JP2022151791A - Method of quantitative analysis of phosphate mineral by morphology - Google Patents

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

The present invention relates to a method for quantitatively analyzing phosphate minerals present in iron ore by morphology.

Iron ore, which is used as a raw material in the steel industry, is composed of multiple iron oxides in nature. ) and other impurities.

Impurities in iron ore degrade the properties of steel materials, so iron ore with a high content of impurities has been avoided until now. there is

Of these, phosphorus is known to exist as phosphate minerals and is removed in the steelmaking process using the converter method. There is a need to understand mineral removal efficiency. For that purpose, it is necessary to grasp the mass fraction of phosphate minerals. Accurate assessment of mineral removal efficiency is difficult. In addition, the phosphate minerals are not evenly distributed, and the phosphate minerals are unevenly distributed in the iron ore, making the measurement of the mass fraction more difficult.

For example, to analyze mineral composition in mining applications such as oil and gas exploration, X-ray fluorescence emitted from irradiating a mineral sample with X-rays and Raman emitted from similarly irradiating a mineral sample with light. There is a method of analyzing compounds in mineral samples using radiation (see Patent Document 1). In addition, in order to identify unidentified minerals in the ore when obtaining high-purity metals (base metals) from ores containing compounds (minerals) such as metal oxides such as copper and nickel and sulfides, A known method is to prepare an ore sample in which the ore is embedded in resin, form a polished surface, measure the EDS spectrum by energy dispersive X-ray spectroscopy (EDS), and measure the Raman spectrum by a micro laser Raman spectrometer. (see Patent Document 2).

Thus, there are known methods for evaluating micromineral phases by combining local elemental analysis methods using X-rays and vibrational spectroscopy such as Raman spectroscopy. It is not possible to accurately measure the mass fraction of phosphate minerals, which are three-dimensionally distributed at , and which are trace amounts.

On the other hand, an automatic mineral analysis device equipped with a scanning electron microscope (SEM) having an energy dispersive X-ray spectrometer (EDS) and a computer that controls them and stores the EDS spectra of various minerals as data. (Mineral Liberation Analyzer: MLA) is used to analyze the mass ratio and concentration of minerals in a raw ore in which multiple types of minerals are mixed (see Patent Document 3 for the device configuration, and the analysis method is described in Patent Document 4).

In this method, first, a sample in which ore powder is solidified with resin is ground, and a backscattered electron image (BSE image) of the ground cross section is measured to store the position of each mineral particle. Next, the EDS spectrum is measured for each polished surface of the discriminated mineral particle, and the obtained result is compared with the EDS spectrum of the mineral list preliminarily built into the MLA, thereby identifying the mineral species of the mineral particle. identify. If the mineral species is identified, the type of metal element contained in the mineral is specified, and the density can be grasped according to the type of metal element, and the size relationship between the densities of each mineral in the sample is obtained. I'm trying

Next, in the above method, an X-ray CT image of the ore powder is obtained using X-ray CT. In this X-ray CT image, since various substances constituting the sample have luminance corresponding to their densities, the luminance magnitude relation is associated with the previously obtained density magnitude relation by MLA. For example, in the MLA measurement, the mineral α having the highest density metal in the sample, the mineral β having the same high density metal, and the mineral γ having the same medium density metal are ranked. Also, in the X-ray CT image, the ranking is made such that particle A has the highest brightness, particle B has the highest brightness but is not as bright as particle A, and particle C has the medium brightness. Linking is performed such that β=particle B and mineral γ=particle C. By doing so, it is possible to three-dimensionally evaluate the mass ratio and concentration of each mineral in the ore.

However, although the method described above can relatively evaluate a plurality of types of minerals present in an ore, it is not possible to directly determine the mass fraction of a specific mineral. In addition, this method is based on the assumption that the number of mineral phases observed by MLA and the number of mineral phases observed by X-ray CT are the same, but the number of mineral phases observed by a two-dimensional observation method like MLA is based on the assumption that Accurate evaluation cannot be performed if the number of mineral phases observed by three-dimensional X-ray CT does not match the number of mineral phases observed.

Japanese Patent Publication No. 2015-519571 JP 2017-090183 A JP 2015-40724 A (paragraph 0012) Japanese Patent Application Laid-Open No. 2020-34372 (paragraphs 0013 to 0020)

In order to effectively utilize low-grade iron ore as a countermeasure against resource deterioration, it is important to correctly evaluate the amount of phosphorus, an impurity, in iron ore. It is difficult to accurately measure the mass fraction of phosphate minerals in iron ore because they are ubiquitous in rocks and in very small amounts. cannot be achieved.

Accordingly, the present inventors have made intensive studies on methods for measuring the mass fraction of phosphate minerals present in iron ore, and as a result, have found the following method. First, reference particles are selected from the iron ore particle group to be analyzed, and the phosphate minerals contained in the reference particles are identified by using SEM/EDS and vibrational spectroscopy. Next, an X-ray CT image is obtained for a specimen of the same type of phosphate mineral as the identified phosphate mineral, and the intensity of brightness corresponding to the identified phosphate mineral is grasped from the contrast histogram. Then, by acquiring an X-ray CT image of the analysis particles to be actually analyzed and measuring the region having the intensity of brightness corresponding to the previously obtained phosphate mineral, the phosphoric acid present in the iron ore The present invention was completed because it became possible to accurately determine the mass fraction of salt minerals. According to the above method, the volume fraction of phosphate minerals present in iron ore can also be obtained in the same manner. It is called a quantitative analysis method by morphology.

