Method for evaluating the quality of sintered ore

Abstract

To improve the accuracy of quality evaluation in a simple method for evaluating the quality of sintered ore using Rietveld analysis.SOLUTION: A method for evaluating the quality of sintered ore is provided, executing the steps of: pulverizing calcined sintered ore to obtain a powder sample; analyzing the powder sample by an X-ray diffraction method to obtain a diffraction pattern; applying Rietveld analysis to the diffraction pattern, and separating multicomponent calcium ferrite into first to third calcium ferrites and determining respective phase fractions; and evaluating the quality of the sintered ore based on the phase fraction of the second calcium ferrite. The first calcium ferrite is multicomponent calcium ferrite in which a spinel layer (S) and a pyroxene layer (P) take a SP crystal alignment. The second calcium ferrite is multicomponent calcium ferrite in which the layers take a SSP crystal alignment. The third calcium ferrite is multicomponent calcium ferrite in which the layers take a SSSP crystal alignment.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for evaluating the quality of sintered ore. [Background technology]

[0002] Sinter accounts for approximately 70% of the iron source charged into a blast furnace. Therefore, to efficiently reduce the iron source in the blast furnace and maintain permeability to stabilize operation, the reducibility of the sinter and its permeability before it is absorbed into the cohesive zone are important. These indices include the reducibility, reduction disintegration, and softening temperature of the sinter. Reducibility is an indicator of the ease with which sinter can be reduced. Using sinter with high reducibility reduces the amount of reducing agent used and CO2 emissions. Reduction disintegration index (RDI) is an indicator of the strength of sinter after reduction. Sinter with low reduction disintegration index is less likely to disintegrate after reduction, improving permeability in the blast furnace. Softening temperature (Ts) is an indicator of the softening phenomenon that occurs during the reduction process of sinter. Sinter with a high softening temperature is more likely to maintain its shape at high temperatures, improving permeability in the blast furnace.

[0003] However, it is not easy to determine these indices through actual testing. For example, the reducibility index (RI), which indicates reducibility, is determined by a reduction test according to JIS M8713. However, this test requires a furnace to heat the sample and gas to reduce the sample, and the reduction time alone takes 180 minutes. The reduction disintegration index (RDI), which indicates reduction disintegration, is determined by a crushing test after reduction according to JIS M8720. However, this crushing test also requires large-scale equipment and considerable labor. Furthermore, the softening temperature is determined by a large-scale drop test, which takes approximately one day per test and requires approximately 500 g of sintered ore with a diameter of 10–15 mm, making it impossible to test with small amounts of sintered ore. As for methods that do not rely on actual testing, for example, the softening temperature is generally believed to correlate with the basicity of sintered ore, but calculating basicity requires chemical analysis, making it difficult to obtain results quickly.

[0004] To solve the above-mentioned problems, methods have been proposed for evaluating the quality of sintered ore based on the mineral phase fractions quantified by Rietveld analysis of diffraction patterns obtained by X-ray diffraction analysis of powder samples obtained by pulverizing sintered ore raw materials. For example, Patent Document 1 describes a method for evaluating the strength of sintered ore from the SFCA phase fraction among the mineral phases. Patent Document 2 describes a method for evaluating the reducibility of sintered ore from the SFCA-I phase fraction among the mineral phases. Furthermore, Patent Document 3 describes a method for evaluating the reduction disintegration property of sintered ore from the SFCA-I phase fraction among the mineral phases. In the methods described in these documents, in the step of determining the mineral phase fractions, SFCA-I, which has a relatively high Fe content, and SFCA, which has a relatively low Fe content, are separated from each other in a multi-component calcium ferrite, and the phase fractions are quantified, thereby improving the accuracy of the quality evaluation of sintered ore. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2018-179690 [Patent Document 2] Japanese Patent Application Publication No. 2018-179691 [Patent Document 3] Japanese Patent Application Publication No. 2018-179692 Summary of the Invention [Problem to be solved by the invention]

[0006] However, even with the methods described in the above documents, there is still room for improvement in the accuracy of the quality evaluation of sintered ore using Rietveld analysis.

