Kaolin - China Clay

KAOLIN

CHINA CLAY

Technical grade

Kaolin is a naturally occurring, fine, white clay dominated by the mineral kaolinite, a 1:1 layered phyllosilicate. It forms from the weathering of feldspar-rich rocks (like granite). Kaolin is used in ceramics, bricks, paint, plastics, rubber, sealants, adhesives, coated paper, as a light diffusing material in white incandescent light bulbs, and as a filler in many other applications. The largest and most common use is in the paper industry. It is the main ingredient in creating "glossy" paper. In the paint industry it is added to act as an extender of titanium dioxide reducing costs and improving rheology. Kaolin is used as a raw material in the manufacture of the pigment ultramarine blue.

• Principal mineral: Kaolinite

• Ideal formula: Al₂Si₂O₅(OH)₄

• Structure: Stacks of silica tetrahedral sheets bonded to alumina octahedral sheets (1:1).

• Charge/CEC: Very low isomorphic substitution → low cation-exchange capacity (typically ~3–15 meq/100 g).

• Surface chemistry: Hydroxyl groups on the octahedral surface; weakly acidic to near-neutral behavior.

Properties of Kaolin

• Synonyms: Kaolin Powder; clay; hydrated aluminium silicate; China Clay; kaolinite
• CAS No.: 1332-58-7
• EINES No.: 310-127-6
• Molecular Weight: 258.16
• Chemical Formula: Al₂Si₂O₅(OH)₄
• Appearance: Soft, fine, white powder (plate-like particles).
• Odour: Odourless
• Solubility: insoluble in water.
• Density (true): ~2.58–2.63 g/cm³.
• Melting Point: 1750 C
• Mohs hardness: ~2–2.5 (very soft).
• Refractive index: ~1.56 (useful as an extender pigment).
• pH (20% slurry): ~4–7

Uses for Kaolin 

Ceramics

• Key clay in porcelain, sanitaryware, tableware, tiles. Provides whiteness, shape, and forms mullite on firing for strength.

Paper

• As coating and filler to improve brightness, opacity, gloss, printability. Calcined grades boost opacity; hydrous grades aid smoothness.

Paints & coatings

• Extender pigment (low RI but excellent spacing), improves opacity, scrub resistance, rheology, and reduces TiO₂ demand (especially with calcined kaolin).

Rubber & plastics

• Functional filler for reinforcement, stiffness, barrier, and cost control; improves processing (wire & cable, automotive parts, films).

Adhesives & sealants

• Rheology control, body, and reinforcement.

Construction & cement

• Metakaolin is a high-reactivity pozzolan: increases concrete strength, lowers permeability, mitigates ASR, improves sulfate and chloride resistance; also used in geopolymers.

Catalysis & refining

• Kaolin matrix in FCC catalysts and as a support/porous component.

Pharmaceuticals & medical

• Historically as a GI adsorbent (now limited); excipient/tablet diluent. Kaolin-impregnated hemostatic dressings promote clotting.

Cosmetics & personal care

• Oil absorber and matting agent in masks, powders, and cleansers; gentle exfoliant.

Agrochemicals & others

• Carrier for pesticides, anti-caking/flow aid, mild adsorbent for environmental uses.