Industrial Applications

Chapter 4.2

Industrial Applications C.C. Harveya and G. Lagalyb a b

Institute of Geological and Nuclear Sciences, Wairakei Research Centre, Taupo, New Zealand Institut fu¨r Anorganische Chemie, Christian-Albrechts-Universita¨t zu Kiel, Kiel, Germany

Chapter Outline 4.2.1. Industrial Uses 453 4.2.1.1. Common Clays 453 4.2.1.2. Kaolins 453 4.2.1.3. Bentonites 457 4.2.1.4. Vermiculites and Micas 467 4.2.1.5. Talc and Pyrophyllite 468 4.2.1.6. Palygorskite and Sepiolite 468 4.2.1.7. Mixtures of Clay Types 468 4.2.2. Processing Industrial Clays 469 4.2.2.1. Purification and Fractionation 469 4.2.2.2. Processing of Kaolins 471 4.2.2.3. Raw and Activated Bentonites 471 4.2.3. Laboratory Evaluation of Clay Samples 478 4.2.4. Categorization of Clay Resources 478 4.2.4.1. Categories of Industrial Clays 479 4.2.4.2. Examples of Different Categories 479

4.2.4.3. Role of Categorization in Assessing Industrial Clay Resources 480 4.2.4.4. Relationship Between Category and Annual Tonnage 481 4.2.4.5. Relationship Between Category and Resource Confidence 481 4.2.4.6. Relationship Between Category and Value 481 4.2.4.7. Relationship Between Category and Pre-Investment Capital 482 4.2.4.8. Relationship Between Category and Investment Capital 482 4.2.5. The Resource Evaluation Process 482 4.2.6. Other Considerations 484

Developments in Clay Science, Vol. 5B. http://dx.doi.org/10.1016/B978-0-08-098259-5.00018-4 © 2013 Elsevier Ltd. All rights reserved.

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4.2.6.1. From Laboratory-Scale Testing to Major Plant Scale 484 4.2.6.2. Level of Applied Technology 484 4.2.6.3. Losses Associated with Applied Processing Steps 485

4.2.6.4. Time to Move from Commissioning to Full Production 4.2.6.5. Reducing Risk During Development 4.2.7. Conclusions References

485 485 486 486

Clays and clay minerals are extensively used in a wide variety of industrial applications (Grim, 1962; van Olphen, 1977; Lagaly and Fahn, 1983; Jepson, 1984; Odom, 1984; Murray, 1986, 1999, 2000, 2003; Harvey and Murray, 1997). Their use falls into two contrasting, broad classes: i. Clays are used because of their inertness and stability. A large variety of industrial uses are also related to the unique rheological properties of clay and clay mineral dispersions. ii. Clays are used because of their reactivity and catalytic activity. In the following section, the various families of clays are discussed in terms of their inert or reactive applications and their unique rheological properties. In many cases, the different clay types are modified to meet required specifications. Pure clays do not usually occur in nature. In terms of tonnage used, we may distinguish four classes of clay. The so-called common clays enjoy the largest use in numerous engineering applications. These clays contain mixtures of different clay minerals such as illite–smectites (I–Sm), kaolinites, smectites, micas and associated minerals. This is followed by ‘industrial kaolins’, which contain relatively high amounts of kaolinite and, sometimes, a small proportion of high-quality kaolin minerals. The third class is ‘bentonite’ with a high smectite, mostly montmorillonite (Mt), content. The fourth class of clays is the ‘palygorskite–sepiolite’, which have many similarities to bentonites and are specifically used because of their surface properties and reactivity. The world production of processed kaolins is about 20 million tons/year and that of bentonites is 13 million tons/year, while palygorskite–sepiolite production is around 2 million tons/year. The amount of common clays used worldwide is difficult to estimate since there are no statistics. However, it is likely to exceed many hundreds of million tons per year. There are also a few deposits of high-purity clays, such as halloysite (used in high-quality porcelain and catalysis) and hectorite (used in cosmetics and pharmaceuticals). Their peculiar properties classify them as high-quality additives rather than bulk industrial minerals. In addition, some finely ground minerals with properties similar to those of some industrial clays are frequently included in industrial clay surveys. They include vermiculite, mica, talc and pyrophyllite. A brief summary of their uses is included here.

Chapter

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4.2

Industrial Applications

453

INDUSTRIAL USES Common Clays

The technologies associated with the engineering properties of clays are not covered in this chapter. Large tonnages of common clays are used in a wide variety of engineering applications including road construction, fill, dam construction and waste containment. The mineralogy and particle size distribution determine their engineering properties. Large tonnages of common clays are used in ceramic production (bricks, tiles, terracotta, earthenware, stoneware, sewer pipes, paving bricks, refractory bricks, etc.). Although these clays are typically impure, they contain sufficient clay minerals to cause them to develop plasticity and to produce adequate strength, porosity and other properties to justify their use. These raw materials may contain high amounts of mixed-layer clay minerals, notably I–Sm. As I–Sm particles can delaminate to a certain extent depending on their layer charge distribution (see Chapter 8 in Volume A), the type of I–Sm may influence the ceramic properties of common clays and their behaviour in dispersions (for casting processes, etc.). A small amount of smectite can be tolerated or is added to improve plasticity. Large amounts of smectite would give undesirable shrinkage and drying properties. The presence of kaolinite is not desirable in clays used for bricks and tiles because kaolinite would increase the firing temperature and a light burnt colour is not acceptable (Grim, 1962).

4.2.1.2

Kaolins

4.2.1.2.1 Kaolins as Filler and Coating Particles Table 4.2.1 provides a general summary of the uses of clays as inert components in industrial systems (Murray, 1986, 1999, 2000; Harvey, 1997; Harvey and Murray, 1997). Amongst the earliest industrial uses of clays are waterbased systems such as paper or water-based paints where the hydrophilic nature of clays enables them to readily disperse in such systems. However, kaolins were long used as fillers for plastics and rubber. To make the hydrophilic surface of the clay mineral compatible with the organic material, the surface is modified by reacting with organic compounds, in most cases by grafting. If the clay mineral particles are highly dispersed in the polymer matrix and the adhesion between the filler particles and the matrix is good, the kaolinite particles act as active fillers, that is, they improve certain mechanical properties of the polymers (Lagaly, 1999). Modern developments in this field not only aim to increase the bonding strength between the filler particles and the polymer matrix but also to produce clay mineral–polymer nanocomposites where the fully delaminated mineral is dispersed in the matrix.

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TABLE 4.2.1 Uses of Clay Minerals as Inert Components Clay family

Industry

Use

Kaolin

Paper, plastics, rubber

Filler

Pesticides

Carrier, diluent

Building industry

Heat insulation, sound dissipation

Package industry

Shock-proof materials, thermal protection, liquid absorption thermal protection

Vermiculite

Foundries Mica

Electrical industry

Insulation

Paints

UV-, heat-stable and under-water paints

Cosmetics

Nacreous pigments

Coating

Corrosion proof polymer coatings, underseal

Talcum, pyrophyllite

Plastics, rubber, paper industry, cosmetics, pharmaceutics refractory industry

Filler Powders, pastes, ointments, lotions Refractories

Palygorskite, sepiolite

Pesticides

Carrier for insecticides and herbicides

Chemical industry

Catalyst carrier, filter material, anti-caking agent

Cosmetics, plastics

Filler

Metakaolinite is commonly used in the preparation of geopolymers1 (Buchwald et al., 2009; Zibouche et al., 2009). Kaolin, bentonite, palygorskite and sepiolite are used as carriers and diluents of pesticides (insecticides, fungicides, herbicides). Enhanced application of herbicides requires particular formulations based on modified clay minerals (see Chapter 5.2). The largest amounts of processed kaolins (more than 60% of the word production) are used in the paper industry as fillers within the network of cellulose fibres and as coating particles. The technical requirements for filler clays are significantly less than for kaolinite particles in the coating colours. Gloss, 1. Geopolymers are synthetic aluminosilicate materials with many potential uses, essentially as a replacement for Portland cement, for ceramic applications and advanced nanocomposites.

