Patent Application
20140033872
The present disclosure generally relates to binder compositions for preparing iron ore pellets and processes for preparing the iron ore pellets.
Iron ore is commonly used in the production of steel. In the first step of the steel-making process, iron is recovered from the ore by smelting in a blast furnace. To be fed directly into the furnace, to the iron ore must be in the form of agglomerates of substantial size. If the ore is in the form of particles that are too small for direct feed, it is necessary to convert the iron ore particles to a sinter or to pellets. With the increasing use of lower grade ores, it has become necessary to grind the ore more finely. For these fine particles, pelletization is a common method of feedstock production for the furnaces.
Binders may be used to pelletize particulate iron ore particles. Generally, the iron ore pellets are formed by adding binder or a binder composition to the fine particulate ore and stirring in the presence of a small amount of water to form a moist mixture, and then pelletizing the mixture to form green (wet) pellets. These green pellets are then fired in a kiln through a temperature range that extends from an inlet temperature typically in the range 200° -400° C. to a final temperature of e.g., 1200° C. Such processes of forming iron ore pellets are described, for example, in European Patent No. 0225171, which is incorporated herein by reference in its entirety.
Common binders used to agglomerate particular ion ore include certain polymers and bentonite, although many binders have been proposed in the literature, for example various clays, ferrous sulphate, lignin sulphate, asphalt, starches, calcium and sodium compounds. Yet, the spalling temperature of bentonite and many known binders is undesirably low. Typically, the inlet temperature of the kiln must be in the range 200° to 400° C. to prevent spalling.
One report (de Souza et al. Mining Engineering, October 1984, pages 1437-1441 describes the use of polymers based on cellulose, in particular carboxymethyl cellulose (Peridur®). The article reported adding Peridur® powder to an aqueous pulp of iron ore before filtration and also reported adding the powder manually to the ore flow. The article noted the need for water soluble polymers to be hydrated and dissolved during mixing and pelletizing. Spalling at 250° C. was reported.
Powdered carboxymethyl cellulose binders can produce irregular particle shapes and size distribution, however, such that the powder does not flow freely. Instead, the dry particles tend to clump together, making it difficult to achieve uniform supply of the low dosages that are required. Moreover, the amount of cellulosic binder required for adequate strength tends to be too high to be cost effective and. some cellulosic polymers undesirably lower surface tension.
There remains a need for binder composition which can be used to economically produce pellets of iron ore fines.
There remains a further need for binder compositions which can be used to address the deficiencies in surface properties of the iron ore pellets produced using binders commonly used in the art.
Disclosed herein are binder compositions for agglomerating iron ore fines comprising: (a) about 30 to about 80% by weight one or more types of anionic or nonionic acrylamide-containing polymer; (b) about 10 to about 35% by weight one or more types of inorganic or organic monomeric electrolyte; and (c) about 10 to about 35% one or more types of finely ground wood fiber. Also disclosed is a process for preparing iron ore pellets with the binder compositions, the process comprising: (i) adding a binder composition to particulate iron ore to form a mixture; and (ii) forming the mixture into pellets.
The disclosure may be understood more readily by reference to the following detailed description of the various features of the disclosure and the examples included therein.
The present disclosure is directed to binder compositions for agglomerating iron ore fines, and processes for preparing iron ore pellets. According to the exemplary embodiments, the binder composition includes one or more types of anionic or nonionic acrylamide-containing polymer; one or more types of inorganic or organic monomeric electrolyte; and one or more types of finely ground wood fiber. The binder compositions and processes described herein can be used to provide iron ore pellets that have improved properties, including: increased dry and/or wet compressive strength, improved abrasion index, improved surface tension, and/or decreased clumping. In certain embodiments, the binder compositions offer economic and performance advantages over other polymer-based binder compositions.
