Iron source manufacturing method

Abstract

To provide an iron source production method enabling sufficient removal of phosphorus, even when the phosphorus existing in iron ore, is coupled with iron.SOLUTION: An iron source production method is provided, comprising: a preparing step of mixing iron ore including phosphorus, and raw material including flux, and preparing a 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 crushing step of crushing the reduced object thereby acquiring a crushed product including a reduced-iron-phase-containing product in which at least some of the slag phase constituting the reduced product has been separated; and a separation / recovery step of separating and recovering the reduced iron phase-containing object from the crushed object, wherein a reduction rate of the iron by the roasting is 10% or lower, and the iron source includes a compound defined as the flux.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention 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 the raw material 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 invention has been made in view of the above-mentioned problems, and an object of the present invention is to realize 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. [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 reduction rate of iron by the roasting is 10% or less, The flux is a method for producing an iron source, and includes at least one selected from the group consisting of an oxide, carbonate, hydroxide, and hydrate of an alkali metal, and an oxide, carbonate, hydroxide, and hydrate of an alkaline earth metal.

[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 a method for producing an iron source according to any one of Aspects 1 to 3, wherein the atmospheric temperature in the reduction step is 850° C. or lower.

[0014] A fifth aspect of the present invention is Aspect 5 is the method for producing an iron source according to any one of Aspects 1 to 4, 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.

[0015] A sixth aspect of the present invention is 6. The method for producing an iron source according to claim 1, wherein the reduction rate of iron after the reduction step is 50% or more.

[0016] A seventh aspect of the present invention is 7. The method for producing an iron source according to claim 1, wherein the reduced product is pulverized using a cage mill in the pulverization step.

[0017] Aspect 8 of the present invention is 8. The method for producing an iron source according to claim 1, wherein the reduction rate of iron after the reduction step is 50% or more. [Effects of the Invention]

[0018] According to the present invention, it is possible to provide a method for producing an iron source to be used in iron manufacturing or the like, which can sufficiently remove phosphorus even when phosphorus present in iron ore is bound to iron. [Brief explanation of the drawings]

[0019] [Figure 1] FIG. 1 is an image diagram that schematically shows the steps of this embodiment. [Figure 2] FIG. 2 is a scanning electron microscope image of the sample of Example 2 after grinding. [Figure 3] FIG. 3 is a diagram showing EDX analysis values ​​at analysis points 1 and 2 in FIG. [Figure 4] FIG. 4 is a diagram showing the X-ray absorption edge spectrum of the sample in the example. [Figure 5] FIG. 5 is a graph showing the relationship between each reduction temperature and the phosphorus removal rate in the examples. [Figure 6] FIG. 6 is a graph showing the relationship between the iron reduction rate and the phosphorus removal rate after the reduction step in the examples. DETAILED DESCRIPTION OF THE INVENTION

[0020] 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 reduction rate of iron by the roasting is 10% or less, The flux contains 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.

[0021] According to this embodiment, the manufacturing method involves 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 components. The reduction process then involves reducing the iron oxide while keeping the phosphorus bound to the slag components. 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, as evaluated in the examples described below, the phosphorus is bound to the slag components, specifically, captured as a complex oxide of phosphorus and calcium oxide (the complex oxide is believed to have a bonding state similar to Ca2P2O7), which is believed to enable sufficient removal of phosphorus from the iron ore.

[0022] 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 explanation of each step may be based on FIG. 1, FIG. 1 is merely an image diagram and does not limit the present invention. 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.

[0023] [Preparation process] A roasting mixture is prepared by mixing phosphorus-containing iron ore and raw materials containing flux, resulting in a roasting mixture of iron ore 11 and flux 12, as shown in FIG. 1A.

[0024] The flux contains one or more compounds selected from the group consisting of oxides, carbonates, hydroxides, and hydrates of alkali metals, and oxides, carbonates, hydroxides, and hydrates of alkaline earth metals. 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, by using SiO2 in iron ore, the aforementioned complex oxide of phosphorus and calcium oxide can be easily formed, allowing for easy immobilization of phosphorus. 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, as described above, and other fluxes. Examples of other fluxes include soda-based fluxes, CaF2, CaCl2, Li2CO3-based fluxes, and BaCO3-based fluxes. The flux size may be any size commonly used in industry.

[0025] 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. The iron ore may be crushed, classified, or the like to achieve a uniform size before mixing with the flux.

[0026] 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.

[0027] The iron ore and the flux may be mixed by an industrially used method, and if necessary, a medium such as water may be further added to the iron ore and the flux to form a granulated product as a mixture for roasting.

