JP7222379B2 - Sintered ore structure evaluation method and sintered ore production method - Google Patents

Description

The present invention provides a sintered ore structure evaluation method for evaluating the sintered ore structure by a simple method, and a high-quality sintered ore by optimizing the operating conditions of the sintering machine based on the evaluation results. It relates to a method for producing a sintered ore that can be produced.

The sintered ore is made by mixing multiple brands of fine iron ore with appropriate amounts of auxiliary raw material powder such as limestone, silica stone, and serpentinite, miscellaneous raw materials such as dust, scale, and return mine, and solid fuel such as coke fine. It is produced by adding water to the sintering compound raw material, mixing and granulating the raw material, and then charging the resulting granulated raw material into a Dwight Lloyd type (DL) sintering machine or the like and sintering it. The sintering blended raw material contains moisture during granulation and aggregates to form pseudo-particles. Good air permeability can be secured, and smooth sintering proceeds.

By the way, fine iron ore, which is a raw material for sintering, has recently been depleted of high-quality iron ore, resulting in a marked decrease in grade, that is, an increase in slag components and a tendency to become finer. It has become. In particular, an increase in the alumina component of iron ore causes a problem of increasing the blast furnace slag ratio and causing an increase in the amount of reducing material to be fed into the blast furnace. Sintered ore to be charged into the blast furnace is required to have a low slag ratio, high reducibility, and high strength from the viewpoint of reducing the production cost of hot metal and reducing the amount of CO ₂ generated. Moreover, from the viewpoint of operational stability of the blast furnace, it is also required to improve the product yield of sintered ore (ratio of sintered ore having a particle size of 5 mm or more that can be put into the blast furnace). Therefore, the productivity of sintered ore can be improved by adjusting the operating conditions such as the blending ratio of raw materials, moisture content, sintering heat pattern, oxygen partial pressure in the atmosphere, air permeability, etc., against the adverse effects of the low grade of raw iron ore. There is a need for measures to improve quality and product yield without sacrificing quality.

Sintered ore is composed of main mineral phases such as magnetite, hematite, calcium ferrite, and slag, and pores (also referred to as voids), and has a complex morphology. It is known that the reducibility, strength, and productivity of sintered ore are related to each other, and all of them are closely related to the morphology of the sinter (Non-Patent Document 1). Non-Patent Document 2 discloses that the yield of sintered ore can be estimated using the strength and porosity of sintered ore obtained by a tablet firing test. Therefore, in order to improve the productivity, quality and product yield of sintered ore, it is important to evaluate the morphology of the produced sintered ore and appropriately adjust the manufacturing conditions based on the evaluation results. be.

As a method for evaluating the structure of sintered ore, quantitative analysis of the main mineral phase by powder X-ray diffraction, quantitative analysis of the structure by optical microscope, electron microscope, electron probe microanalyzer (EPMA), and methods using these in combination have been reported. there is For example, in Patent Document 1, using the abundance ratio of each constituent phase obtained from the X-ray diffraction pattern, the boundary value of each constituent phase is determined from the brightness histogram in the tissue image obtained by an optical microscope, and the tissue image is made to correspond to the constituent phase. A method of quaternarizing is disclosed. Patent Document 2 discloses a method of correcting the mass ratio of each constituent phase obtained from the X-ray diffraction pattern by the average particle size and mass absorption coefficient of each constituent phase obtained from the characteristic X-ray mapping of the sintered ore. there is On the other hand, Patent Literature 3 discloses a method of determining the apparent density in a cross section of sintered ore using microfocus X-ray CT, and determining the content of each mineral phase from the apparent density.

JP 2014-137344 A JP 2018-44855 A JP 2009-30104 A

Sasaki et al.: Tetsu to Hagane, 68 (1982) p. 563. Oyama et al.: Tetsu to Hagane, 82 (1996), p. 719.

