Method for improving hydrogen-based reduction whole ball rate of high-grade iron concentrate oxidized pellets

Abstract

This invention discloses a method for improving the hydrogen-based reduction pelletizing rate of high-grade iron concentrate oxide pellets, comprising the following steps: (1) mixing high-grade iron concentrate with water and then subjecting it to mechanical activation pretreatment to obtain pretreated high-grade iron concentrate; wherein the mechanical activation pretreatment satisfies the following condition (a) or (b), and the specific surface area of ​​the pretreated high-grade iron concentrate is 1500-2000 cm². 2 / g: (a) Perform at least two high-pressure roller millings; (b) Perform one high-pressure roller milling, combined with a side material recycling process; (2) Mix the pretreated high-grade iron concentrate with a binder and pelletize to obtain green pellets; (3) Dry and roast the green pellets in sequence to obtain oxidized pellets. This method achieves the optimization window of specific surface area for hydrogen-based reduction of high-grade ore, and constructs a uniform and tough pellet structure that can resist reduction stress at the microscopic level, thereby increasing the reduction pelletization rate to >60% and significantly improving the iron grade of the product.

Description

Technical Field

[0001] This invention relates to the field of iron and steel metallurgy technology, and in particular to a method for improving the hydrogen-based reduction pelletizing rate of high-grade iron concentrate oxide pellets. Background Technology

[0002] Against the backdrop of deepening global strategic initiatives, the steel industry, as a key sector of energy consumption and carbon emissions, is inevitably undergoing a low-carbon transformation. Currently, the long-process steelmaking method centered on blast furnaces and converters results in high carbon emissions per ton of steel, while the short-process method, represented by all-hydrogen shaft furnaces and electric arc furnaces, is considered a disruptive frontier technology for achieving green development in the steel industry because it can reduce carbon emissions per ton of steel by more than 50%. In this process, iron ore pellets are a high-quality charge for hydrogen-based shaft furnace smelting, and their performance directly affects the quality of direct reduced iron (DRI) and the stable operation of the shaft furnace. To maximize the benefits of hydrogen metallurgy, using high-grade iron concentrate (total iron grade >67 wt.%, extremely low gangue content) to prepare oxide pellets to obtain high-grade direct reduced iron is an important development direction for the industry.

[0003] However, while high-grade iron concentrate offers advantages in terms of high iron content, its characteristics such as low gangue content, predominantly solid-phase sintering, and insufficient liquid-phase generation make it more prone to generating significant internal stress during hydrogen-based shaft furnace reduction, especially during the lattice reconstruction stage of Fe2O3 to Fe3O4 transformation. This leads to severe pulverization. Practice shows that the "bulk ball ratio" of high-grade pellets prepared by traditional processes after gas-based shaft furnace reduction is often less than 50%. This not only causes turbulent airflow and increased pressure differential within the shaft furnace, disrupting production, but also allows a large amount of powder to enter the subsequent electric furnace, worsening the smelting environment and reducing production efficiency. Current technologies often use bentonite as a binder to improve green ball strength, but this introduces large amounts of acidic gangue such as SiO2 and Al2O3, leading to a decrease in the iron grade of the pellets and the final DRI, thus deviating from the original intention of using high-grade ore. Furthermore, although some studies have attempted to improve raw material properties through pretreatment methods such as grinding, the improvement in the hydrogen-reduced pelletizing rate of the resulting pellets after a single treatment is limited, making it difficult to meet the stringent requirements of high pelletizing rate and high grade for industrial production. Therefore, how to significantly improve the hydrogen-based reduction pelletizing rate of high-grade oxide pellets while ensuring or even improving the iron grade of the pellets has become a key technical bottleneck restricting the high-quality development of hydrogen-based vertical shaft furnace short-process production, and there is an urgent need to develop an efficient, economical, and easily integrated intensification technology and method. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a method for improving the hydrogen-based reduction pelletizing rate of high-grade iron concentrate oxide pellets, so as to effectively improve the hydrogen-based reduction pelletizing rate of high-grade oxide pellets.

