Method for producing ironmaking raw material

Abstract

To provide a method for producing an iron-making raw material in which gangue contained in low-grade iron ore is sufficiently removed and a gangue ratio is sufficiently suppressed under a production condition in which energy consumption is suppressed.SOLUTION: A pulverization step of pulverizing the reduced product to obtain a pulverized product containing iron-containing particles having a volume-based cumulative particle size 1A of 100 μm or more, and a magnetic separation step of magnetically separating the pulverized product to recover the iron-containing particles as a magnetically attractable substance, the iron-containing particles having a volume-based cumulative particle size Fe3O4 of 100 μm or more, and the iron-containing particles having a gangue ratio of 10% or more, the gangue ratio being determined by the following formula (D50Fe): Gangue ratio of iron ores (%) = (SiO2 + Al2O3) / T. Fe * 100 (1A) In the formula (1A), SiO2, Al2O3, and T. Fe represent the amount of SiO2 (mass%), the amount of Al2O3 (mass%), and the total amount of iron (mass%) in the iron ores, respectively.SELECTED DRAWING: Figure 7

Description

[Technical Field]

[0001] The present disclosure relates to a method for producing raw materials for iron making. [Background technology]

[0002] In recent years, with the depletion of high-quality iron sources, it has become increasingly difficult to obtain iron ore with few impurities, such as gangue, as a raw material for steel products. The impurity content of iron ore is expected to increase in the future. In the existing blast furnace-converter process, gangue components (e.g., SiO2, Al2O3) in iron ore are separated and discharged as a low-density liquid phase (slag) above the molten iron when the iron ore is reduced and melted in a blast furnace. However, an increase in the amount of slag leads to a deterioration in the gas permeability of the blast furnace, necessitating measures such as increasing the amount of coke input to ensure gas permeability. However, increasing the amount of coke input increases production costs and CO2 emissions. Therefore, when using low-grade iron ore containing a large amount of gangue for steelmaking, it is desirable to reduce the amount of gangue in the iron ore as a pretreatment method.

[0003] As a technique for effectively separating reduced iron from slag containing gangue components, for example, Patent Document 1 discloses a method for producing a mixture of reduced iron and slag, which includes, in this order, a step of agglomerating a raw material mixture containing a substance containing iron oxide and titanium oxide, a carbonaceous material, and a melting point adjuster, and a step of heating the obtained agglomerates so that a portion of the agglomerates melts, thereby reducing the iron oxide contained in the agglomerates.

[0004] Furthermore, Patent Document 2 discloses a method for pre-treating iron ore for steelmaking, in which gangue-containing iron ore is reduced with gas, crushed, and then magnetically separated to remove the gangue and improve the iron quality of the iron ore. In this method, the reduction time [min] of the iron ore is defined as t, and the H2 partial pressure [atm] of the reducing gas is defined as P H2 The CO partial pressure [atm] of the reducing gas is P CO It is shown that the reduction treatment is controlled so that a parameter X indicating the relationship between the reduction time of the iron ore and the reducing gas satisfies a predetermined formula (1) when

[0005] Furthermore, Patent Document 3 discloses a method for producing a high-quality iron source, in which inferior quality iron ore having a gangue ratio of 15% or more, expressed as (SiO2 + Al2O3) / Total.Fe × 100 using the total iron amount Total.Fe, SiO2 amount, and Al2O3 amount (mass %) relative to the raw ore, is reduced, the reduced raw ore is crushed, and the crushed raw ore is magnetically separated to produce a high-quality iron source having a gangue ratio of 10% or less. In this method, the cumulative weight average diameter D of the crushed raw ore is 50 It is indicated that the powder should be crushed so that the particle size is less than 200 μm. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2013-249496 [Patent Document 2] Japanese Patent Application Publication No. 2018-012850 [Patent Document 3] Japanese Patent Application Publication No. 2018-095893 Summary of the Invention [Problem to be solved by the invention]

[0007] The method of Patent Document 1 requires high temperatures of 1200°C or higher to melt a portion of the iron ore. However, from the viewpoint of reducing energy consumption, processing at lower temperatures is desired. Furthermore, the method of Patent Document 1 requires a step of agglomerating a raw material mixture containing a melting point adjuster, which makes the process complicated.

[0008] Patent Document 2 discloses a technique for removing gangue without heating iron ore to high temperatures, i.e., without melting the iron ore. This technique requires the use of large amounts of highly reducing gases, such as H2 and CO, to produce metallic iron. However, since these gases, which are also valuable energy sources, are used in large quantities, this technique is considered to be undesirable from an energy standpoint. Patent Document 3 also relates to a technique for removing gangue without melting iron ore, and provides guidelines for controlling the particle size of the entire sample. However, further study is considered necessary to obtain raw materials for steelmaking with a sufficiently reduced gangue ratio.

