Overview

Kaolin is a significant industrial clay that mainly contains a hydrated aluminum silicate mineral named as kaolinite (Al2Si2O5(OH)4)^{[1, 2]}. Other kaolinminerals include dickite, nacrite, and halloysite. Pure forms of these minerals are not as ubiquitous as kaolinite, and are usually found along with kaolinite in hydrothermal deposits^[1]. Kaolin may form in residual or sedimentary modes. In the former type, kaolinite is created by in-situ weathering or hydrothermal alteration of aluminosilicate parent rocks like granite; though, in the latter, the mineral is produced by the deposition of kaolinite formed elsewhere^{[2, 3]}.
Unique mineralogy, morphology, chemical and physical specifications of kaolin make it a versatile raw material appropriate for many different applications [1, 4], such as ceramic, paper coating and fillers, pigment extender in water-based interior latex paints and oil-based exterior industrial primer. In addition, kaolin is applied in non-black rubber, medicines and pharmaceuticals, cosmetics, crayons, fertilizers, detergents, pesticides, white cement, ink, catalysts, and many other products^{[1, 3, 4]}. These properties are greatly affected by the mode of clay formation which controls the kaolin quality through varying the kaolinite and impurity contents. For instance, kaolinite content of the residual and sedimentary kaolins differs from 20% to 60%, respectively^[3]. High quality kaolins are also low in iron-bearing minerals.
The existence of iron oxides in kaolin adversely affects the clay color, and reduces its brightness and refractoriness ^{[4, 5]}.
These cause a dramatic decrease in its commercial price^[6]. Even an amount of 0.4% of oxides, hydroxides and hydrated oxides of ferric iron may be enough to impart a red to yellow pigmentation to clay deposits. These iron oxide/hydroxides may be hematite (red), maghemite (reddish brown), goethite (brownish yellow), lepidocrocite (orange), ferrihydrate (brownish red), etc.^[7] Similarly, iron ores such as hematite may contain clays like kaolin as contamination which cause problems in the operation of blast furnaces. Therefore, the first beneficiation step to make these raw materials commercially valuable is to effectively eliminate iron oxides from kaolinite clays and vice versa.

Structure and physical properties

Kaolin is a plastic raw material, particularly consisting of the clay mineral kaolinite. The chemical formula is Al2O3.2SiO2.2H2O (39.5% Al2O3, 46.5% SiO2, 14.0% H2O). In systemic mineralogy, kaolinite ranks among phyllosilicates, which are stratified clay minerals formed by a net of tetrahedral and octahedral layers. Phyllosilicates are classified into the main groups according to the type of the layers, interlayer content, charge of the layers and chemical formulas. Besides kaolinite groups, serpentine, halloysite, pyrofylite, mica, and montmorillonite groups also rank among phyllosilicates. Group of kaolinites includes di-octahedral minerals (1:1) with two layers, one silica[SiO4] tetrahedral layer and one aluminium[Al2(OH)4] octahedral layer. The layers are bonded together by sharing oxygen anion between Al and Si. Together, these two layers are called platelets^{[8, 9]}.
The 1:1 platelets of kaolinite are held together strongly via hydrogen bonding between the OH of the octahedral layer and the O of the tetrahedral layer. Due to this strong attraction, these platelets do not expand when hydrated and kaolinite only has external surface area. Also, kaolinite has very little isomorphic substitution of Al for Si in the tetrahedral layer. Accordingly, it has a low cation exchange capacity. Kaolinite easily adsorbs water and forms a plastic, paste-like substance^{[8, 9]}.