[0028] [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 to prevent equipment deterioration. 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.

[0029] The roasting atmosphere in this embodiment refers to an atmosphere in which the reduction rate of iron oxide by roasting (referred to herein as the "iron reduction rate") is 10% or less. In this embodiment, the reduction of iron oxide is suppressed in the roasting stage, the roasting process is separated from the reduction process, and the iron oxide is reduced in the reduction process. This separates phosphorus from the iron phase contained in or derived from iron ore (hereinafter simply referred to as the "iron phase") and prevents the incorporation of phosphorus into the iron phase. The reduction rate is preferably 8% or less, more preferably 5% or less, and may even be 0%. The aforementioned methods for achieving the reduction rate include controlling the atmosphere and temperature.

[0030] The atmosphere may be an oxygen-containing atmosphere. For example, the atmosphere may be air. In the roasting step, for example, a carbonaceous material may be used as a heat source. When this carbonaceous material is used, the atmosphere may be slightly more reducing than air, 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. may be used.

[0031] [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.

[0032] 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 binding with iron due to a reduced oxygen partial pressure, and is thought to result in maintaining the phosphorus in a chemically separated state.

[0033] 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.

[0034] 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.

[0035] 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.

[0036] 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 the furnace used for reduction. Preferably, the atmospheric temperature in the reduction step is 850°C or lower. As will be explained in the Examples below, when the atmospheric temperature was 900°C, signs of Fe-P phase formation were observed. From this, it is considered that if the temperature during reduction is too high, there is a risk that phosphorus that has migrated to and fixed in the slag phase (impurity phase) during the roasting step may recombine with the iron phase. From the viewpoint of promoting reduction, the lower limit of the atmospheric temperature in the reduction step is preferably 650°C or higher.

[0037] The reduction time can be appropriately determined depending on the amount of material to be processed. After the reduction at the above-mentioned ambient temperature is completed, the cooling to room temperature can be performed in a non-oxidizing atmosphere, and is not limited to a reducing gas atmosphere. For example, an atmosphere of N2 gas or other inert gases such as Ar can be used.

[0038] The reduction rate of the iron oxide after reduction in the reduction step (referred to herein as the "iron reduction rate") is preferably 50% or higher. It is believed that increasing the reduction rate of iron through reduction increases the proportion of reduced iron phase, which has different grinding characteristics from the reduced slag phase containing phosphorus, resulting in a reduced product with many reduced iron and reduced slag phases, i.e., metal-oxide interfaces. Furthermore, as described in detail below, in the grinding step of the reduced product, cracks are more likely to occur at the metal-oxide interfaces than at the interfaces between oxide phases, such as the iron oxide and reduced slag phases, allowing for efficient separation of the reduced iron and reduced slag phases. The reduction rate is more preferably 70% or higher, even more preferably 80% or higher, even more preferably 90% or higher, and most preferably 100%. The reduction rate can be determined by the method described in the Examples section below.

[0039] [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 between different phases may form. 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 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 in which a portion of the reduced slag phase 17 remains 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. Of these pulverization equipment, it is preferable to pulverize the reduced material using a cage mill. It is believed that pulverization using an impact-type cage mill produces a force that generates cracks at the interface between the reduced iron phase and the slag phase more efficiently than pulverization using, for example, a grinding-type ball mill.

[0040] [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.

[0041] 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]

[0042] The present invention will be described in more detail below with reference to examples. The present invention is not limited to the following examples, and can be practiced with appropriate modifications within the scope of the above-mentioned and below-mentioned aims, and all such modifications are included in the technical scope of the present invention.

[0043] In the following examples, laboratory tests were conducted to remove phosphorus from iron ore and obtain a reduced iron phase containing material.

[0044] [Preparation process] Iron ore, the target of phosphorus removal, was iron ore of brands A and B, with chemical compositions shown in Table 1. Both brands were produced in Australia. Seven laboratory tests, Nos. 1 to 7, were conducted using iron ore of brand A or B. In Nos. 1 to 5, the iron ore was sieved to less than 2 mm. In Nos. 6 and 7, the iron ore was sieved to less than 0.5 mm. Furthermore, in Nos. 1 to 5, CaCO3 reagent (less than 45 μm) manufactured by Fujifilm Wako Pure Chemical Corporation was used as the flux. On the other hand, in Nos. 6 and 7, industrial limestone (2 mm or more on the sieve, less than 4 mm on the sieve) was used as the flux. The iron ore and flux were mixed so that the CaO / SiO2 ratio of the roasting mixture was 2.0, to obtain a roasting mixture.

