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WO1992005290A1 - Liant a base d'amidon naturel modifie utilise pour agglomerer en boulettes un materiau mineral - Google Patents

Liant a base d'amidon naturel modifie utilise pour agglomerer en boulettes un materiau mineral Download PDF

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Publication number
WO1992005290A1
WO1992005290A1 PCT/US1990/005466 US9005466W WO9205290A1 WO 1992005290 A1 WO1992005290 A1 WO 1992005290A1 US 9005466 W US9005466 W US 9005466W WO 9205290 A1 WO9205290 A1 WO 9205290A1
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WO
WIPO (PCT)
Prior art keywords
water
dispersible
mineral
binder
starch
Prior art date
Application number
PCT/US1990/005466
Other languages
English (en)
Inventor
David L. Dingeman
William E. Skagerberg
Original Assignee
Oriox Technologies, Inc.
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Oriox Technologies, Inc. filed Critical Oriox Technologies, Inc.
Priority to PCT/US1990/005466 priority Critical patent/WO1992005290A1/fr
Priority to US07/852,269 priority patent/US5306327A/en
Priority to CA002069482A priority patent/CA2069482C/fr
Publication of WO1992005290A1 publication Critical patent/WO1992005290A1/fr

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Classifications

    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22B—PRODUCTION AND REFINING OF METALS; PRETREATMENT OF RAW MATERIALS
    • C22B1/00—Preliminary treatment of ores or scrap
    • C22B1/14—Agglomerating; Briquetting; Binding; Granulating
    • C22B1/24—Binding; Briquetting ; Granulating
    • C22B1/242—Binding; Briquetting ; Granulating with binders
    • C22B1/244—Binding; Briquetting ; Granulating with binders organic

