Method for removing phosphorus from iron ore

Abstract

This invention provides a method for removing phosphorus from iron ore. [Solution] By supplying a reducing gas to a heating furnace into which iron ore containing phosphorus has been introduced, phosphorus is removed from the iron ore. The temperature of the reducing gas is set to 600°C or higher and less than 750°C. Furthermore, the composition of the reducing gas and the processing time of the reduction treatment are set so that the reduction rate of iron in the iron ore is 7.4% or higher and 56.1% or lower, and the metallization rate of iron in the iron ore is 0.4% or higher and 41.2% or lower. Here, the composition of the reducing gas can be fixed and the processing time can be set, or the processing time can be fixed and the composition of the reducing gas can be set.

Description

[Technical Field]

[0001] This invention relates to a method for removing phosphorus from iron ore. [Background technology]

[0002] The phosphorus contained in iron ore, a raw material for blast furnaces, is one of the important components for quality control of molten iron produced in blast furnaces. Because phosphorus has a high affinity for iron, when steel is manufactured from iron ore via molten iron, phosphorus tends to remain in the steel. This residual phosphorus can cause low-temperature brittle fracture of the steel, potentially impairing its quality.

[0003] Patent Document 1 describes removing phosphorus from a phosphorus-containing substance (such as iron ore) by reacting it with a nitrogen-containing gas at a processing temperature T below the melting temperature Tm of the phosphorus-containing substance (specifically, 750°C ≤ T ≤ 0.95 × Tm). Patent Document 2 describes performing the dephosphorization treatment in a temperature range of approximately 1000°C or higher. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] International Publication No. 2019 / 131128 [Patent Document 2] Japanese Patent Publication No. 2020-20010 [Overview of the project] [Problems that the invention aims to solve]

[0005] The inventors have discovered that phosphorus can be efficiently removed from iron ore at low temperatures (specifically, below 750°C), and have completed the present invention. [Means for solving the problem]

[0006] The present invention relates to a dephosphorization method for removing phosphorus from iron ore by supplying a reducing gas to a heating furnace into which phosphorus-containing iron ore has been introduced. Here, the temperature of the reducing gas is set to 600°C or higher and less than 750°C. The composition of the reducing gas and the processing time of the reduction treatment are set so that the reduction rate of iron in the iron ore is 7.4% or higher and 56.1% or lower, and the metallization rate of iron in the iron ore is 0.4% or higher and 41.2% or lower.

[0007] The composition of the reducing gas can be fixed, and the processing time can be set so that the reduction rate is between 7.4% and 56.1%, and the metallization rate is between 0.4% and 41.2%. Alternatively, the processing time can be fixed, and the composition of the reducing gas can be set so that the reduction rate is between 7.4% and 56.1%, and the metallization rate is between 0.4% and 41.2%.

[0008] The reducing gas can include CO gas or CO2 gas and an inert gas. The processing time can be 10 to 180 minutes. [Effects of the Invention]

[0009] According to the present invention, in the reduction treatment of iron ore where the temperature of the reducing gas is 600°C or higher and less than 750°C, the dephosphorization rate of the iron ore can be improved. [Brief explanation of the drawing]

[0010] [Figure 1] This figure shows the relationship between the reduction rate and dephosphorization rate of iron in iron ore. [Figure 2] This figure shows the relationship between the metallization rate and dephosphorization rate of iron in iron ore. [Modes for carrying out the invention]

[0011] This embodiment is a dephosphorization method for removing phosphorus from iron ore in a low-temperature range where the temperature of the reducing gas is 600°C or higher and less than 750°C by supplying the reducing gas to a heating furnace into which iron ore containing phosphorus is charged. Here, by setting the composition of the reducing gas and the treatment time of the reduction treatment so that each of the reduction rate and the metallization rate of iron in the iron ore satisfies a predetermined numerical range, the dephosphorization rate is improved. Hereinafter, the dephosphorization method of this embodiment will be specifically described.

[0012] (Heating furnace) As the heating furnace, any furnace that can supply a reducing gas to heat the iron ore may be used. Specifically, as the heating furnace, a stationary, kiln-type or fluidized-bed type heating furnace can be used. Here, the heating furnace can be selectively used according to the particle size of the iron ore.

[0013] As the kiln-type heating furnace, for example, there is a method (internal combustion type) of directly supplying the reducing gas into the heating furnace. In this heating furnace, the reducing gas may be circulated from the supply port of the iron ore toward the discharge port, or may be circulated from the discharge port of the iron ore toward the supply port. As the fluidized-bed type heating furnace, for example, there is a method (direct heating type) of directly applying heat to the iron ore in the heating furnace. In the fluidized-bed type, a method of circulating the iron ore may be used.

