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

Method for removing phosphorus from ore

[0001] The present invention relates to a method for removing phosphorus from an ore.

[0002] Phosphorus contained in sintered ore, a raw material for blast furnace steel, is one of the important components for quality control of the molten iron produced in the blast furnace. Phosphorus has a strong affinity with iron. Therefore, when steel is produced from sintered ore via molten iron, phosphorus tends to remain in the steel. Residual phosphorus in the steel can cause low-temperature brittle fracture, impairing the quality of the steel.

[0003] As a method for reducing phosphorus contained in iron ore, Non-Patent Document 1 discloses a method for reducing iron ore containing phosphorus by supplying a hydrogen-steam mixed gas to the iron ore, thereby removing the phosphorus as a gas. Patent Document 1 also describes a CO gas reduction equilibrium diagram of iron oxide and diphosphorus pentaoxide for high-phosphorus iron ore, and a H gas reduction equilibrium diagram of iron oxide and diphosphorus pentaoxide for high-phosphorus iron ore. ２ Gas reduction equilibrium diagram and / or CO-H of iron oxide and diphosphorus pentoxide ２ P of mixed gas reduction equilibrium diagram ２ The phosphorus compounds are reduced, vaporized and removed by supplying a gas in the gas equilibrium region and the FeO equilibrium region for reduction.

[0004] Japanese Patent Application Laid-Open No. 2020-20010

[0005] "Direct removal of phosphorus from high-phosphorus iron ore," Iron and Steel, Vol. 100 (2014) No. 2, pp. 325-330

[0006] An object of the present invention is to provide a method for removing phosphorus from ore.

[0007] The gist of the present invention is as follows. (1) A method for dephosphorizing ore according to one embodiment of the present disclosure includes a step of heating ore at a temperature of 100°C or higher in a kiln-type or fluidized-bed heating furnace. (2) Preferably, in the method for dephosphorizing ore described in (1) above, a reducing gas is supplied into the heating furnace during the step of heating the ore. (3) Preferably, in the method for dephosphorizing ore described in (1) or (2) above, a non-reducing gas is supplied into the heating furnace during the step of heating the ore. (4) Preferably, in the ore dephosphorization method described in any one of (1) to (3) above, the heating furnace comprises 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 step, 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 ore dephosphorization method described in (4) above further comprises a step of classifying the ore into a coarse particle fraction and a fine particle fraction finer than the coarse particle fraction after heating in the first heating furnace and before supplying it to the second heating furnace, and the coarse particle fraction is removed from the ore supplied to the second heating furnace. (6) Preferably, in the method for dephosphorizing ore described in (5) above, a sieve having a mesh size of 0.5 mm or more and 3.0 mm or less is used in the step of classifying the ore after heating in the first heating furnace and before supplying it to the second heating furnace. (7) Preferably, the method for dephosphorizing ore described in any one of (1) to (6) above further comprises a step of classifying the ore into a coarse particle fraction and a fine particle fraction using a sieve having a mesh size of 3.0 mm or more and 5.0 mm or less before the step of heating the ore in the heating furnace, wherein the heating furnace is a kiln-type heating furnace, only the coarse particle fraction is supplied to the heating furnace, and the heating temperature of the coarse particle fraction in the heating furnace is 400°C or more. (8) Preferably, in the method for dephosphorizing ore according to any one of (1) to (7) above, the ore contains two or more types of ore, and the ore contains goethite, and the method further comprises a step of selecting the ore having the highest phosphorus concentration in the goethite before the step of heating the ore in the heating furnace, and the ore having the highest phosphorus concentration in the goethite is preferentially supplied to the heating furnace.(9) Preferably, in the method for dephosphorizing an ore according to any one of (1) to (8) above, the ore contains goethite, and only the ore having a phosphorus concentration of 1.0 mass% or more in the goethite is supplied to the heating furnace.

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

[0009] Fig. 1 is a diagram illustrating an example of equipment for carrying out a dephosphorization method. Fig. 2 is a diagram illustrating another example of equipment for carrying out a dephosphorization method. Fig. 3 is a diagram illustrating another example of equipment for carrying out a dephosphorization method. Fig. 4 is a diagram illustrating another example of equipment for carrying out a dephosphorization method.

[0010] In an embodiment of the present disclosure, the ore dephosphorization method involves heating the ore at a temperature of 100°C or higher in a kiln or fluidized bed heating furnace. Heating the ore in a kiln or fluidized bed heating furnace applies a physical impact to the ore. This separates phosphorus-containing fine powder from the ore. Physically separating the phosphorus-containing fine powder from the ore allows phosphorus to be released from the ore. Here, the "physical impact" refers to an impact applied to the ore by fluidizing the ore. Furthermore, the "fine powder" refers to ore with a diameter small enough to be removed by blowing gas. The dephosphorization method of this embodiment will now be described in detail.

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

[0012] (Kiln-type heating furnace) In a kiln-type heating furnace, the heating furnace rotates, causing the ore inside the furnace to flow. This causes physical shocks to the ore. These physical shocks include shocks when the ore collides with the inner wall of the heating furnace and shocks when ore particles collide with each other.

[0013] Kiln-type heating furnaces are divided into internal combustion and external combustion furnaces. Internal combustion furnaces are furnaces in which combustion gas is introduced directly into the furnace. External combustion furnaces are furnaces in which heat is added from outside the furnace.

[0014] (Fluidized Bed Furnace) In a fluidized bed furnace, hot gas is blown onto ore particles. The gas causes the ore particles to flow, forming a fluidized bed. The gas also heats the ore. In a fluidized bed furnace, the ore is subjected to physical shocks by flowing inside the furnace. These physical shocks include the shocks caused when the ore collides with the inner walls of the furnace and when the ore particles collide with each other.

