A method for preparing iron powder based on hydrogen reduction of iron concentrate coupled with activation

Abstract

The application discloses a method for preparing iron powder by hydrogen reduction of iron concentrate based on coupling activation, which comprises the following steps: sequentially performing high-pressure roller grinding activation and oxidation activation on iron concentrate raw materials, and then performing hydrogen reduction roasting to obtain the iron powder. The method can improve the reaction activity of the iron concentrate, reduce the hydrogen reduction temperature, and effectively solve the problem of iron powder hardening in the conventional high-temperature hydrogen reduction process without greatly reducing the particle size of the iron concentrate by means of coupling activation of high-pressure roller grinding and oxidation. After reduction, the iron concentrate does not need secondary grinding treatment, and the conventional particle size high-purity iron powder with good dispersion can be obtained. The method has the advantages of simple process flow, low energy consumption and green environmental protection.

Description

Technical Field

[0001] This invention relates to a method for preparing iron powder by hydrogen reduction of iron concentrate, and particularly to a method for improving the hydrogen reduction activity of coarse-grained iron concentrate and reducing the hydrogen reduction temperature by mechanical activation coupled with oxidative activation, thereby obtaining highly dispersible conventional particle-sized iron powder, which belongs to the field of metal powder material preparation technology. Background Technology

[0002] Reduced iron powder is one of the most widely used metallic materials in modern industry, applicable to powder metallurgy, welding materials, soft magnetic materials, flame cutting and stainless steel cutting, diamond tools, and cemented carbide fields. Statistics show that in 2020, my country's iron powder exports accounted for approximately 29% of the world's total, with production showing a year-on-year growth trend. Reduced iron powder accounted for over 50% of total iron powder production. With the high-quality development of my country's industry and manufacturing sector, the demand for reduced iron powder will inevitably continue to increase.

[0003] Currently, reduced iron powder is generally prepared from iron scale or ultrapure iron concentrate through a two-step carbon-hydrogen reduction method. In the future, the preparation process of reduced iron powder will inevitably move towards all-hydrogen reduction. On the other hand, iron scale, as a byproduct of the steel rolling process, also suffers from large performance fluctuations and limited production. With advancements in iron concentrate mining and beneficiation technologies, the output of ultrapure iron concentrate is increasing year by year, its properties are relatively stable, and the metallurgical industry is developing towards green and low-carbon practices. Therefore, the production of iron powder using hydrogen reduction of ultrapure iron concentrate has broad development and application prospects.

[0004] Reduced iron powder is classified into different categories according to particle size: coarse powder (150–500 μm), medium powder (45–150 μm), fine powder (10–45 μm), ultrafine powder (0.5–10 μm), and ultrafine powder (less than 0.5 μm). Among these, conventional reduced iron powder with a particle size greater than 10 μm is in the largest demand, accounting for over 85% of the total reduced iron powder production. Because the iron powder obtained from low-temperature reduction has low purity, current conventional reduced iron powder preparation processes are carried out at high temperatures above 900℃ to obtain higher purity. This not only results in high energy consumption but also causes particle agglomeration and adhesion due to factors such as localized melting of ultrapure iron concentrate particles and the formation of iron whiskers on the surface during high-temperature reduction, leading to iron powder caking. Furthermore, the higher the temperature, the more severe the caking, often requiring grinding after reduction to obtain well-dispersed iron powder. However, due to the good ductility of iron itself, it is difficult to grind caking iron powder at low cost, resulting in high grinding energy consumption. At the same time, special protective mechanisms or methods are needed to prevent the introduction of oxygen and other impurities during the grinding process, such as using a nitrogen air classifier or crushing in a nitrogen chamber, which also increases the process cost.

[0005] Currently, existing methods for lowering the hydrogen reduction temperature of ultrapure iron concentrate mainly involve reducing the particle size of the concentrate to below 10 μm through ultrafine grinding, thereby significantly increasing the specific surface area and reactivity of the concentrate and lowering the hydrogen reduction temperature. However, due to the extremely fine particle size of ultrapure iron concentrate, its application in the preparation of conventional particle size iron powder also faces challenges in terms of adaptability and economic cost.