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80

60

325 mesh

Mass percent finer than

100

Filler

Coating

Thin particles

40 Thick particles

20

0 100

50

20 10 5 2 1 Equivalent spherical diameter (µm)

0.5

0.2

0.1

FIGURE 4.2.1 Typical particle size distribution of filler and coating grade kaolins. From Murray (1986).

brightness, opacity and smoothness generally improve with increasing coat mass and decreasing particle size. The
2 mm fraction is particularly important in coating kaolins and high-glossing paint kaolins. More than 70% (m/m) of the coating particles should be smaller than 2 mm. Very finely divided kaolins can cause technical problems. Filler clays typically have 50–70% particles >2 mm (Jepson, 1984; Murray, 1986, 1999, 2000) and the optimum particle size for lodging within paper fibres is 5–7 mm. Typical particle size distributions of industrially processed filler and coating kaolins from the sedimentary kaolin deposits in Georgia (USA) are illustrated in Fig. 4.2.1. Coating of paper is done at very high speeds (1200 m/min and even more) using large machines (Bundy, 1993). As such, it requires an exact tuning of the rheological properties of the highly concentrated slurries. In blade coating, the rate of shear can reach 106 s1 along the line of contact of the blade with the paper. The relation between bulk kaolin properties and coating colour rheology is complex. Particle shape, size, size distribution and particle packing are critical factors. For the same clay content, dispersions of thin, large particles have higher viscosities than those of blocky particles. The more platy the particle shape, the lower is the shear rate at which shear thickening starts. To prepare homogeneous slurries of kaolin with up to 70% (m/m) solids, anionic macromolecules, mainly polyphosphates and polyacrylates,2 are added. This enhances the negative charge density at particle edges, providing steric stabilization to the dispersion (see Chapter 8 in Volume A). It is necessary to select appropriate size fractions and particle shapes to obtain the 2. Some polyphosphate-containing kaolin slurries can form gels within a few hours if left undisturbed, producing discharge problems. Gelation is retarded or impeded by adding sodium polyacrylates.

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required rheological properties (yield value, viscosity, thixotropy). One also has to consider the interaction of the coating particles with the thickeners (often carboxy methylcellulose and starch), as this plays a key role in controlling the rheological and dewatering properties (Li et al., 2001).

4.2.1.2.2 Kaolins in Ceramics A major use for high-purity kaolins is for ceramic products such as porcelain, bone china, vitreous sanitary ware and earthenware. Low-quality kaolins are also used as fillers in a wide range of ceramic products including brick, pipes and tiles. Refractory clays are predominantly composed of kaolins with low levels of iron, alkali and alkaline-earth cations. High levels of such metals would reduce the fusion point. Delamination of kaolinite particles3 improves the quality of porcelain. Delamination of kaolinite particles by intercalation of urea was used by Chinese ceramists to produce very thin (eggshell) porcelain of high mechanical stability (see Chapter 10.3 in Volume A). Delamination was also used in the production of specialty paper clays. Delamination of kaolin stacks of large particle size can convert filler clay into high-surface-area platelets with superior opacity in lightweight coatings (Bundy, 1993). The presence of smectites in commercially exploited kaolin resources is undesirable for most industrial applications. The smectites may therefore have to be removed in order to meet the required specifications. As these minerals are generally concentrated in the finest size fractions (<0.5 mm) of kaolins (Fig. 4.2.2), size fractionation can help to reduce the smectite content. Chemical modification of the smectites was also proposed to reduce their negative effect (Jepson, 1984). Historically, mainly in China and Eastern Asia, clays and kaolins for the production of fine ceramics were traditionally matured by placement in humid pits for several years. The improvement in properties is caused by the modification of particle size (and possibly composition) through the action of microorganisms. This beneficiation process is currently attracting the attention of scientists (Groudeva and Groudev, 1995; Lee et al., 2002). Ceramic masses can be shaped because of the unique ability of clay mineral particles to form ‘card house’ or band-type networks (see Chapter 8 in Volume A). On the other hand, the ease with which clay mineral particles form stable colloidal dispersions also allows the production of ceramics by casting, especially porcelain and vitreous sanitary ware. The deflocculated slip (total solid content 70% (m/m) is poured into a porous plaster mould so that a filter cake builds up on the plaster surface. The mould is inverted, and the excess slip is allowed to drain. After de-watering in the mould, the cast is removed, and, 3. In terms of strength, ‘delamination’ describes the splitting of the particles into single silicate layers (see Chapter 1). In industrial applications, ‘delamination’ stands for the splitting of aggregates into single particles or smaller aggregates.

4.2

Composition (% mass)

Chapter

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80

K M 40

S

F,Q 0 100

10 1 Equivalent spherical diameter (µm)

0.1

FIGURE 4.2.2 Variation in mineral composition with particle size for Cornish kaolin. F, feldspars; Q, quartz; M, mica; S, smectite; K, kaolinite. From Jepson (1984).

after a few further steps, is sprayed with glaze and fired (Jepson, 1984). This technique needs fluid colloidal dispersions with clay contents as high as possible. Liquefaction requires the addition of sodium salts and a pH above 6. At the same water content, a sodium kaolinite dispersion can be fluid whereas calcium kaolinite forms a plastic mass (see Chapter 8 in Volume A). This behaviour was first described by von Liebig (1865). Fine ceramics produced by slip casting commonly have a higher dry breaking strength than shaped ceramics. The filter cake built up during slip casting consists of kaolinite particles that are more densely packed in parallel orientation as compared with moulded plastic masses in the presence of calcium ions (Hofmann, 1962a). In technical processes, the charge on particle edges is changed from positive to negative by the addition of multivalent anions, particularly oligo- and polyphosphates as well as polyanions such as polyacrylate and less well-defined macromolecular compounds such as humic substances. These additives often impart a certain amount of steric stabilization to the dispersion (see Chapter 8 in Volume A). One of the most effective dispersants for modern highperformance ceramics is oxidized fish oil (Bo¨hnlein-Mauß et al., 1992). Liquefaction of a mass of 100 g kaolinite (China clay) in 200 ml water by 1 g tetrasodium diphosphate (Na4P2O710 H2O) is illustrated in Fig. 4.2.3. The fluid dispersion can stiffen again by the addition of salts such as KCl (in this case 3 g/100 g clay), causing the clay mineral particles to coagulate.

4.2.1.3

Bentonites

World production tonnages for bentonites are very difficult to obtain. Our best estimate is 13 million tons and the major uses are iron ore pelletizing, foundry

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C

Shear rate (s−1)

B

A 100 g China Clay 200ml water

+ 1 g Na4P2O7.10 H2O

500 + 3 g KCl

100 0 0

50 100 Shear stress (Pa)

150

FIGURE 4.2.3 Liquefaction of kaolin by tetrasodium diphosphate. (A) 100-g China Clay in 200 ml water. (B) Liquefaction by addition of 1 g Na4P2O7 10 H2O. (C) Again stiffening by addition of 3 g KCl. Data from M. Mu¨ller-Vonmoos, ETH Zurich. From Jasmund and Lagaly (1993).

Adsorbents 29.4%

Foundry 23.5%

Refining 3.1%

Iron ore pelletising 13.3%

Agronomy 7.3% Building industry 3.4%

Drilling fluids 13.2% Other 6.9%

FIGURE 4.2.4 Use of bentonite. World production may have been 13 million tons in 1993 (Courtesy N. Schall, Su¨d-Chemie AG, Germany).

mouldings and oil-well drilling (Fig. 4.2.4). However, the use of bentonite in numerous environmental applications is growing fast. Large volumes are needed for filtering, decolourizing and clarifying (mostly in the form of bleaching earths), pelletizing animal feed, as pet litter adsorbent,4 pesticide carrier and oil and grease adsorbent. Smaller amounts of bentonites are needed for paints, pharmaceutical and cosmetic uses, waste disposal, lubricants, as additives for cement and mortar, as catalysts and catalyst supports, water purification, fertilizers, animal nutrition (Kim et al., 2009; Slamova et al., 2011), ceramics and 4. The effectiveness of clays for pet litter may also be related to the deactivation of enzymes that convert urea to ammonia.

