2672 XXXI International Mineral Processing Congress 2024 Proceedings/Washington, DC/Sep 29–Oct 3
pH values achieved, around 6.5–7.0, did not significantly
desorb calcium or magnesium.
Yet, the reduction in dispersion did increase the filtra-
tion throughput by up to 23%. Product quality was not
impacted, allowing for greater throughput of on-spec mate-
rial. The limiting factor for this improvement was the rate
of CO2 addition.
The primary contribution of the CO2 was that the
lowered pH brought the filter cake material closer to its
isoelectric point, lowering the intensity of the dispersion
introduced on it by the flotation process taking place at
around pH 11. The contrasting conditions required by
flotation and filtration should serve to further emphasize
how interconnected every part of the iron ore concentra-
tion process is.
Note also that this increase in filtration rate is by
mechanisms which are orthogonal to the typical activity of
dewatering agents. For example, Patra et al. (2015) report
a very successful improvement in dewatering efficiency
using sodium dodecyl sulfate as a dewatering agent for iron
ore fines by completely different mechanisms and largely
without mention of the potential impacts of calcium and
magnesium. It is likely that the use of one strategy does not
preclude the other in this case.
It is worth noting that calcium is sometimes added (as
calcium chloride) to the dry materials in iron ore concen-
trators as a dust suppressant, to great effect (Copeland et
al., 2009). This is usually ascribed to the hygroscopic nature
of calcium chloride, drawing moisture towards the fines,
making it more difficult for dust to become airborne.
CASE 3: DISPERSION AND
FLOCCULATION
The consistent theme of iron ore concentration is the use of
surface chemistry to promote the separation and agglom-
eration of specific materials. In grinding, dispersion aids in
the separation of particles from each other and themselves,
such as by reducing the impact of slime formation.
In selective flocculation and dispersion desliming,
dispersion is used to keep gangue slimes afloat while the
valuable iron-bearing minerals are flocculated and sunk
(Krishnan and Iwasaki, 1984 Haselhuhn et al., 2012b
Haselhuhn and Kawatra, 2015). This process is very sensi-
tive to the water chemistry, being dependent on a careful
balance where one material can be dispersed while another
flocculates.
In reverse cationic flotation, the dispersion is main-
tained to ensure that iron-bearing mineral surfaces are not
coated by gangue minerals, or vice-versa, which would pre-
vent effective separation (Zhang et al., 2021). At the same
time, the most used iron depressant in reverse cationic flo-
tation, starch, is also a selective flocculant which primarily
depresses hematite and magnetite.
As mentioned previously, the impact of (over)disper-
sion on filtration is also directly observed, as reducing the
extent of dispersion has such an immediately apparent
impact on filtration rates.
Even past filtration, in agglomeration processes such
as pelletization where the ore is recombined to form easily
transportable product, the role of flocculation and disper-
sion remains vital. The formation of pellets is a complex
interplay of rheological and surface chemistry effects, where
the addition of reagents which affect either or both is likely
to have a considerable effect (De Moraes et al., 2013).
Although in agglomeration it may seem straightfor-
ward the process is overall one of flocculation, studies have
found that dispersion results in the formation of smoother,
stronger, and more abrasion resistant pellets for a variety of
binders (Halt and Kawatra, 2017). The addition of floc-
culants instead seemed to promote the formation of weaker
and dustier pellets, suggesting that the influence of floccu-
lants in creating pellets more rapidly was overall detrimen-
tal to their internal structure.
Throughout the reverse cationic flotation process iron
ore is dispersed (in grinding), flocculated (in desliming),
re-dispersed (in flotation), re-flocculated (in filtration),
and then dispersed again (potentially, in agglomeration) to
make a useful final product. It cannot be overstated how
important these surface chemistry effects are to the overall
process.
There is tremendous opportunity to optimize the over-
all process by understanding the overarching, shared behav-
ior between each of these distinct steps and accounting for
it in each potential optimization. It also leads to questions
of how these back-and-forth cycles between dispersing and
flocculating conditions could potentially be avoided or
eliminated. Perhaps the most drastic optimization would be
to consider entirely different processes from the ground up,
such as the pig iron nugget process (Anameric and Kawatra,
2006 Anameric et al., 2006), a process which may also
have applications in processing other iron-bearing but dif-
ficult materials such as Bayer process red mud (Archambo
and Kawatra, 2021)
SUMMARY
Iron ore processing depends on maintaining the highest
possible recoveries while still making high quality product.
