Preparation method of sintered return mine cold-bonded pellets based on precise gradation

Abstract

The invention discloses a preparation method of sintered return mine cold-bonded pellets based on precise gradation. Aiming at the problems of insufficient pellet strength, overproof alkali metal and the like caused by unreasonable grading in the prior art, the method is characterized by screening and grading sintered return ores into five particle size grades of 0-1mm, 1-2mm, 2-3mm, 3-4mm and 4-5mm, determining a preset grading scheme based on a grading index n = 0.4-0.6 and blending the ores; the graded sintering return mine and defective glass fibers are mixed and ground, liquid sodium silicate, pre-gelatinized cassava starch and water are added to prepare a ball pressing mixture, and sintering flue gas or annular cold flue gas is used for drying and consolidation after double-roller compression molding. Through precise gradation optimization of a particle stacking structure and cooperative enhancement of the composite adhesive, the green pellet drop strength of the prepared pellets is larger than or equal to 5 times / P, the dry pellet compressive strength is larger than or equal to 2200 N / P, the alkali metal content is smaller than 0.4%, cooperative resource utilization of sintered return mine, defective glass fibers and industrial waste gas is achieved, existing steel equipment is compatible, the cost is controllable, and the method is suitable for large-scale popularization and application. The method is suitable for large-scale production and assists green low-carbon transformation in the iron and steel industry.

Description

Technical Field

[0001] This invention belongs to the field of cold-bonded pellet preparation and metallurgical solid waste resource utilization technology. Specifically, it relates to a method for preparing high-strength, low-alkali metal cold-bonded pellets by optimizing the particle packing structure of sintered return ore through a preset precise gradation scheme and combining composite binders with synergistic processes. Background Technology

[0002] Sintered ore return is industrial solid waste with a particle size of <5mm generated during sintering production. Because it cannot be directly fed into the furnace, it needs to be recycled and re-burned, which not only reduces sintering capacity by 20-30% but also increases CO2 and pollutant emissions, contradicting the steel industry's need for green and low-carbon transformation. Cold-bonded pelletizing technology provides an effective path for the resource utilization of sintered ore return, but existing technologies face key bottlenecks: Current sintering return ore blending lacks scientific gradation design, often employing random mixing or single-size range blending, resulting in high particle porosity and insufficient density. Fine particles cannot effectively fill the gaps between coarse particles, reducing the contact area between the binder and particles, lowering the consolidation effect, and making the internal structure of the pellets loose. Ultimately, this leads to insufficient green pellet drop strength and difficulty in consistently meeting the blast furnace smelting requirements (>2200 N / P) for dry pellets. At the same time, unreasonable gradation exacerbates the agglomeration of fiber-reinforced materials, further deteriorating pellet performance.

[0003] While some existing technologies attempt to improve pellet strength through binder optimization or surface modification, they fail to recognize the decisive role of gradation design in particle packing structure and subsequent consolidation effect. This results in limited improvement in pellet strength and makes it difficult to balance low alkali metal content with the needs of large-scale production. Therefore, developing a method for preparing sintered return ore cold-consolidated pellets based on a precise gradation scheme, which optimizes particle packing structure and synergistically combines binders and reinforcing materials to achieve breakthroughs in pellet performance, has significant industrial application value. Summary of the Invention

[0004] This invention aims to solve the problems of loose particle packing, low bonding efficiency, and insufficient pellet strength caused by unreasonable gradation in the preparation of cold-consolidated pellets from sintered ore. It provides a method for preparing cold-consolidated pellets with high strength, low alkali metal content, and resource utilization by pre-setting a precise gradation scheme, combined with composite binders and synergistic processes.