[0007] Therefore, an object of the present invention is to provide a new and improved method for evaluating the quality of sintered ore, which is a simple method for evaluating the quality of sintered ore using Rietveld analysis and can further improve the accuracy of the quality evaluation. [Means for solving the problem]

[0008] [1] A sample grinding step of grinding sintered ore obtained by granulating and firing raw materials containing iron-containing raw materials, auxiliary raw materials, and carbonaceous materials to obtain a powder sample; an X-ray diffraction pattern measurement step of analyzing the powder sample by X-ray diffraction to obtain a diffraction pattern; a Rietveld analysis step of applying Rietveld analysis to the diffraction pattern to separate a multi-component calcium ferrite containing Fe, Ca, Si, and Al among the mineral phases into a first calcium ferrite, a second calcium ferrite, and a third calcium ferrite, and quantifying the phase fractions of each; and a Rietveld analysis step of quantifying the phase fraction of the second calcium ferrite based on the phase fraction of the second calcium ferrite. a sinter ore quality evaluation process for evaluating the quality of sinter ore, wherein the first calcium ferrite is a multi-component calcium ferrite in which the spinel layer (S) and the pyroxene layer (P) have an SP crystal arrangement, the second calcium ferrite is a multi-component calcium ferrite in which the spinel layer (S) and the pyroxene layer (P) have an SSP crystal arrangement, and the third calcium ferrite is a multi-component calcium ferrite in which the spinel layer (S) and the pyroxene layer (P) have an SSSP crystal arrangement. [2] The method for evaluating the quality of sintered ore according to [1], wherein the sintered ore quality evaluation step evaluates the reducibility of the sintered ore. [3] The method for evaluating the quality of sintered ore according to [1] or [2], wherein the sintered ore quality evaluation step evaluates the reduction disintegration property of the sintered ore. [4] The method for evaluating the quality of sintered ore according to any one of [1] to [3], wherein the sintered ore quality evaluation step evaluates the softening start temperature of the sintered ore. [Effects of the Invention]

[0009] According to the above configuration, the third calcium ferrite is separated in addition to the first calcium ferrite (SFCA) and the second calcium ferrite (SFCA-I) in the Rietveld analysis. This allows the phase fraction of the second calcium ferrite (SFCA-I), which is correlated with multiple qualities of sintered ore, to be quantified with higher accuracy, further improving the accuracy of quality evaluation. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is a flow chart showing an outline of a method for evaluating the quality of sintered ore according to an embodiment of the present invention. [Figure 2] FIG. 1 is a graph showing the relationship between the 1200° C. reduction rate and the SFCA-I fraction in Examples. [Figure 3] FIG. 1 is a graph showing the relationship between the reduction degradation index RDI and the SFCA-I fraction in an example. [Figure 4] FIG. 1 is a graph showing the relationship between the softening start temperature Ts and the SFCA-I fraction in the examples. DETAILED DESCRIPTION OF THE INVENTION

[0011] Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. In this specification and drawings, components having substantially the same functional configurations are designated by the same reference numerals, and redundant description will be omitted.

[0012] In one embodiment of the present invention described below, the quality of sinter ore is evaluated by evaluating its reducibility, reduction disintegration property, and softening start temperature. These indices correlate with the fraction of SFCA-I (Silico-Ferrite of Calcium and Aluminum - I) phase (hereinafter simply referred to as the SFCA-I fraction) among mineral phases, which is quantified by Rietveld analysis of the XRD pattern obtained by analyzing a powder sample obtained by crushing sinter ore using X-ray diffraction (XRD). In principle, sinter ore with a high SFCA-I fraction is thought to have a high content of low-gangue calcium ferrite phase. Since calcium ferrite is more easily reduced and has a higher melting point with a low gangue content, the greater the content of low-gangue calcium ferrite phase, the higher the reducibility and softening start temperature. Furthermore, while reduction disintegration property is thought to be worsened by secondary hematite crystallizing from the melt during sintering at temperatures above 1300°C, SFCA-I is formed at temperatures lower than this, around 1200°C to 1300°C. Therefore, it is thought that the structure of sintered ore with a high SFCA-I fraction contains relatively little secondary hematite and is less susceptible to deterioration in reduction disintegration.

