Studies on Countercurrent Electromigration of Molten Salts with an aim of High Enrichment of <^6Li>

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Although enriched <^6Li> is useful, no method has been established in Japan even on a laboratory scale. Countercurrent electromigration of molten salts is promissing for enrichment particularly of isotopes of alkali metals and hence of <^6Li> . However, enrichment of <^6Li> , which is to be held at the cathode, is not so easy as that of <^7Li> because of inevitable low current density there. To avoid this, the method of <^6Li> enrichment around the boundary between molten <LiNO_3> and molten <NH_4> <NO_3> at the cathode was previously devised by us. In this study, electromigration cells of "horizontal type" was made; the separation tube was placed nearly horizontally in which the boundary was established near the relatively large cathode compartment containing molten <NH_4> <NO_3> . The part of the separation tube was heated at about 300 ゜C, while the part of the cathode compartment was heated at about 180 ゜C. Lithium-6 was enriched from 7.4% to 82% in 31 days without corrosion trouble. The enrichment took place around the rather sharp boundary between <LiNO_3> and <NH_4> <NO_3> . The elementry separation factor, that is, the relative difference in internal mobilities of <^6Li> and <^7Li> in neat <LiNO_3> , <LiNO_3> - <NH_4> <NO_3> mixture and <LiNO_3> - <KNO_3> mixture melts, was measured.The effect of mixing on the separation factor is not clear. The separation factor increases with rising temperature. This can be interpreted microscopically with molecular dynamics simulation. The following methods are to be found in the future:(1) detecting the boundary between <LiNO_3> and <NH_4> <NO_3> from the outside and (2) the extracting very small amount of enriched <^6Li> from molten <NH_4> <NO_3> at the cathode. If these are solved, <^6Li> could be enriched more effectively.