Electrochemical separation of uranium from lanthanide (La, Eu, Gd) fluorides in molten LiCl-KCl

The electrochemical behaviors of a series of lanthanide fluorides in molten LiCl-KCl were investigated, and the results on the separation of uranium from molten LiCl-KCl-UF4-LaF3-GdF3-EuF3 by electrolysis were provided. On the basis of the cyclic voltammetry and square wave voltammetry measurements, LaF3 and GdF3 undergo a three-electron reduction to metal in molten LiCl-KCl while the fluoride of europium (III) can only be reduced to europium (II) via single electron transfer. Compared with the relatively simple electrochemical behaviors of individual LaF3, GdF3 or EuF3 in molten LiCl-KCl, the cyclic voltammograms of LaF3, UF4, GdF3 and EuF3 coexisting in the LiCl-KCl melt are complicated by the presence of F ions which cause the appearance of new peaks especially in the oxidation processes. Potentiostatic electrolysis of the LiCl-KCl-UF4-LaF3-GdF3-EuF3 melt using the tungsten sheet electrode resulted in the formation of metallic deposits that are composed of uranium as well as small amount of UO2 according to the X-ray diffraction and scanning electron microscope analysis, suggesting that uranium can be successfully separated from lanthanide fluorides in the LiCl-KCl molten salt.