[0013] SFCA-I is a type of multicomponent calcium ferrite containing Fe, Ca, Si, and Al among the mineral phases in sinter. As mentioned above, when quantifying the mineral phase fraction by Rietveld analysis of the XRD pattern of sinter, the SFCA-I fraction can be calculated more accurately by separating the SFCA-I phase, which has a relatively high Fe content, from the SFCA phase, which has a relatively low Fe content. However, SFCA-I and SFCA are not the only types of multicomponent calcium ferrites found in sinter. For example, V. Kahlenberg et al., "Structural elucidation of triclinic and monoclinic SFCA-III—killing two birds with one stone," Acta Crystallographica Section B: Structural Science, Crystal Engineering and Materials 75.6 (2019): 1126-1136, reported SFCA-III, which, along with SFCA and SFCA-I, is a homologue of the aenigmatite structure.

[0014] The inventors considered that, when quantifying the SFCA-I fraction by Rietveld analysis of the XRD patterns of sinter, a more accurate calculation of the SFCA-I fraction could be achieved by separating another type of multi-component calcium ferrite in addition to SFCA. In the following explanation, SFCA will be referred to as the "first calcium ferrite" and SFCA-I as the "second calcium ferrite," and this other type of calcium ferrite will also be referred to as the "third calcium ferrite." Note that the SFCA-III reported in the literature is high in Al and Mg, and therefore unlikely to be present in large quantities in sinter. Therefore, the "third calcium ferrite" is not necessarily identical to the SFCA-III reported in the literature.

[0015] As mentioned above, the Fe content differs between SFCA and SFCA-I, but the crystal structure also differs. Specifically, multi-component calcium ferrite is composed of a layered structure of a spinel structure (S) and a pyroxene structure (P). The spinel structure is M4T2O8, and the pyroxene structure is Ca2M2T4O 12 Here, M stands for octahedral site, T stands for tetrahedral site, O stands for oxygen, and Ca stands for calcium. Elements such as Fe, Al, Si, and Mg are dissolved in the M and T sites to form a multi-component calcium ferrite composition. In SFCA, the spinel layer (S) and pyroxene layer (P) are stacked in an SP-SP-... arrangement (hereinafter, this is also referred to as the "SP crystal arrangement"). In SFCA-I, the spinel layer (S) and pyroxene layer (P) are stacked in an SSP-SSP-... arrangement (hereinafter, this is also referred to as the "SSP crystal arrangement").

[0016] Furthermore, in the "third calcium ferrite" of this embodiment, spinel layers (S) and pyroxene layers (P) are stacked in an SSSP-SSSP-... arrangement (hereinafter, this is also referred to as "SSSP crystal arrangement"). SFCA-III (triclinic crystal) reported in the literature has an SSSP crystal arrangement and therefore can be included in the "third calcium ferrite," but as mentioned above, it is unlikely to be present in large amounts in sintered ore. As will be explained below, in this embodiment, the SFCA-I fraction is quantified with higher accuracy by separating the mineral phases in Rietveld analysis into "first calcium ferrite" (SFCA), which has an SP crystal arrangement, "second calcium ferrite" (SFCA-I), which has an SSP crystal arrangement, and "third calcium ferrite" which has an SSSP crystal arrangement.

[0017] FIG. 1 is a flow diagram showing an outline of a method for evaluating the quality of sintered ore according to one embodiment of the present invention. As shown in the figure, in the quality evaluation method, first, sintered ore obtained by firing granulated raw materials is pulverized to obtain a powder sample (step S1: sample pulverization step). Next, the powdered sample is analyzed by X-ray diffraction (XRD) to obtain an XRD pattern (step S2: XRD pattern measurement step). Furthermore, Rietveld analysis is applied to the XRD pattern to determine the mineral phase fraction (step S3: Rietveld analysis step). Finally, the quality of the sintered ore, specifically, at least one of reducibility, reduction disintegration property, and softening start temperature, is evaluated based on the SFCA-I fraction obtained by Rietveld analysis (step S4: sintered ore quality evaluation step). Each step will be described in detail below.

