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Kaolinite

Kaolinite is a clay mineral with chemical composition Al2Si2O5(OH)4. It is an important industrial mineral. Rocks rich in kaolinite are called kaolin. Kaolinite, common group of clay minerals that are hydrated aluminum silicates; they contain the main components of kaolin (china clay). The group includes kaolinite, which is chemically similar but amorphous to kaolinite, and its rarer forms, stalagmite and nacrite, halloysite and allophane.

It is a layered silicate mineral with a tetrahedral silica layer (SiO4) bonded to an octahedral layer of alumina (AlO6) octahedra through oxygen atoms.

Kaolinite, nacrite, and dickite occur as compact or granular masses and mica-like clumps as small, sometimes elongated, hexagonal plates. Feldspars are natural change products of feldspathoids and other silicates. Anoxide, previously considered a kaolinite group mineral with a higher-than-normal silica-to-alumina ratio, is now considered kaolinite and free silica (mainly non-crystalline). For chemical formula and detailed physical properties

Kaolinite is the raw material of brick, pottery and tile.It has played a vital role in the development of human civilization.The most important of these minerals is kaolinite. Kaolinite It forms white, microscopic, pseudo-hexagonal plates.

compact or granular masses and mica-like clumps. Three other minerals – stalagmite, nacrite and halloysite – chemically identical to kaolinite, but monoclinic system. Four found together and often visually indistinguishable.

Kaolinite is a natural product of mica degradation. plagioclase and sodium-potassium feldspars under Effect of water, dissolved carbon dioxide and organic matter acids. Used in agriculture; as a filler in foods such as chocolate; mixed with pectin as an antidiarrheal; as paint expander; as a reinforcing agent in rubber; and as powder agent in foundry operations

Name: The name kaolin is derived from Gaoling. Chinese village near Jingdezhen in southeastern China’s Jiangxi Province. The name entered English in 1727 from the French version of the word: kaolin.

Kaolinite has low shrinkage-swelling capacity and low cation exchange capacity (1–15 meq/100 g). A soft, earthy, usually white mineral (dioctahedral phyllosilicate clay) produced by chemical weathering of aluminum silicate minerals such as feldspar. In many parts of the world it is pink-orange-red with iron oxide, giving it a distinctive rust color. Lighter concentrations give white, yellow or light orange colors. Alternating layers are sometimes found, as in Providence Canyon State Park in Georgia, United States. Commercial grades of kaolin are supplied and transported as dry powder, semi-dry noodles or liquid slurry.

Association: Quartz, feldspar, muscovite.

Polymorphism & Series: Dickite, halloysite, and nacrite are polymorphs

Mineral Group: Kaolinite-serpentine group.

Cell Data: Space Group: P1: a = 5.15 b = 8.95 c = 7.39 ® = 91:8 ± ¯ = 104:5 ±¡105:0 ± ° = 90 ± Z = [2]

X-ray Powder Pattern: Scalby, Yorkshire, England (1A). 7.16 (vvs), 3.573 (vvs), 4.336 (vs), 2.491 (s), 2.289 (s), 2.558 (ms), 2.379 (ms)

Chemical Properties

Chemical ClassificationPhyllosilicates Kaolinite-serpentine group
FormulaAl2Si2O5(OH)4
Common ImpuritiesFe,Mg,Na,K,Ti,Ca,H2O

Kaolinite structure showing interlayer hydrogen bonds

Compared to other clay minerals, kaolinite is chemically and structurally simple. It is defined as a 1:1 or TO clay mineral because its crystals consist of stacked layers of RO. Each TO layer consists of a tetrahedral (T) sheet of silicon and oxygen ions bonded to an octahedral (O) sheet of oxygen, aluminum, and hydroxyl ions. The T layer is so named because each silicon ion is surrounded by four oxygen ions forming a tetrahedron. The O layer is so named because each aluminum ion is surrounded by six oxygen or hydroxyl ions arranged at the corners of an octahedron. The two layers in each layer are strongly bonded to each other via shared oxygen ions, while the layers are bonded via hydrogen bonding between the oxygen on the outer face of the T layer of one layer and the hydroxyl on the outer face of the O layer of the next layer.