[0005] To solve the above-mentioned technical problems, the technical solution adopted by the present invention includes the following steps: (1) mixing high-grade iron concentrate with water and then performing mechanical activation pretreatment to obtain pretreated high-grade iron concentrate; the mechanical activation pretreatment satisfies the following condition (a) or (b), and the specific surface area of ​​the pretreated high-grade iron concentrate is 1500-2000 cm². 2 / g: (a) Perform at least two high-pressure roller milling operations; (b) Perform a high-pressure roller mill and combine it with an edge material recycling process; (2) The pretreated high-grade iron concentrate is mixed with a binder and pelletized to obtain green pellets; (3) The green pellets are dried and roasted in sequence to obtain oxidized pellets.

[0006] Furthermore, in the edge material recycling process of step (1), the proportion of edge material returned for re-rolling is 20% to 40% of the total output mass.

[0007] Furthermore, in step (1), the water volume is 4.5–8%, and the pressure of the high-pressure roller mill is 0.8–1.5 N / mm. 2 .

[0008] Furthermore, in step (2), the amount of adhesive added is 0.5 to 2.0 wt% of the total mass of the green pellets.

[0009] Furthermore, in step (2), the adhesive is selected from at least one of bentonite, organic adhesive, and organic-inorganic composite adhesive.

[0010] Furthermore, the adhesive is an organic-inorganic composite adhesive, wherein the organic component is selected from at least one of sodium carboxymethyl cellulose, polyacrylamide, sodium humate, and dextrin.

[0011] Furthermore, the roasting process in step (2) is as follows: first, preheating roasting is carried out at 800-1000℃, and then oxidative roasting is carried out at 1150℃-1250℃.

[0012] Furthermore, the preheating and roasting time is 6–18 min, and the oxidative roasting time is 12–18 min.

[0013] The design principle of this invention is as follows: the mechanical activation pretreatment is not simply a reduction in particle size, but rather, through the cumulative shear force of at least two high-pressure roller milling processes, or the lamination and kneading effect generated by a high proportion of edge material circulation, high-density lattice distortion and dislocations are induced within the particles while maintaining high-grade ore (extremely low gangue). This activated state allows the newly formed hematite microcrystals to achieve deep solid-phase bonding across particles during subsequent oxidative roasting, forming a tough crystalline network capable of absorbing the internal stress of hydrogen reduction volume expansion.

[0014] Unlike existing technologies that blindly pursue high specific surface area, this invention discovers that high-grade iron concentrate (Fe > 67 wt.%) possesses a specific 'critical point for reduction performance'. When the specific surface area is below 1500 cm²... 2 At a density of / g, the recrystallized network is sparse; excessive machining will over-increase the water demand of the green pellets and cause blockage of the interconnected pores in the early stages of calcination. This invention achieves this through precise measurement of 1500–2000 cm⁻¹. 2 / g window control achieves a structural balance of 'strong connectivity + micropores' inside the pellets, which is key to improving the whole pellet rate of hydrogen-based reduction.

[0015] Specifically, mechanical activation within this optimized window not only significantly increases the specific surface area of ​​the raw material, but more importantly, it creates a high density of lattice defects and surface microcracks within the particles, providing a large number of highly active sites. These highly active sites greatly promote the efficient and uniform transformation of Fe3O4 to α-Fe2O3 and the diffusion and bonding of newly formed hematite microcrystals during subsequent oxidative roasting, thereby constructing a highly uniform and dense hematite recrystallization network framework within the pellets. Simultaneously, the long-chain molecules of the organic composite binder strengthen the bridging between particles during the pelletizing stage, and provide additional impetus for solid-phase diffusion through decomposition or carbonization during the roasting stage, further consolidating this strengthened framework, while introducing almost no gangue components that lower the grade.

[0016] The method of this invention actively constructs a uniform and robust microstructure, endowing the final oxidized pellets with excellent resistance to reduction stress. When the pellets undergo a dramatic lattice transformation (accompanied by approximately 10% volume expansion) from Fe2O3 to Fe3O4 in a hydrogen-based vertical shaft furnace, this reinforced structure effectively disperses and buffers internal stress, thereby fundamentally inhibiting the initiation and propagation of microcracks. This directly leads to a significant leap in the macroscopic integrity (bulk pellet ratio) of the reduced pellets: as shown in the examples, the bulk pellet ratio increases dramatically from Comparative Example 1 (conventional grinding, specific surface area 1137 cm²)... 2 The percentage of / g) surged from 14.88% in Examples 1 and 2 (specific surface areas of 1705 cm², respectively) to 14.88%. 2 / g、1876cm 2The iron content of the oxidized pellets was increased by more than 400% to 75.49% and 80.49% respectively, and the iron content of the oxidized pellets was also improved simultaneously due to the optimization of the binder.

