Coated raw material for direct reduction ironmaking and its manufacturing method

Abstract

Provided is a coating material that is for use in direct-reduction iron production, and that does not inhibit carburizing of obtained reduced iron. The coating material has a material containing iron oxide, and a coating layer containing particles adhering to the surface of the material. The particles contain at least one selected from the group consisting of calcium compounds and cements, and have a particle size of at least 0.010 mm. The particle size of the particles is preferably at least 0.050 mm. The adhered amount of the particles is preferably 0.10-3.00 mass% with respect to the material. The calcium compounds preferably include at least one selected from the group consisting of calcium oxide and calcium hydroxide.

Description

[Technical field]

[0001] The present invention relates to a coated feedstock for use in direct reduced iron making and a method for producing the same. [Background technology]

[0002] In recent years, against the backdrop of global environmental issues and the problem of depletion of fossil fuels, there has been a strong demand for energy conservation in steelmaking.

[0003] The raw material for iron is mainly iron oxide such as iron ore. The ironmaking process includes a reduction process to reduce the iron oxide as an essential process. The most common ironmaking process in the world is the blast furnace process, which uses a blast furnace. In the tuyere of a blast furnace, coke or pulverized coal reacts with oxygen in hot air (air heated to about 1200°C) to produce CO and H2 gas (reducing gas). The resulting reducing gas then reduces the raw materials (iron ore, etc.) in the blast furnace. Thanks to recent improvements in blast furnace operation technology, the reducing agent rate (the amount of coke and pulverized coal used per ton of molten iron produced) has been reduced to around 500 kg / t. However, the reducing agent rate has already reached its lower limit, and no further significant reduction in the reducing agent rate can be expected.

[0004] On the other hand, in recent years, the direct reduction ironmaking process (also called the "direct reduction process" or "direct ironmaking process") has been developed as an ironmaking method different from the blast furnace process. The direct reduction ironmaking process involves filling a reduction furnace (direct reduction furnace) with raw materials containing iron oxide (such as iron ore), blowing in reducing gas to reduce the raw materials and produce reduced iron, and then melting the reduced iron in an electric furnace. As the reduction furnace, a shaft furnace is mainly used. Natural gas is mainly used as a source of reducing gas. The natural gas is heated and reformed inside the thermal reformer together with the furnace top gas discharged from the top of the shaft furnace. In this way, reducing gas containing CO and H2 is generated. The resulting reducing gas is blown into the shaft furnace and reacts with the raw material (iron oxide) supplied from the top of the shaft furnace, thus reducing the raw material (iron oxide) to produce reduced iron. The produced reduced iron is cooled in a region (cooling zone) below the position where the reducing gas is blown into the shaft furnace, and is then discharged from the bottom of the shaft furnace.

[0005] The raw materials charged into the shaft furnace include lump iron ore (lump ore) and pellets (powdered iron ore solidified into a spherical shape). These raw materials often undergo clustering in the high-temperature reducing atmosphere in the shaft furnace. Clustering is a phenomenon in which these raw materials fuse together in the high-temperature reducing atmosphere in the shaft furnace to form large lumps. When clustering occurs, it may become difficult to discharge the reduced iron from the shaft furnace. In addition, the raw materials may bridge each other in the shaft furnace (also called "hanging"), hindering smooth unloading. In either case, the operability of the shaft furnace is significantly reduced.

[0006] For this reason, in normal shaft furnace operation, the maximum reduction temperature is kept low to prevent the occurrence of clustering, but this makes it difficult to sufficiently increase the reduction rate and therefore difficult to improve productivity to a satisfactory level.

