Powdered iron ore

Abstract

To provide iron ore that can be reduced in a shorter time when reduced by a hydrogen reduction method. Powdered iron ore that satisfies the following requirements (A), (B), (C), and (D): (A) The average particle size is 1.0 μm to 5.0 mm. (B) The surface area ratio (surface area determined by nitrogen adsorption / desorption isotherm / external surface area) is 20 to 400. (C) The pore volume ratio determined by a nitrogen adsorption / desorption isotherm is 20 to 400. (D) The molar ratio of the amount of O to the amount of Fe (O / Fe) is 1.35 to 1.55.

Description

[Technical Field]

[0001] The present disclosure relates to powdered iron ore. [Background technology]

[0002] The blast furnace method using coke is commonly used to reduce iron ore, but this method generates carbon dioxide during the reduction of iron ore, which poses a significant environmental burden.

[0003] Therefore, a method of reducing iron ore using a reducing gas containing hydrogen gas instead of coke (hereinafter referred to as "hydrogen reduction method") has been investigated. The hydrogen reduction method has the advantage of having a smaller environmental impact than the blast furnace method because water is produced when reducing iron ore. Furthermore, a fluidized bed reduction furnace or the like is used to reduce iron ore using the hydrogen reduction method. In particular, reduction in a fluidized bed reduction furnace involves maintaining powdered iron ore of a few millimeters or less in a fluidized state with hydrogen gas to promote the reduction reaction. Therefore, reduction in a fluidized bed reduction furnace has the advantage of eliminating the process of sintering the iron ore to form strong pellets, as is done in a shaft furnace, and also of having a large contact area between the powdered iron ore and the hydrogen gas, resulting in a high reaction rate for reduction by hydrogen gas.

[0004] As an iron ore reduction technique using the hydrogen reduction method, for example, Patent Document 1 discloses "a method for producing sintered ore by reducing iron ore containing crystal water with a reducing gas containing hydrogen and using the resulting reduced ore as a sintering raw material to produce sintered ore." Patent Document 1 also discloses the use of a fluidized bed reduction furnace for the reduction of iron ore. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2009-249725 Summary of the Invention [Problem to be solved by the invention]

[0006] In recent years, the steel industry has been required to reduce emissions of carbon dioxide (CO2), a greenhouse gas, and this has led to a demand for practical application of the hydrogen reduction method for iron ore. One of the challenges in achieving this is shortening the reduction time for powdered iron ore. Therefore, an object of the present disclosure is to provide iron ore that can be reduced in a shorter reduction time when reduced by a hydrogen reduction method. [Means for solving the problem]

[0007] The above problems are solved by the following means: <1> Powdered iron ore that meets the following requirements (A), (B), (C), and (D). (A) The average particle size is 1.0 μm to 5.0 mm. (B) The surface area ratio (surface area determined by nitrogen adsorption / desorption isotherm / external surface area) is 20 to 400. (C) The pore volume ratio determined by a nitrogen adsorption / desorption isotherm is 20 to 400. (D) The molar ratio of the amount of O to the amount of Fe (O / Fe) is 1.35 to 1.55. <2> The above-mentioned items satisfying the requirements of (E) below. <1> 1. Powdered iron ore according to claim 1. (E) The micropore volume fraction determined by a nitrogen adsorption / desorption isotherm is 0.020 to 0.120. <3> The above-mentioned items satisfying the requirements of (F) below. <1> or <2> 1. Powdered iron ore according to claim 1. (F) The mesopore volume ratio determined by the nitrogen adsorption / desorption isotherm is 0.10 to 0.50. [Effects of the Invention]

[0008] According to the present disclosure, iron ore is provided that can shorten the reduction time when the iron ore is reduced by a hydrogen reduction method. DETAILED DESCRIPTION OF THE INVENTION

[0009] Hereinafter, an embodiment that is an example of the present disclosure will be described. In this specification, a numerical range expressed using "to" means a range that includes the numerical values before and after "to" as the lower and upper limits. In numerical ranges described in stages, the upper limit value described in one numerical range may be replaced with the upper limit value of another numerical range described in stages, and the lower limit value described in one numerical range may be replaced with the lower limit value of another numerical range described in stages. In a numerical range, the upper or lower limit value described in a certain numerical range may be replaced with a value shown in the examples. The term "process" includes not only an independent process but also a process that cannot be clearly distinguished from other processes as long as the intended purpose of the process is achieved. According to the definitions of the International Union of Pure and Applied Chemistry (IUPAC), "micropores" (also called micropores) refer to pores with a pore diameter of less than 2 nm, "mesopores" refer to pores with a pore diameter of 2 to 50 nm, and "macropores" refer to pores with a pore diameter of more than 50 nm.

[0010] <Powdered iron ore> The powdered iron ore according to this embodiment (hereinafter also simply referred to as "specific iron ore") satisfies the following requirements (A), (B), (C), and (D). (A) The average particle size is 1.0 μm to 5.0 mm. (B) The surface area ratio (surface area determined by nitrogen adsorption / desorption isotherm / external surface area) is 20 to 400. (C) The pore volume ratio determined by a nitrogen adsorption / desorption isotherm is 20 to 400. (D) The molar ratio of the amount of O to the amount of Fe (O / Fe) is 1.35 to 1.55. With the above-described configuration, the specific iron ore can be reduced in a shorter reduction time using a reducing gas.