[0017] The innovativeness of this mechanical activation invention lies in its abandonment of the path relying on chemical grinding aids. Through purely physical, multi-frequency shearing, it increases the surface free energy of the particle cluster without pollution. Instead of pursuing optimal power consumption, this invention takes "hydrogen reduction stress resistance" as its ultimate goal, deeply coupling machining parameters with the thermodynamic evolution of the pellets. Under harsh conditions of extremely low gangue content and lack of liquid-phase lubrication, mechanical activation compensates for the insufficient driving force of solid-phase sintering, solving the industry problem of easy pulverization during the reduction of high-grade pellets.

[0018] The beneficial effects of adopting the above technical solution are as follows: This invention achieves an optimized specific surface area window for the hydrogen-based reduction of high-grade minerals through high-pressure roller milling (at least twice) or high-pressure roller mill edge material recycling; and then, in synergy with low-addition binders, especially organic-inorganic composite binders, a uniform and tough pellet structure that can resist reduction stress is constructed at the microscopic level, and a dual breakthrough is achieved at the macroscopic level, simultaneously increasing the reduction pellet rate from <50% to >60% and significantly improving the iron content of the product.

[0019] This invention, through precise design and synergistic enhancement of microstructure, successfully unifies the high pellet ratio and high iron content that are difficult to achieve simultaneously in high-grade pellets. The effect is significant and not obvious, providing a high-performance key feedstock for short-process hydrogen-based vertical shaft furnaces, and has significant industrial application value. Attached Figure Description

[0020] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments.

[0021] Figure 1 This is a schematic diagram of the process flow of the present invention. Detailed Implementation

[0022] Figure 1 As shown, the method for improving the hydrogen-based reduction pelletizing rate of high-grade iron concentrate oxide pellets includes the following steps: (1) The total iron grade of the high-grade iron concentrate is greater than 67 wt.%, and the total content of SiO2 and Al2O3 is less than 2.5 wt.%. The high-grade iron concentrate is mixed with water and then subjected to mechanical activation pretreatment, with the mass of water accounting for 4.5 to 8% of the total mass of the high-grade iron concentrate and water, to obtain pretreated high-grade iron concentrate; the mechanical activation pretreatment meets the following conditions (a) or (b), and the specific surface area of ​​the pretreated high-grade iron concentrate is 1500 to 2000 cm². 2 / g: (a) Perform at least two high-pressure roller millings, preferably two or three; it can also be combined with an edge material recycling process, in which the proportion of edge material returned for re-rolling is 20% to 40% of the total output mass; (b) Perform a high-pressure roller mill and combine it with the edge material recycling process. The proportion of edge material returned for roller milling is 20% to 40% of the total output mass. That is, the edge material close to both sides of the roller mill is roller milled again once.

[0023] The pressure of the high-pressure roller mill is 0.8–1.5 N / mm. 2 The feeding speed is 4–8 kg / min. The pressure of the high-pressure roller mill described in this method is lower than that of conventional processes. It adopts a low-pressure multi-pass roller milling strategy instead of a high-pressure single pass, combined with precise water control of 4.5–8%, to ensure that the material is in a continuous 'pressure-dissociation-re-pressure' cycle in the roller gap. This specific mechanical work input mode ensures the uniform distribution of active sites on the particle surface, and the reduction of whole particles is increased to more than 60%, which has a significant synergistic effect.

