A double-layer filler fluorine-phosphorus calcium crystallization depth defluorination system and method thereof

Abstract

The application belongs to the field of industrial wastewater, and particularly relates to a double-layer filler calcium fluorophosphate crystallization deep fluorine removal system and a method thereof. The mixing distribution area of the fluidized bed system is provided with a water inlet pipe, the water inlet pipe is respectively provided with a first dosing pipe and a second dosing pipe, and the dosing pipes are connected with the water inlet pipe through a pipeline mixer. The first dosing pipe adds phosphates and inorganic acid, and the second dosing pipe adds calcium salt. Industrial fluorine-containing wastewater enters the mixing distribution area, the reagent in the first dosing pipe makes the pH value of the wastewater acidic, avoiding pipeline blockage; then the wastewater enters the pH adjusting area and contacts with the first layer of filler, the pH value of the wastewater changes to neutral to alkaline; then the wastewater enters the induced crystallization area, the fluorine ions in the wastewater generate calcium fluorophosphate crystals with the phosphates and the calcium salt on the surface of the filler, realizing efficient fluorine removal. Through the principle of acidic pH in the mixing distribution area and neutral to alkaline pH in the induced crystallization area, the application guarantees smooth water inlet and deep fluorine removal of the wastewater.

Description

Technical Field

[0001] This invention belongs to the field of industrial wastewater, specifically relating to a double-layer packing calcium fluorophosphate crystallization deep defluorination system and method. Background Technology

[0002] Fluorine is a trace element essential for the human body and crucial for human health. The suitable fluoride concentration in drinking water is 0.5~1.0 mg / L. Long-term consumption of water with fluoride concentrations exceeding 1.0 mg / L can lead to dental fluorosis, skeletal fluorosis, and other diseases. With the rapid development of high-tech industries such as electronics manufacturing, photovoltaics, and lithium batteries, the large amounts of fluoride-containing wastewater generated during these production processes pose a serious environmental challenge.

[0003] Currently, common methods for advanced defluoridation include chemical precipitation, membrane separation, adsorption, ion exchange, and electrochemical methods. While these methods can remove fluoride from wastewater, they all suffer from drawbacks such as high energy consumption, low efficiency, or high cost. Among these, chemical precipitation is the most widely used due to its simplicity. This method typically involves adding calcium salts to react with fluoride ions to produce CaF2 precipitate, reducing the fluoride concentration in the water from hundreds to thousands of milligrams per liter to just tens of milligrams per liter. However, the effluent still requires further advanced defluoridation.

[0004] To overcome the shortcomings of traditional chemical precipitation methods, induced crystallization has emerged, with fluidized bed systems being the most common. Adding a crystal to a fluidized bed reactor causes the target pollutant to precipitate as crystals on the packing surface. This system offers advantages such as high product purity, low water content, and easy resource recovery. Currently, existing fluidized beds consist of a mixing and distribution zone, an induced crystallization zone, and a clarified effluent zone from bottom to top. The mixing and distribution zone is used to adjust the pH of the wastewater. Chemicals are added in the induced crystallization zone to induce the target pollutant to precipitate as crystals on the packing surface. However, directly adding chemicals in the induced crystallization zone leads to uneven mixing of the chemicals and wastewater, and can cause blockage at the dosing port, resulting in low chemical utilization and reduced defluorination efficiency. Furthermore, induced crystallization defluorination technologies often focus on removing and recovering fluoride in the form of calcium fluoride. Due to solubility limitations, this method can only reduce fluoride levels to around ten milligrams per liter. Summary of the Invention

[0005] To address the aforementioned technical problems, this invention provides a system and method for deep defluorination of calcium fluorophosphate crystals using a double-layer packing.

[0006] The first aspect of this invention provides a double-layer packing calcium fluorophosphate crystallization deep defluorination system, comprising a sulfurized bed system. The mixing and distribution zone of the sulfurized bed system is equipped with an inlet pipe. A first dosing pipe and a second dosing pipe are connected to the inlet pipe via a mixer, with the second dosing pipe located close to the mixing and distribution zone. The mixer ensures that the reagent and wastewater can be rapidly and uniformly mixed within a short time. The second dosing pipe is used to add calcium salts, and the first dosing pipe is used to add phosphates and inorganic acids. During the dosing process, phosphates and inorganic acids are first added through the first dosing pipe, and then calcium salts are added through the second dosing pipe.

