296 XXXI International Mineral Processing Congress 2024 Proceedings/Washington, DC/Sep 29–Oct 3
CO2 as a flotation gas
CO2 was studied as a conditioning gas instead of air during
nickel froth-flotation resulting in the conversion of mono-
hydroxide complexes of divalent ions such as Ca2+ and
Mg2+ from recycled water to their respective carbonates
(Wani et al., 2022). This led to the electrostatic repulsion
between the nickel-containing mineral and the unwanted
serpentine, leading to its lower slime coating and enhanced
froth flotation nickel recovery and grade by 10 and 4 wt.%.
Since recycled water is used in industry, their study pro-
vided insight into a vital phenomenon of Ca2+ and Mg2+
ions’ detrimental effect on the froth flotation of nickel,
which is mitigated during CO2 conditioning and the miti-
gation of serpentine slime coating.
Possible Nickel Processing Pathways for Reducing CO2
Emissions
The CO2 sequestration technologies discussed in the sec-
tions above are characterized (Table 2) based on various
parameters such as CO2 source, CO2 availability (avail-
ability of CO2 for sequestration), process modifications
required (based on technical acceptance), time for seques-
tration (fast or slow), and the value addition (source of rev-
enue it brings to existing process). With the technologies
being mainly emerging, a qualitative analysis is provided.
The CO2 source for the carbonation of ore, tailings,
and froth-flotation gas, will be mainly process power gener-
ation, while for the carbonation of laterite ores, the source
will be a combination of power generation (natural gas or
diesel) and neutralization reaction between sulfuric acid and
calcite (Eqn. 7). In doing so, the emissions which would
otherwise escape to the atmosphere, can be repurposed in
carbonation reactions with Mg2+ ions leached from the ore.
Captured CO2 availability would be a combination
of factors such as the volume and the purification of CO2
required for sequestration. For the carbonation of ore and
tailings, the CO2 from power generation would require
additional treatment, including dehydration before com-
pression. In contrast, CO2 used as a flotation gas would
need less treatment. Similarly, since the laterite ores neu-
tralization will release high-purity CO2, the availability
would be high.
Process modifications will require capital expendi-
tures (capex), which will be a significant factor in deter-
mining the feasibility of process addition. For carbonation
of ore before flotation, installation of process equipment
and change of flowsheet would be required, increasing the
capex. However, the process would benefit from the exist-
ing plant infrastructure. In the case of tailings carbonation,
existing plant processes will not require significant modifi-
cations, but a separate plant near the tailing’s storage facility
with its power generation, carbonated product processing
facility, etc., will be required, which will increase the capex.
For CO2 flotation, the costs will be lower due to minor
process adjustments, while moderate adjustments would be
needed for the carbonation of laterite ores at ambient con-
ditions and the presence of divalent magnesium ions from
leaching.
Based on the current state of CO2 sequestration, the
time for CO2 sequestration would be fast due to the accel-
erated carbonation of nickel sulfide and nickel laterite
ores, whereas tailings carbonation would take more time at
ambient conditions. Although CO2 gas will assist flotation,
the conversion of CO2 to magnesite in flotation would be
slower than the accelerated carbonation of ores.
Regarding value addition, the carbonation of ore and
CO2 as flotation gas shows promising results in improving
Table 2. Comparative analysis of CO2 sequestration pathways in nickel processing
Sequestration
Route CO
2 Source
Captured CO
2 Availability
Process Modifications
Required
Time for
Sequestration Value Addition
1 Carbonation
of Ore before
Flotation
Power Generation Moderate Considerable adjustments
given the In-Process
Installation
Fast Additional Ni
Revenue
2 Carbonation of
Tailings
Power Generation Moderate Considerable adjustments
to establish infrastructure
at TSF
Moderate Carbon Offset
Revenue
3 CO
2 as a
Flotation gas
Power Generation High Minor adjustments needed Moderate Additional Ni
Revenue
4 Carbonation of
Nickel Laterite
Ore
Power Generation
+Neutralization
Reaction
High Moderate adjustments
needed
Fast Carbon Offset
Revenue
CO2 as a flotation gas
CO2 was studied as a conditioning gas instead of air during
nickel froth-flotation resulting in the conversion of mono-
hydroxide complexes of divalent ions such as Ca2+ and
Mg2+ from recycled water to their respective carbonates
(Wani et al., 2022). This led to the electrostatic repulsion
between the nickel-containing mineral and the unwanted
serpentine, leading to its lower slime coating and enhanced
froth flotation nickel recovery and grade by 10 and 4 wt.%.
