Pellet and preparation method thereof

Abstract

The invention belongs to the technical field of blast furnace burdens, and particularly relates to pellets and a preparation method thereof. The pellet consists of the following raw materials: 75-82 wt% of fine iron powder; 17 to 22 wt% of modified phosphogypsum; 1-3 wt% of a composite binder; the modified ardealite is prepared by the following preparation processes: drying and crushing ardealite, adding the crushed ardealite into water, stirring, filtering, and drying to obtain pretreated ardealite; and mixing the pretreated ardealite with blast furnace ash and sodium hydroxide, and calcining to obtain the modified ardealite. The prepared pellets are high in iron grade and excellent in strength.

Description

Technical Field

[0001] This invention belongs to the field of blast furnace charge technology, specifically relating to a pellet ore and its preparation method. Background Technology

[0002] Iron and steel materials possess advantages such as abundant mineral resources, excellent mechanical properties, and good processing performance, and are widely used in everything from daily necessities to high-end fields, making them an important pillar of the modern industrial system. As blast furnaces in the iron and steel industry develop towards larger scales, and as research into blast furnace ironmaking technology delves deeper into areas such as longevity, low consumption, and high output, researchers are increasingly emphasizing the optimization of blast furnace burdens. As a result, iron ore pellets have gained increasing importance in the ferrous metal smelting industry and have become a crucial ironmaking raw material in the blast furnace production process.

[0003] Iron pellets offer several advantages as furnace feedstock in ironmaking processes: superior metallurgical properties, with significantly higher porosity and reducibility than sinter, effectively reducing the blast furnace fuel ratio; significant environmental benefits, with sulfur dioxide emissions only 1 / 5 that of sintering and dust emissions reduced by 70%; and high production efficiency, high iron content, and high bulk density, which helps reduce blast furnace slag, heat loss, coke ratio, and pig iron production. However, iron pellets also have significant limitations: firstly, acidic pellets require flux to adjust slag basicity, increasing the complexity of blast furnace operation; secondly, roasting consumes more energy, and reliance on binders such as bentonite can lead to a decrease in iron content. Current technological improvements for iron pellets mainly focus on the following directions: firstly, developing new binders to reduce bentonite usage and improve iron content; secondly, optimizing the pellet structure, adjusting the raw material mineral phases, and improving the metallurgical properties of the pellets; and thirdly, improving the roasting process to reduce production costs and energy consumption. Optimizing the composition and structure of iron ore pellets using appropriate methods will further expand their application in steel production. Summary of the Invention

[0004] The primary objective of this invention is to provide a pellet ore with high iron grade and excellent strength, which can reduce ironmaking costs and improve steel quality.

[0005] The second objective of this invention is to provide a method for preparing pellets.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A type of ore pellet, composed of the following raw materials: 75-82 wt% iron concentrate; 17-22 wt% modified phosphogypsum; and 1-3 wt% composite binder. The modified phosphogypsum is prepared by the following process: After drying and pulverizing phosphogypsum, it is added to water, stirred, filtered, and dried to obtain pretreated phosphogypsum; the pretreated phosphogypsum is mixed with blast furnace ash and sodium hydroxide, and calcined to obtain modified phosphogypsum.

[0007] Furthermore, the ratio of phosphogypsum to water is 1 g: (3-5) mL; the stirring time is 8-10 h.

[0008] Furthermore, the mass ratio of the pretreated phosphogypsum, blast furnace ash, and sodium hydroxide is 1:(0.4-2):(0.05-0.1); the calcination temperature is 400-600 ℃, and the time is 1-3 h.

[0009] Furthermore, the composite adhesive is prepared by the following process: (1) Degummed silk fibroin was added to lithium bromide solution and heated to dissolve. After cooling, dialysis, and concentration under reduced pressure, a degummed silk fibroin solution was obtained. (2) Lanthanum oxide particles and silane coupling agent were added to ethanol, ultrasonically treated under heating conditions, filtered, washed and dried to obtain surface-modified lanthanum oxide particles. (3) The surface-modified lanthanum oxide particles are added to the degummed silk fibroin solution, the pH is adjusted to 7-9, and the reaction is carried out under stirring conditions; then bentonite is added to the reaction solution, ultrasonically dispersed, and freeze-dried to obtain the composite binder.

