A multi-effect three-phase crystallization defluorination and fluorine recovery device and method

Abstract

The present invention discloses a multi-effect three-phase crystallization defluorination and fluorine recovery device and method, which belongs to the field of sewage treatment and resource recovery. The device is provided with a water distribution and air distribution area, a defluorination reaction area and an enhanced precipitation area from bottom to top. The water distribution and air distribution area is provided with a crystal discharge port, a downflow liquid circulation guide tube, an aeration device, and a water inlet and dosing device. The defluorination reaction area is provided with a carrier reaction area and a deep defluorination area, and the cross-sectional area of ​​the deep defluorination area is larger than that of the carrier reaction area. The enhanced precipitation area is provided with three layers of enhanced precipitation plates, a precipitation area, a guide cover and a vent pipe. Fluorine-containing wastewater and defluorination agent enter the device through the water inlet pipe and the dosing pipe. After the reaction, the solid and liquid mixture enters the carrier reaction area to condense and crystallize to form larger particles of calcium fluoride, which are recovered through the carrier. The treated wastewater is discharged from the device through the enhanced precipitation area. The device provided by the present invention integrates high-efficiency fluoride removal and recovery of calcium fluoride resources. The functions of each unit are complementary, the structure is compact, the floor space is small, and the pollution reduction and resource recovery effects are good.

Description

Technical Field

[0001] The present invention belongs to the field of sewage treatment and resource recovery, and in particular relates to a multi-effect three-phase crystallization fluorine removal and fluorine recovery device and method. Background Art

[0002] The booming development of emerging industries such as photovoltaics and chip manufacturing has generated a significant amount of industrial wastewater with high concentrations, complex composition, and significant challenges to manage. Fluoride-containing wastewater is a significant component, with fluoride ion levels reaching as high as 30,000-50,000 mg / L. Fluoride inhibits crop respiration and photosynthesis, and has a range of adverse effects on the human kidneys, liver, and brain, among other negative impacts. Therefore, the discharge of fluoride into water bodies can cause serious ecological pollution, and the effectiveness of treating fluoride-contaminated wastewater will directly impact downstream biological treatment units (such as biological denitrification).

[0003] Since fluoride ions cannot be effectively removed through biological treatment, physical and chemical processes are often used to treat fluoride-containing wastewater, including chemical precipitation, coagulation and sedimentation, adsorption, and ion exchange. Among them, adsorption and ion exchange methods produce hazardous solid wastes such as waste adsorbents and waste resins, and have high disposal costs. The chemical precipitation method mainly removes fluoride ions from the wastewater by adding calcium salts such as lime and calcium chloride to the fluoride-containing wastewater after acid-base balance, and uses the reaction of calcium ions and fluoride ions to form precipitates to ensure that the effluent water quality meets the standards. Therefore, the chemical precipitation process has become the preferred choice for the treatment of fluoride-containing wastewater.

[0004] On the other hand, the precipitate produced by calcium salt defluoridation - calcium fluoride (CaF2, also known as fluorite) is a usable material with a wide range of uses in metallurgy, chemical industry, building materials and light industry. Therefore, the recovery of calcium fluoride from fluoride-containing wastewater for resource recovery has important practical significance, and is also in line with the country's overall guidance requirements for resource utilization of wastewater treatment. At present, CaF2 has economic value when its content is >60%, and its selling price can reach several thousand yuan per ton as the purity increases (>80%). Crystallization is an effective method to improve the purity of precipitates, and it has been widely used in wastewater treatment (such as crystallization for phosphorus removal, etc.). Applying it to the calcium precipitation defluoridation process will improve the purity of the product and its recovery value. Calcium crystallization defluoridation can provide technical support for improving the purity of precipitates and their recovery value.

[0005] Therefore, chemical precipitation defluoridation can be combined with calcium crystallization defluoridation, and the calcium crystallization defluoridation can be induced by adding crystal nuclei (endogenous and exogenous). Summary of the Invention

[0006] The present invention aims to address the shortcomings of the prior art by providing a multi-effect three-phase crystallization defluorination and fluorine recovery device and method. This device not only simplifies equipment and reduces investment costs, but also enhances wastewater defluorination and reduces operating expenses. By recovering calcium fluoride as a resource product, resource recycling is achieved, improving economic efficiency.

