XXXI International Mineral Processing Congress 2024 Proceedings/Washington, DC/Sep 29–Oct 3 2213
et al., 2020). Pyrite floatability may be controlled in selec-
tive flotation of complex sulfide ores via adjusting the pulp
potential by oxygen purging during grinding (Altun, 2010
Moslemi &Gharabaghi, 2017).
When the electrochemical potential increases, pyrite
can be activated through either dissolved copper (Cu) or
lead (Pb) ions or be depressed through the formation of
hydrophilic complexes (Iron oxyhydroxides). Changes in
electrochemical potential also have a negative impact on the
adsorption of xanthate on both activated and non-activated
surfaces, highlighting the importance of optimizing elec-
trochemical conditions is therefore, very important. The
intensity of these electrochemical interactions is influenced
by factors such as pH, solid percentage, particle size dis-
tribution, flotation time, reagent type and concentration,
oxygen content, and grinding conditions (Altun, 2010).
Furthermore, electrical characteristics at the pyrite-
water interface impact its floatability as it impacts its inter-
action with reagents and ions in the flotation pulp and
therefore, hydrophobic-hydrophilic properties (Fuerstenau
et al., 2009). Fresh pyrite is negatively charged, however,
when exposed to oxygen, water, pH change, and surfac-
tants, its surface charge change due to the formation of
various species on its surface which consequently affects
its hydrophobicity (Fuerstenau et al., 2009 Parks, 1965).
The hydrophilic and hydrophobic species that form as a
result of pH change are formed due to electrochemical reac-
tions. Depending on the extent of the oxidation process
on the sulfide mineral (DS), partial oxidation will produce
low metal sulfides such as (D1–nS), polysulfide (Dn2–), or
elemental sulfur (S0), which will render the pyrite surface
hydrophobic and consequently lead to its flotation with-
out any interaction with collector (Castellón et al., 2022
Moslemi &Gharabaghi, 2017). Equation (1) shows sul-
fide’s surface reactions in acidic conditions where metal
ions (nD2+) move to the surface of the mineral and sub-
sequently dissolve in solution, leaving behind a sulfur-rich
mineral surface that is hydrophobic (Castellón et al., 2022).
The pyrite reactions that occur are generated using
Eh-pH measurements from pyrite in aqueous solutions
with elemental sulfur as metastable phase. Generating sta-
bility boundaries for different chemical species present in
the solution when their concentration is 10–4 mol/L in a
collector-less flotation of pyrite (Castellón et al., 2022).
The reactions occur as follows:
DS 2nH 2
n O D S nD nH O
2 1 n
2+
2 )+++++
-(1)
At conditions above a pH of 7, the ions shown in equa-
tion (1) react with oxygen and water to produce a metal
hydroxide layer which is hydrophilic. This is demonstrated
in equation (2):
DS H O 2
1 O D S nD(OH)
2 2 1 n 2 )+++
-(2)
Complete oxidation leads to the formation of sulphates
and metal hydroxides which are hydrophilic complexes
that favor the depression of pyrite. And this is shown by
equation (3) and (4) (Castellón et al., 2022 Moslemi &
Gharabaghi, 2017).
FeS 3H O Fe S O 6H 6e E
0.344 0.059pHhV
2 2
2+
2 3
2-
h "++++
=-
+-
^
(3)
FeS2 6H2O Fe^OHh3 S O
9H 7e E
0.076pHhV
2 3
2-
h
"++
++
=-
+-
^0.48
(4)
Increasing pH of the solution leads to a higher rate
of precipitation of ferric hydroxide as a protective coat-
ing on the pyrite surface, which prevents further oxidation
of pyrite (Moslemi &Gharabaghi, 2017 Nakhaei et al.,
2023).
Additionally, the pulp pH has a substantial effect on
floatability of pyrite (Jiang et al., 2023). Pyrite naturally
floats at acidic pH due to the formation of sulfur rich
and Fe-deficient hydrophobic species (Ozun et al., 2019).
Conversely, as the pH increases, floatability decreases due
to the formation of hydrophilic Fe-hydroxides and/or sul-
phoxy species at neutral and alkaline pH. The formation of
hydrophobic and hydrophilic compounds at different pH
is substantiated by research on contact angle measurements
by (Jiang et al., 2023) where it has been shown that under
acidic conditions at pH =2, the contact angle of pyrite
is approximately (63.0°) and as the pH increases from 2.0
to 7.0, the contact angle decreases to (57.0°). As pH fur-
ther increases to 12.0, a notable decrease in contact angle is
observed (39.0°).
Flotation of pyrite is also impacted by interaction with
surfactants such as xanthates which are commonly used
as collectors. Xanthate reverses the positive surface charge
of pyrite in acidic pH pulps, making it more negative at
neutral and alkaline pH with increasing xanthate con-
centration (Bulut et al., 2004). Although the majority of
research conducted on pyrite flotation using xanthate has
consistently shown that the primary hydrophobic surface
species is dixanthogen, it is important to note that fur-
ther investigations can reveal additional surface species
(Moslemi &Gharabaghi, 2017). Ferric xanthate (FeX3)
and ferric-hydroxy xanthate (FeOHX2) and (Fe(OH)2X)
are additional hydrophobic complexes that are anticipated
et al., 2020). Pyrite floatability may be controlled in selec-
tive flotation of complex sulfide ores via adjusting the pulp
potential by oxygen purging during grinding (Altun, 2010
Moslemi &Gharabaghi, 2017).
