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Title: Transformation of uranium under Fe(III)-reducing conditions: Reduction of U(VI) by biogenic green rust

Authors:
; ;
Publication Date:
Research Org.:
University of Iowa, Iowa City, IA
Sponsoring Org.:
USDOE Office of Science (SC)
OSTI Identifier:
894287
Report Number(s):
CONF-ERSP2006-12
Resource Type:
Conference
Resource Relation:
Conference: Annual Environmental Remediation Sciences Program PI Meeting, April 3-5, 2006, Warrenton, VA
Country of Publication:
United States
Language:
English
Subject:
59 BASIC BIOLOGICAL SCIENCES; 54 ENVIRONMENTAL SCIENCES

Citation Formats

O'Loughlin, Edward, Kemner, Kenneth M., and Scherer, Michelle M. Transformation of uranium under Fe(III)-reducing conditions: Reduction of U(VI) by biogenic green rust. United States: N. p., 2006. Web.
O'Loughlin, Edward, Kemner, Kenneth M., & Scherer, Michelle M. Transformation of uranium under Fe(III)-reducing conditions: Reduction of U(VI) by biogenic green rust. United States.
O'Loughlin, Edward, Kemner, Kenneth M., and Scherer, Michelle M. Tue . "Transformation of uranium under Fe(III)-reducing conditions: Reduction of U(VI) by biogenic green rust". United States. doi:. https://www.osti.gov/servlets/purl/894287.
@article{osti_894287,
title = {Transformation of uranium under Fe(III)-reducing conditions: Reduction of U(VI) by biogenic green rust},
author = {O'Loughlin, Edward and Kemner, Kenneth M. and Scherer, Michelle M.},
abstractNote = {},
doi = {},
journal = {},
number = ,
volume = ,
place = {United States},
year = {Tue Apr 04 00:00:00 EDT 2006},
month = {Tue Apr 04 00:00:00 EDT 2006}
}

