Powdery iron ore

Abstract

Provided is an iron ore capable of shortening reduction time during reduction of iron ore by a hydrogen reduction method.　A powdery iron ore according to the present invention satisfies requirements (A), (B), (C), and (D) below. (A) The average particle diameter is 1.0 μm to 5.0 mm. (B) The surface area ratio (surface area / outer surface area as determined by nitrogen adsorption / desorption isotherms) is 20 to 400. (C) The pore volume ratio determined by the nitrogen adsorption / desorption isotherms is 20 to 400. (D) The molar ratio (O / Fe) of the amount of O to the amount of Fe is 1.35 to 1.55.

Description

Powdered iron ore

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

[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 the "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 during the reduction of iron ore. For the reduction of iron ore using the hydrogen reduction method, a fluidized bed reduction furnace or the like is used. 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 eliminates the need for a shaft furnace to sinter the iron ore into strong pellets. Furthermore, the contact area between the powdered iron ore and the hydrogen gas is large, resulting in a high reaction rate for reduction by hydrogen gas.

[0004] As an iron ore reduction technique using a 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.

[0005] JP 2009-249725 A

[0006] In recent years, the steel industry has been focusing on carbon dioxide (CO ２ Since there is a demand for reducing emissions of CO₂, there is a demand for practical application of the reduction of iron ore by a hydrogen reduction method. One of the challenges in achieving practical application is shortening the reduction time of 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.

[0007] The above problems are solved by the following means. That is, <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 / external surface area determined by nitrogen adsorption / desorption isotherm) is 20 to 400. (C) The micropore volume ratio determined by nitrogen adsorption / desorption isotherm is 20 to 400. (D) The molar ratio of O to Fe (O / Fe) is 1.35 to 1.55. <2> Powdered iron ore according to <1> above, which satisfies the following requirement (E): (E) The micropore volume ratio determined by nitrogen adsorption / desorption isotherm is 0.020 to 0.120. <3> Powdered iron ore according to <1> or <2> above, which satisfies the following requirement (F): (F) The mesopore volume ratio determined by a nitrogen adsorption / desorption isotherm is 0.10 to 0.50.

[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.

[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 ​​written before and after "to" as the lower and upper limits. In a numerical range that is written in stages, the upper limit value written in a certain numerical range may be replaced with the upper limit value of another numerical range that is written in stages. Furthermore, the lower limit value written in a certain numerical range may be replaced with the lower limit value of another numerical range that is written in stages. In a numerical range, the upper or lower limit value written 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 definition of the International Union of Pure and Applied Chemistry (IUPAC), "micropores", also called micropores, refer to, for example, pores with a pore diameter of less than 2 nm, "mesopores" refer to, for example, pores with a pore diameter of 2 nm to 50 nm, and "macropores" refer to, for example, 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 / external surface area determined by nitrogen adsorption / desorption isotherm) is 20 to 400. (C) The pore volume ratio determined by nitrogen adsorption / desorption isotherm is 20 to 400. (D) The molar ratio of O to Fe (O / Fe) is 1.35 to 1.55. Due to the above-mentioned configuration, the specific iron ore can shorten the reduction time when reduced using a reducing gas.

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

[0012] One of the methods for reducing iron ore using the hydrogen reduction method is a method using a fluidized bed reduction furnace. When reducing using a fluidized bed reduction furnace, iron ore is usually used in powder form with a size of submicron to about 8.0 mm, 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, and the iron oxide is classified into goethite (FeO(OH)), hematite (FeO(OH)), and tetrahydrofuran (TeO(OH)). ２ O ３ ), magnetite (Fe ３ O ４ As iron oxide is reduced, the oxygen content decreases and it eventually becomes iron.

[0013] The reduction of iron ore by hydrogen reduction 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 in a single grain of iron ore. Subsequent reduction results in a second stage in which magnetite and wüstite are mixed in a single grain of iron ore. Subsequent reduction results in a third stage in which wüstite and iron are mixed in a single grain of iron ore. Further reduction results in a fourth stage in which all the ore is reduced to iron.

