Showing papers on "Hematite published in 1986"

Organic matter mineralization with reduction of ferric iron in anaerobic sediments.

Abstract: The potential for ferric iron reduction with fermentable substrates, fermentation products, and complex organic matter as electron donors was investigated with sediments from freshwater and brackish water sites in the Potomac River Estuary. In enrichments with glucose and hematite, iron reduction was a minor pathway for electron flow, and fermentation products accumulated. The substitution of amorphous ferric oxyhydroxide for hematite in glucose enrichments increased iron reduction 50-fold because the fermentation products could also be metabolized with concomitant iron reduction. Acetate, hydrogen, propionate, butyrate, ethanol, methanol, and trimethylamine stimulated the reduction of amorphous ferric oxyhydroxide in enrichments inoculated with sediments but not in uninoculated or heat-killed controls. The addition of ferric iron inhibited methane production in sediments. The degree of inhibition of methane production by various forms of ferric iron was related to the effectiveness of these ferric compounds as electron acceptors for the metabolism of acetate. The addition of acetate or hydrogen relieved the inhibition of methane production by ferric iron. The decrease of electron equivalents proceeding to methane in sediments supplemented with amorphous ferric oxyhydroxides was compensated for by a corresponding increase of electron equivalents in ferrous iron. These results indicate that iron reduction can outcompete methanogenic food chains for sediment organic matter. Thus, when amorphous ferric oxyhydroxides are available in anaerobic sediments, the transfer of electrons from organic matter to ferric iron can be a major pathway for organic matter decomposition.

Use of the Kubelka—Munk theory to study the influence of iron oxides on soil colour

Abstract: SUMMARY The Kubelka–Munk theory, which is commonly applied to ‘pigment mixtures’, adequately predicted the colour of mixtures of synthetic haematite, synthetic goethite and deferrated soil powders. The theory illustrated the higher pigmenting effect of haematite compared with goethite. In mixtures containing haematite the calculated colour coordinates could be combined into simple ‘redness’ indices that were highly correlated with haematite content and were not appreciably influenced by goethite. The theory was also applied to the study of the chromatic characteristics of 98 soils, differing widely in their origin but having an organic matter content <2% in which haematite or goethite was the dominant Fe oxide. The theory showed that the average ‘soil’ haematite and ‘soil’ goethite had colours similar to those of their synthetic counter-parts, whereas the rest of the soil components could be considered as an essentially ‘grey’ matrix. It was also useful in predicting the haematite and goethite contents of soils either from several reflectance measurements of soil-white standard mixtures or from the indices of redness developed for the synthetic mixtures.

Raman Spectroscopy of Thin Corrosion Films on Iron at 100 to 150 C in Air

Abstract: Laser Raman spectroscopy (LRS) has been applied for the detection and characterization of thin corrosion films formed on iron in air at a temperature range from 100 to 150 C. In situ ellipsometric measurements have also been conducted for quantitative estimations of the film growth kinetics. It is found that (1) the oxidation of iron in dry air leads to the formation of a surface oxide film composed primarily of magnetite and (2) the water vapor in air accelerates the formation of hematite. The ratio of magnetite to hematite in the surface oxide film appears to increase with (1) increasing water vapor pressure, (2) ascending temperature, and (3) extending oxidation time.

Alteration of detrital Fe-Ti oxides in sedimentary rocks

Abstract: Scanning electron microscope study has revealed that in Proterozoic sandstones, shales, and carbonate rocks of the Visingso Group in southern Sweden, detrital Fe-Ti oxides have undergone alteration by dissolution and/or replacement mainly by titanium oxides, hematite (reddish rocks), or pyrite (greenish sandstones, shales, and carbonate rocks). The titanium oxides occur as either poorly crystalline masses, cryptocrystalline aggregates, or discrete, euhedral crystals of anatase, brookite, and rutile that attain a variety of crystal habits. Microprobe analyses have shown that the alteration of ilmenite occurs through several intermediate phases, each successively enriched in titanium and depleted in iron, to an almost pure form of TiO 2 . Some of the iron and titanium which is released during alteration of the Fe-Ti oxides is incorporated in associated clay minerals.

