Thesis--Wisconsin. / Includes bibliographical references (leaves 78-80).

The dissolution of hematite (⍺ -Fe203) in hydrochloric acid solutions has been investigated. Sintered compacts, single crystals and particulate specimens were subjected to leaching over a range of temperatures and acid concentrations. The effects of varying the hydrogen and chloride ion concentrations independently were also investigated. The dissolution was found to be highly anisotropic, the basal (0001) plane dissolving at a rate an order of magnitude greater than that of any of the other surfaces examined. Qualitative experiments indicated that this effect is also characteristic of dissolution in nitric, sulphuric and perchloric acids. The effect is attributed to the presence of a greater number of active dissolution sites on the basal plane, resulting from the anisotropic nature of the hematite crystal structure, and possibly also from the presence of a greater number of dislocations terminating on the basal plane. The reaction rate was found to depend strongly on the acid concentration, increasing as the 2.5th power of the acid normality in the range 0.2-7.ON, an to vary independently with hydrogen and chloride ion concentrations. At acidities below 2N, the rate appears to vary with the product of hydrogen and chloride ion activities, while at concentrations in the range 2-7N, a linear dependence on hydrogen ion activity was observed. A tentative mechanism is proposed, in which protonation of the hydrated oxide surface is followed by adsorption of a chloride ion and desorption of a ferric-chloride complex. / Applied Science, Faculty of / Materials Engineering, Department of / Graduate

Thesis (Ph. D.)--University of Wisconsin--Madison, 1970. / Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references.

The direct dissolution of various samples of hematite and goethite in hydrochloric, sulphuric and perchloric acids using a particulate (-65, + 150 mesh) feed has been investigated. The reductive dissolution of hematite samples using acidified sulphur dioxide solutions was also investigated. Goethite and hematite leached by a common mechanism with comparable rates. The various shapes of leaching curves obtained for different hematite samples can be correlated with their grain size to particle size ratio. An increasing rate of dissolution was found for a large number of grains per particle, and an approximately constant rate was observed for particles containing relatively few grains per particle. The effect of acid concentration on the rate of dissolution for different acids has led to the modification of a previously proposed chemical mechanism dependent on the complexing power of the anion of the acid with iron. The increase in dissolution rate for a weak complexer was proportional to the acid concentration e.g. HCIO₄, and for a strong complexer, if was proportional to the acid concentration squared e.g. HCl. The rate of dissolution in the presence of sulphur dioxide was extremely rapid compared with the acid dissolution. / Applied Science, Faculty of / Materials Engineering, Department of / Graduate

M.Sc. (Chemistry) / Please refer to full text to view abstract

<p> The kinetics of the hematite to rnagnetite reduction have been studied in H2-H2O, and H2-H2O-N2 gas mixtures, using natural as well as synthetic specimens. The reactivity of hematite was found to be related to the structural defects formed during the preparation of the specimens. The type of defects formed and their effect on reactivity are discussed. Kinetic studies are performed on the specimens with reproducible properties. Rate expressions based upon suitable reaction mechanisms are derived and their validity checked with the experimental data. Reaction rate parameters for the expressions accurately interpreting the experimental results are evaluated, and the effect of nitrogen is separately established. Values of enthalpies and entropies for the mechanistic steps a.re calculated from the temperature dependence of these parameters, which reasonably support the proposed mechanism. </p> / Thesis / Doctor of Philosophy (PhD)

The crystallization kinetics of hydronium jarosite have been studied in the area of the Fe₂O₃-SO₃-H₂O phase diagram where hematite is the stable phase. Hydronium jarosite has been shown to be a kinetically favored intermediate to hematite over a wide range of chemical and thermal conditions. A model useful for predicting the crystal size distribution as a function of temperature, free acid and iron concentrations, and residence time has been developed. Hydronium, sodium, and potassium jarosite have been shown to convert, via a solid phase reaction, to hematite. A model useful for predicting the conversion rate as a function of temperature, free acid concentration, and particle size has been developed. A predictive model, the growing core model, has been developed. It is useful for predicting the crystal size distribution and the product split between hydronium jarosite and hematite when both crystallization and conversion are occurring simultaneously. The cardinal assumption in this model is that crystal growth and conversion occur at separate cites on the crystal surface simultaneously. The model, with only one adjustable constant, has been verified with experimental results. The effect of double draw off (DDO) operation in this system has been demonstrated. It has been shown, via the growing core model and experimental results, that DDO operation can produce a high iron, low sulfur product. Without DDO operation, this high product quality can only be achieved through higher operating temperature, high neutralization rates, or very large vessel size.