[0024] (2) The pretreated high-grade iron concentrate is mixed with a binder and pelletized to obtain green pellets; the amount of binder added is 0.5-2.0 wt% of the total mass of the pretreated high-grade iron concentrate and the binder, that is, the amount of binder added is 0.5-2.0 wt% of the total mass of the green pellets. The binder is selected from at least one of bentonite, organic binder and organic-inorganic composite binder, preferably organic-inorganic composite binder. The organic binder is selected from at least one of sodium carboxymethyl cellulose, polyacrylamide, sodium humate and dextrin. In the organic-inorganic composite binder, the organic component is selected from at least one of sodium carboxymethyl cellulose, polyacrylamide, sodium humate and dextrin, and the inorganic component is bentonite. The pelletizing time is 8-14 min. The diameter of the green pellets is 10-16 mm, the moisture content is 7.5-10 wt.%; the drop strength of the green pellets is greater than or equal to 4 times / 0.5 m, the compressive strength is greater than or equal to 10 N / pellet, and the bursting temperature is greater than or equal to 500℃.

[0025] (3) A simulated chain grate-rotary kiln process is adopted, in which the green pellets are dried and calcined sequentially to obtain oxidized pellets. The drying temperature is 280℃~310℃ and the time is 5~10min. The calcination adopts preheating calcination + oxidation calcination; the preheating calcination temperature is 800~1000℃ and the time is 6~18min, with an air velocity of 2.0~2.4m / s; the oxidation calcination temperature is 1150℃~1250℃ and the time is 12~18min, with an air velocity of 2.0~2.4m / s.

[0026] (4) The compressive strength of the obtained oxide pellets is ≥2800N / piece, and the compressive strength is preferably 2800~3200N / piece; after the obtained oxide pellets are gas-based reduced in a hydrogen-based vertical furnace, the pellet wholeness rate is greater than 60%.

[0027] The raw material properties of the high-grade iron concentrate used in the following examples and comparative examples are as follows: Chemical composition: Total iron content 70.16 wt.%, SiO2 1.38 wt.%, Al2O3 0.88 wt.%; Physical properties: The raw ore particle size of -0.074mm is 94.78wt.%, and the specific surface area is 1099cm³. 2 / g.

[0028] Example 1: The method for improving the pelletizing rate of high-grade iron concentrate oxide pellets by hydrogen-based reduction is as follows: (1) Add an appropriate amount of water to the high-grade iron concentrate and adjust the water content to 8.0 wt.% to obtain magnetite concentrate; feed the magnetite concentrate into a high-pressure roller mill with a roller mill pressure of 1.17 N / mm. 2 The feeding speed was 6 kg / min, and the roller milling was performed twice. The pretreated magnetite concentrate had a -0.074 mm content of 97.51 wt.% and a specific surface area of ​​1705 cm³. 2 / g; (2) Add 1.2 wt.% bentonite to the pretreated magnetite concentrate and mix the material thoroughly. Pelletize the dispersed mixture on a disc pelletizer for 12 minutes, adding atomized water during the process to obtain qualified green pellets with a diameter of 10–16 mm and a moisture content of 9.0 wt.%. The resulting green pellets have a drop strength of 6.7 times / (0.5 m), a compressive strength higher than 10 N / pellet, and a bursting temperature higher than 600℃. (3) Using a simulated chain grate machine-rotary kiln process, the green pellets are dried at 300℃ for 6 min and preheated at 950℃ for 5 min to obtain preheated pellets with a compressive strength between 500 and 700 N / piece, and the compressive strength of the preheated pellets is 564 N / piece; the preheated pellets are then oxidized and calcined at 1150℃ for 15 min, and after cooling, oxidized pellets with a compressive strength between 2800 and 3200 N / piece are obtained, with a compressive strength of 2884 N / piece and an iron content of 67.20 wt.%.

[0029] In this embodiment, the oxidized pellets were subjected to gas-based reduction in a hydrogen-based vertical shaft furnace to determine the reduction pelletization rate. The results showed that the reduction pelletization rate was 75.49%.

