JP5000410B2 - Method for evaluating mineral structure of iron ore for sintering by X-ray CT and method for producing sintered ore - Google Patents

Description

  The present invention is a method for evaluating the characteristics of various brands of iron ore used for the production of sintered ore for blast furnace raw materials, and the distribution of the iron ore using the method for producing sintered ore, The invention relates to a method for producing sintered ore under compounding.

Generally, the sintered ore for blast furnace raw material is manufactured as follows. First, powdered iron ore is mixed with CaO-containing auxiliary materials such as lime powder, SiO _2- containing auxiliary materials such as silica and serpentine, and carbon materials such as coke powder, and an appropriate amount of water is added and mixed. Granulate. This granulated compounded raw material (sintered raw material) is filled to a predetermined thickness on the pallet of a Dwytroid type sintering machine, ignited the charcoal on the surface part of the packed bed, and then air downwards. The carbonaceous material in the packed bed is burned while sucking the slag, and the blended raw material is sintered by the combustion heat to obtain a sintered cake. Then, by crushing and sizing the sintered cake, a product sintered ore having a particle size of several mm or more can be obtained.

  In this sintering process, in order to produce stable sinter operations and to produce sintered ore that satisfies the qualities required for blast furnace raw materials such as strength, reducibility, and reduced powdering properties, For iron ore imported from one foreign country, chemical analysis and grain size analysis are performed at the time of receiving each ship. This analysis method is defined in detail in, for example, JIS-Z8815, JIS-M8211 to JIS-M8213.

  In Patent Document 1, in order to evaluate the iron ore closer to the actual sintering process, a low melting point material formed on the formed fine iron ore is placed, and 1000 ° C. or higher in the air or in a low oxygen atmosphere. To melt the low melting point material, melt the melt into the iron ore powder, and measure one or more of the distance, cross-sectional area and volume penetrated by the melt, A method for evaluating the melt penetration into iron ore powder has been proposed.

In addition, since not only the chemical composition and particle size but also the ore species has a great influence on the sinterability, among the ore species, in particular, as a method for analyzing martite (γ-Fe ₂ O ₃ : maghemite) A method using both differential thermal analysis and X-ray diffraction analysis has been proposed (see Patent Document 2).

  Patent Document 3 proposes a method of obtaining the two-dimensional porosity of a sintered body by using an X-ray CT apparatus and controlling the generation of unsintered parts. In this method, an arbitrary cross section of a sintered body is imaged using X-ray CT, and the ratio of pores having an equivalent circle diameter of 5 mm or more is obtained from the obtained image, and the porosity does not exceed 40%. Thus, the sintering process is controlled.

However, in recent years, iron ores mainly composed of hematite (α-Fe ₂ O ₃ : hematite) and magnetite (Fe ₃ O ₄ : magnetite), which are high-quality iron ores, are heading for depletion. Iron ore is expected to be shipped as a product blended at the foot of a maramamba ore containing 5-9% crystal water with abundant reserves. For this reason, imported iron ore is expected to be a product in which high grade or low grade ore is mixed in one brand.

  On the other hand, Non-Patent Document 1 clarifies that the blending ratio of low-grade ore species in the same brand adversely affects the production of sintered ore. If the amount of low-grade ore in one brand increases in the future, there is a concern that the productivity of sintered ore will decrease.

  Conventionally, evaluation of ore species has been performed by embedding a target iron ore in a resin or the like, cutting the surface, polishing the surface, and observing under a microscope. However, this method has a strong empirical factor, and the criteria for discrimination are ambiguous, so quantitative evaluation is not performed.

  The method for analyzing the composition for sintering in Patent Document 1 and Patent Document 2 has few empirical elements and can be quantitatively evaluated. However, the amount of the sample used in this method is about several grams. When it is adopted in an iron making process for processing a large amount of iron ore, it is difficult to say that the target ore can be evaluated depending on the accuracy of shrinkage, and it takes time to evaluate.

JP 59-153845 A JP 2006-257477 A Japanese Unexamined Patent Publication No. 61-110729 Iron and steel Vol. 92 (2006) No. 12 p21-28

  In the present invention, based on the above-mentioned problems of the prior art, it is possible to provide a simple and efficient method for evaluating iron ore by quantifying the amount of hematite ore in the ore mixed with multiple ore species. The first purpose. Furthermore, the second object is to provide a method for quantitatively predicting and evaluating the sintering characteristics using the evaluation in the present invention.