[0006] Therefore, if the reactivity of ultrapure iron concentrate can be increased and the hydrogen reduction temperature can be lowered without significantly reducing the particle size of ultrapure iron concentrate, the agglomeration of iron powder in the traditional hydrogen reduction process can be alleviated. Well-dispersed conventional particle size iron powder can be directly prepared in one step, thereby reducing process energy consumption and cost. This is of great significance for the development of low-carbon and green preparation technology of conventional particle size reduced iron powder above 10μm. Summary of the Invention

[0007] To address the problems of easy agglomeration of conventional reduced iron powder with particle size greater than 10μm at high temperatures, high energy consumption and cost of secondary grinding, and difficulty in meeting the required purity of iron powder during low-temperature reduction, the present invention aims to provide a method for preparing iron powder by hydrogen reduction of iron concentrate based on coupled activation. This method uses coupled activation of iron concentrate through high-pressure roller milling and oxidation to promote the generation of microcracks, increase the active surface, activate the crystal lattice, and amorphize the iron concentrate. This improves the reactivity of the iron concentrate without significantly reducing its particle size, lowers the hydrogen reduction temperature, and obtains well-dispersed conventional particle size iron powder without secondary grinding. This reduces the energy consumption and cost of conventional reduced iron powder preparation processes and has the advantages of simple process, energy saving and environmental protection.

[0008] To achieve the above-mentioned technical objectives, the present invention provides a method for preparing iron powder by hydrogen reduction of iron concentrate based on coupled activation. The method involves sequentially subjecting iron concentrate raw materials to high-pressure roller mill activation and oxidative activation, followed by hydrogen reduction roasting to obtain iron powder.

[0009] The key to this invention lies in the coupled activation technology of high-pressure roller milling and oxidation, which promotes the generation of microcracks, increases the active surface area, activates the crystal lattice, and amorphizes the iron concentrate, thus benefiting the subsequent hydrogen reduction process. On one hand, high-pressure roller milling differs from mechanical activation methods such as ball milling, stirred milling, and vibratory milling, which rely primarily on the interaction between the grinding media and the powder. High-pressure roller milling activation is a layer-pressing pulverization method where the interaction between powder particles is the main factor. The mechanical force has a relatively small impact on the particle size, primarily acting on the generation of microcracks within the particles, increasing the surface roughness of the particles, and causing lattice distortion and amorphization. This increases the active surface area of ​​the iron concentrate without significantly reducing its particle size, thereby enhancing its gas-solid reaction activity. On the other hand, the crystal transformation and volume shrinkage of Fe3O4 during the oxidation activation process improves the particle surface and pore structure. Simultaneously, the α-Fe2O3 formed after oxidation activation undergoes a crystal structure transformation and volume expansion during the subsequent hydrogen reduction process, further generating internal cracks and crystal structure defects in the ultrapure iron concentrate, which is beneficial for gas-phase diffusion and the reduction reaction. Thirdly, high-pressure roller milling activation and oxidation activation have a coupling effect. After high-pressure roller milling activation, the generation of microcracks, the increase of active surfaces, and the amorphization of the crystal lattice in ultrapure iron concentrate are all conducive to the pre-oxidation reaction, which can reduce the pre-oxidation temperature and thus avoid the agglomeration of the material layer after pre-oxidation. Furthermore, the iron concentrate after coupled activation has higher reactivity, which is beneficial to reducing the subsequent hydrogen reduction temperature. In summary, after using the coupled activation technology of high-pressure roller milling and oxidation, the reactivity of iron concentrate can be improved without significantly reducing its particle size, the hydrogen reduction temperature in the preparation process of reduced iron powder can be reduced, and well-dispersed iron powder can be obtained without secondary grinding.

