Method for improving stability of steel slag at normal temperature and pressure, product obtained and application thereof

Abstract

The application discloses a method for improving the stability of steel slag at normal temperature and pressure, and products and applications thereof, and the method is performed in a carbonization box. Steel slag is ball milled and sieved to control the particle size, and steel slag powder is obtained, which is mixed with water, and then is placed in the carbonization box for carbonization, and then is dried, ball milled and sieved to obtain modified steel slag. The implementation process of the method is simple, and the effect is obvious. The volume stability of the modified steel slag meets the requirements of relevant standards, and the modified steel slag has good early mechanical properties, and can be used in cement paste, mortar and concrete, so that the utilization rate of the steel slag is greatly improved.

Description

Technical Field

[0001] This invention relates to a method for improving the stability of steel slag under normal temperature and pressure, as well as the resulting products and applications, belonging to the field of building materials technology. Background Technology

[0002] Steel slag is an industrial byproduct generated during the steelmaking process, accounting for approximately 15-20% of steel production. China's annual crude steel production in 2020 was 1.06 Gt, resulting in a steel slag production of 0.16 Gt. However, over 70% of this steel slag was not effectively utilized. Most steel slag is disposed of through landfilling or stockpiling, which not only occupies valuable land resources but also wastes resources.

[0003] With the rapid development of the global economy and industrialization, human demand for energy has increased significantly, leading to the large-scale use of fossil fuels and a continuous increase in atmospheric CO2 concentration, exacerbating the global greenhouse effect. Reducing carbon emissions has become a common global concern. Currently, more than 8% of CO2 emissions are related to cement and concrete production, making the reduction of carbon emissions from the cement industry of significant importance. To this end, many scholars have proposed using steel slag as an auxiliary cementitious material to replace a portion of the cement.

[0004] The main components of steel slag vary depending on the processing technology, but they primarily include tricalcium silicate (C3S), dicalcium silicate (C2S), tetracalcium aluminoferrite (C4AF), calcium iron oxide (C2F), and RO phase, exhibiting certain hydraulic properties and making it suitable for use as a building material. However, the presence of a certain amount of f-CaO within steel slag has led to volume stability issues that have consistently limited its application in the building materials field.

[0005] The stability of steel slag can be addressed through carbonization. Commonly used steel slag carbonization methods can be divided into direct carbonization and indirect carbonization. In direct carbonization, steel slag or its aqueous slurry reacts directly with gaseous CO2. In indirect carbonization, calcium ions are first extracted from the steel slag using appropriate chemicals under acidic conditions, and then the extracted calcium ions are carbonated under alkaline conditions to form calcium carbonate precipitate, achieving carbon fixation. Compared to indirect carbonization, direct carbonization has the advantages of a shorter process and no introduction of new impurities. However, current steel slag carbonization often employs high-temperature or high-pressure methods, which are complex to operate, have high energy costs, and are difficult to promote in practice. Therefore, effectively and conveniently solving the stability problem of steel slag has become a key aspect of its widespread application. Summary of the Invention

[0006] Objectives of the Invention: The first objective of this invention is to provide a method for improving the stability of steel slag under normal temperature and pressure; the second objective of this invention is to provide a modified steel slag obtained by this method; the third objective of this invention is to provide the application of this modified steel slag in the preparation of cement-based materials, thereby expanding the application scope of steel slag in the building materials field.

[0007] Technical Solution: To achieve the above objectives, this invention provides a method for improving the stability of steel slag under normal temperature and pressure, comprising the following steps:

[0008] (1) Grind and sieve the steel slag to obtain steel slag powder;

[0009] (2) Mix water and steel slag powder, stir evenly to obtain steel slag slurry;

[0010] (3) Spread the steel slag slurry from step (2) on the breathable membrane and place it in the carbonization box for carbonization using CO2;

[0011] (4) After carbonization, the steel slag is dried, ball-milled, and sieved to obtain modified steel slag.

[0012] In step (1), the particle size of the steel slag powder is D50≤30μm; the mass of CaO in the steel slag is more than 30%.

[0013] In step (2), the mass ratio of water to steel slag powder is 1 to 1.5:10.

[0014] In step (2), the mixing is carried out in a paste mixer for 3 to 5 minutes.

[0015] In step (3), the CO2 concentration during carbonization is above 20%.

