Iron source manufacturing method

Abstract

To provide an iron source production method enabling phosphorus existing in iron ore to be sufficiently removed, even when the phosphorus is coupled to iron.SOLUTION: An iron source production method is provided, comprising: a preparing step of mixing iron ore including phosphorus, and raw material including flux, thereby preparing mixture for roasting; a roasting step of roasting the mixture for roasting, thereby acquiring a roasted object; a reduction step of reducing the roasted object in atmosphere including at least one of, CO gas and hydrogen gas, thereby acquiring a reduced object including a reduced iron phase and a slag phase; a disintegrating step of disintegrating the reduced object, thereby acquiring a disintegrated object including a reduced iron phase-containing object in which, at least a part of the slag phase forming the reduced object is separated; and a selection / recovery step of selecting and recovering the reduced iron phase-containing object from the disintegrated object, wherein the flux includes a prescribed compound, and an average particle diameter of the flux is larger than an average particle diameter of the iron ore.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to a method for producing an iron source, and more particularly to a method for producing an iron source having a reduced phosphorus content compared to raw iron ore. [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, and the impurity content of iron ore is expected to increase in the future. Patent Document 1, for example, describes a pre-treatment method for converting low-grade iron ore containing a large amount of gangue into high-grade iron ore for direct ironmaking, in which iron ore charged into a reduction furnace is reduced with reducing gas generated from a hydrocarbon-containing fuel to directly obtain a raw material for ironmaking without going through a pig iron production process. The method includes the steps of: introducing high-temperature furnace gas discharged from the reduction furnace into a reduction roasting furnace and reducing and roasting hematite ore supplied from a storage yard with reducing components remaining in the furnace gas to produce magnetite ore; crushing the magnetite ore to a particle size suitable for magnetic separation and magnetically separating it using a magnetic separator; and agglomerating and firing the magnetite concentrate obtained by magnetic separation to form pellets, which are then fed to the reduction furnace.

[0003] Phosphorus is one of the components that reduces the quality of iron ore. In the existing blast furnace-converter process, almost all of the phosphorus in iron ore is transferred to the molten iron in the blast furnace, and is generally removed in the subsequent molten iron pretreatment and converter processes. However, as the amount of phosphorus in the raw iron ore increases, the cost of phosphorus removal in these processes increases and productivity decreases. Therefore, there is a need to develop a technology to remove phosphorus from iron ore used in steelmaking.

[0004] For example, Patent Document 2 describes a method for removing phosphorus from iron ore by wet processing. Specifically, the method describes a phosphorus-containing iron ore treatment process in which high-phosphorus iron ore is crushed to 0.5 mm or less, water is added to the crushed ore to a pulp concentration of approximately 35%, H2SO4 or HCl is added as a solvent, and the resulting mixture is reacted at a pH of 2.0 or less to decompose and dissolve the contained phosphorus minerals (mainly apatite). Magnetic separation is then performed to collect magnetized materials such as magnetite, and non-magnetic materials such as SiO2 or Al2O3 are separated and separated as slime. Furthermore, the phosphorus dissolved in the solution is neutralized by adding slaked lime or quicklime at a pH of 5.0 to 10.0, and separated and recovered as calcium phosphate. However, the method described in Patent Document 2 has the drawback of being difficult to ensure productivity due to its wet processing.

[0005] Meanwhile, methods for removing phosphorus from iron ore using dry processes have also been proposed. For example, Non-Patent Document 1 proposes a process for separating phosphorus from iron ore by concentrating it in a dicalcium silicate (C2S) phase. Specifically, the basicity of the iron ore and the blending ratio of the carbonaceous material are adjusted, particularly with regard to the basicity, by adding an amount of CaO based on the SiO2 contained in the fine ore so that the basicity (C / S) becomes 2.0, and then heating at a high temperature. This results in the coexistence of a dicalcium silicate phase (2CaO-SiO2, C2S) as a solid phase in the molten slag, and P is concentrated as a solid solution (C2S-C3P solid solution) with a calcium phosphate phase (3CaO-P2O5, C3P). [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Publication No. 53-103915 [Patent Document 2] Japanese Patent Application Publication No. 60-261501 [Non-patent literature]

