Binder composition for iron ore agglomeration

Abstract

The present invention relates to a binder composition for iron ore pellet production, comprising: a) at least two organic binders LO in the form of solid particles, at least a water-soluble anionic polymer P1 having a mass average molecular weight of 500 to 200,000 daltons, and a water-soluble anionic polymer P2 having a mass average molecular weight exceeding 500,000 daltons, the organic binder LO; and b) at least one inorganic binder LI in the form of solid particles, wherein the solid particles of the binder LO have a number median diameter exceeding 500 micrometers, and the particles of the binder LI have a number median diameter less than one-third of the number median diameter of the solid particles of the binder LO.

Description

Technical Field

[0001] The present invention relates to a binder composition for producing iron ore pellets. More specifically, the binder composition contains at least two organic binders and at least one inorganic binder. These binders have specific properties.

Background Art

[0002] Iron ore should be in the form of large pellets when charged into a blast furnace. If the ore is in the form of particles that are too small to be introduced directly into the blast furnace, they must be processed into pellets. The increasing use of lower-quality ores has made it necessary to grind the ore more finely. Pelletization (or granulation) is the only satisfactory way to produce furnace raw materials from these fine particles.

[0003] Pellets are produced by adding a binder to fine ore particles, stirring it in the presence of a small amount of water (usually the moisture from the ore) to form a wet mix, and then collecting the mix, for example, with a shovel inside a pelletizing drum or a disk pelletizer. Subsequently, green pellets (or so-called raw material pellets before they are sintered by firing) are fired in a furnace over a temperature range from an inlet temperature, typically 200 to 400 degrees Celsius, to a high final temperature, for example, 1,200 degrees Celsius.

[0004] Important pellet properties are the initial or wet strength, the dry strength (after drying the green pellets in an oven at 105 °C), and the tendency for the pellets to break into powder (or explode or flake) when the pellets are exposed to the furnace firing temperature. The tendency to flake can be defined by determining the lowest temperature at which flaking occurs or by observing the proportion of fines formed during a particular firing cycle. The moisture content of the mix and the porosity of the pellets must be carefully selected. A high "drop number" is desirable for green pellets. For cost reasons, the amount of binder should be as low as possible, and for ensuring certain properties, the flow properties of the binder should be such that the binder can be easily added uniformly in this small amount.

[0005] Binders have traditionally been clay (usually bentonite), cement (usually Portland cement), or lime. However, various proposals have been made for using organic polymers as binders. Thus, natural polymers are considered in certain cellulose polymers, but natural polymers are not entirely satisfactory. Indeed, it can be very difficult to accurately adjust the addition of natural polymers to particulate materials. Synthetic polymers (generally water-soluble linear anionic polymers having a molecular weight of 1 million to 20 million in powder form) have also been proposed for many years. However, the use of synthetic polymers also involves difficulties.

[0006] For example, WO2017 / 037207 discloses a binder composition comprising a water-soluble polymer having a molecular weight of 1,000 to 20,000 Da, a copolymer having a molecular weight greater than 300,000 Da, and an inorganic pelletization aid. In the same field, US5,002,607 describes a binder composition comprising a water-soluble polymer having a molecular weight of less than 50,000 Da, a binder polymer having a molecular weight greater than 1 million Da, and an inorganic pelletization aid.

[0007] The size of the polymer particles is generally relatively large, typically larger than 700 μm. The results obtained with products of such large particle sizes are not entirely satisfactory. Indeed, the pellets obtained tend to adhere to the surface of the pellets and are then contaminated by the dust blown out from the pellets in subsequent metallurgical applications of the pellets. This problem is thought to be due to pellets having a stickier surface than is desirable. Whatever the cause, the drawback of the pellets is that when the outside air blows through the pellet layer, metal ore dust is carried by the outside air and from the furnace. This can cause pollution problems and undesirable wear to the fans and other parts of the furnace, and related equipment.

[0008] In EP0225171 and EP288150, specific synthetic polymers have been proposed, and the dry particle size of these polymers must be between 20 and 300 μm. This size is preferably less than 100 μm at a ratio of at least 50% by mass.

