Dephosphorization method for ore

Abstract

A dephosphorization method for an ore according to one embodiment of the present disclosure includes a step in which the ore is heated at a temperature of 100°C or higher in a kiln-type or fluidized-bed heating furnace. Preferably, in the step of heating the ore, a reducing gas or a non-reducing gas is supplied to the inside of the heating furnace. Preferably, the heating furnace is composed of a first heating furnace and a second heating furnace, the non-reducing gas is supplied to the first heating furnace, the reducing gas is supplied to the second heating furnace, and in the heating step, the ore is supplied to the first heating furnace and heated and the ore heated in the first heating furnace is subsequently supplied to the second heating furnace and heated.

Description

TITLE OF INVENTION: DEPHOSPHORIZATION METHOD FOR ORE TECHNICAL FIELD

[0001] The present invention relates to a dephosphorization method for removing phosphorus contained in an ore. BACKGROUND ART

[0002] Phosphorus contained in sintered ore as a steelmaking raw material for a blast furnace is one of important components in terms of quality control of molten iron produced in the blast furnace. Phosphorus has high affinity for iron. Therefore, when a steel material is produced from the sintered ore through the molten iron, phosphorus is likely to remain in the steel material. Phosphorus remaining in the steel material may cause low-temperature brittle fracture of the steel material and impair the quality of the steel material.

[0003] As a method for reducing phosphorus contained in iron ore, in Non Patent Document 1, phosphorus is removed as a gas by supplying a hydrogen-steam mixed gas to iron ore containing phosphorus and reducing the iron ore. In addition, in Patent Document 1, a phosphorus compound is reduced, vaporized, and removed by supplying, to high-phosphorus iron ore, a gas present in a P2 gas equilibrium region and an FeO equilibrium region in a CO gas reduction equilibrium diagram of iron oxide and diphosphorus pentoxide, an H2 gas reduction equilibrium diagram of iron oxide and diphosphorus pentoxide, and / or a CO-H2 mixed gas reduction equilibrium diagram of iron oxide and diphosphorus pentoxide, and reducing the high-phosphorus iron ore. Citation List Patent Document

[0004] Patent Document 1: Japanese Unexamined Patent Application, First Publication No. 2020-20010 Non Patent Document

[0005] Non Patent Document 1: “Direct Dephosphorization from Iron Ore Containing Higher Concentration of Phosphorus”, Tetsu-to-Hagane, Vol. 100 (2014), No. 2, pp. 325 to 330. SUMMARY OF INVENTION Technical Problem

[0006] An object of the present invention is to provide a dephosphorization method for removing phosphorus contained in ore. Solution to Problem

[0007] The gist of the present invention is as follows. (1) A dephosphorization method for ore according to the present disclosure includes: heating ore at a temperature of 100°C or higher in a kiln-type or fluidized-bed-type heating furnace. (2) Preferably, in the dephosphorization method for ore according to (1), during the heating of the ore, a reducing gas is supplied into the heating furnace. (3) Preferably, in the dephosphorization method for ore according to (1) or (2), during the heating of the ore, a non-reducing gas is supplied into the heating furnace. (4) Preferably, in the dephosphorization method for ore according to any one of (1) to (3), the heating furnace includes a first heating furnace and a second heating furnace, a non-reducing gas is supplied to the first heating furnace, a reducing gas is supplied to the second heating furnace, and in the heating, the ore is first supplied to the first heating furnace and heated, and then the ore heated in the first heating furnace is supplied to the second heating furnace and heated. (5) Preferably, the dephosphorization method for ore according to (4) further includes: classifying the ore into a coarse fraction and a fine fraction finer than the coarse fraction after the ore is heated in the first heating furnace and before the ore is supplied to the second heating furnace, in which the coarse fraction is excluded from the ore supplied to the second heating furnace. (6) Preferably, in the dephosphorization method for ore according to (5), in the classifying the ore after the ore is heated in the first heating furnace and before the ore is supplied to the second heating furnace, a sieving device having a sieve opening of 0.5 mm or more and 3.0 mm or less is used. (7) Preferably, the dephosphorization method for ore according to any one of (1) to (6) further includes: before the heating the ore in the heating furnace, classifying the ore into a coarse fraction and a fine fraction using a sieving device having a sieve opening of 3.0 mm or more and 5.0 mm or less, in which the kiln-type heating furnace is used as the heating furnace, only the coarse fraction is supplied to the heating furnace, and a heating temperature of the coarse fraction in the heating furnace is 400°C or higher. (8) Preferably, in the dephosphorization method for ore according to any one of (1) to (7), there are two or more types of ore, the ore contains goethite, the dephosphorization method further includes, before the heating the ore in the heating furnace, selecting the ore having a highest phosphorus concentration in the goethite, and the ore having the highest phosphorus concentration in the goethite is preferentially supplied to the heating furnace. (9) Preferably, in the dephosphorization method for ore according to any one of (1) to (8), the ore contains goethite, and only the ore having a phosphorus concentration in the goethite of 1.0% by mass or more is supplied to the heating furnace. Advantageous Effects of Invention

[0008] According to the present invention, phosphorus contained in ore can be separated from the ore. BRIEF DESCRIPTION OF DRAWINGS

[0009] [FIG. 1] A diagram showing an example of equipment for carrying out a dephosphorization method. [FIG. 2] A diagram showing another example of the equipment for carrying out the dephosphorization method. [FIG. 3] A diagram showing still another example of the equipment for carrying out the dephosphorization method. [FIG. 4] A diagram showing still another example of the equipment for carrying out the dephosphorization method. DESCRIPTION OF EMBODIMENTS

[0010] A dephosphorization method for ore according to an embodiment of the present disclosure is a dephosphorization method for ore, in which the ore is heated in a heating furnace of a kiln-type or a fluidized-bed-type at a temperature of 100°C or higher. By heating the ore in the heating furnace of a kiln-type or a fluidized-bed-type, a physical impact is applied to the ore. In this manner, fine powder containing phosphorus is separated from the ore. Phosphorus can be removed from the ore by physically separating the fine powder containing phosphorus from the ore. Here, the "physical impact" is an impact applied to the ore by causing the ore to flow. In addition, the "fine powder" is ore having a fine diameter to an extent that the ore can be removed by blowing gas. Hereinafter, the dephosphorization method of the present embodiment will be described in detail.

[0011] (Heating Furnace) The heating furnace may be any furnace as long as the heating furnace can heat the ore to a predetermined temperature of 100°C or higher and can apply the physical impact to the ore. Specifically, a kiln-type or fluidized-bed-type heating furnace can be used as the heating furnace.

[0012] (Kiln-Type Heating Furnace) In the kiln-type heating furnace, the heating furnace rotates to cause the ore in the heating furnace to flow. As a result, the physical impact is applied to the ore. This physical impact includes an impact when the ore collides with an inner wall surface of the heating furnace and an impact when particles of the ore collide with each other.

[0013] The kiln-type heating furnace includes an internal combustion heating furnace and an external combustion heating furnace. The internal combustion heating furnace is a heating furnace of a type in which a combustion gas is directly introduced into the heating furnace. The external combustion heating furnace is a heating furnace of a type in which heat is applied from the outside of the heating furnace.

