BLEACHING OF BRAZILIAN KAOLINS USING ORGANIC-ACIDS AND FERMENTED MEDIUM

The use of kaolin for both coating and filler applications in the pape r industry requires a high brightness grade, so that treatment for the removal of iron, which adds color to the mineral decreasing its comme rcial value, is required. Bleaching of kaolin is usually carried out b y reductive leaching of iron, producing effluents of considerable envi ronmental concern. Despite little investigation, the use of organic ac ids Seems to be a good alternative for the iron removal with the addit ional advantage of producing less-aggressive effluents. This paper pre sents a study of bleaching treatments with different samples of Brazil ian kaolins using organic acids and fermented medium from Aspergillus niger cultivation as the leaching agent. The studies showed more effec tiveness when oxalic acid and fermented medium were used. The brightne ss of a kaolin sample reached the levels for filler clay (sample nor s ubmitted to magnetic separation) and coating clay (sample submitted to magnetic separation), when fermented medium and oxalic acid were used as a bleaching agent. These results could not be obtained by more con ventional methods. Copyright (C) 1996 Elsevier Science Ltd