[0007] Therefore, in order to suppress the occurrence of clustering, techniques have been developed for coating the surface of raw materials (such as iron ore) containing iron oxide (Patent Documents 1 to 3). Clustering is a sintering phenomenon that occurs when raw materials such as iron ore are reduced to produce reduced iron (metallic iron). It is believed that providing a coating layer on the raw materials reduces the contact surface between the resulting reduced iron particles, suppressing sintering and thereby suppressing clustering. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Japanese Unexamined Patent Publication No. 62-7806 [Patent Document 2] Japanese Patent Application Publication No. 63-262426 [Patent Document 3] International Publication No. 2015 / 16145 Summary of the Invention [Problem to be solved by the invention]

[0009] In the direct reduction ironmaking process, as mentioned above, the reduced iron produced by reduction in a reduction furnace is melted in an electric furnace. Therefore, carburization (addition of carbon) of the reduced iron is essential to improve the efficiency of the electric furnace operation. In other words, by carburizing the reduced iron, the melting point of the reduced iron is lowered; the iron oxide remaining in the reduced iron is reduced; and when melting in an electric furnace, oxygen is blown in to burn the carbon, generating a lot of energy and shortening the melting time.

[0010] Specifically, the carburization of the reduced iron is carried out, for example, by flowing a carburizing gas (such as CH4) in a cooling zone in the lower part of a shaft furnace. However, when a coated raw material having a coating layer (Patent Documents 1 to 3) is used as a raw material for reduced iron, the coating layer acts as a barrier and may inhibit carburization of the resulting reduced iron.

[0011] The present invention has been made in consideration of the above-mentioned points, and an object of the present invention is to provide a coated raw material for use in direct reduction ironmaking, in which carburization of the resulting reduced iron is not inhibited, and a method for producing the same. [Means for solving the problem]

[0012] As a result of extensive investigations, the present inventors have found that the above object can be achieved by employing the following configuration, and have completed the present invention.

[0013] That is, the present invention provides the following [1] to [8]. [1] A coated raw material for use in direct reduction iron making, comprising: a raw material containing iron oxide; and a coating layer containing particles adhered to a surface of the raw material, the particles containing at least one type selected from the group consisting of calcium compounds and cement and having a particle size of 0.010 mm or more. [2] The coating material according to [1] above, wherein the particle size of the particles is 0.050 mm or more. [3] The coated raw material according to [1] or [2] above, wherein the amount of the particles adhering to the raw material is 0.10% by mass or more and 3.00% by mass or less. [4] The coating material according to any one of the above [1] to [3], wherein the calcium compound contains at least one selected from the group consisting of calcium oxide and calcium hydroxide. [5] A method for producing a coated raw material for use in direct reduction iron making, comprising the steps of: suspending particles containing at least one type selected from the group consisting of calcium compounds and cement and having a particle size of 0.010 mm or more in water to produce a slurry-like treatment liquid; coating the surface of a raw material containing iron oxide with the treatment liquid; and heating the raw material coated with the treatment liquid to remove water contained in the treatment liquid. [6] The method for producing a coated raw material according to [5] above, wherein the particle size of the particles is 0.050 mm or more. [7] The method for producing a coated raw material according to [5] or [6] above, wherein the calcium compound contains at least one selected from the group consisting of calcium oxide and calcium hydroxide. [8] The method for producing a coated raw material according to any one of [5] to [7] above, wherein the treatment liquid is applied to the surface of the raw material by immersion or spraying. Effect of the Invention

[0014] According to the present invention, it is possible to provide a coated raw material for use in direct reduction ironmaking, which does not inhibit carburization of the resulting reduced iron, and a method for producing the same. [Brief description of the drawings]

[0015] [Figure 1]FIG. 2 is a block diagram showing a facility for producing coated raw material together with a shaft furnace for reducing the coated raw material. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] [Coating materials] The coated raw material of the present invention is a coated raw material used in direct reduction ironmaking, which comprises a raw material containing iron oxide and a coating layer containing particles adhered to the surface of the raw material, the particles containing at least one type selected from the group consisting of calcium compounds and cement and having a particle size of 0.010 mm or more.

[0017] <Raw materials> The coated raw material of the present invention has a raw material containing iron oxide (hereinafter simply referred to as "raw material"). The raw material is, for example, iron ore, and specific examples thereof include lump iron ore (lump ore) and pellets (iron ore powder solidified into a spherical shape). The grade (iron content) of the iron ore used as the raw material is not particularly limited, but from the viewpoint of reduction in a shaft furnace, it is generally preferably 65 mass % or more.