[0014] The reduction process from the first to third stages proceeds in a short period of time. This is 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, converting them to magnetite. The outside of the iron ore particles shrinks as they convert to magnetite, while the hematite inside expands upon heating. This causes cracks to form on the outside of the iron ore particles. (b) The cracks allow reducing gas to easily penetrate into the iron ore particles. Therefore, in the first stage, reduction of the iron ore particles proceeds quickly, leading to the second stage. At this time, the cracks expand as reducing gas penetrates through the cracks, forming pores that extend to the interior of the iron ore particles. (c) In the second stage, the pores formed by (a) and (b) allow reducing gas to easily penetrate into the iron ore particles. Therefore, in the second stage, reduction of the iron ore particles progresses rapidly to the inside, and the process moves to the third stage.

[0015] However, the reduction from the third stage to the fourth stage takes a long time. The reason for this is presumed to be as follows: As the reduction progresses, a dense iron film forms in the pores formed by steps (a) and (b). This prevents the reduction 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 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 the 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 a low temperature promotes the formation of mesopores and macropores that connect to the interior of the particles. Reduction at a low temperature converts iron oxide to iron without passing through wustite. This results in a larger volumetric shrinkage rate than when the iron ore passes through wustite. Therefore, cracks that occur during the reduction of iron ore are more likely to expand, promoting the formation of mesopores and macropores that connect to the interior of the particles. The subsequent process of rapidly oxidizing the iron ore at a high temperature forms micropores while maintaining the shape of the mesopores and macropores formed in the reduction process. This oxidation process rapidly oxidizes the iron coating formed in the reduction process to hematite. When the iron coating turns into hematite, it undergoes a rapid volume expansion. This causes cracks on the surface of the iron ore and on the surfaces of the mesopores and macropores, forming micropores. In other words, the specific iron ore must be oxidized until micropores are formed, so it 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 this range, the specific iron ore is easily reduced, for example, when a fluidized bed reduction furnace is used in the reduction of iron ore by hydrogen reduction. If the average particle size is less than 1.0 μm, many particles are carried away by the flow of reducing gas during reduction using a fluidized bed reduction furnace, making it difficult to maintain a stable fluidized state. If the average particle size exceeds 5.0 mm, many particles do not float even with the flow of reducing gas during reduction 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 carried away by the gas flow during reduction using a fluidized bed reduction furnace. Here, to shorten the reduction time of the iron ore, particles with an average particle size of 0.1 to 1.0 mm (e.g., alumina, zirconia, etc.), which are not involved in the reaction but are easily fluidized themselves, may be inserted into the fluidized bed reduction furnace as auxiliary particles, 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, further shortening the reduction time of the iron ore. The average particle size of the iron ore is preferably 3.0 mm or less, more preferably 2.0 mm or less, from the viewpoint of floating the particles with the gas flow and achieving a sufficient fluidized state during reduction 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 the value obtained by dividing the surface area determined by 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 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 has numerous pores inside the particles. This promotes the penetration of reducing gas into the particles during reduction of 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, hindering the penetration of reducing gas into the iron ore particles. If the surface area ratio of the specific iron ore exceeds 400, the powdered iron ore becomes brittle, causing a so-called pulverization phenomenon during reduction. While the iron ore is fluidized to match its original particle size, the small iron ore particles resulting from 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 of the specific iron ore (surface area determined by nitrogen adsorption / desorption isotherm / external surface area) is preferably 20 to 350, and 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 as determined by a nitrogen adsorption / desorption isotherm is the adsorption amount V at a relative pressure of 0.995 as determined by the nitrogen adsorption / desorption isotherm. ０．９９５ (mL / g) divided by the reciprocal of the density of the 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. This promotes the penetration of reducing gas into the iron ore particles during reduction of 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, hindering the penetration of reducing gas into the iron ore particles. If the pore volume ratio of the specific iron ore determined by the nitrogen adsorption / desorption isotherm exceeds 400, the powdered iron ore will become brittle and will be crushed during the fluidization process. Therefore, powdered iron ore with a pore volume ratio exceeding 400 cannot be substantially 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 described in the manufacturing method of the specific iron ore described below, by setting the molar ratio of O to Fe (O / Fe) within this range, the number of micropores increases. Therefore, in the reduction of iron ore by hydrogen reduction, the penetration of reducing gas into the iron ore particles is promoted, and the reduction time can be shortened.

