Evaluation of alkaline electro-activated water and eggshell as acid mine drainage neutralization and mine tailing remediation agents Thèse

Alexey Kastyuchik

Doctorat en sols et environnement Philosophiae Doctor (Ph.D.)

Québec, Canada

© Alexey Kastyuchik, 2015

Résumé Cette étude visait à étudier la capacité d’un biodéchet calcitique seul ou en mélange avec de matériaux chimiques alcalins ainsi que l’efficacité du procédé d’électro-activation dans la neutralisation de l’acidité et le maintien de conditions alcalines dans un résidu minier sulfuré (RMS). Dans une première série d'expériences, l’évolution du pH du RMS traité avec divers amendements a été suivie en fonction de doses croissantes de coquilles d'œufs de poule (COP) ajoutées seules (2, 4, 6, 8 et 10%) ou en mélange avec 1 et 2% de ciment Portland, 1 et 2% d’oxyde de magnésium (MgO), 1 et 2% de chaux calcique et 1 et 2% de chaux dolomitique. La plus forte dose de COP (10 %) a augmenté la valeur de pH de 2,61 (sans ajout d’amendement) à 7,24. Cependant, les échantillons de RMS mélangés avec COP + ciment (1 – 2%) ou COP + MgO (1 – 2%) avaient un pH très élevé (≥ 8). Les résultats suggèrent que les composés de magnésium ou les produits calcaires riches en oxydes, en hydroxydes et en carbonates, présents dans les RMS chaulés, fournissent une protection à longue terme contre l’acidification anthropique des RMS chaulés. Dans une deuxième série d'expériences, plusieurs essais ont été effectués pour évaluer l’efficacité du procédé d’électro-activation utilisant deux compartiments, l’anode et la cathode, et certains paramètres géométriques, électriques, qualitatifs et quantitatifs, dans la neutralisation de l’acidité des suspensions de RMS introduites dans le compartiment cathodique. Tous les traitements ont influencé de façon significative les valeurs de pHcatholyte. Les résultats ont démontré que l’électro-activation permettait de neutraliser efficacement l’acidité du RMS seul ou en mélange avec COP et également d’obtenir des valeurs de pH fortement alcalines (pHcatholyte 8,0 – 10,0). En outre, l’électro-activation utilisant trois compartiments a permis d’éliminer 80% du fer ferreux d’une solution de FeSO4·7H2O.

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Abstract This study aimed to investigate the capacity of a calcite biowaste alone or mixed with alkaline chemical materials and the efficiency of the electro-activation process in neutralizing acidity and maintaining alkaline conditions in a sulfide mine tailing (SMT). In a first set of experiments, chicken eggshell residue (CES) alone (2, 4, 6, 8 and 10%) or mixed with cement concrete (1 – 2%), MgO (1 – 2%), calcitic limestone (1 – 2%) or dolomitic limestone (1 – 2%) was used to neutralize sulfide mine tailing (SMT) acidity and to precipitate trace metallic elements. The highest rate of CES (10%) increased the initial tailing pH value from 2.61 (without amendment) to 7.24, indicating that CES had sufficient lime value to increase the pH of acid SMT. However, the SMT samples mixed with either CES + cement (1 – 2%) or CES + MgO (1 – 2%) had a high pH (≥ 8). The results suggested that magnesium compounds and calcareous products rich in hydroxides, oxides and carbonates present in limed SMT would provide long-term protection against acid deposition or reacidification of limed SMT. In a second set of experiments, several trials were carried out to assess the effectiveness of electro-activation process composed by two compartments, anode and cathode, under different electric, geometrical, quantitative and qualitative parameters, in neutralizing acidity and maintaining alkaline conditions in a SMT alone or mixed with CES introduced into the cathode compartment. All treatments significantly influenced the pHcatholyte. The results demonstrated that electro-activation process is capable of neutralizing the acidity of RMS alone or mixed with COP and also to achieve alkaline pH conditions (pHcatholyte 8.0 – 10.0). In addition, the electro- activation process using three compartments can remove up to 80% of ferrous iron from an aqueous FeSO4·7H2O solution.

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Acknowledgments It is done. The three years doctoral research is finished and thesis is written. My scientific development could be clearly observed through the pages of my dissertation. But it is just one side of the medal. Another side is the people that I met and that have supported me on this long and sometimes difficult life period. The first person, that I want to thank, is my beloved wife Christiana. It was necessary cross the ocean (one half of the world) to find her here in Canada. In the most difficult moment of my residence here (like and all time) she gave me moral support. And finally, she made the best present of my life - my son Serge. Very impressive event in my life, of course, was arriving in Canada. It was a dream of my childhood. Because of that I want to express special gratitude to my professor Mohammed Aider. He accepted my candidacy to work in his research team and proposed very interesting project throughout of my last experience in the electrochemistry. I also want to thank him for his guidance, patience, flexibility, accessibility and criticism. I do gratefully acknowledge to my co-advisor professor Antoine Karam. For this short three years he has done too much for me. Maybe without his contribution to my fortune it was impossible arrive at the final point of my doctorate program. In the complicated moment he breathed life into the project. His wisdom, altruism, presence, useful accurate hints were always in time. His laboratory, that was accessible for me, had almost all needed equipment and materials. He considerably enriched my mental outlook as a researcher. I would like to thank Dr Lotfi Khiari for agreement to pre-read this thesis and for his valuable comments. My appreciation also goes to the members of my thesis committee: Dr Alfred Jaouich and Dr Mathieu Quenum. They have given their time and offered valuable advice and suggestions.

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Thanks very much to Daniel Marcotte, Alain Brousseau and Marie-Hélène Lamontagne for their assistance in the special analysis and to Normand Massicotte for his help in the technical questions. I cannot forget the role of my friends and colleagues Shyam Suwal, Sergey Mikhailin, Luca Lo Verso, Marina Bergoli, Amara Aït Aissa, Alina Gerzhova, Valerie Carnovale, Julien Chamberland, Catherine Couturier, Nassim Naderi, Élizabeth Parent, Sabrine Naimi, Stéphanie Dudonné, Cédric Leterme, Sébastien Goumon, Cheslav Liato et al. The separation with homeland was not so heavy because of you. My deep appreciation must also be expressed to the faculty direction and especially to vicedoyen Pierre-Mathieu Charest for the foreign student assistance. And finally I want to thank the most important persons in the life of each man - parents. Galina Alekseevna and Sergey Aleksandrovich, I am deeply grateful to you for all.

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Table of contents Résumé.................................................................................................................................. iii Abstract ................................................................................................................................... v Acknowledgments ............................................................................................................... vii Table of contents ....................................................................................................................ix Index of tables ..................................................................................................................... xiii Index of figures ..................................................................................................................... xv List of abbreviations ............................................................................................................xix Introduction ............................................................................................................................. 1 Chapter 1 : Review of literature .............................................................................................. 5 1.1 Importance of Canadian mine activity .......................................................................... 5 1.2 Impacts of mining on environment ............................................................................... 5 1.3 Acid mine drainage generation ..................................................................................... 5 1.3.1 General consideration ......................................................................................... 5 1.3.2 Chemistry of pyrite oxidation ............................................................................. 7 1.3.2.1 Geochemistry of iron ...................................................................................... 7 1.3.2.2 Formation of pyrite ....................................................................................... 11 1.3.2.3 Weathering and oxidation of pyritic tailings under natural conditions ........ 14 1.3.2.3.1 Reaction 1: Oxidation of pyrite ............................................................. 16 1.3.2.3.2 Reaction 2: Oxidation of the ferrous sulfate .......................................... 17 1.3.2.3.3 Reaction 3: precipitation of Fe(III) ........................................................ 18 1.3.2.4 Pyrite oxidation in neutral and alkaline medium .......................................... 20 1.3.2.5 Role of carbonate in the reaction of pyrite oxidation ................................... 21 1.3.2.6 Biological oxidation of metallic sulfides ...................................................... 23 1.3.2.7 Factors affecting the oxidation of pyrite ....................................................... 23 1.4 Prevention and mitigation of acid mine drainage generation ..................................... 24 1.5 Treatment of acid mine waters and acid mine tailings for environmental control ..... 28 1.5.1 Passive treatments ............................................................................................. 30 1.5.2 Active systems .................................................................................................. 33 1.5.2.1 Aeration ........................................................................................................ 33 1.5.2.2 Neutralization technologies .......................................................................... 34 1.5.2.2.1 Alkaline neutralization of mine water and acid mine drainage ............. 34 1.5.2.2.2 Lime neutralization processes and high density sludge method ............ 37 1.5.2.2.3 Neutralization of acid mine tailing ........................................................ 39 1.5.2.2.4 Metal precipitation ................................................................................. 40 1.5.2.2.5 Alkaline industrial waste as neutralizing agents .................................... 43 1.5.3 Electro-activated aqueous solutions.................................................................. 46 1.5.3.1 Base of electro-activated aqueous solutions ................................................. 46 1.5.3.2 Applications of electro-activated solutions................................................... 49 1.5.3.3 Application of electro-activated water to acid mine neutralization .............. 50 Chapter 2 : Research hypotheses, objectives and significance of the study ......................... 53 2.1 Hypothesis .................................................................................................................. 53 2.2 Objectives ................................................................................................................... 53 2.3 Expected results .......................................................................................................... 54 2.3.1 Hypothesis 1 ..................................................................................................... 54

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2.3.2 Hypothesis 2 ..................................................................................................... 54 2.4 Communications......................................................................................................... 55 2.5 Significance of the study ............................................................................................ 56 2.6 Research motivation ................................................................................................... 56 Chapter 3 : Effectiveness of chicken eggshell residue mixed with alkaline amendments in acid mine drainage remediation ........................................................................................... 57 3.1 Résumé ....................................................................................................................... 57 3.2 Abstract ...................................................................................................................... 59 3.3 Introduction ................................................................................................................ 61 3.4 Materials and methods ............................................................................................... 65 3.4.1 Sulfide mine tailing .......................................................................................... 65 3.4.2 Alkaline amendments ....................................................................................... 68 3.4.3 Methodology .................................................................................................... 68 3.4.3.1 Treatments .................................................................................................... 68 3.4.3.2 Use of chicken eggshell residues mixed with alkaline amendments as acidneutralising agents .................................................................................................... 69 3.4.3.3 Buffering capacity of sulfide mine tailing amended with alkaline materials70 3.5 Results and discussion ................................................................................................ 71 3.5.1 Use of chicken eggshell residue mixed with alkaline amendments as acidneutralizing agent ......................................................................................................... 71 3.5.2 Buffering capacity of sulfide mine tailing amended with alkaline materials ... 79 3.6 Conclusions ................................................................................................................ 83 Chapter 4 : Electro-activation technology in AMD treatment ............................................. 85 4.1 Résumé ....................................................................................................................... 85 4.2 Abstract ...................................................................................................................... 87 4.3 Introduction ................................................................................................................ 89 4.4 Materials and methods ............................................................................................... 92 4.4.1 Mining tailing and eggshell .............................................................................. 92 4.4.2 Separator membranes ....................................................................................... 92 4.5 Methodology .............................................................................................................. 94 4.5.1 Removal of Fe(II) from aqueous FeSO4 solution by electro-activation process 94 4.5.2 Neutralization of acid aqueous sulfide mine tailing and precipitation of toxic metals using electro-activation process ........................................................................ 99 4.5.2.1 Experiment 1: Electroneutralization of acid sulfide mine tailing under variable electro-activation conditions including the amount of solid tailing to be treated ....................................................................................................................... 99 4.5.2.2 Experiment 2: Electroneutralization of acid aqueous sulfide mine tailing previously treated with 0, 4 and 10% chicken eggshell (CES) under variable electroactivation conditions .............................................................................................. 101 4.5.2.3 Experiment 3: Electroneutralization of acid aqueous sulfide mine tailing previously treated with 4% chicken eggshell residue under variable cathodes and membrane type conditions ..................................................................................... 103 4.6 Results and discussion .............................................................................................. 106 4.6.1 Removal of Fe(II) from aqueous FeSO4 solution by electro-activation process 106 4.6.1.1 Evolution of pH of electrolyte solutions .................................................... 107 x

4.6.1.2 Concentration of Fe in anolyte and central solution ................................... 110 4.6.2 Neutralization of acid aqueous sulfide mine tailing and precipitation of toxic metals using electro-activation process ...................................................................... 118 4.6.2.1 Experiment 1: Electroneutralization of acid sulfide mine tailing under variable electro-activation conditions including the amount of solid tailing to be treated...................................................................................................................... 118 4.6.2.2 Experiment 2: Electroneutralization of acid aqueous sulfide mine tailing previously treated with 0, 4 and 10% chicken eggshell (CES) under variable electroactivation conditions ............................................................................................... 129 4.6.2.3 Experiment 3: Electroneutralization of acid aqueous sulfide mine tailing previously treated with 4% chicken eggshell residue under variable cathodes and membrane type conditions ...................................................................................... 143 4.6.2.3.1 General results ..................................................................................... 143 4.6.2.3.2 Electro-activation process using cation-exchange membrane as a separator .............................................................................................................. 144 4.6.2.3.3 Electro-activation process using nanofiltration membrane as a separator ............................................................................................................................ 145 4.6.2.3.4 Electro-activation process using anion-exchange membrane as a separator .............................................................................................................. 149 General conclusions ............................................................................................................ 153 References ........................................................................................................................... 157

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Index of tables Table 1.1. Chemicals for AMD neutralization (Bise, 2013) ................................................. 34 Table 1.2. Characteristics of chemical compounds used in AMD treatment (Jacobs et al., 2014). .................................................................................................................................... 35 Table 1.3. Element composition of cement kiln dust and red mud bauxite (Doye and Duchesne, 2003). .................................................................................................................. 44 Table 3.1. Chemical composition of the Solbec-Cupra tailing (Karam and Guay, 1994) .... 67 Table 3.2. Chemical composition (%) of alkaline amendments ........................................... 68 Table 3.3. Experimental treatments ...................................................................................... 69 Table 3.4. Effect of CES mixed with four alkaline amendments on pHTS of aqueous tailing suspensions ........................................................................................................................... 76 Table 3.5. Values of pHAA of aqueous treated tailing suspensions before and after addition of 0.025 mmol of acid ........................................................................................................... 80 Table 4.1. Composites of ion-exchange membranes MK-40 and MA-40 (Saldadze et al., 1960; Dyomina et al., 2002; Berezina et al., 2008). ............................................................. 93 Table 4.2. Manufacturer characteristics of ion-exchange membranes (Pokonova, 2007; Shekino-AZOT, 2015) .......................................................................................................... 94 Table 4.3. Experimental parameters studied in experiment 1. ............................................ 101 Table 4.4. Experimental parameters studied in experiment 2. ............................................ 103 Table 4.5. Experimental parameters studied in experiment 3. ............................................ 106 Table 4.6. Analysis of variance on the influence of current intensity and anode-CEM distance on the pH values of anolyte and electrolyte solution in central compartment at t = 120 minutes. ........................................................................................................................ 107 Table 4.7. ANOVA results (F-value) on concentration of total Fe in central and anolyte compartments at two electro-activation times. ................................................................... 110 Table 4.8. ANOVA results (F-value) on the influence of current intensity, solid SMT:water ratio, and rotation speed of stirrer on the pH values of catholyte at six electro-activation times. ................................................................................................................................... 119 Table 4.9. A partial activity series of elements (Lide, 2000). ............................................. 123 Table 4.10. ANOVA results (F-value) on the influence of CES content of SMT, active membrane surface, cathode-AEM distance on the pH values of catholyte at six electroactivation times. .................................................................................................................. 130 Table 4.11. ANOVA results (F-value) on the influence of membrane type, voltage and electrode material, on the pH values of catholyte at six electro-activation times. ............. 144 Table 4.12. Values of initial pH and pHcatholyte at the end of electro-activation process .... 147 Table 4.13. Values of initial pH and pHcatholyte at the end of electro-activation process using AEM and variable voltage values and electrode materials. ................................................ 151

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Index of figures Figure 1.1. Acid mine drainage process (MWC, 2006) .......................................................... 7 Figure 1.2. Sulfur transformations. 1) Chemolitotrophic oxididation, 2) Phototrophic and chemotrophic oxidation. Adapted from Muyzer and Stams (2008) ..................................... 12 Figure 1.3. Schematic representation of the mechanism of pyrite oxidation in carbonate solutions (Caldeira et al., 2010) ............................................................................................ 22 Figure 1.4. Scheme of dry cover in the abandoned Kettara mine, Marocco (Bosse et al., 2013) ..................................................................................................................................... 27 Figure 1.5. Classification of mine drainage treatment technologies (INAP, 2014) .............. 29 Figure 1.6. Scheme of a mine-waste impoundment with a combined remediation complex (Blowes et al., 2014) ............................................................................................................. 32 Figure 1.7. Pond treatment (Aubé and Zinck, 1999) ............................................................ 37 Figure 1.8. Conventional treatment plant (Aubé and Zinck, 1999) ...................................... 38 Figure 1.9. Solubility of the common heavy metal hydroxides in dependence of pH (HEI, 2012) ..................................................................................................................................... 42 Figure 1.10. Schematic representation of electro-activation apparatus ................................ 47 Figure 3.1. The Solbec-Cupra site (position A) .................................................................... 65 Figure 3.2. Oxidized sulfide tailings on the surface of the site (1994) ................................. 66 Figure 3.3. Yellow and grey colored sulfide tailings (Karam and Guay, 1994) ................... 66 Figure 3.4. Effect of alkaline amendments on tailing pH ..................................................... 72 Figure 3.5. Tailing pH values as a function of time for different rates and sources of alkaline amendments............................................................................................................. 74 Figure 3.6. Potentiometric titration curves of acid sulfide mine tailing ............................... 83 Figure 4.1. The schematic diagram of electro-activation cell units ...................................... 96 Figure 4.2. Plates that function as the anode and the cathode electrodes ............................. 96 Figure 4.3. Cation- and anion-exchange membranes ........................................................... 97 Figure 4.4. The experimental set-up of the reactor ............................................................... 97 Figure 4.5. Schematic representation of the two-compartment cell units .......................... 100 Figure 4.6. Schematic representation of the two-compartment cell units using CEM (a) and NFM (b) .............................................................................................................................. 105 Figure 4.7. Evolution of pH of solution in the anode (A) and central (B) compartments as a function of electro-activation time ...................................................................................... 108 Figure 4.8. Evolution of Fetotal concentration in the anolyte as a function of electroactivation time..................................................................................................................... 111 Figure 4.9. Evolution of Fe2+ concentration in the central solution as a function of electroactivation time..................................................................................................................... 112 Figure 4.10. Precipitation of Fe(OH)3 on the CEM from the anode side. (A): Anode-CEM distance = 3 cm and I = 150 mA; (B): Anode-CEM distance = 5 cm, I=250 mA and t=120 minutes ................................................................................................................................ 114 Figure 4.11. Scanning electron microscope image of two zones: A and B (Fe(OH)3 – light crystals) ............................................................................................................................... 115 Figure 4.12. EDS spectrum of the grey colored zone (Figure 4.11) ................................... 116 Figure 4.13. EDS spectrum of white crystal (Figure 4.11) ................................................. 116 Figure 4.14. Precipitation of Fe on CEM (anode side) surface under the following conditions: Anode-CEM distance = 5 cm, V = 126 volts, t = 6 minutes ............................ 117

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Figure 4.15. Effect of the current intensity on pHcatholyte values as a function of electroactivation time. R = 0.1:1, 0.2:1 and 0.3:1 ......................................................................... 120 Figure 4.16. Effect of the amount of SMT in cathode compartment on pHcatholyte as a function of electro-activation time. I = 50 mA, 100 mA and 150 mA ............................... 121 Figure 4.17. Effect of current intensity on voltage as a function of electro-activation time. R = 0.1:1, 0.2:1 and 0.3:1....................................................................................................... 126 Figure 4.18. Effect of solid SMT/water ratios on voltage as a function of electro-activation time. I = 50mA, 100mA and 150 mA ................................................................................ 127 Figure 4.19 Evolution of sulfur concentration in the cathode compartment ...................... 129 Figure 4.20. Effect of the CES rate in SMT in cathode compartment on pHcatholyte values as a function of electro-activation time. DC = 3, 4 and 5 cm. AS = 25% ............................... 131 Figure 4.21. Effect of the CES content of SMT in cathode compartment on pHcatholyte values as a function of electro-activation time. DC = 3, 4 and 5 cm. AS = 50% ........................... 132 Figure 4.22. Effect of the CES content of SMT in cathode compartment on pHcatholyte values of catholyte as a function of electro-activation time. DC = 3, 4 and 5 cm. AS = 100% ..... 133 Figure 4.23. Effect of DC on pHcatholyte values as a function of electro-activation time. CES rate = 0, 4 and 10%. AS = 25% ........................................................................................ 134 Figure 4.24. Effect of DC on pHcatholyte values as a function of electro-activation time. CES rate = 0, 4 and 10%. AS = 50% .......................................................................................... 135 Figure 4.25. Effect of DC on pHcatholyte values as a function of electro-activation time. CES rate = 0, 4 and 10%. AS = 100% ...................................................................................... 136 Figure 4.26. Evolution of voltage as a function of electro-activation time. DC = 3, 4 and 5 cm. AS = 50% .................................................................................................................... 138 Figure 4.27. Evolution of voltage as a function of electro-activation time. CES = 0, 4 and 10%. Dc = 3 cm .................................................................................................................. 139 Figure 4.28. Sulfur concentration in the catholyte under variable electro-activation conditions at the end of electro-activation treatment. Initial solution = catholyte before starting electro-activation ................................................................................................... 141 Figure 4.29. Calcium concentration in the catholyte under variable electro-activation conditions at the end of electro-activation treatment. Initial solution = catholyte before starting electro-activation ................................................................................................... 142 Figure 4.30. Evolution of pHcatholyte as a function of electro-activation time under variable conditions using CEM as a separator and a stainless steel cathode material ..................... 145 Figure 4.31. Evolution of pH as a function of electro-activation time under variable conditions using nanofiltration membrane as a separator and a stainless steel cathode material ............................................................................................................................... 146 Figure 4.32. Evolution of current intensity as a function of electro-activation time when applying three different voltages (15 V, 30 V and 60 V) under variable conditions using nanofiltration membrane as a separator ............................................................................. 147 Figure 4.33. Sulfur concentration in catholyte at the end of electro-activation treatment, using nanofiltration membrane and stainless steel cathode, as a function of voltage. Initial solution = catholyte before starting electro-activation ....................................................... 149 Figure 4.34. Calcium concentration in catholyte at the end of electro-activation treatment, using nanofiltration membrane and stainless steel cathode, as a function of voltage. Initial solution = catholyte before starting electro-activation ....................................................... 149

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Figure 4.35. Evolution of pH as a function of electro-activation time under variable conditions using anion-exchange membrane as a separator and a stainless steel cathode material ............................................................................................................................... 150 Figure 4.36. Evolution of current intensity as a function of electro-activation time when applying three different voltages (15, 30 and 60 V) under variable conditions using AEM as a separator ........................................................................................................................... 151

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List of abbreviations A: identification (electro-activation treatment with AEM) AA: alkaline additions AC: alkaline carbonate AEM: anion-exchange membrane ALDs: anoxic limestone drains AMD: acid mine drainage AS: active membrane surface, % BC: buffer capacity C’: electrolyte concentration, mol/L CAL: calcitic limestone CCM: calcareous products CEM: cation-exchange membrane COP: coquilles d’œufs de poule CES: chicken eggshell residue CKD: cement kiln dust CPC: ciment riche en produits calcaires D: diffusion constant of electrolytes dissolving in a solution, cm2/s DC: direct current DA: anode-membrane distance, cm DC: cathode-membrane distance, cm DMA: drainage minier acide DOL: dolomitic limestone ECCE: effective calcium carbonate equivalent EDS: energy-dispersive X-ray spectroscopy F: Faraday constant, 9.64853399(24)x104 C mol−1 I: current intensity, mA ilim: limiting current density KU-2: cation-exchange resin LD: limestone drain LR: lime requirement MA-40: anion-exchange membrane MGO: magnesium oxide MK-40: cation-exchange membrane MT: mine tailing N: identification (electro-activation treatment with nanofiltration membrane) N30F: nanofiltration membrane NFM: nanofiltration membrane OLCs: open limestone channels OM: organic matter pHAA: pH of aqueous alkaline amended tailing suspensions pHTS: pH of tailing suspension pHS: pH de suspensions R: SMT/water ratio in the cathode compartment, w/v R’: resistance, ohm

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RMB: red mud bauxite RMA: résidus miniers générateurs d’acide RMS: résidus miniers sulfurés SAPS: successive alkalinity producing systems SMT: sulfide mine tailing t: time of treatment, min T: treatment t-- and t-: the transport number of anions in the anion-exchange membrane and in the solution TS: tailing suspension V: voltage voltage of the electro-activation system, V δ: boundary layer thickness, cm. φ0: standard electrode potential, V

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Introduction As it is known, oxidation of sulfide minerals, particularly pyrite, which is the most abundant sulfide mineral on the planet (Johnson and Hallberg, 2005), is the major cause of acid mine drainage (AMD) generation (Ritcey, 1989). Sulfide minerals are unstable when exposed to air (oxygen) and rainfall (water), and begin to react almost immediately. This reaction yields high level of sulfuric acid and causes the leaching of heavy metals, in concentrations which may be toxic to aquatic life (Sheoran and Sheoran, 2006; Sadak, 2008). For many years, the Canadian mining industry is facing to management of large amounts of sulfidic mine tailings. In Québec, the regulations of the Ministère du Développement Durable, de l’Environnement et de la Lutte contre les Changements Climatiques (MDDELCC) require that acid mine tailings do not contaminate surface water and groundwater. Since the adoption of the policy of rehabilitation of contaminated land by the MDDELCC in 1988, the restoration of degraded sites has become a government priority. Acid mine drainage is of particular concern in Canadian mine areas because its high level of acidity, heavy metals (iron, aluminium, copper, and manganese, and possibly other heavy metals) and metalloids (of which arsenic is generally of greatest concern) has adverse effects in the terrestrial and aquatic environments. The most widespread method used to treat acidic mine tailing effluents or to mitigate the generation of AMD, is an active treatment process involving addition of a chemicalneutralizing agents. There are a large number of alkaline compounds that have been used in neutralizing acid mine drainage or acid generated from sulfidic wastes. These include agricultural lime, dolomite, fly ash, lime marl, soda ash, red mud, unactivated attapulgite and by-product lime from various industrial processes (Adams et al., 1972; Mays and Bengtson, 1978; Ritcey, 1989; Bellaoui et al., 1996; Skousen et al., 2000; Potgieter-Vermaaka et al., 2006; Karam et al., 2009; Fytas, 2010; Falayi and Ntuli, 2014). However, information on acid neutralization of sulfide mine tailings using eco-friendly agro-waste such as chicken eggshells which are rich in calcium carbonate is quite limited. In the context of sustainable development, there is an increasing interest in the recycling of agrifood waste with high concentration of calcium carbonate such as chicken eggshells.