[0014] (Fluidized-Bed-Type Heating Furnace) In the fluidized-bed-type heating furnace, a high-temperature gas is blown to particles of the ore. The gas fluidizes the particles of the ore to form a fluidized bed. Further, the gas heats the ore. In the fluidized-bed-type heating furnace, the ore is fluidized in the heating furnace, so that the physical impact is applied to the ore. This physical impact includes an impact when the ore collides with an inner wall surface of the heating furnace and an impact when particles of the ore collide with each other.

[0015] The fluidized-bed-type heating furnace includes a direct-heating heating furnace and an indirect-heating heating furnace. The direct-heating heating furnace is a heating furnace of a type in which heat is directly applied to the ore in the heating furnace. The indirect-heating heating furnace is a heating furnace of a type in which heat is indirectly applied to the ore in the heating furnace. Further, the fluidized-bed-type heating furnace may be a type in which the ore is circulated.

[0016] (Heating Temperature of Ore) The heating temperature of the ore in the heating furnace is set to 100°C or higher. By heating the ore to a predetermined temperature of 100°C or higher, the ore can be dried, and fine powder adhering to the ore with water can be brought into a state where the fine powder is easily detached. By applying the physical impact to the ore in a dried state, the fine powder can be efficiently detached from the ore. Since a fine powder portion is likely to contain a high concentration of phosphorus, the phosphorus can be detached from the ore by physically separating the fine powder from the ore. In addition, by heating the ore at a predetermined temperature of 100°C or higher in the fluidized-bed-type or kiln-type heating furnace, a dehydration reaction can be caused to remove phosphorus in goethite contained in the ore. Goethite is a type of mineral constituting the ore, and a chemical composition thereof is FeO(OH). JIS M 8700:2013 “Iron ores and reduced iron - Terms” classifies goethite as hydrous iron oxide.

[0017] The ore may be heated to a predetermined temperature of 300°C or higher. As a result, it is preferable that the combined water contained in the ore is further evaporated to embrittle the goethite portion, which is a portion containing the combined water. In a state where the portion containing the combined water is embrittled, the embrittled portion can be pulverized by applying the physical impact to the ore. Accordingly, the separation of fine powder from the ore is further promoted. A portion containing the combined water is likely to contain a high concentration of phosphorus. Therefore, as described above, the pulverized fine powder is likely to contain a high concentration of phosphorus. Accordingly, the phosphorus can be detached from the ore by physically separating the pulverized fine powder from the ore.

[0018] An upper limit of the predetermined temperature at which the ore is heated is not particularly limited. For example, from the viewpoint of the durability of the heating furnace, the phosphorus detachment efficiency described in the following Examples, and the like, the heating temperature is preferably 1000°C or lower. In addition, although details will be described in Examples, in a range where the heating temperature exceeds 750°C, a ratio of an increase rate of a dephosphorization rate to an increase amount of the temperature is lower than that in a range of 750°C or lower. That is, in the temperature range exceeding 750°C, the improvement of the phosphorus removal effect with respect to the increase in the heating temperature is limited as compared with a case of 750°C or lower. This phenomenon occurs regardless of whether the atmosphere of the heating furnace is non-reducing or reducing atmosphere. Therefore, the heating temperature can be more preferably set to 750°C or lower. Further, as will be described later, the dephosphorization effect can be obtained in a range of about 100°C to 500°C regardless of the atmosphere of the heating furnace. Therefore, the ore may be heated in a range of 100°C or higher and 500°C or lower or in a range of 100°C or higher and 300°C or lower from the viewpoint of the energy cost and the like in the heating furnace.

[0019] A temperature rising rate when the ore is heated to the predetermined temperature can be determined as appropriate. A time for heating the ore at the predetermined temperature, that is, a time for maintaining the temperature of the ore at the predetermined temperature is not particularly limited, but is preferably a time that allows the combined water contained in the ore to be sufficiently evaporated, as will be described later. This time can be, for example, 5 min or longer.

[0020] (Type of Gas Supplied into Heating Furnace) The atmosphere in the heating furnace can be determined as appropriate. For example, the atmosphere in the heating furnace can be a non-reducing or reducing atmosphere. The term “non-reducing atmosphere” is a concept encompassing both an oxidizing atmosphere and an inert atmosphere.

[0021] For example, by supplying a gas containing oxygen gas, which is one type of oxidizing gas, air, or the like into the heating furnace, the atmosphere in the heating furnace can be the oxidizing atmosphere. In addition, by supplying a nitrogen gas, an argon gas, or the like, which is one type of inert gas, into the heating furnace, the atmosphere in the heating furnace can be set to the inert atmosphere. Hereinafter, the term “non-reducing gas” is used as a concept encompassing both an inert gas and an oxidizing gas.

[0022] In addition, by supplying a gas containing hydrogen gas, which is one type of reducing gas, a gas containing carbon monoxide, or the like into the heating furnace, the atmosphere in the heating furnace can be set to the reducing atmosphere. Here, by setting the atmosphere in the heating furnace to the reducing atmosphere, in addition to the detachment of phosphorus by the dephosphorization method of the present embodiment, that is, the detachment of phosphorus accompanying the heating of the ore and the physical impact applied to the ore, the detachment of phosphorus described in Non Patent Document 1, that is, the removal of phosphorus from the ore as a gas, can be performed. That is, by heating the ore in the reducing atmosphere, the phosphate contained in the ore can be reduced and decomposed and removed.

[0023] The method for supplying the reducing gas or the non-reducing gas into the heating furnace is not particularly limited. In a case where the heating furnace is of a fluidized-bed-type, the gas for fluidizing the ore may be the reducing gas or the nonreducing gas. In a case where the heating furnace is of a kiln-type, as shown in FIG. 1, the reducing gas or the non-reducing gas may be blown from an inlet or an outlet of the heating furnace toward the ore. In a case where the reducing gas or the non-reducing gas is supplied to the heating furnace and the gas is allowed to flow inside the heating furnace, the fine powder separated from the ore can be moved together with the gas, that is, pneumatic conveyance of the fine powder can be performed. As a result, the effect of further facilitating the removal of the fine powder from the ore can also be obtained.

[0024] (Post-Heating Classification Treatment) The ore discharged from the heating furnace may be subjected to the classification treatment. The classification treatment can separate the fine powder separated from the ore from the ore. As a result, the fine powder separated from the ore can be removed. Unlike intermediate classification treatment described later, it is not assumed that the ore is further heated after the post-heating classification treatment. When the ore is heated two or more times, the post-heating classification treatment is performed after all the heat treatments are completed.

[0025] As a method for performing the post-heating classification treatment, for example, a sieving device can be used. The sieve opening of the sieving device can be determined as appropriate in consideration of the particle diameter of the fine powder separated from the ore, and for example, in the post-heating classification treatment, the sieve opening can be set to 0.125 mm to 0.25 mm.

[0026] Hereinafter, an example of equipment for performing the dephosphorization method for ore according to the present embodiment will be described with reference to FIG. 1.

