Fluorine-containing wastewater pretreatment system

Abstract

The utility model relates to a kind of fluorine-containing wastewater pretreatment systems, including the pipeline connection of horizontal flow type grit chamber, first intermediate pool, first hydrocyclone, second intermediate pool, second hydrocyclone and waste sand collection and treatment device in proper order, waste sand collection and treatment device are connected with the pipeline of three bottom sand discharge port respectively;Horizontal flow type grit chamber receives quartz sand pickling fluorine-containing wastewater and separates coarse sand, first hydrocyclone separates medium sand, second hydrocyclone separates fine sand, upper overflow effluent enters fluorine-containing wastewater treatment device, after sand grain grading treatment by waste sand collection and treatment device, coarse sand is used as fluidized bed seed, and medium sand and fine sand are recycled for high-purity quartz sand production.The system is separated by three-stage gradient physics, effectively avoids quartz sand particle to influence subsequent treatment system stability, without secondary pollution and realizes resource high-value utilization.

Description

Technical Field

[0001] This utility model relates to the field of wastewater treatment technology, and in particular to a pretreatment system for fluoride-containing wastewater. Background Technology

[0002] High-purity quartz sand has extremely high industrial value and is currently widely used in industries such as semiconductors and photovoltaics. The production of high-purity quartz sand generates a large amount of wastewater containing fluorine and silicon. This wastewater contains a large number of quartz sand particles, and improper treatment can paralyze subsequent fluoride wastewater treatment systems, affecting normal production and even causing environmental pollution.

[0003] In actual production processes, fluoride- and silicon-containing wastewater is mainly generated from the high-purity quartz sand pickling process. Treatment of this wastewater primarily utilizes lime precipitation or calcium chloride precipitation to remove fluorides and ensure compliant discharge. However, the importance of the pretreatment system is often overlooked. A large amount of quartz sand particles remain in the wastewater, leading to a waste of mineral resources, pipe blockages, damage to power equipment, and impacting the stable operation of the wastewater treatment system.

[0004] Existing pretreatment technologies mainly include gravity sedimentation and filtration. Simple gravity sedimentation has a long hydraulic retention time, requires a large building area, and can only remove larger particles of quartz sand. Simple filtration can effectively retain granular quartz sand, but the packing material is quickly clogged. A combination of gravity sedimentation and filtration can remove granular quartz sand of different sizes in stages, but the system still suffers from problems such as easy clogging of the packing material, high backwashing frequency, cumbersome operation, and unstable process.

[0005] Therefore, it is essential to provide a stable and feasible pretreatment system to address the problem of difficult treatment of quartz sand particles in the existing quartz sand pickling fluoride wastewater treatment process. Summary of the Invention

[0006] The purpose of this application is to solve the problem of difficult treatment of fluoride-containing wastewater carried by quartz sand pickling.

[0007] To achieve the above objectives, this application employs the following technical solution: This application provides a fluoride-containing wastewater pretreatment system, including a horizontal flow grit chamber, a primary intermediate water tank, a primary hydrocyclone, a secondary intermediate water tank, a secondary hydrocyclone, and a waste sand collection and treatment device. The components are sequentially connected by pipelines to form a wastewater treatment flow path; wherein: The waste sand collection and treatment device is connected to the bottom sand discharge port pipes of the horizontal flow sedimentation tank, the first-stage hydrocyclone, and the second-stage hydrocyclone, respectively. The inlet of the horizontal flow grit chamber is connected to the outlet of the quartz sand pickling process. It is used to receive fluoride-containing wastewater from the quartz sand pickling process and separate coarse sand from the wastewater by gravity sedimentation. The coarse sand is discharged from the bottom sand discharge port to the waste sand collection and treatment device, and the water overflows from the top. The inlet of the primary intermediate water tank is connected to the upper overflow outlet of the horizontal flow grit chamber, and is used to receive wastewater after the removal of coarse sand. The inlet of the first-stage hydrocyclone is connected to the outlet of the first-stage intermediate water tank through the first water pump. Its structure is a short and wide cavity, which is used to receive the wastewater after removing coarse sand and separate the medium sand in the wastewater. The medium sand is discharged from the bottom sand discharge port to the waste sand collection and treatment device, and the water overflows from the top. The inlet of the secondary intermediate water tank is connected to the upper overflow outlet of the primary hydrocyclone and is used to receive wastewater after the removal of medium sand. The inlet of the secondary hydrocyclone is connected to the outlet of the secondary intermediate water tank through a second water pump. Its structure is a slender small cavity, which is used to receive the wastewater after removing the medium sand and separate the fine sand in the wastewater. The fine sand is discharged from the bottom sand discharge port to the waste sand collection and treatment device, and the overflow water from the top enters the fluoride-containing wastewater treatment device. The waste sand collection and treatment device is connected to the fluorine-containing wastewater treatment device and is used to classify the collected coarse sand, medium sand and fine sand. The treated coarse sand is used as seed crystals in the fluidized bed of the fluorine-containing wastewater treatment device, and the treated medium sand and fine sand are used for the production of high-purity quartz sand.