Accordingly, an object of the present invention is to provide a method for quantitatively analyzing phosphate minerals according to morphology, which can accurately measure the mass fraction or volume fraction of phosphate minerals present in iron ore. .

That is, the gist of the present invention is as follows.
(1) A method for quantitatively analyzing phosphate minerals according to morphology for measuring the mass fraction or volume fraction of phosphate minerals present in iron ore,
A step of selecting reference particles from 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;
obtaining an X-ray CT image of a specimen of a phosphate mineral that is the same as the identified identified phosphate mineral;
creating a contrast histogram of brightness intensity and brightness frequency from an X-ray CT image obtained from the specimen to identify the brightness intensity corresponding to the identified phosphate mineral;
a step of selecting analysis particles from the iron ore particle group and obtaining an X-ray CT image of the analysis particles;
Based on the X-ray CT image obtained with the analysis particles, the volume of the region having the brightness intensity corresponding to the identified phosphate mineral in the analysis particles is measured, and the identification in the analysis particles is performed. determining the mass fraction or volume fraction of the phosphate mineral;
A quantitative analysis method for each morphology of phosphate minerals present in iron ore, characterized by comprising:
(2) Prior to the step of identifying the brightness intensity corresponding to the identified phosphate mineral, the cross-section of the specimen is analyzed by SEM/EDS and vibrational spectroscopy, and the contrast of the X-ray CT image of the specimen is The method for quantitatively analyzing phosphate minerals present in iron ore according to form according to (1), comprising the step of specifying the brightness of the phosphate minerals to be analyzed from.
(3) In the step of determining the mass fraction or volume fraction of the identified phosphate mineral in the analysis particles, the contrast histogram of the X-ray CT image obtained with the specimen, or the X-ray obtained with the analysis particles (1) or (2), after correcting one of the contrast histograms of the CT image, measuring the region having the brightness intensity corresponding to the identified phosphate mineral in the X-ray CT image of the analysis particle; Quantitative analysis method according to morphology of phosphate minerals described in .
(4) In the step of identifying the 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. A quantitative analysis method according to morphology of phosphate minerals according to (1) or (2) for identification.
(5) in the step of identifying phosphate minerals contained in the reference particles, selecting a plurality of reference particles and analyzing based on aggregated particle cross sections having cross sections of the plurality of reference particles; (1) or (2) ) quantitative analysis method for each morphology of phosphate minerals described in ).

According to the present invention, it is possible to accurately measure the mass fraction or volume fraction of phosphate minerals that are contained in iron ore in a very small amount and are unevenly distributed in iron ore. become able to. In particular, there is no known quantitative analysis method for morphology of phosphate minerals that measures the mass fraction and volume fraction of phosphate minerals present in iron ore. This is an extremely useful invention for achieving effective utilization.

FIG. 1 is a photograph and an EDS map showing the appearance of reference particles in Example 1 (the lower frame indicates the position of each upper figure). FIG. 2 shows Raman spectra in Example 1, the upper row is for the hydroxyapatite standard reagent, and the lower row is for the Ca/P coexistence region in the reference particles. 3 is a contrast histogram created from a three-dimensional CT image of a hydroxyapatite sample obtained by X-ray CT in Example 1. FIG. 4 is an X-ray CT image of analysis particles in Example 1. FIG. FIG. 5 compares the mass fraction of hydroxyapatite determined by the method of the present invention in Example 1 and the mass fraction of hydroxyapatite determined by XRD measurement. FIG. 6 shows the results of elemental analysis by μ-XRF of the reference particles in Example 2, and the lower part is an enlarged part of the upper part. FIG. 7 shows the result of elemental analysis by SEM/EDS of the vicinity of the phosphate mineral of the reference particles in Example 2. FIG. FIG. 8 shows the results of micro-Raman analysis of the reference particles in Example 2. FIG. FIG. 9 is the contrast histogram of the _YPO4 mineral specimen and the contrast histogram of the analyzed particles in Example 2; FIG. 10 is an enlarged partial view comparing the contrast histogram of the _YPO4 mineral specimen with the contrast histogram of the analyzed particles. 11 is an X-ray CT image of analysis particles in Example 2. FIG.

The present invention will be described in detail below.
The present invention is a method for quantitatively analyzing phosphate minerals according to morphology for measuring the mass fraction or volume fraction of phosphate minerals present in iron ore, comprising the following steps i) to v). It is a thing.
i) selecting reference particles from the group of iron ore particles to be analyzed and analyzing the cross section of the reference particles by SEM/EDS and vibrational spectroscopy to identify the phosphate mineral contained in the reference particles;
ii) obtaining an X-ray CT image of a specimen of a phosphate mineral that is congruent with the identified identified phosphate mineral;
iii) creating a contrast histogram of brightness intensity and brightness frequency from the X-ray CT image obtained from the specimen to identify the brightness intensity corresponding to the identified phosphate mineral;
iv) selecting analysis particles from the iron ore particle group and acquiring an X-ray CT image of the analysis particles;
v) Based on the X-ray CT image obtained with the analysis particles, a region having a luminance intensity corresponding to the identified phosphate mineral is measured to determine the mass of the identified phosphate mineral in the analysis particles. Determining fraction or volume fraction.