[0007] The specific technical solutions adopted in the present invention are as follows:

[0008] In a first aspect, the present invention provides a multi-effect three-phase crystallization defluorination and fluorine recovery device, wherein the device body is sequentially provided with a water and gas distribution zone, a defluorination reaction zone and an enhanced precipitation zone from bottom to top.

[0009] The water and air distribution area is equipped, from bottom to top, with a crystal discharge port, a downflow liquid circulation guide tube, an aeration pipe, a water inlet pipe, and a dosing pipe. The crystal discharge port is located at the bottom of the device body and is connected vertically to the aeration head at one end of the aeration pipe. Below the aeration head is an aeration head support frame. Above the aeration head are a water inlet pipe for introducing fluoride-containing wastewater and a dosing pipe for adding defluoridation agents. The downflow liquid circulation guide tube is an inverted triangle structure with a larger top and a smaller bottom, which is used to drain the calcium fluoride granular sludge generated in the defluoridation reaction zone.

[0010] The defluorination reaction zone consists of a carrier reaction zone and a deep defluorination zone, with the deep defluorination zone having a larger cross-sectional area than the carrier reaction zone. A support frame for calcium fluoride seed crystals is located at the bottom of the carrier reaction zone, and the area where the calcium fluoride seed crystals are placed serves as the carrier chamber. The support frame can be opened and closed to discharge calcium fluoride crystals that have reached a threshold, and is equipped with a diversion hole.

[0011] The enhanced sedimentation zone is provided with a first enhanced sedimentation plate, a second enhanced sedimentation plate, a third enhanced sedimentation plate, a sedimentation zone, a flow guide cover and a vent pipe. Above the carrier reaction zone is the sedimentation zone, in which the first enhanced sedimentation plate, the second enhanced sedimentation plate and the third enhanced sedimentation plate are arranged in an inclined manner, and inter-plate gaps are left between the first enhanced sedimentation plate and the second enhanced sedimentation plate, as well as between the second enhanced sedimentation plate and the third enhanced sedimentation plate to prevent particle accumulation. The flow guide cover is connected above the third enhanced sedimentation plate. The vent pipe is connected above the flow guide cover so that the vent pipe is connected to the carrier reaction zone to ensure that the device body is in balance with the external air pressure. The enhanced sedimentation zone is also provided with a water outlet weir, and the water outlet weir is arranged on the inner wall of the device body at a position higher than the sedimentation zone.

[0012] Preferably, a water distributor is provided at the water outlet of the water inlet pipe. A dosing water distributor is provided at the dosing outlet of the dosing pipe.

[0013] Furthermore, the diameter ratios of the water inlet distributor and the dosing water distributor to the carrier reaction zone are both 1 / 4 to 1 / 3.

[0014] Preferably, the cross-sectional area ratio of the aeration head to the carrier reaction zone is 1 / 10 to 1 / 4.

[0015] Preferably, the carrier chamber is located at 1 / 5 to 2 / 3 of the carrier reaction zone from bottom to top.

[0016] Preferably, the cross-sectional area ratio of the above-mentioned carrier reaction zone to the deep defluorination zone is 2 / 5 to 4 / 5.

[0017] Preferably, the inter-plate gap widths between the first and second reinforced precipitation plates, and between the second and third reinforced precipitation plates are both greater than 5 cm.

[0018] Preferably, the inclination angle β of the first strengthening precipitation plate, the second strengthening precipitation plate and the third strengthening precipitation plate is 60°.

[0019] Preferably, the bottom angle α of the downflow liquid circulation guide tube is 60°, and the inclination angle γ of the guide cover is 60°.

[0020] In a second aspect, the present invention provides a method for recovering fluorine using the device described in the first aspect, the specific steps of which are as follows:

[0021] S1: Fluoride-containing wastewater enters the mixing chamber below the defluorination reaction zone through the inlet pipe and water distributor. The defluoridation agent enters the mixing chamber below the defluoridation reaction zone through the dosing pipe and water distributor. The high-speed water flow creates a negative pressure in the mixing chamber below the defluoridation reaction zone, drawing the calcium fluoride granular sludge generated in the defluoridation reaction zone into the mixing chamber through a downflow liquid circulation guide tube. The sludge mixes with the fluoride-containing wastewater and defluoridation agent to form a mud-water mixture.

