Showing papers on "Hematite published in 1971"

Transformation of hematite to goethite in soils.

Abstract: IN many parts of the world, especially in those that were not glaciated during the Pleistocene epoch, red hematitic soils that formed in a previous climate (different from the present one) still exist. In regions where the present climate is cooler and more humid than the previous one, the red colour seems to be disappearing and being replaced by more yellowish-brown colours that indicate the mineralogical transformation of hematite (α-Fe2O3) to goethite (α-FeOOH).

Gaseous reduction of iron oxides: Part I. Reduction of hematite in hydrogen

Abstract: The reduction of high-grade hematite ore in hydrogen has been investigated. There is an unusual temperature effect for small granules with a dip in the rate at about 700°C, similar to those reported by previous investigators for different types of iron oxides. The particlesize effect on the time of reduction suggests that there are three major limiting rate-controlling processes: i) uniform internal reduction, ii) limiting mixed control and iii) gas diffusion in porous iron layer. Processes (ii) and (iii) are special cases of a so-called topochemical mode of reduction associated with the formation of product layers. Unidirectional reduction experiments revealed the significant role played by gas diffusion in porous iron layer as a rate-controlling process. The effective H2-H2O diffusivity in porous iron derived from, the reduction data is found to decrease markedly with decreasing reduction temperature. This is consistent with the fracture surfaces of porous iron as viewed by scanning electron microscopy. The present interpretation of the rate of reduction of hematite ore is found to apply equally well to previously published data on the hydrogen-reduction of natural and synthetic hematite pellets.

Gaseous reduction of iron oxides: Part II. Pore characteristics of iron reduced from hematite in hydrogen

Abstract: The pore structure of iron reduced from hematite ore by hydrogen is charactertized from measurements of pore volume, pore area and effective gas diffusivity. The measured connected pore volume within the range 0.22 to 0.34 cu cm per g is about the same as the total pore volume; that is, most of the pores in the reduced iron are interconnected. The pore area measured by the BET technique increases with decreasing reduction temperature,e.g. from 0.1 sq m per g at 1200°C to 39 sq m per g at 200°C. The effective H2−H2O diffusivity, measured directly at 600°C after reduction of the ore in hydrogen at the same temperature, is in excellent agreement with that derived from the reduction data. The pore-diffusivity measurements were also made at room temperature using iron samples reduced in hydrogen at 800° and 1000°C. On the basis of the pore properties measured, it appears that the reduced iron has a regular pore structure which becomes finer with decreasing reduction temperature. The effective diffusivities computed on the basis of a simple pore structure are found to be in accord with those derived previously from the reduction data.

The kinetics of reduction of hematite by carbon

Abstract: Reduction kinetics of mixtures of hematite and carbon powders were investigated in the temperature range of 850° to 1087°C. Experiments were carried out under argon atmosphere and the isothermal weight loss of the samples was determined as a function of time. The effects of carbon particle size, hematite/carbon ratio of the mixture, and addition of promotive or inhibitive reagents were also investigated. The results were summarized in the form of fractional reaction vs time plots. A kinetic model developed on the basis of carbon solution-loss reaction as rate-controlling represented the results fairly well. An enthalpy of activation of 72 kcal/per mole was calculated, within the range of 957° to 1087°C. The observed effects of Li2O and FeS on the reduction kinetics are consistent with the influence these reagents are known to exercise on the solution-loss reaction.

The Recently Discovered Serra dos Carajas Iron Deposits, Northern Brazil

Abstract: Hematite as main ore, formation from Precambrian itabirite leached of silica by meteoric water with residual enrichment of iron oxides

Evidence of Single-Domain Magnetite in the Michikamau Anorthosite

Abstract: The Michikamau anorthosite possesses very stable natural remanent magnetization, some of which resists alternating fields up to 1800 Oe. The rock contains two types of opaque grains, fine opaque needles of order 10 × 0.5 μ in the plagioclase felspar, and large equidimensional magnetite particles. Ore microscope studies suggest, but do not establish, that the needles are composed of magnetite. Saturation isothermal remanence and thermal demagnetization studies indicate magnetite as the carrier of remanent magnetization. In order to distinguish the effects of the large grains from those of the needles, mineral separation was used to show that an artificial specimen of essentially pure plagioclase had very similar isothermal remanent magnetization properties to the whole rock. Both indicated magnetite as the magnetic mineral. Thermoremanent properties of the separated mineral fractions indicated magnetite as the dominant magnetic constituent but showed some evidence of laboratory-produced hematite. Theoretic...

Jarosite-geoethite stabilities at 25 °C, 1 ATM

Abstract: Eh, pH and log activity diagrams were calculated to demonstrate the equilibrium relationships between jarosite-goethite-pyrite at 25 °C, 1 atm. Interpretation of these diagrams in light of natural occurrences of iron minerals in the oxidation zone of a sulfide deposit indicates that goethite (or hematite) is the stable mineral in the normal weathering environment. Jarosite is shown to be stable in an acid (pH<3) medium which is moderate to highly oxidizing (Eh-pH). It appears that the persistence of jarosite outside its stability field is due to the sluggishness of the reaction jarosite → goethite.