The gist of the present invention for achieving the above object is as follows.
(1) A method of taking a cross-sectional image of a sintered iron ore using microfocus X-ray CT, and evaluating the mineral structure of the iron ore from the cross-sectional image,
(I) Under the condition that the tube voltage is 150 kV or higher, the X-ray generated from the X-ray source is passed through a filter having a density ρ and a thickness L with a filter index F defined by the following formula (1) of 0.89 or higher. Irradiating the iron ore from a plurality of directions,
(Ii) Obtain the spatial distribution of CT values corresponding to the X-ray absorption coefficient inside the iron ore from the intensity of the irradiated X-ray and the transmitted X-ray intensity of the iron ore, and further, the space of the X-ray absorption coefficient CT value From the distribution, find the apparent density in the iron ore section,
(Iii) Based on the apparent density, the mineral structure of the iron ore is specified, and the content of the mineral structure is obtained from the area ratio of the specified mineral structure to the entire iron ore section. Evaluation method of mineral structure of iron ore for sintering by wire CT.
F = ρ × L (1)
Where ρ: filter density (g / cm ³ )
L: Filter thickness (cm)

(2) The apparent density ρz is obtained from the measured value of the X-ray absorption coefficient CT using the following equation (2), and the iron ore for sintering by X-ray CT according to (1) above Method for evaluating the mineral structure of stone.
ρz = ρair + (ρc−ρair) / (CTc−CTair) × (CT−CTair)
... (2)
Where ρz: apparent density of mineral structure (g / cm ³ )
ρair: density of air (= 1.3 × 10 ⁻³ ) (g / cm ³ )
ρc: Density of calibration sample (g / cm ³ )
CT: CT value of mineral structure
CTair: CT value of air
CTc: CT value of the calibration sample

(3) The mineral structure having an apparent density of 4.4 g / cm ³ or more is hematite, and the mineral structure having an apparent density of 3.5 g / cm ³ or more and less than 4.4 g / cm ³ is goethite and hematite. And a mineral structure having an apparent density of 2.8 g / cm ³ or more and less than 3.5 g / cm ³ as a goethite, and an apparent density of 1.5 g / cm ³ or more and 2.8 g / cm 2. Sintering by X-ray CT according to (1) or (2) above, wherein the mineral structure of less than cm ³ is a gangue mineral and the apparent density is less than 1.5 g / cm ^3. Mineral structure evaluation method for iron ore.

(4) In the method for producing sintered ore,
(I) Using the method for evaluating the mineral structure of iron ore for sintering by X-ray CT as described in (3) above, iron-containing raw materials (but excluding returning minerals and under-slags) included in the sintered raw materials Measure the hematite content in iron ore with a grain size of 1 mm or more collected from the iron ore of brand I
(Ii) From the measured value ai of the hematite content, the cumulative mass% bi of iron ore having a particle size of 1 mm or more in the iron ore of brand i, and the blending ratio Xi of the iron ore of brand i, the following formula (3) is obtained. The hematite content WH in the iron ore having a particle size of 1 mm or more in the total iron-containing raw material is used,
(Iii) A sintered ore characterized by adjusting the blending ratio Xi of the iron ore of the brand i constituting the iron-containing raw material so that the WH becomes 35% or more, and then firing the blended coal sintering machine. Manufacturing method.
WH = Σ _{i = 1 to n} (ai × bi) × Xi (3)
However, ai: Hematai in iron ore with a particle size of 1mm or more collected from iron ore of brand i
G content (% by mass)
bi: Accumulation (% by mass) of iron ore having a particle size of 1 mm or more in the iron ore of brand i
Xi: Mixing ratio of iron ore of brand i (mass%)
Σ _{i = 1 to n} (ai × bi) × Xi: Weighting of (ai × bi) by blending ratio Xi
Average value (i = 1 to n)

  According to the present invention, it is possible to quickly and accurately analyze the abundance ratio of high-grade ore species existing in the incoming ore that contribute to the improvement of sinterability, and the coarse particles of the raw ore blended in the sintered raw material By controlling the amount of dense ore, sintered ore can be produced with high productivity regardless of the type of raw ore.

  Hereinafter, embodiments of the present invention will be described in detail.

  FIG. 1 shows an example of an embodiment of the present invention using microfocus X-ray CT.

