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 an iron-containing substance and a gangue phase having a volume-based cumulative particle diameter 1A of 82 μm or more, and a magnetic separation step of magnetically separating the pulverized product to recover the iron-containing substance as a magnetically attractable substance, wherein the iron-containing phase and the iron-containing substance contain at least metallic, and the gangue ratio is 10% or more and 60% or less, the gangue ratio being determined by the following formula (D50G): 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 5

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 pre-treatment.

[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 COIt 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] The method of Patent Document 2 requires a high reduction temperature of 950°C, and does not include analysis that takes into account the reduction rate, nor does it consider the morphology of the crushed ore. Patent Document 3 also relates to a technology for removing gangue from iron ore without melting it, but it only provides guidelines for crushing reduced ore with a metallization rate of 59.3% in the reduction process, or a reduction rate of 68.8% or more. Further investigation is considered necessary to obtain raw materials for ironmaking with a sufficiently low gangue rate.

[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 of reducing iron ore having a gangue ratio of 10% or more calculated from the following formula (1A) at a reduction rate of 60% or less to obtain a reduced product containing metallic iron and a gangue phase; a pulverization step of pulverizing the reduced product to obtain a pulverized product having a cumulative volume particle size D50G of the gangue phase of 82 μm or more; and a magnetic separation step of magnetically separating the pulverized material and recovering iron-containing materials including metallic iron as magnetically attracted materials. Iron ore gangue ratio (%) = [(SiO2 + Al2O3) / T.Fe] x 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 carried out at a reduction temperature of 900° C. or less.

[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 gangue removal rate of the magnetized material calculated from the following formula (2) is 40% or more: Gangue removal rate (%) = (1 - gangue rate of magnetic material (%) / gangue rate of iron ore (%)) × 100 (2) In formula (2), the gangue ratio of the magnetized material is calculated from formula (1B) below, and the gangue ratio of the iron ore is calculated from formula (1A) above. 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. [Effects of the Invention]

[0013] 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]

[0014] [Figure 1] FIG. 1 is an image diagram that schematically shows the steps of this embodiment. [Figure 2] Figure 2 is a reference spectrum of the SiO2 phase. [Figure 3] Figure 3 is a reference spectrum of the Al2O3 phase. [Figure 4] Figure 4 shows the reference spectrum of the Si-Al-O phase. [Figure 5] Figure 5 is a graph showing the relationship between the cumulative volumetric particle size D50G of the gangue phase and the gangue removal rate. [Figure 6] FIG. 6 is a mineral phase analysis map of Comparative Example 1. [Figure 7] FIG. 7 is a mineral phase analysis map of Example 7. DETAILED DESCRIPTION OF THE INVENTION

[0015] The method for producing raw materials for iron making according to this embodiment includes the steps of: a reduction step of reducing iron ore having a gangue ratio of 10% or more calculated from the following formula (1A) at a reduction rate of 60% or less to obtain a reduced product containing metallic iron and a gangue phase; a pulverization step of pulverizing the reduced product to obtain a pulverized product having a cumulative volume particle size D50G of the gangue phase of 82 μm or more; and a magnetic separation step of magnetically separating the pulverized material and recovering iron-containing materials containing metallic iron as magnetically attracted materials. According to the production method of this embodiment, the reduction rate in the reduction step is set to 60% or less, and gangue contained in low-grade iron ore can be sufficiently removed under production conditions that reduce energy consumption, thereby producing an ironmaking raw material (iron-containing material) with a sufficiently reduced gangue rate. 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.

[0016] The technology of the present disclosure is a technology that focuses particularly on the state of the gangue phase after crushing. According to a preferred embodiment of the present disclosure, the above-mentioned raw material for iron making can be produced without heating to a high temperature during the production process.

[0017] 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 explanation 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 the gangue phase and the iron-containing phase are not completely separated by pulverization, and a portion of the gangue phase remains, for example, on the surface of the iron-containing phase. These aspects are naturally acceptable, and the manufacturing method according to this embodiment may also include these aspects.

