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Title: Influence of uranyl speciation and iron oxides on uranium biogeochemical redox reactions

Abstract

Uranium is a pollutant of concern to both human and ecosystem health. Uranium's redox state often dictates its partitioning between the aqueous- and solid-phases, and thus controls its dissolved concentration and, coupled with groundwater flow, its migration within the environment. In anaerobic environments, the more oxidized and mobile form of uranium (UO{sub 2}{sup 2+} and associated species) may be reduced, directly or indirectly, by microorganisms to U(IV) with subsequent precipitation of UO{sub 2}. However, various factors within soils and sediments may limit biological reduction of U(VI), inclusive of alterations in U(VI) speciation and competitive electron acceptors. Here we elucidate the impact of U(VI) speciation on the extent and rate of reduction with specific emphasis on speciation changes induced by dissolved Ca, and we examine the impact of Fe(III) (hydr)oxides (ferrihydrite, goethite and hematite) varying in free energies of formation on U reduction. The amount of uranium removed from solution during 100 h of incubation with S. putrefaciens was 77% with no Ca or ferrihydrite present but only 24% (with ferrihydrite) and 14% (no ferrihydrite) were removed for systems with 0.8 mM Ca. Imparting an important criterion on uranium reduction, goethite and hematite decrease the dissolved concentration of calcium through adsorptionmore » and thus tend to diminish the effect of calcium on uranium reduction. Dissimilatory reduction of Fe(III) and U(VI) can proceed through different enzyme pathways, even within a single organism, thus providing a potential second means by which Fe(III) bearing minerals may impact U(VI) reduction. We quantify rate coefficients for simultaneous dissimilatory reduction of Fe(III) and U(VI) in systems varying in Ca concentration (0 to 0.8 mM), and using a mathematical construct implemented with the reactive transport code MIN3P, we reveal the predominant influence of uranyl speciation, specifically the formation of uranyl-calcium-carbonato complexes, and ferrihydrite on the rate and extent of uranium reduction in complex geochemical systems.« less

Authors:
; ; ;
Publication Date:
Research Org.:
Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)
Sponsoring Org.:
Earth Sciences Division
OSTI Identifier:
993851
Report Number(s):
LBNL-3549E
Journal ID: ISSN 0149-0451; GEJODG; TRN: US201024%%170
DOE Contract Number:  
DE-AC02-05CH11231
Resource Type:
Journal Article
Journal Name:
Geomicrobiology Journal
Additional Journal Information:
Related Information: Journal Publication Date: 2010; Journal ID: ISSN 0149-0451
Country of Publication:
United States
Language:
English
Subject:
54; 58; ADSORPTION; BINDING ENERGY; CALCIUM; ECOSYSTEMS; ELECTRONS; ENZYMES; GOETHITE; HEMATITE; INCUBATION; IRON OXIDES; MICROORGANISMS; POLLUTANTS; PRECIPITATION; REDOX REACTIONS; SEDIMENTS; SOILS; URANIUM; URANIUM 228; VALENCE

Citation Formats

Stewart, B D, Amos, R T, Nico, P S, and Fendorf, S. Influence of uranyl speciation and iron oxides on uranium biogeochemical redox reactions. United States: N. p., 2010. Web.
Stewart, B D, Amos, R T, Nico, P S, & Fendorf, S. Influence of uranyl speciation and iron oxides on uranium biogeochemical redox reactions. United States.
Stewart, B D, Amos, R T, Nico, P S, and Fendorf, S. 2010. "Influence of uranyl speciation and iron oxides on uranium biogeochemical redox reactions". United States. https://www.osti.gov/servlets/purl/993851.
@article{osti_993851,
title = {Influence of uranyl speciation and iron oxides on uranium biogeochemical redox reactions},
author = {Stewart, B D and Amos, R T and Nico, P S and Fendorf, S},
abstractNote = {Uranium is a pollutant of concern to both human and ecosystem health. Uranium's redox state often dictates its partitioning between the aqueous- and solid-phases, and thus controls its dissolved concentration and, coupled with groundwater flow, its migration within the environment. In anaerobic environments, the more oxidized and mobile form of uranium (UO{sub 2}{sup 2+} and associated species) may be reduced, directly or indirectly, by microorganisms to U(IV) with subsequent precipitation of UO{sub 2}. However, various factors within soils and sediments may limit biological reduction of U(VI), inclusive of alterations in U(VI) speciation and competitive electron acceptors. Here we elucidate the impact of U(VI) speciation on the extent and rate of reduction with specific emphasis on speciation changes induced by dissolved Ca, and we examine the impact of Fe(III) (hydr)oxides (ferrihydrite, goethite and hematite) varying in free energies of formation on U reduction. The amount of uranium removed from solution during 100 h of incubation with S. putrefaciens was 77% with no Ca or ferrihydrite present but only 24% (with ferrihydrite) and 14% (no ferrihydrite) were removed for systems with 0.8 mM Ca. Imparting an important criterion on uranium reduction, goethite and hematite decrease the dissolved concentration of calcium through adsorption and thus tend to diminish the effect of calcium on uranium reduction. Dissimilatory reduction of Fe(III) and U(VI) can proceed through different enzyme pathways, even within a single organism, thus providing a potential second means by which Fe(III) bearing minerals may impact U(VI) reduction. We quantify rate coefficients for simultaneous dissimilatory reduction of Fe(III) and U(VI) in systems varying in Ca concentration (0 to 0.8 mM), and using a mathematical construct implemented with the reactive transport code MIN3P, we reveal the predominant influence of uranyl speciation, specifically the formation of uranyl-calcium-carbonato complexes, and ferrihydrite on the rate and extent of uranium reduction in complex geochemical systems.},
doi = {},
url = {https://www.osti.gov/biblio/993851}, journal = {Geomicrobiology Journal},
issn = {0149-0451},
number = ,
volume = ,
place = {United States},
year = {Mon Mar 15 00:00:00 EDT 2010},
month = {Mon Mar 15 00:00:00 EDT 2010}
}