Method for sorting iron ore

Abstract

To identify iron ore having high dephosphorization efficiency by a reduction heat treatment method.SOLUTION: The present invention relates to a method for sorting iron ore that facilitates removal of phosphorus by a reduction heat treatment technique, the method including an X-ray diffraction measurement step of performing X-ray diffraction measurement on the iron ore. The iron ore is determined to be more easily subjected to phosphorus removal by the reduction heat treatment technique as a shift, relative to a goethite reference peak, of at least one peak attributed to goethite observed in an X-ray diffraction pattern becomes larger.SELECTED DRAWING: Figure 1A

Description

[Technical Field]

[0001] The present invention relates to a method for sorting iron ore, and more particularly to a method for sorting iron ore from which phosphorus is easily removed by a reduction heat treatment method. [Background technology]

[0002] Iron ore, which is used as a raw material in the steel industry, is naturally composed of multiple iron oxides and exists in a state where, in addition to its main component iron (Fe), it also contains impurities such as aluminum (Al), silicon (Si), and phosphorus (P).While it is predicted that the Fe content of iron ore will decrease and the P concentration will increase in the future, there is a possibility that iron ore resources with high Fe and P concentrations remain, and it is hoped that iron ore with high P concentrations (high-P iron ore) will be effectively utilized as a countermeasure to the deterioration of resources.

[0003] When high-P iron ore is used in current blast furnace operation, it causes disadvantages such as increased processing costs due to the increased amount of slag in the steelmaking process and an increased load in the dephosphorization process in high-grade steel production. Therefore, when using high-P iron ore as a raw material, it is desirable to remove P from the iron ore beforehand before using it in the steelmaking process.

[0004] On the other hand, it is known that P exists in several forms in iron ore (see Non-Patent Documents 1 and 2, etc.). Known methods for dephosphorizing iron ore include alkaline hydrothermal treatment, flotation, and reduction heat treatment. The dephosphorization efficiency of each of these dephosphorization methods differs depending on the form of P in the iron ore.

[0005] Patent Document 1 proposes a method for quickly and accurately identifying P chemically adsorbed to α-FeOOH contained in iron ore composed of multiple iron oxides. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Patent Publication No. 2021-107770 [Non-patent literature]

[0007] [Non-Patent Document 1] JM Arroyave et al. :Spectrochimica Acta PartA, 199 (2018) 57-64. [Non-patent document 2] Carina Luego et al.:Journal of Colloid and Interface Science, 300 (2006) 511. Summary of the Invention [Problem to be solved by the invention]

[0008] Iron ore contains Fe as oxides such as hematite, magnetite, and goethite (α-FeOOH). Depending on the origin and brand of iron ore, some contain relatively high amounts of hematite, while others contain relatively high amounts of α-FeOOH. P chemisorbed to α-FeOOH is considered to be one of the main causes of increased P concentration in iron ore. Among various dephosphorization methods, reduction heat treatment is a method in which P is vaporized at high temperatures using a rotary kiln or other device in a reducing atmosphere such as H2-CO2-N2. Reduction heat treatment is considered to be the most suitable method for removing P chemisorbed to α-FeOOH. Therefore, if iron ore is identified as containing a large amount of P chemisorbed to α-FeOOH, applying reduction heat treatment to that iron ore is expected to achieve high dephosphorization efficiency.

[0009] More specifically, an object of the present invention is to provide a method for sorting iron ore that can identify iron ore with a high deP efficiency by reduction heat treatment. [Means for solving the problem]

[0010] To solve the above-mentioned problems, the present inventors conducted extensive research and discovered the following: Among the forms of P contained in α-FeOOH iron ore containing P-adsorbed α-FeOOH, P-adsorbed α-FeOOH containing Al (referred to herein as "P-adsorbed α-(Fe,Al)OOH") has a smaller bond energy between α-FeOOH and phosphate ions than P-adsorbed α-FeOOH without Al. Therefore, iron ore containing α-(Fe,Al)OOH is more likely to release P during reduction heat treatment than iron ore containing only α-FeOOH. Furthermore, the higher the content of α-(Fe,Al)OOH, the more easily P is released during reduction heat treatment. Based on this finding, the present invention was conceived.

[0011] That is, the gist of the present invention is as follows. In this specification, goethite is used as a term indicating α-FeOOH or α-(Fe,Al)OOH, and α-(Fe,Al)OOH is used as a term indicating α-FeOOH containing Al (i.e., Fe is partly substituted with Al).

