Quick Search
Kaolin is a significant industrial clay that mainly contains a hydrated aluminum silicate mineral named as kaolinite (Al2Si2O5(OH)4).
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.
CAS: 1332-58-7
MF: H2Al2O8Si2.H2O
MW: 258.16
EINECS: 310-194-1
Synonyms
Anhydrol;Argilla;Bilt-cote;Bilt-plates;Buca;Catalpo;Chinaclaypowder;PAR CLAY
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.
Unique mineralogy, morphology, chemical and physical specifications of kaolin make it a versatile raw material appropriate for many different applications, 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.
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.
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.
These cause a dramatic decrease in its commercial price.
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.
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.
Kaolin is formed under acidic conditions through weathering or hydrothermal changes of feldspars, and – to a lower extent – also other aluminosilicates.
Kaolin 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.
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.
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):
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).
Kaolin 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.
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 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.
Kaolin provides a matte surface effect, which can slightly reduce sheen left by some talc products.
A fine-grained deposit consistingchiefly of clay minerals.
Kaolin 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.
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.
Odorless white to yellowish or grayish powder.
Contains mainly the clay mineral KAOLINite (Al2O3 SiO2)2 H2O)2), a hydrous aluminosilicate.
Kaolin has mp 740-1785°C and density: 2.65 g cm-3.
Kaolin is insoluble in water but darkens and develops a earthy odor when wet.
Kaolin is a clay mineral, with the chemical composition Al2Si2O5(OH)4.
Kaolin is a layered silicate mineral, with one "tetrahedral" sheet of silicate tetrahedrons (SiO4) linked to one "octahedral" sheet of aluminate octahedrons (AlO2(OH)4) through oxygen atoms on one side, and another such sheet through hydrogen bonds on the other side.
Kaolinite is a soft, earthy, usually white, mineral (dioctahedral phyllosilicate clay), produced by the chemical weathering of aluminium silicate minerals like feldspar.
Kaolin has a low shrink–swell capacity and a low cation-exchange capacity.
Rocks that are rich in kaolinite, and halloysite, are known as kaolin (/ˈkeɪ.əlɪn/) or china clay.
In many parts of the world kaolin is colored pink-orange-red by iron oxide, giving it a distinct rust hue.
Lower concentrations of iron oxide yield the white, yellow, or light orange colors of kaolin.
Alternating lighter and darker layers are sometimes found, as at Providence Canyon State Park in Georgia, United States.
Kaolin is an important raw material in many industries and applications.
Commercial grades of kaolin are supplied and transported as powder, lumps, semi-dried noodle or slurry.
Global production of kaolin in 2021 was estimated to be 45 million tonnes, with a total market value of US $4.24 billion.
Kaolin is a naturally occurring clay mineral famously used in cosmetics for its absorbent properties.
Kaolin is particularly popular in facial masks targeted at reducing skin’s surface oil.
While its absorbent properties are helpful for those with oily skin, Kaolin can be drying for other skin types (especially if used in very high amounts).
To avoid this issue, some formulators pair kaolin with hydrating/soothing ingredients which work to offset some of its absorbency so skin benefits without feeling dry or tight.
Kaolin Chemical Properties
Melting point: 1750 °C
Density: 2,6 g/cm3
Bulk density: 470kg/m3
Refractive index: 1.6200
Storage temp.: no restrictions.
Solubility: Practically insoluble in diethyl ether, ethanol (95%), water, other organic solvents, cold dilute acids, and solutions of alkali hydroxides.
Form: Powder
Color: 75-96, Hunter Brightness
PH: 6-7 (50g/l, H2O, 20℃)(slurry)
Water Solubility: insoluble H2O, dilute acids and alkali hydroxides [HAW93]
Dielectric constant: 1.8 - 2.8（0.0℃）
Stability: Stable. Substances to be avoided include strong oxidizing agents.
InChI: InChI=1S/2Al.O5Si2.2H2O.2O/c;;1-6(2)5-7(3)4;;;;/h;;;2*1H2;;/q2*+1;-2;;;;
InChIKey: NLYAJNPCOHFWQQ-UHFFFAOYSA-N
EPA Substance Registry System: Kaolin (1332-58-7)
Kaolin occurs as a white to grayish-white colored, unctuous powder free from gritty particles.
Kaolin has a characteristic earthy or claylike taste, and when moistened with water it becomes darker in color and develops a claylike odor.
