Preparation method and application of aluminum-magnesium-based composite gel fluorine removal agent

Abstract

The invention discloses a preparation method and application of an aluminum-magnesium-based composite gel fluorine removal agent, Al (OH) 3-Mg (OH) 2 coprecipitation gel is prepared from an aluminum source and a magnesium source, then the Al (OH) 3-Mg (OH) 2 coprecipitation gel and a pore forming agent are mixed and aged, and finally a phosphoric acid solution is used for etching to obtain the aluminum-magnesium-based composite gel fluorine removal agent with a 2-5nm mesoporous structure and porosity improved by 10-15%, and the aluminum-magnesium-based composite gel fluorine removal agent can be directly used for defluorination of phosphogypsum. The prepared aluminum-magnesium-based composite gel fluorine removal agent can form three synergistic fluorine removal mechanisms of precipitation, adsorption and lattice immobilization with fluorine in ardealite, the fluorine in the ardealite leachate is efficiently reduced, the fluorine in the ardealite leachate is stabilized below 10 ppm and is stable and not repeated, and the aluminum-magnesium-based composite gel fluorine removal agent has the advantages of deep and stable fluorine removal and resource circulation.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of phosphogypsum defluorination, and particularly relates to a preparation method and application of an aluminum-magnesium-based composite gel defluorination agent. BACKGROUND

[0002] Phosphogypsum is a main industrial by-product in the production of wet-process phosphoric acid by using phosphate rock as raw material. The main component of phosphogypsum is calcium sulfate dihydrate. During the reaction of phosphate rock and sulfuric acid, fluoride (such as fluoride in fluorapatite) is released in the form of hydrofluoric acid (HF) or fluorosilicic acid (H2SiF6). These fluoride-containing substances subsequently combine with calcium, sodium, aluminum and other ions in the reaction system to form insoluble or soluble fluorides, which are finally retained in phosphogypsum. Common fluoride-containing compounds include calcium fluoride, sodium fluorosilicate, etc. At present, the main treatment method for phosphogypsum is stockpiling. The residual soluble fluorides in phosphogypsum can be leached into groundwater and surrounding soil with rainwater, causing serious environmental pollution and threatening the health of animals, plants and humans. It may lead to diseases such as fluorosis and dental fluorosis. When phosphogypsum is used as a resource, the residual fluorine will also have a negative impact. For example, when phosphogypsum is used to prepare building materials, fluorides will affect the setting time and strength of cement and gypsum building materials, resulting in unstable product performance. When phosphogypsum is used to improve alkaline soil, excessive fluorine will poison soil microorganisms and crops, causing secondary pollution.

[0003] At present, various physical, chemical and thermal treatment methods have been developed for phosphogypsum defluorination. For example, water washing method: the fluorine content is reduced by multiple water washing, but the water consumption is large, the wastewater treatment cost is high, and the fluorine removal rate is only 60%-70%; lime neutralization method: adding lime (CaO) to generate CaF2 precipitate, but the fluorine in the leaching solution still reaches 50-80 mg / L, and the pH value of the gypsum is high; adsorption method: using activated alumina, zeolite and other adsorbents, but the adsorption capacity is low (<15 mg / g) and the fluorine in the leaching solution is high. Therefore, defluorination agents are generally prepared for phosphogypsum defluorination at present.

[0004] Chinese patent CN118184065A discloses a phosphogypsum slag fluorine fixation and phosphorus locking and wastewater deep treatment system and method, which adds a fluorine fixation and phosphorus locking agent to the phosphogypsum to fix fluorine, wherein the fluorine fixation and phosphorus locking agent is a polymer, and the production ratio is modified clay: lanthanum: polyaluminum ferric chloride = 20:1:2, and polyacrylamide (PAM) is additionally added, and the dosage is 0.8 kg of fluorine fixation and phosphorus locking agent and 15 g of polyacrylamide per ton of phosphogypsum slag. After the fluorine fixation and phosphorus locking treatment, the fluorine content of the phosphogypsum can be reduced from about 3000 mg / L to about 1000 mg / L, and the phosphorus content can be reduced from about 1500 mg / L to about 600 mg / L. However, it needs to be filtered through multiple layers of steel wire mesh layers for liquid flow flocculation reaction and then flows out, and is diffused into the phosphogypsum slag heap, and can only prevent the diffusion of high fluorine and high phosphorus and is limited to the field of phosphogypsum storage, and the leachate and wastewater still need to be separately deep treated.

