A method for removing fluorine and silicon from wastewater in polysilicon production

Abstract

The application relates to the technical field of industrial wastewater treatment, and particularly discloses a method for removing fluorine and silicon from polysilicon production wastewater in a cooperative manner, which comprises the following steps: introducing the polysilicon production wastewater into a homogenizing adjusting tank to balance water quantity and water quality; sending the water discharged from the homogenizing adjusting tank into a fluidized bed crystallization reactor, and then into a solid-liquid separation zone for solid-liquid separation; sending part of overflow from the solid-liquid separation zone into a bypass ultrasonic depolymerization tank for ultrasonic depolymerization treatment; and sending the rest of the overflow from the solid-liquid separation zone which does not enter the bypass ultrasonic depolymerization tank into a clarifying tank for flocculation and sedimentation. The method adopts a fluidized bed crystallization reactor, promotes nucleation and crystallization of fluorine-containing substances by means of lime milk and ultrasonic action in a reaction zone, and introduces part of the overflow into a bypass ultrasonic depolymerization tank for ultrasonic depolymerization with high intensity, so that the stability of the process for removing fluorine and silicon in a cooperative manner can be maintained.

Description

Technical Field

[0001] This application relates to the field of industrial wastewater treatment technology, and more specifically, it relates to a method for the combined treatment of polysilicon production wastewater by removing fluoride and silicon. Background Technology

[0002] Polysilicon production generates fluoride- and silicon-containing wastewater, which is typically acidic. The fluoride ions and silicon-containing components require treatment before discharge or reuse. Therefore, effectively removing fluoride and silicon from polysilicon production wastewater is a crucial technical aspect of polysilicon production wastewater treatment.

[0003] Currently, polysilicon production wastewater is typically treated by adding calcium source precipitant in conjunction with precipitation, crystallization, and subsequent flocculation. Fluorescent bed treatment allows fluoride-containing crystals to nucleate and continue growing on the support surface, achieving fluoride ion removal while simultaneously treating silicon-containing components. However, during crystallization, fine crystal nuclei and particles are easily formed. Some of these fine particles are prone to agglomeration or being carried away by the liquid flow, affecting the number of effective crystal nuclei that can continue to participate in crystal growth and the circulation state of bed particles. This, in turn, affects the stability of the synergistic treatment process for fluoride and silicon removal in polysilicon production wastewater. Summary of the Invention

[0004] To address the issue of existing polysilicon production wastewater treatment methods affecting the stability of the combined defluorination and desiliconization process, this application provides a method for the combined defluorination and desiliconization treatment of polysilicon production wastewater.

[0005] This application provides a method for the combined treatment of fluoride and silicon removal from polysilicon production wastewater, which adopts the following technical solution: A method for the combined treatment of defluorination and silicon removal in polysilicon production wastewater includes the following steps: S1. Introduce polysilicon production wastewater into a homogenization and equalization tank to balance the water quantity and quality. S2. The effluent from the homogenization equalization tank is fed into the fluidized bed crystallization reactor. The fluidized bed crystallization reactor is divided into a reaction zone, a crystal growth zone, and a solid-liquid separation zone from bottom to top. The reactor is filled with silica sand support. The wastewater flows from the bottom to the top, so that the support is in a fluidized state. In the reaction zone, lime milk is added to the wastewater as a calcium source precipitant. The pH value in the reaction zone is controlled at 8.5 to 9.5, and ultrasound is applied. The mixed liquid after being treated in the reaction zone enters the crystal growth zone for crystal growth, and then enters the solid-liquid separation zone for solid-liquid separation. S3. A portion of the overflow from the solid-liquid separation zone is sent to a bypass ultrasonic depolymerization tank for ultrasonic depolymerization treatment. The volume power density of the bypass ultrasonic depolymerization treatment is higher than that of the ultrasonic treatment in the reaction zone. The mixture after ultrasonic depolymerization treatment is returned to the bottom of the fluidized bed crystallizer. S4. The remaining portion of the solid-liquid separation zone overflow that does not enter the bypass ultrasonic depolymerization tank is sent to the clarification tank for flocculation and sedimentation. The effluent from the clarification tank is discharged or reused.

[0006] By adopting the above technical solution, the fluidized bed crystallization reactor allows wastewater to sequentially pass through the reaction zone, crystal growth zone, and solid-liquid separation zone. In the reaction zone, lime slurry and ultrasound promote the nucleation and crystallization of fluoride-containing substances. Simultaneously, a portion of the overflow is introduced into a bypass ultrasonic depolymerization tank for high-intensity ultrasonic depolymerization, and the treated mixture is returned to the bottom of the reactor, allowing fine crystal nuclei and crystal particles to re-participate in the crystallization process. The remaining overflow undergoes further treatment through flocculation and sedimentation. Therefore, nucleation, crystal growth, solid-liquid separation, fine particle depolymerization and reflux, and subsequent flocculation treatment can be seamlessly integrated, which is beneficial for maintaining the stability of the synergistic treatment process of fluoride and silicon removal. This solves the problem that the state of fine crystal nuclei and fine crystal particles is difficult to effectively control during the treatment of polysilicon production wastewater, thus affecting the stability of the synergistic treatment of fluoride and silicon removal.

