Aluminium recycling is the process of making new aluminium from old or no longer useful aluminium, such as scrap metal. This process involves melting the metal again, which uses less energy and costs less than creating new aluminium from raw materials. New aluminium is usually made by using electricity to separate alumina (Al₂O₃) from raw bauxite, a process that involves the Bayer and Hall–Héroult methods.
Making aluminium from recycled scrap uses only 5% of the energy needed to create new aluminium from raw ore. In 2022, the United States produced 3.86 metric tons of recycled aluminium for every metric ton of newly made aluminium. During the same time, recycled aluminium made up 34% of all new aluminium available in the country, including imported materials. Used drink containers are the biggest part of recycled aluminium scrap, and most of this material is turned back into aluminium cans.
Recycling process
The first step in aluminum recycling is gathering and separating aluminum scrap from different sources. Aluminum scrap comes mainly from two sources: manufacturing waste or old products. These old products can be things like cars, building materials, or items people use every day. Manufacturing waste includes pieces like shreds, shavings, and leftover aluminum from making products. Post-consumer scrap includes old or thrown-away aluminum items. Aluminum cans are a major source of recyclable aluminum scrap. After being collected, aluminum scrap is sorted based on its type of alloy, quality, and impurity levels. Sorting can be done by hand or using machines like eddy current separators, air classifiers, and density separators. The scrap is divided into groups such as wrought alloy scrap, casting alloy scrap, used beverage cans, automobile scrap, and mixed scrap. Sorting is important to create high-quality recycled aluminum.
After sorting, the scrap may go through pre-treatment steps to prepare it for melting. These steps can include baling, shredding, crushing, granulating, decoating, and demagnetizing. Shredding and crushing break the scrap into smaller pieces, making it easier to separate from other materials, while granulating makes fine particles that are good for melting. Thermal decoating removes coatings like paint and plastic from aluminum surfaces. Demagnetizing removes iron particles that stick to the aluminum scrap. Pre-treatment increases the density of the scrap and removes impurities, leading to faster melting, cleaner metal, less waste, and lower energy use.
Once pre-treated, the aluminum scrap is melted and treated to make refined aluminum alloy suitable for casting or reprocessing. Different types of furnaces are used depending on the type of scrap, the quality of the metal needed, and cost. Smaller pieces are usually melted in rotary or reverberatory gas-fired furnaces, while large pieces can be placed directly into reverb furnaces through side openings. Electric induction furnaces are also used. As the scrap melts, substances called fluxes are added to bind and remove impurities, which float to the top as dross. Chlorine gas may be added to remove impurities through flotation. The melted metal can then be refined further using methods like flux injection to reduce hydrogen and impurities. Degassing removes hydrogen, and chemical filtration removes solid impurities and small particles. The final result is molten aluminum alloy ready for casting.
The molten recycled aluminum is cast into solid forms like ingots, sows, or directly into sheets or extrusion billets. Direct-chill casting is often used to solidify liquid aluminum into large cylindrical billets for extrusion or rolling. This method sprays water onto the hot metal as it exits the mold, quickly cooling it into a solid billet. For ingots, book molds are used to create slab-shaped ingots that are suitable for remelting or rolling. Continuous casting shapes the aluminum directly into rolling slabs without an extra step of making ingots. Twin-belt or twin-roll strip casting makes thin alloy strips, 6-7mm thick, directly from the melt for rolling later. The casting method depends on how the recycled aluminum will be used next.
History
Although pure aluminum was made as early as 1825, recycling aluminum became more common when methods to produce aluminum in large amounts were developed. These methods combined the Bayer process and the Hall-Héroult process. The Hall-Héroult process, which turns alumina into aluminum, was created in 1886 by Charles Hall and Paul Héroult. Carl Josef Bayer developed a method in 1888 to change raw bauxite into alumina. As aluminum production increased with these methods, recycling aluminum also increased. In 1904, the first two aluminum can recycling plants were built in the United States. One was in Chicago, Illinois, and the other was in Cleveland, Ohio. Aluminum recycling increased the most during World War I when metal supplies were low. The U.S. government asked people to donate old items like aluminum pots, pans, boats, vehicles, and toys to recycle for making airplane parts.
Advantages
Aluminum is a material that can be recycled endlessly. Recycling aluminum uses up to 95% less energy than making new aluminum from raw materials, which also reduces emissions, including greenhouse gases. Today, about 75% of all aluminum ever produced, nearly a billion tons, is still being used.
Recycling aluminum usually saves money compared to making new aluminum, even after considering the costs of collecting, sorting, and processing it. Over time, recycling also helps save money nationally by reducing the costs of landfills, mining, and transporting raw aluminum across the world.
