Method for producing iron ore pellets

Abstract

To provide a manufacturing method of an iron ore pellet excellent in reducibility and high in collapse strength.SOLUTION: A method for manufacturing iron ore pellets according to one aspect of the present invention is used for blast furnace operation, and produces iron ore pellets having a CaO / SiO2 mass ratio of 0.8 or more and a MgO / SiO2 mass ratio of 0.4 or more. The manufacturing method comprising a granulation step of granulating raw pellets by adding granulation water to the iron ore raw materials and dolomite, and a firing step of firing the raw pellets, where the dolomite has properties of being finely divided and existing inside.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a method for producing iron ore pellets.

Background Art

[0002] As a blast furnace operation, a method is known in which a first layer containing an ore raw material and a second layer containing coke are alternately laminated in a blast furnace, and auxiliary fuel is blown into the blast furnace from a tuyere while melting the ore raw material using hot air to produce pig iron. In this pig iron production method, the ore raw material supplied as iron ore pellets is reduced to produce pig iron. At this time, the coke functions as a reducing agent and also serves as a spacer for ensuring air permeability.

[0003] The above iron ore pellets are required to have high reducibility in order to improve the production efficiency of pig iron. As iron ore pellets with enhanced reducibility, for example, dolomite is added to make the CaO / SiO 2 mass ratio 0.8 or more and the MgO / SiO 2 mass ratio 0.4 or more (see Japanese Patent Application Laid-Open No. 1-136936). The above publication also states that the reducibility can be improved by increasing the porosity of the iron ore pellets.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] Due to the increasing awareness of environmental problems in recent years, even in blast furnace operations, CO, a greenhouse gas 2It is required to reduce emissions of CO2, specifically, to operate at a low reducing agent ratio. If iron ore pellets break down in the blast furnace, it leads to a decrease in gas permeability, and it becomes necessary to charge a large amount of coke as a spacer to ensure gas permeability. If the amount of coke charged, which is also a reducing agent, increases, the reducing agent ratio becomes higher, making it difficult to operate at a low reducing agent ratio. Therefore, in order to operate at a low reducing agent ratio, the iron ore pellets are required to have high crushing strength so as not to break down.

[0006] However, the addition of dolomite tends to decrease the crushing strength, and increasing the porosity of the iron ore pellets inevitably decreases the crushing strength.

[0007] The present invention has been made in view of the above-mentioned circumstances, and an object of the present invention is to provide a method for producing iron ore pellets having excellent reducibility and high crushing strength. [Means for solving the problem]

[0008] The present inventors have intensively studied iron ore pellets with improved reducibility by adding dolomite, and have found that the crushing strength can be increased by adding dolomite that has been treated so that it is finely divided and exists in the pellet structure before firing. Although the exact reason is unclear, the present inventors speculate that by subjecting dolomite to a certain treatment, MgO originating from dolomite is finely divided and exists inside the iron ore pellets, which acts to increase the binding strength of the pellet structure of the iron ore pellets during firing. In other words, it is believed that the fineness of MgO increases the reactivity of MgO, making it easier to generate magnesioferrite compounds and contributing to the binding of the pellet structure, and / or that MgO, which has a weak binding strength and can become a starting point of pellet fracture, is finely divided and less likely to become a starting point of fracture, thereby improving the binding strength of the pellet structure.

[0009] That is, the method for producing iron ore pellets according to one embodiment of the present invention is used in blast furnace operation, and is a method for producing iron ore pellets using CaO / SiO 2 Mass ratio is 0.8 or more and MgO / SiO 2A method for manufacturing an iron ore pellet having a mass ratio of 0.4 or more, comprising a granulation step of granulating a green pellet by adding granulation water to an iron ore raw material and dolomite, and a firing step of firing the green pellet, wherein the dolomite has a property of being refined and present in the green pellet structure.

[0010] In the method for manufacturing the iron ore pellet, by adding dolomite that is refined and present in the green pellet structure before firing and that causes the binding force of the pellet structure of the iron ore pellet to increase, the crushing strength of the manufactured iron ore pellet can be increased. Further, the iron ore pellet manufactured by the method for manufacturing the iron ore pellet has a CaO / SiO 2 mass ratio of 0.8 or more and an MgO / SiO 2 mass ratio of 0.4 or more, so it has high reducibility.