[0018] [Reduction process] As shown schematically in Figure 1, in the reduction step, iron ore 1, which is a raw material and contains gangue phase 3 and unreduced iron oxide 5, is reduced under predetermined conditions to obtain a reduced product 7, which contains an iron-containing phase 9 containing metallic iron and the gangue phase 3, as shown in B in Figure 1. By undergoing the reduction step represented by arrow a from A to B in Figure 1, a reduced product 7 containing the iron-containing phase 9 that contains at least metallic iron and may further contain FeOx and Fe3O4 is obtained.

[0019] The raw material iron ore 1 containing a gangue phase 3 and unreduced iron oxide 5 has a gangue ratio of 10% or more, calculated from 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.

[0020] The inventors have conducted research to obtain a pulverized product in which the iron-containing phase and gangue phase are easily separable while maintaining a low reduction rate. In this embodiment, a reduction rate of 60% or less is sufficient in the reduction process. For the purpose of removing gangue from iron ore, maintaining a low reduction rate leads to energy savings, such as lowering the temperature and reducing the consumption of reducing gas. Iron ore and the iron-making raw materials obtained from the iron ore contain four iron-containing substances: iron oxides (also called "iron oxides") Fe2O3, Fe3O4, and FeO, and metallic iron (Fe). Of these, Fe3O4 and metallic iron (Fe) exhibit ferromagnetic properties. In the method for producing raw materials for iron making disclosed herein, the iron ore (raw material) is reduced to a level where metallic iron is partially contained, rather than until the iron oxide contained in the iron ore is completely reduced to metallic iron. Therefore, energy costs and production time can be reduced compared to when the iron oxide contained in the iron ore is completely reduced to metallic iron, and magnetic separation (magnetic separation) can be used, allowing for efficient separation and recovery. The reduction rate can be, for example, 55% or less, or even 50% or less.

[0021] The lower limit of the reduction rate is preferably 20% or more, more preferably 25% or more, from the viewpoint of increasing the proportion of ferromagnetic metallic iron (Fe) and improving the separation efficiency in the magnetic separation process. If the reduction rate is too low, the proportion of non-magnetic FeO increases, and the proportion of magnetically attracted particles decreases. When Fe2O3, the iron oxide with the highest oxidation degree, is used as the standard, the reduction rate when all of the Fe2O3 is reduced to FeO is 33.3%. However, in reality, reduction is not uniform, and metallic iron can be generated even when the reduction rate is below 33.3%. Therefore, from the viewpoint of sufficiently recovering magnetically attracted materials in the magnetic separation process, the preferred lower limit of the reduction rate is set to 20%.

[0022] The reduction rate is calculated from the following formula (3): The FeO amount, total iron amount (T.Fe), and metallic iron amount (M.Fe) in the following formula (3) are measured by the method described in the examples below.

[0023]

number

[0024] The reduction conditions in the reduction step are the type of gas used in the reduction step and the ambient temperature in the reduction step, which are conditions that produce metallic iron and achieve the above reduction rate. The gas constituting the atmosphere in the reduction step needs only to contain at least one of the CO gas and H gas described above, and the remaining gas components are not particularly limited. Since the purpose is reduction, it is preferable that the remaining gas components are gases that do not have an oxidizing effect. Examples of the remaining gas components include the above-mentioned CO, N, and H. For example, CO-CO, H-H, or H-H-O-CO-CO gases can be used for reduction.

[0025] According to the manufacturing method of the present disclosure, the reduction step can be performed at a reduction temperature of 900°C or lower. As a result, heating at high temperatures exceeding 1000°C, as in Patent Document 1, is not required, thereby reducing energy costs. Furthermore, since most practical gas reduction processes operate at temperatures below 900°C, lowering the temperature allows for the adoption of vertical furnaces, such as shaft-type reduction furnaces, in which the material to be reduced is stacked vertically in a cylindrical container and gas flows in a direction opposite the downward flow of the material, thereby broadening the options for processes that can be used in the reduction step. The ambient temperature in the reduction step can be, for example, 500°C or higher, or even 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 the furnace used for reduction. The ambient temperature in the reduction step can also be, for example, 850°C or lower, or even 800°C or lower, or even 750°C or lower, or even 700°C or lower.

