Aluminium recycling.html



Aluminium recycling is the process by which scrap aluminium can 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 electrolysis of aluminium oxide (Al₂O₃), which must first be mined from bauxite ore and then refined using the bayer process. Recycling scrap aluminum requires only 5% of the energy used to make new aluminium. ¹ For this reason, approximately 31% of all aluminium produced in the United States comes from recycled scrap. ²

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. ³

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.⁴

Ideological Barriers

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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 toxic fumes.^{citation needed} Most of the aluminium that is recycled comes from pre-consumer factory waste.^{citation needed}

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 stockpile scrap 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.

Baled cans ready for transport

Shredded aluminium beverage cans

Advantages

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.⁵ Over the long term, even larger national savings are made when the reduction in the capital costs associated with landfills, mines and international shipping of 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)⁵. Also, open-cut mining is most often used for obtaining aluminium ore, which destroys large sections of the world's natural land.

Process

Aluminium beverage cans are usually recycled in the following basic way:⁶

1. Cans are first separated from municipal waste, using an eddy current separator.
2. Cans are shredded into small, uniform pieces to reduce volume and simplify automated handling by machines.
3. Pieces are mechanically and/or chemically cleaned to reduce contamination impurities.
4. Pieces are compressed into blocks to minimize oxidation losses when melted. (The surface of aluminium readily oxidizes back into aluminium oxide when exposed to oxygen. ⁷)
5. Blocks are loaded into the furnace and heated to 750 °C ± 100 °C to produce molten aluminium.
6. Dross is removed and the dissolved hydrogen is degassed. (Molten aluminium readily disassociates hydrogen from water vapor and hydrocarbon contaminants.) This is typically done with chlorine and nitrogen gas. Hexachloroethane tablets are normally used as the source for chlorine. Ammonium perchlorate can also be used, as it decomposes mainly into chlorine, nitrogen, and oxygen when heated.⁸
7. Samples are taken for spectroscopic analysis. Depending on the final product desired, high purity aluminium, copper, zinc, manganese, silicon, and/or magnesium is added to alter the molten composition to the proper alloy specification. The top 5 aluminium alloys produced are apparently 6061, 7075, 1100, 6063, and 2024.⁹
8. 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.¹⁰

Ingot production using reverberatory furnaces

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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.

Trivia

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• The average person consumes 43,371 aluminium beverage cans (12 pack every week) in their lifetime.¹¹
  • 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.^{citation needed}
• The average life cycle of an aluminium can is 30 days, from its placement on the store shelf to its return to be recycled.^{citation needed}
• An empty aluminum can weighs approximately a half-ounce (15 g). There are roughly 30 empty aluminum cans to an avoirdupois pound (450 g).^{citation needed}

References

External links

• Eddy current separator for Aluminium recycling and separation - Videos available
• Industrial shredder shredding compressed blocks of aluminium Youtube Video
• Industrial shredder shredding aluminium cans Youtube Video
• How aluminum cans are made Youtube Video
• How new aluminium is made Youtube Video
• Youcanchangetheplanet.org - A non-profit sustainable conservation organization promoting aluminum recycling and the rehabilitation of damaged ecosystems.