Method for producing iron-making raw material

Abstract

A method for producing an iron-making raw material comprising: a reduction step for reducing an iron ore having a gangue ratio of 10% or more as determined from formula (1A) at a temperature and gas composition condition at which Fe3O4 becomes a stable phase to obtain a reduced product including an iron-containing phase; a pulverization step for pulverizing the reduced product to obtain a pulverized product including iron-containing particles having an integrated volume particle diameter D50 Fe of not less than 100 µm; and a magnetic separation step for magnetically separating the pulverized product to recover the iron-containing particles as magnetized products.　(1A): Gangue ratio of iron ore (%)=(SiO2+Al2O3) / T.Fe×100 In formula (1A), SiO2, Al2O3, and T.Fe respectively represent the SiO2 amount (mass%), the Al2O3 amount (mass%), and the total iron amount (mass%) 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] Patent Document 2 discloses a technique for removing gangue without heating iron ore to a high temperature, i.e., without melting the iron ore. In this technique, for example, H ２ However, this method is considered to be undesirable from an energy standpoint because it requires the use of large amounts of gases with high reducing power, such as SiO2 and CO, which are also valuable energy sources. Patent Document 3 also relates to a technique for removing gangue without melting the iron ore, and provides guidelines for controlling the particle size of the entire sample, but further investigation is considered necessary to obtain raw materials for ironmaking 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.

[0010] In the first aspect of the present invention, iron ore having a gangue ratio of 10% or more calculated from the following formula (1A) is treated with Fe ３ O ４ The method for producing raw materials for iron making includes the steps of: a reduction step of reducing iron ore under conditions of a temperature and gas composition such that (SiO) is in a stable phase to obtain a reduced product containing an iron-containing phase; a crushing step of crushing the reduced product to obtain a crushed product containing iron-containing particles including the iron-containing phase, the iron-containing phase having an integrated volume particle diameter D50Fe of 100 μm or more; and a magnetic separation step of magnetically separating the crushed product and recovering the iron-containing particles as magnetically separated materials. 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] In the second aspect of the present invention, in the reduction step, Fe calculated from the following formula (2) is ３ O ４ The method for producing a raw material for iron making according to aspect 1, wherein the reduction is carried out so that the conversion rate is 40% or more. 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.

[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 gas used in the reduction step includes a top gas of a blast furnace.

[0013] A fourth aspect of the present invention is the method for producing raw materials for iron making according to any one of the first to third aspects, wherein the reduction step is carried out at a reduction temperature of 900° C. or less.

[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.

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

[0016] In the method for producing raw materials for iron making according to the present embodiment, iron ore having a gangue ratio of 10% or more calculated by the following formula (1A) is mixed with Fe ３ O ４ The method includes a reduction step of reducing iron ore under conditions of a temperature and gas composition where the iron ore is in 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, the iron-containing phase having an integrated volume particle diameter D50Fe of 100 μm or more, and a magnetic separation step of magnetically separating the pulverized product and recovering the iron-containing particles as magnetically separated products. 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.

[0017] According to the manufacturing 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 manufactured.

[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. 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, when unreduced iron oxide is completely converted to Fe by reduction, ３ O ４ In some cases, the sintered material is not completely reduced to the original state, or the sintered material is not completely separated into gangue and the iron-containing phase by pulverization, with some of the gangue remaining on, for example, the surface of the iron-containing phase. These situations are naturally acceptable, and the production method according to this embodiment can also include these situations.

[0020] [Reduction Step] As shown in Fig. 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 Fig. 1B. By going through the reduction step indicated by the arrow a from A to B in Fig. 1, for example, Fe ２ O ３ The unreduced iron oxide 5 such as is reduced to Fe ３ O ４ The reduced product 7 is obtained, which contains an iron-containing phase 9 such as

[0021] The raw material iron ore 1 containing gangue 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 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. 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.

[0022] In the method for producing raw materials for iron making disclosed herein, iron ore (raw material) is not reduced to metallic iron, but to Fe, which is iron oxide with a high iron content. ３ O ４ The iron ore and the iron-making raw materials obtained from the iron ore contain iron-containing substances, such as oxides of Fe ２ O ３ , Fe ３ O ４ There are four types: FeO, Fe, and metallic iron. ３ O ４ Metallic iron (Fe) exhibits ferromagnetism. ３ O ４ By reducing iron ore (raw material) to Fe, it is possible to reduce energy costs and production time compared to when reducing iron to metallic iron, and magnetic separation (magnetic separation) can be used, allowing efficient separation and recovery. ３ O ４ By limiting the reduction rate to 100%, it is possible to use a gas with low reducing power, such as the top gas of a blast furnace, and to utilize waste gas.

