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

Herein, 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. We observed that Sr could be extracted by decreasing the activity of the deposited metal Sr on the reactive electrode, although 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, respectively, with no codeposition of Li observed. Based on the density functional theory calculations, both Zn₁₃Sr and Al₄Sr were identified as stable intermetallic compounds with Zn-/Al-rich phases. In LiCl–KCl molten salt containing 3wt% SrCl₂, the coulombic efficiency of Sr in the Zn electrode was ~54%. The depolarization values for Sr on Zn and Al electrodes were 0.864 and 0.485 V, respectively, exhibiting a stronger chemical interaction between Zn and Sr than between Al and Sr. This study suggests that using reactive electrodes can facilitate extraction of Sr accumulated while electrorefining molten salts, thereby enabling the purification and reuse of the salt and decreasing the volume of the nuclear waste.