Organic complexation of U(VI) in reducing soils at a natural analogue site: Implications for uranium transport

Research output: Contribution to journalArticlepeer-review

  • External authors:
  • Adam J. Fuller
  • Peter Leary
  • Neil D. Gray
  • Helena S. Davies
  • J. Frederick W. Mosselmans
  • Clare M. Mccann
  • Michael Muir
  • Margaret C. Graham
  • Satoshi Utsunomiya
  • William R. Bower
  • Pieter Bots
  • Francis R. Livens
  • Gareth T.w. Law

Abstract

Understanding the long-term fate, stability, and bioavailability of uranium (U) in the environment is important for the management of nuclear legacy sites and radioactive wastes. Analysis of U behavior at natural analogue sites permits evaluation of U biogeochemistry under conditions more representative of long-term equilibrium. Here, we have used bulk geochemical and microbial community analysis of soils, coupled with X-ray absorption spectroscopy and μ-focus X-ray fluorescence mapping, to gain a mechanistic understanding of the fate of U transported into an organic-rich soil from a pitchblende vein at the UK Needle's Eye Natural Analogue site. U is highly enriched in the Needle's Eye soils (∼1600 mg kg−1). We show that this enrichment is largely controlled by U(VI) complexation with soil organic matter and not U(VI) bioreduction. Instead, organic-associated U(VI) seems to remain stable under microbially-mediated Fe(III)-reducing conditions. U(IV) (as non-crystalline U(IV)) was only observed at greater depths at the site (>25 cm); the soil here was comparatively mineral-rich, organic-poor, and sulfate-reducing/methanogenic. Furthermore, nanocrystalline UO2, an alternative product of U(VI) reduction in soils, was not observed at the site, and U did not appear to be associated with Fe-bearing minerals. Organic-rich soils appear to have the potential to impede U groundwater transport, irrespective of ambient redox conditions.

Bibliographical metadata

Original languageEnglish
Article number126859
JournalChemosphere
Volume254
Early online date28 Apr 2020
DOIs
Publication statusPublished - 6 May 2020