An Investigation into the Sulphation Roasting of Enargite Concentrates
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Potential new ore deposits containing significant levels of enargite, a copper arsenic sulphide mineral, are being considered for development. The processing of high arsenic copper concentrates directly in copper smelters is difficult due to environmental concerns. This thesis investigates a process using sulphation roasting as an alternative method for processing enargite concentrates; copper is recovered from the calcine by acid leaching, gold is extracted from the leach residue by conventional cyanidation and arsenic is either fixed in the calcine or precipitated from process emissions. In this research, sulphation roasting between the temperatures of 300-800oC, with varying oxygen and sulphur dioxide partial pressures, was investigated. Experiments indicated that high levels of copper extraction, as well as arsenic fixation, could be achieved from the produced calcines through hydrometallurgical processes. At operating temperatures between 400-550oC copper sulphate, copper arsenate, iron sulphate, hematite and iron arsenate form in the calcine, as well as some arsenic being volatilized as arsenic trioxide. At processing temperatures between 475-575oC, greater than 80% of the arsenic was retained in the calcine as copper and iron arsenates. Copper arsenate would be weak-acid soluble and fixed in an effluent treatment plant along with arsenic captured in the wet-gas scrubber bleed solution. As operating temperatures increase above 650oC copper sulphates were converted into oxysulphates, oxides and ferrites, hematite production was favoured, and arsenic was primarily volatilized. Increasing the sulphur dioxide addition in the reaction atmosphere resulted in additional sulphate formation and increased sulphate stability at higher temperatures. Sulphation roaster heat balances were developed for calcines produced at two temperatures, 500 and 750oC. They indicated that while high copper extraction and arsenic fixation rates could be achieved, the sulphation roasting reactions are highly exothermic and significant cooling water would need to be added. Due to these issues, it is likely that partial roasting operations would be economically favourable in greenfield operations. However, niche applications of this process in operations with existing copper SX/EW facilities in good acid markets, have the potential to be economically favourable.