A method for preparing high-purity ultrafine reduced iron powder

Abstract

The present application relates to powder metallurgy and industrial waste high value utilization technical field, disclose a kind of preparation high-purity superfine reduced iron powder method.The method is prepared with the oxidized iron powder of cold-rolled pickling waste liquid as raw material, after granulation, sequentially through primary reduction, primary crushing, secondary reduction, secondary crushing, tertiary reduction and tertiary crushing, to obtain reduced iron powder.Reducing gas is hydrogen, crushing is carried out under nitrogen protection, and the temperature of tertiary reduction is gradually reduced, and hydrogen gradient circulation step is provided.The method is alternately carried out with reduction and crushing, break sintering neck and agglomerate, promote deep reduction and particle size refinement, and the purity of the prepared reduced iron powder is ≥99.5%, the average particle size is <10 μm and the oxygen content is low, which can replace part of carbonyl iron powder, realize high value utilization of industrial waste.

Description

Technical Field

[0001] This invention relates to the field of powder metallurgy and high-value utilization of industrial waste, specifically to a method for preparing high-purity ultrafine reduced iron powder. Background Technology

[0002] In the desiliconization and pickling process of cold-rolled steel sheets in the steel industry, a large amount of pickling waste liquid is generated. Currently, advanced resource utilization technologies in the industry (such as the desiliconization-spray roasting process) can efficiently convert this waste liquid into high-purity iron oxide powder (commonly known as "iron red"). This iron oxide powder, derived from industrial waste, after refining treatment such as desiliconization and impurity removal, has excellent purity (e.g., Fe2O3 content ≥ 99.4wt%), physical and chemical properties, and can be stably used as a main raw material in fields such as soft magnetic ferrites, realizing the high-value utilization of waste.

[0003] However, the application areas and market value of ferrite materials are somewhat limited. With technological advancements, the demand for high-performance metal powders (such as high-purity, ultrafine, low-oxygen reduced iron powder) is increasing. These powders are widely used in higher value-added fields such as powder metallurgy, metal injection molding, high-frequency magnetic cores, microwave absorption, and 3D printing. Currently, the supply of high-end iron powder for these fields mainly relies on the carbonyl process, but the carbonyl process is costly, complex, and involves hazardous materials, posing safety and environmental risks.

[0004] Therefore, there is an urgent need in this field for a high-end iron powder preparation route that can break the monopoly of the carbonyl method, is more cost-effective, and more environmentally friendly. If a new refining and purification process can be developed, starting with iron oxide, which already possesses a high purity base, and transforming it into high-purity ultrafine reduced iron powder with performance comparable to carbonyl iron powder, it will not only open up new application markets but also achieve a leapfrog improvement in product value, which is of great significance for promoting resource recycling and the localization of high-end materials. Summary of the Invention

[0005] To address the above technical problems, this invention provides a method for preparing high-purity ultrafine reduced iron powder, which overcomes the limitations of existing high-end iron powder preparation methods and is more in line with the concept of green environmental protection.

[0006] The specific technical solution of the present invention is as follows: According to one aspect of the present invention, a method for preparing high-purity ultrafine reduced iron powder is provided, comprising the following steps: After granulation, iron oxide powder is subjected to primary reduction, primary crushing, secondary reduction, secondary crushing, tertiary reduction and tertiary crushing in sequence to obtain reduced iron powder.

[0007] In the above technical solution, the purity of the reduced iron powder is ≥99.5%, and the average particle size is <10μm.

[0008] In the above technical solution, the reducing gas used in the primary reduction, secondary reduction and tertiary reduction processes each independently includes hydrogen.

[0009] In the above technical solution, the primary crushing, secondary crushing and tertiary crushing processes are each carried out independently in an inert gas.

[0010] In the above technical solution, the inert gas includes nitrogen.

[0011] In the above technical solution, the temperature of the first-stage reduction is 840~860℃.

[0012] In the above technical solution, the temperature of the secondary reduction is 810~830℃.

[0013] In the above technical solution, the temperature of the three-stage reduction is 780~820℃.

[0014] In the above technical solution, the time for the first-level restoration is 1.5~2.5h.

[0015] In the above technical solution, the secondary restoration time is 1~2 hours.

[0016] In the above technical solution, the time for the three-stage restoration is 0.5~1.5h.

[0017] In the above technical solution, the temperatures of the first-stage reduction, second-stage reduction, and third-stage reduction decrease step by step.

