Efficient solvent-based removal of epoxy polymer coatings for the recycling of neodymium-iron-boron magnets

Conventional fossil-fuel driven transportation is responsible for ∼25 % of global carbon dioxide emissions. Electrification of transport is one solution for reducing emissions and minimising global warming. However, the production of electric vehicle (EV) motors has dramatically increased the demand for Rare Earth Elements (REEs); rare earth permanent magnets such as neodymium iron boron (NdFeB) are essential constituents of EV motors. There is a growing increase in recycling of these materials to meet demand, improve supply security, and mitigate the environmental impacts of mining. NdFeB magnets are often coated with crosslinked epoxy polymers to enhance corrosion resistance. NdFeB magnets can be recycled via the hydrogen processing magnet scrap method (HPMS). However, the epoxy polymer coatings tend to be only partially removed via sieving. Residual carbon will negatively impact the processing and properties of the recycled magnet; hence it is desirable to remove this coating prior to HPMS treatment. A solvolysis treatment offers the potential to remove organic coatings from magnets, which is explored in depth in this paper.

Epoxy polymer coated N42SH-grade NdFeB magnet samples from industrial motors were solvolysed in a batch reactor with isopropanol, achieving full coating removal at temperatures as low as 175 °C and times as short as 5–10 min. A kinetic model was developed using a Logistic Growth equation. This enabled the calculation of a relatively low activation energy of 11.62 kJ/mol. This work demonstrates the proof of concept of a solvent-based pre-treatment for coating removal during the recycling of NdFeB magnets with epoxy polymer coatings.