Phosphogypsum-steel slag solid waste-based aggregate and preparation method thereof

Abstract

The application discloses a kind of phosphogypsum-steel slag solid waste base aggregate and preparation method thereof, belong to solid waste resource utilization and green building material technical field.Preparation method includes: phosphogypsum and steel slag powder are mixed, and solid waste raw material is obtained, then solid waste raw material and water are mixed uniformly, granulation, and aggregate blank is obtained;Aggregate blank is placed in mineralization reactor, and sequentially carries out first hydration, mineralization, secondary hydration maintenance, and is prepared.The wet aggregate particle after granulation of the application is placed in the same mineralization reactor, by sequentially switching the input order of air and CO2-containing flue gas, so that the aggregate continuously completes the first hydration, mineralization and secondary hydration maintenance process in the same device.Compared with the traditional curing method, the application does not need to transfer the aggregate or change the curing device, but by regulating the cutting-in time of CO2 flue gas, the coupling regulation of the hydration product formation process and the carbonate mineralization product generation process inside the aggregate is realized, which is conducive to improving the controllability of the curing process.

Description

Technical Field

[0001] This invention belongs to the field of solid waste resource utilization and green building materials technology, specifically relating to a phosphogypsum-steel slag solid waste-based aggregate and its preparation method. Background Technology

[0002] In response to global climate change, CO2 emission reduction and the resource utilization of industrial solid waste have become important research directions in the field of building materials. CO2 mineralization curing technology can utilize the active calcium source in industrial solid waste to react with CO2 to generate stable carbonates, thereby immobilizing CO2 and improving the pore structure and mechanical properties of building materials. Phosphogypsum, as a byproduct of phosphoric acid production, has a large annual emission and contains soluble phosphorus, fluorine, and acidic impurities. Long-term storage not only occupies land but also poses environmental risks. Therefore, achieving efficient resource utilization and performance improvement of phosphogypsum has become an urgent technical problem to be solved.

[0003] Currently, phosphogypsum is mainly used in building materials such as cement retarders, gypsum blocks, and cementitious materials, but its utilization at high dosages is limited. Studies have shown that when the phosphogypsum content exceeds 25%, the 28-day compressive strength of mortar or cementitious materials decreases significantly. Although related studies have attempted to improve this issue by adding slag, silica fume, or optimizing the dosage of admixtures, it is difficult to fundamentally address the demands for high dosage, high strength, and low cost.

[0004] The sulfate components in phosphogypsum can participate in the system reaction and promote the formation of sulfate-containing hydrated products and crystal structures, enhancing the early structure of aggregates. Steel slag contains dicalcium silicate, tricalcium silicate, and free CaO, which can react with water to form CSH gel and calcium hydroxide, providing a framework and pore filling, while also providing a calcium source for subsequent CO2 mineralization. However, traditional phosphogypsum-steel slag building material preparation often adopts a fixed segmented process of "hydration first, then mineralization," making it difficult to match the mineralization intervention time with the phosphogypsum-steel slag system, resulting in low curing efficiency, incomplete mineralization reaction, and problems with optimizing the material's microstructure.

[0005] Therefore, there is an urgent need to provide a mineralization-hydration curing method that can match the phosphogypsum-steel slag system. By reasonably controlling the time of air curing and mineralization curing, the formation of hydration products and carbonate precipitation can be carried out in synergy without increasing the total curing time, thereby improving the aggregate strength and structural density, and realizing the resource utilization of industrial solid wastes such as phosphogypsum and steel slag as well as CO2 fixation. Summary of the Invention

[0006] In order to overcome the above-mentioned shortcomings of the existing technology, the purpose of this invention is to provide a phosphogypsum-steel slag solid waste-based aggregate and its preparation method, so as to solve the problems of low early strength, insufficient structural density, low traditional curing efficiency and difficulty in controlling the mineralization reaction of existing phosphogypsum-based aggregates.

