Quantitative analysis methods for phosphate minerals based on their morphology

Abstract

To provide a method capable of precisely measuring the mass fraction or volume fraction of a phosphate mineral included in iron ore.SOLUTION: A method of a quantitative analysis of phosphate mineral by morphology includes: a step of selecting reference particles out of iron ore particles as the subject to analysis, analyzing by SEM / EDS and vibrational spectroscopy, and identifying phosphate mineral contained in the reference particle; a step of obtaining X-ray CT images of a specimen of the phosphate mineral of the same type as the identified phosphate mineral; a step of creating a contrast histogram relevant to the luminance intensity and luminance frequency from the obtained X-ray CT images and identifying the luminance intensity corresponding to the identified phosphate mineral; a step of selecting analysis particles out of the iron ore particles and obtaining X-ray CT images; and a step of measuring the area with the luminance intensity corresponding to the identified phosphate mineral, and calculating the mass fraction or volume fraction of the identified phosphate mineral based on the obtained X-ray CT image.SELECTED DRAWING: Figure 5

Description

Technical Field

[0001] This invention relates to a method for quantitatively analyzing phosphate minerals in iron ore by form.

Background Art

[0002] Iron ore used as a raw material in the steel industry is composed of multiple iron oxides in nature. In addition to iron (Fe) as the main component, it contains impurities such as aluminum (Al), silicon (Si), and phosphorus (P) as gangue components.

[0003] Since the impurities in iron ore deteriorate the properties of steel, those with a high content have been avoided so far. However, as a measure against resource degradation, the effective utilization of such low-grade iron ore has attracted attention.

[0004] Among these, phosphorus is known to exist as phosphate minerals and is removed in the steelmaking process by the converter method. However, in order to enhance the dephosphorization process, it is necessary to understand the removal efficiency of phosphate minerals in iron ore. For this purpose, the mass fraction of phosphate minerals must be grasped. However, since the phosphate minerals present in iron ore are 1 mass% or less of the whole, it is difficult to accurately evaluate the removal efficiency of phosphate minerals using the bulk analysis method. In addition, phosphate minerals are not uniformly distributed, and phosphate minerals may be unevenly distributed within iron ore, making it more difficult to measure their mass fraction.

[0005] For example, in mining applications such as oil and gas exploration, there is a method for analyzing the composition of mineral samples by using X-ray fluorescence emitted when the mineral sample is irradiated with X-rays and Raman radiation emitted when the mineral sample is irradiated with light to analyze the compounds in the mineral sample (see Patent Document 1). In addition, when obtaining high-purity metals (ingots) from ores containing compounds (minerals) such as metal oxides and sulfides of copper and nickel, a method is known in which an ore sample is prepared by embedding the ore in resin, a polished surface is formed, and the EDS spectrum is measured by energy-dispersive X-ray analysis (EDS), as well as the Raman spectrum is measured by a micro-laser Raman spectrometer, in order to identify unidentified minerals present in the ore (see Patent Document 2).

[0006] Thus, methods for evaluating minute mineral phases by combining X-ray local elemental analysis and vibrational spectroscopy such as Raman spectroscopy are known. However, even with these methods, it is not possible to accurately measure the mass fraction of phosphate minerals, which are distributed three-dimensionally within iron ore particles and present in trace amounts.

[0007] On the other hand, there is a method of analyzing the mass ratio and concentration of minerals in raw ore containing a mixture of multiple types of minerals using a Mineral Liberation Analyzer (MLA), which is equipped with a scanning electron microscope (SEM) having an energy-dispersive X-ray analyzer (EDS) and a computer that controls these and stores EDS spectra of various minerals as data (see Patent Document 3 for the device configuration and Patent Document 4 for the analysis method).

[0008] In this method, first, a sample of ore powder solidified with resin is polished, and the backscattered electron image (BSE image) of the polished cross-section is measured to record the position of each mineral particle. Next, the EDS spectrum is measured for each polished surface of the identified mineral particles, and the mineral species of the mineral particle is identified by comparing the obtained results with the EDS spectra of the mineral list pre-installed in the MLA. Once the mineral species is identified, the type of metallic element contained in that mineral is determined, and the density can be determined according to the type of metallic element, thereby obtaining the relative densities of each mineral in the sample.

[0009] Next, the above method uses X-ray CT to obtain an X-ray CT image of the ore powder. Since the various substances constituting the sample have brightness corresponding to their density, the relationship between the magnitudes of these brightnesses is correlated with the relationship between the magnitudes of densities determined earlier by MLA. For example, in the MLA measurement, minerals are ranked as follows: mineral α, which has the highest density of metal in the sample; mineral β, which also has a high density of metal; and mineral γ, which has a medium density of metal. Similarly, in the X-ray CT image, particles are ranked as follows: particle A, which has the highest brightness; particle B, which has a high brightness but not as high as particle A; and particle C, which has a medium brightness. A relationship is then established between these particles, such as mineral α = particle A, mineral β = particle B, and mineral γ = particle C. In this way, it is possible to evaluate the mass ratio and concentration of each mineral in the ore in three dimensions.