Geochemistry of oolitic iron ores, an electron microprobe study

Abstract: Oolitic iron ores are made up of silicate, oxide, and carbonate minerals that are part of solid solution series. The compositions of the minerals can depart from pure end members and show variation among deposits. This variability can be quantified using electron microprobe techniques. Iron silicates are represented by chamositic clays, both berthierine and chamosite. Glauconite was not seen in any of these samples. Berthierine predominates in younger deposits, whereas the Paleozoic ores studied contained only chamosite. Compositions of the chamositic clays, however, were independent of age. Iron oxides are mostly goethite in younger deposits or hematite in older deposits. Both minerals lack appreciable Al in solid solution. Most analyses show small amounts of Al but usually balanced by Si in the same proportion as in chamosite, indicating a slight admixture of clay. Iron carbonates are siderite with appreciable substitution of Ca and Mg but not of Mn. Apatite is common, but no iron phosphates were found. The compositions of the silicates and carbonates are close to those reported for early diagenetic minerals from other types of sedimentary rocks, indicating that ironstone formation does not require unusual chemical conditions other than a large supply of iron.The analytical results can be used to argue against several hypotheses of ironstone genesis. The lack of Al in the goethitic and hematitic ooliths is inconsistent with an origin either by redeposition of soil ooliths or by oxidation and leaching of earlier chamositic ooliths. The presence of high Al contents in the chamositic ooliths shows that they cannot have formed from earlier aragonitic ooliths, and the presence of small amounts of chamositic clay and apatite as discrete laminae in goethitic and hematitic ooliths suggests that this type of oolith could also not have formed by replacement of aragonite.Times of ironstone deposition show a correlation with climate and sea-level stands that suggests a mechanism for generating locally high iron concentrations in seawater. A combination of a warm, humid climate and low average continental relief would intensify lateritic weathering and the formation of iron-enriched detritus. Coincidence of this increased detrital iron supply with intensification and shallowing of the oxygen minimum layer in the ocean could lead to mobilization of iron from offshore shelf clastics, to be redeposited near the shoreline in intertidal to shallow subtidal environments.

Dissolution of kaolinites and accumulation of iron oxides in lateritic-ferruginous nodules : mineralogical

Abstract: Muller, J.-P. and Bocquier, G., 1986. Dissolution of kaolinites and accumulation of iron oxides in lateritic-ferruginous nodules: mineralogical and microstructural transformations. Geoderma, 37: 113-136. Insitu geochemical and structural microanalysis of non-disturbed samples of laterite and mineralogical identifications of microsamples demonstrate an orderly succession of mineralogical and structural transformations. These transformations result in the formation of Fe-nodules. They start from a micaceous phase whose micropores are occupied by hematite. Because the source of iron is external to micas this hematite corresponds to an absolute accumulation (in the meaning of Brewer, 1964). The following transformations constitute a succession of three mineral phases corresponding to relative accumulations with the removal of some components and in-situ reutilization of residual materials. ' (1) Phase of Fe-kaolinite accumulation during which the structures inherited from micas are preserved. (2) Phase of Al-hematite accumulation resulting from a dissolution of Fe-kaolinite, with development of pedoplasma and vesicular porosity. (3) Phase of accumulation of more or less aluminous goethite which ultimately results in the crystallization of geodes at the borders of voids.

57Fe Mössbauer effect study of Mn-substituted goethite and hematite

Abstract: 57Fe Mossbauer spectroscopy is performed on synthetic Mn-substituted goethites, α-(Fe1−cMnc)OOH, and hematites, α-(Fe1−cMnc)2O3, with c up to 0.08. The hyperfine parameters and in particular the magnetic hyperfine field are found to be less influenced by Mn substitution than in the case of Al. On the other hand, Mn substitution suppresses drastically the Morin transition in hematite which results in a weakly-ferromagnetic state at 80K for compositions with c>0.04.

