XXXI International Mineral Processing Congress 2024 Proceedings/Washington, DC/Sep 29–Oct 3 3371
Effects of Sulfuric Acid on the Dissolution of Claystone
Sulfuric acid was used to leach the claystone. Sulfuric acid
is a commercially available and cheap leaching agent that
is used commonly in the industry for metal leaching. The
results in Figure 4 show the dissolution of the 5 elements
under study (Li, Mg, Ca, iron Fe, and Al) with sulfuric acid.
In 1 hour, over 90% Li extraction was achieved, and as time
increased from 1 hour to 24 hours, there was no signifi-
cant increase in Li extraction observed. Mg had an extrac-
tion of 77% in 1 hour, then subsequently made a slight
increase as time increased to 24 hours. About 60% of iron
and aluminum was extracted in 1 hour, with an increase in
dissolution as time increased. The trend in both elements
was very similar. Calcium was the element with the low-
est extraction, with just less than 20% extraction over 24
hours. Sulfuric acid has a negative pka value (Equation 2),
meaning it is considered a strong acid that can be easily
deprotonated. This acidic strength can be used to explain
sulfuric acid’s excellent leaching efficiency.
H2SO4 → HSO4 – +H+ (pKa1 =–3) (2)
HSO4 – → SO4 2– +H+ (pKa1 =1.99) (3)
Effects of Organic Acids on the dissolution of claystone
Citric Acid
Citric acid, an organic tricarboxylic acid, readily dissolves
in water and is commonly employed as a raw material in
various manufacturing processes. It is a common metabo-
lite found in plants and animals [36]. Naturally occurring
in fruits, citric acid has a low molecular weight of 210.14g/
mol, and a high solubility of 1477 g L−1 in water and is
generated through microbial fermentation, constituting a
biodegradable organic product. Citric acid has been used in
recent years in the leaching of ores due to its considerable
leaching performance and strong chelating abilities [37]. Its
applications across different fields and its high solubility in
water make it an appropriate leaching agent [35].
The leaching of Li-bearing sedimentary clays with citric
acid has not been seen in the literature yet, but other sedi-
mentary rocks such as calcareous phosphate ores have been
beneficiated from organic acid leaching [38]. However, this
acid has been widely used for the leaching of other ores and
materials such as nickel ores, spent Li-ion batteries, zinc
and lead ores, etc. [39, 40].
Citric acid leaching was carried out and the dissolu-
tion of the 5 main elements of interest was recorded across
the chosen times, as shown in Figure 5. Li and Mg follow
very similar trends and similar extraction rates, and it can
be seen that after 8 hours, their increase in extraction rates
was not very significant. To note, calcium demonstrated
maximum extraction rate compared to the other elements.
In 1 hour, more than 90% of Ca was already dissolved in
the solution, while the extraction was roughly constant over
time. Al and Fe on the other hand had the lowest extraction
rate recording less than 60% for Al and less than 70% for
Fe, as maximum extraction. Their trends across time were
also very similar, hence Al is concomitant to Fe as Li is
concomitant to Mg.
Comparing the dissolution rates of citric acid and sul-
furic acid, it can be suggested that citric acid forms stable
0
20
40
60
80
100
0 4 8 12 16 20 24 28
Time, hour
Sulfuric Acid
Al
Ca
Fe
Li
Mg
Figure 4. Dissolution rates of main elements in claystone using sulfuric acid. 1M acid,
80 °C, 10 L/S
Extraction,
%
Effects of Sulfuric Acid on the Dissolution of Claystone
Sulfuric acid was used to leach the claystone. Sulfuric acid
is a commercially available and cheap leaching agent that
is used commonly in the industry for metal leaching. The
results in Figure 4 show the dissolution of the 5 elements
under study (Li, Mg, Ca, iron Fe, and Al) with sulfuric acid.
In 1 hour, over 90% Li extraction was achieved, and as time
increased from 1 hour to 24 hours, there was no signifi-
cant increase in Li extraction observed. Mg had an extrac-
tion of 77% in 1 hour, then subsequently made a slight
increase as time increased to 24 hours. About 60% of iron
and aluminum was extracted in 1 hour, with an increase in
dissolution as time increased. The trend in both elements
was very similar. Calcium was the element with the low-
est extraction, with just less than 20% extraction over 24
hours. Sulfuric acid has a negative pka value (Equation 2),
meaning it is considered a strong acid that can be easily
deprotonated. This acidic strength can be used to explain
sulfuric acid’s excellent leaching efficiency.
H2SO4 → HSO4 – +H+ (pKa1 =–3) (2)
HSO4 – → SO4 2– +H+ (pKa1 =1.99) (3)
Effects of Organic Acids on the dissolution of claystone
Citric Acid
Citric acid, an organic tricarboxylic acid, readily dissolves
in water and is commonly employed as a raw material in
various manufacturing processes. It is a common metabo-
lite found in plants and animals [36]. Naturally occurring
in fruits, citric acid has a low molecular weight of 210.14g/
mol, and a high solubility of 1477 g L−1 in water and is
generated through microbial fermentation, constituting a
biodegradable organic product. Citric acid has been used in
recent years in the leaching of ores due to its considerable
leaching performance and strong chelating abilities [37]. Its
applications across different fields and its high solubility in
water make it an appropriate leaching agent [35].
The leaching of Li-bearing sedimentary clays with citric
acid has not been seen in the literature yet, but other sedi-
mentary rocks such as calcareous phosphate ores have been
beneficiated from organic acid leaching [38]. However, this
acid has been widely used for the leaching of other ores and
materials such as nickel ores, spent Li-ion batteries, zinc
and lead ores, etc. [39, 40].
Citric acid leaching was carried out and the dissolu-
tion of the 5 main elements of interest was recorded across
the chosen times, as shown in Figure 5. Li and Mg follow
very similar trends and similar extraction rates, and it can
be seen that after 8 hours, their increase in extraction rates
was not very significant. To note, calcium demonstrated
maximum extraction rate compared to the other elements.
In 1 hour, more than 90% of Ca was already dissolved in
the solution, while the extraction was roughly constant over
time. Al and Fe on the other hand had the lowest extraction
rate recording less than 60% for Al and less than 70% for
Fe, as maximum extraction. Their trends across time were
also very similar, hence Al is concomitant to Fe as Li is
concomitant to Mg.
Comparing the dissolution rates of citric acid and sul-
furic acid, it can be suggested that citric acid forms stable
0
20
40
60
80
100
0 4 8 12 16 20 24 28
Time, hour
Sulfuric Acid
Al
Ca
Fe
Li
Mg
Figure 4. Dissolution rates of main elements in claystone using sulfuric acid. 1M acid,
80 °C, 10 L/S
Extraction,
%