[0011] The specific iron ore was discovered based on the following findings.

[0012] One method for reducing iron ore using hydrogen reduction is to use a fluidized bed reduction furnace. When reducing iron ore using a fluidized bed reduction furnace, iron ore powder with a particle size of submicron to 8.0 mm is usually used, and powder with an average particle size of 1.0 μm to 5.0 mm can be used. Here, the main component of iron ore is iron oxide, which exists in any one of the following states in order of increasing oxygen content: goethite (FeO(OH)), hematite (Fe2O3), magnetite (Fe3O4), and wustite (FeO). As the iron oxide is reduced, the oxygen content decreases, and it eventually becomes iron.

[0013] The reduction of iron ore using a hydrogen reduction method using a fluidized bed reduction furnace will be described using the reduction of powdered iron ore primarily composed of hematite as a specific example. Powdered iron ore primarily composed of hematite is reduced by spraying hydrogen as a reducing gas at a flow rate of 100 mL / min at 800°C. As a result, in the first stage, hematite and magnetite are mixed within each particle of iron ore. Subsequent reduction results in a second stage in which magnetite and wüstite are mixed within each particle of iron ore. Subsequent reduction results in a third stage in which wüstite and iron are mixed within each particle of iron ore. Further reduction results in a fourth stage in which all the ore is reduced to iron.

[0014] The reduction from the first to the third steps proceeds in a short time due to the following (a) to (c). (a) In the first stage, small cracks are formed on the outside of the iron ore particles. The cracks are formed as follows: Reduction begins from the outside of the iron ore particles, causing them to change into magnetite. The outside of the iron ore particles shrinks as they change into magnetite, but the hematite inside expands when heated. This causes cracks to form on the outside of the iron ore particles. (b) The cracks allow the reducing gas to penetrate more easily into the iron ore particles. Therefore, in the first stage, the reduction inside the iron ore particles proceeds quickly, and the process moves to the second stage. At this time, the cracks expand due to the penetration of the reducing gas through the cracks, and form pores that connect to the inside of the iron ore particles. (c) In the second stage, the holes formed by (a) and (b) allow the reducing gas to penetrate easily into the iron ore particles, so that the reduction of the iron ore particles progresses rapidly to the interior in the second stage, and the process moves to the third stage.

[0015] However, the reduction from the third to the fourth stage takes a long time, and the reason for this is presumed to be as follows. As the reduction proceeds, a dense iron coating is formed in the pores formed by (a) and (b), which prevents the reducing gas from penetrating into the iron ore particles, making it difficult for the reduction to proceed.

[0016] Therefore, the present inventors have investigated a method for producing iron ore that allows a reducing gas to penetrate into the interior of iron ore particles. Specifically, they have investigated the production of iron ore having an average particle size of 1.0 μm to 5.0 mm (i.e., satisfying requirement (A)) by a process of reducing raw iron ore at a low temperature and a subsequent process of rapidly oxidizing the raw iron ore at a high temperature. As a result, they have obtained the following findings. First, the process of reducing the raw iron ore at low temperatures promotes the formation of mesopores and macropores that connect to the interior of the particles. Reduction at low temperatures causes iron oxide to become iron without passing through wustite. This results in a larger volumetric shrinkage rate than when iron ore passes through wustite. This makes it easier for cracks that occur during the reduction of iron ore to expand, promoting the formation of mesopores and macropores that connect to the interior of the particles. The subsequent step of rapid oxidation at high temperatures forms micropores while maintaining the shape of the mesopores and macropores formed in the reduction step. The oxidation step rapidly oxidizes the iron coating formed in the reduction step, converting it to hematite. When the iron coating becomes hematite, it undergoes a rapid volume expansion. This causes cracks to form on the surface of the iron ore and on the surfaces of the mesopores and macropores, forming micropores. In other words, because oxidation is necessary until micropores are formed, the specified iron ore satisfies the requirement (D) above.

[0017] As described above, the specific iron ore obtained by the oxidation step and the reduction step has a large number of micropores, mesopores, and macropores inside, and has a structure with a larger number of fine pores inside than conventional iron ores. In other words, the specific iron ore satisfies the requirements (B) and (C). Therefore, the specific iron ore more easily allows the reducing gas to penetrate into the interior of the particles, and the reduction of the iron ore by the reducing gas more rapidly progresses.

[0018] Based on the above findings, it has been discovered that the specific iron ore can shorten the reduction time when reducing iron ore by hydrogen reduction.

[0019] The specific iron ore will be explained in detail below.

[0020] (Requirement (A)) The average particle size of the specific iron ore is 1.0 μm to 5.0 mm. By setting the average particle size of the specific iron ore within the above range, the iron ore can be easily reduced, for example, when a fluidized bed reduction furnace is used in the reduction of the iron ore by hydrogen reduction. If the average particle size is less than 1.0 μm, when reduction is carried out using a fluidized bed reduction furnace, many particles are carried away by the flow of reducing gas, making it difficult to maintain a stable fluidized state. If the average particle size exceeds 5.0 mm, many particles will not float even with the flow of reducing gas when reduction is carried out using a fluidized bed reduction furnace, making it difficult to achieve a sufficient fluidized state.

