Large-dosage ardealite curing agent and application thereof

Abstract

The invention provides a high-dosage ardealite curing agent and application thereof, and belongs to the technical field of curing agents. The curing agent comprises a polymer synergistic solution, a hydrophobic modifier, a coagulant and an alkaline stabilizer; wherein the polymer synergistic liquid is prepared from sodium polyacrylate and polyvinyl acetate emulsion; the hydrophobic modifier is prepared from dimethyl tetrachlorodisilane, trimethyl trichlorodisilane and an organic solvent; the coagulant comprises sodium aluminate and sodium silicate; the alkaline stabilizer comprises sodium hydroxide and polyaluminum chloride powder. Through the synergistic effect of the four components, on the premise that the phosphogypsum doping amount is larger than or equal to 90%, the early mechanical property, the water stability and the harmful element curing capacity of the phosphogypsum base road material are remarkably improved. According to the invention, a large amount of industrial solid waste phosphogypsum is consumed, environmental pollution is reduced, and reliable technical support is provided for green, high-value and large-scale application of phosphogypsum.

Description

Technical Field

[0001] This invention relates to the field of curing agents, specifically to a high-dosage phosphogypsum curing agent and its application. Background Technology

[0002] Phosphogypsum is an industrial byproduct of wet-process phosphoric acid production. Its main component is calcium sulfate dihydrate (CaSO4·2H2O), and it contains small amounts of impurities such as phosphorus and fluorine. Due to the lack of efficient and economical resource utilization pathways, the primary method of disposal for phosphogypsum is currently stockpiling. This not only occupies a large amount of land resources but also poses a risk of leachate pollution. With the continuous increase in stockpiles and limited comprehensive utilization, phosphogypsum has become a prominent environmental problem restricting the green development of the phosphorus chemical industry.

[0003] In recent years, research on the resource utilization of phosphogypsum has deepened, and its applications have expanded to building materials, chemicals, agriculture, and environmental functional materials. Among these, using phosphogypsum in road base construction is one of the important directions for achieving its large-scale resource utilization. In particular, high-volume aggregate-free phosphogypsum base structures (phosphogypsum content ≥90%) show great potential due to their large phosphogypsum consumption capacity and low cost. However, the impurities contained in phosphogypsum pose multiple challenges to its application as a cementitious substrate: the impurities in phosphogypsum will seriously delay cement hydration, resulting in the following key problems: (1) significant retarding effect and low early strength: soluble phosphorus and other impurities form a coating layer on the surface of cement particles, which seriously inhibits cement hydration, resulting in slow early strength development of the base material and failure to meet the construction progress requirements; (2) poor water resistance: the hydration products of phosphogypsum itself have poor water resistance, and the impurities delay the formation of dense hydration products, resulting in a low softening coefficient and a significant decrease in strength after contact with water; (3) prominent environmental risks: harmful ions in phosphogypsum have the risk of continuous leaching under long-term service or rainwater leaching conditions, which may cause secondary pollution to groundwater and surrounding soil; the above problems seriously limit the large-scale application of phosphogypsum in road engineering.

[0004] In existing technologies, numerous attempts have been made to improve the performance of phosphogypsum base materials through composite modification. Patent CN119241197A discloses a modified phosphogypsum cement-stabilized material and its preparation method and application, which is composed of phosphogypsum, cement, sodium silicate, quicklime and water, wherein the mass ratio of phosphogypsum to cement is 85~95:5~15. Although it improves the material performance to a certain extent, the 7-day unconfined compressive strength is only 3.8-4.7 MPa, and the strength growth at 14 days and 28 days is limited, making it difficult to meet the higher requirements of high-grade highway base courses for early strength and long-term load-bearing capacity. Moreover, it does not provide systematic test data on the leaching concentration of harmful elements, and it is impossible to clarify its pollution risk under long-term service or rainwater leaching conditions. Patent CN112125630A discloses a high-dosage phosphogypsum-based stabilized material and its application in road base courses. It uses 64-74% undisturbed phosphogypsum, 13-20% slag, 7-13% cement, and a composite modifier composed of calcium chloride, petroleum coke desulfurization ash, bentonite, talc, and casein. The 21-day unconfined compressive strength reaches up to 4.12 MPa, and it significantly reduces the leaching concentration of fluorine and phosphorus. However, the simultaneous curing effect of multiple heavy metals (such as chromium, lead, cadmium, arsenic, and mercury) has not been systematically investigated, and further verification of its leaching of harmful elements in complex environments is still needed.

