Rare earth elements

You have to come very close to see the type of screenings that Prof. YongXiang Yang (3mE) is shaking back and forth in a plastic bottle. If you look carefully, you can see fragments of copper wire, green motherboard pellets and transistor particles. As the recycling expert can tell you, neodymium is also amongst the pulverised computer particles.

Yang’s job is to extract this rare silver-coloured earth element. It has been processed into the magnet of the hard-disk drive. The magnets in windmills and electric automobiles also contain this element.
In addition to the computer powder, Yang has hundreds of hard-drive magnets lying around in his laboratory. All of the materials are delivered to him by a Spanish recycling company.

Although neodymium is a scarce substance, this material is not yet being recycled from PCs. There is no industrial method for doing so. Yang has several ideas for how it could be done. In 2013, he received two EU grants to conduct research here, in collaboration with several European partners. The team, which also includes four TU Delft doctoral candidates, is investigating two methods. In both cases, the magnets must first be demagnetised and converted into a powder. This can be done by heating the hard disks to 450–500 °C. ‘The powder that is created in this way can be extracted from the casings by shaking them hard in a rotating drum’, explains Yang. ‘We can also obtain the magnet powder by exposing the magnets to high concentrations of hydrogen’, the professor continues. ‘The neodymium then forms a powdery metal hydride and expands considerably’.

The powder, with iron and the black metalloid boron in addition to neodymium, is then purified through an electrolytic reaction and a long series of treatments with solvents. ‘The techniques appear to be very promising, although we do not yet know how efficient these processes would be on an industrial scale. The study will continue until 2016.’
The researchers are simultaneously testing comparable methods of extracting rare earth metals out of waste (tailings) from an iron mine in Sweden.


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