2374 XXXI International Mineral Processing Congress 2024 Proceedings/Washington, DC/Sep 29–Oct 3
grinding and flotation tests with the addition of copper
ions but without sulfidization were also tested. Figure 3
shows these results.
Figure 3 shows a total sulfur recovery of 36.2% and
57.8% at the end of flotation with the addition of 200 g/t
Cu(II) and Cu(I) during grinding without subsequent
sulfidization, respectively. Compared to the baseline flota-
tion of the oxidized ore producing a total sulfur recovery
of 45.7% at the end of flotation without sulfidization, the
addition of Cu(II) (in the absence of sulfidization) in fact
decreased total sulfur recovery, but the addition of Cu(I)
(in the absence of sulfidization) increased total sulfur recov-
ery. Obviously, Cu(II) had a depressing effect on oxidized
pyrite, but Cu(I) had an activating effect without sulfidi-
zation. With sulfidization, the addition of 200 g/t Cu(II)
increased total sulfur recovery to 62.8%, while the addition
of 200 g/t Cu(I) (with sulfidization) increased total sulfur
recovery to 68.4%. Compared to a total sulfur recovery of
55.4% achieved by sulfidization at –300 mV alone, sul-
fidization resulted in Cu(II) behaving as an activator in the
flotation of oxidized pyrite, while enhancing the activating
role of Cu(I).
Flotation results so far indicated that conventional
potential control sulfidization was still beneficial to the flo-
tation of the oxidized pyritic gold ore, but that the ben-
efit was limited. The addition of Cu(II) during grinding
in conjunction with potential control sulfidization further
improved the flotation of the oxidized pyrite. It was inter-
esting that Cu(I) behaved differently to Cu(II) when added
during grinding in conjunction with potential control sul-
fidization, providing the best opportunity to improve flota-
tion of the oxidized ore. It was expected that a new metal
sulfide phase was formed on oxidized pyrite surfaces during
sulfidization when copper ions especially Cu(I) ions were
present, which facilitated collector adsorption. This aspect
was investigated by electrochemical studies as presented in
the next section.
Formation of Copper Sulfide on Oxidized
Pyrite Surfaces
Formation of Cu(I)S on Pyrite Surfaces Without
Sulfidization
The electrochemical study started with CV test work
on fresh pyrite in the presence of Cu(II) ions to establish
the peak for the newly formed Cu(I)S. It is well known
that Cu(II) ions can easily activate fresh pyrite by forming
Cu(I)S (von Oertzen et al., 2007). Figure 4 shows the cyclic
voltammograms of fresh pyrite and oxidized pyrite in the
presence of Cu(II) ions. The oxidized pyrite was obtained
by polarizing the fresh pyrite at 700 mV for 600 seconds
as established previously by Huai and Peng (2020). The
CV scan in this work was initialized in a positive direction
from the open circuit potential (OCP) of pyrite to ensure
the initial oxidation of possibly formed Cu(I)S. As shown
in Figure 4, an anodic peak A1 and a cathodic peak C1
appeared on the cyclic voltammogram of fresh pyrite in the
presence of Cu(II) ions. The appearance of Peak A1 indi-
cates the formation of Cu(I)S which was oxidized during
the anodic scan through Reactions (2) and (3) (Hicyilmat et
al., 2004). The reverse of the scan from positive to negative
produced Peak C1, attributed to the reverse of Reactions
(2) and (3). On oxidized pyrite, Peaks A1 and C1 did not
appear although the same amount of Cu(II) ions was pres-
ent. Instead, a cathodic peak C2 and an anodic peak A2
appeared. Peak C2 indicates the existence of ferric oxide/
hydroxide which was electrochemically reduced through
Figure 3. Total sulfur grade as a function of total sulfur recovery with the addition of copper ions during grinding with and
without subsequent sulfidization at –300 mV: the addition of Cu (II) ions (left) and the addition of Cu (I) ions (right)
grinding and flotation tests with the addition of copper
ions but without sulfidization were also tested. Figure 3
shows these results.
Figure 3 shows a total sulfur recovery of 36.2% and
57.8% at the end of flotation with the addition of 200 g/t
Cu(II) and Cu(I) during grinding without subsequent
sulfidization, respectively. Compared to the baseline flota-
tion of the oxidized ore producing a total sulfur recovery
of 45.7% at the end of flotation without sulfidization, the
addition of Cu(II) (in the absence of sulfidization) in fact
decreased total sulfur recovery, but the addition of Cu(I)
(in the absence of sulfidization) increased total sulfur recov-
ery. Obviously, Cu(II) had a depressing effect on oxidized
pyrite, but Cu(I) had an activating effect without sulfidi-
zation. With sulfidization, the addition of 200 g/t Cu(II)
increased total sulfur recovery to 62.8%, while the addition
of 200 g/t Cu(I) (with sulfidization) increased total sulfur
recovery to 68.4%. Compared to a total sulfur recovery of
55.4% achieved by sulfidization at –300 mV alone, sul-
fidization resulted in Cu(II) behaving as an activator in the
flotation of oxidized pyrite, while enhancing the activating
role of Cu(I).
Flotation results so far indicated that conventional
potential control sulfidization was still beneficial to the flo-
tation of the oxidized pyritic gold ore, but that the ben-
efit was limited. The addition of Cu(II) during grinding
in conjunction with potential control sulfidization further
improved the flotation of the oxidized pyrite. It was inter-
esting that Cu(I) behaved differently to Cu(II) when added
during grinding in conjunction with potential control sul-
fidization, providing the best opportunity to improve flota-
tion of the oxidized ore. It was expected that a new metal
sulfide phase was formed on oxidized pyrite surfaces during
sulfidization when copper ions especially Cu(I) ions were
present, which facilitated collector adsorption. This aspect
was investigated by electrochemical studies as presented in
the next section.
Formation of Copper Sulfide on Oxidized
Pyrite Surfaces
Formation of Cu(I)S on Pyrite Surfaces Without
Sulfidization
The electrochemical study started with CV test work
on fresh pyrite in the presence of Cu(II) ions to establish
the peak for the newly formed Cu(I)S. It is well known
that Cu(II) ions can easily activate fresh pyrite by forming
Cu(I)S (von Oertzen et al., 2007). Figure 4 shows the cyclic
voltammograms of fresh pyrite and oxidized pyrite in the
presence of Cu(II) ions. The oxidized pyrite was obtained
by polarizing the fresh pyrite at 700 mV for 600 seconds
as established previously by Huai and Peng (2020). The
CV scan in this work was initialized in a positive direction
from the open circuit potential (OCP) of pyrite to ensure
the initial oxidation of possibly formed Cu(I)S. As shown
in Figure 4, an anodic peak A1 and a cathodic peak C1
appeared on the cyclic voltammogram of fresh pyrite in the
presence of Cu(II) ions. The appearance of Peak A1 indi-
cates the formation of Cu(I)S which was oxidized during
the anodic scan through Reactions (2) and (3) (Hicyilmat et
al., 2004). The reverse of the scan from positive to negative
produced Peak C1, attributed to the reverse of Reactions
(2) and (3). On oxidized pyrite, Peaks A1 and C1 did not
appear although the same amount of Cu(II) ions was pres-
ent. Instead, a cathodic peak C2 and an anodic peak A2
appeared. Peak C2 indicates the existence of ferric oxide/
hydroxide which was electrochemically reduced through
Figure 3. Total sulfur grade as a function of total sulfur recovery with the addition of copper ions during grinding with and
without subsequent sulfidization at –300 mV: the addition of Cu (II) ions (left) and the addition of Cu (I) ions (right)