Effect of Hydrogen Ion Concentration on Cation Exchange in Clay Salts

Abstract

THE lyotrope series is usually observed in the exchange of cations from clays and permutites^1,2. Deviations from this series have also been reported^3,4. These have been attributed to the structural peculiarities of the clays^{2, 3} and variations in the hydration of cations⁴. Differences in the relative effects of Ba++ and Ca++ ions in the interaction of hydrogen clays with neutral salts and bases have been observed^{5, 6, 7}, depending on the prevailing pH of the system. Symmetry values³ of a number of clay salts against various electrolytes (chlorides) have been measured with and without adjustment of the pH of the system at a constant value by the addition of the requisite amount of hydrochloric acid. When a constant pH is not maintained, deviations from the normal lyotrope series often occur, especially in clays containing montmorillonite as judged from X-ray analysis. The deviations disappear when the symmetry values measured at a constant pH ranging from 6·0 to 7·0 are compared. At a constant pH between 3·0 and 5·0, all the cations examined give the same symmetry value, and the cation effect as envisaged in the lyotrope series altogether disappears.