Process for synthesizing fluorapatite from wastewater and equipment used in process

Abstract

The invention discloses a process and equipment for synthesizing fluorapatite from wastewater, the equipment comprises a blending tank, a dispensing tank, a crystallization fluidized bed reactor, a reaction tank, a coagulation tank, a flocculation tank, a sedimentation tank, a pH detection device, a lift pump and a control system, fluorine-containing sewage and phosphorus-containing sewage are mixed in the blending tank, so that the molar ratio of fluorine to phosphorus is 0.34-0.4; the method comprises the following steps: adding fluorapatite into a reaction tank, adjusting the pH value to 7.5-8.5, pumping the fluorapatite and lime slurry into a crystallization fluidized bed reactor according to a calcium-phosphorus molar ratio of (3-3.5): 1, carrying out a crystallization reaction, naturally airing the generated fluorapatite crystals, carrying out a reaction on crystallization treatment water and the lime slurry in the reaction tank to remove fluorine and phosphorus, carrying out coagulation, flocculation and precipitation treatment, and discharging the effluent after reaching the standard. The high-quality fluorapatite product is prepared from the fluorine-containing sewage and the phosphorus-containing sewage, so that the preparation cost is low, and resourceful treatment of the fluorine-containing sewage and the phosphorus-containing sewage is realized.

Description

Technical Field

[0001] This invention relates to a wastewater treatment technology, and more particularly to a process for synthesizing fluorapatite from wastewater and the equipment used therein. Background Technology

[0002] Industries such as phosphorus chemicals, semiconductor electronics manufacturing, metal surface treatment, and fluorochemicals use raw materials containing fluorine or phosphorus in their production processes, resulting in wastewater containing both phosphorus and fluorine. Treatment of fluorine- and phosphorus-containing wastewater typically employs a coagulation and sedimentation process with lime addition. This process separates the fluorine and phosphorus in the wastewater into calcium fluoride and calcium phosphate sludge, respectively, achieving compliant wastewater discharge.

[0003] The primary goal of wastewater treatment is to achieve compliance with standards for fluoride and phosphorus levels. Therefore, excessive calcium sources are added to wastewater when removing fluoride and phosphorus. While this method is effective for treatment, the calcium fluoride and calcium phosphate sludge produced by this method are of low grade and can only be treated as solid waste. This increases the cost of wastewater treatment and wastes fluoride and phosphorus resources.

[0004] Fluorapatite, with the chemical formula Ca5(PO4)3F, is a mineral containing both phosphorus and fluorine. It belongs to the apatite ore family and often occurs mixed with hydroxyapatite and chloroapatite. Fluorapatite has numerous applications. In biomedicine, it is frequently used as a material for preventing tooth decay and for bone repair. In agriculture, it is a raw material for producing superphosphate and ammonium phosphate, or used directly as a slow-release fertilizer. Industrially, it serves as a catalyst carrier in petrochemicals and a flux in the ceramics and glass industries. Furthermore, due to its hexagonal crystal system and stable structure, fluorapatite is often used as a solidification material for radioactive nuclides such as uranium, thorium, and actinium.

[0005] Currently, there are two main methods for preparing fluorapatite:

[0006] The first method involves using specific substances to prepare a fluorine- and phosphorus-containing mixed solution of a specific concentration. The mixed solution is then mixed with a calcium source prepared with calcium nitrate tetrahydrate. Under natural mixing pH conditions and reflux at 60°C, the mixture is magnetically stirred and microwaved for 30 minutes. The solid-liquid mixture is then centrifuged, washed with water, dried, and ground to obtain a nano-fluorapatite system.

[0007] The second method involves preparing a mixed transparent solution containing fluorine and phosphorus using ammonium fluoride and diammonium hydrogen phosphate. A calcium source prepared with calcium nitrate is added to the mixed solution, and the pH value of the system is controlled to be 9-12. The mixed system is aged to obtain fluorapatite. The mixed system is then separated into solid and liquid components, washed, and dried to obtain a fluorapatite precursor. The precursor is then calcined at high temperature to obtain nano-sized fluorapatite.

