Method for improving stability of steel slag based on dissolved oxygen regulation

Abstract

This invention relates to the field of solid waste application technology, and particularly to a method for improving the stability of steel slag based on dissolved oxygen regulation using microorganisms. The method includes the following steps: crushing and screening waste steel slag, washing, drying, sterilizing, and drying to constant weight to obtain steel slag aggregate; preparing a liquid culture medium, adjusting the pH value of the liquid culture medium to be approximately equal to the pH value of the steel slag aggregate; inoculating microorganisms into the liquid culture medium for cultivation; centrifuging the cultured microbial solution; diluting the bacterial sludge with 0.9% physiological saline or resuspending it with a sterilized 5g / L yeast extract solution; adjusting the OD600 value of the bacterial solution to 0.8~1.2; using a vacuum negative pressure adsorption device and surface spraying to ensure full contact between the bacterial solution and the steel slag aggregate and adsorption to saturation; preparing a mineralizing nutrient solution to mineralize the steel slag aggregate after adsorption of the bacterial solution, resulting in stabilized steel slag aggregate. This invention utilizes a microbial dissolved oxygen response regulation strategy to maximize and improve the stabilization efficiency of microbially modified steel slag.

Description

Technical Field

[0001] This invention relates to the field of solid waste application technology, and in particular to a method for improving the stability of steel slag based on dissolved oxygen regulation using microorganisms. Background Technology

[0002] The steel industry is an energy-intensive industry and a pillar industry of the national economy. Steel slag is a large-scale alkaline solid waste generated in the steelmaking industry. It is grayish-brown, microporous, dense, and heavy. Every ton of crude steel produced generates 0.1-0.15 tons of steel slag and emits 1.85 tons of carbon dioxide. As a major steel producer, China's annual steel slag emissions exceeded 150 million tons by 2024, with a cumulative stockpile exceeding 2 billion tons. Due to the complex composition, large quality fluctuations, poor stability, and low activity of steel slag, its resource utilization rate is less than 30%. The high content of free oxides in steel slag reacts with water or water vapor, resulting in significant volume expansion. This characteristic makes it difficult to use steel slag and its treated tailings for large-scale building material production, thus affecting the comprehensive utilization rate of steel slag and leading to large-scale stockpiling. If not properly disposed of, it will cause serious environmental and social harm, and the harmful elements and substances in steel slag will also have adverse effects on the ecological environment and human health.

[0003] In existing technologies, the utilization of steel slag as a building material requires improved volume stability. The key lies in inhibiting or transforming its unstable components, such as free oxides. Steel slag mineralization technology accelerates its reaction with carbon dioxide to generate stable carbonate minerals, thereby directly reducing the risk of expansion and improving volume stability.

[0004] Currently, methods for improving volume stability mainly include mechanical grinding, high-temperature activation, alkali activation, acid activation, organic activation, and carbonation activation. For example, mechanical grinding physically disrupts the crystal structure of steel slag, reduces particle size, and increases specific surface area, thereby promoting hydration reactions. High-temperature activation, alkali activation, acid activation, organic activation, and carbonation activation alter the state of steel slag, making it more active and facilitating mineralization reactions. In particular, the method of microbial-induced carbonate precipitation utilizes the metabolic activity of microorganisms to drive the carbonate mineralization process, with the microbial metabolism producing CO3. 2− The technique of combining with free cations in the environment to form carbonate precipitates utilizes the negative charge on the surface of microorganisms, which allows them to spontaneously combine with free positive ions in the environment, especially in saturated environments, to form carbonate mineralization, thus playing a stabilizing role. However, the modification process involved in mineralization has problems such as low reaction efficiency, long reaction cycle, and difficulty in control. Summary of the Invention

[0005] The purpose of this invention is to provide a method for improving the stability of steel slag based on dissolved oxygen regulation using microorganisms, so as to solve the problems mentioned in the background art.

[0006] To achieve the above objectives, the present invention provides the following technical solution: A method for improving the stability of steel slag based on dissolved oxygen regulation by microorganisms includes the following steps: S1: The waste steel slag is crushed, ground, and screened to obtain steel slag aggregates of different grades; the required grade of steel slag aggregate is selected and the floating ash is cleaned using ultrasonic equipment; it is dried, sterilized, and dried to constant weight before being cooled to room temperature; S2: Prepare the appropriate liquid culture medium according to the type of microorganism to be used for modification, and sterilize the liquid culture medium. Adjust the pH value of the liquid culture medium to be approximately equal to the pH value of the steel slag aggregate using a 1 mol / L sodium hydroxide solution. S3: Inoculate the microorganisms into the corresponding liquid culture medium according to their type and culture them to obtain the corresponding microbial inoculum. The microorganisms are urease-producing bacteria, aerobic lactobacilli, or denitrifying bacteria. S4: Centrifuge the cultured microbial solution in a centrifuge to separate the bacterial solution. Dilute the bacterial sludge at the bottom of the test tube with 0.9% physiological saline or resuspend it with a sterilized 5g / L yeast extract solution. Adjust the OD600 value of the bacterial solution to 0.8~1.2 to obtain the corresponding bacterial solution for steel slag modification. S5: The bacterial solution for steel slag modification is applied using a vacuum negative pressure adsorption device and surface spraying to ensure that the steel slag aggregate is fully in contact with and adsorbed to saturation; the corresponding mineralization nutrient solution is prepared according to the type of microorganism to be used for modification, and the steel slag aggregate after adsorbing the bacterial solution for steel slag modification is mineralized using the mineralization nutrient solution. S6: Based on the type of microorganism, a mineralization oxygenation method is adopted. The mineralization oxygenation method involves adding calcium peroxide oxygenating agent, pure oxygen, or air to the mineralization nutrient solution to adjust the dissolved oxygen content of the mineralization environment to be greater than or equal to the set value. The dissolved oxygen meter is used to monitor in real time to ensure that the dissolved oxygen content of the environment is sufficient during the modification process. The steel slag aggregate modified with bacterial solution after mineralization is rinsed with clean water and dried to constant weight to obtain stabilized steel slag aggregate.