[0023] From the above, in the reduction process, iron ore is reduced to Fe ３ O ４ The reduction is carried out under the conditions of temperature and gas composition in which Fe is a stable phase, thereby obtaining a reduced product containing an iron-containing phase (reduced iron oxide phase). ３ O ４ For example, as shown in Figure 2 (Yoichi Ono, "Rist Operation Diagram (I)", Iron and Steel, Vol. 79, 1993, No. 9, N618, Figure 3 (reduction equilibrium diagram of iron oxide)), the temperature and the gas composition are such that the temperature and CO / (CO + CO ２ ) using the Fe-C-O equilibrium diagram represented by３ O ４ The region where Fe is stable is shown as the shaded region in FIG. ３ O ４ In Figure 2, the horizontal axis indicates "CO" and "CO ２ " are CO gas, CO ２ In FIG. 2, for example, the CO ２ / (CO + CO ２ ) is 70%, temperature: 600 ° C, 700 ° C, Fe ３ O ４ Therefore, for example, when the temperature is 600°C or 700°C and the gas composition is CO ２ / (CO + CO ２ ) = 70% is Fe ３ O ４ The temperature and gas composition conditions for the stable phase are as follows. ２ / (CO + CO ２ ) is, for example, 70% and the temperature is 800°C, FeO is the stable phase and Fe ３ O ４ is not a stable phase, so this condition is ３ O ４ However, it cannot be said that the temperature and gas composition conditions are such that the phase becomes stable.

[0024] The gases constituting the atmosphere in the reduction step are the above-mentioned CO gas and H ２ The remaining gas components are not particularly limited as long as the gas contains at least one of the following gases: ２ , N ２ , H ２ The gas may include at least the top gas of a blast furnace.

[0025] The type of gas is CO2-CO ２ Instead of the system, H ２ -H ２ O series or H ２ -H ２ O-CO-CO ２ The reduction may be carried out as a system. ２ -H ２ O series, H ２ -H２ O-CO-CO ２ In the case of the CO-CO system, ２ As with the system, Fe ３ O ４ It is possible to determine the temperature and gas composition conditions under which H becomes a stable phase. ２ -H ２ O-CO-CO ２ In the reduction of the system (H ２ +H ２ O) and (CO + CO ２ ) and discuss the position of the equilibrium line using the weighted average.

[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 even 700°C or lower.

[0027] 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.

[0028] In the reduction step, Fe calculated from the following formula (2) ３ O ４ It is preferable to carry out the reduction so that the conversion rate is 40% or more. In the present disclosure, the reduction degree in the reduction step is ３ O ４ Evaluated by conversion rate. ２ O ３ is Fe ３ O ４ The conversion (reduction) rate is as follows:３ O ４ A conversion rate of 40% or more is preferable because iron contained in iron ore can be sufficiently recovered. ３ O ４ The conversion rate is more preferably 60% or more, and even more preferably 80% or more, with the upper limit being 100%. 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.

[0029] [Crushing Step] As schematically shown in FIG. 1 , the reduced material 7 is crushed in the crushing step indicated by the arrow b from B to C in FIG. 1 to obtain a crushed material 11 containing iron-containing particles 13 including an iron-containing phase 9. In the method of the present disclosure, crushing is required so that the iron-containing phase 9 has an integrated volume particle diameter D50Fe of 100 μm or more. In this specification, the iron-containing particles are sufficient as long as they contain at least 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 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 crushed material 11 also includes gangue particles that do not contain the iron-containing phase 9 but contain gangue 3. The crushing 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 or the like 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 a high-speed collation function can be used as a method for distinguishing between the iron-containing phase and gangue and evaluating the size of the iron-containing phase. 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 volume particle diameter D50Fe of the iron-containing phase in the pulverized material is 100 μm or more. It is believed that when a large amount of fine iron-containing phase is present in the pulverized material, 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 volume particle diameter D50Fe of the iron-containing phase in the pulverized material is 100 μm or more, magnetic attraction is not inhibited, resulting in a high magnetic attraction rate during the magnetic separation process. The cumulative volume particle diameter D50Fe is preferably 1000 μm or less. This is because if the cumulative volume 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, but can take various shapes, such as polygonal, acicular, or having recesses. The shape of the iron-containing particles is also not limited to spherical, but can take various shapes, such as polygonal, acicular, or having 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] The cage mill can be used regardless of the conditions of the reduction step other than the pulverization step, and the pulverization conditions can be, for example, preferably a rotation speed of 1000 rpm or more, preferably 4000 rpm or less. Within this range of rotation speed, the dosage of the sample to be pulverized, the number of pulverizations, etc. may be adjusted. On the other hand, when a ball mill is used, Fe ３ O ４ Depending on the conversion rate, the above D50Fe may not be achieved. When using a ball mill, the Fe content of the reduced product to be milled is ３ O ４A higher conversion rate is preferable, and is preferably 40% or more, more preferably 50% or more, even more preferably 60% or more, and even more preferably 70% or more. When a ball mill is used, the rotation speed can be, for example, preferably 30 rpm or more, more preferably 40 rpm or more, and preferably 100 rpm or less, more preferably 80 rpm or less, and the amount of sample to be ground, operation time, number of grinding operations, etc. may be adjusted within this rotation speed range.