Thesis (M.S.)--Missouri University of Science and Technology, 2009. / Vita. The entire thesis text is included in file. Title from title screen of thesis/dissertation PDF file (viewed November 11, 2009) Includes bibliographical references (p. 85-87).

At this study three samples of hematite nanorods were deposited on the silicon substrates with different varieties of glancing angle deposition techniques. One sample (S1) was prepared by using thermal deposition with partially ionized beam (PIB) and substrate rotation. The second sample (S2) was synthesized by using thermal deposition with PIB and no substrate rotation. The third sample (S3) was obtained by using E-beam deposition, PIB and rotating substrate. In addition, one sample of magnetite nanorods (S4) has been prepared in order to compare the magnetic properties of the two different iron oxides. S4 was prepared by using thermal deposition and fixed glancing angle deposition, but no PIB was applied. The hysteresis loop has been studied for all samples and the temperature dependent magnetic properties of one of the hematite samples and the magnetite been studied, too. The studies of the magnetic hysteresis for S1, S2, S3 and S4 showed that all of the samples have hysteresis loops but with dissimilar values of the saturation magnetization Ms, remanence MR, and coercivity HC. Furthermore, the hysteresis loops of all four samples showed different behaviors as the nanorods of the samples change the orientation with respect to the magnetic field. In addition to that fact, the hysteresis loop demonstrated that samples that have similar morphology have like behavior of the hysteresis loop. Also, it has found that S2 has the largest hysteresis loop of all hematite samples and it has large hysteresis loop in the perpendicular and parallel directions with the field as well. However, the magnetite hysteresis loops are significant larger than the ones of the hematite. Likewise, the studies of the temperature dependence magnetic properties of S2 and S4 showed that the ZFC and FC M-T curves of S1and S4 behaved differently when the direction of the nanorods changed from perpendicular to parallel with the field. In addition, the ZFC and FC M-T curves of hematite were different than the ZFC and FC M-T curves of magnetite.

M.Sc. / High-grade hematite ores at the Thabazimbi Mine, Limpopo Province, occur as stratabound bodies in the Early Paleoproterozoic Penge Iron Formation of the Transvaal Supergroup. Iron ores occur at three distinct positions in the Penge Iron Formation (i) basal ore bodies located immediately above a thin oxidised shale unit that marks the base of the Penge Iron Formation in the Thabazimbi area and that may be interpreted as a structural contact towards the underlying dolostones of the Malmani Subgroup; (ii) ore bodies developed immediately above a prominent mafic sill in the Penge Iron Formation; (iii) small, lenticular ore bodies developed in the iron-formation without apparent structural control. Ore bodies in all three stratigraphic positions formed on the expense of the Penge Iron Formation protore, they share very similar mineralogical and textural attributes and can be subdivided into three major ore types with respect to their mineralogy and physical characteristics, namely, (a) carbonate-hematite ore; (b) hard hematite ore; (c) supergene modified ore. Further subdivision into subtypes is possible based on textural attributes. The first stage of iron ore formation at the Thabazimbi deposit is marked by oxidation of ferrous minerals (carbonates and grunerite) and their replacement by hematite. Efficient leaching and replacement of chert in the iron-formation to produce high-grade hematite ores characterizes the second stage of alteration. Stable isotope and fluid inclusion evidence point to a hydrothermal origin of the iron ores. Two hydrothermal fluids were identified, namely a highly saline Ca-Mg-rich brine (S = 27 wt% NaClequiv, TH = 160ºC) and a Nadominated fluid of intermediate salinity (S = 10 wt% NaClequiv, TH = 130ºC) that is possibly of meteoric origin. The results obtained in this study are used to propose the following sequence of mineralising events for the Thabazimbi iron ore deposit: (i) Deposition of iron-formation and diagenesis; (ii) contact metamorphic alteration related to the intrusion of the Bushveld igneous complex; (iii) metasomatic oxidation, leaching and residual upgrading that is tentatively linked to structurallycontrolled hydrothermal fluid flow; (iv) supergene modification of existing high-grade ore bodies in post-Gondwana times along the old African land surface.