[0007] Preferably, the vacuum adsorption device in S5 is equipped with an automatic spraying device. The automatic spraying device can evenly spray the bacterial solution for steel slag modification onto the steel slag aggregate, and fully adsorb it under negative pressure. The automatic spraying device controls the bacterial solution for steel slag modification to spray once at a set interval, and the total number of sprays is greater than or equal to 12.

[0008] Preferably, the method for mineralizing and oxygenating steel slag aggregate for adsorbing urease-producing bacteria involves adding calcium peroxide to the mineralization nutrient solution at a dosage of 30 g / m³. 3The mineralization and oxygenation method for steel slag aggregate used to adsorb aerobic lactic acid bacteria involves introducing pure oxygen into the mineralization nutrient solution at a rate of approximately 1-2 L / min. The mineralization and oxygenation method for steel slag aggregate used to adsorb denitrifying bacteria involves introducing air into the mineralization nutrient solution at a rate of approximately 20-30 L / min.

[0009] Preferably, in S1, the fine aggregate particles have a particle size of less than 4.75 mm, the medium-coarse aggregate particles have a particle size of 4.75-9.5 mm, and the extra-coarse aggregate particles have a particle size of 9.5-19.0 mm.

[0010] Preferably, the urease-producing bacteria is one of Bacillus pasteurellii, Bacillus spheroides, or Bacillus subtilis; the aerobic lactobacillus is one of Bacillus coli or Bacillus pseudostrongylus; and the denitrifying bacteria is Pseudomonas aeruginosa.

[0011] Preferably, the liquid culture medium for urease-producing bacteria is prepared by mixing 3-8 g / L soybean peptone, 4-6 g / L sodium chloride, 10-20 g / L tryptone, and 10-30 g / L urea, sterilizing in an autoclave at 121°C, and then adjusting the pH to 12 with sodium hydroxide solution; the liquid culture medium for aerobic lactobacillus is prepared by mixing 5-10 g / L yeast extract, 5-10 g / L sodium chloride, and 10-15 g / L tryptone, sterilizing, and then adjusting the pH to 11 with sodium hydroxide solution; the liquid culture medium for denitrifying bacteria is prepared by mixing 2-3 g / L potassium nitrate, 0.2-0.5 g / L magnesium sulfate heptahydrate, 20-25 g / L potassium sodium tartrate tetrahydrate, and 0.5-0.8 g / L potassium dihydrogen phosphate, sterilizing, and then adjusting the pH to 10 with sodium hydroxide solution.

[0012] Preferably, the amount of microorganisms in S3 is 1%~1.5%; the liquid culture medium is shaken and cultured in a full-temperature shaker at a constant temperature of 30-40℃ for 48-72 hours.

[0013] Preferably, the centrifugation time of the microbial culture is set to 8-12 min, and the centrifugation speed is set to 4000-6000 r / min.

[0014] Preferably, the mineralized nutrient solution used for adsorbing urease-producing bacteria in steel slag aggregate has the following composition: 1-2 mol / L urea and 1-2 mol / L calcium nitrate; the mineralized nutrient solution used for adsorbing aerobic lactic acid bacteria in steel slag aggregate has the following composition: 0.5-1.5 mol / L lactic acid, 0.2-0.5 mol / L calcium nitrate and 0.2-0.5 mol / L calcium lactate; and the mineralized nutrient solution used for adsorbing denitrifying bacteria in steel slag aggregate has the following composition: 0.8-1.2 mol / L acetic acid, 0.3-0.5 mol / L sucrose and 0.5-0.8 mol / L calcium nitrate.

[0015] Compared with the prior art, the present invention has the following beneficial effects: This invention provides a method for improving the stability of steel slag based on dissolved oxygen regulation by microorganisms. Based on the dissolved oxygen response regulation of microorganisms, it adopts microorganisms such as urease-producing bacteria, aerobic lactobacilli and denitrifying bacteria. The growth and proliferation activity and mineralization reaction rate of the microorganisms are dominated by the dissolved oxygen content in the saturated environment. Vacuum adsorption, soaking and spraying strategies are used to fully combine the bacterial solution and steel slag, which greatly shortens the modification and stabilization cycle.

