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Selectively Oxidizing and Depressing High-Concentration Pyrite
in Copper Flotation
Richard Li Jie Lee, Yongjun Peng
School of Chemical Engineering, The University of Queensland Australia
ABSTRACT: Pyrite is an iron sulfide gangue mineral to be depressed in copper (Cu) flotation. With the
depletion of high-grade Cu ores and the increasing demand for Cu globally, Cu concentrators are processing
high-pyrite-containing ores, and pyrite depression has been challenging due to strong copper activation on
pyrite and unselective mineral oxidation produced by conventional pyrite depression methods. For the first
time, this research developed a new pyrite depression method which selectively and strongly oxidized pyrite
with limited effects on chalcopyrite during flotation. This method explored the unique capability of potassium
peroxymonosulfate (PMS), which can produce hydroxyl (•OH, E0 =2.8 V) and sulfate (SO4•–, 2.5 V E0
3.1 V) radicals, strong oxidants, catalyzed by iron ions. Flotation tests indicated that the addition of 500 g/t
PMS in the flotation cell strongly depressed high-concentration pyrite in chalcopyrite flotation while improving
chalcopyrite flotation. This is because the radicals were generated on pyrite, a cathodic mineral on which iron
ions were drawn, and oxidized the pyrite surface including the copper-activating species. At the same time,
mild oxidation occurred on the chalcopyrite surface, producing hydrophobic sulfur oxidation products which
are beneficial to chalcopyrite flotation. However, the addition of 500 g/t PMS in the mill improved both
chalcopyrite and pyrite flotation without showing a selectivity. This is because the reducing grinding condition
limited the production of radicals, promoting copper activation on the pyrite surface and also preventing
chalcopyrite from being overly oxidized. The research recommends a new method be applied in the selective
flotation of base metal sulfide minerals against pyrite.
INTRODUCTION
Pyrite (FeS2) is one of the most common sulfide gangue
minerals that need to be rejected in copper (Cu) flotation
if not associated with any precious elements such as gold
or silver (Bicak et al., 2007 Chandra and Gerson, 2010).
Depression of pyrite in Cu flotation is difficult owing to
copper activation, a process where Cu(II) produced from
the oxidation of Cu sulfides is reduced to Cu(I) which
interacts with sulfur content from pyrite to form a Cu-S
entity (Mu et al., 2016). Consequently, Cu flotation collec-
tors are able to adsorb on the surface of Cu-activated pyrite
via Cu-S, resulting in enhanced pyrite flotation and dilu-
tion of flotation concentrates. To effectively depress pyrite
in Cu flotation, copper activation must be minimized.
Copper activation on pyrite surface in flotation can be
restricted by promoting pyrite oxidation to form hydro-
philic species (e.g., iron hydroxides, Fe(OH)2,3 and sulfate
ions, SO42–) and oxidizing Cu-S species on pyrite surface
(Peng et al., 2012), which can be accomplished via creating
an oxidizing redox environment (high Eh) in the mill and
flotation cell (Owusu et al., 2013). In practice, inert grind-
ing media are employed to produce an oxidizing pulp. This
Selectively Oxidizing and Depressing High-Concentration Pyrite
in Copper Flotation
Richard Li Jie Lee, Yongjun Peng
School of Chemical Engineering, The University of Queensland Australia
ABSTRACT: Pyrite is an iron sulfide gangue mineral to be depressed in copper (Cu) flotation. With the
depletion of high-grade Cu ores and the increasing demand for Cu globally, Cu concentrators are processing
high-pyrite-containing ores, and pyrite depression has been challenging due to strong copper activation on
pyrite and unselective mineral oxidation produced by conventional pyrite depression methods. For the first
time, this research developed a new pyrite depression method which selectively and strongly oxidized pyrite
with limited effects on chalcopyrite during flotation. This method explored the unique capability of potassium
peroxymonosulfate (PMS), which can produce hydroxyl (•OH, E0 =2.8 V) and sulfate (SO4•–, 2.5 V E0
3.1 V) radicals, strong oxidants, catalyzed by iron ions. Flotation tests indicated that the addition of 500 g/t
PMS in the flotation cell strongly depressed high-concentration pyrite in chalcopyrite flotation while improving
chalcopyrite flotation. This is because the radicals were generated on pyrite, a cathodic mineral on which iron
ions were drawn, and oxidized the pyrite surface including the copper-activating species. At the same time,
mild oxidation occurred on the chalcopyrite surface, producing hydrophobic sulfur oxidation products which
are beneficial to chalcopyrite flotation. However, the addition of 500 g/t PMS in the mill improved both
chalcopyrite and pyrite flotation without showing a selectivity. This is because the reducing grinding condition
limited the production of radicals, promoting copper activation on the pyrite surface and also preventing
chalcopyrite from being overly oxidized. The research recommends a new method be applied in the selective
flotation of base metal sulfide minerals against pyrite.
INTRODUCTION
Pyrite (FeS2) is one of the most common sulfide gangue
minerals that need to be rejected in copper (Cu) flotation
if not associated with any precious elements such as gold
or silver (Bicak et al., 2007 Chandra and Gerson, 2010).
Depression of pyrite in Cu flotation is difficult owing to
copper activation, a process where Cu(II) produced from
the oxidation of Cu sulfides is reduced to Cu(I) which
interacts with sulfur content from pyrite to form a Cu-S
entity (Mu et al., 2016). Consequently, Cu flotation collec-
tors are able to adsorb on the surface of Cu-activated pyrite
via Cu-S, resulting in enhanced pyrite flotation and dilu-
tion of flotation concentrates. To effectively depress pyrite
in Cu flotation, copper activation must be minimized.
Copper activation on pyrite surface in flotation can be
restricted by promoting pyrite oxidation to form hydro-
philic species (e.g., iron hydroxides, Fe(OH)2,3 and sulfate
ions, SO42–) and oxidizing Cu-S species on pyrite surface
(Peng et al., 2012), which can be accomplished via creating
an oxidizing redox environment (high Eh) in the mill and
flotation cell (Owusu et al., 2013). In practice, inert grind-
ing media are employed to produce an oxidizing pulp. This