High-early-strength acid-resistant filling material suitable for phosphate mine, preparation method and application

Abstract

The application discloses a high-early-strength acid-resistant phosphorite filling and grouting material and a preparation method and application thereof. The material takes sulphoaluminate cement, modified phosphogypsum and steel slag powder as main components, and is supplemented with an alkali activator, nano silicon dioxide, a composite acid-resistant agent, a water reducing agent, a suspending agent and a retarder. The material has a 1-day compressive strength of no less than 3.0 MPa, a 3-day compressive strength of no less than 15 MPa and a 28-day compressive strength of no less than 28 MPa; the strength loss rate is no more than 14.3% after being soaked in a sulfuric acid solution for 28 days, and the material has excellent high-temperature and high-humidity stability and freeze-thaw cycle stability. The high-early-strength is derived from the rapid hydration of sulphoaluminate cement to generate ettringite and Al(OH)3 gel, and the acid resistance is realized through the physical blocking and chemical gel filling of the composite acid-resistant agent, and the material can be efficiently applied to phosphorite filling mining, and meets the requirements of rapid support and long-term acid erosion resistance.

Description

Technical Field

[0001] This invention relates to the field of mine backfilling materials technology, specifically to a high early strength, acid-resistant grouting material for phosphate mine backfilling, its preparation method, and its application. Background Technology

[0002] Phosphate ore backfilling technology is an important means of solving the problem of goaf in mines, mainly including methods such as strip backfilling, layered backfilling, and subsequent backfilling. Phosphate ore backfilling faces two major challenges: First, the groundwater in phosphate mining areas is generally acidic (low pH value). Acidic solutions (such as sulfuric acid and hydrochloric acid) will react with hydration products such as ettringite and calcium hydroxide in the backfill material, leading to their decomposition and loss, destroying the cementing structure of the material, thus significantly reducing the compressive strength and durability of the backfill. Moreover, acid corrosion increases the porosity of the material, forming interconnected channels and microcracks. This not only further weakens the mechanical properties of the material, but also provides channels for the migration and leaching of harmful substances inside. This places extremely high demands on the long-term acid corrosion resistance of the backfill. Second, in order to meet the process cycle requirements of efficient mining, the backfill must have high early strength so as to quickly replace the stope and assume the role of roof support.

[0003] With the rapid development of the phosphate chemical industry, the resource utilization of solid wastes such as phosphogypsum has attracted much attention. Traditional phosphate mine backfill materials mainly use ordinary silicate cement as cementing material, supplemented by industrial waste residue and tailings sand. However, these materials have the following significant defects in the acidic environment of phosphate mines. (1) Ordinary silicate cement-based backfill materials have slow early strength development, and their hydration product, calcium hydroxide, has poor acid resistance. Under the erosion of acidic mine water, it is easy to undergo neutralization and dissolution and gypsum-type corrosion, resulting in structural deterioration and a sharp drop in strength. (2) Other systems, such as low-alkalinity materials (silica fume + limestone powder + slag), can improve the problem of slow setting, but after long-term soaking, the strength may be reduced due to the decomposition of ettringite or the corrosion of calcium hydroxide. The compressive strength is low and far from meeting the requirements of rapid support, and the acid resistance is still insufficient. These defects together restrict the safe and reliable application of traditional materials in phosphate mine backfilling.

[0004] To address these issues, researchers have explored various modification methods, such as adding lime to neutralize acidity, optimizing aggregate gradation to improve density, and using nanomaterials like silica fume to fill pores. However, these methods often only solve part of the problem and fail to achieve a synergistic improvement in early strength, acid resistance, and long-term stability. Summary of the Invention

[0005] This invention addresses the challenges posed by the highly acidic geological conditions in phosphate mine backfilling and the shortcomings of existing backfilling materials. It provides a high early strength and acid-resistant backfilling material suitable for phosphate mines, achieving a synergistic improvement in early strength, acid resistance, and long-term stability.