Prior Art Documents

Patent Documents

[0009]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Summary of the Invention

Problems to be Solved by the Invention

[0010] Using smaller particles tends to provide better granulation performance (including resolved dust problems), but causes some handling problems. The particles are generally pulverized gel particles. However, handling very finely pulverized gel particles can itself pose problems. On the one hand, there is a risk of polymer fines spraying out during the mixing step, on the other hand, the flow characteristics of the particles are not entirely satisfactory, and ultimately accurate metering of the particles into the fine particle material can be difficult.

Means for Solving the Problems

[0011] The applicant unexpectedly discovered that a binder composition for producing iron ore pellets containing at least two organic binders and at least one inorganic binder (these binders have specific properties) can maintain satisfactory granulation performance, minimize dust problems, facilitate handling, and enable the use of large polymer particles. Furthermore, the pellets can have a more consistent shape within the scope of the present invention than when using other polymer-based binders.

[0012] More specifically, the present invention relates to a binder composition for producing iron ore pellets, a) at least two organic binders LO in the form of solid particles, at least, - a water-soluble anionic polymer P1 having a mass average molecular weight of 500 to 200,000 daltons, and - an anionic or amphoteric water-soluble polymer P2 having a mass average molecular weight exceeding 500,000 daltons which is the organic binder LO and b) at least one inorganic binder LI in the form of solid particles and comprising, - the solid particles of the binder LO have a number median diameter exceeding 500 micrometers, - the particles of the binder LI have a number median diameter less than one-third of the number median diameter of the solid particles of the binder LO, relates to a binder composition for producing iron ore pellets.

[0013] Therefore, this binder composition contains a mixture of an anionic water-soluble polymer P1, an anionic or amphoteric water-soluble polymer P2, and an inorganic binder LI.

[0014] Another aspect of the present invention relates to iron ore pellets containing the binder composition of the present invention at 50 to 5,000 ppm.

Mode for Carrying Out the Invention

[0015] The term "polymer" means both homopolymers and copolymers of at least two different monomers.

[0016] As used herein, the term "water-soluble polymer" is understood to be a polymer that, when stirred at 25°C for 4 hours and dissolved at a concentration of 20 g / L in deionized water, results in an aqueous solution free of insoluble particles. -1

[0017] Ranges of values include the lower and upper limits. Thus, ranges of values such as "between 0.1 and 1.0" and "0.1 to 1" include the values 0.1 and 1.0.

[0018] According to the present invention, the weight average molecular weights of the water-soluble polymers P1 and P2 are determined by measuring the intrinsic viscosity. The intrinsic viscosity can be measured by methods known to those skilled in the art, in particular, by a graphical method consisting of plotting values of low viscosity (on the vertical axis) as a function of concentration (on the horizontal axis), and by extrapolating the curve to zero concentration to calculate the values of low viscosity for different concentrations. The intrinsic viscosity value is read on the vertical axis or using the least squares method. Thereafter, the weight average molecular weight is calculated using the Mark-Houwink equation: [η]=KM α (wherein [η] represents the intrinsic viscosity of the polymer determined by solution viscosity measurement, K represents an experimental constant, M represents the molecular weight of the polymer, α represents the Mark-Houwink coefficient, ​α and K depend on a specific polymer solvent system) and can be determined by. Tables known to those skilled in the art give the values of α and K for the polymer solvent system.

[0019] The water-soluble polymer P1 has a mass average molecular weight of 500 to 200,000 Daltons, more preferably 1,000 to 50,000 Daltons, and even more preferably 1,000 to 10,000 Daltons.

[0020] The water-soluble polymer P2 has a mass average molecular weight greater than 500,000 Daltons, more preferably greater than 1 million Daltons. The water-soluble polymer P2 usually has a mass average molecular weight of less than 40 million Daltons, preferably less than 30 million Daltons.

[0021] The water-soluble polymer P1 is anionic. Therefore, the water-soluble polymer P1 contains an anionic monomer and optionally a nonionic monomer.

[0022] Advantageously, the polymer P1 contains 50 to 100 mol%, more preferably 70 to 100 mol%, and even more preferably 90 to 100 mol% of the anionic monomer.

[0023] The nonionic monomer of the water-soluble polymer P1 is preferably selected from the group consisting of acrylamide, methacrylamide, N-alkylacrylamide, N-alkylmethacrylamide, N,N-dialkylacrylamide, N,N-dialkylmethacrylamide, alkoxylated esters of acrylic acid, alkoxylated esters of methacrylic acid, N-vinylpyridine, N-vinylpyrrolidone, hydroxyalkyl acrylate, hydroxyalkyl methacrylate, and mixtures thereof. Among these nonionic monomers, the alkyl group is advantageously C 1 ~C 5 and more advantageously C 1 ~C 3 The alkyl group is preferably a straight-chain alkyl group.

