Method for reduction vaporization dephosphorization of iron ore

Abstract

To provide a method for reduction vaporization dephosphorization of iron ore which is excellent in dephosphorization efficiency.SOLUTION: The method for reduction vaporization dephosphorization of iron ore is characterized in that (1) when the phosphorus concentration α of iron ore is defined by the following formula: α(-)=Wp(+3 mm) / Wp (wherein Wp(+3 mm) is phosphorus concentration (mass%) of coarse-grained iron ore having a particle size of 3 mm or more, and Wp is phosphorus concentration (mass%) of iron ore of average particle size), iron ore with an α of 1.04 or more is dephosphorized by the method for reduction vaporization dephosphorization.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a method for reducing and vaporizing iron ore to remove phosphorus. [Background technology]

[0002] In recent years, the concentration of phosphorus contained in iron ore has been increasing. Since phosphorus is an element that reduces the quality of steel, such as reducing the strength of steel, various methods for dephosphorizing iron ore have been proposed. For example, known methods for dephosphorizing iron ore include a leaching method using acid, a bioleaching method using bacteria, a roasting reduction method in which iron ore is roasted to concentrate the phosphorus components and then the phosphorus components are separated from the iron content by reduction magnetic separation, a reduction vaporization method in which heating is performed under a controlled atmosphere, and an alkaline hydrothermal reaction method in which an alkaline hydrothermal reaction is applied to iron ore (see Patent Documents 1 to 5). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Special Publication No. 45-21174 [Patent Document 2] JP 2000-119759 A [Patent Document 3] Special Publication No. 2016-529396 [Patent Document 4] JP 2020-20010 A [Patent Document 5] JP 2018-95893 A Summary of the Invention [Problem to be solved by the invention]

[0004] However, all of these methods have the problem of insufficient phosphorus removal efficiency. For example, the leaching and bioleaching methods have problems such as the time-consuming post-treatment required for acid use and insufficient productivity, and have not yet been put to practical use. Both the roasting reduction method and the reduction-vaporization method require heating the iron ore to over 1000°C, which means high energy consumption.

[0005] The present invention has been made in view of the above problems, and an object of the present invention is to provide a method for dephosphorization of iron ore by reduction and vaporization, which is excellent in dephosphorization efficiency. [Means for solving the problem]

[0006] The gist of the present invention is as follows. (1) When the phosphorus concentration of iron ore, α, is defined as follows: α(-)=Wp(+3mm) / Wp Wp(+3mm): Phosphorus concentration (mass%) of coarse iron ore with a particle size of 3mm or more Wp: Total particle size average phosphorus concentration of iron ore (mass%) A method for dephosphorization of iron ore by reduction and vaporization, comprising the steps of: dephosphorizing the iron ore having an α value of 1.04 or more by a reduction and vaporization dephosphorization method. (2) The method for reducing and vaporizing dephosphorization of iron ore according to (1), characterized in that the iron ore having an α value of 1.04 or more is classified using a sieve having an opening of 3 mm to obtain the coarse iron ore, and the coarse iron ore is dephosphorized by the reduction and vaporization dephosphorization method. (3) The method for reducing and vaporizing dephosphorization of iron ore according to (2), characterized in that yellow iron ore is selected from the coarse iron ore, and the yellow iron ore is dephosphorized by the reducing and vaporizing dephosphorization method. (4) The method for reducing and vaporizing dephosphorization of iron ore according to any one of (1) to (3), wherein the reduction temperature in the reduction and vaporization dephosphorization method is 500 to 700°C. Effect of the Invention

[0007] According to the above-mentioned aspects of the present invention, it is possible to provide a method for dephosphorization of iron ore by reduction and vaporization, which is excellent in dephosphorization efficiency. [Brief description of the drawings]

[0008] [Figure 1] 1 is a graph showing the correlation between particle size fraction of iron ore and dephosphorization rate. [Diagram 2] 1 is a graph showing the correlation between the phosphorus concentration degree α and the dephosphorization rate. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] A preferred embodiment of the present invention will be described in detail below with reference to the accompanying drawings. In this embodiment, "AB" indicating a particle size range means A or more and less than B. In addition, in classification using a sieve, the particle size of iron ore remaining on a sieve with an opening size of X mm is X mm or more, and the particle size of iron ore that falls through the sieve is less than X mm.

