XXXI International Mineral Processing Congress 2024 Proceedings/Washington, DC/Sep 29–Oct 3 3329
reverse flotation, the mixed NaOL/DAA collector demon-
strated the highest lithium recovery of 29.40% Li2O, sig-
nificantly outperforming the single collectors. The use of
either NaOL or DAA alone proved insufficient for effec-
tive spodumene separation from silicate gangue minerals
due to the intricate surface chemistry of aluminosilicates
(Xie et al., 2021). Spodumene typically carries a negative
surface charge over a wide pH range, leading to electro-
static repulsion with anionic collectors NaOL. Conversely,
cationic collectors such as DAA weakly adhere to mineral
surfaces through electrostatic forces, resulting in subop-
timal reverse flotation performance (Bian et al., 2023).
Mixed collectors, however, show a synergistic interaction
that enhances performance. In the mixed NaOL/DAA
system, NaOL initially reacts with aluminum sites on the
mineral surface, followed by DAA forming an electroneu-
tral complex with NaOL and co-adsorbing onto the Stern
layer through NaOL’s chemisorption (Xu et al., 2013).
The use of mixed collectors modifies the zeta potential of
spodumene, reducing the electrostatic repulsion between
the negatively charged spodumene and the anionic collec-
tor component in reverse flotation. The cationic collector
in the mixture can neutralize the surface charge of spodu-
mene or even impart a positive charge. This modification
facilitates the adsorption of the anionic collector through
electrostatic attraction and complex formation. This change
in surface charge enhances the preferential attachment of
gangue minerals to air bubbles, leading to their flotation,
thereby improving the separation efficiency and recovery
of spodumene through reverse flotation. Many researchers
have found that the mixed NaOL/DDA collector exhibited
better surface activity and reduced the negative effect of
feldspar slime on spodumene flotation compared to NaOL
alone (Moon et al., 2003, Xu et al., 2016, Xu et al., 2016,
Zhu et al., 2020, Jia et al., 2021).
Effects of pH on the Recovery of Lithium
Figure 7 illustrates the flotation behavior of spodumene
across different pH levels using NaOL, DAA, and a mixture
of NaOL/DAA as collectors, each at a 1000 g/t dosage. The
maximum lithium recovery from direct flotation, reaching
around 40%, was obtained using NaOL at an initial pH
of 6.75 with the highest grade of 0.52% Li2O. This is due
to NaOL’s constrained effectiveness in selectively separat-
ing spodumene from associated gangue minerals like feld-
spar, quartz, and muscovite. In contrast, in reverse flotation
using DAA alone improved the lithium grade to 0.92%
Li2O at pH 8, although the recovery was a mere 5%. The
pH level of the pulp is crucial for reverse flotation recovery
of lithium from low-grade spodumene ore. Within the pH
range of 4 to 8, lithium recovery initially decreases slightly
as the lithium grade increases, but then sharply increases
at pH 8 when using NaOL/DAA in reverse flotation. It is
attributed to the role of electrical double-layer forces and
the solution chemistry of flotation agents, both of which
dependent on pH (Rai et al., 2011). At pH 10, lithium
recovery in reverse flotation reached around 30% with a
grade of 1%, suggesting acid-soap species formation in
alkaline environments enhances adsorption and flotation
(Kulkarni et al., 1980). The mixed NaOL/DAA collec-
tor system outperforms single collectors, indicating the
potential of combining collectors for improved flotation
efficiency in spodumene processing. This highlights the
importance of optimizing pH and collector type for effec-
tive spodumene recovery, potentially leading to more effi-
cient lithium extraction strategies.
