No description available.

No description available.

No description available.

No description available.

Sulfide minerals are a major source of metals; however, certain sulfide minerals, such as pyrite and pyrrhotite, are less desirable. Froth flotation is a commonly used separation technique, which requires the use of several reagents to float and depress different sulfide minerals. Xanthate, a thiol collector, has gained immense usage in sulfide minerals flotation. However, some sulfides are naturally hydrophobic and may float without a collector. Iron sulfides, such as pyrite and pyrrhotite, are few of the most abundant minerals, yet economically insignificant. Their existence with other sulfide minerals leads to an inefficient separation process as well as environmental problems, such as acid mine drainage during mining and processing and SO2 emissions during smelting process. A part of the present study is focused on understanding their behavior, which leads to undesired flotation and difficulties in separation. The major reasons for the undesired flotation are attributed to the collectorless hydrophobicity and the activation with heavy metal ions. To better understand the collectorless hydrophobicity of pyrite, Electrochemical Impedance Spectroscopy (EIS) of freshly fractured pyrite electrodes was used to study the oxidation and reduction of the mineral. The EIS results showed that the rate of reaction increases with oxidation and reduction. At moderate oxidizing potentials, the rate of reaction is too slow to replenish hydrophilic iron species leaving hydrophobic sulfur species on the surface. However, at higher potentials, iron species are replaced fast enough to depress its flotation. Effects of pH and polishing were also explored using EIS. Besides collectorless hydrophobicity, the activation of pyrrhotite with nickel ions and interaction with xanthate ions makes the separation more difficult. DETA and SO2 are commonly used as pyrrhotite depressants; however, the mechanism is not very well understood. Contact angle measurements, cyclic voltammetry and Tafel studies have been used to elucidate the depressing action of DETA and SO2. It was observed that DETA and SO2 complement each other in maintaining lower pulp potentials and removing polysulfides. DETA also helps in deactivating pyrrhotite. Therefore, the combined use of DETA and SO2 leads to the inhibition of both the collectorless flotation and the adsorption of xanthate. The adsorption of xanthate on sulfide minerals is a mixed-potential mechanism, i.e., the anodic oxidation of xanthate requires a cathodic counterpart. Normally, the cathodic reaction is provided by the reduction of oxygen. However, oxygen can be replaced by other oxidants. Ferric ions are normally present in the flotation pulp. Their source could be either iron from the grinding circuit or the ore itself. The galvanic studies were carried out to test the possibility of using ferric ions as oxidants and positive results were obtained. Tafel studies were carried out to measure the activation energies for the adsorption of ethylxanthate on several sulfide minerals. Pyrite, pyrrhotite (pure and nickel activated), chalcocite and covellite were studied in 10-4 M ethylxanthate solution at pH 6.8 at temperatures in the range of 22 – 30 0C. The Tafel studies showed that xanthate adsorbs as dixanthogen (X2) on pyrite and pyrrhotite, nickel dixanthate (NiX2) on nickel-activated pyrrhotite and cuprous xanthate (CuX) on both chalcocite and covellite. However, the mechanism for xanthate adsorption on each mineral is different. The free energy of reaction estimated from the activation energies are in good agreement with thermodynamically calculated ones. / Ph. D.

