Thesis (M.S.)--University of Missouri-Columbia, 2008. / The entire dissertation/thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file (which also appears in the research.pdf); a non-technical general description, or public abstract, appears in the public.pdf file. Title from title screen of research.pdf file (viewed July 14, 2009). Includes bibliographical references.

Thesis (Ph.D.)--York University, 2008. Graduate Programme in Earth and Space Science and Engineering. / Typescript. Includes bibliographical references (leaves123-134). Also available on the Internet. MODE OF ACCESS via web browser by entering the following URL: http://gateway.proquest.com/openurl?url_ver=Z39.88-2004&res_dat=xri:pqdiss&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&rft_dat=xri:pqdiss:NR46019

Thesis (M. Sc.)(Chemistry)--University of Pretoria, 2003. / Title from opening screen (viewed March 22, 2006). Summaries in English and Afrikaans. Includes bibliographical references.

The flotation of chalcopyrite and sphalerite has been accomplished without the use of collectors. Of the six chalcopyrite ores tested in the present work, some floated well using only a frother, while others required the addition of sodium sulfide, presumably to remove the hydrophilic surface oxidation products. On the other hand, the flotation of sphalerite ores was found to require both sodium sulfide treatment and copper-activation. The ratio of these two reagents was most critical, the optimum Cu²⁺/S²⁻ atomic ratio being approximately 0.17 over a wide range of reagent dosages. Potential measurements taken during both batch and micro-flotation experiments demonstrated that the collectorless flotation of chalcopyrite was possible only in oxidizing conditions, which confirms an earlier finding by Heyes and Trahar (1977). In relation to this phenomenon, three possible mechanisms have been discussed: i) elemental sulfur formed under oxidizing conditions is responsible for the collectorless flotation, ii) polysulfide ions formed during the incipient surface oxidation process render the mineral hydrophobic, and iii) HS⁻ ions, which may render the mineral hydrophilic upon adsorption, are removed from the system under oxidizing conditions. The first mechanism may operate primarily in acidic solutions, while the second mechanism operates in alkaline solutions where elemental sulfur is thermodynamically unstable. The third mechanism is based on the assumption that a clean, unoxidized surface is inherently hydrophobic. Spectroscopic evidence has been presented to support these proposed mechanisms. / Master of Science

The flotation of sphalerite has been demonstrated without the use of collectors. The effect of redox potential, pH, and copper-activation have been investigated in tests using samples of pure mineral. It has been found that in general, collectorless flotation of sphalerite can be accomplished at potentials greater than -200 mV, SHE, and is more readily carried out in acidic solutions. It has also been shown that although copper-activation was necessary to achieve flotation recoveries above 35%, an excessive addition of cupric ions may result in a decrease in floatability. Batch flotation experiments conducted using Elmwood Mine sphalerite ore have shown that in addition to copper-activation, the addition of sodium sulfide was required to obtain high grades and recoveries. If the ratio of the addition of these reagents is maintained such that the atomic ratio of cupric ions to sulfide ions is 0.31, good flotation is observed over a range of reagent dosages. X-ray photoelectron spectroscopy (XPS) was conducted on pure mineral samples after microflotation testing. Based on the sulfur species identified on highly flotable samples, possible mechanisms for collectorless flotation of sphalerite have been suggested. These include: i) elemental sulfur formed under oxidizing conditions is responsible for collectorless flotation; ii) polysulfides or metal-deficient sulfides formed as a result of mineral oxidation are responsible for collectorless flotation; and iii) removal of HS- ions, which may render the surface hydrophilic, under oxidizing conditions. The third mechanism is based on the assumption that clean, unoxidized sphalerite surfaces are naturally hydrophobic. Evidence has been presented to suggest that the first mechanism may be responsible for collectorless flotation in acidic solutions, while the second mechanism may be of greater importance in nearly neutral or basic solutions where elemental sulfur is thermodynamically less stable. / Master of Science

