Acid strength at clay mineral surfaces

Abstract

The interactions of ,{1 3+ -montmorillonite, Na+ - montmorillonite and Na+ -kaolinite with selected Hammett indicators have been reinvestigated. The use of a series of indicators with different acid strengths, Ho, to determine the activity of protons on the clay surface was basid on the assumption that the activity of H+ on the clay surface is equivalent to activity in solution. The results show that A13+- montmorillonite had the hiehest acid strength, especially after drying at 1lfc. Na+-kaolinite had Ih" lo*r"rt acid strength, at two moisture levels: befirre washing with ethanol and u{"l g1lporation of this alcohol. At all moisture levels the acid strength of A1'* -montmorillonite was greater than that of either Nai - montmorillonite or Na+ - kaolinite.