A model has been developed to obtain the thermodynamic parameters, i.e., th
e equilibrium constant and solid-phase activity coefficients, that describe
binary ion exchange reactions. The model is based on the thermodynamic fra
mework for adsorption exchange reactions developed by Gaines and Thomas (19
53. Journal of Chemical Physics, 21, 714-718). The Wilson activity coeffici
ent model is used for the adsorbed phase and the stoichiometry of the excha
nge reaction is taken into account. The solid solution model parameters are
regressed with a new data reduction technique, based on the use of the Van
selow selectivity coefficient calculated at various points on the isotherm
equilibrium surface. Additionally, a consistency test is developed for anal
yzing the selectivity coefficient plots. For the estimation of the selectiv
ity coefficient, the Bromley-Zemaitis model is used for calculating the act
ivity coefficients in the aqueous phase. Also, the speciation of the aqueou
s systems is taken into account. The equilibrium constants are calculated u
sing their relationship with the selectivity coefficients and the activity
coefficients in the solid phase. In addition to accurate representation of
experimental data, the data reduction of binary pairs from three ternary sy
stems has been shown to satisfy the triangular rule consistency test. Uptak
e graphs of the investigated systems have been accurately predicted. (C) 20
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