Process and system for recovering phosphorus and fluorine from phosphogypsum leachate

Abstract

The invention discloses a process and system for recovering phosphorus and fluorine from ardealite leachate, which comprises the following steps: feeding the ardealite leachate into an induced crystallization reactor for induced crystallization, discharging generated large-particle fluorapatite crystals from a crystal discharge port at the bottom of the induced crystallization reactor, and collecting and recycling; aluminum hydroxide flocs and fine-particle fluorapatite crystals enter a cyclone separator along with the effluent, the fine-particle fluorapatite crystals are separated and then flow back to the induced crystallization reactor, the aluminum hydroxide flocs form precipitates in the flocculation sedimentation tank through flocculation to be removed, and the effluent of the flocculation sedimentation tank enters a multi-stage treatment system. According to the method disclosed by the invention, fluorine and phosphorus in the phosphogypsum leachate are recovered together, the recovered fluorapatite finished product is high in purity and can be recycled, and the amount of chemical sludge is also greatly reduced, so that the treatment cost of the sludge is reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of wastewater treatment, and in particular to a process and system for recovering phosphorus and fluorine from phosphogypsum leachate. Background Art

[0002] Phosphogypsum is a solid waste generated during the wet-process phosphoric acid production process. Its formation involves treating phosphate rock with sulfuric acid to produce phosphoric acid. Every ton of phosphoric acid produced produces approximately 4.0 to 5.0 tons of phosphogypsum, its primary component being calcium sulfate dihydrate. In addition to calcium sulfate, phosphogypsum also contains impurities such as incompletely decomposed phosphate rock, residual phosphoric acid, fluoride, and organic matter. my country's annual phosphogypsum production exceeds 5,000 tons, but only 10% is effectively utilized, with the vast majority being dumped as waste. During the storage of phosphogypsum, the erosion and leaching of precipitation, as well as the effects of sedimentation and compression, causes the phosphogypsum to carry moisture and form a large amount of phosphogypsum leachate. This leachate has a complex composition and high acidity, containing not only large amounts of phosphorus but also fluorine and some metal elements. If anti-seepage measures are not implemented or the impermeable layer is damaged, it poses a serious threat to the safety of soil, groundwater, and surrounding surface water.

[0003] At present, for the treatment of phosphogypsum leachate, the industry usually adopts multi-stage chemical precipitation treatment represented by lime precipitation method, that is, by adding lime emulsion into the leachate to make it chemically react with various pollutants in the water to remove pollutants such as phosphorus and fluorine.

[0004] Patent CN 218879624 U provides a system for treating high-concentration phosphogypsum leachate. While maintaining the existing chemical precipitation process, it adds a pretreatment system. The alkaline substance lime is used to deeply precipitate and remove orthophosphate and fluoride ions from the phosphogypsum leachate. Chemical agents and flocculants are then added to remove suspended solids (SS) from the wastewater, as well as insoluble substances generated by the pretreatment unit.

[0005] This type of process can ensure the removal rate of fluoride ions and orthophosphates and achieve standard discharge of wastewater, but it does not take resource recovery into consideration. Pollutants such as fluoride and phosphorus in the water are converted into chemical sludge, which not only causes problems such as large sludge volume and high wastewater treatment costs, but also a large amount of phosphorus and fluorine elements in the leachate are transferred into the chemical sludge, resulting in a huge waste of fluorine and phosphorus resources.

[0006] Fluorine and phosphorus are non-renewable scarce resources. If the pollutants in wastewater are removed and they are recycled and reused as resources, it will be of great significance to the sustainable development of enterprises and society. Summary of the Invention

[0007] In order to overcome the above-mentioned defects, the present invention provides a process and system for recovering phosphorus and fluorine from phosphogypsum leachate. The process flow for recovering phosphorus and fluorine from phosphogypsum leachate is simple and can achieve the purpose of co-recovery of fluorine and phosphorus and resource utilization of sludge.

[0008] The present invention adopts a technical solution to solve the technical problem: a process for recovering phosphorus and fluorine from phosphogypsum leachate, comprising the following steps:

[0009] Step 1: first add induced crystal seeds into the induced crystallization reactor, then feed the phosphogypsum leachate into the induced crystallization reactor, and continuously add CaCl2 solution and NaOH solution into the induced crystallization reactor, the calcium-fluorine molar ratio is controlled within the range of 1 to 2, and the pH of the solution in the induced crystallization reactor is continuously maintained at a neutral condition;

[0010] Step 2: The crystals produced in the induced crystallization reactor are wrapped around the seed crystals to form large-particle fluorapatite crystals. The large-particle fluorapatite crystals are discharged from the crystal discharge port at the bottom of the induced crystallization reactor and recovered as fluorapatite crystals or reused within the factory. At the same time, the effluent from the induced crystallization reactor enters the crystal sedimentation tank.