[0021] The average particle size of the iron ore is preferably 1.0 μm or more, more preferably 10 μm or more, and even more preferably 50 μm or more, from the viewpoint of suppressing particles being carried away by the gas flow when reduction is performed using a fluidized bed reduction furnace. Here, in order to shorten the reduction time of the iron ore, auxiliary particles (e.g., alumina, zirconia, etc.) that do not participate in the reaction but that are easily fluidized themselves and have an average particle size of 0.1 to 1.0 mm may be inserted into the fluidized bed reduction furnace, and iron ore powder may be added to the fluidized auxiliary particles for reduction. In particular, when the average particle size of the iron ore is less than 1.0 μm, the addition of auxiliary particles is effective, and the reduction time of the iron ore can be further shortened. The average particle size of the iron ore is preferably 3.0 mm or less, and more preferably 2.0 mm or less, from the viewpoint of floating the iron ore by the flow of gas and achieving a sufficient fluidized state when the iron ore is reduced using a fluidized bed reduction furnace.

[0022] Here, the average particle size of the iron ore is measured by the measurement method shown in the examples below.

[0023] (Requirement (B)) The specific iron ore has a surface area ratio (surface area determined by nitrogen adsorption / desorption isotherm / external surface area) of 10 to 400. Here, the surface area ratio is a value obtained by dividing the surface area determined by the nitrogen adsorption / desorption isotherm by the external surface area.

[0024] The surface area determined by the nitrogen adsorption / desorption isotherm is measured in accordance with the multipoint method of nitrogen gas adsorption described in ASTM D6556-21 (July 7, 2021), and is the surface area per unit mass calculated by BET analysis of the adsorption isotherm of the nitrogen adsorption / desorption isotherm, as described in detail in the Examples below. The external surface area is the surface area per unit mass of a spherical iron ore whose diameter is the average particle size of the specific iron ore measured by the above-mentioned method.

[0025] By setting the surface area ratio (surface area determined by nitrogen adsorption / desorption isotherm / external surface area) of the specific iron ore within the above range, the iron ore will have many pores inside the particles, which will promote the penetration of reducing gas into the particles during reduction of the iron ore by hydrogen reduction, thereby shortening the reduction time. If the surface area ratio of the specific iron ore is less than 20, the pores inside the iron ore particles are not sufficiently developed, and the penetration of the reducing gas into the inside of the iron ore particles is inhibited. If the surface area ratio of the specific iron ore exceeds 400, the powdered iron ore becomes brittle, causing the so-called pulverization phenomenon during reduction. When the iron ore is fluidized to match its original particle size, the small iron ore particles produced by pulverization are released outside the system by the fluidization gas, resulting in a decrease in the yield of the iron ore itself.

[0026] The surface area ratio (surface area determined by nitrogen adsorption / desorption isotherm / external surface area) of the specific iron ore is preferably 20 to 350, more preferably 25 to 350, from the viewpoint of obtaining iron ore having a large number of pores inside the iron ore particles.

[0027] Here, the surface area ratio (surface area determined by nitrogen adsorption / desorption isotherm / external surface area) of the specific iron ore is measured by the measurement method shown in the examples below.

[0028] (Requirement (C)) The specific iron ore has a pore volume ratio of 20 to 400 as determined by a nitrogen adsorption / desorption isotherm. Here, the pore volume ratio obtained from the nitrogen adsorption / desorption isotherm is the adsorption amount V at a relative pressure of 0.995 obtained from the nitrogen adsorption / desorption isotherm. 0.995 (mL / g) is the density of iron ore (For example, 5.24 g / mL for hematite and 5.17 g / mL for magnetite)

[0029] By setting the pore volume ratio of the specific iron ore determined by the nitrogen adsorption / desorption isotherm within the above range, the iron ore will have a large number of pores inside the particles, which will promote the penetration of reducing gas into the iron ore particles during reduction of the iron ore by hydrogen reduction, thereby shortening the reduction time. If the pore volume ratio of the specific iron ore determined by the nitrogen adsorption / desorption isotherm is less than 20, the pores inside the iron ore particles will not be sufficiently developed, and the penetration of reducing gas into the iron ore particles will be hindered. If the pore volume ratio of the specific iron ore determined by the nitrogen adsorption / desorption isotherm exceeds 400, the powdered iron ore becomes brittle and is crushed during the fluidization process. Therefore, powdered iron ore having a pore volume ratio exceeding 400 cannot be obtained.

[0030] The pore volume ratio determined by the nitrogen adsorption / desorption isotherm is preferably 25 to 350, more preferably 25 to 300, from the viewpoint of obtaining iron ore having a large number of pores inside the iron ore particles.

[0031] Here, the pore volume ratio determined from the nitrogen adsorption / desorption isotherm is measured by the measurement method shown in the examples below.

[0032] (Requirement (D)) The specific iron ore has a molar ratio of O to Fe (O / Fe) of 1.35 to 1.55. As will be described later in the section on the method for producing a specific iron ore, by setting the molar ratio of O to Fe (O / Fe) within the above range, the number of micropores increases, which promotes the penetration of reducing gas into the iron ore particles during reduction of iron ore by hydrogen reduction, thereby shortening the reduction time.

[0033] The molar ratio of O to Fe (O / Fe) of the specific iron ore is preferably 1.40 to 1.55, more preferably 1.40 to 1.50, from the viewpoint of increasing the micropores of the specific iron ore.

[0034] Here, the molar ratio of the amount of O to the amount of Fe (O / Fe) of the specific iron ore is measured by the measurement method shown in the examples described later.

