The oxidation of thin rectangular plates of pyrrhotite by sulphur dioxide between 700 and 900°C has been studied at sulphur dioxide partial pressures ranging from 0.25 to 1.0 atm. As reaction proceeded, an outer layer of magnetite thickened at the expense of pyrrhotite, sample dimensions remaining constant. Observations of partially oxidized samples have indicated a linear reaction front and the lack of retained pyrrhotite. Weight loss curves have indicated two types of behaviour: constant rate with increasing porosity at high sample densities, and increasing rate with increasing porosity at lower sample densities. Analysis by a transport control model has shown that chemical processes have no effect on the reaction rate and that the rate is controlled by gaseous diffusion through a laminar gas film at onset of reaction of low density samples. As the magnetite layer thickens, control shifts to that of gaseous diffusion through the porous magnetite. By correlation of observations and effective diffusion coefficients, it is demonstrated that the structure of magnetite varies as a function of its thickness and is dependent on reaction temperature and pressure. The primary mode of diffusion in the porous magnetite layer is determined to be transitional for the range of pyrrhotite densities investigated. High density samples are subject to rupturing. This causes approximately linear reaction rates which are independent of sample density. It is proposed that reaction is cyclic in that it proceeds by the transport of oxide ions to the reaction front, subsequent rupturing, and gaseous diffusion until pore distributions prohibit Knudsen diffusion. / Applied Science, Faculty of / Materials Engineering, Department of / Graduate

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Self-heating of sulphide minerals has a potential for serious impact on environment and safety in mining of ores, and storage and transport of concentrates. A research program, focused on the investigation of the conditions under which the H2S is produced from pyrrhotite-rich materials, has been initiated using the self-heating facility and technology developed at the Noranda Technology Centre. It is hypothesized that H 2S production could be important in self-heating as the exothermic heat of oxidation of H2S to SO2 is greater than that for oxidation of S to SO2. / The hypothesis of liberation of H2S was tested using copper (as metal pieces and sulphate solution) as a detector, both in the self-heating apparatus and in a "weathering" apparatus at 40°C. X-ray diffraction and scanning electron microscopy analysis of coatings and precipitates confirmed the formation of copper sulphide and therefore indicated the release of H 2S. Release of H2S involves acid conditions and the possible origin of the acidity was discussed. / Prior work had suggested that the level of exposure to oxygen was a factor in self-heating. Tests were conducted to explore the role of oxygen level. Three tests were conducted in the weathering apparatus at 40°C with covers of no hole, 3 holes and 128 holes to control access the air. Weight gain was recorded every two days and stage B self-heating tests were conducted on the samples after a month of weathering. Under limited air access (no hole and 3 hole covers), the samples showed higher weight gain, higher degree of oxidation (by colour change) and higher self-heating rates compared with the sample with more exposure to air (128 hole cover). X-ray diffraction analysis identified the oxidation products elemental sulphur, maghemite and goethite in the samples under the limited air conditions. A series of non-standard self-heating tests were conducted in the self-heating apparatus under different air flow rates of Stage A. These showed that the samples weathered under low air flow rates yielded significantly higher self-heating rates in both stage A and B. / All the experiments indicate that a high level of exposure to air dose not promote self-heating but rather suppress it. Less oxidative conditions play a critical role in the self-heating of pyrrhotite-rich materials.

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Removing pyrite from coal and pyrrhotite from pentlandite play a critical role in coal and nickel production, respectively, to meet the stringent restriction on SO2 emission. The present project investigates first the mechanism of xanthate adsorption on gold using Atomic Force Microscope (AFM), then the depression of pyrite and pyrrhotite using the synthetic polymers developed by Cytec Industries. The results show that for xanthate/gold system, dixanthogen is the only species that renders the surface hydrophobic. Chemisorbed xanthate is observed on the gold surface but is hydrophilic. The synthetic polymers may adsorb on pyrite and pyrrhotite possibly through the hydrophobic interaction between the hydrophobic moiety of the polymer and the mineral surface that has been hydrophobized by collector adsorption. The hydrophilic moieties of the polymer are exposed to the aqueous phase and render the surface hydrophilic. / Master of Science