[0007] [Non-Patent Document 1] Nobuhiro Maruoka et al., "Enrichment of phosphorus in iron ore into the dicalcium silicate phase by partial reduction treatment," Iron and Steel, Vol. 107 (2021), No. 6, pp. 527-533 Summary of the Invention [Problem to be solved by the invention]

[0008] The method of Patent Document 1 is effective when phosphorus is bound to elements other than iron, but has the problem that it cannot remove phosphorus when bound to iron. Furthermore, the method of Non-Patent Document 1 has the problem that it is difficult to adjust the oxygen partial pressure due to the use of carbonaceous materials, etc., which makes it easy for phosphorus to be mixed into the iron phase, making it difficult to remove phosphorus. In addition, the use of carbonaceous materials causes problems such as the inclusion of sulfur and the emission of greenhouse gases.

[0009] The present disclosure has been made in view of the above-mentioned problems, and an object of the present disclosure is to realize a method for producing an iron source to be used in iron production and the like, which can sufficiently remove phosphorus even when the phosphorus present in iron ore is bound to iron. [Means for solving the problem]

[0010] Aspect 1 of the present invention is a preparation step of mixing phosphorus-containing iron ore and a raw material containing flux to prepare a roasting mixture; a roasting step of roasting the mixture to be roasted to obtain a roasted product; a reduction step of reducing the roasted product in an atmosphere containing at least one of CO gas and hydrogen gas to obtain a reduced product containing a reduced iron phase and a slag phase; a pulverization step of pulverizing the reduced material to obtain a pulverized material containing a reduced iron phase from which at least a portion of the slag phase constituting the reduced material has been separated; a sorting and recovery step of sorting and recovering the reduced iron phase-containing material from the pulverized material, The flux comprises at least one selected from the group consisting of oxides, carbonates, hydroxides, and hydrates of alkali metals, and oxides, carbonates, hydroxides, and hydrates of alkaline earth metals; and In the method for producing an iron source, the average particle size of the flux is larger than the average particle size of the iron ore.

[0011] Aspect 2 of the present invention is A method for producing an iron source according to aspect 1, wherein the flux is one or more selected from the group consisting of CaO, CaCO 3 , and Ca(OH) 2 .

[0012] Aspect 3 of the present invention is Aspect 3 is a method for producing an iron source according to aspect 1 or 2, wherein the sorting and recovery step employs magnetic separation as a method for sorting and recovery.

[0013] A fourth aspect of the present invention is Aspect 4 is the method for producing an iron source according to any one of Aspects 1 to 3, wherein in the preparing step, the iron ore and the flux are mixed together so that the mixture for roasting has a basicity CaO / SiO2 in the range of 1.0 to 5.0. [Effects of the Invention]

[0014] According to the present disclosure, it is possible to provide a method for producing an iron source to be used in iron production or the like, which can sufficiently remove phosphorus even when phosphorus present in iron ore is bound to iron. [Brief explanation of the drawings]

[0015] [Figure 1] FIG. 1 is an image diagram that schematically shows the steps of this embodiment. [Figure 2A] FIG. 2A is a scanning electron microscope image of Comparative Example 1. [Figure 2B] FIG. 2B is a scanning electron microscope image of Example 5. [Figure 3A] FIG. 3A is a diagram showing EDX analysis values ​​at analysis points denoted by symbols 1 to 3 in FIG. 2A. [Figure 3B] FIG. 3B is a diagram showing EDX analysis values ​​at analysis points denoted by symbols 1 to 3 in FIG. 2B. [Figure 4] FIG. 4 is a graph showing the relationship between the flux, the average particle size of the iron ore, and the phosphorus removal rate. DETAILED DESCRIPTION OF THE INVENTION

