A long-lasting stable filler for phosphate mining, its preparation method and application

Abstract

This invention discloses a long-lasting stable filler for phosphate mining, its preparation method, and its application. The material uses cement, slag powder, phosphogypsum, and fly ash as matrix components, supplemented with nano-modifying liquid and additives such as retarders and early-strength agents. Its 3-day compressive strength reaches 4.6-5.5 MPa, and its 28-day compressive strength is 13.5-15.5 MPa. In a simulated acidic environment, its 90-day strength retention rate is ≥84%, and its volume shrinkage rate is ≤0.5%, exhibiting both high early strength and excellent long-term acid resistance. Through the synergistic effect of the "nano-micro" composite structure, nanoparticles fill pores and promote secondary hydration, basalt fibers bridge and resist cracking, and nano-montmorillonite blocks acid corrosion, achieving a balance between high early strength and long-term acid resistance. The material has a simple preparation process and can be efficiently applied to phosphate mine backfilling, meeting the requirements for rapid support and long-term resistance to acidic media erosion.

Description

Technical Field

[0001] This invention relates to the field of mine backfill materials technology, specifically to a long-lasting stable filler for phosphate mining, its preparation method, and its application. This filler is particularly suitable for phosphate mining backfilling, and can maintain stable mechanical properties and structural integrity over a long period in the acidic environment of phosphate mines. Background Technology

[0002] Phosphate rock is an important non-metallic mineral resource. Its mining commonly employs methods such as backfilling after the site has been exposed to prevent soil erosion, improve recovery rates, and manage solid waste. Phosphate rock layers and their surrounding rocks often contain sulfides such as pyrite, which are easily oxidized during mining to generate acidic mine drainage. This drainage typically has a pH value between 2.0 and 4.0 and is rich in sulfate, phosphate, and various heavy metal ions, creating a highly corrosive chemical environment that gradually erodes the backfill material, leading to a significant decrease in strength and insufficient long-term stability. Currently, traditional cement-based fillers, with cement as the main cementing material, are widely used for backfilling phosphate mine goafs. A typical formula consists of ordinary Portland cement, phosphate tailings aggregate, and water mixed in a certain proportion. To reduce costs and dispose of solid waste, phosphogypsum, a byproduct of phosphate chemical production, is often used as a partial substitute for aggregate or admixture. However, extensive engineering practice and research have shown that traditional cement-based fillers or phosphogypsum exhibit serious durability problems in this long-term acidic water environment. Their insufficient long-term stability has become a key technical bottleneck restricting the safe production and sustainable development of phosphate mines.

[0003] The failure of traditional cement-based fillers in the acidic aquatic environment of phosphate rock is a complex physicochemical process, mainly manifested as chemical corrosion and the resulting gradual deterioration of the microstructure. Under acidic conditions, calcium hydroxide and CSH gel in cement hydration products react with H+. + The reaction causes a rapid decrease in the alkalinity of the system, disrupting the stable environment of the gel. Simultaneously, phosphate ions react with calcium ions to form insoluble calcium phosphate salts, consuming the cementing calcium ions, while sulfate ions may generate expansive products, all contributing to the gradual disintegration of the gel system. These chemical reactions further lead to continuous damage to the microstructure. Acidic ions penetrate inward along pores and microcracks, dissolving soluble components to form new pores. Insoluble products precipitate locally and may generate crystallization pressure, increasing porosity, coarsening pore size, and expanding and connecting microcracks, ultimately making the material's internal structure loose and porous. Macroscopically, this process manifests as a sharp decline in mechanical properties and volume instability. For example, in an acidic environment with pH 2-4, the compressive strength of traditional fillers often decreases by more than 30% after 90 days of immersion, accompanied by uneven shrinkage or expansion, and in severe cases, complete collapse, posing a serious threat to the long-term safety of mines.

