Powdered iron ore

Abstract

An iron ore is provided that can shorten the reduction time in the reduction of iron ore using the hydrogen reduction method. A powdered iron ore satisfies the following requirements (A), (B), (C), and (D): (A) Average particle size of 1.0 μm to 5.0 mm. (B) Surface area ratio (surface area / external surface area determined by nitrogen adsorption-desorption isotherms) of 20 to 400. (C) Pore volume fraction determined by nitrogen adsorption-desorption isotherms of 20 to 400. (D) Molar ratio of O to Fe (O / Fe) of 1.35 to 1.55.

Description

Technical Field

[0001] This disclosure relates to powdered iron ore. Background Technology

[0002] Iron ore reduction typically uses the blast furnace method, which utilizes coke. However, the blast furnace method has the problem of generating carbon dioxide during iron ore reduction, resulting in a significant environmental impact.

[0003] Therefore, a method for reducing iron ore using a reducing gas containing hydrogen instead of coke is being studied (hereinafter referred to as "hydrogen reduction"). Hydrogen reduction generates water during the reduction of iron ore, thus having the advantage of a lower environmental impact compared to the blast furnace method. Furthermore, fluidized bed reduction furnaces and similar equipment can be used in the reduction of iron ore using hydrogen reduction.

[0004] In particular, the reduction in a fluidized bed reduction furnace is carried out by maintaining powdered iron ore, smaller than a few millimeters in size, in a fluidized state using hydrogen gas. Therefore, the process of sintering iron ore into strong granules, as in a shaft furnace, can be omitted in the reduction in a fluidized bed reduction furnace. Furthermore, it has the advantages of a large contact area between powdered iron ore and hydrogen gas and a high reaction rate utilizing hydrogen gas for reduction.

[0005] As a reduction technology for iron ore based on hydrogen reduction, for example, Patent Document 1 discloses "a method for manufacturing sinter by reducing iron ore containing water of crystallization using a hydrogen-containing reducing gas and using the resulting reduced ore as a sintering raw material." Moreover, Patent Document 1 discloses the use of a fluidized bed reduction furnace in the reduction of iron ore.

[0006] Existing technical documents Patent documents Patent Document 1: Japanese Patent Application Publication No. 2009-249725 Summary of the Invention

[0007] The problem that the invention aims to solve In recent years, the steel industry has faced demands for reducing emissions of carbon dioxide (CO2), a greenhouse gas, leading to a need for the practical application of hydrogen reduction-based iron ore reduction methods. One key area for this practical application is shortening the reduction time for powdered iron ore.

[0008] Therefore, the objective of this disclosure is to provide an iron ore that can shorten the reduction time in the reduction of iron ore based on hydrogen reduction.

[0009] Methods for solving problems The above-mentioned problem is solved through the following means. That is, <1> A powdered iron ore that satisfies the following requirements (A), (B), (C), and (D): (A) Average particle size is 1.0 μm to 5.0 mm. (B) The surface area ratio (surface area / external surface area obtained from nitrogen adsorption-desorption isotherms) is 20~400. (C) The micropore volume fraction determined by nitrogen adsorption-desorption isotherms is 20~400. (D) The molar ratio of O to Fe (O / Fe) is 1.35~1.55.

[0010] <2> As mentioned above <1> The powdered iron ore described herein satisfies the following requirement (E): (E) The micropore volume fraction determined by nitrogen adsorption-desorption isotherms is 0.020~0.120.

[0011] <3> As mentioned above <1> or <2> The powdered iron ore described herein satisfies the following requirement (F): (F) The mesoporous volume fraction determined by the nitrogen adsorption-desorption isotherm is 0.10~0.50.

[0012] Invention Effects According to this disclosure, an iron ore is provided that can shorten the reduction time in the reduction of iron ore based on hydrogen reduction. Detailed Implementation

[0013] The following describes an embodiment as an example of this disclosure.

[0014] It should be noted that, in this specification, the numerical range represented by "~" refers to the range that includes the values ​​recorded before and after "~" as the lower and upper limits.

[0015] Within a range of values ​​recorded in stages, the upper limit value recorded in one range can be replaced by the upper limit value of another range of values ​​recorded in stages. Similarly, the lower limit value recorded in one range can be replaced by the lower limit value of another range of values ​​recorded in stages.

[0016] Within a numerical range, the upper or lower limit value recorded in a certain numerical range can be replaced with the value shown in the embodiment.

[0017] The term "process" not only includes independent processes, but also includes processes that cannot be clearly distinguished from other processes, as long as the desired purpose of the process can be achieved.

[0018] According to the definition of the International Union of Pure and Applied Chemistry (IUPAC), "micropore" is also called micropore, for example, referring to pores with a diameter of less than 2 nm; "mesopore" refers to pores with a diameter of less than 2 nm and less than 50 nm; and "macropore" refers to pores with a diameter of more than 50 nm.

[0019] <Powdered iron ore> The powdered iron ore of this embodiment (hereinafter also referred to as "specific iron ore") satisfies the requirements of (A), (B), (C) and (D) below.

[0020] (A) The average particle size is 1.0 μm to 5.0 mm.

[0021] (B) The surface area ratio (surface area / external surface area obtained by nitrogen adsorption-desorption isotherms) is 20~400.

[0022] (C) The micropore volume fraction determined by nitrogen adsorption-desorption isotherms is 20~400.

