Abstract: A selected kaolin crude or crude fraction is purified by physical or physical/chemical means, such as froth flotation and/or selective flocculation, to remove discrete particles of TiO.sub.2 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.

Abstract: A process for reacting metallic iron with sulfur dioxide (SO.sub.2) gas in the presence of water and bleachable matter, especially iron-contaminated kaolin clay, whereby the kaolin or the like is bleached in situ and the viscosity of the kaolin is less than it would be if bleached in a conventional manner.

Abstract: An improved method for improving the brightness of clay of the type that is capable of being bleached by an oxidative reagent such as Georgia gray kaolin. Such clay, in the form of a dispersed slurry, is treated with a combination of sodium silicate, sodium hypochlorite and ozone, most preferably followed by magnetic purification and a reduction bleach. Sodium hypochlorite is added shortly before ozonation.

Abstract: A process for reacting metallic iron with sulfur dioxide (SO.sub.2) gas in the presence of water and bleachable matter, especially iron-contaminated kaolin clay, whereby the kaolin or the like is bleached in situ.