[0016] This invention provides a method for improving the stability of steel slag using microorganisms based on dissolved oxygen regulation. Compared to low-oxygen natural environments, the modification cycle is reduced under saturated dissolved oxygen conditions, maximizing and improving the stabilization efficiency of microbially modified steel slag, while avoiding the high-temperature and high-pressure reaction conditions of traditional steel slag disposal strategies. Furthermore, some extracellular polymers secreted by microorganisms during their growth can undergo complexation reactions with metal ions in the steel slag, forming crystal nuclei on or around the microbial cell surface. This causes the metal ions to precipitate as minerals, filling the pores of the steel slag and forming a dense structure. This restricts the expansion space of residual free oxides, indirectly promoting the volume stabilization of the steel slag.

[0017] This invention provides a method for improving the stability of steel slag based on dissolved oxygen regulation using microorganisms. Microbial dissolved oxygen response regulation significantly improves stability and increases comprehensive utilization, reducing the risks associated with the application of steel slag aggregate in building materials. Furthermore, the process of stabilizing steel slag using microbial technology does not involve high-temperature and high-pressure reactions, resulting in high efficiency, low energy consumption, and no secondary pollution, effectively reducing the environmental harm caused by steel slag. Simultaneously, microbial treatment of steel slag can also reduce carbon dioxide emissions, thus having a certain carbon reduction effect. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the process for improving the stability of steel slag using microorganisms based on dissolved oxygen regulation, as described in this invention. Detailed Implementation

[0019] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0020] In the following description of the invention, it should be noted that the terms "upper," "lower," "left," "right," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, and are only for the convenience of describing the invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation or be constructed and operated in a specific orientation. The term "connection" simply indicates a connection between devices and has no special meaning.

[0021] Furthermore, the technical fields and installation methods involved in the embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0022] Example 1 A method for improving the stability of steel slag based on dissolved oxygen regulation by microorganisms includes the following steps: S1: The waste steel slag is crushed, ground, and screened to obtain fine aggregate particles of different grades; the fine aggregate particles are cleaned of floating ash using ultrasonic equipment; dried, sterilized, and dried to constant weight before being cooled to room temperature; Specifically, the raw steel slag blocks are crushed, ground, and screened to obtain fine aggregate particles with a particle size of less than 4.75 mm. The screening process removes impurities and ensures that the fine aggregate particles are of uniform size, which is conducive to the full contact between microorganisms and fine aggregate particles.

[0023] Specifically, the fine aggregate particles are rinsed with an ultrasonic cleaner with a frequency of 16kHz to remove surface dust, dirt and other impurities. The cleaned fine aggregate particles are then placed in an oven with a temperature controlled at 105℃±5℃ and dried to constant weight. After that, they are taken out and cooled to room temperature.

[0024] S2: Prepare a liquid culture medium according to the urease-producing strain to be used for modification, and sterilize the liquid culture medium. Adjust the pH value of the liquid culture medium to be approximately equal to the pH value of the fine aggregate particles using a 1 mol / L sodium hydroxide solution. Specifically, the liquid culture medium is prepared by mixing 5 g / L soybean peptone, 15 g / L tryptone, 5 g / L sodium chloride, and 20 g / L urea evenly, and then sterilizing the liquid culture medium and experimental vessels using a high-pressure steam sterilizer. The sterilization conditions are set at a temperature of 121°C and a time of 15-20 min. The pH value of the liquid culture medium is adjusted with a 1 mol / L sodium hydroxide solution. The pH value of the liquid culture medium is the same as that of the fine aggregate particle leachate. In this example, the pH value of the fine aggregate particle leachate is approximately 12. S3: Inoculate urease-producing bacteria into liquid culture medium and culture them to obtain a well-cultured microbial solution; Specifically, after high-temperature sterilization, urease-producing bacteria, such as Bacillus pasteurellii, Bacillus spheroides, or Bacillus subtilis, are inoculated into liquid culture medium at an inoculation rate of 1% in an ultra-clean workbench. Furthermore, the inoculated liquid culture medium was cultured in a full-temperature shaker at a constant temperature of 30°C for 48 hours, with the shaker speed set to 120 r / min.

[0025] S4: Centrifuge the cultured microbial solution in a centrifuge to separate the bacterial solution. Dilute the bacterial sludge at the bottom of the test tube with 0.9% physiological saline and adjust the OD600 value of the bacterial solution to 1.0 to obtain the bacterial solution for steel slag modification. Specifically, after the microbial culture is cultured, it is taken out and centrifuged in a centrifuge for 10 minutes. The centrifuge speed is set to 6000 r / min. After centrifugation, the bacterial sludge at the bottom of the test tube is diluted with 0.9% physiological saline. Finally, the OD600 value of the bacterial culture is tested with an ultraviolet spectrophotometer and adjusted to 1.0 as required for the experiment. The bacterial culture for steel slag modification used in the experiment can then be obtained.

