Lightweight high-strength self-compacting ardealite base fertilizer trough backfill material and preparation method and construction process thereof

Abstract

The invention discloses a light high-strength self-compacting ardealite-based backfill material as well as a preparation method and a construction process thereof, and belongs to the technical field of industrial solid waste recycling and constructional engineering. The light high-strength self-compacting ardealite-based backfill material is prepared from the following components in parts by mass: 60 to 70 parts of ardealite, 20 to 30 parts of a cementing material, 0.5 to 1 part of a polycarboxylate superplasticizer, 0.1 to 0.3 part of a hydroxypropyl methyl cellulose thickening agent, 0.01 to 0.05 part of an air entraining agent, 0.3 to 0.5 part of reinforced fibers, 3 to 8 parts of a composite curing agent, 15 to 25 parts of lightweight aggregate and 25 to 35 parts of water. The ardealite is used as a main raw material, the slump expansion degree is larger than or equal to 500 mm, the density is not higher than 1200 kg / m < 3 >, and the 28-day compressive strength is larger than or equal to 10 MPa. A double-stage stirring method is adopted in the preparation process, complex foundation trenches can be filled without vibration during construction, efficiency is remarkably improved, industrial solid waste is consumed, and the concrete is suitable for engineering such as building foundation trenches, underground pipe galleries and pipeline backfilling and has remarkable environmental protection and economic benefits.

Description

Technical Field

[0001] The present invention belongs to the technical fields of industrial solid waste resource utilization and construction engineering, and particularly relates to a lightweight and high-strength self-compacting phosphogypsum backfill material for foundation trenches, a preparation method thereof, and a construction process. Background Art

[0002] Phosphogypsum is an industrial by-product generated during the production of wet-process phosphoric acid. Approximately 4.5 - 5.5 tons of phosphogypsum are discharged for every 1 ton of phosphoric acid produced. According to the statistics of the International Fertilizer Industry Association (IFA), the global annual production of phosphogypsum has been continuously increasing since the 1990s and reached approximately 320 million tons in 2020, with the total historical stockpiles exceeding 7 billion tons. As the world's largest phosphate fertilizer producer, China has a particularly prominent phosphogypsum problem. In 2021, the newly generated amount reached 75 million tons, and the comprehensive utilization rate was only about 40%, far lower than the average level of 70% in developed countries. These mountainous phosphogypsum piles are usually disposed of by open-air stacking, occupying more than 20,000 hectares of land. There are more than 200 large phosphogypsum repositories distributed only along the Yangtze River Economic Belt, and leakage risks have occurred in some of the reservoir areas. The soluble phosphorus (0.5% - 2.5%), fluorides (0.3% - 1.8%), and trace heavy metals (such as arsenic, cadmium, lead, etc.) contained in phosphogypsum form acidic leachate (pH value can be as low as 2.5) after being washed by rainwater during long-term stacking, resulting in acidification of the surrounding soil, groundwater pollution, and damage to the ecosystem.

[0003] In the field of construction engineering, the backfill materials for building foundation trenches mainly use plain soil compaction or ordinary concrete. The former has the risk of settlement caused by uneven compaction degree, while the latter generates a large additional load on the side walls of underground structures due to its high material density (2200 - 2500 kg / m 3 ). To reduce the material density, the engineering community has successively tried lightweight solutions such as foamed concrete (dry density 600 - 1200 kg / m 3 ), EPS particle lightweight soil (dry density 300 - 800 kg / m 3 ), etc. However, these materials have obvious defects: Foamed concrete relies on aluminum powder or hydrogen peroxide for foaming, generating a large amount of CO2 emissions during the production process, and the 28-day compressive strength is generally lower than 2 MPa, making it difficult to meet the strength requirements for mechanical backfilling; Although EPS lightweight soil has excellent load reduction effects, the interfacial bonding between polystyrene particles and the cement matrix is weak, and problems such as particle floating and segregation are likely to occur during long-term use.