[0005] Chinese patent CN118908390A discloses a preparation method and application of a phosphogypsum leachate defluorination agent, which utilizes phosphogypsum and ammonium carbonate to obtain calcium carbonate slag, and then mixes the calcium carbonate slag, phosphorus tailings, cerium sulfate, and a pH adjusting agent for wet grinding, filters the mixture, and then adds an activator and 3-sulfopropyl potassium methacrylate to the filter residue for calcination to obtain the defluorination agent. The defluorination agent has the advantages of low silicon and fluorine dissolution rate, stable structure, many surface pores, and many adsorption sites, can effectively remove fluorine ions in the phosphogypsum leachate, has a low phosphorus loss rate in the phosphogypsum leachate, has a small amount of sludge, has a significant effect on alleviating fluorine and silicate scaling of the membrane treatment system, and finally has a fluorine removal rate of more than 97%. However, the defluorination agent is used for defluorination of the phosphogypsum leachate and cannot be directly mixed with the phosphogypsum for defluorination. Therefore, it is important to develop a defluorination agent that is efficient, low-cost, anti-interference, and can directly act on phosphogypsum with high solid content, realizes efficient and stable fluorine removal, does not affect the subsequent resource utilization of the phosphogypsum, and promotes the resource utilization of the phosphogypsum. SUMMARY

[0006] To solve the above technical problems, the application provides a preparation method and application of an aluminum-magnesium-based composite gel defluorination agent, which realizes efficient reduction of fluorine in phosphogypsum, stabilizes fluorine in the phosphogypsum leachate at less than 10 ppm, and has the advantages of deep and stable defluorination and resource recycling.

[0007] To achieve the above purpose, the application provides a preparation method of an aluminum-magnesium-based composite gel defluorination agent, which comprises the following steps: (1) Dissolve an aluminum source and a magnesium source in water and stir until uniform, then gradually adjust the pH value with lye, and control the pH value at 9-9.5 to obtain Al(OH)3-Mg(OH)2 coprecipitated gel; (2) Add a pore-forming agent, and age at 60°C for 12 h to induce the gel to form a porous structure (micropores and mesopores), increase the specific surface area and porosity, and collect the gel precipitate; - Provide more diffusion channels and adsorption sites, while stabilizing the gel skeleton; (3) Soak the gel precipitate in a phosphoric acid solution for 1-3 h, then wash with water until neutral, dry at 80-105°C, crush to 100-200 mesh, and obtain an aluminum-magnesium-based composite gel fluoride removal agent.

[0008] Preferably, the molar ratio of the aluminum source to the magnesium source in step (1) is 1-2.5:1, and the total concentration of aluminum ions and magnesium ions (Al 3+ and Mg 2+ ) after being dissolved in water is 0.5 mol / L.

[0009] Further preferably, the aluminum source is any one of aluminum sulfate, aluminum chloride, polyaluminum sulfate, polyaluminum chloride, and aluminum nitrate, and the magnesium source is any one of magnesium chloride, magnesium sulfate, and magnesium nitrate.

[0010] Preferably, the amount of the pore-forming agent in step (2) is 4-7% of the mass of the Al(OH)3-Mg(OH)2 coprecipitated gel.

[0011] Further preferably, the pore-forming agent in step (2) is any one of an organic polymer, an inorganic salt, or a carbonaceous material.

[0012] More preferably, the organic polymer is polyethylene glycol, the inorganic salt is ammonium bicarbonate, and the carbonaceous material is starch.

[0013] More preferably, the molecular weight of the polyethylene glycol is 200-2000, preferably 200-400, and more preferably 400.

[0014] Preferably, the concentration of the phosphoric acid solution in step (3) is 0.1-0.5 mol / L.

[0015] The application also provides an application of the aluminum-magnesium-based composite gel fluoride removal agent, which is an application in phosphogypsum fluoride removal.

[0016] Preferably, the solid content of the phosphogypsum is 75-90%.

[0017] Preferably, the application comprises the following steps: (1) Prepare the aluminum-magnesium-based composite gel fluoride removal agent into a fluoride removal solution with a mass concentration of 40-60%; (2) Adjust the pH of the phosphogypsum to 6-8, then add the fluoride removal agent solution, stir, and separate the solid and liquid to complete the fluoride removal.