  An apparatus for microfocus X-ray CT (Computerized Tomography) includes a microfocus X-ray source 1 composed of a vacuum tube having a cathode and an anode for generating X-rays 5, and a filter for removing low energy components of X-rays 5. 2 and the iron ore sample 3 are fixed, the iron ore sample 3 is rotated around its central axis, and the irradiation stage of the X-ray 5 can be changed, and the iron ore sample 3 is transmitted. X-ray detector 4 (hereinafter referred to as an image intensifier (II) type) having an outer diameter of 230 mm for converting the X-ray 5 (hereinafter referred to as transmitted X-ray) into a visible light image. Called detector).

  In the microfocus X-ray source 1, the electron beam generated at the cathode under vacuum and high voltage is converged, accelerated, and collided with the focus of the anode target (tungsten or the like) to generate the X-ray 5. In the present invention, since the sample to be measured is a high-density iron ore, a microfocus X-ray source having a high tube voltage as high as 225 kV and a minimum focal size as small as 4 μm is used as the X-ray source. It is preferable to do.

  The X-ray 5 generated by the microfocus X-ray source 1 is irradiated on the iron ore sample from a plurality of directions, and the transmitted X-ray transmitted through the iron ore sample is visualized by the II type detector 4. The spatial distribution of the X-ray absorption coefficient inside the iron ore sample is obtained from the intensity of the irradiated X-ray and the intensity of the transmitted X-ray by reconstruction calculation.

  In normal X-ray CT, the X-ray absorption coefficient is calculated based on water so that the CT value of water (density = 1) is 0 and the CT value of air (density≈0) is −1000. The cross-sectional image of the iron ore sample is displayed as a grayscale (brightness) image having 256 gradations (CT = 0 (CT of air) to 255) according to the CT value.

  The cross-sectional image of the iron ore sample is displayed so as to be bright (white) in a pixel region having a high CT value and dark (black) in a pixel region having a low CT value.

In general, the X-ray absorption obtained from the following equation (4) from the intensity I ₀ of the irradiated X-ray of the iron ore sample, the intensity I of the transmitted X-ray, and the X-ray optical path length (sample thickness) L in the iron ore sample In the case of a single wavelength (single energy), the coefficient μ is proportional to the density of the iron ore sample, and as the X-ray absorption coefficient μ (corresponding to the CT value) increases, the density also increases as shown in FIG. Get higher.
I = I ₀ × exp (−μ · L) (4)

  The CT value of the iron ore sample obtained by microfocus X-ray CT can be converted to density as follows.

For example, as shown in FIG. 2, the density of aluminum (density: 2.7 g / cm ³ ), acrylic (density: 1.1 g / cm ³ ), water (density: 1 g / cm ³ ), etc. is known. Before measuring the CT value of the iron ore sample using the calibration sample, the CT value CTc of the calibration sample and the CT value CTair of the air are measured in advance. The CT value of the iron ore sample can be converted into a density.

The calibration sample is not particularly limited to a specific one, but aluminum (density: 2.7 g / cm ³ ) is preferable from the viewpoints of no variation in density and handling and availability.
ρz = ρair + (ρc−ρair) / (CTc−CTair) × (CT−CTair)
... (2)
ρz: Mineral structure density (g / cm ³ )
ρair: density of air (= 1.3 × 10 ⁻³ ) (g / cm ³ )
ρc: Density of calibration sample (g / cm ³ )
CT: CT value of mineral structure CTair: CT value of air CTc: CT value of calibration sample

  The present invention captures a cross-sectional image of a sintered iron ore using microfocus X-ray CT and evaluates the mineral structure of the iron ore from the cross-sectional image. In order to obtain the resolution and accuracy of CT for quantification, the conditions of the tube voltage of the X-ray source and the density ρ and thickness L of the filter are particularly optimized as described below.

<Filter density ρ and thickness L>
As described above, the X-ray absorption coefficient μ obtained by the above equation (4) is proportional to the density of the iron ore sample in the case of a single wavelength (single energy).

  However, the X-rays generated from the microfocus X-ray source actually contain a long wavelength (low energy) component. When the CT value of an iron ore sample is measured, this long wavelength (low energy) ) Component is selectively absorbed particularly in the vicinity of the periphery of the sample, so that the apparent X-ray absorption coefficient is increased, and as a result, the spatial resolution of CT is decreased.

