Aluminium
See also Aluminium recycling tips
- Recycle Aluminum Cans - Use of recycled aluminum in the manufacturing process requires saves 95% less energy, generate 95% less emission and create 97% less water pollution than producing the new metal from ore. Recycling one ton of aluminum eliminates the need for 5 tons of bauxite ore to be mined. One ton of recycled Aluminum saves 14,000 KWH of Energy, 40 barrels of oil, 238 million BTUs of Energy and 10 cubic yards of landfill space. Wash and squash cans before recycling. Only recycle clean aluminium foil.
- Separate aluminium (drinks cans) - non-magnetic, from steel (food tins) - magnetic. Aerosols can be made from either, so test by using a magnet. Write to recycle-more@valpak.co.uk to request a free magnet. Never pierce or crush aerosols even when empty. Only put empty aerosols in recycling schemes i.e. when you cannot get any more out by pressing the button.
- Crisp wrappers (metallised plastic film) cannot be recycled. Metallised plastic springs back when scrunched. Advice: contact Alupro for details of their Cash for Cans scheme and BAMA for any aerosol queries.
- Join the Voluntary Aluminium Industrial Partnership, an innovative pollution prevention program developed jointly by the US Environmental Protection Agency (EPA) and the primary aluminum industry.
- In the UK, we use 35,000 tonnes of aluminium foil a year to wrap food, but recycle just 12 per cent of that. Aluminium can be recycled over and over again with no loss of quality, but if you'd rather avoid it completely, try these ideas. Wrap packed lunches and picnic food with greaseproof paper - and then compost it afterwards. Store leftovers in the fridge in an empty margarine tub or tupperware container - or simply cover your leftovers with a plate.
Aluminium does not exist naturally, but is found in mineral compounds (silicate and oxide) that are very stable. The most economically important form of an aluminum hydroxide is the aluminum ore, called bauxite. Bauxite is plentiful and occurs mainly in tropical and sub-tropical areas such as West Africa, West Indies, South America and Australia. It is mined then refined into alumina using the Bayer Process, and then electrolytically reduced into metallic aluminium. This abundance is due to the fact that the element Aluminum, (Al), makes up 10% of the Earth’s crust. The range of forms the metal can take (castings, extrusions and tubes, sheet & plate, foil, powder, forgings etc) and variety of surface finishes available (coatings, anodizing, polishing etc) means it lends itself to a wide range of products, many of which we use every day of our lives. In fact, it is the world’s second most used metal after steel. In 2006, 50 million tons were produced compared with 17 million tons of copper, 8 million tons of lead and 0.4 million tons of tin. Of the 50 million total, 16 million, or 32%, is recycled aluminium production while 34 million tons of new aluminium is produced.
Aluminum is one of the most reusable sources available as it can be used over and over and over again indefinitely without losing its properties. Two very commonly recycled materials, paper (because of the fibers) and plastic (because of its molecular structure), are limited in the number of times they can be recycled, and the quality eventually degrades to a non-reusable state. Moreover, aluminium recycling require 95% less energy, generate 95% less emission and create 97% less water pollution than producing the new metal from naturally occuring aluminium ore. Recycling one ton of aluminum eliminates the need for 5 tons of bauxite ore to be mined, the generation of nearly 2 tons of “red mud” byproduct, 9800 kg of carbon dioxide equivalent emission, and 64 kilogram of sulfur dioxide of emission, and the disturbance of about 1 square meters of land. Moreover, if pre-treated and/or sorted, aluminium products can be recycled for use in almost all aluminium applications since the metal’s atomic structure is not altered during melting. Recycled aluminium can be back as new products in as little as 60 days after it enters the recycling cycle. It should be noted that though the recycled product may be the same as the original product (e.g. window frame recycled back into a window frame or can to can), it is more often that it comes back a completely different product (cylinder head recycled into a gearbox). Aluminium that cannot be collected or recycled includes that used in powder, paste and for deoxidation purposes as, after use, it loses its metallic properties.
As aluminium has been recycled since the days it was first commercially produced, 70% of the aluminum produced in the world since the industry began a century ago is still in use today. Today, recycled aluminium accounts for one-third of global aluminium usage per year and US aluminium recyclers are earning almost $1 billion a year.
Containers and packaging (80 million tons or 31.7% of total generation) make up the major portion of US solid waste. The recovery of containers and packaging is at 40.2%. High recycling achievers were: 72% corrugated boxes, 63% steel packaging (predominately steel cans), 45% aluminum beverage cans. There still much more potential for recycling, as only 52% of aluminium cans in the US are recycled -nearly 48 billion beverage cans a year goes to waste.