Definitions

  • 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.
  • taconite which is abundant in Minnesota's Iron Range, typically contains about 25% magnetic iron as compared to the roughly 50-70% iron content of some higher grade iron ores. In order to use 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 in 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 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 agglomeration 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 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 matrices which provide strength to enable the pellets to survive significant handling at shipping and receiving sites during transshipment.
  • 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 iron particles within the pellet. This phenomenon adversely affects the ability of blast furnace reducing gasses to enter the pellets, thereby lowering blast furnace productivity.
  • Bentonite 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.
  • copolymers of sodium acrylate and acrylamide, used in conjunction with soda ash also show promise as binding agents.
  • 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.
  • 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.
  • modified native starches generally exhibit strong binding characteristics which are desirable in good binders.
  • starch binders generally result in excessive tackiness on the surface of "green" pellets. This allows excessive amounts of mineral concentrate fragments to collect on the surface of green balls when sufficient starch binders are added to maintain acceptable drop strength and dry compression strength at typical concentrate moisture levels.
  • 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.
  • 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 transshipment due to abrasion between adjacent pellet surfaces.
  • starch base binders are generally considered to be unacceptable in the art.
  • a need has been demonstrated for an inexpensive organic binder for pelletizing 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 pelletizing industry.
  • the present invention addresses these and other needs and problems associated with the formation and use of mineral ore pellets in the pelletizing industry.
  • the present invention also offers other advantages over the prior art and solves other problems associated therewith.
  • the present invention provides a binder for pelletizing 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.
  • 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.
  • 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.
  • the binder of the present invention provides many advantages over the prior art binders. It is preferably an substantially inorganic binder containing none of the undesirable constituents found in clay 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.
  • 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, 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 average green ball drop strength of 5 or better at about 9.5% moisture content is generally desireable in many industry pelletizing operations.
  • 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) .
  • 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 pelletizing operations.
  • the pellets should have a relatively smooth outer surface to minimize abrasion or "dust" losses after the pellets are fired. If the pellet surface is too rough, as has commonly been the case with prior art pelletizing 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 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 operations, thereby creating greater transportation and/or transshipment tonnage losses which further degrade pellet quality.
  • Binders must generally accommodate some 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.
  • 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.
  • 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.
  • pellets having a binder comprising modified 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 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.
  • 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.
  • 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.
  • native starch means starch which can be found in nature.
  • 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.
  • water-dispersible 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.
  • percent means percent by weight.
  • aqueous means having water as a primary solvent.
  • organic binder means a binder which is substantially without significant metal (including alkali metal) or silicate content.
  • 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.
  • 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 pellet A being an iron ore 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.
  • a modified native starch base binder for pelletizing 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 ore 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 consisting of ammonium lignin sulfonate, calcium lignin sulfonate, sodium lignin sulfonate and any combination thereof.
  • Binders of the present invention may further comprise about 0.2-40% of soda ash, or sodium carbonate (Na 2 C0 3 ), preferably about 1-25%, and more preferably about 5-20%.
  • the binder of the present invention is preferably used for pelletizing particulate mineral 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 8-11%, 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.
  • 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%.
  • 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.
  • the mineral ore pellet includes about 0.001-1.0%, 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 45%, more prefer bly about 50% iron.
  • 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%, preferably about 8-10%; 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 iron ore pellets include a modified native starch base binder.
  • the iron ore pellet may further comprise about 0.001- 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 mays), 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 starch 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 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.
  • 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.
  • modified native starch is believed to be an unacceptable binder, as has been discussed hereinabove.
  • 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 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.
  • 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
  • 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.
  • 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.
  • Fig. 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.
  • 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.
  • 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.
  • the pellet without 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 peel” effect which is considered unacceptable in the pelletizing industry.
  • 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 or the present invention possess a more even or smooth surface, lacking the "cratering" or the "orange peel” effect generally observed on the surfaces of the pellets having simple starch base binders. In 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.
  • 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.
  • 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 0.001-0.1%, 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 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.
  • the step involving forming mineral ore pellets includes balling the mineral 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 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- 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%, more 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 6-12%, 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 0.01-10.0%, preferably about 0.01-1.0% modified native starch and about 0.001-0.1% of water-dispersible polymer material.
  • 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 with the present 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.
  • 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 processing by mixing them with a relatively small amount of water and then extruded through a screw extrusion device such as a Wenger Extruder (Wenger Manufacturing, Inc., Sabetha, KS) which generates sufficient heat and pressure to gelatinize the starch. A sample of the extruded starch is weighed, and dried and weighed again to determine its moisture content which was about 7%. The extrusion process generated sufficient heat to "flash" off most of the moisture. The starch was then ground to a fine size in a Pitchford blender and screened on a 44 micron screen (U.S. standard No.
  • 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 550 (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 in 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 procedure. 750 g of 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 14 grams, was mixed into the head sample so as to produce green pellets having a moisture content in the range of 8.8 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 15 minutes at approximately 25 rpm until approximately 500 grams of pellets were formed. The finished pellets were screened using a U.S.
  • 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 pellets 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 observations of pellet surface characteristics and weights of water added to obtain desired pellet moistures.
  • 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.
  • 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.
  • 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.
  • 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 polyacryla ide-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 properly.
  • 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 starch/polymer pellets raises the dry compression strength of the pellet by about 1-2 pounds.
  • 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.
  • 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 growth and wet, tacky surfaces which produce fragile, erodible pellet surfaces when dried.
  • 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.
  • moist, "green” balls are fed onto a steel conveyer or grate which travels into 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.
  • the pellets will reach a temperature of about 2200-2400°F (1200-1300°C) which 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 stabilize operations or low quality production must be accepted. Dust losses in the furnace, in this situation, would be severe.
  • the resistance to abrasion and dust losses of pellets in the drying zone of the furnace is simulated by the DRY ABRASION TEST. Iron ore pellets were prepared as described above for 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 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.
  • 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 observed to be consistent with those needed to produce high quality pellets and did not display the negative characteristics previously seen with starch bound pellets.
  • the growth rate was similar to that seen using bentonite as a binding agent, and the balls did not display the characteristics rapid growth rate, tackiness and orange peel characteristics of starch bound pellets. Samples of the green pellet were collected and analyzed to determine their characteristics.
  • Standardization is abbreviated ISO.
  • the test procedures referenced are well known in the art.
  • Figure 1 is a picture of two fired pellets. Both pellets contain 0.147% binder by weight. The pellet on the left (A) contains 0.147% extruded wheat starch and the pellet on the right (B) contains 0.118% extruded wheat starch and 0.029% guar gum. Both sets of pellets were produced 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.
  • the starch bound pellet (A) surface has significant areas of rough, orange peel surface while the starch/polymer pellet (B) is relatively smooth.
  • the critical improvement appears to be related to the ability of small amounts of water-dispersible polymer material to control the green pellet growth rate 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.
  • 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.
  • 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.
  • 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 lb. 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.
  • lignosulfonate compounds in combination with binders to 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 aqueous medium and cause such suspensions to become more fluid.
  • 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.
  • 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 1 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.
  • Example 1 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.
  • Example 1 Example 1
  • Binder Addition Rate 0.148% (dry basis) Ore Concentrate Source: LTV, Hoyt Lakes, MN Typical Moisture and Strength Results:
  • Binder Composition Guar gum (Rantec D-l)
  • Guar gum (Rantec D-l) 20% Finely-ground, modified (extruded), secondary wheat starch 80%
  • Binder Addition Rate 0.148% (dry basis) Ore Concentrate Source: Eveleth Taconite, Eveleth, MN
  • Binder Addition Rate 0.148% (dry basis) Ore Concentrate Source: Eveleth Taconite
  • Binder Addition Rate 0.148% (dry basis) Ore Concentrate Source: Eveleth Taconite
  • Binder Addition Rate 0.148% (dry basis) Ore Concentrate Source: Eveleth Taconite, Eveleth, MN

