2670 XXXI International Mineral Processing Congress 2024 Proceedings/Washington, DC/Sep 29–Oct 3
context of seasonal changes, can impact the performance of
hydrocyclone separators found in typical grinding circuits,
impacting the grind size targeted by the cyclones (Kawatra
and Eisele, 1988).
The reverse cationic flotation process used in many
North American iron ore processing plants uses pH to
maintain a dispersing environment as well, primarily to
allow for easier separation of gangue materials from iron-
bearing minerals. At lower pH values, the surface charges
of the iron-bearing minerals are less negative, and if the pH
drops below a certain point (the isoelectric point) then the
surface charge becomes positive. If the gangue and iron-
bearing minerals have opposing charges, then the charge
difference will attract them to each other making separation
far more difficult. However, while this level of dispersion is
necessary for efficient desliming and the flotation process,
it is often achieved with simple inorganic compounds like
caustic soda.
Caustic soda’s chemistry is relatively simple as a dis-
persant, however. Its interactions with other reagents in
the process are relatively minimal or well understood, such
as the causticization of starch to improve solubility. The
structure of more complex dispersants, especially organic
polymers, can be far more involved. The impact of many
different types of reagents on the surface charge of iron ore
minerals is reported in Carlson and Kawatra (2013), high-
lighting the considerable impact even reagents not typically
chosen for surface chemical interactions can have on the
mineral’s surface. Thus, the introduction of potent, dedi-
cated dispersants can have far reaching effects on the flota-
tion process if these interactions are not accounted for.
The authors are aware of a plant trial at an iron ore
concentrator where a grinding aid was introduced into
the comminution process. The grinding efficiency was
improved considerably, by approximately 10% above
their baseline from their existing grinding procedures. The
plant management was quite impressed with the increase.
However, the grinding aid was never implemented by plant
operations. Even though the grinding was significantly
improved, when the additive reached the flotation circuit
the froth completely died.
Because the flotation was so negatively affected, this
10% improvement in grinding efficiency could not be
used. It would have been a completely different story at,
for example, a coal crushing plant with no need to main-
tain the material for downstream flotation. But in iron ore
processing, the processed material needs to work with the
downstream processes. Whether it is adding a grinding aid
at comminution or adding a new reagent in flotation, it
needs to work downstream whether in deslime and flota-
tion or in the thickeners and filtration.
Consider, however, how the situation differs for coal
water fuels. With the addition of grinding aids, the coal
water fuels can be pumped at a higher percent solids directly
resulting in increased profits. In this process, there is no flo-
tation step, which makes the gains very obvious.
This gap in the research between the impact of grind-
ing aids on grinding and the impact of grinding aids on the
subsequent iron ore flotation has been noted elsewhere in
the literature (Chipakwe et al., 2022). There are grinding
aids which are effective in iron ore processing, and there
certainly may be some which can achieve similar improve-
ments to the anecdote mentioned prior without destroying
the flotation.
Chipakwe et al. (2022) reports that polysaccharide-
based reagent (in the same general family of chemicals as
modified starches or celluloses) presents benefits in both
the grinding and the reverse cationic flotation processes for
magnetite ores. Bench scale studies found that the poly-
saccharide-based reagent allowed for a narrower and finer
particle size distribution, and that 86% Fe recovery could
be achieved even without the addition of starch.
Chipakwe et al. (2023) reports on another promising
reagent based on polyacrylic acid, achieving an 18% reduc-
tion in grinding energy consumption in benchtop tests
with magnetite/quartz mixtures. In this case the reagent is
also effective as a quartz collector, but it is also a strong
dispersant. It may be worth noting that if it preferentially
adsorbs to quartz, it may be mostly removed during the
flotation process in full scale studies. If it remains strongly
with the magnetite as well then it may potentially pose a
challenge during filtration, due to the dispersing effects,
though the effect may be small compared to the existing
pH-related dispersion.
It must be emphasized that the flotation process is
sensitive to almost any change in the water chemistry, and
the impact of a grinding aid on that needs to be evaluated.
Grinding aids introduced at the head of process may influ-
ence any downstream process, depending on how sensitive
the processes are to their presence and depending on where
the grinding aids tend to deport to as they pass through the
process.
