Recycling Bonded Nd-Fe-B Magnet Wastes by Chemical Reaction and Its Mechanism

The difficulty of short-process bonded Nd-Fe-Bmagnetwaste recycling lies in the effective removal of the cured polymermatrix while protecting the magnetic powder. In this study, the polymermatrix in bonded Nd-Fe-B magnet waste was destroyedusing sodium hydroxide ethanol solution, and the effect of the recyclingprocess on the magnetic powders was studied. The nonmagnetic polymermatrix was removed, while the magnetic phase was not destroyed. Thecarbon and oxygen contents of the recycled magnetic powders decreasedby 92.96 and 89.30%, respectively, while the M (S) (saturation magnetization), M (r) (remanence), and H (cj) (coercivity) valuesof the recycled magnetic powders were 99.8, 98.5, and 95.9% of theoriginal magnetic powders, respectively. The curing and decompositionprocesses of the polymer matrix were also analyzed. During the curingprocess, dicyandiamide and bisphenol A epoxy resin acted as bridgesand skeletons, respectively, finally forming a thermosetting three-dimensionalnetwork structure. In the alkaline alcohol solution, the bridges andskeletons were destroyed by the free hydroxyl groups and free hydrogenradicals in ethanol, and small molecular products were dissolved inthe solution.

Automated summary

The difficulty in recycling short-process bonded Nd-Fe-B magnet waste lies in removing the polymer matrix while protecting the magnetic powder. This study used a sodium hydroxide ethanol solution to destroy the polymer matrix and examined its effect on the magnetic powders. The nonmagnetic polymer matrix was successfully removed without damaging the magnetic phase, resulting in a significant decrease in carbon and oxygen contents while preserving most of the magnetic properties.