XXXI International Mineral Processing Congress 2024 Proceedings/Washington, DC/Sep 29–Oct 3 3389
groups, are extremely common (Al-Ani and Sarapää 2008
Brindley and Brown 1984).
In smectites, lithium can be present in two different
locations: (i) in the structural octahedral site as a substitu-
tion for Mg2+ (structural lithium), and (ii) as an exchange-
able cation in the interlayer space (exchangeable lithium).
As seen in Table 1, if structural lithium is present, the
mineral is typically classified as hectorite. Any of the other
smectites, including hectorite itself, could theoretically
contain exchangeable lithium (Vigier et al. 2008 Brindley
and Brown 1984).
Mineral acids are most commonly considered for the
direct leaching of lithium from lithium-bearing clay depos-
its. While hydrochloric acid is deemed to be a potentially
viable leaching agent for some of the commercial projects
under development, leaching results published thus far
have focused on sulphuric acid as lixiviant (Noram Lithium
Corporation 2022, 2021 Fayram et al. 2020 Hawkstone
Mining Ltd. 2019 Ehsani et al. 2018).
Sulphuric acid-based processing routes typically
yield high lithium recoveries of ≥ 85% (Noram Lithium
Corporation 2022, 2021 Fayram et al. 2020) however,
drawbacks of this process include high acid consumption
as well as environmental management challenges. Using
alternative leaching reagents, such as organic acids, could
potentially lead to reduced acid consumption, reduced
environmental impact of processing and opportunity for
reagent regeneration and recycling. Very limited informa-
tion about suitable alternative leaching reagents for lithium
recovery from clays are available in the published literature.
The aim of this study was to evaluate a range of organic
acids for the recovery of lithium from montmorillonite
clays at different process conditions. The leaching perfor-
mance of these alternative reagents were compared with
that of sulphuric acid.
EXPERIMENTAL
Experimental Planning
Screening Leaching Tests
Based on published literature, six organic acids were
identified as potentially suitable lixiviants for leach-
ing screening tests, and are shown in Table 2. Organic
acids have been ranked in order of decreasing acidity
(A B C D E F), where organic acid A has the
lowest pKa value, and is therefore the strongest of the six
organic acids investigated.
Seven different acids types (sulphuric acid and six
organic acids) were tested at two temperature levels (25°C
and 60°C) and two oxidant types (no oxidant added, and
1 vol% hydrogen peroxide fed at predetermined intervals).
All tests were conducted at an acid concentration of 1 M
and 2% solids.
Leaching Optimisation Tests
Based on the outcomes of the leaching screening tests,
organic acid A was selected as the most suitable organic
acid for further testwork. Leaching optimisation tests were
performed using two acid types (sulphuric acid and organic
acid A), at two temperature levels (25°C and 60°C), four
acid concentrations (0.5 M, 1 M, 1.5 M, 2 M) and two sol-
ids content levels (8% and 12% solids) in the absence of an
oxidant. However, due to the limited solubility of organic
acid A in water at lower temperatures, the tests using con-
centrations of 1.5 M and 2 M of organic acid A were con-
ducted at temperatures of 30°C and 40°C, respectively. An
upper limit of 12% solids was selected, as the clay’s swell-
ing properties caused the slurry to become highly viscous
beyond this point.
Materials
The feed material used for the leaching screening tests and
leaching optimisation tests had an average lithium con-
tent of 1,400 ppm (100% passing 45 μm) and 960 ppm
(100% passing 10 μm), respectively. Using X-ray diffrac-
tion (XRD), the feed was shown to consist predominantly
of montmorillonite, dolomite, calcite and anorthite, with
small amounts of quartz, orthoclase and muscovite.
Acid solutions of the desired concentration were pre-
pared using demineralised water, 98% sulphuric acid, and
organic acids with a purity ≥ 98.5%. The residual acid con-
centration after leaching was determined by titration using
a 1 M solution of 98% sodium hydroxide as titrant and
phenolphthalein as indicator.
Experimental Setup and Procedure
Screening leaching tests were performed in a shaking incu-
bator that controlled the temperature within 0.5°C of the
setpoint temperature. 1 M acid solutions, of 100 mL each,
were prepared in Erlenmeyer flasks. The flasks were then
placed in the shaking incubator until the desired setpoint
Table 2. Organic acids used in the screening tests
Organic Acid (OA)
Identifier Organic Acid Class
A Dicarboxylic acid
B Tricarboxylic acid
C Dicarboxylic acid
D Monocarboxylic acid
E Monocarboxylic acid
F Amino acid
groups, are extremely common (Al-Ani and Sarapää 2008
Brindley and Brown 1984).
