Method for directly reducing micro-fine-particle iron powder from high-purity iron ore concentrate through hydrogen-based low-temperature fluidization

Abstract

The invention relates to a method for directly reducing micro-fine-particle iron powder from high-purity iron ore concentrate through hydrogen-based low-temperature fluidization, belongs to the technical field of mineral processing, and mainly relates to five stages of nitrogen replacement of air, preheating dehydration, low-temperature fluidization direct reduction, inert cooling and ore grinding screening. And fluidization direct reduction at the low temperature of 570-620 DEG C into metal iron powder is achieved, efficient ore grinding is conducted on the basis, and the micro-fine-particle iron powder with the particle size D50 smaller than or equal to 3 micrometers is prepared. Compared with a conventional 800-1400 DEG C high-temperature preparation process of the reduced iron powder, the energy consumption and the material consumption are greatly reduced, and meanwhile bonding and flow loss are effectively avoided. According to the technological method, H2 serves as reducing gas, fluidized roasting is adopted, and the technological method has the advantages of being simple in technological process, free of carbon emission, high in reduction efficiency and the like.

Description

Technical Field

[0001] The invention belongs to the technical field of mineral processing, and particularly relates to a method for directly reducing fine iron powder by hydrogen-based low-temperature fluidization of high-purity iron concentrate. Background Art

[0002] Iron is one of the most widely used metal materials in modern industry and can be used in powder metallurgy, welding material production, machinery manufacturing, construction and transportation, pharmaceutical and chemical industries. Among them, fine iron powder is mainly used to make high-performance stealth materials, infrared stealth materials, structural stealth materials, and mobile phone radiation shielding materials due to its high coercivity, high specific saturation magnetization, high signal-to-noise ratio, and good oxidation resistance. With the high-quality development of my country's industry and manufacturing industry, the demand for fine reduced iron powder is increasing year by year.

[0003] Traditional blast furnace-coking-sintering ironmaking requires high-quality iron ore as raw material, and is heavily dependent on metallurgical coke as an energy source and reducing agent, causing serious pollution problems during the ironmaking process. The Chinese invention patent with publication number CN105907947A proposes a "method for preparing iron powder and a system for preparing iron powder", which mixes iron concentrate with a reducing agent, limestone, additives and a binder to form a ball and perform reduction smelting treatment to obtain metallized pellets, and then grinds and magnetically separates the metallized pellets to prepare iron powder. The preparation process is relatively complicated and cumbersome. Direct reduction ironmaking is a non-blast furnace ironmaking process that directly reduces iron oxides to metallic iron. It can directly reduce high-purity iron concentrate to spongy metallic iron, and has the characteristics of simple process, low energy consumption and low pollution emissions.

[0004] At present, the preparation process of conventional reduced iron powder is carried out under high temperature conditions of 800-1400℃. The Chinese invention patent with publication number CN118305319A proposes "A device and method for preparing iron powder using iron concentrate powder as raw material". The high temperature H2 reduction temperature used is greater than 800℃. Not only is the process energy consumption high, but the iron ore powder will cause adhesion loss due to the precipitation of metallic iron during the high temperature fluidized reduction process, which will affect production. The higher the reduction temperature, the more serious the adhesion loss phenomenon. At present, the main measures to avoid adhesion loss are to lower the reduction temperature, add inert coating, increase external force field stirring, etc. The Chinese invention patent with publication number CN117867269A proposes "A raw material suitable for fluidized bed direct reduction ironmaking and its preparation method", using a binder and a coating agent to reduce adhesion loss. However, adding inert coating or increasing external force field stirring requires additional processes and increases process production costs. In comparison, lowering the reduction temperature is undoubtedly a simpler and more economical way.