[0018] Preferably, the amount of the defluorination agent in step (2) is 1-5% of the mass of the phosphogypsum.

[0019] The present application has the following advantages: 1. The traditional aluminum salt defluorination agent is compounded with magnesium salt. The Mg 2+ introduced by the magnesium salt can ion exchange with fluoride ions (F - ). The Mg 2+ has a certain ion exchange capacity, which can displace F - adsorbed on the surface of the material and combine with F - itself, thereby increasing the adsorption sites of the material for F - . Compared with a single aluminum salt defluorination agent, the fluoride adsorption capacity is significantly improved after adding magnesium salt, which can reach 25-35 mg / g, while a single aluminum-based material usually only has 10-15 mg / g.

[0020] 2. The addition of pore-forming agents can form a mesoporous structure of 2-5 nm, and the porosity can be increased from 40% to 50-55%, thereby increasing the specific surface area of the defluorination agent, promoting the diffusion and adsorption of F - in the pore channel, and improving the adsorption capacity. Phosphoric acid can preferentially dissolve the amorphous components in the gel, exposing high-activity Al-OH and Mg-OH sites, and generating aluminum magnesium phosphate (such as Mg3(PO4)2, AlPO4) framework, thereby enhancing the mechanical strength of the material. After crushing, more than 80% of the initial porosity can be retained, while a low-strength gel may only retain 50%.

[0021] 3. The porous gel structure is formed by aluminum-magnesium coprecipitation coupled with phosphoric acid activation, and the three synergistic defluorination mechanisms of precipitation, adsorption, and lattice fixation with fluorine in phosphogypsum are realized, thereby achieving efficient reduction of fluorine in phosphogypsum. The fluorine in the leaching solution of the phosphogypsum is stably maintained at less than 10 ppm and does not repeat, and the advantages of deep and stable defluorination and resource recycling are combined. BRIEF DESCRIPTION OF DRAWINGS

[0022] Figure 1 The flowchart of the present application is shown. DETAILED DESCRIPTION

[0023] The technical solutions of the present application will be further explained and described below in combination with the drawings and specific embodiments. It should be noted that the following embodiments are only preferred embodiments of the present application and should not be understood as limiting the present application. The protection scope of the present application should be based on the content recited in the claims. Modifications and replacements of the technical solutions of the present application made by those skilled in the art without creative labor fall within the protection scope of the present application.

[0024] In the following examples, phosphogypsum is sourced from Yidu Xingfa Chemical Co., Ltd. factory, and the main component is calcium sulfate dihydrate (CaSO4·2H2O), with a content of 85-90%, and F-content of 0.2-0.3%.

[0025] Example 1 (1) Dissolve aluminum sulfate and magnesium chloride in water at a molar ratio of 1:1, and prepare a 0.5 mol / L mixed solution. Slowly adjust the pH to 9.0 with a NaOH solution (concentration of 0.1 mol / L) to form an Al(OH)3-Mg(OH)2 co-precipitation gel; (2) Add polyethylene glycol (PEG400) and age at 60°C for 12h. Centrifuge the mixed system at 3000rpm for 10min, and collect the wet gel precipitate; the amount of polyethylene glycol is 5% of the mass of the Al(OH)3-Mg(OH)2 co-precipitation gel; (3) Soak the aged gel in a 0.1 mol / L phosphoric acid solution for 2h, then wash with water until neutral, and then dry at 80°C until the gel powder is not sticky and the water content is less than 5%. Finally, obtain a stable structure, high specific surface area fluoride removal agent, and crush to 100 mesh to obtain an aluminum-magnesium-based composite gel fluoride removal agent.

[0026] Example 2 (1) Dissolve aluminum sulfate and magnesium chloride in water at a molar ratio of 2.5:1, and prepare a 0.5 mol / L mixed solution. Slowly adjust the pH to 9.0 with a NaOH solution (concentration of 0.1 mol / L) to form an Al(OH)3-Mg(OH)2 co-precipitation gel; (2) Add polyethylene glycol (PEG-400) and age at 60°C for 12h. Filter the mixed system with a Buchner funnel to obtain the aged gel; the amount of polyethylene glycol is 5% of the mass of the Al(OH)3-Mg(OH)2 co-precipitation gel; (3) Soak the aged gel in a 0.1 mol / L phosphoric acid solution for 2h, then wash with water until neutral, and then dry at 90°C until the gel powder is not sticky and the water content is less than 5%. Crush to 100 mesh to obtain an aluminum-magnesium-based composite gel fluoride removal agent.