[0023] (D) The molar ratio of O to Fe (O / Fe) is 1.35~1.55.

[0024] With the above-described structure, the reduction time of certain iron ores can be shortened during reduction using reducing gas.

[0025] The specific iron ore was discovered through the following insights.

[0026] One method for reducing iron ore based on hydrogen reduction is the use of a fluidized bed reduction furnace. When using a fluidized bed reduction furnace, the iron ore is typically used in submicron to 8.0 mm powder form, with an average particle size of 1.0 μm to 5.0 mm.

[0027] Here, the main component of iron ore is iron oxide, which, in descending order of oxygen content, can be any of the following states: goethite (FeO(OH)), hematite (Fe2O3), magnetite (Fe3O4), and ferruginous iron (FeO). Moreover, as iron oxide is reduced, its oxygen content decreases, eventually becoming iron.

[0028] Regarding the reduction of iron ore using hydrogen reduction in a fluidized bed reduction furnace, the reduction of powdered iron ore, primarily composed of hematite, will be illustrated as a specific example. Powdered iron ore, primarily composed of hematite, is reduced by blowing hydrogen as a reducing gas at a flow rate of 100 mL / min at 800°C. In the first stage, hematite and magnetite are mixed in a single grain of iron ore. In the second stage, magnetite and aragonite are mixed in a single grain of iron ore. In the third stage, aragonite and iron are mixed in a single grain of iron ore. Finally, if further reduction is carried out, in the fourth stage, all iron is reduced to iron.

[0029] The reduction from the first stage to the third stage is carried out in a short period of time. It is based on the following (a) to (c).

[0030] (a) In the first stage, small cracks form on the outer side of the iron ore particles. It should be noted that the above cracks are formed as follows.

[0031] The iron ore particles are reduced from the outside to magnetite. During this reduction process, the outer surface of the iron ore particles contracts, while the inner hematite expands due to heating. Therefore, cracks form on the outer surface of the iron ore particles.

[0032] (b) Reducing gases readily penetrate the interior of the iron ore particles through the aforementioned cracks. Therefore, in the first stage, reduction occurs rapidly inside the iron ore particles, transitioning to the second stage. At this point, the cracks widen due to the intrusion of reducing gases from the cracks, connecting to the interior of the iron ore particles and forming pores.

[0033] (c) In the second stage, the reducing gas easily penetrates into the interior of the iron ore particles through the pores formed by (a) and (b) above. Therefore, in the second stage, the reduction of the iron ore particles proceeds rapidly into the interior, transferring to the third stage.

[0034] However, the transition from stage three to stage four takes a long time. The reasons for this are speculated to be as follows.

[0035] Through the reduction process, a dense iron film is formed in the pores created by (a) and (b) above. This hinders the penetration of reducing gas into the iron ore particles, making reduction difficult.

[0036] Therefore, the inventors investigated a method for manufacturing iron ore in which reducing gas can penetrate into the interior of iron ore particles. Specifically, they investigated a method for manufacturing iron ore with 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 followed by a process of rapidly oxidizing it at a high temperature. As a result, the following insights were obtained.

[0037] 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. Through low-temperature reduction, iron oxide becomes iron without passing through aragonite. Consequently, the volume shrinkage rate is greater compared to the case via aragonite. Therefore, cracks generated during the reduction of iron ore are more likely to propagate, further promoting the formation of mesopores and macropores that connect to the interior of the particles.

[0038] Next, through a rapid oxidation process at high temperature, micropores are formed while maintaining the shape of the mesopores and macropores produced by the reduction process described above. This oxidation process rapidly oxidizes the iron coating formed by the reduction process, producing hematite. When the iron coating becomes hematite, a rapid volume expansion occurs. As a result, cracks are generated on the surface of the iron ore, the surfaces of the mesopores and macropores, forming micropores. That is, oxidation to the point of forming micropores is required; therefore, a specific iron ore must satisfy the requirement (D) above.

[0039] As described above, the specific iron ore obtained through the oxidation and reduction processes has a large number of micropores, mesopores, and macropores inside, resulting in a structure with a large number of fine pores compared to conventional iron ore. That is, the specific iron ore satisfies the requirements of (B) and (C) above. Therefore, the specific iron ore further promotes the penetration of reducing gas into the particles, further reducing the iron ore.

[0040] Based on the above insights, it was found that the reduction time of certain iron ores can be shortened in the reduction of iron ore using the hydrogen reduction method.

[0041] The following is a detailed description of a specific iron ore.

[0042] (Requirement (A)) The average particle size of a specific iron ore is 1.0 μm to 5.0 mm.

[0043] By ensuring that the average particle size of a particular iron ore is within the aforementioned range, for example, in the reduction of iron ore based on hydrogen reduction, it is easily reduced when using a fluidized bed reduction furnace.

[0044] When the average particle size is less than 1.0 μm, the number of particles transported out due to the flow of reducing gas increases when using a fluidized bed reduction furnace for reduction, making it difficult to maintain a stable flow state.

[0045] When the average particle size exceeds 5.0 mm, even with the flow of reducing gas, the number of unfloated particles increases when using a fluidized bed reduction furnace for reduction, making it difficult to achieve a sufficient flow state.

[0046] From the viewpoint of suppressing particles transported out due to gas flow during reduction in a fluidized bed reduction furnace, 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.

