5
isobutyl carbinol (MIBC), polyglycols, pine oils, or other
materials as dedicated frothers to separate the responsibili-
ties of the frother and the collectors. Several of these tests
managed to improve recovery without sacrificing product
grade, but the specific theory behind optimally choosing
these reagents remains unclear (Zhang et al., 2021).
There is also significant room to explore other collectors
to either improve the selectivity over that of the etheramine
collectors, or to make more environmentally and biologi-
cally manageable reagents (Zhang et al., 2021).
AGGLOMERATION
The final step before metallurgical processing is transform-
ing the iron concentrate into a form which is convenient
for shipping and handling, and which has the necessary
geometric and metallurgical properties for effective pro-
cessing. This is agglomeration, where the fine iron ore
concentrates are agglomerated into larger materials (Eisele
and Kawatra, 2003), usually pellets or sinter. For fine iron
ore concentrates, pelletization is usually the agglomeration
method of choice.
Pelletization involves rolling a moist (usually 7–9%
water content by weight) iron concentrate in a drum or
disk. As flotation proceeds at higher moisture contents, the
material first needs to be dewatered, almost always by filtra-
tion. Notably, the water chemistry which supports efficient
filtration of iron ores is somewhat at odds with the water
chemistry that supports effective flotation or effective pel-
letization. Filtration proceeds most rapidly at flocculating
conditions, but the alkaline conditions of flotation prefer
dispersing conditions. As an example, the addition of car-
bon dioxide as an acidifying reagent to the thickener under-
flow feeding a filtration line at one iron ore concentration
plant improved the throughput by about 23% overall
(Carlson and Kawatra, 2011) by reducing this dispersion
effect.
Once dried, the concentrate is mixed with a selection
of binders, fluxes, and other reagents meant to prepare the
material for metallurgical processing. The rolling action of
the pellet in the disk or drum then allows the water in the
concentrate to utilize capillary action to bring the material
together and form the agglomerate (Eisele and Kawatra,
2003 Claremboux and Kawatra, 2022).
The most typical binder in the U.S. is sodium benton-
ite (Claremboux and Kawatra, 2022). The role of sodium
bentonite is to expand throughout the pellet by absorb-
ing the water to expand as the pellet grows, and then to
be undergo partial recrystallization during the indura-
tion phase to form a strong silicate matrix that lends the
pellet sufficient strength to survive blast furnace processing
(400 lbf or 1780 N compression strength Claremboux
and Kawatra, 2022).
However, a very large variety of materials can be applied
as binders. Most successful are polysaccharide chemistries
(modified starches and carboxymethylcellulose) or cementi-
tious chemistries (e.g., molasses and lime). The former are
generally preferred as surface active reagents, but the latter
can be used for cold bonding – achieving the final required
pellet strength without an energy intensive thermal indura-
tion step (Claremboux and Kawatra, 2022).
Mixed binders have also been studied and found effec-
tive so long as they are compatible overall. Surface active
binders (particularly bentonite and starch as in McDonald
and Kawatra, 2017) are generally compatible because their
mechanisms improve pellet strength whether the binders
interact with the pellet material or each other more or less
equally well. However, incompatible chemistries such as
the cementitious reaction of fly-ash with calcium and the
surface active binding of sodium bentonite (which is signif-
icantly and negatively impacted by the presence of calcium
ions, notably), can have even worse performance than the
binders would have if they were used separately (Ripke and
Kawatra, 2000).
Outside of the United States, sodium bentonite is also
far less available. Most bentonite deposits are calcium ben-
tonites, which exhibit far less swelling behavior and thus
spread much less readily through the pellet as they absorb
water (Eisele and Kawatra, 2003). This tends to push the
choice of binder towards these organic alternatives such
as starches or carboxymethylcelluloses, as they are more
globally available. The increased cost of these compared to
bentonite is justified by much lower binder dosage require-
ments in general. A typical organic binder dosage may be
less than 1/10th by weight the dosage required for sodium
bentonite, which in turn is usually less than half the dosage
required for effective performance of calcium bentonites.
The requirements of an effective binder generally appear
to be (as reported in Claremboux and Kawatra, 2022):
• The binder must be able to provide strength to the
pellet that will be retained long enough to support
the metallurgical processing of the pellet.
• The binder must be able to spread through the pel-
let and bind the whole pellet, requiring some water-
phase mobility.
