2394 XXXI International Mineral Processing Congress 2024 Proceedings/Washington, DC/Sep 29–Oct 3
implies a positive total interaction between serpentine and
pentlandite i.e., a repulsive force (Alvarez-Silva et al. 2016).
Additionally, the effect of CO2 gas after 5 mins con-
ditioning was also investigated and the results revealed a
zeta potential value of –30 mV, –34 mV, –23 mV, –50 mV
for serpentine, pentlandite, brucite, and silica respectively
(Figure 6). By reversing the charge of serpentine from a pos-
itive to a negative zeta potential, CO2 facilitated serpentine
suppression and should prevent slime coating of pentland-
ite by serpentine in flotation tests just like in the STPP case.
Thus, a few minutes conditioning of the mineral suspen-
sion with CO2 gas reverses the charge on serpentine’s sur-
face, thereby limiting slime coating on pentlandite’s surface
and enhancing overall pentlandite recovery plus grade. It
can therefore be inferred that the detrimental effects (slime
coating effect) caused by the presence of magnesium cat-
ions can be addressed by conditioning the mineral suspen-
sion with CO2, which converts the magnesium cations into
mineral carbonates, and remove any metal-monohydroxide
complexes on the surface of pentlandite (Wani et al. 2022).
Hence, the use of CO2 as both a conditioning reagent for
serpentine suppression and its use as a flotation gas is also
explored in flotation tests.
Microflotation tests
Figure 7 shows the cumulative nickel contained in the con-
centrates for all the experimental types and it clearly shows
that the CO2 only case attained the highest nickel recovery
(88%) which is 20% increase from the baseline case, fol-
lowed by the Air +STPP case (83%) and closely by the Air
+CO2 case (78%). Leading up to the first 50 s, a similar
flotation rate was observed for all the cases until about 100 s
where the flotation rate for the Air +CO2 case experienced
the highest rate. As the flotation time increased, both the
flotation recovery and rates for the CO2 only case became
increasingly better than other cases. This shows that CO2
bubbles are better at enhancing the recovery of pentlandite
than air bubbles or in the presence of STPP reagent.
Enhanced pentlandite recovery implies that the CO2
fine bubbles acted by either enhancing dispersion of slimes
on pentlandite’s surface or by facilitating the aggregation
of pentlandite particles, thereby increasing their hydropho-
bicity and floatability. It is not clear which is the leading
mechanism or if both occur simultaneously at the same
rate. However, it has been demonstrated in previous stud-
ies that by continuously bubbling the flotation system
with CO2, they nucleate and grow simultaneously on
-60
-50
-40
-30
-20
-10
0
Serpentine Pentlandite Brucite Silica
Mineral
Figure 6. Zeta potential measurements of different mineral suspensions after
conditioning with CO
2 gas
Zeta
potential
(mV)
implies a positive total interaction between serpentine and
pentlandite i.e., a repulsive force (Alvarez-Silva et al. 2016).
Additionally, the effect of CO2 gas after 5 mins con-
ditioning was also investigated and the results revealed a
zeta potential value of –30 mV, –34 mV, –23 mV, –50 mV
for serpentine, pentlandite, brucite, and silica respectively
(Figure 6). By reversing the charge of serpentine from a pos-
itive to a negative zeta potential, CO2 facilitated serpentine
suppression and should prevent slime coating of pentland-
ite by serpentine in flotation tests just like in the STPP case.
Thus, a few minutes conditioning of the mineral suspen-
sion with CO2 gas reverses the charge on serpentine’s sur-
face, thereby limiting slime coating on pentlandite’s surface
and enhancing overall pentlandite recovery plus grade. It
can therefore be inferred that the detrimental effects (slime
coating effect) caused by the presence of magnesium cat-
ions can be addressed by conditioning the mineral suspen-
sion with CO2, which converts the magnesium cations into
mineral carbonates, and remove any metal-monohydroxide
complexes on the surface of pentlandite (Wani et al. 2022).
Hence, the use of CO2 as both a conditioning reagent for
serpentine suppression and its use as a flotation gas is also
explored in flotation tests.
Microflotation tests
Figure 7 shows the cumulative nickel contained in the con-
centrates for all the experimental types and it clearly shows
that the CO2 only case attained the highest nickel recovery
(88%) which is 20% increase from the baseline case, fol-
lowed by the Air +STPP case (83%) and closely by the Air
+CO2 case (78%). Leading up to the first 50 s, a similar
flotation rate was observed for all the cases until about 100 s
where the flotation rate for the Air +CO2 case experienced
the highest rate. As the flotation time increased, both the
flotation recovery and rates for the CO2 only case became
increasingly better than other cases. This shows that CO2
bubbles are better at enhancing the recovery of pentlandite
than air bubbles or in the presence of STPP reagent.
Enhanced pentlandite recovery implies that the CO2
fine bubbles acted by either enhancing dispersion of slimes
on pentlandite’s surface or by facilitating the aggregation
of pentlandite particles, thereby increasing their hydropho-
bicity and floatability. It is not clear which is the leading
mechanism or if both occur simultaneously at the same
rate. However, it has been demonstrated in previous stud-
ies that by continuously bubbling the flotation system
with CO2, they nucleate and grow simultaneously on
-60
-50
-40
-30
-20
-10
0
Serpentine Pentlandite Brucite Silica
Mineral
Figure 6. Zeta potential measurements of different mineral suspensions after
conditioning with CO
2 gas
Zeta
potential
(mV)