Abstract
The role of Np(v) concentration as a potential chemical driver of Np(v) disproportionation was investigated by probing Np redox chemistry in two different acid media using visible-near-infrared absorbance spectroscopy. In situ spectroscopy of chemically and electrochemically manipulated Np oxidation states at molar concentrations of Np underscores the difficulty in stabilizing pure Np(v), even in dilute acid. A Np(vi) component coexisting with the majority Np(v) component was observed in both HNO3 and HCl. Electrochemical tuning and subsequent spectroscopic analysis of the Np(VI/V) ratio revealed neptunyl self-complexation as a key mechanism occurring in both acid media. Chemical reduction of the Np(vi) component and stabilization of a minor Np(iv) component in HNO3 were observed; however, spectral data indicated that these two oxidation states were not observed to coexist, and pure Np(v) was stabilized only briefly. These findings demonstrate that high Np concentrations significantly affect the redox chemistry of Np in acidic solutions. Finally, the occurrence of Np(v) disproportionation could not be definitely determined by spectral data, but other mechanisms such as self-complexation and radiolysis, which potentially compete with disproportionation, must be considered.
| Original language | English |
|---|---|
| Pages (from-to) | 16040-16049 |
| Number of pages | 10 |
| Journal | RSC Advances |
| Volume | 16 |
| Issue number | 18 |
| DOIs | |
| State | Published - 2026 |
Funding
Funding for this research was provided by the Science Mission Directorate of the National Aeronautics and Space Administration and administered by the US Department of Energy, Office of Nuclear Energy, under contract DEAC05-00OR22725. S. E. G. wishes to acknowledge the Glenn T. Seaborg Initiative for support through a postdoctoral fellowship. This work used the facilities and resources at the Radiochemical Engineering Development Center operated by the US Department of Energy's Oak Ridge National Laboratory. The authors wish to thank the Transuranic Analytical Laboratory Group staff for conducting the alpha spectroscopy of the Np stock solutions and Albert Wolff for providing the calculation for approximate energy deposited into solution from237Np and233Pa decay. S.E.G. wishes to thank Leigh Martin and Kathryn Lawson for helpful scientific discussions. Funding for this research was provided by the Science Mission Directorate of the National Aeronautics and Space Administration and administered by the US Department of Energy, Office of Nuclear Energy, under contract DEAC05-00OR22725. S. E. G. wishes to acknowledge the Glenn T. Seaborg Initiative for support through a postdoctoral fellowship. This work used the facilities and resources at the Radiochemical Engineering Development Center operated by the US Department of Energy's Oak Ridge National Laboratory. The authors wish to thank the Transuranic Analytical Laboratory Group staff for conducting the alpha spectroscopy of the Np stock solutions and Albert Wolff for providing the calculation for approximate energy deposited into solution from Np and Pa decay. S.E.G. wishes to thank Leigh Martin and Kathryn Lawson for helpful scientific discussions. This manuscript has been authored by UT-Battelle, LLC, under contract DE-AC05-00OR22725 with the US Department of Energy (DOE). The US government retains and the publisher, by accepting the article for publication, acknowledges that the US government retains a nonexclusive, paid-up, irrevocable, worldwide license to publish or reproduce the published form of this manuscript, or allow others to do so, for US government purposes. DOE will provide public access to these results of federally sponsored research in accordance with the DOE Public Access Plan ( https://www.energy.gov/doe-public-access-plan ).
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