A low-alkalinity, early-strength phosphogypsum filling and solidifying material and its preparation method

Abstract

The present invention belongs to the technical field of new building materials, and provides a low-alkalinity and early-strength phosphogypsum filling and solidifying material and a preparation method thereof. The raw material formula of the low-alkalinity and early-strength phosphogypsum filling and solidifying material includes phosphogypsum, a curing agent and water. Among them, the curing agent includes silica fume, limestone powder, ultra-fine granulated blast furnace slag powder, metakaolin, calcium aluminate powder, Portland cement clinker powder, a suspension stabilizer, and hydroxypropyl methyl cellulose ether. The present invention can solve the problems of setting retardation, low early strength, and high alkalinity of ordinary cement-based phosphogypsum filling materials, and meet the technical requirements of phosphogypsum cemented filling technology.

Description

Technical Field

[0001] The present invention belongs to the technical field of new building materials, and more specifically, relates to a low-alkalinity, early-strength phosphogypsum filling and solidifying material and a preparation method thereof. Background Art

[0002] The phosphogypsum cemented filling technology is an effective way to harmlessly utilize phosphogypsum proposed in recent years. The phosphogypsum filling technology uses phosphogypsum as the main raw material, and uses solidifying materials (such as portland cement, fly ash, etc.) and other additives (such as activators, water reducers, etc.). After the above materials are mixed with water to form a homogeneous mixed slurry, it is backfilled into the mined-out area of the underground mine. As the hydration reaction proceeds, the filling body gradually forms strength. After solidification and hardening, it supports the roof of the underground mined-out area, prevents surface subsidence, and improves the recovery rate of phosphate rock. It not only realizes the safe and efficient recovery of resources, but also effectively alleviates the environmental problems caused by the stacking of surface solid waste.

[0003] However, conventional solidifying materials such as portland cement are difficult to meet the requirements of the phosphogypsum cemented filling technology:

[0004] ① The setting retardation phenomenon of the phosphogypsum filling body with conventional portland cement as the solidifying material is serious. In the case of a large amount of phosphogypsum, the initial setting time of the filling slurry is usually above 48h.

[0005] ② The overall alkalinity of the phosphogypsum filling body with conventional portland cement as the solidifying material is high, and the pH of its leachate is usually about 12.5. After the hydroxide ions in the filling body dissolve out, they will affect the pH value of the surrounding groundwater.

[0006] ③ The bleeding rate of the phosphogypsum with conventional portland cement as the solidifying material is high, and pollutants such as soluble fluorine, phosphorus, and heavy metals in the gypsum filling body affect the water and soil environment through bleeding, etc.

[0007] To solve the above problems of phosphogypsum cemented filling, it is urgent to develop a new type of phosphogypsum filling and solidifying material. Summary of the Invention

[0008] One of the purposes of the present invention is to overcome the above-mentioned disadvantages of the existing technology and provide a low-alkalinity, early-strength phosphogypsum filling and solidifying material.

[0009] One aspect of the present invention provides a low-alkalinity and early-strength phosphogypsum filling and solidifying material. The raw material formula of the low-alkalinity and early-strength phosphogypsum filling and solidifying material includes phosphogypsum, a curing agent, and water. The phosphogypsum is dihydrate phosphogypsum, and the phosphogypsum is 65-75 parts by dry basis, the curing agent is 25-35 parts, and the water accounts for 27%-34% by weight of the sum of the phosphogypsum and the curing agent. Among them, the curing agent includes silica fume, limestone powder, superfine granulated blast furnace slag powder, metakaolin, aluminate cement, Portland cement clinker powder, suspension stabilizer, and hydroxypropyl methyl cellulose ether. By mass percentage, the content of aluminate cement is 6%-8%, and the content of Portland cement clinker powder is 28%-32%. The aluminate cement includes calcium aluminate powder, and the calcium aluminate powder includes monocalcium aluminate and / or monocalcium dialuminate. The calcium carbonate content of the limestone powder is ≥80%.

[0010] In the embodiment, the specific surface area of the calcium aluminate powder is ≥400 m 2 / kg, and Al2O3≥50%. In the embodiment, the curing agent can be composed of the following components by mass percentage: silica fume 4%-6%, limestone powder 9%-11%, superfine granulated blast furnace slag powder 36%-41%, metakaolin 8%-12%, calcium aluminate powder 6%-8%, Portland cement clinker powder 28%-32%, suspension stabilizer 0.3‰-3‰, and hydroxypropyl methyl cellulose ether 0.5‰-1.5‰.

[0011] In the embodiment, the silica fume can be semi-densified or fully densified silica fume, the silica dioxide content is ≥95%, the activity index is ≥110%, and the water demand ratio is ≤125%; the fineness of the limestone powder is 1000 mesh and above; the specific surface area of the superfine granulated blast furnace slag powder is ≥600 m 2 / kg, and the 28d activity index is ≥105%; the Al2O3 in the metakaolin powder is ≥35%, the specific surface area is ≥600 m 2 / kg, and the 28d activity index is ≥105%; the tricalcium silicate content in the Portland cement clinker powder is ≥55%, and the specific surface area is ≥350 m 2 / kg; the particle size of the phosphogypsum is ≤4.75 mm.

[0012] In the embodiment, the phosphogypsum can account for ≥65% of the dry material mass. The dry material can include phosphogypsum and a curing agent. The initial setting time of the phosphogypsum filling and solidifying material is ≤8 h, the 3d compressive strength is ≥1 MPa, the 7d compressive strength is ≥3 MPa, the 28d strength is ≥5 MPa, the spread of the filling slurry is ≥800 mm, the bleeding rate of the slurry is ≤0.5%, and the pH value of the leaching solution of the 28d filling body is ≤10.

[0013] According to another aspect of the present invention, a preparation method of a low-alkalinity and early-strength phosphogypsum filling and solidifying material is provided. The preparation method includes: uniformly mixing silica fume, limestone powder, superfine granulated blast furnace slag powder, metakaolin, aluminate cement, Portland cement clinker powder, suspension stabilizer, and hydroxypropyl methyl cellulose ether to form a solidifying agent powder. The aluminate cement includes calcium aluminate powder, and the calcium aluminate powder includes calcium monoaluminate and / or calcium hemialuminate. The calcium carbonate content of the limestone powder is ≥80%. By mass percentage, the content of the aluminate cement is 6-8%, and the content of the Portland cement clinker powder is 28-32%. Uniformly mixing water and the solidifying agent powder to obtain a solidifying agent slurry; and adding phosphogypsum to the solidifying agent slurry until the slurry is uniformly mixed to obtain a phosphogypsum filling slurry. Wherein, the phosphogypsum is dihydrate phosphogypsum. The phosphogypsum is 65-75 parts by dry basis, the solidifying agent is 25-35 parts, and the water accounts for 27%-34% of the sum of the phosphogypsum and the solidifying agent by weight ratio.

[0014] In the embodiment, the specific surface area of the calcium aluminate powder is ≥400m 2 / kg, and Al2O3 ≥50%.