[0016] In step (3), the breathable membrane is one of PTFE waterproof and breathable membrane, ePTFE waterproof and breathable membrane, and PVDF membrane.

[0017] In step (3), the amount of steel slag slurry spread on the breathable membrane is 6-13 kg / m³. 2 .

[0018] In step (3), the carbonization temperature is 20-30℃, the humidity is 60-80%, and the carbonization time is 2-24h.

[0019] In step (4), the drying temperature is above 100°C and the drying time is above 24 hours.

[0020] In step (4), the particle size D50 is controlled to be ≤30μm during sieving.

[0021] The modified steel slag obtained by the method for improving the stability of steel slag under normal temperature and pressure as described in this invention.

[0022] The application of the modified steel slag described in this invention in the preparation of cement.

[0023] Beneficial effects: Compared with the prior art, the present invention has the following significant advantages:

[0024] (1) Compared with the carbonization method under high temperature and high pressure, the present invention carbonizes steel slag at normal temperature and pressure, resulting in stable product quality, safety and reliability, simple equipment and easy operation, which is convenient for practical application in engineering projects.

[0025] (2) In the carbonization process, the f-CaO in the steel slag reacts with CO2 to generate CaCO3, which effectively reduces the f-CaO content in the steel slag and improves the stability of the steel slag.

[0026] (3) The CaCO3 crystal form generated during the carbonization process in this invention is calcite, which has high strength and can improve the early strength of cement-based materials.

[0027] (4) In the carbonization process, the present invention encapsulates CO2 in the form of CaCO3 in the steel slag, which reduces carbon emissions in the production process and is environmentally friendly. Attached Figure Description

[0028] Figure 1 Here is a SEM image of the uncarbonized steel slag in Example 3;

[0029] Figure 2 This is a SEM image of the modified steel slag C after carbonization in Example 3.

[0030] Figure 3 The XRD patterns of steel slag before and after carbonization in Examples 1-6 and Comparative Example 1 are shown. Detailed Implementation

[0031] The technical solution of the present invention will be further described below with reference to the accompanying drawings.

[0032] The chemical composition of the steel slag used in the following examples and comparative examples is shown in Table 1.

[0033] Table 1 Chemical composition of steel slag

[0034]

[0035] In the following examples and comparative examples, the cement material used was P·Ⅰ42.5 type cement produced by Fushun Cement Co., Ltd., whose main oxide components were CaO, SiO2 and Al2O3, and whose main mineral phase components were C3S, C2S, C3A and C4AF.

[0036] In the following examples and comparative examples, the soundness test of steel slag was conducted in accordance with the standards GB / T 1346-2011 "Standard Consistency Water Requirement, Setting Time and Soundness Test Methods for Cement" and GB / T 20491-2017 "Steel Slag Powder for Cement and Concrete".

[0037] In the following examples and comparative examples, the compressive strength test of steel slag-cement paste was conducted in accordance with the standard GB / T 17671-2021, "Test Method for Strength of Cement Mortar".

[0038] Example 1

[0039] 1. The specific implementation process is as follows:

[0040] (1) The steel slag was ball-milled at 400 r / min for 2 h and sieved through a 100 mesh sieve to obtain steel slag powder with a particle size D50≤30μm.

[0041] (2) Weigh 1 part by weight of water and 10 parts by weight of steel slag, mix them together and add them to a paste mixer. First, stir slowly for 150 seconds, then stir quickly for 30 seconds to make them evenly mixed and obtain steel slag slurry.

[0042] (3) The steel slag slurry, after being evenly mixed with water, is spread evenly on a PTFE waterproof and breathable membrane with a pore size of 0.1 μm, and placed in a carbonization box for carbonization under conditions of 20% CO2 concentration, 20℃ temperature, and 70% humidity; the amount of steel slag slurry spread on the breathable membrane is 9.55 kg / m. 2 ;

[0043] (4) After carbonization for 2 hours, the PTFE waterproof and breathable membrane with steel slag is taken out of the carbonization box, the steel slag is poured into a tray and placed in an oven, and dried at 110°C for 24 hours.

[0044] (5) Take the dried steel slag out of the oven, ball mill it at 300 r / min for 4 min, and sieve it through a 100 mesh sieve to control the particle size D50≤30μm to obtain modified steel slag A.

[0045] 2. The stability of modified steel slag A was determined, and the results are shown in Table 2.

