JP7765699B2 - Method for evaluating the quality of sintered ore - Google Patents

Description

The present invention relates to a method for evaluating the quality of sintered ore.

Sintered ore accounts for approximately 70% of the iron source charged into a blast furnace. Therefore, in order to efficiently reduce the iron source in the blast furnace and maintain permeability to stabilize operation, the reducibility of the sintered ore and its permeability until it is incorporated into the cohesive zone are important. Examples of indicators include the reducibility, reduction disintegration, and softening start temperature of the sintered ore. Reducibility is an indicator of the ease with which sintered ore can be reduced. Using sintered ore with high reducibility reduces the amount of reducing agent used and _CO2 emissions. Reduction disintegration index (RDI) is an indicator of the strength of sintered ore after reduction. Sintered ore with low reduction disintegration index is less likely to disintegrate after reduction, improving permeability in the blast furnace. Softening start temperature (Ts) is an indicator of the softening phenomenon that occurs during the reduction of sintered ore. Sintered ore with a high softening start temperature easily maintains its shape even at high temperatures, improving permeability in the blast furnace.

However, it is not easy to determine the above-mentioned indices through actual testing. For example, the reducibility index (RI), which indicates reducibility, is determined through a reduction test in accordance with 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 through a post-reduction crushing test in accordance with JIS M8720. However, this crushing test also requires large-scale equipment and a great deal of effort. Furthermore, the softening onset temperature is determined through 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 onset 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.

To address the above-mentioned issues, 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. Patent Document 3 describes a method for evaluating the reduction disintegration properties of sintered ore from the SFCA-I phase fraction among the mineral phases. In the methods described in these documents, the accuracy of sintered ore quality evaluation is improved by quantifying the phase fractions of SFCA-I, which has a relatively high Fe content, and SFCA, which has a relatively low Fe content, separately in the process of determining the mineral phase fractions.

JP 2018-179690 A Japanese Patent Application Laid-Open No. 2018-179691 Japanese Patent Application Laid-Open No. 2018-179692

However, even with the methods described in the above documents, there was still room for improvement in the accuracy of sinter quality evaluation using Rietveld analysis.

The present invention therefore aims 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 which can further improve the accuracy of quality evaluation.

[1] A sample grinding step of grinding sintered ore obtained by granulating and firing raw materials containing 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 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; a sinter ore quality evaluation step 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.

According to the above configuration, in addition to the first calcium ferrite (SFCA) and the second calcium ferrite (SFCA-I), the third calcium ferrite is separated in the Rietveld analysis. This allows the phase fraction of the second calcium ferrite (SFCA-I), which correlates with multiple qualities of sintered ore, to be quantified with greater accuracy, further improving the accuracy of quality assessment.

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. FIG. 1 is a graph showing the relationship between the 1200° C. reduction rate and the SFCA-I fraction in the examples. FIG. 1 is a graph showing the relationship between the reduction degradation index RDI and the SFCA-I fraction in the examples. FIG. 1 is a graph showing the relationship between the softening starting temperature Ts and the SFCA-I fraction in the examples.

Preferred embodiments of the present invention will be described in detail below with reference to the accompanying drawings. Note that in this specification and drawings, components that have substantially the same functional configuration will be assigned the same reference numerals, and redundant explanations will be omitted.

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 onset temperature. These indices correlate with the SFCA-I (Silico-Ferrite of Calcium and Aluminum - I) phase fraction (hereinafter simply referred to as the SFCA-I fraction) among mineral phases, which is quantified by applying Rietveld analysis to the XRD patterns obtained by analyzing powder samples of pulverized 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. The lower the gangue content of calcium ferrite, the more easily it is reduced and has a high melting point. Therefore, the greater the content of low-gangue calcium ferrite phase, the higher the reducibility and softening onset temperature. Furthermore, while reduction disintegration property is thought to be worsened by secondary hematite crystallizing from the melt during sintering reactions at temperatures above 1300°C, SFCA-I is generated 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, making it less susceptible to deterioration due to reduction disintegration.

