XXXI International Mineral Processing Congress 2024 Proceedings/Washington, DC/Sep 29–Oct 3 2371
known that the oxidation of the sulfidizer will form oxysul-
phide species such as sulfites, thiosulfates and sulfate which
not only impart surface hydrophilicity, but also consume
the sulfidizer and inhibit the formation of the new metal
sulfide phase (Zhou and Chander, 1993). As a result, the
addition of Cu(II) during the sulfidization might still have
some limitations in being able to promote the flotation of
oxidized pyrite. However, the limitation could be overcome
by directly adding Cu(I) with sulfidization so that Cu(I)
can react with the sulfidizer to form a Cu(I)S phase without
needing to oxidize the sulfidizer.
Therefore, the objectives of the work were to investi-
gate the effects of the addition of Cu(II) and Cu(I) ions
along with sulfidization of oxidized pyrite on the formation
of a new metal sulfide phase on the surface of pyrite and the
subsequent flotation behavior. While Cyclic Voltammetry
(CV) analyses were conducted to understand the formation
of the new metal sulfide phase on the surface of oxidized
pyrite, flotation tests on fresh and oxidized pyritic gold ores
were conducted to evaluate the effect of the new sulfidiza-
tion process on pyrite flotation. The results from this work
will provide recommendations on how to more effectively
float oxidized pyritic gold ores. Although this work focused
on oxidized pyritic gold ores, outcomes from this work will
also provide new insights into sulfidization and flotation of
metal oxides and other oxidized sulfide minerals.
METHODOLOGY
Materials
A fresh pyritic gold ore and an oxidized pyritic gold ore
were supplied by a gold mining operation. The fresh ore
was collected from an active mining bench, while the oxi-
dized ore was from stockpiles that had been undisturbed
for more than 5 years. The ore deposit for this mine is
regarded as dominantly refractory with gold being con-
tained in solid-solution in pyrite. The ores were crushed
to –3.25 mm particles which were mixed thoroughly, split
into 1 kg bags and stored in a freezer with the tempera-
ture below –18°C. Table 1 shows the elemental composi-
tions of the two ore samples analyzed at ALS Geochemistry,
Brisbane, Australia. As can be seen, the fresh ore consists of
6.8% sulfide sulfur and 7.2% total sulfur with their ratio
being about 95%, while the oxidized ore consists of 3.2%
sulfide sulfur and 6.2% total sulfur with their ratio being
about 51%. Since the total sulfur is composed of sulfide
sulfur and the sulfur from sulfide oxidation products, the
lower ratio of sulfide sulfur to total sulfur is indicative that
significant surface oxidation had occurred.
Potassium amyl xanthate (PAX) and Aerofroth were
used as the collector and frother, respectively, in flotation
tests. A.R. grade disodium tetraborate decahydrate and
hydrochloric acid were used to prepare pH 8 and 9 buf-
fer solutions with 0.1 M KCl as the supporting electrolyte.
The chosen buffer pH values considered the flotation pH
at 8 without sulfidization and 9 with sulfidization after the
addition of Na2S. In addition, A.R. grade sodium sulfide
nonahydrate (Na2S·9H2O) was used as the sulfidizer. All
chemical solutions were prepared daily just prior to the
experiment in de-ionized water.
Methods
Grinding and Flotation
A grinding and flotation test procedure was developed to
simulate plant operation. For each test, 1 kg crushed ore
sample was wet ground using a laboratory rod mill with
forged steel grinding media at a solid concentration of 60%
to achieve a P80 (80% passing size) of 150 μm. Copper
ions were added in the mill at different dosages when they
were required during sulfidization. After grinding, the mill
discharge was relocated to a 2.5 L mechanical flotation cell
and mixed at 1000 rpm. The pulp pH was adjusted and
maintained at 8.0 using a small amount of NaOH solu-
tion. When sulfidization was applied, Na2S was added to
achieve a predetermined potential (SHE) which was then
maintained for 5 min. After sulfidization, 85 g/t PAX and
15 g/t Aerofroth were added to the pulp sequentially and
each was conditioned for 2 min. Then air was purged at 3
L/min to start flotation and the first flotation concentrate
was collected for 2 min. Then the air flowrate was increased
to 3.5 L/min and more flotation concentrates were col-
lected at cumulative flotation times of 4, 10, 16, 22 and 28
min. Before concentrates 3 to 5 were collected, additional
PAX (25 g/t) was added to the flotation cell and condi-
tioned for 1 min to maximize gold recovery. All flotation
tests were performed in duplicate, and the standard error
of gold grade and recovery was around 0.3 ppm and 0.5%,
respectively. In terms of sulfide flotation, the standard error
of grade and recovery was around 0.1 and 1%, respectively.