[0018] In the above technical solution, the temperature of the first-stage reduction is 850°C.

[0019] In the above technical solution, the temperature of the secondary reduction is 820℃.

[0020] In the above technical solution, the temperature of the three-stage reduction is 800℃.

[0021] In the above technical solution, the time for the first-level restoration is 2 hours.

[0022] In the above technical solution, the secondary restoration time is 1.5 hours.

[0023] In the above technical solution, the time for the three-stage restoration is 1 hour.

[0024] The method for preparing high-purity ultrafine reduced iron powder in the above technical solution also includes a hydrogen circulation step: Fresh hydrogen gas is introduced into the third-stage reduction, and the gas produced after the reaction is introduced into the second-stage reduction. The gas produced after the second-stage reduction is then introduced into the first-stage reduction and the third-stage reduction, respectively. The exhaust gas discharged from the first-stage reduction is treated to recover hydrogen gas, which is then reintroduced into the third-stage reduction.

[0025] Compared with existing technologies, this invention provides a method for preparing high-purity ultrafine reduced iron powder. First, the reduction and crushing processes are designed to be carried out alternately and complement each other, continuously breaking down the sintering necks and agglomerates formed during the reduction process. This not only effectively controls the particle size but also greatly increases the reactivity and promotes deep reduction, jointly ensuring the high purity and ultrafine characteristics of the final product. In the first-stage reduction process, iron oxide is initially reduced to porous sponge iron, and then the large sintered material is crushed in the first-stage crushing. The second-stage reduction process is a deep reduction process, further deepening the reduction degree, and the second-stage crushing further homogenizes the material. Finally, the third-stage reduction ensures that the iron powder is completely reduced, and the third-stage crushing further refines the material, ultimately obtaining ultrafine iron powder.

[0026] Secondly, the invention successfully transforms ferrite raw materials, which already possess significant market value, into high-purity ultrafine iron powder with higher technological content and profit margins, achieving high-value utilization of raw materials and expanding product application scenarios. Furthermore, it provides a process route that can partially replace carbonyl iron powder, solving the inherent cost, safety, and environmental issues of the carbonyl method. Simultaneously, based on low-cost, readily available, high-quality raw materials, combined with efficient hydrogen recycling technology, the overall production cost possesses strong market competitiveness. This invention expands and improves the resource utilization path of industrial waste, sequentially converting industrial waste into ferrite raw materials, and then further processing them into high-end metal powders, thus practicing the concept of green manufacturing. Attached Figure Description

[0027] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments.

[0028] Figure 1 This is a process flow diagram of Embodiment 1 of the present invention. Detailed Implementation

[0029] To make the objectives, technical solutions, and advantages of this invention more apparent, the invention is described in detail below. It should be understood that the invention is not limited to the description herein.

[0030] Iron oxide powder The iron oxide powder used in this invention is a type of iron oxide powder known in the art for preparing high-purity ultrafine reduced iron powder. In the method for preparing high-purity ultrafine reduced iron powder in this invention, the iron oxide powder is obtained by roasting and purifying cold-rolled desilicate pickling waste liquid. Specifically, the cold-rolled desilicate pickling waste liquid is roasted at high temperature in a spray roasting furnace at 650~750℃ for 3~6s to obtain crude iron oxide powder; the crude iron oxide powder is then washed with water, magnetically separated, and dried to obtain high-purity iron oxide powder with an Fe2O3 content ≥99.4wt%.

[0031] This invention provides a method for preparing high-purity ultrafine reduced iron powder, comprising the following steps: After granulation, iron oxide powder is subjected to primary reduction, primary crushing, secondary reduction, secondary crushing, tertiary reduction and tertiary crushing in sequence to obtain reduced iron powder.

[0032] In the method for preparing high-purity ultrafine reduced iron powder, the step of granulation of iron oxide powder includes: mixing iron oxide powder with petroleum coke powder at a mass ratio of 100:5~15, adding a binder, and granulating by roller pressing to obtain granules with a particle size of 5~20mm.

[0033] In this invention, water is used as the binder in the granulation process of iron oxide powder; the mass ratio of iron oxide powder to petroleum coke powder is 100:5~15, for example, it can be 100:5, 100:6, 100:7, 100:8, 100:9, 100:10, 100:11, 100:12, 100:13, 100:14, 100:15, preferably 100:8~12, and more preferably 100:10.