[0007] The water-to-powder volume ratio in the inlet pipe is 100-500:1 to save on reagent consumption and ensure crystallization efficiency.

[0008] The distance between the mixer on the second dosing pipe and the inlet of the mixing and distribution zone is ≤1m, so as to minimize the residence time of the mixture in the pipe.

[0009] In another preferred embodiment, the phosphate is one of NaH2PO4·2H2O, NaH2PO4·H2O, NaH2PO4 and KH2PO4, the calcium salt is one of CaCl2·6H2O, CaCl2·4H2O and CaCl2, and the inorganic acid is one or a mixture of several of hydrochloric acid, sulfuric acid, carbonic acid and phosphoric acid.

[0010] In another preferred embodiment, the fluidized bed system further includes a pH adjustment zone, an induced crystallization zone, and a clarified effluent zone arranged sequentially above the mixing and distribution zone.

[0011] In another preferred embodiment, the pH adjustment zone is provided with calcium carbonate particles with a particle size of 0.5 mm to 10 mm to adjust the pH value of the wastewater; specifically, the calcium carbonate particles are natural calcium carbonate particles such as seashells and snail shells, or mineral calcium carbonate particles such as calcite, limestone and marble.

[0012] The induced crystallization zone is equipped with phosphate rock particles with a particle size of 0.1 mm to 2 mm to induce crystallization for the removal and recovery of fluorine.

[0013] The volume ratio of the calcium carbonate particles to the pH adjustment zone is 1~4:10; the volume ratio of the phosphate rock particles to the induced crystallization zone is 1~4:10.

[0014] In another preferred embodiment, the induced crystallization zone is provided with a sampling port along the longitudinal direction.

[0015] In another preferred embodiment, the connection between the induced crystallization zone and the clarified effluent zone is made by a gradually expanding pipe.

[0016] In another preferred embodiment, the clarified water outlet area is provided with a water outlet.

[0017] In another preferred embodiment, the diameter ratio of the clarified water effluent zone to the induced crystallization zone is 1.5:1; the diameter of the mixing and distribution zone is the same as that of the pH adjustment zone and the induced crystallization zone.

[0018] A second aspect of the present invention provides a method for treating fluoride-containing wastewater using the fluidized bed apparatus, comprising the following steps:

[0019] S1, industrial fluoride-containing wastewater is injected into the mixing and distribution zone. Phosphates and inorganic acids enter the mixing and distribution zone through the first dosing pipe, and calcium salts enter the mixing and distribution zone through the second dosing pipe.

[0020] The specific process of S1 is as follows:

[0021] S11, Fluorine-containing wastewater enters the mixing and distribution zone through the inlet of the inlet pipe;

[0022] S12, phosphate and hydrochloric acid enter the first pipeline mixer through the first dosing pipe, and calcium chloride enters the second pipeline mixer through the second dosing pipe and then enters the mixing and distribution area;

[0023] S13, in the mixing and distribution zone, industrial fluoride wastewater, phosphate and hydrochloric acid mixed acid solution and calcium chloride solution are mixed evenly;

[0024] S14. The influent and chemical flow rates are monitored by an electromagnetic flow meter to ensure the correct flow ratio. The influent to chemical flow rate ratio is 100 to 500:1. The chemical flow rate refers to the flow rate of phosphate, hydrochloric acid and calcium chloride added to the first and second dosing pipes. The influent refers to fluoride-containing industrial wastewater.

