A process and device for recycling phosphochemical wastewater

Abstract

A process and device for recycling phosphochemical wastewater. A combined process of "chemical precipitation + freeze crystallization separation + membrane separation" is used to separately treat the phosphorus-containing wastewater. Pollutants such as phosphorus and fluorine precipitate out as calcium phosphate and fluoride slag in the chemical precipitation process section, and it is ensured that the lime content therein is very low. Salts such as calcium, magnesium, and sodium are frozen and concentrated and precipitated out in the freeze crystallization process section. At the same time, water is transformed into ice and further forms light brine, and then water is extracted in the membrane separation process section to produce industrial recycled water meeting the industrial recycled water standard. Compared with the traditional process, its advantage lies in the generation of calcium phosphate and fluoride slag with low lime content, which can be reused as crude phosphate rock, and other salts are also separately recovered. Basically, all water can be recycled. While recycling phosphorus, fluorine, other salts, and water, since waste is turned into treasure, certain economic benefits are formed, achieving the dual effects of environmental protection and economy, and the environmental protection and economic benefits are very remarkable.

Description

Technical Field

[0001] The present invention belongs to the field of environmental protection technology - wastewater treatment technology, and particularly relates to a process and device for recycling phosphochemical wastewater. Background Art

[0002] Phosphorite is a mineral resource, and its downstream industries mainly include phosphate fertilizers, pesticides, phosphates, phosphoric acid, etc., which are widely used in industries such as agriculture, food, flame retardants, detergents, and electronics; at present, the proven reserves of phosphorite in China are about 3.2 billion tons, and the production capacity is about 85 million tons / year. As a non-renewable resource, the sustainable development and utilization of phosphorite are directly related to food security and production and life.

[0003] The phosphorite mined from nature contains a large amount of impurities. Therefore, before using phosphorite to produce products, it is necessary to wash and select the phosphorite, and a large amount of washing wastewater containing phosphorus and fluorine is produced as a by-product. During the production process of phosphochemical products, a large amount of phosphogypsum is also produced as a by-product, and a large amount of phosphogypsum leachate is generated at the same time. In addition, a large amount of other phosphorus-containing wastewater is also generated in the phosphochemical industry chain. Due to the physical properties of phosphorite and the characteristics of phosphochemical processes, common phosphochemical wastewater contains a large amount of pollutants such as phosphorus, fluorine, and acid. If these pollutants are directly discharged into the environment, it will bring great ecological disasters. Therefore, it is imperative to effectively treat phosphochemical wastewater.

[0004] The conventional process for treating phosphochemical wastewater is to use the lime precipitation method. That is: directly add lime to the phosphochemical wastewater. Since pollutants such as phosphorus and fluorine will react with calcium to form precipitates and precipitate out, and at the same time, since lime is alkaline, it also neutralizes the acid in the wastewater, and finally the wastewater can meet the discharge standards for all indicators. The chemical reactions that occur are as follows:

[0005] H + + Ca(OH)2→Ca 2+ +H2O,

[0006] Ca 2+ +PO4 3- →Ca3(PO4)↓,

[0007] Ca 2+ +F - →CaF2↓.

[0008] Chinese Patent CN102328984A discloses a method for treating phosphochemical wastewater, which mixes the acidic wastewater from the sulfuric acid process titanium dioxide industry with phosphochemical wastewater, and then adds lime milk or carbide slag for neutralization. The reaction system is settled and the solid-liquid separation is carried out to obtain wastewater meeting the discharge standard; Chinese Patent CN105254073A discloses a phosphochemical wastewater treatment and reuse system and its implementation method, which obtains wastewater meeting the discharge standard through steps such as lime neutralization, flocculation, precipitation, and chemical phosphorus removal of phosphochemical wastewater; Chinese Patent CN102690000A discloses a method for recovering phosphorus in phosphochemical wastewater by using struvite production process, which removes inorganic fluoride ions in the wastewater by the quicklime method after preliminary sedimentation and separation of phosphochemical wastewater, and then removes inorganic cations by the cation exchange method. Finally, the obtained wastewater is used to prepare phosphatase particle waste in a struvite reactor, and the effluent of the struvite reaction can be directly discharged up to the standard.

