RIGOROUS MODEL FOR ION-EXCHANGE EQUILIBRIA OF STRONG AND WEAK ELECTROLYTES

A thermodynamics-based equilibrium model was developed to describe ion exchange equilibria of strong and weak electrolytes. It is applicable to binary and multicomponent systems, using selectivity coefficients for all ion pairs and distribution coefficients for all neutral specie s as parameters. The model was successfully tested for a strong-base a nion exchange resin with the strong electrolyte NaCl and the weak elec trolytes acetic acid and N-acetylmethionine in a wide concentration ra nge. Compared to conventional models, this model is more advantageous because it takes into account the uptake of all species, counterions a s well coions and neutral species, thus making it possible to calculat e the intraparticle pH. Especially when weak electrolytes are involved and when electrolyte concentrations strongly exceed the resin capacit y, it is superior to conventional ones, whereas for dilute systems it converges to the conventional stoichiometric displacement model.