Conference:
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  • The research we are proposing addresses fundamental aspects of the effects of coupled biotic and abiotic processes on U speciation in subsurface environments where Fe redox cycling is significant. The long-term objective of this research is to evaluate whether reduction of U{sup VI} by biogenic GRs is a significant immobilization mechanism in subsurface environments. Our preliminary experiments have shown that biogenic GRs can reduce U{sup VI} to U{sup IV}; however, little is known about how biogeochemical conditions (such as pH, U concentration, carbonate concentration, and the presence of cocontaminants) and GR composition affect the rate and products of U{sup VI}more » reduction by GRs. It is also unclear which biogeochemical conditions favor formation of GR over other non-reactive Fe-bearing biomineralization products from the reduction of Fe{sup III} by DIRB. To address these issues, the following objectives are proposed: (1) Identify the geochemical conditions that favor the formation of biogenic GRs from the reduction of Fe{sup III} oxyhydroxides by DIRB (e.g., Shewanella and Geobacter species). (2) Characterize the chemical composition of biogenic GRs (e.g., Fe{sup II}:Fe{sup III} ratios and interlayer anions) and the effects of compositional variability on the rate and extent of U{sup VI} reduction. (3) Evaluate the effects of variations in geochemical conditions--particularly pH, U concentration, carbonate concentration, the presence of organic ligands, and the presence of reducible co-contaminants--both on the kinetics of U{sup VI} reduction by biogenic GR and on the composition of U-bearing mineral phases. Particular attention will be given to examining geochemical conditions relevant to conditions at DOE field sites. (4) Determine the potential for coupling the reduction of Fe{sup III} by DIRB to the reduction of U{sup VI} via biogenic Fe{sup II} species (including biogenic GRs). The objectives outlined above will be achieved by testing the following hypotheses: (1) The formation of GRs by dissimilatory Fe{sup III} reduction is controlled by Fe{sup III} speciation, solution composition, and microbial physiology. (2) The chemical composition and structural properties of biogenic GRs are variable and depend on the conditions under which they were formed. (3) The rate of U{sup VI} reduction by biogenic GRs varies depending on their chemical composition and structure, particularly with respect to the Fe{sup II}/Fe{sup III} ratio and the nature of the interlayer anions. (4) The rate of U{sup VI} reduction by a given biogenic GR is affected by the solution composition (e.g., pH, uranium concentration, the concentration of carbonate and other ligands, and the presence of other potential oxidants). Moreover, the solution composition affects both the speciation of U{sup VI} and U{sup IV} and the stability of the GR. (5) The reduction of UVI to UIV can be coupled to dissimilatory FeIII reduction under conditions that promote the formation of biogenic GR and other reactive Fe{sup II} species. The results of this research will increase our understanding of the coupling of biotic and abiotic processes with respect to the speciation of U in Fe{sup III}-reducing environments. This information has direct applications to understanding contaminant transport and the development of in situ bioremediation technologies for treatment of subsurface U contamination.« less
  • The recent identification of green rusts (GRs) as products of the reduction of FeIII oxyhydroxides by dissimilatory iron-reducing bacteria, coupled with the ability of synthetic (GR) to reduce UVI species to insoluble UO2, suggests that biogenic green rusts (BioGRs) may play an important role in the speciation (and thus mobility) of U in FeIII-reducing environments. The objective of our research was to examine the potential for BioGR to affect the speciation of U under FeIII-reducing conditions. To meet this objective, we designed and executed a hypothesis-driven experimental program to identify key factors leading to the formation of BioGRs as productsmore » of dissimilatory FeIII reduction, to determine the key factors controlling the reduction of UVI to UIV by GRs, and to identify the resulting U-bearing mineral phases. The results of this research significantly increase our understanding of the coupling of biotic and abiotic processes with respect to the speciation of U in iron-reducing environments. In particular, the reduction of UVI to UIV by BioGR with the subsequent formation of U-bearing mineral phases may be effective for immobilizing U in suboxic subsurface environments. This information has direct applications to contaminant transport modeling and bioremediation engineering for natural or enhanced in situ remediation of subsurface contamination.« less
  • Dissimilatory metal-reducing microorganisms may be useful in processes designed for selective removal of uranium from aqueous streams. These bacteria can use U(VI) as an electron acceptor and thereby reduce soluble U(VI) to insoluble U(IV). While significant research has been devoted to demonstrating and describing the mechanism of dissimilatory metal reduction, the reaction kinetics necessary to apply this for remediation processes have not been adequately defined. In this study, pure culture Shewanella alga strain BrY reduced U(VI) under non-growth conditions in the presence of excess lactate as the electron donor. Initial U(VI) concentrations ranged from 13 to 1,680{micro}M. A maximum specificmore » U(VI) reduction rate of 2.37 {micro}mole-U(VI)/(mg-biomass h) and Monod half-saturation coefficient of 132 {micro}M-U(VI) were calculated from measured U(VI) reduction rates. U(VI) reduction activity was sustained at 60% of this rate for at least 80 h. The initial presence of oxygen at a concentration equal to atmospheric saturation at 22 C delays but does not prevent U(VI) reduction. The rate of U(VI) reduction by BrY is comparable or better than rates reported for other metal reducing species. BrY reduces U(VI) at a rate that is 30% of its Fe(III) reduction rate.« less
  • U(VI) dissolved in a modified lactate-C medium (either sulfate- or lactate-limited) was reacted with a mixture of an Fe(III)-(hydr)oxide mineral (hematite, goethite, or ferrihydrite) and quartz under anoxic conditions and equivalent mineral surface areas. After sorption equilibration, the suspensions were inoculated with a sulfate-reducing bacterium (SRB, Desulfovibrio desulfuricans G20). Inoculation of the suspensions containing sulfate-limited medium yielded significant SRB growth, along with concomitant reduction of sulfate and removal of U(VI) from solution. Inoculation of the suspensions containing lactate-limited medium yielded similar results while lactate was still present. Once the lactate was depleted, however, some of the U that had beenmore » removed from solution was re-solubilized in the hematite treatment and, to a lesser extent, in the goethite treatment. No re-solubilization was observed in the lactate-limited ferrihydrite treatment even after a prolonged incubation of four months. Analysis by U L3-edge XANES spectroscopy of mineral specimens sampled without inoculation yielded a typical U(VI) spectrum. Mineral specimens sampled at the end of the experiment yielded spectra similar to that of uraninite, thus providing strong evidence for SRB-promoted removal of U(VI) from solution by reductive precipitation of uraninite. Consequently, U re-solubilization was attributed to re-oxidation of the uraninite by Fe(III) present in the (hydr)oxide phases. Our results thus suggest that inoculation with SRB mediates reduction of soluble U(VI) to an insoluble U(IV) oxide so long as a suitable electron donor is available. Depletion of the electron donor may result in partial re-oxidation of the U(IV) to soluble U(VI) species when the surfaces of crystalline Fe(III) (hydr)oxides are incompletely reduced by reaction with SRB-generated sulfide.« less