A phosphogypsum-fly ash-based mine filling cementing material and a preparation method thereof

Abstract

The application belongs to the technical field of building materials, and particularly relates to a phosphogypsum-fly ash-based mine filling cementing material and a preparation method thereof, which comprises a component a and a component b, and the mass ratio of the component a to the component b is 1:4-6; the component a comprises the following components by weight: activated phosphogypsum 40-50 parts, alkali-activated fly ash 20-30 parts, blast furnace slag 20-30 parts, modified steel slag 5-10 parts, composite activator 3-6 parts, polycarboxylic acid water reducer 0.3-0.8 parts, and foam stabilizing and water retaining agent 0.2-0.5 parts; wherein the activated phosphogypsum is modified through calcination-alkali spraying in a hot state-organic coating, the alkali-activated fly ash is pre-activated, and the modified steel slag is treated through aging and grinding aid. The material significantly improves the fluidity of the filling slurry, greatly improves the mechanical strength and long-term stability of the filling body, and has significant economic and environmental benefits.

Description

Technical Field

[0001] This invention relates to the field of building materials technology, specifically to a phosphogypsum-fly ash based mine filling cementitious material and its preparation method. Background Technology

[0002] Phosphogypsum is a large-scale industrial solid waste generated during the wet-process phosphoric acid production process, and fly ash is a typical emission from coal-fired power plants. Both have huge annual production volumes, and their stockpiling not only occupies land but also poses potential environmental risks to soil and groundwater due to their soluble impurities. Using these industrial solid wastes to prepare mine backfill cementitious materials to replace traditional cement is an important way to achieve "waste treatment and green mining," offering both environmental and economic benefits. However, directly or simply combining phosphogypsum and fly ash for mine backfill faces a series of key technical bottlenecks. First, the soluble phosphorus and fluorine impurities in phosphogypsum severely delay the hydration process of the cementitious system, resulting in phosphogypsum-based backfill with inherent defects such as extremely low early strength and excessively long setting time, making it difficult to meet the stringent requirements of mining processes for the early self-supporting properties of backfill. Second, undisturbed fly ash has low pozzolanic activity and reacts slowly at room temperature, contributing little to the early strength of the backfill, thus limiting its high-volume application in cementitious materials.

[0003] Patent application CN202110290842.5 provides a high-concentration self-flowing backfill cementitious material for phosphate mines, comprising the following raw materials: 24-40 wt% phosphogypsum, 30-40 wt% phosphate slag powder, 8-18 wt% cement, 3-15 wt% alkaline activator, 1-2 wt% air-entraining component, and 1-3 wt% modified plant gum. The modified plant gum is prepared from plant gum, esterified monomers, and sodium methacryloyl sulfonate. This invention provides a cementitious material specifically designed for high-concentration self-flowing backfilling processes (slurry mass concentration ≥80%). By adding modified plant gum, the tailings remain stable in the cementitious material for a long time without sedimentation and with almost no bleeding. The prepared tailings backfill slurry has good fluidity, requires no pumping, and is more conducive to transportation and backfilling, thus better meeting the requirements for mine backfill connection. However, this invention directly uses phosphogypsum as a raw material. Phosphogypsum contains soluble phosphorus and fluorine impurities, which severely delays setting time, resulting in slow early strength development. Patent application CN202210679055.4 discloses a solid waste backfill material and its preparation method. The gel material includes desulfurized gypsum, fly ash, slag, steel slag, magnesium slag, carbide slag, water-reducing agent, water-retaining dispersant, and alkaline activator, with tailings as the aggregate. This invention rationally utilizes the theory of synergistic complementarity of chemical components from multiple solid waste sources. Under the action of the alkaline activator, the silicon-rich and calcium-rich phases in the slag and fly ash structures react to generate stronger AFm crystals. The water-retaining dispersant effectively solves the segregation and bleeding problems of the solid waste backfill material, giving it good water retention and uniform dispersion. The addition of an appropriate amount of fly ash allows it to exert a ball-bead effect, increasing the fluidity of the backfill slurry. However, the dense glassy structure of fly ash and its extremely low pozzolanic activity at room temperature result in a slow reaction under the action of the compounded alkaline activator, leading to a minimal contribution of fly ash to early strength development.

[0004] Therefore, the development of a high-performance cementitious material suitable for mine backfilling, which simultaneously meets multiple engineering requirements such as the fluidity of the backfill slurry, controllable setting time, early and late mechanical strength, and long-term stability, has become a key technical challenge that urgently needs to be solved in this field. Summary of the Invention

[0005] To address the aforementioned problems, this invention provides a phosphogypsum-fly ash-based mine backfill cementitious material and its preparation method. By combining activated phosphogypsum, alkali-activated fly ash, modified steel slag, and compound activators, polycarboxylate superplasticizers, and multifunctional foam stabilizers and water-retaining agents in optimized proportions, a phosphogypsum-fly ash-based mine backfill cementitious material with excellent working performance, superior mechanical properties, good long-term stability, and high comprehensive solid waste utilization rate is obtained.

