XXXI International Mineral Processing Congress 2024 Proceedings/Washington, DC/Sep 29–Oct 3 1787
Mg(OH)2 showed a decrease in pH over time after passing
through the column.
Samples with 0.05 gMg(OH)2/gore of Mg(OH)2 and a
pH of 9.5, as shown in Figure 8 (c), exhibited nearly 0 mM
of Cu during the test period, despite having slightly elevated
pH levels. Also, it should be noted that the experimental
procedure employed a lower concentration of thiosulfate
(50 mM). As seen in previous experiments, the pH level
could impact thiosulfate stability and Cu concentration. It
is believed that this concentration is insufficient to stabilize
the thiosulfate-copper complex in the presence of increased
pH levels, resulting in the precipitation of Cu. Figure 8 (d)
reveals that all conditions resulted in a similar decrease in
thiosulfate concentration. This result shows that Mg(OH)2
did not form a complex with thiosulfate, which is consis-
tent with the bench scale tests. This suggests that the appro-
priate amount of Mg(OH)2 is crucial in this system when
using lower thiosulfate and copper concentrations.
Effect of Thiosulfate Concentration
The results of this test confirm that the concentration of thio-
sulfate has a significant effect on column leaching. Figure 9
(a) illustrates that, regardless of the thiosulfate concentra-
tion, the pH behavior during the test followed a similar
pattern. Figure 9 (b) demonstrates that higher thiosulfate
concentrations experienced a more drastic decrease, with
100 mM decreasing to 70 mM in 8 days. Meanwhile,
lower initial thiosulfate concentrations remained stable for
throughout test. This is consistent with previous research,
indicating that lower thiosulfate concentrations undergo
less decomposition over time [14].
Although Cu concentration decreased then increased
over time for all conditions, higher thiosulfate concentra-
tion resulted in higher Cu concentration on the same day
(in Figure 9 (c)). Although the Cu concentration decreased
to almost zero under all conditions, the condition with the
higher thiosulfate concentration exhibited a higher Cu con-
centration. This can be attributed to the ability of thiosul-
fate to stabilize the thiosulfate-copper complex [15,26,26,27].
The recovery of Au followed a similar pattern, reaching
58% within a week, except for the lowest condition, which
was 10 mM as illustrated in Figure 9 (d). In the lowest thio-
sulfate concentration, the Au slowly leached out to 50% at
the end of two weeks.
Effect of Cu Concentration
This study investigates the impact of Cu concentration on
the system’s behavior. Figure 10 (a) showcases the recovery
of Au, with higher Cu amounts resulting in more remark-
able recovery. For instance, 1 mM of Cu produced 56%
Figure 9. Kinetic plots of leaching at various thiosulfate concentration, a) pH, b) thiosulfate concentration, c) Cu
concentration and d) Au recovery (Test condition: 10-100 mM S
2 O
3 2–, 1 mM Cu, 0.02 g
Mg(OH)2 /g
Ore Mg(OH)
2 ,20±3°C)
Mg(OH)2 showed a decrease in pH over time after passing
through the column.
Samples with 0.05 gMg(OH)2/gore of Mg(OH)2 and a
pH of 9.5, as shown in Figure 8 (c), exhibited nearly 0 mM
of Cu during the test period, despite having slightly elevated
pH levels. Also, it should be noted that the experimental
procedure employed a lower concentration of thiosulfate
(50 mM). As seen in previous experiments, the pH level
could impact thiosulfate stability and Cu concentration. It
is believed that this concentration is insufficient to stabilize
the thiosulfate-copper complex in the presence of increased
pH levels, resulting in the precipitation of Cu. Figure 8 (d)
reveals that all conditions resulted in a similar decrease in
thiosulfate concentration. This result shows that Mg(OH)2
did not form a complex with thiosulfate, which is consis-
tent with the bench scale tests. This suggests that the appro-
priate amount of Mg(OH)2 is crucial in this system when
using lower thiosulfate and copper concentrations.
Effect of Thiosulfate Concentration
The results of this test confirm that the concentration of thio-
sulfate has a significant effect on column leaching. Figure 9
(a) illustrates that, regardless of the thiosulfate concentra-
tion, the pH behavior during the test followed a similar
pattern. Figure 9 (b) demonstrates that higher thiosulfate
concentrations experienced a more drastic decrease, with
100 mM decreasing to 70 mM in 8 days. Meanwhile,
lower initial thiosulfate concentrations remained stable for
throughout test. This is consistent with previous research,
indicating that lower thiosulfate concentrations undergo
less decomposition over time [14].
Although Cu concentration decreased then increased
over time for all conditions, higher thiosulfate concentra-
tion resulted in higher Cu concentration on the same day
(in Figure 9 (c)). Although the Cu concentration decreased
to almost zero under all conditions, the condition with the
higher thiosulfate concentration exhibited a higher Cu con-
centration. This can be attributed to the ability of thiosul-
fate to stabilize the thiosulfate-copper complex [15,26,26,27].
The recovery of Au followed a similar pattern, reaching
58% within a week, except for the lowest condition, which
was 10 mM as illustrated in Figure 9 (d). In the lowest thio-
sulfate concentration, the Au slowly leached out to 50% at
the end of two weeks.
Effect of Cu Concentration
This study investigates the impact of Cu concentration on
the system’s behavior. Figure 10 (a) showcases the recovery
of Au, with higher Cu amounts resulting in more remark-
able recovery. For instance, 1 mM of Cu produced 56%
Figure 9. Kinetic plots of leaching at various thiosulfate concentration, a) pH, b) thiosulfate concentration, c) Cu
concentration and d) Au recovery (Test condition: 10-100 mM S
2 O
3 2–, 1 mM Cu, 0.02 g
Mg(OH)2 /g
Ore Mg(OH)
2 ,20±3°C)