SEPARATION OF LIGHT RARE-EARTH ELEMENTS FROM RARE-EARTH MIXTURE SOLUTION BY USE OF ELECTRODIALYSIS WITH COMPLEXING AGENTS

Lanthanum and neodymium, light rare-earth elements, have been separated from lanthanum-yttrium and neodymium-gadolinium-yttrium solution, respectively, containing lactic acid or EDTA as a chelator by the electrodialysis. EDTA is so effective in the separation as to be used in most of the experiment. In the lanthanum-yttrium system, the separation factor of lanthanum to yttrium increased with an increase in EDTA concentration, attaining over 100 under the concentrations of complexing ratio higher than 60% and pH 3. The separation fator was also affected by the hydrogen-ion concentration: it increased with increasing pH to the maximum at pH 4. In the neodymium-gadolinium-yttrium system, the separation factor of neodymium to neodmium, gadolinium and yttrium mixture varied with the concentration fraction of neodymium. The separation characteristics were explained by the difference of free-ion (uncomplexed ion) concentrations which was caused by the difference of stability constants for complexes of rare-earth elements.