Preparation and application of carbon-mineralized phosphogypsum mine filling material

Abstract

The application relates to the field of mine filling, in particular to preparation and application of carbon-mineralized phosphogypsum mine filling material, which is prepared from the following raw materials in parts by mass: 70-100 parts of red mud, 20-40 parts of yellow phosphorus slag, 1-10 parts of fly ash, 1-10 parts of slag, 5-20 parts of compound activator, 4-8 parts of modified cellulose, 10-30 parts of activated phosphogypsum, 8-16 parts of fine aggregate, 3-8 parts of modified biochar, 1-5 parts of water reducing agent and 50-100 parts of water; the modified cellulose is prepared from AlCl3, sodium hypophosphite, 1,4-butanediol diglycidyl ether and butane tetracarboxylic acid. In the high-alkaline environment, P and F are simultaneously and efficiently solidified, the fine aggregate cementing material is mixed into filling slurry, CO2 is introduced, free calcium oxide in the steel slag and calcium carbide slag is reacted with the calcium sulfate hemihydrate in the phosphogypsum to form calcium carbonate, the strength of the filling body is rapidly improved, and the solidification of CO2 is completed.

Description

Technical Field

[0001] This invention relates to the field of mine backfilling applications, and more specifically, to the preparation and application of a carbon mineralized phosphogypsum mine backfilling material. Background Technology

[0002] Red mud is a highly alkaline solid waste unavoidably generated during alumina production, producing approximately 1 to 1.5 tons of red mud for every ton of alumina produced. Taking the widely used Bayer process as an example, red mud, as a byproduct of this alkaline process, is extremely alkaline and characterized by fine particle size and high heavy metal content. Large stockpiles of red mud not only occupy valuable land resources, but their highly alkaline chemical components can also seep into the soil and groundwater systems, posing a serious threat to the surrounding environment. Therefore, exploring low-cost, environmentally friendly methods for large-scale treatment and resource utilization of red mud has become an urgent technical challenge.

[0003] In recent years, researchers have been actively engaged in the research of resource utilization of red mud solid waste, striving to transform it into a high-value resource. Currently, the research focus both domestically and internationally is mainly on using red mud to produce building materials, ceramic products, adsorbent materials, and new functional materials, as well as recovering iron, aluminum, titanium, sodium, and even rare metal elements from red mud. In existing technologies for producing building materials using red mud as a raw material, most involve partially replacing cement with red mud as a cementing material. For example, Chinese patent application CN118479817A proposes a red mud high-content hazardous waste solidification filling material and its preparation method. The filling material includes a solid phase component and water. The mass percentages of each component in the solid phase component are: 50-80 parts Bayer process red mud, 10-30 parts coal slag, 20 parts cement, 0-1 part water-reducing agent, and 0-0.15 parts chelated fiber. The mass ratio of water to the solid phase component is 62:100. For example, Chinese patent application CN118108476A discloses a red mud synergistic multi-source solid filling material and its preparation method, which, by weight parts, includes 50-60 parts red mud, 10-25 parts desulfurization ash, 15-25 parts cement, 2-5 parts sodium dodecyl sulfate, 2-5 parts mirabilite, 2-5 parts gypsum, 3-5 parts cementitious material, 5-6 parts mineral powder, 5-6 parts activator, 2-3 parts activator, 5-8 parts quick-setting agent, 35-45 parts water, and 0.9-1.5 parts water-reducing agent.

[0004] In existing technologies, phosphogypsum-based cementitious materials easily absorb water and swell, exhibiting insufficient impermeability and frost resistance. Long-term use can lead to cracks and structural damage, limiting their reliability in humid or low-temperature mining environments. While carbon-mineralized phosphogypsum has potential advantages in reducing carbon emissions and utilizing resources as a mine backfill material, it suffers from deficiencies in raw material stability, mechanical properties, and water stability. Summary of the Invention

[0005] This invention provides a method for preparing and applying a carbon-mineralized phosphogypsum mine backfill material. During the backfilling process, calcium carbonate precipitate is added using an alkaline activator, causing the calcium in the phosphogypsum to react with carbon dioxide to form stable calcium carbonate minerals, thus achieving solid carbon sequestration. This significantly enhances the CO2 emission reduction potential while maintaining or improving the material's mechanical properties.

