Polyfunctionality of resin carboyxl sites in ion exchange with alkali metal ions

Abstract

The ion-exchange behaviour of a weak acid-type cation-exchange resin with alkali metal ion was obtained as a function of pH by titration. The behaviour was analyzed with a model that assumes that the resin has two types of carboxyl sites (1 and II) with different reactivities (polyfunctionality) and that the ion exchange at each site is suppressed steadily with progress of ion exchange owing to electrostatic lateral interactions between the species in the solid/solution interphase. The ion-exchange parameters in the model were determined by multi-parametric curve fitting. The values indicate that the type I sites are much more reactive than the type II sites and are more subject to suppression. The polyfunctionality was ascribed to the micropore structure of the resin: the type I sites are distributed in wider pores where hydrated ions can be adsorbed electrostatically with larger lateral interactions and the type II sites in narrower pores where dehydrated ions are adsorbed by forming coordination-type chemical bonds with smaller laterl interactions. The activity coefficients of interphase spcies are discussed in terms of the electrostatic lateral interactions between these species.