Note: Descriptions are shown in the official language in which they were submitted.
WO 92/05290 ~ ~ 6 ~ ~ ~ ~ PCT/U59Q~J~P~~.~!~
MODIFIED NATIVE STARCH BASE BINDER FOR
PELLETIZING MINERAL MATERIAL
Field of the Invention
The present invention relates to modified "'
native starch base binders for pelletizing particulate
mineral materials and to mineral ore concentrates and
mineral ore pellets containing the novel binders.
Methods of using the novel binder are also disclosed.
Background of the Invention
In order to reduce impure deposits of iron ore
to commercially usable grades of iron, impure deposits
of iron ore are generally concentrated and pelletized
prior to reduction processing in blast furnaces.
Pelletizing impure mineral deposits has grown into a
very large industry since the end of World War II.
Mineral ores of various kinds are pelletized for ore
production but the process is most commonly with impure
iron ores, such as taconite. Approximately 40 million
tons of iron ore pellets are produced annually in the
United States and another 30 million tons are produced
in Canada. Other significant pellet production
facilities exist in several other countries including
Hrazil, Australia, Turkey, India, Norway and Japan.
High grade iron ore depasits in the United
States were severely depleted by the war effort during
World War II. In order to continue to produce steel in
blast furnace operations in the U.S., alternate sources
of iron were needed to feed the blast furnaces. The
University of Minnesota and a number of steel companies
concentrated their efforts on developing technology to
upgrade low grade magnetic ores, commonly called
taconite, into an acceptable iron ore feed for these
blast furnaces. Taconite, which is abundant in
Minnesota's Iron Range, typically contains about 25$
magnetic iron as compared to the roughly SO-70~ iron
content of some higher grade iron ores. In order to use
W092/05290 ~~~' PC.'f/~J~~!~!~!~'~..
20~ -
2
taconite in place of the higher grade ores in commercial
reduction processes, the iron content of the taconite
needed to be concentrated.
The process for concentrating the iron i..
taconite evolved to include blasting the taconite and
crushing it into particles small enough to liberate most
of the grains of magnetite. The pulverized ore is then
upgraded to an iron content in excess of preferably y
about 67~ iron in a series of concentrating steps. The
resulting mineral material is typically an aqueous
slurry which is filtered or otherwise reduced to a
moisture content of between about 9-10~ by weight.
This material cannot be added directly to a
blast furnace because the average particle size is so
small, typically in a range of about 10-40 microns in
diameter. Small particles such as these can plug a
blast furnace. In addition, they are often lost as air
entrained dust when fed directly into a blast furnace.
It was believed, however, that this problem could be
overcome by agglomerating the resulting mineral
material. The need for some method of agglomerating
this material subsequently led to the development of the
iron ore pelletizing industry.
The commercial pelletizing or agglameration
process is generally a continuous process in which
filtered mineral material is conveyed into balling drums
or "disks" to form pellets. The rotating drum or disk
causes the concentrated mineral material to roll into
balls, typically called "green" or undried balls or
pellets.
Green ball growth is somewhat similar to the
growth of a snowball when it is rolled in wet snow. .As
the ball is rolled, successive layers are added as the
ball grows to form a large ball. Seed pellets are
initially formed from the mineral material by the
rolling action of the drum. During commercial
operation, pellets are typically screened at the drum
WO 92/05290 ~~ ~ ~ ~ PCT/1.~59Q~,/~~''%~~''
3
discharge and the undersized pellets are recycled back
into the drum as seed pellets until they have grown to
form a ball having a diameter of about 1/2 inch (about
1.25 cm).
These green pellets are typically screened to
remove pellet fines, dried at increasingly higher
temperatures, and "fired" at a temperature of about
2400°F (1315°C). When the pellets are fired, the iron
grains grow together to form somewhat porous iron .
t0 matrices which provide strength to enable the pellets to
survive significant handling at shipping and receiving
sites during transshipment.
Barly in the development of the pelletizing
industry, it was recognized that green pellets without
"binding" agents were not suitable for subsequent
processing steps. For example, the green pellets often
broke during the balling process or during the initial
stages of the drying process. Therefore, it became
necessary to add a binding agent or "binder" to the
moist mineral material fed into the balling drum. Many
different additives were tested before it was determined
that bentonite clay or "bentonite" would provide the
binding strength required. Subsequently, bentonite
became the standard balling additive or binder used in
the pelletizing industry. Bentonite clay is typically
added to the mineral material at rates of somewhere
between about 10-25 pounds per long ton (2,240 pounds)
of pellets.
Unfortunately, bentonite contains significant
amounts of certain materials which shorten the useful
life and lower the performance of blast furnaces. One
of these materials is silica which is undesirable
because excessive amounts of silica result in excessive
amounts of slag which must be removed from blast
furnaces during processing. The silica in bentonite
also has the undesirable effect of melting and reforming
into a glassy coating which can coat the surface of the
NCO 93/05290 ~, ~ ~ Av~~ ~ Pcrius~oio~~~~
4
iron particles within the pellet. This phenomenon
adversely affects the ability of blast furnace reducing
gasses to enter the pellets, thereby lowering blast ,
furnaces productivity. Bantonite is about 60~ silica.
Bentonite also contains other undesirable elements such
as sodium and potassium. Sodium and potassium
apparently react with the refractory linings of blast
furnaces, thereby reducing the useful life of each
furnace lining. In addition, these elements are
believed to cause pellets to exhibit undesirable
"swelling" when processed in blast furnaces.
Over the years, there has been intensive
research to develop a binder that does not have these
undesirable characteristics. Among the many inorganic
and organic binders which have been tested are clays,
paint rock, soda ash, limestone, lime, hydrated lime,
iron sulfates, amines, amine carboxolates, animal
proteins (e. g: dried blood), manures, cereal grains,
flours, hulls, corn cobs, gelatins, glues, gums, humic
acids, lignins, lignosulfonates, pulp, polyacroleins,
polyacrylamides, polyamines, starch, sugar, surfactants,
wood chips, wood flour, carboxymethylcellulose (CMC),
molasses,. corn syrup, graft copolymers of acrylic acid,
possuolan, cement, tar, pitch, polyvinyl alcohols,
dolomite, synthetic organic dispersants and high
molecular weight substantially straight chain water-
soluble polymers.
The complexity and difficulty of finding a
practical and functional substitute for bentonite,
however, has been demonstrated by the continued use of
bentonite as a binder. Today, bentonite remains the
principal commercial binding agent used in industry.
Progress has been made toward resolving the
complex technical problems inhibiting the use of organic
binders, however. See, for example, Haas, et al.,
"Effectiveness of Organic Binders for Iron Ore ,
Pelletization" in Report of Investigations 1989, U.S.
- ,.: :: , : ..,.
WO 92/05290 - PC'T/US90/O5~b6d~
Dept. Interior, Bureau of Mines (19$9). Sodium
carboxymethylcellulose (CMC), used in conjunction with
soda ash, or sodium carbonate (NazC03), has proven to be
a:~ acceptable binder in some operations and cor.tinuc~ to
be used in several commercial operations today.
Similarly, copolyrlers of sodium acrylate and acrylamide,
used in conjunction with soda ash, also show promise as
binding agents.
Efforts to use other binders, however, such as
starch in particular, have not been favorably received.
Modified native starch would appear to be an excellent
candidate as a binding agent. Substantial supplies of
native starch of a consistent quality are widely
available at a relatively low cost, especially as
compared to synthetically produced organic binders such
as those mentioned hereinabove. Starches do not contain
significant amounts of silica, sodium or potassium. In
addition, starches are also believed to be relatively
insensitive to variations in the "water chemistry" or
ion concentration levels of the moisture contained in
the concentrated mineral materials. Furthermore,
modified native starches generally exhibit strong
binding characteristics which axe desirable in good
binders.