[0004] The particularity of the backfilling scenario of building backfill trenches poses higher requirements for the material properties. The typical width of a backfill trench is usually 0.5 - 1.2 m, with a narrow working space and fragile structural layers such as waterproof coiled materials often existing. The traditional construction method of vibration compaction is prone to causing structural damage. This requires that the backfill material must have both high fluidity (slump > 240 mm) and good self - compacting property. However, existing phosphogypsum - based materials have high viscosity and poor water retention, and often need to add excessive mixing water (water - solid ratio > 0.45) during construction, resulting in an increase in porosity and a decrease in strength after hardening. In addition, the backfill body in underground engineering needs to bear the surrounding soil pressure and groundwater erosion for a long time. Besides meeting the strength requirements, the material also needs to have low water absorption (water absorption rate < 15%) and impermeability (permeability coefficient < 1×10 -6 cm / s). How to achieve the coordinated optimization of phosphogypsum content, construction performance, and long - term durability while ensuring the material properties has become the key to breaking through the industry's technical barriers. Summary of the Invention

[0005] The main purpose of the present invention is to provide a lightweight, high - strength, self - compacting phosphogypsum - based backfill material for backfill trenches, its preparation method, and construction technology, to solve the problems of poor fluidity, the need for vibration compaction construction, and high resource consumption of existing materials, and to achieve multiple performance improvements such as self - compacting molding, lightweight, high - strength, and environmental protection and low - carbon.

[0006] To solve the above - mentioned technical problems, the technical solution provided by the present invention is: a lightweight, high - strength phosphogypsum - based backfill material for backfill trenches, which, by mass fraction, comprises the following components: 60 - 70 parts of phosphogypsum, 20 - 30 parts of cementitious material, 15 - 25 parts of lightweight aggregate, 0.5 - 1 part of polycarboxylate - based superplasticizer, 0.1 - 0.3 part of hydroxypropyl methylcellulose thickener, 0.01 - 0.05 part of air - entraining agent, 0.3 - 0.5 part of reinforcing fiber, 3 - 8 parts of composite curing agent, and 25 - 35 parts of water.

[0007] In a preferred embodiment, the phosphogypsum is pretreated to remove soluble fluorides, heavy metals, and organic matter, and has a specific surface area of 4000 - 4500 cm 2 / g.

[0008] In a further preferred embodiment, the pretreatment of the phosphogypsum includes the following steps: mixing the phosphogypsum with water at a solid-liquid ratio of 1:2 to 5, putting it into a stirring device, and stirring at a speed of 150 to 250 r / min for 20 to 40 min; after stirring, performing solid-liquid separation to obtain a phosphogypsum filter cake with preliminary defluorination and partial heavy metal removal, drying the filter cake at a temperature of 35 to 45 °C for 20 to 26 h; adding a sodium dodecylbenzenesulfonate solution accounting for 0.5% of its mass to the dried phosphogypsum and stirring at a speed of 250 to 350 r / min for 10 to 20 min; grinding and activating the phosphogypsum after washing and flotation treatment to obtain the product. During the washing process, most of the soluble fluorides in the phosphogypsum, such as NaF, CaF2, and some heavy metal ions, will dissolve in water and can be removed; while sodium dodecylbenzenesulfonate is an anionic surfactant that can selectively adsorb on the surface of organic matter, making the surface of the organic matter hydrophilic, and then removing the organic matter; during the ball milling process, the phosphogypsum particles are continuously broken and refined, which not only increases the specific surface area but also exposes the active sites on the particle surface, enhancing its gelling activity.

[0009] In a preferred embodiment, the cementitious material is composed of a sulfoaluminate cement and a slag micro-powder mixed in a mass ratio of 1:1 to 2.

[0010] In a preferred embodiment, the reinforcing fiber is a chopped basalt fiber with a length of 6 to 12 mm.

[0011] In a preferred embodiment, the composite curing agent is composed of quicklime and sodium silicate mixed in a mass ratio of 3:1.

[0012] In a preferred embodiment, the lightweight aggregate is composed of fly ash ceramsite with a particle size of 0.5 to 5 mm and expanded perlite mixed in a mass ratio of 2:1, and the density ≤ 800 kg / m 3 。 Another technical solution provided by the present invention is: the preparation method of the lightweight and high-strength self-compacting phosphogypsum base fertilizer tank backfilling material includes the following steps: S1. Weigh the phosphogypsum, 50% of the cementitious material, and the lightweight aggregate according to the ratio and stir at a speed of 100 to 150 r / min for 2 to 4 min; S2. Dissolve the polycarboxylate-based superplasticizer, hydroxypropyl methylcellulose thickener, and air-entraining agent in water to prepare an admixture solution, add it to step S1, increase the speed to 300 to 400 r / min, and stir for 3 to 5 min; S3. Dissolve the composite curing agent in the remaining water, add it to step S2, continue stirring for 0.5 - 1 min, then add the reinforcing fiber and the remaining 50% of the gelling material, and continue stirring until the slump flow of the slurry is 550 - 650 mm and there is no delamination or segregation, thus obtaining the mixture of the lightweight and high-strength self-compacting phosphogypsum base fertilizer tank backfill material.