[0009] The present disclosure has been made in view of the above-mentioned problems, and an object of the present disclosure is to provide a method for producing raw materials for ironmaking with a sufficiently reduced gangue ratio by sufficiently removing gangue contained in low-grade iron ore under production conditions with reduced energy consumption. [Means for solving the problem]

[0010] Aspect 1 of the present invention is a reduction step in which iron ore having a gangue ratio of 10% or more calculated from the following formula (1A) is reduced under conditions of temperature and gas composition in which Fe3O4 becomes a stable phase, to obtain a reduced product containing an iron-containing phase; a pulverization step of pulverizing the reduced product to obtain a pulverized product containing iron-containing particles including an iron-containing phase, wherein the iron-containing phase has a cumulative volume particle size D50Fe of 100 μm or more; and a magnetic separation step of magnetically separating the pulverized material and recovering the iron-containing particles as magnetically attracted material. Iron ore gangue ratio (%) = (SiO2 + Al2O3) / T.Fe × 100 (1A) In formula (1A), SiO2, Al2O3, and T.Fe represent the amount of SiO2 (mass%), the amount of Al2O3 (mass%), and the total amount of iron (mass%) in the iron ore, respectively.

[0011] Aspect 2 of the present invention is In the method for producing a raw material for iron making according to aspect 1, the reduction step is performed so that the Fe3O4 conversion rate calculated from the following formula (2) is 40% or more.

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[0012] Aspect 3 of the present invention is In the method for producing a raw material for iron making according to aspect 1 or 2, the gas used in the reduction step includes a top gas of a blast furnace.

[0013] A fourth aspect of the present invention is In the method for producing a raw material for iron making according to any one of Aspects 1 to 3, the reduction step is carried out at a reduction temperature of 900° C. or less. [Effects of the Invention]

[0014] According to the present disclosure, it is possible to provide a method for producing raw materials for ironmaking with a sufficiently reduced gangue ratio by sufficiently removing gangue contained in low-grade iron ore under production conditions with reduced energy consumption. [Brief explanation of the drawings]

[0015] [Figure 1] FIG. 1 is an image diagram that schematically shows the steps of this embodiment. [Figure 2] Figure 2 is Figure 3 (reduction equilibrium diagram of iron oxide) from Yoichi Ono, "Rist Operation Diagram (I)," Iron and Steel, Vol. 79, 1993, No. 9, N618. [Figure 3] Figure 3 is a reference spectrum of iron oxide. [Figure 4] Figure 4 is a reference spectrum of another iron oxide. [Figure 5] FIG. 5 is a mineral phase analysis map of Comparative Example 2. [Figure 6] FIG. 6 is a mineral phase analysis map of Example 2. [Figure 7] FIG. 7 is a graph showing the relationship between the cumulative volume particle diameter D50Fe of the iron-containing phase and the magnetic susceptibility. DETAILED DESCRIPTION OF THE INVENTION

[0016] The method for producing raw materials for iron making according to this embodiment includes the steps of: a reduction step in which iron ore having a gangue ratio of 10% or more calculated from the following formula (1A) is reduced under conditions of temperature and gas composition in which Fe3O4 becomes a stable phase, to obtain a reduced product containing an iron-containing phase; a pulverization step of pulverizing the reduced product to obtain a pulverized product containing iron-containing particles including an iron-containing phase, wherein the iron-containing phase has a cumulative volume particle size D50Fe of 100 μm or more; and a magnetic separation step of magnetically separating the pulverized material and recovering the iron-containing particles as magnetically attracted material. Iron ore gangue ratio (%) = (SiO2 + Al2O3) / T.Fe × 100 (1A) In formula (1A), SiO2, Al2O3, and T.Fe represent the amount of SiO2 (mass%), the amount of Al2O3 (mass%), and the total amount of iron (mass%) in the iron ore, respectively.

[0017] According to the production method of this embodiment, gangue contained in low-grade iron ore can be sufficiently removed, and ironmaking raw material (iron-containing particles) with a sufficiently reduced gangue ratio can be produced.

[0018] The technology of the present disclosure is particularly focused on the state of the iron-containing phase after pulverization. According to a preferred embodiment of the present disclosure, a raw material for ironmaking with sufficiently reduced gangue can be produced without using high temperatures in the production process, particularly in the reduction step. Furthermore, according to a preferred embodiment of the present disclosure, gangue components can be sufficiently removed from iron ore without using a gas with high reducing power in the production process.

