Phosphorite filling agent with pH response as well as preparation method and application thereof

Abstract

The invention discloses a pH sensitive microcapsule and an application thereof in a pH response type intelligent control phosphorite filling agent, and aims to solve the problems that a traditional filling agent is poor in acid resistance and cannot dynamically cope with acid corrosion. The filling agent is prepared by mixing 40-60 parts of a basic gel system, 1-10 parts of pH sensitive microcapsules, 80-120 parts of aggregate and 3-8 parts of an additive. The pH sensitive microcapsule is inert in a neutral / alkalescent environment, an alumina shell layer is subjected to acidolysis and rupture in an acidic environment, nano calcium carbonate rapidly neutralizes acid, and calcium sulphoaluminate is hydrated for the second time to generate ettringite to repair cracks. The 28-day compressive strength of the filling agent is 13.8-14.5 MPa, the strength retention rates of acid soaking and freezing and thawing cycles are larger than or equal to 85.3% and larger than or equal to 86.2% respectively, waste resource utilization is achieved, the filling agent is suitable for phosphorite goaf filling, and the long-term stability of a filling body is remarkably improved.

Description

Technical Field

[0001] This invention relates to the field of mining backfill materials technology, specifically to a smart material for phosphate mine backfilling, and more particularly to a pH-responsive smart backfill agent that can respond to changes in environmental pH and autonomously regulate its properties to improve the long-term stability of the backfill. Background Technology

[0002] In phosphate mining, backfilling technology is a crucial element in ensuring mine safety and environmental friendliness. Traditional phosphate mine backfilling materials primarily use industrial waste such as cement and slag as binders, consolidating aggregates (such as tailings and waste rock) into a backfill body with a certain strength through physical and chemical processes. However, acidic seepage water often occurs during phosphate mining, which severely corrodes the backfill body, leading to decreased strength and structural damage, thus affecting mine safety and service life.

[0003] Phosphate deposits often contain sulfide minerals such as pyrite. After mining, blasting, and other engineering activities, these sulfides are exposed to air and water, undergoing oxidation reactions to produce sulfuric acid, resulting in mine seepage water exhibiting a significantly acidic characteristic. In phosphate mine backfill environments, the corrosion mechanism of acidic seepage water on the backfill body is mainly manifested in the following aspects: First, H... + It will react with hydration products (such as Ca(OH)2, CSH gel, etc.) in the filling material, leading to the decomposition of the hydration products; secondly, acid radicals (such as SO42-) 2- It will react with metal ions (such as Al) in the filling material. 3+ Ca 2+ The acidic environment generates water-soluble salts, which exacerbate the corrosion of the filling material. Finally, the acidic environment destroys the microstructure of the filling material, increases porosity, and reduces the density and strength of the filling material.

[0004] Traditional phosphate rock backfill materials exhibit low compressive strength and poor acid resistance in acidic environments. Long-term exposure to acidic environments can lead to structural damage and functional loss of the backfill. Furthermore, they lack self-regulation; once corroded by acidic environments, their performance cannot be restored or improved, requiring external intervention for repair. To address these issues, existing technologies primarily employ the following methods: First, increasing the alkalinity of the backfill material, such as by adding alkaline substances like quicklime or carbide slag, to neutralize acidic substances and improve the backfill's acid resistance. Second, optimizing the backfill material's composition, such as adjusting the ratio of fly ash, slag, and cement, to enhance the backfill's compressive strength. Third, using composite cementitious materials, such as geopolymers and self-healing materials, to improve the backfill's durability.

[0005] However, these traditional methods all have certain limitations: first, static proportioning cannot dynamically respond to changes in acidic environments; second, external intervention for remediation is costly and inefficient; and third, the performance improvement of composite cementitious materials is limited, making it difficult to meet the requirements for long-term stability. Therefore, developing a filling agent that can intelligently adjust its performance according to changes in environmental pH is of great significance for solving the problem of insufficient long-term stability of phosphate rock backfills. Summary of the Invention

[0006] This invention addresses the inability of existing phosphate rock backfill materials to dynamically respond to changes in acidic environments by providing a pH-responsive intelligent phosphate rock backfill agent and its preparation method. This backfill agent, through the introduction of pH-sensitive microcapsules, achieves intelligent response to the acidic environment of phosphate rock, releasing the agent as needed under acidic conditions to neutralize acidic substances and strengthen the backfill structure, significantly improving the long-term stability of the backfill.

