Method for preparing iron-containing burden with high proportion of specularite concentrate and near zero carbon

Abstract

The application discloses a kind of high proportion specular iron ore concentrate near zero carbon preparation iron-containing furnace charge method, belong to steel metallurgy technical field, the method is carried out surface activation pretreatment to specular iron ore concentrate and is mixed evenly with iron-containing carbon-containing dust and magnetite concentrate, further mixed with organic-inorganic composite binder and water and forms mixed material;The mixed material is formed by pressing, low-temperature consolidation, and cold briquetting is obtained;The method can prepare high proportion specular iron ore concentrate into cold briquetting with high strength, good reduction performance, low reduction expansion, compared with the existing specular iron ore concentrate high-temperature briquetting process, the process flow is short, the preparation temperature is low (<300 DEG C), and the carbon emission is extremely low, while large-scale processing specular iron ore, iron-containing carbon-containing solid waste resources can also be treated simultaneously, to provide a new technical route for green and low-carbon transformation of steel industry.

Description

Technical Field

[0001] This invention relates to a method for preparing iron-containing furnace charge, and particularly to a method for preparing iron-containing furnace charge by room temperature forming and low temperature consolidation of high proportion specular iron concentrate, belonging to the field of iron and steel metallurgy. Background Technology

[0002] With the rapid development of the steel industry, steel companies are increasingly reliant on imported iron ore. In recent years, high-quality iron ore resources with high iron content, good granulation performance, and excellent high-temperature reactivity have become increasingly scarce. The coexistence of tight supply and rising costs of high-quality furnace feed has put pressure on optimizing the structure of blast furnace feed and ensuring stable production.

[0003] Specularite, a subspecies of hematite, is relatively abundant, and specularite concentrate typically exhibits high iron content, high iron oxidation degree, and relatively low price, making it a potential source of high-grade furnace feed. However, specularite concentrate generally possesses mineralogical characteristics such as well-formed crystals, dense structure, relatively smooth surface, and low specific surface area, resulting in poor hydrophilicity and pelletizing properties. It is not easy for it to form pellets on its own or adhere to the surface of other mineral particles. At the same time, its high-temperature reactivity is weak, making it difficult to generate a low-melting-point liquid phase or achieve high-temperature crystal interconnection. This makes it prone to causing a decrease in product strength and metallurgical properties during traditional high-temperature agglomeration processes such as sintering and pelletizing, often accompanied by the cost of increasing roasting / sintering temperatures or increasing the amount of binder. It belongs to the traditional difficult-to-process and difficult-to-utilize iron ore resources, and therefore the proportion of specularite concentrate added in industrial applications has long been limited.

[0004] Currently, the mainstream route for specular hematite concentrate to enter the blast furnace burden system is still mainly through high-temperature agglomeration processes such as sintering or roasting pellets, with a relatively low proportion and small processing scale. These routes typically require fuel heating (such as sintering solid fuel, pellet roasting gas, etc.), resulting in relatively long processes, high energy consumption, and significant CO2 emissions. Traditional high-temperature agglomeration routes face even greater pressure in terms of energy consumption and carbon emissions when consuming specular hematite concentrate on a large scale. For example, a Chinese patent application (application publication number: CN101570821A) discloses a sintering method for high-proportion specular hematite concentrate. After pretreatment by high-pressure roller milling, the specular hematite concentrate is pelletized. Other iron-containing raw materials, fluxes, coke powder, etc., are mixed and granulated according to traditional processes. Then, the green pellets and granulated mixture are mixed evenly, spread on a sintering machine, ignited, and sintered to prepare blast furnace burden composed of a mixture of high-basicity sinter, acidic pellets, and sintered pellet composite ore. The utilization rate of specular hematite in the iron-containing raw materials of this method is only 30-50%, and it requires fuel heating, with a relatively long process, high energy consumption, and significant CO2 emissions.

[0005] In the existing technology, there are no reports of using specular hematite to prepare cold-pressed briquettes. This is mainly because: on the one hand, specular hematite has a dense crystal structure and low porosity, and the cold-pressed briquettes prepared using specular hematite concentrate have low strength and poor reduction performance; on the other hand, the chemical composition of specular hematite is mainly Fe2O3, which will still be converted into Fe3O4 during the reduction process, resulting in a crystal transformation and severe expansion.

