Method for producing raw material for iron-making

Abstract

This method for producing a raw material for iron-making includes a reduction step for reducing an iron ore having a gangue ratio derived from formula (1A) of 10% or greater at a reduction rate of 60% or less to obtain a reduced product that includes an iron-containing phase, a pulverization step for pulverizing the reduced product to obtain a pulverized product that contains an iron-containing substance and a gangue phase having a cumulative volume particle diameter D50G of 82 μm or greater, and a magnetic separation step for magnetically separating the pulverized product and recovering the iron-containing substance as a magnetically attracted material. The iron-containing phase and the iron-containing substance contain at least metallic iron.　Formula 1A: Gangue ratio (%) of iron ore = [(SiO2 + Al2O3) / T.Fe] × 100. In formula (1A), SiO2, Al2O3, and T.Fe respectively represent the amount (mass%) of SiO2, the amount (mass%) of Al2O3, and the total amount (mass%) of iron in the iron ore.

Description

Method of manufacturing raw materials for ironmaking

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

[0002] In recent years, with the depletion of high-quality iron sources, it has become difficult to obtain iron ore with few impurities such as gangue as a raw material for steel products, and the impurity content of iron ore is expected to increase in the future. In the existing blast furnace-converter process, gangue components (SiO ２ , Al ２ O ３ When iron ore is reduced and melted in a blast furnace, these substances are separated as a low-density liquid phase (slag) on ​​top of the molten iron and discharged. However, an increase in the amount of slag leads to a deterioration in the gas permeability inside the blast furnace, and measures such as increasing the amount of coke charged are required to ensure gas permeability. However, increasing the amount of coke charged increases production costs and CO2 emissions. ２ Therefore, when low-grade iron ore containing a large amount of gangue is subjected to 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, as a pretreatment of iron ore for steelmaking, Patent Document 2 discloses a method for improving the iron quality of the iron ore by subjecting the iron ore containing gangue to reduction treatment with a gas, crushing the resulting mixture, and then magnetic separation to remove the gangue. In this method, the reduction time [min] of the iron ore is defined as t, and the H ２ Partial pressure [atm] is P Ｈ２ and the CO partial pressure [atm] of the reducing gas is P ＣＯ In this case, 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).

[0005] Furthermore, Patent Document 3 discloses that the total iron content of the raw ore is ２ Amount, Al ２ O ３ Using the amount (mass%), (SiO ２ +Al ２ O ３ The present invention discloses a method for producing a high-quality iron source, in which a low-quality iron ore having a gangue ratio of 15% or more, represented by (a) / Total.Fe×100, is reduced as a raw ore, 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. ５０ It is shown that the pulverization is carried out so that the particle size is less than 200 μm.

[0006] JP 2013-249496 A JP 2018-012850 A JP 2018-095893 A

[0007] The method of Patent Document 1 requires a high temperature of 1200°C or higher to melt a portion of the iron ore. However, from the viewpoint of reducing energy consumption, it is desirable to treat the iron ore at a lower temperature. 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 any 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 Patent Document 3 only provides guidelines for crushing reduced ore with a metallization rate of 59.3% in the reduction step, or a reduction rate of 68.8% or more. Further investigation is considered necessary to obtain a raw material for ironmaking with a sufficiently reduced 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.

[0010] A first aspect of the present invention is a method for producing raw materials for iron making, comprising: a reduction step of reducing iron ore having a gangue ratio of 10% or more, calculated from the following formula (1A), at a reduction ratio of 60% or less to obtain a reduced product containing metallic iron and a gangue phase; a crushing step of crushing the reduced product to obtain a crushed product having a gangue phase cumulative volume particle diameter D50G of 82 μm or more; and a magnetic separation step of magnetically separating the crushed product to recover iron-containing materials including metallic iron as magnetically separated materials. Gangue ratio (%) of iron ore = [(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.