[0005] In summary, existing technologies still have significant shortcomings in early strength development, long-term water stability assurance, and synergistic solidification of multiple pollutants. Therefore, the development of a novel aggregate-free base material with high phosphogypsum content that can simultaneously achieve early strength, high water stability, and low pollution is of great practical significance. Summary of the Invention

[0006] The main objective of this invention is to provide a high-dosage phosphogypsum curing agent and its application, addressing the problems mentioned in the background section. The curing agent of this invention comprises a polymer synergist, a hydrophobic modifier, a setting accelerator, and an alkaline stabilizer. Through the synergistic effects of these components in dispersion toughening, hydrophobic protection, early strength setting, and multi-pollutant synergistic curing, the proportions can be flexibly adjusted to significantly improve the overall performance of aggregate-free road base materials with high-dosage phosphogypsum. The prepared road base material exhibits excellent mechanical strength, long-term water stability, and environmental safety, providing technical support for the resource utilization of phosphogypsum.

[0007] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows:

[0008] A high-dosage phosphogypsum curing agent comprises a polymer synergist, a hydrophobic modifier, a coagulant accelerator, and an alkaline stabilizer in a mass ratio of 1-4:2-6:1-4:2-6.

[0009] Preferably, the polymer synergist comprises sodium polyacrylate, polyvinyl acetate emulsion, and water in a mass ratio of 6-9:3-6:85-91.

[0010] More preferably, the mass ratio of sodium polyacrylate, polyvinyl acetate emulsion and water is 8:4:88.

[0011] In the above technical solution, sodium polyacrylate, as an anionic polymeric dispersant, has its molecular chains adsorbed on the surface of phosphogypsum and cement particles. Through electrostatic repulsion and steric hindrance, it effectively breaks down particle flocculation, releases encapsulated water, and greatly improves the uniformity and flowability of the mixture. Polyvinyl acetate emulsion, as a film-forming polymer, has its emulsion particles demulsified and fused in the acidic environment created by the system's dehydration and hydrophobic modifier. This forms a continuous and flexible polymer film between the rigid network and the inorganic particle interface, significantly improving the material's toughness, crack resistance, and strength.

[0012] Preferably, the polymer synergist is prepared by the following method: dissolving sodium polyacrylate powder in water, stirring and mixing evenly, then adding polyvinyl acetate emulsion and stirring and mixing evenly again to obtain the product.

[0013] Preferably, the hydrophobic modifier comprises dimethyltetrachlorodisilane, trimethyltrichlorodisilane, and an organic solvent in a mass ratio of 5-8:3-5:12-26.

[0014] More preferably, the organic solvent is toluene; the mass ratio of dimethyltetrachlorodisilane, trimethyltrichlorodisilane and toluene is 5:5:15.

[0015] In the above technical solution, dimethyltetrachlorodisilane can form a rigid siloxane network with high cross-linking density after hydrolysis, which helps to form a hydrophobic framework and promotes the formation of early strength; trimethyltrichlorodisilane can participate in network formation after hydrolysis, and because it contains three methyl groups, it can also act as a network terminator, effectively regulating the density and flexibility of the network structure and avoiding embrittlement; toluene, as a carrier, not only solvents the silane monomer, but also helps to uniformly disperse the hydrophobic silane in the hydrophilic mixture in the form of tiny droplets, ensuring the efficient distribution and reaction of the hydrophobic modifier.

[0016] Preferably, the hydrophobic modifier is prepared by the following method: adding dimethyltetrachlorodisilane and trimethyltrichlorodisilane to an organic solvent and stirring and mixing them evenly at room temperature.