To achieve these recoveries does require that each section
of the process be optimized as much as possible. Yet, these
sections are all critically interwoven with each other, and
pH values achieved, around 6.5–7.0, did not significantly
desorb calcium or magnesium.
Yet, the reduction in dispersion did increase the filtra-
tion throughput by up to 23%. Product quality was not
impacted, allowing for greater throughput of on-spec mate-
rial. The limiting factor for this improvement was the rate
of CO2 addition.
The primary contribution of the CO2 was that the
lowered pH brought the filter cake material closer to its
isoelectric point, lowering the intensity of the dispersion
introduced on it by the flotation process taking place at
around pH 11. The contrasting conditions required by
flotation and filtration should serve to further emphasize
how interconnected every part of the iron ore concentra-
tion process is.
Note also that this increase in filtration rate is by
mechanisms which are orthogonal to the typical activity of
dewatering agents. For example, Patra et al. (2015) report
a very successful improvement in dewatering efficiency
using sodium dodecyl sulfate as a dewatering agent for iron
ore fines by completely different mechanisms and largely
without mention of the potential impacts of calcium and
magnesium. It is likely that the use of one strategy does not
preclude the other in this case.
It is worth noting that calcium is sometimes added (as
calcium chloride) to the dry materials in iron ore concen-
trators as a dust suppressant, to great effect (Copeland et
al., 2009). This is usually ascribed to the hygroscopic nature
of calcium chloride, drawing moisture towards the fines,
making it more difficult for dust to become airborne.
CASE 3: DISPERSION AND
FLOCCULATION
The consistent theme of iron ore concentration is the use of
surface chemistry to promote the separation and agglom-
eration of specific materials. In grinding, dispersion aids in
the separation of particles from each other and themselves,
such as by reducing the impact of slime formation.
In selective flocculation and dispersion desliming,
dispersion is used to keep gangue slimes afloat while the
valuable iron-bearing minerals are flocculated and sunk
(Krishnan and Iwasaki, 1984 Haselhuhn et al., 2012b
Haselhuhn and Kawatra, 2015). This process is very sensi-
tive to the water chemistry, being dependent on a careful
balance where one material can be dispersed while another
flocculates.
In reverse cationic flotation, the dispersion is main-
tained to ensure that iron-bearing mineral surfaces are not
coated by gangue minerals, or vice-versa, which would pre-
vent effective separation (Zhang et al., 2021). At the same
time, the most used iron depressant in reverse cationic flo-
tation, starch, is also a selective flocculant which primarily
depresses hematite and magnetite.
As mentioned previously, the impact of (over)disper-
sion on filtration is also directly observed, as reducing the
extent of dispersion has such an immediately apparent
impact on filtration rates.
Even past filtration, in agglomeration processes such
as pelletization where the ore is recombined to form easily
transportable product, the role of flocculation and disper-
sion remains vital. The formation of pellets is a complex
interplay of rheological and surface chemistry effects, where
the addition of reagents which affect either or both is likely
to have a considerable effect (De Moraes et al., 2013).
Although in agglomeration it may seem straightfor-
ward the process is overall one of flocculation, studies have
found that dispersion results in the formation of smoother,
stronger, and more abrasion resistant pellets for a variety of
binders (Halt and Kawatra, 2017). The addition of floc-
culants instead seemed to promote the formation of weaker
and dustier pellets, suggesting that the influence of floccu-
lants in creating pellets more rapidly was overall detrimen-
tal to their internal structure.
Throughout the reverse cationic flotation process iron
ore is dispersed (in grinding), flocculated (in desliming),
re-dispersed (in flotation), re-flocculated (in filtration),
and then dispersed again (potentially, in agglomeration) to
make a useful final product. It cannot be overstated how
important these surface chemistry effects are to the overall
process.
There is tremendous opportunity to optimize the over-
all process by understanding the overarching, shared behav-
ior between each of these distinct steps and accounting for
it in each potential optimization. It also leads to questions
of how these back-and-forth cycles between dispersing and
flocculating conditions could potentially be avoided or
eliminated. Perhaps the most drastic optimization would be
to consider entirely different processes from the ground up,
such as the pig iron nugget process (Anameric and Kawatra,
2006 Anameric et al., 2006), a process which may also
have applications in processing other iron-bearing but dif-
ficult materials such as Bayer process red mud (Archambo
and Kawatra, 2021)
SUMMARY
Iron ore processing depends on maintaining the highest
possible recoveries while still making high quality product.
To achieve these recoveries does require that each section
of the process be optimized as much as possible. Yet, these
sections are all critically interwoven with each other, and