When the electrochemical potential increases, pyrite
can be activated through either dissolved copper (Cu) or
lead (Pb) ions or be depressed through the formation of
hydrophilic complexes (Iron oxyhydroxides). Changes in
electrochemical potential also have a negative impact on the
adsorption of xanthate on both activated and non-activated
surfaces, highlighting the importance of optimizing elec-
trochemical conditions is therefore, very important. The
intensity of these electrochemical interactions is influenced
by factors such as pH, solid percentage, particle size dis-
tribution, flotation time, reagent type and concentration,
oxygen content, and grinding conditions (Altun, 2010).
Furthermore, electrical characteristics at the pyrite-
water interface impact its floatability as it impacts its inter-
action with reagents and ions in the flotation pulp and
therefore, hydrophobic-hydrophilic properties (Fuerstenau
et al., 2009). Fresh pyrite is negatively charged, however,
when exposed to oxygen, water, pH change, and surfac-
tants, its surface charge change due to the formation of
various species on its surface which consequently affects
its hydrophobicity (Fuerstenau et al., 2009 Parks, 1965).
The hydrophilic and hydrophobic species that form as a
result of pH change are formed due to electrochemical reac-
tions. Depending on the extent of the oxidation process
on the sulfide mineral (DS), partial oxidation will produce
low metal sulfides such as (D1–nS), polysulfide (Dn2–), or
elemental sulfur (S0), which will render the pyrite surface
hydrophobic and consequently lead to its flotation with-
out any interaction with collector (Castellón et al., 2022
Moslemi &Gharabaghi, 2017). Equation (1) shows sul-
fide’s surface reactions in acidic conditions where metal
ions (nD2+) move to the surface of the mineral and sub-
sequently dissolve in solution, leaving behind a sulfur-rich
mineral surface that is hydrophobic (Castellón et al., 2022).
The pyrite reactions that occur are generated using
Eh-pH measurements from pyrite in aqueous solutions
with elemental sulfur as metastable phase. Generating sta-
bility boundaries for different chemical species present in
the solution when their concentration is 10–4 mol/L in a
collector-less flotation of pyrite (Castellón et al., 2022).
The reactions occur as follows:
DS 2nH 2
n O D S nD nH O
2 1 n
2+
2 )+++++
-(1)
At conditions above a pH of 7, the ions shown in equa-
tion (1) react with oxygen and water to produce a metal
hydroxide layer which is hydrophilic. This is demonstrated
in equation (2):
DS H O 2
1 O D S nD(OH)
2 2 1 n 2 )+++
-(2)
Complete oxidation leads to the formation of sulphates
and metal hydroxides which are hydrophilic complexes
that favor the depression of pyrite. And this is shown by
equation (3) and (4) (Castellón et al., 2022 Moslemi &
Gharabaghi, 2017).
FeS 3H O Fe S O 6H 6e E
0.344 0.059pHhV
2 2
2+
2 3
2-
h "++++
=-
+-
^
(3)
FeS2 6H2O Fe^OHh3 S O
9H 7e E
0.076pHhV
2 3
2-
h
"++
++
=-
+-
^0.48
(4)
Increasing pH of the solution leads to a higher rate
of precipitation of ferric hydroxide as a protective coat-
ing on the pyrite surface, which prevents further oxidation
of pyrite (Moslemi &Gharabaghi, 2017 Nakhaei et al.,
2023).
Additionally, the pulp pH has a substantial effect on
floatability of pyrite (Jiang et al., 2023). Pyrite naturally
floats at acidic pH due to the formation of sulfur rich
and Fe-deficient hydrophobic species (Ozun et al., 2019).
Conversely, as the pH increases, floatability decreases due
to the formation of hydrophilic Fe-hydroxides and/or sul-
phoxy species at neutral and alkaline pH. The formation of
hydrophobic and hydrophilic compounds at different pH
is substantiated by research on contact angle measurements
by (Jiang et al., 2023) where it has been shown that under
acidic conditions at pH =2, the contact angle of pyrite
is approximately (63.0°) and as the pH increases from 2.0
to 7.0, the contact angle decreases to (57.0°). As pH fur-
ther increases to 12.0, a notable decrease in contact angle is
observed (39.0°).
Flotation of pyrite is also impacted by interaction with
surfactants such as xanthates which are commonly used
as collectors. Xanthate reverses the positive surface charge
of pyrite in acidic pH pulps, making it more negative at
neutral and alkaline pH with increasing xanthate con-
centration (Bulut et al., 2004). Although the majority of
research conducted on pyrite flotation using xanthate has
consistently shown that the primary hydrophobic surface
species is dixanthogen, it is important to note that fur-
ther investigations can reveal additional surface species
(Moslemi &Gharabaghi, 2017). Ferric xanthate (FeX3)
and ferric-hydroxy xanthate (FeOHX2) and (Fe(OH)2X)
are additional hydrophobic complexes that are anticipated