[0027] A storage tank 1 stores the ore to be subjected to the dephosphorization. The ore discharged from the storage tank 1 is conveyed to the kiln-type heating furnace 2. The ore is supplied into the heating furnace 2 from a supply port 2a positioned at one end of the heating furnace 2. Thereafter, the ore is heated at a predetermined temperature of 100°C or higher and subjected to a tumbling action caused by rotation of the heating furnace 2, whereby a physical impact is applied to the ore. Inside the heating furnace 2, the fine powder is separated from the ore by the evaporation and pulverization of the combined water described above. The ore moves from the supply port 2a of the heating furnace 2 toward a discharge port 2b positioned at the other end of the heating furnace 2, and is discharged from the discharge port 2b.

[0028] A gas supply device 3 supplies the gas into the heating furnace 2. The gas is the non-reducing gas or the reducing gas. The gas from the gas supply device 3 is supplied into the heating furnace 2 from the discharge port 2b of the heating furnace 2, moves along a rotation axis direction of the heating furnace 2, and is then discharged from the supply port 2a of the heating furnace 2. The fine powder separated from the ore moves together with the gas by the gas flowing inside the heating furnace 2 as described above. An exhaust gas, which is the gas discharged from the heating furnace 2, and the fine powder are guided to a dust collector 4. In the dust collector 4, the fine powder discharged from the heating furnace 2 is collected. In the equipment shown in FIG. 1, the gas flows from the discharge port 2b toward the supply port 2a, but the gas can also flow from the supply port 2a toward the discharge port 2b.

[0029] The ore discharged from the discharge port 2b of the heating furnace 2 may be conveyed to the sieving device 5 for classification. The sieving device 5 has a sieve opening of a predetermined size. The sieve opening of the sieving device 5 is, for example, in a range of 0.125 mm to 0.25 mm. The sieving device 5 removes the fine powder having a predetermined size or less from the ore among the ore conveyed to the sieving device 5. The ore on the sieve of the sieving device 5 is ore from which phosphorus has been removed. The ore from which phosphorus has been removed is used for producing sintered ore or pellet, which is an iron raw material to be charged into the blast furnace.

[0030] The heating furnace 2 may be the fluidized-bed-type heating furnace as described above. By causing the ore to be fluidized by the gas supplied into the heating furnace, the physical impact can be applied to the ore. Accordingly, similarly to the case of the kiln-type, the fluidized-bed-type heating furnace can separate fine powder from ore and perform dephosphorization.

[0031] (Combination of First Heating Furnace in Non-Reducing Atmosphere and Second Heating Furnace in Reducing Atmosphere) In the above-described embodiment shown in FIG. 1, the ore is heated once in the heating furnace in either the non-reducing atmosphere or the reducing atmosphere. However, the dephosphorization method for ore according to the present embodiment is not limited to this configuration. For example, after the ore is heated in the nonreducing atmosphere, the ore may be heated in the reducing atmosphere.

[0032] The heating in the non-reducing atmosphere and the heating in the reducing atmosphere may be performed in separate heating furnaces. The volumes, types, and the like of the first heating furnace and the second heating furnace may be the same as or different from each other. For example, one heating furnace may be the kiln-type heating furnace, and the other heating furnace may be the fluidized-bed-type heating furnace.

[0033] On the other hand, the heating in the non-reducing atmosphere and the heating in the reducing atmosphere may be performed in the same heating furnace. In this case, the second heating need only be performed by changing, after the first heating, the type of the gas supplied to the heating furnace. In this case, the heating furnace in a state where the non-reducing gas is blown is regarded as the first heating furnace, and the heating furnace in a state where the reducing gas is blown is regarded as the second heating furnace.

[0034] A case where the heating in the non-reducing atmosphere and the heating in the reducing atmosphere are performed in separate heating furnaces will be described with reference to FIG. 2. In the equipment shown in FIG. 2, the heating furnace is composed of two units, a first heating furnace 21 and a second heating furnace 22. The first heating furnace 21 and the second heating furnace 22 are connected in series. In the following description, descriptions of portions overlapping with those in the case of FIG. 1 are omitted. In addition, as an example, the first heating furnace 21 and the second heating furnace 22 will be described as being of the kiln-type. On the other hand, any one or both of the first heating furnace 21 and the second heating furnace 22 may be the fluidized-bed-type heating furnace.

[0035] First, the ore is supplied from the storage tank 1 to the first heating furnace 21. In the first heating furnace 21, the ore is heated at the predetermined temperature of 100°C or higher. The non-reducing gas is supplied from the non-reducing gas supply device 31 to the first heating furnace 21. In the first heating furnace 21, the ore is heated in the non-reducing atmosphere. Then, the ore is subjected to a tumbling action by rotation of the first heating furnace 21, whereby the physical impact is applied to the ore. As a result, the fine powder is separated from the ore. The fine powder is discharged together with the gas, and is collected by a dust collector 41. The gas discharged together with the fine powder is referred to as the exhaust gas. As a result, a part of the phosphorus contained in the ore is detached. In FIG. 2, the non-reducing gas is caused to flow from the discharge port 21b of the first heating furnace 21 toward the supply port 21a, but the exhaust gas may be caused to flow from the supply port 21a toward the discharge port 21b.

[0036] The ore discharged from the discharge port 21b of the first heating furnace 21 is supplied into the second heating furnace 22 from the supply port 22a positioned at one end of the second heating furnace 22. Thereafter, in the second heating furnace 22, the ore is heated in the reducing atmosphere at the predetermined temperature of 100°C or higher, and is subjected to the tumbling action by the rotation of the second heating furnace 22, and the physical impact is applied. The ore moves from the supply port 22a toward the discharge port 22b positioned at the other end inside the second heating furnace 22, and is discharged from the discharge port 22b.

[0037] The reducing gas supply device 32 supplies the reducing gas into the second heating furnace 22. The reducing gas from the reducing gas supply device 32 is supplied from the discharge port 22b of the second heating furnace 22 into the second heating furnace 22, moves along the rotation axis direction of the second heating furnace 22, and is then discharged from the supply port 22a. As described above, the fine powder separated from the ore moves together with the gas by the gas flowing inside the second heating furnace 22. The exhaust gas, which is the gas discharged from the second heating furnace 22, and the fine powder are guided to the dust collector 42. Then, the fine powder discharged from the second heating furnace 22 is collected by the dust collector 42. In the equipment shown in FIG. 2, the gas is caused to flow from the discharge port 22b of the second heating furnace 22 toward the supply port 22a, but the gas can also be caused to flow from the supply port 22a toward the discharge port 22b.

[0038] The ore discharged from the discharge port 22b of the second heating furnace 22 may be conveyed to the sieving device 5 for classification. The sieving device 5 has a sieve opening of a predetermined size. The sieve opening of the sieving device 5 is, for example, in a range of 0.125 mm to 0.25 mm. The sieving device 5 removes the fine powder having a predetermined size or less from the ore among the ore conveyed to the sieving device 5. The ore on the sieve of the sieving device 5 is ore from which phosphorus has been removed. The ore from which phosphorus has been removed is used for producing sintered ore or pellet, which is an iron raw material to be charged into the blast furnace.

