Electrolytic extraction of dysprosium and thermodynamic evaluation of Cu–Dy intermetallic compound in eutectic LiCl–KCl

The electrochemical reduction of dysprosium(iii) was studied on W and Cu electrodes in eutectic LiCl-KCl by transient electrochemical methods. Cyclic voltammogram and current reversal chronopotentiogram results demonstrated that dysprosium(iii) was directly reduced to dysprosium (0) on the W electrode through a single-step process with the transfer of three electrons. Electrochemical measurements on the Cu electrode showed that different Cu-Dy intermetallics are formed. Moreover, the thermodynamic properties of Cu-Dy intermetallic compounds were estimated by open circuit chronopotentiometry in a temperature range of 773-863 K. Using the linear polarization method, the exchange current density (j ₀) of dysprosium in eutectic LiCl-KCl on the Cu electrode was estimated, and the temperature dependence of j ₀ was studied to estimate the activation energies associated with Dy(iii)/Cu₅Dy and Dy(iii)/Cu9/2Dy couples. In addition, potentiostatic electrolysis was conducted to extract dysprosium on the Cu electrode, and five Cu-Dy intermetallic compounds, CuDy, Cu₂Dy, Cu9/2Dy, Cu₅Dy and Cu0.99Dy0.01 were identified by X-ray diffraction, scanning electron microscopy and energy dispersive spectrometry. Meanwhile, the change of dysprosium(iii) concentration was monitored using inductively coupled plasma-atomic emission spectrometry, and the maximum extraction efficiency of dysprosium was found to reach 99.2%.