Method for producing carbonized electric furnace oxidizing slag, and method for producing mortar containing the same, and concrete

Abstract

To provide a method for fixing CO2 into an electric furnace oxidizing slag, that is, a method for carbonizing the electric furnace oxidizing slag, aiming to develop a technology that achieves both effective utilization of industrial by-products and reduction of CO2 concentration in the atmosphere.SOLUTION: A method for producing a carbonized electric furnace oxidizing slag includes: a grinding step of grinding the electric furnace oxidizing slag to produce ground slag; and a wet carbonization step of wet-processing the ground slag to carbonize the same.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a method for producing carbonated electric furnace oxidizing slag, and to a method for producing mortar and concrete containing carbonated electric furnace oxidizing slag. [Background technology]

[0002] In recent years, in order to build a recycling-oriented society, there has been a demand to reduce, reuse, and recycle industrial by-products (reduce, reuse, recycle (3R)). The cement industry is playing a major role in building a recycling-oriented society, for example, by replacing part of the cement with industrial by-products. In addition, because CO2 is inevitably emitted during the cement manufacturing process, replacing cement with industrial by-products and reducing the amount of cement used reduces CO2 emissions, contributing to low carbonization and the prevention of global warming.

[0003] Furthermore, as reducing CO2 emissions has become an urgent issue, there is a growing need for CO2 fixation technology that reduces atmospheric CO2 by fixing it as a carbon compound, in addition to technology that reduces CO2 emissions themselves.

[0004] Meanwhile, JIS A 5011 specifies blast furnace slag aggregate, ferronickel slag aggregate, copper slag aggregate, electric furnace oxidizing slag aggregate, and coal gasification slag aggregate as industrial by-products. In recent years, the amount of crude steel produced by electric furnaces has increased, replacing blast furnaces, and an increase in the amount of electric furnace slag discarded is expected. Electric furnace slag includes oxidizing slag produced during oxidizing refining, and reducing slag produced during reducing refining.

[0005] As examples of cement compositions containing electric furnace oxidized slag, Patent Documents 1 and 2 describe advance materials for pumping concrete, which contain cement, ground granulated blast furnace slag, and electric furnace oxidized slag fine aggregate, while Patent Document 3 describes a cement composition containing a binder made of Portland cement, ground granulated blast furnace slag, and finely ground shirasu, electric furnace oxidized slag fine aggregate, and a polymer for cement admixture. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 2023-000648 [Patent Document 2] Japanese Patent Publication No. 2023-001410 [Patent Document 3] Japanese Patent Application Publication No. 2023-146634 Summary of the Invention [Problem to be solved by the invention]

[0007] The object of the present invention is to provide a method for immobilizing CO2 in electric furnace oxidizing slag, i.e., a method for carbonating electric furnace oxidizing slag, with the aim of developing a technology that achieves both the effective utilization of industrial by-products and the reduction of atmospheric CO2 concentration. [Means for solving the problem]

[0008] Preferred embodiments of the present invention are as follows. 1. A grinding step of grinding electric furnace oxidizing slag to produce ground slag; a wet carbonation step of wet treating the ground slag to carbonate it; A method for producing carbonated electric furnace oxidized slag, comprising: 2. A method for producing carbonated electric furnace oxidizing slag according to the above item 1, A method for producing carbonated electric furnace oxidized slag, wherein the particle size of the pulverized slag is 200 μm or less. 3. A method for producing carbonated electric furnace oxidizing slag according to 1 or 2 above, The method for producing carbonated electric furnace oxidizing slag, wherein the wet carbonation step is carried out by mixing electric furnace oxidizing slag with a carbonate solution. 4. The method for producing carbonated electric furnace oxidizing slag according to 3 above, wherein the carbonate is one or more selected from potassium carbonate, sodium carbonate, sodium bicarbonate, and calcium bicarbonate. 5. A method for producing carbonated electric furnace oxidizing slag according to any one of 1 to 4 above, A method for producing carbonated electric furnace oxidizing slag, further comprising a pretreatment step of subjecting the electric furnace oxidizing slag to autoclave treatment. 6. The method for producing carbonated electric furnace oxidizing slag according to 5 above, wherein the autoclave treatment is carried out at a temperature of 200°C and a pressure of 2 MPa for 3 hours. 7. A method for producing carbonated electric furnace oxidizing slag according to any one of 1 to 6 above, The method for producing carbonated electric furnace oxidizing slag, wherein the electric furnace oxidizing slag is slowly cooled electric furnace oxidizing slag. 8. A method for producing mortar, comprising the step of mixing carbonated electric furnace oxidized slag produced by the method according to any one of the above items 1 to 7, with water and cement. 9. A method for producing concrete, comprising the step of mixing carbonated electric furnace oxidizing slag produced by the method according to any one of the above items 1 to 8 with coarse aggregate, water, and cement. [Effects of the Invention]