Despite extensive testing of starch binders
during the past thirty plus years, however, starch has
yet to find commercial acceptability as a binder in the
pelletizing industry. In spite of its broad
availability, attractive cost, lack of undesirable
constituents, general insensitivity to water chemistry,
and strong binding characteristics, starch is generally
believed to be unacceptable as a binder for pelletizing
particulate mineral material. Some of the reasons why
starch is believed to be an unacceptable binder, include
the following negative characteristics of starch
binders:
WO 92/05290 '~, PCT/US9~lo~~~~~
6
1. Starch binders generally result in excessive
tackiness on the surface of "green" pellets.
This allows excessive amounts of mineral
concentrate fragments to collec t o.~, the s~.:rface
of green balls when sufficient starch binders
are added to maintain acceptable drop strength
and dry compression strength at typical
concentrate moisture levels. It is believed,
but not relied upon. that starches do not
readily retain water in the interior of the
green balls. This is believed to result in
unacceptably low green ball moisture content in
the interior of the balls and unacceptably high
moisture content on the surfaces which tend to
be considered wet or tacky.
2. Starches exhibit the unacceptable
characteristic of encouraging rapid and
uneven ball growth during balling
operations. This is thought to be due to
excessive tackiness on the surface of the
balls which is characteristic of pellets
made from mineral concentrates including
starch base binders, and generally results
in pellets which display poor strength
characteristics.
3. Pellets bound with starch generally have a
rough surface exhibiting surface
"cratering" and a surface characteristic
commonly referred to as "orange peel".
Such rough surface characteristics
commonly result in unacceptable tonnage
losses during transshiprnent due to
abrasion between adaacent pellet surfaces.
Because of these and other problems associated
with the use of starch binders to palletize particulate
mineral material, starch base binders are generally
considered to be unacceptable in the art. A need has
~criu~9oi~
wo 9zio~z9o
been demonstrated for an inexpensive organic binder for
palletizing mineral ores. Therefore, because of the
attractive characteristics of native starch, discussed
above, a need also exists for a starch base binder and a
method of using native starch as a binder for
particulate mineral material which will prove to be
acceptable within the palletizing industry. The present
invention addresses these and other needs and problems
associated With the formation and use of mineral ore
pellets in the palletizing industry. The present
invention also offers other advantages over the prior
art and solves other problems associated therewith.
S_umm_ary of the Invention
The present invention provides a binder for
palletizing particulate mineral material. The binder
comprises about 30-99.5 modified native starch, and
about 0.2-80$ of water-dispersible polymer material
selected from the group consisting of water-dispersible
natural gums, water-dispersible pectins, water-
dispersible starch derivatives, water-dispersible
cellulose derivatives, water-dispersible vinyl polymers,
water-dispersible acrylic polymers and mixtures thereof.
Preferably, the polymer material is selected from the
group consisting of water-dispersible acrylic polymers,
water-dispersible vinyl polymers, water-dispersible
cellulose derivatives, water-dispersible natural gums
and mixtures thereof. In certain preferred embodiments,
the binder is substantially free of inorganic elements,
preferably substantially free of potassium, sodium and
silica. Other preferred embodiments include an amount
of lignosulfonates which are either effective to improve
water retention characteristics so as to improve balling
characteristics or surface characteristics or improve
the dry compression strength of the resulting pellets
while permitting the reduction of the amount of starch
in the binder.
9V0 92/05290 PCTlUS90/05466
The binder .of the present invention provides
many advantages over the prior art binders. It is
preferably an substantially inorganic binder containing
none ~f the undesirable constituents found in clay
5~ binders such as bentonite. As stated in the Background
of this specification, starch is readily available and
quite inexpensive as compared to synthetic organic
binders. In addition, the quality of the starch may be
consistently maintained. Furthermore, native starches
are relatively insensitive to variations in water
chemistry and they exhibit desirable binding
characteristics.
In order to find commercial acceptability
within the palletizing industry, however, mineral ore
pellets are generally required to have the
characteristics which are discussed below. In the past,
starch base binders were not used because pellets made
with such binders did not meet these requirements. The
inventive pellets, however, do meet these requirements.
Therefore, it is deemed to be extremely likely that
pellets made in accordance with the present invention
will find acceptability within the palletizing industry
after introduction of the novel binder. The
characteristics which are believed to be critical for
good quality pellets include the following. Green
pellets must be able to survive repeated drops without
cracking as they pass over a number of conveyors between
the balling drums or disks and the firing furnace. If
the pellets are not strong enough to resists cracking
prior to being fired, the fired pellets will have low
physical strength and may break during transshipment.
Such breakage generally results from "microcracks" which
develop in the green balls as they are conveyed to the
furnace. Their resistance to cracking is measured by
the "18 inch drop test". This test measures the number
of times a green ball or pellet can be dropped 18 inches
onto a hard, flat surface without cracking. Typically,
WO 92/05290 ~cr/US9o/o5a66
20 balls will be dropped until they crack. The drop
strength of the balls is then calculated by averaging
the number of times each of the 20 balls can be dropped
before each ball cracks. An aa:erage gree.~. ball drop
strength of 5 or better at about 9.5$ moisture content
is generally desireable in many industry palletizing
operations.
In addition, the pellet must be strong enough
to survive the drying process and to maintain sufficient
strength to prevent collapse of the pellet structure
during "firing" until the iron oxide particles grow
together and provide the high compressive strength
required for the pellet to survive transshipment to the
blast furnace locations. This characteristic is
commonly referred to as the "dry strength" and is
determined by measuring the fracture strength of pellets
in the minus 1/2 inch plus 7/16 inch category (balls
smaller than 1/2 inch and larger than 7/16 inch).
Typically, 20 green pellets are pre-dried at 105°C and
then compressed until they break. The average dry
strength is reported in "pounds compression". A dry
strength of 5 or better is generally desired by most
palletizing operations.
Furthermore, the pellets should have a
relatively smooth outer surface to minimize abrasion or
"dust" losses after the pellets are tired. If the
pellet surface is too rough, as has commonly been the
case with prior art palletizing methods utilizing
starch, the pellet will chip and abrade along the
surface during transshipment. This results in severe
tonnage losses. Because it is essential to limit these
tonnage losses, the pellet surface is generally
considered to be unacceptable if it is "cratered" or
includes rough protrusions.
In addition, the green pellet surface must not
be wet or "tacky". If the surface is tacky, pellet and
concentrate fragments will stick to the tacky pellet
n
WO 92/05 ~~ ~317~ ~,~ PCT/TJ~~~kf~~°~'~.,._.
a
surface and be carried over the screens which are used
to remove and recycle green pellet fines from the
furnace feed. Fines stuck to the pellets will
eventually break off of fired pellets during subsequent
5 operations, thereby creating greater transportation
and/or transshipment tonnage losses which further
degrade pellet quality.
Also, variations in concentrate moisture can
have a significant effect on balling action and
10 subsequent ball quality. Binders must generally
accommodate same fluctuation in moisture content in
order to allow rough estimation of this parameter in
every day balling operations. Therefore, it is
important that the binder be able to compensate for
fluctuations in concentrate moisture by producing stable
quality green balls over a fluctuating range of green
ball moisture levels of about 9.0-10.0 moisture.
Furthermore, the binder must not cause the
green ball to grow too rapidly during the balling
process. Stronger balls are believed to be formed when
the diameters of the green pellets are increased in
relatively small increments. Such balls have
relatively thin conchoidal layers, whereas rapid ball
growth generally results in weaker pellets having
relatively thick conchoidal layers. These pellets are.
subject to erosion or disintegration drying process, and
may spall during firing. In addition, the fired pellets
should have significant resistance to abrasion, as
measured by the tumble test, relatively high porosity,
and a high compressive strength. they should also
reduce to iron rapidly as measured by the reducibility
test, have high resistance to degradation in the upper
area of the blast furnace as measured by the low
temperature degradation test and have low swelling
characteristics as measured by the swelling test.
Unlike pellets having binders consisting solely
of starch, pellets having a binder comprising modified
WO 92/0290 PCT/U590/06
2069482
11
native starch and water-dispersible polymer material in
accordance with the present invention, generally possess
the desired characteristics set forth above and lack the
undesirable ones. Experimental evidence indicates that
the use of the water-dispersible polymer material to
modify the characteristics of modified native starch
base binders results in green pellets which do not have
excessively tacky surfaces. Such pellets grow at a much
slower rate of growth during conventional balling
processes than pellets having binders consisting solely
of starch. They are also less erodible as measured by
the tumble test.
