Technology development for kaolin processing

Abstract

Kaolins or china clays are naturally-occurring earthy materials predominantly containing the mineral kaolinite, Al2O3 2SiO2 2H2O. The material is characterized by unique properties such as colloidal particle size, thin platelet shape, high brightness, etc. and is used as coating, filling, diluent and carrying material in a number of industrial and consumer products. Although most important in paper making, kaolin is also used extensively in ceramics, paint, rubber, plastics etc. The mined china clay normally contains different types of impurities. Technology development for the processing of kaolin is essentially the development for sequentilised flow sheet for its beneficiation so that all unwanted impurities are removed and the required properties of the processed material is ensured by suitable sizing, brightness improvement, surface modifications and other operations. Typical impurities present in china clay are quartz, various iron oxides and sulphides, titanoferrous minerals, mica, feldspar, organic matter etc. Hence for all value-added applications, kaolin is to be processed to obtain end products which satisfy prescribed specifications. Modern methods of (wet route) china clay beneficiation make use of a number of techniques such as crushing/attrition, blunging, screening or mechanical classification, centrifugal separations, magnetic separation, selective flocculation, froth flotation, oxidative and/ or reductive bleaching etc. Additional techniques such as attrition/delamination, pugging, calcination, surface modification etc. are also employed for enhancing the properties of the end product. The selection and sequentialisation of the techniques depend upon the type of the impurities present and the end use of the product clay. The present paper discusses about technology development work carried out for different china clays with some case studies such as those for Mamuara clay, Kutch (Gujarat), Thonnakkal Pink clay, Trivandrum (Kerala), Thonnakkal Grey clay. Trivandrum (Kerala), Koraput clay (Orissa) and KCCPL clay, Kannur (Kerala).