[0009] The method for producing carbonated electric furnace oxidized slag of the present invention makes it possible to effectively utilize industrial by-products while reducing atmospheric CO2 concentrations, thereby contributing to the creation of a recycling-oriented society, low carbonization, and the prevention of global warming.

[0010] Using electric furnace oxidized slag fine aggregate, a by-product of the electric furnace manufacturing process, as an alternative to crushed sand, which is a natural resource, contributes to the conservation of natural aggregate resources. It also reduces the amount of cement used, which contributes to reducing CO2 emissions.

[0011] Furthermore, by using electric furnace oxidized slag fine aggregate in mortar and concrete, not only is fluidity improved and workability improved, but the unit water content can also be reduced, resulting in increased durability such as reduced drying shrinkage (reduced cracking) and suppression of carbonation. [Brief explanation of the drawings]

[0012] [Figure 1] FIG. 1 shows the analysis results of EFS1 by X-ray diffraction (XRD). [Figure 2] FIG. 2 shows the results of measuring the pore radius of EFS1 by mercury intrusion porosimetry (MIP). [Figure 3] FIG. 3 shows the adsorption / desorption isotherm of EFS1 measured using a nitrogen adsorption apparatus, BELSORP. [Figure 4] FIG. 4 shows the results of thermogravimetry and differential thermal analysis (TG-DTA) of ground EFS1 before and after dry carbonation. [Figure 5] FIG. 5 shows the results of thermogravimetry and differential thermal analysis (TG-DTA) of EFS1 after wet carbonation and ground EFS1. [Figure 6] FIG. 6 shows the X-ray diffraction (XRD) results for EFS1, EFS1 after wet carbonation, and milled EFS1. [Figure 7] FIG. 7 shows the TG and DTG results before and after carbonation for EFS1 that was carbonated after steam curing. [Figure 8] FIG. 8 shows the TG and DTG results before and after carbonation for EFS2 that was carbonated after steam curing. [Figure 9] FIG. 9 shows the X-ray diffraction (XRD) analysis of EFS2 carbonated after autoclave curing. [Figure 10] FIG. 10 shows the results of thermogravimetry (TG) of EFS2 carbonated after autoclave curing. DETAILED DESCRIPTION OF THE INVENTION

[0013] The method for producing carbonated electric furnace oxidizing slag of the present invention comprises: a grinding step of grinding the electric furnace oxidizing slag to produce ground slag; a wet carbonation step of wet treating the ground slag to carbonate it; Includes:

[0014] [Electric furnace oxidizing slag] Electric furnace oxidized slag is a by-product obtained during the oxidation refining process in an electric furnace. Because lime is used during refining, it is known that undissolved lime and lime that crystallizes during cooling remain in electric furnace oxidized slag as free calcium oxide. Electric furnace oxidized slag is standardized as JIS A5011-4 (Slag aggregate for concrete - Part 4).

[0015] Electric furnace oxidizing slag is divided into slow-cooled slag and quenched slag depending on the cooling method used for the molten slag discharged from the electric furnace.Slow-cooled slag is made by discharging molten oxidizing slag into a dirt floor or steel pan, then solidifying it with water spray cooling and air cooling.Quick-cooled slag is made by blowing molten oxidizing slag with a high-speed rotating impeller, then rapidly cooling and solidifying it with water and air mist.