[0011] The method further comprises a preparation step of preparing the dolomite, and in the preparation step, the dolomite may be pulverized so that the Blaine specific surface area is 4000 cm 2 / g or more. By setting the Blaine specific surface area of the dolomite to be equal to or greater than the above lower limit in this way, the dolomite is refined and incorporated into the pellet structure. Thereby, the reactivity of the dolomite can be enhanced, and it is possible to prevent MgO from becoming a fracture initiation point in the manufactured iron ore pellet. Therefore, the binding force of the pellet structure of the iron ore pellet can be enhanced, and the crushing strength of the iron ore pellet can be increased. Here, the "Blaine specific surface area" means a value measured in accordance with JIS-R-5201:2015, and in the case where the object is composed of a plurality of powders, it refers to the minimum value among the individual powders.

[0012] The method further comprises a preparation step of preparing the dolomite, and in the preparation step, the dolomite may be calcined at a temperature of 900 °C or higher. "Calcination" refers to a heat treatment process in which a solid such as an ore is heated to cause thermal decomposition, phase transition, or removal of volatile components. Dolomite is a carbonate mineral and is represented by CaMg(CO 3 ) 2 When the dolomite is calcined, CaCO 3 →CaO + CO 2 、MgCO 3 →MgO + CO 2 undergoes the reaction and thermally decomposes. The MgO produced by this calcination undergoes hydration at the granulation process stage and changes to Mg(OH) 2 while being refined (reduction in the size of large-sized dolomite). This enhances the reactivity of dolomite and can refine MgO that is generated in the firing process and can serve as a fracture initiation point in the produced iron ore pellets. Therefore, the binding force of the pellet structure of the produced iron ore pellets can be enhanced, and the crushing strength of the iron ore pellets can be increased.

[0013] As the firing temperature in the above firing process, 1250 °C or higher is preferable. By setting the firing temperature in the above firing process to be equal to or higher than the above lower limit, the crushing strength can be further enhanced.

Advantages of the Invention

[0014] As described above, by using the method for producing iron ore pellets of the present invention, it is possible to produce iron ore pellets having excellent reducibility and high crushing strength.

Brief Description of the Drawings

[0015]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Embodiments for Carrying Out the Invention

[0016] Hereinafter, the pig iron manufacturing method according to each embodiment of the present invention will be described.

[0017] [First Embodiment] The method for manufacturing iron ore pellets shown in FIG. 1 includes a preparation step S1, a granulation step S2, a firing step S3, and a cooling step S4. For example, as shown in FIG. 2, the method for manufacturing the iron ore pellets is used in blast furnace operation, and the CaO / SiO 2 mass ratio is 0.8 or more, and the MgO / SiO 2 iron ore pellets 1 with a mass ratio of 0.4 or more can be manufactured using a grate kiln type manufacturing apparatus (hereinafter, also simply referred to as "manufacturing apparatus 2"). The manufacturing apparatus 2 includes a pan pelletizer 3, a grate furnace 4, a kiln 5, and an annular cooler 6.

[0018] <Iron Ore Pellets> The iron ore pellets 1 are obtained by granulating fine ore and firing it into a lump ore with high strength. In the production of the iron ore pellets 1, a CaO-containing compound such as limestone is added to the iron ore raw material, and the CaO / SiO 2 When the mass ratio is increased, it is known that the reducibility of the iron ore pellets 1 is improved (see Patent Document 1). Based on this finding, in the method for manufacturing the iron ore pellets, iron ore pellets 1 with a CaO / SiO 2 mass ratio of 0.8 or more are manufactured.

[0019] When the raw materials are iron ore (iron oxide) and limestone (CaO-containing compound), in the firing process, calcium ferrite-based compounds are formed by the solid-phase reaction between CaO generated by thermal decomposition and iron oxide, and at the same time, they are bonded by solid-phase diffusion bonding at the contact points. This bonding is local, and the fine pores that existed before firing are maintained after firing, and the iron ore pellets 1 become a porous body in which the fine pores are relatively uniformly present.

