Cemented ardealite, preparation method thereof and application of cemented ardealite in heavy metal repair

Abstract

The invention discloses cemented ardealite, a preparation method thereof and application of the cemented ardealite in heavy metal repair. The cemented ardealite is prepared from ardealite, cement and sand as raw materials. The preparation method comprises the following steps: crushing, grinding and drying caked phosphogypsum to obtain pretreated phosphogypsum; mixing the pretreated ardealite and cement according to a preset proportion, and then grinding and drying to obtain mixed powder; granulating the mixed powder to obtain a molded granular product; and curing the formed particle product to obtain the cemented phosphogypsum. The invention also discloses an application of the cemented ardealite in heavy metal repair. According to the invention, different modified cementing materials are selected to prepare the cemented phosphogypsum filler, and the influence of the selection of the cementing materials on the structure and the release of active components is researched, so that the safe and efficient application of the phosphogypsum-based solid waste filler in heavy metal repair is realized.

Description

Technical Field

[0001] The present invention belongs to the field of solid waste resource recovery and heavy metal treatment, and specifically relates to a cemented phosphogypsum, a preparation method thereof, and an application thereof in heavy metal remediation. Background Art

[0002] Heavy metal pollution refers to environmental contamination caused by heavy metals or their compounds, primarily due to human factors such as mining, smelting, and wastewater discharge. The adverse impacts on aquatic and soil environments are particularly severe. These heavy metals are difficult to decompose in soil and water, and therefore migrate between the environment and organisms in different valence states, ultimately affecting the entire ecosystem. Currently, heavy metal pollution in my country primarily includes lead, cadmium, copper, arsenic, and antimony. According to the "China Ecological Environment Bulletin (2023)", the rate of excess pollution of heavy metals such as total lead, total cadmium, total arsenic, and total zinc in surface water nationwide is 3% to 15%. In recent years, heavy metal levels have intermittently exceeded standards in the Yangtze River, Yellow River, and Pearl River basins. Concentrations of lead, cadmium, arsenic, and antimony in water bodies near some urban industrial zones and mineral resource development areas have significantly exceeded environmental quality standards. The cadmium content in wastewater discharged by some metallurgical, mining and chemical enterprises in central my country reached above 0.05 mg / L, significantly exceeding the cadmium limit of 0.005 mg / L for Class III water bodies stipulated in the "Surface Water Environmental Quality Standard" (GB 3838-2002).

[0003] Solid waste resource utilization refers to the conversion of industrial byproducts and waste into usable resources through technological means, achieving reduction, harmlessness, and reuse, offering a new approach for environmental remediation. In recent years, remediation materials have been developed from industrial solid wastes, such as phosphogypsum. These materials effectively immobilize or remove heavy metal ions from water bodies through adsorption, ion exchange, and complexation precipitation, reducing their bioavailability and mobility. Due to their rich functional groups, excellent cementing properties, and easy modifiability, phosphogypsum-based materials have become important materials for the remediation of heavy metal-contaminated water bodies, offering significant benefits in both resource utilization and environmental remediation. Phosphogypsum (PG), a major byproduct of wet phosphoric acid production, is primarily composed of calcium sulfate dihydrate (CaSO₄·2H₂O). However, PG often introduces a significant number of impurities, such as phosphoric acid, fluoride, organic matter, and heavy metals. Its surface possesses numerous active sites, such as hydroxyl groups and sulfate groups, which can undergo surface complexation or ion exchange reactions with heavy metal anions. Although phosphogypsum has good adsorption capacity and resource utilization advantages in the process of remediating heavy metal pollution, its application also faces some problems. In particular, in actual use, phosphogypsum often contains a certain amount of impurity ions, such as F - 、SO4 2- PO4 3-During contact with heavy metals, impurity ions may be released. These impurities can cause secondary pollution, impacting the safety of the aquatic environment, and interfere with the heavy metal fixation effect of phosphogypsum, reducing the effectiveness and stability of the remediation process. Therefore, inhibiting or controlling the release of impurity ions in phosphogypsum and improving its environmental compatibility are key to achieving its efficient and safe remediation of heavy metal contamination.