Aluminium scrap destined for recycling can be described as either “new” or “old”. New scrap is the surplus material that is discarded during the fabrication and manufacturing of aluminium alloys (e.g. the splinters of sheet edge trimmings). Most new scrap reaching the recycling industry comes directly from the manufacturing industry. It is usually of known quality and composition and often uncoated. It can therefore be melted down with little preparation. 100 % of the scrap arising from fabrication and manufacturing processes is remelted by the aluminium industry. Old scrap is the material that is collected after an aluminium containing product has reached the end of its useful life. With the variability in the chemical composition and price of scrap, both refiners and remelters have become increasingly specialised over the years. These specialists now apply scrap-specific treatment processes and melting. If a particular type of scrap is not available in the area where a plant is located, as is often the case, importing the scrap may be the best solution.
Scrap must be of appropriate quality before it can be melted down. To obtain this level of quality, all adherent materials must be removed. Depending on scrap type, aluminium losses of about 2% to 10% may be incurred during separation of aluminium from other materials. End-of-life products are often not mechanically separable into single material output fractions resulting to a dilution of foreign materials within each output. Clean scrap may be shredded or baled to assist subsequent handling. Turnings are
treated in special processing facilities, where they are freed of all adherents, degreased, dried and separated from any iron particles using a magnetic separator. Large scrap pieces (e.g. engine blocks) are fragmentised in order to separate foreign iron from the aluminium. If it is difficult to separate unwanted iron mechanically or manually from aluminium scrap, the scrap is fed into a special furnace that separates the iron thermally. Usually, it is more difficult to separate other non-ferrous metals from aluminium. For this purpose, heavy media separation is used, where scrap can be separated from impurities by density. For the separation of aluminium from non-metallic pieces eddy current installations are used which separate materials with different electrical conductivity.
With aluminium cans, lacquered and laminated scrap are often cleaned to remove coatings and residues to minimise metal losses during remelting. The industry uses three principal de-coating technologies: Rotary kiln, belt and fluidized bed de-coater. Aluminium contained in multi-material packaging (e.g. beverage cartons) can be separated by pyrolysis. In this case, the non-metallic components are removed from the aluminium by evaporation. A newer technology is the thermal plasma process here all three components –aluminium, plastic and paper – are separated into distinct fractions.
Almost all aluminium used commercially contains one or more alloying elements to enhance its strength or other properties. Basically, there are two types of aluminium alloys. Casting alloys are used for the production of castings, i.e. products at or near their finished shape, formed by solidification of the metal in a mould or a die. They have an an alloy concentration of up to 20%,
mostly silicon, magnesium and copper. Typical castings are cylinder heads, engine blocks and gearboxes in cars, components used in the mechanical and electrical engineering industries, components for household equipment and many other applications. the second type are wrought alloys. These alloys are primarily used for wrought products by hot and/or cold working and have an alloy concentration of up to 10%, mostly manganese, magnesium, silicon, copper and zinc.. Aluminium recycling therefore contributes to the sustainable use of these alloying metals, such as copper, iron, magnesium, manganese, silicon, zinc and other elements. This effectively means that with a recycled metal production of 4.7 million tonnes, 230 000 tonnes of alloying elements are simultaneously conserved by the aluminium industry in Europe every year. Many of the alloying elements do, however, limit the usability of recycled aluminium in the production of fabricated goods, like extrusion billets or rolling ingots. Therefore, aluminium scrap with an alloy composition corresponding to that of wrought alloys is separated whenever possible.
| Region | Number of Recycling Plants, 2008 |
|---|---|
| North America | 316 |
| Europe | 273 |
| Latin America & Caribbean | 117 |
| Japan | 120 |
| China | 71 |
| Middle East | 50 |
| CIS | 22 |
| Rest of Asia | 495 |
| Africa | 46 |
| Oceania | 56 |
Before being loaded into the furnace, it is standard practice for alloy-specific scrap batches to be combined in order to ensure
a precise alloy composition in the final product. This type of computer-assisted optimisation of selection and mixing of scrap types enables the aluminium recycling industry to work as economically as possible. It also serves to minimise environmental impact, since limited alloy corrections need to be made after melting. A new process being developed to sort aluminium scrap metallurgically utilises laser and spectroscopic technology. This technology, is now at an advanced stage of development, and looks very promising.
