Metals of all types have the unique quality of not just being recyclable, but infinitely recyclable. No matter how many times they’re melted down the reprocessed metal is just as good as when it was smelted from ore dug out of the ground. This advantage means that metals are one of the most sustainable materials that humans use, and this is especially so of aluminum whose lightweight strength means that it is cost effective to move around, and thus to use as packaging. Hence aluminum’s widespread use and continuing use as a beverage container.
The aluminum scrap recycling process is a vital part of maintaining a sustainable industry that already exists. It is estimated that some seventy-five percent of all the aluminum ever mined is still circulating in the aluminum market. With sustainability becoming a growing concern, lightweight aluminum will play an even greater role, and while existing recycling practices are outstanding, there is always room for improvement in the aluminum scrap recycling process.
The Aluminum Scrap Recycling Process
At the surface level the aluminum scrap recycling process is very simple. The aluminum needs to be gathered, it needs to be cleaned, and then it can be remelted. This is true in the broadest sense. In the details it is a little more complicated. Aluminum is used in a variety of different roles, and it does need to be processed to remove potential contaminants before it can be reprocessed into a fresh aluminum product. Examples of these contaminants are:
|Non-Aluminum Metals||Non-aluminum metals, like iron, can cause problems during aluminum recycling. These metals can be introduced in aluminum turnings—chips left over from machining—after being scraped from tooling. Magnetic processes can remove iron from the recycling process, and sink-float tanks can separate non-magnetic metals.|
|Paints and Lacquers||Paints, coatings, lacquers and other organic materials are commonly applied to aluminum beverage cans. These must be removed before recycling in order to avoid contaminating the metal and producing fumes. This removal is usually accomplished through mechanical means.|
|Water and Moisture||Water and moisture can create hydrogen gas, which can lead to porosity and other defects in the recycled aluminum. Typically metal is heated and dried to remove any chance of moisture.|
|Grease and Oils||Oils and coolants are part of the machining process and these can be introduced into aluminum turnings that are sent for recycling. A combination of heat treatments and mechanical processes can remove these oils before recycling.|
In addition to processing to remove these potential contaminants, recycled aluminum can also be processed differently depending on its source, its quality, and its composition. Alloys that are heavily mixed with other materials besides aluminum may be melted in furnaces with heavy fluxing and filtration to separate other metals from the aluminum. Higher grade metals, like turnings from machine shops whose composition are known, are recycled in high-heat, rapid-mixing furnaces that minimize oxidation during the remelt.
Although recycling is a little more complicated than the sort, shred, and melt that it is usually made out to be, it is in fact vastly more energy efficient than making aluminum from virgin ore. However, direct reuse of metals as they are is even more energy efficient. It is also an option that is underutilized by many metal workers in industry.
Productions of Virgin Aluminum and the Importance of Recycling
In nature aluminum is most typically found in the form aluminum oxide. Sapphire gemstones are aluminum oxides and are in effect transparent aluminum, but metallic aluminum is refined from an aluminum oxide ore called bauxite. Bauxite isn’t pure aluminum oxide but also contains iron, silicates, magnesium, titanium, and other metals. Separating the aluminum from the ore isn’t simply a matter of crushing and heating the ore until the aluminum melts out but a multistage process—called the Bayer process—where the ore is first dissolved into a series of chemical solutions:
- Digestion: Crushed bauxite ore is mixed with caustic soda (sodium hydroxide) and heated to 300°F to 400 °F in large tanks. This creates sodium aluminate while impurities like silicates settle to the bottom of the tank where they are removed.
- Clarification: The slurry is then passed through a series of settling tanks, where the sodium aluminate decomposes into aluminum hydroxide and sodium hydroxide. The aluminum hydroxide settles to the bottom of the tank where it can be removed.
- Calcination: The aluminum hydroxide is heated in a kiln at high temperatures (~1,160°F) to remove hydrates and convert it to pure aluminum oxide powder.
This final aluminum oxide powder can then be smelted to create metallic aluminum. This aluminum oxide powder is then subjected to an additional, and separate high heat chemical process—the Hall-Heroult Process—where aluminum oxide is dissolved into molten, cryolite a sodium-aluminum salt. Then through a process of electrolysis, or a direct correct current induced chemical reaction, nearly pure metallic aluminum is formed and allowed to cool into ingot. This metallic aluminum ingot can then be sent to a foundry where an electric-arc furnace can melt it alongside trace percentages of other metals into aluminum alloys like the 3000 series aluminums used in drink cans, 6061 or 6063 structural and architectural aluminums, or 5000 series aluminum alloys used to cast tooling plate.
Production of virgin—from ore—aluminum is a three step process with every step of the process being energy intensive. Additionally many parts of the process offer a double carbon emission penalty both from the electrical production required for the process, and as part of the chemical action needed to production. Recycling aluminum is vastly less energy intensive. The existing aluminum can simply be melted down and used to produce a new aluminum product without a lot of repeated chemical reaction needed.
Direct Reuse Is the Best Aluminum Recycling
Reduce, reuse, and recycle is an old saw in environmentalism. Of the three, reuse is the most preferred but most underutilized. Aluminum comes from the foundries in standard shapes and size. Typically, at least some of this isn’t used, and sent to be recycled. While this is a worthy use, directly reusing the metal would be a worthier use of the metal still. The remnant aluminum leftover after cutting or machining has removed parts is the same as new metal for all intents and purposes.
This metal can be directly reused as it is. The only difference between remnant aluminum and new aluminum is that it is a nonstandard size, and possibly cosmetic issues like scratches. Direct reuse of this metal means an energy savings and reduction of carbon emissions that improves on even that of recycling aluminum into new aluminum products. All that is to ensure that this reclaimed remnant aluminum is the alloy needed for the job. Ensuring the use of 6061 instead of 7075 or vice versa where needed, or 6061 aluminum vs. 6063 or Alca 5 vs. 6061, and many other examples besides. So long as you use aluminum where the alloy can be verified there should be no issue with the use of remnant aluminum.
Industrial Metal Service is a long time metal recycler that offers collection and scrap metal pick up service to industrial firms. In addition to these services, IMS also offers cut to order sawing of new and remnant aluminum. The remnant aluminum’s contents are verified by an XRF scanner so you know what type of aluminum you’re getting. Our cutting service also allows you to buy precision cut and process ready aluminum that can be worked on directly after delivery. It is the ultimate in time, energy, costs, and carbon saving for metal workshops nationwide.