[0006] The technical solution of the present invention to solve the above problems is as follows: A phosphogypsum-fly ash based mine filling cementitious material includes component A and component B, wherein the mass ratio of component A to component B is 1:4-6; component A comprises the following components by weight: 40-50 parts activated phosphogypsum, 20-30 parts alkali-activated fly ash, 20-30 parts blast furnace slag, 5-10 parts modified steel slag, 3-6 parts composite activator, 0.3-0.8 parts polycarboxylate superplasticizer, and 0.2-0.5 parts foam stabilizer and water retainer; The method for preparing the activated phosphogypsum is as follows: Step S1: Dry the phosphogypsum at 80-100℃ until the moisture content is less than 1%, grind it to a specific surface area of ​​300-350m2 / kg, and then keep it at 650-710℃ for 1.5-2.0h; Step S2: Cool the material obtained in step S1 after heat preservation (air cooling). When the temperature drops to 150-200℃, add sodium hydroxide solution and then cool to 60-75℃ to obtain calcined-alkali activated phosphogypsum. Step S3: Add the composite modifier to the calcined-alkali activated phosphogypsum obtained in step S2 at 60-75℃, stir for 15-25 minutes, and then age for 6-12 hours to obtain activated phosphogypsum.

[0007] Further, the mass ratio of the sodium hydroxide solution in step S2 to the phosphogypsum in step S1 is 0.015-0.025:1, and the concentration of the sodium hydroxide solution is 9.5-10.5%.

[0008] Further, the composite modifier mentioned in step S3 is composed of calcium stearate, silane coupling agent KH-550, and silicon dioxide in a mass ratio of 1.0-1.5:0.3-0.5:1.0-2.0, and the mass ratio of the composite modifier to the calcined-alkali activated phosphogypsum obtained in step S2 is 0.025-0.04:1.

[0009] Furthermore, the preparation method of the alkali-activated fly ash is as follows: fly ash is mixed with a composite alkali activator, deionized water is added to adjust the liquid-solid ratio to 0.25-0.30:1, and the mixture is stirred and activated at 75-85℃ for 12-18 hours. After post-treatment, alkali-activated fly ash is obtained.

[0010] Furthermore, the mass ratio of fly ash to composite alkali activator is 1:0.08-0.12, and the composite alkali activator is composed of sodium hydroxide and water glass in a molar ratio of 0.8-1.2:1.

[0011] Furthermore, the modified steel slag is prepared by aging the steel slag until the free calcium oxide content does not exceed 3%, then adding a grinding aid and grinding it until the specific surface area is 350-450 m2 / kg to obtain the modified steel slag.

[0012] Furthermore, the grinding aid is triethanolamine and gypsum, and the mass ratio of steel slag, triethanolamine and gypsum is 1:0.003-0.007:0.001-0.005.

[0013] Furthermore, the composite activator is composed of component A and component B in a mass ratio of 1.8-2.2:1; component A is an alkaline activator, composed of water glass, sodium hydroxide and water in a mass ratio of 60-70:10-15:20-30; component B is a sulfate activator, composed of anhydrous sodium sulfate, hemihydrate gypsum powder and silica fume in a mass ratio of 40-50:30-40:10-20.

[0014] Further, component b is tailings; the polycarboxylate superplasticizer is a polycarboxylate-based high-performance superplasticizer; the foam stabilizer and water retainer is composed of hydroxypropyl methylcellulose, nano-bentonite, air-entraining agent and defoamer in a mass ratio of 40-50:30-40:5-10:0.5-1, the air-entraining agent is rosin thermal polymer or triterpenoid saponin, and the defoamer is a polyether defoamer.

[0015] The preparation method of the above-mentioned phosphogypsum-fly ash based mine filling cementitious material includes the following steps: dry mixing activated phosphogypsum, alkali-activated fly ash, blast furnace slag, modified steel slag and component b to obtain mixture A; dry mixing composite activator, polycarboxylate superplasticizer and foam stabilizer and water-retaining agent to obtain mixture B; first adding a portion of water to mix with mixture A and mixture B, then adding the remaining water and continuing to stir to obtain the final product.

[0016] The present invention has the following beneficial effects: This invention achieves functional reshaping and performance enhancement of three core solid waste components by modifying activated phosphogypsum, alkali-activated fly ash, and modified steel slag separately. Specifically, the activated phosphogypsum undergoes synergistic modification through "calcination-hot alkali spraying-organic coating." First, calcination at 650-710℃ transforms dihydrate gypsum into hemihydrate gypsum with higher hydration activity, while simultaneously converting soluble phosphorus and fluorine impurities into inert insoluble substances, completely eliminating their retardation effect on the hydration reaction and potential threat to long-term stability. Then, atomized sodium hydroxide solution is sprayed at the discharge temperature of 150-200℃, utilizing residual heat to achieve hot alkali pre-activation, generating active hydration on the gypsum surface. The nucleation process neutralizes residual acidic impurities, significantly reducing the nucleation barrier of the hydration reaction. Finally, a composite modifier consisting of calcium stearate, silane coupling agent KH-550, and nano-silica is applied at high speed (60-75℃) to coat the gypsum surface, constructing a hybrid hydrophobic layer of "chemical anchoring-organic crosslinking-inorganic filling." This hydrophobic layer releases free water adsorbed by the particles to improve slurry fluidity and acts as a flexible transition layer to enhance the interfacial bonding between hydration products and gypsum particles. Alkali-activated fly ash undergoes pre-activation treatment with a composite alkali activator of sodium hydroxide and water glass at 75-85℃ for 12-18 hours. This effectively disrupts the glassy structure, releasing a large amount of active silica-alumina components and generating gel precursors in advance, achieving effective cementation of the fly ash. This allows the fly ash to participate in the reaction in the early stages of hydration and continuously contribute to the later strength. Modified steel slag undergoes aging treatment to fully dissolve free calcium oxide, and is simultaneously ground to a suitable specific surface area with the synergistic grinding aid of triethanolamine and gypsum. This completely eliminates potential volume stability issues and activates the cementitious activity of silicate minerals in the steel slag. These three modifying components complement each other in terms of chemical composition and surface properties: activated phosphogypsum provides a sulfate source and hydrophobic interface, alkali-activated fly ash provides active silica and alumina and pre-formed crystal nuclei, and modified steel slag provides a stable alkaline environment and cementitious activity, collectively laying a solid foundation for the excellent performance of the entire cementing system.

