The Science of Persulfate Activation Philip Block, PhD Director of Technology FMC’s Environmental Solutions Division
Brant Smith, PhD Sr. Project Manager XDD
April 24, 2013
Bios Philip Block is the director of technology for FMC's Environmental Solutions Division. The Environmental Solutions Division provides integrated products and solutions in three major focus areas: soil and groundwater remediation, wastewater and industrial water treatment, and air pollution. He holds a PhD in physical chemistry and a BS in Philip Block, Ph.D chemical engineering. FMC Environmental Solutions
[email protected] (215) 299-6645 Dr. Smith specializes in water chemistry and hazardous waste remediation with a particular emphasis on in situ chemical oxidation and reduction technologies. He is the Director of XDD's treatability laboratory in Stratham, NH and has over 12 years experience with remedial technologies. He holds a PhD in civil engineering. Brant Smith, P.E., Ph.D XDD, LLC
[email protected] (603) 778-1100
April 24, 2013
Introduction to Klozur® Persulfate
• Klozur® Persulfate is a strong oxidant used for in situ and ex situ destruction of contaminants in soil and groundwater • Provides the strength of “Fenton’s Chemistry” but with extended subsurface lifetime (3 – 4 months) and little to no heat or gas evolution • Applicable across a broad range of organic contaminants
April 24, 2013
Introduction to Klozur® Persulfate Examples of Contaminants Destroyed by Klozur Persulfate Chlorinated Solvents PCE, TCE, DCE TCA, DCA Vinyl chloride Carbon tetrachloride Chloroform Chloroethane Chloromethane Dichloropropane Trichloropropane Methylene chloride
TPH BTEX GRO DRO ORO creosote
Others Carbon disulfide PFOS / PFOA Aniline PVA/ TNT / DNT
Freons
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Oxygenates MTBE TBA
Chlorobenzenes Chlorobenzene Dichlorobenzene trichlorobenzene Phenols phenol Pentachlorophenol nitrophenol PAHs Anthracene Benzopyrene Styrene Naphthalene Pyrene Chrysene trimethylbenzene
Pesticides DDT Chlordane Heptachlor Lindane Toxaphene MCPA Bromoxynil
Chemistry and Stoichiometry
Persulfate Oxidation Principles: S2O8-2 + 2H+ + 2e- 2HSO4-1 persulfate anion
Examples 15 S2O8-2 + C6H6 + 12 H2O 6 CO2 + 30 HSO4-1
45 lb / lb
benzene
2 S2O8-2 + C2Cl4 + 4 H2O 2 CO2 + 4 Cl- + 4 H+ + 4 HSO4-1 PCE
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3 lb / lb
Chemistry and Stoichiometry However, persulfate anion kinetics are generally too slow for most contaminants. As a result, you must activate persulfate to form the sulfate radical.
Activated Persulfate produces a radical which is more powerful and kinetically fast FMC always recommends using an activator proper activation method is based on contaminant, site lithology, and hydrogeology 2.6 eV
S2O8-2 + activator SO4•- + (SO4•- or SO4-2) Heat
Iron
H2O2
High pH
One of strongest oxidants available.
Purchase of FMC’s Klozur® Persulfate includes rights to practice the inventions covered by global patents in the purchase price of the product.