[0004] The cementation process provides an effective solution to the problem of impurity ion release during the remediation of heavy metals using phosphogypsum. Through cementation, impurities in phosphogypsum are encapsulated or solidified within the dense material structure, significantly reducing the free release of impurity ions and thus minimizing the risk of secondary contamination. Furthermore, the stable structure formed by cementation improves the material's water resistance and mechanical strength, helping to maintain the sustained adsorption and slow release of heavy metal ions, enabling controlled and sustained release of components. Furthermore, the cementation process enhances the material's adsorption properties and selectivity, effectively improving the remediation effectiveness of heavy metals. This ensures structural stability in the granulated material, controlled release of active component ions, guaranteed leaching of impurity ions, and effective contaminant fixation. However, phosphogypsum reacts with tricalcium aluminate and tetracalcium aluminoferrite in cement to form calcium aluminate hydrate, forming ettringite precipitates. This precipitate adheres to the surface of cement particles, hindering their contact with water and slowing the hydration rate of the cement clinker, thereby retarding the setting process. Furthermore, phosphogypsum contains small amounts of soluble impurities, such as phosphorus, fluorine, and organic matter, which prolong the retarding time of the cementation process and reduce the strength of the filler. In response to the above problems, we urgently need to develop a preparation method for cemented phosphogypsum, so as to realize the safe and efficient application of phosphogypsum-based solid waste fillers in heavy metal remediation. Summary of the Invention

[0005] One of the purposes of the present invention is to address the above-mentioned problems and provide a cemented phosphogypsum to achieve the safe and efficient application of phosphogypsum-based solid waste fillers in heavy metal remediation.

[0006] A second object of the present invention is to provide a method for preparing the cementitious phosphogypsum.

[0007] The third object of the present invention is to provide the application of the cemented phosphogypsum in heavy metal repair.

[0008] The present invention provides a cemented phosphogypsum. The cemented phosphogypsum is prepared using phosphogypsum, cement and sand as raw materials. The phosphogypsum is an original phosphogypsum material. The cement is ordinary Portland cement, sulphoaluminate cement or modified slag Portland cement.

[0009] The modified silicate slag cement is prepared by uniformly mixing silicate slag cement, water glass and quicklime in proportion.

[0010] In the modified slag silicate cement, the content of slag silicate cement is 75-85wt%, the content of water glass is 10-15wt%, and the content of quicklime is 5-10wt%.

[0011] In modified slag silicate cement, water glass is an alkaline activator. It acts as both an activator and a reactant. The Na2O in the water glass breaks the Si-O bond and Al-O bond in the slag, dissolving elements such as Si and Al. The siliceous components in the water glass act as a reactant with the Ca dissolved in the slag. 2+ Reacts to generate hydrated calcium silicate gel, and the dissolved Al 3+ and Si 4+ It penetrates deep into the vicinity of the water glass nucleus and, under dehydration, undergoes a polymerization reaction with the SiO2 in the nucleus. The polymerization products of adjacent nuclei overlap to form a whole, forming a stable cementing structure. Lime is added because the soluble phosphorus and fluorine in phosphogypsum slow the early hydration rate of minerals such as C3A and C3S. Lime can neutralize the soluble phosphorus and convert it into insoluble calcium phosphate minerals. At the same time, the calcium material also has a bonding effect, which strengthens the solidification of phosphogypsum.

[0012] The present invention also provides a method for preparing cemented phosphogypsum, comprising the following steps:

[0013] S1. The agglomerated phosphogypsum is crushed, ground, and dried to obtain pretreated phosphogypsum;

[0014] S2. The pretreated phosphogypsum and cement are mixed in a preset ratio, and then ground and dried to obtain a mixed powder;

[0015] S3. After adding sand to the granulation equipment, the mixed powder is added for granulation to obtain a molded granular product;

[0016] S4. Curing the formed particle product to obtain the cemented phosphogypsum.

