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

Summary

The cyclic voltammetric behavior of uranyl ion was investigated at hanging mercury drop electrode in perchlorate supporting electrolyte. The standard heterogeneous electron transfer rate constant “k_s” for the reduction of uranyl ion in perchlorate medium was (2.74±0.03)×10⁻³ cm s⁻¹ while in acetate and formate medium the value of k_s was (2.83±0.02)×10⁻³ and (2.66±0.02)×10⁻³ cm s⁻¹, respectively. The effect of temperature on the values of k_s was 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⁻¹ K⁻¹ and 15.02±0.07 kJ mol⁻¹ in simple perchlorate medium and 3.67±0.02 kJ mol⁻¹, −38.04±0.05 J mol⁻¹ K⁻¹, and 15.01±0.03 kJ mol⁻¹ in acetate medium and 0.79±0.02 kJ mol⁻¹, −48.24±0.04 J mol⁻¹ K⁻¹ and 15.17±0.02 kJ mol⁻¹ in 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 logβ₁ and logβ₂ values for 1:1 and 1:2 uranyl acetate complexes were 2.67±0.04 and 4.71±0.01, respectively. The values of logβ₁ and logβ₂ of uranyl formate complex were 1.61±0.02 and 2.57±0.01, respectively, which are reported for the first time.