[0006] In a first aspect, the present invention provides a carbon-mineralized phosphogypsum mine backfill material, comprising the following raw materials in parts by weight: 70-100 parts red mud, 20-40 parts yellow phosphorus slag, 1-10 parts fly ash, 1-10 parts slag, 5-20 parts compound activator, 4-8 parts modified cellulose, 10-30 parts activated phosphogypsum, 8-16 parts fine aggregate, 3-8 parts modified biochar, 1-5 parts water-reducing agent, and 50-100 parts water; wherein the modified cellulose is prepared by modifying cellulose with AlCl3, sodium hypophosphite, 1,4-butanediol diglycidyl ether and butanetetracarboxylic acid.

[0007] Preferably, the mass ratio of AlCl3, sodium hypophosphite, 1,4-butanediol diglycidyl ether, butanetetracarboxylic acid, and cellulose is 1~2:1:2~3:1~2:5~8.

[0008] Preferably, the compound activator includes polyphosphate, sodium methylsilicate, sodium metasilicate and gypsum powder, and the mass ratio of polyphosphate, sodium methylsilicate, sodium metasilicate and gypsum powder is 2~5:1~3:1:1~2.

[0009] Preferably, the modified biochar is prepared by modifying biochar with phosphate ester and 3-aminopropyltriethoxysilane, wherein the mass ratio of phosphate ester, 3-aminopropyltriethoxysilane and biochar is 1:1~2:3~5.

[0010] Preferably, the red mud has a D50 particle size of 20~100 μm and a moisture content of ≤5%; the yellow phosphorus slag has a D50 particle size of 0.03~0.2 mm; the fly ash has a D50 particle size of 5~160µm; and the slag has a D50 particle size of 30~70µm.

[0011] Preferably, the method for preparing the activated phosphogypsum includes the following steps: neutralizing the phosphogypsum by adding calcium oxide or sodium hydroxide, with a pH of 7.0 to 9.0, a solid-liquid ratio of 1:0.5 to 2.5, stirring for 0.5 to 5 hours, adding 1% to 5% aluminate coupling agent, heating at 90°C to 120°C for 20 to 40 minutes, washing with water to remove residual soluble salts, and finally drying at 40°C to 60°C to obtain the activated phosphogypsum.

[0012] Preferably, the water-reducing agent is selected from at least one of polycarboxylate, naphthalene sulfonate, or silicate.

[0013] Secondly, the present invention provides a method for preparing a carbon-mineralized phosphogypsum mine backfill material, comprising the following steps: According to the mass ratio, red mud, yellow phosphorus slag, fly ash, slag, compound activator, modified cellulose, activated phosphogypsum, fine aggregate, modified biochar, water-reducing agent and water are mixed to obtain a filling slurry; the filling slurry is cured to obtain carbonized phosphogypsum mine filling material.

[0014] Preferably, the mixing speed is 300~500 rpm; the curing conditions include: temperature of 20~40°C, humidity ≥95%, and time ≥28 days.

[0015] Thirdly, the present invention provides a carbon mineralized phosphogypsum mine filling material for mine filling.

[0016] In summary, the present invention has the following beneficial effects: 1. This invention employs a bifunctional modification process involving AlCl3 / sodium hypophosphite catalytic crosslinking and 1,4-butanediol diglycidyl ether / butanetetracarboxylic acid copolymerization. This process enables the formation of a high-strength, low-permeability, and sustainable carbon-capturing composite network structure within phosphogypsum-based fillers, significantly improving the material's mechanical properties, durability, carbon mineralization efficiency, and environmental friendliness. The AlCl3 / sodium hypophosphite catalytic crosslinking process utilizes these two Lewis acids to activate the hydroxyl groups of cellulose at low temperatures (≤80°C), forming phenolic crosslinking bridges (Al-OC), significantly enhancing the thermal stability and alkali resistance of cellulose. AlCl3 primarily targets epoxy ring-opening, while sodium hypophosphite primarily targets carboxylic acid esterification; their functions are clearly defined, do not interfere with each other, and synergistically enhance each other's effectiveness. 1,4-Butanediol diglycidyl ether (BDGE) is a bifunctional epoxidizing agent that can perform epoxy ring-opening crosslinking on the cellulose hydroxyl groups, forming diethyl ether bonds (-O-CH2-CH2-O-), improving flexibility and providing an adjustable elastic modulus. Butanetetracarboxylic acid (BTCA) is a polycarboxylic acid crosslinking agent that forms ester bonds (-COO-) with cellulose hydroxyl groups at high temperatures (120-150°C), generating a high-density carboxyl network, which plays a key role in CO2 adsorption / carbonate precipitation.