In the present invention, first, in step i) above, reference particles are selected from the iron ore particle group to be analyzed, and the distribution of elements is analyzed with a scanning electron microscope (SEM/EDS) equipped with an EDS. Target elements are, for example, Fe, Si, P, Ca, and Al. Other elements such as Na, Mg, Ti, Mn, and rare earths are also selected according to the mineral phase contained in the phosphate minerals and iron ores to be analyzed.
Here, FIG. 1 shows an example of observation results. In the figure, the upper left (1) is a photograph showing a polished surface obtained by embedding the reference particles in resin and polishing the cross section, and the upper center (2) is a photograph showing one particle on the polished surface [indicated by an arrow in (1) attached] is an SEM image (magnification: 30 times). In addition, the upper right (3), the lower left (4), the lower center (5), and the lower right (6) show the EDS phase analysis results (EDS map) of the particle cross section of (2), and (3) is Ca element, (4) is P element, (5) is Fe element, and (6) is Si element. 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) are confirmed. The existence of Si in (6) has not been confirmed.

After analyzing the contained elements by SEM/EDS as described above, in step i) above, the region having the elements constituting the phosphate mineral is analyzed by vibrational spectroscopy. This vibrational spectroscopy may be any method that can analyze the molecular structure by irradiating an object to be analyzed with an electromagnetic wave and obtaining a spectrum by spectroscopically transmitting or reflecting the light. Raman spectroscopy, Fourier transform infrared spectroscopy, and the like can be mentioned, but from the viewpoint of analyzing phosphate minerals in iron ore, preferably Raman spectroscopy or Fourier transform infrared spectroscopy. , most preferably Raman spectroscopy.

In the previous example, FIG. 2 shows the results of Raman spectrum measurement for the Ca/P coexistence region (white circles in the figure) where the coexistence of Ca and P was confirmed in the particle cross section. In FIG. 2, the upper spectrum is obtained by measuring a standard reagent of hydroxyapatite [Ca ₅ (PO ₄ ) ₃ (OH)]. The spectrum in the lower row is obtained by measuring the Ca/P coexistence region of the reference particles, and since both coincide, the phosphate mineral contained in the reference particles is identified as hydroxyapatite.

By the way, the number of published standard spectra for Raman spectroscopy is overwhelmingly smaller than that for infrared absorption spectra, and in particular for phosphate minerals, standard spectra for identifying them have not been prepared. Therefore, in the present invention, the phosphate mineral is estimated from the contained elements based on the result of elemental analysis by SEM/EDS. In this example, assuming that the mineral composed of Ca and P is hydroxyapatite (hydroxyapatite is representative of phosphate minerals composed of Ca and P in iron ore), a commercially available standard reagent for hydroxyapatite After measuring the Raman spectroscopy at , the reference particles are also measured to identify the phosphate minerals contained in the iron ore particles. Phosphate minerals present in iron ore include hydroxyapatite as described above, as well as Xenotime (YPO ₄ ) and Vivianite (Fe ₃ (PO ₄ ) 2.8H ₂ O), Wavellite (Al ₃ (PO ₄ ) ₂ (OH, F) _{3.5H 2} O), etc. _are representatively known, but are the subject of the present invention. Phosphate minerals to be used are not limited to these. In particular, in the contrast histogram obtained by X-ray CT, as long as the brightness regions of the target phosphate minerals do not overlap, even if the number of mineral phases present in the reference particles and the analysis particles do not match, the phosphate Mineral identification is possible.

Here, the reference particles used as samples in step i) are arbitrarily selected from the iron ore particle group to be analyzed. In general, the iron ore used in the steelmaking process is mainly powdered ore (iron ore particles) of 5 mm or less, which is mixed with a small amount of lime powder and baked to a certain size. Solidify to make sintered ore. Therefore, most of the iron ore particles to be analyzed are about 5 mm or less. It is theoretically possible to observe the cross section of one of these iron ore particles with SEM/EDS, but since the amount of phosphate minerals contained in iron ore is small, phosphate minerals are present. It is not easy to find a cross section that does.

Therefore, as shown in FIG. 1(1) above, a plurality of reference particles are selected, preferably at least 50 reference particles of about 1 to 3 mm are selected, embedded in resin, and their cross sections are polished. Preferably, step i) is performed based on an aggregated grain cross-section having a cross-section of a plurality of reference grains so as to form a sample. More specifically, it is preferable that the total area of the cross sections of the reference particles in the cross section of the aggregated particles is 400 mm ² or more. This makes it possible to more reliably observe the cross section of the reference grain in which the phosphate mineral is present. Considering that the probability of catching phosphate minerals in such two-dimensional observation increases, it is of course more desirable that the total area of the cross section of the reference particles is larger. Considering these factors, the substantial upper limit of the total area is about 1200 mm ² . In step i), as in general measurement, a backscattered electron image or the like of a cross section of a resin-embedded reference particle is obtained by SEM in advance, and then the position of the reference particle is specified and the element is measured by EDS. analysis can be performed.

