Activated steel slag as well as preparation method and application thereof

Abstract

The invention relates to the technical field of cement-based material admixtures, in particular to activated steel slag and a preparation method and application thereof.The activated steel slag is subjected to two-stage microbiological treatment, specifically, firstly, the steel slag is soaked with acid-producing microorganisms to be pretreated, then the pretreated steel slag is carbonized with mineralized microorganisms, and the carbonized steel slag is obtained; the activity of the steel slag is improved, the volume stability of the steel slag is improved, the safety of the steel slag in a concrete structure is ensured, the service life of a steel slag test piece is prolonged, and the resource utilization of the steel slag is improved.

Description

Technical Field

[0001] The invention relates to the technical field of cement-based material admixtures, in particular to activated steel slag and a preparation method and application thereof. Background Art

[0002] Steel slag, a byproduct of steel production, is currently primarily used in building materials, road construction, soil improvement, and wastewater treatment. However, compared to other industrial solid wastes such as fly ash and slag, its utilization rate remains relatively low, leaving large quantities of slag unused and stockpiled. This not only wastes resources but also poses serious environmental risks due to the metal ions contained in the slag after weathering. During high-temperature steelmaking, the divalent metal solid solution (RO phase) formed exhibits poor abrasive properties, hindering the activation of the slag. Furthermore, the free calcium oxide (f-CaO) contained in the slag expands during hydration, leading to stability issues such as cracking and deformation in building materials like concrete. This makes it difficult for steel slag to meet practical engineering application standards when used in building materials. Therefore, modifying the slag to increase its activity index and improve its volume stability is an important approach to promoting its application in building materials.

[0003] Currently, the primary method for treating steel slag is natural aging, which utilizes the moisture and temperature of the natural environment to hydrate the free calcium oxide (f-CaO) within it, thereby reducing its volume expansion. After aging, crushing and screening are required to reduce the particle size. This method is time- and environmentally-intensive, and the consumption rate is typically lower than the production rate. Driven by relevant policies, some steel mills and processing plants have begun adopting wet carbonization to treat steel slag. This involves stacking freshly fired slag in a hot, humid pit at elevated temperatures, covering it with a hot, humidifying cover and spraying water. This rapidly hydrates the free calcium oxide and free magnesium oxide within the pit in the high-temperature, humid, and hot environment. This method is highly efficient, but places high demands on the equipment. In addition, autoclaving, alkali activation, and acid activation have been widely studied, but the equipment requirements and processing costs have limited their practical application. Therefore, wet carbonization is currently the mainstream method for treating steel slag and promoting its resource utilization.

[0004] In recent years, microbial induced calcium carbonate precipitation (MICP) technology has gradually been explored. Many domestic universities have conducted research on microbial mineralization and modification of steel slag. For example, Southeast University has widely studied the use of Bacillus to metabolize carbonic anhydrase (CA) to capture CO2 and promote the conversion of f-CaO in steel slag into CaCO3, thereby improving the stability of steel slag during use. Patent applications have been filed for existing technologies such as CN111847915A, CN113860779A, CN119638238A, and CN119822655A. However, while microbial carbonization accelerates steel slag, a thin layer of CaCO3 is also formed around the f-CaO, preventing further carbonization. This encapsulated free calcium oxide still poses a significant risk of expansion. In addition, commonly used mineralizing bacteria have limited ability to decompose the mineral phase in steel slag, resulting in poor slag activation. Summary of the Invention

[0005] In order to solve the problems existing in the prior art, the present invention provides a preparation method of activated steel slag. The steel slag is subjected to two-stage microbial treatment. First, the steel slag is pretreated by soaking it with acid-producing microorganisms, and then the pretreated steel slag is carbonized using mineralizing microorganisms. This improves the activity of the steel slag and improves the volume stability of the steel slag, thereby ensuring the safety of the steel slag in concrete structures, extending the service life of the steel slag specimens, and improving the resource utilization of the steel slag.

[0006] Specifically, the method for preparing activated steel slag of the present invention comprises the following steps:

[0007] 1) Cultivate acid-producing microorganisms and mineralizing microorganisms to obtain acid-producing microbial culture liquid and mineralizing microbial culture liquid,

[0008] 2) Soak the steel slag powder in acid-producing microbial liquid, filter, and wash to obtain acid-hydrolyzed steel slag powder.

[0009] 3) The acid-decomposed steel slag powder is soaked in a carbonization environment using a mineralized microbial solution, filtered, and washed to obtain the product.