[0033] The molar ratio of the O amount to the Fe amount (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 O amount to the Fe amount (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 as determined by a nitrogen adsorption / desorption isotherm by the adsorption amount (mL / g) at a relative pressure of 0.995 as determined by 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 more preferably 0.025 to 0.110, and even more preferably 0.025 to 0.100, from the viewpoint of increasing the proportion of micropores while maintaining the proportion of mesopores and macropores in all pores.

[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 as determined by a nitrogen adsorption / desorption isotherm is the adsorption amount V at a relative pressure of 0.96 as determined by 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 calculated by the nitrogen adsorption / desorption isotherm, and the adsorption amount V at a relative pressure of 0.995 is calculated by 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 described later.

[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 for producing specific iron ore) Next, an example of a method for producing 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 a specific iron ore, the raw material iron ore is reduced at a low temperature in the reduction step to effectively develop mesopores and macropores inside the iron ore particles, while the oxidation step oxidizes the iron ore to an oxidation state exceeding magnetite, i.e., a mixture of magnetite and hematite (ideally, an oxidation state oxidized to a single hematite phase), thereby effectively developing micropores while maintaining the mesopores and macropores developed in the reduction step.

[0046] Here, magnetite transforms into wüstite by high-temperature reduction at 570°C or higher. During this process, the change in the crystal lattice constant is small, and the degree of shrinkage associated with the transformation is small, so cracking is unlikely to occur. As a result, even when reduced at high temperatures, pores for the diffusion of reducing gas into the iron ore particles do not develop, and an improvement in the reduction rate cannot be expected. In contrast, magnetite transforms into iron by low-temperature reduction at 550°C or lower. However, the transformation from magnetite to iron is accompanied by a large volumetric shrinkage, so cracking is likely to occur. As a result, when reduced at low temperatures, pores for the diffusion of reducing gas into the iron ore particles develop, improving the reduction rate.

[0047] On the other hand, the transformation from hematite to magnetite due to reduction causes the crystals to shrink, creating nano-sized cracks (pores) deep inside the iron ore particles. Similarly, the transformation from magnetite to hematite due to oxidation also causes the crystals to shrink, further developing the pores created by reduction.

[0048] Thus, to obtain iron ore with pores developed 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 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 step, it is effective to slowly oxidize the ore at a low temperature of about 300°C with an oxygen concentration lower than that of air, or to oxidize the ore to a state close to hematite in a short time at a high temperature of 700°C or more with an oxygen concentration of several percent or less in order to maintain and further develop the pores developed in the reduction step. By undergoing these reduction and oxidation steps, a specific iron ore can be obtained that satisfies the above requirements (A) to (D) (preferably the above requirements (A) to (F)) and allows for a shorter reduction time.

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

[0050] - Reduction Step - 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 rate of 15 to 40% at a temperature of 300 to 550°C. If the reduction rate is less than 15%, the pores (mesopores and macropores) are not sufficiently developed, 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 reduction 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 with the highest content. From the viewpoint of increasing the proportion of mesopores and macropores in the specific iron ore, iron ores containing hematite or magnetite as a main component are preferred as the raw iron ore.

[0052] The reduction process is carried out at a temperature of 300 to 550°C. By carrying out reduction under these temperature conditions, iron oxide becomes iron without passing through wüstite, and the formation of mesopores and macropores that connect to the interior of the iron ore particles is promoted. Since 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 within a reduction ratio range of 10 to 45% is suitable for satisfying requirements (B) to (C). A reduction ratio of 15 to 40% is more preferable. If the oxidation step is performed under conditions conducive to pore development (e.g., an oxygen concentration of 5 to 10%, oxidation at an oxidation temperature of 300°C for several hours), a pore structure satisfying the above requirements (B) to (C) (preferably the above requirements (B) to (C) and (E) to (F)) may be formed in the iron ore even when the reduction ratio 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 without using energy. Therefore, 45% is essentially set as an upper limit for reduction in pretreatment. Here, the reduction ratio refers to the percentage of the oxygen content of the raw iron ore that is reduced by the reduction step. Limiting the reduction ratio to 10 to 45% shortens the time required for the reduction step. The reduction ratio is measured using the measurement method described 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 the fluid, the linear velocity of the reducing gas is preferably 10 to 100 cm / sec.