[0013] Another technical solution provided by the present invention is: the construction process of the lightweight and high-strength self-compacting phosphogypsum base fertilizer tank backfill material, including the following steps: P1. Foundation trench pretreatment: Lay a 1 - 2 mm thick HDPE anti-seepage membrane on the base, with an overlap width ≥ 20 cm, and bond the joints with bentonite sealant to prevent groundwater erosion; Brush 1:10 neat cement slurry on the side walls of the foundation trench to enhance the bonding force between the lightweight and high-strength self-compacting phosphogypsum base fertilizer tank backfill material and the structural interface; P2. Layered construction: Directly pour the mixture of the lightweight and high-strength self-compacting phosphogypsum base fertilizer tank backfill material into the foundation trench, and let it flow and fill naturally. The single-layer pouring thickness does not exceed 50 cm, and the construction interval between adjacent layers is 4 - 8 h to avoid settlement of the upper layer caused by the unhardened lower layer; P3. Cover with a plastic film after the final setting of the last layer, and cure for 7 days in an environment with a humidity ≥ 90%, and then cure naturally until 28 days.

[0014] In the preferred solution, the pouring in step P2 guides the flow of the mixture of the lightweight and high-strength self-compacting phosphogypsum base fertilizer tank backfill material through a foundation trench slope or diversion groove with an angle ≥ 5°, ensuring filling without dead corners, especially suitable for narrow areas with a width < 50 cm. In the preferred solution, when the ambient temperature < 10 °C, the construction interval between adjacent layers in step P2 is 6 - 8 h.

[0015] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. The present invention reduces the water-binder ratio through polycarboxylate water reducer, maintains the cohesion with hydroxypropyl methylcellulose, and optimizes the particle lubrication with air-entraining agent, achieving a slump flow ≥ 500 mm, and can flow and fill complex foundation trenches naturally without vibration, especially suitable for narrow areas, significantly simplifying the construction process and reducing the labor intensity.

[0016] 2. The lightweight and high-strength self-compacting phosphogypsum base fertilizer tank backfill material provided by the present invention has a material density not higher than 1200 kg / m 3 by introducing lightweight aggregates, meeting the lightweight requirements; at the same time, the sulphoaluminate cement, slag powder and composite curing agent enhance the gelling activity, the chopped basalt fiber enhances the toughness, and the secondary slurry coating method is adopted to achieve the combination of light weight and high strength.

[0017] 3. The leaching solution of the lightweight, high-strength and self-compacting phosphogypsum base fertilizer tank backfill material provided by the present invention has a fluoride ion content of ≤ 10 mg / L, an internal irradiation index of radioactive substances of ≤ 1.0, and a phosphogypsum content of ≥ 60%, which can consume industrial solid waste and reduce the consumption of natural sand and gravel at the same time. Detailed implementation mode

[0018] The technical solution of the present invention will be further described and illustrated below through examples. All raw materials used in the examples can be purchased commercially or prepared by conventional methods.

[0019] The phosphogypsum used in the following examples is pretreated to remove soluble fluorides, heavy metals and organic matter, and its specific surface area is 4000 - 4500 cm 2 / g; the pretreatment of the phosphogypsum includes the following steps: mixing the phosphogypsum and water at a solid-liquid ratio of 1:2 - 5, putting it into a stirring device, and stirring at a speed of 200 r / min for 30 min; after stirring, separating the solid and liquid to obtain a phosphogypsum filter cake with preliminary defluorination and partial heavy metal removal, drying the filter cake at a temperature of 40 °C for 23 h; adding a sodium dodecylbenzenesulfonate solution accounting for 0.5% of its mass to the dried phosphogypsum and stirring at a speed of 300 r / min for 15 min; grinding and activating the phosphogypsum after washing and flotation treatment to obtain the product. The lightweight aggregate used is composed of fly ash ceramsite with a particle size of 0.5 - 5 mm and expanded perlite in a mass ratio of 2:1, and its density is ≤ 800 kg / m 3 . The composite curing agent used is composed of quicklime and sodium silicate in a mass ratio of 3:1.

