Low-alkalinity high-strength filling material, and preparation method and application thereof

Abstract

The application discloses a kind of low alkalinity high-strength filling material and preparation method and application thereof, belong to mine filling material and solid waste resource utilization technical field, the filling material includes cementitious material, aggregate and water, the mass ratio of cementitious material and aggregate is 1:4~1:8, slurry solid phase mass concentration is 65~72%.Cementitious material includes slag, fly ash, phosphogypsum, acetic acid, phosphate and alkaline regulator.Acid main activator accelerates hydration, inhibits shrinkage, phosphate auxiliary solidification will Ca 2+ Permanent solidification into insoluble calcium phosphate, realize multiple synergy activation.The material of the application 28d compressive strength is ≥2.5MPa, leaching solution pH value is ≤9, pH value is still stable after long-term immersion 180d 9 below, 60d drying shrinkage strain is 385~450×10 ‑6 , solid waste utilization rate is high, process is simple, without special maintenance, effectively solve the technical problem that traditional filling material is high in alkalinity, long-term return alkali.

Description

Technical Field

[0001] This invention belongs to the technical field of mine backfill materials and solid waste resource utilization, and particularly relates to a low-alkalinity, high-strength backfill material, its preparation method, and its application. Background Technology

[0002] With the continuous development of mineral resources, backfilling of mined-out areas has become a key technology for ensuring mine safety and environmental protection. Currently, the most commonly used cementing materials for mine backfilling mainly include ordinary Portland cement (OPC) and alkali-activated cementing materials (such as cementitious powder) made from slag and fly ash. OPC production is energy-intensive and generates large carbon emissions, and its hydration products contain a large amount of Ca(OH)2, resulting in a strongly alkaline leachate with a pH value often greater than 12. While cementitious powder activated by strong alkalis such as sodium hydroxide and sodium silicate can effectively utilize the activity of slag, it also suffers from a high alkali metal ion leaching rate, with the pH value of the leachate typically above 10.

[0003] Highly alkaline backfill materials, when exposed to groundwater for extended periods, continuously leach alkaline substances (primarily Ca(OH)2), causing the pH of surrounding groundwater and soil to rise beyond the requirements of Class III (pH=6.5–8.5) or even Class IV (pH=5.5–9.0) water in the Groundwater Quality Standard (GB / T 14848-2017). This leads to soil salinization, inhibits plant growth, and may promote the leaching of harmful heavy metal ions, posing a serious environmental threat. Simultaneously, some mines require high strength in backfill materials (e.g., 28-day compressive strength ≥2.5 MPa), while existing low-alkalinity materials often struggle to balance high strength with low alkalinity.

[0004] In existing technologies, while acetic acid activation alone can achieve good early strength and shrinkage inhibition, the soluble calcium acetate formed by the reaction of acetic acid with Ca(OH)2 poses a long-term risk of alkali reversion. While phosphoric acid activation alone can achieve permanent alkali fixation by generating insoluble Ca3(PO4)2, it suffers from high cost, complex processes, and the need for high-temperature curing. Therefore, developing a synergistic activation system that combines the advantages of both methods—high strength, low alkalinity, simple process, and long-term stability—has become a pressing technical challenge in this field. Summary of the Invention

[0005] To address the aforementioned technical problems, this invention proposes a low-alkalinity, high-strength filling material, its preparation method, and its application.

[0006] To achieve the above objectives, the present invention provides the following technical solution: One objective is to provide a low-alkalinity, high-strength backfill material, comprising cementitious material, aggregate, and water; wherein the mass ratio of the cementitious material to the aggregate is 1:4 to 1:8; the amount of water used is such that the solid phase mass concentration of the backfill material is 65% to 72%; the cementitious material comprises slag, fly ash, phosphogypsum, acetic acid, phosphate, and an alkalinity regulator.

[0007] This invention accelerates the early hydration of slag and fly ash by using acetic acid as the main activator, while using phosphate as an auxiliary solidifying agent to remove Ca from the system. 2+ Permanently solidified into insoluble calcium phosphate, it fully utilizes the activity of slag and fly ash while effectively controlling the alkalinity of the system, increasing the 28-day compressive strength of the filling body to over 2.5 MPa, and stably controlling the pH value of the leachate below 9, with a low risk of long-term alkali return, thus achieving efficient utilization of industrial solid waste and green and low-carbon mine filling.

[0008] Further, by mass, the cementitious material comprises the following components: slag: 70-85 parts; fly ash: 5-20 parts; phosphogypsum: 8-15 parts; acetic acid: 3-6 parts; phosphate: 0.2-1.0 parts; alkaline regulator: 0-2 parts.