[0005] To achieve the above method, the present invention provides a method for preparing cold-consolidated pellets from sintered return ore based on precise gradation, comprising the following steps: S1. The sintered return ore is screened and graded into five particle size grades: 0-1mm, 1-2mm, 2-3mm, 3-4mm, and 4-5mm. Graded sintered return ore is then blended according to a preset gradation scheme to obtain graded sintered return ore. The preset gradation scheme is determined based on a gradation index n = 0.4-0.6, and the mass percentage of each particle size grade is as follows: when n = 0.4, 0-1mm accounts for 52.53%, 1-2mm accounts for 16.78%, 2-3mm accounts for 12.20%, and 3-4mm accounts for 9.9%. 4% for 0-1mm and 8.54% for 4-5mm; when n=0.5, 44.72% for 0-1mm, 18.52% for 1-2mm, 14.21% for 2-3mm, 11.98% for 3-4mm, and 10.56% for 4-5mm; when n=0.6, 38.07% for 0-1mm, 19.63% for 1-2mm, 15.89% for 2-3mm, 13.87% for 3-4mm, and 12.53% for 4-5mm. S2. The graded sintered return ore is mixed with substandard glass fiber and then ground in a cylindrical drum to obtain a mixture. S3. Add liquid sodium silicate and pregelatinized cassava starch to the mixture, adjust the moisture content, and mix evenly to obtain the pelletizing mixture; S4. Press the briquetting mixture into shape to obtain cold-consolidated green pellets; S5. The green pellets are dried and consolidated using industrial waste gas to obtain cold-consolidated dry pellets.

[0006] When the gradation index n = 0.4-0.6, following the particle gradation theory, coarse particles (3-5mm) form a skeletal structure, medium particles (1-3mm) fill the gaps between coarse particles, and fine particles (0-1mm) further fill the remaining voids, maximizing particle packing density, reducing internal voids in the pellets, and laying a structural foundation for improved mechanical strength. Dense packing increases the contact area between particles, allowing liquid sodium silicate to uniformly cover the particle surface and fully react to generate strong Fe-O-Si chemical bonds. Simultaneously, the viscous colloid effect of pregelatinized cassava starch rapidly improves the strength of green pellets, preventing breakage during transportation. The uniformly packed particles provide a uniformly distributed carrier for the ground, substandard glass fibers. The fibers form a three-dimensional network reinforcement structure between the particles, synergistically working with the three-dimensional network structure formed by the dehydration condensation of sodium silicate, similar to the reinforced concrete effect, significantly improving the compressive strength of dry pellets. Furthermore, the reaction of the active SiO2 in the fibers with sodium silicate enhances (SiO4). 4- The concentration further enhances the consolidation effect.

[0007] Furthermore, in step S1, the gradation index n is set to 0.5. After mixing each particle size grade according to its corresponding mass proportion, the particle packing porosity is ≤35%. The essence of gradation design is to achieve a three-level packing effect by controlling the proportion of coarse, medium, and fine particles, with coarse particles providing skeletal support, medium particles filling the gaps, and fine particles sealing the micropores. The particle size proportion of n=0.5 precisely achieves the peak of this effect, with coarse particles (3-5mm) accounting for 22.54%, fine particles (0-1mm) accounting for 44.72%, and medium particles (1-3mm) accounting for 32.73%. These three particles form the optimal ratio of skeleton-filling-sealing, resulting in the lowest porosity inside the pellets and the highest density of contact points between particles, providing the densest structural carrier for subsequent binder consolidation and fiber reinforcement.

[0008] Furthermore, the defective glass fiber is waste generated during steel production or glass processing, with an initial length of 0.1-3mm, and a length ≤0.1mm after grinding in step S2.

[0009] Furthermore, in step S2, the diameter of the cylindrical drum is 10-30cm, the grinding speed is 5-20r / min, and the grinding time is 5-20min.

