Effect of Ore Grade on Water Consumption
Just as a decline in metallic ore grade increases the embodied energy of primary metal production, so too does the embodied water increase due to the additional amount of material that has to be treated in the mineral processing stage. This is shown in Figure 8.11 for copper and nickel (see also Figure 8.5). The increase in embodied water with falling ore grade parallels the effect on embodied energy shown in Figure 8.10.
Deteriorating Ore Resources and Greenhouse Gas Emissions
As fossil fuels can be expected to be the primary energy source for metal production well into the future, a primary issue relating to the deterioration in quality of the world's ore resources is greenhouse gas emissions. This is illustrated in Figure 8.10, if one applies appropriate conversion factors for greenhouse gas emissions. Given the obvious connection between fossil fuels and greenhouse gases, the trends in these figures for embodied energy and those for global warming potential, as ore grade and grind size fall, are very similar.
However, although increased greenhouse gas emissions that result from the deterioration in quality of base metal ores (such as copper, nickel, lead, and zinc) will contribute appreciably to global emissions, they will still be less than the current emissions from aluminium and steel production, as illustrated in Figure 8.12. Figure 8.12 was prepared using average Australian ore grades (Fe 64.0%, Al 17.4%, Cu 2.8%, Ni 1.8%, Pb 5.5% and Zn 8.6%; global production-weighted mean base metal ore grade of 5.2%) and world annual production rates of the metals by the various processing routes. Figure 8.12 is only a first approximation to illustrate the relative impacts of the various metals assuming copper 80% pyro, 20% hydro; nickel 60% pyro, 40% hydro; lead 89% BF, 11% ISP; zinc 90% electrolytic, 10% ISP. Reducing the mean base metal ore grade
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