The Influence of Aluminum on Iron Oxides. Part XVI: Hydroxyl and Aluminum Substitution in Synthetic Hematites

Stanjek, Helge; Schwertmann, U.

doi:10.1346/ccmn.1992.0400316

Cited by 102 publications

(100 citation statements)

References 33 publications

(33 reference statements)

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“…6, inset), thus indicating the lengthening of unit-cell parameters, and thus the probable decrease of Al-for-Fe substitution, since the ionic radius of Al is smaller than Fe (Shannon, 1976). The extent of this substitution was assessed for the two oxides by refinement of the unit-cell parameters and empirical relations between the Al content and the lattice parameters (Schulze, 1984;Stanjek and Schwertmann, 1992). Al substitutions in hematite decreased from 17 mol% (surface) to 10 mol% (deep alteritic horizons) and were almost constant (~20 mol%) over the entire profile for goethite.…”

Section: Granulometry Chemistry and Mineralogymentioning

confidence: 99%

Mercury speciation in a tropical soil association; Consequence of gold mining on Hg distribution in French Guiana

et al. 2009

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Mercury (Hg) speciation was compared in French Guiana pristine soils and in Hg contaminated soils impacted by former (~1950's) gold-mining activities which used Hg for gold amalgamation. Four selective extractions were performed on soil samples to assess the fraction of Hg present as Hg(II) and bond to organic matter (extracted by NH 4 OH and KOH), to amorphous iron oxides (ascorbate) and to soil components other than refractory minerals (HCl/HNO 3 ). In addition, pyrolysis was used to quantify the content of elemental Hg in contaminated soils. X-ray diffraction (XRD) and X-ray fluorescence micro-mapping (µXRF) were used in combination to selective extractions to assess the nature of targeted components, the possible overlaps between the different extraction procedures and the spatial correlation between Si, K, Fe, Au and Hg.In soil profiles from pristine toposequences, Hg concentrations (0.01-0.49 µg.g -1 ) decreased with increasing depth in soil matrix. Hg concentrations also decreased from ferralsols to acrisols and further to gleysols. In pristine soil matrix, Hg was mainly associated to the clay size fraction (< 2 µm) which was mainly constituted of amorphous and crystalline Fe oxides (Al-substituted goethite and hematite), gibbsite and fine organic matter (OM), whose relative abundances vary along the soil association. Total Hg concentration was positively correlated with sulfurs and organic carbon suggesting the association of Hg with OM sulfur-bearing functional groups.Gleysols were depleted in Hg because of the prevailing reducing conditions that lead to the dissolution of iron oxides. In the same soil profiles, Hg concentrations in ferruginous nodules, which make up most of the soil coarse fraction (> 2 mm), were similar to those reported in the pristine soil matrix. These nodules mainly contained Al-substituted hematite and goethite and were especially abundant upslope in 2 ferralsols and acrisols. Gold-mined gleysols were strongly disorganized by former activities as neither the original structure nor the texture was preserved. Soil granulometry was dominated by gravels, sands and silts. Hg concentrations (0.09-9.22 µg.g -1 ) largely exceeded those in pristine soils. µXRF allowed the identification of Au-amalgamated Hg and of elemental Hg droplets. Pyrolysis confirmed Hg to be mainly present in its elemental form in contaminated soils. Selective extractions showed additional minor contributions of Hg(II) associated to OM, and to Al or Fe oxides. The combination of selective extractions with XRD and µXRF data showed that extraction efficiency is strongly dependent on the soil type, and that this efficiency needs to be determined on a soil-by-soil basis for Hg speciation studies.KOH extraction was especially delicate as crystalline and amorphous oxides were extracted together with organic matter.

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Section: Granulometry Chemistry and Mineralogymentioning

confidence: 99%

Mercury speciation in a tropical soil association; Consequence of gold mining on Hg distribution in French Guiana

et al. 2009

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“…A low sensitivity or even an erratic behaviour of c compared to a, i.e., perpendicular to as against within the oxygen sheets, was also observed for ?d-substituted hematite (Schwertmann et al 1979, Stanjek andSchwertmann 1992).…”

Section: Crystal Size and Unit Cell Edge Lengthmentioning

confidence: 99%

Iron Substitution in Soil and Synthetic Anatase

Schwertmann

1995

Clays and clay miner.