[0010] The present invention first uses acid-producing microorganisms to digest the structure of steel slag powder, and then uses Bacillus to treat the pretreated steel slag powder again to promote the carbonization degree of the steel slag powder. In the existing technology, acid excitation mainly uses organic weak acid or dilute strong acid, which is highly polluting and costly, and will reduce the alkalinity of the steel slag and cannot optimize the morphology of the steel slag powder particles. Compared with the use of acid excitation, the acid-producing microbial digestion of the present invention can achieve particle size refinement, while promoting the exposure of activation sites, and the calcium-magnesium alkaline particles are more rounded. The carbonate generated after the Bacillus treatment can play a lubricating role, improve the fluidity of the slurry, and promote the release of activity, thereby improving the stability. Compared with the alkali excitation technology, the present invention has less impact on the workability of the mortar, is conducive to construction, and does not involve the use of high concentrations of chemical reagents, so it will not cause secondary pollution. Compared with the carbonization technology, the present invention has a better activation effect on the steel slag powder and a simpler maintenance system. Compared with the single Bacillus mineralization treatment, the present invention can promote the carbonization ability of Bacillus on the steel slag powder, shorten the carbonization time and improve efficiency.

[0011] Preferably, the acid-producing microorganism in step 1) is at least one of Thiobacillus ferrooxidans and Aspergillus niger.

[0012] Preferably, the mineralizing microorganism in step 1) is a Bacillus. More preferably, the Bacillus is selected from at least one of Bacillus pasteurianus, Bacillus mucilaginosus, and Bacillus alkaliphilus, and all strains are commercially available products in the prior art.

[0013] Preferably, the concentration of live bacteria in the acid-producing microbial solution and the mineralizing microbial solution in step 1) is 1.5×10 8 cfu / mL-4.6×10 12 cfu / mL.

[0014] Preferably, the steel slag powder in step 2) is obtained by crushing, washing and drying the steel slag.

[0015] Preferably, in step 2), the mass ratio of the steel slag powder to the acid-producing microbial liquid is 1:(8-15).

[0016] Preferably, the soaking time in step 2) is 24-36 hours, and the washing is performed 3-4 times with distilled water.

[0017] Preferably, in step 3), the mass ratio of the acid-hydrolyzed steel slag powder to the mineralized microbial liquid is 1:(8-15).

[0018] Preferably, the carbonization environment in step 3) is a relative humidity of 60±5%, a CO2 volume fraction of more than 90%, a pressure of 0.05-0.2 MPa, a soaking time of 24-48 hours, and washing with distilled water for 3-4 times.

[0019] The present invention also relates to activated steel slag, which is specifically prepared by the above-mentioned preparation method.

[0020] The present invention also relates to the use of the activated steel slag in the preparation of cement-based products, preferably including but not limited to its use as a cement admixture, admixture, alkali-activated material, or geopolymer matrix in the preparation of slurry, mortar, concrete, and various building materials.

[0021] The present invention has the following technical advantages:

[0022] 1. The activity of the activated steel slag of the present invention is significantly improved, with the activity index exceeding 100% at 28 days. In addition, the particle size of the steel slag powder is reduced and the specific surface area is increased under the digestion of organic acids produced by the metabolism of acid-producing microorganisms.

[0023] 2. The contents of f-CaO and f-MgO in the activated steel slag of the present invention are significantly reduced, and the volume stability is improved.

[0024] 3. The fluidity of the cement-based mortar specimens prepared from the activated steel slag of the present invention meets the requirements of the specification, and the setting time is slightly extended, which is beneficial to the transportation of the slurry and on-site construction. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] In order to more clearly illustrate the specific embodiments of the present invention or the technical solutions in related technologies, the following briefly introduces the drawings required for use in the specific embodiments or related technical descriptions. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0026] Figure 1 The microscopic morphology of steel slag after being treated with Thiobacillus ferrooxidans and Bacillus pasteurianus

[0027] Figure 2 The microscopic morphology of steel slag after being treated with Thiobacillus ferrooxidans

