Electrochemical and Kinetic Analysis of Pr(III) Recovery by Liquid In-Bi Alloy Electrode in LiCl-KCl Melt

Abstract Effective recovery of the rare earth fission product praseodymium during the pyroprocessing of irradiated nuclear fuel is crucial for the purification of waste salts and the safe disposal of nuclear waste. This study introduces a novel liquid indium-bismuth alloy (In-52.5wt% Bi eutectic) cathode for effective recovery of praseodymium from electrorefining waste molten salts. The underpotential deposition mechanism of praseodymium on liquid In, Bi, and the In-Bi alloy electrode was investigated using steady-state and transient electrochemical methods in molten LiCl-KCl eutectic. Additionally, the reduction kinetics parameters of Pr(III)/Pr(0) on liquid In-52.5wt% Bi, In, and Bi were elucidated, along with the thermodynamic properties of binary In-Pr, Bi-Pr, and ternary In-Bi-Pr alloys. Praseodymium was efficiently recovered and separated from simulated electrorefining waste molten salts using constant current electrolysis and pulse potential electrolysis. The recovered products were analyzed using X-ray diffraction, scanning electron microscopy, and inductively coupled plasma optical emission spectrometry. The extraction efficiency of praseodymium on the liquid In-52.5wt% Bi cathode exceeds 99%, and the liquid In-52.5wt% Bi alloy electrode material demonstrated better stability than individual liquid In and Bi.