Method for manufacturing slag products and slag products

Abstract

This invention provides a method for producing usable slag products from steelmaking slag with a high alumina content. [Solution] The method for manufacturing slag products comprises a step of air-cooling steelmaking slag containing, by mass%, Al2O3: 15.0-35.0%, CaO: 30.0-50.0%, MgO: 3.0-7.0%, and SiO2: 5.0-20.0%, without adding water, until the surface temperature reaches 50°C or below.

Description

Technical Field

[0001] The present invention relates to a method for manufacturing a slag product and a slag product, and more particularly, to a method for manufacturing a slag product and a slag product using steelmaking slag having a high alumina content as a raw material.

Background Art

[0002] Steel slag is a by-product generated in the process of manufacturing steel products from iron ore, and is effectively used for various purposes according to its type (see, for example, Non-Patent Documents 1 and 2). In this specification, all products using steel slag as a raw material are referred to as "slag products".

[0003] Steel slag is roughly classified into "blast furnace slag" generated when producing pig iron from iron ore and "steelmaking slag" generated when refining pig iron or scrap to produce steel. Further, blast furnace slag is divided into "quenched blast furnace slag" and "slow-cooled blast furnace slag" according to its treatment method.

[0004] Quenched blast furnace slag is mainly used as a material for cement (a blending material for blast furnace cement), which is called "blast furnace cement".

[0005] Slow-cooled blast furnace slag is used as a roadbed material for roads, a material for civil engineering works, a concrete aggregate, etc.

[0006] Steelmaking slag is reused as an iron source in the steelmaking process, and is also used as a roadbed material for roads, a material for civil engineering works, a ground improvement material, etc.

[0007] In addition to the uses mentioned above (such as road base materials), blast furnace slow-cooled slag and steelmaking slag are also used for "cementation" (see pages 4 and 7 of Non-Patent Document 2). However, this differs in meaning from the use of "cementation" in the context of granulated blast furnace slag. Granulated blast furnace slag itself has properties similar to cement and is used as "blast furnace cement" when mixed with ordinary cement (Portland cement). In contrast, blast furnace slow-cooled slag and steelmaking slag are used as raw materials (alumina source and iron source) for producing clinker, an intermediate product of ordinary cement (Portland cement). Although blast furnace slow-cooled slag and steelmaking slag themselves have hydraulic properties, they do not possess the strong hydraulic properties of cement.

[0008] Japanese Patent Publication No. 6-199548 (Patent Document 1) discloses a cement alumina raw material consisting of steelmaking slag with an alumina content of 15% or more and an alkali content of 1.5% or less. The technology disclosed in this publication involves utilizing steelmaking slag with a high alumina content, which is produced when molten steel is deoxidized and desulfurized by blowing in auxiliary materials such as quicklime and aluminum, as an alumina source for cement (the clinker mentioned above). [Prior art documents] [Patent Documents]

[0009] [Patent Document 1] Japanese Patent Application Publication No. 6-199548 [Non-patent literature]

[0010] [Non-Patent Document 1] Japan Iron and Steel Slag Association, "Characteristics and Usefulness of Iron and Steel Slag Products," published in 2015, [online], [searched July 2024], Internet<URL:https: / / www.slg.jp / publication / pamphlet.html> [Non-Patent Document 2] Japan Iron and Steel Slag Association, "Annual Report of Iron and Steel Slag Statistics (2022 Edition)," published October 2023, [online], [searched July 2024], Internet.<URL:https: / / www.slg.jp / statistics / report.html> [Non-Patent Document 3] Michihiro Aimoto et al., "Development of Analytical Techniques Related to Steel Slag," Nippon Steel & Sumitomo Metal Technical Report No. 399 (2014), p. 14. [Overview of the project] [Problems that the invention aims to solve]

[0011] Steel slag is mainly composed of lime (CaO) and silica (SiO2). In addition to these, blast furnace slag contains relatively large amounts of alumina (Al2O3) and magnesium oxide (MgO), while steelmaking slag contains relatively large amounts of iron oxide (FeO). Non-patent document 1 describes an example of the chemical composition of steelmaking slag (converter slag) as follows: CaO: 45.8%, SiO2: 11.0%, T-Fe: 17.4%, MgO: 6.5%, Al2O3: 1.9%, S: 0.06%, P2O5: 1.7%, MnO: 5.3%. On the other hand, as described in Japanese Patent Publication No. 6-199548 (Patent document 1), depending on the refining method, slag containing a large amount of alumina may be produced even in the case of steelmaking slag.