[0010] As a preferred embodiment, the iron concentrate raw material is primarily magnetite, with a TFe content greater than 71.5% by mass, a particle size of 20–150 μm, and a particle size D. 50 The particle size should be no less than 45 μm, and the moisture content should be 6.5%–7.5% by mass. The iron concentrate raw material is conventional iron concentrate with a particle size of 10 μm or larger, with a preferred particle size of 20–150 μm. The iron concentrate raw material is ultrapure iron concentrate with a TFe content greater than 71.5% by mass. The higher the purity of the iron concentrate, the higher the purity of the reduced iron powder that can be obtained. Controlling the moisture content within a suitable range is beneficial to the high-pressure roller milling process. A suitable moisture content helps to increase the molecular and capillary forces between particles, thereby obtaining higher interparticle shear stress during the lamination and crushing process and improving the activation effect of the roller mill. However, when the moisture content is too high, the plasticity of the cake formed by the extrusion of the material layer increases, and the activation efficiency of the high-pressure roller mill decreases.

[0011] As a preferred embodiment, the activation conditions for the high-pressure roller mill are: pressure of 2.1–2.45 MPa and roller speed of 20–23 r / min. As a further preferred embodiment, the high-pressure roller mill is a high-pressure roller mill using alloy steel inlaid with hard alloy studs, with a roller spacing of 1–2 mm. Alloy stud rollers have better wear resistance, and controlling a reasonable roller spacing is beneficial to improving the mechanical force efficiency of the high-pressure roller mill. During the activation process, sufficient roller mill pressure can ensure the full activation of ultra-pure iron concentrate. However, excessively high roller mill pressure will result in excessively fine ultra-pure iron concentrate particle size, and simultaneously reduce the energy efficiency of the roller mill process. Therefore, the upper and lower limits of the roller mill pressure must be strictly controlled. During the activation process of the high-pressure roller mill, as the roller speed of the high-pressure roller mill increases, the material layer pressurization speed increases, and the roller mill processing capacity increases. However, when the roller speed is too high, the activation effect of the roller mill is poor.

[0012] As a preferred embodiment, the particle size D of the iron concentrate obtained by the high-pressure roller mill activation is... 50 The microcrack content growth rate ξ is greater than 30μm. H =(L H -L0) / L0, relative change in particle roughness R H =(F H -F0) / F0, the amorphousness increase ratio η H =(x H -x0) / x0; where L0 and L H The microcrack content of the iron concentrate raw material and the iron concentrate activated by high-pressure roller milling are respectively expressed in cm³. 3 / g;F0 and F H x0 and x1 are the fractal dimensions of the raw iron concentrate and the iron concentrate activated by high-pressure roller milling, respectively, dimensionless; H The figures show the crystal amorphism of the raw iron concentrate and the iron concentrate after high-pressure roller mill activation, respectively, in percentage (%). By adjusting the appropriate mechanical activation process parameters of the high-pressure roller mill, the increase of active surface area, lattice activation, and amorphization of the iron concentrate can be promoted, thereby improving the reactivity of the iron concentrate. Furthermore, due to the increased reactivity, the suitable temperature for subsequent oxidation activation is reduced to T. pr =850-150×[0.5×(ξ) H 2 +R H 2 )] 0.5 -120×η H .

[0013] As a preferred embodiment, the growth rate ξ of the microcrack content in the iron concentrate obtained by high-pressure roller mill activation is... H Not less than 30%, relative change in particle roughness R H Not less than 15%, the amorphousness increases by a certain percentage η H Greater than 50%.

[0014] As a preferred embodiment, the conditions for the oxidation activation are: temperature T pr =850-150×[0.5×(ξ) H 2 +R H 2 )] 0.5 -120×η H The unit is ℃, and the time is 10-20 min. Excessive oxidation activation time or temperature can easily lead to iron concentrate caking, while insufficient activation temperature or time will not achieve the desired effect. Based on high-pressure roller mill activation, oxidation activation can be achieved at a relatively low temperature while avoiding iron concentrate caking.

