1870 XXXI International Mineral Processing Congress 2024 Proceedings/Washington, DC/Sep 29–Oct 3
The magnet powder after oxidative roasting was
leached in EG-MA DES, resulting in only 7.91% of Nd
and 0.35% of Fe being leached. This suggests that, unlike
Nd2O3, NdFeO3 has a low solubility in EG-MA, and the
formation of NdFeO3 should be suppressed for Nd recov-
ery from NdFeB magnets.
During the oxidative roasting of NdFeB magnet,
NdFeO3 is formed according to Eqs. 2–4 (Parida et al.,
2002 Tanvar and Dhawan, 2021).
Nd Fe B 2
3 O
12Fe Fe B Nd O
2 14 2^gh
2 2 3^sh
)+
++
^sh
^sh
^sh
(2)
2
3 2Fe O Fe2O3^sh
s 2 )+
^^gh h (3)
2
1 Nd2 O Fe 4
3 O NdFeO3^sh
s g 3^ 2 )++
^sh ^h h (4)
First, by roasting NdFeB, it decomposes according to Eq.
2, and Nd2O3 and Fe forms NdFeO3. Then, the excess Fe
forms Fe2O3. Due to the nature of NdFeB magnets, which
contain an excess of Fe compared to Nd, Fe reacts with
Nd2O3 to form NdFeO3 first (Eq. 4), and the remaining Fe
is converted to Fe2O3 (Eq. 3), ultimately forming NdFeO3
and Fe2O3. Thus, in order to suppress the formation of
NdFeO3 and form individual oxides of Nd and Fe, pre-
treatment to separate the Nd2O3 and Fe phases should be
applied before roasting.
Leaching of NaOH Digestion-Roasted Magnet
NaOH digestion is a method of converting REEs into rare
earth hydroxides, and it mainly used for pretreatment of
monazite (Yu and Chen, 1995). Post NaOH digestion, the
elements in NdFeB magnets are converted into Nd(OH)3
and Fe3O4 according to Eqs. 5–7 (Kim et al., 2022
Thompson, 1940).
Nd 3H2 O Nd(OH) 1.5H2^gh
s s 3^ )++
^^l h h h (5)
3Fe 2H O 3Fe(OH) H
s 2 2^ s 2^gh )++
^^lh h h (6)
3Fe(OH) Fe O 2H O H
2 sh 3 4^s 2 l 2^gh )++
^^h h
(7)
Figure 3 demonstrates that Nd(OH)3 and Fe3O4 were
formed after NaOH digestion, and upon oxidative roast-
ing, were converted into Nd2O3 and Fe2O3.
Unlike the oxidative roasted magnets, the formation of
NdFeO3 was not observed after NaOH digestion-roasting,
and Nd2O3 and Fe2O3, which are crystal structures that
can be selectively leached, were formed. As a result of leach-
ing NaOH digestion-roasted magnet using EG-MA DES,
97.69% Nd and 0.72% Fe were leached, and selective
leaching of Nd was possible. Therefore, applying NaOH
digestion-roasting pretreatment, the separated oxides of Nd
and Fe were formed, and Nd could be selectively leached
using EG-MA DES.
Effect of Solid-Liquid (S/L) Ratio
In the previous chapter, selective leaching of Nd from
NdFeB magnets was possible, applying NaOH digestion-
roasting. The leaching of NdFeB magnets using DESs was
mostly performed at the 5–50 mL scale in other previous
studies (Liu et al., 2020 Riaño et al., 2017 Yang et al.,
2023), and 40 mL glass vials were also used in the previous
chapter of this study. Therefore, in this chapter, the leaching
Figure 3. XRD patterns of NdFeB magnets after NaOH digestion and NaOH digestion-roasting
The magnet powder after oxidative roasting was
leached in EG-MA DES, resulting in only 7.91% of Nd
and 0.35% of Fe being leached. This suggests that, unlike
Nd2O3, NdFeO3 has a low solubility in EG-MA, and the
formation of NdFeO3 should be suppressed for Nd recov-
ery from NdFeB magnets.
During the oxidative roasting of NdFeB magnet,
NdFeO3 is formed according to Eqs. 2–4 (Parida et al.,
2002 Tanvar and Dhawan, 2021).
Nd Fe B 2
3 O
12Fe Fe B Nd O
2 14 2^gh
2 2 3^sh
)+
++
^sh
^sh
^sh
(2)
2
3 2Fe O Fe2O3^sh
s 2 )+
^^gh h (3)
2
1 Nd2 O Fe 4
3 O NdFeO3^sh
s g 3^ 2 )++
^sh ^h h (4)
First, by roasting NdFeB, it decomposes according to Eq.
2, and Nd2O3 and Fe forms NdFeO3. Then, the excess Fe
forms Fe2O3. Due to the nature of NdFeB magnets, which
contain an excess of Fe compared to Nd, Fe reacts with
Nd2O3 to form NdFeO3 first (Eq. 4), and the remaining Fe
is converted to Fe2O3 (Eq. 3), ultimately forming NdFeO3
and Fe2O3. Thus, in order to suppress the formation of
NdFeO3 and form individual oxides of Nd and Fe, pre-
treatment to separate the Nd2O3 and Fe phases should be
applied before roasting.
Leaching of NaOH Digestion-Roasted Magnet
NaOH digestion is a method of converting REEs into rare
earth hydroxides, and it mainly used for pretreatment of
monazite (Yu and Chen, 1995). Post NaOH digestion, the
elements in NdFeB magnets are converted into Nd(OH)3
and Fe3O4 according to Eqs. 5–7 (Kim et al., 2022
Thompson, 1940).
Nd 3H2 O Nd(OH) 1.5H2^gh
s s 3^ )++
^^l h h h (5)
3Fe 2H O 3Fe(OH) H
s 2 2^ s 2^gh )++
^^lh h h (6)
3Fe(OH) Fe O 2H O H
2 sh 3 4^s 2 l 2^gh )++
^^h h
(7)
Figure 3 demonstrates that Nd(OH)3 and Fe3O4 were
formed after NaOH digestion, and upon oxidative roast-
ing, were converted into Nd2O3 and Fe2O3.
Unlike the oxidative roasted magnets, the formation of
NdFeO3 was not observed after NaOH digestion-roasting,
and Nd2O3 and Fe2O3, which are crystal structures that
can be selectively leached, were formed. As a result of leach-
ing NaOH digestion-roasted magnet using EG-MA DES,
97.69% Nd and 0.72% Fe were leached, and selective
leaching of Nd was possible. Therefore, applying NaOH
digestion-roasting pretreatment, the separated oxides of Nd
and Fe were formed, and Nd could be selectively leached
using EG-MA DES.
Effect of Solid-Liquid (S/L) Ratio
In the previous chapter, selective leaching of Nd from
NdFeB magnets was possible, applying NaOH digestion-
roasting. The leaching of NdFeB magnets using DESs was
mostly performed at the 5–50 mL scale in other previous
studies (Liu et al., 2020 Riaño et al., 2017 Yang et al.,
2023), and 40 mL glass vials were also used in the previous
chapter of this study. Therefore, in this chapter, the leaching
Figure 3. XRD patterns of NdFeB magnets after NaOH digestion and NaOH digestion-roasting