Composite binder with high iron and low silicon for iron ore pellets and its preparation method

Abstract

The present invention belongs to the technical field of binders, and particularly relates to a high-iron and low-silicon composite binder for iron ore pellets and a preparation method thereof. On the basis of the existing technology, the present invention uses citric acid-crosslinked starch and cyclodextrin to obtain modified starch. After preparing magnesium iron hydrotalcite, it is calcined and oxidized and then intercalated with p-hydroxycinnamic acid to obtain modified magnesium iron hydrotalcite. The cavity structure of cyclodextrin and the carboxyl functional group of citric acid in the modified starch can undergo a complexation reaction with metal ions on the surface of iron ore powder, enhancing the bonding strength of the pellets; the intercalation of p-hydroxycinnamic acid into magnesium iron hydrotalcite improves the thermal stability and dispersion performance of magnesium iron hydrotalcite. The high-iron and low-silicon composite binder for iron ore pellets obtained by compounding modified starch, modified magnesium iron hydrotalcite, bentonite, sodium carboxymethylcellulose and a dispersant has excellent bonding performance, reduces the addition amount of bentonite and increases the iron content of iron ore pellets, and improves the green pellet strength and thermal stability of iron ore pellets.

Description

Technical Field

[0001] The present invention belongs to the technical field of binders, and particularly relates to a high-iron and low-silicon composite binder for iron ore pellets and a preparation method thereof. Background Art

[0002] The ore powder after beneficiation cannot be directly charged into the furnace for smelting. The particle size of the ore powder is too fine. Directly putting it into the blast furnace will reduce the gas permeability of the burden column. Therefore, it is necessary to knead the iron ore powder into iron ore pellets to make more full use of iron ore resources. After mixing the ore powder and the binder and adding them into a pelletizer, small particle ore powder is bonded into large particles in a humid environment. During the rolling process, the large particles continuously bond the ore powder to form green pellets. The green pellets are maintained together by surface tension and capillary force. The hard pellets formed after calcination and drying are iron ore pellets. At present, bentonite is the most commonly used binder in the production of iron ore pellets. However, for every 1% addition of bentonite, the grade of iron ore pellets will be reduced by 0.6 - 0.7%. And since most of the iron ores in China have a low grade, more bentonite needs to be added to make the iron ore pellets reach the required hardness and strength for production, resulting in a significant increase in the steel smelting cost. Therefore, it is necessary to develop a new binder to reduce the amount of binder used while ensuring that the metallurgical properties of the pellet ore will not be weakened.

[0003] The Chinese invention patent with the publication number CN114854984B discloses a preparation method and an application method of a composite binder for producing oxidized pellets, belonging to the technical field of binders. Sodium lignosulfonate and sodium carbonate are evenly mixed to obtain a mixture; the mixture and water are mixed and stirred to dissolve to obtain a mixture solution A; sodium bicarbonate is placed in distilled water to prepare a sodium bicarbonate solution with a concentration of 5-15 g / L; then sodium pyrophosphate is added to the sodium bicarbonate solution and stirred until completely dissolved to obtain a mixed solution B; the mixed solution B is added to the mixture solution A, stirred, and then evaporated to dryness to obtain a composite binder for producing oxidized pellets. The composite binder is used for pelletizing in limonite powder and can effectively improve the pellet strength at each stage. The Chinese invention patent with the publication number CN110629020B discloses an iron-based composite binder for pellet ore and its preparation and use methods. The iron-based composite binder for pellet ore is composed of the following components according to the dry basis weight percentage: 95% - 97% of converter OG sludge, 1% - 2.2% of hydroxypropyl methylcellulose, and 1% - 2.9% of instant sodium carboxymethylcellulose. The invention uses converter OG sludge without extrusion dehydration as an iron-containing raw material, adds hydroxypropyl methylcellulose solution and instant sodium carboxymethylcellulose solution without dehydration and drying, and obtains an iron-based composite binder for pellet ore after deep fusion by microwave radiation heating and heap leaching reaction, which not only realizes the efficient recycling of converter OG sludge, simplifies and shortens the production process of the iron-based composite binder, but also is beneficial to improving the quality of pellets and reducing the production cost of iron and steel integrated enterprises. However, the existing technology has the technical problem that the starch structure in the starch composite binder is not further compound-modified to improve the green pellet strength and pellet grade of iron ore pellets. Summary of the Invention

[0004] The purpose of the present invention is to provide a rich-iron and low-silicon composite binder for iron ore pellets and its preparation method, which is used to solve the technical problem in the existing technology that the starch structure in the starch composite binder is not further compound-modified to improve the green pellet strength and pellet grade of iron ore pellets.

