Adsorption of silicic acid on iron(III) hydroxide from aqueous solution and polymerization of adsorbed silicic acid were affected by pH, concentration of silicic acid before and after adsorption, or the relative amount of silicic acid and iron(III) hydroxide. The amount of adsorbed silicic acid and the rate of its polymerization were maximum at pH 9. The polymerization reaction of silicic acid on the surface of iron(III) hydroxide was found to consist of two steps: (1) polymerization of adsorbed monosilicic acid and (2) polymerization between monosilicic acid in the solution and silicic species already present on the surface of iron(III) hydroxide, giving a three-dimensional gel structure.
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