Showing papers on "Hematite published in 1972"

Gaseous reduction of iron oxides: Part III. Reduction-oxidation of porous and dense iron oxides and iron

Abstract: The internal reduction of high-grade granular hematite ore in hydrogen and carbon monoxide, and also the internal oxidation of porous iron granules in CO2-CO mixtures have been investigated. To assist the interpretation of the rate data for porous iron and iron oxides, rate measurements have been made also with dense wustite, previously grown on iron by oxidation. The iron formed by reduction of dense wustite is porous, similar to that observed when porous hematite is reduced. It is found that the rate of dissociation or formation of water vapor or carbon dioxide on the iron surface is about an order of magnitude greater than that on the surface of wustite. The results of the previous investigations using dense iron and wustite are in general accord with the present findings. The rate of reduction of hematite increases with increasing pore surface area of the reduced oxide. The results indicate that the rate of reduction of granules is controlled primarily by the formation of H2O or CO2 on the pore walls of wustite. The specific rate constants evaluated from internal reduction, using the total pore surface area, are about 1/50 to 1/100 of those for dense wustite. These findings indicate that with porous wustite or iron, the effective pore surface area utilized is about 1 to 2 pct of the total pore surface area. The rate of reduction in H2-CO mixtures is in accord with that derived from the rate constants for reduction in H2 and CO.

Direct‐Current Conductivity and Iron Tracer Diffusion in Hematite at High Temperatures

Abstract: The dc conductivity of natural single-crystal α-Fe2O3 was measured as a function of O partial pressure from 10−4 to 1 atm at 950° to 1422°C. The conductivity was independent of O2 partial pressure, indicating that hematite is an intrinsic semiconductor with lattice defect concentrations much lower than the concentration of intrinsic electrons (holes). The activation energy of the dc conductivity was 1.18 eV. The iron tracer (55Fe) diffusion coefficients, measured as a function of O2 partial pressure at 1200° and 1300°C, increased as the O2 partial pressure decreased, with a pressure dependence of -0.75; the iron therefore migrates interstitially.

Gaseous reduction of iron oxides: Part IV. mathematical analysis of partial internal reduction-diffusion control

Abstract: In this mathematical analysis of gaseous reduction of iron oxides, the partial internal reduction of the porous oxide and gas diffusion in the porous iron layer are considered simultaneously in deriving the rate equation. The rate equation, derived by partly analytical and partly numerical solutions, is well substantiated by the experimental results obtained previously. The following parameters, determined previously, are used in the application of the rate equation: i) specific rate constant for the gas reaction on the pore walls of wustite, ii) pore surface area of wustite, iii) effective gas diffusivity in the porous wustite formed during reduction of hematite, and iv) effective gas diffusivity in the porous iron layer. The effective depth of the internal reduction zone at the wustite-iron diffuse interface increases steeply with the progress of reduction beyond about 50 pct O removal. For reduction of 1 to 2 cm diam hematite spheroids in 100 pct H2, the gas composition at the diffuse iron-wustite interface is within 10 to 20 pct of that for the iron-wustite equilibrium; beyond about 50 pct O removal, the rate of reduction is controlled primarily by gas diffusion in the porous iron layer. From the mathematical analysis it is found that the relative depth of internal reduction increases with decreasing particle size and increasing temperature.

Iron and Clay in Tropical Savanna Alluvium, Northern Colombia: A Contribution to The Origin of Red Beds

Abstract: Along the flanks of Sierra Nevada de Santa Marta, northern Colombia, tropical savanna uplands with reddish to reddish-brown soils yield brown alluvium which contains relatively abundant grains of fresh iron-bearing minerals: magnetite, amphibole, and biotite, with subordinate chlorite and ilmenite. They constitute about 4.5 weight percent of bulk samples and 8.8 weight percent of sand-silt fractions. In older terrace deposits bleached biotite is common, amphibole is rare, and some magnetite has been oxidized to specular hematite. Clay minerals consist of varying amounts of montmorillonite, illite, mixed-layer clay, kaolinite, and chlorite. Amorphous to very disordered aluminosihcate constitutes 10 to 26 percent of the clay fraction. Total iron makes up 3.1 to 7.6 percent of bulk samples which is considerably higher than that in Sonoran Desert alluvium (0.7 to 4.7 percent), and its upper range exceeds that in many ancient red beds. With few exceptions most of the total iron is in the clay fractions and about 75 percent of that is combined in clay minerals. Total iron in clay fractions averages about 6.6 percent: 5.5 to 8.0 percent in alluvium in transit, 4.8 to 9.0 percent in flood-plain sediments, and 3.0 to 5.8 percent in older terrace deposits. Free (extractable) iron in brown pigment constitutes 0.7 to 3.2 percent of clay fractions and averages about 0.75 percent of bulk samples. This is about twice that in bulk samples of Sonoran Desert alluvium (0.38 percent mean) and it is more than that in many ancient red beds (0.67 percent mean). According to these data there is enough free brown hydrated ferric oxide in tropical savanna alluvium to produce hematite pigment in a red bed simply by post-depositional dehydration and crystallization in an oxidizing environment of burial.

