Showing papers on "Hematite published in 1979"
TL;DR: In this article, it was shown that acids can induce hematite formation by linking di-and tricarboxylic acid linking ferrihydrite particles in an immobile network.
Abstract: Hydroxy-carboxylic acids inhibit the crystallization of ferrihydrite in the pH range 9–11 in the order $$citric >meso\,tartaric >L - tartaric \gg lactic$$
and favor hematite formation relative to goethite in the order $$L - tartaric >citric >meso\,tartaric >lactic.$$
The crystal shape of hematite can change from hexagonal plates to acicular in the presence of these acids. The influence of the acids on the crystallization rises with increasing concentration and with falling pH. The effectiveness in suppressing crystallization depends on whether and how strongly the acid adsorbs on ferrihydrite and how strongly it complexes with Fe3+ in solution. Inhibition of crystallization of hematite is believed to be due to the di- and tricarboxylic acid linking ferrihydrite particles in an immobile network. Goethite formation is suppressed by the acid complexing with Fe in solution and hindering nucleation; strongly adsorbing acids also adsorb on the nuclei and hinder further growth. Certain acids can induce hematite formation because they contain a group which acts as a template for nucleation of hematite.
204 citations
TL;DR: Birnessite and hematite have been identified as the Mn-and Fe-oxide phases in desert varnish by IR spectroscopic and chemical techniques as discussed by the authors, and these oxides are in intimate physical association with the mixed-layer illite-montmorillonite clay minerals.
159 citations
TL;DR: In this paper, the location of the characteristic IR absorption bands, in the low frequency region (<600 cm−1), which could be used as fingerprints in the identification of hematite, was investigated.
Abstract: Hematite, α-Fe2O3, one of the most abundant forms of iron oxides in this planet, has been studied and used since ancient times. A search through the pertinent literature reveals many discrepancies on the location of the characteristic IR absorption bands, in the low frequency region (<600 cm−1), which could be used as fingerprints in the identification of hematite. For example, McDevitt and Baun characterize hematite by maxima at 325, 370, 468, and 560 cm−1. Liese, however, locates absorption bands at 312, 391, 449, and 532 cm−1. Schwertmann and Taylor locate them at 345, 470, and 540 cm−1 whereas Bogdanovich et al. assign bands at 475, 520, and 580 cm−1 as characteristic for hematite. It seems that in addition to isomorphous substitution and impurities, crystal defects and the degree of crystallinity may also cause the differences in the locations of the absorption bands. The present work was undertaken to examine the latter assumption and to determine whether IR spectroscopy can be applied to distinguish between well and poorly crystalline hematites.
105 citations
TL;DR: In this article, Ferrihydrite was transformed to goethite and/or hematite at various temperatures, (OH), and IAl, and a straight line was obtained for all preparations independent of (OH).
Abstract: Ferrihydrite was transformed to goethite and/or hematite at various temperatures, (OH), and IAl). Increasing temperature and (AI) favored hematite, increasing (OH) favored goethite. A given (AI) induces hematite more effectively at lower (OH). AI substitution in goethites increased linearly with log(All, but was independent of temperature. At a givea (All, substitution increased with decreasing (OH). In a plot of AI/Fe in the goethite against (AI)/(Fe(OH)C) in solution a straight line was obtained for all preparations independent of (OH).
89 citations
TL;DR: The reliability and utility of diffuse reflectance spectra are briefly but critically reviewed in this article, where the results of measurements for wustite, magnetite, hematite, maghemite, ilmenite, ulvospinel, and α-FeO · OH (goethite), β -FeO 7sd OH, γ-feO · OP (lepidocrocite), and δ-Fe O · OP have been assigned by reference to simplified molecularorbital energy-level diagrams derived from recent SCF-Xα calculations.
Abstract: The reliability and utility of diffuse reflectance spectra are briefly but critically reviewed. The results of measurements of diffuse reflectance over the wavelength range 200 < λ < 2500 nm are reported for wustite, magnetite, hematite, maghemite, ilmenite, ulvospinel, and α-FeO · OH (goethite), β-FeO 7sd OH, γ-FeO · OH (lepidocrocite), and δ-FeO · OH. The spectra have been assigned by reference to simplified molecular-orbital energy-level diagrams derived from recent SCF-Xα calculations. The specular reflectances reported in the Quantitative Data File (Henry, 1977) are related to the diffuse reflectance spectra in a rational way. Minerals that absorb strongly throughout the visible display little dispersion of specular reflectance, and their powders are dark (wustite, magnetite, ilmenite, ulvospinel); those that absorb much more strongly in the near ultraviolet than in the visible have specular reflectances that decrease monotonically from blue to red according to a simple dispersion relation derived by combining the Sellmeier dispersion and Fresnel reflexion equations; their powders are strongly coloured (hematite, maghemite, lepidocrocite, goethite) and their optical anisotropy is closely related to crystal structure.