[0030] Example 2: The method for improving the pelletizing rate of high-grade iron concentrate oxide pellets by hydrogen-based reduction is as follows: (1) Add an appropriate amount of water to the high-grade iron concentrate and adjust the water content to 8.0 wt.% to obtain magnetite concentrate; feed the magnetite concentrate into a high-pressure roller mill with a roller mill pressure of 1.17 N / mm. 2 The feeding speed was 6 kg / min, and the roller milling was performed three times. The pretreated magnetite concentrate had a -0.074 mm content of 98.42 wt.% and a specific surface area of ​​1876 cm³. 2 / g; (2) Add 1.2 wt.% bentonite to the pretreated magnetite concentrate and mix the material thoroughly. Pelletize the dispersed mixture on a disc pelletizer for 12 minutes, adding atomized water during the process to obtain qualified green pellets with a diameter of 10–16 mm and a moisture content of 9.0 wt.%. The resulting green pellets have a drop strength of 6.7 times / (0.5 m), a compressive strength higher than 10 N / pellet, and a bursting temperature higher than 600℃. (3) Using a simulated chain grate machine-rotary kiln process, the green pellets are dried at 280℃ for 10 min and then preheated and roasted at 950℃ for 15 min to obtain preheated pellets with a compressive strength between 500 and 700 N / piece, and the compressive strength of the preheated pellets is 572 N / piece; the preheated pellets are oxidized and roasted at 1160℃ for 15 min, and after cooling, oxidized pellets with a compressive strength between 2800 and 3200 N / piece are obtained, with a compressive strength of 2984 N / piece and an iron content of 67.20 wt.%.

[0031] In this embodiment, the oxidized pellets obtained were subjected to gas-based reduction in a hydrogen-based vertical shaft furnace to determine the reduction pelletization rate. The results showed that the reduction pelletization rate was 80.49%.

[0032] Example 3: The method for improving the hydrogen-based reduction pelletizing rate of high-grade iron concentrate oxide pellets is as follows: (1) Add an appropriate amount of water to the high-grade iron concentrate and adjust the moisture content to 8.0 wt.% to obtain magnetite concentrate; send the magnetite concentrate into a high-pressure roller mill for one high-pressure roller milling + one edge material circulation high-pressure roller milling, wherein the roller milling pressure is 1.17 N / mm 2 The feeding rate is 6 kg / min; the pretreated magnetite concentrate has a -0.074 mm content of 96.89 wt.% and a specific surface area of ​​1511 cm³. 2 / g; where, edge material circulation high-pressure roller milling refers to repeatedly roller milling the edge material close to both sides of the roller mill once; (2) 1.2 wt.% bentonite was added to the magnetite concentrate after high-pressure roller mill pretreatment, and the material was thoroughly mixed. The dispersed mixture was pelletized on a disc pelletizer for 12 min, with atomized water added during the process, to obtain qualified green pellets with a diameter of 10-16 mm and a moisture content of 9.0 wt.%. The drop strength of the obtained green pellets was 6.9 times / (0.5 m), the compressive strength was higher than 10 N / pellet, and the bursting temperature was higher than 600℃; (3) Using a simulated chain grate machine-rotary kiln process, the green pellets are dried at 350℃ for 5 min and then preheated and roasted at 950℃ for 15 min to obtain preheated pellets with a compressive strength between 500 and 700 N / piece, and the compressive strength of the preheated pellets is 553 N / piece; the preheated pellets are oxidized and roasted at 1200℃ for 15 min and then cooled to obtain oxidized pellets with a compressive strength between 2800 and 3200 N / piece, and the compressive strength of the oxidized pellets is 2864 N / piece, with an iron content of 67.20 wt.%.

[0033] In this embodiment, the oxidized pellets obtained were subjected to gas-based reduction in a hydrogen-based vertical shaft furnace to determine the reduction pelletization rate. The results showed that the reduction pelletization rate was 60.66%.

[0034] Example 4: The method for improving the hydrogen-based reduction pelletizing rate of high-grade iron concentrate oxide pellets is as follows: (1) Add an appropriate amount of water to the high-grade iron concentrate and adjust the water content to 8.0 wt.% to obtain magnetite concentrate; feed the magnetite concentrate into a high-pressure roller mill with a roller mill pressure of 1.17 N / mm. 2 The feeding speed was 6 kg / min, and the roller milling was performed twice. The pretreated magnetite concentrate had a -0.074 mm content of 97.51 wt.% and a specific surface area of ​​1705 cm³. 2 / g; (2) Add 0.9 wt.% of an organic-inorganic composite binder to the pretreated magnetite concentrate, specifically 0.35 wt.% sodium carboxymethyl cellulose (CMC) + 0.35 wt.% sodium humate + 0.20 wt.% bentonite, and mix the materials thoroughly. Pelletize the dispersed mixture on a disc pelletizer for 12 minutes, adding atomized water during the process to obtain qualified green pellets with a diameter of 10–16 mm and a moisture content of 9.0 wt.%. The resulting green pellets have a drop strength of 7.2 times / (0.5 m), a compressive strength higher than 10 N / pellet, and a bursting temperature higher than 570℃. (3) Using a simulated chain grate machine-rotary kiln process, the green pellets are dried at 300℃ for 6 min and then preheated and roasted at 950℃ for 18 min to obtain preheated pellets with a compressive strength between 500 and 700 N / piece, specifically 514 N / piece; the preheated pellets are oxidized and roasted at 1250℃ for 15 min and then cooled to obtain oxidized pellets with a compressive strength between 2800 and 3200 N / piece, specifically 2813 N / piece and 67.71 wt.% iron content.

