Aug 15 2006
Background
To illustrate the aluminium life cycle, what can be more relevant than the myth of the Fountain of Youth. In this myth, old persons enter a fountain of youth and are transformed back to their young and healthy selves. This myth is a good metaphor for recycling : considering that used aluminium is an old person, recycling gives it the same effect as the Fountain of Youth.
A “cradle to cradle” cycle of an aluminium product system can be modelled using different process steps as outlined in the flowchart below. It should be noted that “grave” relates here to the end of life of the product, not of the material aluminium since it is being recycled.
Figure 1. Aluminium life cycle.
Bauxite Mining
The mining of bauxite is the first step in aluminium production.
At 8% of the earth’s crust, aluminium is the third most abundant element in nature.
The ore from which aluminium is produced is bauxite. Disregarding various quality grades, bauxite reserve estimates indicate adequate supply for at least 400 years. More than 130 million tonnes of bauxite are mined each year, the major deposits being in the tropics and sub-tropics. Bauxite is currently being extracted in Australia, Central and South America (Jamaica, Brazil, Surinam, Venezuela and Guyana), Africa (Guinea), Asia (India, China), CIS and parts of Europe (Greece and Hungary). In many of these regions bauxite extraction is the only valuable natural resource.
Alumina Production
Alumina, the raw material for primary aluminium production, is extracted from bauxite.
Bauxite has to be processed into pure aluminium oxide (alumina) before it can be converted to aluminium by electrolysis. This is achieved through the use of the Bayer chemical process in alumina refineries. The aluminium oxide is released from the other substances in bauxite in a caustic soda solution, which is filtered to remove all insoluble particles. The aluminium hydroxide is then precipitated from the soda solution, washed and dried while the soda solution is recycled. After calcination, the end-product, aluminium oxide (Al2O3), is a fine grained white powder.
Four tonnes of bauxite are required to produce two tonnes of alumina which in turn produces one tonne of aluminium at the primary smelter. In 2003, 59 million tonnes of alumina were produced world-wide.
The main production areas are:
Figure 2. Breakdown of global alumina production.
Primary Aluminium Production
Primary aluminium is produced by electrolysis .
Primary aluminium is produced in reduction plants (or "smelters"), where pure aluminium is extracted from alumina. The reduction of alumina into liquid aluminium is operated at around 950 degrees Celsius in a fluorinated bath under high intensity electrical current. This process takes place in electrolytic cells (or “pots”), where carbon cathodes form the bottom of the pot and act as the negative electrode. Anodes (positive electrodes) are held at the top of the pot and are consumed during the process when they react with the oxygen coming from the alumina.
At regular intervals, molten aluminium tapped from the pots is transported to the cast house where it is alloyed in holding furnaces by the addition of other metals (according to the user’s needs), cleaned of oxides and gases, and then cast into ingots.
Aluminium output has increased by a factor of 13 since 1950, making aluminium the most widely used non-ferrous metal. In 2003, world-wide production of primary aluminium was about 28 million tonnes.
Figure 3. Worldwide production of aluminium.
The main production areas are China (5.5 million tonnes), North America (5.5 million tonnes), CIS (3.9 million tonnes), EU25 (2.9 million tonnes), Asia (2.3 million tonnes), Central and South America, Australia and Africa. In Europe the main producing countries are France, Germany and Norway. World-wide, production plants are mainly located where suitable electrical energy resources are available.
Semi-Fabrication
This encompasses several industrial processes: rolling, casting and extrusion .
Rolling
Rolled products, i.e. sheet, plate and foil constitute almost 50 % of all aluminium alloys used. In North America and Western Europe, the packaging industry consumes the majority of the sheet and foil for making beverage cans, foil containers and foil wrapping. Sheet is also used extensively in building for roofing and siding, in mass transport for airframes, road and rail vehicles, in marine applications, including offshore platforms, and superstructures and hulls of boats. Plate is used for airframes, military vehicles and bridges, ship superstructures, cryogenic and chemical vessels and as tooling plate for the production of plastic products. Foil applications outside packaging include electrical equipment, insulation for buildings, lithographic plate and foil for heat exchangers.