[0007] This invention provides a method for preparing pH-sensitive microcapsules for use as phosphate rock fillers. The core layer of the pH-sensitive microcapsules is composed of nano-calcium carbonate and calcium sulfoaluminate, and the core layer is composed of alumina. The method includes the following steps: S1. Add nano-calcium carbonate powder and calcium sulfoaluminate powder to deionized water, add a dispersant, and after stirring and ultrasonic treatment, obtain a uniformly dispersed core suspension. S2. Under nitrogen protection, aluminum salt solution is added dropwise to the core layer suspension in step S1, followed by ammonia water to adjust the pH value to 9-10. The mixture is stirred and aged at room temperature for 3-5 hours. After centrifugation, washing and drying, microcapsule precursors coated with aluminum hydroxide are obtained. S3. The microcapsule precursor is calcined at 500-700℃ for 1-3 hours, cooled, ground and sieved to obtain the pH-sensitive microcapsules.

[0008] Preferably, in step S1, the mass ratio of nano-calcium carbonate to calcium sulfoaluminate is 1:1 to 3:1, and the amount of deionized water used is 5 to 20 times the total mass of nano-calcium carbonate and calcium sulfoaluminate.

[0009] Preferably, the average particle size of the nano-calcium carbonate is 50-200 nm; the average particle size of the calcium sulfoaluminate is 50-100 nm.

[0010] Preferably, the dispersant in step S1 is at least one of sodium polyacrylate, polyepoxysuccinic acid, and sodium dodecylbenzenesulfonate, and the amount of dispersant added is 0.5% - 2.0% of the total mass of the core layer powder (nano-calcium carbonate powder and calcium sulfoaluminate powder).

[0011] Preferably, in step S2, the aluminum salt is at least one of aluminum chloride, aluminum sulfate, and aluminum nitrate, and its concentration is 0.5-1.0 mol / L; the mass of the aluminum salt solution is 10-30% of the total mass of the core layer prepared in step S1.

[0012] This invention also provides a pH-responsive intelligent phosphate rock filling agent, the raw materials of which, by weight, include: 40-60 parts of basic gelling system, 1-10 parts of pH-sensitive microcapsules, 80-120 parts of aggregate, and 3-8 parts of admixture.

[0013] Preferably, the admixture includes at least one of water-reducing agent, suspending agent, and setting regulator.

[0014] 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.

[0015] Preferably, the suspending agent is at least one of sodium carboxymethyl cellulose, polyacrylamide, and bentonite.

[0016] Preferably, the setting agent is at least one of citric acid, potassium sodium tartrate, and sodium gluconate.

[0017] Preferably, the basic cementitious system consists of 30-45 parts of sulfoaluminate cement, 5-10 parts of slag powder, and 3-5 parts of fly ash.

[0018] Preferably, the aggregate is at least one of phosphate rock tailings, phosphogypsum, and metakaolin. The preferred aggregate particle size is 5-20 mm.

[0019] In the preparation of the pH-sensitive microcapsules of this invention, a dispersant is first added and adsorbed onto the surface of inorganic powder. Electrostatic repulsion and steric hindrance prevent particle agglomeration, thus ensuring good dispersion of the core material particles at the nanoscale. Subsequently, under alkaline conditions, aluminum ions hydrolyze to form aluminum hydroxide sol-gel, which gradually deposits on the surface of the core material particles, completing the initial coating. Then, the coating is continuously stirred and aged at room temperature for 4-5 hours to further homogenize and densify the coating layer. Finally, calcination at 500-700℃ decomposes the amorphous aluminum hydroxide in the coating layer, transforming it into crystalline alumina, forming a dense and stable inorganic alumina shell. This method not only achieves structural control of the microcapsules but also avoids the problem of poor dispersibility in cement-based cementitious systems when using organic polymer shells.

[0020] The present invention also provides a method for preparing the above-mentioned pH-responsive intelligent phosphate rock filling agent, comprising the following steps: Weigh out the basic cementitious system, aggregates and admixtures by weight and mix them evenly; then add pH-sensitive microcapsules and stir evenly to obtain a pH-responsive intelligent phosphate rock filler.

[0021] This invention also provides the application of pH-responsive intelligent phosphate rock filling agent in the filling of phosphate rock goaf areas, including mixing the pH-responsive intelligent phosphate rock filling agent with water, adjusting the mass concentration of the slurry to 50-70%, and injecting the slurry into the area to be filled.