  Generally, such changes in the X-ray spectrum and CT value due to absorption of low energy components contained in X-rays are known as a phenomenon of hardening of the beam (beam hardening). In CT imaging using a high-density material such as stone as a sample, it was confirmed that the influence becomes significant.

FIG. 3 shows a microfocus X-ray CT cross-sectional image of a reagent hematite fired body sample having an average equivalent circle diameter of 4.1 mm when imaged under a condition where no filter is used. 4 is the same as the above sample in the case of imaging using a copper filter having a density ρ of 8.9 g / cm ³ and a thickness of 2 mm and removing a long wavelength (low energy) component in X-rays. The microfocus X-ray CT cross-sectional image of a sample is shown. The reagent hematite fired body sample is a sample having a uniform density with an average true density (the density of the solid portion excluding pores) of 5.3.

  FIG. 3 shows that the CT cross-sectional image of the sample imaged without using the filter shown in FIG. 3 displays the outer periphery of the sample in white, and the apparent density of the periphery of the sample is high (linear hardening phenomenon). . On the other hand, as shown in FIG. 4, by using the filter, a CT image with a uniform luminance (CT value) distribution that reproduces the calcined reagent hematite with a uniform density is obtained by using the filter. .

  Furthermore, the present inventors have provided a filter that can suppress the hardening of the iron ore sample in X-ray CT and ensure the spatial resolution of the CT value necessary for accurately quantifying the mineral structure in the sample. The conditions of density ρ and thickness L were examined.

  FIG. 5 shows the relationship between the thickness of the copper filter used in the microfocus X-ray CT of the reagent hematite fired body sample and the relative standard deviation RSD of CT.

  Relative Standard Deviation (RSD) is the standard deviation (σ) divided by the mean value (μ) (σ / μ), and generally evaluates the measurement accuracy and the extent of distribution relatively. It is used as an indicator for

  FIG. 6 shows the average true density of the above-described reagent hematite fired body and main iron ore used as a sintering raw material. In addition, an average true density shows the average density of the solid part except the porosity calculated | required by the liquid phase substitution method.

From FIG. 6, the average true density of MBR-PF, Carajas, and Mt Newman is 4.4 g / cm ³ or more. Generally, it is known that the mineral composition of these iron ores is mainly hematite.

The reason why the average true density of MBR-PF, Carajas, and Mt Newman having a mineral structure mainly composed of hematite is lower than the average true density (5.3 g / cm ³ ) of the reagent hematite sintered body is that This is because MBR-PF, Carajas, and Mt Newman contain gangue minerals in addition to hematite.

Further, the density of W Angelus and the lobe river is 3.5 g / cm ³ or more and less than 4.4 g / cm ³ . Generally, the mineral structure of these iron ores is a mixed structure of hematite and goethite (note that hematite has a porous structure and may be called martite).

  In the present invention, 2 of Mt Newman (Australian hematite ore) and W Angelus (Australian Malabamba ore), which have the closest average density difference X of about 7% among the main iron ores shown in FIG. In order to distinguish brands with a confidence level of 95.4%, four times the relative standard deviation (σ / μ) of CT values (4σ / μ) is 7% or less, that is, iron ore per brand. The relative standard deviation (σ / μ) of the CT value needs to be 1.75% or less.

Therefore, from the relationship between the thickness of a copper filter having a density ρ of 8.9 g / cm ³ and the relative standard deviation RSD of CT shown in FIG. 5, two kinds of mineral structures having an average density difference of 7% are represented by 95.4. It can be seen that the thickness of the copper filter needs to be 1 mm or more in order to stably secure a relative standard deviation RSD of 1.75% or less that can be distinguished with a reliability of%.

FIG. 5 shows the relationship between the thickness of a copper filter having a density ρ of 8.9 g / cm ³ and the relative standard deviation RSD of CT, but the filter density ρ is increased without changing the filter thickness. Similarly, the effect of reducing the relative standard deviation RSD of CT, that is, improving the spatial resolution of CT can be obtained.

FIG. 11 shows the relationship between the F value obtained by the following equation (1) and the relative standard deviation RSD of CT in the microfocus X-ray CT of the reagent hematite fired body sample.
F = ρ × L (1)
Where ρ: filter density (g / cm ³ )
L: Filter thickness (cm)

From FIG. 11, the thickness of a copper filter having a density ρ of 0.89 g / cm ³ shown in FIG. 5 corresponds to 1 mm or more, “the filter index F defined by the above formula (1) is 0.89 or more. It can be seen that the effect of reducing the relative standard deviation RSD of CT, that is, the effect of improving the spatial resolution of CT can be obtained by using the “filter having density ρ and thickness L”.

