Method for preparing high-reactivity blast furnace burden from low-carbon magnetite concentrate and blast furnace burden

Abstract

This invention discloses a method for preparing high-reactivity blast furnace charge from magnetite concentrate with low carbon content, and the blast furnace charge itself, belonging to the field of iron and steel metallurgical technology. The method involves sequentially mixing iron-containing raw materials with an organic-inorganic composite binder, multifunctional additives, and water, followed by high-pressure roller molding and solidification to obtain the finished cold-pressed briquettes. By optimizing the particle size distribution of the raw materials and adding multifunctional additives, this method can significantly improve the strength and reducibility of the cold-pressed briquettes. The process is simple, requires no high-temperature treatment, and has low carbon emissions.

Description

Technical Field

[0001] This invention relates to a blast furnace charge, particularly to a high-reactivity blast furnace charge, and also to a method for preparing a high-reactivity blast furnace charge from magnetite concentrate with low carbon content, belonging to the field of iron and steel metallurgy. Background Technology

[0002] Currently, magnetite concentrate is mainly used to produce oxidized iron ore pellets. After pelletizing, the concentrate needs to be oxidized and roasted at a high temperature of 1200-1300℃, consuming 35-45 kgce per ton of ore and directly generating 120-150 kg of CO2 emissions. This traditional process requires multiple high-temperature heat treatments, resulting in high energy consumption and carbon emissions, which does not meet the current development requirements of carbon reduction, emission reduction, and green transformation in the steel industry. Oxidized iron ore pellets are further used in blast furnace ironmaking or direct reduction processes.

[0003] As a key carbon-emitting industry, the steel industry is accelerating raw material and process innovation aimed at reducing carbon emissions and saving energy. Cold briquetting technology is gaining widespread attention due to its advantages such as eliminating the need for high-temperature roasting, high raw material utilization efficiency, and a streamlined process. Currently, cold briquetting technology is mainly used to process secondary resources in steel plants (such as sintering return ore and dust collector ash). For example, Chinese patent (CN103103310B) discloses a method for preparing vanadium-extracting cold briquetting briquettes. This method involves uniformly mixing dust collector ash, iron oxide scale, and a binder; pelletizing the resulting mixture to obtain wet briquettes; and then drying the wet briquettes. This method effectively utilizes dry dust collector ash to produce vanadium-extracting cold briquetting briquettes, effectively solving the problem of reusing dust collector ash and iron oxide scale in the steel industry. Furthermore, it produces vanadium-extracting cold briquetting briquettes with high mechanical strength and cooling strength without the addition of vanadium-containing iron concentrate powder, thus reducing the cost of vanadium extraction to a certain extent. In existing technologies, research on cold-pressed briquettes using magnetite concentrate as the main raw material is extremely scarce. This is mainly because magnetite concentrate has inherent defects; its dense Fe3O4 crystal structure leads to poor reduction kinetics, resulting in a significant lag in the reduction rate of magnetite cold-pressed briquettes in the blast furnace. This causes problems such as the downward shift of the softening zone and deterioration of permeability, ultimately leading to an increase in coke ratio and hindering the development of large-scale blast furnaces. At the same time, the traditional particle size distribution of magnetite concentrate (-200 mesh ≥ 85%) results in an unreasonable internal structure of the cold-pressed briquettes, making it difficult for the compressive strength of the finished cold-pressed briquettes to meet the requirements of blast furnace burden.

[0004] In summary, existing technologies have not solved the problem of synergistic optimization of strength and reducibility of cold-pressed magnetite concentrate briquettes, making it difficult to use them directly as blast furnace feed. Summary of the Invention

[0005] In view of the above-mentioned defects in the existing field of blast furnace charge preparation from magnetite concentrate, the first objective of this invention is to provide a blast furnace charge with high strength and reducibility and high reactivity.

[0006] The second objective of this invention is to provide a method for preparing high-reactivity blast furnace charge from magnetite concentrate with low carbon content. This method uses magnetite concentrate as the main raw material, and by adding multifunctional additives and optimizing the particle size distribution and composition of the raw material, and by adding an organic-inorganic composite binder for high-pressure roller forming and low-temperature consolidation, the strength and reducibility of cold-pressed magnetite concentrate briquettes can be significantly improved to obtain high-reactivity blast furnace charge. Compared with high-temperature processes such as sintering and pelletizing, this method has the advantages of simple process and low carbon emissions.

[0007] To achieve the above-mentioned technical objectives, the present invention provides a method for preparing high-reactivity blast furnace charge from magnetite concentrate with low carbon content. The method involves mixing iron-containing raw materials with an organic-inorganic composite binder, a multifunctional additive and water in sequence, followed by high-pressure roller molding and solidification to obtain the finished cold-pressed block.