[0010] Further, in step (1), the concentration of the lithium bromide solution is 9.3-9.5 mol / L; the mass ratio of the degummed silk fibroin to the lithium bromide solution is 1:5-10; the concentration of the degummed silk fibroin solution is 4-8 w / v%; the heating and dissolving temperature is 50-70 ℃; the cooling temperature is 0-5 ℃; and the dialysis time is 40-80 h.

[0011] Further, in step (2), the ratio of lanthanum oxide particles to silane coupling agent is 1 g: (0.5-1) mL; the heating temperature is 50-60 ℃, and the ultrasonic treatment time is 3-5 h; the silane coupling agent is 3-aminopropyltriethoxysilane.

[0012] Further, in step (3), the ratio of the surface-modified lanthanum oxide particles, the degummed silk fibroin solution, and the bentonite is 1 g: (400-600) mL: (100-200) g.

[0013] The above-mentioned method for preparing pellets includes the following steps: According to the proportion of each component, the raw materials of each component are mixed to obtain a mixture; water is added to the mixture, pellets are formed and sieved to obtain green pellets of 9-15 mm; the green pellets are dried, preheated, roasted and cooled to obtain the pellet ore.

[0014] Furthermore, the drying temperature is 300-400 ℃ and the time is 8-10 min; the preheating temperature is 800-1000 ℃ and the time is 10-15 min; the calcination temperature is 1150-1300 ℃ and the time is 20-30 min.

[0015] The beneficial technical effects of this invention are as follows: 1. This invention involves adding modified phosphogypsum to the raw materials for preparing pellets, wherein the Ca in the phosphogypsum... 2+ and SO4 2- During the roasting process of ore pellets, calcium ferrates are generated, which can optimize the pore structure of the pellets, improve their reducibility and compressive strength, facilitate storage and transportation, generate less dust, and have high thermal energy utilization. However, phosphogypsum has a high decomposition temperature, and impurities such as fluorides and phosphoric acid can reduce the strength of the pellets and may corrode equipment. Phosphogypsum is washed with water to remove impurities and then roasted and modified with blast furnace ash. The carbon in the blast furnace ash can react with phosphogypsum to generate CaO and SO2. CaO can increase the alkalinity of the system, neutralize the free acid in phosphogypsum, reduce its corrosiveness, and promote the conversion of dihydrate calcium sulfate to hemihydrate gypsum in phosphogypsum; SO2 escapes directly in gaseous form, which can reduce sulfur residue in the pellets and can also be recovered for acid production. Furthermore, the silica-alumina active components in the blast furnace ash can react with CaO under alkaline conditions. 2+ The reaction produces ettringite and CSH gel, which can fill pores and enhance the strength of the pellets. Furthermore, phosphogypsum and blast furnace ash are both solid waste resources, and blast furnace ash contains approximately 40% iron. Using them as raw materials for pellets not only achieves waste-to-waste treatment but also fully recovers and utilizes iron resources, reducing production costs.

[0016] 2. This invention uses a composite of surface-modified lanthanum oxide particles, degummed silk fibroin, and bentonite as a binder for iron ore pellets; the natural polymer chain structure of the degummed silk fibroin can form chemical bonds with the surface of the iron concentrate; La 3+It can coordinate with the active groups of degummed silk fibroin to form a more stable cross-linked network, improving the bonding strength and thermal stability of degummed silk fibroin; while the montmorillonite interlayer structure of bentonite provides physical adsorption support and can maintain the stability of the skeleton at high temperatures. The combination of the three can significantly improve the compressive strength of green pellets. Moreover, the porous structure formed after the high-temperature decomposition of degummed silk fibroin helps gas diffusion, reduces pellet calcination cracks, and almost completely volatilizes after calcination, without the chemical residue problems of organic binders. The mineralization effect of lanthanum oxide promotes the growth of iron oxide grains and adsorbs and reduces sodium, potassium and heavy metal impurities in bentonite, which can effectively improve iron grade, reduce tailings pollution, and enhance the reducibility and mechanical strength of pellets. Attached Figure Description