[0017] Preferably, the coagulant comprises sodium aluminate, sodium silicate, and water in a mass ratio of 6-9:2-4:87-92.

[0018] More preferably, the mass ratio of sodium aluminate, sodium silicate and water is 7:3:90.

[0019] In the above technical solution, sodium aluminate can react rapidly with the gypsum component in cement under alkaline conditions to quickly generate a large number of needle-like ettringite crystals, which is the core component for achieving early strength and rapid setting; sodium silicate not only provides alkalinity to stimulate the activity of sodium aluminate and cement, but also reacts with cement hydration products to generate calcium silicate gel, synergistically improving the early mechanical strength of the material.

[0020] Preferably, the coagulant is prepared by the following method: dissolving sodium aluminate powder in water, stirring and mixing evenly, then adding liquid sodium silicate and stirring and mixing evenly again to obtain the coagulant.

[0021] Preferably, the alkaline stabilizer comprises sodium hydroxide, polyaluminum chloride powder, and water in a mass ratio of 5-8:3-6:86-92.

[0022] More preferably, the mass ratio of sodium hydroxide, polyaluminum chloride and water is 6:4:90.

[0023] In the above technical solution, sodium hydroxide provides a high concentration of OH. - It rapidly increases the pH value of the system, creating favorable alkaline conditions for cement hydration and the function of polyaluminum chloride, while neutralizing the acidity of phosphogypsum and inhibiting the dissolution of harmful substances. Under alkaline conditions, the hydrolysis products generated by polyaluminum chloride react with soluble phosphate and fluoride ions to form water-insoluble precipitates. At the same time, the high-valent polycations it contains can effectively adsorb negatively charged colloidal particles and impurity ions, destabilizing and agglomerating them through charge neutralization and adsorption bridging, and fixing them in the hardened body, thus achieving simultaneous passivation and solidification of multiple pollutants.

[0024] Preferably, the mass ratio of the polymer synergist, hydrophobic modifier, coagulant accelerator, and alkaline stabilizer is 2:3:2:3.

[0025] Preferably, the alkaline stabilizer is prepared by the following method: dissolving solid sodium hydroxide in water, stirring and mixing evenly, cooling to room temperature, and then adding polyaluminum chloride powder and stirring and mixing evenly again.

[0026] The second aspect of this invention provides the application of a high-dosage phosphogypsum curing agent in the preparation of aggregate-free road base materials with high dosage phosphogypsum, comprising the following steps: S1. Mix the raw phosphogypsum and cement evenly to obtain the first mixture; S2. The polymer synergist is atomized and sprayed into the first mixture and stirred until evenly mixed to obtain the second mixture; S3. After atomizing the coagulant and alkaline stabilizer in sequence, spray them into the second mixture and stir to mix evenly to obtain the third mixture. S4. Add the hydrophobic modifier to the third mixture and stir until evenly mixed to obtain a high-volume phosphogypsum aggregate-free road base material.

[0027] In the above technical solution, a polymer synergist is first added to effectively disperse the aggregate and cement particles, ensuring good flowability and uniformity of the mixture. Then, a setting accelerator is added to rapidly activate cement hydration in a fully wetted environment, accelerating the formation of ettringite and CSH gel to build an early strength framework. Next, an alkaline stabilizer is added to further increase the alkalinity of the system, enhancing the hydration reaction while synergistically fixing harmful ions such as phosphorus, fluorine, and heavy metals. Finally, a hydrophobic modifier is added dropwise under high-speed stirring to prevent premature hydrolysis or agglomeration in highly alkaline environments or during prolonged stirring, ensuring that the organosilane forms a dense, continuous hydrophobic network in situ before molding. This order of addition effectively avoids mutual interference between functional components, achieving a temporal match and synergistic effect of dispersion toughening, early setting acceleration, pollutant solidification, and hydrophobic protection. This provides a guarantee for the high strength, high water stability, and high environmental safety of aggregate-free road base materials with high phosphogypsum content.

