3014 XXXI International Mineral Processing Congress 2024 Proceedings/Washington, DC/Sep 29–Oct 3
regulation by aeration with air, remarkable wavenumbers
were found at 155, 220 and 472 cm−1 when the stirring
time was prolonged from 1 min to 3 min, causing a slight
increase in Eh from about –300 to –298 mV .This find-
ing indicated that the generated polysulfides could stably
exist in alkaline and low-Eh pulp media. As illustrated in
Figure 6E-F, three pronounced characteristic peaks at about
155, 220 and 472 cm−1 of polysulfides could be distin-
guished in the filtrate of pulp stirred for 1 and 2 min. In the
sample stirred for 3 min, the peaks at about 155 and 220
cm−1 were not found in the Raman spectrum results of pulp
filtrate when Eh was regulated by aerating the pulp with air
(with 8.84 L/min aeration rate). The Eh rapidly increased
from about –300 mV to 7 mV when the aeration time was
extended from 1 min to 3 min. For the peak at 472 cm–1,
the intensity markedly weakened when the aeration time
was extended to 3 min or more, and the corresponding Eh
exceeded 0 mV the single wavenumber 472 cm–1 could be
due to SO3 2– or CO3 2–. The oxidation of polysulfides was
seen as one of the major reasons for the continuous decline
of DO within the start of Eh regulation during pyrite/pyr-
rhotite depression with lime. As the generated polysulfides
were completely oxidised by oxygen from the aerated air
and dissolved oxygen (DO) of pulp, they disappeared since
3 min. As such, DO rapidly recovered and increased sub-
sequently, supporting previous observed phenomena and
conclusions.
Effect of Polysulfides on Subsequent Cu-Activation
Cupric ion or copper hydroxide (Cu-OH) served as the
active constituents of CuSO4 during the activation of
sphalerite in acid or alkaline pulp. However, without Eh
regulation by aeration, the polysulfides generated in pyrite/
pyrrhotite depression stage were stable and rapidly con-
verted the active Cu-bearing species into the inactive cop-
per sulfide species such as CuS (shown as Reaction (1) and
(2)). In this regard, the pulp filtrate was obtained after
stirring for 3 min with lime and slowly added with 5%
CuSO4 solution. CuSO4 instantly reacted with the yellow
pulp filtrate containing S
n
2- ,forming brown precipitates,
whose main component was identified as CuS by XRD.
Without copper activation, sphalerite responds poorly to
xanthate collectors (Chandra and Gerson, 2009 Ejtemaei
and Nguyen, 2017 Laskowski et al., 1997 Zhang et al.,
2022), leading to unsatisfactory flotation results. After the
pulp was aerated for 3 min or more, S
n
2- was exhausted
and removed from the pulp before the addition of CuSO4,
which created a favourable pulp environment for CuSO4
activation and effectively activated the sphalerite flotation.
These findings explained the improvements in Zn-S selec-
tive flotation.
1hS S Cu CuS
n
2 2+ ".+^n +--(1)
S Cu CuS
n n
2 2+ ".+-(2)
0 200 400 600 800 1000 1200 1400 1600 1800 2000
C
B
180
1640 980
472
220
Wave Number (cm-1)
155
A
Figure 5. Raman spectrum results of pulp filtrate without or with lime: A-5% CaS
n (n=2~8), B-without lime (pH 6), C-with lime (pH 12). Permission from Li et al.
(2023b)
Intensity
(a.u.)
regulation by aeration with air, remarkable wavenumbers
were found at 155, 220 and 472 cm−1 when the stirring
time was prolonged from 1 min to 3 min, causing a slight
increase in Eh from about –300 to –298 mV .This find-
ing indicated that the generated polysulfides could stably
exist in alkaline and low-Eh pulp media. As illustrated in
Figure 6E-F, three pronounced characteristic peaks at about
155, 220 and 472 cm−1 of polysulfides could be distin-
guished in the filtrate of pulp stirred for 1 and 2 min. In the
sample stirred for 3 min, the peaks at about 155 and 220
cm−1 were not found in the Raman spectrum results of pulp
filtrate when Eh was regulated by aerating the pulp with air
(with 8.84 L/min aeration rate). The Eh rapidly increased
from about –300 mV to 7 mV when the aeration time was
extended from 1 min to 3 min. For the peak at 472 cm–1,
the intensity markedly weakened when the aeration time
was extended to 3 min or more, and the corresponding Eh
exceeded 0 mV the single wavenumber 472 cm–1 could be
due to SO3 2– or CO3 2–. The oxidation of polysulfides was
seen as one of the major reasons for the continuous decline
of DO within the start of Eh regulation during pyrite/pyr-
rhotite depression with lime. As the generated polysulfides
were completely oxidised by oxygen from the aerated air
and dissolved oxygen (DO) of pulp, they disappeared since
3 min. As such, DO rapidly recovered and increased sub-
sequently, supporting previous observed phenomena and
conclusions.
Effect of Polysulfides on Subsequent Cu-Activation
Cupric ion or copper hydroxide (Cu-OH) served as the
active constituents of CuSO4 during the activation of
sphalerite in acid or alkaline pulp. However, without Eh
regulation by aeration, the polysulfides generated in pyrite/
pyrrhotite depression stage were stable and rapidly con-
verted the active Cu-bearing species into the inactive cop-
per sulfide species such as CuS (shown as Reaction (1) and
(2)). In this regard, the pulp filtrate was obtained after
stirring for 3 min with lime and slowly added with 5%
CuSO4 solution. CuSO4 instantly reacted with the yellow
pulp filtrate containing S
n
2- ,forming brown precipitates,
whose main component was identified as CuS by XRD.
Without copper activation, sphalerite responds poorly to
xanthate collectors (Chandra and Gerson, 2009 Ejtemaei
and Nguyen, 2017 Laskowski et al., 1997 Zhang et al.,
2022), leading to unsatisfactory flotation results. After the
pulp was aerated for 3 min or more, S
n
2- was exhausted
and removed from the pulp before the addition of CuSO4,
which created a favourable pulp environment for CuSO4
activation and effectively activated the sphalerite flotation.
These findings explained the improvements in Zn-S selec-
tive flotation.
1hS S Cu CuS
n
2 2+ ".+^n +--(1)
S Cu CuS
n n
2 2+ ".+-(2)
0 200 400 600 800 1000 1200 1400 1600 1800 2000
C
B
180
1640 980
472
220
Wave Number (cm-1)
155
A
Figure 5. Raman spectrum results of pulp filtrate without or with lime: A-5% CaS
n (n=2~8), B-without lime (pH 6), C-with lime (pH 12). Permission from Li et al.
(2023b)
Intensity
(a.u.)