A highly sensitive reflection-absorption infrared spectrophotometric technique was used to investigate the adsorption of sodium oleate from aqueous solutions onto magnesium carbonate (magnesite) thin film substrates. Valuable qualitative results were obtained, regarding the nature of the adsorbed species and their molecular orientation. However, this orientation effect strongly influenced the relative intensities of the infrared absorption bands; this prevented precise quantitative determinations. Under moderately acidic conditions, the original surface charge of magnesite was positive and near zero. The anionic collector was chemisorbed, forming only one type of complex, very similar to the bulk magnesium oleate. The hydrocarbon chains were oriented nearly parallel to the substrate, forming a homogeneous partially polymerized epoxide-polyether layer, strongly laterally bound, at the sites of the former C=C double bonds. The C-0 bonds were formed following a partial oxidation of the oleate in solution, by oxygen from the air. This adsorbed film converted the carbonate surface to a strongly hydrophobic condition, which was responsible for the high flotation recoveries obtained. Under basic conditions, the original magnesite surface was negatively charged. This limited the formation of the chemisorbed collector complex to a lower amount; different complexes, probably physically adsorbed, joined in forming a film. However, this was a more heterogenous film, showing different molecular orientations - - from nearly parallel, to closer to the normal to the adsorbent's surface. These aspects caused a net decrease in the degree of hydrophobicity, in comparison to the acidic conditions. The same oxidation and polymerization effects were observed, although to a lower extent. The film was also very stable. These properties of the adsorbed film were consistent with the lower flotation response observed under basic conditions. Therefore, more concentrated collector solutions were needed, to reach the same high recoveries obtained under moderately acidic conditions. / Applied Science, Faculty of / Mining Engineering, Keevil Institute of / Graduate

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Thesis (M.Sc.)--Memorial University of Newfoundland, 1996. / Typescript. Bibliography: leaves 141-145. Also available online.

Thesis (Ph. D.) - Harvard University, 1960. / Bibliography: leaves [90-93]

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Dans ce travail est présentée une étude systématique de la réactivité des carbonates de magnésium. La constant d'équilibre d'hydromagnésite a été déterminée en réacteurs fermés en fonction de la température de 22,5-75°C et à des pH compris entre 8,6-10,7. L'effet de Ca aqueux sur la cinétique de croissance de la magnésite à 100°C et pH ~ 7,7 a été déterminé en utilisant la microscopie à force atomique hydrothermale et des réacteurs hydrothermaux à circulation. La vitesse d'avancement des marches obtuses et les vitesses de croissance de la magnésite ne varient pas significativement avec la concentration en Ca2+. La solubilité de dolomite a été déterminée de 50-175°C en utilisant une cellule de concentration à électrode d'hydrogène. La valeur du produit de solubilité de la réaction CaMg(CO3)2 = Ca2+ + Mg2+ + 2CO32- générée dans cette étude est à peu près égale à celle prédite par SUPCRT92 à 200ºC mais elle est environ d'un ordre de grandeur plus élevée à 50°C. / This thesis presents a systematic study on the reactivity of Mg-carbonates. The equilibrium constant of hydromagnesite was determined in closed-system reactors as a function of temperature (22.5-75°C) and pH (8.6-10.7). The effect of aqueous Ca on the growth kinetics of magnesite at 100°C and pH ~ 7.7 was determined using hydrothermal atomic force microscopy and hydrothermal mixed-flow reactors. Both, the advancement rates of obtuse steps and the growth kinetics of magnesite are not significantly influenced by the concentration of aqueous Ca. Furthermore, the solubility of dolomite was determined from 50-175°C using a hydrogen concentration cell. The value of the solubility product of the reaction CaMg(CO3)2 = Ca2+ + Mg2+ + 2CO32- derived from this study is nearly equal to that predicted by SUPCRT92 at 200ºC but about one order of magnitude higher at 50°C, suggesting that dolomite is somewhat less stable than previously assumed.

MESMEG / Department of Mining and Environmental Geology / Muyexe magnesite deposit is situated in the Giyani Greenstone Belt in South Africa. Despite mining activities currently taking place at Muyexe magnesite deposit, little information is available about the geology and geochemistry of the deposit. This has resulted in a gap of information about the nature and character of magnesite, namely; its geology, mineralogy, geochemistry and mode of occurrence. Consequently, there is a need for further investigation of the magnesite deposit. The main objective of the study was to establish the geology and geochemistry of the Muyexe magnesite deposit and to ascertain its mode of occurrence. Further work involved undertaking detailed geological mapping, magnesite and rock sampling for petrographic and geochemical studies using petrographic microscopy and X-ray fluorescence spectrometry and identification of minerals in rocks and magnesite through X-ray diffractometry. A total of 20 magnesite and 4 host rock samples were collected from the Muyexe magnesite deposit. Furthermore, 62 rock samples were collected during geological field mapping of which 16 representative samples were selected for further analysis. X-ray fluorescence spectrometry was conducted on all selected samples of magnesite and rocks. XRD analysis was conducted on 12 rocks and 2 magnesite samples. Mineralogy of the rocks was also confirmed using petrographic microscopy. Detailed geological map of the Muyexe area revealed that the area is dominated by metamorphic ultramafic and mafic rocks. Basalt and peridotite are intrusions within the rock. The serpentinites and peridotites were found to be the source rock for magnesite mineralization, while the peridotite is the source rock for serpentinites rocks. XRD analysis revealed that magnesite in the Muyexe magnesite deposit is associated with silica and dolomite, while XRF data revealed that the following major oxides are present in magnesite as impurities; silicon dioxide (SiO2), calcium oxide (CaO), and iron oxide (Fe2O3). These oxides reduce the quality of magnesite, thus, their removal is necessary during processing. Magnesite of this deposit was found to be of good quality, with an average value of 54.02 wt. %. Magnesite at Muyexe was formed due to precipitation of Mg2+ along the fractures of serpentinites and peridotites due to CO2rich hydrothermal fluids. Magnesite occurs as a cryptocrystalline of the Kraubathtype. / NRF

No description available.

Tez (Doktora) - Süleyman Demirel Üniversitesi, Fen Bilimleri Enstitüsü, Jeoloji Mühendisliği Anabilim Dalı, 2008. / Kaynakça var.