GB1115694A - Clay improvement - Google Patents

Abstract

Kaolin clay containing Ti is purified by incorporating into a slurry of the clay containing 10-50% solids an amount of a peptizing agent in excess of that required to obtain minimum viscosity, i.e. maximum dispersion, and allowing the impurities to settle. Two methods are described: (a) a crude slurry is initially treated with e.g. 0.5-6 lb/ton of a peptizing agent (i.e. not excess) and fractionated. The portion containing at least 90% minus 2m particles, with a 20-45% solids content, is then mixed with the excess peptizing agent (5-25 lb/ton), allowed to stand, and drawn off from the deposit (Examples 1-47); (b) a crude slurry is fractionated and treated at the same time. The excess peptizing agent is added to the slurry, and on standing, coarse particles and impurities settle, and the slurry is drawn off. The treatment may be repeated with the addition of 0.5 to 1.5 lb/ton sulphuric acid (Examples 48-70). In either case, the slurry is then flocculated with sulphuric acid (0.2-7 lb/ton) and/or aluminium sulphate (3-45 lb/ton), and filtered. The clay may be bleached before or after treatment. In all the examples, the filtered clay was reslurried to 22-32% solids and bleached with zinc hydrosulphite (8-15 lb/ton) with or without aluminium sulphate (0.8-6 lb/ton). Peptizing agents exemplified are: sodium hexametaphosphate alone (Examples 1, 2, 6-9, 11, 12, 14, 17, 20-24, 28, 31, 39, 40, 45, 49, 51-55, 57, 65-66), with tetrasodium pyrophosphate (3, 59, 60, 62), with sodium hydroxide (4, 15, 18, 26, 32, 44, 61, 63, 64), and with sodium carbonate (47, 68); sodium hypochlorite (30); sodium silicate (35-38, 42, 70); tetrasodium pyrophosphate (34, 46); and an organic polyphosphate (41).