Aluminum smelter
An aluminum smelter (also called aluminum smelter ) is a large-scale industrial facility in which pure aluminum is produced. This is done by fused -salt electrolysis using the Hall-Héroult process , a process dating back to 1886.
Worldwide, 36.9 million tons of pure aluminum were produced in 2009, 520,000 tons of which in Germany. In 2008, aluminum was used in the world in construction (36%), transportation (28%) (including automobiles with 16%), mechanical engineering and cables (28%) and for packaging (1%).
The production of aluminum is extremely energy-intensive; an average of 15,700 kWh of electrical energy is required to produce one ton of aluminum .
Aluminum smelters
The bauxite ore that is extracted in mines is the basis of aluminum production. In refineries, bauxite is separated from other components in the Bayer process from hematite and boehmite , whereby 1.5 tons of red mud are produced per ton of aluminum oxide , which has to be disposed of. Then aluminum oxide is transported to the smelters.
An aluminum smelter usually consists of 300 lined steel containers for aluminum smelting, called potlines , with a capacity of 150,000 tons of aluminum per year. The newer potlines are capable of producing 200,000 to 300,000 tons. The larger aluminum smelters run several potlines and can produce 1,000,000 and more tons annually.
To produce one ton of pure aluminum, an average of 15,700 kWh are required. Aluminum recycling requires only 5 percent of this energy. The aluminum smelters are characterized by high energy consumption and, due to economic constraints, production is being relocated to countries with low electricity costs. For example, the generated power plant Alba of Aluminum Bahrain at the site in Bahrain 2,225 MW and operation of the Australian Portland Aluminum Smelter and Point Henry smelter consumes 18 to 25 percent of the electric energy of the entire state of Victoria .
Different energy sources are used to produce aluminum. For example, in Australia energy is generated from gas , coal and lignite , the Anglesey aluminum smelter in Wales in Great Britain uses electricity from the Wylfa nuclear power plant and in South American countries hydropower plants are being built for this purpose.
Aluminum manufacturing
Aluminum oxide is produced from bauxite in aluminum refineries using the Bayer process . In the aluminum smelters, aluminum oxide is reduced to pure aluminum in the Hall-Héroult process using fused- salt electrolysis . Here, aluminum oxide, which has a melting temperature of 2045 ° C, is mixed with cryolite (Na 3 AlF 6 ) in order to reduce the melting temperature to 950 ° C. The pure aluminum produced has a melting point of 650 ° C.
During electrolysis, aluminum is produced at the cathode and oxygen at the anode , which reacts with the carbon of the graphite anode to form carbon dioxide and carbon monoxide . The graphite blocks that make up the anode slowly burn off. Graphite is also used as the cathode, but it only needs to be replaced after about 6 to 7 years. The liquid aluminum obtained in this process collects at the bottom of the troughs and is removed using suction pipes. It contains 0.1 to 1 percent impurities, mainly iron , silicon and titanium .
Since this process requires a lot of electrical energy, aluminum production is mainly carried out in places where the energy is available in sufficient quantities and at affordable prices. Aluminum smelters cannot be switched off, but have to be operated day and night. If the process is stopped for more than around four hours, irreparable damage to the systems occurs because the metal solidifies.
It is viewed critically that the large purchases of electricity due to state subsidies in Germany fall below the cost prices.
environment
Different environmental problems arise at all stages of the production of aluminum, from mining to refineries and aluminum smelters.
When mining bauxite, there is extensive intervention in nature, as the bauxite deposits are about half a meter below the topsoil with an average thickness of 4 to 6 meters. The large natural areas can then be recultivated again when the topsoil is dumped. In addition, dams are being built in South America to generate energy for aluminum production, which irreparably damage the local ecology.
The bauxite ore extracted in mines is ground, mixed with caustic soda and heated to 180 ° C to produce red mud . Red mud contains caustic caustic soda , toxic heavy metal oxides and about one percent heavy metal hydroxides. Furthermore, ore dusts can get into the environment during transport and the toxic components such as fluorides , arsenates , chromates and vanadates can be washed out of the sludge. The aluminum ions are harmful to microorganisms and toxic to animals and plants. Red mud landfills should therefore be covered on their surface and have no contact with groundwater. On October 4, 2010, the Kolontár dam burst in Hungary, as a result of which 40 square kilometers were flooded with red mud; ten people died, 150 people were injured and 400 people had to be brought to safety.
The energy consumption of 1 ton of aluminum is four times as high as producing 1 ton of paper, ten times as high as producing 1 ton of tinplate and 27 times as high as producing 1 ton of glass.
Air pollutants and greenhouse gases such as carbon monoxide and carbon dioxide (CO 2 ) are also emitted. For every ton of aluminum produced, 0.7 tons of CO 2 are released into the atmosphere. Fluorine and hydrogen fluoride also escape from the aluminum smelters , which cannot be avoided entirely. An output of less than 0.5 kg per ton of aluminum is expected in the best plants from 2007 and more than 4.0 kg in plants before 1974.
Protests against aluminum production range from conservationists against the establishment of Australian bauxite mines in Western Australia since 1975, residents who live near the Wagerup alumina refinery and who have long complained about health problems and illnesses caused by air pollution, to Indian farmers who Demanded compensation for their land contaminated by an aluminum hut in 2003 and 2008.
See also
Web links
- Prebake Cell Technology: A Global Review: List of Processes Used in Most of the World's Aluminum Smelters
Individual evidence
- ↑ minerals.usgs.gov (PDF; 89 kB): Aluminum , in English, accessed on April 18, 2012
- ↑ world-aluminium.org ( Memento of the original from January 26, 2011 in the Internet Archive ) Info: The archive link was automatically inserted and not yet checked. Please check the original and archive link according to the instructions and then remove this notice. : Aluminum for Future Generations (2009 update) , in English, accessed April 16, 2012
- ↑ world-aluminium.org ( Memento of the original dated April 2, 2012 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. : Smelting.
- ↑ Eutectic aluminum oxide / cryolite ( Memento of the original from April 19, 2015 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice.
- ↑ a b c Umweltlexikon-online.de : Aluminum production , accessed on January 18, 2014
- ↑ Frank Muster: Rotschlamm. Residual material from aluminum oxide production - ecological backpack or input for production processes? kassel university press GmbH, Kassel 2007, ISBN 978-3-89958-359-5
- ↑ spiegel.de : Environmental disaster in Hungary. Toxic sludge reaches the Danube from October 7, 2010, accessed on April 17, 2012
- ↑ a b merinews.com ( Memento of the original from January 19, 2017 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. : Sankar pani: Toxic gas from smelter plant damages crop in Hirakud , in English, accessed April 17, 2012
- ↑ researchrepository.murdoch.edu.au (PDF; 6.9 MB): Ron Chapman: Fighting for the Forest. A History of The West Australian Forest Protest Movement 1975-2001 , pp. 132 ff., In English, accessed on April 14, 2012
- ↑ perthnow.au ( Memento of the original dated August 13, 2011 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. : John Flint: A 5KM buffer zone around the refinery - as the Health Department wants - would wipe Yarloop, Hamel and Cookernup off the map , in English, accessed April 9, 2012
- ↑ abc.net.au ( Memento of the original dated November 12, 2011 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. : Quentin McDermott: Something in the air , broadcast March 10, 2005, in English, accessed April 17, 2012