[0017] Figure 1 This is a scanning electron microscope image of the modified phosphogypsum prepared in Example 1 of the present invention; Figure 2 This is a scanning electron microscope image of the composite adhesive prepared in Example 1 of the present invention. Detailed Implementation

[0018] The following is a further detailed description of the present invention in conjunction with specific preferred embodiments, and it should not be construed that the specific implementation of the present invention is limited to these descriptions. For those skilled in the art, various simple deductions or substitutions can be made without departing from the concept of the present invention, and all such modifications and substitutions should be considered within the scope of protection of the present invention. Specific conditions not specified in the embodiments are performed according to conventional conditions or conditions recommended by the manufacturer. Unless otherwise specified, all reagents or instruments used are conventional products obtained through commercial channels.

[0019] The preparation method of degummed silk fibroin in the following examples and comparative examples is as follows: silk fibroin is immersed in sodium carbonate aqueous solution and boiled for 90 minutes to degumme the silk fibroin. The degummed silk fibroin is washed three times with distilled water to remove sericin from the surface of the silk fibroin. After washing, it is kept in an oven at 60°C for 12 hours to remove moisture, and degummed silk fibroin is obtained.

[0020] (I) Implementation Examples Example 1 Example 1 provides a pellet ore, composed of the following raw materials: 78 wt% iron concentrate; 20 wt% modified phosphogypsum; 2 wt% composite binder; The modified phosphogypsum is prepared by the following process: After drying, the phosphogypsum was pulverized to 0.2 mm. The phosphogypsum was added to water at a ratio of 1 g to 4 mL, and the mixture was shaken and stirred for 9 h to remove impurities. The mixture was then filtered and dried to obtain pretreated phosphogypsum. The pretreated phosphogypsum, blast furnace ash, and sodium hydroxide were then mixed evenly at a mass ratio of 1:1.6:0.08 and calcined at 500 °C for 2 h to obtain modified phosphogypsum.

[0021] Figure 1 The above-mentioned scanning electron microscope image of modified phosphogypsum shows that the morphology and uniform size of the dihydrate gypsum crystals in the modified phosphogypsum are destroyed, the structure becomes loose and the porosity is high, and there are molten aggregates formed by mineralization reaction on the surface.

[0022] The above-mentioned composite adhesive is prepared by the following process: (1) According to the mass ratio of degummed silk fibroin to lithium bromide solution of 1:8, degummed silk fibroin was added to lithium bromide solution with a concentration of 9.4 mol / L, heated and stirred at 60 ℃ to dissolve, and then the solution was cooled to 3 ℃ and dialyzed in pure water for 60 h. The dialysate was concentrated under reduced pressure to obtain a degummed silk fibroin solution with a concentration of 7 w / v%. (2) Lanthanum oxide particles, silane coupling agent KH550 and ethanol were added to ethanol at a ratio of 1 g: 0.8 mL: 60 mL. The mixture was ultrasonically reacted at 50 °C for 4 h. After filtration, washing and drying, the surface-modified lanthanum oxide particles were obtained. (3) According to the ratio of surface-modified lanthanum oxide particles, degummed silk fibroin solution and bentonite 1 g: 500 mL: 150 g, the surface-modified lanthanum oxide particles and degummed silk fibroin solution were mixed, and sodium hydroxide solution was added dropwise to adjust the pH to 8. After stirring and reacting for 1 h, bentonite was added for ultrasonic dispersion. After uniform dispersion, the mixture was freeze-dried to obtain the composite binder.

[0023] Figure 2 The scanning electron microscope image of the above composite binder shows that the freeze-dried degummed silk fibroin has a porous structure and contains granular bentonite inside the gel. The porous structure indicates that the binder has good water absorption and impurity adsorption properties, and the small pore size indicates that the structure is compact and the cross-linking is good.

[0024] This embodiment also provides a method for preparing the above-mentioned pellets, including the following steps: According to the above component proportions, the raw material components are mixed to obtain a mixture; 8% water by mass of the mixture is added to the mixture, pelletized and sieved to obtain green pellets of 12 mm; the green pellets are dried at 300 ℃ for 8 min, then preheated at 800 ℃ for 12 min, then roasted at 1200 ℃ for 20 min, and cooled to obtain pellet ore.