Availability, mining and processing

Kaolin is formed under acidic conditions through weathering or hydrothermal changes of feldspars, and – to a lower extent – also other aluminosilicates. It can form independent weathered kaolin deposits, kaolinite clays or may be a compound of kaolinite sandstones and oolitic ironstones, and less frequently also of pegmatites and hydrothermal deposits. The most significant kaolin deposits were formed through intensive weathering of rocks rich in feldspar (granite, arkose, certain types of ortho-gneisses, and migmatites). Millions of years ago, original material was decomposed by weathering, giving rise to kaolin and silica combined with higher or lower amounts of admixtures. Mechanical erosion formed the rock under the tropical climate of that era and at increased temperatures, chemical corrosion occurred under the activity of water saturated with CO2 and humic acids which eluted from water^{[9, 10]}.
World renowned deposits in the Czech Republic are especially situated in the district of Karlovy Vary (Sedlec, Podlesi, and Otovice). Kaolin deposits in the area of Karlovy Vary are primary, i.e. kaolin remained in the place of its formation. Extracted raw material contains 20 to 30% kaolin; the remainder is silica sand which is an integral part of the raw material. Deeper deposits tend to be less kaolinized. Larger areas with kaolin material contents of 15 to 35% formed through weathering of arkoses are found in the vicinity of Horni Briza, Kaznejov, and Chotikov. Lower quality kaolin deposites are near Nova Role, Vidnava, Kadan, Podborany, Znojmo, and Veverska Bityska^{[9, 10]}.
Kaolin was obtained from extracted kaolinite or kaolinite-illitic gritstone or pudding-stone from the "mine U" in southern Moravia using the following procedure (unpublished data):

1. Superficial soil layer (about 50 cm) was removed, and the raw material was floated to a suction pump by water cannon (water source was a pond formed on the surface of the mine after kaolin extraction).
2. It was transported in the form of dense slurry through about 150 m long pipeline with about 20 cm in diameter to the processing plant halls.
3. After kaolin washing, classification and separation steps according to the particle size, kaolin sedimentation, addition of colloid agent, and kaolin drying in wire baskets, the product was finished and could be dispatched to customers.

Kaolin added to diet fed to farm animals

Due to its adsorbent capability and lack of primary toxicity, kaolin is considered a simple and effective means to prevent or ameliorate the adverse effects exerted by many toxic agents, not only those from the environment, but also those from the living organisms. Kaolin based medication often combined with pectin is commonly used as a palliative for diarrhea and digestive problems in humans[11]. Kaolin, given to the animals in the diet, firmly and selectively binds compounds present in the diets which are noxious to the intestine and thus decreases their absorption through intestinal mucosa into the organism and subsequently prevents their toxic mode of action. A number of studies confirmed
kaolin capability to decontaminate aflatoxins^[12], plant metabolites (alkaloids, tannins), diarrhea causing enterotoxins^[13], pathogenic microorganisms, heavy metals^[14] and poisons^[15]. In contrast, vitamin B12 adsorption by kaolinite clays is very low^[16].
Few studies have investigated the effects of kaolin-feeding on farm animals. Savory (1984)^[17]investigated the effect of kaolin feeding on adult roosters. That author did not register any change in the live body weight gain when 100 and 200 g kaolin/kg of the diet was fed. Although in the initial phase of the experiment when animals ingested 300 g kaolin/kg of the diet their weight did not increase, and when the animals ingested 400 g kaolin/kg of the diet, the live body weight of the animals even decreased; the differences were gradually compensated, primarily by increased feed intakes. Although it was not possible to completely compensate the body weight differences by increased feed intake, compensation was reached by significant increase in digestibility of basal diet. That effect was observed in a group fed 100 g kaolin/kg of the diet within a couple of days when more than 200 and 300 g of kaolin per week and 400 g per three weeks, was consumed, respectively. Sakata (1986)^[18] registered stimulation of the live weight gain in rats given kaolin combined with the diet (100 mg/g) with concurrent proportional increase in the weight of the tissues of some digestive organs.