[0008] As a further improvement of this application, the waste sand collection and treatment device includes a centrifugal dewatering unit, a drying unit and a screening unit connected in sequence. The screening unit is used to classify the sand particles after passing through the centrifugal dewatering unit and the drying unit into coarse sand, medium sand and fine sand according to their particle size.

[0009] As a further improvement of this application, the cylindrical section of the first-stage hydrocyclone has an inner diameter of 80-150 mm, a cone angle of 15°-25°, a length-to-diameter ratio of 1.2-1.8, and a cavity volume of 5-12 L; the cylindrical section of the second-stage hydrocyclone has an inner diameter of 30-60 mm, a cone angle of 6°-12°, a length-to-diameter ratio of 2.5-3.5, and a cavity volume of 0.8-2.5 L.

[0010] As a further improvement of this application, a first flow regulating valve is provided at the inlet of the first-stage hydrocyclone, and a second flow regulating valve is provided at the inlet of the second-stage hydrocyclone. The flow velocities of the first flow regulating valve and the second flow regulating valve are both controlled between 1.5 and 3.0 m / s.

[0011] As a further improvement of this application, the bottom of the horizontal flow sedimentation tank is provided with a V-shaped sand discharge slope with an inclination angle of 30° to 60°.

[0012] As a further improvement of this application, the primary intermediate water tank is provided with a first stirrer and a first liquid level controller, and the secondary intermediate water tank is provided with a second stirrer and a second liquid level controller.

[0013] As a further improvement of this application, both the first agitator and the second agitator are submersible agitators with a stirring speed of 100 r / min to 300 r / min.

[0014] As a further improvement of this application, both the first liquid level controller and the second liquid level controller are float-type liquid level switches, used to control the liquid level in the pool to be within a preset range.

[0015] As a further improvement of this application, both the first water pump and the second water pump are corrosion-resistant centrifugal pumps.

[0016] As a further improvement of this application, the particle size range of the coarse sand is greater than 200 μm, the particle size range of the medium sand is 50 μm to 200 μm, and the particle size range of the fine sand is 2 μm to 50 μm.

[0017] The beneficial effect of this application is that it provides a fluoride-containing wastewater pretreatment system, including a horizontal flow grit chamber, a primary intermediate water tank, a primary hydrocyclone, a secondary intermediate water tank, a secondary hydrocyclone, and a waste sand collection and treatment device connected in sequence by pipelines. The waste sand collection and treatment device is connected to the bottom sand discharge port pipelines of the three. The horizontal flow grit chamber receives fluoride-containing wastewater from quartz sand acid washing and separates coarse sand. The primary hydrocyclone separates medium sand, and the secondary hydrocyclone separates fine sand. The overflow water from the top enters the fluoride-containing wastewater treatment device. After the waste sand collection and treatment device classifies the sand particles, the coarse sand is used as fluidized bed seed crystals, and the medium and fine sand are recycled for high-purity quartz sand production.

