British Geological Survey TECHNICAL REPORT WG/92/39 Mineralogy and Petrology Series

Industrial Minerals Laboratory Manual

DIATOMITE S D J Inglethorpe

Mineralogy and Petrology Group British Geological Survey

Keyworth Nottingham UnitedKingdom NG12 5GG

British Geological Survey TECHNICAL REPORT WG/92/39 Mineralogy and Petrology Series

Industrial Minerals Laboratory Manual

DIATOMITE S D J Inglethorpe A Report prepared for the Overseas Development Administration under the ODA/BGS Technology Development and Research Programme, Project 91/1

ODA Classzjkation: Subsector: Others Subject: Geoscience Theme: Mineral resources Project title: Minerals for Development Reference number:R5541

Bibliographic reference: Inglethorpe, S D J Industrial MineralsLaboratory Manual: Diatomite BGS Technical Report WG/92/39 Subject index: Industrial minerals, diatomite, laboratory techniques Cover illustration: SEM photomicrograph of the Rio Chiquito DeLas Nubes diatomite, Costa Rica. The presenceof genus Melosira sp. diatoms indicates fresh, deep water environment. The predominance of whole diatoms suggests that accumulation was by low-energy pelagic sedimentation. 0 NERC 1993

Keyworth, Nottingham, British Geological Survey, 1993

CONTENTS

Page 1. INTRODUCTION

1

2. BIOLOGY AND ECOLOGY OF DIATOMS

2

3. GEOLOGICAL, OCCURRENCE

3

4. INDUSTRIAL APPLICATIONS

6

5. LABORATORY CHARACTERISATION

9

6. LABORATORY TESTS RELATINGTO INDUSTRIAL APPLICATIONS

15

7. CASE STUDY

22

8. CONCLUSIONS

24

REFERENCES

25

APPENDICES: 1. Preparation of diatomite for examinationby optical microscope 27 2. Measurement gravity of specific

28

3. Measurement of bulk density

30

4. Sample preparation and calcination

31

5. Filtration theory

33

6. Measurement of permeability and wet cake density

34

7. Determination of oil absorption values

36

Preface Industrial mineral raw materials are essential for economic development. Infrastructure improvement and growth of the manufacturing sector requires a reliable supplyof good quality construction minerals and a wide range of other industrial mineral raw materials. Although many less developed countries have significant potential industrial mineral resources, some continue to import these materials to supply their industries. Indigenous resources may not be exploited (or are exploited ineffectively) because they do not meet industrial specifications, and facilities and expertise to carry out the necessary evaluation and testwork are unavailable. Unlike metallic and energy minerals, the suitability of industrial minerals generally depends on physical behaviour, as well as on chemical and mineralogical properties. Laboratory evaluation often involvesdetemination of a wide rangeof inter-related propertiesand must be carried outwith knowledge of the requirements of consuming industries. Evaluation may also include investigation of likely processing required to enable the commodity to meet industry specifications. Overthelast 10 years, funding from the Overseas Development Administration has enabled the British Geological Survey to provide assistance to less developed counties in the evaluationof their industrial mineral resources. This series of laboratory manuals sets out experience gained during this period. The manuals are intended to be practical bench-top guidesfor use by organisations such as Geological Surveys and Mines Departments and are not exhaustive in their coverage of every test and specification. The following manuals have been published to date: Limestone Flake Graphite Diatomite Kaolin Bentonite A complementary seriesof Exploration Guidesis also being produced. These are intended to provide ideas and advice for geoscientists involved in the identification and field evaluation of industrial minerals in the developing world. The following guide has been published to date: Biogenic Sedimentary Rocks A J Bloodworth Series Editor

D J Morgan Project Manager

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Industrial Minerals Laboratory Manual

Diatomite 1. INTRODUCTION

Diatomite is a pale coloured, soft, light-weight rock composed principally of the silica microfossils of aquatic unicellular algae known as diatoms.It has a unique combination of physical and chemical properties (high porosity, high permeability, small particle-size, large surface area, low thermal conductivity and chemical inertness) that make it suitable for a wide range of industrial applications. Its main uses are as a filter-aidin the processing of liquid foodstuffs and chemical fluids, as a filler in plastics and paints, and as a raw material for the production of insulation bricks.

This manual defines the petrographic, mineralogical, chemical and physical characteristicsof diatomite and describes simple test procedures for determining industrial specifications. Experimental results from as recent studiesin Thailand and Central America are included examples. This manual is one of a series produced as part of the BGS/ODA R&D Project ‘Minerals for Development’.