[0028] Preferably, the stirring speed in step S1 is 20-30 rpm, and the stirring time is 2-3 min; The stirring speed in steps S2 and S3 is 150-250 rpm, and stirring continues for 3-5 minutes after spraying is completed.

[0029] In step S4, the stirring speed is ≥300 rpm, and stirring continues for 2-3 minutes after all the hydrophobic modifier has been added.

[0030] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. This invention effectively disperses particles and releases encapsulated water through sodium polyacrylate in the polymer synergist, improving the uniformity and flowability of the mixture; after the polyvinyl acetate emulsion forms a film, it bridges the inorganic phase, giving the material good toughness and resistance to drying shrinkage cracking, thus improving the long-term service performance of the base structure; sodium hydroxide in the alkaline stabilizer raises the pH value of the system to inhibit the leaching of phosphorus and fluorine, while polyaluminum chloride simultaneously fixes phosphate, fluoride ions and various heavy metals such as Cr, Pb, Cd, and As through precipitation, adsorption and complexation. The concentration of various pollutants in the leachate meets the requirements of the "Technical Specification for Application of Phosphogypsum Road Base Materials" (DB42 / T 1991-2023), and has high environmental safety.

[0031] 2. This invention utilizes a highly efficient coagulating system composed of sodium aluminate and sodium silicate to rapidly generate ettringite and CSH gel under a strongly alkaline environment. This enables base course materials with ≥90% phosphogypsum content to achieve an unconfined compressive strength of over 7 MPa at 7 days, meeting the early bearing capacity requirements of high-grade highway base courses. Furthermore, the invention employs the hydrolysis and condensation of organosilanes in the hydrophobic modifier within the mixture to construct a dense, cross-linked hydrophobic silica network on the surface of phosphogypsum particles. The flexible membrane structure formed by the synergistic polymer enhancer creates a dual protection mechanism, resulting in a softening coefficient as high as 0.90 and a water softening strength loss of less than 10%. The overall performance is significantly superior to conventional cement-stabilized phosphogypsum materials.

[0032] 3. This invention effectively solves the technical problems of slow setting, low strength, poor water resistance and high environmental risk of high-dosage phosphogypsum base materials by means of the synergistic effect of the dispersion toughening of polymer toughening liquid, the hydrophobic protection of hydrophobic modifier, the early strength activation of coagulation accelerator and the solidification of pollutants by alkaline stabilizer. It provides reliable technical support for the green, high-value and large-scale application of phosphogypsum in road construction.

[0033] 4. This invention achieves a phosphogypsum content of up to 90% without using natural aggregates, which not only enables the efficient utilization of bulk industrial solid waste but also significantly reduces solid waste stockpiling and natural sand and gravel mining, resulting in significant environmental and economic benefits. Detailed Implementation

[0034] The present invention will be further illustrated below with reference to the embodiments, but the following embodiments are only used to explain the present invention and are not intended to limit the scope of protection of the present invention.

[0035] A curing agent for road base materials with high dosage of phosphogypsum comprises a polymer synergist, a hydrophobic modifier, a coagulant accelerator, and an alkaline stabilizer in a mass ratio of 1-4:2-6:1-4:2-6; wherein the polymer synergist comprises sodium polyacrylate, polyvinyl acetate emulsion, and water in a mass ratio of 6-9:3-6:85-91; the hydrophobic modifier comprises dimethyltetrachlorodisilane, trimethyltrichlorodisilane, and an organic solvent in a mass ratio of 5-8:3-5:12-26; the coagulant accelerator comprises sodium aluminate, sodium silicate, and water in a mass ratio of 6-9:2-4:87-92; and the alkaline stabilizer comprises sodium hydroxide, polyaluminum chloride powder, and water in a mass ratio of 5-8:3-6:86-92.