  FIG. 10 shows a case where the filter index F is less than 0.89 (F <0.89) (A) and a case where the filter index F is 0.89 or more (F ≧ 0.89) (B). The distribution of X-ray CT values of mineral structure 1 (average density: X1) and mineral structure 2 (average density: X2) with a difference in average density of X% is shown.

  When the filter index F is less than 0.89 (F <0.89), for example, when X = 2σ / μ (A), the two mineral structures can be distinguished (separated), the region A becomes wide, and the X-ray CT The reliability when separating the mineral structure 1 and the mineral structure 2 from the density calculated from the values is as low as about 68.3%.

  On the other hand, when the filter index F is 0.89 or more, for example, X = 4σ / μ (B), the two mineral structures can be distinguished (separated), the region A becomes smaller, and is calculated from the X-ray CT value. The reliability at the time of separating the mineral structure 1 and the mineral structure 2 from the obtained density is 95.4% or more, and a sufficient density resolution of CT can be ensured.

A filter having a density ρ and a thickness L with a filter index F defined by the above formula (1) of 0.89 or more is not particularly limited to a specific material and shape, but the density ρ is 8 in .9g / cm ^3, and, in addition the thickness L is equal to or greater than the copper filter 1 mm, a density ρ is 2.7 g / cm ^3, and the thickness L is 3mm or more aluminum made filter, the density ρ is 7 An iron filter having a thickness L of 1.2 mm or more can be applied at 0.8 g / cm ³ .

  In the present invention, since X-ray CT is measured with high sensitivity using a filter having a filter index F defined by the above formula (1) of 0.89 or more for a high-density iron ore sample, In consideration of the attenuation of X-rays due to filter transmission, it is necessary to have an X-ray transmission capability that can sufficiently transmit an iron ore sample.

  FIG. 7 shows the relationship between the thickness of the copper filter and the ability of transmitting X-ray hematite generated at a tube voltage of 80 to 210 kV.

  Here, the hematite permeation ability means a limit thickness that allows hematite to pass through when the hematite is irradiated with X-rays generated under each tube voltage condition.

  The maximum particle size of powdered iron ore used for ordinary sintered ore is 10 mm. For this reason, in order to ensure both the spatial resolution and sensitivity of the CT value, from FIG. 7, the F value obtained by the above equation (1) is 0.89 or more, and the thickness of the copper filter is 1 mm or more, In addition, it is necessary to irradiate high energy X-rays having sufficient transmission ability under the condition that the tube voltage is 150 kV or higher.

  As described above, the present invention eliminates the long-wavelength (low energy) component of X-rays, thereby ensuring a sufficient spatial resolution of CT values for accurately quantifying mineral texture, and having a high density. In order to ensure the X-ray penetration ability that can sufficiently penetrate the iron ore sample, the tube voltage of the X-ray source is set to 150 kV or more, and the filter index F defined by the above formula (1) is 0.89 or more. It is a characteristic requirement to use a filter having a density ρ and a thickness L.

  As a result, in X-ray CT cross-sectional imaging of iron ore samples, the average density difference X in the iron ore samples is about 7%, and the CT values that can distinguish mineral structures that are in a close relationship with a reliability of 95.4%. Can be ensured, and good CT value sensitivity can be ensured even for high-density iron ore of 10 mm at the maximum.

  In this invention, it becomes possible to quantify the mineral structure of the iron ore constituting the raw material for sintering with high accuracy using the above-described method for evaluating the structure of iron ore by X-ray CT. In general, the mineral structure of iron ore greatly affects the ease of granulation (granulating property) and the strength of the granulated product when the raw material for sintering is granulated. It is known that the air permeability, productivity, and product yield at the time of firing a sintered raw material with a kneading machine are affected.

  In addition, the granulation property and the strength of the granulated product, which is a granulated product in the sintered ore process, is a pseudo particle (a granulated product in which fine particles of less than 1 mm are attached around a core particle of 1 mm or more). The degree of influence of the mineral structure of the iron ore differs greatly between the core particles and the fine particles constituting the pseudo particles.