[0012] (1) A method for selecting iron ore from which phosphorus is easily removed by a reduction heat treatment method, comprising: performing X-ray diffraction measurement on the iron ore; and determining that the iron ore is easier to remove phosphorus by a reduction heat treatment method as the shift of at least one peak attributed to goethite observed in the X-ray diffraction pattern from the goethite reference peak increases.

[0013] (2) The method for sorting iron ore according to (1), further comprising an element concentration measurement step of measuring the element concentration of the iron ore, and sorting iron ore whose element concentration of phosphorus obtained in the element concentration measurement step is equal to or greater than [Threshold 1] as iron ore to be removed from by a reduction heat treatment method.

[0014] (3) a sample preparation step of preparing a sample having an analysis surface from the iron ore; an infrared absorption spectrum acquisition step of observing the analysis surface with an infrared microscope to acquire an infrared absorption spectrum a; a goethite presence field identification step of identifying a goethite presence field by comparing the infrared absorption spectrum a with an infrared absorption standard spectrum b of goethite; an infrared absorption spectrum averaging step of averaging the infrared absorption spectrum c1 of the goethite presence field to acquire an average infrared absorption spectrum c2; and an infrared absorption spectrum averaging step of averaging the average infrared absorption spectrum c2 at a wave number of 950 cm. -1 More than 1200cm -1 and an adsorption P peak intensity acquisition step of acquiring an adsorption P peak intensity by calculating the sum of the intensities of peaks observed in the following regions, and determining that P is adsorbed to α-FeOOH or α-(Fe,Al)OOH when the adsorption P peak intensity is equal to or greater than a predetermined [threshold 2].

[0015] (4) The iron ore sorting method according to (3), further comprising the steps of: prior to the infrared absorption spectrum acquisition step, scanningly irradiating the analysis surface obtained in the sample preparation step with an electron beam probe or an X-ray probe to acquire a characteristic X-ray spectrum at each analysis point; identifying and storing Fe-P-Al coexistence analysis points where the element concentrations of Fe, P, and Al are equal to or greater than predetermined thresholds [threshold 3], [threshold 4], and [threshold 5]; and setting a region for acquiring the infrared absorption spectrum a in the infrared absorption spectrum acquisition step so as to include the Fe-P-Al coexistence analysis points. [Effects of the Invention]

[0016] According to the present invention, it is possible to determine whether iron ore is suitable for reduction heat treatment based on the content of α-(Fe,Al)OOH in the iron ore, and to reliably select iron ore that is easy to be reduced and dephosphorized. [Brief explanation of the drawings]

[0017] [Figure 1A]FIG. 1 is a flow diagram for selecting iron ore from which phosphorus is easily removed by a reduction heat treatment method according to a first embodiment of the present invention. [Figure 1B] FIG. 1 is a flow chart for selecting iron ore from which phosphorus is easily removed by a reduction heat treatment method according to a second embodiment of the present invention. [Figure 1C] FIG. 10 is a flow chart for selecting iron ore from which phosphorus is easily removed by a reduction heat treatment method according to a third embodiment of the present invention. [Figure 2A] FIG. 1 is a diagram showing 2θ (°) at the 002 peak of three types of iron ore. [Figure 2B] FIG. 1 is a diagram showing 2θ (°) at the 221 peak of three types of iron ore. [Figure 3A] FIG. 1 is a diagram showing the relationship between 2θ (°) at the 002 peak of three types of iron ore and the dephosphorization rate (%) by reduction heat treatment. [Figure 3B] FIG. 1 is a diagram showing the relationship between 2θ (°) at the 221 peak of three types of iron ore and the dephosphorization rate (%) by reduction heat treatment. [Figure 4] 1 is an optical microscope image of the analyzed surface of iron ore obtained with an infrared microscope. [Figure 5] This is an example of an infrared absorption spectrum in the wavenumber range of 950 cm −1 to 1200 cm −1 . DETAILED DESCRIPTION OF THE INVENTION

[0018] The present invention will be described in detail below.

[0019] The present invention is a method for selecting iron ore from which phosphorus can be easily removed by reduction heat treatment.

[0020] First, the circumstances that led to the creation of the present invention will be explained.

[0021] <Background of the invention> Patent Document 1 and the like disclose a method for rapidly identifying P chemisorbed to α-FeOOH contained in iron ore composed of multiple iron oxides, iron hydroxides, etc. However, even when iron ore is determined to contain α-FeOOH chemisorbed with P by this method (hereinafter referred to as "P-adsorbed α-FeOOH ore"), the dephosphorization efficiency by reduction heat treatment is not necessarily the same.