[0025] Example 2 Example 2 provides a pellet ore composed of the following raw materials: 75 wt% iron concentrate; 22 wt% modified phosphogypsum; and 3 wt% composite binder. The modified phosphogypsum is prepared by the following process: After drying, the phosphogypsum was pulverized to 0.2 mm. The phosphogypsum was added to water at a ratio of 1 g to 3 mL, and the mixture was shaken and stirred for 8 h to remove impurities. The mixture was then filtered and dried to obtain pretreated phosphogypsum. The pretreated phosphogypsum, blast furnace ash, and sodium hydroxide were then mixed evenly at a mass ratio of 1:0.4:0.05 and calcined at 400 °C for 1 h to obtain modified phosphogypsum.

[0026] The above-mentioned composite adhesive is prepared by the following process: (1) According to the mass ratio of degummed silk fibroin to lithium bromide solution of 1:5, degummed silk fibroin was added to lithium bromide solution with a concentration of 9.5 mol / L, heated and stirred at 50 ℃ to dissolve, and then the solution was cooled to 0 ℃ and dialyzed in pure water for 40 h. The dialysate was concentrated under reduced pressure to obtain a degummed silk fibroin solution with a concentration of 4 w / v%. (2) Lanthanum oxide particles, silane coupling agent KH550 and ethanol were added to ethanol at a ratio of 1 g: 0.5 mL: 50 mL. The mixture was ultrasonically reacted at 50 °C for 3 h. After filtration, washing and drying, the surface-modified lanthanum oxide particles were obtained. (3) According to the ratio of surface-modified lanthanum oxide particles, degummed silk fibroin solution and bentonite 1 g: 400 mL: 100 g, the surface-modified lanthanum oxide particles and degummed silk fibroin solution were mixed, and sodium hydroxide solution was added dropwise to adjust the pH to 7. After stirring and reacting for 1 h, bentonite was added for ultrasonic dispersion. After uniform dispersion, the mixture was freeze-dried to obtain the composite binder.

[0027] This embodiment also provides a method for preparing the above-mentioned pellets, including the following steps: According to the above component proportions, the raw material components are mixed to obtain a mixture; 7.5% water by mass of the mixture is added to the mixture, pelletized and sieved to obtain green pellets of 9 mm; the green pellets are dried at 300 ℃ for 8 min, then preheated at 800 ℃ for 10 min, and then roasted at 1150 ℃ for 20 min, and then cooled to obtain pellet ore.

[0028] Example 3 Example 3 provides a pellet ore composed of the following raw materials: 82 wt% iron concentrate; 17 wt% modified phosphogypsum; and 1 wt% composite binder. The modified phosphogypsum is prepared by the following process: After drying, the phosphogypsum was pulverized to 0.3 mm. The phosphogypsum was added to water at a ratio of 1 g to 5 mL, and the mixture was shaken and stirred for 10 h to remove impurities. The mixture was then filtered and dried to obtain pretreated phosphogypsum. The pretreated phosphogypsum, blast furnace ash, and sodium hydroxide were mixed evenly at a mass ratio of 1:2:0.1 and calcined at 600 °C for 3 h to obtain modified phosphogypsum.

[0029] The above-mentioned composite adhesive is prepared by the following process: (1) According to the mass ratio of degummed silk fibroin to lithium bromide solution of 1:10, degummed silk fibroin was added to lithium bromide solution with a concentration of 9.5 mol / L, heated and stirred at 70 ℃ to dissolve, and then the solution was cooled to 5 ℃ and dialyzed in pure water for 80 h. The dialysate was concentrated under reduced pressure to obtain a degummed silk fibroin solution with a concentration of 8 w / v%. (2) Lanthanum oxide particles, silane coupling agent KH550 and ethanol were added to ethanol at a ratio of 1 g: 1 mL: 80 mL. The mixture was ultrasonically reacted at 60 °C for 5 h. After filtration, washing and drying, the surface-modified lanthanum oxide particles were obtained. (3) According to the ratio of surface-modified lanthanum oxide particles, degummed silk fibroin solution and bentonite 1 g: 600 mL: 200 g, the surface-modified lanthanum oxide particles and degummed silk fibroin solution were mixed, and sodium hydroxide solution was added dropwise to adjust the pH to 9. After stirring and reacting for 2 h, bentonite was added and ultrasonically dispersed evenly. After even dispersion, the mixture was freeze-dried to obtain the composite binder.