[0016] The method for producing an iron source according to this embodiment includes the steps of: a preparation step of mixing phosphorus-containing iron ore and a raw material containing flux to prepare a roasting mixture; a roasting step of roasting the mixture to be roasted to obtain a roasted product; a reduction step of reducing the roasted product in an atmosphere containing at least one of CO gas and hydrogen gas to obtain a reduced product containing a reduced iron phase and a slag phase; a pulverization step of pulverizing the reduced material to obtain a pulverized material containing a reduced iron phase from which at least a portion of the slag phase constituting the reduced material has been separated; a sorting and recovery step of sorting and recovering the reduced iron phase-containing material from the pulverized material, The flux comprises at least one selected from the group consisting of oxides, carbonates, hydroxides, and hydrates of alkali metals, and oxides, carbonates, hydroxides, and hydrates of alkaline earth metals; and The average particle size of the flux is larger than the average particle size of the iron ore.

[0017] According to this embodiment, the manufacturing method involves two separate steps: a roasting process in which a roasting mixture containing flux and iron ore is oxidized and roasted; and a reduction process in which reduction is performed in a controlled atmosphere containing at least one of CO gas and hydrogen gas. As a result, phosphorus bound to iron in the iron ore is transferred to the slag phase (components other than iron, impurities) formed by the flux roasting (oxidizing roasting) and bound to the slag. The reduction process then involves reducing the iron oxide while keeping the phosphorus bound to the slag. This chemical separation of the phosphorus and the iron phase is achieved, and the resulting material is then crushed and separated to obtain a reduced iron phase-containing material as an iron source. In this embodiment, the phosphorus is captured as a complex oxide of phosphorus and calcium oxide (which is believed to be in a bonding state similar to Ca2P2O7), which is believed to enable sufficient removal of phosphorus from the iron ore.

[0018] Each step of the production method according to this embodiment will be described in detail below. FIG. 1 is an image diagram that schematically illustrates each step of the production method according to this embodiment. While the following description of each step may be based on FIG. 1, FIG. 1 is merely an image diagram and does not limit the present disclosure. For example, there may be cases where phosphorus does not completely migrate to the slag phase after roasting, or where the slag phase and the reduced iron phase do not completely separate after pulverization, with part of the slag phase remaining bound to the reduced iron phase. However, such situations are naturally acceptable, and the production method according to this embodiment may also include these situations.

[0019] [Preparation process] A roasting mixture is prepared by mixing phosphorus-containing iron ore and a raw material containing a flux. In this embodiment, the average particle size of the flux is larger than that of the iron ore. By increasing the average particle size of the flux relative to the average particle size of the iron ore, when the phosphorus component is fixed in the impurity phase during roasting, the melt region expands, increasing the size of the impurity phase. This also coarsens the phosphorus-enriched phase, which is a crystallized product, making it easier to separate phosphorus after roasting. The average particle size of the flux should be larger than that of the iron ore. For example, the average particle size of the flux can be preferably 1.1 times or more, more preferably 1.5 times or more, and even 3.0 times or more, the average particle size of the iron ore. The upper limit is not particularly limited, but from the viewpoint of improving the mixability of the raw materials, it can be 30 times or less, or even 20 times or less.

[0020] In the present disclosure, the average values ​​of the minimum and maximum particle sizes of the particles constituting the flux and iron ore are defined as the average particle sizes of the flux and iron ore, respectively. The minimum and maximum particle sizes can be determined using a sieve, as shown in the examples described below. The sizes of the iron ore and flux can be adjusted by crushing, classifying, or the like before mixing so as to satisfy the above relationship.