  In general, when the mineral structure of coarse iron ore with a particle size of 1 mm or more corresponding to the core particles constituting the pseudo particles is dense hematite, the granulation property and the strength of the granulated material are improved. In the case of goethite with a lot of water, the granulation property and the strength of the granulated product are lowered.

  Therefore, by using the above-mentioned method for evaluating the mineral structure of iron ore by X-ray CT, among the iron ores constituting the raw material for sintering, the mineral structure of coarse iron ore of 1 mm or more is quantified to sinter Predicting the granulation properties of the raw materials and the strength of the granulated material, and based on these predictions, the productivity and product yield of the sintered ore are improved, and the quality of the sintered ore such as cold strength is improved. Can be maintained.

  Below, an example of embodiment at the time of applying the mineral structure evaluation method of the iron ore by the said X-ray CT to the manufacturing method of a sintered ore is demonstrated.

  First, the hematite content in an iron ore having a particle size of 1 mm or more collected from the iron ore of the brand i constituting the iron-containing raw material (excluding returning or sieving iron) mixed with the sintered raw material is measured. Here, the iron ore having a particle size of 1 mm or more plays a role of forming a core of pseudo particles (a granulated product in which fine powder adheres around the core particles) when the sintered raw material is granulated.

  Next, from the measured value ai of the hematite content, the cumulative mass% bi of iron ore having a particle size of 1 mm or more in the iron ore of brand i, and the blending ratio Xi of the iron ore of brand i, the following formula (3) is obtained. The hematite content WH in the iron ore having a particle size of 1 mm or more in the total iron-containing raw material is obtained.

Furthermore, the blending ratio Xi of the brand ore iron ore constituting the iron-containing raw material is adjusted so that the hematite content WH is 35% or more, and then fired by the blended carbon sintering machine.
WH = Σ _{i = 1 to n} (ai × bi) × Xi (3)
However, ai: Hematai in iron ore with a particle size of 1mm or more collected from iron ore of brand i
G content (% by mass)
bi: Accumulation (% by mass) of iron ore having a particle size of 1 mm or more in the iron ore of brand i
Xi: Mixing ratio of iron ore of brand i (mass%)
Σ _{i = 1 to n} (ai × bi) × Xi: Weighting of (ai × bi) by blending ratio Xi
Average value (i = 1 to n)

  FIG. 9 shows the hematite content WH in iron ore having a particle size of 1 mm or more in the total iron-containing raw material obtained by the above formula (3), and the production rate when sintering the sintered raw material containing this iron-containing raw material. The relationship is shown.

  Sintering was performed using a 300 mmφ sintering test pan, a layer thickness of 600 mm, a coke blending amount of 4.5%, and a suction negative pressure of 1.3 kPa.

From FIG. 9, when the hematite content WH in the iron ore having a particle size of 1 mm or more in the total iron-containing raw material obtained by the above formula (3) is controlled to 35% or more, a high production rate of 28 t / d / m ² or more is stable. It can be seen that it can be maintained.

[Example 1]
CT of a mixture sample in which Brazilian hematite ore with an average particle size of 2.8 to 3 mm and Australian pisolite ore (mainly goethite ore) are mixed 1: 1 using the microfocus X-ray CT shown in FIG. The spatial distribution of was measured. At this time, the tube voltage of the X-ray source is 210 kV, the tube current is 70 μA, and the filter is a copper filter having a density ρ: 0.89 g / cm ³ and a thickness L: 2 mm (F value of the above (1): 1. 78 g / cm ² ) was used.

Further, before the measurement of this sample, the CT value CTc of aluminum for measurement calibration (density ρc: 2.7 g / cm ³ ) and the CT value CTair of air (density ρair: 1.3 × 10 ⁻³ ) Were measured, and from these values (CTc = 1056, CTair = 1000), the CT value of the sample was converted to density by the above equation (2).

Further, the obtained mineral structure having an apparent density of 4.4 g / cm ³ or more is hematite, and the mineral structure having an apparent density of 3.5 g / cm ³ or more and less than 4.4 g / cm ³ is composed of goethite and hematite. A mineral structure having a mixed structure with an apparent density of 2.8 g / cm ³ or more and less than 3.5 g / cm ³ is a goethite, and an apparent density of 1.5 g / cm ³ or more and less than 2.8 g / cm ^3. The mineral structure of each sample was gangue mineral, and the apparent density was less than 1.5 g / cm ^3, and the content of each mineral structure in the sample (area% with respect to the cross section of the total iron ore) was measured.

