XXXI International Mineral Processing Congress 2024 Proceedings/Washington, DC/Sep 29–Oct 3 2203
is because inert grinding media is less electrochemically
active compared to forged steel grinding media and con-
sumes less oxygen in the mill, producing higher pulp Eh,
which is more effective in depressing pyrite in Cu flotation
(Peng et al., 2003). In recent years, due to mine depletion,
pyrite head grade in Cu ores has been increasing dramati-
cally from below 10% to above 18% and could reach as
high as 80% (Bakalarz, 2021 Lee et al., 2022) nonetheless,
inert grinding media becomes less effective when treating
high-pyrite-containing Cu ores. Lee and Peng (2023) dis-
covered that when coupled with a type of inert grinding
media, pyrite of a higher grade becomes more cathodic or
less oxidized, favouring copper activation. At the same time,
copper sulfides become more anodic or oxidized, leading to
depression. Hence, the depression of high-concentration
pyrite in Cu flotation requires stronger but more selective
oxidation on pyrite rather than copper sulfides.
In fact, radicals that are catalyzed by specific ions
may be developed as selective and strong oxidants. A wide
range of inorganic radicals produced from advanced oxi-
dation processes exists (Deng and Zhao, 2015 Ghanbari
and Moradi, 2017). Among the oxidants in nature, per-
oxymonosulfate (HSO5, – denoted as PMS) is a strong one
with a standard reduction potential (E0) of 1.82 V (Devi et
al., 2016 Wang and Wang, 2018). More importantly, PMS
can be catalyzed by Fe(OH)3 to produce sulfate radical
(SO4•–, E0 =2.5 – 3.1 V), and hydroxyl radical (•OH, E0 =
2.80), which are two of the most potent oxidants (Devi et
al., 2016 Ghanbari and Moradi, 2017 Matzek and Carter,
2016 Oh et al., 2016). The introduction of PMS in the
flotation system may selectively oxidize and depress pyrite
owing to the high Fe(OH)3 coverage on the pyrite surface
due to pyrite being a cathodic mineral on which oxygen
reduction takes place to produce OH– ions drawing iron
(Fe) ions (Ekmekçi and Demirel, 1997 Fuchida et al.,
2022). During flotation, the majority of Fe ions originate
from grinding media, and in the absence of grinding media,
the Fe(OH)3 on the pyrite surface may catalyze PMS to
produce radicals selectively oxidizing pyrite. During grind-
ing, due to the contact of grinding media with all minerals,
the selectivity of PMS may not be good.
In this paper, PMS was tested to selectively oxidize
and depress pyrite in Cu flotation. The depression ability
of PMS was first examined on an artificial Cu ore contain-
ing chalcopyrite (a typical primary copper sulfide mineral),
pyrite (an iron sulfide gangue mineral), and quartz (a com-
mon non-sulfide gangue mineral). The Cu and pyrite head
grades were fixed at 1.7 and 25%, respectively, in line with
the values in a high-pyrite-containing Cu ore processed by
an Australian Cu flotation plant. Pyrite depression by PMS
in Cu flotation was evaluated by adding the reagent during
grinding or flotation at different dosages. Electrochemical
measurements were also employed to identify the reactions
involving PMS on pyrite and chalcopyrite surfaces.
EXPERIMENTAL METHODOLOGY
Materials and Reagents
Chalcopyrite and pyrite samples were purchased from Geo
Discoveries, Australia and a quartz sample was sourced
from Nuway Landscape Supplies Paver &Wall Westerns,
Australia. All these samples have more than 95% purity
according to X-ray Diffraction and metal inductively cou-
pled plasma (ME-ICP) analyses. They were crushed by a
jaw crusher, followed by a roller crusher, and then screened
to acquire the particles between 0.6 and 3.35 mm in size
fractions. Crushed chalcopyrite and pyrite samples were
stored in a freezer (below 0°C) to avoid further oxidation.
Seven forged steel grinding media were used during the
grinding stage to produce Fe ions, which can catalyze PMS
to produce radicals.
PMS used in this study was purchased from
ChemSupply Australia Pty Ltd. I-propyl ethyl thionocarba-
mate (IPETC) and a polyfroth alcohol ethoxylates (W34)
were used in the flotation as the collector and frother,
respectively. Sodium hydroxide (NaOH) was used as a pH
regulator. In the electrochemical studies, the background
electrolyte consisted of 0.1 M sodium tetraborate decahy-
drate (Barax) and 0.1 M potassium chloride (KCl). Cu and
Fe ions were introduced to the electrolyte in the forms of
copper sulfate pentahydrate (CuSO4·5H2O) and ferrous
chloride tetrahydrate (FeCl2·4H2O), respectively, during
the electrochemical measurements.
Experiments
Grinding and Flotation Tests
A chalcopyrite-pyrite-quartz (Cpy-Py-Q) mixture was
made with 1.7% Cu and 25% pyrite. 1 kg of the mix-
ture and Brisbane tap water with pre-adjusted pH were
added into a laboratory stainless steel grinding mill with
seven forged steel grinding media at a two-to-one ratio
for grinding. PMS was added to the mill when required.
The grinding produced P80=106 µm with a pulp pH
value of 9. The mill discharge was transferred into a 1.5 L
laboratory mechanical flotation cell. The flotation cell was
topped up with Brisbane tap water to produce a pulp den-
sity of approximately 32%, and the pulp was agitated at
1000 rpm. The flotation pulp pH was maintained at pH 9.