[0026] S5: The bacterial solution for steel slag modification is used with a vacuum negative pressure adsorption device to ensure that the fine aggregate particles are fully contacted and adsorbed to saturation. A mineralized nutrient solution is prepared for adsorbing fine aggregate particles of urease-producing bacteria. The mineralized nutrient solution is used to mineralize the fine aggregate particles after adsorbing the bacterial solution for steel slag modification. Specifically, fine aggregate particles cooled to room temperature are placed in a vacuum adsorption device equipped with an automatic spraying system. This system evenly sprays the steel slag modification bacterial solution onto the fine aggregate particles. The spraying interval is 1 hour per cycle, with a total of 12 sprays or more. The pressure inside the vacuum adsorption device is reduced to -0.1 MPa to create a negative pressure environment. This negative pressure environment removes air from the surface of the fine aggregate particles and the surrounding microorganisms, allowing the microorganisms to adhere more tightly to the surface of the fine aggregate particles. This increases the contact area and bonding force between the two, which helps the microorganisms to colonize and grow better on the fine aggregate particles, thus more efficiently exerting the stabilizing effect of the microorganisms on the steel slag.

[0027] Under negative pressure, the automatic spraying equipment is turned on so that the bacterial solution for steel slag modification is evenly sprayed onto the surface of the fine aggregate particles until the bacterial solution for steel slag modification covers the fine aggregate particles. After 15-30 minutes, the fine aggregate particles that have absorbed the bacterial solution for steel slag modification are taken out. In this embodiment, the adsorption time is set to 20 minutes.

[0028] The fine aggregate particles after adsorbing the bacterial solution for steel slag modification were placed in a constant temperature water bath, and a prepared mineralization nutrient solution was added. In this embodiment, the mineralization nutrient solution was prepared using 1 mol / L urea and 1 mol / L calcium nitrate. The mineralization nutrient solution provides the substances required for the mineralization of the fine aggregate particles after adsorbing the bacterial solution for steel slag modification. The temperature inside the constant temperature water bath was maintained at 30°C, and the mineralization was enhanced for 3 days.

[0029] S6: Calcium peroxide oxygenating agent is used to adjust the dissolved oxygen content of the mineralization environment to be greater than or equal to 3mg / L to ensure sufficient dissolved oxygen content during the modification process; the fine aggregate particles of the mineralized adsorbed steel slag modified with bacterial solution are washed with clean water and dried to constant weight to obtain stabilized steel slag aggregate.

[0030] Specifically, to ensure mineralization efficiency and improve the stabilization rate of steel slag, it is necessary to ensure sufficient dissolved oxygen in the environmental medium during the modification process to enhance the reactivity of mineralizing bacteria; calcium peroxide oxygenating agent is added to the mineralization nutrient solution at a dosage of approximately 30 g / m³. 3 To ensure that the dissolved oxygen level in the environment is not less than 3 mg / L during the modification process, a dissolved oxygen meter is used for real-time monitoring to ensure sufficient dissolved oxygen in the reaction medium and provide an additional calcium source, which greatly reduces the modification cycle of fine aggregate particles under normal temperature and pressure for microbial mineralization and stabilization.

[0031] Furthermore, after drying the steel slag aggregate to constant weight, basic performance tests were conducted on its water absorption rate, apparent density, and crushing index. The results showed that during the 3-day modification process, the water absorption rate decreased by 76.13%, and the apparent density increased by 133.7 kg / m³. 3 The crushing index of fine aggregate particles with gradations of 1.18-2.36mm and 2.36-4.75mm was reduced by 64.6% and 19.5%, respectively. Under the same mix proportion, the concrete prepared by microbially modified steel slag showed an increase of 21% and 6% in compressive strength at 7 days and 28 days, respectively, compared with the concrete prepared by natural crushed stone and river sand. No cracking caused by poor stability occurred after boiling at 105℃ for 3 hours. The test results are compared with the basic properties of unmodified fine aggregate particles in Table 1. Table 1. Comparison of basic properties of microbially modified steel slag and unmodified fine aggregate particles

[0032] Based on the above-mentioned equal proportions, the steel slag aggregate is mineralized and modified using urease-producing bacteria. When the dissolved oxygen content of the environmental medium is not controlled during the modification process, the mineralization treatment time is 5-7 days. Ensuring sufficient dissolved oxygen in the environmental medium during the modification process greatly reduces the modification cycle by 70%.

[0033] Example 2 A method for improving the stability of steel slag based on dissolved oxygen regulation by microorganisms includes the following steps: S1: The waste steel slag is crushed, ground, and screened to obtain medium and coarse aggregate particles of different grades; the medium and coarse aggregate particles are cleaned of floating ash using ultrasonic equipment; dried, sterilized, and dried to constant weight before being cooled to room temperature; Specifically, the steel slag raw material blocks are crushed, ground, and screened to obtain medium-coarse aggregate particles with a particle size of 4.75-9.5mm. The screening process removes impurities and ensures that the medium-coarse aggregate particles are of uniform size, which is conducive to the full contact between microorganisms and the medium-coarse aggregate particles.

