Electrochemical behavior and electrowinning of uranium(IV) from FLiNaK molten salt

The electrochemical behaviors and electrowinning of uranium from LiF–NaF–KF (46.5–11.5–42.0 mol%, FLiNaK) molten salt were investigated. Cyclic voltammetric and chronopotentiometric studies revealed the presence of two steps during the electro-reduction of UF4 on W electode. U(IV) undergoes a one-electron reduction to form U(III) followed by a three-electron reduction to form U(0). The diffusion coefficient (D) of U(IV) ion was determined to be 1.33 × 10−6 cm2 s−1 at 550 °C. Based on the electrochemical behaviors of U(IV) in FLiNaK melt, pulse current electrolysis was carried out using Ni electrode. The black bulks obtained as electrolysis products were characterized to contain metallic U. Consecutive electrolysis experiments demonstrated up to 74.7% U can be separated from the fluoride melt.