As used herein, the phrase “iron ore fines” refers to substantially iron-based or iron ore materials that are in particulate form. In exemplary embodiments, the iron ore fines are particles of iron ore that are substantially of small particle size, for example less than about 250 μm. Iron ores are rocks and minerals from which metallic iron can be economically extracted. The ores are usually rich in iron oxides and vary in color from dark grey, bright yellow, deep purple, to rusty red. The iron itself is usually found in the form of magnetite (Fe3O4), hematite (Fe2O3), goethite (FeO(OH)), limonite (FeO(OH).n(H2O)) or siderite (FeCO3). Taconite is an iron-bearing sedimentary rock in which the iron minerals are interlayered with quartz, chert, or carbonate. Itabirite, also known as banded-quartz hematite and hematite schist, is an iron and quartz formation in which the iron is present as thin layers of hematite, magnetite, or martite. Any of these types of iron are suitable for use in forming the pellet as described herein. In exemplary embodiments, the iron ore fines are substantially magnetite, hematite, taconite or itabirite. In exemplary embodiments, the iron ore fines can be contaminated with clay.
As used herein, the term “pellet” refers to a small particle created by agglomerating the mixture comprising iron ore fines, the binder and a liquid, such as water. Such mixtures may also be agglomerated or compressed into shapes other than pellets, for example briquettes or other appropriate shapes. As will be understood by those of skill in the art, the shape of the agglomerated particle is not particularly limited. In exemplary embodiments, the final particle size of the pellet, or agglomerated particle, is about 5 to about 19 mm.
As used herein, the term “binder” or “binder composition” refers to a composition or a system of components that is added to the iron ore fines in order to draw them together in such a way that the mixture maintains a uniform consistency. The binder composition may be added to the iron ore fines as a mixture of the components or the components of the binder composition may be added separately to the iron ore composition and in any order deemed suitable by one of skill in the art. In exemplary embodiments, the binder composition is a dry mixture or is a substantially dry mixture.
In exemplary embodiments, the binder composition comprises one or more types of anionic or nonionic acrylamide-containing polymer; one or more types of inorganic or organic monomeric electrolyte; and one or more types of finely ground wood fiber. The optimal proportions of these components may vary depending on the identity of each of the components, the source of iron ore fines, the moisture content, the surface area, the particle size and the impurities. In exemplary embodiments, the binder composition comprises: (a) about 30 to about 80% by weight one or more types of anionic or nonionic acrylamide-containing polymer; (b) about 10 to about 35% by weight one or more types of inorganic or organic monomeric electrolyte; and (c) about 10 to about 35% one or more types of finely ground wood fiber.
In exemplary embodiments, the anionic or nonionic acrylamide-containing polymer is an anionic acrylamide-containing polymer. In other exemplary embodiments, the anionic or nonionic acrylamide-containing polymer is a nonionic acrylamide-containing polymer. In exemplary embodiments, the anionic or nonionic acrylamide-containing polymer is polyacrylamide. In exemplary embodiments, the anionic or nonionic acrylamide-containing polymer is a copolymer of acrylamide and an ethylenically unsaturated anionic monomer. In exemplary embodiments, the anionic or nonionic acrylamide-containing polymer is a copolymer of sodium acrylate and acrylamide, for example a polymer that contains about 30 to about 50% by weight sodium acrylate and about 50 to about 70% by weight acrylamide. In certain embodiments, the anionic or nonionic acrylamide-containing polymer has a low molecular weight and/or a low ionic charge.
As used herein, the terms “polymer,” “polymers,” “polymeric,” and similar terms are used in their ordinary sense as understood by one skilled in the art, and thus may be used herein to refer to or describe a large molecule (or group of such molecules) that contains recurring units. Polymers may be formed in various ways, including by polymerizing monomers and/or by chemically modifying one or more recurring units of a precursor polymer. A polymer may be a “homopolymer” comprising substantially identical recurring units formed by, e.g., polymerizing a particular monomer. A polymer may also be a “copolymer” comprising two or more different recurring units formed by, e.g., copolymerizing two or more different monomers, and/or by chemically modifying one or more recurring units of a precursor polymer. The term “terpolymer” may be used herein to refer to polymers containing three or more different recurring units.