[0009] Since calcium hydroxide (Ca(OH)2) is slightly soluble in water and has limited solubility in water, in order to make the phosphorus and fluorine in the final product water meet the standards, the pH value of the reaction needs to be controlled above 10. Therefore, a large amount of lime needs to be added, resulting in a large amount of unreacted lime in the final phosphorus-fluorine slag, thus bringing the problem of a large amount of slag production. In addition, due to the unreacted lime mixing into the phosphorus-fluorine waste slag, the resulting alkaline phosphorus-fluorine slag cannot be directly recycled into production, and the formed alkaline hazardous waste needs to be further disposed of. If backfilled into a landfill, pollutants will gradually accumulate in the system, bringing great risks to the treatment system. At the same time, since there are still a large amount of calcium, magnesium, and sodium ions in the water, although pollutants such as phosphorus and fluorine have been removed, the salt content is relatively high and it still cannot be recycled for production. This part of the brine can only be discharged. Therefore, the traditional process not only causes a large amount of water resource waste, but also brings a large amount of salt to the natural water body. In summary, although the traditional process can make the water quality meet the standard for external discharge when treating phosphochemical wastewater, there are problems such as high treatment costs, ineffective recovery and utilization of phosphorus and fluorine resources, large amounts of hazardous waste slag production, water resource waste, and environmental unfriendliness. Summary of the Invention

[0010] In order to solve the above technical problems, the present invention provides a process and device for recycling phosphochemical wastewater, which separately recovers the phosphorus, fluorine, calcium, magnesium, and sodium components in the wastewater in the form of phosphorus-fluorine mixed salts (mainly calcium phosphate and calcium fluoride) and calcium-magnesium-sodium mixed salts (mainly magnesium sulfate, calcium sulfate, sodium chloride, and sodium sulfate), and all the water resources are recycled as industrial recycled water and no longer discharged externally.

[0011] The technical solution adopted by the present invention is as follows:

[0012] The present invention provides a process for recycling phosphochemical wastewater, specifically including the following steps:

[0013] (1)Add lime milk with a concentration of 1% - 30% to the phosphochemical wastewater, control the reaction pH to 3.5 - 7.0, react, precipitate and separate to obtain a phosphorus-fluorine mixed salt and a primary clear liquid;

[0014] (2)The primary clear liquid is frozen and crystallized at -40°C to 0°C, separated to obtain solid ice and a concentrated mother liquor. The solid ice is melted to obtain a secondary clear liquid. The concentrated mother liquor is divided into three paths. One path is that the reflux concentrated mother liquor exchanges heat with the primary clear liquid and then returns to step (1) for secondary reaction to precipitate and separate phosphorus and fluorine elements. One path is that the circulating concentrated mother liquor provides cooling capacity through circulating cooling. One path is that after solid-liquid separation, concentrated water and a calcium-magnesium-sodium mixed salt are obtained, and the concentrated water continues to be frozen and crystallized;

[0015] (3)The secondary clear liquid is divided into two paths. One path is that the circulating secondary clear liquid is circulated and heated. The other path is the externally sent secondary clear liquid, which exchanges heat with the primary clear liquid and then undergoes reverse osmosis membrane separation for desalination to obtain concentrated water and industrial recycled water, and the concentrated water returns to step (2) for secondary freezing and crystallization.

[0016] Preferably, the freezing and ice formation rate in step (2) is 5% - 60%; the flow rate of the circulating concentrated mother liquor is 2 - 30 times that of the primary clear liquid; the flow rate of the reflux concentrated mother liquor is 40% - 95% of that of the primary clear liquid.

[0017] Preferably, the flow rate of the circulating secondary clear liquid in step (3) is 1 - 35 times that of the primary clear liquid.

[0018] According to the above process, the present invention also provides a device for recycling phosphochemical wastewater. The bottom discharge port of the lime silo is connected to the feed port of the lime screw conveyor. The discharge port of the lime screw conveyor is connected to the feed port at the top of the lime milk pulping tank. The bottom outlet of the lime milk pulping tank is connected to the phosphorous-fluorine reaction tank through a lime milk delivery pump; the slurry outlet of the phosphorous-fluorine reaction tank is connected to the upper inlet of the phosphorous-fluorine sedimentation tank; one side of the phosphorous-fluorine sedimentation tank is provided with a clear liquid outlet, which is fixedly connected to the primary clear liquid tank through a pipeline. The primary clear liquid tank is connected to a secondary clear liquid heat exchanger and a reflux concentrated mother liquor heat exchanger respectively through a primary clear liquid delivery pump. The secondary clear liquid heat exchanger and the reflux concentrated mother liquor heat exchanger are connected to an integrated freezing and crystallization separator through pipelines. One side of the upper part of the integrated freezing and crystallization separator is provided with a floating ice outlet and is connected to a defrosting tank. The defrosting tank is sequentially connected to the secondary clear liquid tank through a secondary clear liquid delivery pump and a secondary clear liquid heat exchanger. The secondary clear liquid tank is connected to a reverse osmosis membrane module through a reverse osmosis feed water pump and a reverse osmosis booster pump.

