Kinetic and thermodynamic study of Lu on W and Zn electrodes and its electrochemical extraction

ABSRACT To extract lutetium (Lu) from LiCl-KCl fused salt, the electrode reaction mechanisms of Lu on W and liquid Zn electrodes were systematically investigated using a series of electrochemical methods such as cycle voltammetry (CV), square wave voltammetry (SWV), reverse chronopotentiometry (RCP), etc. The diffusion coefficient and diffusion activation energy of Lu(III) in LiCl-KCl fused salt were measured by CV. The results of CV, SWV and open circuit chronopotentiometry (OCP) confirmed that seven Lu-Zn intermetallic compounds were formed when Lu was deposited on Zn film electrode. Kinetic data of Lu(III)/Lu on W and liquid Zn electrodes, i.e., exchange current density, charge transfer resistance and reaction activation energy, were determined and compared by linear polarization (LP) at 773-848 K. Furthermore, the thermodynamic date such as equilibrium potential and formation Gibbs free energy of Lu-Zn alloys were also calculated and analyzed according to the OCP. The results demonstrate that the liquid Zn electrode is conducive to extract Lu from LiCl-KCl fused salt. Thus, constant potential electrolysis (CPE) was conducted at -1.58 V for 9 h on liquid Zn cathode to extract Lu from fused salt. The electrolytic product was composed of Zn and LuZn12 phases checked by XRD and SEM-EDS. The extraction rate of Lu is reached up to 98.37% based on the concentration change of Lu(III) in fused salt, which confirmed the feasibility to extract Lu employing liquid Zn electrode.