[0055] Examples of the reducing gas include hydrogen, carbon monoxide, etc. From the viewpoint of reducing the burden on the environment, hydrogen is preferred as the reducing gas.

[0056] - Oxidation Step - 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] Examples of oxidizing agents used in the oxidation process include air, pure oxygen, and ozone. From the viewpoint of promoting the formation of micropores, pure oxygen or ozone is preferred as the oxidizing agent. Here, 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 performed for several hours, the pores are hardly collapsed and can be further developed. On the other hand, when oxidizing iron ore at high temperatures, for example, above 700°C, the temperature-induced atomic migration is significant, so nanometer-sized pores are easily collapsed. Therefore, in the case of high-temperature oxidation, since the oxidation reaction is fast, it is preferable to reduce the oxidizing gas concentration (for example, in the case of oxygen or ozone, the oxidizing gas concentration is reduced to about 1 to 2%) and shorten the treatment time as much as possible. Furthermore, in order to achieve an O / Fe ratio of 1.35 or more, it is effective to limit the treatment time to a few minutes to a maximum of about 10 minutes. If this condition is not met, the pores inside the iron ore particles that were developed during the reduction process will collapse.

[0058] The oxidation step is preferably carried out using, for example, a fluidized bed reduction furnace in which the oxidizing agent is used 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 acceptable for the raw iron ore before reduction, the iron ore of the present disclosure can be obtained by the oxidation treatment alone, without the reduction treatment. Specifically, if an oxidation treatment is acceptable for the raw iron ore before reduction under oxidation treatment conditions of a low oxidation treatment temperature, an extremely low oxygen concentration, and a long treatment time, the iron ore of the present disclosure can be obtained by the oxidation treatment alone, without the reduction treatment. Such 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 a treatment time of 150 hours or more.

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

[0061] <Method for measuring each parameter> (Method for measuring average particle size) Since the appropriate measurement method for measuring 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 particles from small particles. The particles on the 11.1 mm sieve were excluded because they are practically difficult to fluidize in a fluidized bed. The particles separated on the 1.0 mm sieve under the 11.1 mm sieve were further sieved using dry sieves with different openings to measure the particle size distribution. The sieves used were standard sieves according to the Japanese Industrial Standards (JIS Z8801). On the other hand, for small particles under the 1.0 mm sieve, the average particle size was measured using a laser diffraction particle size distribution analyzer (e.g., 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 values ​​from the device were 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 was 50% was defined as the average particle size, based on the particle size distribution measurement results from both the dry sieve and the laser diffraction particle size distribution analyzer.

[0062] (Method for measuring nitrogen adsorption / desorption isotherm) Basically, nitrogen adsorption / desorption isotherm was measured by a method conforming to the multipoint method described in ASTM D6556-21 (Jul 07, 2021). Specifically, about 1 g of sample (about 5 g for samples with small surface areas) was measured, inserted into a predetermined measurement sample tube, and vacuum dried at 120 ° C. for 2 hours. Next, the sample tube was set in an automatic specific surface area measuring device (Microtrackbell, BELSORP MAX), and nitrogen adsorption / desorption isotherm was measured using nitrogen gas as the adsorbate and liquid nitrogen as the measurement temperature. High-purity nitrogen gas (Taiyo Nippon Sanso G1 grade, impurity concentration 0.2 vol. ppm or less) was used as the nitrogen gas used for the measurement, and the relative pressure was 1 × 10 －５ ~1 x 10 －２Up to 1000 kJ / s, measurements were taken at approximately 30 points at equal logarithmic intervals, and above that, measurements were taken at one point every 0.02 relative pressure, increasing the number of measurement points to improve the accuracy of the BET analysis. In measuring the nitrogen adsorption / desorption isotherm, fixed points were taken at measurement intervals of 0.005 relative pressure.

