Electrochemical extracting variable valence ytterbium from LiCl–KCl–YbCl3 melt on Cu electrode

Abstract

The electrochemical behavior of Yb(III) in LiCl–KCl–YbCl3 melt was studied on inert W and reactive Cu electrodes by cyclic voltammetry, square wave voltammetry and open circuit chronopotentiometry. The results indicated that the reduction of Yb(III) on W electrode takes place in only one step of Yb(III) to Yb(II). The system of Yb(II)/Yb(0) was not observed within the electrochemical windows, which inhibits the extraction of Yb from the melt on an inert electrode. In contrast, the electroreduction of Yb(II) occured at a more positive potential on Cu electrode than that on W electrode, due to the formation of various Yb–Cu intermetallic compounds. The extraction of ytterbium on Cu electrode was performed by galvanostatic and potentiostatic electrolysis to prepare Yb–Cu alloys, respectively. These samples were characterized by X–ray diffraction (XRD) and scanning electron microscopy (SEM) equipped with energy dispersive spectrometry (EDS). XRD results showed that the Yb-Cu compounds, YbCu, YbCu2, YbCu5, YbCu6.5 and Yb0.1Cu0.99, were obtained. The working electrode was replaced and characterized by SEM and XRD during electroextraction every 3h. It was found that thermodynamic metastable phase was easily formed even if the concentration of Yb(III) decreases to 3.95×10−8molcm−3 in LiCl–KCl melt. The extraction efficiency was about 99.9% for Yb(III) after potentiostatic electrolysis at −2.3V for 18h.