Recycling Nd-Fe-B End-of-Life Magnets with Different Levels of Oxidation Using the Magnet-to-Magnet Approach

The recycling of Nd-Fe-B end-of-life magnets through powder metallurgy can aid in reducing the usage of primary raw minerals, decreasing environmental damage, and redirecting otherwise discarded materials towards high-tech applications. This work assesses the process of recycling discarded Nd-Fe-B magnets at various stages of oxidation. It uses a magnet-to-magnet approach, starting with the hydrogen decrepitation method and ending with the sintering of the recycled magnets. The research findings suggest that the properties of recycled magnets largely depend on the oxidation content of the raw material. Recycled magnets with the highest oxidation content (27400 ppm) demonstrated poor properties
$\text{EoL} (\rho=5.35\mathrm{g}/\text{cm}^{3}$
, Br
$=0.11\mathrm{T}$
, and
$\mathrm{H}_{\text{cJ}}=15\text{kA}/\mathrm{m})$
. However, starting with magnets that have a low oxidation content (4900 ppm) resulted in notable properties
$(\rho=7.35\mathrm{g}/\text{cm}^{3}$
, Br
$=1.16\mathrm{T}$
, and
$\mathrm{H}_{\text{cJ}}=900\text{kA}/\mathrm{m})$
. This resulted in a 100% remanence recovery of the end-of-life magnet and 78% coercivity recovery. In summary, the feasibility of recycling these magnets is directly associated to the oxygen content of the original end-of-life magnet.