A method for preparing high-activity mineral slurry from wet carbonized steel slag

Abstract

A method for preparing a high-activity mineral slurry from wet-process carbonized steel slag, which relates to a method for preparing a mineral slurry, is intended to solve the technical problems of low carbon fixation efficiency and low volcanic ash activity in existing wet-process carbonized steel slag. The method comprises the following steps: first preparing steel slag powder and biochar particles; then adding the biochar, steel slag, and water to a high-pressure reactor, introducing CO2 gas into the reactor, and continuously stirring to obtain a high-activity mineral slurry. The loose and porous structure of the biochar in the present invention also allows for better precipitation of solid CaCO3, thereby improving the carbon fixation efficiency. At the same time, after the outer dense CaCO3 layer is peeled off, the calcium silicate minerals with hydration activity inside the steel slag can also better contact with the water in the slurry, undergoing a hydration reaction, thereby significantly improving the volcanic ash activity of the slurry. The high-activity mineral slurry prepared by the present invention can partially replace cement and improve the early strength of cement-based materials. It can be used in the construction field.

Description

Technical Field

[0001] The invention relates to a preparation method of high-activity mineral slurry based on wet carbonized steel slag. Background Art

[0002] In recent years, the growing greenhouse effect has led to increasingly severe global warming. Carbon capture and storage (CCS) is an important approach to reducing greenhouse gases, and mineral carbon sequestration is an effective method for this purpose. The basic principle of this method is to utilize mineral materials rich in alkali metals such as calcium and magnesium to chemically react with dissolved or ionized CO2; in this process, the CO2 is captured and converted into carbonate precipitates.

[0003] Steel slag is a solid waste produced during the steelmaking process. It is considered to be an ideal mineral carbon fixation material because it contains a large amount of calcium and magnesium compounds. Carbonized steel slag as an auxiliary cementitious material has attracted the attention of many scholars. The existing steel slag carbonization processes can be divided into two categories: dry carbonization and wet carbonization. The dry carbonization process is relatively simple and has low economic costs, but it has shortcomings such as long reaction time, strict requirements on carbonization pressure and humidity, and low carbon fixation efficiency. The wet carbonization process of steel slag is relatively complicated. It requires dispersing the steel slag in water to form a mixed slurry, and then continuously introducing high-concentration CO2 into the slurry.

[0004] As carbonization continues, CaCO3 gradually deposits on the surface of slag particles, forming a dense layer of carbonized products, which affects the hydration and carbonization activity of the slag inside. Therefore, existing wet carbonization technologies suffer from long reaction times and low carbonization efficiency. How to achieve efficient CO2 capture using simple, low-cost wet carbonization technology is a pressing challenge. Summary of the Invention

[0005] The present invention aims to solve the technical problems of low carbon fixation efficiency and low volcanic ash activity in the existing wet carbonized steel slag, and provides a method for preparing a high-activity mineral slurry of wet carbonized steel slag.

[0006] The method for preparing the high-activity mineral slurry of wet-process carbonized steel slag of the present invention is carried out according to the following steps:

[0007] 1. Dry, crush and sieve the steel slag to obtain steel slag powder with a particle size of less than 100 μm; crush and sieve the biochar to obtain biochar particles with a particle size of less than 150 μm;

[0008] 1% to 4% biochar, 10% to 30% steel slag, and 66% to 89% water were weighed by mass and added to a high-pressure reactor equipped with a stirring device. The stirring device was first adjusted to 50 to 100 r / min, and the mixture was stirred at a low speed for 60 ± 2s to ensure preliminary mixing. Then, CO2 gas with a volume percentage concentration of 20% to 99% was introduced into the reactor until the pressure gauge of the reactor showed that the air pressure in the reactor reached 0.5 to 3 MPa, and the ventilation was stopped. The stirring device was then adjusted to 200 to 300 r / min and stirred continuously for 30 to 180 minutes to ensure that the slurry in the reactor and the CO2 gas were fully mixed and reacted. The CO2 gas in the reactor was then released to obtain a highly active mineral slurry.

[0009] Furthermore, the steel slag described in step 1 is electric furnace steel slag, open-hearth steel slag or converter steel slag with a basicity of more than 1.8.

[0010] Furthermore, the biochar described in step one is plant-based biochar prepared from corn stalks, bamboo, reeds, rice husks, and coconut shells.