[0018] <Coating layer> The coated feedstock of the present invention further comprises a coating layer adhered to the surface of the feedstock. The coating layer includes particles as described below.

[0019] <Types of particles> The particles contained in the coating layer contain at least one type selected from the group consisting of calcium compounds and cement.

[0020] (Calcium compounds) Examples of calcium compounds include calcium oxide, calcium hydroxide, and Ca x Fe y O z Among them, at least one selected from the group consisting of calcium oxide and calcium hydroxide is preferred. When calcium hydroxide is used as the calcium compound, it becomes calcium oxide when it is heated and a dehydration reaction occurs during the production process of the coating raw material, as described below. Even if a dehydration reaction does not occur during the process of producing the coated raw material, the inside of a reduction furnace such as a shaft furnace is at 700°C to 1000°C, so a dehydration reaction easily occurs and most of the calcium hydroxide becomes calcium oxide.

[0021] (cement) Examples of cement include self-hardening cement (Portland cement); latent hydraulic cement (such as blast furnace cement); fine powders of blast furnace slag, blast furnace slag, and steel slag; and among these, Portland cement is preferred. Examples of Portland cement include ordinary Portland cement, high-early-strength Portland cement, and high-strength Portland cement. These contain a large amount of 3CaO·SiO2, which shows a strong hydration reaction, and have excellent hydraulic properties, so they have good adhesion to raw materials (iron ore, etc.). They are also cheap and easily available.

[0022] (Other Ingredients) The particles contained in the coating layer may further contain magnesium compounds such as magnesium oxide and magnesium hydroxide; aluminum compounds such as aluminum oxide and aluminum hydroxide; silicas; iron oxide; and the like.

[0023] Particle size The particle size of the particles contained in the coating layer is 0.010 mm or more. The reason for this is explained below.

[0024] As mentioned above, calcium oxide (CaO) can be easily produced by the dehydration reaction of calcium hydroxide. It is also contained in cement such as Portland cement. Calcium oxide (CaO) consumes carburizing gas (CH4) by inducing the reaction represented by the following formula (1), which causes the reaction represented by the following formula (2) (carburizing reaction) to stagnate, inhibiting the carburization of reduced iron. 3CH4+CaO→CaC2+CO+6H2...(1) CH4 → C + 2H2 (2)

[0025] The reaction of formula (1) above occurs on the surface of calcium oxide (CaO) particles. When the particle size of calcium oxide (CaO) particles on the surface of reduced iron is small, the reaction area per unit mass increases, the reaction of formula (1) above is accelerated, and the amount of carburizing gas (CH4) present near the reduced iron decreases. This causes the rate of diffusion of the carburizing gas (CH4) to become limited, and the reaction of formula (2) above stagnates.

[0026] Therefore, the particle size is increased, which reduces the reaction area per unit mass and suppresses the reaction of formula (1) above, and as a result, the stagnation of the reaction of formula (2) above can be avoided. In other words, the carburization of reduced iron is not inhibited. Furthermore, the larger the particle size, the greater the porosity of the gaps between the reduced iron and the particles, making it easier for the carburizing gas (CH4) to diffuse to the surface of the reduced iron, and making it easier for the carburizing reaction of formula (2) to occur.

[0027] For these reasons, the particle size of the particles contained in the coating layer is 0.010 mm or more, preferably 0.050 mm or more, and more preferably 0.100 mm or more.

[0028] There is no particular upper limit to the particle size of the particles contained in the coating layer. However, calcium oxide and other components of the particles are impurities in reduced iron, and if the particle size is too large, the proportion of impurities increases, which may result in a decrease in the quality (iron purity) of the reduced iron obtained. Therefore, from the viewpoint of improving the quality of the obtained reduced iron, the particle size of the particles contained in the coating layer is, for example, 3.000 mm or less, preferably 1.000 mm or less, more preferably 0.800 mm or less, and even more preferably 0.200 mm or less.