[0006] This invention provides a high early strength acid-resistant backfill material suitable for phosphate mines, comprising the following raw materials by weight: 10-30 parts of sulfoaluminate cement, 50-75 parts of modified phosphogypsum, 15-49 parts of steel slag powder, 1-5 parts of alkali activator, 0.5-3 parts of nano silica, 5-15 parts of acid-resistant agent, 0.2-1 parts of water-reducing agent, 1-5 parts of suspending agent, and 0.5-3 parts of retarder.

[0007] The preparation method of the modified phosphogypsum includes the following steps: After pulverizing and mixing phosphogypsum, fly ash and carbide slag separately, the resulting mixture is fed into a rotary kiln and calcined at 160-190℃ for 1-2 hours. Finally, after grinding and sieving, modified phosphogypsum rich in hemihydrate phosphogypsum is obtained.

[0008] Preferably, the sum of the sulfoaluminate cement, modified phosphogypsum, and steel slag powder is 100 parts.

[0009] Preferably, the modified phosphogypsum has the following raw material mass fraction ratio: phosphogypsum 60%~85%; fly ash 5%~15%; and carbide slag 10%~25%. Preferably, the sieving is performed using a 200-mesh sieve.

[0010] Preferably, the chemical composition of the carbide slag, by mass fraction, includes: CaO 60-80%, SiO2 5-15%, and Al2O3 2-8%. Preferably, the average particle size of the carbide slag is 10-50 micrometers.

[0011] Preferably, the chemical composition of the fly ash, by mass fraction, includes: SiO2 40%-60%, Al2O3 20%-30%, Fe2O3 4%-10%, and CaO 5%-15%. Preferably, the average particle size of the fly ash is 5-30 micrometers.

[0012] Preferably, the phosphogypsum contains 70% to 90% calcium sulfate dihydrate (CaSO4·2H2O) by mass. Preferably, the average particle size of the phosphogypsum is 30-60 micrometers.

[0013] Preferably, the chemical composition of the sulfoaluminate cement, by mass fraction, includes: Al2O3 30%-50%, CaO 30%-45%, SiO2 5%-10%, and SO3 8-15%. The particle size of the sulfoaluminate cement is 15-30 micrometers.

[0014] Preferably, the chemical composition of the steel slag powder, by mass fraction, includes: CaO 30%-50%, SiO2 15%-25%, Al2O3 3%-10%, and Fe2O3 15%-30%. Preferably, the average particle size of the steel slag powder is 10-30 micrometers.

[0015] Preferably, the total amount of the sulfoaluminate cement, modified phosphogypsum, and steel slag powder is 100 parts.

[0016] Preferably, the acid-resistant agent is a mixture of fluorite powder and sodium silicate in a mass ratio of 1:1-3.

[0017] Preferably, the fluorite powder contains ≥85% CaF2 and has an average particle size of 10-20 micrometers.

[0018] Preferably, the nano-silica has a particle size of 15nm-100nm and a specific surface area of ​​150-400 m². 2 / g, SiO2 content ≥98%.

[0019] Preferably, the alkaline activator is at least one selected from potassium hydroxide, sodium hydroxide, sodium carbonate, and calcium oxide.

[0020] Preferably, the water-reducing agent includes at least one of naphthalene-based water-reducing agents, melamine-based water-reducing agents, or polycarboxylate-based water-reducing agents.

[0021] Preferably, the suspending agent includes at least one of sodium carboxymethyl cellulose or hydroxymethyl cellulose.

[0022] Preferably, the retarder is at least one of borax and boric acid.

[0023] This invention also provides a method for preparing a high early strength acid-resistant phosphate rock filling grouting material, comprising the following steps: mixing sulfoaluminate cement, modified phosphogypsum, steel slag powder, alkali activator, nano silica, acid resistant agent, water reducing agent, suspending agent, and retarder evenly to obtain the high early strength acid-resistant phosphate rock filling grouting material.

[0024] The present invention also provides an application of a high early strength acid-resistant phosphate rock filling grouting material in phosphate mine filling, comprising mixing the filling grouting material with water and adjusting the mass concentration of the grout to 50-70% to meet the filling requirements of phosphate mines.