[0008] The above-mentioned process for preparing fluorapatite requires the use of a large amount of inorganic salts containing phosphate and fluoride ions to prepare a mixed solution containing fluoride and phosphorus. Calcium nitrate is also required as a calcium source, resulting in high raw material costs. Furthermore, the process requires stringent auxiliary conditions such as high temperature, microwave, centrifugation, and drying, leading to high energy consumption and complex technology.

[0009] If fluorapatite can be extracted from wastewater while removing phosphorus and fluoride, and then reused as a raw material, not only can the resources of fluoride and phosphorus in wastewater be utilized, but also higher economic benefits can be generated.

[0010] If the current fluorapatite preparation process is followed, it is clear that heating the wastewater would incur significant costs for such a large volume of wastewater. Furthermore, the extraction of calcium fluorophosphate requires solid-liquid separation, washing, and drying, all of which are challenging, complex, and difficult to control in wastewater extraction. Summary of the Invention

[0011] To overcome the above-mentioned defects, the present invention provides a process for synthesizing fluorapatite from wastewater and the equipment used therein. This process for synthesizing fluorapatite from wastewater can not only achieve the standard treatment of fluorine and phosphorus in wastewater, but also extract high-grade fluorapatite in a low-energy-consumption manner.

[0012] The technical solution adopted by this invention to solve its technical problem is: a process for synthesizing fluorapatite from wastewater, comprising the following steps:

[0013] Step 1: Pour the fluoride-containing wastewater and the phosphorus-containing wastewater into the mixing tank, so that the fluoride-phosphorus molar ratio of the mixed wastewater in the mixing tank is between 0.34 and 0.4;

[0014] Step 2: Add sodium hydroxide, potassium hydroxide, or sulfuric acid to the mixing tank to adjust the pH of the mixed wastewater to the range of 7.5 to 8.5;

[0015] Step 3: The mixed wastewater containing fluoride and phosphorus prepared in the mixing tank is fed into the crystallization fluidized bed reactor. At the same time, lime slurry is added to the crystallization fluidized bed reactor according to the calcium-fluoride molar ratio of 4.2 to 5.0. The mixed wastewater and lime slurry react in the crystallization fluidized bed reactor to produce fluorapatite crystals and crystallized treated water.

[0016] Step 4: Fluoroapatite crystals are discharged from the crystallization fluidized bed reactor and air-dried naturally; crystallization treatment water is pumped into the reaction tank, and lime slurry is added to the reaction tank at a calcium-to-phosphorus molar ratio of 3-3.5:1. Fluorine and phosphorus in the crystallization treatment water react with lime slurry to form precipitates, and the fluorine and phosphorus content of the treated water in the reaction tank is below the standard line.

[0017] Step 5: The mud-water mixture discharged from the reaction tank undergoes further coagulation, flocculation, and sedimentation treatment to remove calcium fluoride and calcium phosphate sludge, resulting in effluent that meets discharge standards.

[0018] As a further improvement of the present invention, in step one, sodium fluoride, potassium fluoride or hydrofluoric acid is added to the mixing tank as soluble fluorides to help adjust the fluoride-phosphorus molar ratio of the mixed wastewater.

[0019] As a further improvement of the present invention, the mass percentage concentration of the lime slurry used in step three is 0.5-3%.

[0020] As a further improvement of the present invention, the lime slurry is prepared by mixing and blending dry lime powder with tap water, crystallization treatment water in step three, or effluent from step five in a mixing tank.

[0021] As a further improvement of the present invention, in step four, sulfuric acid is injected into the reaction tank to adjust the pH of the treated water to 6.5-7.5.