[0018] (Step S1: Sample crushing process) In the sample grinding process, iron-containing raw materials such as iron ore and return ore, auxiliary raw materials such as limestone, and carbonaceous materials such as coke are granulated and then fired to obtain sintered ore. Sintering equipment, such as a Dwight Lloyd (DL) sintering machine or a sintering pot, can be used. Sintered ore samples are collected from the sintered cake (or from the sintered ore lump in the case of a sintering pot). The following describes the case where samples are collected from the sintered cake. To minimize the impact of particle size and the thermal history of the sintering reaction on the quality of the sintered ore, it is preferable to collect samples from the same area of ​​the sintered cake for each firing lot. The sampling range and amount of the sample should be the same as those for powder samples for chemical analysis, for example, to obtain valid representative values.

[0019] Next, the collected sintered ore sample is crushed and mixed to obtain a powder sample. In the crushing process, crushing equipment such as a vibration mill, ball mill (rotary mill), or stamp mill is used. Because crushing and mixing are performed simultaneously with crushing using a vibration mill or ball mill, the crushing time can be reduced compared to stamp mills. The particle size of the powder sample is determined so that analysis by XRD can be performed appropriately. If the particle size is too coarse, orientation will affect the XRD pattern, while if the particle size is too fine (on the nanometer order), the crystallinity will deteriorate, resulting in an amorphous-like XRD pattern. Specifically, for example, crushing is preferably performed so that the average particle size of the powder sample is approximately 20 μm to 125 μm. The mixing process after crushing can be performed simply by mixing the powder sample using a mortar or pestle. As mentioned above, crushing and mixing are performed simultaneously using a vibration mill or ball mill, so a separate mixing process is not necessary. When crushing using a stamp mill or other crushing equipment, it is preferable to perform a mixing process after crushing to homogenize the sample. If the crushing process is performed multiple times, a mixing process is preferably performed regardless of the crushing method to homogenize the sample.

[0020] (Step S2: XRD pattern measurement process) In the XRD pattern measurement process, the powder sample is packed into a sample holder and XRD measurements are performed. The material of the sample holder is not particularly limited as long as it does not affect the XRD measurement; for example, a glass sample holder is commonly used. When packing the sample powder into the sample holder, it is preferable not to pack it too tightly, as this will affect the XRD pattern due to orientation. It is preferable to smooth the surface of the sample after packing it into the sample holder. Surface irregularities will cause the X-ray penetration depth to become inconsistent, affecting the XRD pattern. Sintered ore powder is not particularly prone to orientation, so no special structure or method is required to prevent orientation beyond the above. When using a Cu tube X-ray source for XRD, the penetration depth of the incident X-rays is approximately 1 μm. Therefore, the thickness of the sample in the sample holder should be at least 0.2 mm. The sample holder packed with the powder sample is then placed in the X-ray diffractometer and the XRD pattern is measured.

[0021] For example, a diffractometer (focusing method) is used to measure the XRD pattern. A wide 2θ measurement range is preferred because Rietveld analysis is performed later to refine the entire XRD pattern. For example, measurements are preferably performed over a 2θ range of 10° to 140°. The step increment Δ2θ is set to, for example, Δ2θ = 0.02° to 0.04°. The scan type can be either step scan or continuous scan. The detector exposure time (for step scan) or scan speed (for continuous scan) is set to achieve a maximum intensity of 20,000 to 30,000 counts. The slit conditions are such that the irradiated area of ​​the incident X-rays does not exceed the sample area. For example, CuKα or CoKα radiation is used as the X-ray source. In this case, it is preferable to insert a Kβ filter (Ni plate for Cu radiation source) tailored to the element of the X-ray source to reduce the Kβ radiation.