[0015] In the embodiment, in the step of forming the solidifying agent powder, by mass percentage, silica fume is 4-6%, limestone powder is 9-11%, superfine granulated blast furnace slag powder is 36-41%, metakaolin is 8-12%, calcium aluminate powder is 6-8%, Portland cement clinker powder is 28-32%, suspension stabilizer is 0.3-3‰, and hydroxypropyl methyl cellulose ether is 0.5-1.5‰.

[0016] In the embodiment, the silica fume can be semi-densified or fully densified silica fume, the silicon dioxide content is ≥95%, the activity index is ≥110%, and the water demand ratio is ≤125%; the fineness of the limestone powder is 1000 mesh and above; the specific surface area of the superfine granulated blast furnace slag powder is ≥600m 2 / kg, and the 28d activity index is ≥105%; the metakaolin powder can be a powder material mainly composed of amorphous aluminosilicate obtained by calcining kaolin minerals at 600-900°C. The Al2O3 in the metakaolin powder is ≥35%, the specific surface area is ≥600m 2 / kg, and the 28d activity index is ≥105%; the tricalcium silicate content of the Portland cement clinker powder is ≥55%, and the specific surface area is ≥350m 2 / kg; the particle size of the phosphogypsum is ≤4.75mm.

[0017] In the embodiment, the phosphogypsum may account for ≥65% of the dry material mass. The dry material may include phosphogypsum and a curing agent. The initial setting time of the filling of the phosphogypsum filling and curing material is ≤8 h, the 3-day compressive strength is ≥1 MPa, the 7-day compressive strength is ≥3 MPa, the 28-day strength is ≥5 MPa, the spread of the filling slurry is ≥800 mm, the bleeding rate of the slurry is ≤0.5%, and the pH value of the leachate of the 28-day filling body is ≤10.

[0018] Compared with the prior art, the beneficial effects of the present invention are as follows: The present invention can solve the problems of retarding setting, low early strength, and high alkalinity in the filling of ordinary cement-based phosphogypsum. It can achieve that when the filling slurry has a large dosage of phosphogypsum (phosphogypsum accounts for ≥65% of the dry material mass), the initial setting time of the filling is ≤8 h, the 3-day compressive strength is ≥1 MPa, the 7-day compressive strength is ≥3 MPa, the 28-day strength is ≥5 MPa, the spread of the filling slurry is ≥800 mm, the bleeding rate of the slurry is ≤0.5%, and the pH of the leachate of the 28-day filling body is ≤10, meeting the technical requirements of phosphogypsum cemented filling technology. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] The drawings illustrate exemplary embodiments of the inventive concept and, together with the description, are used to explain the principles of the inventive concept. The drawings are included to provide a further understanding of the inventive concept, and the drawings are incorporated into and form a part of this specification.

[0020] Figure 1 Shows the material test results of the phosphogypsum filling and curing materials according to the examples and comparative examples of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0021] In the ranges disclosed herein, the endpoints and any values are not limited to the exact ranges or values. These ranges or values should be understood to include values close to these ranges or values. For numerical ranges, between the endpoint values of each range, between the endpoint values of each range and individual point values, and between individual point values, they can be combined with each other to obtain one or more new numerical ranges, and these numerical ranges should be regarded as specifically disclosed herein.

[0022] Reasons for using the phosphogypsum filling curing agent: The main component of phosphogypsum is calcium sulfate dihydrate (CaSO4·2H2O), which does not have hydraulicity. The filling slurry formed after mixing with water has no strength, and a curing material needs to be added to cement the phosphogypsum so that the filling slurry forms strength.

[0023] Problems of pure silicate cement as a filling and solidifying agent: The conventional solidifying agent, microsilicate cement, is a representative hydraulic material. However, when using a single cementitious material of silicate cement to solidify a large amount of phosphogypsum, the initial setting time of the filling slurry is usually more than 48 hours. This is because the gypsum component and soluble phosphorus in phosphogypsum react with silicate cement, hindering and delaying the hydration reaction process of silicate cement, resulting in a significant delay in the setting time and a significant reduction in early strength. At the same time, the hydration products of this system contain a large amount of Ca(OH)2, leading to a high pH value, making it difficult to meet the performance application requirements such as setting time, early strength, and pH value.

[0024] Problems of "portland cement + granulated blast furnace slag powder" or "portland cement + lime + granulated blast furnace slag powder" as filling and solidifying agents: Granulated blast furnace slag powder reacts with phosphogypsum and the hydration products Ca(OH)2 of cement or lime to form hydration products such as ettringite and C-(A)-S-H gel. This system can achieve a certain degree of improvement in the mechanical properties of the hardened cementitious body. However, this system still has not solved the problems of long setting time, high alkalinity, and low early strength caused by the hindrance of phosphogypsum to the hydration reaction of the composite cementitious material.

[0025] To solve the above problems, the technical concept of the present invention is:

[0026] On the one hand, the present invention provides a low-alkalinity and early-strength phosphogypsum filling and solidifying material. In an exemplary embodiment, the raw material formula of the low-alkalinity and early-strength phosphogypsum filling and solidifying material includes phosphogypsum, a solidifying agent, and water. Among them, the solidifying agent includes silica fume, limestone powder, ultrafine granulated blast furnace slag powder, metakaolin, calcium aluminate powder, portland cement clinker powder, a suspension stabilizer, and hydroxypropyl methylcellulose ether.

[0027] The exemplary embodiment of the present invention can solve the technical problems of phosphogypsum retarding, low early strength, and high alkalinity to meet the technical requirements of phosphogypsum cemented filling technology.

[0028] The mechanism of the exemplary embodiment of the present invention to solve the retarding and low early strength of conventional phosphogypsum:

[0029] (1) Based on the characteristics of sufficient phosphogypsum and water in the phosphogypsum filling slurry, the components of "portland cement, aluminate cement, granulated blast furnace slag powder, and metakaolin" in the solidifying agent react with the gypsum phase under sufficient water conditions to achieve a cementing and solidifying effect.

[0030] The C3A component in portland cement forms calcium aluminate hydrate (C3AH6) during hydration, which continues to react with gypsum and water to form a high-hydration reaction product - ettringite (C6AS3H 32), the generated ettringite usually covers the surface of cement particles, hindering the further reaction of Portland cement particles. At the same time, the soluble phosphorus in phosphogypsum will also react with Portland cement to form insoluble substances, hindering the reaction and resulting in serious setting retardation of the phosphogypsum filling body. In this invention, aluminate cement is introduced. Aluminate cement is a cement mainly composed of calcium aluminate, and its main components are calcium monoaluminate (CA) and calcium dialuminate (C2A). It will also react with gypsum in this system to produce ettringite to cover the surface. However, there is sufficient aluminum phase in aluminate cement particles, and some aluminate ions dissolve into the water through osmosis, dissolution, etc. and continue to react with the gypsum phase to form hydrated products that interweave and build between various particles, greatly shortening the initial setting time of the system and ensuring its early strength. At the same time, granulated blast furnace slag powder and metakaolin in the curing agent dissolve out aluminosilicate ions, silicate ions, etc. under the action of calcium hydroxide in the cement hydrated products and react with the gypsum phase to produce hydrated products C-(A)-S-H gel and ettringite, making the phosphogypsum filling body continuously compact and increasing the later strength.