In exemplary embodiments, the anionic or nonionic acrylamide-containing polymer can be introduced to the binder composition as a powder or as a dispersion, for example a dispersion of the polymer in powder form in oil. In exemplary embodiments, particles of the polymer powder can be relatively large, for example about 20 μm to about 1000 μm, about 20 μm to about 500 μm, about 20 μm to about 300 μm, about 20 μm to about 100 μm, or about 20 μm to about 100 μm. In exemplary embodiments, substantially all, or at least 90% by weight, of the individual polymer particles are in the range 20 to 150 μm or, preferably, 20 to 100 μm. These individual polymer particles may be introduced into the mixture as friable aggregates of several particles, these aggregates breaking down into the individual particles during mixing with the insoluble particulate material.
In exemplary embodiments, the anionic or nonionic acrylamide-containing polymer is made by polymerization in conventional manner or known in the art, such as reverse phase polymerization followed by drying and, optionally, comminution; or by bulk gel polymerization followed by drying and comminution. If the polymers are made by comminution it may be necessary to sieve the particles to give desired particle size. In certain embodiments, the anionic or nonionic acrylamide-containing polymer is in the form of beads, for example substantially spherical beads, made by reverse phase polymerization. In certain embodiments, the anionic or nonionic acrylamide-containing polymer is a free-flowing powder.
In exemplary embodiments, the anionic or nonionic acrylamide-containing polymer comprises a blend of nonionic and anionic monomers. In exemplary embodiments, the polymer contains up to 95% by weight nonionic monomers and at least 5% by weight anionic monomers. In exemplary embodiments, the nonionic monomer is acrylamide, another nonionic ethylenically unsaturated monomers or a mixture thereof. In exemplary embodiments, the anionic monomer is acrylic acid, methacrylic acid, sulphonic acid, an ethylenically unsaturated carboxylic acid, a mixture thereof, or salts thereof. The anionic monomer may be used in the form of a salt, for example a water soluble salt such as a sodium salt, a potassium salt, or an ammonium salt. The anionic monomer may be used partially or wholly in the form of free acid. In certain embodiments, other anionic monomers, or even cationic monomers, may form part of the polymer but the amounts of them should be sufficiently low that they do not deleteriously affect the performance properties.
In exemplary embodiments, the amount of the anionic monomer in the polymer is about 5 to about 60%, about 5 to about 50%, about 5 to about 40%, about 5 to about 30%, about 5 to about 25%, about 5 to about 20%, or about 5 to about 15% by weight.
In exemplary embodiments, the amount of the nonionic monomer in the polymer is about 40 to about 95%, about 50 to about 95%, about 60 to about 95%, about 70 to about 95%, about 75 to about 95%, about 80 to about 95%, or about 85 to about 95% by weight.
In exemplary embodiments, the polymer has an intrinsic viscosity of about 2 dl/g to about 16 dl/g, about 2 dl/g to about 8 dl/g, about 2 dl/g to about 7 dl/g, about 3 dl/g to about 6 dl/g, or about 3 dl/g to about 5 dl/g. Intrinsic viscosity may be determined by any methods know in the art, for example, using a suspended level viscometer.
In certain embodiments, the anionic or nonionic acrylamide-containing polymer is a copolymers of 95 to 85% by weight acrylamide and 5 to 15% by weight sodium acrylate having intrinsic viscosity of from about 2 dl/g to about 7 dl/g.
In certain embodiments, the amount of the one or more anionic or nonionic acrylamide-containing polymer is about 0.005 to about 0.2%, about 0.005 to about 0.15%, or about 0.01 to about 0.1% by weight of the iron ore fines.