[0039] The heating temperatures of the first heating furnace 21 and the second heating furnace 22 may be the same as or different from each other. In addition, both the heating in the non-reducing atmosphere and the heating in the reducing atmosphere may be performed in the same one heating furnace. In this case as well, the heating temperatures in the respective atmospheres may be the same as or different from each other. However, the heating temperature during the second heating, which is the heating in the reducing atmosphere, is preferably 300°C or higher. That is, it is preferable that the first heating temperature is set to 100°C or higher, and the second heating temperature is set to 300°C or higher. The term “second heating” means both the heating in the second heating furnace 22 in a case where the ore is sequentially heated using two heating furnaces and the second heating in a case where the ore is heated twice using one heating furnace. This is because, by setting the second heating temperature to 300°C or higher, from the ore in which a part of phosphorus is separated from the goethite portion by the first heating, the remaining phosphorus can be more efficiently separated.

[0040] Further, the heating time of the first heating and the heating time of the second heating are not particularly limited. In addition, the first heating time and the second heating time may be the same as or different from each other. The term “first heating” means both the heating in the first heating furnace 21 in a case where the ore is sequentially heated using two heating furnaces and the first heating in a case where the ore is heated twice using one heating furnace.

[0041] As described above, phosphorus contained in the ore may be separated by a method of first heating in the non-reducing atmosphere and then heating in the reducing atmosphere. Compared to a case of one-time heating in either the non-reducing atmosphere or the reducing atmosphere, in a case where heating in the non-reducing atmosphere and heating in the reducing atmosphere are combined, a larger amount of phosphorus can be separated from the ore. In addition, first, heating is performed in the non-reducing atmosphere, which is generally less expensive than the reducing atmosphere, to remove phosphorus by heating and decomposing goethite in which a large amount of phosphorus is present, and then heating is performed in the reducing atmosphere to remove phosphorus or phosphorus oxide that remains without being removed, thereby enabling more efficient removal of phosphorus while minimizing the use of the reducing gas, which is more expensive. Therefore, in accordance with the method of the embodiment in which heating is performed twice as described above, it is possible to further save energy and reduce costs compared to a case of one-time heating. That is, in a case where the heating the ore includes first heating the ore in the nonreducing atmosphere and then second heating the ore in the reducing atmosphere, the amount of reducing gas required for the reduction decomposition of the phosphate present in the ore can be reduced. Since the non-reducing gas is less expensive than the reducing gas, the reduction in the amount of reducing gas used by using the first heating furnace reduces the dephosphorization cost.

[0042] In addition, in a case of heating in the reducing atmosphere, the reduction of iron oxide in the ore may also occur. Since metallic iron generated by reduction combines with phosphorus, heating in the reducing atmosphere may instead decrease the dephosphorization rate. Therefore, by setting a part of the entire heating process to the non-reducing atmosphere, the reduction reaction to metallic iron, which leads to the decrease in the dephosphorization rate, is suppressed, and only the dephosphorization reaction can be efficiently advanced, which is also advantageous.

[0043] (Intermediate Classification Treatment) The intermediate classification treatment may be further performed between the first heating furnace 21 and the second heating furnace 22. The intermediate classification treatment is treatment of separating the ore discharged from the first heating furnace 21 into the coarse fraction and the fine fraction. Unlike the abovedescribed post-heating classification treatment, the second heating of the ore is always performed after the intermediate classification treatment. The intermediate classification treatment is defined as classifying the ore after the ore is heated in the first heating furnace and before the ore is supplied to the second heating furnace.

[0044] FIG. 3 is a process diagram showing steps of the dephosphorization method for ore according to the embodiment when the intermediate classification treatment is performed. The ore heated and discharged in the first heating furnace 21 is supplied to the sieving device 6 which is a classification device. The sieving device 6 performs the intermediate classification treatment of classifying the ore heated in the first heating furnace 21 into the coarse fraction and the fine fraction. Then, the coarse fraction of the ore classified in the sieving device 6 is supplied to the second heating furnace 22 and subjected to the reduction treatment. The fine fraction is removed from the ore supplied to the second heating furnace 22.

[0045] In the sieving device 6 used in the intermediate classification treatment, the size of the sieve opening is preferably 0.5 mm or more and 3.0 mm or less. In the sieving device 6, particles that do not pass through the sieve opening are the coarse fraction, and particles that pass through the sieve opening are the fine fraction. The particle size can be adjusted by the size of the sieve opening of the sieving device 6. By using the sieving device having a sieve opening range of 0.5 mm or more and 3.0 mm or less, the particle size of the fine fraction can be set to 0.5 mm or more and 3.0 mm or less. The sieve opening of the sieving device 6 that performs the intermediate classification treatment is larger than the sieve opening of the sieving device 5 that performs the post-heating classification treatment performed for removing the fine powder. The classification device that performs the intermediate classification treatment is not limited to the sieving device, and other classification devices may be used. In general, in ore that has been heated in the first heating furnace 21 and from which fine powder has been removed, the smaller the particle size, the lower the phosphorus content. Stated another way, the ore having a smaller particle size has a higher dephosphorization rate. Therefore, by the above-described intermediate classification treatment, the ore discharged from the first heating furnace 21 can be separated into the coarse fraction having a relatively low dephosphorization rate and the fine fraction having a relatively high dephosphorization rate. By performing the intermediate classification treatment, only the coarse fraction that requires the dephosphorization treatment can be preferentially supplied to the second heating furnace 22. This makes it possible to limit the object of dephosphorization to a portion of the entire iron ore that requires further dephosphorization treatment by reduction, in other words, a portion in which dephosphorization is less likely to progress and to which dephosphorization treatment by reduction should be preferentially applied, thereby enabling more effective dephosphorization treatment. By heating only the coarse fraction in the second heating furnace 22, the dephosphorization treatment can be more efficiently performed in terms of the overall energy efficiency and the gas unit consumption than in a case where all of the ore is heated in the second heating furnace 22. That is, in a case where the ore is classified after the first heating and before the second heating, the fine powder is removed from the ore, so that the reaction efficiency between the ore particles and the reducing gas is increased. As a result, the amount of reducing gas required for the reduction decomposition of the phosphate present in the ore can be further reduced.

[0047] The fine fraction separated by the intermediate classification treatment in the present embodiment has a sufficiently high dephosphorization rate, and thus can be used as it is as dephosphorized iron ore for a raw material for pellets, briquettes, sintering, or the like. The post-heating classification treatment by the sieving device 5 shown in FIG. 3 may be omitted.

[0048] (Pre-Heating Classification) The dephosphorization method for ore according to the present embodiment may further include classifying the ore into a coarse fraction and a fine fraction before the heating the ore in the heating furnace. Hereinafter, the classification treatment of the ore before being heated is referred to as “pre-heating classification treatment”. FIG. 4 shows a process chart of the dephosphorization method for ore in which the pre-heating classification treatment is performed.

[0049] First, the configuration of the dephosphorization method for ore in which the pre-heating classification treatment is performed will be described with reference to FIG. 4. A storage tank 1 stores the ore to be subjected to the dephosphorization. The ore discharged from the storage tank 1 is conveyed to the sieving device 7 before being conveyed to the kiln-type heating furnace 2. The sieving device 7 for the pre-heating classification treatment has a sieve opening of 3.0 mm or more and 5.0 mm or less. The sieving device 7 classifies the ore before being heated into the coarse fraction and the fine fraction.

