Zeta potential of kaolinite in the presence of alkali, alkaline earth and hydrolyzable metal ions

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 using electrophoretic mobility in the salt and heavy metals ions as functions 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 negative with 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 potential values in the presence of NaCl and LiCl than in water. However, the zeta potential of kaolinite decreased with divalent cations such as Ca2+ and Mg2+. The zeta potential of kaolinite with heavy metal ions such as Cu2+, Co2+ and Pb2+ showed a similar trend, i.e., increase in the concentration of these ions caused a decrease in the zeta potential up to neutral pH, then it became positive. In highly basic environments, the zeta 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).