Chemical, Mineralogical and Morphological Characterisation of kaolinitic clays

Abstract

Kaolin is one of the most important white minerals which has got applications in a variety of industries. The nature of kaolin and the ancillary mineral contarnuratits depend upon (i) the genesis / origin of the mineral ie., from feldspathic or micaceous rocks, and (ii) the nature of the deposit ie., primary, secondary or hydro-thermal. The present investigation is on a kaolin sample from India and another from Germany A systematic study on physical, chemical and mineralogical characterisation showed that both the clays are highly kaolinitic, but the ancillary mineral contaminants are different- The German clay is already being processed for various applications whereas the optimal utilisation of the Indian clay is under study. The trace elements in the clays were also estimated to get some idea about the genesis of the clay. Iron containing titania was found to be the major colouring impurity in the Indian clay while orthoclase feldspar., mica and quartz were found in the German clay. Attempts were also made to find out whether the iron in the clay is "free" or "structural". The poor response to citrate-dithionite-bicarbonate dissolution method indicated that most of the iron in both the clays is structural. The magnetic fraction separated form the Indian clay was also characterised for identifying the mineral impurities. X-ray Diffraction, Thermal Analysis, Electron Microscopy & Chemical Analysis studies substantiated the findings.