[0050] After the pre-heating classification treatment, the coarse fraction is supplied to the heating furnace 2. It is preferable that the fine fraction is removed from the ore supplied to the heating furnace 2. The fine fraction may be added to the ore conveyed out from the heating furnace 2. In addition, the fine fraction may not be used as ore of a steelmaking raw material. The heating furnace 2 is the kiln-type heating furnace. Further, the heating temperature of the coarse fraction in the heating furnace 2 is set to 400°C or higher. More preferably, the heating temperature is set in a range of 600°C to 1000°C.

[0051] The atmosphere inside the heating furnace 2 is not particularly limited. For example, it is preferable to supply the reducing gas to the heating furnace 2 to set the inside of the heating furnace 2 to the reducing atmosphere. Examples of the reducing gas include a hydrogen gas, a CO gas, and a mixed gas thereof. In the kiln-type heating furnace, the best dephosphorization efficiency is achieved by heating the ore to 400°C or higher while blowing in the reducing gas.

[0052] The above-described various configurations may be combined with a configuration in which the pre-heating classification treatment is performed.

[0053] For example, in a case where the heating furnace includes the first heating furnace 21 and the second heating furnace 22, the ore may be classified before the ore is supplied to the first heating furnace 21. In this case, at least one of the first heating furnace 21 and the second heating furnace 22 may be of the kiln-type, and the heating temperature thereof may be set to 400°C or higher. More preferably, the first heating furnace 21 is of the kiln-type, and the heating temperature thereof is set to 400°C or higher.

[0054] For example, in addition to the pre-heating classification treatment, one or both of the intermediate classification treatment and the post-heating classification treatment may be performed. When a plurality of classification treatments are performed, all the classification treatments may be performed by one sieving device. However, the sieve opening suitable for the pre-heating classification treatment does not necessarily match the sieve opening suitable for the intermediate classification treatment and the sieve opening suitable for the post-heating classification treatment. This is because the state of the ore to be subjected to these classification treatments and the purpose of these classification treatments are different. In particular, the pre-heating classification treatment is intended to maintain tumbling properties in the furnace and improve reactivity with gas, whereas the post-heating classification treatment is intended to enable efficient phosphorus removal by selectively charging only particles in which phosphorus removal has not progressed into the heating furnace 2, by excluding particles in which phosphorus removal has progressed. Therefore, it is most preferable to independently install the sieving device 7 for the pre-heating classification treatment, the sieving device 6 for the intermediate classification treatment, and the sieving device 5 for the postheating classification treatment.

[0055] Next, the technical idea and the operations and effects of the dephosphorization method for ore in which the pre-heating classification treatment is performed will be described. The present inventors have found that, in a case where the dephosphorization of the ore is performed using the kiln-type heating furnace at 400°C or higher, the dephosphorization efficiency is decreased when the particle size of the ore to be charged into the heating furnace is lower than a specific threshold value. This is a phenomenon contrary to the technical common knowledge of a person skilled in the art. In a case where the ore is reduced using the kiln-type heating furnace, it is considered that the smaller the particle size of the ore, the higher the reduction efficiency. This is because the smaller the particle size of the ore, the larger the surface area per unit weight of the ore. Therefore, in accordance with the technical common knowledge, it is expected that the smaller the particle size of the ore, the easier it is to perform the dephosphorization of the ore.

[0056] Based on the above findings of the present inventors, it is preferable to remove the fine fraction of the ore before performing the dephosphorization of the ore using the kiln-type heating furnace at 400°C or higher. By subjecting only the coarse fraction, which is a portion for which the dephosphorization rate can be easily increased, to dephosphorization, dephosphorization efficiency can be increased, and more efficient dephosphorization treatment can be performed from the viewpoints of overall energy efficiency and gas consumption rate. Based on the findings of the present inventors through experiments, the above-described effects can be suitably obtained by performing the classification treatment using a sieve opening of 3 mm or more and 5 mm or more and supplying only the coarse fraction remaining on the sieve opening to the heating furnace.

[0057] (Selection of Ore Before Heating) In the dephosphorization method for ore according to the present embodiment, in a case where there are two or more types of ores, the dephosphorization method may further include selecting ore having a highest phosphorus concentration in goethite before the heating the ore in the heating furnace, and the ore having the highest phosphorus concentration in goethite may be preferentially supplied to the heating furnace. Hereinafter, a specific configuration of the embodiment in which the ore is sorted before heating the ore will be described in detail.

[0058] The types of ore are distinguished based on, for example, working faces formed when mining ore in an ore deposit. The working face is a work site in a mine, such as a coal mine or metal mine, where coal, ore, or the like is mined or where tunnel excavation is being performed (see JIS M 0102:2000 “Glossary of Mining Terms”). The grade of the ore may vary depending on the working face from which the ore is mined. Further, the types of ore may be distinguished based on the place of production of the ores.

[0059] In a case where there are two or more types of ore, ore having a high phosphorus concentration in goethite is selected as a target of dephosphorization treatment. The criterion for selecting ore is the phosphorus concentration in goethite in the ore, and not the phosphorus content of the ore. For example, when there are ore A, which has a low goethite content but a high phosphorus concentration in the goethite, and ore B, which has a high goethite content but a low phosphorus concentration in the goethite, ore A is selected as the dephosphorization target. Even when the total amount of phosphorus contained in ore B is larger than that in ore A, ore A is preferentially subjected to dephosphorization treatment based on the phosphorus concentration in goethite contained in the ore, from the viewpoints of efficiency and energy saving.

[0060] In a case where the phosphorus concentration in goethite in the ore is unknown, the dephosphorization method for ore may further include measuring the phosphorus concentration in goethite. The means for measuring the phosphorus concentration of goethite may be, for example, a mineral liberation analyzer (MLA). The mineral liberation analyzer includes a scanning electron microscope (SEM) having an energy 25 dispersive X-ray spectrometer (EDS), and a computer configured to control these components and store, as data, EDS spectra of respective mineral species. Japanese Unexamined Patent Application, First Publication No. 2015-40724 discloses an example of the MLA. Japanese Unexamined Patent Application, First Publication No. 202034372 discloses an example of an analysis method using the MLA.

[0061] By performing elemental analysis of a polished cross-sectional sample of iron ore using the MLA, the amount of goethite per unit mass of the iron ore and the distribution of goethite can be specified. In addition, by cross sectional analysis using the MLA, the amount of phosphorus per unit mass of the iron ore and the distribution of phosphorus can also be specified. By collating the analysis result of goethite and the analysis result of phosphorus, the phosphorus concentration of goethite can be specified.

[0062] The ore having the highest phosphorus concentration in goethite, which is selected by the above-described procedure, is preferentially supplied to the heating furnace for dephosphorization. Specifically, first, the ore having the highest phosphorus concentration in goethite is supplied to the heating furnace. Then, after all of the ore is supplied to the heating furnace, the ore having the highest phosphorus concentration in goethite among the remaining ores is selected and supplied to the heating furnace. That is, the order of supplying the ores to the heating furnace is determined in descending order of the phosphorus concentration in goethite. In a case where a different type of ore is received before all types of ores are supplied to the heating furnace, the dephosphorization target is selected from the group including the new ore by the abovedescribed means. Next, the operation and effect of the embodiment in which the ore is selected before heating the ore will be described. In the dephosphorization method for ore according to the present embodiment, the phosphorus concentration of goethite in the ore is used as a criterion for selecting the type of ore to be supplied to the heating furnace. This is because the kiln-type or fluidized-bed-type heating furnace is less likely to remove phosphorus contained in minerals other than goethite. On the other hand, the phosphorus concentration of goethite has a significant influence on the dephosphorization efficiency of the ore using the kiln-type or fluidized-bed-type heating furnace. The higher the phosphorus concentration of goethite in the ore, the easier it is to perform dephosphorization using the kiln-type or fluidized-bed-type heating furnace.