[0005] The Chinese invention patent with publication number CN118460811A proposes "A method for pre-treatment of iron ore powder - efficient and low-carbon direct reduction". Before direct reduction roasting, the iron ore powder raw material, reduction dust collection material, additives and water need to be mixed and granulated, roasted and consolidated, and cooled to obtain an iron ore consolidation material. The Chinese invention patent with publication number CN105925743A proposes "A method for producing ultra-pure iron by direct reduction of ultra-high-grade iron concentrate in a gas-based vertical furnace". It uses ultra-high-grade iron concentrate as raw material, adds organic binder, pelletizes, and oxidizes and roasts to produce oxidized pellets, and then directly reduces them in a gas-based vertical furnace. Different from the above invention patents, the present invention utilizes the characteristic of fluidization that can directly process powder ore. It uses high-purity iron concentrate as raw material, without the need for pelletizing and granulation. Under the action of high-speed hydrogen gas flow, fluidization is directly reduced to obtain metallic iron, and then grinding is used to prepare particles with a diameter of D 50 ≤3μm fine iron powder. This process has the advantages of no carbon emission, low roasting temperature, not easy to stick and lose flow, high reduction efficiency, simple process, etc., and has broad development and application prospects. Summary of the invention

[0006] In view of the shortcomings of the prior art, the present invention provides a method for preparing fine-grained iron powder by hydrogen-based low-temperature fluidized direct reduction of high-purity iron concentrate. By using highly efficient and environmentally friendly H2 as a reducing agent and controlling the roasting temperature to 570-620°C, the problem of sticking and fluid loss is effectively avoided, and the low-temperature fluidized direct reduction of iron concentrate to iron powder is achieved, and then efficient grinding is used to prepare fine-grained iron powder, making the direct reduction of iron powder process more economical and environmentally friendly.

[0007] The method for direct reduction of fine iron powder by hydrogen-based low-temperature fluidization of high-purity iron concentrate of the present invention comprises the following steps:

[0008] Step 1: Feeding Operation

[0009] Open the upper connecting valve of the roasting tube of the fluidized roasting device, feed the iron concentrate onto the porous medium plate inside the roasting tube to make the iron concentrate loosely distributed, and close the upper connecting valve;

[0010] Step 2: Nitrogen replacement of air

[0011] Open the switch of the N2 gas cylinder, let in N2, and exhaust the air in the roasting tube;

[0012] Step 3: Preheat and dehydrate

[0013] The temperature controller of the fluidized roasting device is started, and the electric heating wire heats the roasting tube at a temperature of 570-620°C. When the temperature in the roasting tube rises to a preset temperature, the temperature rise is stopped and kept constant for 10-30 minutes. The speed and heat of the high-temperature airflow are used to fluidize the iron ore concentrate, and the adsorbed water and other volatile components in the iron ore concentrate are removed to obtain a dry material.

[0014] Step 4: Hydrogen-based low-temperature fluidized direct reduction operation

[0015] Open the switch of the H2 gas cylinder, introduce H2 into the roasting tube, adjust the total gas volume of H2 and N2 and the volume percentage of hydrogen, and carry out reduction roasting for 60 to 80 minutes at a roasting temperature of 570 to 620°C and under the action of the airflow of H2 and N2. At this time, the iron minerals in the iron concentrate are in a low-temperature fluidized environment and undergo a reduction reaction with H2 to generate reduced iron powder;

[0016] Step 5: Inert Cooling Operation

[0017] After the roasting is completed, the introduction of H2 into the roasting tube is stopped, and the roasting tube is taken out of the fluidized roasting device, and the reduced iron powder is cooled to room temperature under the protection of N2;

[0018] Step 6: Grinding and Screening Operations

[0019] Weigh the reduced iron powder according to the mass ratio of grinding ball: reduced iron powder = 15:1, put it into the planetary ball mill for grinding, set the mill speed to 500r / min, and the grinding time ≥12h. After the ball milling is completed, sieve to separate the reduced iron powder from the grinding balls to obtain a particle size D 50 Fine reduced iron powder ≤3μm.

[0020] Furthermore, the iron concentrate described in step 1 is magnetite powder, the TFe grade is ≥71.00%, the content of other impurities is ≤0.5%, and the content of iron concentrate with a particle size of 60 to 20 μm accounts for more than 80%.

[0021] Furthermore, the gas flow rate of N2 introduced in step 2 is ≥1000mL / min, and the evacuation time is ≥3min.

[0022] Furthermore, the total gas volume of H2 and N2 in step 4 is ≥1000 mL / min, and the volume percentage of hydrogen is ≥60%.

[0023] Furthermore, in step 4, three chemical reactions mainly occur in the hydrogen-based low-temperature fluidized direct reduction operation: first, magnetite directly reacts with hydrogen to generate reduced iron powder; second, magnetite reacts with hydrogen to generate fusate; third, fusate generated by the reaction of magnetite with hydrogen further undergoes a reduction reaction with hydrogen to generate reduced iron powder.