[0020] Example 1 A lightweight, high-strength phosphogypsum base fertilizer tank backfill material, by mass, includes the following components: 65 parts of phosphogypsum, 25 parts of a cementitious material (composed of sulfoaluminate cement and slag micro-powder in a mass ratio of 1:1), 20 parts of lightweight aggregate, 0.8 part of polycarboxylate superplasticizer, 0.2 part of hydroxypropyl methylcellulose thickener, 0.03 part of alkylbenzene sulfonate air-entraining agent, 0.4 part of short-cut basalt fiber with a length of 9 mm, 5 parts of composite curing agent, and 30 parts of water.

[0021] The preparation method of the lightweight, high-strength and self-compacting phosphogypsum base fertilizer tank backfill material includes the following steps: S1. Weigh the phosphogypsum, 50% of the cementitious material and the lightweight aggregate according to the ratio and stir at a speed of 120 r / min for 3 min; S2. Dissolve the polycarboxylate superplasticizer, hydroxypropyl methylcellulose thickener and air-entraining agent in water to make an admixture solution, add it to step S1, increase the speed to 350 r / min, and stir for 4 min; S3. Dissolve the composite curing agent in the remaining water, add it to step S2, continue stirring for 1 min, then add the reinforcing fiber and the remaining 50% of the cementitious material, and continue stirring until the slump flow of the slurry reaches 600 mm and there is no delamination or segregation, thus obtaining the mixture of the lightweight, high-strength and self-compacting phosphogypsum base fertilizer tank backfill material.

[0022] The construction technology of the lightweight, high-strength and self-compacting phosphogypsum base fertilizer tank backfill material includes the following steps: P1. Foundation trench pretreatment: Lay a 1-mm-thick HDPE anti-seepage membrane on the base, with a lap width of 20 cm, and bond the joints with bentonite sealant to prevent groundwater erosion; Brush the side walls of the foundation trench with neat cement slurry of 1:10 to enhance the bonding force between the lightweight, high-strength and self-compacting phosphogypsum base fertilizer tank backfill material and the structural interface. P2. Layered construction: Pour the mixture of the lightweight, high-strength and self-compacting phosphogypsum base fertilizer tank backfill material directly into the foundation trench along the slope of the foundation trench (with an angle of 5°), and let it fill by natural flow. The single-layer pouring thickness is 50 cm, and the construction interval between adjacent layers is 5 h. P3. Cover with a plastic film after the final layer starts to set, and cure for 7 days in an environment with a humidity ≥ 90%, and then cure naturally until 28 days.

[0023] After testing, the density of the lightweight, high-strength and self-compacting phosphogypsum base fertilizer tank backfill material is 880 kg / m 3 , the 7-day compressive strength is 3.5 MPa, the 28-day compressive strength is 5.5 MPa, the water absorption rate is 18%, and the fluoride ion concentration in the leachate is 8 mg / L.

[0024] Example 2 A lightweight, high-strength phosphogypsum base fertilizer tank backfill material, by mass, includes the following components: 60 parts of phosphogypsum, 30 parts of cementitious material (composed of sulfoaluminate cement and slag micro-powder mixed in a mass ratio of 1:2), 15 parts of lightweight aggregate, 1 part of polycarboxylate-based superplasticizer, 0.1 part of hydroxypropyl methylcellulose thickener, 0.05 part of alkylbenzene sulfonate air-entraining agent, 0.3 part of chopped basalt fiber with a length of 6 mm, 8 parts of composite curing agent, and 25 parts of water.

[0025] The preparation method of the lightweight, high-strength and self-compacting phosphogypsum base fertilizer tank backfill material includes the following steps: S1. Weigh phosphogypsum, 50% of the cementitious material and the lightweight aggregate according to the ratio, and stir at a speed of 120 r / min for 3 min. S2. Dissolve the polycarboxylate-based superplasticizer, hydroxypropyl methylcellulose thickener and air-entraining agent in water to make an admixture solution, add it to step S1, increase the speed to 350 r / min, and stir for 4 min. S3. Dissolve the composite curing agent in the remaining water, add it to step S2, continue stirring for 1 min, then add the reinforcing fiber and the remaining 50% of the gelling material, and continue stirring until the slump flow of the slurry reaches 600 mm and there is no delamination or segregation, thus obtaining the mixture of the lightweight and high-strength self-compacting phosphogypsum base fertilizer tank backfilling material.