[0029] <Amount of particle adhesion> If the amount of particles contained in the coating layer is too small, it is difficult to obtain the effect of suppressing clustering. Therefore, in order to obtain excellent resistance to clustering, the amount of particles attached is preferably 0.03 mass% or more, more preferably 0.07 mass% or more, and even more preferably 0.10 mass% or more, based on the raw material.

[0030] On the other hand, if the coating layer contains too many particles, the reaction of the above formula (1) may proceed excessively, and the amount of carburizing gas (CH4) may become insufficient, inhibiting the reaction of the above formula (2). In addition, the reducibility of the raw material may decrease, which may result in a decrease in productivity. For this reason, the amount of attached particles is preferably 8.00% by mass or less, more preferably 5.50% by mass or less, and even more preferably 3.00% by mass or less, based on the raw material.

[0031] [Method of manufacturing the coated raw material] Next, a method for producing the above-mentioned coated raw material of the present invention will be described with reference to FIG. FIG. 1 is a configuration diagram showing a facility for producing coated raw material, together with a shaft furnace 7 for reducing the coated raw material. The facility for producing coated raw material generally comprises a raw material tank 1, a coating treatment tank 3, a heating furnace 5, and a dehydration furnace 6, as shown in FIG.

[0032] Raw material is stored in the raw material tank 1. The raw material is, for example, iron ore such as pellets or lump ore. Below the raw material tank 1, a charging conveyor 2 is installed. The input conveyor 2 carries the raw material supplied from the raw material tank 1 up to a drop-in position above the coating treatment tank 3. The coating treatment tank 3 stores a treatment liquid containing the above-mentioned particles.

[0033] The above-mentioned particles are suspended in water in advance to prepare a slurry-like treatment liquid, which is then stored in the coating treatment tank 3 . As mentioned above, the calcium compounds constituting the particles include calcium oxide, calcium hydroxide, calcium iron compounds (Ca x Fe y O zCalcium oxide reacts with water to form calcium hydroxide. The type of cement constituting the particles is also as described above.

[0034] The particle size of the particles in the treatment liquid does not change in the steps described below (the step of coating the surface of the raw material with the treatment liquid, and the step of heating the raw material whose surface is coated with the treatment liquid). Therefore, for example, when the particle size of the particles contained in the coating layer of the finally obtained coating raw material is to be 0.010 mm or more, the particle size of the treatment liquid is also to be 0.010 mm or more.

[0035] The concentration of the particles in the treatment liquid is not particularly limited, and is appropriately adjusted depending on the desired amount of adhesion.

[0036] The raw material fed from the feeding conveyor 2 to the coating treatment tank 3 is immersed in the treatment liquid. This results in a raw material whose surface is coated with the treatment liquid (hereinafter referred to as "treated raw material"). The method for coating the surface of the raw material with the treatment liquid is not limited to the immersion method, and for example, a method using spraying (spray method) may be used. However, the dipping method is preferred because it allows the coating layer to be formed uniformly and the amount of coating to be easily controlled.

[0037] The treated raw material is carried out to the heating furnace 5 by the carrying-out conveyor 4a, and is heated (dried) in the heating furnace 5. In this way, moisture in the treated raw material (particularly the processing liquid that covers the raw material) is evaporated and removed. The method for heating the treated raw material is not particularly limited, and examples thereof include methods using steam heating, electric heating, microwaves, and induction current. The heating temperature in the heating furnace 5 is preferably 100°C or higher from the viewpoint of evaporating moisture from the treated raw material. The atmospheric gas inside the heating furnace 5 is preferably a gas with a low CO2 concentration, and more preferably a gas with a CO2 concentration of 1000 ppm by volume or less (e.g., inert gas, air, combustion gas from which CO2 has been removed, heated steam, etc.).

