XXXI International Mineral Processing Congress 2024 Proceedings/Washington, DC/Sep 29–Oct 3 649
not fully utilized by the industry to address the ongoing
copper recovery challenges in copper operations.
Processing of sulphide copper, molybdenum and
precious metal ores typically involves flotation of copper
bearing minerals while depressing non-sulphide and other
non-copper sulphide minerals such as pyrite, pyrrhotite and
sometimes arsenopyrite. Though in many precious metal
ores, the values are in these sulphide minerals as well. The
conventional method employed in the industry to produce
a saleable copper concentrate requires depression of these
non-copper sulphide minerals using an alkaline pH above
9.5, though 10.5 to 11.5 is more common. Alkalinity is
controlled by the addition of a pH modifier. Lime is nor-
mally employed as a pH modifier due to its relatively low
cost however, the costs associated with adding lime can
be significant and the effectiveness of lime as a depressant
could be drastically reduced when the process water sup-
plied to the flotation circuit contains high level of dissolved
salts. In some cases, a small amount of cyanide is used along
with lime to depress non-copper sulphide minerals espe-
cially when its proportion to copper sulphide minerals in
the ore is higher than three.
As ore bodies are becoming more complex, use of lime
or cyanide based non-copper sulphide mineral depres-
sion methods are not effective in situations where there is
a significant amount of clay minerals in the ore or where
pyrite gets activated due to the presence of high amounts
of copper, magnesium or other ions in solutions. The need
for using raw sea water, brackish or poor quality munici-
pal waste water, due to lack of fresh water availability or
the desire to avoid using limited fresh water available for
community purposes, is becoming essential to obtain the
“license to operate.” The challenge, however, is that the
conventional copper flotation schemes are sometimes inef-
fective with these challenging water sources. This could be
mainly attributed to pH buffering issues and precipitation
of certain undesirable ions in solutions.
The need for an alternative to high lime or cyanide
based pyrite depressant is critical for selective flotation of
copper from these complex ore bodies using problematic
non-conventional water sources. This paper presents a
solution that was advanced through rigorous development
work carried out on various ore types followed by exten-
sive proof-of-concept validation using bench and piloting
program, which has now allowed two commercial applica-
tions. The technology that emanated from this earlier work
(Gorain et al., 2016) has now been developed further and
is presently trademarked as Flotation Advanced Recovery
Technology (FLOT-ART), the main subject of this paper.
Flotation with Sea Water
To better understand the impact of non-conventional
sources on flotation, it is best to first ascertain the status
quo on the relevant research work carried out in this area.
The effect of seawater on flotation performance has
been investigated by some researchers and many of the
findings tend to corroborate well with the experiences
obtained during the development of this FLOT-ART pro-
cess. Castro (2012) suggested that the two most important
chemical factors of seawater that may affect the flotation
processes are known as the buffering effect of seawater and
the precipitation of secondary ions at alkaline pH with the
depressing effect on flotation of some sulphide minerals.
Bıçak et al. (2012) stated that increased froth stability can
be obtained more easily in seawater with relatively lower
amount of frother required in comparison with tap water
due to the high ionic strength of seawater. This agrees with
the conclusion from various earlier studies (Laskowski,
1966 Pugh et al., 1997) and the observations we made
during the FLOT-ART development work.
While lime is widely used as a mean to control pH
for pyrite depression in copper flotation using fresh water,
in the case of sea water, added OH– ions from lime are
consumed by other reactions resulting in significant higher
dosage of lime required to reach to the desired alkaline pH,
as demonstrated in Figure 1.
The buffering effect of sea water is known to be due to
the presence of the couples carbonate /bicarbonate ions
(HCO3– /CO32–) and boric acid /borate ions (B(OH)3
/B(OH)4–) (Pytkowicz &Atlas, 1975). But the most
important contribution to the measured effect is deemed to
come from the precipitation of Mg(OH)2, as the solubil-
ity product of magnesium hydroxide is much smaller than
the solubility product of calcium hydroxide and therefore
any introduction of lime must initiate the precipitation of
magnesium hydroxo-complexes and magnesium hydroxide
in seawater (Castro, 2012). Figure 2 shows the concentra-
tion of both Ca2+ and Mg2+ ions in seawater when its pH is
increased by lime addition.
This agrees with the previous findings by Parraguez et
al. (2009) when they suggested that the formation of mag-
nesium carbonates and magnesium hydroxide prevented
the increase in pH values when lime was used. They have
suggested the reason for lime to be less effective as a pyrite
depressant when seawater is used in flotation is because of
the pyrite surface modifier, Ca2+, is consumed in part of the
chemical reactions with various mineral species instead of
being consumed entirely by the surface of pyrite.
not fully utilized by the industry to address the ongoing
copper recovery challenges in copper operations.