[0004] To address the failure of traditional fillers in acidic environments, high-alumina cement, magnesium phosphate cement, or large amounts of slag and fly ash are often used to reduce the calcium content and alkalinity of the system, thereby improving corrosion resistance. However, these materials exhibit slow early strength development and are insufficient against the synergistic corrosion of multiple ions in acidic water. Furthermore, methods that use polymer emulsions to block seepage paths are limited by the stability of polymers in long-term acidic, high-mineralization environments and their high cost. Therefore, developing a novel filler material that combines high early strength, excellent long-term corrosion resistance, good volume stability, and controllable cost has become an urgent technical requirement in the field of phosphate rock backfilling. Summary of the Invention

[0005] The purpose of this invention is to provide a long-lasting stable filler for phosphate mining, its preparation method, and its application. By introducing a nano-modified liquid, the high specific surface area, high activity, and special interface effect of nanomaterials are utilized to form a dense "nano-micro" composite structure with cement-based matrix components. This solves the technical problems of poor long-term stability and severe strength loss of traditional fillers in the acidic environment of phosphate mines, and overcomes the technical bottleneck of "short-term compliance and long-term failure" in existing fillers.

[0006] This invention provides a long-lasting stable filler for phosphate mining, comprising the following raw materials in parts by weight: 100-150 parts of matrix component, 5-10 parts of nano-modified liquid, and 1-6 parts of additive.

[0007] Preferably, the matrix component comprises the following raw materials in parts by weight: 15-30 parts cement, 25-35 parts slag powder, 30-65 parts phosphogypsum, 10-30 parts fly ash, 2-5 parts activator, and 0.5-1.5 parts water-reducing agent.

[0008] Preferably, the nano-modified liquid comprises the following raw materials in parts by weight: 2-5 parts of nano-silica, 0.2-1 parts of nano-calcium fluoride, 0.5-3 parts of nano-montmorillonite, 0.3-1.5 parts of basalt fiber, 0.5-1.5 parts of dispersant, 0.1-0.5 parts of surface modifier, and 10-20 parts of deionized oil.

[0009] Preferably, the cement is at least one of sulfoaluminate cement and aluminate cement, with an average particle size of 10-30 μm; the slag powder is granulated blast furnace slag powder, with an average particle size of 15-60 μm and a specific surface area ≥400 m². 2 / kg; the phosphogypsum contains 60%~90% calcium sulfate dihydrate (CaSO4·2H2O) by mass, with an average particle size of 30-70 micrometers; the fly ash is Grade I or Grade II fly ash, with an average particle size of 0.5-10μm.

[0010] Preferably, the activator is at least one of sodium hydroxide, potassium hydroxide, sodium carbonate, or sodium sulfate; and the water-reducing agent is at least one of polycarboxylate water-reducing agent or naphthalene-based water-reducing agent.

[0011] Preferably, the additive comprises 1-2 parts of a retarder, 1-3 parts of an accelerator, and 0.5-1 parts of a thickener. Preferably, the retarder is at least one of borax, boric acid, and citric acid; preferably, the accelerator is one or more of triethanolamine, aluminum sulfate, and calcium formate; preferably, the thickener is at least one of carboxymethyl cellulose, polyacrylic acid, and xanthan gum.

[0012] Preferably, the nano-silica is fumed nano-silica with a particle size of 10-20 nm and a specific surface area ≥300 m² / g; the nano-calcium fluoride is nano-calcium fluoride with a particle size of 20-40 nm and a purity ≥99%; the nano-montmorillonite is organically modified nano-montmorillonite with a particle size of 50-100 nm; and the basalt fiber is short-cut basalt fiber with a length of 1-5 mm and a diameter of 10-20 μm.

[0013] Preferably, the dispersant is at least one of sodium polyacrylate, polyethylene glycol, polyvinylpyrrolidone, and lignin sulfonate.

[0014] Preferably, the surface modifier is at least one of silane coupling agent, titanate coupling agent, sodium stearate, and stearic acid.

[0015] Preferably, the method for preparing the nano-modified liquid includes the following steps: mixing water, dispersant and surface modifier, and dispersing by low-speed stirring; then adding nano-silica, nano-calcium fluoride and nano-montmorillonite in sequence, and dispersing under ultrasonic assistance for 30-60 minutes to obtain a uniform and stable nano slurry; finally adding basalt fiber and dispersing by high-speed stirring to obtain the nano-modified liquid.

[0016] Preferably, the low-speed stirring dispersion is carried out at a speed of 300-500 r / min and a temperature of 40-60℃ for 15-30 min. The high-speed stirring dispersion is carried out at a speed of 800-1200 r / min and a temperature of 40-60℃ for 30-60 min. The ultrasonic power is 300-500 W, and the ultrasonic treatment lasts for 20-45 min.