In exemplary embodiments, the one or more inorganic or organic monomeric electrolyte is a water soluble salt of an acid, for example a salt of a weak organic acid or carbonic acid. In certain embodiments, one or more inorganic or organic monomeric electrolyte is not a salt of a strong acid. In exemplary embodiments, the one or more inorganic or organic monomeric electrolyte is an inorganic water soluble salts of carboxylic, dicarboxylic, and tricarboxylic acids. In exemplary embodiments, the one or more inorganic or organic monomeric electrolyte is selected from the group consisting of: sodium carbonate, sodium bicarbonate, sodium citrate, sodium hydroxide, sodium oxalate, sodium tartrate, sodium benzoate, sodium stearate, sodium silicate, and the corresponding ammonium, potassium, calcium or magnesium salts of the preceding salts, calcium oxide, and mixtures thereof. In certain embodiments, the one or more inorganic or organic monomeric electrolyte comprises sodium carbonate. In certain embodiments, the one or more inorganic or organic monomeric electrolyte comprises sodium citrate. In certain embodiments, the one or more inorganic or organic monomeric electrolyte comprises sodium carbonate and sodium citrate. In certain embodiments, the amount of the one or more inorganic or organic monomeric electrolyte is about 5 to about 60% by weight of the one or more anionic or nonionic acrylamide-containing polymer.
As used herein, “finely ground wood fiber” refers to finely ground, or micronized, lignocellulose or plant biomass that is composed of cellulose, hemicellulose, and lignin. The type or source of wood fiber may be any type or source which one of skill in the art would understand to be useful in the compositions described herein. In exemplary embodiments, the finely ground wood fiber consists of fibers, or particles, of which the majority of the fibers are about 10 to about 150 μm, about 50 to about 150 μm, about 10 to about 100 μm, about 10 to about 70 μm, about 40 to about 70 μm, or about 20 to about 40 μm in length. In exemplary embodiments, about 95% of the fibers are less than 150 μm in length and about 80% of the fibers are more than less than 10 μm in length. In exemplary embodiments, about 95% of the fibers are less than 150 μm in length and about 80% of the fibers are more than 50 μm in length. In certain embodiments, about 95% of the fibers are less than 100 μm in length and about 80% of the fibers are more than 10 μm in length. In certain embodiments, about 95% of the fibers are less than 70 μm in length and about 80% of the fibers are more than 10 μm in length. In certain embodiments, about 95% of the fibers are less than 70 μm in length and about 80% of the fibers are more than 40 μm in length. In certain embodiments, about 95% of the fibers are less than 40 μm in length and about 80% of the fibers are more than 20 μm in length.
In exemplary embodiments, the wood fiber is a mixture of one or more types of wood fibers. In one embodiment, the wood fiber is tree bark, for example spruce bark or balsam fir bark. In exemplary embodiments, the wood fiber is a commercially available lignocellulose product or mixture, for example Arbocel C750 FP, Arbocel C100 SG, Arbocel CW 630 PU, Arbocel C350 SR, Arbocel C500 SR, Vemissa E 150, Vemissa E 100/150, Vemissa B 100/150. In one embodiment, the wood fiber is a mixture of lignocellulose and raw cellulose.
The wood fiber is in a finely divided form and may be reduced to a powder by grinding or shredding in a disc refiner. The size of the fibers has been found to have an impact on the performance of the iron ore pellets. The wood fiber may be subjected to a plurality of pretreatments, depending on the nature of the wood fiber chosen and the degree of binding required. These procedures may include organic solvent extraction to remove resins and other organic solvent-soluble materials, or treatment with alkali, such as sodium hydroxide solution.
In exemplary embodiments, the binder composition may comprise any additives necessary or desired. Additives suitable for use in the compositions described herein would be known to those of skill in the art. In certain embodiments, the binder composition further comprises bentonite. In certain embodiments, the binder composition does not comprise bentonite. In certain embodiments, the binder composition does not comprise carboxymethyl cellulose.
In exemplary embodiments, the binder composition may be added to iron ore fines to provide a pellet. In exemplary embodiments, the pellet comprises about 0.005 to about 0.2%, about 0.01 to about 0.1%, about 0.02 to about 0.08%, or about 0.03 to about 0.06% binder composition per kilogram of iron ore fines.