[0022] Therefore, the inventors conducted further studies to explore the cause of this difference. As a result, they found that P-adsorbed α-FeOOH ores containing relatively high amounts of Al tend to exhibit high dephosphorization efficiencies by reduction heat treatment. Therefore, we next focused on α-FeOOH, in which part of the Fe is replaced by Al (i.e., α-(Fe,Al)OOH). First, infrared absorption spectroscopy was performed to identify the specific chemical adsorption mode of phosphate ions on α-FeOOH and α-(Fe,Al)OOH. The results showed that P adsorbs to Fe in a monodentate phosphate ion configuration in both α-FeOOH and α-(Fe,Al)OOH. Therefore, we calculated the bond energy between Fe and the oxygen of the phosphate ion for the monodentate phosphate ions on α-FeOOH and α-(Fe,Al)OOH by quantum chemical calculation. We found that the bond energy between Fe and the oxygen of the phosphate ion was smaller when adsorbed on α-(Fe,Al)OOH than when adsorbed on α-FeOOH. Therefore, it was concluded that the more α-(Fe,Al)OOH contained in α-FeOOH contained in iron ore, the easier it is to deP by reduction heat treatment, and the higher the deP efficiency can be obtained. Based on the above findings, the present invention provides a method for selecting iron ore that can achieve a high deP efficiency by reduction heat treatment.

[0023] On the one hand, in α-(Fe,Al)OOH, it is known that Al exists in a form substituting a part of Fe. Also, in α-(Fe,Al)OOH, when Al substitutes a part of Fe, the 002 peak and 221 peak observed on the X-ray diffraction pattern of α-FeOOH shift to the high angle side, and it has been clarified that the greater the substitution rate of Al, the more these two peaks shift to the high angle side. Therefore, if the X-ray diffraction pattern of an iron ore is obtained and diffraction peaks corresponding to α-FeOOH are observed, and it can be confirmed that their positions (2θ) are shifted to the high angle side with respect to the standard α-FeOOH, it can be said that there is a high possibility that the iron ore contains P-adsorbed α-(Fe,Al)OOH.

[0024] In addition, when it is unclear whether the iron ore to be separated is an α-FeOOH ore containing a relatively large amount of α-FeOOH, or whether it contains a relatively large amount of P and Al, prior to obtaining the above X-ray diffraction pattern, the iron ore may be subjected to elemental analysis to measure the elemental concentrations. Or, from the above X-ray diffraction pattern, for example, the phase fraction of α-FeOOH may be determined using the Rietveld method, and based on the result, it may be determined whether it is an α-FeOOH ore containing a relatively large amount of α-FeOOH.

[0025] However, P is not always chemisorbed to α-FeOOH. Therefore, in another embodiment of the present invention, infrared microscopic observation is performed to identify the α-FeOOH region and confirm the presence of P adsorbed to α-FeOOH. According to this embodiment, it becomes possible to more reliably select an iron ore that can obtain a high P removal rate by dephosphorization in the reduction heat treatment method.

[0026] Hereinafter, with reference to the drawings, a method for separating an iron ore that is easy to remove P by the reduction heat treatment method according to this embodiment will be described. First, the first embodiment of the present invention will be described. Hereinafter, examples of specific methods will be shown, but this method is not limited to its content.

[0027] <X-ray Diffraction Measurement Step> FIG. 1A shows a flow diagram of a method for sorting iron ore according to a first embodiment of the present invention. X-ray diffraction measurement is performed on the iron ore powder to be sorted. The larger the shift of the peak (2θ) attributable to α-FeOOH relative to the α-FeOOH reference peak observed in the obtained X-ray diffraction pattern, the easier it is to select the iron ore for phosphorus removal by reduction heat treatment. Whether or not the iron ore contains aluminum-substituted goethite (hereinafter referred to as "aluminum-substituted goethite-containing iron ore") can be determined, for example, by determining whether the shift of the peak (2θ) attributable to α-FeOOH relative to the α-FeOOH reference peak is equal to or greater than a predetermined threshold. The threshold may be set, for example, as three times the measurement device error. Specifically, powder X-ray diffraction measurement of iron ore involves powdering the iron ore to be sorted using a mortar and an automatic grinder, and then subjecting the powder to an X-ray diffractometer to obtain an X-ray diffraction pattern. After identifying the α-FeOOH peaks in the obtained X-ray diffraction pattern, the 2θ value of at least one of the α-FeOOH-derived 002 and 221 peaks observed in the X-ray diffraction pattern is calculated, and the 2θ shift from the α-FeOOH reference peak (α-FeOOH reference peak) is determined to identify the aluminum-substituted goethite-containing iron ore. Instead of calculating the 2θ shift, the ratio of change in peak position observed in powder X-ray diffraction measurement of the iron ore to be sorted can be calculated using the peak position of α-FeOOH without Al as a reference. The X-ray source used in the X-ray diffraction measurement is not particularly limited, but cobalt (Co), chromium (Cr), copper (Cu), etc. can be used.

