Industrial solid waste-based phosphogypsum-based curing agent as well as preparation method and application thereof

Abstract

The invention discloses an industrial solid waste-based phosphogypsum-based curing agent as well as a preparation method and application thereof. According to the curing agent, industrial solid wastes such as slag powder, fly ash and steel slag powder are used as main inorganic gelling components, and are matched with a sodium carboxymethyl cellulose-waterborne epoxy resin organic modification system, a nano-modified silicon dioxide-graphene oxide reinforcing component and a silane coupling agent interface modifier; the curing agent is prepared through a low-temperature grinding activation and ultrasonic dispersion process, and through the cooperation of a quaternary system of multi-element industrial solid waste cooperative activation-organic / inorganic interface enhancement-nanomaterial functionalization-toxicity reduction synergistic effect, the problems that an ardealite base layer is low in strength, poor in water resistance and high in environmental protection risk are solved; the method is suitable for heavy traffic base engineering such as expressways, and efficient recycling and low-carbon preparation of industrial solid waste are achieved.

Description

Technical Field

[0001] This invention belongs to the field of road engineering materials technology, specifically relating to an industrial solid waste-based phosphogypsum base curing agent and its preparation method and application, which is particularly suitable for heavy-duty traffic base engineering such as highways. Background Technology

[0002] Phosphogypsum, a byproduct of wet-process phosphoric acid production, has a huge annual output. Open-air stockpiling not only occupies land but also poses a risk of pollution from soluble phosphorus, fluorine, and heavy metals. Using phosphogypsum in road construction materials is an important way to utilize it on a large scale, but it faces many technical bottlenecks, such as insufficient strength and durability, low utilization rate of industrial solid waste, significant environmental risks, and poor interfacial compatibility with other aggregates. When traditional cement-based curing agents cure phosphogypsum, the soluble phosphorus in the phosphogypsum delays cement hydration, resulting in low early strength and significant strength loss upon contact with water, failing to meet the strength and water resistance requirements of highway base courses. In existing technologies, the amount of industrial solid waste (such as slag and fly ash) added is usually <50%, and it is mostly dominated by single solid wastes, failing to form a multi-component solid waste synergistic activation system, making it difficult to simultaneously improve strength and utilize solid waste. Soluble phosphorus and fluorine in phosphogypsum are easily leached out. Although traditional chemical precipitation methods can reduce the leaching concentration, it is difficult to achieve long-term stable curing and may lead to excessively high alkalinity in the cured body. The weak interfacial bonding between organic polymers and inorganic cementitious materials easily leads to the formation of a weak layer, resulting in poor crack resistance of the cured body and an inability to adapt to the deformation requirements of the base layer.

[0003] Therefore, there is an urgent need to develop a phosphogypsum base curing agent that combines "high industrial solid waste content, high strength and water resistance, low toxicity release, and synergistic interface enhancement" to meet the stringent requirements of highway base courses for material performance and environmental protection. Summary of the Invention

[0004] This invention provides an organic-inorganic synergistic industrial solid waste-based phosphogypsum base layer solidifying agent, featuring a quaternary system of "multi-element industrial solid waste synergistic activation - organic / inorganic interface enhancement - nanomaterial functionalization - detoxification synergistic effect," overcoming the shortcomings of existing technologies. Specifically, the solidifying agent is composed of an inorganic cementing component and an organic modifying component. The inorganic cementing component, by weight, includes 35-45 parts of slag powder, 20-30 parts of fly ash, 10-15 parts of steel slag powder, and 5-15 parts of sulfoaluminate cement. The organic modified component, by weight, includes: 0.5-1 parts sodium carboxymethyl cellulose and 1-2 parts waterborne epoxy resin; nano-reinforcing components: 0.8-1.2 parts nano-modified silica and 0.05-0.1 parts graphene oxide; interface modifier KH560 silane coupling agent 0.3-0.6 parts; detoxifying agent: 5-8 parts calcium carbide slag and 2-3 parts magnesium chloride, wherein the nano-modified silica and graphene oxide contain carboxyl groups.