[0022] This invention selects sulfoaluminate cement as the main cementing material based on its rapid hardening and early strength, good impermeability, and excellent corrosion resistance, especially its superior performance against sulfate attack compared to ordinary silicate cement. The cement's hydration products are mainly ettringite, which possesses a certain degree of resistance to acid and alkali attack. To further improve performance, active mineral admixtures such as slag powder and fly ash are incorporated: on the one hand, they can generate more CSH gel through secondary hydration reactions, refining the pore structure and enhancing the compactness of the filling, thereby physically hindering the penetration of acidic media; on the other hand, they can consume some calcium hydroxide, reducing the alkalinity of the system and decreasing weak points susceptible to acid attack.

[0023] As a further optimization, the aggregate is selected from one or more combinations of phosphate mine tailings, phosphogypsum, or metakaolin, with a particle size controlled between 5-20 mm. This fully utilizes solid waste generated from phosphate mining, such as phosphate mine tailings and phosphogypsum, to reduce material costs and achieve green backfilling. Meanwhile, metakaolin, as a highly reactive pozzolanic material, can participate in the cementation reaction, helping to improve the later-stage strength and durability of the backfill.

[0024] The pH-sensitive microcapsules of this invention have an alumina shell. Under neutral or weakly alkaline conditions, the alumina shell is chemically stable and dense, effectively encapsulating and isolating the core material. In this state, the microcapsules act like inert micro-aggregates, uniformly distributed within the filling matrix, without participating in the initial hydration reaction and without affecting the normal setting, hardening, and strength development of the filling. When external acidic mine water permeates into the filling, causing a significant drop in pH in localized areas, the amphoteric alumina shell reacts with H... + An acid hydrolysis reaction occurs, and the shell is gradually corroded and dissolved until it cracks, thus exposing the internal core repair agent.

[0025] The nano-calcium carbonate in the core layer has a high specific surface area and rapidly reacts with invading H₂. + A neutralization reaction occurs, rapidly consuming acidic substances and effectively preventing a drop in local pH, thus protecting the cement matrix from continuous acid corrosion. On the other hand, the calcium sulfoaluminate released from the core layer reacts with the Ca produced in the neutralization reaction. 2+ It undergoes secondary hydration reactions with water in the surrounding environment to generate new ettringite, which can fill the microcracks and pores caused by acid etching, and form a network structure, thereby strengthening and densifying the matrix, thus restoring and maintaining the mechanical properties of the damaged area and improving its strength and stability.

[0026] The advantages or beneficial effects of the phosphate rock backfill grouting material of the present invention include at least the following: This invention introduces pH-sensitive microcapsule technology. These microcapsules automatically release a repair agent triggered by an acidic environment inside the filling material. The released nano-calcium carbonate rapidly neutralizes acidic substances, while active ingredients such as calcium sulfoaluminate undergo synergistic secondary hydration with the matrix, generating a dense CSH gel and ettringite network. This not only repairs damage but also further strengthens the filling structure, significantly improving its long-term stability. The material maintains excellent stability even under long-term acidic erosion, with an acid immersion strength retention rate ≥85.3% and a freeze-thaw cycle strength retention rate ≥86.2%. By utilizing industrial waste such as phosphate mine tailings and phosphogypsum as aggregates, the filling cost is effectively reduced, and waste resource utilization is achieved, aligning with current green mine construction concepts. Detailed Implementation

[0027] 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.

[0028] 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.

[0029] Table 1 shows that the fly ash used in the examples had an average particle size of 30 micrometers and the following chemical composition:

[0030] Table 2 shows that the average particle size of the sulfoaluminate cement used in the examples is 25 micrometers, and its chemical composition is as follows:

[0031] The chemical composition of phosphogypsum is as follows: the mass percentage of calcium sulfate dihydrate (CaSO4·2H2O) in phosphogypsum is 80%, and the average particle size of phosphogypsum is 30-50 micrometers.

[0032] Water-reducing agent: Polycarboxylate-based water-reducing agent, commercially available.

[0033] Suspension agent: Polyacrylamide, commercially available.

[0034] Setting agent: Sodium gluconate, commercially available.

[0035] Slag powder: S95 grade, purchased from Wuhan Weishen Technology Development Co., Ltd.