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2. BIOLOGY AND ECOLOGY

OF DIATOMS

Diatoms are classified within the Kingdom Protista which also includes protozoans, moulds andfungi (Brazier, 1990). They are single-celled organisms consisting ofa softbody (cytoplasm, oil globules and chloroplasts) enclosedby an opaline exoskeleton. The exoskeleton or frustule is composedof two halves, the smaller half fitting inside the in larger half. Frustules are either circular (centric) or elliptical (pennate) form, and are ornamented with sieve-like perforations (punctae) and intricate rib structures (costae). Diatoms create their food by combining carbon (obtained fiom photosynthesis of carbon dioxide) with nutrients extracted from seawater. They form the foundation of the Oceanic food chain as they are the staple diet of krill (tiny shrimp-like crustaceans) which support many marine vertebrates. Diatoms are adapted to a wide range of aquatic environments including marine, brackish and fresh waters. The organisms require suitable environmental conditionsif they are to flourish including appropriate temperature and photic conditions,a narrow salinity and acidity range, and a stable supplyof nutrients including silica, nitrogen, phosphorus, iron, oxygen and carbon dioxide. Diatoms inhabit the photic zone at depths down to 200m and thrive in cold watersin sub-polar and temperate regions. Recent studies have used diatom assemblages as environmental indicators in Quaternary and present-day freshwater lakes (Abella, 1988; Stager, 1988).

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Diatomite

3. GEOLOGICAL OCCURRENCE At the end of their life-cycle, opaline diatom exoskeletons settle through the water column and accumulate as ooze on the floor of the depositional environment, a process known as pelagic sedimentation; Kadey (1983) suggests an average sedimentation rate of 1-4mm per year. Diatomite,a sedimentary rock, forms by dewatering and compaction of this ooze.

Diatoms first appearsin the geological record about one hundred million years ago during the Upper Cretaceous, but most economic deposits are of Miocene-Pleistocene age. Diatomite deposits are frequently associated with volcanic activity,with air-fall ash, run-off waters and spring waters providing a source of dissolved silica to replenish that extracted by diatoms (Talliaferro, 1933). The purity of a diatomiteis chiefly controlled by clastic and/or volcanogenic input during deposition. Calcareous micro-organisms which co-exist with diatoms in equatorial marine environments also affect purity. At the present day, diatom-rich marine sediments accumulate in ocean basins in regions associated with the upwelling of nutrients, such as the in the sub-antarctic (Figure 1). Ocean zone of ocean current divergence floor areas are free from strong water movements which would introduce temgenous sediment, and are also deep enough to allow the dissolution of calcareous microfossils. However, the extensive marine Miocene-Pliocene deposits of California are known to have formed in a shallow-water neritic environment. Conger (1942) suggested that freshwater diatomite is likelyto accumulatein mountain or crater lakes, free of sediment-bearing streams or rivers, where water inflow is by seepage (Figure2). Most world deposits are of lacustrine origin. Marine in size. Gradual, deposits, although less common, are generally larger is necessary to prolonged subsidenceof marine and freshwater basins allow development of thick accumulations of diatomite.

The effect of post-depositional processes on diatomite deposits is poorly understood. Diagenetic alteration is likely to influence the porosity and degree of cementation through dissolution, mobilisation and reprecipitation of diatomaceous silica, and in extreme cases is likely to convert diatomite to chert (Mathers, 1989). Diatomaceous ooze has been reported to containa substantial proportion of organic matter derived from diatom soft bodies and so is a possible source rocks for petroleum deposits (Talliafen-o,1933). Conger (1942) reports that uplift and exposure of diatomite under good drainage conditions removes organic impurities by oxidation and leaching.

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.

-

I

.

.

.

. .. . . .. . . .. . . .

.. .. . .

Figure 1. Concentration of diatoms in surfacesedimentsofoceansat the present day (after Brazier, 1991).