[0026] 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.

[0027] [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 an iron-containing material 13 including an iron-containing phase 9 and a gangue phase 3. The iron-containing phase 9 refers to a phase of metallic iron and iron oxide. The iron-containing material 13 may further contain one or more of a gangue phase and other mineral phases (mineral phases other than metallic iron, iron oxide, and the gangue phase). In addition to the iron-containing material 13, the pulverized material 11 also contains gangue particles. The gangue particles are particles that contain the gangue phase 3 but do not contain the iron-containing phase. In other words, the gangue particles do not contain metallic iron or iron oxide. The gangue particles may be composed of the gangue phase 3 or may be composed of the gangue phase 3 and other mineral phases. In this embodiment, as described above, the reduction rate in the reduction step is suppressed, and the iron-containing material 13 containing at least metallic iron (Fe) obtained by reduction at a low reduction rate is sufficiently recovered in the magnetic separation step. To achieve this, it is necessary to obtain a pulverized product 11 in which the iron-containing phase 9 and the gangue phase 3 are sufficiently separated in the pulverization step. From this perspective, in the method of the present disclosure, it is necessary to pulverize the pulverized product 11 so that the cumulative volume particle size D50G ("G" stands for gangue) of the gangue phase 3 is 82 μm or more. The pulverization conditions are described in detail below.

[0028] The inventors have previously conducted research and found that the morphology of the gangue 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 the gangue phase. In contrast, the present embodiment distinguishes between the iron-containing phase and the gangue phase while evaluating the size of the gangue phase obtained by pulverization. This allows for the control of the morphology of the gangue phase, thereby improving the magnetic separation efficiency in the magnetic separation process. As such, a mineral analysing apparatus (MLA) combining elemental analysis using an electron microscope with a high-speed collation function can be used as a method for distinguishing between the iron-containing phase and the gangue phase and evaluating the size of the gangue phase obtained by pulverization. The cumulative volumetric particle diameter D50G of the gangue phase in this disclosure is determined by the method described in the Examples below, and is obtained from a cross-sectional image in the observation field. The MLA and the method for measuring the cumulative volumetric particle diameter D50G of the gangue phase are described in detail in the Examples.

[0029] Experiments have demonstrated that a cumulative volumetric particle diameter D50G of the gangue phase in the pulverized material of 82 μm or greater can achieve high magnetic separation efficiency and, as a result, a high gangue removal rate. When the pulverized material contains a large amount of fine gangue phase, the fine gangue phase is mixed with other mineral phases, resulting in a greater static electricity-induced magnetic attraction inhibition effect, which is thought to reduce the magnetic attraction rate during the magnetic separation process. On the other hand, when the gangue phase in the pulverized material is 82 μm or greater, magnetic attraction is not inhibited, resulting in a high magnetic attraction rate during the magnetic separation process. While it is reasonable to consider that there is no upper limit to the cumulative volumetric particle diameter D50G of the gangue phase based on the removal mechanism described above, the reduced material can be pulverized, and therefore the size can be, for example, 3000 μm or less, 2000 μm or less, 1000 μm or less, or 500 μm or less. The shape of the gangue phase is not limited to spherical but can take various forms, such as polygonal, acicular, or concave.

[0030] To obtain a pulverized product with a cumulative volumetric particle diameter D50G of the gangue phase of 82 μm or more, it is advisable to investigate the cumulative volumetric particle diameter D50G of the gangue phase after pulverization in advance for each type of mill, operating conditions, and reduction conditions used, and to determine appropriate reduction and pulverization conditions. Pulverization can be performed using pulverization equipment such as a cage mill, ball mill, or disc mill. It is preferable not to increase the pulverization energy too much during the pulverization process. 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. Furthermore, the pulverization conditions for the cage mill can be, for example, preferably a rotation speed of 1000 rpm or more and preferably 4000 rpm or less. The amount of sample to be pulverized, the operating time, the number of pulverization cycles, etc. can be adjusted within this rotation speed range. The pulverization conditions for the ball mill can be, for example, preferably a rotation speed of 30 rpm or more, more preferably 40 rpm or more, and preferably 100 rpm or less, more preferably 80 rpm or less. The amount of sample to be pulverized, the operating time, the number of pulverization cycles, etc. can be adjusted within this rotation speed range. The grinding conditions for the disc mill can be adjusted by adjusting the amount of sample to be ground, operation time (grinding time), number of grinding operations, etc. In the case of a disc mill, it is preferable to set conditions that are weaker than those for the cage mill and ball mill described above, and for example, this can be achieved by increasing the amount of sample to be ground and reducing the operation time compared to the grinding conditions for the cage mill and ball mill.