[0045] [Table 1]

[0046] [Roasting process] A resistance-type electric heating furnace was used for roasting. The roasting mixture was placed in a dense MgO container manufactured by Nikkato Corporation, and heated to 1300°C (furnace atmosphere temperature) at a heating rate of 10°C / min in an air atmosphere, and then held at 1300°C for 30 minutes. The mixture was then cooled to room temperature to obtain a roasted sample.

[0047] (Analysis of chemical components) The chemical composition of the roasted samples was analyzed as follows. The total iron (T.Fe) content was determined by titanium (III) chloride reduction potassium dichromate titration, the FeO content by potassium dichromate titration, and the metallic iron (M.Fe) content by bromine methanol decomposition-EDTA titration. Phosphorus was quantified according to JIS M8216 (absorption spectrophotometry). When FeO and M.Fe were found to be below the detection limit of 0.10 mass%, they were deemed to be 0.10%.

[0048] The reduction rate of iron was calculated using the following formula: The results are shown in Table 2.

[0049]

number

[0050] In the above formula, (FeO%), (T.Fe%), and (M.Fe%) represent the mass% of FeO, T.Fe, and M.Fe after each step (after roasting in Table 2, and after reduction in Table 3 described below).

[0051] [Table 2]

[0052] [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

[0053] The chemical composition of the reduced sample was analyzed in the same manner as that of the roasted sample, and the results are shown in Table 3.

[0054] [Table 3]

[0055] [Crushing process] The reduced samples were pulverized using a cage mill manufactured by Masuno Seisakusho Co., Ltd. or a ball mill manufactured by Yoshida Seisakusho Co., Ltd. When using a cage mill, the rotation speed was 2850 rpm. 200 g of sample was fed into the cage mill at a time, and the sample after being pulverized in the cage mill was fed back into the cage mill, so that the entire sample passed through the cage mill a total of three times to obtain a pulverized sample. When using a ball mill, steel balls were filled as pulverizing balls, and the mill was operated at a rotation speed of 68 rpm for 60 seconds to pulverize the sample. 140 g of sample was fed.

[0056] [Sorting and recovery (magnetic separation) process] Magnetic separation was performed as a separation and recovery method to obtain material containing reduced iron phase. Magnetic separation was performed by loading the pulverized sample into a dry drum magnetic separator. The rotation speed of the dry drum magnetic separator was 80 rpm. The amount of pulverized material fed to the dry drum magnetic separator was 50 g per run, and this was performed twice. The magnetic attraction rate was measured for each run (N1, N2) and the chemical components (T. Fe and P) were analyzed. The magnetic attraction rate was calculated using the following formula. The chemical components were also calculated in the same manner as the chemical component analysis of the roasted sample. The results are shown in Table 4.

[0057]

number

[0058] [Table 4]

[0059] Furthermore, the phosphorus removal rate and iron recovery rate were calculated using the following formula. The phosphorus removal rate and iron recovery rate were calculated using the average values ​​obtained by performing magnetic separation twice. The results are shown in Table 5.

[0060]

number

[0061]

number

[0062] [Table 5]

[0063] From the results of a laboratory test of phosphorus removal from iron ore conducted by the above-described method, a phosphorus removal rate of 15% or more could be achieved by performing sorting and recovery after the roasting step and reduction step according to the manufacturing method of this embodiment.

[0064] [Microscopic observation and EDX analysis] The sample pulverized after roasting and reduction in Example 2 was embedded in resin, the cross section polished, and then observed with a scanning electron microscope. The results are shown in Figure 2. Furthermore, the components at each of the analysis points marked with symbols 1 and 2 in Figure 2 were analyzed by EDX (energy dispersive X-ray spectroscopy). The results are shown in Figure 3. The EDX semi-quantitative analysis values ​​in Figure 3 were calculated from the amount of each element other than oxygen, assuming that each element formed an oxide as shown in the legend of Figure 3.

[0065] 2 and 3, it was confirmed that the gray area indicated by reference numeral 1 in Fig. 2 is the phosphorus-concentrated phase, and the white area indicated by reference numeral 2 in Fig. 2 is the iron phase. Furthermore, based on the results in Fig. 2 and 3 and Table 5, the reason why a high phosphorus removal rate was achieved by performing selective recovery after oxidizing roasting and reduction is thought to be that the oxidizing roasting and reduction process causes phosphorus in the iron ore to migrate to the impurity phase and fix it without bonding to iron, i.e., the phosphorus is sufficiently separated and removed chemically, and the subsequent crushing and selective recovery process separates and removes the phosphorus-containing slag phase, allowing the magnetic reduced iron phase to be recovered.

