XXXI International Mineral Processing Congress 2024 Proceedings/Washington, DC/Sep 29–Oct 3 2395
hydrophobic mineral surfaces, thereby enhancing inter-
actions between neighboring hydrophobic valuable min-
erals making them to aggregate and to float (Hassas and
Miller 2019). Since the effect of introducing CO2 gas is
more pronounced towards improving pentlandite recovery
rather than depressing serpentine, it can be concluded that
facilitating pentlandites’ aggregation through hydrophobic
interactions is the leading mechanism (Figure 12) for the
improved recovery observed in the CO2-assisted flotation
cases.
Serpentine recovery was also monitored by following
the cumulative release of magnesium in the ICP-OES anal-
ysis. The results clearly show that the case of Air +STPP was
the most effective serpentine depressant. STPP decreased
magnesium recovery from 77% to 72%, a difference of 5%
which is the highest reduction observed among all treated
cases (Figure 8). This validates the results observed in the
zeta potential measurements where the introduction of
STPP was more effective in reversing the surface charge
on serpentine (Figure 5) than CO2 conditioned suspen-
sion (Figure 6). STPP acts by chelating and complexing
the magnesium cations on serpentine surfaces through its
phosphate group (Equation 1), limiting serpentine’s elec-
trostatic attraction with pentlandite and rendering serpen-
tine particles more hydrophilic (Li et al. 2022). Because
some serpentine particles are no longer heterogeneously
agglomerated with pentlandite particles, they are no longer
recovered together when air bubbles attach to pentlandite
through hydrophobic interactions.
Furthermore, introduction of the reagents (STPP and
CO2) in the treated cases increased the nickel grade from
below 10% in the baseline case to about 15% in both STPP
and CO2 cases (Figure 9). The poor recovery of nickel in
the baseline case is an indication of the high slime coating
effect of the serpentine minerals on pentlandite, resulting
in both minerals reporting to the froth phase, and thereby
diluting the nickel grade. Thus, the use of STPP as depres-
sant and the use of CO2 as both a depressant and a flota-
tion gas, did not only enhance the recovery of nickel, but
they also helped to improve the overall nickel grade in the
concentrate. This implies that the electrostatic interactions
between serpentine particles and pentlandite minerals were
reduced upon introduction of either STPP or CO2 gas
resulting in a lesser amount of serpentine particles to report
to the froth phase. Therefore, nickel grade was improved as
compared to the baseline case (Figure 9).
XPS Analysis
Both zeta potential measurements and flotation tests were
validated by performing XPS analyses (different peaks are
provided in Table S1). The results as shown in Figure 10
revealed a significant decrease of the Mg 2s peak area from
13533.15 CPS.eV in the baseline case to 7207.25 CPS.eV
in the STPP treated serpentine, which agrees with study
0
20
40
60
80
100
0 100 200 300 400 500
Time (s)
Ni (Baseline)
Ni (Air +CO2)
Ni (Air +STPP)
Ni (CO2 only)
Figure 7. Cumulative nickel recovery vs flotation time for baseline case (air flotation
with no depressant), Air +CO
2 (air flotation with CO
2 as a depressant), Air +STPP (air
flotation with STPP as the depressant), CO
2 only (CO
2 gas for both flotation and as a
depressant)
Recovery
(%)
hydrophobic mineral surfaces, thereby enhancing inter-
actions between neighboring hydrophobic valuable min-
erals making them to aggregate and to float (Hassas and
Miller 2019). Since the effect of introducing CO2 gas is
more pronounced towards improving pentlandite recovery
rather than depressing serpentine, it can be concluded that
facilitating pentlandites’ aggregation through hydrophobic
interactions is the leading mechanism (Figure 12) for the
improved recovery observed in the CO2-assisted flotation
cases.
Serpentine recovery was also monitored by following
the cumulative release of magnesium in the ICP-OES anal-
ysis. The results clearly show that the case of Air +STPP was
the most effective serpentine depressant. STPP decreased
magnesium recovery from 77% to 72%, a difference of 5%
which is the highest reduction observed among all treated
cases (Figure 8). This validates the results observed in the
zeta potential measurements where the introduction of
STPP was more effective in reversing the surface charge
on serpentine (Figure 5) than CO2 conditioned suspen-
sion (Figure 6). STPP acts by chelating and complexing
the magnesium cations on serpentine surfaces through its
phosphate group (Equation 1), limiting serpentine’s elec-
trostatic attraction with pentlandite and rendering serpen-
tine particles more hydrophilic (Li et al. 2022). Because
some serpentine particles are no longer heterogeneously
agglomerated with pentlandite particles, they are no longer
recovered together when air bubbles attach to pentlandite
through hydrophobic interactions.
Furthermore, introduction of the reagents (STPP and
CO2) in the treated cases increased the nickel grade from
below 10% in the baseline case to about 15% in both STPP
and CO2 cases (Figure 9). The poor recovery of nickel in
the baseline case is an indication of the high slime coating
effect of the serpentine minerals on pentlandite, resulting
in both minerals reporting to the froth phase, and thereby
diluting the nickel grade. Thus, the use of STPP as depres-
sant and the use of CO2 as both a depressant and a flota-
tion gas, did not only enhance the recovery of nickel, but
they also helped to improve the overall nickel grade in the
concentrate. This implies that the electrostatic interactions
between serpentine particles and pentlandite minerals were
reduced upon introduction of either STPP or CO2 gas
resulting in a lesser amount of serpentine particles to report
to the froth phase. Therefore, nickel grade was improved as
compared to the baseline case (Figure 9).
XPS Analysis
Both zeta potential measurements and flotation tests were
validated by performing XPS analyses (different peaks are
provided in Table S1). The results as shown in Figure 10
revealed a significant decrease of the Mg 2s peak area from
13533.15 CPS.eV in the baseline case to 7207.25 CPS.eV
in the STPP treated serpentine, which agrees with study
0
20
40
60
80
100
0 100 200 300 400 500
Time (s)
Ni (Baseline)
Ni (Air +CO2)
Ni (Air +STPP)
Ni (CO2 only)
Figure 7. Cumulative nickel recovery vs flotation time for baseline case (air flotation
with no depressant), Air +CO
2 (air flotation with CO
2 as a depressant), Air +STPP (air
flotation with STPP as the depressant), CO
2 only (CO
2 gas for both flotation and as a
depressant)
Recovery
(%)