Polymerization of Silicic Acid Adsorbed on Aluminium Hydroxide

Abstract

Abstract Factors controlling the absorption of silicic acid on aluminium hydroxide from aqueous solution and the polymerization of adsorbed silicic acid were studied. Measurements included the amount of silicic acid adsorbed on aluminium hydroxide, the amount and size distribution of the polysilicic acid formed, and the differential thermal analysis curve of aluminium hydroxide which had adsorbed silicic acid. The adsorption and the polymerization of silicic acid are affected by pH, the relative amounts of silicic acid and aluminium hydroxide, the reaction time between monosilicic acid and aluminium hydroxide, and the formation of amorphous aluminosilicate. The amount of adsorbed silicic acid and the rate of its polymerization are maximum at pH 9.0–9.5. A part of adsorbed monosilicic acid reacts with aluminium hydroxide to form an aluminosilicate. In an early stage of the polymerization of the adsorbed silicic acid, the polymerization mainly proceeds by the reactions between monosilicic acids and between monosilicic and polysilicic acids; the particle sizes of polysilicic acids gradually increase with time. When the polymer particles grow large enough to touch neighboring polymers, the growth rate of polymer particles becomes faster due to the polymer-polymer reactions.