[0026] The construction process of the lightweight and high-strength self-compacting phosphogypsum base fertilizer tank backfilling material includes the following steps: P1. Foundation trench pretreatment: Lay a 1-mm-thick HDPE anti-seepage membrane on the base, with a lap width of 20 cm, and bond the joints with bentonite sealant to prevent groundwater erosion; coat the side walls of the foundation trench with neat cement slurry of 1:10 to enhance the bonding force between the lightweight and high-strength self-compacting phosphogypsum base fertilizer tank backfilling material and the structural interface. P2. Layered construction: Guide and pour the mixture of the lightweight and high-strength self-compacting phosphogypsum base fertilizer tank backfilling material into the foundation trench along the diversion trough, and fill it by natural flow. The single-layer pouring thickness is 50 cm, and the construction interval between adjacent layers is 5 h. P3. Cover with a plastic film after the final layer starts to set, and cure for 7 days in an environment with a humidity ≥ 90%, and then cure naturally until 28 days.

[0027] After testing, the density of the lightweight and high-strength self-compacting phosphogypsum base fertilizer tank backfilling material is 890 kg / m 3 , the 7-day compressive strength is 4 MPa, the 28-day compressive strength is 6 MPa, the water absorption rate is 16%, and the fluoride ion concentration in the leachate is 7 mg / L.

[0028] Example 3 A lightweight and high-strength phosphogypsum base fertilizer tank backfilling material, by mass, includes the following components: 70 parts of phosphogypsum, 20 parts of gelling material (composed of sulfoaluminate cement and slag micro-powder mixed in a mass ratio of 1:1.5), 25 parts of lightweight aggregate, 0.5 part of polycarboxylate-based superplasticizer, 0.3 part of hydroxypropyl methylcellulose thickener, 0.01 part of alkylbenzene sulfonate air-entraining agent, 0.5 part of chopped basalt fiber with a length of 12 mm, 3 parts of composite curing agent, and 35 parts of water.

[0029] The preparation method of the lightweight and high-strength self-compacting phosphogypsum base fertilizer tank backfilling material includes the following steps: S1. Weigh phosphogypsum, 50% of the gelling material, and the lightweight aggregate according to the ratio and stir at a speed of 120 r / min for 3 min. S2. Dissolve the polycarboxylate-based superplasticizer, hydroxypropyl methylcellulose thickener, and air-entraining agent in water to make an admixture solution, add it to step S1, increase the speed to 350 r / min, and stir for 4 min. S3. Dissolve the composite curing agent in the remaining water, add it to step S2, continue stirring for 1 min, then add the reinforcing fiber and the remaining 50% of the gelling material, and continue stirring until the slump flow of the slurry reaches 600 mm and there is no delamination or segregation to obtain the mixture of the lightweight and high-strength self-compacting phosphogypsum base fertilizer tank backfill material.

[0030] The construction process of the lightweight and high-strength self-compacting phosphogypsum base fertilizer tank backfill material includes the following steps: P1. Foundation trench pretreatment: Lay a 1-mm-thick HDPE anti-seepage membrane on the base, with a lap width of 20 cm, and bond the joints with bentonite sealant to prevent groundwater erosion; brush 1:10 neat cement slurry on the side walls of the foundation trench to enhance the bonding force between the lightweight and high-strength self-compacting phosphogypsum base fertilizer tank backfill material and the structural interface. P2. Layered construction: Guide and pour the mixture of the lightweight and high-strength self-compacting phosphogypsum base fertilizer tank backfill material into the foundation trench along the diversion groove, and let it fill naturally by gravity. The single-layer pouring thickness is 50 cm, and the construction interval between adjacent layers is 5 h. P3. After the final layer starts to set, cover it with a plastic film and cure it for 7 days in an environment with a humidity ≥ 90%, and then cure it naturally until 28 days.

[0031] After testing, the density of the lightweight and high-strength self-compacting phosphogypsum base fertilizer tank backfill material is 820 kg / m 3 , the 7-day compressive strength is 3 MPa, the 28-day compressive strength is 5 MPa, the water absorption rate is 20%, and the fluoride ion concentration in the leachate is 9 mg / L.

