Neodymium recovery from scrap magnet using ammonium persulfate

This study proposes a novel leaching methodology to recover neodymium from scrap magnet using ammonium persulfate ((NH4)2S2O8) solutions. The NdFeB magnets from obsolete Hard-Disk-Drives were physically treated by thermal demagnetization (400 °C, 45 min) and mechanical crushing (< 420 μm). The chemical composition of the ground sample was Nd: 31.5 wt%, Fe: 64.8 wt%, Co: 1.9 wt%, Ni: 0.6 wt%. Diagrams of equilibrium phases (Eh vs. pH) were designed to determine the predominance of the formed species in the (NH4)2S2O8 system. Ammonium persulfate aqueous solutions were prepared to generate oxidative sulfate radicals. These radicals allowed to leach the ground samples of NdFeB magnets and recover of neodymium sulfate. The influence of (NH4)2S2O8 concentration (0.7–1.3 M), temperature (25–75 °C) and L/S ratio (25–50 mL/g) on NdFeB magnets leaching was investigated employing analysis of variance in a 23 full factorial experimental design. At the optimal conditions, quantities >98% of NdFeB magnets were leached after 15 min reaction time. Neodymium sulfate was selectively recovered as crystals, and evaluated by chemical and crystallographic analyses. The findings presented in this investigation suggest that neodymium could be recovered from scrap magnet using an eco-friendly leaching methodology assisted by ammonium persulfate.