Preparation method of solid waste-based foam concrete based on carbonized steel slag tailings

Abstract

This application relates to a method for preparing solid waste-based foamed concrete based on carbonized steel slag tailings, belonging to the field of building materials technology. The method includes: sequentially crushing and magnetically separating undisturbed steel slag to extract metallic iron, obtaining iron-extracted tailings; wet-milling the iron-extracted tailings to obtain steel slag tailings of a predetermined fineness; mixing the steel slag tailings with water to form a slurry, and subjecting the slurry to a carbonization and solidification reaction to obtain carbonized steel slag tailings; grinding various solid wastes including siliceous aluminum solid waste, calcareous solid waste, and sulfate solid waste to obtain a solid waste-based cementitious material with a specific surface area meeting preset requirements; and sequentially mixing and stirring the carbonized steel slag tailings, the solid waste-based cementitious material, a high-efficiency water-reducing agent, a foaming agent, a foam stabilizer, and water, pouring and molding the mixture, and then curing it to obtain solid waste-based foamed concrete.

Description

Technical Field

[0001] This application relates to the field of building materials technology, and in particular to a method for preparing solid waste-based foamed concrete based on carbonized steel slag tailings. Background Technology

[0002] Foamed concrete is a lightweight porous building material made by introducing a large number of uniform closed pores into a cementitious matrix. Due to its low density, low thermal conductivity, and good sound insulation properties, it is widely used in building insulation, non-load-bearing filling, and roadbed backfilling. However, traditional foamed concrete typically uses Portland cement as the main cementing component. Its production not only consumes large amounts of natural resources such as limestone and clay, but also generates significant carbon dioxide emissions during the cement clinker firing process, contradicting the urgent need for energy conservation and emission reduction in the current construction industry.

[0003] To reduce environmental impact and save costs, utilizing industrial solid waste to replace or partially replace cement in the preparation of foamed concrete has become an important research direction. The steel industry generates massive amounts of steel slag annually, which is rich in oxides such as silicon and calcium and possesses potential cementitious activity. However, the direct utilization of steel slag faces several technical bottlenecks: First, its mineral composition fluctuates greatly, leading to unstable product performance; second, steel slag has a high content of free calcium oxide and magnesium oxide, which easily undergoes hydration or carbonization expansion in later stages, causing product cracking and poor volume stability; third, the early hydration activity of steel slag is usually low, limiting its application in foamed concrete requiring rapid demolding and early strength. Summary of the Invention

[0004] This application provides a method for preparing solid waste-based foamed concrete based on carbonized steel slag tailings to solve the following technical problem: how to develop a foamed concrete preparation technology that can simultaneously achieve high utilization of industrial solid waste and has excellent comprehensive performance.

[0005] This application provides a method for preparing solid waste-based foamed concrete based on carbide steel slag tailings, the method comprising:

[0006] The undisturbed steel slag is crushed and magnetically separated to extract the metallic iron from the undisturbed steel slag, thus obtaining the iron extraction tailings. The iron extraction tailings are wet-milled to obtain steel slag tailings of a predetermined fineness. The steel slag tailings are mixed with water to form a slurry, and the slurry is subjected to a carbonization and solidification reaction to obtain carbonized steel slag tailings. Multiple solid wastes, including siliceous aluminum solid waste, calcareous solid waste and sulfate solid waste, are ground to obtain solid waste-based cementitious materials with a specific surface area that meets the preset requirements. The carbide steel slag tailings, the solid waste-based cementitious material, the high-efficiency water-reducing agent, the foaming agent, the foam stabilizer and water are mixed and stirred in sequence, poured and molded and cured to obtain solid waste-based foamed concrete; The raw material composition of the solid waste-based foamed concrete, by mass fraction, is as follows: 10%–40% solid waste-based cementitious material, 10%–50% carbonized steel slag tailings, 20%–50% water, 0.01%–1% high-efficiency water-reducing agent, 0.01%–1% foaming agent, and 0.01%–1% foam stabilizer.

[0007] Optionally, the mass fraction of steel slag tailings in the slurry is 30% to 60%; the temperature of the carbonization and solidification reaction is 20℃ to 80℃; the time of the carbonization and solidification reaction is 1h to 8h; and the carbon fixation rate of the carbonization and solidification reaction is >15%.

[0008] Optionally, the iron extraction tailings shall meet the following requirements: total iron content <1%, free calcium oxide content <3%, and alkalinity coefficient >2.

[0009] Optionally, in the steel slag tailings, the mass fraction of particles with a particle size of less than 200 micrometers is >80%.

[0010] Optionally, by mass fraction, the solid waste-based cementitious material includes: 30%–80% siliceous aluminous solid waste, 10%–60% calcareous solid waste, 5%–40% sulfate solid waste, and ≤30% iron tailings from mines.

[0011] Optionally, the silica-alumina solid waste is at least one of slag and fly ash; the calcareous solid waste is at least one of steel slag, desulfurization slag from molten iron, and dust removal ash; and the sulfate solid waste is at least one of gypsum and desulfurization gypsum.