[0009] Furthermore, the slag is granulated blast furnace slag with a specific surface area ≥ 450 m². 2 / kg, with a 28-day activity index ≥98%, preferably S95 grade or higher slag powder. Highly active slag ensures rapid disintegration under acetic acid erosion, releasing sufficient Ca. 2+ [SiO4] 4- [AlO2] - It participates in the hydration reaction.

[0010] Furthermore, the fly ash is low-calcium type F fly ash, with a water requirement ratio ≤105% and a 45μm sieve residue ≤15%, preferably Grade I or Grade II fly ash. The microsphere effect of fly ash can improve slurry fluidity, and its active components participate in the secondary hydration reaction in the later stage, refining the pore structure.

[0011] Furthermore, the phosphogypsum is a hemihydrate phosphogypsum that has been dried and ground, with a specific surface area ≥400 m². 2 / kg, such as 400-500m 2 / kg, P2O5 content ≤1.0%, pH value 4–5.5. Phosphogypsum, as a sulfate activator, provides SO42-. 2- With dissolved AlO2 - Ca 2+ The reaction produces ettringite (AFt), which makes a core contribution to strength development.

[0012] Furthermore, the acetic acid is industrial grade acetic acid with a concentration of 4-10%, preferably 4-6%. Acetic acid acts as the main activator, and its functions include: (1) eroding the surface of slag and fly ash particles, increasing the hydration contact surface, and accelerating the disintegration of the glassy structure; (2) reacting with Ca(OH)2 to generate soluble calcium acetate, reducing the alkalinity of the system; and (3) inhibiting the drying shrinkage of the filling material and improving its volume stability.

[0013] Further, the phosphate is potassium dihydrogen phosphate or sodium dihydrogen phosphate, preferably potassium dihydrogen phosphate. The phosphate acts as a co-curing agent, its functions including: (1) reducing the PO4 produced by hydrolysis. 3- With Ca in the system 2+ The reaction produces a sparingly soluble Ca3(PO4)2 precipitate, permanently solidifying the alkaline ions; (2) reacts with Mg dissolved in the slag 2+ K + The reaction produces struvite-like minerals, which further fill the pores.

[0014] Furthermore, the alkaline regulator is calcium oxide and / or magnesium oxide, and its amount does not exceed 1 / 2 of the mass of acetic acid. It is used to regulate the reaction rate, ensure early strength development, and provide the necessary alkaline environment for later hydration.

[0015] Furthermore, the aggregate is fine-grained tailings, which is tailings from metal mine beneficiation, and its D... V (50) = 35~45μm.

[0016] Mechanism of action of the present invention: (1) Acetic acid as the main activator: accelerates hydration and inhibits contraction. Surface etching and activation: H+ ions from the ionization of acetic acid molecules (CH3COOH) + It reacts with alkaline oxides such as CaO and MgO on the surface of slag and fly ash particles, eroding the particle surface, producing an uneven morphology, increasing the specific surface area and reaction contact surface, accelerating the disintegration of the glassy structure, and promoting the Ca... 2+ [SiO4] 4- [AlO2] - Early dissolution.

[0017] Sulfate synergy: Phosphogypsum contains calcium sulfate, which provides SO4 through dissolution. 2- With dissolved AlO2 - Ca 2+ The rapid reaction forms ettringite (AFt), which provides a core contribution to early strength. The presence of acetic acid modulates the reaction rate, preventing the loose structure caused by excessively rapid ettringite formation.

[0018] Shrinkage inhibition: Studies have shown that when the acetic acid content is in the range of 3 to 6%, it has a significant inhibitory effect on the drying shrinkage of cement-based materials, which is beneficial to the volume stability of the filling and reduces the risk of cracking.

[0019] (2) Phosphate-assisted solidification: permanent alkali fixation, long-term stability Alkaline ionic curing: Potassium dihydrogen phosphate (KH2PO4) hydrolyzes to produce H2O. + and PO4 3- H + It can neutralize some of the OH in the system - To reduce the alkalinity of the liquid phase; PO4 3- With Ca 2+ The reaction produces a sparingly soluble Ca3(PO4)2 precipitate, which will permanently solidify the highly alkaline calcium ions in the mineral phase, thus blocking the leaching of alkali at the source.

[0020] Synergistic mineral formation: Phosphates can also react with Mg dissolved in slag. 2+ K + The reaction generates K-struvite (MgKPO4·6H2O) minerals, which further fill the pores and improve the density of the structure.

