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In the past two decades a depletion of rich ore materials has led to a decrease in mining productivity and a commensurate increase in costs, as the industry moves to extraction from lower economic ores. To sustain productivity, these inherently higher energy costs and expenditures must be limited by ensuring a deep understanding of ore material composition, and optimization of extraction processes. To this end, this thesis is aimed at optimising the thermal decomposition process of cobalt-rich pyrite sourced from the Thackaringa mine in Broken Hill, being one step in the patented process of sulfur and cobalt extraction by our industry partner Cobalt Blue Holdings (Ltd). The precursor material to thermal treatment was a pyrite ore concentrate powder constituting a complex multiphase composition, which needed to be characterized in terms of materials present and particle size distribution to identify influences on pyrite thermal decomposition to pyrrhotite. Main phases of pyrite (82.7(3) wt.%), albite (8.3(2) wt.%), quartz (4.96(12) wt.%), pyrrhotite 4M (3.06(10) wt.%), and rutile (0.923(14) wt.%) were identified and found consistent across a 50 kg aliquot obtained from the ‘Pyrite Hill’ subsite. Particle size distribution is broad (1 - 1000 µm), with 50(8) wt.% of the available pyrite manifesting in the 106 - 250 µm range, which was an essential result given how particle size influences the underlying ‘unreacted core’ reaction mechanism associated with pyrite particle decomposition. Powder X-ray diffraction was the primary characterization method used here, whereby a 7-min ball milling preparation technique was optimized to attain reproduceable results within 0.3 wt.% for main phases. Analysis of thermal treatment indicated no change in gangue phases when treated between 450 - 750 °C. Reaction was seen commencing > 450 °C, though sometimes as low as 300 °C in the special case of reduced particle size and ideal particle-gas interfacing known to improve pyrite decomposition. Activation energies, as in the Arrhenius relation, of 220 - 250(50) kJ/mol and pre-exponential factors between 1.9(2)x1012 - 2.2(2)x1015 sec-1 were obtained and coincide with those found in literature. The progression of reaction is best described by a combination of volumetric shrinking sphere mechanics at < 50 - 70 % pyrite conversion, and 3-dimensional diffusion limiting mechanics at > 50 - 70 % pyrite conversion when treated between 450 - 550 °C. Enhancing interaction between concentrate particles and carrier gas appears to be greatest influence on thermal decomposition across all experimental designs increasing degree of reaction by 22% and 58% at 600- and 650 °C respectively. |
