XXXI International Mineral Processing Congress 2024 Proceedings/Washington, DC/Sep 29–Oct 3 1761
ferrous iron. Under high-temperature conditions of up to
80 °C, in the presence of an oxygen environment, the fer-
rous iron is converted to ferric iron, which facilitates the
dissolution of pyrite.
4Fe2+ +O2 +4H+ → 4Fe3+ +2H2O (6)
However, as the redox potential decreases, the rate of pyrite
oxidation slows and eventually stops. In bioleaching pro-
cesses, bacteria oxidize ferrous iron back into ferric iron,
maintaining a high redox potential. To facilitate this high
redox potential and the conversion of ferrous iron into fer-
ric iron, a catalyst such as manganese (IV) oxide is used.
The results indicated that the use of manganese (IV) oxide
as a catalyst, in the presence of ferric ions and oxygen,
significantly increased gold extraction from 44% to 91%
(Figure 6).
Recovery of Gold from the Pregnant Solution
Using Pyrite
To achieve a sustainable and eco-friendly gold process, tail-
ing (i.e., non-valuables) was utilized for the recovery of gold
ions from the thiosulfate solution. First, the recovery of gold
ions using a model pyrite sample by time was carried out to
identify whether pyrite can recover gold ions in the thiosul-
fate system. The results showed that the gold recovery rate
increased from 60% to 83% between 2–12 h. period.
CONCLUSION
In conclusion, this study presents an innovative and envi-
ronmentally sustainable methodology for the extraction
of gold from flotation concentrates. Initially, the leaching
phase employed a copper-ammoniacal-thiosulfate solution,
with optimal conditions determined through a series of
variable tests. This optimal environment resulted in a direct
leaching efficiency of 44% with the following conditions:
0.05 M S2O32–, 0.3 M NH3, 1.0 mM Cu2+, pH 9.5 and 8
hours. Subsequently, a pretreatment involving a ferric solu-
tion and catalysts under various operational conditions was
conducted to enhance the gold extraction. Pretreatment
with a ferric solution in the presence of manganese (IV)
oxide significantly improved the leaching efficiency from
44% to 91%. For gold recovery after leaching, a novel
recovery technique was developed by utilizing tailings, and
the results showed that about 83% of gold was recovered
and upgraded by pyrite.
44%
91%
0%
20%
40%
60%
80%
100%
Without pretreatment With pretreatment
Pretreatment experiment condition: 10% pulp density, 180 rpm shaking rate, 80 °C temperature, 12 hours, pH
level 1.2. Reagents concentrations: 6 g/L Fe3+ solution, 0.05 M MnO
2 Leaching experiment condition: 10% pulp density, 180 rpm shaking rate, 25 °C temperature, 4 hours, pH level
9.5. Reagents concentrations: 0.05 M S
2 O
3 2–, 0.3 M NH
3 ,1.0 mM Cu2+
Figure 6. Gold extraction results with and without pretreatment
Leaching
eiciency
(%)
ferrous iron. Under high-temperature conditions of up to
80 °C, in the presence of an oxygen environment, the fer-
rous iron is converted to ferric iron, which facilitates the
dissolution of pyrite.
4Fe2+ +O2 +4H+ → 4Fe3+ +2H2O (6)
However, as the redox potential decreases, the rate of pyrite
oxidation slows and eventually stops. In bioleaching pro-
cesses, bacteria oxidize ferrous iron back into ferric iron,
maintaining a high redox potential. To facilitate this high
redox potential and the conversion of ferrous iron into fer-
ric iron, a catalyst such as manganese (IV) oxide is used.
The results indicated that the use of manganese (IV) oxide
as a catalyst, in the presence of ferric ions and oxygen,
significantly increased gold extraction from 44% to 91%
(Figure 6).
Recovery of Gold from the Pregnant Solution
Using Pyrite
To achieve a sustainable and eco-friendly gold process, tail-
ing (i.e., non-valuables) was utilized for the recovery of gold
ions from the thiosulfate solution. First, the recovery of gold
ions using a model pyrite sample by time was carried out to
identify whether pyrite can recover gold ions in the thiosul-
fate system. The results showed that the gold recovery rate
increased from 60% to 83% between 2–12 h. period.
CONCLUSION
In conclusion, this study presents an innovative and envi-
ronmentally sustainable methodology for the extraction
of gold from flotation concentrates. Initially, the leaching
phase employed a copper-ammoniacal-thiosulfate solution,
with optimal conditions determined through a series of
variable tests. This optimal environment resulted in a direct
leaching efficiency of 44% with the following conditions:
0.05 M S2O32–, 0.3 M NH3, 1.0 mM Cu2+, pH 9.5 and 8
hours. Subsequently, a pretreatment involving a ferric solu-
tion and catalysts under various operational conditions was
conducted to enhance the gold extraction. Pretreatment
with a ferric solution in the presence of manganese (IV)
oxide significantly improved the leaching efficiency from
44% to 91%. For gold recovery after leaching, a novel
recovery technique was developed by utilizing tailings, and
the results showed that about 83% of gold was recovered
and upgraded by pyrite.
44%
91%
0%
20%
40%
60%
80%
100%
Without pretreatment With pretreatment
Pretreatment experiment condition: 10% pulp density, 180 rpm shaking rate, 80 °C temperature, 12 hours, pH
level 1.2. Reagents concentrations: 6 g/L Fe3+ solution, 0.05 M MnO
2 Leaching experiment condition: 10% pulp density, 180 rpm shaking rate, 25 °C temperature, 4 hours, pH level
9.5. Reagents concentrations: 0.05 M S
2 O
3 2–, 0.3 M NH
3 ,1.0 mM Cu2+
Figure 6. Gold extraction results with and without pretreatment
Leaching
eiciency
(%)