[0064] In accordance with the dephosphorization method for ore according to the present embodiment, it is possible to preferentially dephosphorize an ore having a high dephosphorization efficiency. Therefore, the efficiency of the dephosphorization process can be further improved.

[0065] Instead of relatively comparing the phosphorus concentrations of goethite in a plurality of types of ore, the dephosphorization treatment may be performed only in a case where the phosphorus concentration of goethite in the ore is equal to or higher than a predetermined value. Specifically, only the ore having a phosphorus concentration of goethite of 1.0% by mass or more may be supplied to the heating furnace. In this case, the type of ore may be only one. In a case where there is no ore having a phosphorus concentration of goethite of 1.0% by mass or more, the dephosphorization treatment may be stopped.

[0066] Based on the experimental results of the present inventors, by using only the ore having a phosphorus concentration of goethite of 1.0% by mass or more as a target of the dephosphorization treatment using the kiln-type or fluidized-bed-type heating furnace, the dephosphorization efficiency can be further improved, and the energy for dephosphorization can be reduced.

[0067] The above-described various configurations and the configuration of selecting the ore before heating may be combined as appropriate. Examples

[0068] The effects of one aspect of the present disclosure will be further described in detail with reference to Examples. However, conditions in Examples are merely one set of conditions employed to confirm the feasibility and effects of the present disclosure. The present disclosure is not limited to this one set of conditions. The present disclosure may adopt various conditions as long as the conditions do not depart from the gist thereof and achieve the object thereof.

[0069] (Experiment 1) (Ore) In Comparative Example and Examples 1 to 5 described later, ore having components shown in Table 1 was used. In Comparative Example, a batch-type heating furnace described later was filled with 2 kg of ore. In Examples 1 to 4, the ore was supplied to the kiln-type heating furnace described later at a constant supply rate of 300 kg / h.

[0070] [Table 1] Component Iron P SiO2 AI2O3 Combined water (CW) [% by mass] 61 0.1 3.5 2.3 5.1

[0071] (Heating Furnace) In Comparative Example, a batch-type box-type furnace that only heats the ore without fluidizing the ore was used as the heating furnace. An inner diameter of the box-type furnace was set to a width of 300 mm, a depth of 300 mm, and a height of 300 mm. In Examples 1 to 4, an external combustion kiln was used as the heating furnace. An internal space of the kiln had a diameter of 0.90 m and a length of 2.0 m. Further, the rotation speed of the kiln was set to 2.0 rpm.

[0072] (Number of Heating Furnaces and Heating Atmosphere Condition) In Comparative Example and Example 1, the number of heating furnaces was set to one. In Comparative Example and Example 1, air, which is an oxidizing gas, was supplied into the heating furnace at a flow rate of 15 Nm3 / h, and the atmosphere in the heating furnace was set to the non-reducing atmosphere. In Example 2, the number of heating furnaces was set to one. In Example 2, a reducing gas containing 33% of H2 and the remainder of N2 was supplied into the heating furnace at a flow rate of 15 Nm3 / h, and the atmosphere in the heating furnace was set to the reducing atmosphere. In Examples 3 and 4, the number of heating furnaces was set to two. In the first heating furnace, the heat treatment was performed in the non-reducing atmosphere under the conditions of Example 1. Thereafter, the ore was cooled to the room temperature. Then, in the second heating furnace, the heat treatment was performed in the reducing atmosphere under the conditions of Example 2.

[0073] (Heating Temperature Condition) In Comparative Example and Examples 1 to 4, a plurality of temperatures were set as the temperature for heating the ore. Specifically, in the heating furnace, the temperature was raised to each of 100°C, 300°C, 500°C, 750°C, 1000°C, and 1100°C, and then the temperature was maintained. In Examples 3 and 4, the heating temperature in the non-reducing atmosphere and the heating temperature in the reducing atmosphere were the same as each other.

[0074] (Heating Time Condition) In Examples 1 and 2, the holding time of the ore in the heating furnace was set to 120 min. In Examples 3 and 4, the total holding time of the ore in the first heating furnace and the second heating furnace was set to 120 min. In Examples 3 and 4, the heating in the non-reducing atmosphere in the first heating furnace was performed for 60 min, and the heating in the reducing atmosphere in the second heating furnace was performed for 60 min. In Comparative Example, the heating time in the heating furnace was set to 120 min.

[0075] (Intermediate Classification Treatment) In Example 5, after the heat treatment in the non-reducing atmosphere in the first heating furnace, the ore was discharged from the first heating furnace, and the intermediate classification treatment was performed using a sieving device having a sieve opening of 3.0 mm. In the intermediate classification treatment, the ore was separated into the fine fraction and the coarse fraction. Then, only the coarse fraction was charged into the second heating furnace, and the heat treatment was performed in the reducing atmosphere. In Comparative Example and Examples 1 to 4, the intermediate 5 classification treatment was not performed.

[0076] Neither the pre-heating classification treatment nor the post-heating classification treatment was performed in any example.

[0077] 10           Table 2 summarizes the above-described test conditions. [Table 2] Comparative Example Example 1 Example 2 Example 3 Example 4 Pre-heating classification treatment Absent Number of heating furnaces 1 1 1 2 2 First heating furnace Type Batch-type Kiln-type Kiln-type Kiln-type Kiln-type Atmosphere Non-reducing Nonreducing Reducing Nonreducing Nonreducing Heating temperature (°C) 100, 300, 500, 750, 1000, or 1100 Heating time (minutes) 120 120 120 60 60 Intermediate classification treatment Absent Present (sieve opening 3 mm) Second heating furnace Type Kiln-type Kiln-type Atmosphere Reducing Reducing Heating temperature (°C) Same as in first heating furnace Heating time (minutes) 60 60 Total heating time 120 Post-heating classification treatment Absent

[0079] (Measurement of Dephosphorization Rate) 5            The dephosphorization rate was measured for the ore subjected to the heat treatment in the heating furnace. In Comparative Example and Examples 1 to 3, the dephosphorization rate was measured for the ore discharged from the heating furnace. The dephosphorization rate of Example 4 was obtained by the following 10 procedure. First, the dephosphorization rate of the fine fraction, which was obtained by the intermediate classification treatment after heating in the non-reducing atmosphere in the first heating furnace, was obtained. In addition, the dephosphorization rate of the coarse fraction after the intermediate classification treatment, which was obtained by heating the coarse fraction in the second heating furnace in the reducing atmosphere, was obtained. The overall dephosphorization rate of Example 5 was obtained from both the dephosphorization rate of the fine fraction and the dephosphorization rate of the coarse fraction after heating. The overall dephosphorization rate was determined as the sum of values obtained by multiplying the mass ratio of each of the coarse fraction and the fine fraction by the corresponding dephosphorization rate. That is, the overall dephosphorization rate was obtained by the following expression. (Overall dephosphorization rate) = {(Dephosphorization rate of fine fraction) x (Weight of fine fraction) + (Dephosphorization rate of coarse fraction) x (Weight of coarse fraction)} / {(Weight of fine fraction) + (Weight of coarse fraction)}

[0080] The dephosphorization rate is represented by Expression (1).