[0005] Slag powder provides Ca 2+ Al is supplemented by active SiO2, fly ash and steel slag powder. 3+ In the alkaline environment (pH=10~12) of sulfoaluminate cement, cementitious products are generated through the following reaction: , Fe in steel slag powder 3+ With F in phosphogypsum - It forms a stable complex (FeF3), reducing the risk of fluorine leaching.

[0006] The silane coupling agent KH560 hydrolyzes to generate silanol groups (Si-OH), which react with the carboxyl groups of oxygen-containing functional groups in nano-modified silica and graphene oxide to form Si-OC covalent bonds, thereby improving the interfacial adhesion strength. The reaction formula is as follows: , The hydroxyl groups (-OH) of sodium carboxymethyl cellulose form hydrogen bonds with the silicon-oxygen bonds (Si-O-Si) of the Ca-Si-H gel. After curing with waterborne epoxy resin, a three-dimensional network is formed, filling the pores of the inorganic framework and reducing the thickness of the interfacial transition zone. Simultaneously, nano-modified silica fills the gel pores, increasing the density of the cured body and reducing the permeability coefficient. The high specific surface area of ​​graphene oxide can adsorb soluble phosphorus, which, combined with the Ca from carbide slag... 2+ Hydroxyapatite is formed, which reduces the concentration of soluble phosphorus leaching.

[0007] Adjust the pH of the carbide slag system to 8-9 to promote Mg 2+ With F - It produces sparingly soluble MgF2, while Mg... 2+ SO4 in phosphogypsum 2- The formation of MgSO4·H2O fills the pores and inhibits the dissolution of MgSO4·H2O; magnesium chloride reacts with carbide slag to form Mg(OH)2 colloid, which adsorbs heavy metal ions (such as Pb). 2+ Cd 2+ ), forming hydroxide precipitates.

[0008] Furthermore, the slag powder is grade S95 with a specific surface area ≥500m². 2 / kg; fly ash is Class F, Grade I, with a loss on ignition ≤5%; steel slag powder is Grade II, with a free calcium oxide content ≤3%. The preferred amount is 23-28 parts, and the effective components of the fly ash are preferably Al2O3, CaO, SiO2, and Fe2O3; the preferred amount of sulfoaluminate cement is 7-12 parts, and the effective components of the sulfoaluminate cement are preferably Al2O3, CaO, SiO2, and SO3; the preferred sulfoaluminate cement is rapid-hardening sulfoaluminate cement.

[0009] Furthermore, the sodium carboxymethyl cellulose is preferably 0.51 to 0.83 parts, the substitution value (DS) of the sodium carboxymethyl cellulose is 0.7 to 1.2, preferably 0.7 to 1.0; the waterborne epoxy resin is preferably 1.2 to 1.8 parts, the solid content is ≥60%, preferably 63.6%, and the epoxy equivalent is 80 to 220 g / eq.

[0010] Furthermore, the nano-modified silica is preferably 0.86~1.08 parts, with a particle size of 10~30 nm and a specific surface area of ​​600~1000 m². 2 / g, SiO2 purity ≥99.8%; graphene oxide layers ≤10, oxygen-containing functional group content ≥30%, specific surface area 100~300m² 2 / g, preferably 763.2m 2 / g.

[0011] Furthermore, the hydrolysis rate of the KH560 silane coupling agent is ≥90%; the refractive index of the KH560 silane coupling agent is preferably 1.4260~1.4300, more preferably 1.4283; and the Ca(OH)2 content of the carbide slag is ≥80%.

