XXXI International Mineral Processing Congress 2024 Proceedings/Washington, DC/Sep 29–Oct 3 1783
ammonia could have a negative impact, as it stabilizes the
copper(I)-ammonia complex, as explained in previous
studies [16].
Effect of Mg(OH)2 Concentration
The results displayed in Figure 3 (a) to (d) explain how
Mg(OH)2 impacts at consistent pH levels but different
leaching parameters over time. Without Mg(OH)2, the
pH level gradually decreases from 10.0 to 9.3. To achieve
efficient Au dissolution, the pH range between 9 and 10
is desirable and unsaturated Mg(OH)2 helps to maintain
the pH level within this range and leads to increased gold
leaching from 73.1% to 78.3% when 0.05 M Mg(OH)2
is added to the solution (Figure 3 (d)). However, when
Mg(OH)2 is present, the pH level remains stable around
10.0, regardless of concentration.
Thiosulfate concentration and behavior remain con-
stant for all conditions, irrespective of magnesium concen-
tration (Figure 3 (c)). Previous studies have suggested that
thiosulfate complexes can form with various metals in the
ammoniacal thiosulfate system [12,18]. But Mg(II) has a low
stability constant for thiosulfate complexes, indicating that
Mg(OH)2 has less tendency to form a complex with thio-
sulfate and has a minimal effect on thiosulfate [18]. The pres-
ence of Mg(OH)2 results in a lower copper concentration
compared to its absence (Figure 3 (b)), which is related to
the gradual decrease in pH from 10.0 to 9.5 over time.
Effect of Thiosulfate Concentration
Figure 4 (a) to (d) show the leaching kinetics of gold at three
thiosulfate concentrations and three pH levels. Figure 5 (a)
to (b) show Au leaching efficiency and Cu concentration
after 24 hours. Results showed that as pH levels increased,
gold recovery decreased. However, for the same pH level,
increasing thiosulfate concentration led to improved gold
recovery. This supports previous research indicating a posi-
tive relationship between gold dissolution and thiosulfate
concentration [12,23,26]. Additionally, it was observed that
increasing thiosulfate concentration from 0.05 M to 0.2 M
resulted in higher copper concentration after 24 hours. This
can be attributed to thiosulfate’s ability to stabilize gold(I)
by forming a complex with Cu and Au in solution [18,24].
As a result, controlling copper content in the thiosulfate
solution is crucial for enhancing gold dissolution and maxi-
mizing copper’s role as a catalytic oxidant [10].
Effect of Cu Concentration
Figure 6 (a) to (d) showcase the results of the impact of
copper concentration on leaching. As seen in Figure 6 (a),
gold leaching showed similar behavior across all conditions,
Figure 3. Kinetic plots of leaching at different Mg(OH)2 concentrations, a) Au concentration b) Cu concentration, c) thiosulfate
concentration, and d) pH (Test condition: 0.1 M S2O32–, 1 mM Cu, 0-0.05 gMg(OH)2/gOre Mg(OH)2, pH 10.0, 20±3°C)
ammonia could have a negative impact, as it stabilizes the
copper(I)-ammonia complex, as explained in previous
studies [16].
Effect of Mg(OH)2 Concentration
The results displayed in Figure 3 (a) to (d) explain how
Mg(OH)2 impacts at consistent pH levels but different
leaching parameters over time. Without Mg(OH)2, the
pH level gradually decreases from 10.0 to 9.3. To achieve
efficient Au dissolution, the pH range between 9 and 10
is desirable and unsaturated Mg(OH)2 helps to maintain
the pH level within this range and leads to increased gold
leaching from 73.1% to 78.3% when 0.05 M Mg(OH)2
is added to the solution (Figure 3 (d)). However, when
Mg(OH)2 is present, the pH level remains stable around
10.0, regardless of concentration.
Thiosulfate concentration and behavior remain con-
stant for all conditions, irrespective of magnesium concen-
tration (Figure 3 (c)). Previous studies have suggested that
thiosulfate complexes can form with various metals in the
ammoniacal thiosulfate system [12,18]. But Mg(II) has a low
stability constant for thiosulfate complexes, indicating that
Mg(OH)2 has less tendency to form a complex with thio-
sulfate and has a minimal effect on thiosulfate [18]. The pres-
ence of Mg(OH)2 results in a lower copper concentration
compared to its absence (Figure 3 (b)), which is related to
the gradual decrease in pH from 10.0 to 9.5 over time.
Effect of Thiosulfate Concentration
Figure 4 (a) to (d) show the leaching kinetics of gold at three
thiosulfate concentrations and three pH levels. Figure 5 (a)
to (b) show Au leaching efficiency and Cu concentration
after 24 hours. Results showed that as pH levels increased,
gold recovery decreased. However, for the same pH level,
increasing thiosulfate concentration led to improved gold
recovery. This supports previous research indicating a posi-
tive relationship between gold dissolution and thiosulfate
concentration [12,23,26]. Additionally, it was observed that
increasing thiosulfate concentration from 0.05 M to 0.2 M
resulted in higher copper concentration after 24 hours. This
can be attributed to thiosulfate’s ability to stabilize gold(I)
by forming a complex with Cu and Au in solution [18,24].
As a result, controlling copper content in the thiosulfate
solution is crucial for enhancing gold dissolution and maxi-
mizing copper’s role as a catalytic oxidant [10].
Effect of Cu Concentration
Figure 6 (a) to (d) showcase the results of the impact of
copper concentration on leaching. As seen in Figure 6 (a),
gold leaching showed similar behavior across all conditions,
Figure 3. Kinetic plots of leaching at different Mg(OH)2 concentrations, a) Au concentration b) Cu concentration, c) thiosulfate
concentration, and d) pH (Test condition: 0.1 M S2O32–, 1 mM Cu, 0-0.05 gMg(OH)2/gOre Mg(OH)2, pH 10.0, 20±3°C)