[0007] The technical solution of this invention to solve the above-mentioned technical problems is as follows: A method for preparing phosphogypsum-steel slag solid waste-based aggregate is provided, comprising the following steps: S1. Mix phosphogypsum and steel slag powder to obtain solid waste raw materials. Then mix the solid waste raw materials with water, granulate, and obtain aggregate blanks. S2. The aggregate blanks are placed in a mineralization reactor and subjected to primary hydration, mineralization, and secondary hydration curing in sequence to obtain phosphogypsum-steel slag solid waste-based aggregate. The conditions for primary and secondary hydration are: pressure 0.1 MPa, temperature 20~30℃, relative humidity 60~80%, and CO2 concentration in the gas ≤5%. The conditions for mineralization are: pressure 0.1 MPa, temperature 60~70℃, relative humidity 85~95%RH, and CO2 concentration in the gas ≥10%. The times for primary hydration, mineralization, and secondary hydration are 12~48h, 6~12h, and 12~54h, respectively.

[0008] The curing gas of this invention is composed of a mixture of low-concentration flue gas and high-concentration CO2 at the reactor inlet. The low-concentration flue gas is emitted from the steel industry, with a CO2 concentration of ≤5%, while the high-concentration CO2 is gas from a carbon capture device with a concentration of 99.5%. Temperature is controlled by a heat exchanger at the reactor inlet, and relative humidity is controlled by a humidifier installed at the reactor inlet.

[0009] Based on the above technical solution, the present invention can be further improved as follows: Furthermore, in step S1, the free fluoride ions in the phosphogypsum are ≤0.5%, and the particle size is ≤150μm; the steel slag powder has a particle size of ≤75μm and a specific surface area of ​​≥400m². 2 / kg.

[0010] Furthermore, step S1 also includes the following treatment of phosphogypsum and steel slag powder: drying phosphogypsum and steel slag powder at 120-150℃ for 5-8 hours respectively.

[0011] Furthermore, the phosphogypsum and steel slag powder were dried at 120℃ for 6 hours.

[0012] Furthermore, the mass percentages of phosphogypsum and steel slag powder in the solid waste raw materials are 50%–90% and 10%–50%, respectively; water accounts for 15%–20% of the dry weight of the solid waste raw materials.

[0013] Furthermore, the mass percentages of phosphogypsum and steel slag powder in the solid waste raw materials are 50% and 50%, respectively; water accounts for 15% of the dry weight of the solid waste raw materials.

[0014] Furthermore, the total time for primary hydration, mineralization, and secondary hydration is 72 hours.

[0015] Furthermore, the conditions for primary hydration were: pressure 0.1 MPa, temperature 20 °C, relative humidity 60%, CO2 concentration in the gas 5%, and time 12 h.

[0016] Furthermore, the conditions for secondary hydration were all: pressure 0.1 MPa, temperature 20 °C, relative humidity 60%, CO2 concentration in the gas 5%, and time 48 h.

[0017] Furthermore, the mineralization conditions were: pressure 0.1 MPa, temperature 60℃, relative humidity 95% RH, CO2 concentration in the gas 12%, and time 12 h.

[0018] The present invention has the following beneficial effects: (1) This invention achieves synergistic regulation of the hydration reaction and CO2 mineralization reaction of phosphogypsum-steel slag solid waste-based aggregates through atmosphere switching curing. In this invention, granulated wet aggregate particles are placed in the same mineralization reactor. By sequentially switching the order of air and CO2-containing flue gas introduction, the aggregates continuously complete the primary hydration curing, mineralization curing, and secondary hydration curing processes within the same device. Compared with traditional curing methods, this invention does not require transferring aggregates or changing curing devices; instead, the aggregates are directly fed into the reactor for curing without pre-curing or pre-drying. By controlling the CO2 flue gas inlet time, the coupling regulation of the formation process of hydration products and the generation process of carbonate mineralization products within the aggregates is achieved, which is beneficial to improving the controllability of the curing process.

[0019] (2) This invention can utilize the complementary effect between phosphogypsum and steel slag to improve the early structural strength of aggregates. The main mineral component of phosphogypsum is calcium sulfate dihydrate, which can provide sulfate and calcium sources for the system; steel slag contains alkaline calcium-containing components such as dicalcium silicate, tricalcium silicate, and free calcium oxide, which can undergo hydration reactions in the presence of water to generate hydrated calcium silicate gel, calcium hydroxide, and aluminum sulfate hydration products. The above hydration products can gradually form a cemented network inside the aggregate particles and between the particles, filling capillary pores and microcracks, and improving the cohesion, initial compressive strength, and structural stability of the aggregates. The mineralization reaction further refines the pore structure, improving the strength and water resistance of the aggregates. After CO2-containing flue gas is introduced, the calcium hydroxide already formed inside the aggregate, the calcium-containing hydration products, and the unreacted calcium-containing active components in the steel slag can undergo a mineralization reaction with CO2 to generate mineral products such as calcium carbonate. These products can further fill the pores, improve the density of the internal structure of the aggregate, thereby increasing the compressive strength of the aggregate and helping to reduce the water absorption rate.