Magnetite and Ilmenite in the Sudbury Nickel Irruptive

Abstract: Magnetite and ilmenite occur throughout the Sudbury Nickel Irruptive. The magnetite almost invariably contains oriented lamellae of ilmenite and the ilmenite often contains lamellae of oxide magnetite and/or hematite. The upper and oxide-rich gabbros and the micropegmatite contain between 1 and 10 percent oxide minerals with magnetite far in excess of ilmenite. The felsic and south range norites contain 0.1 to 2 percent oxide minerals with ilmenite in excess of magnetite. The mafic norite, a unit developed intermittently around the perimeter of the north range of the intrusion, contains 0.5 to 1 percent oxide (largely magnetite) while the quartz-rich norite, developed continuously along the margin of the south range, contains the same amount of oxide, largely ilmenite.Electron microprobe data on magnetite, coupled with estimates of the proportion of ilmenite lamellae developed within grains, indicates that magnetite from the upper levels of the Irruptive was very much richer in titanium at the time of its crystallization than that from lower levels. Chromium shows the reverse trend. Magnetite from the upper part of the mafic norite contains 8 to 13 percent Cr 2 O 3 but this decreases rapidly to less than 2 percent across the 10-50 ft transition zone between the mafic and over-lying felsic norite and then falls more gradually to less than 0.1 percent in the micro-pegmatite. Magnetite from the upper part of the quartz-rich norite and lower south range norite is also rich in Cr 2 O 3 (3-5 wt %) and this decreases upwards to less than 1.5 percent halfway up this unit. These variations in magnetite composition support previous evidence (Naldrett et al., 1970) of cryptic variation in the Irruptive.The final partitioning of iron and titanium between magnetite and ilmenite occurred at high ( nearly equal 900 degrees C) temperatures on the north range and much lower (<600 degrees C) temperatures on the south range, indicating a very different cooling history for the two ranges. This is consistent with the hypothesis that the Irruptive is funnel shaped and that the south range is a section through a deeper, thicker portion of the funnel.

Magnetite thin films

Abstract: A low temperature process for converting hematite (α-Fe 2 O 3 ) thin films into magnetite (Fe 3 O 4 is described. The films produced are unambiguously identified as magnetite by several complementary methods of analysis. These include α-backscattering spectrography, X-ray powder diffractometry, and observations of electrical, magnetic, and optical properties.

Artificial meteor ablation studies: Iron oxides

Abstract: Artificial meteor ablation was performed on natural minerals composed predominantly of magnetite and hematite by using an arc-heated plasma stream of air. Analysis indicates that most of the ablated debris was composed of two or more minerals. Wustite, a metastable mineral, was found to occur as a common product. The 'magnetite' sample, which was 80% magnetite, 14% hematite, 4% apatite, and 2% quartz, yielded ablated products consisting of more than 12 different minerals. Magnetite occurred in 91% of the specimens examined, hematite in 16%, and wustite in 30%. The 'hematite' sample, which was 96% hematite and 3% quartz, yielded ablated products consisting of more than 13 different minerals. Hematite occurred in 47% of the specimens examined, magnetite in 60%, and wustite in 28%. The more volatile elements (Si, P, and Cl) were depleted by about 50%. This study has shown that artificially created ablation products from iron oxides exhibit unique properties that can be used for identification.

Refining hematite pig iron

Abstract: A process for refining hematite pig iron in a convertor by blowing oxygen into a bath of molten hematite pig iron through the bottom and/or through the side wall of the vessel, below the top surface of the bath, and in which a quantity of pieces of lime, at most 10 percent of the pieces of lime averaging less than 2 mm in particle size, is introduced into the bath through the mouth of the convertor, the quantity being sufficient to give a slag with a CaO/SiO2 between 2.5 and 5; the total quantity of pig iron and scrap, and iron in the form of ore (if any), charged into the convertor is such that the specific volume of the convertor exceeds 0.85 m3/ton. By hematite pig iron, is meant a low phosphorus pig iron. With a process in which oxygen is injected through the bottom, the refining of high phosphorus pig iron does not give problems to the steelmaker; only for hematite pig iron, it was necessary to find a way of preventing severe ejections of steel and slag out of the converter.