[0025] This invention utilizes carbide slag and fly ash to provide a stable alkaline environment, promoting the directional transformation of phosphogypsum into highly active hemihydrate gypsum under calcination conditions of 160-190℃. This lays the foundation for the early strength of the material and simultaneously stimulates the pozzolanic activity of the fly ash. During the subsequent addition of water to form a slurry, the carbide slag and fly ash further neutralize acidic impurities such as free phosphoric acid in the phosphogypsum. The three components form a dense skeletal structure, which, together with steel slag powder and sulfoaluminate cement, enhances the early strength, acid resistance, and long-term stability of the backfill material, making it suitable for the backfilling needs of acidic phosphate mines.

[0026] This invention selects sulfoaluminate cement clinker as the cementitious material, whose main mineral components are C4A3S and C2S. On the one hand, C4A3S undergoes a hydration reaction with water and calcium sulfate hemihydrate in modified phosphogypsum to generate a large amount of ettringite and Al(OH)3 gel, thereby rapidly forming high early strength. On the other hand, the Al(OH)3 gel formed by the reaction can neutralize more H+. + Simultaneously, a protective layer can be formed on the surface to delay acid penetration, which not only improves the long-term stability of the filler but also significantly enhances the material's resistance to acid corrosion. Furthermore, the nano-silica added in this invention can act as a nucleation agent, accelerating the hydration of the sulfoaluminate cement and modified phosphogypsum cementitious system, thereby promoting early strength development. At the same time, the nanoparticles can effectively fill the micropores between hydration products, significantly improving the compactness of the filler's microstructure and thus enhancing its long-term stability.

[0027] In the phosphate mine backfill material of this invention, fluorite powder and sodium silicate, as composite acid-resistant agents, can exert a synergistic effect, improving the acid resistance and long-term stability of the material through both physical barrier and chemical stabilization pathways. Fluorite powder primarily functions through physical barrier and chemical inertness: its fluorite particles can uniformly cover the surface of the material particles, forming a continuous inert protective layer that directly blocks the contact and erosion of acidic media; simultaneously, its stable properties enhance the overall density and compressive strength of the material, improving long-term stability. Sodium silicate mainly relies on chemical reaction and gel filling: under acidic conditions, it hydrolyzes to generate silica (or silicic acid) gel. This gel forms a stable acid-resistant protective layer on the particle surface, achieving physical isolation; on the other hand, it effectively fills the pores inside the material, reducing permeability, thereby significantly improving the material's resistance to H+. + SO4 2- It enhances the resistance to harmful ion erosion and increases compressive strength. The synergistic use of these two methods comprehensively improves both surface protection and structural reinforcement, giving the filler superior acid resistance and durability in acidic mining environments.

[0028] The advantages or beneficial effects of the phosphate mine filling grouting material of the present invention include at least the following: the 1-day compressive strength of the filling material of the present invention is ≥3.0MPa, the 3-day compressive strength is ≥15MPa, the 28-day compressive strength is ≥28MPa, and the 28-day acid immersion compressive strength loss rate is ≤14.3%; at the same time, it has excellent long-term stability, with a strength loss rate of ≤4.3% after 3 months of high temperature and high humidity curing and a strength loss rate of ≤10.1% after 50 freeze-thaw cycles, achieving a synergistic improvement in early strength, acid resistance and long-term stability, which can quickly provide phosphate mine support strength and resist the erosion of complex working conditions such as acidic environment, high temperature and high humidity and freeze-thaw cycles for a long time. Detailed Implementation

[0029] 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.

[0030] 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.

[0031] Table 1 shows that the fly ash used in the examples had an average particle size of 20 micrometers and the following chemical composition:

[0032] Table 2 shows that the average particle size of the carbide slag used in the examples is 30 micrometers, and its chemical composition is as follows:

[0033] Table 3 shows that the average particle size of the steel slag powder used in the examples is 15 micrometers, and its chemical composition is as follows:

[0034] Table 4 shows the particle size of the sulfoaluminate cement used in the examples, which is 20 micrometers, and its chemical composition is as follows:

[0035] The chemical composition of the phosphogypsum used in this invention is as follows: the mass percentage of calcium sulfate dihydrate (CaSO4·2H2O) in the phosphogypsum is 85%, and the average particle size of the phosphogypsum is 40 micrometers.