However, conventional texture evaluation techniques for sintered ore have the following problems. For example, in the method of evaluating the structure from images taken with an optical microscope or scanning electron microscope (SEM), since the structure is distinguished from a slight difference in contrast on the polished surface, the condition of the polished surface and the imaging conditions (light intensity, acceleration voltage) etc.), and mineralogy knowledge and skill are required to distinguish the structure In addition, the method of estimating the structure from the results of quantitative structure analysis by EPMA has a large number of quantitative elements, and when distinguishing between hematite and magnetite, it is necessary to correct for the oxide constituent elements such as Al and Mg that are slightly contained. For example, there is a problem that the quantification work is complicated and it takes time to evaluate. Patent Documents 1 and 2 use the results of elemental mapping using X-ray diffraction and characteristic X-rays to determine and correct thresholds such as the contrast and brightness of the above image. Therefore, there is a problem that it takes time to evaluate. Further, in Patent Document 3, since a powerful X-ray source of 150 kV or more is required, there is a problem that the equipment becomes large-scaled and cannot be carried out on the machine side of the sintering machine.

An object of the present invention is to propose a sintered ore structure evaluation method for quickly and simply evaluating the structure of the produced sintered ore, and to adjust the operating conditions of the sintering machine based on the evaluation results. It is to propose a method for producing ore.

Therefore, in the present invention, in order to solve the above-mentioned problems that the conventional technology has and to achieve the above objects, the structure of the sintered ore is evaluated using a rapid and more objective index. It reached the conclusion that it is effective to sinter while feeding back to the operation of , and came to develop the present invention. That is, the inventors paid attention to the optical microscope from the viewpoint of simplicity, paid attention to the fact that the image contrast and color tone are changed by adjusting the sample, and decided to use it.

That is, the present invention smoothes any surface of sintered ore, acquires an optical microscope image of the smoothed surface, and provides an optical microscope image of the surface after applying a light-transmitting thin film to the smoothed surface. is acquired, and based on the contrast of both optical microscope images, the area ratio for each structure of the sintered ore is obtained as a structural fraction.

In addition, in the method for evaluating the structure of sintered ore according to the present invention configured as described above,
(1) the light transmissive thin film is a carbon thin film;
(2) the structure of the sintered ore is hematite, magnetite, slag, voids, and the balance is calcium ferrite;
(3) Of the texture of the sintered ore, the area ratios of hematite and magnetite are obtained from the contrast of the optical microscope image of the smoothed surface, and the area ratios of slag and voids are obtained by light on the smoothed surface. Obtaining from an optical microscope image of the surface after application of the transparent thin film;
is considered to be a more preferable solution.

In addition, the present invention relates to a granule obtained by adding water to a sintered mixed raw material obtained by mixing a powdery substance containing iron ore, auxiliary raw materials, miscellaneous raw materials and solid fuel, and mixing and granulating. A certain pseudo-particle is sintered to form a sintered ore, and the tissue fractions of hematite, magnetite, slag, voids and calcium ferrite in the sintered ore are evaluated by the above-described sintered ore texture evaluation method, and based on the evaluation results A method for producing sintered ore, characterized by adjusting the production conditions for sintered ore.

In addition, in the method for producing sintered ore according to the present invention configured as described above,
(1) the adjustment of the production conditions includes changing the blending ratio of coke and / or lime;
is considered to be a more preferable solution.

According to the sintered ore structure evaluation method of the present invention, the structure morphology of the sintered ore can be evaluated quickly and simply, so that it can be reflected in the adjustment of the operating conditions. As a result, the quality of the sintered ore is improved, and it is possible to reduce the production cost of the sintered ore and improve productivity.

It is a photograph showing an example of an optical microscope image of sintered ore, (a) is a photograph showing an optical microscope image of a sample as polished, and (b) is a photograph showing an optical microscope image of the same field of view of a sample after carbon deposition. is. It is a figure which shows the dispersion|variation of the intensity|strength (TI value) of the sintered ore of an invention example and a comparative example.

In developing the present invention, the inventors diligently studied a method for quickly and accurately evaluating the texture fraction of each mineral phase of sintered ore and the morphology of some of the mineral phases. Focusing on the optical microscope from the viewpoint of simplicity, we investigated the change in image contrast and color tone by adjusting the sample in the same field of view. As a result, as shown in comparison with FIGS. 1(a) and 1(b), it was found that when carbon vapor deposition is applied to the observation surface (polished surface), the contrast and color tone change significantly compared to the image before vapor deposition. rice field.

