zpravodajství životního prostředí již od roku 1999

Těžba hliníku a životní prostředí

21.07.2006
Geologie
Těžba hliníku a životní prostředí

Background With a share of 8 %, aluminium is the third most abundant element in the earth?s crust. Thus, the availability of raw material supplies for the production of aluminium is almost unlimited.Production OverviewThe common raw material for aluminium production, bauxite is composed primarily of one or more aluminium hydroxide compounds, plus silica, iron and titanium oxides as the main impurities. It is used to produce aluminium oxide through the Bayer chemical process and subsequently aluminium through the Hall-Heroult electrolytic Process. On a world-wide average 4 to 5 tonnes of bauxite are needed to produce two tonnes of alumina, from which one tonne of aluminium can be produced. In Europe, usually the average bauxite consumption is 4.1 tonnes per tonne of aluminium.Bauxite ProductionMore than 100 million tonnes of bauxite are mined each year. The major locations of deposits are found in a wide belt around the equator. Bauxite is currently being extracted in Australia (in excess of 40 million tonnes per year), Central and South America (Jamaica, Brazil, Surinam, Venezuela, Guyana), Africa (Guinea), Asia (India, China), Russia, Kazakhstan and Europe (Greece).The material is mainly extracted by open-cast mining, which has a variable and highly site-specific effect on the local environment. The primary ecological concerns connected to this operation are related to the clearing of vegetation, affect on local flora and fauna, and soil erosion.Table 1. Breakdown of global bauxite production in 1998.Country Production(million tonnes/year) Australia 44.5 Guinea 17 Jamaica 12.6 Brazil 12 China 9 India 6 Venezuela 4.8 Surinam 3.9 Russia 3.6 Kazachstan 3.4 Guyana 2.3 Greece 1.8 Total 120.9 Bauxite Mining in Forest AreasThe conservation of rain forests is a key concern often voiced with regard to bauxite mining. Only about 6 % of the world?s bauxite mining is today conducted in rain forest regions, affecting a total area of around 1.5 km2 per year. The total area of the globe currently covered by rain forest is about 18 million km2.The original flora and fauna of much of the land involved in bauxite mining is restored once mining operations have ceased. For all forest areas used for bauxite mining, 80% is returned to native forests, the rest is replaced by agriculture, commercial forest, or recreational area, thereby making the area more productive for the local community. As far as rain forests in particular are concerned, however, the area used for bauxite mining in rain forests is almost totally reverted back to rain forest.RevegetationDuring the preparation of a site for open-cast mining, the surface soil is removed to get access to the bauxite. In order to avoid soil erosion and to ensure that vegetation is returned to the land, many companies have water drainage practices during mining operations, separate removal of top soil (50 per cent reuse it directly after the mining operation) and over 60 per cent have their own nursery plant facilities. Rehabilitation plans are established prior to the start-up of operations and the investments required to implement these plans are built into mining costs.Proof of the Aluminium Industry?s Commitment to the EnvironmentAlcoa won for example in 1990 the United Nations Environmental Programmes ?Global 500 Roll of Honour for Environmental Achievement? award for exemplary reforestation and recultivation of its bauxite mines in Western Australia. A computer-based system that integrates mining with environmental management was developed: the Geographical Information System (GIS). It helps engineers and scientists to produce accurate mine plans that consider biological diversity, land use value, and water quality.The Aluminium Industry and Land ReclamationA company such as Alcan has developed what is now one of the most successful land reclamation projects in Brazil thanks to employee education, surveys of flora and fauna, and the creation of on-site plant nursery and seed collection programmes. Over 450 of the 950 hectares of mined land are already completely restores to forest with 1.2 million transplants of at least 350 native species of vegetation.

ZDROJ: European Alumuniun Association

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