[0012] Optionally, the surface area of ​​the solid waste-based cementitious material is 450 m². 2 / kg~650 m 2 / kg.

[0013] Optionally, the foamed concrete meets at least one of the following properties: dry density <650 kg / m³ 3 The compressive strength is >10MPa, the thermal conductivity is <0.12W / (m·K), the average pore size is 0.1mm~0.5mm, and the closed-cell rate is >80%.

[0014] Optionally, the foaming agent is at least one of organic foaming agents, inorganic foaming agents, and composite foaming agents.

[0015] Optionally, the high-efficiency water-reducing agent is at least one of melamine-based high-efficiency water-reducing agents, aminosulfonate-based high-efficiency water-reducing agents, polycarboxylate high-efficiency water-reducing agents, and naphthalene-based high-efficiency water-reducing agents.

[0016] The technical solutions provided in this application have the following advantages compared with the prior art: This application provides a method for preparing solid waste-based foamed concrete based on carbonized steel slag tailings. The method includes: sequentially crushing and magnetically separating undisturbed steel slag to extract metallic iron, obtaining iron-extracted tailings; wet-grinding the iron-extracted tailings to obtain steel slag tailings of a predetermined fineness; mixing the steel slag tailings with water to form a slurry, and subjecting the slurry to a carbonization and solidification reaction to obtain carbonized steel slag tailings; grinding various solid wastes including siliceous aluminum solid waste, calcareous solid waste, and sulfate solid waste to obtain a solid waste-based cementitious material with a specific surface area meeting preset requirements; and sequentially mixing and stirring the carbonized steel slag tailings, the solid waste-based cementitious material, a high-efficiency water-reducing agent, a foaming agent, a foam stabilizer, and water, pouring and molding the mixture, and then curing it to obtain solid waste-based foamed concrete. The undisturbed steel slag is sequentially crushed and magnetically separated to extract iron, significantly reducing the residual iron content in the resulting iron-extracting tailings. This reduces the adverse effects of metallic impurities on subsequent chemical reactions and the long-term stability of the product. Subsequently, the tailings are wet-milled to a specific fineness, greatly increasing their specific surface area and exposing more active surfaces, creating sufficient interfacial conditions for the subsequent carbonization and solidification reaction. Next, the steel slag tailings are mixed with water to form a slurry, which is then carbonized and solidified in a controlled carbon dioxide environment. This allows the active calcium oxide and calcium hydroxide in the tailings to react with carbon dioxide to form calcium carbonate. This reaction not only consumes the key component causing later volume expansion—free calcium oxide—essentially improving the material's volume stability, but also fixes carbon dioxide in a stable mineral form within the material, giving the product "carbon-negative" characteristics. Simultaneously, the generated calcium carbonate crystals fill the interparticle gaps, forming an early skeletal structure, effectively improving the matrix's density and initial strength. Furthermore, various solid wastes, including siliceous aluminate solid waste, calcareous solid waste, and sulfate solid waste, are ground to prepare solid waste-based cementitious materials. By optimizing the component ratio and controlling the grinding fineness, the synergistic hydration effect among the multiple solid wastes is stimulated, constructing a fully solid waste cementing system with high cementing activity. Finally, carbide steel slag tailings, solid waste-based cementitious materials, water, high-efficiency water-reducing agents, foaming agents, and foam stabilizers are mixed, stirred, cast, and cured according to a specific mass ratio. The high-efficiency water-reducing agent ensures the workability of the mixture under low water-cement ratio conditions. Relying on the synergistic effect of foaming agents and foam stabilizers, a uniform pore structure with a high closed-cell rate is introduced and stabilized, thus forming a multi-scale composite system with carbide steel slag tailings as the reinforcing phase, fully solid waste synergistic hydration products as the continuous cementing phase, and stable closed pores as the thermal insulation unit. This synergistically achieves the unity of low dry density, high compressive strength, low thermal conductivity, and high carbon fixation performance in solid waste-based foamed concrete. Attached Figure Description

[0017] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this application and, together with the description, serve to explain the principles of this application.

[0018] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, for those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0019] Figure 1 This is a schematic flowchart illustrating a method for preparing solid waste-based foamed concrete based on carbonized steel slag tailings, as provided in an embodiment of this application. Detailed Implementation

[0020] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0021] The range descriptions used herein, such as numerical ranges and proportional ranges, include all possible sub-ranges and single numerical values ​​within that range. For example, the range descriptions of "1 to 6" or "1~6" cover all sub-ranges (such as 1 to 3, 2 to 5, etc.) and single numbers (such as 1, 2, 3, 4, 5, 6) between 1 and 6. Unless otherwise specified, the terms "including" and "contains" as used herein mean "including but not limited to"; relational terms such as "first" and "second" are used only to distinguish different entities or operations and do not imply an actual order or relationship; "and / or" indicates that multiple situations can exist individually or simultaneously; expressions such as "at least one," "multiple," and "at least one" refer to any combination of the corresponding objects, including combinations of single or multiple objects. The proportional relationships mentioned herein, such as mass ratios and molar ratios, should be understood as the correspondence between the first and second terms of a proportional formula, according to the order of description. The raw materials, reagents, instruments, and equipment used herein can all be obtained through commercial purchase or prepared using existing methods.