[0020] During blast furnace operation, the reduction gas diffuses and penetrates into these fine pores, causing the reduction reaction to proceed from the outer surface to the interior of the iron ore pellet 1. As oxygen is removed from iron oxide by the reduction reaction, the existing fine pores expand and new fine pores are generated, while metallic iron is produced. In the process of shrinkage of the outer shape of the iron ore pellet 1 due to the aggregation of this metallic iron, the fine pores begin to decrease. As a result, the diffusion of the reduction gas into the interior of the iron ore pellet 1 is suppressed, and the reduction is likely to stagnate.

[0021] To suppress this reduction stagnation, it is effective to add a high melting point component that suppresses the disappearance of fine pores during the aggregation process of metallic iron. In particular, adding dolomite as a MgO source, which is a high melting point component, and increasing the MgO / SiO 2 mass ratio of the iron ore pellet 1 can obtain a high reduction stagnation suppression effect (see Patent Document 1). Based on this finding, in the manufacturing method of the iron ore pellet, an iron ore pellet 1 with a MgO / SiO 2 mass ratio of 0.4 or more is manufactured.

[0022] The produced iron ore pellet 1 is preferably self - fluxing. By making the iron ore pellet 1 self - fluxing in this way, the melting and dissolution of the reduced iron are likely to be promoted. Note that the self - fluxing property of the iron ore pellet 1 is determined by auxiliary raw materials and the like.

[0023] <Preparation Step> In the preparation step S1, dolomite is prepared. In the manufacturing method of the iron ore pellet, the dolomite has a property such that it is refined and exists within the structure of the green pellet P granulated in the granulation step S2 described later. In the preparation step S1, this property is imparted to the dolomite. Specifically, in the preparation step S1, the dolomite is pulverized so that the Blaine specific surface area becomes a predetermined value or more. Note that the pulverization can be performed using a known pulverizer.

[0024] As the above - mentioned predetermined value, 4000 cm 2 / g is preferable, and 6000 cm 2 / g is more preferable. Increasing the specific surface area is considered to be equivalent to substantially refining the dolomite. This refinement can enhance the reactivity of the dolomite and prevent MgO from becoming a fracture initiation point in the produced iron ore pellet 1. Therefore, the bonding strength of the pellet structure of the produced iron ore pellet 1 can be enhanced, and the crushing strength of the iron ore pellet 1 can be increased. Note that the upper limit of the Blaine specific surface area of the dolomite after pulverization is not particularly limited, but considering manufacturing costs and the like, the Blaine specific surface area of the dolomite after pulverization is 10,000 cm 2 / g or less.

[0025] In the pulverized dolomite, the lower limit of the proportion of particles with a particle size of 20 μm or less is preferably 35% by volume, more preferably 45% by volume, and even more preferably 55% by volume. When the proportion of particles with a particle size of 20 μm or less is at or above the above lower limit, it is easy to increase the crushing strength of the iron ore pellet 1. Note that the "proportion of particles with a particle size of 20 μm or less" refers to a value obtained from the particle size distribution measured by a particle size distribution measuring device (Microtrac).

[0026] The upper limit of the D50 particle size of the pulverized dolomite is preferably 50 μm, more preferably 20 μm. When the D50 particle size of the dolomite is at or below the above upper limit, it is easy to increase the crushing strength of the iron ore pellet 1. Note that the "D50 particle size" refers to a value obtained from the particle size distribution measured by a particle size distribution measuring device (Microtrac).

[0027] <Pelletizing process> In the pelletizing process S2, green pellets P are pelletized by adding granulation water to the iron ore raw material and the above dolomite. As described above, auxiliary raw materials such as limestone may be added to make the CaO / SiO 2 mass ratio 0.8 or more. The MgO / SiO 2 mass ratio can be mainly adjusted by dolomite.

[0028] Specifically, in the granulation step S2, after adding granulation water to the iron ore raw material and dolomite, this granulation water-containing mixture (iron ore raw material and dolomite containing granulation water) is put into and tumbled in a pan pelletizer 3, which is a granulator, to produce doughnut-shaped green pellets P.