[0015] As a preferred embodiment, the crack content growth rate ξ of the iron concentrate obtained by oxidation activation is... M =(L M -L0) / L0, relative change in particle roughness R M =(F M -F0) / F0, degree of oxidation w M =(W0-W M ) / W0; L0 and L M The microcrack content is shown in cm³ for raw iron concentrate and oxidized and activated iron concentrate, respectively. 3 / g;F0 and F M , respectively, are the fractal dimensions of the raw iron concentrate and the oxidized and activated iron concentrate, dimensionless; W0 and W M The FeO mass content of iron concentrate before and after oxidation activation is shown in %.

[0016] As a preferred embodiment, the degree of oxidation w of the iron concentrate obtained by the oxidation activation is... M Greater than 85%. During the oxidation activation process, the improvement of particle surface and pore structure is accompanied by Fe3O4 crystal transformation and volume shrinkage. The higher the degree of oxidation, the better the activation effect of iron concentrate.

[0017] As a preferred embodiment, the conditions for the hydrogen reduction roasting are: temperature T re =950-120×[0.5×(ξ) M 2 +R M 2 )] 0.5 -90×w M 2 The unit is ℃, the time is 2-4 hours, and the hydrogen flow rate is 800-1200 Nm³. 3 / t iron concentrate; of which ξ M =(LM -L0) / L0, R M =(F M -F0) / F0, w M =(W0-W M ) / W0; L0 and L M The microcrack content is shown in cm³ for raw iron concentrate and oxidized and activated iron concentrate, respectively. 3 / g;F0 and F M , respectively, are the fractal dimensions of the raw iron concentrate and the oxidized and activated iron concentrate, dimensionless; W0 and W M The figures show the FeO mass content of the iron concentrate before and after oxidation activation, respectively, in percentages (%). The hydrogen reduction roasting process of this invention reduces the iron concentrate obtained through high-pressure roller mill activation coupled with oxidation activation. This significantly improves the pore structure of the iron concentrate, increasing its newly formed active surface, amorphousness, and lattice activation degree, allowing the suitable temperature for subsequent hydrogen reduction to be lowered to T. re =950-120×[0.5×(ξ) M 2 +R M 2 )] 0.5 -90×w M 2 Hydrogen reduction roasting for more than 2 hours can ensure sufficient reduction of iron powder, but excessively long hydrogen reduction times can easily lead to iron powder caking. A further preferred approach is to preheat the hydrogen to the reduction temperature during the hydrogen reduction roasting process of the iron concentrate using a hydrogen preheater. Since the hydrogen reduction reaction is endothermic, preheating the hydrogen to the reduction temperature can prevent the temperature drop of the iron concentrate due to heat exchange, thereby improving the efficiency of the reduction reaction.

[0018] As a preferred embodiment, the oxidation activation and hydrogen reduction roasting are carried out in a steel belt atmosphere furnace or a pusher boat atmosphere furnace, with the iron concentrate raw material thickness being 5–15 mm. Pre-oxidation and hydrogen reduction are conducted in a steel belt atmosphere furnace or a pusher boat atmosphere furnace, which is beneficial for the full progress of the reduction reaction. The thickness of the iron concentrate raw material affects the permeability of the material layer, therefore it should not be too high, preferably controlled below 15 mm.

[0019] Compared with the prior art, the advantages of the technical solution of the present invention are as follows:

[0020] (1) This invention utilizes the mechanical activation method of "mainly based on the interaction between powders" during the layer-by-layer crushing process of high pressure roller mill. By using mechanical force to generate microcracks inside the particles, increase the surface roughness of the particles, and cause lattice distortion and amorphization, the active surface of ultrapure iron concentrate can be increased without significantly reducing the particle size of iron concentrate, thereby improving its gas-solid reaction activity. At the same time, since the high pressure roller mill adopts a continuous extrusion discharge process, it has higher mechanical activation efficiency and working capacity.

[0021] (2) This invention utilizes the crystal transformation and volume shrinkage of Fe3O4 during the pre-oxidation process to improve the particle surface and pore structure, promote the lattice distortion and amorphization of ultrapure iron concentrate, and the α-Fe2O3 formed after pre-oxidation will undergo crystal structure transformation and volume expansion again during hydrogen reduction, further generating internal cracks and crystal structure defects, which is conducive to the diffusion of gas phase and the subsequent reduction reaction, and reduces the hydrogen reduction temperature.

