Patent ID: 7732495

Claim:
A process for producing an aqueous silica-based sol containing aggregated silica-based particles which comprises: (a) providing a cationic ion exchange resin having at least part of the ion exchange capacity in hydrogen form; (b) bringing said ion exchange resin in contact with an aqueous solution of alkali metal silicate having a pH above 12 in a reaction vessel equipped with means for stirring 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) adjusting the pH of said aqueous phase to above 9.0; and (e) separating said ion exchange resin from the aqueous phase after step (c) or after step (d).