[0017] This invention also provides a method for preparing a long-lasting stable filler for phosphate mining, comprising the following steps: After the matrix components are dry-mixed evenly, the nano-modification liquid and additives are added, and the mixture is stirred and mixed evenly to obtain the long-lasting stable filler.

[0018] The present invention also provides an application of a long-acting stable filler in phosphate mine backfilling, comprising the following steps: mixing the filler with water, adjusting the mass concentration of the slurry to 60-75%, and using it for backfilling operations in phosphate mine mining.

[0019] This invention is the first to apply a composite of nano-SiO2, nano-CaF2, and nano-montmorillonite to phosphate rock fillers. Utilizing their high specific surface area, high activity, and unique interfacial effects, they form a dense "nano-micro" composite structure with micron-sized matrix components. The nanoparticles can fill the tiny pores between matrix components, reduce interconnected pores, and form a dense microstructure that effectively prevents the penetration of acidic media, improves the erosion resistance of the filler material, and effectively solves the stability problem of traditional fillers in acidic environments.

[0020] In the nano-modified liquid used in this invention, nano-SiO2, with its high surface activity and pozzolanic activity, can not only fill the pores of the material, but also undergo a secondary reaction with Ca(OH)2 in the cement hydration products, promoting the formation of more CSH gel, thereby significantly improving the material's density, impermeability, and overall strength. Nano-CaF2 exhibits excellent chemical stability in acidic environments such as phosphate rock, and the F it releases... - The ions can react with C3A in cement to form calcium fluoroaluminate and ettringite crystals, while simultaneously forming a stable framework structure within the material. This dual effect effectively inhibits the erosion of hydration products, especially CSH gel, by acidic media, significantly improving the long-term acid resistance of the filler.

[0021] Basalt fiber, characterized by high strength, high modulus, and good corrosion resistance, can act as a "bridging" agent in filling materials, dispersing stress concentration and inhibiting the generation and propagation of microcracks, thereby preventing brittle failure of the filling material under stress. Especially in acidic environments, its corrosion resistance helps prevent further crack propagation and structural damage, ensuring the long-term durability of the material. Nano-montmorillonite, with its unique layered structure, can fill material pores, forming a physical barrier layer that effectively blocks the penetration of moisture and acidic media; simultaneously, its interlayer forces enhance the compressive strength and crack resistance of the material, both contributing to improved crack resistance and acid resistance of the filling material.

[0022] In the modified liquid used in this invention, the dispersant effectively prevents the agglomeration of nanoparticles and the clumping of fibers, ensuring that the nano-components and fibers are uniformly dispersed in the system, thereby avoiding the decrease in modification effect caused by agglomeration. In addition, the surface modifier can act as a "bridging" agent between nanoparticles, basalt fibers and cement matrix, significantly improving the interfacial compatibility between the two and the matrix, enhancing the interfacial bonding strength, and ensuring that each component can fully exert its reinforcing effect.

[0023] The advantages or beneficial effects of using a long-lasting stable filler in phosphate mining according to the present invention include at least the following: By constructing a "nano-micro" composite structure by combining composite nanomaterials with micron-sized matrix components, and synergistically formulating with multi-component nanofillers, the material achieves a 28-day compressive strength of 13.5-15.5 MPa, a 3-day compressive strength of 4.6-5.5 MPa, a 90-day acid immersion strength retention rate of ≥84%, and a volume shrinkage rate of ≤0.5%. It balances high early strength, excellent acid resistance, and volume stability, exhibiting good long-term stability and solving the technical problem of traditional materials achieving "short-term performance but long-term failure." Furthermore, using industrial solid waste such as phosphogypsum and slag powder as core components, it effectively disposes of solid waste and reduces costs, embodying the concept of green mining. Its preparation requires only simple mixing and stirring; during application, adjusting the slurry concentration allows for large-scale filling. The process is simple, cost-controllable, and suitable for complex phosphate mining applications. Detailed Implementation

[0024] To more clearly illustrate the purpose, technical solution, and advantages of this invention, the technical solution of this invention will be described in detail below through specific embodiments. It should be noted that these embodiments are only for illustrating this invention and not for limiting its scope of protection; the actual scope of protection of this invention should be determined by the claims.