[0030] This embodiment also provides a method for preparing the above-mentioned pellets, including the following steps: According to the above component proportions, the raw material components are mixed to obtain a mixture; 8.5% water by mass of the mixture is added to the mixture, pelletized and sieved to obtain green pellets of 15 mm; the green pellets are dried at 400 ℃ for 10 min, then preheated at 1000 ℃ for 15 min, and then roasted at 1300 ℃ for 30 min, and cooled to obtain pellet ore.

[0031] (ii) Comparative Example Comparative Example 1 Comparative Example 1 is basically the same as Example 1, except that the modified phosphogypsum is replaced with a mixture of phosphogypsum and blast furnace ash, and the ratio of phosphogypsum to blast furnace ash is the same as in Example 1.

[0032] Comparative Example 2 Comparative Example 2 is basically the same as Example 1, except that the composite binder is replaced with bentonite.

[0033] Comparative Example 3 Comparative Example 3 is basically the same as Example 1, except that step (2) is omitted when preparing the composite binder, and the surface-modified lanthanum oxide particles are omitted in step (3).

[0034] (III) Experimental Examples The pellets prepared in Examples 1-3 and Comparative Examples 1-3 were tested as follows: (1) Iron grade: The iron grade of the finished pellets was determined according to the national standard GB / T 6730.65-2009 "Determination of total iron content in iron ore by titration of potassium dichromate reduced by titanium trichloride (conventional method)". The results are shown in Table 1.

[0035] (2) Drop strength of green balls: Green balls are dropped from a height of 0.5 m onto a 1 cm thick steel plate until the ball cracks or breaks on the nth drop. The drop strength of the ball is (n-1) times / 0.5 m. The average value of the drop strength of 20 green balls is taken. The results are shown in Table 1.

[0036] (3) Compressive strength test: The compressive strength of green pellets and roasted pellets was determined in accordance with the national standard GB / T14201-2018 "Determination of compressive strength of iron pellets for blast furnace and direct reduction". The results are shown in Table 1.

[0037] Table 1

[0038] As shown in Table 1, the pellets prepared using Examples 1-3 of the present invention have high iron content and excellent pellet strength.

[0039] Compared to Example 1, Comparative Example 1 replaced the modified phosphogypsum with a mixture of phosphogypsum and blast furnace ash; Comparative Example 2 replaced the composite binder with bentonite; and Comparative Example 3 used a degummed silk fibroin-bentonite composite binder. The resulting pellets had lower iron content and poorer pellet strength. These results demonstrate that by using modified phosphogypsum and a composite binder, the present invention significantly improves the performance of pellets. Specifically, the modified phosphogypsum of the present invention is obtained by washing and removing impurities from phosphogypsum with water and then modifying it by calcination with blast furnace ash. The carbon in the blast furnace ash can undergo a reduction reaction with phosphogypsum to generate CaO and SO2. CaO can increase the alkalinity of the system, neutralize the free acid in the phosphogypsum, reduce its corrosiveness, and promote the conversion of dihydrate calcium sulfate to hemihydrate gypsum in the phosphogypsum. SO2 escapes directly in gaseous form, reducing sulfur residue in the pellets and allowing for simultaneous recovery for acid production. Furthermore, the silica-alumina active components in the blast furnace ash can react with CaO under alkaline conditions. 2+The reaction produces ettringite and CSH gel, which can fill pores and enhance the strength of the pellets. In the composite binder prepared in this invention, the natural polymer chain structure of degummed silk fibroin can form chemical bonds with the surface of iron concentrate, La 3+ It can coordinate with the active groups of degummed silk fibroin to form a more stable cross-linked network, improving the bonding strength and thermal stability of degummed silk fibroin; while the montmorillonite interlayer structure of bentonite provides physical adsorption support and can maintain the stability of the skeleton at high temperatures. The combination of the three can significantly improve the compressive strength of green pellets. Moreover, the porous structure formed after the high-temperature decomposition of degummed silk fibroin helps gas diffusion, reduces pellet calcination cracks, and almost completely volatilizes after calcination, without the chemical residue problems of organic binders. The mineralization effect of lanthanum oxide promotes the growth of iron oxide grains and adsorbs and reduces sodium, potassium and heavy metal impurities in bentonite, which can effectively improve iron grade, reduce tailings pollution, and enhance the reducibility and mechanical strength of pellets.