[0015] Fluidized bed furnaces include direct heating furnaces and indirect heating furnaces. Direct heating furnaces are furnaces that apply heat directly to the ore inside the furnace. Indirect heating furnaces are furnaces that apply heat indirectly to the ore inside the furnace. Fluidized bed furnaces may also be furnaces that circulate the ore.

[0016] (Ore Heating Temperature) The ore heating temperature in the heating furnace is 100°C or higher. Heating the ore to a predetermined temperature of 100°C or higher dries the ore, making it easier to remove fine particles adhering to the ore with water. Applying physical impact to the ore in a dry state can efficiently remove the fine particles from the ore. Because the fine particles tend to contain high concentrations of phosphorus, physically separating the fine particles from the ore can remove the phosphorus from the ore. Furthermore, heating the ore to a predetermined temperature of 100°C or higher in a fluidized bed or kiln-type heating furnace causes a dehydration reaction, which can remove the phosphorus from the goethite contained in the ore. Goethite is a mineral that constitutes ore and has the chemical composition FeO(OH). JIS M 8700:2013, "Iron ore and reduced iron - Terminology," classifies goethite as a hydrous iron oxide.

[0017] The ore may be heated to a predetermined temperature of 300°C or higher. This is preferable because it further evaporates the crystal water contained in the ore and embrittles the goethite portion, which is the portion containing the crystal water. When the portion containing the crystal water is in an embrittled state, the embrittled portion can be pulverized by applying a physical impact to the ore. This further promotes separation of the fine powder from the ore. The portion containing the crystal 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. Therefore, by physically separating the pulverized fine powder from the ore, phosphorus can be removed from the ore.

[0018] The upper limit of the predetermined temperature for heating the ore is not particularly limited. For example, considering the durability of the heating furnace and the phosphorus removal efficiency described in the examples below, the heating temperature is preferably 1000°C or less. Furthermore, as will be described in detail in the examples, when the heating temperature exceeds 750°C, the ratio of the increase in dephosphorization rate to the increase in temperature is lower than when the heating temperature is below 750°C. In other words, when the heating temperature exceeds 750°C, the improvement in the phosphorus removal effect with increasing heating temperature is limited compared to when the heating temperature is below 750°C. This phenomenon occurs whether the heating furnace atmosphere is non-reducing or reducing. Therefore, it is more preferable to set the heating temperature to 750°C or less. Furthermore, as will be described later, even in the range of approximately 100°C to 500°C, the dephosphorization effect can be obtained regardless of the heating furnace atmosphere. Therefore, taking into consideration the energy costs in the heating furnace, the ore may be heated in the range of 100°C to 500°C, or in the range of 100°C to 300°C.

[0019] The rate of temperature rise when heating the ore to a predetermined temperature can be determined as appropriate. The time for heating the ore at the predetermined temperature, i.e., the time for maintaining the temperature of the ore at the predetermined temperature, is not particularly limited, but is preferably a time that allows sufficient evaporation of the water of crystallization contained in the ore, as described below. This time can be, for example, 5 minutes or more.

[0020] (Type of gas supplied into heating furnace) The atmosphere in the heating furnace can be determined appropriately. For example, the atmosphere in the heating furnace can be a non-reducing atmosphere or a reducing atmosphere. The term "non-reducing atmosphere" is a concept that encompasses both an oxidizing atmosphere and an inert atmosphere.

[0021] For example, the atmosphere in the heating furnace can be made into an oxidizing atmosphere by supplying a gas containing oxygen gas, which is a type of oxidizing gas, or the air into the heating furnace. Furthermore, the atmosphere in the heating furnace can be made into an inert atmosphere by supplying a type of inert gas, such as nitrogen gas or argon gas, into the heating furnace. Hereinafter, the term "non-reducing gas" will be used as a concept that encompasses both inert gases and oxidizing gases.

[0022] Furthermore, by supplying a reducing gas, such as a hydrogen-containing gas or a carbon monoxide-containing gas, into the heating furnace, the atmosphere inside the heating furnace can be made a reducing atmosphere. By making the atmosphere inside the heating furnace a reducing atmosphere, in addition to the phosphorus removal according to the dephosphorization method of this embodiment, i.e., phosphorus removal due to heating the ore and physical impact on the ore, the phosphorus removal described in Non-Patent Document 1, i.e., removal of phosphorus from the ore as a gas, can be achieved. That is, by heating the ore in a reducing atmosphere, the phosphate contained in the ore can be reduced, decomposed, and removed.

[0023] The means for supplying a reducing gas or a non-reducing gas into the heating furnace is not particularly limited. When the heating furnace is of a fluidized bed type, the gas for fluidizing the ore may be a reducing gas or a non-reducing gas. When the heating furnace is of a kiln type, as exemplified in FIG. 1, the reducing gas or the non-reducing gas may be sprayed toward the ore from the inlet or outlet of the heating furnace. Note that, if a reducing gas or a non-reducing gas is supplied to the heating furnace and the gas is made to flow inside the heating furnace, the fine powder separated from the ore can be moved together with the gas, i.e., the fine powder can be conveyed by airflow. This also has the effect of making it easier to remove the fine powder from the ore.

[0024] (Classification after heating) The ore discharged from the heating furnace may be subjected to classification. By the classification, fine powder separated from the ore can be separated from the ore. This allows the fine powder separated from the ore to be removed. Unlike the intermediate classification described below, it is not expected that the ore will be further heated after the classification after heating. If the ore is heated two or more times, the classification after heating is performed after all heating processes are completed.

[0025] As a means for carrying out classification treatment after heating, for example, a sieve can be used. The mesh size of the sieve can be appropriately determined taking into consideration the particle size of the fine powder to be separated from the ore. For example, in classification treatment after heating, the mesh size can be set to 0.125 [mm] to 0.25 [mm].

[0026] Next, an example of equipment for carrying out the method for dephosphorizing ore according to the present embodiment will be described with reference to FIG.