[0028] Figure 3 The original morphology of steel slag DETAILED DESCRIPTION

[0029] In order to characterize the technical effect of the present invention, activated steel slag was prepared and its performance was tested. The main chemical composition of the steel slag powder was CaO37.8%, SiO215.22%, Al2O34.36%, MgO8.59%, Fe2O323.4%, and MnO5.0%. The testing process was carried out in accordance with the following standards: the f-CaO content in the steel slag powder was tested in accordance with GB / T 38216.3-2023 "Determination of free calcium oxide content in steel slag - EDTA titration and thermogravimetric analysis"; the f-CaO content in the steel slag powder was tested in accordance with GB / T The activity index of steel slag powder was tested according to 51003-2014 "Technical Specifications for the Application of Mineral Admixtures". 30% steel slag powder and 70% cement were mixed into a cementitious material to prepare mortar specimens. The fluidity and setting time of the mortar were tested according to GB / T1346-2011 "Test Methods for Water Consumption, Setting Time and Soundness of Cement Standard Consistency". During the test, the viable bacteria concentration of the acid-producing microbial culture and the mineralizing microbial culture was raised to 2×10 12 About cfu / mL.

[0030] The present invention selected no treatment, alkali stimulation, carbonization, and Bacillus mineralization as controls and set up a total of 4 comparison groups. The single acid-producing microorganism treatment, acid-producing + mineralizing bacteria composite microorganism treatment, and dilute acid + mineralizing bacteria treatment were selected to set up a total of 6 experimental groups. The specific experimental conditions of each group are abbreviated as follows:

[0031] Experiment 1: Steel slag powder was treated by immersion in a Thiobacillus ferrooxidans bacterial solution, filtered, washed, and dried. The immersion ratio of steel slag powder to bacterial solution was 1:10, and the immersion time was 48 hours.

[0032] Experiment 2: Steel slag powder was treated by soaking in Aspergillus niger solution, filtered, washed, and dried. The mass ratio of steel slag powder to bacterial solution was 1:10, and the soaking time was 48 hours.

[0033] Experiment 3: The steel slag powder was treated by immersing it in a bacterial solution of Thiobacillus ferrooxidans at a mass ratio of 10:1. After immersion for 24 hours, the slag powder was filtered, washed, and dried. The slag powder was then treated by immersing it in an environment of 60±5% relative humidity, 95.0% CO2 volume fraction, and 0.1 MPa pressure for 24 hours using a bacterial solution of Bacillus pasteurianus at a mass ratio of 10:1.

[0034] Test 4: The steel slag powder was treated by soaking it in Aspergillus niger liquid at a mass ratio of 10:1. After soaking for 24 hours, the powder was filtered, washed, and dried. The powder was then soaked in Bacillus pasteurianus at a mass ratio of 10:1 for 24 hours in an environment with a relative humidity of 60±5%, a CO2 volume fraction of 95.0%, and a pressure of 0.1 MPa.

[0035] Test 5: The steel slag powder was treated by soaking in dilute acid at a mass ratio of 10:1. After soaking for 24 hours, the slag powder was filtered, washed, and dried. The slag powder was then soaked in an environment with a relative humidity of 60±5%, a CO2 volume fraction of 95.0%, and a pressure of 0.1 MPa using Bacillus pasteurianus at a mass ratio of 10:1 for 24 hours. The dilute acid used was dilute nitric acid with a mass concentration of 0.5%.

[0036] Test 6: The steel slag powder was treated by soaking in dilute acid at a mass ratio of 10:1. After soaking for 24 hours, the steel slag powder was filtered, washed, and dried. The steel slag powder was then soaked in an environment with a relative humidity of 60±5%, a CO2 volume fraction of 95.0%, and a pressure of 0.1 MPa using Bacillus pasteurianus at a mass ratio of 10:1 for 24 hours. The dilute acid used was citric acid with a mass concentration of 0.5%.

[0037] Comparison 1: Untreated steel slag powder.

[0038] Comparison 2: Activation was performed using an activator containing 8% by mass of steel slag powder. The activator composition consisted of 10 mol / L NaOH solution and Na2SiO3 solution. The modulus of the Na2SiO3 solution used was Ms=1.3 (Ms=SiO2 / Na2O=1.3), and SH (NaOH):SS(Na2SiO3)=0.16.

[0039] Comparison 3: Using carbonized activated steel slag powder, the carbonization conditions are relative humidity 60±5%, CO2 volume fraction 95.0%, pressure 0.1 MPa, and carbonization for 48 hours.

[0040] Comparison 4: Using Bacillus pasteurianus to mineralize steel slag powder, the steel slag powder was soaked in a ratio of steel slag powder to bacterial solution = 1:10 for 48 hours, filtered, washed, and dried in an immersion environment with a relative humidity of 60±5%, a CO2 volume fraction of 95.0%, and a pressure of 0.1 MPa.