[0031] (2) "Aluminate cement, metakaolin, and limestone" in the curing agent can react with "gypsum and Portland cement hydrated products" in the system to achieve a cementing and curing effect.

[0032] In the exemplary embodiment of the present invention, calcium aluminate reacts with ultrafine limestone powder (mainly composed of calcium carbonate) and calcium hydroxide to form calcium carboaluminate hydrate. This reaction mainly occurs in the early stage of hydration with a relatively fast hydration rate, and can regulate the early setting time and early strength of the phosphogypsum filling slurry. Amorphous aluminosilicate (AlSi2O) in metakaolin dissolves out under alkaline conditions and can react with calcium hydroxide, gypsum, and limestone powder (calcium carbonate) to form C-(A)-S-H, calcium carboaluminate hydrate, and ettringite to form strength. The formed calcium carboaluminate hydrate is relatively dense and provides strength for the filling body. This reaction mainly occurs in the middle and later stages of the system reaction.

[0033] In the embodiment, the phosphogypsum is the original state phosphogypsum without high-temperature treatment such as calcination. The phosphogypsum can be dihydrate phosphogypsum obtained by drying wet phosphogypsum to constant weight within 40°C. The phosphogypsum accounts for ≥65% of the dry material mass, where the dry material refers to phosphogypsum and the curing agent.

[0034] In the embodiment, the production raw material formula can include the following components in the mass fraction ratio: phosphogypsum (dry basis) 65 - 75 parts, curing agent 25 - 35 parts, and water accounts for 27% - 34% of the sum of the phosphogypsum and the curing agent by weight.

[0035] Among them, the curing agent can be composed of the following components by mass percentage: silica fume 4 - 6%, limestone powder 9 - 11%, superfine granulated blast furnace slag powder 36 - 41%, metakaolin 8 - 12%, calcium aluminate powder 6 - 8%, Portland cement clinker powder 28 - 32%, suspension stabilizer 0.3 - 3‰, hydroxypropyl methyl cellulose ether 0.5 - 1.5‰.

[0036] Exemplarily, the silica fume can be semi - densified or fully - densified silica fume, with a silica content ≥95%, an activity index ≥110%, and a water demand ratio ≤125%.

[0037] Exemplarily, the calcium carbonate content of the limestone powder ≥80%, and the fineness is 1000 mesh and above.

[0038] Exemplarily, the specific surface area of the superfine granulated blast furnace slag powder ≥600m 2 / kg, and the 28 - day activity index ≥105%. In this specific surface area range, granulated blast furnace slag is more likely to react and be activated.

[0039] Exemplarily, the metakaolin powder can be a powder material mainly composed of amorphous aluminosilicate obtained by calcining kaolin - type minerals at 600 - 900°C. In the metakaolin powder, Al2O3 ≥35%, the specific surface area ≥600m 2 / kg, and the 28 - day activity index ≥105%.

[0040] Exemplarily, the calcium aluminate powder can include calcium monoaluminate and / or calcium hemialuminate, with a specific surface area ≥400m 2 / kg, and Al2O3 ≥50%.

[0041] Exemplarily, the content of tricalcium silicate in the Portland cement clinker powder ≥55%, and the specific surface area ≥350m 2 / kg. Exemplarily, the Portland cement clinker powder can include 50 - 70% tricalcium silicate, 20 - 40% dicalcium silicate, 6 - 12% tricalcium aluminate, and 10 - 20% tetracalcium aluminoferrite.

[0042] Exemplarily, the suspension stabilizer (also known as suspension dispersant) can be a light - yellow powder, and adding it can improve the suspension performance and stability of particles in the filling slurry. For example, the suspension stabilizer can include modified vinyl alcohol - based polymers, vinyl ester polymers, maltodextrin, etc.

[0043] Exemplarily, hydroxypropyl methyl cellulose ether (HPMC) can be a white powder, with a viscosity specification of 200,000 and industrial - pure purity.

[0044] Exemplarily, the particle size of the phosphogypsum ≤4.75mm, and other indicators should meet the technical requirements of the current national standard GB / T23456 "Phosphogypsum".

[0045] Exemplarily, the water may be water that meets the requirements of the current industry standard "Standard for Water Used in Concrete" JGJ 63.

[0046] The mechanism by which the exemplary embodiment of the present invention solves the problem of high alkalinity in the conventional cement-based phosphogypsum filling system:

[0047] The main reactant that generates alkalinity in the reaction system of the exemplary embodiment of the present invention is portland cement, which itself only accounts for 28 - 32% of the curing agent and 7 - 12% of the phosphogypsum filling body, with a relatively low relative content. Its reaction product calcium hydroxide is the main source of alkalinity, while silica fume, metakaolin, and granulated blast furnace slag in the curing agent all react with calcium hydroxide to reduce the alkalinity of the system. At the same time, the aluminous cement and limestone powder that provide strength in the exemplary embodiment of the present invention, whose main hydration products are calcium carboaluminate and ettringite, do not generate calcium hydroxide, so the alkalinity of the entire system is relatively low.

[0048] The mechanism of the good working performance of the low-alkalinity and early-strength phosphogypsum filling and curing material in the exemplary embodiment of the present invention: The contents of portland cement and aluminous cement in this reaction system are scientific, and the setting time is controllable under the phosphogypsum filling system without flash setting. The silica fume in the system plays a lubricating role like glass microspheres, and the suspension dispersant in the system can make the phosphogypsum better suspended in water to stabilize the slurry, making the slurry have a better flow state. Hydroxyethyl methyl cellulose can play a water retention role to reduce bleeding in the system.

[0049] In the embodiment, the phosphogypsum may account for ≥65% of the dry material mass. The dry material may include phosphogypsum and a curing agent. The initial setting time of the phosphogypsum filling and curing material is ≤8 h, the 3-day compressive strength is ≥1 MPa, the 7-day compressive strength is ≥3 MPa, the 28-day strength is ≥5 MPa, the spread of the filling slurry is ≥800 mm, the bleeding rate of the slurry is ≤0.5%, and the pH value of the leachate of the 28-day filling body is ≤10.

[0050] According to another aspect of the present invention, a preparation method of a low-alkalinity and early-strength phosphogypsum filling and curing material is provided. The preparation method includes: uniformly mixing silica fume, limestone powder, ultra-fine granulated blast furnace slag powder, metakaolin, calcium aluminate powder, portland cement clinker powder, a suspension stabilizer, and hydroxypropyl methyl cellulose ether to form a curing agent powder; uniformly mixing water and the curing agent powder to obtain a curing agent slurry; adding phosphogypsum to the curing agent slurry until the slurry is uniformly mixed to obtain a phosphogypsum filling slurry.

[0051] In the exemplary embodiment, the phosphogypsum accounts for ≥65% of the dry material mass. The dry material includes phosphogypsum and a curing agent.