[0029] The above iron ore raw material is the main raw material of the iron ore pellet 1 and is composed of iron ore powder (for example, 90% by mass or more of the whole is powder with a particle size of 0.5 mm or less). Although the surface properties of iron ore vary greatly depending on the mining area and the crushing and transportation methods, the surface properties of the iron ore in the manufacturing method of the iron ore pellet are not particularly limited.

[0030] The above granulation water forms a water-based cross-link between the particles of the iron ore raw material. The green pellets P granulated in the granulation step S2 maintain their strength due to the adhesion force acting between the particles by this cross-link. That is, the bond between the particles is manifested by the surface tension of the water existing between the particles, and the adhesion force between the particles is ensured by the value obtained by multiplying the surface tension by the number of contact points between the particles.

[0031] <Firing step> In the firing step S3, the green pellets P are fired. In the firing step S3, a grate furnace 4 and a kiln 5 are used.

[0032] (Grate furnace) As shown in FIG. 2, the grate furnace 4 includes a traveling grate 41, a drying chamber 42, a water separation chamber 43, and a preheating chamber 44.

[0033] The traveling grate 41 is configured in an endless shape, and the green pellets P placed on the traveling grate 41 can be moved in the order of the drying chamber 42, the water separation chamber 43, and the preheating chamber 44.

[0034] In the drying chamber 42, the water separation chamber 43, and the preheating chamber 44, the green pellets P are dried, water-separated, and preheated by the heating gas G1 to obtain preheated pellets H having a strength capable of withstanding tumbling in the kiln 5.

[0035] Specifically, it is carried out according to the following procedure. First, in the drying chamber 42, the green pellets P are dried at an ambient temperature of about 250°C. Next, in the water separation chamber 43, the temperature of the dried green pellets P is raised to about 450°C to decompose and remove mainly the crystal water in the iron ore. Further, in the preheating chamber 44, the temperature of the green pellets P is raised to about 1100°C to decompose the carbonates contained in limestone, dolomite, etc. to remove carbon dioxide and oxidize the magnetite in the iron ore. Thereby, the preheated pellets H are obtained.

[0036] As shown in FIG. 2, as the heating gas G1 for the drying chamber 42, the heating gas G1 used in the water separation chamber 43 is diverted. Similarly, the heating gas G1 for the water separation chamber 43 has the heating gas G1 for the preheating chamber 44 diverted, and the heating gas G1 for the preheating chamber 44 has the combustion exhaust gas G2 used in the kiln 5 diverted. By diverting the high-temperature heating gas G1 or combustion exhaust gas G2 on the downstream side in this way, the heating cost of the heating gas G1 can be reduced. Note that a burner 45 may be provided in each chamber to control the temperature of the heating gas G1. In FIG. 2, burners 45 are provided in the water separation chamber 43 and the preheating chamber 44. Further, the heating gas G1 used in the drying chamber 42 is finally discharged from the chimney C.

[0037] (Kiln) The kiln 5 is directly connected to the grate furnace 4 and is a cylindrical rotary furnace with a gradient. The kiln 5 fires the preheated pellets H discharged from the preheating chamber 44 of the grate furnace 4. Specifically, the preheated pellets H are fired by combustion by a kiln burner (not shown) disposed on the outlet side. Thereby, the high-temperature iron ore pellets 1 are obtained.

[0038] As the lower limit of the firing temperature for firing the preheated pellets H, 1250°C is preferable, and 1300°C is more preferable. By setting the firing temperature to be equal to or higher than the above lower limit, the crushing strength can be further increased. On the other hand, the upper limit of the firing temperature is not particularly limited, but for example, it can be 1500°C. If the firing temperature exceeds the above upper limit, the effect of improving the crushing strength tends to saturate, and there is a risk that the effect will be insufficient with respect to the increase in manufacturing cost. Further, from the viewpoint of reducing the amount of fusion of the iron ore pellets 1 with the increase in temperature, it is more preferable that the above upper limit be 1400°C.

[0039] In the kiln 5, as the combustion air, the atmosphere which is the cooling gas G3 used in the annular cooler 6 is used. Further, the high-temperature combustion exhaust gas G2 used for firing the preheated pellets H is sent to the preheating chamber 44 as the heating gas G1.