[0025] Unless otherwise specified, the materials and reagents used in the following examples and comparative examples are commercially available. Unless otherwise specified, the amount of each component in the following examples is 1 g per part by weight.

[0026] Cement: Sulfoaluminate cement, purchased from Tangshan Liujiu Cement Co., Ltd., with an average particle size of 20μm. Slag powder: S95 grade, purchased from Wuhan Weishen Technology Development Co., Ltd., with an average particle size of 45μm and a specific surface area of ​​450m². 2 / kg.

[0027] The chemical composition of phosphogypsum is as follows: the mass percentage of calcium sulfate dihydrate (CaSO4·2H2O) in phosphogypsum is 70%, and the average particle size of phosphogypsum is 50μm.

[0028] Fly ash: Grade I fly ash, with an average particle size of 3-5 μm.

[0029] Nano-silica: Vapor-phase nano-silica with an average particle size of 20 nm and a specific surface area of ​​400 m². 2 / g.

[0030] Nano calcium fluoride: Nano calcium fluoride with an average particle size of 40nm and a purity of ≥99%.

[0031] Nano-montmorillonite: Nano-montmorillonite with an average particle size of 80 nm, modified with 3% CTAB.

[0032] Basalt fiber: Short-cut basalt fibers with a length of 3 mm and a diameter of 15 μm.

[0033] Water-reducing agent: Polycarboxylate-based water-reducing agent, commercially available.

[0034] Retarder: Borax, commercially available.

[0035] Early strength agent: Triethanolamine, commercially available.

[0036] Thickener: Carboxymethyl cellulose, commercially available.

[0037] Other reagents: dispersants, surface modifiers, activators, etc., are all of analytical grade.

[0038] I. Experimental examples and comparative examples of preparing phosphate rock using long-acting stable fillers.

[0039] Example 1 A long-lasting stable filler for phosphate mining, with the following raw material composition by mass: 121.8 parts matrix component, 7.2 parts nano-modified liquid, and 3.3 parts additives.

[0040] The matrix components consist of: 18 parts sulfoaluminate cement, 28 parts slag powder, 60 parts phosphogypsum, 12 parts Class I fly ash, 3 parts sodium hydroxide, and 0.8 parts polycarboxylate superplasticizer.

[0041] The preparation method of the nano-modified liquid is as follows: 15 parts of deionized water, 0.7 parts of dispersant sodium polyacrylate and 0.2 parts of surface modifier silane coupling agent are mixed and dispersed at low speed at 350 r / min and 45℃ for 20 minutes; then 3 parts of nano silica, 0.5 parts of nano calcium fluoride and 1 part of nano montmorillonite are added in sequence, and dispersed with ultrasonic power of 350W for 40 minutes to obtain a uniform and stable nano slurry; finally, 0.8 parts of basalt fiber are added and dispersed at high speed at 1000 r / min and 45℃ for 45 minutes to obtain the final product.

[0042] The preparation method of the filler in this embodiment is as follows: After the raw materials of the matrix components are dry mixed evenly, the above-prepared nano-modified liquid, 1.2 parts of retarder, 1.5 parts of early strength agent, and 0.6 parts of thickener are added, and the mixture is stirred for 15 minutes until it is evenly mixed to obtain a long-lasting stable filler for phosphate rock.

[0043] When using, mix the filler with water and adjust the slurry mass concentration to 65% for use in filling operations in goaf areas of phosphate mines.

[0044] Example 2 A long-lasting stable filler for phosphate mining, with the following raw material composition by mass: 113.5 parts matrix component, 6.3 parts nano-modified liquid, and 4.3 parts additives.

[0045] The matrix components consist of: 22 parts sulfoaluminate cement, 32 parts slag powder, 46 parts phosphogypsum, 10 parts Class I fly ash, 2.5 parts sodium carbonate, and 1 part polycarboxylate superplasticizer.

[0046] The preparation method of the nano-modified liquid is as follows: 18 parts of deionized water, 1 part of dispersant polyethylene glycol, and 0.3 parts of surface modifier titanate coupling agent are mixed and dispersed at low speed at 400 r / min and 42℃ for 25 minutes; then 2.5 parts of nano silica, 0.8 parts of nano calcium fluoride, and 1.5 parts of nano montmorillonite are added sequentially, and dispersed under ultrasonic power of 400W for 35 minutes to obtain a uniform and stable nano slurry; finally, 1 part of basalt fiber is added and dispersed at high speed at 900 r / min and 45℃ for 50 minutes to obtain the final product.

