Magnesium slag-based aggregate and preparation method thereof

Abstract

The present application relates to solid waste resource utilization and building material technical field, specifically relates to a kind of magnesium slag-based aggregate and its preparation method.The specific technical scheme is: industrial magnesium slag is ground into powder;Surface activation and organic-inorganic hybrid coating modification are carried out on waste tire rubber powder;Magnesium slag powder, modified rubber powder and chemical foaming agent are graded and mixed to obtain composite dry material;Composite dry material is mixed and granulated with specially-made bio-based composite cementing solution;Finally, green balls are placed in alkaline carbon dioxide-rich atmosphere for low-temperature carbonization curing.The bio-based cementing solution is stabilized and solidified by ion crosslinking, mineralization induction and organic-inorganic network interpenetration mechanisms.The obtained aggregate has a "dense shell" structure, with a bulk density of 650-850 kg / m 3 , a cylinder pressure strength of 6-12 MPa, a water absorption of less than 10%, and excellent impact toughness, achieving efficient and collaborative utilization of various solid wastes, and the process does not require high-temperature sintering, which is low-carbon and energy-saving.

Description

Technical Field

[0001] This invention relates to the fields of solid waste resource utilization and building materials technology, specifically to a magnesium slag-based aggregate and its preparation method. Background Technology

[0002] Industrial magnesium slag is a waste residue generated during the smelting of metallic magnesium. Rich in calcium oxide and active magnesium components, it possesses certain cementitious activity, but suffers from slow hydration and poor volume stability, hindering its large-scale, high-value utilization. Currently, magnesium slag is mainly used in low-value-added products such as cementitious admixtures, roadbed materials, or unfired bricks.

[0003] Lightweight aggregates can reduce the self-weight of concrete and improve its thermal insulation performance. Traditional artificial ceramsite (such as shale ceramsite and clay ceramsite) requires high-temperature sintering at 1100-1300℃, resulting in high energy consumption and carbon emissions; although fly ash ceramsite can utilize solid waste, it generally suffers from low strength and high water absorption.

[0004] Rubber granules are often used to improve the toughness of building materials, but unmodified rubber powder has an inert and hydrophobic surface, resulting in weak interfacial adhesion with inorganic cementitious matrices. Direct incorporation often leads to a significant decrease in strength. Existing chemical modification methods (such as silane coupling agents) are costly, complex, and difficult to coordinate with green mineralization processes.

[0005] Therefore, developing a lightweight, high-strength, and high-toughness aggregate that can synergistically utilize magnesium slag and waste tire rubber, with low-carbon processing and excellent product performance has become an urgent technical problem to be solved in the field of building materials and solid waste resource utilization. Summary of the Invention

[0006] To address the shortcomings of existing technologies, this invention provides a magnesium slag-based aggregate and its preparation method. This method solves the problem of weak interfacial bonding between rubber and inorganic matrix by synergistically combining rubber powder interface modification, bio-based composite bonding, and alkaline carbonation processes, thereby achieving the regulation of magnesium carbonate / calcium carbonate crystal forms and preparing lightweight aggregates with excellent comprehensive performance.

[0007] To achieve the above objectives, the present invention provides the following technical solution:

[0008] This invention discloses a method for preparing magnesium slag-based aggregate, comprising the following steps:

[0009] S1: Magnesium slag powder, modified rubber powder and physical foaming agent are graded and mixed to obtain composite dry material;

[0010] S2: The composite dry material is mixed with the bio-based composite cementing solution and granulated to form raw material balls; the bio-based composite cementing solution is an organic-inorganic composite solution;

[0011] S3: The raw material pellets are placed in an alkaline environment with a carbon dioxide-rich atmosphere for carbonization treatment to obtain lightweight, high-strength, and high-toughness aggregate.

[0012] Preferably, in step S1, the dry weight percentages are: 100 parts magnesium slag powder, 5-15 parts modified rubber powder, and 0.5-2.0 parts chemical foaming agent.

[0013] Preferably, in step S1, the chemical foaming agent is a composite of solid hydrogen peroxide and aluminum powder, wherein the amount of aluminum powder is 30%-40% of the total mass of the chemical foaming agent.