[0010] <1. Findings by the Inventor> First, the findings of the present inventor, which are the basis of the present embodiment, will be described. The present inventor focused on the reduction vaporization dephosphorization method as a method for dephosphorization of iron ore. The reduction vaporization dephosphorization method is, in outline, a method for dephosphorization of iron ore by heating the iron ore and then placing the iron ore under a reducing atmosphere. Furthermore, the present inventor classified the iron ore into a plurality of particle size divisions by sieving, and observed the iron ore of each particle size division. The observation of the iron ore was performed by MLA (Mineral Liberation Analysis). As a result, it was found that phosphorus aggregates in goethite, and this tendency is particularly prominent in coarse iron ore (iron ore with a particle size of 3 mm or more). Such phosphorus is chemically adsorbed to goethite, and is considered to be easily desorbed by heating, i.e., reduction vaporization. In addition, it is considered that large cracks are easily generated in the coarse iron ore due to reduction disintegration during reduction vaporization dephosphorization, and phosphorus is easily desorbed from these cracks. In addition, it is believed that in fine iron ore, the stress caused by reduction and disintegration during reduction and vaporization dephosphorization is dispersed and does not lead to the occurrence of cracks. Therefore, it is believed that the more phosphorus contained in coarse iron ore, the more likely dephosphorization occurs.

[0011] Therefore, the present inventors have defined phosphorus concentration α as a parameter indicating the ease of dephosphorization of iron ore. The phosphorus concentration α is expressed by the following formula. Here, the phosphorus concentration of coarse iron ore is the value (%) obtained by dividing the mass of phosphorus contained in the coarse iron ore by the total mass of the coarse iron ore. The mass of phosphorus is measured by fluorescent X-ray analysis (JIS K 0119:2008). The total particle size average phosphorus concentration is the value (%) obtained by dividing the mass of phosphorus contained in all iron ore by the total mass of all iron ore. The phosphorus concentration α increases as the phosphorus concentration of the coarse iron ore increases. α(-)=Wp(+3mm) / Wp Wp(+3mm): Phosphorus concentration (mass%) of coarse iron ore with a particle size of 3mm or more Wp: Total particle size average phosphorus concentration of iron ore (mass%)

[0012] Next, the inventors prepared several types of iron ore (Ore A to C) with different phosphorus states. Table 1 shows the phosphorus concentration by particle size division of each iron ore (mass of phosphorus contained in each particle size division / mass of iron ore in each particle size division), the abundance ratio of each particle size division (mass of iron ore in each particle size division / total mass of iron ore in all particle size divisions), the average phosphorus concentration of all particle sizes (mass of phosphorus contained in iron ore in all particle size divisions / total mass of iron ore in all particle size divisions), and the phosphorus concentration α.

[0013] [Table 1]

[0014] Next, a reduction vaporization dephosphorization treatment was carried out under the following treatment conditions. The iron ore used was in granular form (grain size less than 10 mm). The sample weight was 100 g. The composition of the reducing gas was H2: 25% by volume, CO2: 25% by volume, and N2: 50% by volume. This reducing gas was blown onto the iron ore for the reduction time shown below. However, N2 gas was blown onto the iron ore while the temperature of the iron ore was rising. The reduction temperature (temperature of the iron ore during the reduction vaporization dephosphorization process) was set to 600°C. The reduction time (time for reduction vaporization dephosphorization treatment) was set to 1 hour. Note that the reduction time here does not include the time for heating the iron ore. The dephosphorization rate was measured for each particle size of iron ore. The dephosphorization rate for each particle size was defined as the rate of change in P / Fe (P mass / Fe mass) for each particle size before and after reduction vaporization dephosphorization treatment. P mass is the mass of P contained in the iron ore, and was measured using the method described above. Fe mass is the mass of Fe contained in the iron ore, and was measured using X-ray fluorescence analysis (JIS K 0119:2008).

[0015] Figure 1 shows the relationship between particle size classification (mm) and dephosphorization rate (%) for various iron ores. The horizontal axis shows particle size classification, and the vertical axis shows the dephosphorization rate for each particle size classification. As is clear from Figure 1, Ore A, which has a phosphorus concentration level α of 1.04 or more, has the highest dephosphorization rate, and the larger the particle size, the higher the dephosphorization rate. In particular, it can be seen that the dephosphorization rate increases significantly when the particle size is 3 mm or more. In other words, the dephosphorization efficiency becomes extremely high.

