MOLTEN-SALT REGULAR MIXTURE THEORY APPLIED TO ION-EXCHANGE MEMBRANES

Exchange equilibria between a cation exchange membrane and an aqueous solution were studied experimentally and theoretically. By using thermodynamic components in terms of the Gibbs phase rule, and a suitable reference state, a convenient method for data treatment was obtained. Thermodynamic mixture properties were derived for one membrane with four pairs of monovalent cations. The results show that when the difference in cation size is small, the cation exchange membrane behaves nearly ideal. For larger differences, the membrane may be described as a regular mixture. Activity coefficients for membrane mixtures can be obtained easily for regular mixtures.