[0025] S2, industrial fluoride-containing wastewater enters the mixing and distribution zone. The concentration ratio of calcium salts and phosphates to fluoride in the wastewater in the mixing and distribution zone is maintained at 3–15:2–8:1. Inorganic acid is added to adjust the pH of the wastewater in the mixing and distribution zone to 3.0–6.0 to prevent the formation of homogeneous crystals of calcium fluorophosphate, thus avoiding clogging of the mixer and distributor caused by homogeneous crystallization, extending the reactor's service life, and reducing operation and maintenance costs. The industrial fluoride-containing wastewater then enters the pH adjustment zone through the distribution plate, contacting the packing material to increase the pH from 3.0–6.0 to 6.5–9.0. After passing through the distribution plate, the industrial fluoride-containing wastewater undergoes pH adjustment by natural calcium carbonate or mineral calcium carbonate packing material, satisfying the following chemical equation: H + +CaCO3=HCO3 - +Ca 2+ CaCO3 + H2O = Ca 2+ +HCO3 - +OH -The pH value of the wastewater increased from 3-6 to 6.5-9.

[0026] In S3, industrial fluoride-containing wastewater enters the induced crystallization zone. The phosphate rock packing material is in a fluidized state. Fluoride ions in the wastewater react with calcium salts and phosphates on the surface of the phosphate rock to form calcium fluorophosphate crystals, producing calcium fluorophosphate coatings.

[0027] S4: Wastewater treated by S3 enters the clarification effluent zone. A diffuser is installed to prevent the packing material from overflowing. Water exits from the top side of the diffuser in the clarification effluent zone, with a pH value of 6.5~9.0 and a fluoride concentration of less than 1.0 mg / L. The effluent is stored in a flushing tank and then discharged through the top of the tank. The clarification effluent zone enhances solid-liquid separation, reducing turbidity and suspended solids concentration in the effluent; it also prevents overflow of the packing material caused by flushing.

[0028] S5, repeat S1~S4, after a 12h~48h operating cycle, water is introduced from the flushing water tank to flush the packing material to avoid packing material clumping or hardening and to ensure smooth water intake.

[0029] Compared with the prior art, the present invention has the following beneficial effects:

[0030] This invention employs a dosing principle of adding phosphate first and then calcium salt in the mixing and distribution zone, with the distance between the remote mixer and the inlet of the mixing and distribution zone ≤1m. By mixing phosphate with inorganic acid, the pH of the influent system is lowered to 3-6.0, ensuring smooth influent flow and preventing clogging of the inlet pipe and mixer. The pH adjustment zone adjusts the system pH from 3-6.0 to 6.5-9.0, ensuring efficient operation of fluoride removal and recovery in the induced crystallization zone, satisfying the following chemical equation: 10Ca²⁺ + +6PO4 3- +2F - =Ca 10 (PO4)6F2 generates calcium fluorophosphate, resulting in an effluent pH of 6.5–9 that meets national discharge standards without requiring secondary adjustment. The effluent fluoride concentration is less than 1.0 mg / L, achieving deep defluorination. A flushing tank is installed after effluent discharge for periodic flushing to prevent the packing material from clumping and hardening.

[0031] The reactor in this invention has a simple structure, small footprint, convenient operation, low reagent cost, and high treatment efficiency, and can achieve deep defluorination and recovery of calcium fluorophosphate. Attached Figure Description

[0032] Figure 1 The present invention provides a fluidized bed device for fluorine recovery from calcium fluorophosphate crystallization using a double-layer packing structure.

[0033] Figure 2 This is a schematic diagram of the water distribution plate in the device of the present invention.

[0034] In the diagram: 1-First dosing pipe; 2-Second dosing pipe; 3-Inlet; 4-Inspection port; 5-Water distribution plate; 6-Pack material outlet; 7-Sampling port along the flow path; 8-Outlet; 001-Mixing and distribution zone; 002-pH adjustment zone; 003-Induced crystallization zone; 004-Clarified water outlet zone. Detailed Implementation

[0035] To enable those skilled in the art to better understand and implement the technical solutions of the present invention, the present invention will be further described below with reference to specific embodiments and accompanying drawings. However, the embodiments described are not intended to limit the present invention. Unless otherwise specified, the experimental methods and detection methods described in the following embodiments are conventional methods; unless otherwise specified, the reagents and materials described are commercially available.