[0024] Furthermore, the reduced iron powder in step 5 has a TFe grade of ≥95%, and is a single-grain sponge-like reduced iron powder.

[0025] Furthermore, the planetary ball mill described in step 6 uses a stainless steel tank and stainless steel grinding balls, the diameters of the grinding balls are 10 mm, 5 mm and 2.5 mm respectively, and the mass ratio thereof is 1:2:1.

[0026] Furthermore, the fluidized roasting device includes a roasting tube, a porous medium plate, a heating device, a thermal insulation material and an exhaust pipe. The roasting tube is a cylindrical tube with a detachable upper connecting valve and a lower connecting valve at both ends, and a porous medium plate is provided inside. The lower end of the roasting tube is provided with an air inlet, and the upper end is provided with an exhaust port. The heating device includes a thermocouple and a heating wire arranged on the outside of the roasting tube, and a thermal insulation material is provided on the outer layer of the heating wire; the temperature controller is connected to the thermocouple and the heating wire.

[0027] Furthermore, the gas storage device includes an N2 gas cylinder and an H2 gas cylinder, and the gas flow controller is arranged between the gas storage device and the fluidized bed roasting device. The N2 gas cylinder and the H2 gas cylinder are connected to the gas inlet of the gas flow controller through an N2 pipeline and an H2 pipeline respectively, and a switch and a pressure dividing valve are respectively provided on the N2 pipeline and the H2 pipeline; the gas outlet of the gas flow controller is connected to the fluidized bed roasting tube through the roasting air inlet pipeline.

[0028] Compared with the prior art, the advantages of the present invention are:

[0029] 1. The raw material for preparing fine-grained reduced iron powder is iron concentrate, with TFe grade ≥71.00% and trace impurity content, which effectively avoids the interference of impurities in the process of reducing iron concentrate to iron powder, thereby obtaining a higher metal conversion rate. At the same time, the content of iron concentrate with a particle size of 60-20μm accounts for more than 80%, and the narrow particle size of iron concentrate ensures good fluidization.

[0030] 2. Based on the hydrogen-based reduction system and method designed and developed by the present invention, the roasting temperature is controlled at 570-620°C, realizing the preparation of iron powder by low-temperature direct reduction. Compared with the conventional high-temperature preparation process of 800-1400°C for reducing iron powder, it greatly reduces energy consumption and material consumption and improves production efficiency. Compared with adding inert agents and increasing external force fields, lowering the reduction temperature is a simpler and more effective way to avoid adhesion loss.

[0031] 3. The present invention uses H2-rich gas as reducing gas. Compared with CO, H2 has the advantages of high energy density, fast mass transfer speed and environmentally friendly reduction products. The reaction product is water, does not involve carbon-containing energy and reducing agents, and has no carbon emissions. Related studies have shown that the use of H2-rich reducing gas can reduce the occurrence of adhesion loss.

[0032] 4. The present invention adopts a planetary ball mill with high grinding efficiency and excellent uniformity, so that it can efficiently and stably prepare fine iron powder. The fluidized device is used for reduction roasting, which has high heat and mass transfer efficiency, sufficient gas-solid contact between particles, more thorough reaction, and can significantly improve resource utilization. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1Schematic diagram of the process flow of an embodiment of the present invention.

[0034] Figure 2 This is the surface morphology of fine iron powder.

[0035] Figure 3 This is the particle size distribution diagram of fine iron powder.

[0036] Figure 4 Schematic diagram of the structure of a direct reduction roasting system according to an embodiment of the present invention.

[0037] In the figure: 1. N2 gas cylinder, 2. H2 gas cylinder, 3. N2 pipeline, 4. H2 pipeline, 5. gas flow controller, 6. roasting air inlet pipeline, 7. porous medium plate, 8. iron concentrate, 9. roasting tube, 10. heating wire, 11. thermocouple, 12. thermal insulation material, 13. temperature controller, 14. exhaust pipe, 15. N2 pressure dividing valve, 16. H2 pressure dividing valve. DETAILED DESCRIPTION

[0038] The technical solutions in the embodiments of the present invention will be described clearly and completely below in conjunction with the embodiments of the present invention. It should be noted that the examples described in the present invention are only used to further explain and illustrate, rather than to limit the scope of application. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in the field without creative work are within the scope of protection of the present invention.