Refiners melt mixed casting and wrought alloy scrap, while remelters use mainly clean and sorted wrought alloy scrap, as well as some primary metal. The chemical composition of wrought alloys are generally characterised, among others things, by their low tolerance for certain alloying elements. Remelters select the appropriate quantity and quality of scrap to correlate with the chemical composition of the wrought alloy to be produced. With vehicles recycling it might be needed to separate the wrought alloys from the casting alloys, a technology not applied nor needed at present, as little of the aluminium contained in today’s vehicles is in the form of wrought alloys but new technology in the form of laser and x-ray sorting is under development for future application. Since 2003, the European Standard EN 13920 (parts 1–16) on aluminium and aluminium scrap, which covers all scrap types, has been considered the norm for scrap classification. In addition, further classifications at national and international level have been developed on the basis of bilateral agreements.
Scrap is melted in dry hearth, closed-well, electric induction, rotary or tilting rotary furnaces. Refiners most commonly use the rotary furnace, which melts aluminium scrap under a salt layer, while remelters favour the hearth furnace. Selection of the most appropriate furnace type is determined by the oxide content, type and content of foreign material (e.g. organic content), geometry of the scrap (mass to surface ratio), frequency of change in alloy composition and operating conditions.
The result of contact with the oxygen in air, aluminium is covered with a thin layer of aluminium oxides. This chemical reaction occurs particularly at high temperatures during melting, be it primary melting, foundry casting or recycling. This is the reason why molten aluminium is protected from further oxidation in the furnace. The generated fine mixture of oxide skins, metal (in equal amounts) and gas on the surface of the melt in the furnace is termed skimmings or aluminium dross. These skimmings have to be removed before the metal is cast. This by-product is collected and recycled into aluminium alloys and aluminium oxides (used in the cement industry) in special refineries. Using salt during the melting process reduces the amount of oxides generated and removes
impurities from the liquid metal.
During melting, samples are regularly taken and analysed using the latest computer-controlled technology, before it is awarded the necessary certification. Even the smallest discrepancy with the specified alloy composition, down to the parts-per-million range, can be detected and adjusted. Typical metal losses during scrap melting including the recycling of skimmings and salt slag range from 1 to 5% depending on the application and the furnace technology.
Alloy production in the melting furnace is followed by a refining process. The molten metal is transferred to a holding furnace, where the chemical composition is adjusted and the metal purified by the addition of refining agents or with the use of filters. For example, the introduction of fine bubbles of chlorine, argon and nitrogen removes unwanted elements, such as calcium and magnesium, and degasses the molten metal. Different grain refiners and modifiers are added in order to guarantee the desired metallurgical
structure of the resulting product.
As a final step, molten aluminium casting alloys are cast into ingots (4 kg to 25 kg) or directly transported to the foundry as molten metal. Indeed, refiners often deliver aluminium in its molten state to be turned into castings immediately upon arrival at the foundry. In the right circumstances this saves money and reduces environmental impact. Sometimes aluminium oxides trapped within the metal are filtered out during the casting process. Most casting alloys are produced exclusively by the aluminium recycling industry, as the primary industry is often unable to produce the diversity of alloys required by the foundry industry. Foundries are the main customers of refiners. They produce a wide variety of castings which are principally used in the transport sector.
Molten aluminium wrought alloys are cast into extrusion billets and rolling ingots, which may need to undergo heat treatmentfor various metallurgical reasons before hot working.
As aluminium is used in the steel industry to eliminate unwanted oxygen because of its high affinity for oxygen, special aluminium alloys are also cast into small ingots or other specific shapes for deoxidation purposes to produce high quality steel. In order to produce one tonne of steel in a basic oxygen furnace, around 1.8 kg of aluminium is needed for deoxidation purposes. Due to its high affinity for oxygen, aluminium always forms an oxide layer, one of the reasons why it has such excellent corrosion resistance qualities. This results, however, in loss of metal during use and melting.
The most significant emissions resulting from the aluminium recycling process are emissions released into the air. These include dust and smoke, metal compounds, organic materials, nitrogen oxides, sulphur dioxides and chlorides. State-of-the-art technology is used to extract fumes and other emissions and to reduce fugitive emissions. European refiners and remelters are equipped with state-of-the-art air filter equipment to clean exhaust gases of dust, acidic gases (HCl, HF, SO2), volatile organic carbon, dioxins, and furans. Filter dust, which arises during the cleaning and de-acidification of gaseous combustion products, is deemed to be hazardous waste and is partly landfilled or recycled. Skimmings and, in some cases, furnace linings are recycled within the aluminium recycling industry. The International Aluminium Institute projects that greenhouse gas emissions from the world wide aluminium industry will be fully offset through a combination of reduction measures, increased recycling and the use of aluminium in transport by around 2020.