[0011] A second aspect of the present invention is the method for producing raw materials for iron making according to the first aspect, wherein the reduction step is carried out at a reduction temperature of 900°C or less.

[0012] A third aspect of the present invention is the method for producing raw materials for iron making according to the first or second aspect, 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 magnetized material / gangue rate (%) of iron ore) × 100 (2) In formula (2), the gangue rate of the magnetized material is calculated from the following formula (1B), and the gangue rate of the iron ore is calculated from the above formula (1A). Gangue rate (%) of magnetized 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.

[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.

[0014] FIG. 1 is an image diagram showing the process of this embodiment. ２ FIG. 3 shows the reference spectrum of the Al phase. ２ O ３ FIG. 4 is a reference spectrum of the Si—Al—O phase. FIG. 5 is a graph showing the relationship between the cumulative volume particle size D50G of the gangue phase and the gangue removal rate. FIG. 6 is a mineral phase analysis map of Comparative Example 1. FIG. 7 is a mineral phase analysis map of Example 7.

[0015] The method for producing raw materials for ironmaking according to this embodiment includes the steps 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; pulverizing the reduced product to obtain a pulverized product having a gangue phase cumulative volume particle diameter D50G of 82 μm or more; and magnetic separation step of magnetically separating the pulverized product to recover an iron-containing material containing metallic iron as a magnetic material. 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 with reduced energy consumption, thereby producing raw materials for ironmaking (iron-containing material) with a sufficiently reduced gangue ratio. Gangue ratio of iron ore (%) = (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.

[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 using high temperatures in 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. In the following description of each step, the explanation may be based on FIG. 1, but 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 Step] As shown in Fig. 1, in the reduction step, iron ore 1 containing gangue phase 3 and unreduced iron oxide 5 as a raw material is reduced under predetermined conditions to obtain a reduced product 7 containing an iron-containing phase 9 containing metallic iron and gangue phase 3, as shown in Fig. 1B. By going through the reduction step indicated by arrow a from A to B in Fig. 1, a reduced product 7 containing at least metallic iron and further containing FeOx, Fe ３ O ４ A reduction product 7 is obtained which contains an iron-containing phase 9 which may contain:

[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, and 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 raw material for steelmaking 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. Gangue ratio (%) of iron ore = (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.

[0020] The present inventors have conducted research to obtain a pulverized product in which the iron-containing phase and gangue phase are highly separable while maintaining a low reduction rate. In this embodiment, the reduction step only requires a reduction rate of 60% or less. If the reduction rate can be maintained low for the purpose of removing gangue from iron ore, this leads to energy savings such as a decrease in temperature and a reduction in reducing gas consumption. Iron ore and iron-making raw materials obtained from the iron ore contain iron oxide (also called "iron oxide"), Fe ２ O ３ , Fe ３ O ４ There are four types: FeO and metallic iron Fe, of which Fe ３ O ４ and metallic iron (Fe) exhibit ferromagnetism. In the method for producing raw materials for iron making disclosed herein, reduction of iron ore (raw material) is not carried out until the iron oxide contained in the iron ore is completely reduced to metallic iron, but is carried out to the extent that metallic iron is partially contained. Therefore, compared to the case where the iron oxide contained in the iron ore is completely reduced to metallic iron, energy costs and production time can be reduced, 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 metallic iron (Fe) that exhibits ferromagnetism and improving the separation efficiency in the magnetic separation step. If the reduction rate is too low, the proportion of FeO that does not exhibit magnetism increases, and the proportion of particles that are magnetically attracted decreases. Note that Fe, which is the iron oxide with the highest oxidation degree, ２ O ３ When based on Fe ２ O ３ When the entire amount of iron is reduced to FeO, the reduction rate is 33.3%, but in reality, reduction does not occur uniformly, and metallic iron can be produced even when the reduction rate is below 33.3%. Therefore, from the viewpoint of being able to sufficiently recover the magnetically attracted matter in the magnetic separation step, the preferable 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] In formula (3), "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.