[0022] (Step S3: Rietveld analysis process) In the Rietveld analysis process, the factors of the calculated XRD pattern are optimized using the least-squares method so that it matches the XRD pattern obtained by measurement (the measured XRD pattern). This process is also called refinement. By appropriately refining the calculated XRD pattern, the mineral phase fraction can be quantified with higher accuracy than, for example, conventional peak intensity comparisons. For quantification by Rietveld analysis, the Whole Powder Pattern Fitting (WPPF) method, which allows for mineral phase quantification without the addition of standard materials, is preferably used. For example, PDXL-2 (manufactured by Rigaku Corporation) is used as the analysis software for Rietveld analysis. For example, the Powder Diffraction File (PDF) (registered trademark) created by the International Centre for Diffraction Data (ICDD) (registered trademark) is used as the crystalline phase database. The following describes the procedure for Rietveld analysis using the above software and database; however, other software and databases available for Rietveld analysis can also be used.

[0023] The specific procedures for Rietveld analysis using the software and database described above are described below. The specific procedures include (1) initial setup of the calculated XRD pattern, (2) determination of the initial mineral phase, (3) determination of the refinement conditions, and (4) refinement of the pattern.

[0024] (1) Initial setting of calculated XRD pattern When a measured XRD pattern is loaded into PDXL-2, a calculated XRD pattern that closely matches the measured pattern is automatically calculated. If a peak present in the measured XRD pattern does not exist in the calculated XRD pattern, or if an anomaly is found in the background, the calculated XRD data can be manually corrected. For example, in PDXL-2, the peak position addition function can be used to add peaks that do not exist in the automatically calculated pattern. Peaks between 2θ = 30° and 50° are often overlooked in automatic calculations, so compare the measured XRD pattern and add peaks as needed. Conversely, if the background is mistakenly detected as a peak, the peak position deletion function can be used. Furthermore, if an obvious anomaly is found in the background, even though it is rare, the background editing function can be used to correct it.

[0025] (2) Determination of the initial mineral phase PDXL-2 has a function that, when selecting elements contained in mineral phases, lists candidate mineral phases that match the calculated XRD pattern set in (1) above. This function is used to determine the initial mineral phases and their order. The order of the initial mineral phases also affects the results of the Rietveld analysis. Generally, selecting the initial mineral phases in order of increasing abundance will improve the accuracy of the results. The major mineral phases in sinter are hematite (α-Fe2O3), magnetite (Fe3O4), multicomponent calcium ferrite, and silicate slag (Ca2SiO4). Depending on the production conditions, trace amounts (approximately 3% by mass or less) of wüstite (FeO) and binary calcium ferrite may also be produced. While the exact abundance fractions are unknown at this point, the general trend is hematite, magnetite, multicomponent calcium ferrite, and silicate slag, so it is recommended to select the mineral phases in this order. Trace amounts of wüstite and binary calcium ferrite may be included in the analysis, but they must be included after the major mineral phases. Furthermore, these trace phases have almost no effect on the quality of the sintered ore evaluated in this embodiment, so they do not need to be included in the analysis unless their diffraction peaks are clearly detected.

[0026] As already mentioned, there are multiple types of multi-component calcium ferrites. For example, if a multi-component calcium ferrite is separated into two types, SFCA and SFCA-I, the initial mineral phases are set to five types, hematite, magnetite, SFCA, SFCA-I, and silicate slag, in this order. On the other hand, in this embodiment, the multi-component calcium ferrite is separated into three types, SFCA (first calcium ferrite), SFCA-I (second calcium ferrite), and a third calcium ferrite. Therefore, the initial mineral phases are preferably set to six types, hematite, magnetite, SFCA, SFCA-I, the third calcium ferrite, and silicate slag, in this order, although the order may be changed as described below.

[0027] The following points should be considered when selecting the initial mineral phase. First, for hematite and magnetite, many mineral phases with similar crystal structures exist in the database. However, any mineral phase can be selected because the crystal structure will be refined in a later step. Generally, hematite has a maximum peak near 2θ = 33°, and magnetite has a maximum peak near 2θ = 35°. When selecting hematite and magnetite as initial mineral phases, the general peak positions mentioned above and the figure of merit (FOM) of the XRD pattern should be taken into consideration. Here, the FOM is a value that quantitatively indicates the difference between the XRD pattern of the sample and that of the candidate mineral phase. The smaller the FOM, the more likely the mineral phase is contained in the sample.