[0016] In the present invention, the electric furnace oxidizing slag may be either slowly cooled slag or rapidly cooled slag, but slowly cooled electric furnace oxidizing slag is particularly preferred.

[0017] [Crushing process] In the method for producing carbonated electric furnace oxidized slag of the present invention, electric furnace oxidized slag (EFS) is pulverized before carbonation. Because EFS has few voids, carbonation may not be achieved. However, pulverization can ensure sufficient carbonation of the EFS. The pulverization method for EFS is not particularly limited, and it can be performed using, for example, a ball mill, rod mill, bead mill, conical mill, disk mill, edge mill, hammer mill, mortar, pellet mill, VSI mill, Willy mill, roller mill, jet mill, mass colloider, or the like. Among these, pulverization using a disk mill is preferred. The particle size of the pulverized slag is preferably 200 μm or less, more preferably 100 μm or less.

[0018] [Carbonation process] In the method for producing carbonated electric furnace oxidized slag of the present invention, pulverized electric furnace oxidized slag (pulverized EFS) is carbonated by wet treatment. Wet carbonation is a method of carbonation by contacting CO2 with pulverized EFS via a solution. Unlike dry carbonation, which carbonates by directly contacting CO2 gas with EFS and causing a reaction, wet carbonation is a method of carbonation by converting CO2 into CO3 2- The wet carbonation step of the present invention is preferably carried out by mixing electric furnace oxidizing slag with a carbonate solution, although this is not limited thereto. The carbonate is preferably one or more selected from potassium carbonate, sodium carbonate, sodium bicarbonate, and calcium bicarbonate, and particularly preferably sodium carbonate.

[0019] [Pretreatment process] In the method for producing carbonated electric furnace oxidized slag of the present invention, it is further preferable to carry out a pretreatment step. The pretreatment step is preferably an autoclave treatment. The temperature conditions for the autoclave treatment are, for example, preferably 100 to 300°C, more preferably 150 to 250°C. The pressure conditions for the autoclave treatment are, for example, preferably 0.5 to 9.0 MPa, more preferably 1.0 to 8.0 MPa. The time conditions for the autoclave treatment are, for example, preferably 1 to 5 hours, more preferably 2 to 4 hours.

[0020] [Methods of manufacturing mortar and concrete] The method for producing mortar of the present invention includes a step of mixing the carbonated electric furnace oxidizing slag produced by the above method, water, and cement. The method for producing concrete of the present invention includes a step of mixing the carbonated electric furnace oxidizing slag produced by the above method with coarse aggregate, water, and cement.

[0021] Mortar and concrete formed using the above-mentioned carbonated electric furnace oxidized slag not only have improved fluidity and workability, but also have a reduced unit water content, which makes it possible to achieve high durability by reducing drying shrinkage (reducing cracking) and inhibiting carbonation.

[0022] Cement refers to a powder that hardens by hydration or polymerization with water or a liquid agent. The cement is not particularly limited, but examples that can be used include ordinary Portland cement, high-early-strength Portland cement, ultra-high-early-strength Portland cement, moderate-heat Portland cement, low-heat Portland cement, sulfate-resistant cement, white cement, blended cement, and alumina cement, as specified in JIS R 5210. Among these, ordinary Portland cement is preferred. One type of cement may be used alone, or two or more types may be used in combination.

[0023] The water used is not particularly limited, but examples thereof include tap water, distilled water, deionized water, etc. By appropriately adjusting the water content in the mortar and concrete, desired properties (fluidity, air content, etc.) and formability can be ensured.

[0024] The coarse aggregate is not particularly limited, but for example, coarse aggregates specified in JIS A 5005 "Crushed Stone and Crushed Sand for Concrete" can be used. Examples of coarse aggregates include natural aggregates such as river gravel, mountain gravel, and sea gravel, artificial aggregates such as crushed stone such as sandstone, hard limestone, basalt, and andesite, and recycled aggregates. One type of coarse aggregate may be used alone, or two or more types may be used in combination.

[0025] The mortar and concrete may further contain fine aggregate other than carbonated electric furnace oxidized slag, admixtures, hardening accelerators, and the like.