[0031] The means for making the cumulative volume particle diameter D50G of the gangue phase in the pulverized material 82 μm or more is not limited to the above-described method, and any other method may be adopted that can obtain a pulverized material having a cumulative volume particle diameter D50G of the gangue phase of 82 μm or more.

[0032] [Magnetic selection process] Magnetic separation (magnetic separation) is used as a method for separating and recovering the iron-containing material. The iron-containing material obtained by the reduction, including metallic iron, becomes magnetic, which enables magnetic separation of the iron-containing material. 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 allows separation of the iron-containing material from the gangue phase. For example, hand magnetic separation is also acceptable, but when large-scale processing is required, large-scale magnetic separators such as drum magnetic separators and rotary magnetic separators may be used.

[0033] In the manufacturing method of the present disclosure, it is sufficient to use iron ore with a gangue ratio of 10% or more, and to obtain a magnetized product from which gangue has been sufficiently removed. The degree of gangue removal is evaluated by the gangue removal ratio calculated from the following formula (2). 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 (2) In formula (2), the gangue ratio of the magnetized material is calculated from formula (1B) below, and the gangue ratio of the iron ore is calculated from formula (1A) above. 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.

[0034] 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 material 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]

[0035] 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.

[0036] In this example, a test was carried out to remove gangue from iron ore and obtain an iron-containing material.

[0037] (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.

[0038] [Table 1]

[0039] (2) Reduction process The pre-reduction sample was reduced using a drum-type rotary heating furnace (size: inner diameter 258 mmφ x length 620 mm). 100% H2 gas was introduced into the furnace as the reducing gas. The reducing gas was introduced immediately after the temperature increase started. 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 is the atmospheric temperature inside the furnace. Rotation speed of drum type rotary heating furnace: 0.5 rpm - Sample amount for reduction: 1.0 kg Reducing gas flow rate: 10NL / min

[0040] [Calculation of the return 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 (3) to determine the reduction 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

[0041]

number

[0042] [Table 2]

[0043] (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.

[0044] 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.

[0045] When using a ball mill, the operating conditions were a 100 g sample charge, steel balls were used as grinding balls, and grinding was performed for 60 seconds at a rotation speed of 68 rpm.When using a disk mill, the operating conditions were a 100 g sample charge and grinding for 30 seconds.

[0046] (4) Sorting and recovery (magnetic separation) process The crushed sample was loaded into a dry drum magnetic separator, and magnetic separation was performed as a sorting and recovery method to obtain iron-containing material as a magnetically attached material. The rotation speed of the dry drum magnetic separator was 80 rpm. The amount of crushed material fed to the dry drum magnetic separator was 50 g per run, and the run was performed once. The magnetic attachment rate was then measured, and the chemical composition of the magnetically attached material (Fe, SiO2, Al2O3) was analyzed, and the gangue rate was calculated.

[0047] The magnetic attraction rate 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 SiO2 and Al2O3 contents were calculated by measuring the Si and Al contents using ICP emission spectrometry, which were then converted into the respective oxides SiO2 and Al2O3. Using these chemical component values, the gangue rate of the magnetized material was calculated from the following formula (1B). Furthermore, the gangue rate of the magnetized material and the gangue rate of the iron ore raw material were used to calculate the gangue removal rate from the specified formula (2). The results are shown in Table 3. In this embodiment, the magnetic attraction rate is preferably 40% or more, more preferably 50% or more, and even more preferably 70% or more.

[0048]

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[0049] 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 material).