[0036] Fluorite powder: CaF2 content is 95%, and particle size is 15μm.

[0037] Nano-silica: SiO2 content is 98%, average particle size is 50nm, and specific surface area is 300m². 2 / g.

[0038] Alkali activator: Sodium carbonate.

[0039] Water-reducing agent: Polycarboxylate-based water-reducing agent.

[0040] Suspension agent: Sodium carboxymethyl cellulose Retarder: Borax.

[0041] I. Examples and comparative examples of phosphate rock backfill grouting materials.

[0042] Example 1 The high early strength acid-resistant phosphate rock backfill material, by weight, consists of the following raw materials: 20 parts sulfoaluminate cement, 60 parts modified phosphogypsum, 20 parts steel slag powder, 3 parts alkali activator, 1.5 parts nano silica, 10 parts acid-resistant agent (fluorite powder and sodium silicate mixed at a mass ratio of 1:2), 0.6 parts water-reducing agent, 3 parts suspending agent, and 1.5 parts retarder.

[0043] The preparation steps of modified phosphogypsum are as follows: Phosphogypsum, fly ash, and carbide slag are mixed in a mass ratio (75% phosphogypsum, 10% fly ash, and 15% carbide slag) in a mixer and stirred for 30 minutes until uniformly mixed to obtain a mixture. The mixture is then fed into a rotary kiln and calcined at 180°C for 1.5 hours. The calcined product is then removed, allowed to cool naturally to room temperature, and ground in a ball mill. After grinding, the mixture is sieved through a 200-mesh sieve, and the sieved material is collected. This sieve-undersized material is the modified phosphogypsum rich in hemihydrate phosphogypsum.

[0044] The preparation method of this embodiment is as follows: the above raw materials are put into a forced mixer according to the proportion and stirred for 40 minutes until they are mixed evenly to obtain a high early strength acid-resistant phosphate rock filling grouting material; when using, the filling grouting material is mixed with water and the grout mass concentration is adjusted to 60% for use in phosphate mine filling.

[0045] Example 2 The high early strength acid-resistant phosphate rock backfill material, by weight, consists of the following raw materials: 30 parts sulfoaluminate cement, 50 parts modified phosphogypsum, 20 parts steel slag powder, 5 parts alkali activator, 3 parts nano silica, 15 parts acid-resistant agent (fluorite powder and sodium silicate mixed at a mass ratio of 1:3), 1 part water-reducing agent, 5 parts suspending agent, and 0.5 parts retarder. The preparation steps of modified phosphogypsum are as follows: Phosphogypsum, fly ash, and carbide slag are mixed in a mass ratio (80% phosphogypsum, 5% fly ash, and 15% carbide slag) in a mixer and stirred for 20 minutes until uniformly mixed to obtain a mixture. The mixture is then fed into a rotary kiln and calcined at a controlled temperature of 190°C for 1 hour. The calcined product is then removed, allowed to cool naturally to room temperature, and ground in a ball mill. After grinding, the mixture is sieved through a 200-mesh sieve, and the sieved material is collected. This sieve-undersized material is modified phosphogypsum rich in hemihydrate phosphogypsum. The preparation method of this embodiment is as follows: the above raw materials are put into a mixer according to the proportion and stirred at high speed for 25 minutes until they are mixed evenly to obtain a high early strength acid-resistant phosphate rock filling grouting material; when using, the filling grouting material is mixed with water and the grout mass concentration is adjusted to 65% for rapid filling of phosphate mines.