[0027] The ore to be dephosphorized is stored in a storage tank 1. The ore discharged from the storage tank 1 is transported to a kiln-type heating furnace 2. The ore is supplied into the heating furnace 2 from a supply port 2a located at one end of the heating furnace 2. The ore is then heated to a predetermined temperature of 100°C or higher, and is subjected to a rolling action by the rotation of the heating furnace 2, thereby giving rise to physical impacts. Inside the heating furnace 2, the water of crystallization evaporates and pulverizes as described above, separating fine powder from the ore. The ore moves from the supply port 2a of the heating furnace 2 toward a discharge port 2b located at the other end of the heating furnace 2, and is discharged from the discharge port 2b.

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

[0029] The ore discharged from the discharge port 2b of the heating furnace 2 may be transported to a sieve 5 for classification. The sieve 5 has meshes of a predetermined size. The meshes of the sieve 5 are, for example, in the range of 0.125 mm to 0.25 mm. The sieve 5 removes fine particles of a predetermined size or less from the ore transported to the sieve 5. The ore remaining on the sieve of the sieve 5 has had phosphorus removed from it. The ore from which phosphorus has been removed is used to produce sintered ore or pellets, which are iron raw materials to be charged into a blast furnace.

[0030] The heating furnace 2 may be a fluidized bed type heating furnace as described above. The gas supplied into the heating furnace causes the ore to flow, thereby applying physical shock to the ore. Therefore, a fluidized bed type heating furnace can separate fine particles from the ore and dephosphorize it, just like a kiln type.

[0031] (Combined Use of a First Heating Furnace with a Non-Reducing Atmosphere and a Second Heating Furnace with a Reducing Atmosphere) In the embodiment illustrated in Fig. 1, the ore is heated in the heating furnace once in either a non-reducing atmosphere or a reducing atmosphere. However, the ore dephosphorization method according to this embodiment is not limited to this configuration. For example, the ore may be heated in a non-reducing atmosphere and then heated in a reducing atmosphere.

[0032] The heating in a non-reducing atmosphere and the heating in a reducing atmosphere may be performed in separate heating furnaces. The first and second heating furnaces may be the same in volume, type, etc., or may be different. For example, one heating furnace may be a kiln-type heating furnace and the other heating furnace may be a fluidized-bed type heating furnace.

[0033] Alternatively, heating under a non-reducing atmosphere and heating under a reducing atmosphere may be performed in the same heating furnace. In this case, after the first heating, the type of gas supplied to the heating furnace is changed, and then the second heating is performed. In this case, the heating furnace into which the non-reducing gas is blown is considered to be the first heating furnace, and the heating furnace into which the reducing gas is blown is considered to be the second heating furnace.

[0034] A case where heating under a non-reducing atmosphere and heating under a reducing atmosphere are performed in separate heating furnaces will be described with reference to Figure 2. The equipment shown in Figure 2 is composed of two heating furnaces, 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 explanation, explanations of parts that overlap with the case of Figure 1 will be omitted. Also, as an example, the first heating furnace 21 and the second heating furnace 22 will be described as being kiln-type. However, either or both of the first heating furnace 21 and the second heating furnace 22 may be fluidized bed-type heating furnaces.

[0035] First, ore is supplied from the storage tank 1 to the first heating furnace 21. In the first heating furnace 21, the ore is heated to a predetermined temperature of 100°C or higher. A non-reducing gas is supplied to the first heating furnace 21 from the non-reducing gas supply unit 31. In the first heating furnace 21, the ore is heated in a non-reducing atmosphere. The rotation of the first heating furnace 21 causes the ore to be subjected to a rolling action, which imparts physical impact to the ore. This separates fine powder from the ore. The fine powder is discharged together with gas and collected in the dust collector 41. The gas discharged together with the fine powder is referred to as exhaust gas. This releases some of the phosphorus contained in the ore. Note that in FIG. 2, the non-reducing gas flows from the exhaust port 21b of the first heating furnace 21 toward the supply port 21a, but the exhaust gas may also flow from the supply port 21a toward the exhaust 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 located at one end of the second heating furnace 22. Thereafter, in the second heating furnace 22, the ore is heated in a reducing atmosphere at a predetermined temperature of 100°C or higher, and is subjected to a rolling action and physical shock by the rotation of the second heating furnace 22. The ore moves from the supply port 22a inside the second heating furnace 22 toward the discharge port 22b located at the other end, and is discharged from the discharge port 22b.

[0037] The reducing gas supplier 32 supplies reducing gas to the interior of the second heating furnace 22. The reducing gas from the reducing gas supplier 32 is supplied into the interior of the second heating furnace 22 through the exhaust port 22b of the second heating furnace 22, moves along the rotational axis direction of the second heating furnace 22, and is then discharged through the supply port 22a. As the gas flows through the interior of the second heating furnace 22, the fine powder separated from the ore, as described above, moves along with the gas. 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. The fine powder discharged from the second heating furnace 22 is then collected by the dust collector 42. Note that, although the gas flows from the exhaust port 22b of the second heating furnace 22 toward the supply port 22a, it is also possible to flow the gas from the supply port 22a toward the exhaust port 22b.

[0038] The ore discharged from the discharge port 22b of the second heating furnace 22 may be transported to a sieve 5 for classification. The sieve 5 has meshes of a predetermined size. The meshes of the sieve 5 are, for example, in the range of 0.125 mm to 0.25 mm. The sieve 5 removes fine particles of a predetermined size or less from the ore transported to the sieve 5. The ore remaining on the sieve of the sieve 5 has had phosphorus removed from it. The ore from which phosphorus has been removed is used to produce sintered ore or pellets, which are iron raw materials to be charged into a blast furnace.