[0017] This invention constructs a multi-dimensional synergistic solid waste cementing system by combining the above three core modified components with blast furnace slag, a composite activator, a polycarboxylate superplasticizer, and a foam stabilizer and water-retaining agent. Blast furnace slag, as a highly active cementing component, rapidly depolymerizes its glassy structure to release active silica and aluminum under the synergistic activation of alkaline-sulfate reactions provided by the composite activator. This reacts with sulfate ions provided by activated phosphogypsum to form ettringite, and with calcium ions provided by alkaline-activated fly ash and modified steel slag to form a gel, resulting in a dense three-dimensional network structure. The composite activator, using a specific ratio of alkaline and sulfate activators, achieves a step-by-step activation process of "first alkaline activation to break the glassy structure, then sulfate to promote ettringite formation." This ensures an orderly connection between the hydration reactions in terms of time and product types, guaranteeing rapid early strength development and promoting continuous strength growth in later stages. The synergistic effect of polycarboxylate superplasticizer and foam stabilizer / water retainer further optimizes the rheological properties of the slurry based on the hydrophobic layer of activated phosphogypsum, forming a stable spatial network structure that effectively inhibits tailings settling and free water precipitation. In this invention, the hydrophobic layer of activated phosphogypsum and the ball-bearing effect of alkali-activated fly ash synergistically improve fluidity and slump, giving the slurry excellent pipeline transport performance; the nucleation induction of activated phosphogypsum and the pre-formed precursor of alkali-activated fly ash synergistically shorten setting time and improve early strength, enabling the backfill to quickly bear load; the alkaline environment of modified steel slag and the stepwise activation of the composite activator synergistically promote the depolymerization of the vitreous body of slag and fly ash, achieving efficient and orderly hydration reactions; the impurity solidification of activated phosphogypsum and the dissolution of free calcium oxide in modified steel slag jointly ensure long-term stability, preventing the backfill from failing due to expansion and cracking during service; the organic-inorganic hybrid coating layer and the CSH gel network synergistically enhance interfacial bonding, simultaneously improving flexural and compressive strength. The overall solution achieves synergistic effects from all dimensions of solid waste activation, component compatibility, and preparation process. The resulting cementitious material has a moderate setting time, qualified stability, and excellent mechanical strength, realizing the synergistic use of industrial solid waste and mine tailings. It has environmental benefits, economic benefits, and engineering practicality, and is suitable for large-scale application in various mine backfilling projects. Attached Figure Description

[0018] Figure 1 This is a comparison chart of the setting time test results of Examples 1-4 and Comparative Examples 1-5; Figure 2 The graph shows a comparison of the compressive and flexural strength test results of Examples 1-4 and Comparative Examples 1-5 at different ages. Detailed Implementation

[0019] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0020] All raw materials used in the following examples are commercially available products. Blast furnace slag, 98% effective component content, particle size 2000μm, Lingshou County Oukai Mineral Products Sales Department; phosphogypsum, >90% effective component content, Fuzhou Persian Gulf Chemical Co., Ltd.; fly ash, 88% effective component content, particle size 325 mesh, Lingshou County Haibin Mineral Products Trading Co., Ltd.; water glass, 99% effective component content, modulus 2.2-2.5, Shandong Hongmei Mining Equipment Co., Ltd.; steel slag, 99% purity, particle size 20-40 mesh, Lingshou County Zhanxing Mineral Products Co., Ltd.; gypsum, 200 mesh particle size, Anhui Province Lujiang County Guzhen Mineral Products Co., Ltd.; hemihydrate gypsum powder, whiteness 85, hardness 5, Zaozhuang Xinghao New Materials Co., Ltd.; silica fume, 1250 mesh particle size, silicon content ≥91%, Hebei Leijiang New Materials Technology Co., Ltd.; tailings, apparent density 2.71g / cm³. 3 The bulk density is 1.63 g / cm³. 3 The tailings were dried to a moisture content of less than 2%, with particle size distribution of d10=2.82μm, d30=18.35μm, d50=26.18μm, d60=44.52μm, and d90=145.06μm, uniformity coefficient Cu=15.79, and curvature coefficient Cc=2.68; the polycarboxylate-based high-performance water-reducing agent had a solid content of 96% and a water reduction rate of ≥32%, produced by Wuhan Huaxuan High-Tech Co., Ltd.; hydroxypropyl methylcellulose had a water retention of 96%, produced by Jinzhou Xingdong Building Materials Technology Co., Ltd.; nano-bentonite had an effective component content of 92% and a particle size of 600 mesh, produced by Hebei Leijiang New Materials Technology Co., Ltd.; rosin thermal polymer had a solid content of 50±2%, produced by Shaoxing Shangyu Zhengyuan Building Materials Co., Ltd.; triterpenoid saponins had an effective component content of 99%, produced by Jinan Daorong Chemical Co., Ltd.; and polyether defoamer had a solid content of 99% and a moisture content of ≤5%, produced by Nanjing Chuhai New Materials Technology Co., Ltd.

