Indian China Clays: Vagaries in Process and Flow Sheet Development

Abstract

Process and flow sheet development for the beneficiation of China clay remains always unique to each deposit since the mineral characteristics changes from deposit to deposit. The difference in characteristics has got a great bearing on the geological formation, setting and the transformation of the resource over millions of years. Each clay deposit differs in its type and extent of impurities, particle size distribution, pH and other characteristics. Hence it is imperative that flow sheet for beneficiation for any clay can be made only after detailed laboratory processing studies. The present paper discusses about the above mentioned aspect by carrying out process development studies on five typical clays from different states of India, viz., Mamuara clay from Kutch (Gujarat), Thonnakkal Pink clay from Trivandrum (Kerala), Thonnakkal Grey clay from Trivandrum (Kerala), Koraput clay from Orissa and Guda clay from Bikaner, Rajasthan so as to bring out the vagaries in process and develop flow sheet. Studies shows that, besides the normal operations, high gradient magnetic separation and calcination are essential for Mamuara clay so as to get a premium grade calcined clay, reductive bleaching is unavoidable for Thonnakkal Pink clay, shear-floc flotation is required for Thonnakkal Grey clay to remove graphite and a non-conventional (pH controlled) water washing is required for Koraput clay even before blunging since it is highly acidic (pH 1.7). Finally, Guda clay responds only to magnetic separation and can not be upgraded to any premium grade Incidentally, reductive bleaching, flotation and selective flocculation are not effective for Guda clay. Thus the investigations reveal that each deposit needs different unit operations and hence different beneficiation flow sheets.