[0026] Further fine aggregates that can be used include those specified in JIS A 5005 "Crushed Stone and Crushed Sand for Concrete." Examples of fine aggregates include river sand, land sand, sea sand, crushed sand, silica sand, hard blast furnace slag fine aggregate, blast furnace slag fine aggregate, and copper slag fine aggregate. One type of fine aggregate may be used alone, or two or more types may be used in combination.

[0027] Examples of the admixture include air-entraining agents, water-reducing agents, air-entraining water-reducing agents, high-performance water-reducing agents, superplasticizers, antifoaming agents, shrinkage-reducing agents, setting accelerators, setting retarders, and thickeners. Depending on the required performance, one type of admixture may be used alone, or two or more types may be used in combination.

[0028] Examples of hardening accelerators include potassium sulfate, sodium sulfate, lithium sulfate, anhydrous gypsum, quicklime, slaked lime, calcium nitrite, calcium nitrate, calcium chloride, alkali aluminate, alkali carbonate, triethanolamine, triisopropanolamine, methyldiethanolamine, diethanolisopropanolamine, calcium formate, maleic anhydride, calcium rhodanate, CSH nanoparticles, calcium thiocyanate, etc. One hardening accelerator may be used alone, or two or more may be used in combination.

[0029] The mixing of the various components in the mixing step may be carried out using a mixer such as a pan mixer, a tilting mixer, a ribbon mixer, etc. The mixing order of the various components may be adjusted as appropriate.

[0030] In this specification, the numerical ranges "XX to △△" for temperature, pressure, time, particle size, etc. mean "not less than XX and not more than △△." [Example]

[0031] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples.

[0032] [1] Electric furnace oxidizing slag (EFS) used in the examples and its abbreviation (1) Electric furnace quenched oxidized slag (EFS1): Windstars (Hoshino Sansho Co., Ltd.) Oxidized slag, a by-product obtained from electric furnace steelworks, is melted at around 1500°C and blown out with a high-pressure blower, rapidly cooled with mist, and then crushed into black, spherical slag with particle sizes of 0.3mm to 5mm or less.

[0033] Table 1 shows the physical properties of EFS1, and Table 2 shows the results of its chemical analysis. The chemical composition of EFS1 was determined using an XRF (X-ray fluorescence analyzer) in accordance with JIS R5204 (X-ray fluorescence analysis of cement). SO3 content was measured according to JIS R5202 (chemical analysis of cement). The analysis was performed using the fundamental parameter (FP) method.

[0034] [Table 1]

[0035] [Table 2]

[0036] The results of the XRD analysis of EFS1 are shown in Figure 1. The analysis results confirmed that the mineral contained calcium silicate.

[0037] Figure 2 shows the results of measuring the pore radius of EFS1 using mercury intrusion porosimetry (MIP). The measurement results confirmed that EFS1 mainly contains pores of 100 to 1000 nm. Furthermore, pores were hardly found on the aggregate surface, and the total void volume was confirmed to be extremely low at 0.77%.

[0038] Figure 3 shows the adsorption / desorption isotherm of EFS1 measured using the BELSORP nitrogen adsorption apparatus. The shape of the adsorption isotherm obtained by analysis confirmed that the adsorption isotherm of EFS1 corresponds to Type II (non-porous) according to the IUPAC classification. Combined with the results of the MIP analysis described above, it was confirmed that there are almost no voids in EFS1.

[0039] (2) Electric furnace slowly cooled oxidizing slag (EFS2): Ecostar (Hoshino Sansho Co., Ltd.) Oxidized slag, a by-product obtained from electric furnace steelworks, is poured from a molten state at around 1500°C into a vat-shaped container called a slag pan, slowly cooled, and then crushed to produce black, angular slag with a particle size of 5mm or less.

[0040] Table 3 shows the physical properties of EFS2, and Table 4 shows an example of the chemical composition analysis of EFS2.

[0041] [Table 3]

[0042] [Table 4]

[0043] In this example, the above-mentioned electric furnace quenched oxidized slag (EFS1) and electric furnace slowly cooled oxidized slag (EFS2), as well as those crushed to 90 μm or less using a disc mill (hereinafter referred to as crushed EFS1 and crushed EFS2), were used.