[0021] The flux contains one or more compounds selected from the group consisting of alkali metal oxides, carbonates, hydroxides, and hydrates, and alkaline earth metal oxides, carbonates, hydroxides, and hydrates. These alkaline earth metal oxides are compounds that readily bind with phosphorus. Examples of the alkali metal compounds include Na2O, K2O, Li2CO3, Na2CO3, K2CO3, NaOH, and KOH. Examples of the alkaline earth metal compounds include CaO (quicklime), CaCO3 (limestone), and Ca(OH)2 (slaked lime). The flux is preferably one or more compounds selected from the group consisting of CaO, CaCO3, and Ca(OH)2. CaO, CaCO3, and Ca(OH)2 are preferred because they readily bind with phosphorus and are readily available industrially. Furthermore, the addition of SiO2 in iron ore facilitates the formation of the aforementioned complex oxide of phosphorus and calcium oxide, thereby enabling phosphorus to be easily immobilized. CaCO3, which is widely used industrially, is more preferred. The flux may be a mixture of one or more selected from the group consisting of oxides, carbonates, hydroxides, and hydrates of alkali metals and oxides, carbonates, hydroxides, and hydrates of alkaline earth metals, and other fluxes, such as soda-based fluxes, CaF2, CaCl2, Li2CO3-based fluxes, and BaCO3-based fluxes.

[0022] The iron ore and flux are preferably mixed so that the basicity (CaO / SiO2) of the roasting mixture is in the range of 1.0 to 5.0. For example, depending on the amount of SiO2 contained in the iron ore, the flux may be preferably one or more selected from the group consisting of CaO, CaCO3, and Ca(OH)2, more preferably one or more of CaO and CaCO3, so as to achieve the basicity within the above range. Alternatively, depending on the amount of SiO2 contained in the iron ore, the flux may be preferably one or more selected from the group consisting of CaO, CaCO3, and Ca(OH)2, more preferably one or more of CaO and CaCO3, and another of the above-mentioned fluxes so as to achieve the basicity within the above range. By achieving the basicity of the roasting mixture in the above range, a complex oxide of phosphorus and calcium oxide close to Ca2P2O7 can be easily formed. CaO / SiO2 is more preferably 3.0 or less. When calculating the basicity (CaO / SiO2), Ca-containing compounds other than CaO are calculated in terms of CaO. This is because the Ca-containing compounds contained in the flux, such as CaCO3 and Ca(OH)2, other than CaO, also decompose when heated to form CaO.

[0023] The iron ore and the flux may be mixed by an industrially used method. As a result of mixing, a roasting mixture containing iron ore 11 and flux 12 is obtained, as shown in Fig. 1A. As the roasting mixture, if necessary, a medium such as water may be further added to the iron ore and flux to form a granule.

[0024] The phosphorus-containing iron ore may contain, for example, 0.05% by mass or more of phosphorus. According to this embodiment, even when the amount of phosphorus in the iron ore is as high as 0.10% by mass or more, or even 0.15% by mass or more, the phosphorus can be sufficiently reduced.

[0025] [Roasting process] In the roasting step, the roasting mixture is roasted to obtain a roasted product as shown in FIG. 1B. In the roasting step indicated by arrow a from A to B in FIG. 1, iron ore 11 containing phosphorus bound to iron is roasted together with flux 12 (oxidizing roasting). This leads to phosphorus migration 15, specifically, phosphorus in iron ore 11 migrates to a slag phase 14 (an impurity phase mainly composed of components other than iron, hereinafter referred to as the "roasted slag phase") formed by the roasting of the flux, and is believed to bond with the roasted slag phase 14. To achieve this effect, the roasting temperature is preferably 1150°C or higher, at which at least a portion of the mixture can melt. The temperature may even be 1200°C or higher. The upper limit of the roasting temperature is not particularly limited from the viewpoint of transferring phosphorus from the iron ore to the slag phase. For example, the upper limit of the temperature may be approximately 1500°C from the viewpoint of preventing deterioration of equipment. The roasting temperature refers to the temperature of the packed bed of the mixture of iron ore and flux, and in the examples described below, this temperature was controlled by the ambient temperature of the furnace used.

[0026] The roasting atmosphere may be any oxygen-containing atmosphere. For example, the air atmosphere can be used. In the roasting step, for example, a carbonaceous material can be used as a heat source. When this carbonaceous material is used, the atmosphere may be slightly more reducing than the air atmosphere, and such an atmosphere is also acceptable. As equipment for roasting, for example, an electric resistance furnace (externally heated), a burner-type heating furnace, a Dwight Lloyd sintering machine, a pot-type sintering machine, etc. can be used.