[0012] The component analysis of slag is generally performed using X-ray fluorescence (XRF). In XRF, information on the analytical components is obtained as signals from each element being measured, and quantitative analysis of light elements such as oxygen is difficult. Therefore, when indicating the content in slag, it is common practice to convert the quantitative values ​​of each element into oxides (see Non-Patent Literature 3).

[0013] Steelmaking slag is generally processed in much the same way as blast furnace slow-cooled slag. Specifically, the slag is first poured into a cooling yard or pit and cooled by natural cooling and appropriate water spraying (see pages 2 and 3 of Non-Patent Document 1). After cooling, the steelmaking slag is crystalline and has a rock-like structure, which is then crushed to adjust the particle size before being used for various purposes.

[0014] On the one hand, steelmaking slag with a high alumina content (hereinafter referred to as "high-alumina steelmaking slag") becomes powdery after cooling. In addition to being difficult to handle in powder form, high-alumina steelmaking slag exhibits significant water immersion swelling, making it difficult to be used as a roadbed material, which is a major application of steelmaking slag.

[0015] An object of the present invention is to provide a method for manufacturing a slag product that can be effectively utilized from high-alumina steelmaking slag and an effectively utilizable slag product.

Means for Solving the Problems

[0016] The method for manufacturing a slag product according to an embodiment of the present invention includes a step of air-cooling steelmaking slag containing, in mass%, Al2O3: 15.0 to 35.0%, CaO: 30.0 to 50.0%, MgO: 3.0 to 7.0%, and SiO2: 5.0 to 20.0% without water injection until the surface temperature becomes 50°C or lower.

[0017] The slag product according to an embodiment of the present invention contains, in mass%, Al2O3: 15.0 to 35.0%, CaO: 30.0 to 50.0%, MgO: 3.0 to 7.0%, and SiO2: 5.0 to 20.0%, and a peak of Ca3(Al(OH6))2 is observed by analysis using X-ray diffraction method.

Effects of the Invention

[0018] According to the present invention, a slag product that can be effectively utilized can be obtained from high-alumina steelmaking slag.

Brief Description of the Drawings

[0019] [Figure 1] FIG. 1 is an X-ray diffraction pattern of one sample prepared by crushing an air-cooled slag solid. [Figure 2] FIG. 2 is an X-ray diffraction pattern of another sample prepared by crushing an air-cooled slag solid. [Figure 3]Figure 3 is another X-ray diffraction pattern of a sample prepared by crushing an air-cooled slag solidified body. [Figure 4] Figure 4 is the X-ray diffraction pattern of a sample that did not harden. [Figure 5] Figure 5 is the X-ray diffraction pattern of a sample prepared from general steelmaking slag.

Embodiments for Carrying Out the Invention

[0020] Steelmaking slag is often described as being processed "in substantially the same manner as blast furnace slowly cooled slag" (see, for example, page 3 of Non-Patent Document 1). From the term "slowly cooled," it may seem that no water cooling is done at all. However, in both the cases of blast furnace slowly cooled slag and steelmaking slag, after pouring into the cooling yard, it is common to perform water injection also for the purpose of dust suppression (Non-Patent Document 1 also has an explanation regarding blast furnace slowly cooled slag, which states "cooling by natural air cooling and appropriate water spraying").