The Applicants have also observed that the
binder of the present invention reduces or eliminates
the undesirable rough pellet surface characteristics
generally observed for pellets with starch binders. The
surfaces of dried pellets made with the inventive binder
are smoother than the rough surfaces of pellets having
binders consisting solely of starch, and result in
reduced abrasion losses. In addition, because modified
native starch base binders are not very sensitive to
variations in "water chemistry", the novel binder is
particularly desirable in respect to binding
consistency. Furthermore, the present binders
preferably contain substantially no sodium or potassium,
thereby minimizing the tendency for the pellets to swell
during firing, and substantially no sodium or potassium,
thereby minimizing the production of slag and other
undesirable characteristics associated with their
presence.
As used herein, the following terms have the
following meanings. The term "native starch" means
starch which can be found in nature. The terms
"modified native starch" and °'pregellatinized starch"
and "pre-gelled starch" mean native starch which is at
least partially gelatinized such that the binding
characteristics of the native starch are improved.
WO 92/05290 ~~~ ~~~, . , P~f/US90/054661
12
Starch which is "extruded" or "roll dried," is native
starch which has been subjected to processing at
elevated temperatures so as to produce pregelatinized or
pre-gelled starch. The term "mater-disper~ibl° polymer
material" means material including water-dispersible
polymers. "Water-dispersible" means either dispersible
in water or other aqueous media, or soluble in water or
other aqueous media. The term "percent" (symbolized by
~) means percent by weight._ In addition, the term
"aqueous" means having water as a primary solvent. The
term "organic binder" means a binder which is
substantially without significant metal (including
alkali metal) or silicate content. The term "rate of
growth" means the rate at which green balls of a certain
size are generated from concentrate in comparative
experimental balling operations. Additional terms are
defined hereinbelow.
The above described features and advantages
along with various other advantages and features of
novelty are pointed out with particularity in the claims
of the present application. However, for a better
understanding of the invention, its advantages, and
objects attained by its use, reference should be made to
the drawings which form a further part of the present
application and to the accompanying descriptive matter
in which there is illustrated and described preferred
embodiments of the present invention.
Brief Description of the Drawings
In the drawings, in which like and primed
~.etters indicate corresponding embodiments of the
present invention and the prior art throughout the
several view,
Figure 1 is a photographic depiction of a
magnified view of two pellets having binders including
modified wheat starch, pellet B being a preferred iron
ore pellet in accordance with the present invention and
WO 92/05290 PCT/U590/05A66
13
pellet A being an iron are pellet made with a modified
starch base binder not within the scope of the present
invention; and
Figure 2 is a photographic depiction of a
magnified view of two pellets having binders including
modified corn starch, pellet B' being a preferred iron
ore pellet in accordance with the present invention and
pellet A' being an iron ore pellet made with a modified
starch base binder not within the scope of the present
invention.
Detailed Description of the Preferred Embodiments
of the Invention
In accordance with the present invention, a
modified native starch base binder is provided for
palletizing particulate material, preferably particulate
mineral material. The binder comprises, and can be
prepared by mixing about 20-99.8, preferably.about 30-
99.8$, more preferably about 50-99.5, even more
preferably about 75-99.5 modified native starch, and
about 0.2-80~, preferably about 0.2-70~, more preferably
about 0.5-50$, even more preferably about 0.5-40~ of a
binding modifier which is preferably water-dispersible
polymer material. The binding modifier will preferably
include an amount of water-dispersible polymer material
effective to reduce the rate of growth of mineral are
pellets during conventional balling processes when said
pellets include modified native starch base binders. It
is further preferred that the binder comprises about
0.2-80$, preferably 0.5-50~, and more preferably about
5-40$ lignosulfonate. Preferred lignosulfonates for the
binder are lignin sulfonate salts, preferably lignin
sulfonate salts selected from the group cansisting of
ammonium lignin sulfonate, calcium lignin sulfonate,
sodium lignin sulfonate and any combination thereof.
Binders of the present invention, especially those which
contain lignosulfonates, may further comprise about
~~ 92/05290 ~~~q ~~~ PCT/US90/054~6._
14
0.2-40~ of soda ash, or sodium carbonate (Na~C03),
preferably about 1-25~, and more preferably about 5-20$.
The binder of the present invention is
preferably used for pelietizing particulate .~,iineral
material such as iron ores including taconite and the
like, as well as other mineral ores, for reduction in
metal ore reduction processes such as blast furnace
operations common to the United States and many other
countries.
Also in accordance with the present invention,
an iron ore concentrate for forming iron ore pellets is
provided. The concentrate comprises about 50-99.98,
preferably about 80-99.98$, more preferably about
90-99.98$ mineral material including about 6-12~,
preferably about 8-ll~k, more preferably about 9-10~
moisture, and at least about 35~, preferably about 45$,
more preferably about 50$, and most preferably about 60~
iron; about 0.01-0.5$, preferably about 0.02-0..5~
modified native starch; and an amount of water-
dispersible polymer material effective to reduce the
rate of growth of green pellets during conventional
balling processes when said green pellets have modified
native starch base binders. Preferably, the concentrate
includes about 0.001-0.1~, more preferably about 0.002-
0.08 of water-dispersible polymer material. It is
further preferred that the concentrate comprises about
0.001-0.2~ lignosulfonate, preferably about 0.002-0.1~.
In addition, the present invention provides a
mineral ore pellet comprising about 50-99.98,
preferably about 80-99.98 mineral material; about 0.01-
10.0~, preferably about 0.01-1.0$, more preferably about
0.01-0.5~ modified native starch; and an amount of
water-dispersible polymer material effective to reduce
the rate of growth of mineral ore pellets during
conventional balling processes when said pellets include
a modified native starch base binder. Preferably, the
.~ ~ ~ ~ PCf/L»S9~/~~!~r~r
WO 92/05290
mineral ore pellet includes about 0.001-1.0'x, more
preferably about 0.001-0.5$, most preferably about
0.001-0.1~ of water-dispersible polymer material and at
least about 35~, preferably about ASg, more prefer3blY
5 about 50~ iron. Alternatively, the present invention
provides an iron ore pellet comprising 9-99.98 mineral
material including at least about 50$ iron and having a
moisture content of about 6-12~p preferably about 8-10~;
about 0.01-0.5~ modified native starch; and, an amount
10 of water-dispersible polymer material effective to
reduce the rate of growth of mineral ore pellets during
conventional balling processes when said iron ore
pellets include a modified native starch base binder.
The iron ore pellet may further comprise about 0.001-
15 0.2~ lignosulfonate.
Native starch is any starch which can be found
in nature. Such starch includes, but is not limited to,
starch from the following sources: corn (Zea mat's),
wheat, triticale, tubers, rice, or the like. Native
starch is virtually insoluble in cold water. Modified
native starch is native starch which has been at least
partially gelatinized such that the binding
characteristics of the native starch are improved. When
starch is heated it tends to become soluble in water
forming as colloidal solution which may form a gel on
cooling. During heating, the amylose and amylopectin
moieties of the staxch granule depolymerize to one
degree or another. This process is called
gelatinization. Starch can be gelatinized by
depolymerizing the amylose and amylopectin in several
ways. Heat is most commonly used to gelatinize starch,
however, a hydrolysis reaction depolymerizing amylose
and amylopectin may also occur when the starch is
treated with acids, enzymes, or other well known
chemical agents. Starch is gelatinized during heat
processing when a starch-water mixture is heated to a
temperature exceeding the temperature at which the
vvo 92iosigo ~~ ~ Pc~i~»~~~r~P~~~,~
16
quasi-crystalline or aggregate structure of the water-
swollen starch granules are irreversibly destroyed.
