Electrochemistry and Spectroelectrochemistry of the Pu (III/IV) and (IV/VI) Couples in Nitric Acid Systems

Abstract

The solution chemistry of Pu in nitric acid is explored via electrochemistry and spectroelectrochemistry. By utilizing and comparing these techniques, an improved understanding of Pu behavior and its dependence on nitric acid concentration can be achieved. Here the Pu (III/IV) couple is characterized using cyclic voltammetry, square wave voltammetry, and a spectroelectrochemical Nernst step. Results indicate the formal reduction potential of the couple shifts negative with increasing acid concentration and reversible electrochemistry is no longer attainable above 6 M HNO3. Spectroelectrochemistry is also used to explore the irreversible oxidation of Pu(IV) to Pu(VI) and shine light on the mechanism and acid dependence of the redox reaction.

Overcoming Oxidation State-Dependent Spectral Interferences: Online Monitoring of U(VI) Reduction to U(IV) via Raman and UV–vis Spectroscopy

“…Fortunately, U­(VI) can also be monitored via Raman spectroscopy but due to the absorbance of the Raman excitation laser by U­(IV), the signal may be drastically attenuated. Advanced data analysis techniques can be employed to overcome spectral complexities and accurately quantify target analytes. − Our research group is focused on building optical monitoring probes for highly complex processes. ,− The inclusion of multiple forms of spectroscopy expands capabilities to analyze for multiple target species in complex environments, building on the capabilities already demonstrated for solo Raman and solo absorbance approaches.…”

Mechanisms of Plutonium Redox Reactions in Nitric Acid Solutions

“…The redox behavior of Pu 4+ /Pu 3+ in 1 M HNO 3 was first reported by Artyukhin et al Later, Kim et al reported the Pu 4+ /Pu 3+ redox couple to demonstrate a quasi-reversible electrochemical process in 1 M HNO 3 on a glassy carbon (GC) electrode with a formal redox potential value of 0.721 V (vs Ag/AgCl) . Lines et al further expanded the work to HNO 3 media, exploring the behavior of Pu 4+ /Pu 3+ redox couples across a range of HNO 3 concentrations varying from 1 to 6 M . The value of the analogous Pu 4+ /Pu 3+ redox was observed by Lines et al at 0.703 V (vs Ag/AgCl) in 1 M HNO 3 on a Pt mesh electrode.…”

Measuring Nd(III) Solution Concentration in the Presence of Interfering Er(III) and Cu(II) Ions: A Partial Least Squares Analysis of Ultraviolet–Visible Spectra

“…15,16 However, the efficacy of all optical approaches is limited by signal interferences which can hinder accurate data analysis. 10,[17][18][19][20][21][22] Numerous data analysis approaches have been developed to overcome these challenges and expand the effective utilization of optical spectroscopy for complex sample analysis. Of greatest interest is chemometric analysis, which was first introduced in 1972, that applies mathematical and statistical methods to obtain the maximum relevant system information by analyzing multiple wavelengths simultaneously.…”

“…While chemometric modeling has been used to complete the spectral analysis of many systems, 10,11,[13][14][15][16][17][18][19][20] open questions remain regarding what their limits are in relation to accurate analysis of complex samples. Herein these limits are explored in the context of impacts that could be expected in off-normal processing conditions or unanticipated research system changes.…”