The Fraunhofer Institute for Silicate Research ISC, based in Alzenau, Germany, has reported a new, simplified process route for the recycling of permanent magnets that is claimed to enable the fast and cost-effective recycling of the rare earth elements neodymium and dysprosium.
Currently, methods of recycling permanent magnets involve extracting the rare earth elements from the magnet in a laborious and expensive process. The scientists of the Fraunhofer Project Group for Materials Recycling and Resource Strategies IWKS in Alzenau and Hanau of the Fraunhofer Institute for Silicate Research ISC are now pursuing a different approach. “Instead of trying to regain each individual type of rare earth, we focus on recycling the entire material, meaning the complete magnet – and this in only a few steps,” stated Oliver Diehl, a scientist in the Project Group IWKS. “This process is much easier and more efficient, because the composition of the material is already almost as it should be.”
The new recycling method utilises the melt spinning process, also known as rapid solidification, where researchers begin by melting the magnet. The liquefied material, heated to more than 1000°C, is directed via a nozzle onto a water-cooled copper wheel that rotates at a speed of 10 to 35 metres per second. As soon as the melted droplet comes into contact with the copper, it transfers its heat to the metal within fractions of a second and solidifies into flakes.
If the melted material was allowed to solidify in the normal way the atoms would line up in rows, in a crystal lattice. In the melt spinning procedure, however, crystallisation is avoided with either an amorphous structure being formed in which the atoms are completely irregularly arranged, or a nanocrystalline structure in which the atoms arrange themselves in nanometer-sized grains to form a crystalline structure.
The advantage is that the grain sizes – meaning the areas with the same crystalline structure – can be specifically varied and can be used to change the properties of the permanent magnet. In a further step, the researchers mill the flakes into a powder, which can then be further processed. “We press it into its final shape,” Diehl added.
A demonstration plant has already been established. “The demo system can process up to half a kilogram of molten material and is somewhere between a lab and a large-scale plant,” stated Diehl. The researchers are now optimising the properties of the recycled magnets by varying the melt spinning process – such as the speed of the copper wheel or the temperature of the melted material during the rapid solidification process. Both influence the cooling rate and consequentially also the crystalline structure of the solidified material.
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