[0022] S2: The sludge-water mixture from step S1 enters the carrier chamber, where it reacts with the calcium fluoride seed crystals inside to produce calcium fluoride. It then enters the enhanced sedimentation zone. Solid-liquid separation occurs between the first, second, and third enhanced sedimentation plates, and the clarified wastewater is discharged through the effluent weir. Due to the increased cross-sectional area of ​​the deep defluoridation zone, the water flow rate slows down within the zone, promoting the flocculation and crystallization of large calcium fluoride crystals. The resulting calcium fluoride granular sludge passes through the deep defluoridation zone and enters the downflow liquid circulation guide tube, where it can be drawn back into the mixing chamber for circulation.

[0023] S3: When the calcium fluoride crystals in the carrier chamber accumulate to a threshold, the support frame is opened and the crystals are discharged through the crystal discharge port.

[0024] Compared with the prior art, the present invention has the following beneficial effects:

[0025] (1) The multi-effect three-phase crystallization defluorination and fluorine recovery device provided by the present invention is divided into three units from top to bottom: a water and gas distribution zone, a defluorination reaction zone, and an enhanced precipitation zone. The adjacent units complement each other in function, integrating crystallization defluorination and fluorine recovery. The overall structure of the device is compact and occupies a small area.

[0026] (2) The multi-effect three-phase crystallization defluorination and fluorine recovery device provided by the present invention uses a sedimentation plate composed of three layers of parallel conical covers, which has a compact structure, a small separation zone volume, and a good solid-liquid separation effect;

[0027] (3) The multi-effect three-phase crystallization defluorination and fluorine recovery device provided by the present invention is provided with a carrier reaction zone. After the reacted calcium fluoride crystals in the carrier chamber in this zone accumulate to a threshold value, they can be discharged through the crystal discharge port, which can effectively recover the calcium fluoride crystals and realize resource utilization;

[0028] (4) The defluorination method provided by the present invention uses calcium fluoride seed crystals as a crystallization defluorination carrier, which can improve the crystallization defluorination efficiency and crystal purity; adopts the "continuous feeding-intermittent aeration" operation mode to enhance the mixing effect of fluorine-containing wastewater and defluorination agent, and promotes the precipitation and reflux of calcium fluoride, while effectively preventing the calcium fluoride precipitation from agglomerating, which is beneficial to the desorption and recovery of crystals on the carrier; during the reaction process, the generated calcium fluoride granular sludge can be sucked into the mixing chamber again through the downflow liquid circulation guide tube for circulation, thereby improving the volumetric crystallization defluorination efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 A cross-sectional view of the structure of the multi-effect three-phase crystallization defluorination and fluorine recovery device provided by the present invention;

[0030] Figure 2 for Figure 1 Middle AA cross-section;

[0031] In the figure: crystal discharge port 1, downflow liquid circulation guide tube 2, aeration head support frame 3, aeration head 4, aeration pipe 5, water inlet distributor 6, water inlet pipe 7, dosing water distributor 8, dosing pipe 9, support frame 10, carrier chamber 11, deep fluorine removal zone 12, carrier reaction zone 13, first enhanced sedimentation plate 14, second enhanced sedimentation plate 15, third enhanced sedimentation plate 16, sedimentation zone 17, guide cover 18, water outlet weir 19, vent pipe 20. DETAILED DESCRIPTION

[0032] The present invention will be further described and illustrated below with reference to the accompanying drawings and specific embodiments. The technical features of each embodiment of the present invention may be combined accordingly, provided that there is no conflict between them.

[0033] like Figure 1 As shown, this embodiment, as a preferred embodiment of a specific embodiment, provides a multi-effect three-phase crystallization defluorination and fluorine recovery device. The device body comprises, from bottom to top, interconnected water and gas distribution zone I, defluorination reaction zone II, and enhanced precipitation zone III. The structure and connection method of each device are described in detail below.

[0034] From bottom to top, the water and gas distribution area I is equipped with a crystal discharge port 1, a downflow liquid circulation guide tube 2, an aeration pipe 5, a water inlet pipe 7, and a dosing pipe 9. The crystal discharge port 1 is located at the bottom of the device body. To facilitate the discharge of calcium fluoride crystals that have reached the threshold, the bottom of the device body has an inverted triangle structure, with the crystal discharge port 1 located at the lowest point of the inverted triangle.