References

1. Murray, H.H., 2006b. Chapter 5 — kaolin applications. In: Haydn, H.M. (Ed.), Developments in Clay Science. Elsevier, pp. 85–109.
2. Zegeye, A., Yahaya, S., Fialips, C.I., White, M.L., Gray, N.D., Manning, D.A.C., 2013. Refinement of industrial kaolin by microbial removal of iron-bearing impurities. Appl. Clay Sci. 86, 47–53.
3. Bloodworth, A.J., Highley, D.E., Mitchell, C.J., 1993. Industrial minerals laboratory manual: kaolin, mineralogy and petrology series. British Geological Survey, Nottingham.
4. Ryu, H.W., Cho, K.S., Chang, Y.K., Kim, S.D., Mori, T., 1995. Refinement of low-grade clay by microbial removal of sulfur and iron compounds using Thiobacillus ferrooxidans. J. Ferment. Bioeng. 80, 46–52.
5. de Mesquita, L.M.S., Rodrigues, T., Gomes, S.S., 1996. Bleaching of Brazilian kaolins using organic acids and fermented medium. Miner. Eng. 9, 965–971.
6. Guo, M.R., Lin, Y.M., Xu, X.P., Chen, Z.L., 2010. Bioleaching of iron from kaolin using Fe (III)-reducing bacteria with various carbon nitrogen sources. Appl. Clay Sci. 48, 379–383.
7. Ambikadevi, V.R., Lalithambika, M., 2000. Effect of organic acids on ferric iron removal from iron-stained kaolinite. Appl. Clay Sci. 16, 133–145
8. Klein C., Hurlbut C.S. (1993): Manual of Mineralogy. 21st ed. John Wiley and Sons, Inc., New York. 681 pp.
9. Slivka V. (2002): Mining and treatment of silicate (in Czech). Silikatovy Svaz, Praha. 443 pp.
10. Bernard J.H., Rost R. (1992): Encyclopaedic knowledge of minerals (in Czech). 1st ed. Academia, Prague. 704 pp.
11. Heimann G. (1984): Pharmacotherapy of acute infant enteritis (in German). Montss??r. Kinderheilkd., 132, 303–305.
12. Phillips T.D. (1999): Dietary clay in the chemoprevention of aflatoxin-induced disease. Toxicol. Sci., 52, 118– 126.
13. Dominy N.J., Davoust E., Minekus M. (2004): Adaptive function of soil consumption: an in vitro study modelling the human stomach and small intestine. J. Exp. Biol., 207, 319–324.
14. Katsumata H., Kaneco S., Inomata K., Itoh K., Funasaka K., Masuyama K., Suzuki T., Ohta K. (2003): Removal of heavy metals in rinsing wastewater from plating factory by adsorption with economical viable materials. J. Environ. Manage., 69, 187–191.
15. Knezevich D.L., Tadic V. (1994): Decontamination with clay or alcoholate of pigs percutaneously poisoned with VX and soman (in Croatian). Vojnosanit. Pregl., 51, 488–491.
16. Hashsham S.A., Freedman D.L. (2003): Adsorption of vitamin B12 to alumina, kaolinite, sand and sandy soil. Water. Res., 37, 3189–3193.
17. Savory C.J. (1984): Regulation of food intake by brown Leghorn cockerels in response to dietary dilution with kaolin. Brit. Poult. Sci., 25, 253–258.
18. Sakata T. (1986): Effects of unpalatable dietary bulk and short chain fatty acids on the tissue weight and epithelial cell proliferation rate of the digestive tract in rats. J. Nutr. Sci. Vitaminol. (Tokyo), 32, 355–362.

Description

Kaolin or china clay is a naturally occurring, almost white, hydrated aluminum silicate. This material does not exhibit a high degree of slip. Kaolin boasts good absorbency, is dense, and is sometimes used to reduce the bulk densities in loose powder products. It provides a matte surface effect, which can slightly reduce sheen left by some talc products.

Chemical Properties

off-white powder

Chemical Properties

Kaolin occurs as a white to grayish-white colored, unctuous powder free from gritty particles. It has a characteristic earthy or claylike taste, and when moistened with water it becomes darker in color and develops a claylike odor.

Physical properties

Sericite is a mineral similar to white mica in shape and composition. It has a very fine grain size and a silky shine. This material is soft and smooth and has a slippery feel on the skin. Sericite may be coated with silicone and other treatments for enhanced water repellency and skin adhesion.

Occurrence

Kaolin is a naturally occurring clay that is treated for impurities.

