Study looks at preventing contamination in recycling


Researchers at the Massachusetts Institute of Technology in the United States have looked at ways to prevent the accumulation of impurities in recycling aluminium.

A major aluminium producer requested this analysis from MIT researchers Randolph Kirchain and Elsa Olivetti to help decide whether to install improved separation systems to prepare for impurities that could become more serious over time as the metal is recycled over and over again. These impurities can include everything from paint and labels on cans to other metals that are accidentally mixed in.


The team found that even though the business case did not currently exist to install the separation equipment, it would make sense to install such systems in anticipation of future changes.

For now the problem remains manageable because different uses require different grades of aluminium. For example, aluminium engine blocks can be made from metal with relatively high levels of impurities without suffering any loss of performance or durability. But more specialised applications for electronic circuits or aerospace materials require much higher purity.

And although the technologies exist to separate material based on purity, the researchers found it was better to install it in new built plants rather than as a retrofit to an existing plant.

Randolph Kirchain said: “We’re continuing to collect more and more scrap which suggests we’re likely to have more and more problems with accumulating impurities. So far the operators of aluminium smelting plants have been able to accommodate variations in quality. If material comes in that’s more contaminated, they’ll divert that toward more forgiving applications. The cleanest material is reserved for the most specialised applications such as aeroplane parts.”

Although directed specifically at aluminium, the research is also an attempt to develop methods for analysing the lifecycle of other materials that are becoming more significant parts of the recycling stream.”