[0021] First, the inventor attempted to collect samples before and after water injection for the purpose of mineral composition investigation. For sample collection before and after water injection, after pouring high alumina steelmaking slag into the cooling yard, it was cooled only by air cooling (natural air cooling) for a predetermined period, and then water injection was performed. The slag cooled only by air cooling was also powdery, but when water was injected into this slag, it was found that the entire slag changed into a strong solid.

[0022] It is known that blast furnace granulated slag has properties similar to cement, but there has been no prior knowledge that steelmaking slag reacts with water and hardens like cement. Based on this result, when investigating the relationship between the length of the air cooling period and the hardening characteristics, it was found that high alumina steelmaking slag shows the property of reacting with water and hardening when air cooled until the surface temperature becomes 50°C or lower. Hereinafter, high alumina steelmaking slag air cooled without water injection until the surface temperature becomes 50°C or lower is called "air-cooled slag," and the hardened product obtained by adding water to the air-cooled slag and hardening it is called "air-cooled slag solidified body."

[0023] The inventors investigated the properties of air-cooled slag and solidified air-cooled slag. Specifically, they conducted mortar tests using air-cooled slag, referring to JIS R 5201:2015. As a result, the mortar produced using air-cooled slag had a yield of approximately 30 N / mm² after 28 days of curing. 2 The compressive strength was demonstrated. In other words, it was found that air-cooled slag, unlike general steelmaking slag, has hardening properties similar to cement. From this, specific uses for air-cooled slag and solidified air-cooled slag can be considered, such as using air-cooled slag like cement (for use in ready-mix concrete) or using solidified air-cooled slag as molded products such as blocks and artificial stone.

[0024] As mentioned above, air-cooled slag has the property of hardening when water is added, like cement. On the other hand, even with high-alumina steelmaking slag, slag that has been water-cooled during the cooling process until the surface temperature reaches 50°C or below in a cooling yard (hereinafter referred to as "water-cooled slag") does not harden when water is added. When the hardened material (solidified air-cooled slag) and the non-hardened material (a mixture of water-cooled slag and water) were analyzed by X-ray diffraction, it was found that the solidified air-cooled slag contains Ca3(Al(OH6))2 (Ca3(Al(OH6))2 is produced in reaction with water), whereas the non-hardened material does not contain Ca3(Al(OH6))2 (Ca3(Al(OH6))2 is not produced even when water is added). Although the detailed mechanism is not clear, it is thought that Ca3(Al(OH6))2 is involved in the hardening process.

[0025] The present invention was completed based on the above findings. Below, a slag product and a method for manufacturing the same according to one embodiment of the present invention will be described.

[0026] [Manufacturing method for slag products] A method for producing a slag product according to one embodiment of the present invention comprises a step of air-cooling a steelmaking slag containing, by mass%, Al2O3: 15.0-35.0%, CaO: 30.0-50.0%, MgO: 3.0-7.0%, and SiO2: 5.0-20.0% until the surface temperature reaches 50°C or below, without adding water.

[0027] The slag used as a raw material for the slag product according to this embodiment is slag generated in the steelmaking process (steelmaking slag), and contains, by mass%, Al2O3: 15.0-35.0%, CaO: 30.0-50.0%, MgO: 3.0-7.0%, and SiO2: 5.0-20.0%. Here, "steelmaking slag" includes not only slag produced in converters, but also molten iron pretreatment slag, slag produced in electric furnaces, and slag produced in secondary refining equipment such as RH vacuum degassing units. Preferably, the steelmaking slag used as a raw material for the slag product according to this embodiment is steelmaking slag produced in secondary refining equipment.

[0028] The steelmaking slag used as a raw material for the slag product according to this embodiment is characterized by a higher alumina (Al2O3) content compared to general steelmaking slag. Hereinafter, this slag will be referred to as "high-alumina steelmaking slag." High-alumina steelmaking slag may be produced in the steelmaking process when aluminum is used as a secondary material. The lower limit of the Al2O3 content of high-alumina steelmaking slag is preferably 18.0%, more preferably 20.0%, and even more preferably 22.0%.

