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Source of energy
In pyrometallurgical extraction thermal energy is required. Fossil fuel is the source of energy. Fossil fuels are the non renewable source of energy and hence their optimum utilization is important. Further thermal energy from fossil fuel is derived by combustion which leads to production of products of combustion like CO, CO2, NOx etc. Large energy requirement demands higher consumption of fossil fuel.
Thus optimum utilization of fossil fuel in pyrometallurgical extraction is important from the point of view of conservation of natural resources and cleanliness of the environment.
Environmental issues
The production of metals from natural reserves results in the formation of emissions, unwanted solids, liquids and gases like CO, CO2, NOx SO2, SO3 etc directly (during mining and processing) and indirectly(associated with the consumption of raw materials and utilities), for example in the generation of electric power. In the supply chains of metal needs, mineral resource extraction and processing are particularly critical stages for the potential release of gas, liquid and solid emissions.Sulphurus gases can cause acidic rains. NOx is a group of different gases formed due to different levels of nitrogen and oxygen. Commonly formed gases are nitrogen dioxide and nitric oxide.NOx is given off in many forms such as smog or particles.NOx cobributes to global warming, hampers the growth of plants and forms acid rains. It is harmful to humans as well. It can cause nausea, irritated eyes and major respiratory problems.
Environment impact of the process depends on metal grade of ore, electrical energy source, fuel types and material transport as well as processing technology. As higher grade ore reserves of metal decrease, there will be a dramatic effect on the energy consumption and accompanying greenhouse emissions from metal production processes.
The environment impacts for cradle-to-gate metal production (cradle-to-gate is an assessment of a partial production life cycle from resource extraction to the factory gate) are given in the following table:
Environmental impacts for “cradle-to-gate” metal production
Metal |
Process |
GER *
(MJ/kg) |
GWP$
(kg CO2 e/ kg) |
AP#
(kg SO2e/kg) |
SWB##
(kg/kg) |
Nickel |
flash furnace smelting and sherritt Gordon refining |
114 |
11.4 |
0.130 |
65 |
Copper |
pressure acid leaching Sx/Ew
Smelting /converting and electro –refining
Heap leaching and Sx/Ew |
194
33
64 |
16.2
3.3
6.2 |
-
0.040
-
|
351
64
125 |
Lead |
Lead blast furnace
Imperial smelting process |
20
32 |
2.1
3.2 |
0.022
0.035 |
14.8
15.9 |
Zinc |
Electrolytic process
Imperial smelting process |
48 |
4.6 |
0.055 |
29.3 |
Aluminum |
Bayer refining ,Hall- Heroult smelting |
36
211 |
3.3
22.4 |
0.036
0.131 |
15.4
4.5 |
Titanium |
Beecher and Kroll process |
361 |
35.7 |
0.230 |
16.9 |
Steel |
Integrated route (BF and BOF)
|
23 |
2.3 |
0.020 |
2.4 |
Stainless steel
|
Electric furnace and Argon–Oxygen decarburization |
75 |
6.8 |
0.051 |
6.4 |
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* GER: Gross energy requirement
$ GWP: Global warming potential.
# AP: Acidification potential.
## SWB: solid waste burden.
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