[0028] Here, the 2θ of the 002 peak of goethite of Ore1 to Ore3, which are examples of α-FeOOH ores, is shown in Fig. 2A, and the 2θ of the 221 peak is shown in Fig. 2B. In this embodiment, the iron ore is selected as having a higher deP efficiency by reduction heat treatment when the shift of the diffraction peak derived from α-FeOOH relative to the α-FeOOH reference peak is larger.

[0029] Prior to or after the X-ray diffraction measurement step, the element concentrations of the iron ore to be sorted may be measured. This step is the "element concentration measurement step" described below.

[0030] <Element concentration measurement process> As shown in FIG. 1A, chemical analysis of iron ore is performed to determine the average P element concentration (more preferably, the element concentrations of Fe, P, and Al) contained in the iron ore. Specifically, if the Fe concentration is within a predetermined range (e.g., 30% by mass or more and 60% by mass or less), the iron ore can be determined to be a high-α-FeOOH ore containing a relatively large amount of α-FeOOH phase. In this case, P is likely to be chemisorbed onto α-FeOOH, and the ore can be determined to be suitable for dephosphorization by reduction heat treatment.

[0031] Table 1 shows the chemical analysis values ​​of the iron ores (Ore1 to Ore4). Iron ores Ore1, Ore2, and Ore3 are α-FeOOH ores, and Ore4 is α-Fe2O3 ore. As shown in Table 1, the Fe concentration of the α-FeOOH ore and the Al-substituted α-FeOOH ore is between 30% and 60% by mass, while the Fe concentration of the α-Fe2O3 ore is over 60% by mass (64.49% by mass).

[0032] [Table 1]

[0033] Furthermore, iron ore with a P concentration equal to or greater than a predetermined threshold [Threshold 1] is determined to require dephosphorization (i.e., iron ore from which phosphorus is to be removed by reduction heat treatment). The P concentration [Threshold 1] may be determined, for example, from a range of 0.06 to 0.08% by mass. A P concentration of 0.06% by mass or greater imposes significant burdens on the ironmaking and steelmaking processes, such as dephosphorization. However, the P concentration [Threshold 1] may be appropriately determined depending on the ironmaking and steelmaking equipment capacity and operating conditions. Ore 3 is a high-α-FeOOH ore, and its Al concentration is more than twice that of Ore 1 and Ore 2. Therefore, it is expected to contain α-(Fe,Al)OOH. While Ore 4 contains 0.05% by mass or more of P, its Fe concentration suggests that it contains a relatively high amount of hematite. Therefore, in this embodiment, it is not determined that a high dephosphorization efficiency can be achieved by reduction heat treatment.

[0034] Various techniques can be used for chemical analysis, including inductively coupled plasma (ICP) emission spectroscopy, X-ray fluorescence analysis using the glass bead method, and atomic absorption spectrometry. However, if it is known in advance that the iron ore contains more than a predetermined amount of Al and P and is a goethite ore containing a relatively large amount of goethite, the element concentration measurement can be omitted.

[0035] This article explains X-ray fluorescence analysis using the glass bead method. X-ray fluorescence analysis is a quantitative analytical method for analyzing the elements that make up a material by measuring the fluorescent X-rays generated by irradiating a sample with X-rays. There are various techniques for measuring X-ray fluorescence, but the glass bead method, which involves melting and vitrifying the sample with an alkaline flux, is commonly used for X-ray fluorescence analysis of ores, rocks, and refractories. This analytical technique uniformly disperses the powdered sample within the glass structure, reducing the sample's heterogeneity, eliminating particle size effects, and mitigating matrix effects, resulting in accurate and reproducible analytical results. Various alkaline fluxes are used, but lithium tetraborate is commonly used. Quantitative analysis using X-ray fluorescence analysis often involves the use of a calibration curve. This method involves creating a calibration curve using a standard sample and then measuring the content of a specific element in an unknown sample. For X-ray fluorescence analysis, a standard sample with a similar chemical composition to the measurement sample (unknown sample) is used, and a relationship between the fluorescent X-ray intensity and the content is first established. The quantitative value of an unknown sample can be determined using the calibration curve and the fluorescent X-ray intensity of the unknown sample obtained by measurement.