[0021] Risk control of alkali return: Unlike the solubility of calcium acetate, Ca3(PO4)2 has extremely low solubility (Ksp≈2.0×10). -29 It hardly dissolves under long-term leaching conditions in groundwater, fundamentally solving the problem of alkali return in traditional acetic acid activation systems.

[0022] (3) Multi-faceted synergistic effect Strength contribution: Acetic acid accelerates hydration → more ettringite and CASH gel formation; phosphate formation generates struvite to fill pores; phosphogypsum sulfate activation continuously provides SO4. 2- The three components work synergistically to ensure a 28-day compressive strength ≥ 2.5 MPa.

[0023] Alkalinity control: Acetic acid neutralizes some of the OH-. - ; Phosphate-cured Ca 2+ The two work together to keep the pH of the leachate stable below 9.

[0024] Long-term stability: Acetic acid inhibits shrinkage, phosphate permanently stabilizes the alkali, and phosphogypsum sulfate continuously stimulates the filling. The three work together to ensure long-term volume stability, alkalinity stability, and strength stability of the filling.

[0025] Objective 2: A method for preparing a low-alkalinity, high-strength filling material, comprising the following steps: (1) Mix acetic acid with the first part of water to obtain an aqueous solution of acetic acid; dissolve phosphate with the second part of water to obtain an aqueous solution of phosphate; (2) Mix slag, fly ash, phosphogypsum and alkaline regulator to obtain composite cementitious material dry powder; (3) Mix the dry powder of the composite cementitious material with the aggregate, then add the acetic acid aqueous solution and the phosphate aqueous solution in sequence, replenish the remaining water, stir evenly, and obtain a filling slurry with a solid mass concentration of 65-72%.

[0026] Furthermore, the mass ratio of the acetic acid to the first portion of water is 1:3 to 1:5.

[0027] Furthermore, the mass ratio of the phosphate to the second portion of water is 1:4 to 1:7 (it is necessary to ensure that the phosphate can be completely dissolved in the water).

[0028] Third objective: Application of a low-alkalinity, high-strength filling material in mine backfilling.

[0029] Furthermore, the specific operating steps of the application are as follows: the low-alkalinity high-strength filling material is transported to the goaf through a pipeline and cured under natural conditions or standard curing conditions to the specified age.

[0030] Compared with the prior art, the present invention has the following advantages and technical effects: (1) Environmentally friendly and with long-term stable alkalinity: Through the multi-component synergistic activation of acetic acid and phosphate, acetic acid neutralizes part of the OH groups. - phosphates will cause Ca 2+ The material permanently solidifies into a sparingly soluble Ca3(PO4)2 precipitate. The pH value of the leachate from the filling material can be stably controlled below 9 after 28 days, and the pH value still meets the Class IV water requirements (≤9) after long-term soaking for 180 days. This fundamentally solves the problem of alkali return in traditional acetic acid activation systems and effectively avoids alkaline pollution of groundwater and soil in the mining area.

[0031] (2) High strength, meeting high-requirement backfilling scenarios: Acetic acid accelerates early hydration by eroding the slag surface, generating sufficient ettringite and CASH gel; phosphate generates struvite-like minerals to fill pores; phosphogypsum provides continuous sulfate activation. The three work synergistically, and the 28-day compressive strength can reach more than 2.5 MPa, and can reach more than 4.0 MPa under the optimal ratio, which can meet the high-strength backfilling scenarios such as roof support and pillar mining.

[0032] (3) Shrinkage suppression and good volume stability: When the acetic acid content is in the range of 3 to 6 parts, it has a significant effect on suppressing the drying shrinkage of the filling material. The 60-day drying shrinkage strain can be reduced by 30 to 40% compared with the pure cement system, effectively reducing the risk of cracking of the filling body and improving the top connection rate.

[0033] (4) High utilization rate of solid waste and controllable cost: The total proportion of industrial solid waste such as slag, fly ash and phosphogypsum in cementitious materials can reach more than 90%. Acetic acid can be selected from industrial by-product acetic acid, and the amount of phosphate used is very small (0.2 to 1.0 parts). The overall material cost can be reduced by 30 to 50% compared with the cement system.

[0034] (5) The process is simple and easy to industrialize: The preparation process of this invention is compatible with existing mine filling systems, requires no special curing conditions (room temperature curing is sufficient), does not require the addition of complex equipment, and can be directly promoted and applied in existing filling stations.

[0035] (6) Good durability and excellent corrosion resistance: The hydration products are mainly ettringite, CASH gel and insoluble calcium phosphate. The structure is dense and stable, with good resistance to sulfate corrosion and long-term durability. Detailed Implementation

[0036] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0037] It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the invention. Furthermore, with respect to numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Every smaller range between any stated value or intermediate value within a stated range, and any other stated value or intermediate value within said range, is also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0038] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.

