Multicomponent ion exchange in zeolites. Part 2.—Prediction of exchange equilibria over a range of solution concentrations

Abstract

Using a recently derived thermodynamic model for ternary ion exchange, equations are formulated which facilitate the prediction of ternary exchange equilibria in zeolites at a given constant temperature. The implicit equations (which allow predictions over a range of solution concentrations and compositions) can be solved iteratively, and the conditions and constraints which must be applied to the iteration procedures are described. The prediction method is then tested using experimental data on the ternary Na/Ca/Mg–zeolite A system which were reported in Part 1 of this series. The prediction procedure is shown to work satisfactorily. In addition, it is shown that normalisation procedures (widely used for cases of partial exchange in binary systems) are irrelevant for the prediction of either binary or ternary equilibrium exchange behaviour. Finally some shortcomings in the fitting procedures which are currently employed to fit experimental data are discussed.