Abstract
A previous statistical thermodynamic relationship between the ionic fraction of species in solution and in the resin phase for uni-bivalent anion exchange processes has been extended for exchange in media of constant equivalent concentration. From this relationship, a method of obtaining the standard free energy and enthalpy of exchange has been developed, such that the thermodynamic parameters found are referred to the same standard state for any given anion exchanger. Values of the standard enthalpy of exchange and of the heat of swelling of resins have also been found by means of a calorimetric technique. In general, changes in standard free energy and enthalpy with selectivity are in accordance with those predicted by the theory and a relationship between selectivity and the water-regain value of a resin has been observed. It has been possible to transform the selectivity expression into the same form as the semi-empirical expression due to Kielland and into the expression, derived by a rigorous thermodynamic treatment, due to Gaines and Thomas.