[0019] Each step of the manufacturing method according to this embodiment will be described in detail below. FIG. 1 is an image diagram that schematically illustrates each step of the manufacturing method according to this embodiment. While the following description of each step may be based on FIG. 1, FIG. 1 is merely an image diagram and does not limit the present disclosure. For example, there may be cases where unreduced iron oxide is not completely reduced to Fe3O4 by reduction, or where grinding does not completely separate the gangue and the iron-containing phase, with some of the gangue remaining, for example, on the surface of the iron-containing phase. These situations are naturally acceptable, and the manufacturing method according to this embodiment may also include these situations.

[0020] [Reduction process] As shown schematically in Figure 1, in the reduction step, the raw material, iron ore 1 containing gangue 3 and unreduced iron oxide 5, is reduced under predetermined conditions to obtain a reduced product 7 containing an iron-containing phase 9 shown in B in Figure 1. By going through the reduction step represented by arrow a from A to B in Figure 1, unreduced iron oxide 5, such as Fe2O3, is reduced to obtain a reduced product 7 containing an iron-containing phase 9, such as Fe3O4.

[0021] The raw material, iron ore 1 containing gangue 3 and unreduced iron oxide 5, has a gangue ratio of 10% or more as calculated by the following formula (1A). The gangue ratio may be 13.0% or more, even 15.0% or more, or even 18.0% or more. The upper limit of the gangue ratio may be, for example, 40.0%. According to the present disclosure, even when iron ore containing such a large amount of gangue is used as the raw material, it is possible to produce a steelmaking raw material from which gangue has been sufficiently removed. The iron ore may be crushed, classified, or the like before being subjected to reduction to achieve a uniform size. Iron ore gangue ratio (%) = (SiO2 + Al2O3) / T.Fe × 100 (1A) In formula (1A), SiO2, Al2O3, and T.Fe represent the amount of SiO2 (mass%), the amount of Al2O3 (mass%), and the total amount of iron (mass%) in the iron ore, respectively.

[0022] In the method for producing raw materials for ironmaking disclosed herein, iron ore (raw material) is reduced not to metallic iron but to Fe3O4, an iron oxide with a high iron content. Iron ore and the raw materials for ironmaking obtained from the iron ore contain four iron-containing compounds: Fe2O3, Fe3O4, and FeO, which are oxides, and metallic iron (Fe). Of these, Fe3O4 and metallic iron (Fe) are ferromagnetic. Therefore, reducing iron ore to Fe3O4 reduces energy costs and production time compared to reducing iron to metallic iron, and magnetic separation (magnetic separation) can be used, allowing for efficient separation and recovery. Furthermore, reducing iron ore to Fe3O4 allows for the use of gases with low reducing power, such as blast furnace top gas, thereby enabling the utilization of waste gas.

[0023] Based on the above, in the reduction process, iron ore is reduced under conditions of temperature and gas composition where Fe3O4 is the stable phase, to obtain a reduced product containing an iron-containing phase (reduced iron oxide phase). These conditions may be any temperature and gas composition where Fe3O4 is the stable phase. For example, as shown in Figure 2 (Yoichi Ono, "Rist Operating Diagram (I)," Iron and Steel, Vol. 79, No. 9, N618, 1993, Figure 3 (Iron Oxide Reduction Equilibrium Diagram)), reduction can be performed by combining the temperature and gas composition in the region where Fe3O4 is the stable phase, such as the Fe3O4 region shown as the shaded area in Figure 2, using an Fe-CO equilibrium diagram represented by temperature and CO / (CO + CO2). In Figure 2, the horizontal axes "CO" and "CO2" represent the partial pressures of CO gas and CO2 gas, respectively. In Figure 2, for example, when CO2 / (CO+CO2) shown on the horizontal axis is 70%, Fe3O4 is stable at temperatures of 600°C and 700°C. Therefore, for example, temperatures of 600°C and 700°C and a gas composition of CO2 / (CO+CO2) = 70% can be said to be the temperature and gas composition conditions under which Fe3O4 becomes a stable phase. On the other hand, when CO2 / (CO+CO2) is, for example, 70% and the temperature is 800°C, FeO is the stable phase, but Fe3O4 cannot be said to be a stable phase, so these conditions cannot be said to be the temperature and gas composition conditions under which Fe3O4 becomes a stable phase.

[0024] The gas constituting the atmosphere in the reduction step may contain at least one of the CO gas and H gas described above, and the remaining gas components are not particularly limited. Examples of the remaining gas components include CO, N, and H0. The gas may also contain at least the top gas of a blast furnace.

[0025] Instead of the CO-CO2 system, reduction can be performed using an H2-H2O system or an H2-H2O-CO-CO2 system. The temperature and gas composition conditions for Fe3O4 to become a stable phase can be determined in the same way as for the CO-CO2 system. When reducing an H2-H2O-CO-CO2 system, the position of the equilibrium line can be determined using the weighted average of (H2 + H2O) and (CO + CO2).