[0035] In this embodiment, the oxidized pellets obtained were subjected to gas-based reduction in a hydrogen-based vertical shaft furnace to determine the reduction pelletization rate. The results showed that the reduction pelletization rate was 72.31%.

[0036] Comparative Example 1: (1) Add an appropriate amount of water to the high-grade iron concentrate and adjust the moisture content to 8.0 wt.% to obtain magnetite concentrate; send the magnetite concentrate into a grinding mill with a filling rate of 25% and a grinding time of 8 min; the pretreated magnetite concentrate has a -0.074 mm content of 95.20 wt.% and a specific surface area of ​​1137 cm². 2 / g; (2) Add 1.2 wt.% bentonite to the pretreated magnetite concentrate and mix the material thoroughly. Pelletize the dispersed mixture on a disc pelletizer for 12 minutes, adding atomized water during the process to obtain qualified green pellets with a diameter of 10–16 mm and a moisture content of 9.0 wt.%. The resulting green pellets have a drop strength of 2.5 times / (0.5 m), a compressive strength higher than 14.56 N / pellet, and a bursting temperature higher than 600℃. (3) Using a simulated chain grate machine-rotary kiln process, the green pellets are dried at 300℃ for 6 min and then preheated at 950℃ for 15 min to obtain preheated pellets with a compressive strength between 500 and 700 N / piece. The specific compressive strength of the preheated pellets is 539 N / piece. The preheated pellets are calcined at 1150℃ for 15 min and then cooled to obtain oxidized pellets. The compressive strength of the oxidized pellets is 3039 N / piece, and the iron content is 67.20 wt.%.

[0037] The oxidized pellets obtained in this comparative example were subjected to gas-based reduction in a hydrogen-based vertical shaft furnace to determine the reduction pelletization rate. The results showed that the reduction pelletization rate was 14.88%, which did not meet the standard.

[0038] Comparative Example 2: (1) Add an appropriate amount of water to the high-grade iron concentrate and adjust the water content to 8.0 wt.% to obtain magnetite concentrate; feed the magnetite concentrate into a high-pressure roller mill with a roller mill pressure of 1.17 N / mm. 2The feeding speed is 6 kg / min, and the number of roller milling cycles is one. The pretreated magnetite concentrate has a -0.074 mm content of 96.23 wt.% and a specific surface area of ​​1361 cm³. 2 / g; (2) 1.2 wt.% bentonite was added to the magnetite concentrate after high-pressure roller mill pretreatment, and the material was thoroughly mixed. The dispersed mixture was pelletized on a disc pelletizer for 12 min, with atomized water added during the process, to obtain qualified green pellets with a diameter of 10-16 mm and a moisture content of 9.0 wt.%. The resulting green pellets had a drop strength of 5.9 times / (0.5 m), a compressive strength higher than 10 N / pellet, and a bursting temperature higher than 600 °C. (3) Using a simulated chain grate-rotary kiln process, the green pellets are dried at 300℃ for 6 min and then preheated at 950℃ for 15 min to obtain preheated pellets with a compressive strength between 500 and 700 N / piece, and the specific compressive strength of the preheated pellets is 535 N / piece; the preheated pellets are calcined at 1150℃ for 15 min and cooled to obtain oxidized pellets with a compressive strength between 2800 and 3200 N / piece; the specific compressive strength of the obtained oxidized pellets is 2835 N / piece, and the iron content is 67.20 wt.%.