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Canada produces a significant amount of poultry eggshells that are composed primarily of calcium carbonate, which is highly alkaline and neutralizes acid. Eggshells are waste materials from hatcheries, homes and fast food industries (Amu et al., 2005; King’ori, 2011). In 2007, Canadian production of eggs for consumption reached 521.1 million dozen (EFC, 2008). Canada has approximately 1,100 egg farmers, the majority of farms are located in Quebec and Ontario (Farm Credit Canada, 2012). Poultry eggshells are all at once: i) a problem due to the need to manage and ii) a potential source of neutralizing substances and calcium. Several studies have shown that eggshells could be employed : (i) as a natural and ecofriendly adsorbent material for the removal of either organics (Arami et al., 2006; Zulfikar and Setiyanto, 2013) or heavy metals from aqueous solutions (Rao et al., 2010; Nduwayezu et al., 2013; Ipeaiyeda and Tesi, 2014; Bolboli et al., 2015), (ii) as an alternative soil stabilizer like lime (King’ori, 2011) or as subgrade material for road construction (Olarewaju et al., 2011). Relatively little research has been devoted to assess short-term effect of chicken eggshell waste on acid neutralization and chemical precipitation of heavy metals. In particular, little is known about the effectiveness of chicken eggshell mixed with by-product alkaline materials such as cement concrete rich in calcareous products (Portland cement) or magnesium oxide for acid sulfide mine tailing remediation. Although most of the research to date has focused on using conventional active and passive treatments, evidence was presented in few studies suggesting that electrochemically activating water technology using ion-exchange membranes could remove metals from AMD (Bunce et al., 2001; Chartrand and Bunce, 2003). The base of electro-activated aqueous solution is electrolysis and it is possible to produce acidic, neutral or alkaline solution at electrode compartment (pH 2 – 12). Electrochemical applications basically use an electrochemical cell with two electrodes submerged in an electrolyte (Doering et al., 2001). Catholyte is an alkaline solution (pH 7 – 12) with a high reduction potential (Marais and Williams, 2001). Electrolysis remediation is often regarded as environmentally friendly technology for remediating sites polluted by heavy metals. However, little is known about the effectiveness of electro-activation for neutralizing tailing acidity and the influence of electro-activation conditions (e.g. current intensity, active membrane surface, distance 2

between the electrode and the membrane (ion-exchange or nanofiltration membrane), electrode materials and solid/water ratio) on neutralization of sulfide mine tailings amended with chicken eggshell. This thesis investigates the application of alkaline amendments (chapter 3) and electroactivation technology (chapter 4) in remediation of acid sulfide mine tailings.

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Chapter 1 : Review of literature 1.1 Importance of Canadian mine activity Mining is an important economic activity in many developed and developing countries. Internationally, Canada is one of the leading mining countries and one of the largest producers of minerals and metals. Quebec is a great place for mining (Marshall, 2013). Mining and exploration activities contribute significant economic and social benefits to Canada's provinces and territories (MiningFacts.org, 2012a; Marshall, 2013). Mining also remains an important source of employment in Canada.

1.2 Impacts of mining on environment The Canadian mineral industry generates annually a significant amount of waste rock and tailings. After being removed, waste rock and tailings are usually stored above ground in large free-draining piles. According to information of the mining association of Quebec, overburden, waste rock and mine tailings were disposed on the surface which was equal 8000 hectares in 1991 (Doye, 2005). As most waste rock and tailings contain metal sulfide minerals, the production of acidic metal-rich mine drainage waters (AMD) generated from sulfide mine tailing piles, as a result of weathering and oxidation of sulfides, constitute an environmental problem to the immediate environment and receiving waters (Ritcey, 1989). AMD severely degrades water quality, and can kill aquatic life and make water virtually unusable (SDWF, 2015).

1.3 Acid mine drainage generation 1.3.1 General consideration Metal sulfide minerals, primarily pyrites and other sulfide ores, can be oxidized when they come in contact with oxygen (O2) and water (Ritcey, 1989). The oxidation reaction produces significant amount of sulfuric acid (H2SO4) reducing tailing pH and generating metal-rich acid infiltration water (e.g. AMD).

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Acidity in AMD is comprised of hydrogen ion acidity or H2SO4 and mineral acidity (iron, aluminum, manganese, and other metals depending on the specific geologic setting and metal sulfide (Skousen et al., 1996). The primary factors directly involved in the formation of AMD are the presence, abundance and reactivity or tendency of sulfide minerals to oxidize. The sulfides oxidation reactions are catalyzed by the iron- and sulfur-oxidizing microorganisms (Jacobs et al., 2014). Oxidation of sulfides can be provided by oxygen from the atmosphere and by oxygen that is solubilized in the seepage waters as well as oxidizing inorganic components present in tailings, such as ferric iron, manganese, nitrates, etc. (Ritcey, 1989). The sulfides responsible for acid generation include (Ritcey, 1989; Udayabhanu and Prasad, 2010): pyrite (FeS2), pyrrhotite (FexSs), arsenopyrite (FeAsS2), chalcopyrite (CuFeS2), sphalerite (ZnS), galena (PbS), chalcosite (Cu2S), covelite (CuS), molybdenite (MoS2), millerite (NiS). There are four processes by which sulfides may be oxidized (Ritcey, 1989): 1) chemical oxidation, 2) biological (bacterial) oxidation, 3) electrochemical oxidation, and 4) a combination of chemical, bacterial and electrochemical oxidation. If uncontrolled, the AMD may runoff into streams or rivers or leach into groundwater (Coil et al., 2014). The resulting fluids may be highly toxic and, when mixed with groundwater, surface water and soil, may have harmful effects on humans, animals and plants. Acid mine drainage can develop at several points throughout the mining process: in underground workings, open pit mine faces, waste rock dumps, tailings deposits, and ore stockpiles. Acid generation can last for decades, centuries, or longer, and its impacts can travel many miles downstream. Roman mine sites in Great Britain continue to generate acid drainage 2,000 years after mining ceased (Figure 1.1) (MWC, 2006). That is why AMD is a priority ecological problem for many countries (Leopold and Lapakko, 2001).

6

Figure 1.1. Acid mine drainage process (MWC, 2006)

1.3.2 Chemistry of pyrite oxidation 1.3.2.1 Geochemistry of iron Fe is one of the most abundant elements in the lithosphere, and its common range in magmatic rocks is 1.4 to 10% (Kabata-Pendias, 2011). Its highest concentrations are usually associated with ultramafic rocks. In nature, Fe readily undergoes oxidation or reduction, depending upon prevailing environmental physicochemical parameters, such as pH, oxygen concentration, availability of electrons and redox potential (Eh) (Ritcey, 1989; Stumm and Morgan, 1996; Hedrich et al., 2011; Kabata-Pendias, 2011). Its oxidized and reduced forms are referred to as ferric (Fe3+) and ferrous (Fe2+) iron, respectively. Fe readily participates in subsurface redox reactions (Vance, 1994). The reactions of Fe in processes of weathering are dependent largely on the availability of electrons, the Eh-pH system of the environment and on the stage of oxidation of Fe compounds involved (Kabata-Pendias, 2011). Redox reactions involving Fe and S can be catalyzed by enzymes (Bohn et al., 1985). Oxygen has a great affinity for electrons and is the primarily and strongest electron acceptor in nature (lithosphere) because it generates the

7

greatest Gibbs free energy change and produces the most energy. Under aerobic conditions, it accepts electrons according to the following reaction (Ebsworth et al., 2013): O2 + 4 e- + 4H+ ↔ 2H2O (Eh0 = 1,229V)

[1.1]

Oxidizing agents have high electrode potentials and are electron acceptors. In aqueous solutions O2 is thermodynamically a powerful oxidizing agent (Ebsworth et al., 2013). In chemical industries, atmospheric O2 is by far the cheapest oxidizing agent since other oxidizing agents such as H2SO4, HNO3, MnO2 and H2O2 need O2 for their preparation, resulting in higher investment (Nayak and Rao, 2003). Oxygen is supplied to the surface water layers and soils primarily from the air (Rowell, 1981). However, some biological processes occurring in aerobic soils could oxidize water under dark conditions releasing O2 (Fleischer et al., 2013). It has been suggested that O2 is produced by dismutation of nitric oxide (NO) in anaerobic methane oxidisers (Ettwig et al., 2010; Ettwig et al., 2012). NO and nitrous oxide (N2O) in soils are among nature's most powerful electron acceptors (Ettwig et al., 2012). NO dismutase has been involved in O2 production in soils containing nitrate and nitrite (Fleischer et al., 2013). Oxic conditions occur when the supply of O2 exceeds the consumption (Dillmann et al., 2013). Aerobic conditions prevails in aerated soils, well drained soils, coarse-textured soils, areas with a low water table, and any other waterlogged or flooded media. Ferrous iron (Fe2+) is a soluble form of Fe that is stable at extremely low values of pH or under anaerobic conditions (Boundless.com, 2014). Anaerobic conditions prevails in aquatic ecosystems and terrestrial ecosystems such as wetland soils, paddy soils, organic soils, poorly drained soils, clayed soils, areas with a high water table, soils amended with heavy rates of organic materials, and any other waterlogged or flooded media (Inglett et al., 2005). Under aerobic and moderate pH conditions, Fe2+, as Fe(OH)2, is susceptible to spontaneous chemical oxidation by molecular oxygen (O2), which acts as electron acceptor, to the ferric form, according to simple rate law following the reaction path (Nayak and Rao, 2003): Fe(OH)2 + ¼O2 + ½H2O → Fe(OH)3

8

[1.2]

In natural water, the rate at which the spontaneous chemical oxidation occurs depends on the temperature and concentrations of protons (pH), dissolved oxygen and Fe2+ (Stumm and Morgan, 1996):

[1.3] where k is a temperature-dependent constant (3×10−12 mol. l−1 min−1 at 20 °C). Oxidation of Fe2+ is easily carried out by contact with air (Wong, 1984) or by oxygenation. During oxidation of Fe2+ salt aqueous solutions, poor soluble compounds including Fe3+ oxides are formed (Domingo et al., 1994). Alicilar et al. (2008) studied the air oxidation of Fe2+ ions in water. While the maximum yield of 86 % is catalytically achieved by blowing air at a neutral medium, the oxidation was almost completed in an alkaline solution even at stationary atmosphere. The reaction was first order with respect to Fe2+. In aerobic soils, Fe(II) minerals in parent material slowly oxidize spontaneously (Bohn et al., 1985). In most environments, rates of spontaneous chemical oxidation of Fe2+ are very low at pH

k1(Fe(CO3)22-) >

21

k1(Fe(CO3)(OH)-). The contribution of each compound is 20, 40 and 40% respectively. Thus, the carbonate contained particles play the main role in the ferrous iron oxidation (80%). It is possible due to the less energy bond between ferrous iron and hydroxide ion or carbonate (bicarbonate) ion that is formed in the high spin complexes (Caldeira et al., 2010). In addition, the buffering properties of carbonate minimize pH changing in the solution and preserve favorable conditions for oxidation of pyrite. Hydroxide ions produced in the anodic reaction will be bounded in HCO3- (Caldeira et al., 2010). Carbonate complexes of iron also are more soluble in the water solutions under alkaline conditions. It makes iron more available to the chemical reactions. A schematic model of the pyrite oxidation process proposed by Caldeira et al. (2010) is shown in Figure 1.3.

Figure 1.3. Schematic representation of the mechanism of pyrite oxidation in carbonate solutions (Caldeira et al., 2010)

Fe(III) carbonate complexes (electron acceptors) are adsorbed on the pyrite surface in the presence of carbonate. Electron transfer from anodic to cathodic side of pyrite surface reduces the Fe(III)-CO3 to Fe(II)-CO3. Produced Fe(II) carbonate complex is oxidized by oxygen. It forms the cycle of electron transfer from the pyrite sulfur to dissolved oxygen. The water or OH- adsorption from the anodic side leads to radical formation on the iron site and further radical transport to sulfur. It results in thiosulfate formation and pyrite dissolution (Caldeira et al., 2010).

22

1.3.2.6 Biological oxidation of metallic sulfides Several sulfide minerals can biologically be oxidized and generating acid mine drainage. These include (Ritcey, 1989): arsenopyrite, bornite, bravoite, chalcosite, chalcopyrite, cobaltite, covellite, enargite, marcasite, marmatite, millerite, molybdenite, orpiment, pyrite, phyrrhotite, sphalerite, stannite, tetrahedrite and violarite. Many common metals may participate in sedimentation and generation of H+ ions during reactions of hydrolysis. These reactions usually occur in the area of blending of acidic waters with 3 major dissolved metals mix with cleaner waters resulting in metal hydroxides precipitation on stream channel substrates. Al3+ + 3H2O ↔ Al(OH)3(s) + 3H+

[1.22]

Fe2+ + 0.25O2 + 2.5H2O ↔ Fe(OH)3(s) + 2H+

[1.23]

Mn2+ + 0.25O2 + 2.5H2O ↔ Mn(OH)3(s) + 2H+

[1.24]

Metal sulfide minerals like pyrite may interact with valuable mineral deposits and some of these minerals may also fabricate acidity and sulfate ions. Oxidation and hydrolysis of metal sulfide minerals pyrrhotite (Fe1-xS), chalcopyrite (CuFeS2), sphalerite [(Zn, Fe)S] and others release metals such as zinc, lead, nickel, and copper into solution in addition to acidity and SO42- (Jennings et al., 2000; Younger et al., 2002).

1.3.2.7 Factors affecting the oxidation of pyrite There are several factors that can influence the kinetics of pyrite oxidation. These include (Ritcey, 1989): oxygen content of the gas phase, if saturation is less than 100 %, oxygen concentration in the water phase, degree of surface saturation with water, pH of the solution in contact with pyrite, temperature, chemical activity of Fe3+, surface area of exposed metal sulfide, chemical activation energy required to initiate acid generation and bacterial activity (Akcil and Koldas, 2006). There are a number of common microscopic bacteria which oxidize sulfide minerals as a source of energy. These bacteria can accelerate the rate of S oxidation and are an important factor in pyrite oxidation and consequently in AMD formation. The kinetics of microbial oxidation of pyrite are influenced by many factors, including (Ritcey, 1989): oxygen

23

availability, carbon dioxide requirements, temperature dependence, pyrite reactivity, amount of pyrite and its surface area, bacterial contact with pyrite, inhibitors.

1.4 Prevention and mitigation of acid mine drainage generation Preventing and controlling AMD is a concern at operating mine sites and after mine closure. Advances continue to be made in research and the development of technology to improve ARD prediction, prevention, and treatment. The prevention and mitigation of AMD generation is based on the methods that minimize the presence of the primary reactants for sulfide oxidation (water and oxygen), and/or maximize the quantity and availability of acid neutralizing reactants. These methods could be classified as shown below (Ritcey, 1989; Lottermoser, 2012): 1) minimizing oxygen penetration by diffusion or advection; 2) minimizing water infiltration and leaching (water as a reactant and a transport agent); 3) minimizing, removing, or isolating sulfide minerals; 4) controlling pore water solution pH by addition of lime, limestone, etc.; 5) maximizing availability of acid neutralizing minerals and pore water alkalinity; 6) controlling bacteria and biogeochemical processes (bactericides using): organic chemicals designed to kill or to inhibit sulfide-oxidizing bacteria activity have been applied to sulfide wastes in order to slow the rate of AMD generation. However, there is concern that some of these chemicals may kill beneficial microorganisms in the environment, thus becoming pollutants themselves. Various approaches have been evaluated for inhibition of pyrite oxidation or to prevent or minimise the generation of AMD from pyritic tailings. Such techniques are known collectively as ‘source control’ measures. These include (Ritcey, 1989; Johnson and Hallberg, 2005; Lottermoser, 2012; MiningFacts.org, 2012b): 1) mixing acid-producing materials with acid-buffering materials, combining sulfide wastes with limestone or calcite can result in AMD neutralization on site; 2) total solidification of tailings; 3) underwater storage of mine tailings that are potentially acid producing;

24

4) flooding/sealing of underground mines; 5) land-based storage in sealed waste heaps; 6) covering waste rock: installing a cover of clay, plastic, or soil over piles of waste rock prevents rain and other precipitation from contributing to AMD formation and transport, and reduces the amount of O2 available to react with the sulfide minerals. 7) blending of pyritic mine wastes with solid-phase phosphates (such as apatite) to precipitate Fe3+ as ferric phosphate, thereby reducing its potential to act as an oxidant of sulfide minerals; 8) application of anionic surfactants, microencapsulation (coating), and application of alkaline materials. Controlling pH by addition of alkaline materials such as lime, limestone, phosphates, and other calcareous amendments have been shown to be effective for restricting oxygen and reducing permeability (Ritcey, 1989). As limestone raises the pH of the bulk solution and heavy metals are present, precipitation of the metal hydroxides (with extremely low solubilities) is normally accelerated. As it was mentioned above, migration of oxygen through the sulfur-bearing wastes in the presence of water promotes to the AMD generation. Thus, oxygen and water are the limiting factors of pyrite oxidation reaction. Control of these factors has a potential to AMD release limit. Different physical barriers have found application to realize this control. In practice of oxygen penetration blocking, the most popular barriers are: 1) water covering systems, 2) soil material composed covers (dry covers), 3) synthetic and dry covers and 4) systems composed of materials that consume oxygen (Peppas et al., 2000). A low diffusion coefficient of O2 into the different materials (mediums) plays a principal role in the action mechanism of these barriers (except: consume oxygen systems). For example, the diffusion coefficient of O2 in the water and air is 2·10-9 and 1.78·10-5 m2s-1 respectively. The difference between aqueous and air medium shows that the water will significantly delay

25

O2 migration to the mine waste surface. Thus, an aqueous covering will decrease mine tailing oxidation rate. In the publication of Vigneault et al. (2001) this rate for the flooded tailing at a depth of 0.3 m and less is approximately 2000 times higher than in the humid conditions. Dry covers in general consist of soil material layers with different grain-size composition (Ritcey, 1989). The high density (fine-grain fraction) and poorness of the soil in the gas phase decrease the oxygen transport depthward the mine tailing layer (oxygen availability to pyrite oxidation reaction). Fine-grained cover was made at Whiteis waste rock heap, Rum Jungle, Northern Territory, Australia (Taylor et al., 2003). The migration of oxygen from cover layers into the heap of waste rock was observed. The experimental data demonstrated reducing of oxygen transport by dry layers cover using to 20 – 23% in comparison with the exposed waste. Season humidity changing makes a contribution to the intensity of oxygen flow in the applied dry cover layers (gravelly sand - 15 cm, sandy clay loam - 15 – 25 cm and lateritic clay - 15 – 25 cm). In the last day of wet season the oxygen flow was 4 times lower than in the last day of dry season (Taylor et al., 2003). Application of this method in the humid climate of Québec for oxygen flows control was investigated as an alternative of water cover method (Demers et al., 2009). In this study, acid generating wastes were covered by a single low-sulfide tailing layer (cover thickness from 0.5 to 1.0 m). The efficiency of low sulfide tailing in the oxygen flow control was observed in the presence of elevated water table. Dry covers also found its application as a physical water infiltration barrier in a semiarid climate. The operating principle of these covers is in water retention during the wet season and evaporation (emission) of accumulated moisture during the dry season. For example, Kettara mine wastes were covered by dry (store-and-release) cover produced from phosphate mine wastes situated close to contaminated site. After 1.5 year period, the effectiveness of water store-and-release cover was 94% (Bosse et al., 2013). It means that 246.5 mm of water precipitation was evaporated to the atmosphere. The scheme of this cover is shown in the Figure 1.4.

26

Figure 1.4. Scheme of dry cover in the abandoned Kettara mine, Marocco (Bosse et al., 2013)

Synthetic covers are used for mine tailing protection from both oxygen and water infiltration. Polymer materials (high-density polyethylene, linear low-density polyethylene, polyvinyl chloride), concrete and asphalt are the base components of impermeable layers. These impermeable layers could not be used alone because of their specific character of installation. They are a part of complex cover system with a protective clay cover, a granular stabilization layer etc. This method has found popularity in humid climate as in Québec, Canada (Benzaazoua et al., 2008; Heerten and Koemer, 2008; Mazzieri et al., 2013). Desulphurization of mine tailing and cement backfill technology were combined to control of AMD generation in the Doyon mine of the Abitibi region, Québec, Canada. As the end products of mine tailing desulphurization, it was produced non-acid generating low sulfide tailing and sulfide concentrate. It was found that the low sulfide wastes (0.3 wt% of sulphur) could be used as a cover material. The sulfide concentrate (≈ 45% of pyrite) found its application in the cement paste backfill (Benzaazoua et al., 2008). Oxygen consumed materials are the same organic materials that will be discussed below in the section of permeable reactive barriers. The decomposition of organic material could be realized in the aerobic (in the presence of oxygen) and anaerobic (in the absence of oxygen) conditions. The microorganisms consumed oxygen degrade organic material with carbonic acid gas and water production according to reaction (Peppas et al., 2000):

27

C6H12O6 + 6O2 → 6CO2 + 6H2O

[1.25]

Thus, the anaerobic microorganisms use all accessible oxygen and block its migration to the covered mine tailing (Peppas et al., 2000). The practice of cover barriers exploitation shows that discussed covers are used separately (Demers et al., 2009) or in the combinations (Bosse et al., 2013). Effectiveness of these barriers is justified but it is still inadequately understood on the long term.

1.5 Treatment of acid mine waters and acid mine tailings for environmental control Treating AMD requires neutralizing the acid and precipitating out metal ions. A wide range of acidic mine effluent, tailing slurry, waste rock and sulfide tailings treatment technologies has been developed, proven, and applied to many different applications in the different countries. Information regarding technologies is furnished by INAP (2014). In Figure 1.5 is depicted the major treatment categories of mine tailings, which may be divided into those that use either chemical or biological mechanisms to neutralise AMD and remove metals from solution. Within the major categories that use chemical or biological mechanisms to neutralise AMD and remove metals from solution, there are processes that may be described as either ‘active’ or ‘passive’.

