2390 XXXI International Mineral Processing Congress 2024 Proceedings/Washington, DC/Sep 29–Oct 3
and brucite) was added into a 100 mL beaker containing
40 mL KCl solution in the presence or absence of serpen-
tine depressants. The pH of the individual mineral suspen-
sion was adjusted to pH 10.1 with NaOH (or HCl when
necessary) and stirred for 30 mins using a magnetic stir-
rer. The suspension was then allowed to settle for 10 mins,
the supernatant collected and sonicated using Fisherbrand
CPX5800 Ultrasonic Bath to remove any bubbles before
zeta potential measurements. The experiments were per-
formed in triplicates
Microflotation Tests
Microflotation experiments were performed in a 120 ml
column with a collection chamber and a tube opening fit-
ted at the upper part of the column to allow collection of
the froth. A frit was constructed at the lower part of the
column which allowed small bubbles to be generated when
flotation gas was introduced at the lower tube opening.
All experiments were performed with a 1.5:1 mass ratio
of serpentine and pentlandite in 10 mM KCl solution as
background electrolyte at pH 10.1. Since they are separate
minerals, the ratio of 1.5:1 was chosen to imitate the con-
centrations of serpentine and pentlandite in a real ultra-
mafic nickel ore (Dai et al. 2009). A feed particle size of
–38 μm was used in the flotation tests. The different flota-
tion experimental types with varying conditions used in this
work are summarized in the Table 1. After flotation tests,
the concentrates were dried and subjected to Inductively
Coupled Plasma Optical Emission Spectrometry (ICP-
OES) analysis. To perform ICP-OES analysis, about 0.1g
of the dried mineral samples were digested overnight in
5 mL of trace metal grade concentrated HNO3 and diluted
to 25 mL with milliQ water (EPA 3051a modified EPA
6010d modified). The results are presented appropriately.
X-Ray Photoelectron Spectroscopy (XPS) Tests
XPS is an analytical method used to identify any alterations
in the chemical compositions of sample surfaces, such as
mineral powder (Li et al. 2022). To get the samples ready
for XPS analysis, 1 g of mineral was added to a 40 mL
deionized water in the presence or absence of a depressant,
the pH adjusted to 10.1 with NaOH or HCl solution and
the suspension was continuously stirred for 5 min. For
the STPP case, 50 mg/L of STPP depressant was used. In
the CO2 case, the suspensions were continuously bubbled
with CO2 gas as a depressant for 5 mins while stirring and
the pH was maintained at pH 10.1 with NaOH or HCl
solution. The baseline case did not employ the use of any
depressant. After 5 mins stirring or conditioning, the sus-
pension was filtered, the mineral samples were dried below
40 °C in a vacuum oven, and the dried mineral samples
were vacuum preserved prior to XPS analysis. XPS analyses
of the serpentine samples were performed using Kratos Axis
(Ultra) spectrometer. A Shirley background was applied to
obtain core-level peaks. Marquardt Algorithm (CasaXPS)
was used to determine the peak model parameters like
peak positions, intensities, and widths. Compositions were
calculated from the survey spectra using major elemental
peaks and sensitivity factors provided by the database (S
Table 1).
RESULTS AND DISCUSSION
X-Ray Diffraction
The mineral samples were subject to XRD, and the pat-
tern revealed the three polymorphs of serpentine namely:
chrysotile, antigorite and lizardite (Figure 1a). Chrysotile
and antigorite are monoclinic in their crystal lattice while
lizardite exhibits a hexagonal crystal lattice. Peaks at 12°,
19.8°, 24.3°, 35.4°, and 60.1°corresponds to chrysotile,
peaks at 12.1°, 24.7°, and 35.6° corresponds to antigorite,
while lizardite peaks at 12.2°, 24.5°, 35.8°, 42°, 50.9°, and
59.9°. For the pentlandite sample, patterns of pentlandite
and pyrrhotite with cubic and orthorhombic crystal lattice
respectively, are shown in (Figure 1b). Pentlandite peaked
at 15.3°, 39.1°, 29.4°, 30.8°, 46.9°, 51.4°, 72.1°, and 75.6°,
while the peaks at 29.9°, 33.8°, 43.7° and 53° corresponds
to pyrrhotite. Sharp peaks at 20.8° and 26.6° were detected
for quartz in the silica sample (Figure 2a), while peaks for
brucite occur at 18.6°, 38°, and 50.8° (Figure 2b). Both
silica and brucite samples have hexagonal crystal lattices.
Table 1. Four conditions used in the flotation test
Experiment type Gas Depressant Description
Baseline Air none Serpentine and pentlandite mixture in air flotation.
Air +STPP case Air STPP Serpentine, pentlandite and 50 mg/L of STPP in air
flotation.
Air +CO
2 case Air CO
2 Serpentine, pentlandite and 5 mins of CO
2 conditioning prior to air flotation.