Sericite is a mineral similar to white mica in shape and composition.
Kaolin 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.
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.
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, Kaolin has a low cation exchange capacity.
Kaolinite easily adsorbs water and forms a plastic, paste-like substance.
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.
Kaolin is a mixture of various aluminum silicates.
Kaolin 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.
Kaolin adheres well to the skin’s surface, yet is easily removed with normal cleansing procedures.
Kaolin is considered a non-comedogenic raw material.
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; Kaolin 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.
Main
In 2009, up to 70% of kaolin was used in the production of paper.
Following reduced demand from the paper industry, resulting from both competing minerals and the effect of digital media, in 2016 the market share was reported to be: paper, 36%; ceramics, 31%; paint, 7% and other, 26%.
According to the USGS, in 2021 the global production of kaolin was estimated to be around 45 million tonnes.
Paper applications require high-brightness, low abrasion and delaminated kaolins.
For paper coatings it is used to enhance the gloss, brilliance, smoothness and receptability to inks; Kaolin can account for 25% of mass of the paper.
As a paper filler Kaolin is used as a pulp extender, and to increase opacity; it can account for 15% of mass.
In whiteware ceramic bodies, kaolin can constitute up to 50% of the raw materials.
In unfired bodies Kaolin contributes to the green strength, plasticity and rheological properties, such as the casting rate.
During firing Kaolin reacts with other body components to form the crystal and glass phases.
With suitable firing schedules Kaolin is key to the formation of mullite.
The most valued grades have low contents of chromophoric oxides such that the fired material has high whiteness.
In glazes Kaolin is primarily used as a rheology control agent, but also contributes some green strength.
In both glazes and frits Kaolin contributes some SiO2 as a glass network former, and Al2O3 as both a network former and modifier.
Other industrial
As a raw material for the production of an insulation material called Kaowool (a form of mineral wool).
An additive to some paints to extend the titanium dioxide (TiO2) white pigment and modify gloss levels.
An additive to modify the properties of rubber upon vulcanization.
An additive to adhesives to modify rheology.
As adsorbents in water and wastewater treatment.
In its altered metakaolin form, as a pozzolan; when added to a concrete mix, metakaolin accelerates the hydration of Portland cement and takes part in the pozzolanic reaction with the portlandite formed in the hydration of the main cement minerals.
Metakaolin is also a base component for geopolymer compounds.
Medical
To soothe an upset stomach, similar to the way parrots (and later, humans) in South America originally used Kaolin (more recently, industrially produced).
Kaolin-based preparations are used for treatment of diarrhea.
An ingredient in 'pre-work' skin protection and barrier creams.
To induce and accelerate blood clotting.
In April 2008 the US Naval Medical Research Institute announced the successful use of a kaolinite-derived aluminosilicate infusion in traditional gauze.
which is still the hemostat of choice for all branches of the US military.
As a mild abrasive in toothpaste.
Cosmetics
As a filler in cosmetics.
For facial masks or soap.
for spa body treatments, such as body wraps, cocoons, or spot treatments.
Archaeology
As an indicator in radiological dating since kaolinite can contain very small traces of uranium and thorium.
Geophagy
Humans sometimes eat kaolin for pleasure or to suppress hunger, a practice known as geophagy.
In Africa, kaolin used for such purposes is known as kalaba (in Gabon and Cameroon), calaba, and calabachop (in Equatorial Guinea).
Consumption is greater among women, especially during pregnancy, and its use is sometimes said by women of the region to be a habit analogous to cigarette smoking among men.
The practice has also been observed within a small population of African-American women in the Southern United States, especially Georgia, likely brought with the traditions of the aforementioned Africans via slavery.
There, the kaolin is called white dirt, chalk or white clay.
Geotechnical engineering
Research results show that the utilization of kaolinite in geotechnical engineering can be alternatively replaced by safer illite, especially if its presence is less than 10.8% of the total rock mass.
Small-scale uses
As a light-diffusing material in white incandescent light bulbs.
In organic farming as a spray applied to crops to deter insect damage, and in the case of apples, to prevent sun scald.
As whitewash in traditional stone masonry homes in Nepal.
As a filler in Edison Diamond Discs.
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.
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.
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.
Kaolin is normally sold in pelletized form with a pellet size ranging from 6 to 12 mm.
