Arsenic(III) and Arsenic(V) Speciation during Transformation of Lepidocrocite to Magnetite

Wang, Yuheng; Morin, Guillaume; Ona-Nguéma, Georges; Brown, Gordon E.

doi:10.1021/es5033629

Cited by 68 publications

(43 citation statements)

References 45 publications

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“…S6) revealed that the initial adsorbed As was not released back into the aqueous phase. Previous studies have shown that adsorbed As can slow down or inhibit the transformation of GR minerals to other iron (oxyhydr)oxides such as magnetite (Su and Wilkin, 2005;Wang et al, 2014), which explains the stability of the As-interacted GR SO4 even after 90 days in our study. In addition, our results are also consistent with long-term batch experiments of Su and Wilkin (2005), who showed that As-interacted GR CO3 remained stable for up to 60 days.…”

Section: Long-term Batch Adsorption Experimentssupporting

confidence: 56%

The interfacial reactivity of arsenic species with green rust sulfate (GRSO4)

Perez

Freeman

Schuessler

et al. 2019

Science of The Total Environment

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GR SO4 is among the best performing Febearing minerals for As removal.• Both pH and the presence of competing aqueous ions affect As removal efficiency. • Long term experiments showed that GR SO4 with As adsorbed onto its surface is stable for up to 90 days. • High-resolution electron microscopy revealed that As is preferentially adsorbed at the GR particle edges.Editor: José Virgílio Cruz Arsenic (As) contamination in groundwater is a significant health and environmental concern worldwide because of its wide distribution and toxicity. The fate and mobility of As is greatly influenced by its interaction with redox-active mineral phases, among which green rust (GR), an Fe II -Fe III layered double hydroxide mineral, plays a crucial role. However, the controlling parameters of As uptake by GR are not yet fully understood. To fill this gap, we determined the interfacial reactions between GR sulfate (GR SO4 ) and aqueous inorganic As(III) and As(V) through batch adsorption experiments, under environmentally-relevant groundwater conditions. Our data showed that, under anoxic conditions, GR SO4 is a stable and effective mineral adsorbent for the removal of As(III) and As(V). At an initial concentration of 10 mg L −1 , As(III) removal was higher at alkaline pH conditions (~95% removal at pH 9) while As(V) was more efficiently removed at near-neutral conditions (N99% at pH 7). The calculated maximum As adsorption capacities on GR SO4 were 160 mg g −1 (pH 8-9) for As(III) and 105 mg g −1 (pH 7) for As(V). The presence of other common groundwater ions such as Mg 2+ and PO 4 3− reduces the efficiency of As removal, especially at high ionic strengths. Long-term batch adsorption experiments (up to 90 days) revealed that As-interacted GR SO4 remained stable, with no mineral transformation or release of adsorbed As species. Overall, our work shows that GR SO4 is one of the most effective As adsorbents among iron (oxyhydr)oxide phases.

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Section: Long-term Batch Adsorption Experimentssupporting

confidence: 56%

The interfacial reactivity of arsenic species with green rust sulfate (GRSO4)

Perez

Freeman

Schuessler

et al. 2019

Science of The Total Environment

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“…Hence, arsenic species are found adsorbed onto these FeOOH compounds mainly As(III) but to a lesser extent As(V) species. Such findings are in agreement with arsenic adsorptive behaviors characteristic under different environmental conditions (e.g., Dixit and Hering 2003;Ona-Nguema et al 2005;Lin et al 2008;Wang et al 2014).…”

