Calcination of Kaolin:
Calcination of Kaolin increases hardness, increases whiteness, improves electrical properties, and alters the size of Kaolin particles. Calcined Kaolin is produced by heating the natural Kaolin to high temperature in Kilns. Market uses of calcined Kaolin is in Rubber, Paint and Plastic industries. Calcined Kaolin is also used as a filler in plaster boards. Characteristics of Calcined Kaolin
Specific Gravity – 2.6
Refractive index – 1.56
MOH Hardness – 4 to 5
Moisture (max %) – 0.5
pH – 6 to 8
During calcination the Kaolin transforms to other amorphous or crystalline phases. At about 500C the transformation of dehydroxylization of kaolinite to metakaolinite occurs and at 1000C crystallization of metakaolinite into mullite takes place. Calcination of kaolin is generally done in horizontal rotary kilns or vertical Herreshoff kilns.
