Separation, characterization and initial reaction studies of magnetite particles from Hanford sediments

Baer, Donald R.; Grosz, A.E.; Ilton, Eugene S.; Krupka, Kenneth M.; Liu, Juan; Penn, R. Lee; Pepin, Alex

doi:10.1016/j.pce.2010.04.010

Cited by 13 publications

(13 citation statements)

References 21 publications

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“…The remaining candidate is solid phase Fe(II), e.g., Fe(II) minerals or sorbed Fe(II), which has been shown (as stronger reductants than aqueous Fe(II)) to reduce a variety of organic compounds, including redox mediators that are analogous to I2S. 48,49 Complete oxidation of solid Fe(II) results in Fe(III) oxyhyroxide, which suggests the following overall reaction between Fe(0) and I2S ox .…”

Section: ■ Experimental Sectionmentioning

confidence: 99%

Field Deployable Chemical Redox Probe for Quantitative Characterization of Carboxymethylcellulose Modified Nano Zerovalent Iron

Fan

Chen

Johnson

et al. 2015

Environ. Sci. Technol.

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Nano zerovalent iron synthesized with carboxymethylcelluose (CMC-nZVI) is among the leading formulations of nZVI currently used for in situ groundwater remediation. The main advantage of CMC-nZVI is that it forms stable suspensions, which are relatively mobile in porous media. Rapid contaminant reduction by CMC-nZVI is well documented, but the fate of the CMC-nZVI (including "aging" and "reductant demand") is not well characterized. Improved understanding of CMC-nZVI fate requires methods with greater specificity for Fe(0), less vulnerability to sampling/recovery artifacts, and more practical application in the field. These criteria can be met with a simple and specific colorimetric approach using indigo-5,5'-disulfonate (I2S) as a chemical redox probe (CRP). The measured stoichiometric ratio for reaction between I2S and nZVI is 1.45 ± 0.03, suggesting complete oxidation of nZVI to Fe(III) species. However, near pH 7, reduction of I2S is diagnostic for Fe(0), because aqueous Fe(II) reduces I2S much more slowly than Fe(0). At that pH, adding Fe(II) increased I2S reduction rates by Fe(0), consistent with depassivation of nZVI, but did not affect the stoichiometry. Using the I2S assay to quantify changes in the Fe(0) content of CMC-nZVI, the rate of Fe(0) oxidation by water was found to be orders of magnitude faster than previously reported values for other types of nZVI.

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Section: ■ Experimental Sectionmentioning

confidence: 99%

Field Deployable Chemical Redox Probe for Quantitative Characterization of Carboxymethylcellulose Modified Nano Zerovalent Iron

Fan

Chen

Johnson

et al. 2015

Environ. Sci. Technol.

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“…Specifically, magnetite has the inverse spinel structure, A (Fe 3+ ) B (Fe 2+ Fe 3+ )O 4 , where A and B refer to tetrahedral and octahedral sites, respectively. Natural magnetites are invariably impure, with Ti(IV) a major structural substituent (Cornell and Schwertmann, 2003;Pearce et al, 2006), particularly in sediments derived from basalt such as at the Hanford site (Baer et al, 2010). Replacement of Fe(III) by Ti(IV) in the lattice yields titanomagnetites (Fe 3Àx Ti x O 4 ), phase intermediates along the binary join with ulvö spinel (Fe 2 TiO 4 ).…”

Section: Introductionmentioning

confidence: 99%

Tc(VII) reduction kinetics by titanomagnetite (Fe3−xTixO4) nanoparticles

Liu

Pearce

Qafoku

et al. 2012

Geochimica et Cosmochimica Acta

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Technetium contamination remains a major environmental problem at nuclear reprocessing sites, such as at the Hanford nuclear reservation, Washington, USA. Here we investigate the heterogeneous reduction of the highly soluble pertechnetate anion [Tc(VII)O 4 À ] to sparingly soluble Tc(IV)-bearing solids by a novel and well-characterized set of mixed-valent titaniumdoped magnetite nanoparticles, structurally and chemically analogous to titanomagnetites naturally present in Hanford sediments. Titanomagnetite (Fe 3Àx Ti x O 4 ) nanoparticles (10-12 nm) with varying Ti content (0 6 x 6 0.53) were synthesized in aqueous suspension. Reaction with 10 and 30 lM Tc(VII) solution yielded fast exponentially decaying reduction kinetics with rates that increased with increasing solid-state Fe(II)/Fe(III) ratio in the nanoparticles, a characteristic systematically controlled by the Ti-content. Nanoparticles before and after reduction experiments and surface-associated products of Tc(VII) reduction were characterized using transmission electron microscopy (TEM), X-ray absorption near-edge spectroscopy (XANES), extended X-ray absorption fine structure spectroscopy (EXAFS), micro X-ray diffraction (l-XRD), X-ray absorption (XA) and X-ray magnetic circular dichroism (XMCD). A mechanistic reaction model was developed involving reduction of Tc(VII) to form Tc(IV)/Fe(III) solids by structural Fe(II) enriched at the nanoparticle surface, a reactive Fe(II) pool that during reaction is resupplied and sustained by outward migration of Fe(II) from the particle interior with concurrent inward migration of charge-balancing cationic vacancies in a ratio of 3:1. The reaction process was quantitatively linked to mass and electron balanced changes in the Fe 3Àx Ti x O 4 nanoparticles, and the accessibility of structural Fe(II) from these phases was determined.

