Preliminary Study On Purification Of Ce Alloy By Molten Salt Electrorefining

Recovery of actinide metal by molten salt electrorefining has been an important method for dealing with spent nuclear fuel in the last few decades.This study carried out preliminary research on purification of cerium gallium alloy as simulated material by molten salt electrorefining in the NaCl-KCl molten system.Fistly,chlorination of cerium indicated that liquid cerium can react with HCl gas rapidly and completely proving that introduction of CeCl3 by HCl gas bubbling into liquid cerium is feasible.The study found when HCl feed rate exceeds a certain value,there would be HCl detected in the exhaust gas which was the discharge of unreacted HCl.This phenomenon indicated that it was important to control the HCl flow speed and the amount of HCl gas to ensure full contact between HCl gas and liquid cerium.Secondly,cyclic voltammetry,square wave voltammetry and chronopotentiometry were carried out to investigate the cathode reduction process of cerium ions and gallium ions in NaCl-KCl molten salts.The results showed that Ce3+was reduced to Ce in a reversible one-step process exchanging three electrons on the molybdenum electrode.The electrochemical reduction process was limited by the diffusion of Ce3+ in the solution with diffusion coefficient of 0.12 ×10-5 cm2·s-1.The temperature dependence of apparent reduction potential was Eo'=-2.535 + 5.458 × 10-4 T(?);Ga3+was reduced to Ga in a two-step reversible reactions i.e.,Ga3++ 2e-? Ga+,and Ga+ + e? Ga.The two reactions were both limited by the diffusion of Ga3+and Ga3+ ions.The diffusion coefficient of Ga3+ was 0.16 X 10-5 cm2·s-1.The temperature dependence of the apparent reduction potentials for the two-step reaction were respectively E°'2c =-0.732 + 5.40 × 10-4 T(?)and Eo'3c =-2.129 +1.21 × 10-3 T(?).Finally,molten salt electrorefining of cerium gallium alloy in NaCl(39.2%)-KCl(30.8%)-CeCl3(30wt%)molten salt system was conducted in the temperature range of 1123K-1173K.The average straight recovery rate of cerium and cathode current efficiency were found to be 64.3%and about 63.5%under current efficiency of 6-9 A/cm2.Purity of the obtained cerium metal products reached 99.9%.The separation factor of gallium reached 104.Metal impurities were mainly aluminum,molybdenum and sodium.