This temperature is commonly referred to as the
gelatinization temperature. The gelatinization
temperature can be reduced by including hydrolytic
agents in the starch-water mixture. Such agents
include, but are not limited to acids, alkalies,
amylolytic enzymes and the like. For example, it is
possible to dissolve caustic soda in a starch-water .
mixture in order to reduce the gelatinization
temperature to about 20-30'C. In such a case, no
heating is required if the ambient temperature exceeds
the gelatinization temperature. In addition to
gelatinizing the starch, the hydrolytic agents reduce
the molecular weight or chain length of the resulting
carbohydrate molecules. Therefore, gelatinized starch
may be the product of treatment with heat,
enzymes, acids, or other chemical agents. This treatment
will improve the binding characteristics of the starch
so that it can be used to bind particulate mineral
material together to form pellets.
Unfortunately, modified native starch is
believed to be an unacceptable binder, as has been
discussed hereinabove. In order to modify the
characteristics of modified native starch base binders,
the applicants have included about 0.2-70~ preferably
about 0.5-50~, more preferably about 0.5-25~ of a
binding modifier. The binding modifier includes an
amount of water-dispersible polymer material effective
to reduce the rate of growth of mineral ore pellets
during conventional balling processes when the pellets
include modified native starch base binders. The water-
dispersible polymer materials of the present invention
include, but are not limited to, water-dispersible
natural gums, water-dispersible pectins, water-
dispersible starch derivatives, water-dispersible
cellulose derivatives, water-dispersible acrylic
WO 9/05290 ~'CT/1;~~9~=.'~r~..,'~
_ 1' 2069182
polymers, and water-dispersible lignosulfonates. The
natural gums include: terrestrial plant exudates
including, but not limited to, gum arabic (acacia), gum
tragacanth, gum karaya, and the like; terrestrial plant
seed mucilages, including but not limited, to psyllium
seed gum, flax seed gum, guar gum, locust bean gum,
tamarind kernel powder, okra, and the like; derived
marine plant mucilages, including but not limited to,
algin, alginates, carrageenan, agar, furcellaran, and
the like; other terrestrial plant extracts including but
not limited to arabinogalactan, pectin, and 'the like;
microbial fermentation products including but not
limited to xanthan, dextran, scleroglucan, and the like.
Cellulose derivatives include chemical derivatives of
cellulose, including but not limited to, alkyl,
carboxyalkyl, hydroxyalkyl and combination ethers, and
the sulfonate and phosphate esters. Water-dispersible ,
starch derivatives include, but are not limited to,
alkyl, carboxyalkyl, hydroxyalkyl and combination ethers
of starch, phosphate or sulfonate esters of starch and
the like which are prepared by various chemical or
enzymatic reaction processes. Water-dispersible acrylic
and vinyl polymers, include but are not limited to the
homo-, co-, and ter- polymers of acrylic acid, vinyl
alcohol, vinyl acetate, Dimethyl Diacrylyl Ammonium
Chloride (DMDAAC), Acrylaminyl Propyl Sulfonate (AMPS)
and the like, and combinations thereof. Lignosulfonates
include, but are not limited to, lignin sulfonate salts
such as ammonium lignin sulfonate, and alkali metal and
alkaline earth metal salts of lignosulfonic acid, such
as sodium lignin sulfonate, calcium lignin sulfonate and
the like, and combinations thereof. It may be
preferable, in certain circumstances, to use ammonium
lignin sulfonate in~order to avoid the addition of
inorganic materials such as calcium and sodium,
particularly sodium.
~criu~.. :.; ~ , .. .
wo 9aeos29o
18
The inclusion of the binding modifier in the
modified native starch base binder has been shown to
improve the binding characteristics of the binder.
Experimental results shcw that the "cratering" affect is
absent or reduced, as is the "orange peel" effect in the
surface of pellets prepared in accordance with the
present invention. Figs. 1 and 2 provide comparisons of
pellets which were made using modified native starch
base binders with (B and B'~) and without (A and A') a
binding modifier in accord with the present invention.
In Fig. 1, a representative pellet (A) containing 0.15
modified wheat starch is compared to another pellet (B)
containing 0.12 modified wheat starch and 0.03 guar
gum. In Fig. 2, a representative pellet (A') containing
0.147$ modified corn starch is compared to another
pellet (B') containing 0.118 modified corn starch and
0.029 guar gum. Each of the comparisons was made
employing the same ingredients under similar conditions,
except as noted. Tn each comparison, the pellet without
' 20 the binding modifier, guar gum, displays a rougher
surface than is displayed by the pellet including both
starch and guar gum. The pellets without 'the modifier
show a "cratered" surface and the rough "orange geel"
effect which is considered unacceptable in the
palletizing industry.
It is believed, but not relied upon, that the
binding modifier of the present invention modifies the
water retention characteristics of the modified native
starch base binder. How and why this occurs are not
known. It is apparent that the binding modifier
modifies the binding characteristics of modified native
starch based binders such that the rate of growth of
mineral ore pellets can be reduced during conventional
balling processes. At the same time, it is apparent
that the pellets which are produced using the binder ar
the present invention possess a more even or smooth
surface, lacking the "cratering° or the "orange peel"
.,.,,
WO 92/05290 ~ P~T/U~~O~W'"
~j'!~82
19
effect generally observed on the surfaces of the pellets
having simple starch base binders. Tn addition, the
surface of green pellets made in accordance with the
present invention do not exhibit the tackiness generally
associated with high moisture content green pellets
using simple starch base binders.
It is believed, but not relied upon, that
starch binders somehow allow or encourage excessive
water migration away from the interior of the green
balls. during and/or after balling. It is believed that
this effect results in the rapid growth rates associated
with starch binders, the "cratering" effect, the "orange
peel" effect and the surface tackiness observed on the
surface of green pellets prepared with starch binders.
It is not known how the binding modifier of the present
invention modifies the binding characteristics of starch
binders, however, empirical results indicate that a
desirable effect occurs. In addition, the drop. strength
and dry strength of pellets made with binders in
accordance with the present invention are not only
acceptable, but appear to be quite desirable.
Furthermore, experiments indicates that mineral
materials containing moisture having significantly
different ionic characteristics have little effect upon
the binding characteristics of the binder of the present
invention. therefore, it may be concluded that the
binder of the present invention is relatively
insensitive to variations in the ioninicity of the
moisture in the concentrate, or to "water chemistry".
An alternate embodiment of the present
invention provides a mineral ore pellet prepared by a
process comprising the steps of forming a mineral
concentrate including about 50-99.98$, preferably about
80-99.98 mineral material having a moisture content of
about 6-12~, preferably about 8-10~; about 0.01-10.0,
preferably about 0.01--1.0$, more preferably about 0.01-
0.5$ modified native starch; and about 0.00?-0.1~,
~'Cf/U.~: .; i _,.:'~,~
WO 92/05290
preferably about 0.001-0.05 of water-dispersible
polymer material selected from the group consisting of
natural gums and water-dispersible synthetic polymers;
and forming mineral ore pellets from the mineral
5 concentrate. It is further preferred that the
concentrate comprises about 0.001-0.2$ lignosulfonate.
The concentrate may further comprise about 0.001-0.1$ of
soda ash. Preferably, the step involving forming
mineral ore pellets includes balling the mineral
10 concentrate in a conventional balling apparatus.
Another embodiment of the present invention
provides a mineral ore pellet prepared by a process
comprising the steps of extruding native starch at a
temperature effective to modify said native starch so
15 that said starch is at least partially gelatinized; .
combining said modified native starch with water-
dispersible polymer material and particulate mineral
material to thereby form a mineral concentrate including
about 0.01-0.5~ modified native starch and about 0.001-
20 0.1~ of water-dispersible polymer material, and forming
mineral ore pellets from the mineral concentrate. The
mineral ore concentrate preferably has an iron content
of at least about 35$, mare preferably about 50~ and
most preferably about 60~ iron. It is further preferred
that the mineral ore concentrate contain
lignosulfonates. The concentrate may further contain
soda ash.