The conceptual overlap of each step of the iron ore
concentration process is important to recognize here. The
dispersion behavior in the grinding is the same kind of
chemical phenomenon as the dispersion in desliming, in
flotation, and in agglomeration. This is both the reason
why these sorts of problems can occur, and key to under-
standing how to solve them.
context of seasonal changes, can impact the performance of
hydrocyclone separators found in typical grinding circuits,
impacting the grind size targeted by the cyclones (Kawatra
and Eisele, 1988).
The reverse cationic flotation process used in many
North American iron ore processing plants uses pH to
maintain a dispersing environment as well, primarily to
allow for easier separation of gangue materials from iron-
bearing minerals. At lower pH values, the surface charges
of the iron-bearing minerals are less negative, and if the pH
drops below a certain point (the isoelectric point) then the
surface charge becomes positive. If the gangue and iron-
bearing minerals have opposing charges, then the charge
difference will attract them to each other making separation
far more difficult. However, while this level of dispersion is
necessary for efficient desliming and the flotation process,
it is often achieved with simple inorganic compounds like
caustic soda.
Caustic soda’s chemistry is relatively simple as a dis-
persant, however. Its interactions with other reagents in
the process are relatively minimal or well understood, such
as the causticization of starch to improve solubility. The
structure of more complex dispersants, especially organic
polymers, can be far more involved. The impact of many
different types of reagents on the surface charge of iron ore
minerals is reported in Carlson and Kawatra (2013), high-
lighting the considerable impact even reagents not typically
chosen for surface chemical interactions can have on the
mineral’s surface. Thus, the introduction of potent, dedi-
cated dispersants can have far reaching effects on the flota-
tion process if these interactions are not accounted for.
The authors are aware of a plant trial at an iron ore
concentrator where a grinding aid was introduced into
the comminution process. The grinding efficiency was
improved considerably, by approximately 10% above
their baseline from their existing grinding procedures. The
plant management was quite impressed with the increase.
However, the grinding aid was never implemented by plant
operations. Even though the grinding was significantly
improved, when the additive reached the flotation circuit
the froth completely died.
Because the flotation was so negatively affected, this
10% improvement in grinding efficiency could not be
used. It would have been a completely different story at,
for example, a coal crushing plant with no need to main-
tain the material for downstream flotation. But in iron ore
processing, the processed material needs to work with the
downstream processes. Whether it is adding a grinding aid
at comminution or adding a new reagent in flotation, it
needs to work downstream whether in deslime and flota-
tion or in the thickeners and filtration.
Consider, however, how the situation differs for coal
water fuels. With the addition of grinding aids, the coal
water fuels can be pumped at a higher percent solids directly
resulting in increased profits. In this process, there is no flo-
tation step, which makes the gains very obvious.
This gap in the research between the impact of grind-
ing aids on grinding and the impact of grinding aids on the
subsequent iron ore flotation has been noted elsewhere in
the literature (Chipakwe et al., 2022). There are grinding
aids which are effective in iron ore processing, and there
certainly may be some which can achieve similar improve-
ments to the anecdote mentioned prior without destroying
the flotation.
Chipakwe et al. (2022) reports that polysaccharide-
based reagent (in the same general family of chemicals as
modified starches or celluloses) presents benefits in both
the grinding and the reverse cationic flotation processes for
magnetite ores. Bench scale studies found that the poly-
saccharide-based reagent allowed for a narrower and finer
particle size distribution, and that 86% Fe recovery could
be achieved even without the addition of starch.
Chipakwe et al. (2023) reports on another promising
reagent based on polyacrylic acid, achieving an 18% reduc-
tion in grinding energy consumption in benchtop tests
with magnetite/quartz mixtures. In this case the reagent is
also effective as a quartz collector, but it is also a strong
dispersant. It may be worth noting that if it preferentially
adsorbs to quartz, it may be mostly removed during the
flotation process in full scale studies. If it remains strongly
with the magnetite as well then it may potentially pose a
challenge during filtration, due to the dispersing effects,
though the effect may be small compared to the existing
pH-related dispersion.
It must be emphasized that the flotation process is
sensitive to almost any change in the water chemistry, and
the impact of a grinding aid on that needs to be evaluated.
Grinding aids introduced at the head of process may influ-
ence any downstream process, depending on how sensitive
the processes are to their presence and depending on where
the grinding aids tend to deport to as they pass through the
process.
The conceptual overlap of each step of the iron ore
concentration process is important to recognize here. The
dispersion behavior in the grinding is the same kind of
chemical phenomenon as the dispersion in desliming, in
flotation, and in agglomeration. This is both the reason
why these sorts of problems can occur, and key to under-
standing how to solve them.