[0039] The heating temperatures of the first heating furnace 21 and the second heating furnace 22 may be the same or different. Furthermore, both heating in a non-reducing atmosphere and heating in a reducing atmosphere may be performed in the same heating furnace. In this case, the heating temperatures in each atmosphere may be the same or different. However, the heating temperature in the second heating, which is heating in a reducing atmosphere, is preferably 300°C or higher. That is, it is preferable that the first heating temperature be 100°C or higher and the second heating temperature be 300°C or higher. The term "second heating" refers to both the heating in the second heating furnace 22 when two heating furnaces are used to sequentially heat the ore, and the second heating when one heating furnace is used to heat the ore twice. By setting the second heating temperature to 300°C or higher, the remaining phosphorus can be more efficiently removed from the goethite portion of the ore in the first heating.

[0040] Furthermore, the heating time of the first heating and the heating time of the second heating are not particularly limited. Furthermore, the first heating time and the second heating time may be the same or different. Note that the "first heating" refers to both the heating in the first heating furnace 21 when two heating furnaces are used to sequentially heat the ore, and the first heating when one heating furnace is used to heat the ore twice.

[0041] As described above, phosphorus contained in the ore may be removed by first heating in a non-reducing atmosphere and then heating in a reducing atmosphere. Compared to a single heating in either a non-reducing or reducing atmosphere, combining heating in a non-reducing atmosphere and heating in a reducing atmosphere can remove more phosphorus from the ore. Furthermore, first heating in a non-reducing atmosphere, which is generally cheaper than a reducing atmosphere, removes phosphorus by thermal decomposition of goethite, where most of the phosphorus is present, and then removing the remaining phosphorus and phosphorus oxides by heating in a reducing atmosphere. This allows for more efficient phosphorus removal while minimizing the use of more expensive reducing gas. Therefore, the method of the above-described embodiment in which two heating steps are performed can achieve further energy and cost savings compared to a single heating step. That is, when the ore heating step includes first heating the ore in a non-reducing atmosphere and then second heating the ore in a reducing atmosphere after the first heating, the amount of reducing gas required to reduce and decompose the phosphates present in the ore can be reduced. Since non-reducing gases are cheaper than reducing gases, reducing the amount of reducing gas used using the first heating furnace reduces dephosphorization costs.

[0042] Furthermore, heating in a reducing atmosphere can also reduce iron oxide in the ore. Because the metallic iron produced by reduction binds with phosphorus, heating in a reducing atmosphere can actually decrease the dephosphorization rate. Therefore, by using a non-reducing atmosphere for part of the entire heating process, the reduction reaction to metallic iron, which leads to a decrease in the dephosphorization rate, can be suppressed, and the dephosphorization reaction alone can be efficiently promoted, which is an advantage.

[0043] (Intermediate classification process) An intermediate classification process may be further performed between the first heating furnace 21 and the second heating furnace 22. The intermediate classification process is a process of separating the ore discharged from the first heating furnace 21 into a coarse particle fraction and a fine particle fraction. Unlike the classification process after heating described above, the ore is always subjected to a second heating process after the intermediate classification process. The intermediate classification process is defined as a process of classifying the ore after it has been heated in the first heating furnace and before it is supplied to the second heating furnace.

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

[0045] In the sieve 6 used in the intermediate classification process, the mesh size is preferably 0.5 mm or more and 3.0 mm or less. Particles that do not pass through the sieve mesh in the sieve 6 are the coarse particle portion, and particles that pass through the sieve mesh are the fine particle portion. The particle size can be adjusted by the mesh size of the sieve 6. By using a sieve with a mesh range of 0.5 mm or more and 3.0 mm or less, the particle size of the fine particle portion can be set to 0.5 mm or more and 3.0 mm or less. The mesh size of the sieve 6 used in the intermediate classification process is larger than the mesh size of the sieve 5 used in the classification process after heating to remove fine powder. The classification device used in the intermediate classification process is not limited to a sieve, and other classification devices may be used.

[0046] Typically, in ore heated in the first heating furnace 21 and from which fine particles have been removed, the smaller the particle size, the lower the phosphorus content. In other words, the smaller the particle size of the ore, the higher the dephosphorization rate. Therefore, the intermediate classification process described above can separate the ore discharged from the first heating furnace 21 into a coarse particle fraction with a relatively low dephosphorization rate and a fine particle fraction with a relatively high dephosphorization rate. By performing the intermediate classification process, only the coarse particle fraction that requires dephosphorization can be preferentially fed to the second heating furnace 22. This allows for more effective dephosphorization by focusing on the portion of the entire iron ore that requires further dephosphorization by reduction—in other words, the portion where dephosphorization is difficult to proceed and where dephosphorization by reduction should be performed with higher priority. Furthermore, by heating only the coarse particle fraction in the second heating furnace 22, more efficient dephosphorization can be achieved in terms of overall energy efficiency and gas consumption than when all the ore is heated in the second heating furnace 22. That is, when the ore is classified after the first heating and before the second heating, the removal of fine particles from the ore increases the reaction efficiency between the ore particles and the reducing gas, thereby further reducing the amount of reducing gas required to reduce and decompose the phosphates present in the ore.

[0047] The fine particles separated by the intermediate classification treatment in this embodiment have a sufficiently high dephosphorization rate, and can be used as dephosphorized iron ore directly for pellets, briquettes, raw material for sintering, etc. Note that the classification treatment after heating using the sieve 5 shown in Fig. 3 may be omitted.

[0048] (Classification before heating) The method for dephosphorizing ore according to this embodiment may further include a step of classifying the ore into a coarse particle portion and a fine particle portion before the step of heating the ore in a heating furnace. Hereinafter, the classification process of the ore before heating is referred to as the "classification process before heating." Figure 4 shows an exemplary process diagram of the method for dephosphorizing ore that performs classification process before heating.