[0027] [Reduction process] In the reduction step, the roasted product is reduced in an atmosphere containing at least one of CO gas and hydrogen gas to obtain the reduced product shown in C in FIG. 1, i.e., a reduced product containing a reduced iron phase and a slag phase. Through the reduction step indicated by arrow b from B to C in FIG. 1, the iron oxide-containing phase 13 is reduced to obtain a reduced product formed of a reduced iron phase 16 and a reduced slag phase 17 in which phosphorus remains fixed (the slag phase after the roasted slag phase 14 has undergone this reduction step). The reasons why the roasting step and the reduction step are separated and reduction is performed in the above atmosphere in the reduction step in this embodiment enable easy chemical separation of phosphorus are described in detail below.

[0028] When the oxygen partial pressure drops during reduction, oxygen dissociates from P2O5 in the slag, generating phosphorus. This phosphorus easily binds with Fe, making it difficult to remove from the iron ore. Therefore, it is necessary to suppress fluctuations in the oxygen partial pressure during reduction. However, the method of Non-Patent Document 1 is thought to be prone to fluctuations in the oxygen partial pressure during reduction. This is because the method of Non-Patent Document 1 uses a carbonaceous material, which can locally decrease the oxygen partial pressure around the carbonaceous material during reduction, and heating the carbonaceous material can produce CO gas and CO2 gas, resulting in unpredictable oxygen consumption. On the other hand, this embodiment uses a gaseous reducing agent, such as CO gas or hydrogen gas, for reduction. This suppresses fluctuations in the oxygen partial pressure during reduction, preventing phosphorus from recombining with iron due to the reduced oxygen partial pressure, and is thought to maintain the phosphorus in a chemically separated state.

[0029] The gas constituting the atmosphere in the reduction step needs only to contain at least one of CO gas and hydrogen gas, 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 CO gas and N gas. In the examples described below, CO gas alone or a mixture of CO gas and hydrogen gas is used as the reducing gas, but the reducing gas may be hydrogen gas alone, for example, 10% hydrogen gas with the remainder being N gas. According to this embodiment, when hydrogen is used as the reducing gas, it contributes to a reduction in greenhouse gas emissions compared to when a carbonaceous material is used as a reducing agent as in Non-Patent Document 1.

[0030] By carrying out reduction under the above conditions, the migration of SiO2 and Al2O3 to the reduced slag phase 17 proceeds, and the reduction of the iron oxide-containing phase 13 proceeds with most of the phosphorus fixed in the reduced slag phase 17, resulting in a reduced iron phase 16 mainly composed of, for example, M.Fe (metallic iron) or Fe3O4. In other words, the above oxidizing roasting and reduction steps produce a reduced product that is chemically sufficiently separated into phosphorus fixed in the reduced slag phase 17 and reduced iron phase 16.

[0031] In this embodiment, the reduced iron phase may contain not only M.Fe (metallic iron), but also FeO, in addition to the FeO obtained by reducing FeO. The reduced iron phase may also contain impurities such as oxides of elements other than iron.

[0032] The atmospheric temperature in the reduction step can be, for example, in the range of 600°C or higher and 900°C or lower. The atmospheric temperature in the reduction step refers to the atmospheric temperature in a furnace used for reduction. The atmospheric temperature in the reduction step is preferably 650°C or higher and preferably 850°C or lower.

[0033] 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 inert gas atmosphere such as N2 gas or Ar can be used.