[0081]

[0082] In Expression (1), r|p is a dephosphorization rate [% by mass], (Cp)o is a concentration of phosphorus [% by mass] contained in the ore before the heating and the reduction are performed, and (Cp)t is a concentration of phosphorus [% by mass] contained in the ore after the heating and the reduction are performed.

[0083] The phosphorus concentration Cp shown in Expression (1) is represented by Expression (2). That is, the phosphorus concentration Cp is a value obtained by normalizing a content rate of phosphorus by a content rate of iron.

[0084] %p C„ =-------- ... (2) p %T.Fe 1 }

[0085] 5           In Expression (2), %P is the content rate (measured value) of phosphorus [% by mass], and %T.Fe is the content rate (measured value) of iron (Fe2+, Fe3+, and M.Fe) [% by mass]. The content rate %P of phosphorus was measured in accordance with the provisions of JIS M 8216. The content rate [% by mass] of Fe2+ (FeO) was measured in accordance with the provisions of JIS M 8213. The content rate [% by mass] of Fes+ 10 (Fe2Os) was measured by X-ray fluorescence analysis. The content rate [% by mass] of M.Fe was measured in accordance with the provisions of JIS M 8212.

[0086] The measurement results of the dephosphorization rate are shown in Table 3 below. 15

[0087] [Table 3] Dephosphorization rate pp [% by mass] Comparative Example Example 1 Example 2 Example 3 Example 4 Heating temperature [°C] 100 1.2 2.0 2.2 - - 300 1.9 2.5 2.6 2.7 2.8 500 - 6.4 6.7 7.0 7.2 750 - 10.5 14.1 14.6 14.8 1000 - 12.2 16.1 16.7 17.0 1100 - 13.1 16.9 17.5 17.8 Note:    indicates unmeasured. When the heating temperature was 100°C, the dephosphorization rate r|p in Examples 1 and 2 was higher than the dephosphorization rate r|p in Comparative Example. When the heating temperature was lower than 100°C, since the surface of the ore was not sufficiently dried, it is presumed that the fine powder containing phosphorus (fine powder having a particle diameter of 0.25 mm or less) was less likely to be separated from the surface of the ore, and the dephosphorization effect was small.

[0089] In any of the examples, the dephosphorization rate r|p increased as the heating temperature became higher than 100°C. Here, when the heating temperature was 300°C, the dephosphorization rate r|p in Examples 1 to 4 was higher than the dephosphorization rate r|p in Comparative Example. It is presumed that this is because the combined water of the goethite portion in the ore was evaporated (dehydrated) and embrittled at 300°C or higher, and the fine powder containing phosphorus was further separated and removed by the physical impact.

[0090] As described above, the dephosphorization rate r|p increases as the heating temperature increases, but in consideration of the increase rate of the dephosphorization rate with respect to the increase amount of the heating temperature, the heating temperature need not be excessively increased. Table 4 shows the increase rate Ar|p [% by mass / 10°C] of the dephosphorization rate when the heating temperature was increased by 10°C, which was calculated based on the results shown in Table 3.

[0091] [Table 4] Comparative Example Example 1 Example 2 Example 3 Example 4 Rate of increase in dephosphorization rate when temperature is raised from 100°C to 300°C 0.035 0.025 0.020 - - Rate of increase in dephosphorization rate when temperature is raised from 300°C to 500°C - 0.195 0.205 0.215 0.223 Rate of increase in dephosphorization rate when temperature is raised from 500°C to 750°C - 0.164 0.296 0.304 0.313 Rate of increase in dephosphorization rate when temperature is raised from 750°C to 1000°C - 0.068 0.080 0.084 0.086 Rate of increase in dephosphorization rate when temperature is raised from 1000°C to 1100°C - 0.090 0.080 0.080 0.081 Unit: % by mass / 10°C

[0092] Based on the results shown in Table 4, the increase rate Ar|p increases as long as the heating temperature is 750°C or lower. However, the increase rate Ar|p decreases when the heating temperature exceeds 750°C. Therefore, in consideration of the 5 increase rate, the upper limit of the heating temperature can be set to 750°C. On the other hand, in consideration of the points described below, the upper limit of the heating temperature can be set to 1000°C.

[0093] When the heating temperature is higher than 1000°C, the temperature of the ore 10 exceeds 950°C, which is the reference temperature for measurement in the Karl Fischer method (see JIS M 8211:1995 “Iron ores-Method for determination of combined water content”). Therefore, in the ore heated to 950°C or higher, the embrittlement due to the evaporation of the combined water described above is already completed. In addition, when the ore is heated in a reducing atmosphere, at a heating temperature higher than 1000°C, it is considered that the reduction reaction is excessively promoted and generation of metallic iron progresses, whereby detachment of phosphorus from the ore is likely to be inhibited. In consideration of these points, the upper limit of the heating temperature can be set to 1000°C.

[0094] In Example 2 in which the atmosphere in the heating furnace was the reducing atmosphere, the dephosphorization rate r|p was improved in a range of 750°C or higher as compared with Example 1. In Example 3, the dephosphorization rate r|p was improved as compared with Example 1 in a range of 750°C or higher, and the dephosphorization rate r|p was also improved as compared with Example 2. On the other hand, in Examples 1 to 3, the dephosphorization rates pp at the same temperature were equivalent regardless of the atmosphere of the heating furnace in a temperature range in which the heating temperature is 100°C or higher and 500°C or lower.

[0095] The dephosphorization rate qp in Example 4 was the highest among Examples 1 to 4 at the same heating temperature. By performing the intermediate classification treatment of separating the ore into the fine fraction and the coarse fraction after the first heating in the non-reducing atmosphere, the dephosphorization rate can be further improved.

[0096] (Experiment 2) The operation and effect of the pre-heating classification treatment will be verified below using the results of the offline experiment.

[0097] (Raw Material) The ore to be subjected to dephosphorization was Australian iron ore fines. The components of the ore were iron: 62.6%, P: 0.29%, SiCh: 2.7%, alumina: 2.2%, and combined water [CW]: 4.5%.

[0098] (Classification Method) The pre-heating classification treatment was performed using the sieving device. The sieve opening of the sieving device was set to 2 mm, 3 mm, 5 mm, or 7 mm.