[0005] In order to achieve the above purpose, the present invention adopts the following technical solutions:

[0006] The rich-iron and low-silicon composite binder for iron ore pellets is prepared from the following components by mass:

[0007] 7 - 13 parts of bentonite, 5 - 6 parts of sodium carboxymethylcellulose, 10 - 15 parts of modified starch, 5 - 6 parts of modified magnesium iron hydrotalcite, and 1 - 4 parts of dispersant.

[0008] The montmorillonite content of the bentonite is 70 - 80 wt%, the swelling capacity is 9 - 10 mL / g, the water absorption rate in 2 h is 300 - 350%, the blue absorption amount is 30 - 35 g / 100 g, and the colloid index is 20 - 25% / 3 g.

[0009] The type of the sodium carboxymethyl cellulose is one or more combinations of CMC-M6, CMC-IH800, and CMC-IH1500.

[0010] The dispersant is one or more combinations of sodium citrate, sodium tripolyphosphate, and sodium silicate.

[0011] Preferably, the preparation method of the modified starch includes the following steps:

[0012] S11: Add starch into an aqueous sodium chloride solution with a concentration of 2.5 - 3.5 wt% to prepare a starch solution with a concentration of 20 - 30 wt%. Let it stand and swell at 30 - 40 °C for 1 - 2 h, and then perform microwave activation treatment for 60 - 120 s to obtain a pretreated starch solution.

[0013] S12: By mass, add citric acid into deionized water to prepare a citric acid solution with a concentration of 30 - 40 wt%. Add a sodium hydroxide solution to adjust the pH to 3 - 3.5. Mix 20 - 30 parts of the pretreated starch solution with 40 - 50 parts of the citric acid solution evenly. Add 20 - 40 parts of cyclodextrin and 1 - 3 parts of sodium dihydrogen phosphate. Stir at 40 - 50 °C until the cyclodextrin is completely dissolved, then let it stand at room temperature for 12 - 18 h, and react at 120 - 140 °C for 4 - 6 h. After the reaction, filter to collect the precipitate, wash it with distilled water, dry it at 40 - 50 °C, and grind it through a 100 - 160 - mesh sieve to obtain the modified starch.

[0014] Preferably, the microwave power in S11 is 300 - 500 W.

[0015] Preferably, the cyclodextrin in S12 is either α - cyclodextrin or β - cyclodextrin.

[0016] Preferably, the preparation method of the modified magnesium - iron hydrotalcite includes the following steps:

[0017] S21: By mass, add 14 - 18 parts of magnesium nitrate and 7 - 9 parts of iron nitrate into 100 - 200 parts of deionized water. While stirring, drop a mixed solution of 150 - 200 parts of sodium hydroxide and sodium carbonate into the system, and keep the pH between 10.8 - 11.2 during the dropping process. After the dropping is completed, react at 80 - 90 °C for 8 - 10 h. Centrifuge and filter to collect the precipitate, wash it with deionized water, and then dry it under vacuum at 40 - 60 °C and grind it to obtain magnesium - iron hydrotalcite.

[0018] S22. By mass parts, calcine magnesium iron hydrotalcite at 600 - 650 °C for 10 - 12 h to obtain layered oxide. Add 0.3 - 0.5 parts of p-hydroxycinnamic acid to 50 - 100 parts of deionized water and mix evenly, then add 10 - 15 parts of the layered oxide, react at 70 - 80 °C for 4 - 6 h, filter to collect the solid, wash with deionized water, and then dry in vacuum at 40 - 60 °C, and grind to obtain modified magnesium iron hydrotalcite.

[0019] Preferably, the mixed solution of sodium hydroxide and sodium carbonate in S21 is prepared by adding 16 - 20 parts of sodium hydroxide and 5.3 - 6.6 parts of sodium carbonate to 130 - 180 parts of deionized water.

[0020] The preparation method of the iron ore pellet with iron-rich and low-silica composite binder includes the following steps:

[0021] S1. Pretreat bentonite: Grind bentonite to remove large impurities, then add it to deionized water to prepare a 20 - 30 wt% bentonite suspension. Let the bentonite suspension stand for 10 - 12 h, pass through a 100 - 160 mesh sieve, add it to a hydrocyclone for step-by-step purification, dry at 80 - 90 °C, and grind through a 100 - 160 mesh sieve to obtain pretreated bentonite.

[0022] S2. By mass parts, mix 7 - 13 parts of bentonite, 5 - 6 parts of sodium carboxymethylcellulose, 10 - 15 parts of modified starch, 5 - 6 parts of modified magnesium iron hydrotalcite and 1 - 4 parts of dispersant to obtain the iron ore pellet with iron-rich and low-silica composite binder.

[0023] Preferably, in S1, the hydrocyclone uses cyclones with inner diameters of 100 mm, 75 mm, 50 mm, and 25 mm for step-by-step purification.