[0021] Example 1 A phosphogypsum-fly ash based mine filling cementitious material includes component A and component B, wherein the mass ratio of component A to component B is 1:4; component A comprises the following components by weight: 40 parts activated phosphogypsum, 20 parts alkali activated fly ash, 20 parts blast furnace slag, 5 parts modified steel slag, 3 parts composite activator, 0.3 parts polycarboxylate superplasticizer, and 0.2 parts foam stabilizer and water retainer; The method for preparing the activated phosphogypsum is as follows: Step S1: Dry the phosphogypsum at 90℃ until the moisture content is less than 1%, and ball mill it until the specific surface area is 300-350 m². 2 / kg, the ball-to-material ratio is 5:1, high-chromium cast iron balls are selected, the diameters of large, medium and small balls are 40mm, 30mm and 10mm respectively, the ratio of large, medium and small balls is 2:5:3, and then it is kept at 680℃ for 1.8h; Step S2: The material obtained in step S1 after heat preservation is cooled by air cooling. When the temperature drops to 180°C, sodium hydroxide solution is sprayed in, followed by rapid cooling to 70°C to obtain calcined-alkali activated phosphogypsum. The mass ratio of sodium hydroxide solution to phosphogypsum from step S1 is 0.02:1, and the concentration of sodium hydroxide solution is 10%. Step S3: Add the composite modifier to the calcined-alkali activated phosphogypsum obtained in step S2 at 70℃, stir at high speed for 20 minutes at a speed of 4000 r / min, and then age in a sealed container for 9 hours to obtain activated phosphogypsum. The composite modifier is composed of calcium stearate, silane coupling agent KH-550, and silicon dioxide in a mass ratio of 1.3:0.4:1.5, and the mass ratio of the composite modifier to the calcined-alkali activated phosphogypsum obtained in step S2 is 0.03:1.

[0022] The preparation method of the alkali-activated fly ash is as follows: fly ash is mixed with a composite alkali activator, deionized water is added to adjust the liquid-solid ratio to 0.27:1, and the mixture is stirred and activated at 80℃ for 15 hours. Then, it is dried at 105℃ until the moisture content is less than 1%, and ball-milled until the specific surface area is 450-550 m². 2 / kg, the ball-to-material ratio is 6:1, high-chromium cast iron balls are selected, the diameters of large, medium and small balls are 30mm, 20mm and 15mm respectively, and the ratio of large, medium and small balls is 3:4:3 to obtain alkali activated fly ash, in which the mass ratio of fly ash to composite alkali activator is 1:0.1, and the composite alkali activator is composed of sodium hydroxide and water glass in a molar ratio of 1:1.

[0023] The modified steel slag is prepared by aging the steel slag until the free calcium oxide content does not exceed 3%, then adding a grinding aid and ball milling it to a specific surface area of ​​350-450 m². 2 / kg, the ball-to-material ratio is 6:1, high-chromium cast iron balls are selected, the diameters of large, medium and small balls are 20mm, 15mm and 10mm respectively, and the ratio of large, medium and small balls is 3:4:3 to obtain modified steel slag, in which the grinding aids are triethanolamine and gypsum, and the mass ratio of steel slag, triethanolamine and gypsum is 1:0.005:0.003.

[0024] The composite activator is composed of component A and component B in a mass ratio of 2:1; component A is an alkaline activator, composed of water glass, sodium hydroxide and water in a mass ratio of 65:13:25; component B is a sulfate activator, composed of anhydrous sodium sulfate, hemihydrate gypsum powder and silica fume in a mass ratio of 45:35:15.

[0025] Component b is tailings; the polycarboxylate superplasticizer is a polycarboxylate-based high-performance superplasticizer; the foam stabilizer and water retainer is composed of hydroxypropyl methylcellulose, nano-bentonite, air-entraining agent and defoamer in a mass ratio of 45:35:8:0.8, the air-entraining agent is rosin thermal polymer, and the defoamer is a polyether defoamer.

[0026] The preparation method of the above-mentioned phosphogypsum-fly ash based mine filling cementitious material includes the following steps: dry mixing activated phosphogypsum, alkali-activated fly ash, blast furnace slag, modified steel slag and tailings for 90s at a speed of 100r / min to obtain mixture A; dry mixing composite activator, polycarboxylate superplasticizer and foam stabilizer / water retainer for 60s at a speed of 130r / min to obtain mixture B; first adding water accounting for 80% of the total mixing water and mixing it with mixture A and mixture B, stirring at a speed of 50r / min for 60s, then adding the remaining water and continuing to stir for 90s to obtain the final product, wherein the mass ratio of the total mixing water to the solid material is 0.75:1.

[0027] Example 2 A phosphogypsum-fly ash based mine filling cementitious material includes component A and component B, wherein the mass ratio of component A to component B is 1:6; component A comprises the following components by weight: 50 parts activated phosphogypsum, 30 parts alkali activated fly ash, 30 parts blast furnace slag, 10 parts modified steel slag, 6 parts composite activator, 0.8 parts polycarboxylate superplasticizer, and 0.5 parts foam stabilizer and water retainer; The rest is the same as in Example 1.

