MIT: Time to Act on Contaminants in Recycled Aluminium

New MIT research has shown that while aluminium has long been the poster child of recycling, problems may arise unless measures are taken to reduce impurities that can build up.


For now, the problem of contamination in recycled aluminium remains manageable because different uses require different grades
Credit: Shutterstock/ Nadja Antonova 03 April 2012

New research by the Massachusetts Institute of Technology (MIT) has shown that while aluminium has long been the poster child of recycling, problems may arise unless measures are taken to reduce impurities that can build up as aluminium is recycled over and over again.

According to the Institute, about half of all aluminium used in the U.S. is now recycled, with clear and dramatic benefits. For example, weight for weight, it takes anywhere from nine to 18 times as much energy to produce aluminium from raw ore as from recycled material.

Because it saves so much energy - and therefore money - aluminium recycling has continued to expand.

However, new MIT analysis finds that this expansion could run into problems unless measures are taken to reduce impurities that can build up as aluminium is recycled over and over again. These impurities include everything from paint and labels on cans to other metals that are accidentally mixed in.

According to MIT researchers, while such impurities will continue to increase, they can be managed so as to keep the accumulation to acceptable levels if extra steps are taken while the recycled goods are sorted, 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 scientific journal Resources, Conservation and Recycling.

According to MIT, the analysis was produced in response to a request from a major aluminium producer to help it decide whether to install improved separation systems to prepare for impurities that could become more serious over time.

"They couldn't make the business case based on what's happening today," said Kirchain - but his team's analysis showed that it would indeed make sense to install such systems in anticipation of future changes.

For now, the problem remains manageable, explained Kirchain, because different uses require different grades of aluminium.

For example, aluminium 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 specialised applications, such as electronic circuits or aerospace materials, require much higher purity.

"There is a huge range of impurity tolerance," added Olivetti. "The question is, how will the balance of such markets over time compare with the kinds of materials coming through the recycling stream?"

Conclusions

The study found many techniques available to reduce impurities in recycled aluminium.

In some cases, these technologies are simply extensions of those already used in the initial separation of aluminium from raw ore; others are extensions of processes used to separate different materials in the recycling stream.

The study found that most of these systems are difficult retrofit to existing plants, so it makes more economic sense to add them as new plants are built, even if they are not yet needed.

Although directed specifically at aluminium, Kirchain said that his team's analysis is also an attempt to develop methods for analysing the life cycle of other materials that are becoming more significant parts of the recycling collections.

This includes analysis of the social factors governing people's decisions on disposal of materials, which can affect how much contaminating material ends up in a given waste stream - or whether potentially useful material ends up in a landfill instead of being reused.

The study found that in order to maximise the utility of recycled aluminium, as well as other recycled materials, there is a need for more research on reducing accumulated contaminants.

"This is a technological area that has been underinvested in," he says. "Technology for dealing with garbage is not an exciting, high-profile field, but there is real value in investing in this," concluded Kirchain.


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