[0034] In the method for preparing high-purity ultrafine reduced iron powder, the reducing gases used in the primary reduction, secondary reduction and tertiary reduction processes each independently include hydrogen.

[0035] In the method for preparing high-purity ultrafine reduced iron powder, the primary crushing, secondary crushing and tertiary crushing processes are carried out independently in an inert gas, including nitrogen.

[0036] In the method for preparing high-purity ultrafine reduced iron powder, the temperature for the first-stage reduction is 840~860℃, and the time is 1.5~2.5h; the temperature for the second-stage reduction is 810~830℃, and the time is 1~2h; the temperature for the third-stage reduction is 780~820℃, and the time is 0.5~1.5h. The temperatures for the first, second, and third-stage reductions decrease progressively. Preferably, the temperature for the first-stage reduction is 850℃, and the time is 2h; the temperature for the second-stage reduction is 820℃, and the time is 1.5h; and the temperature for the third-stage reduction is 800℃, and the time is 1h. The progressively decreasing temperature during the first, second, and third-stage reductions not only ensures the complete reduction of the iron powder, but also reduces fluctuations in the powder's physical properties by allowing for gradual temperature changes, thus guaranteeing the stability of the reduced iron powder's quality and physical properties.

[0037] The method for preparing high-purity ultrafine reduced iron powder also includes a hydrogen circulation step: Fresh hydrogen is introduced into a three-stage reduction furnace, and the reacted gas is introduced into a two-stage reduction furnace. The gas from the two-stage reduction furnace is then introduced into both the first-stage and third-stage reduction furnaces. The exhaust gas from the first-stage reduction furnace is treated to recover hydrogen, which is then reintroduced into the third-stage reduction furnace. In this process, fresh hydrogen is introduced from the third-stage hydrogen reduction furnace, and the reacted gas is sequentially introduced into the second-stage and first-stage reduction furnaces in reverse order, enabling the cascade utilization of hydrogen. Simultaneously, the exhaust gas from the first-stage reduction furnace is purified through condensation, dust removal, deoxygenation, and pressure swing adsorption. The recovered high-purity hydrogen is then returned to the third-stage reduction furnace, forming a highly efficient closed-loop cycle that significantly reduces hydrogen consumption and production costs.

[0038] The present invention also provides an apparatus for implementing the method for preparing high-purity ultrafine reduced iron powder as described above, comprising a primary hydrogen reduction furnace, a primary crusher, a secondary hydrogen reduction furnace, a secondary crusher, a tertiary hydrogen reduction furnace, and a tertiary crusher connected in sequence; a hydrogen source is connected to the tertiary hydrogen reduction furnace, the exhaust port of the tertiary hydrogen reduction furnace is connected to the inlet of the secondary hydrogen reduction furnace, the exhaust port of the secondary hydrogen reduction furnace is connected to the inlets of the tertiary hydrogen reduction furnace and the primary hydrogen reduction furnace in sequence through a hydrogen-rich condenser dust collector and a hydrogen-rich deoxygenation booster device, and the exhaust port of the primary hydrogen reduction furnace is connected to the inlet of the tertiary hydrogen reduction furnace in sequence through a tail gas condenser dust collector, a tail gas microfiltration deoxygenation device, and a pressure swing adsorption device.

[0039] To further illustrate the present invention, the following examples will provide a detailed description. The raw materials used in the following examples and comparative examples are all commercially available products. The iron oxide powder is produced by a steel company's cold rolling mill using a desilication-spray roasting-purification process. Testing showed that the raw material powder had an Fe2O3 content of 99.45 wt%, and low levels of key impurities such as silicon and chlorine. All its indicators met the YHT1 grade standard in GB / T 24244-2009.