[0035] The crystal discharge port 1 is vertically connected to the aeration head 4 at one end of the aeration tube 5. Below the aeration head 4, an aeration head support frame 3 is provided for supporting the aeration head 4. Above the aeration head 4, an inlet pipe 7 for introducing fluoride-containing wastewater and a dosing pipe 9 for adding a defluoridation agent are provided. In this embodiment, the cross-sectional area ratio of the aeration head 4 to the carrier reaction zone 13 within the defluoridation reaction zone II ranges from 1 / 10 to 1 / 4.

[0036] The downflow liquid circulation draft tube 2 connects the water and gas distribution zone I with the defluorination reaction zone II. This downflow liquid circulation draft tube 2 has an inverted triangular structure with a larger top and a smaller bottom. It is used to drain the calcium fluoride granular sludge generated in the defluorination reaction zone II. In this embodiment, the base angle α of the downflow liquid circulation draft tube 2 is 60°.

[0037] To ensure uniform distribution of water entering the device, a water inlet distributor 6 is provided at the outlet of the water inlet pipe 7, and a dosing distributor 8 is provided at the outlet of the dosing pipe 9. In this embodiment, the diameter ratio of the water inlet distributor 6 and the dosing distributor 8 to the carrier reaction zone 13 within the defluorination reaction zone II is in the range of 1 / 4 to 1 / 3.

[0038] like Figure 2 As shown, defluorination reaction zone II is provided with a carrier reaction zone 13 and a deep defluorination zone 12, with the cross-sectional area of ​​deep defluorination zone 12 being larger than that of carrier reaction zone 13. Because the cross-sectional area of ​​deep defluorination zone 12 is larger than that of carrier reaction zone 13, the water velocity slows when it reaches deep defluorination zone 12, promoting the flocculation and crystallization of large calcium fluoride crystals. In this embodiment, the cross-sectional area ratio of carrier reaction zone 13 to deep defluorination zone 12 ranges from 2 / 5 to 4 / 5.

[0039] A support frame 10 for holding calcium fluoride seed crystals is located at the bottom of the carrier reaction zone 13. The area housing the calcium fluoride seed crystals forms a carrier chamber 11. Carrier chamber 11 is positioned between 1 / 5 and 2 / 3 of the way up the carrier reaction zone 13. The support frame 10 is openable and features diversion holes to facilitate the discharge of calcium fluoride crystals that have reached a threshold value after the reaction is complete.

[0040] The enhanced sedimentation zone III is provided with a first enhanced sedimentation plate 14 , a second enhanced sedimentation plate 15 , a third enhanced sedimentation plate 16 , a sedimentation zone 17 , a guide cover 18 , a water outlet weir 19 and a vent pipe 20 .

[0041] Above the carrier reaction zone 13 is a sedimentation zone 17 for achieving solid-liquid separation, and a sedimentation plate composed of three layers of parallel conical covers is provided in the sedimentation zone 17. This structure can achieve efficient separation of solid and liquid phases, has a compact structure, a small separation zone volume, and saves space. The sedimentation plates composed of the three layers of parallel conical covers are the first reinforced sedimentation plate 14, the second reinforced sedimentation plate 15, and the third reinforced sedimentation plate 16, which are arranged in an inclined manner. An inter-plate gap is left between the first reinforced sedimentation plate 14 and the second reinforced sedimentation plate 15 to avoid particle accumulation, and an inter-plate gap is also left between the second reinforced sedimentation plate 15 and the third reinforced sedimentation plate 16 to avoid particle accumulation. The width of the inter-plate gap is more than 5 cm. In this embodiment, the inclination angle β of the first reinforced sedimentation plate 14, the second reinforced sedimentation plate 15, and the third reinforced sedimentation plate 16 are all 60°, which is conducive to solid-liquid separation.

[0042] A flow guide 18 is connected above the third enhanced precipitation plate 16, and a vent pipe 20 is connected above the flow guide 18, so that the vent pipe 20 is connected to the carrier reaction zone 13 to ensure that the pressure of the device body is balanced with the external air pressure. In this embodiment, the inclination angle γ of the flow guide 18 is 60°.

[0043] The enhanced sedimentation zone III is further provided with a water outlet weir 19 , and the water outlet weir 19 is arranged at a position higher than the sedimentation zone 17 on the inner wall of the device body, for controlling the elevation of the water level in the device.