[0034] [Crushing process] In the milling process, the reduced material is milled to obtain a milled material containing a reduced iron phase, from which at least a portion of the slag phase constituting the reduced material has been separated. The milling process, indicated by arrow c from C to D in Figure 1, separates the reduced slag phase 17 and the reduced iron phase 16 due to the impact of the milling process, as shown in Figure 1D. This milling process, followed by the sorting and recovery process described below, physically separates phosphorus. The reduced material is composed of substances with different milling characteristics, such as metals and oxides, and a phase boundary may form between the two. While the reduced iron phase and the slag phase remain bonded together as shown in Figure 1C in the as-reduced state, milling facilitates efficient separation at the interface between the reduced slag phase 17 and the reduced iron phase 16. After separation, the reduced iron phase 16 can be easily recovered in the sorting and recovery process described below. As mentioned above, Figure 1 is a conceptual diagram, and in addition to the complete separation of the reduced slag phase 17 and the reduced iron phase 16 as shown in Figure 1, it is also possible for some of the reduced slag phase 17 to remain in the reduced iron phase 16. In this embodiment, the reduced iron phase 16 completely separated from the reduced slag phase 17 and the reduced iron phase 16 with a portion of the reduced slag phase 17 remaining are collectively referred to as "reduced iron phase-containing material." The pulverization is performed using pulverization equipment such as a cage mill, a ball mill, a rotary mill, or a jet mill.

[0035] [Sorting and collection process] In the sorting and recovery step, a material containing a reduced iron phase is sorted and recovered from the pulverized material. The sorting and recovery step, indicated by the arrow d from D to E in Figure 1, yields a material containing a reduced iron phase (only reduced iron phase 16 is shown in Figure 1E as an example). Because metallic iron is magnetic, magnetic separation can be used as a method for sorting and recovery. The iron phase becomes magnetic due to the previous reduction step, making magnetic separation possible. Magnetic separation is known to have higher separation efficiency than gravity separation and other methods. Note that if the reduction step is insufficient and the reduced iron phase is primarily composed of Fe3O4, for example, the formation of a phase boundary to promote pulverization is insufficient. However, because Fe3O4 is magnetic like metallic iron, magnetic separation can still be used. This embodiment also encompasses such a configuration. The material containing a reduced iron phase may be subjected to additional processing to produce an iron source.

[0036] The magnetic separation method is not particularly limited as long as it allows separation of the reduced iron phase and the reduced slag phase. For example, hand magnetic separation is acceptable, but when large-scale processing is required, a large-scale magnetic separator such as a drum-type magnetic separator or a rotary-type magnetic separator may be used. [Example]

[0037] The present embodiment will be described in more detail below with reference to examples. The present disclosure is not limited to the following examples, and appropriate modifications can be made within the scope of the above-mentioned and below-mentioned aims, and all such modifications are within the technical scope of the present disclosure.

[0038] In the following examples, laboratory tests were conducted to remove phosphorus from iron ore and obtain a reduced iron phase containing material.

[0039] [Preparation process] Two types of iron ore, brand A and brand B, with the chemical compositions shown in Table 1 were used as the iron ore to be removed from. Both brands were produced in Australia. CaCO3 reagent manufactured by Fujifilm Wako Pure Chemical Industries, Ltd. or industrial limestone was used as the flux. In this example, the size of the iron ore and flux was adjusted using a sieve. The notation "-xx mm" (where "xx" is a number) in the "Sieve" column of Table 2 refers to the material obtained by sieving through a sieve with an opening size of xx mm, with a size of less than xx mm. The notation "xx-xx mm" (where "xx" and "xx" are numbers) refers to the material obtained by sieving through a sieve with an opening size of xx mm, with a size of less than xx mm, and remaining on the sieve after sieving through a sieve with an opening size of xx mm. The average particle size of each of the iron ore and flux in Table 2 was calculated by measuring the minimum and maximum particle sizes of the constituent particles of each of the iron ore and flux using a sieve and then averaging the minimum and maximum particle sizes.

[0040] As shown in Table 2, iron ores with various average particle sizes and fluxes were blended and mixed to obtain a mixture for roasting so that the CaO / SiO2 ratio of the mixture for roasting was 2.0. In this example, for each of iron ores of brands A and B, processes from mixing the iron ore and flux to magnetic separation were carried out under the conditions of Nos. 1 to 5, including those in Tables 2 and 3, to obtain a material containing a reduced iron phase, and the phosphorus removal rate was determined. The average value of the phosphorus removal rates for brands A and B carried out under the same conditions of Nos. 1 to 5 was taken as the phosphorus removal rate under each of the conditions of Nos. 1 to 5.

