US20240158886A1 - Method for producing iron ore pellets - Google Patents

Method for producing iron ore pellets Download PDF

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US20240158886A1
US20240158886A1 US18/552,247 US202118552247A US2024158886A1 US 20240158886 A1 US20240158886 A1 US 20240158886A1 US 202118552247 A US202118552247 A US 202118552247A US 2024158886 A1 US2024158886 A1 US 2024158886A1
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iron ore
dolomite
ore pellets
pellets
equal
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Hitoshi TOYOTA
Tsugunori KATO
Rikizo TADAI
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Kobe Steel Ltd
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Kobe Steel Ltd
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Assigned to KABUSHIKI KAISHA KOBE SEIKO SHO (KOBE STEEL, LTD.) reassignment KABUSHIKI KAISHA KOBE SEIKO SHO (KOBE STEEL, LTD.) ASSIGNMENT OF ASSIGNORS INTEREST (SEE DOCUMENT FOR DETAILS). Assignors: KATO, TSUGUNORI, TADAI, RIKIZO, TOYOTA, Hitoshi
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    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22B—PRODUCTION AND REFINING OF METALS; PRETREATMENT OF RAW MATERIALS
    • C22B1/00—Preliminary treatment of ores or scrap
    • C22B1/14—Agglomerating; Briquetting; Binding; Granulating
    • C22B1/24—Binding; Briquetting ; Granulating
    • C22B1/242—Binding; Briquetting ; Granulating with binders
    • C22B1/243—Binding; Briquetting ; Granulating with binders inorganic
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22B—PRODUCTION AND REFINING OF METALS; PRETREATMENT OF RAW MATERIALS
    • C22B1/00—Preliminary treatment of ores or scrap
    • C22B1/14—Agglomerating; Briquetting; Binding; Granulating
    • C22B1/24—Binding; Briquetting ; Granulating
    • C22B1/2406—Binding; Briquetting ; Granulating pelletizing
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22B—PRODUCTION AND REFINING OF METALS; PRETREATMENT OF RAW MATERIALS
    • C22B1/00—Preliminary treatment of ores or scrap
    • C22B1/02—Roasting processes
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22B—PRODUCTION AND REFINING OF METALS; PRETREATMENT OF RAW MATERIALS
    • C22B1/00—Preliminary treatment of ores or scrap
    • C22B1/14—Agglomerating; Briquetting; Binding; Granulating
    • C22B1/16—Sintering; Agglomerating
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22B—PRODUCTION AND REFINING OF METALS; PRETREATMENT OF RAW MATERIALS
    • C22B1/00—Preliminary treatment of ores or scrap
    • C22B1/14—Agglomerating; Briquetting; Binding; Granulating
    • C22B1/16—Sintering; Agglomerating
    • C22B1/20—Sintering; Agglomerating in sintering machines with movable grates
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22B—PRODUCTION AND REFINING OF METALS; PRETREATMENT OF RAW MATERIALS
    • C22B1/00—Preliminary treatment of ores or scrap
    • C22B1/14—Agglomerating; Briquetting; Binding; Granulating
    • C22B1/16—Sintering; Agglomerating
    • C22B1/216—Sintering; Agglomerating in rotary furnaces
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22B—PRODUCTION AND REFINING OF METALS; PRETREATMENT OF RAW MATERIALS
    • C22B1/00—Preliminary treatment of ores or scrap
    • C22B1/14—Agglomerating; Briquetting; Binding; Granulating
    • C22B1/24—Binding; Briquetting ; Granulating
    • C22B1/2413—Binding; Briquetting ; Granulating enduration of pellets

Definitions

  • the present invention relates to a method for producing iron ore pellets.
  • a method is well-known in which pig iron is produced by: alternately stacking, in a blast furnace, a first layer containing an iron ore material, and a second layer containing coke; and injecting an auxiliary reductant into the blast furnace from a tuyere and melting the iron ore material by using resulting hot blasts.
  • the iron ore material being supplied as iron ore pellets, is reduced, whereby the pig iron is produced.
  • the coke functions as a reduction agent and serves as a spacer to secure gas permeability.
  • the iron ore pellets need to have high reducibility in order to improve production efficiency of pig iron.
  • iron ore pellets having improved reducibility for example, iron ore pellets obtained by adding dolomite to make a CaO/SiO 2 mass ratio greater than or equal to 0.8 and a MgO/SiO 2 mass ratio greater than or equal to 0.4 are known (see Japanese Unexamined Patent Application Publication No. H1-136936).
