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 is dephosphorized by the method for reduction vaporization dephosphorization at reduction temperature T (°C) in the range of the following formula: -3333×α+4111≤T≤-3333×α+4211.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 vaporization, characterized in that the reduction temperature T (°C) is set in the range of the following formula, and iron ore is dephosphorized by the reduction vaporization dephosphorization method. -3333×α+4111≦T≦-3333×α+4211 (2) 1. The method for dephosphorization of iron ore by reduction and vaporization according to claim 1, wherein iron ore having a phosphorus concentration α of 0.95 or more and 1.10 or less is dephosphorized by the reduction and vaporization dephosphorization method. (3) The method for reducing and vaporizing dephosphorization of iron ore according to (1) or (2), characterized in that the iron ore is classified using a sieve with a mesh size of 3 mm to obtain the coarse iron ore, and the coarse iron ore is dephosphorized by the reduction and vaporization dephosphorization method. (4) The method for reducing and vaporizing dephosphorization of iron ore according to (3), 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. 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 reduction temperature and dephosphorization rate. [Diagram 2] 1 is a graph showing the correlation between phosphorus concentration α and reduction temperature. 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 iron ore during reduction vaporization dephosphorization treatment) was set to 500 to 1000°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 iron ore was measured. The dephosphorization rate was defined as the rate of change in P / Fe (P mass / Fe mass) before and after the reduction vaporization dephosphorization treatment. P mass is the mass of P contained in the iron ore, and was measured by the method described above. Fe mass is the mass of Fe contained in the iron ore, and was measured by X-ray fluorescence analysis (JIS K 0119:2008).

[0015] Figure 1 shows the relationship between the reduction temperature (℃) and the dephosphorization rate (%) for various iron ores. The horizontal axis shows the reduction temperature, and the vertical axis shows the dephosphorization rate at each reduction temperature. As is clear from Figure 1, in OreA with a phosphorus concentration α of 1.07 (coarse iron ore containing a lot of phosphorus), the dephosphorization rate was highest when the reduction temperature was 600℃, and the achieved dephosphorization rate (maximum dephosphorization rate) reached 22%. In OreB with a phosphorus concentration α of 0.98 (phosphorus is almost uniformly present regardless of particle size classification), the dephosphorization rate was highest when the reduction temperature was 900℃, but the achieved dephosphorization rate was limited to 15%. In OreC with a phosphorus concentration α of 0.82 (fine iron ore containing a lot of phosphorus), the dephosphorization rate was highest when the reduction temperature was 1000℃, but the achieved dephosphorization rate was limited to 8%. From these results, it became clear that there is a correlation between the reduction temperature Topt at which the ultimate dephosphorization rate is achieved (the dephosphorization rate is at its maximum) and the phosphorus concentration α. ​​Specifically, the following equation (1) was obtained as the relation between the reduction temperature Topt at which the ultimate dephosphorization rate is achieved and the phosphorus concentration α. Topt(℃)=-3333·α+4166 ···(1)

[0016] That is, in iron ore (e.g., Ore A) with a high phosphorus concentration α (coarse iron ore containing a large amount of phosphorus), a high ultimate dephosphorization rate can be achieved by reduction vaporization dephosphorization treatment at a low reduction temperature. When the phosphorus concentration α is low and around 1 (in this case, for example, Ore B, where the phosphorus concentration is uniform across each particle size range), not only does the ultimate dephosphorization rate decrease, but a high reduction temperature is required to achieve the ultimate dephosphorization rate. When the reduction temperature increases, not only is phosphorus desorbed, but Fe3(PO4)2 is more likely to be generated. This results in a lower ultimate dephosphorization rate. When the phosphorus concentration α is even lower, less than 1 (in this case, for example, Ore C, where fine iron ore contains a large amount of phosphorus), the above tendency becomes even stronger.

[0017] Therefore, when iron ore is dephosphorized by the reduction vaporization dephosphorization method, the phosphorus concentration α is first measured, and a preferred reduction temperature (=Topt) is determined based on the phosphorus concentration α and formula (1). However, in actual operation, it is difficult to always maintain the reduction temperature at Topt. On the other hand, it is considered that the dephosphorization rate will not vary significantly even if the reduction temperature fluctuates slightly. Therefore, it is preferable to maintain the reduction temperature T within the range of the following formula (2), i.e., (3). Topt-50≦T(℃)≦Topt+50 (2) -3333×α+4111≦T≦-3333×α+4211 (3)