[0036] Nano-calcium carbonate: average particle size 50nm, purchased from Hubei Jingjing Calcium Industry Co., Ltd.

[0037] Calcium sulfoaluminate: average particle size 100nm, purchased from Fuzhou Persian Gulf Chemical Co., Ltd.

[0038] Other reagents: Deionized water, aluminum salts, ammonia, etc., were all of analytical grade.

[0039] I. Experimental examples and comparative examples for preparing pH-sensitive microcapsules.

[0040] Experimental Example 1 S1. Add 67g of nano-calcium carbonate powder and 33g of calcium sulfoaluminate powder to 800mL of deionized water, stir at 700rpm, and sonicate for 40 minutes after dissolution. Then add sodium polyacrylate at 1.2% of the total mass of the powder materials and continue stirring for 1.5 hours to obtain the core layer. S2. Prepare a 0.8 mol / L aluminum chloride solution. Slowly add 20% of the total mass of the core layer aluminum chloride solution to the core layer in step S1 while purging with nitrogen gas (flow rate 120 mL / min). Then, add ammonia water dropwise to the reaction system until the pH reaches 9.5. Stir and age the mixture at room temperature for 4 hours. After the reaction is complete, centrifuge the mixture, wash it four times with ethanol, and vacuum dry it to obtain the microcapsule precursor. S3. Place the microcapsule precursor in a muffle furnace, heat it at a rate of 5℃ / min to 600℃, and keep it at that temperature for 2 hours. After cooling, grind it through a 200-mesh sieve to obtain pH-sensitive microcapsules 1.

[0041] Experiment Example 2 S1. Add 75g of nano calcium carbonate powder and 25g of calcium sulfoaluminate powder to 900mL of deionized water, stir at 900rpm, and sonicate for 30 minutes after dissolution. Then add 0.8% of the total mass of the powder materials of polyepoxysuccinic acid and continue stirring for 1 hour to obtain the core layer. S2. Prepare a 1.0 mol / L aluminum sulfate solution. Slowly add 15% of the total mass of the core layer aluminum sulfate solution to the core layer in step S1 while purging with nitrogen (flow rate 90 mL / min). Then, add ammonia to the reaction system until the pH reaches 9. Stir and age the mixture at room temperature for 3 hours. After the reaction is complete, centrifuge the mixture, wash it three times with ethanol, and vacuum dry it to obtain the microcapsule precursor. S3. Place the microcapsule precursor in a muffle furnace, heat it at a rate of 5℃ / min to 500℃, and keep it at that temperature for 3 hours. After cooling, grind it through a 200-mesh sieve to obtain pH-sensitive microcapsules 2.

[0042] Experimental Example 3 S1. Add 50g of nano calcium carbonate powder and 50g of calcium sulfoaluminate powder to 600mL of deionized water, stir at 850rpm, and sonicate for 50 minutes after dissolution. Then add sodium dodecylbenzenesulfonate at 1.5% of the total mass of the powder materials and continue stirring for 1.2 hours to obtain the core layer. S2. Prepare a 0.5 mol / L aluminum nitrate solution. Slowly add 25% of the total mass of the core layer aluminum nitrate solution to the core layer in step S1 while purging with nitrogen gas (flow rate 110 mL / min). Then, add ammonia water dropwise to the reaction system until the pH reaches 10. Stir and age the mixture at room temperature for 4.5 hours. After the reaction is complete, centrifuge the mixture, wash it twice with ethanol, and vacuum dry it to obtain the microcapsule precursor. S3. Place the microcapsule precursor in a muffle furnace, heat it at a rate of 5℃ / min to 650℃, and hold it at that temperature for 1.5 hours. After cooling, grind it through a 200-mesh sieve to obtain pH-sensitive microcapsules 3.