[0020] (3) This invention avoids the adverse effects of premature or delayed mineralization by controlling the timing of CO2 mineralization initiation. If CO2 is introduced too early, the hydration reaction inside the aggregate has not yet been fully carried out, and the aggregate has not yet formed a stable initial cemented skeleton. CO2 tends to react rapidly on or near the surface of the particles, forming a relatively dense carbonate layer, which hinders the continued diffusion of water and CO2 into the interior, resulting in insufficient internal hydration and mineralization. If CO2 is introduced too late, there are already a lot of hydration products inside the aggregate, and the pore channels are partially filled or closed. The diffusion of CO2 into the interior of the aggregate is limited, and the depth of the mineralization reaction and the amount of carbonate generated decrease. By controlling the curing conditions and curing time of hydration-mineralization-hydration, the curing state of the aggregate can be controlled under conditions where pre-curing and pre-drying are not required.

[0021] (4) This invention can improve curing efficiency while keeping the total curing time constant. This invention does not simply extend the air curing time or the mineralization curing time, but rather, under the premise of a fixed total curing time, it regulates the sequential matching relationship between the hydration and mineralization reactions by changing the ingress time of the CO2 flue gas. The air curing stage is mainly used to form the initial hydration cementitious structure, the CO2 mineralization stage is mainly used to generate carbonates and fill pores, and the subsequent air curing stage is beneficial for the continued hydration of incompletely reacted components and for stabilizing the aggregate structure. The three stages work together to enable the aggregate to obtain higher strength in a shorter time, which is beneficial for the rapid preparation of phosphogypsum-based aggregates.

[0022] (5) This invention can improve the resource utilization level of phosphogypsum and steel slag, and realize CO2 fixation and utilization. This invention uses industrial solid waste such as phosphogypsum and steel slag as the main raw materials to prepare artificial aggregates. On the one hand, it increases the utilization ratio of phosphogypsum and steel slag in building materials and reduces the land occupation and environmental risks caused by their stockpiling; on the other hand, it uses CO2-containing flue gas to mineralize and maintain the aggregates, so that CO2 is fixed in the form of carbonates inside the aggregates, realizing the synergy of solid waste resource utilization and CO2 emission reduction. Compared with traditional natural aggregates, the phosphogypsum-based mineralized aggregates prepared by this invention have the advantages of low cost, low carbonization preparation and high value utilization of solid waste, and are suitable for road materials, building materials and concrete aggregates. Attached Figure Description

[0023] Figure 1 Flowchart for the preparation of phosphogypsum-based aggregates for CO2 mineralization and curing. Detailed Implementation

[0024] The examples given below are for illustrative purposes only and are not intended to limit the scope of the invention. Unless otherwise specified, conditions in the examples are performed under standard conditions or as recommended by the manufacturer. Reagents or instruments whose manufacturers are not specified are all commercially available products.

[0025] Example 1:

[0026] A method for preparing phosphogypsum-steel slag solid waste-based aggregate includes the following steps: S1. The phosphogypsum and steel slag powder are screened separately to obtain phosphogypsum with a particle size ≤150μm (free fluoride ions ≤0.5%) and steel slag powder with a particle size ≤75μm (specific surface area ≥400m²). 2 The solid waste raw material powder was obtained by drying it at 120℃ for 6 hours ( / kg). S2. Weigh 900g of phosphogypsum and 100g of steel slag powder after drying in step S1, and put them into the mixer and mix for 60 minutes. Then transfer the raw material mixture to the granulator and spray 150g of water to make water mist to wet the aggregate material with a moisture content of 15% and a particle size of 5~15mm. S3. Place the aggregate blanks into the mineralization reactor, set the reaction pressure of the mineralization reactor to 0.1 MPa, use a flow controller to adjust the inlet ratio of low-concentration flue gas to high-concentration CO2, and use a heat exchanger and humidifier to control the temperature and humidity in the reactor: first, hydrate the aggregate for 12 hours at a temperature of 20℃, relative humidity of 60%RH, and CO2 concentration of 5% in the gas. Then, adjust the curing conditions to a temperature of 60℃, relative humidity of 95%RH, and CO2 concentration of 12% in the gas for mineralization curing for 12 hours. Finally, adjust the curing conditions to a temperature of 20℃, relative humidity of 60%RH, and CO2 concentration of 5% in the gas for secondary hydration for 48 hours. After curing, the phosphogypsum-steel slag solid waste-based aggregate is obtained.