28

Figure 1.5. Classification of mine drainage treatment technologies (INAP, 2014)

These technologies can be grouped according to the following (Johnson and Hallberg, 2005): 

Active systems, referring to the continuous application of alkaline materials (e.g., aeration and lime addition) to neutralise acidic mine waters and precipitate metals (abiotic method), and off-line of sulfidogenic bioreactors (biological method).



Passive systems, referring to the use of anoxic lime drains (abiotic method) or biological methods such as natural and constructed aerobic wetland ecosystems, compost reactors, anoxic lime drains, permeable reactive barriers, packed bed iron-oxidation bioreactors.

The major differences between active and passive treatment are that active treatment refers to technologies requiring ongoing human operations, maintenance and monitoring based on external sources of energy (electrical power) using different infrastructures and engineered systems. In all systems alkalinity is increased, either by limestone (CaCO3) dissolution,

29

bacterial transformation of organic carbon to bicarbonate, or photosynthetic release of OH(Gillmore, 2011).

1.5.1 Passive treatments Passive treatments are based on natural processes and do not require constant application of chemicals. However, they take longer, use more space, and are not as reliable. The following are a few examples of passive treatments to neutralize acidic mine drainage, and to remediate mine water and ground water containing metals and other pollutants (Ritcey, 1989; Aubertin et al., 1997; Catalan and Yin, 2003; Conca et al., 2003; Cravotta, 2003; Molson et al., 2004; Johnson and Hallberg, 2005; Gillmore, 2011): constructed wetlands, anoxic limestone drains (ALDs), successive alkalinity producing systems (SAPS), limestone ponds, open limestone channels (OLCs), diversion wells are large vertical tanks filled with grains of limestone, limestone dumping, capillary barriers and permeable reactive barriers. Information regarding passive treatments is furnished by Mission 2017: Global Water Security (MIT, 2015) as follows: ‘Constructed wetlands consist of flooded gravel, soil, and organic matter along with wetland plants’. Aerobic wetlands, consisting of vegetation in shallow, impermeable soil, are used for alkaline mine water. As the water collects, the metals inside are oxidized by the aerated water, and they settle out. Anaerobic wetlands include a layer of limestone in the organic sediment, so they are used with acidic water. ALDs work by allowing anoxic water (water without oxygen) to flow through buried limestone cells. The limestone cells passively produce alkaline bicarbonates that react with the AMD. Successive alkalinity producing systems (SAPS) are a combination of the organic matter found in wetlands and in ALD. Limestone ponds are built over a seep: the seep is covered in limestone, so the water coming out of the seep that fills the limestone pond must pass through (and be neutralized by) the limestone. OLCs are surface ditches lined with limestone. Natural wetlands are the water-saturated soils or sediments whose vegetation is suited to reducing conditions of rhizosphere. Man-made ecosystems are constructed wetlands that were produced to mimic their analog in the nature. As a rule they consist of shallow excavations filled with a flooded gravel, soil, and organic matter to support wetland plants, such as Typha, Juncus, and Scirpus sp. (Skousen et al., 2000). AMD treatment process

30

depends on active biogeochemical interactions as polluted water is moved through the constructed wetland. ALDs are abiotic systems consisting of buried limestone cells that passively produce bicarbonate alkalinity as anoxic water streams through. In Marocco, phosphate carbonated wastes were found their application as a limestone in the drain system (Ouakibi et al., 2014). Successive progress of alkalinity-producing systems consists in combine treatment concepts from both wetlands and anoxic limestone drains. Oxygenated water pre-treatment is implemented by organic substance that removes oxygen and Fe3+, and then the anoxic water flows through an anoxic limestone drain at the base of the system. Ponds built over the upwelling of a seep are limestone ponds, which are filled with limestone for treatment process. OLCs are surface channels or ditches filled that contain limestone. Fe compound precipitation on the limestone surface decreases limestone dissolution from 20 to 50%. There are needed more long channels and more limestone for water treatment (Skousen et al., 2000). Permeable reactive barrier is a technology for the mine drainage treatment within waterbearing horizon (Blowes et al., 2014). These systems must be integrated in the aquifer downstream from the waste disposal (Blowes et al., 2000). The base of permeable reactive barrier is a mixture that could be: 1) Organic carbon in the different forms (composted municipal wastes, wood wastes and by-products from pulp-and-paper manufacturing) (Blowes and Ptacek, 1994; Bennett et al., 1999). The reactive material will contain a bio-available organic carbon substrate and alkalinity source, with coarser materials sometimes added to increase porosity. The structure of organic carbon barriers plays a role of support for the bacterially mediated reduction of sulfate and the precipitation of metal sulfides (Blowes and Ptacek, 1994; Waybrant et al., 1998; Cocos et al., 2002; Waybrant et al., 2002). Sulfate-reducing bacteria activity conduces to organic carbon oxidation in the presence of SO42- (electron acceptor). The end products of this reaction are H2S and inorganic carbon. Released in the solution inorganic carbon promotes to the pH

31

augmentation and precipitation of some metal carbonates (Example: FeCO3, MnCO3) (Waybrant et al., 2002). 2) Zerovalent iron (Puls et al., 1999; Blowes et al., 2000; Morrison et al., 2003; Naftz et al., 2003). 3) Limestone and phosphate-based adsorbent materials (Conca et al., 2003). 4) Red mud (BauxsolTM) as a reactive material (Lapointe et al., 2005, 2006; Fytas, 2010). Column test was applied to simulate groundwater seepage flow through the permeable reactive barrier (Lapointe et al., 2005, 2006; Fytas, 2010). The permeable reactive barrier with the pH 12 – 13 was made from red mud pellets (BauxsolTM). The acid waste effluent (pH 2.2) was taken from the Doyon Mine in Val d’Or (Québec, Canada) to imitate contaminated groundwater flow. Used red mud showed a potential in the pH augmentation and metal removal over a long period during the AMD treatment. At their present period of development, there aren’t the passive systems that can be reliably realized as a single permanent solution for the most AMD problems to meet effluent limits (Skousen et al., 2000), for example (Figure 1.6).

Figure 1.6. Scheme of a mine-waste impoundment with a combined remediation complex (Blowes et al., 2014)

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1.5.2 Active systems Chemical neutralization of AMD is a common approach to dealing with mine wastes containing pyrites. In general, any base will neutralize sulfuric acid (or any acid). Reagents that have been used for neutralization of acidic effluents include lime, limestone, sodium carbonate and sodium hydroxide. In some cases it may be advantageous to use mixtures, e.g. limestone and lime (Wilmoth and Roger, 1974; Wilmoth, 1978; Ritcey, 1989) in order to provide reagent cost reduction over the lime treatment route (Ritcey, 1989). Amendments that have been used for neutralization of acid sulfide mine tailings deposits on include limestone (CaCO3), lime, dolomite or magnesium hydroxide (Mg(OH)2). Active treatment technologies are presented by aeration and neutralization, which often subdivide into metal precipitation, metals removal, chemical precipitation, membrane processes, ion exchange treatment, and biological sulphate removal (INAP, 2014).

1.5.2.1 Aeration Ferrous hydroxides are not so stable as ferric hydroxides when the sludge is exposed to acidic waters or natural precipitation. For this reason, aeration is often applied to oxidise the iron to the ferric iron form that is deposited as a less soluble Fe(OH)3. As usually the principal contaminant is dissolved ferrous iron, a significant aspect of treating AMD is aeration. Only about 9 mg/L of oxygen can dissolve in water (20 ºC), so if the concentration of Fe2+ is more than about 50 mg/L, the water must be oxygenated. Using of aeration even at lower Fe2+ concentrations increases the level of dissolved oxygen and promotes oxidation of iron and manganese, increases chemical treatment efficiency, and decreases financial costs. Aeration can drive off dissolved CO2, which is generally present in mine water coming from underground. This increases the pH and can significantly reduce amount of used reagents (INAP, 2014). Aeration can be used as a pre-treatment or during the treatment. It can be realised by gravity or mechanical aeration/mixing devices application. Venturi-based jet pumps and static mixers (in-line systems) can be a cost-effective alternative due to possibility of neutralizing agent addition in the aeration process. It will increase operational efficiency (Ackman and Kleinmann, 1984, 1991).

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1.5.2.2 Neutralization technologies 1.5.2.2.1 Alkaline neutralization of mine water and acid mine drainage Although many different chemical, biological and electrochemical technologies exist for treatment of tailings containing pyrite, lime neutralisation remains by far the most widely applied treatment method (Johnson and Hallberg, 2005). This is largely due to the high efficiency in removal of dissolved heavy metals (metallic sulfates) combined with the fact that lime costs are low in comparison to alternatives. Table 1.1 shows a variety of alkaline compounds used in AMD treatment (acidic water). Table 1.1. Chemicals for AMD neutralization (Bise, 2013) Name

Chemical formula

Comments

Limestone

CaCO3

Used in anoxic limestone drains and open limestone channels.

Hydrated lime

Ca(OH)2

Cost effective reagent, but requires mixing.

Pebble quick lime

CaO

Very reactive, needs metering equipment.

Soda ash briquettes

Na2CO3

System for remote locations, but expensive.

Caustic soda

NaOH

Very soluble, comes as a solid in drums, beads, or flakes, or as a 20% or 50% liquid. Cheaper in the liquid form.

Ammonia

NH3 or NH4OH

Very reactive and soluble; also purchased as aqua ammonia.

Potassium hydroxide

KOH

Similar to caustic.

Magnesium

Mg(OH)2

Similar to hydrated lime.

Magna lime

MgO

Similar to pebble quicklime.

Calcium peroxide

CaO2

Used as a neutralizer and oxidant; either powder or

hydroxide

briquettes. Kiln dust

CaO, Ca(OH)2

Waste

product

of

limestone

industry.

Active

ingredient is CaO with various amounts of other constituents. Fly ash

34

CaCO3, Ca(OH)2

Neutralization value varies with each product.

All alkaline reagents have their specific characteristics that could be more or less applicable in different mine sites. To make the best choice, technical and economic factors must be estimated together. The technical factors are acidity, flow, drainage composition, preparatory rate and degree of chemical treatment, and required final water quality. The economic factors are prices of chemicals, manpower, transport, analysis, equipment, treatment period, the interest rate, and risk factors (Table 1.2). Table 1.2. Characteristics of chemical compounds used in AMD treatment (Jacobs et al., 2014). Common name

Chemical name

Formula

Conversion

Neutralization

Factor1

Efficiency2 (%)

2010 Cost3 ($ per ton or gallon)

Limestone

Calcium carbonate

CaCO3

1

30

60

Hydrated Lime

Calcium hydroxide

Ca(OH)2

0.74

90

275

Pebble quick lime

Calcium oxide

CaO

0.56

90

355

Soda ash

Sodium carbonate

Na2CO3

1.06

60

840

Caustic soda (solid)

Sodium hydroxide

NaOH

0.8

100

1240

20% Liquid caustic

Sodium hydroxide

NaOH

784

100

0.95

50% Liquid caustic

Sodium hydroxide

NaOH

256

100

2.35

NH3

0.34

100

1000

Ammonia

Anhydrous ammonia

1

The conversion factor may be multiplied by the estimated tons acid/yr to get tons of chemical needed for neutralization per year. For liquid caustic, the conversion factor gives gallons needed for neutralization. 2

Neutralization Efficiency estimates the relative effectiveness of the chemical in neutralizing AMD acidity. For example, if 100 tons of acid/yr was the amount of acid to be neutralized, then it can be estimated that 82 tons of hydrated lime would be needed to neutralize the acidity in the water (100(0.74)/0.90). 3

Price of chemical depends on the quantity being delivered. Liquid caustic prices are for gallons. Others in tons.

Hydrated lime is the most popular neutralizer reagent in AMD treatment. More than 90% of worldwide AMD treatment is realized by hydrated lime. This reagent is produced in the form of powder and exhibits a tendency to hydrophobic properties that leads to necessity of intense mechanical agitation until suspension (Jacobs et al., 2014).

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Pebble quicklime (CaO) has found its application in combination with the Aquafix Water Treatment System (Skousen et al., 1993). The feature of this system is a water wheel concept. Initially, this kind of treatment was used for small quantity of high acid solutions because of high reactive ability of pebble quicklime. Development of water wheel system technology has promoted high flow AMD treatment (Mills and Davis, 2000; Jacobs et al., 2014). Caustic soda (NaOH) can be used commercially in the form of concentrated liquid or water soluble pellets. This reagent finds a use only in remote sites (in the absence of electricity), and in low flow, high acidity situations, especially where long-term AMD treatment may not be necessary or where Mn concentrations are high. Advantages of caustic soda are high solubility in water, rapid dispersion, and fast increasing of the water pH. The dense of chemical is more than water therefore it should be applied at the surface of water body. The disadvantages of caustic soda for coal mine drainage treatment are relatively high cost, potentially dangerous for personal contact and relatively high freezing point. The high freezing point problem could be decided by three methods: KOH addition (35% of the solution), concentration changing from 50 to 20% (from 0 to -37ºC) and solid caustic soda utilisation (Skousen et al., 1996). It is necessary to mark that high concentration of Na is not desirable for the plants. The general application of soda ash (Na2CO3) is only treatment of coal mine drainage in remote areas with low flow and low concentrations of hydrogen and metals ions. Selection of Na2CO3 for AMD treating is usually based on convenience and simplicity of utilization. Soda ash in the form of solid briquettes is gravity fed into water by the use of bins or barrels. The flow rate and quality of the incoming water determine the certain number of briquettes to be used. This system requires less control of the amount of chemical used (Skousen et al., 2000). As in case of NaOH, the relatively high concentrations of Na are dangerous for the plants. Ammonia (NH3 or NH4OH) has been applied in the same cases as caustic soda. But it has several of the significant drawbacks: consequences of excessive application rates, additional protective measures for personnel and environment, potential biological implications (Skousen et al., 2000; Jacobs et al., 2014). NH4OH has less density than water and because of that it should be injected into water flow at the pond entrance (Jacobs et al., 2014).

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Magnesium hydroxide can lead to a lower volume and denser metal hydroxide sludge when it is properly applied in the system of neutralization. Magnesium sulfate, which is more soluble than calcium sulfate, forms in the process and magnesium hydroxide can also remove metals through surface adsorption. Negative moment of this process is the rate of neutralization. It is slow and the buffering capability of magnesium hydroxide prevents the pH from exceeding 9. Magnesium hydroxide can be used in conjunction with NaOH in the requirement case (pH > 9). Mg(OH)2 is popular reagent to employ in treatment plants, such as Canadian Copper Refinery in Montreal east, where the disposal cost of sludge generated is high, in order to reduce sludge disposal costs (Volesky, 1990). 1.5.2.2.2 Lime neutralization processes and high density sludge method Lime neutralization processes consists in the using of lime in the form of quick lime (CaO) or hydrated lime (Ca(OH)2). It is more popular neutralizer agents than other because of their high reactivity and abundance (Kuyucak, 2001; Kuyucak et al., 2001). Metals (e.g., Fe2+, Fe3+, Zn, Cu, Al, and Pb) are precipitated in the form of metal hydroxides during acid neutralization. The resulting mixture of this process ("sludge") contains CaSO4 (gypsum) and metal hydroxides. Lime neutralization facilities can vary greatly in degrees of complexity because of the presence of site depending factors. They range from the elementary operation of lime addition to the tailings pipe lines to plants consisting of reactors, clarifiers, and sludge dewatering equipment as depicted in Figure 1.7 and Figure 1.8.

Figure 1.7. Pond treatment (Aubé and Zinck, 1999)

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Figure 1.8. Conventional treatment plant (Aubé and Zinck, 1999)

The metal contention in the water and the effectiveness of treatment process influence the solid percent of sludge (''sludge density''). Because of that sludge have solids in the range 130 %. To reduce until minimum the formation of big volumes of sludge, the process parameters are set to optimum to obtain denser sludges. The sludge formation depends on the following characteristics: the oxidation rate; the rate of neutralization; the ratio Fe2+:Fe3+; the ion concentrations; aging, recycling of settled sludge; temperature; and crystal formation (Kuyucak, 2006). The current state-of-the-art lime neutralization process treating of AMD and other acidic waters in the works of Aubé and Zinck (1999) is called the "High Density Sludge" process that is capable of producing more compacted sludges than traditional methods of liming. As a rule in the high density sludge process, more than one reactor is used to perform the neutralization. A part of the new produced sludge is recycled from the clarifier underflow to the process and is used along with lime like the alkaline reagent. Fe2+ is oxidized by aeration in the reactors of neutralization. pH must be continuously monitored. The neutralized AMD contained metal precipitates on the next step is flocculated with a polymer and is separated by clarifier/thickener using. The solid content in this sludge is considerably higher (e.g. 10 – 30 %) as contrasted to the case not including sludge recycle. Sludge recycling can be facilitated by either using it alone to partially neutralize AMD or after blending with lime. As practise shows, the site specific and usually multiple step neutralization methods are

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needed for best results in the high strength AMD treatment. It is recommended the pilot tests for determining of design purposes (Kuyucak, 2006). Almost all high density sludge systems lead to decreasing of the SO42- content in the acid water to values lower than theoretical solubility limit of gypsum (i.e., 2000 mg/L CaSO4). It is a condition for gypsum precipitation. White colour crystal particles of the precipitate are visible to naked eye. Further dehydration of sludge can be done by a drum ''vacuum'' filter. It helps decrease the value and increase solids content more than 50%. In the practice of Kristineberg site in Sweden the high density sludge is returned to the mine for conclusive disposal and storing before mixing with tailings. The Falun high density sludge system generates sand-like granulated sludge with 60 – 70 % solids content which is landfilled. The quality of effluent produced in these systems often better than permitted effluent quality objectives (Kuyucak, 2006). Kuyucak (2006) supposed that the tendency of AMD treatment in the mining industry is to use the high density sludge processes or to upgrade the existing treatment systems to the high density sludge production. In addition to the improved characteristics of sludge and purified water, this technology has the cost advantages. Also it economizes the quantity of lime used per unit of water treated. 1.5.2.2.3 Neutralization of acid mine tailing There is a variety of alkaline compounds used in acid tailing treatment. Limestone has largely been used to prevent sulfide oxidation within tailings and consequent acidification (Ritcey, 1989; Ward et al., 2002). Other alkalinity sources may include dolomite (CaMg(CO3)2), quicklime (CaO), hydrated lime, crushed concrete, pulp waste, oyster shells or any other soluble acidity-consuming compounds (Catalan and Yin, 2003; Gillmore, 2011). Alkaline materials applied to surface and depth of mine tailings, or thoroughly mixed in mine tailings, provide alkalinity to infiltrating water. Alkaline materials have to be placed over the long term. As limestone raises the pH of the bulk solution (tailing pore water) and heavy metals are present, precipitation of the metal hydroxides (with extremely low solubilities) is normally accelerated.

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Limestone dissolution results in the production of calcium and bicarbonate alkalinity. In waters of pH ±1000 mV), high concentration of dissolved oxygen, is produced from the anode section. Moreover, electro-activated water with high pH value (10.0 – 11.5), high dissolved hydrogen, and negative oxidation-reduction potential (-800 to -900 mV), is produced from the cathode section (Huang et al., 2008). In the works of Bakhir et al. (Janoschek et al., 1972; Bakhir et al., 1981; Delimarskii, 1982; Bakhir, 1994; Prilutckiy and Bakhir, 1995; Prilutckiy, 1996; Bakhir, 1997; Prilutsky and Bakhir, 1997; Bakhir, 2009), it was assigned some factors that are responsible for the properties of electro-activated solutions: 1) Electrochemical production of alkaline catholyte and acid anolyte: Their concentration is a function of water mineral contention and applying electricity in the process of electro-activation. 2) Extremely active oxidative (for anolyte) and reductive (for catholyte) metastable compounds: Preservation of these compounds leads to gradually transformation of their initial condition to a stable stage. It is a result of some structural energetic and chemical conversions that have spontaneous character. They can play role of catalyzer, initiators and reagents. Thus, these metastable compounds intensify oxidative and reductive properties of electrochemical solutions. 3) Electrically synthesized microbubbles of electrolytic gases (hydrogen, oxygen, etc.): The gas bubble size is in the range from 0.2 to 5 mm. 4) Metastable water structure that is produced: It was determined that catholyte maintains the structural changes and the properties of the electron-donor environment appeared by electric field of high intensity. The relaxation time is up to several dozen hours. It is the same for the anolyte that has the electron-acceptor properties. This factor improves capability of electro-activated solutions to percolate into intermolecular spaces of different substances (also in biological membranes), to stretch out the hydrate cover of separate ions and molecules and on the interface of phases, to increase the solubility, to promote the extraction ability of electro-activated water solutions.

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1.5.3.2 Applications of electro-activated solutions Properties of electro-activated solutions described above characterize their application fields that can be divided to two main groups: oxidative with acid and neutral pH and reductive with alkaline pH. In the early seventies, the Russian engineer Bakhir detected special properties of electroactivated aqueous solutions when he looked for a method of amelioration of drilling agent preparation in the oil industry (Mamadzhanov et al., 1978; Leonov, 1997). The pH of received catholyte was 14. It was detected that the best application of this alkaline solution could be realized in the first 8 – 10 min. Because after this period part of electro-activated solution properties will be lost in the recombination reaction of unbalanced OH- ions (equation 1.33). The object of electro-activated alkaline solution treatment in this work was a clay powder (d < 1 mm) that was mixed with catholyte in the separate tank by machine mixer. The author declared a reagent economy of applied electro-activation method (Mamadzhanov et al., 1978). Subsequent development of discussed method was realized in the direct treatment of clay suspension in the cathode section of electro-activation cell (Mamadzhanov et al., 1982). The property control of directly activated clay drilling agent was also an object of investigation (Bakhir, 1983). The negative oxidation-reduction potential (-800 to -1000 mV) of electro-activated suspension was achieved by the electrode potential in the range from 6 to 100 V. Additional voltage rise was not expedient due to the maximum value of ORP. It was detected that the mixing of electro-treated and untreated clay drilling agent decreases the relaxation time of electro-activated catholyte to 0.5 – 12 hours. This time was also under the influence of the mixing period, volume of untreated drilling agent and applied voltage. High voltage, small volume and short period of mixing gave the highest period of relaxation (Bakhir, 1983). In 1979, Mamadzhanov and Bakhir published the patent of natural gas cleaning from H2S (Mamadzhanov and Bakhir, 1981). The natural gas passed through the cathode section of electro-activator. The hydrogen sulfide was removed in the reaction with catholyte, according to the following equations: H2S + 2Cl- → 2HCl + S

[1.36]

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H2S + 2OH- → 2H2O + S

[1.37]

Alkaline catholyte was applied as closing liquid for the concretes. Contradictory experimental data were published (Ryzhakov et al., 2009, 2010). In the first work, 12% rise of concrete durability was observed when usual water was changed by electro-activated solution in the concrete preparation (Ryzhakov et al., 2009). In the second, the authors stated a fact that there is no significant difference in the property of concrete prepared with electroactivated and untreated water (Ryzhakov et al., 2010). Electro-activated solutions found wide applications in the food industry and medicine (as a disinfectant): 1) antioxidant enzymes activation (Khasanov, 1986; Podkolzin et al., 2001); 2) yeast inactivation (Guillou and El Murr, 2002; Guillou et al., 2003); 3) electrochemical inactivation of bacteria, viruses and bacteriophages (Grahl and Märkl, 1996; Beuchat et al., 2001; Bari et al., 2003; Drees et al., 2003); 4) biofilms prevention/treatment (Kim et al., 2001; Ayebah et al., 2005; Ayebah et al., 2006); 5) inactivation of endospore-forming bacteria and toxins (Rogers et al., 2006); 6) protein extraction (Nabok and Plutahin, 2009); 7) synthesis of lactulose from lactose isomerization (Aït Aissa and Aïder, 2013, 2014b); 8) electro-activation of zebrafish (Danio rerio) eggs (Cardona-Costa et al., 2011); 9) canning of vegetables (Liato et al., 2015); 10) non-invasive extraction of plant proteins (Gerzhova et al., 2015).

