2398 XXXI International Mineral Processing Congress 2024 Proceedings/Washington, DC/Sep 29–Oct 3
flotation, and this phenomenon has been confirmed by a
study where CO2 bubbles induction time was faster than
other bubbles (Hassas and Miller 2019). Additionally,
faster induction time relates to higher hydrophobic interac-
tion which is the underlying interaction for bubble-particle
attachment (Verrelli et al. 2011). Also, bubbling the min-
eral suspension with CO2 at pH 10.1 precipitates Mg2+
because of the dominant CO32– species, and therefore car-
bonation of the mineral suspension will produce MgCO3
and SiO2 (Equation 2) (Wani et al. 2022).
Mg3Si2O5(OH)4 +3CO2 →
3MgCO3 +2SiO2 +2H2O (2)
Thus, through enhanced hydrophobic interactions of
CO2 bubbles, there was high collision probability and high
attachment efficiency of CO2 bubbles with pentlandite
particles which resulted in the aggregation of the mineral
particles and remains an underlying mechanisms why the
highest flotation recoveries were achieved for the CO2 only
case (Figure 12) .
Furthermore, STPP effect was also effective in improv-
ing the recovery of pentlandite. By introducing STPP, the
negative phosphate groups in STPP chelated the magne-
sium cations on serpentine’s surface through the generation
of P-O-Mg bonds which is agrees with a previous study (Li
et al. 2022), thereby decomposing Mg2+ from the bulk ser-
pentine (Figure 13). These actions resulted in a negatively
charged serpentine’s surface, meaning that the hetero-
coagulation between pentlandite and fine serpentine was
reversed because a new electrostatic repulsion now exists
between them (Figure 13). Therefore, the pentlandite par-
ticles have renewed surfaces to better adsorb to PAX collec-
tors and attach to air bubbles, facilitating overall improved
pentlandite recovery. At the same time, the recovery of ser-
pentine particles was also reduced.
CONCLUSION
The use of STPP and CO2 gas help to improve flotation
processes in many ways as demonstrated in the study.
Conditioning and floating the mineral suspension with
CO2 converted the monohydroxide complexes to magne-
sium carbonate, resulting in improved pentlandite recovery
because MgCO3 is negatively charged and is not known to
slime coat pentlandite. This improved the recovery of pent-
landite by 20% and depressed serpentine by 3%, thereby
improving the cumulative nickel grade. In the experiment
where CO2 was used only in the conditioning stage (Air
+CO2 case), pentlandite recovery was improved by 10%
and serpentine depression by 4%. It provides a proof of
concept that CO2 can be permanently stored in the form
Figure 11. Peak concentrations of Mg 2s of serpentine before and after treatment with
STPP and CO
2
flotation, and this phenomenon has been confirmed by a
study where CO2 bubbles induction time was faster than
other bubbles (Hassas and Miller 2019). Additionally,
faster induction time relates to higher hydrophobic interac-
tion which is the underlying interaction for bubble-particle
attachment (Verrelli et al. 2011). Also, bubbling the min-
eral suspension with CO2 at pH 10.1 precipitates Mg2+
because of the dominant CO32– species, and therefore car-
bonation of the mineral suspension will produce MgCO3
and SiO2 (Equation 2) (Wani et al. 2022).
Mg3Si2O5(OH)4 +3CO2 →
3MgCO3 +2SiO2 +2H2O (2)
Thus, through enhanced hydrophobic interactions of
CO2 bubbles, there was high collision probability and high
attachment efficiency of CO2 bubbles with pentlandite
particles which resulted in the aggregation of the mineral
particles and remains an underlying mechanisms why the
highest flotation recoveries were achieved for the CO2 only
case (Figure 12) .
Furthermore, STPP effect was also effective in improv-
ing the recovery of pentlandite. By introducing STPP, the
negative phosphate groups in STPP chelated the magne-
sium cations on serpentine’s surface through the generation
of P-O-Mg bonds which is agrees with a previous study (Li
et al. 2022), thereby decomposing Mg2+ from the bulk ser-
pentine (Figure 13). These actions resulted in a negatively
charged serpentine’s surface, meaning that the hetero-
coagulation between pentlandite and fine serpentine was
reversed because a new electrostatic repulsion now exists
between them (Figure 13). Therefore, the pentlandite par-
ticles have renewed surfaces to better adsorb to PAX collec-
tors and attach to air bubbles, facilitating overall improved
pentlandite recovery. At the same time, the recovery of ser-
pentine particles was also reduced.
CONCLUSION
The use of STPP and CO2 gas help to improve flotation
processes in many ways as demonstrated in the study.
Conditioning and floating the mineral suspension with
CO2 converted the monohydroxide complexes to magne-
sium carbonate, resulting in improved pentlandite recovery
because MgCO3 is negatively charged and is not known to
slime coat pentlandite. This improved the recovery of pent-
landite by 20% and depressed serpentine by 3%, thereby
improving the cumulative nickel grade. In the experiment
where CO2 was used only in the conditioning stage (Air
+CO2 case), pentlandite recovery was improved by 10%
and serpentine depression by 4%. It provides a proof of
concept that CO2 can be permanently stored in the form
Figure 11. Peak concentrations of Mg 2s of serpentine before and after treatment with
STPP and CO
2