- Aluminium recycling
Aluminium recycling is the process by which
scrap aluminiumcan be reused in products after its initial production. The process involves simply re-melting the metal, which is far less expensive and energy intensive than creating new aluminium through the electrolysisof aluminium oxide(aluminium2oxygen3), which must first be mined from bauxiteore and then refined using the bayer process. Recyclingscrap aluminum requires only 5% of the energy used to make new aluminium. [ [http://www.economist.com/opinion/displaystory.cfm?story_id=9302727 Recycling | The price of virtue | Economist.com ] ] For this reason, approximately 31% of all aluminium produced in the United Statescomes from recycled scrap. [http://minerals.usgs.gov/minerals/pubs/commodity/aluminum/mcs-2008-alumi.pdf minerals.usgs.gov]
A common practice since the early 1900s and extensively capitalized during
World War II, aluminium recycling is not new. It was, however, a low-profile activity until the late 1960s when the exploding popularity of aluminium beverage cans finally placed recycling into the public consciousness. [cite book |last=Schlesinger |first=Mark |title=Aluminum Recycling |year=2006 |url=http://books.google.com/books?id=DtX1nbel49kC |publisher=CRC Press |language=English |isbn=9780849396625 |pages=248]
Sources for recycled aluminium include
aircraft, automobiles, bicycles, boats, computers, cookware, gutters, siding, wire, and many other products that require a strong light weight material, or a material with high thermal conductivity. As recycling does not damage the metal's structure, aluminium can be recycled indefinitely and still be used to produce any product for which new aluminium could have been used. [ [http://www.wasteonline.org.uk/resources/InformationSheets/metals.htm WasteOnline: Metals aluminium and steel recycling] ]
The recycling of aluminium generally produces significant cost savings over the production of new aluminium even when the cost of collection, separation and recycling are taken into account. [http://www.world-aluminium.org/environment/recycling/ International Aluminium Institute: Aluminium Recycling Facts] ] Over the long term, even larger national savings are made when the reduction in the capital costs associated with
landfills, mines and international shippingof raw aluminium are considered.
The environmental benefits of recycling aluminium are also enormous. Only around 5% of the CO2 is produced during the recycling process compared to producing raw aluminium (and an even smaller percentage when considering the complete cycle of mining and transporting the aluminium). Also, open-cut mining is most often used for obtaining aluminium ore, which destroys large sections of world's natural land.
One of the reasons why only 31% of scrap aluminum is recycled is economics: for the aluminium producer, it is cheaper to make new aluminium than it is to find, collect, identify, separate, and clean the aluminium parts in old products. Recycling is further complicated with painted aluminium, as re-melting these products releases highly
toxicfumes.Fact|date=April 2008 Most of the aluminium that is recycled comes from pre-consumer factory waste.Fact|date=April 2008
Aluminium lasts practically forever: 500-year-old aluminium is just as good as aluminium made 50 years ago, due to its resistance to
corrosion. Strategic planning may dictate that it is most economical to stockpilescrap aluminium for future use while energy is still relatively cheap. Whatever the case may be, the global supply of easily accessible scrap aluminium is not enough to meet current demands for aluminium.
Aluminium beverage cans are usually recycled in the following basic way: [ [http://www.aluminum.org/Content/NavigationMenu/News_and_Stats/CansForHabitat_org/Aluminum_Recycling/How_Is_An_Aluminum_Can_Recycled_/How_Is_An_Aluminum_Can_Recycled_.htm aluminum.org: How Is An Aluminum Can Recycled?] ]
#Cans are first separated from
municipal waste, using an eddy currentseparator.
#Cans are shredded into small, uniform pieces to reduce volume and simplify automated handling by machines.
#Pieces are mechanically and/or chemically cleaned to reduce contamination impurities.
#Pieces are compressed into blocks to minimize
oxidationlosses when melted. (The surface of aluminium readily oxidizes back into aluminium oxide when exposed to oxygen. [ [http://www.metalwebnews.com/howto/furnace2/melting.html www.metalwebnews.com: Melting Practice] ] )
#Blocks are loaded into the furnace and heated to 750 °C ± 100 °C to produce molten aluminium.
