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Biogenic sulfidation of U(VI) and ferrihydrite mediated by sulfate-reducing bacteria at elevated pH

DOI: 10.1021/acsearthspacechem.1c00126 DOI Help

Authors: Luke T. Townsend (The University of Manchester) , Gina Kuippers (The University of Manchester) , Jonathan R. Lloyd (The University of Manchester) , Louise S. Natrajan (The University of Manchester) , Christopher Boothman (The University of Manchester) , J. Frederick W. Mosselmans (Diamond Light Source) , Samuel Shaw (The University of Manchester) , Katherine Morris (University of Manchester)
Co-authored by industrial partner: No

Type: Journal Paper
Journal: Acs Earth And Space Chemistry , VOL 2

State: Published (Approved)
Published: October 2021
Diamond Proposal Number(s): 17243

Open Access Open Access

Abstract: Globally, the need for radioactive waste disposal and contaminated land management is clear. Here, gaining an improved understanding of how biogeochemical processes, such as Fe(III) and sulfate reduction, may control the environmental mobility of radionuclides is important. Uranium (U), typically the most abundant radionuclide by mass in radioactive wastes and contaminated land scenarios, may have its environmental mobility impacted by biogeochemical processes within the subsurface. This study investigated the fate of U(VI) in an alkaline (pH ∼9.6) sulfate-reducing enrichment culture obtained from a high-pH environment. To explore the mobility of U(VI) under alkaline conditions where iron minerals are ubiquitous, a range of conditions were tested, including high (30 mM) and low (1 mM) carbonate concentrations and the presence and absence of Fe(III). At high carbonate concentrations, the pH was buffered to approximately pH 9.6, which delayed the onset of sulfate reduction and meant that the reduction of U(VI)(aq) to poorly soluble U(IV)(s) was slowed. Low carbonate conditions allowed microbial sulfate reduction to proceed and caused the pH to fall to ∼7.5. This drop in pH was likely due to the presence of volatile fatty acids from the microbial respiration of gluconate. Here, aqueous sulfide accumulated and U was removed from solution as a mixture of U(IV) and U(VI) phosphate species. In addition, sulfate-reducing bacteria, such as Desulfosporosinus species, were enriched during development of sulfate-reducing conditions. Results highlight the impact of carbonate concentrations on U speciation and solubility in alkaline conditions, informing intermediate-level radioactive waste disposal and radioactively contaminated land management.

Journal Keywords: Redox reactions; Phosphates; Inorganic carbon compounds; Wastes; Anions

Subject Areas: Materials, Chemistry, Environment

Instruments: B18-Core EXAFS

Added On: 25/10/2021 08:50


Discipline Tags:

Inorganic Chemistry Earth Sciences & Environment Geology Desertification & Pollution Nuclear Waste Materials Science Radioactive Materials Chemistry Geochemistry

Technical Tags:

Spectroscopy X-ray Absorption Spectroscopy (XAS)