[0008] The iron-containing raw material comprises magnetite concentrate A and magnetite concentrate B;

[0009] The particle size distribution and mass percentage of each particle size fraction of the magnetite concentrate A are +74μm:+45μm~-74μm:-45μm = 25%~45%:25%~45%:30%~50%;

[0010] The particle size distribution and mass percentage of each particle size fraction of the magnetite concentrate B are +74μm: +45μm to -74μm: -45μm = 0% to 20%: 26% to 46%: 54% to 74%;

[0011] The multifunctional additive includes a filler, highly reactive biochar, and low-reactive biochar.

[0012] The filler is a mineral containing magnesium carbonate and / or calcium carbonate;

[0013] The particle size distribution and mass percentage of each particle size of the filler are: +0.7mm~-1.0mm: +0.4mm~-0.7mm:-0.4mm = 10%~30%: 25%~45%: 45%~65%;

[0014] The highly reactive biochar has a fixed carbon content of 55% to 70%, a volatile matter content of 10% to 25%, and an ash content of 20% to 35%.

[0015] The low-reactive biochar has a fixed carbon content of 75% to 85%, a volatile matter content of 5% to 15%, and an ash content of 10% to 20%.

[0016] The particle size distribution involved in this invention is obtained by sieving and grading. The "+" refers to the material that passes through the sieve, and the "-" refers to the material that passes through the sieve.

[0017] The key to the technical solution of this invention, which enables the preparation of high-reactivity blast furnace charge from magnetite, lies in: by controlling the particle size distribution of magnetite concentrate and adding multifunctional additives to further optimize the composition and particle size of the raw material system, and by utilizing the efficient coupling effect between multifunctional additives and binders, the process energy consumption can be reduced, the strength of cold-pressed briquettes can be improved, and their reduction performance can be enhanced, thereby producing iron-containing charge that meets the requirements of blast furnaces in a low-carbon manner.

[0018] Regarding reducing process energy consumption: Compared to agglomeration processes such as sintering and pelletizing, the process of this invention does not require high-temperature processes, which can significantly reduce carbon dioxide and other pollutant emissions. Furthermore, the process of this invention uses magnetite concentrate as the iron-containing raw material, and compared to other processes that use magnetite concentrate to prepare blast furnace burdens, it does not require a high-temperature oxidation process to improve reducibility, resulting in a significant reduction in process energy consumption. In particular, the biochar in the multifunctional additive is a renewable energy source, which can reduce the blast furnace coke ratio, further reducing fossil fuel consumption and carbon emissions.

[0019] Regarding improving the strength of cold-pressed briquettes: On the one hand, by adjusting the ratio of the two types of magnetite concentrate, the particle size distribution of the iron-containing raw materials is made to conform to the Fourier distribution, and the multifunctional additive can also improve the particle size distribution and optimize the structure of the cold-pressed briquettes. Compared with the smaller particle size of the iron-containing raw materials, the multifunctional additive has a larger particle size, which can act as a core particle in the cold-pressed briquettes, making the particle size distribution of the mixture more in line with the Fourier distribution, further improving the overall performance of the cold-pressed briquettes and reducing the amount of binder used. On the other hand, the biochar in the multifunctional additive can couple with the organic binder components in the binder to enhance the compressive strength of the cold-pressed briquettes. For example, the hydroxyl groups in the organic binder and the oxygen-containing functional groups (carboxyl groups, phenolic hydroxyl groups) on the surface of the biochar form a network of hydrogen bonds, which can significantly improve the cold strength.

[0020] Regarding improving the reducibility of cold-pressed briquettes: During blast furnace reduction, the biochar inside the cold-pressed briquettes undergoes both direct and indirect reduction reactions, effectively improving reducibility. High-reactivity biochar has relatively low fixed carbon and relatively high ash and volatile matter content, participating in the reduction reaction at lower temperatures. Low-reactivity biochar has relatively high fixed carbon and relatively low ash content, participating in the reduction reaction at higher temperatures. The combination of these two types of biochar helps maintain high-temperature strength. The staged reduction process of the cold-pressed briquettes avoids concentrated reduction at the same temperature, preventing the generation of large amounts of gas that could damage the briquette structure. Furthermore, the filler in the additives decomposes at high temperatures to generate CO2, which then reacts with the biochar to produce CO, accelerating the reduction process. In addition, both filler decomposition and biochar reduction increase the porosity inside the cold-pressed briquettes, further improving reducibility.

