Environmental Effects of Bauxite Mining
Bauxite is generally found fairly close to the surface and so opencast mining methods are used, but the mines are often in environmentally sensitive regions. Of the land disturbed by mining, 76% is forested, and disruption to wildlife is inevitable. There is particular concern about mining in Brazilian rain forest, though in fact this accounts for only 3% of production, and at any one time only 5km2 will be mined, with new forest being planted afterwards.
Mining companies recognise their responsibilities, and over 90% of mines have an environmental rehabilitation plan, with 60% operating plant nurseries for this purpose. The majority of mines also operate wildlife reserves and fund monitoring and research.
Extracting aluminium oxide from bauxite (the "Bayer Process") produces large quantities of "red mud", which is bauxite ore with the aluminium oxide removed. The trend is towards building "Bayer" plants closer to the mining area so that the "mud" can be used to reconstruct the landscape from which it was taken.
Primary aluminium production requires a lot of energy, particularly electrical energy. A range of energy sources is used for this - click here for more detail. Refinements in cell technology have resulted in a steady reduction in energy consumption, and modern plants now require 10-15 kWh per kg of aluminium produced. Further reductions will be possible with the development of inert anodes.
The increase in secondary aluminium production, recovery from scrap, is particularly beneficial in this respect as the process uses only 5% of the energy used by primary production from bauxite.
Greenhouse Gas Emissions
Carbon Dioxide - Globally about 45% of aluminium production relies on electricity generated from carbon-based fuels (coal, oil and gas), though the figure is lower in Europe (35%). In addition, the use of carbon anodes adds to the carbon dioxide generated during aluminium production. Making 1 tonne of aluminium can result in 1.5 tonnes of carbon dioxide being released to the atmosphere.
PFCs - If a cell is run at less than optimum conditions, fluorine in the electrolyte can react with carbon in the anodes, resulting in "perfluorocarbons" (PFC) being produced. Though these materials are not toxic to people, PFCs are greenhouse gases with much higher global warming potentials than carbon dioxide. Making 1 tonne of aluminium can result in PFC emissions that are the equivalent of releasing 2 tonnes of carbon dioxide, though the actual quantity of PFC is much smaller than this.
It must also be borne in mind that the increased use of aluminium in
transport, including cars, lorries, trains and aeroplanes, has resulted
in weight decreases that have reduced carbon dioxide emissions from
these vehicles. It is estimated that a 100kg reduction in the weight
of a car would save 0.6 litres fuel for every 100km travelled, and reduce
carbon dioxide emissions by about 2,000 kg over the life of the vehicle.
Aluminium has always been recycled, as off-cuts from manufacturing are returned to the smelters and re-cast. Over recent years, however, there has been an increase in the amount of used aluminium products being returned for re-use. This is from vehicles, building, printing plates and packaging, in particular drinks cans.
Methods for Reduction
The considerable reduction in energy requirements has had a significant
impact on carbon dioxide emissions. The use of sensors and computerised
control to optimise conditions has helped to reduce production of PFCs.
Enclosed hoods are increasingly being incorporated on cells so that
all waste gases can be captured and treated. This has resulted in a
60% reduction in PFC emissions (as CO2 equivalents) in the last 10 years.