4
cutoff size to reject primarily the colloidal material, or by
selective flocculation and dispersion desliming. The hydro-
cyclone approach faces significant challenges for target sizes
much below the fine liberation sizes required for the more
difficult iron ore bodies, and as such selective flocculation
and dispersion desliming is often used in these scenarios.
Selective flocculation and dispersion desliming involves
utilizing a dispersant to disperse all of the materials along-
side a selective flocculant for the iron-bearing minerals to
sink them. For hematite and silica, the traditional disper-
sant choice is caustic soda and the traditional flocculant
choice is starch. Other dispersant chemistries have been
used at operating facilities, including modified sodium sili-
cates, tripolyphosphates, and polyacrylamide chemistries
(Zhang et al., 2021).
These alternative chemistries can have various positive
impacts on the process, such as by having a greater dispers-
ing effect per unit of reagent or by helping to sequester cal-
cium and magnesium cations in the solution. In general, so
long as the solution is properly dispersed (either from the
impact of the dispersant directly or via a maintained alka-
linity of the solution) and the selectivity of the flocculant
is maintained (which is strongly dependent on activating
species such as the previously mentioned calcium and mag-
nesium), the selective flocculation and desliming process is
very effective at rejecting gangue slimes.
The impact of calcium and magnesium, and the water
chemistry in general, cannot be understated here (Haselhuhn
and Kawatra, 2015 a,b,c). Green and Colombo (1984) had
identified that the concentrations of calcium and magne-
sium should be maintained below 15ppm for good results
in the desliming process. Recent studies in adjacent flota-
tion work on the impact of calcium and magnesium would
suggest that both can negatively impact the selectivity of
starch at even lower concentrations (Parra-Álvarez et al.,
2023). In flotation, a small amount of calcium (roughly
5ppm) may be slightly advantageous, but any amount of
magnesium appears to be detrimental in the flotation step.
As the selectivity of the starch is the key concern here, it is
likely that these results are at least partially mirrored in the
desliming process.
Once the slimes are removed, additional separations can
proceed. Flotation can proceed by several routes, though
the most common in the west is reverse cationic flotation
(Zhang et al., 2021). The slurry is raised to alkaline pH via
caustic soda or similar basic reagent, the gangue materials
are collected typically via etheramines (for hematite ores)
or etherdiamines (for magnetite ores), which also act as the
frother for bubble formation. The hematite or magnetite
is simultaneously suppressed using a selective depressant,
which is again typically a modified starch. Goethite-rich
materials can also be processed via this method, but the
chemically bound water in goethite can provide additional
challenges in induration later.
Siderite ores are usually processed via a stepped flota-
tion process (Shao, 2013 Zhang et al., 2021), where the
siderites are directly floated first and then the remaining
iron minerals are treated with standard techniques. Siderite
slimes formed during the grinding process are particularly
problematic, as they depress silica in typical desliming pro-
cesses (Yin et al., 2010 Zhang et al., 2021).
Opportunities in Flotation
Reverse cationic flotation floats silica or other gangues away
from the iron-rich minerals in several scavenging stages.
Flotation recovery is limited primarily by the effectiveness
of the depressant and the minimization of entrainment and
entrapment of valuables in the froth phase. Product grade
is primarily limited by the selectivity of the depressant and
the effectiveness of the collector.
Existing depressants utilizing starches as a basis likely
rely on a very convenient coincidence in the structure of
pyranose (the primary functional ring in the amylose and
amylopectin that compose starch) and hematite, which
share a compatible surface site spacing of 283–285pm
(Zhang et al., 2021). This similarity appears to be key for
the very good selectivity of most starches for hematite and
other iron oxides versus silicates or other common gangues.
There are some organic materials that outperform starches
for iron ore depression (such as zein, a specific protein
found in corn starch Peres and Corra, 1996), but they are
usually relatively high cost compared to starches.
There are opportunities to be had with the choice of
collector in reverse cationic flotation. While etheramines
chemistries are effective, their selectivity is generally not as
precise as could be desired, and they also have significant
frothing power. While in one sense the frothing power is
positive, as it eliminates the strict need for a separate frother,
it also limits the options to control the overall frother dos-
ing. In the case when more frother is desired, the addition
of etheramines (which are relatively expensive reagents
compared to common frothers) for the sake of increasing
frothing is relatively wasteful and can potentially reduce
recovery due to overcollection reaching the iron-bearing
minerals.