  FIG. 8 shows a cross-sectional image of microfocus X-ray CT of a mixed sample of hematite ore and pisolite ore (mainly goethite ore).

  Table 1 shows the apparent density and content (area% relative to the cross section of the total iron ore) of each mineral structure in the sample. Table 2 shows the content of each mineral structure calculated by chemical analysis using the same sample for comparison.

  In FIG. 8, H is hematite, G is goethite, H + G is a mixed structure of hematite and goethite, S is gangue, and P is a pore.

  In the cross-sectional image of X-ray CT, the CT value and the apparent density increase in the order of pore (P), gangue (S), hematite (H), mixed structure of hematite and goethite (H + G), and goethite (G). Correspondingly, an image with bright (white) brightness is obtained.

  In chemical analysis, the mixed structure and pores of hematite and goethite cannot be discriminated, so a direct comparison is not possible. However, as shown in Table 2, when compared at a ratio excluding the mixed structure and pores of hematite and goethite, As for the content of each mineral structure obtained from the CT value, a result with almost the same measurement accuracy as the content of each mineral structure calculated by chemical analysis using the same sample was obtained.

  As described above, according to the method of the present invention, the content of hematite, goethite, and gangue can be measured with the same degree of accuracy as chemical analysis, and the mixed structure and pores of matite and goethite that cannot be distinguished by chemical analysis. Can be measured simultaneously.

[Example 2]
Like the compounding example shown in Table 1, the iron-containing raw materials (ores A to F) and the auxiliary raw materials (limestone, serpentine, and silica) constituting the sintered raw materials are mixed at a predetermined ratio. The ratio was adjusted so that the ratio of SiO ₂ , CaO / SiO ₂ , and MgO in the sintered ore was not significantly changed.

  The sintered raw material was mixed and granulated with a drum mixer while adjusting the water content to 7.2%, and then sintered. Sintering was performed using a 300 mmφ sintering test pan, a layer thickness of 600 mm, a coke blending amount of 4.4%, and a suction negative pressure of 15 kPa. The sintered ore after sintering was measured for its cold strength, and the product yield and production rate during sintering were measured.

  Table 1 shows the iron ore having a particle size of 1 mm or more in the iron-containing raw materials (ores A to F) constituting the sintered raw material according to the formula (3) using the method for evaluating iron ore by X-ray CT of the present invention. The results of the determination of the hematite content WH in, the cold strength of the sintered ore after sintering, the product yield during sintering, and the measurement results of the production rate are also shown.

  As shown in Table 1, using the iron ore evaluation method by X-ray CT of the present invention, the hematite content WH determined by the above formula (3) is higher than that of the comparative example deviating from the scope of the present invention. In the present inventions 1 and 2 in which the WH is within the scope of the present invention, the cold strength of the sintered ore, the product yield at the time of sintering, and the production rate are all good.

  From this, based on the evaluation method of iron ore by X-ray CT of the present invention, by adjusting the composition of the iron-containing raw material constituting the sintered raw material, the quality such as the cold strength of the sintered ore, It can be seen that both the product yield and the production rate at the time of conjugation can be stably and satisfactorily maintained.

  According to the present invention, as described above, a sintered ore can be produced with high productivity regardless of the type of raw ore. Therefore, the present invention has great applicability in the steel industry.

It is a figure which shows an example of embodiment of this invention using micro focus X-ray CT. It is a figure which shows the relationship between a density and CT value. It is a figure which shows the micro focus X-ray CT cross-section image of the reagent hematite baking body sample of the hand circle equivalent diameter of 4.1 mm imaged on the conditions which do not use a filter. It is a figure which shows the micro focus X-ray CT cross-sectional image of the said hematite baking body sample (reagent) imaged using the copper filter. It is a figure which shows the relationship between the thickness of the copper filter used in micro focus X-ray CT, and the relative standard deviation RSD of said CT. It is a figure which shows the average true density (g / cm < ³ >) of the main iron ore used for a reagent hematite sintered body and a sintering raw material. It is a figure which shows the relationship between the thickness of a copper filter, and the hematite transmission capability of the X-ray | X_line generate | occur | produced with the tube voltage of 80-210 kV. It is a figure which shows an example of the cross-sectional image of micro focus X-ray CT. It is a figure which shows the relationship between hematite content and the production rate at the time of sintering. It is a figure which shows X-ray CT value distribution of the mineral structure 1 and the mineral structure 2 whose difference in average density is X%. (A) shows a case where the filter index F is less than 0.89, and (B) shows a case where the filter index F is 0.89 or more. It is a figure which shows the relationship between F value (= SxL) of a filter, and the relative standard deviation of micro focus X-ray CT.

