Patent ID: 7893114

Claim:
A process for producing an aqueous silica-based sol containing aggregated silica-based particles which comprises: (a) providing a reaction vessel equipped with means for stirring; (b) adding to said reaction vessel: (i) a cationic ion exchange resin having at least part of its ion exchange capacity in hydrogen form, and (ii) an aqueous solution of alkali metal silicate, to form an aqueous slurry; (c) stirring said aqueous slurry in said reaction vessel to allow particle aggregation and until the pH of the aqueous phase is in the range of from 5.0 to 8.0; (d) adding one or more materials to the aqueous phase obtained after step (c) to form an aqueous phase having a pH of above 9.0; and separating said ion exchange resin from the aqueous phase after step (c) or after step (d).