Application of liquid Ga-Pb cathode for selective separation of samarium fission products from molten alkali metal chlorides

The efficient separation of the rare earth element Sm from spent nuclear fuel is of strategic importance for the nuclear industries. This study explored the feasibility of a novel liquid Ga-Pb hybrid electrode for electrochemical extraction of samarium compounds, and the electrochemical reduction mechanism and dynamic properties of Sm(III) ions were provided in NaCl-2CsCl molten salt. It was established that the reduction mechanisms of Sm(III) to Sm(II) and Pb(II) to Pb(0) on the Mo cathode were a one-step reaction processes, respectively, while Ga(III) to Ga(0) was a two-step reaction process. The co-deposition mechanisms of Sm(III), Ga(III) and Pb(II) ions on the Mo cathode were identified, and the types of intermetallic compounds, formation potentials and reaction processes were analyzed. The deposition potential of Sm on Ga-Pb mixed cathode is determined, and the value of its depolarization was greater than on the liquid Pb electrode. Simultaneously, Sm ions have higher exchange current densities and lower activation energies for electrode reactions on the liquid Ga-Pb mixed electrodes than on the liquid Pb electrodes. Furthermore, the electro-separation of NaCl-2CsCl-SmCl₃ molten salt was executed via potentiostatic electrolysis technique, and the separation efficiency and the effect of cathode product type were analyzed and compared in Ga-Pb hybrid electrode and Pb electrode. It was obtained that the maximum extraction efficiency on the Ga-Pb hybrid electrode and the separation efficiency of Sm could reach 91.3 % after 8 h of electrolysis.