Aluminium smelting

(Also called aluminum hut) An aluminum smelter is a large industrial plant in which, the production of pure aluminum. This is done by electrolysis according to the Hall - Heroult process, a method from the year 1886.

Worldwide in 2009 36.9 million tons of pure aluminum were produced, of which the Federal Republic of 520,000 tons. 2008 aluminum in the world in the construction industry (36%), transportation ( 28%) received ( including automobiles with 16 % ), machinery and cables ( 28%) and packaging (1 %) was used.

The production of aluminum is extremely energy intensive to produce one tonne of aluminum average of 15,700 kWh consumed.

Aluminum smelters

The bauxite ore that is mined in mines, is the basis of aluminum production. Bauxite is separated from other components in refineries in the Bayer process of hematite and boehmite, with per tonne alumina 1.5 tons of red mud arise that must be landfilled. Then alumina is transported to the huts.

An aluminum smelter normally consists of 300 lined steel containers for molten aluminum potline be called and a capacity of 150,000 tonnes of aluminum annually have. The newer potlines are able to produce 200,000 to 300,000 tons in the situation. The larger smelters perform several potlines and can produce 1 million tonnes per year and more.

To produce one ton of pure aluminum, an average of 15,700 kWh are required. Aluminium recycling requires only 5 percent of this energy. The smelters are characterized by high energy consumption and find it for economic reasons the relocation of production to countries with lower electricity costs instead. For example, create the four power plants in the Alba smelter Aluminium Bahrain on site in Bahrain consumes 2,225 MW and operation of the Australian Portland aluminum smelter and Point Henry aluminum smelter 18 to 25 percent of the electric energy of the entire state of Victoria.

For aluminum production different energy sources are used. For example, energy is generated by gas, coal and brown coal in Australia, the Anglesey aluminum smelter in Wales in the UK uses electricity from the Wylfa nuclear power plant and hydroelectric plants in South American countries this built.

Aluminum production

From bauxite to produce alumina in Bayer process in alumina refineries. In the aluminum smelters in the Hall - Heroult process with fused-salt electrolysis, the reduction of alumina to aluminum and wood. In this case, aluminum, which has a melting temperature of 2045 ° C, mixed with cryolite ( Na3AlF6 ), to lower the melting temperature to 950 ° C. The pure aluminum is after it has been created, a melting point of 650 ° C.

In the electrolysis of aluminum forms on the cathode and oxygen at the anode, reacts with the graphite (carbon ) of the anode to carbon dioxide and carbon monoxide. The graphite blocks that form the anode burn, because of the oxygen produced slowly. As a cathode, graphite is used, which must be replaced after about 6 to 7 years. The collecting in this process at the bottom liquid aluminum is sucked with a suction pipe and contains 0.1 to 1 percent of contaminants, especially of iron, silicon and titanium.

Since in this process, a high energy consumption arises aluminum production is mainly carried out in places where sufficient energy is available and this is economically available. Aluminum smelters can not be turned off, but must be operated day and night. If the process is stopped for more than about four hours, there will be irreparable damage to the equipment, as the metal solidifies.

In Germany, approximately 1.4 million tonnes of aluminum are produced. According to estimates of the energy consumer, the aluminum smelters in Germany consume the amount of electricity used for lighting and cooking. Critical is seen that the major decreases of power by government subsidies in Germany fall below the purchase price.

Environment

At all stages of production of aluminum, from the mines to refineries to the smelters produce different environmental problems.

When bauxite mining is a large scale intervention in nature, since the bauxite deposits are located about half a meter below the topsoil with an average thickness of 4 to 6 meters. Although the large natural areas can be revegetated then again when the topsoil is deposited. Furthermore, to be built, for example, in South America for energy for aluminum production dams that damage the local ecology beyond repair.

Funded in mines bauxite ore is ground, mixed with sodium hydroxide solution and heated to 180 ° C and causes a red mud. Red mud contains caustic soda lye, toxic heavy metal oxides and about one percent Schwermetallhydroxide. Furthermore, iron ore dust can get on transport in the environment and toxic components such as fluorides, arsenates, vanadates and chromates can be washed out of the mud. The aluminum ions are harmful and toxic to animals and plants to microorganisms. Red mud should therefore be covered on their surface and have no contact with groundwater. On October 4, 2010, there was Kolontár - dam failure in Hungary, as a result 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 the production of 1 ton of paper, ten times as high as the production of 1 ton of tinplate and 27 times as high as the production of one ton of glass.

In addition, air pollutants and greenhouse gases such as carbon monoxide and carbon dioxide ( CO2) are ejected. Per tonne of aluminum reach 0.7 tons of CO2 into the atmosphere. Also escaping the smelters fluorine and hydrogen fluoride, which can not be avoided in its entirety. It is calculated with an output of less than 0.5 kg per ton of aluminum in the best equipment from 2007 and with more than 4.0 kg in the plants before 1974.

Protests against the aluminum production ranging from conservationists to the establishment of the Australian bauxite mines in Western Australia since 1975, on residents who live near the Wagerup aluminum refinery and has long been complaining about adverse health effects and diseases caused by air pollution, and Indian farmers who compensations for their contaminated by an aluminum hut country in 2003 and 2008 called for.

Of particular importance is the use of aluminum in automobile, which is already an average of about 140 kg of aluminum are in a car and the interest organizations of the aluminum industry to emphasize that the more weight savings by using aluminum components reduce fuel consumption by 9 percent per vehicle by 10 percent would.