The influence of aluminium substitution and crystallinity on the Mössbauer spectra of goethite

Murad, E.; Schwertmann, U.

doi:10.1180/claymin.1983.018.3.07

Cited by 134 publications

(87 citation statements)

References 27 publications

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“…Therefore, it is conceivable that the presently observed linear variation contains a contribution from the decreasing crystallinity. Murad and Schwertmann (1983) correlated the hyperfine field at 4.2 K, obtained by fitting a single Lorentzian-shaped sextet to the MS, of A1 goethites to both the Al concentration, x, and the surface area, S, expressed in m2/g: Hhf = 505.4 -33x -0.036S r = -0.98, for n = 19)…”

Section: Resultsmentioning

confidence: 97%

⁵⁷Fe Mössbauer Effect Study of Al-Substituted Lepidocrocites

Grave

1996

Clays and clay miner.

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Abstract--Seven A|-containing lepidocrocite samples, ~/-Fe,_xAlxOOH, prepared from FeC12/AI(NO3)3 solutions with initial A1/(A1 + Fe) mole ratios C~ of 0.0025, 0.01, 0.025, 0.05, 0.075, 0.10 and 0.15 tool/ mol, were examined by means of M6ssbauer spectroscopy at room temperature (RT) and at various temperatures in the range of 8 to 80 K. The spectra at RT and 80~ consist of broadened quadrupole doublets and were analyzed in terms of a single doublet and of a model-independent quadrupole-splitting distribution, the latter yielding the best fit. The observed variations of the quadrupole-splitting parameters with increasing C i are inconclusive as to whether the A1 cations are substituting into the structure. The temperature at which the onset of magnetic ordering is reflected in the spectra, was measured by the therrnoscan method with zero source velocity. A gradual shift from 50 K for Ci = 0.0025 mol/mol to 44 K for Ci = 0.10 mol/mol was observed for that temperature. As compared to earlier studies of Al-free ~-FeOOH samples with similar morphological characteristics, the fractional doublet area in the mixed sextet-doublet spectra at 35 K is significantly higher for the present lepidocrocites. This observation is ascribed to the substitution of A1 cations into the lepidocrocite structure. A similar conclusion is inferred from the variation with C~ of the maximum-probability hyperfine field derived from the spectra recorded at 8 K and fitted with a model-independent hyperfine-field distribution. The magnetic results suggest that for the sample corresponding to Ci = 0.15 mol/mol, not all of the initially present A1 has been incorporated into the structure.

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Section: Resultsmentioning

confidence: 97%

⁵⁷Fe Mössbauer Effect Study of Al-Substituted Lepidocrocites

Grave

1996

Clays and clay miner.

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“…Lowering the measurement temperature reduces relaxation ef- 2919 Bacterial reduction of Al-goethite fects. Fysh and Clark (1982) proposed that the relaxation effects for Al-goethite were negligible at 4.2 K. Murad and Schwertmann (1983), in contrast, argued that the particle size effects were not completely removed at 4.2 K. Both Fysh and Clark, and Murad and Schwertmann proposed equations to calculate the Al content of synthetic Al-goethites from spectra collected at 4.2 K. Murad and Schwertmann further suggested that crystallinity information (surface area or MCD) data were essential for the calculation of Al content.…”

Section: Properties Of the Sediment Goethite Fractionmentioning

confidence: 99%

“…Lorentzian modeling of the 4.2 spectrum was performed to allow comparison with the work of Fysh and Clark (1982) and Murad and Schwertmann (1983). The B hf values obtained for the inner (49.55 T) and outer sextets (53.02 T) were typical of Al-goethite and hematite.…”

Section: Properties Of the Sediment Goethite Fractionmentioning

confidence: 99%

Dissimilatory bacterial reduction of Al-substituted goethite in subsurface sediments

Kukkadapu

Zachara

Smith

et al. 2001

Geochimica et Cosmochimica Acta

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Abstract-The microbiologic reduction of a 0.2 to 2.0 m size fraction of an Atlantic coastal plain sediment (Eatontown) was investigated using a dissimilatory Fe(III)-reducing bacterium (Shewanella putrefaciens, strain CN32) to evaluate mineralogic controls on the rate and extent of Fe(III) reduction and the resulting distribution of biogenic Fe(II). Mössbauer spectroscopy and X-ray diffraction (XRD) were used to show that the sedimentary Fe(III) oxide was Al-substituted goethite (13-17% Al) that existed as 1-to 5-m aggregates of indistinct morphology. Bioreduction experiments were performed in two buffers [HCO 3 Ϫ ; 1,4-piperazinediethansulfonic acid (PIPES)] both without and with 2,6-anthraquinone disulfonate (AQDS) as an electron shuttle. The production of biogenic Fe(II) and the distribution of Al (aqueous and sorbed) were followed over time, as was the formation of Fe(II) biominerals and physical/chemical changes to the goethite.The extent of reduction was comparable in both buffers. The reducibility (rate and extent) was enhanced by AQDS; 9% of dithionite-citrate-bicarbonate (DCB) extractable Fe(III) was reduced without AQDS whereas 15% was reduced in the presence of AQDS. XRD and Mössbauer spectroscopy were used to monitor the disposition of biogenic Fe(II) and changes to the Al-goethite. Fe(II) biomineralization was not evident by XRD. Biomineralization was observed by Mössbauer when sorbed Fe(II) concentrations exceeded a threshold value. The biomineralization products displayed Mössbauer spectra consistent with siderite FeCO 3 (HCO 3 Ϫ buffer only) and green rust . Adsorption of biogenic Fe(II) to accessory mineral phases (e.g., kaolinite) and bacterial surfaces appeared to limit biomineralization. Al evolved during reduction was sorbed, and extractable Al increased with reduction. XRD analysis indicated that neither crystallite size or the Al content of the goethite was affected by bacterial reduction, i.e., Al release was congruent with Fe(II).