[0024] The present invention also provides the application of the iron ore pellet with iron-rich and low-silica composite binder in the production and preparation of iron ore pellets. The preparation method of iron ore pellets includes the following steps:

[0025] S31. Pretreatment: Respectively dry iron concentrate, the iron ore pellet with iron-rich and low-silica composite binder, dephosphorizer and steel slag through a dryer, and then put them into a silo for standby.

[0026] S32. Grinding and compounding: After proportioning iron concentrate, the iron ore pellet with iron-rich and low-silica composite binder, dephosphorizer and steel slag, add them to a mill, grind and screen until more than 90 wt% of the powder passes through a 100 - 120 mesh sieve to obtain a mixed material.

[0027] S33. Pelletizing: By mass, put 2000 - 3000 parts of the mixed material into a disc pelletizer, drip industrial water to form mother balls. Stop dripping water after the total volume of the mother balls is greater than the total volume of the remaining mixed material. Divide 1000 - 2000 parts of the mixed material into three portions, each portion with an interval of 3 - 5 minutes, and slowly add them into the disc pelletizer. Spray water to make the mother balls grow within 10 - 17 minutes to obtain green pellets. Stop feeding after the green pellets grow to an average diameter of 10 - 12 mm, continue to roll and compact for 2 - 5 minutes, and then take out and screen to collect green pellets with an average diameter of 10 - 15 mm;

[0028] S34. Roasting: Put the green pellets into a roasting furnace, heat up to 200 - 300 °C for drying for 30 - 40 minutes, then heat up to 600 - 700 °C for preheating for 30 - 40 minutes, and finally heat up to 1250 - 1300 °C for roasting for 20 - 30 minutes. After cooling with the furnace, iron ore pellets are obtained.

[0029] Preferably, the chemical compositions of the iron concentrate and steel slag in S31 are shown in Table 1:

[0030] Table 1 Chemical Compositions of Iron Concentrate and Steel Slag

[0031] Component TFe FeO <![CDATA[SiO2]]> P S <![CDATA[Al2O3]]> MgO CaO Others Iron Concentrate 63.43 26.69 3.87 0.019 0.92 1.55 0.86 1.23 1.431 Steel Slag 80.94 4.88 3.61 0.005 0.35 0.21 1.97 6.99 1.048

[0032] Preferably, the dephosphorizer in S31 is prepared by mixing calcium chloride and coke powder in a mass ratio of 1:5 - 7.

[0033] Preferably, the mass ratio of the iron concentrate, iron ore pellets, the iron-rich and low-silicon composite binder, the dephosphorizer and the steel slag in S32 is 100:0.9 - 1.1:2 - 5:20 - 30.

[0034] Preferably, the inclination angle of the disc pelletizer in S33 is 30 - 50°, and the rotation speed is 30 - 60 r / min.

[0035] Preferably, the total amount of industrial water used in S33 is 9 - 13% of the total mass of the mixed material.

[0036] In summary, due to the adoption of the above technical solutions, the beneficial effects of the present invention are:

[0037] 1. Based on the prior art, the present invention uses citric acid-crosslinked starch and cyclodextrin to obtain modified starch. After preparing magnesium-iron hydrotalcite, it is calcined and oxidized, and then p-hydroxycinnamic acid is added for intercalation to obtain modified magnesium-iron hydrotalcite. The cavity structure of cyclodextrin and the carboxyl functional group of citric acid in the modified starch can undergo complexation reactions with metal ions on the surface of iron ore powder, forming chemical bonding, which enhances the bonding strength of the pellets; p-hydroxycinnamic acid intercalated magnesium-iron hydrotalcite improves the thermal stability and dispersion performance of magnesium-iron hydrotalcite, and can partially replace bentonite when used in composite binders. The iron ore pellets obtained by compounding modified starch, modified magnesium-iron hydrotalcite, bentonite, sodium carboxymethylcellulose and dispersant with a rich-iron and low-silicon composite binder have excellent bonding performance, reduce the addition amount of bentonite and increase the iron content of the iron ore pellets, and improve the green strength and thermal stability of the iron ore pellets.

[0038] 2. The present invention activates starch by microwave treatment, which improves the degree of depolymerization and hydrophilic performance of the functional groups of starch. Then, citric acid-crosslinked starch and cyclodextrin are used to introduce the cavity structure of cyclodextrin and the carboxyl functional group of citric acid, which can undergo complexation reactions with metal ions on the surface of iron ore powder particles, forming chemical bonding, thereby enhancing the bonding strength of the pellets. The raw materials of the modified starch have a wide source and relatively low cost, and can improve the green strength of iron ore pellets when used to prepare composite binders.

