Having grown up with reduce, reuse, recycle campaigns (Tweety’s Global Patrol circa 1990), recycling is part of my daily routine. In fact, I’ve even spent time at a Japanese university lab where aluminum foil is thrown out separately from plastic wrap and gloves.
But how well is metal being recycled, and are we doing enough?
I recently read a paper in Science by Barbara K. Reck and Thomas E. Graedel, both of Yale University’s Centre for Industrial Ecology, School of Forestry and Environmental Studies, reviewing the current state of metal recycling. They offer some great insight on what’s been achieved and how metal recycling can be improved.
How much is going on?
This figure summarizes which elements have been recycled and their approximate recycling rates.
You can see only about half of the elements in the periodic are ever recycled. Of the ones that are recycled, base metals such as iron, copper, zinc have decently high recycling rates—around 50% and higher. But the remainder of the elements are rarely recycled. These elements are typically used in very precise technological purposes such as high-strength magnets, thin-film solar cells, computer chips, etc.
is that the elements highly mixed and technologically or economically challenging to recover.
What are the trends?
Certain metals have high overall recycling rates because they are used in large quantities in applications that make it easy to identify individual metals (think: steel beams, copper wiring). Metals used in large quantities such as steel, aluminum, copper, zinc, lead, nickel are straightforward to remelt and recycled the most (>50%) because of economies of scale.
Specialty metals such as indium and other rare earth elements used in jet engines, solar cells, or consumer electronics are generally used in small amounts so recycling is unfavorable economically. Another reason there’s limited recycling of elements used for precise technological purposes is because these elements are highly mixed, making them technologically or economically challenging to recover. However, metals used in small amounts but have high economic value such as precious metals like gold or platinum provide large incentives for recycling are have high recycling rates (60% Au, 50%Pt). There’s also a move towards replacing scarce metals with common metals, such as substituting indium tin oxide in LCDs with aluminum-doped zinc oxides.
What are the limitations?
Metals can be recycled infinitely in principle; however, recycling rates are limited by social behavior, product design, recycling technologies, and the thermodynamics of metal separation.
Of these limitations, the thermodynamics of metals cannot be altered. Thermodynamics describe the tendency of metals to stay in certain form, and determines the amount of work required to separate a mixture of materials. Metals with similar thermodynamic behaviours are very energy-intensive or difficult/practically impossible to separate individually. This is common problem, as most metals are used in combinations as alloys and/or reprocessed as mixtures. Sometimes it’s possible to separate elements in the slag or gas phase, but they often can’t be separated in the metal phase, leading to problems later on. For example, aluminum alloys containing manganese are used for only 5% of all aluminum applications (e.g.heat exchangers in vehicles) . However manganese cannot be separated from aluminum during recycling, and this aluminum alloy would be inappropriate for the majority of aluminum applications. So aluminum alloys containing manganese would have be recycled separately from other aluminum alloys.
Is a closed-loop materials economy possible?
A closed-loop materials economy refers to the idea that discarded mixed materials are restored to their original pure forms for reuse. The authors believe we are currently far away from a closed-loop material system. However, strict worldwide regulations have led to 90-95% collection and pre-processing rates of lead, making lead a near closed-loop system. While a lot can be done to improve recycling rates, the authors believe the limitation described earlier prevent a completely closed-loop system.
What can be done?
The authors believe there are three ways to significantly improve metal recycling:
#1Improve collection methods to increase recyclability rates
This method has the most potential for improve recycling, especially for metals used in small amounts in products containing large mixture of materials. . Collection efficiencies greatly depend on social and governmental influences (recall lead has 90-95% collection rates). Collection efficiency needs to be improved and conducted in a way that avoids creating even more difficult mixtures to separate during the reprocessing steps.
#2 Choose materials with recycling and recyclability in mind
Designers need to take metal combinations that can’t be recycled into considerations in their designs.
Back in school, I remember using a materials selection program that graphs a bunch of materials from the database relative to certain performance criteria. Typical criteria were costs, strength, weight, etc. But I don’t remember recyclability being a performance criterion. I agree with the authors, materials should be selected based on economics and function but also on how easily or readily they can be recycled.
#3 Establish collaborations between corporations, universities, governments to improve recycling technology
There’s a need for continued research on improving recycling technologies. Current recycling technologies are divided into basic and advanced methods. Basic technologies like shredding, crushing, magnetic sorting often used because scale and economically favourable. However, advanced technologies like laser, near-infrared, x-ray are limited to select metals because the technologies are most costly, even though better sorting can be achieved using advanced technologies.
In the end, recycling is about collecting and reusing all metals/materials. The authors stress that recycling rates can improve by stopping the practice of using large amounts of energy, time, technology, money to mine (scare) metals and then throwing them away after a single use.
American Welding Society. (1995-2012). Understanding Aluminum Alloys. Retrieved August 29, 2012, from http://www.aws.org/wj/amwelder/04-02/feature1.html
Reck BK, & Graedel TE (2012). Challenges in metal recycling. Science (New York, N.Y.), 337 (6095), 690-5 PMID: 22879508
Featured image source: Wikipedia user Borvan53