[0040] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them. The basic principles and main features of the present invention have been described above with specific implementation schemes. Based on the present invention, some modifications or substitutions can be made, but these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of protection claimed by the present invention.

Claims

1. A type of pelletized ore, characterized in that, Composed of the following raw materials: 75-82 wt% iron concentrate; 17-22 wt% modified phosphogypsum; 1-3 wt% composite binder; The modified phosphogypsum is prepared by the following process: After drying and pulverizing phosphogypsum, it is added to water, stirred, filtered, and dried to obtain pretreated phosphogypsum; the pretreated phosphogypsum is mixed with blast furnace ash and sodium hydroxide, and calcined to obtain modified phosphogypsum.

2. The pelletized ore according to claim 1, characterized in that, The ratio of phosphogypsum to water is 1 g: (3-5) mL; the stirring time is 8-10 h.

3. The pelletized ore according to claim 1, characterized in that, The mass ratio of the pretreated phosphogypsum, blast furnace ash, and sodium hydroxide is 1:(0.4-2):(0.05-0.1); the calcination temperature is 400-600 ℃, and the time is 1-3 h.

4. The pelletized ore according to claim 1, characterized in that, The composite adhesive is prepared by the following process: (1) Degummed silk fibroin was added to lithium bromide solution and heated to dissolve. After cooling, dialysis, and concentration under reduced pressure, a degummed silk fibroin solution was obtained. (2) Lanthanum oxide particles and silane coupling agent were added to ethanol, ultrasonically treated under heating conditions, filtered, washed and dried to obtain surface-modified lanthanum oxide particles. (3) The surface-modified lanthanum oxide particles are added to the degummed silk fibroin solution, the pH is adjusted to 7-9, and the reaction is carried out under stirring conditions; then bentonite is added to the reaction solution, ultrasonically dispersed, and freeze-dried to obtain the composite binder.

5. The pelletized ore according to claim 4, characterized in that, The concentration of the lithium bromide solution in step (1) is 9.3-9.5 mol / L; the mass ratio of the degummed silk fibroin to the lithium bromide solution is 1:5-10; the concentration of the degummed silk fibroin solution is 4-8 w / v%; the heating and dissolving temperature is 50-70 ℃; the cooling temperature is 0-5 ℃; and the dialysis time is 40-80 h.

6. The pelletized ore according to claim 4, characterized in that, In step (2), the ratio of lanthanum oxide particles to silane coupling agent is 1 g: (0.5-1) mL; the heating temperature is 50-60 ℃, and the ultrasonic treatment time is 3-5 h; the silane coupling agent is 3-aminopropyltriethoxysilane.

7. The pelletized ore according to claim 4, characterized in that, The ratio of the surface-modified lanthanum oxide particles, degummed silk fibroin solution and bentonite used in step (3) is 1 g: (400-600) mL: (100-200) g.

8. The method for preparing pellets according to any one of claims 1-7, characterized in that, Includes the following steps: According to the proportion of each component, the raw materials of each component are mixed to obtain a mixture; water is added to the mixture, pellets are formed and sieved to obtain green pellets of 9-15 mm; the green pellets are dried, preheated, roasted and cooled to obtain the pellet ore.

9. The method for preparing pellets according to claim 8, characterized in that, The drying temperature is 300-400℃ and the time is 8-10 min; the preheating temperature is 800-1000℃ and the time is 10-15 min; the calcination temperature is 1150-1300℃ and the time is 20-30 min.

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