Thesis (M.Sc.)--Memorial University of Newfoundland, 2005. / Restricted until October 2006. Bibliography: leaves 280-292. Also available online.

Thesis (M.S.)--West Virginia University, 2004. / Title from document title page. Document formatted into pages; contains xiv, 74 p. : ill. (some col.). Includes abstract. Includes bibliographical references (p. 69-71).

A thesis submitted to the Faculty of Science, University of the Witwatersrand; Johannesburg, in fulfilment of the requirements for the degree of Doctor of Philosophy. July 1991 / Precipitated-iron Fischer- Tropsch catalysts were sulfided in the range 500 - 20000 ppm S/Fe with an aqueous sulfide source (Na2S, (NB4)zS, (NB4)zS5) during the precipitation process. Sulfidation was performed at pH 10.75, 8.5 and 6.9. Sodium ions were removed by centrifugation, and atomic absorption analysis confirmed low sodium levels (0-51 ppm). Based on solution speciation models, ferrous sulfide (FeS) which formed from aqueous HS' species, was found to influence the iron-oxyhydroxide crystallite morphology. It is proposed that, when sulfide was added at pH 10.75, FeS molecules functioned as nuclei for crystallite growth, while a pH 6.9 they assisted 'with the aggregation of particles. The processes of nucleation and aggregation appeared to be in competition following sulfidation at pH 8.5, resulting in a composite morphology that produced an inactive catalyst. The bulk structure of the catalysts was elucidated using XRD, SEM and nitrogen porosimetry, All sulfided catalysts exhibited enhanced BET surface areas and total pore volumes with a maximum at 2000 ppm S (surface area = 166 m2/g,total pore volume = 0.254 cm3/g) compared to an unsulfided catalyst (surface area = 58 m2/g, total pore volume = 0.184 cm3/g), Furthermore, for any series of catalysts at the same level of sulfidation, the BET surface areas were observed to decrease as the pH of sulfide addition decreased. Increasing levels of sulfidation (to 20000 ppm) brought about an increase in crystallite size and therefore, improved crystallinity as determined by XRD measurements. Materials with larger crystallites possess smaller surface areas, and thus the crystallinity was found to increase as the pH of sulfidation decreased. Surface characterisation by XPS after calcination at 400°C and reduction (400°C), revealed sulfate species (169.4 eV) on catalysts sulfided with 500-2000 ppm, while sulfide species (162.O eV) emerged at higher sulfide content. No sulfates were observed on reduced catalysts following calcination at 200 C. [Abbreviated Abstract. Open document to view full version]

Thesis (doctoral)--Technische Universiteit Delft, 1998. / Includes bibliographical references.

Thesis (doctoral)--Technische Universiteit Delft, 1998. / Includes bibliographical references.

The Miguel Auza mine, located in Zacatecas State, Mexico, is a vein-type polymetallic epithermal deposit hosted in deformed argillite, siltstone and greywacke of the Cretaceous Caracol Formation. Silver-rich base metal veins (0.2 m to >1.5 m wide) are spatially associated with NE-striking, steeply SE- dipping (70-80º) faults over a strike length of 1.6 km and a depth of 460 m. Three distinct structural stages are correlated with hydrothermal mineral deposition: Stage I is characterized by normal faulting and early hypogene alteration of the sedimentary rock. Stage II is associated with reverse-sense reactivation of early normal faults, dilation of bedding planes/fractures, and deposition of barren calcite + pyrite veinlets. Sub-stages IIA and IIB are related to the development of reverse-fault-hosted quartz-carbonate sulphide veins and characterize the main stage of mineralization. Associated hydrothermal minerals during the main stage of mineral deposition are quartz, muscovite, and calcite. Stage III involves late NW-SE striking block faulting, brecciation and calcite veining. Later supergene oxidation of veins led to deposition of Fe-oxides and hydroxides. The main Ag-bearing minerals comprise pyrargyrite, tetrahedrite- freibergite, polybasite-antimonpearceite, and acanthite, with associated sulphides including galena, sphalerite, chalcopyrite, arsenopyrite and pyrite. In the main ore zone, base metal sulphides are commonly intergrown with the Ag-bearing sulfosalts. Compositions of Ag-rich tetrahedrite + pyrargyrite + sphalerite indicate a primary depositional temperature around 325-350ºC for the late phase of sub-stage IIB. 40Ar/39Ar dating of wall-rock illite associated with stage I alteration yields an age of 46.58 ± 0.30 Ma. Ages of 46.01 ± 0.55 Ma, and 44.55 ± 0.22 Ma were obtained for vein muscovite related to the main stage (sub-stage IIB) of ore deposition. These ages correspond to the later stage of the Laramide orogeny in Northern Mexico. The geometric relationship between the various structures, vein types, and the regional Miguel Auza fault zone suggest episodic reverse-sense reactivation of normal faults. Based on (1) the tectonic setting, (2) spatially related igneous rocks, (3) ore and gangue mineralogy, and textures (4) geochemical signature, and (5) inferred temperature of formation, the Miguel Auza deposit is interpreted to be an intermediate-sulfidation type deposit. / Thesis (Master, Geological Sciences & Geological Engineering) -- Queen's University, 2010-04-15 13:04:06.104