Uses

Adsorbant.

Uses

kaolin (China clay) is a mixture of various aluminum silicates. It is often used in powders and masks given its absorbent, abrasive, bulking, and opacifying properties. This white, soft powder has good coverage and absorption abilities for both water and oil, making it an appropriate absorber of the oil and sweat secreted by the skin. It adheres well to the skin’s surface, yet is easily removed with normal cleansing procedures. Kaolin is considered a non-comedogenic raw material.

Uses

Kaolin has been used:

• For preparing synthetic turbid water that is employed to evaluate the biosorption capacity of Moringa oleifera leaves.
• In combination with carrageenan to induce arthritic inflammation in a rat model for evaluating the activity of JAK3 (janus kinase 3) inhibitors.
• In a study to assess its utility for microparticle-enhanced cultivation (MPEC) of 2-phenylethanol and 6-pentyl-α-pyrone.

Preparation

The extraction of KAOLIN (china clay) from its deposits is usually performed in three steps: open-pit mining, mineral processing and beneficiation, and drying.
Open-pit operations require the removal of ground overlying the clay (i.e., overburden). The exposed clay is then mined by a hydraulic mining process, that is, a high-pressure water jet from a water cannon called a monitor erodes the faces of the pit. This liberates from the quarry face the china clay, together with sand and mica. The slurry formed flows to the lowest part of the pit or sink, where it is pumped by centrifugal pumps to classifiers, where coarse silica sand is removed. The silica sand is later reused for landscape rehabilitation. The remaining suspension of clay is transported by underground pipeline to the mineral-processing and beneficiation plant, where a series of gravity separation techniques are used to remove particulate materials such as quartz, mica, and feldspars. Sometimes the purified clay slurry undergoes an additional chemical bleaching process that greatly improves its whiteness. The refined clay suspension is then filtrated, and the filtration cake with a moisture content of about 25 wt.% passes through a thermal drier fired by natural gas to yield a final product with 10 wt.% moisture. The end product is normally sold in pelletized form with a pellet size ranging from 6 to 12 mm.

Definition

A mixture of clays, quartz, and feldspar usually containing at least 25% alumina. Ball and china clays are ordinarily used. A slip or slurry is formed with water to form a plastic, moldable mass, which is then glazed and fired to a hard, smooth solid.

Production Methods

Kaolin is a hydrated aluminum silicate obtained by mining naturally occurring mineral deposits. Large deposits are found in Georgia, USA and in Cornwall, England.
Mined kaolin is powdered and freed of coarse, gritty particles either by elutriation or by screening. Impurities such as ferric oxide, calcium carbonate, and magnesium carbonate are removed with an electromagnet and by treatment with hydrochloric acid and/or sulfuric acids.

Indications

Kaolin is a naturally occurring hydrated aluminum silicate that is prepared for medicinal use as a very finely divided powder. The rationale behind its use in acute nonspecific diarrhea stems from its ability to adsorb some of the bacterial toxins that often cause the condition.

Definition

clay: A fine-grained deposit consistingchiefly of clay minerals. It ischaracteristically plastic and virtuallyimpermeable when wet and crackswhen it dries out. In geology the sizeof the constituent particles is usuallytaken to be less than 1/256 mm. Insoil science clay is regarded as a soilwith particles less than 0.002 mm insize.

brand name

Vanclay (Vanderbilt);Biskapect;Chloropect;Collodyne;Diaguard forte;Diastat;Donnagel pg liquid;Donnagel-mb;Donnagel-pg;Enterosan;Fissan;Kaodinnon-narcotic;Kaolin w/pectin;Kaomagma with pectin;Kaomycin;Kaoneo;Kaopectate n;Kaoprompt-h;Kao-spen;Kapetolin;Kc;Kln;Medipect;Noventerol;Parepectolin;Pectrolyte;Peterpect;Streptomagma.