[0034] Specifically, the medium and coarse aggregate particles are rinsed with an ultrasonic cleaner with a frequency of 24kHz to remove surface dust, dirt and other impurities. The cleaned medium and coarse aggregate particles are then placed in an oven with a temperature controlled at 105℃±5℃ and dried to constant weight. After that, they are taken out and cooled to room temperature.

[0035] S2: Prepare a liquid culture medium based on the aerobic lactic acid bacteria to be used in the modification, and sterilize the liquid culture medium. Adjust the pH value of the liquid culture medium to be approximately equal to the pH value of the aggregate particles using a 1 mol / L sodium hydroxide solution. Specifically, the liquid culture medium is prepared by mixing 8 g / L yeast extract, 5 g / L sodium chloride, and 15 g / L tryptone evenly, and then sterilizing the liquid culture medium and experimental vessels using a high-pressure steam sterilizer. The sterilization conditions are set at a temperature of 121°C and a time of 20 min. The pH of the liquid culture medium is adjusted to be consistent with the pH of the leachate from the coarse and medium aggregate particles using a 1 mol / L sodium hydroxide solution. In this example, the pH of the leachate from the coarse aggregate particles is approximately 11. S3: Inoculate aerobic lactobacilli into liquid culture medium and culture them to obtain a well-cultured microbial solution; Specifically, after high-temperature sterilization, aerobic lactobacilli, such as Bacillus coli and Bacillus pseudostrongylus, are inoculated into liquid culture medium at an inoculation rate of 1.5% in an ultra-clean workbench.

[0036] Furthermore, the inoculated liquid culture medium was cultured in a full-temperature shaker at a constant temperature of 30°C for 48 hours, with the shaker speed set to 120 r / min.

[0037] S4: Centrifuge the cultured microbial solution in a centrifuge to separate the microbial solution, resuspend it in a sterilized 5g / L yeast extract solution, and adjust the OD600 value of the microbial solution to 1.0 to obtain the microbial solution for steel slag modification. Specifically, after the microbial culture is cultured, it is taken out and centrifuged in a centrifuge for 10 minutes at a speed of 5000 r / min. After centrifugation, the bacterial sludge at the bottom of the test tube is resuspended in a sterilized yeast extract solution with a concentration of 5 g / L. The OD600 value of the bacterial culture is measured and adjusted to 1.0 as required for the experiment using an ultraviolet spectrophotometer to obtain the bacterial culture for steel slag modification used in the experiment.

[0038] S5: The bacterial solution for steel slag modification is used with a vacuum negative pressure adsorption device to ensure that the medium and coarse aggregate particles are fully contacted and adsorbed to saturation. A mineralized nutrient solution is prepared for adsorbing the medium and coarse aggregate particles of aerobic lactic acid bacteria. The mineralized nutrient solution is used to mineralize the medium and coarse aggregate particles after adsorbing the bacterial solution for steel slag modification. Specifically, medium and coarse aggregate particles cooled to room temperature are placed in a vacuum adsorption device. An automatic spraying device can evenly spray the bacterial solution for steel slag modification onto the medium and coarse aggregate particles. The spraying interval of the automatic spraying device is 1 hour / time, and the total number of spraying times is greater than or equal to 12 times. The pressure inside the vacuum adsorption device is pumped to -0.06MPa. After vacuum adsorption for 20 minutes, the medium and coarse aggregate particles adsorbed with the bacterial solution for steel slag modification are taken out. The medium and coarse aggregate particles after adsorbing the bacterial solution for steel slag modification were placed in a glass tank in a constant temperature water bath, and a prepared mineralization nutrient solution was added. In this embodiment, the mineralization nutrient solution consisted of 0.5 mol / L lactic acid, 0.2 mol / L calcium nitrate, and 0.2 mol / L calcium lactate. The mineralization nutrient solution provided the substances required for the mineralization of the medium and coarse aggregate particles after adsorbing the bacterial solution for steel slag modification. The solution temperature in the tank was kept constant at 33°C, and the mineralization was enhanced for 3 days.

[0039] S6: Pure oxygen is used to adjust the dissolved oxygen content of the mineralization environment to be greater than or equal to 3mg / L to ensure sufficient dissolved oxygen content during the modification process; the medium and coarse aggregate particles of the mineralized adsorbed steel slag modified with bacterial solution are washed with clean water and dried to constant weight to obtain stabilized steel slag aggregate.

[0040] Furthermore, to ensure mineralization efficiency and improve the stabilization rate of steel slag, it is necessary to ensure sufficient dissolved oxygen in the environmental medium during the modification process to enhance the reactivity of mineralizing bacteria. Pure oxygen is introduced into the reaction mineralization nutrient solution using a pure oxygen cylinder and flow meter at a rate of approximately 1-2 L / min to ensure that the dissolved oxygen content in the environment during the modification process is not less than 3 mg / L. A dissolved oxygen meter is used for real-time monitoring to ensure sufficient dissolved oxygen in the reaction medium and full reaction of dissolved calcium sources in the environmental medium, which greatly reduces the modification cycle of steel slag under normal temperature and pressure microbial mineralization stabilization.

