Extraction of gadolinium on Cu electrode from LiCl-KCl melts by formation of Cu-Gd alloys

Abstract

Electrochemical behavior of gadolinium was studied on W and Cu electrodes in LiCl-KCl melts 823 K via cyclic voltammetry, square wave voltammetry, and open circuit chronopotentiometry. The reduction of Gd(III) ions was found to be through a one-step process: Gd(III) + 3e− = Gd(0). The equilibrium potential of the Gd(III)/Gd(0) redox couple was measured via open circuit chronopotentiometry in the temperature range of 773–893 K, with subsequent calculation of the apparent standard potential, $$ {E}_{\mathrm{Gd}\left(\mathrm{III}\right)/\mathrm{Gd}(0)}^{\ast 0} $$ , and the apparent Gibbs free energy of formation for GdCl3, $$ \varDelta {G}_f^{\ast 0}\left({\mathrm{GdCl}}_3\right) $$ . Three reduction peaks, corresponding to the formation of GdxCuy intermetallic compounds, were detected from cyclic voltammogram and square wave voltammogram obtained by co-reduction of Gd(III) and Cu(II) ions or electrodeposition of Gd(III) on Cu electrode. Potentiostatic/galvanostatic electrolysis was performed on Cu electrode with different electrolytic conditions. The results indicate that the Cu-Gd alloys are comprised of CuGd, Cu2Gd, and Cu6Gd phases. The morphology and micro-zone chemical analysis of the deposits were characterized by scanning electron microscopy (SEM) equipped with energy dispersive spectrometry (EDS). The highest extraction efficiency of metallic Gd could reach about 99.60% at − 2.20 V for 12 h at 823 K. Therefore, employing electrochemical deposition of Gd(III) on reactive Cu electrode to extract Gd is feasible.