  • the aforementioned publication further discloses that increasing porosity of the iron ore pellets can improve reducibility.
  • the present invention was made in view of the foregoing circumstances, and an objective thereof is to provide a method for producing iron ore pellets superior in reducibility and high in crushing strength.
  • the present inventors have thoroughly investigated iron ore pellets obtained by adding dolomite to increase reducibility, and found that adding dolomite treated to be present in a miniaturized state in a pellet structure prior to firing increases crushing strength. Although an exact reason is not clear, the present inventors infer that, by subjecting dolomite to a predetermined treatment, MgO derived from the dolomite is present in a miniaturized state in the iron ore pellets, whereby an effect of increasing a bonding strength of the pellet structure of the iron ore pellets is produced during firing.
  • the bonding strength of the pellet structure is considered to be increased due to the fact that: MgO being miniaturized increases reactivity of MgO and facilitates generation of a magnesioferrite compound, thus contributing to bonding of the pellet structure; and/or MgO having a low bonding strength that may be an origin of fracture of the pellet is miniaturized and less likely to be the origin of fracture.
  • a method for producing iron ore pellets used for operation of a blast furnace and in which a CaO/SiO 2 mass ratio is greater than or equal to 0.8 and a MgO/SiO 2 mass ratio is greater than or equal to 0.4 includes: balling green pellets by adding, to an iron ore material and dolomite, water for use in the balling; and firing the green pellets, in which the dolomite has a characteristic of being present in a miniaturized state in a structure of the green pellets.
  • the method for producing iron ore pellets enables increasing crushing strength of the iron ore pellets to be produced, by adding dolomite that is present in a miniaturized state in a structure of the green pellets prior to firing and produces an effect of increasing the bonding strength of the pellet structure of the iron ore pellets.
  • a CaO/SiO 2 mass ratio is greater than or equal to 0.8 and a MgO/SiO 2 mass ratio is greater than or equal to 0.4, resulting in high reducibility.
  • the method for producing iron ore pellets further includes preparing the dolomite, in which in the preparing, the dolomite is pulverized such that a Blaine specific surface area is greater than or equal to 4,000 cm 2 /g. Due to the Blaine specific surface area of the dolomite being greater than or equal to the lower limit, the dolomite is miniaturized and integrated into the pellet structure. As a result, reactivity of dolomite can be increased, and MgO can be inhibited from functioning as an origin of fracture in the iron ore pellets to be produced. Therefore, the bonding strength of the pellet structure of the iron ore pellets is increased, whereby the crushing strength of the iron ore pellets can be increased.
  • a “Blaine specific surface area” means a value obtained by measurement in accordance with JIS-R-5201:2015, and, in a case in which a target object is composed of a plurality of powders, indicates a minimum value for an individual powder.
  • the method for producing iron ore pellets further includes preparing the dolomite, wherein the dolomite is calcined at a temperature greater than or equal to 900° C. in the preparing.
  • “calcination” means a heat treatment process of heating a solid such as ore to cause thermal decomposition and phase transition, and to remove volatile components.
  • Dolomite is a carbonate mineral and represented by CaMg(CO 3 ) 2 . When dolomite is calcined, the following reaction takes place
  • dolomite is thermally decomposed.
  • water is added to MgO generated by the calcination, resulting in a transformation into Mg(OH) 2 and miniaturization (dolomite having a large grain size is reduced).
  • dolomite having a large grain size is reduced.
  • reactivity of dolomite can be increased, and MgO which is generated in the firing and can function as an origin of fracture in the iron ore pellets to be produced can be miniaturized. Therefore, the bonding strength of the pellet structure of the iron ore pellets to be produced is increased, whereby the crushing strength of the iron ore pellets can be increased.
  • the firing temperature in the firing preferably higher than or equal to 1,250° C. Due to the firing temperature in the firing being higher than or equal to the aforementioned lower limit, the crushing strength can further be increased.
  • iron ore pellets superior in reducibility and having high crushing strength can be produced.
  • FIG. 1 is a flow chart illustrating a method for producing iron ore pellets according to an embodiment of the present invention.
  • FIG. 2 is a schematic view illustrating a structure of a production apparatus used in the method for producing iron ore pellets illustrated in FIG. 1 .
  • FIG. 3 is a graph showing a grain size distribution of dolomite before and after the calcination.