[0040] Example 1 Iron oxide powder and petroleum coke powder were mixed at a mass ratio of 100:10, with water added as a binder. The mixture was then granulated by roller pressing to obtain particles with a diameter of 5-20 mm. These particles were then fed into a primary hydrogen reduction furnace at a controlled temperature of 840℃ for 2.5 hours under nitrogen protection. Afterward, they were subjected to primary crushing in a jaw crusher (resulting in particles with a diameter of 2-5 mm). Following this, they were fed into a secondary hydrogen reduction furnace at a controlled temperature of 810℃ for 2 hours. Then, under nitrogen protection, they were fed into a ball mill for secondary crushing (resulting in particles with a diameter of 80-150 μm). Finally, they were fed into a tertiary hydrogen reduction furnace at a controlled temperature of 780℃ for 1.5 hours. Finally, under nitrogen protection, the iron powder is ultra-finely pulverized using an air jet mill to obtain reduced iron powder. During this process, fresh hydrogen enters from the inlet of the tertiary hydrogen reduction furnace, then flows from its exhaust port to the inlet of the secondary hydrogen reduction furnace. After passing through the exhaust port of the secondary hydrogen reduction furnace, the hydrogen passes sequentially through a hydrogen-rich condenser dust collector and a hydrogen-rich deoxygenation booster before connecting to the inlets of the tertiary and primary hydrogen reduction furnaces. The hydrogen from the primary hydrogen reduction furnace, after passing through its exhaust port, flows sequentially through a tail gas condenser dust collector, a tail gas microfiltration deoxygenation device, and a pressure swing adsorption device before connecting to the inlet of the tertiary hydrogen reduction furnace, thus achieving hydrogen recycling. The process flow diagram is shown below. Figure 1 As shown.

[0041] Example 2 Iron oxide powder and petroleum coke powder were mixed at a mass ratio of 100:10, with water added as a binder. The mixture was then granulated by roller pressing to obtain particles with a diameter of 5-20 mm. These particles were then fed into a primary hydrogen reduction furnace at a controlled temperature of 850℃ for 2 hours under nitrogen protection. Afterward, they were subjected to primary crushing in a jaw crusher (resulting in particles with a diameter of 2-5 mm). Following this, they were fed into a secondary hydrogen reduction furnace at a controlled temperature of 820℃ for 1.5 hours. Under nitrogen protection, they were then subjected to secondary crushing in a ball mill (resulting in particles with a diameter of 60-120 μm). Finally, they were fed into a tertiary hydrogen reduction furnace at a controlled temperature of 800℃ for 1 hour of further reduction. h. Finally, under nitrogen protection, the iron is ultra-finely pulverized using an air jet mill to obtain reduced iron powder. During this process, fresh hydrogen enters from the inlet of the three-stage hydrogen reduction furnace, and then connects to the inlet of the two-stage hydrogen reduction furnace from the exhaust port of the three-stage hydrogen reduction furnace. After passing through the exhaust port of the two-stage hydrogen reduction furnace, the hydrogen passes sequentially through a hydrogen-rich condenser dust collector and a hydrogen-rich deoxygenation booster to the inlets of the three-stage and one-stage hydrogen reduction furnaces. The hydrogen in the one-stage hydrogen reduction furnace passes sequentially through a tail gas condenser dust collector, a tail gas microfiltration deoxygenation device, and a pressure swing adsorption device from the exhaust port of the one-stage hydrogen reduction furnace to the inlet of the three-stage hydrogen reduction furnace, thus realizing the recycling of hydrogen.

[0042] Example 3 Iron oxide powder and petroleum coke powder were mixed at a mass ratio of 100:10, and water was added as a binder. The mixture was then granulated by roller pressing to obtain granules with a particle size of 5~20mm. These granules were then fed into a primary hydrogen reduction furnace at a controlled temperature of 860℃ for 1.5h. Under nitrogen protection, the mixture was then fed into a jaw crusher for primary crushing (the crushed particle size was 2~5mm). After that, it was fed into a secondary hydrogen reduction furnace at a controlled temperature of 830℃ for 1h. Under nitrogen protection, it was fed into a ball mill for secondary crushing (the crushed particle size was 80~160μm). Finally, it was fed into a tertiary hydrogen reduction furnace at a controlled temperature of 820℃ for further reduction. After 5 hours, under nitrogen protection, the iron powder is further pulverized using an air jet mill to obtain reduced iron powder. During this process, fresh hydrogen enters from the inlet of the tertiary hydrogen reduction furnace and then connects to the inlet of the secondary hydrogen reduction furnace from the exhaust port of the tertiary hydrogen reduction furnace. After passing through the exhaust port of the secondary hydrogen reduction furnace, the hydrogen passes sequentially through a hydrogen-rich condenser dust collector and a hydrogen-rich deoxygenation pressurization device, connecting to the inlets of the tertiary and primary hydrogen reduction furnaces. The hydrogen in the primary hydrogen reduction furnace passes sequentially through a tail gas condenser dust collector, a tail gas microfiltration deoxygenation device, and a pressure swing adsorption device from the exhaust port of the primary hydrogen reduction furnace, connecting to the inlet of the tertiary hydrogen reduction furnace, thus achieving hydrogen recycling.