[0006] In summary, existing processing methods for specular hematite concentrate mainly rely on high-temperature agglomeration routes such as sintering or pelletizing, which still generally suffer from common problems such as long process length, high temperature, high energy consumption and carbon emissions. Cold briquetting processes also have the disadvantage of poor metallurgical performance. Summary of the Invention

[0007] The existing technologies for processing specular hematite concentrate mainly involve high-temperature agglomeration routes such as sintering or pelletizing, which generally suffer from common problems such as long process lengths, high temperatures, high energy consumption, and high carbon emissions. The purpose of this invention is to provide a method for preparing iron-containing furnace charge with a high proportion of specular hematite concentrate and near-zero carbon content. This method combines specular hematite concentrate with an appropriate amount of magnetite concentrate and iron-containing carbon dust to prepare cold-pressed briquettes, which can effectively improve the reduction performance of the cold-pressed specular hematite concentrate briquettes and inhibit their reduction expansion. At the same time, by performing surface activation treatment on specular hematite and optimizing the particle size distribution of the iron-containing mixture, the strength of the cold-pressed specular hematite concentrate briquettes can be improved, making them meet the process application requirements of blast furnace reduction, gas-based vertical shaft furnace direct reduction, and coal-based rotary kiln direct reduction.

[0008] This invention provides a method for preparing iron-containing furnace charge from specular hematite concentrate through compression molding and low-temperature consolidation. Compared with traditional specular hematite processing processes (sintering process, pelletizing process), this method has the advantages of a shorter process flow, lower preparation temperature, and near-zero carbon emissions. It can also co-process solid waste resources such as iron-containing and carbon-containing dust while processing specular hematite concentrate on a large scale.

[0009] To achieve the above-mentioned technical objectives, this invention provides a method for preparing iron-containing furnace charge from high-proportion specular hematite concentrate with near-zero carbon content. The method involves pre-treating the specular hematite concentrate with surface activation to obtain activated specular hematite concentrate; mixing the activated specular hematite concentrate with iron-containing carbon dust and magnetite concentrate to obtain iron-containing raw materials; mixing the iron-containing raw materials with an organic-inorganic composite binder and water to form a mixture; pressing the mixture into wet lumps; and solidifying the wet lumps to obtain cold-pressed blocks.

[0010] in,

[0011] The mass percentage composition of activated specular hematite concentrate, iron-containing carbon dust, and magnetite concentrate is: 68%~84% : 2%~10% : 14%~22%;

[0012] The activated specular hematite concentrate has the following particle size distribution: -74μm by mass not less than 20%, +0.25mm by mass not more than 40%, and a specific surface area not less than 1000 cm². 2 ·g -1 ;

[0013] The particle size of iron- and carbon-containing dust shall meet the following requirements: the mass proportion of -74μm shall not be less than 60%, the mass proportion of +0.2mm shall not be more than 25%, and the fixed carbon mass content shall not be less than 1%.

[0014] The magnetite concentrate has a particle size distribution that meets the following requirements: -74μm mass ratio not less than 70%, +0.1mm mass ratio not more than 20%, and Fe3O4 phase mass content not less than 80%.

[0015] This invention primarily addresses the technical problems of low strength, poor reducibility, and severe reduction expansion in cold-pressed briquettes prepared from specular hematite concentrate. As a difficult-to-process iron ore resource, specular hematite concentrate is typically processed using conventional high-temperature briquetting methods such as sintering or pelletizing. This invention successfully produces cold-pressed briquettes from specular hematite concentrate, enabling large-scale processing of this resource and offering significant near-zero carbon advantages: Firstly, the lower temperature of the cold-pressing process avoids the large fuel consumption and emissions associated with high-temperature processes like sintering, significantly reducing energy consumption and CO2 emissions. Hot air consolidation can directly utilize existing low-temperature waste gas from steel plants as a heat source, virtually eliminating the need for additional fossil fuel consumption and reducing direct carbon emissions during the consolidation stage to extremely low levels. Secondly, the high proportion of specular hematite concentrate in the cold-pressing process allows for large-scale processing compared to conventional sintering and pelletizing processes. Furthermore, by incorporating iron- and carbon-containing dust and other solid waste, iron resource recovery and carbon resource utilization can be achieved, reducing solid waste accumulation and resulting in significant environmental benefits. Furthermore, the cold-pressed briquettes prepared by this invention have a wide range of applications. They can be used as iron-containing furnace charge in blast furnace reduction processes, as well as in various reduction processes such as direct reduction in gas-based vertical shaft furnaces and direct reduction in coal-based rotary kilns.