[0039] 3. After preparing magnesium-iron hydrotalcite by reacting ferric nitrate and magnesium nitrate under alkaline conditions, the present invention calcines and oxidizes it, and then adds p-hydroxycinnamic acid for intercalation to obtain modified magnesium-iron hydrotalcite, which improves the thermal stability and dispersion performance of the modified magnesium-iron hydrotalcite in iron ore powder, enables the modified magnesium-iron hydrotalcite to withstand the sintering process of iron ore pellets at high temperatures, and can improve the green strength and thermal stability of iron ore pellets when used to prepare composite binders. Specific Embodiments

[0040] The technical solutions in the embodiments of the present invention are clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0041] Example 1. The rich-iron and low-silicon composite binder for iron ore pellets in this example is prepared from the following components by mass:

[0042] 9 g of bentonite, 5.5 g of sodium carboxymethylcellulose, 13 g of modified starch, 5.5 g of modified magnesium-iron hydrotalcite and 3 g of dispersant.

[0043] The bentonite has a montmorillonite content of 77.9 wt%, a swelling capacity of 10 mL / g, a water absorption rate of 335% in 2 h, a blue absorption amount of 33 g / 100 g, and a colloid index of 24% / 3 g; the sodium carboxymethyl cellulose has a model of CMC-IH800; the dispersant is sodium tripolyphosphate.

[0044] The preparation method of the modified starch in this example includes the following steps:

[0045] S11. By mass, add 7.5 g of starch to 22.5 g of 3 wt% sodium chloride aqueous solution to prepare a 25 wt% starch solution. Let it stand and swell at 35 °C for 1 h, and activate it with a microwave power of 300 W for 90 s to obtain a pretreated starch solution;

[0046] S12. By mass, add 13.5 g of citric acid to 31.5 g of deionized water to prepare a 30 wt% citric acid solution. Add sodium hydroxide solution to adjust the pH to 3.5. Mix 30 g of the pretreated starch solution and 45 g of the citric acid solution evenly, add 30 g of β-cyclodextrin and 2 g of sodium dihydrogen phosphate. Stir at 40 °C until the cyclodextrin is completely dissolved, then let it stand at room temperature for 12 h, react at 120 °C for 4 h. After the reaction is completed, filter and collect the precipitate, wash it with distilled water, dry it at 40 °C, grind it, and pass through a 100-mesh sieve to obtain the modified starch.

[0047] The preparation method of the modified magnesium-iron hydrotalcite in this example includes the following steps:

[0048] S21. By mass, add 15 g of magnesium nitrate and 8 g of iron nitrate to 200 g of deionized water. Add 20 g of sodium hydroxide and 6.6 g of sodium carbonate to 173.4 g of deionized water to prepare a mixed solution of sodium hydroxide and sodium carbonate. Drop 200 g of the mixed solution of sodium hydroxide and sodium carbonate into the system under stirring, and keep the pH between 11 during the dropping process. After the dropping is completed, react at 80 °C for 10 h, centrifuge and filter to collect the precipitate, wash it with deionized water, and then dry it in vacuum at 50 °C and grind it to obtain magnesium-iron hydrotalcite;

[0049] S22. By mass, calcine the magnesium-iron hydrotalcite at 650 °C for 12 h to obtain layered oxides. Add 0.5 g of p-hydroxycinnamic acid to 100 g of deionized water, mix evenly, then add 15 g of the layered oxides, react at 80 °C for 4 h, filter and collect the solid, wash it with deionized water, and then dry it in vacuum at 60 °C and grind it to obtain the modified magnesium-iron hydrotalcite.

[0050] The method for preparing iron ore pellets with a rich-iron and low-silica composite binder for iron ore pellets in this example includes the following steps:

[0051] S1. Pretreat bentonite: Grind the bentonite to remove large impurities, then add it to deionized water to prepare a 20 - 30 wt% bentonite suspension. Let the bentonite suspension stand for 12 h, pass it through a 100 - mesh sieve, add it to a hydrocyclone, and use hydrocyclones with inner diameters of 100 mm, 75 mm, 50 mm, and 25 mm for step - by - step purification. Dry it at 90 °C and grind it through a 100 - mesh sieve to obtain pretreated bentonite;

[0052] S2. By mass, mix 9 g of bentonite, 5.5 g of sodium carboxymethyl cellulose, 13 g of modified starch, 5.5 parts of modified magnesium - iron hydrotalcite, and 3 g of dispersant to prepare a rich - iron and low - silicon composite binder for iron ore pellets.