[0021] In summary, when using the process of this invention, magnetite concentrate does not need to go through a process from low temperature to high temperature (high temperature oxidation, about 1300°C) and then back to low temperature (cooling to room temperature), thereby avoiding energy waste and reducing carbon emissions. At the same time, it can also utilize clean and environmentally friendly biomass resources, reduce fossil energy consumption, and further reduce the energy consumption of steel production processes.

[0022] As a preferred embodiment, the iron-containing raw material is composed of magnetite concentrate A and magnetite concentrate B in a mass percentage ratio of 30%~50%:50%~70%. For the roll forming process, the cold-pressed briquettes with the highest strength are obtained when the particle size distribution of the raw materials conforms to the Fourier distribution. Magnetite concentrate A has a relatively large particle size. When its proportion is too low, it cannot play a role in adjusting the particle size distribution, resulting in lower strength of the cold-pressed briquettes. When its proportion is too high, the lack of fine-grained materials in the raw material system will also affect the strength of the cold-pressed briquettes. Therefore, optimizing the particle size of the iron-containing raw material is beneficial for obtaining high-strength cold-pressed briquettes.

[0023] As a preferred embodiment, the multifunctional additive is composed of a filler, highly reactive biochar, and low-reactive biochar in a mass percentage ratio of 45%~60%:5%~20%:35%~50%. The components and proportions of the multifunctional additive of this invention are optimized, and the components have highly efficient coupling functions, which can significantly improve the strength and reducibility of the cold-pressed block. The filler not only improves the particle size distribution of the raw material and enhances the strength of the cold-pressed block, but also decomposes at high temperatures to produce CO2, which can react with biochar to generate CO, enhancing the reduction efficiency. Simultaneously, the decomposition of the filler and the reduction of the biochar both increase the porosity inside the cold-pressed block, further improving its reducibility. The appropriate ratio of highly reactive and low-reactive biochar helps maintain the high-temperature strength of the cold-pressed block and allows for staged reduction during the reduction process, avoiding concentrated reduction at the same temperature, which could generate a large amount of gas inside and damage the cold-pressed block structure. If the proportion of highly reactive biochar is too low, most of the biochar will react at lower temperatures. The reaction rate at low temperatures is slower, reducing the overall reduction efficiency. Conversely, if the proportion of highly reactive biochar is too low, the biochar will react intensively at high temperatures, resulting in excessive gas generation inside the cold-pressed blocks, which can damage the block structure and affect its strength. Furthermore, if the filler ratio is too high, there will be too much coarse material, and the raw material particle size distribution will not conform to the Fourier distribution. Conversely, if the filler ratio is too low, the amount of coarse material will be too small, failing to improve the raw material particle size distribution.

[0024] As a preferred embodiment, the mass of the multifunctional additive accounts for 3% to 8% of the mass of the iron-containing raw material. When the amount of multifunctional additive added is too small, the improvement effect on the strength and reducibility of the cold-pressed block is limited; when the amount of multifunctional additive added is too large, too many pores are generated after decomposition at high temperature, which will affect the strength of the cold-pressed block.

[0025] As a preferred embodiment, the filler includes at least one selected from calcite, limestone, dolomite, and magnesite. The preferred fillers are all carbonate minerals, which readily decompose at high temperatures to produce carbon dioxide and simultaneously generate alkaline oxides that can regulate the alkalinity of the blast furnace charge.

[0026] As a preferred embodiment, the particle size of the highly reactive biochar and the low reactive biochar shall meet the requirement that the mass percentage of the -1mm particle size is not less than 90%.

[0027] The difference between the high-reactivity and low-reactivity biochar of this invention lies in their fixed carbon, volatile matter, and ash content, both of which can be selected from one or more of wood charcoal, straw charcoal, bamboo charcoal, rice husk charcoal, etc. The particle size distribution of the biochar selected in this invention must be matched with the cold-pressing process. If the +1mm portion of the biochar accounts for too high a proportion, it will be difficult to distribute it evenly, affecting the structure of the cold-pressed blocks.

[0028] As a preferred embodiment, the organic-inorganic composite adhesive is composed of organic adhesive and inorganic adhesive in a mass percentage ratio of 5%~20%:80%~95%.

[0029] As a preferred embodiment, the organic-inorganic composite binder accounts for 2% to 6% of the mass of the iron-containing raw material.