[0019] Preferably, the bottom of the phosphorous-fluorine sedimentation tank is provided with a mixed liquid outlet, and is transported to a phosphorous-fluorine mixed salt filter through a phosphorous-fluorine mixed salt delivery pump; the bottom of the phosphorous-fluorine mixed salt filter is provided with a mixed salt outlet to discharge solid substances, and one side is provided with a clear liquid outlet and is connected to the phosphorous-fluorine sedimentation tank through a pipeline.

[0020] Preferably, the lower part of one side of the integrated freezing crystallization separator is connected to the circulating concentrated mother liquor cooler through a concentrated mother liquor transfer pump, and the circulating concentrated mother liquor cooler is then connected to the inlet pipeline on one side of the integrated freezing crystallization separator; the integrated freezing crystallization separator is also connected to the cold-side inlet of the reflux concentrated mother liquor heat exchanger through a concentrated mother liquor transfer pump, and the cold-side outlet of the reflux concentrated mother liquor heat exchanger is connected to the phosphorus and fluorine reaction tank through a pipeline; an automatic ice scraper is also provided inside the integrated freezing crystallization separator.

[0021] Preferably, the bottom of the integrated freezing crystallization separator is connected to the calcium, magnesium and sodium mixed salt filter through a mixed salt transfer pump. The bottom of the calcium, magnesium and sodium mixed salt filter is provided with a mixed salt outlet for discharging solid substances, and a clear liquid outlet is provided on one side and is connected to the integrated freezing crystallization separator through a pipeline.

[0022] Preferably, the ice melting tank is also connected to the refrigeration unit through a secondary clear liquid transfer pump. The secondary clear liquid is heated up after heat exchange in the refrigeration unit and then transported back to the ice melting tank from the refrigeration unit. The refrigeration unit contains a secondary coolant. After the secondary coolant is cooled down in the refrigeration unit, it is transported to the secondary coolant tank through a pipeline. The secondary coolant tank is connected to the circulating concentrated mother liquor cooler through a secondary coolant circulation pump, and the circulating concentrated mother liquor cooler is then connected to the refrigeration unit.

[0023] Preferably, the bottom of the reverse osmosis membrane module is provided with a concentrated water outlet. A part of the outflowing concentrated water is mixed with the water pumped out by the reverse osmosis circulation pump and the reverse osmosis booster pump and enters the reverse osmosis membrane module for secondary concentration separation; the other part is transported back to the primary clear liquid tank through a pipeline for secondary freezing crystallization.

[0024] Beneficial effects

[0025] 1. The present invention adopts chemical precipitation to precipitate valuable mineral resources such as phosphorus and fluorine in the phosphorus chemical wastewater with a relatively high purity. The lime content in the phosphorus and fluorine mixed salt does not exceed 1%. The phosphorus and fluorine mixed salt can be returned to other phosphorus chemical production process systems as crude phosphate rock, effectively improving the utilization rate of resources such as phosphorus and fluorine. At the same time, there is no need to landfill phosphorus and fluorine ore slag, greatly reducing the environmental protection pressure of the slag yard.

[0026] 2. The present invention adopts freezing crystallization separation to desalinate the primary clear liquid obtained after chemical precipitation. The produced clear liquid can be applied to the membrane separation system without fouling, and the water resources can be recycled. At the same time, two concentrated water refluxes are built in to ensure that all the water can finally be produced in the form of industrial recycled water, and the utilization rate of water resources reaches more than 98%. It effectively alleviates the environmental protection problem of discharging saline wastewater into the environment, saves water resources at the same time, and realizes zero discharge of waste liquid.

[0027] 3. The present invention enables salts with high solubility such as calcium, magnesium, and sodium to be concentrated and precipitated at low temperature through the form of low-temperature concentration and crystallization. The mixed salts can be used as raw materials for extracting magnesium salts, sodium salts, etc., thereby further reducing the comprehensive cost of treating phosphorus-containing wastewater and reducing the environmental protection pressure on enterprises.