[0017] Furthermore, in step S1, the grinding process conditions are specifically as follows: grinding the agglomerated phosphogypsum to below 300 mesh; and the drying process conditions are as follows: drying the moisture content to below 10%.

[0018] Furthermore, in step S2, the mass ratio of the pretreated phosphogypsum to cement is (1:2 to 2:1); and the particle size of the mixed powder is less than 30 meshes.

[0019] Furthermore, step S3 is specifically as follows: feeding the mixed powder into a disc granulation device, setting the speed to 600-700 rpm, maintaining the temperature at 20°C-30°C, spraying water intermittently during the granulation process, setting the mass ratio of the mixed powder to sand to (1:3-3:1), regulating the moisture content of the mixture to about 3%, and disc granulating for 30-60 minutes.

[0020] Furthermore, in step S4, the curing is specifically as follows: placing the formed particle product in a curing box for curing for 7-10 days; the temperature and humidity conditions in the curing box are: 25°C, and the humidity is not less than 90%.

[0021] Relatively constant humidity and temperature conditions are typically maintained within the curing chamber to ensure that the cementing reaction proceeds continuously and that the surface does not dry out or crack due to rapid water evaporation. Appropriate regulation of temperature and humidity facilitates the in-depth hydration reaction of cement-based binders, gradually densifying the material's internal skeleton structure and improving its overall mechanical strength. During the curing period, active components such as tricalcium silicate (C3S) and belite (C2S) in binders such as cement react with water to form products such as hydrated calcium silicate gel (CS-Hgel) and calcium hydroxide. These hydration products can encapsulate and fix phosphogypsum particles and other impurities, significantly reducing the release of harmful ions.

[0022] The present invention also provides an application of the cemented phosphogypsum in heavy metal repair.

[0023] The specific application scenarios of the application include surface water remediation application scenarios and groundwater remediation application scenarios.

[0024] In the surface water remediation application scenario, the cemented phosphogypsum is applied to surface water bodies that are lightly to moderately contaminated by heavy metals.

[0025] The application scenario of the application in surface water remediation is specifically as follows: using a filtration treatment method, the particles of the cemented phosphogypsum are filled in a dedicated filtration device, and the filtration device is arranged in a water body contaminated by heavy metals. By filling the filter layer of the cemented phosphogypsum, the polluted water flow is fully in contact with the material particles, and the heavy metal ions are efficiently removed through mechanisms such as adsorption, complexation and precipitation.

[0026] The filtering equipment includes a special water filter bed, an artificial wetland matrix layer or a mobile filter cartridge; the heavy metal-contaminated water passes through the filtering device under natural or artificial drainage conditions.

[0027] In the application scenario of groundwater remediation, the cemented phosphogypsum is used for heavy metal-contaminated water bodies where the concentration of pollutants such as cadmium, lead, zinc, arsenic, and antimony exceeds the standard by 5 to 10 times, the flow rate range is 0.01m / d-0.1m / d, and the filler has an effective period of 5 to 10 years.

[0028] The application scenario of the application in groundwater remediation is specifically as follows: in the downstream or migration channel of the groundwater pollution plume, a trench is excavated and filled with the cemented phosphogypsum to construct a reaction wall that runs through the width of the pollution plume.

[0029] As groundwater flows through the permeable reactive wall, heavy metal ions come into contact with the material, undergoing processes such as adsorption, ion exchange, complexation, and chemical precipitation, effectively immobilizing or converting them into insoluble forms. The material's sustained-release properties and dense structure ensure long-term, highly effective in-situ remediation performance and effectively curb the further expansion of the contamination plume.

