Effect of hydroxides of alkali metals on the kinetics of silica depolymerization

The kinetics of silica depolymerization in aqueous solutions of alkaline hy droxides is a complex process including steps of the interaction of alkalin e hydroxides with active sites on the surface of the particles and in their bulk (of the "solid-phase reaction" type) and the dissolution of colloidal particles. The effect of alkaline hydroxides on the rate of the "solid-pha se reaction" increases with the basicity constants of hydroxides (in the se ries LiOH < NaOH < KOH), while the silica dissolution rate increases with t he degree of cation hydration (in the series K+ < Na+ < Li+). The depolymer ization results in the breaking of the siloxane bonds and the formation of surface polysilicate anions and gel structures both on the surface of the s ilica particles and in their bulk.