Since recycled water is used in industry, their study pro-
vided insight into a vital phenomenon of Ca2+ and Mg2+
ions’ detrimental effect on the froth flotation of nickel,
which is mitigated during CO2 conditioning and the miti-
gation of serpentine slime coating.
Possible Nickel Processing Pathways for Reducing CO2
Emissions
The CO2 sequestration technologies discussed in the sec-
tions above are characterized (Table 2) based on various
parameters such as CO2 source, CO2 availability (avail-
ability of CO2 for sequestration), process modifications
required (based on technical acceptance), time for seques-
tration (fast or slow), and the value addition (source of rev-
enue it brings to existing process). With the technologies
being mainly emerging, a qualitative analysis is provided.
The CO2 source for the carbonation of ore, tailings,
and froth-flotation gas, will be mainly process power gener-
ation, while for the carbonation of laterite ores, the source
will be a combination of power generation (natural gas or
diesel) and neutralization reaction between sulfuric acid and
calcite (Eqn. 7). In doing so, the emissions which would
otherwise escape to the atmosphere, can be repurposed in
carbonation reactions with Mg2+ ions leached from the ore.
Captured CO2 availability would be a combination
of factors such as the volume and the purification of CO2
required for sequestration. For the carbonation of ore and
tailings, the CO2 from power generation would require
additional treatment, including dehydration before com-
pression. In contrast, CO2 used as a flotation gas would
need less treatment. Similarly, since the laterite ores neu-
tralization will release high-purity CO2, the availability
would be high.
Process modifications will require capital expendi-
tures (capex), which will be a significant factor in deter-
mining the feasibility of process addition. For carbonation
of ore before flotation, installation of process equipment
and change of flowsheet would be required, increasing the
capex. However, the process would benefit from the exist-
ing plant infrastructure. In the case of tailings carbonation,
existing plant processes will not require significant modifi-
cations, but a separate plant near the tailing’s storage facility
with its power generation, carbonated product processing
facility, etc., will be required, which will increase the capex.
For CO2 flotation, the costs will be lower due to minor
process adjustments, while moderate adjustments would be
needed for the carbonation of laterite ores at ambient con-
ditions and the presence of divalent magnesium ions from
leaching.
Based on the current state of CO2 sequestration, the
time for CO2 sequestration would be fast due to the accel-
erated carbonation of nickel sulfide and nickel laterite
ores, whereas tailings carbonation would take more time at
ambient conditions. Although CO2 gas will assist flotation,
the conversion of CO2 to magnesite in flotation would be
slower than the accelerated carbonation of ores.
Regarding value addition, the carbonation of ore and
CO2 as flotation gas shows promising results in improving
Table 2. Comparative analysis of CO2 sequestration pathways in nickel processing
Sequestration
Route CO
2 Source
Captured CO
2 Availability
Process Modifications
Required
Time for
Sequestration Value Addition
1 Carbonation
of Ore before
Flotation
Power Generation Moderate Considerable adjustments
given the In-Process
Installation
Fast Additional Ni
Revenue
2 Carbonation of
Tailings
Power Generation Moderate Considerable adjustments
to establish infrastructure
at TSF
Moderate Carbon Offset
Revenue
3 CO
2 as a
Flotation gas
Power Generation High Minor adjustments needed Moderate Additional Ni
Revenue
4 Carbonation of
Nickel Laterite
Ore
Power Generation
+Neutralization
Reaction
High Moderate adjustments
needed
Fast Carbon Offset
Revenue