[0030] The dosage and composition of the organic-inorganic composite binder of this invention are optimized based on comprehensive considerations such as cost, bonding effect, and impurity content. The advantages of the organic binder component are that it can significantly improve the green pellet performance and has low impurity content; the disadvantages are that it is relatively expensive and has poor high-temperature resistance, easily decomposing at high temperatures. The advantages of the inorganic binder component are that it is inexpensive and does not decompose at high temperatures, providing high-temperature strength for the cold-pressed block; however, the disadvantage is that it has a higher impurity content. Therefore, throughout the entire process of cold pressing from room temperature molding to high-temperature reduction, by controlling the ratio of organic and inorganic binders, functional complementarity can be achieved through the synergistic effect of chemical bonds. Furthermore, regarding the dosage of the composite binder, if the dosage is too low, the strength of the cold-pressed block will be too low to meet the requirements; if the dosage is too high, the cost will be too high.

[0031] As a preferred embodiment, the organic binder includes at least one of sodium humate, sodium carboxymethyl starch, sodium carboxymethyl cellulose, gelatinized starch, epoxy resin, and polyacrylamide.

[0032] As a preferred embodiment, the inorganic binder includes at least one of sodium silicate, sodium silicate, potassium silicate, silica sol, bentonite, and clay.

[0033] The organic and inorganic binders preferred in this invention are common types of binders in the prior art and are commercial products.

[0034] As a preferred embodiment, the linear pressure during the high-pressure roller forming process is 0.5t / mm to 1.3t / mm. Too high a forming pressure or too low a forming pressure is unsuitable; too high a pressure will cause large particles in the additives to break, while too low a pressure will result in insufficient forming, both of which will affect the strength of the cold-pressed block.

[0035] As a preferred option, the moisture content of the wet briquettes obtained by high-pressure rolling is 4wt.%~9wt.%, and the shape is oblate, with dimensions of: major axis × minor axis × height = 14~32mm × 12~24mm × 10~16mm. The forming moisture content should not be too low or too high. If it is too low, the binder will not be able to function effectively; if it is too high, the binder will be lost during high-pressure forming and will also have a lubricating effect, inhibiting the mechanical wedging effect between raw material particles, both of which will affect the strength of the cold-pressed briquettes. The size of the cold-pressed briquettes should not be too large or too small. If they are too large, the reduction performance will be poor; if they are too small, the permeability of the blast furnace burden will be affected.

[0036] As a preferred embodiment, the consolidation is performed using microwave or hot air heating at a temperature of 100℃ to 250℃ for a time of 10 to 40 minutes. The consolidation temperature should not be too low or too high. Too low a temperature results in low consolidation efficiency, while too high a temperature leads to excessive internal air pressure in the cold-pressed block during consolidation, which can damage the structure and affect strength. The consolidation time should also not be too short or too long. Too short a time results in incomplete consolidation, while too long a time increases process energy consumption.

[0037] The present invention also provides a blast furnace charge obtained by the aforementioned preparation method. The resulting blast furnace charge exhibits high reactivity.

[0038] The method for preparing high-reactivity blast furnace charge from magnetite concentrate using low-carbon methods provided by this invention includes the following specific steps:

[0039] (1) Magnetite concentrate A and magnetite concentrate B are mixed in a mass percentage ratio of 30%~50%:50%~70% to obtain iron-containing raw materials. Additives are then added in a proportion of 3%~8% of the mass of the iron-containing raw materials to obtain mixture 1. Among them, the particle size distribution and mass percentage of each particle size of magnetite concentrate A are +74μm:+45μm~-74μm:-45μm=25%~45%:25%~45%:30%~50%; the particle size distribution and mass percentage of each particle size of magnetite concentrate B are +74μm:+45μm~-74μm:-45μm=0%~20%:26%~46%:54%~74%. The additives are composed of fillers and highly reactive biochar and low reactive biochar in a mass percentage ratio of 45%~60%:5%~20%:35%~50%. The filler includes one or more of calcite, limestone, dolomite, and magnesite. The particle size distribution and mass percentage of each particle size fraction of the filler are +0.7 mm to -1 mm: +0.4 mm to -0.7 mm: -0.4 mm = 10% to 30%: 25% to 45%: 45% to 65%. Both highly reactive and low-reactive biochar include one or more of charcoal, straw charcoal, bamboo charcoal, and rice husk charcoal, with the -1 mm fraction accounting for more than 90% of the mass. High-reactive biochar has a fixed carbon content of 55% to 70%, a volatile matter content of 10% to 25%, and an ash content of 20% to 35%. Low-reactive biochar has a fixed carbon content of 75% to 85%, a volatile matter content of 5% to 15%, and an ash content of 10% to 20%.