[0039] Various modifications and variations can be made to the specific embodiments described in this specification without departing from the scope or spirit of the invention, as will be apparent to those skilled in the art. Other embodiments derived from this specification will also be apparent to those skilled in the art. This specification and embodiments are merely exemplary.

[0040] The terms “include,” “including,” “have,” “contain,” etc., used in this article are all open-ended terms, meaning that they include but are not limited to.

[0041] This invention provides a low-alkalinity, high-strength filling material, comprising cementitious material, aggregate, and water; wherein the mass ratio of cementitious material to aggregate is 1:4 to 1:8 (e.g., 1:5, 1:6, 1:7, or 1:8); the amount of water used is such that the solid phase mass concentration of the filling slurry is 65% to 72% (e.g., 65%, 68%, or 70%); the cementitious material includes slag, fly ash, phosphogypsum, acetic acid, phosphate, and an alkaline modifier. The cementitious material comprises the following components by weight: slag: 70-85 parts (e.g., 70, 78, or 80 parts); fly ash: 5-20 parts (e.g., 10 or 15 parts); phosphogypsum: 8-15 parts (e.g., 12 parts); acetic acid: 3-6 parts (e.g., 4, 5, or 6 parts); phosphate: 0.2-1.0 parts (e.g., 0.3, 0.4, 0.5, or 0.6 parts); and alkaline regulator: 0-2 parts (e.g., 1 or 1.5 parts).

[0042] In the following optional embodiments of the present invention, the slag is granulated blast furnace slag with a specific surface area ≥ 450 m². 2 / kg, 28-day activity index ≥98%, preferably S95 grade or higher slag powder. Exemplarily, in the following preferred embodiments of the present invention, the slag specific surface area is 460 m². 2 / kg, with an activity index of 99% after 28 days.

[0043] In the following optional embodiments of the present invention, the fly ash is low-calcium type F fly ash, with a water requirement ratio ≤105% and a 45μm sieve residue ≤15%, preferably Grade I or Grade II fly ash. For example, in the following preferred embodiments of the present invention, the fly ash is Grade I fly ash, with a 45μm sieve residue of 8% and a water requirement ratio of 95%.

[0044] In the following optional embodiments of the present invention, the phosphogypsum is a hemihydrate phosphogypsum that has been dried and ground, and has a specific surface area ≥400 m². 2 / kg, such as 400-500m 2 / kg, P2O5 content ≤1.0%, pH value 4~5.5. Exemplarily, in the following preferred embodiments of the present invention, the phosphogypsum has a specific surface area of ​​420m². 2 / kg, with a P2O5 content of 0.8%.

[0045] In the following optional embodiments of the present invention, the acetic acid is industrial grade acetic acid with a concentration of 4-10%, preferably 4-6%. Exemplarily, in the following preferred embodiments of the present invention, the acetic acid concentration is 4%.

[0046] In the following optional embodiments of the present invention, the phosphate is potassium dihydrogen phosphate or sodium dihydrogen phosphate; exemplaryly, in the following preferred embodiments of the present invention, the phosphate is potassium dihydrogen phosphate.

[0047] In the following optional embodiments of the present invention, the alkalinity regulator is calcium oxide and / or magnesium oxide, and its amount does not exceed 1 / 2 of the mass of acetic acid. Exemplarily, in the following preferred embodiments of the present invention, the alkalinity regulator is calcium oxide or a mixture of calcium oxide and magnesium oxide (mass ratio 1:1).

[0048] In the following optional embodiments of the present invention, the aggregate is tailings from metal mine beneficiation, D V (50) = 35~45μm. Exemplarily, in the following preferred embodiments of the invention, the D of the aggregate... V (50) = 38.7 μm.

[0049] The preparation method of the above-mentioned low-alkalinity, high-strength filling material includes the following steps: (1) Raw material pretreatment: Dry the phosphogypsum at 100-120℃ (e.g., 105℃) to constant weight, and then grind it to achieve a specific surface area of ​​400-500 m². 2 / kg (e.g., 420m) 2 / kg); dilute and mix acetic acid with the first part of water at a mass ratio of 1:3 to 1:5 (e.g., 1:4) to obtain an acetic acid aqueous solution; mix phosphate with the second part of water at a mass ratio of 1:4 to 1:7 (e.g., 1:5, ensuring that the phosphate is completely dissolved in the water) to obtain a phosphate aqueous solution; (2) Dry material mixing: The slag, fly ash, phosphogypsum and alkaline regulator weighed according to the proportion are thoroughly mixed to obtain composite cementitious material dry powder; (3) Slurry preparation: The dry powder of composite cementitious material is mixed with aggregate (fine-grained tailings) in proportion, and diluted acetic acid aqueous solution and phosphate aqueous solution are added in sequence. The remaining water is replenished and stirred evenly to make a filling slurry. The solid mass concentration of the filling slurry is 65-72%.