[0024] The anionic monomers of the water-soluble polymer P1 are preferably selected from the group consisting of monomers having a carboxylic acid functional group, including acrylic acid, methacrylic acid, itaconic acid, maleic acid, and their salts; monomers having a sulfonic acid functional group, including acrylamide-tert-butylsulfonic acid (ATBS), allylsulfonic acid, methallylsulfonic acid, and their salts; and monomers having a phosphonic acid functional group and their salts.

[0025] The salt may be an alkali metal or alkaline earth metal salt. The term "alkali" should be understood as an alkali metal, preferably lithium, sodium, or potassium. The term "alkaline earth" should be understood as an alkaline earth metal, preferably calcium or magnesium.

[0026] Preferably, the polymer P1 is a polymer of at least one anionic monomer containing at least one carboxylate functional group -C(=O)-O - X + (wherein X is an alkali metal) and at least one carboxylate functional group -C(=O)-O - X' + (wherein X' is an alkaline earth metal).

[0027] Therefore, this does not exclude the presence of anionic monomers in the polymer P1 containing carboxylic acid functional groups (not neutralized). In other words, it is possible for anionic monomers with carboxylic acid functional groups and anionic monomers with carboxylate functional groups to coexist.

[0028] Advantageously, when the anionic monomers of the polymer P1 are present in both their carboxylic acid form and their carboxylate salt form, the proportion in the carboxylate salt form is 10 to 100 mol%, more advantageously 20 to 100 mol%, based on the carboxylate salt and carboxylic acid forms.

[0029] Advantageously, 40 to 60 mol% of the carboxylate functional groups of polymer P1 are neutralized by an alkali salt, and 40 to 60 mol% of the carboxylate functional groups are neutralized by an alkaline earth salt.

[0030] Even more preferably, at least one of the anionic monomers of polymer P1 containing a carboxylate functional group is an acrylate.

[0031] Polymer P1 is advantageously a polymer of a mixture of at least one of an alkali metal salt (preferably sodium) and an alkaline earth metal salt (preferably calcium) of acrylic acid CH 2 =CH-C(=O)OH.

[0032] According to a preferred embodiment, the carboxylate functional groups of polymer P1 are neutralized with sodium and calcium.

[0033] Advantageously, polymer P1 contains at least sodium acrylate and calcium acrylate.

[0034] Polymer P1 may be linear or structured by at least one structuring agent, and may advantageously be selected from the group containing polyethylene unsaturated monomers such as vinyl, allyl, acrylic, and epoxy functional groups (having at least two unsaturated functional groups), for example, sodium allyl sulfonate, sodium methallyl sulfonate, sodium methallyl disulfonate, methylene bisacrylamide, diallylamine, triallylamine, triallylammonium chloride, tetraallylammonium chloride, or macroinitiators such as polyperoxide and polyazoic, and polyintroducers such as polymercaptan polymers, or hydroxyalkyl acrylate and epoxy vinyl.

[0035] Polymer P1 may also be constituted using controlled radical polymerization techniques (CRP, the initials of "controlled radical polymerization") or, more particularly, the RAFT type (the initials of "reversible addition-fragmentation chain transfer").

[0036] The solid polymer particles P1 are in powder form. These particulate forms are obtained by techniques known to those skilled in the art.

[0037] The powder form of the polymer P1 may be obtained by polymerization in an aqueous solution, followed by drum drying, spray drying, radiation drying such as microwave drying, or fluidized bed drying.

[0038] Preferably, the polymer P1 is in powder form resulting from polymerization in an aqueous solution followed by drum drying.

[0039] The polymerization to obtain the polymer P1 of the present invention is generally carried out by a radical route. This includes free radical polymerization using UV, azo, redox, or thermal initiators, and CRP, or more particularly, RAFT type polymerization techniques.

[0040] Some additives known to those skilled in the art (azo compounds, oxidation / reduction couples, transfer agents, terminators, etc.) may be advantageously added during the polymerization of the polymer P1. Some of them may contain sulfur such as sodium bisulfite, sodium metabisulfite, or sodium persulfate.