[0028] Next, regarding SFCA (first calcium ferrite), since it is a continuous solid solution, many phases with different compositions have been confirmed, but it is basically Ca2(Ca,Fe,Al)6(Fe,Al,Si)6O 20 For example, Calcium Iron Aluminum Silicate (chemical formula: Ca 2.8 Fe 8.7 Al 1.2 Si 0.8 O 20 ,No:08-1-080-0850) (Fe2O3 / CaO=1.6) is selected. Similarly, many phases with different compositions have been confirmed for SFCA-I (second calcium ferrite), but basically Ca3(Ca,Fe)(Fe,Al) 16 O 28 For example, the chemical formula: Ca 3.18 Fe 15.48 Al 1.34 O 28 , No: 00-052-1258 is selected. For the third calcium ferrite, unlike SFCA and SFCA-I, no crystal structure has been identified that is valid for phases of different compositions. Therefore, for example, a crystal structure in which Al and Mg are replaced with Fe in SFCA-III reported in the literature is tentatively selected, and refined in a later process.

[0029] For silicate slag, dicalcium silicate (Ca2SiO4) accounts for the majority of sintered ore. Among these, larnite (Ca2SiO4), which has a strong diffraction peak near 2θ = 32°, is easily compatible with the XRD pattern of typical sintered ore, so if there are no particular issues, larnite should be selected. As with hematite and magnetite, there are many mineral phases in the database with similar crystal structures for larnite, so the initial mineral phase is set taking into account the general peak position and the FOM of the XRD pattern.

[0030] (3) Determining refinement conditions The conditions for Rietveld analysis are set for the initial mineral phase determined above. The formula for calculating the theoretical diffraction intensity used in the calculated XRD pattern in Rietveld analysis is shown in Equation (1). In Equation (1), s is the scale factor, S R (θ i ) is the correction factor for the sample surface roughness, A(θ i ) is the absorption factor, D(θ i ) is the constant illumination correction factor, K is the number of reflections that contribute to the Bragg reflection intensity, m k is the multiplicity of Bragg reflections, F k is the crystal structure factor, P k is the preferred orientation function, L(θ k ) is the Lorentz polarization factor, θ k is the Bragg angle, Φ(Δ2θ ik ) is the profile function, y b (2θ i ) is the background function.

[0031]

number

[0032] In this embodiment, the lattice constant and profile function are selected as refinement factors in the Rietveld analysis of the XRD pattern. These factors are expressed in the following equations (2) and (3) in equation (1). However, the symmetry profile parameters U, V, and W incorporated into the profile function of equation (3) are factors related to the instrument conditions and do not change under common instrument conditions, so they are excluded from the refinement target. Furthermore, since the crystal structures of the three phases of calcium ferrite are similar and there is a possibility that the refinement results will diverge, the crystal structure factors are excluded from the refinement target, and the profile function is common between SFCA, SFCA-I, and the third calcium ferrite. In addition, η incorporated into the profile function of equation (3) is also excluded from the refinement target.

[0033]

number

[0034] (4) Pattern refinement As described above, the factors for refining the pattern in this embodiment are the lattice constant and the profile function. The refinement of the lattice constant and the profile function is performed simultaneously. Furthermore, the refinement is performed in the order in which the initial mineral phases are selected. Table 1 shows an example of a specific refinement order. As described above, in this embodiment, the initial mineral phases are set to be hematite, magnetite, SFCA, SFCA-I, the third calcium ferrite, and silicate slag in this order, so the refinement is also performed in this order. Note that the initial refinement of hematite and magnetite may be performed simultaneously. Furthermore, the order shown in Table 1 is merely an example, and the order of refinement may be changed depending on the sample.