[0010] However, while the methods described above can relatively evaluate multiple types of minerals present in ore, they cannot directly determine the mass fraction of a specific mineral. Furthermore, these methods are based on the assumption that the number of mineral phases observed by MLA matches the number of mineral phases observed by X-ray CT. If the number of mineral phases observed by a two-dimensional observation method like MLA does not match the number of mineral phases observed by a three-dimensional X-ray CT, accurate evaluation is not possible. [Prior art documents] [Patent Documents]

[0011] [Patent Document 1] Special Publication No. 2015-519571 [Patent Document 2] Japanese Patent Publication No. 2017-090183 [Patent Document 3] Japanese Patent Publication No. 2015-40724 (paragraph 0012) [Patent Document 4] Japanese Patent Publication No. 2020-34372 (paragraphs 0013-0020) [Overview of the Initiative] [Problems that the invention aims to solve]

[0012] In order to effectively utilize low-grade iron ore as a measure against resource deterioration, it is important to accurately assess the amount of phosphorus, an impurity, contained in the iron ore. However, because phosphate minerals are unevenly distributed in iron ore and are present in trace amounts, it is difficult to accurately measure the mass fraction of phosphate minerals in iron ore, and this cannot be achieved with currently known methods.

[0013] Therefore, the inventors diligently studied methods for measuring the mass fraction of phosphate minerals present in iron ore and, as a result, discovered the following method. First, a reference particle is selected from the group of iron ore particles to be analyzed, and the phosphate minerals contained in the reference particle are identified using SEM / EDS and vibrational spectroscopy. Next, an X-ray CT image is obtained of a sample of the same type of phosphate mineral as the identified phosphate mineral, and the intensity of brightness corresponding to the identified phosphate mineral is determined from the contrast histogram. Then, an X-ray CT image is obtained of the analytical particle to be actually analyzed, and the region having the intensity of brightness corresponding to the previously determined phosphate mineral is measured, thereby enabling the accurate determination of the mass fraction of phosphate minerals present in iron ore, thus completing the present invention. Furthermore, since the volume fraction of phosphate minerals present in iron ore can also be determined in the same manner using the above method, the present invention collectively refers to these as a method for quantitative analysis of phosphate minerals in iron ore by morphology.

[0014] Therefore, the object of the present invention is to provide a morphological quantitative analysis method for phosphate minerals that can accurately measure the mass fraction or volume fraction of phosphate minerals present in iron ore. [Means for solving the problem]

[0015] In other words, the gist of the present invention is as follows: (1) A method for quantitative analysis of phosphate minerals by morphology, which involves measuring the mass fraction or volume fraction of phosphate minerals present in iron ore, A step of selecting a reference particle from a group of iron ore particles to be analyzed, and analyzing the cross-section of the reference particle using SEM / EDS and vibrational spectroscopy to identify the phosphate minerals contained in the reference particle, A step of obtaining an X-ray CT image of a phosphate mineral specimen that is the same type as the identified phosphate mineral, A step of creating a contrast histogram relating brightness intensity and brightness frequency from the X-ray CT image obtained from the aforementioned specimen, and identifying the brightness intensity corresponding to the identified phosphate mineral, The process involves selecting analytical particles from the group of iron ore particles and obtaining an X-ray CT image of the analytical particles. A step of determining the mass fraction or volume fraction of the identified phosphate mineral in the analyzed particle by measuring the volume of the region having a brightness intensity corresponding to the identified phosphate mineral in the analyzed particle based on the X-ray CT image obtained from the analyzed particle, A method for quantitative analysis of phosphate minerals present in iron ore, characterized by comprising the following features. (2) A method for quantitative analysis of phosphate minerals present in iron ore according to (1), comprising the step of analyzing a cross-section of the specimen by SEM / EDS and vibrational spectroscopy prior to the step of determining the intensity of brightness corresponding to the identified phosphate mineral, and determining the brightness of the phosphate mineral to be analyzed from the contrast of the X-ray CT image of the specimen. (3) In the step of obtaining the mass fraction or volume fraction of the identified phosphate mineral in the analyzed particles, after correcting either the contrast histogram of the X-ray CT image obtained from the specimen or the contrast histogram of the X-ray CT image obtained from the analyzed particles, the region having the intensity of the luminance corresponding to the identified phosphate mineral in the X-ray CT image of the analyzed particles is measured. The method for quantitatively analyzing the morphology of the phosphate mineral according to (1) or (2). (4) In the step of identifying the phosphate mineral contained in the reference particles, after subjecting the cross-section of the reference particles to elemental analysis by fluorescent X-ray analysis, the phosphate mineral is identified by SEM / EDS and vibrational spectroscopy. The method for quantitatively analyzing the morphology of the phosphate mineral according to (1) or (2). (5) In the step of identifying the phosphate mineral contained in the reference particles, a plurality of reference particles are selected and analyzed based on the cross-section of the aggregate particles having the cross-sections of the plurality of reference particles. The method for quantitatively analyzing the morphology of the phosphate mineral according to (1) or (2).

Advantages of the Invention

[0016] According to the present invention, it becomes possible to accurately measure the mass fraction or volume fraction of a phosphate mineral contained in an iron ore in a very small amount and unevenly distributed in the iron ore. In particular, there has been no known method for quantitatively analyzing the morphology of a phosphate mineral for measuring the mass fraction or volume fraction of a phosphate mineral present in an iron ore, and it is an extremely useful invention for realizing the effective utilization of low-grade iron ore in the future.