[0022] (3) The high-pressure roller mill activation and oxidation activation used in this invention have a significant coupling effect. On the one hand, after high-pressure roller mill activation, the generation of microcracks inside the ultrapure iron concentrate, the increase of active surface, and the amorphization of the crystal lattice are all conducive to the pre-oxidation reaction, thereby reducing the pre-oxidation temperature and avoiding the agglomeration of the material layer after pre-oxidation. On the other hand, the improvement of the surface and pore structure of the ultrapure iron concentrate after pre-oxidation and the volume expansion of α-Fe2O3 during the reduction process can compensate for the unfavorable factors such as the dense material layer structure caused by the finer particle size of the iron concentrate after high-pressure roller milling. Moreover, the iron concentrate after coupled activation has higher reactivity, which is conducive to the subsequent reduction of hydrogen reduction temperature.

[0023] (4) This invention employs a coupled activation method of high-pressure roller milling and oxidation, which can promote the generation of microcracks, increase the active surface, activate the lattice, and create amorphous structures in the iron concentrate. This improves the reactivity of the iron concentrate without significantly reducing its particle size and lowers the hydrogen reduction temperature. Simultaneously, the oxidation activation process preheats the ultrapure iron concentrate, avoiding the low hydrogen utilization rate problem in traditional hydrogen reduction heating processes. Combined with hydrogen preheating, this results in a more uniform and stable temperature field in the feed bed, improving hydrogen utilization and facilitating the rapid and complete hydrogen reduction reaction at low temperatures.

[0024] In summary, this invention utilizes the mechanical activation principle of high-pressure roller mill lamination and pulverization coupled with pre-oxidation activation to improve the reactivity of iron concentrate without significantly reducing its particle size. Simultaneously, by combining hydrogen preheating in the reduction process, the hydrogen reduction temperature of conventional particle size ultrapure iron concentrate can be lowered to below 850℃. After reduction, well-dispersed high-purity iron powder can be obtained without secondary grinding, reducing the energy consumption and cost of conventional particle size reduced iron powder preparation processes. This invention offers the advantages of simple process, energy saving, and environmental friendliness. Attached Figure Description

[0025] Figure 1 The images show the particle morphology of the iron powder obtained in Comparative Example 1 and Example 1. Detailed Implementation

[0026] To further illustrate the present invention, the following description, in conjunction with preferred embodiments, will provide a more comprehensive and detailed account. However, the scope of protection of the present invention is not limited to the specific embodiments described below. Unless otherwise defined, all technical terms used herein have the same meaning as commonly understood by those skilled in the art. The technical terms used herein are for the purpose of describing specific embodiments only and are not intended to limit the scope of protection of the present invention.

[0027] The parameter testing methods used in the following embodiments are all conventional testing methods in the art:

[0028] Among them, the microcrack content L is the micropore and mesopore volume of iron concentrate measured by the BET method.

[0029] The fractal dimension F is obtained by statistically analyzing the area S and perimeter A of iron concentrate particles (no fewer than 3000) using image processing software, plotting lnS against lnA, and fitting the straight line using the least squares method. The slope of the resulting line is the fractal dimension of the iron concentrate particles.

[0030] The crystal amorphism x is calculated based on the XRD diffraction pattern of iron concentrate (scanning speed not exceeding 2° / min), which is the rate of change of the diffraction peak area of ​​activated iron concentrate relative to unactivated standard magnetite. That is, crystal amorphism = (diffraction peak area of ​​unactivated standard magnetite - diffraction peak area of ​​activated iron concentrate) / (diffraction peak area of ​​unactivated standard magnetite).

[0031] The FeO content was determined according to GB / T 6730.8-2016.