[0022] As a further improvement of the present invention, the crystallization fluidized bed reactor used in step three is a crystallization reactor in which pure water provides fluidization power or a mechanically stirred fluidized bed crystallization reactor.

[0023] As a further improvement of the present invention, in step three, the initial packing material in the crystallization fluidized bed reactor is 10-20 μm quartz sand or fluorapatite, and the packing material accounts for 20%-50% of the volume in the crystallization fluidized bed reactor. The reflux power provided in the reaction zone of the crystallization fluidized bed reactor is 20-100 m / h, and the power is a vertically upward macroscopic thrust.

[0024] As a further improvement of the present invention, in step three, after the fluoride ions and phosphate ions in the influent water and the calcium ions in the lime slurry are diluted by internal reflux, the ratio of the activity product of fluoride ions, phosphate ions and calcium ions in the fluorophosphate to the solubility product constant of fluorophosphate is controlled to be between 20 and 100.

[0025] As a further improvement of the present invention, in step three, sodium hydroxide or sulfuric acid is added to the crystallization fluidized bed reactor to control the pH of the mixed liquid in the crystallization fluidized bed reactor to be between 8.0 and 8.5, and the residence time of the mixed liquid in the crystallization fluidized bed reactor is not less than 20 minutes.

[0026] A device for synthesizing fluorapatite from wastewater includes an mixing tank, a dosing tank, a crystallization fluidized bed reactor, a reaction tank, a coagulation tank, a flocculation tank, a sedimentation tank, a pH monitoring device, a booster pump, and a control system. The mixing tank is equipped with a wastewater inlet, a dosing inlet, and a mixed wastewater outlet. Fluoride-containing and phosphorus-containing wastewater enter the mixing tank through the wastewater inlet and mix with the reagents entering through the dosing inlet. The dosing tank is equipped with a lime powder dosing inlet, a purified water inlet, and a lime slurry outlet. A stirrer is also installed in the mixing tank to mix the lime powder and purified water. The crystallization fluidized bed reactor is equipped with a mixing inlet, a dosing inlet, an outlet, and a crystal discharge outlet. The mixing inlet of the crystallization fluidized bed reactor is connected to the mixed wastewater outlet of the mixing tank, and the dosing inlet of the crystallization fluidized bed reactor is connected to the lime slurry outlet of the dosing tank. The booster pump can pump the mixed wastewater from the mixing tank and the lime slurry from the dosing tank into the crystallization tank. Crystallization occurs within a fluidized bed reactor. Large crystal particles settle and are periodically discharged through the crystal discharge port. The reaction tank, coagulation tank, flocculation tank, and sedimentation tank are sequentially connected. Each of the reaction tank, coagulation tank, and flocculation tank has a dosing port. The sedimentation tank has an effluent discharge port and a sludge discharge port at its upper and lower ends, respectively. The effluent outlet of the crystallization fluidized bed reactor is connected to the reaction tank via a pipe. The dosing port of the reaction tank is connected to the lime slurry outlet of the mixing tank. A booster pump can pump lime slurry from the mixing tank into the reaction tank. PAC and PAM agents can be added to the coagulation tank and flocculation tank through their respective dosing ports for coagulation and flocculation reactions. The effluent outlet of the sedimentation tank is connected to the purified water inlet of the mixing tank via a branch pipe. A pH detection device is installed in the mixing tank, the crystallization fluidized bed reactor, and the reaction tank to monitor the pH of the liquid in real time. The pH detection device communicates with the control system, which controls the start / stop and flow rate of the booster pump.