[0052] Each component is in parts by mass: 65 - 75 parts of phosphogypsum (dry basis), 25 - 35 parts of curing agent, and water accounts for 27% - 34% by weight of the sum of the phosphogypsum and the curing agent.

[0053] In the step of forming the curing agent powder, by mass percentage, silica fume is 4 - 6%, limestone powder is 9 - 11%, superfine granulated blast furnace slag powder is 36 - 41%, metakaolin is 8 - 12%, calcium aluminate powder is 6 - 8%, Portland cement clinker powder is 28 - 32%, suspension stabilizer is 0.3 - 3‰, and hydroxypropyl methyl cellulose ether is 0.5 - 1.5‰.

[0054] Exemplarily, the limestone powder can be semi - dense or fully - dense silica fume, with a silica content of ≥95%, an activity index of ≥110%, and a water demand ratio of ≤125%.

[0055] Exemplarily, the calcium carbonate content of the limestone powder is ≥80%, and the fineness is 1000 mesh or more.

[0056] Exemplarily, the specific surface area of the superfine granulated blast furnace slag powder is ≥600m 2 / kg, and the 28 - day activity index is ≥105%.

[0057] Exemplarily, the metakaolin powder can be a powder material mainly composed of amorphous aluminosilicate obtained by calcining kaolin - type minerals at 600 - 900°C. In the metakaolin powder, Al2O3 ≥ 35%, the specific surface area is ≥600m 2 / kg, and the 28 - day activity index is ≥105%.

[0058] Exemplarily, the calcium aluminate powder can include calcium monoaluminate and / or calcium hemialuminate, with a specific surface area of ≥400m 2 / kg, and Al2O3 ≥ 50%.

[0059] Exemplarily, the tricalcium silicate content of the Portland cement clinker powder is ≥55%, and the specific surface area is ≥350m 2 / kg.

[0060] Exemplarily, the suspension stabilizer can be a light - yellow powder, and adding it can improve the suspension performance and stability of particles in the filling slurry. For example, the suspension stabilizer can include modified vinyl alcohol - based polymers, vinyl ester polymers, maltodextrin, etc.

[0061] Exemplarily, hydroxypropyl methyl cellulose ether (HPMC) can be a white powder, with a viscosity of 200,000 and industrial - grade purity.

[0062] Exemplarily, the particle size of the phosphogypsum is ≤4.75mm, and other indicators should meet the technical requirements of the current national standard GB / T23456 "Phosphogypsum".

[0063] Exemplarily, the water can be water that meets the requirements of the current industry standard "Standard for Water Used in Concrete" JGJ 63.

[0064] In an embodiment, the phosphogypsum can account for ≥ 65% of the dry material mass. The dry material can include phosphogypsum and a curing agent. The initial setting time of the filling of the phosphogypsum filling and curing material ≤ 8h, the 3d compressive strength ≥ 1MPa, the 7d compressive strength ≥ 3MPa, the 28d strength ≥ 5MPa, the spread of the filling slurry ≥ 800mm, the bleeding rate of the slurry ≤ 0.5%, and the pH value of the leachate of the 28d filling body ≤ 10.

[0065] In another exemplary embodiment, the method for preparing the low-alkalinity, early-strength phosphogypsum filling and curing material as described in the above exemplary embodiment includes the following steps:

[0066] S1. The wet phosphogypsum should be dried to a constant weight within 40°C, and its moisture content should be calculated.

[0067] S2. Weigh each raw material according to the production raw material formula amount, where the weighed phosphogypsum raw material is the dry-based phosphogypsum mass converted by the moisture content, and the weighed water should discount the moisture contained in the wet phosphogypsum.

[0068] S3. Mix the silica fume, limestone powder, ultra-fine granulated blast furnace slag powder, metakaolin, calcium aluminate powder, Portland cement clinker powder, suspension stabilizer, and hydroxypropyl methyl cellulose ether required for the curing agent component evenly in a dry mixing device to form a filling and curing agent powder.

[0069] S4. Mix the water and the curing agent powder evenly in a stirring device to obtain a curing agent slurry.

[0070] S5. Add the phosphogypsum to the curing agent slurry at a constant speed until the slurry is evenly mixed to obtain a phosphogypsum filling slurry.

[0071] S6. Inject the phosphogypsum filling slurry into the position to be filled, and after forming and curing to an age of 3d and above, a filling body with strength is obtained.

[0072] In an exemplary embodiment, for the method for preparing the low-alkalinity, early-strength phosphogypsum filling and curing material, the obtained phosphogypsum filling slurry can be backfilled into the mined-out area of the underground mine. As the hydration reaction proceeds, the filling body gradually forms strength, and after consolidation and hardening, it supports the roof of the underground mined-out area, prevents surface settlement, and improves the recovery rate of phosphate ore. It not only realizes the safe and efficient recovery of resources but also can effectively alleviate the environmental problems caused by the stacking of surface solid waste.

[0073] In an exemplary embodiment, the low-alkalinity, early-strength phosphogypsum filling and curing material can be prepared by the above preparation method.

[0074] In an exemplary embodiment, the low-alkalinity and early-strength phosphogypsum filling and solidifying material prepared by the preparation method as described above, or the low-alkalinity and early-strength phosphogypsum filling and solidifying material as described above, is used in the solidifying material adopted in the phosphogypsum cemented filling technology.

[0075] In the embodiment, the above can be backfilled into the mined-out area of the underground mine; as the hydration reaction proceeds, the filling body gradually forms strength, and after consolidation and hardening, it supports the roof of the underground mined-out area.

[0076] To better understand the above exemplary embodiments of the present invention, the following further illustrates them with specific examples. It should be noted that the sources of raw materials and the specific component compositions adopted in the following examples are the same. For example, the Portland cement clinker powder in Example 1 is the same as the Portland cement clinker powder in Example 2 itself.

[0077] Example 1

[0078] Prepare the low-alkalinity and early-strength phosphogypsum filling and solidifying material according to the following steps:

[0079] S1. The wet phosphogypsum should be dried to a constant weight within 40°C, and its moisture content should be calculated.

[0080] S2. 70 parts of dihydrate phosphogypsum (based on dry basis), 30 parts of the curing agent component; water accounts for 32% by weight of the sum of phosphogypsum and the curing agent. Among them, according to the mass ratio, the curing agent is 5% of silica fume, 10% of limestone powder, 38% of ultrafine granulated blast furnace slag powder, 10% of metakaolin, 7% of calcium aluminate powder, 30% of Portland cement clinker powder, 1‰ of suspension stabilizer, and 1‰ of hydroxypropyl methylcellulose ether. Weigh each raw material, where the weighed phosphogypsum raw material is the dry basis phosphogypsum mass converted by the moisture content, and the weighed water should deduct the moisture contained in the wet phosphogypsum.

[0081] S3. Mix the silica fume, limestone powder, ultrafine granulated blast furnace slag powder, metakaolin, calcium aluminate powder, Portland cement clinker powder, suspension stabilizer, and hydroxypropyl methylcellulose ether required for the curing agent component evenly in a dry mixing device to form a filling and solidifying agent powder.