[0032] Example 4 A lightweight and high-strength phosphogypsum base fertilizer tank backfill material, by mass, includes the following components: 63 parts of phosphogypsum, 27 parts of gelling material (composed of sulfoaluminate cement and slag micro-powder mixed in a mass ratio of 1:1), 18 parts of lightweight aggregate, 0.7 part of polycarboxylate-based superplasticizer, 0.25 part of hydroxypropyl methylcellulose thickener, 0.02 part of alkylbenzene sulfonate air-entraining agent, 0.45 part of chopped basalt fiber with a length of 8 mm, 6 parts of composite curing agent, and 32 parts of water.

[0033] The preparation method of the lightweight and high-strength self-compacting phosphogypsum base fertilizer tank backfill material includes the following steps: S1. Weigh phosphogypsum, 50% of the gelling material, and the lightweight aggregate according to the ratio and stir at a speed of 120 r / min for 3 min. S2. Dissolve the polycarboxylate-based superplasticizer, hydroxypropyl methylcellulose thickener, and air-entraining agent in water to make an admixture solution, add it to step S1, increase the speed to 350 r / min, and stir for 4 min. S3. Dissolve the composite curing agent in the remaining water, add it to step S2, continue stirring for 1 min, then add the reinforcing fiber and the remaining 50% of the cementitious material, and continue stirring until the slump flow of the slurry reaches 600 mm and there is no delamination or segregation to obtain the mixture of the lightweight and high-strength self-compacting phosphogypsum base fertilizer tank backfilling material.

[0034] The construction process of the lightweight and high-strength self-compacting phosphogypsum base fertilizer tank backfilling material includes the following steps: P1. Foundation trench pretreatment: Lay a 1-mm-thick HDPE anti-seepage membrane on the base, with a lap width of 20 cm, and bond the joints with bentonite sealant to prevent groundwater erosion; coat the side walls of the foundation trench with 1:10 neat cement slurry to enhance the bonding force between the lightweight and high-strength self-compacting phosphogypsum base fertilizer tank backfilling material and the structural interface; P2. Layered construction: Guide and pour the mixture of the lightweight and high-strength self-compacting phosphogypsum base fertilizer tank backfilling material into the foundation trench along the diversion trough, and let it fill by natural flow. The single-layer pouring thickness is 50 cm, and the construction interval between adjacent layers is 5 h; P3. After the final layer starts to set, cover it with a plastic film and cure it for 7 days in an environment with a humidity ≥ 90%, and then cure it naturally until 28 days.

[0035] After testing, the density of the lightweight and high-strength self-compacting phosphogypsum base fertilizer tank backfilling material is 850 kg / m 3 , the 7-day compressive strength is 3.2 MPa, the 28-day compressive strength is 5.2 MPa, the water absorption rate is 17%, and the fluoride ion concentration in the leachate is 6 mg / L.

[0036] It should be understood that the above embodiments are only used to illustrate the content of the present invention and not to limit the protection scope of the present invention. In addition, it should be understood that after reading the content taught by the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent forms also fall within the scope defined by the appended claims of this application.

Claims

1. A lightweight and high-strength self-compacting backfill material for phosphogypsum base fertilizer tanks, characterized in that, By mass parts, it includes the following components: 60 - 70 parts of phosphogypsum, 20 - 30 parts of cementitious material, 15 - 25 parts of lightweight aggregate, 0.5 - 1 part of polycarboxylate superplasticizer, 0.1 - 0.3 part of hydroxypropyl methylcellulose thickener, 0.01 - 0.05 part of air-entraining agent, 0.3 - 0.5 part of reinforcing fiber, 3 - 8 parts of composite curing agent, and 25 - 35 parts of water.

2. The light-weight and high-strength self-compacting phosphogypsum base fertilizer tank backfill material according to claim 1, wherein The phosphogypsum described above is pretreated to remove soluble fluorides, heavy metals and organic matter, and has a specific surface area of 4000 - 4500 cm 2 / g.