[0047] To shorten the reduction time of iron ore, particles with an average particle size of 0.1 to 1.0 mm (such as particles of alumina or zirconium oxide) that do not participate in the reaction but are easily fluidized can be inserted as auxiliary particles into the fluidized bed reduction furnace. Iron ore powder is then added to these 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 can further shorten the reduction time of the iron ore.

[0048] From the viewpoint that the iron ore floats and achieves a fully fluid state through the flow of gas during reduction in a fluidized bed reduction furnace, the average particle size of the iron ore is preferably 3.0 mm or less, and more preferably 2.0 mm or less.

[0049] Here, the average particle size of the iron ore is determined by the determination method shown in the examples described later.

[0050] (Requirement (B)) The surface area ratio (surface area / external surface area obtained by nitrogen adsorption-desorption isotherms) of a certain iron ore is 10~400.

[0051] Here, the above surface area ratio is the value obtained by dividing the surface area obtained from the nitrogen adsorption-desorption isotherm by the outer surface area.

[0052] The surface area obtained by the nitrogen adsorption-desorption isotherm refers to the surface area per unit mass determined by the multi-point method of nitrogen adsorption as described in ASTM D6556-21 (Jul 07, 2021), as detailed in the examples described later, by performing BET analysis on the adsorption isotherm of the nitrogen adsorption-desorption isotherm.

[0053] The external surface area is the surface area per unit mass of a spherical iron ore with a diameter equal to the average grain size of a specific iron ore as determined by the above method.

[0054] By ensuring that the surface area ratio (surface area / external surface area obtained through nitrogen adsorption-desorption isotherms) of a specific iron ore is within the aforementioned range, the iron ore becomes an iron ore with numerous fine pores within its particles. Therefore, in the reduction of iron ore based on the hydrogen reduction method, the penetration of reducing gas into the particle interior can be promoted, shortening the reduction time.

[0055] If the surface area ratio of a particular iron ore is less than 20, the micropores inside the iron ore particles are not well developed, and the intrusion of reducing gas into the iron ore particles is hindered.

[0056] If the surface area ratio of a particular iron ore exceeds 400, the powdered iron ore becomes brittle, thus producing a so-called pulverization phenomenon during the reduction process. During the process of fluidizing the iron ore according to its original particle size, small iron ore particles generated by pulverization are released out of the system through the fluidizing gas, reducing the yield of the iron ore itself.

[0057] From the viewpoint of producing iron ore with a large number of fine pores inside the iron ore particles, the surface area ratio (surface area / external surface area obtained by nitrogen adsorption-desorption isotherms) of a particular iron ore is preferably 20 to 350, more preferably 25 to 350.

[0058] Here, the surface area ratio (surface area / external surface area obtained by nitrogen adsorption-desorption isotherms) of a specific iron ore is determined by the determination method shown in the examples described later.

[0059] (Requirement (C)) The micropore volume ratio of a specific iron ore, determined by nitrogen adsorption-desorption isotherms, is 20-400.

[0060] Here, the pore volume fraction obtained from the nitrogen adsorption-desorption isotherm refers to the amount of adsorption V at a relative pressure of 0.995 obtained from the nitrogen adsorption-desorption isotherm. 0.995 The value is obtained by dividing (mL / g) by the reciprocal of the density of the iron ore (e.g., 5.24 g / mL in the case of hematite and 5.17 g / mL in the case of magnetite).

[0061] By ensuring that the pore volume fraction of a specific iron ore, determined through nitrogen adsorption-desorption isotherms, falls within the aforementioned range, the ore becomes an iron ore with numerous fine pores within its particles. Consequently, in the reduction of iron ore based on hydrogen reduction, the penetration of reducing gas into the iron ore particles can be promoted, shortening the reduction time.

[0062] If the micropore volume fraction of a specific iron ore, as determined by nitrogen adsorption-desorption isotherms, is less than 20, then the micropores inside the iron ore particles are not sufficiently developed, and the intrusion of reducing gas into the iron ore particles is hindered.

[0063] If the pore volume ratio of a specific iron ore, determined by nitrogen adsorption-desorption isotherms, exceeds 400, the powdered iron ore becomes brittle and collapses during the fluidization process. Therefore, it is practically impossible to obtain powdered iron ore with a pore volume ratio exceeding 400.

[0064] From the viewpoint of producing iron ore with a large number of fine pores inside the iron ore particles, the fine pore volume ratio determined by nitrogen adsorption-desorption isotherms is preferably 25 to 350, more preferably 25 to 300.

[0065] Here, the pore volume fraction obtained by nitrogen adsorption-desorption isotherms is determined by the measurement method shown in the examples described later.

[0066] (Requirement (D)) The molar ratio (O / Fe) of a specific iron ore is 1.35 to 1.55.

[0067] As described later in the specific iron ore manufacturing method, by keeping the molar ratio of O to Fe (O / Fe) within the aforementioned range, the micropores are enlarged. Therefore, in the reduction of iron ore based on hydrogen reduction, the penetration of reducing gas into the interior of the iron ore particles can be promoted, shortening the reduction time.

[0068] From the viewpoint of increasing the micropores of a particular iron ore, the molar ratio (O / Fe) of the amount of O to the amount of Fe in the particular iron ore is preferably 1.40 to 1.55, more preferably 1.40 to 1.50.

