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

Daniel Scott Alessi, Rizlan Bernier-Latmani, Elena Suvorova Buffat, Harish Veeramani
Elsevier, 2010
Conference paper

Abstract

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 UO2, 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 UO2. 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. (C) 2011 Elsevier Ltd. All rights reserved.

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Daniel Scott Alessi, Rizlan Bernier-Latmani, Elena Suvorova Buffat, Harish Veeramani
Elsevier, 2010
Conference paper

Abstract

Official source

https://infoscience.epfl.ch/record/149738?ln=en

About this result

Related concepts (18)

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

Daniel Scott Alessi, Rizlan Bernier-Latmani, Jonathan Sharp, Elena Suvorova Buffat, Harish Veeramani

Elsevier2011

The product of microbial uranium reduction includes multiple species with U(IV)-phosphate coordination

Daniel Scott Alessi, Rizlan Bernier-Latmani

Until recently, the reduction of U(VI) to U(IV) during bioremediation was assumed to produce solely the sparingly soluble mineral uraninite, UO2(s). However, results from several laboratories reveal other species of U(IV) characterized by the absence of an EXAFS U-U pair correlation (referred to here as noncrystalline U(IV)). Because it lacks the crystalline structure of uraninite, this species is likely to be more labile and susceptible to reoxidation. In the case of single species cultures, analyses of U extended X-ray fine structure (EXAFS) spectra have previously suggested U(IV) coordination to carboxyl, phosphoryl or carbonate groups. In spite of this evidence, little is understood about the species that make up noncrystalline U(IV), their structural chemistry and the nature of the U(IV)-ligand interactions. Here, we use infrared spectroscopy (IR), uranium L-III-edge X-ray absorption spectroscopy (XAS), and phosphorus K-edge XAS analyses to constrain the binding environments of phosphate and uranium associated with Shewanella oneidensis MR-1 bacterial cells. Systems tested as a function of pH included: cells under metal-reducing conditions without uranium, cells under reducing conditions that produced primarily uraninite, and cells under reducing conditions that produced primarily biomass-associated noncrystalline U(IV). P X-ray absorption near-edge structure (XANES) results provided clear and direct evidence of U(IV) coordination to phosphate. Infrared (IR) spectroscopy revealed a pronounced perturbation of phosphate functional groups in the presence of uranium. Analysis of these data provides evidence that U(IV) is coordinated to a range of phosphate species, including monomers and polymerized networks. U EXAFS analyses and a chemical extraction measurements support these conclusions. The results of this study provide new insights into the binding mechanisms of biomass-associated U(IV) species which in turn sheds light on the mechanisms of biological U(VI) reduction. (C) 2014 Elsevier Ltd. All rights reserved.

Elsevier2014

Decades of uranium (U) mining, milling and military use left a legacy of U contamination around the world. The radioactivity and chemical toxicity of U at contaminated sites pose an acute and long-term hazard to human health and the surrounding environment. In order to diminish the risk, in situ bioremediation methods, which contribute to contaminant immobilization, are proposed. Nevertheless, the reported prevalent formation of labile and non-crystalline U(IV) species as a result of microbial U(VI) reduction, in contrast to more stable and crystalline uraninite, undermines the effectiveness of the applied bioremediation. Therefore, a holistic understanding of the controls and mechanisms that govern the formation of non-crystalline U(IV) in the environment is at the core of this thesis. Presence of common groundwater solutes (sulfate, silicate and phosphate) were shown to induce the production of bacterial extracellular polymeric substances (biofilm matrix components), which in turn increases the formation of non-crystalline U(IV) as a result of microbial U reduction. In contrast, a field study suggested that non-crystalline U(IV) was a product of abiotic U reduction followed by the sequestration of U(IV) ions by the biofilm matrix. Those contrasting theories, motivated us to look for an indicator capable of differentiating between biotic and abiotic U reduction in the environment. Uranium isotope fractionation proved to be an excellent tool. Based on our results, the isotopic signature of biotic U reduction (accumulation of 238U in the reduced phase) is easily distinguishable from the abiotic U reduction signature (either no isotopic fractionation or fractionation in the opposite direction). When contrasted with U isotope signatures recorded in the sediments, the findings of this study indicated that biological activity contributed to the formation of many ancient and modern U(IV) deposits. Equipped with a tool capable of assessing the origin of the U(IV) product, and with an understanding of the relationship between the biofilm matrix and the formation of non-crystalline U(IV), we embarked on a project to validate the mechanism responsible for non-crystalline U(IV) formation in the subsurface. Results show that regardless whether U is reduced enzymatically or though abiotic agents, the formed U(IV) species are always non-crystalline if the biofilm matrix is present. However, according to our experiments, biological U reduction resulted in better immobilization and overall reduction of U. The mechanism of U reduction in our systems was shown to be controlled by U speciation, which in turn, is govern by the presence of bicarbonate. Under low carbonate concentrations, the majority of U(VI) adsorbs onto the mineral phase thus promoting abiotic U reduction mediated by redox active minerals. However, at higher carbonate concentrations, most of U(VI) is present as aqueous U(VI)-carbonate complexes precluding sorption and thus allowing for enhanced enzymatic U reduction. The results obtained here shed light on the processes occurring at U-contaminated sites and have several field implications. The effectiveness of applied bioremediation was shown to depend on the geochemical conditions at the field site. However, the injection of bicarbonate during in situ clean-up operation enhances microbial U reduction and by this, the overall reductive immobilization of U.

EPFL2015

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

Daniel Scott Alessi, Rizlan Bernier-Latmani, Jonathan Sharp, Elena Suvorova Buffat, Harish Veeramani

Elsevier2011

The product of microbial uranium reduction includes multiple species with U(IV)-phosphate coordination

Daniel Scott Alessi, Rizlan Bernier-Latmani

Elsevier2014

EPFL2015