Comparison Study of Zeta Potential Values of Bentonite in Salt Solutions

Abstract

The electrokinetic mobility (EM) was measured and then zeta potential (ZP) was calculated for laboratory grade bentonite particles by varying pH between 4 and 10 and at 0.001, 0.01, and 0.1 M salt (NaCl, Na2SO4, LiCl, KCl, and CaCl2) concentrations. In all tests, bentonite particles displayed a negative zeta potential. No charge reversal was observed at any stage. The ZP values showed low sensitivity to pH in salt solutions. Zeta potential calculation of bentonite particles in distilled water showed an increase in ZP value beyond pH >8, which could be due to charge development at the edges by direct transfer of H+ from clay to water. For all salts, at a concentration of 0.1 M, and for all tested concentrations of CaCl2, bentonite particles showed a zero zeta potential. For NaCl and Na2SO4, at 75, 200, and 325 mg/L bentonite particle concentrations, increasing the salt concentration from 0.001 to 0.01 M did not affect the ZP value of the bentonite particles. For the same cation such as Na+, the presence of monovalent anions (Cl−) or divalent anions (SO4 −2) did not affect the zeta potential value of the clay for the tested conditions. In salt solutions containing common anions but different cations (LiCl, NaCl, and KCl), bentonite particles displayed a higher ZP value for NaCl than KCl, whereas no ZP difference was observed for bentonite particles in LiCl and NaCl at the experimental conditions.