[0029] High-alumina steelmaking slag may contain components other than Al2O3, CaO, MgO, and SiO2. For example, high-alumina steelmaking slag may further contain, by mass%, T-Fe: 0-5.0% and MnO: 0-5.0%. The lower limit of the T-Fe content is preferably 0.3%, more preferably 0.5%, and even more preferably 2.0%.

[0030] High-alumina steelmaking slag discharged from converters, electric furnaces, or secondary smelting equipment is transported to a cooling yard or cooling pit (hereinafter referred to as "cooling yard, etc.") and poured into the cooling yard, etc. The surface temperature of the high-alumina steelmaking slag immediately after being poured into the cooling yard, etc. depends on the elapsed time since discharge from the converter, etc., but is for example 300 to 1200°C. If the slag temperature is too low, its fluidity decreases, which may make it difficult to pour into the cooling yard, etc. The surface temperature of the high-alumina steelmaking slag immediately after being poured into the cooling yard, etc. is preferably 350°C or higher, and more preferably 400°C or higher.

[0031] High-alumina steelmaking slag poured into a cooling yard, etc., is air-cooled without adding water until the surface temperature drops below 50°C. That is, high-alumina steelmaking slag poured into a cooling yard, etc., is cooled by air cooling alone until the surface temperature drops below 50°C. It is preferable to air-cool the high-alumina steelmaking slag without adding water until the surface temperature drops below 45°C, and more preferably to air-cool it without adding water until the surface temperature drops below 40°C.

[0032] The air cooling process, from when the high-alumina steelmaking slag is poured into a cooling yard until its surface temperature drops below 50°C, can be natural cooling in the atmosphere or by blowing in air or an inert gas. Of these, natural cooling is preferred because it is cost-effective and efficient. If the surface temperature immediately after pouring into the cooling yard is 400-600°C, natural cooling for approximately 24 hours or more will reduce the surface temperature to below 50°C, although this depends on the environment of the cooling yard. Furthermore, when natural cooling is performed outdoors, rain may fall during the cooling process, but this is not considered "water injection." Rainfall only wets the very surface of the slag and does not penetrate into the interior of the slag, so the slag obtained after cooling is substantially the same as if no water had been injected at all.

[0033] High-alumina steelmaking slag that has been air-cooled to a predetermined temperature without adding water becomes powdery. Hereafter, this powdery high-alumina steelmaking slag will be referred to as "air-cooled slag." Air-cooled slag has the property of hardening when water is added, like cement. Hereafter, the hardened product obtained by adding water to air-cooled slag will be referred to as "air-cooled slag solidified body."

[0034] While not limited to these uses, one example of how this air-cooled slag and its solidified form can be used is its application similar to cement. Immediately after adding water, air-cooled slag exhibits properties very similar to mortar. By using ordinary steel slag or natural stone as aggregate, and mixing air-cooled slag with the aggregate and kneading it with water, a mixture with properties very similar to concrete can be obtained. These mixtures can be molded before the hardening reaction progresses to form structures such as blocks or artificial stones.

[0035] When mixing air-cooled slag with water, the ratio of the weight of water to the weight of air-cooled slag is preferably 40-60%, and more preferably 50-60% because this ratio maximizes the strength after hardening.

[0036] Fine aggregate or coarse aggregate may be added to the mixture of air-cooled slag and water as needed.

[0037] When using air-cooled slag as a substitute for cement, it is not possible to achieve the same level of strength as when using cement. Therefore, it is acceptable to replace a portion of the air-cooled slag with cement. Here, "cement" refers to common types of cement such as ordinary cement (Portland cement), blast furnace cement, alumina cement, and fly ash cement.

[0038] The resulting mixture can be used, for example, in the manufacture of road paving, blocks, artificial stone, and the like.

[0039] [Slag products] A slag product according to one embodiment of the present invention contains, by mass%, Al2O3: 15.0-35.0%, CaO: 30.0-50.0%, MgO: 3.0-7.0%, and SiO2: 5.0-20.0%, and a peak of Ca3(Al(OH6))2 is observed by analysis by X-ray diffraction.