[0039] The method for direct reduction of fine iron powder by hydrogen-based low-temperature fluidization of high-purity iron concentrate of the present invention comprises the following steps:

[0040] Step 1: Feeding Operation

[0041] Open the upper connecting valve of the roasting tube 9 of the fluidized roasting device, feed the iron ore concentrate to the porous medium plate 7 inside the roasting tube 9, make the iron ore concentrate 8 loosely distributed, and close the upper connecting valve;

[0042] The iron concentrate 8 is magnetite powder, with a TFe grade of ≥71.00%, other impurities content of ≤0.5%, and the content of iron concentrate particles with a diameter of 60 to 20 μm accounting for more than 80%;

[0043] Step 2: Nitrogen replacement of air

[0044] Open the switch of N2 gas cylinder 1, let in N2, and exhaust the air in the roasting tube 9. The gas flow rate of N2 is ≥1000mL / min, and the exhaust time is ≥3min;

[0045] Step 3: Preheat and dehydrate

[0046] The temperature controller 13 of the fluidized roasting device is started, and the electric heating wire 10 heats the roasting tube 9 at a heating temperature of 570-620° C. When the temperature in the roasting tube 9 rises to a preset temperature, the temperature rise is stopped and maintained at a constant temperature for 10-30 minutes. The speed and heat of the high-temperature airflow are used to fluidize the iron ore concentrate, and the adsorbed water and other volatile components in the iron ore concentrate are removed to obtain a dry material.

[0047] The main reaction for removing adsorbed water from the iron ore concentrate is:

[0048] H2O(l)=H2O(g) (1);

[0049] Step 4: Hydrogen-based low-temperature fluidized direct reduction operation

[0050] Open the switch of H2 gas cylinder 2, introduce H2 into the roasting tube, adjust the total amount of H2 and N2 and the volume percentage of hydrogen, and carry out reduction roasting for 60 to 80 minutes at a roasting temperature of 570 to 620°C and under the action of the airflow of H2 and N2. At this time, the iron minerals in the iron concentrate are in a low-temperature fluidized environment and undergo a reduction reaction with H2 to generate reduced iron powder;

[0051] The total gas volume of H2 and N2 is ≥1000mL / min, and the volume percentage of hydrogen is ≥60%.

[0052] In the hydrogen-based low-temperature fluidized direct reduction operation, three chemical reactions mainly occur: first, magnetite directly reacts with hydrogen to generate reduced iron powder; second, magnetite reacts with hydrogen to generate fusinite; third, the fusinite generated by the reaction of magnetite with hydrogen further undergoes a reduction reaction with hydrogen to generate reduced iron powder;

[0053] Step 5: Inert Cooling Operation

[0054] After the roasting is completed, the H2 is stopped from being introduced into the roasting tube 9, and the roasting tube is taken out from the fluidized roasting device, and the reduced iron powder is cooled to room temperature under the protection of N2; the TFe grade of the reduced iron powder in step 5 is ≥95%, and it is a single sponge-like reduced iron powder;

[0055] Step 6: Grinding and Screening Operations

[0056] Weigh the reduced iron powder according to the mass ratio of grinding ball: reduced iron powder = 15:1, put it into the planetary ball mill for grinding, set the mill speed to 500r / min, and the grinding time ≥12h. After the ball milling is completed, sieve to separate the reduced iron powder from the grinding balls to obtain a particle size D 50 Fine reduced iron powder ≤3μm.

[0057] The planetary ball mill adopts a stainless steel tank and stainless steel grinding balls, the diameters of the grinding balls are 10 mm, 5 mm and 2.5 mm respectively, and the mass ratio thereof is 1:2:1.

