Positive Electrokinetic Charge of Silica in the Presence of Chlorides.

The presence of chlorides promotes a positive electrokinetic charge of silica. Silica shows an isoelectric point (iep) at pH 2 in the presence of HCl but at pH < 1.5, if any, in the presence of HClO4 and HNO3. The iep of silica in the presence of different 1:1 salts depends on the nature and concentration of the salt. The highest value of pH, 5.5, was observed for 0.1 mol dm-3 cesium chloride and nitrate. A larger increase in cesium salt concentration shifts the iep back to low pH values and at >0.5 mol dm-3 there is no iep (only negative zeta potentials). Copyright 1998 Academic Press.