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Abstract

Liant servant à agglomérer en boulettes un matériau minéral particulaire. Le liant comprend environ 30 à 99,5 % d'amidon naturel modifié et environ 0,2 à 80 % d'un matériau polymère pouvant se disperser dans l'eau choisi dans le groupe constitué de gommes naturelles pouvant se disperser dans l'eau, de pectines pouvant se disperser dans l'eau, de dérivés d'amidon pouvant se disperser dans l'eau, de dérivés de cellulose pouvant se disperser dans l'eau, de polymères de vinyle pouvant se disperser dans l'eau, de polymères acryliques pouvant se disperser dans l'eau et de mélanges de ces derniers. D'autres compositions possibles renferment environ 0,5 à 50 % de lignosulfonates et/ou environ 0,2 à 40 % de soude à l'ammoniaque. L'invention concerne également un concentré de minerai minéral ainsi que des boulettes de minerai minéral et de minerai de fer. En outre, des procédés pour lier un matériau minéral particulaire et pour fabriquer des boulettes de minerai minéral sont également décrits.
PCT/US1990/005466 1990-09-26 1990-09-26 Liant a base d'amidon naturel modifie utilise pour agglomerer en boulettes un materiau mineral WO1992005290A1 (fr)

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PCT/US1990/005466 WO1992005290A1 (fr) 1990-09-26 1990-09-26 Liant a base d'amidon naturel modifie utilise pour agglomerer en boulettes un materiau mineral
US07/852,269 US5306327A (en) 1990-09-26 1990-09-26 Modified native starch base binder for pelletizing mineral material
CA002069482A CA2069482C (fr) 1990-09-26 1990-09-26 Liant a base d'amidon naturel modifie servant a la pelletisation de matiere minerale

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Cited By (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO1994021831A1 (fr) * 1993-03-16 1994-09-29 Linde Aktiengesellschaft Briquette s'utilisant comme materiau generateur de laitier dans des fours de fusion et procede pour sa fabrication
EP0656072A4 (fr) * 1992-08-06 1996-06-26 Akzo Nobel Nv Composition de liant et procede d'agglomeration de matiere particulaire.
US7261759B2 (en) * 2001-05-21 2007-08-28 React-Nti, Llc Powder metal mixture including micronized starch
US8221831B2 (en) 2004-09-17 2012-07-17 Envirobond Products Corporation Materials for travelled surfaces
CN114196822A (zh) * 2021-12-03 2022-03-18 河南锦瀚环保科技有限公司 一种圆盘造球烧结球团矿新型粘合剂及其制备方法
CN114737055A (zh) * 2022-05-11 2022-07-12 兰州理工大学 用于冶金球团的高纯度复合粘结剂及使用方法
CN115279928A (zh) * 2020-05-18 2022-11-01 日本制铁株式会社 团块物的制造方法及团块物
CN116348433A (zh) * 2020-11-23 2023-06-27 可耐福石膏两合公司 淀粉作为用于基材的底漆

