Method for producing high brightness low abrasion calcined kaolin pigment

Abstract

A process for preparing a high brightness, low abrasion calcined kaolin. A cretaceous crude is wet beneficiated by subjecting same as an aqueous slurry to degritting, classification, magnetic separation, and scrub grinding. The slurry from the foregoing is diluted to less than 15% solids and subjected while well dispersed to a separation in a centrifuge to yield an underflow and an overflow fine fraction having less than 5% solids and a P.S.D. such that at least 85% by weight are of <0.5 .mu.m E.S.D. and at least 30% by weight are of <0.25 .mu.m E.S.D. The overflow fine fraction slurry of dispersed kaolin is subjected to a partial filtration by passing same in cross flow relation to a microporous membrane through which substantially none of the suspended kaolin particles pass, to raise the solids content of the said slurry to at least 20%. This slurry is combined with up to 90% on a dry weight basis of a slurry of a fine particle size tertiary kaolin, and is then bleached, flocculated and filtered to yield a filter cake, which is redispersed, dried and milled to provide a calciner feed. The feed is calcined at temperatures above the kaolin exotherm to yield a calcined product having a brightness of at least 92 and an Einleiner Abrasion less than 24.