Phosphogypsum-based nano geopolymer backfill material and backfill method thereof

Abstract

The invention provides an ardealite-based nano geopolymer backfill material, and relates to the field of backfill materials. The material is prepared from the following raw materials in percentage by mass: 90-97% of ardealite; 2%-9% of ground cement clinker; 0.1%-0.3% of nano silicon dioxide; and 0.5%-2% of calcium chloride. The utilization rate of phosphogypsum is high, the dissolution amount of fluorine ions is low, and the compressive strength is high.

Description

Technical Field

[0001] The present invention relates to the field of backfill materials, in particular to a phosphogypsum-based nano-geopolymer backfill material and a backfill method thereof. Background Art

[0002] Phosphogypsum production exceeds 100 million tons annually. Its storage occupies land and contains soluble pollutants such as fluorine and phosphorus (fluoride ion leaching concentration > 100 mg / L, pH < 4 or > 11), posing environmental risks. Traditional phosphogypsum utilization technologies (such as for building materials) require high-temperature calcination or chemical modification, resulting in high costs and a utilization rate of less than 10%.

[0003] Backfill materials refer to materials used to fill gaps in the foundations of buildings or structures, basements, pipes, trenches, etc. Their selection must be based on a comprehensive consideration of multiple factors including engineering requirements, material properties, environmental friendliness and cost.

[0004] Existing backfill materials include natural materials such as sand, stone, and soil, which are low-cost and readily available. Industrial waste materials such as fly ash, slag, and steel slag are byproducts of industrial production and offer advantages in environmental protection and resource recycling. Synthetic materials such as foamed concrete, lightweight soil, and expanded clay are manufactured through artificial synthesis or processing and possess specific performance advantages.

[0005] With the improvement of environmental awareness, the use of environmentally friendly backfill materials such as industrial waste will gradually increase. However, industrial waste contains heavy metal ions, which may pollute the environment through long-term dissolution. Therefore, there is an urgent need to provide an environmentally friendly backfill material that can reuse industrial waste. Summary of the Invention

[0006] The object of the present invention is to provide a phosphogypsum-based nano-geopolymer backfill material, which has high utilization rate of phosphogypsum, low fluoride ion dissolution amount and high compressive strength.

[0007] Another object of the present invention is to provide a backfilling method for phosphogypsum-based nano-geopolymer backfill material, which compacts the backfill material through layered paving and vibration rolling, thereby improving the stability of the backfill material.

[0008] The present invention solves the technical problem by adopting the following technical solutions.

[0009] In one aspect, an embodiment of the present invention provides a phosphogypsum-based nano-geopolymer backfill material comprising the following raw materials, calculated by mass fraction:

[0010] Phosphogypsum 90%-97%; ground cement clinker 2%-9%; nano silicon dioxide 0.1%-0.3%; calcium chloride 0.5%-2%.

[0011] In some embodiments of the present invention, the following raw materials are included, calculated by mass: 95% phosphogypsum; 4% ground cement clinker; 0.2% nano-silicon dioxide; and 0.8% calcium chloride.

[0012] In some embodiments of the present invention, the following raw materials are included, calculated by mass: 97% phosphogypsum; 2% ground cement clinker; 0.3% nano-silicon dioxide; and 0.7% calcium chloride.

[0013] On the other hand, an embodiment of the present invention provides a backfilling method for a phosphogypsum-based nano-geopolymer backfill material, comprising the following steps:

[0014] S1, naturally air-drying the phosphogypsum to a moisture content of ≤5%, and then crushing and screening the phosphogypsum to a particle size of <2 mm;

[0015] S2, dry-mix the raw materials for 10-20 seconds, then add water and wet-mix for 40-60 seconds to obtain backfill material;

[0016] S3, transport the backfill material to the construction site under mixing conditions, and then backfill in layers;

[0017] S4, vibration compaction, natural curing.

[0018] In some embodiments of the present invention, in step S3, when backfilling in layers, the thickness of each layer is ≤30 cm.

[0019] In some embodiments of the present invention, in step S4, the pressure of the vibration rolling is ≥ 200 kN.