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“…Electron diffraction studies (Goltztaub, 1935;van Oosterhout, 1960;Cornell et al, 1983) have shown that goethite crystals are commonly elongated in the [001 ] direction, although factors such as pH, temperature, and the presence of foreign elements in the synthetic system can influence the morphology of the final product. Synthetic goethites doped with A1 have been widely studied (e.g., Fysh and Clark, 1982;Fysh and Fredericks, 1983;Murad and Schwertmann, 1983;Schulze, 1984;Mann, 1983). AI substitutes directly in goethite for Fe in octahedral sites because the ionic radius of A1 (0.67 A) (Shannon and Prewitt, 1969) is similar to that of Fe 3 § (0.78 A).…”

Section: Introductionmentioning

confidence: 99%

“…AI substitutes directly in goethite for Fe in octahedral sites because the ionic radius of A1 (0.67 A) (Shannon and Prewitt, 1969) is similar to that of Fe 3 § (0.78 A). M/Sssbauer spectroscopy (Taylor and Schwertmann, 1974;Murad and Schwertmann, 1983) have shown that A1 substitution has the same effect on the magnetic propCopyright 9 1988, The Clay Minerals Society erties of goethite as does poor crystallinity, namely, that it reduces the saturation internal hyperfine field.…”

Section: Introductionmentioning

confidence: 99%

Influence of Silicon and Phosphorus on Structural and Magnetic Properties of Synthetic Goethite and Related Oxides

Quin

1988

Clays and clay miner.

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Abstract--A series of synthetic goethites containing varying amounts of Si and P dopants were characterized by X-ray powder diffraction, electron diffraction, microbeam electron diffraction, and M6ssbauer spectroscopy. Very low level incorporation produced materials having structural and spectral properties similar to those of poorly crystalline synthetic or natural goethite. At higher incorporation levels, mixtures of noncrystalline materials were obtained which exhibited M6ssbauer spectra typical of noncrystalline materials mixed with a superparamagnetic component. Microbeam electron diffraction indicated that these mixtures contained poorly crystalline goethite, poorly crystalline ferrihydrite, and a noncrystalline component. If the material was prepared with no aging of the alkaline Fe 3+ solution before the addition of Na2HPO4 or Na2SiO3, materials were obtained containing little if any superparamagnetic component. If the alkaline Fe 3+ solution was aged for 48 hr before the addition, goethite nuclei formed and apparently promoted the precipitation of a superparamagnetic phase. The M6ssbauer-effect hyperfine parameters and the saturation internal-hyperfine field obtained at 4.2 K were typical of those of goethite; however, the M6ssbauer spectra indicated that the ordering temperature, as reflected in the relaxation rate and/or the blocking temperature, decreased with increasing incorporation of Si and P. The complete loss of crystallinity indicates that Si and P did not substitute for Fe, but rather adsorbed on crystal-growth sites, thereby preventing uniform crystal growth.

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The influence of aluminium substitution and crystallinity on the Mössbauer spectra of goethite

Cited by 134 publications

References 27 publications

⁵⁷Fe Mössbauer Effect Study of Al-Substituted Lepidocrocites

⁵⁷Fe Mössbauer Effect Study of Al-Substituted Lepidocrocites

Dissimilatory bacterial reduction of Al-substituted goethite in subsurface sediments

Influence of Silicon and Phosphorus on Structural and Magnetic Properties of Synthetic Goethite and Related Oxides

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The influence of aluminium substitution and crystallinity on the Mössbauer spectra of goethite

Cited by 134 publications

References 27 publications

57Fe Mössbauer Effect Study of Al-Substituted Lepidocrocites

57Fe Mössbauer Effect Study of Al-Substituted Lepidocrocites

Dissimilatory bacterial reduction of Al-substituted goethite in subsurface sediments

Influence of Silicon and Phosphorus on Structural and Magnetic Properties of Synthetic Goethite and Related Oxides

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⁵⁷Fe Mössbauer Effect Study of Al-Substituted Lepidocrocites

⁵⁷Fe Mössbauer Effect Study of Al-Substituted Lepidocrocites