High ionic strength electrokinetics of clay minerals

The electrokinetic potential of kaolin and montmorillonite at high ionic strengths (up to 2 M of 1-1 electrolyte) was measured as a function of pH by means of three instruments. The present results indicate that the electrokinetic potential does not cease at high ionic strengths. Potassium and cesium salts induced a shift in the IEP of kaolin to high pH. Similar shifts were observed for montmorillonite, but only in the presence of cesium. The increase in 1-1 electrolyte concentration resulted in depression of the absolute value of the zeta potential of kaolin and montmorillonite at neutral and basic pH. However, zeta potentials at high ionic strengths were surprisingly high in the absolute value. Namely, the negative zeta potentials up to -20 mV were measured in 1 M solutions of Li and Na salts. (c) 2006 Elsevier B.V. All rights reserved.