[0038] The treated raw material is heated in the heating furnace 5, and then transported by the discharge conveyor 4b to the dehydration furnace 6, where it is further heated. Heating in the dehydration furnace 6 causes a dehydration reaction represented by the following formula (3) to form a dense and porous coating layer. In this way, a coated raw material is obtained in which the coating layer is attached to the surface of the raw material. Since the reaction of the following formula (3) proceeds at 580° C. under atmospheric pressure, the heating temperature in the dehydration furnace 6 is preferably 580° C. or higher. Ca(OH)2 →CaO+H2O (3)

[0039] [Direct reduction ironmaking] The coating raw material is then transported to a vertical shaft furnace 7, and reduced by a reducing gas while descending from a furnace top 7a of the shaft furnace 7. Below, we will explain the MIDREX process, a representative direct reduction ironmaking process.

[0040] The shaft furnace 7 is equipped with a gas outlet 8 and a gas inlet 9 . The gas inlet 9 is provided at approximately the middle position in the vertical direction of the shaft furnace 7, and supplies reducing gas into the shaft furnace 7. Examples of the reducing gas that can be used include natural gas; reformed gas obtained by reforming natural gas and containing CO and H2 as main components; and coal gas (gas generated when coal is gasified). The composition of the reformed gas is, for example, a total concentration of H2 and CO of about 90 mol %, a molar ratio of H2 / (H2+CO) of 0.52 to 0.71, and a CO2 concentration of 0.5 to 3.0 mol %. The temperature of the reducing gas blown in from the gas blowing port 9 is, for example, 700° C. to 1200° C. The reducing gas reduces the coating raw material charged from the furnace top part 7a, and is then exhausted from the gas exhaust port 8 as exhaust gas.

[0041] A gas inlet 12 and a gas suction port 11 are provided in the cooling zone 7b at the lower part of the shaft furnace 7. Cooling gas and carburizing gas are blown into the shaft furnace 7 from the gas inlet 12. The gas suction port 11 sucks these gases so that they do not enter the furnace top portion 7a. The reduced iron produced by reducing the coating raw material is cooled by the cooling gas in the cooling zone 7b and carburized by the carburizing gas. The cooling gas is generally N2, and the carburizing gas is mainly CH4, which may contain CO.

[0042] A reduced iron discharge port 13 is provided at the bottom of the shaft furnace 7. The reduced iron 14 after being cooled and carburized is discharged from a reduced iron discharge port 13 .

[0043] As a measure against clustering, a cluster breaker 10 is installed inside the shaft furnace 7 to mechanically break up any clusters that are generated.

[0044] As described above, a method using a shaft furnace 7 has been described as a direct reduction ironmaking process. However, the type of reduction furnace (direct reduction furnace) is not limited to this, and a method using a fluidized bed, a rotary kiln, a rotary hearth furnace (RHF), or the like may also be used. EXAMPLES

[0045] The present invention will be specifically described below with reference to examples, although the present invention is not limited to the examples described below.

[0046] <Raw materials> The raw iron ore used was pellets from Brazil with a particle size of 10.0 to 15.0 mm. The pellets had the following composition by mass: T.Fe: 66%, FeO: 0.63%, SiO2: 2.0%, CaO: 2.1%, Al2O3: 0.5%, MgO: 0.16%.

[0047] Processing Solution Commercially available calcium hydroxide and cement (Portland cement) were pulverized to the particle size ranges shown in Table 1 below, and the resulting particles were suspended in water at the concentrations shown in Table 1 below to prepare a slurry-like treatment liquid.

[0048] <Coating materials> 500 g of raw material (pellets) was weighed and immersed in the treatment liquid for 30 seconds to obtain a treated raw material. The obtained treated raw material was heated in a heating furnace set at 80° C. for 30 minutes and dried. When a treatment liquid containing calcium hydroxide particles was used, after immersion and drying, the sample was further heated in a dehydration furnace set at 600° C. for 1 hour. In this manner, moisture was removed from the treated raw material to obtain a coated raw material.