[0024] The reduction conditions in the reduction step are the type of gas used in the reduction step and the atmospheric temperature in the reduction step, which are conditions that allow metallic iron to be produced and achieve the above reduction rate. ２ The remaining gas components are not particularly limited as long as they contain at least one of the above gases. Since the purpose is reduction, it is preferable that the remaining gas components are gases that do not have an oxidizing effect. The remaining gas components include the above-mentioned CO ２ , N ２ , H ２ For example, CO-CO ２ System, H ２ -H ２ O series or H ２ -H ２ O-CO-CO ２ The gas in the system 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 treated. After the reduction at the above atmospheric 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, N ２ The atmosphere may be an atmosphere of gas or other inert gas such as Ar.

[0027] [Crushing Step] As schematically shown in FIG. 1 , the reduced material 7 is crushed in a crushing step indicated by an arrow b from B to C in FIG. 1 to obtain a crushed 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 crushed 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 formed 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" is the initial letter of gangue) of the gangue phase 3 is 82 μm or more. The pulverization conditions are described in detail below.

[0028] The inventors of the present invention have previously 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 or the like without distinguishing between the iron oxide phase and the gangue phase. In contrast, in the present embodiment, by distinguishing between the iron-containing phase and the gangue phase and evaluating the size of the gangue phase obtained by pulverization, it is possible to control the morphology of the gangue phase, thereby improving the magnetic separation efficiency in the magnetic separation process. As described above, 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 the present disclosure is determined by the method described in the Examples below, and is determined 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 when the cumulative volume particle diameter D50G of the gangue phase in the pulverized material is 82 μm or more, high magnetic separation efficiency can be achieved, resulting in 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, which increases the static electricity-induced magnetic attraction inhibition effect, resulting in a lower magnetic attraction rate in the magnetic separation process. On the other hand, when the gangue phase in the pulverized material is 82 μm or more in size, magnetic attraction is not inhibited, resulting in a high magnetic attraction rate in the magnetic separation process. While it is reasonable to consider that there is no upper limit to the cumulative volume particle diameter D50G of the gangue phase based on the above-mentioned removal mechanism, due to the pulverization of the reduced material, it 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 shapes such as polygonal, acicular, and shapes with recesses.

[0030] To obtain a pulverized product having a cumulative volume particle diameter D50G of the gangue phase of 82 μm or more, it is advisable to investigate in advance the cumulative volume particle diameter D50G of the gangue phase after pulverization for each type of mill, operating conditions, and reduction conditions used, and 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. In the pulverization process, it is preferable not to increase the pulverization energy too much. 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, a rotation speed of 1000 rpm or more, preferably 4000 rpm or less. The amount of sample to be pulverized, the operating time, the number of pulverizations, etc., can be adjusted within this rotation speed range. The grinding conditions for the ball mill can be, for example, preferably a rotation speed of 30 rpm or more, more preferably 40 rpm or more, preferably 100 rpm or less, more preferably 80 rpm or less, and the amount of sample to be ground, operating time, number of grinding operations, etc. can be adjusted within this range of rotation speed. The grinding conditions for the disk mill can be adjusted by adjusting the amount of sample to be ground, operating time (grinding time), number of grinding operations, etc. In the case of a disk mill, it is preferable to use conditions that are even weaker in grinding than the grinding conditions for the cage mill and ball mill described above, and for example, the amount of sample to be ground can be increased and the operating time can be reduced 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 product 82 μm or more is not limited to the above-described method, and any other method may be adopted that can obtain a pulverized product having a cumulative volume particle diameter D50G of the gangue phase of 82 μm or more.

[0032] [Magnetic Separation Step] 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 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, when 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 magnetized material (%) / gangue rate of iron ore (%)) × 100 (2) In formula (2), the gangue rate of magnetized material is calculated from the following formula (1B), and the gangue rate of iron ore is calculated from the above formula (1A). Gangue rate of magnetized 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.

