A Study on Electrochemical Reduction of Rare Earth Oxides in Molten LiCl-Li₂O Salt

In this study, the electrochemical reduction of RE₂O₃ (RE = Nd or Ce) has been conducted via co-reduction NiO to increase the reduction degree of the rare earth oxides in molten molten LiCl containing 1wt% Li₂O. The electrochemical reduction behavior of the mixed RE₂O₃-NiO oxide has been investigated and the reduction path of RE₂O₃ has been proposed. An electorchemical spent fuel processing technology, pyroprocessing, has been developed for recycling of spent fuel to be applied to a sodium-cooled fast reactor. The spent fuel is reduced in the oxide reduction process. It is well known that the rare earth oxides are hardly reduced due to their electrochemical and thermodynamic stability. The rare earth oxides unreduced in the reduction process can cause problems via reaction with UCl₃ in the electrorefiner. To tackle those problems, the electrochemical reduction of rare earth oxide has been conducted via co-reduction of NiO in LiCl molten salt containing 1 wt% Li₂O. The reduction of the oxide mixture starts from the reduction of NiO to Ni, followed by that of RE₂O₃ on the produced Ni to form intermetallic RENi₅. The mixed oxide pellets were successfully reduced to the RENi5 alloy by constant electrolysis at 3.0 V at 650 .deg. C. The crucial aspect to these results is that the thermodynamically stable rare-earth oxide, Nd₂O₃ was successfully converted to the metal in the presence of NiO.