XXXI International Mineral Processing Congress 2024 Proceedings/Washington, DC/Sep 29–Oct 3 3391
dissolution was achieved with sulphuric acid, the strongest
acid, followed by organic acid A, which is the strongest
organic acid that was evaluated. This trend is to be expected,
since the predominant leaching mechanism of lithium from
montmorillonite is considered to be ion exchange between
H+ and exchangeable lithium (Zhao et al. 2023).
Figure 3 shows the percentage lithium dissolution as a
function of time and acid type, for sulphuric acid and the
top three performing organic acids, without oxidant addi-
tion. The lithium dissolution rates are comparable for sul-
phuric acid and organic acid A, while organic acids B and C
exhibit similar rates of lithium dissolution. The pKa1 values
for organic acid B and C are within 10% of each other, and
more than double that of organic acid A. Organic acid A is
therefore a significantly stronger acid than organic acid B
and organic acid C.
Based on the outcomes of the leaching screening tests,
organic acid A and organic acid B were selected as poten-
tially suitable organic acids for further test work. While
organic acid C yielded 74% lithium dissolution at 60°C
in the presence of hydrogen peroxide, this specific organic
acid was excluded from further testwork due to its high
cost and lack of availability, relative to organic acid A and
organic acid B. During preliminary downstream process-
ing tests, pregnant leach solutions containing organic acid
B became extremely viscous after evaporation and difficult
to handle consequently, organic acid B was also excluded
from the leaching optimisation tests.
Leaching Optimisation Tests
Figure 4 and Figure 5 show the percentage lithium dissolu-
tion as a function of time, acid type, and acid concentration,
for tests performed at 8% solids and 12% solids, respec-
tively. In general, the rate and extent of lithium dissolu-
tion is higher using sulphuric acid as lixiviant, compared
to organic acid A. This is expected, since sulphuric acid is
a stronger acid than organic acid A, and the predominant
mechanism of lithium leaching is considered to be ion
exchange between H+ and exchangeable lithium, as men-
tioned previously.
From the figures, it can be seen that lithium dissolution
tends to decrease with increasing solids content, for both
acid types investigated. For sulphuric acid, lithium dissolu-
tion generally increases with increasing acid concentration,
and this effect is more pronounced at the higher solids con-
tent of 12%. The effect of increasing the concentration of
organic acid A above 1 M is not clear.
Using sulphuric acid, greater than 90% lithium disso-
lution was achieved after 2 hours, at acid concentrations
of at least 1.5 M, temperatures of both 25°C and 60°C,
and 8% solids. A maximum of 82% lithium dissolution
was achieved after 6 hours using organic acid A at 2 M,
40°C and 8% solids. One further test using organic acid
A was performed at an increased temperature of 80°C, but
lithium dissolution did not increase.
Table 3 shows the metal concentrations in solution at
conditions where the highest extents of lithium dissolution
of 99% and 82% were achieved after 6 hours, for sulphuric
acid and organic acid A, respectively. A lithium concen-
tration of 88.7 mg/L was achieved using sulphuric acid,
and 69.1 mg/L lithium using organic acid A. Depending
on the downstream processes selected, higher lithium
concentrations might be desirable. Higher lithium con-
centrations were achieved with the higher solids content
0
20
40
60
80
100
0 1 2 3 4 5 6 7
Time (h)
(a) (b)
0
20
40
60
80
100
0 1 2 3 4 5 6 7
Time (h)
Figure 3. Percentage lithium dissolution as a function of time and acid type at (a) 25°C and (b) 60°C, with an acid
concentration of 1 M and 2% solids, in the absence of an oxidant
Li
dissolug415on
(%)
Li
dissolug415on
(%)
dissolution was achieved with sulphuric acid, the strongest
acid, followed by organic acid A, which is the strongest
organic acid that was evaluated. This trend is to be expected,
since the predominant leaching mechanism of lithium from
montmorillonite is considered to be ion exchange between
H+ and exchangeable lithium (Zhao et al. 2023).
Figure 3 shows the percentage lithium dissolution as a
function of time and acid type, for sulphuric acid and the
top three performing organic acids, without oxidant addi-
tion. The lithium dissolution rates are comparable for sul-
phuric acid and organic acid A, while organic acids B and C
exhibit similar rates of lithium dissolution. The pKa1 values
for organic acid B and C are within 10% of each other, and
more than double that of organic acid A. Organic acid A is
therefore a significantly stronger acid than organic acid B
and organic acid C.
Based on the outcomes of the leaching screening tests,
organic acid A and organic acid B were selected as poten-
tially suitable organic acids for further test work. While
organic acid C yielded 74% lithium dissolution at 60°C
in the presence of hydrogen peroxide, this specific organic
acid was excluded from further testwork due to its high
cost and lack of availability, relative to organic acid A and
organic acid B. During preliminary downstream process-
ing tests, pregnant leach solutions containing organic acid
B became extremely viscous after evaporation and difficult
to handle consequently, organic acid B was also excluded
from the leaching optimisation tests.
Leaching Optimisation Tests
Figure 4 and Figure 5 show the percentage lithium dissolu-
tion as a function of time, acid type, and acid concentration,
for tests performed at 8% solids and 12% solids, respec-
tively. In general, the rate and extent of lithium dissolu-
tion is higher using sulphuric acid as lixiviant, compared
to organic acid A. This is expected, since sulphuric acid is
a stronger acid than organic acid A, and the predominant
mechanism of lithium leaching is considered to be ion
exchange between H+ and exchangeable lithium, as men-
tioned previously.
From the figures, it can be seen that lithium dissolution
tends to decrease with increasing solids content, for both
acid types investigated. For sulphuric acid, lithium dissolu-
tion generally increases with increasing acid concentration,
and this effect is more pronounced at the higher solids con-
tent of 12%. The effect of increasing the concentration of
organic acid A above 1 M is not clear.
Using sulphuric acid, greater than 90% lithium disso-
lution was achieved after 2 hours, at acid concentrations
of at least 1.5 M, temperatures of both 25°C and 60°C,
and 8% solids. A maximum of 82% lithium dissolution
was achieved after 6 hours using organic acid A at 2 M,
40°C and 8% solids. One further test using organic acid
A was performed at an increased temperature of 80°C, but
lithium dissolution did not increase.
Table 3 shows the metal concentrations in solution at
conditions where the highest extents of lithium dissolution
of 99% and 82% were achieved after 6 hours, for sulphuric
acid and organic acid A, respectively. A lithium concen-
tration of 88.7 mg/L was achieved using sulphuric acid,
and 69.1 mg/L lithium using organic acid A. Depending
on the downstream processes selected, higher lithium
concentrations might be desirable. Higher lithium con-
centrations were achieved with the higher solids content
0
20
40
60
80
100
0 1 2 3 4 5 6 7
Time (h)
(a) (b)
0
20
40
60
80
100
0 1 2 3 4 5 6 7
Time (h)
Figure 3. Percentage lithium dissolution as a function of time and acid type at (a) 25°C and (b) 60°C, with an acid
concentration of 1 M and 2% solids, in the absence of an oxidant
Li
dissolug415on
(%)
Li
dissolug415on
(%)