[0028] Example 3 A phosphogypsum-fly ash based mine filling cementitious material includes component A and component B, wherein the mass ratio of component A to component B is 1:5; component A comprises the following components by weight: 45 parts activated phosphogypsum, 25 parts alkali activated fly ash, 25 parts blast furnace slag, 8 parts modified steel slag, 4 parts composite activator, 0.5 parts polycarboxylate superplasticizer, and 0.3 parts foam stabilizer and water retainer; The rest is the same as in Example 1.

[0029] Example 4 A phosphogypsum-fly ash based mine filling cementitious material includes component A and component B, wherein the mass ratio of component A to component B is 1:5; component A comprises the following components by weight: 45 parts activated phosphogypsum, 25 parts alkali activated fly ash, 25 parts blast furnace slag, 8 parts modified steel slag, 4 parts composite activator, 0.5 parts polycarboxylate superplasticizer, and 0.3 parts foam stabilizer and water retainer; The method for preparing the activated phosphogypsum is as follows: Step S1: Dry the phosphogypsum at 100℃ until the moisture content is less than 1%, and ball mill it until the specific surface area is 300-350 m². 2 / kg, the ball-to-material ratio is 5:1, high-chromium cast iron balls are selected, the diameters of large, medium and small balls are 40mm, 30mm and 10mm respectively, the ratio of large, medium and small balls is 2:5:3, and then it is kept at 710℃ for 2.0h; Step S2: The material obtained in step S1 after heat preservation is cooled by air cooling. When the temperature drops to 200℃, sodium hydroxide solution is sprayed in, followed by rapid cooling to 75℃ to obtain calcined-alkali activated phosphogypsum. The mass ratio of sodium hydroxide solution to phosphogypsum from step S1 is 0.025:1, and the concentration of sodium hydroxide solution is 10.5%. Step S3: Add the composite modifier to the calcined-alkali activated phosphogypsum obtained in step S2 at 75℃, stir at high speed for 25 minutes at a speed of 4000 r / min, and then age in a sealed container for 12 hours to obtain activated phosphogypsum. The composite modifier is composed of calcium stearate, silane coupling agent KH-550, and silicon dioxide in a mass ratio of 1.5:0.5:2.0, and the mass ratio of the composite modifier to the calcined-alkali activated phosphogypsum obtained in step S2 is 0.04:1.

[0030] The preparation method of the alkali-activated fly ash is as follows: fly ash is mixed with a composite alkali activator, deionized water is added to adjust the liquid-solid ratio to 0.30:1, and the mixture is stirred and activated at 85°C for 18 hours. Then, it is dried at 105°C until the moisture content is less than 1%, and ball-milled until the specific surface area is 450-550 m². 2 / kg, the ball-to-material ratio is 6:1, high-chromium cast iron balls are selected, the diameters of large, medium and small balls are 30mm, 20mm and 15mm respectively, and the ratio of large, medium and small balls is 3:4:3 to obtain alkali activated fly ash, in which the mass ratio of fly ash to composite alkali activator is 1:0.12, and the composite alkali activator is composed of sodium hydroxide and water glass in a molar ratio of 1.2:1.

[0031] The modified steel slag is prepared by aging the steel slag until the free calcium oxide content does not exceed 3%, then adding a grinding aid and ball milling it to a specific surface area of ​​350-450 m². 2 / kg, the ball-to-material ratio is 6:1, high-chromium cast iron balls are selected, the diameters of large, medium and small balls are 20mm, 15mm and 10mm respectively, and the ratio of large, medium and small balls is 3:4:3 to obtain modified steel slag, in which the grinding aids are triethanolamine and gypsum, and the mass ratio of steel slag, triethanolamine and gypsum is 1:0.007:0.005.

[0032] The composite activator is composed of component A and component B in a mass ratio of 2.2:1; component A is an alkaline activator, composed of water glass, sodium hydroxide and water in a mass ratio of 70:15:30; component B is a sulfate activator, composed of anhydrous sodium sulfate, hemihydrate gypsum powder and silica fume in a mass ratio of 50:40:20.

[0033] Component b is tailings; the polycarboxylate superplasticizer is a polycarboxylate-based high-performance superplasticizer; the foam stabilizer and water retainer is composed of hydroxypropyl methylcellulose, nano-bentonite, air-entraining agent and defoamer in a mass ratio of 50:40:10:1, the air-entraining agent is a triterpenoid saponin, and the defoamer is a polyether defoamer.

[0034] The preparation method of the above-mentioned phosphogypsum-fly ash based mine filling cementitious material is the same as in Example 1.

[0035] Comparative Example 1 A phosphogypsum-fly ash based mine filling cementitious material includes component A and component B, wherein the mass ratio of component A to component B is 1:1; component A comprises the following components by weight: 20 parts activated phosphogypsum, 15 parts alkali activated fly ash, 25 parts blast furnace slag, 8 parts modified steel slag, 4 parts composite activator, 0.5 parts polycarboxylate superplasticizer, and 0.3 parts foam stabilizer and water retainer; The method for preparing the activated phosphogypsum is as follows: Step S1: Dry the phosphogypsum at 50℃ until the moisture content is less than 1%, and ball mill it until the specific surface area is 300-350 m². 2 / kg, the ball-to-material ratio is 5:1, high-chromium cast iron balls are selected, the diameters of large, medium and small balls are 40mm, 30mm and 10mm respectively, the ratio of large, medium and small balls is 2:5:3, and then it is kept at 710℃ for 2.0h; Step S2: The material obtained in step S1 after heat preservation is cooled by air cooling. When the temperature drops to 100°C, sodium hydroxide solution is sprayed in, followed by rapid cooling to 75°C to obtain calcined-alkali activated phosphogypsum. The mass ratio of sodium hydroxide solution to phosphogypsum from step S1 is 0.01:1, and the concentration of sodium hydroxide solution is 11%. Step S3: Add the composite modifier to the calcined-alkali activated phosphogypsum obtained in step S2 at 75℃, stir at high speed for 25 minutes at a speed of 400 r / min, and then age in a sealed container for 12 hours to obtain activated phosphogypsum. The composite modifier is composed of calcium stearate, silane coupling agent KH-550, and silicon dioxide in a mass ratio of 0.5:0.5:2.0, and the mass ratio of the composite modifier to the calcined-alkali activated phosphogypsum obtained in step S2 is 0.04:1.