[0011] Step 3: Aluminum hydroxide flocs and fine-grained fluorapatite crystals formed by the reaction of phosphogypsum leachate in the induced crystallization reactor are discharged from the outlet of the induced crystallization reactor along with the effluent water and enter the cyclone separator. The lightweight aluminum hydroxide flocs flow out of the cyclone separator along with the water and enter the flocculation sedimentation tank. The fine-grained fluorapatite crystals enter the bottom of the cyclone separator and are discharged from the crystal discharge port of the cyclone separator. The fine-grained fluorapatite crystals are finally returned to the induced crystallization reactor for use as induced crystal seeds.

[0012] Step 4: Add PAM solution to the inlet of the flocculation sedimentation tank to form large-particle flocs of aluminum hydroxide and precipitate in the flocculation sedimentation tank;

[0013] Step 5: The effluent from the flocculation sedimentation tank enters a multi-stage treatment system. After chemical defluorination and dephosphorization treatment, the fluoride ions, phosphorus ions and aluminum ions in the wastewater meet the discharge standards.

[0014] Phosphogypsum leachate contains high concentrations of impurities such as phosphate, fluorine, and aluminum. The phosphorus content can reach 2000-5000 mg / L, the fluoride ion content is as high as 1500-3000 mg / L, and the aluminum content is about 1350-1600 mg / L.

[0015] The fluorine and phosphorus in the phosphogypsum leachate react in the induced crystallization reactor to form fluorapatite crystals, and the aluminum in the wastewater forms aluminum hydroxide flocs during the reaction. The generated fluorapatite crystals directly adhere to the induced crystal seeds (the induced crystal seeds are preferably fluorapatite induced crystal seeds, and calcium fluoride induced crystal seeds can also be selected) to form large-grained fluorapatite crystals. The large-grained fluorapatite crystals sink in the induced crystallization reactor and are discharged through the crystal discharge port at the bottom of the induced crystallization reactor. In this way, the fluorine and phosphorus in the wastewater are efficiently removed while the fluorine and phosphorus are recovered in the form of fluorapatite crystals. The fluorapatite crystals can also be recycled within the mine to achieve resource reuse.

[0016] By setting up a process for removing impure aluminum, that is, utilizing the different properties of the products formed by various components in the phosphogypsum leachate during the chemical precipitation reaction, lightweight aluminum hydroxide flocs are discharged from the effluent of the induced crystallization reactor, effectively removing impurities (aluminum hydroxide flocs) in the target material, and thus obtaining higher-purity fluorapatite crystals. The aluminum content in the large-particle fluorapatite crystals discharged from the induced crystallization reactor is less than 0.1%.

[0017] The fine-grained fluorapatite crystals and aluminum hydroxide flocs discharged with the effluent from the induced crystallization reactor are further separated by a cyclone separator using their density difference. The fine-grained fluorapatite crystals are returned to the induced crystallization reactor for use as seed crystals, reducing the amount of subsequent sludge to be processed while recovering as much fluorine and phosphorus in the water as possible. The aluminum hydroxide flocs are removed by flocculation and sedimentation in the flocculation sedimentation tank. In the effluent from the flocculation sedimentation tank, aluminum ions are fully removed and meet standards, and the fluorine and phosphorus removal rates both reach over 80%. The small amount of fluorine and phosphorus remaining in the phosphogypsum leachate after the above treatment is further removed by chemical reaction in a subsequent multi-stage treatment system. Ultimately, the fluorine ions, phosphorus ions, and aluminum ions in the phosphogypsum leachate are all fully removed and meet discharge standards. Since the fluorine and phosphorus concentrations in the phosphogypsum leachate have been effectively reduced by induced crystallization, the load of the subsequent multi-stage treatment system is effectively reduced, ensuring effluent stability and significantly reducing the output of chemical sludge, thereby reducing the subsequent treatment cost of the chemical sludge.

[0018] As a further improvement of the present invention, the multi-stage treatment system includes a primary defluorination and phosphorus removal reaction tank, a primary sedimentation tank, a secondary defluorination and phosphorus removal reaction tank and a secondary sedimentation tank. The effluent from the flocculation sedimentation tank enters the primary defluorination and phosphorus removal reaction tank, and lime is added to the primary defluorination and phosphorus removal reaction tank to generate insoluble calcium hydroxyphosphate and calcium fluoride precipitates. The wastewater after the reaction in the primary defluorination and phosphorus removal reaction tank enters the primary sedimentation tank for sedimentation treatment. The effluent from the primary sedimentation tank enters the secondary defluorination and phosphorus removal reaction tank, and calcium chloride is added to the secondary defluorination and phosphorus removal reaction tank to react and generate insoluble phosphate and calcium fluoride precipitates to further remove residual orthophosphate and fluoride ions in the wastewater. The wastewater after the reaction in the secondary defluorination and phosphorus removal reaction tank enters the secondary sedimentation tank for sedimentation treatment, and the effluent from the secondary sedimentation tank meets the discharge standards.