[0036] This section explains ICP optical emission spectroscopy. This analytical method consists of a pretreatment step in which a sample is melted using a mixed flux of sodium carbonate and sodium tetraborate, and then the melt is dissolved in hydrochloric acid. A portion of the solution is then sprayed and introduced into the argon plasma of an ICP optical emission spectrometer, where the emission intensity of the analytical line of the quantitative component or the ratio of the emission intensity of the analytical line of the quantitative component to the emission intensity of the internal standard element (emission intensity ratio) is measured. There are various types of ICP optical emission spectrometers, including sequential and multichannel types, but the type is not important here.

[0037] Next, a second embodiment of the present invention will be described.

[0038] In a second embodiment of the present invention, an iron ore sample is measured using an infrared microscope before or after the first embodiment. FIG. 1B shows a flow diagram of an example of an iron ore sorting method according to the second embodiment of the present invention. The flow diagram shown in FIG. 1B includes a sample preparation step, an infrared absorption spectrum acquisition step, a goethite presence field identification step, an infrared absorption spectrum averaging step, and an adsorption P peak intensity acquisition step after the first embodiment (i.e., the X-ray diffraction measurement step and the element concentration measurement step). Hereinafter, the second embodiment of the present invention will be described, starting with the sample preparation step.

[0039] <Sample preparation process> In the sample preparation process, a smooth cross section of the iron ore is prepared as the analysis surface to obtain a sample with an analysis surface. Various methods, such as thin section processing, can be used to prepare the analysis surface. For example, a resin-embedded sample embedded in resin may be prepared. Specifically, the iron ore to be sorted is embedded in resin and polished to create the analysis surface, thereby preparing the sample for analysis. Various resins can be used, including thermosetting resins, thermoplastic resins, and photocurable resins, but thermoplastic resins are commonly used. Once the resin-embedded sample with the iron ore particles embedded in the resin has solidified, it is polished to obtain a polished surface. A conductive film may be formed on the polished surface by vapor deposition.

[0040] <Infrared absorption spectrum acquisition process> The analytical surface of the prepared sample is measured using an infrared microscope, and an infrared absorption spectrum a is obtained for each field of view.

[0041] <Gamesite presence visual field identification process> Next, the infrared absorption spectrum a of each field of view acquired in the infrared absorption spectrum acquisition step is compared with the infrared absorption standard spectrum b of goethite, which is the infrared absorption spectrum of the goethite standard reagent, to evaluate the degree of match. That is, the correlation coefficient between the infrared absorption spectrum a of each field of view and the infrared absorption standard spectrum b of goethite is calculated, and the field of view where the calculated correlation coefficient is equal to or greater than a predetermined threshold is identified as the field of view where goethite is present. In this case, a commercially available goethite standard reagent can be used. The method for measuring the infrared absorption spectrum of the goethite standard reagent is not limited, but it is preferable to measure it using the same method as the method used to analyze the iron ore to be sorted.

[0042] In the goethite-containing field identification step, a correlation coefficient is used to evaluate the degree of agreement between the infrared absorption spectrum a for each field acquired in the previous infrared absorption spectrum acquisition step and the infrared absorption standard spectrum b for goethite. This correlation coefficient can be calculated from the covariance and standard deviation. In both cases of positive and negative correlation, the closer the absolute value of the correlation coefficient is to 1, the more the two spectra match, and the closer it is to zero, the less correlation there is. The iron ore sample to be measured in this invention is generally composed of multiple iron oxides. Therefore, to identify goethite based on the presence or absence of the characteristic peaks of goethite, a threshold value for determining goethite is determined in advance through a preliminary test using the analytical device to be used. The threshold value can be determined by measuring the infrared absorption spectrum of an iron ore sample and calculating the correlation coefficients for each field, and then using the smallest correlation coefficient at which the characteristic peaks of goethite are observed.