[0036] The preparation method of the alkali-activated fly ash is as follows: fly ash is mixed with a composite alkali activator, deionized water is added to adjust the liquid-solid ratio to 0.1:1, and the mixture is stirred and activated at 85°C for 18 hours. Then, it is dried at 105°C until the moisture content is less than 1%, and ball-milled until the specific surface area is 450-550 m². 2 / kg, with a ball-to-material ratio of 6:1, using high-chromium cast iron balls, with diameters of 30mm, 20mm, and 15mm for large, medium, and small balls respectively, and a ball-to-material ratio of 3:4:3, to obtain alkali-activated fly ash, wherein the mass ratio of fly ash to composite alkali activator is 1:0.05, and the composite alkali activator is composed of sodium hydroxide and water glass in a molar ratio of 1.2:1.

[0037] The modified steel slag is prepared by aging the steel slag until the free calcium oxide content does not exceed 3%, then adding a grinding aid and ball milling it to a specific surface area of ​​350-450 m². 2 / kg, the ball-to-material ratio is 6:1, high-chromium cast iron balls are selected, the diameters of large, medium and small balls are 20mm, 15mm and 10mm respectively, and the ratio of large, medium and small balls is 3:4:3 to obtain modified steel slag, in which the grinding aids are triethanolamine and gypsum, and the mass ratio of steel slag, triethanolamine and gypsum is 1:0.001:0.005.

[0038] The composite activator is composed of component A and component B in a mass ratio of 1:1; component A is an alkaline activator, composed of water glass, sodium hydroxide and water in a mass ratio of 70:15:30; component B is a sulfate activator, composed of anhydrous sodium sulfate, hemihydrate gypsum powder and silica fume in a mass ratio of 20:40:20.

[0039] Component b is tailings; the polycarboxylate superplasticizer is a polycarboxylate-based high-performance superplasticizer; the foam stabilizer and water retainer is composed of hydroxypropyl methylcellulose, nano-bentonite, air-entraining agent and defoamer in a mass ratio of 50:10:10:1, the air-entraining agent is rosin thermal polymer, and the defoamer is a polyether defoamer.

[0040] The preparation method of the above-mentioned phosphogypsum-fly ash based mine filling cementitious material is the same as in Example 1.

[0041] Comparative Example 2 A phosphogypsum-fly ash based mine filling cementitious material, wherein activated phosphogypsum is replaced with commercially available phosphogypsum, and the rest is the same as in Example 1.

[0042] Comparative Example 3 A phosphogypsum-fly ash based mine filling cementitious material, wherein the alkali-activated fly ash is replaced with commercially available fly ash, and the rest is the same as in Example 1.

[0043] Comparative Example 4 A phosphogypsum-fly ash based mine filling cementitious material, wherein modified steel slag is replaced with commercially available steel slag, and the rest is the same as in Example 1.

[0044] Comparative Example 5 A phosphogypsum-fly ash based mine filling cementitious material, wherein modified phosphogypsum is replaced with commercially available phosphogypsum, alkali-activated fly ash is replaced with commercially available fly ash, and modified steel slag is replaced with commercially available steel slag, and the rest is the same as in Example 1.

[0045] Performance testing Flowability: The flowability was determined according to the requirements of GB / T 2419-2005 "Test Method for Flowability of Cement Mortar", and the results are shown in Table 1. Setting time and soundness: The setting time and soundness of each sample were determined according to the requirements of GB / T 1346-2024 "Test Methods for Standard Consistency Water Requirement, Setting Time and Soundness of Cement". The results are shown in Table 1. Compressive strength (3d, 7d, 28d) and flexural strength (3d, 7d, 28d): Samples were prepared and cured according to the requirements of GB / T 17671-2021 "Test Method for Strength of Cement Mortar (ISO Method)". The flexural strength and compressive strength of each sample were measured, and the results are shown in Table 2. Slump: The slump of concrete made with the cementitious material prepared by this invention as one of the raw materials was determined according to the requirements of GB / T 50080-2016 "Standard for Test Methods of Performance of Ordinary Concrete Mixtures". The results are shown in Table 2.

[0046] Table 1. Flowability, setting time, and stability

[0047] Table 2 Compressive strength, flexural strength, and slump

[0048] From Tables 1 and 2 and Figure 1 , 2It can be seen that the performance of Comparative Example 1 declined across the board. The root cause was that multiple key process parameters and formulation ratios deviated from the preferred range of the present invention at the same time, resulting in a cumulative negative effect. The superposition of these multiple factors led to a significant decrease in the fluidity and slump of the filling slurry, abnormal setting time, and although the stability was barely qualified, the compressive strength and flexural strength were greatly reduced, which manifested as a loose filling structure, weak interfacial bonding, and insufficient generation of hydration products.