Plumes of s e d i m e n t - r i c h river water e n t e r i n g l a k e as u n d e r , i n t e r a n d o v e r f l o w s , depending on d e n s i t y relative t o l a k e w a t e r

Figure 2. Sedimentological model for accumulation of diatomite in a caldera lake environment (afterMathers,1989)

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3.1 Major economic deposits

The following countries are major producers of diatomite and are responsible for 98% of world production:USA (approx. 33%), France, Romania, former USSR (CIS), Spain, Denmark, Korea, Mexico, Gemany, Italy, Iceland, Brazil (Harben, 1992). World production for 1988 was estimated at 2 Mt. with reserves of 2000 A Mt. brief survey of some commercial depositsis made below. A more comprehensive reviewof world production of diatomite is givenin Anon. (1987). 3.1.1 USA

The most extensive deposits of commercial diatomite are the late Miocene-early Pliocene marine diatomites of the Sisquoc Formation located in the foothills of the Santa Ynez mountains south of Lompoc valley, western Santa Barbera County, California, USA (Taylor, 1981; Burnett, 1991). Commercial deposits over 1000 ft. thick are extracted by the Johns-Manville Corp. and Grefco Inc. (who market M thei t e and DicaZite range of products respectively) for filter-aid and fiier production. In mid-1986 Grefco also began to extract a high-quality Miocene-Pleistocene freshwater diatomite at Lake Britton, northeast of Burney, Shasta County, for filter-aid production. 3.1.2 Romania

Romania is the largest producer in Europe with lacustrine deposits located at Adamclisis Constanta, Patiragele Buxau and Minis-Arad. in the former USSR) arealmost Diatomite products in Romania (and exclusively consumed by the construction industry.

3.1.3 France ‘Carbonisation de Actifs SA’ (Ceca) produces high-quality filter-aid grade diatomite from underground mining of a Miocene lacustrine deposit at Rioms-les-Montagnes. Ceca also operate an opencast diatomite mine at St. Bauzille on the east side of the Andance mountains. ‘Manville de France SA’ are France’s second largest producer with a mine at Murat, Cantal.

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Diatomite

4. INDUSTRIAL APPLICATIONS

In the United Statesin 1985,66%of diatomite produced was used in filtration, 21%for fillers, 1% for insulation and12%for miscellaneous uses (Anon, 1987). The world market for diatomite is increasing, although there is competition from perlite, calcined kaolin, talc, and other forms of silica (Harben, 1992). 4.1

Industrial processing

Raw diatomiteis processed using the following methods:

Primary crushing After extraction the diatomite is crushed to aggregate-size piecesin roller or hammer mills. Simultarleous drying and milling Crude diatomite (typically containing in excessof 40% moisture) is carriedby a stream of hot gases produced byan air-blower coupled to a furnace, and is simultaneously dried and milled. Air-classification The filter-aid and filler markets require powdered diatomite in different particle-size grades. These are produced by airclassification. For example, Lompoc diatomite isair classified to produce various gradesof calcined filter-aidswith different particlesize characteristics.A proportion of the dried, milled, air-classified powder is packaged and sold as ‘natural’ diatomite mainly for the filler market. Calcination Following air classification, diatomite is calcinedat 8701 100°C in a rotary kiln. The process transforms amorphous silica to crystalline a-cristobalite, reduces surface area, increases mean particle-size and increases hardness from 4.5-5.0 to 5.5-6.0 (Mohs’ scale).The main purpose of calcination is to increase filter-aid flowrate, improve the strength of fillers and increase abrasive properties. Greater changein physical properties is obtained by adding ‘soda ash’ [Na2C03] asa flux. Calcined and flux-calcined end-products are marketed both as filter-aids and as fillers. 4.2 Filtration

Diatomite is used as a filter-aid to process a wideofrange industrial and non-industrial fluids including inorganic/organic chemicals, pharmaceuticals, beer, wine, whisky, fruit juices, vegetable juices, fuels, oils,dry cleaning solventsand swimming pool waters.A filterbed of diatomite whose purpose is to aid is essentially a permeable

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Diatomite

remove fine-grained particles from a suspension and producea clear filtrate at high flowrates. 4.3 Fillers

Diatomite is usedas a fillerin paints, plastics, rubber, pharmaceuticals, toothpastes and polishes. Diatomite fillers are marketedasboth natural grades (e.g. Celite266) and as flux-calcined grades (e.g. Celite 499, 281, White Mist). In certain applications diatomite is added to modify the physical properties of the product and is therefore referred toa as ‘functional’ filler.

