Adsorption Interactions of Monosilicic and Boric Acid on Hydrous Oxides of Iron and Aluminum

Abstract

AbstractReactions of monosilicic acid and boric acid with hydrous oxides of aluminum and iron were studied. Adsorption of B by hydrous iron oxides was satisfactorily described by the Langmuir equation over the range of equilibrium solution concentrations investigated (0–14mM). Adsorption by hydrous aluminum oxides conformed to the Langmuir equation at equilibrium solution concentrations less than 6mM B. Maximum adsorption of boric acid by aluminum hydrous oxides was found to occur at approximately pH 7.5. Aging freshly precipitated hydrous aluminum and iron oxides up to 12 hours markedly reduced B adsorption; beyond 12 hours the effects of aging diminished.Successive treatments with 1.4mM solutions of Si(OH)4 were applied to freshly precipitated aluminum‐ and ironhydrous oxides until an apparent saturation was attained. The adsorption of Si followed the Langmuir equation, with maximum adsorption of 2.96 and 2.67 millimoles of Si per gram of aluminum and iron hydrous oxide, respectively. Boric acid at concentrations of 1.85 and 18.5mM were applied to individual samples after each Si(OH)4 treatment. Aluminum‐ and iron‐Si complexes retained less B as the amount of adsorbed Si on these hydrous oxides increased.