[0049] First, the configuration of a method for dephosphorizing ore by pre-heating classification will be described with reference to Figure 4. The ore to be dephosphorized is stored in a storage tank 1. The ore discharged from the storage tank 1 is transported to a sieve 7 before being transported to a kiln-type heating furnace 2. The sieve 7 for pre-heating classification has sieve openings of 3.0 mm or more and 5.0 mm or less. The sieve 7 classifies the ore before heating into a coarse particle fraction and a fine particle fraction.

[0050] After classification before heating, the coarse particle portion is supplied to the heating furnace 2. It is preferable that the fine particle portion is removed from the ore supplied to the heating furnace 2. The fine particle portion may be added to the ore discharged from the heating furnace 2. The fine particle portion does not have to be used as ore for steel production. The heating furnace 2 is a kiln-type heating furnace. The heating temperature of the coarse particle portion in the heating furnace 2 is set to 400°C or higher. More preferably, the heating temperature is set to a range of 600 to 1000°C.

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

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

[0053] For example, when the heating furnace is composed of a first heating furnace 21 and a second heating furnace 22, the ore may be classified before being 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 a kiln type, and the heating temperature thereof may be 400° C. or higher. More preferably, the first heating furnace 21 may be a kiln type, and the heating temperature thereof may be 400° C. or higher.

[0054] For example, in addition to the classification treatment before heating, one or both of intermediate classification treatment and classification treatment after heating may be performed. When multiple classification treatments are performed, all classification treatments may be performed using a single sieve. However, the sieve mesh suitable for the classification treatment before heating is not necessarily the same as the sieve mesh suitable for the intermediate classification treatment and the classification treatment after heating. This is because the conditions of the ore to be classified and the purposes of these classification treatments are different. In particular, the classification treatment before heating is intended to maintain the rolling ability in the furnace and improve reactivity with gas, while the classification treatment after heating is intended to remove particles in which phosphorus removal has progressed, thereby selectively introducing only particles in which phosphorus removal has not progressed into the heating furnace 2, thereby enabling efficient phosphorus removal. Therefore, it is most preferable to independently install the sieve 7 for the classification treatment before heating, the sieve 6 for the intermediate classification treatment, and the sieve 5 for the classification treatment after heating.

[0055] Next, the technical concept and effects of the method for dephosphorizing ore by pre-heating classification will be described. The inventors discovered that when dephosphorizing ore using a kiln-type heating furnace at 400°C or higher, the dephosphorization efficiency decreases when the particle size of the ore fed into the heating furnace is below a certain threshold. This phenomenon contradicts the common general knowledge of those skilled in the art. When reducing ore using a kiln-type heating furnace, it is believed 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 greater the surface area per weight of the ore. Therefore, common general knowledge predicted that the smaller the particle size of the ore, the easier it would be to dephosphorize the ore.

[0056] Based on the above-mentioned findings of the present inventors, it is preferable to remove the fine particle portion of the ore before dephosphorizing the ore using a kiln-type heating furnace at 400°C or higher. By targeting only the coarse particle portion, which is the portion where the dephosphorization rate can be easily increased, the dephosphorization efficiency can be increased, and a more efficient dephosphorization process can be implemented in terms of overall energy efficiency and gas consumption. As revealed through experiments by the present inventors, the above-mentioned effects can be preferably obtained by performing classification using a sieve with openings of 3 mm to 5 mm and supplying only the coarse particle portion remaining on the sieve openings to the heating furnace.

[0057] (Selection of Ore Before Heating) When there are two or more types of ore, the method for dephosphorizing ore according to this embodiment may further include a step of selecting the ore having the highest goethite phosphorus concentration before the step of heating the ore in the heating furnace, and the ore having the highest goethite phosphorus concentration may be preferentially supplied to the heating furnace. Specific configurations of an embodiment in which the ore is selected before being heated will be described in detail below.

[0058] The types of ore are distinguished based on the face formed when the ore is mined within the deposit. A face is a working area in a coal, metal, or other mine where coal, ore, etc. is mined or tunnels are excavated (see JIS M 0102:2000 "Mine Terminology"). The grade of the ore may vary depending on the face from which the ore is mined. The types of ore may also be distinguished based on the origin of the ore.

[0059] When there are two or more types of ores, the ore with the highest phosphorus concentration in the goethite is selected as the target for dephosphorization. It should be noted that the criterion for selecting the ore is the phosphorus concentration in the goethite in the ore, not the phosphorus content of the ore. For example, if there are ore A with a low goethite content but a high phosphorus concentration in the goethite and ore B with a high goethite content but a low phosphorus concentration in the goethite, ore A is selected as the target for dephosphorization. Even if the total amount of phosphorus contained in ore B is greater than that of ore A, ore A is preferentially subjected to dephosphorization based on the phosphorus concentration in the goethite contained in the ore from the viewpoints of efficiency and energy conservation.

[0060] When the phosphorus concentration of goethite in the ore is unknown, the method for dephosphorizing the ore may further include a step of measuring the phosphorus concentration of 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 dispersive X-ray analyzer (EDS), and a computer that controls the SEM and stores EDS spectra of each mineral species as data. Japanese Patent Application Laid-Open Publication No. 2015-40724 discloses an example of an MLA. Japanese Patent Application Laid-Open Publication No. 2020-34372 discloses an example of an analysis method using an MLA.

[0061] By performing elemental analysis of a cross-sectional polished sample of iron ore using MLA, it is possible to identify the amount of goethite per unit mass of iron ore and the location of goethite. Furthermore, by cross-sectional analysis using MLA, it is possible to identify the amount of phosphorus per unit mass of iron ore and the location of phosphorus. By comparing the analysis results of goethite and phosphorus, it is possible to identify the phosphorus concentration in goethite.

