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 ζ potential of kaolin and montmorillonite at neutral and basic pH. However, ζ potentials at high ionic strengths were surprisingly high in the absolute value. Namely, the negative ζ potentials up to −20 mV were measured in 1 M solutions of Li and Na salts.