APPLICATION OF THE SURFACE COMPLEX-FORMATION MODEL TO EXCHANGE EQUILIBRIA ON ION-EXCHANGE RESINS .2. CHELATING RESINS

Multicomponent equilibria on ordinary weak-acid ion exchange resins can be predicted accurately by means of the surface complex formation model, as demonstrated extensively in Part I of this series. In Part II this theoretical approach is extended to include chelating exchange resins with iminodiacetic functional groups. For systems with protons and divalent metal counterions, linear relationships have been found to exist between a logarithmic equilibrium parameter and the resin loading. The two parameters obtained from a graphical representation of this interdependence are valid for a broad spectrum of initial liquid phase compositions. Combination of several of these H+-metal ion equilibria allows multicomponent equilibria to be predicted in a simple way. Owing to the two steps of dissociation of the functional groups of chelating resins, not considered in the present approach, the agreement between experimental data and predicted multicomponent equilibria is not quite as good as for ordinary weak-acid resins.