Brief Description of the Drawings

[0017] [Figure 1] FIG. 1 is a photograph and an EDS map showing the appearance of the reference particles in Example 1 (the lower framed part is for indicating the positions of the respective upper figures). [Figure 2] FIG. 2 is a Raman spectrum in Example 1. The upper part is the case of a standard reagent of hydroxyapatite, and the lower part is that of the Ca / P coexisting region in the reference particles. [Figure 3]Figure 3 is a contrast histogram created from the three-dimensional CT image of the hydroxyapatite specimen obtained by X-ray CT in Example 1. [Figure 4] Figure 4 is an X-ray CT image of the analysis particles in Example 1. [Figure 5] Figure 5 compares the mass fraction of hydroxyapatite determined by the method of the present invention in Example 1 with the mass fraction of hydroxyapatite determined by XRD measurement. [Figure 6] Figure 6 shows the results of elemental analysis of the reference particles in Example 2 by μ-XRF. The lower part is an enlarged view of a part of the upper part. [Figure 7] Figure 7 shows the results of elemental analysis of the vicinity of the phosphate mineral of the reference particles in Example 2 by SEM / EDS. [Figure 8] Figure 8 shows the results of analyzing the reference particles in Example 2 by micro-Raman. [Figure 9] Figure 9 is a contrast histogram of the YPO4 mineral specimen and a contrast histogram of the analysis particles in Example 2. [Figure 10] Figure 10 is a partially enlarged view comparing the contrast histogram of the YPO4 mineral specimen and the contrast histogram of the analysis particles. [Figure 11] Figure 11 is an X-ray CT image of the analysis particles in Example 2.

Modes for Carrying Out the Invention

[0018] Hereinafter, the present invention will be described in detail. The present invention is a method for quantitatively analyzing the morphological form of a phosphate mineral by measuring the mass fraction or volume fraction of the phosphate mineral present in an iron ore, and comprises the following steps i) to v). i) A step of selecting reference particles from among the iron ore particle group to be analyzed, analyzing the cross-section of the reference particles by SEM / EDS and vibrational spectroscopy, and identifying the phosphate mineral contained in the reference particles. ii) A step of obtaining an X-ray CT image of a phosphate mineral specimen that is the same species as the identified phosphate mineral, iii) A step of creating a contrast histogram relating brightness intensity and brightness frequency from the X-ray CT images obtained from the specimen, and identifying the brightness intensity corresponding to the identified phosphate mineral. iv) A step of selecting analytical particles from the group of iron ore particles and obtaining an X-ray CT image of the analytical particles, and v) A step of determining the mass fraction or volume fraction of the identified phosphate mineral in the analyzed particle by measuring the region having a brightness intensity corresponding to the identified phosphate mineral based on the X-ray CT image obtained from the analyzed particle.

[0019] In this invention, first, in step i) above, a reference particle is selected from the group of iron ore particles to be analyzed, and the distribution of elements is analyzed using a scanning electron microscope (SEM / EDS) equipped with an EDS. The elements to be analyzed are, for example, Fe, Si, P, Ca, and Al. For other elements such as Na, Mg, Ti, Mn, and rare earth elements, the elements are selected depending on the mineral phase contained in the phosphate mineral or iron ore to be analyzed. Here, Figure 1 shows an example of the observation results. The upper left (1) in the figure is a photograph showing the polished surface after embedding a reference particle in resin and polishing its cross-section, and the upper center (2) is an SEM image (30x magnification) of a single particle on the polished surface [indicated by the arrow in (1)]. The upper right (3), lower left (4), lower center (5), and lower right (6) show the EDS phase analysis results (EDS maps) of the particle cross-section of (2), with (3) representing Ca, (4) P, (5) Fe, and (6) Si. In this reference particle, in addition to Fe (5), the coexistence of Ca (3) and P (4) (regions indicated by white circles in the figure) is confirmed. The presence of Si (6) is not confirmed.

[0020] As described above, after analyzing the constituent elements by SEM / EDS, in step i) above, vibrational spectroscopy is performed on the region containing the elements that make up the phosphate mineral. Any vibrational spectroscopy method that can analyze the molecular structure by irradiating the analyte with electromagnetic waves and spectrally analyzing the transmitted or reflected light to obtain a spectrum is acceptable. Typical examples include Raman spectroscopy and Fourier transform infrared spectroscopy. However, from the viewpoint of analyzing phosphate minerals in iron ore, Raman spectroscopy or Fourier transform infrared spectroscopy is preferred, and Raman spectroscopy is most preferred.

[0021] In the previous example, Figure 2 shows the results of Raman spectroscopy measurements performed on the Ca / P coexistence region (white circle in the figure) where the coexistence of Ca and P was confirmed in the particle cross-section. In Figure 2, the upper spectrum is the measurement of the standard reagent for hydroxyapatite [Ca5(PO4)3(OH)]. The lower spectrum is the measurement of the Ca / P coexistence region of the reference particle. Since the two spectra match, the phosphate mineral contained in this reference particle is identified as hydroxyapatite.

[0022] Incidentally, the number of publicly available standard Raman spectra is overwhelmingly smaller compared to infrared absorption spectra, and in particular, standard spectra for identifying phosphate minerals have not been developed. Therefore, in this invention, phosphate minerals are inferred from the constituent elements based on the results of elemental analysis by SEM / EDS. In this example, the mineral composed of Ca and P is inferred to be hydroxyapatite (hydroxyapatite is a representative example of a phosphate mineral composed of Ca and P in iron ore), and the Raman spectrum is measured using a commercially available standard reagent for hydroxyapatite, and then the phosphate mineral contained in the iron ore particles is identified by measuring it on a reference particle. In addition to hydroxyapatite as described above, other representative phosphate minerals present in iron ore include xenotime (YPO4), vivianite (Fe3(PO4)2·8H2O), and wavellite (Al3(PO4)2(OH,F)3·5H2O), as shown in the examples described later, but the phosphate minerals targeted in this invention are not limited to these. In particular, as long as the brightness regions of the target phosphate minerals do not overlap in the contrast histogram obtained by X-ray CT, it is possible to identify phosphate minerals even if the number of mineral phases present in the reference particles and analyte particles does not match.