[0082] S4. Mix the water and the filling and solidifying agent powder evenly in a stirring device to obtain a curing agent slurry.

[0083] S5. Add the phosphogypsum to the curing agent slurry at a constant speed until the slurry is evenly mixed to obtain a phosphogypsum filling slurry.

[0084] S6. Take a portion of the filling material slurry to test its spread, and take another portion of the filling material slurry to test its bleeding rate. The remaining phosphogypsum filling slurry is filled into a setting time mold and a 70.7×70.7×70.7 mm triple mold respectively for setting time test and compressive strength test. After curing to the specified age, test the compressive strength and the pH value of the leachate.

[0085] The testing methods for the above items are carried out as follows: The testing methods for the spread and bleeding rate of the filling slurry are carried out in accordance with the current national standard "Standard Test Method for Properties of Ordinary Concrete Mixtures" GB / T 50080. The testing method for the setting time of the filling slurry is carried out in accordance with the current national standard "Test Methods for Water Requirement for Normal Consistency, Setting Time and Soundness of Cement" GB / T 1346. The compressive strength test is carried out in accordance with the current industry standard "Test Methods for Basic Properties of Building Mortar" JGJ70. For pH testing, the test blocks cured to 28 days of age are crushed to a maximum particle size not exceeding 4.75 mm, mixed with deionized water at a solid-liquid ratio of 1:10, and after standing for 24 days, take the supernatant and test its pH value with a pH meter.

[0086] Example 2

[0087] Prepare a low-alkalinity, early-strength phosphogypsum filling and solidifying material according to the following steps:

[0088] S1. The wet phosphogypsum should be dried to a constant weight within 40°C and calculate its moisture content.

[0089] S2. 65 parts of dihydrate phosphogypsum (dry basis), 35 parts of curing agent components; water accounts for 31% of the sum of phosphogypsum and curing agent by weight. Among them, 5% of silica fume, 10% of limestone powder, 36% of ultra-fine granulated blast furnace slag powder, 9% of metakaolin, 8% of calcium aluminate powder, 32% of Portland cement clinker powder, 0.5‰ of suspension stabilizer, and 0.8‰ of hydroxypropyl methyl cellulose ether in the curing agent. Weigh each raw material, and the weighed phosphogypsum raw material is the dry basis phosphogypsum quality converted by the moisture content. The weighed water should deduct the moisture contained in the wet phosphogypsum.

[0090] S3. Mix the silica fume, limestone powder, ultra-fine granulated blast furnace slag powder, metakaolin, calcium aluminate powder, Portland cement clinker powder, suspension stabilizer, and hydroxypropyl methyl cellulose ether required for the curing agent components evenly in a dry mixing device to form a filling and solidifying agent powder.

[0091] S4. Mix the water and the filling and solidifying agent powder evenly in a stirring device to obtain a curing agent slurry.

[0092] S5. Slowly add the phosphogypsum to the curing agent slurry until the slurry is evenly mixed to obtain a phosphogypsum filling slurry.

[0093] S6. Take part of the filling material slurry to test its spread, and take another part of the filling material slurry to test its bleeding rate. The remaining phosphogypsum filling slurry is filled into a setting time mold and a 70.7×70.7×70.7 mm triple mold respectively for setting time test and compressive strength test. After curing to the specified age, test the compressive strength and the pH value of the leachate.

[0094] The material testing method is the same as that in Example 1 and will not be elaborated here.

[0095] Example 3

[0096] Prepare a low-alkalinity and early-strength phosphogypsum filling and solidifying material according to the following steps:

[0097] S1. The wet phosphogypsum should be dried to constant weight at 40°C, and its moisture content should be calculated.

[0098] S2. 75 parts of dihydrate phosphogypsum (on dry basis), 25 parts of curing agent components; water accounts for 32% by weight of the sum of phosphogypsum and curing agent. Among them, silica fume in the curing agent is 4%, limestone powder is 9%, ultra-fine granulated blast furnace slag powder is 41%, metakaolin is 8%, calcium aluminate powder is 6%, Portland cement clinker powder is 32%, suspension stabilizer is 0.5‰, and hydroxypropyl methylcellulose ether is 0.8‰. Weigh each raw material, where the weighed phosphogypsum raw material is the dry basis phosphogypsum quality converted by the moisture content, and the weighed water should deduct the moisture contained in the wet phosphogypsum.

[0099] S3. Mix the silica fume, limestone powder, ultra-fine granulated blast furnace slag powder, metakaolin, calcium aluminate powder, Portland cement clinker powder, suspension stabilizer, and hydroxypropyl methylcellulose ether required for the curing agent components evenly in a dry mixing device to form a filling and solidifying agent powder.

[0100] S4. Mix the water and the curing agent powder evenly in a stirring device to obtain a curing agent slurry.

[0101] S5. Add the phosphogypsum to the curing agent slurry at a constant speed until the slurry is mixed evenly to obtain a phosphogypsum filling slurry.

[0102] S6. Take part of the filling slurry to test its spread, and take another part of the filling slurry to test its bleeding rate. The remaining phosphogypsum filling slurry is filled into a setting time mold and a 70.7×70.7×70.7 mm triple mold respectively for setting time test and compressive strength test. After curing to the specified age, test the compressive strength and the pH value of the leachate.

[0103] The material testing method is the same as that in Example 1 and will not be elaborated here.

[0104] Example 4

[0105] Prepare a low-alkalinity and early-strength phosphogypsum filling and solidifying material according to the following steps:

[0106] S1. The wet phosphogypsum should be dried to a constant weight at 40 °C, and its moisture content should be calculated.

[0107] S2. 65 parts of dihydrate phosphogypsum (dry basis), 35 parts of solidifying agent components; water accounts for 30% of the sum of phosphogypsum and solidifying agent by weight. Among them, silica fume is 4%, limestone powder is 9%, ultra-fine granulated blast furnace slag powder is 39%, metakaolin is 8%, calcium aluminate powder is 8%, Portland cement clinker powder is 32%, suspension stabilizer is 0.5‰, and hydroxypropyl methyl cellulose ether is 0.8‰ in the solidifying agent. Weigh each raw material, where the weighed phosphogypsum raw material is the dry basis phosphogypsum quality converted by the moisture content, and the weighed water should deduct the moisture contained in the wet phosphogypsum.

[0108] S3. Mix the silica fume, limestone powder, ultra-fine granulated blast furnace slag powder, metakaolin, calcium aluminate powder, Portland cement clinker powder, suspension stabilizer, and hydroxypropyl methyl cellulose ether required for the solidifying agent components evenly in a dry mixing device to form a filling and solidifying agent powder.

[0109] S4. Mix the water and the solidifying agent powder evenly in a stirring device to obtain a solidifying agent slurry.

[0110] S5. Add the phosphogypsum to the solidifying agent slurry at a uniform speed until the slurry is mixed evenly to obtain a phosphogypsum filling slurry.