[0034] When using a disk mill, the Fe content of the reduced material to be milled is the same as in the case of a ball mill. ３ O ４ A higher conversion rate is preferable. The milling conditions may be adjusted by adjusting the amount of sample to be milled, the operation time (milling time), the number of times of milling, etc. 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 may be increased and the operation time may be reduced compared to the 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-described 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 Separation Step] Magnetic separation (magnetic separation) is used as a method for separating and recovering the magnetic material. ３ O ４ The inclusion of α-tocopherol in the iron-containing particles makes magnetic separation possible. 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 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.

[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 rate calculated from the following formula (3). The gangue removal rate 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 rate of the magnetized product itself is not particularly limited. For example, if the gangue rate of the iron ore is quite high, the gangue rate of the obtained magnetized product may be 10% or more. Even in such cases, the gangue removal rate is preferably 40% or more. The gangue rate of the magnetized product depends on the gangue rate 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 product / 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.

[0039] 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.

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

[0041] (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.

[0042]

[0043] (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). The reducing gas was a CO:CO mixture at room temperature. ２The mixture was mixed to a reducing gas composition of 10:90 (vol %) and then introduced into the furnace. The reducing gas was introduced immediately after the start of temperature increase. The temperature was increased at a rate of about 450°C / h to the reduction temperature shown in Table 2 below. After maintaining the temperature at the reduction temperature shown in Table 2 below for 60 minutes (min), N ２ The sample 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 atmospheric temperature in the furnace. The reducing gas and reduction temperature in this example were Fe ３ O ４ These are the conditions for a stable phase. 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

[0044] [Fe ３ O ４ Calculation of Conversion Rate] The metallic iron amount M.Fe (mass%), FeO amount (mass%), and total iron amount T.Fe (mass%) of the reduced sample (reduced product) were determined by the following analytical method. The obtained values ​​were substituted into the following formula (2) to calculate Fe ３ O ４ The conversion rate was determined, and the results are shown in Table 2. M. Fe content analysis method: bromine methanol decomposition-potassium dichromate titration method FeO content analysis method: potassium dichromate titration method T. Fe content analysis method: titanium (III) chloride reduction-potassium dichromate titration method

[0045] 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.

[0046]

[0047] (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.

[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 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.

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

[0050] (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 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 cycle, and this cycle was carried out once. The magnetic adsorption rate of the obtained magnetic material was measured, and the chemical components (T.Fe, SiO ２ , Al ２ O ３ ) and calculated the gangue rate.

[0051] 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 , 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 ratio of the magnetized material was calculated by converting the amount of the chemical components into the amount of the gangue ratio of the magnetized material. The gangue ratio was calculated by using the values ​​of these chemical component amounts according to the following formula (1B). The results are shown in Table 3. In this embodiment, the magnetization ratio is preferably 40% or more, more preferably 50% or more, and even more preferably 70% or more.

[0052]

[0053] 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 particles), respectively. ２ Amount (mass%), Al ２ O ３ The amount (mass%) of iron and the total amount (mass%) of iron are shown.

[0054] (5) Mineral phase analysis (measurement of cumulative volume particle diameter D50Fe) First, mineral phase analysis was performed to determine the cumulative volume particle diameter D50Fe. 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 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 device that uses EDX as the measurement principle, it was possible to measure iron oxides (iron oxides) with different oxidation forms, such as Fe ２ O ３ , Fe ３ O ４ , 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, Fe ３ O ４ The reduction is carried out under conditions in which Fe becomes a stable phase, and the iron-containing particles are obtained as magnetic particles by magnetic separation. ３ O ４ Since the conversion rate is 40% or more, the "iron-containing phase" and "iron-containing particles" in this specification include oxides (e.g., Fe ２ O ３ ) is reduced in the reduction step to obtain Fe３ O ４ (also called "reduced oxides").

