1794 XXXI International Mineral Processing Congress 2024 Proceedings/Washington, DC/Sep 29–Oct 3
gold needs to be oxidized, and thiocyanate is suitable for
leaching under acidic system. Therefore, in this experimen-
tal study, the higher potential and more commonly used
oxidizing agent -manganese dioxide as the oxidizing agent
for leaching, and dilute sulfuric acid to adjust the pH of
the leaching system, and systematically study the change
rule of the gold extraction under various conditions, mainly
including the number of reagents, the system pH, the liq-
uid-solid ratio and the leaching time. The test results are
shown in Table 3. It should be noted that, unless otherwise
specified, the conditions of all leaching tests were: 1.2 mol/L
NaSCN, 4.0 mmol/L MnO2, pH=1.0, liquid-solid ratio
6:1 mL/g, leaching time 24 h, stirring rate 300 rpm, room
temperature.
According to the results shown in Table 3, the reagent
dosage and system pH had a greater influence on the
extraction of gold, and the gold extraction increased with
the increase of reagent dosage, so it was more favorable to
maintain a higher reagent concentration during the leach-
ing process. The extraction of gold was 92.75% at the con-
centration of NaSCN of 1.2 mol/L, and the change of the
extraction of gold was not significant when the NaSCN
dosage was increased further. Therefore, the optimum dos-
age of NaSCN was 1.2 mol/L. Continuing to increase the
concentration of MnO2 because of 4.0 mmol/L, the gold
hardly changed, so the optimum dosage of MnO2 was
4.0 mmol/L. From the results of the pH condition test for
the leaching of thiocyanate under acidic, the higher the pH
of the system, the lower the gold extraction, and the highest
extraction was found when the pH=1.0. The highest extrac-
tion was found at pH=1.0, so the optimum pH for leaching
in this test was 1.0.
The effects of liquid-solid ratio and stirring rate on the
gold extraction were small, indicating that the mass transfer
in the leaching process had been enough and the reaction
had been more complete, to improve the processing capac-
ity as much as possible, so 3:1 mL/g and 300 rpm were
selected as the optimal liquid-solid ratio conditions and the
optimal stirring rate. In the process of increasing the leach-
ing time from 12 h to 24 h, the gold extraction increased
about 8.65%, but the gold extraction did not change when
the leaching time was increased after 24 h. Therefore, the
optimal leaching time was chosen to be 24 h.
Therefore, according to the experimental study of the
above conditions, the optimal conditions for conventional
cyanide-free leaching were: 1.2 mol/L NaSCN, 4.0 mmol/L
MnO2, pH=1.0, liquid-solid ratio 3:1 mL/g, leaching time
24 h, stirring rate 300 rpm, room temperature. Under the
optimal conditions, the extraction of gold was 94.74% and
that of silver was 89.44%, and the leaching effect of gold
and silver was better.
Mechanical Activation Cyanide Free Leaching Test
According to the above study, the extraction of gold and
silver under conventional conditions has not reached the
optimal value, so in this section, mechanical activation is
used to enhance the leaching of gold and silver and the
leaching conditions are systematically optimized to maxi-
mize the efficient leaching of gold and silver. The results
of the mechanical activation enhanced leaching conditions
tests are shown in Table 4. It should be noted that, unless
otherwise specified, all leaching tests were conducted under
the following conditions: 1.0 mol/L NaSCN, 2.0 mmol/L
MnO2, pH=1.0, liquid-solid ratio of 6:1 mL/g, leaching
time of 6 h, ball milling tank rotational rate of 150 rpm/
min, and ball milling tank autorotation rate of 300 rpm/
min, at room temperature.
As can be seen from Table 4, the overall improvement
of gold extraction is more obvious under the reinforcement
of mechanical activation. According to the optimization
results of the condition test, the extraction of gold was
96.13% when the concentration of NaSCN was 1.2 mol/L.
Further increasing the dosage of sodium thiocyanate, the
change of gold extraction was not significant, so the opti-
mal dosage of NaSCN was 1.2 mol/L. Continuing to
increase the concentration of MnO2 since 4.0 mmol/L,
Table 2. Cyanide leaching gold test results
NaCN, g/L 0.5 1.0 1.5 2.0 2.5
Gold extraction, %92.95 90.91 91.08 92.42 94.93
Table 3. Conventional cyanide-free leaching test results
Conditions Gold Extraction, %
NaSCN, mol/L 0.6 86.95
1.2 92.75
1.8 94.44
MnO
2 ,mmol/L 2.0 90.51
4.0 94.61
6.0 94.73
pH 1.0 92.13
2.0 90.51
3.0 87.21
Liquid-solid ratio,
mL/g
3 90.19
6 90.51
9 91.31
Leaching time, h 12 85.86
24 94.51
48 93.97
Stirring rate, rpm 200 88.12
300 90.51
400 90.01
gold needs to be oxidized, and thiocyanate is suitable for
leaching under acidic system. Therefore, in this experimen-
tal study, the higher potential and more commonly used
oxidizing agent -manganese dioxide as the oxidizing agent
for leaching, and dilute sulfuric acid to adjust the pH of
the leaching system, and systematically study the change
rule of the gold extraction under various conditions, mainly
including the number of reagents, the system pH, the liq-
uid-solid ratio and the leaching time. The test results are
shown in Table 3. It should be noted that, unless otherwise
specified, the conditions of all leaching tests were: 1.2 mol/L
NaSCN, 4.0 mmol/L MnO2, pH=1.0, liquid-solid ratio
6:1 mL/g, leaching time 24 h, stirring rate 300 rpm, room
temperature.