[0046] Example 3 The high early strength acid-resistant phosphate rock backfill material, by weight, consists of the following raw materials: 10 parts sulfoaluminate cement, 75 parts modified phosphogypsum, 15 parts steel slag powder, 1 part alkali activator, 0.5 parts nano silica, 5 parts acid-resistant agent (fluorite powder and sodium silicate mixed at a mass ratio of 1:1), 0.2 parts water-reducing agent, 1 part suspending agent, and 3 parts retarder. The preparation steps of modified phosphogypsum are as follows: Phosphogypsum, fly ash, and carbide slag are mixed in a mass ratio (65% phosphogypsum, 15% fly ash, and 20% carbide slag) in a mixer and stirred for 30 minutes until uniformly mixed to obtain a mixture. The mixture is then fed into a rotary kiln and calcined at 160°C for 2 hours. The calcined product is then removed, allowed to cool naturally to room temperature, and ground in a ball mill. After grinding, the mixture is sieved through a 200-mesh sieve, and the sieved material is collected. This sieve-undersized material is modified phosphogypsum rich in hemihydrate phosphogypsum. The preparation method of this embodiment is as follows: put the above raw materials into a mixer according to the proportion and stir for 25 minutes until they are evenly mixed to obtain a high early strength acid-resistant phosphate rock filling grouting material; when using, mix the filling grouting material with water and adjust the grout mass concentration to 55% for filling of phosphate mines with strong acidity.

[0047] Example 4 The high early strength acid-resistant phosphate rock backfill material, by weight, consists of the following raw materials: 25 parts sulfoaluminate cement, 55 parts modified phosphogypsum, 20 parts steel slag powder, 4 parts alkali activator, 2 parts nano silica, 12 parts acid-resistant agent (fluorite powder and sodium silicate mixed at a mass ratio of 1:2.5), 0.8 parts water-reducing agent, 4 parts suspending agent, and 1 part retarder. The preparation steps of modified phosphogypsum are as follows: Phosphogypsum, fly ash, and carbide slag are mixed in a mass ratio (70% phosphogypsum, 12% fly ash, and 18% carbide slag) in a mixer and stirred for 25 minutes until uniformly mixed to obtain a mixture. The mixture is then fed into a rotary kiln and calcined at 185°C for 1.2 hours. The calcined product is then removed, allowed to cool naturally to room temperature, and ground in a ball mill. After grinding, the mixture is sieved through a 200-mesh sieve, and the sieved material is collected. This sieve-undersized material is the modified phosphogypsum rich in hemihydrate phosphogypsum. The preparation method of this embodiment is as follows: put the above raw materials into a forced mixer according to the proportion and stir for 30 minutes until they are evenly mixed to obtain a high early strength acid-resistant phosphate rock filling grouting material; when using, mix the filling grouting material with water and adjust the grout mass concentration to 62% for conventional filling operations in medium acid phosphate mines. Example 5

[0048] The high early strength acid-resistant phosphate rock backfill material, by weight, consists of the following raw materials: 18 parts sulfoaluminate cement, 62 parts modified phosphogypsum, 20 parts steel slag powder, 3.5 parts alkali activator, 1.2 parts nano silica, 8 parts acid-resistant agent (fluorite powder and sodium silicate mixed at a mass ratio of 1:1.8), 0.5 parts water-reducing agent, 3 parts suspending agent, and 1.8 parts retarder. The preparation steps of modified phosphogypsum are as follows: Phosphogypsum, fly ash, and carbide slag are mixed in a mass ratio (78% phosphogypsum, 8% fly ash, and 14% carbide slag) in a mixer and stirred for 30 minutes until uniformly mixed to obtain a mixture. The mixture is then fed into a rotary kiln and calcined at 170°C for 1.5 hours. The calcined product is then removed, allowed to cool naturally to room temperature, and ground in a ball mill. After grinding, the mixture is sieved through a 200-mesh screen, and the sieved material is collected. This sieve material is the modified phosphogypsum rich in hemihydrate phosphogypsum. The preparation method of this embodiment is as follows: put the above raw materials into a mixer according to the proportion and stir for 35 minutes until they are mixed evenly to obtain a high early strength acid-resistant phosphate rock filling grouting material; when using, mix the filling grouting material with water and adjust the grout mass concentration to 58%, which is suitable for phosphate mine filling with low energy consumption production requirements.

[0049] Comparative Example 1 The formulation and preparation method are basically the same as those in Example 1. The only difference is that modified phosphogypsum was not used. Instead, phosphogypsum, carbide slag and fly ash were directly mixed and passed through a 200-mesh sieve and added directly as raw materials.