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other miscellaneous applications such as additives in washing powders, for newspaper recycling, cleaning waste water from car washes and as flocculation aids, often together with soluble flocculating agents such as polyions, alum (aluminium sulphate) and iron chloride (Tables 4.2.2A, 4.2.2B and 4.2.3) (Grim, 1962; Odom, 1984; Fahn and Schall, 1985; Murray, 1986, 1999, 2000; Schall, 1988; Harvey and Murray, 1997; Caine et al., 1999; Panpanit and Visvanathan, 2001; Philippakopoulou et al., 2003). Recent developments aim to use smectites, mainly Mt, in the preparation of electrodes useable as sensors (Fitch, 1990; Fitch et al., 1998; Fendler, 2001; Mousty, 2004; Darder et al., 2005; Yao et al., 2006; Muralidharan et al., 2008; Xu et al., 2008), for immobilization of enzymes (Chang et al., 2007; Gopinath and Sugunan, 2007; Xu et al., 2008; Ghiaci et al., 2009a,b; Sedaghat et al., 2009a,b; Wicklein et al., 2010), as bactericidal materials (Zhou et al., 2004; Dizman et al., 2007; Meng et al., 2009; Holesˇova´ et al., 2010; Miyoshi et al., 2010), as adsorbents of toxins (Zhou et al., 2005; Jaynes et al., 2007; Dixon et al., 2008), and for biomedicinal applications (Kim et al., 2009; Long et al., 2009).

4.2.1.3.1 Bentonite as Binding Agents Bentonites are extensively used as binding agents in the pelletization of iron ore, other fine-grained solids and animal feed. The sands are prepared with about 2% bentonite. The Mt layers ensure adhesion between the particles in a similar way as described for moulding sands (see below). Natural sodium and sodiumexchanged calcium bentonites are preferred for iron ore pelletizing because of their high capacity for removing excess water from the powdered ore. In other cases, both sodium and calcium bentonites are used. Bentonite added to animal feeds can increase their nutritional value (Slamova et al., 2011). TABLE 4.2.2A Uses of Clay Minerals Based on Their Rheological Properties Clay family

Industry

Uses

Common clays

Ceramics

Tiles, bricks, earthenware, stoneware, sewer pipes, sanitary ware, refractory bricks

Kaolins

Paper

Coating

Ceramics

Porcelain, bone china, vitreous sanitary ware, earthenware

Bentonites

See Table 4.2.2B

Palygorskite, sepiolite

Paints, chemical and mineral oil industry

Thickening and thixotropic additive, dispersing and anti-settling agent, drilling fluids

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TABLE 4.2.2B Uses of Bentonites Based on Their Rheological Properties Area of applications

Uses

Activationa

Agriculture, horticulture

Soil improvement

r, s

Building industry

Supporting dispersions for cut-off diaphragms

r, s

Wall constructions, shield tunneling, subsoil sealing, antifriction agents for pipejacking and shaft sinking additions to concrete and mortar

r, s

Ceramics

Plasticizing of organic masses, improvement of strength, fluxing agents

r, a

Foundries

Binding agents for moulding and core sands

r, s

Binding agents for anhydrous casting sands

o

Thickening of blackwashes

o

Mineral oil industry

Drilling fluids, thickening of greases

r, a, o o

Paints, varnishes

Thickening, thixotroping, stabilizing, antisettling agents

s, o

Coating materials, sealing cement, additives for waxes and adhesives

s, o

Pharmaceutical industry, cosmetics

Bases of creams, ointments and cosmetics

r, a, s

Stabilization of emulsions

r, o

Tar exploitation

Emulsification and thixotroping of tar–water emulsions, tar and asphalt coatings, additives for bitumen

a, o

a

r, raw bentonite; a, acid-activated bentonite; s, soda-activated bentonite; o, organo-bentonite.

In foundry moulding sands, the clay mineral particles have to make the sand plastic and cohesive so that the sand can be moulded around a pattern. The bentonite also gives the sand sufficient strength to resist the thermal stress of the molten metal. Green compression strength, dry compression strength, wet tensile strength, hot compression strength, flowability and durability (clay-bonded moulding sands are recycled many times) are crucial properties in foundry usage. Again, the Naþ/Ca2þ ratio is very important to adjust these properties (Odom, 1984). Natural sodium bentonites have better durability and higher fusion temperature and are favoured for use in steel foundries. Bentonites containing Ca2þ ions are preferred for preparing moulds for iron casting. Many foundries use specified blends of specific types of sodium and calcium smectites to achieve the optimum moulding sand properties.

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TABLE 4.2.3 Uses of Clay Minerals Based on Their Adsorption Properties and Reactivity Activationa

Clay family

Industry

Uses

Kaolin

Fibre glass

Source of alumina

Petrochemicals

Catalyst support

Chemical industry

Zeolite synthesis

Building industry

Additive in cement

Agriculture, horticulture

Soil improvement, composting adsorption of mycotoxins

r, s o

Chemical industry

Sulphur production: refining, decolouration, bitumen extraction

r, a

Catalysts

r, a, s

Carriers for pesticides

r, a, s, o

Dehydrating agents

r, a, s

Adsorbents for radioactive materials

r, a, s, o

Regeneration of organic fluids for dry cleaning

a

Polish and dressings

r, s

Additives for washing and cleaning agents and soap production

r, s

Forest and water conservation: fireextinguishing powders, binding agents for oil on water

r, a

Animal husbandry, manure treatment, cat litter

r, s

Water and waste water purification

r, s, a

Sewage sludge pelletizing

r, a

Barriers

r, s

Refining, decolouration and stabilization of vegetable and animal oils and fats, animal nutrition

r, a

Fining of wine, juices, beer stabilization, purification of saccharine juice and syrup

r, a, s

Bentonite

Cleaning industry

Environmental technology

Food industry

Continued

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TABLE 4.2.3 Uses of Clay Minerals Based on Their Adsorption Properties and Reactivity—Cont’d Clay family

Palygorskite and sepiolite

Industry

Uses

Activation

Mineral oil industry

Refining, decolouration, purification and stabilization of mineral oils, fats, waxes and paraffins

r, a

Paper making

Pigment and colour developer for carbonless copying paper

a

Adsorption of impurities in circulating water

r, a, s

De-inking in waste-paper recycling

r, a, s

Cosmetics, pharmaceutics

Powders, tablets, drug carrier, odour control, liquid absorption

r, a, s, o

Environment

Chemical industry decolouration, anti-caking agent Cigarette filters (sepiolite), cat box litter

Adsorbent, carrier, bleaching

a

r, raw bentonite; a, acid-activated bentonite; s, soda-activated bentonite; o, organo-bentonite.

The importance of having sodium ions in the interlayer space was described by Hofmann and Endell (1935, 1936). Adding soda ash (Na2CO3) to German bentonites that are not suited for foundry-moulding sands should make such clays suitable for use as a moulding sand binder.

4.2.1.3.2 Bentonite in Drilling Muds Oil-well drilling fluids are colloidal dispersions of a complex composition (van Olphen, 1977; Odom, 1984; Darley and Gray, 1991; Karagu¨zel et al., 2010). First of all, the fluid acts as a lubricant to reduce the friction between the drilling string and the side of the hole. The drilling fluid is circulated to bring the drill cuttings from beneath the bit up to the separation site and to cool the bit. Therefore, drilling fluids must have a relatively high density to carry the fine cuttings. The drilling fluid builds up an impermeable filter cake of Mt particles on the side of the hole, preventing the loss of fluid into the permeable rock (see Chapter 8 in Volume A). It also prevents the inflow of fluids (oil, gas or water) from permeable rocks. When the drilling operation is interrupted before the drill cuttings and sand were circulated out of the hole, the thixotropic stiffening (see Chapter 8 in Volume A) of the drilling fluid prevents settling of the fine material. In offshore drilling or drilling through salt domes, the fluid must be protected against destabilization by salts.

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463

Drilling fluids are mainly based on dispersed sodium bentonites. The particular requirements can only be fulfilled by components whose properties may, in some cases, be counteractive. For instance, the thixotropic property of the fluid requires conditions that are adverse to optimal plastering. When calcium and/or barium sulphate are added to enhance the density, or calcium and barium hydroxide are added to reduce the large increase of viscosity at the high temperatures in deeper holes, the divalent cations would cause coagulation of the dispersed particles. This effect is usually overcome by the addition of complexing macromolecular compounds, which also impart a high degree of steric stabilization. A well-known additive is carboxymethyl cellulose. Other macromolecular compounds such as polyphosphates are less effective as steric stabilizers but they improve the salt stability by reversing the edges of the clay mineral particles from positive to negative, or by increasing the negative edge charge density. The common Quebracho tannates in the red muds exert both effects (see Chapter 8 in Volume A).