[0012] On the other hand, the present invention also provides a method for preparing the curing agent as described above, comprising the following steps: (1) After mixing slag powder, fly ash and steel slag powder, grind them in a ball mill for 20-30 minutes until the specific surface area is ≥450m². 2 / kg, add sulfoaluminate cement, carbide slag, and magnesium chloride, stir for 10-15 minutes to form an inorganic mixture; (2) Dissolve sodium carboxymethyl cellulose in deionized water at 80-90°C, stir until completely dissolved, cool to 25-30°C and add waterborne epoxy resin, stir for 20-30 minutes to prepare an organic solution, wherein the solid-liquid ratio of the organic solution is 1:8-10. (3) Add nano-modified silica, graphene oxide and KH560 silane coupling agent to the inorganic mixture obtained in step (1), ball mill at 300-400 r / min for 30-40 min, then add the organic solution obtained in step (2), stir and dry at 50-60℃ until the moisture content is ≤5%, pulverize and pass through a 100 mesh sieve to obtain curing agent powder.

[0013] Furthermore, in step (1), the grinding media are zirconia balls with a diameter of 5 to 10 mm and a ball-to-material ratio of 5:1; in step (3), the grinding media are alumina balls with a diameter of 2 to 5 mm and a ball-to-material ratio of 8:1.

[0014] This invention also provides a phosphogypsum base material, which is prepared by mixing phosphogypsum and the above-mentioned curing agent at a mass ratio of 100:10-15, and then statically pressing it at a pressure of 15-20 MPa for 60-120 seconds, followed by curing at 20-26°C and relative humidity ≥85% for 5-28 days. The base material has an unconfined compressive strength of ≥8 MPa after 14 days, an unconfined compressive strength of ≥10 MPa after 28 days, and a softening coefficient of ≥0.9. The molding speed is 10 mm / min, and the molding time is preferably 70-90 seconds.

[0015] In this invention, the curing temperature is preferably 20-26°C, more preferably 25°C; the relative humidity is preferably ≥85%, more preferably 90%-95%; and the curing time is preferably 7-28 days, more preferably 14 days.

[0016] In this invention, the moisture content of the phosphogypsum solidified body is preferably 14.86% to 16.22%.

[0017] Furthermore, the industrial solid waste content of the base material accounts for more than 70% of the total mass of the curing agent; the permeability coefficient is ≤5×10⁻⁶. -6 cm / s; freeze-thaw cycle strength ratio ≥90% after 25 cycles at -15℃ to 20℃; wet-dry cycle strength ratio ≥90%; fluoride leaching concentration ≤1.5mg / L, total phosphorus leaching concentration ≤0.1mg / L.

[0018] The present invention also provides an application of the curing agent described above or the phosphogypsum base material described above in heavy-duty traffic base engineering of highways.

[0019] The beneficial effects of this invention are: (1) Synergistic activation of multiple industrial solid wastes: using slag powder, fly ash, and steel slag powder as the main inorganic cementing components, activation is achieved through low-temperature grinding in the alkaline environment provided by sulfoaluminate cement, promoting the " "Gel" and " The formation of a "gel" dual-gel system enhances the strength of the cured body.

[0020] (2) Organic-inorganic interface enhancement: The hydroxyl groups in sodium carboxymethyl cellulose are bonded to CSH gel through hydrogen bonds. After the waterborne epoxy resin is cured, a three-dimensional network is formed to fill the pores. Combined with KH560 silane coupling, the organic-inorganic phase is connected through Si-OC covalent bonds, which reduces the thickness of the interface transition zone and improves water resistance.

[0021] (3) Functionalization of nanomaterials: Nano-modified silica fills the pores of the gel, reducing the permeability coefficient; graphene oxide, with oxygen functional groups ≥30%, adsorbs soluble phosphorus through its high specific surface area, synergistically enhancing the Ca content of carbide slag. 2+ Hydroxyapatite is generated, which stabilizes and solidifies the pollutants.

