Pulverization of Permanent Magnets by Solvothermal Chemistry for Direct Recycling

Abstract

To face the growing need for NdFeB permanent magnets in devices in our everyday life, while considering the fluctuating market of rare earth elements such as neodymium (Nd), their recycling is strategic, especially for countries devoid of mines. Here, we report the proof of concept for permanent magnets’ direct recycling through solvothermal chemistry. Compared to existing processes requiring either the use of acids or dihydrogen, this greener approach is only based on the use of a water/ethanol mixture under pressure (250 bar) and temperature (250 °C) treatment. The mechanism consists of the hydrolysis of an intergranular Nd-rich phase, consuming it to form a Nd(OH)₃ powder together with a lattice expansion due to hydrogen insertion (Nd₂Fe₁₄BH_x), leading to the collapse of the ceramic into a Nd₂Fe₁₄B-based powder. This powder can then be directly reused and mixed with a virgin one to make new permanent magnets with interesting magnetic performance.