4.2.1.3.3 Bentonite in Engineering Bentonite dispersions are used in many civil engineering applications. Most impressive is the diaphragm-walling technique. A thixotropic bentonite dispersion is used as an intermediate supporting material, obviating the need for revetting (retaining wall) when the trench is excavated. In addition, the plastering effect (see Chapter 8 in Volume A) is important. The slurry penetrates only to some extent into the trench sides and forms an impermeable filter cake of clay mineral layers on the walls so that excessive loss of fluid to the surrounding formation is prevented. In the next step, the bentonite dispersion is displaced by the concrete (Fig. 4.2.5). Concrete walls about 100 m deep and 0.8–1.5 m thick are built up by this technique. (It is interesting to note that the stabilizing effect of bentonite dispersions was observed in the middle of the nineteenth century. The first patent was issued in 1912 but the technique was only widely applied since about 1950.) In other applications, bentonite dispersions are used to grout cracks and fissures in rocks, for soil injection, or to impede water and waste water movement through soils, sand or gravel. Examples are sealing waste deposits, sewage ponds or ornamental ponds. The dispersions are used as lubricants not only in drilling fluids but also to lubricate caissons (Fig. 4.2.6) and piles or cables as well as pipes for pulling through conduit. In shield tunneling the thixotropic bentonite supports the soil in front of the shield until it is removed by the tools of the rotating shield. It also has to keep back ground water and transport the excavated soil to a separation plant above ground. Bentonite can be added to waterproof concrete walls and floors, or added to mortar to increase its plasticity (Kryer et al., 2003). Bentonite also serves as an important additive in bitumen emulsions. The properties of bentonite that are most significant in the above-mentioned civil engineering applications are viscosity, yield value, thixotropy, plastering

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FIGURE 4.2.5 Diaphragm walling. Excavation of a trench and its subsequent lining with a thixotropic bentonite slurry.

ability and plasticity. Thus, only natural sodium bentonites and certain sodiumexchanged calcium (magnesium) bentonites are suited for the purpose.

4.2.1.3.4 Bentonite as a Thickener Bentonites are added to paints and enamel paints not only as thickening agents and gellants but also to impart a certain degree of thixotropy to the dispersion thereby impeding sagging of the paints (Jones, 1983) (Fig. 4.2.7). In non-polar systems, the clay mineral particles have to be hydrophobized.

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Industrial Applications

Bentonite dispersion as lubricant Caisson Cutting

FIGURE 4.2.6 Caisson sinking and pipe checking. A highly viscous bentonite slurry reduces the friction between the building structure and soil (outer light-shaded piece). Shown is the cutting face of the caisson to be sunk or the pipe to be checked.

FIGURE 4.2.7 Addition of a thixotropic agent. It impedes sagging of the paints. From Lagaly et al. (1997).

4.2.1.3.5 Activated Bentonites, Fuller’s Earth and Catalysis A large number of diverse of applications are related to the adsorption capacity and chemical reactivity of bentonites (Table 4.2.3). Their ability to adsorb proteins and high molecular weight compounds is useful for stabilizing beer,5 5. When the proteins are not removed from beer, their decomposition makes the beer undrinkable.

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and improving the taste and quality of juices and even cheap wines (Rankine, 1995; Sarmento et al., 2000). An up-coming important application is the use of modified bentonites as adsorbent of mycotoxins. These excretions of certain moulds on cereal grains and oil seeds are extremely toxic and enter the food chain of both animals and humans. Most important is the use of acid-activated bentonites (‘bleaching earths’, see Chapter 10.1 in Volume A) for decolourizing vegetable and mineral oils (Fahn, 1963, 1973; Sarier and Gu¨ler, 1988; Srasra et al., 1989; Jovanovic´ and Janackovic´, 1991; Mokaya et al., 1994; Theng and Wells, 1995; Erdogan et al., 1996; Christidis et al., 1997; Ravichandran and Sivasankar, 1997; Falaras et al., 1999, 2000; Jozefaciuk and Bowanko, 2002; Christidis and Kosiari, 2003). The removal of pigments not only decolourizes vegetable oils but also improves taste and stability. A natural bleaching earth containing sepiolite was found suitable for fast filtration and bio-separation of larger proteins (Emmerich et al., 2010). Sepiolite also represents a support for immobilizing enzymes (Sedaghat et al., 2009b). Fuller’s earth was used for centuries to remove fat from animal wool (fulling) and is a mixture of different clay minerals (palygorskite, sepiolite, smectites). The composition of fuller’s earth varies between different localities. Fuller’s earth was used for oil refining before the industrial production of acid-activated bentonites. The history of fuller’s earths has been described by Robertson (1986) and Beneke and Lagaly (2002). Clays are used as catalysts and catalyst supports in many organic syntheses. Mt is the most important clay mineral for these uses. The acid forms can provide environment-friendly alternatives to liquid Brnsted acids. ‘Clayfen’ and ‘Claycop’ are not catalysts but useful Mt-supported reagents (see Chapter 4.3). Carbonless copying papers are composed of paper sheets with different coatings on the back of the upper sheet (CB) and on the front of the lower sheet (CF) (Fig. 4.2.8). CB is coated with microcapsules (1–10 mm) of gelatine or polyurethane. The capsules contain a solution of leuco dyes, commonly crystal violet lactone or N-benzoyl leuco methylene blue. CF is

CB CF FIGURE 4.2.8 Carbonless copying paper. The back of the upper sheet is coated with microcapsules containing the leuco dye, and the front of the lower sheet is coated with an acid-activated bentonite. From Fahn and Fenderl (1983).

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covered with a coating colour consisting of an acid-activated bentonite (adjusted to pH 9–10) together with water and binders. The pressure of a pencil or the stroke of a typewriter breaks the microcapsules at the point of contact. As the solution is released, the dye is adsorbed on the coating colour of the CF front page, and the colour (crystal violet or methylene blue) develops at this point (Fahn and Fenderl, 1983).

4.2.1.4

Vermiculites and Micas

Vermiculites are commonly used in the form of expanded particles as shown in Fig. 4.2.9. The vermiculite flakes are expanded by rapid heating from 250 to 1500  C followed by immediate cooling to 400  C. The evaporating water expands the particles in worm-like (vermiform) manner (Grim, 1968; Bergaya et al., 2001) and increases the volume by up to 1500 times. Extremely short heating periods are required to avoid the decomposition of structural OH groups (Klose, 1982). Expanded vermiculite is used in the building industry for heat insulation and sound dissipation. In the packaging industry, it is used as a thermal protecting and shock-proof-filling material for glass containers and vessels. The high liquid absorption capacity of expanded vermiculite reduces damage by breaking containers. In metallurgy, the surface of molten metals is covered with vermiculite for thermal protection. Wet or dry finely ground micas, typically with a particle size similar to that of filler clays, are found in heat-stable, UV-stable and under-water paints. Nacreous (pearlescent) pigments (Perlglanzpigmente), especially used in

FIGURE 4.2.9 Shock-heated expanded vermiculite flakes (Courtesy K. Beneke, University Kiel).

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cosmetics, obtain their exceptional optical properties from parallel oriented mica particles. Ground micas are also used in corrosion-proof materials, polymer coatings, underseal and as an insulating material.

4.2.1.5 Talc and Pyrophyllite Talc and pyrophyllite are important filler materials for polymer and rubber. Talc is also used extensively in cosmetic and pharmaceutical powders. In pharmaceutical technology, talc is needed as an indispensable slip additive.

