XXXI International Mineral Processing Congress 2024 Proceedings/Washington, DC/Sep 29–Oct 3 2389
INTRODUCTION
Liberating pentlandite ((Fe,Ni)9S8) from low-grade ultra-
mafic nickel ores results in generation of fine particles in
addition to the slime coating effect of the MgO-bearing
serpentine (Mg3Si2O5(OH)4) (Bobicki et al. 2014). One
main parameter that has been proven to promote improve-
ments in fine mineral flotation recovery over the last decade
is the addition of fine bubbles (Maoming et al. 2010). In
terms of fine bubbles for froth flotation, CO2 tends to
produce finer or smaller bubbles when compared to other
gasses/air because of its increased solubility (Snoswell et at.
2005).
Aside from improved solubility and ability to produce
finer bubbles, CO2 can interact with divalent cations and
reduce their negative impacts (Freitas et al. 2020). At the
same time, CO2 can be permanently stored in mineral
form as carbonates, a strategy to mitigate GHG emissions
(Wani et al. 2022). Due to many benefits of CO2 bubbles,
they have been tested in the processing of various minerals.
In an experiment to investigate CO2 attachment at pyrite
surfaces, it was reported that the formation of CO2 nano-
bubbles at the surface of the pyrite improved the flotation
recovery of pyrite (Hassas and Miller 2019). Another study
reported shorter bubble attachment time and high adsorp-
tion potential of CO2 bubbles which resulted in improved
coal recovery and reduced ash content when compared with
air or nitrogen gas (Miller and Misra 1985). CO2 has been
used for other purposes such as a depressant (Matiolo et al.
2016). In a two-stage flotation process of siliceous carbon-
ate phosphate ore for example, CO2 was used as an apatite
depressant to specifically float calcite/dolomite followed by
apatite flotation with other additives (Matiolo et al. 2016).
CO2 gas has also been used in a preconditioning stage prior
to air flotation to improve pentlandite recovery (Wani et al.
2022). Their results provided a good background to further
explore the use of CO2 as a flotation gas instead of air in the
processing of ultramafic nickel ores.
STPP on the other hand, can interact and form com-
plexes with or chelate calcium ions and magnesium ions,
thereby reversing the surface charge on the divalent cations
bearing gangue minerals (Li et al. 2022). By promoting
surface charge reversal of the gangue minerals, their elec-
trostatic interactions with valuable minerals are decreased
and the floatability of the valuable minerals is enhanced.
To address the issue of poor flotation kinetics of ultramafic
nickel ores, this study will explore the use of CO2 fine bub-
bles as a flotation gas and STPP as a serpentine depressant
are used in separate experiments to facilitate the removal of
slimes from pentlandite’ surface and improve the aggrega-
tion of pentlandite to the froth phase.
MATERIALS AND METHODS
Ore Samples
The ore samples used in this research were obtained as
separate minerals. Pentlandite was obtained from the Vale
Voisey’s bay operations, and the serpentine samples were
supplied by FPX Nickel from their Baptiste deposit in
British Columbia, Canada. Brucite samples were obtained
from Fengcheng City Hequi Brucite Mining CO., Ltd.,
while silica samples were purchased from US Silica. Further
size reduction of the samples (pentlandite and serpentine)
involved crushing and pulverizing using a bb 200 jaw
crusher and a dm 200-disc mill. The milled samples were
then classified using the Ro-Tap method to obtain – 38 μm
samples used for flotation tests and XPS measurements. The
– 38 μm powdered mineral samples were further reduced
with mortar and pestle to obtain – 2 μm particle size used
for zeta potential measurements. To remove potential sur-
face oxidation of the pentlandite samples, the sample was
washed in 0.1 M hydrochloric acid (HCl) solution for
about 6 hours, rinsed with deionized (DI) water, freeze-
dried for 48 hours, and was stored in a –80 °C freezer prior
to experiments. Mineralogical characterization of samples
was performed by X-ray diffraction (XRD) with a Bruker
D8 Discover diffraction system at 2theta range of 5 and 80
degrees, 0.05 step size and 3 degrees/min scan speed.
Reagents
Flotation reagents including methyl isobutyl carbinol
(MIBC) and potassium amyl xanthate (PAX) were sup-
plied by Flottec. Reagent-grade hydrochloric acid (HCl)
was supplied by ACP Chemicals, while sodium hydroxide
(NaOH) was obtained from Fisher Scientific. Both were
used as pH modifiers for all experiments performed in this
work. Analytical grade Sodium tripolyphosphate (STPP) of
≥ 98.0% purity was purchased from Fisher Scientific and
was used as serpentine depressant in this work. Research
grade carbon dioxide cylinder from PRAXAIR was sup-
plied by Linde Canada Inc.
Zeta Potential Measurements
Zeta potential measurements were performed using the
Malvern Zetasizer Nano particle characterization system.
The device measures the zeta potential by obtaining the
electrophoretic mobility which is then converted to zeta
potential by applying the Henry’s equation (Smoluchowski
approximation). Zeta potential measurement allows us to
predict the interaction of different gangue minerals with
the valuable mineral.