[0062] The ore with the highest goethite phosphorus concentration selected by the above procedure is preferentially supplied to the heating furnace for dephosphorization. Specifically, the ore with the highest goethite phosphorus concentration is supplied to the heating furnace first. Next, after all of the ores have been supplied to the heating furnace, the ore with the highest goethite phosphorus concentration is selected from the remaining ores and supplied to the heating furnace. In other words, the order in which the ores are supplied to the heating furnace is determined in descending order of goethite phosphorus concentration. If a different type of ore arrives before all types of ore have been supplied to the heating furnace, the ore to be dephosphorized is selected from the group including the new ore by the above method.

[0063] Next, the effects of an embodiment in which the ore is sorted before being heated will be described. In the ore dephosphorization method according to this embodiment, the criterion for selecting the type of ore to be supplied to the heating furnace is the phosphorus concentration of goethite in the ore. This is because kiln-type or fluidized-bed heating furnaces have difficulty removing phosphorus contained in minerals other than goethite. On the other hand, the phosphorus concentration of goethite significantly affects the efficiency of dephosphorization of ore using a kiln-type or fluidized-bed heating furnace. The higher the phosphorus concentration of goethite in the ore, the easier it is to perform dephosphorization using a kiln-type or fluidized-bed heating furnace.

[0064] According to the method for dephosphorizing ore of this embodiment, ore with high dephosphorization efficiency can be preferentially dephosphorized, thereby further increasing the efficiency of the dephosphorization process.

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

[0066] According to the results of experiments conducted by the present inventors, by subjecting only goethite ores having a phosphorus concentration of 1.0 mass% or more to dephosphorization treatment using a kiln-type or fluidized-bed heating furnace, it is possible to further increase the dephosphorization efficiency and reduce the energy required for dephosphorization.

[0067] The various configurations described above may be appropriately combined with the configuration of selecting the ore before heating.

[0068] The effects of one embodiment of the present disclosure will be explained in more detail using examples. However, the conditions in the examples are merely examples of conditions adopted to confirm the feasibility and effects of the present disclosure. The present disclosure is not limited to this example of conditions. Various conditions may be adopted in the present disclosure as long as they do not deviate from the gist of the disclosure and achieve the purpose.

[0069] (Experiment 1) (Ore) In the comparative example and examples 1 to 5 described below, ore having the components shown in Table 1 below was used. In the comparative example, 2 kg of ore was charged into a batch-type heating furnace described below. In examples 1 to 4, the ore was supplied to a kiln-type heating furnace described below at a constant supply rate of 300 kg / h.

[0070]

[0071] (Heating furnace) In the comparative example, a batch-type box furnace was used as the heating furnace, which only heats the ore without fluidizing it. The inner diameter of the box furnace was 300 mm wide, 300 mm deep, and 300 mm high. In Examples 1 to 4, an external combustion kiln was used as the heating furnace. The internal space of the kiln had a diameter of 0.90 m and a length of 2.0 m. The rotation speed of the kiln was 2.0 rpm.

[0072] (Number of heating furnaces and heating atmosphere conditions) In the comparative example and Example 1, the number of heating furnaces was 1. In the comparative example and Example 1, air, which is an oxidizing gas, was used at a flow rate of 15 [Nm ３ The atmosphere in the heating furnace was a non-reducing atmosphere. In Example 2, the number of heating furnaces was 1. In Example 2, 33% H ２ and the remainder is N ２ The reducing gas is 15 [Nm ３ The ore was supplied into the heating furnace at a flow rate of [1 / h], and the atmosphere in the heating furnace was a reducing atmosphere. In Examples 3 and 4, the number of heating furnaces was two. In the first heating furnace, heat treatment was performed in a non-reducing atmosphere under the conditions of Example 1. The ore was then cooled to room temperature. Then, in the second heating furnace, heat treatment was performed in a reducing atmosphere under the conditions of Example 2.

[0073] (Heating Temperature Conditions) In the comparative example and Examples 1 to 4, a plurality of temperatures were set as the temperature to which the ore was heated. Specifically, in the heating furnace, the temperature was raised to 100°C, 300°C, 500°C, 750°C, 1000°C, and 1100°C, and then maintained at these temperatures. In Examples 3 and 4, the heating temperature in the non-reducing atmosphere was the same as the heating temperature in the reducing atmosphere.

[0074] (Heating time conditions) In Examples 1 and 2, the residence time of the ore in the heating furnace was 120 min. In Examples 3 and 4, the total residence time of the ore in the first heating furnace and the second heating furnace was 120 min. In Examples 3 and 4, heating in a non-reducing atmosphere in the first heating furnace was performed for 60 min, and heating in a reducing atmosphere in the second heating furnace was performed for 60 min. In the comparative example, the heating time in the heating furnaces was 120 min.

[0075] (Intermediate classification treatment) In Example 5, after heat treatment in a non-reducing atmosphere in the first heating furnace, the ore was discharged from the first heating furnace and subjected to intermediate classification treatment using a sieve with 3.0 mm mesh. In the intermediate classification treatment, the ore was separated into a fine particle portion and a coarse particle portion. Then, only the coarse particle portion was placed in a second heating furnace and subjected to heat treatment in a reducing atmosphere. Note that the intermediate classification treatment was not performed for the comparative example and Examples 1 to 4.

[0076] In all the examples, classification treatment before heating and classification treatment after heating were not carried out.

[0077] Table 2 below summarizes the test conditions described above.