[0022] Figure 1 This is a schematic flowchart illustrating a method for preparing solid waste-based foamed concrete based on carbonized steel slag tailings, as provided in an embodiment of this application.

[0023] like Figure 1As shown in the figure, this application provides a method for preparing solid waste-based foamed concrete based on carbide steel slag tailings, the method comprising: S1. The original steel slag is crushed and magnetically separated to extract iron, so as to separate the metallic iron from the original steel slag and obtain the iron extraction tailings. S2. The iron extraction tailings are wet-milled to obtain steel slag tailings of a predetermined fineness. S3. The steel slag tailings are mixed with water to form a slurry, and the slurry is subjected to a carbonization and solidification reaction to obtain carbonized steel slag tailings. S4. Grind various solid wastes, including siliceous aluminum solid waste, calcareous solid waste and sulfate solid waste, to obtain a solid waste-based cementitious material with a specific surface area that meets the preset requirements. S5. The carbide steel slag tailings, the solid waste-based cementitious material, the high-efficiency water-reducing agent, the foaming agent, the foam stabilizer and water are mixed and stirred in sequence, poured into molds and cured to obtain solid waste-based foamed concrete. The raw material composition of the solid waste-based foamed concrete, by mass fraction, is as follows: 10%–40% solid waste-based cementitious material, 10%–50% carbonized steel slag tailings, 20%–50% water, 0.01%–1% high-efficiency water-reducing agent, 0.01%–1% foaming agent, and 0.01%–1% foam stabilizer.

[0024] Raw steel slag refers to the initial steel slag discharged directly from the steel smelting production line without any iron extraction or stabilization treatment. Raw steel slag has a large particle size, with metallic iron trapped inside, resulting in low efficiency for direct magnetic separation. Crushing can reduce the particle size of raw steel slag, fully releasing and exposing the trapped metallic iron, achieving a particle size range suitable for effective separation by subsequent magnetic separation equipment (usually crushed to all particles less than 10mm).

[0025] Magnetic separation for iron extraction can maximize the separation and recovery of magnetic iron particles from crushed steel slag where the metallic iron has been fully dissociated. The crushed steel slag particles smaller than 10mm undergo "multi-cycle magnetic separation," meaning multiple magnetic separation processes with varying magnetic field strengths to achieve efficient, step-by-step capture of coarse and fine iron particles. This process is purely physical separation.

[0026] After crushing and magnetic separation, the interference of metallic iron impurities in the iron extraction tailings has been largely eliminated, but the particle size is usually still in the millimeter range, the specific surface area is limited, and the chemical activity is not fully activated. Wet grinding, through high-intensity grinding, destroys the inert layer on the surface of the iron extraction tailings particles, significantly increasing the specific surface area and surface defects of the iron extraction tailings, exposing more active sites (especially free calcium oxide, etc.), and optimizing the particle morphology and gradation of the iron extraction tailings.

[0027] The carbonization and solidification reaction involves a chemical reaction between the steel slag tailings in the slurry and carbon dioxide gas. The core reaction is the reaction of the active calcium components in the steel slag tailings (mainly free calcium oxide f-CaO and calcium hydroxide) with CO2 to generate calcium carbonate (CaCO3). This process achieves two purposes: first, solidification (stabilization), consuming the unstable f-CaO that causes the steel slag to expand in volume; and second, carbon fixation, permanently storing gaseous CO2 in the form of stable carbonate minerals.

[0028] In solid waste-based cementitious materials, silicoaluminate solid waste serves as the main active component, providing the silicon and aluminum sources for the formation of cementitious products such as hydrated calcium silicate and hydrated calcium aluminate. The activity of silicoaluminate solid waste determines the long-term strength development of the cementitious material. Calcium solid waste, as a key alkaline activator and calcium source, provides OH- ions to activate the dissolution of silicoaluminate solid waste and provides Ca... 2+ Ions form hydration products. Sulfate solid waste acts as a sulfate activator, providing SO4. 2- Ions promote the early formation of products such as ettringite, accelerate setting and hardening, and contribute to early strength. Iron tailings from mines are used as micro-aggregates or fillers to adjust particle size distribution and reduce costs, but the amount of iron tailings added is limited to avoid affecting the overall activity.

[0029] Finally, the carbonized steel slag tailings, solid waste-based cementitious materials, high-efficiency water-reducing agents, foaming agents, foam stabilizers, and water are mixed, stirred, poured, and cured sequentially to obtain solid waste-based foamed concrete. The solid waste-based cementitious materials (10%–40%) provide the main body of the bonding capacity. A mass fraction below 10% results in insufficient bonding and low strength; a mass fraction above 40% may make the system too dense, hindering foaming and reducing density. The carbonized steel slag tailings (10%–50%) serve as the core aggregate and functional filler, forming the material's skeleton. Together with the cementitious materials, they form a solid matrix, and the amount of carbonized steel slag tailings directly affects the material's density and strength. Water (20%–50%) satisfies the hydration reaction of the cementitious materials and provides the necessary workability. The water volume needs to be precisely matched with the dosages of the cementitious materials and water-reducing agents to ensure that the slurry can effectively encapsulate the foam without being too thin, which could lead to foam collapse or reduced strength. High-efficiency water-reducing agent (0.01%–1%), foaming agent (0.01%–1%), and foam stabilizer (0.01%–1%) are all key chemical modifiers added in small amounts. With extremely small dosages, they have a decisive influence on the rheology, porosity, and pore stability of the slurry, respectively, and are indispensable elements for achieving the contradictory unity of low density, high strength, and excellent thermal insulation. Solid waste-based foamed concrete can be obtained by curing at room temperature for 28 days after casting.