[0050] The low-alkalinity, high-strength backfill material prepared by the above method can be used in mine backfilling. The specific operation steps are as follows: the low-alkalinity, high-strength backfill material is transported to the goaf through pipeline and cured under natural conditions or standard curing conditions until the specified age.

[0051] Unless otherwise specified, "room temperature" and "normal temperature" in this invention refer to 25±2℃.

[0052] Unless otherwise specified, the term "parts" in this invention refers to parts by weight.

[0053] All raw materials used in this invention were purchased from the market.

[0054] The technical solution of the present invention will be further illustrated by the following embodiments.

[0055] Example 1 (Core Proportioning Standard) A low-alkalinity, high-strength filler material, with the following composition: (a) Cementitious materials: Slag: S95 grade slag (specific surface area 460m²) 2 78 samples ( / kg, 28d activity index 99%); Fly ash: 10 parts of Grade I fly ash (8% residue on 45μm sieve, 95% water requirement); Phosphogypsum: (dried and ground, specific surface area 420m²) 2 / kg, P2O5 content 0.8%) 12 portions; Acetic acid: 5 parts of industrial grade acetic acid (4% concentration) (equivalent to 0.2% of the total mass of pure acetic acid in the cementitious material). Phosphate: 0.5 parts potassium dihydrogen phosphate (0.5% of the total mass of cementitious materials); Alkalinity regulator: 1 part calcium oxide; (ii) Aggregates: Fine-grained tailings from a certain iron ore mine, its D V (50) = 38.7 μm; the mass ratio of cementitious material to aggregate is 1:6; (iii) Water: Calculated based on a filling mass concentration of 68%.

[0056] A method for preparing a low-alkalinity, high-strength filling material includes the following steps: (1) Dry the phosphogypsum in an oven at 105℃ for 24 hours, and then grind it with a ball mill to a specific surface area of ​​420 m². 2 / kg; (2) Dilute and mix acetic acid with a portion of water at a mass ratio of 1:4 (i.e., the amount of water used is 20 parts) to obtain an acetic acid aqueous solution; dissolve potassium dihydrogen phosphate with a portion of water at a mass ratio of 1:5 (i.e., the amount of water used is 2.5 parts) to obtain a phosphate solution; (3) Weigh out the slag, fly ash, phosphogypsum and calcium oxide according to the proportion, mix them evenly in the mixer to obtain composite cementitious material dry powder; (4) Mix the dry powder of composite cementitious material with fine-grained tailings at a mass ratio of 1:6, then add acetic acid aqueous solution, phosphate solution and remaining water, and stir evenly with a mixer to obtain a filling slurry with a solid mass concentration of 68%. (5) Pour the slurry into a 70.7mm×70.7mm×70.7mm triple mold and cure it for 28 days under standard curing conditions (20±2℃, relative humidity ≥95%).

[0057] Example 2 (High Slag, High Strength Type) A low-alkalinity, high-strength filler material, with the following composition: (a) Cementitious materials: Slag: S95 grade slag (specific surface area 460m²) 2 / kg, 28d activity index 99%) 82 samples; Fly ash: 8 parts of Grade I fly ash (8% residue on 45μm sieve, 95% water requirement); Phosphogypsum: (dried and ground, specific surface area 420m²) 2 / kg, P2O5 content 0.8%) 10 portions; Acetic acid: 4 parts of industrial grade acetic acid (4% concentration); Phosphate: 0.4 parts potassium dihydrogen phosphate; Alkalinity regulator: 1 part calcium oxide; (ii) Aggregates: Fine-grained tailings from a certain iron ore mine, its D V (50) = 38.7 μm; the mass ratio of cementitious material to aggregate is 1:5; (iii) Water: Calculated based on a filling mass concentration of 70%.

[0058] The preparation method is the same as in Example 1.