SFCA-I is a type of multi-component calcium ferrite that contains Fe, Ca, Si, and Al among the mineral phases in sintered ore. As already mentioned, when applying Rietveld analysis to the XRD pattern of sintered ore to quantify the phase fraction of the mineral phase, the SFCA-I fraction can be calculated more accurately by separating SFCA-I, which has a relatively high Fe content, from SFCA, which has a relatively low Fe content, and quantifying the phase fraction. However, SFCA-I and SFCA are not the only types of multi-component calcium ferrite contained in sintered ore. 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, reports SFCA-III, which, along with SFCA and SFCA-I, constitutes a homologue of the aenigmatite structure.

When quantifying the SFCA-I fraction by applying Rietveld analysis to the XRD pattern of sintered ore, the inventors believed that a more accurate SFCA-I fraction could be calculated 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 sintered ore. Therefore, the "third calcium ferrite" is not necessarily identical to the SFCA-III reported in the literature.

As mentioned above, SFCA and SFCA-I differ in Fe content, but their crystal structures also differ. 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 _Ca2M2T4O12 . 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 the multi-component calcium ferrite composition. In SFCA, the spinel layer (S) and pyroxene layer (P) are layered in an SP-SP-... arrangement (hereinafter, this is also referred to as the "SP crystal arrangement"). In SFCA-I, spinel layers (S) and pyroxene layers (P) are laminated in an SSP-SSP-... arrangement (hereinafter, this is also referred to as "SSP crystal arrangement").

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"). Note that SFCA-III (triclinic crystals) reported in the literature has an SSSP crystal arrangement and therefore could be included in the "third calcium ferrite," but as mentioned above, it is unlikely to be present in large quantities in sintered ore. As 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.

Figure 1 is a flow diagram outlining a sinter quality evaluation method according to one embodiment of the present invention. As shown in the figure, the quality evaluation method first involves pulverizing the sinter obtained by firing granulated raw materials to obtain a powder sample (Step S1: Sample Pulverization Step). Next, the powder 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 sinter, specifically at least one of the reducibility, reduction disintegration property, and softening start temperature, is evaluated based on the SFCA-I fraction obtained by Rietveld analysis (Step S4: Sinter Quality Evaluation Step). Each step is described in detail below.

(Step S1: Sample crushing step)
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 sample collection range and amount should be the same as those for powder samples for chemical analysis, for example, to obtain valid representative values.

Next, the collected sintered ore sample is crushed and mixed to obtain a powder sample. The crushing process uses crushing equipment such as a vibration mill, ball mill (rotary mill), or stamp mill. Because crushing and mixing are performed simultaneously with crushing using a vibration mill or ball mill, 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 can affect the XRD pattern, while if the particle size is too fine (on the nanometer order), crystallinity deteriorates, resulting in an amorphous-like XRD pattern. Specifically, for example, crushing is 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 as simple as mixing the powder sample using a mortar or other device. 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 device, a mixing process after crushing is preferably performed 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.

(Step S2: XRD pattern measurement step)
In the XRD pattern measurement process, the powder sample is packed into a sample holder and XRD measurement is 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 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. Since sintered ore powder is not particularly prone to orientation, no special structure or method is required to prevent orientation other than the above. When the X-ray source used in XRD is a Cu tube, the penetration depth of the incident X-rays is approximately 1 μm. Therefore, the thickness of the sample in the sample holder should be 0.2 mm or more. The sample holder packed with the powder sample is then placed in the X-ray diffractometer, and the XRD pattern is measured.

To measure the XRD pattern, a diffractometer (focusing method) is used, for example. Since Rietveld analysis is performed later to refine the entire XRD pattern, a wide measurement range of 2θ for the XRD pattern is preferable. For example, measurement is preferably performed in the range of 2θ = 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 so that the maximum intensity is 20,000 to 30,000 counts. The slit conditions are such that the irradiated area of the incident X-rays does not exceed the area of the sample. 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 Kβ radiation.

(Step S3: Rietveld analysis step)
In the Rietveld analysis process, the factors of the calculated XRD pattern are optimized by 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, general peak intensity comparison. For quantification by Rietveld analysis, it is preferable to use the Whole Powder Pattern Fitting (WPPF) method, which allows for mineral phase quantification without mixing a standard substance. For example, PDXL-2, manufactured by Rigaku Corporation, is used as the analysis software for Rietveld analysis. For example, PDF (Powder Diffraction File) (registered trademark) created by ICDD (International Centre for Diffraction Data) (registered trademark) is used as the crystalline phase database. Note that the procedure for Rietveld analysis using the above software and database is described below; however, other software and databases available for Rietveld analysis can also be used.