[0027] Example 3 (1) Dissolve aluminum chloride and magnesium sulfate in water at a molar ratio of 1.8:1, and prepare a 0.5 mol / L mixed solution. Adjust the pH to 9.5 with a 0.1 mol / L NaOH solution to form an Al(OH)3-Mg(OH)2 co-precipitation gel; (2) Add polyethylene glycol (PEG-400) and age at 60°C for 12h. Centrifuge the mixed system at 5000rpm for 10min to obtain the aged gel; the amount of polyethylene glycol is 4% of the mass of the Al(OH)3-Mg(OH)2 co-precipitation gel; (3) The aged gel was soaked in 0.3 mol / L phosphoric acid solution for 2 h, washed with water to neutral, dried at 100°C, and then crushed to 150 mesh to obtain the aluminum-magnesium-based composite gel fluoride removal agent.

[0028] Example 4 (1) Aluminum sulfate and magnesium chloride were dissolved in water in a 2:1 molar ratio to form a 0.5 mol / L mixed solution, and the pH was adjusted to 9.5 with a 0.1 mol / L NaOH solution to form an Al(OH)3-Mg(OH)2 coprecipitated gel; (2) Polyethylene glycol (PEG-400) was added, and the mixture was aged at 60°C for 12 h. The mixture was centrifuged at 4000 rpm for 10 min to obtain an aged gel. The amount of polyethylene glycol was 7% of the mass of the Al(OH)3-Mg(OH)2 coprecipitated gel; (3) The aged gel was soaked in 0.5 mol / L phosphoric acid solution for 2 h, washed with water to neutral, dried at 105°C, and then crushed to 200 mesh to obtain the aluminum-magnesium-based composite gel fluoride removal agent.

[0029] Comparative Example 1 (1) Aluminum sulfate was dissolved in water to form a 0.5 mol / L mixed solution, and the pH was adjusted to 9.0 with a 0.1 mol / L NaOH solution to form an Al(OH)3 gel; (2) Polyethylene glycol (PEG-400) was added, and the mixture was aged at 60°C for 12 h to obtain an aged gel. The amount of polyethylene glycol was 5% of the mass of the Al(OH)3 gel; (3) The aged gel was soaked in 0.1 mol / L phosphoric acid solution for 2 h, washed with water to neutral, dried at 80°C, and then crushed to 100 mesh to obtain the aluminum-based gel fluoride removal agent.

[0030] Comparative Example 2 (1) Magnesium chloride was dissolved in water to form a 0.5 mol / L mixed solution, and the pH was adjusted to 9.0 with a 0.1 mol / L NaOH solution to form an Mg(OH)2 gel; (2) Polyethylene glycol (PEG-400) was added, and the mixture was aged at 60°C for 12 h to obtain an aged gel. The amount of polyethylene glycol was 5% of the mass of the Mg(OH)2 gel; (3) The aged gel was soaked in 0.1 mol / L phosphoric acid solution for 2 h, washed with water to neutral, dried at 80°C, and then crushed to 100 mesh to obtain the magnesium-based gel fluoride removal agent.

[0031] Comparative Example 3 (1) aluminum sulfate and magnesium chloride were dissolved in water according to a 1:1 molar ratio to form a 0.5 mol / L mixed solution, and the pH was adjusted to 9.0 with a 0.1 mol / L NaOH solution to form an Al(OH)3-Mg(OH)2 coprecipitation gel; (2) polyethylene glycol (PEG-400) was added, and the aged gel was obtained after aging at 60°C for 12 h; the amount of polyethylene glycol was 5% of the mass of the Al(OH)3-Mg(OH)2 coprecipitation gel; (3) the aged gel was washed to neutral, then dried at 80°C, and crushed to 100 mesh to obtain an aluminum-magnesium-based gel fluoride removal agent.

[0032] Comparative Example 4 (1) aluminum sulfate and magnesium chloride were dissolved in water according to a 1:1 molar ratio to form a 0.5 mol / L mixed solution, and the pH was adjusted to 9.0 with a 0.1 mol / L NaOH solution to form an Al(OH)3-Mg(OH)2 coprecipitation gel; (2) the Al(OH)3-Mg(OH)2 coprecipitation gel was washed to neutral, then dried at 80°C, and crushed to 100 mesh to obtain an aluminum-magnesium-based gel fluoride removal agent.