[0043] Experiment Example 4 S1. Add 60g of nano-calcium carbonate powder and 40g of calcium sulfoaluminate powder to 750mL of deionized water, stir at 750rpm, and sonicate for 45 minutes after dissolving. Then add 1.0% of the total mass of the powder materials of the compound dispersant (sodium polyacrylate and sodium dodecylbenzene sulfonate in a mass ratio of 1:1) and continue stirring for 1.3 hours to obtain the core layer. S2. Prepare a 0.7 mol / L aluminum chloride-aluminum sulfate mixed solution (aluminum chloride to aluminum sulfate mass ratio 2:1). Slowly add 18% of the total mass of the aluminum salt mixed solution of the core layer to the core layer of step S1, while simultaneously purging with nitrogen gas (flow rate 105 mL / min). Then, add ammonia water dropwise to the reaction system until the pH reaches 9.5, and continue stirring and aging at room temperature for 5 hours. After the reaction is completed, centrifuge, wash three times with ethanol, and vacuum dry to obtain the microcapsule precursor. S3. Place the microcapsule precursor in a muffle furnace, heat it at a rate of 5℃ / min to 620℃, and hold it at that temperature for 2.5 hours. After cooling, grind it through a 200-mesh sieve to obtain pH-sensitive microcapsules 4.

[0044] Experimental Example 5 S1. Add 55g of nano-calcium carbonate powder and 45g of calcium sulfoaluminate powder to 680mL of deionized water, stir at 820rpm, and sonicate for 55 minutes after dissolution. Then add 0.5% of the total mass of the powder materials of polyepoxysuccinic acid and continue stirring for 0.8 hours to obtain the core layer. S2. Prepare a 0.6 mol / L aluminum nitrate solution. Slowly add 28% of the total mass of the core layer aluminum nitrate solution to the core layer in step S1 while purging with nitrogen gas (flow rate 130 mL / min). Then, add ammonia water dropwise to the reaction system until the pH reaches 9.5. Stir and age the mixture at room temperature for 3.5 hours. After the reaction is complete, centrifuge the mixture, wash it four times with ethanol, and vacuum dry it to obtain the microcapsule precursor. S3. Place the microcapsule precursor in a muffle furnace, heat it at a rate of 5℃ / min to 550℃, and hold it at that temperature for 2 hours. After cooling, grind it through a 200-mesh sieve to obtain pH-sensitive microcapsules 5.

[0045] Comparative Experiment Example 1 The difference from Experimental Example 2 is that an equal amount of nano-calcium carbonate powder was used instead of calcium sulfoaluminate powder to obtain pH-sensitive microcapsules 6.

[0046] Comparative Experiment Example 2 The difference from Experimental Example 2 is that an equal amount of calcium sulfoaluminate powder was used instead of nano-calcium carbonate powder to obtain pH-sensitive microcapsules 7.

[0047] Comparative Experiment Example 3 The difference from Experimental Example 2 is that the calcination temperature in step S3 is 1000℃, and the holding time is 3h. Other conditions are the same as in Experimental Example 2, and pH-sensitive microcapsules 8 are obtained. II. Examples and Comparative Examples of Preparing pH-Responsive Intelligent Regulated Phosphate Rock Filling Agents The preparation method of the pH-responsive intelligent phosphate rock filling agent in the examples and comparative examples includes the following steps: weigh the basic cementitious system, aggregate and admixture according to the weight ratio in Table 3 and mix them evenly; then add pH-sensitive microcapsules and stir evenly to obtain the pH-responsive intelligent phosphate rock filling agent.

[0048] Table 3: The mass fractions (g) of each component in Examples 1-6 are as follows.

[0049]

[0050] Table 4: The mass fractions (g) of each component in Comparative Examples 1-4 are as follows.

[0051]

[0052] Comparative Example 5: 4 parts by weight of nano-calcium carbonate were used instead of pH-sensitive microcapsules, and everything else was the same as in Example 2.

[0053] Comparative Example 6: 4 parts by weight of calcium sulfoaluminate were used instead of pH-sensitive microcapsules, and the rest was the same as in Example 2.

[0054] Comparative Example 7: 3 parts by weight of nano-calcium carbonate and 1 part by weight of calcium sulfoaluminate were used instead of pH-sensitive microcapsules, and the rest was the same as in Example 2.

[0055] III. Performance Testing 1. Preparation of filling material: Add water to the filling agent and stir to form a filling agent slurry. The water-solid ratio is controlled between 0.5 and 0.6. Prepare 40×40×160mm test blocks according to GB / T 17671-2020 standard.

[0056] 2. Compressive strength test: The test blocks were cured at 20℃ and 90% humidity for 28 days, and the compressive strength was tested according to GB / T 17671-2020 standard. Three parallel test samples were tested and the average value was taken.

[0057] 3. Acid Cycling Test: The test block is alternately immersed in an acidic solution with pH=3 and a neutral solution with pH=8 for 24 hours each time, for a total of 50 cycles. After each cycle, the test block is thoroughly dried, and the compressive strength retention rate is tested.