[0019] The residual fluoride and phosphorus in the wastewater are chemically treated through a multi-stage treatment system to form precipitation, which is removed as chemical sludge, which can fully ensure the stability of the effluent. During the treatment process, it is best to monitor the fluoride, phosphorus and aluminum content in the effluent in real time, and adjust the multi-stage treatment system according to actual conditions. For example, the multi-stage treatment system can adopt two-stage fluoride and phosphorus removal, or three-stage fluoride and phosphorus removal to ensure that the effluent meets the standards.

[0020] As a further improvement of the present invention, in step 1, fluorapatite induction seeds or calcium fluoride induction seeds with a particle size of 60 to 120 μm are added.

[0021] As a further improvement of the present invention, a stirrer is provided in the induced crystallization reactor to stir the phosphogypsum leachate at a stirring speed of 20 to 60 r / min. The phosphogypsum leachate is reacted in the induced crystallization reactor for 0.5 to 2 hours. Through sufficient stirring, the fluorine, phosphorus, and aluminum ions in the phosphogypsum leachate fully react with the CaCl2 solution and the NaOH solution. Simultaneously, the induced crystal seeds are evenly distributed in the induced crystallization reactor, allowing the reaction product to fully crystallize on the surface of the induced crystal seeds.

[0022] As a further improvement of the present invention, the rotation speed of the cyclone separator in step 3 is set to 400-600 r / min. This rotation speed can quickly and fully separate the fine-grained fluorapatite crystals from the aluminum hydroxide flocs.

[0023] As a further improvement of the present invention, the mass percent concentration of the PAM solution is 0.1% to 0.2%, and the dosage of the PAM solution is 5 to 20 ppm. Aluminum hydroxide flocs flocculate in a flocculation sedimentation tank to form large flocs, which then settle in the sedimentation tank to achieve mud-water separation, thereby effectively removing aluminum from the phosphogypsum leachate.

[0024] As a further improvement of the present invention, the large fluorapatite crystals discharged from the crystal discharge port at the bottom of the induced crystallization reactor in step 2 are collected in a crystal collection pool. The collected large fluorapatite crystals are filtered, cleaned, and dehydrated to achieve co-recovery of fluorine and phosphorus in the form of fluorapatite. The large fluorapatite crystals are post-processed to achieve higher purity, directly forming a high-purity, low-water-content fluorapatite product that can be sold and reused within the factory.

[0025] A system for recovering phosphorus and fluorine from phosphogypsum leachate, comprising a phosphogypsum leachate collection tank, an induced crystallization reactor, a crystal collection tank, a cyclone separator, a flocculation sedimentation tank, a multi-stage treatment system, a sludge collection tank, a first lifting pump, a first dosing pump, a second dosing pump, a third dosing pump, and a control system. The phosphogypsum leachate collection tank is used to collect phosphogypsum leachate, and the phosphogypsum leachate collection tank is connected to the liquid inlet of the induced crystallization reactor through a pipeline. The first lifting pump can continuously transport the phosphogypsum leachate in the phosphogypsum leachate collection tank to the induced crystallization reactor. The induced crystallization reactor is also provided with a dosing port, a water outlet, a crystal discharge port, and a return port. The first dosing pump and the second dosing pump can respectively add the CaCl2 solution and the NaOH solution into the induced crystallization reactor through the dosing port, the crystal discharge port at the bottom of the induced crystallization reactor is connected with the crystal collection pool through a pipeline, the crystal discharge port of the induced crystallization reactor can be opened to discharge large-particle fluorapatite crystals into the crystal collection pool, the water outlet of the induced crystallization reactor is connected with the water inlet of the cyclone separator through a pipeline, the crystal discharge port at the bottom of the cyclone separator is connected with the reflux port of the induced crystallization reactor through a reflux pipeline, and the fine-particle fluorapatite crystals separated by the cyclone separator can return to the induced crystallization reactor through the reflux pipeline. In the reactor, the water outlet of the cyclone separator is connected to the water inlet of the flocculation sedimentation tank through a pipeline, and the lightweight aluminum hydroxide flocs separated in the cyclone separator enter the flocculation sedimentation tank with the outlet water. The flocculation sedimentation tank is provided with a flocculant addition port, and the third dosing pump can add the PAM solution into the flocculation sedimentation tank through the flocculant addition port. The water outlet of the flocculation sedimentation tank is connected to the water inlet of the multi-stage treatment system through a pipeline, and the mud discharge port of the flocculation sedimentation tank and the mud discharge port of the multi-stage treatment system are respectively connected to the sludge collection tank through pipelines. The sludge formed by the mud-water separation of the flocculation sedimentation tank and the multi-stage treatment system can be discharged to the sludge collection tank through the mud discharge port. The wastewater is collected and processed in a unified manner. The multi-stage treatment system can chemically remove fluorine and phosphorus from the wastewater therein. The outlet of the multi-stage treatment system can discharge treated water that meets the standards. A pH meter is provided in the induced crystallization reactor. The pH meter can detect the pH of the liquid in the induced crystallization reactor in real time and transmit the detection result to the control system. The control system can control the flow of the first dosing pump, the second dosing pump and the third dosing pump according to the real-time pH of the liquid in the induced crystallization reactor and the flow of the first lifting pump. The control system can also control the crystal discharge port of the induced crystallization reactor and the sludge discharge port of the flocculation sedimentation tank and the multi-stage treatment system to open at regular intervals.

