Electrolytic reduction of CrF3 and Cr2O3 in molten fluoride salt

Abstract

The electrochemical behavior of Cr³⁺ in molten LiF–NaF–KF (46.5 : 11.5 : 42 mol%) (FLiNaK) was studied by cyclic voltammetry (CV) at 600 °C. With an acceptable solubility and a relatively positive reduction potential of solute Cr³⁺, the electrolytic reduction of chromium in FLiNaK-CrF₃ melt was performed on a tungsten electrode by potentiostatic electrolysis. After electrolysis for 21.5 h, the Cr³⁺ in the melt was effectively removed as confirmed by ICP-OES and CV. Then, the solubility of Cr₂O₃ in FLiNaK with ZrF₄ additive was analyzed by CV. The results showed that the solubility of Cr₂O₃ was greatly promoted by ZrF₄ and the reduction potential of zirconium is far more negative than that of chromium, which makes the electrolysis of chromium from Cr₂O₃ material possible. Thus, the electrolytic reduction of Cr in a FLiNaK-Cr₂O₃-ZrF₄ system was further performed by potentiostatic electrolysis on a nickel electrode. After electrolysis for 5 h, a thin layer of chromium metal (with a thickness of c.a. 20 μm) was deposited on the electrode, as confirmed by SEM-EDS and XRD techniques. This study verified the feasibility of electroextraction of Cr from the FLiNaK-CrF₃ and FLiNaK-Cr₂O₃-ZrF₄ molten salt systems.