[0078]

[0079] (Measurement of dephosphorization rate) The dephosphorization rate was measured for the ore that had been heat-treated in the heating furnace. In the comparative example and Examples 1 to 3, the dephosphorization rate was measured for the ore discharged from the heating furnace. The dephosphorization rate for Example 4 was determined by the following procedure. First, the dephosphorization rate of the fine particle portion obtained by intermediate classification after heating in a non-reducing atmosphere in the first heating furnace was determined. The dephosphorization rate of the coarse particle portion obtained by heating in a reducing atmosphere in the second heating furnace was also determined. The overall dephosphorization rate for Example 5 was determined from both the dephosphorization rate of the fine particle portion and the dephosphorization rate of the coarse particle portion after heating. The overall dephosphorization rate was calculated as the sum of the values ​​obtained by multiplying the mass ratio of the coarse particle portion to the fine particle portion by each dephosphorization rate. That is, the overall dephosphorization rate was calculated using the following formula: (Total dephosphorization rate) = {(Dephosphorization rate of fine particle portion) × (weight of fine particle portion) + (Dephosphorization rate of coarse particle portion) × (weight of coarse particle portion)} / {(weight of fine particle portion) + (weight of coarse particle portion)}

[0080] The dephosphorization rate is expressed by the following formula (1).

[0081]

[0082] In the above formula (1), η ｐ is the dephosphorization rate [mass%], (C ｐ ) ０ is the concentration of phosphorus in the ore before heating and reduction [mass%], (C ｐ ) ｔ is the concentration of phosphorus in the ore after heating and reduction [mass %].

[0083] The phosphorus concentration C shown in the above formula (1) ｐ is expressed by the following formula (2): ｐ is the value obtained by normalizing the phosphorus content by the iron content.

[0084]

[0085] In the above formula (2), %P is the phosphorus content (measured value) [mass %], %T.Fe is the iron content (Fe ２＋ , Fe ３＋and M. Fe) content (measured value) [mass %]. The phosphorus content %P was measured in accordance with the provisions of JIS M8216. Fe ２＋ The content of (FeO) [mass %] was measured in accordance with the standard of JIS M8213. ３＋ (Fe ２ O ３ The content [mass%] of M. Fe was measured by fluorescent X-ray analysis. The content [mass%] of M. Fe was measured in accordance with the provisions of JIS M8212.

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

[0087]

[0088] When the heating temperature is 100°C, the dephosphorization rate η in Examples 1 and 2 ｐ is the dephosphorization rate η in the comparative example ｐ It is presumed that when the heating temperature is less than 100°C, the surface of the ore is not sufficiently dried, making it difficult to separate fine powder containing phosphorus (fine powder with a particle size of 0.25 mm or less) from the surface of the ore, and the dephosphorization effect is small.

[0089] In all the examples, the higher the heating temperature is above 100°C, the higher the dephosphorization rate η ｐ When the heating temperature was 300°C, the dephosphorization rate η ｐ is the dephosphorization rate η in the comparative example ｐ This is presumably because the crystal water in the goethite ore evaporated (dehydrated) at temperatures above 300°C, causing embrittlement, and the fine powder containing phosphorus was further separated and removed by physical impact.

[0090] As mentioned above, the higher the heating temperature, the higher the dephosphorization rate η ｐ However, taking into consideration the rate of increase in the dephosphorization rate relative to the increase in the heating temperature, the heating temperature does not need to be set too high. Table 4 below shows the rate of increase Δη in the dephosphorization rate when the heating temperature is increased by 10°C based on the results shown in Table 3 above. ｐ The value was calculated as [mass % / 10°C].

[0091]

[0092] According to the results shown in Table 4, if the heating temperature is up to 750°C, the rate of increase Δη ｐ However, when the heating temperature exceeds 750°C, the rate of increase Δη ｐ Therefore, taking into consideration the rate of increase, the upper limit of the heating temperature can be set to 750°C. On the other hand, taking into consideration 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 exceeds 950°C, which is the measurement standard temperature in the Karl Fischer method (see JIS M 8211:1995 "Iron ore - Method for determining water of synthesis"). Therefore, in the ore heated to 950°C or higher, the embrittlement caused by the evaporation of the water of crystallization described above has already been completed. Furthermore, when heating the ore in a reducing atmosphere, a heating temperature higher than 1000°C is thought to excessively promote the reduction reaction, leading to the advancement of metallic iron production and thus to the inhibition of phosphorus removal from the ore. Taking these points into consideration, 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 a reducing atmosphere, the dephosphorization rate η was higher than that in Example 1 in the range of 750 [°C] or higher. ｐ Furthermore, Example 3 also showed a higher dephosphorization rate η than Example 1 in the range of 750°C or higher. ｐ The dephosphorization rate η ｐ On the other hand, in Examples 1 to 3, in the temperature range of 100°C or more and 500°C or less, the dephosphorization rate η ｐ were equivalent.

[0095] At the same heating temperature, the dephosphorization rate η in Example 4 among Examples 1 to 4 ｐ The dephosphorization rate can be further improved by performing intermediate classification to separate the fine particle fraction and the coarse particle fraction after the initial heating in a non-reducing atmosphere.

[0096] (Experiment 2) The effect of classification before heating will be verified below using the results of an offline experiment.

[0097] (Raw material) The ore to be dephosphorized was Australian iron ore fines. The ore had the following components: iron: 62.6%, phosphorus: 0.29%, SiO ２ : 2.7%, alumina: 2.2%, and crystal moisture [CW]: 4.5%.

[0098] (Classification Method) Classification before heating was carried out using a sieve with sieve openings of 2 mm, 3 mm, 5 mm, or 7 mm.

[0099] (Heat treatment device, heating conditions) The heating furnace was a kiln type. The heating conditions were as follows: Size of the inner space of the heating furnace: diameter 0.90 m, length 2.0 m Rotation speed of the heating furnace: 2.0 rpm Number of heating furnaces: 1 Amount of ore fed into the heating furnace: 1 kg / h (constant feeding rate) Type of gas fed into the heating furnace: reducing gas (N ２ -33%H ２ ) Flow rate of gas supplied to the heating furnace: 15 Nm ３ / h Heating temperature: 700 ° C. Residence time at the above heating temperature: 60 min

[0100] The dephosphorization rate was measured in the same manner as in Example 4 of Experiment 1. That is, the dephosphorization rate of the fine particle portion obtained by classification before heating and the dephosphorization rate of the coarse particle portion after heating were measured. These values ​​were substituted into the following formula to obtain a value, which is shown in Table 5 as the dephosphorization rate. (Total dephosphorization rate) = {(Dephosphorization rate of the fine particle portion) × (Weight of the fine particle portion) + (Dephosphorization rate of the coarse particle portion) × (Weight of the coarse particle portion)} / {(Weight of the fine particle portion) + (Weight of the coarse particle portion)} The experimental results are shown in Table 5.

