Technique for recovering rare-earth metals from spent sintered Nd-Fe-B magnets without external heating

•Rare-earths were recovered as oxalates from spent sintered Nd-Fe-B magnets.•Mechano-chemical treatment with HCl(COOH)2 aqueous solution is used.•This approach is very effective and no external heating is needed.•Optimal concentrations of HCl and (COOH)2 were 0.2 and 0.25 mol/dm3, respectively.•Recovery rate and purity of the rare-earths were 95.3 and 95.0 mass%, respectively.

To selectively recover rare-earth metals with higher purity from spent sintered Nd-Fe-B magnets without external heating, we investigated the mechano-chemical treatment of spent sintered Nd-Fe-B magnet powder with a reaction solution of HCl and (COOH)2 at room temperature. The results of various experiments showed that the mechano-chemical treatment with HCl and (COOH)2 is very effective for recovering the rare-earth metals contained in spent sintered Nd-Fe-B magnet powder; the recovery rate and purity of the rare-earth metals were 95.3 and 95.0 mass%, respectively, under optimal conditions ([HCl] = 0.2 mol/dm3 and [(COOH)2] = 0.25 mol/dm3).