Separation of alkali metal ions by constant current electromigration in an ion exchange membrane

A strip of homogeneous cation-permselective ion exchange membrane of the hydrogen form (Ashiplex CK-1, 2 cm in width, 0.02 cm in thickness and 30 -- 50 cm in length) was placed in a migration apparatus (Fig. 1). The behaviour of the mixed band containing two alkali metal ions (couples of Cs+-K+, Rb+-K+ and Na+-K+) followed by Li+-band, was observed by passing a constant direct current of 20 mA. As the electromigration proceeded, the length of the mixed band decreased and two new bands, each of which consisted of single alkali metal ion, appeared at the front and the rear of the mixed band. It was also observed that the sum of transport numbers of cations in the mixed band was unity and each band moved with all the same constant velocity, in other words, with an ideal ''isothachophoresis''. The order of the mobility in the membrane, K+>Rb+>Cs+>Na+>Li+, was ascertained both by electromigration experiments and by conductivity experiments (Table 1). It was demonstrated that the couple of Rb+-Cs+ was easily separated to produce pure alkali metal ion by the present procedure without using any complex forming reagent. (auth.)