Next, in step ii), an X-ray CT image of a specimen of a phosphate mineral that is the same as the identified phosphate mineral identified in step i) is obtained. X-ray CT utilizes differences in the easiness of transmission and easiness of absorption of X-rays when they pass through the object to be analyzed, and examines the material and structure of the object to be analyzed. This step ii) is carried out to understand how much the identified phosphate mineral identified in step i) transmits (absorbs) X-rays, and step iv) described later. 3, an X-ray CT image of the particles to be analyzed is actually obtained so that the amount of the identified phosphate mineral contained in the particles to be analyzed can be correctly evaluated. However, X-ray CT is susceptible to material density, which changes the spatial resolution, field of view, and contrast of the image. Therefore, in the present invention, the acquisition conditions for the X-ray CT images in the ii) step and the iv) step are matched, and among others, the size of the evaluation material (here, the analysis particle) and the standard material (here, the mineral specimen) , and the measurement conditions (especially the incident X-ray voltage and output, and the spatial resolution of the image) should be as similar as possible for the evaluation material (here, analysis particles) and the reference material (here, mineral specimen). Better to

Here, the phosphate mineral sample used in step ii) can be one collected from natural minerals. Among them, it is preferable that the material is substantially single-phase and massive, and is commercially available as a mineral specimen. Although there is no particular limitation, for example, they can be obtained from general stores specializing in the sale of mineral specimens and meteorite specimens. In the previous example, it is a sample of hydroxyapatite, and as such a sample, preferably, the name is described as hydroxyapatite or (hydroxy)apatite, and is equivalent to the analysis particles that are the evaluation materials. size and shape.

Next, in step iii), based on the X-ray CT image of the specimen obtained by the X-ray CT in step ii), a contrast histogram regarding brightness intensity and brightness frequency is created to identify the phosphate mineral. Identify the luminance intensity corresponding to . As described above, there are differences in the transmission and absorption of X-rays depending on the material that constitutes the object to be analyzed, and in X-ray CT, a three-dimensional CT image (grayscale image) is formed based on the brightness corresponding to the difference. be. Therefore, using the image analysis software etc. attached to the X-ray CT, read out the luminance input to the voxels that make up the 3D CT image. Create a contrast histogram on the axis.

As ii) and iii) steps, FIG. Contrast histograms are shown, constructed with intensity on the horizontal axis and luminance frequency on the vertical axis. In FIG. 3, the peak at approximately the center is the X-ray transmitted through the mineral phase of hydroxyapatite. The peak to the left of it is just the x-ray passing through the atmosphere. When such a contrast histogram is created, the mineral phase peaks are always brighter than the atmospheric peaks.

As described above, in the contrast histogram of FIG. 3, the luminance intensity (horizontal axis) region of 30000 to 40000 is identified as corresponding to hydroxyapatite. Since this area is used to measure the identified phosphate minerals in the actual analysis particles in the later step v), the determination is based on the three-dimensional CT image of the analysis particles measured in the later-described step iv). can be determined to match the peak corresponding to the identified phosphate mineral (hydroxyapatite in this case) when a contrast histogram similar to that described above is created in step v). Alternatively, a region sandwiched by two inflection points on both sides of the peak position corresponding to hydroxyapatite may be determined as a region of intensity of luminance corresponding to hydroxyapatite. Specifically, in the example of FIG. 3, the point where the second derivative becomes negative on the side where the brightness is higher than the peak of hydroxyapatite (that is, the intensity of brightness = 32000), and the point on the side where the brightness is lower than the peak of hydroxyapatite. The region (32000 to 36000) sandwiched by the point where the second differentiation becomes positive (ie, intensity of luminance = 36000) may be determined as the hydroxyapatite signal. Further, the half-value width of the peak corresponding to the identified phosphate mineral may be selected and the corresponding one taken as the region of brightness intensity.

Here, in identifying the brightness intensity corresponding to the identified phosphate mineral in step iii), after analyzing the cross section of the mineral specimen by SEM / EDS and vibrational spectroscopy, the X-ray CT image of the mineral specimen The brightness of the phosphate mineral to be analyzed may be specified from the contrast. It is possible to more reliably determine which regions correspond to identified phosphate minerals, such as when a mineral specimen contains multiple mineral phases.

Next, in step iv), particles to be analyzed are selected from the iron ore particle group to be analyzed, and X-ray CT images are acquired. The particles to be analyzed here are those of the same brand as those of the reference particles selected in step i), which have the same collection location and collection time. In step i), it is necessary to form a cross-section for analysis by SEM/EDS or vibrational spectroscopy, but in step iv), an X-ray CT image of the iron ore particles to be analyzed is obtained in a non-destructive manner. be able to. Therefore, it is sufficient to acquire an X-ray CT image with one analysis particle, but a plurality of analysis particles are selected, each X-ray CT image is acquired, and the mass fraction of the identified phosphate mineral obtained in step v) described later. The rate may be obtained as an average value or the like. The acquisition of the X-ray CT image in step iv) may be performed under the same conditions as the acquisition of the X-ray CT image in step ii) above, except for the difference in the target sample.