[0111] S6. Take part of the filling slurry to test its spread, take another part of the filling slurry to test its bleeding rate, and load the remaining phosphogypsum filling slurry into a setting time mold and a 70.7×70.7×70.7 mm triple mold respectively for setting time test and compressive strength test. After curing to the specified age, test the compressive strength and the pH value of the leaching solution.

[0112] The material testing method is the same as that in Example 1 and will not be elaborated here.

[0113] Comparative Example 1:

[0114] S1. The wet phosphogypsum should be dried to a constant weight at 40 °C, and its moisture content should be calculated.

[0115] S2. 70 parts of dihydrate phosphogypsum (dry basis), 30 parts of P·O 42.5 ordinary Portland cement components; water accounts for 34% of the sum of phosphogypsum and P·O 42.5 ordinary Portland cement by weight. Weigh each raw material, where the weighed phosphogypsum raw material is the dry basis phosphogypsum quality converted by the moisture content, and the weighed water should deduct the moisture contained in the wet phosphogypsum.

[0116] S3. Mix water and P·O 42.5 ordinary portland cement powder evenly in a stirring device to obtain a slurry.

[0117] S4. Slowly add the phosphogypsum to the slurry until the slurry is evenly mixed to obtain a phosphogypsum filling slurry.

[0118] S5. Take part of the filling slurry to test its spread, take another part of the filling slurry to test its bleeding rate, and put the remaining phosphogypsum filling slurry into a setting time mold and a 70.7×70.7×70.7 mm triple mold respectively for setting time test and compressive strength test. After curing to the specified age, test the compressive strength and the pH value of the leaching solution.

[0119] The material testing method is the same as that in Example 1 and will not be elaborated here.

[0120] Comparative Example 2

[0121] S1. The wet phosphogypsum should be dried to constant weight at 40°C and its moisture content should be calculated.

[0122] S2. 70 parts of dihydrate phosphogypsum (dry basis), 30 parts of curing agent. Among the curing agent, 60% is granulated blast furnace slag powder, 30% is P·O 42.5 ordinary portland cement component, and 10% is lime; water accounts for 34% by weight of the sum of phosphogypsum and P·O 42.5 ordinary portland cement. Weigh each raw material, and the weighed phosphogypsum raw material is the dry basis phosphogypsum quality converted by the moisture content. The weighed water should be discounted by the moisture contained in the wet phosphogypsum.

[0123] S3. Mix water and P·O 42.5 ordinary portland cement powder evenly in a stirring device to obtain a slurry.

[0124] S4. Slowly add the phosphogypsum to the slurry until the slurry is evenly mixed to obtain a phosphogypsum filling slurry.

[0125] S5. Take part of the filling slurry to test its spread, take another part of the filling slurry to test its bleeding rate, and put the remaining phosphogypsum filling slurry into a setting time mold and a 70.7×70.7×70.7 mm triple mold respectively for setting time test and compressive strength test. After curing to the specified age, test the compressive strength and the pH value of the leaching solution.

[0126] The material testing method is the same as that in Example 1 and will not be elaborated here.

[0127] Comparative Example 3

[0128] S1. The wet phosphogypsum should be dried to constant weight at 40°C and its moisture content should be calculated.

[0129] S2. 65 parts of dihydrate phosphogypsum (dry basis), 35 parts of curing agent components; water accounts for 34% of the sum of phosphogypsum and curing agent by weight. 5% of silica fume, 10% of limestone powder, 35% of ultra-fine granulated blast furnace slag powder, 20% of metakaolin, 15% of calcium aluminate powder, 15% of Portland cement clinker powder, 0.5‰ of suspension stabilizer, 0.8‰ of hydroxypropyl methyl cellulose ether.

[0130] Weigh each raw material, where the weighed phosphogypsum raw material is the dry basis phosphogypsum quality converted by moisture content, and the weighed water should deduct the moisture contained in the wet phosphogypsum.

[0131] S3. Mix the silica fume, limestone powder, ultra-fine granulated blast furnace slag powder, metakaolin, calcium aluminate powder, Portland cement clinker powder, suspension stabilizer, and hydroxypropyl methyl cellulose ether required for the curing agent components evenly in a dry mixing device to form a filled curing agent powder.

[0132] S4. Mix the water and the cured agent powder evenly in a stirring device to obtain a cured agent slurry.

[0133] S5. Slowly add the phosphogypsum to the cured agent slurry at a uniform speed until the slurry is evenly mixed to obtain a phosphogypsum filling slurry.

[0134] S6. Take part of the filling slurry to test its spread, take another part of the filling slurry to test its bleeding rate, and put the remaining phosphogypsum filling slurry into a setting time mold and a 70.7×70.7×70.7mm triple mold respectively for setting time test and compressive strength test, and test the compressive strength and the pH value of the leaching solution after curing to the specified age.

[0135] The material testing method is the same as that in Example 1 and will not be elaborated here.

[0136] Comparative Example 4

[0137] S1. The wet phosphogypsum should be dried to constant weight at 40°C to calculate its moisture content.

[0138] S2. 80 parts of dihydrate phosphogypsum (dry basis), 20 parts of curing agent components; water accounts for 32% of the sum of phosphogypsum and curing agent by weight. Among them, the curing agent is in a mass ratio of 5% of silica fume, 10% of limestone powder, 38% of ultra-fine granulated blast furnace slag powder, 10% of metakaolin, 7% of calcium aluminate powder, 30% of Portland cement clinker powder, 1‰ of suspension stabilizer, 1‰ of hydroxypropyl methyl cellulose ether. Weigh each raw material, where the weighed phosphogypsum raw material is the dry basis phosphogypsum quality converted by moisture content, and the weighed water should deduct the moisture contained in the wet phosphogypsum.

[0139] Weigh each raw material, where the weighed phosphogypsum raw material is the dry basis phosphogypsum quality converted by moisture content, and the weighed water should deduct the moisture contained in the wet phosphogypsum.

[0140] S3. Mix the silica fume, limestone powder, ultra-fine granulated blast furnace slag powder, metakaolin, calcium aluminate powder, portland cement clinker powder, suspension stabilizer, and hydroxypropyl methylcellulose ether required for the curing agent component evenly in a dry mixing device to form a filling curing agent powder.

[0141] S4. Mix water and the curing agent powder evenly in a stirring device to obtain a curing agent slurry.

[0142] S5. Add the phosphogypsum to the curing agent slurry at a constant speed until the slurry is evenly mixed to obtain a phosphogypsum filling slurry.

[0143] S6. Take a part of the filling slurry to test its spread, take another part of the filling slurry to test its bleeding rate, and put the remaining phosphogypsum filling slurry into a setting time mold and a 70.7×70.7×70.7mm triple mold respectively for setting time test and compressive strength test. After curing to the specified age, test the compressive strength and the pH value of the leaching solution.

[0144] The material testing method is the same as that in Example 1 and will not be elaborated here.

[0145] Comparative Example 5

[0146] S1. The wet phosphogypsum should be dried to a constant weight at 40°C and its moisture content should be calculated.

