2454 XXXI International Mineral Processing Congress 2024 Proceedings/Washington, DC/Sep 29–Oct 3
23.5% Fe and 29.9% S (Table 1). These percentages were
used to calculate the amount of nickel associated with the
iron and this was designated as pentlandite nickel. Millerite
content was then calculated by subtracting the amount of
the pentlandite nickel from the total nickel. Quartz content
was calculated by difference. The accuracy of this method
was tested by QXRD. Two flotation products were analysed
by QXRD, and the results compared to the mineral con-
tent as calculated from the assays (Table 2). There was good
agreement between both methods.
QXRD analysis
The samples were ground in ethanol in a McCrone micron-
izing mill. The resulting slurries were oven dried at 60°C
then thoroughly mixed in an agate mortar and pestle before
being lightly back pressed into stainless-steel sample holders
for presentation to the X-ray beam. The XRD patterns of
the micronized samples were collected with a PANalytical
X’Pert Pro Multi-purpose Diffractometer using Fe filtered
Co Ka radiation, automatic divergence slit, 2° anti-scatter
slit and fast X’Celerator Si strip detector. Patterns were col-
lected from 4 to 80° in steps of 0.017° 2θ with a count-
ing time of 0.5 s per step, for an overall counting time of
approximately 35 min. Phase identification was performed
using PANalytical Highscore Plus© software (V4.8) which
interfaces with the International Centre for Diffraction
Data (ICDD) PDF 4+ 2020 database. Quantitative phase
analysis (QPA) was carried out via the Rietveld method
using TOPAS V6 software.
Sizing
Where sizing was required, sub-samples were sized using
the modified cyclosizing procedure of Kelsall et al. (1974).
RESULTS AND DISCUSSION
Effect of Pulp Potential
The effect of pulp potential on millerite and pentlandite flo-
tability in single mineral tests at pH 9 with ethyl xanthate
as collector is shown in Figure 2 as a plot of mineral recov-
ery at 8 minutes against pulp potential. Data for millerite
is taken from Smith et al. (2011) and for pentlandite from
Senior et al. (1994). The air set potential for these systems is
between +200 and +300 mV SHE. Under reducing condi-
tions, millerite produces a flotation edge below –100 mV
SHE as the mineral goes from being non-flotable to being
strongly flotable. The threshold potential for the transition,
which we define here as the potential at which recovery
after 8 min is 50%, is about –100 mV SHE. As far as it was
tested (up to +400 mV SHE), no upper limiting potential
for millerite was found. In contrast, the threshold potential
for the pentlandite transition is about +200 mV. The upper
limiting potential for pentlandite was not determined.
It is normal for sulphide minerals to exhibit a lower
limiting threshold potential with xanthate collectors. What
is unusual about the data here for millerite is that this
potential is relatively low in comparison with that for pent-
landite (about 300 mV SHE below the pentlandite edge).
The results of Figure 2 indicate that, by adjusting the pulp
potential, it should be possible to separate pentlandite and
millerite at a potential around 0 mV SHE. It is important
to note that these results relate to single mineral flotation
tests using only millerite and quartz diluent or pentlandite
and quartz diluent. Using potential control as a means of
separating one mineral from another will depend largely
upon the extent to which the sulphide minerals present
interact—this is normally determined in mixed mineral
flotation tests. Finally, it is noted that the data shown are
for millerite flotation at pH 9. The flotation response of
millerite as a function of Eh at different pH values has not
been determined but theoretically the threshold potential,
which is related to the oxidation potential of the mineral,
should be dependent on pH although as can be seen from
Figure 2 this was not the case for pentlandite.
The aim of the current study was to determine if pent-
landite and millerite could indeed be separated by flotation
using changes in pulp potential. The effect of pulp potential
on the flotation of pentlandite and millerite from the nickel
sulphide sample used in this study using KeX at pH 9 is
shown in Figure 3. It is evident that the region of separation
at low potential, which was expected from the single min-
eral tests, has disappeared, presumably due to interaction
between the two minerals.