  • FIG. 4 is a graph showing a relationship between the Blaine specific surface area and the crushing strength in EXAMPLES.
  • FIG. 5 is a graph showing a relationship between a rate of dolomite particles having a grain size of less than or equal to 20 m and the crushing strength in EXAMPLES.
  • the method for producing iron ore pellets illustrated in FIG. 1 includes a preparing step S 1 , a balling step S 2 , a firing step S 3 , and a cooling step S 4 .
  • the method for producing iron ore pellets is used for operation of a blast furnace, and can produce iron ore pellets 1 in which a CaO/SiO 2 mass ratio is greater than or equal to 0.8 and a MgO/SiO 2 mass ratio is greater than or equal to 0.4, by using a production apparatus with a grate kiln system (hereinafter, may be also merely referred to as “production apparatus 2 ”).
  • the production apparatus 2 includes: a pan pelletizer 3 ; a traveling grate furnace 4 ; a kiln 5 ; and an annular cooler 6 .
  • the iron ore pellets 1 are obtained by balling and firing finely pulverized ore to form agglomerated ore having a great strength.
  • a CaO-containing compound such as limestone
  • adding a CaO-containing compound such as limestone to an iron ore material to increase a CaO/SiO 2 mass ratio in the iron ore pellets 1 improves reducibility of the iron ore pellets 1 (see Patent Document 1).
  • the present method for producing iron ore pellets produces the iron ore pellets 1 having the CaO/SiO 2 mass ratio of greater than or equal to 0.8.
  • the raw materials are iron ore (iron oxide) and limestone (CaO-containing compound)
  • a calcium ferrite compound is generated by a solid phase reaction between CaO generated by the thermal decomposition and iron oxide in the firing, and is simultaneously bound through solid phase diffusion bonding at an interface thereof. Since the bonding is local, fine pores which were present prior to the firing are retained even after the firing, whereby the iron ore pellets 1 are porous bodies in which fine pores are present relatively uniformly.
  • a reducing gas enters the fine pores diffusively, whereby a reduction reaction proceeds from an outer surface to an inner portion of the iron ore pellets 1 . Due to removal of oxygen from the iron oxide by the reduction reaction, the existing fine pores are enlarged and new fine pores are generated, while metallic iron is generated. In a process of shrinkage of an external shape of the iron ore pellets 1 due to aggregation of the metallic iron, the fine pores start to decrease. As a result, diffusion of the reduction gas into the iron ore pellets 1 is suppressed, whereby the reduction is likely to stagnate.
  • the iron ore pellets to be produced are self-fluxing. Due to the iron ore pellets 1 being self-fluxing, melting down of reduced iron is likely to be accelerated. Note that the self-fluxing property of the iron ore pellets 1 is determined by an auxiliary material and/or the like.
  • dolomite is prepared.
  • the dolomite has a characteristic of being present in a miniaturized state in a structure of green pellets P to be balled in the balling step S 2 described later.
  • this characteristic is imparted to the dolomite.
  • the dolomite is pulverized such that a Blaine specific surface area is greater than or equal to a predetermined value. Note that the pulverization can be carried out by using a known pulverizer.
  • the predetermined value is preferably 4,000 cm 2 /g, and more preferably 6,000 cm 2 /g.
  • Increasing the specific surface area is considered to be substantially the same as miniaturizing the dolomite. Due to the miniaturization, reactivity of dolomite can be increased, and MgO can be inhibited from functioning as an origin of fracture in the iron ore pellets 1 to be produced. Therefore, the bonding strength of the pellet structure of the iron ore pellets 1 to be produced is increased, whereby the crushing strength of the iron ore pellets 1 can be increased.
  • an upper limit of the Blaine specific surface area of the pulverized dolomite is not particularly limited, but in view of production cost and the like, the Blaine specific surface area of the pulverized dolomite is less than or equal to 10,000 cm 2 /g.
  • a lower limit of a percentage of particles having a grain size of less than or equal to m in the pulverized dolomite is preferably 35% by volume, more preferably 45% by volume, and further preferably 55% by volume.
  • the percentage of particles having a grain size of less than or equal to 20 ⁇ m being greater than or equal to the lower limit facilitates an increase in the crushing strength of the iron ore pellets 1 .
  • the “percentage of particles having a grain size of less than or equal to 20 ⁇ m” indicates a value obtained from a grain size distribution measured by a grain size distribution measurement apparatus (Microtrac).