The Nature and Origin of the Blue Dust in Precambrian Sedimentary Iron Ores

Abstract: In the course of study of the Precambrian sedimentary iron ore deposits of Noamundi in Singhbhum district of Bihar and of Goa, extensive occurrences of powdery iron ores known as Blue Dust have been observed and examined. Field features like the nature of occurrence, textural, structural, and mineralogical character of the Blue Dust have been observed in detail. Shape and size analysis of the mineral grains of the powdery ore have been made and their chemical, X-ray and DTA data presented to explain the mineralogy and chemistry. Etch tests and dissolution experiments have been carried out on standard ore pieces at different pH and temperature for different lengths of time to produce material equivalent to the powdery iron ore. From the above data and experiments, and with the theory of anisotropic dissolution of hematite, the mechanism of formation of the Blue Dust has been explained.

On the Reduction of Ground Particles of Hematite with Hydrogen Gas

Abstract: 緻密なヘマタイト粉砕試料の水素還元 (還元温度350～500℃) を行ない, 化学分析 (臭素-メタノール法) および顕微鏡観察により反応進行状態を調べた結果, 反応ガス中の水蒸気量が少ないと固体中心より, ヘマタイト, マグネタイトおよび金属鉄の三層がならび, 殻状モデルによる取り扱いが可能であった。しかし, 水蒸気量が増すとマグネタイト層内に金属鉄が点在するようになり, 殻状の金属鉄層は存在しなかった。

Study on the manganese nodule V. Thermal studies of the iron-manganese phase

Abstract: The thermal phase transformation of the iron-manganese phase of the Pacific Ocean manganese nodules were studied by the differential thermal and X-ray diffraction methods. X-ray powder patterns of the heated samples at the temperature of 600°C to 1000°C show the occurrence of hematite, bixbyite and cubic and tetragonal (Fe, Mn)3O4. Bixbyite produced by the heat treatment of the iron-manganese phase gives an abnormal X-ray pattern in comparison with the standard sample of bixbyite. Cubic (Fe, Mn)3O4 is produced not only by the reaction of bixbyite with hematite over 900°C, but also at the lower temperature, such as 600°C. While, tetragonal (Fe, Mn)3O4 is a reaction product of cubic (Fe, Mn)3O4 with bixbyite over 900°C in the case of manganese rich nodules. The species and quantities of the products after the heat treatment are assumed to be mostly influenced by the relative contents of iron and manganese in the manganese nodule.

Direct Observation of Iron Oxide Reduction Using High Voltage Microscopy.

Abstract: : The microstructure of reaction products resulting from gaseous reduction of iron oxide has been examined in situ and ex situ by high voltage electron microscopy (HVEM). In order to perform in situ experiments it was necessary to construct a special environmental cell for the AEI EM7 electron microscope. There have been no previous transmission electron microscopy studies of iron ores and whenever possible, micrographs of samples from various localities were obtained although not all the samples were used in reduction experiments. When hematite (Fe2O3) is heated in a reducing atmosphere, magnetite (Fe3O4) nucleates epitaxially at surfaces in contact with the gas. The morphology and rate of growth of the lower oxides were studied.

Crystal structure and magnetic properties of lepidocrocite upon thermal transformation to hematite

Abstract: Synthesized lepidocrocite (γ-FeOOH) has a unit cell of the rhombic system (a = 3.86 A, b = 12.49, and c = 3.36). In the 230–250°C region the structure of lepidocrocite is reconstructed to cubic (a = 8.331 ± 0.003 A) maghemite (γ-Fe2O3), which at 375°C is transformed completely to hematite (α-Fe2O3) with a hexagonal structure which becomes more perfect with further heating (a = 5.0330 ± 0.002 A, c = 13.748 ± 0.002 A). Lepidocrocite occurs in a paramagnetic state. The intermediate substance of its thermal transformation, maghemite, as a consequence of high dispersion, is characterized by superparamagnetic properties and the end product, hematite, owing to the presence of Dzialoshinski's moment, has weak ferromagnetism.