Cr(VI) Reduction and Immobilization by Magnetite under Alkaline pH Conditions:  The Role of Passivation

He, Yufei; Traina, Samuel J.

doi:10.1021/es0483692

Cited by 159 publications

(105 citation statements)

References 29 publications

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“…These results are consistent with the formation of a passivating layer during metal reduction. [32][33][34] Nanoparticulate UO 2 growth rates observed by AFM are consistent with U(VI) reduction rates determined by the GI-XANES analysis; the U L III -edge position moves to lower energy values within 2-4 hours after exposure of U(VI) to the magnetite (111) surface (Fig. 2) but reached a plateau around 8 hours, roughly the same time that the AFM data indicated slowing precipitate formation.…”

Section: Nanoparticulate Uo 2 Growth and U(vi) Reduction Ratessupporting

confidence: 81%

U(VI) Sorption and Reduction Kinetics on the Magnetite (111) Surface

Singer

Chatman

Ilton

et al. 2012

Environ. Sci. Technol.

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continuous batch-flow conditions. We observed, in real-time and in situ, adsorption and reduction of U(VI) and subsequent growth of UO 2 nanoprecipitates using atomic force microscopy (AFM) and newly developed batch-flow U L III -edge grazing-incidence x-ray absorption spectroscopy near-edge structure (GI-XANES) spectroscopy. U(VI) reduction occurred with and without CO 3 present, and coincided with nucleation and growth of UO 2 particles. When Ca and CO 3 were both present no U(VI) reduction occurred and the U surface loading was lower. In situ batch-flow AFM data indicated that UO 2 particles achieved a maximum height of 4-5 nm after about 8 hours of exposure, however, aggregates continued to grow laterally after 8 hours reaching up to about 300 nm in diameter. The combination of techniques indicated that U uptake is divided into three-stages; (1) initial adsorption of U(VI),(2) reduction of U(VI) to UO 2 nanoprecipitates at surface-specific sites after 2-3 hours of exposure, and (3) completion of U(VI) reduction after ~6-8 hours. U(VI) reduction also corresponded to detectable increases in Fe released to solution and surface topography changes.Redox reactions are proposed that explicitly couple the reduction of U(VI) to enhanced release of Fe(II) from magnetite. Although counter intuitive, the proposed reaction stoichiometry was shown to be largely consistent with the experimental results. In addition to providing molecularscale details about U sorption on magnetite, this work also presents novel advances for collecting surface sensitive molecular-scale information in real-time under batch-flow conditions. 3

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Section: Nanoparticulate Uo 2 Growth and U(vi) Reduction Ratessupporting

confidence: 81%

U(VI) Sorption and Reduction Kinetics on the Magnetite (111) Surface

Singer

Chatman

Ilton

et al. 2012

Environ. Sci. Technol.

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“…No dissolved Cr(III) was detected during the reaction, which suggests that all the Cr(III) was co-precipitated with Fe(III). This observation is consistent with those reported previously (Williams and Scherer 2001;He and Trainas 2005). It can be concluded that iron hydroxide and chromium hydroxide could be the final and predominant products of Cr(VI) reduction by CMC-stabilized Fe 0 nanoparticles.…”

Section: Resultssupporting

confidence: 93%

Conjunctive effect of CMC–zero-valent iron nanoparticles and FYM in the remediation of chromium-contaminated soils

et al. 2013

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Chromium is an important industrial metal used in various products and processes but at the same time causing lethal environmental hazards. Remediation of Cr-contaminated soils poses both technological and economic challenges, as conventional methods are often too expensive and difficult to operate. Zero-valent iron particles at nanoscale are proposed to be one of the important reductants of Cr(VI), transforming the same into nontoxic Cr(III). In the present investigation, soils contaminated with Cr(VI) are allowed to react with the various loadings of zero-valent iron nanoparticles (Fe 0 ) for a reaction period of 24 h. Fe 0 nanoparticles were synthesized by the reduction of ferrous sulfate in the presence of sodium borohydride and stabilized with carboxy methyl cellulose and were characterized by scanning electron microscopy, energy dispersion spectroscopy, X-ray diffraction, UV-vis spectrophotometer, Fourier transform-infra red spectrophotometer, Raman spectroscopy, dynamic light scattering technique and zeta potential. Further, this work demonstrates the potential utilization of farm yard manure (FYM) and Fe 0 nanoparticles in combination and individually for the effective remediation of Cr(VI)-contaminated soils. An increase in the reduction of Cr(VI) from 60 to 80 % was recorded with the increase in the loading of Fe 0 nanoparticles from 0.1 to 0.3 mg/100 g individually and in combination with FYM ranging from 50 to 100 mg/100 g soil.

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“…This passivation reaction converts metallic iron to a composite oxyhydroxide of iron(III)-chromium(III) with low electrical conductivity that prevents passage of electrons from Fe(0) to Cr(VI). Similar passivation has been reported during reduction by magnetite also (He and Traina 2005).…”

Section: Introductionsupporting

confidence: 82%

Commercial steel wool for reduction of hexavalent chromium in wastewater: batch kinetic studies and rate model

Mitra¹,

Banerjee²,

Sarkar³

et al. 2013

Int. J. Environ. Sci. Technol.

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The present study aims at searching the potential of commercial grade steel wool in reducing hexavalent chromium in aqueous phase under batch mode. About 30 % of the initial hexavalent chromium was found to reduce within 2 h at a pH of 3. However, on testing the combined effects of different process parameters, namely the solution pH, wool loading, etc., the optimum batch parametric condition has been fixed. A moving boundary type kinetic model, which takes into account the effect of passivation along with the direct reduction mechanism to simulate the gross uptake profile of Cr(VI) from the bulk solution is proposed. The effective pore diffusivity of Cr(VI) in commercial steel wool was determined by a suitable global optimization technique. Additionally, the model is also capable to simulate the decline of active external surface area of the wool caused by passivation with time. A good match of the experimental data and model-simulated transient bulk concentration of Cr(VI) (under optimum parametric condition only) establishes the general validity of the proposed model.

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Cr(VI) Reduction and Immobilization by Magnetite under Alkaline pH Conditions: The Role of Passivation

Cited by 159 publications

References 29 publications

U(VI) Sorption and Reduction Kinetics on the Magnetite (111) Surface

U(VI) Sorption and Reduction Kinetics on the Magnetite (111) Surface

Conjunctive effect of CMC–zero-valent iron nanoparticles and FYM in the remediation of chromium-contaminated soils

Commercial steel wool for reduction of hexavalent chromium in wastewater: batch kinetic studies and rate model

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