[0050] Comparative Example 2 The formulation and preparation method are basically the same as those in Example 1, except that an equal amount of ordinary silicate cement (model P.O52.5, purchased from Anhui Conch Cement Co., Ltd.) is used instead of sulfoaluminate cement.

[0051] Comparative Example 3 The formulation and preparation method are basically the same as those in Example 1, except that nano-silica is not added to the raw materials. The types, proportions and preparation steps of the other raw materials are the same as those in Example 1. Comparative Example 4 The formulation and preparation method are basically the same as those in Example 1, except that the antacid is 10 parts of single fluorite powder and no sodium silicate is added. The types, proportions and preparation steps of the other raw materials are the same as those in Example 1.

[0052] Comparative Example 5 The formulation and preparation method are basically the same as those in Example 1, except that the antacid is 10 parts sodium silicate and no fluorite powder is added. The types, proportions and preparation steps of the other raw materials are the same as those in Example 1.

[0053] Comparative Example 6 The formulation and preparation method are basically the same as those in Example 1. The only difference is that the calcination temperature is adjusted to 120°C and the calcination time is still 1.5 hours in the preparation process of modified phosphogypsum. The other preparation steps and raw material parameters are the same as those in Example 1.

[0054] Comparative Example 7 The formulation and preparation method are basically the same as those in Example 1, except that steel slag powder is not added to the raw materials, and the amount of modified phosphogypsum is adjusted to 80 parts. The types, proportions, and preparation steps of the other raw materials are the same as those in Example 1. II. Performance Testing 1. Compressive strength: According to GB / T 17671-2021 "Test method for strength of cement mortar (ISO method)", 40mm×40mm×40mm specimens were prepared and cured under standard curing conditions for 24h, 3d and 28d respectively. The compressive strength was then determined by a pressure testing machine.

[0055] 2. Acid resistance test (1) Specimen preparation: Prepare 40mm×40mm×40mm specimens according to the above compressive strength test method, and cure them for 28 days before use; (2) Acid soaking treatment: The cured specimens are soaked in H2SO4 solution with pH=2. The solution volume is 5 times the volume of the specimens. The solution is changed every 7 days and soaked for 28 days. (3) Performance test: Take out the soaked specimen, wipe off the surface moisture, measure its compressive strength, and calculate the strength loss rate (strength loss rate (%) = (strength before soaking - strength after soaking) / strength before soaking × 100%).

[0056] 3. Long-term stability test (1) Specimen preparation: Prepare 40mm×40mm×40mm specimens according to the above compressive strength test method, and cure them for 28 days before use; (2) High temperature and high humidity curing test: Place the spare specimens in a constant temperature and humidity curing chamber, set the curing conditions to 60℃ and 95%RH, and continue curing for 3 months; after curing, take out the specimens, let them cool naturally to room temperature, measure their compressive strength, and calculate the strength loss rate (the calculation method is the same as the acid resistance test). (3) Cyclic freeze-thaw test: According to GB / T 50082-2009 "Standard for Test Methods of Long-term Performance and Durability of Ordinary Concrete", 50 freeze-thaw cycles were performed on the spare specimens. The freeze-thaw cycle parameters were: freezing stage temperature -20℃, duration 4h; thawing stage temperature 20℃, duration 4h. After 50 cycles, the compressive strength of the specimens was measured and the strength loss rate was calculated. Table 5 shows the performance of the examples and comparative examples.

[0057] The test results of Examples 1-5 show that the material has a 1-day compressive strength ≥3.0MPa, a 3-day compressive strength ≥15MPa, a 28-day compressive strength ≥28MPa, and a 28-day acid immersion compressive strength loss rate ≤14.3%. It also has excellent long-term stability, with a 3-month high-temperature and high-humidity curing strength loss rate ≤4.3% and a 50-cycle freeze-thaw cycle strength loss rate ≤10.1%. It can quickly provide support strength for phosphate mines and resist the erosion of complex working conditions such as acidic environment, high temperature and high humidity, and freeze-thaw cycles for a long time.

