Electrochemical Behavior and Separation of Ytterbium from Nacl-Cacl2 Molten Salt by Reactive Electrodes

Abstract

To electro-extract Yb from NaCl–CaCl2 molten salt, the electrochemical behavior of Yb(III) was studied by cyclic voltammetry (CV), square wave voltammetry (SWV), chronopotentiometry (CP) and open circuit chronopotentiometry (OCP) on inert Mo and reactive Ni and Cu electrodes in NaCl–CaCl2 molten salt at 923 K. It was found that Yb(III) was reduced to Yb(II) on the Mo electrode and no Yb metal was formed prior to the reduction of Na+/Ca2+ ions, suggesting that the electroreduction of Yb(II) to Yb on inert Mo electrode is impossible. The diffusion coefficient of Yb(III) was determined by CV and CP and the results by the two methods showed good consistency. However, the reduction peaks of four Ni-Yb and five Cu-Yb intermetallic compounds were formed on reactive electrodes Ni and Cu, respectively. Thus, the reduction of Yb(II)/Yb became possible by this cathodic alloying method. To investigate the feasibility of the separation of ytterbium from this molten salt, potentiostatic electrolysis were carried out at -1.83 V, -2.0 V, -2.2 V, and -2.4 V (vs. Ag/AgCl) respectively on the Ni electrode and at -2.1 V (vs. Ag/AgCl) on the Cu electrode. The results showed that the yield of Yb atoms in the electrolytic alloy layer becomes higher when the applied potential shifts negatively, and Ni electrode is confirmed more suitable than Cu material for Yb separation in NaCl–CaCl2 molten salt.

Keywords: NaCl-CaCl2, Yb, electrochemical behavior and separation, potentiostatic electrolysis, reactive electrodes, Ni-Yb and Cu-Yb intermetallic compounds