[0040] (2) Mix mixture 1 thoroughly with the composite binder and water in a certain proportion to obtain mixture 2. The composite binder accounts for 2% to 6% of the mass of the iron-containing raw materials, and the water content of mixture 2 is 4 wt.% to 9 wt.%. The composite binder consists of organic binder and inorganic binder in a mass percentage ratio of 5% to 20% and 80% to 95%. The organic binder includes one or more of sodium humate, sodium carboxymethyl starch, sodium carboxymethyl cellulose, gelatinized starch, epoxy resin, and polyacrylamide. The inorganic binder includes one or more of sodium silicate, sodium silicate, potassium silicate, silica sol, bentonite, and clay.

[0041] (3) The mixture 2 is subjected to high-pressure roller molding, and the molded material is screened. The undersize material is returned to step (2) for remolding, and the oversize material is the green ball. The molding line pressure is 0.5t / mm~1.3t / mm. The green ball is oblate, and the size is: long axis × short axis × height = 14~32mm × 12~24mm × 10~16mm. The obtained green balls are solidified at low temperature by microwave or hot air to obtain cold-pressed blocks. The solidification temperature is 100℃~250℃, and the solidification time is 10min~40min. The compressive strength of the cold-pressed block is not less than 2500N / P, the drum index (+6.3mm) is not less than 80%, the wear resistance index is not higher than 8%, the low-temperature reduction pulverization index (+3.15mm) is not less than 70%, and the reduction degree is not less than 75%.

[0042] Compared with the prior art, the technical solution of the present invention brings the following beneficial effects:

[0043] (1) This invention uses a cold briquetting process to prepare blast furnace burden, which is simple and has a short production flow. Compared with briquetting processes such as sintering and pelletizing, the process of this invention does not require a high-temperature process, which can significantly reduce carbon dioxide and other pollutant emissions. Moreover, this invention uses magnetite concentrate as an iron-containing raw material. Compared with other processes that use magnetite concentrate to prepare blast furnace burden, it does not require a high-temperature oxidation process to improve reducibility, which significantly reduces energy consumption. Furthermore, the biochar in the multifunctional additives used is a renewable energy source, which can reduce the blast furnace coke ratio and further reduce fossil energy consumption and carbon emissions.

[0044] (2) This invention can effectively improve the performance of cold-pressed briquettes by controlling the particle size distribution of raw materials. On the one hand, by adjusting the ratio of the two magnetite concentrates, the particle size distribution of the iron-containing raw materials conforms to the Fourier distribution. On the other hand, additives can also improve the particle size distribution and optimize the structure of cold-pressed briquettes. Compared with the iron-containing raw materials with smaller particle size, the additives have larger particle size and can act as core particles in cold-pressed briquettes, making the particle size distribution of the mixture more conform to the Fourier distribution, further improving the overall performance of cold-pressed briquettes and reducing the amount of binder used.

[0045] (3) This invention addresses the poor reducibility of cold-pressed magnetite briquettes by introducing special multifunctional additives to significantly improve their reducibility. During blast furnace reduction, the biochar inside the cold-pressed briquettes undergoes both direct and indirect reduction reactions, effectively improving reducibility. High-reactivity biochar has relatively low fixed carbon and relatively high ash and volatile matter content, participating in reduction reactions at lower temperatures. Low-reactivity biochar has relatively high fixed carbon and relatively low ash content, participating in reduction reactions at higher temperatures. The combination of these two types of biochar helps maintain their high-temperature strength. The cold-pressed briquettes are reduced in stages during the reduction process, avoiding concentrated reduction at the same temperature, which would generate a large amount of gas and damage the briquette structure. Furthermore, the filler in the additive decomposes at high temperatures to generate CO2, which then reacts with the biochar to generate CO, accelerating the reduction process. In addition, both filler decomposition and biochar reduction increase the porosity inside the cold-pressed briquettes, further improving reducibility.

[0046] (4) This invention employs an organic-inorganic composite binder to achieve functional complementarity between different components, and the binder and multifunctional additives can be efficiently coupled. Throughout the entire process of cold pressing from room temperature molding to high temperature reduction, the organic binder and inorganic binder achieve functional complementarity through the relay synergy of chemical bonds. In the low-temperature stage (<300℃), the long molecular chains of the organic binder bridge the magnetite particles through a hydrogen bond network and synergistically form a three-dimensional gel structure with the inorganic binder, giving the cold pressing block initial high strength. When entering the high-temperature stage (>800℃), the inorganic binder will not decompose, and the residual strength of the cold pressing block remains high. In addition, the biochar in the additives can couple with the organic components in the binder to enhance the compressive strength of the cold pressing block. The hydroxyl groups in the organic binder and the oxygen-containing functional groups (carboxyl groups, phenolic hydroxyl groups) on the surface of the biochar form a connection through a hydrogen bond network, which can significantly improve the cold strength. Detailed Implementation

[0047] To facilitate understanding of the present invention, the present invention will be described more fully and in detail below with reference to specific embodiments, but the scope of protection of the present invention is not limited to the following specific embodiments.