[0026] According to the manufacturing method of the present disclosure, reduction can be performed at a reduction temperature of 900°C or lower in the reduction step. As a result, heating at high temperatures exceeding 1000°C as in Patent Document 1 is not required, thereby reducing energy costs. Furthermore, since many practical gas reduction processes are operated at 900°C or lower, lowering the temperature broadens the range of processes that can be used in the reduction step. The ambient temperature in the reduction step can be, for example, 500°C or higher, further 550°C or higher, or even 580°C or higher, but not higher than 900°C. The ambient temperature in the reduction step refers to the ambient temperature in a furnace used for reduction. The ambient temperature in the reduction step can also be, for example, 850°C or lower, further 800°C or lower, further 750°C or lower, or further 700°C or lower.

[0027] The reduction time can be appropriately determined depending on the amount of material to be processed. After the reduction at the above-mentioned ambient temperature is completed, the cooling to room temperature can be performed in a non-oxidizing atmosphere, and is not limited to a reducing gas atmosphere. For example, an atmosphere of N2 gas or other inert gases such as Ar can be used.

[0028] In the reduction step, it is preferable to carry out reduction so that the Fe3O4 conversion rate calculated from the following formula (2) is 40% or more. In the present disclosure, the degree of reduction in the reduction step is evaluated by this Fe3O4 conversion rate. When the Fe3O4 conversion rate below, which is the rate at which Fe2O3 is converted (reduced) to Fe3O4, is 40% or more, iron contained in the iron ore can be sufficiently recovered, which is preferable. The Fe3O4 conversion rate is more preferably 60% or more, and even more preferably 80% or more, with the upper limit being 100%.

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[0029] [Crushing process] As shown schematically in FIG. 1 , the reduced material 7 is pulverized in a pulverization step indicated by the arrow b from B to C in FIG. 1 to obtain a pulverized material 11 containing iron-containing particles 13 including an iron-containing phase 9. In the method of the present disclosure, the iron-containing phase 9 needs to be pulverized so that its cumulative volume particle diameter D50Fe is 100 μm or more. In this specification, the iron-containing particles need only contain an iron-containing phase. Therefore, examples of the iron-containing particles include those consisting only of the iron-containing phase, as well as those containing both the iron-containing phase and a phase other than the iron-containing phase (such as gangue). In addition to the iron-containing particles 13, the pulverized material 11 also includes gangue particles that do not contain the iron-containing phase 9 but contain gangue 3. The pulverization conditions are described in detail below.

[0030] The inventors have previously conducted research and found that the morphology of the iron-containing phase obtained by pulverization in the pulverization process performed prior to the magnetic separation process significantly affects the magnetic separation efficiency in the magnetic separation process. Previously reported techniques have only measured the overall particle size distribution using laser diffraction methods, without distinguishing between the iron oxide phase and gangue. In contrast, the present embodiment distinguishes between the iron-containing phase and gangue while evaluating the size of the iron-containing phase, thereby controlling the morphology of the iron-containing phase to improve the magnetic separation efficiency in the magnetic separation process. As such, a mineral analysing instrument (MLA) combining elemental analysis using an electron microscope with high-speed collation capabilities can be used as a method for distinguishing between the iron-containing phase and gangue and evaluating its size. The cumulative volumetric particle diameter D50Fe of the iron-containing phase in this disclosure is determined by the method described in the Examples below, and is determined from a cross-sectional image in the observation field. The methods for measuring the MLA and cumulative volumetric particle diameter D50Fe are described in detail in the Examples.

[0031] Experiments have demonstrated that high magnetic separation efficiency can be achieved when the cumulative volumetric particle diameter D50Fe of the iron-containing phase in the pulverized material is 100 μm or greater. When the pulverized material contains a large amount of fine iron-containing phase, the fine iron-containing phase is mixed with other minerals, which increases the static electricity-induced magnetic attraction inhibition effect, resulting in a decrease in the magnetic attraction rate during the magnetic separation process. On the other hand, when the cumulative volumetric particle diameter D50Fe of the iron-containing phase in the pulverized material is 100 μm or greater, magnetic attraction is not inhibited, resulting in a high magnetic attraction rate during the magnetic separation process. The cumulative volumetric particle diameter D50Fe is preferably 1000 μm or less. This is because if the cumulative volumetric particle diameter D50Fe is too large, it becomes difficult to isolate gangue from the iron-containing particles. The shape of the iron-containing phase is not limited to spherical and can take various shapes, such as polygonal, acicular, or with recesses. The shape of the iron-containing particles is also not limited to spherical and can take various shapes, such as polygonal, acicular, or with recesses.

