3384 XXXI International Mineral Processing Congress 2024 Proceedings/Washington, DC/Sep 29–Oct 3
size of 70 mm produced a remarkably high nickel grade of
53.8% which is four times higher than published values
for ultramafic deposits containing nickel sulfide minerals
(Selby and White 2011, Crundwell, et al. 2011, Warner, et
al. 2007). This significant improvement translates to poten-
tial economic advantages like lower refining costs. While
this achievement is promising, further work is needed to
explore strategies for optimizing the process and potentially
reaching even higher grades.
Figure 3 reveals an additional benefit for Sample C:
scavenger magnetic separation could significantly con-
tribute to nickel recovery since over 30% of the nickel in
Sample C was recovered by flotation. Notably, this “extra”
nickel translates into a potentially saleable product, as the
concentrate achieved a grade of 12.4% nickel after grind-
ing to a P80 of 49 mm, which falls within the typical grade
for nickel sulfide concentrates. Also, the concentrate from
Sample C can be combined with the concentrate of Sample
B for further processing. This alternative is explored in the
test performed for Sample D.
Table 2 shows the acid consumption for the flotation
tests reported in Figure 3 for Samples B and C. For all grind
sizes, both samples required lower acid consumption com-
pared to Sample A. The consumption in flotation for Sample
B at a P80 of 140 mm (8.7 kg/t) is more than 3 times lower
than the measured consumption for Sample A at a similar
grind size (P80 of 150 mm, 27.2 kg/t). Furthermore, con-
sidering that the LIMS concentrate (Sample B) represents
only 10% of the overall fresh feed plays a crucial role in this
reduced acid consumption, highlighting the efficiency of
this approach in terms of acid consumption.
Table 3 presents the results of cleaner flotation on
Sample D. The flotation sample was obtained by two clean-
ing regrinding and magnetic cleaning stages of the LIMS
and MIMS concentrate (Samples B and C). This step of
magnetic separation cleaning was aimed at removing most
gangue minerals, especially serpentine, only 5% of the total
fresh feed mass reports to the magnetic cleaner concentrate.
The cleaner flotation of this magnetic product achieved a
significantly higher nickel grade of 59.1% Ni compared
to Sample B (53.8%). However, it is important to note
that achieving this high-grade product might come at the
expense of recovery. The table also shows higher acid con-
sumption for Sample D compared to Samples B and C.
This can be attributed to the fine particle size of the mate-
rial (98% below 38 mm), as finer particles have a larger
surface area that is available for reactions with acid. Further
investigation is needed to understand the potential trade-
offs between grade, recovery, and acid consumption for this
process.
Flotation of Awaruite—Activation with Ammonium
Sulfate and Thiosulfate
The results presented above show clear relationships
between grind size, preconcentration by magnetic separa-
tion and acid consumption. There is therefore an interest to
investigate the potential for flotation at neutral pH levels.
Awaruite flotation with xanthate collector requires
weakly acidic conditions (pH 4.5) to achieve hydropho-
bicity. The first stage of the project demonstrated that the
awaruite surface becomes passivated with mixed iron and
nickel oxide layers, predominantly NiO, under neutral and
alkaline conditions, hindering collector adsorption (Seiler,
et al., 2022). Similar nickel-iron alloys exhibit rapid pas-
sivation within minutes at neutral and alkaline pH, sup-
porting this mechanism. As a result, an investigation was
conducted to evaluate potential flotation activators to float
awaruite at neutral or alkaline conditions.
It was demonstrated that awaruite can be selectively
floated under neutral pH conditions using a novel acti-
vation approach with low concentrations of ammonium
sulfate and thiosulfate. Electrochemical analysis revealed
that these activators induce passivation layer dissolution,
primarily through pitting or crevice corrosion, enabling
interaction with the xanthate collector and subsequent
hydrophobicity. While citrate effectively enhances passiv-
ation layer dissolution, it does not participate in the collec-
tor reaction. Microflotation and bench-scale flotation tests
confirmed the findings from the electrochemical character-
ization, demonstrating selective awaruite flotation under
neutral pH conditions.
The best rougher flotation performance on fresh feed
was achieved at pH 6.5 with 5 kg/t of ammonium sulfate
and 100 g/t of sodium thiosulfate. The nickel recovery on
these conditions was 61%, with a nickel grade of 1.05%.