as flat emulsions, Diatomite is commonly added to paint products such varnishes and primers because it has excellent ‘flatting’ properties (i.e. it reduce gloss and sheen), extends the ‘hiding power’ (opacity) of the primary pigment, improves adhesionof subsequent coats (‘good tooth’) and has good sanding properties. Moreland(1987) estimates that 15% of the total industrial usageof diatomite is as a filler for plastics. Its major useis as an ‘anti-blocking’ agentin production of low-density polyethylene film; diatomite is typically added 500-3000 at ppm film. concentration and prevents self-adhesion of the 4.4 Insulation,absorbentpowders

and granules

The Danish companies Skamol and Damolin produce insulation bricks from a raw material known as ‘moler’- a natural mixture of diatomaceous silica and20-25%‘plastic’ clay (Griffiths,1990). Insulation bricks are produced as follows: (1) crude moler is fed from a hopper to a primary crusher and reduced to a particle-sizeof 2-3 mm; (2) up to 50% pinewood sawdustis added to increasethe porosityof the final product through gases generated during firing;(3) the with steam to improve plasticity, moler/sawdust blend is then mixed extruded and wire cut into lengths; (4) these ‘green’ bricks are dried at 90°C for 2-5 days and then fired. Moler isalso used to produce kiln-dried absorbent powders/granules (uses: industrial absorption, animal feed, pesticides, cat litter) and calcined powders (uses: explosives, seed coating, chemicals industry). It is likely that current uses for moler were developed because it is not 1983). sufficiently pure for filtration and filler applications (Lefond,

4.5 Miscellaneous Diatomite is also used asa mild abrasive (toothpaste and metal polish) anti-caking agentin fertilizer prills, pozzolana/concrete additive to Mineralogy and Petrology Group, British GeologicalSurvey 0 NERC 1992

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Diatomite

improves plasticand hardened properties, stabilising agent in explosives, chromatography support media, pitch controlin paper manufacture, andas a catalyst carrier (for nickel catalyst in vegetable oil in sulphuric acid manufactureand for hydrogenation, for vanadium phosphoric acidin petroleum refining).

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Diatomite

5. LABORATORYCHARACTERISATION

This section describes the mineralogical, chemical and physical properties of diatomite. Appropriate methods for the laboratory assessment of diatomite are outlined in Figure 3. Diatomite has distinctive chemical and physical characteristics, including high silica content in combination witha low SG. An optical or scanning electron microscope is usually required to detect the presence of diatoms, and XRD analysis is necessary to identify diatomaceous silica (opal A). 5.1 Chemistry

The prime criterion for judging potential industrial is uses chemical composition. Typical chemical analyses of diatomites used by industry are shownin Table 1. Diatomites used in filtration and filler applications generally contain>85% silica. Theune& Bellet (1988) define maximum of filter-aids: (1) 4 % CaO to levels for several chemical constituents prevent turbidity in beer filtration resulting from oxalic acid formation and precipitationof tartaric acid crystalsin the filterbed during wine filtration; (2) 63 pm fractionof the alter particle-size distribution. The substantial Nan Jo diatomite (Table2) is due to cementation of particles by goethite, and its largeQ pm fraction is a result of a high clay mineral content. Pure diatomite hasan SG value of 2.0-2.1, >80% porosity (total void volume) and a bulk density between 0.2-0.4 gJcm3. The presenceof mineral impurities increasesSG and bulk density values and lowers porosity. SG is generally the most reliable indicator of purity, since both influenced by particle-size bulk density and porosity are

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Diatomite

distribution as wellas mineral content. Proceduresfor the determination of specific gravity and bulk density are given in Appendices 2 and 3. High-purity diatomites are typically white, buff or greyin colour (in the as illustrated by the Burney diatomite natural state and after calcination) (Table 3). The colourof calcined diatomite is particularly affected by iron content; for example, the low brightness values of calcined Lorna Camastro diatomite are due to a pink colouration imparted by hematite (formed from thermal decompositionof alunite-group minerals). Addition of a ‘soda ash’ flux may improve the colour of the calcined product. A procedure for sample preparation and calcination of diatomite for physical propertytesting is given in Appendix4.

Table 1. Chemicalcomposition

of naturaldiatomites.

(C)

(A) Element (%) CeliteNatural Bumey 91.39 0.10 1.97 0.48 0.002 0.04 0.5 1 NA 0.07 0.00 4.18

266 86.9 0.18 3.1 1.1 NA 0.65 0.4 1

3 o.88 0.15 3.8

@)

Skamol Damolin 68-80 NA 8-10 5-7 NA 1-1.5 1-3.5

3 2-3 NA 0.5-3.5

74 1.o 11 7.O NA 2.0

1.o 0.5 1.5 NA 1.o

(A) Burney diatomitefrom Shasta County, CA, USA, extracted for filter-aid production by Grefco Inc. (BGS analysis.) (B) Johns-Manville diatomite paint filler @emmers & Kranich, 1986). (C)& (D)Dansk Moler Industriand Skamol-Skarrehenge Moler-vaerk technical literature.