[0032] Comparative Example 1

[0033] The ultrapure iron concentrate from Table 1 was used and activated by high-pressure roller milling under the conditions of 2.1 MPa pressure, 7.5% moisture content, 23 r / min roller speed, and 1.5 mm roller spacing. The mechanically activated ultrapure iron concentrate D... 50 The microcrack content growth rate ξ is 43 μm. H The relative change in particle roughness R is 31%. H The amorphousness increases by 15%, η. H It is 52%.

[0034] Mechanically activated ultrapure iron concentrate was subjected to hydrogen reduction in a steel strip atmosphere furnace with a material layer height of 5 mm. Due to the lack of oxidation activation treatment, the microcrack content of the activated ultrapure iron concentrate increased by ξ. H The relative change in particle roughness R is 31%.H The oxidation level is 15%, w M The value is 0%. At the hydrogen reduction temperature of 950–120 × [0.5 × (0.31)], the value is 0%. 2 +0.15 2 )] 0.5 -90×0 2 =921 (unit is °C), reduction time 2h, hydrogen consumption is 800Nm 3 Under conditions of / t ultrapure iron concentrate, the iron powder obtained after reduction agglomerates, such as Figure 1 As shown, the iron powder purity is 95.53%.

[0035] Comparative Example 2

[0036] Using the ultrapure iron concentrate from Table 1, it was sequentially pre-oxidized and hydrogen-reduced in a steel strip atmosphere furnace, with a material layer height of 5 mm. Under the conditions of a pre-oxidation temperature of 751℃ and a pre-oxidation time of 10 min, the growth rate ξ of the microcrack content in the activated ultrapure iron concentrate was [not specified]. H The relative change in particle roughness R is 7%. H The oxidation level is 14%, w M It is 75%.

[0037] Furthermore, at a hydrogen reduction temperature of 950–120 × [0.5 × (0.07)] 2 +0.14 2 )] 0.5 -90×0.75 2 =886 (unit is °C), reduction time 2h, hydrogen consumption is 800Nm 3 Under the condition of / t ultrapure iron concentrate, the iron powder obtained after reduction agglomerates, and the purity of the iron powder is 95.11%.

[0038] Comparative Example 3

[0039] The ultrapure iron concentrate from Table 1 was used and activated by high-pressure roller milling under the conditions of 1.7 MPa pressure, 5.5% moisture content, 20 r / min roller speed, and 2 mm roller spacing. The mechanically activated ultrapure iron concentrate D... 50 The microcrack content growth rate ξ is 47 μm. H The relative change in particle roughness R is 23%. H The amorphousness increases by η, which is 11%. H It is 31%.

[0040] The mechanically activated ultrapure iron concentrate was pre-oxidized and hydrogen-reduced in a pusher-type atmosphere heater with a material layer height of 5 mm. The pre-oxidation temperature was 850-150 × [0.5 × (0.23)]. 2 +0.11 2 )] 0.5-120 × 0.31 = 786 (unit: °C), under the condition of a pre-oxidation time of 10 min, the growth rate ξ of the microcrack content in the coupled activated ultrapure iron concentrate is... H The relative change in particle roughness R is 29%. H The oxidation level is 26%, w M It is 82%.

[0041] Furthermore, at a hydrogen reduction temperature of 950–120 × [0.5 × (0.29)] 2 +0.26 2 )] 0.5 -90×0.82 2 =856 (unit is °C), reduction time 3h, hydrogen consumption is 1000Nm 3 Under the condition of / t ultrapure iron concentrate, the iron powder obtained after reduction has no agglomeration phenomenon and the purity of the iron powder is 97.01%.

[0042] Due to the low pressure of the roller mill and the low moisture content of the iron concentrate, the particle shear stress was insufficient during the lamination and crushing process. This resulted in a relatively low increase in particle microcracks, roughness, and amorphousness, leading to poor mechanical activation. After pre-oxidation activation under suitable conditions, the oxidation degree of the iron concentrate was only 82%, indicating insufficient activity in the coupled-activated iron concentrate. Under the corresponding hydrogen reduction regime, although the obtained iron powder did not exhibit agglomeration, its purity was low.