[0027] The beneficial effects of this invention are as follows: This invention collects and mixes fluoride-containing wastewater and phosphorus-containing wastewater to form a mixed wastewater with a specific fluoride-phosphorus molar ratio. The mixed wastewater is then reacted with lime slurry in a crystallization fluidized bed reactor to generate high-purity fluorapatite crystals. After the fluorapatite crystals are discharged from the crystallization fluidized bed reactor, they are naturally air-dried to obtain a high-quality fluorapatite product. No additional centrifugation and drying dehydration treatment is required. The entire process is simple and effectively avoids the harsh auxiliary conditions such as high temperature, microwave, centrifugation, and drying required in traditional fluorapatite extraction. At the same time, it achieves the standard treatment of fluoride and phosphorus in wastewater. This invention uses fluoride-containing wastewater and phosphorus-containing wastewater to prepare high-quality fluorapatite products, with low preparation cost, and realizes the resource-based treatment of fluoride-containing wastewater and phosphorus-containing wastewater. Attached Figure Description

[0028] Figure 1 This is a process flow diagram of the present invention. Detailed Implementation

[0029] Example: A process for synthesizing fluorapatite from wastewater, characterized by the following steps:

[0030] Step 1: Introduce fluoride-containing wastewater and phosphorus-containing wastewater into a mixing tank, ensuring the fluoride-to-phosphorus molar ratio is between 0.34 and 0.4. This ensures a slight excess of fluoride ions and phosphate ions in the mixed wastewater compared to the fluoride-to-phosphate ratio in fluorapatite, maximizing the utilization of fluoride and phosphorus in both types of wastewater. This also reduces the amount of sludge generated during subsequent fluoride and phosphorus removal processes. If the fluoride ion content in the mixed wastewater is too low, causing the fluoride-to-phosphorus molar ratio to not meet the requirements, add sodium fluoride, potassium fluoride, or hydrofluoric acid to the mixing tank as soluble fluorides to help adjust the fluoride-to-phosphorus molar ratio, ensuring that the phosphate ions in the wastewater are fully utilized.

[0031] Step 2: Add sodium hydroxide, potassium hydroxide, or sulfuric acid to the mixing tank to adjust the pH of the mixed wastewater to the range of 7.5 to 8.5;

[0032] Step 3: The mixed wastewater containing fluoride and phosphorus prepared in the mixing tank is fed into the crystallization fluidized bed reactor. At the same time, lime slurry is added to the crystallization fluidized bed reactor according to the calcium-fluoride molar ratio of 4.2 to 5.0. The mass percentage concentration of lime slurry is 0.5% to 3%. The mixed wastewater and lime slurry react in the crystallization fluidized bed reactor to produce fluorapatite crystals and crystallized water. The addition of lime slurry (calcium hydroxide) provides a calcium source. Fluoroapatite (calcium fluorophosphate) crystals are precipitated in the liquid phase when the three free particles of phosphate, fluoride, and calcium ions reach the solubility product of calcium fluorophosphate.

[0033] Step 4: Fluoroapatite crystals are discharged from the crystallization fluidized bed reactor and allowed to air dry naturally. Crystallization-treated water is pumped into the reaction tank, and lime slurry is simultaneously added to the reaction tank at a calcium-to-phosphorus molar ratio of 3–3.5:1. Sulfuric acid is injected into the reaction tank to adjust the pH of the treated water to 6.5–7.5. Fluorine and phosphorus in the crystallization-treated water react with the lime slurry to form precipitates. The fluorine and phosphorus content of the treated water in the reaction tank is below the standard. Due to the addition of a large amount of lime slurry, the pH of the treated water in the reaction tank is high. Sulfuric acid is injected to adjust the pH of the treated water to neutral water. The discharge port of the crystallization fluidized bed reactor can be opened periodically to periodically discharge the fluoroapatite crystals. The fluoroapatite crystals only need to air dry naturally; no further centrifugation, drying, or dehydration is required, saving energy. Residual fluoride ions and phosphate ions in the crystallization-treated water continue to react with the lime slurry in the reaction tank to generate calcium fluoride and calcium phosphate precipitates, effectively removing fluoride ions and phosphate ions from the wastewater and ensuring that the fluorine and phosphorus content in the wastewater meets the discharge standards.