[0047] The preparation method of the filler in this embodiment is as follows: After the raw materials of the matrix components are dry mixed evenly, the above-prepared nano-modified liquid, 1.5 parts of retarder, 2 parts of early strength agent, and 0.8 parts of thickener are added, and the mixture is stirred for 15 minutes until it is evenly mixed, thus obtaining the long-lasting stable filler for phosphate mining.

[0048] When using, mix the filler with water and adjust the slurry mass concentration to 68% for use in filling operations in goaf areas of phosphate mines.

[0049] Example 3 A long-lasting stable filler for phosphate mining, by mass, has the following raw material composition: 117 parts matrix component, 8.8 parts nano-modification liquid, and 4.2 parts additives.

[0050] The matrix components consist of: 25 parts aluminate cement, 25 parts slag powder, 49.4 parts phosphogypsum, 13 parts Class I fly ash, 4 parts activator (sodium hydroxide + sodium carbonate compounded in a mass ratio of 2:1), and 0.6 parts polycarboxylate superplasticizer.

[0051] The preparation method of the nano-modified liquid is as follows: 12 parts of deionized water, 0.9 parts of dispersant polyvinylpyrrolidone, and 0.4 parts of surface modifier sodium stearate are mixed and dispersed at low speed for 18 minutes at a speed of 380 r / min and a temperature of 48℃; then 4 parts of nano silica, 0.3 parts of nano calcium fluoride, and 2 parts of nano montmorillonite are added sequentially, and dispersed under ultrasonic power of 450W for 30 minutes to obtain a uniform and stable nano slurry; finally, 0.5 parts of basalt fiber are added and dispersed at high speed at a speed of 1100 r / min and a temperature of 48℃ for 35 minutes to obtain the final product.

[0052] The preparation method of the filler in this embodiment is as follows: After the raw materials of the matrix components are dry mixed evenly, the above-prepared nano-modified liquid, 1 part of retarder, 2.5 parts of early strength agent, and 0.7 parts of thickener are added, and the mixture is stirred for 20 minutes until it is evenly mixed, thus obtaining the long-lasting stable filler for phosphate mining.

[0053] When using, mix the filler with water and adjust the slurry mass concentration to 72% for use in filling operations in goaf areas of phosphate mines.

[0054] Example 4 A long-lasting stable filler for phosphate mining, with the following raw material composition by mass: 117.7 parts matrix component, 6.6 parts nano-modified liquid, and 3.5 parts additives.

[0055] The matrix components consist of: 15 parts sulfoaluminate cement, 35 parts slag powder, 53 parts phosphogypsum, 10 parts Class I fly ash, 3.5 parts sodium sulfate, and 1.2 parts polycarboxylate superplasticizer.

[0056] The preparation method of the nano-modified liquid is as follows: 16 parts of deionized water, 1.3 parts of dispersant lignin sulfonate and 0.2 parts of surface modifier stearic acid are mixed and dispersed at low speed for 22 minutes at 450 r / min and 40℃; then 2 parts of nano silica, 1 part of nano calcium fluoride and 0.8 parts of nano montmorillonite are added sequentially and dispersed with ultrasonic power of 380W for 45 minutes to obtain a uniform and stable nano slurry; finally, 1.2 parts of basalt fiber are added and dispersed at high speed for 55 minutes at 850 r / min and 40℃ to obtain the final product.

[0057] The preparation method of the filler in this embodiment is as follows: After the raw materials of the matrix components are dry mixed evenly, the above-prepared nano-modified liquid, 1.8 parts of retarder, 1.2 parts of early strength agent, and 0.5 parts of thickener are added, and the mixture is stirred for 10 minutes until it is evenly mixed, thus obtaining the long-lasting stable filler for phosphate mining.

[0058] When using, mix the filler with water and adjust the slurry mass concentration to 62% for use in filling operations in goaf areas of phosphate mines.

[0059] Example 5 A long-lasting stable filler for phosphate mining, by mass, has the following raw material composition: 120 parts matrix component, 9.9 parts nano-modification liquid, and 6 parts additives.