  • An upper limit of a D50 grain size of the pulverized dolomite is preferably 50 m and more preferably 20 m.
  • the D50 grain size of the dolomite being less than or equal to the upper limit facilitates an increase in the crushing strength of the iron ore pellets 1 .
  • the “D50 grain size” indicates a value obtained from a grain size distribution measured by a grain size distribution measurement apparatus (Microtrac).
  • green pellets P are balled by adding water for use in the balling to an iron ore material and the dolomite.
  • an auxiliary material such as limestone may be added to obtain the CaO/SiO 2 mass ratio of greater than or equal to 0.8.
  • the MgO/SiO 2 mass ratio can be adjusted mainly by the dolomite.
  • the water is added to the iron ore material and the dolomite, and then this water-containing mixture (the iron ore material and the dolomite containing the water) is charged into the pan pelletizer 3 , serving as the pelletizer, and rolled to produce the green pellets P, having a ball shape.
  • the iron ore material is a main material of the iron ore pellets 1 , and composed of powder of the iron ore (for example, powder of which at least 90% by mass of the total has a grain size of less than or equal to 0.5 mm).
  • powder of the iron ore for example, powder of which at least 90% by mass of the total has a grain size of less than or equal to 0.5 mm.
  • surface characteristics of the iron ore vary greatly depending upon a mining region and a pulverizing/transporting method, the surface characteristics of the iron ore are not particularly limited in the present method for producing iron ore pellets.
  • the water constitutes bridges between particles of the iron ore material. Strength of the green pellets P balled in the balling step S 2 is maintained due to an adhesion force acting between the particles, resulting from this bridging. In other words, a bond between the particles is expressed by means of surface tension of the water between the particles, and the adhesion force between the particles is ensured by a value obtained by multiplying the surface tension by the number of points of contact between the particles.
  • the green pellets P are fired.
  • the traveling grate furnace 4 and the kiln 5 are used.
  • the traveling grate furnace 4 has: a traveling grate 41 ; a drying chamber 42 ; a dehydrating chamber 43 : and a preheating chamber 44 .
  • the traveling grate 41 is configured to be endless, and the green pellets P placed on this traveling grate 41 can be transferred to the drying chamber 42 , the dehydrating chamber 43 , and the preheating chamber 44 , in this order.
  • the green pellets P are subjected to: drying by a heating gas G 1 ; dehydrating; and preheating, whereby preheated pellets H are obtained having strength, imparted to the green pellets P, sufficient to resist the rotation in the kiln 5 .
  • the green pellets P are dried at an atmospheric temperature of about 250° C.
  • the green pellets P after the drying are heated to about 450° C. in order to mainly decompose and remove combined water in the iron ore.
  • the preheating chamber 44 the green pellets P are heated to about 1,100° C., whereby carbonate contained in limestone, dolomite, and/or the like is degraded to remove carbon dioxide, and magnetite in the iron ore is oxidized. Accordingly, the preheated pellets H are obtained.
  • the heating gas G 1 used in the dehydrating chamber 43 is reused as the heating gas G 1 in the drying chamber 42 .
  • the heating gas G 1 in the preheating chamber 44 is reused as the heating gas G 1 in the dehydrating chamber 43
  • a combustion exhaust gas G 2 used in the kiln 5 is reused as the heating gas G 1 in the preheating chamber 44 .
  • burner(s) may be provided in each chamber to control the temperature of the heating gas G 1 .
  • burners 45 are provided in the dehydrating chamber 43 and the preheating chamber 44 .
  • the heating gas G 1 used in the drying chamber 42 is finally discharged from a smokestack C.
  • the kiln 5 is directly connected to the traveling grate furnace 4 , and is a rotary furnace having a sloped cylindrical shape.
  • the kiln 5 fires the preheated pellets H which are discharged from the preheating chamber 44 of the traveling grate furnace 4 .
  • the preheated pellets H are fired by combustion with a kiln burner (not shown in the figure) provided on an outlet side of the kiln 5 . Accordingly, high-temperature iron ore pellets 1 are obtained.
  • a lower limit of the firing temperature for firing the preheated pellets H is preferably 1,250° C., and more preferably 1,300° C. Due to the firing temperature being higher than or equal to the aforementioned lower limit, the crushing strength can further be increased.
  • the upper limit of the firing temperature is not particularly limited, and may be, for example, 1,500° C. When the firing temperature is higher than the upper limit, the effect of increasing the crushing temperature tends to be saturated and the effect may be insufficient with respect to the increase in the production cost.
