Zeta Potential of Kaolinite in the Presence of Alkali, Alkaline Earth and Hydrolyzable Metal Ions

Abstract

Electrokinetic remediation is one of the promising subsurface clean up techniques whose efficiency is directly affected by the zeta potential of clay minerals. To determine the factors affecting the zeta potential, in turn, electrokinetic remediation, the zeta potential of kaolinite is determined usingelectrophoretic mobility in the salt and heavy metals ions asfunctions of pH and concentration. The zeta potential of kaolinite ranged from -25 mV (pH 3) to -42 mV (pH 11) in water. The zeta potential of kaolinite became more negativewith increasing pH. The zeta potential of kaolinite was also found to be sensitive to the valence of ions. Results, furthermore, revealed that kaolinite has higher zeta potentialvalues in the presence of NaCl and LiCl than in water. However, the zeta potential of kaolinite decreased with divalent cationssuch as Ca²⁺ and Mg²⁺. The zeta potential of kaolinitewith heavy metal ions such as Cu²⁺, Co²⁺ and Pb²⁺ showed a similar trend, i.e., increase in the concentration ofthese ions caused a decrease in the zeta potential up to neutral pH, then it became positive. In highly basic environments, thezeta potential became negative again, giving two apparent pzcs. One of two apparent pzcs was attributed to kaolinite and the other one to the precipitation of these ions in highly basic solutions (pH ≥ 9).