[0030] In some embodiments, the mass fraction of steel slag tailings in the slurry is 30% to 60%; the temperature of the carbonization and solidification reaction is 20°C to 80°C; the time of the carbonization and solidification reaction is 1h to 8h; and the carbon fixation rate of the carbonization and solidification reaction is >15%.

[0031] Carbonization and solidification is a technology that uses materials containing alkaline components (such as CaO, Ca(OH)2, etc.) to react chemically with CO2 under specific conditions to generate stable carbonates (such as CaCO3), thereby achieving material solidification, performance improvement, and carbon sequestration. In the embodiments of this application, this process is mainly applied to the treatment of steel slag tailings. The specific process is as follows: the steel slag tailings are prepared into a slurry and placed in a carbonization reactor, allowing the calcium-rich components in the steel slag tailings to undergo a carbonization and solidification reaction with CO2, generating a robust CaCO3 network structure. This process not only fixes CO2 (the carbon fixation rate of steel slag tailings is greater than 15%), but also improves the density, strength, and volume stability of the steel slag tailings, laying the foundation for the subsequent preparation of foamed concrete.

[0032] Mixing steel slag tailings with water to form a slurry creates a uniform and operable reaction system for the carbonization and solidification reaction. Mixing finely ground steel slag tailings with water forms a suspension (slurry) with a certain degree of fluidity, ensuring that carbon dioxide gas can be effectively dispersed and contact the surface of the steel slag tailings particles. The mass fraction of steel slag tailings in the slurry is 30%–60%, and this range is crucial for balancing reaction efficiency and mass transfer resistance. If the mass fraction of steel slag tailings is below 30%, the reactant per unit volume is low, resulting in low efficiency; if the mass fraction is above 60%, the slurry viscosity is high, hindering the diffusion of carbon dioxide into the slurry interior. The carbonization and solidification reaction is a chemical reaction, and its rate increases with increasing temperature. The temperature range of 20℃ to 80℃ covers the area from room temperature to medium temperature, avoiding the problems of excessively slow reaction rates and excessively long reaction times at excessively low temperatures (such as below 20℃), and also avoiding the potential for excessively high energy consumption, excessive moisture evaporation, and unnecessary requirements on reaction equipment at excessively high temperatures (such as above 80℃), thus achieving a reasonable balance between efficiency and energy consumption. The carbonization and solidification reaction requires time to complete the processes of gas diffusion, interfacial reaction, and product formation. One hour is the minimum necessary reaction time to ensure the reaction starts and forms a certain amount of product; eight hours sets the upper limit for the sufficient reaction time required to achieve a higher conversion rate.

[0033] A carbon fixation rate >15% in the carbonization and solidification reaction is a mandatory requirement for the final effectiveness of the reaction step, defined as the percentage of fixed carbon dioxide mass relative to the mass of the raw steel slag tailings being greater than 15%. The gas source for the carbonization and solidification reaction can be pure carbon dioxide or a mixture of carbon dioxide and air. If a mixture is used, to ensure reaction efficiency, the volume concentration of carbon dioxide in the mixture should be between 20% and 100%. Generally, increasing the carbon dioxide concentration is beneficial for promoting the forward reaction.

[0034] In some embodiments, the iron extraction tailings meet the following requirements: total iron content <1%, free calcium oxide content <3%, and alkalinity coefficient >2.

[0035] The iron extraction tailings after crushing and magnetic separation meet the requirement of total iron content <1%, indicating that the magnetic separation iron extraction effect is significant and the metallic iron is thoroughly removed.

[0036] When free calcium oxide hydrates to form calcium hydroxide, its volume expansion rate can reach over 98%, which is a major cause of cracking and collapse in steel slag-based building materials. Limiting the free calcium oxide content to a low level of less than 3% significantly reduces the inherent volume stability risk of the material from the raw material stage. Even if a small amount of free calcium oxide remains, it will preferentially react with carbon dioxide in the subsequent carbonization and solidification reaction steps, being converted into stable calcium carbonate and further "digested." A free calcium oxide content of <3% provides a controllable burden for completely resolving the expansion problem in the carbonization and solidification process.

[0037] An alkalinity coefficient (usually expressed as the ratio of CaO to SiO2 content) greater than 2 stipulates that iron ore tailings must possess calcium-rich alkaline chemical characteristics. An alkalinity coefficient >2 means that the iron ore tailings are rich in alkaline oxides such as calcium oxide, which provides a sufficient source of active calcium that can react with carbon dioxide for subsequent carbonization and solidification reaction steps, ensuring a high carbon fixation rate (>15%).