[0023] Here, the reference particles used as samples in step i) are arbitrarily selected from the group of iron ore particles to be analyzed. Generally, the iron ore used in the steelmaking process is mainly in the form of powdered ore (iron ore particles) of 5 mm or less, which are mixed with a small amount of lime powder and sintered to a certain size. Therefore, most of the iron ore particles to be analyzed are about 5 mm or less. In theory, it is possible to observe the cross-section of one of these iron ore particles using SEM / EDS, but because the amount of phosphate minerals contained in iron ore is small, it is not easy to find a cross-section in which phosphate minerals are present.

[0024] Therefore, as shown in Figure 1(1) above, it is preferable to select multiple reference particles, preferably at least 50 reference particles of about 1 to 3 mm in size, embed them in resin, and polish their cross-sections to form a sample, and then perform step i) based on a composite particle cross-section having the cross-sections of multiple reference particles. More specifically, in this composite particle cross-section, the total area of ​​the cross-sections of the reference particles is 400 mm². 2 It is preferable to have the above configuration. This allows for more reliable observation of the cross-section of the reference particle containing phosphate minerals. While a larger total area of ​​the reference particle's cross-section is desirable to increase the probability of detecting phosphate minerals in such two-dimensional observation, considering the effort and workability involved in actual measurement, this total area of ​​1200 mm² is preferable. 2 This degree represents the practical upper limit. Furthermore, in step i), similar to general measurements, it is possible to first obtain a backscattered electron image of the cross-section of the resin-embedded reference particle using SEM, then identify the position of the reference particle, and perform elemental analysis using EDS.

[0025] Next, in step ii), an X-ray CT image is obtained of a phosphate mineral specimen that is the same type as the identified phosphate mineral identified in step i). X-ray CT uses the differences in how easily X-rays are transmitted or absorbed when X-rays pass through the analyte to investigate the material and structure that make up the analyte. This step ii) is performed to understand how much X-rays the identified phosphate mineral identified in step i) transmits (absorbs), so that in step iv), which will be described later, an X-ray CT image of the actual analyte particles is obtained so that the extent to which the identified phosphate mineral is contained in the analyte particles can be accurately evaluated. However, X-ray CT is easily affected by material density, which changes the spatial resolution, field of view, and contrast of the image. Therefore, in the present invention, the conditions for acquiring X-ray CT images in steps ii) and iv) should be made the same, and in particular, the size of the evaluation material (in this case, analytical particles) and the standard material (in this case, mineral specimens), and the measurement conditions (especially the voltage and output of the incident X-rays, and the spatial resolution of the image) should be made as similar as possible for the evaluation material (in this case, analytical particles) and the standard material (in this case, mineral specimens).

[0026] Here, the phosphate mineral specimen used in step ii) can be one collected from a natural mineral. Preferably, it should be a nearly single-phase, massive specimen that is commercially available as a mineral specimen. There are no particular restrictions, but for example, it can be obtained from a specialty store that sells general mineral specimens and meteorite specimens. In the example above, it would be a hydroxyapatite specimen, and such a specimen is preferably one whose name is written as hydroxyapatite or (hydroxy)apatite, and which is of the same size and shape as the analytical particles used as evaluation material.

[0027] Next, in step iii), a contrast histogram is created based on the X-ray CT image of the specimen obtained in step ii) to determine the intensity of brightness and the frequency of brightness, thereby identifying the intensity of brightness corresponding to the identified phosphate mineral. As mentioned earlier, there are differences in X-ray transmission and absorption depending on the material that makes up the object of analysis, and in X-ray CT, a 3D CT image (grayscale image) is formed based on the brightness corresponding to these differences. Therefore, using image analysis software attached to the X-ray CT, the brightness input into the voxels that make up the 3D CT image is read out, and a contrast histogram is created with brightness intensity on the horizontal axis and brightness frequency on the vertical axis.

[0028] Figure 3 shows a contrast histogram created using image analysis software for a 3D CT image of a specimen (mineral specimen) consisting of the mineral phase of natural hydroxyapatite obtained by X-ray CT in steps ii) and iii). The histogram plots brightness intensity on the x-axis and brightness frequency on the y-axis. In Figure 3, the peak near the center represents X-rays that have passed through the mineral phase of hydroxyapatite. The peak to its left represents X-rays that have only passed through the atmosphere. When such a contrast histogram is created, the peak of the mineral phase is always brighter than the peak that has passed through the atmosphere.

[0029] As described above, in the contrast histogram of Figure 3, the region of brightness intensity (horizontal axis) between 30,000 and 40,000 is identified as corresponding to hydroxyapatite. Since this region will be used in step v) later to measure the identified phosphate mineral in the actual analytical particles, its determination can be made by creating a contrast histogram similar to the one described above in step v) based on the 3D CT image of the analytical particles measured in step iv) below, and determining it so that it matches the peak corresponding to the identified phosphate mineral (in this case, hydroxyapatite). Alternatively, the region of brightness intensity corresponding to hydroxyapatite can be determined by centering the peak position corresponding to hydroxyapatite and defining the region between the two inflection points on either side of it. Specifically, in the example in Figure 3, the region between the point where the second derivative is negative on the side with a higher brightness than the hydroxyapatite peak (i.e., brightness intensity = 32000) and the point where the second derivative is positive on the side with a lower brightness than the same peak (i.e., brightness intensity = 36000) (32000 to 36000) may be determined as the signal for hydroxyapatite. Furthermore, the full width at half maximum of the peak corresponding to the identified phosphate mineral may be selected, and the corresponding region of brightness intensity may be used.