[0014] Preferably, in step S2, the mass ratio of the composite dry material to the bio-based composite cementing solution is 1:0.3-0.5.

[0015] Preferably, in step S3, the alkaline environment is an atomized alkaline environment or an alkaline solution environment with a pH value of 9-11; the carbonization treatment conditions are: carbon dioxide concentration not less than 20%, temperature 50±5℃, and treatment time 48-72h.

[0016] Preferably, the modified rubber powder is prepared by the following method:

[0017] S11: Place the rubber powder in a sodium hydroxide solution and treat it at 40-60℃ for 30-60 minutes, then wash and dry.

[0018] S22: The rubber micro powder treated by S11 is immersed in an aqueous solution containing tannic acid and calcium lignosulfonate for adsorption treatment. Under the conditions of 40-60℃, it is dispersed by ultrasonic vibration and reacted for 30-90 minutes.

[0019] S33: After completing S22, separate and remove the supernatant, disperse the obtained wetted rubber powder in a 0.2-0.3 mol / L MgCl2 solution, stir continuously, adjust the pH to 8.5-9.5, and continue the reaction;

[0020] S44: After the reaction is complete, the product is subjected to solid-liquid separation, and then washed and dried to obtain the modified rubber micro powder.

[0021] Preferably, in step S22, the mass ratio of tannic acid to calcium lignosulfonate in the aqueous solution is 1:0.5-1.0, and the total mass concentration of the two is 1.0%-3.0%.

[0022] Preferably, the bio-based composite cementing solution is prepared by the following method:

[0023] P1: Xanthan gum solution, guar gum solution and aspartic acid solution were left to stand at room temperature to mature; then they were mixed and stirred to form a homogeneous ternary composite solution.

[0024] P2: Mix mineral powder and calcium carbide slag powder evenly to obtain composite inorganic powder;

[0025] P3: Add the composite inorganic powder obtained in step P2 into the ternary composite solution; use the steps of first wetting at 200-300 rpm and then shearing and dispersing at 1000-2000 rpm, and continue the treatment for 20-30 minutes to obtain a homogeneous and stable suspended composite slurry.

[0026] P4: Disperse the composite slurry obtained in step P3 into uniform droplets with a particle size range of 100-200μm;

[0027] P5: Disperse the droplets obtained in step P4 in a MgCl2 solution with a concentration of 0.1-0.15 mol / L, and stir to form the bio-based composite cemented solution.

[0028] Preferably, in step P1, the volume ratio of the xanthan gum solution, guar gum solution, and aspartic acid solution is 1:0.5-1.0:0.2-0.5; in step P2, the mass ratio of the mineral powder to the calcium carbide slag powder is 1:0.2-0.5; in step P3, the composite inorganic powder accounts for 10%-15% of the total mass of the ternary composite solution; and in step P5, the molar ratio of magnesium ions to aspartic acid in the system is controlled to be 1:0.5-1.0.

[0029] Accordingly, a magnesium slag-based aggregate prepared by the aforementioned method has a continuous porous structure, with its outer surface covered by a dense mineralized shell layer of 2-5 mm thickness; the bulk density of the aggregate is 650-850 kg / m³. 3 The compressive strength of the aggregate is 6-12 MPa, and the water absorption rate is less than 10%. The strength retention rate of the aggregate after soaking in water for 28 days is not less than 90%, and its impact toughness index is not less than 15 times.

[0030] The bio-based composite binder solution prepared in this invention and its curing process in aggregates involve complex physicochemical processes, the core curing mechanism of which can be explained as follows:

[0031] (1) Ion crosslinking and organic network reinforcement: During the preparation and subsequent granulation process, the calcium carbide slag powder rapidly provides an alkaline environment and releases calcium ions (Ca ions) upon contact with water. 2+ ), while the magnesium ions (Mg) present in the system 2+ ) and Ca 2+ The bridging effect of polyvalent cations on the carboxyl groups of xanthan gum and aspartic acid molecules leads to a highly efficient ionic cross-linking reaction. This bridging effect of polyvalent cations significantly strengthens the initial organic network structure based on xanthan gum and guar gum, greatly improving its mechanical strength and stability.

