As aluminium is generally the core material used in the majority of façades and windows it is important that the sustainability and embodied energy of aluminium as a material is considered.
Aluminium originates in the earth in the form of a red or brownish clay called Bauxite. Bauxite ore is found in abundance in the Caribbean, Australia and Africa and estimated figures suggest that 8% of the earth’s surface contains this red clay. Bauxite is an ore, rich in aluminium oxide formed over millions of years by chemical weathering of rocks containing aluminium silicates.
From 4 tons of bauxite it is possible to obtain approximately 1 ton of aluminium. That 1 ton of aluminium is enough to make over 60,000 of the types of cans used to hold soft drinks. It is also enough to make the space frames for 7 large cars, or enough to make 40,000 computer memory disks capable of storing all the books ever published. All this from a truckload of clay..!! Alumina chemicals are also used to purify water and to make refractory bricks, ceramics, catalysts and fire retardant fillers for fabrics.
Bauxite was first mined in France but has since been found all over the world. Today the majority of bauxite is mined in the Caribbean, Australia and Africa. To convert bauxite into alumina the ore is ground and mixed with lime and caustic soda and the mix is pumped into high pressure containers and heated. The aluminium oxide required is dissolved by the caustic soda, then extracted from this solution, washed and heated to drive off water. What is left is a sugar-like white powder called alumina or aluminium oxide.
Alumina powder becomes aluminium in an electrolytic reduction process known as smelting. Alumina is dissolved in a cryolite bath inside large, carbon lined cells called pots. When a powerful electric current is passed through the bath aluminium metal separates from the chemical solution and is siphoned off.
This slide gives an indication of the production and life cycle of aluminium from the mining of the bauxite, through to its primary smelting and production and on to the various manufacturing industries where the alloy is used. From here any scrap metal produced can be reintroduced into the process for secondary smelting and the process can start again.
Aluminium goes from the smelting pots into furnaces and is mixed with other metals to form various alloys with specific properties designed for particular uses. Further fabrication may include casting, rolling, forging, drawing, or extruding – to make thousands of different finished products.
Aluminium compounds form 8% of the earth’s crust and aluminium is the third most common element on the planet. The world’s known deposits of bauxite are sufficient to support the current production rate for a further 300 years. The method of mining the bauxite is generally with open cast mines and great care is taken to reinstate land after the bauxite has been removed.
Bauxite occurs mainly in tropical and sub-tropical areas. Where mining takes place in rainforest areas, only 5 Sq. Km is mined at any one time and is restored with indigenous flora and fauna after use. Primary smelters use extensive pollution control equipment to ensure the environment is protected.
Two notable examples of where aluminium is still in service to this day after over a century of exposure to the elements are the capping on top of the Washington monument and the San Gioacchino church in Rome. Eros in Piccadilly Circus has also lasted the test of time and has only recently been renovated.
It is important to bear in mind that the quality of aluminium is not impaired by recycling as the constituents of the alloy are not altered during reprocessing.
Re-smelting aluminium conserves up to 95 % of the energy needed to produce the primary product so it pays to recycle.
It is the most cost-effective material to recycle and one of the most abundant.
The overall market for used aluminium is steadily growing, so the more aluminium there is in a product, the more likely it is to be recycled.
Aluminium extrusion is collected by scrap contractors (whether mill finish, anodised or painted). It is segregated and then used as raw material for furnace production where it is made into aluminium alloy ingots for the casting industry. The extrusion is used in selected proportions along with other raw materials to form a "charge" for the furnaces.
The recycling rate of used aluminium products in building is now over 80 %. In fact, research carried out by the University of Delft in the Netherlands has found that that, depending on the type of building, the recycle rate can be as much as 92% (over 95% in transportation and 30 % in packaging).
30% of the 1.9m tonnes of aluminium used in Europe in 1997 came from recycling*.
In the UK, over 150,000 tonnes of aluminium are used by the building and construction industry each year, a large proportion of which is in the form of extruded and rolled products*.
*Figures courtesy of the CAB Council for Aluminium in Building