[0039] The oxide pellets obtained in this comparative example were subjected to gas-based reduction in a hydrogen-based vertical shaft furnace to determine the reduction pelletization rate. The results showed that the reduction pelletization rate was 27.28%.

[0040] Comparative Example 3: (1) Add an appropriate amount of water to the high-grade iron concentrate and adjust the water content to 8.0 wt.% to obtain magnetite concentrate; feed the magnetite concentrate into a high-pressure roller mill with a roller mill pressure of 1.17 N / mm. 2 The feeding speed was 6 kg / min, the number of roller milling cycles was four, and the pretreated magnetite concentrate had a -0.074 mm content of 99.84 wt.% and a specific surface area of ​​2015 cm³. 2 / g; (2) 1.2 wt.% bentonite was added to the magnetite concentrate after high-pressure roller mill pretreatment, and the material was thoroughly mixed. The dispersed mixture was pelletized on a disc pelletizer for 12 min, with atomized water added during the process, to obtain qualified green pellets with a diameter of 10-16 mm and a moisture content of 9.0 wt.%. The resulting green pellets had a drop strength of 5.9 times / (0.5 m), a compressive strength higher than 10 N / pellet, and a bursting temperature higher than 600 °C. (3) Using a simulated chain grate-rotary kiln process, the green pellets are dried at 300℃ for 6 min and then preheated at 950℃ for 15 min to obtain preheated pellets with a compressive strength between 500 and 700 N / piece. Specifically, the compressive strength of the preheated pellets is 541 N / piece, and the iron content is 67.20 wt.%. The preheated pellets are calcined at 1150℃ for 15 min and then cooled to obtain oxidized pellets with a compressive strength between 2800 and 3200 N / piece. Specifically, the compressive strength of the obtained oxidized pellets is 3023 N / piece, and the iron content is 67.20 wt.%.

[0041] The oxide pellets obtained in this comparative example were subjected to gas-based reduction in a hydrogen-based vertical shaft furnace to determine the reduction pelletization rate. The results showed that the reduction pelletization rate was 47.28%.

[0042] Results analysis: Comparative Examples 1 and 2 show that the pelletizing rates of both Comparative Example 1 (moistening and grinding) and Comparative Example 2 (high pressure once) are below 30%, indicating severe pellet pulverization during reduction. The specific surface areas of Comparative Examples 1 and 2 are insufficient (1137 cm², respectively). 2 / g、1361cm 2 / g)) means that the particles are relatively coarse, with low surface energy and few active sites; the capillary force between particles is weak during the pelletizing stage, resulting in a loose initial structure and large pores in the green pellets; the solid-phase reaction of Fe3O4 to Fe2O3 during the roasting stage is insufficient, and the growth of newly formed hematite microcrystals is limited, resulting in a sparse and low-strength hematite recrystallization network; when Fe2O3 is reduced to Fe3O4, the internal stress generated by the volume expansion directly acts on the fragile network, causing cracks to propagate rapidly and the structure to collapse, resulting in an extremely low pellet rate.

[0043] Comparative Example 3 shows that although the whole pellet rate (47.28%) of Comparative Example 3 (high pressure 4 times) is better than that of Comparative Examples 1 and 2, it still does not meet the standard, and the pellets show abnormal stratification and surface peeling. The specific surface area of ​​Comparative Example 3 is too high (2015 cm²). 2 The excessively fine particle size ( / g) results in overly dense green pellets with poor permeability during pelletizing. Oxygen during roasting has difficulty diffusing into the pellets, leading to a shell-core layered structure characterized by complete external oxidation and insufficient internal oxidation. The outer layer is a dense hematite shell, while the inner layer remains predominantly magnetite. Due to differences in mineral composition and density, the shell and core layers shrink asynchronously during reduction, generating significant shear stress. Ultimately, this causes the outer layer to crack and peel off at the layering interface. This demonstrates that stronger activation is not always better; there exists an optimal range.