[0032] (2) Mineralization induction and microstructure regulation: Aspartic acid in solution can react with Mg 2+ Coordination occurs preferentially, forming a stable aspartic acid-Mg group. 2+ The complex, acting as a highly efficient crystal form inducer, plays a crucial role in the subsequent inorganic phase precipitation process. Under alkaline conditions, the Ca provided by the calcium carbide slag powder... 2+ It reacts with the active silicon / aluminum phase dissolved from mineral powder to produce products such as hydrated calcium silicate. Aspartic acid-Mg 2+ The complex can guide and regulate the nucleation sites, growth rate and crystal morphology of these inorganic minerals, promoting the formation of specific crystal forms or microstructures that are smaller, more uniformly distributed, denser and more thermodynamically stable, thereby optimizing the cementing performance of the inorganic phase.

[0033] (3) Network Interpenetration and Chemical Bonding: The ionic cross-linking enhancement process of the organic network and the controlled mineralization process of the inorganic phase do not occur in isolation, but rather proceed simultaneously and mutually promote each other in an alkaline environment. The alkaline environment also stimulates the potential cementitious activity of the mineral powder. Ultimately, a unique "organic biological network-inorganic mineralization structure" interpenetrating composite cross-linking system was successfully constructed inside and on the surface of the droplets. This system not only achieves the tight interweaving of the organic and inorganic phases at the microscale, but also firmly binds them together through chemical bonding such as ionic bonds and coordination bonds, thereby forming a bio-based composite cementing solution with highly stable performance and excellent bonding strength. This solution, as a bonding medium, is key to imparting initial strength to the raw material pellets and influencing the final aggregate performance.

[0034] The magnesium slag-based aggregate prepared by the above method has a continuous porous structure, with a dense mineralized shell layer of 2-5 mm thickness, mainly composed of high-strength magnesite, calcium carbonate crystals, and hydrated calcium silicate. The uniformly dispersed modified rubber powder inside acts as an elastic functional component, effectively inducing crack deflection and passivation when the aggregate is subjected to external impact, and absorbing a large amount of energy through its own elastic deformation. This unique structure gives it excellent performance: a bulk density of 650-850 kg / m³. 3 The compressive strength is 6-12 MPa, and the water absorption rate is <10%. At the same time, the aggregate exhibits strong durability and toughness, with a strength retention rate of no less than 90% after soaking in water for 28 days. Its impact toughness index (based on the simple drop hammer method) is more than 100% higher than that of similar aggregates without modified rubber powder.

[0035] The present invention has the following beneficial effects:

[0036] 1. Using industrial magnesium slag and waste tire rubber as the main raw materials, the synergistic high-value utilization of these two difficult-to-treat solid wastes has been achieved, resulting in a high degree of solid waste resource utilization and environmental friendliness.

[0037] 2. The core curing process adopts low-temperature carbonization curing, which completely abandons the traditional high-temperature sintering process of ceramic particles, significantly reducing energy consumption and carbon emissions.

[0038] 3. Through the combination of chemical foaming and modified rubber, a continuous porous structure is formed, which, together with a dense mineralized shell, results in an aggregate bulk density of 650-850 kg / m³. 3 The compressive strength can reach 6-12 MPa, achieving a balance between lightweight and high strength. The dense mineralized shell on the surface effectively prevents water intrusion, with a water absorption rate of less than 10%. After long-term immersion in water, the strength retention rate is not less than 90%, and the volume stability is good. The introduction of surface-modified rubber powder as an elastic component can buffer stress, ensuring that the impact toughness index of the aggregate is not less than 15 times, thus improving its impact resistance and crack resistance.