[0058] 4. Cyclic freeze-thaw test: In accordance with GB / T 50082-2009 "Standard for Test Methods of Long-term Performance and Durability of Ordinary Concrete", 100 freeze-thaw cycles were conducted on the spare specimens. The freeze-thaw cycle parameters were: freezing stage temperature -20℃, duration 4h; thawing stage temperature 20℃, duration 4h. After completing 100 cycles, the compressive strength of the specimens was measured and the compressive strength retention rate was calculated.

[0059] Table 5 shows the performance of the examples and comparative examples.

[0060] As shown in Table 5, the pH-responsive intelligent phosphate rock filling agent of the embodiments achieves a comprehensive improvement in mechanical properties, corrosion resistance, and environmental adaptability through the synergistic design of pH-sensitive microcapsules, basic cementitious system, and industrial waste aggregate. The compressive strength of this filling agent remains stable between 13.8 and 14.5 MPa after 28 days, meeting the structural load-bearing requirements for filling phosphate mine goaf areas and providing reliable mechanical protection for safe mining. Regarding corrosion resistance, after 50 alternating cycles of soaking in acidic solution (pH=3) and neutral solution (pH=8), the strength retention rate is not less than 85.3%, with Example 4 reaching the highest at 91.4%, effectively overcoming the strength decay problem caused by acidic mine water. Simultaneously, the material exhibits a strength retention rate of ≥86.2% after 100 freeze-thaw cycles, demonstrating good adaptability to alternating temperature and humidity environments, expanding its application range under complex mining geographical and climatic conditions. Furthermore, this filler uses industrial solid waste such as phosphate mine tailings and phosphogypsum as aggregates, which not only reduces raw material costs but also realizes the resource utilization of waste, aligning with the concept of green mine construction. The pH-sensitive microcapsules used in this invention remain inert in neutral to weakly alkaline environments, without affecting the normal setting and hardening of the filler; only when triggered by an acidic environment does their alumina shell undergo acidolysis and rupture, thereby releasing the core material as needed. This mechanism enables autonomous and precise control of the filler material's performance without external intervention, providing intelligent, efficient, and reliable response.

[0061] A comparison of Example 2 with Comparative Examples 1-4 reveals significant differences in long-term durability despite similar initial compressive strength. Comparative Example 1, lacking pH-sensitive microcapsules and relying solely on a basic cementitious system composed of sulfoaluminate cement, slag powder, and fly ash, exhibits limited inherent corrosion resistance. Under the influence of acidic seepage water from the phosphate rock, hydration products such as CSH gel in the backfill react directly with the acid, leading to product decomposition, the formation of soluble salts, microstructural damage, and increased porosity, resulting in a significant decrease in acid resistance and freeze-thaw cycle resistance. While Comparative Example 2 incorporated microcapsules with nano-calcium carbonate as the core material, which could neutralize some acidic substances and slow corrosion, the lack of calcium sulfoaluminate prevented the repair of structural damage such as pore enlargement and microcracks caused by acid corrosion. With increasing acidic cycles, damage accumulated, leading to a decline in acid resistance and freeze-thaw resistance.

[0062] The microcapsule core material of Comparative Example 3 contains only calcium sulfoaluminate and lacks the calcium carbonate component that can rapidly neutralize acids, resulting in a lack of rapid H2 consumption. +The ability of the filler substrate to withstand corrosion is limited. In acidic environments, the substrate of the filler gradually becomes damaged due to continuous corrosion. Even if calcium sulfoaluminate can undergo secondary hydration and produce some repair effect, the repair effect is significantly limited because the substrate has already suffered significant corrosion, ultimately leading to a continuous decrease in the strength of the filler. In Comparative Example 4, due to excessively high calcination temperature, the calcium carbonate in the core layer decomposes (the decomposition temperature of calcium carbonate is about 825℃), generating calcium oxide and water. This process damages the internal structure of the microcapsules, causing them to lose their pH response function, ultimately resulting in a decrease in acid resistance and freeze-thaw cycle resistance.

[0063] Comparative Examples 5-7 did not employ microencapsulation technology; instead, calcium sulfoaluminate and / or calcium carbonate were directly incorporated into the system. These components participate in the reaction prematurely during the hardening process of the filling material and cannot be released as needed under acidic conditions later. Therefore, the synergistic effect of neutralization reaction and structural repair cannot be achieved during acid erosion, ultimately resulting in a significant reduction in both acid immersion strength retention and freeze-thaw cycle strength retention.