[0038] In some embodiments, the mass fraction of particles with a diameter of less than 200 micrometers in the steel slag tailings is >80%.

[0039] The requirement that the mass fraction of particles smaller than 200 micrometers in steel slag tailings be >80% provides a unique, clear, and measurable quantitative standard for the "predetermined fineness" in "steel slag tailings of predetermined fineness." Carbonization and solidification is a gas-liquid-solid multiphase reaction, and its rate is severely limited by the specific surface area of ​​the solid reactants (steel slag tailings). A particle size of less than 200 micrometers exceeding 80% signifies a significant increase in the average specific surface area of ​​the steel slag tailings. This extremely high specific surface area directly leads to: a geometrical increase in the number of reactive sites (such as the surface of free calcium oxide particles); and a significantly shortened diffusion distance of carbon dioxide gas from the slurry to the reaction interface. This provides the necessary physical conditions and kinetic advantages for achieving a high-efficiency carbonization and solidification reaction with a carbon fixation rate >15%.

[0040] In some embodiments, the solid waste-based cementitious material comprises, by mass fraction: 30%–80% siliceous aluminous solid waste, 10%–60% calcareous solid waste, 5%–40% sulfate solid waste, and ≤30% iron tailings from mines.

[0041] Silica-alumina solid waste (30%–80%), as the most important active component in the system, provides the silicon and aluminum sources required for the formation of major strength phases such as hydrated calcium silicate (CSH) and hydrated calcium aluminate. Calcium-rich solid waste (10%–60%) provides the alkaline environment (OH-) required for the hydration reaction. - ions) and the main calcium ion (Ca ions) 2+ Sulfate solid waste (5%–40%) provides sulfate ions (SO4). 2- In an alkaline environment, it participates in the reaction to generate early-strength hydration products such as ettringite, accelerating solidification and hardening, and improving early strength. Iron tailings from mines (≤30%), as a low-activity or inert micro-aggregate, mainly play a physical filling role, optimizing particle size distribution, and can improve the overall utilization rate of solid waste and reduce material costs without significantly impairing activity.

[0042] By limiting the proportions of solid waste-based cementitious materials, a dynamic equilibrium system was constructed, with siliceous-aluminate solid waste as the active component, calcareous solid waste as the activation medium, sulfate solid waste as the early strength driving force, and mine iron tailings as a limited filler. Within the specified mass fraction range, the components mutually restrict and synergistically influence each other: siliceous-aluminate and calcareous solid wastes jointly determine the type, quantity, and structure of the system's hydration products; sulfate solid waste is activated in this alkaline calcareous environment, contributing to early strength; and the limited incorporation of mine iron tailings must be carried out while ensuring the dominant position of the first three types of active components.

[0043] In some embodiments, the siliceous-aluminous solid waste is at least one of slag and fly ash; the calcareous solid waste is at least one of steel slag, desulfurization slag from molten iron, and dust removal ash; and the sulfate solid waste is at least one of gypsum and desulfurized gypsum.

[0044] Slag (usually referring to blast furnace slag) and fly ash are recognized industrial byproducts with potential hydraulic or pozzolanic activity. Specificifying aluminosilicate solid waste into these two materials clarifies the primary and reliable source of core cementitious activity (i.e., the generation of strength phases such as hydrated calcium silicate) for solid waste-based cementitious materials. This limitation excludes other aluminosilicate wastes with potentially unclear or fluctuating activity, ensuring the stability and predictability of the activity base of the cementing system.

[0045] Steel slag, desulfurization slag from molten iron, and dust removal ash are all materials originating from the iron and steel metallurgical process and are rich in alkaline components such as calcium oxide. Calcareous solid waste provides a necessary calcium source (Ca) for solid waste-based cementitious material systems. 2+ Secondly, calcium-based solid waste provides an alkaline environment (OH-) to form products such as hydrated calcium silicate. - This process is used to stimulate the dissolution and reactivity of siliceous aluminous solid wastes such as slag and fly ash. It is important to note that the steel slag used here, as a source of calcareous solid waste, is distinct from the "carburized steel slag tailings" used as aggregate after magnetic separation for iron extraction and carbonization solidification. This reflects a "differentiated utilization" strategy for the same bulk of solid waste (steel slag). The steel slag and desulfurization slag from molten iron here require cyclic magnetic separation to remove iron impurities, ensuring the grinding quality and chemical purity of the solid waste-based cementitious materials.

[0046] Gypsum and desulfurized gypsum provide sulfate ions (SO42-). 2- Sulfate ions are an effective source of sulfur dioxide, and can participate in the reaction to generate early hydration products such as ettringite, which are crucial for accelerating system coagulation and improving early strength. As a large-scale industrial byproduct, the use of desulfurized gypsum particularly embodies the environmental protection concept of treating waste with waste.

[0047] In some embodiments, the surface area of ​​the solid waste-based cementitious material is 450 m². 2 / kg~650 m 2 / kg.