[0035] [Table 1]

[0036] The accuracy of refinement is evaluated by the S value shown in formula (5). i is the diffraction intensity, w i is 1 / y i, N is the total number of data, and P is the number of parameters to be refined. The closer the calculated XRD pattern is to the measured XRD pattern, the smaller the S value (minimum is 1). For general sintered ore, an S value of 2 to 3 can be considered to be sufficient precision of refinement. However, depending on the sample, the S value may exceed 3 even if the refinement is appropriate.

[0037]

number

[0038] (Step S4: Sinter quality evaluation process) Once the Rietveld analysis is deemed to have reached sufficient accuracy based on the S value, the quality of the sinter is evaluated based on the SFCA-I (secondary calcium ferrite) phase fraction. Specifically, sinter with a high SFCA-I fraction can be evaluated as having high reducibility, low reduction disintegration, and a high softening temperature. Regarding reducibility, the reduction degree at 900°C is specified as the relative reducibility in JIS M8713. Furthermore, because reduction in an actual blast furnace proceeds even at temperatures above 1200°C, the reduction degree at 1200°C is also used. Regarding reduction disintegration, the reduction disintegration index (RDI) specified in JIS M8720 is used. Regarding the softening temperature, the softening temperature Ts measured by a large-scale dropping test using a 1 kg sinter sample is used.

[0039] By analyzing multiple sinters using the above evaluation criteria, it is possible to derive correlations between reducibility, reduction disintegration, and softening start temperature and the SFCA-I fraction. By applying the correlation curve obtained by this method, it is possible to evaluate the reducibility, reduction disintegration, and softening start temperature of new sinters from the SFCA-I fraction obtained by Rietveld analysis.

[0040] In one embodiment of the present invention described above, by quantifying the SFCA-I fraction by applying Rietveld analysis to the XRD pattern of sintered ore, it is possible to evaluate at least one of the reducibility, reduction disintegration property, and softening start temperature of the sintered ore more simply than by actual testing. Furthermore, in this embodiment, the Rietveld analysis separates a third calcium ferrite in addition to SFCA (first calcium ferrite) and SFCA-I (second calcium ferrite), so the SFCA-I fraction can be quantified with higher accuracy. [Example]

[0041] As an example of the present invention, XRD pattern measurements and Rietveld analysis were carried out on several sintered ore samples in addition to actual tests to evaluate the correlation between the SFCA-I phase fraction and the reducibility, reduction disintegration index (RDI), and softening temperature (Ts) of the sintered ore. The specific procedure is as follows.

[0042] First, iron ore, an iron-containing raw material, was granulated with limestone as an auxiliary material in a range of 9.0% to 11.0% by mass and coke as a carbonaceous material in an amount of 4.0% to 5.5% by mass, and then fired in a DL-type sintering machine. For each of the 16 firing lots (lot names: Sinter 1 to Sinter 16), the sintered cake was removed from the pallet, crushed, and 3 kg of the crushed cake was collected as a sintered ore sample, with a diameter of 5 mm or less.

[0043] The following measurements were carried out on each lot of sintered ore sample. (XRD Measurement and Rietveld Analysis) Approximately 1 g of sintered ore sample was taken from each lot, and XRD measurement and Rietveld analysis were carried out under the measurement conditions described below to determine the phase fraction of each mineral phase. (Measurement of reducibility) 500 g of sintered ore sample from each lot was sampled and subjected to a reduction test under a temperature condition of 1200°C in accordance with JIS M8713 except for the reduction temperature, to measure the achieved reduction degree (1200°C reduction degree). (Measurement of Reduction Disintegration Property) 2 kg of sintered ore sample was taken from each lot, and after reduction at 550° C., a crushing test was carried out using a drum crusher in accordance with JIS M8720 to measure the reduction disintegration index (RDI). (Measurement of softening temperature) The softening temperature was determined by a high-temperature load softening test using 500 g of sintered ore sample from each lot. In detail, a 500 g iron source sample was placed in a crucible with an inner diameter of 70 mm and a height of 70 mm, sandwiched between coke, and a constant pressure of 1 kgf / cm was applied to the crucible. 2 While applying a load of 98 kPa, CO gas was supplied at 8 L / min, N 2 The gas was fed at a flow rate of 24.5 L / min, and the temperature was increased at 5°C / min (heated up to 1400°C), and the temperature at which the pressure loss reached 200 mmH2O (1960 Pa) was taken as the softening initiation temperature.