[0035] (Requirement (E)) The specific iron ore preferably has a micropore volume ratio of 0.020 to 0.120 as determined by a nitrogen adsorption / desorption isotherm. Here, the micropore volume ratio is the value obtained by dividing the adsorption amount (mL / g) at a relative pressure of 0.1 obtained from the nitrogen adsorption / desorption isotherm by the adsorption amount (mL / g) at a relative pressure of 0.995 obtained from the nitrogen adsorption / desorption isotherm.

[0036] By setting the micropore volume ratio of the specific iron ore, determined by the nitrogen adsorption / desorption isotherm, within the above range, it is possible to increase the proportion of micropores while maintaining the proportion of mesopores and macropores in the total pores, which in turn promotes the penetration of reducing gas into the iron ore particles during reduction of iron ore by hydrogen reduction, thereby shortening the reduction time.

[0037] The micropore volume ratio of the specific iron ore determined by the nitrogen adsorption / desorption isotherm is set to 0.02 from the viewpoint of increasing the proportion of micropores while maintaining the proportion of mesopores and macropores in the total pores. It is more preferably 5 to 0.110, and even more preferably 0.025 to 0.100.

[0038] Here, the micropore volume fraction of the specific iron ore, which is determined from the nitrogen adsorption / desorption isotherm, is measured by the measurement method shown in the examples described later.

[0039] (Requirement (F)) The specific iron ore preferably has a mesopore volume ratio of 0.10 to 0.50 as determined by a nitrogen adsorption / desorption isotherm. Here, the mesopore volume ratio obtained from the nitrogen adsorption / desorption isotherm is the adsorption amount V at a relative pressure of 0.96 obtained from the nitrogen adsorption / desorption isotherm. 0.96 (mL / g) and the adsorption amount V at a relative pressure of 0.1 obtained from the nitrogen adsorption / desorption isotherm 0.1(mL / g) (V 0.96 -V 0.1 ) is the adsorption amount V at a relative pressure of 0.995 obtained from the nitrogen adsorption / desorption isotherm. 0.995 The value is divided by (mL / g).

[0040] By setting the mesopore volume ratio of the specific iron ore, determined by the nitrogen adsorption / desorption isotherm, within the above range, it is possible to increase the proportion of mesopores while maintaining the proportion of macropores in all pores, which in turn promotes the penetration of reducing gas into the iron ore particles during reduction of iron ore by hydrogen reduction, thereby shortening the reduction time.

[0041] The mesopore volume ratio of the specific iron ore determined by the nitrogen adsorption / desorption isotherm is more preferably 0.15 to 0.45, and even more preferably 0.20 to 0.45, from the viewpoint of increasing the proportion of mesopores while maintaining the proportion of macropores in all pores.

[0042] Here, the mesopore volume ratio of the specific iron ore determined from the nitrogen adsorption / desorption isotherm is measured by the measurement method shown in the examples below.

[0043] Here, the mesopore volume ratio of the specific iron ore, which is determined from the nitrogen adsorption / desorption isotherm, is measured by the measurement method shown in the examples described later.

[0044] (Method of manufacturing specific iron ore) Next, an example of a method for producing the specific iron ore will be described. The specific iron ore is produced, for example, through a reduction step in which raw iron ore is reduced at a low temperature, and an oxidation step in which the iron ore is oxidized after the reduction step.

[0045] In the method for producing the specific iron ore, in the reduction step, raw material iron ore is reduced at a low temperature to effectively develop mesopores and macropores inside the iron ore particles. On the other hand, in the oxidation process, the material is oxidized to a mixed oxidation state of magnetite and hematite (ideally, an oxidation state in which the material is oxidized to a single hematite phase), which exceeds at least magnetite, thereby effectively developing micropores while maintaining the mesopores and macropores developed in the reduction process.

[0046] Magnetite transforms into wüstite through high-temperature reduction at 570°C or higher, but the change in the crystal lattice constant is small and the degree of shrinkage associated with the transformation is small, making it less likely to crack. As a result, even when reduced at high temperatures, pores for the diffusion of reducing gas within the iron ore particles do not develop, making it impossible to improve the reduction rate. In contrast, magnetite transforms into iron through low-temperature reduction at temperatures below 550°C, but the transformation from magnetite to iron is accompanied by a large volumetric shrinkage, making it prone to cracking. As a result, when reduction is carried out at low temperatures, pores develop inside the iron ore particles that allow the reducing gas to diffuse, improving the reduction rate.

[0047] On the other hand, in the transformation from hematite to magnetite due to reduction, the crystal shrinks, causing nano-sized cracks (pores) to form deep inside the iron ore particles. Similarly, in the transformation from magnetite to hematite due to oxidation, the pores created by reduction further develop due to the shrinkage of the crystals.

[0048] Thus, in order to obtain iron ore with well-developed pores inside the particles, which effectively improves the reduction rate of iron ore, it is effective to reduce the raw iron ore at a low temperature and then oxidize it to an oxidation state close to that of hematite. That is, as will be described in detail below, it is effective to maintain and further develop the pores developed in the reduction step by low-temperature reduction at about 550°C or less in the oxidation step. In the oxidation process, it is effective to oxidize slowly at a low temperature of around 300°C with an oxygen concentration lower than that of air, or to oxidize to a state close to hematite in a short time at a high temperature of 700°C or higher with an oxygen concentration of a few percent or less, in order to maintain and further develop the pores developed in the reduction process. By undergoing these reduction and oxidation steps, a specific iron ore that satisfies the above requirements (A) to (D) (preferably the above requirements (A) to (F)) and allows the reduction time to be shortened can be obtained.