[0017] 2. The activated phosphogypsum of this invention is rich in rapidly released Ca. 2+ , for CO2 and Ca 2+ The formation of calcium carbonate provides an ample calcium source. The addition of activated phosphogypsum significantly enhances the CO2 mitigation potential of the infill material and accelerates the carbon mineralization rate. Using waste phosphogypsum and modified biochar as the main aggregates can substantially reduce the use of traditional infill materials such as purchased cement and sand, improving resource utilization and resulting in significant economic and environmental benefits.

[0018] 3. The carbon-mineralized phosphogypsum mine backfill material prepared by this invention incorporates calcium carbonate precipitate with an alkaline activator during the backfilling process. This allows the calcium in the phosphogypsum to react with carbon dioxide to form stable calcium carbonate minerals, achieving solid carbon sequestration. This significantly enhances the CO2 emission reduction potential while maintaining or improving the material's mechanical properties. Simultaneously and efficiently solidifying phosphorus and phosphorus (P and F) under a highly alkaline environment, and mixing with fine aggregate cementitious materials to form a backfill slurry, CO2 is introduced. This causes the free calcium oxide in steel slag and carbide slag to react with the hemihydrate calcium sulfate in the phosphogypsum to form calcium carbonate, rapidly increasing the strength of the backfill while simultaneously solidifying the CO2.

[0019] It should be understood that the above general description and the following detailed description are exemplary and explanatory only, and do not limit the scope of protection of the present invention. Detailed Implementation

[0020] The present invention will be further described in detail below with reference to the embodiments. It should be noted that: unless otherwise specified, the conditions in the following embodiments are carried out according to conventional conditions or the conditions recommended by the manufacturer. Unless otherwise specified, the raw materials used in the following embodiments can be obtained from commercially available sources.

[0021] Example Example 1 A carbon mineralized phosphogypsum mine backfill material comprises the following raw materials in parts by weight: 70 parts red mud, 20 parts yellow phosphorus slag, 1 part fly ash, 1 part slag, 5 parts compound activator, 4 parts modified cellulose, 10 parts activated phosphogypsum, 8 parts fine aggregate, 3 parts modified biochar, 1 part water reducing agent, and 50 parts water. Modified cellulose was prepared by modifying cellulose with AlCl3, sodium hypophosphite, 1,4-butanediol diglycidyl ether and butanetetracarboxylic acid; the mass ratio of AlCl3, sodium hypophosphite, 1,4-butanediol diglycidyl ether, butanetetracarboxylic acid and cellulose was 1:1:2:1:5.

[0022] The compound activator includes polyphosphate, sodium methylsilicate, sodium metasilicate, and gypsum powder, with a mass ratio of 2:1:1:1.

[0023] Modified biochar was prepared by modifying biochar with phosphate ester and 3-aminopropyltriethoxysilane, with a mass ratio of phosphate ester, 3-aminopropyltriethoxysilane and biochar of 1:1:3.

[0024] The D50 particle size of red mud is 20 μm and the moisture content is ≤5%; the D50 particle size of yellow phosphorus slag is 0.03 mm; the D50 particle size of fly ash is 5 µm; and the D50 particle size of slag is 30 µm.

[0025] The water-reducing agent is selected from polycarboxylate. The preparation method of activated phosphogypsum includes the following steps: neutralizing phosphogypsum by adding calcium oxide, pH=7.2, solid-liquid ratio of 1:0.5, stirring reaction time of 0.5 h, adding 1% aluminate coupling agent, heating treatment at 90℃ for 20 min, washing with water to remove residual soluble salts, and finally drying at 40℃ to obtain activated phosphogypsum.

[0026] A method for preparing a carbon-mineralized phosphogypsum mine backfill material includes the following steps: According to the mass ratio, red mud, yellow phosphorus slag, fly ash, slag, compound activator, modified cellulose, activated phosphogypsum, fine aggregate, modified biochar, water-reducing agent and water are mixed at a speed of 300 rpm to obtain filling slurry; the filling slurry is then cured under the following conditions: temperature 20°C, humidity ≥95%, time ≥28 days to obtain carbonized phosphogypsum mine filling material.

[0027] Example 2 A carbon-mineralized phosphogypsum mine backfill material comprises the following raw materials in parts by weight: 90 parts red mud, 30 parts yellow phosphorus slag, 5 parts fly ash, 5 parts slag, 10 parts compound activator, 5 parts modified cellulose, 20 parts activated phosphogypsum, 12 parts fine aggregate, 5 parts modified biochar, 3 parts water-reducing agent, and 80 parts water. Modified cellulose was prepared by modifying cellulose with AlCl3, sodium hypophosphite, 1,4-butanediol diglycidyl ether and butanetetracarboxylic acid; the mass ratio of AlCl3, sodium hypophosphite, 1,4-butanediol diglycidyl ether, butanetetracarboxylic acid and cellulose was 2:1:2:1:7.

