Spectroelectrochemical Behavior of Cr, Fe, Co, and Ni in LiCl-KCl Molten Salt for Decontaminating Radioactive Metallic Wastes

Abstract

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. 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. The order of the diffusion coefficients was 10–5 cm2 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. UV–vis-NIR absorption spectroscopy of the metallic constituents was performed to derive molar absorption coefficients and molecular structures in molten salt media. 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). 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. The findings of this study will be directly used for designing a decontamination process to produce acceptable waste forms and reduce waste volume.

Determination of the Diffusion Coefficient in Electrodeposition Reactions by Electrochemical Impedance Spectroscopy: A Case Study of Cobalt in Molten LiCl-KCl Salt

“…7. [29][30][31][32][33][34] Overall, D Co(II) values in the literature and our present analyses are distributed within the range of 10 −5 cm 2 /s. This implies that our approach to determining the D of metal ions in molten LiCl-KCl by EIS is practically valid.…”

In Situ Corrosion Monitoring of the T91 Alloy in a Molten Chloride Salt Using a Miniaturized Electrochemical Probe for High-Throughput Applications

“…Considering that the T91 sample mainly consists of two elements, Fe and Cr, the extra redox peak should be attributed to the redox reaction of Cr 2+ /Cr or Fe 2+ /Fe. Based on previous studies, , the equilibrium potential of Cr 2+ /Cr is about 0.3 V lower than that of Fe 2+ /Fe in the LiCl–KCl eutectic molten salt. However, this difference between the two equilibrium potentials was based on the conditions of equal concentrations of Cr 2+ and Fe 2+ in the molten salt and equal activity of Cr and Fe on the inert electrode (activity is unity, assuming pure metals).…”

Chronoamperometric determination of the diffusion coefficient in molten chlorides

“…The electrochemical reduction of Cr 2+ to Cr 0 in molten chlorides is a quasi-reversible reaction. [22][23][24] Consequently, the previously proposed CV-based method for the determination of D generates results with intolerable errors. [7] The determination of D by CA under pure diffusion-controlled conditions generated by applying a su ciently high overpotential overcomes this limitation by mitigating the in uence of the reaction rate constant.…”