[0018] Employing a three-stage gradient separation architecture consisting of a horizontal flow grit chamber and two-stage hydrocyclones, this system precisely removes coarse, medium, and fine sand in stages. This prevents quartz sand particles from clogging pipes and equipment in subsequent fluoride-containing wastewater treatment units, significantly improving the overall system's operational stability. The purely physical separation method requires no chemical additives, produces no additional sludge, completely eliminates secondary pollution, and reduces environmental protection pressure. It enables graded recycling and high-value utilization of waste sand resources: coarse sand is suitable for the fluidized bed seeding requirements in fluoride-containing wastewater treatment units, while medium and fine sand are recycled for high-purity quartz sand production, maximizing resource recovery and avoiding mineral resource waste. The components are sequentially connected via pipelines to form a closed-loop flow path, resulting in a compact structure and smooth flow, suitable for the continuous production needs of high-purity quartz sand production lines. This also reduces equipment maintenance frequency and labor costs, combining environmental benefits with economic value. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of the flow structure of the fluoride-containing wastewater pretreatment system of this application.

[0020] In the diagram: 1. Horizontal flow grit chamber; 11. V-shaped grit discharge slope; 2. Primary intermediate water tank; 21. First agitator; 3. Primary hydrocyclone; 31. First flow regulating valve; 4. Secondary intermediate water tank; 41. Second agitator; 5. Secondary hydrocyclone; 51. Second flow regulating valve; 6. Waste sand collection and treatment device; 61. Centrifugal dewatering unit; 62. Drying unit; 63. Screening unit; 7. Fluoride-containing wastewater treatment device; 71. Third intermediate water tank; 72. Third water pump; 73. Fluorinated bed; 8. First water pump; 9. Second water pump. Detailed Implementation

[0021] As can be seen from the background technology, existing pretreatment technologies for treating fluoride-containing wastewater from quartz sand pickling are hampered by difficulties in handling quartz sand particles. These technologies suffer from problems such as high water consumption, large footprint, easy clogging of packing materials, and unstable removal efficiency. To address these issues, this application provides a fluoride-containing wastewater pretreatment system, comprising a horizontal flow grit chamber, a primary intermediate water tank, a primary hydrocyclone, a secondary intermediate water tank, a secondary hydrocyclone, and a waste sand collection and treatment device. These components are sequentially connected by pipelines to form a wastewater treatment flow path. The waste sand collection and treatment device is connected to the bottom sand discharge port pipes of the horizontal flow sedimentation tank, the first-stage hydrocyclone, and the second-stage hydrocyclone, respectively. The inlet of the horizontal flow grit chamber is connected to the outlet of the quartz sand pickling process. It is used to receive fluoride-containing wastewater from the quartz sand pickling process and separate coarse sand from the wastewater by gravity sedimentation. The coarse sand is discharged from the bottom sand discharge port to the waste sand collection and treatment device, and the water overflows from the top. The inlet of the primary intermediate water tank is connected to the upper overflow outlet of the horizontal flow grit chamber, and is used to receive wastewater after the removal of coarse sand. The inlet of the first-stage hydrocyclone is connected to the outlet of the first-stage intermediate water tank through the first water pump. Its structure is a short and wide cavity, which is used to receive the wastewater after removing coarse sand and separate the medium sand in the wastewater. The medium sand is discharged from the bottom sand discharge port to the waste sand collection and treatment device, and the water overflows from the top. The inlet of the secondary intermediate water tank is connected to the upper overflow outlet of the primary hydrocyclone and is used to receive wastewater after the removal of medium sand. The inlet of the secondary hydrocyclone is connected to the outlet of the secondary intermediate water tank through a second water pump. Its structure is a slender small cavity, which is used to receive the wastewater after removing the medium sand and separate the fine sand in the wastewater. The fine sand is discharged from the bottom sand discharge port to the waste sand collection and treatment device, and the overflow water from the top enters the fluoride-containing wastewater treatment device. The waste sand collection and treatment device is connected to the fluorine-containing wastewater treatment device and is used to classify the collected coarse sand, medium sand and fine sand. The treated coarse sand is used as seed crystals in the fluidized bed of the fluorine-containing wastewater treatment device, and the treated medium sand and fine sand are used for the production of high-purity quartz sand.

