Investigations on a kaolin sample from kerala for possible value addition

Abstract

Kaolin or china clay is a versatile industrial mineral with wide technological applications. The major mineral in kaolin is kaolinite (Al2O3.2SiO2.2H2O). The common ancillary/impurity minerals occurring with kaolin include parent rocks like feldspar and mica, quartz, ferruginous, titanoferrous and carbonaceous materials etc. The most deleterious impurities in kaolin are iron minerals which imparts colour to the white kaolin. Kaolin finds extensive applications in paper, paint, rubber, ceramics, plastics etc. One of the highest value additions for kaolin is as pigment in paper and paint industries. Particle size distribution and optical properties are the critical parameters which decides its suitability for the above application. Hence, removal of the coloured minerals is of prime importance in the value addition and optimum utilization of kaolin. The coloring effect as well as the mode of removal of these impurities depends on the “species” of the ion and/or the type of mineral. Therefore, identification/quantification of the impurity minerals has got a major role in the selection and sequentialisation of beneficiation processes. Present paper deals with the investigations carried out on a kaolin sample from Kannur district of Kerala State. Studies have shown that the clay is highly kaolinitic in nature and the major impurity minerals present in the sample are oxides, hydroxides and oxy-hydroxides of iron. Dithionite-Citrate-Bicarbonate (DCB) treatment of the sample shows that most of the iron in the sample is in “free” form. Studies have shown that the product clay after size classification (1" hydrocycloning) and chemical leaching by DCBT is found to be of acceptable grade for filler industry with respect to chemical assay, optical properties and particle size distribution. This shows that the clay can be value added to filler grade by employing suitable deferration technique like Super Conducting High Gradient Magnetic Separation (SC-HGMS) after sizing.