[0034] The manufacturing method of the present disclosure is not limited as long as it includes at least the reduction step, the crushing 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.

[0035] The present disclosure will be described in more detail below with reference to examples. The present disclosure is not limited to the following examples, and can be implemented by making 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 disclosure.

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

[0037] (1) Preparation Step As iron ore (raw material) from which gangue was to be removed, iron ore produced in 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]

[0039] (2) Reduction Step 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). ２ 100% gas was introduced into the furnace. Immediately after the start of temperature increase, reducing gas was introduced. The temperature was increased at a rate of about 450°C / h up to the reduction temperature shown in Table 2 below. After maintaining the reduction temperature shown in Table 2 below for 60 minutes (min), N ２ The mixture was cooled to room temperature in an atmosphere to obtain a reduced sample. Other conditions in the reduction step were as follows. The reduction temperature was the ambient temperature inside the furnace. Rotation speed of the drum-type rotary heating furnace: 0.5 rpm. Amount of sample to be reduced: 1.0 kg. Flow rate of the reducing gas: 10 NL / min.

[0040] [Calculation of Reduction Rate] The metallic iron amount M.Fe (mass%), FeO amount (mass%), and total iron amount T.Fe (mass%) of the post-reduction sample (reduced product) were determined by the following analytical methods. The obtained values ​​were substituted into the following formula (3) to determine the reduction rate. The results are also shown in Table 2. - Analysis method for M.Fe amount: Bromine methanol decomposition-potassium dichromate titration method - Analysis method for FeO amount: Potassium dichromate titration method - Analysis method for T.Fe amount: Titanium (III) chloride reduction-potassium dichromate titration method

[0041] In formula (3), "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.

[0042]

[0043] (3) Pulverization Test The reduced samples were pulverized using one of three 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 pulverized samples.

[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 to the cage mill, so that the entire sample passed through the cage mill three times in total, 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) step: The pulverized sample was placed in a dry drum magnetic separator, and magnetic separation was carried out as a sorting and recovery method to obtain iron-containing materials as magnetically attached materials. 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 cycle, and this cycle was carried out once. The magnetic attachment rate and the chemical composition (T.Fe, SiO) of the magnetically attached materials were measured. ２ , Al ２ O ３) and calculated the gangue rate.

[0047] The magnetic susceptibility was calculated from the following formula (4). Regarding the chemical components, the T.Fe content was analyzed by the above-mentioned titanium (III) chloride reduction potassium dichromate titration method, SiO ２ Amount, Al ２ O ３ The amounts of Si and Al were determined by ICP emission spectrometry, and the respective oxides SiO ２ , Al ２ O ３ The gangue removal rate was calculated by converting the amount of the magnetized material into the amount of the magnetic material. The gangue removal rate was calculated from the following formula (1B) using the values ​​of these chemical component amounts. Furthermore, the gangue removal rate was calculated from the predetermined formula (2) using the gangue removal rate of the magnetized material and the gangue removal rate of the iron ore, which is the raw material. The results are shown in Table 3. In this embodiment, the magnetic removal rate is preferably 40% or more, more preferably 50% or more, and even more preferably 70% or more.

[0048]

[0049] 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 are the SiO in the magnetized material (iron-containing material), respectively. ２ Amount (mass%), Al ２ O ３ The amount (mass%) of iron and the total amount (mass%) of iron are shown.