Processing of sulphide copper, molybdenum and
precious metal ores typically involves flotation of copper
bearing minerals while depressing non-sulphide and other
non-copper sulphide minerals such as pyrite, pyrrhotite and
sometimes arsenopyrite. Though in many precious metal
ores, the values are in these sulphide minerals as well. The
conventional method employed in the industry to produce
a saleable copper concentrate requires depression of these
non-copper sulphide minerals using an alkaline pH above
9.5, though 10.5 to 11.5 is more common. Alkalinity is
controlled by the addition of a pH modifier. Lime is nor-
mally employed as a pH modifier due to its relatively low
cost however, the costs associated with adding lime can
be significant and the effectiveness of lime as a depressant
could be drastically reduced when the process water sup-
plied to the flotation circuit contains high level of dissolved
salts. In some cases, a small amount of cyanide is used along
with lime to depress non-copper sulphide minerals espe-
cially when its proportion to copper sulphide minerals in
the ore is higher than three.
As ore bodies are becoming more complex, use of lime
or cyanide based non-copper sulphide mineral depres-
sion methods are not effective in situations where there is
a significant amount of clay minerals in the ore or where
pyrite gets activated due to the presence of high amounts
of copper, magnesium or other ions in solutions. The need
for using raw sea water, brackish or poor quality munici-
pal waste water, due to lack of fresh water availability or
the desire to avoid using limited fresh water available for
community purposes, is becoming essential to obtain the
“license to operate.” The challenge, however, is that the
conventional copper flotation schemes are sometimes inef-
fective with these challenging water sources. This could be
mainly attributed to pH buffering issues and precipitation
of certain undesirable ions in solutions.
The need for an alternative to high lime or cyanide
based pyrite depressant is critical for selective flotation of
copper from these complex ore bodies using problematic
non-conventional water sources. This paper presents a
solution that was advanced through rigorous development
work carried out on various ore types followed by exten-
sive proof-of-concept validation using bench and piloting
program, which has now allowed two commercial applica-
tions. The technology that emanated from this earlier work
(Gorain et al., 2016) has now been developed further and
is presently trademarked as Flotation Advanced Recovery
Technology (FLOT-ART), the main subject of this paper.
Flotation with Sea Water
To better understand the impact of non-conventional
sources on flotation, it is best to first ascertain the status
quo on the relevant research work carried out in this area.
The effect of seawater on flotation performance has
been investigated by some researchers and many of the
findings tend to corroborate well with the experiences
obtained during the development of this FLOT-ART pro-
cess. Castro (2012) suggested that the two most important
chemical factors of seawater that may affect the flotation
processes are known as the buffering effect of seawater and
the precipitation of secondary ions at alkaline pH with the
depressing effect on flotation of some sulphide minerals.
Bıçak et al. (2012) stated that increased froth stability can
be obtained more easily in seawater with relatively lower
amount of frother required in comparison with tap water
due to the high ionic strength of seawater. This agrees with
the conclusion from various earlier studies (Laskowski,
1966 Pugh et al., 1997) and the observations we made
during the FLOT-ART development work.
While lime is widely used as a mean to control pH
for pyrite depression in copper flotation using fresh water,
in the case of sea water, added OH– ions from lime are
consumed by other reactions resulting in significant higher
dosage of lime required to reach to the desired alkaline pH,
as demonstrated in Figure 1.
The buffering effect of sea water is known to be due to
the presence of the couples carbonate /bicarbonate ions
(HCO3– /CO32–) and boric acid /borate ions (B(OH)3
/B(OH)4–) (Pytkowicz &Atlas, 1975). But the most
important contribution to the measured effect is deemed to
come from the precipitation of Mg(OH)2, as the solubil-
ity product of magnesium hydroxide is much smaller than
the solubility product of calcium hydroxide and therefore
any introduction of lime must initiate the precipitation of
magnesium hydroxo-complexes and magnesium hydroxide
in seawater (Castro, 2012). Figure 2 shows the concentra-
tion of both Ca2+ and Mg2+ ions in seawater when its pH is
increased by lime addition.
This agrees with the previous findings by Parraguez et
al. (2009) when they suggested that the formation of mag-
nesium carbonates and magnesium hydroxide prevented
the increase in pH values when lime was used. They have
suggested the reason for lime to be less effective as a pyrite
depressant when seawater is used in flotation is because of
the pyrite surface modifier, Ca2+, is consumed in part of the
chemical reactions with various mineral species instead of
being consumed entirely by the surface of pyrite.