[0043] Example 4 Iron oxide powder and petroleum coke powder were mixed at a mass ratio of 100:10, with water added as a binder. The mixture was then granulated by roller pressing to obtain particles with a diameter of 5-20 mm. These particles were then fed into a primary hydrogen reduction furnace at a controlled temperature of 800℃ for 2 hours under nitrogen protection. Afterward, they were subjected to primary crushing in a jaw crusher (resulting in particles with a diameter of 2-5 mm). Following this, they were fed into a secondary hydrogen reduction furnace at a controlled temperature of 820℃ for 1.5 hours. Under nitrogen protection, they were then subjected to secondary crushing in a ball mill (resulting in particles with a diameter of 100-200 μm). Finally, they were fed into a tertiary hydrogen reduction furnace at a controlled temperature of 850℃ for 1 hour of further reduction. h. Finally, under nitrogen protection, the iron is ultra-finely pulverized using an air jet mill to obtain reduced iron powder. During this process, fresh hydrogen enters from the inlet of the three-stage hydrogen reduction furnace, and then connects to the inlet of the two-stage hydrogen reduction furnace from the exhaust port of the three-stage hydrogen reduction furnace. After passing through the exhaust port of the two-stage hydrogen reduction furnace, the hydrogen passes sequentially through a hydrogen-rich condenser dust collector and a hydrogen-rich deoxygenation booster to the inlets of the three-stage and one-stage hydrogen reduction furnaces. The hydrogen in the one-stage hydrogen reduction furnace passes sequentially through a tail gas condenser dust collector, a tail gas microfiltration deoxygenation device, and a pressure swing adsorption device from the exhaust port of the one-stage hydrogen reduction furnace to the inlet of the three-stage hydrogen reduction furnace, thus realizing the recycling of hydrogen.

[0044] Example 5 Iron oxide powder and petroleum coke powder were mixed at a mass ratio of 100:10, with water added as a binder. The mixture was then granulated by roller pressing to obtain particles with a diameter of 5-20 mm. These particles were then fed into a primary hydrogen reduction furnace at a controlled temperature of 850℃ for 2 hours under nitrogen protection. After primary crushing in a jaw crusher (resulting in particles with a diameter of 2-5 mm), the mixture was further fed into a secondary hydrogen reduction furnace at a controlled temperature of 850℃ for 1.5 hours. Under nitrogen protection, the mixture was then fed into a ball mill for secondary crushing (resulting in particles with a diameter of 90-180 μm). Finally, the mixture was fed into a tertiary hydrogen reduction furnace at a controlled temperature of 850℃ for 1 hour of further reduction. h. Finally, under nitrogen protection, the iron is ultra-finely pulverized using an air jet mill to obtain reduced iron powder. During this process, fresh hydrogen enters from the inlet of the three-stage hydrogen reduction furnace, and then connects to the inlet of the two-stage hydrogen reduction furnace from the exhaust port of the three-stage hydrogen reduction furnace. After passing through the exhaust port of the two-stage hydrogen reduction furnace, the hydrogen passes sequentially through a hydrogen-rich condenser dust collector and a hydrogen-rich deoxygenation booster to the inlets of the three-stage and one-stage hydrogen reduction furnaces. The hydrogen in the one-stage hydrogen reduction furnace passes sequentially through a tail gas condenser dust collector, a tail gas microfiltration deoxygenation device, and a pressure swing adsorption device from the exhaust port of the one-stage hydrogen reduction furnace to the inlet of the three-stage hydrogen reduction furnace, thus realizing the recycling of hydrogen.