[0033] Comparative Example 5 (1) aluminum sulfate and magnesium chloride were dissolved in water according to a 3:1 molar ratio to form a 0.5 mol / L mixed solution, and the pH was adjusted to 9.0 with a 0.1 mol / L NaOH solution to form an Al(OH)3-Mg(OH)2 coprecipitation gel; (2) polyethylene glycol (PEG-400) was added, and the aged gel was obtained after aging at 60°C for 12 h; the amount of polyethylene glycol was 5% of the mass of the Al(OH)3-Mg(OH)2 coprecipitation gel; (3) the aged gel was soaked in a 0.1 mol / L phosphoric acid solution for 2 h, then washed to neutral, then dried at 80°C, and crushed to 100 mesh to obtain an aluminum-magnesium-based composite gel fluoride removal agent.

[0034] Comparative Example 6 (1) aluminum sulfate and magnesium chloride were dissolved in water according to a 1:2 molar ratio to form a 0.5 mol / L mixed solution, and the pH was adjusted to 9.0 with a 0.1 mol / L NaOH solution to form an Al(OH)3-Mg(OH)2 coprecipitation gel; (2) polyethylene glycol (PEG-400) was added, and the aged gel was obtained after aging at 60°C for 12 h; the amount of polyethylene glycol was 5% of the mass of the Al(OH)3-Mg(OH)2 coprecipitation gel; (3) the aged gel was soaked in a 0.1 mol / L phosphoric acid solution for 2 h, then washed to neutral, then dried at 80°C, and crushed to 100 mesh to obtain an aluminum-magnesium-based composite gel fluoride removal agent.

[0035] Comparative Example 7 (1) Dissolve aluminum sulfate and magnesium chloride in water at a molar ratio of 1:1 to prepare a 0.5 mol / L mixed solution. Adjust the pH to 9.0 with 0.1 mol / L NaOH solution to form an Al(OH)3-Mg(OH)2 coprecipitate gel. (2) Polyethylene glycol (PEG-400) was added and aged at 60°C for 12 hours to obtain an aged gel; the amount of polyethylene glycol used was 10% of the mass of the Al(OH)3-Mg(OH)2 coprecipitated gel. (3) Soak the aged gel in 0.1 mol / L phosphoric acid solution for 2 hours, wash it with water until it is neutral, dry it at 80℃, and pulverize it to 100 mesh to obtain aluminum-magnesium-based composite gel defluorinating agent.

[0036] Comparative Example 8 (1) Dissolve aluminum sulfate and magnesium chloride in water at a molar ratio of 1:1 to prepare a 0.5 mol / L mixed solution. Adjust the pH to 9.0 with 0.1 mol / L NaOH solution to form an Al(OH)3-Mg(OH)2 coprecipitate gel. (2) Polyethylene glycol (PEG-400) was added and aged at 60°C for 12 hours to obtain an aged gel; the amount of polyethylene glycol used was 5% of the mass of the Al(OH)3-Mg(OH)2 coprecipitated gel; (3) Soak the aged gel in 1.0 mol / L phosphoric acid solution for 2 hours, wash it with water until it is neutral, dry it at 80°C, and pulverize it to 100 mesh to obtain aluminum-magnesium-based composite gel defluorinating agent.

[0037] Example 5 The defluorinating agents prepared in the above examples and comparative examples were tested for porosity and mesopore diameter before and after pulverization using the BET method, and their adsorption capacity was tested using a fluoride ion meter. The results are shown in Table 1. Table 1 Physicochemical properties of defluorinating agents

[0038] The results showed that adding magnesium salt to traditional aluminum salt defluorinating agents resulted in the introduction of Mg by the magnesium salt. 2+ Can react with fluoride ions (F - Ion exchange occurs, enhancing adsorption. Compared to single aluminum salt defluorinators, the addition of magnesium salt increases fluoride adsorption capacity. Adding an appropriate amount of pore-forming agent creates a 2-5 nm mesoporous structure in the gel, increasing porosity and promoting fluoride adsorption. - Diffusion and adsorption within the pores enhance adsorption capacity, but excessive pore-forming agent results in mesopores <2nm, leading to reduced F0. -The adsorption capacity is reduced; the phosphoric acid can preferentially dissolve the amorphous phase components in the gel, exposing high-activity Al-OH and Mg-OH sites, and generating aluminum magnesium phosphate (such as Mg3(PO4)2, AlPO4) frameworks, enhancing the mechanical strength of the material, and after crushing, more than 80% of the initial porosity can be retained, while the low-strength gel without the addition of phosphoric acid only retains 50%.

