Mössbauer Study of the Low-Temperature Phase of Magnetite

Srivastava, C. M.; Shringi, S.N.; Babu, M. V.

doi:10.1515/9783112492925-040

Cited by 2 publications

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“…Treatments with 5 mM Fe(II) resulted in significant magnetite precipitation (Figure 3). Owing to the complexity of the magnetite Mossbauer spectrum at liquid helium temperatures, 68,69 these samples could not be fitted unambiguously, and thus Fh, Fh−PGA_0.05, and Fh− PGA_0.7 are shown only as measured data in the Supporting Information (Figure S18). In contrast to XRD, which only detects phases with some degree of crystallinity, Mossbauer spectroscopy is sensitive to atomic nuclei capable of recoilless absorption and emission of γ-radiation; i.e., in our case, every type of solid containing structural or adsorbed 57 Fe.…”

Section: Environmental Science and Technologysupporting

confidence: 87%

Impact of Organic Matter on Iron(II)-Catalyzed Mineral Transformations in Ferrihydrite–Organic Matter Coprecipitates

ThomasArrigo

Byrne

Kappler

et al. 2018

Environ. Sci. Technol.

172

191

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Poorly crystalline Fe(III) (oxyhydr)oxides like ferrihydrite are abundant in soils and sediments and are often associated with organic matter (OM) in the form of mineralorganic aggregates. Under anoxic conditions, interactions between aqueous Fe(II) and ferrihydrite lead to the formation of crystalline secondary minerals, like lepidocrocite, goethite, or magnetite. However, the extent to which Fe(II)-catalyzed mineral transformations are influenced by ferrihydrite-associated OM is not well understood. We therefore reacted ferrihydrite-PGA coprecipitates (PGA = polygalacturonic acid, C:Fe molar ratios = 0−2.5) and natural Fe-rich organic flocs (C:Fe molar ratio = 2.2) with 0.5−5.0 mM isotopically labeled 57 Fe(II) at pH 7 for 5 weeks. Relying on the combination of stable Fe isotope tracers, a novel application of the PONKCS method to Rietveld fitting of X-ray diffraction (XRD) patterns, and 57 Fe Mossbauer spectroscopy, we sought to follow the temporal evolution in Fe mineralogy and elucidate the fate of adsorbed 57 Fe(II). At low C:Fe molar ratios (0−0.05), rapid oxidation of surface-adsorbed 57 Fe(II) resulted in 57 Feenriched crystalline minerals and nearly complete mineral transformation within days. With increasing OM content, the atom exchange between the added aqueous 57 Fe(II) and Fe in the organic-rich solids still occurred; however, XRD analysis showed that crystalline mineral precipitation was strongly inhibited. For high OM-content materials (C:Fe ≥ 1.2), Mossbauer spectroscopy revealed up to 39% lepidocrocite in the final Fe(II)-reacted samples. Because lepidocrocite was not detectable by XRD, we suggest that the Mossbauer-detected lepidocrocite consisted of nanosized clusters with lepidocrocite-like local structure, similar to the lepidocrocite found in natural flocs. Collectively, our results demonstrate that the C content of ferrihydrite−OM coprecipitates strongly impacts the degree and pathways of Fe mineral transformations and iron atom exchange during reactions with aqueous Fe(II).

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Section: Environmental Science and Technologysupporting

confidence: 87%

Impact of Organic Matter on Iron(II)-Catalyzed Mineral Transformations in Ferrihydrite–Organic Matter Coprecipitates

ThomasArrigo

Byrne

Kappler

et al. 2018

Environ. Sci. Technol.

172

191

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“…The spectrum at 140 K for stoichiometric magnetite has an Fe(II)Fe(III) oct sextet with δ ∼0.72 mm/s, ε ∼ −0.02 mm/s, and B hf of 47.4 T combined with a Fe tet sextet with δ ∼0.38 mm/s, ε ∼ 0.00 mm/s, and B hf of 50.2 T. 35 As the measurement temperature decreases below the Verwey transition (∼121 K), the Fe(II)Fe(III) oct splits into two sextets, resulting in the low temperature spectrum having at least three distinct sextets. 342 It is possible to calculate the Fe(II)/Fe(III) ratio from a magnetite spectrum based on the relative areas of the Fe(II)Fe(III) oct and Fe(III) tet sextets 35 according to the formula Fe(II)/Fe(III) = [0.5 × Fe(II)Fe(III) oct ]/[0.5 × Fe(II)Fe(III) oct +Fe(III) tet ]. However, the calculation is most effectively applied when the sample is fully magnetically ordered and above T v , thus ideally a spectrum obtained at 140 K is considered to be the most effective for determining Fe(II)/Fe(III).…”

Section: Mossbauer Spectroscopymentioning

confidence: 99%

Magnetite and Green Rust: Synthesis, Properties, and Environmental Applications of Mixed-Valent Iron Minerals

et al. 2018

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Mixed-valent iron [Fe(II)-Fe(III)] minerals such as magnetite and green rust have received a significant amount of attention over recent decades, especially in the environmental sciences. These mineral phases are intrinsic and essential parts of biogeochemical cycling of metals and organic carbon and play an important role regarding the mobility, toxicity, and redox transformation of organic and inorganic pollutants. The formation pathways, mineral properties, and applications of magnetite and green rust are currently active areas of research in geochemistry, environmental mineralogy, geomicrobiology, material sciences, environmental engineering, and environmental remediation. These aspects ultimately dictate the reactivity of magnetite and green rust in the environment, which has important consequences for the application of these mineral phases, for example in remediation strategies. In this review we discuss the properties, occurrence, formation by biotic as well as abiotic pathways, characterization techniques, and environmental applications of magnetite and green rust in the environment. The aim is to present a detailed overview of the key aspects related to these mineral phases which can be used as an important resource for researchers working in a diverse range of fields dealing with mixed-valent iron minerals.

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Mössbauer Study of the Low-Temperature Phase of Magnetite

Cited by 2 publications

References 0 publications

Impact of Organic Matter on Iron(II)-Catalyzed Mineral Transformations in Ferrihydrite–Organic Matter Coprecipitates

Impact of Organic Matter on Iron(II)-Catalyzed Mineral Transformations in Ferrihydrite–Organic Matter Coprecipitates

Magnetite and Green Rust: Synthesis, Properties, and Environmental Applications of Mixed-Valent Iron Minerals

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