[0016] In order to confirm that the dephosphorization rate becomes significantly higher when the phosphorus concentration α is 1.04 or more, the inventor further prepared several types of iron ore and subjected these iron ores to the above-mentioned reduction vaporization dephosphorization treatment. The results are shown in FIG. 2. The horizontal axis of FIG. 2 indicates the phosphorus concentration α, and the vertical axis indicates the dephosphorization rate. Note that the dephosphorization rate here is the particle size average dephosphorization rate. In other words, it is the rate of change before and after the reduction vaporization dephosphorization treatment of the P mass contained in the total iron ore / the Fe mass contained in the total iron ore. As is clear from FIG. 2, the dephosphorization rate rises sharply when the phosphorus concentration α is 1.04 or more. In other words, the dephosphorization efficiency is extremely high.

[0017] If the phosphorus concentration α is less than 1.04, the concentration of phosphorus in the coarse iron ore is insufficient, and a high dephosphorization rate of the coarse iron ore cannot be obtained. In other words, the particle size dependency of the dephosphorization rate is small. As a result, the dephosphorization rate remains low when viewed on an average particle size basis. On the other hand, if the phosphorus concentration α is 1.04 or more, the concentration of phosphorus in the coarse iron ore is sufficiently high, and a high dephosphorization rate of the coarse iron ore can be obtained. As a result, a high dephosphorization rate can be obtained when viewed on an average particle size basis.

[0018] Therefore, when performing the reduction vaporization dephosphorization treatment of iron ore, it is preferable to first measure the phosphorus concentration α of each iron ore and select as a raw material iron ore having a phosphorus concentration α of 1.04 or more. Furthermore, since the dephosphorization rate of coarse iron ore is higher than that of iron ores of other particle sizes, it is more preferable to classify the coarse iron ore by sieving in advance and perform the reduction vaporization dephosphorization treatment on the coarse iron ore obtained thereby. Furthermore, it is more preferable to select yellow iron ore from the coarse iron ores and perform the reduction vaporization dephosphorization treatment. This is because the dephosphorization rate of yellow iron ore is particularly high, as shown in the examples described later. This is thought to be because yellow iron ore contains a lot of goethite, which adsorbs a lot of phosphorus.

[0019] Here, an example of a method for sorting yellow iron ore is a sorting method using RGB information of a color image. The sorting method is outlined below. Here, the sorting method may be performed using a computer having software relating to the sorting method recorded therein. As the software, for example, general image analysis software capable of separating and extracting the intensity values ​​of each RGB component, such as "WinROOF" or "Image J" manufactured by Mitani Shoji Co., Ltd., may be used.

[0020] First, a plurality of discrimination iron ores are extracted from the coarse iron ore to be subjected to the reduction vaporization dephosphorization treatment. Here, it is preferable to wash and dry the discrimination iron ore in advance. This is to enable the discrimination iron ore to be properly imaged. Next, the discrimination iron ore is visually classified into yellowish iron ore, reddish iron ore, and blackish iron ore. Here, "yellowish iron ore", "reddish iron ore", and "blackish iron ore" refer to iron ore whose external color is yellowish, reddish, and blackish. Next, each iron ore is imaged to obtain an image for threshold determination. The imaging is preferably performed in an environment where light emitted from a daylight white, daylight white, daylight white, or white light source is irradiated, or in an environment where sunlight is irradiated, in an environment where light emitted from a daylight white or white light source is irradiated, or in an environment where sunlight is irradiated. Next, a threshold value R for the intensity value of the R component among the RGB components of the threshold determination image is determined. t1 Here, the intensity value of the R component of the threshold determination image corresponding to yellowish iron ore is the threshold value R t1 As a result, the intensity values ​​of the R component of the threshold determination image corresponding to the reddish iron ore and the blackish iron ore are equal to the threshold R t1 A threshold R is set so that t1 Specifically, for example, the average value of the intensity value of the R component of the threshold determination image corresponding to at least yellowish iron ore and the average value of the intensity value of the R component of the threshold determination image corresponding to reddish iron ore are calculated. Then, these average values ​​are further averaged. The value obtained in this way is called the threshold value R. t1 Let us assume that.

[0021] Threshold R t1 As another method for determining R, for example, the following method can be mentioned. For example, the entire iron ore to be identified (yellow, red, and black mixed) is imaged to obtain a threshold determination image. Next, the minimum value is subtracted from the maximum value of the R component of each pixel constituting the threshold determination image. Next, the value obtained by this subtraction is subtracted from the maximum value of the R component. The value obtained in this way is called the threshold R. t1 Let us assume that.