Salt slag, which used to be land filled, is now recycled. Aluminium salt slag is a mixture of salts, aluminium oxide, metallic aluminium and impurities, extracted from aluminium scrap during melting. It is the typical residue left behind when aluminium scrap is melted in a rotary furnace. Rotary furnaces are commonly employed for aluminium scrap containing foreign materials. Depending on the kind of rotary furnace used and the type of scrap being melted, anything up to 500 kg of salt slag can be generated in the production of one tonne of aluminium metal. Fluxing salt is used mainly for refining in rotating furnaces in order to: 1. cover the molten metal to prevent oxidation, 2. increase the net metal yield, 3. clean the metal from non-metallic inclusions and dissolved metallic impurities (e.g. calcium and magnesium) and 4. enhance thermal efficiency in the furnace. The salt that is applied during melting can be completely recovered and used again for the same purpose by the refiner. The metallic aluminium is also recovered and utilised to produce aluminium alloys. The remaining residues, mainly aluminium oxide and impurities, are rendered inert and subsequently used by the cement industry or, if this is not possible, landfilled. In the landfill, aluminium oxidises to aluminium oxide. This oxide is inert.
The aluminium industry, in collaboration with various universities, is currently designing a model to track aluminium throughout its life cycle from mining to use to recycling. More than 90 processes (including sub-processes) and 300 aluminium flows will be investigated in Europe. The main objective of the study is to quantify the aluminium collection rate, as well as the metal losses incurred during the treatment and melting of scrap. This will help the industry to understand more fully, and continue to improve,
the diversity of processes required for recycled aluminium production
Transportation is the most important field of application for aluminium worldwide. Aluminium used in transportation is collected separately at end-of-life, when commercial vehicles, aircraft, railway coaches, ships, etc. are dismantled. As the aluminium parts are often too large to be directly melted in the furnace, they must first be reduced to small pieces by processes such as shearing. Scrap collected using various separation procedures is today mainly processed into aluminium casting alloys, which serve as pre-material for the production of castings. Typical applications include engines and gearboxes. Due to the increased use of aluminium wrought alloys in car bodies, a growing volume of wrought alloy scrap is anticipated.
The main uses of aluminium in the building industry are in the construction of windows, doors and facades, closely followed by roofs and walls. Other structural uses range from a glazed shop front to the superstructure of anything from a shopping centre to a
stadium. Aluminium can also be found in door handles, window catches, staircases, roller shutters and sun-shading systems, heating and air-conditioning systems and more recently in the support structures for solar panels, solar collectors and light shelves. The collection rate of aluminium in building can be determined by comparing of the mass of aluminium scrap dismantled from an end-of-life building with the mass aluminium identified in this building before starting to demolish it. Globally, aluminium enjoys a high
collection rate of 85% in the building industry. Today the global building market uses some 11 million tons of final aluminium products annually.
Aluminium possesses unique barrier and physical properties and is therefore used extensively for the packaging of food, beverages and pharmaceuticals. It effectively protects contents against the quality-reducing effects of oxygen, light, moisture, micro-organisms and unwanted aromas. The amount of aluminium packaging effectively recycled depends greatly upon individual national circumstances and the efficiency of the collection schemes, and therefore rates vary from 25% to 85% across the globe. The collection rates of used beverage cans vary from country to country from 30% to close to 100%, with a global average of close to 70%.
Two different types of aluminium packaging can be distinguished. There is the rigid and semi-rigid packaging such as food and beverage cans, aerosol cans, closures and menu trays which consist mainly of aluminium. This type of packaging scrap has a high aluminium content and therefore of high market value. There is also the flexible packaging such as a packaging where a thin aluminium foil is laminated as a barrier material to plastics or cardboard. With its very low content of aluminium. aluminium in most of this type of packaging is not recycled because the pack will have been sent for recycling to the reprocessor of the predominant material, for example drinks cartons containing a thin barrier layer of foil will usually go to the paper industry, and aluminium caps on glass bottles will go to the glass industry. Alternatively, such a packaging is economically incinerated with a recovery of the combustion heat. Because of its low thickness, the aluminium barrier will be oxidized completely, and the combustion heat of aluminium can be recovered. Incineration and energy recovery is often preferable to the recovery of the minute amount of aluminium metal. However if the aluminium is separated during reprocessing, it can certainly be recycled. Aluminium can be extracted from laminates by pyrolysis and thermal plasma techniques.