[0069] Here, the molar ratio (O / Fe) of the amount of O to the amount of Fe in a particular iron ore is determined by the determination method shown in the examples described later.

[0070] (Requirement (E)) For a specific iron ore, the micropore volume ratio determined by nitrogen adsorption-desorption isotherms is preferably 0.020~0.120.

[0071] Here, micropore volume fraction refers to the value obtained by dividing the amount of adsorption (mL / g) at a relative pressure of 0.1 obtained by the nitrogen adsorption-desorption isotherm by the amount of adsorption (mL / g) at a relative pressure of 0.995 obtained by the nitrogen adsorption-desorption isotherm.

[0072] By ensuring that the micropore volume fraction of a specific iron ore, determined through nitrogen adsorption-desorption isotherms, falls within the aforementioned range, the proportion of micropores can be increased while maintaining the proportion of mesopores and macropores in all micropores. Consequently, in the reduction of iron ore based on hydrogen reduction, the penetration of reducing gas into the iron ore particles is further promoted, further shortening the reduction time.

[0073] From the viewpoint of increasing the proportion of micropores while maintaining the proportion of mesopores and macropores in all micropores, the micropore volume fraction of a specific iron ore, as determined by nitrogen adsorption-desorption isotherms, is more preferably 0.025 to 0.110, and even more preferably 0.025 to 0.100.

[0074] Here, the micropore volume fraction of a specific iron ore, determined by nitrogen adsorption-desorption isotherms, is determined by the method shown in the examples described later.

[0075] (Requirement (F)) For a specific iron ore, the preferred mesopore volume fraction is 0.10~0.50, determined by nitrogen adsorption-desorption isotherms.

[0076] Here, the mesoporous volume fraction obtained from the nitrogen adsorption-desorption isotherm refers to the amount of adsorption V at a relative pressure of 0.96 obtained from the nitrogen adsorption-desorption isotherm. 0.96 (mL / g) and the adsorption capacity V at a relative pressure of 0.1, determined by the nitrogen adsorption-desorption isotherm. 0.1 The difference (mL / g) (V) 0.96 -V 0.1 Divide by the adsorption amount V at a relative pressure of 0.995 obtained from the nitrogen adsorption-desorption isotherm. 0.995 The value obtained is (mL / g).

[0077] By setting the mesopore volume ratio, determined using nitrogen adsorption-desorption isotherms for a specific iron ore, within the aforementioned range, it is possible to increase the proportion of mesopores while maintaining the proportion of macropores among all micropores. Consequently, in the reduction of iron ore based on hydrogen reduction, this further promotes the penetration of reducing gas into the iron ore particles, further shortening the reduction time.

[0078] From the viewpoint of increasing the proportion of mesopores while maintaining the proportion of macropores in all micropores, the mesopore volume fraction of a specific iron ore, as determined by nitrogen adsorption-desorption isotherms, is more preferably 0.15 to 0.45, and even more preferably 0.20 to 0.45.

[0079] Here, the mesoporous volume fraction of a specific iron ore, obtained by nitrogen adsorption-desorption isotherms, is determined by the measurement method shown in the examples described later.

[0080] Here, the mesopore volume fraction of a specific iron ore, determined by nitrogen adsorption-desorption isotherms, is determined by the method shown in the examples described later.

[0081] (Methods for manufacturing specific iron ore) Next, an example of a method for manufacturing a specific iron ore will be described.

[0082] A specific iron ore is manufactured, for example, through a reduction process in which the raw iron ore is reduced at low temperature and an oxidation process in which the iron ore is oxidized after the reduction process.

[0083] In a specific iron ore manufacturing method, during the reduction process, the raw iron ore is reduced at low temperature, thereby effectively developing mesopores and macropores within the iron ore particles.

[0084] On the other hand, in the oxidation process, by oxidizing to an oxidation state that is at least greater than magnetite and a mixture of magnetite and hematite (ideally oxidizing to a single-phase oxidation state of hematite), micropores are effectively developed while maintaining the well-developed mesopores and macropores in the reduction process.

[0085] Here, magnetite undergoes a phase transformation into aragonite through high-temperature reduction above 570℃. At this point, the change in the lattice constant of the crystal is small, and the shrinkage associated with the phase transformation is minimal, thus reducing the likelihood of cracking. Consequently, even with high-temperature reduction, the micropores for the diffusion of reducing gas within the iron ore particles are underdeveloped, and an improvement in the reduction rate cannot be expected.

[0086] In contrast, magnetite is reduced to iron at low temperatures below 550°C, but this transformation is accompanied by significant volume shrinkage, making it prone to cracking. Consequently, reduction at low temperatures results in well-developed pores for the diffusion of reducing gas into the iron ore particles, thus improving the reduction rate.

[0087] On the other hand, during the reduction phase transition from hematite to magnetite, tiny nanoscale cracks (pores) are generated within the iron ore particles due to crystal shrinkage. Similarly, during the oxidation phase transition from magnetite to hematite, crystal shrinkage also occurs. The pores generated by reduction are further developed.

[0088] In order to obtain iron ore with well-developed fine pores inside the particles that effectively improves the reduction rate of iron ore, it is effective to reduce the raw iron ore at low temperature and then oxidize it to an oxidation state close to that of hematite.

[0089] In other words, as detailed below, it is effective to maintain and further develop the fine pores that are developed through low-temperature reduction at around 550°C or below in the reduction process during the oxidation process.

