1782 XXXI International Mineral Processing Congress 2024 Proceedings/Washington, DC/Sep 29–Oct 3
Cyanidation Test
The purpose of the cyanidation test was to evaluate the
leachability and refractoriness of the sample. To achieve
this, sodium hydroxide was added to adjust the pH of the
leaching reactor to 11.0, followed by the introduction of 2
g/t of sodium cyanide. Throughout the test, the pH level
was kept constant. The bench test was conducted at 25°C
and 100 rpm, using 150 g of the sample and 150 ml of
solution for 24 hours. The column test, which lasted for
7 days, utilized the same setup as the thiosulfate tests. The
feed solution was comprised of pH 11.0 and 2 g/t of sodium
cyanide. The results of both tests revealed that 67.3% and
64.9%, respectively, of the gold could be leached from the
ore under these conditions.
RESULTS AND DISCUSSION
Bench Scale Test Results
Effect of Initial pH
The behavior of various parameters in thiosulfate leaching
tests conducted at different pH values adjusted by Ca(OH)2
are depicted in Figure 2 (a) to (d). It was observed that the
pH of the solution decreased during the first 30 minutes
of leaching when the initial pH was above 9.0, as shown in
Figure 2 (a). Conversely, an increasing trend was observed
in the initial pH of 9.0.
Figure 2 (b) shows that similar gold dissolution patterns
and leaching efficiencies of around 65% were measured at
all initial pH values, except for the experiment conducted
at an initial pH of 11.5, in which a sharp decrease of gold
recovery to 28% was obtained. Most of the copper precipi-
tates within 30 minutes when the initial pH increases from
9.5 to 10.3, as shown in Figure 2 (c). According to the
previous research, the precipitation of Cu as CuS and CuO
could hinder gold dissolution at this pH level [21]. Despite
the interaction between copper and thiosulfate, several
investigations have found that higher copper concentra-
tions benefit gold leaching [22–25]. This could support the
higher gold recoveries obtained at pH 9.0 and pH 9.5 with
higher Cu contents. Molleman and Dreisinger explained
that the favorable pH range for thiosulfate leaching with
copper is 9.0 to 10 [16].
Thiosulfate decomposition displayed similar trends at
all pH levels (Figure 2 (d)), and 0.03 M of ammonium
thiosulfate was consumed during leaching. This demon-
strated that similar mechanisms of thiosulfate decomposi-
tion occurred from pH 9.0 to pH 10.3. A specific range of
ammonia to thiosulfate ratio should be maintained to allow
regeneration of the cupric ion. However, over-concentrated
Figure 2. Kinetic plots of leaching at various pH levels adjusted by Ca(OH)
2 ,a) pH, b) Au recovery, c) Cu concentration,
d) thiosulfate concentration (Test condition: 0.1 M S
2 O
3 2–, 1 mM Cu, 0.01 g
Mg(OH)2 /g
Ore Mg(OH)
2 ,20±3°C)
Cyanidation Test
The purpose of the cyanidation test was to evaluate the
leachability and refractoriness of the sample. To achieve
this, sodium hydroxide was added to adjust the pH of the
leaching reactor to 11.0, followed by the introduction of 2
g/t of sodium cyanide. Throughout the test, the pH level
was kept constant. The bench test was conducted at 25°C
and 100 rpm, using 150 g of the sample and 150 ml of
solution for 24 hours. The column test, which lasted for
7 days, utilized the same setup as the thiosulfate tests. The
feed solution was comprised of pH 11.0 and 2 g/t of sodium
cyanide. The results of both tests revealed that 67.3% and
64.9%, respectively, of the gold could be leached from the
ore under these conditions.
RESULTS AND DISCUSSION
Bench Scale Test Results
Effect of Initial pH
The behavior of various parameters in thiosulfate leaching
tests conducted at different pH values adjusted by Ca(OH)2
are depicted in Figure 2 (a) to (d). It was observed that the
pH of the solution decreased during the first 30 minutes
of leaching when the initial pH was above 9.0, as shown in
Figure 2 (a). Conversely, an increasing trend was observed
in the initial pH of 9.0.
Figure 2 (b) shows that similar gold dissolution patterns
and leaching efficiencies of around 65% were measured at
all initial pH values, except for the experiment conducted
at an initial pH of 11.5, in which a sharp decrease of gold
recovery to 28% was obtained. Most of the copper precipi-
tates within 30 minutes when the initial pH increases from
9.5 to 10.3, as shown in Figure 2 (c). According to the
previous research, the precipitation of Cu as CuS and CuO
could hinder gold dissolution at this pH level [21]. Despite
the interaction between copper and thiosulfate, several
investigations have found that higher copper concentra-
tions benefit gold leaching [22–25]. This could support the
higher gold recoveries obtained at pH 9.0 and pH 9.5 with
higher Cu contents. Molleman and Dreisinger explained
that the favorable pH range for thiosulfate leaching with
copper is 9.0 to 10 [16].
Thiosulfate decomposition displayed similar trends at
all pH levels (Figure 2 (d)), and 0.03 M of ammonium
thiosulfate was consumed during leaching. This demon-
strated that similar mechanisms of thiosulfate decomposi-
tion occurred from pH 9.0 to pH 10.3. A specific range of
ammonia to thiosulfate ratio should be maintained to allow
regeneration of the cupric ion. However, over-concentrated
Figure 2. Kinetic plots of leaching at various pH levels adjusted by Ca(OH)
2 ,a) pH, b) Au recovery, c) Cu concentration,
d) thiosulfate concentration (Test condition: 0.1 M S
2 O
3 2–, 1 mM Cu, 0.01 g
Mg(OH)2 /g
Ore Mg(OH)
2 ,20±3°C)