[0026] The phosphogypsum leachate is first collected and stored in the phosphogypsum leachate collection tank, which is convenient for subsequent treatment and can also play a role in homogenization. The dosing port of the induced crystallization reactor realizes automatic dosing of CaCl2 solution and NaOH solution through the first dosing pump and the second dosing pump, and the dosing amount of CaCl2 solution and NaOH solution is automatically adjusted according to the flow rate of the first lifting pump and the pH value of the liquid in the induced crystallization reactor. The flocculant dosing port on the flocculation sedimentation tank automatically adds PAM solution through the third dosing pump, and the dosage of PAM solution is controlled according to the flow rate of the first lifting pump. That is, the third dosing pump automatically controls the dosing according to the amount of wastewater and the amount of aluminum hydroxide flocs in the flocculation sedimentation tank. As the system runs, more and more large-particle fluorapatite crystals accumulate at the bottom of the induced crystallization reactor, and more and more sludge accumulates in the flocculation sedimentation tank and the multi-stage treatment system. The control system controls the crystal discharge port at the bottom of the induced crystallization reactor, the sludge discharge port of the flocculation sedimentation tank, and the sludge discharge port of the multi-stage treatment system to open at a fixed time, so as to realize the automatic discharge and collection of large-particle fluorapatite crystals and sludge. The above system realizes automated and intelligent operation, ensures sufficient reaction, and saves labor.

[0027] As a further improvement of the present invention, the multi-stage treatment system includes a primary defluorination and phosphorus removal reaction tank, a primary sedimentation tank, a secondary defluorination and phosphorus removal reaction tank, a secondary sedimentation tank, a second lift pump, a third lift pump, a fourth dosing pump, a fifth dosing pump and a fluorine and phosphorus ion concentration detection device, the water outlet of the flocculation sedimentation tank is connected to the water inlet of the primary defluorination and phosphorus removal reaction tank through a pipeline, the water outlet of the primary defluorination and phosphorus removal reaction tank is connected to the water inlet of the primary sedimentation tank through a pipeline, the water outlet of the primary sedimentation tank is connected to the water inlet of the secondary defluorination and phosphorus removal reaction tank through a pipeline, the water outlet of the secondary defluorination and phosphorus removal reaction tank is connected to the water inlet of the secondary sedimentation tank through a pipeline, the wastewater after the reaction in the primary defluorination and phosphorus removal reaction tank is completed can be sent to the primary sedimentation tank via the second lift pump, the wastewater after the reaction in the secondary defluorination and phosphorus removal reaction tank is completed can be sent to the secondary sedimentation tank via the third lift pump, the primary defluorination and phosphorus removal The reaction tank and the secondary defluorination and phosphorus removal reaction tank are both provided with a dosing port for adding defluorination and phosphorus removal agents. The fourth dosing pump and the fifth dosing pump can respectively deliver the defluorination and phosphorus removal agents into the dosing ports of the primary defluorination and phosphorus removal reaction tank and the secondary defluorination and phosphorus removal reaction tank. The sludge discharge ports of the primary sedimentation tank and the secondary sedimentation tank are respectively connected to the sludge collection tank through pipelines. The water outlet of the secondary sedimentation tank can discharge treated water that meets the standards. The primary defluorination and phosphorus removal reaction tank and the secondary defluorination and phosphorus removal reaction tank are also respectively provided with fluorine and phosphorus ion concentration detection devices. The fluorine and phosphorus ion concentration detection devices can detect the fluorine and phosphorus ion concentrations of the wastewater in the primary defluorination and phosphorus removal reaction tank and the secondary defluorination and phosphorus removal reaction tank. The fluorine and phosphorus ion concentration detection devices can transmit the detection data to the control system. The control system controls the flow rates of the fourth dosing pump and the fifth dosing pump, and the start and stop of the second lift pump and the third lift pump.