[0044] [2] Study of the carbonation process (1) Dry carbonation test Using a carbonation acceleration test device used for concrete carbonation tests, EFS was brought into contact with CO2 gas and left to stand for 7 days at a temperature of 20°C, humidity of 60%, and CO2 concentration of 5%.

[0045] (2) Wet carbonation test EFS was mixed with 500 mL of 5% sodium carbonate solution for 90 minutes. After the reaction, the mixture was filtered and dried in a high-temperature oven at 105°C for 24 hours.

[0046] In the present invention, the "carbonation rate" refers to the rate at which CaO in electric furnace oxidizing slag (EFS) is carbonated, and is defined by Equation 1. When all the CaO in the EFS is carbonated to form CaCO3, the carbonation rate is 100%.

[0047]

number

[0048] Two types of carbonation tests, dry and wet, were carried out on EFS1 and crushed EFS1.

[0049] Figure 4 shows the TG-DTA analysis results for ground EFS1 before and after dry carbonation. The TG data confirmed a mass loss in ground EFS1 after carbonation at temperatures between 600 and 800°C, likely due to the decarbonation of CaCO3 (Figure 4, right). The difference in mass gain before and after carbonation was approximately 0.28%, and assuming this difference to be the mass loss rate in TG-DTA, the carbonation rate for ground EFS1 using the dry carbonation method was 1.4%. Furthermore, XRD showed almost no change in peaks before and after dry carbonation (not shown).

[0050] Figure 5 shows the TG-DTA results for EFS1 and pulverized EFS1 after wet carbonation. The TG data showed no mass loss for EFS1 (right side of Figure 5), but a mass loss of approximately 0.7% was observed for pulverized EFS1 at temperatures between 600 and 700°C, likely due to the decarbonation of CaCO3 (left side of Figure 5). The carbonation rate for pulverized EFS1 after wet carbonation was approximately 4%.

[0051] The XRD results for EFS1, wet-carbonated EFS1, and crushed EFS1 are shown in Figure 6. When EFS1 was wet-carbonated, only the same peaks as before carbonation were observed, but when crushed EFS1 was wet-carbonated, a calcite (CaCO3) peak appeared (circle), confirming that the carbonation of Ca within EFS1 had progressed.

[0052] Furthermore, EFS1, which was not crushed, did not carbonate using either the dry or wet carbonation method. Carbonation requires voids inside the aggregate for CO2 to penetrate, but as mentioned above, EFS1 has an extremely small total void volume and no voids extending from the surface to the interior, which is presumably why it did not carbonate.

[0053] Thus, it was found that to enable carbonation, it is necessary to pulverize the electric furnace oxidizing slag before carbonation, and that the particle size of the pulverized slag should preferably be 200 μm or less. It was also confirmed that wet carbonation is the most suitable carbonation method.

[0054] [3] Consideration of pre-treatment process The effect of pretreatment of EFS on carbonation was investigated. Steam curing or autoclave curing was used as the pretreatment method. Each curing method is as follows. (1) Steam curing 100 g of EFS and 500 mL of water were placed in a sealed container and left to stand in a steam curing tank set at 60°C or 80°C for 3 days. (2) Autoclave curing 100g of EFS was placed in a stainless steel beaker and placed in an autoclave. After the lid of the autoclave was fixed, heating was started, and when the temperature reached 200°C, the discharge valve was closed and pressure application was started. When the pressure inside the vessel reached 2MPa, it was left to stand for 3 hours.

[0055] [4] Study on types of electric furnace oxidizing slag Furthermore, to investigate whether the type of EFS affects the carbonation rate, carbonation was carried out using the two types of EFS mentioned above (EFS1 (electric furnace quenched oxidizing slag) and EFS2 (electric furnace slowly cooled oxidizing slag)). After pretreatment with each method, the EFS was dried at 105°C for 24 hours and then carbonation was carried out. After carbonation, the EFS was crushed and analyzed by TG-DTA to calculate the carbonation rate.