Next, in step v), based on the three-dimensional CT image of the analysis particles obtained by the X-ray CT in step iv), a region having a luminance intensity corresponding to the identified phosphate mineral is measured. , to determine the mass fraction of identified phosphate minerals in the analyzed particles. The three-dimensional CT image of the particles to be analyzed should have the same resolution as the three-dimensional CT image obtained in the previous step iii). Then, in this step v), using image analysis software attached to the X-ray CT, from the three-dimensional CT image of the analyzed particles, the brightness intensity corresponding to the identified phosphate mineral obtained in the step iii) Determine the regions that have At that time, as in the case of step iii), a contrast histogram relating to brightness intensity and brightness frequency may be created from the three-dimensional CT image of the analysis particle, and the identified phosphor in the analysis particle may be obtained without creating a contrast histogram. A region corresponding to acid salt minerals may be obtained.

Here, FIG. 4 shows a CT image of analysis particles in the previous example. In this CT image, the region corresponding to hydroxyapatite is mapped, and in fact the hydroxyapatite region is shown in red, and other mineral phases containing iron oxide are shown in light blue (Fig. 4, top). is an actual CT image, and the lower part is an explanatory diagram showing the hydroxyapatite region). In FIG. 4, the luminance intensity region corresponding to hydroxyapatite obtained in step iii), specifically, the luminance of the region sandwiched between two inflection points on both sides of the hydroxyapatite peak. Those corresponding to the strength (32,000 to 36,000) are identified as hydroxyapatite, and others are identified as other mineral phases containing iron oxide.

In addition, in determining the mass fraction or volume fraction of the identified phosphate mineral in the analysis particles, the contrast histogram of the X-ray CT image obtained with the specimen, or the contrast histogram of the X-ray CT image obtained with the analysis particles After correcting either one of the above, the region having the brightness intensity corresponding to the identified phosphate mineral in the X-ray CT image of the analysis particle may be measured. As mentioned earlier, X-ray CT is sensitive to material density, which can change the spatial resolution, field of view, and contrast of the image. Therefore, when acquiring an X-ray CT image, if there is a difference in size, shape, etc. between the sample and the analysis particles, it is preferable to perform correction to match the baseline. For example, it is possible to correct the brightness by translating the spectrum so that the brightness at the boundary between the sample and the space in each spectrum becomes equal.

In this way, by measuring the volume of the identified phosphate mineral contained in one analyzed particle by X-ray CT of the analyzed particle, and multiplying the volume of the identified phosphate mineral by its density, one analyzed particle contains The mass of the identified phosphate mineral can be calculated. For example, by obtaining the mass of one analysis particle measured by X-ray CT and dividing the mass of the identified phosphate mineral by the mass of one analysis particle, the mass fraction of the identified phosphate mineral in the analysis particle can be asked for. In addition, as a method of obtaining the mass fraction of the identified phosphate minerals in the analyzed particles, if there is only one mineral phase other than phosphate minerals contained in the iron ore particles, The volume fraction of the mineral phase is determined by CT image processing, and these values are multiplied by the density of each mineral phase to determine the mass fraction of the identified phosphate mineral in the analyzed particles. . It is of course possible to determine the volume fraction of the identified phosphate mineral contained in one analysis particle from the volume of the identified phosphate mineral obtained above.

In the present invention, in step i) above, the cross section of the reference particle may be subjected to elemental analysis by fluorescent X-ray analysis, and then the phosphate mineral may be identified by SEM/EDS and vibrational spectroscopy. Since elemental analysis of a relatively large area is possible with fluorescent X-ray analysis, prior to observation with EDS, a section of a reference particle is previously elementally analyzed by fluorescent X-ray analysis (screened). ), the regions where the constituent elements of the phosphate mineral are detected are analyzed by EDS and vibrational spectroscopy as described above. As a result, the time and effort required to identify the phosphate minerals contained in the reference particles can be greatly reduced. Such fluorescent X-ray analysis includes, for example, microscopic fluorescent X-ray analysis (μ-XRF).

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

(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 reference particle is selected from the iron ore particle group to be analyzed, the cross section of the reference particle is subjected to elemental analysis by μ-XRF, and then the region where the element constituting the phosphate mineral is detected is subjected to SEM / analyzing with EDS and vibrational spectroscopy to identify the phosphate minerals contained in the reference particles;
ii) obtaining an X-ray CT image of a specimen of a phosphate mineral that is congruent with the identified identified phosphate mineral;
iii) a step of creating a contrast histogram regarding brightness intensity and brightness frequency from the three-dimensional CT image of the specimen obtained by X-ray CT in ii), and identifying the brightness intensity corresponding to the identified phosphate mineral;
iv) selecting analysis particles from the iron ore particle group and acquiring an X-ray CT image of the analysis particles;
v) Based on the three-dimensional CT image of the analysis particle obtained by the X-ray CT in iv), the area having the brightness intensity corresponding to the identified phosphate mineral is measured to identify the analysis particle. A step of determining the mass fraction of phosphate minerals.