[0040] <Cooling process> In the cooling process S4, the high-temperature iron ore pellets 1 obtained in the firing process S3 are cooled. In the cooling process S4, the annular cooler 6 is used. The iron ore pellets 1 cooled in the cooling process S4 are aggregated and used for blast furnace operation.

[0041] In the annular cooler 6, while moving the high-temperature iron ore pellets 1 discharged from the kiln 5, the iron ore pellets 1 can be cooled by ventilating the atmosphere which is the cooling gas G3 with a ventilator 61.

[0042] Note that the cooling gas G3 whose temperature has risen and is used in the annular cooler 6 is sent to the kiln 5 and used as combustion air.

[0043] <Advantages> In the method for manufacturing the iron ore pellets, dolomite is added which is finely divided and present in the pellet structure of the iron ore pellets 1 and has the function of increasing the binding force of the pellet structure of the iron ore pellets 1. Specifically, the Blaine specific surface area of the dolomite is 4000 cm 2By setting it to / g or more, the dolomite is refined and incorporated into the pellet structure. As a result, the reactivity of the dolomite can be enhanced, and it is possible to prevent MgO from becoming a fracture initiation point in the produced iron ore pellet 1. Therefore, the bonding strength of the pellet structure of the iron ore pellet 1 can be enhanced, and the crushing strength of the iron ore pellet 1 can be increased. Further, the iron ore pellet 1 produced by the method for producing the iron ore pellet has a CaO / SiO 2 mass ratio of 0.8 or more, and MgO / SiO 2 Since the mass ratio is 0.4 or more, the reducibility is high.

[0044] [Second Embodiment] A method for producing an iron ore pellet according to another embodiment of the present invention is used for blast furnace operation, and has a CaO / SiO 2 mass ratio of 0.8 or more and a MgO / SiO 2 mass ratio of 0.4 or more. As shown in FIG. 1, it includes a preparation step S1 of preparing dolomite, a granulation step S2 of granulating green pellets by adding granulation water to the iron ore raw material and the dolomite, a firing step S3 of firing the green pellets, and a cooling step S4 of cooling the high-temperature iron ore pellets obtained in the firing step S3. Further, the dolomite has a property of being refined and present in the green pellet structure.

[0045] In the method for producing the iron ore pellet, each step except the preparation step S1 is the same as each corresponding step in the method for producing the iron ore pellet of the first embodiment. Hereinafter, the preparation step S1 will be described, and the description of the other steps will be omitted.

[0046] <Preparation Step> In the preparation step S1 of the method for producing the iron ore pellet, the dolomite is calcined at a temperature equal to or higher than a predetermined value. The present inventors have found that by this treatment, the dolomite is imparted with a property of being refined and present in the green pellet structure, and the crushing strength of the produced iron ore pellet can be increased.

[0047] As the above-mentioned specified value, 900°C is preferable and 1100°C is more preferable. Although the upper limit of the calcination temperature is not particularly limited, considering the manufacturing cost and the like, the calcination temperature is set to 1500°C or lower.

[0048] Consider the effect of increasing the crushing strength of iron ore pellets produced by calcination. Dolomite is a carbonate mineral and is represented by CaMg(CO 3 ) 2 . When dolomite is calcined, CaCO 3 →CaO + CO 2 , MgCO 3 →MgO + CO 2 reactions occur and it thermally decomposes. The MgO generated by this calcination undergoes hydration at the granulation step S3, MgO + H 2 O → Mg(OH) 2 hydration reaction occurs and it becomes magnesium hydroxide.

[0049] The inventors of the present invention have found that the hydration reaction causes the refinement of dolomite in calcined dolomite. Fig. 3 shows the results of measuring the particle size distribution of calcined dolomite before and after the hydration reaction by Microtrac. As shown in Fig. 3, before the hydration reaction, there is no significant change in the particle size distribution after calcination compared to that of dolomite after the hydration reaction without calcination. However, a change in particle size is observed, which is presumably due to a change in the crystal structure caused by the hydration reaction. For example, it can be seen that the number of particles with a large particle size exceeding 20 μm decreases, that is, the refinement progresses. This refinement enhances the reactivity of dolomite and can refine MgO that is generated in the firing process and can be a fracture initiation point in the produced iron ore pellets. Therefore, the binding force of the pellet structure of the produced iron ore pellets can be enhanced, and the crushing strength of the iron ore pellets can be increased.

