Effect of alkali, alkali-earth and zinc cations on the dissolution rate of silica gel in aqueous solution

Dissolution rate of silica gel with alkali, alkali-earth, and zinc chloride solution was examined. The dissolution rate depends on the concentration of the cation in solution. In each series, the larger the ionic radius, the higher is the dissolution rate. In solutions containing alkali cations, a high charge density prevents the hydrolysis of the Si-O bond because the water molecules cannot move freely. On the other hand, the dissolution rates of the silica gel in Ca and Sr chloride solutions are very high. The rates in alkaline-earth and zinc chloride solutions vary over a wider range than that for the alkali chloride solutions. This suggests that the mechanism of dissolution of silica gel in Ca and Sr chloride solutions is different from that in Mg, Zn and alkaline chloride solutions.