[0041] The test results are shown in the following table:

[0042] 7d activity index (%) 28d activity index (%) <![CDATA[Specific surface area (m 2 / kg)]]> f-CaO content (%) f-MgO content (%) Flowability (mm) Initial setting time (min) Final setting time (min) Test 1 93.34 100.61 749 0.93 0.85 148.5 152 254 Test 2 94.63 109.77 792 1.01 0.71 150.0 161 268 Test 3 90.35 125.33 663 0.32 0.56 162.5 148 293 Test 4 91.87 139.79 681 0.57 0.45 165.0 160 296 Test 5 89.76 98.22 658 0.83 0.73 149.0 153 336 Test 6 87.98 95.73 632 0.76 0.69 151.5 182 401 Comparison 1 63.41 75.66 512 4.04 1.97 155.0 125 202 Comparison 2 95.23 113.55 573 2.35 1.53 135.0 102 163 Contrast 3 75.23 82.79 509 1.93 1.32 161.5 150 251 Contrast 4 89.13 90.56 478 0.85 1.09 152.5 165 384

[0043] The results in the table show that the activity of untreated steel slag is poor, with an activity index of only 75.66% at 28 days, classifying it as Class II steel slag. The activity of the steel slag powder after alkaline activation treatment was significantly improved, reaching an activity index of 113.55% at 28 days. Comparative data from Experiment 3 show a slight increase in the activity of the steel slag powder after carbonization treatment. Comparative data from Experiment 4 also show that the activity was further enhanced after Bacillus mineralization treatment, with the 28-day activity index increasing from 75.66% to 90.56%. The 28-day activity indices of the steel slag powder from Experiments 1 and 2 were 100.61% and 109.77%, respectively. The improvement in activity after acidogenic microbial treatment was significantly greater than that after Bacillus treatment. The higher activity improvement in Experiment 2 is attributed to the complex pellet-mycelium structure of Aspergillus niger, which allows it to decompose the steel slag powder through acid hydrolysis and microbial corrosion, resulting in a stronger ability to destruct the structure and release active substances encapsulated by the RO phase. Experiments 1-4 and Comparison 4 revealed that the breakdown of the slag powder structure by acidogenic microorganisms facilitated Bacillus' mineralization of the slag powder, further enhancing its 7-day and 28-day activity indices compared to those obtained with a single acidogenic microorganism. Because acidogenic microorganisms can disrupt the slag powder structure, the surface area test results of Experiments 1 and 2, as well as the accompanying figures, indicate that the treated slag particles are smaller in size, providing more CaCO3 nucleation sites and thus promoting Bacillus' mineralization. The results of Experiments 5 and 6 indicate that the activity of slag powder treated with inorganic and organic dilute acids followed by mineralization is lower than that achieved with treatment using acidogenic microorganisms.

[0044] f-CaO and f-MgO in steel slag powder undergo hydration upon contact with water to form Ca(OH)₂ and Mg(OH)₂. This process causes significant volume expansion, and therefore f-CaO and f-MgO are the primary contributors to poor volume stability. In Comparison 1, the f-CaO content in the untreated raw steel slag reached 4.04%, and the f-MgO content reached 1.97%, both exceeding the standard requirements and posing a significant risk of volume expansion. After alkaline activation treatment, the f-CaO and f-MgO contents in the steel slag powder decreased somewhat, but only slightly below the standard requirement. This is primarily due to the alkaline nature of f-CaO and f-MgO, making alkaline activation insufficiently destructive. Comparisons 3 and 4 demonstrate that Bacillus can promote the carbonization of f-CaO, with a significant decrease after treatment. However, the decrease in f-MgO was less pronounced. This is primarily due to the f-MgO being dissolved in the RO phase, which Bacillus lacks the ability to destruct the RO phase, resulting in a less pronounced effect on the carbonization of f-MgO. The data from Experiments 1 and 2 demonstrate that acidogenic microorganisms significantly degrade f-CaO and f-MgO, with their contents significantly decreasing after treatment. However, the f-CaO content remained slightly higher than that in the steel slag treated with Bacillus spores. This is primarily because the two acidogenic microorganisms can only decompose the steel slag and f-CaO through the organic acids they produce, lacking the carbonization-promoting ability similar to Bacillus spores. Furthermore, the f-MgO content was lower than that in the steel slag treated with Bacillus spores, indicating that the acidogenic microorganisms disrupted the structure of the steel slag, exposing the internal f-MgO for acidolysis. In Experiments 3 and 4, the f-CaO and f-MgO contents in the steel slag treated with the composite microorganisms further decreased. This directly demonstrates that the corrosive degradation of the steel slag by acidogenic microorganisms can accelerate the carbonization of the Bacillus spores, achieving a shorter degradation of f-CaO and f-MgO in the steel slag, significantly improving the treatment efficiency of the steel slag. Experiments 5 and 6 show that although dilute acid treatment can also reduce the f-CaO and f-MgO contents, its effect on improving other properties is relatively poor.