[0032] To obtain a pulverized product having an iron-containing phase with a cumulative volume particle diameter D50Fe of 100 μm or more, it is advisable to investigate in advance the cumulative volume particle diameter D50Fe of the iron-containing phase after pulverization for each type of mill, operating conditions, and reduction conditions to determine appropriate reduction and pulverization conditions. Pulverization can be carried out using pulverization equipment such as a cage mill, ball mill, or disc mill. From the viewpoint of reducing the pulverization energy and achieving milder pulverization conditions, a cage mill is most preferred, followed by a ball mill, and then a disc mill.

[0033] A cage mill can be used regardless of the conditions of the reduction step other than the grinding step. The grinding conditions can be, for example, a rotation speed of preferably 1000 rpm or higher and preferably 4000 rpm or lower. The amount of sample to be ground, the number of grinding cycles, etc., can be adjusted within this rotation speed range. On the other hand, when a ball mill is used, depending on the Fe3O4 conversion rate, it may not be possible to achieve the above D50Fe. When using a ball mill, the Fe3O4 conversion rate of the reduced product to be ground is preferably high, preferably 40% or higher, more preferably 50% or higher, even more preferably 60% or higher, and even more preferably 70% or higher. When using a ball mill, the rotation speed can be, for example, preferably 30 rpm or higher, more preferably 40 rpm or higher, and preferably 100 rpm or lower, more preferably 80 rpm or lower. The amount of sample to be ground, the operating time, the number of grinding cycles, etc., can be adjusted within this rotation speed range.

[0034] When using a disk mill, it is preferable that the Fe3O4 conversion rate of the reduced material to be milled is high, as in the case of a ball mill. Furthermore, the milling conditions, such as the amount of sample to be milled, the operating time (milling time), and the number of times of milling, can be adjusted. In the case of a disk mill, it is preferable to use conditions that are weaker than those used in the cage mill and ball mill described above. For example, the amount of sample to be milled can be increased and the operating time can be reduced compared to the milling conditions used in the cage mill and ball mill.

[0035] The means for making the cumulative volume particle size of the iron-containing phase in the pulverized product 100 μm or more is not limited to the above method, and any other method may be adopted as long as it is possible to obtain a pulverized product in which the cumulative volume particle size of the iron-containing phase is 100 μm or more.

[0036] [Magnetic selection process] Magnetic separation (magnetic separation) is used as a method for separating and recovering the iron-containing particles. Magnetic separation is possible when magnetic substances such as Fe3O4 are contained in the iron-containing particles due to the reduction. Magnetic separation is known to have higher separation efficiency than gravity separation and the like. The magnetic separation method is not particularly limited as long as it can separate the iron-containing particles from the gangue. For example, hand magnetic separation is acceptable, but when large-scale processing is required, large-scale magnetic separators such as drum magnetic separators and rotary magnetic separators may be used.

[0037] In the manufacturing method of the present disclosure, it is sufficient to use iron ore with a gangue ratio of 10% or more, and obtain a magnetized product from which gangue has been sufficiently removed. The degree of gangue removal can be evaluated by the gangue removal ratio calculated from the following formula (3). The gangue removal ratio is preferably 40% or more, more preferably 50% or more, even more preferably 60% or more, even more preferably 70% or more, and particularly preferably 75% or more. The gangue ratio of the magnetized product itself is not particularly limited. For example, if the gangue ratio of the iron ore is quite high, the gangue ratio of the obtained magnetized product may be 10% or more. Even in such cases, the gangue removal ratio is preferably 40% or more. The gangue ratio of the magnetized product depends on the gangue ratio of the raw material (iron ore), but may be, for example, 20% or less, further 15% or less, further 10% or less, or even 8% or less. Gangue removal rate [%] = (1 - gangue rate of magnetic material [%] / gangue rate of iron ore [%]) × 100 (3)

[0038] The manufacturing method of the present disclosure is not limited as long as it includes at least the reduction step, the pulverization step, and the magnetic separation step. Therefore, the iron-containing particles obtained in the magnetic separation step can be used as a raw material for iron making as is, or can be used as a raw material for iron making after undergoing further steps. [Example]

[0039] The present invention will be described in more detail below with reference to examples. The present invention is not limited to the following examples, and can be practiced with appropriate modifications within the scope of the above-mentioned and below-mentioned aims, and all such modifications are included in the technical scope of the present invention.

[0040] In this example, a test was carried out to remove gangue from iron ore and obtain iron-containing particles.

[0041] (1) Preparation process As the iron ore (raw material) from which gangue was to be removed, iron ore from South America having the chemical composition (unit: mass%) shown in Table 1 below was sieved to a size of less than 2 mm (-2 mm) to prepare a pre-reduction sample.