Structural Transformations

Kaolinite group clays undergo a series of phase transformations after heat treatment in air at atmospheric pressure.

Milling

Grinding kaolinite results in the formation of a mechanochemically amorphous phase similar to metakaolin, although the properties of this solid are quite different. Great energy is required to convert kaolinite into metakaolin.

Drying

Below 100 °C (212 °F), exposure to dry air will slowly remove liquid water from the kaolin. The final state of this transformation is called “skin dryness”. Between 100 °C and about 550 °C (1,022 °F), the remaining liquid water is expelled from the kaolinite. The final state of this transformation is called “bone dryness”. Over this temperature range, the removal of water is reversible: if kaolin is exposed to liquid water, it will be reabsorbed and decomposed into fine particle form. Subsequent transformations represent irreversible and permanent chemical changes.

Metakaolin

Endothermic dehydration of kaolinite begins at 550-600 °C and produces disordered metakaolin, but continuous loss of hydroxyl is observed up to 900 °C (1,650 °F). Although historically there has been much disagreement about the nature of the metakaolin phase, extensive research has led to general consensus that metakaolin is not a simple mixture of amorphous silica (SiO2) and alumina (Al2O3), but rather a complex amorphous structure that retains some of it. longer range order (but certainly not crystalline) due to stacking of hexagonal layers.

Physical Properties

Crystal habit 
ColourWhite to cream and pale-yellow, also often stained various hues, tans and browns being common.
StreakWhite, or paler than the sample.
Hardness2 – 2½
LusterWaxy, Pearly, Dull, Earthy
CleavagePerfect on {001}.
DiaphaneityTranslucent, Opaque
Crystal SystemTriclinic
TenacityFlexible but inelastic
Density2.63 g/cm3 (Calculated)
FractureIrregular/Uneven, Conchoidal, Sub-Conchoidal, Micaceous

Optical Properties

TypeBiaxial (-)
Color / PleochroismTransparent to translucent as single crystals
2V:Measured: 24° to 50°, Calculated: 44°
RI values:nα = 1.553 – 1.563 nβ = 1.559 – 1.569 nγ = 1.560 – 1.570
Birefringence0.017
ReliefLow
Dispersion:none

Occurrence

It replaces other aluminosilicate minerals during hydrothermal alteration and weathering. A common component from which the clay-size fraction of sediments can form by direct precipitation

Kaolinite is one of the most common minerals; As kaolin, it is mined in Malaysia, Pakistan, Vietnam, Brazil, Bulgaria, Bangladesh, France, United Kingdom, Iran, Germany, India, Australia, South Korea, People’s Republic of China, Czech Republic, Spain, South. Africa, Tanzania and the United States.

Kaolinitic saprolite mantles are common in Western and Northern Europe. The ages of these mantles are from Mesozoic to Early Cenozoic.

Kaolinite clay is abundant in soils formed by chemical erosion of rocks in hot and humid climates, such as tropical rainforests. When comparing soils along a slope towards increasingly cooler or drier climates, the proportion of kaolinite decreases while the proportion of other clay minerals such as illite (in colder climates) or smectite (in drier climates) increases. Such climatically relevant differences in clay mineral content are often used to reveal changes in climates in the geological past, where ancient soils were buried and preserved.

