Ion-exchange equilibria in zeolites and clay minerals. Different concentration scales and derived thermodynamic functions

Abstract

Treatments have been made of the thermodynamics of ion exchange which use mole fractions and equivalent cation fractions as concentration scales. Recently, substantial criticisms have been made of the widely used equivalent-fraction scale in ion exchange. These criticisms require an examination of the treatments based on the two scales and of the criticisms of one of these. It is shown that the criticisms are not valid and that the two approaches are completely equivalent and compatible. Reasons are given for preferring equivalent cation fractions as the concentration scale for zeolite exchangers where cations are often distributed among a number of sub-lattices.