1.5.3.3 Application of electro-activated water to acid mine neutralization As was mentioned above, only solution from the cathode section (catholyte) can be used for AMD neutralization because of its alkaline properties. The catholyte can be applied for metal precipitation under neutral and alkaline conditions since many of them lose their solubility at these pH values. The key difference in the AMD treatment (view of chemistry) is unstable condition of electrolyzed water with lapse of time. It is the advantage and disadvantage at the same time. Decreasing catholyte pH to neutral after few days eliminates long-term storage and transport for a long distance (Fabrizio and Cutter, 2003). In turn, simplicity of

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electrolyzer construction enables to produce electro-activated aqueous solutions on-site of contamination. The ability of catholyte to turn into the common water condition, during its relaxation period through the different reactions of metastable compounds, makes this reagent the most ecological. Generation of acid electro-active solutions in the presence of selective ion-exchange membranes has a potential in the controlled solid compound dissolution and thus in the end product extraction (synthesis). Anolyte will be as renewable acid dissolvent for suspended components and as regenerative reagent for the applied ion-exchange membrane (anionexchange membrane). Simplicity of electro-activation cell construction has a big practical significance for the industrial application that decreases production cost, installation costs, manpower requirements and material saving. The problem is just in the geometrical parameters and material selection of the electrodes and membranes. The geometric parameters (form, distance between electrode and membrane, dimensions) must be selected in terms of treated solution (suspension) properties, volume flow and resource of the electric current source. The choice of electrode material is dependent on: 1) electrical conductance, 2) catalytic activity, 3) selectivity to the target chemical reaction(s), 4) strength properties, 5) price, 6) form (maximum of effective surface), 7) chemical inertness (for the anodes) (Aider et al, 2012). The membranes are used to separate the solutions of different sections. They must be possessed of: 1) high selective permeability, 2) high strength properties, 3) low price,

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4) chemical inertness and, 5) low working surface. The important property of electro-activated catholyte solution is the negative oxidationreduction potential that could have a beneficial effect on the vital activity. Many studies have examined the effects of water catholyte on the germination of grains and development of plants (Filonenko and Baykovskaya, 1997; Novobranova et al., 1997). The positive electroactivated aqueous solution can improve vital activity processes. Novobranova et al. (1997) found in a study of irrigation of tomato plants that electro-activated water (catholyte) stimulated shoot length (132%), root length (115%), total length (127%) and plant weight (177%) when compared with the potable water (water without electrolysis). Thereby reductive metastable compounds and high pH value makes catholyte very attractive for acidity correction of artificial wetlands, where wetland biomass may experience chemical shock (Example: emergency blowdown and increasing of acid concentration).

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Chapter 2 : Research hypotheses, significance of the study

objectives

and

2.1 Hypothesis The hypotheses for the study were: 1. Calcium carbonate from chicken eggshell (CES) is cost-effective acid neutralizing. However, CES is less powerful acid neutralization agent than cement or Mg-bearing material such as MgO. 2. Electro-activation method, operated under appropriate conditions, has a high potential to neutralize (alkalize) acid aqueous suspension of CES-amended sulfide mine tailing and to remove heavy metals from aqueous media.

2.2 Objectives The main objectives of this study were: 1. To examine the ability of eggshell alone or in the mixture with alkaline amendments (commercial cement, dolomitic limestone, calcitic limestone and magnesium oxide) to neutralize acidity and to maintain alkaline or neutral conditions within the SMT. 2. To assess the acid buffering capacity of sulfide mine tailing (SMT) samples after their stabilization with CES, commercial concrete cement rich in calcareous products, dolomitic limestone, calcitic limestone and magnesium oxide. 3. The capability of electro-activation cell to produce special conditions for extraction of Fe2+ from Fe rich water without precipitate formation at the membrane or electrode surface. 4. The effectiveness of electro-activation cell under some different geometrical (cathodemembrane distance, active membrane surface, rotation speed of magnetic stirrer), quantitative (mine tailing/water ratio in the cathode compartment, rate of CES in SMT), qualitative (cathode material, nanofiltration membrane, and ion-exchange membrane type) and electric (current intensity, voltage) parameters in increasing pH of CES-amended mine tailing suspensions over 8.

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2.3 Expected results 2.3.1 Hypothesis 1 1. CES should have the same neutralizing effect as calcium carbonate. Application of CES should significantly increase acid sulfide mine tailing pH. 2. Application of cement and Mg-bearing materials should result in considerably higher tailing pH than application of CES. 3. The capacity of CES to neutralize acid SMT or to resist changes in pH could be enhanced by mixing with cement concrete or magnesium oxide. 4. Sulfide mine tailing amended with cement or magnesium oxide is more highly buffered and resistant against anthropogenic re-acidification than SMT amended with chicken eggshell, calcitic limestone or dolomitic limestone.

2.3.2 Hypothesis 2 1. The electro-activation of aqueous FeSO4 using three compartments separated by 2 different ion-exchange membranes should generate acidic solution in the anode and central compartments and an alkaline solution in the cathode compartment, and the recovery of most Fe in a soluble form in the central compartment. Under the effect of electric field, Fe2+ and Fe3+ ions, due to their affinity toward the cathode, pass through the cation-exchange membrane and the concentration of Fe becomes enhanced (enriched). 2. Several geometrical, electric, qualitative and quantitative parameters could promote the electro-activated neutralization (alkalization) of CES-amended mine tailing. These include one or more of the following parameters: time of electro-activation, current intensity, voltage, cathode materials, cathode-membrane distance, mine tailing/water ratio, chicken eggshell rate, rotation speed of magnetic stirrer in the cathode compartment, active membrane surface, nanofiltration membrane, and ion-exchange membrane type.

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3. The pH of catholyte should increase progressively with current, due to electrochemical reduction of H+ ions to elemental hydrogen at the cathode and consequently the production of OH- ions. OH- is a strong base.

2.4 Communications The results of this study were presented at national (Quebec) and international (Bulgaria) conferences for a total of two papers, four posters and one oral presentation. Kastyuchik A., Karam A., Aider M., Jaouich A. 2014. Effectiveness of eggshell residues mixed with alkaline amendments in acid mine drainage remediation. 14th International Multidisciplinary Scientific GeoConference-SGEM 2014. 17 – 26 June 2014, Albena, Bulgaria. Conference Proceedings, ISBN 978-619-7105-16-2. Vol. II, pp. 35 – 41. Published by STEF92 Technology Ltd., Sofia, Bulgaria. Kastyuchik A., Karam A., Aider M., Jaouich A. 2014. Buffering capacity of sulfide mine tailing amended with alkaline materials. 14th International Multidisciplinary Scientific GeoConference-SGEM 2014. 17 – 26 June 2014, Albena, Bulgaria. Conference Proceedings, ISBN 978-619-7105-16-2. Vol. II, pp. 65 – 72. Published by STEF92 Technology Ltd., Sofia, Bulgaria. Kastyuchik A., Aider M., Karam A. 2015. Electro-neutralization of acid aqueous sulfide mine tailing under variable conditions. 4th International Earth Science and Climate Change. June 16-18, 2015. Melia Alicante, Spain. Kastyuchik A., Aider M., Karam A. 2014. Extraction du fer par électro-migration contrôlée avec des membranes échangeuses d’ions. 28e congrès annuel de l’Association Québécoise de Spécialistes en Sciences du Sol : Qualité des sols et productivité des cultures. 26 – 29 mai 2014, Victoriaville, Québec, p. 53. Kastyuchik A., Aider M., Karam A. 2014. Neutralisation de l’Acidité de résidus miniers sulfurés par électrolyse. 18e Colloque annuel du Chapitre Fleuve Saint-Laurent SRASETAC, 5 et 6 juin 2014, Québec, Québec, p. 54.

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2.5 Significance of the study The findings of this study are useful to industry who possess small sizes of land, and have difficulties in managing acidic mine tailings. The findings will also contribute to the existing knowledge on neutralization of acid mine drainage and chemical precipitation of toxic metals. In addition, the information is envisaged to be used by the regional mining field staff and/or managers, government agencies and consulting organizations and tailings & mine waste practitioners in advising industry on how to manage acidic mine tailings.

2.6 Research motivation Research into the use of bio-waste materials such eggshell is of interest both from the environmental standpoint, since it reduces the environmental impact of the material, and from a financial standpoint. The latter is in close connection with the potential cost savings on disposal of those waste materials. Of growing interest in recent years is the use of electroactivation technology in removing or sequestering environmental contaminants.

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Chapter 3 : Effectiveness of chicken eggshell residue mixed with alkaline amendments in acid mine drainage remediation 3.1 Résumé Le drainage minier acide (DMA) généré par la réaction d’oxydation de la pyrite et autres minéraux sulfurés présents dans les résidus miniers est un problème géo-environnemental majeur au Canada. Cette eau est caractérisée par un pH très bas, généralement inférieur à 3,5, et par une concentration élevée de métaux. Le chaulage au moyen d’une chaux calcaire ou dolomitique est une condition requise pour la neutralisation de l’acidité et le maintien des conditions alcalines dans les résidus miniers générateurs d’acide (RMA). La chaux calcique ou dolomitique est un composé de calcium ou de calcium et de magnésium capable de neutraliser les formes d’acidité produites dans le RMA. L'utilisation de bio-déchets et de sous-produits industriels riches en carbonate ou en oxydes et hydroxydes de calcium devient de plus en plus attrayant comme une alternative à la chaux calcique dans la réhabilitation des parcs à résidus miniers acides. Dans la présente étude, nous avons comparé les capacités chaulantes et stabilisatrices de 5 amendements ajoutés à un RMA. Deux séries d'expériences ont été effectuées en laboratoire pour évaluer l'efficacité de résidus de coquilles d'œuf de poule (COP) ajoutés seuls ou en combinaison avec quatre autres agents neutralisants pour : 1) neutraliser l'acidité et prévenir la mobilisation de quelques éléments traces dans un RMA provenant de l’ancienne mine Solbec située à Thetford-Mines (Québec, Canada) et 2) évaluer la capacité tampon (résistance à la ré-acidification anthropique) de quatorze échantillons de RMA après leur stabilisation avec des agents neutralisants. Les traitements étaient les suivants: RMA sans agents de neutralisation; 1, 2, 4, 8 et 10% de COP ajoutés seuls ou en combinaison avec 1 et 2% de ciment riche en produits calcaires (CPC), 1 et 2% d'oxyde de magnésium (MgO), 1 et 2% de chaux dolomitique (DOL) ou 1 et 2% de chaux calcique (CAL); 1, 2, 4, 8 et 10% de CPC); 1 et 2% de CAL; 1 et 2% de DOL; 1 et 2% de MgO.

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L’expérience de neutralisation de l’acidité du résidu minier a été réalisée en mélangeant 10 g d'échantillon de RMA ayant reçu des doses d’amendements alcalins (RMAT) avec 25 mL d'eau bidistillée. Les suspensions de RMAT-eau ont été laissées à l’équilibre pendant 70 jours à la température ambiante avec agitation occasionnelle. Les valeurs de pH de ces suspensions (pHs) ont été mesurées après 1 h, 7 jrs, 14 jrs, 21 jrs, 35 jrs, 56 jrs, et 70 jrs. Les résultats sont présentés ci-après. Après 70 jours d’équilibre, l’application singulière de la dose la plus élevée de COP (i.e. 10%) a augmenté le pHs de 2,61 (témoin) à 7,24. Cependant, lorsque les COP ont été mélangés avec 2% de ciment ou 2% de MgO, les valeurs de pHs ont augmenté considérablement, allant de 7,24 pour le RMA traité avec 10% COP à 8,78 ou 8,54 pour le RMA traité avec 10% COP + 2% ciment ou 10% COP + 2% MgO, respectivement. L'augmentation de pHs était généralement plus importante dans le cas des échantillons de résidus miniers amendés avec du ciment (pH 8,35 à 11,52). Les valeurs de pHs les plus basses ont été obtenues avec les échantillons de résidus miniers amendées avec les COP (7,18 à 7,24). Les échantillons de résidus miniers amendés avec un mélange de COP et de ciment ou de MgO sont plus efficaces à maintenir des conditions alcalines (pHs > 8) dans le résidu minier que les traitements COP + CAL ou COP + DOL, due probablement à la capacité de neutralisation très élevée du ciment et de l’oxyde de magnésium. Les concentrations des éléments métalliques (aluminium, cuivre, fer, manganèse et zinc) dans les suspensions aqueuses de résidus miniers traités avec les amendements alcalins étaient inférieures au seuil de détection par spectrophotométrie d’absorption atomique, sans doute en raison de leur précipitation chimique. Les matériaux de chaulage alternatifs tels que les coquilles d’œufs de poule mélangés avec du ciment et de l'oxyde peuvent être utilisés comme un amendement alcalin pour neutraliser les résidus miniers produisant de l’acide. Cette étude a montré que les échantillons de RMA traités avec du ciment ou de l’oxyde de magnésium sont plus fortement tamponnés et résistants contre la ré-acidification anthropique que les échantillons amendés avec des COP. Ces résultats pourraient avoir des implications pratiques dans la gestion des résidus miniers. Les matériaux riches en MgO ou en oxydes, hydroxydes et carbonates mélangés avec des coquilles d’œufs peuvent conférer aux résidus miniers sulfurés une protection à long terme contre les dépôts atmosphériques acides ou les conditions de ré-acidification.

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3.2 Abstract Acid mine drainage (AMD) generated from pyrite oxidation in sulfide mine tailings is a major geoenvironmental problem in Canada. This AMD is characterized by a low pH, typically below 3.5 and by a high concentration of trace elements. Liming is a prerequisite for sustainable stabilization and neutralization of acid-producing sulfide mine tailings. Limestone is a compound of calcium or calcium and magnesium capable of neutralizing acid compounds in the sulfide mine tailing. Addition of limestone involves the pH change resulting in immobilization of toxic trace elements. The use of agrifood waste and industrial by-products rich calcium carbonate or calcium oxides and hydroxides becomes more and more attractive as an alternative limestone in the remediation of acid mine tailing impoundments. Addition effect of five different types of alkaline amendments into sulfide mine tailing (SMT) was compared. Two series of laboratory experiments were conducted on SMT originated from the Solbec site at Thetford-Mines (Quebec, Canada), to evaluate the use of chicken eggshell residue (CES) alone or in combination with neutralizing agents to neutralize acidity and prevent mobilization of trace elements in SMT. The purpose of the first laboratory experiment was to monitor pH changes of the SMT amended with chicken CES alone or mixed with four alkaline materials, while the second one was to assess the acid buffering capacity of fourteen SMT samples after their stabilization with neutralizing agents. The treatments were as follows: SMT without neutralizing agents; 1, 2, 4, 8 and 10% CES alone or in combination with 1 and 2% cement concrete rich in calcareous products (CCM), 1 and 2% magnesium oxide (MGO), 1 and 2% dolomitic limestone (DOL) or 1 and 2% calcitic limestone (CAL); 1, 2, 4, 8 and 10% CCM; 1 and 2% CAL; 1 and 2% DOL; 1 and 2% MGO. Acid tailing neutralization experiment was carried out by mixing 10 g of treated tailing samples with 25 mL of double distilled water. The tailing suspensions were allowed to equilibrate for 70 d at room temperature with occasional shaking. Tailing suspension pH (pHTS) was measured after 1 h, 7 d, 14 d, 21 d, 35 d, 56 d, and 70 d. Application of the highest

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rate of CES (10%) alone increased pHTS from 2.61 (control) to 7.24 in 70 days. However, when adding 2% of cement or 2% MGO to the CES-amended tailing, pHTS values increased from 7.24 (10% CES) to 8.78 or 8.54, respectively. The increase in pHTS was generally greater for tailing samples receiving CCM alone (pH 8.35 – 11.52). The lowest pHTS was obtained with CES-treated tailings (7.18 – 7.24). CES mixed with CCM or MGO are more efficient in maintaining alkaline conditions (pHTS > 8) in the tailing than CES + CAL or CES + DOL, due probably to the higher neutralizing capacity of magnesium oxide and cement. Two days after the addition of 0.5 ml of 0.05 mol/L sulfuric acid to fourteen amended-tailing samples, the decrease in pH ranged over several orders of magnitude in SMT amended with CES and CAL. In general, the lowest values of pHTS were recorded in SMT amended with 2% and 4% CES (pH 3.3 and 3.5 respectively) and 2% CAL (pH 3.9). The pH TS of all acidified aqueous SMT samples increased gradually over time. Chicken eggshell residue mixed with MgO or cement was considerably more efficient in neutralizing sulfuric acid than CES alone. At the end of the equilibration period (56 days), the pHTS values of aqueous SMT + 2% AM suspensions (solid:liquid ratio of 1:20, w/v) decreased in the following order: SMT + 2% MGO (pHTS 9.0) > SMT + 2% CCM (pHTS 8.6) > SMT + 2% limestone (CAL or DOL) (pHTS 7.3 – 7.5) > SMT + 2% CES (pHTS 7.0). Aluminum, copper, iron, manganese and zinc were not detected in aqueous suspensions of alkaline amended-tailing samples, due probably to their chemical precipitation. Alternative liming materials such as chicken eggshells mixed with cement or magnesium oxide may be used as an alkaline amendment to neutralize acid-producing mine tailings. This study showed that tailing samples amended with cement or magnesium oxide are more highly buffered and resistant against anthropogenic re- acidification than tailing samples amended with CES, CAL or DOL. These results may have practical implications in tailing management for the reduction of acid generation and trace metal mobility in sulfide mine drainage system and of water contamination risk. Materials rich in oxides, hydroxides and carbonates mixed with eggshells may confer to SMT long-term protection against acid atmospheric deposition or re-acidification of limed SMT.

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3.3 Introduction The importance of calcareous materials in supplying carbonates and calcium (Ca) ions to neutralize acidity, and contributing to buffer capacity of geological media (soil, mine tailing) is well recognized. Carbonate anion is a fairly strong base and plays a key role in the pHbuffering of either natural ecosystem (Stumm and Morgan, 1996; Calvet, 2013). Several studies of acid sulfate soils containing pyrite demonstrated that Ca ion was the most important alkaline cation that reacted with acidity (Janjirawuttikul et al., 2011). In agricultural soils, Ca is the most important acid neutralizing element (Bates and Johnston, 1997). Buffering capacity is the ability of soils, surface water or seawater to resist rapid changes of pH when adding acid or base (Donahue et al., 1977; Stumm and Morgan, 1996). Precisely, the buffer capacity (BC) of soils refers to the impact that addition of either acid or alkaline material has on the soil pH (Hill, 2003). In soil system, the amount of liming material required to neutralize soil acidity depends on the neutralizing value of the liming material and pH buffering capacity of the soil (Bolan et al., 2003). Various constituents such as carbonates of basic cations (CaCO3 in calcareous soils), clay, namely phyllosilicates, organic matter, basic cation-containing aluminosilicates, and iron, aluminum and manganese oxides contribute to pH buffering of soils at different pH values (Barrow, 1969; Donahue et al., 1977; McLean, 1982; Kim, 2000; Calvet, 2013). Generally, soils with high clay and/or 2:1 type of clays (smectites, vermiculites, micas, and chlorites), organic matter (OM) or alkaline carbonate (AC) contents exhibit higher BC than those with low clay, OM and AC. Soils with high BC require a greater amount of lime to be added than a soil with a lower BC for the same incremental change in pH. Soil acidity is corrected by the application of liming materials (Edmeades and Ridley, 2003) such as limestone (CaCO3), lime (Ca(OH)2), or dolomite (CaMg (CO3)2) (Goulding and Annis, 1998; Bolan et al., 2003) according to a common soil test (quick) method, namely lime requirement (LR). The LR of an acid soil is the amount of agricultural limestone or any other basic material, required to neutralize that fraction of the total acidity (McLean, 1982) that must be neutralized to attain a desired soil pH that is favorable for crop growth and optimum yield production (Donahue et al., 1977; McLean, 1982). Many chemical methods have been developed and successfully used worldwide to determine LR of acid soils (Van Lierop,

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1990). Soil-buffer equilibration is the most commonly used method for acid mineral and organic soils in Quebec, Canada (Tran and Van Lierop, 1981; Van Lierop and Tran, 1983; Van Lierop, 1990; Ziadi and Tran, 2008). In the laboratory, LR of an acid soil is usually determined by adding certain weight of soil to specified volume of a buffer solution composed of para-nitrophenol, potassium chromate, calcium chloride dehydrate, calcium acetate, and triethanolamine adjusted to pH 7.5 (Shoemaker et al., 1961; Ziadi and Tran, 2008) and noting the reduction in pH of the buffer. From the initial pH of the soil and reduction of pH of the buffer solution, the lime requirement could be calculated using standard tables (Adams and Evans, 1962; Van Lierop, 1990; Ziadi and Tran, 2008). Whether a mine tailing is acidic, neutral, or basic has much to do with the occurrence of minerals producing acidity and alkalinity, the solubility of various compounds, and the buffer capacity (BC) of the tailing which is controlled by the different buffering minerals in mine tailing (Dold, 2014). These factors will ultimately control the quality of coal mine drainage (Caruccio and Geidel, 1978; Jurjevec, 2002). Strong mineral acid (sulfuric acid) in the sulfide mine tailing is normally the result of oxidation and hydrolysis of sulfides (Tucker et al., 1987). Generally, tailings with low BC or acid-neutralizing minerals are more adversely affected by high acidity than tailings with high acid-neutralizing mineral contents. Controlling acid mine drainage (AMD) and neutralization of acid after its formation in tailing is feasible by applying either limestone (Ritcey, 1989) or acid-neutralizing materials (Nehdi and Tariq, 2007). Limestone has often been used in passive systems to neutralize acid mine drainage. A few examples of treated acid coal mine drainage with different types of passive systems using limestone drain (LD) are given in Bernier et al. (2002). A limestone drain typically comprises a trench filled with crushed limestone rocks surrounded by impervious materials. The main purpose of a LD is to generate bicarbonate alkalinity that will increase the pH of pore water emanating from mine tailings water pHTS from acidic conditions to net neutral or alkaline water. In mine waste system, the buffer capacity of tailings is a function of their mineralogical and chemical composition. Laboratory testing and numerical simulation model highlighted the importance of the infiltration rate, the oxygen diffusion rate, the location of acidity production, and the buffering capacity of the engineered cover and tailings material in

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assessing acidity and metals production from cover and tailings profile (Dobchuk et al., 2003). Acid-buffering minerals such as calcite, dolomite, carbonate or bicarbonate in tailings provide high buffering capacity resulting in rapid neutralization of pore and surface water (Ritcey, 1989; Wilkin, 2007). Jurjovec et al. (1995) found that the dissolution of (Ca,Mn,Mg,Fe)CO3, Al(OH)3, and aluminosilicate minerals controls the pHTS of the mine effluent water. The results showed that the buffering capacity of unoxidixed mill-tailings was consumed more rapidly when natrojarosite, an acid-producing reaction, was added to the tailings collected at the Kidd Creek metallurgical site, near Timmins, Ontario. In another study conducted in laboratory on the same tailings, Jurjovec et al. (2004) assessed the acid neutralization reactions in the absence of sulfide oxidation using a fully-saturated laboratory column experiment. The column was packed with fresh unoxidixed tailings and 0.1 M sulfuric acid was passed through the column continuously. Based on mineralogical analysis, the authors concluded that the pHTS of effluent water is buffered by a consistent series of minerals such as ankerite-dolomite, siderite, gibbsite and chlorite, present in the tailings. Caruccio and Geidel (1978) reported that calcium carbonate content of coals and strata containing pyrite has the potential of generating an alkaline, highly buffered, and potentially neutralizing drainage. A study of pHTS buffering capacity of copper-mine tailing containing calcite (CaCO3) amended with a peat-moss and shrimp wastes compost, De Coninck et al. (2008) have shown that calcite mineral collected from the tailing site exhibited much higher buffering capacity than compost, mine tailing and compost-amended tailing. They concluded that carbonate buffer system was the major factor controlling the ability of copper-mine tailing system to withstand a large change in pHTS when acid was added. Unlike copper-mine tailing and carbonaceous tailings, pHTS buffer capacity of sulfide mine tailings (SMT) is low because they lack natural alkalinity, and therefore cannot neutralize acid naturally (Ritcey, 1989). A range of management practices has been proposed to enhance the pHTS of acid SMT or to control and mitigate AMD. Liming material (agricultural limestone) has undoubtedly received most attention, but other options that have been suggested include the application of alternative Ca-containing compounds such as cement concrete, stabilized alkaline byproducts or bio-waste rich in calcium carbonate (Dinel et al., 2000; Casséus and Karam, 2006; Golab et al., 2006; Nehdi and Tariq, 2007).

