Energy Consumption In Metal Production

Abstract:

Energy is consumed at all stages in the production of metals – mining, beneficiation and chemical extraction – both directly in the processes and indirectly through the production of inputs (such as electricity and reagents) used in the processes. The sum of the direct and indirect energies of the individual stages along the value chain is the embodied energy of the commodity. It is used for comparing the energy intensiveness of commodities. ¬The embodied energy of the common metals varies widely, from typically around 20 MJ per kilogram for lead and steel to over 200 MJ per kilogram for aluminium, with the chemical transformation stages (leaching, smelting, electrowinning, etc) contributing the largest component and mining the least. Factors affecting the embodied energy include the stability of the minerals, the ore grade and the degree of beneficiation (particularly grinding) required. The quantity of greenhouse gases produced frequently follows closely the trends in embodied energy though for those metals which require a high component of electrical energy, such as aluminium, the source of electrical energy (coal, hydro, nuclear, etc) has a major impact on the quantities of greenhouse gases produced. Globally, of all the metals, steel production contributes the greatest quantity of greenhouse gases (about 7% of global CO2 produced from fossil fuels) since, although it has a low embodied energy content it is produced in huge quantities (about one billion tonnes per year) . Aluminium production produces around 3% of global CO2. The energy required to recycle metals is a relatively small fraction of the energy required to produce metals from their ores since energy is required largely only for melting and not chemical transformation. However, when the energy required for collection and separation of scrap is included, the embodied energy of recycled metals increases as the fraction of scrap collected increases since transportation and separation costs progressively increase. Technology plays an important role in reducing the embodied energy content of metals and greenhouse gas production and there has been progressive improvement over many decades. However, without step changes in technology incremental improvements in energy efficiency become harder and harder to achieve.

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