Kinetics of chromate reduction by ferrous ions derived from hematite and biotite at 25 degrees C

Eary, L. E.; Rai, Dhanpat

doi:10.2475/ajs.289.2.180

Cited by 221 publications

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“…Among numerous soil minerals including clay minerals and metal (hydr)oxides, iron oxides and other ironcontaining components could be particularly important for Cr(VI) reduction. Eary and Rai (1989) observed Cr(VI) reduction by hematite and biotite over a wide pH range from 3.5 to 11. They proposed that the dissolution of ferrous iron from solid phases into the aqueous phase should take place prior to Cr(VI) reduction and the reduction occurs in the solution phase rather than at surface sites.…”

Section: Introductionmentioning

confidence: 97%

Kinetic study of hexavalent Cr(VI) reduction by hydrogen sulfide through goethite surface catalytic reaction

Kim¹,

Lan²,

Deng³

2007

Geochem. J.

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Hexavalent chromium reduction by sulfide in the presence of goethite was studied through several batch experiments. Under our specific experimental conditions including 20 µM of hexavalent chromium, 560-1117 µM of sulfide and 10.61-37.13 m 2 /L of goethite at pH of 8.45 controlled by 0.1 M borate buffer, the obtained hexavalent chromium disappearance1.5 and the determined overall rate constant (k) was 31.9 ± 4.2 (min). Among the potential major reducing agents in our comprehensive heterogeneous system such as aqueous phase sulfide, surface-associated sulfide, dissolved ferrous iron, ferrous iron on the goethite surface, as well as fresh ferrous sulfide in the solution, it was considered that the surface ferrous irons which could be produced following sulfide adsorption, played a leading role for Cr(VI) reduction as primary electron donors. In addition, no proof of the preliminary dissolution of ferrous iron from goethite to aqueous phase was observed in the experiments. Elemental sulfur was detected as the final stabilized product of sulfide and it took in charge for the promoted Cr(VI) disappearance for the successive addition of Cr(VI) at later stage.

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Section: Introductionmentioning

confidence: 97%

Kinetic study of hexavalent Cr(VI) reduction by hydrogen sulfide through goethite surface catalytic reaction

Kim¹,

Lan²,

Deng³

2007

Geochem. J.

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“…Rai (1989, 1991) showed that Fe(II)-containing minerals, dissolving under acid conditions, released Fe(II) into solution, which rapidly reduced Cr(VI) to Cr(III). Under neutral and alkaline conditions, mineral dissolution and Fe(II) release become less significant, yet Cr(VI) reduction still occurs in soils and clays (Eary and Rai, 1989;Anderson et al, 1994;Cifuents et al, 1996). White and Yee (1985) proposed an electron-cation transfer mechanism where the electron transfer from structural Fe(II) to aqueous Fe(III) was coupled by cation release from silicates to solution.…”

Section: Introductionmentioning

confidence: 99%

Chromate Removal by Dithionite-Reduced Clays: Evidence from Direct X-Ray Adsorption Near Edge Spectroscopy (XANES) of Chromate Reduction at Clay Surfaces

Taylor

2000

Clays and clay miner.

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Abstract--Chromium(VI) in the environment is of particular concern because it is toxic to both plants and animals, even at low concentrations. As a redox-sensitive element, the fate and toxicity of chromium is controlled by soil reduction-oxidation (redox) reactions, ln-situ remediation of chromium combines reduction of Cr(VI) to Cr(III) and immobilization of chromium on mineral surfaces. In this study, Fetich smectite, montmorillonite, illite, vermiculite, and kaolinite were examined to determine reactivity in sorption-reduction of Cr(VI). The clays were compared to forms that were reduced by sodium dithionite. Clays containing Fe(lI) efficiently removed soluble Cr(VI) from solution. Chromium K-edge X-ray absorption near edge structure (XANES) suggested that clays containing Fe(II) reduced Cr(VI) to Cr(III), immobilizing Cr at the clay/water interface. Adsorption of Cr(VI) by the Fe(II)-containing clay was a prerequisite for the coupled sorption-reduction reaction. Sodium dithionite added directly to aqueous suspensions of non-reduced clays reduced Cr(VI) to Cr(III), but did not immobilize Cr on clay surfaces. The capacity of clays to reduce Cr(VI) is correlated with the ferrous iron content of the clays. For dithionite-reduced smectite, the exchangeable cation influenced the sorption reaction, and thus it also influenced the coupled sorption-reduction reaction of Cr(VI). The pH of the aqueous system affected both the amount of Cr(VI) reduced to Cr(III) and the partition of Cr(llI) between aqueous and adsorbed species. A plot of pH vs. amount (adsorption envelope) adsorbed for the coupled sorption-reduction reaction of Cr by reduced smectite exhibited a similar pattern to that of typical anion-sorption.

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“…Chromium is readily immobilized as (Fe,Cr)(OH) 3 under ferruginous conditions (19,20) and will be reduced and rendered insoluble by reaction with a wide range of other reductants under sulfidic or even denitrifying conditions (21)(22)(23). Thus, comparing Mo enrichments in independently constrained euxinic shales and Cr enrichments in independently constrained anoxic shales can offer a unique and complementary perspective on the global redox landscape of the ocean.…”

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confidence: 99%

Proterozoic ocean redox and biogeochemical stasis

Reinhard

Planavsky

Robbins

et al. 2013

Proc. Natl. Acad. Sci. U.S.A.

444

423

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The partial pressure of oxygen in Earth's atmosphere has increased dramatically through time, and this increase is thought to have occurred in two rapid steps at both ends of the Proterozoic Eon (∼2.5-0.543 Ga). However, the trajectory and mechanisms of Earth's oxygenation are still poorly constrained, and little is known regarding attendant changes in ocean ventilation and seafloor redox. We have a particularly poor understanding of ocean chemistry during the mid-Proterozoic (∼1.8-0.8 Ga). Given the coupling between redoxsensitive trace element cycles and planktonic productivity, various models for mid-Proterozoic ocean chemistry imply different effects on the biogeochemical cycling of major and trace nutrients, with potential ecological constraints on emerging eukaryotic life. Here, we exploit the differing redox behavior of molybdenum and chromium to provide constraints on seafloor redox evolution by coupling a large database of sedimentary metal enrichments to a mass balance model that includes spatially variant metal burial rates. We find that the metal enrichment record implies a Proterozoic deep ocean characterized by pervasive anoxia relative to the Phanerozoic (at least ∼30-40% of modern seafloor area) but a relatively small extent of euxinic (anoxic and sulfidic) seafloor (less than ∼1-10% of modern seafloor area). Our model suggests that the oceanic Mo reservoir is extremely sensitive to perturbations in the extent of sulfidic seafloor and that the record of Mo and chromium enrichments through time is consistent with the possibility of a Mo-N colimited marine biosphere during many periods of Earth's history.paleoceanography | geobiology

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Kinetics of chromate reduction by ferrous ions derived from hematite and biotite at 25 degrees C

Cited by 221 publications

References 0 publications

Kinetic study of hexavalent Cr(VI) reduction by hydrogen sulfide through goethite surface catalytic reaction

Kinetic study of hexavalent Cr(VI) reduction by hydrogen sulfide through goethite surface catalytic reaction

Chromate Removal by Dithionite-Reduced Clays: Evidence from Direct X-Ray Adsorption Near Edge Spectroscopy (XANES) of Chromate Reduction at Clay Surfaces

Proterozoic ocean redox and biogeochemical stasis

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