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Agrifood wastes such as eggshells are a pressing environmental, social and economic issue. Increasing consumption and a developing economy continue to generate large amounts of waste materials (Stanica-Ezeanu et al., 2014). While agrifood waste is viewed as disposable in the past, today it is increasingly recognized as a resource. In the last decades, a variety of wastes was introduced in cement and concrete, including agricultural waste and industrial by-products for reducing landfill (Kanning et al., 2014; Lepadatu et al., 2014). Eggshells and cement concrete are very important source of calcareous materials and their recycling by mine land application will have a positive impact on the preservation of mine drainage quality. Eggs are used by enormous number of food industries and restaurants and the eggshell is discards as waste. Most of the eggshell waste from egg processors and food industries in Quebec are directed to landfills. Eggshells are approximately 95 percent calcium carbonate and 4.5 percent membrane The chemical composition of eggshell (approximately 95% calcium carbonate, 1% magnesium carbonate) as well as the porous nature of eggshell structure (7000 – 17000 pores) (Burley and Vadehra, 1989; William and Owen, 1995) makes it an attractive material to serve as an adsorbent agent (Salman et al., 2012; Karam et al., 2014) or acid-neutralizing agent and chemical precipitation agent (Karam and Jaouich, 2009). Land application may be an alternative method to recycle eggshell wastes. The calcium carbonate in the eggshell would be a substitute for mined minerals that improve tailing acidity and drainage water quality. The main objectives of this study are: (i) to investigate the possibility of utilizing powdered chicken eggshells alone or mixed with four alkaline materials as a liming material on acidic sulfide mine tailing (SMT) and (ii) to assess the acid buffering capacity of SMT samples after their stabilization with chicken eggshell residue, commercial concrete cement rich in calcareous products, dolomitic limestone, calcitic limestone and magnesium oxide. The sensitivity of SMT amended with calcareous materials to pHTS changes is important to know in order to design proper tailing management schemes when these tailings are cultivated or phytoremediated. In addition, buffering capacity is an indication of the limed tailing’s capacity to resist re-acidification by either natural (oxidation of pyrite) or anthropogenic (acid deposition) means. The term re-acidification here refers to the acidification process of a

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tailing pile, after a period of liming. Acid rain of pH 4,5 or lower is common in industrial regions in which SO2 and NO are released by fuel combustion and smelting (Bohn et al., 1985), and may increase the weathering of minerals in tailings with low acid-buffering capacities.

3.4 Materials and methods 3.4.1 Sulfide mine tailing The sulfide mine tailing (SMT) used in the present study originated from the Solbec-Cupra site at Thetford-Mines in the province of Quebec (Canada). It is situated 2 km to the north of Stratford city and 3 km to the east of Aylmer lake (Figure 3.1) (ltee and CRM, 1987).

Figure 3.1. The Solbec-Cupra site (position A)

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The site surface is characterized by the presence of oxidized sulfide tailings which can be occur at a depth of some cm (1-5) until 25 cm. These tailings have a characteristic color from yellow until orange (Figure 3.2); otherwise unoxidized tailings have a grey-blue color (Figure 3.3). For the laboratory analysis and investigations it was taken oxidized sulfide tailings (Karam and Guay, 1994).

Figure 3.2. Oxidized sulfide tailings on the surface of the site (1994)

Figure 3.3. Yellow and grey colored sulfide tailings (Karam and Guay, 1994)

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The original Cu-Zn-Pb ore body, consisting of pyrite, chalcopyrite, sphalerite, galena and pyrrhotite, has predetermined final chemical properties of the tailings. They have a 100 μm median grain-size (appearance of fine sand) and a rate of 20% sulfide and 2 – 5% heavy metals (Marcoux and Grenier, 1990). The main chemical components of this tailing are presented in the Table 3.1. Table 3.1. Chemical composition of the Solbec-Cupra tailing (Karam and Guay, 1994) Element

Concentration (ppm)

Iron (Fe)

>10*

Sulfur (S)

5.75*

Gold (Au)

140**

Iridium (Ir)

9) for tailing samples receiving 2% MGO, 4% CCM, 10% CCM and 10% CES + 2% CCM. In all limed tailing samples maximum decrease in pH of the tailing suspension after 56 days did not exceed 0.33 unit (Table 3.5). On the other hand, it was noted that the values of pHAA-56d of aqueous SMT+ 2% alkaline amendment suspensions (T1, T7, T4, T5 and T6) decreased in the following order: SMT + 2% MGO (pHAA 9.0) > SMT + 2% CCM (pHAA 8.6) > SMT + 2% DOL (pHAA 7.5) > SMT + 2% CAL (pHAA 7.3) > SMT + 2% CES (pHAA 7.0). This result indicates that chicken eggshell residue (CES) mixed with MgO or cement was considerably more efficient in neutralizing sulfuric acid input than low amount (2%) of CES alone. On a weight basis CES possess lower alkalizing power than cement or MgO in terms of its ability to neutralize acid or elevate tailing pHST suspension. Application of the highest rate of CES (10%) was more efficient than the lower rates (Table 3.5) in pH buffering against re-acidification of tailings. The positive correlation between the final pH (pHAA-56d) and both: (i) concentration of Ca (r = 0.64*) and (ii) concentration of Ca + Mg (r = 0.83**) of the aqueous amended-SMT (t = 56 days) provided further evidence the alkaline amendments act as a pool of strongly base ions. Consequently, the limed tailing would become more resistant to re-acidification. This interpretation is supported by De Coninck and Karam (2006) who concluded that

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acidification of flooded tailing (e.g., oxidation of pyrite) is not to be expected if the limed tailing is well buffered over time. Aqueous tailing solution from T3 (10% cement) and T4 (2% MgO) had enough high alkalinity to neutralize anthropogenic acid (Table 3.5), indicating that sulfide mine tailing treated with MgO or cement was stable and well buffered to acidifying input. It is recognized that cement concretes contain highly alkaline pore water (Hong and Glasser, 1999; Shehataa and Thomas, 2008) due to the dissolution of alkalis. Alkali ions such as K+, Na+, Ca2+ and OH- are the most abundant ions in the pore solution (liquid phase) of cement (Chen and Brouwers, 2010). When dry cement is exposed to water, a chemical reaction called hydration takes place releasing strongly alkaline ions (CCI, 2009). In aqueous solution, CaO from cement is converted to Ca(OH)2 : CaO + H2O = Ca(OH)2. The dissociation of Ca2+ and OHions increases the pH of the solution and maintains an alkaline environment. Furthermore, Ca(OH)2 present in cement which is a highly soluble mineral (Lamond and Pielert, 2006) also contributes to neutralize acidic water solution. Like CaO, MgO (from cement or chemical powder) is able to react with water to form Mg(OH)2 : MgO + H2O = Mg(OH)2. The dissociation of Mg2+ and OH- ions increases the pH of the solution and maintains an alkaline environment. However, Ca(OH)2 is more effective at neutralizing tailing water solution than Mg(OH)2 (Figure 3.6). It is known that Ca(OH)2 dissolves in water more than Mg(OH)2. Compared to earth alkaline hydroxides, NaOH was more effective in neutralizing acidic aqueous tailing suspension (Figure 3.6) due to its high solubility. It is known that the solubility of alkalis in water decreases in the following order: NaOH > Ca(OH)2 > Mg(OH)2 (Aphane, 2007). Davison and House (1988) developed a computer model to calculate the final alkalinity of waters at equilibrium with air and solid phase calcite, after neutralization by a sodium or calcium-based product. They found that waters which were initially very acid, and deficient in calcium, could sustain a much higher final alkalinity, a measure of the water's resistance to further supply of acid, if they were neutralized by either sodium hydroxide or sodium carbonate rather than calcium hydroxide or calcium carbonate. They concluded that soft waters acidified by acid rain, and acid mine waters low in calcium, would benefit most from using sodium-based neutralizing agents.

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Figure 3.6. Potentiometric titration curves of acid sulfide mine tailing

Titration of aqueous tailing suspension with 65 ml of 0.001 N NaOH, 158 mL of 0.001 N Ca(OH)2 and 326 mL of 0.001 N Mg(OH)2 raises the pH of aqueous tailing suspension from 3.62 (without alkali addition) to 7.05, 7.06 and 7.01, respectively (Figure 3.6). In all aqueous tailing suspension, consumption of OH- (neutralization of H+) was linearly increased to pH 7 for all alkali reagents, suggesting that alkaline conditions would be achieved more quickly with alkaline amendment supplying a substantial amount of hydroxide ions in solution.

3.6 Conclusions Alternative liming materials such as chicken eggshell mixed with cement and magnesium oxide may be used as an alkaline amendment to neutralize acid-producing mine tailings. Chicken eggshell, cement and MgO have a sufficient lime value. The study showed that sulfide mine tailing treated with magnesium oxide or cement was stable and well buffered to acidifying input. Sources of limed tailing buffering are the amount and nature of the inorganic amendment. The results suggested that magnesium compounds

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and calcareous products rich in hydroxides, oxides and carbonates present in SMT would provide long-term protection against acid deposition. Alkaline material incorporated in the tailing acts as a buffer. Therefore, a limed tailing with a high buffering capacity would resist to anthropogenic acidification. To avoid re-acidification, excess alkaline compounds should be applied. These results may have practical implications in tailing management for the reduction of acid generation and trace metal mobility in sulfide mine drainage system and of water contamination risk.

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Chapter 4 : Electro-activation technology in AMD treatment 4.1 Résumé Le drainage minier acide (DMA) est une préoccupation géo-environnementale majeure car, elle peut dégrader la qualité des eaux de surface en raison de sa forte acidité et de son contenu élevé en acide sulfurique, en fer, en certains métaux et métalloïdes. La neutralisation de l'acidité, l'élimination des sulfates et la précipitation des métaux présents dans le DMA ou les résidus miniers confinés dans le parc à résidus miniers peuvent être réalisées par la méthode d’électro-activation de l’eau dans un réacteur équipé de membranes échangeuses d'ions. La méthode est basée sur le principe d'auto-génération d'acide et de base aux interfaces solutions/électrodes qui crée des conditions propices pour: 1) la neutralisation de l'acidité et la précipitation d’éléments traces métalliques, et 2) la séparation et l'extraction d'éléments chargés tels que le fer (Fe) et le calcium (Ca). Les objectifs principaux de cette étude sont : (i) d’évaluer l'efficacité du processus d'électroactivation pour extraire le Fe d’une solution modèle de FeSO4 en utilisant un électroactivateur à trois compartiments électrolytiques et (ii) de déterminer l'efficacité du procédé d’électro-activation en utilisant deux compartiments électrolytiques en fonction d’une combinaison de deux ou plus de paramètres analytiques pour neutraliser l’acidité et rehausser le pH de la suspension de RMS à des valeurs alcalines (pH 8.0 – 10). Ces paramètres comprennent: le temps d'électro-activation (t), l'intensité du courant (I), le voltage (V), la quantité de coquilles d’œufs de poule (COP) dans le RMS, le rapport RMS/eau (R) dans le compartiment cathodique, la nature du matériel de l’électrode, la distance entre la cathode et la membranes (DC), la distance entre l’anode et la membranes (DA), la vitesse de l’agitateur dans le compartiment cathodique (ω), la surface active de la membrane (SA) et le type de membranes : nanofiltration, échange de cations (MEC) et échange d'anions (MEA) . L'électro-activation de la solution de FeSO4 utilisant trois compartiments a généré des solutions acides dans les compartiments anodique et central. En général, la récupération du Fe dans le compartiment central a augmenté avec l'augmentation de I, t et D. La plus forte concentration de Fe (800 mg/L) dans la solution du compartiment central a été obtenue avec 85

les conditions opératoires suivantes: t = 120 min; I = 150 mA; DA (anode-CEM) = 7 cm; pH = 1,5. L'électro-activation du résidu minier amendé avec COP en utilisant deux unités de cellules électrolytiques a généré une solution alcaline dans le compartiment de la cathode. Le premier essai expérimental a mis en évidence le rôle des paramètres R et I dans l’augmentation du pH de la suspension aqueuse de RMS amendé avec COP jusqu’à l’atteinte d’une solution alcaline (pHcatholyte ˃ 7.8). À la fin du traitement d'électro-activation (t = 60 min), la valeur de pHcatholyte la plus élevée (pH 9,1) a été obtenue avec les conditions suivantes: R = 0,1:1; I = 100 mA et 150 mA. Le deuxième essai expérimental a mis en évidence le rôle des paramètres DC (distance entre la membrane et la cathode) et SA dans l’augmentation du pH de la suspension aqueuse de RMS amendé avec COP jusqu’à l’atteinte d’une solution alcaline (pHcatholyte ˃ 7.8). Les plus fortes valeurs de pHcatholyte (9.5 à 9.6) ont été obtenues avec les conditions suivantes: t = 60 min; RMS amendé avec 10 % COP, DC = 3 cm et SA = 50% (pH 9,6) ou SA = 100 % (pH 9,5). Le troisième essai expérimental a mis en évidence le rôle de la membrane échangeuses d'anions (MEA), la membrane nanofiltration (NFM) et le voltage (V) dans l’augmentation du pH de la suspension aqueuse de RMS amendé avec COP jusqu’à l’atteinte d’une solution alcaline. Les valeurs de pHcatholyte les plus élevées (pH ≥ 7,9) ont été obtenues avec les conditions suivantes: (i) t = 60 min; membrane de nanofiltration + 60V + électrode d’acier inoxydable, de titane ou de cuivre (pH 8,9 à 9,1); (ii) MEA + 15 V, 30 V ou 60 V + électrode d’acier inoxydable, de titane ou de cuivre (pH 7,9 – 10,1). L'absence de Fe et d'autres éléments traces métalliques dans le catholyte démontre l’efficacité de l’électro-activation dans la neutralisation de l’acidité du résidu minier et la précipitation de métaux toxiques dans le compartiment cathodique. Même si cette approche n’a pas été appliquée à l’échelle réelle, l’incorporation de biosolide calcaire dans le résidu minier acide suivi de l’électro-activation de l’effluent peut être une approche économiquement intéressante pour neutraliser les effluents acides car, elle est axée sur les principes du développement durable. 86

4.2 Abstract The acid mine drainage (AMD) production by the sulfide mine tailing (SMT) is a major environmental preoccupation, because it can degrade the water surface quality on account of its strong acidity and its advanced content in sulfide, iron (Fe) and other metals and metalloids. The acid neutralization and precipitation of metals present in the AMD can be carried out by electro-activation with ion-exchange membranes. This method is based on a self-generation principle which produces conditions for: 1) acid neutralization and metal precipitation, 2) separation and extraction of charged elements including Fe and calcium (Ca). The main objectives of this study are: (i) to evaluate the effectiveness of electro-activation cell for extraction of Fe from FeSO4 rich water using three-compartment cell units, (ii) to determine the effectiveness of electro-activation process using two- compartment cell units as a function of a combination of two or more of several parameters to raise the pH of acid CES-amended mine tailing to alkaline range (8.0 – 10). These include: time of electroactivation (t), current intensity (I), voltage (V), cathode materials (CM), cathode-membrane distance (DC), anode-membrane distance (DA), SMT:water ratio (R), CES rate, rotation speed of magnetic stirrer in the cathode compartment (ω), active membrane surface (AS), nanofiltration membrane, cation-exchange membrane (CEM) and anion-exchange membrane (AEM). The electro-activation of FeSO4 solution using three-compartments generated strong acid solutions in anode and central compartments. In general, recovery of Fe in central compartment increased with increasing I, t and D. The highest Fe concentration (800 mg/L) in central solution was recorded with the following conditions: t = 120 min; I = 150 mA; anode-CEM distance = 7 cm; pH = 1.5. The electro-activation of CES-amended SMT using two-electro-activation cell units generated alkaline solution in cathode compartment. The first experimental trial highlighted the role of R and I in raising the pH of CES-amended SMT to alkaline range. At the end of the electro-activation treatment (t = 60 min), the higher pHcatholyte (9.1) values were recorded with the following conditions: R = 0.1:1, and I = 100 and 150 mA. The second experimental 87

trial highlighted the role of DC and AS in raising the pH of CES-amended SMT to alkaline range. The higher pHcatholyte values (9.5 – 9.6) were recorded with the following conditions: t = 60 min, SMT + 10% CES, DC = 3 cm and either 50% AS (pH 9.6) or 100% AS (pH 9.5). The third experimental trial highlighted the role of anion-exchange membrane, nanofiltration membrane and voltage of the electro-activation system (V) in raising the pH of CES-amended SMT to alkaline range. At the end of the electro-activation treatment (t = 60 min), the higher pHcatholyte values (pH ≥ 7.9) were obtained with the following conditions: Nanofiltration membrane + 60V + stainless steel, titanium or copper electrode (pH 8.9 – 9.1); AEM + 15 V, 30V or 60V + stainless steel, titanium or copper electrode (pH 7.9 – 10.1). The absence of Fe and other trace metal ions in the catholyte provide evidence that electroactivation of SMT promotes precipitation of insoluble trace metals in the cathode compartment. While this approach has not been applied in real scale, a combination of pre-treatment SMT applications, where biological calcareous amendments are available, followed by electroactivation of acid effluent may be feasible, cost-effective approach for SMT neutralization as it focuses on sustainable development.

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4.3 Introduction Acid mine drainage (AMD) is a result of sulfur bearing minerals oxidation in the presence of water. This process could be considerably accelerated by bacteria (Thiobacillus ferrooxidans, Thiobacillus thiooxidans) activity. AMD contains high concentrations of heavy metals such as iron (Fe), lead (Pb), nickel (Ni), chromium (Cr), etc... It is a serious hazard to the people and the nature. At the same moment, this drainage is a promising source of dissolved metals. Among the different approaches that could solve the problem of AMD negative influence, electrochemical treatment becomes more and more useful. Broad experience of electrochemical application in the restoration of various industrial wastewaters and polluted soils could be very usable in the case of AMD. As it was discussed in the work of Walsh and Reade (1994), electrochemical technique is not capable to provide a single solution of metal containing solution treatment because of some adverse factors: 1) strong dependence on composition and temperature of treated solutions, 2) joule heating problems (an excessive cell voltage due to resistance increasing), 3) small electrode area (material economy), 4) limited chemical and mechanical stability of cell materials and components (electrode, membrane). At the present time, economical (high prices of recovered materials) and ecological factors simultaneously with new engineering decisions lead to the rise of electrochemical treatment applications despite these problems. This type of treatment could be divided into two general parts: electrodialysis and electrolysis based processes (Kurniawan et al., 2006). Electrolysis is a process that uses the direct electric current to drive otherwise unfavorable chemical reactions. The base of electrolysis is oxidation-reduction reactions near the electrode surfaces. The electrode (anode) could be consumed or inactive. In some cases, positive and negative electrode areas could be separated by the inactive (filtration, porous) membranes or selective ion-exchange membranes that leads to the establishing of special (required) conditions in the controlled sections. The heavy metal ions are derived from the polluted water in the form of metal deposition on the cathode (Britto-Costa and Ruotolo,

89

2014; Leahy and Schwarz, 2014; Mokmeli et al., 2015) or in the form of slightly soluble substances in the bulk solution (Bunce et al., 2001; Chartrand and Bunce, 2003). Metal deposition (plating) of the target element extracted from the solution on the cathode is a very popular practice (Luptakova et al., 2012; Haghighi et al., 2013; Britto-Costa et al., 2014; Leahy and Schwarz, 2014). For example, the part of world copper production by electrowinning was nearly 15% in the middle eighties (Cooper, 1985). Significant number of research works was devoted to this process. Some of them proposed using of Fe sacrificial anode (Shelp et al., 1996). Shelp et al. (1996) evaluated the effectiveness of an electrowinning technique to eliminate negative impact of AMD. The authors used a massive sulfide-graphite rock from Sherman open pit iron mine (Temagami, Ontario, Canada) as the cathode, scrap iron as a sacrificial anode and collected acidic leachate as the electrolyte. The experiments were accompanied by the pH increasing from 3.0 to 5.6 and significant decreasing of redox potential from > 650 to < 300 mV. Iron was precipitated in the form of sulfate with a concomitant decrease of solution concentration for Cd, Al, Co, Cu and Ni. Canadian research group (Bunce et al., 2001; Chartrand and Bunce, 2003) investigated the electrochemical remediation of AMD (synthetic AMD solution) by means of electrolysis with ion-exchange membranes. In their work, Bunce et al. (2001) and Chartrand and Bunce (2003) described electrolytic reduction of solutions of synthetic AMD, comprising FeSO4/H2SO4 and CuSO4/H2SO4, in flow-through cells whose anode and cathode compartments were separated using either cation- or anion-exchange membranes. The effluent pH increased in step with increases in the applied current. Cathodic reduction lowered the acidity of the synthetic AMD, and pH values > 7 were readily achieved. The heavy metals (iron, copper, nickel) were precipitated n the hydroxide forms in the cathode section compartment due to elevated OH- ion levels under produced alkaline conditions in the hydroxide forms. The effectiveness of iron and copper ion removing reached 100%. In case of Ni and Cu, hydroxide precipitation dominated over electrodeposition. Reelectrolysis or chemical precipitation was recommended for nickel. Sparging of electrolysed catholyte was applied to remove the precipitate outside of electrolyzer. Removal of metal was achieved by sparging air or gas into the catholyte effluent, thereby precipitating metal outside the electrochemical cell.The experiments with copper, graphite and carbon cathodes showed 90

similar results (for the iron precipitation) (Chartrand and Bunce, 2003). It was also found that the efficiency of the process (rise of pH and metal precipitation) was higher with anionexchange membrane than with cation-exchange membrane. Cell design, optimization of mass transfer, new materials application was assigned by authors as a necessity in the development of AMD electro-remediation (Bunce et al., 2001; Chartrand and Bunce, 2003). Electrodialysis is also applicable for the wastewater treatment as electrolysis but this method is based on the selective separation of charged dissolved components by ion-exchange membranes under electric current. This method gives an efficiency more than 97% in the purification of recovering water from acid mine drainage (Buzzi et al., 2013). Electrodialysis has one significant limitation in the AMD treatment. It is a precipitate formation at the surface of cation-exchange membrane that leads to the blocking of ion migration through this membrane and to the cell resistance rise (increasing of power inputs) (Buzzi et al., 2013; Marti-Calatayud et al., 2014). Hansen et al. (2007) have shown that three-section electrodialysis cell can mobilize heavy metals from the polluted soils and different mining tailings placed in the central section. The copper was extracted in the greatest extent from the mine tailing with low pH. H2O was more efficient as an extracting solution in comparison with NH4Cl, H2SO4 (Hansen et al., 2007). Another kind of possible electrochemical treatment of AMD could be realized by the electroactivated water technology. As and for electrowinning, electro-activation is based on the electrolysis of activated water (Tanaka et al., 1996a). The distinctive feature of this technology is a water splitting reaction at the electrode surfaces and extremely active oxidative (for anolyte) and reductive (for catholyte) metastable compounds of electroactivated solution. Effectiveness of electrolysis in the AMD neutralization was shown (Bunce et al., 2001; Chartrand and Bunce, 2003). Dominance of water splitting reaction (generation of H+ and OH-) in aggregate with ion flow correction (control) by electro-activator with ionexchange membranes could be more effective in the special condition formations that are necessary for AMD neutralization (high pH) and metal extraction. The main objectives of this study are: (i) to evaluate the effectiveness of electro-activation process for extraction of Fe from FeSO4 rich water using three-compartment cell units, (ii) to determine the effectiveness of electro-activation process using two- compartment cell units 91

as a function of a combination of two or more of several parameters to raise the pH of acid CES-amended mine tailing to alkaline range (8.0 – 10). These include: current intensity (I), voltage (V), electro-activation time (t), amount of CES in SMT, SMT/water ratio, electrode materials, distance between electrodes and ion-exchange membranes, rotation speed of magnetic stirrer in the cathode compartment, type of the membrane materials and active surface area of the ion-exchange membrane.

4.4 Materials and methods 4.4.1 Mining tailing and eggshell The sulfide mine tailing (SMT) used in the present study originated from the Solbec-Cupra site at Thetford-Mines in the province of Quebec (Canada). The main chemical properties of SMT were reported in chapter 3. Applied chicken eggshell (CES) was taken from the market, washed, dried in an oven and then finely ground (< 2 mm). CES was used as tailing amendment in the previous experiment (chapter 3).