The present invention also provides a method of
binding particulate mineral material comprising the
steps of mixing modified native starch, water--
dispersible polymer material and particulate mineral
material having a moisture content of about 6-120,
preferably about 8-10~, to form a mineral concentrate;
and, balling the mineral concentrate to form agglomerate
mineral ore pellets. The mineral concentrate includes
about 0.01-lO.Og, preferably about 0.01-1.0~ modified
native starch and about 0.001-0.1~ of water-dispersible
Pcr/us9~a/~~A
!~'O 92/05290
21
polymer material. Alternatively, the present invention
provides a method of making mineral ore pellets having
modified native starch base binders comprising the steps
of preparing a binder in accordance Hith tha pras2nt
invention, mixing the binder with mineral material
having a moisture content of about 6-12~, preferably
about 9-10~, to form a mineral concentrate, and forming
mineral ore pellets from the concentrate. The mineral '
concentrate preferably includes about 80-99.98 mineral
material and about 0.01-10.0$, preferably about 0.01-
1.0$ of a binder.
The invention will be further described by
reference to the following detailed experimental
results.
_Experimental
Samples of iron ore mineral material from
production facilities in Northern Minnesota are.obtained
to test various modified native starch base binders.
The samples are stored in airtight containers to ensure
that evaporative losses did not occur prior to mixing
the samples with binder. The moisture content of the
mineral material is determined by weighing a sample of
concentrate drying it, and then weighing it again. Data
from particle size analyses of the mineral material are
obtained from production records based on U.S. Standard
Sieve Analyses. Data regarding iron content obtained
from production records which report the results of
standard iron analyses as a percent of iron (dry basis).
The samples typically had moisture contents of about
9.5~, particle sizes of 82-92~ less than 44 microns in
diameter (U. S. standard No.' 325 mesh), and iron contents
of 67-68$.
Binders are prepared using two pregelatinized
native starches. Each of the native starches, secondary
wheat starch and corn starch, had been previously
modified using heat professing by mixing them with a
CA 02069482 2002-07-16
WO 92/05290 PCT/1JS90/05466
22
relatively small amount of water a.nd then extruded
through a screw extrusion device such as a Wenger
Extruder (Wenger Manufacturing, Inc., Sabetha, KS) which
generates sufficient heat a..~.d pressure to gelati.~.ize the
starch. A sample of the extruded starch is weighed, and
dried and weighed again to determine ir_s moisture
content which was about ?'~. The extrusion process
generated sufficient heat to "flas:h" off most of the
moisture. The starch was then graund to a fine size in
a Pitchford~'' blender and screened on a 44 micron screen
(U. S. standard No. 325 mesh). The plus 44 micron starch
was discarded and the minus 44 micron starch was used to
prepare modified native starch base binders in accord
with the present invention. Some "dextrinization" or
head degradation of the modified or gelatinized product
was evident from the slight "browning" of the samples.
Two different binding modifiers were used.
Each was ground in a Pitchford blender and screened
through a 44 micron screen. The plus 44 micron material
was discarded and the minus 44 micron material was used
to prepare the binders of the present invention. The
first binding modifier was milled endosperm of guar seed
which has been wet flaked, dried, and pulverized
(hereinafter "guar gum"). The other binding modifier is
a synthetic water-soluble nonionic, high molecular
weight, polyacrylamide Calgon~" 55U (obtained from Calgon
Corporation, Pittsburgh, PA).
The binders were prepared by combining the
various weight proportions of the components and.
thoroughly mixing. It will be appreciated,. however,
that the specific components of the binders need not be
mixed together prior to use, but may instead be mixed
with the mineral material individually; either i.n series
or simultaneously, both prior to or during agglomeration
processes such as normal balling processes and the like.
Green pellets were prepared using each of the
binders with the following balling pro~~~edure. T5U g of
1V0 92/05290 P4:T/U590105~~5~
23 2os9~~~
particulate mineral material having a moisture content
of about 9.5~ used as a head sample. A measured
quantity of additional water, which varied between 6 and
1~ grams, was mixed into the head sample so as to
produce green pellets having a moisture content in the
range of S.8 to 10.1. The desired quantity of binder
was added to the head sample and mixed into the sample
over a two minute period of time to form a mineral
material including the desired quantity of binder.
Approximately 75 g of the concentrate was balled to form
seed pellets in an airplane tire balling drum rotating
at approximately 25 rpm. Additional measured amounts of
water were added as required to obtain good ball growth.
Additional concentrate was then added along with
additional measured spray water to increase the average
pellet diameter. The pellets were then screened on a 6
mesh sieve to remove undersized pellets. The larger
pellets were then returned to the balling drum with
additional concentrate and rotated for about l5 minutes
at approximately 25 rpm until approximately 500 grams of
pellets were formed. The finished pellets were screened
using a U.S. Standard Sieve Analysis and the --1/2 +716
inch pellets were collected and re-rolled for 20 seconds
to randomize the pellets for subsequent random selection
far further testing. Approximately 300 grams of
finished green pellets were prepared in this manner for
each of the mineral materials listed in Table 1 below.
The finished pellets were sealed in an air-
tight container to maintain their moisture content.
Twenty pellets from each batch of newly prepared green
pellets were immediately tested for drop strength.
Thirty pellets from each batch were weighed, dried at
105°C, reweighed, and compressed to determine their
average fracture strength. Before and after drying,
observations were made regarding the surface
characteristics of the pellets. The moisture content
was calculated by comparing the weight of the moist
WG~ 92/05290 PCT/US90/!~~%s65
p Nets to the weight of the dry pellets. The average
fracture strength was calculated by averaging the
fracture strength of the 30 pellets which were tested.
Other observations were also made including obssrvatio~~
of pellet surface characteristics and weights of water
added to obtain desired pellet moistures.
It was evident that the pellets containing the
binder of the present invention showed improved surface
characteristics. The "cratering" effect and the "orange
peel" effect which were both evident on the surfaces of
the pellets made with the binders which included only
wheat starch or corn starch, were eliminated or at least
minimized or reduced on the surfaces of pellets
containing the binders of the present invention.
Furthermore, the wet or "tacky" green pellet surface,
typical of high moisture green pellets containing
binders comprising solely modified native starch was
also eliminated or minimized in green pellets containing .
the binders of the present invention. The drop strength
and dry strength were also found to be acceptable for
those pellets using binders in accordance with the
present invention. Furthermore, the growth rates seen
with concentrates including the binder of the present
invention were more acceptable than those for
concentrates including binders consisting solely of
modified starch. Table I hereinbelow lists some of the
empirical observations with respect to the surface
characteristics of iron ore pellets which were prepared
using common mineral material.
PCT/'IJS9~/05~~6
WO 92/05290
TABLE 1
Surface Characteristics of Iron Ore Pellets
with Modified Native Starch Base Binders
5 Percent of Binder Observed Surface
Components Added Characteristics
None Used WET, SEVERE ROUGHNESS,
LUMPY
0.126$ extruded wheat WET, TACKY, SEVERE
ROUGHNESS, starch PROTRUSIONS
ATTACHED, RAPID
GROWTH
0.022 guar gum SOME CRATERTNG, GENERALLY
SMOOTH SURFACE, SOME
LUMPINESS
0.012 nonionic, high MODERATE SURFACE
ROUGHNESS
molecular weight
polyacrylamide
0.126 extruded SMOOTH SURFACE, DRY, NO
wheat starch & PROTRUSIONS
0.022 guar gum
0.126$ extruded corn SMOOTH SURFACE, DRY, NO
starch & 0.022 PROTRUSIONS
guar gum
0.136 extruded wheat SMOOTH SURFACE, DRY, NO
starch & 0.0128 PROTRUSIONS
nonionic, high
molecular weight
polyacrylamide
wo 9aia~~~~~ PCT/US90/OSa~r6
26
SODIUhS FREE PELLETS
The sodium CMC binders being marketed today
contain significant quantities of sodium carbonate,
typically 15-30~ by weight in addition to the sodium
contained in the polymer. The acrylamide binders
contain as much as 50~ sodium carbonate. The negative
effects of alkalis on iron ore pellet characteristics
have been described by A. Jersch et al. (1985, 4th
International Symposium on Agglomerations, Iron and
Steel Society Journal, pp. 259-266). The authors state
that it has been widely documented that the potassium,
and sodium contents in commercial pellets have very
undesirable effects of swelling and sticking in the
upper regions of the charge, and occasional blocking of
the shaft of the furnace in the temperature range from
700-800°C, incurring increased maintenance and
operations difficulties.