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

(1) Initial Setting of Calculated XRD Pattern When a measured XRD pattern is loaded into PDXL-2, a calculated XRD pattern that is similar to the measured XRD pattern is automatically calculated. If a peak present in the measured XRD pattern is not present in the calculated XRD pattern, or if an abnormality is observed in the background, the calculated XRD data can be manually corrected. For example, in PDXL-2, peaks that are not present in the automatically calculated pattern can be added using the peak position addition function. Peaks between 2θ = 30° and 50° are easily overlooked in automatic calculations, so peaks can be added as needed by comparing them with the measured XRD pattern. Conversely, if the background is mistakenly detected as a peak, the peak position deletion function can be used. Furthermore, if a clear abnormality is observed in the background, although this is rare, the background editing function can be used to correct it.

(2) Determining the Initial Mineral Phases. PDXL-2 has a function that, when elements contained in the mineral phases are selected, 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 improves the accuracy of the results. The major mineral phases in sinter are hematite (α-Fe ₂ O ₃ ), magnetite (Fe ₃ O ₄ ), multicomponent calcium ferrite, and silicate slag (Ca ₂ SiO ₄ ). 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 wustite and binary calcium ferrite may be included in the analysis, but they will 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.

As mentioned above, there are multiple types of multi-component calcium ferrites. For example, if multi-component calcium ferrite is separated into two types, SFCA and SFCA-I, the initial mineral phases are set as follows: hematite, magnetite, SFCA, SFCA-I, and silicate slag, in that order. In contrast, in this embodiment, 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 as follows: hematite, magnetite, SFCA, SFCA-I, the third calcium ferrite, and silicate slag, in that order; however, the order may be changed, as described below.

Points to note when selecting the initial mineral phase are explained below. First, for hematite and magnetite, there are many mineral phases in the database with similar crystal structures, but any mineral phase can be selected since the crystal structure will be refined in a later process. Generally, hematite has a maximum peak near 2θ = 33°, and magnetite has a maximum peak near 2θ = 35°. When selecting hematite and magnetite as the initial mineral phase, the above general peak positions and the FOM (Figure of Merit) of the XRD pattern are taken into consideration. Here, FOM is a value that quantitatively indicates the difference between the XRD pattern of the sample and the XRD pattern of the candidate mineral phase; the smaller the FOM, the more likely it is that the mineral phase is contained in the sample.

Next, with regard to SFCA (first calcium ferrite), since it is a continuous solid solution, many phases of different compositions have been confirmed, but _{it basically has a crystal structure that satisfies the structural formula of Ca2(Ca,Fe,Al)6(Fe,Al,Si)6O20 , so for example ,} Calcium Iron Aluminum Silicate _{( chemical} formula: _{Ca2.8Fe8.7Al1.2Si0.8O20} , No: 08-1-080-0850) ( _Fe2O3 / _CaO =1.6) is selected. Similarly, many phases of different compositions have been confirmed for SFCA-I (second calcium ferrite), but since it basically has a crystal structure that satisfies the structural formula of _Ca3 (Ca,Fe)(Fe,Al) _{16O28 ,} for example, chemical formula: _{Ca3.18Fe15.48Al1.34O28} , No: 00-052-1258 is selected. For the third calcium ferrite, unlike SFCA and SFCA-I _{, no} crystal structure that _is appropriate for phases of different compositions has been identified, so 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 then refined in a later process.

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 general sintered ore, so if there are no particular problems, larnite is selected. As with hematite and magnetite, there are many mineral phases in the database that have similar crystal structures to larnite, so the initial mineral phase is set taking into account the general peak position and the FOM of the XRD pattern.

(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 formula (1). In formula (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 irradiation correction factor, K is the reflection number contributing to the Bragg reflection intensity, m _k is the multiplicity of the Bragg reflection, 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, and y _b (2θ _i ) is the background function.

In this embodiment, the lattice constant and profile function are selected as refinement factors in 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 in 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, because the crystal structures of the three phases of calcium ferrite are similar and there is a possibility that refinement will diverge, the crystal structure factor is excluded from the refinement target, and the profile function is common between SFCA, SFCA-I, and the third calcium ferrite. η incorporated into the profile function in equation (3) is also excluded from the refinement target.