When sulfide minerals are exposed to the oxidizing conditions of the earth's surface, their metal ions are released into solution and the S²⁻ is oxidized to either elemental sulfur or sulfate. The experiments described here used a mixed flow reactor system to determine the oxidation rates of galena and sphalerite under conditions similar to that expected in a weathering ore deposit . The specific surface area of the run solids was determined by N₂ BET procedure and the surface textures observed by SEM. The amount of Fe³⁺ converted to Fe²⁺ by the oxidation reaction was determined using an Eh electrode. Solid reaction products include, orthorhombic S(s) and anglesite (PbSO₄) from the galena oxidation and minor orthorhombic S(s) from the sphalerite oxidation. The rate equations describing the 25°C data are: dn_Fe³⁺/dt = -5.5 ± 1.1 × 10⁻³ (A)(a<sub>Fe³⁺</sub)^{1.06 ± 0.16} for galena, and dn_Fe³⁺/dt = -1.8 ± 0.3 × 10⁻⁶ (A)(a_Fe³⁺)^{0.47 ± 0.08} for sphalerite. Where dn_Fe³⁺/dt is the rate of reduction of Fe³⁺ (moles sec⁻¹), and A is the surface area of the solid (m²). The calculated E_a for galena oxidation is 48 kJ mol⁻¹ (25 - 40°C) and is 84 kJ mol⁻¹ (25 -60°C) for sphalerite oxidation. Although galena and sphalerite are both simple, cubic, monosulfides their reaction rate with ferric iron differs by about 2.5 orders of magnitude for m_Fe³⁺ = 10⁻³. / M.S.

No description available.

Chen, Yanmin. / Thesis (Ph.D.)--Chinese University of Hong Kong, 2011. / Includes bibliographical references (leaves 140-160). / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Abstract also in Chinese.

Thesis (M.S.)--University of Missouri, School of Mines and Metallurgy, 1930. / The entire thesis text is included in file. Typescript. Title from title screen of thesis/dissertation PDF file (viewed February 10, 2010) Includes bibliographical references (p. 63-64).

Carbon matrix composite (CMC) electrode and surface conducting (SC) electrode have been developed to study the copper-activation and the subsequent xanthate adsorption on insulating sphalerite. Fabricating CMC electrode involves embedding sphalerite particles in carbon to form a carbon matrix composite; and SC electrode is designed by contacting a platinum wire to the sphalerite surface. When these electrodes are activated by heavy metal ions such as copper, a conducting layer is formed on the mineral surfaces that allows dynamic electrochemical studies to be conducted. Voltammetric studies on the copper activated CMC:ZnS electrodes in inert electrolytes show that although the activation product and kinetics may differ with pH, copper-activation occurs at all pH ranges. At acidic pH, a Cu2S-like activation product was formed at open circuit. When activation was conducted at near neutral and alkaline pH at open circuit, the surface products formed were identified to be CuS-like. It was also established that the amount of copper uptaken by sphalerite is strongly dependent on the time of activation and on the electrochemical potential applied during activation. Activation at potentials positive of the rest potential decreases the amount of copper on the surface. Indeed, activation at potentials of 50 to 100 mV more positive of the rest potential in the activating solution completely inhibits copper activation. This result is consistent with the anodic stripping voltammetry that shows copper can be removed from the surface of sphalerite at oxidizing potentials. Activation at potentials mildly negative of the rest potential causes a progressive increase in the amount of copper on the surface, consistent with the diffusion controlled reduction process between ZnS and Cu2+ ions observed in the activating solution. At very low potentials, however, elemental copper is formed, which may worsen the selectivity of the sphalerite flotation. Controlled potential contact angle measurements showed that xanthate adsorption does occur on copper-activated sphalerite at all pH ranges. However, the contact angles and flotation recovery decrease at near neutral pH. This problem is caused by the adsorption of the copper-hydroxy species on the activated sphalerite surface. It was found that addition of small amount of complexing reagent can improve the flotation recovery at the near neutral pH. The results obtained in the present work show that potential control of the activation process can provide a means of controlling copper uptake and, hence, the selectivity and recovery of sphalerite flotation. The development of CMC:ZnS and SC:ZnS electrodes provides a practical and reliable way to quantitatively estimate the amount of copper uptake on sphalerite surface after activation. / Ph. D.