[0016] This invention addresses the mineral and compositional characteristics of specular hematite, such as its dense crystals, high density, large particle size, and poor reducibility. Furthermore, specular hematite concentrate's main component is Fe2O3, which undergoes a crystal transformation during reduction to Fe3O4, leading to severe reduction expansion. Consequently, cold-pressed briquettes prepared using specular hematite concentrate exhibit low strength, poor reducibility, and severe expansion, failing to meet furnace charge performance requirements. The key improvements of this invention are: firstly, optimizing the cold-pressed briquette composition. This involves adding appropriate amounts of carbon-containing iron-containing dust and magnetite concentrate to a high proportion of specular hematite concentrate, improving the reducibility and expansion properties of the cold-pressed briquettes. The carbon-containing dust itself contains a certain amount of fixed carbon, which accelerates the reduction reaction from within during the reduction process, thus improving the reducibility of the cold-pressed briquettes. Magnetite concentrate, whose main component is Fe3O4, does not require the reduction of Fe2O3 to Fe3O4 during the reduction process; therefore, adding an appropriate proportion of magnetite concentrate can alleviate the expansion phenomenon of the cold-pressed briquettes to some extent. Secondly, optimizing the particle size distribution of the raw materials. By strictly controlling the particle size distribution of activated specular hematite concentrate and iron- and carbon-containing dust and magnetite concentrate, an appropriate proportion of finer iron- and carbon-containing dust and magnetite concentrate is embedded in the coarser, harder specular hematite concentrate to achieve optimal particle size distribution, thereby improving the strength of cold-pressed briquettes. Thirdly, the surface activation treatment of specular hematite concentrate involves mechanically breaking and refining the particle size. During this process, numerous sharp edges are generated, transforming the relatively smooth and dense particle morphology into a more irregular and coarser one. This strengthens the mechanical interlocking during the pressing process, increasing the strength of the cold-pressed briquettes. Simultaneously, mechanical energy accumulates in the specular hematite lattice, causing dislocations, vacancies, and grain boundary distortions, forming high-energy new surfaces and a larger specific surface area. This significantly enhances surface reactivity, providing a rapid channel for the diffusion of reducing gases and the renewal of reaction interfaces, reducing the apparent resistance to solid-phase diffusion and interfacial reactions, and thus improving the reduction performance of the cold-pressed briquettes.

[0017] The composition ratio of activated specular hematite concentrate, iron- and carbon-containing dust, and magnetite concentrate in this invention is optimized. If the proportion of specular hematite concentrate is too high, the reducibility and reductive expansion properties of the prepared cold-pressed briquettes are poor. If the proportion of specular hematite concentrate is too low, the purpose of large-scale processing of specular hematite concentrate cannot be achieved. If the amount of iron- and carbon-containing dust added is too small, the effect on improving the reducibility of the cold-pressed briquettes is limited. If the amount of iron- and carbon-containing dust added is too large, it will increase the amount of fine-grained material in the cold-pressed briquette mixture, affecting the particle size distribution. If the amount of magnetite concentrate added is too small, the effect on improving the reductive expansion properties is limited. If the amount of magnetite concentrate added is too large, it will deteriorate the reducibility of the cold-pressed briquettes.

[0018] As a preferred embodiment, the surface activation pretreatment employs at least one of high-pressure roller milling, wet milling, and ball milling. The specular hematite concentrate is surface activated and pretreated using methods such as high-pressure roller milling, wet milling, or ball milling to ensure that the particle size distribution meets the following requirements: -74μm particle size accounts for no less than 20% by mass, +0.25mm particle size accounts for no more than 40% by mass, and the specific surface area is no less than 1000 cm². 2 ·g -1 Preferred high-pressure roller milling conditions: pressure 5~15MPa, roller speed 15~25r / min. Preferred lubrication milling conditions: material filling rate 40~60%, speed 10~20r / min. Preferred ball milling conditions: material filling rate 20~40%, ball-to-material mass ratio 1:1~2, speed 10~25r / min. Under high-pressure roller milling, lubrication milling, and ball milling, specular hematite concentrate can be selectively crushed, resulting in finer particle size and numerous sharp edges. The particle morphology changes from relatively smooth and dense to more irregular and coarser, thereby strengthening the mechanical interlocking effect during the pressing process, improving the strength of the cold-pressed blocks. Simultaneously, through the accumulation of mechanical energy in the specular hematite concentrate lattice, dislocations, vacancies, and grain boundary distortions occur, forming high-energy new surfaces and a larger specific surface area, significantly enhancing surface reactivity. This provides a rapid channel for the diffusion of reducing gases and the renewal of reaction interfaces, reducing the apparent resistance to solid-phase diffusion and interfacial reactions, thus improving the reduction performance of the cold-pressed blocks. The particle size distribution of activated specular hematite concentrate needs to meet certain conditions. The mass proportion of -74μm particles should not be too low, and the mass proportion of +0.25mm particles should not be too high. Within the preferred particle size distribution, it is more conducive to obtaining cold-pressed briquettes with high strength and good reduction performance.

