Difference in the influence of Na and Ca ions on the zeta potentials of Anatolian bentonitic clays

The values of the zeta potentials for bentonitic clay particles suspended in solutions of NaCl, (NaPO3)(n) and CaCl2 at different electrolyte concentrations and constant pH(similar to 7) were measured. When Ca salts were added to the clay solutions in increasing concentrations, the double layers of particle surfaces gradually contract, become narrower and the zeta potential value decreases. When Na salts were used, the zeta potential increased with increasing concentration.