Table 2. Acid consumption for Sample B (LIMS) and C
(MIMS) at different grinding times
Grinding Time,
min
Acid Consumption, kg/t
Sample B Sample C
10 8.7 7.5
20 13.7 11.2
30 16.4 15.0
Table 3. Flotation results for Sample D
Grinding
Time,
min
Cleaner Flotation Concentra`vte
Nickel
Recovery, %
Nickel
Grade, %
Acid Consumption,
kg/t
10 71.1 59.1 23.8
size of 70 mm produced a remarkably high nickel grade of
53.8% which is four times higher than published values
for ultramafic deposits containing nickel sulfide minerals
(Selby and White 2011, Crundwell, et al. 2011, Warner, et
al. 2007). This significant improvement translates to poten-
tial economic advantages like lower refining costs. While
this achievement is promising, further work is needed to
explore strategies for optimizing the process and potentially
reaching even higher grades.
Figure 3 reveals an additional benefit for Sample C:
scavenger magnetic separation could significantly con-
tribute to nickel recovery since over 30% of the nickel in
Sample C was recovered by flotation. Notably, this “extra”
nickel translates into a potentially saleable product, as the
concentrate achieved a grade of 12.4% nickel after grind-
ing to a P80 of 49 mm, which falls within the typical grade
for nickel sulfide concentrates. Also, the concentrate from
Sample C can be combined with the concentrate of Sample
B for further processing. This alternative is explored in the
test performed for Sample D.
Table 2 shows the acid consumption for the flotation
tests reported in Figure 3 for Samples B and C. For all grind
sizes, both samples required lower acid consumption com-
pared to Sample A. The consumption in flotation for Sample
B at a P80 of 140 mm (8.7 kg/t) is more than 3 times lower
than the measured consumption for Sample A at a similar
grind size (P80 of 150 mm, 27.2 kg/t). Furthermore, con-
sidering that the LIMS concentrate (Sample B) represents
only 10% of the overall fresh feed plays a crucial role in this
reduced acid consumption, highlighting the efficiency of
this approach in terms of acid consumption.
Table 3 presents the results of cleaner flotation on
Sample D. The flotation sample was obtained by two clean-
ing regrinding and magnetic cleaning stages of the LIMS
and MIMS concentrate (Samples B and C). This step of
magnetic separation cleaning was aimed at removing most
gangue minerals, especially serpentine, only 5% of the total
fresh feed mass reports to the magnetic cleaner concentrate.
The cleaner flotation of this magnetic product achieved a
significantly higher nickel grade of 59.1% Ni compared
to Sample B (53.8%). However, it is important to note
that achieving this high-grade product might come at the
expense of recovery. The table also shows higher acid con-
sumption for Sample D compared to Samples B and C.
This can be attributed to the fine particle size of the mate-
rial (98% below 38 mm), as finer particles have a larger
surface area that is available for reactions with acid. Further
investigation is needed to understand the potential trade-
offs between grade, recovery, and acid consumption for this
process.
Flotation of Awaruite—Activation with Ammonium
Sulfate and Thiosulfate
The results presented above show clear relationships
between grind size, preconcentration by magnetic separa-
tion and acid consumption. There is therefore an interest to
investigate the potential for flotation at neutral pH levels.
Awaruite flotation with xanthate collector requires
weakly acidic conditions (pH 4.5) to achieve hydropho-
bicity. The first stage of the project demonstrated that the
awaruite surface becomes passivated with mixed iron and
nickel oxide layers, predominantly NiO, under neutral and
alkaline conditions, hindering collector adsorption (Seiler,
et al., 2022). Similar nickel-iron alloys exhibit rapid pas-
sivation within minutes at neutral and alkaline pH, sup-
porting this mechanism. As a result, an investigation was
conducted to evaluate potential flotation activators to float
awaruite at neutral or alkaline conditions.
It was demonstrated that awaruite can be selectively
floated under neutral pH conditions using a novel acti-
vation approach with low concentrations of ammonium
sulfate and thiosulfate. Electrochemical analysis revealed
that these activators induce passivation layer dissolution,
primarily through pitting or crevice corrosion, enabling
interaction with the xanthate collector and subsequent
hydrophobicity. While citrate effectively enhances passiv-
ation layer dissolution, it does not participate in the collec-
tor reaction. Microflotation and bench-scale flotation tests
confirmed the findings from the electrochemical character-
ization, demonstrating selective awaruite flotation under
neutral pH conditions.
The best rougher flotation performance on fresh feed
was achieved at pH 6.5 with 5 kg/t of ammonium sulfate
and 100 g/t of sodium thiosulfate. The nickel recovery on
these conditions was 61%, with a nickel grade of 1.05%.
Table 2. Acid consumption for Sample B (LIMS) and C
(MIMS) at different grinding times
Grinding Time,
min
Acid Consumption, kg/t
Sample B Sample C
10 8.7 7.5
20 13.7 11.2
30 16.4 15.0
Table 3. Flotation results for Sample D
Grinding
Time,
min
Cleaner Flotation Concentra`vte
Nickel
Recovery, %
Nickel
Grade, %
Acid Consumption,
kg/t
10 71.1 59.1 23.8