Drossis removed and the dissolved hydrogenis degassed. (Molten aluminium readily disassociates hydrogen from water vaporand hydrocarbon contaminants.) This is typically done with chlorine and nitrogen gas. Hexachloroethanetablets are normally used as the source for chlorine. Ammonium perchloratecan also be used, as it decomposes mainly into chlorine, nitrogen, and oxygen when heated. [ [http://www.key-to-metals.com/Article83.htm key-to-metals.com: Aluminum Casting Problems ] ]
#Samples are taken for
spectroscopic analysis. Depending on the final product desired, high purity aluminium, copper, zinc, manganese, silicon, and/or magnesiumis added to alter the molten composition to the proper alloyspecification. The top 5 aluminium alloysproduced are apparently 6061, 7075, 1100, 6063, and 2024. [http://en.wikipedia.org/wiki/Aluminium_alloy]
#The furnace is tapped, the molten aluminium poured out, and the process is repeated again for the next batch. Depending on the end product it may be cast into
ingots, billets, or rods, formed into large slabs for rolling, atomized into powder, sent to an extruder, or transported in its molten state to manufacturing facilities for further processing. [ [http://www.alcoa.com/primary_na/en/products/products.asp Alcoa Primary Aluminum - North America: Products ] ]
Ingot production using reverberatory furnaces
The scrap aluminium is separated into a range of categories i.e. irony aluminium (engine blocks etc), alloy wheels, "clean aluminium"Depending on the specification of the required ingot casting will depend on the type of scrap used in the start melt.Generally the scrap is charged to a
reverberatory furnace(other methods appear to be either less economical and/ or dangerous) and melted down to form a "bath". the molten metal is tested using spectroscopy on a sample taken from the melt to determine what refinements are needed to produce the final casts.After the refinements have been added the melt may be tested several times to be able to fine tune the batch to the specific standard
Once the correct "recipe" of metal is available the furnace is tapped and poured into ingot moulds, usually via a casting machine. The melt is then left to cool, stacked and sold on as cast silicon aluminium ingot to various industries for re-use.
*The average person consumes 43,371 aluminium beverage cans (12 pack every week) in their lifetime. [cite video |date2=2008-04-14 |title=The Human Footprint |url=http://www.natgeohumanfootprint.com |medium=Documentary |publisher = National Geographic Channel |accessdate = 2008-04-14]
** 43,371 cans is approximately 1,434 pounds of aluminium.
** The recycle value of 43,371 cans is approximately $731 if loose, $1,355 if shredded.
** If a person recycled all the aluminium cans they consumed it could power a TV for 130,000 hours.
* One kilogram of recycled aluminium, prevents the extraction of five kilograms of bauxite.Fact|date=April 2008
* The average life cycle of an aluminium can is 30 days, from its placement on the store shelf to its return to be recycled.Fact|date=April 2008
* An empty aluminum can weighs approximately a half-ounce (15 g). There are roughly 30 empty aluminum cans to an avoirdupois pound (450 g). Fact|date=April 2008
* [http://www.cogelme.com/eng/e-eddy-current-separators.htm Eddy current separator for Aluminium recycling and separation - Videos available]
* [http://www.youtube.com/watch?v=U8o9DckXSgo&fmt=18 Industrial shredder shredding compressed blocks of aluminium] Youtube Video
* [http://www.youtube.com/watch?v=M4rt-ZthhF4&fmt=18 Industrial shredder shredding aluminium cans] Youtube Video
* [http://www.youtube.com/watch?v=SJNwsZH53-A&fmt=18 How aluminum cans are made] Youtube Video
* [http://www.youtube.com/watch?v=oTiRznsxauc&fmt=18 How new aluminium is made] Youtube Video
* [http://www.youcanchangetheplanet.org Youcanchangetheplanet.org] - A non-profit sustainable conservation organization promoting aluminum recycling and the rehabilitation of damaged ecosystems.
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