In smectites, lithium can be present in two different
locations: (i) in the structural octahedral site as a substitu-
tion for Mg2+ (structural lithium), and (ii) as an exchange-
able cation in the interlayer space (exchangeable lithium).
As seen in Table 1, if structural lithium is present, the
mineral is typically classified as hectorite. Any of the other
smectites, including hectorite itself, could theoretically
contain exchangeable lithium (Vigier et al. 2008 Brindley
and Brown 1984).
Mineral acids are most commonly considered for the
direct leaching of lithium from lithium-bearing clay depos-
its. While hydrochloric acid is deemed to be a potentially
viable leaching agent for some of the commercial projects
under development, leaching results published thus far
have focused on sulphuric acid as lixiviant (Noram Lithium
Corporation 2022, 2021 Fayram et al. 2020 Hawkstone
Mining Ltd. 2019 Ehsani et al. 2018).
Sulphuric acid-based processing routes typically
yield high lithium recoveries of ≥ 85% (Noram Lithium
Corporation 2022, 2021 Fayram et al. 2020) however,
drawbacks of this process include high acid consumption
as well as environmental management challenges. Using
alternative leaching reagents, such as organic acids, could
potentially lead to reduced acid consumption, reduced
environmental impact of processing and opportunity for
reagent regeneration and recycling. Very limited informa-
tion about suitable alternative leaching reagents for lithium
recovery from clays are available in the published literature.
The aim of this study was to evaluate a range of organic
acids for the recovery of lithium from montmorillonite
clays at different process conditions. The leaching perfor-
mance of these alternative reagents were compared with
that of sulphuric acid.
EXPERIMENTAL
Experimental Planning
Screening Leaching Tests
Based on published literature, six organic acids were
identified as potentially suitable lixiviants for leach-
ing screening tests, and are shown in Table 2. Organic
acids have been ranked in order of decreasing acidity
(A B C D E F), where organic acid A has the
lowest pKa value, and is therefore the strongest of the six
organic acids investigated.
Seven different acids types (sulphuric acid and six
organic acids) were tested at two temperature levels (25°C
and 60°C) and two oxidant types (no oxidant added, and
1 vol% hydrogen peroxide fed at predetermined intervals).
All tests were conducted at an acid concentration of 1 M
and 2% solids.
Leaching Optimisation Tests
Based on the outcomes of the leaching screening tests,
organic acid A was selected as the most suitable organic
acid for further testwork. Leaching optimisation tests were
performed using two acid types (sulphuric acid and organic
acid A), at two temperature levels (25°C and 60°C), four
acid concentrations (0.5 M, 1 M, 1.5 M, 2 M) and two sol-
ids content levels (8% and 12% solids) in the absence of an
oxidant. However, due to the limited solubility of organic
acid A in water at lower temperatures, the tests using con-
centrations of 1.5 M and 2 M of organic acid A were con-
ducted at temperatures of 30°C and 40°C, respectively. An
upper limit of 12% solids was selected, as the clay’s swell-
ing properties caused the slurry to become highly viscous
beyond this point.
Materials
The feed material used for the leaching screening tests and
leaching optimisation tests had an average lithium con-
tent of 1,400 ppm (100% passing 45 μm) and 960 ppm
(100% passing 10 μm), respectively. Using X-ray diffrac-
tion (XRD), the feed was shown to consist predominantly
of montmorillonite, dolomite, calcite and anorthite, with
small amounts of quartz, orthoclase and muscovite.
Acid solutions of the desired concentration were pre-
pared using demineralised water, 98% sulphuric acid, and
organic acids with a purity ≥ 98.5%. The residual acid con-
centration after leaching was determined by titration using
a 1 M solution of 98% sodium hydroxide as titrant and
phenolphthalein as indicator.
Experimental Setup and Procedure
Screening leaching tests were performed in a shaking incu-
bator that controlled the temperature within 0.5°C of the
setpoint temperature. 1 M acid solutions, of 100 mL each,
were prepared in Erlenmeyer flasks. The flasks were then
placed in the shaking incubator until the desired setpoint
Table 2. Organic acids used in the screening tests
Organic Acid (OA)
Identifier Organic Acid Class
A Dicarboxylic acid
B Tricarboxylic acid
C Dicarboxylic acid
D Monocarboxylic acid
E Monocarboxylic acid
F Amino acid