[0022] Based on the above technical solution, a three-stage gradient separation architecture using a horizontal flow grit chamber and two-stage hydrocyclones is adopted to accurately remove coarse, medium, and fine sand in stages. This prevents quartz sand particles from clogging the pipes and equipment of subsequent fluoride-containing wastewater treatment devices, significantly improving the overall operational stability of the process system. The purely physical separation mode requires no chemical additives, produces no additional sludge, completely eliminates secondary pollution, and reduces environmental protection pressure. It achieves graded recycling and high-value utilization of waste sand resources: coarse sand is suitable for the fluidized bed seeding requirements in fluoride-containing wastewater treatment devices, while medium and fine sand are recycled for high-purity quartz sand production, maximizing resource recovery and avoiding mineral resource waste. All components are sequentially connected via pipelines to form a closed-loop flow path, resulting in a compact structure and smooth flow, suitable for the continuous production requirements of high-purity quartz sand production lines.

[0023] In an optional implementation, the waste sand collection and treatment device includes a centrifugal dewatering unit, a drying unit, and a screening unit connected in sequence. The screening unit is used to classify the sand particles after passing through the centrifugal dewatering unit and the drying unit into coarse sand, medium sand, and fine sand according to their particle size. This clarifies the three-stage treatment process of centrifugal dewatering, drying, and screening in the waste sand collection and treatment device, ensuring thorough dewatering and achieving the required dryness, thus preventing wet sand from clumping and affecting subsequent classification and utilization. The screening unit specifically achieves precise classification of coarse, medium, and fine sand, ensuring the suitability of sand particles of different sizes for various applications and providing quality assurance for subsequent high-value utilization.

[0024] In an optional implementation, the cylindrical section of the first-stage hydrocyclone has an inner diameter of 80–150 mm, a cone angle of 15°–25°, an aspect ratio of 1.2–1.8, and a cavity volume of 5–12 L; the cylindrical section of the second-stage hydrocyclone has an inner diameter of 30–60 mm, a cone angle of 6°–12°, an aspect ratio of 2.5–3.5, and a cavity volume of 0.8–2.5 L. By quantifying key structural parameters such as the inner diameter of the cylindrical section, the cone angle, the aspect ratio, and the cavity volume, the design of a short, wide, large-cavity first-stage hydrocyclone and a slender, small-cavity second-stage hydrocyclone can be implemented. The large inner diameter, large cone angle, and small length-to-diameter ratio of the first-stage hydrocyclone are suitable for the efficient separation of medium sand ranging from 50μm to 200μm; the small inner diameter, small cone angle, and large length-to-diameter ratio of the second-stage hydrocyclone are used to precisely trap fine sand ranging from 2μm to 50μm, achieving targeted separation of sand particles of different sizes and improving separation efficiency and accuracy.

[0025] In an optional implementation, a first flow regulating valve is provided at the inlet of the first-stage hydrocyclone, and a second flow regulating valve is provided at the inlet of the second-stage hydrocyclone. The flow velocities of both the first and second flow regulating valves are controlled within the range of 1.5–3.0 m / s. The inlet flow regulating valves allow for flexible adjustment of the feed flow rate, stabilizing it within the optimal separation range of 1.5–3.0 m / s. This ensures a stable centrifugal field within the hydrocyclone, preventing a decrease in separation efficiency due to flow rate fluctuations. The two-stage independent flow regulation design allows for dynamic adjustment based on the sand concentration and particle size distribution in the wastewater, enhancing the system's adaptability to water quality fluctuations and improving process stability.

[0026] In an optional implementation, the bottom of the horizontal flow grit chamber is provided with a V-shaped sand discharge slope with an inclination angle of 30° to 60°. Gravity guides coarse sand to gather at the bottom discharge port, preventing coarse sand from settling and agglomerating at the bottom of the chamber, improving sand discharge efficiency, and reducing the cleaning frequency and maintenance costs of the horizontal flow grit chamber.

