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

Fuller, A. J. et al. (2020) Organic complexation of U(VI) in reducing soils at a natural analogue site: implications for uranium transport. Chemosphere, 254, 126859. (doi: 10.1016/j.chemosphere.2020.126859)

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.

• Item Type: Articles
• Additional Information: This work was funded as part of the LO-RISE (Long-lived Radionuclides in the Surface Environment; NE/L000202/1) consortium under the UK NERC RATE programme (Radioactivity and the Environment), co-funded by the UK Environment Agency and Radioactive Waste Management Ltd. Synchrotron data was collected at Diamond Light Source on beamline B18 (SP10163 and SP12767), I18 (SP12477), and at the MARS beamline, Synchrotron Soleil (20150125). Law also thanks the UK STFC and NERC for funding through the Environmental Radioactivity Network (ST/K001787/1) and grant NE/M014088/1.
• Status: Published
• Refereed: Yes
• Glasgow Author(s) Enlighten ID: Muir, Dr Michael
• Authors: Fuller, A. J., Leary, P., Gray, N. D., Davies, H. S., Mosselmans, J. F. W., Cox, F., Robinson, C. H., Pittman, J. K., McCann, C. M., Muir, M., Graham, M. C., Utsunomiya, S., Bower, W. R., Morris, K., Shaw, S., Bots, P., Livens, F. R., and Law, G. T.W.
• College/School: College of Social Sciences > School of Interdisciplinary Studies
• Journal Name: Chemosphere
• Publisher: Elsevier
• ISSN: 0045-6535
• ISSN (Online): 1879-1298
• Published Online: 28 April 2020
• Copyright Holders: Copyright © 2020 The Authors
• First Published: First published in Chemosphere 254: 126859
• Publisher Policy: Reproduced under a Creative Commons License