[0019] As a preferred embodiment, the iron- and carbon-containing dust includes at least one of the following: sintering dust, blast furnace dust, converter dust, electric furnace dust, iron oxide scale, coke oven dust, and municipal sludge. The fixed carbon content of the iron- and carbon-containing dust should not be too low; if it is too low, the reduction effect will be limited.

[0020] As a preferred embodiment, the organic-inorganic composite binder is composed of an organic binder and an inorganic binder in a mass percentage ratio of 11%~28% : 72%~89%. Organic binders are more expensive but can effectively improve the strength of wet lumps, though they are not heat-resistant. Inorganic binders are less expensive but can effectively improve the strength of solidified lumps and have good heat resistance, although excessive amounts can reduce the iron grade of the cold-pressed briquettes. Therefore, this invention optimizes the composition and ratio of the composite binder under constraints such as cost, wet lump strength, solidified lump strength, high-temperature strength, and iron grade. The composite binder combines the advantages of improving wet lump strength, solidified lump strength, and high-temperature strength without significantly affecting iron grade, and is also less expensive. Ultimately, cold-pressed briquettes with high wet lump strength, solidified lump strength, and high-temperature strength are obtained under conditions of a lower composite binder ratio.

[0021] As a preferred embodiment, the organic binder includes at least one of gelatinized starch, hydroxypropyl / methylcellulose, carboxymethylcellulose, lignin sulfonate, polyvinyl alcohol, polyacrylamide, phenolic resin, and urea-formaldehyde resin.

[0022] As a preferred embodiment, the inorganic binder includes at least one of silicate cement, aluminate cement, modified bentonite, polyphosphate, sodium silicate, water glass, sodium humate, quicklime, and kaolin.

[0023] As a preferred embodiment, the amount of the organic-inorganic composite binder accounts for 1.2% to 3.5% of the mass of the mixture.

[0024] As a preferred embodiment, the amount of water used accounts for 4.0% to 9.5% of the mass of the mixture.

[0025] As a preferred option, the pressing and forming process employs roll forming, extrusion forming, or stamping forming.

[0026] As a preferred embodiment, the size of the wet pellets is (10~40) mm × (10~35) mm × (10~28) mm. The size of the wet pellets is optimized; if the size is too large, it will increase the drying and consolidation time and affect the reducibility, while if the size of the cold-pressed pellets is too small, it will affect the output of the cold-pressed pellet forming process.

[0027] As a preferred embodiment, the consolidation is performed using microwave consolidation or hot air consolidation, with a consolidation temperature of 120~300℃ and a consolidation time of 30~80min. When using hot air consolidation, the existing low-temperature hot waste gas from the steel plant can be used as a heat source. Under the preferred consolidation conditions, the compressive strength of the cold-pressed block is not less than 2500N / P, the drum index (+6.3mm) is not less than 85%, the reduction performance is not less than 70%, and the reduction expansion index is not higher than 20%.

[0028] In this invention, the particle size of materials is described using "+" and "-", which are conventional expressions for particle size classification. "+" indicates oversize and "-" indicates undersize. For example, -74μm particle size indicates undersize material that passes through a 74μm mesh, and +0.25mm particle size indicates oversize material that passes through a 0.25mm mesh.

[0029] The cold-pressed blocks of the present invention can be used in processes such as blast furnace reduction, direct reduction in gas-based vertical shaft furnaces, and direct reduction in coal-based rotary kilns.

[0030] This invention provides a method for preparing iron-bearing furnace charge from high-proportion specular hematite concentrate with near-zero carbon content, comprising the following specific steps:

[0031] (1) Surface activation pretreatment is performed on the specular hematite concentrate to obtain activated specular hematite concentrate. The surface activation pretreatment is one or more of the following: high-pressure roller milling, wet milling, ball milling, etc. The activated specular hematite concentrate has a -74μm ratio of not less than 20%, a +0.25mm ratio of not more than 40%, and a specific surface area of ​​not less than 1000cm². 2 ·g -1 The activated specular hematite concentrate, iron-containing carbon dust, and magnetite concentrate are mixed uniformly in a ratio of 68wt.%~84wt.% : 2wt.%~10wt.% : 14wt.%~22wt.% to obtain an iron-containing mixture. The iron-containing carbon dust includes one or more of the following: sintering dust, blast furnace dust, converter dust, electric furnace dust, iron oxide scale, coke oven dust, and municipal sludge. The iron-containing carbon dust contains at least 60% -74μm particles and at least 25% +0.2mm particles, with a fixed carbon content of at least 1wt.%. The magnetite concentrate contains at least 80wt.% Fe3O4 phase, at least 70% -74μm particles, and at least 20% +0.1mm particles.