[0060] The matrix components consist of: 28 parts of sulfoaluminate cement, 30 parts of slag powder, 44.3 parts of phosphogypsum, 15 parts of Class I fly ash, 2 parts of activator (sodium carbonate + sodium sulfate compounded in a mass ratio of 1:1), and 0.7 parts of polycarboxylate superplasticizer.

[0061] The preparation method of the nano-modified liquid is as follows: 19 parts of deionized water, 0.6 parts of dispersant (sodium polyacrylate and polyethylene glycol in a mass ratio of 2:1) and 0.5 parts of surface modifier (silane coupling agent and titanate coupling agent in a mass ratio of 1:1) are mixed and dispersed at low speed at 480 r / min and 45℃ for 28 minutes; then 3.5 parts of nano silica, 0.6 parts of nano calcium fluoride and 2.5 parts of nano montmorillonite are added sequentially, and dispersed under ultrasonic power of 480W for 38 minutes to obtain a uniform and stable nano slurry; finally, 1.5 parts of basalt fiber are added and dispersed at high speed at 1150 r / min and 40℃ for 40 minutes to obtain the final product.

[0062] The preparation method of the filler in this embodiment is as follows: After the raw materials of the matrix components are dry mixed evenly, the above-prepared nano-modified liquid, 2 parts of retarder, 3 parts of early strength agent, and 1 part of thickener are added, and the mixture is stirred for 10 minutes until it is evenly mixed, thus obtaining the long-lasting stable filler for phosphate mining.

[0063] When using, mix the filler with water and adjust the slurry mass concentration to 75% for use in filling operations in goaf areas of phosphate mines.

[0064] Comparative Example 1 The difference from Example 1 is that no nano-modification liquid is added, while the other conditions are the same as in Example 1.

[0065] Comparative Example 2 The difference from Example 1 is that, in the preparation of the nano-modified liquid, an equal amount of nano-silica was used instead of nano-calcium fluoride, while other conditions were the same as in Example 1.

[0066] Comparative Example 3 The difference from Example 1 is that, in the preparation of the nano-modified liquid, an equal amount of nano-silica was used instead of nano-montmorillonite, while other conditions were the same as in Example 1.

[0067] Comparative Example 4 The difference from Example 1 is that, in the preparation of the nano-modified liquid, an equal amount of nano-silica was used instead of basalt fiber, while other conditions were the same as in Example 1.

[0068] Comparative Example 5 The difference from Example 1 is that the dispersant sodium polyacrylate and the surface modifier silane coupling agent were omitted in the preparation of the nano-modified liquid, while the other conditions were the same as in Example 1.

[0069] II. Performance Testing 1. Perform compressive strength testing according to GB / T 17671-2020 standard, test three parallel specimens, and take the average value.

[0070] 2. Acid resistance test Prepare a simulated acidic solution: 0.05 mol / L H₂SO₄ + 0.02 mol / L H₃PO₄ + 0.01 mol / L Fe 2+ +0.03mol / L Ca 2+ +0.02mol / L Mg 2+ Adjust the pH to 3.0 using H2SO4 or NaOH. Immerse the specimens after 28 days of standard curing in simulated acidic leachate; maintain a constant temperature (25±2℃) during immersion, and change the acid solution regularly to maintain the pH; remove the specimens at 30d, 60d, and 90d respectively, rinse with clean water, dry the surface, test the remaining compressive strength, and calculate the strength loss rate.

[0071] 3. Volume shrinkage rate The volume shrinkage rate of the sample was determined according to GB / T 29417-2012 "Test Method for Shrinkage Performance of Cement-based Grouting Materials".

[0072] Table 1 shows the performance of the examples and comparative examples.

[0073] The long-lasting stable fillers used in Examples 1-5 exhibit excellent comprehensive performance in phosphate mine mining, with 3-day compressive strength reaching 4.6-5.5 MPa and 28-day compressive strength reaching 13.5-15.5 MPa, quickly meeting the early strength requirements of phosphate mine support. In a simulated acidic environment of phosphate mines at pH 3.0, the strength retention rate is ≥93.5% at 30 days, ≥87.4% at 60 days, and ≥84.3% at 90 days, with a strength loss rate of only 11%-16%, far superior to traditional fillers. The volume shrinkage rate of the filling material is less than 0.50%, demonstrating excellent long-term volume stability and good long-term structural integrity. Through the synergistic effect of the "nano-micro" composite structure, it combines high early strength, excellent acid resistance, and strong volume stability, making it perfectly suited for the complex filling conditions of acidic phosphate mines with multiple corrosive ions.