[0048] At 450 m 2 / kg~650 m 2 Within a specific surface area range of / kg, solid waste-based cementitious materials possess sufficiently high surface energy, enabling rapid dissolution, ion exchange, and hydration reactions upon contact with water, ensuring adequate early reaction rates and final cementitious strength. Secondly, the high specific surface area of ​​the fine particles allows for better encapsulation of carbide steel slag tailings, improving the workability of the fresh mixture and acting as a micro-filler in the hardened body, reducing porosity. The fine-particle cementitious slurry can also more thoroughly wet and encapsulate relatively coarse carbide steel slag tailings particles, forming a strong interfacial transition zone through hydration reactions.

[0049] In some embodiments, the foamed concrete satisfies at least one of the following properties: dry density <650 kg / m³ 3 The compressive strength is >10MPa, the thermal conductivity is <0.12W / (m·K), the average pore size is 0.1mm~0.5mm, and the closed-cell rate is >80%.

[0050] Dry density <650kg / m³ 3 This means that foamed concrete has significant lightweight properties.

[0051] The high strength threshold of compressive strength >10MPa (far exceeding the C3-C5 grade of conventional lightweight concrete) can overcome the limitation of the low strength of traditional foamed concrete and expand the application possibilities of foamed concrete in the embodiments of this application in a wider range of fields such as low-rise load-bearing structures and integrated thermal insulation and load-bearing components.

[0052] A thermal conductivity of less than 0.12 W / (m·K) indicates that foamed concrete has excellent thermal insulation capabilities.

[0053] The average pore size defines the optimal range for pore size. If the pore size is too small, it may affect the lightweight design, while if it is too large, it will significantly weaken the strength. The average pore size range of 0.1 mm to 0.5 mm is the balance between lightweight and high strength.

[0054] A closed-cell ratio >80% means that the bubble walls are intact and the bubbles are independent of each other. This brings three major benefits: First, it significantly reduces the thermal conductivity (closed air is an excellent insulator); second, it improves impermeability and durability; and third, under pressure, closed bubbles have better deformation and load-bearing capacity than interconnected pores.

[0055] In some embodiments, the foaming agent is at least one of organic foaming agents, inorganic foaming agents, and composite foaming agents.

[0056] The three types of foaming agents listed are all mature, commercially available products in the building materials field with known performance. Organic foaming agents (such as protein-based and synthetic surfactant-based agents) have high expansion ratios and relatively stable foams; inorganic foaming agents (such as aluminum powder and hydrogen peroxide) generate gas through chemical reactions; composite foaming agents (combinations of the aforementioned two or more substances) optimize performance through compounding. Implementers can select one or more suitable foaming agents from this range based on local raw material supply, cost, and the specific pore structure requirements (such as average pore size and closed-cell ratio). All of these can achieve the core functions of introducing gas, forming foam, and ultimately creating pores in solid waste-based foamed concrete.

[0057] In some embodiments, the high-efficiency water-reducing agent is at least one of melamine-based high-efficiency water-reducing agents, aminosulfonate-based high-efficiency water-reducing agents, polycarboxylate high-efficiency water-reducing agents, and naphthalene-based high-efficiency water-reducing agents.

[0058] Melamine-based, aminosulfonate-based, polycarboxylate-based, and naphthalene-based high-efficiency water-reducing agents are the four major types of high-efficiency water-reducing agents in the concrete and building materials industry, which have been validated over a long period and have clearly defined technical standards. The core function of high-efficiency water-reducing agents is to significantly improve the fluidity of a mixture of solid waste-based cementitious materials and carbide steel slag tailings at low water-cement ratios. All four types of high-efficiency water-reducing agents can efficiently adsorb onto the surface of cementitious material particles, achieving excellent dispersion through electrostatic repulsion or steric hindrance, thus reliably fulfilling this function. These four types of high-efficiency water-reducing agents each have their own characteristics in terms of water reduction rate, slump retention, adaptability, and compatibility with specific solid waste components. Implementers can select the most suitable one or use a compound formulation based on the specific properties of the solid waste-based cementitious materials and carbide steel slag tailings used, as well as the desired performance indicators (such as strength and pore structure). The following specific embodiments further illustrate this application. Unless otherwise specified, the experimental methods described in the following examples are generally performed in accordance with national / industry standards. If there is no corresponding national / industry standard, they are performed in accordance with general international standards, conventional conditions, or conditions recommended by the manufacturer.

[0059] Example 1 Preparation of iron ore tailings: Raw steel slag from a steel plant's converter (with uneven particle size, the largest particle size being approximately 300 mm) was coarsely crushed using a jaw crusher to produce particles smaller than 10 mm. A vibrating screen was then used for grading; coarse particles larger than 10 mm were returned to the jaw crusher for further crushing, while fine particles smaller than 10 mm were further crushed using a hammer crusher until all material particles were smaller than 10 mm.

[0060] The crushed steel slag particles smaller than 10mm are sequentially passed through an open-type composite magnetic separator and a multi-stage roller magnetic separator for multiple cycles of magnetic separation to separate and recover metallic iron. The iron-extraction tailings obtained after magnetic separation are tested and found to have a total iron content of 0.8%, a free calcium oxide (f-CaO) content of 2.5%, and an alkalinity coefficient (CaO / (SiO2)) of 2.3.