[0041] The initiation of the polymerization of the polymer P1 may be carried out in the presence of an oxidation / reduction couple. One preferred sulfur-containing oxidizing agent is sodium persulfate.

[0042] Preferably, the polymer P1 contains sulfur up to 2% by mass, more preferably up to 1% by mass, and the sulfur is derived from sodium bisulfite and / or sodium metabisulfite and / or sodium persulfate.

[0043] "A and / or B" means A or B, or A and B.

[0044] The water-soluble polymer P2 is anionic or amphoteric. Thus, the water-soluble polymer P2 contains anionic monomers, optionally cationic monomers, and optionally non-ionic monomers.

[0045] The nonionic monomers of the water-soluble polymer P2 are preferably selected from the group consisting of acrylamide, methacrylamide, N-alkylacrylamide, N-alkylmethacrylamide, N,N-dialkylacrylamide, N,N-dialkylmethacrylamide, alkoxylated esters of acrylic acid, alkoxylated esters of methacrylic acid, N-vinylpyridine, N-vinylpyrrolidone, hydroxyalkyl acrylate, hydroxyalkyl methacrylate, and mixtures thereof. Among these nonionic monomers, the alkyl group is preferably C 1 ~C 5 and more preferably C 1 ~C 3 . The alkyl group is preferably a linear alkyl group. The nonionic monomer is preferably acrylamide.

[0046] The anionic monomers of the water-soluble polymer P2 are monomers having a carboxylic acid functional group including acrylic acid, methacrylic acid, itaconic acid, maleic acid and their salts; monomers having a sulfonic acid functional group including acrylamide-tert-butylsulfonic acid (ATBS), allylsulfonic acid, methallylsulfonic acid, and their salts; and monomers having a phosphonic acid functional group and their salts, and are preferably selected from the group consisting of these. Preferred anionic monomers are acrylic acid and their salts.

[0047] The salt may be an alkali metal or alkaline earth metal salt. Advantageously, the alkali metal is sodium.

[0048] The cationic monomers of the water-soluble polymer P2 are preferably selected from the group consisting of quaternized or chlorinated dimethylaminoethyl acrylate (ADAME), quaternized or chlorinated dimethylaminoethyl methacrylate (MADAME), diallyldimethylammonium chloride (DADMAC), acrylamidopropyltrimethylammonium chloride (APTAC), and methacrylamidopropyltrimethylammonium chloride (MAPTAC).

[0049] Advantageously, the cationic monomer of polymer P2 has a halide as a counter ion, preferably chloride ion. A preferred cationic monomer is dimethylaminoethyl acrylate (ADAME) quaternized with methyl chloride.

[0050] Preferably, polymer P2 is a copolymer of acrylamide and sodium acrylate.

[0051] Polymer P2 may be linear or structured by at least one structuring agent, and can preferably be selected advantageously from the group comprising ethylenically unsaturated monomers (having at least two unsaturated functional groups) such as vinyl, allyl, acrylic, and epoxy functional groups, for example, sodium allyl sulfonate, sodium methallyl sulfonate, sodium methallyl disulfonate, methylene bisacrylamide, diallylamine, triallylamine, triallylammonium chloride, tetraallylammonium chloride, or macroinitiators such as polyperoxides, polyazoics and polyintroducing agents such as polymercaptan polymers or hydroxyalkyl acrylates and epoxy vinyls.

[0052] Polymer P2 may also be constituted using CRP polymerization techniques, or more particularly RAFT type.

[0053] Advantageously, polymer P2 is constituted in the form of a star having a central part (core) and polymer-based arms extending radially from said central part.

[0054] The water-soluble polymer P2 is advantageously a copolymer of at least one nonionic monomer (preferably acrylamide) and at least one anionic monomer (preferably acrylic acid and / or its salt).

[0055] The polymeric microgel preferably contains 0 to 100 mol%, preferably 0 to 80 mol%, more preferably 0 to 60 mol%, and even more preferably 0 to 50 mol% of cationic monomers. In particular, Polymer P2 preferably contains less than 5 to 100 mol% (excluding 100%) of sodium acrylate, more preferably 10 to 80 mol%, and even more preferably 20 to 60 mol%; and acrylamide in an amount exceeding 0 and not more than 95 mol% (excluding 0%), more preferably 20 to 90 mol%, and even more preferably 40 to 80 mol%.

[0056] The solid particles of Polymer P2 are in the form of powder or microbeads. These particulate forms can be obtained by techniques known to those skilled in the art.