[0030] Principle of the present invention:

[0031] The present invention uses phosphogypsum, cement and sand as raw materials to prepare cementitious phosphogypsum-based materials, and removes heavy metal pollutants in water environment remediation. Three types of cement are selected as the cementing material, namely silicate cement, sulfoaluminate cement and modified slag silicate cement. During the granulation and curing process of phosphogypsum-based materials, cement is not only responsible for structural bonding, but the retarder it contains (mainly calcium sulfate, CaSO4) has a key regulatory effect on the early reaction characteristics of the material and the subsequent component release behavior. Under different coagulation and curing times, the presence of the retarder can not only prevent the agglomeration and structural unevenness caused by premature setting of the material, but also promote the material to obtain ideal fluidity and encapsulation in the early stage, and improve the degree of uniform mixing and dense consolidation of each component. A longer coagulation time can make the Ca in the cement system 2+ and SO4 2- Plasma is continuously released into the system and reacts with phosphogypsum and heavy metal ions, forming more surface complexes and precipitation-fixed structures, thereby enhancing the long-term adsorption and fixation of heavy metals. Furthermore, a reasonable retarder content effectively controls shrinkage and crack formation during curing, ensuring the mechanical strength and environmental stability of the final product.

[0032] The removal mechanism of heavy metals by cemented phosphogypsum mainly includes adsorption and chemical precipitation. In terms of adsorption, heavy metal ions can interact with phosphogypsum and its surface active sites such as hydroxyl groups, sulfate groups and other functional groups through mechanisms such as surface complexation and ion exchange, and be firmly adsorbed on the surface or in the pores of the material. Chemical precipitation is manifested as the Ca in phosphogypsum 2+ Metal ions and heavy metal anions in water such as CrO4 2- 、AsO4 3- 、SbO4 3-Reactions occur, such as with water, to form insoluble or low-solubility metal precipitates, effectively inhibiting the migration and release of heavy metals. Furthermore, the porous structure and large specific surface area of ​​cementitious phosphogypsum provide more channels and reaction sites for the diffusion and capture of heavy metal ions, significantly enhancing its ability to remove a variety of heavy metals. The choice of different cementitious materials allows for the controlled release of active component ions from the granulated material and the leaching of impurity ions to meet standards.

[0033] Beneficial effects of the present invention

[0034] (1) The present invention utilizes solid wastes such as phosphogypsum and slag to prepare cemented phosphogypsum. The preparation method is green and environmentally friendly, and provides a new channel for the recycling and reuse of solid wastes.

[0035] (2) The present invention proposes for the first time the use of cemented phosphogypsum prepared from solid waste for heavy metal pollution control. It not only recycles the solid waste, but also reuses the characteristics of phosphogypsum. The formula of phosphogypsum and cement is designed so that the obtained cemented phosphogypsum has the ability to remove heavy metals. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 This is the XRD analysis diagram of the cementitious phosphogypsum material in Example 1;

[0037] Figure 2 This is a scanning electron microscope image of cementitious phosphogypsum material No. 2 in Example 1;

[0038] Figure 3 This is a fitting diagram of the adsorption kinetic model of As by the cemented phosphogypsum material obtained in Example 4;

[0039] Figure 4 This is a fitting diagram of the adsorption kinetic model of Sb by the cemented phosphogypsum material obtained in Example 4;

[0040] Figure 5 This is a graph showing the relationship between the antimony and arsenic concentrations in the effluent and time in Example 5. DETAILED DESCRIPTION

[0041] The present invention is further described in detail below by way of specific embodiments, which are intended to further illustrate the present invention rather than to limit the present invention.

[0042] Example 1: Preparation of cemented phosphogypsum. The present invention provides a method for preparing cemented phosphogypsum, comprising the following steps:

[0043] The raw phosphogypsum is air-dried under natural ventilation or dried in a drying oven at 40°C to 60°C for 24-48 hours to remove excess moisture. The dried phosphogypsum is then pulverized using mechanical crushing equipment, reducing bulky material to a particle size of less than 2 mm to improve uniformity and reactivity. The pulverized phosphogypsum is then passed through a 100-mesh sieve using a screening device to obtain pretreated phosphogypsum.