[0036] Existing fluoride wastewater treatment technologies still have significant shortcomings in achieving deep fluoride removal and resource recovery. First, the calcium fluoride crystallization method is limited by the solubility product, making it difficult to consistently maintain an effluent fluoride concentration below 10 mg / L, failing to meet increasingly stringent environmental requirements. Second, existing calcium fluorophosphate reactors suffer from complex structures, susceptibility to clogging, and high operating costs. Specifically, the reagent dosing inlet of the reactor is prone to clogging due to crystal adhesion, affecting continuous and stable operation; the pH of the effluent is too high (9.0–10.0), requiring additional neutralizing agents to adjust the pH to 6.0–9.0 to meet discharge standards, increasing treatment costs and operational complexity. Furthermore, fluoride removal technologies such as chemical precipitation, adsorption, membrane separation, and ion exchange often separate fluoride as sludge or waste, failing to achieve effective fluoride resource recovery and generally suffering from high treatment costs, high energy consumption, and significant risks of secondary pollution.

[0037] To address the shortcomings of the aforementioned technologies, this invention provides a well-structured, highly resistant, and resource-recoverable double-layer packed bed system for deep defluorination using calcium fluorophosphate crystallization. Its main objective is to optimize the reactor's internal structure and reagent dosing method, employing a double-layer packed bed fluidized bed reactor. This system maintains a low pH value in the mixing and distribution zone to prevent pipe blockage. After passing through the pH adjustment zone, the system maintains neutral to alkaline conditions in the induced crystallization zone to achieve efficient fluoride removal and recovery. While achieving a fluoride concentration of <1.0 mg / L in the defluorinated effluent, the pH value of the effluent remains stable between 6.5 and 9.0, allowing for discharge without additional adjustment. Finally, fluoride is recovered in the form of high-purity calcium fluorophosphate crystals, reducing treatment costs. Compared to existing deep defluorination processes, this invention not only simplifies operation and management but also offers significant advantages in terms of overall treatment costs and control stability.

[0038] The following is a detailed description of a defluorination system and method for calcium fluorophosphate crystallization depth using a double-layer packing.

[0039] like Figure 1As shown, a double-layer packing calcium fluorophosphate crystallization deep defluorination system includes, from bottom to top, a mixing and distribution zone 001, a pH adjustment zone 002, an induced crystallization zone 003, and a clarified effluent zone 004 connected in sequence. The induced crystallization zone 003 and the clarified effluent zone 004 are connected by a diffuser pipe; the induced crystallization zone 003 is provided with a sampling port 7 along the longitudinal direction.

[0040] The mixing and distribution zone 001 is equipped with an inlet pipe 3, on which a first dosing pipe 1 and a second dosing pipe 2 are respectively installed, with the second dosing pipe 2 being close to the mixing and distribution zone 001. The second dosing pipe 2 is used to add calcium salts, and the first dosing pipe 1 is used to add phosphates and inorganic acids. Specifically, the inlet pipe 3 is located on the middle side wall of the mixing and distribution zone; the first dosing pipe 1 and the second dosing pipe 2 are arranged perpendicularly to the inlet pipe 3 at 90° and are connected to the inlet pipe 3 through mixers to achieve rapid and uniform mixing of the reagents and wastewater. The inspection port 4 is located on the middle side wall of the mixing and distribution zone 001, facing the inlet of the inlet pipe 3.

[0041] A discharge port 6 is provided at the bottom of the pH adjustment zone 002; a water distribution plate 5 is provided at the connection between the mixing and distribution zone 001 and the pH adjustment zone 002, such as... Figure 2 As shown, the water distribution plate 5 has multiple holes, and short-handled filter heads are installed to achieve uniform water distribution.

[0042] The induced crystallization zone 003 contains phosphate rock filler with a particle size of 0.1 mm to 2.0 mm, while the pH adjustment zone 002 contains natural calcium carbonate particles from seashells and snails with a particle size of 0.5 mm to 10.0 mm, or calcium carbonate particles from calcite, limestone, and marble. The volume ratio of the filler in the pH adjustment zone to that in the pH adjustment zone is 1 to 4:10, and the volume ratio of the filler in the induced crystallization zone to that in the induced crystallization zone is also 1 to 4:10. The clarified water outlet zone 004 has an outlet 8. The diameter ratio of the clarified water outlet zone 004 to the induced crystallization zone 003 is 1.5:1; the mixing and distribution zone 001, pH adjustment zone 002, and induced crystallization zone 003 have the same diameter.

