The production of metals from metalliferous ores typically involves the stages of mining, mineral processing/concentrating, metal extraction, and refining. Both pyrometallurgical and hydrometallurgical processing routes are used; the former involves smelting of metal concentrates at high temperatures whereas the latter involves leaching of ores and concentrates into aqueous solution at temperatures generally not too far removed from ambient (shown schematically in Figure 8.3). The choice as to which processing route should be used is invariably based on economic considerations, which are strongly influenced by issues such as ore grade and mineralogy.
Sustainability concerns have focused attention on the supply chains and life cycles of metal production and product manufacture, which highlights the need to take a life cycle approach in determining the true energy consumption required for primary metal production. This approach takes into account energy inputs occurring externally to or upstream of the metal production stage—the so-called indirect inputs. Life cycle assessment (LCA) is a methodology that has been developed in recent years and can be used for this purpose. Figure 8.4 shows the results of a number of LCA studies concerning the production of a number of primary metals by various processing routes, in terms of embodied energy or gross energy requirement (GER).4 The GER results shown in Figure 8.4 are broken down to show the contributions of the mining/mineral
In-situ leaching |-
Leaching (heap, pressure)
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