PMS was then added to the pulp, if required, with 5 min of
conditioning. Then, 16.4 IPETC and 3.33 g/t W34 were
added subsequently with 3 min and 1 min of conditioning,
is because inert grinding media is less electrochemically
active compared to forged steel grinding media and con-
sumes less oxygen in the mill, producing higher pulp Eh,
which is more effective in depressing pyrite in Cu flotation
(Peng et al., 2003). In recent years, due to mine depletion,
pyrite head grade in Cu ores has been increasing dramati-
cally from below 10% to above 18% and could reach as
high as 80% (Bakalarz, 2021 Lee et al., 2022) nonetheless,
inert grinding media becomes less effective when treating
high-pyrite-containing Cu ores. Lee and Peng (2023) dis-
covered that when coupled with a type of inert grinding
media, pyrite of a higher grade becomes more cathodic or
less oxidized, favouring copper activation. At the same time,
copper sulfides become more anodic or oxidized, leading to
depression. Hence, the depression of high-concentration
pyrite in Cu flotation requires stronger but more selective
oxidation on pyrite rather than copper sulfides.
In fact, radicals that are catalyzed by specific ions
may be developed as selective and strong oxidants. A wide
range of inorganic radicals produced from advanced oxi-
dation processes exists (Deng and Zhao, 2015 Ghanbari
and Moradi, 2017). Among the oxidants in nature, per-
oxymonosulfate (HSO5, – denoted as PMS) is a strong one
with a standard reduction potential (E0) of 1.82 V (Devi et
al., 2016 Wang and Wang, 2018). More importantly, PMS
can be catalyzed by Fe(OH)3 to produce sulfate radical
(SO4•–, E0 =2.5 – 3.1 V), and hydroxyl radical (•OH, E0 =
2.80), which are two of the most potent oxidants (Devi et
al., 2016 Ghanbari and Moradi, 2017 Matzek and Carter,
2016 Oh et al., 2016). The introduction of PMS in the
flotation system may selectively oxidize and depress pyrite
owing to the high Fe(OH)3 coverage on the pyrite surface
due to pyrite being a cathodic mineral on which oxygen
reduction takes place to produce OH– ions drawing iron
(Fe) ions (Ekmekçi and Demirel, 1997 Fuchida et al.,
2022). During flotation, the majority of Fe ions originate
from grinding media, and in the absence of grinding media,
the Fe(OH)3 on the pyrite surface may catalyze PMS to
produce radicals selectively oxidizing pyrite. During grind-
ing, due to the contact of grinding media with all minerals,
the selectivity of PMS may not be good.
In this paper, PMS was tested to selectively oxidize
and depress pyrite in Cu flotation. The depression ability
of PMS was first examined on an artificial Cu ore contain-
ing chalcopyrite (a typical primary copper sulfide mineral),
pyrite (an iron sulfide gangue mineral), and quartz (a com-
mon non-sulfide gangue mineral). The Cu and pyrite head
grades were fixed at 1.7 and 25%, respectively, in line with
the values in a high-pyrite-containing Cu ore processed by
an Australian Cu flotation plant. Pyrite depression by PMS
in Cu flotation was evaluated by adding the reagent during
grinding or flotation at different dosages. Electrochemical
measurements were also employed to identify the reactions
involving PMS on pyrite and chalcopyrite surfaces.
EXPERIMENTAL METHODOLOGY
Materials and Reagents
Chalcopyrite and pyrite samples were purchased from Geo
Discoveries, Australia and a quartz sample was sourced
from Nuway Landscape Supplies Paver &Wall Westerns,
Australia. All these samples have more than 95% purity
according to X-ray Diffraction and metal inductively cou-
pled plasma (ME-ICP) analyses. They were crushed by a
jaw crusher, followed by a roller crusher, and then screened
to acquire the particles between 0.6 and 3.35 mm in size
fractions. Crushed chalcopyrite and pyrite samples were
stored in a freezer (below 0°C) to avoid further oxidation.
Seven forged steel grinding media were used during the
grinding stage to produce Fe ions, which can catalyze PMS
to produce radicals.
PMS used in this study was purchased from
ChemSupply Australia Pty Ltd. I-propyl ethyl thionocarba-
mate (IPETC) and a polyfroth alcohol ethoxylates (W34)
were used in the flotation as the collector and frother,
respectively. Sodium hydroxide (NaOH) was used as a pH
regulator. In the electrochemical studies, the background
electrolyte consisted of 0.1 M sodium tetraborate decahy-
drate (Barax) and 0.1 M potassium chloride (KCl). Cu and
Fe ions were introduced to the electrolyte in the forms of
copper sulfate pentahydrate (CuSO4·5H2O) and ferrous
chloride tetrahydrate (FeCl2·4H2O), respectively, during
the electrochemical measurements.
Experiments
Grinding and Flotation Tests
A chalcopyrite-pyrite-quartz (Cpy-Py-Q) mixture was
made with 1.7% Cu and 25% pyrite. 1 kg of the mix-
ture and Brisbane tap water with pre-adjusted pH were
added into a laboratory stainless steel grinding mill with
seven forged steel grinding media at a two-to-one ratio
for grinding. PMS was added to the mill when required.
The grinding produced P80=106 µm with a pulp pH
value of 9. The mill discharge was transferred into a 1.5 L
laboratory mechanical flotation cell. The flotation cell was
topped up with Brisbane tap water to produce a pulp den-
sity of approximately 32%, and the pulp was agitated at
1000 rpm. The flotation pulp pH was maintained at pH 9.
PMS was then added to the pulp, if required, with 5 min of
conditioning. Then, 16.4 IPETC and 3.33 g/t W34 were
added subsequently with 3 min and 1 min of conditioning,