[0010] Furthermore, based on the total mass of the pelletized mixture, the amount of liquid sodium silicate added in step S3 is 2-5 wt%, the amount of pregelatinized cassava starch added is 0.5-2 wt%, and the amount of substandard glass fiber added is 0.5-2 wt%. The glass fiber, after grinding, retains its fibrous structure and is uniformly distributed in the cold-consolidated pellets, forming a three-dimensional network fiber structure. Similarly, sodium silicate, after dehydration and condensation solidification, also forms a three-dimensional network structure. The two complement each other, forming a structure similar to reinforced concrete, which can significantly improve the compressive strength of the cold-consolidated dry pellets. Chemically, liquid sodium silicate is composed of (SiO4). 4- Composed of tetrahedral units, partly (SiO4). 4- It reacts with Fe-OH on the surface of the sintered return ore to form strong chemical bonds Fe-O-Si bonds, partly (SiO4). 4- The molecules dehydrate and condense to form polymers, gradually developing into a three-dimensional network structure. Therefore, sodium silicate primarily provides mechanical strength to cold-bonded pellets through strong Fe-O-Si bonds and the three-dimensional network structure. Glass fiber, on the other hand, is essentially composed of active SiO2. When mixed with sodium silicate, the OH- ions in the alkaline environment of the sodium silicate react chemically with the glass fiber to form (SiO4). 4- Tetrahedral units, which significantly improve the concentration of (SiO4) in sodium silicate solution. 4- Density can promote (SiO4) 4- It forms Fe-O-Si bonds with sintered return ore and increases (SiO4) content. 4-The strength of the three-dimensional network structure formed after dehydration and condensation. Macroscopically, this is reflected in the significant increase in the compressive strength of the dry pellets in the sintered return ore cold-consolidated pellets after the addition of glass fibers. Liquid sodium silicate is used to complement the synergistic effect of the active SiO2 in the glass fibers (the reaction between glass fibers and sodium silicate increases (SiO4)). 4- Concentration (strengthening the three-dimensional network structure) can ensure stable compressive strength of dry pellets and avoid insufficient strength and pellet breakage before entering the furnace due to insufficient dosage; Furthermore, the grinding in step S2 employs a stepped grinding process, specifically comprising two stages: The first stage is pre-dispersion grinding. The rotation speed of the cylindrical drum is controlled at 5-10 r / min and the grinding time is 8-15 min. The particle collision and preliminary shearing of the graded sintered return ore are used to make the substandard glass fiber evenly dispersed among the sintered return ore particles and avoid local agglomeration. The second stage is fine shearing and grinding. The rotation speed of the cylindrical drum is increased to 15-20 r / min, and the grinding time is 3-8 min. The sharp edge of the graded sintered return ore is used to precisely shear the dispersed substandard glass fibers, so that the final length of the glass fibers is uniformly controlled within the required range and tightly attached to the porous structure surface of the graded sintered return ore.

[0011] Traditional single-speed grinding has two major drawbacks: First, when high-speed grinding is used directly, substandard glass fibers (initial length 0.1-3mm) are prone to entanglement and agglomeration due to excessive instantaneous shear force, forming local fiber clusters that cannot be evenly distributed among the sintered return ore particles, resulting in uneven strength within the pellets. Second, while low-speed grinding can reduce agglomeration, the shear force is insufficient, making it difficult to control the fiber length within the target range of ≤0.1mm. Furthermore, it cannot effectively shear through the sharp edges of the sintered return ore, resulting in weak fiber adhesion to the return ore surface and hindering the effective three-dimensional network reinforcement. Stepped grinding addresses these issues through a two-stage design: low-speed pre-dispersion and high-speed fine shearing. The first stage prioritizes breaking down fiber agglomerations, creating a foundation for uniform distribution during subsequent shearing. The second stage precisely controls fiber length while simultaneously enhancing the adhesion between the fibers and the return ore. The first stage of pre-dispersion grinding (low speed, long duration) is mainly to break up agglomerates and achieve uniform distribution. The sintered return ore, after precise gradation, forms a dense aggregate with a coarse particle skeleton, medium particles filling, and fine particles blocking, with uniform micro-gaps between particles. The pre-dispersion fiber bundles can initially fill these gaps, preventing the fibers from agglomerating again during subsequent shearing. At the same time, low-speed grinding does not damage the sharp edges of the sintered return ore (providing protection for the second stage of shearing) nor cause excessive fiber breakage, ensuring that the fibers retain sufficient length to form a three-dimensional reinforcement structure. The second stage, fine shearing and grinding (high speed, short time), is mainly for precise length control and enhanced adhesion. On the one hand, the precisely sheared short fibers can be more tightly embedded into the porous structure surface of the sintered return ore. The dense packing of graded return ore makes the pore distribution on the particle surface uniform, and the short fibers can be attached to the pores through physical adsorption and mechanical interlocking, preventing them from falling off during drying and molding. On the other hand, particle collision at high speed allows the fibers to fully contact the return ore surface, creating conditions for the subsequent composite binder to act: the alkaline environment of liquid sodium silicate can react with the active SiO2 of the fibers to generate (SiO4). 4- This further strengthens the chemical bond between the fiber and the recycled minerals, while the colloidal effect of pregelatinized cassava starch can coat the fiber and recycled mineral particles, thereby increasing the strength of the green pellets.

[0012] Furthermore, in step S4, a roller briquetting machine is used for pressing and forming, with a forming pressure of 20-50 MPa.

