Electrochemical extraction and separation of praseodymium and erbium on reactive magnesium electrode in molten salts

The electrochemical behaviors of Pr(III) and Er(III) in LiCl-KCl melts were studied on inert tungsten and reactive magnesium electrodes by cyclic voltammetry, square wave voltammetry, and open-circuit chronopotentiometry at 823 K. On a W electrode, the reduction of Pr(III) and Er(III) were found to be through a one-step process: Pr(III) + 3 e(-) -> aEuro parts per thousand Pr, Er(III) + 3e (-) -> aEuro parts per thousand Er. On a Mg electrode, the reduction potentials of Pr(III)/Pr and Er(III)/Er were observed at more positive potential values than those on W electrode, due to the formation of Mg-Pr and Mg-Er intermetallic compounds when Pr(III) and Er(III) ions were reduced to Pr and Er metal and then react with the Mg substrate, respectively. The extraction of Pr(III) and Er(III) in LiCl-KCl melts were performed by galvanostatic electrolysis on Mg electrode, respectively. The Mg3Pr and Mg24Er5 intermetallic compounds were obtained, which characterized by X-ray diffraction (XRD) and scanning electron microscopy equipped with energy-dispersive spectrometry (SEM-EDS). In order to separate the Pr(III) and Er(III), potentiostatic electrolysis was performed at -1.9 V in LiCl-KCl-PrCl3-ErCl3 melts on a Mg electrode, only one Mg-Pr intermetallic compound, Mg12Pr, was found in the deposit. The separation efficiency was evaluated via inductively coupled plasma atomic emission spectrometer (ICP-AES) analysis at different electrolysis time during potentiostatic electrolysis at -1.9 V. The separation efficiency of Pr(III) was about 95.3 % from the mixture of PrCl3-ErCl3 in LiCl-KCl melts.