1867
Recovery of Rare Earth Elements from Waste NdFeB Permanent
Magnets Using Deep Eutectic Solvents
Seojin Heo, Rina Kim, Sujeong Lee, Kyeong Woo Chung
University of Science and Technology
Korea Institute of Geoscience and Mineral Resources
Ho-Sung Yoon, Chul-Joo Kim
Korea Institute of Geoscience and Mineral Resources
ABSTRACT: Hydrometallurgical techniques have been advanced for recycling NdFeB magnets using inorganic
acids, but they generally consume a lot of resources such as chemicals and water. Consequently, there has been
an upsurge in interest for deep eutectic solvents (DESs), a non-aqueous alternative capable of substituting
conventional lixiviants. In this study, rare earth elements (REEs) recovery from waste NdFeB magnets through
selective leaching using DESs was investigated. Two types of DESs were employed for preliminary leaching tests,
and it was confirmed that selective leaching of Nd from Fe was available once they are present as their oxide,
Nd2O3 and Fe2O3, respectively. So, Nd and Fe contained in the magnets were converted into oxide forms
ahead of DES leaching, applying NaOH digestion-roasting pretreatment. Leaching the pretreated magnets in
two DESs, ethylene glycol-maleic acid and guanidine hydrochloride-lactic acid, selective leaching of Nd was
viable, and ethylene glycol-maleic acid DES exhibiting superior selectivity, with a leaching efficiency of Nd
97.69% and Fe 0.72%. In DESs, relatively difficult to disperse the powder due to its high viscosity, evaluating
the amount of solid sample available to be leached in one batch is crucial to assess the scalability. Accordingly,
as a result of assessing the effect of solid/liquid (S/L) ratio at increased leaching scale, the leaching efficiency was
97% for Nd, 96% for Pr, 95% for Dy and 0.6% for Fe in the range of 0.01–0.3 g/g. The leaching efficiency and
leaching rate were similar at all S/L ratio, while the subsequent S/L separation was difficult at high S/L ratio due
to the high viscosity of the DES. In this study, S/L ratio of 0.2 g/g was determined to be optimal.
INTRODUCTION
Rare earth elements (REEs) are key materials for high-
tech industries including clean energy technology (solar,
wind, and electric vehicle, etc.) (Mudali et al., 2021). As
the transition to clean energy accelerates, the demand
for NdFeB magnets used in wind turbines and electric
vehicle motors is increasing. Accordingly, the demand of
Nd, Pr and Dy, vital for NdFeB magnets, is projected to
triple by 2050 (IEA, 2022). Therefore, recovery of REEs
from secondary resources is essential to meet the growing
demand (Pimassoni et al., 2023). In this respect, waste
NdFeB permanent magnets, with the rare earth contents of
27–32 wt.%, are suitable secondary resources for the recov-
ery of Nd, Pr, and Dy (Zhang et al., 2020).
The hydrometallurgical method is mainly used to
recover REEs from waste NdFeB magnets, but it gener-
ates wastewater and has low selectivity (Binnemans and
Jones, 2017). In the efforts to reduce the environmental
Recovery of Rare Earth Elements from Waste NdFeB Permanent
Magnets Using Deep Eutectic Solvents
Seojin Heo, Rina Kim, Sujeong Lee, Kyeong Woo Chung
University of Science and Technology
Korea Institute of Geoscience and Mineral Resources
Ho-Sung Yoon, Chul-Joo Kim
Korea Institute of Geoscience and Mineral Resources
ABSTRACT: Hydrometallurgical techniques have been advanced for recycling NdFeB magnets using inorganic
acids, but they generally consume a lot of resources such as chemicals and water. Consequently, there has been
an upsurge in interest for deep eutectic solvents (DESs), a non-aqueous alternative capable of substituting
conventional lixiviants. In this study, rare earth elements (REEs) recovery from waste NdFeB magnets through
selective leaching using DESs was investigated. Two types of DESs were employed for preliminary leaching tests,
and it was confirmed that selective leaching of Nd from Fe was available once they are present as their oxide,
Nd2O3 and Fe2O3, respectively. So, Nd and Fe contained in the magnets were converted into oxide forms
ahead of DES leaching, applying NaOH digestion-roasting pretreatment. Leaching the pretreated magnets in
two DESs, ethylene glycol-maleic acid and guanidine hydrochloride-lactic acid, selective leaching of Nd was
viable, and ethylene glycol-maleic acid DES exhibiting superior selectivity, with a leaching efficiency of Nd
97.69% and Fe 0.72%. In DESs, relatively difficult to disperse the powder due to its high viscosity, evaluating
the amount of solid sample available to be leached in one batch is crucial to assess the scalability. Accordingly,
as a result of assessing the effect of solid/liquid (S/L) ratio at increased leaching scale, the leaching efficiency was
97% for Nd, 96% for Pr, 95% for Dy and 0.6% for Fe in the range of 0.01–0.3 g/g. The leaching efficiency and
leaching rate were similar at all S/L ratio, while the subsequent S/L separation was difficult at high S/L ratio due
to the high viscosity of the DES. In this study, S/L ratio of 0.2 g/g was determined to be optimal.
INTRODUCTION
Rare earth elements (REEs) are key materials for high-
tech industries including clean energy technology (solar,
wind, and electric vehicle, etc.) (Mudali et al., 2021). As
the transition to clean energy accelerates, the demand
for NdFeB magnets used in wind turbines and electric
vehicle motors is increasing. Accordingly, the demand of
Nd, Pr and Dy, vital for NdFeB magnets, is projected to
triple by 2050 (IEA, 2022). Therefore, recovery of REEs
from secondary resources is essential to meet the growing
demand (Pimassoni et al., 2023). In this respect, waste
NdFeB permanent magnets, with the rare earth contents of
27–32 wt.%, are suitable secondary resources for the recov-
ery of Nd, Pr, and Dy (Zhang et al., 2020).
The hydrometallurgical method is mainly used to
recover REEs from waste NdFeB magnets, but it gener-
ates wastewater and has low selectivity (Binnemans and
Jones, 2017). In the efforts to reduce the environmental
