Recovery of Terbium from LiCl-KCl-TbCl₃ System by Electrodeposition Using Different Electrodes

Abstract

To extract terbium from LiCl-KCl-TbCl3 molten salts, the electrochemistry of Tb(III) was investigated on Cu and Zn coated W electrodes by a range of electrochemical techniques. A depolarization effect for Tb(III) reduction was observed on the two electrodes owing to the formation of Cu-Tb and Zn-Tb intermetallics. The Gibbs energies of formation for Zn12Tb and Cu5Tb were calculated by open circuit chronopotentiomery, and showed that the formation of Zn12Tb on Zn electrode is easier than the one of Cu5Tb on Cu electrode. The exchange current intensities for Tb(III)/Zn12Tb and Tb(III)/Cu5Tb couples were estimated using linear polarization technique. It was found that j0(Tb(III)/Zn12Tb) > j0(Tb(III)/Cu5Tb), which revealed that the reaction rate of Tb(III) on Zn electrode is faster than that on Cu electrode. The electroextraction of Tb was conducted on the two electrodes under the same conditions, and the extraction rates and efficiencies on liquid Zn electrode are higher than those on Cu electrode when electroextraction time is less than 3 h. The products were checked by XRD and SEM with EDS, and are comprised of Zn and Zn17Tb2 in the Zn-Tb alloy and CuTb and Cu2Tb in Cu-Tb alloy, respectively.