[0027] Example 2:

[0028] The only difference between Example 2 and Example 1 is that 800g of phosphogypsum and 200g of steel slag powder are weighed in step S2; the remaining steps and the amount of raw materials added are the same as in Example 1.

[0029] Example 3:

[0030] The only difference between Example 3 and Example 1 is that 700g of phosphogypsum and 300g of steel slag powder are weighed in step S2; the remaining steps and the amount of raw materials added are the same as in Example 1.

[0031] Example 4:

[0032] The only difference between Example 4 and Example 1 is that 600g of phosphogypsum and 400g of steel slag powder are weighed in step S2; the remaining steps and the amount of raw materials added are the same as in Example 1.

[0033] Example 5:

[0034] The only difference between Example 5 and Example 1 is that 500g of phosphogypsum and 500g of steel slag powder are weighed in step S2; the remaining steps and the amount of raw materials added are the same as in Example 1.

[0035] Example 6:

[0036] The difference between Example 6 and Example 3 is that in step S3, the aggregate is first hydrated for 12 hours at a temperature of 30°C, a relative humidity of 70%RH, and a CO2 concentration of 5% in the gas. Then, the curing conditions are adjusted to a temperature of 60°C, a relative humidity of 95%RH, and a CO2 concentration of 12% in the gas for mineralization curing for 12 hours. Finally, the curing conditions are adjusted to a temperature of 30°C, a relative humidity of 70%RH, and a CO2 concentration of 5% in the gas for secondary hydration for 48 hours. After curing, phosphogypsum-steel slag solid waste-based aggregate is obtained.

[0037] Example 7:

[0038] The difference between Example 7 and Example 3 is that in step S3, the aggregate is first hydrated for 12 hours at a temperature of 20°C, a relative humidity of 80%RH, and a CO2 concentration of 5% in the gas. Then, the curing conditions are adjusted to a temperature of 70°C, a relative humidity of 95%RH, and a CO2 concentration of 12% in the gas for mineralization curing for 12 hours. Finally, the curing conditions are adjusted to a temperature of 20°C, a relative humidity of 80%RH, and a CO2 concentration of 5% in the gas for secondary hydration for 48 hours. After curing, phosphogypsum-steel slag solid waste-based aggregate is obtained.

[0039] Example 8:

[0040] The difference between Example 8 and Example 3 is that in step S3, the aggregate is first hydrated for 12 hours at a temperature of 20°C, a relative humidity of 70%RH, and a CO2 concentration of 5% in the gas. Then, the curing conditions are adjusted to a temperature of 70°C, a relative humidity of 85%RH, and a CO2 concentration of 12% in the gas for mineralization curing for 12 hours. Finally, the curing conditions are adjusted to a temperature of 20°C, a relative humidity of 70%RH, and a CO2 concentration of 5% in the gas for secondary hydration for 48 hours. After curing is completed, phosphogypsum-steel slag solid waste-based aggregate is obtained.

[0041] Example 9:

[0042] The difference between Example 9 and Example 3 is that in step S3, the aggregate is first hydrated for 12 hours at a temperature of 20°C, a relative humidity of 60%RH, and a CO2 concentration of 5% in the gas. Then, the curing conditions are adjusted to a temperature of 60°C, a relative humidity of 95%RH, and a CO2 concentration of 15% in the gas for mineralization curing for 6 hours. Finally, the curing conditions are adjusted to a temperature of 20°C, a relative humidity of 60%RH, and a CO2 concentration of 5% in the gas for secondary hydration for 54 hours. After curing, the phosphogypsum-steel slag solid waste-based aggregate is obtained.

