A systematic study of HDDR processing conditions for the recycling of end-of-life Nd-Fe-B magnets

Scrap rare earth permanent magnets from various sources and applications were collected and processed for recycling using hydrogen decrepitation (HD) and hydrogenation disproportionation desorption and recombination (HDDR) processes. The effects of the principle HDDR processing parameters hydrogen pressure, hydrogen desorption rate and temperatures on the magnetic properties of the recycled materials have been investigated systematically. The optimum hydrogen pressures required for the complete disproportionation of the various magnet compositions were determined. We found that a hydrogen heat treatment composed of two steps (780 °C and 840 °C) and a moderate desorption rate can be used for the magnets having a higher Dy and Co content to obtain high quality anisotropic HDDR powders for resin bonded magnet production.