The Giant Mine near Yellowknife, NWT generated 237 000 tonnes of arsenic-trioxide (As₂O₃)-rich dust as a by-product of gold mining during its years of operation (1948 - 2004). Arsenic trioxide is a relatively soluble form of arsenic (As) and is currently stored in the mine, posing a threat of contamination to the adjacent Great Slave Lake. This research investigates the potential for permanent remediation of the As₂O₃ using sulfidation to transform it to arsenic trisulfide (As₂S₃). Knowing that aqueous As₂O₃ readily reacts with sulfide (Ostermeyer, 2021), it was determined that the most practical and effective method to achieve sulfidation of the Giant Mine dust is to first dissolve the As₂O₃ and then conduct the reaction with sulfide. The optimal conditions at which to dissolve As₂O₃ were investigated. The solubility and dissolution rate in water were shown to increase with temperature, with solubility increasing from 185.7 g As₂O₃/kg water at 140 °C to 250.6 g As₂O₃/kg water at 180 °C. Qualitative demonstrations of the rate of dissolution show that ≥ 90 % of the As₂O₃ dissolved within 5 minutes at 140 °C, and 4 minutes at 180 °C; previous research indicates that time to equilibrium is > 24 hours at 60 °C (CANMET, 2000). Reaction of Giant-Mine material in water at elevated temperatures (140 °C - 200 °C) for 10 to 30 minutes consistently resulted in dissolution of approximately 80 wt. % of the initial solid-phase As concentrations, representing almost all the As₂O₃, yielding undissolved residues (≈ 40 wt. % of initial mass). The persistence of As in these residues is likely due to it being hosted in As₂O₃ - Sb₂O₃ solid solutions and low-solubility Fe-oxide phases in the initial sample (CANMET, 2000; Poirier, 2004).

This thesis study is concerned with the genetic investigation of two epithermal gold deposits (Madendag and Kartaldag) in &Ccedil / anakkale, NW Turkey. The methodology comprises field and integrated laboratory studies including mineralogic-petrographic, geochemical, isotopic, and fluid inclusion analysis. Kartaldag deposit, hosted by dacite porphyry, is a typical vein deposit associated with four main alteration types: i) propylitic, ii) quartz-kaolin, iii) quartz-alunitepyrophyllite, iv) silicification, the latter being characterized by two distinct quartz generations as early (vuggy) and late (banded, colloform). Primary sulfide minerals are pyrite, covellite and sphalerite. Oxygen and sulfur isotope analyses, performed on quartz (&delta / 18O: 7.93- 8.95 &permil / ) and pyrite (&delta / 34S: -4.8 &permil / ) separates, suggest a magmatic source for the fluid. Microthermometric analysis performed on quartz yield a temperature range of 250-285 &ordm / C, and 0-1.7 wt % NaCl eqv. salinity. Madendag deposit, hosted by micaschists, is also vein type associated with two main alteration types: illite and kaolin dominated argillization and silicification, characterized by two distinct quartz phases as early and late. Oxygen isotope analyses on quartz (&delta / 18O: 9.55-18.19 &permil / ) indicate contribution from a metamorphic source. Microthermometric analysis on quartz yield a temperature range of 235-255 &ordm / C and 0.0-0.7 wt % NaCl eqv. salinity. The presence of alunite, pyrophyllite and kaolinite, vuggy quartz and covellite suggest a high-sulfidation epithermal system for Kartaldag. On the other hand, Madendag is identified as a low- sulfidation type owing to the presence of neutral pH clays and typical low temperature textures (e.g. colloform, comb, banded quartz).