[0027] In an optional implementation, the primary intermediate water tank is equipped with a first agitator and a first level controller, and the secondary intermediate water tank is equipped with a second agitator and a second level controller. The agitator prevents fine sand particles remaining in the wastewater from settling and accumulating in the intermediate water tank, ensuring uniform wastewater quality and guaranteeing stable feeding for the subsequent hydrocyclone. The level controller monitors the water tank level in real time, preventing overflow due to excessively high levels or idling of the water pump due to excessively low levels, ensuring continuous and stable operation of the entire pretreatment system.

[0028] In an optional implementation, both the first and second agitators are submersible agitators with a mixing speed of 100 r / min to 300 r / min. Submersible agitators are suitable for underwater working environments in intermediate water tanks, are corrosion-resistant, operate stably, and the speed range of 100 r / min to 300 r / min effectively prevents sand sedimentation without generating unnecessary energy consumption due to excessively high speeds.

[0029] In an optional implementation, both the first and second level controllers are float-type level switches used to control the water level in the pool within a preset range. Float-type level switches are simple in structure, highly responsive, and can accurately control the water level within the preset range without requiring real-time manual monitoring, thus reducing operational difficulty and labor costs. Stable level control provides constant suction conditions for the water pump, preventing unstable pump head due to level fluctuations and extending the pump's service life.

[0030] In an optional implementation, both the first and second water pumps are corrosion-resistant centrifugal pumps. These corrosion-resistant centrifugal pumps are suitable for the acidic and corrosive environment of fluoride-containing wastewater from quartz sand pickling, effectively resisting the erosion of the pump body by the wastewater, extending equipment lifespan, and reducing equipment maintenance and replacement costs. The centrifugal pumps feature stable head and uniform flow rate, providing continuous and stable feed power to the hydrocyclone, ensuring consistent separation performance.

[0031] In an optional implementation, the coarse sand has a particle size range greater than 200 μm, the medium sand has a particle size range of 50 μm to 200 μm, and the fine sand has a particle size range of 2 μm to 50 μm. Clearly defining the particle size ranges of coarse, medium, and fine sand makes the goal of three-stage separation clearer, providing a clear basis for the design of hydrocyclone parameters and the selection of screens for screening units, ensuring the precise implementation of the technical solution. Precise matching of the particle size range with subsequent applications (e.g., coarse sand >200 μm is suitable for fluidized bed seed crystal requirements) ensures the utilization effect of the recovered sand particles and maximizes the value of resource recovery.

[0032] To make the objectives, technical solutions, and advantages of this application clearer, the technical solutions of this application will be clearly and completely described below in conjunction with specific embodiments and accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this application, not all of them, and are not intended to limit the scope of this application. All other embodiments obtained by those skilled in the art based on the embodiments of this application without creative effort are within the scope of protection of this application.

