Characterizing pulse reverse-pulse uranium recovery in molten LiCl-KCl with intermittent electrochemical impedance spectroscopy

Abstract

In this work, EIS was applied to characterize the temporal recovery of uranium from UCl4 onto a tungsten electrode in molten LiCl-KCl salt between sets of pulse reverse-pulse (PRP) deposition steps. Impedance measurements were fitted to an equivalent circuit (EC) model of the electrode interface using Simplex optimization to calculate the double layer capacitance, charge transfer resistance, Warburg impedance, and CPE-restricted diffusion. Diffusion of uranium towards the electrode surface dominated the surface interactions for the first 80 cycles, followed by a transition to kinetic control for the remaining 520 cycles. A decrease in the Warburg impedance showed depletion of uranium from the bulk melt, which was confirmed to be a 52.5% reduction through ICP-OES. Reduction in the phasance from CPE-restricted diffusion suggested the formation of pores in the uranium deposits, which was confirmed through SEM characterization.

Keywords

• Actinide
• Uranium
• Lanthanum
• Electrochemical impedance spectroscopy
• Molten salt
• LiCl-KCl