In order to clarify which mineral phase the image contrast and color tone change correspond to, the element concentration was analyzed by an electron probe microanalyzer (EPMA). From the optical microscope image of the as-polished sample (Fig. 1(a)), hematite, which is the main structure in the sintered ore, can be identified as the white region with the brightest contrast, and magnetite can be identified as the light gray region with the second brightest contrast. have understood. Calcium ferrite, slag and voids have different contrast (dark gray area and black area) from hematite and magnetite, but it was difficult to classify them clearly. On the other hand, from the optical microscope image (FIG. 1(b)) of the sample subjected to carbon vapor deposition, the slag was clearly distinguished from other tissues as white areas and voids as black areas. This is because the contrast of the slag changed from black to white due to carbon deposition. Based on the above results, it is possible to identify all the major structures of sintered ore by identifying hematite and magnetite from the image of the as-polished sample, identifying slag and voids from the image after carbon deposition, and identifying the remainder as calcium ferrite. I found out.

The inventors considered the reason why the image contrast and color tone of an optical microscope change by applying carbon vapor deposition as follows. The contrast in the optical microscope image of the as-polished sintered ore sample is due to the difference in the light absorption and reflection characteristics of each mineral phase (black because all voids absorb). It is presumed that the incident light and reflected light of specific wavelengths are absorbed depending on the vapor deposition species and film thickness, and the absorption/reflection spectrum of the slag changes, making it possible to distinguish it from the voids. In addition, since the deposited film formed this time has a thickness shorter than the wavelength of light, not only simple scattering absorption but also the state of the sample/deposited film interface affects the scattering, absorption, and reflection of light. For this reason, although the detailed mechanism is unknown, it is presumed that the difference in contrast was formed due to the change in the surface state due to the mineral species caused by the carbon deposition.

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described in detail. The following description shows a preferred embodiment of the present invention, and the present invention is not limited by the following description.

The sintered ore discharged from the sintering machine is roughly pulverized by a crusher and introduced into a cooler for cooling. In order to collect sintered ore in an actual machine, it is not limited to collecting with a special box-shaped sampler. It may be a method of collecting the sintered ore that is present by some means. For example, a robot arm may be used to continuously sample a portion of the sinter flowing on the belt, or a sample container that has been graded for strength measurement may be continuously sampled using the arm. Selective sampling may be performed. Further, the method may be a method in which the operator manually collects the sample from the sample container, and the sample is collected regularly and continuously. Collect multiple samples from the same lot if it is necessary to assess tissue variability.

In evaluating the texture of sintered ore, first, the surface of the sintered ore sample, which serves as an observation surface, is polished to a mirror surface. Since sintered ore is irregular and easily crumbles, a sample in which sintered ore is embedded in resin in advance may be polished.

Next, the surface of the polished sample is observed with an optical microscope. An ordinary metallographic microscope may be used as the optical microscope. It is preferable to attach a camera or the like to the eyepiece position in order to take an image. It is preferable to adjust the observation magnification appropriately according to the size of the tissue so that the average information of the tissue can be obtained. White areas are distinguished from hematite, light gray areas from magnetite and the rest based on the contrast and color tone of the captured optical microscope images.

For specific identification, it is preferable to use an image processing device. In the identification using an image processing device, the brightest contrast area and the next brightest contrast area are extracted so that the contrast is hematite, magnetite, and other contrasts, and the rest is divided into the other areas. value. Quaternarization may also be performed in which the darkest area (black area) is also extracted. At this time, since the brightness of the image changes depending on the sample preparation conditions and the imaging conditions, the contrast threshold cannot be set constant. is easy to set.

In addition to the above, after performing image processing, it is also possible to obtain a luminance profile and identify each region with the highest luminance peak as hematite and the next highest luminance peak as magnetite. In this case, since the black area clearly differs in contrast from the surroundings, the black area may be included in the quaternary image processing. From the ternary or quaternarized image thus obtained, the area ratios of hematite and magnetite are obtained and used as the respective tissue fractions. Further, as shape parameters, an average equivalent circle diameter, an average Feret diameter, an average aspect ratio, and the like can be obtained. In addition, a polarizing filter or the like can be used to further facilitate tissue identification.