[0039] 4. The organic-inorganic hybrid layer on the surface of the modified rubber powder significantly improves the interfacial adhesion between the hydrophobic rubber and the hydrophilic inorganic matrix. The bio-based composite cementing solution constructs an interpenetrating composite cross-linking system of "organic biological network-inorganic mineralization," exhibiting strong and stable adhesion. The carbonization process takes place in an alkaline, CO2-rich environment, promoting the formation of dense products such as magnesite, calcium carbonate crystals, and hydrated calcium silicate from active MgO and CaO in the magnesium slag. This forms a hard shell on the aggregate surface and a porous, high-strength structure inside. Attached Figure Description

[0040] Figure 1 This is a SEM image of the aggregate prepared in Example 1. Detailed Implementation

[0041] 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.

[0042] Unless otherwise specified, the technical means used in the implementation examples are conventional means well known to those skilled in the art.

[0043] This invention relates to a method and products for preparing lightweight, high-strength, and high-toughness aggregates using industrial magnesium slag and waste tire rubber powder as main raw materials through bio-based bonding and carbonization curing technology.

[0044] This invention discloses a method for preparing magnesium slag-based aggregate, comprising the following steps:

[0045] S1: Dry and grind industrial magnesium slag to a particle size ≤150μm to obtain magnesium slag powder, so as to improve its specific surface area and reactivity.

[0046] S2: Surface activation and bridging treatment of waste tire rubber powder to obtain modified rubber powder, so as to improve its interfacial bonding with the inorganic cementitious phase.

[0047] S3: Magnesium slag powder, modified rubber powder and chemical foaming agent are graded and mixed to obtain composite dry material;

[0048] By dry basis mass fractions: 100 parts magnesium slag powder, 5-15 parts modified rubber powder, and 0.5-2.0 parts chemical foaming agent. The chemical foaming agent is a composite of hydrogen peroxide and aluminum powder, and the amount of aluminum powder is 30%-40% of the total mass of the chemical foaming agent.

[0049] S4: The composite dry material is mixed with the bio-based composite cementing solution and rolled into granules to form raw material balls; the bio-based composite cementing solution is an organic-inorganic composite solution; the bio-based composite cementing solution is an organic-inorganic composite solution, which has the functions of bonding, foaming synergy and mineralization induction; the mixing mass ratio of the composite dry material to the bio-based composite cementing solution is 1:0.3-0.5.

[0050] S5: The raw material pellets are placed in an alkaline environment with a carbon dioxide-rich atmosphere for carbonization treatment to obtain lightweight, high-strength, and high-toughness aggregate.

[0051] The alkaline environment is a mist-like alkaline environment or an alkaline solution environment with a pH of 9-11. The carbonization treatment conditions are: a carbon dioxide concentration of not less than 20%, a temperature of 50±5℃, and a treatment time of 48-72 hours. In this step, the alkaline environment ensures that the carbonization reaction (CO2+Mg(OH)2→MgCO3+H2O) proceeds at a high speed in the positive direction, significantly improving the CO2 fixation efficiency, carbonization depth, and product density. The dense carbonized layer further strengthens the aggregate shell, protects the internal structure, and works synergistically with the internal modified rubber powder to contribute to the overall high strength and high toughness.

[0052] Furthermore, in step S3, the modified rubber powder is prepared by the following method:

[0053] S11: Place rubber powder with a particle size of 40-80 mesh in a sodium hydroxide solution with a mass concentration of 2%-5% and treat it at 40-60℃ for 30-60 minutes. Then clean and dry it to remove surface impurities and introduce hydroxyl active sites.

[0054] S22: The rubber micro powder treated by S11 is immersed in an aqueous solution containing tannic acid and calcium lignosulfonate for adsorption treatment. The mass ratio of tannic acid to calcium lignosulfonate in the aqueous solution is 1:0.5-1.0, and the total mass concentration of the two is 1.0%-3.0%. Under the condition of 40-60℃, ultrasonic vibration is used for dispersion, and the reaction is carried out for 30-90 minutes to allow organic molecules to be adsorbed on the rubber surface.

[0055] S33: After completing S22, separate and remove the supernatant, disperse the resulting wetted rubber micropowder in a 0.2-0.3 mol / L MgCl2 solution, and carry out ionic crosslinking reaction by continuous stirring at 25-35℃; then add dilute ammonia to the system to adjust the pH to 8.5-9.5, and continue the reaction to form an organic-inorganic hybrid coating layer on the surface of the rubber micropowder;

[0056] S44: After the reaction is complete, the product is subjected to solid-liquid separation, and then washed and dried to obtain the modified rubber micro powder.

