- ^ _ „ separate ore materials

Figure 8.2 Effect of ore grade and the "mineralogical barrier" (Skinner 1976).

Figure 8.2 Effect of ore grade and the "mineralogical barrier" (Skinner 1976).

Resources of metallic minerals and energy are classified as abiotic resources.3 Although abiotic energy resources such as oil, gas, coal, and uranium are essentially used in a destructive manner, abiotic nonenergy resources (e.g., copper and iron) are mainly used in a dissipative way. Thus, metals cannot be depleted, they can only be dissipated. Most abiotic resources have functional value only to humans; that is, they are valuable because they enable us to achieve other goals that have intrinsic value, such as human welfare, human health, or existence values of the natural environment.

Energy Required for Primary Metal Production

In general, metals consume significantly more energy in their production than both ceramic and plastic materials. There are important physical and chemical reasons for the high energy consumption associated with metal production, namely, chemical stability, availability, and the extraction process used. The oxides and sulfides of the important industrial metals from which they are commonly produced are chemically stable, and significant energy is required to break the chemical bonds to produce metal. While the Gibbs free energy is the ultimate measure of chemical stability, the heat of formation normally dictates the minimum energy requirements for a process. For example, the heat of formation for the reduction of alumina to aluminium is 31.2 MJ/kg compared to 7.3 MJ/kg for the reduction of iron oxide to iron. This difference partly explains the higher energy consumption required for the production of aluminium compared to iron or steel.

Abiotic resources are the product of past biological processes (coal, oil, and gas) or of past physical/chemical processes (deposits of metal ores).

Pyrometallurgical route Hydrometallurgical route - Ore deposit -


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