[0049] Each step of the method for producing the specific iron ore will be described in detail below.

[0050] - Reduction process - In the reduction step, raw iron ore having an average particle size of 1.0 μm to 5.0 mm is reduced to a reduction degree of 15 to 40% under a temperature condition of 300 to 550° C. If the reduction degree is less than 15%, the development of pores (mesopores and macropores) is insufficient, and it is not possible to form a pore structure in the iron ore that satisfies the above requirements (B) to (C) (preferably the above requirements (B) to (C) and (E) to (F)). This reduction step increases the proportion of mesopores and macropores in the specific iron ore compared to when reduction is performed under high temperature conditions.

[0051] The raw iron ore is not limited, but examples thereof include iron ores containing goethite, hematite, or magnetite as a main component. Here, the term "main component" refers to the component contained in the iron ore in the largest amount. From the viewpoint of increasing the proportion of mesopores and macropores in the specific iron ore, the raw material iron ore is preferably iron ore containing hematite or magnetite as a main component.

[0052] The reduction step is carried out under temperature conditions of 300 to 550°C. By carrying out reduction under these temperature conditions, iron oxide is converted to iron without passing through wüstite, promoting the formation of mesopores and macropores that connect to the interior of the iron ore particles. Because the transformation of magnetite to iron is accompanied by a large volumetric shrinkage, it is presumed that pores (voids) are formed inside the iron ore particles.

[0053] In the reduction step, reduction at a reduction rate in the range of 10 to 45% is suitable for satisfying requirements (B) to (C). A reduction rate of 15 to 40% is more preferable. If the oxidation step is carried out under conditions that develop pores (for example, conditions of an oxygen concentration of 5 to 10% and oxidation at an oxidation temperature of 300°C for several hours), it may be possible to form a pore structure in the iron ore that satisfies the above requirements (B) to (C) (preferably the above requirements (B) to (C) and (E) to (F)) even when the reduction rate is reduced to 50% or more. However, from a practical standpoint, it is effective to shorten the reduction time efficiently using a low-cost pretreatment that does not require much energy, so 45% is essentially set as one upper limit for reduction as a pretreatment. Here, the reduction rate is the amount of oxygen contained in the raw iron ore that has been reduced by the reduction process. Indicates the percentage of oxygen content. By keeping the reduction rate between 10 and 45%, the time required for the reduction process can be shortened. The reduction rate is measured by the measurement method shown in the Examples below.

[0054] The reduction step is preferably carried out using, for example, a fluidized bed reduction furnace using a reducing gas as the fluid. When reduction is carried out using a fluidized bed reduction furnace using a reducing gas as a fluid, the linear velocity of the reducing gas is preferably 10 to 100 cm / sec.

[0055] The reducing gas may include hydrogen, carbon monoxide, and the like. From the viewpoint of reducing the burden on the environment, hydrogen is preferred as the reducing gas.

[0056] -Oxidation process- In the oxidation step, the iron ore after the reduction step is substantially oxidized at a temperature of 300°C or higher. This oxidation step forms micropores while maintaining the shapes of the mesopores and macropores formed in the reduction step.

[0057] The oxidizing agent used in the oxidation step may be air, pure oxygen, ozone, or the like. From the viewpoint of promoting the formation of micropores, the oxidizing agent is preferably pure oxygen or ozone. In the oxidation process, controlling the concentration of the oxidizing gas according to the temperature is effective for maintaining the pores. Specifically, for example, when oxidizing iron ore at 300°C, if the oxygen concentration is about 5 to 10% and the oxidation is carried out for several hours, the pores are hardly collapsed and can be further developed. On the other hand, when iron ore is oxidized at high temperatures exceeding 700°C, for example, the temperature-induced atomic migration is so rapid that nanometer-sized pores are easily collapsed. Therefore, in the case of high-temperature oxidation, the oxidation reaction is rapid, so it is preferable to reduce the oxidizing gas concentration (for example, to about 1-2% in the case of oxygen or ozone) and shorten the treatment time as much as possible. Furthermore, in order to achieve an O / Fe ratio of 1.35 or higher, it is effective to limit the treatment time to a few minutes to a maximum of 10 minutes. If this condition is not met, the pores inside the iron ore particles developed during the reduction process will collapse.

[0058] The oxidation step is preferably carried out using, for example, a fluidized bed reduction furnace using the oxidizing agent as a fluid. When reduction is carried out using a fluidized bed reduction furnace in which the oxidizing agent is used as a fluid, the linear velocity of the fluid is preferably 10 to 100 cm / sec.

[0059] However, if an extremely long oxidation treatment time is permitted for the raw iron ore before reduction, the iron ore of the present disclosure can be obtained by the oxidation step alone, without going through the reduction step. Specifically, if oxidation treatment is permitted for raw iron ore before reduction under oxidation treatment conditions in which the oxidation treatment temperature is low, the oxygen concentration is extremely low, and the treatment time is long, the iron ore disclosed herein can be obtained through the oxidation process alone, without going through the reduction process. The oxidation treatment conditions are preferably an oxidation treatment temperature of 250 to 350°C, an oxygen concentration of 1 to 5%, and an oxidation treatment time of more than 100 hours, and more preferably a treatment temperature of 300 to 350°C, an oxygen concentration of 3 to 5%, and an oxidation treatment time of 150 hours or more. [Example]

[0060] Examples will be described below, but the present disclosure is not limited to these examples in any way.

