PURPOSE: To remove impurities such as sulfur, lead and arsenic contained in a clay mineral and to decolor the mineral by treating the mineral with an acidic aq. soln. of a peroxide.

CONSTITUTION: A clay mineral such as kaoline, talc or mica is treated with an acidic aq. soln. of a peroxide such as hydrogen peroxide, sodium percarbonate, sodium perborate, performic acid or peracetic acid. Hydrogen peroxide is esp. pref. used, and the concn. thereof is pref. 3W10%. The acid applied may be hydrochloric acid, sulfuric acid, nitric acid, phosphoric acid, malic acid, acetic acid or propionic acid, and the concn. thereof is 0W50, pref. 1W20%. More than twice, pref. about 5 times as much the soln. as the mineral is used. The treatment temp. ranges from 0W80°C, yet the mineral can be treated at room temp. without requiring a temp. rise.