[0043] Example 10:

[0044] The difference between Example 10 and Example 3 is that in step S3, the aggregate is first hydrated for 24 hours at a temperature of 20°C, a relative humidity of 60%RH, and a CO2 concentration of 5% in the gas. Then, the curing conditions are adjusted to a temperature of 60°C, a relative humidity of 95%RH, and a CO2 concentration of 20% in the gas for mineralization curing for 12 hours. Finally, the curing conditions are adjusted to a temperature of 20°C, a relative humidity of 60%RH, and a CO2 concentration of 5% in the gas for secondary hydration for 36 hours. After curing, phosphogypsum-steel slag solid waste-based aggregate is obtained.

[0045] Example 11:

[0046] The difference between Example 11 and Example 3 is that in step S3, the aggregate is first hydrated for 36 hours at a temperature of 20°C, a relative humidity of 60%RH, and a CO2 concentration of 5% in the gas. Then, the curing conditions are adjusted to a temperature of 60°C, a relative humidity of 95%RH, and a CO2 concentration of 12% in the gas for mineralization curing for 12 hours. Finally, the curing conditions are adjusted to a temperature of 20°C, a relative humidity of 60%RH, and a CO2 concentration of 5% in the gas for secondary hydration for 24 hours. After curing is completed, phosphogypsum-steel slag solid waste-based aggregate is obtained.

[0047] Example 12:

[0048] The difference between Example 12 and Example 3 is that in step S3, the aggregate is first hydrated for 48 hours at a temperature of 20°C, a relative humidity of 60%RH, and a CO2 concentration of 5% in the gas. Then, the curing conditions are adjusted to a temperature of 60°C, a relative humidity of 95%RH, and a CO2 concentration of 12% in the gas for mineralization curing for 12 hours. Finally, the curing conditions are adjusted to a temperature of 20°C, a relative humidity of 60%RH, and a CO2 concentration of 5% in the gas for secondary hydration for 12 hours. After curing, phosphogypsum-steel slag solid waste-based aggregate is obtained.

[0049] Example 13:

[0050] The difference between Example 13 and Example 3 is that in step S3, the aggregate is first hydrated for 48 hours at a temperature of 20°C, a relative humidity of 60%RH, and a CO2 concentration of 5% in the gas. Then, the curing conditions are adjusted to a temperature of 60°C, a relative humidity of 95%RH, and a CO2 concentration of 12% in the gas for mineralization curing for 6 hours. Finally, the curing conditions are adjusted to a temperature of 20°C, a relative humidity of 60%RH, and a CO2 concentration of 5% in the gas for secondary hydration for 18 hours. After curing, phosphogypsum-steel slag solid waste-based aggregate is obtained.

[0051] Example 14:

[0052] The difference between Example 14 and Example 5 is that in step S3, the aggregate is first hydrated for 24 hours at a temperature of 20°C, a relative humidity of 70%RH, and a CO2 concentration of 5% in the gas. Then, the curing conditions are adjusted to a temperature of 60°C, a relative humidity of 95%RH, and a CO2 concentration of 12% in the gas for mineralization curing for 12 hours. Finally, the curing conditions are adjusted to a temperature of 20°C, a relative humidity of 70%RH, and a CO2 concentration of 5% in the gas for secondary hydration for 36 hours. After curing, phosphogypsum-steel slag solid waste-based aggregate is obtained.

[0053] Example 15:

[0054] The difference between Example 15 and Example 5 is that in step S3, the aggregate is first hydrated for 36 hours at a temperature of 20°C, a relative humidity of 70%RH, and a CO2 concentration of 5% in the gas. Then, the curing conditions are adjusted to a temperature of 60°C, a relative humidity of 95%RH, and a CO2 concentration of 12% in the gas for mineralization curing for 12 hours. Finally, the curing conditions are adjusted to a temperature of 20°C, a relative humidity of 70%RH, and a CO2 concentration of 5% in the gas for secondary hydration for 24 hours. After curing is completed, phosphogypsum-steel slag solid waste-based aggregate is obtained.

[0055] Example 16:

[0056] The difference between Example 16 and Example 5 is that in step S3, the aggregate is first hydrated for 48 hours at a temperature of 20°C, a relative humidity of 70%RH, and a CO2 concentration of 5% in the gas. Then, the curing conditions are adjusted to a temperature of 60°C, a relative humidity of 95%RH, and a CO2 concentration of 12% in the gas for mineralization curing for 12 hours. Finally, the curing conditions are adjusted to a temperature of 20°C, a relative humidity of 70%RH, and a CO2 concentration of 5% in the gas for secondary hydration for 12 hours. After curing is completed, phosphogypsum-steel slag solid waste-based aggregate is obtained.