[0036] The preparation method of the polymer synergist is as follows: Sodium polyacrylate powder is slowly and evenly added to water at a speed of 100-200 rpm. After the addition is complete, the mixture is stirred continuously at a speed of 200-300 rpm for 10-15 minutes until the sodium polyacrylate is completely dissolved, forming a homogeneous, transparent, viscous solution. Then, polyvinyl acetate emulsion is slowly added at a speed of 100-200 rpm, and the mixture is stirred continuously at a speed of 100-200 rpm for 5-10 minutes until a stable mixture with uniform components, no layering, and no flocculation is obtained, which is the polymer synergist.

[0037] The hydrophobic modifier is prepared as follows: Dimethyltetrachlorodisilane and trimethyltrichlorodisilane are slowly added to toluene and stirred until homogeneous to obtain the hydrophobic modifier.

[0038] The preparation method of the coagulant is as follows: at a speed of 100-200 rpm, solid sodium aluminate powder is slowly added to a portion of water and stirred until it is completely dissolved; then liquid sodium silicate is added, and the container holding the sodium silicate is rinsed with the remaining water, and the rinsing liquid is poured into the mixture to make up the total water volume to 90 parts. Stirring is continued for 5-10 minutes until the solution is completely homogeneous to obtain the coagulant.

[0039] The alkaline stabilizer is prepared as follows: at a speed of 100-200 rpm, solid sodium hydroxide is slowly and in batches added to water. After it is completely dissolved and cooled to room temperature, polyaluminum chloride powder is slowly added. At a speed of 200-300 rpm, stirring is continued for 5-10 minutes until the polyaluminum chloride powder is completely dissolved and a homogeneous solution is formed, thus obtaining the alkaline stabilizer.

[0040] In the following examples and comparative examples, a road base material with a high dosage of phosphogypsum was prepared with a mix ratio of 90% phosphogypsum, 10% cement, and 1% external curing agent. The base structure with dimensions of 2000mm×1000mm×200mm was prepared. The undisturbed phosphogypsum was obtained from Huangmailing Phosphate Chemical Co., Ltd., with a CaSO4·2H2O content of 89.26%, a soluble phosphorus content of 0.17%, a crystal water content of 18.68%, an attached water content of 8-10%, and an SO3 content of 43.04%.

[0041] Example 1: A high-dosage phosphogypsum curing agent comprises a polymer synergist, a hydrophobic modifier, a coagulant accelerator, and an alkaline stabilizer in a mass ratio of 2:3:2:3; wherein the polymer synergist comprises sodium polyacrylate, polyvinyl acetate emulsion, and water in a mass ratio of 8:4:88; the hydrophobic modifier comprises dimethyltetrachlorodisilane, trimethyltrichlorodisilane, and an organic solvent in a mass ratio of 6:4:15; the coagulant accelerator comprises sodium aluminate, sodium silicate, and water in a mass ratio of 7:3:90; and the alkaline stabilizer comprises sodium hydroxide, polyaluminum chloride powder, and water in a mass ratio of 6:4:90.

[0042] The application of the high-dosage phosphogypsum curing agent in the preparation of aggregate-free road base materials with high dosage phosphogypsum includes the following steps: S1. Weigh 900 kg of raw phosphogypsum (natural water content 8%) and 100 kg of cement, and add them to a forced mixer equipped with a spray system. Mix at 25 rpm for 2.5 min to obtain the first mixture. Tests showed that the maximum dry density and optimum moisture content of the mixture were 1.58 g / cm³. 3 The wet density at 13.0%, i.e., the optimum moisture content, is 1.58 × (1 + 13%) = 1.79 g / cm³. 3 The additional water required is (13%-8%)×(900kg+100kg)=50kg; S2. Dissolve 2 kg of polymer synergist in 10 kg of water and add it to the spray system of the mixer. The polymer synergist is then evenly atomized and sprayed into the first mixture through the spray system. After spraying, continue stirring at 200 rpm for 4 minutes to obtain the second mixture. S3. Dissolve 2 kg of coagulant and 3 kg of alkaline stabilizer in 20 kg of water respectively. Then, spray the water-dissolved coagulant and alkaline stabilizer into the second mixture in an atomized form through a spray system. After spraying, continue stirring at 200 rpm for 4 minutes to obtain the third mixture. S4. Slowly add 3 kg of hydrophobic modifier to the center of the stirring vortex of the third mixture in a thin stream. Stir and mix evenly at a speed of 500 rpm. After the addition is completed, continue stirring for 2.5 min to obtain the aggregate-free road base material with high phosphogypsum content.

