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

DOI: 10.1016/j.chemosphere.2020.126859 DOI Help

Authors: Adam J. Fuller (The University of Manchester) , Peter Leary (Newcastle University) , Neil D. Gray (Newcastle University) , Helena S. Davies (The University of Manchester) , J. Frederick W. Mosselmans (Diamond Light Source) , Filipa Cox (The University of Manchester) , Clare H. Robinson (The University of Manchester) , Jon K. Pittman (The University of Manchester) , Clare M. Mccann (Newcastle University) , Michael Muir (University of Edinburgh) , Margaret C. Graham (University of Edinburgh) , Satoshi Utsunomiya (Kyushu University) , William R. Bower (The University of Manchester; The University of Helsinki) , Katherine Morris (The University of Manchester) , Samuel Shaw (The University of Manchester) , Pieter Bots (The University of Manchester) , Francis R. Livens (The University of Manchester) , Gareth T. W. Law (The University of Manchester; The University of Helsinki)
Co-authored by industrial partner: No

Type: Journal Paper
Journal: Chemosphere

State: Published (Approved)
Published: April 2020
Diamond Proposal Number(s): 10163 , 12767 , 12477

Open Access Open Access

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.

Journal Keywords: Uranium; Radionuclide biogeochemistry; Natural analogue site; Needle's eye

Subject Areas: Chemistry, Earth Science, Environment


Instruments: B18-Core EXAFS , I18-Microfocus Spectroscopy

Other Facilities: SOLEIL

Documents:
1-s2.0-S0045653520310523-main.pdf