[0090] It should be noted that in the oxidation process, slow oxidation is achieved by keeping the oxygen concentration below that of air at a low temperature of around 300°C; or by oxidizing to the vicinity of hematite in a short time at a high temperature above 700°C with an oxygen concentration of less than a few percent. These methods are effective in maintaining and further developing the fine pores that have been developed in the reduction process.

[0091] Through these reduction and oxidation processes, a specific iron ore that meets the above requirements (A) to (D) (preferably meeting the above requirements (A) to (F)) and can shorten the reduction time can be obtained.

[0092] The following details the process of manufacturing a specific iron ore.

[0093] -Reduction Process- In the reduction process, raw iron ore with 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. When the reduction rate is less than 15%, the development of micropores (mesopores and macropores) is insufficient, and it is impossible to form a microporous structure in the iron ore that satisfies the above requirements (B) to (C) (preferably the above requirements (B) to (C) and (E) to (F)).

[0094] Through this reduction process, the proportion of mesopores and macropores in a particular iron ore increases compared to reduction under high-temperature conditions.

[0095] There is no limitation on the iron ore used as raw material; for example, iron ore containing goethite, hematite, or magnetite as its main components can be listed. Here, the main component refers to the component with the highest content among the components contained in the iron ore.

[0096] From the viewpoint of increasing the proportion of mesopores and macropores in a particular iron ore, iron ore used as raw material is preferably iron ore containing hematite or magnetite as the main component.

[0097] The reduction process is carried out at a temperature of 300~550℃.

[0098] By reducing the iron oxide at this temperature, iron oxide becomes iron without passing through ferromagnetite, promoting the formation of mesopores and macropores connected to the interior of the iron ore particles. The transformation from magnetite to iron is accompanied by a large volume shrinkage, thus it is speculated that fine pores (voids) are formed inside the iron ore particles.

[0099] To satisfy conditions (B) to (C), the reduction process is suitable to be carried out in the range of 10% to 45%. More preferably, the reduction rate is 15% to 40%. If the oxidation process is carried out under conditions that promote the development of fine pores (e.g., oxidation at an oxygen concentration of 5% to 10% and an oxidation temperature of 300°C for several hours), even if the reduction rate is reduced to more than 50%, it is sometimes possible to form a fine pore structure in the iron ore that satisfies the above conditions (B) to (C) (preferably the above conditions (B) to (C) and (E) to (F)). However, from a practical point of view, it is effective to shorten the reduction time effectively with low cost and no energy application in the pretreatment. Therefore, 45% is essentially set as an upper limit for the reduction in the pretreatment.

[0100] Here, the reduction rate refers to the proportion of oxygen in the raw iron ore that is reduced due to the reduction process.

[0101] By keeping the reduction rate between 10% and 45%, the time required for the reduction process can be shortened.

[0102] The reduction rate was determined using the measurement method shown in the examples described later.

[0103] The reduction process is preferably carried out using a fluidized bed reduction furnace with reducing gas as the fluid.

[0104] When using a fluidized bed reduction furnace with reducing gas as the fluid for reduction, the linear velocity of the reducing gas is preferably 10~100 cm / s.

[0105] Examples of reducing gases include hydrogen and carbon monoxide.

[0106] From the perspective of reducing the environmental impact, hydrogen is preferred as a reducing gas.

[0107] -Oxidation Process- In the oxidation process, the iron ore after the reduction process is essentially oxidized at a temperature above 300°C.

[0108] Through this oxidation process, micropores are formed while maintaining the shape of the mesopores and macropores produced by the reduction process described above.

[0109] Examples of oxidants used in oxidation processes include air, pure oxygen, and ozone.

[0110] From the perspective of promoting the formation of micropores, pure oxygen or ozone is preferred as an oxidant.

[0111] In this process, managing the concentration of oxidizing gas corresponding to the temperature is effective for maintaining micropores. Specifically, for example, when oxidizing iron ore at 300°C, setting the oxygen concentration to around 5-10% and oxidizing for several hours results in micropores that hardly collapse, further promoting micropore development.

[0112] On the other hand, when iron ore is oxidized at temperatures exceeding 700°C, significant atomic movement occurs due to temperature, easily disrupting nanoscale pores. Therefore, in high-temperature oxidation, the oxidation reaction is rapid, making it preferable to reduce the concentration of oxidizing gas (e.g., to approximately 1-2% if oxygen or ozone is used) and minimize processing time. Furthermore, suppressing the oxidation for several minutes to a maximum of about 10 minutes is effective to achieve an O / Fe ratio of 1.35 or higher. If this condition is not met, the fine pores within the iron ore particles, which are developed during the reduction process, will collapse.

[0113] The oxidation process is preferably carried out using a fluidized bed reduction furnace with the aforementioned oxidant as the fluid.

[0114] When using a fluidized bed reduction furnace with the above-mentioned oxidant as the fluid for reduction, the linear velocity of the fluid is preferably 10 to 100 cm / s.

[0115] However, for iron ore raw materials before reduction, under conditions where extremely long oxidation treatment is allowed, it is possible to obtain the iron ore disclosed herein through oxidation alone without a reduction process.

[0116] Specifically, under oxidation treatment conditions of low temperature, extremely low oxygen concentration, and extended treatment time, and when the raw iron ore before reduction is allowed to undergo oxidation treatment, the iron ore disclosed herein can be obtained solely through an oxidation process without a reduction process.

