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This study proposes a novel leaching methodology to recover neodymium from scrap magnet using ammonium persulfate ((NH4)2S2O8) solutions. The Nd-Fe-B 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 Nd-Fe-B 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 Nd-Fe-B magnets leaching was investigated employing analysis of variance in a 2 3 full factorial experimental design. At the optimal conditions, quantities greater than 98% of Nd-Fe-B 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.

In this study, a pressure oxidative system with ammonium persulfate (NH4)2S2O8 was developed in order to recover nonleaching gold from electronic waste. The effects of (NH4)2S2O8 concentration (0.66-1.31 M), pressure (0-103 kPa) and liquid/solid ratio (15-25 mL/g) on the recovery of gold were studied in two different levels through a full factorial 2 3 experimental design. The optimum conditions for gold recovery were established in 0.66 M, 103 kPa and 25 mL/g for a reaction time of 5 minutes. With these conditions the metallic substrate (Cu, Fe, and Ni) was oxidized and gold was recovered as a fine coating in a 99.36%. The resulting solution was treated with a precipitation process to produced non-pollutants by-products (CuSO4:5H2O(C); FeSO4:7H2O(C); NiSO4:7H2O(C)

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