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

Lookup NU author(s): Dr Peter Leary, Professor Neil Gray

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This work is licensed under a Creative Commons Attribution 4.0 International License (CC BY 4.0).


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.


Publication metadata

Author(s): Fuller AJ, Leary P, Gray ND, Davies HS, Mosselmans JFW, Cox F, Robinson CH, Pittman JK, McCann CM, Muir M, Graham MC, Utsunomiya S, Bower WR, Morris K, Shaw S, Bots P, Livens FR, Law GTW

Publication type: Article

Publication status: Published

Journal: Chemosphere

Year: 2020

Volume: 254

Print publication date: 01/09/2020

Online publication date: 28/04/2020

Acceptance date: 19/04/2020

Date deposited: 30/04/2020

ISSN (print): 0045-6535

Publisher: Elsevier

URL: https://doi.org/10.1016/j.chemosphere.2020.126859

DOI: 10.1016/j.chemosphere.2020.126859


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