Role for Fe(III) Minerals in Nitrate-Dependent Microbial U(IV) Oxidation

Senko, John M.; Mohamed, Y.; Dewers, Thomas; Krumholz, Lee R.

doi:10.1021/es048906i

Cited by 116 publications

(133 citation statements)

References 74 publications

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“…As noted above, ferrihydrite may either compete as an electron acceptor in microbial respiration or may act as an oxidant of biogenic UO 2 . A series of recent reports indicate reoxidation of uraninite by Fe(III) at high concentrations of HCO 3 -resulting from bacterial respiration (Sani et al, 2005;Senko et al, 2005;. However, under the conditions of our study (HCO 3 -< 6 mM, 0.168 U(VI), and pH 7), even the oxidation of biogenic UO 2 to Ca 2 UO 2 (CO 3 ) 3 by ferrihydrite, the most viable reaction, would be thermodynamically favorable only at Fe(II) concentrations less than 0.025 mM Fe(II) during the initial stages of reduction and 0.050 mM at late stages.…”

Section: Impact Of Fe(iii) (Hydr)oxides On U(vi) Reductionmentioning

confidence: 99%

Influence of Uranyl Speciation and Iron Oxides on Uranium Biogeochemical Redox Reactions

Stewart

Amos

Nico

et al. 2011

Geomicrobiology Journal

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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 2 2+ and associated species) may be reduced, directly or indirectly, by microorganisms to U(IV) with subsequent precipitation of UO 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, 2 specifically the formation of uranyl-calcium-carbonato complexes, and ferrihydrite on the rate and extent of uranium reduction in complex geochemical systems.3

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Section: Impact Of Fe(iii) (Hydr)oxides On U(vi) Reductionmentioning

confidence: 99%

Influence of Uranyl Speciation and Iron Oxides on Uranium Biogeochemical Redox Reactions

Stewart

Amos

Nico

et al. 2011

Geomicrobiology Journal

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“…In contrast to A. ferrooxidans, Fe(III) reducing Geobacter metallireducens, nitrate reducing Klebsiella sp., and sulfur oxidizing nitrate reducing Thiobacillus denitrificans enzymatically oxidize U(IV) at a near neutral pH under anaerobic conditions (Finneran et al, 2002b;Beller, 2005;Senko et al, 2005a). The enzymatic U(IV) oxidation is coupled to nitrate reduction and is not linked to energy conservation required for cell growth.…”

Section: Direct Enzymatic Control Of the Redox Transformations Of Umentioning

confidence: 99%

Geomicrobiological factors that control uranium mobility in the environment: Update on recent advances in the bioremediation of uranium-contaminated sites

Suzuki

Suko

2006

Journal of Mineralogical and Petrological Sciences

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Understanding the behavior of uranium (U) in the environment is essential not only for the protection of aquifers from U contamination but also for predicting the fate of U and other actinides disposed of in deep geological settings. It has long been believed that the redox chemistry of U can be simply predicted by thermodynamics and that the development of a low redox potential is a sufficient condition for U reduction. However, recent studies have demonstrated that redox transformations of U are controlled by kinetic factors that are strongly influenced by microbial activity. Although abiological U oxidation proceeds efficiently under oxygenic conditions, abiological reduction of U is inhibited by the formation of negatively charged U(VI) CO 3 complexes that prevail in nature. Phylogenetically diverse microorganisms are capable of enzymatically reducing U(VI) CO 3 complexes to form U(IV) bearing minerals such as uraninite (UO 2+x . This complex is mainly produced by the microbial reduction of Fe(III) in natural systems. Thus, U(VI) reduction is controlled both directly and indirectly, at least in part, by microbial activity. Several mechanisms of U oxidation under anoxic conditions have been revealed recently by laboratory and field studies. U(IV) is abiologically oxidized by Fe(III) and Mn(IV) oxides. Microbial reduction of nitrate to molecular nitrogen, which occurs following the depletion of O 2 , produces nitrogen intermediates including nitrite (NO 2 -), nitrous oxide (NO), and nitric oxide (N 2 O). Although the nitrogen intermediates oxidize U(IV), poorly crystalline Fe(III) oxide minerals resulting from the oxidation of aqueous Fe(II) species by the nitrogen intermediates oxidize U(IV) more efficiently than the nitrogen intermediates alone. Remarkably, the formation of Ca U(VI) CO 3 complexes resulting from increased levels of Ca 2+ and/or HCO 3 -leads to the reoxidation of bioreduced U(IV) under reducing conditions. These geomicrobiological factors pose challenges in manipulating and/or predicting the mobility and fate of U in complex and heterogeneous environmental settings.