[0064] 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 method for preparing pH-sensitive microcapsules for phosphate rock filling agents, characterized in that, The core layer of the pH-sensitive microgel is composed of nano-calcium carbonate and calcium sulfoaluminate, and the core layer is aluminum oxide. The process includes the following steps: S1. Add nano-calcium carbonate powder and calcium sulfoaluminate powder to deionized water, add a dispersant, and after stirring and ultrasonic treatment, obtain a uniformly dispersed core suspension. S2. Under nitrogen protection, aluminum salt solution is added dropwise to the core layer suspension in step S1, followed by ammonia water to adjust the pH value to 9-10. The mixture is stirred and aged at room temperature for 3-5 hours. After centrifugation, washing and drying, microcapsule precursors coated with aluminum hydroxide are obtained. S3. The microcapsule precursor is calcined at 500-700℃ for 1-3 hours, cooled, ground and sieved to obtain pH-sensitive microcapsules.

2. The method for preparing pH-sensitive microcapsules for phosphate rock filling agents as described in claim 1, characterized in that, In step S1, the mass ratio of nano-calcium carbonate to calcium sulfoaluminate is 1:1 to 3:1, and the amount of deionized water used is 5 to 20 times the total mass of nano-calcium carbonate and calcium sulfoaluminate.

3. The method for preparing pH-sensitive microcapsules for phosphate rock filling agents as described in claim 1, characterized in that, The average particle size of the nano-calcium carbonate is 50-200 nm; the average particle size of the calcium sulfoaluminate is 50-100 nm.

4. The method for preparing pH-sensitive microcapsules for phosphate rock filling agents according to any one of claims 1-3, characterized in that, In step S1, the dispersant is at least one of sodium polyacrylate, polyepoxysuccinic acid, and sodium dodecylbenzenesulfonate, and the amount of dispersant added is 0.5% - 2.0% of the total mass of the core layer powder.

5. The method for preparing pH-sensitive microcapsules for phosphate rock filling agents according to any one of claims 1-3, characterized in that, In step S2, the aluminum salt is at least one of aluminum chloride, aluminum sulfate, and aluminum nitrate, with a concentration of 0.5-1.0 mol / L; the mass of the aluminum salt solution is 10-30% of the total mass of the core layer prepared in step S1.

6. A pH-responsive intelligent phosphate rock filling agent, characterized in that, The raw materials, by weight, include: 40-60 parts of basic gelling system, 1-10 parts of pH-sensitive microcapsules, 80-120 parts of aggregate, and 3-8 parts of additives; the pH-sensitive microcapsules are prepared by any one of the methods in claims 1-5.

7. The pH-responsive intelligent phosphate rock filling agent as described in claim 6, characterized in that, The admixture includes at least one of water-reducing agent, suspending agent, and setting regulator; preferably, the water-reducing agent includes at least one of naphthalene-based water-reducing agent, melamine-based water-reducing agent, or polycarboxylate-based water-reducing agent; the suspending agent is at least one of sodium carboxymethyl cellulose, polyacrylamide, and bentonite; and the setting regulator is at least one of citric acid, potassium sodium tartrate, and sodium gluconate.

8. The pH-responsive intelligent phosphate rock filling agent as described in claim 6, characterized in that, The basic cementitious system consists of 30-45 parts of sulfoaluminate cement, 5-10 parts of slag powder, and 3-5 parts of fly ash; the aggregate is at least one of phosphate rock tailings, phosphogypsum, and metakaolin; the preferred aggregate particle size is 5-20 mm.

9. A method for preparing a pH-responsive intelligent phosphate rock filling agent as described in any one of claims 6-8, characterized in that, Includes the following steps: Weigh out the basic cementitious system, aggregates and admixtures according to the weight parts and mix them evenly; then add pH-sensitive microcapsules and stir evenly to obtain pH-responsive intelligent phosphate rock filling agent.

10. The application of a pH-responsive intelligent phosphate rock filling agent as described in any one of claims 6-8 in the filling of phosphate rock goaf areas, characterized in that, This includes mixing the pH-responsive intelligent phosphate rock filling agent with water, adjusting the mass concentration of the slurry to 50-70%, and then injecting the slurry into the area to be filled.

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