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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