Effect of ligands on the production of oxidants from oxygenation of reduced Fe-bearing clay mineral nontronite

Zeng, Qiang; Dong, Hailiang; Xi, Wang

doi:10.1016/j.gca.2019.02.032

Cited by 72 publications

(103 citation statements)

References 93 publications

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“…Pyrite (FeS 2 ) oxidation also leads to formation of ·OH, with various ligands accelerating the process. Similar results were observed for structural Fe(II) in reduced nonronite. , …”

Section: Introductionsupporting

confidence: 85%

“…Similar results were observed for structural Fe(II) in reduced nonronite. 13,14 Exposure of electrochemically reduced dissolved organic matter (DOM) to oxygen has been shown to yield of 42 to 160 mmol of •OH produced per mole of electrons transferred from the reduced organic matter. 9 For arctic soil waters, both increasing levels of dissolved organic carbon (DOC) and Fe(II) led to larger •OH yields.…”

Section: ■ Introductionmentioning

confidence: 99%

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Determination of Hydroxyl Radical Production from Sulfide Oxidation Relevant to Sulfidic Porewaters

Lombardo

Vindedahl

Arnold

2020

ACS Earth Space Chem.

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Hydroxyl radical (·OH) production from the reaction between aqueous total sulfide ([H2S]T = [H2S] + [HS–] + [S2–]) and dissolved oxygen is potentially an environmentally important reaction when anoxic, sulfidic water is exposed to oxygen. Using hydroxyterephthalate (hTPA) formation from the reaction of terephthalic acid (TPA) with ·OH as a probe for ·OH production, hydrogen peroxide was verified as an essential intermediate, and the production of free ·OH, versus lower energy hydroxylating agents, was established. The optimal conditions for the quantification of ·OH production kinetics and yield were determined by varying TPA and total sulfide concentrations. An initial total sulfide concentration of 10 μM and TPA concentration of 2 mM was used to find a yield of 15 mmol of ·OH per mole [H2S]T. Additionally, a pseudo-first-order model elucidated a maximum rate of production of 1.04 (±0.05) × 10–4 moles of ·OH per hour per mole of [H2S]T. Experiments with sulfidic wetland porewaters containing up to 294 mg/L of dissolved organic carbon (DOC) revealed that [H2S]T, and not reduced DOC, was the dominant source of ·OH. A simple model considering a water containing [H2S]T, DOC, and methane exposed to a constant concentration of oxygen (∼50 μM) gave steady state values of [·OH] ranging from 5.7 × 10–19 to 3.2 × 10–18 M. The results indicate that [H2S]T should be considered a source of dark formation of ·OH in addition to ferrous iron and reduced DOC.

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“…Pyrite (FeS 2 ) oxidation also leads to formation of ·OH, with various ligands accelerating the process. Similar results were observed for structural Fe(II) in reduced nonronite. , …”

Section: Introductionsupporting

confidence: 85%

Section: ■ Introductionmentioning

confidence: 99%

Determination of Hydroxyl Radical Production from Sulfide Oxidation Relevant to Sulfidic Porewaters

Lombardo

Vindedahl

Arnold

2020

ACS Earth Space Chem.

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“…In this sense, soluble Fe 2+ − and Fe 3+ −ligand complexes would serve as electron shuttles to enhance Fe(III) bioreduction (Figure S2a), similar to their role in abiotic Fe(II) oxidation. 56 The similar levels of aqueous Fe 2+ and total aqueous Fe suggest a negligible level of aqueous Fe 3+ . This result suggests that the bioreduction rate of the Fe 3+ −ligand complex to the Fe 2+ −ligand complex (R1 in Figure S2a) is faster than the abiotic oxidation rate of the Fe 2+ −ligand complex to the Fe 3+ −ligand complex by structural Fe(III) in NAu-2 (R2 in Figure S2a), consistent with previous observations that IET is a slow process.…”