The Ducktown mining district, located in the southeastern corner of Tennessee within the Blue Ridge Province of the southern Appalachians, contains some of the largest metamorphosed pyrrhotite-pyrite-rich massive sultide deposits in the Appalachian-Caledonian orogen. Oxygen isotope temperatures of 530±20°C are consistent with previous estimates based on mineral thermobarometers (540±40°C; 6-7 kb) suggesting that minerals attained oxygen isotopic equilibrium during peak metamorphism and underwent little retrograde exchange. Fluid inclusion and petrologic data do not support the previous interpretation that low δ¹⁸O zones near orebodies are synmetamorphic, rather, a premetamorphic origin is indicated. Integrated fluid/rock ratios were low enough during and after metamorphism that premetamorphic spatial variations in δ¹⁸O were retained. However, hydrogen and carbon isotopes were homogenized throughout the area during or before metamorphism. The low δ¹⁸O zones surrounding the orebodies appear to have formed during sea—fIoor hydrothermal activity associated with ore deposition. The δ¹⁸O value of the fluid responsible for ore deposition, assuming a temperature of 300°C, is calculated to be -1 to +2 per mil, consistent with the interpretation that the ore fluid was modified seawater. Calculation of theoretical C-O-H-S fluid speciation suggests that the fluid in equilibrium with clinopyroxene-bearing rocks was essentially H₂O+CO₂with XCO₂ = 0.10. However, primary fluid inclusions located in clinopyroxene contain signifticant quantities of CH₄. This discrepancy is explained by hydrogen diffusion into primary fluid inclusions and subsequent conversion of CO₂ to CH₄ during uplift in response to an fH₂ gradient between inclusion and matrix fluids. Low δD values of primary fluid inclusions are consistent with diffusive addition of isotopically light hydrogen after trapping. Secondary inclusions in metamorphic quartz record a complex uplift history involving a variety of fluids in the C-O-H-N-salt system. lsochores calculated for these inclusions constrain the uplift path to have been initially concave toward the temperature axis. Over the pressure range 2.3 to 1.0 kb the uplift path became nearly isothermal at 215±20°C. lmmiscible H₂O-CH₄-N₂-NaCl fluids present during the isothermal stage of the uplift history were derived during Alleghanian thrusting by expulsion of pore fluids and maturation of organic matter in lower plate sedimentary rocks proposed to underlie the deposits. Average uplift rates of 0.1 mm/yr are suggested by the uplift path and available geochronologic data. / Ph. D.

No description available.