It is noted that the starch binder compositions
of the present invention have very low, preferably
substantially no sodium and potassium contents. An
example is the starch/guar mixture. This binder is
substantially sodium and potassium free as compared to
the approximate 15-30~ Na content of CMC-soda ash and
polyacrylamide-soda ash binders being marketed and,
therefore, will not contribute to the negative effects
of alkali on the swelling characteristics of pellets,
particularly fired pellets (see minimal swelling
characteristics recorded for pellets with this binder in
Table 6).
The starch/acrylamide and starch/CMC binders of
the present invention contain small amounts of sodium in
the polymer, but do not require sodium carbonate to ,
function pxoperly. Adding sodium carbonate to the
starch binders will result in increased dry compression
strengths, but this increase in strength is not
considered necessary for most operations. Test data
shows that adding 0.024 soda ash to starch and
WO 92/05290 ~ ~ ~~ ~ ~ ~('T/US90/OS~b~F~
27
starch/polymer pellets raises the dry compression
strength of the pellet by about 1-2 pounds. 2t will be
understood that all of the binders of the present
invention can be used in conjunction with other binders
and additives, such as bentonite, limestone or dolomite.
If lignosulfonates are added to the binder, ammonium
lignin sulfonate will be preferred in order to minimize
sodium content. '
DRIED PELLET SURFACE EFFECTS
Starch bound pellets produced without the
addition of a small amount of water-dispersible polymer
material as per the present invention, exhibit the
negative phenomena of rapid and uncontrollable pellet
1S growth and wet, tacky surfaces which produce fragile,
erodible pellet surfaces when dried.
Several different types of pelletizing furnaces
are used in the industry. The two principal furnaces
are; the traveling grate in which the entire drying,
preheating, firing, and cooling operation takes place on
the grate; and the grate kiln in which the pellets are
dried and preheated on a grate and then fired in a
rotary kiln. In either case, moist, "green" balls are
fed onto a steel conveyer or grate which travels into
2S the furnace. The pellet bed depth is typically in the
range of 12-16 inches deep on the grate. Hot, high
velocity air is blown through the pellets as the grate
travels forward. The air temperature is initially quite
low, in the range of about 400°F (200°C). The air dries
the pellets at a rate slow enough to prevent steam
explosions from causing catastrophic failure of the
pellets. The temperature is increased as the pellets
dry and as the bed moves forward, initiating a process
which starts grain growth between iron ore particles and
increases strength. Eventually, the pellets will reach
a temperature of about 2200-2400°F (1200-1300°C) which
WO 92/05290 PCT/LJS90/05d66
28
is sufficient to provide the necessary oxidation and
grain growth required to produce a "hard" pellet.
The drying and preheat zone of the furnace is a
critical area. Dried pellets are quite fragile, thus
the need for "dry strength" and "smooth surfaces". The
high air velocities in a furnace will erode loosely
attached material on the surface of the dried pellet.
Starch pellets have historically displayed this
characteristic. Eroded pellets will collapse and allow
air channeling in the pellet bed. Air channeling then
increases the velocity in the eroded area since the
resistance to air flow is decreased. This can result in
catastrophic failure of the pellet bed. When this
occurs, the furnace production must be slowed to
13 stabilize operations or low quality production must be
accepted. Dust losses in the furnace, in this
situation, would be severe.
Applicant's observations indicate that the
addition of small amounts of water-dispersible~polymer
material in accordance with the present invention
significantly reduces the surface erosion
characteristics of starch bound pellets.
PEhLET GROWTH RATES
"Starch" pellets are characterized by "rapid
pellet growth" during balling and "wet" or "tacky" .'.
surfaces. Tt appears that these phenomena are related
to the quality of the pellet surface. Therefore, a ,
series of pellet growth rate tests, described were
conducted with binders including various binding
modifiers and modified starch base binders to determine
their respective effects on growth rates.
In each growth rate test, 750 grams of 9.5~
moisture iron ore miner material was mixed with 14 g of
additional water. A measured quantity of binder was
then blended into the mixture. 100 g of the resulting
mixture was then added to the balling drum which was
PCT/~J~~~C!~'
WO 92/05290
206982
29
operating at 25 rpm and 40 g of minus 4 mesh plus 6 mesh
seed pellets were generated. The 40 grams of seed
pellets were then added back to the balling drum and
another 500 grams of blended concentrate was added to
the drum over a 15 second period. The balling process
was allowed to continue for 90 seconds from the time the
500 gram sample addition was begun. This process was
repeated for each of the binders listed in Table 2
below.
The pellets were then removed from the drum and
screened through 1/4 inch, U.S. No. 4 mesh, and U.S. No.
6 mesh screens. The cumulative percentage of green
balls retained on each screen is reported in Table 2
below.
The results, reported in Table 2 below,
indicate that there is a correlation between ball growth
rate, starch content, and binding modifier or water-
dispersible polymer type and quantity. The data is
believed to establish that small quantities of water-
dispersible polymer material can significantly slow the
balling rate of starch pellets as compared to comparable
quantities of additional starch. It is also believed
that the charge and molecular weight of the polymer
material used affects the balling rate.
WO 92/05290
JPCI('/~.J~~'~/t~~~~~,
. 30 -
TABLE 2
Ball Growth Rate
Modified Native Starch Base
Binder Iron Ore Pellets
Percent of Starch and
Modifier in the Blended ~ + ~ +
Concentrate 1~4" 4 mesh 6
mesh
ZO None (100 Concentrate) 90
0.118 extruded corn starch 71
0.147$ extruded corn starch 79
0.199$ extruded corn starch 76
0.118$ extruded corn starch
& 0.013$ guar gum 48
0.118 extruded corn starch
& 0.029 guar gum 26
0.118$ extruded corn starch
& 0.081$ guar gum 11
0.118$ extruded corn starch
& 0.029 high molecular
weight anionic acrylamide 68 88 99
0.118$ extruded corn starch
& 0.029 low molecular ....
weight anionic acrylamide 30 69 91
0.118$ extruded corn starch
& 0.029 medium molecular "
weight anionic acrylamide 15 50 84
0.118 extruded corn starch
& 0.029$ medium molecular
weight cationic acrylamide 11 46 81
0.118 extruded corn starch
& 0.029 high molecular
weight cationic acrylamide 8 27 64
0.118 extruded corn starch
&
0.029 high molecular weight
nonionic polyacrylamide 6 23 63
0.118~k extruded corn starch
&
0.029 high molecular weight
anionic polyacrylamide 4 14 38
WO 92/05290 PCT/U590105~56
31 2~~.~~g~
DRY PELLET AHRASION TESTS
The resistance to abrasion and dust losses of
pellets in the drying zone of the furnace is simulated
by the DRY .AERASIO:; TEST. Iron ore pellets ~~:ere
prepared as described above fox tests to determine
pellet growth rates. The green pellets were then
thoroughly dried at 105° C, weighed, and their abrasion
resistance was measured by tumbling the dried pellets
for 4 revolutions in a 20 cm balling disk rotating at 16
rpm at a 45° angle. The percent weight loss was used to
evaluate the relative abrasion resistance of the dried
but unfired pellet.
The dry abrasion data, reported in Table 3
below, shows that pure polymer added at equivalent
percentages to those used in the starch/polymer binders
provide little dry abrasion strength to the pellets.