According to the results shown in Table 3, the reagent
dosage and system pH had a greater influence on the
extraction of gold, and the gold extraction increased with
the increase of reagent dosage, so it was more favorable to
maintain a higher reagent concentration during the leach-
ing process. The extraction of gold was 92.75% at the con-
centration of NaSCN of 1.2 mol/L, and the change of the
extraction of gold was not significant when the NaSCN
dosage was increased further. Therefore, the optimum dos-
age of NaSCN was 1.2 mol/L. Continuing to increase the
concentration of MnO2 because of 4.0 mmol/L, the gold
hardly changed, so the optimum dosage of MnO2 was
4.0 mmol/L. From the results of the pH condition test for
the leaching of thiocyanate under acidic, the higher the pH
of the system, the lower the gold extraction, and the highest
extraction was found when the pH=1.0. The highest extrac-
tion was found at pH=1.0, so the optimum pH for leaching
in this test was 1.0.
The effects of liquid-solid ratio and stirring rate on the
gold extraction were small, indicating that the mass transfer
in the leaching process had been enough and the reaction
had been more complete, to improve the processing capac-
ity as much as possible, so 3:1 mL/g and 300 rpm were
selected as the optimal liquid-solid ratio conditions and the
optimal stirring rate. In the process of increasing the leach-
ing time from 12 h to 24 h, the gold extraction increased
about 8.65%, but the gold extraction did not change when
the leaching time was increased after 24 h. Therefore, the
optimal leaching time was chosen to be 24 h.
Therefore, according to the experimental study of the
above conditions, the optimal conditions for conventional
cyanide-free leaching were: 1.2 mol/L NaSCN, 4.0 mmol/L
MnO2, pH=1.0, liquid-solid ratio 3:1 mL/g, leaching time
24 h, stirring rate 300 rpm, room temperature. Under the
optimal conditions, the extraction of gold was 94.74% and
that of silver was 89.44%, and the leaching effect of gold
and silver was better.
Mechanical Activation Cyanide Free Leaching Test
According to the above study, the extraction of gold and
silver under conventional conditions has not reached the
optimal value, so in this section, mechanical activation is
used to enhance the leaching of gold and silver and the
leaching conditions are systematically optimized to maxi-
mize the efficient leaching of gold and silver. The results
of the mechanical activation enhanced leaching conditions
tests are shown in Table 4. It should be noted that, unless
otherwise specified, all leaching tests were conducted under
the following conditions: 1.0 mol/L NaSCN, 2.0 mmol/L
MnO2, pH=1.0, liquid-solid ratio of 6:1 mL/g, leaching
time of 6 h, ball milling tank rotational rate of 150 rpm/
min, and ball milling tank autorotation rate of 300 rpm/
min, at room temperature.
As can be seen from Table 4, the overall improvement
of gold extraction is more obvious under the reinforcement
of mechanical activation. According to the optimization
results of the condition test, the extraction of gold was
96.13% when the concentration of NaSCN was 1.2 mol/L.
Further increasing the dosage of sodium thiocyanate, the
change of gold extraction was not significant, so the opti-
mal dosage of NaSCN was 1.2 mol/L. Continuing to
increase the concentration of MnO2 since 4.0 mmol/L,
Table 2. Cyanide leaching gold test results
NaCN, g/L 0.5 1.0 1.5 2.0 2.5
Gold extraction, %92.95 90.91 91.08 92.42 94.93
Table 3. Conventional cyanide-free leaching test results
Conditions Gold Extraction, %
NaSCN, mol/L 0.6 86.95
1.2 92.75
1.8 94.44
MnO
2 ,mmol/L 2.0 90.51
4.0 94.61
6.0 94.73
pH 1.0 92.13
2.0 90.51
3.0 87.21
Liquid-solid ratio,
mL/g
3 90.19
6 90.51
9 91.31
Leaching time, h 12 85.86
24 94.51
48 93.97
Stirring rate, rpm 200 88.12
300 90.51
400 90.01