Development of a rate law for arsenite oxidation by manganese oxides

Owings, Shannon M.; Luther, George W.; Taillefert, Martial

doi:10.1016/j.gca.2019.02.003

Cited by 22 publications

(17 citation statements)

References 75 publications

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“…Furthermore, the low abundance of Mn oxides in the Early Pleistocene confined aquifer of the Songnen Basin (<0.262 mmol/kg; Table S3 in Supporting Information ) may also facilitate the reductive dissolution of Fe(III) oxides and be beneficial to As enrichment. The trace amount of Mn oxides, one of the important oxidants in aquifers (Gao, Guo, et al., 2020; Owings et al., 2019), favors groundwater As remaining as As(III) species, which is less adsorbed and thus is more mobile than As(V) (Dixit & Hering, 2003). On the other hand, the low abundant Mn oxides facilitate reduction of As‐bearing Fe(III) oxides based on the classical redox sequence (Lee et al., 2007), which thus leads to As release into groundwater.…”

Section: Discussionmentioning

confidence: 99%

Abundant Fe(III) Oxide‐Bound Arsenic and Depleted Mn Oxides Facilitate Arsenic Enrichment in Groundwater From a Sand‐Gravel Confined Aquifer

et al. 2022

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Section: Discussionmentioning

confidence: 99%

Abundant Fe(III) Oxide‐Bound Arsenic and Depleted Mn Oxides Facilitate Arsenic Enrichment in Groundwater From a Sand‐Gravel Confined Aquifer

et al. 2022

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“…In these experiments, the oxidation of As(III) to As(V) by OH • , which represents 81% of the oxidant species (Figure S4), was favorable despite the presence of 100 μM of Mn(II) in solution. Arsenic(III) oxidation could also have been mediated by Mn(III, IV) if Mn(II) oxidation by OH • , were faster than As(III) oxidation. Additionally, faster As removal from the dissolved phase occurred in the presence of Mn (10As100Mn; Figure A (A-4)) than in its absence (10As0Mn, Figure (A-1)).…”

Section: Resultsmentioning

confidence: 99%

Coupled As and Mn Redox Transformations in an Fe(0) Electrocoagulation System: Competition for Reactive Oxidants and Sorption Sites

Catrouillet

Hirosue

Manetti

et al. 2020

Environ. Sci. Technol.

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Iron electrocoagulation (EC) can be used for the decentralized treatment of arsenic(As)-contaminated groundwater. Iron EC involves the electrolytic dissolution of an Fe(0) electrode to Fe(II). This process produces reactive oxidants, which oxidize As(III) and Fe(II) to As(V) and a range of Fe(III) (oxyhydr)oxide phases. Here, we investigated the impact of manganese (Mn) on As removal, since the two often co-occur in groundwater. In the absence of Mn(II), we observed rapid As(III) oxidation and the formation of As(V)–Fe(III) polymers. Arsenic removal was achieved upon aggregation of the As(V)–Fe(III) polymers. In the presence of Mn, the mechanism of As removal varied with pH. At pH 4.5, As(III) was oxidized rapidly by OH• and the aggregation of the resulting As(V)–Fe(III) polymers was enhanced by the presence of Mn. At pH 8.5, As(III) and Mn(II) competed for Fe(IV), which led As(III) to persist in solution. The As(V) that did form was incorporated into a mixture of As(V)–Fe(III) polymers and a ferrihydrite-like phase that incorporated 8% Mn(III); some As(III) was also sorbed by these phases. At intermediate pH values, As(III) and Mn(II) also competed for the oxidants, but Mn(III) behaved as a reactive intermediate that reacted with Fe(II) or As(III). This result can explain the presence of As(V) in the solid phase. This detailed understanding of the As removal mechanisms in the presence of Mn can be used to tune the operating conditions of Fe EC for As removal under typical groundwater conditions.

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“…This is in contrast to the work on chemical mechanisms of solid-phase oxidized Mn (e.g., MnO2) with other reductants; e.g. H2S (Herzsage and Afonso 2003; Millero 1993, 1995;Luther et al 2018), organic compounds (Matocha et al 2001; Morgan 1984 a b), and As(III) (Owings et al 2019). Interestingly, all these studies did not include isotope studies although they discussed electron transfer, intermediates, and molecular mechanisms.…”

Section: Links Among Various Elemental Cycles Are a Hallmark Of Bioge...mentioning

confidence: 95%

The Abiotic Nitrite Oxidation by Ligand-Bound Manganese (III): The Chemical Mechanism

et al. 2021

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Given their environmental abundances, it has been long hypothesized that geochemical interactions between reactive forms of manganese and nitrogen may play important roles in the cycling of these elements. Indeed recent studies have begun shedding light on the possible role of soluble, ligand bound Mn(III) in promoting abiotic transformations under environmentally relevant conditions. Here, using the kinetic data of Karolewski et al. (2021), we provide the chemical mechanism for the abiotic oxidation of nitrite (NO2 -) by Mn(III)-pyrophosphate, Mn III PP, to form nitrate (NO3 -). Nitrous acid (HNO2), not NO2 -, is the reductant in the reaction, based on thermodynamic and kinetic considerations. As soluble Mn(III) complexes react in a one-electron transfer reaction, two one-electron transfer steps must occur. In step one, HNO2 is first oxidized to nitrogen dioxide, NO2, a free radical via a hydrogen atom transfer (HAT) reaction. We show that this inner sphere reaction process is the rate limiting step in the reaction sequence. In step two, NO2 reacts with a second Mn III PP complex to form the nitronium ion (NO2 + ), which is isoelectronic with CO2. Unlike the poor electron accepting capability of CO2, NO2 + is an excellent electron acceptor for both OHand H2O, so NO2 + reacts quickly with water to form the end-product NO3 -(step 3 in the reaction sequence). Thus, water provides the O atom in this nitrification reaction in accordance with the O-isotope data. This work provides mechanistic perspective on a potentially important interaction between Mn and nitrogen species, thereby offering a framework in which to interpret kinetic and isotopic data and to further investigate the relevance of this reaction under environmental conditions.

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Development of a rate law for arsenite oxidation by manganese oxides

Cited by 22 publications

References 75 publications

Abundant Fe(III) Oxide‐Bound Arsenic and Depleted Mn Oxides Facilitate Arsenic Enrichment in Groundwater From a Sand‐Gravel Confined Aquifer

Abundant Fe(III) Oxide‐Bound Arsenic and Depleted Mn Oxides Facilitate Arsenic Enrichment in Groundwater From a Sand‐Gravel Confined Aquifer

Coupled As and Mn Redox Transformations in an Fe(0) Electrocoagulation System: Competition for Reactive Oxidants and Sorption Sites

The Abiotic Nitrite Oxidation by Ligand-Bound Manganese (III): The Chemical Mechanism

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