[0059] Example 3 (High fly ash, high phosphate gypsum type) A low-alkalinity, high-strength filler material, with the following composition: (a) Cementitious materials: Slag: S95 grade slag (specific surface area 460m²) 2 70 samples ( / kg, 28d activity index 99%); Fly ash: 15 parts of Grade I fly ash (8% residue on 45μm sieve, 95% water requirement); Phosphogypsum: (dried and ground, specific surface area 420m²) 2 / kg, P2O5 content 0.8%) 15 portions; Acetic acid: 5 parts of industrial grade acetic acid (4% concentration); Phosphate: 0.6 parts potassium dihydrogen phosphate; Alkalinity regulator: 1.5 parts calcium oxide; (ii) Aggregates: Fine-grained tailings from a certain iron ore mine, its D V (50) = 38.7 μm; the mass ratio of cementitious material to aggregate is 1:7; (iii) Water: Calculated based on a filling mass concentration of 66%.

[0060] The preparation method is the same as in Example 1.

[0061] Example 4 (High acetic acid content, low phosphate type) A low-alkalinity, high-strength filler material, with the following composition: (a) Cementitious materials: Slag: S95 grade slag (specific surface area 460m²) 2 78 samples ( / kg, 28d activity index 99%); Fly ash: 10 parts of Grade I fly ash (8% residue on 45μm sieve, 95% water requirement); Phosphogypsum: (dried and ground, specific surface area 420m²) 2 / kg, P2O5 content 0.8%) 12 portions; Acetic acid: 6 parts of industrial grade acetic acid (4% concentration); Phosphate: 0.3 parts potassium dihydrogen phosphate; Alkalinity regulator: 1 part calcium oxide; (ii) Aggregates: Fine-grained tailings from a certain iron ore mine, its D V (50) = 38.7 μm; the mass ratio of cementitious material to aggregate is 1:6; (iii) Water: Calculated based on a filling mass concentration of 68%.

[0062] The preparation method is the same as in Example 1.

[0063] Example 5 (Magnesium oxide composite alkaline regulator) A low-alkalinity, high-strength filler material, with the following composition: (a) Cementitious materials: Slag: S95 grade slag (specific surface area 460m²) 2 78 samples ( / kg, 28d activity index 99%); Fly ash: 10 parts of Grade I fly ash (8% residue on 45μm sieve, 95% water requirement); Phosphogypsum: (dried and ground, specific surface area 420m²) 2 / kg, P2O5 content 0.8%) 12 portions; Acetic acid: 5 parts of industrial grade acetic acid (4% concentration); Phosphate: 0.5 parts potassium dihydrogen phosphate; Alkalinity regulator: 0.5 parts calcium oxide, 0.5 parts magnesium oxide; (ii) Aggregates: Fine-grained tailings from a certain iron ore mine, its D V (50) = 38.7 μm; the mass ratio of cementitious material to aggregate is 1:6; (iii) Water: Calculated based on a filling mass concentration of 68%.

[0064] The preparation method is the same as in Example 1.

[0065] Example 6 (Low cementitious material to aggregate mass ratio, low filling mass concentration boundary type) A low-alkalinity, high-strength filler material, with the following composition: (a) Cementitious materials: Same as in Example 1; (ii) Aggregates: Fine-grained tailings from a certain iron ore mine, its D V (50) = 38.7 μm; the mass ratio of cementitious material to aggregate is 1:8; (iii) Water: Calculated based on a filling mass concentration of 65%.

[0066] The preparation method is the same as in Example 1.

[0067] Comparative Example 1 (Ordinary Portland Cement) Same as Example 1, except that the cementitious material is replaced with ordinary Portland cement (P·O42.5) by mass.

[0068] The preparation method is the same as in Example 1.

[0069] Comparative Example 2 (Slag-based Alkali-activated Cementitious Powder for Mine Backfilling) Same as Example 1, except that the same mass of cementing material is replaced with slag-based alkali-activated cementing powder for mine backfilling (purchased from Anshan Shuangshuo New Material Technology Co., Ltd.).

[0070] The preparation method is the same as in Example 1.

[0071] Comparative Example 3 (Activated by monoacetic acid, without phosphate) Same as Example 1, except that potassium dihydrogen phosphate is not added, and the amount of acetic acid is adjusted to 5.5 parts (to keep the total amount of activator equivalent).

[0072] The preparation method is the same as in Example 1.

[0073] Comparative Example 4 (monophosphate activation, without acetic acid) Same as Example 1, except that acetic acid is not added and the amount of potassium dihydrogen phosphate is adjusted to 5.5 parts.