[0043] The above-mentioned double-layer packing calcium fluorophosphate crystallization depth defluorination system for treating fluoride-containing wastewater includes the following steps:

[0044] S1, industrial fluoride-containing wastewater is injected into the mixing and distribution zone 001. Phosphates and inorganic acids enter the mixing and distribution zone 001 through the first dosing pipe 1, and calcium salts enter the mixing and distribution zone 001 through the second dosing pipe 2.

[0045] The specific process of S1 is as follows:

[0046] S11, fluoride-containing wastewater enters the mixing and distribution zone through the inlet.

[0047] S12, phosphate and hydrochloric acid enter the mixer through the first dosing tube 1, and calcium chloride enters the mixing and distribution zone 001 through the mixer through the second dosing tube 2.

[0048] S13, in the mixing and distribution zone 001, industrial fluoride-containing wastewater, a mixed solution of phosphate and hydrochloric acid, and a calcium chloride solution are mixed evenly; the phosphate is one of NaH2PO4·2H2O, NaH2PO4·H2O, NaH2PO4, and KH2PO4, the calcium salt is one of CaCl2·6H2O, CaCl2·4H2O, and CaCl2, and the inorganic acid is one or a mixture of several of hydrochloric acid, sulfuric acid, carbonic acid, and phosphoric acid.

[0049] S14. The inlet water and the inlet drug flow rate are monitored by an electromagnetic flow meter to ensure the correct flow ratio. The ratio of inlet water to inlet drug flow rate is 100 to 500:1.

[0050] S2, industrial fluoride-containing wastewater enters the mixing and distribution zone 001. The calcium and phosphorus added to the system maintain a concentration ratio of 3-15:2-8:1 with the fluoride in the wastewater. Hydrochloric acid is added to maintain the pH of the wastewater in mixing and distribution zone 001 at 3.0-6.0, preventing the formation of homogeneous crystals of calcium fluorophosphate, eliminating blockages in the mixer and distributor caused by homogeneous crystallization, extending the reactor's service life, and reducing operation and maintenance costs. The industrial fluoride-containing wastewater then enters the pH adjustment zone 002 through the distribution plate 5. Through the pH adjustment effect of natural calcium carbonate or mineral calcium carbonate packing, the following chemical equation is satisfied: H... + +CaCO3=HCO3 - +Ca 2+ CaCO3 + H2O = Ca 2+ +HCO3 - +OH - The pH value of industrial fluoride-containing wastewater increased from 3-6 to 6.5-9.

[0051] S3, industrial fluoride-containing wastewater enters the induced crystallization zone 003, the phosphate rock packing is in a fluidized state, the fluoride ions in the industrial fluoride-containing wastewater react with the reagents to form calcium fluorophosphate crystals on the surface of the phosphate rock, producing calcium fluorophosphate coatings.

[0052] S4: Industrial fluoride-containing wastewater treated by S3 enters the clarification effluent zone 004. A diffuser is installed to prevent the packing material from overflowing. Water exits from the top side of the diffuser in the clarification effluent zone 004. The effluent pH is 6.5~9.0, and the fluoride concentration is less than 1.0 mg / L. After being stored in a flushing tank, the effluent is discharged through the top of the tank. The clarification effluent zone enhances solid-liquid separation, reducing turbidity and suspended solids concentration in the effluent; it also prevents overflow of the packing material caused by flushing.

[0053] S5, repeat S1~S4, after 12~48h operation cycle, water is introduced from the flushing water tank to flush the packing to avoid packing clumping or caking and to ensure smooth water intake.

[0054] Application Example: Wastewater from an integrated circuit factory in Guangdong Province: fluoride ion concentration 2.2 mg / L~6.7 mg / L, pH value 7.1~7.8. The specific implementation steps of this fluidized bed system are as follows:

[0055] S1, the pH adjustment zone 002 of the fluidized bed is filled with seashell packing, and the induced crystallization zone 003 is filled with phosphate rock packing.