[0061] Wet grinding of steel slag tailings: The iron-extraction tailings after magnetic separation are fed into a wet ball mill, and an appropriate amount of water is added to control the solid content of the slurry to about 65% (i.e., the mass fraction of the iron-extraction tailings is 65%). After grinding, the mass fraction of particles with a particle size of less than 200 micrometers in the steel slag tailings slurry reaches more than 85%.

[0062] Preparation of tailings from carbide steel slag: The obtained steel slag tailings slurry was adjusted to a solid content of 50% (i.e., the mass fraction of steel slag tailings was 50%), stirred evenly, and then injected into a carbonization and solidification reactor. The reactor temperature was set to 30℃, and a mixture of carbon dioxide and air was introduced to carry out the carbonization and solidification reaction. The volume concentration of carbon dioxide in the mixed gas was 40%, and the reaction time was 4 hours. After the reaction was completed, the carbonization product was removed, dried, crushed, and sieved to obtain carbonized steel slag tailings powder with a particle size of less than 2 mm. The carbon fixation rate was determined to be 18% by thermogravimetric analysis.

[0063] Preparation of solid waste-based cementitious materials: Weigh out the following solid waste raw materials according to the following mass percentages: slag 55%, fly ash 15%, steel slag (after magnetic separation to remove iron) 10%, dust collector ash 5%, gypsum 10%, and iron tailings from the mine 5%. After mixing the above materials evenly, dry grind them using a vertical roller mill to obtain a specific surface area of ​​600 m². 2 / kg of solid waste-based cementitious materials.

[0064] Preparation and properties of solid waste-based foamed concrete: The raw material composition of 1 cubic meter of solid waste-based foamed concrete is as follows: 225 kg of solid waste-based cementitious material, 390 kg of carbonized steel slag tailings, 260 kg of water, 9.5 kg of foaming agent, 0.72 kg of foam stabilizer, and 1.44 kg of water-reducing agent.

[0065] The preparation process is as follows: solid waste-based cementitious material and carbide steel slag tailings are mixed with water and water-reducing agent to form a uniform slurry; foaming agent, foam stabilizer and water are mixed separately to form foam water, which is then added to the above uniform slurry to form foamed concrete slurry.

[0066] Foamed concrete slurry was poured into a 100mm×100mm×100mm cube mold and gently vibrated to eliminate large air bubbles. The molded concrete was left to stand in a standard curing room at a temperature of (20±2)℃ and a relative humidity of >90% for 48 hours before being demolded, and then continued to be cured under the same temperature and humidity conditions for 28 days.

[0067] The performance of the 28-day-old foamed concrete specimens was tested, and the results are as follows: Dry density: 580 kg / m³ 3 Compressive strength: 12 MPa, thermal conductivity: 0.10 W / (m·K), average pore size (microscopic method): 0.25 mm, closed-cell ratio (calculated according to GB / T 3810.3): 85%.

[0068] Example 2 The difference between this embodiment and Embodiment 1 is that: The raw material mass percentages for the solid waste-based cementitious material are: slag 55%, fly ash 10%, steel slag (after magnetic separation to remove iron) 15%, desulfurized gypsum 15%, and iron tailings from the mine 5%. The specific surface area after grinding is 650 m². 2 / kg.

[0069] The raw material composition of 1 cubic meter of solid waste-based foamed concrete is as follows: 185 kg of solid waste-based cementitious material, 420 kg of carbonized steel slag tailings, 230 kg of water, 1.28 kg of naphthalene-based high-efficiency water-reducing agent, 8.0 kg of foaming agent, and 0.65 kg of foam stabilizer.

[0070] Performance test results: Dry density 600 kg / m³ 3 The compressive strength is 10 MPa, the thermal conductivity is 0.12 W / (m·K), the average pore size (microscopic method) is 0.2 mm, and the closed-cell ratio (calculated according to GB / T 3810.3) is 82%.

[0071] Example 3 The difference between this embodiment and Embodiment 1 is that: The raw material mass percentages of the solid waste-based cementitious material are: slag 65%, fly ash 15%, steel slag (after magnetic separation to remove iron) 10%, and gypsum 10%. The specific surface area after grinding is 650 m². 2 / kg.

[0072] The raw material composition of 1 cubic meter of foamed concrete is as follows: 160 kg of solid waste-based cementitious material, 450 kg of carbonized steel slag tailings, 250 kg of water, 1.1 kg of polycarboxylate superplasticizer, 8.8 kg of foaming agent, and 0.7 kg of foam stabilizer.

[0073] Performance test results: Dry density 620 kg / m³ 3 The compressive strength is 12 MPa, the thermal conductivity is 0.10 W / (m·K), the average pore size (microscopic method) is 0.3 mm, and the closed-cell rate (calculated according to GB / T 3810.3) is 85%.

