Abstract
Two Indian kaolins of different origins and containing different types of iron minerals were subjected to leaching by citrate-dithionite-bicarbonate (CDB) method and also using dilute sulphuric acid. The kaolins were calcined at various temperatures from 400° to 1200°C and the products were also chemically leaured in a similar way. The percentages of iron and aluminium in the clays and their calcined products before and after leaching were determined. The change in optical properties of the samples on CDB treatment was also found out. The removal of iron and aluminium was correlated with the structural change occurring in kaolinite during calcination. The optical properties were found to improve by the removal of iron, which was again dependent on the temperature of calcination.
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