[0032] (2) Add an appropriate amount of composite binder and water to the iron-containing mixture, and mix thoroughly to obtain a mixture. The amount of composite binder added accounts for 1.2 wt.%~3.5 wt.% of the mixture, and the moisture content of the mixture is 4.0 wt.%~9.5 wt.%. The composite binder is composed of organic binder and inorganic binder in a ratio of 11 wt.%~28 wt.% : 72 wt.%~89 wt.%. The organic binder is composed of one or more of the following: gelatinized starch, hydroxypropyl / methylcellulose, carboxymethylcellulose, lignin sulfonate, polyvinyl alcohol, polyacrylamide, phenolic resin, urea-formaldehyde resin, etc. The inorganic binder is composed of one or more of the following: silicate cement, aluminate cement, modified bentonite, polyphosphate, sodium silicate, water glass, sodium humate, quicklime, kaolin, etc. Further molding at room temperature yields wet lumps. The room temperature forming method is any one of roll forming, extrusion forming, or stamping forming, with the wet agglomerate size being (10~40) mm × (10~35) mm × (10~28) mm. The wet agglomerate is then solidified at low temperature to obtain a cold-pressed block. The low-temperature solidification method is one or more of microwave solidification and hot air solidification, with a solidification temperature of 120~300℃ and a solidification time of 30~80 min.

[0033] Compared with the prior art, the technical solution of the present invention brings the following beneficial effects:

[0034] (1) This invention is the first to successfully prepare cold-pressed briquettes with good reduction performance, high strength and low reduction expansion of specular iron concentrate. It solves the technical problems that the processing of specular iron concentrate in the prior art mainly relies on high-temperature briquetting routes such as sintering or pelletizing, which still generally have long process, high temperature, high energy consumption and high carbon emissions. This invention not only enables the processing of specular hematite concentrate resources on a larger scale, but also has a significant "near-zero carbon" advantage compared to existing high-temperature briquetting methods: On the one hand, the cold briquetting process has a lower temperature, avoiding the large amount of fuel consumption and process emissions caused by high-temperature steps such as sintering or roasting, significantly reducing energy consumption and CO2 emissions. Hot air consolidation can directly utilize the existing low-temperature hot waste gas from steel plants as a heat source, with virtually no additional fossil fuel consumption, reducing direct carbon emissions during the consolidation stage to an extremely low level. On the other hand, the high proportion of specular hematite concentrate in the cold briquetting process allows for large-scale processing compared to conventional sintering and pelletizing processes. At the same time, by blending in solid waste such as iron- and carbon-containing dust, iron resource recovery and carbon resource utilization can be achieved, reducing solid waste accumulation and resulting in significant environmental benefits.

[0035] (2) This invention significantly improves the performance of cold-pressed briquettes prepared from specular hematite concentrate by optimizing the ore blending, addressing defects such as poor reduction performance and severe expansion. Based on the characteristics of specular hematite concentrate—its relatively dense crystals, high density, and large particle size, resulting in poor reduction performance—and the fact that its main component is Fe2O3, which undergoes a crystal transformation leading to severe expansion during reduction to Fe3O4, this invention improves the reduction and expansion performance of cold-pressed briquettes by adding appropriate amounts of carbon-containing iron dust and magnetite concentrate. Specifically, the addition of carbon-containing dust accelerates the reduction reaction from within, thereby improving the reducibility of the cold-pressed briquettes. Since magnetite concentrate's main component is Fe3O4, it does not require the reduction of Fe2O3 to Fe3O4 during the reduction process; therefore, the addition of magnetite concentrate alleviates the expansion phenomenon of the cold-pressed briquettes.

[0036] (3) The present invention significantly improves the strength of cold-pressed briquettes prepared from specular iron concentrate by optimizing the particle size distribution of the ore. That is, a suitable proportion of fine iron and carbon dust and magnetite concentrate is embedded in specular iron concentrate with coarse particle size and high hardness to meet the optimal particle size distribution and improve the strength of cold-pressed briquettes.

[0037] (4) The surface-activated pretreatment of specular hematite concentrate used in this invention can effectively improve the reduction performance and strength of cold-pressed blocks. On the one hand, the strong mechanical force during the surface activation pretreatment process causes selective crushing of specular hematite concentrate, resulting in finer particle size and a large number of sharp edges. The particle morphology changes from relatively smooth and dense to a more irregular and rougher morphology, thereby strengthening the mechanical interlocking effect during the pressing process and improving the strength of the cold-pressed blocks. On the other hand, mechanical energy accumulates in the specular hematite lattice, causing defects such as lattice dislocations, vacancies and grain boundary distortions, and forming high-energy new surfaces and a larger specific surface area, significantly improving surface reactivity. This provides a fast channel for the diffusion of reducing gas and the renewal of the reaction interface, reduces the apparent resistance of solid-phase diffusion and interface reaction, and thus improves the reduction performance of cold-pressed blocks.