[0014] (Treatment conditions for dephosphorization treatment) The treatment conditions for performing the dephosphorization treatment will be described. These treatment conditions include the temperature of the reducing gas, the composition of the reducing gas, and the treatment time of the reduction treatment by the reducing gas. Hereinafter, each treatment condition will be specifically described.

[0015] (Temperature of the reducing gas) The temperature of the reducing gas supplied to the heating furnace is set to between 600°C and 750°C. This ensures that the reduction treatment of the iron ore takes place within the temperature range of 600°C to 750°C. When the reducing gas temperature is below 600°C, the rate at which phosphorus is removed from the iron ore (dephosphorization rate) tends to be slow, making it difficult to obtain a sufficient dephosphorization effect within a practical time (e.g., 1 to 2 hours). On the other hand, when the reducing gas temperature is above 750°C, the reduction rate of iron in the iron ore increases too much, making it difficult to adjust the reduction rate of iron within the numerical range described later. Here, it is preferable that the reducing gas temperature be between 700°C and 750°C.

[0016] (Composition of reducing gas and processing time) In this embodiment, the composition of the reducing gas and the processing time for the reduction treatment are determined such that the reduction rate of iron in the iron ore is 7.4% to 56.1%, and the metallization rate of iron is 0.4% to 41.2%. Here, the upper limit of the reduction rate is preferably 45%, more preferably 30%. The lower limit of the reduction rate is preferably 20%. On the other hand, the upper limit of the metallization rate is preferably 30%, more preferably 20%, and even more preferably 10%.

[0017] Since the reduction rate and metallization rate each depend on the composition of the reducing gas and the processing time under temperature conditions where the reducing gas temperature is between 600°C and 750°C, at least one of the reducing gas composition and processing time can be determined so that each of the reduction rate and metallization rate falls within the aforementioned numerical range. This makes it possible to improve the dephosphorization rate of iron ore in the low temperature range where the reducing gas temperature is between 600°C and 750°C.

[0018] The following describes how to determine the composition of the reducing gas and the processing time.

[0019] As a first method, the correlation between at least one of the reducing gas composition and processing time, the reduction rate, and the metallization rate can be determined experimentally in advance, and the reducing gas composition and processing time can be determined when the reduction rate and metallization rate each fall within the aforementioned numerical range. In the aforementioned correlation, the reducing gas composition can be fixed and the effect of processing time on the reduction rate and metallization rate can be considered, or the processing time can be fixed and the effect of the reducing gas composition on the reduction rate and metallization rate can be considered.

[0020] As a second method, the reduction rate and metallization rate of the iron ore after dephosphorization can be measured during the dephosphorization operation, and the composition of the reducing gas and the treatment time can be adjusted based on these measurement results.

[0021] Specifically, if the measured reduction rate is higher than the upper limit mentioned above (e.g., 56.1%), or if the measured metallization rate is higher than the upper limit mentioned above (e.g., 41.2%), the composition of the reducing gas can be changed or the processing time can be shortened to reduce the reducing power of the reducing gas. On the other hand, if the measured reduction rate is lower than the lower limit mentioned above (e.g., 7.4%), or if the measured metallization rate is lower than the lower limit mentioned above (e.g., 0.4%), the composition of the reducing gas can be changed or the processing time can be extended to increase the reducing power of the reducing gas.

[0022] The reduction rate of iron in iron ore is expressed by the following formula (1).

[0023]

number

[0024] In the above equation (1), Rr is the reduction rate of iron [%], and O e O is the amount of oxygen removed by the reduction reaction of iron ore (hereinafter referred to as the amount of removed oxygen) [mass%], i This is the initial amount of oxygen used in the reduction reaction of iron ore (hereinafter referred to as the initial amount of oxygen to be reduced) [mass%]. Amount of oxygen removed ☐e and the initial reducible oxygen amount O i Each of them is the ratio of the oxygen amount to the total mass of the iron ore before the reduction reaction occurs.

[0025] Oxygen removal amount O e As methods for obtaining the oxygen removal amount O, several methods can be mentioned. As the first method, the oxygen removal amount O e can be obtained by performing chemical analysis on the iron ore before and after the reduction reaction. As the second method, the oxygen removal amount O e can be obtained by performing gas analysis on the exhaust gas discharged during the reduction reaction. As the third method, the oxygen removal amount O e can be obtained based on the weight change of the iron ore before and after the reduction reaction.

