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Figure 8.4 Gross energy requirement (GER) for the production of various primary metals (Norgate et al. 2007).

processing and metal extraction/refining stages.5 For most metals with the typical Australian ore grades used in the LCAs, the metal extraction and refining stages (particularly the former) make the greater contribution to the GER.

Water Required for Primary Metal Production

Relatively little water is used in most types of mining; the majority of water is used in mineral processing and refining. In particular, operations such as grinding, fl otation, gravity concentration, dense medium separation, and hy-drometallurgical processes all consume substantial amounts of water. Factors that contribute to make water the fluid of choice for mineral processing are:

• Water is an efficient (low energy, low cost) way of transporting particles within and between processes, mixing particles, and supplying reactants to the site of a reaction.

• Water is a medium that can provide a suitable vehicle for the selective action of a distributed force field (e.g., gravity or centrifugal force).

• Water is an essential chemical ingredient in some processes.

Figure 8.5 shows the results of the previously mentioned LCA studies in terms of embodied water consumption. This time, however, it is broken down to show the direct (i.e., from within the process) and indirect (i.e., external to the

Based on electricity generated from black coal (35% efficiency).

Figure 8.5 Embodied water for the production of various primary metals.

process, primarily from electricity generation) contributions. Because of the high value for gold (252,000 l/kg gold), and to a lesser extent nickel (377 l/kg nickel, hydrometallurgical route), compared to the other metals, the values for these two metals are not plotted in Figure 8.5.

The embodied water results in Figure 8.5 were used in conjunction with Australian production data for the various metals to give the annual embodied water results for metal production in Australia for all the metals combined, broken down into the three processing stages (Figure 8.6). Figure 8.6 clearly shows that the mineral processing stage makes the greatest contribution to the embodied water for metal production.

Mining Mineral processing Metal production

Figure 8.6 Contribution of processing stages to embodied water for metal production.

Mining Mineral processing Metal production

Figure 8.6 Contribution of processing stages to embodied water for metal production.

Impact of Deteriorating Ore Quality on Energy and Water Effect of Ore Grade on Energy Consumption

Future energy requirements for primary metal production from ores will be dependent primarily on the following factors:

• A decline in ore grades will increase energy requirements.

• Smaller metal seams and higher overburden layers will increase energy requirements.

• Ores with higher chemical energy will increase energy for metal extraction.

• Remote deposits will require more transportation energy.

• Improvement of technology will decrease energy requirements.

The focus here is on the increase in energy requirements due to the anticipated fall in ore grades in the future.

Using the pyrometallurgical production of copper as an example, the GER or embodied energy for copper metal production may be expressed as:

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