Casting
Aluminium casting processes are classified as ingot casting or mould casting. During the first process, primary or aluminium is cast into rolling ingot (slab), extrusion ingot (billet) and wire bar ingot which are subsequently transformed in semi- and finished products.
The second process is used in the foundries for producing cast products. This is the oldest and simplest mean of manufacturing shaped components.
Aluminium castings are very powerful and versatile techniques for manufacturing semi- or finished products with intricate shapes. Those techniques are continuously improved and developed to satisfy the user needs and to penetrate new markets.
Extrusion
The term extrusion is usually applied to both the process, and the product obtained, when a hot cylindrical billet of aluminium is pushed through a shaped die. The resulting section can be used in long lengths or cut into short parts for use in structures, vehicles or components. Also, extrusions are used for the starting stock for drawn rod, cold extruded and forged products.
Extruded products constitute more than 50 % of the market for aluminium products in Europe of which the building industry consumes the majority.
Aluminium extrusions are used in commercial and domestic buildings for window and door frames.
Product Manufacture
Aluminium is then formed into products.
The aluminium unique combination of properties has enabled designers and manufacturers to develop products that enhance the quality of life. Many applications in transportation, medicine, food preservation and electricity distribution would not have been possible if a material with aluminium’s high strength-to-weight characteristic, outstanding barrier properties, good conductivity and corrosion resistance had not been available.
Use Phase
The major outlets for aluminium products are in transport, building and construction, packaging and engineering .
The real impact on the environment of a product or material can only be judged from a life cycle perspective. The energy requirements of all aluminium production stages - from the mining of the raw material to the transport of the metal - must be considered in combination with the possible energy savings enabled during the lifetime of the finished aluminium product. Account must be taken of the energy saving potential of recycling the aluminium after the product has been used.
Recycling
Recycling is a major consideration in continued aluminium use, representing one of the key attributes of this ubiquitous metal, with far-reaching economic, ecological and social implications. More than half of all the aluminium currently produced in the European Union originates from recycled raw materials and that trend is on the increase. In view of domestic energy constraints, growing aluminium end-use demand and the small number of bauxite mines in this part of the world, Europe has a huge stake in maximising the collection of all available aluminium, and developing the most resource-efficient scrap treatments and melting processes.
Aluminium can be recycled over and over again without loss of properties. The high value of aluminium scrap is a key incentive and major economic impetus for recycling. Aluminium recycling benefits present and future generations by conserving energy and other natural resources. It saves up to 95% of the energy required for primary aluminium production, thereby avoiding corresponding emissions, including greenhouse gases. The growing markets for aluminium are supplied by both primary and recycled metal sources. Increasing demand for aluminium and the long lifetime of many products mean that, for the foreseeable future, the overall volume of primary metal produced from bauxite will continue to be substantially greater than the volume of available recycled metal. Industry continues to recycle, without subsidy, all the aluminium it can collect from used products, as well as fabrication and manufacturing processes. However, with the help of appropriate authorities, local communities and society as a whole, the amount of aluminium collected could be increased further.
Global aluminium recycling rates are high, approximately 90% for transport and construction applications and about 60% for beverage cans.
Used aluminium is valuable - it is easily and endlessly recycled without quality loss. Aluminium makes a major and unique contribution to support product recycling into the future and to the benefit of society as a whole.
• Aluminium has unique recycling qualities: the quality of aluminium is not impaired by recycling -it can be repeatedly recycled.
• Aluminium recycling saves energy: remelting used aluminium saves up to 95% of the energy needed to produce the primary product.
• Aluminium recycling is economical: it uses less energy and recycling is self-supported because of the high value of used aluminium.
Source: European Aluminium Association.
For more information on this source please visit European Aluminium Association.