[0056] S2, fluoride-containing wastewater enters the mixing and distribution zone 001 through the inlet pipe 3, the mixed solution of sodium dihydrogen phosphate and hydrochloric acid is mixed through the mixer on the first dosing pipe 1 and enters the mixing and distribution zone 001, the calcium chloride solution is mixed through the mixer on the second dosing pipe 2 and enters the mixing and distribution zone 001, and the volume ratio of fluoride-containing wastewater to solution is 300:1; the pH of fluoride-containing wastewater changes from neutral to acidic.

[0057] S3, the fluoride-containing wastewater, the mixed solution of sodium dihydrogen phosphate and hydrochloric acid, and the calcium chloride solution enter the pH adjustment zone 002 through the mixing and distribution zone 001, and the pH of the wastewater changes from acidic to neutral to alkaline.

[0058] S4, then the neutral to alkaline fluoride-containing wastewater enters the induced crystallization zone 003, where calcium fluorophosphate coatings are formed on the surface of the phosphate rock, achieving deep defluorination.

[0059] S5, the treated wastewater exits through the top side of the clarification effluent zone 004.

[0060] Results: The fluoride concentration in the effluent of the fluoride-containing wastewater treated by this fluidized bed system was reduced to 0.3~0.8 mg / L, and the pH value of the effluent was 6.5~8.

[0061] Comparative example: Simulated fluoride-containing wastewater: fluoride ion concentration 9.2 mg / L~10.3 mg / L, pH value 6.7~7.3. The specific implementation steps of this fluidized bed system are as follows:

[0062] S1, the pH adjustment zone 002 of the fluidized bed is filled with seashell packing, and the induced crystallization zone 003 is filled with phosphate rock packing.

[0063] S2. Fluorine-containing wastewater enters the mixing and distribution zone 001 through the inlet pipe 3. The mixed solution of sodium dihydrogen phosphate and hydrochloric acid is mixed through the mixer on the first dosing pipe 1 and enters the mixing and distribution zone 001. The calcium chloride solution is mixed through the mixer on the second dosing pipe 2 and enters the mixing and distribution zone 001. The pH of the wastewater changes from neutral to acidic.

[0064] S3. Fluorine-containing wastewater and reagents enter pH adjustment zone 002 through mixing and distribution zone 001, and the pH of the wastewater changes from acidic to neutral to alkaline.

[0065] S4. Subsequently, the neutral to alkaline fluoride-containing wastewater enters the induced crystallization zone 003, where a calcium fluorophosphate coating is formed on the surface of the phosphate rock, achieving deep defluorination.

[0066] S5. The treated wastewater exits through the top side of the clarification effluent zone 004.

[0067] Results: After fluidized bed treatment, the fluoride concentration of fluoride-containing wastewater was reduced to 0.4~0.9 mg / L, and the pH of the effluent was 6.5~7.0.

[0068] As can be seen from the above embodiments and comparative examples, the double-layer packing calcium fluorophosphate crystallization deep defluorination system and method provided by the present invention can deeply treat low-concentration fluoride-containing wastewater, achieving an effluent fluoride concentration of 0.3 mg / L~0.9 mg / L and an effluent pH of 6.5~8, meeting the direct discharge standards for industrial wastewater. It has low operating costs and a simple system structure.

[0069] Although preferred embodiments of the invention have been described, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including both the preferred embodiments and all changes and modifications falling within the scope of the invention.