[0058] The fluidized calcining device of the present invention comprises a calcining tube 9, a porous medium plate 7, a heating device, a heat insulating material 12 and an exhaust pipe 14. The calcining tube 9 is a cylindrical tube with a detachable upper connecting valve and a lower connecting valve at both ends, and a porous medium plate 7 is arranged inside. The lower end of the calcining tube is provided with an air inlet, and the upper end is provided with an exhaust port 14. The heating device comprises a thermocouple 11 and a heating wire 10 arranged outside the calcining tube, and a heat insulating material 12 is arranged on the outer layer of the heating wire 10; the temperature controller 13 is connected to the thermocouple 11 and the heating wire 10;

[0059] The gas storage device comprises an N2 gas cylinder 1 and an H2 gas cylinder 2, which are connected to a gas flow controller 5 through an N2 pipeline 3 and an H2 pipeline 4, respectively. A switch and an N2 pressure dividing valve 15 and an H2 pressure dividing valve 16 are respectively provided on the N2 pipeline 3 and the H2 pipeline 4;

[0060] The gas storage device includes an N2 gas cylinder 1 and an H2 gas cylinder 2. The gas flow controller 5 is arranged between the gas storage device and the fluidized roasting device. The N2 gas cylinder 1 and the H2 gas cylinder 2 are connected to the gas inlet of the gas flow controller 5 through an N2 pipeline 3 and an H2 pipeline 4, respectively. A switch and an N2 pressure dividing valve 15 and an H2 pressure dividing valve 16 are respectively provided on the N2 pipeline 3 and the H2 pipeline 4; the gas outlet of the gas flow controller 5 is connected to the roasting tube 9 through the roasting air inlet pipeline 6.

[0061] Embodiment 1:

[0062] A method for direct reduction of fine iron powder by hydrogen-based low-temperature fluidization of high-purity iron concentrate adopts the above system, takes an iron concentrate from Liaoning as raw material, wherein the TFe grade is 71.22%, the content of other impurities is ≤0.5%, and the content of iron concentrate particles with a diameter of 60 to 20 μm accounts for 82.35%, and comprises the following steps:

[0063] (1) Ore feeding operation: open the upper connecting valve of the roasting tube, feed the iron ore concentrate onto the porous medium plate inside the fluidized roasting tube, make the iron ore concentrate loosely distributed, and reconnect the upper connecting valve;

[0064] (2) Nitrogen replacement of air: Connect the gas channel of the roasting device and ensure that the pipeline is unobstructed. Turn on the switch of the N2 gas cylinder and introduce N2 into the roasting tube at a gas flow rate of 1500 mL / min. The evacuation time is 5 min to exhaust the air in the roasting tube.

[0065] (3) Preheating and dehydration operation: Start the temperature control system of the fluidized bed roasting device and set the reduction roasting temperature to 575°C. When the temperature in the roasting system rises to the preset temperature, stop heating and maintain a constant temperature. Place the fluidized bed roasting tube in the roasting system for 10 minutes to fluidize the iron ore concentrate and remove the adsorbed water and other volatile components in the iron ore concentrate to obtain dry material.

[0066] (4) Hydrogen-based low-temperature fluidized direct reduction operation: Turn on the H2 gas cylinder switch and introduce H2 into the roasting tube at a total gas volume of 1200 mL / min and a hydrogen volume percentage of 60%. Perform reduction roasting for 60 min. At this time, the iron ore concentrate reacts with H2 to generate reduced iron powder;

[0067] (5) Inert cooling operation: After the roasting is completed, the introduction of H2 is stopped, and the roasting tube is taken out of the roasting device, and the reduced iron powder generated by the reduction is cooled to room temperature under the protection of N2 to obtain reduced iron powder with a TFe grade of 95.26%.

[0068] (6) Grinding and screening: The reduced iron powder is placed in a planetary ball mill and ground at a speed of 500 r / min for 12 h. After the ball milling is completed, the grinding balls are separated by sieving to obtain a particle size of D 50 =2.97μm fine reduced iron powder.

[0069] Embodiment 2:

[0070] A method for direct reduction of fine iron powder by hydrogen-based low-temperature fluidization of high-purity iron concentrate adopts the above system, takes an iron concentrate from Shandong as raw material, wherein the TFe grade is 71.56%, the content of other impurities is ≤0.5%, and the content of iron concentrate particles with a diameter of 60 to 20 μm accounts for 85.76%, and comprises the following steps:

[0071] (1) Ore feeding operation: Open the upper connecting valve of the roasting tube, feed the iron ore concentrate to the porous medium plate inside the roasting tube, so that the iron ore concentrate is loosely distributed, and then connect the upper connecting valve again.