Uses Area

  • The main use of the mineral kaolinite (about 50% of the time) is in paper production; Its use provides shine on some coated paper types.
    • in ceramics (main component of porcelain)
    • in toothpaste
    • as a light-emitting material in white incandescent bulbs
    • in cosmetics
    • In industrial insulation material called Kaowool (a type of mineral wool)
    • in ‘pre-work’ skin protection and barrier creams
    • in paint to prolong titanium dioxide white pigment and change gloss levels
    • to change the properties of rubber upon vulcanization
    • in adhesives to change the rheology
    • as a spray applied to crops to prevent insect damage in organic farming and to prevent sunburn on apples
  • As a whitewash in traditional stone-walled houses in Nepal (most common method is to paint the top with white kaolin clay and the middle with red clay; the red clay can extend to the bottom or the bottom can be painted black)
  • As a filler or as a coating to improve the surface in papermaking, as a filler in Edison Diamond Discs Because kaolinite may contain very small traces of uranium and thorium, as an indicator in radiological dating, it was common to treat stomach upset (more recently, industrially produced preparations of kaolinite for the treatment of diarrhea), similar to what parrots (and later humans) originally used in South America.
  • for face masks or soap (known as “White Clay”) body wraps, spa body treatments like cocoons or just spot treatments like feet, back or hands. Essential oil can be added to add a pleasant aroma, or seaweed can be added to increase the nutritional values ​​of the treat.
  • as an adsorbent in water and wastewater treatment to promote blood coagulation in diagnostic procedures, e.g. Kaolin clotting time
  • in the form of metakaolin modified as a pozzolan; When added to a concrete mix, metakaolin accelerates the hydration of Portland cement and takes part in the pozzolanic reaction with portlandite, which is formed in the hydration of the main cement minerals (e.g. alite).
  • in the form of modified metakaolin as a basic ingredient for geopolymer compounds

Safety

People can be exposed to kaolin in the workplace by breathing in the powder or from skin or eye contact.

The Occupational Safety and Health

The Occupational Safety and Health Administration (OSHA) has set the statutory limit (permissible exposure limit) for workplace kaolin exposure as 15 mg/m3 total exposure and 5 mg/m3 respiratory exposure in an 8-hour workday. The National Institute of Occupational Safety and Health (NIOSH) has set a recommended exposure limit (REL) as 10 mg/m3 total exposure TWA 5 mg/m3 respiratory exposure during an 8-hour workday.

Geotechnical engineering

Araştırma sonuçları, kaolinitin jeoteknik mühendisliğinde kullanımının alternatif olarak, özellikle mevcudiyeti toplam kaya kütlesinin %10,8’inden az ise, daha güvenli illit ile değiştirilebileceğini göstermektedir.

Distribution

Pure material from many localities, including:

  • at Kauling, Kiangsi Province,China.
  • In numerous china-clay pits in Cornwall and Devon, England.
  • At Limoges, Haute-Vienne,France.
  • Near Dresden, Kemmlitz, and Zettlitz, Saxony, and elsewhere in Germany.
  • Large deposits in the Donets Basin, Ukraine.
  • In the USA, at Macon, Bibb Co., Georgia; at the Dixie Clay Company mine, and in the Lamar Pit, near Bath, Aikin Co., South Carolina; near Webster, Jackson Co., North Carolina; near Murfreesboro, Pike Co., and at Greenwood, Sebastian Co., Arkansas; from Mesa Alta, Rio Arriba Co., New Mexico.
  • At Huberdeau, Quebec, and near Walton, Nova Scotia, Canada

References

  • Britannica, T. Editors of Encyclopaedia (2018, January 25). Kaolinite. Encyclopedia Britannica. https://www.britannica.com/science/kaolinite
  • Bonewitz, R. (2012). Rocks and minerals. 2nd ed. London: DK Publishing.
  • Dana, J. D. (1864). Manual of Mineralogy… Wiley.
  • Handbookofmineralogy.org. (2019). Handbook of Mineralogy. [online] Available at: http://www.handbookofmineralogy.org [Accessed 4 Mar. 2019].
  • Mindat.org. (2019): Mineral information, data and localities.. [online] Available at: https://www.mindat.org/ [Accessed. 2019].
  • Smith.edu. (2019). Geosciences | Smith College. [online] Available at: https://www.smith.edu/academics/geosciences [Accessed 15 Mar. 2019].