by Choy Wing Hong. / Thesis (M.Phil.)--Chinese University of Hong Kong, 1998. / Includes bibliographical references (leaves 95-102). / Text in English; abstract also in Chinese. / by Choy Wing Hong. / ABSTRACT --- p.vi / ACKNOWLEDGEMENTS --- p.x / LIST OF FIGURES --- p.xi / LIST OF TABLES --- p.xiii / Chapter Chapter 1 --- Introduction --- p.1 / Chapter 1.1 --- Background --- p.1 / Chapter 1.2 --- Surface passivation techniques --- p.2 / Chapter 1.2.1 --- Sulfide solution passivation --- p.2 / Chapter 1.2.2 --- Gas-phase sulfide passivation --- p.3 / Chapter 1.2.3 --- Ultra-violet and ozone exposure --- p.4 / Chapter 1.3 --- Surface structure of sulfide-passivated surface --- p.5 / Chapter 1.4 --- Surface structure of ultra-violet/ozone oxidation --- p.8 / Chapter 1.5 --- Objectives of present study --- p.10 / Chapter Chapter 2 --- Instrumentation --- p.12 / Chapter 2.1 --- Introduction --- p.12 / Chapter 2.2 --- Atomic force microscopy (AFM) --- p.12 / Chapter 2.2.1 --- The development of AFM --- p.12 / Chapter 2.2.2 --- Basic principles of AFM --- p.12 / Chapter 2.2.3 --- Forces and their relevance to atomic force microscopy --- p.13 / Chapter 2.2.3.1 --- Van Der Waals forces --- p.15 / Chapter 2.2.3.2 --- Repulsive forces --- p.15 / Chapter 2.2.3.3 --- Capillary forces --- p.15 / Chapter 2.2.4 --- Displacement sensor of AFM --- p.15 / Chapter 2.2.4.1 --- Electron tunneling --- p.16 / Chapter 2.2.4.2 --- Optical interference --- p.16 / Chapter 2.2.4.3 --- Laser beam deflection --- p.16 / Chapter 2.2.5 --- Instrument specification --- p.17 / Chapter 2.2.5.1 --- Contact mode AFM --- p.17 / Chapter 2.3 --- X-ray photoelectron spectroscopy --- p.19 / Chapter 2.3.1 --- The development of XPS --- p.19 / Chapter 2.3.2 --- Basic principles of XPS --- p.19 / Chapter 2.3.3 --- XPS experiments --- p.23 / Chapter 2.3.4 --- Quantitative analysis --- p.26 / Chapter 2.3.4.1 --- Atomic concentration of a homogenous materials --- p.26 / Chapter 2.3.4.2 --- Layer structure --- p.27 / Chapter 2.4 --- Rutherford backscattering spectrometry (RBS) --- p.29 / Chapter 2.4.1 --- Basic principles --- p.29 / Chapter 2.4.2 --- Kinematics --- p.29 / Chapter 2.4.3 --- Channeling --- p.31 / Chapter Chapter 3 --- Surface treatments --- p.32 / Chapter 3.1 --- Semiconductor wafer --- p.32 / Chapter 3.2 --- Cleaning procedures --- p.32 / Chapter 3.3 --- Polysulfide passivation --- p.34 / Chapter 3.4 --- UV/Ozone oxidation --- p.39 / Chapter Chapter 4 --- Surface roughness and oxide contents of sulfide passivation --- p.41 / Chapter 4.1 --- Introduction --- p.41 / Chapter 4.2 --- Experimental methodology --- p.42 / Chapter 4.3 --- Etching --- p.44 / Chapter 4.3.1 --- Etching effect of polysulfide solution --- p.45 / Chapter 4.3.2 --- Possible consequences of the etching effect --- p.45 / Chapter 4.4 --- Oxide contents --- p.47 / Chapter 4.4.1 --- Oxide gained during polysulfide solution treatment --- p.47 / Chapter 4.4.2 --- Oxide gained after polysulfide passivation --- p.47 / Chapter 4.5 --- Surface roughness --- p.49 / Chapter 4.5.1 --- Surface roughness after different passivation methods --- p.49 / Chapter 4.5.2 --- The sticking probability after different passivations --- p.51 / Chapter 4.6 --- The spiral ladder of solution-phase passivation --- p.55 / Chapter 4.7 --- Conclusions --- p.58 / Chapter Chapter 5 --- Sulfide on Ge/GaAs heterojunction --- p.59 / Chapter 5.1 --- Introduction --- p.59 / Chapter 5.1.1 --- Band structure of Ge/GaAs heteroj unction --- p.59 / Chapter 5.1.2 --- Lattice match of Ge/GaAs heteroj unction --- p.60 / Chapter 5.1.3 --- The growth of Ge on GaAs using molecular beam epitaxy --- p.62 / Chapter 5.2 --- The growth of Ge on GaAs using thermal pulse annealing --- p.63 / Chapter 5.3 --- Sulfide as an atomic interdiffusion barrier --- p.65 / Chapter 5.3.1 --- Experimental methodology --- p.65 / Chapter 5.3.2 --- Crystallinity of Ge --- p.67 / Chapter 5.3.3 --- Results and discussions --- p.67 / Chapter 5.3.3.1 --- RBS and XPS results --- p.67 / Chapter 5.3.3.2 --- AFM and I-V results --- p.71 / Chapter 5.4 --- Conclusions --- p.71 / Chapter Chapter 6 --- UV/03 on Ge/GaAs heterojunction --- p.72 / Chapter 6.1 --- Introduction of UV/o3 oxidation --- p.72 / Chapter 6.2 --- UV/o3 oxidation on GaAs --- p.74 / Chapter 6.3 --- Ge on UV/o3 treated GaAs --- p.76 / Chapter 6.3.1 --- Experimental methodology --- p.76 / Chapter 6.3.2 --- Crystallinity of Ge --- p.77 / Chapter 6.3.3 --- AFM results --- p.77 / Chapter 6.3.4 --- RBS results --- p.80 / Chapter 6.4 --- Diodes --- p.82 / Chapter 6.4.1 --- Fabrication of diode --- p.82 / Chapter 6.4.2 --- Diode characteristics --- p.84 / Chapter 6.4.3 --- I-V characteristics --- p.90 / Chapter 6.5 --- Conclusions --- p.90 / Chapter Chapter 7 --- Conclusion and future work --- p.93 / Chapter 7.1 --- Conclusions --- p.93 / Chapter 7.2 --- Future works --- p.94 / Reference --- p.95