[0072] (2) Nitrogen replacement of air: Connect the gas channel of the roasting device and ensure that the pipeline is unobstructed. Turn on the switch of the N2 gas cylinder and introduce N2 into the roasting tube with a gas flow rate of 1500 mL / min. The evacuation time is 5 minutes to exhaust the air in the roasting tube.

[0073] (3) Preheating and dehydration operation: Start the temperature control system of the fluidized roasting device and set the reduction roasting temperature to 580°C. When the temperature in the roasting system rises to the preset temperature, stop heating and maintain a constant temperature. Place the roasting tube in the roasting system for 15 minutes to fluidize the iron ore concentrate and remove the adsorbed water and other volatile components in the iron ore concentrate to obtain dry material.

[0074] (4) Hydrogen-based low-temperature fluidized direct reduction operation: Turn on the H2 gas cylinder switch, introduce H2 into the roasting tube, the total gas volume is 1200mL / min, the volume percentage of hydrogen is 65%, and carry out reduction roasting for 65 minutes. At this time, the iron ore concentrate reacts with H2 to generate reduced iron powder.

[0075] (5) Inert cooling operation: After the roasting is completed, the introduction of H2 is stopped, and the roasting tube is taken out of the roasting device, and the reduced iron powder generated by the reduction is cooled to room temperature under the protection of N2 to obtain reduced iron powder with a TFe grade of 96.83%.

[0076] (6) Grinding and screening: The reduced iron powder is placed in a planetary ball mill and ground at a speed of 500 r / min for 16 h. After the ball milling is completed, the grinding balls are separated by sieving to obtain a particle size of D 50 =2.36μm fine reduced iron powder.

[0077] Embodiment 3:

[0078] A method for direct reduction of fine iron powder by hydrogen-based low-temperature fluidization of high-purity iron concentrate adopts the above system, takes an iron concentrate from Hebei as raw material, wherein the TFe grade is 71.12%, the content of other impurities is ≤0.5%, and the content of iron concentrate particle size of 60 to 20 μm accounts for 81.23%, and comprises the following steps:

[0079] (1) Ore feeding operation: open the upper connecting valve of the roasting tube, feed the iron concentrate to the porous medium plate inside the roasting tube, make the iron concentrate loosely distributed, and connect the upper connecting valve again;

[0080] (2) Nitrogen replacement of air: Connect the gas channel of the roasting device and ensure that the pipeline is unobstructed. Turn on the switch of the N2 gas cylinder and introduce N2 into the roasting tube at a gas flow rate of 1200 mL / min. The evacuation time is 8 minutes to exhaust the air in the roasting tube.

[0081] (3) Preheating and dehydration operation: Start the temperature control system of the fluidized roasting device and set the reduction roasting temperature to 610°C. When the temperature in the roasting system rises to the preset temperature, stop heating and keep the temperature constant. Put the roasting tube into the roasting system for 20 minutes to make the iron concentrate in a fluidized state, remove the adsorbed water and other volatile components in the iron concentrate, and obtain dry material;

[0082] (4) Hydrogen-based low-temperature fluidized direct reduction operation: Turn on the H2 gas cylinder switch, introduce H2 into the roasting tube, the total gas volume is 1500mL / min, the volume percentage of hydrogen is 70%, and carry out reduction roasting for 70 minutes. At this time, the iron ore concentrate reacts with H2 to generate reduced iron powder;

[0083] (5) Inert cooling operation: After the roasting is completed, the introduction of H2 is stopped, and the roasting tube is taken out of the roasting device, and the reduced iron powder generated by the reduction is cooled to room temperature under the protection of N2 to obtain reduced iron powder with a TFe grade of 95.37%.

[0084] (6) Grinding and screening: The reduced iron powder is placed in a planetary ball mill and ground at a speed of 500 r / min for 14 h. After the ball milling is completed, the grinding balls are separated by sieving to obtain a particle size of D 50 =2.66μm fine-grained reduced iron powder.