[0028] The dosing ports of the primary defluorination and dephosphorization reaction tank and the secondary defluorination and dephosphorization reaction tank are respectively automatically dosed with drugs through the fourth dosing pump and the fifth dosing pump. The amount of drugs added in the primary defluorination and dephosphorization reaction tank and the secondary defluorination and dephosphorization reaction tank is adjusted by the control system automatically controlling the flow of the fourth dosing pump and the fifth dosing pump based on the detection data of the fluorine and phosphorus ion concentration detection device. It is also best to monitor the fluorine, phosphorus and aluminum ion concentrations in the effluent of the secondary sedimentation tank in real time to ensure that the effluent is stable and meets the standards.

[0029] As a further improvement of the present invention, a filter press, a conveying device, a cleaning device and a dehydration device are further provided. The large-particle fluorapatite crystals collected in the crystal collection pool can be discharged into the filter press through a conveying device. The filter press can perform filter pressure treatment on the large-particle fluorapatite crystals containing water. The large-particle fluorapatite crystals after the filter pressure treatment can be conveyed into the cleaning device by the conveying device. The cleaning device can clean the large-particle fluorapatite crystals at least once with clean water. The cleaned large-particle fluorapatite crystals can be conveyed into the dehydration device through another conveying device for dehydration treatment to form a fluorapatite finished product with a moisture content that meets the requirements. When large-particle fluorapatite crystals are discharged from the crystal discharge port at the bottom of the induced crystallization reactor, some wastewater will be discharged together. The wastewater contained in the wastewater can be removed by filtering it through a filter press, and the wastewater can be returned to the phosphogypsum leachate collection tank. Then, the large-particle fluorapatite crystals are cleaned by a cleaning device to further remove the wastewater remaining on their surface. Finally, the pure large-particle fluorapatite crystals are dehydrated by a dehydration device to finally obtain a fluorapatite product with high purity and low water content.

[0030] The beneficial effects of the present invention are as follows: the present invention efficiently removes fluorine and phosphorus from phosphogypsum leachate by induced crystallization, and realizes the recovery of fluorine and phosphorus in the form of fluorapatite crystals. The fluorapatite crystals obtained by induced crystallization can be recycled in the mine to achieve resource reuse; the present invention also provides a process for removing impurity aluminum, and utilizes the density difference between fine-grained fluorapatite crystals and aluminum hydroxide flocs to separate the fine-grained fluorapatite crystals and aluminum hydroxide flocs mixed in the effluent of the induced crystallization reactor through a hydrocyclone separator, and the recovered fine-grained fluorapatite crystals are returned to the induced crystallization reactor. The reactor is used as an induced crystal seed, which reduces the subsequent sludge processing volume. In addition, the aluminum in the fine-grained fluorapatite crystals is removed, so that the aluminum content in the finally obtained large-grained fluorapatite crystals is reduced to below 0.1%, thereby ensuring the purity of the fluorapatite product. At the same time, as much fluorine and phosphorus as possible are recovered in the water. The present invention effectively reduces the fluorine and phosphorus concentrations in the phosphogypsum leachate by inducing crystallization, thereby reducing the load of the subsequent treatment process and ensuring that the effluent meets the discharge standards. The above process realizes the co-recovery of fluorine and phosphorus, greatly reduces the amount of chemical sludge, and thus reduces the sludge treatment cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 This is a schematic diagram of the prior art system;

[0032] Figure 2 This is a system principle diagram of the present invention.

[0033] Figure numerals: phosphogypsum leachate collection tank--1; induced crystallization reactor--2; crystal collection tank--3; cyclone separator--4; flocculation sedimentation tank--5; sludge collection tank--6; primary fluorine and phosphorus removal reaction tank--7; primary sedimentation tank--8; secondary fluorine and phosphorus removal reaction tank--9; secondary sedimentation tank--10. DETAILED DESCRIPTION

[0034] The following describes specific embodiments of the present invention in detail. It should be noted that the embodiments described here are only some embodiments of the present invention, not all embodiments. Based on the following embodiments, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0035] Example: The phosphorus content in the phosphogypsum leachate of a certain enterprise is 3265-3758 mg / L, the fluorine content is 2405-2588 mg / L, and the aluminum content is 1455-1562 mg / L, which is collected and processed.

[0036] The original treatment process is: first pre-treat the collected phosphogypsum leachate, then send the phosphogypsum leachate to the primary reaction tank, add drugs to remove fluorine and phosphorus, then send the wastewater after the reaction in the primary reaction tank to the primary sedimentation tank 8 for sedimentation treatment, then send the effluent from the primary sedimentation tank 8 to the secondary reaction tank, add drugs to remove fluorine and phosphorus, then send the wastewater after the reaction in the secondary reaction tank to the secondary sedimentation tank 10 for sedimentation treatment, then send the effluent from the secondary sedimentation tank 10 to the tertiary reaction tank, add drugs to remove fluorine and phosphorus, then send the wastewater after the reaction in the tertiary reaction tank to the tertiary sedimentation tank for sedimentation treatment, the effluent from the tertiary sedimentation tank is discharged after sand filtration and pH adjustment. The original treatment process for fluorine and phosphorus removal mainly uses the lime method for treatment, and the fluorine, phosphorus and aluminum in the wastewater are eventually converted into chemical sludge.