[0040] The slag product according to this embodiment is, for example, a hardened product (i.e., a solidified air-cooled slag) obtained by adding water to the air-cooled slag described above and allowing it to harden. The slag product according to this embodiment may also contain other components (e.g., aggregate) in addition to the air-cooled slag and water described above. The slag product according to this embodiment may also be obtained by crushing the solidified air-cooled slag into granules.

[0041] The air-cooled slag solidified body can be manufactured, for example, as follows: First, holes (pits) with predetermined bottom area and depth are formed in the cooling yard, and high-alumina steelmaking slag is poured into these pits. Then, it is air-cooled without adding water until the surface temperature drops below 50°C, forming air-cooled slag in the pits. After that, water is injected into the pits.

[0042] The amount of water injected is preferably such that the mixture of air-cooled slag and water becomes a concrete-like (slurry-like) mixture. More preferably, the amount of water injected is such that the weight of the air-cooled slag becomes 40-60%, and even more preferably 50-60%. When injecting the water, it is preferable to agitate the air-cooled slag and water with heavy machinery or the like.

[0043] After mixing the air-cooled slag with water, the mixture is left to stand until the air-cooled slag hardens. It is preferable to allow the mixture to cure for at least one day, and more preferably for at least seven days. This yields a solidified air-cooled slag product (i.e., the slag product according to this embodiment).

[0044] In the slag product according to this embodiment, a peak of Ca3(Al(OH6))2 is observed in analysis by X-ray diffraction. As previously described, the component analysis of slag is generally performed by XRF, and the analytical results obtained by XRF are expressed as the concentration of each element converted to oxide. On the other hand, these elements often form complex oxides. Complex oxides are expected to be in various chemical states depending on differences in cooling treatment, etc. The properties of a slag product are greatly influenced not only by the elements it contains, but also by the type of mineral phase it forms. X-ray diffraction (XRD) is a simple and effective method for identifying the type of mineral phase that has been formed (see Non-Patent Literature 3).

[0045] As mentioned above, air-cooled slag has the property of hardening when water is added, like cement. On the other hand, even with high-alumina steelmaking slag, slag that has been water-cooled during the cooling process until the surface temperature reaches 50°C or below in a cooling yard (hereinafter referred to as "water-cooled slag") does not harden when water is added. When the hardened material (solidified air-cooled slag) and the non-hardened material (a mixture of water-cooled slag and water) were analyzed by X-ray diffraction, it was found that the solidified air-cooled slag contains Ca3(Al(OH6))2 (Ca3(Al(OH6))2 is produced in reaction with water), whereas the non-hardened material does not contain Ca3(Al(OH6))2 (Ca3(Al(OH6))2 is not produced even when water is added). Although the detailed mechanism is not clear, it is thought that Ca3(Al(OH6))2 is involved in the hardening process.

[0046] The above describes a method for manufacturing slag products and a slag product according to one embodiment of the present invention. According to this embodiment, a slag product that can be effectively used can be obtained from high-alumina steelmaking slag. [Examples]

[0047] The present invention will be described more specifically below with reference to examples. The present invention is not limited to these examples.

[0048] High-alumina steelmaking slag was poured into a cooling yard and then air-cooled without adding water until the surface temperature dropped below 50°C to produce air-cooled slag. Specifically, the slag poured into the cooling yard was air-cooled for 24 hours. The surface temperature immediately after pouring into the cooling yard was 480°C, and the surface temperature after air-cooling was 48°C.

[0049] The main components of air-cooled slag are shown in Table 1 (the units of the values ​​in the table are in mass%). For comparison, the components of typical steelmaking slag are also listed in Table 1.

[0050] [Table 1]

[0051] The air-cooled slag and a comparative steelmaking slag were dried at 100°C for 24 hours, then crushed to a particle size of less than 75 μm. Mortar specimens were prepared according to the mortar testing method of JIS R 5201:2015, and the compressive strength was compared at 3 days of curing (3 days old), 7 days of curing (7 days old), and 28 days of curing (28 days old). Specifically, mortar specimens were prepared with the mix designs shown in Table 2 below, and the compressive strength tests were performed.