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Table 2. Physicalproperties

(1)> 63 Cun (%I 63-10 (2) (%) (3) 1 0 - 2 p (%) (4) 2 lun (%I

(5) Graphic mean(w) (9Bulk density (g/cm3) (7) SG (8) Porosity (%) (9) Surface area (m2/g)

of diatomite (BGS data).

1.2 5.0 21.7 72.1 1.5 0.250

0.8 9.9 68.5 20.8 4.8 0.298 2.0 1 85 13.1

0 7.0 88.0 5.0 5.3 0.296 NA 79 3.4

18.2 3.3 19.6 58.9 1.5 0.245 2.26 89 NA

NA NA 59.8

0 24.0 66.5 9 .o 6.8 0.407 NA NA 4.7

(A) Burney diatomite, Shasta County, CA, USA. High purity: extracted by Grefco Inc. for fiter-&d production. (B) Loma Comastro, diatomite,NE of Liberia, Costa Rica. Impure: 22% clay mineral content plus alunitegroup minerals (Inglethorpe, 1990). (C) Nan Jo diatomite, Lampang,Thailand. Impure: 3040% clay mineral content plus 12% quartz and 6% goethite (Inglethorpe,1991). (D)& (E) show values for samples calcinedat 1100°C for 1hour. (1)-(4) Particle-size distributionby wet sieving and sedimentation. ( 5 ) Mean particle-size of e63 p n fraction. (6)-(9) Values fordry powdered samples.

-

Table 3. Brightnessvalues

of natural and calcineddiatomites ~

~~

~

602 filter

~

605 fiiter

606 filter

(4900 A)

(5500 A)

(4800 A)

Yellow Yellow-green Blue-green Blue Sample

(4700 A)

69.8 Burney Bumey, calcined 66.1 Loma Camastro 74.7 Loma Camastro, 30.2 calcined

69.1 66.0 75.6 32.4

~~

603filter

74.2 78.6 78.8 46.0

Mineralogy and Petrology Group, British Geological Survey0 NERC 7992

72.1 73.4 78.1 36.6

.

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Diatomite

6. LABORATORYTESTSRELATING APPLICATIONS

TO INDUSTRIAL

6.1 Filtration

Diatomite filter-aids have two functions: (1) precoat as a - a thin bed of diatomite used to filter fluids by removing suspended particles,(2)and as a bodyfeed - diatomite added to the fluid to maintain the porosity of the filter.A schematic diagram ofan industrial filtration processis shown in Figure 6. The Brewing Research Foundation(BRF) Surrey, England, has developed a modelof filtration characteristics usingpermeability and mean hydraulic radius as the principal parameters (Reed and Picksley, 1987; Picksley and Reed, 1989). These two properties control ‘flowrate’ and ‘clarity’ respectively . These are key properties referred to by manufacturers and consuming industries. An outline of 5. filtration theory is given in Appendix Permeability is defined as ‘the ability of a granular materialallow to the rate of passage of a fluid’, andis the property which determines the flow of a fluid through a filter-aid. Manufacturers and consuming industries often refer to permeability in terms of ‘flowrate’ or ‘relative flowrate’. Mean hydraulic radius is the average void size within a filteraid andis ameasure of ‘cut-off size’- the smallest size of particle that the filter-aid is able to remove from suspension. In industry this property is often referredto as ‘clarification ability’ or ‘filtrate clarity’. 6.1 .I Filtration properties

The physical propertiesof diatomite filter-aids are summarised in Table 4. In a preliminary investigation,it is not practical to determine all the will give parameters given in Table4. Permeability and wet cake density a good indication of likely filtration performance. Parameters such as mean hydraulic radiusand effective void volume are useful theoretical concepts (Appendix5)’ but are not essential to a preliminary investigation of diatomite forfilter aids. Table4 shows that increasing the particle-sizeof a filter-aid raises‘flowmte’ by increasing permeability, and lessens ‘clarity’ by increasing mean hydraulic radius. Procedures for the determination of permeability and wet density values of calcined diatomites are given in Appendix 6. Theune & Bellet (1988) state that calcined diatomite filter-aids have permeability values 9.03 pm* and wet density values (the density of a filter-aid precoat) between 0.35-0.5 gJcm3. The authors suggest that high permeability values are required for fast flowrates, and that low wet density values are Mineralogy and Petrology Group, British GeologicalSurvey 0 NERC 1992

