VALUE ADDITION OF PAPER COATING GRADE KAOLINS BY THE REMOVAL OF ULTRAFINE COLORING IMPURITIES

Two kaolin samples from the southern part of Kerala (A and B) have bee n characterised. The colouring impurities present were found to be car bonaceous and ferruginous, being also present in ultrafine size ranges . Modern beneficiation techniques such as ultra flotation and high gra dient magnetic separation (HGMS) have been carried out to reduce the l evel of these contaminants and to increase the brightness of the produ ct clays. The results showed that nearly 70% of the ultrafine carbonac eous matter in A, which originally contains 0.13% carbon (as fixed car bon), could be removed by shear floc-flotation, HGMS treatment could r emove similar to 45% of the iron minerals (feed assay 0.58% Fe2O3). Sa mple B contained 0.32% Fe2O3 and 0.19% carbon. The shear floc-flotatio n was found to be the only effective method by which similar to 75% of the carbon could be floated out. This sample did not respond to HGMS which may be because of the 'structural' nature of the iron present. B oth the kaolins, after processing, were found suitable for paper coati ng. Another important aspect of this work is the establishment of the maximum permissible level for carbon in paper coating grade clays sinc e the standard specifications do not give any limiting value. (C) 1997 Elsevier Science B.V.