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 phas e is considered to be an important contributor to the deprotonation process . Estimation of the salt transfer was based on the principle of equal activ ity of the salt in both phases at equilibrium. Two assumptions were made: s orbed alkali metal ions are not associated with functional groups, while al l hydrogen ions are associated with functional groups. The associated hydro gen ions and functional groups do not contribute to the internal ionic stre ngth value. Two thermodynamic models, describing the deprotonation of ion-e xchange resin, were used and compared: the Gibbs-Donnan-based model of Buka ta and Marinsky and the model proposed by Erik Hogfeldt. Thermodynamic char acteristics of the resins' deprotonation are obtained using two different t hermodynamic approaches. Hogfeldt's three-parameter model provides a better agreement with experimental data. The fitting of the data to Marinsky's me thod can be improved by taking into account the influence of the resins' ma croporosity; however, this requires an additional empirical parameter to de scribe the resin.