[0085] Embodiment 4:

[0086] A method for direct reduction of fine iron powder by hydrogen-based low-temperature fluidization of high-purity iron concentrate adopts the above system, takes an iron concentrate from Shanxi as raw material, wherein the TFe grade is 71.07%, the content of other impurities is ≤0.5%, and the content of iron concentrate particle size of 60 to 20 μm accounts for 82.98%, and comprises the following steps:

[0087] (1) Ore feeding operation: open the upper connecting valve of the roasting tube, feed the iron concentrate to the porous medium plate inside the roasting tube, make the iron concentrate loosely distributed, and connect the upper connecting valve again;

[0088] (2) Nitrogen replacement of air: Connect the gas channel of the roasting device and ensure that the pipeline is unobstructed. Turn on the switch of the N2 gas cylinder and introduce N2 into the roasting tube at a gas flow rate of 1500 mL / min. The evacuation time is 6 minutes to exhaust the air in the roasting tube.

[0089] (3) Preheating and dehydration operation: Start the temperature control system of the fluidized roasting device and set the reduction roasting temperature to 590°C. When the temperature in the roasting system rises to the preset temperature, stop heating and keep the temperature constant. Put the roasting tube into the roasting system for 15 minutes to make the iron concentrate in a fluidized state, remove the adsorbed water and other volatile components in the iron concentrate, and obtain dry material;

[0090] (4) Hydrogen-based low-temperature fluidized direct reduction operation: Turn on the H2 gas cylinder switch, introduce H2 into the roasting tube, the total gas volume is 1600mL / min, the volume percentage of hydrogen is 75%, and carry out reduction roasting for 75 minutes. At this time, the iron ore concentrate reacts with H2 to generate reduced iron powder;

[0091] (5) Inert cooling operation: After the roasting is completed, the introduction of H2 is stopped, and the roasting tube is taken out of the roasting device, and the reduced iron powder generated by the reduction is cooled to room temperature under the protection of N2 to obtain reduced iron powder with a TFe grade of 95.15%.

[0092] (6) Grinding and screening: The reduced iron powder is placed in a planetary ball mill and ground at a speed of 500 r / min for 20 h. After the ball milling is completed, the grinding balls are separated by sieving to obtain a particle size of D 50 =1.87μm fine reduced iron powder.

[0093] Embodiment 5:

[0094] The system and method used in this embodiment are the same as those in Embodiment 1, except that:

[0095] An iron concentrate from Anhui was used as raw material, with a TFe grade of 71.42%, other impurities ≤0.5%, and iron concentrate particles with a diameter of 60-20 μm accounting for 84.05%; the reduction roasting temperature was set to 580 ° C, and the preheating and dehydration time was 15 min to obtain a dry material; the H2 gas cylinder switch was turned on, the total gas volume was 1300 mL / min, the volume percentage of hydrogen was 65%, and the reduction roasting was performed for 65 min. The iron concentrate reacted with H2 to generate reduced iron powder. After inert cooling, the reduced iron powder was placed in a planetary ball mill for 15 h to obtain fine reduced iron powder with a TFe grade of 95.78% and a particle size of D 50 =2.45μm.

[0096] Embodiment 6:

[0097] The system and method used in this embodiment are the same as those in Embodiment 1, except that:

[0098] An iron concentrate from Henan was used as raw material, with a TFe grade of 71.69%, other impurities ≤0.5%, and iron concentrate particles with a diameter of 60-20 μm accounting for 85.21%; the reduction roasting temperature was set to 585 °C, and the preheating and dehydration time was 12 min to obtain a dry material; the H2 gas cylinder switch was turned on, with a total gas volume of 1200 mL / min and a hydrogen volume percentage of 65%, and the reduction roasting was performed for 70 min. The iron concentrate reacted with H2 to generate reduced iron powder. After inert cooling, the reduced iron powder was placed in a planetary ball mill for 18 h to obtain fine reduced iron powder with a TFe grade of 97.11% and a particle size of D 50 =2.11μm.