Metal-based nanoparticles (MNPs) are becoming increasingly common in commercial products. Release of these materials into the environment raises concerns about the potential risks they pose to aquatic life. Predicting these risks requires an understanding of MNPs' chemical transformations. In this study, arrays of immobilized MNPs fabricated by nanosphere lithography (NSL) were used to investigate environmental transformations of MNPs. Specifically, sulfidation of silver nanoparticles (Ag NPs) and dissolution of copper-based nanoparticles (Cu NPs) were investigated. Atomic force microscopy (AFM) and transmission electron microscopy were the primary analytical techniques for these investigations. Because the MNPs were immobilized on a solid surface, the samples were field deployable, environmentally relevant metal concentrations were maintained, and the confounding influence of MNP aggregation was eliminated. Ag NP samples were deployed in a full-scale wastewater treatment plant. Sulfidation occurred almost exclusively in anaerobic zones of the WWTP, where the initial sulfidation rate was 11-14 nm of Ag converted to Ag2S per day. Conversion to Ag2S was complete within 7-10 d. Dissolution rates of Cu-based NPs were measured in situ over a range of pH by flow-cell AFM. Based on the measured rates, CuO/Cu(OH)2 NPs dissolve completely within a matter of hours at any pH, metallic Cu NPs persist for a few hours to days, and CuxS NPs do not dissolve significantly over the time scales studied. Field deployment of samples in a freshwater stream confirmed these conclusions for a natural aquatic system. This research demonstrates that environmental transformations of MNPs will be a key factor in determining the ultimate form and concentration of NPs that aquatic organisms will be exposed to. / Ph. D.

Parmi les biocarburants de deuxième génération, la chaîne "biomass to liquid" vise à convertir les résidus agricoles en carburant. Cette voie suppose une première étape de gazéification de la biomasse en un gaz de synthèse, mélange de CO et de H2. Ce gaz doit ensuite être désulfuré, afin de ne pas endommager le catalyseur Fischer-Tropsch, à l'aide d'oxydes métalliques tel que l'oxyde de zinc, qui se sulfure selon la réaction suivante : ZnO(s) + H2S(g) → ZnS(s) + H2O(g) a l'heure actuelle, aucune étude ne décrit les mécanismes de la réaction. le but de ce travail a donc été d'identifier les différentes étapes du mécanisme de sulfuration puis d'établir une loi de vitesse de réaction. L'étude cinétique a été réalisée par thermogravimétrie. La formation de cavités au cœur des particules sulfurées a été observée par MEB et MET, mettant en évidence une croissance externe de la phase de ZnS. Un mécanisme de sulfuration en huit étapes élémentaires a été proposé avec diffusion des atomes de zinc et d'oxygène de l'interface interne ZnO/ZnS vers la surface externe du ZnS formé. Le régime limitant de la réaction a été déterminé via l'étude de l'influence des pressions partielles de H2S et de H2O sur la vitesse de réaction. Un régime mixte sur la base de deux étapes élémentaires a été envisagé : une réaction d'interface externe avec désorption des molécules d'eau et la diffusion des atomes d'oxygène. la formation de cavités à l'interface interne ZnO/ZnS entraînant une diminution de la surface de contact entre les phases ZnO et ZnS a été mise en évidence, phénomène probablement à l'origine du ralentissement de la réaction observé sur les courbes cinétiques. / Among the second generation biofuels processes, the "biomass to liquid" process aims at turning agricultural wastes into fuels. This process comprises a first step of feed gasification into a synthesis gas, composed of CO and H2. Sulfur compounds such as H2S are also present in the synthesis gas and must be removed, in order to prevent Fischer-Tropsch catalyst poisoning. deep desulfurization is achieved with metal oxides such as zinc oxide, which reacts with H2S according to the reaction: ZnO(s) + H2S(g) → ZnS(s) + H2O(g) nevertheless to our knowledge, most of the studies found in the literature do not describe accurately the mechanism involved at a crystal scale. The aim of this work was to determine the elementary steps of the ZnO sulfidation reaction, and in fine to establish a kinetic rate model in agreement with the proposed mechanism. The sulfidation reaction has been studied through thermogravimetric experiments. SEM and TEM characterizations of sulfided ZnO have revealed the presence of voids inside particles, that is evidence an external growth of ZnS phase. A sulfidation mechanism with eight elementary steps has been proposed, based on zinc and oxygen diffusion through the ZnS layer from the internal ZnO/ZnS interface to the ZnS surface. The rate determining step of the reaction was determined from the study of the influence of H2S and H2O partial pressures on the reaction rate. A "mixed kinetics" based on two elementary steps was considered: external interface reaction with H2O desorption and oxygen diffusion. Cavities formation at the internal ZnO/ZnS interface leading to a decreasing contact zone between ZnO and ZnS phases might be responsible for the reaction rate blocking observed on the kinetic curves.