[0044] The pretreated phosphogypsum sample was mixed with ordinary Portland cement (filler number: 1), modified slag Portland cement (filler number: 2), and sulfoaluminate cement (filler number: 3) in a 1:1 mass ratio, finely ground in a grinder, and then passed through a 0.25 mm sieve to obtain mixed powders 1, 2, and 3 for later use. Sand (particle size: 1-2 mm) was weighed and sprayed with a water mist at a mass of 0.5-5 wt% of the sand mass to moisten the surface. 10 wt% of mixed powders 1, 2, and 3 were then added to each of the pellets, and the mixture was mixed at 80 rpm to obtain cores 1, 2, and 3. These cores were then added to a disc granulator at a speed of 400-500 rpm. The cores in the disc granulator were sprayed with a water mist at a mass of 0.5-5 wt% of the total mass of the sand and mixed powders to slightly moisten the surface. Repeat the above steps until all the powder is added and the particles are round and full, to obtain shaped particle products 1, 2, and 3.

[0045] The formed particle products 1, 2, and 3 were placed in a curing box and cured for 8 days to finally obtain formed cementitious phosphogypsum materials 1, 2, and 3.

[0046] Example 2: Sustained-release experiment of cementitious phosphogypsum material. The sustained-release experiment of the cementitious phosphogypsum material is as follows:

[0047] 10g of each of the cementitious phosphogypsum materials No. 1 to No. 3 prepared in Example 1 was placed in a disposable plastic cup, with two parallel groups set up for each experiment. Immediately after adding 100mL of deionized water, a timer was started. 5mL samples were taken at 0.5, 1, 2, 3, 6, 9, 12, 24, 36, and 48 hours, and 5mL of deionized water was immediately replenished. The pH of the samples was measured using a pH meter, and the concentrations of Fe, Ca, Na, Mg, Al, F, S, and P in the samples were determined using ICP-OES. The results are shown in Tables 1 and 2.

[0048] Table 1 pH value of cemented phosphogypsum material slow-release experiment

[0049]

[0050] Table 2 Ca ion concentration (ppm) in the sustained-release experiment of cemented phosphogypsum materials

[0051]

[0052] As can be seen from the table, the slow-release solution of cemented phosphogypsum is alkaline, and the pH value is relatively stable at different slow-release times, indicating that it can better adapt to the remediation environment contaminated by alkaline heavy metals. The slow-release amount of the three materials can reach a stable state in a short period of time, indicating that the chemical reaction and ion release process inside the filler are relatively rapid, and with the increase of immersion time, its slow-release performance is improved, showing that the material has good stability and sustainability.

[0053] Example 3: Toxicity leaching test of cementitious phosphogypsum material. The toxicity leaching test is as follows:

[0054] Leaching experiments were conducted using the acetic acid buffer solution method (HJ / T 300-2007). 100g each of the phosphogypsum materials 1, 2, and 3 prepared in Example 1 were placed in a 2L polyethylene (PE) wide-mouth bottle and mixed with the leaching agent at a solid-to-liquid ratio of 1:20. The bottle was capped and fixed in an oscillating box at a speed of 30±2 rpm. The oscillating box was then incubated at 23±2°C for 18±2 hours. After 2 hours of static storage, the sample was filtered using a vacuum filter pump. After filtering through 0.6μm filter paper, the sample was stored at 4°C. According to the leaching toxicity identification standard (GB5085.3-2007), the following six hazardous ions were selected as detection indicators: total phosphorus and fluoride were determined by ammonium molybdate spectrophotometry (GB / T11893-1989) and ion chromatography (GB / T5085.3-2007), respectively; hexavalent chromium was determined by diphenylcarbazide spectrophotometry (GB / T15555.4-1995); total chromium and total barium concentrations were both determined by inductively coupled plasma atomic emission spectrometry in (GB / T5085.3-2007); and total arsenic was determined by atomic fluorescence spectrometry.

[0055] After cementation and granulation, the leachate from the cemented phosphogypsum filler contained 0.08 mg / L of total phosphorus, 0.09 mg / L of soluble fluoride, 0.06 mg / L of hexavalent chromium, 0.06 mg / L of total chromium, 0.01 mg / L of total barium, and 0.01 mg / L of total arsenic. These results are all below the corresponding standards for Class IV water as specified in the Identification Standard for Leaching Toxicity (GB 5085.3-2007) and the Groundwater Quality Standard (GB / T 14848-2017).