[0057] Furthermore, in step S4, the bio-based composite cementing solution is prepared by the following method:

[0058] P1: Prepare xanthan gum solution (0.1% by mass), guar gum solution (0.05% by mass), and aspartic acid solution (0.05% by mass) separately, and let them stand at room temperature for 12-24 hours to mature. Then, mix the three matured solutions at a volume ratio of 1:0.5-1.0:0.2-0.5 and stir at 200-300 rpm for 20-30 minutes at room temperature to form a homogeneous ternary composite solution.

[0059] P2: Dry the mineral powder and calcium carbide slag powder separately, and ball mill them to a specific surface area ≥ 500 m². 2 / kg, and then the two are uniformly mixed at a mass ratio of 1:0.2-0.5 to obtain composite inorganic powder; the mineral powder is S95 grade or above granulated blast furnace slag powder.

[0060] P3: The composite inorganic powder obtained in step P2 is slowly added to the ternary composite solution under stirring at a ratio of 10%-15% of the total mass of the ternary composite solution obtained in step P1; the process is carried out by first wetting at 200-300 rpm and then shearing and dispersing at 1000-2000 rpm for 20-30 minutes to obtain a homogeneous and stable suspended composite slurry.

[0061] P4: Disperse the composite slurry obtained in step P3 into uniform droplets with a particle size range of 100-200μm using a pressure or centrifugal atomizer.

[0062] P5: Disperse the droplets obtained in step P4 in a MgCl2 solution with a concentration of 0.1-0.15 mol / L; under stirring conditions of 30-40℃ and 100-200 rpm, continue stirring for 20-30 min, and control the molar ratio of magnesium ions to aspartic acid in the system to be 1:0.5-1.0, so as to promote the organic network cross-linking and inorganic phase mineralization inside the droplets and form a stable bio-based composite cemented solution.

[0063] This invention provides a magnesium slag-based aggregate prepared by the aforementioned method. The aggregate has a continuous porous structure and is coated with a dense mineralized shell with a thickness of 2-5 mm. The bulk density of the aggregate is 650-850 kg / m³. 3 The compressive strength of the aggregate is 6-12 MPa, and the water absorption rate is less than 10%. The strength retention rate of the aggregate after soaking in water for 28 days is not less than 90%, and its impact toughness index is not less than 15 times.

[0064] The present invention will be further described below with reference to specific embodiments.

[0065] Example 1

[0066] Preparation of a magnesium slag-based lightweight high-strength and high-toughness aggregate

[0067] 1. Raw material preparation:

[0068] Magnesium slag powder: Take industrial magnesium slag, dry it at 105℃, and then grind it to a particle size ≤150μm.

[0069] Modified rubber powder: Take 100g of 40-60 mesh waste tire rubber powder, place it in 500mL of 3% NaOH solution, treat at 50℃ for 45min, wash with water until neutral, and dry. Immerse the treated rubber powder in 500mL of an aqueous solution containing 1.5% tannic acid and 1.5% calcium lignosulfonate (mass ratio 1:1), and sonicate at 55℃ for 60min. After separation, add the wetted rubber powder to 500mL of 0.25mol / L MgCl2 solution, stir at 30℃ for 30min, add dilute ammonia dropwise to adjust the pH to 9.0, and continue the reaction for 60min. Filter, wash with water, and dry at 60℃ to obtain modified rubber powder.

[0070] Bio-based composite cementing solution:

[0071] P1: Prepare 1 L each of 0.1% xanthan gum solution, 0.05% guar gum solution, and 0.05% aspartic acid solution, and mature for 24 h. Mix them at a volume ratio of 1:0.8:0.4 and stir at 250 rpm for 25 min.

[0072] P2: Mix S95 slag powder and calcium carbide slag powder (dried and ground to a specific surface area of ​​550m²) 2Mix ( / kg) at a mass ratio of 1:0.3 to obtain composite inorganic powder.