Section: Discussionsupporting

confidence: 88%

Arsenopyrite weathering under conditions of simulated calcareous soil

Lara¹,

Velázquez²,

Vazquez‐Arenas³

et al. 2015

Environ Sci Pollut Res

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Mining activities release arsenopyrite into calcareous soils where it undergoes weathering generating toxic compounds. The research evaluates the environmental impacts of these processes under semi-alkaline carbonated conditions. Electrochemical (cyclic voltammetry, chronoamperometry, EIS), spectroscopic (Raman, XPS), and microscopic (SEM, AFM, TEM) techniques are combined along with chemical analyses of leachates collected from simulated arsenopyrite weathering to comprehensively examine the interfacial mechanisms. Early oxidation stages enhance mineral reactivity through the formation of surface sulfur phases (e.g., S n (2-)/S(0)) with semiconductor properties, leading to oscillatory mineral reactivity. Subsequent steps entail the generation of intermediate siderite (FeCO3)-like, followed by the formation of low-compact mass sub-micro ferric oxyhydroxides (α, γ-FeOOH) with adsorbed arsenic (mainly As(III), and lower amounts of As(V)). In addition, weathering reactions can be influenced by accessible arsenic resulting in the formation of a symplesite (Fe3(AsO4)3)-like compound which is dependent on the amount of accessible arsenic in the system. It is proposed that arsenic release occurs via diffusion across secondary α, γ-FeOOH structures during arsenopyrite weathering. We suggest weathering mechanisms of arsenopyrite in calcareous soil and environmental implications based on experimental data.

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“…Fe(II)-induced conversion of lepidocrocite to magnetite has also been observed for pure lepidocrocite under slightly alkaline conditions similar to our experimental conditions (pH > 7.3) [ 37 ]. Under alkaline conditions the conversion of lepidocrocite to magnetite (via a green rust intermediate) in the presence of Fe(II) is rapid and complete after 10 min [ 44 ]. Sustained oxidation of Fe(II) confirms that after cumulative addition of 27 mM Fe(II), which exceeds the electron accepting capacity of original pyrolusite particles [1 g L −1 = 23 mM e − for conversion of Mn(IV) to Mn(II)], some of the final Fe(II) added to the system was oxidized.…”

Section: Resultsmentioning

confidence: 99%

Fe(II) reduction of pyrolusite (β-MnO2) and secondary mineral evolution

2017

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Iron (Fe) and manganese (Mn) are the two most common redox-active elements in the Earth’s crust and are well known to influence mineral formation and dissolution, trace metal sequestration, and contaminant transformations in soils and sediments. Here, we characterized the reaction of aqueous Fe(II) with pyrolusite (β-MnO2) using electron microscopy, X-ray diffraction, aqueous Fe and Mn analyses, and 57Fe Mössbauer spectroscopy. We reacted pyrolusite solids repeatedly with 3 mM Fe(II) at pH 7.5 to evaluate whether electron transfer occurs and to track the evolving reactivity of the Mn/Fe solids. We used Fe isotopes (56 and 57) in conjunction with 57Fe Mössbauer spectroscopy to isolate oxidation of Fe(II) by Fe(III) precipitates or pyrolusite. Using these complementary techniques, we determined that Fe(II) is initially oxidized by pyrolusite and that lepidocrocite is the dominant Fe oxidation product. Additional Fe(II) exposures result in an increasing proportion of magnetite on the pyrolusite surface. Over a series of nine 3 mM Fe(II) additions, Fe(II) continued to be oxidized by the Mn/Fe particles suggesting that Mn/Fe phases are not fully passivated and remain redox active even after extensive surface coverage by Fe(III) oxides. Interestingly, the initial Fe(III) oxide precipitates became further reduced as Fe(II) was added and additional Mn was released into solution suggesting that both the Fe oxide coating and underlying Mn phase continue to participate in redox reactions when freshly exposed to Fe(II). Our findings indicate that Fe and Mn chemistry is influenced by sustained reactions of Fe(II) with Mn/Fe oxides. Electronic supplementary materialThe online version of this article (10.1186/s12932-017-0045-0) contains supplementary material, which is available to authorized users.

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Arsenic(III) and Arsenic(V) Speciation during Transformation of Lepidocrocite to Magnetite

Cited by 68 publications

References 45 publications

The interfacial reactivity of arsenic species with green rust sulfate (GRSO4)

The interfacial reactivity of arsenic species with green rust sulfate (GRSO4)

Arsenopyrite weathering under conditions of simulated calcareous soil

Fe(II) reduction of pyrolusite (β-MnO2) and secondary mineral evolution

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