Pellets that include the exemplary binder composition have improved properties. Common properties of the pellets include the initial or wet strength, the dry strength (after drying the green pellets in an oven at 105° C.) and the tendency of the pellets to spall (or burst) upon exposure to firing temperatures. Generally, a higher spalling temperature is a desirable quality. The tendency for spalling can be defined by determining the minimum temperature at which spalling occurs or by observing the percentage of fines formed during a particular firing cycle. Other properties of the pellets include the moisture content of the mixture and the porosity of the pellets. Another property of pellets is a “drop number.”—generally, a high drop number for the green pellets is desirable. To ensure uniform properties, the binder's flow properties must be such that it can easily be added uniformly in low quantities.
In exemplary embodiments, the pellets comprising a mixture of iron ore fines and the binder compositions described herein, have satisfactorily high wet strength and dry strength (measured after drying in an oven) and a satisfactorily high drop number when wet (indicating the number of drops before they shatter). In exemplary embodiments, the sintered pellets prepared by the processes described herein have improved (higher) abrasion index, such as when compared to the similar pellets made with a sodium carboxymethylcellulose binder. In exemplary embodiments, the pellets prepared by the processes described herein have increased compressive strength, including wet and dry compressive strength, such as when compared to similar pellets made with sodium carboxymethylcellulose binder. In exemplary embodiments, the pellets prepared by the processes described herein have improved moisture retention properties.
In exemplary embodiments, a process for preparing pellets of iron ore comprising: (i) adding a binder composition to iron ore fines to form a mixture; and (ii) forming the mixture into pellets. According to the embodiments, the binder composition comprises: (a) about 30 to about 80% by weight one or more types of anionic or nonionic acrylamide-containing polymer; (b) about 10 to about 35% by weight one or more types of inorganic or organic monomeric electrolyte; and (c) about 10 to about 35% one or more types of finely ground wood fiber.
In exemplary embodiments, the components of the binder composition may be blended and added to the iron ore fines as a blend. In certain embodiments, the components of the binder may be added separately to the iron ore fines.
According to the embodiments, the process steps of adding the binder composition to iron ore fines to form a mixture or forming the mixture into pellets can be carried out in the conventional or known methods in the art of agglomeration. In exemplary embodiments, the process further comprises the step of mixing, stirring or agitating the mixture after the addition of the binder composition. In certain embodiments, the binder composition may be added to the iron ore fines prior to or during mixing of the mixture. In exemplary embodiments, the binder composition can be blended with the iron ore fines by scattering the binder composition powder or dispersion on to the iron ore fines as it is carried toward a mixer, such as a paddle mixer with stators. In exemplary embodiments, the mixture comprising the iron ore fines and the binder composition is mixed for about 2 minutes to about 20 minutes.
In exemplary embodiments, the process further comprises the step of adding water, which may be added before, during or after the addition of the binder to the iron ore fines. The amount of water added is the amount required to bring the moisture content to the optimum level for the particular mixture. In exemplary embodiments, the iron ore fines, prior to adding the binder composition, already has the desired final moisture content of about 5 to about 15%, or about 6 to about 10%, by weight based on the weight of the iron ore. The moisture content is the moisture as measured by heating up to 105° C. If the iron ore fines initially do not contain the desired final moisture content, water may be added to increase the moisture content.
In exemplary embodiments, the forming of the mixture into pellets, or the agglomeration step, may be conducted with or without compression, by balling on a disc, or balling in a drum. In exemplary embodiments, the process may further comprise drying and firing the pellets, for example by any methods known in the art such as heating the pellets to about 1000° C., about 1200° C. For this purpose, the pellets can be introduced to a kiln or other firing apparatus and fired in the conventional manner. It is desirable to be able to introduce It is desirable to be able to introduce them into this furnace at the highest possible inlet temperature with the minimum risk of spalling. The inlet temperature at which spalling becomes significant can be referred to as the spalling temperature and a particular advantage of the invention is that it is possible to make pellets having a spalling temperature higher than can conveniently be obtained by the use of bentonite and other known binders.