81 citations
TL;DR: Biotite in deeply weathered granitic rocks in southwestern Australia has altered to exfoliated grains composed of biotite, mixed-layer clay minerals, kaolinite, vermiculite, gibbsite, goethite, and hematite as discussed by the authors.
Abstract: Biotite in deeply weathered granitic rocks in southwestern Australia has altered to exfoliated grains composed of biotite, mixed-layer clay minerals, kaolinite, vermiculite, gibbsite, goethite, and hematite. Discrete vermiculite and vermiculite-dominant mixed-layer clay minerals are not major weathering products. Oxidation of octahedral iron in biotite is associated with ejection of octahedral cations, loss of interlayer K, and a contraction of the b-dimension of the biotite sheet. Si, Mg, Ca, Mn, K, and Na are lost from biotite during weathering, and Ti, Al, Ni, and Cr are retained. Fe and water have been added to the grains during weathering. Much Fe occurs as aggregates of microcystalline, aluminum-rich goethite particles on flake surfaces and within etchpits, with smaller amounts occurring as hexagonal arrangements of lath-shaped crystals of goethite on flake surfaces.
76 citations
TL;DR: In this article, a study by means of electron microscopy at high resolution has enabled the analysis of the microstructure of hematite as produced by dehydration from goethite.
63 citations
TL;DR: In this article, it was shown that the satellites observed in the diffraction pattern of the dehydrated single crystal of the mineral goethite are better interpreted in terms of small angle scattering by a "texture" of the dehydration product hematite.
49 citations
01 Sep 1979-Metallurgical and Materials Transactions B-process Metallurgy and Materials Processing Science
TL;DR: In this paper, a laboratory study was carried out on the conversion of ammonium jarosite to iron oxide with recovery of reagents as byproducts, which resulted in the development of three process possibilities: 1) thermal decomposition with separate recovery of hematite, ammonia and sulfur dioxide, 2) decomposition of jarosite in an aqueous slurry to hematitic and ammonium sulfate, or 3) decomposition in an acid-based slurgharge to magnetite, ammonium and magnetite.
Abstract: Precipitation of iron as a jarosite is used in various hydrometallurgical processes. There are several advantages to this route, for example excellent liquid-solid separation characteristics, selective precipitation of iron in environmentally more stable form, recovery of sulfur as sulfuric acid and higher zinc extraction. However, jarosite precipitation also has disadvantages, the major being the high cost of reagents. A laboratory study was therefore carried out on the conversion of ammonium jarosite to iron oxide with recovery of reagents as byproducts. The investigation resulted in the development of three process possibilities: 1) thermal decomposition with separate recovery of hematite, ammonia and sulfur dioxide, 2) decomposition of jarosite in an aqueous slurry to hematite and ammonium sulfate, or 3) decomposition in an aqueous slurry to magnetite and ammonium sulfate. The conditions affecting the decomposition of jarosite by all three methods have been defined and the chemical, mineralogical and physical characteristics of the iron products are identified.
45 citations
TL;DR: In this article, the authors examined several soils in detail by electron microscope and microprobe to assess the nature of clay size particles and microaggregates and determined their morphology, analytical composition, identity and association between particles.