[0066] [Evaluation of the chemical bonding state of phosphorus using XAFS] The above laboratory test was conducted using brand B iron ore. Samples were taken before and after roasting, and after reduction at temperatures of 600°C, 700°C, 800°C, and 900°C. X-ray absorption fine structure (XAFS) analysis was performed using synchrotron radiation to evaluate the chemical bonding state of phosphorus. The equipment and method for XAFS measurements are described below. The results are shown in Figure 4. Similar analyses were also performed on the compounds Fe3P, Fe2P, and Ca2P2O7, which were also evaluated in Figure 4. Facility: Ritsumeikan University SR Center Beamline: BL-13 Absorption edge: P K-edge, Si K-edge, Al K-edge at room temperature Measurement method: Fluorescence method

[0067] The shoulder of the spectrum near 2145 to 2150 eV, indicated by arrow Q in Fig. 4, indicates that phosphorus forms iron phosphate in the iron ore before roasting. According to this embodiment, roasting the iron ore in the presence of flux causes the absorption of the band indicated by arrow Q to disappear, resulting in a bonding state close to Ca2P2O7, indicated by the peak shown by the solid line, i.e., phosphorus is fixed to Ca.

[0068] [About reduction temperature] 4, no energy absorption near 2145 to 2150 eV was observed in the sample reduced at a temperature of 800°C or lower, but in the sample reduced at 900°C, energy absorption was observed at the same position as the peak of the Fe-P compound indicated by arrow R, as shown by arrow Z in Fig. 4, suggesting that an Fe-P compound was formed in this sample. This shows that a reduction temperature lower than 900°C is preferable in order to suppress bonding of phosphorus with iron during reduction.

[0069] Furthermore, Fig. 5 shows a graph summarizing the relationship between the reduction temperature and the phosphorus removal rate based on the data in Tables 3 and 5. Fig. 5 shows that if the reduction temperature is too high, the phosphorus removal rate tends to decrease, and that from the perspective of achieving a higher phosphorus removal rate, for example, a higher phosphorus removal rate of about 20% or more, it is preferable to set the reduction temperature to 850°C or less.

[0070] Furthermore, Figure 6 shows a graph summarizing the relationship between the reduction rate of iron after the reduction process and the phosphorus removal rate based on the data in Tables 3 and 5. Figure 6 indicates that a reduction rate of iron after the reduction process of 50% or higher can increase the phosphorus removal rate, even achieving a higher phosphorus removal rate of approximately 20% or higher. As mentioned above, this is thought to be because, as the reduction rate increases, the proportion of reduced iron phase, which has different milling characteristics from the reduced slag phase containing phosphorus, increases. This results in a reduced product with many metal-oxide interfaces. This interface is prone to cracking during milling, allowing for efficient separation of the reduced iron phase and the reduced slag phase. Note that although No. 3 had a high reduction rate, as mentioned above, the reduction temperature was higher, resulting in a lower phosphorus removal rate than No. 2 and other samples.

[0071] 6, when the phosphorus removal rates of samples with similar reduction rates are compared, a comparison of No. 2, which has a reduction rate of approximately 90%, with Nos. 6 and 7 reveals that the phosphorus removal rate of sample No. 2 is higher. This is thought to be because, in the crushing process, the reduced material was crushed preferably using a cage mill, which efficiently generated a force that caused cracks at the interface between the reduced iron phase and the slag phase, allowing the phosphorus-containing slag phase to be sufficiently separated. [Explanation of symbols]

[0072] 1. Phosphorus-rich phase 2 Iron Phase 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, In the preparation step, the iron ore and the flux are mixed so that the basicity of the roasting mixture, CaO / SiO 2 , is in the range of 1.0 to 5.0; The atmospheric temperature in the reduction step is 900°C or less, The reduction rate of iron by the roasting is 10% or less, The method for producing an iron source, wherein the flux is at least one selected from the group consisting of an oxide, a carbonate, a hydroxide, and a hydrate of an alkali metal, and an oxide, a carbonate, a hydroxide, and a hydrate of an alkaline earth metal.

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. 3. The method for producing an iron source according to claim 1, wherein the reduction rate of iron after the reduction step is 50% or more.

5. The method for producing an iron source according to claim 1 or 2, wherein the reduced product is pulverized using a cage mill in the pulverization step.

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