[0117] The preferred oxidation conditions are an oxidation temperature of 250-350°C, an oxygen concentration of 1-5%, and an oxidation time of more than 100 hours. More preferably, the conditions are an oxidation temperature of 300-350°C, an oxygen concentration of 3-5%, and an oxidation time of more than 150 hours.

[0118] Example The following describes the embodiments, but this disclosure is not limited to these embodiments in any way.

[0119] <Methods for measuring each parameter> (Method for determining average particle size) In determining the average particle size, different methods are used depending on the particle size. Therefore, to separate large and small particles, dry sieves with mesh sizes of 11.1 mm and 1.0 mm are used. The 11.1 mm sieve is excluded due to difficulties in fluidization in a fluidized bed. Particles that pass through the 11.1 mm sieve but are separated onto the 1.0 mm sieve are further sieved using dry sieves with different mesh sizes to determine the particle size distribution. The sieves used conform to the Japanese Industrial Standard (JIS Z8801).

[0120] On the other hand, for small-diameter particles passing through a 1.0 mm sieve, the average particle size is determined using a laser diffraction particle size distribution measuring device (e.g., Shimadzu SALD-2300).

[0121] Specifically, a dispersion is prepared by dispersing 1-2 drops of a specific iron ore and, as needed, a neutral household detergent (trade name: Mamaremon) in a dispersion medium such as water. The amount of iron ore powder is adjusted to bring the measured values ​​of the device within a specified frequency range. The particle size distribution of this dispersion is then measured using a laser diffraction particle size distribution measuring device.

[0122] It should be noted that for the particle size distribution measurement results of both dry sieve and laser diffraction particle size distribution measuring device, the average particle size will be the particle size at which the cumulative relative particle amount is 50% based on volume.

[0123] (Method for determining nitrogen adsorption-desorption isotherms) The nitrogen adsorption-desorption isotherm was determined using the multi-point 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 measured and inserted into a specified sample tube for testing, and then vacuum-dried at 120°C for 2 hours. Next, the sample tube was placed in an automated specific surface area measuring device (MicrotracBEL, BELSORP MAX), with nitrogen gas used as the adsorbate and liquid nitrogen as the measurement temperature, to determine the nitrogen adsorption-desorption isotherm. High-purity nitrogen gas (G1 grade, Taiyo Nippon Sanso, impurity concentration below 0.2 vol. ppm) was used in the test at a relative pressure of 1 × 10⁻⁶. -5 ~1×10 -2 Approximately 30 points are measured at logarithmic intervals. When the number of points exceeds this, a measurement condition of 1 point is set for every 0.02 relative pressures to increase the number of measurement points and improve the accuracy of BET analysis.

[0124] In the determination of nitrogen adsorption-desorption isotherms, fixed points were set at measurement intervals of 0.005 relative pressures.

[0125] (Method for determining surface area ratio) The surface area ratio (surface area / external surface area obtained by nitrogen adsorption-desorption isotherms) is determined according to the following steps.

[0126] First, calculate the surface area obtained from the nitrogen adsorption-desorption isotherm.

[0127] The nitrogen adsorption-desorption isotherm was determined using the method described above. The surface area derived from the nitrogen adsorption isotherm was calculated by performing BET analysis on the nitrogen adsorption isotherm within a relative pressure range of 0.05–0.20. It should be noted that the BET analysis was performed using the analysis software provided with the measuring apparatus.

[0128] Next, the external surface area is calculated. The average particle size of the sample is determined using the method described above. The surface area S and volume V of a sphere with the calculated average particle size as its diameter are calculated. The volume V is then multiplied by the density of the sample (5.24 g / cm³ in the case of hematite). 3 In the case of magnetite, it is 5.17 g / cm³. 3The reciprocal of the obtained value is taken as the number of spheres per unit mass. The outer surface area is obtained by multiplying the number of spheres per unit mass by the surface area S.

[0129] Then, the surface area obtained by the nitrogen adsorption-desorption isotherm is divided by the surface area to calculate the surface area ratio (surface area obtained by the nitrogen adsorption-desorption isotherm / surface area).

[0130] Here, the units for surface area and external surface area derived from nitrogen adsorption-desorption isotherms are set to be the same. The unit used is m. 2 / g.

[0131] (Method for determining the pore volume fraction by means of nitrogen adsorption-desorption isotherms) The determination of the pore volume fraction obtained by nitrogen adsorption-desorption isotherms is carried out according to the following steps.

[0132] First, the nitrogen adsorption-desorption isotherm was determined using the method described above. Using this isotherm, the adsorption capacity V at a relative pressure of 0.995 was calculated. 0.995 (mL / g). The above adsorption amount V 0.995 The value obtained by dividing by the reciprocal of the sample density (5.24 g / mL for hematite and 5.17 g / mL for magnetite) is used as the pore volume fraction determined by the nitrogen adsorption-desorption isotherm.

[0133] (Method for determining the molar ratio of O to Fe (O / Fe)) According to JIS M8212 (2005), the iron content in the raw iron ore is calculated in mass% (%). Based on the above-mentioned iron content value and chemical composition of the raw iron ore (Fe2O3 in the case of hematite and Fe3O4 in the case of magnetite), the oxygen content in the raw iron ore is calculated in mass% (%).

