CHARACTERISTIC COEFFICIENTS OF CATION-EXCHANGE MEMBRANES FOR BIVALENT-CATIONS IN EQUILIBRIUM BETWEEN THE MEMBRANE AND SOLUTION

Characteristic coefficients of four cation-exchange membranes (Neosepta C66-5T, Selemion CMV, Aciplex K101, and Nafion 417 membranes) for three bivalent cations in equilibrium between the membrane and solution were measured. The order of the exchange affinities of the bivalent cations was Mg2+ < Cu2+ < Ca2+ for all the membranes studied. The selectivity coefficients between bivalent cation-bivalent cation systems (e.g., K(Ca)Mg) for each membrane remained constant over a 3-order variation of the concentrations of the total cations in solution. The ratios of selectivity coefficients (eg., K(Ca)Mg(K(Ca)Cu)-1) were constant among various kinds of membranes for Na+-H+, Na+-K+, K+-H+, Ca2+-Mg2+, Ca2+-Cu2+, and Mg2+-Cu2+ systeMs. In addition, the exchange capacity, water content, density, and thickness of the Aciplex K101 membrane were measured, and compared to those of the Neosepta C66-5T, Selemion CMV, and Nafion 417 membranes.