[0038] (5) The present invention also found that, based on the high hardness of specular hematite, compared with conventional iron ores such as hematite and magnetite, cold-pressed blocks prepared with a high proportion of specular hematite concentrate as raw material have higher strength, which can reduce the proportion of binder added. Detailed Implementation

[0039] To facilitate understanding of the present invention, the present invention will be described more fully and in detail below with reference to preferred embodiments, but the scope of protection of the present invention is not limited to the following specific embodiments.

[0040] 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.

[0041] 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.

[0042] The following examples specify the relevant standards for performance testing of cold-pressed blocks: compressive strength testing standard is GB / T 14201-2018, ISO 4700:2015; drum and abrasion resistance index testing standard is GB / T 24531-2009, ISO 3271:2007; low-temperature reduction pulverization index testing standard is GB / T 31923-2015; reduction performance testing standard is GB / T 13241-2017; reduction expansion performance testing standard is GB / T 13240-2018, ISO 4698:2007.

[0043] Example 1

[0044] Specular hematite concentrate underwent surface activation pretreatment, specifically high-pressure roller milling at a pressure of 10 MPa and a roller speed of 20 r / min, to obtain activated specular hematite concentrate. The roller milling controlled the particle size to meet the following requirements: -74 μm proportion 35%, +0.25 mm proportion 17%, and specific surface area 1410 cm². 2 ·g -1 The activated specular hematite concentrate, iron-containing carbon dust, and magnetite concentrate were mixed uniformly in a ratio of 70 wt.% : 8 wt.% : 22 wt.% to obtain an iron-containing mixture. The iron-containing carbon dust consisted of blast furnace dust and sintering dust in a ratio of 50 wt.% : 50 wt.%, with 70% being -74 μm, 8% being +0.2 mm, and a fixed carbon content of 8 wt.%. The magnetite concentrate had an Fe3O4 phase content of 83 wt.%, with 78% being -74 μm and 7% being +0.1 mm. An appropriate amount of composite binder and water were added to the iron-containing mixture, and the mixture was further mixed uniformly to obtain a final mixture. The composite binder accounted for 1.3 wt.% of the mixture, and the moisture content of the mixture was 4.0 wt.%. The composite binder consisted of organic binder and inorganic binder in a ratio of 15 wt.% : 85 wt.%. The organic binder consisted of gelatinized starch and phenolic resin in a ratio of 10 wt.% : 90 wt.%, while the inorganic binder consisted of silicate cement, modified bentonite, and sodium silicate in a ratio of 10 wt.% : 10 wt.% : 80 wt.%. Further, room-temperature roller molding was performed to obtain wet lumps with dimensions of 25 × 20 × 13 mm. These wet lumps were then subjected to low-temperature consolidation to obtain cold-pressed blocks. The low-temperature consolidation method was hot air consolidation at a temperature of 200℃ for 40 minutes.

[0045] The cold-pressed block has a compressive strength of 2950 N / P, a drum index (+6.3 mm) of 88.6%, a reduction degree of 74%, and a reduction expansion index of 17.5%.

[0046] Example 2

[0047] Specular hematite concentrate was pretreated with surface activation, specifically by swirl milling at a filling rate of 50% and a rotation speed of 15 r / min to obtain activated specular hematite concentrate. The swirl milling controlled the particle size to meet the following requirements: -74 μm proportion of 41%, +0.25 mm proportion of 10.5%, and specific surface area of ​​1690 cm². 2 ·g -1The activated specular hematite concentrate, iron-containing carbon dust, and magnetite concentrate were mixed evenly in a ratio of 79 wt.% : 6 wt.% : 15 wt.% to obtain an iron-containing mixture. The iron-containing carbon dust was electric furnace dust, with 90% of the particles at -74 μm, 1% at +0.2 mm, and a fixed carbon content of 5 wt.%. The magnetite concentrate had an Fe3O4 phase content of 85 wt.%, with 76% at -74 μm and 10% at +0.1 mm. An appropriate amount of composite binder and water were added to the iron-containing mixture, and the mixture was further mixed evenly to obtain a final mixture. The composite binder accounted for 3.2 wt.% of the mixture, and the moisture content of the mixture was 4.5 wt.%. The composite binder consisted of organic and inorganic binders in a ratio of 11 wt.% : 89 wt.%. The organic binder consisted of hydroxymethyl cellulose and polyacrylamide in a ratio of 30 wt.% : 70 wt.%, while the inorganic binder consisted of silicate cement, polyphosphate, and water glass in a ratio of 8 wt.% : 5 wt.% : 87 wt.%. Further, room-temperature stamping was performed to obtain wet lumps with dimensions of 15×15×14 mm. The wet lumps were then subjected to low-temperature microwave consolidation to obtain cold-pressed blocks. The consolidation temperature was 130℃, and the consolidation time was 30 min.