[0043] Example 2: This embodiment is the same as Example 1, except that the mass ratio of polymer synergist, hydrophobic modifier, coagulant accelerator and alkaline stabilizer is 4:3:2:3.

[0044] Example 3: This embodiment is the same as Example 1, except that the mass ratio of polymer synergist, hydrophobic modifier, coagulant accelerator and alkaline stabilizer is 2:5:2:3.

[0045] Example 4: This embodiment is the same as Example 1, except that the mass ratio of polymer synergist, hydrophobic modifier, coagulant accelerator and alkaline stabilizer is 2:3:4:3.

[0046] Example 5: This embodiment is the same as Example 1, except that the mass ratio of polymer synergist, hydrophobic modifier, coagulant accelerator and alkaline stabilizer is 2:3:2:5.

[0047] Example 6: This embodiment is the same as Example 1, except that the ratio of sodium polyacrylate, polyvinyl acetate emulsion and water in the polymer synergist is 6:6:88.

[0048] Example 7: This embodiment is the same as Example 1, except that the ratio of sodium polyacrylate, polyvinyl acetate emulsion and water in the polymer synergist is 9:3:88.

[0049] Example 8: This embodiment is the same as Example 1, except that the ratio of dimethyltetrachlorodisilane, trimethyltrichlorodisilane and organic solvent in the hydrophobic modifier is 5:5:15.

[0050] Example 9: This embodiment is the same as Example 1, except that the ratio of dimethyltetrachlorodisilane, trimethyltrichlorodisilane and organic solvent in the hydrophobic modifier is 7:3:15.

[0051] Example 10: This embodiment is the same as Embodiment 1, except that the ratio of sodium aluminate, sodium silicate and water in the coagulant is 6:4:90.

[0052] Example 11: This embodiment is the same as Embodiment 1, except that the ratio of sodium aluminate, sodium silicate and water in the coagulant is 8:2:90.

[0053] Example 12: This embodiment is the same as Example 1, except that the ratio of sodium hydroxide, polyaluminum chloride powder and water in the alkaline stabilizer is 5:5:90.

[0054] Example 13: This embodiment is the same as Embodiment 1, except that the ratio of sodium hydroxide, polyaluminum chloride powder and water in the alkaline stabilizer is 7:3:90.

[0055] Comparative Example 1: This comparative example is the same as Example 1, except that no polymer synergist is added.

[0056] Comparative Example 2: This comparative example is the same as Example 1, except that no hydrophobic modifier is added.

[0057] Comparative Example 3: This comparative example is the same as Example 1, except that no coagulant is added.

[0058] Comparative Example 4: This comparative example is the same as Example 1, except that no alkaline stabilizer is added.

[0059] Comparative Example 5: This comparative example is the same as Example 1, except that no polymer synergist, hydrophobic modifier, coagulant accelerator, or alkaline stabilizer is added.

[0060] Comparative Example 6: This comparative example is the same as Example 1, except that the ratio of polymer synergist, hydrophobic modifier, coagulant accelerator and alkaline stabilizer is 5:3:2:2.

[0061] Comparative Example 7: This comparative example is the same as Example 1, except that the ratio of polymer synergist, hydrophobic modifier, coagulant and alkaline stabilizer is 2:7:1:2.

[0062] Comparative Example 8: This comparative example is the same as Example 1, except that the ratio of polymer synergist, hydrophobic modifier, coagulant and alkaline stabilizer is 2:2:6:2.

[0063] Comparative Example 9: This comparative example is the same as Example 1, except that the ratio of polymer synergist, hydrophobic modifier, coagulant and alkaline stabilizer is 1:2:2:7.