April 24, 2013
Presentation Overview • Activation Methods of Activated Persulfate – Overview – Chemistry – Discussion
• Bench testing activated persulfate • Case study – Industrial site with chlorinated ethanes, ethenes and 1,4-dioxane
April 24, 2013
Activation Methods of Persulfate • Persulfate is a peroxygen, and similar to hydrogen peroxide, it can be split at the O-O bond: -O S-O-O-SO 3 3
-O3S-O• •O-SO3-
• Reaction is facilitated by activation methods, which include: – – – – –
Reduced metals (Iron and Iron-Chelate) Alkaline/high pH Heat Hydrogen peroxide Others (photolysis) 8
Iron/Iron Chelate Activation: Overview • Sodium persulfate (2.05 V) is activated by the a reduced iron, Fe(II) is most common, to form the sulfate radical (SO4•; 2.6 V) • Has been shown to be reactive with: – – – –
Reduced organics (PAHs, BTEX, TPH, etc) Chlorinated ethenes (PCE, TCE, DCE, and VC) Oxygenates (MTBE, 1,4-Dioxane, etc) Perfluorinated acids (PFOA, PFBA, etc)
• FMC guidance of 150 mg/L Fe to 600 mg/L Fe
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Iron/Iron Chelate Activation: Chemistry • Iron/Iron Chelate S2O82- + Fe(II) Fe(III) + SO4- + SO4• • Chelate or not to chelate: – At pH >~2.7 Fe (III) will precipitate – EDTA, citrate, or other chelates help keep iron in solution
• How does Fe(III) cycle back to Fe(II)? – Likely reaction with destabilized organics
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Iron/Iron-Chelate Activation: Discussion • Reactivity due to sulfate radical • Field application is well established • Minimized health and safety concerns
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• Does not react with chlorinated ethanes or methanes such as 1,1,1TCA or carbon tetrachloride • Does not typically include anything to neutralize the acid that is formed during the decomposition of persulfate (more of a concern as concentrations increase) • Formation of halomethanes has been observed if halides are present
Alkaline Activation: Overview • Sodium persulfate is activated when the solution is raised to pH > 10.5 • Has been shown to be reactive with: – Reduced organics (PAHs, BTEX, TPH, etc) – Chlorinated ethenes (PCE, TCE, DCE, and VC) – Chlorinated methanes or ethanes (CT, 1,1,1-TCA, etc) – Oxygenates (MTBE, 1,4-Dioxane, etc) – Perfluorinated acids (PFOA, PFBA, etc) • Sufficient base needs to be added to account for buffering capacity of the soil plus the acid that is generated during the decomposition of sodium persulfate
April 24, 2013
Alkaline Activation: Chemistry • Alkaline Activation-simple version: pH >10.5 S2O82- 2SO4• • Alkaline Activation-complex version (Furman et al., 2010): OH-
S2O8 2H2O HO2- + 2SO42- + 3 H+ HO2- + S2O82- SO4- + SO42- + H++ O2SO4- + OH- OH + SO422- +
(note: H2O2 HO2- + H+ pKa = 11.7)
• Complex version of the reaction results in the transient oxygen species of SO4- , OH , O2- , and HO2• Analogous to the chemistry that has been studied with catalyzed hydrogen peroxide (CHP)
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Alkaline Activation: Discussion • Generates reductive (O2-), nucleophilic (HO2-), and oxidative (SO4-; OH) species to react with broad suite of contaminants • As a result AAP can treat CT, and 1,1,1TCA • Ease of implementation April 24, 2013
• Health and safety risk of NaOH or other base. • Additional cost of NaOH • Typically has increased non-target demand from soils • Site pH following application
Heat Activation: Overview • Heat activated persulfate used in certain TOC analyses • Subsurface heated to desired temperature • Persulfate degrades to form different compounds as the temperature increases Block et al, 2004
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Activation with Heat: Chemistry • Heat (>35°C sulfate radical; >80°C multiple oxidants) S2O82- 2SO4• • Two schools of thought: – Different oxidants formed at elevated temperatures – Kinetics (ie. Arrhenius equation)
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Heat Activation: Discussion • Arguably the most effective activation method, especially in the lab setting • Reacts with wide variety of compounds depending upon the temperature • Can be used as part of a combined remedy with thermal treatments
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• Soils/silica are good insulators • Typically requires dual system to heat the subsurface • Introduces unique failure mechanisms such as thermal sinks/losses/distribution • Health and safety associated with heat source
Hydrogen Peroxide Activation: Overview • “Activation” – Addition of hydrogen peroxide to react with (donate an electron) sodium persulfate – Heat
• Combination of two proven ISCO technologies • Ratio between the two reagents determines application characteristics April 24, 2013
Hydrogen Peroxide Activation: Catalyzed Hydrogen Peroxide Chemistry Fundamental Fenton’s reaction (hydroxyl radical)
Fe2+ + H2O2 Fe3+ + OH. + OHPerhydroxyl Radical
OH• + H2O2 HO2• + H2O Fe3+ + H2O2 HO2• + Fe2+ + H+
Superoxide HO2• O2•-+ H+ pKa 4.8 OH• + HO2- O2•-+ H2O
Hydroperoxide
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HO2• + Fe2+ Fe3+ + HO2HO2• + O2•- O2+ HO2-
19
Hydrogen Peroxide Activation: Chemistry • Hydrogen peroxide can donate electrons going to oxygen or accept electrons to become water e-
e-
2e-
O2 O2 H2O2 H2O •-
• If hydrogen peroxide is present in sufficient quantities, the reaction should result in the transient species of SO4- , OH , O2- , and HO2-
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Hydrogen Peroxide Activation: Discussion • Various reactive species should allow for the destruction of a wide variety of site COCs • Thermodynamic energy could be used to generate heat activated persulfate
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• Design engineers needs to be concerned with overlapping ROIs • Issues associated with the application of hydrogen peroxide
Summary of Activation Methods Several commonly used activation methods allows the activation method to be selected by the design engineer on a site specific basis – Iron/Iron chelate: Less expensive, effective on petroleum compounds and chlorinated ethenes – Alkaline: Effective in treating most chlorinated and petroleum compounds. Proper alkaline dose should return site to near neutral pH.