[0034] Step 5: The sludge-water mixture discharged from the reaction tank undergoes further coagulation, flocculation, and sedimentation treatment to remove calcium fluoride and calcium phosphate sludge. The effluent meets discharge standards. By adding PAC and PAM to the sludge-water mixture discharged from the reaction tank for coagulation and flocculation treatment, the calcium fluoride, calcium phosphate, and SS in the sludge-water mixture are solidified to form sludge. The final effluent can be directly discharged or recycled within the plant.

[0035] The lime slurry is prepared by mixing dry lime powder with tap water, crystallization treatment water from step three, or effluent from step five in a mixing tank. Initially, the lime slurry is prepared by mixing dry lime powder with tap water, and later by mixing dry lime powder with effluent from step five, thus saving water resources.

[0036] The crystallization fluidized bed reactor used in step three is either a crystallization reactor powered by pure water or a mechanically stirred fluidized bed crystallization reactor. The initial packing material in the crystallization fluidized bed reactor is 10-20 μm quartz sand or fluorapatite, and the packing material accounts for 20%-50% of the volume in the crystallization fluidized bed reactor. The reflux power provided in the reaction zone of the crystallization fluidized bed reactor is 20-100 m / h, and the power is a vertically upward macroscopic thrust. Adding quartz sand or fluorapatite to the crystallization fluidized bed reactor can serve as seed crystals, which is conducive to the rapid adhesion and crystallization of fluorapatite. The mixed wastewater enters from the bottom of the crystallization fluidized bed reactor and flows from bottom to top. The water flow makes the seed crystals evenly distributed in the reaction zone of the crystallization fluidized bed reactor. At the same time, the mixed wastewater and lime slurry are fully mixed to carry out the crystallization reaction. The calcium fluorophosphate formed by the reaction quickly adheres to the surface of the seed crystals, realizing the rapid growth of large crystal particles. After the large crystal particles sink, they are discharged to prevent the fluorapatite crystals from flowing out with the water at the top of the crystallization fluidized bed reactor.

[0037] In step three, after the fluoride and phosphate ions in the influent water and the calcium ions in the lime slurry are diluted by internal reflux, the ratio of the activity product of fluoride, phosphate and calcium ions in the reactor to the solubility product constant of calcium fluorophosphate is controlled to a power of 1 / 9 between 20 and 100. This is conducive to the rapid combination of fluoride, phosphate and calcium ions to form calcium fluorophosphate.

[0038] In step three, sodium hydroxide or sulfuric acid is added to the crystallization fluidized bed reactor to control the pH of the mixed liquid in the reactor between 8.0 and 8.5, and the residence time of the mixed liquid in the crystallization fluidized bed reactor is not less than 20 minutes. This ensures that fluoride ions, phosphate ions and calcium ions in the mixed liquid fully react to form calcium fluorophosphate, avoiding insufficient reaction that would cause fluoride ions and phosphate ions to be discharged with the water flow, and also avoiding calcium ions that have not fully reacted and settle down to mix with fluorapatite, which would affect the final purity of fluorapatite.