Table 2. Validation of method for determining pentlandite and millerite content from assays
Flotation Product
Content as Measured by QXRD (%)Content as Estimated from Assays (%)
Pentlandite Millerite Quartz Pentlandite Millerite Quartz
Test 2/1
0.5 min con
11 72 17 14 71 15
Test 2/6
air-set potential con
63 4 32 64 3 33
23.5% Fe and 29.9% S (Table 1). These percentages were
used to calculate the amount of nickel associated with the
iron and this was designated as pentlandite nickel. Millerite
content was then calculated by subtracting the amount of
the pentlandite nickel from the total nickel. Quartz content
was calculated by difference. The accuracy of this method
was tested by QXRD. Two flotation products were analysed
by QXRD, and the results compared to the mineral con-
tent as calculated from the assays (Table 2). There was good
agreement between both methods.
QXRD analysis
The samples were ground in ethanol in a McCrone micron-
izing mill. The resulting slurries were oven dried at 60°C
then thoroughly mixed in an agate mortar and pestle before
being lightly back pressed into stainless-steel sample holders
for presentation to the X-ray beam. The XRD patterns of
the micronized samples were collected with a PANalytical
X’Pert Pro Multi-purpose Diffractometer using Fe filtered
Co Ka radiation, automatic divergence slit, 2° anti-scatter
slit and fast X’Celerator Si strip detector. Patterns were col-
lected from 4 to 80° in steps of 0.017° 2θ with a count-
ing time of 0.5 s per step, for an overall counting time of
approximately 35 min. Phase identification was performed
using PANalytical Highscore Plus© software (V4.8) which
interfaces with the International Centre for Diffraction
Data (ICDD) PDF 4+ 2020 database. Quantitative phase
analysis (QPA) was carried out via the Rietveld method
using TOPAS V6 software.
Sizing
Where sizing was required, sub-samples were sized using
the modified cyclosizing procedure of Kelsall et al. (1974).
RESULTS AND DISCUSSION
Effect of Pulp Potential
The effect of pulp potential on millerite and pentlandite flo-
tability in single mineral tests at pH 9 with ethyl xanthate
as collector is shown in Figure 2 as a plot of mineral recov-
ery at 8 minutes against pulp potential. Data for millerite
is taken from Smith et al. (2011) and for pentlandite from
Senior et al. (1994). The air set potential for these systems is
between +200 and +300 mV SHE. Under reducing condi-
tions, millerite produces a flotation edge below –100 mV
SHE as the mineral goes from being non-flotable to being
strongly flotable. The threshold potential for the transition,
which we define here as the potential at which recovery
after 8 min is 50%, is about –100 mV SHE. As far as it was
tested (up to +400 mV SHE), no upper limiting potential
for millerite was found. In contrast, the threshold potential
for the pentlandite transition is about +200 mV. The upper
limiting potential for pentlandite was not determined.
It is normal for sulphide minerals to exhibit a lower
limiting threshold potential with xanthate collectors. What
is unusual about the data here for millerite is that this
potential is relatively low in comparison with that for pent-
landite (about 300 mV SHE below the pentlandite edge).
The results of Figure 2 indicate that, by adjusting the pulp
potential, it should be possible to separate pentlandite and
millerite at a potential around 0 mV SHE. It is important
to note that these results relate to single mineral flotation
tests using only millerite and quartz diluent or pentlandite
and quartz diluent. Using potential control as a means of
separating one mineral from another will depend largely
upon the extent to which the sulphide minerals present
interact—this is normally determined in mixed mineral
flotation tests. Finally, it is noted that the data shown are
for millerite flotation at pH 9. The flotation response of
millerite as a function of Eh at different pH values has not
been determined but theoretically the threshold potential,
which is related to the oxidation potential of the mineral,
should be dependent on pH although as can be seen from
Figure 2 this was not the case for pentlandite.
The aim of the current study was to determine if pent-
landite and millerite could indeed be separated by flotation
using changes in pulp potential. The effect of pulp potential
on the flotation of pentlandite and millerite from the nickel
sulphide sample used in this study using KeX at pH 9 is
shown in Figure 3. It is evident that the region of separation
at low potential, which was expected from the single min-
eral tests, has disappeared, presumably due to interaction
between the two minerals.
Table 2. Validation of method for determining pentlandite and millerite content from assays
Flotation Product
Content as Measured by QXRD (%)Content as Estimated from Assays (%)
Pentlandite Millerite Quartz Pentlandite Millerite Quartz
Test 2/1
0.5 min con
11 72 17 14 71 15
Test 2/6
air-set potential con
63 4 32 64 3 33