[0030] Here, in step iii) to determine the intensity of brightness corresponding to the identified phosphate mineral, the cross-section of the mineral specimen may be analyzed using SEM / EDS and vibrational spectroscopy, and the brightness of the phosphate mineral to be analyzed may be determined from the contrast of the X-ray CT image of the mineral specimen. This allows for a more reliable determination of which region corresponds to the identified phosphate mineral, especially when the mineral specimen contains multiple mineral phases.

[0031] Next, in step iv), analytical particles are selected from the group of iron ore particles to be analyzed, and an X-ray CT image is obtained. The analytical particles here are of the same type, sampled at the same location and time as the reference particles selected in step i). In step i), it is necessary to form a cross-section for analysis using SEM / EDS or vibrational spectroscopy, but in step iv), an X-ray CT image of the iron ore particles to be analyzed can be obtained non-destructively. Therefore, it is sufficient to obtain an X-ray CT image from one analytical particle, but it is also possible to select multiple analytical particles, obtain an X-ray CT image from each, and then determine the mass fraction of the identified phosphate mineral obtained in step v) described later as an average value, etc. Furthermore, the acquisition of the X-ray CT image in step iv) should be carried out under the same conditions as the acquisition of the X-ray CT image in step ii), except for the difference in the sample being analyzed.

[0032] Next, in step v), based on the 3D CT image of the analytical particles obtained by X-ray CT in step iv), the region having a brightness intensity corresponding to the identified phosphate mineral is measured to determine the mass fraction of the identified phosphate mineral in the analytical particles. The resolution and other properties of this 3D CT image of the analytical particles should be the same as those of the 3D CT image obtained in step iii). Then, in step v), image analysis software attached to the X-ray CT is used to identify the region having a brightness intensity corresponding to the identified phosphate mineral determined in step iii) from the 3D CT image of the analytical particles. At this time, as in step iii), a contrast histogram relating brightness intensity and brightness frequency may be created from the 3D CT image of the analytical particles, or the region corresponding to the identified phosphate mineral in the analytical particles may be determined without creating a contrast histogram.

[0033] Here, Figure 4 shows the CT image of the analyzed particles in the previous example. In this CT image, the region corresponding to hydroxyapatite is mapped, and in reality, the hydroxyapatite region is shown in red, while other mineral phases containing iron oxide are shown in light blue (the upper part of Figure 4 is the actual CT image, and the lower part is an explanatory diagram showing the hydroxyapatite region). In Figure 4, the region with brightness intensity corresponding to hydroxyapatite obtained in step iii), specifically the brightness intensity of the region between the two inflection points on either side of the hydroxyapatite peak (32000~36000), is identified as hydroxyapatite, and everything else is identified as other mineral phases containing iron oxide.

[0034] Furthermore, when determining the mass fraction or volume fraction of the identified phosphate mineral in the analyzed particles, it is also possible to correct either the contrast histogram of the X-ray CT image acquired from the sample or the contrast histogram of the X-ray CT image acquired from the analyzed particles, and then measure the region in the X-ray CT image of the analyzed particles that has a brightness intensity corresponding to the identified phosphate mineral. As mentioned earlier, X-ray CT is easily affected by material density, which can cause changes in the spatial resolution, field of view, and contrast of the image. Therefore, when acquiring X-ray CT images, if there are differences in size, shape, etc., between the sample and the analyzed particles, it is advisable to perform a correction to match the baseline. For example, brightness can be corrected by shifting the spectrum so that the brightness at the boundary between the sample and space is equal in each spectrum.

[0035] In this way, by measuring the volume of the identified phosphate mineral contained in each analytical particle using X-ray CT of the analytical particle, the mass of the identified phosphate mineral contained in each analytical particle can be calculated by multiplying the volume of the identified phosphate mineral by its density. For example, by determining the mass of one analytical particle measured by X-ray CT, the mass of the identified phosphate mineral can be divided by the mass of one analytical particle to determine the mass fraction of the identified phosphate mineral in the analytical particle. Alternatively, as a method for determining the mass fraction of the identified phosphate mineral in the analytical particle, if the mineral phase other than the phosphate mineral contained in the iron ore particle is singular, the volume fractions of the phosphate mineral and the other mineral phases can be determined by CT image processing, and these values ​​can be multiplied by the density of each mineral phase to determine the mass fraction of the identified phosphate mineral in the analytical particle. Of course, it is also possible to determine the volume fraction of the identified phosphate mineral contained in each analytical particle from the volume of the identified phosphate mineral obtained above.

[0036] In the present invention, in step i) above, the cross-section of the reference particle may be elementally analyzed by X-ray fluorescence analysis, and then the phosphate mineral may be identified by SEM / EDS and vibrational spectroscopy. Since X-ray fluorescence analysis allows for elemental analysis of a relatively large area, the cross-section of the reference particle may be elementally analyzed (screened) by X-ray fluorescence analysis in advance of observation with EDS, and then the regions in which the constituent elements of the phosphate mineral are detected may be analyzed by EDS and vibrational spectroscopy as described above. This significantly reduces the time and effort required to identify the phosphate mineral contained in the reference particle. Examples of such X-ray fluorescence analysis include micro-X-ray fluorescence analysis (μ-XRF). [Examples]

[0037] The present invention will be described more specifically below based on examples, but the present invention is not limited to these examples.

