Characterization of uranium redox state in organic-rich Eocene sediments

Cumberland, S. A., Etschmann, B., Brugger, J., Douglas, G., Evans, K., Fisher, L., Kappen, P. and Moreau, J. W. (2018) Characterization of uranium redox state in organic-rich Eocene sediments. Chemosphere, 194, pp. 602-613. (doi: 10.1016/j.chemosphere.2017.12.012) (PMID:29241135)

Abstract

The presence of organic matter (OM) has a profound impact on uranium (U) redox cycling, either limiting or promoting the mobility of U via binding, reduction, or complexation. To understand the interactions between OM and U, we characterised U oxidation state and speciation in nine OM-rich sediment cores (18 samples), plus a lignite sample from the Mulga Rock polymetallic deposit in Western Australia. Uranium was unevenly dispersed within the analysed samples with 84% of the total U occurring in samples containing >21 wt % OM. Analyses of U speciation, including x-ray absorption spectroscopy and bicarbonate extractions, revealed that U existed predominately (∼71%) as U(VI), despite the low pH (4.5) and nominally reducing conditions within the sediments. Furthermore, low extractability by water, but high extractability by a bi-carbonate solution, indicated a strong association of U with particulate OM. The unexpectedly high proportion of U(VI) relative to U(IV) within the OM-rich sediments implies that OM itself does not readily reduce U, and the reduction of U is not a requirement for immobilizing uranium in OM-rich deposits. The fact that OM can play a significant role in limiting the mobility and reduction of U(VI) in sediments is important for both U-mining and remediation.

• Item Type: Articles
• Status: Published
• Refereed: Yes
• Glasgow Author(s) Enlighten ID: Moreau, Dr John
• Authors: Cumberland, S. A., Etschmann, B., Brugger, J., Douglas, G., Evans, K., Fisher, L., Kappen, P., and Moreau, J. W.
• College/School: College of Science and Engineering > School of Geographical and Earth Sciences > Earth Sciences
• Journal Name: Chemosphere
• Publisher: Elsevier
• ISSN: 0045-6535
• ISSN (Online): 1879-1298
• Published Online: 05 December 2017