Increasing the starch content of the pure starch pellets
does not significantly improve the abrasion resistance
of those pellets. Yet, the data show that the addition
of small amounts of polymer to starch pellets
significantly improves the loss on abrasion, a result
that could not be predicated from drop and dry strength
data since the pure starch pellets had equivalent or
better drop and dry strengths as compared to the
starch/polymer pellets evaluated in those tests.
iVVO 92/0S290 P~/~»~~~'~~~'~'
'
32
BLB 3
TA
Dry Abrasion Test
Modified Native Starch Base
Binder Iron Ore Pellets
Percent of Starch and
Modifier in the Blended
Concentrate Percent Loss on
Abrasion
0.015 nonionic acrylamide 3.41
0.029 guar gum 3.73
0.074$ guar gum 1.24
0.118 extruded corn starch 1.16
0.147$ extruded corn starch 1.01
0.140$ extruded corn starch &
0.007 guar gum 0.89
0.133$ extruded corn starch &
0.015$ guar gum 0.82
0.118$ extruded corn starch &
0.029$ guar gum 0.79
0.074$ extruded corn starch &
0.074$ guar gum 0.25
0.133$ extruded corn starch &
0.015$ nonionic acrylamide 0.73
0.118 extruded corn starch &
0.029~C nonionic acrylamide 0.62
Fired Pellet Characteristics
A binder including 80 percent extruded corn
starch/20 percent guar gum was added at a rate of 0.16
percent by weight to 600 pounds of iron ore concentrate
from National Steel Pellet Co. (Keewatin, MN) along with
1 percent by weight ground limestone and thoroughly
mixed in a mueller mixer. This material was then
continuously conveyed to an industrial standard, 4 foot
diameter pelletizing disk where it was formed into green
balls. Water was added as required to maintain stable
balling action. Pellet growth characteristics were
CA 02069482 2002-07-16
WO 92/05290 PCf/US90/05d66
33
observed to be consistent with those needed to produce
high quality pellet, and did not display the negative
characteristics previously seen with starch bound
pellets. In particular, the growl:: rat° was sy...ilar to
that seen using bentonite as a binding agent, and the
balls did not display the characteristics rapid growth
rate, tackiness anc; orange peel characteristics of
starch bound pellets. Samples of the green pellet were
collected and analyzed to determine their
characteristics.
Sixty-five and one-half pounds of green pellets
were fired in a 1 foot square, McKee~'' type pot furnace to
evaluate the characteristics of the fired pellets. This
test simulated the actual drying and. firing air flows
and temperature cycles seen in Grates'' Kiln palletizing
machine. A 4-inch-thick hearth layer of. prefired
pellets separated the green pellets from the grate bars
and was separated from the green pellets by nichrome
wire screen to prevent mixing of the hearth layer and
green pellets. A six-inch bed of green pellets was
placed on the hearth layer pellets and fired under the
conditions reported in Table 4. Green pellet quality
measurements for pellets produced in the 4-foot balling
disk are reported in Table 5. Fire pellet quality
measurements for fired pellets from the pot furnace cast
are reported in Table 6.
Test procedures used in obtaining the results
in Table 6 are referenced parenthetically. In those
references American Society for Testing and Materials is
abbreviated ASTM, and .'.nternational Organization for
Standardization is abbreviated TSO. The test procedures
referenced are well known in the art.
Fired pellet quality was excellent with the
high compression strengths and high reducibility rates
indicating that the fuel rate coin>i be reduced.
PCT/iJS9Q~!~~~~'
WO 92/05290
34
TABLE 4
Firing Cycle
Pressure Drop
Location (Inches of Input Time at Temp Actual
Test PhaseWater Displaced) (Min Temp.F
-Sec.)
_ Dry 10 2 36 615
Downdraft -
Bed Top 700 ,
DowndraftDry 8.5 1 34 1260
-
Bed Top 1350
DowndraftDry 7 0 34 1320
-
Bed Top 1350
Preheat 7 2 36 1250
-
UnderBed 1950
Firing 5 6 30 2170
-
UnderBed 2075
Firing 5 6 30 2235
-
UnderBed 2300
Firing 6 6 - 30 2295
UnderBed 2375
~
Firing 5 6 - 30 2315
UnderBed 2300
Cooling 11 10 - 0 695
Bed Top Ambient
TABLE 5
Green Pellet Measurements
Percent Moisture - Percent by weight 9.41
18" Drop Strength 6.2
Wet Compression Strength - pounds 1.66
Dry Compression Strength - pounds 11.12
WO 92/05290 PCT!~J590!~~66
TABLE 6
Fired Pellet Measurements
And Visual Observations
5 Top of Pellet Bed No cracking, Minor clustering
Middle of Pellet Bed Minor cracking, Minor clustering
Bottom of Pellet Bed Minor cracking, Minor clustering
Crushing Strength (ASTM E382-80) Pounds 1000
10 Swelling (ISO Dp 4698) percent volume 13.1
R40 Reducibility (ISO Dp 4695) percent
oxygen loss per minute at 40~ reduction 1.10
Low Temperature Degradation (ISO Dp 4697)
Porosity as Measured by Air Comparison
15 Pycnometer (percent voids) 27.0?
Bulk Density - Grams/0.1 cubic foot 5145
Tumble Test (ASTM E 279-691
Screen Analysis before Tumble -
20 Percent by Weight
+1/2 inch 28.6
-1/2 inch + 3/8 inch 68.9
-3/8 inch + 1/4 inch - 2.3
-1/4 inch + 28 Mesh 0.1
25 -28 Mesh 0.1
Screen Analysis after Tumble -
Percent by Weight
+1/2 inch 19.1
-1/2 inch + 3/8 inch 68.6
30 -3/8 inch + 1/4 inch 6.4
-1/4 inch + 2B Mesh 1.5
-28 Mesh 4.4
WO 92/05290 ~~~ ~~~ PC'f/US90/~D.~9~O6
36
SURFACE ROUGHNESS OF STARCH ANA STARCH/POLYMER PELLETS
Figure 1 is a picture of two fired pellets.
Both pellets contain 0.147 binder by weight. The
pellet on the left (A) contain s 0.14?a extruded :':h°at
starch and the pellet on the right (B) contains 0.118
extruded wheat starch and 0.029 guar gum. Both sets of
pellets were groduced under identical conditions using
the same concentrates water addition rates and
controlling other variables. to maintain similar balling
conditions. The green pellets were screened to minus
1/2 inch plus 7/16 inch, placed in one, multi-
compartment wire basket, and insert in a muffle furnace
preheated to 65° C. The pellets were than heated to
1265° C at a rate of 9° per minute, removed from the
furnace and air cooled.
As is apparent from an examination of Figure 1,
the starch bound pellet (A) surface has significant
areas of rough, orange peel surface while the
starch/polymer pellet (B) is relatively smooth. One can
. 20 see from the rough surface of the starch bound pellet
that it would be fragile and easily erodible during the
drying and preheating process. This fact is confirmed
by the dr-y abrasion tests previously described. Again,
the critical improvement appears to be related to the
ability of small amounts of water-dispersible polymer
material to control the green pellet growth rats and the
quantity of moisture on the surface of the green pellets
during the balling process, a factor which greatly
reduce surface irregularities on the pellets.
Figure 2 is a picture of two fire pellets
containing extruded corn starch in place of the wheat
starch, and the same amounts of everything else.
WO 92/05290 ~ ~ ~ ~ ~ PCI'/US90/05~~6~
37
ENHANCEMENT OF BINDER PERFORMANCE WITH LIGNOSULFONATE
Lignosulfonates are water-soluble, sulfonated
polymers generally produced by chemical dissolution of
lignin from wood by sulfite pulping processes. They are
generally part of the spent sulfite liquors that are
separated from the pulp as a water-soluble form of
lignin, and are precipitated out from an evaporated
concentrate of the liquor. The precipitant may be
further purified to remove sugars and other byproducts
of the pulping process. Lignosulfonates are usually
anionic polymers of a phenolic type that have molecular
weight distributions ranging from 100 to 100,000, with a
median molecular weight of about 10,000, that being a '
relatively low molecular weight polymer.
7.5 Lignosulfonates are most often commercially sold in the
form of ammonium, alkali metal and alkaline earth metal
salts of the lignosulfonic acid. Frequently, such salts
contain portions of both types of metal cations. It is
preferred that the binder comprise a lignosulfonate
salt, preferably ammonium lignin sulfonate, sodium
lignin sulfonate, calcium lignin sulfonate and any
combination thereof.