[0074] Furthermore, one or more technical solutions in the embodiments of the present invention have at least the following technical effects or advantages: The solid waste-based foamed concrete prepared in this embodiment of the invention has a dry density of <650 kg / m³. 3 The compressive strength is >10MPa, and the thermal conductivity is <0.12W / (m·K). These performance indicators are outstanding among lightweight materials based on solid waste, overcoming the technical contradiction that traditional foamed concrete or existing solid waste foamed concrete products cannot simultaneously achieve low density and high strength.

[0075] This invention achieves a carbon fixation rate of over 15% through the carbonization reaction of calcium-rich components in steel slag tailings with carbon dioxide. This carbon fixation rate is higher than that of similar solid waste negative carbon foam concrete technologies that have been disclosed, providing an effective carbon emission reduction technology approach for the building materials field.

[0076] In the preparation method of this invention, the solid waste-based cementitious material is composed entirely of siliceous aluminate solid waste, calcareous solid waste, and sulfate solid waste, with carbide steel slag tailings as aggregate, achieving 100% utilization of industrial solid waste within the specified proportions. This significantly enhances the synergistic disposal capacity and added value of single and multiple types of solid waste, helping to alleviate the stockpiling pressure and environmental problems associated with bulk solid wastes such as steel slag.

[0077] The solid waste-based foamed concrete prepared in this embodiment of the invention has a uniform pore size distribution, with an average pore size of 0.1 mm to 0.5 mm and a closed-cell rate of more than 80%.

[0078] The embodiments of this invention not only consume industrial solid waste on a large scale and seal carbon dioxide, but also, during the carbonization and solidification reaction of steel slag tailings, heavy metal ions that may be contained can be fixed in the newly generated carbonate and silicate network structure, which can effectively reduce the risk of heavy metal leaching, avoid secondary pollution, and achieve the unity of resource utilization and environmental safety.

[0079] The above description is merely a specific embodiment of this application, enabling those skilled in the art to understand or implement this application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of this application. Therefore, this application is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features claimed in this application.

Claims

1. A method for preparing solid waste-based foamed concrete based on carbide steel slag tailings, characterized in that, The method includes: The undisturbed steel slag is crushed and magnetically separated to extract the metallic iron from the undisturbed steel slag, thus obtaining the iron extraction tailings. The iron extraction tailings are wet-milled to obtain steel slag tailings of a predetermined fineness. The steel slag tailings are mixed with water to form a slurry, and the slurry is subjected to a carbonization and solidification reaction to obtain carbonized steel slag tailings. Multiple solid wastes, including siliceous aluminum solid waste, calcareous solid waste and sulfate solid waste, are ground to obtain solid waste-based cementitious materials with a specific surface area that meets the preset requirements. The carbide steel slag tailings, the solid waste-based cementitious material, the high-efficiency water-reducing agent, the foaming agent, the foam stabilizer and water are mixed and stirred in sequence, poured and molded and cured to obtain solid waste-based foamed concrete; The raw material composition of the solid waste-based foamed concrete, by mass fraction, is as follows: 10%–40% solid waste-based cementitious material, 10%–50% carbonized steel slag tailings, 20%–50% water, 0.01%–1% high-efficiency water-reducing agent, 0.01%–1% foaming agent, and 0.01%–1% foam stabilizer.

2. The method according to claim 1, characterized in that, The mass fraction of steel slag tailings in the slurry is 30% to 60%; the temperature of the carbonization and solidification reaction is 20℃ to 80℃; the time of the carbonization and solidification reaction is 1h to 8h; and the carbon fixation rate of the carbonization and solidification reaction is >15%.

3. The method according to claim 1, characterized in that, The iron extraction tailings meet the following requirements: total iron content <1%, free calcium oxide content <3%, and alkalinity coefficient >2.

4. The method according to claim 1, characterized in that, In the steel slag tailings, the mass fraction of particles with a diameter of less than 200 micrometers is >80%.

5. The method according to claim 1, characterized in that, By mass fraction, the solid waste-based cementitious material comprises: 30%–80% siliceous aluminum solid waste, 10%–60% calcareous solid waste, 5%–40% sulfate solid waste, and ≤30% iron tailings from mines.

6. The method according to claim 5, characterized in that, The siliceous-aluminate solid waste is at least one of slag and fly ash; the calcareous solid waste is at least one of steel slag, desulfurization slag from molten iron, and dust removal ash; the sulfate solid waste is at least one of gypsum and desulfurization gypsum.

7. The method according to claim 1, characterized in that, The solid waste-based cementitious material has a surface area of ​​450 m². 2 / kg~650 m 2 / kg.

8. The method according to claim 1, characterized in that, The foamed concrete meets at least one of the following properties: dry density <650kg / m³ 3 The compressive strength is >10MPa, the thermal conductivity is <0.12W / (m·K), the average pore size is 0.1mm~0.5mm, and the closed-cell rate is >80%.

9. The method according to claim 1, characterized in that, The foaming agent is at least one of organic foaming agents, inorganic foaming agents, and composite foaming agents.

10. The method according to claim 1, characterized in that, The high-efficiency water-reducing agent is at least one of melamine-based high-efficiency water-reducing agents, aminosulfonate-based high-efficiency water-reducing agents, polycarboxylate high-efficiency water-reducing agents, and naphthalene-based high-efficiency water-reducing agents.

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