[0044] As can be seen from Examples 1-3, the specific surface area can be precisely controlled within the range of 1500-2000 cm². 2 / g optimization window (1705cm in Example 1) 2 / g, Example 2 is 1876cm2 / g, Example 3 is 1511cm 2 / g), which is the key to obtaining a high pellet percentage (60.66%~80.49%). Under this window, high-pressure roller milling generates an appropriate amount of microcracks on the particle surface and introduces high-density lattice defects, creating an ideal raw material state of "high activity but not dense". During preheating and oxidative roasting, the highly active sites promote the rapid and uniform transformation of Fe3O4 to α-Fe2O3. The newly formed hematite microcrystals form a hematite network with tight intergranular bonding, uniform and fine pores, and a strong overall structure through sufficient solid-phase diffusion. The above-mentioned homogeneous and strong structure can uniformly disperse and absorb the volume expansion stress generated by the reduction phase transformation (Fe2O3→Fe3O4), effectively suppressing the generation of macroscopic cracks, thus exhibiting a high reduction pellet percentage.

[0045] As shown in Example 4, based on optimized activation, 0.9 wt.% of an organic-inorganic composite binder (CMC / sodium humate / bentonite ≈ 0.35:0.35:0.20) was used. CMC and sodium humate exerted a super strong organic bond, ensuring excellent green pellet performance (drop strength 7.2 times) even with a significant reduction of 83% in bentonite usage. After the organic components decomposed, the remaining small amount of bentonite (0.20 wt.%) and the hematite network formed by the mineral powder itself constituted a stable high-temperature skeleton, ensuring the strength of the oxidized pellets (2813 N / pellet). This scheme not only ensured a high pellet rate (72.31%) through optimized activation, but also directly increased the iron grade of the oxidized pellets by 0.51 percentage points (to 67.71%) by reducing the introduction of bentonite impurities by 83% from the source, perfectly achieving the unity of "high strength" and "high grade".

Claims

1. A method for improving the hydrogen-based reduction pelletizing rate of high-grade iron concentrate oxide pellets, characterized in that, The process includes the following steps: (1) mixing high-grade iron concentrate with water and then subjecting it to mechanical activation pretreatment to obtain pretreated high-grade iron concentrate; the mechanical activation pretreatment satisfies either condition (a) or (b) below, and the specific surface area of ​​the pretreated high-grade iron concentrate is 1500-2000 cm². 2 / g: (a) Perform at least two high-pressure roller milling operations; (b) Perform a high-pressure roller mill and combine it with an edge material recycling process; (2) The pretreated high-grade iron concentrate is mixed with a binder and pelletized to obtain green pellets; (3) The green pellets are dried and roasted in sequence to obtain oxidized pellets.

2. The method for improving the hydrogen-based reduction pelletizing rate of high-grade iron concentrate oxide pellets according to claim 1, characterized in that: In the edge material recycling process of step (1), the proportion of edge material returned for re-rolling is 20% to 40% of the total output mass.

3. The method for improving the hydrogen-based reduction pelletizing rate of high-grade iron concentrate oxide pellets according to claim 1, characterized in that: In step (1), the water volume is 4.5-8%, and the pressure of the high-pressure roller mill is 0.8-1.5 N / mm. 2 .

4. The method for improving the hydrogen-based reduction pelletizing rate of high-grade iron concentrate oxide pellets according to claim 1, characterized in that: In step (2), the amount of adhesive added is 0.5 to 2.0 wt% of the total mass of the green pellets.

5. The method for improving the hydrogen-based reduction pelletizing rate of high-grade iron concentrate oxide pellets according to claim 1, characterized in that: In step (2), the adhesive is selected from at least one of bentonite, organic adhesive, and organic-inorganic composite adhesive.

6. The method for improving the hydrogen-based reduction pelletizing rate of high-grade iron concentrate oxide pellets according to claim 5, characterized in that: The adhesive is an organic-inorganic composite adhesive, wherein the organic component is selected from at least one of sodium carboxymethyl cellulose, polyacrylamide, sodium humate and dextrin.

7. A method for improving the hydrogen-based reduction pelletizing rate of high-grade iron concentrate oxide pellets according to any one of claims 1-6, characterized in that, The roasting process in step (2) is as follows: first, preheating roasting is carried out at 800-1000℃, and then oxidative roasting is carried out at 1150-1250℃.

8. The method for improving the hydrogen-based reduction pelletizing rate of high-grade iron concentrate oxide pellets according to claim 7, characterized in that: The preheating and roasting time is 6–18 min, and the oxidation and roasting time is 12–18 min.

Images