[0041] Furthermore, after drying the steel slag aggregate to constant weight, basic performance tests were conducted on its water absorption rate, apparent density, and crushing index. The results showed that during the 3-day modification process, the water absorption rate decreased by 65.19%, and the bulk density increased by 122.6 kg / m³.3 The crushing index decreased by 57.1%. Under the same mix proportion, the concrete prepared by microbially modified steel slag showed a 6% and 34% increase in compressive strength at 7 days and 28 days, respectively, compared with the concrete prepared by natural crushed stone and river sand. No cracking caused by poor stability occurred after boiling at 105℃ for 3 hours. The test results are compared with the basic properties of unmodified medium and coarse aggregate particles in Table 2.

[0042] Table 2. Comparison of basic properties of microbially modified steel slag and unmodified medium and coarse aggregate particles parameter Water absorption rate (%) <![CDATA[Apparent density (kg / m 3 )]]> Crushing index (%) 7-day compressive strength of concrete (MPa) 28-day compressive strength of concrete (MPa) Medium and coarse aggregate particles 1.35 3430 14.7 36.5 46.6 Microbial modified steel slag 0.47 3552.6 6.3 38.7 62.2 Based on the above-mentioned equivalent proportions, the steel slag aggregate is mineralized and modified using aerobic lactic acid bacteria. When the dissolved oxygen content of the environmental medium is not controlled during the modification process, the mineralization treatment time is 5-7 days. Ensuring sufficient dissolved oxygen in the environmental medium during the modification process greatly reduces the modification cycle by 70%.

[0043] Example 3 A method for improving the stability of steel slag based on dissolved oxygen regulation by microorganisms includes the following steps: S1: The waste steel slag is crushed, ground, and screened to obtain extra-coarse aggregate particles of different grades; the extra-coarse aggregate particles are washed with running water to remove floating ash; dried, sterilized, and dried to constant weight before being cooled to room temperature; Specifically, the steel slag raw material blocks are crushed, ground, and screened to obtain extra-coarse aggregate particles with a particle size of 9.5-19.0 mm. The screening process removes impurities and ensures that the extra-coarse aggregate particles are of uniform size, which is conducive to the full contact between microorganisms and extra-coarse aggregate particles.

[0044] The surface dust of the extra-coarse aggregate particles is washed with running water, and then dried and sterilized in a constant temperature drying oven at 105℃±5℃. After drying to constant weight, the particles are removed and cooled to room temperature.

[0045] S2: Prepare a liquid culture medium according to the denitrifying bacteria to be used in the modification, and sterilize the liquid culture medium. Adjust the pH value of the liquid culture medium to be approximately equal to the pH value of the extra coarse aggregate particles using a 1 mol / L sodium hydroxide solution. Specifically, the liquid culture medium is prepared by mixing 2 g / L potassium nitrate, 0.2 g / L magnesium sulfate heptahydrate, 20 g / L sodium potassium tartrate tetrahydrate, and 0.5 g / L potassium dihydrogen phosphate until homogeneous. The liquid culture medium and experimental vessels are then sterilized using a high-pressure steam sterilizer at 121°C for 20 minutes. The pH of the liquid culture medium is adjusted to match the pH of the leachate from the extra-coarse aggregate particles using a 1 mol / L sodium hydroxide solution. In this example, the pH of the leachate from the extra-coarse aggregate particles is approximately 10. S3: Inoculate denitrifying bacteria into liquid culture medium and culture them to obtain a cultured microbial solution; Specifically, after high-temperature sterilization, denitrifying bacteria such as Pseudomonas aeruginosa are inoculated into liquid culture medium at an inoculation rate of 1.5% in an ultra-clean workbench.

[0046] Furthermore, the inoculated liquid culture was cultured in a full-temperature shaker at a constant temperature of 30°C for 48 hours, with the shaker speed set to 120 r / min.

[0047] S4: Centrifuge the cultured microbial solution in a centrifuge to separate the microbial solution, resuspend it in a sterilized 5g / L yeast extract solution, and adjust the OD600 value of the microbial solution to 1.0 to obtain the microbial solution for steel slag modification. Specifically, after the microbial culture is cultured, it is taken out and centrifuged in a centrifuge for 10 minutes at a speed of 5000 r / min. After centrifugation, the bacterial sludge layer at the bottom of the test tube is resuspended in a sterilized yeast extract solution with a concentration of 5 g / L. The OD600 value of the bacterial culture is measured and adjusted to 1.0 as required for the experiment using an ultraviolet spectrophotometer to obtain the bacterial culture for steel slag modification used in the experiment.