[0048] Unless otherwise defined, all technical terms used herein have the same meaning as commonly understood by those skilled in the art. The patent terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the scope of the invention.

[0049] Unless otherwise specified, the various reagents and raw materials used in this invention are commercially available products or products that can be prepared by known methods.

[0050] The relevant standards for performance testing of cold-pressed blocks in the following embodiments are as follows: compressive strength test standard is GB / T 14201-2018, ISO 4700:2015; drum and abrasion resistance index test standard is GB / T 24531-2009, ISO 3271:2007; low temperature reduction pulverization index test standard is GB / T 31923-2015; reduction performance test standard is GB / T 13241-2017.

[0051] Example 1

[0052] Magnetite concentrate A and magnetite concentrate B are mixed in a mass percentage ratio of 35%:65% to obtain iron-containing raw materials. A multifunctional additive is then added at a mass percentage of 4.0% of the iron-containing raw materials to obtain mixture 1. The particle size distribution and mass percentage of each particle size fraction of magnetite concentrate A are +74μm:+45μm ~74μm:-45μm = 35%:35%:30%; the particle size distribution and mass percentage of each particle size fraction of magnetite concentrate B are +74μm:+45~-74μm:-45μm = 15%:30%:55%. The multifunctional additive is composed of filler and highly reactive biochar and low-reactive biochar in a mass percentage ratio of 55%:10%:35%. The filler is limestone, and its particle size distribution and mass percentage of each particle size are +0.7mm~-1mm:+0.4mm~-0.7mm:-0.4mm = 20%:35%:45%. The highly reactive biochar and the low-reactive biochar are charcoal, with the -1mm portion accounting for 95% of their mass. The highly reactive biochar has a fixed carbon content of 65%, a volatile matter content of 15%, and an ash content of 20%. The low-reactive biochar has a fixed carbon content of 80%, a volatile matter content of 10%, and an ash content of 10%. Mixture 1 is thoroughly mixed with the composite binder and water in a certain proportion to obtain mixture 2. The composite binder accounts for 4% of the iron-containing raw material mass, and the water content of mixture 2 is 5.0 wt.%. The composite binder consists of an organic binder and an inorganic binder in a mass percentage ratio of 10%:90%. The organic binder is sodium carboxymethyl cellulose. The inorganic binder consists of 70 wt% sodium silicate and 30 wt% bentonite. Mixture 2 is subjected to high-pressure roller molding, and the molded material is sieved; the material remaining on the sieve is the green pellet. The molding line pressure is 1.0 t / mm. The green pellets are oblate in shape, with dimensions of: major axis × minor axis × height = 22 mm × 17 mm × 14 mm. The resulting green pellets are then subjected to low-temperature consolidation with hot air to obtain cold-pressed blocks. The consolidation temperature is 150℃, and the consolidation time is 25 min. The compressive strength of the cold-pressed blocks is 2706 N / P, the drum index (+6.3 mm) is 90%, the abrasion resistance index is 7%, the low-temperature reduction pulverization index (+3.15 mm) is 91%, and the reduction degree is 77%.