[0046] 3. The modified steel slag A obtained was used to replace part of the cement by internal admixture. Cement paste was formed at a water-cement ratio of 0.4 and a steel slag content of 30%. The compressive strength was measured after curing for 3 days and 7 days. The results are shown in Table 2.

[0047] Example 2

[0048] 1. Specific implementation process: Except that the carbonization time is changed to 8 hours, the process is the same as in Example 1, and modified steel slag B is obtained.

[0049] 2. The stability of modified steel slag B was determined, and the results are shown in Table 2.

[0050] 3. The modified steel slag B obtained was used to replace part of the cement by internal admixture. Cement paste was formed at a water-cement ratio of 0.4 and a steel slag content of 30%. The compressive strength was measured after curing for 3 days and 7 days. The results are shown in Table 2.

[0051] Example 3

[0052] 1. Specific implementation process: Except that the carbonization time is changed to 24h, the process is the same as in Example 1, and modified steel slag C is obtained.

[0053] 2. The stability of modified steel slag C was determined, and the results are shown in Table 2.

[0054] 3. The modified steel slag C obtained was used to replace part of the cement by internal admixture. Cement paste was formed at a water-cement ratio of 0.4 and a steel slag content of 30%. The compressive strength was measured after curing for 3 days and 7 days. The results are shown in Table 2.

[0055] Scanning electron microscopy analysis was performed on the uncarburized steel slag and modified steel slag C of this embodiment. The results are as follows: Figure 1-2 As shown. Figure 1 The images shown are SEM images of the uncarbonized steel slag in Example 3; where a is the SEM image at 20 μm and b is the SEM image at 5 μm. Figure 2 The images show SEM images of modified steel slag C after carbonization in Example 3, where a is an SEM image at 20 μm, b is an SEM image at 10 μm, and c is an SEM image at 5 μm. Figures 1-2 It is evident that after carbonization, CaCO3 crystals are formed on the surface of the steel slag, with the crystal form being calcite type, resulting in high strength.

[0056] Example 4

[0057] 1. The specific implementation process is as follows:

[0058] (1) The steel slag was ball-milled at 400 r / min for 2 h and sieved through a 100 mesh sieve to obtain steel slag powder with a particle size D50≤30μm.

[0059] (2) Weigh 1.5 parts by weight of water and 10 parts by weight of steel slag, mix them together and add them to a paste mixer. First, stir slowly for 150 seconds, then stir quickly for 30 seconds to make them evenly mixed and obtain steel slag slurry.

[0060] (3) The steel slag slurry, after being evenly mixed with water, is spread evenly on a PTFE waterproof and breathable membrane with a pore size of 0.1 μm, and placed in a carbonization box for carbonization under conditions of 20% CO2 concentration, 20℃ temperature, and 70% humidity; the amount of steel slag slurry spread on the breathable membrane is 9.55 kg / m. 2;

[0061] (4) After carbonization for 2 hours, the PTFE waterproof and breathable membrane with steel slag is taken out of the carbonization box, the steel slag is poured into a tray and placed in an oven, and dried at 110°C for 24 hours.

[0062] (5) Take the dried steel slag out of the oven, ball mill it at 300 r / min for 4 min, and sieve it through a 100 mesh sieve to control the particle size D50≤30μm to obtain modified steel slag D.

[0063] 2. The stability of modified steel slag D was determined, and the results are shown in Table 2.

[0064] 3. The modified steel slag D obtained was used to replace part of the cement by internal admixture. Cement paste was formed at a water-cement ratio of 0.4 and a steel slag content of 30%. The compressive strength was measured after curing for 3 days and 7 days. The results are shown in Table 2.

[0065] Example 5

[0066] 1. Specific implementation process: Except that the carbonization time is changed to 8h, the process is the same as in Example 4, and modified steel slag E is obtained.

[0067] 2. The stability of modified steel slag E was determined, and the results are shown in Table 2.

[0068] 3. The modified steel slag E obtained was used to replace part of the cement by internal admixture. Cement paste was formed at a water-cement ratio of 0.4 and a steel slag content of 30%. The compressive strength was measured after curing for 3 days and 7 days. The results are shown in Table 2.

[0069] Example 6

[0070] 1. Specific implementation process: Except that the carbonization time is changed to 24h, the process is the same as in Example 4, and modified steel slag F is obtained.

[0071] 2. The stability of modified steel slag F was determined, and the results are shown in Table 2.