[0053] The application of the rich - iron and low - silicon composite binder for iron ore pellets in this example is used for the production and preparation of iron ore pellets. The preparation method of iron ore pellets includes the following steps:

[0054] S31. Pretreatment: Mix calcium chloride and coke powder in a mass ratio of 1:5 to prepare a dephosphorizer. After drying the iron concentrate, the rich - iron and low - silicon composite binder for iron ore pellets, the dephosphorizer, and steel slag respectively through a dryer, put them into a storage bin for standby;

[0055] S32. Grinding and compounding: Put 5 kg of iron concentrate, 45 g of the rich - iron and low - silicon composite binder for iron ore pellets, 100 g of the dephosphorizer, and 1 kg of steel slag into a mill, grind and screen until more than 90 wt% of the powder passes through a 100 - mesh sieve to obtain a mixture;

[0056] S33. Pelletizing: By mass, put 3 kg of the mixture into a disk pelletizer with an inclination angle of 40° and a rotation speed of 50 r / min, drip industrial water to form mother balls. Stop dripping water after the total volume of the mother balls is greater than the total volume of the remaining mixture. Add 2 kg of the mixture to the disk pelletizer in three times, with an interval of 4 min each time, and spray water to make the mother balls grow within 15 min to obtain green pellets. Stop feeding after the green pellets grow to an average diameter of 10 mm. The total consumption of industrial water is 11% of the total mass of the mixture. Continue to roll and compact for 3 min, take out and screen to collect green pellets with an average diameter of 13 mm;

[0057] S34. Roasting: Put the green pellets into a roasting furnace, heat up to 200 °C for drying for 30 min, then heat up to 600 °C for preheating for 30 min, and finally heat up to 1250 °C for roasting for 30 min. After cooling with the furnace, obtain iron ore pellets.

[0058] Example 2. The rich - iron and low - silicon composite binder for iron ore pellets in this example is prepared from the following components by mass:

[0059] 7 g of bentonite, 5 g of sodium carboxymethyl cellulose, 10 g of modified starch, 5 g of modified magnesium - iron hydrotalcite, and 1 g of dispersant.

[0060] The bentonite has a montmorillonite content of 71 wt%, a swelling capacity of 9.9 mL / g, a water absorption rate of 312% in 2 h, a blue absorption amount of 31.3 g / 100 g, and a colloid index of 23% / 3 g; the sodium carboxymethyl cellulose has a model of CMC-M6; the dispersant is sodium silicate.

[0061] The preparation method of the iron ore pellet with a rich iron and low silicon composite binder in this example includes the following steps:

[0062] S1. Pretreat the bentonite: Grind the bentonite to remove large impurities, then add it to deionized water to prepare a 20 wt% bentonite suspension. Let the bentonite suspension stand for 10 h, pass through a 120-mesh sieve, add it to a hydrocyclone, and use hydrocyclones with inner diameters of 100 mm, 75 mm, 50 mm, and 25 mm for step-by-step purification. Dry it at 85 °C and grind it through a 120-mesh sieve to obtain the pretreated bentonite.

[0063] S2. Mix 7 g of bentonite, 5 g of sodium carboxymethyl cellulose, 10 g of modified starch, 5 g of modified magnesium iron hydrotalcite, and 1 g of dispersant by mass to obtain the rich iron and low silicon composite binder for iron ore pellets.

[0064] The method for preparing iron ore pellets with the rich iron and low silicon composite binder in this example includes the following steps:

[0065] S31. Pretreatment: Mix calcium chloride and coke powder according to a mass ratio of 1:6 to obtain a dephosphorizer. After drying the iron concentrate, the rich iron and low silicon composite binder for iron ore pellets, the dephosphorizer, and the steel slag through a dryer respectively, put them into a storage bin for standby.

[0066] S32. Grinding and compounding: Add 3 kg of iron concentrate, 28 g of the rich iron and low silicon composite binder for iron ore pellets, 60 g of the dephosphorizer, and 0.9 kg of steel slag into a mill, grind and screen until more than 90 wt% of the powder passes through a 120-mesh sieve to obtain a mixture.

[0067] S33. Pelletizing: Put 2 kg of the mixture into a disk pelletizer with an inclination angle of 30° and a rotation speed of 30 r / min, drip industrial water to form mother balls. Stop dripping water after the total volume of the mother balls is greater than the total volume of the remaining mixture. Add 1 kg of the mixture into the disk pelletizer in three times at intervals of 3 min, and spray water to make the mother balls grow within 10 min to obtain green pellets. Stop feeding after the green pellets grow to an average particle size of 10 mm. The total amount of industrial water used is 9% of the total mass of the mixture. Continue to roll and compact for 2 min, take out and screen to collect green pellets with an average particle size of 11 mm.

[0068] S34. Roasting: Put the green pellets into a roasting furnace, heat up to 250°C for drying for 35 min, then heat up to 650°C for preheating for 30 min, and finally heat up to 1260°C for roasting for 25 min. After cooling with the furnace, iron ore pellets are obtained.

[0069] The difference between the modified starch in this example and that in Example 1 is that cyclodextrin is replaced by α-cyclodextrin.

[0070] The preparation method of the modified magnesium-iron hydrotalcite in this example is the same as that of the modified magnesium-iron hydrotalcite in Example 1.

