Aluminium recycling
Encyclopedia
Scrap
Scrap is a term used to describe recyclable and other materials left over from every manner of product consumption, such as parts of vehicles, building supplies, and surplus materials. Unlike waste, scrap has significant monetary value...
aluminium
Aluminium
Aluminium or aluminum is a silvery white member of the boron group of chemical elements. It has the symbol Al, and its atomic number is 13. It is not soluble in water under normal circumstances....
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
Electrolysis
In chemistry and manufacturing, electrolysis is a method of using a direct electric current to drive an otherwise non-spontaneous chemical reaction...
of aluminium oxide
Aluminium oxide
Aluminium oxide is an amphoteric oxide with the chemical formula 23. It is commonly referred to as alumina, or corundum in its crystalline form, as well as many other names, reflecting its widespread occurrence in nature and industry...
(23), which must first be mined from bauxite
Bauxite
Bauxite is an aluminium ore and is the main source of aluminium. This form of rock consists mostly of the minerals gibbsite Al3, boehmite γ-AlO, and diaspore α-AlO, in a mixture with the two iron oxides goethite and hematite, the clay mineral kaolinite, and small amounts of anatase TiO2...
ore and then refined using the Bayer process
Bayer process
The Bayer process is the principal industrial means of refining bauxite to produce alumina .Bauxite, the most important ore of aluminium, contains only 30–54% alumina, Al2O3, the rest being a mixture of silica, various iron oxides, and titanium dioxide. The alumina must be purified before it can...
. Recycling
Recycling
Recycling is processing used materials into new products to prevent waste of potentially useful materials, reduce the consumption of fresh raw materials, reduce energy usage, reduce air pollution and water pollution by reducing the need for "conventional" waste disposal, and lower greenhouse...
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
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...
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
World War II
World War II, or the Second World War , was a global conflict lasting from 1939 to 1945, involving most of the world's nations—including all of the great powers—eventually forming two opposing military alliances: the Allies and the Axis...
, aluminium recycling is not new. It was, however, a low-profile activity until the late 1960s when the exploding popularity of aluminium beverage can
Beverage can
A beverage can is a tin can designed to hold a specific portion of a beverage. Beverage cans are made of tin-plated steel or aluminium.- History :...
s finally placed recycling into the public consciousness.
Aircraft
An aircraft is a vehicle that is able to fly by gaining support from the air, or, in general, the atmosphere of a planet. An aircraft counters the force of gravity by using either static lift or by using the dynamic lift of an airfoil, or in a few cases the downward thrust from jet engines.Although...
, automobiles, bicycles, boats, computers, cookware, gutters
Rain gutter
A rain gutter is a narrow channel, or trough, forming the component of a roof system which collects and diverts rainwater shed by the roof....
, siding
Siding
Siding is the outer covering or cladding of a house meant to shed water and protect from the effects of weather. On a building that uses siding, it may act as a key element in the aesthetic beauty of the structure and directly influence its property value....
, wire
Wire
A wire is a single, usually cylindrical, flexible strand or rod of metal. Wires are used to bear mechanical loads and to carry electricity and telecommunications signals. Wire is commonly formed by drawing the metal through a hole in a die or draw plate. Standard sizes are determined by various...
, and many other products that require a strong light weight material, or a material with high thermal conductivity
Thermal conductivity
In physics, thermal conductivity, k, is the property of a material's ability to conduct heat. It appears primarily in Fourier's Law for heat conduction....
. 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.
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 landfillLandfill
A landfill site , is a site for the disposal of waste materials by burial and is the oldest form of waste treatment...
s, mines and international shipping
Shipping
Shipping has multiple meanings. It can be a physical process of transporting commodities and merchandise goods and cargo, by land, air, and sea. It also can describe the movement of objects by ship.Land or "ground" shipping can be by train or by truck...
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. Just how much is vividly shown when aluminium oxidises, in ThermiteThermite
Thermite is a pyrotechnic composition of a metal powder and a metal oxide that produces an exothermic oxidation-reduction reaction known as a thermite reaction. If aluminium is the reducing agent it is called an aluminothermic reaction...
and Ammonium perchlorate composite propellant
Ammonium Perchlorate Composite Propellant
Ammonium perchlorate composite propellant is a modern solid rocket propellant used in both manned and unmanned rocket vehicles. It differs from many traditional solid rocket propellants such as black powder or Zinc-Sulfur, not only in chemical composition and overall performance, but also by the...
.
Environmental savings
If energy is 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:- Cans are first divided from municipal waste, usually through an eddy current separatorEddy current separatorAn eddy current separator uses a powerful magnetic field to separate metals from non-metals in garbage. The device makes use of eddy currents to effect the separation....
, and cut into little, equal pieces to lessen the volume and make it easier for the machines that separate them. - 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 oxygenOxygenOxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...
.). - Blocks are loaded into the furnace and heated to 750 °C ± 100 °C to produce molten aluminium.
- DrossDrossDross is a mass of solid impurities floating on a molten metal. It appears usually on the melting of low-melting-point metals or alloys such as tin, lead, zinc or aluminium, or by oxidation of the metal. It can also consist of impurities such as paint leftovers...
is removed and the dissolved hydrogenHydrogenHydrogen is the chemical element with atomic number 1. It is represented by the symbol H. With an average atomic weight of , hydrogen is the lightest and most abundant chemical element, constituting roughly 75% of the Universe's chemical elemental mass. Stars in the main sequence are mainly...
is degassedDegasificationDegasification is the removal of dissolved gases from liquids, especially water or aqueous solutions, in the fields of science and engineering. There are numerous possible methods for such removal of gases from solids....