[0056] The TG test results for EFS1 and EFS2, which were carbonated after steam curing, are shown in Figures 7 and 8, respectively. Since almost no change was observed in the TG curves in either case, the DTG curves are also shown. In the case of EFS1 (electric furnace quenched oxidized slag), no mass loss was observed before and after carbonation from the DTG curve (Figure 7), but in the case of EFS2 (electric furnace slowly cooled oxidized slag), a mass loss due to the decarbonation of CaCO3 was observed around 600-800°C (Figure 8). This indicates that EFS2 has a higher carbonation reactivity than EFS1.

[0057] The results of XRD analysis of EFS2 carbonated after autoclave curing are shown in Figure 9. Almost no change was observed in the crystal structure before and after autoclave curing, or before and after wet and dry carbonation.

[0058] Figure 10 shows the TG analysis results for EFS2 that was carbonated after autoclave curing. In Figure 10, the data for wet carbonation overlaps with the data for no carbonation. After dry carbonation, EFS2 was found to have a mass loss of approximately 0.25% due to the decarbonation of CaCO3 at around 600°C, and the carbonation rate for EFS2 using the dry carbonation method was 1.7%. Since the XRD analysis results in Figure 9 showed no changes in the crystal group of EFS, it is believed that autoclave curing did not change the crystal structure, but rather changed the condition of the aggregate surface, which promoted carbonation.

[0059] As described above, it has been confirmed that in the method for producing carbonated electric furnace oxidizing slag of the present invention, it is preferable to perform pretreatment in an autoclave, and that the electric furnace oxidizing slag is preferably slowly cooled electric furnace oxidizing slag.

[0060] From the above, the inventors' experiments have revealed for the first time a method for immobilizing CO2 in electric furnace oxidizing slag.

[0061] While preferred embodiments of the present invention are described herein, it will be apparent to those skilled in the art that such embodiments are provided by way of example only, and that various modifications, changes, and substitutions may be made by those skilled in the art without departing from the invention. It should be understood that various alternative embodiments of the invention described herein may be used in practicing the invention. Furthermore, the contents of all publications, including patents and patent applications, referenced herein should be construed as incorporated by reference as if expressly set forth herein.

Claims

1. a grinding step of grinding the electric furnace oxidizing slag to produce ground slag; a wet carbonation step of wet treating the ground slag to carbonate it; A method for producing carbonated electric furnace oxidized slag, comprising:

2. 2. The method for producing carbonated electric furnace oxidizing slag according to claim 1, A method for producing carbonated electric furnace oxidized slag, wherein the particle size of the pulverized slag is 200 μm or less.

3. 3. The method for producing carbonated electric furnace oxidizing slag according to claim 1 or 2, The method for producing carbonated electric furnace oxidizing slag, wherein the wet carbonation step is carried out by mixing electric furnace oxidizing slag with a carbonate solution.

4. 4. The method for producing carbonated electric furnace oxidized slag according to claim 3, wherein the carbonate is one or more selected from the group consisting of potassium carbonate, sodium carbonate, sodium bicarbonate, and calcium bicarbonate.

5. 3. The method for producing carbonated electric furnace oxidizing slag according to claim 1 or 2, A method for producing carbonated electric furnace oxidizing slag, further comprising a pretreatment step of subjecting the electric furnace oxidizing slag to autoclave treatment.

6. 6. The method for producing carbonated electric furnace oxidized slag according to claim 5, wherein the autoclave treatment is carried out at a temperature of 150 to 300°C under saturated steam pressure for 1 to 5 hours.

7. 3. The method for producing carbonated electric furnace oxidizing slag according to claim 1 or 2, The method for producing carbonated electric furnace oxidizing slag, wherein the electric furnace oxidizing slag is slowly cooled electric furnace oxidizing slag.

8. A method for producing mortar, comprising the step of mixing the carbonated electric furnace oxidizing slag produced by the method according to claim 1 or 2 with water and cement.

9. A method for producing concrete, comprising the step of mixing the carbonated electric furnace oxidizing slag produced by the method according to claim 1 or 2 with coarse aggregate, water, and cement.

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