[0050] (6) Mineral phase analysis (measurement of D50G) First, mineral phase analysis was performed to determine the cumulative volume particle diameter D50G. For the mineral phase analysis, an SEM-EDX with a mineral phase analysis function was used. In this analysis, an MLA 650F (hereinafter referred to as MLA) manufactured by FEI was used. This MLA will be explained first. The MLA has the function of distinguishing different mineral phases from the color tone of the backscattered electron image, acquiring characteristic X-ray spectra by EDX, and comparing them with a pre-registered reference spectrum to determine the type of mineral phase. For the measurement, three types of minerals thought to be typical gangue phases were visually selected, and the spectra shown in Figures 2 to 4 were obtained and used as reference spectra. In Figure 2, peaks of Si and O were confirmed, so SiO ２ , Similarly, Fig. 3 shows Al ２ O ３ It is thought that this is the case. Figure 4 shows large peaks for Si, Al, and O, and is therefore presumed to be a clay mineral such as kaolinite. Trace amounts of Ca, Fe, and Mg were also detected. These are thought to be picking up on the surrounding EDX spectrum, as clay minerals are generally extremely fine, but this does not pose a problem in determining the mineral phase. In this specification, phases that are determined to match the spectra in Figures 2 to 4 are referred to as "gangue phases."

[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 analysis is performed. 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 even if the number of reference spectra of other mineral phases registered differs. 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 shape analysis function "Create Database → Dataview." However, as long as a colored mineral phase map is obtained, it can also be determined by ordinary 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 in this case was approximately 2 square millimeters.

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

[0054] In this embodiment, the cumulative volume particle diameter D50G [μm] was used as an index representing the particle size distribution of the gangue phase. The cumulative volume particle diameter D50G was calculated by calculating the equivalent spherical 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 the cross-sectional image obtained by mineral phase mapping. ２ ].

[0055]

[0056] Fig. 6 shows a mineral phase map of Comparative Example 1, and Fig. 7 shows a mineral phase map of Example 7. In Fig. 6 and Fig. 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 Fig. 6 and Fig. 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 volume particle diameter D50G of the gangue phase obtained using the above MLA is also shown in Table 3. The relationship between this D50G value and the gangue removal rate is shown in Figure 5. From Figure 5, it can be seen that when D50G is below 82 μm, the gangue removal rate decreases.

[0058]

[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 in a state in which iron-containing materials and fine gangue phases are mixed together. When iron-containing materials and fine gangue phases are mixed together, static electricity causes the gangue phase to adhere to the magnetic iron-containing materials, increasing the proportion of the gangue phase that is mixed in, and as a result, it is thought that the gangue removal rate decreases.

[0060] On the other hand, when the gangue is not excessively crushed in the crushing step and the gangue phase has a size of 82 μm or more as in Example 7, the gangue phase is not entangled with the magnetized material 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 ensure that the cumulative volume particle size D50G of the pulverized material (pulverized sample) exceeds 82 μm, it is believed that it is necessary to select an appropriate mill and set operating conditions as pulverization conditions depending on the state after reduction. First, we will consider the case where a cage mill is used as the mill. 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, the operating conditions when a ball mill is used as the mill will be considered. 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, the operating conditions when a disk mill is used as the mill will be considered. The operating conditions of 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).

[0064] This application claims priority from Japanese Patent Application No. 2024-126135, which is incorporated herein by reference.

[0065] 1 Iron ore 3 Gangue phase 5 Unreduced iron oxide 7 Reduced material 9 Iron-containing phase 11 Crushed material 13 Iron-containing material

Claims

1. A method for producing raw materials for iron making, comprising: a reduction step of reducing iron ore having a gangue ratio of 10% or more, calculated from the following formula (1A), at a reduction ratio of 60% or less to obtain a reduced product containing metallic iron and a gangue phase; a crushing step of crushing the reduced product to obtain a crushed product having a gangue phase cumulative volume particle diameter D50G of 82 μm or more; and a magnetic separation step of magnetically separating the crushed product to recover iron-containing materials including metallic iron as magnetically separated materials. Gangue ratio (%) of iron ore = [(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. The method for producing raw materials for iron making according to claim 1 or 2, 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 magnetized material (%) / gangue rate of iron ore (%)) × 100 (2) In formula (2), the gangue rate of magnetized material is calculated from the following formula (1B), and the gangue rate of iron ore is calculated from the above formula (1A). Gangue rate of magnetized 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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