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Diatomite

necessary to provide porosity for the retention of particles removedfrom fluid during filtration. ‘Total void volume’is calculated fromSG and wet density values as follows:

Total void volume(% porosity)= [1-(wet density/SG)]* 100/1 Permeability canbe measured with simple experimental apparatus using Darcy’s Law: Permeability (13)[pm2] = p U L * 1012

AP

p = viscosity of water at20 O C U = superficial velocity= (volumetric flowrate [m3/s] / cross-sectional area [m*]) AI? = pressure drop across bed L = depth of bed [m] Diatomite shouldbe prepared for thesetests using the preparation and calcination procedure described in Appendix 4. During the test only volumetric flowrate(U) and depthof bed (L) are recorded, as the other parameters are constant. The apparatus usedcany to out permeability and wet density determinationsis illustrated in Figure 7. Procedures for particle size measurement of mineral powders are given elsewhere in this series of manuals.

Mineralogy and Petrology Group, British Geological Survey 0 NERC 1992

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Diatomite

diatomite particle

- liquor particle Liquor + bodyfeed

Precoat

Filtrate

M

Glossarv: Filter septum - a wire mesh or cloth screen upon which precoatis deposited Precoat - a thin permeable bed of diatomite particles deposited on fiter septum prior to filtration Filtration - process for removing suspended particles from a liquor liquor - industrial fluid containing particles in suspension Body feed - diatomite added to the liquor to maintain flowrate by increasing porosity of the filter-cake.

Filter-cake - a layer comprised of diatomite and liquor particles which builds up on the ofsurface the precoat during filtration

Filtrate - clear liquor that has passed through the precoat Flowrate - volume of filtrate that passes through precoat with respect to time Clarity - amount/or lack of particles present in filtrate

Figure 6. Schematic diagram of an industrial filtrationprocess

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..

.. ......

.

.

.~

,

. ..;.

.

.

..

,..

. ... .

~

.. .

- .

,

Diatomite

Table 4. Filtrationproperties literature).