[0056] Example 4: Treatment experiment of heavy metal wastewater with cemented phosphogypsum material. The treatment experiment of heavy metal wastewater with cemented phosphogypsum material is as follows:

[0057] Take 1g of each of No. 1, 2, and 3 cemented phosphogypsum materials prepared in Example 1 and place them in 50mL centrifuge tubes. Set 10 time points, set two parallel samples at each time point, and add 15mL of diluted ten-fold contaminated water samples. The water sample is taken from a contaminated water sample of a tin mine in Central China. The centrifuge tube is placed in a shaking box and oscillated at a constant temperature (150r / min) at 25°C. The water sample in the corresponding centrifuge tube is taken out at the corresponding time points of 30min, 1h, 2h, 3h, 6h, 9h, 12h, 24h, 36h, and 48h and filtered. About 4-5mL of filtrate is collected with a 5mL centrifuge tube, and the Fe, Ca, Na, Mg, Al, Sb, and As concentrations in the sample are measured using ICP-OES. Fit the adsorption kinetic model. The corresponding adsorption results are shown in Table 3.

[0058] Table 3 Material adsorption effect after 48 hours of adsorption

[0059]

[0060] The adsorption kinetic model fitting diagram of three cemented phosphogypsum materials for arsenic and antimony is shown in the figure below. Figure 3 、 Figure 4 shown.

[0061] As shown in the table, all three cemented phosphogypsum materials exhibit significant adsorption effects on arsenic and antimony. Arsenic concentrations in water samples adsorbed by materials No. 2 and No. 3 were ≤ 0.05 mg / L, meeting the standard for Class I water specified in the "Surface Water Environmental Quality Standard" (GB 3838-2002). Antimony concentrations were all ≤ 0.5 mg / L after adsorption by all three materials, demonstrating excellent adsorption capacity and ability to treat heavy metal pollution in water bodies.

[0062] Example 5: Simulated column experiment of heavy metal wastewater treatment using cemented phosphogypsum material. The simulated column experiment is as follows:

[0063] A PRB indoor simulation experiment was carried out using an experimental column (35 cm long, 4 cm in diameter) filled with phosphogypsum-based materials and quartz sand. The particle size of the quartz sand is 0.5-2 mm. Both ends are filled with 5 cm thick quartz sand to separate the reaction mixture from the water inlet and outlet, while ensuring uniform water distribution. The rest of the column (25 cm) is filled with the cemented phosphogypsum-based material prepared in Example 1 to remove heavy metals such as antimony and arsenic from the water flowing through. The total solid mass in the experimental column (including phosphogypsum material and quartz sand) is 600 g, and the PV value is calculated based on the mass increased in the column after saturation (1PV = 200-220 mL). Under an environment of 25±2°C, the contaminated groundwater is concentrated at a rate of 0.5 mL min -1 The flow rate (about 0.57md -1) passes through the experimental column. Samples are taken from the end of the experimental column at different time points, and the concentration of heavy metals in the samples is measured. The dynamic monitoring process uses the Class IV standard limit in the "Surface Water Environmental Quality Standard" (GB3838-2002) as a reference value, and records the water inflection point (i.e. the time point when the heavy metal concentration exceeds the standard limit). The corresponding experimental results are as follows Figure 5 shown.

[0064] like Figure 5 As shown in the simulated column experiments, all three cemented phosphogypsum materials demonstrated excellent arsenic removal efficiency, reaching over 95% and achieving effluent concentrations that met the Class I standard for water specified in the Environmental Quality Standard for Surface Water (GB3838-2002). Their CRMlast values ​​were 12584.23, 12690.51, and 12564.91 μg, respectively. Antimony removal was less efficient than arsenic, but effluent concentrations were all ≤0.5 mg / L, with removal efficiencies of 32.3%, 58.1%, and 40.6%, respectively, demonstrating excellent heavy metal removal potential.

[0065] The above is only a preferred embodiment of the present invention, and the scope of protection of the present invention is not limited to the above embodiment. For those skilled in the art, improvements and modifications obtained without departing from the technical concept of the present invention should also be considered as the scope of protection of the present invention.