[0074] A method for preparing a filling material includes the following steps: (1) Dry the phosphogypsum in an oven at 105℃ for 24 hours, and then grind it with a ball mill to a specific surface area of ​​420 m². 2 / kg; (2) Dissolve potassium dihydrogen phosphate in a mixture of potassium dihydrogen phosphate and water in a mass ratio of 1:5 (i.e., the amount of water used is 27.5 parts) to obtain a phosphate solution; (3) Weigh out the slag, fly ash, phosphogypsum and calcium oxide according to the proportion, mix them evenly in the mixer to obtain composite cementitious material dry powder; (4) Mix the dry powder of composite cementitious material with fine-grained tailings at a mass ratio of 1:6, add phosphate solution and remaining water, and stir evenly with a mixer to obtain a filling slurry with a solid mass concentration of 68%. (5) Pour the slurry into a 70.7mm×70.7mm×70.7mm triple mold, seal it at room temperature for 2 days, then cure it at 60℃ for 24 hours, and then cure it under standard curing conditions (20±2℃, relative humidity ≥95%) for 28 days.

[0075] This method involves complex processes and is costly.

[0076] Comparative Example 5 (no acid activation, only sulfate activation) A filling material, the composition of which is as follows: (a) Cementitious materials: Slag: S95 grade slag (specific surface area 460m²) 2 80 samples ( / kg, 28d activity index 99%); Fly ash: 12 parts of Grade I fly ash (8% residue on 45μm sieve, 95% water requirement); Phosphogypsum: (dried and ground, specific surface area 420m²) 2 8 portions ( / kg, P2O5 content 0.8%); Alkalinity regulator: 2 parts calcium oxide; (ii) Aggregates: Fine-grained tailings from a certain iron ore mine, its D V (50) = 38.7 μm; the mass ratio of cementitious material to aggregate is 1:6; (iii) Water: Calculated based on a filling mass concentration of 68%.

[0077] The preparation method is the same as in Example 1, except that the preparation and addition of potassium dihydrogen phosphate solution and acetic acid aqueous solution are omitted.

[0078] Performance testing: (1) Uniaxial compressive strength: The uniaxial compressive strength of the consolidated paste was tested according to the provisions of JGJ / T 70 for 28 days.

[0079] (2) pH value of leachate: The test block cured for 28 days was crushed to a particle size of less than 3 mm. The leachate was prepared according to HJ 557-2010 "Leaching Toxicity of Solid Waste - Horizontal Oscillation Method" and measured with a pH meter.

[0080] (3) Long-term alkali return test: The test block was soaked in deionized water, the soaking water was changed every 30 days and the pH value was measured. The pH value of the soaking water was measured after 180 days.

[0081] (4) Drying shrinkage: Refer to GB / T 50082-2009 to test the drying shrinkage strain of the sample after 60 days.

[0082] Table 1. Test results of the filling materials prepared in Examples 1-6 and Comparative Examples 1-5 As can be seen from Table 1, Example 1 is the benchmark ratio of the present invention. Under the condition of appropriate proportions of slag, fly ash and phosphogypsum, it achieves a comprehensive performance of 3.4 MPa compressive strength, pH value of 8.5, long-term stability and good shrinkage, which represents the typical technical effect of the present invention.

[0083] Example 2 increases the proportion of slag and the mass ratio of cementitious materials to aggregates, increasing the compressive strength to 4.8 MPa, making it suitable for filling scenarios with high strength requirements (such as roof support and pillar mining).

[0084] Example 3 increases the proportion of fly ash and phosphogypsum, resulting in higher solid waste utilization. The compressive strength is 2.8 MPa, which still meets the requirement of ≥2.5 MPa, making it suitable for filling scenarios with relatively low strength requirements.

[0085] Example 4 showed that increasing the acetic acid content and decreasing the phosphate content resulted in a more significant effect of acetic acid in inhibiting shrinkage (60-day shrinkage of 395 × 10⁻⁶). -6 Meanwhile, phosphates can still effectively solidify alkaline ions, and the pH value remains stable at 8.5 after long-term soaking.

[0086] Example 5 uses a composite alkaline regulator of calcium oxide and magnesium oxide. Magnesium oxide and phosphate synergistically generate struvite minerals to fill the pores, resulting in a slight increase in strength (3.7 MPa), demonstrating the optimization effect of the alkaline regulator.

[0087] Example 6 is a boundary condition test. The mass ratio of cementitious material to aggregate is reduced to 1:8, the filling mass concentration is reduced to 65%, the compressive strength is 2.6MPa, which just meets the requirement of ≥2.5MPa, and the pH value remains stable at 8.6, which reflects the wide applicability of the technical solution of the present invention.

[0088] The following conclusions can be drawn from the above analysis: The technical solution of this invention has wide applicability: within the range of 70-80 parts slag, 10-15 parts fly ash, 12 parts phosphogypsum, 4-6 parts acetic acid, 0.3-0.6 parts phosphate, a mass ratio of cementitious material to aggregate of 1:5-1:8, and a filling mass concentration of 65-70%, the target of 28-day compressive strength ≥2.5MPa and leachate pH value ≤9 can be achieved.