[0026] Initial reducible oxygen amount O i can be obtained based on the chemical analysis of the iron ore before the reduction reaction. Here, the initial reducible oxygen amount O i is represented by the following formula (2).

[0027]

Number

[0028] In the above formula (2), O i is the initial reducible oxygen amount [mass%], T.Fe is the content rate of total iron contained in the iron ore [mass%], M.Fe is the content rate of metallic iron contained in the iron ore [mass%], and FeO is the content rate of FeO contained in the iron ore [mass%]. The content rate T.Fe [mass%] can be measured according to the provisions of JIS M8212, the content rate M.Fe [mass%] can be measured according to the provisions of JIS M8212, and the content rate FeO [mass%] can be measured according to the provisions of JIS M8213.

[0029] On the other hand, the metallization rate of iron is represented by the following formula (3).

[0030]

Number

[0031] In equation (3) above, Rm is the metallization rate [%], M.Fe is the content of metallic iron in the iron ore [mass%], and T.Fe is the content of total iron in the iron ore [mass%]. The methods for measuring the content M.Fe and T.Fe are as described above.

[0032] (Composition of reducing gas) The composition of the reducing gas supplied to the heating furnace can be any gas capable of reducing iron ore, and can be appropriately determined under the condition that the reduction rate and metallization rate each satisfy the numerical ranges described above. For example, the reducing gas may contain 25% or more by volume of CO gas or 25% or more by volume of CO2 gas. The remainder of the reducing gas can be an inert gas such as N2 gas or Ar gas, and may contain a portion of H2 gas or H2O (water vapor) in equilibrium with H2.

[0033] As the reducing gas, blast furnace by-product gas (BFG) can be used. Furthermore, as the inert gas mentioned above, purchased gas or inert gas contained in by-product gas from manufacturing facilities can be used. On the other hand, when adjusting the composition of the reducing gas, the types of gas components contained in the reducing gas can be changed, or the content ratio of the gas components can be changed.

[0034] (Processing time) The processing time is set appropriately under the condition that the reduction rate and the metallization rate each satisfy the numerical ranges described above, but for example, it can be set to 10 to 180 minutes, preferably 30 to 90 minutes. [Examples]

[0035] (Iron ore) In Examples 1-6 and Comparative Examples 1-3, described later, two types of iron ore, A and B, were used. Iron ore A had a phosphorus content of 0.270 [mass%], and iron ore B had a phosphorus content of 0.191 [mass%]. The particle sizes of iron ore A and B were adjusted to 5-10 [mm].

[0036] (heating furnace) A kiln-type heating furnace was used to continuously flow the iron ore. This furnace had a diameter of 0.90 m and a length of 2.0 m. The inclination angle of the reaction tube (chamber) was set to 1°, and the kiln rotation speed was set to 2.0 rpm.

[0037] (Reduction treatment) Iron ore was fed into the heating furnace at a rate of 1 kg / h using a feeder for 3 hours, while reducing gas was supplied into the heating furnace at a flow rate of 60 NL / min. The temperature of the reducing gas was set to 700 °C.

[0038] In Examples 1-4 and 6, a reducing gas consisting of 25% by volume of H2 gas, 25% by volume of CO2 gas, and the remainder of N2 gas was used. In Example 5, a reducing gas consisting of 25% by volume of CO gas, 25% by volume of CO2 gas, and the remainder of N2 gas was used. In Comparative Examples 1 and 3, N2 gas was used as the reducing gas, and in Comparative Example 2, a reducing gas consisting of 75% by volume of H2 gas and the remainder of N2 gas was used.

[0039] The processing time was 32 minutes for Examples 1 and 5, 44 minutes for Example 2, 57 minutes for Example 3, 69 minutes for Example 4, and 53 minutes for Example 6. On the other hand, the processing time for Comparative Examples 1 and 2 was 32 minutes, and the processing time for Comparative Example 3 was 53 minutes.

[0040] (Measurement of phosphorus removal rate) The dephosphorization rate was calculated for iron ore that underwent reduction treatment in a heating furnace (Examples 1-6 and Comparative Examples 1-3). The dephosphorization rate was determined using the following formula (4).

[0041]

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[0042] In the above equation (4), η p This is the phosphorus removal rate [mass%], and (C p )0 is the concentration of phosphorus [mass%] contained in the iron ore before dephosphorization treatment, and (C p ) t This represents the phosphorus concentration [mass%] in the iron ore after dephosphorization.

[0043] Phosphorus concentration C shown in formula (4) above p This is expressed by the following equation (5). That is, phosphorus concentration C p The phosphorus content is compared to the iron content (Fe 2+ Fe 3+ This value is normalized by the content of M.Fe.

