The previously presented theory that, in countercurrent electromigration of molten common anion binary mixtures, the lighter isotope of the less mobile cation should anoma lously enrich in a zone next to the anode, has been substan tiated for the K isotopes in molten (Li, K)N03.Until Lunden and Ljubimov's discovery of 'nonideal behaviour" some twenty years ago [1,2], it had generally been believed that, in countercurrent elec tromigration of pure or mixture melts with an initially uniform distribution along a separation tube, the lighter and heavier isotopes of the cation enrich only at the cathode and anode, respectively. They discov ered in countercurrent electromigration of molten (Li, K)(SO4)0 5 that on the anode side of the separa tion tube the gradient of 41K/39K is slightly positive before it becomes zero.In a previous paper [3] we have argued that in elec tromigration of molten systems consisting of two ca tions A and B and a common anion, enrichment of the lighter isotope of the less mobile cation B should oc cur in the region where dcB/dz < 0, where cB is con centration of B, and z is the distance taken from the anode towards the cathode. For more general cases, including temperature gradients, the reasons for such changes in composition in countercurrent electromi gration have been discussed by Klemm and Lunden [4] with essentially the same conclusion for the above mentioned case.Our argument was experimentally substantiated by enrichment of 6Li in the range where dcLj/dz < 0 in electromigration of molten binary mixtures (Li, K)C1 and (Li, K )N 0 3; the condition dcLi/dz < 0 was real Reprint requests to Prof. Isao Okada, Department of Elec tronic Chemistry, Tokyo Institute of Technology at Naga tsuta, Midori-ku, Yokohama.ized, if the Li+ ions were less mobile than the K + ions. In case where at low temperature the K + ions were less mobile, however, enrichment of 39K was not clearly detected (see Table 2 in [3]). This is presumably because the precision of the used mass spectrometer was not good enough.Thus, the purpose of the present work is to substan tiate our theoretical equations in [3] by showing ex perimentally that an anomalous enrichment of 39K actually occurs at the place where dcK/dz < 0; in the present work we have used a mass spectrometer with much better accuracy and precision.(Li, K )N 0 3 of the eutectic composition (mole frac tion of L iN 03, xLi = 0.58) was chosen. Since bu > bK below ca. 520 K [5], at lower temperatures K + ions are expected to enrich with respect to Li+ ions on the anode side in a separation tube, and there the condi tion of dcK/dz < 0 (and therefore d.xK/dz < 0) being realized, 39K should enrich in this region. Thus, electromigrations were performed at 450 K. The experi mental procedures were similar to those in the pre vious study [5], The separation tube was inserted into a large vessel containing catholytes of a mixture of (Li, K )N 0 3 of the eutectic composition + NH4N 0 3 (about 50mol% of the total mixture); since the tem perature of the electromigration wa...

Relative differences in the internal cation mobilities in the molten binary system (Na, NH4)NO3 have been measured by Klemm's countercurrent electromigration method at NaNO3 mole fractions 0 0.3 and temperatures 433-453 K. Also the densities and electric conductivities of this system have been measured. From these data the internal cation mobilities, bNa and bNH₄, were calculated. Under all accessible conditions, bNH₄ is greater than bNa. The results are discussed in terms of the interaction between unlike ions and free space.

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High enrichment of 6Li was attempted by improvement a previously used countercurrent electromigration method in molten LiNO3. In order to prevent a possible outflow of Li § ions into a large cathode compartment which contained NH4NO3 melt by electromigration, a small zone of NaNO3 was formed between molten LiNO3 and NH4NO3 in a separation tube. The electromigration cell was reformed so that the temperature in the separation tube could be kept at an intended value. 6Li was enriched from 7.4 to 91.2% in 39 days without any trouble with material corrosion.

Internal cation mobility ratios in molten (Li, Pb(II))Cl at 650 °C have been remeasured by Klemm's column method. From these and available data on the densities and conductivities, the internal mobilities b