[0022] (4) Synergistic effect of detoxification: The calcium carbide slag Ca(OH)2 ≥ 80% adjusts the pH to 8-9, promoting the Mg content of magnesium chloride. 2+ With F - Insoluble MgF2 is formed; at the same time, Mg 2+ With SO4 2－ The formation of MgSO4·H2O fills the pores and inhibits the dissolution of gypsum. Detailed Implementation

[0023] The present invention will be further described in detail below through embodiments, but it should not be construed as limiting the scope of the subject matter of the present invention to the following embodiments. All technologies implemented based on the above content of the present invention fall within the scope of the present invention.

[0024] Unless otherwise specified, the experimental methods used in the following examples are conventional methods, and the reagents, methods and equipment used are conventional reagents, methods and equipment in this technical field.

[0025] Example 1:

[0026] Inorganic cementitious component: slag powder (S95 grade, 500m³) 2 / kg) 40 parts, fly ash (Class I, Loss on ignition 4%) 25 parts, steel slag powder (Class II, Free CaO 2.5%) 12 parts, sulfoaluminate cement (rapid hardening type) 10 parts; Organic modifying components: 0.7 parts sodium carboxymethyl cellulose (DS=0.9), 1.5 parts waterborne epoxy resin (solid content 63.6%, epoxy equivalent 150g / eq); Nano-reinforcing component: Nano-modified silica (20nm, 800m) 2 / g, purity 99.9%) 1.0 part, graphene oxide (5 layers, oxygen-containing functional groups 35%, 200m 2 / g) 0.08 parts; Interface modifier: 0.45 parts of KH560 silane coupling agent (hydrolysis rate 92%, refractive index 1.4283); Detoxification agent: 6.5 parts of 85% Ca(OH)2 from carbide slag and 2.5 parts of magnesium chloride.

[0027] Comparative Example 1 The difference from Example 1 is that it does not contain nano-modified silica and graphene oxide; otherwise, it is the same as Example 1.

[0028] Comparative Example 2 The difference from Example 1 is that it does not contain sodium carboxymethyl cellulose and waterborne epoxy resin; otherwise, it is the same as Example 1.

[0029] Comparative Example 3 The difference from Example 1 is that the detoxifying agent uses only carbide slag and does not contain magnesium chloride; otherwise, it is the same as Example 1.

[0030] Comparative Example 4 The difference from Example 1 is that 42.5 grade ordinary Portland cement is used instead of sulfoaluminate cement, while the rest is the same as Example 1.

[0031] In the following examples and comparative examples, all samples were prepared as phosphogypsum base materials according to the method described in this invention, i.e., phosphogypsum:curing agent = 100:12, molding pressure 18 MPa, holding pressure for 90 s, and curing at 25°C and 90% relative humidity. Tests were conducted according to the following standards: "JTGE51-2009 Test Procedure for Inorganic Binder Stabilized Materials in Highway Engineering", "T-CECSG-D45-02-2022 Technical Specification for Stabilized Base Materials of Hypersulfurized Phosphogypsum Cementitious Materials for Roads", "DB42T1991-2023 Technical Specification for Application of Phosphogypsum Composite Stabilized Base Materials for Highways", and "Design Specification for Rolled Earth-Rock Dams". The test results are shown in Table 1. Performance indicators Example 1 Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 14-day unconfined compressive strength (MPa) 9.2 7.5 6.8 9.0 5.5 28-day unconfined compressive strength (MPa) 11.5 9.0 8.5 11.2 7.2 Softening coefficient 0.93 0.85 0.78 0.92 0.65 Permeability coefficient (cm / s) <![CDATA[3.2×10 -6 ]]> <![CDATA[8.6×10 -6 ]]> <![CDATA[9.1×10 -6 ]]> <![CDATA[3.5×10 -6 ]]> <![CDATA[12.5×10 -6 ]]> Strength ratio after 25 freeze-thaw cycles (%) 92 85 78 91 65 Dry-wet cycle intensity ratio (%) 93 86 79 92 68 Fluoride leaching concentration (mg / L) 1.2 1.3 1.2 2.8 3.0 Total phosphorus leaching concentration (mg / L) 0.08 0.25 0.09 0.08 0.35 .