[0050] (6) Mineral phase analysis (D50G measurement) To determine the cumulative volumetric particle diameter D50G, mineral phase analysis was first performed. A SEM-EDX with mineral phase analysis function was used. For this analysis, an FEI MLA 650F (hereafter referred to as MLA) was used. First, we will explain the MLA. The MLA distinguishes different mineral phases based on the color tone of the backscattered electron image, acquires characteristic X-ray spectra using EDX, and compares them with pre-registered reference spectra to identify the mineral phase. For the measurement, three minerals thought to be representative gangue phases were visually selected and used as reference spectra, as shown in Figures 2–4. Figure 2 shows peaks for Si and O, suggesting SiO2, while Figure 3 shows Al2O3. Figure 4 shows large peaks for Si, Al, and O, suggesting clay minerals such as kaolinite. Traces of Ca, Fe, and Mg were also detected. These are likely picking up on the surrounding EDX spectra due to the generally very fine size of clay minerals, but this does not pose a problem for mineral phase identification. In this specification, the phase determined to match the spectra in Figures 2 to 4 is referred to as a "gangue phase."

[0051] Although only the reference spectrum of the gangue used to calculate the particle size distribution is shown above, in MLA measurements, reference spectra of many other mineral phases are registered and analyzed. Those skilled in the art can register the reference spectra of other mineral phases using roughly similar procedures, and the measurement results of the gangue morphology do not change significantly depending on the number of registered reference spectra of other mineral phases. In this example, the mineral phases for which reference spectra are registered are listed as follows: iron oxide, metallic iron, kaolinite, calcium ferrite, fayrite, silicate slag, calcium phosphate, solid solution of dicalcium silicate and calcium phosphate, and aluminum phosphate.

[0052] 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.

[0053] In the shape analysis, the boundaries of the mineral phases were first identified from the contrast difference in the backscattered electron image, and the phase whose EDX spectrum at one central point was determined to match the spectra in Figures 2 to 4 as described above was determined to be the gangue phase, and the particle size distribution in the gangue phase region was calculated.

[0054] In this embodiment, the cumulative volumetric particle size D50G [μm] was used as an index representing the particle size distribution of the gangue phase. The cumulative volumetric particle size D50G was calculated by calculating the spherical equivalent volume V using the following formula, and then integrating the volumes of the gangue phases in order from the smallest particle size. The particle size at which the integrated volume first exceeded 50% of the total volume of the gangue phase was defined as D50G. In the formula below, A is the area [μm] of the gangue phase in question in the cross-sectional image obtained by mineral phase mapping. 2 ].

[0055]

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[0056] Fig. 6 shows a mineral phase map of Comparative Example 1, and Fig. 7 shows a mineral phase map of Example 7. In Figs. 6 and 7, gray indicates the iron-containing phase, red indicates the gangue phase, and black indicates the unidentifiable phase. In calculating the equivalent spherical volume V, in Figs. 6 and 7, for particles having the iron-containing phase and other mineral phases attached to the surface (surrounding) of the gangue phase, the region of the iron-containing phase and other mineral phases was excluded, and the equivalent spherical volume V of only the gangue phase was calculated.

[0057] The cumulative volumetric particle size D50G values ​​of the gangue phase obtained using the above MLA are also shown in Table 3. The relationship between this D50G value and the gangue removal rate is shown in Figure 5. Figure 5 shows that the gangue removal rate decreases when D50G falls below 82 μm.

[0058] [Table 3]

[0059] A small cumulative volume particle diameter D50G means that the gangue phase is small. In Comparative Example 1, the cumulative volume particle diameter D50G is small, below 82 μm, and there is a large amount of fine gangue phase. In this case, the pulverized material subjected to magnetic separation is a mixture of iron-containing materials and fine gangue phase. When the iron-containing materials and fine gangue phase are mixed together, static electricity causes the gangue phase to adhere to the magnetic iron-containing materials, increasing the proportion of the mixed-in material, which is thought to result in a decrease in the gangue removal rate.

[0060] On the other hand, when the gangue is not excessively crushed in the crushing process and the gangue phase has a size of 82 μm or more, as in Example 7, the gangue phase is not entangled in the magnetized matter due to static electricity, and a high gangue removal rate can be achieved.

