Reduction of U(VI) to U(IV) on the surface of magnetite

Scott, Thomas Bligh; Allen, GC; Heard, Peter J; Randell, MG

doi:10.1016/j.gca.2005.07.003

Cited by 238 publications

(170 citation statements)

References 25 publications

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“…Aqueous uranium, commonly found as the UO 2 2+ uranyl ion, can form hydroxide and water complexes which have been shown to sorb strongly to Fe 3+ -oxide surfaces, including magnetite [49,50]. Magnetite (Fe 3 O 4 ) is an interesting mineral to consider as it is a common corrosion product of steel, formed during anoxic water-steel interaction via the following reaction:…”

Section: U-incorporation Into Fe-oxide Minerals *mentioning

confidence: 99%

Quantum-Mechanical Methods for Quantifying Incorporation of Contaminants in Proximal Minerals

et al. 2014

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Abstract:Incorporation reactions play an important role in dictating immobilization and release pathways for chemical species in low-temperature geologic environments. Quantum-mechanical investigations of incorporation seek to characterize the stability and geometry of incorporated structures, as well as the thermodynamics and kinetics of the reactions themselves. For a thermodynamic treatment of incorporation reactions, a source of the incorporated ion and a sink for the released ion is necessary. These sources/sinks in a real geochemical system can be solids, but more commonly, they are charged aqueous species. In this contribution, we review the current methods for ab initio calculations of incorporation reactions, many of which do not consider incorporation from aqueous species. We detail a recently-developed approach for the calculation of incorporation reactions and expand on the part that is modeling the interaction of periodic solids with aqueous source and sink phases and present new research using this approach. To model these interactions, a systematic series of calculations must be done to transform periodic solid source and sink phases to aqueous-phase clusters. Examples of this process are provided for three case studies: (1) neptunyl incorporation into studtite and boltwoodite: for the layered boltwoodite, the incorporation energies are smaller (more favorable) for reactions using environmentally relevant source and sink phases (i.e., ΔE rxn (oxides) > ΔE rxn (silicates) > ΔE rxn (aqueous)). Estimates of the solid-solution behavior of Np to predict the limit of Np-incorporation into boltwoodite (172 and 768 ppm at 300 °C, respectively); (2) uranyl and neptunyl incorporation into carbonates and sulfates: for both carbonates and sulfates, it was found that actinyl incorporation into a defect site is more favorable than incorporation into defect-free periodic structures. In addition, actinyl incorporation into carbonates with aragonite structure is more favorable than into carbonates with calcite structure; and (3)

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Section: U-incorporation Into Fe-oxide Minerals *mentioning

confidence: 99%

Quantum-Mechanical Methods for Quantifying Incorporation of Contaminants in Proximal Minerals

et al. 2014

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“…Magnetite has been applied in the adsorption of various heavy metals, e.g., Cr(VI) [27], Hg(II) [28], As(V) [25], Sb(V) [29], Se(IV) [30] and U(VI) [31]. The adsorption mechanism includes surface site binding [32], electrostatic interaction [33], modified ligand combination [34] and oxidation-reduction interaction [35,36]. Some substitutions have made obvious variations on the physicochemical properties of magnetite surface [26,37].…”

Section: Introductionmentioning

confidence: 99%

The distinct effects of Mn substitution on the reactivity of magnetite in heterogeneous Fenton reaction and Pb(II) adsorption

Liang

Zhu

Wei

et al. 2014

Journal of Colloid and Interface Science

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“…Magnetite formation has also been reported during biooxidation of Fe(II) coupled to denitrification (Chaudhuri et al, 2001). A number of studies have investigated the role of magnetite in uranium reduction and the findings varied greatly ranging from no observable reduction (Dodge et al, 2002) to clear evidence of reduction (Scott et al, 2005;Aamrani et al, 2007;O'Loughlin et al, 2010) to the formation of a mixed-valence U(IV)-U(VI) phase (Missana et al, 2003;Aamrani et al, 2007;Regenspurg et al, 2009) or the formation of U(V) (Ilton et al, 2010). The variation in findings is presumably linked to variability in morphology, specific surface area and phase stoichiometry Scherer, 2009, Gorski et al, 2010) of the magnetite used as well as differences in experimental conditions.…”

Section: Introductionmentioning

confidence: 99%

Products of abiotic U(VI) reduction by biogenic magnetite and vivianite

Veeramani

Alessi

Suvorova

et al. 2011

Geochimica et Cosmochimica Acta

138

122

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Reductive immobilization of uranium by the stimulation of dissimilatory metal-reducing bacteria (DMRB) has been investigated as a remediation strategy for subsurface U(VI) contamination. In those environments, DMRB may utilize a variety of electron acceptors, such as ferric iron which can lead to the formation of reactive biogenic Fe(II) phases. These biogenic phases could potentially mediate abiotic U(VI) reduction. In this work, the DMRB Shewanella putrefaciens strain CN32 was used to synthesize two biogenic Fe(II)-bearing minerals: magnetite (a mixed Fe(II)-Fe(III) oxide) and vivianite (an Fe(II)-phosphate). Analysis of abiotic redox interactions between these biogenic minerals and U(VI) showed that both biogenic minerals reduced U(VI) completely. XAS analysis indicates significant differences in speciation of the reduced uranium after reaction with the two biogenic Fe(II)-bearing minerals. While biogenic magnetite favored the formation of structurally ordered, crystalline UO 2 , biogenic vivianite led to the formation of a monomeric U(IV) species lacking U-U associations in the corresponding EXAFS spectrum. To investigate the role of phosphate in the formation of monomeric U(IV) such as sorbed U(IV) species complexed by mineral surfaces, versus a U(IV) mineral, uranium was reduced by biogenic magnetite that was pre-sorbed with phosphate. XAS analysis of this sample also revealed the formation of monomeric U(IV) species suggesting that the presence of phosphate hinders formation of UO 2 . This work shows that U(VI) reduction products formed during in situ biostimulation can be influenced by the mineralogical and geochemical composition of the surrounding environment, as well as by the interfacial solute-solid chemistry of the solid-phase reductant.

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Reduction of U(VI) to U(IV) on the surface of magnetite

Cited by 238 publications

References 25 publications

Quantum-Mechanical Methods for Quantifying Incorporation of Contaminants in Proximal Minerals

Quantum-Mechanical Methods for Quantifying Incorporation of Contaminants in Proximal Minerals

The distinct effects of Mn substitution on the reactivity of magnetite in heterogeneous Fenton reaction and Pb(II) adsorption

Products of abiotic U(VI) reduction by biogenic magnetite and vivianite

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