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Abstract--Iron nI for Ti TM substitution in the structure of pedogenic and synthetic anatase of up to Fe/ (Ti+Fe) 0.1 mol/mol was indicated by an increase in unit cell size as measured by XRD line shifts. MiSssbauer-and electron paramagnetic resonance spectra at both, 298 K and 4.2 K supported this by the presence of signals typical for octahedrally coordinated Fe I11 in a diamagnetic matrix. Charge compensation was achieved by structural OH, as indicated by FTIR bands at 3360 and 960 cm -~, which were absent in pure anatase and which disappeared on heating. The weight loss on heating amounted to ca. 0.5 mol H20/mol Fe. At 600~ structural Fe was ejected, the unit cell size decreased to that of pure anatase, and pseudobrookite, Fe2TiOs, was formed.

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“…These bands are produced by crystal-field transitions of Fe(III) in an ocCopyright 9 1998, The Clay Minerals Society Bigham et al (1990Bigham et al ( , 1996; Schwertmann et al (1995) Carlson andSchwertmann (1980) Schwertmann and Fischer (1973); Schwertmann et al (1982); Schwertmann and Kiimpf (1983); Carlson and Schwertmann (1981, 1987) Schulze and Schwertmann (1984; Schwertmann et al (1985) Stanjek (1991; Stanjek and Schwertmann (1992); Murad and Schwertmann (1986); Schwertmann (1987) Schwertmann andFitzpatrick (1977); Carlson and Schwertmann (1990);Scbwertmann and Wolska (1990); Schwertmann (1984) Taylor andSchwertmann (1974) Schwertmann and Murad (1990) Bigham et al (1990, 1996; Schwertmann et al (1995) tahedral ligand field (Sherman and Waite 1985). Due to the combination of several polarization planes and particle-dependent scattering, the diffuse reflectance spectra of powders show broad, strongly overlapping bands (Kortiim 1969;Morris et al 1982).…”

Section: Introductionmentioning

confidence: 99%

Use and Limitations of Second-Derivative Diffuse Reflectance Spectroscopy in the Visible to Near-Infrared Range to Identify and Quantify Fe Oxide Minerals in Soils

Scheinost

Chavernas

Barrón

et al. 1998

Clays and clay miner.

378

304

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Abstract--We measured the visible to near-infrared (IR) spectra of 176 synthetic and natural samples of Fe oxides, oxyhydroxides and an oxyhydroxysulfate (here collectively called "Fe oxides"), and of 56 soil samples ranging widely in goethite/hematite and goethite/lepidocrocite ratios. The positions of the second-derivative minima, corresponding to crystal-field bands, varied substantially within each group of the Fe oxide minerals. Because of overlapping band positions, goethite, maghemite and schwertmannite could not be discriminated. Using the positions of the 4Tl<----6AI, 4T2<----6AI, (4E;4AI)4---6A I and the electron pair transition (4T~ h-4Ti)<----(6Ai q-6ml) , at least 80% of the pure akaganeite, feroxyhite, ferrihydrite, hematite and lepidocrocite samples could be correctly classified by discriminant functions. In soils containing mixtures of Fe oxides, however, only hematite and magnetite could be unequivocally discriminated from other Fe oxides. The characteristic features of hematite are the lower wavelengths of the 4"171 transition (848-906 nm) and the higher wavelengths of the electron pair transition (521-565 nm) as compared to the other Fe oxides (909-1022 nm and 479-499 nm, resp.). Magnetite could be identified by a unique band at 1500 nm due to Fe(II) to Fe(III) intervalence charge transfer. As the bands of goethite and hematite are well separated, the goethite/hematite ratio of soils not containing other Fe oxides could be reasonably predicted from the amplitude of the second-derivative bands. The detection limit of these 2 minerals in soils was below 5 g kg t, which is about 1 order of magnitude lower than the detection limit for routine X-ray diffraction (XRD) analysis. This low detection limit, and the little time and effort involved in the measurements, make second-derivative diffuse reflectance spectroscopy a practical means of routinely determining goethite and hematite contents in soils. The identification of other accessory Fe oxide minerals in soils is, however, very restricted.

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The Influence of Aluminum on Iron Oxides. Part XVI: Hydroxyl and Aluminum Substitution in Synthetic Hematites

Cited by 102 publications

References 33 publications

Mercury speciation in a tropical soil association; Consequence of gold mining on Hg distribution in French Guiana

Mercury speciation in a tropical soil association; Consequence of gold mining on Hg distribution in French Guiana

Iron Substitution in Soil and Synthetic Anatase

Use and Limitations of Second-Derivative Diffuse Reflectance Spectroscopy in the Visible to Near-Infrared Range to Identify and Quantify Fe Oxide Minerals in Soils

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