Enrichment of Na and K or 6Li and 7Li by counter current flow of the coexisting phases of Na/K- or 6Li/7Li-ammonia solutions

Metal-ammonia solutions (M-AS) have a miscibility gap, they separate at low temperatures into a diluted, electrolytic phase of high density and a concentrated, metallic phase of low density. In mixed sodium-potassium solutions (Na/K-AS) after phase separation sodium is enriched in the metallic phase, the separation factor αNa/K (Eq. (2)) is the larger, the lower the temperature relative to the critical temperature of the miscibility gap or the wider the miscibility gap. Therefore in deuteroammonia solutions (DAS) with higher critical temperatures the enrichment is more effective than in normal ammonia solutions. In Li-DAS with the two stable isotopes 6Li and 7Li the lighter one is enriched in the metallic phase. The separation factor (Eq. (4)) is αLi∼1.010 at -73 C. By multiplication of the single equilibrium effect in a counter current column, which acts like a solvent-solvent extraction column, the species can be enriched. The counter current operation of the column was enforced by electrochemical means (application of a dc-current through the column), and the enrichment was tested around -74 C with equimolar Na/K-AS and Na/K-DAS for which αNa/K=1.61 and 1.70 resp. and with Li-DAS of natural Li-isotope abundance. The height of the theoretical plate of the column for all three systems was HTP=12.9±0.3 cm. (orig.)