2124 XXXI International Mineral Processing Congress 2024 Proceedings/Washington, DC/Sep 29–Oct 3
waste seems to be a good alternative. However, reprocess-
ing waste means consuming more reagents, energy, and
water (Adrianto et al., 2023 Araya et al., 2021). Several
studies have been carried out related to the bulk flotation
of tailings that already contain acidifying species known as
desulfurization (Benzaazoua et al., 2017, 2000 Nadeif et
al., 2019 Skandrani et al., 2019). For example, Skandrani
et al. (2019) carried out the desulfurization of gold tail-
ings. They identified that the abandoned tailings had
some problems related to the formation of layers on top
of sulfide minerals. These layers allowed a poor affinity of
the sulfide minerals with the collector, reducing flotation
performance. Consequently, they implemented mechani-
cal treatments such as grinding, agitation, and attrition to
remove the oxidized species formed and activate the sur-
face of the sulfide mineral. After this procedure, they dem-
onstrated that it is possible to produce a concentrate rich
in sulfides and gold. Furthermore, the desulphurized tail-
ings did not generate acid due to their high neutralization
potential. However, they conclude that various pretreat-
ments should be used to remove oxidized species formed
on the surfaces of sulfide minerals to improve desulfuriza-
tion performance. Therefore, this aspect makes its repro-
cessing difficult because the desulfurization flotation circuit
requires another crushing stage, which increases energy
consumption and operating costs.
Therefore, this work proposes to carry out the desul-
furization process in an early stage of the flotation process,
called “In-process technology”. This methodology enables
to eliminate the species responsible for AMD in an early
stage if the flotation process and generate a tailing free of
acidifying species. Additionally, this methodology allows
for better control all the physicochemical interactions
that occur between the sulfide minerals and the reagents.
In addition, it enables optimizing the required amount of
each reagent, as well as the order of addition of the reagents,
allowing better control of the pulp potential and, therefore,
achieving a more efficient flotation process with a cleaner
production perspective. However, the bulk concentrate
obtained from desulfurization is challenging from a phys-
ical-chemical point of view since an alternative procedure
is required to selectively separate the pyrite that has already
been floated from the copper sulphide minerals. Since
pyrite is the most common and widely studied metal sul-
fide, it is useful to review the chemistry of pyrite as a start-
ing point for understanding its behavior and evaluating its
environmental impact. The behavior of pyrite depends on
the control of the pulp potential. Pulp potential is strongly
affected by oxidation level and pH. Thus, these parameters
are responsible for pyrite flotation (Cruz et al., 2021
Moslemi and Gharabaghi, 2017).
The oxidation of pyrite comprises a very complex pro-
cess that involves several electrochemical reactions. The
most important reactions in the oxidation of pyrite are the
formation of ions such as Fe2+ and SO42– after the complete
oxidation of pyrite, represented by equation 1 (Egiebor &
Oni, 2007). However, Fe2+ could be further oxidized, pro-
ducing more reactions (equations 2 and 3) (Chernyshova,
2003 Janzen et al., 2000). The third equation shows the
formation of ferric hydroxide, which can precipitate and is
responsible for the depression of pyrite due to the forma-
tion of a passivation layer on the pyrite surface.
FeS2 +3.5 O2 +H2O → Fe2++2SO42−+2H+ (1)
Fe2++ 0.25 O2 +H+→ Fe3+ +0.5 H2O (2)
Fe3++3 H2O→ Fe(OH)3+3H+ (3)
Regarding the effect of pH, it is worth mentioning that
this phenomenon becomes more critical with an increase
in pH. At very acidic pH it can be observed that pyrite
has a natural floatability due to the formation of elemental
sulfur (S0). However, the formation of elemental sulfur (S0)
occurs in a narrow potential range. Then, at higher poten-
tial the SO42− is formed, which affects the natural floatabil-
ity of pyrite. On the other hand, analyzing the floatability
of pyrite at alkaline pH, it can be identified that the spe-
cies formed Fe(OH)3 and SO42− after the oxidation process
become more abundant. Therefore, the formation rate and
stability of these hydrophilic species are strongly dependent
on pH. Fe(OH)3 is electrochemically very stable, forming
passivation of the pyrite surface. Thus, alkaline pH inhib-
its the pyrite floatability (Cruz et al., 2021 Moslemi and
Gharabaghi, 2017).
Pyrite depression has been studied extensively because
pyrite must be separated from copper sulfides. Therefore,
other methods than pH adjustment are implemented to
carry out pyrite depression. For instance, organic and inor-
ganic reagents (Cai et al., 2022 Chapagai et al., 2023). Mu
et al. (2016), present a review of fundamental pyrite depres-
sion studies and common reagents used. Inorganic depres-
sants such as pH modifiers, oxidants, cyanide and sulfoxyl,
and organic depressants including polysaccharide polymers
(starch, dextrin, guar gum, carboxymethylcellulose, and
chitosan), lignosulfonate, polyacrylamides, and diethylene-
triamine are used (Ahmadi et al., 2018 Bulatovic, 1999).