To perform the zeta potential measurements, 40 mg
of each mineral sample (serpentine, pentlandite, silica,
INTRODUCTION
Liberating pentlandite ((Fe,Ni)9S8) from low-grade ultra-
mafic nickel ores results in generation of fine particles in
addition to the slime coating effect of the MgO-bearing
serpentine (Mg3Si2O5(OH)4) (Bobicki et al. 2014). One
main parameter that has been proven to promote improve-
ments in fine mineral flotation recovery over the last decade
is the addition of fine bubbles (Maoming et al. 2010). In
terms of fine bubbles for froth flotation, CO2 tends to
produce finer or smaller bubbles when compared to other
gasses/air because of its increased solubility (Snoswell et at.
2005).
Aside from improved solubility and ability to produce
finer bubbles, CO2 can interact with divalent cations and
reduce their negative impacts (Freitas et al. 2020). At the
same time, CO2 can be permanently stored in mineral
form as carbonates, a strategy to mitigate GHG emissions
(Wani et al. 2022). Due to many benefits of CO2 bubbles,
they have been tested in the processing of various minerals.
In an experiment to investigate CO2 attachment at pyrite
surfaces, it was reported that the formation of CO2 nano-
bubbles at the surface of the pyrite improved the flotation
recovery of pyrite (Hassas and Miller 2019). Another study
reported shorter bubble attachment time and high adsorp-
tion potential of CO2 bubbles which resulted in improved
coal recovery and reduced ash content when compared with
air or nitrogen gas (Miller and Misra 1985). CO2 has been
used for other purposes such as a depressant (Matiolo et al.
2016). In a two-stage flotation process of siliceous carbon-
ate phosphate ore for example, CO2 was used as an apatite
depressant to specifically float calcite/dolomite followed by
apatite flotation with other additives (Matiolo et al. 2016).
CO2 gas has also been used in a preconditioning stage prior
to air flotation to improve pentlandite recovery (Wani et al.
2022). Their results provided a good background to further
explore the use of CO2 as a flotation gas instead of air in the
processing of ultramafic nickel ores.
STPP on the other hand, can interact and form com-
plexes with or chelate calcium ions and magnesium ions,
thereby reversing the surface charge on the divalent cations
bearing gangue minerals (Li et al. 2022). By promoting
surface charge reversal of the gangue minerals, their elec-
trostatic interactions with valuable minerals are decreased
and the floatability of the valuable minerals is enhanced.
To address the issue of poor flotation kinetics of ultramafic
nickel ores, this study will explore the use of CO2 fine bub-
bles as a flotation gas and STPP as a serpentine depressant
are used in separate experiments to facilitate the removal of
slimes from pentlandite’ surface and improve the aggrega-
tion of pentlandite to the froth phase.
MATERIALS AND METHODS
Ore Samples
The ore samples used in this research were obtained as
separate minerals. Pentlandite was obtained from the Vale
Voisey’s bay operations, and the serpentine samples were
supplied by FPX Nickel from their Baptiste deposit in
British Columbia, Canada. Brucite samples were obtained
from Fengcheng City Hequi Brucite Mining CO., Ltd.,
while silica samples were purchased from US Silica. Further
size reduction of the samples (pentlandite and serpentine)
involved crushing and pulverizing using a bb 200 jaw
crusher and a dm 200-disc mill. The milled samples were
then classified using the Ro-Tap method to obtain – 38 μm
samples used for flotation tests and XPS measurements. The
– 38 μm powdered mineral samples were further reduced
with mortar and pestle to obtain – 2 μm particle size used
for zeta potential measurements. To remove potential sur-
face oxidation of the pentlandite samples, the sample was
washed in 0.1 M hydrochloric acid (HCl) solution for
about 6 hours, rinsed with deionized (DI) water, freeze-
dried for 48 hours, and was stored in a –80 °C freezer prior
to experiments. Mineralogical characterization of samples
was performed by X-ray diffraction (XRD) with a Bruker
D8 Discover diffraction system at 2theta range of 5 and 80
degrees, 0.05 step size and 3 degrees/min scan speed.
Reagents
Flotation reagents including methyl isobutyl carbinol
(MIBC) and potassium amyl xanthate (PAX) were sup-
plied by Flottec. Reagent-grade hydrochloric acid (HCl)
was supplied by ACP Chemicals, while sodium hydroxide
(NaOH) was obtained from Fisher Scientific. Both were
used as pH modifiers for all experiments performed in this
work. Analytical grade Sodium tripolyphosphate (STPP) of
≥ 98.0% purity was purchased from Fisher Scientific and
was used as serpentine depressant in this work. Research
grade carbon dioxide cylinder from PRAXAIR was sup-
plied by Linde Canada Inc.
Zeta Potential Measurements
Zeta potential measurements were performed using the
Malvern Zetasizer Nano particle characterization system.
The device measures the zeta potential by obtaining the
electrophoretic mobility which is then converted to zeta
potential by applying the Henry’s equation (Smoluchowski
approximation). Zeta potential measurement allows us to
predict the interaction of different gangue minerals with
the valuable mineral.
To perform the zeta potential measurements, 40 mg
of each mineral sample (serpentine, pentlandite, silica,