[0041] [Table 1]

[0042] [Table 2]

[0043] [Roasting process] A resistance-type electric heating furnace was used for roasting. All of the roasting mixtures No. 1 to 5 were placed in a dense MgO container manufactured by Nikkato Corporation, and roasted in an air atmosphere by heating to 1300°C (the ambient temperature inside the furnace) at a heating rate of 10°C / min and then holding at 1300°C for 30 minutes. After that, the mixtures were cooled to room temperature to obtain roasted samples.

[0044] [Reduction process] The roasted sample was crushed by hand or using a cage mill and sieved to obtain a sample for reduction with a size of less than 2 mm. Reduction was carried out using a drum-type rotary heating furnace with an inner diameter of 130 mm and a length of 200 mm. The reduction conditions were as shown in Table 3. The reducing gas was mixed at room temperature according to the gas composition shown in Table 3 and then introduced into the furnace. The reducing gas was also introduced immediately after the start of the temperature increase. The temperature was increased to the temperature shown in Table 3 at a rate of 450°C / h. After holding at the temperature shown in Table 3 for the time shown in Table 3, the sample was cooled to room temperature in a N2 atmosphere to obtain a reduced sample. Other conditions in the reduction process were as follows. Note that the above temperatures are the atmospheric temperatures inside the furnace. Rotation speed of drum type rotary heating furnace: 12 rpm Sample amount for reduction: 500g Reducing gas flow rate: 10NL / min

[0045] [Table 3]

[0046] [Crushing process] The reduced sample was pulverized at 2850 rpm using a cage mill manufactured by Masuno Seisakusho Co., Ltd. 200 g was fed into the cage mill at a time, and the sample after pulverization was fed into the cage mill again, with the entire sample passing through the cage mill a total of three times to obtain a pulverized sample.

[0047] [Sorting and recovery (magnetic separation) process] Magnetic separation was performed as a sorting and recovery method to obtain materials containing reduced iron phase. Magnetic separation was performed by loading the crushed samples into a dry drum magnetic separator. The rotation speed of the dry drum magnetic separator was 80 rpm. For each brand of iron ore, 50 g of crushed material was fed to the dry drum magnetic separator per run, and magnetic separation was performed twice. In other words, for each No. in Tables 2 and 3, magnetic separation was performed a total of four times for brand A and brand B. [evaluation] For each of Brand A and Brand B, the phosphorus content (P content) of the reduced iron phase material obtained by magnetic separation was determined according to JIS M8216 (absorptiometry). The phosphorus removal rate was calculated as an evaluation index using the following formula. The average value of the phosphorus removal rates determined for each of Brand A and Brand B was calculated. The results are shown in Table 4.

[0048]

number

[0049] [Table 4]

[0050] Laboratory tests of phosphorus removal from iron ore using the above method demonstrated that a phosphorus removal rate of 28.0% or higher could be achieved by performing roasting and reduction followed by sorting and recovery as specified in this embodiment. Figure 4 shows a graph illustrating the relationship between the average particle size of flux and iron ore and the phosphorus removal rate, as determined from the results of Tables 2 and 4 above. Figure 4 indicates that mixing iron ore with a flux having a larger average particle size tends to increase the phosphorus removal rate. Furthermore, when iron ore with an undersize particle size of less than 2 mm was used, the phosphorus removal rate was higher when the flux had an average particle size of 1 mm or more than when it was less than 1 mm. Furthermore, when the average particle size of the flux was the same, the phosphorus removal rate was even higher when iron ore with a smaller particle size, i.e., less than 0.5 mm undersize, was used than when iron ore with an undersize particle size of less than 2 mm was used.