[0101]

[0102] The dephosphorization rates of Examples 12 and 13, in which the sieve openings were in the range of 3 to 5 mm, were higher than those of Example 11, in which the sieve openings were 2 mm, and Example 14, in which the sieve openings were 7 mm. In Example 11, ores with diameters of 2 to 3 mm, which are difficult to dephosphorize, were also subjected to dephosphorization, so it is presumed that the dephosphorization rate was lower than that of Examples 12 and 13. In Example 14, the amount of ore subjected to dephosphorization was small, so it is presumed that the dephosphorization rate was lower than that of Examples 12 and 13.

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

[0104] (Raw material) The high-phosphate ores to be dephosphorized were two types of Australian iron ore fines A and B. The components of high-phosphate ore A were iron: 62.6%, P: 0.29%, SiO ２ The components of high phosphorus ore B were iron: 61.6%, P: 0.19%, SiO2: 2.7%, alumina: 2.2%, and crystalline moisture [CW]: 4.5%. The phosphorus concentration in the goethite contained in high phosphorus ore A was 1.33%. High phosphorus ore A was used as the ore for the invention example. ２ : 1.6%, alumina: 1.8%, crystal moisture [CW]: 7.1%. The phosphorus concentration in the goethite contained in high-phosphate rock B was 0.37%. High-phosphate rock B was used as the ore of the comparative example.

[0105] The ores used in the comparative examples and the inventive examples were all dried at 105°C for 2 hours and then sized to 5 to 10 mm using a vibrating sieve. The weight of the ores was approximately 3 kg.

[0106] (Heat Treatment Device and Method) The heating furnace was a kiln type. The heating conditions were as follows: Size of the inner space of the heating furnace: diameter 0.90 m, length 2.0 m Rotation speed of the heating furnace: 2.0 rpm Number of heating furnaces: 1 Amount of ore fed into the heating furnace: 1 kg / h (constant feeding rate) Type of gas supplied to the heating furnace: air (N ２ -21% O ２ ) or reducing gas (N ２ -30% H ２ ) Flow rate of gas supplied to the heating furnace: 15 Nm if the gas is a reducing gas３ / h, and 6 Nm when the gas is air ３ / h Heating temperature: 700°C when the gas is a reducing gas, 280°C when the gas is air Residence time at steam heating temperature: 55 min when the gas is a reducing gas, 22 min when the gas is air Classification treatment after heating: The iron ore discharged from the heating furnace is classified using a sieve with 0.25 mm mesh

[0107] (Calculation of phosphorus removal amount) The amount of phosphorus removed 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 as described above and then sieving to 5 to 10 mm using a vibrating sieve. The dephosphorization rate was expressed as a percentage, where the phosphorus content was normalized by the iron content (P / Fe), and the difference between before and after treatment was the difference. The results are shown in Table 6.

[0108]

[0109] When goethite ore with a high phosphorus concentration was fed into a kiln-type heating furnace, the dephosphorization rate and amount of phosphorus removed were far greater than those of goethite ore with a low phosphorus concentration.

[0110] 1: storage tank, 2: heating furnace, 21: first heating furnace, 22: second heating furnace, 2a, 21a and 22a: supply port, 2b, 21b and 22b: discharge port, 3: gas supplier, 31: non-reducing gas supplier, 32: reducing gas supplier, 4, 41 and 42: dust collector, 5, 6 and 7: sieves

Claims

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

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

3. The method for dephosphorizing ore according to claim 1, characterized in that a non-reducing gas is supplied into the heating furnace during the step of heating the ore.

4. The method for dephosphorizing ore according to claim 1, characterized in that the heating furnace is composed of a first heating furnace and a second heating furnace, a non-reducing gas is supplied to the first heating furnace, and a reducing gas is supplied to the second heating furnace, and in the heating step, 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 method for dephosphorizing ore according to claim 4, further comprising a step of classifying the ore into a coarse particle fraction and a fine particle fraction finer than the coarse particle fraction after heating in the first heating furnace and before supplying the ore to the second heating furnace, wherein the fine particle fraction is removed from the ore supplied to the second heating furnace.

6. The method for dephosphorizing ore according to claim 5, characterized in that in the step of classifying the ore after heating in the first heating furnace and before supplying it to the second heating furnace, a sieve with mesh sizes of 0.5 mm or more and 3.0 mm or less is used.

7. The method for dephosphorizing ore according to any one of claims 1 to 6, further comprising the step of classifying the ore into a coarse particle fraction and a fine particle fraction using a sieve with a mesh size of 3.0 mm or more and 5.0 mm or less before the step of heating the ore in the heating furnace; the heating furnace is a kiln-type heating furnace; only the coarse particle fraction is supplied to the heating furnace; and the heating temperature of the coarse particle fraction in the heating furnace is 400°C or more.

8. The method for dephosphorizing ore according to any one of claims 1 to 6, characterized in that the ore is of two or more types, the ore contains goethite, and the method further comprises a step of selecting the ore having the highest phosphorus concentration in the goethite before the step of heating the ore in the heating furnace, and the ore having the highest phosphorus concentration in the goethite is preferentially supplied to the heating furnace.

9. A method for dephosphorizing ore according to any one of claims 1 to 6, characterized in that the ore contains goethite, and only the ore having a phosphorus concentration of 1.0 mass% or more in the goethite is supplied to the heating furnace.

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