0
10
20
30
40
50
60
4 6 8 10 12
pH
DAA (1000 g/t)
NaOL (1000 g/t)
NaOL/DAA (1000 g/t)
0.00
0.20
0.40
0.60
0.80
1.00
1.20
4 6 8 10 12
pH
DAA (1000 g/t)
NaOL (1000 g/t)
NaOL/DAA (1000 g/t)
(a) (b)
Figure 7. (a) Lithium recovery and (b) grade as a function of pH in the presence of NaOL, DAA, and NaOL/DAA (ratio of 1:5)
LiO
2
Recovery,
%
Grade
(LiO,
2
%)
reverse flotation, the mixed NaOL/DAA collector demon-
strated the highest lithium recovery of 29.40% Li2O, sig-
nificantly outperforming the single collectors. The use of
either NaOL or DAA alone proved insufficient for effec-
tive spodumene separation from silicate gangue minerals
due to the intricate surface chemistry of aluminosilicates
(Xie et al., 2021). Spodumene typically carries a negative
surface charge over a wide pH range, leading to electro-
static repulsion with anionic collectors NaOL. Conversely,
cationic collectors such as DAA weakly adhere to mineral
surfaces through electrostatic forces, resulting in subop-
timal reverse flotation performance (Bian et al., 2023).
Mixed collectors, however, show a synergistic interaction
that enhances performance. In the mixed NaOL/DAA
system, NaOL initially reacts with aluminum sites on the
mineral surface, followed by DAA forming an electroneu-
tral complex with NaOL and co-adsorbing onto the Stern
layer through NaOL’s chemisorption (Xu et al., 2013).
The use of mixed collectors modifies the zeta potential of
spodumene, reducing the electrostatic repulsion between
the negatively charged spodumene and the anionic collec-
tor component in reverse flotation. The cationic collector
in the mixture can neutralize the surface charge of spodu-
mene or even impart a positive charge. This modification
facilitates the adsorption of the anionic collector through
electrostatic attraction and complex formation. This change
in surface charge enhances the preferential attachment of
gangue minerals to air bubbles, leading to their flotation,
thereby improving the separation efficiency and recovery
of spodumene through reverse flotation. Many researchers
have found that the mixed NaOL/DDA collector exhibited
better surface activity and reduced the negative effect of
feldspar slime on spodumene flotation compared to NaOL
alone (Moon et al., 2003, Xu et al., 2016, Xu et al., 2016,
Zhu et al., 2020, Jia et al., 2021).
Effects of pH on the Recovery of Lithium
Figure 7 illustrates the flotation behavior of spodumene
across different pH levels using NaOL, DAA, and a mixture
of NaOL/DAA as collectors, each at a 1000 g/t dosage. The
maximum lithium recovery from direct flotation, reaching
around 40%, was obtained using NaOL at an initial pH
of 6.75 with the highest grade of 0.52% Li2O. This is due
to NaOL’s constrained effectiveness in selectively separat-
ing spodumene from associated gangue minerals like feld-
spar, quartz, and muscovite. In contrast, in reverse flotation
using DAA alone improved the lithium grade to 0.92%
Li2O at pH 8, although the recovery was a mere 5%. The
pH level of the pulp is crucial for reverse flotation recovery
of lithium from low-grade spodumene ore. Within the pH
range of 4 to 8, lithium recovery initially decreases slightly
as the lithium grade increases, but then sharply increases
at pH 8 when using NaOL/DAA in reverse flotation. It is
attributed to the role of electrical double-layer forces and
the solution chemistry of flotation agents, both of which
dependent on pH (Rai et al., 2011). At pH 10, lithium
recovery in reverse flotation reached around 30% with a
grade of 1%, suggesting acid-soap species formation in
alkaline environments enhances adsorption and flotation
(Kulkarni et al., 1980). The mixed NaOL/DAA collec-
tor system outperforms single collectors, indicating the
potential of combining collectors for improved flotation
efficiency in spodumene processing. This highlights the
importance of optimizing pH and collector type for effec-
tive spodumene recovery, potentially leading to more effi-
cient lithium extraction strategies.
0
10
20
30
40
50
60
4 6 8 10 12
pH
DAA (1000 g/t)
NaOL (1000 g/t)
NaOL/DAA (1000 g/t)
0.00
0.20
0.40
0.60
0.80
1.00
1.20
4 6 8 10 12
pH
DAA (1000 g/t)
NaOL (1000 g/t)
NaOL/DAA (1000 g/t)
(a) (b)
Figure 7. (a) Lithium recovery and (b) grade as a function of pH in the presence of NaOL, DAA, and NaOL/DAA (ratio of 1:5)
LiO
2
Recovery,
%
Grade
(LiO,
2
%)