Abstract: Several soils were examined in detail by electron microscope and microprobe to assess the nature of clay size particles and microaggregates. Morphology, analytical composition, identity and association between particles were determined. Of the mineral oxides, pellets of goethite and hematite about 1 µm in size were most distinctive. They were found in all the soils examined except one. They contained both aluminium and silicon, sometimes in fairly constant proportions, but the presence of adhering fine material made it difficult to assess the extent to which these elements were part of the iron oxide structure. Discrete gibbsite particles of micron size were rarely encountered, although some soils contained appreciable quantities of it in much smaller form. At least a few rutile or anatase particles were found in all soils, while they were common in some. They also were usually contaminated by surface deposits, in contrast to ilmenite and quartz grains which were always relatively clean and were often isolated from other particles. The ratios of ironltitanium in ilmenites were well defined but different from soil to soil. Uncontaminated clay mineral particles were rare. Most had substantial deposits of fine-grained material upon their surfaces, much of it < 200 A in diameter. The most easily detected components of these surface deposits were goethite and hematite, and often they were dominant. Finely divided clay minerals were usually present as well, together in some soils with gibbsite and occasionally with titanium oxides. In one soil where coarser (1 µm) host particles were not readily available to carry it, the fine-grained material formed microaggregates consisting of kaolin, gibbsite and hematite, all of comparable size. Soils containing both kaolin and illite were composed mainly of compact microaggregates of the two clay minerals, which had the appearance of single particles. These results demonstrate the close association frequently existing between micron and submicron soil particles and between submicron particles themselves. The structural units of soil particles were often much smaller than generally supposed.
24 citations
TL;DR: The effect of trivalent ions on the Morin phase transition in hematite was studied by the neutron diffraction method in this article, and it was found that the angle by which the magnetic moments turn out of the basal plane in the MORIN transition decreases with increasing concentration when a critical concentration is reached: 9, 5, 25 and 15 at% for Al, Ga, Cr and In, respectively, the angle becomes zero.
TL;DR: Findings from the pyrolytic release experiment on Mars support the abiotic interpretation of the PR results, which detected the fixation of small amounts of CO2 and/or CO.
Abstract: During its operation on Mars the pyrolytic release experiment (PR) detected the fixation of small amounts of CO2 and/or CO. Laboratory simulations of the experimental conditions were made in an attempt to substantiate the previous conclusion that these reactions were chemical rather than biological. The selection of model substrata for these tests was based on the known properties of the Martian surface material. After pretreatment and incubation under various conditions, pyrolytic analysis was used to indicate the extent of surface catalyzed conversion of14CO2 or14CO to14C-organic compounds. This abiotic synthesis was detected in experiments with three iron oxides, viz. hematite, magnetite and maghemite. When the incubation atmosphere was supplemented with water vapor, the levels of synthesis were in a range comparable to that detected in the Viking PR tests. An abiotic synthesis was also detected in experiments with a mixture of clays and minerals (Mars analog soil) or with montmorillonite artifically enriched in iron. With either substratum the reaction appeared to be the result of a photocatalytic synthesis of14C-organics from14CO and surface hydroxyl groups. This process was not dependent on the presence of water vapor in the incubation atmosphere. Although a duplication of the Viking data has not been achieved, these findings support the abiotic interpretation of the PR results.
TL;DR: In this article, the formation of banded hematite (martite) quartzite has been investigated in the Tomka-Daiteri and Bichakatia areas in Orissa, India.
TL;DR: Mossbauer spectroscopy has been used to characterise the secondary Fe oxides in whole samples of some red (Munsell hue in the range 10R-5YR) and yellow/brown (7.5YR-2.5Y) soil samples from New Zealand as discussed by the authors.
Abstract: Mossbauer spectroscopy has been used to characterise the secondary Fe oxides in whole samples of some red (Munsell hue in the range 10R-5YR) and yellow/brown (7.5YR-2.5Y) soil samples from New Zealand. Dithionite/citrate/bicarbonate treatment of all samples produced whitish-grey to grey residues indicating that the colouring material was present in the “free Fe oxide” fraction of the soils. At room temperature the spectrum of each red sample has a magnetic hyperfine component attributable to hematite. This is absent from the spectra of all yellow/brown samples. At 77K further magnetic hyperfine components are evident in some red samples and in all yellow/brown samples, and are attributable to goethite of very small particle size (superparamagnetic) and/or akaganeite. The Munsell designation can be used to relate colour to the concentration of free Fe oxides with reasonable accuracy (± 25%) for the red samples, but not the yellow/brown samples. In addition, the increasing intensity of redness, judged subjectively, is closely related to increasing concentration of hematite in the red samples.
TL;DR: The mineral composition in the clay fraction of the "terra roxa estruturada" (TRE) soils from Altamira county in the Brazilian Amazon region was discussed by comparing with that of a neighboring red yellow podzolic soil using X-ray diffraction method, differential thermal analysis and chemical analysis.
