Reductive Dissolution and Reactivity of Ferric (Hydr)oxides: New Insights and Implications for Environmental Redox Processes

Peiffer, Stefan; Wan, Moli

doi:10.1002/9783527691395.ch3

Cited by 9 publications

(12 citation statements)

References 64 publications

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“…It appears that high sulfate concentrations in the groundwater, together with the abundance of microbially available organic C within fine-grained, reducing lenses (Supporting Information, Table SI-1), stimulated sulfate reduction within and along the edges of lenses to produce aqueous sulfide that dispersed within the groundwater (Figure ). The sustained sulfide supply drove reductive dissolution of Fe(III) oxides to aqueous Fe(II), producing zero-valent S and releasing adsorbed As, as shown in previous studies. − Zero-valent S is not very stable in the aqueous phase at pH 8, where it will likely react with sulfide to form polysulfides or with other species, such as As(III), unless it is partitioned to the solid phase (as seen in the aquifer sand before the first reducing lens in this study). On the influent (upstream) side of the first fine-grained, reducing lens, it appears that aqueous Fe(II) concentrations were too low to precipitate FeS (Figure ).…”

Section: Resultssupporting

confidence: 59%

Redox Heterogeneities Promote Thioarsenate Formation and Release into Groundwater from Low Arsenic Sediments

Kumar

Noël

Planer-Friedrich

et al. 2020

Environ. Sci. Technol.

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Groundwater contamination by As from natural and anthropogenic sources is a worldwide concern. Redox heterogeneities over space and time are common and can influence the molecular-level speciation of As, and thus, As release/retention but are largely unexplored. Here, we present results from a dual-domain column experiment, with natural organic-rich, fine-grained, and sulfidic sediments embedded as lenses (referred to as "reducing lenses") within natural aquifer sand. We show that redox interfaces in sulfur-rich, alkaline aquifers may release concerning levels of As, even when sediment As concentration is low (<2 mg/kg), due to the formation of mobile thioarsenates at aqueous sulfide/Fe molar ratios <1. In our experiments, this behavior occurred in the aquifer sand between reducing lenses and was attributed to the spreading of sulfidic conditions and subsequent Fe reductive dissolution. In contrast, inside reducing lenses (and some locations in the aquifer) the aqueous sulfide/Fe molar ratios exceeded 1 and aqueous sulfide/As molar ratios exceeded 100, which partitioned As(III)−S to the solid phase (associated with organics or as realgar (As 4 S 4 )). These results highlight the importance of thioarsenates in natural sediments and indicate that redox interfaces and sediment heterogeneities could locally degrade groundwater quality, even in aquifers with unconcerning solid-phase As concentrations.

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Section: Resultssupporting

confidence: 59%

Redox Heterogeneities Promote Thioarsenate Formation and Release into Groundwater from Low Arsenic Sediments

Kumar

Noël

Planer-Friedrich

et al. 2020

Environ. Sci. Technol.

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“…So far, it is commonly accepted for ferritins in general that further oxidation can concomitantly occur through an autocatalytic reaction for which the ferrous ions can enter and be oxidized at the ferric mineral surface in the presence of the oxidant co-substrate,w ithout which no oxidation has been described to be possible.S urprisingly,i nt his work, we demonstrate that even in the absence of co-substrate iron sequestration and mineralization is possible.T he data suggests that not only the 57 Fe II was oxidized, it was also incorporated into the bulk mineral structure,g iven the spectral similarity with the iron reacted with H 2 O 2 sample and the presence of mix-valence species.T his phenomenon has been observed by Silvester et al [34] and Williams and Scherer [35] in abiotic systems.T he authors showed that Fe II could adsorb to the surface of synthetic minerals (goethite and hydrous ferric oxide hydrate) and be completely oxidized in anoxic environments,t hrough electron transfer reactions from the aqueous Fe II to the solid ferric mineral. Thet wo models proposed for the heterogeneous reaction of aqueous Fe II with synthetic ferric iron oxides,r ecently reviewed by Peiffer and Wana nd Gorski and Scherer, [36,37] involve electron transfer between aqueous Fe II ions and the solid ferric mineral. These electrons can be trapped in the ferric oxide structure,aslocalized or delocalized charges,ormay be released into solution in the form of Fe II ions through reductive dissolution.…”

Section: Methodsmentioning

confidence: 99%

“…These electrons can be trapped in the ferric oxide structure,aslocalized or delocalized charges,ormay be released into solution in the form of Fe II ions through reductive dissolution. Adsorption and incorporation of aqueous Fe II ions contributing to the mineral growth, without dissolution of the mineral [36,38] is an alternative model that can lead to mineral transformation. Under the experimental conditions used, our data supports anet oxidation reaction of Fe II ions in the absence of an oxidant co-substrate through detection of delocalized trapped electrons in the core structure and absence of aqueous octahedral Fe II species in the Mçssbauer spectrum ( Supporting Information, Figure S6A).…”