of diatomitefilter-aids

(BGS experimentaldataandtechnical

‘Flowrate’ particle

void

Product ~~

~~~

‘Clarity’ Mean Wet Measured void cake hydraulic permeability radius volume volume density m21 [PI [g/cm31

Total

Effective

Mean

[%I

size [WI

SG

[%I

5.8 5.3 5.9 NA 7.1 * NA 6.8 * 7.5 10.7 *

2.25 2.01 2.25 NA NA NA NA 2.25 #I NA

~

speedflow Hyflo Supercel

0.02 # 0.04 0.04 # 0.069 0 0.07 * 0.20 0 0.22 0 0.22 # 1.62 *

NA NA NA 0.3 0 NA 0.5 0 0.7 0 NA NA

NA 0.42 0.352 NA NA NA NA 0.368 # NA

NA 79 84 NA 83 * NA 86 * 84 86 *

NA NA NA 17 0 27 * 25 0 35 * NA 58 *

Nan Jo (ax)

0.02

NA

0.59

73

NA

Dicalite 215 Bumey Superaid FPlW Celite 578 FP4 Standard Supercel

0

Reed & Freeman (1991).

* Reed & Picksley (1987). # Manufacturer’sdata.

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2.1 3.1

7

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Diatomite

Figure 7. Laboratory filtration apparatus. Components are connected in seriesto a filterpump as follows:(1) conical flask, (2) vacuum regulator unit, (3) bleed valve, (4) vacuum meterand (5) filtration unit.

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6.2. Fillers

General characteristicsof fillers that influence usage include colour oil absorption surface wetting and bonding properties chemicalresistance strength/iability. The physical properties of diatomite fillers summarised are in Table 5; chemical specifications are discussed in section 5.1. Remmers and low Krannich (1986) cite high oil absorption, high silica content and bulk density as important properties of diatomite fillers for paint. A procedure for determination of oil absorption by diatomiteis given in Appendix 7.

of diatomitefillers

Table 5. Physicalpropertyspecifications

for paintsandplastics.

Celite:

NA NA

NA NA NA

NA NA

supmoss* White Silver Frost K 5 * White White White Mist* 266# Grey trace White 499# 28 1# White

0.1 trace trace 0.5 82 1.5

96 99 96

92

NA NA

68

NA NA

Type 1 diatomite* / Type 2 diatomite* /

15 5

70 75

10 20

NA

/ 5

NA NA NA 16 1 3

120 115 160 135 105 110

9-10 9-10 9-10 6.5 9.5 9.5

/ /

60-100 60-100

6.5-10 / 6.5-10 /

* Moreland (1987). #Remmers I &h

i c h (1986).

5 BS 1795 (1976).

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1.48 1.48 1.48 1.42 1.48 1.48

NA NA NA

0.7-3.5 0.7-3.5 0.7-3.5

0.128 0.136 0.136

NA NA NA

NA NA NA NA NA NA

/ /

/ /

1 1

NA NA NA

NA NA NA 15 1

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Diatomite

6.3. Insulation bricks, absorbent powders and granules Insulation bricks are produced from a Danish clay-rich diatomite known as ‘moler’ which is characterised by a lowSi02 content and high levels of Fe2O3 and A1203 compared to other commercial diatomites (Tablel). The physical specifications for insulation bricks are based on bulk density, porosity, cold crushing strength and thermal conductivity (Table 6). The heat resistant properties (or low thermal conductivity) of diatomite The Danish bricks resultfrom their high porosity (or low bulk density). company Skamol produce seven types of insulation brick (with a temperature resistanceof 900-950°C) classified on the basisof bulk density; low bulk density bricks have good heat resistance but only moderate strength whereas high bulk density bricks have better strength of these products arein kiln but lower heat resistance. The main uses and furnace applications.

Table 6. Typicalphysicalproperties

of diatomiteinsulationbricks. ROTOL

HTpoR(450)

Bulk density (kg/m3)

800

Porosity (%) Cold crushing strength (kg/cm2) Modulus of rupture (kglcm2) Thermal conductivity (kcal/m hr “C)

66 100 20 0.17-0.2 1

450 81 8 NA 0.09-0.16 ~~

Data source: Skamol-Skarrehenge Moler-vaerk technical literature. (Thermal conductivity valuesquoted are for temperature range200-80O0C.)

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Diatomite

7. CASE STUDY 7.1 Diatomite, Thailand A 20 kg sample of diatomite was collected from Nan Jo quarry, Mae Tha, Lampang Province, Thailand. A laboratory study was planned to define the chemistry, mineralogy, petrography and physical properties of the diatomite, examine mineral processing techniques to reduce levels of mineral impurities, and evaluate the sample as a potential industrial raw material for filter-aid production (Inglethorpe, 1991). A flowsheet summarizing the laboratory investigation of this material is shown in Figure 8.

Nan Jo quarry is situated to the south of Lampang. Diatomiteis currently extracted for use by the local paper-making industry. The geological map ofthis area is the Department of Mineral Resources (DMR) Changwat Lampang 1:250000 scale sheet. The diatomite sequence is partof the MaeMo Group which consistsof freshwater sandstone, shale, carbonaceous shale and lignite beds of Miocene-Pliocene age. The sample examined in this study was collected from the basalbed of the 10 m high north face of the quarry. Results indicated thatthe Nan Jo diatomite contains30-40% clay minerals, 12% quartz and6% goethite. These impuritiesare probablyof in a relatively high-energy detrital origin. The sample was deposited freshwater environment. Attrition during sediment transport reduced whole diatoms to 10-1 pm size fragments. The sample has aSi02 low and high A 1 2 0 3 and Fe2O3 content compared to diatomites utilised by industry. Mineral processing trials were not effective in upgrading the sample. The filtration performance of the Nan Jo diatomite is poor. Calcined samples are of low permeability (0.02 prnz), high filter-cake density (0.57-0.61 g/cm3) and small average particle-size (2.5-3.7 pm). The iron oxide content ofthis material is above levels acceptable for the processing of foodstuffs. The sampleis therefore unlikely tobe suitable for use in filter-aid applications. However, the chemistry and mineralogy of the Nan Jo sample aresimilar to commercially-mined diatomites usedin the production of insulation bricks.

Mineralogy and Petrology Group, British Geological Survey 0 NERC 1992

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Diatomite

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PETROGRAPHY:

- Optical

I I I ( II

microscopy

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