Electrochemical recovery of dysprosium from LiCl-KCl melt aided by liquid Pb metal

Abstract

To recover Dy from LiCl-KCl melt, the electroreduction mechanism of Dy(III) on liquid Pb electrode was first studied by CV and Tafel methods. Dy(III) was reducted on liquid Pb electrode at about −1.35 V which is more positive than that on W electrode due to the formation of Dy(Pb) solid solution: Dy(III) + Pb + 3e− = Dy(Pb). Tafel method was used to evaluate the exchange current density (j0) and charge transfer coefficient (α) of Dy(III)/Dy(Pb) couple on liquid Pb electrode, the influence of different scanning speeds and temperatures on j0 were studied. The linear dependence of j0 as a function of temperature was observed, from which the activation energy associated with Dy(III)/Dy(Pb) couple was also obtained. Then, the reduction process of Dy(III) on the Pb film coated on the W electrode was also performed to obtain more information of the Pb-Dy intermetallic compounds. Electrochemical signals associated with the formation of Pb3Dy, Pb2Dy, Pb4/5Dy and Pb3/5Dy, were observed. The deposition potentials and equilibrium potentials of different Pb-Dy intermetallic compounds were obtained, which are more positive than those of Dy(III) on W electrode. Thermodynamic properties of Pb-Dy intermetallic compounds at 713 K–803 K were calculated employing the determined equilibrium potentials. The metallic Dy was recovered through galvanostatic and potentiostatic electrolysis on liquid Pb cathode and the products were detected by SEM-EDS and XRD. The recovered Dy was found to be in the form of Pb3Dy intermetallic compound.