[0044]

number

[0045] In the above formula (5), %P is the phosphorus content (measured value) [mass%], and %T.Fe is the iron content (Fe) contained in the iron ore. 2+ Fe 3+ The content of (and M.Fe) is [mass %]. The phosphorus content %P was measured in accordance with the provisions of JIS M8216. 2+ The (FeO) content [mass%] was measured in accordance with the provisions of JIS M8213. 3+ The (Fe2O3) content [mass%] was measured by X-ray fluorescence analysis. The M.Fe content [mass%] was measured in accordance with the provisions of JIS M8212.

[0046] Furthermore, the reduction rate and metallization rate were calculated for the dephosphorized iron ore. The reduction rate was calculated based on formula (1) above, and the metallization rate was calculated based on formula (3) above. The treatment conditions for dephosphorization and the calculated results of the reduction rate, metallization rate, and dephosphorization rate are shown in Table 1 below.

[0047] [Table 1]

[0048] Depending on the iron ore source, an increase in phosphorus concentration in iron ore is predicted in the future (for example, Nippon Steel Technical Report No. 413, 2019, pp. 15-20). Therefore, in this example, the target dephosphorization rate was set to 16.1% to mitigate the increase in phosphorus concentration. For Examples 1-6, the dephosphorization rate was 16.1% or higher, indicating that the target dephosphorization was achieved. On the other hand, for Comparative Examples 1-3, the dephosphorization rate was less than 16.1%, and the target dephosphorization was not achieved.

[0049] In a low-temperature range where the reducing gas temperature is between 600°C and 750°C, by adjusting the composition of the reducing gas and the processing time, it was possible to achieve a reduction rate of 7.4% to 56.1% of iron and a metallization rate of 0.4% to 41.2% of iron, thereby achieving a dephosphorization rate of 16.1% or higher.

[0050] Specifically, as can be seen from Examples 1 and 5 and Comparative Examples 1 and 2, even with the same processing time (32 minutes), by adjusting the composition of the reducing gas, the reduction rate can be set to 7.4% to 56.1% and the metallization rate to 0.4% to 41.2%. Similarly, as can be seen from Example 6 and Comparative Example 3, even with the same processing time (53 minutes), by adjusting the composition of the reducing gas, the reduction rate can be set to 7.4% to 56.1% and the metallization rate to 0.4% to 41.2%.

[0051] Furthermore, as can be seen from Examples 1-4 and 6, even if the composition of the reducing gas is the same (N2-25%H2-25%CO2), the reduction rate and metallization rate can be changed by varying the processing time, and as a result, the dephosphorization rate changes.

[0052] Based on the results shown in Table 1 above, Figure 1 shows the relationship between the reduction rate and the dephosphorization rate. As shown in Figure 1, when the reduction rate was less than 7.4% or higher than 56.1%, the dephosphorization rate fell below 16.1%. Therefore, it was found that there is an appropriate range for the reduction rate to maintain a dephosphorization rate of 16.1% or higher.

[0053] Based on the results shown in Table 1 above, Figure 2 shows the relationship between the metallization rate and the dephosphorization rate. As shown in Figure 2, when the metallization rate was less than 0.4% or higher than 41.2%, the dephosphorization rate fell below 16.1%. Therefore, it was found that there is an appropriate range for the metallization rate to maintain a dephosphorization rate of 16.1% or higher.

Claims

1. A dephosphorization method for removing phosphorus from iron ore containing phosphorus by supplying a reducing gas to a heating furnace into which the iron ore is fed, The temperature of the reducing gas is 600°C or higher and less than 750°C. A method for dephosphorizing iron ore, characterized in that the composition of the reducing gas and the processing time of the reduction treatment are set such that the reduction rate of iron in the iron ore is 7.4% or more and 56.1%, and the metallization rate of iron in the iron ore is 0.4% or more and 41.2%.

2. The method for dephosphorizing iron ore according to claim 1, characterized in that the composition of the reducing gas is fixed, and the processing time is set such that the reduction rate is 7.4% or more and 56.1% or less, and the metallization rate is 0.4% or more and 41.2% or less.

3. The method for dephosphorizing iron ore according to claim 1, characterized in that the processing time is fixed, the composition of the reducing gas is set such that the reduction rate is 7.4% or more and 56.1% or less, and the metallization rate is 0.4% or more and 41.2% or less.

4. The reducing gas is CO gas or CO ２ The method for dephosphorizing iron ore according to claim 1, characterized by comprising a gas and an inert gas.

5. The method for dephosphorizing iron ore according to claim 1, characterized in that the processing time is 10 to 180 minutes.

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