[0053] Example 2

[0054] Magnetite concentrate A and magnetite concentrate B are mixed in a mass percentage ratio of 45%:55% to obtain the iron-containing raw material. A multifunctional additive is then added at a mass percentage of 6% of the iron-containing raw material to obtain mixture 1. The particle size distribution and mass percentage of each particle size fraction of magnetite concentrate A are +74μm:+45μm ~-74μm:-45μm = 40%:30%:30%; the particle size distribution and mass percentage of each particle size fraction of magnetite concentrate B are +74μm:+45μm ~-74μm:-45μm = 10%:30%:60%. The multifunctional additive is composed of filler and highly reactive biochar and low-reactive biochar in a mass percentage ratio of 60%:5%:35%. The filler is magnesite, and its particle size distribution and mass percentage of each particle size are +0.7mm~-1mm:+0.4mm~-0.7mm:-0.4mm = 10%:25%:65%. High-reactivity biochar and low-reactivity biochar are straw char, with the -1mm portion accounting for 90% of their mass. The high-reactivity biochar has a fixed carbon content of 60%, a volatile matter content of 20%, and an ash content of 20%. The low-reactivity biochar has a fixed carbon content of 85%, a volatile matter content of 5%, and an ash content of 10%. Mixture 1 is thoroughly mixed with the composite binder and water in a certain proportion to obtain mixture 2. The composite binder accounts for 5% of the iron-containing raw material mass, and the water content of mixture 2 is 5.5 wt.%. The composite binder consists of organic binder and inorganic binder in a mass percentage ratio of 15%:85%. The organic binder consists of 20 wt% sodium humate, 10 wt% sodium carboxymethyl cellulose, and 70 wt% gelatinized starch. The inorganic binder consists of 85 wt% sodium silicate and 15 wt% clay. Mixture 2 is subjected to high-pressure roller molding, and the molded material is sieved; the material remaining on the sieve is the green pellet. The molding line pressure is 0.9 t / mm. The green pellets are oblate, with dimensions of: major axis × minor axis × height = 15 mm × 13 mm × 11 mm. The obtained green pellets are then subjected to low-temperature consolidation with hot air to obtain cold-pressed blocks. The consolidation temperature is 250℃, and the consolidation time is 18 min. The compressive strength of the cold-pressed blocks is 2810 N / P, the drum index (+6.3 mm) is 91%, the abrasion resistance index is 5%, the low-temperature reduction pulverization index (+3.15 mm) is 88%, and the reduction degree is 79%.

[0055] Example 3

[0056] Magnetite concentrate A and magnetite concentrate B are mixed in a 50%:50% mass ratio to obtain the iron-containing raw material. A multifunctional additive is then added at 5% of the mass of the iron-containing raw material to obtain mixture 1. The particle size distribution and mass percentage of each particle size fraction of magnetite concentrate A are +74μm:+45μm ~-74μm:-45μm = 30%:25%:45%; the particle size distribution and mass percentage of each particle size fraction of magnetite concentrate B are +74μm:-45μm ~-74μm:-45μm = 0%:30%:70%. The multifunctional additive consists of a filler and highly reactive biochar and low-reactive biochar in a 45%:10%:45% mass ratio. The filler consists of 50 wt% limestone and 50 wt% magnesite. The particle size distribution and mass percentage of each particle size fraction are +0.7 mm to -1 mm: +0.4 mm to -0.7 mm: -0.4 mm = 10%:30%:60%. The highly reactive and low-reactive biochar are bamboo charcoal, with the -1 mm portion accounting for 96% of the mass. The highly reactive biochar has a fixed carbon content of 70%, a volatile matter content of 10%, and an ash content of 20%. The low-reactive biochar has a fixed carbon content of 80%, a volatile matter content of 5%, and an ash content of 15%. Mixture 1 is thoroughly mixed with the composite binder and water in a certain proportion to obtain mixture 2. The composite binder accounts for 4% of the iron-containing raw material mass, and the water content of mixture 2 is 4 wt.%. The composite binder consists of organic binder and inorganic binder in a mass percentage ratio of 20%:80%. The organic binder consists of 30 wt% sodium carboxymethyl starch, 60 wt% sodium carboxymethyl cellulose, and 10 wt% epoxy resin. The inorganic binder consists of 10 wt% sodium silicate, 40 wt% sodium silicate, 30 wt% silica sol, and 20 wt% bentonite. Mixture 2 is subjected to high-pressure roller molding, and the molded material is sieved; the material remaining on the sieve is the green pellet. The molding line pressure is 1.1 t / mm. The green pellets are oblate, with dimensions of: major axis × minor axis × height = 26 mm × 20 mm × 15 mm. The obtained green pellets are then subjected to low-temperature microwave consolidation to obtain cold-pressed blocks. The consolidation temperature is 100℃, and the consolidation time is 20 min. The compressive strength of the cold-pressed blocks is 2607 N / P, the drum index (+6.3 mm) is 87%, the abrasion resistance index is 6.5%, the low-temperature reduction pulverization index (+3.15 mm) is 90%, and the reduction degree is 76%.

[0057] Comparative Example 1

[0058] The only difference compared to Example 1 is that no filler (limestone) was added in the magnetite concentrate A and the multifunctional additive. The multifunctional additive accounted for 1.8% of the mass of the iron-containing raw material. The multifunctional additive was composed of high-reactivity biochar and low-reactivity biochar in a mass percentage ratio of 22.22%:77.78%. Specifically, the strength of the cold-pressed briquettes was not improved by optimizing the particle size composition.

[0059] The cold-pressed block has a compressive strength of 2251 N / P, a drum index (+6.3 mm) of 83%, an abrasion resistance index of 10%, a low-temperature reduction pulverization index (+3.15 mm) of 80%, and a reduction degree of 73%.