[0032] Comparing the experimental data of Example 1 and Comparative Example 4, it can be seen that in Example 1, slag powder, fly ash, and steel slag powder generate " " in the alkaline environment of sulfoaluminate cement. "Gel" and " The "gel" dual-cementation system achieved a strength of 11.5 MPa after 28 days; while the comparative example 4, using ordinary cement, had a strength of only 7.2 MPa due to the lack of synergistic activation. This indicates that the combination of multi-component solid waste synergy and sulfoaluminate cement is the core of the strength and high solid waste content.

[0033] Comparing the experimental data of Example 1 and Comparative Example 2, it can be seen that in Example 1, the hydroxyl groups in sodium carboxymethyl cellulose and the three-dimensional network in the waterborne epoxy resin, combined with the Si-O covalent bonds in H560, strengthen the interface, resulting in a softening coefficient of 0.93 and a freeze-thaw / wet-dry strength ratio ≥92%. In Comparative Example 2, due to the absence of organic components, the interface transition zone is thicker, the softening coefficient decreases to 0.78, and the cycle strength ratio is <80%. These experiments demonstrate that organic-inorganic interface reinforcement is key to water resistance and durability.

[0034] Comparing the experimental data of Example 1 and Comparative Example 1, it can be seen that the nano-modified silica in Example 1 fills the pores with a permeability coefficient of 3.2 × 10⁻⁶. -6 Graphene oxide adsorbed phosphorus, with a total phosphorus concentration of 0.08 mg / L and a 28-day strength of 11.5 MPa; Comparative Example 1, lacking nano-components, showed a permeability coefficient increased to 8.6 × 10⁻⁶. -6Total phosphorus leaching reached 0.25 mg / L, and strength decreased by 22%. This indicates that nanomaterials can improve density and reduce pollutant leaching.

[0035] By comparing the experimental data of Example 1 and Comparative Example 3, it can be seen that the Ca in the carbide slag of Example 1... 2+ With Mg in magnesium chloride 2+ In Comparative Example 3, MgF2 was synergistically generated, resulting in a fluoride leaching concentration of 1.2 mg / L. In Comparative Example 3, lacking magnesium chloride, the calcium carbide slag alone could not effectively fix F⁻, leading to a leaching concentration of 2.8 mg / L, exceeding the standard by 1.5 mg / L. This demonstrates that the synergistic effect of detoxifying agents is crucial for controlling fluoride pollution.

[0036] In summary, Example 1 achieves "high strength, high water resistance, and low toxicity" through a quaternary system of "synergistic activation of multiple industrial solid wastes - enhancement of organic / inorganic interfaces - functionalization of nanomaterials - synergistic detoxification," fully meeting the requirements of heavy-load base courses for highways. While ensuring the structural and functional needs of highway subgrades and pavements, it simultaneously realizes the large-scale disposal and high-value-added utilization of phosphogypsum solid waste, and effectively fixes and seals pollutants in phosphogypsum, which has important practical significance for engineering construction and environmental protection.

[0037] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Any simple modifications, equivalent substitutions, and improvements made by those skilled in the art to the above embodiments without departing from the scope of the technical solution of the present invention, based on the technical essence of the present invention, shall still fall within the protection scope of the technical solution of the present invention.

Claims

1. An organic-inorganic synergistic industrial solid waste-based phosphogypsum base layer solidifying agent, characterized in that, The curing agent is composed of an inorganic cementing component and an organic modifying component. The inorganic cementing component, by weight, includes 35-45 parts of slag powder, 20-30 parts of fly ash, 10-15 parts of steel slag powder, and 5-15 parts of sulfoaluminate cement. The organic modifying component, by weight, includes 0.5-1 parts of sodium carboxymethyl cellulose and 1-2 parts of waterborne epoxy resin. Nano-reinforcing components: 0.8-1.2 parts of nano-modified silica and 0.05-0.1 parts of graphene oxide; 0.3-0.6 parts of interface modifier KH560 silane coupling agent; detoxifying agent: 5-8 parts of carbide slag and 2-3 parts of magnesium chloride, wherein the nano-modified silica and graphene oxide contain carboxyl groups.

