Kinetics and electrochemical studies of uranium in acetate and formate media by cyclic voltammetry

Abstract

SummaryThe cyclic voltammetric behavior of uranyl ion was investigated at hanging mercury drop electrode in perchlorate supporting electrolyte. The standard heterogeneous electron transfer rate constant “ks” for the reduction of uranyl ion in perchlorate medium was (2.74±0.03)×10−3cm s−1while in acetate and formate medium the value ofkswas (2.83±0.02)×10−3and (2.66±0.02)×10−3cm s−1, respectively. The effect of temperature on the values ofkswas investigated and thermodynamic constants ΔH*, ΔS* and ΔG298* were evaluated. The values of ΔH*, ΔS*; and ΔG298* were 8.06±0.03 kJ mol−1, −23.42±0.05 J mol−1K−1and 15.02±0.07 kJ mol−1in simple perchlorate medium and 3.67±0.02 kJ mol−1, −38.04±0.05 J mol−1K−1, and 15.01±0.03 kJ mol−1in acetate medium and 0.79±0.02 kJ mol−1, −48.24±0.04 J mol−1K−1and 15.17±0.02 kJ mol−1in formate medium, respectively. The thermodynamic data showed that the process of reduction of uranyl ion at hanging mercury drop electrode was endothermic and non-spontaneous. The stability constants of uranyl acetate and uranyl formate were calculated from an analysis of the shift in peak potential data. The logβ1and logβ2values for 1:1 and 1:2 uranyl acetate complexes were 2.67±0.04 and 4.71±0.01, respectively. The values of logβ1and logβ2of uranyl formate complex were 1.61±0.02 and 2.57±0.01, respectively, which are reported for the first time.