[0049] From Tables 1 and 2 and Figure 1 , 2 It is evident that the performance of Comparative Example 2 decreased after replacing activated phosphogypsum with commercially available phosphogypsum, primarily due to the complete loss of the multiple functional benefits provided by activated phosphogypsum. A large amount of soluble phosphorus and fluorine impurities in commercially available phosphogypsum were not removed. These impurities, in the early stages of hydration, react with calcium ions to form insoluble calcium phosphate precipitates, which coat the surface of slag and fly ash particles, creating a physical barrier that hinders water penetration and ion diffusion, resulting in a significant retarding effect and abnormally shortened and difficult-to-control setting time. Simultaneously, uncalcined commercially available phosphogypsum is mainly dihydrate gypsum, whose hydration activity is far lower than that of hemihydrate gypsum, failing to rapidly generate ettringite to provide crystal nuclei for subsequent hydration, leading to slow early strength development. More importantly… Commercially available phosphogypsum lacks a hydrophobic modification layer on its surface. The strong adsorption of free water by the particles reduces the effective lubricating water in the slurry, resulting in a significant decrease in fluidity and slump. Without organic-inorganic hybrid coating, phosphogypsum particles lack a "flexible transition layer" with hydration products, resulting in weak interfacial bonding. This makes the filler prone to failure along the interface under stress, with a particularly significant decrease in flexural strength. In addition, soluble impurities may migrate and dissolve with water during long-term service, leading to deterioration of the internal structure of the filler and posing a potential threat to long-term stability.

[0050] From Tables 1 and 2 and Figure 1 , 2It can be seen that the performance of Comparative Example 3 decreased after replacing the alkaline activated fly ash with commercially available fly ash. The root cause is that the pozzolanic activity of commercially available fly ash is difficult to fully exert at room temperature, and the "destruction first, reconstruction later" activity release mechanism brought about by pre-activation treatment cannot be realized. Commercially available fly ash without pre-activation has a complete vitreous structure, and the active silica-alumina components are bound by a dense network. In the early stages of hydration, these components hardly participate in the reaction and can only wait for the alkaline and sulfate activators in the system to slowly destroy their structure, leading to a prolonged hydration induction period and severely delayed early strength development. Simultaneously, the lack of pre-activation treatment means that gel precursors cannot be generated in advance. These precursors could have acted as nuclei to promote the formation of ettringite in the early stages of hydration; their absence raises the nucleation barrier throughout the hydration process, significantly reducing the contribution to early strength. Regarding fluidity and slump, although commercially available fly ash can still exert some spherical particle ball-bearing effect, its insufficient particle surface activity weakens its synergistic effect with water-retaining agents, making it difficult to form a stable spatial network structure, resulting in decreased slurry fluidity and slump. In terms of later strength, the pozzolanic reaction of commercially available fly ash requires a long time to gradually activate in an alkaline environment, and the reaction degree is limited. It cannot continuously and efficiently consume calcium hydroxide to generate gel like alkali-activated fly ash, resulting in weak later strength growth; both compressive and flexural strengths are significantly lower than those of the pre-activated system.

[0051] From Tables 1 and 2 and Figure 1 , 2 It can be seen that the performance of Comparative Example 4 decreased after the modified steel slag was replaced with commercially available steel slag. The core reason is that the commercially available steel slag has a high content of free calcium oxide and has not been fully digested. The cementitious activity was not effectively activated, and the divalent metal oxide phase and iron phase minerals in the steel slag were not activated. The early hydration rate was slow and could not provide an alkaline environment and calcium ions in time. As a result, the potential activity of alkali-activated fly ash and blast furnace slag was not fully activated. The early compressive strength and flexural strength developed slowly, and the setting time was prolonged. More importantly, if the aging was not sufficient, the residual free calcium oxide hydrated and expanded in the later stage of hardening, generating volumetric stress, which led to poor stability, specimen cracking, and strength reduction. Even if the short-term strength met the standard, there were serious hidden dangers in the long-term performance.

[0052] From Tables 1 and 2 and Figure 1 , 2It is evident that in Comparative Example 5, replacing activated phosphogypsum, alkali-activated fly ash, and modified steel slag with commercially available products resulted in a precipitous decline in performance. The fundamental reason lies in the complete loss of the functional gains brought about by the individual modifications of the three components, as well as the synergistic effect among them. In the absence of activated phosphogypsum, the soluble phosphorus and fluorine impurities in the commercially available phosphogypsum, without removal, exert a retarding effect; the low hydration activity of dihydrate gypsum prevents the rapid formation of ettringite; the lack of hydrophobic modification on the surface leads to decreased fluidity and slump; and the dissolution of impurities threatens long-term stability. In the absence of alkali-activated fly ash, the glassy structure of the commercially available fly ash remains intact, the active silica-alumina components are bound and cannot be released early, and the pozzolanic reaction can only proceed slowly in the later stages, resulting in severely insufficient early strength. In the absence of modified steel slag, the free calcium oxide in the commercially available steel slag is not dissolved, leading to substandard volume stability and ineffective activation of cementitious activity. More importantly, the three commercially available products cannot form a synergistic chemical-physical-structural system. Activated phosphogypsum cannot provide a sulfate source and hydrophobic interface, alkali-activated fly ash cannot provide active silica and aluminum and pre-generated crystal nuclei, and modified steel slag cannot provide a stable alkaline environment and gelling activity. The entire gelling system degenerates into a simple physical mixture. This superimposed effect of multiple component functional deficiencies minimizes the fluidity and slump of the filling slurry, makes setting time abnormally difficult to control, results in cracks failing stability tests, and significantly reduces compressive and flexural strength. The filling structure is loose, with low hydration product generation and weak interfacial bonding, failing to meet the basic requirements of mine filling engineering. This fully demonstrates the essential characteristics of the present invention: the indispensable and synergistic effects of activated phosphogypsum, alkali-activated fly ash, and modified steel slag.