[0020] In some embodiments of the present invention, in step S2, the moisture content of the backfill material is 12-15%.

[0021] Compared with the prior art, the embodiments of the present invention have at least the following advantages or beneficial effects:

[0022] The backfill material provided by the present invention uses phosphogypsum as its primary raw material, combined with ground cement clinker, nano-silica, and calcium chloride. The ground cement clinker provides alkaline excitation, nano-SiO2 strengthens the geopolymer network, and calcium chloride synergistically solidifies fluoride ions. This backfill material combines high solid waste utilization with environmental friendliness. Its ion leaching concentration is ≤20 mg / L, its pH range is 6-9, and it is pollution-free. After application, the backfill material achieves a compressive strength of ≥1.5 MPa after 7 days and ≥3.0 MPa after 28 days. The phosphogypsum utilization rate is ≥91%, and its cost is 50% lower than that of traditional cement-based materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for use in the embodiments. It should be understood that the following drawings only illustrate certain embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other relevant drawings can be obtained based on these drawings without paying any creative work.

[0024] Figure 1 This is a physical picture of the sample prepared in Example 1 of the present invention. DETAILED DESCRIPTION

[0025] To make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention are described clearly and completely below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer are used. Where the manufacturer of the reagents or instruments is not specified, all are conventional products that can be purchased commercially.

[0026] It should be noted that, in the absence of conflict, the embodiments and features of the embodiments of the present invention can be combined with each other. The present invention will be described in detail below with reference to specific embodiments.

[0027] The embodiment of the present invention provides a phosphogypsum-based nano-geopolymer backfill material, which comprises the following raw materials by mass:

[0028] Phosphogypsum 90%-97%; ground cement clinker 2%-9%; nano silicon dioxide 0.1%-0.3%; calcium chloride 0.5%-2%.

[0029] More preferably, the raw materials are as follows, calculated by mass: 95% phosphogypsum; 4% ground cement clinker; 0.2% nano-silicon dioxide; and 0.8% calcium chloride.

[0030] More preferably, the raw materials are as follows, calculated by mass: 97% phosphogypsum; 2% ground cement clinker; 0.3% nano-silicon dioxide; and 0.7% calcium chloride.

[0031] In the embodiment of the present invention, the functions and effects of the various raw materials in the backfill material are as follows:

[0032] As a backfill material, phosphogypsum can form a high-strength fill, effectively managing open pits and underground goafs, and restoring the ecological environment in mining areas. Furthermore, using phosphogypsum for backfill can eliminate geological hazards, reduce remediation costs, and address the large land occupation caused by phosphogypsum storage, thereby achieving sustainable development in the phosphorus chemical industry. When used for underground backfill and open pit backfill, phosphogypsum can significantly eliminate safety hazards and improve mining safety.

[0033] Ground cement clinker refers to the powder obtained by finely grinding cement clinker through grinding equipment (such as ball mills and vertical mills). Ground cement clinker significantly increases its surface area, allowing it to react more fully with water, accelerating its hydration rate and improving the early strength and overall performance of the backfill material. Refined cement is the key to improving cement quality and reducing energy consumption, contributing to the overall quality of the backfill material.

[0034] Nanosilica, with its extremely small particle size and high specific surface area, can fill the microscopic pores in backfill materials, increasing their density and strength. The addition of nanosilica significantly improves the backfill's impermeability, weather resistance, and durability, extending its service life. By filling and stabilizing the backfill's internal structure, nanosilica helps reduce shrinkage and cracking, improving its stability.

[0035] Calcium chloride reacts with hydration products in cement to form insoluble compounds such as hydrated calcium chloroaluminate. This increases the solid content of the cement slurry, forming a strong skeleton and thus promoting the strength of the backfill material. Calcium chloride has significant early strength enhancement and accelerating setting, improving the early strength of the backfill material and accelerating construction progress. The addition of calcium chloride can also improve the construction properties of the backfill material, such as fluidity and workability, making construction more convenient and efficient.