[0071] Example 3. The iron ore pellets in this example use a composite binder rich in iron and low in silicon, which is prepared from the following components by mass:

[0072] 13 g of bentonite, 6 g of sodium carboxymethylcellulose, 15 g of modified starch, 6 g of modified magnesium-iron hydrotalcite, and 4 g of dispersant.

[0073] The montmorillonite content of the bentonite is 79.6 wt%, the swelling capacity is 9.8 mL / g, the water absorption rate in 2 h is 340%, the blue absorption amount is 35 g / 100 g, and the colloid index is 25% / 3 g; the model of the sodium carboxymethylcellulose is CMC-IH1500; the dispersant is sodium citrate.

[0074] The preparation method of the composite binder rich in iron and low in silicon for the iron ore pellets in this example includes the following steps:

[0075] S1. Pretreatment of bentonite: Grind the bentonite to remove large impurities, then add it to deionized water to prepare a 30 wt% bentonite suspension. Let the bentonite suspension stand for 12 h, pass through a 160-mesh sieve, add it to a hydrocyclone, and use hydrocyclones with inner diameters of 100 mm, 75 mm, 50 mm, and 25 mm for step-by-step purification. Dry it at 90°C and grind it through a 160-mesh sieve to obtain pretreated bentonite.

[0076] S2. Mix 13 g of bentonite, 6 g of sodium carboxymethylcellulose, 15 g of modified starch, 6 g of modified magnesium-iron hydrotalcite, and 4 g of dispersant by mass to obtain a composite binder rich in iron and low in silicon for iron ore pellets.

[0077] The method for preparing iron ore pellets using the composite binder rich in iron and low in silicon for the iron ore pellets in this example includes the following steps:

[0078] S31. Pretreatment: Mix calcium chloride and coke powder according to a mass ratio of 1:7 to obtain a dephosphorizer. After drying the iron ore concentrate, the composite binder rich in iron and low in silicon for iron ore pellets, the dephosphorizer, and the steel slag through a dryer respectively, put them into a storage bin for standby.

[0079] S32. Grinding and compounding: Add 4 kg of iron concentrate, 44 g of iron ore pellets, an iron-rich and low-silica composite binder, 150 g of dephosphorizer, and 1.2 kg of steel slag into a grinding mill, grind and screen until more than 90 wt% of the powder passes through a 120-mesh sieve to obtain a mixture;

[0080] S33. Pelletizing: Put 2.5 kg of the mixture into a disk pelletizer with an inclination angle of 50° and a rotation speed of 40 r / min, drip industrial water to form mother pellets. Stop dripping water after the total volume of the mother pellets is greater than the total volume of the remaining mixture. Add 1.5 kg of the mixture into the disk pelletizer in three times, with an interval of 5 min each time, and spray water to make the mother pellets grow to obtain green pellets within 17 min. Stop feeding after the green pellets grow to an average particle size of 12 mm. The total consumption of industrial water is 13% of the total mass of the mixture. Continue to roll and compact for 5 min, take out and screen to collect green pellets with an average particle size of 15 mm;

[0081] S34. Roasting: Put the green pellets into a roasting furnace, heat up to 300 °C and dry for 40 min, then heat up to 700 °C and preheat for 40 min, and finally heat up to 1300 °C and roast for 20 min. After cooling with the furnace, obtain iron ore pellets.

[0082] The difference between the modified magnesium-iron hydrotalcite in this example and that in Example 1 is that the modified magnesium-iron hydrotalcite is prepared by modifying 10 g of layered oxide with 0.3 g of p-hydroxycinnamic acid.

[0083] The preparation method of the modified starch in this example is the same as that of the modified starch in Example 1.

[0084] Comparative Example 1. The difference between this comparative example and Example 1 is that the modified starch is not added to the composition of the binder.

[0085] Comparative Example 2. The difference between this comparative example and Example 1 is that the modified starch is replaced with corn starch.

[0086] Comparative Example 3. The difference between this comparative example and Example 1 is that no dephosphorizer is added in the preparation of iron ore pellets.

[0087] Performance test

[0088] According to YB / T4848-2020 "Physical Inspection Method for Roasted Green Pellets", drop the green pellets prepared in each example and comparative example from a height of 0.5 m repeatedly until they are broken. Take the average value of the number of times when 20 green pellets do not break as the drop strength of the green pellets.

[0089] According to YB / T4848-2020 "Physical Inspection Method for Roasted Green Pellets", use a compressive strength tester to test the compressive strength of the green pellets prepared in each example and comparative example, and take the average value of the maximum force of 20 green pellets as the compressive strength.

[0090] According to GB / T 14201-93 "Determination of Compressive Strength of Iron Ore Pellets", the compressive strength of the iron ore pellets prepared in each example and comparative example was tested using a compressive strength tester. The average value of the maximum force of 20 iron ore pellets was taken as the compressive strength.

