Kaoline
Description:
- Color: White or very light gray. This is due to minimal impurities like iron oxide, which can cause yellowish or reddish hues in some kaolin varieties.
- Odorless
- Soft and smooth to the touch: Feels slightly greasy or soapy due to its layered structure.
- Fine-grained: Particles are very small, giving it a smooth and powdery texture.
Uses:
Kaolin has a wide range of applications due to its unique properties:
- Papermaking: The primary use of kaolin is as a filler and coating in paper production. It improves whiteness, opacity, and printability of paper.
- Ceramics: Used in the production of whiteware ceramics like porcelain, bone china, and sanitaryware. Kaolin contributes to the white color, smoothness, and strength of ceramic bodies.
- Paints and Coatings: Kaolin can be used as a pigment extender and bulking agent in paints and coatings. It improves viscosity, opacity, and fire resistance.
- Plastics: Some kaolin grades are used as fillers and reinforcing agents in plastics, improving stiffness and heat resistance.
- Rubber: Filler material in some rubber products to improve strength and tear resistance.
- Cosmetics and Pharmaceuticals: Limited use in some cosmetic and pharmaceutical formulations as a thickener, anticaking agent, or absorbent material. Strict regulations and processing are required to ensure safety.
- Pest Control: Certain kaolin types can be used as insecticides due to their dehydrating effect on insects.
- Other Uses: Refractory applications, foundry applications, and as an adsorbent material in some industrial processes.
Chemical Composition:
- Primarily kaolinite (Al2Si2O5(OH)4), a hydrated aluminum silicate mineral.
- The structure consists of alumina (Al2O3) sheets linked to silica (SiO2) sheets through hydroxyl (OH) groups.
- May contain small amounts of other minerals depending on the source rock, such as:
- Quartz (SiO2)
- Mica (KAl2(AlSi3O10)(OH)2)
- Hematite (Fe2O3) – can cause slight color variations.
- Trace amounts of other elements like titanium (Ti) and calcium (Ca).
Physical Properties:
- Crystal System: Triclinic
- Hardness: 2-2.5 on Mohs scale (soft, can be scratched by a fingernail)
- Density: Around 2.2-2.6 g/cm3 (depending on mineral composition and porosity).
- Solubility in Water: Insoluble in pure water. However, can form a suspension in water.
- Melting Point: Decomposes before melting.
- Electrical Conductivity: Poor conductor of electricity
- Thermal Conductivity: Low thermal conductivity
Safety Information:
- Kaolin itself is generally considered non-toxic and non-hazardous.
- However, inhaling kaolin dust can irritate the lungs. Wear a dust mask when handling large quantities of kaolin powder.
- Be aware that some kaolin formations may contain trace amounts of harmful minerals like silica or heavy metals depending on the location. Always refer to safety data sheets (SDS) for specific types of kaolin being used in industrial applications.