[0018] Furthermore, from the results of the above-mentioned experiments, it is found that the phosphorus concentration α is preferably 0.95 or more and 1.10 or less. The lower limit value 0.95 is a value derived from the experimental results of Ore B and Ore C. When the phosphorus concentration α of iron ore is less than 0.95, the reduction temperature approaches 1000°C and the attained dephosphorization rate is also low, so that the reduction vaporization dephosphorization process does not necessarily have to be applied to the iron ore. The preferable lower limit value of the phosphorus concentration α is 1.04. This is because when the phosphorus concentration α is 1.04 or more, the attained dephosphorization rate is particularly remarkably high. When the phosphorus concentration α of iron ore exceeds 1.10, the reduction temperature is 500°C or less, so the dephosphorization promotion effect by reduction disintegration is not exerted, and there is a possibility that a high dephosphorization rate cannot be obtained. From these results, it is found that it is preferable to perform the reduction vaporization dephosphorization process within the range shown in region A in FIG. 2.

[0019] Furthermore, as described above, the higher the phosphorus concentration α, the higher the dephosphorization rate, so the dephosphorization rate of the coarse iron ore is higher than that of iron ores of other particle sizes. Therefore, 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 by this. 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 the yellow iron ore is particularly high, as shown in the examples described later. This is thought to be because the yellow iron ore contains a lot of goethite, which adsorbs a lot of phosphorus.

[0020] 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.

[0021] 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.

[0022] 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.

[0023] 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.

[0024] 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.

[0025] 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.

[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, the phosphorus concentration α of the iron ore to be treated is measured. The iron ore is preferably high phosphorus ore (iron ore having a phosphorus concentration of 0.1 mass% or more). The definition of the phosphorus concentration α is as described above. Here, it is preferable to select iron ore having a phosphorus concentration α of 0.95 to 1.10, preferably 1.04 to 1.10. Furthermore, it is more preferable to select coarse iron ore by classifying the iron ore using a sieve with a mesh size of 3 mm. Furthermore, it is more preferable to select yellowish iron ore from the coarse iron ore by the above-mentioned selection method using RGB information of the color image.

[0028] Next, the range of the reduction temperature in the reduction vaporization dephosphorization process is determined based on the above-mentioned formula (3). Next, the reduction vaporization dephosphorization process is performed on the iron ore to be treated. Here, the reduction temperature is maintained at a value within the determined range. Other treatment conditions are not particularly limited, and may be performed under the same treatment conditions as those described above. For example, the composition of the reduction gas may be CO: 25 vol.%, CO2: 25 vol.%, and N2: 50 vol.%. The reduction time may be 1.5 hours. Note that the reduction time here is the time excluding the time for raising the temperature of the iron ore. However, an inert gas such as N2 gas may be blown onto the iron ore while the temperature of the iron ore is being raised.

[0029] According to the reduction-vaporization dephosphorization method of this embodiment, the reduction temperature of the reduction-vaporization dephosphorization treatment is set so as to satisfy formula (3), so that a reduction-vaporization dephosphorization method for iron ore with excellent dephosphorization efficiency can be provided. EXAMPLES

[0030] Next, examples of this embodiment will be described. First, iron ore to be subjected to reduction vaporization dephosphorization treatment was prepared. In invention example 1, iron ore with a phosphorus concentration degree α of 1.05 was prepared. According to formula (3), the reduction temperature was 611.35 to 711.35°C. In invention example 1, classification was not performed, and the iron ore was treated as it was. All iron ores had a particle size of less than 10 mm. In invention example 2, the iron ore of invention example 1 was classified using a sieve with a mesh size of 3 mm to obtain coarse iron ore, which was treated. In invention example 3, the coarse iron ore was sorted using RGB information of a color image, and yellowish iron ore was treated. Specifically, 10 coarse iron ores visually determined 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 determined as the yellow range. Next, color images of other coarse iron ores were obtained, and those whose R component intensity was within the yellow range were treated as yellow iron ores. The particle size range and phosphorus concentration (phosphorus concentration 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 iron ore during reduction vaporization dephosphorization treatment) was set within the range of reduction temperatures determined above. 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%) A method for dephosphorization of iron ore by reduction vaporization, characterized in that the reduction temperature T (°C) is set in the range of the following formula: -3333 x α + 4111 ≤ T ≤ -3333 x α + 4211

2. 2. The method for dephosphorization of iron ore according to claim 1, wherein the iron ore having a phosphorus concentration α of 0.95 or more and 1.10 or less is dephosphorized by the reduction vaporization dephosphorization method.

3. 3. The method for reducing and vaporizing iron ore according to claim 1 or 2, characterized in that the iron ore 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.

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

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