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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 aluminium requires only 5% of the energy used to make new aluminium. For this reason, approximately 31% of all aluminium produced in the United States comes from recycled scrap. Used beverage containers are the largest component of processed aluminum scrap, with most UBC scrap manufactured back into aluminum cans.
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.
Sources for recycled aluminium include aircraft, automobiles, bicycles, boats, computers, cookware, gutters, siding, wire, and many other products that need a strong light weight material, or a material with high thermal conductivity. As recycling does not transmute the element, aluminium can be recycled indefinitely and still be used to produce any product for which new aluminium could have been used.
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. 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.
Recycling aluminium uses about 5% of the energy required to create aluminium from bauxite; the amount of energy required to convert aluminium oxide into aluminium can be vividly seen when the process is reversed during the combustion of thermite or ammonium perchlorate composite propellant.
Recycled aluminium uses 5% of the energy that would be needed to create a comparable amount from raw materials. The benefit with respect to emissions of carbon dioxide depends on the type of energy used. Electrolysis can be done using electricity from non-fossil-fuel sources, such as nuclear, geothermal, hydroelectric, or solar. Aluminium production is attracted to sources of cheap electricity. Canada, Brazil, Norway, and Venezuela have 61 to 99% hydroelectric power, and are major aluminium producers.
The vast amount of aluminium used means that even small percentage losses are large expenses, so the flow of material is well monitored and accounted for financial reasons. Efficient production and recycling benefits the environment as well.
Aluminium beverage cans are usually recycled in the following basic way:
The scrap aluminium is separated into a range of categories e.g. irony aluminium (engine blocks etc.), clean aluminium (alloy wheels). Depending on the specification of the required ingot casting it 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.
Brazil recycles 98.2% of its aluminium can production, equivalent to 14.7 billion beverage cans per year, ranking first in the world, more than Japan's 82.5% recovery rate. Brazil has topped the aluminium can recycling charts eight years in a row.
White dross from primary aluminium production and from secondary recycling operations still contains useful quantities of aluminium which can be extracted industrially. The process produces aluminium billets, together with a highly complex waste material. This waste is difficult to manage. It reacts with water, releasing a mixture of gases (including, among others, hydrogen, acetylene, and ammonia) which spontaneously ignites on contact with air; contact with damp air results in the release of copious quantities of ammonia gas. Despite these difficulties, however, the waste has found use as a filler in asphalt and concrete.