[0038] (Example 1) In this Example 1, the mass fraction of phosphate minerals present in the iron ore was measured by the following steps i) to v). i) A step to identify the phosphate minerals contained in the reference particle by selecting a reference particle from a group of iron ore particles to be analyzed, performing elemental analysis of the cross-section of the reference particle using μ-XRF, and then analyzing the region in which elements constituting phosphate minerals are detected using SEM / EDS and vibrational spectroscopy. ii) A step of obtaining an X-ray CT image of a phosphate mineral specimen that is the same species as the identified phosphate mineral, iii)ii) A step of creating a contrast histogram relating brightness intensity and brightness frequency from the 3D CT image of the specimen obtained by X-ray CT, and identifying the brightness intensity corresponding to the identified phosphate mineral, iv) A step of selecting analytical particles from a group of iron ore particles and obtaining an X-ray CT image of those analytical particles, and A step in which, based on the three-dimensional CT images of the analyzed particles obtained by X-ray CT in v) and iv), regions with brightness intensity corresponding to the identified phosphate mineral are measured, and the mass fraction of the identified phosphate mineral in the analyzed particles is determined.

[0039] In step i), approximately 60 iron ore particles of about 1-3 mm in size were selected from the iron ore particles of brand X1 to be used as reference particles. These reference particles were embedded in resin to form a cross-section, which was then polished to prepare a sample having a composite particle cross-section containing the cross-sections of multiple reference particles. Of this composite particle cross-section, the total area of ​​the reference particle cross-sections was approximately 500 mm². 2 It was to that extent.

[0040] μ-XRF analysis was performed on the above sample. The μ-XRF analysis conditions were: tube voltage 30kV, spot diameter 100μm, measurement time 500s / frame, number of integrations 50, and number of pixels 256. This suggested the existence of a region where Ca and P coexist, so EDS analysis was performed on that region. For this analysis, the acceleration voltage was 15kV or 5kV, and the low vacuum mode was 30Pa. The results are shown in Figure 1 above, and a Ca / P coexistence region was confirmed.

[0041] Next, the Ca / P coexistence region was analyzed by Raman spectroscopy. The analysis conditions were: excitation laser wavelength 488 nm or 532 nm, laser power 0.01 mW, grading 600 gr / mm, objective lens ×20, and exposure time 60 s. The results are shown in Figure 2 above. As mentioned above, the upper spectrum is the measurement of the standard reagent for hydroxyapatite, and the lower spectrum is the measurement of the Ca / P coexistence region of the reference particle. Since these spectra match, the phosphate mineral contained in this reference particle was identified as hydroxyapatite.

[0042] Next, in step ii), an X-ray CT image was obtained of a phosphate mineral specimen of the same species as the identified phosphate mineral in step i). The phosphate mineral specimen used was hydroxyapatite from Brazil. In acquiring the X-ray CT image, the specimen was irradiated with incident X-rays at a voltage of 140kV and an output of 10W, and multiple CT images were taken in the depth direction of the specimen. 1600 transmission images were reconstructed to obtain a 3D CT image with a pixel size of 10μm.

[0043] Next, in step iii), a contrast histogram relating to brightness intensity and brightness frequency was created using image analysis software based on the 3D CT image of the specimen acquired by X-ray CT in step ii). The results are shown in Figure 3 above. The peak that appeared in the region of brightness intensity (horizontal axis) of 30,000 to 40,000 corresponds to hydroxyapatite, and the region of brightness intensity = 32,000 to 36,000, between the point where the second derivative is negative on the brightness side of this peak (brightness intensity = 32,000) and the point where the second derivative is positive on the brightness side of this peak (brightness intensity = 36,000), corresponds to hydroxyapatite.

[0044] Next, in step iv), one particle was selected from the group of iron ore particles to be analyzed, and an X-ray CT image was obtained. The conditions for obtaining the X-ray CT image were the same as in step ii), with a particle of similar size and shape to the phosphate mineral sample particle being selected as the analysis particle. Multiple CT images were taken in the depth direction of the analysis particle, and 1600 transmission images were reconstructed to obtain a 3D CT image with a pixel size of 10 μm.

[0045] Next, in step v), based on the 3D CT image of the analytical particles obtained by X-ray CT in step iv), a region with a brightness intensity corresponding to hydroxyapatite, the identified phosphate mineral, was identified. Although the diagram is omitted, in this example, a contrast histogram was also created from the 3D CT image obtained by X-ray CT in step iv), similar to the case of the sample in step iii), and it was confirmed that the peak corresponding to hydroxyapatite appeared with the same shape.

[0046] Therefore, using image analysis software attached to the X-ray CT scanner, the 3D CT images of the analyzed particles were identified as hydroxyapatite in the region corresponding to a brightness intensity of 32,000 to 36,000, while the rest were identified as other mineral phases containing iron oxide. As explained earlier, Figure 4 shows one of the CT images of the analyzed particles. As in this example, by multiplying the area of ​​hydroxyapatite in one CT image by the pixel size and summing this up over the number of images taken in the depth direction, the volume of hydroxyapatite contained in one analyzed particle can be determined. Multiplying this volume by the density of hydroxyapatite gives the mass of hydroxyapatite contained in one analyzed particle. In addition, by determining the mass of one analyzed particle from which an X-ray CT image was obtained and dividing the mass of hydroxyapatite by the mass of one analyzed particle, the mass fraction of hydroxyapatite in the analyzed particle can be determined.