[0057] Comparative Example 1: A method for preparing phosphogypsum-steel slag solid waste-based aggregate includes the following steps: S1. The phosphogypsum and steel slag powder are screened separately to obtain phosphogypsum with a particle size ≤150μm (free fluoride ions ≤0.5%) and steel slag powder with a particle size ≤75μm (specific surface area ≥400m²). 2 The solid waste raw material powder was obtained by drying it at 120℃ for 6 hours ( / kg). S2. Weigh 500g of phosphogypsum and 500g of steel slag powder after drying in step S1, and put them into the mixer and mix for 60 minutes. Then transfer the raw material mixture to the granulator and spray 150g of water to make water mist to wet the aggregate material with a moisture content of 15% and a particle size of 5~15mm. S3. Place the aggregate blanks into the mineralization reactor, set the reaction pressure of the mineralization reactor to 0.1 MPa, use a flow controller to adjust the inlet ratio of low-concentration flue gas to high-concentration CO2, and use a heat exchanger and humidifier to control the temperature and humidity in the reactor: make the aggregate undergo a single hydration for 72 hours at a temperature of 20℃, a relative humidity of 60%RH, and a CO2 concentration of 5% in the gas. After curing, the phosphogypsum-steel slag solid waste-based aggregate is obtained.

[0058] Comparative Example 2: The only difference between Comparative Example 2 and Comparative Example 1 is that 600g of phosphogypsum and 400g of steel slag powder are weighed in step S2; the remaining steps and the amount of raw materials added are the same as those in Comparative Example 1.

[0059] Comparative Example 3: The only difference between Comparative Example 3 and Comparative Example 1 is that 700g of phosphogypsum and 300g of steel slag powder are weighed in step S2; the remaining steps and the amount of raw materials added are the same as those in Comparative Example 1.

[0060] Comparative Example 4: The only difference between Comparative Example 4 and Comparative Example 1 is that in step S3, the aggregate is mineralized for 12 hours at a temperature of 60℃, a relative humidity of 95%RH, and a CO2 concentration of 12% in the gas. After curing, phosphogypsum-steel slag solid waste-based aggregate is obtained.

[0061] Comparative Example 5: The only difference between Comparative Example 5 and Comparative Example 1 is that in step S3, the aggregate is first hydrated for 60 hours at a temperature of 20℃, a relative humidity of 60%RH, and a CO2 concentration of 5% in the gas. Then, the curing conditions are adjusted to a temperature of 60℃, a relative humidity of 95%RH, and a CO2 concentration of 12% in the gas for mineralization curing for 12 hours. After curing, phosphogypsum-steel slag solid waste-based aggregate is obtained.

[0062] Comparative Example 6: The only difference between Comparative Example 6 and Comparative Example 1 is that in step S3, the aggregate is first mineralized and cured for 12 hours at a temperature of 60℃, a relative humidity of 95%RH, and a CO2 concentration of 12% in the gas. Then, the curing conditions are adjusted to a temperature of 20℃, a relative humidity of 60%RH, and a CO2 concentration of 5% in the gas for hydration curing for 60 hours. After curing, phosphogypsum-steel slag solid waste-based aggregate is obtained.

[0063] Comparative Example 7: The only difference between Comparative Example 7 and Comparative Example 1 is that in step S3, the aggregate is hydrated once for 120 hours under the conditions of 20°C, 60%RH relative humidity, and 5% CO2 concentration in the gas. After curing, phosphogypsum-steel slag solid waste-based aggregate is obtained.

[0064] Comparative Example 8: The only difference between Comparative Example 8 and Comparative Example 1 is that in step S3, the aggregate is hydrated once for 168 hours under the conditions of 20°C, 60%RH relative humidity, and 5% CO2 concentration in the gas. After curing, phosphogypsum-steel slag solid waste-based aggregate is obtained.