[0064] The high-dosage phosphogypsum road base materials prepared in the above embodiments and comparative examples were poured into special molds, pressed into shape, and compacted to a degree of 95%. Mechanical properties and harmful element content were then measured using the following methods: (1) In accordance with the provisions of the "Test Procedure for Inorganic Binder Stabilized Materials for Highway Engineering" (JTG3441-2024), unconfined compressive strength test and softening coefficient test shall be carried out; (2) The concentration of characteristic elements in the leachate was tested in accordance with the requirements of the Hubei Provincial Local Standard "Technical Specification for Application of Phosphogypsum Road Base Material" (DB42 / T1991-2023). The test results are shown in Table 1-2.

[0065] Table 1. Mechanical property test results of the base materials in the examples and comparative examples.

[0066] Table 2. Elemental concentration test results of the base materials in the examples and comparative examples (unit: mg / L)

[0067] As shown in Tables 1-2, the 7-day unconfined compressive strength of Examples 1-13 is ≥7.0 MPa, and the softening coefficient is 0.85-0.91, meeting the technical requirements for high-grade highway base courses. Meanwhile, the concentrations of total phosphorus, fluoride, and various heavy metals in the leachate are all below the standard limits of the "Technical Specification for Application of Phosphogypsum Road Base Course Materials" (DB42 / T1991-2023), demonstrating excellent environmental friendliness. In particular, Example 8 exhibits a compressive strength of 8.00 MPa and a softening coefficient as high as 0.91, indicating that the composition of this group significantly enhances the mechanical strength and water resistance of the material. Moreover, the leaching concentrations of key pollutants are low, with total phosphorus at 22 mg / L, water-soluble fluoride at 2.5 mg / L, and total cadmium and total arsenic far below the limits. This result demonstrates that the combined action of polymer synergist, hydrophobic modifier, coagulant accelerator, and alkaline stabilizer can significantly improve the 7-day unconfined compressive strength and softening coefficient of phosphogypsum samples, effectively suppress strength loss after immersion in water, and at the same time greatly reduce the concentration of harmful elements such as total phosphorus, water-soluble fluoride, total chromium, total lead, total cadmium, total arsenic, and total mercury in the leachate, thus achieving effective solidification of residual harmful substances in the undisturbed phosphogypsum.

[0068] Compared to the examples, Comparative Example 1 lacked a polymer synergist, resulting in reduced compressive strength and softening coefficient. This was due to the absence of the dispersing effect of sodium polyacrylate and the film-forming bridging effect of polyvinyl acetate emulsion, leading to increased particle flocculation, decreased uniformity of the mixture, and the lack of a flexible polymer network in the hardened body, thus weakening the material's cohesion, crack resistance, and mechanical properties. Comparative Example 2 lacked a hydrophobic modifier, resulting in a softening coefficient of 0.76 and reduced compressive strength. This was due to the inability to form a hydrophobic silica network generated by the hydrolysis and condensation of organosilanes. The phosphogypsum particles had strong hydrophilicity, making them prone to structural softening and interfacial peeling under immersion conditions, thus significantly weakening the material's water resistance stability. Comparative Example 3 lacked a coagulant, resulting in a strength decrease to 6.78 MPa. This was due to the lack of synergistic effects of sodium aluminate and sodium silicate. The rapid hydration reaction slows down the formation rate of ettringite and CSH gel, resulting in insufficient early gel structure development. Comparative Example 4, lacking an alkaline stabilizer, shows a significant increase in pollutant leaching. Due to the low pH of the system, it cannot effectively inhibit the leaching of acidic impurities in phosphogypsum. Furthermore, the lack of polyaluminum chloride-provided polynuclear hydroxyaluminum complexes for the precipitation, adsorption, and complexation of phosphate, fluoride, and heavy metal ions leads to a significant reduction in the curing efficiency of harmful elements. This demonstrates that an alkaline stabilizer can effectively improve the curing ability of harmful elements in phosphogypsum. Comparative Example 5, without any added functional components, exhibits extremely low strength (only 2.88 MPa) and exceeds multiple environmental protection standards, failing to meet engineering and environmental requirements. This indicates that the composite curing agent can effectively control the leaching of harmful elements, ensuring the environmental safety of the material during long-term service. When the component ratios of the composite curing agents in Comparative Examples 6-9 deviate from the scope of this invention, the 7-day strength, softening coefficient, and leaching concentration of harmful elements are all affected to varying degrees. This demonstrates that the proportion range defined in this invention is key to achieving optimized mechanical properties and synergistic curing of multiple pollutants.