[0074] Comparative Example 1, lacking the addition of nano-modifying liquid, showed a 3-day and 28-day decrease in compressive strength compared to Example 1, with reductions of 33.3% and 26.1%, respectively. After 90 days of acid immersion, the strength retention rate was only 58%, and the volume shrinkage rate reached 3.31%. The core reason is that without the nano-modifying liquid, a dense "nano-micro" structure could not be constructed. The pore-filling effect of nanoparticles, the bridging and crack-resistant effect of basalt fibers, the stabilizing framework of nano-CaF2, and the barrier effect of nano-montmorillonite all failed. Acidic ions could freely penetrate and erode hydration products, leading to a loose microstructure, a sharp decline in mechanical properties, and uncontrolled volume shrinkage.

[0075] Comparative Example 2 replaced nano-CaF2 with nano-SiO2. The 3-day and 28-day compressive strengths were comparable to those of Example 1, but the strength retention rate after 90 days of acid immersion was only 62%, and the volume shrinkage rate was 1.92%. A possible reason is that nano-CaF2 can release F in an acidic environment. - It reacts with C3A to form stable calcium fluoroaluminate and ettringite crystals, and forms a rigid framework, thus doubly inhibiting acid corrosion. However, nano-SiO2 can only optimize the early density and cannot replace its chemical stabilizing effect, which leads to the accelerated acid corrosion rate of hydration products and the aggravated strength loss.

[0076] In Comparative Example 3, nano-Montmorillonite was replaced with nano-SiO2. The compressive strength decreased by 10% after 28 days, and the strength retention rate after 90 days of acid immersion was 65%, with a volume shrinkage rate of 1.78% (3.6 times that of Example 1). The main reason is that the layered structure of nano-Montmorillonite can form a physical barrier layer, blocking the penetration of acidic ions and enhancing crack resistance. After replacement, nano-SiO2 alone cannot form a continuous barrier interface, allowing acidic media to easily penetrate along the pores and decompose hydration products. Furthermore, the material's crack resistance decreases, and the propagation of microcracks leads to an increase in volume shrinkage and poorer long-term stability.

[0077] Comparative Example 4, where basalt fibers were replaced with nano-SiO2, showed a 12% decrease in compressive strength after 28 days, a 75% strength retention rate after 90 days of acid immersion, and a volume shrinkage rate of 1.57%. Overall performance was slightly better than in Example 1. The main reason is that the basalt fibers in Example 1 can disperse stress and inhibit microcrack propagation, and the corrosion resistance of basalt fibers helps prevent further crack propagation and structural damage, reducing volume shrinkage and ensuring long-term material durability.

[0078] Comparative Example 5, omitting the dispersant and surface modifier, showed a 20.8% and 22.5% decrease in compressive strength at 3 days and 28 days compared to Example 1, respectively. After 90 days of acid immersion, the strength retention rate was 60%, and the volume shrinkage rate was 2.16% (4.3 times that of Example 1). The main reason for this is that the dispersant prevents the agglomeration of nanoparticles and fibers, and the surface modifier improves their interfacial compatibility with the matrix. Omitting these components leads to agglomeration, hindering their uniform filling and bridging effects. Weak interfacial bonding results in localized defects, allowing acidic ions to easily accumulate and corrode at these defects, leading to a significant decrease in overall performance.

[0079] It should be clarified that the above embodiments are merely illustrative of specific implementations of the present invention and do not constitute a limitation on the scope of protection of the present invention. Based on the technical content disclosed in this invention, those skilled in the art can make various modifications, adjustments, or equivalent substitutions within its basic principles and design concepts. These modifications and improvements need not be listed exhaustively, but should all be considered to fall within the scope of protection of this invention.