Claims

1. A cemented phosphogypsum, characterized in that: The cemented phosphogypsum is prepared using phosphogypsum, cement and sand as raw materials; the phosphogypsum is original phosphogypsum material; and the cement is ordinary Portland cement, sulphoaluminate cement or modified slag Portland cement.

2. The cemented phosphogypsum according to claim 1, characterized in that: The modified slag silicate cement is prepared by uniformly mixing slag silicate cement, water glass and quicklime in proportion; in the modified slag silicate cement, the slag silicate cement content is 75-85wt%, the water glass content is 10-15wt%, and the quicklime content is 5-10wt%.

3. A method for preparing cemented phosphogypsum according to any one of claims 1 or 2, characterized in that: The following steps are involved: S1. The agglomerated phosphogypsum is crushed, ground, and dried to obtain pretreated phosphogypsum; S2. The pretreated phosphogypsum and cement are mixed in a preset ratio, and then ground and dried to obtain a mixed powder; S3. After adding sand to the granulation equipment, the mixed powder is added for granulation to obtain a molded granular product; S4. Curing the formed particle product to obtain the cemented phosphogypsum.

4. The method for preparing cemented phosphogypsum according to claim 3, wherein: In step S1, the grinding process conditions are specifically as follows: grinding the agglomerated phosphogypsum to a size of less than 300 mesh; and the drying process conditions are as follows: drying the moisture content to less than 10%.

5. The method for preparing cemented phosphogypsum according to claim 3, wherein: In step S2, the mass ratio of the pretreated phosphogypsum to cement is (1:2 to 2:1); the particle size of the mixed powder is less than 30 meshes; and the cement is ordinary Portland cement, sulfoaluminate cement or modified slag Portland cement.

6. The method for preparing cemented phosphogypsum according to claim 3, wherein: Step S3 is specifically as follows: feeding the mixed powder into a disc granulation device, setting the speed to 600-700 rpm, maintaining the temperature at 20°C-30°C, spraying water intermittently during the granulation process, setting the mass ratio of the mixed powder to sand to (1:3-3:1), and adjusting the moisture content of the mixture to about 3%, and disc granulating for 30-60 minutes.

7. The method for preparing cemented phosphogypsum according to claim 3, wherein: In step S4, the curing specifically comprises placing the formed granule product in a curing box for curing for 7-10 days; the temperature and humidity conditions in the curing box are: 25° C., and the humidity is not less than 90%.

8. Use of cemented phosphogypsum prepared by the method for preparing cemented phosphogypsum according to any one of claims 3 to 7 in heavy metal remediation.

9. The use according to claim 8, characterized in that The specific application scenarios of the application include surface water remediation application scenarios and groundwater remediation application scenarios.

10. The use according to claim 9, characterized in that In the surface water remediation application scenario, the cemented phosphogypsum is applied to surface water bodies that are lightly to moderately contaminated by heavy metals; The application scenario of the surface water remediation is specifically as follows: using a filtration treatment method, the particles of the cemented phosphogypsum are filled in a dedicated filtration device, and the filtration device is deployed in a water body contaminated by heavy metals. By filling the filter layer of the cemented phosphogypsum, the contaminated water flow is fully in contact with the material particles, and the heavy metal ions are efficiently removed through mechanisms such as adsorption, complexation and precipitation; The filtering equipment includes a dedicated water filter bed, an artificial wetland matrix layer or a mobile filter cartridge; the heavy metal-contaminated water passes through the filtering device under natural or artificial drainage conditions; In the application scenario of groundwater remediation, the cemented phosphogypsum is applied to heavy metal-contaminated water bodies where the concentration of cadmium, lead, zinc, arsenic and antimony pollutants exceeds the standard by 5 to 10 times, the flow rate range is 0.01m / d-0.1m / d, and the filler has an effective period of 5 to 10 years; The application scenario of the application in groundwater remediation is specifically as follows: in the downstream or migration channel of the groundwater pollution plume, a trench is excavated and filled with the cemented phosphogypsum to construct a reaction wall that runs through the width of the pollution plume.

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