Redox Equilibrium of U ⁴⁺ /U ³⁺ in Molten NaCL-2CsCL by UV-Vis Spectrophotometry and Cyclic Voltammetry

Abstract

In order to investigate the redox equilibrium of uranium ions in molten NaCL-2CsCL, UV-Vis absorption spectrophotometry measurements were performed for U4+ and U3+ in molten NaCL-2CsCL at 923 K under simultaneous electrolytic control of their ratio. Prominent absorption bands at 480 and 570 nm were assigned to U3+, and their molar absorptivities were determined to be 1,260±42 and 963±32 mol−1.l.cm−1 respectively. From the dependence of the rest potential of the melt on the spectrophotometrically determined ratio of [U4+]/[U3+], the standard redox potential of the couple U4+/U3+ at 923K was determined to be −1.481±0.004 V vs. Cl2/Cl−. Cyclic voltammetry measurements were carried out for the couple U4+/U3+, and the results agreed well with this standard redox potential value. By the results of cyclic voltammetry, a temperature dependence of the standard redox potential was found to be −2.094+6.639×10−4 T (T=823-923 K).