Rock smelting of copper ores with waste heat recovery

Abstract

It is generally recognised that the grades of metallic ores are falling globally. This trend can be expected to increase the life cycle-based energy requirement for primary metal production due to the additional amount of material that must be handled and treated in the mining and mineral processing stages of the metal production life cycle. Rock (or whole ore) smelting has been suggested as a possible alternative processing route for low grade ores with a potentially lower energy intensity and environmental impact than traditional processing routes. In this processing route, the beneficiation stage is eliminated along with its associated energy consumption and greenhouse gas emissions, but this is partially offset by the need for more solid material to be handled and heated up to smelting temperatures. A life cycle assessment study was carried out to assess the potential energy and greenhouse gas benefits of a conceptual flowsheet of the rock smelting process, using copper ore as an example. Recovery and utilisation of waste heat in the slag (via dry slag granulation) and offgas streams from the smelting step was also included in the study, with the waste heat being utilised either for thermal applications or electricity generation. Based on the assumptions made, the results of the study indicated that this conceptual processing route does offer the potential for significant reductions in the embodied fossil fuel energy and associated greenhouse gas emissions of copper metal production from low grade ores compared to the most likely other competing processing route, heap leaching, for these ores. This is particularly the case where waste sulphide material is available, as the energy from oxidation of the waste sulphide during smelting replaces fossil fuel energy required for smelting. However, in the absence of any waste sulphide material, the embodied energy was only less than for heap leaching when the recovered waste heat was utilised in thermal applications. Other issues, particularly economics, will also play a significant role in determining the viability of this processing route for low grade ores.