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US2833642A (en) * 1954-11-10 1958-05-06 Gen Mills Inc Binder additive for making ore pellets
US2914394A (en) * 1956-04-05 1959-11-24 Dohmen Heinrich Briquetting of ores
US3154403A (en) * 1962-09-24 1964-10-27 Grain Products Inc Process for pelletizing ores
US3585025A (en) * 1967-07-27 1971-06-15 Rheinische Kalksteinwerke Basic aggregate for the production of steel
US3823009A (en) * 1971-02-09 1974-07-09 Bayer Ag Agglomeration of titanium ores containing iron
US4402736A (en) * 1979-11-23 1983-09-06 N. B. Love Industries Pty. Limited Cold bonding mineral pelletization
US4767449A (en) * 1985-05-21 1988-08-30 Union Carbide Corporation Process for agglomerating ore concentrate utilizing clay and dispersions of polymer binders or dry polymer binders
US4802914A (en) * 1985-05-21 1989-02-07 Union Carbide Corporation Process for agglomerating mineral ore concentrate utilizing dispersions of polymer binders or dry polymer binders

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Publication number Priority date Publication date Assignee Title
US2833642A (en) * 1954-11-10 1958-05-06 Gen Mills Inc Binder additive for making ore pellets
US2914394A (en) * 1956-04-05 1959-11-24 Dohmen Heinrich Briquetting of ores
US3154403A (en) * 1962-09-24 1964-10-27 Grain Products Inc Process for pelletizing ores
US3585025A (en) * 1967-07-27 1971-06-15 Rheinische Kalksteinwerke Basic aggregate for the production of steel
US3823009A (en) * 1971-02-09 1974-07-09 Bayer Ag Agglomeration of titanium ores containing iron
US4402736A (en) * 1979-11-23 1983-09-06 N. B. Love Industries Pty. Limited Cold bonding mineral pelletization
US4767449A (en) * 1985-05-21 1988-08-30 Union Carbide Corporation Process for agglomerating ore concentrate utilizing clay and dispersions of polymer binders or dry polymer binders
US4802914A (en) * 1985-05-21 1989-02-07 Union Carbide Corporation Process for agglomerating mineral ore concentrate utilizing dispersions of polymer binders or dry polymer binders

Cited By (10)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0656072A4 (fr) * 1992-08-06 1996-06-26 Akzo Nobel Nv Composition de liant et procede d'agglomeration de matiere particulaire.
WO1994021831A1 (fr) * 1993-03-16 1994-09-29 Linde Aktiengesellschaft Briquette s'utilisant comme materiau generateur de laitier dans des fours de fusion et procede pour sa fabrication
US7261759B2 (en) * 2001-05-21 2007-08-28 React-Nti, Llc Powder metal mixture including micronized starch
US8221831B2 (en) 2004-09-17 2012-07-17 Envirobond Products Corporation Materials for travelled surfaces
CN115279928A (zh) * 2020-05-18 2022-11-01 日本制铁株式会社 团块物的制造方法及团块物
CN115279928B (zh) * 2020-05-18 2024-01-19 日本制铁株式会社 团块物的制造方法及团块物
CN116348433A (zh) * 2020-11-23 2023-06-27 可耐福石膏两合公司 淀粉作为用于基材的底漆
CN114196822A (zh) * 2021-12-03 2022-03-18 河南锦瀚环保科技有限公司 一种圆盘造球烧结球团矿新型粘合剂及其制备方法
CN114737055A (zh) * 2022-05-11 2022-07-12 兰州理工大学 用于冶金球团的高纯度复合粘结剂及使用方法
CN114737055B (zh) * 2022-05-11 2024-03-29 兰州理工大学 用于冶金球团的高纯度复合粘结剂及使用方法

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