Multimodal X-ray microanalysis of a UFeO4: evidence for the environmental stability of ternary U(v) oxides from depleted uranium munitions testing

Environ Sci Process Impacts. 2020 Jul 1;22(7):1577-1585. doi: 10.1039/d0em00243g. Epub 2020 Jul 7.

Abstract

An environmentally aged radioactive particle of UFeO4 recovered from soil contaminated with munitions depleted uranium (DU) was characterised by microbeam synchrotron X-ray analysis. Imaging of uranium speciation by spatially resolved X-ray diffraction (μ-XRD) and X-ray absorption spectroscopy (μ-XAS) was used to localise UFeO4 in the particle, which was coincident with a distribution of U(v). The U oxidation state was confirmed using X-ray Absorption Near Edge Structure (μ-XANES) spectroscopy as +4.9 ± 0.15. Le-Bail fitting of the particle powder XRD pattern confirmed the presence of UFeO4 and a minor alteration product identified as chernikovite (H3O)(UO2)(PO4)·3H2O. Refined unit cell parameters for UFeO4 were in good agreement with previously published values. Uranium-oxygen interatomic distances in the first co-ordination sphere were determined by fitting of Extended X-ray Absorption Fine Structure (μ-EXAFS) spectroscopy. The average first shell U-O distance was 2.148 ± 0.012 Å, corresponding to a U valence of +4.96 ± 0.13 using bond valence sum analysis. Using bond distances from the published structure of UFeO4, U and Fe bond valence sums were calculated as +5.00 and +2.83 respectively, supporting the spectroscopic analysis and confirming the presence of a U(v)/Fe(iii) pair. Overall this investigation provides important evidence for the stability of U(v) ternary oxides, in oxic, variably moist surface environment conditions for at least 25 years.

MeSH terms

  • Electron Probe Microanalysis
  • Ferric Compounds
  • Oxides
  • Soil Pollutants, Radioactive*
  • Uranium*
  • X-Ray Absorption Spectroscopy

Substances

  • Ferric Compounds
  • Oxides
  • Soil Pollutants, Radioactive
  • Uranium