[0061] <Measuring methods for each parameter> (Method for measuring average particle size) Since the appropriate measurement method for the average particle size varies depending on the particle size, first, dry sieves with openings of 11.1 mm and 1.0 mm were used to separate large and small particles, and particles above the 11.1 mm sieve were excluded because it would be difficult to fluidize them in a fluidized bed. The particles below the 11.1 mm sieve that were separated onto the 1.0 mm sieve were further sieved using dry sieves with different openings to measure the particle size distribution. Standard sieves according to the Japanese Industrial Standards (JIS Z8801) were used. On the other hand, for small particles that fall under the 1.0 mm sieve, the average particle size was measured using a laser diffraction particle size distribution measuring device (for example, SALD-2300 manufactured by Shimadzu Corporation). Specifically, a dispersion was prepared by dispersing specific iron ore, and optionally 1-2 drops of household neutral detergent (trade name: Mama Lemon), in a dispersion medium such as water. The amount of iron ore powder was adjusted so that the measurement value of the device was within a predetermined frequency range. The particle size distribution of this dispersion was measured using a laser diffraction particle size distribution analyzer. The particle size at which the cumulative value of the relative particle amount on a volume basis is 50% was defined as the average particle size for the particle size distribution measurement results obtained using both the dry sieve and the laser diffraction particle size distribution analyzer.

[0062] (Method for measuring nitrogen adsorption / desorption isotherm) Nitrogen adsorption / desorption isotherms were measured using a method based on the multipoint method described in ASTM D6556-21 (Jul 07, 2021). Specifically, approximately 1 g of sample (approximately 5 g for samples with small surface areas) was weighed out, inserted into a designated measurement sample tube, and vacuum dried at 120°C for 2 hours. The sample tube was then placed in an automatic specific surface area measuring device (MicrotrackBell, BELSORP MAX), and nitrogen adsorption / desorption isotherms were measured using nitrogen gas as the adsorbate and liquid nitrogen as the measurement temperature. High-purity nitrogen gas (G1 grade, manufactured by Taiyo Nippon Sanso Corporation, impurity concentration 0.2 vol. ppm or less) was used for the measurement, and the relative pressure was 1 x 10-5 ~1×10 -2 Up to this point, measurements were taken at approximately 30 points at equal logarithmic intervals, and above this point, measurements were taken at one point every 0.02 relative pressure, and the accuracy of the BET analysis was improved by increasing the number of measurement points. In measuring the nitrogen adsorption / desorption isotherm, the relative pressure was measured at fixed points at intervals of 0.005.

[0063] (Method for measuring surface area ratio) The surface area ratio (surface area determined by nitrogen adsorption / desorption isotherm / external surface area) was measured by the following procedure. First, the surface area was calculated from the nitrogen adsorption / desorption isotherm. Nitrogen adsorption / desorption isotherms were measured using the method described above. The surface area determined from the nitrogen adsorption / desorption isotherms was calculated by BET analysis of the nitrogen adsorption isotherms in the relative pressure range of 0.05 to 0.20. The BET analysis was performed using the analysis software provided with the measurement device. Next, the external surface area was calculated. The average particle diameter of the sample was measured using the method described above. The surface area S of a true sphere having the calculated average particle diameter as its diameter and the volume V were calculated. The volume V was multiplied by the density of the sample (5.24 g / cm in the case of hematite). 3 , 5.17 g / cm for magnetite 3 The reciprocal of the value obtained by multiplying the surface area S by the number of spheres per unit mass was calculated to obtain the number of spheres per unit mass. The value obtained by multiplying the surface area S by the number of spheres per unit mass was obtained to obtain the outer surface area. Then, the surface area ratio (surface area determined by nitrogen adsorption / desorption isotherm / external surface area) was calculated by dividing the surface area determined by the nitrogen adsorption / desorption isotherm by the external surface area. Here, the surface area determined by the nitrogen adsorption / desorption isotherm and the external surface area were measured in the same unit. 2 / g was used.

[0064] (Method for measuring pore volume ratio obtained from nitrogen adsorption / desorption isotherm) The pore volume ratio determined by the nitrogen adsorption / desorption isotherm was measured by the following procedure. First, the nitrogen adsorption / desorption isotherm was measured by the above-mentioned method. From the nitrogen adsorption / desorption isotherm, the adsorption amount V at a relative pressure of 0.995 was determined. 0.995 (mL / g) was calculated. 0.995 The value obtained by dividing by the reciprocal of the density of the sample (5.24 g / mL for hematite, 5.17 g / mL for magnetite) was taken as the pore volume ratio determined from the nitrogen adsorption / desorption isotherm.