[0134] For the raw iron ore, the mass change is measured before and after the oxidation and reduction processes. This mass change is considered as the change in oxygen content in the iron ore, and the iron and oxygen content in the iron ore after the oxidation and reduction processes is calculated in % by mass. Then, the iron and oxygen content in the iron ore after the oxidation and reduction processes is converted to % by mole. The molar ratio of O to Fe (O / Fe) is calculated by dividing the oxygen content (converted to % by the iron content (converted to % by mole).

[0135] It should be noted that the moisture content of the raw iron ore was determined according to JIS standard (JIS M8211, 1985 edition). The results confirmed that the moisture content of hematite and magnetite was below 0.5%.

[0136] The goethite (the goethite sample used in the experiment) had a moisture content of 9.6%. The goethite was pre-dried under vacuum at 300°C for 60 minutes before the reduction experiment. The dried goethite sample was confirmed as a single-phase hematite by X-ray diffraction. Furthermore, the oxygen content of the goethite was calculated using the chemical composition of Fe₂O₃.

[0137] (Method for determining micropore volume fraction by nitrogen adsorption-desorption isotherms) The determination of micropore volume fraction obtained by nitrogen adsorption-desorption isotherms is carried out according to the following steps.

[0138] First, the nitrogen adsorption-desorption isotherm was determined using the method described above. Using this isotherm, the adsorption amount V at a relative pressure of 0.1 was calculated. 0.1 (mL / g) and adsorption capacity V at a relative pressure of 0.995 0.995 (mL / g). The adsorption capacity V at a relative pressure of 0.1, determined by the nitrogen adsorption-desorption isotherm. 0.1 (mL / g) divided by the adsorption capacity V at a relative pressure of 0.995, obtained from the nitrogen adsorption-desorption isotherm. 0.995 The value obtained (mL / g) is used as the micropore volume fraction determined by the nitrogen adsorption-desorption isotherm.

[0139] (Method for determining mesoporous volume fraction by nitrogen adsorption-desorption isotherms) The mesoporous volume fraction obtained from the nitrogen adsorption-desorption isotherm is determined according to the following steps.

[0140] First, the nitrogen adsorption-desorption isotherm was determined using the method described above. Using this isotherm, the adsorption amount V at a relative pressure of 0.1 was calculated. 0.1 (mL / g), adsorption capacity V at a relative pressure of 0.96 0.96 (mL / g) and adsorption capacity V at a relative pressure of 0.995 0.995 (mL / g). Calculate the adsorption capacity V. 0.96 With the above adsorption amount V 0.1 The difference (V) 0.96 -V 0.1 ), divided by the above adsorption amount V 0.995 The obtained value is used as the mesoporous volume fraction determined by the nitrogen adsorption-desorption isotherm.

[0141] (Method for determining reduction rate) According to JIS M8212 (2005), the iron content in the raw iron ore is calculated in mass% (%). Based on the above-mentioned iron content value and the chemical composition of the raw iron ore (Fe2O3 in the case of hematite, Fe3O4 in the case of magnetite), the oxygen content (O2O4) in the raw iron ore is calculated in mass% (%). A ).

[0142] For raw iron ore, the change in mass is measured before and after the reduction process. This change in mass is considered the change in oxygen content in the iron ore, and the oxygen content (O2) in the iron ore after the reduction process is calculated as a percentage by mass. B Then, from the above oxygen content (O) A Subtract the above oxygen content (O) B (O) A -O B ), divided by the above oxygen content (O A The value obtained by multiplying the value of (O) by 100 is used as the reduction rate [that is, (O)]. A -O B )÷O A ×100].

[0143] <Experimental Example> The types of raw iron ore, reduction process conditions, and oxidation process conditions are set as shown in Tables 1 to 3. The iron ore after oxidation and reduction processes (hereinafter referred to as test iron ore) is obtained through the following steps.

[0144] Prepare in a quartz tube (inner diameter 12mm) The lower part of the reaction tube is welded with a quartz filter for holding the raw iron ore and a device (hereinafter referred to as the reaction tube) through which gas flows from below to keep the raw iron ore in a flowing state. 1.0~2.0g of raw iron ore is placed on the quartz filter inside the reaction tube. Hydrogen is flowed from the lower part of the quartz filter to the upper part of the reaction tube at a linear velocity of 10~100cm / sec, keeping the raw iron ore in a flowing state. With the raw iron ore in a flowing state, the reaction tube is inserted into an electric furnace that has been pre-maintained at the desired reaction temperature to begin the reduction reaction. It should be noted that a thermocouple is inserted inside the reaction tube to measure the internal temperature. After the specified reduction rate is reached, the reaction tube is removed from the electric furnace, and simultaneously, the hydrogen gas is switched to argon gas at the same flow rate, cooling to below 100°C. Then, after maintaining the temperature of the electric furnace at the temperature used for the oxidation process, the reaction tube is inserted into the electric furnace, and the oxidant is flowed at a linear velocity of 10~100cm / sec. After the specified time has elapsed, the reaction tube is removed from the electric furnace, and argon gas is switched to the same flow rate. After cooling to room temperature, the test iron ore is removed.

[0145] In the experimental examples RUN1-1 to 1-48, hematite iron ore with an average particle size of 75 μm and the characteristics shown in Table 1 was used as the raw material iron ore (refer to the reference example).

