GER for pyrometallurgical copper production
GER for mining and mineral processing
0.54 MJ/kg Cu ore
GER for smelting and refining
3.55MJ/kg Cu concentrate
grade of copper ore
grade of copper concentrate
recovery of copper in mining and mineral processing stages
recovery of copper in smelting and refining stages
As the copper concentrate produced at the end of the mineral processing stage (see Figure 8.3) has a relatively constant grade (27.3% assumed here) independent of initial ore grade, the subsequent smelting and refining stages are essentially unaffected by ore grade. Thus the energy for mining and mineral processing is inversely proportional to ore grade, whereas the smelting and refining energy is independent of ore grade. Similarly, the metal concentration in the leach solution going to the solvent extraction stage in the hydrometallurgical processing route (see Figure 8.3) is also relatively constant and independent of the initial ore grade. Thus the subsequent solvent extraction and refining stages are also essentially unaffected by ore grade.
Equation 8.1 and the values given above may be used to illustrate the effect of falling ore grade on the embodied energy for pyrometallurgical copper production, and this is shown in Figure 8.7a. Figure 8.7b illustrates the effect of declining ore grade on the GER of copper and nickel production by the pyrometallurgical route, as predicted by the LCA models (as opposed to Equation 8.1), along with some data reported in the literature. The close similarity between Figures 8.7a and 8.7b, in the case of copper, is apparent. The increase in GER with declining ore grade comes about because of the additional energy that must be consumed in the mining and mineral processing stages to move and treat the additional gangue (waste) material. Figure 8.8a, b illustrates the stage-by-stage embodied energy contributions for copper and nickel production (pyrometallurgical) for ore grades over the range 0.5-3.0% and 0.5-2.3%, respectively.
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