[0073] P3: Take 150g of the composite inorganic powder obtained from P2 (accounting for 15% of the total mass of 1000g of solution P1), slowly add it to solution P1, stir at 250rpm for 5min, and then shear at 1500rpm for 25min.

[0074] P4: The slurry is atomized into droplets of about 150μm through a pressure atomizer.

[0075] P5: Spray the droplets into a 0.12 mol / L MgCl2 solution (Mg 2+ Stirring at 35°C and 150 rpm for 25 minutes with an aspartic acid molar ratio of approximately 1:0.7 to form a stable bio-based composite cemented solution.

[0076] Chemical foaming agent: Solid hydrogen peroxide with a particle size ≤20μm and aluminum powder are prepared for use.

[0077] 2. Grading and mixing: Based on dry basis mass parts, take 100 parts of magnesium slag powder, 10 parts of modified rubber powder, and 1.2 parts of chemical foaming agent (aluminum powder accounts for 30% of the total mass of chemical foaming agent), put them in a mixer and mix them evenly to obtain composite dry material.

[0078] 3. Granulation: In a disc granulator, the composite dry material and the bio-based composite binder solution are mixed at a mass ratio of 1:0.35 and rolled into raw material balls with a particle size of 5-20mm.

[0079] 4. Carbonization Curing: Place the raw material pellets in a curing chamber, introduce gas containing 30% CO2, and simultaneously atomize a dilute Ca(OH)2 solution with pH=10 to maintain an alkaline and humid environment. Control the temperature at 50℃ and perform carbonization treatment for 60 hours.

[0080] 5. Post-processing: After carbonization, the aggregate is removed and air-dried at room temperature to obtain the finished product. The aggregate has a continuous porous structure internally, and its outer surface is covered with a dense mineralized shell layer with a thickness of 3.5 mm. Its SEM image is shown below. Figure 1 As shown.

[0081] Example 2

[0082] The preparation process of magnesium slag-based lightweight high-strength and high-toughness aggregate is the same as in Example 1, except that:

[0083] (1) Composite dry material ratio: 100 parts magnesium slag powder, 5 parts modified rubber powder, 1.5 parts chemical foaming agent (aluminum powder accounts for 30% of the total mass of chemical foaming agent).

[0084] (2) In the bio-based cemented solution, in step P1, the volume ratio of xanthan gum solution, guar gum solution and aspartic acid solution is 1:0.5:0.2.

[0085] (3) Carbonization conditions: CO2 concentration 25%, carbonization treatment for 72h.

[0086] Example 3

[0087] The preparation process of magnesium slag-based lightweight high-strength and high-toughness aggregate is the same as in Example 1, except that:

[0088] (1) Composite dry material ratio: 100 parts magnesium slag powder, 15 parts modified rubber powder, 0.8 parts chemical foaming agent (aluminum powder accounts for 30% of the total mass of chemical foaming agent).

[0089] (2) In the preparation of modified rubber powder, the mass ratio of tannic acid to calcium lignosulfonate is 1:0.5, and the total concentration is 2.0%.

[0090] (3) Carbonization conditions: CO2 concentration 35%, carbonization treatment for 48h.

[0091] Comparative Example 1

[0092] No modified rubber powder was added; otherwise, it was the same as in Example 1.

[0093] Comparative Example 2

[0094] Ordinary tap water was used instead of the bio-based composite cementing solution for granulation, and the rest was the same as in Example 1.

[0095] Comparative Example 3

[0096] The carbonization curing was changed to standard curing (temperature 20±2℃, relative humidity ≥95%), and the curing was carried out for 28 days. The rest was the same as in Example 1.

[0097] Comparative Example 4

[0098] The process is basically the same as in Example 1, except that in step 2, during the gradation mixing, the same mass (10 parts) of untreated, raw 40-60 mesh waste tire rubber powder is used to directly replace the modified rubber powder. The remaining raw materials, proportions, and process steps are exactly the same.