[0048] S5: Use a surface spraying device to ensure that the extra-coarse aggregate particles are fully contacted and adsorbed to saturation by the bacterial solution for steel slag modification. Prepare a mineralized nutrient solution for adsorbing the extra-coarse aggregate particles of denitrifying bacteria. Use the mineralized nutrient solution to mineralize the extra-coarse aggregate particles after adsorbing the bacterial solution for steel slag modification. Specifically, the extra-coarse aggregate particles cooled to room temperature are placed in a vacuum adsorption device. An automatic spraying device can evenly spray the bacterial solution for steel slag modification onto the extra-coarse aggregate particles. The automatic spraying device controls the spraying of the bacterial solution for steel slag modification. The spraying interval is 1 hour / time, and the total number of spraying times is greater than or equal to 12 times. After the extra-coarse aggregate particles adsorb the bacterial solution for steel slag modification in the vacuum adsorption device, they are taken out.

[0049] Furthermore, the extra-coarse aggregate particles after adsorbing the bacterial solution for steel slag modification were placed in a glass tank in a constant temperature water bath, and a prepared mineralization nutrient solution was added. In this embodiment, the mineralization nutrient solution consisted of 0.8 mol / L acetic acid, 0.3 mol / L sucrose, and 0.5 mol / L calcium nitrate. The mineralization nutrient solution provided the substances required for the mineralization of the extra-coarse aggregate particles after adsorbing the bacterial solution for steel slag modification. The solution temperature in the tank was maintained at a constant temperature of 33°C, and the mineralization was enhanced for 3 days.

[0050] S6: The dissolved oxygen content in the mineralization environment is greater than or equal to 3 mg / L to ensure sufficient dissolved oxygen during the modification process; the extra coarse aggregate particles of the mineralized adsorbed steel slag modified with bacterial solution are washed with clean water and dried to constant weight to obtain stabilized steel slag aggregate.

[0051] Specifically, to ensure mineralization efficiency and improve the stabilization rate of steel slag, it is necessary to ensure sufficient dissolved oxygen in the environmental medium during the modification process to enhance the reactivity of mineralizing bacteria. An oxygenation pump is used to introduce air into the reaction mineralization nutrient solution at a rate of approximately 20-30 L / min to ensure that the dissolved oxygen level in the environment during the modification process is not less than 3 mg / L. A dissolved oxygen meter is used for real-time monitoring to ensure sufficient dissolved oxygen in the reaction medium and full reaction of dissolved calcium sources in the environmental medium, which greatly reduces the modification cycle of steel slag under normal temperature and pressure for microbial mineralization stabilization.

[0052] Furthermore, after drying the steel slag aggregate to constant weight, basic performance tests were conducted on its water absorption rate, apparent density, and crushing index. The results showed that during the 3-day modification process, the water absorption rate decreased by 60.20%, and the bulk density increased by 115.8 kg / m³. 3 The crushing index was reduced by 76.8%. Under the same mix proportion, the concrete prepared by microbially modified steel slag showed an increase in compressive strength of 8% and 36% at 7 days and 28 days, respectively, compared with the concrete prepared by natural crushed stone and river sand. No cracking caused by poor stability occurred after boiling at 105℃ for 3 hours. The test results are compared with the basic properties of unmodified extra-coarse aggregate particles in Table 3.

[0053] Table 3. Comparison of basic properties between microbially modified steel slag and unmodified extra-coarse aggregate particles parameter Water absorption rate (%) <![CDATA[Apparent density (kg / m 3 )]]> Crushing index (%) 7-day compressive strength of concrete (MPa) 28-day compressive strength of concrete (MPa) Extra coarse aggregate particles 0.98 3185 13.8 36.5 46.6 Microbial modified steel slag 0.39 3300.8 3.2 39.4 63.4 Based on the above-mentioned equal proportions, the steel slag aggregate is modified by denitrifying bacteria. When the dissolved oxygen content of the environmental medium is not controlled during the modification process, the mineralization treatment time is 5-7 days. Ensuring sufficient dissolved oxygen in the environmental medium during the modification process greatly reduces the modification cycle by 70%.

Claims

1. A method for improving the stability of steel slag based on dissolved oxygen regulation by microorganisms, characterized in that: Includes the following steps: S1: The waste steel slag is crushed, ground, and screened to obtain steel slag aggregates of different grades; the required grade of steel slag aggregate is selected and the floating ash is cleaned using ultrasonic equipment; it is dried, sterilized, and dried to constant weight before being cooled to room temperature; S2: Prepare the appropriate liquid culture medium according to the type of microorganism to be used for modification, and sterilize the liquid culture medium. Adjust the pH value of the liquid culture medium to be approximately equal to the pH value of the steel slag aggregate using a 1 mol / L sodium hydroxide solution. S3: Inoculate the microorganisms into the corresponding liquid culture medium according to their type and culture them to obtain the corresponding microbial inoculum. The microorganisms are urease-producing bacteria, aerobic lactobacilli, or denitrifying bacteria. S4: Centrifuge the cultured microbial solution in a centrifuge to separate the bacterial solution. Dilute the bacterial sludge at the bottom of the test tube with 0.9% physiological saline or resuspend it with a sterilized 5g / L yeast extract solution. Adjust the OD600 value of the bacterial solution to 0.8~1.2 to obtain the corresponding bacterial solution for steel slag modification. S5: The bacterial solution for steel slag modification is applied using a vacuum negative pressure adsorption device and surface spraying to ensure that the steel slag aggregate is fully in contact with and adsorbed to saturation; the corresponding mineralization nutrient solution is prepared according to the type of microorganism to be used for modification, and the steel slag aggregate after adsorbing the bacterial solution for steel slag modification is mineralized using the mineralization nutrient solution. S6: Based on the type of microorganism, a mineralization oxygenation method is adopted. The mineralization oxygenation method involves adding calcium peroxide oxygenating agent, pure oxygen, or air to the mineralization nutrient solution to adjust the dissolved oxygen content of the mineralization environment to be greater than or equal to the set value. The dissolved oxygen meter is used to monitor in real time to ensure that the dissolved oxygen content of the environment is sufficient during the modification process. The steel slag aggregate modified with bacterial solution after mineralization is rinsed with clean water and dried to constant weight to obtain stabilized steel slag aggregate.