[0057] The powder form of Polymer P2 may be obtained by gel polymerization, aqueous solution polymerization, followed by radiation drying such as drum drying, spray drying, or microwave drying, or fluidized bed drying.

[0058] The powder form of the water-soluble Polymer P2 may also be obtained by water-in-oil emulsion polymerization (inverse emulsion), followed by a distillation / concentration step of the resulting liquid and spray drying.

[0059] The P2 polymer microbeads are preferably obtained by inverse suspension polymerization.

[0060] Preferably, Polymer P2 is in the form of powder resulting from gel polymerization or microbeads resulting from inverse suspension polymerization.

[0061] The polymerization to obtain Polymer P2 of the present invention is carried out by a radical route. The radical route includes free radical polymerization using UV, azo, redox, or thermal initiators, and CRP, or more particularly, type polymerization techniques.

[0062] The binder composition of the present invention also contains an inorganic binder LI. This LI binder is preferably non-polymerizable. The LI binder is preferably selected from sodium carbonate, sodium bicarbonate, sodium phosphate, sodium silicate, urea, calcium oxide, bentonite, and mixtures thereof.

[0063] Preferably, the binder composition consists of P1 + P2 + LI, - 2 to 40% by mass of polymer P1, - 20 to 60% by mass of polymer P2, and - 30 to 70% by mass of binder LI and the total mass percentage of P1 + P2 + LI is equal to 100%.

[0064] More preferably, the binder composition - 5 to 30% by mass of polymer P1, - 25 to 55% by mass of polymer P2, and - 35 to 65% by mass of binder LI and the total mass percentage of P1 + P2 + LI is equal to 100%.

[0065] Even more preferably, the binder composition - 8 to 25% by mass of polymer P1, - 35 to 50% by mass of polymer P2, and - 40 to 60% by mass of binder LI and the total mass percentage of P1 + P2 + LI is equal to 100%.

[0066] According to the present invention, the binders LO (P1 and P2) and the binder LI are in the form of solid particles, and the median diameter (D 50 ) of the number of solid particles of the binder LO is greater than 500 micrometers, and the median diameter of the number of particles of the binder LI is less than one-third of the median diameter of the number of solid particles of the binder LO.

[0067] The median diameter of the number of particles (D 50) is defined as the maximum dimension (diameter in the case of spherical particles) such that half of the population (half of the particles) has a value less than this value.

[0068] In the case of spherical particles, the particle size refers to the average diameter measured using a laser diffraction particle analyzer according to the prior art of those skilled in the art. One example of an apparatus for measuring the particle size is the Mastersizer from Malvern Instruments.

[0069] Advantageously, the median diameter of the number of organic binders LO is from 500 to 5,000 micrometers, more preferably from 500 to 2,000 micrometers.

[0070] According to the present invention, the binder composition is generally formed by a simple mixing of its components (each in powder form).

[0071] Finally, the last aspect of the present invention relates to iron ore pellets containing a binder composition in an amount of 50 to 5,000 ppm by mass based on the mass of the iron ore pellets.

[0072] The pellets are typically prepared by adding the binder composition to the fine ore, stirring the fine ore in the presence of a small amount of water (preferably the moisture in the ore) to form a wet mixture, and then pelletizing (granulating) the mixture, for example, in a pellet drum or a disk pelletizer.

[0073] The following examples illustrate the present invention without limiting the scope of the present invention.

Examples

[0074] Synthesis of P1 Polymer As is known to those skilled in the art, the P1 polymer is obtained by a polymerization process of acrylic acid in an aqueous solution. The monomer is introduced by flowing it into a heated reactor in parallel with the introduction of the initiator and the transfer agent solution. The initiator solution consists of ammonium persulfate combined with sodium bisulfite as a reducing agent. The proportion of sulfur in all components involved in the process is strictly less than 2% by mass of the total formulation. The polymer P1 is neutralized with soda to obtain sodium counterions, or with soda and calcium oxide to obtain sodium and calcium counterions of different properties in a 50 / 50 mass ratio. This neutralization is carried out on the polymer before the end of the polymerization. At the end of the polymerization, the polymer solution is drum-dried to obtain the P1 polymer in powder form.

[0075] Four tests leading to the synthesis of four P1 polymers, namely P1-A (according to the present invention), P1-B (according to the present invention), P1-C (comparative), and P1-D (comparative), were thus carried out.