[0043] Example 1

[0044] The ultrapure iron concentrate from Table 1 was used and activated by high-pressure roller milling under the conditions of 2.1 MPa pressure, 7.5% moisture content, 23 r / min roller speed, and 1.5 mm roller spacing. The mechanically activated ultrapure iron concentrate D... 50 The microcrack content growth rate ξ is 43 μm. H The relative change in particle roughness R is 31%. H The amorphousness increases by 15%, η. H It is 52%.

[0045] The mechanically activated ultrapure iron concentrate was pre-oxidized and hydrogen-reduced in a steel strip atmosphere heater, with a material layer height of 5 mm. The pre-oxidation temperature was 850-150 × [0.5 × (0.31)]. 2 +0.15 2 )] 0.5 -120 × 0.52 = 751 (unit: °C) Under the condition of a pre-oxidation temperature of 10 min, the growth rate ξ of the microcrack content in the coupled activated ultrapure iron concentrate is... H The relative change in particle roughness R is 42%. H The oxidation level is 35%, and the degree of oxidation is w. M It is 91%.

[0046] Furthermore, at a hydrogen reduction temperature of 950–120 × [0.5 × (0.42)] 2 +0.35 2 )] 0.5 -90×0.91 2 =829 (unit is °C), reduction time 2h, hydrogen consumption is 800Nm 3 Under conditions of / t ultrapure iron concentrate, the iron powder obtained after reduction does not exhibit agglomeration, such as Figure 1 As shown, the purity of the iron powder is 98.83%.

[0047] Example 2

[0048] The ultrapure iron concentrate from Table 1 was used and activated by high-pressure roller milling under the conditions of 2.45 MPa pressure, 6.5% moisture content, 20 r / min roller speed, and 1 mm roller spacing. The mechanically activated ultrapure iron concentrate D... 50 The microcrack content growth rate ξ is 35μm. H The relative change in particle roughness R is 46%. H The amorphousness increases by η, which is 27%. H It is 72%.

[0049] The mechanically activated ultrapure iron concentrate was pre-oxidized and hydrogen-reduced in a steel strip atmosphere furnace with a material layer height of 15 mm. The pre-oxidation temperature was 850-150 °C. 2 +0.27 2 )] 0.5 -120 × 0.72 = 707 (unit: °C), under the condition of pre-oxidation temperature of 20 min, the growth rate ξ of microcrack content in coupled activated ultrapure iron concentrate is... H The relative change in particle roughness R is 53%. H The oxidation level is 45%, and the degree of oxidation is w. M It is 89%.

[0050] Furthermore, at a hydrogen reduction temperature of 950–120 × [0.5 × (0.53)] 2 +0.45 2 )] 0.5 -90×0.89 2 =820 (unit is °C), reduction time 4h, hydrogen consumption is 1200Nm 3 Under the condition of / t ultrapure iron concentrate, the iron powder obtained after reduction showed no agglomeration and the purity of the iron powder was 98.71%.

[0051] Example 3

[0052] The ultrapure iron concentrate from Table 1 was used and activated by high-pressure roller milling under the following conditions: pressure 2.35 MPa, moisture content 7.5%, roller speed 23 r / min, and roller spacing 1 mm. The mechanically activated ultrapure iron concentrate D... 50 The microcrack content growth rate ξ is 34 μm. H The relative change in particle roughness R is 44%. H The amorphousness increases by η, which is 28%. H It is 70%.

[0053] The mechanically activated ultrapure iron concentrate was pre-oxidized and hydrogen-reduced in a pusher-type atmosphere heater with a material layer height of 5 mm. The pre-oxidation temperature was 850-150 °C. 2 +0.28 2 )] 0.5 -120 × 0.70 = 711 (unit: °C), under the condition of pre-oxidation temperature of 10 min, the growth rate ξ of microcrack content in coupled activated ultrapure iron concentrate is... H The relative change in particle roughness R is 55%. H The oxidation level is 47%, and the degree of oxidation is w. M It is 96%.

