Field Aluminum is an abundant element in the crust but it is rarely found in pure form . This is the third most abundant element in the crust (8% mass) after oxygen and silicon. Aluminum is very difficult to retrieve rocks that contain it and has therefore long been very rare and valuable.
The principal ore of aluminum is bauxite.
Production
The bauxite contains the alumina (Al 2 O 3), it must first be extracted. Why bauxite must be treated with a solution of soda.
A precipitate of Al (OH) 3 which gives the alumina by heating. Aluminium is extracted by electrolysis : the alumina is fed into electrolytic cells with additives such as cryolite (Na 3 AlF 6), calcium fluoride (CaF2), lithium fluoride and aluminum ( Li 3 AlF 6) and aluminum fluoride (AlF 3) in order to lower the melting point of 2040 C to 960 C.
The production of one ton of aluminum requires four to five tonnes of bauxite. It takes between 13 000 and 17 000 kWh (between 47 and 61 GJ ). During electrolysis, are emitted gases such as carbon dioxide (CO 2),carbon monoxide (CO), hydrocarbons (PAHs), and gaseous fluorides. In the best plants, the carbon monoxide (CO) and polycyclic aromatic hydrocarbons (PAHs) are burned or recycled as a carbon source, and fluorides are returned in the electrolysis bath.
Production Statistics
World production of secondary aluminum from recycling amounted to 7.6 Mt in 2005, representing 20% of the total production of this metal.
| Year | Africa | America
North | America
Latin | Asia | Europe
and Russia | Oceania | Total |
|---|
| 1973 | 249 | 5 039 | 229 | 1 439 | 2 757 | 324 | 10 037 |
| 1978 | 336 | 5 409 | 413 | 1 126 | 3 730 | 414 | 11 428 |
| 1982 | 501 | 4 343 | 795 | 1 103 | 3 306 | 548 | 10 496 |
| 1987 | 572 | 4 889 | 1 486 | 927 | 3 462 | 1 273 | 12 604 |
| 1992 | 617 | 6 016 | 1 949 | 1 379 | 3 319 | 1 483 | 14 763 |
| 1997 | 1 106 | 5 930 | 2 116 | 1 910 | 6 613 | 1 804 | 19 479 |
| 2003 | 1 428 | 5 945 | 2 275 | 2 457 | 8 064 | 2 198 | 21 935 |
| 2004 | 1 711 | 5 110 | 2 356 | 2 735 | 8 433 | 2 246 | 22 591 |
| Aluminum Production in thousand tonnes |
Recycling
Aluminum has excellent recyclability theoretical, but you have to collect, sort it and melt it requires a significant amount of energy.
In addition to environmental benefits, the recycling of aluminum is much less expensive than extraction from the ore bauxite. It takes 95% of energy in less and a ton of recycled aluminum saves four tons of bauxite. By skipping the step of electrolysis, which requires a lot of energy, we avoid polluting emissions associated with it. Aluminum is almost endlessly recyclable without losing quality, provided it does not melt even in a bath of alloys of different composition. For this reason the producers refused a significant part of the aluminum recovered from household waste.
The recycling of aluminum began to be practiced in the 1900s and has steadily increased: in aluminum consumption in Europe, the share of home recycling from 50% in 1980 to over 70% in 2000. There are different industrial sectors recovery of aluminum.
After the Second World War the shortage has led to redesign of aluminum alloys to make parts that do not require precise mechanical properties, particularly kitchen utensils. The composition of the alloys obtained was not popular with skiers who called them a "cochonium. Pans and made prided themselves ( pitting ), as a result of the acidity of food. The consequences of contaminated food have already been mentioned.
In France, aluminum shocks and similar industrial waste is recovered is then crushed remelted aluminum refiners to produce the secondary aluminum. The latter is mainly used to make castings for automobile (engine blocks, cylinder heads, pistons, etc..). The aluminum "household" is recovered with the packaging through the sorting. In sorting centers, aluminum is sorted manually or more commonly through sorting machines by eddy currents. In 2010, 20% of the aluminum recovered in the garbage is classified sorting refusal (refused by the industry) and sent to landfill or incineration as it contributes to environmental pollution. In 2009, France, 32% of aluminum containers were recycled, small cans, crushed cans, crumpled aluminum foil, packaging type Nespresso, etc.. are rejected by the sorting process because of their size, as well as foil and various compounds containing aluminum (about 50 000 t / year, only for France). Nespresso, manufacturers of aluminum trays or aluminum roller does not pay the tax eco-packaging , sorting centers are not funded to the end to sort recycling. .
In some developing countries, uncontrolled recycling of materials based on aluminum led to this day to make food with utensils contents harmful elements (nickel, copper, etc.).. However, recycling of aluminum alloys, made seriously, with precise control of composition, gives excellent results.
The five largest producers
In the list of producers of aluminum in the world, the top five are in 2006 :
Pollution
Three types of pollution are generated by the production of aluminum :
- pollution by waste from production of alumina from bauxite , called red mud stored in areas protected by dikes, the sludge are caustic (sodium hydroxide) and contain various metals;
- fluoride pollution in the processing of alumina into aluminum;
- gaseous discharges above the electrolytic cells, which must be captured.
Major incidents related to the aluminum industry
On October 4, 2010, a tank factory production of bauxite-aluminum Ajkai Timfoldgyar Zrt, based in Ajka , 160 kilometers from Budapest ruptured spilling between 600,000 and 700,000 cubic meters of red mud toxic composed any noxious and corrosive that flooded three villages in a radius of 40 sq km before reaching the Danube threatens the ecosystem of the Grand River with an alkali rates slightly above normal , , , .
The human toll is 9 dead, including a girl of 14 months and over 150 injured, the ecosystem near the factory was completely destroyed, the red tide has brought with it livestock and animals farms, thousands of fish died. The Hungarian government declared a state of emergency , . The region remains under the risk of a second similar flooding after several cracks were noticed on the reservoir north threatening to dump 500,000 cubic meters of more red mud , .
References
- a , b and c (in) David R. Lide, CRC Handbook of Chemistry and Physics, CRC Press Inc., 2009, 90th ed. Hardcover, 2804 p. ( ISBN 978-1-420-09084-0 )
- Database Chemical Abstracts via SciFinder Web interviewee December 15, 2009 ( )
- (en) Beatriz Cordero, Vernica Gmez, Ana E. Platero-Prats, Marc Revs, Jorge Echeverra, Eduard Cremades, Flavia Barragn and Santiago Alvarez, "Covalent radii revisited", in Dalton Transactions, 2008, p. 2832-2838 See also
Related articles
- Extractive metallurgy of aluminum
- Aluminum alloy
- Aluminum processing
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