  • the upper limit is more preferably 1400° C.
  • an atmosphere serving as a cooling gas G 3 used in the annular cooler 6 is used. Furthermore, the high-temperature combustion exhaust gas G 2 used for firing the preheated pellets H is sent to the preheating chamber 44 as the heating gas G 1 .
  • the cooling step S 4 the high-temperature iron ore pellets 1 obtained in the firing step S 3 are cooled.
  • the annular cooler 6 is used.
  • the iron ore pellets 1 cooled in the cooling step S 4 are accumulated and used in the blast furnace operation.
  • the iron ore pellets 1 can be cooled by blowing the atmosphere serving as the cooling gas G 3 by using a blowing apparatus 61 , while transferring the high-temperature iron ore pellets 1 discharged from the kiln 5 .
  • cooling gas G 3 which was used in the annular cooler 6 , resulting in an increase in temperature, is sent to the kiln 5 and used as the air for combustion.
  • dolomite being present in a miniaturized state in a structure of the iron ore pellets 1 and producing an effect of increasing the bonding strength of the pellet structure of the iron ore pellets 1 .
  • the dolomite is miniaturized and integrated into the pellet structure.
  • reactivity of dolomite can be increased, and MgO can be inhibited from functioning as an origin of fracture in the iron ore pellets 1 to be produced.
  • the bonding strength of the pellet structure of the iron ore pellets 1 is increased, whereby the crushing strength of the iron ore pellets 1 can be increased.
  • a CaO/SiO 2 mass ratio is greater than or equal to 0.8 and a MgO/SiO 2 mass ratio is greater than or equal to 0.4, resulting in high reducibility.
  • a method for producing iron ore pellets used for operation of a blast furnace and in which a CaO/SiO 2 mass ratio is greater than or equal to 0.8 and a MgO/SiO 2 mass ratio is greater than or equal to 0.4 includes, as illustrated in FIG. 1 : a preparing step S 1 of preparing dolomite; a balling step S 2 of balling green pellets by adding, to an iron ore material and the dolomite, water for use in the balling; a firing step S 3 of firing the green pellets; and a cooling step S 4 of cooling the high-temperature iron ore pellets obtained in the firing step S 3 .
  • the dolomite has a characteristic of being present in a miniaturized state in a structure of the green pellets.
  • the steps except for the preparing step S 1 are the same as the corresponding steps in the method for producing iron ore pellets according to the first embodiment.
  • the preparing step S 1 is described and description for the other steps is omitted.
  • the dolomite is calcined at a temperature greater than or equal to a predetermined value.
  • the present inventors have found that this treatment imparts to the dolomite a characteristic of being present in a miniaturized state in a structure of the green pellets, whereby the crushing strength of the iron ore pellets to be produced can be increased.
  • the predetermined value is preferably 900° C., and more preferably 1,100° C. Note that an upper limit of a calcination temperature is not particularly limited, but in view of production cost and the like, the calcination temperature is less than or equal to 1,500° C.
  • Dolomite is a carbonate mineral and represented by CaMg(CO 3 ) 2 .
  • CaMg(CO 3 ) 2 When dolomite is calcined, the following reaction takes place
  • FIG. 3 shows results of measurement of the grain size distribution of the calcined dolomite by a Microtrac before and after the hydration reaction. As shown in FIG.
  • a lower limit of a treatment time of the calcination is preferably 20 minutes, more preferably 50 minutes, and still more preferably 100 minutes.
  • the upper limit of the treatment time of the calcination is preferably 200 minutes and more preferably 150 minutes.
  • the treatment time of the calcination is less than the lower limit, thermal decomposition may not sufficiently proceed and the improvement in the crushing strength of the iron ore pellets may be insufficient.
  • the treatment time of the calcination is greater than the upper limit, the effect of increasing the crushing temperature tends to be saturated and the effect may be insufficient with respect to the increase in the production cost.
  • a lower limit of a percentage of particles having a grain size of less than or equal to 20 ⁇ m in the dolomite after the hydration reaction (after the balling step S 3 ) is preferably 45% by volume, and more preferably 55% by volume.
  • the percentage of particles having a grain size of less than or equal to 20 m being greater than or equal to the lower limit facilitates an increase in the crushing strength of the iron ore pellets.