[0036] An embodiment of the present invention provides a backfilling method for a phosphogypsum-based nano-geopolymer backfill material, comprising the following steps:

[0037] S1, naturally air-drying the phosphogypsum to a moisture content of ≤5%, and then crushing and screening the phosphogypsum to a particle size of <2 mm;

[0038] S2, dry-mixing the raw materials for 10-20 seconds, then adding water and wet-mixing for 40-60 seconds to obtain a backfill material; the backfill material has a moisture content of 12-15%, preferably 14%.

[0039] In step S3, the backfill material is transported to the construction site while being mixed, and then backfilled in layers. The thickness of each layer should be ≤ 30 cm. Layered paving controls the thickness of each layer, ensuring that each layer is fully compacted, reducing blind spots, and improving the overall density of the backfill.

[0040] S4, vibratory compaction, natural curing, vibratory compaction pressure ≥ 200kN. During construction, high-frequency vibration compaction of the filler material causes the particles to rearrange under the action of dynamic forces, reducing pore volume, increasing density, and enhancing bearing capacity. Vibration causes particles of different sizes to fill pores, and mixed-size particles form a more compact structure under vibration.

[0041] The features and performance of the present invention are further described in detail below with reference to the embodiments.

[0042] Example 1

[0043] Prepare the raw materials of the backfill material of this embodiment according to the following ratio:

[0044] Phosphogypsum 95%; ground cement clinker 4%; nano-silicon dioxide 0.2%; calcium chloride 0.8%;

[0045] Prepare backfill materials and apply as follows:

[0046] S1, naturally air-drying the phosphogypsum to a moisture content of ≤5%, and then crushing and screening the phosphogypsum to a particle size of <2 mm;

[0047] S2, dry-mix the raw materials for 10-20 seconds, then add water and wet-mix for 40-60 seconds to obtain backfill material; the moisture content is controlled at 14%;

[0048] S3, transport the backfill material to the construction site under mixing, and then backfill in layers; the thickness of each layer is 30cm;

[0049] S4, vibration compaction, vibration compaction pressure 300kN, natural curing for 7 days.

[0050] Example 2

[0051] Prepare the raw materials of the backfill material of this embodiment according to the following ratio:

[0052] Phosphogypsum 97%; ground cement clinker 2%; nano-silicon dioxide 0.3%; calcium chloride 0.7%;

[0053] Prepare backfill materials and apply as follows:

[0054] S1, naturally air-drying the phosphogypsum to a moisture content of ≤5%, and then crushing and screening the phosphogypsum to a particle size of <2 mm;

[0055] S2, dry-mix the raw materials for 20 seconds, then add water and wet-mix for 60 seconds to obtain the backfill material; the moisture content is controlled at 14%;

[0056] S3, transport the backfill material to the construction site under mixing, and then backfill in layers; the thickness of each layer is 30cm;

[0057] S4, vibration compaction, vibration compaction pressure 300kN, natural curing for 7 days.

[0058] Example 3

[0059] Prepare the raw materials of the backfill material of this embodiment according to the following ratio:

[0060] Phosphogypsum 97%; ground cement clinker 2%; nano-silicon dioxide 0.2%; calcium chloride 0.8%;

[0061] Prepare backfill materials and apply as follows:

[0062] S1, naturally air-drying the phosphogypsum to a moisture content of ≤5%, and then crushing and screening the phosphogypsum to a particle size of <2 mm;

[0063] S2, dry-mix the raw materials for 10 seconds, then add water and wet-mix for 40 seconds to obtain the backfill material; the moisture content is controlled at 14%;

[0064] S3, transport the backfill material to the construction site under mixing, and then backfill in layers; the thickness of each layer is 30cm;

[0065] S4, vibration compaction, vibration compaction pressure 400kN, natural curing for 7 days.

[0066] Example 4

[0067] Prepare the raw materials of the backfill material of this embodiment according to the following ratio:

[0068] Phosphogypsum 90%; ground cement clinker 8%; nano-silicon dioxide 0.2%; calcium chloride 1.8%;

[0069] Prepare backfill materials and apply as follows:

[0070] S1, naturally air-drying the phosphogypsum to a moisture content of ≤5%, and then crushing and screening the phosphogypsum to a particle size of <2 mm;

[0071] S2, dry-mix the raw materials for 15 seconds, then add water and wet-mix for 50 seconds to obtain the backfill material; the moisture content is controlled at 14%;

[0072] S3, transport the backfill material to the construction site under mixing, and then backfill in layers; the thickness of each layer is 30cm;

[0073] S4, vibration compaction, vibration compaction pressure 300kN, natural curing for 7 days.