[0049] The obtained coated raw material was mechanically polished to expose a cross section. The cross section of the coated raw material was observed at a magnification of 300 times using a SEM (scanning electron microscope) to obtain an SEM image. For the obtained SEM images, the particle diameter (circle equivalent diameter) of the particles adhering to the surface of the raw material was measured, and the average value of 10 particles was taken as the particle diameter of the particles contained in the coating layer.

[0050] Furthermore, the adhesion amount of particles contained in the coating layer (adhesion amount relative to the raw material) was calculated from the difference in mass between the raw material before immersion in the treatment liquid and the finally obtained coated raw material.

[0051] <Amount of carburization> In order to simulate the direct reduction ironmaking process described with reference to FIG. 1, tests were carried out in which the coated raw material was reduced and then carburized using a TG (thermogravimetry) furnace. Specifically, 500 g of the coating raw material was filled into a carbon crucible with a diameter of 80 mm, and reducing gas (CO: 35 vol%, H2: 55 vol%, N2: 10 vol%, gas flow rate: 15 NL / min) was flowed from the bottom of the furnace at a constant temperature of 900°C until the reduction rate reached 100%, obtaining reduced iron. After that, carburizing gas (CH4: 100 vol%, gas flow rate: 5 NL / min) was flowed to carburize the reduced iron. The carbon content in the reduced iron before and after carburization was measured by the infrared absorption method specified in JIS G 1211-3 "Iron and steel - Carbon determination method", and the amount of carbon increased by carburization (amount relative to reduced iron) was calculated as the amount of carburization (unit: mass%). It can be evaluated that the larger the amount of carburization, the more the inhibition of carburization is suppressed.

[0052] The reduction rate was calculated by the following formula. [Reduction rate (unit: %)] = {([Amount of oxygen in coated raw material before reduction (unit: mass%)] - [Amount of oxygen in reduced iron (unit: mass%)]) / [Amount of oxygen in coated raw material before reduction (unit: mass%)]} x 100 The amount of oxygen in the coating raw material was determined as follows. First, chemical analysis was performed to quantify the total Fe and FeO in the coating raw material. Next, Fe2O3 in the coating raw material was quantified by subtracting the Fe in FeO from the total Fe, assuming that the amount was the Fe in Fe2O3. The total amount of oxygen in FeO and Fe2O3 was then determined to be the amount of oxygen in the coating raw material. The amount of oxygen in the reduced iron was determined as follows. First, chemical analysis was performed to quantify T.Fe, FeO, and M.Fe in the reduced iron. Next, Fe3O4 in the reduced iron was quantified by subtracting the Fe in FeO and M.Fe from T.Fe, assuming that the amount is the Fe in Fe3O4. The total amount of oxygen in FeO and Fe3O4 was then determined to be the amount of oxygen in the reduced iron.

[0053] In Table 1 below, symbols such as "◎" are listed according to the amount of carburization. "◎", "○", and "○" are used because the inhibition of carburization is suppressed. - " or "△" is preferred. ◎: Carburized amount is 4% or more by mass ○: Carburization amount is 3 mass% or more and less than 4 mass% ○ - Amount of carburization is 2% or more and less than 3% by mass △: Carburized amount is 1% or more and less than 2% by mass ×: Amount of carburization is less than 1% by mass

[0054] <Clustering resistance> In order to evaluate the clustering resistance of the coating material, a reduction test was carried out using a load-softening tester. Specifically, 500 g of the coating raw material was placed in a carbon crucible with a diameter of 100 mm, and reducing gas (CO: 35% by volume, H2: 55% by volume, N2: 10% by volume, gas flow rate: 15 NL / min) was fed from the bottom of the furnace at a constant temperature of 900°C, and 1.5 kg / cm 2 The reduction was carried out while applying a load of 100% until the reduction rate reached 100%. The reduced iron clusters generated after the test were crushed using an I-type rotary tester and rotated 150 times at 30 rpm. The ratio of the mass of the +15 mm sieve to the total mass of the sample was then calculated as the cluster ratio (unit: %). The smaller the cluster ratio value, the better the clustering resistance can be evaluated.