Next, the sample with the light-transmitting thin film applied to the polished surface is observed with an optical microscope. The sample may be obtained separately and polished to a mirror surface, but it is preferable to continue using the sample used in the observation described above. The thin film is preferably a carbon thin film, and specifically a carbon vapor deposition film. The vapor deposition method is not particularly limited and may be a method of heating a vapor deposition source in a vacuum for vapor deposition or a method using chemical reaction or ion sputtering. The thickness of the thin film is preferably 1 nm or more and 50 nm or less. The film thickness can be controlled using a film thickness meter attached to the apparatus, but the relationship between the deposition time and the film thickness may be determined in advance and controlled by time. The observation magnification is preferably the same magnification as the observation before thin film application. Based on the contrast and color tone of the captured optical microscope image, white areas are identified as slags, black areas as voids, and others. For specific identification, it is preferable to use an image processing device to perform ternary conversion so as to provide contrast between slag, voids, and other tissues. Since the brightness of the image changes depending on the sample preparation conditions and imaging conditions, the threshold cannot be set constant. However, since the contrast of the tissue is clear, it is easy to set the threshold for each image. Specifically, a region with the brightest contrast (white region) and a region with the darkest contrast (black region) are visually extracted, and ternarization is performed by dividing into other regions. Alternatively, after image processing, a luminance profile is obtained, and the peak with the highest luminance is defined as a slag, and the peak with the lowest luminance as a void, and other regions are determined. From the ternarized image in this way, the area ratios of slag and voids are obtained and used as the respective tissue fractions. Further, as shape parameters, an average equivalent circle diameter, an average Feret diameter, an average aspect ratio, and the like can be obtained.

The structural fraction of calcium ferrite is obtained from the area ratio of the remainder obtained by subtracting the area ratios of hematite and magnetite obtained from the sample before thin film application and the area ratio of slag and voids obtained from the sample after thin film application. Here, the constituent elements (impurities) that are not classified into the above five are evaluated as calcium ferrite, but since the constituent elements are in trace amounts, they do not greatly affect the properties of the sintered ore, so the problem is do not have. Note that the observation regions may be different regions before and after the application of the thin film, but it is preferable to observe them in the same region in order to improve the evaluation accuracy of the tissue fraction.

On the other hand, the method for evaluating the structure of sintered ore in the present invention is not limited to hematite, magnetite, slag, voids, and calcium ferrite. , it is possible to obtain the tissue fraction as a new phase by applying the method of the present invention.

<Example 1>
Four types of sintered ore with different sintering conditions were prepared by tablet tests, and the compositional fractions of each mineral phase and voids were measured. After roughly pulverizing the prepared sintered ore, an arbitrary sintered ore sample was embedded in a resin and mirror-polished to obtain an analysis sample.

(Comparative Example 1: EPMA)
EPMA (JXA-8100 manufactured by JEOL Ltd.) was used as a standard for the composition fraction, and quantitative elemental mapping analysis of 400 μm × 300 μm Fe, Ca, Al, Si, Mg and O was performed, and hematite, magnetite, calcium ferrite, The area ratios of slag and voids were determined. Analysis conditions are as follows.
Accelerating voltage: 20 kV
Beam current value: 200nA
Number of measurement points: 200 x 150
Measurement interval: 2 μm
Beam system: 2 μm
Acquisition time/point: 1 sec
Quantification method: ZAF

Mineral phases and voids were identified from the obtained quantitative mapping images as follows. First, the Fe oxide phase (hematite or magnetite) was determined to be a region in which the Fe concentration was 95% or more in terms of the atomic concentration ratio of the elements excluding O and which did not contain Ca or Si. At this time, trace amounts of Al and _Mg were also _detected in the oxide phase of Fe. and subtracted from the total amount of oxygen in the oxide phase of Fe to obtain the O atom concentration distribution bound only to Fe. With respect to the atomic ratio of Fe to O thus obtained, a value of Fe/O of 0.70 or more was determined as a magnetite phase, and a value of less than 0.70 was determined as a hematite phase. The calcium ferrite phase was an oxide region containing Fe, Ca, and Si other than the above. The slag was an oxide region mainly composed of calcium silicate containing Ca, Si: 10 to 30 at%, Al: 5 to 15 at%, Fe: 0 to 10 at%, and Mg: 0 to 5 at%. Since the gap is a region without these elements, it is defined as a region where the strength of each element is significantly reduced.