[0060] Comparative Example 2

[0061] The only difference compared to Example 2 is that no multifunctional additives were added, specifically, the strength and reducibility of the cold-pressed block were improved by adjusting the particle size composition and components of the raw materials.

[0062] The cold-pressed block has a compressive strength of 2087 N / P, a drum index (+6.3 mm) of 80%, an abrasion resistance index of 8%, a low-temperature reduction pulverization index (+3.15 mm) of 88%, and a reduction degree of 67%.

[0063] Comparative Example 3

[0064] The only difference compared to Example 3 is that no organic binder was added. That is, the composite binder is composed of a single inorganic binder, which accounts for 3.2% of the mass of the iron-containing raw material. Specifically, the strength of the cold-pressed block was not improved by adjusting the composition of the composite binder and by not achieving functional coupling with the inorganic binder and biochar.

[0065] The cold-pressed block has a compressive strength of 2115 N / P, a drum index (+6.3 mm) of 81%, an abrasion resistance index of 11%, a low-temperature reduction pulverization index (+3.15 mm) of 85%, and a reduction degree of 80%.

Claims

1. A method for preparing high-reactivity blast furnace charge from magnetite concentrate with low carbon content, characterized in that: Iron-containing raw materials are mixed with organic-inorganic composite binder, multifunctional additives and water in sequence, followed by high-pressure roller molding and solidification to obtain the finished cold-pressed block; The iron-containing raw material is composed of magnetite concentrate A and magnetite concentrate B in a mass percentage ratio of 30%~50%:50%~70%; The particle size distribution and mass percentage of each particle size fraction of the magnetite concentrate A are +74μm: +45μm to -74μm: -45μm = 25% to 45%: 25% to 45%: 30% to 50%; The particle size distribution and mass percentage of each particle size fraction of the magnetite concentrate B are +74μm: +45μm to -74μm: -45μm = 0% to 20%: 26% to 46%: 54% to 74%; The multifunctional additive is composed of filler, highly reactive biochar and low reactive biochar in a mass percentage ratio of 45%~60%: 5%~20%: 35%~50%; The filler is a mineral containing magnesium carbonate and / or calcium carbonate; The particle size distribution and mass percentage of each particle size of the filler are +0.7mm~-1.0mm: +0.4mm~-0.7mm:-0.4mm = 10%~30%: 25%~45%: 45%~65%; The highly reactive biochar has a fixed carbon content of 55% to 70%, a volatile matter content of 10% to 25%, and an ash content of 20% to 35%. The low-reactive biochar has a fixed carbon content of 75% to 85%, a volatile matter content of 5% to 15%, and an ash content of 10% to 20%. The mass of the multifunctional additive accounts for 3% to 8% of the mass of the iron-containing raw material.

2. The method for preparing high-reactivity blast furnace charge from magnetite concentrate with low carbon content according to claim 1, characterized in that: The filler includes at least one of calcite, limestone, dolomite, and magnesite.

3. The method for preparing high-reactivity blast furnace charge from magnetite concentrate with low carbon content according to claim 1, characterized in that: The high-reactivity biochar and the low-reactivity biochar have a particle size distribution that satisfies the requirement that the mass percentage of -1mm particle size is not less than 90%.

4. A method for preparing high-reactivity blast furnace charge from magnetite concentrate with low carbon content according to any one of claims 1 to 3, characterized in that: The organic-inorganic composite adhesive is composed of organic adhesive and inorganic adhesive in a mass percentage ratio of 5%~20%:80%~95%; And / or, The organic-inorganic composite binder accounts for 2% to 6% of the mass of the iron-containing raw material; And / or, The organic binder includes at least one of sodium humate, sodium carboxymethyl starch, sodium carboxymethyl cellulose, gelatinized starch, epoxy resin, and polyacrylamide. And / or, The inorganic binder includes at least one of sodium silicate, sodium silicate, potassium silicate, silica sol, bentonite, and clay.

5. A method for preparing high-reactivity blast furnace charge from magnetite concentrate with low carbon content according to any one of claims 1 to 3, characterized in that: The linear pressure during the high-pressure roller forming process is 0.5t / mm to 1.3t / mm.

6. A method for preparing high-reactivity blast furnace charge from magnetite concentrate with low carbon content according to any one of claims 1 to 3, characterized in that: The consolidation is performed using microwave or hot air heating, with a consolidation temperature of 100℃~250℃ and a consolidation time of 10min~40min.

7. A blast furnace charge, characterized in that: Obtained by the method described in any one of claims 1 to 6.