The following examples are presented for illustrative purposes only, and are not intended to be limiting.
The pellet preparation and testing methods used throughout the Examples described herein are provided below.
Pellet Preparation
In this example, iron ore pellets comprising iron ore and a binder, including binders according to the embodiments described herein, were prepared. The iron ore used in this example was hematite with a moisture content of between 8 to 10 wt. %. The binder was added evenly over 6000 grams (dry weight) iron ore. The dosage of the binder used was 0.05 weight-percent. This mixture was initially mixed by hand and then loaded into a high speed mixer (manufactured by WAM S.p.A Italy) and mixed for about 1 minute. After mixing, the batch was screened to remove large lumps and particles.
A disc pelletizer (disc diameter 0.40 m; manufactured by MarsMinerals USA) was used to prepare pellets from the mixture. The mixture was fed with constant rate to the disc and atomized water was sprayed to disc to assist the pellet formation. Pellets grown to right size range (larger than 8 mm) were constantly removed during the pelletization process. After the pelletization, the whole produced pellet batch was sieved to different size fraction and all analyses work was done with 10-12.5 mm pellet size fraction.
Analysis of Physical Properties
For each type of binder composition used in the pellets, an average of 15 pellets of the same composition were subjected to Drop Number, Wet Compressive Strength and Dry Compressive Strength tests. The Drop Number was determined by repeatedly dropping a wet pellet individually from an 0.45 m height to a steel plate until a crack appeared on the surface of the tested pellet. The number of drops required to produce a crack on the surface of each pellet is the Drop Number.
The Wet Compressive Strength, also called green strength, was determined right after the pelletization and sieving from pellets in the size range 10-12.5 mm. The Wet Compressive Strength was measured by CT3 Texture Analyzer manufactured by Brookfield. For the wet pellets, the analyzer also gave a value for the Deformation i.e. how many percentage the wet pellet can be compressed before it breaks. This value is an indication of plasticity of the wet pellet.
The Dry Compressive Strength was determined by drying pellets over night at 105° C. The Dry Compressive Strength analysis was measured by CT3 Texture Analyzer manufactured by Brookfield. The Compressive Strength of the sintered pellets was also measured. Sintered pellets were prepared by loading the dried pellets into the laboroatory furnace and heating them to 1300° C. and holding the temperature 15 min before cooling down to room temperature. After cooling the compressive strength of the sintered pellets were measured by INSTRON® 3366 compressive strength analyzer.
The compositions and dosage of the binders in the pellet samples are provided in Table 1. The binder dosage used was 0.05 weight-percent in the iron pellet composition. The amounts of polymer, sodium carbonate, sodium citrate and wood fiber in the table are listed as weight percentages of the combined totals of these four components. The polymers used in these samples were a anionic polyacrylamide polymers (dry) or sodium carboxymethylcellulose. The reference samples do not contain wood fibers.
The results of the analysis of physical properties of the pellets are provided in Table 2.
The compositions and dosage of the binders in the pellet samples are provided in Table 3. The binder dosage used was 0.05 weight-percent in the iron pellet composition. The amounts of polymer, sodium carbonate, sodium citrate and wood fiber in the table are listed as weight percentages of the combined totals of these four components. The polymers used in these samples were an anionic polyacrylamide polymer (dry) or sodium carboxymethylcellulose. The wood fiber used was lignocellulose of varying particle sizes and size distributions. The particle size and size distribution of the wood fibers used in each sample are provided in Table 3. The reference samples do not contain wood fibers.
The results of the analysis of physical properties of the pellets are provided in Table 4.
This application claims priority to U.S. Provisional Application No. 61/680,002, filed Aug. 6, 2012.
| Number | Date | Country | |
|---|---|---|---|
| 61680002 | Aug 2012 | US |
