Comparison between heterogeneous and homogeneous MASS action models in theprediction of ternary ion exchange equilibria

In this paper two models for the prediction of multicomponent ion exchange equilibria were compared: one, a heterogeneous model, based on the mass act ion law in which ideal behavior for both the solution and the solid phase a nd the heterogeneity of ion exchange sites has been assumed, and the other a homogeneous model, based on the same mass action law in which nonideal be havior for both the solution and the solid phase has been taken into accoun t. Considering counterions with different valences, the optimum value of th e fraction of functional groups was obtained from binary systems data. It w as shown that the energy distribution was practically symmetric. Likewise, a procedure for decreasing the number of adjustable parameters, based on th e determination of the minimum linearly independent equilibria considering each equilibrium as a heterogeneous reaction, was developed. The adjustable parameters (namely, the equilibrium constants forced to satisfy the triang le rule) were used in the prediction of the ternary equilibrium data. In al l cases the prediction of the heterogeneous model was in good agreement wit h experimental data. However, although the homogeneous model was somewhat s uperior to the heterogeneous model in the prediction of ternary systems, th e comparison between both models did not allow us to distinguish statistica lly between them.