[0091] The test results are shown in Table 2:

[0092] Table 2 Test Results

[0093] Serial Number Drop Strength of Green Pellets (times) Compressive Strength of Green Pellets (N) Compressive Strength of Iron Ore Pellets (N) Example 1 3.6 21.5 1845 Example 2 3.4 21.3 1836 Example 3 3.4 21.6 1841 Comparative Example 1 3.2 20.1 1833 Comparative Example 2 3.1 21.3 1632 Comparative Example 3 3.1 20.4 1624

[0094] From the data in Table 1, it can be seen that the drop strength of the green pellets prepared in Examples 1 to 3 was 3.4 to 3.6 times, and the compressive strength was 21.3 to 21.6 N. In Comparative Example 1, the component of the green pellet binder did not add modified starch, resulting in a drop strength of the green pellets of 3.2 times and a compressive strength of 20.1 N, slightly lower than the drop strength and compressive strength of the green pellets prepared in the examples, indicating that the iron ore pellets prepared by the present invention using the iron-rich and low-silicon composite binder have excellent bonding strength; the compressive strength of the iron ore pellets prepared in Examples 1 to 3 was 1836 to 1845 N. In the preparation of the iron ore pellets in Comparative Example 3, no dephosphorizing agent was added, and the phosphorus element content in the pellets was too high, resulting in an increase in cold brittleness. Therefore, the compressive strength of the iron ore pellets in Comparative Example 3 was 1624 N, lower than the compressive strength of the iron ore pellets prepared in the examples, indicating that the iron ore pellets prepared by the present invention using the iron-rich and low-silicon composite binder have excellent high-temperature bonding performance in the preparation of iron ore pellets.

[0095] The chemical composition of the iron ore pellets prepared in each example and comparative example was detected by a chemical composition analyzer. The test results are shown in Table 3:

[0096] Table 3 Chemical Composition

[0097] Component TFe FeO <![CDATA[SiO2]]> P Others Example 1 66.93 0.96 2.52 0.006 29.484 Example 2 67.48 1.01 2.51 0.007 28.893 Example 3 67.52 0.88 2.55 0.006 28.904 Comparative Example 1 66.67 1.23 2.61 0.009 29.481 Comparative Example 2 66.86 1.16 2.54 0.008 29.432 Comparative Example 3 66.90 1.36 2.53 0.012 29.188

[0098] From the data in Table 3, it can be seen that the TFe content in Examples 1 to 3 was 66.93 to 67.52%, the SiO2 content was 2.51 to 2.55%, and the P content was 0.006 to 0.007%. The iron grade of the iron ore pellets was increased, the content of SiO2 was reduced, and not too much P element was incorporated, indicating that the iron ore pellets prepared by the present invention using the iron-rich and low-silicon composite binder have the properties of being iron-rich and low-silicon in the preparation of iron ore pellets.

[0099] The above is only a preferred specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art within the technical scope disclosed by the present invention, according to the technical solution and inventive concept of the present invention, makes equivalent substitutions or changes, and all should be covered within the protection scope of the present invention.

[0100] The preferred embodiments of the present invention disclosed above are only used to help illustrate the present invention. The preferred embodiments do not describe all the details in detail, nor do they limit the invention to only the specific embodiments. Obviously, many modifications and variations can be made according to the content of this specification. These embodiments are selected and specifically described in this specification to better explain the principles and practical applications of the present invention, so that those skilled in the art can well understand and utilize the present invention. The present invention is only limited by the claims and their full scope and equivalents.

Claims

1. A composite binder rich in iron and low in silicon for iron ore pellets, characterized in that, It is prepared from the following components in parts by mass: 0.7 - 1.5 parts of bentonite, 0.5 - 0.6 parts of sodium carboxymethylcellulose, 1 - 1.5 parts of modified starch, 0.5 - 0.6 parts of modified magnesium - iron hydrotalcite, and 0.1 - 0.4 parts of dispersant; The montmorillonite content of the bentonite is 70 - 80 wt%, the swelling capacity is 9 - 10 mL / g, the water absorption rate in 2 h is 300 - 350%, the blue - absorption amount is 30 - 35 g / 100 g, and the colloid index is 20 - 25% / 3 g; The preparation method of the modified starch includes the following steps: S11: Add starch into a 2.5 - 3.5 wt% sodium chloride aqueous solution to prepare a 20 - 30 wt% starch solution, let it stand and swell at 30 - 40 °C for 1 - 2 h, and perform microwave activation treatment for 60 - 120 s to obtain a pretreated starch solution; S12: By mass, add citric acid into deionized water to prepare a 30 - 40 wt% citric acid solution, add sodium hydroxide solution to adjust the pH to 3 - 3.5, mix 20 - 30 parts of the pretreated starch solution with 40 - 50 parts of the citric acid solution evenly, add 20 - 40 parts of cyclodextrin and 1 - 3 parts of sodium dihydrogen phosphate, stir at 40 - 50 °C until the cyclodextrin is completely dissolved, then let it stand at room temperature for 12 - 18 h, react at 120 - 140 °C for 4 - 6 h. After the reaction, filter and collect the precipitate, wash it with distilled water, dry it at 40 - 50 °C and grind it through a 100 - 160 - mesh sieve to obtain the modified starch.