[0043] In addition, in this step of identifying the field of view where goethite is present, a two-dimensional image profile may be created from a correlation coefficient obtained by comparing the infrared absorption spectrum a of each field of view acquired in the infrared absorption spectrum acquisition step with the infrared absorption standard spectrum b of goethite. This makes it possible to visually and easily grasp the distribution of goethite on the analysis surface obtained in the sample preparation step.

[0044] <Infrared absorption spectrum averaging process> The infrared absorption spectrum c1 in the field of view where goethite is present is averaged to obtain an average infrared absorption spectrum c2. The average infrared absorption spectrum c2 may be obtained using a program included in a commercially available infrared microscope.

[0045] <Adsorption P peak intensity acquisition process> In the average infrared absorption spectrum c2, the wave number is 950 cm -1 More than 1200cm -1 The intensity of the peak derived from phosphate ions observed in the following region is determined as the adsorption P peak intensity. There are various methods for determining a specific peak intensity. These include determining a baseline and determining the peak intensity from the baseline, determining the area between the baseline and the peak as the peak intensity, or determining the absorbance value at a specific wavenumber as the peak intensity. If there are multiple adsorption P peaks, the sum of their peak intensities may be determined. As with the infrared absorption spectrum averaging process, the adsorption P peak intensity acquisition process may also be performed using a program included in a commercially available infrared microscope.

[0046] When the adsorbed P peak intensity in the infrared absorption spectrum c2 is equal to or greater than a predetermined threshold [threshold 2], the presence of goethite-adsorbed P, in which a phosphorus compound is chemically adsorbed to goethite, is identified. Here, there is no particular limitation on the means for setting [threshold 2], but it can preferably be set as follows. That is, in advance, a peak intensity of 950 cm wavenumber is set in the spectrum of goethite without phosphate adsorption within the measurement field of view. -1 More than 1200cm -1 The noise intensity N observed in the following region is calculated in advance. If the adsorption P peak intensity in the infrared absorption spectrum corresponding to each field of view is three times or more the square root of the noise intensity N, √N, it may be determined that phosphate is adsorbed. In other words, [threshold 2] is calculated by multiplying the noise intensity N by 3N. 1 / 2 is.

[0047] In the above-described second embodiment, in addition to the first embodiment, for the sample prepared by sample preparation, an infrared absorption spectrum acquisition step, an infrared absorption spectrum averaging step, and an adsorbed P peak intensity acquisition step are performed, and it can be confirmed that P is adsorbed and present on the gas site (α-FeOOH or α-(Fe,Al)OOH). Therefore, according to the second embodiment, it becomes possible to more reliably select iron ore that is easy to remove phosphorus by the reduction heat treatment method.

[0048] Next, a third embodiment of the present invention will be described.

[0049] In the third embodiment of the present invention, before measuring the sample prepared in the sample preparation step of the second embodiment with an infrared microscope (that is, prior to the infrared absorption spectrum acquisition step), characteristic X-ray spectra are acquired using an electron beam probe or an X-ray probe, and analysis points where Fe, P, and Al coexist are specified within the analysis surface. FIG. 1C shows a flowchart of an example of a method for sorting iron ore according to the third embodiment of the present invention. In the flowchart shown in FIG. 1C, after the sample preparation step, there is an Fe-P-Al coexisting analysis point storage step. Hereinafter, the third embodiment of the present invention will be described starting from the Fe-P-Al coexisting analysis point storage step. Note that the sample preparation step is the same as that of the second embodiment and will be omitted.

[0050] <Fe-P-Al Coexisting Analysis Point Storage Step> The sample prepared in the sample preparation step is placed in a sample chamber of an analytical device equipped with a characteristic X-ray detector, and the characteristic X-ray spectrum is measured. Specifically, an electron probe or X-ray probe is scanned and irradiated onto the analysis surface obtained in the sample preparation step to obtain a characteristic X-ray spectrum at each analysis point. The element concentration distributions of Fe, P, and Al are then determined, and Fe-P-Al coexistence analysis points are identified where the element concentration of Fe is equal to or greater than a threshold value [threshold 3], the element concentration of P is equal to or greater than a threshold value [threshold 4], and the element concentration of Al is equal to or greater than a threshold value [threshold 5]. These Fe-P-Al coexistence analysis points are then stored, and in the infrared absorption spectrum acquisition step, the region (field of view) for acquiring the infrared absorption spectrum a is set to include these Fe-P-Al coexistence analysis points. This allows for the presence of P, and for the P to be detected in the 950-1200 cm range observed in the field of view where Al-substituted goethite is present. -1 This allows for more accurate identification of P derived from phosphorus compounds such as phosphate adsorbed on goethite, which shows a peak at 1000 kJ / cm2. In addition, it also makes it possible to limit the measurement field of the infrared microscope, thereby shortening the time required for infrared microscope measurements.

