Abstract: This invention concerns a process for producing high purity silica with less than 5 ppm of impurities from cheap alkali silicate aqueous solution (water glass) for industrial use, which commonly contains more than 2000 ppm of impurities, by directly adding water glass to a mineral acid solution, such as hydrochloric acid, nitric acid, and sulfuric acid so as to dissolve impurities in the mineral acid solution and form silica precipitate, and then rinsing the silica precipitate with a mineral acid solution, provided that the viscosity of the water glass is adjusted to 10-10000 poise in advance of adding to the mineral acid solution.

Abstract: This invention concerns a process for purifying silica produced from an alkali silicate aqueous solution, which usually contains more than 200 ppm of impurities, to silica containing less than 30 ppm of impurities. Concretely, the purification process of silica comprises: dispersing silica gel, containing a lot of impurities, in water and filtering the solution; dispersing the filtered out silica gel again in an aqueous solution of pH 2 or less and filtering the aqueous solution; putting the silica gel to heat-treatment and acid-treatment with continuous stirring in order to break the inside siloxane link and dissolve out impurities therefrom and filtering the acid solution; rinsing a produced cake with pure water to wash away the inside residual solution and drying the cake.