Abstract: Production of siliceous precipitates, for example sodium aluminosilicates by decomposition of an alkali metal sulfite solution with a solution of a sulfitic species such as sulfur dioxide, sulfurous acid or a salt thereof. Precipitates having excellent properties are obtained and the co-produced aqueous phase is a solution of alkali metal sulfite which has utility in pulp and paper mills. The process is advantageously carried out in proximity to a pulp and paper making operation wherein the siliceous precipitate may be used as a paper making filler and the alkali metal sulfite solution may be used in the pulping process.