Recycling aluminum uses about 5% of the energy needed to make aluminum from bauxite. The energy required to change aluminum oxide into aluminum is clearly shown when this process is reversed in certain reactions, like those in thermite or ammonium perchlorate composite propellant.
Aluminum die extrusion is a method used to reuse aluminum scraps without requiring a lot of energy for melting. In 2003, half of all aluminum products made were made from recycled aluminum.
The amount of carbon dioxide released depends partly on the type of energy used. Electrolysis can use electricity from non-fossil fuel sources, such as nuclear, geothermal, hydroelectric, or solar power. Aluminum production often takes place where electricity is cheap. Countries like Canada, Brazil, Norway, and Venezuela, which have 61 to 99% hydroelectric power, are major aluminum producers. However, the carbon anodes used in the Hall–Héroult process are consumed during production, creating large amounts of carbon dioxide, no matter the electricity source. Work is being done to find alternatives to carbon anodes. Using recycled aluminum also reduces the need to mine and refine bauxite.
Because so much aluminum is used, even small losses can add up to large costs. For this reason, the movement of aluminum material is carefully tracked and recorded for financial purposes. Efficient production and recycling also help protect the environment.
Impact
The aluminium industry contributes about 2% of the world's greenhouse gas emissions, which is around 1.1 billion tons of carbon dioxide each year. This happens because many countries still use coal-powered electricity to produce aluminium. These countries are now trying to reduce the carbon emissions from aluminium production because it is the second most used metal globally, and doing so could help lower overall greenhouse gas emissions and slow climate change.
Aluminium is one of the most recyclable materials in the world. It can be recycled over and over again without losing quality. Making aluminium from recycled material uses only 5% of the energy needed to create new aluminium. Because of this, about 75% of all aluminium ever made is still in use today. In industries like automotive and construction, up to 90% of aluminium is recycled.
Since 1991, the amount of greenhouse gas emissions from aluminium cans has decreased by about 40%, similar to the drop in energy needed to make them. This improvement is due to using less carbon-intensive methods to produce primary aluminium, making manufacturing processes more efficient, and creating lighter cans. Although primary aluminium makes up only 26.6% of a can, it is the main source of the can's carbon footprint. For example, in 2020, 86% of China's aluminium production used coal-powered electricity. In contrast, Canada produces about 90% of its primary aluminium using hydroelectric power, which is considered the most sustainable method.
Aluminium is used in many areas, including defense, construction, and electrical systems. It also plays a key role in products that help reduce emissions, such as electric vehicles and solar panels. Because of this, countries are working to reduce the carbon emissions from aluminium production to help fight climate change.
Recycling aluminium has many economic benefits when done correctly. The Environmental Protection Agency says recycling is a "critical" part of the U.S. economy, helping create tax revenue, jobs, and wages. Recycling improves efficiency by handling scrap materials better, including both materials from the end of a product's life and materials reused during production. This supports a circular economy, which aims to use fewer natural resources and reduce waste. Countries like the European Union, Finland, France, Slovenia, Italy, Germany, and the Netherlands have adopted this approach.
A study in the United States found that aluminium recycling has provided economic benefits. It increased wages in the waste management and recycling industries from $2.1 billion to $5 billion, created over 100,000 jobs in the U.S., and generated $1.6 billion in material sales. Recycling also saves enough energy to power 1.5 million homes each year and keeps more than 1 million tons of waste out of landfills annually.
Recycling rates
According to 2020 data from the International Aluminium Institute, the global recycling rate for aluminium is 76%. Approximately 75% of the nearly 1.5 billion tonnes of aluminium ever made is still being used for its intended purpose today. Brazil recycles 98.2% of its aluminium can production, equal to 14.7 billion cans each year. This makes Brazil the world leader in aluminium can recycling, with a recovery rate higher than Japan’s 82.5%. Brazil has held the top position in aluminium can recycling for eight consecutive years.
Challenges
Recycled aluminum, aside from beverage cans, often comes from a mix of different alloys. These alloys usually contain high amounts of silicon (Si) and need extra processing during shredding, sorting, and refining to remove impurities. After refining, the levels of impurities in these alloys limit their use to castings and extrusions. The aerospace industry often sets a maximum limit of 0.40% for silicon and iron in alloys. Controlling these elements becomes harder and more expensive as the metal is recycled more frequently.
White dross, a leftover material from making aluminum and recycling it, is typically considered waste. However, it still contains useful amounts of aluminum that can be removed using industrial methods. This process creates aluminum billets and a complex waste material that is hard to manage. The waste reacts with water, releasing gases like hydrogen, acetylene, and ammonia. These gases catch fire quickly when they touch air, and contact with damp air causes large amounts of ammonia gas to be released. Despite these challenges, the waste is sometimes used as a filler in asphalt and concrete.