In step i), about 60 iron ore particles having a size of about 1 to 3 mm were selected from the iron ore particles of brand X1 and used as reference particles. These reference particles were embedded in a resin to form a cross section, which was polished to prepare a sample having an aggregated particle cross section including cross sections of a plurality of reference particles. Among the cross sections of the aggregated particles, the total area of the cross sections of the reference particles was approximately 500 mm ² .

μ-XRF analysis was performed on the above samples. The μ-XRF analysis conditions are a tube voltage of 30 kV, a spot diameter of 100 μm, a measurement time of 500 s/frame, 50 integration times, and 256 pixels. Since this suggests the presence of a region where Ca and P coexist, EDS analysis was performed on that region. At that time, the acceleration voltage was 15 kV or 5 kV, and the conditions were a low vacuum mode of 30 Pa. The results are as shown in FIG. 1 above, and a Ca/P coexistence region where Ca and P coexist was confirmed.

Then, this Ca/P coexistence region was analyzed by Raman spectroscopy. The analytical conditions at that time were an excitation laser wavelength of 488 nm or 532 nm, a laser output of 0.01 mW, a grading of 600 gr/mm, an objective lens of ×20, and an exposure time of 60 s. The results are as shown in FIG. 2 above. As described above, the upper spectrum is obtained by measuring the hydroxyapatite standard reagent, and the lower spectrum is obtained by measuring the Ca/P coexistence region of the reference particles. Since these spectra match, the phosphate mineral contained in this reference particle was identified as hydroxyapatite.

Next, as step ii), an X-ray CT image of a specimen of a phosphate mineral of the same type as the identified phosphate mineral identified in step i) was obtained. The phosphate mineral specimen used is Brazilian hydroxyapatite. In acquiring the X-ray CT image, the specimen was irradiated with incident X-rays with a voltage of 140 kV and an output of 10 W, and multiple CT images were taken in the depth direction of the specimen to reconstruct 1600 transmission images. A three-dimensional CT image with a pixel size of 10 μm was obtained.

Next, in step iii), based on the three-dimensional CT image of the specimen obtained by the X-ray CT in step ii), image analysis software was used to create a contrast histogram relating to brightness intensity and brightness frequency. . The results are as shown in FIG. 3 above. The peak that appears in the region where the brightness intensity (horizontal axis) is 30,000 to 40,000 corresponds to hydroxyapatite. = 32000) and the point where the second differential on the side with lower brightness than the same peak becomes positive (intensity of brightness = 36000). It was assumed that

Next, in step iv), one particle to be analyzed was selected from the iron ore particle group to be analyzed, and an X-ray CT image was obtained. At that time, the acquisition conditions for acquiring the X-ray CT image are the same as in the ii) step, and the analysis particles are selected to have the same size and shape as the phosphate mineral sample particles, and the depth of the analysis particles is A three-dimensional CT image with a pixel size of 10 μm was obtained by reconstructing 1600 transmission images while taking multiple CT images in the same direction.

Next, in the step v), based on the three-dimensional CT image of the analysis particles obtained by the X-ray CT in the previous step iv), the brightness intensity corresponding to hydroxyapatite, which is the identified phosphate mineral, is determined. identified areas with Although the drawing is omitted, in this embodiment, a contrast histogram is also created from the three-dimensional CT image obtained by the X-ray CT in step iv) in the same manner as in the specimen in step iii), and hydroxyapatite It is confirmed that peaks corresponding to .

Therefore, for the three-dimensional CT image of the analysis particle, using the image analysis software attached to the X-ray CT, the area corresponding to the brightness intensity = 32000 to 36000 is hydroxyapatite, and the other area contains iron oxide. was identified as other mineral phases. As described above, FIG. 4 shows one of the CT images of analysis particles. As in this example, the area of hydroxyapatite in one CT image is multiplied by the pixel size, and the number of images taken in the depth direction is summed to obtain the volume of hydroxyapatite contained in one analysis particle. can be obtained, and by multiplying the volume by the density of hydroxyapatite, the mass of hydroxyapatite contained in one analytical particle can be calculated. In addition, the mass fraction of hydroxyapatite in the analysis particles can be obtained by obtaining the mass of one analysis particle for which an X-ray CT image has been obtained and dividing the mass of hydroxyapatite by the mass of one analysis particle. can.

FIG. 5 shows the mass fraction of hydroxyapatite in the analysis particles obtained as described above. Iron oxide and other mineral phases (gangue) except for hydroxyapatite. In addition, in order to evaluate the validity of this result, in FIG. 5, the analysis particles for which the X-ray CT image was actually acquired were powdered and XRD was measured, and the result of obtaining the mass fraction of hydroxyapatite is also shown. showing. This XRD measurement was performed using a diffractometer method, CoKα rays, a diffraction angle of 10 to 140°, Δ2θ of 0.04, and a scan speed of 1°/min. Rietveld analysis was used to identify hydroxyapatite and calculate the mass fraction. As can be seen from these results, the mass fractions of hydroxyapatite in both samples showed almost similar values.

