Electrochemical Kinetics and Selective Separation Mechanism of Erbium and Europium on a Liquid Zinc Cathode

The selective separation of rare-earth elements (REEs) from uranium tailings is essential for radioactive waste management and the sustainable development of nuclear energy. This study demonstrates the highly selective electrochemical separation of erbium (Er) and europium (Eu) employing a liquid zinc cathode in molten LiCl-KCl. Through a suite of electrochemical techniques coupled with semi-integral and semidifferential analyses, we systematically elucidated the reduction pathways, product solubility, and underpotential deposition behavior of Er(III) and Eu(III) on the liquid Zn electrode. Electrochemical impedance spectroscopy (EIS) revealed that the exchange current density increases while the charge transfer resistance decreases with increasing temperature. The diffusion coefficient of Er in liquid Zn, determined by anodic chronopotentiometry (ACP), was 1.96 × 10^-5 cm² s^-1, which aligns well with the value determined from molecular dynamics (MD) simulations (3.067 × 10^-5 cm² s^-1). Galvanostatic electrolysis achieved an Er extraction efficiency of 99.2%, an Er/Eu separation factor of 312, and a current efficiency of 84.50%, with the residual Eu being subsequently recoverable. This work provides a theoretical foundation and a viable technological pathway for the precise separation of REEs from uranium tailings and secondary resources, contributing to the closed nuclear fuel cycle and the development of green mining.