[0045] Example 6 Iron oxide powder and petroleum coke powder were mixed at a mass ratio of 100:10, with water added as a binder. The mixture was then granulated by roller pressing to obtain particles with a diameter of 5-20 mm. These particles were then fed into a primary hydrogen reduction furnace at a controlled temperature of 840℃ for 2 hours under nitrogen protection. After primary crushing in a jaw crusher (resulting in particles with a diameter of 2-5 mm), the mixture was further fed into a secondary hydrogen reduction furnace at a controlled temperature of 810℃ for 1.5 hours. Under nitrogen protection, the mixture was then fed into a ball mill for secondary crushing (resulting in particles with a diameter of 80-150 μm). Finally, the mixture was fed into a tertiary hydrogen reduction furnace at a controlled temperature of 780℃ for 1 hour of further reduction. h. Finally, under nitrogen protection, the iron is ultra-finely pulverized using an air jet mill to obtain reduced iron powder. During this process, fresh hydrogen enters from the inlet of the three-stage hydrogen reduction furnace, and then connects to the inlet of the two-stage hydrogen reduction furnace from the exhaust port of the three-stage hydrogen reduction furnace. After passing through the exhaust port of the two-stage hydrogen reduction furnace, the hydrogen passes sequentially through a hydrogen-rich condenser dust collector and a hydrogen-rich deoxygenation booster to the inlets of the three-stage and one-stage hydrogen reduction furnaces. The hydrogen in the one-stage hydrogen reduction furnace passes sequentially through a tail gas condenser dust collector, a tail gas microfiltration deoxygenation device, and a pressure swing adsorption device from the exhaust port of the one-stage hydrogen reduction furnace to the inlet of the three-stage hydrogen reduction furnace, thus realizing the recycling of hydrogen.

[0046] Example 7 Iron oxide powder and petroleum coke powder were mixed at a mass ratio of 100:10, with water added as a binder. The mixture was then granulated by roller pressing to obtain particles with a diameter of 5-20 mm. These particles were then fed into a primary hydrogen reduction furnace at a controlled temperature of 860℃ for 2 hours under nitrogen protection. After primary crushing in a jaw crusher (resulting in particles with a diameter of 2-5 mm), the mixture was further fed into a secondary hydrogen reduction furnace at a controlled temperature of 830℃ for 1.5 hours. Under nitrogen protection, the mixture was then fed into a ball mill for secondary crushing (resulting in particles with a diameter of 80-150 μm). Finally, the mixture was fed into a tertiary hydrogen reduction furnace at a controlled temperature of 820℃ for 1 hour of further reduction. h. Finally, under nitrogen protection, the iron is ultra-finely pulverized using an air jet mill to obtain reduced iron powder. During this process, fresh hydrogen enters from the inlet of the three-stage hydrogen reduction furnace, and then connects to the inlet of the two-stage hydrogen reduction furnace from the exhaust port of the three-stage hydrogen reduction furnace. After passing through the exhaust port of the two-stage hydrogen reduction furnace, the hydrogen passes sequentially through a hydrogen-rich condenser dust collector and a hydrogen-rich deoxygenation booster to the inlets of the three-stage and one-stage hydrogen reduction furnaces. The hydrogen in the one-stage hydrogen reduction furnace passes sequentially through a tail gas condenser dust collector, a tail gas microfiltration deoxygenation device, and a pressure swing adsorption device from the exhaust port of the one-stage hydrogen reduction furnace to the inlet of the three-stage hydrogen reduction furnace, thus realizing the recycling of hydrogen.

[0047] Comparative Example 1 Iron oxide powder and petroleum coke powder are mixed at a mass ratio of 100:10, water is added as a binder, and the mixture is granulated by roller pressing to obtain granules with a particle size of 5~20mm. Then, the granules are reduced in a primary hydrogen reduction furnace at a controlled temperature of 840℃ for 2.5h. Under nitrogen protection, the granules are then crushed in a jaw crusher (the particle size after crushing is 2~5mm). After the primary crushing, the granules are reduced in a secondary hydrogen reduction furnace at a controlled temperature of 810℃ for 2h. Under nitrogen protection, the granules are then crushed in a ball mill to obtain reduced iron powder. In this process, fresh hydrogen enters from the inlet of the secondary hydrogen reduction furnace and then connects to the inlet of the primary hydrogen reduction furnace from the exhaust port of the secondary hydrogen reduction furnace. After passing through the exhaust port of the primary hydrogen reduction furnace, the hydrogen passes through the hydrogen-rich condenser dust collector and the hydrogen-rich deoxygenation pressurization device in sequence and then connects to the inlet of the secondary hydrogen reduction furnace, thus realizing the recycling of hydrogen.