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

First, in step i), about 60 iron ore particles having a size of about 1 to 3 mm were selected from the iron ore particles of brand X2 and used as reference particles. These reference particles were embedded in a resin to form a cross section, which was polished to prepare a sample having an aggregated particle cross section including cross sections of a plurality of reference particles. Among the cross sections of the aggregated particles, the total area of the cross sections of the reference particles was approximately 500 mm ² .

μ-XRF analysis was performed on the above samples. The μ-XRF analysis conditions are a tube voltage of 30 kV, a spot diameter of 100 μm, a measurement time of 500 s/frame, 50 integration times, and 256 pixels. FIG. 6 shows the results of elemental analysis of the reference particles by μ-XRF. In FIG. 6, a Y/P coexistence region where Y and P coexist was confirmed, and the existence of a phosphate mineral containing Y in the reference particles was presumed. In addition, FIG. 7 shows the results of elemental analysis by SEM/EDS in the vicinity of phosphate minerals observed by μ-XRF, and FIG. 8 shows the results of microscopic Raman analysis. It is shown. According to these FIGS. 7 and 8, the phosphate mineral in the reference particles (bright field portion in FIG. 7) is Xenotime (YPO ₄ ), and the mineral phase constituting the reference particles is Hematite ( α-Fe ₂ O ₃ ).

Here, the SEM/EDS analysis was performed under the conditions of an acceleration voltage of 15 kV and a low vacuum mode of 30 Pa. In FIG. It is shown.

On the other hand, the micro Raman analysis conditions were an excitation laser wavelength of 532 nm, a laser output of 0.01 mW, a grading of 600 gr/mm, an objective lens of ×20, and an exposure time of 60 s. FIG. 8 shows a two-dimensional Raman image (upper left) and an optical microscopic image (lower left), and the upper right shows a region assumed to be a Y/P coexistence region in the two-dimensional Raman image (actually are shown in red) Raman spectra are shown. Of this Raman spectrum, the upper one is for the Y/P coexistence region of the reference grain, and the lower one is for the Xenotime (YPO ₄ ) mineral sample. Since these were in good agreement, the phosphate mineral contained in this reference grain was identified as xenotime. In addition, the lower right shows the Raman spectrum of the portion assumed to be hematite (α-Fe ₂ O ₃ ) in the two-dimensional Raman image (the portion actually displayed in green). Among these, the upper part is the measurement of the reference particles, and the lower part is the measurement of the hematite standard reagent. Since these spectra are in agreement, the mineral phase constituting the reference grain was identified as hematite.

Next, as step ii), an X-ray CT image of a specimen of a phosphate mineral of the same type as the identified phosphate mineral identified in step i) was obtained. The phosphate mineral specimens used were xenotime mineral specimens. In acquiring the X-ray CT image, the sample was irradiated with incident X-rays with a voltage of 140 kV and an output of 10 W, and while rotating the sample by 0.225 degrees, an X-ray CT image was taken at each rotation angle. A three-dimensional CT image with a pixel size of 10 μm was obtained by reconstructing the transmitted images.

Next, in step iii), based on the three-dimensional CT image of the mineral specimen obtained by the X-ray CT in step ii), image analysis software is used to create a contrast histogram regarding the intensity and frequency of brightness. did.
Next, in step iv), particles to be analyzed were selected from the iron ore particle group to be analyzed, and X-ray CT images were obtained. Acquisition conditions for X-ray CT image acquisition at that time are the same as in step ii), and 1600 transmission images are reconstructed while taking multiple CT images in the depth direction of the analysis particle. A three-dimensional CT image with a pixel size of 10 μm was obtained. However, since the analysis particles have a size of about 0.5 to 1 mm, a plurality of particles were embedded in resin and an X-ray CT image of one analysis particle was acquired. Since the mineral specimen ( _YPO4 mineral specimen) of (1) is a specimen particle having a size of about 5 mm, an X-ray CT image was obtained with one specimen particle as it was without embedding in resin. Based on the obtained three-dimensional CT images, image analysis software was used to create contrast histograms relating to brightness intensity and brightness frequency. These results are shown in FIG.

FIG. 9 summarizes the contrast histogram of the xenotime mineral specimen ( _YPO4 mineral specimen) obtained in step iii) and the contrast histogram of the analyzed particles obtained in step iv). The dotted line in FIG. 9 is the contrast histogram of the _YPO4 mineral specimen, and the dash-dotted line is the contrast histogram of the analyzed particles. The solid line is the contrast histogram after the contrast histogram of the particles to be analyzed is corrected (contrast histogram after correction). In FIG. 9, the horizontal axis represents intensity of luminance, and the vertical axis represents frequency of luminance.

Here, in the spectrum of the _YPO4 mineral specimen in FIG. 9, the peak observed at a luminance frequency of around 10000 represents the outer space, and the peak observed at a luminance frequency of around 20000 represents the xenotime contained in the _YPO4 mineral specimen (YPO ₄ ) A broad peak from 40,000 to 70,000 derived from substances other than 4) is xenotime (YPO ₄ ). Considering that the measurement conditions for the analysis particles and the _YPO4 mineral sample are different, the spectra were corrected by translating them so that the brightness of the boundary between the sample and the space in each spectrum was equal.