Abstract: The mineral composition in the clay fraction of the “terra roxa estruturada” (TRE) soils from Altamira county in the Brazilian Amazon region was discussed by comparing with that of a neighboring red yellow podzolic soil using X-ray diffraction method, differential thermal analysis and chemical analysis. Kaolinite was dominant in the TRE soils. Hematite and goethite were detected, but gibbsite was not found in these soils. The TRE soils were characterized by relatively high content of hematite which acts as a cementing material, judging from a very rare existence of the microaggregate in the red yellow podzolic soil contained an extremely small amount of hematite. The stable micro-aggregate of the clay particles cemented by hematite results in good physical condition of the TRE soils, and make the soil fertile, although their chemical properties are not always good.
TL;DR: In this paper, five types of spherule were found in Quaternary sediments from the Canada Abyssal Plain, including type A spherules composed of magnetite and hematite surrounding metallic iron cores.
Abstract: Five types of spherule were found in Quaternary sediments from the Canada Abyssal Plain. They include: type A spherules composed of magnetite and hematite surrounding metallic iron cores, exsolutio...
TL;DR: In this article, the authors used a series of different applied fields to study the thermomagnetic curves of nearly pure hematite and found that with increasing applied field the peak sharpness became less marked and the peak temperature decreased.
TL;DR: In the case of pyrolusite (s-MnO2) and hematite (α-Fe2O3) in a humid, oxygen-rich analogue of the Martian atmosphere produced changes in the oxygen and manganese binding energies as measured by x-ray photoelectron (ESCA) spectroscopy as discussed by the authors.
Abstract: Ultraviolet irradiation of pyrolusite (s-MnO2) and hematite (α-Fe2O3 in a humid, oxygen-rich analogue of the Martian atmosphere produced changes in the oxygen (1s) and manganese (3p) binding energies as measured by x-ray photoelectron (ESCA) spectroscopy. The changes in the Mn (3p) spectrum of pyrolusite are consistent with the formation of a surface layer of an oxide of Mn (V) or Mn (VI). The changes in the O (1s) spectrum of hematite may be due to the presence of chemisorbed oxygen. Pyrolusite irradiated in an oxygen-rich Mars nominal atmosphere containing 2 mb. water released considerable quantities of oxygen in the humid mode of the Viking GEX experiment. These results suggest that the surface chemistry of transition metal compounds may have played an important role in the behavior of samples of Martian regolith in the Viking experiments.
TL;DR: In this article, the effects of CaO, Al2O3 and MgO on the rate limiting step of the reduction of pellets from wustite to metallic iron and on the values of rate parameters are studied.
Abstract: The effects of CaO, Al2O3 and MgO, all as the foreign oxide, on the rate limiting step of the reduction of pellets from wustite to metallic iron and on the values of rate parameters are studied.It is confirmed that the reduction behavior of those pellets may be represented either by the unreacted core model or by the uniform reaction model, depending on which kinds of the foreign oxide and the iron oxide are present at the start. The mixed rate control equation of mass transfer in the gas phase, intraparticle gas diffusion, and chemical reaction may be applied to any iron oxides that contain CaO and to hematite and magnetite both containing Al2O3. On the other hand, the reduction rates of the pure iron oxides, wustite containing Al2O3 and any iron oxides containing MgO are controlled by the oxygen diffusion in the metallic iron shell.These results agree with the conclusion of the present authors' previous studies, namely, when a complex oxide that consists of an iron oxide and any one of those foreign oxides precipitates in wustite during reduction, wustite grains are reduced nontopochemically while pellets are reduced topochemically.
TL;DR: In this article, the most stable face of a crystal corresponds to the composition plane for crystals of hematite from Elba, and the choice of the orientation of the reference axes has been made with the help of stereographic projection combined with the morphology of the etch figures on the different faces of the crystal.
Abstract: The reactivity of hematite depends among other factors on the morphology of the crystal. The choice of the orientation of the reference axes has been made with the help of stereographic projection combined with the morphology of the etch figures on the different faces of the crystal. That the most stable face of a crystal corresponds to the composition plane is shown for crystals of hematite from Elba.
01 Oct 1979
Journal Article•
TL;DR: In this article, a first order phase transition between two types of domains was observed by means of elastic coherent scattering of neutrons at new phase "germs" at the Morin point.