[0042] [Table 1]

[0043] (2) Reduction process The reduction of the pre-reduction sample was carried out using a drum-type rotary heating furnace (size: inner diameter 258 mmφ × length 620 mm). The reducing gas was mixed at room temperature to a reducing gas composition of CO:CO2 = 10:90 (volume %) and then introduced into the furnace. The reducing gas was introduced immediately after the start of heating. The temperature was increased at a rate of approximately 450°C / h to the reduction temperature shown in Table 2 below. After holding at the reduction temperature shown in Table 2 below for 60 minutes (min), the sample was cooled to room temperature in an N2 atmosphere to obtain a post-reduction sample. Other conditions in the reduction process were as follows. The reduction temperature was the atmospheric temperature inside the furnace. The reducing gas and reduction temperature in this example were conditions under which Fe3O4 becomes a stable phase. Rotation speed of drum type rotary heating furnace: 0.5 rpm - Sample amount for reduction: 1.0 kg Reducing gas flow rate: 10NL / min

[0044] [Calculation of Fe3O4 conversion rate] The metallic iron content (M.Fe) (mass%), FeO content (mass%), and total iron content (T.Fe) (mass%) of the reduced sample (reduced product) were determined using the following analytical methods. The obtained values ​​were substituted into the following equation (2) to determine the Fe3O4 conversion rate. The results are also shown in Table 2. M.Fe content analysis method: Bromine methanol decomposition - potassium dichromate titration method FeO content analysis method: Potassium dichromate titration method - Analysis method for T.Fe content: Titanium(III) chloride reduction potassium dichromate titration method

[0045]

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[0046] [Table 2]

[0047] (3) Crushing test The reduced sample was pulverized using one of three types of mills: a cage mill manufactured by Masuno Seisakusho, a ball mill manufactured by Yoshida Seisakusho, and a disc mill manufactured by Earth Technica, to obtain a pulverized sample.

[0048] When a cage mill was used, the rotation speed was 2850 rpm. The amount of sample fed to the cage mill at one time was 100 to 200 g, and the sample after being ground in the cage mill was fed back into the cage mill so that the entire sample passed through the cage mill a total of three times, i.e., the number of treatments was three, and a ground sample was obtained.

[0049] The operating conditions for the ball mill were as follows: a sample load of 100 g, steel balls were used as grinding balls, and the sample was ground for 60 seconds at a rotation speed of 68 rpm to obtain a ground sample.The operating conditions for the disk mill were as follows: a sample load of 100 g, and the sample was ground for 30 seconds to obtain a ground sample.

[0050] (4) Sorting and recovery (magnetic separation) process The pulverized sample was loaded into a dry drum magnetic separator, and magnetic separation was performed as a sorting and recovery method to obtain iron-containing particles. The rotation speed of the dry drum magnetic separator was 80 rpm. The amount of pulverized material fed to the dry drum magnetic separator was 50 g per run, and the run was performed once. The magnetic adsorption rate of the obtained magnetic material was then measured, and the chemical components (T.Fe, SiO2, Al2O3) were analyzed, and the gangue rate was calculated.

[0051] The magnetic susceptibility was calculated from the following formula (4). Regarding the chemical components, the T.Fe content was analyzed by the titanium (III) chloride reduction potassium dichromate titration method described above, and the Si and Al contents of SiO2 and Al2O3 were determined by ICP emission spectrometry, which was then converted into the amounts of the respective oxides SiO2 and Al2O3. The gangue percentage of the magnetized material was calculated from the following formula (1B) using the values ​​of these chemical components. The results are shown in Table 3. In this embodiment, the magnetic susceptibility is preferably 40% or more, more preferably 50% or more, and even more preferably 70% or more.

[0052]

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[0053] Gangue ratio of magnetic material (%) = [(SiO2 + Al2O3) / T.Fe] × 100 (1B) In formula (1B), SiO2, Al2O3, and T.Fe respectively represent the amount of SiO2 (mass %), the amount of Al2O3 (mass %), and the total amount of iron (mass %) in the magnetized material (iron-containing particle).

[0054] (5) Mineral phase analysis (measurement of cumulative volume particle size D50Fe) First, mineral phase analysis was performed to determine the cumulative volume particle size D50Fe. For mineral phase analysis, an SEM-EDX with mineral phase analysis function was used. In this analysis, an FEI MLA 650F (hereafter referred to as MLA) was used. First, we will explain this MLA. The MLA has the function of distinguishing different mineral phases from the color tone of the backscattered electron image, acquiring characteristic X-ray spectra using EDX, and comparing them with pre-registered reference spectra to determine the type of mineral phase. For the measurement, two types of iron oxide were visually selected, and their spectra were obtained as shown in Figures 3 and 4. These spectra were used as reference spectra. Note that since the MLA is an analytical instrument that uses EDX as its measurement principle, it was possible to distinguish different oxidation forms of iron oxides (iron oxides), such as Fe2O3, Fe3O4, and FeO. 1-x However, it is possible to determine that the mineral phases that match the references shown in Figures 3 and 4 are at least one of the three types of iron oxide. Therefore, in this embodiment, the phases that are determined to match the spectra in Figure 3 or 4 are referred to as "iron-containing phases."