[0065] Comparative Example 9: The only difference between Comparative Example 9 and Comparative Example 1 is that in step S3, the aggregate is first hydrated for 12 hours at a temperature of 20°C, a relative humidity of 60%RH, and a CO2 concentration of 5% in the gas. Then, the curing conditions are adjusted to a temperature of 60°C, a relative humidity of 95%RH, and a CO2 concentration of 12% in the gas for mineralization curing for 12 hours. After curing, phosphogypsum-steel slag solid waste-based aggregate is obtained.

[0066] Comparative Example 10: The only difference between Comparative Example 10 and Comparative Example 1 is that in step S3, the aggregate is first hydrated for 48 hours at a temperature of 20°C, a relative humidity of 60%RH, and a CO2 concentration of 5% in the gas. Then, the curing conditions are adjusted to a temperature of 60°C, a relative humidity of 95%RH, and a CO2 concentration of 12% in the gas for mineralization curing for 12 hours. After curing, phosphogypsum-steel slag solid waste-based aggregate is obtained.

[0067] The compressive strength of the phosphogypsum-steel slag solid waste-based aggregates prepared in Examples 1-13 and Comparative Examples 1-10 was tested. Specifically, the mechanical properties of the aggregates were measured using a compressive strength tester and calculated using the following formula, with the average value of multiple experiments taken.

[0068]

[0069] Where σ is the compressive strength of a single aggregate particle, in MPa; P is the load applied when the aggregate fractures, in N; and d is the average particle size of the aggregate, in mm. The test results are shown in Table 1. Table 1. Test results of compressive strength of phosphogypsum-steel slag solid waste-based aggregate

[0070] As shown in Examples 1-5, under the same hydration-mineralization-hydration coupled curing conditions, the compressive strength of the aggregate gradually decreases with the increase of phosphogypsum content in the system, indicating that steel slag hydration is the main contributing component to the strength development of the system. When the steel slag content is low, the active calcium source and silicate components in the system are relatively insufficient, and the amount of early hydration products generated is limited. Appropriately extending the air curing time is beneficial to the gradual hydration of active components in the steel slag, forming an initial cemented skeleton, which provides a reaction basis for subsequent CO2 mineralization. Therefore, later CO2 incorporation is more conducive to strength development. Although within a certain range, the higher the steel slag content, the better the aggregate performance, phosphogypsum is cheaper than steel slag. Therefore, considering both performance and raw material price, Example 3 is the optimal case. Based on Example 3, a large number of different conditions were adjusted, resulting in Examples 6-13.

[0071] Examples 3 and 6-8 show that, under the same phosphogypsum and steel slag content, fluctuations in curing temperature and humidity do not significantly affect the compressive strength of the aggregate, which remains above 2.10 MPa. Examples 3 and 9-13 show that when the steel slag content is 30%, as the initial air introduction time increases from 12 h to 48 h, the compressive strength increases from 2.21 MPa to 2.42 MPa, showing a gradual increasing trend. Examples 5 and 14-16 show that when the steel slag content is 50%, as the initial air introduction time increases and the relative humidity changes, the compressive strength first increases and then decreases. This indicates that changing the CO2 mineralization initiation time results in certain differences in the compressive strength of the phosphogypsum-based aggregate, suggesting that the matching relationship between the air curing stage, the CO2 mineralization stage, and the subsequent air curing stage affects the development of aggregate strength.

[0072] As demonstrated in Examples 3-5 and Comparative Examples 1-3, under different ratios of phosphogypsum and steel slag, the method of incorporating mineralization curing into the hydration curing process can effectively improve the compressive strength of the material. In the unmineralized group (Comparative Examples 1-3), the compressive strength was only 0.28-0.75 MPa, while in the mineralized group (Examples 3-5), the compressive strength increased to 2.21-2.80 MPa, which is nearly 10 times that of the unmineralized group. This fully demonstrates that CO2 mineralization can promote the synergistic formation of hydration products and carbonate mineralization products within the aggregate, thereby improving the microstructure of the aggregate.

[0073] As shown in Examples 3 and Comparative Examples 4-6, compared to materials that only undergo mineralization curing, materials that undergo hydration curing followed by mineralization curing, and materials that undergo mineralization curing followed by hydration curing, the coupled hydration-mineralization-hydration curing method can synergistically promote the formation of hydration products and the generation of carbonate mineralization products. If CO2 mineralization curing is initiated too early, the hydration skeleton inside the aggregate has not yet fully formed; if CO2 mineralization curing is initiated too late, some hydration products may have already filled the pores and restricted CO2 diffusion into the interior, resulting in a decrease in the enhancing effect of the mineralization reaction. Therefore, an appropriate CO2 initiation time can promote the generation of carbonate products inside the aggregate and fill the pores, but mineralization that is too early or too late is not conducive to further strength improvement.

