The Solubility of Rare Earth with Variable Valent and Electrochemical Behavior in LiCl–KCl–AlCl3 Melts

The solubility of RE2O3 (RE=Sm, Yb, and Eu) with variable valent in LiCl–KCl melts is extremely low. It is impossible to directly extract variable valent metals from RE2O3 using electrolysis in molten salts. After adding AlCl3 to the melt system, the solubility measurements of RE2O3 in LiCl–KCl and LiCl–KCl– AlCl3 melts indicate that AlCl3 can effectively chloridize RE2O3. Take Yb2O3 as an example, the solubility of Yb2O3 in the LiCl–KCl–AlCl3 melts increases first and decreases afterwards due to the rapid volatility of AlCl3 with increase of temperature. The thermodynamic calculation of the reaction of Yb2O3 and AlCl3 also indicates that the reaction would proceed forward at 753 K. Electrochemical behavior of RE2O3 on a molybdenum electrode in LiCl–KCl melts containing AlCl3 also indicates that RE2O3 is effectively chloridized by AlCl3, and then discharges in the form of RE(III) ions in the cathode. The underpotential deposition of RE on pre-deposited aluminum leads to the formation of Al-RE alloy. The extraction of RE with variable valent from RE oxide in LiCl–KCl melts is proven to be feasible.