[0058] A comparison of Example 1 and Comparative Examples 1-7 shows that, through the synergistic formulation of modified phosphogypsum, sulfoaluminate cement, and composite acid-resistant agent, combined with the microscopic regulation effect of nano-silica, the filling material exhibits superior long-term resistance to acidic environments, high temperature and humidity, and freeze-thaw cycles. Specifically, the performance is as follows: 1. The properties of Comparative Example 1, especially its early strength and acid resistance, are far inferior to those of all other examples. This demonstrates that calcination modification to produce highly active hemihydrate gypsum, and the introduction of carbide slag and fly ash to provide an alkaline environment and active components, are crucial for constructing a high early strength and acid-resistant system. The calcination temperature of Comparative Example 6 was insufficient, failing to form a high-content, highly active hemihydrate gypsum. The performance degradation of Comparative Example 6 also illustrates that suitable calcination conditions are key to achieving effective modification of highly active hemihydrate gypsum.

[0059] 2. In Comparative Example 2, the early strength development of ordinary silicate cement is slow, and the acid resistance and long-term stability are significantly deteriorated. In Example 1, the sulfoaluminate cement hydrates to form ettringite and Al(OH)3 gel, which is beneficial to the long-term stability of "high early strength" and "resistance to acid corrosion and freeze-thaw cycles".

[0060] 3. The early strength, 28-day strength, and long-term stability (especially the freeze-thaw loss rate increased to 18.4%) of Comparative Example 3 without nano-silica were all lower than those of Example 1, which proves the key role of nano-silica in accelerating the hydration, refining pores, and improving the density of the sulfoaluminate cement and modified phosphogypsum cementitious system.

[0061] 4. Comparative Example 4 used fluorite powder alone, and Comparative Example 5 used sodium silicate alone as an acid resistant agent. The acid resistance of Comparative Examples 4 and 5 was significantly worse than that of Example 1, and the long-term stability of Comparative Example 5 was even worse. This indicates that the combined use of the physical barrier of fluorite powder and the gel filling of sodium silicate in the composite acid resistant agent produced a synergistic protective effect, and the dual pathway improved acid resistance and long-term stability.

[0062] 5. Comparative Example 7, which omitted the steel slag powder, showed a decrease in 28-day strength, long-term acid resistance, and freeze-thaw resistance. This indicates that the steel slag powder, in addition to being a filler, provides an alkaline buffer system due to its rich CaO content. This system can directly neutralize acidic media and maintain the alkaline environment inside the material for a long time, inhibiting the decomposition of hydration products. This is conducive to the formation of a stable and dense filling structure, thus improving acid resistance and long-term stability.

[0063] The above embodiments are merely examples to illustrate the present invention and are not intended to limit the possible implementations of the invention. Based on the disclosure of this invention, those skilled in the art can make various modifications and adjustments. It is neither possible nor necessary to list all possible implementations. Any modifications, equivalent substitutions, or improvements made within the basic principles and scope of this invention should be considered to fall within the protection scope of this invention.

Claims

1. A high early strength acid-resistant backfill material suitable for phosphate mines, characterized in that, By weight, it includes the following raw materials: 10-30 parts of sulfoaluminate cement, 50-75 parts of modified phosphogypsum, 15-49 parts of steel slag powder, 1-5 parts of alkali activator, 0.5-3 parts of nano silica, 5-15 parts of acid-resistant agent, 0.2-1 parts of water-reducing agent, 1-5 parts of suspending agent, and 0.5-3 parts of retarder; The preparation method of the modified phosphogypsum includes the following steps: pulverizing and mixing phosphogypsum, fly ash and carbide slag separately, then feeding the resulting mixture into a rotary kiln and calcining it at 160-190℃ for 1-2 hours; finally, after grinding and sieving, modified phosphogypsum rich in hemihydrate phosphogypsum is obtained. The antacid is composed of fluorite powder and sodium silicate mixed in a mass ratio of 1:1-3.

2. The high early strength acid-resistant backfill material suitable for phosphate mines as described in claim 1, characterized in that, The modified phosphogypsum has the following raw material mass fraction ratio: phosphogypsum 60%~85%, fly ash 5%~15%, and carbide slag 10%~25%; the sieving is performed using a 200-mesh sieve.