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“…43.0 wt.% quartz, 30.0 wt.% plagioclase, 7.4 wt.% orthoclase, 4.5 wt.% mica, 2.0 wt.% amphibole, 1.0 wt.% chlorite, 0.1 wt.% magnetite (Baer et al, 2010;McKinley et al, 2007) 300 Area: 55m borehole (South Processing Pond)…”

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confidence: 99%

Characterization of natural titanomagnetites (Fe3−xTixO4) for studying heterogeneous electron transfer to Tc(VII) in the Hanford subsurface

Pearce

Liu

Baer

et al. 2014

Geochimica et Cosmochimica Acta

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Sediments with basaltic provenance, such as those at the Hanford nuclear reservation, Washington, U.S.A, are rich in Fe-bearing minerals of mixed valence. These minerals are redox reactive with aqueous O2 or Fe(II), and have the potential to react with important environmental contaminants including Tc. Here, we isolate, identify and characterize natural Fe(II)/Fe(III)-bearing microparticles from Hanford sediments, develop synthetic analogues and investigate their batch redox reactivity with aqueous Tc(VII). Natural Fe-rich mineral samples were isolated by magnetic separation from sediments collected at several locations on Hanford's central plateau. This magnetic mineral fraction was found to represent up to 1 wt% of the total sediment, and be composed of 90% magnetite with minor ilmenite and hematite, as determined by X-ray diffraction. The magnetite contained variable amounts of transition metal impurities consistent with alio-and isovalent metal substitutions for Fe. X-ray microprobe analysis showed that Ti was the most significant impurity, and that these grains could be described with the titanomagnetite formula Fe3 xTixO4, which falls between endmember magnetite (x = 0) and ulvöspinel (x = 1). The dominant composition was determined to be x = 0.15 by chemical analysis and electron probe microanalysis in the bulk, and by Ledge X-ray absorption spectroscopy and X-ray photoelectron spectroscopy at the surface. Site-level characterization of the titanomagnetites by X-ray magnetic circular dichrosim showed that despite native oxidation, octahedral Fe(II) was detectable within 5 nm of the mineral surface. By testing the effect of contact with oxic Hanford and Ringold groundwaters to reduced Ringold groundwater, it was found that the concentration of this near-surface structural Fe(II) was strongly dependent on aqueous redox condition. This highlights the potential for restoring reducing equivalents and thus reduction capacity to oxidized Fe-mineral surfaces through redox cycling in the natural environment. Reaction of these magnetically-separated natural phases from Hanford sediments with a-1 Tc(VII) showed that they were able to reduce Tc(VII) to Tc(IV) with concurrent oxidation of Fe(II) to Fe(III) at the mineral surface, as were synthetic x = 0.15 microparticle and nanoparticle analogue phases. When differences in the particle surface area to solution volume ratio were taken into consideration, measured Tc(VII) reduction rates for Fe3 xTixO4 (x = 0.15) natural material, synthetic bulk powder and nanoparticles scaled systematically, suggesting possible utility for comprehensive batch and flow reactivity studies.

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Separation, characterization and initial reaction studies of magnetite particles from Hanford sediments

Cited by 13 publications

References 21 publications

Field Deployable Chemical Redox Probe for Quantitative Characterization of Carboxymethylcellulose Modified Nano Zerovalent Iron

Field Deployable Chemical Redox Probe for Quantitative Characterization of Carboxymethylcellulose Modified Nano Zerovalent Iron

Tc(VII) reduction kinetics by titanomagnetite (Fe3−xTixO4) nanoparticles

Characterization of natural titanomagnetites (Fe3−xTixO4) for studying heterogeneous electron transfer to Tc(VII) in the Hanford subsurface

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