A RELATION BETWEEN THE AMOUNTS OF SORBED ALKALI CATIONS AND THE STABILITY OF COLLOIDAL SILICA

The sorption of alkali cations, at various pH values and concentrations (0.1-4.0 mol dm-3), on colloidal silica was investigated by the potentiometric titration method. At the same time the colloidal silica stability in the presence of these cations was determined. The critical coagulation concentration of alkali cations decreases with increasing pH and for all studied cations a common "critical sorption curve" was obtained. The amount of sorbed cations at the critical coagulation concentration was found to correspond to a maximum value of the sorption at a given pH. Therefore, the coagulation of colloidal silica in the presence of alkali cations will occur with the sorption of the maximum possible amount of these ions at given pH values.