Section: ■ Materials and Methodsmentioning

confidence: 95%

“…Understanding these effects on bioreduction is important as U, organic ligands, and Fe(III)–clay minerals are co-present at many contaminated sites . In the absence of ligands, structural Fe in clay minerals can undergo many redox cycles without significant dissolution; , however, ligands such as citrate and EDTA can dissolve a fraction of the structural Fe in nontronite to form soluble Fe–ligand complexes. , Fe–ligand complexes exhibit different sorption capacities, speciation, bioavailability, and Fe(III)/Fe(II) redox potentials, all of which are expected to impact the role of Fe in mediating U redox reactions.…”

Section: Introductionmentioning

confidence: 99%

Combined Effects of Fe(III)-Bearing Clay Minerals and Organic Ligands on U(VI) Bioreduction and U(IV) Speciation

Zhang

Chen

Xia

et al. 2021

Environ. Sci. Technol.

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Reduction of U(VI) to U(IV) drastically reduces its solubility and has been proposed as a method for remediation of uranium contamination. However, much is still unknown about the kinetics, mechanisms, and products of U(VI) bioreduction in complex systems. In this study, U(VI) bioreduction experiments were conducted with Shewanella putrefaciens strain CN32 in the presence of clay minerals and two organic ligands: citrate and EDTA. In reactors with U and Fe(III)−clay minerals, the rate of U(VI) bioreduction was enhanced due to the presence of ligands, likely because soluble Fe 3+ − and Fe 2+ −ligand complexes served as electron shuttles. In the presence of citrate, bioreduced U(IV) formed a soluble U(IV)−citrate complex in experiments with either Fe-rich or Fe-poor clay mineral. In the presence of EDTA, U(IV) occurred as a soluble U(IV)−EDTA complex in Fe-poor montmorillonite experiments. However, U(IV) remained associated with the solid phase in Fe-rich nontronite experiments through the formation of a ternary U(IV)−EDTA−surface complex, as suggested by the EXAFS analysis. Our study indicates that organic ligands and Fe(III)-bearing clays can significantly affect the microbial reduction of U(VI) and the stability of the resulting U(IV) phase.

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“…The compounds were phosphate, tripolyphosphate, nitrilotriacetic acid, and diaminetetraacetic acid. All the compounds increase the oxidant yields, but the mechanisms vary, depending on the compound type (15). Electron transfer mechanism was suggested in a study concerning Fe(II)-goethite systems (16,17).…”

Section: Introductionmentioning

confidence: 99%

Reduction of the Structural Iron in Montmorillonite by Electron Transfer from Catechol and its Derivatives

Hassen¹,

Silver²

2021

Journal of the Turkish Chemical Society Section A: Chemistry

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The structural Fe(III) in montmorillonite (MMT) clay has been reduced using catechol and its derivatives. It was found that the reduction process is pH-dependent and also depends on the ring substituents. If the catecholic ring has electron-donating substituents, reduction happens at high pH; if the catecholic ring has electron-withdrawing substituents, no reduction occurs. The process involves electron transfer from the hydroxy groups on the compounds to the active site at the iron atoms within the MMT lattice. This site acts as an electron acceptor (Lewis acid). Heat treatment of the reduced sample at 100-300 oC showed an enhancement of the Fe2+/Fe3+ ratio, which is attributed to an increase in the proportion of radicalic formation induced by dehydration. The MMT sample was added to the solutions of the catecholic compound and the slurries were stirred for 24 hours in order to reach equilibrium, then filtered, washed, and air-dried. The reactions were monitored using Mössbauer spectroscopy, x-ray powder diffraction, differential thermal analysis, electron spin resonance, infrared, and total surface area determination.

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Effect of ligands on the production of oxidants from oxygenation of reduced Fe-bearing clay mineral nontronite

Cited by 72 publications

References 93 publications

Determination of Hydroxyl Radical Production from Sulfide Oxidation Relevant to Sulfidic Porewaters

Determination of Hydroxyl Radical Production from Sulfide Oxidation Relevant to Sulfidic Porewaters

Combined Effects of Fe(III)-Bearing Clay Minerals and Organic Ligands on U(VI) Bioreduction and U(IV) Speciation

Reduction of the Structural Iron in Montmorillonite by Electron Transfer from Catechol and its Derivatives

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