1872 XXXI International Mineral Processing Congress 2024 Proceedings/Washington, DC/Sep 29–Oct 3
leaching REEs from NaOH digestion-roasted NdFeB mag-
nets. However, as DESs exhibit higher viscosity compared
to aqueous solutions, the viscosity of the leaching solution
increased as REEs dissolved into the leaching solution at
higher S/L ratios. The high viscosity of the leaching solu-
tion can make solid-liquid separation difficult, and may
have a negative impact on the following separation and
purification process. Thus, S/L ratio of 0.2 g/g was deter-
mined to be optimal.
CONCLUSIONS
In this study, the most suitable DES as lixiviant and pre-
treatment method were identified for selective leaching
of REEs from waste NdFeB magnet powder. The leach-
ing efficiency of Nd2O3, Fe2O3, and Fe3O4 was assessed
in EG-MA and GUC-LAC, which are effective in leaching
light REEs. Both DESs dissolved all Nd2O3, while Fe2O3
was insoluble. Unlike GUC-LAC, which dissolve 99%
of Fe3O4, EG-MA, which dissolve 0.04% of Fe3O4, was
determined to be suitable for selective leaching of REEs.
Oxidative roasting and NaOH digestion-roasting pretreat-
ments were applied to convert NdFeB magnets into selec-
tively leachable crystal forms of Nd2O3 and Fe2O3. Post
oxidative roasting, the NdFeB magnet was converted to
NdFeO3/Fe2O3 rather than Nd2O3/Fe2O3, and the leach-
ing efficiency of Nd was 7.91%, revealing that NdFeO3
inhibits the leaching of REEs. To suppress the formation of
NdFeO3, phase separation of Nd and Fe was required, and
for this purpose, NaOH digestion-roasting pretreatment
was applied. This process yielded Nd(OH)3 and Fe3O4
through NaOH digestion, followed by Nd2O3 and Fe2O3
formation via oxidative roasting. The NaOH digestion-
roasted magnet sample showed the leaching efficiency of
97.69% for Nd and 0.72% for Fe in EG-MA DES, and
selective leaching of REEs was possible. After confirming
that selective leaching was possible in a glass vial, the leach-
ing scale was increased, and a leaching test was performed
under the same condition (NaOH digestion-roasted mag-
net, 0.01 g/g, S/L ratio, 70°C) in 250 mL double-jacketed
reactor. The leaching efficiency was 97% for Nd and 0.62%
for Fe, indicating that selective leaching was possible even
at the reactor scale. In addition, it was confirmed that Pr
and Dy can be recovered. Afterwards, the effect of the S/L
ratio was assessed, and the leaching efficiency of Nd was
maintained at 97% even as the S/L ratio was increased from
0.01 to 0.3 g/g, and the leaching rate also remained the
same. Although the leaching efficiency remained unaffected
by the S/L ratio, owing to the nature of DESs, where vis-
cosity rises with the increasing concentration of dissolved
metal, a S/L ratio of 0.2 g/g, conducive to subsequent pro-
cessing, is determined to be optimal.
REFERENCES
Binnemans, K., Jones, P.T. 2017. Solvometallurgy: an
emerging branch of extractive metallurgy. Journal of
Sustainable Metallurgy 3:570–600.
Chen, W., Jiang, J., Lan, X., Zhao, X., Mou, H., Mu, T.
2019. A strategy for the dissolution and separation of
rare earth oxides by novel Brønsted acidic deep eutectic
solvents. Green Chemistry 21(17): 4748–4756.
IEA, 2022. World Energy Outlook 2022. Paris.
Figure 6. Leaching efficiency of Nd over time according to S/L ratio (70°C, 250 rpm, 3h)
leaching REEs from NaOH digestion-roasted NdFeB mag-
nets. However, as DESs exhibit higher viscosity compared
to aqueous solutions, the viscosity of the leaching solution
increased as REEs dissolved into the leaching solution at
higher S/L ratios. The high viscosity of the leaching solu-
tion can make solid-liquid separation difficult, and may
have a negative impact on the following separation and
purification process. Thus, S/L ratio of 0.2 g/g was deter-
mined to be optimal.
CONCLUSIONS
In this study, the most suitable DES as lixiviant and pre-
treatment method were identified for selective leaching
of REEs from waste NdFeB magnet powder. The leach-
ing efficiency of Nd2O3, Fe2O3, and Fe3O4 was assessed
in EG-MA and GUC-LAC, which are effective in leaching
light REEs. Both DESs dissolved all Nd2O3, while Fe2O3
was insoluble. Unlike GUC-LAC, which dissolve 99%
of Fe3O4, EG-MA, which dissolve 0.04% of Fe3O4, was
determined to be suitable for selective leaching of REEs.
Oxidative roasting and NaOH digestion-roasting pretreat-
ments were applied to convert NdFeB magnets into selec-
tively leachable crystal forms of Nd2O3 and Fe2O3. Post
oxidative roasting, the NdFeB magnet was converted to
NdFeO3/Fe2O3 rather than Nd2O3/Fe2O3, and the leach-
ing efficiency of Nd was 7.91%, revealing that NdFeO3
inhibits the leaching of REEs. To suppress the formation of
NdFeO3, phase separation of Nd and Fe was required, and
for this purpose, NaOH digestion-roasting pretreatment
was applied. This process yielded Nd(OH)3 and Fe3O4
through NaOH digestion, followed by Nd2O3 and Fe2O3
formation via oxidative roasting. The NaOH digestion-
roasted magnet sample showed the leaching efficiency of
97.69% for Nd and 0.72% for Fe in EG-MA DES, and
selective leaching of REEs was possible. After confirming
that selective leaching was possible in a glass vial, the leach-
ing scale was increased, and a leaching test was performed
under the same condition (NaOH digestion-roasted mag-
net, 0.01 g/g, S/L ratio, 70°C) in 250 mL double-jacketed
reactor. The leaching efficiency was 97% for Nd and 0.62%
for Fe, indicating that selective leaching was possible even
at the reactor scale. In addition, it was confirmed that Pr
and Dy can be recovered. Afterwards, the effect of the S/L
ratio was assessed, and the leaching efficiency of Nd was
maintained at 97% even as the S/L ratio was increased from
0.01 to 0.3 g/g, and the leaching rate also remained the
same. Although the leaching efficiency remained unaffected
by the S/L ratio, owing to the nature of DESs, where vis-
cosity rises with the increasing concentration of dissolved
metal, a S/L ratio of 0.2 g/g, conducive to subsequent pro-
cessing, is determined to be optimal.
REFERENCES
Binnemans, K., Jones, P.T. 2017. Solvometallurgy: an
emerging branch of extractive metallurgy. Journal of
Sustainable Metallurgy 3:570–600.
Chen, W., Jiang, J., Lan, X., Zhao, X., Mou, H., Mu, T.
2019. A strategy for the dissolution and separation of
rare earth oxides by novel Brønsted acidic deep eutectic
solvents. Green Chemistry 21(17): 4748–4756.
IEA, 2022. World Energy Outlook 2022. Paris.
Figure 6. Leaching efficiency of Nd over time according to S/L ratio (70°C, 250 rpm, 3h)