2206 XXXI International Mineral Processing Congress 2024 Proceedings/Washington, DC/Sep 29–Oct 3
removed the Cu-S species. It is important to note that PMS
itself is a medium-strong oxidant with E0 =1.82 V (Devi et
al., 2016 Wang and Wang, 2018). Hence, the addition of
PMS could oxidize Cu-S species.
When Fe ions were introduced with PMS after pyrite
was activated by Cu ions, the CV curve of pyrite changed
significantly. The presence of Fe ions, in addition to Cu
ions and PMS, transformed peak A2 to A2* with stronger
oxidation. This indicates that the co-presence of Fe ions
and PMS promoted reaction (2) of pyrite. Moreover, the
potential of A2 and C1 shifted negatively after adding 0.5
mM Fe ions, meaning that the presence of 0.5 mM Fe ions
allowed pyrite oxidation by PMS to occur at a less oxidizing
potential.
According to previous studies, Fe ion is an excellent
activator for PMS to produce a series of radicals, including
SO4•–, •OH and peroxymonosulfate anion (SO5•–) (Oh et
al., 2016 Wang and Wang, 2018):
Fe HSO Fe SO OH 2+
5
3+
4
•- "+++--(4)
•OH Fe HSO Fe SO 2+
5
3+
4
2- "+++-(5)
Fe HSO Fe SO H 3+
5
2+
5
•- "+++-+(6)
Among the three radicals produced by PMS, SO4•–and
•OH are two of the most potent oxidants in nature, with an
oxidation potential of up to 3.1 V. The production of these
radicals significantly oxidized the pyrite surface, includ-
ing the Cu-activating species, forming more hydrophilic
Fe(OH)3 and SO42– as indicated from the enhanced peak
(A2*) in Figure 2, leading to improved pyrite depression
when 500 g/t of PMS was added to the flotation pulp after
grinding.
In contrast, PMS promoted pyrite flotation when added
in the mill probably due to the reducing condition pro-
duced during grinding, especially when forged steel grind-
ing media were used. In this study, the Eh was – 40 mV
after grinding. As discussed previously, the reducing con-
ditions promote copper activation on pyrite. In addition,
Figure 2 shows that the oxidation of Cu-activated pyrite
occurred on an oxidizing condition at a potential greater
than 200 mV. Therefore, it is unlikely that PMS could oxi-
dize the Cu-activated pyrite during grinding. Furthermore,
the literature indicates that the radicals produced will wane
rapidly in a few microseconds (µs) without oxidizing (Wang
et al., 2021). As a result, even though some radicals were
produced during grinding, they could not sustain until the
flotation process.
Oxidation of Chalcopyrite by PMS
Figure 3 displays the CV curves of chalcopyrite, which
describe the effect of PMS and its combination with Fe ions
and PMS on chalcopyrite oxidation.
Figure 3 shows a strong anodic peak (A1) and a cathodic
peak (C1) regardless of the presence of Fe ions and PMS.
As reported in the literature, peak A1 is correlated to chal-
copyrite oxidation (Reaction (7)), while peak C1 at about
100 mV is the reduction of the Fe3+, Cu2+ and S0 (Hwang
et al., 2023 Zeng et al., 2020):
3H
3 3e
CuFeS O
CuS Fe^OH S H
2 2
3
0
)+
+++++-h
(7)
Figure 3. CV curves of chalcopyrite in the absence and presence of PMS and its
combination with Fe ions obtained in Borax solution at pH 9
removed the Cu-S species. It is important to note that PMS
itself is a medium-strong oxidant with E0 =1.82 V (Devi et
al., 2016 Wang and Wang, 2018). Hence, the addition of
PMS could oxidize Cu-S species.
When Fe ions were introduced with PMS after pyrite
was activated by Cu ions, the CV curve of pyrite changed
significantly. The presence of Fe ions, in addition to Cu
ions and PMS, transformed peak A2 to A2* with stronger
oxidation. This indicates that the co-presence of Fe ions
and PMS promoted reaction (2) of pyrite. Moreover, the
potential of A2 and C1 shifted negatively after adding 0.5
mM Fe ions, meaning that the presence of 0.5 mM Fe ions
allowed pyrite oxidation by PMS to occur at a less oxidizing
potential.
According to previous studies, Fe ion is an excellent
activator for PMS to produce a series of radicals, including
SO4•–, •OH and peroxymonosulfate anion (SO5•–) (Oh et
al., 2016 Wang and Wang, 2018):
Fe HSO Fe SO OH 2+
5
3+
4
•- "+++--(4)
•OH Fe HSO Fe SO 2+
5
3+
4
2- "+++-(5)
Fe HSO Fe SO H 3+
5
2+
5
•- "+++-+(6)
Among the three radicals produced by PMS, SO4•–and
•OH are two of the most potent oxidants in nature, with an
oxidation potential of up to 3.1 V. The production of these
radicals significantly oxidized the pyrite surface, includ-
ing the Cu-activating species, forming more hydrophilic
Fe(OH)3 and SO42– as indicated from the enhanced peak
(A2*) in Figure 2, leading to improved pyrite depression
when 500 g/t of PMS was added to the flotation pulp after
grinding.
In contrast, PMS promoted pyrite flotation when added
in the mill probably due to the reducing condition pro-
duced during grinding, especially when forged steel grind-
ing media were used. In this study, the Eh was – 40 mV
after grinding. As discussed previously, the reducing con-
ditions promote copper activation on pyrite. In addition,
Figure 2 shows that the oxidation of Cu-activated pyrite
occurred on an oxidizing condition at a potential greater
than 200 mV. Therefore, it is unlikely that PMS could oxi-
dize the Cu-activated pyrite during grinding. Furthermore,
the literature indicates that the radicals produced will wane
rapidly in a few microseconds (µs) without oxidizing (Wang
et al., 2021). As a result, even though some radicals were
produced during grinding, they could not sustain until the
flotation process.
Oxidation of Chalcopyrite by PMS
Figure 3 displays the CV curves of chalcopyrite, which
describe the effect of PMS and its combination with Fe ions
and PMS on chalcopyrite oxidation.
Figure 3 shows a strong anodic peak (A1) and a cathodic
peak (C1) regardless of the presence of Fe ions and PMS.
As reported in the literature, peak A1 is correlated to chal-
copyrite oxidation (Reaction (7)), while peak C1 at about
100 mV is the reduction of the Fe3+, Cu2+ and S0 (Hwang
et al., 2023 Zeng et al., 2020):
3H
3 3e
CuFeS O
CuS Fe^OH S H
2 2
3
0
)+
+++++-h
(7)
Figure 3. CV curves of chalcopyrite in the absence and presence of PMS and its
combination with Fe ions obtained in Borax solution at pH 9