(Comparative Example 2: Conventional method)
Using an optical microscope (manufactured by Nikon: ECLIPSE LV150N), the as-polished sample was photographed at a magnification of 200 to obtain an optical microscope image of a region of 400 μm×300 μm at the center of the sample. The area ratios of hematite, magnetite, calcium ferrite, slag and voids were determined for each acquired image.

(Invention example: the present invention)
An optical microscope image of the as-polished sample was obtained under the same conditions as in Comparative Example 2. Using image analysis software (Digital Micrograph), the brightest contrast area and the next brightest contrast area were extracted from the acquired image, and the area ratio of each area was taken as the area ratio of hematite and magnetite. Then, the observed sample was subjected to carbon vapor deposition to a thickness of about 10 nm, and an optical microscope image was obtained under the same conditions as in Comparative Example 2. Using the above image analysis software, the brightest contrast region and the darkest contrast region were extracted from the acquired image, and the area ratio of each region was defined as the area ratio of slag and voids. The area ratio of calcium ferrite was obtained by subtracting the area ratios of hematite, magnetite, slag, and voids from 100%.

Here, for both the invention examples and comparative examples 1 and 2, the area ratios of each mineral phase and voids were measured for 10 fields of view by the above method, and the average value was taken as the texture fraction. Table 1 below shows the evaluation results of the tissue fractions of the invention examples and comparative examples 1 and 2.

From the difference of the present invention in Table 1, it was found that in the example of the invention, all four mineral phases and voids almost matched within ±2.5% with respect to Comparative Example 1 evaluated by EPMA. In addition, the time required from the measurement to obtaining the tissue fraction was 0.5 hours for the inventive example, which enabled rapid evaluation, whereas the comparative example 1 required 10 hours. On the other hand, from the conventional method difference, in Comparative Example 2, the magnetite and hematite matched those of Comparative Example 1 within ±2.5%, while the calcium ferrite, slag, and void structure fractions It was confirmed in many cases that the difference from 1 exceeded ±2.5%.

<Example 2>
(Preparation of reference sample)
Two types of raw material ores A and B, which have been passed through a sieve to have the same particle size, are blended at a blending ratio of 7:3, and furthermore, 1.0% of lime and 5.0% of coke fine are blended with respect to the raw material ore. was added as a raw material for sintering. Water was added to this sintering compound raw material, mixed and granulated by a conventional method to obtain pseudo-particles, and the pseudo-particles were sintered to prepare sintered ore as a reference sample.

(organizational evaluation)
After coarsely pulverizing the reference sample (sintered ore), 10 samples were arbitrarily selected from the pulverized samples. The selected sample was embedded in resin, mirror-polished, and subjected to structural evaluation. The texture evaluation was performed under the same conditions as in the above-described invention example and comparative example 2, and the average value of the area fractions of magnetite, hematite, calcium ferrite, slag and voids in the 10 samples was obtained and used as the texture fraction.

(strength measurement)
The strength (TI value) of the reference sample (sintered ore) was obtained by a rotational strength test method according to JIS M8712.

(Preparation of test sample)
Next, raw material ores A and B were blended at a compounding ratio of 3:7, and coke fine was added at a rate of 5.0% to the raw ore to obtain a mixed raw material for sintering. This sintering mixed raw material was sintered under the same sintering conditions as the reference sample to prepare a test sample. Each tissue fraction of the test sample was determined according to the invention example and comparative example 2 described above. Determine which of the criteria shown in (a) to (g) below corresponds to the obtained structure fraction, adjust the mixing ratio of lime source and / or coke breeze based on the determination, and then sinter again. made ore. X, Y, and Z described in (a) to (g) below are defined by formulas (1), (2), and (3), respectively. Also, iron oxide in the formula represents magnetite and/or hematite.