[0039] Example 6 (1) The defluorination agent prepared in the above examples and comparative examples was configured into a defluorination agent solution with a mass concentration of 50%; (2) The pH value of the phosphogypsum was adjusted to 6 using limestone, the solid content of the phosphogypsum was 75%, and 3% of the defluorination agent based on the mass of the phosphogypsum was added. After stirring for 30 min, the phosphogypsum leaching solution was collected, the concentration of fluoride ions therein was detected, and the defluorination rate was calculated. The results are shown in Table 2; wherein the initial F - The leaching concentration was 90 mg / L; Table 2 Fluoride ion leaching in phosphogypsum leaching solution

[0040] The results show that: through aluminum-magnesium coprecipitation coupled with phosphoric acid activation, a porous gel structure is formed, which realizes efficient reduction of fluorine in phosphogypsum through three synergistic defluorination mechanisms of precipitation, adsorption, and lattice fixation with fluorine in phosphogypsum, and the defluorination rate is stably above 90%.

[0041] Example 7 (1) The aluminum-magnesium-based composite gel defluorination agent prepared in Example 1 was configured into a defluorination agent solution with a mass concentration of 50%; (2) The pH value of the phosphogypsum was adjusted to 6 using limestone, and 0%, 1%, 3%, 5%, and 8% of the defluorination agent based on the mass of the phosphogypsum was added, respectively. The solid content of the phosphogypsum was 75%, and after stirring for 30 min, the phosphogypsum leaching solution was collected, the concentration of fluoride ions therein was detected, and the defluorination rate was calculated. The results are shown in Table 3; wherein the initial F - The leaching concentration was 90 mg / L; Table 3 Fluoride ion leaching in phosphogypsum leaching solution

[0042] The results show that: the aluminum-magnesium-based composite gel defluorination agent can efficiently solve the high-fluorine problem of phosphogypsum leaching solution, and realize deep defluorination (F - ≤10 mg / L) at a low dosage (1%-5%), and has strong process adaptability (does not need to adjust the pH to strong alkalinity, and can stably operate under a solid content of 75%) Example 8 (1) The aluminum magnesium-based composite gel defluorination agent prepared in Example 1 was configured into a defluorination agent solution with a mass concentration of 50%; (2) The pH value of the phosphogypsum was adjusted to 6 by using limestone, 3% of the defluorination agent was added to the phosphogypsum, and the solid content of the phosphogypsum was adjusted, respectively, the solid content of the phosphogypsum was 50%, 75%, 80%, 85%, and 90%, the phosphogypsum leaching solution was collected after stirring for 30 min, the concentration of the fluorine ion in the phosphogypsum leaching solution was detected, and the defluorination rate was calculated, and the results are shown in Table 4. The initial F - The leaching concentration was 90 mg / L. Table 4 Fluorine ion leaching in phosphogypsum leaching solution

[0043] The results show that the aluminum magnesium-based composite gel defluorination agent can efficiently solve the high fluorine problem of the phosphogypsum leaching solution, the defluorination rate can reach 94.4% under the condition of 50% solid content, and deep defluorination (F - ≤ 10 mg / L) can be achieved under the condition of 75%-90% solid content, which can meet the dry material stirring, and no filter pressing treatment is required after defluorination, and the process adaptability is strong.

[0044] Example 9 (1) The aluminum magnesium-based composite gel defluorination agent prepared in Example 1 was configured into a defluorination agent solution with a mass concentration of 50%; (2) The pH value of the phosphogypsum was adjusted to 4, 6, 8, and 10 by using limestone, 3% of the defluorination agent was added to the phosphogypsum, the solid content of the phosphogypsum was 75%, the phosphogypsum leaching solution was collected after stirring for 30 min, the concentration of the fluorine ion in the phosphogypsum leaching solution was detected, and the defluorination rate was calculated, and the results are shown in Table 5. The initial F - The leaching concentration was 90 mg / L. Table 5 Fluorine ion leaching in phosphogypsum leaching solution

[0045] The results show that the aluminum magnesium-based composite gel defluorination agent has a low defluorination rate at a pH value of 4, can efficiently solve the high fluorine problem of the phosphogypsum leaching solution when the pH value is above 6, the defluorination rate can reach 93.3%, and the defluorination efficiency can be improved by increasing the pH value, but the pH value of the phosphogypsum exceeds the standard.