Claims

1. A double-layer packing system for deep defluorination of calcium fluorophosphate crystals, comprising a fluidized bed system, characterized in that, The mixing and distribution zone (001) of the fluidized bed system is provided with an inlet pipe (3). A first dosing pipe (1) and a second dosing pipe (2) are connected to the inlet pipe (3) via a mixer, and the second dosing pipe (2) is close to the mixing and distribution zone (001). The second dosing pipe (2) is used to add calcium salts, and the first dosing pipe (1) is used to add phosphates and inorganic acids. During the dosing process, phosphates and inorganic acids are added first through the first dosing pipe (1), and then calcium salts are added through the second dosing pipe (2). The volume ratio of water to medicine in the water inlet pipe (3) is 100-500:1; The distance between the mixer on the second dosing pipe (2) and the inlet of the mixing and distribution zone (001) is ≤1m; The fluidized bed system also includes a pH adjustment zone (002), an induced crystallization zone (003), and a clarified effluent zone (004) arranged sequentially on the mixing and distribution zone (001). The pH adjustment zone (002) is equipped with calcium carbonate particles with a particle size of 0.5 mm to 10 mm to adjust the pH value of the wastewater. The induced crystallization zone (003) is equipped with phosphate rock particles with a particle size of 0.1 mm to 2 mm for inducing crystallization to remove and recover fluorine; The volume ratio of the calcium carbonate particles to the pH adjustment zone (002) is 1~4:10; The volume ratio of the phosphate rock particles to the induced crystallization zone (003) is 1~4:

10.

2. The double-layer packing calcium fluorophosphate crystallization depth defluorination system according to claim 1, characterized in that, The phosphate is any one of NaH2PO4·2H2O, NaH2PO4·H2O, NaH2PO4, and KH2PO4; the calcium salt is any one of CaCl2·6H2O, CaCl2·4H2O, and CaCl2; and the inorganic acid is at least one of hydrochloric acid, sulfuric acid, carbonic acid, and phosphoric acid.

3. The double-layer packing calcium fluorophosphate crystallization depth defluorination system according to claim 1, characterized in that, The induced crystallization zone (003) is provided with a sampling port (7) along the longitudinal direction.

4. The double-layer packing calcium fluorophosphate crystallization depth defluorination system according to claim 1, characterized in that, The connection between the induced crystallization zone (003) and the clarified water effluent zone (004) is achieved by a gradually expanding pipe.

5. The double-layer packing calcium fluorophosphate crystallization depth defluorination system according to claim 1, characterized in that, The clarified water outlet (004) is provided with an outlet (8).

6. The double-layer packing calcium fluorophosphate crystallization depth defluorination system according to claim 1, characterized in that, The diameter ratio of the clarified water effluent zone (004) to the induced crystallization zone (003) is 1.5:1; the diameters of the mixing and distribution zone (001), the pH adjustment zone (002), and the induced crystallization zone (003) are the same.

7. A method for treating fluoride-containing wastewater using the fluidized bed system as described in claim 4, characterized in that, Includes the following steps: S1, inject industrial fluoride-containing wastewater into the mixing and distribution zone (001). Phosphate and inorganic acid enter the mixing and distribution zone (001) through the first dosing pipe (1), and calcium salt enters the mixing and distribution zone (001) through the second dosing pipe (2). S2, industrial fluoride-containing wastewater enters the mixing and distribution zone (001). The concentration ratio of calcium salts and phosphates in the mixing and distribution zone (001) to fluoride in the wastewater is maintained at 3-15:2-8:

1. Inorganic acid is added to make the pH value of the wastewater in the mixing and distribution zone (001) 3.0-6.0 to prevent the formation of homogeneous crystallization of calcium fluorophosphate. The industrial fluoride-containing wastewater enters the pH adjustment zone (002) through the water distribution plate (5) and comes into contact with the packing material in the pH adjustment zone (002) to increase the pH value of the wastewater from 3.0-6.0 to 6.5-9.

0. S3, the industrial fluoride-containing wastewater then enters the induced crystallization zone (003), where the phosphate rock packing is in a fluidized state, and fluoride ions in the wastewater react with calcium salts and phosphates to form calcium fluorophosphate crystals on the surface of the phosphate rock. S4: Wastewater treated by S3 enters the clarification effluent zone, where a diffuser is installed to prevent packing material from overflowing. Water exits from the top side of the diffuser in the clarification effluent zone, with a pH value of 6.5~9.0 and a fluoride concentration of less than 1.0 mg / L. S5, repeat S1~S4, after a 12h~48h operating cycle, water is introduced from the flushing water tank to flush the packing material to avoid packing material clumping or hardening and to ensure smooth water intake.

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