TRANSPORT NUMBER OF AN ION ACROSS AN AMPHOTERIC ION-EXCHANGE MEMBRANE IN CACL2-NACL SYSTEM

In an amphoteric membrane-mixed electrolyte system, the ionic concentration within the membrane and the membrane conductance were measured. The additivity concept proposed in our previous paper [ J. Membrane Sci, 48 (1990) 25] was applied to the present mixed electrolyte system and each ion transport number in the mixed system was estimated. The transport number of Ca2+, t(Ca), was larger than t(Na) in the whole range concentration and decreased with increasing concentration of the outer electrolyte solution. Additionally, to ascertain whether the predicted values are reasonable, electrodialysis in the mixed electrolyte system was carried out under the same experimental conditions. The transport numbers estimated in the mixed electrolyte system were approximately in good agreement with the values obtained from the electrodialysis experiments. Furthermore, the transport numbers for two different ionic states in the membrane were evaluated and the concentration dependence of the total transport number, t(M), was discussed on the basis of the results.