[0146] In test examples RUN2-1 to 2-14, magnetite iron ore with an average particle size of 12 μm and the characteristics shown in Table 2 was used as the raw material (refer to the reference example).

[0147] In test examples RUN3-1 to 1-25, goethite iron ore with an average particle size of 135 μm and the characteristics shown in Table 3 was used as the raw material (refer to the reference example).

[0148] However, in test examples RUN1-44 to 1-48, as described below, samples of hematite iron ore with an average particle size adjusted by crushing or classifying raw iron ore with an average particle size of 75 μm were used.

[0149] First, iron ore powder was metered into a 250 mL zirconium oxide container (manufactured by Fritsch Japan) and loaded with 30 mL of the powder. Then, 0.5 mm diameter zirconium oxide balls were inserted into the container and sealed with a silicone rubber gasket. This container was then placed in a planetary ball mill (Fritsch Japan P-4) as the grinding device. Next, the powder was repeatedly ground at 400 rpm for 30 minutes until the iron ore powder reached the target average particle size.

[0150] Samples of iron ore with an average particle size of 0.8 μm (RUN1-44) and an average particle size of 1.2 μm (RUN1-45) were prepared by crushing.

[0151] In addition, the powder of hematite iron ore with an average particle size of 75 μm was classified using a sieve with a mesh size of 4.75 mm, thereby preparing iron ore samples with an average particle size of 4.25 mm (RUN1-47) and iron ore samples with an average particle size of 5.22 mm (RUN1-48).

[0152] In addition, the powder of hematite iron ore with an average particle size of 75 μm was classified using a sieve with a mesh size of 425 μm to prepare a sample of iron ore with an average particle size of 550 μm (RUN1-46).

[0153] It should be noted that although it was possible to make the iron ore samples with an average particle size of 0.8 μm (RUN1-44) and the iron ore samples with an average particle size of 5.22 mm (RUN1-48) flow in the reaction tube, a stable flow state could not be formed, indicating that it could not be applied to the reduction using a fluidized bed reduction furnace.

[0154] In addition, in test examples RUN3-1 to 3-12, goethite iron ore that had been pre-dried and normally dehydrated was subjected to reduction treatment and subsequent oxidation treatment.

[0155] On the other hand, in experimental examples RUN3-13 to 3-15, from the viewpoint of omitting a process, for goethite iron ore, the usual moisture removal process, which is performed before drying, was not carried out, and the reduction process and subsequent oxidation process were performed directly.

[0156] However, in test examples RUN3-6 to 3-9, no oxidation treatment was performed, and in test examples RUN3-10 to 3-13, no reduction treatment was performed.

[0157] In experimental examples RUN3-16 to 3-25, also from the perspective of omitting steps, goethite ore, which underwent pre-drying and the usual moisture removal, was subjected to oxidation treatment only without reduction treatment. However, in order to enhance the suppression of pore collapse, the oxidation treatment was attempted under conditions of low temperature, low concentration of oxidizing gases (oxygen and ozone gases), and long duration.

[0158] <Restore Evaluation> Place 1.0-2.0 g of raw iron ore onto the quartz filter inside the reaction tube used in the preparation of the experimental iron ore. Allow hydrogen to flow from the bottom to the top of the quartz filter in the vertical electric furnace at a linear velocity of 10-100 cm / sec, thus making the raw iron ore flowable. Maintaining the flow of the raw iron ore, insert the reaction tube into the electric furnace heated to an internal temperature of 750°C to begin the reduction reaction. Note that a thermocouple is inserted inside the reaction tube to measure the internal temperature. Then, measure the time required for the raw iron ore to reach a reduction rate of 80%.

[0159] Next, 1.0 g of test iron ore prepared using the same raw material was placed on a quartz filter inside the reaction tube, and the reduction was carried out under the same conditions for the time required to achieve a reduction rate of 80%. Then, hydrogen was switched to argon at the same flow rate, and after cooling to room temperature, the reduced test iron ore was removed. The reduction ratio of the obtained reduced test iron ore was calculated.

[0160] Here, when the reduction rate of the reduced test iron ore is above 84%, it is evaluated as iron ore with a shortened reduction rate.

[0161] Based on the above results, it can be seen that the reduction time of the experimental iron ore in this embodiment can be shortened in the reduction of iron ore based on the hydrogen reduction method.

[0162] It should be noted that the disclosure of Japanese Patent Application No. 2024-050248 is incorporated herein by reference in its entirety.

[0163] All documents, patent applications and technical standards described in this specification are incorporated herein by reference to the same extent as those documents, patent applications and technical standards specifically described therein.

Claims

1. A powdered iron ore that satisfies the following requirements (A), (B), (C), and (D): (A) Average particle size is 1.0 μm to 5.0 mm. (B) The surface area ratio, calculated using nitrogen adsorption-desorption isotherms, is 20~400. (C) The micropore volume fraction determined by nitrogen adsorption-desorption isotherms is 20~400. (D) The molar ratio of O to Fe, i.e., O / Fe, is 1.35~1.

55.

2. The powdered iron ore according to claim 1, wherein it satisfies the following requirement (E): (E) The micropore volume fraction determined by nitrogen adsorption-desorption isotherms is 0.020~0.

120.

3. The powdered iron ore according to claim 1 or claim 2, wherein the following requirement (F) is satisfied: (F) The mesoporous volume fraction determined by the nitrogen adsorption-desorption isotherm is 0.10~0.50.

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