[0048] The cold-pressed block has a compressive strength of 2649 N / P, a drum index (+6.3 mm) of 86.1%, a reduction degree of 76.5%, and a reduction expansion index of 19%.

[0049] Example 3

[0050] Specular hematite concentrate underwent surface activation pretreatment, specifically ball milling, with a filling rate of 30%, a ball-to-material mass ratio of 1:1.1, and a rotation speed of 17 r / min, to obtain activated specular hematite concentrate. The ball milling controlled the particle size distribution to meet the following requirements: -74 μm proportion of 51%, +0.25 mm proportion of 7%, and specific surface area of ​​2130 cm². 2 ·g -1The activated specular hematite concentrate, iron-containing carbon dust, and magnetite concentrate were mixed uniformly in a ratio of 83 wt.% : 3 wt.% : 14 wt.% to obtain an iron-containing mixture. The iron-containing carbon dust consisted of converter dust and blast furnace dust in a ratio of 30 wt.% : 70 wt.%, with 87% being -74 μm, 3% being +0.2 mm, and a fixed carbon content of 13 wt.%. The magnetite concentrate had an Fe3O4 phase content of 91 wt.%, with 84% being -74 μm and 4% being +0.1 mm. An appropriate amount of composite binder and water were added to the iron-containing mixture, and the mixture was further mixed uniformly to obtain a final mixture. The composite binder accounted for 2.8 wt.% of the mixture, and the moisture content of the mixture was 7.5 wt.%. The composite binder consisted of organic binder and inorganic binder in a ratio of 14 wt.% : 86 wt.%. The organic binder consisted of gelatinized starch, carboxymethyl cellulose, and sodium lignosulfonate in a ratio of 24 wt.% : 66 wt.% : 10 wt.%, while the inorganic binder consisted of aluminate cement, sodium silicate, water glass, and sodium humate in a ratio of 10.5 wt.% : 45 wt.% : 39.5 wt.% : 5 wt.%. Further, room-temperature extrusion molding was performed to obtain wet lumps with dimensions of 18×18×15 mm. The wet lumps were then solidified using low-temperature hot air to obtain cold-pressed blocks. The solidification temperature was 230℃, and the solidification time was 45 min.

[0051] The cold-pressed block has a compressive strength of 2870 N / P, a drum index (+6.3 mm) of 89%, a reduction degree of 73.6%, and a reduction expansion index of 18.6%.

[0052] Comparative Example 1

[0053] The only difference compared to Example 1 is that only a single specular iron concentrate was used, and the composition and particle size distribution of the iron-containing mixture were not controlled by optimizing the batching, that is, the strength, reducibility and reductive expansion properties of the cold-pressed briquettes were not improved.

[0054] The cold-pressed block has a compressive strength of 2414 N / P, a drum index (+6.3 mm) of 82.5%, a reduction degree of 68.6%, and a reduction expansion index of 25.8%.

[0055] Comparative Example 2

[0056] The only difference compared to Example 1 is that no iron- and carbon-containing dust was added; that is, the iron-containing mixture consisted of activated specular hematite concentrate and magnetite concentrate in a ratio of 76.09 wt.% : 23.91 wt.%. The composition of the iron-containing mixture was not controlled through optimized batching, thus the reducibility of the cold-pressed briquettes was not improved.

[0057] The cold-pressed block has a compressive strength of 2877 N / P, a drum index (+6.3 mm) of 88.1%, a reduction degree of 64%, and a reduction expansion index of 16.1%.

[0058] Comparative Example 3

[0059] The only difference compared to Example 1 is that magnetite concentrate was not added; the iron-containing mixture consisted of activated specular hematite concentrate and carbon-containing iron dust in a ratio of 89.74 wt.% : 10.26 wt.%. The composition and particle size distribution of the iron-containing mixture were not controlled through optimized batching, thus failing to improve the strength and reductive expansion properties of the cold-pressed briquettes.

[0060] The cold-pressed block has a compressive strength of 2550 N / P, a drum index (+6.3 mm) of 84.1%, a reduction degree of 78%, and a reduction expansion index of 28.3%.