[0013] Furthermore, the characteristic feature is that, in step S5, the industrial waste gas is sintering flue gas or sintering ring-cooled flue gas; the drying and consolidation conditions are: flue gas velocity 20000-40000 m / s. 3 / h, temperature 100-200℃, flue gas moisture content 1-5%, consolidation time 1-10h.

[0014] Furthermore, in step S3, the total water content of the briquetting mixture is 3-8 wt%; the liquid sodium silicate has a modulus of 2.5 and a solid content of 50%. When the modulus is too low (<2.0), the Na2O content is too high, resulting in good solubility but weak reactivity, leading to a loose three-dimensional network structure with insufficient strength. When the modulus is too high (>3.0), the SiO2 content is too high, easily forming gel-like precipitates, making it difficult to mix evenly with sintered return ore and glass fiber, resulting in uneven pellet strength. A modulus of 2.5 is in a balance range between high reactivity and low precipitation risk. It can quickly react with Fe-OH on the surface of sintered return ore to generate strong Fe-O-Si bonds, and can also synergistically enhance the effect with the active SiO2 of glass fiber. Simultaneously, it ensures good fluidity after dilution with water, facilitating uniform mixing with solid raw materials.

[0015] The present invention also provides a sintered return ore cold solidification pellet, which is prepared by the above preparation method. The green pellet drop strength is ≥5 times / P, the dry pellet compressive strength is ≥2200N / P, and the alkali metal content is <0.4%.

[0016] The beneficial effects of this invention are: Based on a precise gradation scheme with a gradation index of n=0.4-0.6, and an optimal n=0.5, the optimal packing effect of coarse, medium, and fine particle skeleton, filling, and sealing is achieved, with a particle packing porosity ≤32%. Combined with the synergistic effect of a composite binder consisting of liquid sodium silicate, pregelatinized cassava starch, and substandard glass fiber, the pellets achieve a drop strength ≥5 times / P and a dry pellet compressive strength ≥2200N / P, fully meeting the core requirements for impact resistance in industrial transportation and high pressure resistance in blast furnace smelting. The thermal stability of sodium silicate and the high-temperature resistance of glass fiber work synergistically, preventing thermal collapse of the pellets in a blast furnace environment of 1000-1200℃, ensuring strong structural integrity and guaranteeing the permeability of the feed column and the reduction efficiency of iron ore during smelting. Precise gradation avoids strength dispersion caused by uneven particle packing. The components of the composite binder complement each other: sodium silicate provides chemical consolidation, starch enhances green pellet strength, and glass fiber provides physical reinforcement, resulting in a strength index fluctuation of ≤5% between different batches of pellets, with stability far exceeding existing random ore blending technologies.

[0017] By improving binder utilization efficiency through gradation and reducing the addition of liquid sodium silicate, the alkali metal content of the pellets is stably controlled at 0.14-0.34%, far below the blast furnace safety threshold of <0.4%. The low alkali metal content also reduces the amount of sodium (Na) in the blast furnace. +The alkali metal cycle formed by volatilization, adhesion, and deposition prevents low-melting-point compounds from clogging the pores of the blast furnace charge and eroding the furnace lining, extending the blast furnace lining life by 10-15% while reducing the incidence of production accidents such as blast furnace bridging and suspended charge. Waste materials (substandard glass fibers) generated during steel production and glass processing are used as reinforcing additives to replace expensive industrial fiber materials, solving the waste disposal problem and reducing raw material costs. Sintering flue gas and annular cooling flue gas (associated waste gas from steel production) are used to replace traditional steam / electric heating for drying and solidification, recovering waste heat while avoiding thermal pollution caused by direct emissions.

[0018] Liquid sodium silicate provides basic strength by generating strong Fe-O-Si chemical bonds and a three-dimensional network structure; pregelatinized cassava starch enhances the impact resistance of raw pellets through its viscous colloid effect; and substandard glass fibers are supplemented with active SiO2 (SiO4). 4- The concentration forms a three-dimensional reinforcing network, and the three work together to form a complete system of chemical consolidation, physical reinforcement and green ball stabilization, which improves the strength compared to single binders or binary composite binders. Detailed Implementation

[0019] The following examples illustrate specific implementations of the present invention. However, these examples are merely for illustrative purposes and do not limit the scope of the invention in any way.