[0055] In this specification, the reduction is carried out under conditions in which Fe3O4 becomes a stable phase, the iron-containing particles are obtained as magnetic particles by magnetic separation, and the Fe3O4 conversion rate is 40% or more. Therefore, the "iron-containing phase" and "iron-containing particles" in this specification may include at least Fe3O4 (also referred to as "reduced oxide") obtained by reducing oxides (e.g., Fe2O3) in the iron ore in the reduction step.

[0056] While only the iron oxide reference spectrum used to calculate the particle size distribution is shown above, MLA measurements are performed by registering reference spectra for numerous other mineral phases. Registering reference spectra for other mineral phases can be performed by those skilled in the art in a similar manner, and the measurement results for the morphology of the iron-containing phases described above do not change significantly depending on the number of registered reference spectra for other mineral phases. In this example, reference spectra were registered for the following mineral phases: silicon dioxide, aluminum oxide, magnesium oxide, kaolinite, calcium ferrite, fayalite, silicate slag, calcium phosphate, a solid solution of dicalcium silicate and calcium phosphate, and aluminum phosphate. Note that, due to its fundamental nature, MLA cannot distinguish between minerals with the same chemical composition but different crystalline structures, such as quartz and siliceous silicate (both with the chemical composition SiO2). Therefore, minerals that are difficult to identify are expressed in terms of their chemical composition, such as "silicon dioxide."

[0057] Based on the results of the MLA analysis, a mineral phase map was obtained and analyzed using the MLA's shape analysis function "Create Database → Dataview." However, once a colored mineral phase map is obtained, it can also be obtained by standard image analysis using general-purpose software. The images used for the analysis had a resolution of 0.138 μm per pixel, and the analysis was performed by combining 80 to 150 1000 x 1000 pixel images. The area examined was approximately 2 square millimeters.

[0058] In the shape analysis, the boundaries of the mineral phases were first identified from the contrast differences in the backscattered electron images, and the mineral phase whose central EDX spectrum showed a high degree of agreement with the spectra in Figures 3 and 4 was determined to be an iron-bearing phase, and the particle size distribution of the iron-bearing phase region was then calculated.

[0059] In this embodiment, the cumulative volume particle diameter D50Fe [μm] was used as an index representing the particle size distribution of the iron-containing phase. The cumulative volume particle diameter D50Fe was calculated by calculating the spherical equivalent volume V using the following formula, and then integrating the volumes of the iron-containing phase starting from the smallest particle size. The particle size at which the integrated volume first exceeded 50% of the total volume of the iron-containing phase was defined as the cumulative volume particle diameter D50Fe. In the formula below, A is the area [μm 2 ].

[0060]

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[0061] Fig. 5 shows a mineral phase map of Comparative Example 2, and Fig. 6 shows a mineral phase map of Example 2. In Figs. 5 and 6, gray indicates the iron-containing phase, red indicates other mineral phases, and black indicates an unidentifiable phase. In calculating the equivalent spherical volume V, in Figs. 5 and 6, for particles in which other mineral phases are attached to the surface (surrounding) of the iron-containing phase, the region of the other mineral phases was excluded and the equivalent spherical volume V of only the iron-containing phase was calculated.

[0062] The cumulative volume particle diameter D50Fe of the iron-containing phase obtained using the above MLA is also shown in Table 3. The relationship between this D50Fe value and the magnetic susceptibility is shown in Figure 7. Figure 7 shows that the magnetic susceptibility drops significantly when the cumulative volume particle diameter D50Fe is below 100 μm.

[0063] [Table 3]

[0064] A small cumulative volume particle diameter D50Fe means that the iron-containing phase is small. In Comparative Example 2, the cumulative volume particle diameter D50Fe is small, well below 100 μm, and there is a large amount of fine iron-containing phase. In this case, the pulverized material subjected to magnetic separation is a mixture of fine iron-containing phase and other mineral phases. It is thought that the mixture of fine iron-containing phase and other mineral phases increases the static electricity-induced magnetization inhibition effect, resulting in a decrease in the magnetic attraction rate.

[0065] On the other hand, when the iron-containing phase is not excessively pulverized in the pulverization step and has a size of 100 μm or more, as in Example 2, the static electricity-induced inhibition of magnetic attraction is suppressed, and a high magnetic attraction rate can be achieved. The gangue rate of the raw iron ore was 26.1%, while the gangue rate of the magnetically attracted iron-containing particles in Examples 1 to 3 was 9.3 to 14.3%, which shows a significant decrease in the gangue rate in all Examples, demonstrating that the goal of sufficient gangue removal was achieved.