[0051] There are various analytical instruments equipped with characteristic X-ray detectors, but the most commonly used are SEM, EPMA, and XRF. In this case, SEM images, backscattered electron images, and optical microscope images of the analysis surface may also be acquired. From the characteristic X-ray spectra obtained for each analysis point, analysis points where the characteristic X-ray intensities of Fe, P, and Al are all equal to or greater than the respective predetermined thresholds [Threshold 3], [Threshold 4], and [Threshold 5] are identified and stored.

[0052] In setting the thresholds for Fe, P, and Al, there are no particular restrictions. For example, the concentrations of Fe, P, and Al can be referred to within any region based on the elemental analysis values. Specifically, in the case of elemental analysis by EPMA, as the [threshold 3], [threshold 4], and [threshold 5] for Fe, P, and Al, the average values of the concentrations of Fe, P, and Al calculated at each analysis point within the EPMA measurement field of view may be used. Alternatively, the [threshold 3], [threshold 4], and [threshold 5] may be determined by other statistical methods using the Fe, P, and Al intensities or concentrations within the EPMA measurement field of view.

[0053] Next, for the region (field of view) where the infrared absorption spectrum a is obtained as set above, in the same manner as in the second embodiment, a gassite presence field identification step and an adsorbed P peak intensity acquisition step are carried out to select iron ore that is easy to remove phosphorus by a reduction heat treatment method. According to the third embodiment, since the measurement field of view of the infrared microscope can be limited, it becomes possible to shorten the required time for infrared microscope measurement.

Examples

[0054] Hereinafter, the present invention will be specifically described based on examples, but the present invention is not limited to the examples.

[0055] (Example 1) (1) Three types of model ores of P-adsorbed α-FeOOH (Al substitution rate 0%), (2) P-adsorbed α-(Fe,Al)OOH (Al substitution rate 3%), and (3) P-adsorbed α-(Fe,Al)OOH (Al substitution rate 9%) were prepared.

[0056] <X-ray diffraction measurement> Each of the above three types of model ores was pulverized in a mortar to prepare a powder sample, and X-ray diffraction measurement was performed. The X-ray source used was a Cr tube target.

[0057] <Reduction heat treatment> The three model ores were subjected to reduction heat treatment at 500°C, 700°C, and 900°C in a H2 (25%), CO2 (25%), and N2 (50%) atmosphere using a simultaneous differential thermal analyzer (TG-DTA). The P concentrations of the model ores before and after the reduction heat treatment were measured using inductively coupled plasma atomic emission spectroscopy (ICP-AES), and the dephosphorization rate was calculated from the difference in P content.

[0058] Figure 3A shows the relationship between the deP ratio and the shift of the diffraction peak observed for each sample relative to the diffraction peak of standard α-FeOOH for the 002 plane of α-FeOOH, and Figure 3B shows the relationship between the shift of the 221 plane and the deP ratio. Figures 3A and 3B confirm that the deP ratio increases with increasing shift for both the 002 and 221 plane diffraction peaks.

[0059] Example 2 For infrared absorption spectrum measurement, the sample was embedded in epoxy resin, heat-cured, and then polished to prepare the analysis surface. The measurement equipment used was a Fourier transform infrared spectrophotometer FT-IR6100 and an infrared microscope IRT-7100 manufactured by JASCO Corporation. The analysis software used was the software installed in the equipment. The measurement conditions were a mid-infrared light source, a linear array detector, and an areal resolution of 12.5 × 12.5 μm.

[0060] Figure 4 shows an optical microscope image of the analysis surface of an iron ore sample acquired with an infrared microscope. The area within the black frame in Figure 4 was observed with the infrared microscope to measure the infrared absorption spectrum a. The infrared absorption spectrum a obtained in each field of view was compared with the standard infrared absorption spectrum b of goethite, which had been previously acquired and stored in a memory device, to determine the correlation coefficient. The area where the correlation coefficient was equal to or greater than a preset threshold (0.20 in this example) was identified as the goethite-existing field. For the area identified as the goethite-existing field, the software installed in the measuring device was used to calculate the average value of the infrared absorption spectrum c1 in the observed area, thereby obtaining the average infrared absorption spectrum c2. Next, the average infrared absorption spectrum c2 in the 950-1200 cm range of the goethite-existing field was measured. -1The presence or absence of a peak was detected within this range, and if a peak was detected, the absorbance value at that wavenumber was calculated, and the sum of all peak intensities within the above wavenumber range was calculated as the adsorbed P peak intensity. Figure 5 shows the infrared absorption spectra of three different samples. The adsorbed P peak intensity for all three samples exceeded the threshold, indicating that P was adsorbed onto the goethite.

