Investigations on Selected Indian Kaolins for their Possible Value Addition

Abstract

Kaolins from Kerala, Orissa, Rajasthan and West Bengal states (designated as KK, OK, RK and WK respectively) were studied for their possible value addition. Size classifica-tion followed by physical, chemical and mineralogical characterization of the ROM clays and various size fract-ions were carried out. All the four samples are found to be kaolinitic with quartz as the major impurity. Small quantity of mica is present in RK and WK whereas pyrite is found in OK Size classification increases the % of <2pm particles and kaolinite content. Conventional hydros blea-ching improved the optical properties only marginally whereas dithionite-citrate-bicarbonate ( DCB) treatment considerably enhanced the same. Significant reduction in Fe content and improvement in optical properties on DCB treatment indicate the presence of 'free iron" as oxides, hydroxides, sulphides etc. in KK, OK and WK where as in RK iron is "structural", in kaolinite and / or in the micaceous mineral. The investigation shows that even after size classification, impurity minerals remain in the products indicating their ultra fine size. Hence, value addition is possible (more in KK, OK and WK and less in RK) by removing the iron impurities using special techni-ques such as high gradient magnetic separation, ultra flotation etc. Selected samples were calcined at 1100 °C and the optical properties of the calcined samples did not show much improvement.