Claims

1. A long-lasting stable filler for phosphate mining, characterized in that, The raw materials include the following parts by weight: 100-150 parts of matrix component, 5-10 parts of nano-modification liquid, and 1-6 parts of additives; The matrix components include the following raw materials in parts by weight: 15-30 parts cement, 25-35 parts slag powder, 30-65 parts phosphogypsum, 10-30 parts fly ash, 2-5 parts activator, and 0.5-1.5 parts water-reducing agent; The nano-modified liquid comprises the following raw materials in parts by weight: 2-5 parts nano-silica, 0.2-1 parts nano-calcium fluoride, 0.5-3 parts nano-montmorillonite, 0.3-1.5 parts basalt fiber, 0.5-1.5 parts dispersant, 0.1-0.5 parts surface modifier, and 10-20 parts deionized oil. The surface modifier is at least one of silane coupling agent, titanate coupling agent, sodium stearate, and stearic acid.

2. The phosphate mining method using a long-lasting stable filler as described in claim 1, characterized in that, The cement is at least one of sulfoaluminate cement and aluminate cement, with an average particle size of 10-30 μm; the slag powder is granulated blast furnace slag powder with an average particle size of 15-60 μm and a specific surface area ≥400 m². 2 / kg; the phosphogypsum contains 60%~90% calcium sulfate dihydrate by mass and has an average particle size of 30-70 micrometers; the fly ash is Grade I or Grade II fly ash with an average particle size of 0.5-10μm.

3. The phosphate mining method using a long-lasting stable filler as described in claim 1, characterized in that, The activator is at least one of sodium hydroxide, potassium hydroxide, sodium carbonate, or sodium sulfate; the water-reducing agent is at least one of polycarboxylate water-reducing agent or naphthalene-based water-reducing agent.

4. The long-lasting stable filler used in phosphate mining as described in any one of claims 1-3, characterized in that, The additives include 1-2 parts of retarder, 1-3 parts of early-strength agent, and 0.5-1 parts of thickener.

5. The phosphate mining method using a long-lasting stable filler as described in claim 4, characterized in that, The retarder is at least one of borax, boric acid, and citric acid.

6. The phosphate mining method using a long-lasting stable filler as described in claim 4, characterized in that, The early strength agent is one or more of triethanolamine, aluminum sulfate, and calcium formate.

7. The phosphate mining method using a long-lasting stable filler as described in claim 4, characterized in that, The thickener is at least one of carboxymethyl cellulose, polyacrylic acid, and xanthan gum.

8. The long-lasting stable filler used in phosphate mining as described in any one of claims 1-3, characterized in that, The nano-silica is fumed silica with a particle size of 10-20 nm and a specific surface area ≥300 m² / g; the nano-calcium fluoride is calcium fluoride with a particle size of 20-40 nm and a purity ≥99%; the nano-montmorillonite is organically modified nano-montmorillonite with a particle size of 50-100 nm; and the basalt fiber is short-cut basalt fiber with a length of 1-5 mm and a diameter of 10-20 μm.

9. The long-lasting stable filler used in phosphate mining as described in any one of claims 1-3, characterized in that, The dispersant is at least one of sodium polyacrylate, polyethylene glycol, polyvinylpyrrolidone, and lignin sulfonate.

10. The long-lasting stable filler used in phosphate mining as described in any one of claims 1-3, characterized in that, The preparation method of the nano-modified liquid includes the following steps: mixing water, dispersant and surface modifier, and stirring and dispersing at low speed; then adding nano-silica, nano-calcium fluoride and nano-montmorillonite in sequence, and dispersing under ultrasonic assistance for 30-60 minutes to obtain a uniform and stable nano slurry; finally adding basalt fiber and stirring and dispersing at high speed to obtain the nano-modified liquid.

11. The long-lasting stable filler used in phosphate mining as described in claim 10, characterized in that, The low-speed stirring dispersion is carried out at a speed of 300-500 r / min and a temperature of 40-60℃ for 15-30 min; the high-speed stirring dispersion is carried out at a speed of 800-1200 r / min and a temperature of 40-60℃ for 30-60 min; the ultrasonic power is 300-500W, and the ultrasonic treatment lasts for 20-45 min.

12. A method for preparing a long-lasting stable filler for phosphate mining as described in any one of claims 1-11, characterized in that, Includes the following steps: After the matrix components are dry-mixed evenly, the nano-modification liquid and additives are added, and the mixture is stirred and mixed evenly to obtain the long-lasting stable filler.

13. An application of a long-acting stable filler in phosphate mine backfilling, comprising the following steps: mixing the filler according to any one of claims 1-11 with water, adjusting the mass concentration of the slurry to 60-75%, and using it for backfilling operations in phosphate mine mining.

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