[0147] S2. 70 parts of dihydrate phosphogypsum (dry basis), 30 parts of curing agent component; water accounts for 32% of the sum of phosphogypsum and curing agent by weight. Among them, for the curing agent, according to the mass ratio, silica fume is 5%, limestone powder is 28%, metakaolin is 30%, calcium aluminate powder is 7%, portland cement clinker powder is 30%, suspension stabilizer is 1‰, and hydroxypropyl methylcellulose ether is 1‰. Weigh each raw material, where the weighed phosphogypsum raw material is the dry basis phosphogypsum mass converted by the moisture content, and the weighed water should deduct the moisture contained in the wet phosphogypsum.

[0148] Weigh each raw material, where the weighed phosphogypsum raw material is the dry basis phosphogypsum mass converted by the moisture content, and the weighed water should deduct the moisture contained in the wet phosphogypsum.

[0149] S3. Mix the silica fume, limestone powder, ultra-fine granulated blast furnace slag powder, metakaolin, calcium aluminate powder, portland cement clinker powder, suspension stabilizer, and hydroxypropyl methylcellulose ether required for the curing agent component evenly in a dry mixing device to form a filling curing agent powder.

[0150] S4. Mix water and the curing agent powder evenly in a stirring device to obtain a curing agent slurry.

[0151] S5. Uniformly add the phosphogypsum into the curing agent slurry until the slurry is evenly mixed to obtain a phosphogypsum filling slurry.

[0152] S6. Take a part of the filling slurry to test its spread, take another part of the filling slurry to test its bleeding rate, and load the remaining phosphogypsum filling slurry into a setting time mold and a 70.7×70.7×70.7 mm triple mold respectively for setting time test and compressive strength test. After curing to the specified age, test the compressive strength and the pH value of the leaching solution.

[0153] The material testing method is the same as that in Example 1 and will not be elaborated here.

[0154] Comparative Example 6

[0155] S1. The wet phosphogypsum should be dried to a constant weight at 40°C and its moisture content should be calculated.

[0156] S2. 70 parts of dihydrate phosphogypsum (dry basis), 30 parts of curing agent components; water accounts for 31% by weight of the sum of phosphogypsum and curing agent. Among them, 5% of silica fume, 19% of limestone powder, 36% of ultra-fine granulated blast furnace slag powder, 8% of calcium aluminate powder, 32% of Portland cement clinker powder, 0.5‰ of suspension stabilizer, and 0.8‰ of hydroxypropyl methylcellulose ether are in the curing agent. Weigh each raw material, where the weighed phosphogypsum raw material is the dry basis phosphogypsum quality converted by the moisture content, and the weighed water should deduct the moisture contained in the wet phosphogypsum.

[0157] S3. Mix the silica fume, limestone powder, ultra-fine granulated blast furnace slag powder, metakaolin, calcium aluminate powder, Portland cement clinker powder, suspension stabilizer, and hydroxypropyl methylcellulose ether required for the curing agent components evenly in a dry mixing device to form a filling curing agent powder.

[0158] S4. Mix the water and the curing agent powder evenly in a stirring device to obtain a curing agent slurry.

[0159] S5. Uniformly add the phosphogypsum into the curing agent slurry until the slurry is evenly mixed to obtain a phosphogypsum filling slurry.

[0160] S6. Take a part of the filling slurry to test its spread, take another part of the filling slurry to test its bleeding rate, and load the remaining phosphogypsum filling slurry into a setting time mold and a 70.7×70.7×70.7 mm triple mold respectively for setting time test and compressive strength test. After curing to the specified age, test the compressive strength and the pH value of the leaching solution.

[0161] The material testing method is the same as that in Example 1 and will not be elaborated here.

[0162] Comparative Example 7

[0163] S1. The wet phosphogypsum shall be dried to a constant weight at a temperature within 40°C, and its moisture content shall be calculated.

[0164] S2. 65 parts of dihydrate phosphogypsum (on a dry basis), 35 parts of the curing agent component; water accounts for 31% of the sum of phosphogypsum and the curing agent by weight. Among them, limestone powder is 10%, ultrafine granulated blast furnace slag powder is 41%, metakaolin is 9%, calcium aluminate powder is 8%, and Portland cement clinker powder is 32%. Weigh each raw material, where the weighed phosphogypsum raw material is the dry basis phosphogypsum mass converted by the moisture content, and the weighed water should deduct the moisture contained in the wet phosphogypsum.

[0165] S3. Mix the silica fume, limestone powder, ultrafine granulated blast furnace slag powder, metakaolin, calcium aluminate powder, Portland cement clinker powder, suspension stabilizer, and hydroxypropyl methyl cellulose ether required for the curing agent component evenly in a dry mixing device to form a filled curing agent powder.

[0166] S4. Mix the water and the curing agent powder evenly in a stirring device to obtain a curing agent slurry.

[0167] S5. Add the phosphogypsum to the curing agent slurry at a constant speed until the slurry is evenly mixed to obtain a phosphogypsum filling slurry.

[0168] S6. Take a part of the filling slurry to test its spread, take another part of the filling slurry to test its bleeding rate, and load the remaining phosphogypsum filling slurry into a setting time mold and a 70.7×70.7×70.7mm triple mold respectively for setting time test and compressive strength test, and test the compressive strength and pH value of the leachate after curing to the specified age.

[0169] The material testing method is the same as that in Example 1 and will not be elaborated here.

[0170] Figure 1 The material test results of the phosphogypsum filling and curing materials according to the examples and comparative examples of the present invention are shown.

[0171] Combined Figure 1 , it can be seen from Comparative Example 1 that the conventional Portland cement has the problems of a long initial setting time (1460 min), low early strength (no strength formed at 3 d), and high strength. It can be seen from Comparative Example 2 that the curing agent system composed of conventional mineral admixtures, lime, and cement still has the problems of low early strength and high alkalinity, and cracks appear in the specimens during the 28-day observation of the test, indicating that this system has a volume stability problem.

[0172] As can be seen from Comparative Example 3, when the reduction value of the proportion of portland cement in the curing agent system is changed by 20%, since the phosphogypsum is acidic as a whole, this system cannot provide sufficient alkalinity to dissolve silicon and aluminosilicate ions from granulated blast furnace slag powder and metakaolin to form hydration products. Moreover, due to the relatively high content of calcium aluminate cement in this system, the hydration reaction quickly covers the curing agent particles, affecting the final strength.

[0173] As can be seen from Comparative Example 4, when the proportion of the curing agent is reduced to 20%, sufficient strength cannot be formed.

[0174] As can be seen from Comparative Example 5, by adjusting the proportion of granulated blast furnace slag powder in the curing agent and increasing the components of limestone powder and metakaolin, due to the lack of reaction between granulated blast furnace slag powder and the hydration products of gypsum and cement, the mechanical properties of the system decrease. Moreover, due to the relatively high water demand of metakaolin, the viscosity of the system also increases, and the slump decreases to 740 mm.

