Electrolytic reduction of CrF(3) and Cr(2)O(3) in molten fluoride salt

The electrochemical behavior of Cr(3+) 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 Cr(3+), the electrolytic reduction of chromium in FLiNaK-CrF(3) melt was performed on a tungsten electrode by potentiostatic electrolysis. After electrolysis for 21.5 h, the Cr(3+) in the melt was effectively removed as confirmed by ICP-OES and CV. Then, the solubility of Cr(2)O(3) in FLiNaK with ZrF(4) additive was analyzed by CV. The results showed that the solubility of Cr(2)O(3) was greatly promoted by ZrF(4) and the reduction potential of zirconium is far more negative than that of chromium, which makes the electrolysis of chromium from Cr(2)O(3) material possible. Thus, the electrolytic reduction of Cr in a FLiNaK-Cr(2)O(3)-ZrF(4) 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-CrF(3) and FLiNaK-Cr(2)O(3)-ZrF(4) molten salt systems.