[0007] Preferably, in step S1, the effective volume of the equalization tank is the treated water volume corresponding to 8-12 hours according to the average treatment flow rate of the wastewater treatment system, and the effluent from the equalization tank is controlled at F. - The concentration is 100-2000 mg / L, the SiO2 concentration is 50-300 mg / L, the pH value is 1-3, and the stirring speed of the stirring device in the homogenization tank is 20-40 rpm.

[0008] By adopting the above technical solution, and by controlling the effective volume of the homogenization equalization tank, the effluent quality, and the stirring conditions, the wastewater entering the subsequent fluidized bed crystallization reactor can be kept relatively stable in terms of water volume, pollutant concentration, and acidity. This provides relatively stable influent conditions for subsequent calcium source addition, ultrasonic action, and crystal growth, which is conducive to maintaining the continuous operation of the defluorination and desiliconization process.

[0009] Preferably, in step S2, the volumes of the reaction zone, crystal growth zone, and solid-liquid separation zone in the fluidized bed crystallization reactor account for 25%–35%, 35%–45%, and 20%–30% of the total effective volume of the reactor, respectively, and the sum of the three is 100%; the support is a silica sand support with a particle size of 0.3–0.8 mm, and the support filling rate is 20%–40% of the effective volume of the reactor; based on the total liquid flow rate entering the bottom of the fluidized bed crystallization reactor, the upward flow velocity of the empty tower in the reaction zone is 8–15 m / h, and the support expansion rate is 15%–30%.

[0010] By adopting the above technical solution, and by coordinating and controlling the volume ratio of each functional area as well as the particle size, filling rate and fluidization state of the silica sand support, the wastewater has the corresponding working space in the reaction, crystal growth and solid-liquid separation process, and the support is kept in a suitable fluidization state, which is conducive to the continued growth of fine crystal nuclei on the support and the surface of the existing crystal layer, and reduces the amount of bed particles carried out with the liquid flow.

[0011] Preferably, in step S2, the calcium source precipitant added to the reaction zone is lime slurry, the mass concentration of which is 5%–15%, and the addition amount is in the ratio of n(Ca):n(F) - The ratio is calculated to be 0.8:1 to 1.2:1, and the F... - The amount of F in the wastewater entering the fluidized bed crystallizer is [amount missing]. - The hydraulic residence time in the reaction zone is estimated to be 10–20 minutes.

[0012] By adopting the above technical solution, and by coordinating the lime slurry concentration, the ratio of calcium to fluoride ions, and the reaction time, the calcium source can fully contact the fluoride ions in the wastewater to form fluoride-containing crystal nuclei. At the same time, it avoids the adverse effects of insufficient or excessive calcium source addition on the subsequent crystallization process, thereby providing conditions for the subsequent growth of crystal nuclei and the separation of fluoride-containing substances.

[0013] Preferably, in step S2, when applying ultrasound, the operating frequency of the ultrasound is 20-40 kHz, the volume power density is 0.5-2 W / L, and the effective distance of the ultrasound does not exceed the height of the reaction zone; the ultrasound operates in an intermittent pulse mode, the pulse period is 90-180 seconds, the ultrasound on time is 30-60 seconds and the stop time is 60-120 seconds in each period.

[0014] By adopting the above technical solution, and by concentrating the intermittent ultrasonic action of corresponding intensity in the reaction zone, the ultrasonic action is combined with the reaction and nucleation process after the addition of lime slurry, which can promote the mass transfer between the liquid phase, calcium source and support, and reduce the disordered agglomeration of fine crystal nuclei during the formation stage, which is conducive to forming a more stable crystal nucleus basis for subsequent crystal growth.

[0015] Preferably, in step S2, a guide tube is provided in the crystal growth zone. The inner diameter of the guide tube is 40% to 60% of the inner diameter of the reactor, and the height of the guide tube is 60% to 80% of the height of the crystal growth zone. Both the upper and lower ends of the guide tube are flared out in a funnel shape with an expansion angle of 30° to 60°. The hydraulic residence time of the crystal growth zone is 20 to 40 minutes.

[0016] By adopting the above technical solution, the mixed liquid entering the crystal growth zone is circulated by the combination of the guide tube structure and the crystal growth time, which prolongs the effective contact process between the micro-crystal nuclei and bed crystal particles and the reaction components in the liquid phase. This is beneficial for the continued growth of crystals on the support and the surface of the existing crystal layer, and promotes the transformation of bed particles to a suitable particle size.