[0044] The conditions for the XRD measurement in this example are as follows. Tube: CoKα (40kV, 36mA) Detector: One-dimensional detector D / tex (manufactured by Rigaku Corporation) 2θ: 10deg~140deg Δ2θ: 0.02 deg Scan speed: 1deg / min

[0045] Next, Rietveld analysis was performed on the XRD patterns obtained by XRD measurement. Rietveld analysis was performed on two samples: one in which the initial mineral phases were hematite, magnetite, SFCA, SFCA-I, a third calcium ferrite (referred to as SFCA-III for convenience, but as mentioned above, this is not necessarily the same as the SFCA-III reported in the literature), and silicate slag (larnite), in this order (Example); and one in which the initial mineral phases were hematite, magnetite, SFCA, SFCA-I, and silicate slag, in this order (Comparative Example). For each of the Examples and Comparative Examples, correlations were determined between the SFCA-I fraction quantified by Rietveld analysis and the 1200°C reduction degree, reduction disintegration index (RDI), and softening start temperature (Ts) measured in actual tests. The results are shown in Tables 2, 3, and 4, as well as Figures 2, 3, and 4.

[0046] [Table 2]

[0047] [Table 3]

[0048] [Table 4]

[0049] As shown in the graphs of Figures 2, 3, and 4, the SFCA-I fraction correlates with the 1200°C reduction rate, the reduction degradation index RDI, and the softening start temperature Ts in both the Examples and Comparative Examples. Furthermore, when comparing the Examples and Comparative Examples, the correlation coefficients for the Examples are higher than those for the Comparative Examples for all of the 1200°C reduction rate, the reduction degradation index RDI, and the softening start temperature Ts, demonstrating that the accuracy of sinter quality evaluation is improved by separating the third calcium ferrite in addition to the first calcium ferrite (SFCA) and the second calcium ferrite (SFCA-I) and performing Rietveld analysis.

[0050] Although the preferred embodiments of the present invention have been described in detail above with reference to the accompanying drawings, the present invention is not limited to these examples. It is clear that a person skilled in the art to which the present invention pertains can conceive of various modifications or alterations within the scope of the technical ideas described in the claims, and it is understood that these also naturally fall within the technical scope of the present invention.

Claims

[Claim 1] a sample crushing step of crushing sintered ore obtained by granulating and firing raw materials including an iron-containing raw material, an auxiliary raw material, and a carbonaceous material to obtain a powder sample; an X-ray diffraction pattern measurement step of analyzing the powder sample by X-ray diffraction to obtain a diffraction pattern; a Rietveld analysis step of applying Rietveld analysis to the diffraction pattern to separate the multi-component calcium ferrite containing Fe, Ca, Si, and Al among the mineral phases into a first calcium ferrite, a second calcium ferrite, and a third calcium ferrite, and quantifying the fractions of each phase; a sinter quality evaluation step of evaluating the quality of the sinter based on the second calcium ferrite phase fraction; A method for evaluating the quality of sintered ore, the first calcium ferrite is a multi-component calcium ferrite in which a spinel layer (S) and a pyroxene layer (P) have an SP crystal arrangement, the second calcium ferrite is a multi-component calcium ferrite in which a spinel layer (S) and a pyroxene layer (P) have an SSP crystal arrangement, The third calcium ferrite is a multi-component calcium ferrite in which a spinel layer (S) and a pyroxene layer (P) have an SSSP crystal arrangement, In the sinter ore quality evaluation step, the sinter ore having a high second calcium ferrite phase fraction is evaluated as having a high reducibility, the sinter ore having a high second calcium ferrite phase fraction is evaluated as having a low reduction disintegration tendency, or the sinter ore having a high second calcium ferrite phase fraction is evaluated as having a high softening start temperature.

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