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Summary of Activation Methods Continued – Heat: Effective in treating most chlorinated, petroleum compounds and perfluorinated acids. Cost and issues with subsurface heating need to be addressed. – Hydrogen peroxide: Effective in treating most chlorinated and petroleum compounds. May work via subsurface heating or direct reaction. Design engineer should evaluate overlap in subsurface distribution of each oxidant April 24, 2013
Bench Scale Tests • Bench Scale Tests can be used to: – Determine interactions of site specific geochemistry with the chemistry of activated persulfate – Generate critical design parameters
• Choosing to not bench test: – Field application design will be based on assumptions or a “standard approach” without the development of site specific design parameters – Moves risk to the field
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Bench Scale Design Parameters • Each activation method: – Non-target demand – Degradation ratio/Persulfate efficiency number
• Additional Design Parameters: – Iron/Iron chelate • Iron:chelate loading or ratios
– Alkaline • Base buffering capacity
– Heat • Treatment temperature • Soil heat capacity
– Hydrogen peroxide • Stability of hydrogen peroxide
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Case Study: AAP at an Active Facility • Key Points – Closure goal – 1 mg/L for each compound (1,1,1TCA, PCE, 1,4-dioxane) – Active, high security facility – 3rd shift/evening applications – Bench tested iron activated persulfate, alkaline activated persulfate, ZVI, calcium peroxide, RegenOx as alternatives. – Focus on safety - recommended alkaline persulfate for indoor application • Eliminate degassing/vapor issues and pressure concerns
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Site Overview • Former Vapor Degreaser • COCs – TCA (101 mg/L), PCE (20 mg/L) and 1,4 Dioxane (3 mg/L) • Fill underlying concrete floor and overlying sands and silts – till layer below – high oxidant demand
XDD identified “transition zone” between upper and lower zones contained majority of COC mass
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Injection Well Layout
• Well Network: 9 shallow and 9 deep 2” PVC injection wells to 20 feet bgs
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Operational Overview • Two injection events in 2007 • 100 to 200 g/L Persulfate • 1st event: 33,000 lbs persulfate • 2nd event: 36,000 lbs persulfate
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Long Term COC Monitoring Results Primary ISCO
Primary ISCO
Polish ISCO
Polish ISCO
• 2-3 Orders Magnitude Reduction • Target compounds remain below 1 mg/L
Primary ISCO Polish ISCO
(3 yrs post application monitoring) 30 April 24, 2013
Long Term Contaminant Monitoring Primary ISCO
Primary ISCO
Polish ISCO Polish ISCO
Primary ISCO Polish ISCO
• 2-3 Orders Magnitude Reduction • Target compounds remain below 1 mg/L (3 yr post application sampling round)
April 24, 2013
Metals Mobilization-3 years post • Monitoring wells in the source zone • Data from 3 years post application • Metals have attenuated, typically in 1 year
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Downgradient Metals Mobilization ISCO Area
Downgradient
As still at Baseline levels
Downgradient
• As and Cr were not observed to migrate downgradient in events 1 yr and 3 yr post (shown) application Downgradie nt
ISCO Area Cr still at Baseline levels
All Concentrations in ug/L April 24, 2013
Summary • Several successful methods to activate sodium persulfate • Characteristics of each method lend themselves to site specific engineered designs • Activated sodium persulfate is a proven technology that has been successfully applied in the field for several years April 24, 2013
Questions???
Philip Block, Ph.D FMC Environmental Solutions
[email protected] (215) 299-6645
April 24, 2013
Brant Smith, P.E., Ph.D XDD, LLC
[email protected] (603) 778-1100