[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 determined by the nitrogen adsorption / desorption isotherm was calculated. The nitrogen adsorption / desorption isotherm was measured by the method described above. The surface area determined by the nitrogen adsorption / desorption isotherm was calculated by BET analysis of the nitrogen adsorption isotherm in the relative pressure range of 0.05 to 0.20. The BET analysis was performed using analysis software attached to the measurement device. Next, the external surface area was calculated. The average particle diameter of the sample was measured by the method described above. The surface area S of a 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 ) was multiplied by the surface area S to calculate the reciprocal of the value, which was taken as the number of spheres per unit mass. The value obtained by multiplying the number of spheres per unit mass by the surface area S was taken as the external surface area. The surface area ratio (surface area obtained by nitrogen adsorption / desorption isotherm / external surface area) was then calculated by dividing the surface area obtained by the nitrogen adsorption / desorption isotherm by the external surface area. Here, the surface area obtained by the nitrogen adsorption / desorption isotherm and the external surface area were in the same unit. The unit was m ２ / g was used.

[0064] (Method for measuring pore volume ratio determined from nitrogen adsorption / desorption isotherm) The pore volume ratio determined from 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 calculated. 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 iron content in the raw iron ore and the chemical composition of the raw iron ore (in the case of hematite, Fe ２ O ３ , in the case of magnetite, Fe ３ O ４ ) to calculate the oxygen content in mass% of the raw iron ore. The mass change of the raw iron ore was measured before and after the oxidation and reduction processes. The mass change was considered to be the change in oxygen content in the iron ore, and the iron and oxygen contents in mass% of the iron ore after the oxidation and reduction processes were calculated. The iron and oxygen contents in the iron ore after the oxidation and reduction processes were then converted to mol%. The molar ratio of O to Fe (O / Fe) was calculated by dividing the oxygen content converted to mol% by the iron content converted to mol%. The moisture content of the raw iron ore was measured in accordance with JIS standards (JIS M8211, 1985). The moisture contents of hematite and magnetite were confirmed to be 0.5% or less. The moisture content of goethite (the goethite sample used in the test) was 9.6%. The goethite samples were vacuum-dried at 300°C for 60 minutes before the reduction experiment. The dried goethite sample was confirmed to be a single phase hematite by X-ray diffraction. The oxygen content of goethite was calculated by dividing the chemical composition by Fe. ２ O ３ It was calculated as:

[0066] (Method for measuring the micropore volume ratio determined from the nitrogen adsorption / desorption isotherm) The micropore volume ratio determined from 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 calculated. 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 calculated. 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 (mL / g) was taken as the micropore volume fraction determined by the nitrogen adsorption / desorption isotherm.

[0067] (Method for measuring mesopore volume ratio determined from nitrogen adsorption / desorption isotherm) The mesopore volume ratio determined from 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 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 The difference between (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 for measuring reduction rate) The iron content in the raw iron ore was calculated in mass% in accordance with JIS M8212 (2005). The iron content in the raw iron ore and the chemical composition of the raw iron ore (Fe in the case of hematite) were calculated. ２ O ３ , in the case of magnetite, Fe ３ O ４ ) from the oxygen content (O Ａ 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 draw (O Ａ -O Ｂ ), the oxygen content (O Ａ The value divided by (O) and multiplied by 100 was used as the reduction rate. Ａ -O Ｂ ) ÷ O Ａ×100].