[0044] This embodiment also provides a method for recovering fluorine using the above device, and the specific steps are as follows:

[0045] S1: Fluoride-containing wastewater enters the mixing chamber below defluorination reaction zone II through inlet pipe 7 and inlet distributor 6. Defluoridation agent enters the mixing chamber below defluoridation reaction zone II through dosing pipe 9 and dosing pipe distributor 8. The high-speed water flow creates a negative pressure in the mixing chamber below defluoridation reaction zone II, drawing the calcium fluoride granular sludge generated in defluoridation reaction zone II into the mixing chamber through the downflow liquid circulation guide tube 2. The calcium fluoride granular sludge mixes with the fluoride-containing wastewater and defluoridation agent to form a mud-water mixture.

[0046] S2: The sludge-water mixture from step S1 enters carrier chamber 11, where it reacts with the calcium fluoride seed crystals within carrier chamber 11 to produce calcium fluoride, which then enters enhanced sedimentation zone III. Solid-liquid separation occurs between first, second, and third enhanced sedimentation plates 14, 15, and 16, and the clarified wastewater is discharged through effluent weir 19. Due to the increased cross-sectional area of ​​deep defluorination zone 12, the water flow rate slows in deep defluorination zone 12, promoting the flocculation and crystallization of large calcium fluoride crystals. The resulting calcium fluoride granular sludge passes through deep defluorination zone 12 and enters the downflow liquid circulation guide tube 2, where it can be drawn back into the mixing chamber for circulation.

[0047] S3: When the calcium fluoride crystals in the carrier chamber 11 accumulate to a threshold value, the support bracket 10 is opened and the crystals are discharged through the crystal discharge port 1 .

[0048] The present invention makes full use of the reaction characteristics and strengthens the mixing effect of fluorine-containing wastewater and defluoridation agent through the arrangement of an aeration device, promotes the precipitation and reflux of calcium fluoride, and prevents the agglomeration of calcium fluoride precipitation; calcium fluoride seed crystals are arranged in the carrier area to strengthen the crystallization of calcium fluoride, and integrates efficient fluoride removal and recovery of calcium fluoride resources. The functions of each unit are complementary, the structure is compact, the footprint is small, and the pollution reduction and resource recovery effects are good.

[0049] The embodiment described above is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Persons skilled in the art may make various changes and modifications without departing from the spirit and scope of the present invention. Therefore, any technical solution obtained by equivalent substitution or equivalent transformation falls within the scope of protection of the present invention.

Claims

1. A multi-effect three-phase crystallization defluorination and fluorine recovery device, characterized in that: The device body is sequentially provided with a water and gas distribution zone (I), a fluorine removal reaction zone (II) and an enhanced precipitation zone (III) from bottom to top; The water and air distribution zone (I) is provided with a crystal discharge port (1), a downflow liquid circulation guide tube (2), an aeration pipe (5), a water inlet pipe (7), and a dosing pipe (9) in sequence from bottom to top; the crystal discharge port (1) is provided at the bottom of the device body and is connected to the aeration head (4) at one end of the aeration pipe (5) in vertical communication; an aeration head support frame (3) for supporting the aeration head (4) is provided below the aeration head (4); a water inlet pipe (7) for introducing fluorine-containing wastewater and a dosing pipe (9) for adding a defluorination agent are provided above the aeration head (4); the downflow liquid circulation guide tube (2) is an inverted triangle structure with a larger upper portion and a smaller lower portion, and is used to drain the calcium fluoride granular sludge generated from the defluorination reaction zone (II); The defluorination reaction zone (II) is provided with a carrier reaction zone (13) and a deep defluorination zone (12), and the cross-sectional area of ​​the deep defluorination zone (12) is larger than that of the carrier reaction zone (13); a support frame (10) for placing calcium fluoride seed crystals is provided at the bottom of the carrier reaction zone (13), and the area for placing the calcium fluoride seed crystals is a carrier chamber (11); the support frame (10) can be opened and closed to discharge calcium fluoride crystals that have reached a threshold value, and a guide hole is provided on the support frame (10); The enhanced precipitation zone (III) is provided with a first enhanced precipitation plate (14), a second enhanced precipitation plate (15), a third enhanced precipitation plate (16), a precipitation zone (17), a flow guide cover (18) and a vent pipe (20); the precipitation zone (17) is located above the carrier reaction zone (13), and the precipitation zone (17) is provided with the first enhanced precipitation plate (14), the second enhanced precipitation plate (15) and the third enhanced precipitation plate (16) in an inclined manner, and the first enhanced precipitation plate (14) and the second enhanced precipitation plate (15) are provided with a space between them. A gap is left between the second enhanced precipitation plate (15) and the third enhanced precipitation plate (16) to prevent particle accumulation; a guide cover (18) is connected above the third enhanced precipitation plate (16); a vent pipe (20) is connected above the guide cover (18), so that the vent pipe (20) is connected to the carrier reaction zone (13) to ensure that the device body and the external air pressure are balanced; the enhanced precipitation zone (III) is also provided with a water outlet weir (19), and the water outlet weir (19) is arranged on the inner wall of the device body at a position higher than the precipitation zone (17).

