Aluminium recycling

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 (Template:Aluminium₂Template:Oxygen₃), 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. The nature of aluminium makes the material one of the few "infinitely recyclable" materials used in society; it can be recycled infinitely with no loss in quality. For this reason, approximately 31% of all aluminium produced in the United States comes from recycled scrap and 75% of all aluminum produced since 1888 is still in use today.

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 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.

Baled cans ready for transport

File:Shredded aluminium cans.png

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. 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.

Energy savings

Recycling aluminium uses about 5% of the energy required to create aluminium from bauxite, because the latter requires a lot of electrical energy to electrolyse aluminium oxide into aluminium. Additionally, recycled aluminium saves 95% of the green house gas emission from primary aluminum production. Just how much is vividly shown when aluminium oxidises, in Thermite and Ammonium perchlorate composite propellant.

Environmental savings

If energy directly equated to carbon dioxide, then recycled aluminium could be said to create 5% of the carbon dioxide produced in the creation from raw materials. In practice, this cannot be assumed. Electrolysis can be done by 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.

Process

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

1. Cans are first divided from municipal waste, usually through an eddy current separator, and cut into little, equal pieces to lessen the volume and make it easier for the machines that separate them.
2. Pieces are cleaned chemically/mechanically, and blocked to minimise oxidation losses when melted. (The surface of aluminium readily oxidizes back into aluminium oxide when exposed to oxygen.).
3. Blocks are loaded into the furnace and heated to 750 °C ± 100 °C to produce molten aluminium.
4. 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.
5. 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.
6. 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.

Ingot production using reverberatory furnaces

The scrap aluminium is separated into a range of categories i.e. irony aluminum (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.

Recycling rates

Brazil accounts for 89% recycling rate in 2001, reaching 10.5 billion beverage cans. Brazil attaches great importance to recycling aluminum beverage cans, 15 million people engaged in recycling aluminum beverage cans in 2001, a return rate of 85%, ranking first in the world, more than Japan's 82.5% recovery rate. Brazil has topped the aluminum can recycling charts eight years in a row with a consistent rate of around 90 percent.

The United States in 2001 recycled aluminum scrap aluminum produced 2.982 million tons, exceeding the primary aluminum production. In 2001 the U.S. recycled aluminum beverage cans accounted for 55.4% of total production, recycling aluminum 755,000 tons.

Secondary aluminium recycling

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.

See also

• Environmental issues with mining
• Baler

External links

• Youcanchangetheplanet.org - an organization promoting aluminium recycling and the rehabilitation of damaged ecosystems.
• Thomasnet.com - Recycled Aluminium in Manufacturing
• Secondary Aluminum Smelters of the World - A list of companies who produce secondary aluminium (i.e., recycled or remelted from scrap metal)