• The binder must be able to interact with the water in
the pellet, particularly to spread it evenly through the
pellet and make it available at the surface of the pellet
to promote pellet growth.
isobutyl carbinol (MIBC), polyglycols, pine oils, or other
materials as dedicated frothers to separate the responsibili-
ties of the frother and the collectors. Several of these tests
managed to improve recovery without sacrificing product
grade, but the specific theory behind optimally choosing
these reagents remains unclear (Zhang et al., 2021).
There is also significant room to explore other collectors
to either improve the selectivity over that of the etheramine
collectors, or to make more environmentally and biologi-
cally manageable reagents (Zhang et al., 2021).
AGGLOMERATION
The final step before metallurgical processing is transform-
ing the iron concentrate into a form which is convenient
for shipping and handling, and which has the necessary
geometric and metallurgical properties for effective pro-
cessing. This is agglomeration, where the fine iron ore
concentrates are agglomerated into larger materials (Eisele
and Kawatra, 2003), usually pellets or sinter. For fine iron
ore concentrates, pelletization is usually the agglomeration
method of choice.
Pelletization involves rolling a moist (usually 7–9%
water content by weight) iron concentrate in a drum or
disk. As flotation proceeds at higher moisture contents, the
material first needs to be dewatered, almost always by filtra-
tion. Notably, the water chemistry which supports efficient
filtration of iron ores is somewhat at odds with the water
chemistry that supports effective flotation or effective pel-
letization. Filtration proceeds most rapidly at flocculating
conditions, but the alkaline conditions of flotation prefer
dispersing conditions. As an example, the addition of car-
bon dioxide as an acidifying reagent to the thickener under-
flow feeding a filtration line at one iron ore concentration
plant improved the throughput by about 23% overall
(Carlson and Kawatra, 2011) by reducing this dispersion
effect.
Once dried, the concentrate is mixed with a selection
of binders, fluxes, and other reagents meant to prepare the
material for metallurgical processing. The rolling action of
the pellet in the disk or drum then allows the water in the
concentrate to utilize capillary action to bring the material
together and form the agglomerate (Eisele and Kawatra,
2003 Claremboux and Kawatra, 2022).
The most typical binder in the U.S. is sodium benton-
ite (Claremboux and Kawatra, 2022). The role of sodium
bentonite is to expand throughout the pellet by absorb-
ing the water to expand as the pellet grows, and then to
be undergo partial recrystallization during the indura-
tion phase to form a strong silicate matrix that lends the
pellet sufficient strength to survive blast furnace processing
(400 lbf or 1780 N compression strength Claremboux
and Kawatra, 2022).
However, a very large variety of materials can be applied
as binders. Most successful are polysaccharide chemistries
(modified starches and carboxymethylcellulose) or cementi-
tious chemistries (e.g., molasses and lime). The former are
generally preferred as surface active reagents, but the latter
can be used for cold bonding – achieving the final required
pellet strength without an energy intensive thermal indura-
tion step (Claremboux and Kawatra, 2022).
Mixed binders have also been studied and found effec-
tive so long as they are compatible overall. Surface active
binders (particularly bentonite and starch as in McDonald
and Kawatra, 2017) are generally compatible because their
mechanisms improve pellet strength whether the binders
interact with the pellet material or each other more or less
equally well. However, incompatible chemistries such as
the cementitious reaction of fly-ash with calcium and the
surface active binding of sodium bentonite (which is signif-
icantly and negatively impacted by the presence of calcium
ions, notably), can have even worse performance than the
binders would have if they were used separately (Ripke and
Kawatra, 2000).
Outside of the United States, sodium bentonite is also
far less available. Most bentonite deposits are calcium ben-
tonites, which exhibit far less swelling behavior and thus
spread much less readily through the pellet as they absorb
water (Eisele and Kawatra, 2003). This tends to push the
choice of binder towards these organic alternatives such
as starches or carboxymethylcelluloses, as they are more
globally available. The increased cost of these compared to
bentonite is justified by much lower binder dosage require-
ments in general. A typical organic binder dosage may be
less than 1/10th by weight the dosage required for sodium
bentonite, which in turn is usually less than half the dosage
required for effective performance of calcium bentonites.
The requirements of an effective binder generally appear
to be (as reported in Claremboux and Kawatra, 2022):
• The binder must be able to provide strength to the
pellet that will be retained long enough to support
the metallurgical processing of the pellet.
• The binder must be able to spread through the pel-
let and bind the whole pellet, requiring some water-
phase mobility.
• The binder must be able to interact with the water in
the pellet, particularly to spread it evenly through the
pellet and make it available at the surface of the pellet
to promote pellet growth.