Specifically, as shown in FIG. 9, the boundary brightness of _YPO4 mineral specimens (areas not analyzed, including stomata) is 14500, the boundary brightness of analyzed particles is 22000, and the brightness of both The difference is 7500. Therefore, the overall brightness of the particles to be analyzed was corrected by -7500. Here, in the histogram of the particles to be analyzed, the reason why the peak of the region other than the sample is unclear is due to the measurement conditions. In this Example 2, although the measurement conditions were the same as described above, the _YPO4 mineral sample and the analysis particles had different sample shapes, so correction was necessary.

Regarding the contrast histogram of the xenotime mineral specimen ( _YPO4 mineral specimen) obtained in step iii), FIG. 10 shows a comparison between the contrast histogram of the _YPO4 mineral specimen and the contrast histogram of the analyzed particles. It is Here, the vertical axis (luminance intensity) is 0 to 30,000. According to this, it can be seen that there is a change point near 35000 on the horizontal axis (frequency of luminance) in the spectrum of the _YPO4 mineral specimen. In addition, when the X-ray CT image and the spectrum were compared by processing using analysis software, the peaks of 35000 to 60000 on the spectrum and YPO ₄ shown in the X-ray CT image were consistent. In 2, the threshold value of _YPO4 in the _YPO4 mineral specimen was set to 35000 to 60000, and the region of brightness intensity = 35000 to 60000 corresponded to xenotime.

Next, in the step v), based on the contrast histogram of the analyzed particles obtained in the previous step iv), the image analysis software attached to the X-ray CT is used to determine the brightness intensity in the region of 35000 to 60000. was defined as xenotime, and other mineral phases containing iron oxide, such as hematite, were identified as other mineral phases. Then, based on the volume of one analysis particle for which the X-ray CT image was obtained, the volume fraction of xenotime in the analysis particles was obtained. rice field. Note that FIG. 11 shows a CT image of the analysis particles obtained in step iv). In this CT image, the region corresponding to xenotime is mapped, and the xenotime region is actually shown in light blue, and other mineral phases containing iron oxide are shown in blue.

When the analysis particles according to Example 2 were powdered and subjected to XRD measurement, the content of xenotime was so small that it could not be detected. The analyzed particles of Example 1 above contained phosphate minerals of a size that can be detected sufficiently by XRD measurement, but as in Example 2, depending on the brand of iron ore, XRD measurement Some contain undetectable fine phosphate minerals. Even in such a case, according to the method of the present invention, even iron ore containing phosphate minerals of a size that cannot be analyzed by conventional techniques can be identified non-destructively.

Claims (5)

A method for quantitatively analyzing phosphate minerals by form for measuring the mass fraction or volume fraction of phosphate minerals present in iron ore,
A step of selecting reference particles from 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;
obtaining an X-ray CT image of a specimen of a phosphate mineral that is the same as the identified identified phosphate mineral;
creating a contrast histogram of brightness intensity and brightness frequency from an X-ray CT image obtained from the specimen to identify the brightness intensity corresponding to the identified phosphate mineral;
a step of selecting analysis particles from the iron ore particle group and obtaining an X-ray CT image of the analysis particles;
Based on the X-ray CT image obtained with the analysis particles, the volume of the region having the brightness intensity corresponding to the identified phosphate mineral in the analysis particles is measured, and the identification in the analysis particles is performed. determining the mass fraction or volume fraction of the phosphate mineral;
A quantitative analysis method for each morphology of phosphate minerals present in iron ore, characterized by comprising: Prior to the step of identifying the brightness intensity corresponding to the identified phosphate mineral, the cross section of the specimen is analyzed by SEM/EDS and vibrational spectroscopy, and the contrast of the X-ray CT image of the specimen is analyzed. 2. The quantitative analysis method for each morphology of phosphate minerals present in iron ore according to claim 1, comprising the step of specifying the brightness of the phosphate minerals. In the step of determining the mass fraction or volume fraction of the identified phosphate mineral in the analysis particles, the contrast histogram of the X-ray CT image obtained with the specimen, or the contrast histogram of the X-ray CT image obtained with the analysis particles 3. The phosphoric acid according to claim 1 or 2, wherein after correcting one of the contrast histograms, a region having a brightness intensity corresponding to the identified phosphate mineral in the X-ray CT image of the analysis particle is measured. Method for quantitative analysis of salt minerals by morphology. In the step of identifying the phosphate mineral contained in the reference particle, elemental analysis is performed on the cross section of the reference particle by fluorescent X-ray analysis, and then the phosphate mineral is identified by SEM/EDS and vibrational spectroscopy. 3. The quantitative analysis method for each morphology of phosphate minerals according to claim 1 or 2. 3. The phosphorus according to claim 1 or 2, wherein in the step of identifying the phosphate mineral contained in the reference particles, a plurality of reference particles are selected and analyzed based on an aggregated particle cross section having the cross section of the plurality of reference particles. Method for quantitative analysis of acid salt minerals by morphology.

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