Electrochemical extraction of strontium from molten salts using reactive zinc and aluminum electrodes

The electrochemical behaviors of Sr on inert W electrode and reactive Zn/Al electrodes were systematically investigated in LiCl-KCl-SrCl2 molten salts at 773 K using various electrochemical methods. The chemical reaction potentials of Li and Sr on reactive Zn/Al electrodes were determined. It was found that Sr could be extracted by decreasing the activity of the deposited metal Sr on the reactive electrode, even though the standard reduction potential of Sr(II)/Sr was more negative than that of Li(I)/Li. The electrochemical extraction products of Sr on reactive Zn and Al electrodes were Zn13Sr and Al4Sr, with no co-deposition of Li observed. Based on density functional theory calculations, both Zn13Sr and Al4Sr were identified as stable intermetallic compounds of rich-Zn/Al phases. In LiCl-KCl molten salt containing 3wt% SrCl2, the coulombic efficiency of Sr in Zn electrode was approximately 54%. The depolarization values for Sr on Zn and Al electrodes were 0.864 V and 0.485 V, respectively, demonstrating a stronger chemical interaction between Zn and Sr. This work suggests that the use of reactive electrodes can facilitate the extraction of Sr accumulated in electrorefining molten salts, thereby enabling the purification and reuse of the salt and reducing the volume of nuclear waste.