It is believed, but not relied upon, that the
numerous and strongly anionic sulfonate groups in the
molecular structure of lignosulfonate impart both a
water-solubility and dispersant functionality to this
polymer. The addition of a lignosulfonate to a wet
taconite concentrate are believed to improved the
performance of both natural gum, preferably guar gum and
combinations of pregelled starch and natural gums as
pellet binders. This enhancement is indicated by the
test results provided in Tables 7, 8 and 9.
CA 02069482 2002-07-16
WO 92/05290 PCT/US90/054b6
38
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/LJS9~/(~~3~~
WO 92/05290
41
The data summarized in Table 7 indicate that a
progressive increase in the treatment levels of calcium
lignosulfonate from zero to 1.00 1b. per ton in a
concentrate treated with 3.50 1b. per ton of a modified .
native starch-guar binder provides a progressive
increase in the wet drop, the dry compression strength,
and the suxfaee smoothness of the resulting pellets.
The data further indicate that the extent of the
enhancement would exceed the binder performance of a
2.00 1b, per ton treatment with Peridur XG-3, from Akzo.
The data summarized in Table 8 indicate that a
combined treatment of the wet concentrate with guar gum
and calcium lignosulfonate improves wet drop, dry
strength and surface smoothness of the pellets over
treatment of the wet concentrate with either guar gum or
a 70/30 combination of modified native starch and guar
gum. The data also indicate that the calcium
lignosulfonate by itself performs poorly as a binder
even at a treatment level of 9.00 1b. per ton. This
compound used by itself failed to slow the balling rate
or significantly increase the wet drop, the dry
compression and the surface smoothness of the pellets
beyond those provided by pellets that contained no
binder.
The data presented in Table 9 also indicates
that a combined treatment of the wet concentrate with
guar gum and calcium lignosulfonate improves wet drop,
dry strength and surface smoothness of the pellets over
treatment of the wet concentrate with guar gum or a
75/25 combination of starch and lignosulfonate. The
data further indicate that the calcium lignosulfonate by
itself performs poorly as a binder. Combinations of
guar gum, pre-gelled starch, and lignosulfonate also
provided improved pellets, as did a guar gum,
lignosulfonate and soda ash combination.
Applicant has discovered that the addition of
lignosulfonate compounds in combination with binders to
WO 92/05290 ~~ ~~ ~ PCT/iJS90/OS~~~ ,
N
42
the wet taconite concentrate increases the plasticity of
the mix. The balls formed from this mix are more easily
deformed by light finger pressure than those balls which
do not contain lignosulfonate. Water-soluble
lignosulfonates may act as dispersants on solid
particulate suspensions in an agueous medium and cause
such suspensions to become more fluid. By contrast,
modified native starch and guar gum appear to act to
flocculate or reduce the mobility of particles in such
aqueous suspensions. The lignosulfonate component acts
to counteract the flocculating action of the modified
native starch and of the guar gum.
It is believed that the action of the
lignosulfonates as a dispersant to increase the
plasticity of the wet taconite pellets and to counter
the flocculating action of the polymers is independent
of the nature of the other binder components which are
used. If the synergistic effect of the lignosulfonate
in the binder is due primarily to the dispersant action
of the lignosulfonate, then this effect should occur
with all combinations of the binder components of the
invention, including a polymer component used alone or
any of the modified native starch-polymer combinations.
Example Formulations
The following example formulations of a water-
dispersible polymer and a pregelatinized starch have
been found to provide satisfactory pellet formation with
wet taconite concentrates. Typical moisture contents
and strength test results are given with these
formulations.
CA 02069482 2002-07-16
WO 92/05290 PC'f/US90/05466
43
Example
1
Binder Composition:
Guar gum (Rantec D-1;.
15 ~s
Finely-ground, modified(extruded),
secondary wheat starch
85~
Binder Addition Rate: {dry basis)
0.148'
Ore Concentrate Source:Hoyt Lakes,
LTV, i~T
Typical Moisture and Results:
Strength
Moisture
9.32
18" Drop (1b.)
5.6
Dry Compression (1b.)
5.2
Example
2
Binder Composition:
Guar gum (Rantec D-1)
20~
Finely-ground, modified(extruded),
secondary wheat starch
80~
Hinder Addition Rate: (dry basic)
0.1.48
Ore Concentrate Source:Hoyt Lakes,
L~TM, t~T
Typical Moisture and Results:
Strength
8 Moisture
9.30
18" Drop (1b.)
6.3
Dry Composition (1b.)
5.6
CA 02069482 2002-07-16
WO 92/05290 PCT/US90/05466
44
Example
3
Hinder Composition:
Guar gum (Rantec D-I)
20%
Finely-ground, moditied (extruded),
secondary wheat starch
80%
, Binder Addition Rate: (dry basis)
0.148%
Ore Concentrate Source:Eveleth~"
Taconite.
EvelethT''s, MN
Typical Moisture and Results:
Strength
% Moisture
9.37
18" Drop (1b.)
6.5
Dry Compression (1b.)
5.2
Example
4
Binder Composition:
Guar gum (Rantec D-1)
15%
Finely-ground, modified (extruded)
corn starch
85%
Binder Addition Rate: (dry basis)
0.148%
Ore Concentrate 9ource:Eveleth~"
Taconite,
EvelethT''', t~1
Typical Moisture and Results:
Strength
% Moisture
9.27
18" Drop (1b.)
5.2
Dry Compression (1b.)
7.1
PCd'/~?~91P/0~~'
WO 92/05290
C~~J ~~~a~~~~~
Example5
Binder Composition:
Pregelatinized tamarind kernal
powder
50$
Modified (extruded) secondary
wheat starch
50$
Binder Addition Rate: 0.148$ (dry basis)
Ore Concentrate Source: LTV, Hoyt Lakes, MN
Typical Moisture and Strength Results:
$ Moisture
9.25
18" Drop
7.2
Dry Compression (1b.)
7.2
Example
6
Binder Composition:
Xanthan (finely--ground Rhodopol 23) 4~
Finely-ground, modified (extruded)
secondary wheat starch
96$
Binder Addition Rate: 0.148 (dry basis)
Ore Concentrate Source: LTV, Hoyt Lakes, MN
Typical Moisture and Strength Results:
Moisture
9.11
18" Drop
4.2
Dry Compression (1b.)
7.0
PCI~/LJS90~/~~!~~
WO 92!05290 ~~~
.. 46
Example 7
Binder Composition:
Polyacrylamide (finely-ground
Calgcn M-550)
10$
Finely-gxound, modified (extruded)
secondary corn starch
90$
Binder Addition Rate: 0.148$ (dry basis)
Ore Concentrate Source: Eveleth Taconite,
Eveleth, MN
Typical Moisture and Strength Results:
$ Moisture
9.17
18" Drop
5.5
7.9
Dry Compression (!b.)
Example 8
Binder Composition:
30~ Acrylic acid/60~ Acrylamide
10 AMPSA
2.5$
Neutralized polyacrylic acid
2.5~
Finely-ground, modified (extruded)
secondary corn starch
95~
Binder Addition Rate: 0.148 (dry basis)
Ore Concentrate Source: Eveleth Taconite,
Eveleth, MN
a
w~ 92iosz9o PCf/iJ~90/05466
20~~~~~2
Typical Moisture and Strength Results:
Moisture
9.2
6.0
o a ~~ prop
Dry Compression (1b.) 5.5
Exam~~le 9
Binder Composition:
Guar gum 14.0$
5 Neutralized polyacrylic acid 1.0~
Finely ground, modified (extruded)
corn starch 85.0
Binder Addition Rate: 0.148 (dry basis)
Ore Concentrate Source: Eveleth Taconite,
Eveleth, MN
Typical Moisture and Strength Results:
Moisture 9'S
18" Drop (1b.) 49
Dry Composition (1b.) 4~
While certain representative embodiments of the
invention have been described herein for purposes
of
illustration, it will be apparent to those skilledthe
in
art that modifications therein may be made without
departing from the spirit and scope of the invention.
