Electrochemical Behavior and Reduction of UO22+ in LiCl-KCl Molten Salt

In this work, we explored the electrochemical behavior and reduction process of uranyl ions UO22+ in molten LiCl-KCl eutectic at 773 K. Cyclic voltammetry (CV) and square wave voltammetry (SWV) results showed that the reduction of UO22+ ions on the inert W electrode was a three-step process: (1) UO22++e(- ) (UO2+)-U- , (2) UO2++ e(- )UO2 and (3) UO2+4e(-) U. Electrolysis experiments further confirmed this reduction mechanism that UO22+ ions were reduced to UO2 on the molybdenum electrode by applying a constant potential of -1.00 V vs Ag/AgCl and subsequently to uranium metal at a more negative potential of -2.35 V vs Ag/AgCl. In addition, UO22+ ions could be thoroughly reduced to uranium metal through a 4-h constant current electrolysis at -18 mA cm(-2). Electronic absorption spectroscopy (EAS) and inductively coupled plasma optical emission spectroscopy (ICP-OES) respectively illustrated that the oxidation state of uranium was unchanged and uranium concentration gradually decreased during the electrolysis. Finally, X-ray diffraction (XRD) and scanning electron microscopy (SEM) were used to characterize the phase composition and microstructure of deposited products. Nano-sized UO2 and U metal particles were successfully obtained by constant potential and current electrolysis. The results of this work further reveal the electrochemical behavior and reduction mechanism of UO22+ ions in molten LiCl-KCl, providing a guiding ideology for the pyrochemical reprocessing of oxide spent fuels.

Automated summary

In this study, the electrochemical behavior and reduction process of uranyl ions UO22+ in molten LiCl-KCl eutectic at 773 K were investigated. The reduction of UO22+ ions on the inert W electrode was found to be a three-step process, and electrolysis experiments confirmed this mechanism and successfully obtained nano-sized UO2 and U metal particles. Electronic absorption spectroscopy and inductively coupled plasma optical emission spectroscopy results showed that the oxidation state of uranium remained unchanged and the uranium concentration gradually decreased during the electrolysis. X-ray diffraction and scanning electron microscopy were used to characterize the phase composition and microstructure of deposited products.