3. The lightweight and high-strength self-compacting phosphogypsum base fertilizer tank backfill material according to claim 2, wherein The pretreatment of the phosphogypsum described above includes the following steps: Mix the phosphogypsum and water at a solid-liquid ratio of 1:2 - 5, put it into a stirring device, and stir at a speed of 150 - 250 r / min for 20 - 40 min; after stirring, perform solid-liquid separation to obtain a phosphogypsum filter cake with preliminary defluorination and partial heavy metal removal, place the filter cake at a temperature of 35 - 45 °C and dry it for 20 - 26 h; add a sodium dodecylbenzenesulfonate solution accounting for 0.5% of its mass to the dried phosphogypsum and stir at a speed of 250 - 350 r / min for 10 - 20 min; perform grinding activation on the phosphogypsum after washing and flotation treatment to obtain the product.

4. The lightweight and high-strength self-compacting phosphogypsum base fertilizer tank backfill material according to claim 1, characterized in that, The cementitious material described above is composed of a sulfoaluminate cement and a slag micro-powder mixed in a mass ratio of 1:1 - 2.

5. The lightweight and high-strength self-compacting phosphogypsum base fertilizer tank backfill material according to claim 1, wherein, The reinforcing fiber described above is a chopped basalt fiber with a length of 6 - 12 mm.

6. The light-weight and high-strength self-compacting backfill material for phosphogypsum base fertilizer tank according to claim 1, wherein, The composite curing agent described above is composed of quicklime and sodium silicate mixed in a mass ratio of 3:

1.

7. The light-weight and high-strength self-compacting phosphogypsum base fertilizer tank backfill material according to claim 1, characterized in that, The light aggregate described above is composed of fly ash ceramsite with a particle size of 0.5 - 5 mm and expanded perlite mixed in a mass ratio of 2:1, and the density ≤ 800 kg / m 3 .

8. A preparation method of the lightweight and high-strength self-compacting phosphogypsum base fertilizer tank backfill material as described in any one of claims 1 to 7, characterized in that, It includes the following steps: S1. Weigh phosphogypsum, 50% of the cementitious material, and lightweight aggregate according to the ratio and stir at a speed of 100 - 150 r / min for 2 - 4 min; S2. Dissolve the polycarboxylate superplasticizer, hydroxypropyl methylcellulose thickener, and air-entraining agent in water to make an admixture solution, add it to step S1, increase the speed to 300 - 400 r / min, and stir for 3 - 5 min; S3. Dissolve the composite curing agent in the remaining water, add it to step S2, continue to stir for 0.5 - 1 min, then add the reinforcing fiber and the remaining 50% of the cementitious material, and continue to stir until the slump flow of the slurry is 550 - 650 mm and there is no delamination or segregation to obtain the mixture of the lightweight and high-strength self-compacting phosphogypsum base fertilizer tank backfill material.

9. Construction process of a lightweight and high-strength self-compacting backfill material for phosphogypsum base fertilizer tank, characterized in that, Adopt the lightweight and high-strength self-compacting phosphogypsum base fertilizer tank backfill material as described in any one of claims 1 - 7. The construction process of the lightweight and high-strength self-compacting phosphogypsum base fertilizer tank backfill material includes the following steps: P1. Foundation trench pretreatment: Lay a 1 - 2 mm thick HDPE anti-seepage membrane on the base, with an overlap width ≥ 20 cm, and bond the joints with bentonite sealant to prevent groundwater erosion; brush a 1:10 neat cement slurry on the side walls of the foundation trench to enhance the bonding force between the lightweight and high-strength self-compacting phosphogypsum base fertilizer tank backfill material and the structural interface; P2. Layered construction: Directly pour the mixture of the lightweight and high-strength self-compacting phosphogypsum base fertilizer tank backfill material into the foundation trench, and fill it by natural flow. The single-layer pouring thickness does not exceed 50 cm, and the construction interval between adjacent layers is 4 - 8 h to avoid settlement of the upper layer caused by the unhardened lower layer; P3. Cover with a plastic film after the final setting of the last layer, cure for 7 days in an environment with a humidity ≥ 90%, and then cure naturally until 28 days.

10. The construction process of the lightweight and high-strength self-compacting phosphogypsum base fertilizer tank backfill material according to claim 9, characterized in that, The pouring described in step P2 guides the flow of the mixture of the light-weight, high-strength and self-compacting phosphogypsum base fertilizer trench backfill material through a foundation trench slope or a diversion trench with an angle ≥ 5°; when the ambient temperature < 10 °C, the construction interval between adjacent layers described in step P2 is 6 - 8 h.