The Effects of NdF2 on Current Efficiency of Nd Extraction from NdF3-LiF-Nd2O3 Melts

In this paper, the cyclic voltammetry was applied to investigate the electrochemical reduction processes of Nd(III) ions in NdF3-LiF melts with or without excessive metal Nd. Equilibrium experiments were carried out in NdF3-LiF melts with excessive spheric metal Nd to investigate the relationship between the NdF3:LiF mass ratio and NdF2 concentration. Electrolysis experiments were performed in NdF3-LiF-Nd2O3 melts with different NdF3:LiF mass ratios to explore the relationship between the NdF2 concentration and the current efficiency.The results indicated that Nd(III) ions in the melts were reduced in two steps, i.e., Nd(III)→Nd(II) and Nd(II)→Nd(0). NdF2 could be formed by the comproportionation reaction between Nd(III) and Nd(0) and could stably exist in NdF3-LiF melts containing metal Nd(0). NdF2 mass concentration in the melts decreased from 45.5% to 36.4% with the increase of NdF3-LiF mass ratio from 7:3 to 9:1 in NdF3-LiF melts containing excessive spheric metal Nd, which resulted in a higher current efficiency during the electrolysis. And the highest current efficiency of about 50% for Nd extraction has been obtained by electrolysis in NdF3-LiF (9:1 mass ratio) melts with Nd2O3 (2%, mass concentration) at 1423 K.