[0076] Synthesis of the P2 polymer As is known to those skilled in the art, the polymer P2 is obtained by gel polymerization of acrylamide and sodium acrylate. At the end of the polymerization, the polymer gel is granulated, dried, pulverized, and sieved to obtain the polymer P2 in powder form.

[0077] Four tests leading to the synthesis of four P2 polymers, namely P2-A (according to the present invention), P2-B (according to the present invention), P2-C (comparative), and P2-D (comparative), were thus carried out.

[0078] Manufacture of pellets In the following examples, green iron ore pellets containing various compounds were prepared in the amounts shown in Table 1. The green pellets were prepared by aggregating the iron ore concentrate in the presence of a binder composition. The binder amounts (in mass percent) shown in Table 1 are based on the total mass of the iron ore concentrate. The iron ore concentrate used in the examples of Table 1 is a concentrate of Brazilian hematite ore.

[0079] The inorganic binder LI used was sodium carbonate obtained from two different sources: LI-1 (according to the present invention) and LI-2 (comparative).

[0080] As explained in Table 2, various comparative binder compositions (CEX 1 to CEX 12) and (C1 to C5) according to the present invention were produced. All of those comparative binder compositions consist of the inorganic binder LI and two organic binders, which are the previously synthesized polymers P1 and P2. In each case, the binder composition is produced by blending using a mixture that enables homogenization of the three components.

[0081] The manufacturing process for green ore pellets is generally known to those skilled in the art. Different green ore pellets were manufactured and different binder compositions were tested.

[0082] First, the binder composition is mixed with the dry ore concentrate and homogenized with the required amount of water (water content of 8 - 9 mass%). The ore concentrate is mixed with the binder composition using a kitchen aid type mixer.

[0083] Next, the pellet precursor (or seed) is formed by putting a small amount of the previously obtained mixture of the ore concentrate and the binder composition into a rotating tire (about 40 cm in diameter), adding spray water, and starting pellet growth. Pellet seeds with a size of 2.5 - 4 mm are formed in this way.

[0084] Next, place 55 grams of pellet seeds on the rotating tire and add a portion of the remaining mixture (mineral concentrate + binder composition) during the 5 - 6 minute growth period to obtain finished green pellets in the size range of 9.5 - 12.5 mm. Add spray water if necessary.

[0085] The water content, number of drops, and wet and dry compressive strengths of the obtained green pellets were measured for each case, and the results were listed in Table 3.

[0086] Number of wet drops (NWD) The number of wet drops was determined by repeatedly dropping wet green pellets sized 11.2 - 12.5 mm from a height of 46 cm onto a horizontally placed steel plate until it fell. Visible cracks form on the surface of the pellet. The number of times required for the pellet to reach its fracture / cracking point was determined. This measurement was determined for 20 pellets. The average of these 20 measurements is called the number of wet drops (NWD).

[0087] Wet compressive strength (WCS) Twenty wet green pellets sized 11.2 - 12.5 mm were stored in an airtight container. The pellets were removed one by one and placed in a standard ANDILOG brand measuring instrument. The maximum applied force at which the pellet cracked was determined. The average of these 20 measurements is called the "wet compressive strength" (WCS).

[0088] Dry compressive strength (DCS) Twenty green pellets sized 11.2 - 12.5 mm were dried in an oven at 105°C for at least 2 hours. After drying, the dried pellets were placed one by one in a standard ANDILOG brand measuring instrument. The maximum applied force at which the pellet cracked was determined. The average of these 20 measurements is called the "dry compressive strength" (DCS).

[0089]

Table 1

[0090]

Table 2

[0091]

Table 3

[0092] Table 3 (Table 3) shows that the green pellets of Examples C1 to C5 have a smoother surface when using the binder composition according to the present invention than the green pellets of Comparative Tests CEX 1 to CEX 12.

[0093] Improving the surface state of the pellets is very important for the operator because granular and / or non-smooth surfaces cause an increase in abrasion and tumbling index, leading to a decrease in the market size of the pellets and an increase in the dust content in the furnace and during handling.

[0094] The dry compressive strength for testing the binder composition according to C1 to C5 of the present invention is improved compared to the tests of Comparative Binder Compositions CEX 1 to CEX 12. This parameter is very important for the operator because it enables determining the behavior of the pellets in the furnace, and a higher dry compressive strength avoids pellet breakage in the layer and produces pellets with greater hardness.