[0045] Cement-based mortars were prepared and their fluidity and setting time were tested. The results showed that the fluidity and setting time of alkali-activated steel slag powder decreased significantly. The high alkalinity and high viscosity of the alkali activator significantly affected the mortar's performance. The data in Comparison 3 show that the mortar prepared with carbonized steel slag powder exhibited improved fluidity and a longer setting time. This is primarily due to the denser and smoother CaCO₃ particles generated by carbonization, which reduces interparticle friction and improves fluidity. However, the CaCO₃ produced by carbonization also adheres to the surface of the steel slag particles, hindering further hydration. Furthermore, the generated CaCO₃ is highly stable, reducing its reactivity and leading to a prolonged setting time. The data in Comparison 4 show that the mortar prepared with Bacillus-mineralized steel slag powder exhibited a further prolonged setting time, but decreased fluidity, compared to Comparison 3. This is attributed to the production of polysaccharides by the metabolism of the Bacillus, which have properties similar to those of water-reducing agents, leading to the prolonged setting time. Experiments 1 and 2 show the results of separate treatments with two acid-producing microorganisms. They show that the reduced particle size of the treated slag enhances its adsorption capacity for free water, leading to a significant decrease in the fluidity of the slurry. Experiments 3 and 4 show that pretreatment with acid-producing microorganisms improves the fluidity of the slurry. This is primarily due to the CaCO₃ generated by the Bacillus immersion, which acts as a lubricant and adheres to the particles. Furthermore, reducing the Bacillus immersion time significantly shortens the coagulation time.

[0046] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the above embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing activated steel slag, characterized in that: The steps include: 1) Cultivating acid-producing microorganisms and mineralizing microorganisms to obtain acid-producing microbial culture liquid and mineralizing microbial culture liquid, wherein the acid-producing microorganism is at least one of Thiobacillus ferrooxidans and Aspergillus niger, and the mineralizing microorganism is Bacillus; 2) Soaking the steel slag powder in an acid-producing microbial solution, filtering, and washing to obtain acid-hydrolyzed steel slag powder; 3) The acid-decomposed steel slag powder is soaked in a carbonization environment using a mineralized microbial solution, filtered, and washed to obtain the product.

2. The method for preparing activated steel slag according to claim 1, wherein: The concentration of live bacteria in the acid-producing microbial solution and the mineralizing microbial solution in step 1) is 1.5×10 8 cfu / mL-4.6×10 12 cfu / mL.

3. The method for preparing activated steel slag according to claim 1, wherein: In step 2), the steel slag powder is obtained by crushing, cleaning and drying the steel slag.

4. The method for preparing activated steel slag according to claim 1, wherein: In the step 2), the mass ratio of the steel slag powder to the acid-producing microbial liquid is 1:(8-15).

5. The method for preparing activated steel slag according to claim 1, wherein: The soaking time in step 2) is 24-36 hours.

6. The method for preparing activated steel slag according to claim 1, characterized in that: In step 2), the washing is performed with distilled water for 3-4 times.

7. The method for preparing activated steel slag according to claim 1, characterized in that: In the step 3), the mass ratio of the acid-decomposed steel slag powder to the mineralized microbial liquid is 1:(8-15).

8. The method for preparing activated steel slag according to claim 1, characterized in that: In step 3), the carbonization environment is set at a relative humidity of 60±5%, a CO2 volume fraction of 90% or more, a pressure of 0.05-0.2 MPa, an immersion time of 24-48 hours, and washing with distilled water for 3-4 times.

9. An activated steel slag, characterized in that: The compound is prepared by the preparation method according to any one of claims 1 to 8.

10. Use of the activated steel slag according to claim 9 in the preparation process of cement-based products.

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