[0099] Comparative Example 5

[0100] The process is essentially the same as in Example 1, except that the addition of composite inorganic powders (S95 slag powder and calcium carbide slag powder) is completely omitted in steps P2 and P3 of preparing the bio-based composite cementing solution. That is, after preparing the ternary composite solution in step P1, steps P2 and P3 are skipped, and the P1 solution is dispersed via an atomizer (equivalent to P4), followed by step P5 (dispersed in MgCl2 solution). The resulting solution is used as a binder for subsequent granulation. The remaining raw materials, proportions, and process steps are the same as in Example 1.

[0101] Performance testing:

[0102] The performance of the aggregate products obtained in Examples 1-3 and Comparative Examples 1-5 was tested, and the results are shown in Table 1. The test methods were in accordance with "Lightweight Aggregates and Test Methods Therefor" (GB / T 17431.1-2010).

[0103] Bulk density: determined according to standard methods.

[0104] Compressive strength: Take aggregate with a particle size of 10-20mm and measure its strength index.

[0105] Water absorption rate: The water absorption rate was measured over 1 hour.

[0106] Strength retention rate: After soaking the aggregate in water for 28 days, test its compressive strength and the ratio to the initial strength.

[0107] Impact toughness index: The number of impacts that the aggregate can withstand before crushing is recorded using an aggregate impact testing machine.

[0108] Table 1. Results of aggregate performance tests

[0109]

[0110] As shown in Table 1, the aggregates prepared in Examples 1-3 of this invention exhibit superior performance compared to the comparative examples. The products of Examples 1-3 are lightweight (bulk density 650-850 kg / m³). 3 It has high strength (cylindrical compressive strength 8-11MPa), low water absorption (<10%), good long-term water stability (strength retention rate ≥90%), and excellent toughness (impact index ≥16 times).

[0111] Comparative Example 1 and Example 2: This demonstrates that the introduction of modified rubber powder significantly improves the toughness of the aggregate (more than doubles the impact index) and slightly reduces the water absorption rate without substantially affecting the strength.

[0112] Comparative Example 2: This demonstrates that the bio-based composite cementing solution is the key binder and mineralization inducing component that ensures the molding of raw material balls and achieves their final excellent performance, and it is irreplaceable.

[0113] Comparative Example 3 illustrates the crucial importance of the low-temperature carbonization curing process of this invention. Standard curing cannot effectively activate the magnesium slag and form dense carbonization products, resulting in aggregates with high density, low strength, and high water absorption, whose performance is far inferior to that of carbonized products.

[0114] Comparative Example 4: Aggregates using unmodified rubber powder exhibited significantly lower compressive strength, water absorption, and strength retention compared to Example 1, particularly with a sharp drop in impact toughness index to 6 times. This directly demonstrates the necessity of surface activation and bridging modification of the rubber powder in this invention. The poor interfacial bonding between the unmodified rubber powder and the inorganic matrix creates weak points, leading to decreased overall strength, increased water absorption channels, and reduced durability, while also failing to effectively exert a toughening effect.

[0115] Comparative Example 5: Aggregates prepared without the addition of inorganic composite mineral powders (slag powder and calcium carbide slag powder) had a compressive strength of only 3.0 MPa, a water absorption rate as high as 21.8%, and a water immersion strength retention rate of only 70%. This confirms the core role of inorganic composite powders in bio-based cementing systems. Without the alkaline environment and calcium ions provided by calcium carbide slag powder, and the active silica-alumina phase provided by slag powder, the system cannot undergo effective ionic cross-linking and controlled mineralization reactions, and cannot form an "organic-inorganic" interpenetrating network structure, resulting in severely insufficient cementing strength and a loose, porous, and unstable structure.

[0116] In summary, this invention successfully prepared high-performance magnesium slag-based lightweight, high-strength, and high-toughness aggregates through unique raw material modification, functional composite cementing solutions (containing necessary inorganic mineralization components), and low-temperature carbonization processes, providing a new, efficient, and low-carbon approach for the resource utilization of bulk industrial solid waste.