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“…In its oxidized form, Tc is present as pertechnetate (Tc(VII)O 4 contaminant at nuclear sites (Fredrickson et al, 2004;Morris et al, 2000;Skomurski et al, 2010;Standring et al, 2002). By contrast, under reducing conditions, poorly soluble Tc(IV) species dominate, with hydrous TcO 2 -like precipitates forming at concentrations greater thañ 5610 À9 mol l À1 (Meyer et al, 1991), Tc(IV) sorption and retention to sediments observed at very low concentrations (<10 À12 mol l…”

Section: Introductionmentioning

confidence: 99%

“…Reoxidation of immobilized radionuclides in contaminated aquifers could occur via transport of oxygenated waters through the sediments, water table fluctuations, or disturbance of the geosphere by construction or erosion (Burke et al, 2006;Wu et al, 2007). Furthermore, reoxidation caused by nitrate, a common pollutant found at nuclear facilities, is also a potential route to radionuclide reoxidation via, for example, biologically mediated Fe(II)-oxidation coupled to NO 3 À reduction (Burke et al, 2006;Geissler et al, 2011;Morris et al, 2008;Senko et al, 2005;Wu et al, 2010;Law et al, 2010b;Law et al, 2011). Recent experimental work on sediments suggests that Tc associated with Fe(II)-bearing sediments is recalcitrant to reoxidation even though significant reoxidation of Fe(II) to Fe(III) occurs during both air and nitrate reoxidation (Burke et al, 2006;Fredrickson et al, 2009;Geissler et al, in press;Jaisi et al, 2009 .…”

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confidence: 99%

Redox interactions of technetium with iron-bearing minerals

et al. 2011

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AbstractIron minerals influence the environmental redox behaviour and mobility of metals including the long-lived radionuclide technetium. Technetium is highly mobile in its oxidized form pertechnetate (Tc(VII)O4–), however, when it is reduced to Tc(IV) it immobilizes readily via precipitation or sorption. In low concentration tracer experiments, and in higher concentration XAS experiments, pertechnetate was added to samples of biogenic and abiotically synthesized Fe(II)-bearing minerals (bio-magnetite, bio-vivianite, bio-siderite and an abiotically precipitated Fe(II) gel). Each mineral scavenged different quantities of Tc(VII) from solution with essentially complete removal in Fe(II)-gel and bio-magnetite systems and with 84±4% removal onto bio-siderite and 68±5% removal onto bio-vivianite over 45 days. In select, higher concentration, Tc XAS experiments, XANES spectra showed reductive precipitation to Tc(IV) in all samples. Furthermore, EXAFS spectra for bio-siderite, bio-vivianite and Fe(II)-gel showed that Tc(IV) was present as short range ordered hydrous Tc(IV)O2-like phases in the minerals and for some systems suggested possible incorporation in an octahedral coordination environment. Low concentration reoxidation experiments with air-, and in the case of the Fe(II) gel, nitrate-oxidation of the Tc(IV)-labelled samples resulted in only partial remobilization of Tc. Upon exposure to air, the Tc bound to the Fe-minerals was resistant to oxidative remobilization with a maximum of ∼15% Tc remobilized in the bio-vivianite system after 45 days of air exposure. Nitrate mediated oxidation of Fe(II)-gel inoculated with a stable consortium of nitrate-reducing, Fe(II)-oxidizing bacteria showed only 3.8±0.4% remobilization of reduced Tc(IV), again highlighting the recalcitrance of Tc(IV) to oxidative remobilization in Fe-bearing systems. The resultant XANES spectra of the reoxidized minerals showed Tc(IV)-like spectra in the reoxidized Fe-phases. Overall, this study highlights the role that Fe-bearing biogenic mineral phases have in controlling reductive scavenging of Tc(VII) to hydrous TcO2-like phases onto a range of Fe(II)-bearing minerals. In addition, it suggests that on reoxidation of these phases, Fe-bound Tc(IV) may be octahedrally coordinated and is largely recalcitrant to reoxidation over medium-term timescales. This has implications when considering remediation approaches and in predictions of the long-term fate of Tc in the nuclear legacy.

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Role for Fe(III) Minerals in Nitrate-Dependent Microbial U(IV) Oxidation

Cited by 116 publications

References 74 publications

Influence of Uranyl Speciation and Iron Oxides on Uranium Biogeochemical Redox Reactions

Influence of Uranyl Speciation and Iron Oxides on Uranium Biogeochemical Redox Reactions

Geomicrobiological factors that control uranium mobility in the environment: Update on recent advances in the bioremediation of uranium-contaminated sites

Redox interactions of technetium with iron-bearing minerals

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