[0020] Example 1: Graded sinter return ore: Based on n=0.4, the ore composition is as follows: 0-1mm accounts for 52.53%, 1-2mm accounts for 16.78%, 2-3mm accounts for 12.20%, 3-4mm accounts for 9.94%, and 4-5mm accounts for 8.54%. Using the total mass of the briquetting mixture as a baseline, the total proportion of graded sinter return ore is 88 wt%. Composite binder: Based on the total mass of the briquetting mixture, 1 wt% of substandard glass fiber, 3 wt% of liquid sodium silicate, and 1 wt% of pregelatinized cassava starch; Moisture adjustment: 7 wt% based on the total mass of the briquetting mixture; Process parameters: Drum grinding speed 10 r / min, time 10 min; forming pressure 30 MPa; drying and consolidation using sintering flue gas, flow rate 30000 m / s. 3 / h, temperature 160℃, moisture content 3%, time 4h.

[0021] Example 2: Graded sintered return ore: Based on n=0.5 ore blending, 0-1mm accounts for 44.72%, 1-2mm for 18.52%, 2-3mm for 14.21%, 3-4mm for 11.98%, and 4-5mm for 10.56%. Using the total mass of the briquetting mixture as a baseline, the total proportion of graded sintered return ore is 89 wt%. Composite binder: Based on the total mass of the briquetting mixture, 1 wt% of substandard glass fiber, 2 wt% of liquid sodium silicate, and 1 wt% of pregelatinized cassava starch; Moisture adjustment: 7 wt% based on the total mass of the briquetting mixture; Process parameters: Drum grinding speed 10 r / min, time 10 min; forming pressure 30 MPa; drying and consolidation using sintering flue gas, flow rate 30000 m / s. 3 / h, temperature 160℃, moisture content 3%, time 4h.

[0022] Example 3: Graded sinter return ore: Based on n=0.6, the ore composition is as follows: 0-1mm accounts for 38.07%, 1-2mm accounts for 19.63%, 2-3mm accounts for 15.89%, 3-4mm accounts for 13.87%, and 4-5mm accounts for 12.53%. Using the total mass of the briquetting mixture as a baseline, the total proportion of graded sinter return ore is 86 wt%. Composite binder: Based on the total mass of the briquetting mixture, 1 wt% of substandard glass fiber, 5 wt% of liquid sodium silicate, and 1 wt% of pregelatinized cassava starch; Moisture adjustment: 7 wt% based on the total mass of the briquetting mixture; Process parameters: Drum grinding speed 10 r / min, time 10 min; forming pressure 30 MPa; drying and consolidation using sintering flue gas, flow rate 30000 m / s. 3 / h, temperature 160℃, moisture content 3%, time 4h.

[0023] Comparative Example 1 Graded sinter return ore: ore is blended at n=0.3, with 0-1mm accounting for 60.12%, 1-2mm for 14.35%, 2-3mm for 10.18%, 3-4mm for 8.25%, and 4-5mm for 7.10%, for a total graded sinter return ore proportion of 88 wt%. The composite binder and process parameters are the same as in Example 1.

[0024] Comparative Example 2 Graded sinter return ore: ore is blended with n=0.7, with 0-1mm accounting for 32.45%, 1-2mm for 20.31%, 2-3mm for 17.56%, 3-4mm for 15.23%, and 4-5mm for 14.45%, for a total graded sinter return ore proportion of 88 wt%. The composite binder and process parameters are the same as in Example 1.

[0025] Comparative Example 3 Sintered return ore: ungraded, randomly mixed, total percentage 88 wt%; The composite binder and process parameters are the same as in Example 1.

[0026] Comparative Example 4 The only difference from Example 2 is that the adhesive does not contain liquid sodium silicate; the other process parameters are the same as in Example 2.

[0027] Comparative Example 5 The only difference from Example 2 is that the binder does not contain pregelatinized cassava starch; the other process parameters are the same as in Example 2.

[0028] Comparative Example 6 The only difference from Example 2 is that the adhesive does not contain substandard glass fiber; all other process parameters are the same as in Example 2.

[0029] Strength data for each embodiment are shown in Table 1: Table 1 shows the components and mechanical properties of the cold-bonded pellet binder in each embodiment.