[0061] Example 3 For an iron ore sample prepared in the same manner as in Example 2, an Fe-P-Al coexistence analysis point storage step was carried out in which an electron beam probe was scanned and irradiated onto the analysis surface, characteristic X-ray spectra were obtained at each analysis point, and Fe-P-Al coexistence analysis points where Fe, P, and Al coexist were identified and stored. Specifically, the step was as follows.

[0062] The measurements were performed using a JXA-8530F (manufactured by JEOL Ltd.), and analysis of the three elements Fe, Al, and P was performed at each analysis point. Measurements were performed in a 300 μm × 300 μm area, and the concentration distribution of these three elements within the field of view was investigated. In this example, the [threshold 3] for Fe was 50 mass%, the [threshold 4] for P was 0.5 mass%, and the [threshold 5] for Al was 1 mass%. Based on these thresholds, Fe-P-Al coexistence analysis points that were above [threshold 3], above [threshold 4], and above [threshold 5] were identified. Of the 300 μm × 300 μm map measurement area, an area equivalent to a total of 50 μm × 50 μm corresponded to these Fe-P-Al coexistence analysis points. In Example 2, the infrared absorption spectrum acquisition step had to be performed for the entire 300 μm × 300 μm measurement region. In contrast, in Example 3, the 50 μm × 50 μm region including these Fe-P-Al coexistence analysis points only needs to be set as the measurement region in the infrared absorption spectrum acquisition step, thereby significantly shortening the measurement time.

Claims

1. A method for selecting iron ore from which phosphorus can be easily removed by reduction heat treatment, comprising the steps of: The method for sorting iron ore includes an X-ray diffraction measurement step of measuring X-ray diffraction of iron ore, and sorting the iron ore so that the larger the shift of at least one peak attributed to goethite observed in the X-ray diffraction pattern relative to the goethite reference peak, the easier it is to remove phosphorus by a reduction heat treatment method.

2. Further, an element concentration measuring step of measuring an element concentration of the iron ore, 2. The iron ore sorting method according to claim 1, wherein iron ore having an elemental concentration of phosphorus obtained in the elemental concentration measurement step that is equal to or greater than [threshold 1] is sorted as iron ore that is a target for phosphorus removal by a reduction heat treatment method.

3. a sample preparation step of preparing a sample having an analysis surface from the iron ore; an infrared absorption spectrum acquisition step of observing the analysis surface with an infrared microscope to acquire an infrared absorption spectrum a; a goethite presence field identifying step of identifying a field of view where goethite is present by comparing the infrared absorption spectrum a with a goethite infrared absorption standard spectrum b; an infrared absorption spectrum averaging step of averaging the infrared absorption spectra c1 in the field of view where goethite is present to obtain an average infrared absorption spectrum c2; For the average infrared absorption spectrum c2, the wave number is 950 cm －１ More than 1200cm －１ and an adsorption P peak intensity acquisition step of obtaining an adsorption P peak intensity by determining the intensity of a peak observed in the following region: The iron ore sorting method according to claim 1 or 2, wherein it is determined that P is adsorbed to α-FeOOH or α-(Fe, Al)OOH when the adsorbed P peak intensity is equal to or greater than a predetermined [threshold 2].

4. Prior to the infrared absorption spectrum acquisition step, an Fe-P-Al coexistence analysis point storage step is performed in which an electron beam probe or an X-ray probe is scanned and irradiated onto the analysis surface obtained in the sample preparation step to acquire a characteristic X-ray spectrum at each analysis point, and Fe-P-Al coexistence analysis points at which the element concentrations of Fe, P, and Al are equal to or greater than predetermined thresholds [threshold 3], [threshold 4], and [threshold 5] are identified and stored; The iron ore sorting method according to claim 3, wherein in the infrared absorption spectrum acquisition step, a region for acquiring the infrared absorption spectrum a is set so as to include the Fe-P-Al coexistence analysis point.

Images