4.2.1.6 Palygorskite and Sepiolite Sepiolite is used as a filler (cosmetics, polyester), a carrier (insecticides, herbicides, catalysts) and as filter material and anti-caking agent. It is also used as a dispersing, antisettling, thickening and thixotropic additive in paints and drilling fluids. The thickening effect mainly results from the fibrous shape of the particles, and hence is much less dependent on salt concentration and cations present than is the case with bentonites. Palygorskite6 is used in similar applications. Sepiolite is further used as adsorbent, for instance in cigarette filters, and as a decolourant, sometimes after acid-activation. Sepiolite in the form of ‘Meerschaum’ is also made into pieces of jewellery and pipe bowls (Gala´n, 1996; Harvey and Murray, 1997).

4.2.1.7 Mixtures of Clay Types It is not unusual for single industrial users to utilize clays for both their inertness and reactivity. For example, in many ceramic applications, kaolins may be used as an inert filler, while the reactive properties of bentonites or ball clays impart plasticity, unfired strength and perhaps critical fired properties. Combinations of clay minerals, such as kaolinite, smectite, talc and palygorskite, are used in the preparation of pastes, ointments and lotions for external use. Cosmetic formulations also take advantage of the softness as well as dispersing, gelling, emulsifying and adsorption properties of clays. Talc is the basis of cosmetic and pharmaceutical powders, often combined with kaolins, bentonites and starch. Highly porous bentonites containing high proportions of amorphous silica can be advantageous in some applications compared to bentonites with high smectite contents (Sohling et al., 2009). Solid particles, in particular combinations of bentonite and layered double hydroxides, are excellent stabilizers of emulsions. The important advantage is that such emulsions can remain stable in the absence of any organic surface-active agents (Abend et al., 1998; Lagaly et al., 1999a,b; Abend and Lagaly, 2001). 6. Technical reports still use the older term ‘attapulgite’.

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Certain clays show a soapy appearance and, in fact, can be used for cleaning.7 In Europe, soap-like materials containing high amounts of clays were used during the World Wars and for some time after. Clays were also used as shampoos, not only by primitive people (Mahjoory, 1996). Actually, clay minerals find increasing use in hair cosmetics. Eating earth or clay is widespread throughout the world. Clays were used for centuries in therapeutic, intestinal and adsorbent preparations (see Chapter 5.5).

4.2.2 4.2.2.1

PROCESSING INDUSTRIAL CLAYS Purification and Fractionation

In most cases, relatively simple techniques are used to investigate the properties of clay mineral dispersions. Clay minerals having a certain degree of purity are separated from the non-clay minerals by sedimentation techniques. Particle size fractionation is necessary to separate the clay minerals from associated minerals and phases. Dry separation processes are effective down to sizes of about 7 mm. However, wet processing is necessary for finer particle sizes or for raw materials requiring chemical treatment for such processes as chemical bleaching or magnetic separation. In wet processing, a decisive step preceding sedimentation is the preparation of a stable dispersion of the clay by replacing the divalent compensating (charge-balancing) cations with sodium ions. The pH of the dispersion must be maintained at 7–8 because the clay mineral particles aggregate at pH <6.5. The stable dispersion of the clay minerals in homo-ionic form may then be fractionated by gravity sedimentation, or, for particle sizes below 1 mm, usually by centrifugation (see Chapters 7.1 in volume A). Naturally occurring clays are typically mixtures of clay minerals and nonclay minerals. Such clays may be cemented by metal hydr(oxides) or carbonates. Before any processing flow sheet can be designed, it is recommended that the clay materials be disaggregated, the cements removed and the clay particles dispersed. It is important to understand the nature of the cements and the composition of the total material so that any processing flow sheet can be designed to remove the non-clay minerals. The following processes may be involved: (i) purification; (ii) wet versus dry processing; (iii) particle size separation (fractionation); (iv) bleaching and magnetic separation; (v) flotation and selective flocculation; (vi) drying and calcination and (vii) chemical modification and activation. A typical dry-processing plant for kaolin or bentonite is shown in Fig. 4.2.10. Once the basic composition of a raw material is understood, a series of processing steps may be introduced. For high-quality clays, the processing may be relatively complex. 7. Saponite is derived from Latin sapo, meaning soap (Grim, 1968; Bergaya et al., 2001).

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A

Feed

Dust collector

Cyclone

Separator

Feed hopper

Product Mill

Roll feeder

Fan B Dust collector Product collector

Product

e

Vent

Classifier

O

ve

rs

iz

Feed

Mill Exhaust fan

Hot air Furnace

FIGURE 4.2.10 Dry processing for kaolin or bentonite. (A) Mill, cyclone and dust collection circuit. (B) Hot-air circuit for drying in grinding mill.

Chapter

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4.2

Industrial Applications

471

Processing of Kaolins

Common clays for production of tiles, bricks and ceramics are generally used without any processing. In some cases, the largest particles are removed by simple sedimentation techniques without pre-purification to obtain homogeneous ceramic bodies. Antique ceramists used advanced processing of common clays to obtain the refined clays for shaping and the slips for decoration. The red/black decoration (‘Glanzton’ technique) of the famous Antique vases with the appealing gloss was produced by using clay masses and slurries with different contents of kaolinite and illite (Hofmann, 1962b; Noll, 1982, 1991). Kaolins for the paper industry now require sophisticated and extensive processing technologies (Table 4.2.4). Figure 4.2.11 summarizes the applied technologies that may be used to refine and improve the industrial properties of kaolins.

4.2.2.3

Raw and Activated Bentonites

Bentonites are fine-sized materials, and hence are generally used without significant size fractionation. As certain properties of bentonites can change between neighbouring pits or between individual layers within a pit, blending is commonly used to maintain a consistent product with standard properties. Bentonites may be used in the raw form (as mined) or they may be activated (Tables 4.2.2B and 4.2.3). Alkali or soda-activation, using sodium carbonate (Na2CO3), transforms the calcium (magnesium) bentonites into sodium– calcium forms. The bentonite with water contents of 35–40% (m/m) is usually kneaded or milled with 1–5% (m/m) sodium carbonate and homogenized (Fig. 4.2.12). This process of soda-activation was first proposed by Hofmann and Endell (1935). Fluid dispersions are usually avoided because sodium bentonite dispersions are extremely difficult to filter because of their high TABLE 4.2.4 Applied Technologies Used in Kaolin Processing Delaminationa High-gradient magnetic separation Selective flocculation Column flotation Ozone bleaching Ultra-fine-particle size separation Surface modification Calcination a

see Footnote 3 in Section 4.2.1.2.

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Drilling Stripping Mining Degritting Storage (tanks) and blending Fractionation and particle size separation Selective flocculation

Magnetic separation

Delamination

Leaching

Flotation Surface treatment

Dewatering (filtration) Deflocculation Drying (apron, rotary, tray)

Drying (spray or drum)

Slurry (high solids)

Particle separation Calcination

Bagging and loading

FIGURE 4.2.11 Flow sheet showing the various stages and complexities in the modern wetprocessing of kaolin.

viscosities. Nevertheless, smaller amounts of high-quality sodium bentonites, or especially hectorites for certain applications, are produced in dispersions after careful selection of the raw bentonite. The quality of the products can be improved by special processing of the raw bentonite (fractionation or hydrocycloning, mechanical treatments, reaction with heated water vapour, etc.). During soda-activation, a large part of the interlayer calcium ions is precipitated as calcium carbonate. As the calcium ions are still present in the system when this bentonite is dispersed in water, the degree of delamination and exfoliation is not optimal, and the colloidal properties depend on the amount of soda added (Fig. 4.2.13). The degree of thixotropy (hysteresis of the flow curves) reaches a maximum as a function of the amount of soda added. The yield value also increases to a maximum at an optimum addition of soda (Fig. 4.2.14). The properties of bentonites respond differently to sodaactivation. This is not only due to differences in particle size distribution

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FIGURE 4.2.12 Activation of bentonite by kneading with soda (Courtesy N. Schall, Su¨dChemie AG, Germany).

100

B

Rate of shear (s−1)

50

0

100

300

500

A

700

C

50

0 100

500 Shear stress (mPa)

FIGURE 4.2.13 Soda-activation of bentonites. Influence of soda addition on the flow behaviour (shear rate vs. shear stress) and thixotropy. 2% dispersions of Amory bentonite (Mississippi, API 22b, Wards). (A) 0.5 mmol Na2CO3/g bentonite. (B) 2.5 mmol Na2CO3/g bentonite. (C) 5 mmol Na2CO3/g bentonite.