[0074] As shown in Example 3 and Comparative Examples 1, 7-10, although extending the hydration time can significantly promote the overall hydration of the material, it is still difficult to achieve the compressive strength required for hydration-mineralization-hydration coupled curing. This is because during the initial hydration process, the material can promote the formation of the initial hydration cementitious structure. During the mineralization curing process, the alkaline components in the system can be consumed, which not only promotes the subsequent hydration of the material but also generates carbonates and fills the pores. The subsequent air curing stage is beneficial for the continued hydration of unreacted components and for stabilizing the aggregate structure. The three factors work together to enable the aggregate to obtain higher strength in a shorter time, which is conducive to the rapid preparation of phosphogypsum-based aggregates.

[0075] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing phosphogypsum-steel slag solid waste-based aggregate, characterized in that, Includes the following steps: S1. Mix phosphogypsum and steel slag powder to obtain solid waste raw materials. Then mix the solid waste raw materials with water, granulate, and obtain aggregate blanks. S2. The aggregate blanks are placed in a mineralization reactor and subjected to primary hydration, mineralization, and secondary hydration curing in sequence to obtain phosphogypsum-steel slag solid waste-based aggregate. The conditions for primary and secondary hydration are: pressure 0.1 MPa, temperature 20~30℃, relative humidity 60~80%, and CO2 concentration in the gas ≤5%. The conditions for mineralization are: pressure 0.1 MPa, temperature 60~70℃, relative humidity 85~95%RH, and CO2 concentration in the gas ≥10%. The times for primary hydration, mineralization, and secondary hydration are 12~48h, 6~12h, and 12~54h, respectively.

2. The method for preparing phosphogypsum-steel slag solid waste-based aggregate according to claim 1, characterized in that, In step S1, the free fluoride ions in the phosphogypsum are ≤0.5%, and the particle size is ≤150μm; the steel slag powder has a particle size of ≤75μm and a specific surface area of ​​≥400m². 2 / kg.

3. The method for preparing phosphogypsum-steel slag solid waste-based aggregate according to claim 1, characterized in that, Step S1 also includes the following treatment of phosphogypsum and steel slag powder: drying phosphogypsum and steel slag powder at 120-150℃ for 5-8 hours respectively.

4. The method for preparing phosphogypsum-steel slag solid waste-based aggregate according to claim 1, characterized in that, The mass percentages of phosphogypsum and steel slag powder in the solid waste raw materials are 50%–90% and 10%–50%, respectively; water accounts for 15%–20% of the dry weight of the solid waste raw materials.

5. The method for preparing phosphogypsum-steel slag solid waste-based aggregate according to claim 4, characterized in that, The mass percentages of phosphogypsum and steel slag powder in the solid waste raw materials are 50% and 50%, respectively; water accounts for 15% of the dry weight of the solid waste raw materials.

6. The method for preparing phosphogypsum-steel slag solid waste-based aggregate according to claim 1, characterized in that, The total time for primary hydration, mineralization, and secondary hydration is 72 hours.

7. The method for preparing phosphogypsum-steel slag solid waste-based aggregate according to claim 1 or 6, characterized in that, The conditions for primary hydration were: pressure 0.1 MPa, temperature 20℃, relative humidity 70%, CO2 concentration in the gas 5%, and time 36 h.

8. The method for preparing phosphogypsum-steel slag solid waste-based aggregate according to claim 1 or 6, characterized in that, The conditions for secondary hydration were 0.1 MPa pressure, 20℃ temperature, 70% relative humidity, 5% CO2 concentration in the gas, and 24 h time.

9. The method for preparing phosphogypsum-steel slag solid waste-based aggregate according to claim 1 or 6, characterized in that, The mineralization conditions were: pressure 0.1 MPa, temperature 60℃, relative humidity 95%RH, CO2 concentration in the gas 12%, and time 12 h.

10. Phosphogypsum-steel slag solid waste aggregate prepared by any one of the preparation methods described in claims 1 to 9.

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