Aluminum is prized for the lightweight metal's versatility to form a wide range of consumer and industrial products -- from soda cans and tin foil to electronic parts to aircraft wings. And, it is easily recycled again and again into an even broader range of products.
But now researchers from the Massachusetts Institute of Technolgy and the Rochester Institute of Technology have released a study exposing recycled aluminum's soft underbelly.
Their analysis finds that inadequate measures are in place to reduce impurities that can build up as aluminum is recycled over and over again -- everything from paint and labels on cans to other metals that are accidentally mixed in.
Such impurities will continue to add up, the MIT researchers say, unless extra measures are taking during sorting of the recycled goods, or during their molten processing.
MIT researchers Randolph Kirchain and Elsa Olivetti, of the Materials Systems Lab, along with Gabrielle Gaustad of the Rochester Institute of Technology, published their findings in the journal Resources, Conservation and Recycling.
To maximize the utility of recycled aluminum, as well as other recycled materials, there is a need for more research on reducing accumulated contaminants, Kirchain says.
"This is a technological area that has been underinvested in," he says. "Technology for dealing with garbage is not an exciting, high-profile field," he says, "but there is real value in investing in this."Aluminum has long been the poster child of recycling.
About half of all aluminum used in the United States is now recycled, and this recycling has clear and dramatic benefits: Pound for pound, it takes anywhere from nine to 18 times as much energy to produce aluminum from raw ore as from recycled material.
Because it works so well, aluminum recycling continues to expand. But this expansion could run into problems, the MIT analysis shows,
For now, the problem remains manageable, Kirchain says, because different uses require different grades of aluminum. For example, aluminum engine blocks, one major market for recycled material, can be made from metal with relatively high levels of impurities without suffering any loss of performance or durability. But more specialized applications, such as for electronic circuits or for aerospace materials, require much higher purity.
"There is a huge range of impurity tolerance," Olivetti says. "The question is, how will the balance of such markets over time compare with the kinds of materials coming through the recycling stream?"
Kirchain says his team's analysis -- although directed specifically at aluminum -- is also an attempt to develop methods for analyzing the lifecycle of other materials that are becoming more significant parts of the recycling stream