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1

Shear stress at a shear rate of 100 s−1

Maximum thixotropy

Dakota

0.5

Amory

Otay Bavaria Cameron 0

1 2.5 5 10 0 0.05 0.25 0.5 Soda addition (mmol/g bentonite)

FIGURE 4.2.14 Rheological properties of 2% dispersions of different bentonites. The curves show the effect of soda addition on shear stress measured at a rate of shear of 100 s1. Arrows: denote maximum thixotropy. . . . . . . . Newtonian flow, – ● – ● – (pseudoplastic), ——– thixotropic, – – – antithixotropic. Bentonite from Amory, Mississippi (API 22b, Wards); Bavaria (Schwaiba, Su¨d-Chemie, Germany); Cameron (Arizona, API 31); Dakota; Otay (California, API 24). From Jasmund and Lagaly (1993).

between raw bentonites but also to the differences in layer arrangement within individual Mt particles. Domains of silicate layers with a certain degree of ordering are separated by areas of loose contacts (breaking points), denoted by arrows in Fig. 4.2.15. Depending on the distribution and the extent of these defects in the parent Mt, soda-activation yields different size distributions of the delaminated particles. The strong dependence of rheological properties on the Naþ/Ca2þ ratio is illustrated in Fig. 4.2.16. Varying the Naþ/Ca2þ ratio is, therefore, an important way to optimize and tailor the properties of soda-activated bentonites for the intended applications. Many applications, listed in Tables 4.2.2B and 4.2.3, require hydrophobized bentonites. To this end, the bentonite is usually reacted with quaternary alkylammonium salts such as dialkyl dimethylammonium, dialkyl benzylmethylammonium, and alkyl benzyldimethylammonium salts. The technical products contain alkyl chains (R) of different lengths. For instance, a technical dioctadecyl dimethylammonium chloride had the composition (% m/m): 1.5C14, 0.8C15, 27.5C16, 2C17, 67C18, 1.2C20 (Favre and Lagaly, 1991). Ditalloyl ammonium salts (derived from by-products of

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475

FIGURE 4.2.15 Montmorillonite particles with inherent ‘breaking points’ (arrows). From Jasmund and Lagaly (1993).

cellulose production from deal and pine wood) are mixtures of dialkyl dimethylammonium surfactants with varied alkyl chain lengths, for instance 65% C18, 30% C16 and 5% C14. The amount of alkylammonium ions added corresponds to the cationexchange capacity (CEC) of the clay, and the exchange is nearly quantitative. Products with smaller amounts of alkylammonium salts can also be obtained. In most cases, the products are not washed after cation exchange so that some free (unreacted) alkylammonium salts may still be present. These free salt influences the properties of the product such as ion-exchange and rheological behaviour. The ratio alkylammonium salt/CEC and the treatment of the organo-bentonite after the exchange reaction are parameters that can be used to tailor these products. Bleaching earths are obtained by treating bentonite with acids in such a way that the layer structure is largely decomposed (see Chapter 10.1 in Volume A). Typically, the bentonite is reacted with hydrochloric acid (up to 17 mmol/g bentonite) at 90–100  C for a few hours, then washed to reach pH 4, dried, milled and sieved. Concentration of the acid, temperature and activation time determine the properties of the product (Fahn, 1973). The specific surface area and bleaching activity usually show maximum values at distinct activation conditions, whereas the pore volume and the silica content increase continuously (Fig. 4.2.17) (Fahn, 1973; Christidis et al., 1997). The large volumes of acidic waste waters, containing aluminium salts that are produced, can give rise to environmental problems. Clays

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A 150

Rate of shear (s−1)

0.5%

0

2.5%

100

200 300 Shear stress (mPa)

400

150

Rate of shear (s−1)

0.5%

1%

2%

1.5%

2.5%

75

0

C

2%

75

0 B

1.5%

0

600

1200 1800 2400 Shear stress (mPa)

3000

3600

150

Rate of shear (s−1)

0.5% 1%

1.5%

2%

2.56%

75

0

0

120

240 360 480 Shear stress (mPa)

600

720

FIGURE 4.2.16 Flow curves of sodium bentonite (Bavaria, Germany) (A) in water, (B) in 0.01 M CaCl2, (C) in 0.025 M CaCl2. Bentonite content 0.5–2.5% (m/m), pH 6.5, 20  C. From Permien and Lagaly (1994).

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Industrial Applications

A 0.5

S (m2 / g)

VP (ml / g)

500

0

0

5

10 mmol HCl / g

15

0

B Content of oxides (mas%)

100

50

0

0

5

10 mmol HCl / g

15

5

10 mmol HCl / g

15

C

Colour number

120

60

0

0

FIGURE 4.2.17 Influence of the acid/bentonite ratio on the properties of bleaching earths. (A) Specific surface area S (○), pore volume (●, <80 nm diameter). (B) Chemical composition, D content of Al2O3 þ Fe2O3, ▲ content of SiO2. (C) Bleaching (Lovibond colour numbers) of soybean oil (□) and linseed oil (▪). After Fahn (1973). From Jasmund and Lagaly (1993).

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of certain localities exhibit similar adsorption properties without acid-activation. Before bleaching earths were produced at an industrial scale, fuller’s earth was used for oil bleaching (Beneke and Lagaly, 2002).

4.2.3 LABORATORY EVALUATION OF CLAY SAMPLES Any clay material may be recognized by some plasticity in its raw state. Some clay materials may meet the required specifications for industrial uses with no processing or blending with other raw materials. Other clays may be components in simple or complex blends of various raw materials. Other clay raw materials require simple or complex processing to remove contaminants or non-clay minerals. The assessment of an undeveloped clay resource requires a series of screening techniques by which the clay technician can progressively move towards the identification of the most suitable uses for the material. The three stages involved are summarized below. Stage 1. Screening, consisting of the following steps: Step 1, colour; Step 2, XRD analysis; Step, 3 chemical analysis; Step 4, mineralogical analysis; and Step 5, mineral distribution with particle size. Stage 2. Initial testing of industrial properties, table of industrial properties. Stage 3. Applied testing.

4.2.4 CATEGORIZATION OF CLAY RESOURCES With the continuing growth in global population, rising urbanization and expanding industrialization, there is an ongoing and growing need throughout the world to develop resources of industrial clays. The development of resources in developed countries during the early to middle part of the twentieth century typically began on a small scale from a low-technology base with the initial market focus towards construction materials or relatively low-quality ceramic products. With increasing levels of industrialization, the level of technology and product sophistication increased with the ultimate objective of achieving high-quality products. Over the past 20 years, the developed world has seen (i) the exhaustion of many natural resources; (ii) the maturation of low-growth markets; (iii) an increase in environmental constraints; (iv) a rise in labour costs and a general movement against mining in many countries. This stimulated interest in the resources of, and encourage investment in, developing countries. In addition, the growth in the gross domestic product of many developing nations provided investment capital for the development of their indigenous clay mineral resources. On the basis of many studies on industrial clay mineral resources carried out in both developed and developing countries, the placement of industrial

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clays into one of four categories is a useful precursor to undertaking technical and economic evaluations of potential resources. Such categorization also benefits the explorer or developer because it – assists in identifying the most suitable development strategy; – provides a general estimate of the time required to move from greenfields development to production; – enables a work programme to be broadly defined; and – permits provisional project cost estimates to be made.

4.2.4.1

Categories of Industrial Clays

Four categories are proposed for industrial clay resources. Category 1. High-quality, high-technology clays requiring major investment for large tonnage production to supply both local and international markets. Category 2. Unique specialty clays requiring advanced technologies for small tonnage niche markets, locally and internationally. Category 3. Relatively low-technology clay of moderate quality that mainly supplies local markets. Category 4. With variable quality. The low-quality materials may justify little or no processing but be suitable for large-tonnage local markets. Some clays of category 4 may be of moderate to high quality but for one or more reasons considered non-economic. These reasons may include isolation from markets, politically or economically unstable locations and unfavourable legislative environment.