2. The iron-rich and low-silica composite binder for iron ore pellets according to claim 1, wherein The type of the sodium carboxymethylcellulose is one or a combination of CMC - M6, CMC - IH800, and CMC - IH1500; the dispersant is one or a combination of sodium citrate, sodium tripolyphosphate, and sodium silicate.

3. The iron-rich and low-silicon composite binder for iron ore pellets according to claim 1, wherein In S11, the microwave power is 300 - 500 W, and in S12, the cyclodextrin is either α - cyclodextrin or β - cyclodextrin.

4. The iron-rich and low-silicon composite binder for iron ore pellets according to claim 1, wherein The preparation method of the modified magnesium - iron hydrotalcite includes the following steps: S21: By mass, add 14 - 18 parts of magnesium nitrate and 7 - 9 parts of iron nitrate into 100 - 200 parts of deionized water, while stirring, drip a mixed solution of 150 - 200 parts of sodium hydroxide and sodium carbonate into the system, keep the pH between 10.8 - 11.2 during the dripping process. After the dripping is completed, react at 80 - 90 °C for 8 - 10 h, centrifuge and filter to collect the precipitate, wash it with deionized water and then vacuum - dry it at 40 - 60 °C, and grind it to obtain magnesium - iron hydrotalcite; S22: By mass, calcine the magnesium - iron hydrotalcite at 600 - 650 °C for 10 - 12 h to obtain layered oxides. Add 0.3 - 0.5 parts of p - hydroxycinnamic acid into 50 - 100 parts of deionized water and mix evenly, then add 10 - 15 parts of the layered oxides, react at 70 - 80 °C for 4 - 6 h, filter and collect the solid, wash it with deionized water and then vacuum - dry it at 40 - 60 °C, and grind it to obtain the modified magnesium - iron hydrotalcite.

5. The iron-rich and low-silica composite binder for iron ore pellets according to claim 4, wherein In S21, the mixed solution of sodium hydroxide and sodium carbonate is prepared by adding 16 - 20 parts of sodium hydroxide and 5.3 - 6.6 parts of sodium carbonate into 130 - 180 parts of deionized water.

6. The iron-rich and low-silicon composite binder for iron ore pellets according to claim 1, characterized in that, The method for preparing iron ore pellets with the iron-rich and low-silicon composite binder comprises the following steps: S31. Pretreatment: After separately drying iron concentrate, iron ore pellets, the iron-rich and low-silicon composite binder, a dephosphorizing agent and steel slag through a dryer, put them into a storage bin for standby; S32. Grinding and compounding: After proportioning iron concentrate, iron ore pellets, the iron-rich and low-silicon composite binder, a dephosphorizing agent and steel slag, add them into a mill, grind and screen until the powder with a particle size of more than 90wt% passes through a 100-120 mesh sieve to obtain a mixed material; S33. Pelletizing: By mass, put 2000-3000 parts of the mixed material into a disc pelletizer, drip industrial water to form mother balls. Stop dripping water after the total volume of the mother balls is greater than the total volume of the remaining mixed material. Add 1000-2000 parts of the mixed material into the disc pelletizer in three times at intervals of 3-5 minutes, and spray water to make the mother balls grow within 10-17 minutes to obtain green pellets. Stop feeding after the green pellets grow to an average particle size of 10-12 mm, continue to roll and compact for 2-5 minutes, take out and screen to collect green pellets with an average particle size of 10-15 mm; S34. Roasting: Put the green pellets into a roasting furnace, heat up to 200-300°C and dry for 30-40 minutes, then heat up to 600-700°C and preheat for 30-40 minutes, and finally heat up to 1250-1300°C and roast for 20-30 minutes. After cooling with the furnace, obtain iron ore pellets.

7. The iron-rich and low-silica composite binder for iron ore pellets according to claim 6, wherein, In the S31, the dephosphorizing agent is prepared by mixing calcium chloride and coke powder according to a mass ratio of 1:5-7; in the S32, the mass ratio of iron concentrate, iron ore pellets, the iron-rich and low-silicon composite binder, a dephosphorizing agent and steel slag is 100:0.9-1.1:2-5:20-30; in the S33, the inclination angle of the disc pelletizer is 30-50°, the rotation speed is 30-60 r / min, and the total consumption of industrial water is 9-13% of the total mass of the mixed material.