[0030] Based on the experimental data above, we can see that when the gradation index n=0.5, the dry ball compressive strength of Example 2 reaches 2258 N / P, which meets the smelting requirement of ≥2200 N / P. The green ball drop strength is 6.3 times / P, which meets the transportation requirement of ≥5 times / P. The alkali metal content is only 0.14%, which is far below the safety threshold of <0.4%. In Comparative Example 1, with n=0.3, fine particles (0-1mm) accounted for as high as 60.12%, the coarse particle skeleton was weak, the internal stress of the pellets was uneven, the green pellet drop strength was only 4.8 times / p, and it was easily broken during transportation. The dry pellet compressive strength was 1850 N / p, which did not meet the smelting requirements. In Comparative Example 2, with n=0.7, the proportion of coarse particles (3-5mm) increased to 29.68%, the fine particle filling was insufficient, the porosity increased by 8-10% compared to n=0.5, the binder contact area decreased by 12-15%, the green pellet drop strength was 4.5 times / p, and the dry pellet compressive strength was 1780 N / p, both indicators did not meet the standards. In Comparative Example 3, there was no grading, the particles were randomly packed, the porosity was the highest, and the green pellet drop strength was only 3.2 times / p. P, with a dry-bulb compressive strength of 1620 N / P, exhibits the worst performance, fully demonstrating the logical chain of insufficient strength caused by the lack of precise gradation and resulting in loose packing. Furthermore, n=0.5 reflects the optimal packing effect of coarse particle skeleton, medium particle filling, and fine particle blocking. Example 1 (n=0.4), although achieving a drop strength of 7.0 times / P, suffers from excessive fine particles leading to microcracks after drying and decreased thermal stability. Example 3 (n=0.6), while achieving a dry-bulb compressive strength of 2805 N / P, requires increasing the sodium silicate content to 5 wt%, resulting in an alkali metal content of 0.34%, close to the safety threshold. Example 2 (n=0.5), without sacrificing any performance indicators, achieves a triple balance of strength, minimum alkali metal content, and stable performance.

[0031] In Comparative Example 4 (without sodium silicate), although starch and glass fiber were retained, the dry ball compressive strength was only 1560 N / P, a decrease of 31.6% compared to Example 2. This was because the strong Fe-O-Si chemical bonds generated by the reaction of sodium silicate with Fe-OH on the sintered return ore surface were lacking, and a three-dimensional network solidification structure could not be formed. At the same time, the alkali metal content decreased to 0.01%, proving that sodium silicate is the main source of alkali metals. Through the optimization of the gradation with n=0.5, this invention only requires 2wt% sodium silicate to meet the standard, avoiding excessive addition of alkali metals.

[0032] In Comparative Example 5 (starch-free), the drop strength of the green pellets was only 3.8 times / p, a 40% decrease compared to Example 2. Although the dry pellet compressive strength still reached 2100 N / p, close to the threshold, it was easily broken during transportation and could not meet the requirements of industrial applications. This is because the viscous colloidal effect of starch can quickly form colloidal bridges at the particle contact points, improving the impact resistance of the green pellets, while the dense packing with n=0.5 further enhances the stability of the colloidal bridges.

[0033] In Comparative Example 6 (without glass fiber), the dry-bulb compressive strength decreased to 1745 N / P, a 22.7% decrease compared to Example 2, demonstrating the indispensable role of the three-dimensional network reinforcement of glass fiber. Glass fiber and sodium silicate synergistically form a reinforced concrete structure, with the active SiO2 reacting with sodium silicate to enhance (SiO4). 4- The concentration enhances the density of the three-dimensional network structure, while the uniform stacking of n=0.5 ensures that the glass fibers do not agglomerate, thus fully exerting the reinforcing effect.

[0034] Experimental data fully verify that the precise gradation of this invention is the foundation for the high strength of the pellets. n=0.5 is the optimal gradation index, which maximizes particle packing density by balancing the proportions of coarse, medium, and fine particles, providing the optimal structural carrier for binder synergy and fiber reinforcement. The three components of the composite binder—sodium silicate, pregelatinized cassava starch, and substandard glass fiber—are indispensable, respectively undertaking the functions of chemical consolidation, green pellet impact resistance, and physical reinforcement. Furthermore, the gradation of n=0.5 further improves the synergistic efficiency. The pellets obtained by this invention simultaneously meet the core indicators of green pellet drop strength ≥5 times / P, dry pellet compressive strength ≥2200N / P, and alkali metal content <0.4%, and achieve solid waste resource utilization and low-carbon production, possessing significant industrial application value.

