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| Titel |
Products of abiotic U(VI) reduction by biogenic Fe(II)-bearing minerals |
| VerfasserIn |
Harish Veeramani, Daniel Alessi, Elena Suvorova, Juan Lezama-Pacheco, Joanne Stubbs, Jonathan Sharp, Urs Dippon, Andreas Kappler, John Bargar, Rizlan Bernier-Latmani |
| Konferenz |
EGU General Assembly 2011
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 13 (2011) |
| Datensatznummer |
250046078
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| Zusammenfassung |
| Uranium is a subsurface pollutant of concern in the US, former East Germany and many
other countries worldwide. In the US, the inventory includes an estimated 475 billion gallons
of contaminated ground water and 75 million cubic meters of contaminated sediments. In
former Eastern Germany, an estimated 100 million tons of uranium-mined material was
reportedly disposed improperly. The need for site remediation is urgent and the scale of the
problem, enormous.
Reductive immobilization of hexavalent uranium [U(VI)] to uraninite (UO2) by
stimulation of indigenous dissimilatory metal-reducing bacteria (DMRB) has been
extensively investigated as a remediation strategy for subsurface U(VI) contamination. These
bacteria gain energy by reducing oxidized metals as terminal electron acceptors, often using
organic electron donors. Thus, when evaluating the potential for in situ uranium remediation,
it is important to understand how the presence of competitive electron acceptors
and corresponding biogenic products affect U(VI) remediation and the long term
reactivity of reduced uranium. Iron, an abundant metal in the subsurface, represents a
substantial sink for electrons from DMRB and the reduction of Fe(III) leads to the
formation of biogenic Fe(II) phases. Indirect abiotic U(VI) reduction by reactive
forms of biogenic Fe(II) minerals is a potentially important process for uranium
immobilization. The DMRB Shewanella putrefaciens CN32 was used to synthesize two
biogenic Fe(II) minerals: magnetite and vivianite. The present work elucidates abiotic
molecular scale redox reactions between biogenic magnetite, vivianite and uranium.
While both biogenic magnetite and vivianite reduced U(VI) completely, X-ray
absorption spectroscopy (XAS) analysis indicated dramatic differences in speciation of
the reduced uranium phase in each case. Biogenic magnetite favored formation of
structurally ordered crystalline UO2 and biogenic vivianite led to the formation of a
U(IV)-sorption complex even though UO2 has generally been considered to be the sole end
product of U(VI) reduction. Biogenic magnetite treated with phosphate also reduced
U(VI) to a U(IV)-sorption complex indicating the interference of phosphates in UO2
formation.
The U(IV)-sorption complex could be potentially more labile than UO2 in sub-oxic
environments and thus may affect the long-term stability of reduced uranium species post
remediation. This observation suggests a new paradigm for U(VI) reduction, one in which the
speciation of reduced uranium is dependent on the bulk mineralogical composition in the
surrounding environment. |
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