Solvolysis as a scalable batch recycling step for removal of epoxy resin coatings from sintered Neodymium-Iron-Boron magnets

Neodymium-Iron-Boron (NdFeB) magnets are playing a crucial role in clean technologies. These materials contain critical materials that are subject to supply chain challenges. Therefore, it has become increasingly important to develop recycling technologies and relieve these accessibility issues. One of the key challenges in achieving this is the removal of polymer coatings which can contaminate the magnetic material through the diffusion of carbon into the NdFeB grain boundaries, which subsequently reduces the magnetic performance of a secondary magnet.

This research is a development on a small-scale solvolysis process which used a 100 mL reaction vessel to successfully remove the epoxy resin coating from individual magnets. The process has now been scaled up by a factor of 50 with a 5 L batch reactor. This has enabled the removal of the epoxy resin coating from 25 samples of sintered NdFeB magnets simultaneously. Subsequent measurement of the magnetic properties demonstrated an insignificant increase in the remanence, coercivity and maximum energy product, of 0.56%, 1.21% and 0.94% respectively, which fell within the expected error of the instrument. By removing the epoxy coating prior to hydrogen decrepitation, the carbon content was also substantially reduced from the initial 2506 ppm to 954 ± 5 ppm. This reduction in carbon content will improve the performance of recycled magnets, preventing the downcycling of these materials into low-value applications. As such, this research represents a step change in the performance of a closed-loop recycling process for materials which are critical to clean technologies.