[0039] A device for synthesizing fluorapatite from wastewater includes an mixing tank, a dosing tank, a crystallization fluidized bed reactor, a reaction tank, a coagulation tank, a flocculation tank, a sedimentation tank, a pH monitoring device, a booster pump, and a control system. The mixing tank is equipped with a wastewater inlet, a dosing inlet, and a mixed wastewater outlet. Fluoride-containing and phosphorus-containing wastewater enter the mixing tank through the wastewater inlet and mix with the reagents entering through the dosing inlet. The dosing tank is equipped with a lime powder dosing inlet, a purified water inlet, and a lime slurry outlet. A stirrer is also installed in the mixing tank to mix the lime powder and purified water. The crystallization fluidized bed reactor is equipped with a mixing inlet, a dosing inlet, an outlet, and a crystal discharge outlet. The mixing inlet of the crystallization fluidized bed reactor is connected to the mixed wastewater outlet of the mixing tank, and the dosing inlet of the crystallization fluidized bed reactor is connected to the lime slurry outlet of the dosing tank. The booster pump can pump the mixed wastewater from the mixing tank and the lime slurry from the dosing tank into the crystallization tank. Crystallization occurs within a fluidized bed reactor. Large crystal particles settle and are periodically discharged through the crystal discharge port. The reaction tank, coagulation tank, flocculation tank, and sedimentation tank are sequentially connected. Each of the reaction tank, coagulation tank, and flocculation tank has a dosing port. The sedimentation tank has an effluent discharge port and a sludge discharge port at its upper and lower ends, respectively. The effluent outlet of the crystallization fluidized bed reactor is connected to the reaction tank via a pipe. The dosing port of the reaction tank is connected to the lime slurry outlet of the mixing tank. A booster pump can pump lime slurry from the mixing tank into the reaction tank. PAC and PAM agents can be added to the coagulation tank and flocculation tank through their respective dosing ports for coagulation and flocculation reactions. The effluent outlet of the sedimentation tank is connected to the purified water inlet of the mixing tank via a branch pipe. A pH detection device is installed in the mixing tank, the crystallization fluidized bed reactor, and the reaction tank to monitor the pH of the liquid in real time. The pH detection device communicates with the control system, which controls the start / stop and flow rate of the booster pump.

[0040] The above system realizes intelligent dosing of reagents and intelligent control of reaction, which fully ensures the reaction is complete, the effluent meets the standards and is stable, and effectively guarantees the purity of fluorapatite.

Claims

1. A process for synthesizing fluorapatite from wastewater, characterized in that: Includes the following steps: Step 1: Pour the fluoride-containing wastewater and the phosphorus-containing wastewater into the mixing tank, so that the fluoride-phosphorus molar ratio of the mixed wastewater in the mixing tank is between 0.34 and 0.4; Step 2: Add sodium hydroxide, potassium hydroxide, or sulfuric acid to the mixing tank to adjust the pH of the mixed wastewater to the range of 7.5 to 8.5; Step 3: The mixed wastewater containing fluoride and phosphorus prepared in the mixing tank is fed into the crystallization fluidized bed reactor. At the same time, lime slurry is added to the crystallization fluidized bed reactor according to the calcium-fluoride molar ratio of 4.2 to 5.

0. The mixed wastewater and lime slurry react in the crystallization fluidized bed reactor to produce fluorapatite crystals and crystallized treated water. Step 4: Fluoroapatite crystals are discharged from the crystallization fluidized bed reactor and then air-dried naturally; The crystallization-treated water is pumped into the reaction tank, and lime slurry is added to the reaction tank at a calcium-to-phosphorus molar ratio of 3 to 3.5:

1. Fluorine and phosphorus in the crystallization-treated water react with the lime slurry to form precipitates, and the fluorine and phosphorus content of the treated water in the reaction tank is below the standard line. Step 5: The mud-water mixture discharged from the reaction tank undergoes further coagulation, flocculation, and sedimentation treatment to remove calcium fluoride and calcium phosphate sludge, resulting in effluent that meets discharge standards.

2. The process for synthesizing fluorapatite from wastewater according to claim 1, characterized in that: In step one, sodium fluoride, potassium fluoride, or hydrofluoric acid are added to the mixing tank as soluble fluorides to help adjust the fluoride-phosphorus molar ratio of the mixed wastewater.

3. The process for synthesizing fluorapatite from wastewater according to claim 1, characterized in that: The lime slurry used in step three has a mass percentage concentration of 0.5% to 3%.

4. The process for synthesizing fluorapatite from wastewater according to claim 1 or 3, characterized in that: The lime slurry is prepared by mixing dry lime powder with tap water, crystallization treatment water from step three, or effluent from step five in a mixing tank.

5. The process for synthesizing fluorapatite from wastewater according to claim 1, characterized in that: In step four, sulfuric acid is injected into the reaction tank to adjust the pH of the treated water to 6.5–7.