[0047] Figure 5 shows the mass fraction of hydroxyapatite in the analyzed particles obtained as described above. Other than hydroxyapatite, the particles are considered to be iron oxide and other mineral phases (gangue). Furthermore, to evaluate the validity of these results, Figure 5 also shows the results of XRD measurement of the analyzed particles from which X-ray CT images were actually obtained, after they were powdered, and the mass fraction of hydroxyapatite was determined. This XRD measurement was performed using a diffractometer, CoKα radiation, diffraction angles of 10-140°, Δ2θ of 0.04, and a scan speed of 1° / min. Rietveld analysis was used for the identification of hydroxyapatite and the calculation of its mass fraction. As can be seen from these results, the mass fractions of hydroxyapatite obtained by both methods were nearly similar.

[0048] (Example 2) As in Example 1, the volume fraction of phosphate minerals present in the iron ore was measured using steps i) to v) above.

[0049] First, in step i), approximately 60 iron ore particles of about 1-3 mm in size were selected from the iron ore particles of brand X2 to be used as reference particles. These reference particles were embedded in resin to form a cross-section, which was then polished to prepare a sample having a aggregate particle cross-section containing the cross-sections of multiple reference particles. Of this aggregate particle cross-section, the total area of ​​the reference particle cross-sections was approximately 500 mm². 2 It was to that extent.

[0050] μ-XRF analysis was performed on the above sample. The μ-XRF analysis conditions were: tube voltage 30kV, spot diameter 100μm, measurement time 500s / frame, number of integrations 50, and number of pixels 256. Figure 6 shows the elemental analysis results of the reference particle by μ-XRF. In Figure 6, a Y / P coexistence region where Y and P coexist was confirmed, suggesting the presence of a phosphate mineral containing Y within the reference particle. Furthermore, Figure 7 shows the results of elemental analysis of the vicinity of the phosphate mineral observed by μ-XRF using SEM / EDS, and Figure 8 shows the results of analysis by micro-Raman. According to Figures 7 and 8, the phosphate mineral within the reference particle (bright-field portion in Figure 7) was found to be xenotime (YPO4), and the mineral phase constituting the reference particle was hematite (α-Fe2O3).

[0051] Here, the SEM / EDS analysis was performed under the conditions of an acceleration voltage of 15kV and a low vacuum mode of 30Pa. Figure 7 shows the proportion of each component constituting the reference particle based on the analysis results at each point shown in the SEM image.

[0052] Meanwhile, the analysis conditions for micro-Raman were: excitation laser wavelength 532 nm, laser power 0.01 mW, grading 600 gr / mm, objective lens ×20, and exposure time 60 s. Figure 8 shows a two-dimensional Raman image (upper left) and an optical microscope image (lower left). The upper right shows the Raman spectrum of the region in the two-dimensional Raman image that is presumed to be the Y / P coexistence region (actually shown in red). Of this Raman spectrum, the upper part is the measurement of the Y / P coexistence region of the reference particle, and the lower part is the measurement of a mineral specimen of xenotime (YPO4). Since these show good agreement, the phosphate mineral contained in this reference particle was identified as xenotime. The lower right shows the Raman spectrum of the region in the two-dimensional Raman image that is presumed to be hematite (α-Fe2O3) (actually shown in green). The upper spectrum shows the measurement of a reference particle, while the lower spectrum shows the measurement of a standard reagent for hematite. Since these spectra match, the mineral phase constituting the reference particle was identified as hematite.

[0053] Next, in step ii), X-ray CT images were obtained of phosphate mineral specimens of the same species as the identified phosphate mineral in step i). The phosphate mineral specimens used were xenotime mineral specimens. In acquiring the X-ray CT images, incident X-rays at a voltage of 140kV and output of 10W were irradiated onto the specimen, and while rotating the specimen in increments of 0.225 degrees, X-ray CT images were taken at each rotation angle. 1600 transmission images were reconstructed to obtain a 3D CT image with a pixel size of 10μm.

[0054] Next, in step iii), a contrast histogram relating to brightness intensity and brightness frequency was created using image analysis software based on the 3D CT images of the mineral specimens obtained by X-ray CT in step ii). Next, in step iv), analytical particles were selected from the group of iron ore particles to be analyzed, and X-ray CT images were acquired. The acquisition conditions for the X-ray CT images were the same as in step ii), and 1600 transmission images were reconstructed while taking multiple CT images in the depth direction of the analytical particles to obtain a 3D CT image with a pixel size of 10 μm. However, since the analytical particles were about 0.5 to 1 mm in size, multiple particles were embedded in resin, and an X-ray CT image of one of the analytical particles was acquired. In contrast, since the xenotime mineral specimen (YPO4 mineral specimen) was a specimen particle about 5 mm in size, an X-ray CT image was acquired of a single specimen particle in its original state without resin embedding. Based on the obtained 3D CT images, a contrast histogram relating the intensity and frequency of brightness was created using image analysis software. These results are shown in Figure 9.

[0055] Figure 9 shows the contrast histogram of the xenotime mineral specimen (YPO4 mineral specimen) obtained in step iii) and the contrast histogram of the analyte particles obtained in step iv) together. In Figure 9, the dotted line is the contrast histogram of the YPO4 mineral specimen, and the dashed line is the contrast histogram of the analyte particles. The solid line is the contrast histogram after correction (corrected contrast histogram) of the analyte particles. In Figure 9, the horizontal axis represents the intensity of brightness, and the vertical axis represents the frequency of brightness.