[0028] The compound activator includes polyphosphate, sodium methylsilicate, sodium metasilicate, and gypsum powder, with a mass ratio of 3:1:1:2.

[0029] Modified biochar was prepared by modifying biochar with phosphate ester and 3-aminopropyltriethoxysilane, with a mass ratio of phosphate ester, 3-aminopropyltriethoxysilane and biochar of 1:2:3.

[0030] The D50 particle size of red mud is 50 μm and the moisture content is ≤5%; the D50 particle size of yellow phosphorus slag is 0.1 mm; the D50 particle size of fly ash is 120 µm; and the D50 particle size of slag is 50 µm.

[0031] The water-reducing agent is selected from polycarboxylate. The preparation method of activated phosphogypsum includes the following steps: neutralizing phosphogypsum by adding calcium oxide, pH=8.0, solid-liquid ratio of 1:1.5, stirring reaction time of 2.5h, adding 3% aluminate coupling agent, heating treatment at 100℃ for 30 min, washing with water to remove residual soluble salts, and finally drying at 50℃ to obtain activated phosphogypsum.

[0032] A method for preparing a carbon-mineralized phosphogypsum mine backfill material includes the following steps: According to the mass ratio, red mud, yellow phosphorus slag, fly ash, slag, compound activator, modified cellulose, activated phosphogypsum, fine aggregate, modified biochar, water-reducing agent and water are mixed at a speed of 400 rpm to obtain filling slurry; the filling slurry is then cured under the following conditions: temperature 30°C, humidity ≥95%, time ≥28 days to obtain carbonized phosphogypsum mine filling material.

[0033] Example 3 A carbon mineralized phosphogypsum mine backfill material comprises the following raw materials in parts by weight: 100 parts red mud, 40 parts yellow phosphorus slag, 10 parts fly ash, 10 parts slag, 20 parts compound activator, 8 parts modified cellulose, 30 parts activated phosphogypsum, 16 parts fine aggregate, 8 parts modified biochar, 5 parts water-reducing agent, and 100 parts water. Modified cellulose was prepared by modifying cellulose with AlCl3, sodium hypophosphite, 1,4-butanediol diglycidyl ether and butanetetracarboxylic acid; the mass ratio of AlCl3, sodium hypophosphite, 1,4-butanediol diglycidyl ether, butanetetracarboxylic acid and cellulose was 2:1:3:2:8.

[0034] The compound activator includes polyphosphate, sodium methylsilicate, sodium metasilicate, and gypsum powder, with a mass ratio of 5:3:1:2.

[0035] Modified biochar was prepared by modifying biochar with phosphate ester and 3-aminopropyltriethoxysilane, with a mass ratio of phosphate ester, 3-aminopropyltriethoxysilane and biochar of 1:2:5.

[0036] The D50 particle size of red mud is 100 μm and the moisture content is ≤5%; the D50 particle size of yellow phosphorus slag is 0.2 mm; the D50 particle size of fly ash is 160 µm; and the D50 particle size of slag is 70 µm.

[0037] The water-reducing agent is selected from polycarboxylate. The preparation method of activated phosphogypsum includes the following steps: neutralizing phosphogypsum by adding calcium oxide, pH=9.0, solid-liquid ratio of 1:2.5, stirring reaction time of 5 h, adding 5% aluminate coupling agent, heating treatment at 120℃ for 40 min, washing with water to remove residual soluble salts, and finally drying at 60℃ to obtain activated phosphogypsum.

[0038] A method for preparing a carbon-mineralized phosphogypsum mine backfill material includes the following steps: According to the mass ratio, red mud, yellow phosphorus slag, fly ash, slag, compound activator, modified cellulose, activated phosphogypsum, fine aggregate, modified biochar, water-reducing agent and water are mixed at a speed of 500 rpm to obtain filling slurry; the filling slurry is then cured under the following conditions: temperature 40°C, humidity ≥95%, time ≥28 days to obtain carbonized phosphogypsum mine filling material.

[0039] Comparative Example 1 Same as Example 1, except that no yellow phosphorus slag was added.

[0040] Comparative Example 2 Same as Example 1, except that no activated phosphogypsum was added.

[0041] Comparative Example 3 Same as Example 1, except that no modified cellulose was added.

[0042] Comparative Example 4 Same as Example 1, except that no compound activator was added.