. (Molten aluminium readily disassociatesDissociation (chemistry)Dissociation in chemistry and biochemistry is a general process in which ionic compounds separate or split into smaller particles, ions, or radicals, usually in a reversible manner...
hydrogen from water vaporWater vaporWater vapor or water vapour , also aqueous vapor, is the gas phase of water. It is one state of water within the hydrosphere. Water vapor can be produced from the evaporation or boiling of liquid water or from the sublimation of ice. Under typical atmospheric conditions, water vapor is continuously...
and hydrocarbon contaminants.) This is typically done with chlorine and nitrogen gas. HexachloroethaneHexachloroethaneHexachloroethane, also known as perchloroethanes , C2Cl6, is a colorless solid at room temperature which is used by the US Military in smoke compositions, e.g...
tablets are normally used as the source for chlorine. Ammonium perchlorateAmmonium perchlorateAmmonium perchlorate is an inorganic compound with the formula NH4ClO4. It is the salt of perchloric acid and ammonia. It is a powerful oxidizer, which is why its main use is in solid propellants...
can also be used, as it decomposes mainly into chlorine, nitrogen, and oxygen when heated. - Samples are taken for spectroscopic analysis. Depending on the final product desired, high purity aluminium, copperCopperCopper is a chemical element with the symbol Cu and atomic number 29. It is a ductile metal with very high thermal and electrical conductivity. Pure copper is soft and malleable; an exposed surface has a reddish-orange tarnish...
, zincZincZinc , or spelter , is a metallic chemical element; it has the symbol Zn and atomic number 30. It is the first element in group 12 of the periodic table. Zinc is, in some respects, chemically similar to magnesium, because its ion is of similar size and its only common oxidation state is +2...
, manganeseManganeseManganese is a chemical element, designated by the symbol Mn. It has the atomic number 25. It is found as a free element in nature , and in many minerals...
, siliconSiliconSilicon is a chemical element with the symbol Si and atomic number 14. A tetravalent metalloid, it is less reactive than its chemical analog carbon, the nonmetal directly above it in the periodic table, but more reactive than germanium, the metalloid directly below it in the table...
, and/or magnesiumMagnesiumMagnesium is a chemical element with the symbol Mg, atomic number 12, and common oxidation number +2. It is an alkaline earth metal and the eighth most abundant element in the Earth's crust and ninth in the known universe as a whole...
is added to alter the molten composition to the proper alloyAlloyAn alloy is a mixture or metallic solid solution composed of two or more elements. Complete solid solution alloys give single solid phase microstructure, while partial solutions give two or more phases that may or may not be homogeneous in distribution, depending on thermal history...
specification. The top 5 aluminium alloys produced are apparently 60616061 aluminum6061 is a precipitation hardening aluminum alloy, containing magnesium and silicon as its major alloying elements. It has good mechanical properties and exhibits good weldability...
, 7075, 1100, 60636063 aluminiumAA 6063 is an aluminium alloy, with magnesium and silicon as the alloying elements. The standard controlling its composition is maintained by The Aluminum Association. It has generally good mechanical properties and is heat treatable and weldable...
, and 2024. - 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, billetsBillet (manufacturing)Semi-finished casting products are intermediate castings produced in a foundry that need further processing before being a finished good. There are four types: ingots, billets, blooms, and slabs.-Ingot:...
, or rods, formed into large slabs for rollingRolling (metalworking)In metalworking, rolling is a metal forming process in which metal stock is passed through a pair of rolls. Rolling is classified according to the temperature of the metal rolled. If the temperature of the metal is above its recrystallization temperature, then the process is termed as hot 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 e.g. irony aluminum (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
Reverberatory furnace
A reverberatory furnace is a metallurgical or process furnace that isolates the material being processed from contact with the fuel, but not from contact with combustion gases...
(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 rateRecycling in Japan
is based on the Japanese Container and Packaging Recycling Law. Plastic, paper, PET bottles, aluminium and glass are collected and recycled.- Container and Packaging Recycling Law :...
. 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, hydrogenHydrogen
Hydrogen is the chemical element with atomic number 1. It is represented by the symbol H. With an average atomic weight of , hydrogen is the lightest and most abundant chemical element, constituting roughly 75% of the Universe's chemical elemental mass. Stars in the main sequence are mainly...
, acetylene
Acetylene
Acetylene is the chemical compound with the formula C2H2. It is a hydrocarbon and the simplest alkyne. This colorless gas is widely used as a fuel and a chemical building block. It is unstable in pure form and thus is usually handled as a solution.As an alkyne, acetylene is unsaturated because...
, and ammonia
Ammonia
Ammonia is a compound of nitrogen and hydrogen with the formula . It is a colourless gas with a characteristic pungent odour. Ammonia contributes significantly to the nutritional needs of terrestrial organisms by serving as a precursor to food and fertilizers. Ammonia, either directly or...
) 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
Asphalt
Asphalt or , also known as bitumen, is a sticky, black and highly viscous liquid or semi-solid that is present in most crude petroleums and in some natural deposits, it is a substance classed as a pitch...
and concrete
Concrete
Concrete is a composite construction material, composed of cement and other cementitious materials such as fly ash and slag cement, aggregate , water and chemical admixtures.The word concrete comes from the Latin word...
.
See also
- Environmental issues with miningEnvironmental issues with miningThe environmental impact of mining includes erosion, formation of sinkholes, loss of biodiversity, and contamination of soil, groundwater and surface water by chemicals from mining processes. In some cases, additional forest logging is done in the vicinity of mines to increase the available room...
- BalerBalerA baler is a piece of farm machinery used to compress a cut and raked crop into compact bales that are easy to handle, transport and store...
- Ferrous metal recyclingFerrous metal recyclingFerrous metals are able to be recycled with steel being one of the most recycled materials in the world,. Ferrous metals contain an appreciable percentage of iron and the addition of carbon and other substances creates steel....
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)