[0175] As can be seen from Comparative Example 6, when there is no metakaolin component in the curing agent system, the reaction with calcium hydroxide, calcium carbonate and calcium aluminate in the hydration products of portland cement clinker powder cannot be exerted, and the mechanical properties of the system decrease.

[0176] As can be seen from Comparative Example 7, when there are no components such as silica fume, hydroxypropyl methyl cellulose ether and suspension stabilizer in the curing agent system, the bleeding rate of the system increases significantly to 3%, and the slump of the slurry decreases.

[0177] The present invention aims at the defects of long initial setting time, low early strength, high pH value and high bleeding rate of phosphogypsum filling materials in the prior art. The technical solution formed by the present invention can achieve that when the filling slurry has a large amount of phosphogypsum (phosphogypsum accounts for ≥ 65% of the dry material mass), the initial setting time of filling is ≤ 8 h, the 3-day compressive strength ≥ 1 MPa, the 7-day compressive strength ≥ 3 MPa, the 28-day strength ≥ 5 MPa, the slump of the filling slurry ≥ 800 mm, the bleeding rate of the slurry ≤ 0.5%, and the pH value of the leachate of the 28-day filling body ≤ 10. Here, d in 3d, 7d and 28d refers to days.

[0178] The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited thereto. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solution of the present invention, including any other suitable combination of each technical feature. These simple modifications and combinations should also be regarded as the content disclosed by the present invention and fall within the protection scope of the present invention.

Claims

1. A low-alkalinity and early-strength phosphogypsum filling and solidifying material, characterized in that, The raw material formula of the low-alkalinity and early-strength phosphogypsum filling and solidifying material includes phosphogypsum, a solidifying agent and water. The phosphogypsum is dihydrate phosphogypsum. The phosphogypsum is 65 - 75 parts by dry basis, the solidifying agent is 25 - 35 parts, and the water accounts for 27% - 34% of the sum of the phosphogypsum and the solidifying agent by weight. The solidifying agent consists of the following components by mass percentage: Silica fume 4 - 6%, limestone powder 9 - 11%, superfine granulated blast furnace slag powder 36 - 41%, metakaolin 8 - 12%, calcium aluminate powder 6 - 8%, Portland cement clinker powder 28 - 32%, suspension stabilizer 0.3 - 3‰, and hydroxypropyl methylcellulose ether 0.5 - 1.5‰. The calcium aluminate powder includes calcium monoaluminate and / or calcium hemialuminate. The calcium carbonate content of the limestone powder is ≥80%.

2. The low-alkalinity and early-strength phosphogypsum filling and solidifying material according to claim 1, wherein The specific surface area of the calcium aluminate powder is ≥ 400 m 2 / kg, and Al2O3 ≥ 50%.

3. The low-alkalinity and early-strength phosphogypsum filling and solidifying material according to claim 1, characterized in that The silica fume is semi-densified or fully densified silica fume, with a silica content of ≥95%, an activity index of ≥110%, and a water demand ratio of ≤125%.

4. The low-alkalinity and early-strength phosphogypsum filling and solidifying material according to claim 1, wherein The fineness of the limestone powder is 1000 mesh and above; The specific surface area of the ultra-fine granulated blast furnace slag powder ≥ 600 m 2 / kg, and the 28-day activity index ≥ 105%; The metakaolin powder contains ≥35% Al2O3, has a specific surface area ≥600 m 2 / kg, and has a 28-day activity index ≥105%; The content of tricalcium silicate in the portland cement clinker powder is ≥ 55%, and the specific surface area is ≥ 350 m 2 / kg; The particle size of the phosphogypsum is ≤4.75 mm.

5. The low-alkalinity and early-strength phosphogypsum filling and solidifying material according to claim 1, characterized in that, The dry materials include phosphogypsum and a solidifying agent. The initial setting time of the phosphogypsum filling and solidifying material is ≤8 h, the 3-day compressive strength is ≥1 MPa, the 7-day compressive strength is ≥3 MPa, the 28-day strength is ≥5 MPa, the spread of the filling slurry is ≥800 mm, the bleeding rate of the slurry is ≤0.5%, and the pH value of the leachate of the 28-day filling body is ≤10.

6. A preparation method of a low-alkalinity and early-strength phosphogypsum filling and solidifying material, characterized in that, The preparation method includes: Mix 4 - 6% of silica fume, 9 - 11% of limestone powder, 36 - 41% of superfine granulated blast furnace slag powder, 8 - 12% of metakaolin, 6 - 8% of calcium aluminate powder, 28 - 32% of Portland cement clinker powder, 0.3 - 3‰ of suspension stabilizer, and 0.5 - 1.5‰ of hydroxypropyl methylcellulose ether evenly by mass percentage to form a solidifying agent powder. The calcium aluminate powder includes calcium monoaluminate and / or calcium hemialuminate. The calcium carbonate content of the limestone powder is ≥80%; Mix the water and the solidifying agent powder evenly to obtain a solidifying agent slurry; and Add the phosphogypsum to the solidifying agent slurry until the slurry is mixed evenly to obtain a phosphogypsum filling slurry. Among them, the phosphogypsum is dihydrate phosphogypsum. The phosphogypsum is 65 - 75 parts by dry basis, the solidifying agent is 25 - 35 parts, and the water accounts for 27% - 34% of the sum of the phosphogypsum and the solidifying agent by weight.

7. The preparation method of the low-alkalinity and early-strength phosphogypsum filling and solidifying material according to claim 6, characterized in that The specific surface area of the calcium aluminate powder is ≥ 400 m 2 / kg, and Al2O3 ≥ 50%.

8. The preparation method of the low-alkalinity and early-strength phosphogypsum filling and solidifying material according to claim 6, characterized in that, The silica fume is semi-densified or fully densified silica fume, with a silica content of ≥95%, an activity index of ≥110%, and a water demand ratio of ≤125%.

9. The preparation method of the low-alkalinity and early-strength phosphogypsum filling and solidifying material according to claim 6, characterized in that, The fineness of the limestone powder is 1000 mesh and above; The specific surface area of the ultra-fine granulated blast furnace slag powder ≥ 600 m 2 / kg, and the 28-day activity index ≥ 105%; The metakaolin powder contains ≥35% Al2O3, has a specific surface area ≥600 m 2 / kg, and has a 28-day activity index ≥105%; The content of tricalcium silicate in the portland cement clinker powder is ≥ 55%, and the specific surface area is ≥ 350 m 2 / kg; The particle size of the phosphogypsum is ≤4.75 mm.

10. The preparation method of the low-alkalinity and early-strength phosphogypsum filling and solidifying material according to claim 6, characterized in that, The dry materials include phosphogypsum and a solidifying agent. The initial setting time of the phosphogypsum filling and solidifying material is ≤8 h, the 3-day compressive strength is ≥1 MPa, the 7-day compressive strength is ≥3 MPa, the 28-day strength is ≥5 MPa, the spread of the filling slurry is ≥800 mm, the bleeding rate of the slurry is ≤0.5%, and the pH value of the leachate of the 28-day filling body is ≤10.

Images