[0056] In the spectrum of the YPO4 mineral sample shown in Figure 9, peaks observed around 10,000 luminance represent the outer space, peaks observed around 20,000 luminance originate from substances other than xenotime (YPO4) contained in the YPO4 mineral sample, and the broad peak from 40,000 to 70,000 luminance represents xenotime (YPO4). Considering that the measurement conditions for the analyzed particles and the YPO4 mineral sample are different, the spectra were corrected by parallel shifting so that the luminance at the boundary between the sample and space in each spectrum is equal.

[0057] More specifically, as shown in Figure 9, the boundary brightness of the YPO4 mineral specimen (including areas not part of the analysis sample, such as pores) is 14500, while the boundary brightness of the analysis particles is 22000, resulting in a brightness difference of 7500. Therefore, the overall brightness of the analysis particles was corrected by subtracting 7500. Here, the unclear peak in the non-sample area in the histogram of the analysis particles is due to the measurement conditions. In this Example 2, although the measurement conditions were the same as described above, correction was necessary because the YPO4 mineral specimen and the analysis particles had different sample shapes.

[0058] Furthermore, regarding the contrast histogram of the xenotime mineral specimen (YPO4 mineral specimen) obtained in step iii), Figure 10 shows a comparison between the contrast histogram of the YPO4 mineral specimen and the contrast histogram of the analyzed particles. Here, the vertical axis (luminance intensity) is set from 0 to 30000. From this, it can be seen that in the spectrum of the YPO4 mineral specimen, there is a change point around 35000 on the horizontal axis (luminance frequency). In addition, when the X-ray CT image and spectrum were compared using analysis software, the peak in the spectrum from 35000 to 60000 coincided with the YPO4 shown in the X-ray CT image. Therefore, in this Example 2, the threshold for YPO4 in the YPO4 mineral specimen was set to 35000 to 60000, and the region of luminance intensity = 35000 to 60000 was considered to correspond to xenotime.

[0059] Next, in step v), based on the contrast histogram of the analytical particles obtained in step iv), the region corresponding to a brightness intensity of 35,000 to 60,000 was identified as xenotime using image analysis software attached to the X-ray CT, and the rest were identified as other mineral phases containing iron oxide, such as hematite. The volume of xenotime contained in one analytical particle was then determined in the same manner as in Example 1. Based on the volume of one analytical particle from which an X-ray CT image was obtained, the volume fraction of xenotime in the analytical particle was determined, and the volume fraction of xenotime relative to the total analytical particle was found to be 6.6%. Figure 11 shows the CT image of the analytical particle obtained in step iv). In this CT image, the region corresponding to xenotime is mapped, and in reality, the region of xenotime is shown in light blue, while other mineral phases containing iron oxide are shown in blue.

[0060] The analytical particles in Example 2 were powdered and subjected to XRD measurement, but xenotime could not be detected due to its low content. The analytical particles in Example 1 contained phosphate minerals of a size that could be sufficiently detected by XRD measurement, but as in Example 2, some iron ore varieties contain fine phosphate minerals that cannot be detected by XRD measurement. Even in such cases, the method of the present invention makes it possible to non-destructively identify iron ore containing phosphate minerals of a size that cannot be analyzed by conventional techniques.

Claims

1. A method for quantitative analysis of phosphate minerals by morphology, which measures the mass fraction or volume fraction of phosphate minerals present in iron ore, A step of selecting a reference particle from a group of iron ore particles to be analyzed, and analyzing the cross-section of the reference particle using SEM / EDS and vibrational spectroscopy to identify the phosphate mineral contained in the reference particle, A step of obtaining an X-ray CT image of a phosphate mineral specimen that is the same type as the identified phosphate mineral, A step of creating a contrast histogram relating brightness intensity and brightness frequency from the X-ray CT image obtained from the aforementioned specimen, and identifying the brightness intensity corresponding to the identified phosphate mineral, The process involves selecting analytical particles from the group of iron ore particles and obtaining an X-ray CT image of the analytical particles. A step of determining the mass fraction or volume fraction of the identified phosphate mineral in the analyzed particle by measuring the volume of the region having a brightness intensity corresponding to the identified phosphate mineral in the analyzed particle based on the X-ray CT image obtained from the analyzed particle, A method for quantitative analysis of phosphate minerals present in iron ore, characterized by comprising the following features.

2. A method for quantitative analysis of phosphate minerals present in iron ore according to claim 1, comprising the step of analyzing a cross-section of the specimen by SEM / EDS and vibrational spectroscopy prior to the step of determining the intensity of brightness corresponding to the identified phosphate mineral, and determining the brightness of the phosphate mineral to be analyzed from the contrast of the X-ray CT image of the specimen.

3. A method for quantitative analysis of phosphate minerals by morphology according to claim 1 or 2, wherein, in the step of determining the mass fraction or volume fraction of the identified phosphate mineral in the analytical particles, the contrast histogram of the X-ray CT image obtained from the sample or the contrast histogram of the X-ray CT image obtained from the analytical particles is corrected, and then the region having a brightness intensity corresponding to the identified phosphate mineral in the X-ray CT image of the analytical particles is measured.

4. A method for quantitative analysis of phosphate minerals by morphology according to claim 1 or 2, wherein, in the step of identifying phosphate minerals contained in the reference particles, the cross-section of the reference particles is subjected to elemental analysis by fluorescent X-ray analysis, and then the phosphate minerals are identified by SEM / EDS and vibrational spectroscopy.

5. A method for quantitative analysis of phosphate minerals by morphology according to claim 1 or 2, wherein, in the step of identifying phosphate minerals contained in the reference particles, a plurality of reference particles are selected and the analysis is performed based on a cross-sectional view of aggregate particles having the cross-sections of the plurality of reference particles.

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