Investigations on the rôle of silicon in plant nutrition. Part II. Adsorption of silica in soluble forms by colloidal oxides of iron and aluminium

Abstract

(1) When a solution of sodium silicate is added to hydrogels of iron oxide or alumina there is considerable adsorption of silicate similar to that observed in the case of the soil. Retention of silica is greater in the case of alumina than with iron oxide gel and the percentage retention decreases with increasing concentration. (2) Similar adsorption of silica occurs in the case of ferric, or aluminium hydroxide gel - silica sol systems. (3) Study of the influence of hydrogen-ion concentration on extent of silica retention shows that as the PH of the medium increases, there is a decrease in the retention of silica by the gel. With alumina gel at high PH, however, there is greater adsorption. This is due to the amphoteric nature of alumina. (4) The adsorbed silicate is firmly retained by the colloidal gel and is not leached out by water. (5) The possible significance of silicate adsorption in relation to phosphorus resorption in soils is indicated.