Explanation of symbols

1 Microfocus X-ray source 2 Filter 3 Iron ore sample 4 Sample stage 5 X-ray 6 X-ray detector H Hematite G Goethite S Venus mineral P Pore R Area where two mineral structures cannot be distinguished (separated)

Claims (4)

A method of capturing a cross-sectional image of a sintered iron ore using microfocus X-ray CT, and evaluating the mineral structure of the iron ore from the cross-sectional image,
(I) Under the condition that the tube voltage is 150 kV or higher, the X-ray generated from the X-ray source is passed through a filter having a density ρ and a thickness L with a filter index F defined by the following formula (1) of 0.89 or higher. Irradiating the iron ore from a plurality of directions,
(Ii) Obtain the spatial distribution of CT values corresponding to the X-ray absorption coefficient inside the iron ore from the intensity of the irradiated X-ray and the transmitted X-ray intensity of the iron ore, and further, the space of the X-ray absorption coefficient CT value From the distribution, find the apparent density in the iron ore section,
(Iii) Based on the apparent density, the mineral structure of the iron ore is specified, and the content of the mineral structure is obtained from the area ratio of the specified mineral structure to the entire iron ore section. Evaluation method of mineral structure of iron ore for sintering by wire CT.
F = ρ × L (1)
Where ρ: filter density (g / cm ³ )
L: Filter thickness (cm) 2. The mineral structure of iron ore for sintering by X-ray CT according to claim 1, wherein the apparent density ρz is obtained from the measured value of the X-ray absorption coefficient CT using the following equation (2): Evaluation methods.
ρz = ρair + (ρc−ρair) / (CTc−CTair) × (CT−CTair)
... (2)
Where ρz: apparent density of mineral structure (g / cm ³ )
ρair: density of air (= 1.3 × 10 ⁻³ ) (g / cm ³ )
ρc: Density of calibration sample (g / cm ³ )
CT: CT value of mineral structure
CTair: CT value of air
CTc: CT value of the calibration sample The mineral structure having an apparent density of 4.4 g / cm ³ or more is hematite, and the mineral structure having an apparent density of 3.5 g / cm ³ or more and less than 4.4 g / cm ³ is a mixed structure of goethite and hematite. And a mineral structure having an apparent density of 2.8 g / cm ³ or more and less than 3.5 g / cm ³ as a goethite, and an apparent density of 1.5 g / cm ³ or more and less than 2.8 g / cm ^{3. 3.} The mineral structure of iron ore for sintering by X-ray CT according to claim 1, wherein the mineral structure is a gangue mineral and the apparent density is less than 1.5 g / cm ^3. Evaluation methods. In the method for producing sintered ore,
(I) Using the X-ray CT mineral mineral structure evaluation method of sintering iron ore according to claim 3 to constitute iron-containing raw materials (excluding returning ore and under sieve) Measuring the hematite content in iron ore with a particle size of 1 mm or more collected from the iron ore of brand i
(Ii) From the measured value ai of the hematite content, the cumulative mass% bi of iron ore having a particle size of 1 mm or more in the iron ore of brand i, and the blending ratio Xi of the iron ore of brand i, the following formula (3) is obtained. The hematite content WH in the iron ore having a particle size of 1 mm or more in the total iron-containing raw material is used,
(Iii) A sintered ore characterized by adjusting the blending ratio Xi of the iron ore of the brand i constituting the iron-containing raw material so that the WH becomes 35% or more, and then firing the blended coal sintering machine. Manufacturing method.
WH = Σ _{i = 1 to n} (ai × bi) × Xi (3)
However, ai: Hematai in iron ore with a particle size of 1mm or more collected from iron ore of brand i
G content (% by mass)
bi: Accumulation (% by mass) of iron ore having a particle size of 1 mm or more in the iron ore of brand i
Xi: Mixing ratio of iron ore of brand i (mass%)
Σ _{i = 1 to n} (ai × bi) × Xi: Weighting of (ai × bi) by blending ratio Xi
Average value (i = 1 to n)