2372 XXXI International Mineral Processing Congress 2024 Proceedings/Washington, DC/Sep 29–Oct 3
Electrochemical Studies
A pyrite electrode was prepared from a high purity pyrite
specimen for electrochemical studies, which were con-
ducted in a traditional three electrodes double jacketed
cell controlled by a CHI 920D (CH Instruments, Inc.,
US) potentiostat with a platinum electrode and Ag/AgCl
electrode as the counter electrode and reference electrode,
respectively, in an ambient condition to match the indus-
trial practice of sulfidization. The measured potentials were
converted to standard hydrogen electrode (SHE) values.
Pyrite oxidation was achieved by polarizing the freshly
polished pyrite surface through chronoamperometry (CA)
at 700 mV for 600 seconds. Sulfidization of the oxidized
pyrite in the absence and presence of copper ions was con-
ducted in a Na2S buffer solution at pH 9 for 300 seconds.
Magnetic stirring at 400 rpm was implemented throughout
the sulfidization process to mimic the agitation in floata-
tion. The pyrite surfaces after being treated in different con-
ditions were then characterized using Cyclic Voltammetry
(CV). All CV experiments were conducted at a scan rate of
10 mV/s in a range of –600 to 700 mV.
RESULT AND DISCUSSION
Flotation of Pyritic Gold Ores
Flotation Without Sulfidization
A flotation test on the oxidized pyritic gold ore was con-
ducted to understand the flotation performance of sulfide
sulfur, total sulfur and gold without sulfidization. For com-
parison, a flotation test on the fresh pyritic gold ore was
also conducted. The results are shown in Figure 1. As can
be seen from Figure 1 (left), the flotation of the oxidized
pyritic gold ore produced a sulfide recovery of 79.4% at
a grade of 18.0% and a total sulfur recovery of 45.7% at
a grade of 19.4% at the end of flotation. In contrast, the
flotation of the fresh pyritic gold ore produced the same
sulfide and total sulfur flotation recovery, 89.2%, at a grade
of 19.1% at the end of flotation. Obviously, both sulfide
flotation and total sulfur flotation for the oxidized pyritic
gold ore was worse compared to the fresh pyritic gold ore.
As shown in Table 1, the oxidized ore was heavily oxidized
with about 50% of the sulfur from sulfide oxidation prod-
ucts, whilst the fresh ore was only slightly oxidized with
less than 5% sulfur from sulfide oxidation products. EDTA
extraction tests also showed a much higher amount of iron
oxidation products extracted from the oxidized ore.
Figure 1 (right) illustrates that gold recovery was much
higher for flotation of the fresh ore with a recovery of
85.6% at the end of flotation. Flotation of the oxidized ore
produced a gold recovery of only about 65.0%. The poor
flotation recovery of gold of oxidized ore is reasonable, con-
sidering that the gold is mainly associated with pyrite and
the oxidized ore has a large portion of oxidized sulfur which
corresponds to the oxidized pyrite and was difficult to float
as mentioned previously.
Overall, the finding from batch flotation test work
was consistent with the observation in the processing plant
where the poor flotation of total sulfur results in the poor
flotation of gold mainly associated with oxidized pyrite. In
order to improve gold flotation from the oxidized ore, it is
essential to improve the flotation performance of the oxi-
dized pyrite. In the next sections, gold flotation results were
not shown since the gold was contained in refractory pyrite
and the objective of the work was to improve the flotation
of oxidized pyrite and its associated gold.
Figure 1. Flotation performance of the fresh pyritic ore and the oxidized pyritic gold ore: sulfide sulfur and total sulfur grades
and recoveries (left) and gold grades and recoveries (right)
Electrochemical Studies
A pyrite electrode was prepared from a high purity pyrite
specimen for electrochemical studies, which were con-
ducted in a traditional three electrodes double jacketed
cell controlled by a CHI 920D (CH Instruments, Inc.,
US) potentiostat with a platinum electrode and Ag/AgCl
electrode as the counter electrode and reference electrode,
respectively, in an ambient condition to match the indus-
trial practice of sulfidization. The measured potentials were
converted to standard hydrogen electrode (SHE) values.
Pyrite oxidation was achieved by polarizing the freshly
polished pyrite surface through chronoamperometry (CA)
at 700 mV for 600 seconds. Sulfidization of the oxidized
pyrite in the absence and presence of copper ions was con-
ducted in a Na2S buffer solution at pH 9 for 300 seconds.
Magnetic stirring at 400 rpm was implemented throughout
the sulfidization process to mimic the agitation in floata-
tion. The pyrite surfaces after being treated in different con-
ditions were then characterized using Cyclic Voltammetry
(CV). All CV experiments were conducted at a scan rate of
10 mV/s in a range of –600 to 700 mV.
RESULT AND DISCUSSION
Flotation of Pyritic Gold Ores
Flotation Without Sulfidization
A flotation test on the oxidized pyritic gold ore was con-
ducted to understand the flotation performance of sulfide
sulfur, total sulfur and gold without sulfidization. For com-
parison, a flotation test on the fresh pyritic gold ore was
also conducted. The results are shown in Figure 1. As can
be seen from Figure 1 (left), the flotation of the oxidized
pyritic gold ore produced a sulfide recovery of 79.4% at
a grade of 18.0% and a total sulfur recovery of 45.7% at
a grade of 19.4% at the end of flotation. In contrast, the
flotation of the fresh pyritic gold ore produced the same
sulfide and total sulfur flotation recovery, 89.2%, at a grade
of 19.1% at the end of flotation. Obviously, both sulfide
flotation and total sulfur flotation for the oxidized pyritic
gold ore was worse compared to the fresh pyritic gold ore.
As shown in Table 1, the oxidized ore was heavily oxidized
with about 50% of the sulfur from sulfide oxidation prod-
ucts, whilst the fresh ore was only slightly oxidized with
less than 5% sulfur from sulfide oxidation products. EDTA
extraction tests also showed a much higher amount of iron
oxidation products extracted from the oxidized ore.
Figure 1 (right) illustrates that gold recovery was much
higher for flotation of the fresh ore with a recovery of
85.6% at the end of flotation. Flotation of the oxidized ore
produced a gold recovery of only about 65.0%. The poor
flotation recovery of gold of oxidized ore is reasonable, con-
sidering that the gold is mainly associated with pyrite and
the oxidized ore has a large portion of oxidized sulfur which
corresponds to the oxidized pyrite and was difficult to float
as mentioned previously.
Overall, the finding from batch flotation test work
was consistent with the observation in the processing plant
where the poor flotation of total sulfur results in the poor
flotation of gold mainly associated with oxidized pyrite. In
order to improve gold flotation from the oxidized ore, it is
essential to improve the flotation performance of the oxi-
dized pyrite. In the next sections, gold flotation results were
not shown since the gold was contained in refractory pyrite
and the objective of the work was to improve the flotation
of oxidized pyrite and its associated gold.
Figure 1. Flotation performance of the fresh pyritic ore and the oxidized pyritic gold ore: sulfide sulfur and total sulfur grades
and recoveries (left) and gold grades and recoveries (right)