[0050] As the lower limit of the roasting treatment time, 20 minutes is preferable, 50 minutes is more preferable, and 100 minutes is even more preferable. On the other hand, as the upper limit of the roasting treatment time, 200 minutes is preferable, and 150 minutes is more preferable. If the roasting treatment time is less than the above lower limit, thermal decomposition may not proceed sufficiently, and the improvement in the crushing strength of the iron ore pellets may be insufficient. Conversely, if the roasting treatment time exceeds the above upper limit, the improvement effect of the crushing strength tends to saturate, and there is a risk that the effect will be insufficient for the increase in manufacturing cost.

[0051] In the dolomite after the hydration reaction (after the granulation step S3), as the lower limit of the proportion of particles with a particle size of 20 μm or less, 45% by volume is preferable, and 55% by volume is more preferable. When the proportion of particles with a particle size of 20 μm or less is equal to or higher than the above lower limit, it is easy to increase the crushing strength of the iron ore pellets.

[0052] <Advantages> In the method for producing the iron ore pellets, by roasting the dolomite at a temperature equal to or higher than a predetermined value in the preparation step S1, the dolomite is refined and present in the pellet structure before firing, and the bonding force of the pellet structure of the iron ore pellets is increased. Thereby, the crushing strength of the produced iron ore pellets can be increased. Further, the iron ore pellets produced by the method for producing the iron ore pellets have a CaO / SiO 2 mass ratio of 0.8 or more and a MgO / SiO 2 mass ratio of 0.4 or more, so the reducibility is high.

[0053] [Other Embodiments] Note that the present invention is not limited to the above embodiments.

[0054] In the first embodiment above, only the method of crushing the dolomite so that the Blaine specific surface area becomes a predetermined value or more in the preparation step is described, and in the second embodiment above, only the method of roasting the dolomite at a temperature equal to or higher than a predetermined value in the preparation step is described, but these methods can also be used in combination.

[0055] In the above-described first embodiment, a method of crushing dolomite in the preparation step was described. However, dolomite having a Blaine specific surface area of a predetermined value or more may be prepared in advance. Similarly, in the above-described second embodiment, calcined dolomite may be prepared. In this case, the preparation step can be omitted.

[0056] Also, as described above, it is considered that the crushing strength of the iron ore pellets produced by the dolomite being refined and present in the green pellet structure before firing can be increased. Therefore, the treatment in the preparation step is not limited to the above embodiment, and other treatments such that the dolomite is refined and present in the pellet structure before firing may be performed.

[0057] In the above embodiment, a method of manufacturing iron ore pellets using a grate-kiln type manufacturing apparatus was described. However, it can also be manufactured using a straight grate type manufacturing apparatus. In the straight grate type manufacturing apparatus, the grate furnace includes a traveling grate, a drying chamber, a water separation chamber, a preheating chamber, and a firing chamber, and the firing process is completed only in the grate furnace. Specifically, in the drying chamber, the water separation chamber, and the preheating chamber, the green pellets are dried, water-separated, and preheated by the heating gas, and finally fired in the firing chamber.

Examples

[0058] Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples.

[0059] [Experiment 1] CaO / SiO 2 Iron ore pellets with a mass ratio of 1.4 and MgO / SiO 2 with a mass ratio of 0.8 were produced according to the procedure shown in FIG. 1. In the preparation step, the Blaine specific surface area was changed by crushing dolomite. The firing temperature was set to 1230 °C or 1250 °C.

[0060] The crushing strength of each of the produced iron ore pellets was measured. The results are shown in FIG. 4.

[0061] From the graph of Figure 4, it can be seen that by setting the Blaine specific surface area of dolomite to 4000 cm 2 / g or more, the crushing strength can be increased. In particular, when the firing temperature is 1250 °C, it can be said that iron ore pellets with a high crushing strength of 270 kg / P or more can be produced by setting the Blaine specific surface area of dolomite to 4000 cm 2 / g or more.