[0046] Example 10 (1) The aluminum magnesium-based composite gel defluorination agent prepared in Example 1 was configured into a defluorination agent solution with a mass concentration of 50%; (2) The pH value of the phosphogypsum is adjusted to 6 by using limestone, 3% of the mass of the phosphogypsum is added with a fluoride removal agent, the solid content of the phosphogypsum is 75%, the phosphogypsum leaching solution is collected after stirring for 30 min, the concentration of the fluoride ions in the phosphogypsum leaching solution is detected, and the fluoride removal rate is calculated; wherein the initial F - The leaching concentration is 90 mg / L, and the total mass of the slurry is 100 t.

[0047] The F - concentration of the phosphogypsum leaching solution after treatment is reduced to 8 mg / L, the fluoride removal rate is 91.1%, and the stability is good.

[0048] Example 11 The phosphogypsum after fluoride removal in the implementation case 10 is leached with different pH value acid water according to a solid-liquid ratio of 1:2, the acid water leaching in the open air is simulated, the leaching solution content in the phosphogypsum after leaching is detected, wherein the initial F - The leaching concentration is 8 mg / L.

[0049] Table 6 Fluoride ion leaching in the phosphogypsum leaching solution

[0050] The results show that the fluorine in the phosphogypsum after fluoride removal treatment is very stable, and the fixed fluorine cannot be released under the action of the acid water.

Claims

1. A method for preparing an aluminum magnesium-based composite gel fluoride removal agent, characterized by comprising the following steps: The method comprises the following steps: ​ (1) dissolving aluminum source and magnesium source in water, adjusting pH to obtain Al(OH)3-Mg(OH)2 co-precipitation gel; (2) adding pore-forming agent, aging and collecting gel precipitate; (3) soaking the gel precipitate in phosphoric acid solution for 1-3 hours, washing to neutral, drying and crushing to obtain aluminum-magnesium-based composite gel fluoride removal agent.

2. The preparation method of the aluminum-magnesium-based composite gel fluoride removal agent according to claim 1, characterized in that: The molar ratio of the aluminum source to the magnesium source in step (1) is 1-2.5:1, and the total concentration of metal ions after being dissolved in water is 0.5 mol / L.

3. The method for preparing an aluminum-magnesium-based composite gel fluoride removal agent according to claim 2, characterized by: The aluminum source is any one of aluminum sulfate, aluminum chloride, polyaluminum sulfate, polyaluminum chloride and aluminum nitrate; and the magnesium source is any one of magnesium chloride, magnesium sulfate and magnesium nitrate.

4. The method for preparing an aluminum-magnesium-based composite gel fluoride removal agent according to claim 1, characterized by: The amount of the pore-forming agent in step (2) is 4-7% of the mass of the Al(OH)3-Mg(OH)2 co-precipitation gel.

5. The method for preparing an aluminum-magnesium-based composite fluoride-removal agent according to claim 4, characterized in that: The pore-forming agent in step (2) is any one of polyethylene glycol, ammonium bicarbonate and starch.

6. The method for preparing an aluminum-magnesium-based composite fluoride-removal agent according to claim 1, characterized in that: The concentration of the phosphoric acid solution in step (3) is 0.1-0.5 mol / L.

7. The application of an aluminum-magnesium based composite gel defluorinator prepared by the preparation method according to any one of claims 1-6, characterized in that: The application is the application in defluorination of phosphogypsum.

8. Use according to claim 7, characterized in that: The solid content of the phosphogypsum is 75-90%.

9. Use according to claim 7, characterized in that: The application comprises the following steps: (1) configuring the aluminum-magnesium-based composite gel fluoride removal agent into a fluoride removal solution with a mass concentration of 40-60%; (2) adjusting the pH of the phosphogypsum, adding the fluoride removal agent solution, stirring and completing defluorination.

10. Use according to claim 9, characterized in that: The amount of the fluoride removal agent in step (2) is 1-5% of the mass of the phosphogypsum.

Images