Some studies (Suardini, 1994 Araujo et al., 2005
Rodrigues et al., 2008 Parra-Álvarez et al., 2020) have
investigated partially replacing the etheramines with methyl
cutoff size to reject primarily the colloidal material, or by
selective flocculation and dispersion desliming. The hydro-
cyclone approach faces significant challenges for target sizes
much below the fine liberation sizes required for the more
difficult iron ore bodies, and as such selective flocculation
and dispersion desliming is often used in these scenarios.
Selective flocculation and dispersion desliming involves
utilizing a dispersant to disperse all of the materials along-
side a selective flocculant for the iron-bearing minerals to
sink them. For hematite and silica, the traditional disper-
sant choice is caustic soda and the traditional flocculant
choice is starch. Other dispersant chemistries have been
used at operating facilities, including modified sodium sili-
cates, tripolyphosphates, and polyacrylamide chemistries
(Zhang et al., 2021).
These alternative chemistries can have various positive
impacts on the process, such as by having a greater dispers-
ing effect per unit of reagent or by helping to sequester cal-
cium and magnesium cations in the solution. In general, so
long as the solution is properly dispersed (either from the
impact of the dispersant directly or via a maintained alka-
linity of the solution) and the selectivity of the flocculant
is maintained (which is strongly dependent on activating
species such as the previously mentioned calcium and mag-
nesium), the selective flocculation and desliming process is
very effective at rejecting gangue slimes.
The impact of calcium and magnesium, and the water
chemistry in general, cannot be understated here (Haselhuhn
and Kawatra, 2015 a,b,c). Green and Colombo (1984) had
identified that the concentrations of calcium and magne-
sium should be maintained below 15ppm for good results
in the desliming process. Recent studies in adjacent flota-
tion work on the impact of calcium and magnesium would
suggest that both can negatively impact the selectivity of
starch at even lower concentrations (Parra-Álvarez et al.,
2023). In flotation, a small amount of calcium (roughly
5ppm) may be slightly advantageous, but any amount of
magnesium appears to be detrimental in the flotation step.
As the selectivity of the starch is the key concern here, it is
likely that these results are at least partially mirrored in the
desliming process.
Once the slimes are removed, additional separations can
proceed. Flotation can proceed by several routes, though
the most common in the west is reverse cationic flotation
(Zhang et al., 2021). The slurry is raised to alkaline pH via
caustic soda or similar basic reagent, the gangue materials
are collected typically via etheramines (for hematite ores)
or etherdiamines (for magnetite ores), which also act as the
frother for bubble formation. The hematite or magnetite
is simultaneously suppressed using a selective depressant,
which is again typically a modified starch. Goethite-rich
materials can also be processed via this method, but the
chemically bound water in goethite can provide additional
challenges in induration later.
Siderite ores are usually processed via a stepped flota-
tion process (Shao, 2013 Zhang et al., 2021), where the
siderites are directly floated first and then the remaining
iron minerals are treated with standard techniques. Siderite
slimes formed during the grinding process are particularly
problematic, as they depress silica in typical desliming pro-
cesses (Yin et al., 2010 Zhang et al., 2021).
Opportunities in Flotation
Reverse cationic flotation floats silica or other gangues away
from the iron-rich minerals in several scavenging stages.
Flotation recovery is limited primarily by the effectiveness
of the depressant and the minimization of entrainment and
entrapment of valuables in the froth phase. Product grade
is primarily limited by the selectivity of the depressant and
the effectiveness of the collector.
Existing depressants utilizing starches as a basis likely
rely on a very convenient coincidence in the structure of
pyranose (the primary functional ring in the amylose and
amylopectin that compose starch) and hematite, which
share a compatible surface site spacing of 283–285pm
(Zhang et al., 2021). This similarity appears to be key for
the very good selectivity of most starches for hematite and
other iron oxides versus silicates or other common gangues.
There are some organic materials that outperform starches
for iron ore depression (such as zein, a specific protein
found in corn starch Peres and Corra, 1996), but they are
usually relatively high cost compared to starches.
There are opportunities to be had with the choice of
collector in reverse cationic flotation. While etheramines
chemistries are effective, their selectivity is generally not as
precise as could be desired, and they also have significant
frothing power. While in one sense the frothing power is
positive, as it eliminates the strict need for a separate frother,
it also limits the options to control the overall frother dos-
ing. In the case when more frother is desired, the addition
of etheramines (which are relatively expensive reagents
compared to common frothers) for the sake of increasing
frothing is relatively wasteful and can potentially reduce
recovery due to overcollection reaching the iron-bearing
minerals.
Some studies (Suardini, 1994 Araujo et al., 2005
Rodrigues et al., 2008 Parra-Álvarez et al., 2020) have
investigated partially replacing the etheramines with methyl