4.4.2 Separator membranes The commercial cation-exchange membrane (MK-40), anion-exchange membrane (MA-40) and nanofiltration membrane (N30F) were used as separator in the electro-activation process. The MK-40 and MA-40 membranes were manufactured by Shchekinoazot Ltd. (Shchekino, Russia). These membranes were chosen because of their mechanical and chemical durability and of low price. For example, the lifetime for heterogeneous polymer membranes MK-40 and MA-40 in the water desalination units was limited by 5 years. The features of membrane composites are represented in Tables 4.1 and 4.2.

92

Table 4.1. Composites of ion-exchange membranes MK-40 and MA-40 (Saldadze et al., 1960; Dyomina et al., 2002; Berezina et al., 2008). Membrane Membrane type MK-40

Ionogenic group

Application

Composites formed from the cation- -SO3-

Electrodialysis

exchange resins KU-2 (polystyrene

separation

(PS)

processes, water

matrix

cross-linked

with

divinylbenzene (DVB) and fixed

desalination

groups), polyethylene and nylon MA-40

Composites on the base of resin EDE- ≡N =NH

Electrodialysis

10P produced via condensation of -N+(CH3)3

separation

diamine

processes, water

with

epichlorhydrine, (20%)

polyethylene and nylon

desalination

Using of membrane materials with additional pre-testing treatment is required because of their contamination with various organic substances. This contamination provokes unstable conditions in the target processes. The pre-testing treatment of membranes is a step-by-step procedure. The heterogeneous polymer membranes were first treated with ethanol for 6 h to extract the monomer residues and surfactant inclusions that usually attend in the material after the synthesis. Then the membranes were treated with the solutions of NaCl (saturated solution, 100 g/L and 30 g/L) (Saldadze et al., 1960). The treatment time in every NaCl solution was 24 h. At the end, the membranes were conditioned by distilled water during 48 h.

93

Table 4.2. Manufacturer characteristics of ion-exchange membranes (Pokonova, 2007; Shekino-AZOT, 2015) Parameter

Units

МК-40

MA-40

Static exchange capacity

mg-eq/g

2.6 ± 0.3

3.8 ± 0,4

Transport numbers of ions

dimensionless

0.98

0.94

Resistivity

ohm·cm

< 220

< 240

Thickness swelling

%

30 ± 5

30 ± 5

Lenght swelling

%

8±2

8±2

Dimension

cm

142 × 45

142 × 45

Rupture strength

kg/cm2

> 130

> 130

The commercial flat sheet nanofiltration membrane, NADIR® N30F, was purchased from NADIR

Filtration

GmbH

(Wiesbaden,

Germany).

A

permanently

hydrophilic

polyethersulfone-polyvinylpromidone copolymer on the polypropylene support was utilized as a material for the selective layer production of this composite membrane (Ernst et al., 2000). The general characteristics of nanofiltration membrane are summarized as follows: Test conditions: 40 bar, 20 °C, stirred cell (700 rpm); material of separating layer: hydrophobic; pure water flux (1/m2 h): 40 – 70; MWCO (DA): 400; NaCl rejection (0.5%): 25 – 35; Na2SO4 rejection (1.0%): 85 – 95; pH range: 0 – 14; maximum temperature: 95°C.

4.5 Methodology 4.5.1 Removal of Fe(II) from aqueous FeSO4 solution by electroactivation process The main objective of this experiment is to evaluate the efficiency of the electro-activation process for the removal of dissolved Fe from aqueous FeSO4 solution as a function of some electrochemical conditions such as current intensity, electro-activation time and distance between the cation-exchange membrane and the electrode of the anodic compartment. AMD solutions are Fe rich because ferric and ferrous iron are very soluble at low pH (< 2.5) (Baker and Banfield, 2003). Ferrous sulfate heptahydrate (FeSO4·7H2O) was used as a source of iron

94

in form of Fe(II) to simulate acidic Fe-rich mine water. Iron occurs in most coal mine drainage waters predominantly as the soluble Fe2+ ion (Stauffer and Lovell, 1968). The experimental electro-activator (Figure 4.1) was composed of a cathode and anode compartments separated by a central compartment. The purpose of using three-compartment cell units is to remove most total Fe from the anodic compartment and to recover it at the central compartment. This method is attractive because the removal of Fe from the anolyte to the central compartment can be done without the need for chemical extractant, special equipment and complex operation and the acidic anolyte can be neutralized, leaving no secondary pollution. Two plates that function as the anode and the cathode electrodes are positioned respectively in the anode and cathode compartments (Figure 4.2). Electrode material used for both anode and cathode was made of titanium coated with a rutheniumiridium layer (Qixin Titanium Co., Ltd., Baoji, China). The central compartment was separated from the anode compartment by a cation-exchange membrane MK-40 (CEM) with an active area of 30 cm2 (Figure 4.3) allowing for cation passage and from the cathode compartment by an anion-exchange membrane MA-40 (AEM) with an active area of 30 cm2 (Figure 4.3) allowing for anion passage. This kind of membrane configuration makes possible selective transfer of metal cations from the anode compartment to central compartment, where further migration will be blocked by the AEM because of its specific permeability for the negative charged ions. The main roles of CEM placed between the anode and AEM (Figures 4.1 and 4.4) are: (i) to prevent anions such as hydroxyl (OH-) generated initially in the cathode compartment as well as chloride (Cl-) present in the central compartment to migrate towards anode compartment (Figure 4.1) and (ii) to allow total Fe (Fe3+ generated by oxidation of Fe2+ and remaining Fe2+) present in anolyte to pass through the membrane, resulting in accumulation of soluble Fe ions in the central compartment. The experimental set-up of the reactor is illustrated in Figure 4.4.

95

Figure 4.1. The schematic diagram of electro-activation cell units

Figure 4.2. Plates that function as the anode and the cathode electrodes

96

Figure 4.3. Cation- and anion-exchange membranes

Figure 4.4. The experimental set-up of the reactor

97

The anode compartment is filled with aqueous FeSO4 solution (200 mL) containing 1000 mg/L of Fe2+ and the supporting electrolyte solution (120 mL of 0.1 and 0.01 M NaCl) was placed in the cathode and central compartments. The concentration of Fe(II) was selected to represent moderate Fe concentration in AMD. Concentration higher than 1000 mg Fe(II)/L has been found in extremely acid mine water (pH < 4.0) from numerous mines. Nordstrom and Alpers (1999) found Fe(II) concentrations up to 9790 mg/L at pH 3.6 and up to 79700 mg/L at pH 0.7 in extremely acid mine water from the Richmond Mine (California). The electrode compartment was made from the different number of constituent parts with the length 1and 3 cm (Figure 4.4) in order to dispose the CEM at three distances from the electrode surface (DA). These are 3, 5 and 7 cm and noted as DA3, DA5 and DA7. The length of both central and cathode compartments was kept constant, 3 cm. The two electrodes were connected externally using a conductive copper wire. The current intensities (I) applied were 50, 100, 150, 200 and 250 mA and noted as I1, I2, I3, I4 and I5. The electro-activation times (t) were 30, 60, 75, 90, 105 and 120 minutes. Experimental treatments were replicated thrice. All the chemicals used were of analytical grade. Ferrous sulfate solution was prepared by dissolving FeSO4·7H2O in double distilled water. The commercial CEM and AEM (MK-40 and MA-40, respectively) were subjected to pre-testing treatment in order to eliminate organic contaminants which provoke unstable conditions in the target processes. At the end of each t and I conditions, the pH values of solutions (anolyte and central solution) were measured using a digital pH meter (Omega PHB-62, OMEGA Technologies Company, Stamford, Connecticut, USA) and an Orion double junction electrode (Orion GD9106BNWP, Thermo Scientific, Beverly, Massachusetts, USA). The concentrations of Fe(II) and Fe(III) (after reduction of Fe(III) with hydroxylamine chlorhydrate) were determined by the o-phenanthroline colorimetric method (Tamura et al., 1974), using Spectronic 20D (Milton Roy Company, Rochester, New York, USA) and a molar absorption coefficient for the Fe(II)–phenanthroline complex of 1.100 x 104 M-1 cm-1 at 510 nm. Total Fe in the anolyte and central solutions was also determined by atomic absorption spectroscopy (AAnalyst 200, Perkin Elmer, Shelton, Connecticut, USA). The results were analyzed statistically using the SAS computer package (SAS, 2008).

98

X-ray diffraction (XRD) and elemental analysis using SEM-EDX (scanning electron microscopy-energy-dispersive X-ray spectroscopy) were used to detect any precipitate that could form on the membrane surfaces. This analysis was realized by scanning electron microscope JEOL (Japan Electro Optic Laboratory, model JSM840A, Peabody, Massachusetts, USA) equipped with an energy dispersive spectrometer (EDS) (Princeton Gamma Tech., Princeton, New Jersey, USA). The experimental conditions for EDS were 15 kV accelerating voltage and a 13-mm working distance. The membrane samples were dried and coated by a thin film of gold/palladium in order to impart them electrically conductivity and to ameliorate the microscopy photograph quality. The membrane sample preparation was the same for SEM and for XRD (Cifuentes-Araya et al., 2011; Aït Aissa and Aïder, 2014a).

4.5.2 Neutralization of acid aqueous sulfide mine tailing and precipitation of toxic metals using electro-activation process Three series of experiments were carried out to assess the effectiveness of electro-activation cell units composed by two compartments, anode and cathode, separated by one or more type of ion-exchange membrane, under different electric (intensity current, voltage), geometrical (anode-membrane distance, active membrane surface, rotation speed of magnetic stirrer in the cathode compartment), quantitative (rate of chicken eggshells in SMT and SMT/water ratio in the cathode compartment), qualitative (cathode material and membrane type) parameters in the pH rise of eggshell-amended mine tailing placed in the cathode compartment.

4.5.2.1 Experiment 1: Electroneutralization of acid sulfide mine tailing under variable electro-activation conditions including the amount of solid tailing to be treated The aim of this experiment is to find out the effect of the quantity of SMT to be treated (e.g. SMT/water ratio in the cathode compartment) (R), current intensity (I), rotation speed of magnetic stirrer in the cathode compartment (ω) and electro-activation time (t) on the effectiveness of electroneutralization of aqueous acid SMT. Electro-activation with anion-exchange membrane (AEM) was used to raise the pH of aqueous suspensions of SMT to a range of 9.0 – 10.0. At this pH range, most toxic metals

99

become insoluble and precipitate. The investigation was carried out in two-compartment electro-activation cell units divided with AEM and equipped with titanium electrodes (Figure 4.5).

Figure 4.5. Schematic representation of the two-compartment cell units

The main roles of AEM (Figure 4.5) are: 1) reduction of hydrogen (H+) ions on the cathode surface; 2) blocking H+ ion transport from the anode to cathode compartment through the AEM; 3) neutralization reactions in the cathode compartment; 4) dominance of SO42transport into the AEM if compared to OH-. The anode compartment was fed with a solution containing 90 mL of 0.005 M K2SO4. The cathode compartment is filled with 150 mL of distilled water containing different quantity of SMT. By setting Dc (i.e. distance between the cathode and AEM) to 5 cm, the volume of distilled water in the cathode compartment remains constant (e.g. 150 mL), regardless of the 100

quantity of SMT to be treated in the cathode compartment. Electro-activation parameters are listed in Table 4.3. After given interval of time, the pH values of the solution in the cathode compartment were measured potentiometrically and samples were taken from catholyte to determine the concentrations of Al, Ca, Cu, Fe, Mn, Mg and Zn by atomic absorption spectroscopy (AAnalyst 200, Perkin Elmer, Shelton, CT). Table 4.3. Experimental parameters studied in experiment 1. Parameter

Conditions

Current intensity (I)

50, 100 and 150 mA

Rotation speed of magnetic stirrer in the cathode 150, 300 and 450 rpm compartment (ω) Mine tailing/ water ratio (R) in the cathode compartment

R1= 0.1:1 (w/v) R2 = 0.2:1 (w/v) R3 = 0.3:1 (w/v)

Rate of chicken eggshells (CES) in the mine tailing

0%

Cathode-membrane distance(DC)

5 cm

Anode-membrane distance (DA)

3 cm

Voltage (V)

Galvanostatic process

Cathode and anode material

Titanium

Ion-exchange membrane type

Anionic (AEM)

Active membrane surface (AS)

100%

Surface area of the membrane

30 cm2

Electro-activation time (t)

10, 20, 30, 40, 50 and 60 min

4.5.2.2 Experiment 2: Electroneutralization of acid aqueous sulfide mine tailing previously treated with 0, 4 and 10% chicken eggshell (CES) under variable electro-activation conditions Electro-activation with anion-exchange membrane (AEM) was used to raise the pH of aqueous suspensions of SMT previously treated with 0, 4 and 10% chicken eggshell (CES) to a range of 9.0 – 10.0.

101

The investigation was carried out in two-compartment electro-activator divided with AEM and equipped with titanium electrodes (Figure 4.5). The ratio of SMT:distilled water in the cathode compartment was 0.2:1 (w/v). The evolution of initial pH values of aqueous SMT (pH = 3.2), SMT + 4% CES (pH = 4.3) and SMT + 10% CES (pH = 5.4) in catholyte (pHcatholyte) were examined as a function of: (i) the cathode distance from the AEM (D) and (ii) the active membrane surface (AS). The anode compartment was fed with a solution containing 90 mL of 0.005 M K2SO4. The electro-activation cell was operated at 50 mA for 60 minutes. Electro-activation parameters are listed in Table 4.4. After given interval of time, the pH values of the solution in the cathode compartment were measured potentiometrically and samples were taken from catholyte to determine the concentrations of Al, Ca, Cu, Fe, Mn, Mg and Zn by atomic absorption spectroscopy (AAnalyst 200, Perkin Elmer, Shelton, CT), and S by ICP.

102

Table 4.4. Experimental parameters studied in experiment 2. Parameters

Conditions

Current intensity (I)

50 mA

Rotation speed of magnetic stirrer in the cathode 300 rpm compartment (ω) Mine tailing/ water ratio (R) in the cathode compartment

0.2:1 (w/v)

Rate of chicken eggshells (CES) in the mine tailing

0, 4 and 10%

Cathode-membrane distance (DC)

DC1= 3 cm DC2= 4 cm DC3= 5 cm

Anode-membrane distance (DA)

3 cm

Voltage (V)

Galvanostatic process

Cathode and anode material

Titanium

Ion-exchange membrane type

Anionic (AEM)

Active membrane surface (AS)

25, 50 and 100%

Surface area of the membrane

30 cm2

Electro-activation time (t)

10, 20, 30, 40, 50 and 60 min

4.5.2.3 Experiment 3: Electroneutralization of acid aqueous sulfide mine tailing previously treated with 4% chicken eggshell residue under variable cathodes and membrane type conditions Different concentrations and geometric parameters were investigated in the first and second experiments. Their contribution to the electroneutralization of aqueous acid SMT treated with CES was highlighted. The effectiveness of electroneutralization of aqueous acid SMT previously treated with 4% CES and trace metal precipitation was studied as a function of voltage, cathode materials, three types of ion-exchange membrane, and electro-activation time. The investigation was carried out using three electro-activation reactors composed of a cathode and anode compartments divided respectively with AEM (Figure 4.5), CEM (Figure

103

4.6 (a)) or NFM (Figure 4.6 (b)). The distance between the membranes and the cathode was kept at 4 cm. For the electro-activator with CEM as a separator of the two compartments, theoretical possible ways of OH- ions accumulation in the cathode section compartment are: 1) reduction of hydrogen ions on the cathode surface; 2) neutralization reaction of hydroxyl and hydrogen ions in the cathode section; 3) blocking of OH- transport from the cathode to anode section through the CEM. The ratio of SMT:distilled water in the cathode compartment was 0.2:1 (w/v). The anode compartment was fed with a solution containing 90 mL of 0.005 M K2SO4. Electro-activation parameters are listed in Table 4.5. After given interval of time, the pH values of the solution in the cathode compartment were measured potentiometrically and samples were taken from catholyte to determine the concentrations of Al, Ca, Cu, Fe, Mn, Mg and Zn by atomic absorption spectroscopy (AAnalyst 200, Perkin Elmer, Shelton, CT), and S by ICP.

104

Figure 4.6. Schematic representation of the two-compartment cell units using CEM (a) and NFM (b)

105

Table 4.5. Experimental parameters studied in experiment 3. Parameters

Conditions

Current intensity (I)

Controlled potential process

Rotation speed of magnetic stirrer in the cathode 300 rpm compartment (ω) Mine tailing/ water ratio (R) in the cathode compartment 0.2:1 (w/v) Rate of chicken eggshells in the mine tailing

4%

Type of membranes

Cationic

(CEM),

anionic

(AEM) Active membrane surface (SA)

and nanofiltration (NFM)

Surface area of the membranes

50%

Cathode-membrane distance(DC)

30 cm2

Anode-membrane distance (DA)

DC = 4 cm DA = 3 cm

Voltage (V)

15, 30 and 60 V

Cathode materials

Titanium, stainless steel, copper

Anode material

Titanium

Electro-activation time (t)

10, 20, 30, 40, 50 and 60 min

4.6 Results and discussion 4.6.1 Removal of Fe(II) from aqueous FeSO4 solution by electroactivation process It is known that the electrolysis reactions cause an acidic solution to be generated near the anode and an alkaline solution near the cathode (Flores et al., 2012). There are a large number of studies dealing with the recovery of metallic iron or an iron-rich alloy, oxygen and sulfuric acid from iron-rich metal sulfate wastes using electrochemical process. In general, electrolyzing the iron-rich metal sulfate solution in conventional two-compartment cell units using a separator allowing for anion passage causes iron to be electrodeposited at the cathode, nascent oxygen gas to evolve at the anode, sulfuric acid to accumulate in the anodic compartment and an iron depleted solution to be produced (Cardarelli, 2011). 106

Most of the data presented here are from two compartments of the electro-activation cell. As expected, the electro-activation reactions of aqueous FeSO4 generated acidic solutions in the anode and central compartments and an alkaline solution in the cathode compartment (section 4.4.1.1), and the recovery of Fe in a soluble form in the anodic compartment (section 4.4.1.2).

4.6.1.1 Evolution of pH of electrolyte solutions All treatments significantly influenced the pH values of anolyte (anode compartment) and electrolyte solution in the central compartment (Table 4.6). Table 4.6. Analysis of variance on the influence of current intensity and anode-CEM distance on the pH values of anolyte and electrolyte solution in central compartment at t = 120 minutes. Source of variation Model Repetition Anode-CEM distance (A) Current intensity (B) AxB Error A Linear Quadratic Cubic B Linear Quadratic Cubic

d.f. 16 2 2

pH central 150.41*** 1.64 316.34***

pH anolyte 218.65*** 0.59 397.83***

4 8 28

393.95*** 24.35***

332.44*** 171.48***

1 1 0

15.79*** 86.27*** -

20.90*** 0.13 -

1 1 1

249.37*** 2.01 1.77

22.28*** 11.40** 1.47

*, **, *** significant at the 0.05, 0.01 and 0.001 level of probability, respectively.

As shown in Figure 4.7, the pH values of FeSO4 solution in the anode compartment (i.e. anolyte) and those of electrolyte solution in the central compartment decreased with I and DA and t. There is an inverse relationship between the current I and the values of pH of anolyte and central solution. In general, at each electro-activation time, the pH values (Figure 4.7) decreased in the following order: I5 (250 mA) ˂ I4 ˂ I3 ˂ I2 ˂ I1 (50 mA). This finding indicates that the electric current gradually lower the pH with increasing electro-activation

107

time, confirming that electro-activation of FeSO4 generates acidity at the anode and central compartments.

(A)

(B)

DA = 3 cm

4.0

DA = 3 cm 5

central solution

3.0

2.5

4

3

pH

pH anolyte

3.5

2 2.0 1 0

20

40

4.0

60

80

100

120

0

20

40

60

80

Time, min

Time, min

DA = 5 cm

DA = 5 cm

100

120

100

120

100

120

5

central solution

pH anolyte

3.5

3.0

3

pH

2.5

4

2 2.0 1 0

20

40

60

80

100

120

0

20

40

Time, min

D = 7 cm

4.0

80

D = 7 cm

4.0

A

A

3.5

pH anolyte

3.5

pH anolyte

60

Time, min

3.0

2.5

3.0

2.5

2.0

2.0 0

20

40

60

80

Time, min

100

120

0

20

40

60

80

Time, min

Figure 4.7. Evolution of pH of solution in the anode (A) and central (B) compartments as a function of electro-activation time

108

These results can be explained by the oxidation of water occurred on the anode surface. As the electrolysis performs, oxidation of water is occurring at the anode according to the reaction shown in the equation 1.35 (2H2O(l) → O2(g) + 4H+(aq) + 4e-). In general, the reaction was more intense when the electric current was higher. The pH values of the central solution are lower (i.e. more acidic) than those of the anolyte, regardless of DA values (Figure 4.7). This result could be attributable to three possible causes, including (i) the continual generation of H+ ions at the anode, (ii) the high mobility of a large amount of H+ ions from the anode to central compartment through the CEM and (iii) the characteristic of the CEM which contain 65% of cation-exchange resin and 35% of polyethylene. It is recognized that a part of H+ ions produced at the anode during the electro-activation migrate to the central compartment through the CEM where they are blocked by the AEM and consequently do not reach the cathode compartment. Thus, the presence of protons (H3O+) in central compartments at high concentration contributes to considerably lower the pH of electrolyte solution. On the other hand, it was found that the H+ ion has a great mobility in the electrolyte solutions and cation-exchange resins. Zundel (1969) explained this phenomenon by the presence of proton conduction in both cation-exchange resin and electrolyte solution. Water is a good conductor of protons, because of the H-bonded networks between water molecules. Thus the proton conduction is carried out through the proton transfer from one water molecule to another. This process is due to a high polarization of hydrogen bond in the H5O2+ group and a proton tunnel junction from one bond to another (Zundel, 1969). It is known that in aqueous solutions of acids, the proton exists as hydronium ion, which is itself hydrated, e.g., as H5O2+ (Wicke et al. (1954) and Zundel (1969), cited by Garczarek et al. (2005) and Choi et al. (2005), respectively). Acid-water hydrogen bonds with proton polarizability are of large significance for the dissociation process of acids. The mobility of the proton is abnormally high as compared with other ions of a size similar to hydronium ion, and is explained in terms of contribution by the so-called Grotthuss mechanism, in which the transport of protons is determined by the rate at which the hydrogen bond between a hydronium ion and a water molecule forms rather than by the slower rate at which hydronium ions may migrate en masse (Choi et al., 2005). 109

4.6.1.2 Concentration of Fe in anolyte and central solution Analysis of variance (ANOVA) revealed a very highly significant effect (P < 0.001) of I and DA on the concentration of Fe as a function of electro-activation time (Table 4.7). Table 4.7. ANOVA results (F-value) on concentration of total Fe in central and anolyte compartments at two electro-activation times. [Fe] in central compartment [Fe] in anolyte Source of variation

d.f. T= 60 min

T= 120 min

T= 60 min T= 120 min

Model Repetition Distance (A) Current intensity (B) AxB Error A Linear Quadratic Cubic B Linear Quadratic Cubic

16 2 2 4 8 28

3543.85*** 0.08 9380.75*** 4560.47*** 2462.26***

2918.59*** 0.08 15094.0*** 1797.14*** 1165.09***

247.60*** 2.91 850.70*** 308.25*** 127.67***

478.78*** 3.06 1449.98*** 409.11*** 389.74***

1 1 0

28.23*** 6.96* -

115.73*** 1.75 -

56.94*** 2.83 -

31.64*** 2.46 -

1 1 1

18.31*** 10.34** 5.56*

0.76 26.58*** 0.01

28.38*** 8.19** 6.61*

4.49* 13.27*** 1.48

*, **, *** significant at the 0.05, 0.01 and 0.001 level of probability, respectively.

Changes in total Fe and Fe2+ ion concentrations in the anode and central compartments are illustrated in Figures 4.8 and 4.9, respectively.