[0054] Furthermore, at a hydrogen reduction temperature of 950–120 × [0.5 × (0.55)] 2 +0.47 2 )] 0.5 -90×0.96 2 =806 (unit is °C), reduction time 2h, hydrogen consumption is 800Nm 3 Under the condition of / t ultrapure iron concentrate, the iron powder obtained after reduction has no agglomeration phenomenon and the purity of the iron powder is 99.07%.

[0055] Table 1. Chemical composition (wt.%) and particle size (μm) of ultrapure iron concentrate

[0056]

Claims

1. A method for preparing iron powder by hydrogen reduction of iron concentrate based on coupled activation, characterized in that: Iron concentrate raw material is sequentially activated by high-pressure roller milling and then by oxidation activation, followed by hydrogen reduction roasting to obtain iron powder; the conditions for oxidation activation are: temperature T pr =850-150×[0.5×( ξ H 2 + R H 2 )] 0.5 -120× η H The unit is ℃, and the time is 10~20min; The activation conditions for the high-pressure roller mill are: pressure of 2.1~2.45MPa and roller speed of 20~23r / min; The particle size D of the iron concentrate obtained by high-pressure roller mill activation 50 The growth rate of microcrack content greater than 30μm ξ H =( L H - L 0) / L 0, relative change in particle roughness R H =( F H - F 0) / F 0, amorphousness increase ratio η H =( x H - x 0) / x 0; in, L 0 and L H The microcrack content of the iron concentrate raw material and the iron concentrate activated by high-pressure roller milling are respectively expressed in cm³. 3 / g; F 0 and F H , respectively, are the fractal dimensions of the raw iron concentrate and the iron concentrate activated by high-pressure roller milling, and are dimensionless; x 0 and x H The crystal amorphism of the iron concentrate raw material and the iron concentrate activated by high-pressure roller milling are respectively expressed in % (%). The conditions for the hydrogen reduction roasting are: temperature T re =950-120×[0.5×( ξ M 2 + R M 2 )] 0.5 -90× w M 2 The unit is ℃, the time is 2~4h, and the hydrogen flow rate is 800~1200Nm. 3 / t iron concentrate; in, ξ M The crack content growth rate of iron concentrate obtained by oxidation and activation. ξ M =( L M - L 0) / L 0； R M The relative change in particle roughness of the iron concentrate obtained by oxidation and activation. R M =( F M - F 0) / F 0; w M The degree of oxidation of the iron concentrate obtained by oxidation activation. w M =( W 0- W M ) / W 0; L 0 and L M The microcrack content is shown in cm³ for raw iron concentrate and oxidized and activated iron concentrate, respectively. 3 / g; F 0 and F M , respectively, are the fractal dimensions of the raw iron concentrate and the oxidized and activated iron concentrate, which are dimensionless; W 0 and W M The values ​​represent the FeO mass content of iron concentrate before and after oxidation activation, respectively, in units of %.

2. The method for preparing iron powder based on hydrogen reduction of iron concentrate using coupled activation as described in claim 1, characterized in that: The iron concentrate raw material is mainly magnetite, with a TFe content greater than 71.5% by mass, a particle size of 20~150μm, and a particle size D. 50 Not less than 45μm, with a moisture content of 6.5~7.5% by mass.

3. The method for preparing iron powder based on hydrogen reduction of iron concentrate using coupled activation as described in claim 1, characterized in that: The growth rate of microcrack content in the iron concentrate obtained by high-pressure roller mill activation ξ H No less than 30%, relative change in particle roughness R H Not less than 15%, amorphous increase ratio η H Greater than 50%.

4. The method for preparing iron powder based on hydrogen reduction of iron concentrate using coupled activation according to claim 1, characterized in that: The degree of oxidation of the iron concentrate obtained by oxidation activation w M Greater than 85%.

5. The method for preparing iron powder based on hydrogen reduction of iron concentrate using coupled activation according to claim 1, characterized in that: The oxidation activation and hydrogen reduction roasting are carried out in a steel strip atmosphere heating furnace or a pusher boat atmosphere heating furnace, and the thickness of the iron concentrate raw material is 5~15mm.

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