[0037] The process of the present invention is used for treatment, and the specific steps are as follows:

[0038] (1) The effluent from the phosphogypsum leachate collection tank 1 is directly pumped into the induced crystallization reactor 2, and calcium fluoride induction crystal seeds with a particle size of 60 μm are added to the induced crystallization reactor 2. At the same time, 30% CaCl2 solution and 32% NaOH solution are continuously added through a pump to control the pH of the liquid in the induced crystallization reactor 2 to be maintained at 6.5-7.0. The stirring speed of the stirrer in the induced crystallization reactor 2 is 60 r / min, and the residence time is 0.5 h.

[0039] (2) The effluent from the induced crystallization reactor 2 enters the subsequent cyclone separator 4, which is set to rotate at a speed of 400 r / min to separate the aluminum hydroxide flocs and the fine-grained fluorapatite crystals. The light aluminum hydroxide flocs flow out with the water and enter the flocculation sedimentation tank 5. The fine-grained fluorapatite crystals enter the bottom of the cyclone separator 4 and are discharged from the crystal discharge port of the cyclone separator 4. The fine-grained fluorapatite crystals flow back to the induced crystallization reactor 2 and are used as induced crystal seeds. The aluminum content of the large-grained fluorapatite crystals discharged from the induced crystallization reactor 2 is less than 0.05%;

[0040] (3) After the effluent from the cyclone separator 4 enters the flocculation sedimentation tank 5, a PAM solution is added to the inlet of the flocculation sedimentation tank 5. The mass percentage concentration of the PAM solution is 0.15%, and the addition amount is 5 ppm. The phosphorus content in the effluent from the flocculation sedimentation tank 5 is 23.04-50.2 mg / L, and the fluorine content is 33.66-43.74 mg / L;

[0041] (4) The effluent from the flocculation sedimentation tank 5 enters the primary defluorination and phosphorus removal reaction tank 7 of the multi-stage treatment system, and lime is added to the primary defluorination and phosphorus removal reaction tank 7 to generate insoluble calcium hydroxyphosphate and calcium fluoride precipitates. After the reaction in the primary defluorination and phosphorus removal reaction tank 7 is completed, the wastewater is pumped into the primary sedimentation tank 8 for sedimentation treatment. The effluent from the primary sedimentation tank 8 enters the secondary defluorination and phosphorus removal reaction tank 9, and calcium chloride is added to the secondary defluorination and phosphorus removal reaction tank 9 to generate insoluble phosphate and calcium fluoride. After the reaction in the secondary defluorination and phosphorus removal reaction tank 9 is completed, the wastewater is pumped into the secondary sedimentation tank 10 for sedimentation treatment and finally meets the discharge standards;

[0042] (5) The large-particle fluorapatite crystals (particle size of 80-100 μm) produced in the induced crystallization reactor 2 are regularly discharged into the crystal collection pool 3 for collection and then returned to the factory for reuse;

[0043] After the phosphogypsum leachate is used to recover the fluorapatite crystals, the sludge production in the primary sedimentation tank 8 and the secondary sedimentation tank 10 is reduced by 72% to 80% compared with the original amount.

Claims

1. A process for recovering phosphorus and fluorine from phosphogypsum leachate, characterized by: The steps include: Step 1: first add induced crystal seeds into the induced crystallization reactor, then feed the phosphogypsum leachate into the induced crystallization reactor, and continuously add CaCl2 solution and NaOH solution into the induced crystallization reactor, the calcium-fluorine molar ratio is controlled within the range of 1 to 2, and the pH of the solution in the induced crystallization reactor is continuously maintained at a neutral condition; Step 2: The crystals produced in the induced crystallization reactor are wrapped around the seed crystals to form large-particle fluorapatite crystals. The large-particle fluorapatite crystals are discharged from the crystal discharge port at the bottom of the induced crystallization reactor and recovered as fluorapatite crystals or reused within the factory. At the same time, the effluent from the induced crystallization reactor enters the crystal sedimentation tank. Step 3: Aluminum hydroxide flocs and fine-grained fluorapatite crystals formed by the reaction of phosphogypsum leachate in the induced crystallization reactor are discharged from the outlet of the induced crystallization reactor along with the effluent water and enter the cyclone separator. The lightweight aluminum hydroxide flocs flow out of the cyclone separator along with the water and enter the flocculation sedimentation tank. The fine-grained fluorapatite crystals enter the bottom of the cyclone separator and are discharged from the crystal discharge port of the cyclone separator. The fine-grained fluorapatite crystals are finally returned to the induced crystallization reactor for use as induced crystal seeds. Step 4: Add PAM solution to the inlet of the flocculation sedimentation tank to form large-particle flocs of aluminum hydroxide and precipitate in the flocculation sedimentation tank; Step 5: The effluent from the flocculation sedimentation tank enters a multi-stage treatment system. After chemical defluorination and dephosphorization treatment, the fluoride ions, phosphorus ions and aluminum ions in the wastewater meet the discharge standards.

