4.7 Article

Paving the way for examination of coupled redox/solid-liquid interface reactions: 1 ppm Np adsorbed on clay studied by Np M5-edge HR-XANES spectroscopy

Journal

ANALYTICA CHIMICA ACTA
Volume 1202, Issue -, Pages -

Publisher

ELSEVIER
DOI: 10.1016/j.aca.2022.339636

Keywords

Illite; Clay; Detection limit for speciation study; Actinides; Neptunium; High-energy resolution X-ray absorption near-edge structure (HR-XANES) spectroscopy

Funding

  1. European Union [847593]

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The recently developed high-energy resolution X-ray absorption near-edge structure (HR-XANES) technique has proven to be a powerful tool for studying the oxidation states of actinide elements. In this study, Np M-5-edge HR-XANES was applied for the first time to investigate the sorption of Np on illite. By optimizing the experimental conditions and employing a cryogenic configuration, the researchers were able to obtain Np M-5-edge HR-XANES spectra of a sample with very low Np loadings, which opens up new possibilities for examining redox reactions and solid-liquid interface reactions of actinide ions.
The recently emerged actinide (An) M-4,M-5-edge high-energy resolution X-ray absorption near-edge structure (HR-XANES) technique has proven to be very powerful for oxidation state studies of acti-nides. In this work, for the first time, Np M-5-edge HR-XANES was applied to study Np sorption on illite. By improving the experimental conditions, notably by operation of the spectrometer under He atmo-sphere, it was possible to measure Np M-5-edge HR-XANES spectra of a sample with similar to 1 mg Np/g illite (1 ppm). This is 30-200 0 times lower than Np loadings on mineral surfaces usually investigated by X-ray absorption spectroscopy. A newly designed cryogenic configuration enabled sample temperatures of 141.2 +/- 1.5 K and successfully prevented beam-induced changes of the Np oxidation state. The described approach paves the way for the examination of coupled redox/solid-liquid interface reactions of actinide ions via An M-4,M-5-edge HR-XANES spectroscopy at low metal ion concentrations, which are of specific relevance for contaminated sites and nuclear waste disposal studies.(c) 2022 The Authors. Published by Elsevier B.V.

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