[0117] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A method for preparing magnesium slag-based aggregate, characterized in that: Includes the following steps: S1: Magnesium slag powder, modified rubber powder and chemical foaming agent are graded and mixed to obtain composite dry material; S2: The composite dry material is mixed with the bio-based composite cementing solution and granulated to form raw material balls; the bio-based composite cementing solution is an organic-inorganic composite solution; S3: The raw material pellets are placed in an alkaline environment with a carbon dioxide-rich atmosphere for carbonization treatment to obtain lightweight, high-strength, and high-toughness aggregate. The modified rubber powder is prepared by the following method: S11: Place the rubber powder in a sodium hydroxide solution and treat it at 40-60℃ for 30-60 minutes, then wash and dry. S22: The rubber micro powder treated by S11 is immersed in an aqueous solution containing tannic acid and calcium lignosulfonate for adsorption treatment. Under the conditions of 40-60℃, it is dispersed by ultrasonic vibration and reacted for 30-90 minutes. S33: After completing S22, separate and remove the supernatant, disperse the obtained wetted rubber powder in a 0.2-0.3 mol / L MgCl2 solution, stir continuously, adjust the pH to 8.5-9.5, and continue the reaction; S44: After the reaction is complete, the product is subjected to solid-liquid separation, and then washed and dried to obtain the modified rubber micro powder. The bio-based composite cementing solution is prepared by the following method: P1: Xanthan gum solution, guar gum solution and aspartic acid solution were left to stand at room temperature to mature; then they were mixed and stirred to form a homogeneous ternary composite solution. P2: Mix mineral powder and calcium carbide slag powder evenly to obtain composite inorganic powder; P3: Add the composite inorganic powder obtained in step P2 into the ternary composite solution; use the steps of first wetting at 200-300 rpm and then shearing and dispersing at 1000-2000 rpm, and continue the treatment for 20-30 minutes to obtain a homogeneous and stable suspended composite slurry. P4: Disperse the composite slurry obtained in step P3 into uniform droplets with a particle size range of 100-200μm; P5: Disperse the droplets obtained in step P4 in a MgCl2 solution with a concentration of 0.1-0.15 mol / L, and stir to form the bio-based composite cemented solution.

2. The preparation method according to claim 1, characterized in that: In step S1, the dry weight percentages are: 100 parts magnesium slag powder, 5-15 parts modified rubber powder, and 0.5-2.0 parts chemical foaming agent.

3. The preparation method according to claim 1 or 2, characterized in that: In step S1, the chemical foaming agent is a composite of solid hydrogen peroxide and aluminum powder, wherein the amount of aluminum powder is 30%-40% of the total mass of the chemical foaming agent.

4. The preparation method according to claim 1, characterized in that: In step S2, the mass ratio of the composite dry material to the bio-based composite cementing solution is 1:0.3-0.

5.

5. The preparation method according to claim 1, characterized in that: In step S3, the alkaline environment is an atomized alkaline environment or an alkaline solution environment with a pH value of 9-11; the carbonization treatment conditions are: carbon dioxide concentration not less than 20%, temperature 50±5℃, and treatment time 48-72h.

6. The preparation method according to claim 1, characterized in that: In step S22, the mass ratio of tannic acid to calcium lignosulfonate in the aqueous solution is 1:0.5-1.0, and the total mass concentration of the two is 1.0%-3.0%.

7. The preparation method according to claim 1, characterized in that: In step P1, the volume ratio of the xanthan gum solution, guar gum solution, and aspartic acid solution is 1:0.5-1.0:0.2-0.5; in step P2, the mass ratio of the mineral powder to the calcium carbide slag powder is 1:0.2-0.5; in step P3, the composite inorganic powder accounts for 10%-15% of the total mass of the ternary composite solution; in step P5, the molar ratio of magnesium ions to aspartic acid in the system is controlled to be 1:0.5-1.

0.

8. A magnesium slag-based aggregate prepared by the preparation method according to any one of claims 1-7, characterized in that, The aggregate has a continuous porous structure, and its outer surface is covered with a dense mineralized shell layer with a thickness of 2-5 mm; the bulk density of the aggregate is 650-850 kg / m³. 3 The compressive strength of the aggregate is 6-12 MPa, and the water absorption rate is less than 10%. The strength retention rate of the aggregate after soaking in water for 28 days is not less than 90%, and its impact toughness index is not less than 15 times.

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