[0053] Although embodiments of this application have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principles and spirit of this application, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A phosphogypsum-fly ash based mine filling cementitious material, characterized in that, It includes component A and component B, wherein the mass ratio of component A to component B is 1:4-6; component A comprises the following components by weight: 40-50 parts activated phosphogypsum, 20-30 parts alkali-activated fly ash, 20-30 parts blast furnace slag, 5-10 parts modified steel slag, 3-6 parts composite activator, 0.3-0.8 parts polycarboxylate superplasticizer, and 0.2-0.5 parts foam stabilizer and water retainer; The method for preparing the activated phosphogypsum is as follows: Step S1: Dry the phosphogypsum at 80-100℃ until the moisture content is less than 1%, and grind it to a specific surface area of ​​300-350 m². 2 / kg, then keep warm at 650-710℃ for 1.5-2.0h; Step S2: Cool the material obtained in step S1 after heat preservation. When the temperature drops to 150-200℃, add sodium hydroxide solution and then cool to 60-75℃ to obtain calcined-alkali activated phosphogypsum. Step S3: Add the composite modifier to the calcined-alkali activated phosphogypsum obtained in step S2 at 60-75℃, stir for 15-25 minutes, and then age for 6-12 hours to obtain activated phosphogypsum.

2. The phosphogypsum-fly ash based mine filling cementitious material according to claim 1, characterized in that, The mass ratio of sodium hydroxide solution in step S2 to phosphogypsum in step S1 is 0.015-0.025:1, and the concentration of sodium hydroxide solution is 9.5-10.5%.

3. The phosphogypsum-fly ash based mine filling cementitious material according to claim 1, characterized in that, The composite modifier mentioned in step S3 is composed of calcium stearate, silane coupling agent KH-550, and silicon dioxide in a mass ratio of 1.0-1.5:0.3-0.5:1.0-2.0, and the mass ratio of the composite modifier to the calcined-alkali activated phosphogypsum obtained in step S2 is 0.025-0.04:

1.

4. The phosphogypsum-fly ash based mine filling cementitious material according to claim 1, characterized in that, The method for preparing the alkali-activated fly ash is as follows: fly ash is mixed with a composite alkali activator, deionized water is added to adjust the liquid-solid ratio to 0.25-0.30:1, and the mixture is stirred and activated at 75-85℃ for 12-18 hours. After post-treatment, the alkali-activated fly ash is obtained.

5. The phosphogypsum-fly ash based mine filling cementitious material according to claim 4, characterized in that, The mass ratio of fly ash to composite alkali activator is 1:0.08-0.12, and the composite alkali activator is composed of sodium hydroxide and water glass in a molar ratio of 0.8-1.2:

1.

6. The phosphogypsum-fly ash based mine filling cementitious material according to claim 1, characterized in that, The modified steel slag is prepared by aging the steel slag until the free calcium oxide content does not exceed 3%, and then adding a grinding aid and grinding it to a specific surface area of ​​350-450 m². 2 / kg, to obtain modified steel slag.

7. The phosphogypsum-fly ash based mine filling cementitious material according to claim 6, characterized in that, The grinding aid is triethanolamine and gypsum, and the mass ratio of steel slag, triethanolamine and gypsum is 1:0.003-0.007:0.001-0.

005.

8. The phosphogypsum-fly ash based mine filling cementitious material according to claim 1, characterized in that, The composite activator is composed of component A and component B in a mass ratio of 1.8-2.2:1; component A is an alkaline activator, composed of water glass, sodium hydroxide and water in a mass ratio of 60-70:10-15:20-30; component B is a sulfate activator, composed of anhydrous sodium sulfate, hemihydrate gypsum powder and silica fume in a mass ratio of 40-50:30-40:10-20.

9. The phosphogypsum-fly ash based mine filling cementitious material according to claim 1, characterized in that, Component b is tailings; the polycarboxylate superplasticizer is a polycarboxylate-based high-performance superplasticizer; the foam stabilizer and water retainer is composed of hydroxypropyl methylcellulose, nano-bentonite, air-entraining agent and defoamer in a mass ratio of 40-50:30-40:5-10:0.5-1, the air-entraining agent is rosin thermal polymer or triterpenoid saponin, and the defoamer is a polyether defoamer.

10. The method for preparing the phosphogypsum-fly ash based mine backfill cementitious material according to any one of claims 1-9, characterized in that, The process includes the following steps: dry mixing activated phosphogypsum, alkali-activated fly ash, blast furnace slag, modified steel slag, and component B to obtain mixture A; dry mixing composite activator, polycarboxylate superplasticizer, and foam stabilizer / water retainer to obtain mixture B; first adding a portion of water to mix with mixture A and mixture B, then adding the remaining water and continuing to stir to obtain the final product.

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