[0022] Next, from the coarse iron ore, the intensity value of the R component is determined to be equal to or greater than the threshold value R t1 The iron ore that is above this level, i.e., yellowish iron ore, is selected. Specifically, for example, an imaging device is placed above and an air gun is placed below, and the coarse iron ore is allowed to fall naturally. Next, the imaging device captures an image of the falling coarse iron ore to obtain a color image. Next, the intensity value of the R component of the color image is measured, and the intensity value and a threshold value R are compared. t1 The intensity value of the R component is compared with the threshold value R t1 If the intensity value of the R component is greater than or equal to the threshold value R, the coarse iron ore is determined to be yellowish iron ore, and air is blown from an air gun onto the coarse iron ore to blow it away. t1 If the color is less than 100%, the coarse iron ore is determined to be red or black and allowed to fall naturally. This allows yellow coarse iron ore to be separated from other colored coarse iron ores.

[0023] The sorting method is not necessarily limited to this method. Other methods include, for example, the following method. That is, a plurality of coarse iron ores visually judged as yellowish from among the coarse iron ores are set as iron ores for discrimination, and color images of these iron ores for discrimination are obtained. Next, the R component of the images of these iron ores for discrimination is measured. Next, the range from the maximum value to the minimum value of these R components is set as the yellowish range. Next, an imaging device is placed above and an air gun is placed below, and the coarse iron ores are allowed to fall naturally. Next, the falling coarse iron ores are imaged by the imaging device, and a color image is obtained. Next, the intensity value of the R component of the color image is measured, and the intensity value is compared with the yellowish range. If the intensity value of the R component is within the yellowish range, the coarse iron ore is judged to be yellowish iron ore, and air is blown from the air gun onto the coarse iron ore to blow it away. On the other hand, if the intensity value of the R component is outside the yellow range, the coarse iron ore is determined to be red or black iron ore, and the coarse iron ore is allowed to fall naturally as it is. This makes it possible to separate the yellow coarse iron ore from the coarse iron ores of other colors.

[0024] Yellow iron ore may be separated from the coarse iron ore by visual observation. Visual observation is preferably performed in an environment irradiated with light emitted from a neutral white, daylight or white light source, or in an environment irradiated with sunlight.

[0025] Furthermore, the higher the reduction temperature, the higher the reaction rate of reduction vaporization dephosphorization. However, if the reduction temperature is too high, Fe3(PO4)2 is generated during reduction vaporization dephosphorization, inhibiting dephosphorization. Furthermore, reduction disintegration is suppressed, and the efficiency of dephosphorization by phosphorus vaporization decreases. From this viewpoint, the reduction temperature is preferably 500 to 700°C. In addition, since the phosphorus concentration degree α of Ore B and Ore C is less than 1.04, phosphorus is not desorbed unless it is heated to a high temperature. Therefore, Fe3(PO4)2 is generated along with phosphorus desorption. Therefore, it is considered that the attained dephosphorization rate is low in Ore B and Ore C, and the reduction temperature at that time is also high.

[0026] The reduction-vaporization dephosphorization method for iron ore according to this embodiment has been completed based on the above findings. Hereinafter, the reduction-vaporization dephosphorization method according to this embodiment will be described.

[0027] <2. Reduction vaporization dephosphorization method> Next, the reduction vaporization dephosphorization method according to the present embodiment will be described. In the reduction vaporization dephosphorization method according to the present embodiment, first, iron ore having a phosphorus concentration α of 1.04 or more is selected. The iron ore is preferably high phosphorus ore (iron ore having a phosphorus concentration of 0.1 mass% or more). The phosphorus concentration α is defined as described above. The selected iron ore is the iron ore to be subjected to the reduction vaporization dephosphorization treatment. Here, the iron ore having a phosphorus concentration α of 1.04 or more is classified using a sieve with a mesh size of 3 mm to obtain coarse iron ore, which may be the iron ore to be subjected to the reduction vaporization dephosphorization treatment. Furthermore, yellowish iron ore may be selected from the coarse iron ore by the above-mentioned selection method using RGB information of the color image, and this may be the iron ore to be subjected to the reduction vaporization dephosphorization treatment.

[0028] Next, the iron ore to be subjected to the reduction vaporization dephosphorization treatment is subjected to the reduction vaporization dephosphorization treatment. The treatment conditions of the reduction vaporization dephosphorization treatment are not particularly limited, and may be the same as the treatment conditions described above. For example, the composition of the reduction gas may be CO: 25 volume %, CO2: 25 volume %, and N2: 50 volume %. The reduction time may be 1.5 hours. The reduction time here is the time excluding the time for raising the temperature of the iron ore. However, during the temperature rise of the iron ore, an inert gas such as N2 gas may be blown onto the iron ore. The reduction temperature is preferably 500 to 700°C. This is because in this case, the dephosphorization efficiency is higher. The higher the reduction temperature, the higher the reaction rate of the reduction vaporization dephosphorization. However, if the reduction temperature is too high, Fe3(PO4)2 is generated during the reduction vaporization dephosphorization, inhibiting the dephosphorization. Furthermore, reduction disintegration is suppressed, and the efficiency of desorption by vaporization of phosphorus is reduced. From this viewpoint, the reduction temperature is preferably 500 to 700°C.