[0061] Comparative Example 4

[0062] The only difference compared to Example 2 is that no surface activation pretreatment was performed on the specular hematite concentrate; that is, the proportion of -74μm specular hematite concentrate was 6%, the proportion of +0.25mm was 46%, and the specific surface area was 480cm². 2 ·g -1 The strength and reduction properties of the cold-pressed block were not improved through surface activation pretreatment.

[0063] The cold-pressed block has a compressive strength of 2439 N / P, a drum index (+6.3 mm) of 85.2%, a reduction degree of 68.2%, and a reduction expansion index of 17%.

Claims

1. A method for preparing iron-bearing furnace charge from high-proportion specular hematite concentrate with near-zero carbon content, characterized in that: Surface activation pretreatment is performed on specular iron concentrate to obtain activated specular iron concentrate; the activated specular iron concentrate is mixed with iron-containing carbon dust and magnetite concentrate to obtain iron-containing raw material; the iron-containing raw material is mixed with organic-inorganic composite binder and water to form a mixture; the mixture is pressed into shape to obtain wet lumps; the wet lumps are solidified to obtain cold-pressed blocks; in, The mass percentage composition of activated specular hematite concentrate, iron-containing carbon dust, and magnetite concentrate is: 68%~84% : 2%~10% : 14%~22%; The activated specular hematite concentrate has the following particle size distribution: -74μm by mass not less than 20%, +0.25mm by mass not more than 40%, and a specific surface area not less than 1000 cm². 2 ·g -1 ; The particle size of iron- and carbon-containing dust shall meet the following requirements: the mass proportion of -74μm shall not be less than 60%, the mass proportion of +0.2mm shall not be more than 25%, and the fixed carbon mass content shall not be less than 1%. The magnetite concentrate has a particle size distribution that meets the following requirements: -74μm mass ratio not less than 70%, +0.1mm mass ratio not more than 20%, and Fe3O4 phase mass content not less than 80%.

2. The method for preparing iron-bearing furnace charge from high-proportion specular hematite concentrate with near-zero carbon according to claim 1, characterized in that: The surface activation pretreatment adopts at least one of high-pressure roller milling, wet milling, and ball milling.

3. The method for preparing iron-bearing furnace charge from high-proportion specular hematite concentrate with near-zero carbon according to claim 1, characterized in that: The iron- and carbon-containing dust includes at least one of the following: sintering dust, blast furnace dust, converter dust, electric furnace dust, iron oxide scale, coke oven dust, and municipal sludge.

4. The method for preparing iron-bearing furnace charge from high-proportion specular hematite concentrate with near-zero carbon according to claim 1, characterized in that: The organic-inorganic composite adhesive is composed of organic adhesive and inorganic adhesive in a mass percentage ratio of 11%~28% : 72%~89%.

5. The method for preparing iron-bearing furnace charge from high-proportion specular hematite concentrate with near-zero carbon according to claim 4, characterized in that: The organic binder includes at least one of the following: gelatinized starch, hydroxypropyl / methylcellulose, carboxymethylcellulose, lignin sulfonate, polyvinyl alcohol, polyacrylamide, phenolic resin, and urea-formaldehyde resin. The inorganic binder includes at least one of silicate cement, aluminate cement, modified bentonite, polyphosphate, sodium silicate, water glass, sodium humate, quicklime, and kaolin.

6. A method for preparing iron-bearing furnace charge from high-proportion specular hematite concentrate with near-zero carbon, as described in claim 1, 4, or 5, characterized in that: The amount of the organic-inorganic composite binder is 1.2% to 3.5% of the mass of the mixture.

7. The method for preparing iron-bearing furnace charge from high-proportion specular hematite concentrate with near-zero carbon according to claim 1, characterized in that: The amount of water used accounts for 4.0% to 9.5% of the mass of the mixture.

8. The method for preparing iron-bearing furnace charge from high-proportion specular hematite concentrate with near-zero carbon according to claim 1, characterized in that: The pressing and forming process employs roller forming, extrusion forming, or stamping forming.

9. The method for preparing iron-bearing furnace charge from high-proportion specular hematite concentrate with near-zero carbon according to claim 1, characterized in that: The size of the wet mass is (10~40) mm × (10~35) mm × (10~28) mm.

10. A method for preparing iron-bearing furnace charge from high-proportion specular hematite concentrate with near-zero carbon content according to claims 1, 2, 3, 4, 5, 7, 8, or 9, characterized in that: The consolidation is performed using microwave consolidation or hot air consolidation, with a consolidation temperature of 120~300℃ and a consolidation time of 30~80min.