[0043] Table 1 Performance Test Results

[0044] As shown in Table 1, the carbon-mineralized phosphogypsum mine backfill material prepared by this invention, through the addition of an alkaline activator during the backfilling process, precipitates calcium carbonate, causing the calcium in the phosphogypsum to react with carbon dioxide to form stable calcium carbonate minerals, thus achieving solid carbon sequestration. This significantly enhances the CO2 emission reduction potential while maintaining or improving the material's mechanical properties. Simultaneously and efficiently solidifying phosphorus and phosphorus (P and F) under a highly alkaline environment, and mixing them with fine aggregate cementitious materials to form a backfill slurry, followed by the introduction of CO2, causes the free calcium oxide in steel slag and carbide slag to react with the hemihydrate calcium sulfate in the phosphogypsum to form calcium carbonate, rapidly increasing the strength of the backfill while simultaneously completing CO2 solidification.

[0045] The above description is merely an exemplary embodiment 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 technical scope 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 carbon-mineralized phosphogypsum mine backfill material, characterized in that, The raw materials comprise the following parts by weight: 70-100 parts red mud, 20-40 parts yellow phosphorus slag, 1-10 parts fly ash, 1-10 parts slag, 5-20 parts compound activator, 4-8 parts modified cellulose, 10-30 parts activated phosphogypsum, 8-16 parts fine aggregate, 3-8 parts modified biochar, 1-5 parts water-reducing agent, and 50-100 parts water; the modified cellulose is prepared by modifying cellulose with AlCl3, sodium hypophosphite, 1,4-butanediol diglycidyl ether and butanetetracarboxylic acid.

2. The carbon-mineralized phosphogypsum mine backfill material according to claim 1, characterized in that, The mass ratio of AlCl3, sodium hypophosphite, 1,4-butanediol diglycidyl ether, butanetetracarboxylic acid, and cellulose is 1~2:1:2~3:1~2:5~8.

3. The carbon-mineralized phosphogypsum mine backfill material according to claim 1, characterized in that, The compound activator includes polyphosphate, sodium methylsilicate, sodium metasilicate, and gypsum powder, wherein the mass ratio of polyphosphate, sodium methylsilicate, sodium metasilicate, and gypsum powder is 2~5:1~3:1:1~2.

4. The carbon-mineralized phosphogypsum mine backfill material according to claim 1, characterized in that, The modified biochar is prepared by modifying biochar with phosphate ester and 3-aminopropyltriethoxysilane, wherein the mass ratio of phosphate ester, 3-aminopropyltriethoxysilane and biochar is 1:1~2:3~5.

5. The carbon-mineralized phosphogypsum mine backfill material according to claim 1, characterized in that, The red mud has a D50 particle size of 20~100 μm and a moisture content of ≤5%; the yellow phosphorus slag has a D50 particle size of 0.03~0.2 mm; the fly ash has a D50 particle size of 5~160µm; and the slag has a D50 particle size of 30~70µm.

6. The carbon-mineralized phosphogypsum mine backfill material according to claim 1, characterized in that, The method for preparing the activated phosphogypsum includes the following steps: neutralizing the phosphogypsum by adding calcium oxide or sodium hydroxide, with a pH of 7.0-9.0, a solid-liquid ratio of 1:0.5-2.5, stirring for 0.5-5 h, adding 1%-5% aluminate coupling agent, heating at 90℃-120℃ for 20-40 min, washing with water to remove residual soluble salts, and finally drying at 40℃-60℃ to obtain the activated phosphogypsum.

7. The carbon-mineralized phosphogypsum mine backfill material according to claim 1, characterized in that, The water-reducing agent is selected from at least one of polycarboxylate, naphthalene sulfonate, or silicate.

8. The method for preparing the carbon-mineralized phosphogypsum mine backfill material according to any one of claims 1 to 7, characterized in that, Includes the following steps: According to the mass ratio, red mud, yellow phosphorus slag, fly ash, slag, compound activator, modified cellulose, activated phosphogypsum, fine aggregate, modified biochar, water-reducing agent and water are mixed to obtain a filling slurry; the filling slurry is cured to obtain carbonized phosphogypsum mine filling material.

9. The method for preparing the carbon-mineralized phosphogypsum mine backfill material according to claim 8, characterized in that, The mixing speed is 300~500 rpm; the curing conditions include: temperature of 20~40°C, humidity ≥95%, and time ≥28 days.

10. The application of the carbon-mineralized phosphogypsum mine backfill material according to any one of claims 1 to 7, characterized in that, The carbon-mineralized phosphogypsum mine filling material is used for mine filling.

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