An improved process for producing an ultra high brightness calcined kaolin pigment from kaolin clay

摘要

pA selected kaolin crude or crude fraction is purifed by physical or physical/chemical means, such as froth flotation and/or selective flocculation, to remove discrete particles of TiO2 and in some cases, discrete iron minerals. The pure (or purified clay) must then be agitated in the presence of water with a particulate grinding media such as, for example, sand, alumina or zirconia beads, to increase the 2 micron content of the kaolin. An intermediate ground product that contains a substantial weight percentage of particles finer than 1 micron is generated as a result of grinding. The particles finer than 1 micron in the ground kaolin also include those particles in the previously pure or purified kaolin that were present in the naturally occurring clay. A pulp of the ground clay is then fractionated to remove particles larger than 2 microns, e.g., to remove at least 95 %, preferably at 100 % by weight, of the particles larger than 2 microns, while minimizing the removal of particles finer than 1 micron. The resulting fine particles size fraction is then treated by conventional series of steps, i.e., optional bleaching, drying, pulverization, calcination and repulverization to produce a low abrasion, ultrahigh brightness (typically 96 %) calcined kaolin pigment./p [WO9702323A1]