[0061] As can be seen from the comparison between the Examples and Comparative Examples, in order to achieve a cumulative volume particle size D50G of the pulverized material (pulverized sample) exceeding 82 μm, it is believed that appropriate mill selection and operating conditions as pulverization conditions are required depending on the state after reduction. First, we consider the case where a cage mill is used. The cage mill operating conditions were a rotation speed of 2850 rpm and three treatments, but in all of Examples 5 to 7, the D50G exceeded 82 μm. Therefore, the operating conditions of the cage mill in these Examples are believed to be within an appropriate range. As mentioned above, from the perspective that pulverization is preferably performed under mild conditions that do not excessively destroy the reduced sample, even when a cage mill is used as the mill, if the rotation speed is set high, for example, to 3000 rpm or more, or the number of treatments is increased to four or more, the pulverization operating conditions may fall outside the appropriate range, and as a result, it is believed that it will be difficult to easily achieve a D50G of 82 μm or more for the pulverized material (pulverized sample).

[0062] Next, we will consider the operating conditions when a ball mill is used as the mill. The operating conditions for the ball mill were a sample charge of 100 g and an operating time of 60 s. Under these operating conditions, the cumulative volumetric particle diameter D50G exceeded 82 μm in all of Examples 2 to 4. Therefore, the operating conditions for the ball mill in these Examples are considered to be within an appropriate range. From the viewpoint that it is preferable to perform pulverization under mild conditions so as not to excessively destroy the reduced sample, even when a ball mill is used as the mill, it is considered that, for example, if the sample charge amount is reduced to 90 g or less or the operating time is increased to 70 seconds or more, it will be difficult to easily achieve a cumulative volumetric particle diameter D50G of 82 μm or more for the pulverized product (pulverized sample).

[0063] Finally, we consider the operating conditions when using a disk mill as the mill. The operating conditions for the disk mill in this example were a sample charge of 100 g and a grinding time of 30 s in both Comparative Examples 1 and 2 and Example 1. In Example 1, the cumulative volumetric particle diameter D50G exceeded 82 μm, while in Comparative Examples 1 and 2, the cumulative volumetric particle diameter D50G was below 82 μm. From these results, it is believed that the appropriate operating conditions for the disk mill are milder conditions that require less grinding energy. Therefore, it is believed that by increasing the operating conditions of the disk mill to milder conditions than those in this example, for example, by increasing the sample charge to 200 g or reducing the grinding time to 20 s or less, it is easier to achieve a cumulative volumetric particle diameter D50G of 82 μm or more for the ground product (ground sample). [Explanation of symbols]

[0064] 1. Iron ore 3 Gangue facies 5 Unreduced iron oxide 7. Reduced Products 9 Iron-containing phases 11 Crushed material 13 Iron-containing substances

Claims

1. a reduction step of reducing iron ore having a gangue rate of 10% or more calculated from the following formula (1A) at a reduction rate of 60% or less to obtain a reduced product containing metallic iron and a gangue phase; a pulverization step of pulverizing the reduced product to obtain a pulverized product having a cumulative volume particle diameter D50G of the gangue phase of 82 μm or more; and a magnetic separation step of magnetically separating the pulverized material and recovering iron-containing materials including metallic iron as magnetic materials. 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. 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.

3. 3. The method for producing raw materials for iron making according to claim 1, wherein the gangue removal rate of the magnetized material calculated from the following formula (2) is 40% or more: Gangue removal rate (%) = (1 - gangue rate (%) of magnetic material / gangue rate (%) of iron ore) × 100 (2) In formula (2), the gangue ratio of the magnetized material is calculated from formula (1B) below, and the gangue ratio of the iron ore is calculated from formula (1A) above. Gangue rate of magnetic material (%) = [(SiO ２ +Al ２ O ３ ) / T. Fe]×100 (1B) In formula (1B), SiO ２ , Al ２ O ３ , T.Fe respectively, SiO in the magnetized material ２ Amount (mass%), Al ２ O ３ The amount (mass%) of iron and the total amount (mass%) of iron are shown.

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