(a) When X≧3 and Y≦−5 were satisfied, it was determined that the amount of heat was excessive, and the blending ratio of coke breeze in the raw material powder was reduced by 0.10%.
(b) When only one of X≧3 or Y≦−5 was satisfied, it was determined that the amount of heat was excessive, and the blending ratio of coke breeze in the raw material powder was reduced by 0.05%.
(c) When −4<X<3 and −5<Y<5 were satisfied, it was judged to be equivalent to the reference sample, and the next sintering was carried out under the same conditions.
(d) If only one of X ≤ -4 or Y ≥ 5 is satisfied and Z ≤ -6 is satisfied, it is determined that the amount of Ca is insufficient and the amount of heat is insufficient, and the mixing ratio of the lime source in the raw material powder was increased by 0.5% and the coke fine blending ratio was increased by 0.08%.
(e) If only one of X ≤ -4 or Y ≥ 5 is satisfied and Z > -6 is satisfied, it is judged that the heat quantity is slightly insufficient, and the coke blending ratio of the raw material powder is increased by 0.04%. bottom.
(f) When X ≤ -4, Y ≥ 5, and Z ≤ -4, it is determined that the amount of Ca is insufficient and the amount of heat is insufficient, and the mixing ratio of the lime source in the raw material powder is increased by 1.0%. The coke breeze blending ratio was increased by 0.10%.
(g) When X≦−4, Y≧5, and Z>−4, it was determined that the amount of heat was slightly insufficient, and the coke mixing ratio of the raw material powder was increased by 0.05%.

Based on the criteria shown in (a) to (g) above, sintered ore was produced by batch processing 20 times. The TI value of the obtained sintered ore was measured according to the JIS M8712 method, the difference from the TI value of the reference sample was obtained, and the standard deviation was taken as the strength variation.

FIG. 2 shows variations in the strength of the sintered ore obtained by the method of the present invention together with the conventional method (Comparative Example 2). In Comparative Example 2, the variation in strength was 1.7%, whereas in the example of the present invention, it was 0.7%, and the variation in strength was able to be improved.

The sintered ore structure evaluation method and the sintered ore production method according to the present invention observe the sintered ore structure and produce the sintered ore while reflecting the information based on the observation results in the operation of the sintering machine. It can be applied not only to the method, but also to the observation of other mineral structures and the manufacturing method of products based on the observation results.

Claims (4)

An arbitrary surface of the sintered ore is smoothed, an optical microscope image of the smoothed surface is obtained, and an optical microscope image of the surface after applying a carbon thin film to the smoothed surface is obtained. Based on the contrast, the area ratio for each structure of the sintered ore is obtained as a structure fraction, and the structure of the sintered ore is hematite, magnetite, slag, and voids, and the balance is calcium ferrite. A method for evaluating the structure of sintered ore. Among the texture of the sintered ore, the area ratios of hematite and magnetite are obtained from the contrast of the optical microscope image of the smoothed surface, and the area ratios of slag and voids are determined by the light transmission properties of the smoothed surface. The method for evaluating the structure of sintered ore according to claim 1 , wherein the evaluation is performed from an optical microscope image of the surface after applying the thin film. Water is added to the sintering compounded raw material, which is a mixture of powdery substances containing iron ore, auxiliary raw materials, miscellaneous raw materials, and solid fuel, and mixed and granulated, and the resulting granules, pseudo-particles, are sintered. The sintered ore is obtained as a sintered ore, and the hematite, magnetite, slag, voids and calcium ferrite structure fractions in the sintered ore are evaluated by the sintered ore structure evaluation method according to claim 1 or 2 , and the evaluation result is A method for producing sintered ore, characterized by adjusting the conditions for producing sintered ore based on. The method for producing sintered ore according to claim 3 , wherein the adjustment of the production conditions includes a change in coke and/or lime blending ratio .

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