Investigation on a gray kaolin from south east India

Abstract Kaolin is mostly associated with minor quantities of ferruginous and carbonaceous impurities which impart color to this white mineral. Hence, their removal is of prime importance in the value addition and optimum utilization of kaolin. The coloring effect as well as the technique for removing these impurities depends on the “species” of the ion and/or the type of mineral. The present paper deals with the investigation on a gray kaolin from south east part of India for its properties and utilization. The sample is found to be highly acidic which creates environmental pollution. The run-of-mines clay was characterized for its physical, chemical, mineralogical and morphological properties. Size classification followed by conventional reductive bleaching gave product clay of fine particle size partly free from coarse impurities which was found suitable for ceramic and filler applications. The impurities were separated by different methods, characterized and identified as quartz and pyrite. The product clay was subjected to dithionite citrate bicarbonate treatment to remove the soluble iron mineral species. The improvement in optical properties achieved thereby indicated that the clay can be beneficiated to pigment grade by adopting advanced techniques of beneficiation. X-ray diffraction, thermal and chemical analyses and microscopic investigations (SEM and TEM-EDS) led to conclusive findings.