[0033] In one specific implementation scheme, this application provides a fluoride-containing wastewater pretreatment system, such as... Figure 1As shown, its configuration is as follows: The inlet of the horizontal flow grit chamber 1 is connected to the outlet of the high-purity quartz sand pickling process via a corrosion-resistant pipe. The chamber is 8m long, 2m wide, and has an effective water depth of 1.5m. A V-shaped grit discharge slope with an inclination angle of 45° is provided at the bottom. The lowest point of the grit discharge slope is connected to a DN150 grit discharge pipe, which is directly connected to the waste sand collection and treatment device 6. After the fluoride-containing wastewater from the quartz sand pickling enters the horizontal flow grit chamber 1, under a hydraulic retention time of 10 minutes, coarse sand with a particle size greater than 200μm is separated by gravity sedimentation. The coarse sand slides down the V-shaped grit discharge slope to the grit discharge pipe and is finally discharged into the waste sand collection and treatment device 6. An overflow weir is installed at the top of the sedimentation tank 1. Wastewater after coarse sand removal flows by gravity into the primary intermediate water tank 2 through the overflow weir. The effective volume of the primary intermediate water tank 2 is 10 m³. It is equipped with a submersible first agitator 21 (model QJB5 / 12-620 / 3-480) with a stirring speed set to 200 r / min. A float-type first liquid level controller (model UQK-03) is also installed to maintain the liquid level in the tank within a preset range of 1.2–1.8 m. The outlet of the primary intermediate water tank 2 is connected to a first water pump 8 via a DN80 pipe. The first water pump 8 is a corrosion-resistant centrifugal pump (model IHF50-32-160). The outlet pipe connects to the inlet of the first-stage hydrocyclone 3. The cylindrical section of the first-stage hydrocyclone 3 has an inner diameter of 100mm, a cone angle of 20°, a length-to-diameter ratio of 1.5, and a cavity volume of 8L. A DN65 first flow regulating valve 31 is installed at the inlet to control the feed velocity at 2.0m / s. After the wastewater enters the first-stage hydrocyclone 3, it is separated into medium sand with a particle size of 50μm to 200μm under centrifugal force. The medium sand is discharged from the bottom sand discharge port to the waste sand collection and treatment device 6, and the overflow water from the top flows into the second-stage intermediate water tank 4 through a pipe. The effective volume of the second-stage intermediate water tank 4 is 8m³, and it is equipped with a submersible tank of the same model as that in the first-stage intermediate water tank 2. The second agitator 41 has a stirring speed of 180 r / min and is equipped with a float-type second liquid level controller of the same model as the first-stage intermediate water tank 2 to ensure that the liquid level is stable at 1.0~1.6m. The outlet of the second-stage intermediate water tank 4 is connected to the second water pump 9 through a DN65 pipe. The second water pump 9 is a corrosion-resistant centrifugal pump of model IHF40-25-160. Its outlet pipe is connected to the inlet of the second-stage hydrocyclone 5. The cylindrical section of the second-stage hydrocyclone 5 has an inner diameter of 45mm, a cone angle of 9°, a length-to-diameter ratio of 3.0, and a cavity volume of 1.5L. A DN50 second flow regulating valve 51 is installed at the inlet to control the feed flow rate at 2.At a speed of 2 m / s, high-intensity centrifugal action separates fine sand with a particle size of 2 μm to 50 μm. The fine sand is discharged from the bottom discharge port to the waste sand collection and treatment device 6. The overflow water from the top enters the third intermediate water tank 71 of the fluoride-containing wastewater treatment device 7 through a pipeline, and then enters the reaction zone of the fluidized bed 73 through the third water pump 72. The waste sand collection and treatment device 6 includes a centrifugal dewatering unit 61, a drying unit 62, and a screening unit 63 connected in sequence by pipelines. The centrifugal dewatering unit 61 uses a horizontal screw discharge centrifuge of model LWL450 to dewater the mixture of coarse sand, medium sand, and fine sand, reducing the moisture content of the sand particles to below 30%, and then sending it to the... Drying unit 62 uses a CT-C hot air circulating oven, set at 120℃, to dry the sand particles until the moisture content is below 5%. The sand then enters screening unit 63, which is equipped with three layers of grading screens with apertures of 200μm, 50μm, and 2μm, sequentially retaining coarse, medium, and fine sand for precise grading. The graded coarse sand is transported via pipeline to the seed crystal addition device of the fluoride-containing wastewater treatment unit 7, where it is used as seed crystals in the fluidized bed 73. The graded medium and fine sand are returned via closed pipeline to the raw material silo of the high-purity quartz sand production workshop for subsequent high-purity quartz sand production processes.

[0034] Although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

[0035] The detailed descriptions listed above are merely specific descriptions of feasible implementation methods of this application and are not intended to limit the scope of protection of this application. All equivalent implementation methods or modifications made without departing from the spirit of the art of this application should be included within the scope of protection of this application.