5.

6. The process for synthesizing fluorapatite from wastewater according to claim 1, characterized in that: The crystallization fluidized bed reactor used in step three is either a crystallization reactor powered by pure water or a mechanically stirred fluidized bed crystallization reactor.

7. The process for synthesizing fluorapatite from wastewater according to claim 1, characterized in that: In step three, the initial packing material in the crystallization fluidized bed reactor is 10-20 μm quartz sand or fluorapatite. The packing material accounts for 20%-50% of the volume of the crystallization fluidized bed reactor. The reflux in the reaction zone of the crystallization fluidized bed reactor provides a power of 20-100 m / h, which is a vertically upward macroscopic thrust.

8. The process for synthesizing fluorapatite from wastewater according to claim 1, characterized in that: In step three, after the fluoride and phosphate ions in the influent water and the calcium ions in the lime slurry are diluted by internal reflux, the ratio of the activity product of fluoride, phosphate and calcium ions in the fluorophosphate to the solubility product constant of fluorophosphate is controlled to be between 20 and 100.

9. The process for synthesizing fluorapatite from wastewater according to claim 1, characterized in that: In step three, sodium hydroxide or sulfuric acid is added to the crystallization fluidized bed reactor to control the pH of the mixed liquid in the crystallization fluidized bed reactor between 8.0 and 8.5, and the residence time of the mixed liquid in the crystallization fluidized bed reactor is not less than 20 minutes.

10. An apparatus for synthesizing fluorapatite from wastewater in the process of synthesizing fluorapatite according to any one of claims 1-9, characterized in that: The system includes an mixing tank, a dosing tank, a crystallization fluidized bed reactor, a reaction tank, a coagulation tank, a flocculation tank, a sedimentation tank, a pH monitoring device, a booster pump, and a control system. The mixing tank is equipped with a wastewater inlet, a dosing inlet, and a mixed wastewater outlet. Fluoride-containing and phosphorus-containing wastewater can enter the mixing tank through the wastewater inlet and mix with the chemicals entering through the dosing inlet. The dosing tank is equipped with a lime powder dosing inlet, a purified water inlet, and a lime slurry outlet. A stirrer is also installed in the mixing tank to mix the lime powder and purified water. The crystallization fluidized bed reactor is equipped with a mixing inlet, a dosing inlet, an outlet, and a crystal discharge outlet. The mixing inlet of the crystallization fluidized bed reactor is connected to the mixed wastewater outlet of the mixing tank, and the dosing inlet of the crystallization fluidized bed reactor is connected to the lime slurry outlet of the dosing tank. The booster pump can pump the mixed wastewater from the mixing tank and the lime slurry from the dosing tank into the crystallization fluidized bed reactor. The crystallization reaction takes place in the fluidized bed reactor. Large crystal particles settle down and are periodically discharged through the crystal discharge port. The reaction tank, coagulation tank, flocculation tank, and sedimentation tank are connected in sequence. Each of the reaction tank, coagulation tank, and flocculation tank is equipped with a dosing port. The sedimentation tank is equipped with an outlet for water discharge and a sludge discharge port at its upper and lower ends, respectively. The outlet of the fluidized bed reactor is connected to the reaction tank through a pipeline. The dosing port of the reaction tank is connected to the lime slurry outlet of the mixing tank. A booster pump can pump lime slurry from the mixing tank into the reaction tank. PAC and PAM agents can be added to the coagulation tank and flocculation tank through the dosing ports, respectively, for coagulation and flocculation reactions. The outlet of the sedimentation tank is connected to the purified water inlet of the mixing tank through a branch pipe. A pH detection device is installed in the mixing tank, the fluidized bed reactor, and the reaction tank to detect the pH of the liquid in real time. The pH detection device communicates with the control system, which controls the start and stop of the booster pump and the flow rate.

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