APPLICATION OF THE SURFACE COMPLEX-FORMATION MODEL TO EXCHANGE EQUILIBRIA ON ION-EXCHANGE RESINS .3. ANION-EXCHANGERS

The surface complexation theory considers the sorption of ions as a lo cal equilibrium reaction, which is caused by the amphoteric behaviour of the surface. Application of this theory to exchange equilibria with ordinary and chelating weak-acid ion exchange resins which can releas e protons has opened the way for a comprehensive description. Binary e quilibria are described by a logarithmic equilibrium parameter, which is a linear function of the composition of the resin phase. Multicompo nent equilibria are considered as a superposition of several binary eq uilibria. The approach considers the pH-dependent dissociation of func tional groups. Furthermore, chemical reactions in the liquid phase in which exchangeable species are involved, can readily be taken into acc ount. In contrast to cation exchange resins, the behaviour of anion ex changers is characterized by the uptake of protons enabling them to al so adsorb anions. As a consequence, anion exchange equilibria can be d escribed in similar way. The evaluation of data demonstrates that simi lar relationships exist between a logarithmic equilibrium parameter an d the resin phase composition. As for cation exchangers, multicomponen t equilibria can be predicted with excellent accuracy from binary para meters.