Orientador: César Augusto Moreira / Resumo: O potencial geológico do Brasil para mineralizações auríferas é mundialmente reconhecido, quer seja pelo seu passado histórico, como por conta do expressivo número de ocorrências, depósitos, minas e as centenas de áreas ativas e inativas distribuídas por todo o país. Na região em que presente estudo foi realizado, já foram detalhados uma série de jazimentos desta natureza, caracterizadas por associações de filões de quartzo e pequenas proporções de óxidos de ferro, pirita e calcopirita. Este trabalho apresenta, portanto, os resultados de um estudo de prospecção geofísica de detalhe realizado a partir da aplicação conjunta dos métodos da Eletrorresistividade e da Polarização Induzida, integrados a análise estrutural. O local estudado consiste numa área potencialmente mineralizada em ouro no Complexo Bossoroca, localizada na zona rural do município de São Sepé (RS). Para obtenção dos dados geofísicos foram realizadas cinco linhas de 400m de comprimento e 10m de espaçamento entre eletrodos, através da técnica de tomografia elétrica em arranjo Schlumberger. O levantamento estrutural, por sua vez, considerou medidas de lineamentos, extraídas a partir de imagem SRTM da área, assim como dados de acamamentos e de fraturas de litotipos pertencente ao Complexo Bossoroca, obtidos a partir de levantamento estrutural sistemático. Os resultados de resistividade não permitiram a definição de zonas mineralizadas, possivelmente devido ao pequeno contraste existente entre a rocha encaixante e ... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: Brazil’s geological potential for auriferous mineralization is recognized worldwide for its historic past, as well as for the number of occurrences, deposits, mines and hundreds of active and inactive areas distributed throughout the country. In the region where the present study was carried out, series of such deposits have already been described, characterized by associations of quartz lodes and small proportions of iron oxides, pyrite and chalcopyrite. This work presents the results of a geophysical prospecting study obtained through the joint application of the DC resistivity and induced polarization methods, integrated to the structural analysis. The studied areas consists of a potentially gold mineralized area in the Bossoroca Complex located in the county of São Sepé (RS). In order to obtain the geophysical data, five lines with 400m in length and 10m of spacing between electrodes were made through the electrical tomography technique in a Schlumberger arrangement. The structural data collecting considered measures of lineaments, extracted from the SRTM image of the area, as well as data of bedding and fractures of lithotypes belonging to the Bossoroca Complex, obtained from a systematic structural data collecting. The results of resistivity did not allow the definition of mineralized zones, possibly due to the small contrast between the rock and the mineralized zone. The chargeability data indicated three zones with high values of load (≥ 4,4 mV / V) located to the eas... (Complete abstract click electronic access below) / Mestre

Today, there is a high demand on clean steel for high performance materialproperties. Thus, steel producers try to deliver a steel product with the highestquality and cleanliness to the market. The number of parameters that affect thesteel cleanliness may vary depending on the required material properties of thefinal product. However, the non-metallic inclusion characteristics represent one ofthe most important parameters. More specifically, the composition, size, numberand morphology affect steel cleanliness. In this work, selected parameters affectingthe inclusion characteristics were studied using the following methods: i)thermodynamic calculations (including computational thermodynamiccalculations), ii) inclusion determinations using a cross sectional (CS) method (2Dinvestigations) and iii) inclusion determinations using an electrolytic extraction(EE) method (3D investigations). The computational thermodynamic calculations of the slag-steel and inclusion-steelequilibriums were carried out using the Thermo-Calc software. With the help ofthese calculations, the influence of the slag carryover on the top slag, aluminumcontent in steel and sulfur distribution ratio as well as predictions of stable phasesof inclusions were studied. In addition, inclusion determinations of tool steel gradesamples collected during various stages of the ladle treatment in a scrap-based steelplant were carried out using both 2D and 3D methods. Furthermore, inclusiondeterminations of bearing steel grade samples from a runner system after ingotcasting were performed using a 2D metallographic method (CS-method). Also, theINCAFeature software was used, when using cross sectional method, in order tocollect more statistics of the inclusion characteristics. It was found that slag carryover has a large influence on the composition of theactual top slag as well as the aluminum content in the steel as well as the sulfurdistribution ratio. In addition, steel and slag were found to be in “near”-equilibriumconditions, after the completion of the vacuum degassing operation. Furthermore,the composition of small-size inclusions in samples taken from tool steel was foundto be very scattered. Moreover, the composition of the large-size inclusions wasfound to be less scattered. Furthermore, closer to the top slag composition insamples collected after vacuum degassing. Finally, the accuracy of the inclusioncomposition determinations of tool steel samples using the electrolytic extractionmethod was found to be better than for the cross sectional method. The worseaccuracy of the CS-method is due to a considerable effect of matrix elements oninclusion composition. / QC 20100709