2. The process for recovering phosphorus and fluorine from phosphogypsum leachate according to claim 1, characterized in that: The multi-stage treatment system includes a primary defluorination and dephosphorization reaction tank, a primary sedimentation tank, a secondary defluorination and dephosphorization reaction tank, and a secondary sedimentation tank. The effluent from the flocculation sedimentation tank enters the primary defluorination and dephosphorization reaction tank, and lime is added to the primary defluorination and dephosphorization reaction tank to generate insoluble calcium hydroxyphosphate and calcium fluoride precipitates. The wastewater after the reaction in the primary defluorination and dephosphorization reaction tank enters the primary sedimentation tank for sedimentation treatment. The effluent from the primary sedimentation tank enters the secondary defluorination and dephosphorization reaction tank, and calcium chloride is added to the secondary defluorination and dephosphorization reaction tank to react and generate insoluble phosphate and calcium fluoride precipitates, thereby further removing residual orthophosphate and fluoride ions in the wastewater. The wastewater after the reaction in the secondary defluorination and dephosphorization reaction tank enters the secondary sedimentation tank for sedimentation treatment, and the effluent from the secondary sedimentation tank meets the discharge standards.

3. The process for recovering phosphorus and fluorine from phosphogypsum leachate according to claim 1, characterized in that: In the step 1, fluorapatite induction seed crystals or calcium fluoride induction seed crystals with a particle size of 60 to 120 μm are added.

4. The process for recovering phosphorus and fluorine from phosphogypsum leachate according to claim 1, characterized in that: The induced crystallization reactor is provided with a stirrer, and the phosphogypsum leachate is stirred by the stirrer at a stirring speed of 20 to 60 r / min. The phosphogypsum leachate reacts in the induced crystallization reactor for 0.5 to 2 hours.

5. The process for recovering phosphorus and fluorine from phosphogypsum leachate according to claim 1, characterized in that: In step 3, the rotation speed of the cyclone separator is set to 400-600 r / min.

6. The process for recovering phosphorus and fluorine from phosphogypsum leachate according to claim 1, characterized in that: The mass percentage concentration of the PAM solution is 0.1% to 0.2%, and the dosage of the PAM solution is 5 to 20 ppm.

7. The process for recovering phosphorus and fluorine from phosphogypsum leachate according to claim 1, characterized in that: The large-particle fluorapatite crystals discharged from the crystal discharge port at the bottom of the induced crystallization reactor in step 2 are collected in a crystal collection pool. The collected large-particle fluorapatite crystals are filtered, cleaned and dehydrated to achieve fluorine and phosphorus co-recovery in the form of fluorapatite.

8. A system for recovering phosphorus and fluorine from phosphogypsum leachate used in the process for recovering phosphorus and fluorine from phosphogypsum leachate according to any one of claims 1 to 7, characterized in that: The invention comprises a phosphogypsum leachate collection tank (1), an induced crystallization reactor (2), a crystal collection tank (3), a cyclone separator (4), a flocculation sedimentation tank (5), a multi-stage treatment system, a sludge collection tank (6), a first lifting pump, a first dosing pump, a second dosing pump, a third dosing pump and a control system. The phosphogypsum leachate collection tank is used to collect phosphogypsum leachate. The phosphogypsum leachate collection tank is connected to the liquid inlet of the induced crystallization reactor through a pipeline. The first lifting pump can continuously transport the phosphogypsum leachate in the phosphogypsum leachate collection tank to the induced crystallization reactor. The induced crystallization reactor is also provided with a dosing port, a water outlet, a crystal discharge port and a control system. The reflux port, the first dosing pump and the second dosing pump can respectively add the CaCl2 solution and the NaOH solution into the induced crystallization reactor through the dosing port, the crystal discharge port at the bottom of the induced crystallization reactor is connected with the crystal collection pool through a pipeline, the crystal discharge port of the induced crystallization reactor can be opened to discharge large-particle fluorapatite crystals into the crystal collection pool, the water outlet of the induced crystallization reactor is connected with the water inlet of the cyclone separator through a pipeline, the crystal discharge port at the bottom of the cyclone separator is connected with the reflux port of the induced crystallization reactor through a reflux pipeline, and the fine-particle fluorapatite crystals separated by the cyclone separator can return to the induced crystallization reactor through the reflux pipeline. In the reactor, the water outlet of the cyclone separator is connected to the water inlet of the flocculation sedimentation tank through a pipeline, and the lightweight aluminum hydroxide flocs separated in the cyclone separator enter the flocculation sedimentation tank with the outlet water. The flocculation sedimentation tank is provided with a flocculant addition port, and the third dosing pump can add the PAM solution into the flocculation sedimentation tank through the flocculant addition port. The water outlet of the flocculation sedimentation tank is connected to the water inlet of the multi-stage treatment system through a pipeline, and the mud discharge port of the flocculation sedimentation tank and the mud discharge port of the multi-stage treatment system are respectively connected to the sludge collection tank through pipelines. The sludge formed by the mud-water separation of the flocculation sedimentation tank and the multi-stage treatment system can be discharged to the sludge collection tank through the mud discharge port. The wastewater is collected and processed in a unified manner. The multi-stage treatment system can chemically remove fluorine and phosphorus from the wastewater therein. The outlet of the multi-stage treatment system can discharge treated water that meets the standards. A pH meter is provided in the induced crystallization reactor. The pH meter can detect the pH of the liquid in the induced crystallization reactor in real time and transmit the detection result to the control system. The control system can control the flow of the first dosing pump, the second dosing pump and the third dosing pump according to the real-time pH of the liquid in the induced crystallization reactor and the flow of the first lifting pump. The control system can also control the crystal discharge port of the induced crystallization reactor and the sludge discharge port of the flocculation sedimentation tank and the multi-stage treatment system to open at regular intervals.