[0066] Furthermore, in Examples 1 and 2, the conditions for the reduction process were different, and the Fe3O4 conversion rate was different, but the pulverization method was performed under the same conditions. Comparing these examples, it can be seen that the magnetic attraction rate can be sufficiently increased by increasing the Fe3O4 conversion rate. This is thought to be because the ratio of paramagnetic Fe2O3 decreased and the ratio of ferromagnetic Fe3O4 increased, making magnetic separation recovery easier.

[0067] As can be seen from the comparison between the Examples and Comparative Examples, achieving a cumulative volume particle diameter D50Fe of 100 μm or more for the pulverized material (pulverized sample) requires the selection of appropriate mills and operating conditions depending on the state after reduction. First, we consider the case where a cage mill is used. The cage mill was operated at a rotation speed of 2850 rpm and with three treatments. However, the cumulative volume particle diameter D50Fe exceeded 100 μm in both Examples 1 and 2. Therefore, the operating conditions of the cage mill are considered to be within an appropriate range. As mentioned above, it is preferable to perform pulverization under mild conditions that do not excessively damage the reduced sample. Even when a cage mill is used, for example, if the rotation speed is set high (e.g., 3000 rpm or higher) or the number of treatments is increased to four or more times, the operating conditions for pulverization may fall outside the appropriate range. As a result, it is considered difficult to easily achieve a cumulative volume particle diameter D50Fe of 100 μm or more for the pulverized material (pulverized sample).

[0068] Next, we will consider the case where a ball mill is used as the mill. The operating conditions for the ball mill are a sample charge of 100 g and an operating time of 60 s. Under these operating conditions, the cumulative volumetric particle diameter D50Fe exceeds 100 μm in Example 3, but the cumulative volumetric particle diameter D50Fe is below 100 μm in Comparative Example 1. Therefore, the appropriate operating conditions for the ball mill are considered to be on the weaker side of pulverization, and improvements can be expected, for example, by increasing the sample charge to 200 g or more and setting the operating time to 30 s or less.

[0069] Finally, we consider the case where a disc mill was used. The operating conditions for the disc mill were a sample charge of 100 g and a grinding time of 30 s, but the cumulative volumetric particle size D50Fe was significantly below 100 μm in both Comparative Examples 2 and 3. This suggests that the appropriate operating conditions for the disc mill are on the weak side of grinding, and improvements can be expected, for example, by increasing the sample charge to 300 g or shortening the grinding time to 10 s or less.

[0070] The present disclosure focuses on the size of the iron-containing phase, which affects magnetic separation efficiency, and performs pulverization while focusing on the reduction conditions and pulverization conditions, and on the iron-containing phase in the pulverization conditions. This differs significantly from Patent Document 3, which evaluated the particle size of the entire pulverized material. [Explanation of symbols]

[0071] 1. Iron ore 3 gangue 5 Unreduced iron oxide 7. Reduced Products 9 Iron-containing phases 11 Crushed material 13 Iron-containing particles

Claims

1. Iron ore having a gangue rate of 10% or more calculated from the following formula (1A) is called Fe ３ O ４ a reduction step of reducing the iron-containing phase under conditions of temperature and gas composition such that the iron-containing phase is stable; a pulverization step of pulverizing the reduced product to obtain a pulverized product containing iron-containing particles including an iron-containing phase, the iron-containing phase having a cumulative volume particle diameter D50Fe of 100 μm or more; and a magnetic separation step of magnetically separating the pulverized material and recovering the iron-containing particles as magnetically separated material. Iron ore gangue rate (%) = (SiO ２ +Al ２ O ３ ) / T. Fe×100 (1A) In formula (1A), SiO ２ , Al ２ O ３ , T.Fe are the SiO in iron ore, respectively. ２ Amount (mass%), Al ２ O ３ The amount (mass%) of iron and the total amount (mass%) of iron are shown.

2. In the reduction step, Fe calculated from the following formula (2) ３ O ４ 2. The method for producing raw materials for iron making according to claim 1, wherein the reduction is carried out so that the conversion rate is 40% or more. [Equation 1] In formula (2), "FeO" represents the amount of FeO (mass %) in the reduced product, "T.Fe" represents the total amount of iron (mass %) in the reduced product, and "M.Fe" represents the amount of metallic iron (mass %) in the reduced product.

3. The method for producing raw materials for iron making according to claim 1 or 2, wherein the gas used in the reduction step includes a top gas of a blast furnace.

4. 3. The method for producing raw materials for iron making according to claim 1, wherein the reduction step is carried out at a reduction temperature of 900°C or less.

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