[0028] 4. The present invention sets multiple coolers and heat exchangers in the freezing crystallization unit, enabling heat exchange between liquids. It can effectively utilize the heat and cold of the liquid itself to achieve heating and cooling, improve the refrigeration efficiency during the freezing crystallization process, and save energy and reduce consumption. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 is a schematic process flow diagram of the present invention.

[0030] Figure 2 is a schematic diagram of the device structure of the present invention.

[0031] In the figure: In the figure, 1 is a lime silo, 2 is a lime screw conveyor, 3 is a lime milk pulping tank, 4 is a lime milk transfer pump, 5 is a phosphorus-fluorine reaction tank, 6 is a phosphorus-fluorine sedimentation tank, 7 is a phosphorus-fluorine mixed salt transfer pump, 8 is a phosphorus-fluorine mixed salt filter, 9 is a primary clear liquid tank, 10 is a primary clear liquid transfer pump, 11 is a secondary clear liquid heat exchanger, 12 is a reflux concentrated mother liquor heat exchanger, 13 is a circulating concentrated mother liquor cooler, 14 is a secondary refrigerant circulation pump, 15 is a secondary refrigerant tank, 16 is a refrigeration unit, 17 is a calcium-magnesium-sodium mixed salt filter, 18 is a concentrated mother liquor transfer pump, 19 is an integrated freezing crystallization separator, 20 is a mixed salt transfer pump, 21 is a defrosting tank, 22 is a secondary clear liquid transfer pump, 23 is a secondary clear liquid tank, 24 is a reverse osmosis feed pump, 25 is a reverse osmosis booster pump, 26 is a reverse osmosis circulation pump, 27 is a reverse osmosis membrane module, 28 is an automatic ice scraper.

[0032] DETAILED DESCRIPTION OF THE EMBODIMENTS

[0033] The following further explains the technical solution of the present invention in conjunction with the drawings and specific embodiments. It should be noted that the following embodiments are only the preferred embodiments of the present invention and should not be construed as limitations on the present invention. The protection scope of the present invention shall be subject to the content recorded in the claims. Modifications and substitutions made by those skilled in the art to the present invention without creative efforts fall within the protection scope of the present invention.

[0034] The characteristic pollutants in the phosphochemical wastewater used in the following embodiments refer to: the phosphorus content (calculated as P) is 50 mg / L to 100000 mg / L, the fluorine content (calculated as F) is 50 mg / L to 100000 mg / L, the magnesium content (calculated as Mg) is 100 mg / L to 100000 mg / L, and the sulfate content (calculated as SO4 2-The dosage (count) is between 500 mg / L and 100,000 mg / L, and the pH value is between 0 and 3.5.

[0035] Example 1

[0036] (1) Store the commercially available lime powder in the lime silo 1. When resource treatment is carried out on the phospho-chemical wastewater, open the valve at the bottom discharge port of the lime silo 1, and the lime powder is conveyed to the lime milk preparation tank 3 by the lime screw conveyor 2, and is stirred and mixed with the phospho-chemical wastewater in the lime milk preparation tank 3 to prepare lime milk with a concentration between 1% and 30%.

[0037] (2) Convey the lime milk in the lime milk preparation tank 3 to the phosphorus-fluorine reaction tank 5 by the lime milk delivery pump 4, and add the phospho-chemical wastewater therein. Control the pH between 3.5 and 7.0. After stirring and reacting for 5 to 60 minutes, discharge the clear liquid from the slurry outlet at the upper part of the phosphorus-fluorine reaction tank 5 and convey it to the phosphorus-fluorine sedimentation tank 6 to sediment and separate the phosphorus-fluorine mixed salt solid and impurities obtained by the reaction.

[0038] (3) The solid impurities sedimented in the phosphorus-fluorine sedimentation tank 6 are conveyed to the phosphorus-fluorine mixed salt filter 8 by the phosphorus-fluorine mixed salt delivery pump 7 for filtration. The filter residue is discharged from the bottom of the phosphorus-fluorine mixed salt filter 8 and recycled as mineral resources. The filtrate is refluxed to the phosphorus-fluorine sedimentation tank 6 through the pipeline for continuous sedimentation and separation.