[0074] Experimental example

[0075] Using the raw material ratios and construction methods of Examples 1-4, rolled samples were prepared in the laboratory. The strength, pH value, fluoride and phosphate content of the samples were tested on the 3rd, 7th, 14th and 28th days, respectively. The results are shown in Table 1.

[0076] Table 1 Backfill material properties of various embodiments

[0077]

[0078]

[0079] As shown in Table 1, the backfill materials provided in Examples 1-4 have a 7-day compressive strength of ≥1.5 MPa and a 28-day compressive strength of ≥3.0 MPa, meeting the requirements of GB / T50123-2019. Fluoride and phosphate dissolution is minimal, with a fluoride ion leaching concentration of ≤10 / L, meeting the requirements of HJ557-2010. The pH range is 6-9, indicating environmental friendliness.

[0080] In summary, the backfill material provided by the embodiments of the present invention uses phosphogypsum as its primary raw material, combined with ground cement clinker, nano-silica, and calcium chloride. The ground cement clinker provides alkaline excitation, nano-SiO2 enhances the geopolymer network, and calcium chloride synergistically solidifies fluoride ions. This backfill material combines high solid waste utilization with environmental friendliness. Its ion leaching concentration is ≤20 mg / L, its pH value is 6-9, and it is free of secondary pollution. After construction, the backfill material has a compressive strength of ≥1.5 MPa after 7 days and ≥3.0 MPa after 28 days. The phosphogypsum utilization rate is ≥91%, and the cost is 50% lower than that of traditional cement-based materials.

[0081] The embodiments described above are some, but not all, of the embodiments of the present invention. The detailed description of the embodiments of the present invention is not intended to limit the scope of the invention as claimed, but rather merely represents selected embodiments of the present invention. All other embodiments derived by persons of ordinary skill in the art based on the embodiments of the present invention without inventive effort are also within the scope of protection of the present invention.

Claims

1. A phosphogypsum-based nano-geopolymer backfill material, characterized in that: Calculated by mass fraction, including the following raw materials: Phosphogypsum 90%-97%; ground cement clinker 2%-9%; nano silicon dioxide 0.1%-0.3%; calcium chloride 0.5%-2%.

2. The phosphogypsum-based nano-geopolymer backfill material according to claim 1, characterized in that: Calculated by mass fraction, including the following raw materials: Phosphogypsum 95%; ground cement clinker 4%; nano-silicon dioxide 0.2%; calcium chloride 0.8%.

3. The phosphogypsum-based nano-geopolymer backfill material according to claim 1, characterized in that: Calculated by mass fraction, including the following raw materials: Phosphogypsum 97%; ground cement clinker 2%; nano-silicon dioxide 0.3%; calcium chloride 0.7%.

4. A backfilling method for the phosphogypsum-based nano-geopolymer backfill material according to any one of claims 1 to 3, characterized in that: The following steps are involved: S1, naturally air-drying the phosphogypsum to a moisture content of ≤5%, and then crushing and screening the phosphogypsum to a particle size of <2 mm; S2, dry-mix the raw materials for 10-20 seconds, then add water and wet-mix for 40-60 seconds to obtain backfill material; S3, transport the backfill material to the construction site under mixing conditions, and then backfill in layers; S4, vibration compaction, natural curing.

5. The backfilling method of the phosphogypsum-based nano-geopolymer backfill material according to claim 4, characterized in that: In step S3, when backfilling in layers, the thickness of each layer is ≤30 cm.

6. The backfilling method of the phosphogypsum-based nano-geopolymer backfill material according to claim 4, characterized in that: In step S4, the pressure of the vibration rolling is ≥200 kN.

7. The method for preparing the phosphogypsum-based nano-geopolymer backfill material according to claim 6, characterized in that: In step S2, the moisture content of the backfill material is 12-15%.

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