[0029] According to the reduction vaporization dephosphorization method of this embodiment, iron ore having a phosphorus concentration level α of 1.04 or more is dephosphorized by the reduction vaporization dephosphorization method, so that dephosphorization can be performed with high dephosphorization efficiency. EXAMPLES

[0030] Next, an example of this embodiment will be described. First, iron ore to be subjected to the reduction vaporization dephosphorization treatment was prepared. In the present invention example 1, iron ore with a phosphorus concentration degree α of 1.05 was prepared. In the present invention example 1, classification was not performed, and the iron ore was treated as it was. The particle size of each iron ore was less than 10 mm. In the present invention example 2, the iron ore of the present invention example 1 was classified using a sieve with a mesh size of 3 mm to obtain coarse iron ore, which was treated. In the present invention example 3, the coarse iron ore was sorted using RGB information of a color image, and yellowish iron ore was treated. Specifically, 10 grains of coarse iron ore that were visually judged to be yellowish from the coarse iron ore were used as discrimination iron ores, and color images of these discrimination iron ores were obtained. Next, the R component of the images of these discrimination iron ores was measured. Next, the range from the maximum value to the minimum value of the R component of these 10 grains was set as the yellowish range. Next, color images of other coarse iron ores were obtained, and those with R component intensity falling within the yellow range were treated as yellow iron ores. The particle size ranges and phosphorus concentrations (phosphorus concentrations before treatment) of the iron ores to be treated are shown in Table 2. Since the phosphorus concentration α of Example 1 of the present invention is 1.04 or more, the phosphorus concentrations of Examples 2 and 3 of the present invention are greater than that of Example 1 of the present invention.

[0031] Next, the iron ore to be treated was subjected to a reduction vaporization dephosphorization treatment under the following treatment conditions. The sample weight was 100 g. The composition of the reducing gas was H2: 25% by volume, CO2: 25% by volume, and N2: 50% by volume. This reducing gas was blown onto the iron ore for the reduction time shown below. However, N2 gas was blown onto the iron ore while the temperature of the iron ore was rising. The reduction temperature (temperature of the iron ore during the reduction vaporization dephosphorization process) was set to 600°C. The reduction time (time for reduction vaporization dephosphorization treatment) was set to 1 hour. Note that the reduction time here does not include the time for heating the iron ore. The dephosphorization rate of each example (the rate of change in P / Fe (P mass / Fe mass) of each example before and after reduction vaporization dephosphorization treatment) was measured.

[0032] The dephosphorization rates are shown in Table 2. As shown in Table 2, very high dephosphorization rates are obtained in all of the examples. Example 2 achieves a higher dephosphorization rate than Example 1, and Example 3 achieves a higher dephosphorization rate than Example 2.

[0033] [Table 2]

[0034] Although the preferred embodiment of the present invention has been described in detail above, the present invention is not limited to such an example. It is clear that a person having ordinary knowledge in the technical field to which the present invention pertains can conceive of various modified or amended examples within the scope of the technical ideas described in the claims, and it is understood that these also naturally fall within the technical scope of the present invention.

Claims

1. When the phosphorus concentration of iron ore, α, is defined as follows: α(-)=Wp(+3mm) / Wp Wp (+3 mm): Phosphorus concentration (mass%) of coarse iron ore with a particle size of 3 mm or more Wp: total particle size average iron ore phosphorus concentration (mass%) The iron ore having an α value of 1.04 or more is dephosphorized by a reduction vaporization dephosphorization method.

2. 2. The method for reducing and vaporizing iron ore according to claim 1, wherein the iron ore having an α value of 1.04 or more is classified using a sieve having an opening of 3 mm to obtain the coarse iron ore, and the coarse iron ore is dephosphorized by the reduction and vaporization dephosphorization method.

3. 3. The method for dephosphorization of iron ore according to claim 2, wherein yellow iron ore is selected from the coarse iron ore, and the yellow iron ore is dephosphorized by the reduction-vaporization dephosphorization method.

4. The method for reducing and vaporizing iron ore according to any one of claims 1 to 3, characterized in that the reduction temperature of the reduction and vaporizing dephosphorization method is 500 to 700°C.

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