2. The method for improving steel slag stability based on dissolved oxygen regulation according to claim 1, characterized in that: The vacuum adsorption device in S5 is equipped with an automatic spraying device. The automatic spraying device can evenly spray the bacterial solution for steel slag modification onto the steel slag aggregate, and fully adsorb it under negative pressure. The automatic spraying device controls the bacterial solution for steel slag modification to spray once at a set interval, and the total number of sprays is greater than or equal to 12.

3. The method for improving steel slag stability based on dissolved oxygen regulation according to claim 1, characterized in that: The method for mineralizing and oxygenating steel slag aggregate for adsorbing urease-producing bacteria involves adding calcium peroxide to the mineralization nutrient solution at a dosage of 30 g / m³. 3 The mineralization and oxygenation method for steel slag aggregate used to adsorb aerobic lactic acid bacteria involves introducing pure oxygen into the mineralization nutrient solution at a rate of approximately 1-2 L / min. The mineralization and oxygenation method for steel slag aggregate used to adsorb denitrifying bacteria involves introducing air into the mineralization nutrient solution at a rate of approximately 20-30 L / min.

4. The method for improving steel slag stability based on dissolved oxygen regulation according to claim 1, characterized in that: In S1, the fine aggregate particles have a particle size of less than 4.75 mm, the medium and coarse aggregate particles have a particle size of 4.75-9.5 mm, and the extra-coarse aggregate particles have a particle size of 9.5-19.0 mm.

5. The method for improving steel slag stability based on dissolved oxygen regulation according to claim 1, characterized in that: The urease-producing bacteria are one of Bacillus pasteurellii, Bacillus spheroidae, or Bacillus subtilis; the aerobic lactobacilli are one of Bacillus coli or Bacillus pseudostrongylus; and the denitrifying bacteria are Pseudomonas aeruginosa.

6. The method for improving steel slag stability based on dissolved oxygen regulation according to claim 1, characterized in that: The liquid culture medium for urease-producing bacteria is prepared by mixing 3-8 g / L soybean peptone, 4-6 g / L sodium chloride, 10-20 g / L tryptone, and 10-30 g / L urea, sterilizing in an autoclave at 121°C, and then adjusting the pH to 12 with sodium hydroxide solution. The liquid culture medium for aerobic lactobacillus is prepared by mixing 5-10 g / L yeast extract, 5-10 g / L sodium chloride, and 10-15 g / L tryptone, sterilizing, and then adjusting the pH to 11 with sodium hydroxide solution. The liquid culture medium for denitrifying bacteria is prepared by mixing 2-3 g / L potassium nitrate, 0.2-0.5 g / L magnesium sulfate heptahydrate, 20-25 g / L potassium sodium tartrate tetrahydrate, and 0.5-0.8 g / L potassium dihydrogen phosphate, sterilizing, and then adjusting the pH to 10 with sodium hydroxide solution.

7. The method for improving steel slag stability based on dissolved oxygen regulation according to claim 1, characterized in that: The microbial inoculation amount in S3 is 1%~1.5%; the liquid culture medium is shaken and cultured in a full-temperature shaker at a constant temperature of 30-40℃ for 48-72 hours.

8. The method for improving steel slag stability based on dissolved oxygen regulation according to claim 1, characterized in that: The centrifugation time for the microbial culture was set to 8-12 min, and the centrifugation speed was set to 4000-6000 r / min.

9. The method for improving steel slag stability based on dissolved oxygen regulation according to claim 1, characterized in that: The mineralized nutrient solution used for adsorbing urease-producing bacteria in steel slag aggregate has the following components: 1-2 mol / L urea and 1-2 mol / L calcium nitrate; the mineralized nutrient solution used for adsorbing aerobic lactic acid bacteria in steel slag aggregate has the following components: 0.5-1.5 mol / L lactic acid, 0.2-0.5 mol / L calcium nitrate, and 0.2-0.5 mol / L calcium lactate; and the mineralized nutrient solution used for adsorbing denitrifying bacteria in steel slag aggregate has the following components: 0.8-1.2 mol / L acetic acid, 0.3-0.5 mol / L sucrose, and 0.5-0.8 mol / L calcium nitrate.

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