[0095] Relatively, Composition C3 makes it possible to improve NWD and DCS compared to Binder Composition C5. Therefore, the selection of the counter ion of Polymer P1 affects the physical properties of the pellets.

[0096] Regarding the tests of Comparative Binder Compositions CEX 2, CEX 3, and CEX 4, it is observed that the selection of the molecular weights of Polymers P1 and P2 is important for having a smooth pellet surface and good physical properties.

[0097] The Comparative Binder Composition CEX 5 test indicates that the ratio of the size of the organic binder to the size of the inorganic binder is essential. When this ratio is outside the claimed range, the surface of the resulting pellet is too fragile and thus brittle.

[0098] The Comparative Binder Composition CEX 6 test indicates that the amount of each binder in the green pellet is also an important criterion. When the amounts of these binders are outside the claimed range, the pellet is very viscous (resulting in reduced productivity) and not strong enough for the operator.

[0099] The Comparative Binder Composition CEX 7, CEX 8, and CEX 9 tests indicate that the presence of at least two organic binders, namely Polymer P1 and Polymer P2, is essential. Without either of these two polymers, the surface of the pellet is not smooth and does not have satisfactory physical properties.

[0100] The Comparative Binder Composition CEX 10 test indicates the extreme importance of the presence of the organic binder LO. Without the organic binder (only the presence of the inorganic binder LI), the surface of the pellet is not smooth and does not have satisfactory mechanical properties.

[0101] Finally, the Comparative Binder Compositions CEX 11 and CEX 12 show that when Polymer P1 or Polymer P2 has a median diameter D 50 less than 500 μm, the surface of the pellet is not smooth and does not have satisfactory mechanical properties.

Claims

1. A binder composition for producing iron ore pellets, comprising: a) At least two organic binders LO in the form of solid particles, at least including: - A water-soluble anionic polymer P1 having a mass average molecular weight of 500 to 200,000 Daltons, and - A water-soluble anionic or amphoteric polymer P2 having a mass average molecular weight exceeding 500,000 Daltons as the organic binder LO, b) At least one inorganic binder LI in the form of solid particles and the solid particles of the binder LO have a number median diameter exceeding 500 micrometers, the particles of the binder LI have a number median diameter less than one-third of the number median diameter of the solid particles of the binder LO, A binder composition for producing iron ore pellets.

2. The polymer P1 is a polymer of at least one anionic monomer containing (1) at least one carboxylate functional group -C(=O)-O - X + (wherein X is a carboxylate functional group which is an alkali metal), and (2) at least one carboxylate functional group -C(=O)-O - X' + (wherein X' is an alkaline earth metal), the binder composition according to claim 1.

3. The polymer P1 is at least a polymer of a mixture of alkali metal and alkaline earth metal salts of acrylic acid CH 2 =CH-C(=O)OH, characterized in that it is the binder composition according to claim 2.

4. The binder composition according to claim 2 or 3, characterized in that the alkali metal is sodium and the alkaline earth metal is calcium.

5. The binder composition according to any one of claims 1 to 4, characterized in that the polymer P1 contains a maximum of 2% by mass of sulfur, and the sulfur is derived from sodium bisulfite and / or sodium metabisulfite and / or sodium persulfate.

6. The binder composition according to any one of claims 1 to 5, characterized in that the polymer P2 is a copolymer of acrylamide and sodium acrylate.

7. The binder composition according to any one of claims 1 to 6, characterized in that the polymer P2 is a copolymer containing 5 to less than 100 mol% of sodium acrylate and more than 0 to 95 mol% of acrylamide.

8. The binder composition according to any one of claims 1 to 7, characterized in that the inorganic binder LI is selected from sodium carbonate, sodium bicarbonate, sodium phosphate, sodium silicate, calcium oxide, bentonite, and mixtures thereof.

9. The binder composition consists of P1 + P2 + LI, - 2 to 40% by mass of the polymer P1, - 20 to 60% by mass of the polymer P2, - 30 to 70% by mass of the binder LI and the total of the mass percentages of P1 + P2 + LI is equal to 100% The binder composition according to any one of claims 1 to 8.

10. An iron ore pellet containing 50 to 5,000 mass ppm of the binder composition according to any one of claims 1 to 9 based on the mass of the iron ore pellet.

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