[0055] In the following Table 1, symbols such as "◎" are used according to the value of the cluster ratio. "◎", "◯" and "△" are preferred because of their excellent resistance to clustering. ◎: Cluster ratio is less than 5% ○: Cluster ratio is 5% or more but less than 10% △: Cluster ratio is between 10% and 30% ×: Cluster ratio is 30% or more

[0056] [Table 1]

[0057] <Summary of evaluation results> As is clear from the results shown in Table 1 above, the coated raw materials Nos. 7 to 28, in which the particle size of the particles contained in the coating layer was 0.010 mm or more, had less inhibition of carburization in the obtained reduced iron, compared to the coated raw materials Nos. 1 to 6, which did not satisfy this requirement. Furthermore, the coated raw materials Nos. 7 to 28 also had good resistance to clustering.

[0058] Looking at the coating materials No. 7 to 28, there was a tendency for the effect of suppressing the inhibition of carburization to be excellent in the following order: No. 7 to 12, which have a particle size of 0.010 mm or more (less than 0.050 mm), No. 13 to 18, which have a particle size of 0.050 mm or more (less than 0.100 mm), and No. 19 to 28, which have a particle size of 0.100 mm or more.

[0059] Looking at the coated raw materials Nos. 7 to 12, the coated raw materials Nos. 9 to 12, which have particle adhesion amounts of 0.10 mass % or more, had better clustering resistance than the coated raw materials Nos. 7 to 8, which did not satisfy this requirement. On the other hand, the coated raw materials Nos. 7 to 10, in which the amount of attached particles was 3.00 mass % or less, were more effective in suppressing the inhibition of carburization than the coated raw materials Nos. 11 to 12, which did not satisfy this requirement. The same was true for the coated raw materials Nos. 13-18, 19-24, and 25-28. [Explanation of symbols]

[0060] 1: Raw material tank 2: Input conveyor 3: Coating treatment tank 4a, 4b: Unloading conveyor 5:Heating furnace 6: Dehydration furnace 7: Shaft furnace 7a: Furnace top 7b: Cooling zone 8: Gas exhaust port 9: Gas inlet 10: Cluster Breaker 11: Gas suction port 12: Gas inlet 13: Reduced iron outlet 14: Reduced iron

Claims

1. A raw material containing iron oxide; A coating layer including particles attached to a surface of the raw material, The particles contain at least one kind selected from the group consisting of a calcium compound and a cement, and have a particle size of 0.010 mm or more and 1.000 mm or less.

2. 2. The coating material according to claim 1, wherein the particles have a diameter of 0.050 mm or more.

3. 3. The coated raw material according to claim 1, wherein the amount of the particles attached is 0.10% by mass or more and 3.00% by mass or less with respect to the raw material.

4. 3. The coating material according to claim 1, wherein the calcium compound contains at least one selected from the group consisting of calcium oxide and calcium hydroxide.

5. The coating material according to claim 3, wherein the calcium compound contains at least one selected from the group consisting of calcium oxide and calcium hydroxide.

6. 1. A method for producing a coated feedstock for use in direct reduced iron making, comprising the steps of: Particles containing at least one selected from the group consisting of a calcium compound and cement and having a particle size of 0.010 mm or more and 1.000 mm or less are suspended in water to prepare a slurry-like treatment liquid; The treatment liquid is applied to a surface of a raw material containing iron oxide, The method for producing a coated raw material comprises heating the raw material coated with the treatment liquid to remove moisture contained in the treatment liquid.

7. The method for producing a coated raw material according to claim 6, wherein the particle size of the particles is 0.050 mm or more.

8. 8. The method for producing a coated raw material according to claim 6, wherein the calcium compound contains at least one selected from the group consisting of calcium oxide and calcium hydroxide.

9. 8. The method for producing a coated raw material according to claim 6, wherein the treatment liquid is coated on the surface of the raw material by using a dipping method or a spraying method.

10. The method for producing a coated raw material according to claim 8, wherein the treatment liquid is coated on the surface of the raw material by using a dipping method or a spraying method.

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