4.2.4.2

Examples of Different Categories

4.2.4.2.1 Category 1 Currently, there are three regions in which kaolin (clays of category 1) are produced. These kaolin provinces are (i) the sedimentary kaolins of south-east Georgia, USA; (ii) the hydrothermal kaolins of Cornwall, UK and (iii) the sedimentary kaolins of the Amazon Basin, Brazil. The limited number of kaolin resources identified in this category confirms the rarity of clays of category 1 presently known on the world scene. 4.2.4.2.2 Category 2 There are also very few resources that might be classified under category 2. These are relatively rare, unique resources of somewhat unusual, but valuable industrial clay minerals. Such deposits are typically of high purity and are found in somewhat unique geological settings. Examples include the halloysite deposits of Northland, New Zealand. These deposits of unusually

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pure halloysite were formed by low-temperature hydrothermal alteration of volcanic ash (Harvey and Murray, 1993; Harvey, 1996). It is wet-processed and supplied to a unique niche market for high-quality ceramics. A second example is hectorite, a lithium-rich smectite (bentonite), formed by hydrothermal alteration of basaltic ash containing elevated concentrations of magnesium and lithium. It is wet- or dry-processed and used in a wide variety of industries (coatings, greases, adhesives and paints) because of its high viscosity, high gel strength and good temperature stability. A third example is white bentonite, which is very rare in nature and commands high prices in colloid applications, detergents, pharmaceuticals and ceramics. For some specialty markets, these bentonites may be wet-processed or surface-modified to achieve the high quality required for such applications.

4.2.4.2.3 Category 3 Resources are numerous and widespread. Their specifications are typically not rigid, and the level of processing is only moderate since the market quality requirements and pricing do not justify high processing costs. All known category 1 resources around the world also contain large tonnages of category 3, clays that are too impure to meet category 1 requirements. Examples of large exploited clays resources of category 3 associated with category 1 are the filler kaolins of Georgia, USA, and Cornwall, UK. Other category 3 resources contain few if any category 1 components. These include the kaolin resources of the Czech Republic, Ukraine and Germany; the filler-grade kaolins of Indonesia; and the bentonite resources of Wyoming and south-eastern USA. An example of a clay of category 3 is the Belitung kaolins of Indonesia. During the 1960s and early 1970s, these primary kaolins were mined as an adjunct to the associated, highly profitable, tin-mining operations. With the radical drop in tin prices during the 1970s and 1980s, more emphasis was placed on the kaolin operations. These clays are currently exploited to supply large ceramic and filler clay markets within Indonesia; they are also exported to adjacent Asian countries including Taiwan, Japan and Korea. 4.2.4.2.4 Category 4 Clays exist in all countries of the world and are typically used as mined.

4.2.4.3 Role of Categorization in Assessing Industrial Clay Resources In any assessment of an industrial clay resource, the explorer or developer has to go through the various stages of resource assessment, raw material testing, assessment of product quality, market size and market demand. All these data must then be integrated into a feasibility study which will recommend that the project proceed or be abandoned.

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An early classification of materials into one or more of the categories can prove to be a useful precursor to establishing development strategies and likely project costs. Such categorizations can provide a useful insight into the complexities of such studies because the different categories have different requirements with respect to the work programme needed and time frame to reach the feasibility study.

4.2.4.4

Relationship Between Category and Annual Tonnage

In any mineral processing operation, the term ‘benefits of scale’ is used to denote the significant economic advantages can be obtained by having larger production volumes and using larger ships. Larger tonnage operations operate with fewer man-hours per ton, while capital costs for larger machines are less than the multiples of their relative production capacities. In order to compete on world markets, category 1 producers must consider the benefits of scale. For example, in the kaolin industry during the 1970s, a 100,000 tons/year operation was considered to be a reasonable commercial operation. For the current developments in Brazil, a minimum plant size of 300,000 tons per year is being quoted. For category 2, the annual tonnage requirement is governed by market size rather than ‘benefits of scale’. Annual productions from such processing operations typically fall between 10,000 and 100,000 tons per year. The sizes of category 3 operations are typically governed by other factors such as market size or accessible market share.

4.2.4.5 Relationship Between Category and Resource Confidence Based on the criteria defined above, the development of a category 1 resource requires a very high level of confidence in the quality and quantity of the raw material. If a minimum resource life of 20 years is required at 300,000 tons per year, then the resource must be of sufficient size to produce 6 million tons of the product. For categories 2 and 3, the industrial clays tonnage requirements may be significantly less and resource confidence may be less. The various levels of resource certainty are internationally recognized in the classification of industrial mineral resources. For resources in categories 1 and 2, it is essential that the knowledge be at the ‘mineable proven resource’ stage. For category 3 resources, the resource certainty may be much less, possibly at the ‘inferred resource’ level or lower.

4.2.4.6

Relationship Between Category and Value

Kaolin products of category 1 command the largest tonnage and high addedvalue positions in the industry. Frequently, however, it is the category 2 products that may command the highest unit value position, although their tonnages may be relatively small. Kaolins of category 3 command an intermediate value between kaolins of categories 1 and 4.

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4.2.4.7 Relationship Between Category and Pre-Investment Capital Category 1 projects require significant pre-investment or ‘risk’ capital. The level of confidence in the resource and markets has to be very high, requiring a level of investment that may well exceed US$1 million. The pay-back time for such investments may be at least 5 years, because of the time required to move from reconnaissance through to commissioning (Table 4.2.5). The preinvestment capital requirements for categories 2–4 become progressively lower as one moves to the lower category clays.

4.2.4.8 Relationship Between Category and Investment Capital The investment capital required for large-tonnage, high-complexity kaolin of category 1 projects is quoted to be as high as US$ 300 per processed ton (Harvey, 1995; Pleeth, 1997). For kaolins of category 2, investment capital costs would depend on the complexity of the process but might range between US $100 and US $500 per processed ton. For kaolins of category 3, the investment level may be of the order of US $50 per finished ton.

4.2.5 THE RESOURCE EVALUATION PROCESS The assessor moves progressively through a series of increasingly more detailed stages. He/she must first look at surface outcrops, and gain a general appreciation of the regional geology. The variability in the outcrops and any indications of the real extent and depth of the resource are then assessed. The credibility of the guide has also to be assessed at this time by asking the following questions: – – – –

Does the person have any idea of what he/she is dealing with? Is he/she technically competent? Is the quality of the material being overstated or exaggerated? What level of confidence can be placed on the quality and quantity of the resource, based on the work that was done?

Other questions that must be addressed are: – What is the local infrastructure? – What local support services are available? – What is the situation regarding land tenure? For example, in north Vietnam, land tenure is relatively straightforward, while in south Vietnam it is a nightmare. – Is a trained workforce available locally?

TABLE 4.2.5 Timetable of Activities and Investments Activity

Category 1

Category 2

Category 3

Category 4

12 months

9 months

6 months

3 months

18–24 months

9 months

9 months

6 months

Feasibility study

24 months

12 months

9 months

3 months

Stage IV: decision to invest

4–5 years

2–2.5 years

2 years

1 year

Design, construction and commissioning

1–2 years

1 year

1 year

1 year

Typical overall project time

5–7 years

3–4 years

2–3 years

1 year

Stage I: reconnaissance geological reconnaissance, property surveys, testing, broad categorization of materials, market surveys and evaluation Decision to proceed Stage II: Exploration (pre-feasibility) Property negotiation, drilling, testing, market surveys, precise material characterizations, process flow sheet development, resource calculations, economic studies and evaluation Pre-feasibility study and decision to proceed Stage III: delineation and feasibility Drilling, testing, market surveys, bulk samples, engineering studies, assessment of products in the marketplace, economic studies and evaluation

Total elapsed time since project initiation

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– If qualified engineers, technologists and managers have to be brought in, could they and their families survive and be content? – What are the local ground rules for joint ventures, taxation and moving profits offshore? All these questions may have a bearing on whether or not a project may be attractive or not. If, however, the project does progress through to Stage II, then the work programme becomes increasingly complex and more costly. It is beyond the scope of this review to discuss this in detail, but the programme will include, property negotiations, exploration drilling, detailed testing (possibly at a site laboratory), detailed market surveys, product categorization, preliminary plant design and engineering studies and preliminary economic studies. All these data are combined into a ‘pre-feasibility study’ on which to base a decision on whether or not to proceed to Stage III, ‘delineation and feasibility’. The Stage III program includes detailed drilling and delineation of the resource, detailed testing and resource calculations, extraction of bulk samples for detailed engineering studies, pilot-scale testing leading to process flow sheet design, market surveys and market negotiations, market product testing and final negotiations for land, leases, joint ventures, etc. All these studies culminate in economic studies and a full ‘feasibility study’.