[0065] (Method for measuring the molar ratio of O to Fe (O / Fe)) The iron content in the raw iron ore was calculated in mass% in accordance with JIS M8212 (2005). The oxygen content in the raw iron ore was calculated in mass% from the iron content in the raw iron ore and the chemical composition of the raw iron ore (Fe2O3 for hematite, Fe3O4 for magnetite). The mass change of the raw iron ore was measured before and after the oxidation and reduction steps. The mass change was considered to be a change in the oxygen content in the iron ore, and the iron and oxygen contents in the iron ore after the oxidation and reduction steps were calculated in mass%. The iron and oxygen contents in the iron ore after the oxidation and reduction steps were then converted to mol%. The molar ratio of the O content to the Fe content was calculated by dividing the oxygen content converted to mol% by the iron content converted to mol%. The ratio (O / Fe) was calculated. The moisture content of the raw iron ore was measured in accordance with the JIS standard (JIS M8211, 1985 edition). As a result, it was confirmed that the moisture content of hematite and magnetite was 0.5% or less. The moisture content of the goethite (the goethite sample used in the test) was 9.6%. The goethite was vacuum dried at 300°C for 60 minutes before the reduction experiment. X-ray diffraction confirmed that the dried goethite sample was a single phase of hematite. The oxygen content of the goethite was calculated assuming the chemical composition to be Fe2O3.

[0066] (Method for measuring micropore volume fraction obtained from nitrogen adsorption / desorption isotherm) The micropore volume ratio determined by nitrogen adsorption / desorption isotherm was measured by the following procedure. First, the nitrogen adsorption / desorption isotherm was measured by the above-mentioned method. From the nitrogen adsorption / desorption isotherm, the adsorption amount V at a relative pressure of 0.1 was determined. 0.1 (mL / g) and the adsorption amount V at a relative pressure of 0.995 0.995 (mL / g) was calculated. The adsorption amount V at a relative pressure of 0.1 obtained from the nitrogen adsorption / desorption isotherm was 0.1 (mL / g) is the adsorption amount V at a relative pressure of 0.995 obtained from the nitrogen adsorption / desorption isotherm. 0.995 The value obtained by dividing by the volume fraction (mL / g) was used as the micropore volume fraction determined by the nitrogen adsorption / desorption isotherm.

[0067] (Method for measuring mesopore volume fraction obtained from nitrogen adsorption / desorption isotherm) The mesopore volume ratio determined by the nitrogen adsorption / desorption isotherm was measured by the following procedure. First, the nitrogen adsorption / desorption isotherm was measured by the above-mentioned method. From the nitrogen adsorption / desorption isotherm, the adsorption amount V at a relative pressure of 0.1 was determined. 0.1 (mL / g) and the adsorption amount V at a relative pressure of 0.96 0.96 (mL / g) and the adsorption amount V at a relative pressure of 0.995 0.995 (mL / g) was calculated. 0.96 and the adsorption amount V 0.1 Difference with (V 0.96 -V 0.1 ) is calculated, and the adsorption amount V 0.995 The value obtained by dividing by this was taken as the mesopore volume ratio determined by the nitrogen adsorption / desorption isotherm.

[0068] (Method of measuring the return rate) The iron content in the raw iron ore was calculated in mass% in accordance with JIS M8212 (2005). The oxygen content (O) in the raw iron ore was calculated from the iron content in the raw iron ore and the chemical composition of the raw iron ore (Fe2O3 for hematite, Fe3O4 for magnetite). A ) was calculated in mass%. The mass change of the raw iron ore was measured before and after the reduction process. The mass change was considered to be the change in the oxygen content in the iron ore, and the oxygen content (O B ) was calculated in mass %. A ) to the oxygen content (O B ) and (O A -O B ), the oxygen content (O A The reduction rate was calculated by dividing the value by 100 and multiplying it by 100. A -O B )÷O A ×100].

[0069] <Test example> Using the types of raw iron ore, reduction step conditions, and oxidation step conditions shown in Tables 1 to 3, iron ore after the oxidation step and reduction step (hereinafter, test iron ore) was obtained according to the following procedure. A quartz filter for placing the raw iron ore was welded to the bottom of a quartz tube (inner diameter 12 mm). A gas flow from below fluidized the raw iron ore (hereafter referred to as the reactor tube) was prepared. 1.0–2.0 g of raw iron ore was placed on the quartz filter inside the reactor tube. Hydrogen was flowed from the bottom to the top of the quartz filter at a linear velocity of 10–100 cm / sec to fluidize the raw iron ore. While the raw iron ore was still fluidized, the reactor tube was inserted into an electric furnace preheated to the desired reaction temperature, and the reduction reaction was initiated. A thermocouple was inserted inside the reactor tube to measure the internal temperature. After the desired reduction rate was reached, the reactor tube was removed from the electric furnace, and the hydrogen was replaced with argon gas at the same flow rate. The reactor was then cooled to below 100°C. Next, after the temperature of the electric furnace was maintained at the temperature for the oxidation step, the reaction tube was inserted into the electric furnace, and at the same time, an oxidizing agent was flowed at a linear velocity of 10 to 100 cm / sec. After a predetermined time had elapsed, The reaction tube was removed from the furnace, and the gas was simultaneously switched to argon gas at the same flow rate to cool to room temperature, after which the test iron ore was removed.

[0070] Here, in Test Examples RUN1-1 to 1-48, hematite iron ore having an average particle size of 75 μm and the properties shown in Table 1 was used as the raw iron ore (see Reference Example). In Test Examples RUN2-1 to 2-14, magnetite iron ore having an average particle size of 12 μm and the properties shown in Table 2 was used as the raw iron ore (see Reference Example). In Test Examples RUN3-1 to RUN3-25, goethite iron ore having an average particle size of 135 μm and the properties shown in Table 3 was used as the raw iron ore (see Reference Example).