Solubilization of Iron-Containing Minerals by Soil Microorganisms

Abstract: Eighty-eight strains of microorganisms were isolated from soils collected in northern and southern Chile, and 10 fungi which showed the highest solubilizing action upon the iron in granodiorite were then selected. These fungi were incubated with the following iron-containing minerals: augite, hornblende, biotite, magnetite, hematite, and the igneous rock granodiorite. The solubility of iron in these minerals depended on their nature, crystalline structure, the concentration of metabolic products, or all three. Complex formation could be the mechanism involved, as a strong cation-exchange resin was not able to extract Fe from culture solutions. This conclusion is also confirmed by the RF values obtained by thin-layer chromatography of iron-containing culture solutions.

Magnetic Transition in Rhodium‐Doped Hematite Single Crystals

Abstract: Single crystals of hematite doped with up to 1.6‐mole% rhodium oxide have been grown by the flux method. The amount of dopant, which electron microprobe measurements show to be nonuniform, is linearly correlated with the Morin transition temperature TM determined by a colloidal technique. The increase in TM by about 50°C/mole% Rh2O3 is suggested to have its origin in the effects of the lattice distortion produced by the larger rhodium ions and characterized by a small average lattice expansion of +0.04%/mole% Rh2O3.Single crystals of hematite doped with up to 1.6‐mole% rhodium oxide have been grown by the flux method. The amount of dopant, which electron microprobe measurements show to be nonuniform, is linearly correlated with the Morin transition temperature TM determined by a colloidal technique. The increase in TM by about 50°C/mole% Rh2O3 is suggested to have its origin in the effects of the lattice distortion produced by the larger rhodium ions and characterized by a small average lattice expansion of +0.04%/mole% Rh2O3.

Temperature Dependence of the Weak Ferromagnetic Moment of Hematite

Abstract: A recent proposal by Searle and Dean, which ascribes the anomalous temperature dependence of the weak ferromagnetic moment of hematite to a large temperature-dependent inclination of the antiferromagnetic axis out of the basal plane above the Morin temperature, is demonstrated to be incompatible with M\"ossbauer data. Some possible explanations of this effect are noted.

A Study of the Fe-Ti Oxides in the Whitestone Anorthosite, Dunchurch, Ontario

Abstract: The Fe–Ti oxides hemo-ilmenite, magnetite, and minor ferrian ilmenite occur predominantly in the foliated oxide-rich, garnet-bearing border facies of the Whitestone anorthosite. The rhombohedral phases comprises 80–90 modal % of the oxides, and shows variation in bulk composition from Ilm90Hem10 to Ilm50Hem50 (mol %), which we interpret to be a result of local variation in . Hemo-ilmenites with bulk compositions more ilmenite rich than approximately Ilm85Hem15 exsolve predominantly by a continuous exsolution mechanism, whereas more hematite rich phases exsolve discontinuously. Along the hematite limb of the solvus, the exsolution mechanism changes at a bulk composition of approximately Hem60Ilm40. The compositions of hematite lamellae and host phase ilmenite in hemo-ilmenite are constant at Hem72Ilm28 and Ilm95Hem5 respectively, as indicated by electron-probe analyses. This suggests that the position of the hematite–ilmenite solvus is at more ilmenite rich compositions than was determined by Carmichael (1...

The influence of domain structure on the magnetic properties of hematite

Abstract: The influence of antiferromagnetic domain structure on the AF (antiferromagnet) WF (weak ferromagnet) phase transition is studied. The antiferromagnetic domain structure is considered as a system of antiferromagnetic domains divided by 180° domain walls. AF WF phase transition occurs by splitting of a 180° wall into two 90° walls and a nucleus of a new phase between 90° walls appears. The structure of the weak ferromagnetic domain wall and its formation from the antiferromagnetic domain structure at the AF WF phase transition is discussed. [Russian Text Ignored].

Artificial Meteor Ablation Studies

Abstract: Artificial meteor ablation was performed on natural minerals, composed predominately of magnetite and hematite, using an arc heated plasma stream of air. Analysis of the ablated debris indicated most was composed of two or more minerals. The more volatile elements were depleted and the relative abundance of Fe increased as a result of both volatile depletion and a reduction in its oxidation state. Hematite was converted to magnetite in the ablation zone, and quartz and apatite minerals were converted to an Fe-rich glass consisting of varying amounts of Si, P, Cl, and Ca, depending upon the accessory minerals available at the time of melting. Artificially created ablation products from iron oxides exhibited unique properties depending on the composition of the original material and the environmental conditions of formation. In addition to the accepted elemental criteria, these properties were morphologic characteristics, textural parameters, and the existence of metastable minerals.