3. The high early strength acid-resistant backfill material suitable for phosphate mines as described in claim 1, characterized in that, The chemical composition of the carbide slag, by mass fraction, includes: CaO 60-80%, SiO2 5-15%, and Al2O3 2-8%.

4. The high early strength acid-resistant backfill material suitable for phosphate mines as described in claim 3, characterized in that, The average particle size of the crushed carbide slag is 10-50 micrometers.

5. The high early strength acid-resistant backfill material suitable for phosphate mines as described in any one of claims 1-3, characterized in that, The chemical composition of the fly ash, by mass fraction, includes: SiO2 40%-60%, Al2O3 20%-30%, Fe2O3 4%-10%, CaO 5%-15%; the average particle size of the fly ash after crushing is 5-30 micrometers; the mass percentage of calcium sulfate dihydrate in the phosphogypsum is 70%~90%.

6. The high early strength acid-resistant backfill material suitable for phosphate mines as described in claim 5, characterized in that, The average particle size of the phosphogypsum is 30-60 micrometers.

7. The high early strength acid-resistant backfill material suitable for phosphate mines as described in any one of claims 1-3, characterized in that, The chemical composition of the sulfoaluminate cement, by mass fraction, includes: Al2O3 30%-50%, CaO 30%-45%, SiO2 5%-10%, and SO3 8-15%.

8. The high early strength acid-resistant backfill material suitable for phosphate mines as described in claim 7, characterized in that, The particle size of the sulfoaluminate cement is 15-30 micrometers.

9. The high early strength acid-resistant backfill material suitable for phosphate mines as described in any one of claims 1-3, characterized in that, The chemical composition of the steel slag powder, by mass fraction, includes: CaO 30%-50%, SiO2 15%-25%, Al2O3 3%-10%, and Fe2O3 15%-30%.

10. The high early strength acid-resistant backfill material suitable for phosphate mines as described in claim 9, characterized in that, The average particle size of the steel slag powder is 10-30 micrometers.

11. The high early strength acid-resistant backfill material suitable for phosphate mines as described in any one of claims 1-3, characterized in that, The fluorite powder contains ≥85% CaF2 and has an average particle size of 10-20 micrometers.

12. The high early strength acid-resistant backfill material suitable for phosphate mines as described in any one of claims 1-3, characterized in that, The nano-silica has a particle size of 15nm-100nm and a specific surface area of ​​150-400 m². 2 / g, SiO2 content ≥98%.

13. The high early strength acid-resistant backfill material suitable for phosphate mines as described in any one of claims 1-3, characterized in that, The alkaline activator is at least one of potassium hydroxide, sodium hydroxide, sodium carbonate, and calcium oxide.

14. The high early strength acid-resistant backfill material suitable for phosphate mines as described in any one of claims 1-3, characterized in that, The water-reducing agent includes at least one of naphthalene-based water-reducing agents, melamine-based water-reducing agents, or polycarboxylate-based water-reducing agents.

15. The high early strength acid-resistant backfill material suitable for phosphate mines as described in any one of claims 1-3, characterized in that, The suspending agent includes at least one of sodium carboxymethyl cellulose or hydroxymethyl cellulose.

16. The high early strength acid-resistant backfill material suitable for phosphate mines as described in any one of claims 1-3, characterized in that, The retarder is at least one of borax and boric acid.

17. A method for preparing a high early strength acid-resistant backfill material suitable for phosphate mines as described in any one of claims 1-16, characterized in that, Specifically, the following steps are included: Sulfoaluminate cement, modified phosphogypsum, steel slag powder, alkali activator, nano silica, acid resistant agent, water reducing agent, suspending agent, and retarder are mixed evenly to obtain a high early strength acid-resistant filling material.

18. The application of a high early strength acid-resistant backfill material as described in any one of claims 1-16 in phosphate mine backfilling, characterized in that, This includes mixing the high early strength acid-resistant filling material with water and adjusting the mass concentration of the slurry to 50-70%.

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