[0071] However, in Test Examples RUN1-44 to 1-48, raw iron ore having an average particle size of 75 μm was subjected to a crushing process or classification process to adjust the average particle size, as follows, to use a hematite iron ore sample. First, 30 mL of iron ore powder was weighed and placed in a 250 mL zirconia container manufactured by Fritsch Japan. Then, 80 mL of 0.5 mm diameter zirconia balls were inserted into the container and sealed with a silicone rubber packing. The container in this state was placed in a planetary ball mill (Fritsch Japan P-4) as a grinding device. Next, the iron ore powder was repeatedly ground at 400 rpm for 30 minutes using this grinding device until it reached the desired average particle size. By crushing, an iron ore sample (RUN1-44) with an average particle size of 0.8 μm and an iron ore sample (RUN1-45) with an average particle size of 1.2 μm were prepared. In addition, hematite iron ore powder with an average particle size of 75 μm was classified using a sieve with a mesh size of 4.75 mm to prepare an iron ore sample with an average particle size of 4.25 mm (RUN1-47) and an iron ore sample with an average particle size of 5.22 mm (RUN1-48). In addition, hematite iron ore powder with an average particle size of 75 μm was classified using a sieve with a mesh size of 425 μm to prepare an iron ore sample (RUN1-46) with an average particle size of 550 μm. An attempt was made to fluidize an iron ore sample (RUN1-44) with an average particle size of 0.8 μm and an iron ore sample (RUN1-48) with an average particle size of 5.22 mm in a reactor tube, but it was not possible to achieve a stable fluidized state, and it was found that these samples were not suitable for reduction in a fluidized bed reduction furnace.

[0072] In Test Examples RUN3-1 to RUN3-12, goethite iron ore that had been dried in advance to remove moisture as is usually done was subjected to a reduction treatment and a subsequent oxidation treatment. On the other hand, in Test Examples RUN3-13 to RUN3-15, from the viewpoint of process omission, the goethite iron ore was directly subjected to reduction treatment and subsequent oxidation treatment without being dried in advance to remove moisture, which is normally done. However, in Test Examples RUN3-6 to RUN3-9, no oxidation treatment was performed, and in Test Examples RUN3-10 to RUN3-13, no reduction treatment was performed. In test examples RUN3-16 to RUN3-25, from the viewpoint of process omission, goethite iron ore was dried in advance to remove moisture, as is usually done, and then only oxidation treatment was performed without reduction treatment. However, in order to further suppress pore collapse, oxidation treatment was attempted under conditions of low temperature, low concentration oxidizing gas (oxygen and ozone gas), and long time.

[0073] <Rebate evaluation> 1.0 to 2.0 g of raw iron ore was placed on a quartz filter in the reaction tube used to prepare the test iron ore. Hydrogen was flowed from the bottom to the top of the quartz filter in a vertical electric furnace at a linear velocity of 10 to 100 cm / sec to fluidize the raw iron ore. While the raw iron ore was still fluidized, the reaction tube was inserted into an electric furnace heated to a temperature of 750°C inside the reaction tube, and the reduction reaction was initiated. A thermocouple was inserted into the reaction tube to measure the internal temperature. The time required for the raw iron ore to reach a reduction rate of 80% was then measured. Next, 1.0 g of test iron ore made from the same raw iron ore was placed on a quartz filter in the reaction tube and reduced under the same conditions for the time required for the raw iron ore to reach an 80% reduction rate. The hydrogen was then replaced with argon gas at the same flow rate, and the test iron ore was cooled to room temperature. The reduced test iron ore was then removed. The reduction ratio of the resulting test iron ore was calculated. Here, if the reduction rate of the test iron ore after reduction is 84% or more, the reduction rate of the iron ore is shortened. It was assessed that a stone was obtained.

[0074] [Table 1-1]

[0075] [Table 1-2]

[0076] [Table 2]

[0077] [Table 3]

[0078] [Table 4]

[0079] From the above results, it can be seen that the test iron ore of this example can shorten the reduction time when reducing iron ore by hydrogen reduction.

[0080] The disclosure of Japanese Patent Application No. 2024-050248 is incorporated herein by reference in its entirety. All publications, patent applications, and technical standards mentioned in this specification are herein incorporated by reference to the same extent as if each individual publication, patent application, or technical standard was specifically and individually indicated to be incorporated by reference.

Claims

1. Powdered iron ore that satisfies the following requirements (A), (B), (C), and (D): (A) The average particle size is 1.0 μm to 5.0 mm. (B) The surface area ratio (surface area determined by nitrogen adsorption / desorption isotherm / external surface area) is 20 to 400. (C) The pore volume ratio determined by a nitrogen adsorption / desorption isotherm is 20 to 400. (D) The molar ratio of the amount of O to the amount of Fe (O / Fe) is 1.35 to 1.

55.

2. The powdered iron ore according to claim 1, which satisfies the following requirement (E): (E) The micropore volume ratio determined by a nitrogen adsorption / desorption isotherm is 0.020 to 0.

120.

3. The powdered iron ore according to claim 1 or claim 2, which satisfies the following requirement (F): (F) The mesopore volume ratio determined by a nitrogen adsorption / desorption isotherm is 0.10 to 0.50.

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