Study of ion transport across amphoteric ion exchange membrane. I. Electroconductive membrane permeability.

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Basic ion transport characteristics of a homogeneous amphoteric ion exchange membrane (Kanegafuchi Chem. Ind. 1.0-PA-29) were studied by measuring the membrane potentials and conductances. Concentration cell systems of NaCl, KCl, CaCl2, and SrCl2 with a concentration range of 10−1–10−3 mol dm−3 were studied and the electroconductive membrane permeabilities were estimated from the electrochemical data. Generally, Cl− is slightly more permeable than cations under the present experimental conditions, except the result that K+ is more permeable at low concentrations. Unlike the usual uniform cation exchange membrane of which transport characteristics to ions strongly depend upon the number of ionic charges, a "1.0-PA-29" amphoteric membrane exhibits different transport properties for the NaCl and KCl systems. In the NaCl system, the membrane was constantly anionic selective, while in the KCl system, biphasic ion selectivities were observed depending upon the external KCl concentration. Fundamental electrochemical properties of the membrane systems were discussed by examining the dependencies of membrane permeability on external electrolyte concentrations and on differences in ionic species. The present result suggests that the ionic size is one of the critical factors determining the transport characteristics across amphoteric ion exchange membrane.
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