Electrochemical Extraction of Fission Element Samarium from Molten NaCl-2CsCl Eutectic Salt Using the Liquid Gallium Cathode

Abstract

The effective extraction of neutron poison samarium from nuclear waste to prevent reactions with metallic uranium is crucial for the sustainable development of nuclear energy. The electrochemical recovery of samarium on the liquid gallium cathode from the NaCl-2CsCl molten salts has been investigated by a variety of electrochemical techniques, and its electrochemical reduction properties and kinetic parameters have been provided. It was revealed that the reduction reaction on the Mo cathode of Ga(III) to Ga(0) and Sm(III) to Sm(II) is a two-step and one-step reaction process, respectively, and both reactions are reversible. The diffusion coefficients of Ga(III)/Ga(II) and Sm(III)/Sm(II) were identified, and the activation energies were 20.07 and 42.96 kJ mol–1, respectively. Simultaneously, the codeposition mechanism of Ga(III) and Sm(III) on the Mo cathode was systematically investigated, and the potential and types of formation of binary intermetallic compounds were explored. Subsequently, it was determined that there are two main reaction processes for Sm(III) on the liquid Ga cathode, and the deposition potential of Sm becomes more positive due to the formation of the alloy. The exchange current density values of Sm(III)/Sm(Ga) obtained by both linear polarity (LP) and Tafel techniques increased with temperature, meanwhile the charge transfer resistance decreased, as well as the transfer coefficient. In addition, the apparent electrode potential of Sm(III)/Sm(Ga) was also calculated. Based on the electrochemical analysis, the fission element Sm was deposited on the liquid Ga cathode by potentiostatic electrolysis at a suitable potential, and the alloy products were verified by X-ray diffraction, scanning electron microscopy, and energy-dispersive spectroscopy. Ultimately, the highest separation efficiency of Sm on the liquid Ga cathode reached 92.43% according to the analysis of inductively coupled plasma atomic emission spectrometry (ICP-AES) results.