Claims

1. A method for directly reducing fine iron powder by hydrogen-based low-temperature fluidization of high-purity iron concentrate, a system for directly reducing fine iron powder by hydrogen-based low-temperature fluidization of high-purity iron concentrate, comprising a fluidized roasting device, a gas storage device and a high-efficiency grinding system, characterized in that: The following steps are involved: Step 1: Feeding Operation Open the upper connecting valve of the roasting tube of the fluidized roasting device, feed the iron concentrate onto the porous medium plate inside the roasting tube to make the iron concentrate loosely distributed, and close the upper connecting valve; Step 2: Nitrogen replacement of air Open the switch of the N2 gas cylinder, let in N2, and exhaust the air in the fluidized bed roasting tube; Step 3: Preheat and dehydrate The temperature controller of the fluidized roasting device is started, and the electric heating wire heats the roasting tube at a temperature of 570-620°C. When the temperature in the roasting tube rises to a preset temperature, the temperature rise is stopped and kept constant for 10-30 minutes. The speed and heat of the high-temperature airflow are used to fluidize the iron ore concentrate, and the adsorbed water and other volatile components in the iron ore concentrate are removed to obtain a dry material. Step 4: Hydrogen-based low-temperature fluidized direct reduction operation Open the switch of the H2 gas cylinder, introduce H2 into the roasting tube, adjust the total gas volume of H2 and N2 and the volume percentage of hydrogen, and carry out reduction roasting for 60 to 80 minutes at a roasting temperature of 570 to 620°C and under the action of the airflow of H2 and N2. At this time, the iron minerals in the iron concentrate are in a low-temperature fluidized environment and undergo a reduction reaction with H2 to generate reduced iron powder; Step 5: Inert Cooling Operation After the roasting is completed, the introduction of H2 into the roasting tube is stopped, and the roasting tube is taken out of the fluidized roasting device, and the reduced iron powder is cooled to room temperature under the protection of N2; Step 6: Grinding and Screening Operations Weigh the reduced iron powder according to the mass ratio of grinding ball: reduced iron powder = 15:1, put it into the planetary ball mill for grinding, set the mill speed to 500r / min, and the grinding time ≥12h. After the ball milling is completed, sieve to separate the reduced iron powder from the grinding balls to obtain a particle size D 50 Fine reduced iron powder ≤3μm.

2. The method according to claim 1, characterized in that The iron concentrate described in step 1 is magnetite powder, with TFe grade ≥71.00%, other impurity contents ≤0.5%, and the content of iron concentrate with a particle size of 60-20 μm accounting for more than 80%.

3. The method according to claim 1, characterized in that The gas flow rate of N2 introduced in step 2 is ≥1000mL / min, and the evacuation time is ≥3min.

4. The method according to claim 1, characterized in that: The total gas volume of H2 and N2 in step 4 is ≥1000 mL / min, and the volume percentage of hydrogen is ≥60%.

5. The method according to claim 1, characterized in that Three chemical reactions mainly occur in the hydrogen-based low-temperature fluidized direct reduction operation described in step 4: first, magnetite directly reacts with hydrogen to generate reduced iron powder; second, magnetite reacts with hydrogen to generate fusate; third, fusate generated by the reaction of magnetite with hydrogen further undergoes a reduction reaction with hydrogen to generate reduced iron powder.

6. The method according to claim 1, characterized in that The reduced iron powder described in step 5 has a TFe grade of ≥95%, and is a single-grain sponge-shaped reduced iron powder.

7. The method according to claim 1, characterized in that The planetary ball mill described in step 6 uses a stainless steel tank and stainless steel grinding balls, the diameters of the grinding balls are 10 mm, 5 mm and 2.5 mm respectively, and the mass ratio is 1:2:.

8. The method according to claim 1, characterized in that The fluidized roasting device comprises a roasting tube, a porous medium plate, a heating device, a heat-insulating material and an exhaust pipe. The roasting tube is a cylindrical tube with a detachable upper connecting valve and a lower connecting valve at both ends, and a porous medium plate is arranged inside. The lower end of the roasting tube is provided with an air inlet, and the upper end is provided with an exhaust port. The heating device comprises a thermocouple and a heating wire arranged on the outside of the roasting tube, and a heat-insulating material is arranged on the outer layer of the heating wire; the temperature controller is connected to the thermocouple and the heating wire.

9. The method according to claim 1, characterized in that: The gas storage device includes an N2 gas cylinder and an H2 gas cylinder. The gas flow controller is arranged between the gas storage device and the fluidized roasting device. The N2 gas cylinder and the H2 gas cylinder are connected to the gas inlet of the gas flow controller through an N2 pipeline and an H2 pipeline respectively. A switch and a pressure dividing valve are respectively provided on the N2 pipeline and the H2 pipeline; the gas outlet of the gas flow controller is connected to the fluidized roasting tube through the roasting air inlet pipeline.

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