Claims

1. A pretreatment system for fluoride-containing wastewater, characterized in that, The system includes a horizontal flow grit chamber, a primary intermediate water tank, a primary hydrocyclone, a secondary intermediate water tank, a secondary hydrocyclone, and a waste sand collection and treatment device. These components are sequentially connected by pipelines to form a wastewater treatment flow path. Among them: The waste sand collection and treatment device is connected to the bottom sand discharge port pipes of the horizontal flow sedimentation tank, the first-stage hydrocyclone, and the second-stage hydrocyclone, respectively. The inlet of the horizontal flow grit chamber is connected to the outlet of the quartz sand pickling process. It is used to receive fluoride-containing wastewater from the quartz sand pickling process and separate coarse sand from the wastewater by gravity sedimentation. The coarse sand is discharged from the bottom sand discharge port to the waste sand collection and treatment device, and the water overflows from the top. The inlet of the primary intermediate water tank is connected to the upper overflow outlet of the horizontal flow grit chamber, and is used to receive wastewater after the removal of coarse sand. The inlet of the first-stage hydrocyclone is connected to the outlet of the first-stage intermediate water tank through the first water pump. Its structure is a short and wide cavity, which is used to receive the wastewater after removing coarse sand and separate the medium sand in the wastewater. The medium sand is discharged from the bottom sand discharge port to the waste sand collection and treatment device, and the water overflows from the top. The inlet of the secondary intermediate water tank is connected to the upper overflow outlet of the primary hydrocyclone and is used to receive wastewater after the removal of medium sand. The inlet of the secondary hydrocyclone is connected to the outlet of the secondary intermediate water tank through a second water pump. Its structure is a slender small cavity, which is used to receive the wastewater after removing the medium sand and separate the fine sand in the wastewater. The fine sand is discharged from the bottom sand discharge port to the waste sand collection and treatment device, and the overflow water from the top enters the fluoride-containing wastewater treatment device. The waste sand collection and treatment device is connected to the fluorine-containing wastewater treatment device and is used to classify the collected coarse sand, medium sand and fine sand. The treated coarse sand is used as seed crystals in the fluidized bed of the fluorine-containing wastewater treatment device, and the treated medium sand and fine sand are used for the production of high-purity quartz sand.

2. The fluoride-containing wastewater pretreatment system according to claim 1, characterized in that, The waste sand collection and treatment device includes a centrifugal dewatering unit, a drying unit, and a screening unit connected in sequence. The screening unit is used to classify the sand particles after passing through the centrifugal dewatering unit and the drying unit into coarse sand, medium sand, and fine sand according to their particle size.

3. The fluoride-containing wastewater pretreatment system according to claim 1, characterized in that, The cylindrical section of the first-stage hydrocyclone has an inner diameter of 80–150 mm, a cone angle of 15°–25°, a length-to-diameter ratio of 1.2–1.8, and a cavity volume of 5–12 L; the cylindrical section of the second-stage hydrocyclone has an inner diameter of 30–60 mm, a cone angle of 6°–12°, a length-to-diameter ratio of 2.5–3.5, and a cavity volume of 0.8–2.5 L.

4. The fluoride-containing wastewater pretreatment system according to claim 1, characterized in that, The inlet of the first-stage hydrocyclone is equipped with a first flow regulating valve, and the inlet of the second-stage hydrocyclone is equipped with a second flow regulating valve. The flow velocities of the first flow regulating valve and the second flow regulating valve are both controlled between 1.5 and 3.0 m / s.

5. The fluoride-containing wastewater pretreatment system according to claim 1, characterized in that, The bottom of the horizontal flow sedimentation tank is provided with a V-shaped sand discharge slope with an inclination angle of 30° to 60°.

6. The fluoride-containing wastewater pretreatment system according to claim 1, characterized in that, The primary intermediate water tank is equipped with a first agitator and a first level controller, and the secondary intermediate water tank is equipped with a second agitator and a second level controller.

7. The fluoride-containing wastewater pretreatment system according to claim 6, characterized in that, Both the first and second agitators are submersible agitators with a stirring speed of 100 r / min to 300 r / min.

8. The fluoride-containing wastewater pretreatment system according to claim 6, characterized in that, Both the first liquid level controller and the second liquid level controller are float-type liquid level switches, used to control the liquid level in the pool to be within a preset range.

9. The fluoride-containing wastewater pretreatment system according to claim 1, characterized in that, Both the first water pump and the second water pump are corrosion-resistant centrifugal pumps.

10. The fluoride-containing wastewater pretreatment system according to claim 1, characterized in that, The coarse sand has a particle size range greater than 200 μm, the medium sand has a particle size range of 50 μm to 200 μm, and the fine sand has a particle size range of 2 μm to 50 μm.

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