[0039] (4) The clear liquid sedimented and separated in the phosphorus-fluorine sedimentation tank 6 is conveyed to the primary clear liquid tank 9 for stirring and mixing to obtain primary clear liquid, and then pumped out by the primary clear liquid delivery pump (10) and divided into two paths. One path is conveyed to the secondary clear liquid heat exchanger 11 for heat exchange, and the other path is conveyed to the reflux concentrated mother liquor heat exchanger 12 for heat exchange. After heat exchange, the primary clear liquid flowing out of the secondary clear liquid heat exchanger 11 and the reflux concentrated mother liquor heat exchanger 12 are converged into one stream and then conveyed to the integrated freezing crystallization separator 19. Control the temperature between -40°C and 0°C, and the freezing rate between 5% and 60%. Calcium salts, magnesium salts and sodium salts precipitate. The clear liquid with low salt concentration freezes and floats, and is scraped by the automatic ice scraper 28 to the outlet of the integrated freezing crystallizer 19 and conveyed to the ice melting tank 21; The solution with high salt concentration and the precipitated calcium salts and magnesium salts are located at the bottom of the integrated freezing crystallizer 19 to form concentrated mother liquor.

[0040] (5) The concentrated mother liquor is divided into three paths. One path is transported by the mixed salt transfer pump 20 to the calcium-magnesium-sodium mixed salt filter 17 for solid-liquid separation. The calcium-magnesium-sodium mixed salt (filter residue) is discharged for recycling, and the concentrated water is transported back to the integrated freezing crystallization separator 19 for further freezing crystallization for desalination treatment. One path is the circulating concentrated mother liquor, which is transported by the concentrated mother liquor transfer pump 17 to the circulating concentrated mother liquor cooler 13 for cooling, and then returned to the integrated freezing crystallization separator 19 to cool the liquid therein, improving the refrigeration efficiency. One path is the reflux concentrated mother liquor, which is transported by the concentrated mother liquor transfer pump 17 to the reflux concentrated mother liquor heat exchanger 12 to exchange heat with the primary clear liquid and then transported to the phosphorus-fluorine reaction tank 5 for secondary reaction sedimentation to ensure that most of the cold energy is recovered.

[0041] (5) The floating ice is stirred and melted into secondary clear liquid in the ice melting tank 21, and then divided into two paths by the secondary clear liquid transfer pump 22. One path is pumped into the refrigeration unit 16 to exchange heat and increase the temperature, and then transported back to the ice melting tank 21. The other path is pumped into the secondary clear liquid heat exchanger 11, exchanged heat with the primary clear liquid, and then transported to the secondary clear liquid tank 23 to ensure that most of the cold energy is recovered.

[0042] (6) The secondary clear liquid stored in the secondary clear liquid tank 23 is successively pumped into the reverse osmosis feed pump 24 and the reverse osmosis booster pump 25 and then into the reverse osmosis membrane module 27 for in-depth desalination of the secondary clear liquid to meet the industrial recycled water standard and be discharged as industrial recycled water. The concentrated water obtained from the treatment of the reverse osmosis membrane module 27 is discharged from its bottom outlet and divided into two paths. One path is pumped into the pipeline by the reverse osmosis circulation pump 26, merged with the water coming out of the reverse osmosis booster pump 25, and then circulated through the reverse osmosis membrane module 27. The other path is transported back to the primary clear liquid tank 9 for freezing crystallization treatment again.

[0043] The refrigeration unit 16 contains a coolant. The coolant exchanges cold energy with the secondary clear liquid in the refrigeration unit 16, is cooled and circulated, and then transported to the coolant tank 15 for storage through a pipeline. The coolant tank 15 is connected to the circulating concentrated mother liquor cooler 13 by the coolant circulation pump 14. The coolant exchanges heat with the circulating concentrated mother liquor in the circulating concentrated mother liquor cooler 13, is heated, and then transported back into the refrigeration unit 16 through a pipeline to circulate and cool the liquid in the device, recovering as much cold energy as possible and improving the refrigeration efficiency of the refrigeration unit 16.