110

DA = 3 cm

[Fe total ] in anolyte, mg/L

1000

800

600

400

200 0

20

40

60

80

100

120

100

120

100

120

Time, min

DA = 5 cm

[Fe total ] in anolyte, mg/L

1000

800

600

400

200 0

20

40

60

80

Time, min

DA = 7 cm

[Fe total ] in anolyte, mg/L

1000 900 800 700 600 500 400 0

20

40

60

80

Time, min

Figure 4.8. Evolution of Fetotal concentration in the anolyte as a function of electro-activation time

111

, mg/L

DA = 3 cm

40 35

2+

[Fe ] in central solution

30 25 20 15 10 5 0 0

20

40

60

80

100

120

100

120

100

120

, mg/L

Time, min

DA = 5 cm

500

300

200

100

2+

[Fe ] in central solution

400

0 0

20

40

60

80

Time, min DA = 7 cm

2+

[Fe ] in central solution

, mg/L

900 800 700 600 500 400 300 200 100 0 0

20

40

60

80

Time, min

Figure 4.9. Evolution of Fe2+ concentration in the central solution as a function of electroactivation time

112

The concentration of Fe in anolyte decreased gradually with time for all I and DA values (Figure 4.8). At the same time the concentration of Fe(II) in the electrolyte solution of the central compartment increased gradually with t, I and DA (Figure 4.9). This result would be attributable to two processes: (i) depletion of Fe2+ in the anode compartment due to oxidation of Fe2+ to Fe3+ and (ii) migration of Fe2+ ion through the CEM to the central compartment. Iron concentration curves differed considerably among I treatments throughout the entire range of electro-activation times. As shown in Figure 4.9, Fe 2+ recovery was the highest under highest I. Recovery was also significantly different among D A treatments throughout the entire range of electro-activation times (Table 4.7). Fe2+ recovery was highest under highest D value. The effect of I on Fe recovery was linear at t = 60 min but curvilinear at t = 120 min (Table 4.7). The lowest Fe2+ concentration (478 mg/L) in central solution was recorded with the following conditions: t = 120 min; I = 200 mA; anode-CEM distance = 5 cm; pH = 1.8. The highest Fe concentration (800 mg/L) in central solution was recorded with the following conditions: t = 120 min; I = 150 mA; anode-CEM distance = 7 cm; pH = 1.5. It is advisable to mention that a part of soluble Fe could precipitate at the interface CEM/anolyte in the anode compartment (Figure 4.10), as Fe(OH)3 (Figure 4.11), blocking the transfer of Fe2+ from the anode to the central compartment.

113

(A)

A (B)

B

A

Figure 4.10. Precipitation of Fe(OH)3 on the CEM from the anode side. (A): Anode-CEM distance = 3 cm and I = 150 mA; (B): Anode-CEM distance = 5 cm, I=250 mA and t=120 minutes

114

(A)

(B)

Figure 4.11. Scanning electron microscope image of two zones: A and B (Fe(OH)3 – light crystals)

The qualitative composition of the precipitate was examined by energy-dispersive X-ray spectroscopy. The grey colored zone (Figure 4.11) has well-defined peaks of S, O, C and Fe (Figure 4.12). The first three elements characterise the ionogenic group –SO3- and polymer matrix of the CEM. The Fe peak is identified as adsorbed Fe2+ ions. The analysis of white 115

crystal (Figure 4.11) shows predominance and pronounced Fe and O peaks (Figure 4.13), demonstrating the presence of iron hydroxide.

Figure 4.12. EDS spectrum of the grey colored zone (Figure 4.11)

Figure 4.13. EDS spectrum of white crystal (Figure 4.11)

116

The formation of Fe(OH)3 is based on the duality I and DA. A high voltage or very high current intensity promotes the precipitation of Fe in a short period of time. Indeed, precipitates were observed at I values > 50 mA and DA = 3 cm. However, at higher DA value (5 or 7 cm), a precipitate was observed at I ˃ 200mA. Precipitate was highest under highest DA value. In a preliminary test, it has been observed that when we applied a very high voltage (126V), the values of I increased from 700 mA to approximately 2600 mA after 6 minutes of electroactivation process, and the surface of CEM (anode side) became black- brown as a result of precipitation of the total amount of Fe (1000 mg/L) and its deposition on the membrane (Figure 4.14).

Figure 4.14. Precipitation of Fe on CEM (anode side) surface under the following conditions: Anode-CEM distance = 5 cm, V = 126 volts, t = 6 minutes

In summary, current intensity and electro-activation time induce decreases in pH of solutions in the anode and central compartments. The distance between the anode and CEM has a significant effect on pH. Generally, recovery of Fe in central compartment increased with increasing I, t and D. The highest Fe concentration (800 mg/L) in central solution was recorded with the following conditions: t = 120 min; I = 150 mA, anode-CEM distance =

117

7 cm; pH = 1.5. The close distance between the anode and CEM (D = 3 cm) together with high value of I promote the precipitation of some amount of Fe.

4.6.2 Neutralization of acid aqueous sulfide mine tailing and precipitation of toxic metals using electro-activation process The objectives of the three following experiments are to determine the electro-activation conditions that can be used in order to achieve a target pH range of 9.0 to 10. At this pH, most toxic metals become insoluble and precipitate.

4.6.2.1 Experiment 1: Electroneutralization of acid sulfide mine tailing under variable electro-activation conditions including the amount of solid tailing to be treated Among all treatments, R and I were the most important factors influencing pHcatholyte as indicated by the higher F value (Table 4.8). At each level of I or R, pHcatholyte increased with increasing t (Figures 4.15 and 4.16).

118

Table 4.8. ANOVA results (F-value) on the influence of current intensity, solid SMT:water ratio, and rotation speed of stirrer on the pH values of catholyte at six electro-activation times. Source of variation Model Repetition Mine tailing/water ratio (A) Rotation speed (B) Current intensity (C) AxB AxC BxC AxBxC Error A Linear Quadratic Cubic B Linear Quadratic Cubic C Linear Quadratic Cubic

d.f.

T= 10 min

T= 20 min

T= 30 min

T= 40 min

T= 50 min

T= 60 min

28 2

22.29*** 4.69*

36.13*** 14.78***

42.00*** 30.33***

47.12*** 40.52***

42.09*** 40.94***

36.90*** 41.91***

2

154.25***

263.86***

303.90***

329.84***

270.96***

216.21***

2

15.17***

3.80*

5.74**

7.55**

5.34**

6.78**

2

95.31***

172.97***

199.97***

227.15***

203.27***

169.85***

4 4 4 8 52

4.89** 12.72*** 0.72 1.50

3.59* 15.33*** 1.43 2.41*

5.30** 9.72*** 3.60* 2.71*

4.31** 10.83*** 5.03** 3.58**

3.85** 13.76*** 7.39*** 4.69***

4.75** 17.56*** 8.12*** 5.23***

1 1 0

146.65*** 15.12*** -

233.34*** 15.49*** -

275.07*** 20.16*** -

275.85*** 18.58*** -

198.55*** 7.32** -

140.92*** 3.52 -

1 1 0

10.08** 5.83* -

2.18 1.40 -

4.22* 1.35 -

4.87* 1.87 -

2.68 1.38 -

2.95 1.59 -

1 1 0

96.42*** 3.53 -

162.34*** 0.77 -

193.30*** 0.97 -

202.24*** 0.52 -

153.66*** 0.78 -

112.41*** 1.06 -

*, **, *** significant at the 0.05, 0.01 and 0.001 level of probability, respectively.

119

R = 0.1:1 (w/v)

10 9

pH catholyte

8 7 6 5 4 3 0

10

20

30

40

50

60

50

60

50

60

Time, min R = 0.2:1 (w/v) 9 8

pH catholyte

7 6 5 4 3 0

10

20

30

40

Time, min

R = 0.3:1 (w/v) 8

pH catholyte

7

5

Membrane surface = 25% 4 D = 5 cm

100

pH catholyte

6

3

D = 3 cm

80

D = 4 cm

CES = 0%

0

10 = 5 20 D cm

30

40

Time, min CES = 10%

CES = 4%

Figure 4.15. Effect of the current intensity on pHcatholyte values as a function of electroV = 60 V V = 30 V V = 15 V activation time. R = 0.1:1, 0.2:1 and 0.3:1

60

I = 50 mA

I = 100 mA

I = 150 mA

40

20

0

120

10

20

30

40

Time, min

50

60

I = 50 mA 8

pH catholyte

7 6 5 4 3 0

10

20

30

40

50

60

50

60

50

60

Time, min I = 100 mA

10 9

pH catholyte

8 7 6 5 4 3 0

10

20

30

40

Time, min I = 150 mA

10 9

pH catholyte

8 7 6 5 4 3 0

10

20

30

40

Time, min

Figure 4.16. Effect of the amount of SMT in cathode compartment on pHcatholyte as a function of electro-activation time. I = 50 mA, 100 mA and 150 mA

121

In general, at each level of R, the pHcatholyte values (Figures 4.15 and 4.16) increased in the following order: I150 > I100 > I50. This finding indicates that the electric current gradually rise the pH with increasing t, confirming that electro-activation of aqueous SMT generates alkalinity in the cathode compartment. The pH rise could be caused by four effects which promote the reduction of H+ concentration and rising OH- concentration. The first effect is a reduction of H+ ions at the cathode surface. This phenomenon is based on the metal position in the activity series (Table 4.9). The metal activity series is a chain in which the metals are arranged in the order of their standard electrode potential rising φ0 for semi reaction of metal cation reduction: Men+ + nē → Me

122

[4.1]

Table 4.9. A partial activity series of elements (Lide, 2000). Metal Cation φ0. V

Reactivity

Electrolysis (on the cathode):

Reaction with water

Hydrogen emission

Cs

Cs+

-3.026

Rb

Rb+

-2.98

K

K+

-2.931

Ba

Ba2+

-2.905

Ca

Ca2+

-2.868

Na

Na+

-2.71

La

La3+

-2.379

Reaction with water acid

Mg

Mg2+

-2.372

solutions

Zr

Zr4+

-1.53

Competition reactions: emission of

Cr

Cr2+

-0.852

hydrogen, deposition of pure metal

Zn

Zn2+

-0.763

Fe

Fe2+

-0.441

Cd

Cd2+

-0.404

Co

Co2+

-0.28

Ni

Ni2+

-0.234

Mo

Mo3+

-0.2

Sn

Sn2+

-0.141

Pb

Pb2+

-0.126

H2

H+

0

W

W3+

+0.11

Sb

Sb3+

+0.240

Ag

Ag+

+0.799

Pb

Pb4+

+0.80

Hg

Hg2+

+0.851

Pt

Pt2+

+0.963

Pd

Pd2+

+0.98

Au

Au3+

+1.498

Au

Au+

+1.69

Low reactivity

Deposition of pure metal

123

In chemistry, the reactivity series is a ranking of the metals in order of their reactivity (from highest to lowest). Most active (most strongly reducing) metals appear on top, and least active metals appear on the bottom. Because of relatively low metal concentrations for the elements disposed below hydrogen (Table 4.9), the process of their deposition on the cathode surface was competed with another elements accumulation (above the hydrogen) already in the beginning of the experiments. But for the metals with negative standard electrode potential, the electrode concretion was accompanied by the hydrogen emission owing to the water splitting on the cathode surface. The emission deposit to electrode reactions increased with decreasing φ0 until the aluminum (φ0 = - 1.7). Subsequent potential drop leads to complete replacement of metal reduction reaction by water splitting reaction. At the same time, hydrogen ion (according to Table 4.9) is in the position under the majority metals which can be presented in the solution. Thus, H+ present in the acid water solution was directly reduced on the cathode with gas emission and promoted to primary reduction of metal concentrations due to their precipitation. The precipitation intensity increased with increasing pHcatholyte. The second effect is the neutralization reaction of OH- and H+ ions in the cathode compartment. As a final product, this reaction produces water molecules. Constant generation of OH- ions and absence or bordering of continues H+ ion flow also generates favorable conditions to produce more alkalinity. Selectivity of AEM to anion transport is the third effect. It is realized by blocking positively charged ions to move from anode to cathode compartment through the AEM due to the electrostatic repulsion between cations and fixed positive charged ionogenic groups of the cell membrane. This phenomenon excludes additional flow of H+ ions from anode to cathode compartment. The last effect is the preferential transport of SO42- across the AEM in comparison to OH(Shaposhnik, 1989). The flow of SO42- is 5 times higher than that of OH- ion. This factor plays a major role only in the presence of sufficient quantity of SO42- nearly the membrane surface. In general, t had a linear effect on pHcatholyte for all values of I and R (Figures 4.16 and 4.17). An exception is observed only for the following conditions: R = 0.1:1 and I = 100 and 150 124

mA. In this case, rapid increase in pH followed by a gradual slowdown. This finding could be explained by three possible processes: (i) complete hydroxyl (OH-) ion migration through the AEM; (ii) irreversible water splitting reaction on the membrane surface that produces OH- and H+ ions; (iii) changes in voltage during the electro-activation period. For the first process, in the absence of initial ions in the electrode compartments, the transport of ions will proceed successfully only by water splitting which results in ion generation (source of charge carriers). Water molecules will be reduced and oxidized on the surface of the cathode and anode, respectively, according to equations 1.34 and 1.35. The second process is observed when the concentration of ions in the solution near the membrane surface (desalination side of treated water) is not sufficient to realize the electric transport. Electric current value in this boundary condition is probably near the limiting current density. Subsequent increasing of current is possible in the case of water molecules splitting (Simons, 1979, 1984, 1985; Shaposhnik, 1989; Tanaka, 2005, 2007, 2010). But for the electrolysis of aqueous solution with periodic loading and galvanostatic conditions, the limiting current density does not have a specified value. Limiting current density (equation 4.2) is a function of electrolyte concentration. [4.2] where ilim – limiting current density, t-- and t- – the transport number of anions in the anion-exchange membrane and in the solution, F – Faraday constant, C’ – electrolyte concentration, D – diffusion constant of electrolytes dissolving in a solution and δ – boundary layer thickness. The third process is related to voltage changing over electro-activation period (Figures 4.17 and 4.18).

125

R = 0.1:1 (w/v)

70

Voltage, V

60

50

40

30

20 0

10

20

30

40

50

60

50

60

50

60

Time, min R = 0.2:1 (w/v)

70 60

Voltage, V

50 40 30 20 10 0

10

20

30

40

Time, min R = 0.3:1 (w/v)

60

Voltage, V

50

40

30

Membrane surface = 25% 20 D = 5 cm

100

10

D = 3 cm

80

CES = 0%

pH catholyte

D0 = 5 10 cm

D = 4 cm

20

30

40

Time, min CES = 10%

CES = 4%

Figure 4.17. Effect of current intensity on voltage as a function of electro-activation time. R V =0.2:1 60 V and 0.3:1 V = 30 V V = 15 V = 0.1:1,

60

I = 50 mA

I = 100 mA

I = 150 mA

40

20

0

10

20

30

40

Time, min

126

50

60

I = 50 mA 50

Voltage, V

40

30

20

10 0

10

20

30

40

50

60

50

60

50

60

Time, min I = 100 mA

60

Voltage, V

50

40

30

20 0

10

20

30

40

Time, min I = 150 mA

Voltage, V

60

50

40

30 0

10

20

30

40

Time, min

Figure 4.18. Effect of solid SMT/water ratios on voltage as a function of electro-activation time. I = 50mA, 100mA and 150 mA

127

In general, the voltage increased with increasing electro-activation time for all I and Dc values (Figures 4.17 and 4.18). At each electro-activation time, the voltage increased in the following order (Figure. 4.17): I3 (150 mA) ˃ I2 (100 mA) ˃ I1 (50 mA). However, as it is shown in Figures 4.18 and 4.19, the voltage drops almost during the first 10 minutes of electro-activation process and then increases gradually with increasing electro-activation time. The rise in voltage is due to the decreasing charge carrier concentration in the cathode compartment. It is known that the resistance of a solution is inversely proportional to ionic strength (conductivity) which in turn is a direct function of ion concentration in a solution. The relationship between potential difference, current and resistance is referred to as the Ohm's law equation (equation 4.3). I = V/R’

[4.3]

The greater the battery voltage (i.e., electric potential difference), the greater the current. And the greater the resistance, the less the current. In the present study, the rise in voltage is recorded until the achievement of the maximum voltage value that remains constant over electro-activation period. This value is 64 V. Subsequent rising of voltage is impossible because of device limit. Thus, the electro-activation process changed from galvanostatic to potentiostatic. A potentiostatic regime is characterized by a constant voltage. The results (Figure 4.16) also showed that the rise in pHcatholyte was highest under lowest amount of acid solid mine tailing (e.g., R) in the cathode compartment. The main effect of R on pHcatholyte was more important than that of I or RSS as indicated by the highest F value (Table 4.8). Sulfur concentration in catholyte increased with increasing R values under all I (Figure 4.19), indicating that SMT generated S in catholyte. However, the concentration of S decreased with increasing I, an important electro-activation parameter that promote the production of OH ions. This finding is in agreement with the observation of Kastyuchik et al. (2007a), Kastyuchik et al. (2007b) and Shaposhnik et al. (2007) that decreasing of S concentration is accompanied with increasing the flow of OH- ions. One may conclude that the efficiency of electroneutralization of SMT can be expected to be affected by the SMT rate in anode compartment.

128

[S] in catholyte, mg/L

400

300

200

100

0 0

25

50

75

100

125

150

Current intensity, mA

Figure 4.19 Evolution of sulfur concentration in the cathode compartment

In summary, R and I are the most important factors influencing pHcatholyte. At the end of the electro-activation treatment (t = 60 min), the lowest pHcatholyte (4.2) was recorded with the following conditions: R = 0.3:1, I = 50 mA. The higher pHcatholyte (9.1) values were recorded with the following conditions: R = 0.1:1, and I = 50 mA and 150 mA. The absence of Fe and other trace metal ions in the catholyte provide evidence that electro-activation of SMT promotes precipitation of insoluble trace metals in the cathode compartment.

4.6.2.2 Experiment 2: Electroneutralization of acid aqueous sulfide mine tailing previously treated with 0, 4 and 10% chicken eggshell (CES) under variable electro-activation conditions The evolution of pH values of aqueous SMT (pH = 3.2), SMT + 4% CES (pH = 4.3) and SMT + 10% CES (pH = 5.4) in catholyte (pHcatholyte) were examined as a function of: (i) the cathode distance from the AEM (DC) and (ii) the membrane active surface area (AS). Among all treatments, CES content of SMT and DC were the most important factors influencing pHcatholyte as indicated by the higher F value (Table 4.10).

129

The positive effect of CES rate on the rise of pHcatholyte over electro-activation time was linear (Table 4.10) for AS values (25%, 50% and 100%) in combination with DC values (3, 4 and 5 cm) (Figures 4.20, 4.21 and 4.22). At t = 60 min, the higher pHcatholyte values (pH 9.5) were obtained under the following conditions: SMT + 10% CES, DC = 3 cm and either 50% AS (pH 9.6) or 100% AS. This result indicates that electro-activation of CES-amended mine tailing generated alkalinity and achieve pH range of 9.0 ˗ 10.0. Table 4.10. ANOVA results (F-value) on the influence of CES content of SMT, active membrane surface, cathode-AEM distance on the pH values of catholyte at six electroactivation times. Source of variation Model Repetition Percentage of eggshells (A) Cathode-AEM distance (B) Membrane surface (C) AxB AxC BxC AxBxC Error A Linear Quadratic Cubic B Linear Quadratic Cubic C Linear Quadratic Cubic

d.f.

T= 10 min

T= 20 min

T= 30 min

T= 40 min

T= 50 min

T= 60 min

28 2

184.66*** 8.89***

174.26*** 25.80***

131.14*** 38.46***

69.05*** 32.62***

67.39*** 56.64***

59.48*** 54.60***

2

2522.31***

2274.41***

1527.28***

696.80***

556.50***

371.78***

2

34.16***

103.38***

190.27***

187.60***

257.35***

296.31***

2

4.54*

12.58***

21.82***

19.95***

32.76***

51.18***

4 4 4 8 52

2.41 1.35 1.52 1.21

2.86* 1.50 4.87** 1.24

11.81*** 6.82*** 6.68*** 1.88

4.63** 4.53** 4.61** 0.56

4.87** 5.32** 8.01*** 0.96

7.09*** 10.31*** 8.39*** 1.82

1 1 0

4356.53*** 28.94*** -

3206.42*** 106.80*** -

1227.99*** 78.74*** -

850.57*** 49.14*** -

555.52*** 49.30*** -

281.90*** 33.53*** -

1 1 0

58.45*** 0.95 -

148.24*** 2.36 -

158.50*** 4.29* -

240.32*** 1.91 -

278.55*** 1.14 -

251.29*** 0.10 -

1 1 0

0.00 7.89** -

1.92 16.41*** -

6.37* 12.30*** -

6.74* 19.02*** -

17.80*** 17.80*** -

29.69*** 13.73*** -

*, **, *** significant at the 0.05, 0.01 and 0.001 level of probability, respectively.

130

DC = 3 cm 9 8

pH catholyte

7 6 5 4 3 0

10

20

30

40

50

60

50

60

50

60

Time, min DC = 4 cm

9 8

pH catholyte

7 6 5 4 3 0

10

20

30

40

Time, min DC = 5 cm

8

pH catholyte

7

6

5

4

3

0 10 20 Membrane surface = 25% D = 5 cm

100

40

Time, min

Figure 4.20. Effect of the CES rate in SMT in cathode compartment on pHcatholyte values as a D = 3of cm D = 4 cm D =D5Ccm function electro-activation time. = 3, 4 and 5 cm. AS = 25%

80

CES = 0%

pH catholyte

30

60

V = 60 V I = 50 mA

CES = 4%

CES = 10%

V = 30 V

V = 15 V

I = 100 mA

I = 150 mA

40

20

0

10

20

30

40

Time, min

50

60

131

DC = 3 cm

10 9

pH catholyte

8 7 6 5 4 3 0

10

20

30

40

50

60

50

60

50

60

Time, min DC = 4 cm 9 8

pH catholyte

7 6 5 4 3 0

10

20

30

40

Time, min DC = 5 cm 8

pH catholyte

7

6

5

4

3

0 10 20 Membrane surface = 25% D = 5 cm

100

40

Time, min

Figure 4.21. Effect of the CES content of SMT in cathode compartment on pHcatholyte values D = 3 cm of electro-activation D = 4 cm Dtime. = 5 cm as a function DC = 3, 4 and 5 cm. AS = 50%

80

CES = 0%

pH catholyte

30

60

V = 60 V I = 50 mA

CES = 4%

CES = 10%

V = 30 V

V = 15 V

I = 100 mA

I = 150 mA

40

20

0

10

132

20

30

40

Time, min

50

60

DC = 3 cm

10 9

pH catholyte

8 7 6 5 4 3 0

10

20

30

40

50

60

50

60

50

60

Time, min DC = 4 cm

9 8

pH catholyte

7 6 5 4 3 0

10

20

30

40

Time, min DC = 5 cm 8

pH catholyte

7

6

5

4

3

10 20 Membrane surface 0= 25% D = 5 cm

100

40

Figure 4.22. Effect of the CES content of SMT in cathode compartment on pHcatholyte values D = 3 cmas a function D = 4 cmof electro-activation D = 5 cm of catholyte time. DC = 3, 4 and 5 cm. AS = 100%

80

CES = 0%

pH catholyte

30

Time, min

60

V = 60 V I = 50 mA

CES = 4%

CES = 10%

V = 30 V

V = 15 V

I = 100 mA

I = 150 mA

40

20

0

10

20

30

40

Time, min

50

60

133

CES = 0%

7

pH catholyte

6

5

4

3

0

10

20

30

40

50

60

50

60

50

60

Time, min

CES = 4% 9

pH catholyte

8 7 6 5 4 0

10

20

30

40

Time, min CES = 10% 9

pH catholyte

8

7

6

5 0

10

20

30

40

Time, min

Figure 4.23. Effect of DC on pHcatholyte values as a function of electro-activation time. CES rate = 0, 4 and 10%. AS = 25%

134

CES = 0% 9 8

pH catholyte

7 6 5 4 3 0

10

20

30

40

50

60

50

60

50

60

Time, min

CES = 4%

10 9

pH catholyte

8 7 6 5 4 0

10

20

30

40

Time, min CES = 10%

10

pH catholyte

9

8

7

6

5 0

10

20

30

40

Time, min

Figure 4.24. Effect of DC on pHcatholyte values as a function of electro-activation time. CES rate = 0, 4 and 10%. AS = 50%

135

CES = 0% 9 8

pH catholyte

7 6 5 4 3 0

10

20

30

40

50

60

50

60

50

60

Time, min

CES = 4%

10 9

pH catholyte

8 7 6 5 4 0

10

20

30

40

Time, min

CES = 10%

10

pH catholyte

9

8

7

6

5 0

10

20

30

40

Time, min

Figure 4.25. Effect of DC on pHcatholyte values as a function of electro-activation time. CES rate = 0, 4 and 10%. AS = 100%

136

As can be seen from Figures 4.20 to 4.25, pHcatholyte increased with increasing the membrane active surface area. For instance, pH values were 4.96 and 9.05, respectively at the lowest and the highest points of trials with 25% AS. And they became 6.05 and 9.63 for the trials with 100% AS. It means that the decreasing of AS conduces to quantitative reduction of active ion-exchange centers needed for ion transport. In this condition, the electric current through the unit of membrane area will increase and in turn, will generate additional H+ ions in the cathode compartment, as mentioned previously. This is in agreement with the voltage increasing values (Figure 4.26). All voltage values obtained with 25% AS over a 50-minute electro-activation period were higher than those obtained with 50% and 100% AS. A sharp increase in V was recorded for DC = 3 cm and AS = 50% and 100%. This can be explained by the intensive desalination process in the cathode compartment that results in the rise of electric resistance of the catholyte.