  • the dolomite is present in a miniaturized state in a pellet structure prior to firing, and an effect of increasing the bonding strength of the pellet structure of the iron ore pellets is produced.
  • the crushing strength of the iron ore pellets to be produced can thus be increased.
  • a CaO/SiO 2 mass ratio is greater than or equal to 0.8 and a MgO/SiO 2 mass ratio is greater than or equal to 0.4, resulting in high reducibility.
  • the method of pulverizing the dolomite in the preparing step has been described; however, dolomite having the Blaine specific surface area greater than or equal to the predetermined value may be prepared in advance. Similarly, in the second embodiment, calcined dolomite may be prepared. In this case, the preparing step may be omitted.
  • the treatment in the preparing step is not limited to those of the aforementioned embodiments, and the dolomite may be subjected to another treatment to be present in a miniaturized state in the pellet structure prior to the firing.
  • the method of producing iron ore pellets by using the production apparatus with the grate kiln system has been described; however, the iron ore pellets may also be produced by using a production apparatus with a straight grate system.
  • the grate furnace includes a traveling grate, a drying chamber, a dehydrating chamber, a preheating chamber, and a firing chamber, and the firing step is completed only in the grate furnace.
  • the green pellets are dried, dehydrated, and preheated by a heating gas in the drying chamber, the dehydrating chamber, and the preheating chamber, and finally fired in the firing chamber.
  • Iron ore pellets in which a CaO/SiO 2 mass ratio was 1.4 and a MgO/SiO 2 mass ratio was 0.8 were produced by the procedure illustrated in FIG. 1 .
  • the Blaine specific surface area was changed by pulverization of the dolomite. Note that the firing temperature was 1,230° C. or 1,250° C.
  • the graph in FIG. 4 shows that the Blaine specific surface area of the dolomite being greater than or equal to 4,000 cm 2 /g can increase the crushing strength. It is concluded that, particularly in the case of the firing temperature being 1,250° C., the Blaine specific surface area of the dolomite being greater than or equal to 4,000 cm 2 /g enables production of the iron ore pellets having a high crushing strength of greater than or equal to 270 kg/P.
  • the CaO/SiO 2 mass ratio was 1.4 and the MgO/SiO 2 mass ratio was 0.8 in the present experiment in the present experiment, it is inferred that since the CaO/SiO 2 mass ratio of 0.8 and the MgO/SiO 2 mass ratio of 0.4, for example, increase the crushing strength, the Blaine specific surface area of the dolomite being greater than or equal to 4,000 cm 2 /g gives the crushing strength of greater than or equal to 270 kg/P even in the case in which the firing temperature is 1,230° C., by reducing the CaO/SiO 2 mass ratio and the MgO/SiO 2 mass ratio.
  • Iron ore pellets in which a CaO/SiO 2 mass ratio was 1.40 and a MgO/SiO 2 mass ratio was 0.83 were produced by the procedure illustrated in FIG. 1 .
  • the dolomite was calcined while changing the calcination condition within ranges of temperature from 900 C.° to 1,110° C. and of the treatment time from 80 minutes to 200 minutes. Note that the firing temperature was 1,230° C. or 1,250° C.
  • the graph in FIG. 5 shows that the calcination at a temperature of greater than or equal to 900° C. can increase the crushing strength. It is concluded that, particularly in the case of the firing temperature being 1,250° C., the percentage of particles having a grain size of less than or equal to 20 ⁇ m in the dolomite after the hydration reaction being greater than or equal to 45% by volume enables production of the iron ore pellets having a high crushing strength of greater than or equal to 270 kg/P.
  • the percentage of particles having a grain size of less than or equal to 20 ⁇ m being greater than or equal to 45% by volume gives the crushing strength of greater than or equal to 270 kg/P by reducing the CaO/SiO 2 mass ratio and the MgO/SiO 2 mass ratio.
  • iron ore pellets superior in reducibility and having high crushing strength can be produced. Therefore, the iron ore pellets produced by the present method for producing iron ore pellets can be used in a blast furnace operated with a low reduction agent ratio.

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US18/552,247 2021-04-01 2021-05-13 Method for producing iron ore pellets Pending US20240158886A1 (en)

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JP2021062578A JP2022158000A (ja) 2021-04-01 2021-04-01 鉄鉱石ペレットの製造方法
JP2021-062578 2021-04-01
PCT/JP2021/018288 WO2022208904A1 (ja) 2021-04-01 2021-05-13 鉄鉱石ペレットの製造方法

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