[0089] The synergistic effect of acetic acid and phosphate is the core technical feature of this invention: acetic acid, as the main activator, provides early strength and shrinkage inhibition, while phosphate, as the auxiliary curing agent, provides long-term alkalinity stability; neither can be dispensed with. Ordinary silicate cement (Comparative Example 1) and mine backfill cement powder (Comparative Example 2) have excessively high alkalinity; acetic acid-only activation (Comparative Example 3) suffers from long-term alkali return; although phosphate-only activation (Comparative Example 4) has low alkalinity, its process is complex, costly, and its strength is relatively low; acid-free activation (Comparative Example 5) has low strength and excessive alkalinity.

[0090] The present invention is superior to the prior art: Compared with comparative examples 1, 2 and 5, the present invention reduces the pH value of the leachate from above 11 to below 9 while ensuring the strength (2.6~3.9MPa); Compared with comparative example 3, the present invention solves the long-term alkali return problem (pH value ≤8.8 after 180 days of soaking); Compared with comparative example 4, the process of the present invention is simpler and the cost is lower.

[0091] This invention has good adaptability to raw materials: Examples 2-5 show that by adjusting the ratio of slag, fly ash, and phosphogypsum, changing the amount of acetic acid and phosphate, and using different alkaline regulators, good performance can be obtained, demonstrating the universality of this invention.

[0092] In summary, the acetic acid-phosphate multi-element synergistic low-alkalinity high-strength filling material provided by this invention can achieve the comprehensive goals of high strength, low alkalinity, long-term stability, and simple process within a wide range of proportions, and has significant industrial application value and environmental protection benefits.

[0093] The above are merely preferred embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A low-alkalinity, high-strength filler material, characterized in that, It includes cementitious materials, aggregates, and water; wherein the mass ratio of the cementitious materials to the aggregates is 1:4 to 1:8; and the amount of water used is such that the solid phase mass concentration of the filling material is 65% to 72%. The cementitious material comprises the following components by weight: slag: 70-85 parts; fly ash: 5-20 parts; phosphogypsum: 8-15 parts; acetic acid: 3-6 parts; phosphate: 0.2-1.0 parts; alkalinity regulator: 0-2 parts; The phosphate is potassium dihydrogen phosphate or sodium dihydrogen phosphate; The alkalinity regulator is calcium oxide or a combination of calcium oxide and magnesium oxide, and its amount does not exceed 1 / 2 of the mass of acetic acid.

2. The low-alkalinity, high-strength filling material according to claim 1, characterized in that, The slag is granulated blast furnace slag with a specific surface area ≥ 450 m². 2 / kg, 28d activity index ≥98%; The fly ash is low-calcium type F fly ash, with a water requirement ratio ≤105% and a 45μm sieve residue ≤15%.

3. The low-alkalinity, high-strength filling material according to claim 1, characterized in that, The phosphogypsum is a hemihydrate phosphogypsum that has been dried and ground, with a specific surface area ≥400m². 2 / kg, P2O5 content ≤1.0%; The acetic acid is industrial grade acetic acid with a mass concentration of 4-10%.

4. The low-alkalinity, high-strength filling material according to claim 1, characterized in that, The aggregate is fine-grained tailings, D V (50) = 35~45μm.

5. A method for preparing a low-alkalinity, high-strength filling material as described in any one of claims 1 to 4, characterized in that, Includes the following steps: (1) Mix acetic acid with the first part of water to obtain an aqueous solution of acetic acid; dissolve phosphate with the second part of water to obtain an aqueous solution of phosphate; (2) Mix slag, fly ash, phosphogypsum and alkaline regulator to obtain composite cementitious material dry powder; (3) Mix the dry powder of the composite cementitious material with the aggregate, then add the acetic acid aqueous solution and the phosphate aqueous solution in sequence, replenish the remaining water, stir evenly, and obtain a filling material with a solid mass concentration of 65-72%.

6. The preparation method according to claim 5, characterized in that, The mass ratio of the acetic acid to the first portion of water is 1:3 to 1:

5.

7. The preparation method according to claim 5, characterized in that, The mass ratio of the phosphate to the second part of water is 1:4 to 1:

7.

8. The application of a low-alkalinity, high-strength backfill material as described in any one of claims 1 to 4 in mine backfilling.

9. The application according to claim 8, characterized in that, The specific operating steps of the application are as follows: the low-alkalinity high-strength filling material is transported to the goaf through a pipeline and cured under natural conditions or standard curing conditions until the specified age.

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