Currently, because organic depressants are biodegrad-
able, they have been used as an environmentally friendly
waste seems to be a good alternative. However, reprocess-
ing waste means consuming more reagents, energy, and
water (Adrianto et al., 2023 Araya et al., 2021). Several
studies have been carried out related to the bulk flotation
of tailings that already contain acidifying species known as
desulfurization (Benzaazoua et al., 2017, 2000 Nadeif et
al., 2019 Skandrani et al., 2019). For example, Skandrani
et al. (2019) carried out the desulfurization of gold tail-
ings. They identified that the abandoned tailings had
some problems related to the formation of layers on top
of sulfide minerals. These layers allowed a poor affinity of
the sulfide minerals with the collector, reducing flotation
performance. Consequently, they implemented mechani-
cal treatments such as grinding, agitation, and attrition to
remove the oxidized species formed and activate the sur-
face of the sulfide mineral. After this procedure, they dem-
onstrated that it is possible to produce a concentrate rich
in sulfides and gold. Furthermore, the desulphurized tail-
ings did not generate acid due to their high neutralization
potential. However, they conclude that various pretreat-
ments should be used to remove oxidized species formed
on the surfaces of sulfide minerals to improve desulfuriza-
tion performance. Therefore, this aspect makes its repro-
cessing difficult because the desulfurization flotation circuit
requires another crushing stage, which increases energy
consumption and operating costs.
Therefore, this work proposes to carry out the desul-
furization process in an early stage of the flotation process,
called “In-process technology”. This methodology enables
to eliminate the species responsible for AMD in an early
stage if the flotation process and generate a tailing free of
acidifying species. Additionally, this methodology allows
for better control all the physicochemical interactions
that occur between the sulfide minerals and the reagents.
In addition, it enables optimizing the required amount of
each reagent, as well as the order of addition of the reagents,
allowing better control of the pulp potential and, therefore,
achieving a more efficient flotation process with a cleaner
production perspective. However, the bulk concentrate
obtained from desulfurization is challenging from a phys-
ical-chemical point of view since an alternative procedure
is required to selectively separate the pyrite that has already
been floated from the copper sulphide minerals. Since
pyrite is the most common and widely studied metal sul-
fide, it is useful to review the chemistry of pyrite as a start-
ing point for understanding its behavior and evaluating its
environmental impact. The behavior of pyrite depends on
the control of the pulp potential. Pulp potential is strongly
affected by oxidation level and pH. Thus, these parameters
are responsible for pyrite flotation (Cruz et al., 2021
Moslemi and Gharabaghi, 2017).
The oxidation of pyrite comprises a very complex pro-
cess that involves several electrochemical reactions. The
most important reactions in the oxidation of pyrite are the
formation of ions such as Fe2+ and SO42– after the complete
oxidation of pyrite, represented by equation 1 (Egiebor &
Oni, 2007). However, Fe2+ could be further oxidized, pro-
ducing more reactions (equations 2 and 3) (Chernyshova,
2003 Janzen et al., 2000). The third equation shows the
formation of ferric hydroxide, which can precipitate and is
responsible for the depression of pyrite due to the forma-
tion of a passivation layer on the pyrite surface.
FeS2 +3.5 O2 +H2O → Fe2++2SO42−+2H+ (1)
Fe2++ 0.25 O2 +H+→ Fe3+ +0.5 H2O (2)
Fe3++3 H2O→ Fe(OH)3+3H+ (3)
Regarding the effect of pH, it is worth mentioning that
this phenomenon becomes more critical with an increase
in pH. At very acidic pH it can be observed that pyrite
has a natural floatability due to the formation of elemental
sulfur (S0). However, the formation of elemental sulfur (S0)
occurs in a narrow potential range. Then, at higher poten-
tial the SO42− is formed, which affects the natural floatabil-
ity of pyrite. On the other hand, analyzing the floatability
of pyrite at alkaline pH, it can be identified that the spe-
cies formed Fe(OH)3 and SO42− after the oxidation process
become more abundant. Therefore, the formation rate and
stability of these hydrophilic species are strongly dependent
on pH. Fe(OH)3 is electrochemically very stable, forming
passivation of the pyrite surface. Thus, alkaline pH inhib-
its the pyrite floatability (Cruz et al., 2021 Moslemi and
Gharabaghi, 2017).
Pyrite depression has been studied extensively because
pyrite must be separated from copper sulfides. Therefore,
other methods than pH adjustment are implemented to
carry out pyrite depression. For instance, organic and inor-
ganic reagents (Cai et al., 2022 Chapagai et al., 2023). Mu
et al. (2016), present a review of fundamental pyrite depres-
sion studies and common reagents used. Inorganic depres-
sants such as pH modifiers, oxidants, cyanide and sulfoxyl,
and organic depressants including polysaccharide polymers
(starch, dextrin, guar gum, carboxymethylcellulose, and
chitosan), lignosulfonate, polyacrylamides, and diethylene-
triamine are used (Ahmadi et al., 2018 Bulatovic, 1999).
Currently, because organic depressants are biodegrad-
able, they have been used as an environmentally friendly