(4) Pattern Refinement In this embodiment, the factors for refining the pattern are the lattice constant and the profile function, as described above. 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 hematite, magnetite, SFCA, SFCA-I, the third calcium ferrite, and silicate slag in this order, and therefore 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.

The accuracy of refinement is evaluated by the S value shown in formula (5). In formula (5), _yi is the diffraction intensity, _wi is 1/ _yi , 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 accuracy of refinement. However, depending on the sample, the S value may exceed 3 even if the refinement is appropriate.

(Step S4: Sintered ore quality evaluation step)
Once it is determined that the refinement of the Rietveld analysis has reached sufficient accuracy based on the S value, the quality of the sintered ore is evaluated based on the SFCA-I (second calcium ferrite) phase fraction. Specifically, sintered ore with a high SFCA-I fraction can be evaluated as having high reducibility, low reduction disintegration, and a high softening start temperature. Regarding reducibility, for example, 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 a maximum temperature of 1200°C or higher, the reduction degree at 1200°C, or the 1200°C reduction degree, is also used. Regarding reduction disintegration, for example, the reduction disintegration index (RDI) specified in JIS M8720 is used. Regarding the softening start temperature, the softening start temperature Ts measured by a large-scale dropping test using a 1 kg sintered ore sample, is used.

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

In one embodiment of the present invention described above, by applying Rietveld analysis to the XRD pattern of sintered ore to quantify the SFCA-I fraction, it is possible to evaluate at least one of the reducibility, reduction disintegration tendency, or softening onset temperature of the sintered ore more easily than through actual testing. Furthermore, in this embodiment, because the Rietveld analysis separates a third calcium ferrite in addition to SFCA (first calcium ferrite) and SFCA-I (second calcium ferrite), it is possible to quantify the SFCA-I fraction with greater accuracy.

As an example of the present invention, actual tests were conducted on multiple sintered ore samples, along with XRD pattern measurements and Rietveld analysis, 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:

First, iron ore, an iron-containing raw material, was mixed with 9.0% to 11.0% by mass of limestone as an auxiliary material and 4.0% to 5.5% by mass of coke as a carbonaceous material, and the mixture was granulated 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.

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 rate (1200°C reduction rate).
(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 start temperature) The softening start temperature was determined by a high-temperature load softening test using 500 g of sintered ore sample from each lot. Specifically, 500 g of the iron source sample was placed in a crucible with an inner diameter of 70 mm and a height of 70 mm, sandwiched between coke. A load of ¹ kgf/cm (98 kPa) was constantly applied to the crucible. CO gas and ^N gas were flowed at a flow rate of 8 L/min and 24.5 L/min, respectively, as reducing gases. The temperature was increased at a rate of 5°C/min (to 1400°C), and the softening start temperature was determined as the temperature at which the pressure drop reached 200 _mmH2O (1960 Pa).

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 to 140deg
Δ2θ: 0.02 deg
Scan speed: 1 deg/min

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 noted 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 Example and Comparative Example, correlations were determined between the SFCA-I fraction quantified by Rietveld analysis and the 1200°C reduction degree, reduction degradation index (RDI), and softening onset temperature (Ts) measured in actual tests. The results are shown in Tables 2, 3, and 4, and Figures 2, 3, and 4.

As shown in the graphs of Figures 2, 3, and 4, in both the Examples and Comparative Examples, the SFCA-I fraction shows a correlation with the 1200°C reduction rate, reduction degradation index RDI, and softening start temperature Ts. 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, reduction degradation index RDI, and softening start temperature Ts. This shows that the accuracy of sinter ore quality evaluation is improved by separating the third calcium ferrite in addition to the first calcium ferrite (SFCA) and second calcium ferrite (SFCA-I) and performing Rietveld analysis.

The above describes in detail preferred embodiments of the present invention with reference to the accompanying drawings, but the present invention is not limited to these examples. It is clear that a person skilled in the art of the technology to which the present invention pertains could conceive of various modifications or alterations within the scope of the technical ideas set forth in the claims, and it is understood that these also naturally fall within the technical scope of the present invention.

Claims (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 ore quality evaluation step of evaluating the quality of the sinter ore based on the second calcium ferrite phase fraction,
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 .