In particular, the redox reaction of Cr(III)/Cr(II) was investigated by combining spectroscopy and electrochemistry in the same unit cell to obtain its formal potential, the number of electrons, and the diffusion coefficient of Cr(II). The molar absorption coefficients and molecular structures of the ions were obtained by UV–vis-NIR absorption spectroscopy (250–950 nm). The diffusion coefficients were obtained and compared in terms of both CV and CA results. The formal potentials and standard rate constants of the redox reactions were measured by CV results from both correlations and numerical fitting. In this study, CV was used to characterize redox reactions of Fe(II)/Fe(0), Ni(II)/Ni(0), Co(II)/Co(0), Cr(II)/Cr(0), and Cr(III)/Cr(II). Moreover, the obtained properties have not been applied to explain observed experimental phenomena to show their applicability and completeness. For this reason, the reversibility of the electrochemical systems according to the scan rates of CV has often been ignored. 24 The rate constants of redox reactions were rarely obtained. The spectroelectrochemical measurements were performed only for some elements such as Eu, 22 Sm, 23 and U. 21 However, few studies have explored electrochemical redox reactions at high temperature molten salts while simultaneously monitoring changes in oxidation state using absorption spectroscopy. investigated the possibility of separating Ni and Co in LiCl-KCl using chronopotentiometry (CA) and cyclic voltammetry (CV). ![]() 15– 20 In 2017, Park et al., examined redox behaviors of Zr, Sn, Cr, Fe, and Co in LiCl-KCl using W working electrodes to develop a Zircaloy-4 decontamination process. Some researchers have attempted to apply electrochemical methods for the metallic constituents of nuclear power plant components in LiCl-KCl. 12– 14 Therefore, the thermodynamic, kinetic, and spectroscopic behavior of reduction-oxidation reactions is significant to design and optimize the decontamination process. The electrode potential is controlled to selectively recover each component by depositing it on the surfaces of a metallic cathode. During electrorefining, the contaminated structural components are dissolved into a lithium chloride-potassium chloride (LiCl-KCl) electrolyte. 3, 5 This process was originally developed for recovering uranium from used nuclear fuel. 6– 11 The concept underlying the process can also be used as a decontamination option when radioactive contaminants exist at levels deeper than the surface oxide layers. 4, 5Īn electrorefining process using molten salt has been developed to treat and recycle nuclear materials in used nuclear fuel. 3 In addition, decontaminating the waste can change waste categories from intermediate level waste to low level waste. Such radioactive waste must be decontaminated to reduce the volume of final waste as well as to meet the waste acceptance criteria of the final repository. In particular, radioactive isotopes are distributed in the volume of the reactor internals and pressure vessels made of steel alloys because of neutron activation reactions. ![]() 1, 2 Structural components containing these metallic elements are activated in volume or contaminated on surfaces. ![]() Radioactive metallic waste produced from nuclear power plants commonly contains Cr, Fe, and Ni as alloying constituents and Co as an impurity. The findings of this study will be directly used for designing a decontamination process to produce acceptable waste forms and reduce waste volume. The obtained reaction properties were used in the numerical modeling of the ECE reaction in a Ni and Co binary system to reproduce the experimental results of CV, revealing the presence of chemical reaction. In particular, the redox reaction of Cr(III)/Cr(II) was investigated by chronoabsorptometry to obtain its formal potential, the number of electrons, and the diffusion coefficient of Cr(II). UV–vis-NIR absorption spectroscopy of the metallic constituents was performed to derive molar absorption coefficients and molecular structures in molten salt media. The order of the diffusion coefficients was 10 –5 cm 2 s −1, which agrees with the existing data and the standard rate constants showed similar values with the order of 10 –3 cm s −1 between experimental correlations and numerical fitting. Cyclic voltammetry combined with numerical fitting was used to obtain the formal potentials, standard rate constants, and diffusion coefficients of redox reactions, Cr(II)/Cr, Fe(II)/Fe(0), Co(II)/Co(0), and Ni(II)/Ni(0), in LiCl-KCl at 773 K. This study examines the thermodynamic, kinetic, and spectroscopic behaviors of Cr, Fe, Co, and Ni to lay the foundation to develop an electrochemical decontamination process for radioactive metallic wastes.
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