[0072] 3. The modified steel slag F obtained was used to replace part of the cement by internal admixture. Cement paste was formed at a water-cement ratio of 0.4 and a steel slag content of 30%. The compressive strength was measured after curing for 3 days and 7 days. The results are shown in Table 2.

[0073] Comparative Example 1

[0074] 1. Specific implementation process: The steel slag is ball-milled at 400 r / min for 2 hours, and then sieved through a 100-mesh sieve. The particle size D50 is controlled to be ≤30μm during sieving to obtain steel slag G.

[0075] 2. The stability of steel slag G was determined, and the results are shown in Table 2.

[0076] 3. The obtained steel slag G was used to replace part of the cement by internal admixture. Cement paste was formed at a water-cement ratio of 0.4 and a steel slag content of 30%. The compressive strength was measured after curing for 3 days and 7 days. The results are shown in Table 2.

[0077] XRD analysis was performed on the steel slag in Examples 1-6 and Comparative Example 1, and the results are as follows: Figure 3 As shown. By Figure 3 It is evident that the intensity of the characteristic peak representing CaCO3 significantly increases, while the characteristic peak representing Ca(OH)2 almost disappears after carbonization, and the intensity of the characteristic peaks representing C2S and C3S decreases. These phenomena indicate that during the carbonization process, C3S, C2S, and Ca(OH)2 in the steel slag react with CO2 to form CaCO3.

[0078] Table 2 compares the stability of steel slag and the early 3-day compressive strength of steel slag-cement paste in the examples and comparative examples.

[0079]

[0080] The stability test results of the steel slag in the above embodiments and comparative examples are shown in Table 2. It can be seen from the test results that the method for improving the stability of steel slag under normal temperature and pressure provided by the present invention has a good effect. The volume stability of the modified steel slag is improved, and the effect of improving the stability of steel slag is more obvious with the extension of carbonization time.

[0081] The compressive strength test results of the above embodiments and comparative examples are shown in Table 2. It can be seen from the test results that, compared with steel slag G (comparative example 1), the 3-day and 7-day compressive strength of the cement paste with modified steel slag of the present invention has been significantly improved. The maximum improvement in 3-day compressive strength is 57.61%, and the maximum improvement in 7-day compressive strength is 46.38%.

[0082] Overall, under the same carbonation time, when the water-to-solid ratio (mass ratio of water to steel slag) during the carbonation process is 0.1, the steel slag stability improvement effect is better, and the cement paste formed by the modified steel slag carbonized at this water-to-solid ratio has higher 3-day and 7-day compressive strength.

Claims

1. A method for improving the stability of steel slag under normal temperature and pressure, characterized in that, Includes the following steps: (1) The steel slag is ball-milled and sieved to obtain steel slag powder; the particle size of the steel slag powder is D50≤30μm; the mass of CaO in the steel slag is more than 30%; (2) Mix water and steel slag powder and stir evenly to obtain steel slag slurry; the mass ratio of water to steel slag powder is 1:10; (3) Spread the steel slag slurry from step (2) evenly on the breathable membrane and place it in the carbonization box for carbonization using CO2; the amount of steel slag slurry spread on the breathable membrane is 9.55 kg / m. 2 The CO2 concentration during carbonization is above 20%, the temperature during carbonization is 20~30℃, the humidity is 60~80%, and the carbonization time is 2~24h. (4) After carbonization, the steel slag is dried, ball-milled, and sieved to obtain modified steel slag.

2. The method for improving the stability of steel slag under normal temperature and pressure according to claim 1, characterized in that, In step (2), the mixing is carried out in a paste mixer for 3 to 5 minutes.

3. The method for improving the stability of steel slag under normal temperature and pressure according to claim 1, characterized in that, In step (3), the breathable membrane is one of PTFE waterproof and breathable membrane, ePTFE waterproof and breathable membrane, and PVDF membrane.

4. The method for improving the stability of steel slag under normal temperature and pressure according to claim 1, characterized in that, In step (4), the drying temperature is above 100°C and the drying time is above 24 hours.

5. The method for improving the stability of steel slag under normal temperature and pressure according to claim 1, characterized in that, In step (4), the particle size D50 is controlled to be ≤30μm during sieving.

6. Modified steel slag obtained by the method for improving the stability of steel slag at room temperature and pressure as described in any one of claims 1-5.

7. The application of the modified steel slag according to claim 6 in the preparation of cement-based materials.

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