[0035] The embodiments described above are some, but not all, embodiments of the present invention. The detailed description of the embodiments of the present invention is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

Claims

1. A method for preparing cold-consolidated pellets from sintered return ore based on precise gradation, characterized in that, Includes the following steps: S1. The sintered return ore is screened and graded into five particle size grades: 0-1mm, 1-2mm, 2-3mm, 3-4mm, and 4-5mm. Graded sintered return ore is then blended according to a preset gradation scheme to obtain graded sintered return ore. The preset gradation scheme is determined based on a gradation index n = 0.4-0.6, and the mass percentage of each particle size grade is as follows: when n = 0.4, 0-1mm accounts for 52.53%, 1-2mm accounts for 16.78%, 2-3mm accounts for 12.20%, and 3-4mm accounts for 9.9%. 4% for 0-1mm and 8.54% for 4-5mm; when n=0.5, 44.72% for 0-1mm, 18.52% for 1-2mm, 14.21% for 2-3mm, 11.98% for 3-4mm, and 10.56% for 4-5mm; when n=0.6, 38.07% for 0-1mm, 19.63% for 1-2mm, 15.89% for 2-3mm, 13.87% for 3-4mm, and 12.53% for 4-5mm. S2. The graded sintered return ore is mixed with substandard glass fiber and then ground in a cylindrical drum to obtain a mixture. S3. Add liquid sodium silicate and pregelatinized cassava starch to the mixture, adjust the moisture content, and mix evenly to obtain the pelletizing mixture; S4. Press the briquetting mixture into shape to obtain cold-consolidated green pellets; S5. The green pellets are dried and consolidated using industrial waste gas to obtain cold-consolidated dry pellets.

2. The preparation method according to claim 1, characterized in that, In step S1, the gradation index n is 0.5, and after mixing each particle size grade according to the corresponding mass ratio, the particle packing porosity is ≤35%.

3. The preparation method according to claim 1, characterized in that, The defective glass fiber is waste generated during steel production or glass processing, with an initial length of 0.1-3mm, and a length ≤0.1mm after grinding in step S2.

4. The preparation method according to claim 1, characterized in that, In step S2, the diameter of the cylindrical drum is 10-30cm, the grinding speed is 5-20r / min, and the grinding time is 5-20min.

5. The preparation method according to claim 1, characterized in that, Based on the total mass of the briquetting mixture, the amount of liquid sodium silicate added in step S3 is 2-5 wt%, the amount of pregelatinized cassava starch added is 0.5-2 wt%, and the amount of substandard glass fiber added is 0.5-2 wt%.

6. The preparation method according to claim 1, characterized in that, In step S2, the grinding process employs a stepped grinding technique, specifically comprising two stages: The first stage is pre-dispersion grinding. The rotation speed of the cylindrical drum is controlled at 5-10 r / min and the grinding time is 8-15 min. The particle collision and preliminary shearing of the graded sintered return ore are used to make the substandard glass fiber evenly dispersed among the sintered return ore particles and avoid local agglomeration. The second stage is fine shearing and grinding. The rotation speed of the cylindrical drum is increased to 15-20 r / min, and the grinding time is 3-8 min. The sharp edge of the graded sintered return ore is used to precisely shear the dispersed substandard glass fibers, so that the final length of the glass fibers is uniformly controlled within the required range and tightly attached to the porous structure surface of the graded sintered return ore.

7. The preparation method according to claim 1, characterized in that, In step S4, a roller briquetting machine is used for pressing and forming, with a forming pressure of 20-50 MPa.

8. The preparation method according to claim 1, characterized in that, In step S5, the industrial waste gas is sintering flue gas or sintering ring-cooled flue gas; the drying and consolidation conditions are: flue gas velocity 20000-40000 m / s. 3 / h, temperature 100-200℃, flue gas moisture content 1-5%, consolidation time 1-10h.

9. The preparation method according to claim 1, characterized in that, In step S3, the total moisture content of the briquetting mixture is 3-8 wt%; the modulus of the liquid sodium silicate is 2.5 and the solid content is 50%.

10. A type of sintered return ore cold-consolidated pellet, characterized in that, The pellets are prepared by the preparation method according to any one of claims 1-9, and the green pellet drop strength is ≥5 times / P, the dry pellet compressive strength is ≥2200N / P, and the alkali metal content is <0.4%.

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