9. The system for recovering phosphorus and fluorine from phosphogypsum leachate according to claim 8, characterized in that: The multi-stage treatment system comprises a primary defluorination and dephosphorization reaction tank (7), a primary sedimentation tank (8), a secondary defluorination and dephosphorization reaction tank (9), a secondary sedimentation tank (10), a second lifting pump, a third lifting pump, a fourth dosing pump, a fifth dosing pump and a fluorine and phosphorus ion concentration detection device. The water outlet of the flocculation sedimentation tank is connected to the water inlet of the primary defluorination and dephosphorization reaction tank through a pipeline, the water outlet of the primary defluorination and dephosphorization reaction tank is connected to the water inlet of the primary sedimentation tank through a pipeline, the water outlet of the primary sedimentation tank is connected to the water inlet of the secondary defluorination and dephosphorization reaction tank through a pipeline, the water outlet of the secondary defluorination and dephosphorization reaction tank is connected to the water inlet of the secondary sedimentation tank through a pipeline, the wastewater after the reaction in the primary defluorination and dephosphorization reaction tank is completed can be sent to the primary sedimentation tank through the second lifting pump, the wastewater after the reaction in the secondary defluorination and dephosphorization reaction tank is completed can be sent to the secondary sedimentation tank through the third lifting pump, the primary defluorination and dephosphorization reaction tank is connected to the water inlet of the secondary sedimentation tank through the pipeline, The phosphorus reaction tank and the secondary defluorination and phosphorus removal reaction tank are both provided with a dosing port for adding defluorination and phosphorus removal agents. The fourth dosing pump and the fifth dosing pump can respectively deliver the defluorination and phosphorus removal agents into the dosing ports of the primary defluorination and phosphorus removal reaction tank and the secondary defluorination and phosphorus removal reaction tank. The sludge discharge ports of the primary sedimentation tank and the secondary sedimentation tank are respectively connected to the sludge collection tank through pipelines. The water outlet of the secondary sedimentation tank can discharge treated water that meets the standards. The primary defluorination and phosphorus removal reaction tank and the secondary defluorination and phosphorus removal reaction tank are also respectively provided with fluorine and phosphorus ion concentration detection devices. The fluorine and phosphorus ion concentration detection devices can detect the fluorine and phosphorus ion concentrations of the wastewater in the primary defluorination and phosphorus removal reaction tank and the secondary defluorination and phosphorus removal reaction tank. The fluorine and phosphorus ion concentration detection devices can transmit the detection data to the control system. The control system controls the flow rates of the fourth dosing pump and the fifth dosing pump, and the start and stop of the second lift pump and the third lift pump.

10. The system for recovering phosphorus and fluorine from phosphogypsum leachate according to claim 8, characterized in that: A filter press, a conveying device, a cleaning device and a dehydration device are also provided. The large-particle fluorapatite crystals collected in the crystal collection pool can be discharged into the filter press through a conveying device. The filter press can perform filter pressure treatment on the large-particle fluorapatite crystals containing water. The large-particle fluorapatite crystals after the filter pressure treatment can be conveyed into the cleaning device by the conveying device. The cleaning device can clean the large-particle fluorapatite crystals at least once with clean water. The cleaned large-particle fluorapatite crystals can be conveyed into the dehydration device through another conveying device for dehydration treatment to form a fluorapatite finished product with a moisture content that meets the requirements.

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