CO2 only case CO2 CO2 Serpentine, pentlandite and 5 mins of CO2
conditioning prior to CO2 flotation.
and brucite) was added into a 100 mL beaker containing
40 mL KCl solution in the presence or absence of serpen-
tine depressants. The pH of the individual mineral suspen-
sion was adjusted to pH 10.1 with NaOH (or HCl when
necessary) and stirred for 30 mins using a magnetic stir-
rer. The suspension was then allowed to settle for 10 mins,
the supernatant collected and sonicated using Fisherbrand
CPX5800 Ultrasonic Bath to remove any bubbles before
zeta potential measurements. The experiments were per-
formed in triplicates
Microflotation Tests
Microflotation experiments were performed in a 120 ml
column with a collection chamber and a tube opening fit-
ted at the upper part of the column to allow collection of
the froth. A frit was constructed at the lower part of the
column which allowed small bubbles to be generated when
flotation gas was introduced at the lower tube opening.
All experiments were performed with a 1.5:1 mass ratio
of serpentine and pentlandite in 10 mM KCl solution as
background electrolyte at pH 10.1. Since they are separate
minerals, the ratio of 1.5:1 was chosen to imitate the con-
centrations of serpentine and pentlandite in a real ultra-
mafic nickel ore (Dai et al. 2009). A feed particle size of
–38 μm was used in the flotation tests. The different flota-
tion experimental types with varying conditions used in this
work are summarized in the Table 1. After flotation tests,
the concentrates were dried and subjected to Inductively
Coupled Plasma Optical Emission Spectrometry (ICP-
OES) analysis. To perform ICP-OES analysis, about 0.1g
of the dried mineral samples were digested overnight in
5 mL of trace metal grade concentrated HNO3 and diluted
to 25 mL with milliQ water (EPA 3051a modified EPA
6010d modified). The results are presented appropriately.
X-Ray Photoelectron Spectroscopy (XPS) Tests
XPS is an analytical method used to identify any alterations
in the chemical compositions of sample surfaces, such as
mineral powder (Li et al. 2022). To get the samples ready
for XPS analysis, 1 g of mineral was added to a 40 mL
deionized water in the presence or absence of a depressant,
the pH adjusted to 10.1 with NaOH or HCl solution and
the suspension was continuously stirred for 5 min. For
the STPP case, 50 mg/L of STPP depressant was used. In
the CO2 case, the suspensions were continuously bubbled
with CO2 gas as a depressant for 5 mins while stirring and
the pH was maintained at pH 10.1 with NaOH or HCl
solution. The baseline case did not employ the use of any
depressant. After 5 mins stirring or conditioning, the sus-
pension was filtered, the mineral samples were dried below
40 °C in a vacuum oven, and the dried mineral samples
were vacuum preserved prior to XPS analysis. XPS analyses
of the serpentine samples were performed using Kratos Axis
(Ultra) spectrometer. A Shirley background was applied to
obtain core-level peaks. Marquardt Algorithm (CasaXPS)
was used to determine the peak model parameters like
peak positions, intensities, and widths. Compositions were
calculated from the survey spectra using major elemental
peaks and sensitivity factors provided by the database (S
Table 1).
RESULTS AND DISCUSSION
X-Ray Diffraction
The mineral samples were subject to XRD, and the pat-
tern revealed the three polymorphs of serpentine namely:
chrysotile, antigorite and lizardite (Figure 1a). Chrysotile
and antigorite are monoclinic in their crystal lattice while
lizardite exhibits a hexagonal crystal lattice. Peaks at 12°,
19.8°, 24.3°, 35.4°, and 60.1°corresponds to chrysotile,
peaks at 12.1°, 24.7°, and 35.6° corresponds to antigorite,
while lizardite peaks at 12.2°, 24.5°, 35.8°, 42°, 50.9°, and
59.9°. For the pentlandite sample, patterns of pentlandite
and pyrrhotite with cubic and orthorhombic crystal lattice
respectively, are shown in (Figure 1b). Pentlandite peaked
at 15.3°, 39.1°, 29.4°, 30.8°, 46.9°, 51.4°, 72.1°, and 75.6°,
while the peaks at 29.9°, 33.8°, 43.7° and 53° corresponds
to pyrrhotite. Sharp peaks at 20.8° and 26.6° were detected
for quartz in the silica sample (Figure 2a), while peaks for
brucite occur at 18.6°, 38°, and 50.8° (Figure 2b). Both
silica and brucite samples have hexagonal crystal lattices.
Table 1. Four conditions used in the flotation test
Experiment type Gas Depressant Description
Baseline Air none Serpentine and pentlandite mixture in air flotation.
Air +STPP case Air STPP Serpentine, pentlandite and 50 mg/L of STPP in air
flotation.
Air +CO
2 case Air CO
2 Serpentine, pentlandite and 5 mins of CO
2 conditioning prior to air flotation.
CO2 only case CO2 CO2 Serpentine, pentlandite and 5 mins of CO2
conditioning prior to CO2 flotation.