2. The multi-effect three-phase crystallization defluorination and fluorine recovery device according to claim 1, characterized in that: A water inlet distributor (6) is provided at the water outlet of the water inlet pipe (7); and a dosing distributor (8) is provided at the dosing outlet of the dosing pipe (9).

3. The multi-effect three-phase crystallization defluorination and fluorine recovery device according to claim 2, characterized in that: The diameter ratios of the water inlet distributor (6) and the drug dosing distributor (8) to the carrier reaction zone (13) are both 1 / 4 to 1 / 3.

4. The multi-effect three-phase crystallization defluorination and fluorine recovery device according to claim 1, characterized in that: The cross-sectional area ratio of the aeration head (4) to the carrier reaction zone (13) is 1 / 10 to 1 / 4.

5. The multi-effect three-phase crystallization defluorination and fluorine recovery device according to claim 1, characterized in that: The carrier chamber (11) is located at 1 / 5 to 2 / 3 of the carrier reaction zone (13) from bottom to top.

6. The multi-effect three-phase crystallization defluorination and fluorine recovery device according to claim 1, characterized in that: The cross-sectional area ratio of the carrier reaction zone (13) to the deep fluorine removal zone (12) is 2 / 5 to 4 / 5.

7. The multi-effect three-phase crystallization defluorination and fluorine recovery device according to claim 1, characterized in that: The inter-plate gap widths between the first reinforced precipitation plate (14) and the second reinforced precipitation plate (15) and between the second reinforced precipitation plate (15) and the third reinforced precipitation plate (16) are both greater than 5 cm.

8. The multi-effect three-phase crystallization defluorination and fluorine recovery device according to claim 1, characterized in that: The inclination angles β of the first strengthening precipitation plate (14), the second strengthening precipitation plate (15) and the third strengthening precipitation plate (16) are all 60°.

9. The multi-effect three-phase crystallization defluorination and fluorine recovery device according to claim 1, characterized in that: The bottom angle α of the downflow liquid circulation guide tube (2) is 60°, and the inclination angle γ of the guide cover (18) is 60°.

10. A method for recovering fluorine using the device according to any one of claims 2 to 9, characterized in that: The specific steps are as follows: S1: Fluorine-containing wastewater enters the mixing chamber below the defluorination reaction zone (II) in the device through the water inlet pipe (7) and the water inlet distributor (6), and the defluorination agent enters the mixing chamber below the defluorination reaction zone (II) in the device through the dosing pipe (9) and the dosing pipe distributor (8); the mixing chamber below the defluorination reaction zone (II) forms a negative pressure due to the high-speed water flow, and the calcium fluoride granular sludge generated in the defluorination reaction zone (II) is sucked into the mixing chamber through the downflow liquid circulation guide tube (2); the sludge is mixed with the fluorine-containing wastewater and the defluorination agent to form a mud-water mixture; S2: The mud-water mixture in step S1 enters the carrier chamber (11), and reacts with the calcium fluoride seed crystals in the carrier chamber (11) to generate calcium fluoride, and then enters the enhanced precipitation zone (III); solid-liquid separation is performed between the first enhanced precipitation plate (14), the second enhanced precipitation plate (15) and the third enhanced precipitation plate (16), and the clarified wastewater is discharged through the outlet weir (19); due to the increase in the cross-sectional area of ​​the deep defluorination zone (12), the water flow velocity in the deep defluorination zone (12) slows down, promoting the flocculation and crystallization of large-particle calcium fluoride crystals, and the generated calcium fluoride granular sludge enters the downflow liquid circulation guide tube (2) through the deep defluorination zone (12), and can be sucked into the mixing chamber for circulation; S3: After the calcium fluoride crystals in the carrier chamber (11) accumulate to a threshold value, the support frame (10) is opened and discharged through the crystal discharge port (1).

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