[0099] (Heat Treatment Device and Heating Condition) The heating furnace was a kiln-type heating furnace. The heating conditions were as follows. • Size of internal space of heating furnace: diameter of 0.90 m and length of 2.0 m • Rotation speed of heating furnace: 2.0 rpm • Number of heating furnaces: 1 • Amount of ore charged into heating furnace: 1 kg / h (constant charging rate) • Type of gas supplied to heating furnace: reducing gas (N2-33%H2) • Flow rate of gas supplied to heating furnace: 15 Nm3 / h • Heating temperature: 700°C • Holding time at heating temperature: 60 min

[0100] The method for measuring the dephosphorization rate was the same as the method in Example 4 of Experiment 1. That is, the dephosphorization rate of the fine fraction obtained by the pre-heating classification treatment, and the dephosphorization rate of the coarse fraction after heating were measured. The values obtained by substituting these values into the following expression are shown in Table 5 as the dephosphorization rates. (Overall dephosphorization rate) = {(Dephosphorization rate of fine fraction) x (Weight of fine fraction) + (Dephosphorization rate of coarse fraction) x (Weight of coarse fraction)} / {(Weight of fine fraction) + (Weight of coarse fraction)} Table 5 shows the experimental results.

[0101] [Table 5] Example 11 Example 12 Example 13 Example 14 Sieve opening (mm) 2 3 5 7 Dephosphorization rate (% by mass) 13.6 15.3 16.1 15.0

[0102] The dephosphorization rates of Examples 12 and 13 in which the sieve openings were in a range of 3 to 5 mm were higher than the dephosphorization rate of Example 11 in which the sieve opening was 2 mm and the dephosphorization rate of Example 14 in which the sieve opening was 7 mm. In Example 11, ore having a diameter of 2 to 3 mm, for which dephosphorization is less likely to occur, was also subjected to dephosphorization, and therefore the dephosphorization rate is presumed to have been lower than those in Examples 12 and 13. In Example 14, the amount of ore subjected to dephosphorization was small, and therefore the dephosphorization rate is presumed to have been lower than those in Examples 12 and 13.

[0103] (Experiment 3) The operation and effect of the sorting of the ore before heating will be verified below using the results of the offline experiment.

[0104] (Raw Material) The high-phosphorus ores to be subjected to dephosphorization were two types of Australian iron ore fines A and B. The components of the high-phosphorus ore A were iron: 62.6%, P: 0.29%, SiCh: 2.7%, alumina: 2.2%, and combined water [CW]: 4.5%. The phosphorus concentration in goethite contained in the high-phosphorus ore A was 1.33%. The high-phosphorus ore A was used as the ore of Inventive Example. The components of the high-phosphorus ore B were iron: 61.6%, P: 0.19%, SiO2: 1.6%, alumina: 1.8%, and combined water [CW]: 7.1%. The phosphorus concentration in goethite contained in the high-phosphorus ore B was 0.37%. The high-phosphorus ore B was used as the ore of Comparative Example.

[0105] Both the ore used in Comparative Example and the ore used in Inventive Example were dried at 105 °C for 2 hours and then sized to 5 to 10 mm using a vibrating sieve. The weight of the ore was about 3 kg.

[0106] (Heat Treatment Device and Method) The heating furnace was a kiln-type heating furnace. The heating conditions were as follows. • Size of internal space of heating furnace: diameter of 0.90 m and length of 2.0 m • Rotation speed of heating furnace: 2.0 rpm • Number of heating furnaces: 1 • Amount of ore charged into heating furnace: 1 kg / h (constant charging rate) • Type of gas supplied to heating furnace: air (N2-21%O2) or reducing gas (N2-30%H2) • Flow rate of gas supplied to heating furnace: 15 Nm3 / h when gas is reducing gas, and 6 Nm3 / h when gas is air • Heating temperature: 700°C when gas is reducing gas, and 280°C when gas is air • Holding time at steam heating temperature: 55 min when gas is reducing gas, and 22 min when gas is air • Post-heating classification treatment: Iron ore discharged from heating furnace was classified using sieving device having sieve opening of 0.25 mm

[0107] (Calculation of Phosphorus Removal Amount) A phosphorus removal amount was calculated by multiplying the obtained dephosphorization rate by the initial phosphorus content of the iron ore. The initial phosphorus content of the iron ore is the phosphorus content of the iron ore after drying at 105°C for 2 hours and then sizing to 5 to 10 mm using the vibrating sieve, as described above. The dephosphorization rate was expressed as a percentage of the difference before and after treatment in a value obtained by normalizing the phosphorus content by the iron content (P / Fe). Table 6 shows the results.

[0108] [Table 6] Comparative Example Example Phosphorus in goethite (% by mass) 0.37 1.33 Phosphorus removal amount (g / t-Ore) 400 530 When ore having a high phosphorus concentration in goethite was charged into the kiln-type heating furnace, the dephosphorization rate and the phosphorus removal amount were far higher than those when ore having a low phosphorus concentration in 5 goethite was charged. REFERENCE SIGNS LIST

[0110] 1 Storage tank 2 Heating furnace 10            21 First heating furnace 22 Second heating furnace 2a, 21a, 22a Supply port 2b, 21b, 22b Discharge port 3 Gas supply device 15           31 Non-reducing gas supply device 32 Reducing gas supply device 4, 41, 42 Dust collector 5, 6, 7 Sieving device

Claims

1. A dephosphorization method for ore, the dephosphorization method comprising:heating ore at a temperature of 100°C or higher in a kiln-type or fluidized-bed-type heating furnace.

2. The dephosphorization method for ore according to Claim 1,wherein, during the heating of the ore, a reducing gas is supplied into the heating furnace.

3. The dephosphorization method for ore according to Claim 1,wherein, during the heating of the ore, a non-reducing gas is supplied into the heating furnace.

4. The dephosphorization method for ore according to Claim 1,wherein the heating furnace includes a first heating furnace and a second heating furnace,a non-reducing gas is supplied to the first heating furnace,a reducing gas is supplied to the second heating furnace, andin the heating, the ore is first supplied to the first heating furnace and heated, and then the ore heated in the first heating furnace is supplied to the second heating furnace and heated.

5. The dephosphorization method for ore according to Claim 4, further comprising:classifying the ore into a coarse fraction and a fine fraction finer than the coarse fraction after the ore is heated in the first heating furnace and before the ore is supplied to the second heating furnace,wherein the fine fraction is excluded from the ore supplied to the second heatingfurnace.

6. The dephosphorization method for ore according to Claim 5,wherein, in the classifying the ore after the ore is heated in the first heating furnace and before the ore is supplied to the second heating furnace, a sieving device having a sieve opening of 0.5 mm or more and 3.0 mm or less is used.

7. The dephosphorization method for ore according to any one of Claims 1 to 6, further comprising:before the heating the ore in the heating furnace, classifying the ore into a coarse fraction and a fine fraction using a sieving device having a sieve opening of 3.0 mm or more and 5.0 mm or less,wherein the kiln-type heating furnace is used as the heating furnace, only the coarse fraction is supplied to the heating furnace, anda heating temperature of the coarse fraction in the heating furnace is 400°C or higher.

8. The dephosphorization method for ore according to any one of Claims 1 to 6, wherein there are two or more types of ore, the ore contains goethite, the dephosphorization method further comprises, before the heating the ore in the heating furnace, selecting the ore having a highest phosphorus concentration in the goethite, andthe ore having the highest phosphorus concentration in the goethite is preferentially supplied to the heating furnace.

9. The dephosphorization method for ore according to any one of Claims 1 to 6, wherein the ore contains goethite, andonly the ore having a phosphorus concentration in the goethite of 1.0% by massor more is supplied to the heating furnace.

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