2. The curing agent according to claim 1, characterized in that, The slag powder is grade S95 with a specific surface area ≥500 m². 2 / kg; fly ash is Class F, Grade I, with a loss on ignition of ≤5%; steel slag powder is Grade II, with a free calcium oxide content of ≤3%.

3. The curing agent according to claim 1, characterized in that, The sodium carboxymethyl cellulose has a substitution value (DS) of 0.7 to 1.2; the waterborne epoxy resin has a solid content of ≥60% and an epoxy equivalent of 80 to 220 g / eq.

4. The curing agent according to claim 1, characterized in that, The nano-modified silica has a particle size of 10–30 nm and a specific surface area of ​​600–1000 m². 2 / g, SiO2 purity ≥99.8%; graphene oxide layers ≤10, oxygen-containing functional group content ≥30%, specific surface area 100~300m² 2 / g.

5. The curing agent according to claim 1, characterized in that, The hydrolysis rate of the KH560 silane coupling agent is ≥90%; the Ca(OH)2 content of the carbide slag is ≥80%.

6. A method for preparing the curing agent according to any one of claims 1 to 5, characterized in that, Includes the following steps: (1) After mixing slag powder, fly ash and steel slag powder, grind them in a ball mill for 20-30 minutes until the specific surface area is ≥450m². 2 / kg, add sulfoaluminate cement, carbide slag, and magnesium chloride, stir for 10-15 minutes to form an inorganic mixture; (2) Dissolve sodium carboxymethyl cellulose in deionized water at 80-90°C, stir until completely dissolved, cool to 25-30°C and add waterborne epoxy resin, stir for 20-30 minutes to prepare an organic solution, wherein the solid-liquid ratio of the organic solution is 1:8-10. (3) Add nano-modified silica, graphene oxide and KH560 silane coupling agent to the inorganic mixture obtained in step (1), ball mill at 300-400 r / min for 30-40 min, then add the organic solution obtained in step (2), stir and dry at 50-60℃ until the moisture content is ≤5%, pulverize and pass through a 100 mesh sieve to obtain curing agent powder.

7. The preparation method according to claim 6, characterized in that, In step (1), the grinding media are zirconia balls with a diameter of 5 to 10 mm and a ball-to-material ratio of 5:1; in step (3), the grinding media are alumina balls with a diameter of 2 to 5 mm and a ball-to-material ratio of 8:

1.

8. A phosphogypsum base material, characterized in that, The base material is prepared by mixing phosphogypsum and the curing agent described in any one of claims 1 to 5 at a mass ratio of 100:10 to 15, followed by static pressing at a pressure of 15 to 20 MPa and a holding time of 60 to 120 seconds, and then curing at 20 to 26°C and relative humidity ≥ 85% for 5 to 28 days. The base material has an unconfined compressive strength of ≥ 8 MPa after 14 days, an unconfined compressive strength of ≥ 10 MPa after 28 days, and a softening coefficient of ≥ 0.

9.

9. The phosphogypsum base material according to claim 8, characterized in that, The industrial solid waste content of the base material accounts for more than 70% of the total mass of the curing agent; the permeability coefficient is ≤5×10 -6 cm / s; freeze-thaw cycle strength ratio ≥90% after 25 cycles at -15℃ to 20℃; wet-dry cycle strength ratio ≥90%; fluoride leaching concentration ≤1.5mg / L, total phosphorus leaching concentration ≤0.1mg / L.

10. The application of the curing agent according to any one of claims 1 to 5 or the phosphogypsum base material according to any one of claims 8 to 9 in the heavy-duty traffic base engineering of highways.