4.2.6 OTHER CONSIDERATIONS 4.2.6.1 From Laboratory-Scale Testing to Major Plant Scale The clay industry has many examples of insufficient scale-up factors being applied to basic laboratory data. This ranges from basic recovery figures to assessments of product quality based on too few laboratory test data. For example, losses during commercial plant operations may be much higher than in small-scale laboratory test equipment. A conservative approach to both laboratory- and pilot-scale test data is essential.

4.2.6.2 Level of Applied Technology Almost anything can be done with a low-grade clay resource if a sufficient number of applied technologies is ‘thrown’ at it. For example, a wide selection of technologies can be applied to upgrade commercial kaolin resources (Fig. 4.2.11). However, when all the various processes are costed into the operation, the total costs (and process losses) may become prohibitive, effectively constraining development of the resource.

Chapter

4.2.6.3

4.2

485

Industrial Applications

Losses Associated with Applied Processing Steps

For each technology introduced into a process, there will be process losses. These may range from 2% to much higher values. If, however, we generalize that each process step loses 4% of the product, then the effects of multi-stage processing on recoveries may be very significant. Also, such losses will be cumulative. For example, a raw material that perhaps has 40% recovery in the laboratory may have, say, five applied technologies incorporated in its process flow sheet. If each technology results in a 4% loss then l l l l l

after after after after after

technology technology technology technology technology

1, 2, 3, 4, 5,

the the the the the

recovery recovery recovery recovery recovery

drops drops drops drops drops

from 40% to 38.4%, to 36.9%; to 35.4%; to 34% and to 32.6%.

Such losses may negatively affect mining costs and overall process profitability.

4.2.6.4

Time to Move from Commissioning to Full Production

Industrial mineral users are often conservative by nature, and do not readily accept new products. For example, the paper industry is a complex technology, and an industrial clay such as kaolin may be just one component in a complex formulation. Purchasing agents have to be convinced that the product is compatible with their formulations and further that the product quality and supply are going to be consistent. The first stage is to convince a company to try your product. To reach this stage, it will be necessary to convince the company of the quality, consistency and value of your product over and above the quality of his existing supplier. In such cases, it may be necessary to compete on the basis of higher quality, lower price, better continuity and better technical support. Even with such strengths, however, the new player in the marketplace still has to deal with buyer conservatism. Therefore, the rate at which a product is accepted may be a combination of good fortune or even luck. For some products, it may take years to gain full market acceptance. For example, recent developments of kaolin (category 1) resources in Brazil (Pleeth, 1997) quote time intervals of at least 5 years to move from initial exploration through to commissioning.

4.2.6.5

Reducing Risk During Development

There are several techniques or procedures for minimizing risk and shortening the time necessary to establish category 1 or category 2 ventures:

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associate, or form a joint venture, with established producers in the industry; associate, or form a joint venture, with major market users of the product; engage specialist consultants for resource evaluation, market surveys, etc.; develop resources adjacent to proven established resources.

4.2.7 CONCLUSIONS This review of conventional applications of clay minerals illustrates the great diversity in compositions and properties of clay minerals and the even greater ranges of processes and products in which they may be used. Clay minerals may be utilized in their as-mined state, as low-cost impure materials because of their engineering, physical and or chemical properties. Indeed, in archaeology, clay utilization became recognized as a means of identifying early human progress and development. At the other end of the spectrum, refined, high-purity clay minerals play an integral part in the highest technological achievements of man, including space capsules, pharmaceuticals, medicine and catalysis.

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Christidis, G.E., Scott, P.W., Dunham, A.C., 1997. Acid activation and bleaching capacity of bentonites from the islands of Milos and Chios, Aegean, Greece. Appl. Clay Sci. 12, 329–347. Darder, M., Colilla, M., Ruiz-Hitzky, E., 2005. Chitosan-clay nanocomposites: application as electrochemical sensors. Appl. Clay Sci. 28, 199–208. Darley, H.C.H., Gray, G.R., 1991. Composition and Properties of Drilling and Completion Fluids, fifth ed. Gulf Publishing Company, Houston. Dixon, J.B., Kannewischer, I., Tenorio Arvide, M.G., Barrientos Velazquez, A.L., 2008. Aflatoxin sequestration in animal feeds by quality-labeled smectite clays: an introductory plan. Appl. Clay Sci. 40, 201–208. Dizman, B., Badger, J.C., Elasri, M.O., Mathias, L.J., 2007. Antibacterial fluoromicas: a novel delivery medium. Appl. Clay Sci. 38, 57–63. Emmerich, K., Steudel, A., Schuhmann, R., Weidler, P.G., Ruf, F., Sohling, U., 2010. Mineralogical and physicochemical characterization of a natural bleaching earth containing sepiolite suitable for fast filtration and bioseparation. Clay Miner. 45, 477–488. Erdogan, B., Demirci, S., Akay, Y., 1996. Treatment of sugar beet juice with bentonite, sepiolite, diatomite and quartamin to remove color and turbidity. Appl. Clay Sci. 11, 55–67. Fahn, R., 1963. Innerkristalline Quellung und Farbstoffadsorption sa¨urebehandelter Montmorillonite. Kolloid-Zeitschrift und Zeitschrift fu¨r Polymere 187, 120–127. Fahn, R., 1973. Einfluß der Struktur und der Morphologie von Bleicherden auf die Bleichwirkung ¨ len und Fetten. Fette, Seifen, Anstrichmittel 75, 77–82. bei O Fahn, R., Fenderl, K., 1983. Reaction products of organic dye molecules with acid-treated montmorillonite. Clay Miner. 18, 447–458. ¨ ber die Verwendung von Bentoniten in Wasch- und ReinigungsmitFahn, R., Schall, N., 1985. U teln. Tenside Detergents 22, 57–61. Falaras, P., Kovanis, I., Lezou, F., Seiragakis, G., 1999. Cottonseed oil bleaching by acidactivated montmorillonite. Clay Miner. 34, 221–232. Falaras, P., Lezou, F., Seiragakis, G., Petrakis, D., 2000. Bleaching properties of aluminapillared acid-activated montmorillonite. Clays Clay Miner. 48, 549–556. Favre, H., Lagaly, G., 1991. Organo-bentonites with quaternary alkylammonium ions. Clay Miner. 26, 19–32. Fendler, J.H., 2001. Chemical self-assembly for electronic applications. Chem. Mater. 13, 3196–3210. Fitch, A., 1990. Clay-modified electrode: a review. Clays Clay Miner. 38, 391–400. Fitch, A., Wang, Y., Park, S., Joo, P., 1998. Intelligent design of thin clay films: transport and tailoring. The Latest Frontiers of Clay Chemistry. In: Yamagishi, A., Aramata, A., Taniguchi, M. (Eds.), The Latest Frontiers of Clay Chemistry. Proceedings of the Sapporo Conference on the Chemistry of Clays and Clay Minerals, Sapporo 1996. The Smectite Forum of Japan, Sendai, Japan, pp. 1–15. Gala´n, E., 1996. Properties and applications of palygorskite-sepiolite clays. Clay Miner. 31, 443–453. Ghiaci, M., Aghael, H., Soleimanian, S., Sedaghat, M.E., 2009a. Enzyme immobilization. Part 1. Modified bentonite as a new and efficient support for immobilization of Candida rugosa lipase. Appl. Clay Sci. 43, 289–295. Ghiaci, M., Aghael, H., Soleimanian, S., Sedaghat, M.E., 2009b. Enzyme immobilization. Part 2. Immobilization of alkaline phosphatase on Na-bentonite and modified bentonite. Appl. Clay Sci. 43, 308–316. Gopinath, S., Sugunan, S., 2007. Enzymes immobilized on montmorillonite K 10: effect of adsorption and grafting on the surface properties and the enzyme activity. Appl. Clay Sci. 35, 67–75.

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