[0056] Although only the reference spectrum of iron oxide 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 in a similar manner, and the measurement results of the morphology of the iron-containing phase do not change significantly depending on the number of registered reference spectra of other mineral phases. In this example, reference spectra were registered for the mineral phases listed below: silicon dioxide, aluminum oxide, magnesium oxide, kaolinite, calcium ferrite, fayrite, silicate slag, calcium phosphate, solid solution of dicalcium silicate and calcium phosphate, and aluminum phosphate. Note that, based on its principles, MLA does not allow for the registration of minerals with the same chemical composition but different crystalline structures, such as quartz and quartzite (both of which have the chemical composition SiO ２ Therefore, minerals that are difficult to identify are expressed by 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 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.

[0058] In the shape analysis, the boundaries of the mineral phases were first identified from the contrast difference in the backscattered electron image, 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-containing phase, and the particle size distribution of the iron-containing phase region was 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]

[0061] Figure 5 shows a mineral phase map of Comparative Example 2, and Figure 6 shows a mineral phase map of Example 2. In Figures 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 Figures 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 phase 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 MLA is also shown in Table 3. The relationship between this D50Fe value and the magnetic susceptibility is shown in Figure 7. From Figure 7, it can be seen that the magnetic susceptibility drops significantly when the cumulative volume particle diameter D50Fe is below 100 μm.

[0063]

[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 in a state in which the fine iron-containing phase and other mineral phases are mixed together. It is thought that the mixture of the fine iron-containing phase and other mineral phases increases the magnetic attraction inhibition effect due to static electricity, and the magnetic attraction rate decreases.

[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 effect of static electricity inhibiting 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] In addition, the conditions of the reduction step are different between Example 1 and Example 2, and Fe ３ O ４ Although the conversion rates are different, the pulverization method was carried out under the same conditions. ３ O ４ It can be seen that the magnetic attraction can be increased sufficiently by increasing the conversion rate. This is because the paramagnetic Fe ２ O ３ The ratio of Fe decreases, and the ferromagnetic ３ O ４ This is thought to be because the increased ratio of , made it easier to recover by magnetic separation.

[0067] As can be seen from the comparison between the Examples and Comparative Examples, in order to achieve a cumulative volume particle diameter D50Fe of 100 μm or more for the pulverized material (pulverized sample), 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 as the mill. The cage mill operating conditions were a rotation speed of 2850 rpm and three treatments, but in both Examples 1 and 2, the cumulative volume particle diameter D50Fe exceeded 100 μm. Therefore, the operating conditions of the cage mill are considered to be within an appropriate range. As described above, from the viewpoint 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 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, it is believed that the appropriate operating conditions for the ball mill are 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 disk mill is used. The operating conditions for the disk mill are a sample charge of 100 g and a grinding time of 30 s, but the cumulative volumetric particle size D50Fe is significantly below 100 μm in both Comparative Examples 2 and 3. Therefore, it is believed that the appropriate operating conditions for the disk mill are on the weak side of grinding, and improvements can be expected, for example, by increasing the sample charge to 300 g or reducing 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, which is significantly different from Patent Document 3, which evaluated the particle size of the entire pulverized material.

[0071] This application claims priority from Japanese Patent Application No. 2024-126136, which is incorporated herein by reference.

[0072] 1 Iron ore 3 Gangue 5 Unreduced iron oxide 7 Reduced material 9 Iron-containing phase 11 Crushed material 13 Iron-containing particles

Claims

1. Iron ore with a gangue ratio of 10% or more calculated from the following formula (1A) is classified as Fe ３ O ４ A method for producing raw materials for iron making, comprising: a reduction step of reducing iron ore under conditions of a temperature and gas composition such that (SiO) is in 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, the iron-containing phase having an integrated volume particle diameter D50Fe of 100 μm or more; and a magnetic separation step of magnetically separating the pulverized product and recovering the iron-containing particles as magnetically separated materials. 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. 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 blast furnace top gas.

4. The method for producing raw materials for iron making according to claim 1 or 2, wherein the reduction step is carried out at a reduction temperature of 900°C or less.

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