Organic Complexation of U(VI) in Reducing Soils at a Natural Analogue Site : Implications for Uranium Transport

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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 & Law , G T W 2020 , ' Organic Complexation of U(VI) in Reducing Soils at a Natural Analogue Site : Implications for Uranium Transport ' , Chemosphere , vol. 254 , 126859 . https://doi.org/10.1016/j.chemosphere.2020.126859

Title: Organic Complexation of U(VI) in Reducing Soils at a Natural Analogue Site : Implications for Uranium Transport
Author: Fuller, Adam J.; Leary, Peter; Gray, Neil D.; Davies, Helena S.; Mosselmans, J. Frederick W.; Cox, Filipa; Robinson, Clare H.; Pittman, Jon K.; McCann, Clare M.; Muir, Michael; Graham, Margaret C.; Utsunomiya, Satoshi; Bower, William R.; Morris, Katherine; Shaw, Samuel; Bots, Pieter; Livens, Francis R.; Law, Gareth T. W.
Contributor: University of Helsinki, Department of Chemistry
University of Helsinki, Department of Chemistry
Date: 2020-09
Language: eng
Number of pages: 9
Belongs to series: Chemosphere
ISSN: 0045-6535
URI: http://hdl.handle.net/10138/316931
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.
Subject: 116 Chemical sciences
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