Section: Methodsmentioning

confidence: 99%

Direct Evidence for Ferrous Ion Oxidation and Incorporation in the Absence of Oxidants by Dps from Marinobacter hydrocarbonoclasticus

Penas

Tavares

2018

Angew Chem Int Ed

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Dps proteins (DNA-binding protein from starved cells) are hollow-sphere-shaped, dodecameric enzymes found in bacteria and archaeal species.They can oxidize ferrous iron in acontrolled manner using hydrogen peroxide or molecular oxygen as co-substrate,a nd most of them confer physical protection through DNAb inding.O xidizedi ron is stored, as am ineral core,i nacentral cavity.D irect evidence is now provided that, furthermore,D ps proteins containing small mineral cores can oxidize and mineralize toxic ferrous ions in anaerobic conditions and in the absence of any additional aqueous oxidant co-substrate.Dps proteins containing cores of 24 irons per dodecamer can oxidize about 5f errous irons per dodecamer,w ith that number approximately doubling for protein particles containing in average 96 irons per protein.This additional activity carries importance as it can be ad etoxification mechanism present during anaerobic or oxygen-limited growth conditions.

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“…This fraction was referred to as 'surface bound Fe(II)' in Poulton et al (2004) or 'excess Fe(II)' in Hellige et al (2012). It was proposed that this excess Fe(II) is associated with the surface (Hellige et al, 2012;Poulton, 2003;Poulton et al, 2004) or consists of electron equivalents stored in the surface layers of the bulk mineral (Peiffer and Wan, 2016).…”

Section: A Novel Pathway For Pyrite Formationmentioning

confidence: 99%

Fe(III):S(-II) concentration ratio controls the pathway and the kinetics of pyrite formation during sulfidation of ferric hydroxides

Wan

Schröder

Peiffer

2017

Geochimica et Cosmochimica Acta

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The formation of pyrite has been extensively studied because of its abundance in many anoxic environments. Yet, there is no consensus on the underlying pathways and kinetics of its formation. We studied the formation of pyrite during the reaction between reactive ferric hydroxides (goethite and lepidocrocite) and aqueous sulfide in an anoxic glove box at neutral pH. The formation of pyrite was monitored with Mössbauer spectroscopy using 57 Fe isotope-enriched ferric (hydr)oxides. The initial molar ratios of Fe(III):S(-II) were adjusted to be 'high' with Fe(III) concentrations in excess of sulfide (HR) and 'low' (LR) with excess of sulfide. Approximately the same surface area was applied in all HR runs in order to compare the mineral reactivity of ferric hydroxides. Electron transfer between aqueous sulfide and ferric hydroxides in the first 2 hours led to the formation of ferrous iron and methanol-extractable oxidized sulfur (MES). Metastable FeS x formed in all of the experiments. Pyrite formed at a different rate in HR and LR runs although the MES and ferrous iron concentrations were rather similar. In all HR runs, pyrite formation started after 48 hours and achieved a maximum concentration after 1 week. In contrast, pyrite started to form only after 2 months in LR runs (Fe(III):S(-II) ~ 0.2) with goethite and no pyrite formation was observed in LR with lepidocrocite after 6 months. Rates in LR runs were at least 2-3 orders of magnitude slower than in HR runs. Sulfide oxidation rates were higher with lepidocrocite than with goethite, but no influence of the mineral type on pyrite formation rates in HR runs could be observed. Pyrite formation rates in HR runs could not be predicted by the classical model of Rickard (1975). We therefore propose a novel ferric-hydroxide-surface (FHS) pathway for rapid pyrite formation that is based on the formation of a precursor species >Fe II S 2-. Its formation is competitive to FeS x precipitation at high aqueous sulfide concentrations and requires that a fraction of the ferric hydroxide surface not be covered by a surface precipitate of FeS x. Hence, pyrite formation rate decreases with decreasing Fe(III):S(-II) aq ratio. In LR runs, pyrite formation appears to follow the model of Rickard (1975) and to be kinetically controlled by the dissolution of FeS. The FHS-pathway will be prominent in many aquatic systems with terrestrial influence, i.e. abundance of ferric iron. We propose that the Fe(III):S(-II) aq ratio can be used as an indicator for rapid pyrite formation during early diagenesis in anoxic/suboxic aquatic systems.

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Reductive Dissolution and Reactivity of Ferric (Hydr)oxides: New Insights and Implications for Environmental Redox Processes

Cited by 9 publications

References 64 publications

Redox Heterogeneities Promote Thioarsenate Formation and Release into Groundwater from Low Arsenic Sediments

Redox Heterogeneities Promote Thioarsenate Formation and Release into Groundwater from Low Arsenic Sediments

Direct Evidence for Ferrous Ion Oxidation and Incorporation in the Absence of Oxidants by Dps from Marinobacter hydrocarbonoclasticus

Fe(III):S(-II) concentration ratio controls the pathway and the kinetics of pyrite formation during sulfidation of ferric hydroxides

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