The Precipitation of Monodispersed α-Iron(III) Oxide Particles from Iron(III) Chloride–Glycine System in Aqueous and 2-Propanol/Water Media

Abstract: Monodispersed α-iron(III) oxide (hematite) particles were prepared by aging iron(III) chloride solutions in the presence of glycine at elevated temperatures, 98–100 °C. An aqueous solution of glycinatoiron (III) complex directly gave monodispersed double spheres of hematite, ≈4 μm in size, under the specified conditions, for example, 2.0×10−2 mol dm−3 FeCl3, 0.60 mol dm−3 glycine, and 0.46 mol dm−3 HCl for 96 h. The hematite particles grew up through the polynuclear layers mechanism. By the forced hydrolysis in 2-propanol/water mixed solution of 30% by volume, monodispersed cuboidal hematite particles, 0.06–0.43 μm in size, were also obtained through the conversion of β-iron(III) hydroxide oxide previously deposited. The nucleation rate was markedly affected by acidity at the latter case. The formation processes of these monodispersed hematite particles are discussed.

Defects and Cation Diffusion in Magnetite (VII): Diffusion Controlled Formation of Magnetite During Reactions in the Iron‐Oxygen System

Abstract: Parabolic rate constants describing the kinetics of the exclusively diffusion controlled growth of magnetite scales during simple reactions in the iron-oxygen system are derived on basis of preceding studies on the defect structure and on the transport properties of this oxide. Furthermore, experimental results for the formation of magnetite by solid state reaction between the iron oxides wustite and hematite are reported and compared with calculated data.

Quantitative Determination of Aluminum-Substituted Goethite-Hematite Mixtures by Mössbauer Spectroscopy

Abstract: Mixtures of synthetic Al-substituted goethite (α-Fe0.814Al0.186OOH) and hematite (α-Fe1.658Al0.342O3) (75, 50, 25, 3% hematite by weight) were studied by Mossbauer spectroscopy to evaluate the use of that technique for quantitative analysis. Mossbauer spectra for these mixtures, obtained in the temperature range 12–130 K, were better fitted by a distribution of magnetic fields than by two magnetic sextets. Spectra at 80 K were equally as good as those from lower temperature to determine the hematitegoethite ratio. The recoil-free fractions of the individual components were about equal at any fixed temperature, but thickness effects caused as much as 30% error in the determination of the ratio of components in mixtures.

Increase in Low-temperature Reduction of Iron Ore Sinter due to Hematite-alumina Solid Solution and Columnar Calcium Ferite

Abstract: Direct observation of lattice images by TEM of magnetite reduced from hematite made clear ultramicroscopic partial distortion due to solid solution of Al2O3. Furthermore, the effect of solid solution of Al2O3 with hematite on strain of magnetite, which had reduced grains of the hematite with a mixture gas of CO-CO2, was estimated by line-broadenings of peaks of X-ray diffraction. It revealed that increasing amounts of Al2O3 increased the strain of magnetite.Fracture strength of the minerals in sintered ore was estimated quantitatively by Vickers indentation, indicating crack propagation-arrest characteristics. Fracture toughness of both glassy silicate and calcium ferrite resulted in values of the same order with a little effect of Al2O3. Calcium ferrite, however, had the lowest value for “critical load”, indicating crack initiation characteristic among all the minerals tested.An experimental study of the crystallization mechanism of skeletal hematite indicated that magnetite coexisting with liquid silicate decomposed, melted and was oxidized at the falling stage of sintering.

Characterization of Goethite and Hematite in a Tunisian Soil Profile by Mössbauer Spectroscopy

Abstract: As part of the characterization of a Tunisian red soil profile, six samples, taken at different depths, were investigated by MSssbauer spectroscopy at room temperature and at 80 K to obtain infor- mation about the various types of Fe oxides present. By considering magnetic hypertine field distributions, the spectra of goethite and hematite were well resolved. Chemical analyses of the samples revealed a partial substitution of Fe by A1 and Mn. The spectral behavior of the goethite was predominantly influenced by crystaUinity and amount of A1 substitution which resulted in a reduction of the magnetic hyperfme field. The effect of Mn substitution was much more pronounced in the hematite spectrum as a consequence of a stronger suppression of the Morin transition by Mn than by AI.