Claims

1. An apparatus for recycling phosphochemical wastewater, characterized in that: The bottom discharge port of the lime silo (1) is connected to the feed port of the lime screw conveyor (2). The discharge port of the lime screw conveyor (2) is connected to the feed port at the top of the lime milk pulping tank (3). The bottom outlet of the lime milk pulping tank (3) is connected to the phosphorus-fluorine reaction tank (5) via the lime milk transfer pump (4). The slurry outlet of the phosphorus-fluorine reaction tank (5) is connected to the upper inlet of the phosphorus-fluorine sedimentation tank (6). One side of the phosphorus-fluorine sedimentation tank (6) is provided with a clear liquid outlet, which is fixedly connected to the primary clear liquid tank (9) via a pipeline. The primary clear liquid tank (9) is connected to the secondary clear liquid heat exchanger (11) and the reflux concentrated mother liquor heat exchanger (12) respectively via the primary clear liquid transfer pump (10). The secondary clear liquid heat exchanger (11) and the reflux concentrated mother liquor heat exchanger (12) are connected to the integrated freezing crystallization separator (19) via pipelines. One side of the upper part of the integrated freezing crystallization separator (19) is provided with a floating ice outlet and is connected to the ice melting tank (21). The ice melting tank (21) is connected to the secondary clear liquid tank (23) via the secondary clear liquid transfer pump (22) and the secondary clear liquid heat exchanger (11) in sequence. The secondary clear liquid tank (23) is connected to the reverse osmosis membrane module (27) via the reverse osmosis feed pump (24) and the reverse osmosis booster pump (25). One side of the lower part of the integrated freezing crystallization separator (19) is connected to the circulating concentrated mother liquor cooler (13) via the concentrated mother liquor transfer pump (18), and the circulating concentrated mother liquor cooler (13) is then connected to the pipeline at the inlet on one side of the integrated freezing crystallization separator (19). The integrated freezing crystallization separator (19) is also connected to the cold side inlet of the reflux concentrated mother liquor heat exchanger (12) via the concentrated mother liquor transfer pump (18). The cold side outlet of the reflux concentrated mother liquor heat exchanger (12) is connected to the phosphorus-fluorine reaction tank (5) via a pipeline. An automatic ice scraping machine (28) is also provided inside the integrated freezing crystallization separator (19). The ice melting tank (21) is also connected to the refrigeration unit (16) via the secondary clear liquid transfer pump (22). The secondary clear liquid is heated after heat exchange in the refrigeration unit (16) and then transported back to the ice melting tank (21) from the refrigeration unit (16). The refrigeration unit (16) contains a secondary coolant. The secondary coolant is cooled in the refrigeration unit (16) and then transported to the secondary coolant tank (15) via a pipeline. The secondary coolant tank (15) is connected to the circulating concentrated mother liquor cooler (13) via the secondary coolant circulation pump (14), and the circulating concentrated mother liquor cooler (13) is then connected to the refrigeration unit (16). The process of recycling phosphorus chemical wastewater using the said device comprises the following steps: (1) Add lime milk to the phosphorus chemical wastewater, react and precipitate to separate phosphorus-fluorine mixed salt and primary clear liquid. (2) Freeze and crystallize the primary clear liquid to separate solid ice and concentrated mother liquor. The solid ice melts to obtain secondary clear liquid. A part of the concentrated mother liquor returns to step (1) for secondary reaction precipitation, a part circulates to obtain cold energy, and a part is separated into concentrated water and calcium-magnesium-sodium mixed salt after solid-liquid separation. The concentrated water continues to be frozen and crystallized. (3) Perform membrane separation and desalination on the secondary clear liquid to obtain concentrated water and industrial recycled water. The concentrated water returns to step (2) for secondary freezing and crystallization.

2. The device according to claim 1, characterized in that: The bottom of the phosphorus-fluorine settling tank (6) is provided with a mixed liquid outlet, which is transported to the phosphorus-fluorine mixed salt filter (8) by a phosphorus-fluorine mixed salt transfer pump (7); the bottom of the phosphorus-fluorine mixed salt filter (8) is provided with a mixed salt outlet to discharge solid substances, and a clear liquid outlet is provided on one side and connected to the phosphorus-fluorine settling tank (6) through a pipeline.

3. The device according to claim 1, characterized in that: The bottom of the integrated freezing crystallization separator (19) is connected to the calcium-magnesium-sodium mixed salt filter (17) by a mixed salt transfer pump (20). The bottom of the calcium-magnesium-sodium mixed salt filter (17) is provided with a mixed salt outlet to discharge solid substances, and a clear liquid outlet is provided on one side and connected to the integrated freezing crystallization separator (19) through a pipeline.

4. The device according to claim 1, characterized in that: The bottom of the reverse osmosis membrane module (27) is provided with a concentrated water outlet. A part of the outflowing concentrated water is mixed with the water pumped out by the reverse osmosis circulation pump (26) and the reverse osmosis booster pump (25) and enters the reverse osmosis membrane module (27) for secondary concentration and separation; the other part is transported back to the primary clear liquid tank (9) through a pipeline for secondary freezing crystallization.

5. The device according to claim 1, characterized in that: The membrane described in step (3) of the process is a reverse osmosis membrane.

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