[0048] Performance testing The reduced iron powders prepared in Examples 1-7 and Comparative Example 1 were subjected to the following performance tests: (1) The purity of reduced iron powder was determined based on GB / T 223.5-2008 "Determination of Acid-Soluble Silicon and Total Silicon Content in Iron and Steel - Spectrophotometric Method of Reduced Silicon Molybdate" and GB / T 20125-2006 "Determination of Multi-Element Content in Low Alloy Steel - Inductively Coupled Plasma Atomic Emission Spectrometry". (2) The average particle size of the reduced iron powder was determined using a laser particle size analyzer (Malvern Mastersizer 3000); (3) The oxygen content was determined in accordance with GB / T 4164-2008 "Determination of Oxygen Content that Can Be Reduced by Hydrogen in Metal Powders"; The test results are shown in Table 1.

[0049] Table 1. Performance test results of reduced iron powder prepared in Examples 1-7 and Comparative Example 1

[0050] Table 1 shows that, compared with Comparative Example 1, the reduced iron powder prepared in Examples 1-7 has higher purity, lower average particle size, and lower oxygen content. The reduced iron powder in Examples 1-7 has a purity of over 99.5%, an average particle size of less than 10 μm, and an oxygen content of less than 0.35%. This indicates that the alternating process of three-stage reduction and crushing (first-stage reduction, first-stage crushing, second-stage reduction, second-stage crushing, third-stage reduction, and third-stage crushing) can effectively improve the purity of the reduced iron powder.

[0051] Compared with Examples 4-5, the reduced iron powder prepared in Examples 1-3 has higher purity and lower average particle size, indicating that the temperature decreases step by step in the primary, secondary and tertiary reduction processes, which can further improve the purity of the reduced iron powder and ultimately further ensure the quality and stability of the reduced iron powder.

[0052] Compared with Examples 6-7, the reduced iron powder prepared in Example 2 has higher purity, lower average particle size, and lower oxygen content. This indicates that when the temperature of the first-stage reduction is 850℃, the temperature of the second-stage reduction is 820℃, and the temperature of the third-stage reduction is 800℃, the purity of the reduced iron powder can be further improved, and the quality and stability of the reduced iron powder can be further guaranteed.

[0053] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing high-purity ultrafine reduced iron powder, characterized in that, Includes the following steps: After granulation, iron oxide powder is subjected to primary reduction, primary crushing, secondary reduction, secondary crushing, tertiary reduction and tertiary crushing in sequence to obtain reduced iron powder.

2. The method for preparing high-purity ultrafine reduced iron powder according to claim 1, characterized in that, The reduced iron powder has a purity of ≥99.5% and an average particle size of <10μm.

3. The method for preparing high-purity ultrafine reduced iron powder according to claim 1, characterized in that, The reducing gases used in the primary, secondary, and tertiary reduction processes each independently include hydrogen.

4. The method for preparing high-purity ultrafine reduced iron powder according to claim 1, characterized in that, The primary, secondary, and tertiary crushing processes are each carried out independently in an inert gas, which includes nitrogen.

5. The method for preparing high-purity ultrafine reduced iron powder according to claim 1, characterized in that, The temperature for the first-stage reduction is 840~860℃; The temperature for the secondary reduction is 810~830℃; The temperature for the three-stage reduction is 780~820℃.

6. The method for preparing high-purity ultrafine reduced iron powder according to claim 1, characterized in that, The time for the first-stage reduction is 1.5~2.5 hours; The secondary reduction time is 1-2 hours; The time for the three-stage reduction is 0.5~1.5h.

7. The method for preparing high-purity ultrafine reduced iron powder according to claim 5, characterized in that, The temperatures of the first-stage reduction, second-stage reduction, and third-stage reduction decrease progressively.

8. The method for preparing high-purity ultrafine reduced iron powder according to claim 7, characterized in that, The temperature for the first-stage reduction is 850°C; The temperature for the secondary reduction is 820℃; The temperature for the three-stage reduction is 800℃.

9. The method for preparing high-purity ultrafine reduced iron powder according to claim 6, characterized in that, The first-level restoration takes 2 hours; The secondary reduction time is 1.5 hours; The time for the three-stage restoration is 1 hour.

10. The method for preparing high-purity ultrafine reduced iron powder according to claim 1, characterized in that, It also includes the hydrogen cycle step: Fresh hydrogen gas is passed into the third-stage reduction, the gas produced by the reaction is passed into the second-stage reduction, and the gas produced by the second-stage reduction is passed into the first-stage reduction and the third-stage reduction respectively. The exhaust gas discharged from the first stage reduction is treated to recover hydrogen and then reintroduced into the third stage reduction.

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