Electrochemical behaviour of erbium(III) and its extraction on Cu electrode in LiCl-KCl melts

Abstract

The electrochemical behaviour of Er(III) was studied on W and Cu electrodes in LiCl-KCl melts by a series of electrochemical techniques. The studies indicated that Er(III) ions were reduced to Er(0) in a one-step diffusion-controlled process exchanging three electrons. The diffusion coefficient of Er(III) was determined and the activation energy for diffusion of Er(III) ions was found to be 35.2 kJ mol−1. The equilibrium potential of the Er(III)/Er(0) redox couple was measured via open circuit chronopotentiometry in the temperature range of 773–923 K, with subsequent calculation of the apparent standard potential, EEr(III)/Er(0)∗0, and the apparent Gibbs free energy of formation for ErCl3, ΔGf∗0(ErCl3). The cyclic voltammogram and square wave voltammogram obtained on Cu electrode, compared with those on W electrode, showed several new pairs of reduction peaks observed at more positive potential, which means that the underpotential deposition of erbium occurs. The thermodynamic properties of the Cu-Er intermetallic compound, Cu5Er, were estimated by open circuit chronopotentiometry. Potentiostatic and galvanostatic electrolysis was performed on Cu electrode to extract erbium. The extraction products, consisting of CuEr, Cu2Er and Cu5Er, were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM) equipped with energy dispersive spectrometry (EDS). Furthermore, the extraction efficiencies were evaluated during potentiostatic electrolysis at different electrolysis times using an inductive coupled plasma atomic emission spectrometer (ICP-AES), which showed that the highest extraction efficiency of Er(III) could reach about 98.92%.