[0069] In summary, this invention, through the synergistic effect of polymer synergist, hydrophobic modifier, coagulant accelerator, and alkaline stabilizer, and through multiple mechanisms including dispersion toughening, hydrophobic protection, early strength coagulation, and synergistic curing of multiple pollutants, successfully optimizes the early mechanical strength, long-term water stability, and curing ability of harmful elements in high-dosage phosphogypsum-based road base materials. This invention not only effectively solves the environmental problems caused by phosphogypsum stockpiling, but also transforms it into a high-value-added road engineering material with good prospects for engineering applications.

[0070] The above embodiments are merely preferred technical solutions of the present invention and should not be considered as limitations on the present invention. The scope of protection of the present invention should be limited to the technical solutions described in the claims, including equivalent substitutions of the technical features described in the claims. That is, equivalent substitutions and improvements within this scope are also within the scope of protection of the present invention.

Claims

1. A high-dosage phosphogypsum curing agent, characterized in that: It includes a polymer synergist, a hydrophobic modifier, a coagulant accelerator, and an alkaline stabilizer in a mass ratio of 1-4:2-6:1-4:2-6.

2. The high-dosage phosphogypsum curing agent according to claim 1, characterized in that: The polymer synergist comprises sodium polyacrylate, polyvinyl acetate emulsion, and water in a mass ratio of 6-9:3-6:85-91.

3. The high-dosage phosphogypsum curing agent according to claim 1, characterized in that: The hydrophobic modifier comprises dimethyltetrachlorodisilane, trimethyltrichlorodisilane, and an organic solvent in a mass ratio of 5-8:3-5:12-26.

4. The high-dosage phosphogypsum curing agent according to claim 1, characterized in that: The coagulant comprises sodium aluminate, sodium silicate, and water in a mass ratio of 6-9:2-4:87-92.

5. The high-dosage phosphogypsum curing agent according to claim 1, characterized in that: The alkaline stabilizer comprises sodium hydroxide, polyaluminum chloride powder, and water in a mass ratio of 5-8:3-6:86-92.

6. The high-dosage phosphogypsum curing agent according to claim 1, characterized in that: The mass ratio of the polymer synergist, hydrophobic modifier, coagulant accelerator, and alkaline stabilizer is 2:3:2:

3.

7. The application of the high-dosage phosphogypsum curing agent according to any one of claims 1 to 6 in the preparation of aggregate-free road base materials with high dosage phosphogypsum, characterized in that: Includes the following steps: S1. Mix the raw phosphogypsum and cement evenly to obtain the first mixture; S2. The polymer synergist is atomized and sprayed into the first mixture and stirred until evenly mixed to obtain the second mixture; S3. After atomizing the coagulant and alkaline stabilizer in sequence, spray them into the second mixture and stir to mix evenly to obtain the third mixture. S4. Add the hydrophobic modifier to the third mixture and stir until evenly mixed to obtain a road base material with high aggregate content and no aggregate phosphogypsum.

8. The application according to claim 7, characterized in that: The stirring speed in step S1 is 20-30 rpm, and the stirring time is 2-3 min.

9. The application according to claim 7, characterized in that: The stirring speed in steps S2 and S3 is 150-250 rpm, and stirring continues for 3-5 minutes after spraying is completed.

10. The application according to claim 7, characterized in that: In step S4, the stirring speed is ≥300 rpm, and stirring continues for 2-3 minutes after all the hydrophobic modifier has been added.

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