Effect of atmosphere on the goethite decomposition and pore structure of product particles

Abstract: The thermal decomposition of synthetic acicular goethite has been studied with special reference to the effect of atmosphere on the particle characteristics of decomposed goethite such as pore structure and surface area. The decomposition was promoted by O2 but retarded by N2 and H2O. The conversion temperature from protohematite to hematite was lowest for H2O followed by N2 and O2. The sequence of pore structure development is described and the effects of atmosphere and SiO2 coating have been explained in terms of surface mobility, which was greatly enhanced by H2O and suppressed by SiO2 coating. The variation of BET surface area with both temperature and atmosphere has been correlated with pore structure change.

Thermally activated viscous remanence in some magnetite‐ and hematite‐bearing dolomites

Abstract: A Brunhes-age viscous remanent magnetization (VRM) carried by magnetite and hematite in the El Paso and Montoya dolomite formations has unblocking temperatures significantly higher than those predicted by single-domain theory. The samples appear to contain a substantial fraction of pseudo-single domain magnetite, suggesting transdomain processes may be responsible for the stable VRM. A strong inverse correlation between the occurrence of high unblocking temperatures and high isothermal remanence fractions acquired above 0.3 Tesla suggests that the hematite grain size may also be important in determining the range of observed temperatures. Larger grains are inferred to have lower coercivities but higher unblocking temperatures. An older, reverse-polarity component is also observed, and appears to be a record of late Cretaceous-Tertiary tectonic activity.

The effect of the particle morphology on the Mössbauer effect in αFe2O3

Abstract: Several samples of hematite, one a natural specimen, are considered in order to study the specific effect of the morphology on the magnetic structure and especially on the Morin transition. It seemed that mainly the weak-ferromagnetic contribution is affected by the morphology, as well as the transition temperature and region.

Interaction of dilute fluoride solutions with hydrous iron oxides

Abstract: The amount of F- retained by hydrous iron oxide suspensions was found to be a function of F- concentration (2-100 mg L-1), pH, and structural form of the iron oxide. Uptake was minimal at pH >7, and increased with decreasing pH (e.g, with 10 mg L-1 NaF in solution, the amount sorbed by freshly precipitated hydrous iron oxide varied between 7 mg/g at pH 6 and 35.5 mg/g at pH 4.5). With fixed pH (between 4.5 and 6) the amount sorbed varied with concentration in accordance with a Langmuir isotherm relationship. The pH effect was countered at lower values by solid dissolution, hence each F- concentration studied exhibited a pH (between 3.5 and 4.5) where uptake was a maximum. Solid dissolution was accompanied by the formation of soluble iron(III) fluoro complexes. In acid media, the amount of F sorbed by hydrous iron oxide >> goethite > limonite >> hematite. In environmental systems, F interaction and retention should thus be most pronounced in acid media, containing recently precipitated hydrous oxides.

Mössbauer Spectroscopic Study of the Iron Mineralogy of Post-Glacial Marine Clays

Abstract: Three post-glacial marine clays from eastern Canada and one marine clay from Japan have been studied by M6ssbauer spectroscopy to ascertain their iron mineralogy. Small amounts of hematite (in two samples) and magnetite (in one sample) were found in the Canadian clays, and hematite was detected in the Japanese clay. The major spectral components were ferrous and ferric doublets, consistent with X-ray powder diffraction results that show chlorite, mica, and amphibole in the Canadian samples and smectite in the Japanese sample. Citrate-dithionite extraction removed hematite and most of the magnetite from these samples. Acid-base extraction also removed chlorite and some mica from the Canadian samples. Samples treated by these extractions had appreciably lower geotechnical yield stresses at given water contents.