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Voltammetric Investigation of U and Pu in Perchloric Acid Media Using Gold Working Electrode
p.385
Elucidating the redox behavior of actinide elements in aqueous solution is important for the safety assessments of nuclear waste disposal. Despite ongoing endeavors for decades, some points of uranium and plutonium redox mechanism are ambiguous and unclear. In this study, the electrochemical redox behaviors of U(VI) and Pu(III and VI) ions in perchloric acid media were investigated by using a gold (Au) working electrode via cyclic voltammetry (CV) and cyclic square wave voltammetry (CSWV) with the temperature control (10–55°C). The cyclic voltammograms of U(V/VI), Pu(III/IV) and Pu(V/VI) redox couple were transformed to semi-integral form to calculate the diffusion coefficient and formal potential in the electrochemical quasi-reversibility prevailed system. The CSWV was additionally used for a more precise interpretation of the redox mechanism. From the investigation of the redox chemistry of U(VI) ions, a clear U(V/VI) redox peak and one unidentified oxidation peak appear around pH 2. With the temperature control and CSWV, the relevance of the oxidation peak and U(IV) was confirmed. In the case of voltammetry of Pu(VI) solution, Pu(V/VI) redox peak and an additional reduction peak appear. The redox behavior resposible for this additional reduction peak are also examined. The cyclic voltammograms of Pu(III) solution show a clear reversible redox reaction of Pu(III/IV) couple. With the temperature control, using the change of formal potential at ionic strength 1 M (ClO4 −), thermodynamic parameters of conditional molar enthalpy and entropy change were evaluated in this system.
