SILICA IN SOIL SOLUTIONS: II. THE ADSORPTION OF MONOSILICIC ACID BY SOIL AND BY OTHER SUBSTANCES

Abstract

A study was made of the adsorption of monosilicic acid from dilute solutions by soils and other solids and the results were applied to a consideration of silica in natural soil solutions. Freshly precipitated hydroxides of polyvalent metal ions were most effective, some soil samples and iron-oxide minerals were moderately effective, and alkaline-earth carbonate minerals were ineffective in adsorbing dissolved silica. The adsorption data approximately conformed to Freundlich's adsorption equation. Adsorption of Si(OH)4 increased throughout the reaction range pH 4 to pH 9 and, with a ferruginous soil sample, adsorption decreased as the pH was increased above 10.The data obtained support the hypothesis that a pH-dependent adsorption reaction is involved in controlling the concentration of silica in soil solutions. Adsorption of Si(OH)4 as soil moisture evaporates may contribute to the accumulation of amorphous coatings on soil particle surfaces.