[0011] In the present invention, carbonization will cause the surface of the steel slag particles to be coated with many CaCO3 particles. After the dense CaCO3 layer is formed, it is difficult for CO2 to react with the internal steel slag particles. However, after adding biochar, much of the CaCO3 produced by carbonization can be scattered into the loose and porous structure of the biochar. After the CaCO3 on the surface of the steel slag particles is peeled off, there is no dense external CaCO3 layer, and CO2 can better contact the internal steel slag particles, so the carbonization efficiency of the steel slag is further improved. In addition, the biochar in the present invention can also play a physical adsorption role for gaseous CO2, but the more important role of biochar is to provide an attachment platform for the precipitated solid CaCO3. The loose and porous structure of the biochar in the present invention also allows solid CaCO3 to precipitate better, so the carbonization efficiency is improved. At the same time, after the dense external CaCO3 layer is peeled off, the calcium silicate minerals with hydration activity inside the steel slag can also better contact with the water in the slurry, and a hydration reaction occurs. Therefore, the pozzolanic activity of the slurry can also be significantly improved. The high-activity mineral slurry prepared by the present invention can partially replace cement and improve the early strength of cement-based materials.

[0012] This invention combines biochar with wet steel slag carbonization technology, using a high-pressure reactor to produce a low-cost, high-carbon-fixing, and highly active mineral slurry that effectively enhances the strength of concrete products. The carbon-fixed mineral slurry is applied to cement concrete. The nucleation and filling effects of the solid CaCO₃ can effectively accelerate the cement hydration process and fill the pores of the product, thereby improving the strength and durability of the concrete, as well as its carbon capture capacity. The highly effective synergistic effect of steel slag and biochar can improve the resource utilization of steel slag and reduce CO₂ emissions from industrial exhaust gases.

[0013] The present invention's substitution of biochar and steel slag for cementitious materials can also effectively reduce the production cost of concrete products. The method is simple to operate, has a short testing time, a wide range of applications, and is relatively low in cost. It significantly improves the strength and carbon sequestration of cement specimens and has potential applications in the construction industry. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 This is a scanning electron microscope photograph of the steel slag powder obtained in step 1 of Example 1;

[0015] Figure 2 This is a scanning electron microscope photograph of the steel slag powder in the highly active mineral slurry obtained in step 2 of Example 1;

[0016] Figure 3 is a scanning electron microscope photograph of the biochar particles obtained in step 1 of Example 1;

[0017] Figure 4 This is a scanning electron microscope photograph of the biochar particles in the highly active mineral slurry obtained in step 2 of Example 1. Implementation Method

[0018] The beneficial effects of the present invention are demonstrated with the following examples.

[0019] Example 1: The method for preparing the high-activity mineral slurry of wet-process carbonized steel slag in this embodiment is carried out according to the following steps:

[0020] First, electric furnace steel slag with a basicity of 1.9 was dried and crushed, and passed through a sieve with an aperture of 80 μm to obtain steel slag fine powder with a particle size of 10 to 80 μm; rice husk biochar particles were crushed and passed through a sieve with an aperture of 150 μm to obtain biochar particles with a particle size of less than 150 μm;

[0021] 2. Weigh 40 grams of rice husk biochar, 600 grams of steel slag and 1600 grams of water and add them to a high-pressure reactor with a stirring device. First, adjust the speed of the stirring device to 80 r / min and stir at low speed for 60 seconds to ensure that the materials are initially mixed evenly; then, introduce CO2 gas with a volume percentage concentration of 99% into the reactor until the pressure gauge of the reactor shows that the air pressure in the reactor reaches 3 MPa. Close the air inlet valve and increase the speed of the stirring device to 250 r / min. Continue stirring for 120 minutes to allow the slurry in the reactor to fully mix and react with the CO2 gas. Then release the CO2 gas in the reactor body. After the pressure inside the reactor body returns to atmospheric pressure, pour out the slurry in the reactor to obtain a highly active mineral slurry, which is then sealed and stored.

[0022] Control group 1: The slurry of this control group was prepared according to the following steps:

[0023] 1. Dry and crush the electric furnace steel slag with a basicity of 1.9, and pass it through a sieve with an aperture of 80 μm to obtain steel slag powder with a particle size of 10 ~ 80 μm;

[0024] 2. Weigh 640 g of steel slag and 1600 g of water and mix them evenly to obtain control slurry No. 1.

[0025] Control group 2: The slurry of this control group was prepared according to the following steps:

[0026] 1. Dry and crush the electric furnace steel slag with a basicity of 1.9, and pass it through a sieve with an aperture of 80 μm to obtain steel slag powder with a particle size of 10 ~ 80 μm;

[0027] 2. Weigh 640 grams of steel slag and 1600 grams of water and add them to a high-pressure reactor with a stirring device. First, adjust the speed of the stirring device to 80 r / min and stir at low speed for 60 seconds to ensure that the materials are initially mixed evenly; then, introduce CO2 gas with a volume percentage concentration of 99% into the reactor until the pressure gauge of the reactor shows that the air pressure in the reactor reaches 3 MPa. Close the air inlet valve and increase the speed of the stirring device to 250 r / min. Continue stirring for 120 minutes to allow the slurry in the reactor to be fully mixed and reacted with the CO2 gas, and then release the CO2 gas in the reactor to obtain control slurry No. 2.

