ESTIMATION OF DEPROTONATION COEFFICIENTS FOR CHELATING ION EXCHANGE RESINS. COMPARISON OF DIFFERENT THERMODYNAMIC MODEL

The deprotonation of quinolic resin P-127 and iminodiacetic resin Amberlite IRC-718 has been studied. The process of salt transfer into the resin phase is considered to be an important contributor to the deprotonation process. Estimation of the salt transfer was based on the principle of equal activity of the salt in both phases at equilibrium. Two assumptions were made: sorbed alkali metal ions are not associated with functional groups, while all hydrogen ions are associated with functional groups. The associated hydrogen ions and functional groups do not contribute to the internal ionic strength value. Two thermodynamic models, describing the deprotonation of ion-exchange resin, were used and compared: the Gibbs-Donnan-based model of Bukata and Marinsky and the model proposed by Erik Hogfeldt. Thermodynamic characteristics of the resins’ deprotonation are obtained using two different thermodynamic approaches. Ho¨gfeldt’s three-parameter model provides a better agreement with experimental data. The fitting of the data to Marinsky’s method can be improved by taking into account the influence of the resins’ macroporosity; however, this requires an additional empirical parameter to describe the resin.