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)/Cu(5)Dy and Dy(iii)/Cu(9/2)Dy couples. In addition, potentiostatic electrolysis was conducted to extract dysprosium on the Cu electrode, and five Cu–Dy intermetallic compounds, CuDy, Cu(2)Dy, Cu(9/2)Dy, Cu(5)Dy and Cu(0.99)Dy(0.01) 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%.