137

DC = 3 cm

35

Voltage, V

30

25

20

15

10 0

10

20

30

40

50

60

50

60

50

60

Time, min DC = 4 cm 22.5

Voltage, V

20.0

17.5

15.0

12.5 0

10

20

30

40

Time, min DC = 5 cm 22

Voltage, V

20

18

16

14 20 30 40 Membrane surface0 =1025% Time, min D = 5 cm

100

Figure 4.26. Evolution of voltage as a function of electro-activation time. DC = 3, 4 and 5 D ==350% cm D = 4 cm D = 5 cm cm. AS

80

pH catholyte

CES = 0%

60

V = 60 V I = 50 mA

CES = 4%

CES = 10%

V = 30 V

V = 15 V

I = 100 mA

I = 150 mA

40

20

0

10

138

20

30

40

Time, min

50

60

Voltage, V

CES = 0%

35

Voltage, V

30

25

20

15

10 0

10

20

30

40

50

60

50

60

50

60

Time, min CES = 4%

35 30

Voltage, V

25 20 15 10 5 0

10

20

30

40

Time, min CES = 10%

35 30

Voltage, V

25 20 15 10 5

DC = 3 cm

300

0

10

20

30

40

Time, min

Figure 4.27. Evolution of voltage as a function of electro-activation time. CES = 0, 4 and 10%. Dc = 3 cm

250

AS = 25%

AS = 50%

AS = 100%

200 150 100 50

0

10

20

30

40

Time, min

50

60

139

The effect of DC on pHcatholyte over electro-activation time was linear (Table 4.7) for each AS value (25%, 50% and 100%) in combination with CES rate in SMT (0, 4 and 10%) (Figures 4.23, 4.24 and 4.25). For example, 4% CES and 50% AS generated pHcatholyte values of 7.29, 8.59 and 9.49 for DC = 5, 4 and 3 cm, respectively. This finding could be attributable to the amount of OH- generated at the cathode surface. The amount of OH- ions produced by the water splitting reaction is a function of the electric current density and qualitative and quantitative composition of the initial solution (Tanaka, 2010). In the present trial, only the ion quantity is a variable parameter. Because of constant initial concentration and different volume of solution, the overall number of ions is lower in the compartment with the smallest geometric parameters. It means that fewer initial ions will reach the cathode surface to be reduced and more OH- will be produced to support electric current without changing. More OH- ions will be present in the small volume of electro-activation cell unit. As it is mentioned previously, the changes in pH depend on the electrolyte concentration. The SO42- ions make the major contribution to this process due to their electro-migration from the cathode section, resulting in pH increase. As can be seen from Figure 4.28, the degree of S desalination increased as the cathode-AEM distance decreased and as the AS increased. The maximum S desalination (elimination from the catholyte) from 384 to 46 ppm was recorded with CES = 10%, DC = 3 cm and AS = 100%. The absence of S desalination was observed in the case of CES = 4%, DC = 5 cm and AS = 25%. This result was due to the competition in the ion transport through the anion-exchange membrane between carbonate, sulfate and hydroxyl ions. The carbonate ions from CES could accelerate this reaction; a fact which is confirmed by the rise in S concentration from 257 to 385 mg/L with increasing CES from 0 to 10%, respectively.

140

Figure 4.28. Sulfur concentration in the catholyte under variable electro-activation conditions at the end of electro-activation treatment. Initial solution = catholyte before starting electroactivation

141

Like S concentration, Ca concentration in catholyte at the end of electro-activation treatment was decreased with decreasing DC and increasing AS (Figure 4.29).

Figure 4.29. Calcium concentration in the catholyte under variable electro-activation conditions at the end of electro-activation treatment. Initial solution = catholyte before starting electro-activation

142

The lowest (73 mg/L) and highest (302 ppm) Ca concentrations for CES = 10% were recorded respectively with the following conditions: DC = 3 cm and AS = 100%, DC = 5 cm and AS = 25%. Initial Ca content increased from 87 mg/L for the solution with CES = 0% to 232 ppm with CES = 10%. This finding indicates that electro-activation of CES-amended SMT could extract Ca from tailing. In summary, treatments significantly influenced the pHcatholyte. At each level of CES, pHcatholyte increased with decreasing DC and with increasing AS. For each DC value, pHcatholyte increased with increasing CES rate. The higher pHcatholyte values were obtained under the following conditions: SMT + 10% CES, DC = 3 cm and either 50% AS (pH 9.6) or 100% AS (pH 9.5). The absence of Fe and other trace metal ions in the catholyte provide evidence that electro-activation of SMT under the studied parameter conditions promotes precipitation of insoluble trace metals in the cathode compartment. A combination of pre-treatment SMT applications, where biological calcareous amendments are available, followed by electroactivation of effluent may be feasible, cost-effective approach for SMT neutralization.

4.6.2.3 Experiment 3: Electroneutralization of acid aqueous sulfide mine tailing previously treated with 4% chicken eggshell residue under variable cathodes and membrane type conditions 4.6.2.3.1 General results Among all treatments, membrane type and voltage of the electro-activation system (V) were the most important factors influencing pHcatholyte as indicated by the higher F value (Table 4.11). The absence of trace metal ions in the catholyte provide evidence that electroactivation of SMT under the studied parameter conditions promotes precipitation of insoluble trace metals in the cathode compartment.

143

Table 4.11. ANOVA results (F-value) on the influence of membrane type, voltage and electrode material, on the pH values of catholyte at six electro-activation times. Source of variation Model Repetition Cathode material (A) Membrane (B) Voltage (C) AxB AxC BxC AxBxC Error A Linear Quadratic Cubic B Linear Quadratic Cubic C Linear Quadratic Cubic

d.f.

T= 10 min

T= 20 min

T= 30 min

T= 40 min

T= 50 min

T= 60 min

28 2

66.52*** 0.44

127.12*** 0.58

213.44*** 3.00

279.67*** 5.04**

381.62*** 8.03***

374.36*** 9.61***

2

4.36*

1.37

0.26

0.69

1.07

1.87

2 2 4 4 4 8 52

652.21*** 117.69*** 5.93*** 1.82 67.60*** 1.48

1283.38*** 260.59*** 5.91*** 2.07 106.11*** 1.40

2217.33*** 432.18*** 5.56*** 1.97 153.31*** 3.42**

2916.44*** 569.32*** 5.57*** 1.19 198.85*** 3.15*

4021.46*** 771.05*** 6.93*** 2.42 253.30*** 3.95***

4062.09*** 638.85*** 8.21*** 2.51 246.26*** 3.65**

1 1 0

0.76 0.96 -

0.29 0.10 -

0.01 0.04 -

0.00 0.11 -

0.00 0.14 -

0.01 0.24 -

1 1 0

120.47*** 136.67*** -

139.82*** 215.87*** -

158.32*** 283.49*** -

145.33*** 321.47*** -

136.18*** 374.41*** -

122.06*** 405.33*** -

1 1 0

46.39*** 0.01 -

71.99*** 0.24 -

85.80*** 0.32 -

90.99*** 0.14 -

97.66*** 0.24 -

82.63*** 0.32 -

*, **, *** significant at the 0.05, 0.01 and 0.001 level of probability, respectively.

4.6.2.3.2 Electro-activation process using cation-exchange membrane as a separator For all combinations of the studied parameters, after 1 hour of electro-activation, pHcatholyte values using CEM varied from 4.1 (before electro-activation process) to a range of 4.6 - 5.1 (Figure 4.30). The slow generation of alkalinity in cathode compartment under the selected conditions could be due to the transfer of H+ from the anode to cathode compartment through the CEM and neutralization of OH- produced at the cathode compartment.

144

S. steel cathode

5.0

pH catholyte

4.8

4.6

4.4

4.2

Membrane surface = 25% 4.0 D = 5 cm 0 10 20

100

D = 3 cm

pH catholyte

80

D = 4 cm

D = 5 cm

30

40

50

60

Time, min

Figure 4.30. Evolution of pHcatholyte as a function of electro-activation time under variable CES = 0% CES = 4% CES = 10% conditions using CEM as a separator and a stainless steel cathode material

60

V = 60 V I = 50 mA

V = 30 V

V = 15 V

I = 100 mA

I = 150 mA

40

4.6.2.3.3 Electro-activation process using nanofiltration membrane as a separator 20

The electroneuralization of CES (4%)-amended SMT pattern was similar for electroactivation conditions using nanofiltration membrane, regardless the type of electrode 0

10

20

30

40

50

60

material (e.g., stainless steel, titanium, copper). The results (Figure 4.31) obtained from

minusing nanofiltration membrane and stainless steel cathode electro-activationTime, conditions material will be presented in order to reduce the amount of similar data in the thesis. As shown in Table 4.12 and Figure 4.31, pHcatholyte increased with increasing electroactivation time and achieve alkaline pH range of 8.9 – 9.1 when using nanofiltration membrane as a separator and stainless steel, copper or titanium as a cathode material (Table 4.12). The increase in pHcatholyte was lowest with 15V and highest with 60V. Compared to 60 V, the current intensity produced from 15 V and 30 V was more stable (Figure 4.32). According to Pokonova (2007), the nanofiltration membranes are more useful for separation of multi-charged ions from mono-charged ions in a solution, and their separation efficiency is decreased with increasing ion concentration. In the absence of ionogenic groups in the structure of nanofiltration membrane (NFM), the transfer of ions can be realized in both 145

ways: to cathode and to anode). Thus the OH- and H+ ions flows generated on the anode and cathode surfaces respectively will migrate through the membrane easier than other ions. The overall possible ions flows in the cathode compartment result in increasing OH- concentration with increasing electro-activation time and voltage (Figure 4.31).

S. steel cathode 9

pH catholyte

8 7 6 5

Membrane surface = 25% 4 D = 5 cm0 10 20

pH catholyte

100

30

40

50

60

Time, min D = 3 cm

80

D = 4 cm

D = 5 cm

Figure 4.31. Evolution of pH as a function of electro-activation time under variable CES = 0% CES = 4% CES = 10% conditions using nanofiltration membrane as a separator and a stainless steel cathode material

60

V = 60 V I = 50 mA

V = 30 V

V = 15 V

I = 100 mA

I = 150 mA

40

20

0

10

20

30

40

Time, min

146

50

60

450

S. steel cathode

400

Current intensity, mA

350

250 200 150 100 50

0 Membrane surface = 25% 0 10 20 D = 5 cm

100

30

40

50

60

Time, min

Figure of current as a function of electro-activation time when D = 34.32. cm Evolution D = 4 cm D =intensity 5 cm applying three different voltages (15 V, 30 V and 60 V) under variable conditions using CES = 0% CES = 4% CES = 10% nanofiltration membrane as a separator

80

pH catholyte

300

60

V = 60 V I = 50 mA

V = 30 V I = 100 mA

V = 15 V I = 150 mA

40

Table 4.12. Values of initial pH and pHcatholyte at the end of electro-activation process 20

using nanofiltration membrane and variable voltage values and electrode materials.

0

Identification Electro-activation conditions

Initial pH

pH at t = 60 min

10 N1

4.12

5.68

4.12

5.96

N2

20

30 volts 40 50 steel 60 15 + stainless electrode

15 volts + titanium electrode Time, min

N3

15 volts + copper electrode

4.12

5.57

N4

30 volts + stainless steel electrode

4.12

6.48

N5

30 volts + titanium electrode

4.12

6.91

N6

30 volts + copper electrode

4.12

6.31

N7

60 volts + stainless steel electrode

4.12

8.94

N8

60 volts + titanium electrode

4.12

9.08

N9

60 volts + copper electrode

4.12

9.06

147

Changes in pH were different among voltages and electrode materials throughout the entire range of electro-activation times. A shown in Table 4.12, pHcatholyte values after 60 min were higher with 60V in combination with electrode materials (e.g., N7, N8 and N9). When considering all treatments related to nanofiltration membrane (Table 4.12), the values of pHcatholyte varied from 4.1 (initial pH of aqueous CES(4%)-amended SMT) to a range of: 5.6 – 6.0, 6.3 – 7.0 and 9.0 – 9.1 for 15 V (N1, N2 and N3), 30 V (N4, N5 and N6) and 60 V (N7, N8 and N9), respectively. The lowest pHcatholyte value (pH 5.6) was recorded in 15 volts + copper electrode treatment. The pHcatholyte was greatest (pH > 8) in N7, N8 and N9. Among all treatments having nanofiltration membrane, the voltage of electro-activation system (V) was the most important factor influencing pHcatholyte. In general, V had a significant positive linear effect on pH (Table 4.11). The electro-activation of acid mine tailing previously treated with CES contributes not only to neutralize their acidity but also to increase the concentration of Ca and S in the solution. However, the electro-activation process using a higher voltage (e.g, 60 V) maintains a lower concentration of these elements than lower voltage or initial solution (Figures 4.33 and 4.34). The concentration of both S (Figure 4.33) and Ca (Figure 4.34) in catholyte increases in the following order: V15V ˃ V 30V ˃ initial solution (without V). The higher Ca concentrations (331 – 337 mg/L) were recorded with the following conditions: nanofiltration membrane + 15 V + copper or stainless steel electrode material. This finding indicates that it is possible to extract Ca from mine tailings treated with chicken eggshell residue by the currently electro-activation process using nanofiltration membrane as a separator. The absence of Fe and other trace metal ions in the catholyte provide evidence that electro-activation of SMT under the studied parameter conditions promotes precipitation of insoluble trace metals in the cathode compartment. These results are consistent with those obtained in the previous section.

148

Figure 4.33. Sulfur concentration in catholyte at the end of electro-activation treatment, using nanofiltration membrane and stainless steel cathode, as a function of voltage. Initial solution = catholyte before starting electro-activation

Figure 4.34. Calcium concentration in catholyte at the end of electro-activation treatment, using nanofiltration membrane and stainless steel cathode, as a function of voltage. Initial solution = catholyte before starting electro-activation

4.6.2.3.4 Electro-activation process using anion-exchange membrane as a separator The electroneuralization of CES(4%)-amended SMT pattern was similar for electroactivation conditions using AEM, regardless the type of electrode material (e.g., stainless steel, titanium, copper). The results (figures) obtained from electro-activation conditions using AEM and stainless steel cathode material will be presented in order to reduce the amount of similar data in the thesis.

149

As shown in Figure 4.35 and Table 4.13, pHcatholyte increased with increasing electroactivation time and achieve alkaline pH range of 7.9 – 10.1 when using AEM as a separator and stainless steel, copper or titanium as a cathode material (Table 4.13). Similar findings have been reported by (Bunce et al., 2001; Chartrand and Bunce, 2003), who found that the rise in pH was dependent on the current intensity. When electricity is applied to the solution, OH- ions in anolyte will move toward the cathode compartment. As a consequence, the catholyte becomes alkaline. These pHcatholyte values (Table 4.13) are higher than those obtained with nanofiltration membrane (Table 4.12). The increase in pHcatholyte was lowest with 15 V and highest with 60 V. Compared to 60 V and 30 V, the increase in current intensity produced from 15 V was stable (Figure 4.36). The overall possible ions flows in the cathode compartment result in increasing OH- concentration with increasing electro-activation time and voltage (Figure 4.35).

S. steel cathode

11 10

pH catholyte

9 8 7 6 5 4

Membrane surface = 25% 0 10 20 D = 5 cm

pH catholyte

100

30

40

50

60

Time, min

Figure function of electro-activation time under variable D = 34.35. cm Evolution D = 4 cmof pH Das = 5a cm conditions using anion-exchange membrane as a separator and a stainless steel cathode CES = 0% CES = 4% CES = 10% material

80

60

V = 60 V I = 50 mA

V = 30 V

V = 15 V

I = 100 mA

I = 150 mA

40

20

150 0

10

20

30

40

Time, min

50

60

250

S. steel cathode

Current intensity, mA

200

100

50

Membrane surface = 25% 0 0 10 20 D = 5 cm

100

30

40

50

60

Time, min

Figure of current as a function of electro-activation time when D = 34.36. cm Evolution D = 4 cm D =intensity 5 cm applying three different voltages (15, 30 and 60 V) under variable conditions using AEM as CES = 0% CES = 4% CES = 10% a separator

80

pH catholyte

150

60

V = 60 V I = 50 mA

V = 30 V I = 100 mA

V = 15 V I = 150 mA

40

Table 4.13. Values of initial pH and pHcatholyte at the end of electro-activation process using AEM and variable voltage values and electrode materials.

20

0

Identification Electro-activation conditions

Initial pH

pH at t = 60 min

A1 10

15 + stainless electrode 30volts 40 50 steel 60

4.12

7.87

15 volts + titanium electrode

4.12

8.06

A3

15 volts + copper electrode

4.12

8.30

A4

30 volts + stainless steel electrode

4.12

9.86

A5

30 volts + titanium electrode

4.12

9.17

A6

30 volts + copper electrode

4.12

9.64

A7

60 volts + stainless steel electrode

4.12

10.12

A8

60 volts + titanium electrode

4.12

9.84

A9

60 volts + copper electrode

4.12

9.88

A2

20

Time, min

Changes in pH were different among voltages and electrode materials throughout the entire range of electro-activation times. As shown in Table 4.13, pHcatholyte values after 60 min were higher with 60V in combination with electrode materials (e.g., A7, A8 and A9). 151

When considering all treatments having AEM (Table 4.13), the values of pHcatholyte varied from 4.1 (initial pH of aqueous CES(4%)-amended SMT) to a range of: 7.9 – 8.3, 9.2 – 9.9 and 9.8 – 10.1 for 15 V (A1, A2 and A3), 30 V (A4, A5 and A6) and 60 V (A7, A8 and A9), respectively. The lowest pHcatholyte value (pH 7.9) was recorded in 15 volts + stainless steel electrode treatment (A1). The pHcatholyte was greatest (pH > 9.9) in A7, A8 and A9. These values are much higher than those obtained with nanofiltration membrane and cationexchange membrane under the same electro-activation conditions. It is possible that that a part of OH- generated did not participate in water spitting and were not transferred across the AEM. As a result, the remaining OH- ions have made the catholyte more alkaline. In a laboratory experiment, Iurash et al. (1999) studied the desalination channel of an electrodialyzer stack with ion-exchange bed formed by a smooth anion-exchange membrane MA–40 and cation-exchange membrane MK–40 positioned at the distance h = 0.8 mm. They found that anion-exchange membrane may cause a misbalance of cations and anions, resulting in pH growth of the desalted solution. Among all treatments having AEM, the voltage of electro-activation system (V) was the most important factor influencing pHcatholyte. In general. V had a significant positive linear effect on pH (Table 4.11). These results are consistent with those obtained in the previous section. In summary, anion-exchange membrane, nanofiltration membrane, and voltage of the electro-activation system (V), regardless of cathode material, were the most important factors that contribute to neutralize efficiently the acidity and to achieve target alkaline pH range. The higher pHcatholyte values (pH ≥ 7.9) were obtained with the following conditions: (i)

Nanofiltration membrane + 60 V + stainless steel, titanium or copper electrode (pH

8.9 – 9.1); (ii) 10.1).

152

AEM + 15 V, 30 V or 60 V + stainless steel, titanium or copper electrode (pH 7.9 –

General conclusions The research described in this doctoral dissertation could be reduced to three general groups of conclusions: (i) neutralization of sulfide mine tailing (SMT) acidity through application of chicken eggshell residue (CES) alone or mixed with cement, MgO, dolomite and limestone, (ii) effectiveness of electro-activation process to raise the pH of CES-amended SMT to an alkaline level, and (iii) removal of Fe(II) from aqueous FeSO4 solution by electroactivation process. 

CES amendment

Chicken eggshell (CES) alone (2, 4, 6, 8 and 10%) or mixed with cement concrete (1 – 2%), MgO (1 – 2%), calcitic limestone (1 – 2%) or dolomitic limestone (1 – 2%) are efficient to neutralize SMT acidity and to precipitate trace metallic elements. The application of CES to SMT had an immediately effect on tailing pH. Chicken eggshell, cement and MgO had a sufficient lime value. The target neutral pH condition (pH 7.0 – 7.5) can be obtained with 10% or less of CES. The study showed that SMT treated with magnesium oxide or cement was stable and well buffered to acidifying input. Alkaline material such as CES, cement and MgO incorporated in the tailing acts as a buffer. The addition of cement or MgO to CES tends to increase CES-tailing’s buffering capacity against pH drop. Therefore, a limed tailing with a high buffering capacity would resist to anthropogenic acidification. To avoid reacidification, excess alkaline compounds should be applied. Use of CES to neutralize acidproducing mine tailings can be preferred as sustainable alternative over land filling. 

Electro-activated pH increasing of CES-amended mine tailing

This thesis contains one approach that electro-activation technology can increase alkalinity (neutralize) of acid mine tailing suspensions amended by CES to pH values > 8. Several geometrical, electric, qualitative and quantitative parameters could promote the electro-activated neutralization (alkalization) of CES-amended SMT. These include one or more of the following parameters: time of electro-activation (t), current intensity (I), voltage (V), cathode materials, cathode-membrane distance, mine tailing/water ratio, chicken

153

eggshell rate, rotation speed of magnetic stirrer in the cathode compartment, active membrane surface, nanofiltration membrane, and ion-exchange membrane type. The pH of catholyte increased progressively with t and I, due to electrochemical reduction of H+ ions to elemental hydrogen at the cathode and consequently the production of OH- ions. OH- is a strong base. Anion-exchange membrane (AEM), nanofiltration membrane, and voltage of the electroactivation system, regardless of cathode material, were the most important factors that contribute to neutralize efficiently the acidity and to achieve target alkaline pH range. Decreasing of cathode-membrane distance led to reducing of cathode section volume and thus to the intensification of catholyte saturation by hydroxyl ions. The active membrane surface reduction of AEM was attended by the decreasing of active ion-exchange centers that resulted in water splitting reaction on the membrane surface and finally to the slowdown of pH rise. The values of pHcatholyte varied inversely with SMT/water ratio (R). Adding SMT to catholyte water gives more acidic compounds and drop the pHcatholyte. Conversely, the increase of CES in SMT resulted in increased pHcatholyte. After 60 min of electro-activation treatment of CES-amended SMT the pHcatholyte values were higher than 7 Among all treatments (trials) the highest pHcatholyte value (10.1) is obtained under the following electroactivation conditions: t = 60 min, V = 60 volts, I = controlled potential process, R = 0.2:1 (w/v), CES = 4%, AS = 50%, membrane = AEM, DC = 4 cm, DA = 3 cm, ω = 300 rpm, cathode material = stainless steel electrode. 

Iron extraction by electro-activation technology

The selective permeability of ion-exchange membranes and water splitting reaction on the anode surface in the electro-activation technology gave one approach that three section electro-activation cell could be applied under certain conditions for iron ion (Fe(II)) extracting from the treated solution. The hydrogen ion produced in the water splitting reaction at the anode surface played an important role in this process that created favorable conditions to avoid precipitation of Fe(OH)3 on the membrane surface or dissolution of slightly soluble compounds of target elements. The electro-activation method showed

154

positive results in selective Fe(II) extraction from the modeling FeSO 4 solution. The maximum concentration of Fe(II) (800 ppm) recovered in the central section was obtained under the following experimental conditions: t = 120 min, DA = 7 cm and I = 150 mA. The results of this doctoral dissertation may have practical implications in tailing management: for the reduction of acid generation and trace metal mobility in sulfide mine drainage system and of water contamination risk.

155

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