[0069] <Test Example> Using the type of raw iron ore, reduction process conditions, and oxidation process conditions shown in Tables 1 to 3, iron ore after the oxidation and reduction processes (hereinafter referred to as 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), and an apparatus (hereinafter referred to as a reaction tube) capable of fluidizing the raw iron ore by flowing gas from below was prepared. 1.0 to 2.0 g of raw iron ore was placed on the quartz filter inside the reaction tube. Hydrogen was flowed from the bottom to the top of the quartz filter of the reaction tube at a linear velocity of 10 to 100 cm / sec to fluidize the raw iron ore. While the raw iron ore was kept fluidized, the reaction tube was inserted into an electric furnace pre-maintained at the desired reaction temperature, and the reduction reaction was initiated. A thermocouple was inserted inside the reaction tube to measure the internal temperature. After the predetermined reduction rate was reached, the reaction tube was removed from the electric furnace, and simultaneously, hydrogen was replaced with argon gas at the same flow rate, and the mixture was cooled to 100°C or below. Next, the temperature of the electric furnace was maintained at the temperature for the oxidation step, and then the reaction tube was inserted into the electric furnace, and simultaneously, 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 electric furnace, and simultaneously, argon gas was replaced at the same flow rate, and the mixture was cooled to room temperature, and the test iron ore was then removed.

[0070] Here, in Test Examples RUN 1-1 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 RUN 2-1 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 RUN 3-1 to 1-25, 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 RUN 1-44 to 1-48, a sample of hematite iron ore was used in which the average particle size was adjusted by pulverizing or classifying raw iron ore with an average particle size of 75 μm, as follows. First, a 30 mL volume of iron ore powder was measured and charged into a zirconia container with an internal volume of 250 mL manufactured by Fritsch Japan Co., Ltd., and then 80 mL of zirconia balls with a diameter of 0.5 mm were measured and inserted into the container and sealed with a silicone rubber packing. The container in this state was set in a planetary ball mill (Fritsch Japan Co., Ltd. P-4) as a pulverizer. Next, using this pulverizer, pulverization was repeated for 30 minutes at 400 rpm until the iron ore powder reached the desired average particle size. By pulverization, 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. Furthermore, 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 (RUN1-47) with an average particle size of 4.25 mm and an iron ore sample (RUN1-48) with an average particle size of 5.22 mm. Furthermore, 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) having an average particle size of 0.8 μm and an iron ore sample (RUN1-48) having an average particle size of 5.22 mm in a reaction tube, but a stable fluidized state could not be achieved, and it was found that these samples were not applicable to reduction using a fluidized bed reduction furnace.

[0072] In addition, in Test Examples RUN 3-1 to 3-12, goethite iron ore that had been dried in advance to remove moisture as in the usual case was subjected to a reduction treatment and a subsequent oxidation treatment. On the other hand, in Test Examples RUN 3-13 to 3-15, from the perspective of process omission, goethite iron ore was subjected to a reduction treatment and a subsequent oxidation treatment without being dried in advance to remove moisture as in the usual case. However, in Test Examples RUN 3-6 to 3-9, no oxidation treatment was performed, and in Test Examples RUN 3-10 to 3-13, no reduction treatment was performed. In Test Examples RUN 3-16 to 3-25, also from the perspective of process omission, goethite iron ore that had been dried in advance to remove moisture as in the usual case was subjected to only an oxidation treatment without a reduction treatment. However, in order to further suppress pore collapse, the oxidation treatment was attempted under conditions of low temperature, low concentration oxidizing gas (oxygen and ozone gas), and long time.

[0073] <Reduction 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, fluidizing the raw iron ore. While the raw iron ore was still fluidized, the reaction tube was inserted into an electric furnace heated to 750°C to initiate the reduction reaction. 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 prepared using the same raw iron ore was placed on the quartz filter in the reaction tube, and reduction was performed under the same conditions for the time required for the raw iron ore to reach a reduction rate of 80%. The hydrogen was then switched to argon gas at the same flow rate, and the reduced test iron ore was removed after cooling to room temperature. The reduction ratio of the test iron ore after reduction was calculated. When the reduction ratio of the test iron ore after reduction was 84% ​​or more, it was evaluated that the iron ore had a shortened reduction rate.

[0074]

[0075]

[0076]

[0077]

[0078]

[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 documents, patent applications, and technical standards described herein are incorporated herein by reference to the same extent as if each individual document, patent application, and 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 / external surface area determined by nitrogen adsorption / desorption isotherm) is 20 to 400. (C) The pore volume ratio determined by nitrogen adsorption / desorption isotherm is 20 to 400. (D) The molar ratio of O to 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 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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