The need to extend the study of greenhouse impacts of mining and mineral processing to hydraulic streams: long distance pipelines count

Abstract

Mining operations are major producers of greenhouse gases and energy consumers. Norgate and Haque (2010, 2012) make a strong point regarding the impact and the potential for reductions in energy consumption and greenhouse gas emissions in the mining industry. For the copper concentrate production, they have distinguished different sub-processes, including drilling, basting, loading & hauling, ventilation, dewatering, crushing & grinding, and concentration. They conclude that the loading & hauling stage is the mostenergy-intensive, and that the crushing & grinding stage has the highest potential for energy saving. Although notexactly featuring at the core of the production processes, ore concentrate transport might be an energy-intensive activity when sufficiently long slurry transport lines are installed. In several South American countries, including Chile, Brazil, Peru and Argentina, it is very common for ore concentrate plants to deliver copper, iron or bauxite concentrate through complex topographies connecting distances above 100 km (Jacobs, 1991; Derammelaere and Shou, 2002; Abulnaga, 2002; Santos et al., 2009). Taking into account inventory bases from USA, Australia and Canada, Table 3 in Norgate and Haque (2010) shows, for copper concentrate, an energy consumption of 140 MJ/t at the concentrating stage and 673 MJ/t for dewatering. When applicable, the aforementioned transport process fits between both. Recently, Ihle and Tamburrino (2012) identified specific energy consumptions due to slurry transport in the order of 0.5 MJ/(t km) for a 6 inch nominal diameter pipeline for a dry throughput of 36.7 kg/ s, or about 1.1 million tons per year with a 95% utilization rate. A similar result was obtained by Wu et al. (2010) using a 158 mm internal diameter loop in a laboratory facility. This gives an energy requirement in the order of 50 MJ/t per 100 km pipeline, which can actually reach about twice the value for many long distance concentrate pipeline operations, thus competing with other energy consumption items referred to in Norgate and Haque (2010). Here, there is also significant room for energy efficient design and operation (Ihle and Tamburrino, 2012), and embodied energy and greenhouse gas emissions need to be accounted for and optimized as well. In the particular case of the hydraulic transport of concentrates, it is also necessary to consider the relation between water requirements and energy consumption: less of a water implies less water footprint but, on the other hand, higher energy consumptions, greenhouse gas emissions and embodied energy associated with the final product, the concentrate. A question being pursued in research currently being undertaken by the author is what is the optimal balance between the different elements that minimize the overall environmental impact of new infrastructure and process.