[0052] [Table 2]

[0053] Table 3 shows the results of the compressive strength test. In the mortar specimens made from steelmaking slag for comparison (Case 2), the shape of the mortar specimens could not be maintained at 3 days, 7 days, and 28 days of age, and the compressive strength could not be measured. In contrast, the mortar specimens made from air-cooled slag (Case 1), although inferior to the mortar specimens made from Portland cement (standard), showed an increase in compressive strength as the age progressed, reaching 30 N / mm² at 28 days of age. 2 The above compressive strength was demonstrated.

[0054] [Table 3]

[0055] X-ray diffraction was performed to investigate the compounds contained in the solidified air-cooled slag. Specifically, as described above, high-alumina steelmaking slag was first poured into a cooling yard and then air-cooled without adding water until the surface temperature fell below 50°C to produce air-cooled slag. However, some of the air-cooled slag was exposed to rainfall during the cooling period.

[0056] 500g of air-cooled slag was mixed with 250g of water to produce a solidified air-cooled slag body. Some of the air-cooled slag did not harden even after water was added. This is thought to be because, during the aforementioned air-cooling period, the slag came into contact with rainwater while cooling to 50°C, resulting in localized areas where the cooling conditions were not met.

[0057] For hardened samples, X-ray diffraction was performed after crushing them into powder. For samples that did not harden, X-ray diffraction was performed after thorough drying. For comparison, 500g of crushed general steelmaking slag powder was mixed with 250g of water. This mixture did not harden. This sample was also thoroughly dried and then X-ray diffraction was performed.

[0058] Figures 1 to 5 show the X-ray diffraction patterns of each sample along with the analysis results. The X-ray source used was CuKα, 40kV × 30mA. Figures 1 to 3 show samples obtained by crushing air-cooled slag solidification, Figure 4 shows a sample that did not solidify, and Figure 5 shows a sample prepared from general steelmaking slag.

[0059] The hardened samples (Figures 1-3) all contain Ca3(Al(OH6))2, whereas the unhardened samples (Figures 4 and 5) do not. This suggests that Ca3(Al(OH6))2 is involved in the hardening process.

[0060] The embodiments of the present invention have been described above. The embodiments described above are merely illustrative examples for carrying out the present invention. Therefore, the present invention is not limited to the embodiments described above, and it is possible to carry out the present invention by appropriately modifying the embodiments described above within the scope of the invention.

Claims

1. In mass%, Al ２ O ３ : 15.0–35.0%, CaO: 30.0–50.0%, MgO: 3.0–7.0%, and SiO ２ A method for manufacturing slag products, comprising a step of air-cooling steelmaking slag containing 5.0 to 20.0% without adding water until the surface temperature reaches 50°C or below.

2. A method for manufacturing a slag product according to claim 1, A method for manufacturing slag products, wherein the air cooling is natural cooling in the atmosphere or cooling by blowing in air or an inert gas.

3. A method for manufacturing a slag product according to claim 1 or 2, A method for manufacturing a slag product, further comprising the step of kneading the air-cooled slag with water.

4. A method for manufacturing a slag product according to claim 3, A method for producing slag products, characterized in that a hardening reaction proceeds by mixing the air-cooled slag with water and leaving it to stand, thereby obtaining a hardened product without using cement.

5. A method for manufacturing a slag product according to claim 3, A method for manufacturing slag products, further comprising the step of forming a structure by adding water to the aforementioned steelmaking slag, kneading it, and then leaving it to stand.

6. In mass%, Al ２ O ３ : 15.0–35.0%, CaO: 30.0–50.0%, MgO: 3.0–7.0%, and SiO ２ : Contains 5.0-20.0%, Analysis by X-ray diffraction shows a peak of Ca ３ (Al(OH ６ )) ２ in the slag product observed.

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