[0051] [Microscopic observation and EDX analysis] The reason for the results shown in Figure 1 above is thought to be the coarsening of the phosphorus-enriched phase. To verify this, we conducted microscopic observation and EDX analysis using roasted samples. Specifically, for Comparative Example 1 (No. 1 in Tables 2 to 4) and Example 5 (No. 5 in Tables 2 to 4) in a laboratory test using brand B iron ore, roasted but unreduced samples were embedded in resin, cross-sections were polished, and then observed with a scanning electron microscope equipped with elemental analysis capabilities (SEM-EDX).

[0052] Scanning electron microscope images of Comparative Example 1 and Example 5 are shown in Figures 2A and 2B, respectively. The components at each of the analysis points marked with symbols 1 to 3 in Figures 2A and 2B were analyzed by EDX (energy dispersive X-ray spectroscopy). The results are shown in Figures 3A and 3B for Comparative Example 1 and Example 5, respectively. The EDX semi-quantitative analysis values ​​in Figures 3A and 3B were calculated from the amounts of each element except oxygen, assuming that each element forms an oxide as shown in the legends of Figures 3A and 3B.

[0053] The light gray phase in Figures 2A and 2B is a phase called "calcium ferrite," formed when Fe2O3 and CaO form a molten liquid with small amounts of SiO2 and Al2O3 dissolved in it. It is known that CaO, SiO2, and Al2O3 separate from iron during reduction. Therefore, even if such a phase is formed, it does not cause any problems in recovering iron. Furthermore, the results in Figures 2A, 2B, 3A, and 3B indicate that the dark gray phase in Figures 2A and 2B is a phosphorus-concentrated phase.

[0054] Comparing Figures 2A and 2B, it can be seen that the phosphorus-concentrated phase, shown as the dark gray area in Figure 2B, is coarsened by increasing the average particle size of the flux in the raw material compared to the average particle size of the iron ore. The reason for this is believed to be as follows: When a compound containing CaO is added as flux, it reacts with SiO2 in the iron ore to form a 2CaO·SiO2 compound, and phosphorus is trapped therein in the form of a 3CaO·P2O5-2CaO·SiO2 solid solution (corresponding to the phosphorus-concentrated phase described above). According to the present disclosure, by increasing the average particle size of the added flux and relatively reducing the average particle size of the iron ore, the region of the molten liquid formed during roasting is expanded. This expansion of the molten liquid region increases and coarsens the phosphorus-concentrated phase, which is a crystallized product from the molten liquid, resulting in an increased phosphorus removal rate. [Explanation of symbols]

[0055] 11. Iron Ore 12 Flux 13 Iron oxide-containing phase 14 Roasted slag phase 15 Phosphorus Transfer 16 Reduced iron phase 17 Reduced slag phase a. Roasting b. Reduction c. Crushing d. Selective collection

Claims

1. a preparation step of mixing phosphorus-containing iron ore and a raw material containing flux to prepare a roasting mixture; a roasting step of roasting the mixture to be roasted to obtain a roasted product; a reduction step of reducing the roasted product in an atmosphere containing at least one of CO gas and hydrogen gas to obtain a reduced product containing a reduced iron phase and a slag phase; a pulverization step of pulverizing the reduced material to obtain a pulverized material containing a reduced iron phase from which at least a portion of the slag phase constituting the reduced material has been separated; a sorting and recovery step of sorting and recovering the reduced iron phase-containing material from the pulverized material, The flux contains at least one selected from the group consisting of oxides, carbonates, hydroxides, and hydrates of alkali metals, and oxides, carbonates, hydroxides, and hydrates of alkaline earth metals; and The method for producing an iron source, wherein the flux has an average particle size larger than an average particle size of the iron ore.

2. The flux is CaO, CaCO ３ and Ca(OH) ２ The method for producing an iron source according to claim 1, wherein the iron source is one or more selected from the group consisting of:

3. The method for producing an iron source according to claim 1 or 2, wherein the sorting and recovery step comprises magnetic separation as a method for sorting and recovering the iron.

4. In the preparation step, the basicity of the roasting mixture is ２ 3. The method for producing an iron source according to claim 1, wherein the iron ore and the flux are mixed so that the saturation coefficient is in the range of 1.0 to 5.0.

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