[0028] Control group 3: The slurry of this control group was prepared according to the following steps:

[0029] First, electric furnace steel slag with a basicity of 1.9 was dried and crushed, and passed through a sieve with an aperture of 80 μm to obtain steel slag fine powder with a particle size of 10 to 80 μm; rice husk biochar particles were crushed and passed through a sieve with an aperture of 150 μm to obtain biochar particles with a particle size of less than 150 μm;

[0030] 2. Weigh 40 grams of rice husk biochar, 600 grams of steel slag and 1600 grams of water according to mass percentage and mix them evenly to obtain mineral slurry No. 3.

[0031] The scanning electron microscope photograph of the steel slag powder obtained in step 1 of this embodiment 1 is as follows: Figure 1 As shown, from Figure 1 It can be seen that before carbonization, the surface of the slag particles is smooth and dense, with clear corners and edges.

[0032] The scanning electron microscope photograph of the steel slag powder in the high-activity mineral slurry obtained in step 2 of this embodiment 1 is as follows: Figure 2 As shown, from Figure 2 It can be seen that the surface of the steel slag has undergone obvious changes. The original two-dimensional plane has expanded into a three-dimensional curved surface, which is covered with tiny CaCO3 particles and is rough and uneven overall.

[0033] The scanning electron microscope photograph of the biochar particles obtained in step 1 of this embodiment 1 is as follows Figure 3 As shown, from Figure 3 It can be seen that the interior and surface of biochar particles are loose and porous, with a large number of holes and channels.

[0034] The scanning electron microscope photograph of the biochar particles in the highly active mineral slurry obtained in step 2 of this embodiment 1 is as follows: Figure 4 As shown, from Figure 4 It can be seen that much of the CaCO3 produced by carbonization can be scattered into the loose and porous structure of biochar.

[0035] The slurries prepared in Example 1 and Comparative Groups 1, 2, and 3 were subjected to TG-DTG testing to obtain the amount of CO2 contained in every 100 g of slurry, which is listed in Table 1. The slurries prepared in Example 1 and Comparative Groups 1, 2, and 3 were each uniformly mixed with 3360 g of cement without adding additional water to prepare cement specimens. After standard curing for 7 days, the strength of the cement specimens was tested, and the results are also shown in Table 1. The resulting carbonization-activated slurries were used.

[0036] Table 1 Properties of slurries prepared in Example 1 and comparison groups 1, 2, and 3

[0037]

[0038] Comparing the data in Table 1, it can be seen that the slurry prepared in Example 1 has a high carbon fixation capacity and a good effect on improving the activity of cement specimens. In Example 1, the porous structure of biochar and the large number of surface functional groups make it an excellent CO2

[0039] Capture material, adding an appropriate amount of biochar during the wet carbonization process of steel slag can not only adsorb more CO2 into the steel slag slurry, but also provide new nucleation sites for CaCO3 originally attached to the surface of the steel slag particles. After the CaCO3 originally tightly wrapped on the surface of the steel slag particles migrates into the pores of the biochar, the calcium ions inside the steel slag can be smoothly leached, and the carbonization efficiency and hydration activity of the steel slag can be further improved. The biochar-steel slag high-activity mineral slurry can not only significantly improve the early strength of the cement specimens, but also effectively increase the CO2 capture capacity of the specimens under the same conditions.

Claims

1. A method for preparing a high-activity mineral slurry of wet-process carbonized steel slag, characterized in that: The method proceeds as follows:

1. Dry, crush and sieve the steel slag to obtain steel slag powder with a particle size of less than 100 μm; crush and sieve the biochar to obtain biochar particles with a particle size of less than 150 μm; 2. Weigh 1% to 4% biochar, 10% to 30% steel slag, and 66% to 89% water by mass and add them to a high-pressure reactor with a stirring device. First, adjust the speed of the stirring device to 50 to 100 r / min and stir at a low speed for 60 ± 2s to mix the materials uniformly. Then, introduce CO2 gas with a volume percentage concentration of 20% to 99% into the reactor until the pressure gauge of the reactor shows that the air pressure in the reactor reaches 0.5 to 3 MPa, and then stop ventilation. Then adjust the speed of the stirring device to 200 to 300 r / min and continue stirring for 30 to 180 minutes to fully mix and react the slurry in the reactor with the CO2 gas, and then release the CO2 gas in the reactor to obtain a highly active mineral slurry. The steel slag described in step 1 is electric furnace steel slag, open-hearth steel slag or converter steel slag with a basicity of more than 1.

8.

2. The method for preparing a high-activity mineral slurry from wet carbonized steel slag according to claim 1, characterized in that: The biochar described in step 1 is plant-based biochar prepared from corn stalks, bamboo, reeds, rice husks, and coconut shells.

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