Table 1. Elemental compositions of the pyritic gold ore samples
Au, ppm Stotal, %Sulfide S, %As, ppm S2–/Stotal, %
Fresh ore 2.61 7.2 6.8 830 95.0
Oxidized ore 1.81 6.2 3.2 502 51.5
known that the oxidation of the sulfidizer will form oxysul-
phide species such as sulfites, thiosulfates and sulfate which
not only impart surface hydrophilicity, but also consume
the sulfidizer and inhibit the formation of the new metal
sulfide phase (Zhou and Chander, 1993). As a result, the
addition of Cu(II) during the sulfidization might still have
some limitations in being able to promote the flotation of
oxidized pyrite. However, the limitation could be overcome
by directly adding Cu(I) with sulfidization so that Cu(I)
can react with the sulfidizer to form a Cu(I)S phase without
needing to oxidize the sulfidizer.
Therefore, the objectives of the work were to investi-
gate the effects of the addition of Cu(II) and Cu(I) ions
along with sulfidization of oxidized pyrite on the formation
of a new metal sulfide phase on the surface of pyrite and the
subsequent flotation behavior. While Cyclic Voltammetry
(CV) analyses were conducted to understand the formation
of the new metal sulfide phase on the surface of oxidized
pyrite, flotation tests on fresh and oxidized pyritic gold ores
were conducted to evaluate the effect of the new sulfidiza-
tion process on pyrite flotation. The results from this work
will provide recommendations on how to more effectively
float oxidized pyritic gold ores. Although this work focused
on oxidized pyritic gold ores, outcomes from this work will
also provide new insights into sulfidization and flotation of
metal oxides and other oxidized sulfide minerals.
METHODOLOGY
Materials
A fresh pyritic gold ore and an oxidized pyritic gold ore
were supplied by a gold mining operation. The fresh ore
was collected from an active mining bench, while the oxi-
dized ore was from stockpiles that had been undisturbed
for more than 5 years. The ore deposit for this mine is
regarded as dominantly refractory with gold being con-
tained in solid-solution in pyrite. The ores were crushed
to –3.25 mm particles which were mixed thoroughly, split
into 1 kg bags and stored in a freezer with the tempera-
ture below –18°C. Table 1 shows the elemental composi-
tions of the two ore samples analyzed at ALS Geochemistry,
Brisbane, Australia. As can be seen, the fresh ore consists of
6.8% sulfide sulfur and 7.2% total sulfur with their ratio
being about 95%, while the oxidized ore consists of 3.2%
sulfide sulfur and 6.2% total sulfur with their ratio being
about 51%. Since the total sulfur is composed of sulfide
sulfur and the sulfur from sulfide oxidation products, the
lower ratio of sulfide sulfur to total sulfur is indicative that
significant surface oxidation had occurred.
Potassium amyl xanthate (PAX) and Aerofroth were
used as the collector and frother, respectively, in flotation
tests. A.R. grade disodium tetraborate decahydrate and
hydrochloric acid were used to prepare pH 8 and 9 buf-
fer solutions with 0.1 M KCl as the supporting electrolyte.
The chosen buffer pH values considered the flotation pH
at 8 without sulfidization and 9 with sulfidization after the
addition of Na2S. In addition, A.R. grade sodium sulfide
nonahydrate (Na2S·9H2O) was used as the sulfidizer. All
chemical solutions were prepared daily just prior to the
experiment in de-ionized water.
Methods
Grinding and Flotation
A grinding and flotation test procedure was developed to
simulate plant operation. For each test, 1 kg crushed ore
sample was wet ground using a laboratory rod mill with
forged steel grinding media at a solid concentration of 60%
to achieve a P80 (80% passing size) of 150 μm. Copper
ions were added in the mill at different dosages when they
were required during sulfidization. After grinding, the mill
discharge was relocated to a 2.5 L mechanical flotation cell
and mixed at 1000 rpm. The pulp pH was adjusted and
maintained at 8.0 using a small amount of NaOH solu-
tion. When sulfidization was applied, Na2S was added to
achieve a predetermined potential (SHE) which was then
maintained for 5 min. After sulfidization, 85 g/t PAX and
15 g/t Aerofroth were added to the pulp sequentially and
each was conditioned for 2 min. Then air was purged at 3
L/min to start flotation and the first flotation concentrate
was collected for 2 min. Then the air flowrate was increased
to 3.5 L/min and more flotation concentrates were col-
lected at cumulative flotation times of 4, 10, 16, 22 and 28
min. Before concentrates 3 to 5 were collected, additional
PAX (25 g/t) was added to the flotation cell and condi-
tioned for 1 min to maximize gold recovery. All flotation
tests were performed in duplicate, and the standard error
of gold grade and recovery was around 0.3 ppm and 0.5%,
respectively. In terms of sulfide flotation, the standard error
of grade and recovery was around 0.1 and 1%, respectively.
Table 1. Elemental compositions of the pyritic gold ore samples
Au, ppm Stotal, %Sulfide S, %As, ppm S2–/Stotal, %
Fresh ore 2.61 7.2 6.8 830 95.0
Oxidized ore 1.81 6.2 3.2 502 51.5