World Health Organization (WHO)

Kaolin, a hydrated aluminium silicate, is an absorbent and has been used to treat diarrhoea because of its ability to bind and inactivate bacterial toxins. However, it has been shown to induce only a slight change in stool consistency and there is no evidence that it can reduce the duration or the severity of diarrhoeal disease. It does not reduce fluid and electrolyte losses. It cannot be recommended in the treatment of diarrhoea.

General Description

Odorless white to yellowish or grayish powder. Contains mainly the clay mineral KAOLINite (Al2O3 SiO2)2 H2O)2), a hydrous aluminosilicate. KAOLINite has mp 740-1785°C and density: 2.65 g cm-3. KAOLINe is insoluble in water but darkens and develops a earthy odor when wet.

Reactivity Profile

KAOLIN is stable and chemically unreactive under ordinary conditions.

Hazard

Respirable fraction; questionable carcinogen.

Pharmaceutical Applications

Kaolin is a naturally occurring mineral used in oral and topical pharmaceutical formulations.
In oral medicines, kaolin has been used as a diluent in tablet and capsule formulations; it has also been used as a suspending vehicle. In topical preparations, sterilized kaolin has been used in poultices and as a dusting powder. Therapeutically, kaolin has been used in oral antidiarrheal preparations.

Industrial uses

The name kaolin comes from the two Chinese words kao-ling, meaning high ridge, and was originally a local term used to describe the region from which the clay was obtained. Kaolin (Al₂O₃2SiO₂2 H₂O) usually contains less than 2% alkalies and smaller quantities of iron, lime, magnesia, and titanium. Because of its purity, kaolin has a high fusion point and is the most refractory of all clays. Lone kaolins are widely used in casting sanitaryware, ceramics, and refractories.
Georgia china clay is one of the most uniform kaolins to be found. Generally speaking, there are two types of Georgia-sourced kaolin, both of which are widely used for casting and other processes. One type imparts unusually high strength and plasticity, and is used for both casting and jiggering where a high degree of workability is required. The other type typically is a fractionated, controlled particle size clay that also behaves well in casting, dries uniformly, and reduces cracking of ware.

Side effects

It is almost harmless and is effective in many cases of diarrhea if taken in large enough doses (2–10 g initially, followed by the same amount after every bowel movement). The adsorbents are generally safe, but they may interfere with the absorption of some drugs from the GI tract.

Safety

Kaolin is used in oral and topical pharmaceutical formulations and is generally regarded as an essentially nontoxic and nonirritant material. Oral doses of about 2–6 g of kaolin every 4 hours have been administered in the treatment of diarrhea.

Veterinary Drugs and Treatments

Although its efficacy is in question, kaolin/pectin is used primarily in veterinary medicine as an oral anti-diarrheal agent. It has also been used as an adsorbent agent following the ingestion of certain toxins. Administration may be difficult due to the large volumes that may be necessary to give orally.

Source

Premier-quality deposits of kaolin such as those mined in Cornwall in the United Kingdom, Georgia and the Carolinas in the southe astern United States, and the Amazon Basin of Brazil.
Other suppliers of quality kaolin include France, Germany, the Czech Republic, Malaysia, and Australia.

storage

Kaolin is a stable material. Since it is a naturally occurring material, kaolin is commonly contaminated with microorganisms such as Bacillus anthracis, Clostridium tetani, and Clostridium welchii. However, kaolin may be sterilized by heating at a temperature greater than 160°C for not less than 1 hour. When moistened with water, kaolin darkens and becomes plastic.
Kaolin should be stored in a well-closed container in a cool, dry place.

Incompatibilities

The adsorbent properties of kaolin may influence the absorption of other orally administered drugs. Drugs reportedly affected by kaolin include amoxicillin; ampicillin;cimetidine; digoxin; lincomycin; phenytoin; and tetracycline. Warfarin absorption by rat intestine in vitro was reported not to be affected by kaolin. With clindamycin, the rate (but not the amount) of absorption was affected by kaolin.

Regulatory Status

Accepted in Europe as a food additive in certain applications. Included in the FDA Inactive Ingredients Database (oral capsules, powders, syrups, and tablets; topical preparations). Included in nonparenteral medicines licensed in the UK.