[0062] In this experiment, the mass ratio of CaO / SiO 2 in the iron ore pellets was 1.4, and the mass ratio of MgO / SiO 2 was 0.8. However, for example, when the mass ratio of CaO / SiO 2 is 0.8 and the mass ratio of MgO / SiO 2 is 0.4, the crushing strength increases. Therefore, even when the firing temperature is 1230 °C, by lowering the mass ratio of CaO / SiO 2 and / or the mass ratio of MgO / SiO 2 , it is presumed that an iron ore pellet with a Blaine specific surface area of dolomite of 4000 cm 2 / g or more and a crushing strength of 270 kg / P or more can be obtained.

[0063] [Experiment 2] Iron ore pellets with a CaO / SiO 2 mass ratio of 1.40 and a MgO / SiO 2 mass ratio of 0.83 were produced according to the procedure shown in Figure 1. In the preparation process, dolomite was calcined while changing the calcination conditions in the range of a temperature of 900 °C to 1100 °C and a treatment time of 80 minutes to 200 minutes. The firing temperature was set to 1230 °C or 1250 °C.

[0064] For each of the produced iron ore pellets, the ratio of particles with a particle size of 20 μm or less of dolomite after the hydration reaction in the granulation process and the crushing strength were measured. The results are shown in Figure 5.

[0065] From the graph of Fig. 5, it can be seen that the crushing strength can be increased by performing roasting at 900°C or higher. In particular, when the firing temperature is 1250°C, it can be said that iron ore pellets having a high crushing strength of 270 kg / P or more can be produced by setting the proportion of particles having a particle size of 20 μm or less in dolomite after the hydration reaction to 45% by volume or more. Further, even when the firing temperature is 1230°C, by reducing the CaO / SiO 2 mass ratio and / or MgO / SiO 2 mass ratio, it is presumed that a particle ratio of 45% by volume or more with a particle size of 20 μm or less and a crushing strength of 270 kg / P or more can be obtained.

Industrial Applicability

[0066] By using the method for producing iron ore pellets of the present invention, iron ore pellets excellent in reducibility and having a high crushing strength can be produced. Therefore, the iron ore pellets produced by the method for producing iron ore pellets can be suitably used in blast furnaces operating with low reducing materials.

Explanation of Symbols

[0067] 1 Iron ore pellet 2 Manufacturing apparatus 3 Pan pelletizer 4 Grate furnace 41 Traveling grate 42 Drying chamber 43 Dewatering chamber 44 Preheating chamber 45 Burner 5 Kiln 6 Annular cooler 61 Ventilation device P Green pellet H Preheated pellet G1 Heating gas G2 Combustion exhaust gas G3 Cooling gas C Chimney

Claims

1. Used in blast furnace operation, CaO / SiO ２ with a mass ratio of 0.8 or more, and MgO / SiO ２ A method for producing iron ore pellets with a mass ratio of 0.4 or more, A preparation step of preparing dolomite, A granulation step of granulating green pellets by adding granulation water to an iron ore raw material and the dolomite, A firing step of firing the green pellets, comprising: In the preparation step, the dolomite is pulverized so that the Blaine specific surface area is 4000 cm2 / g or more, and the dolomite has a property of being present in a refined state within the green pellet structure. A method for producing iron ore pellets.

2. Used in blast furnace operation, CaO / SiO ２ with a mass ratio of 0.8 or more, and MgO / SiO ２ A method for producing iron ore pellets with a mass ratio of 0.4 or more, A preparation step of preparing dolomite, A granulation step of granulating green pellets by adding granulation water to an iron ore raw material and the dolomite, A firing step of firing the green pellets, comprising: In the preparation step, the dolomite is calcined at a temperature of 900°C or higher, and the dolomite has a property of being present in a refined state within the green pellet structure. A method for producing iron ore pellets.

3. The method for producing iron ore pellets according to claim 1 or claim 2, wherein the firing temperature in the firing step is 1250°C or higher.

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