The characterization of binary and ternary ion exchange equilibria

Abstract

Accurate correlation and prediction of multicomponent ion exchange equilibria are essential for design and development of ion exchange processes. Several methods for expressing ion exchange equilibrium are reviewed and assessed against a collection of experimental data. The most satisfactory expression is based on the Debye-Hückel relationship for solution phase activity coefficients and the Wilson equation for the resin phase. This method successfully characterized binary experimental data for 48 binary systems covering five resins, three concentration levels and nine counter-ions. Five ternary systems were well correlated by the method. The major drawback of this procedure is that (N 2 − 1) parameters are required to characterize an N-component system. A reciprocal relationship between the Wilson parameters for a binary system was observed and a rationalization for this phenomenon is given. This relationship, when used with the Hála constraint, reduces the number of parameters required to characterize fully an ion exchange equilibrium to 2(N − 1), with little loss in the quality of fit.