[0017] Preferably, in step S2, the effective cross-sectional area of ​​the solid-liquid separation zone is set such that the upward flow velocity of the liquid phase in the solid-liquid separation zone is 2-4 m / h, and an overflow weir is provided at the top of the solid-liquid separation zone, with a weir loading of 5-15 m. 3 / (m·h).

[0018] By adopting the above technical solution, by controlling the liquid phase rising velocity and overflow weir load in the solid-liquid separation zone, larger particles that have completed crystal growth can return to the bed under gravity, while the liquid phase is discharged more evenly from the top, thereby reducing the loss of crystal particles with overflow and providing more stable effluent conditions for subsequent bypass depolymerization and clarification treatment.

[0019] Preferably, in step S2, the fluidized bed crystallizing reactor discharges material from the bottom once every 4 to 12 hours, with each discharge amount being 1% to 5% of the total amount of crystallized particles in the reactor bed; the discharged crystallized particles are wet-screened and classified using two layers of screens, with the upper screen having a mesh size of 1.5 mm and the lower screen having a mesh size of 0.3 mm; after classification, the crystallized particles with a particle size of 0.3 to 1.5 mm are returned to the bottom of the reactor.

[0020] By adopting the above technical solution, through the combination of periodic discharge, wet screening and appropriate particle size recirculation, larger particles can be discharged in a timely manner, while bed crystallization particles suitable for continued growth are returned to the reactor to participate in crystallization. This adjusts the particle size composition of the bed particles, which is beneficial to maintaining the fluidization state of the bed and the stability of the crystallization process.

[0021] Preferably, in step S3, the portion is 10% to 25% of the total overflow from the solid-liquid separation zone; the frequency of the ultrasonic waves in the bypass ultrasonic depolymerization tank is 20 to 40 kHz, and the volumetric power density is 2.5 to 4 W / L; the bypass ultrasonic depolymerization tank adopts a batch operation, and each operating cycle includes 5 to 15 minutes of liquid inlet, 5 to 15 minutes of ultrasonic treatment, 3 to 10 minutes of drainage, and 2 to 5 minutes of standby.

[0022] By adopting the above technical solution, by controlling the bypass diversion ratio, ultrasonic intensity and sequential batch operation process, the micro-nuclei and micro-crystal particles carried out with the overflow can be deagglomerated by high-intensity ultrasonic action, and then returned to the bottom of the fluidized bed to re-participate in crystallization after treatment, thereby improving the recycling status of micro-particles and forming a connection between the nucleation process in the reaction zone.

[0023] Preferably, in step S4, the surface loading of the clarification tank is 0.8–1.5 m³. 3 / (m 2 The hydraulic retention time is 1–2.5 hours; the flocculation and sedimentation are carried out by adding polyaluminum chloride and anionic polyacrylamide to the inlet pipe of the clarifier, and the mass concentration of polyaluminum chloride, calculated as Al2O3, is 8%–12%, and the dosage is 1–2 L / m³. 3 For wastewater, anionic polyacrylamide with a molecular weight of 8 million to 15 million Daltons is added at a dosage of 0.5 to 1 mg / L based on the active ingredient.

[0024] By adopting the above technical solution, and by coordinating the operating conditions of the clarifier with the addition conditions of polyaluminum chloride and anionic polyacrylamide, the fine fluoride-containing particles, silica-containing particles, and suspended particles remaining after fluidized bed crystallization treatment are made into flocs that are easy to settle and then separated into solid and liquid phases. This allows for further treatment of the fluidized bed effluent, which is beneficial to improving the defluorination and desiliconization treatment effect of polysilicon production wastewater.

[0025] In summary, this application has the following beneficial effects: 1. Because this application uses a fluidized bed crystallization reactor, the wastewater sequentially passes through the reaction zone, crystal growth zone, and solid-liquid separation zone. In the reaction zone, lime slurry and ultrasound promote the nucleation and crystallization of fluoride-containing substances. Simultaneously, part of the overflow is introduced into a bypass ultrasonic depolymerization tank for high-intensity ultrasonic depolymerization, and the treated mixture is returned to the bottom of the reactor, allowing the fine crystal nuclei and crystal particles to re-participate in the crystallization process. The remaining overflow is further treated by flocculation and sedimentation. Therefore, nucleation, crystal growth, solid-liquid separation, fine particle depolymerization and reflux, and subsequent flocculation treatment can be interconnected, which is beneficial to maintaining the stability of the synergistic treatment process of fluoride and silicon removal. This solves the problem that the state of fine crystal nuclei and fine crystal particles is difficult to effectively control during the treatment of polysilicon production wastewater, thus affecting the stability of the synergistic treatment of fluoride and silicon removal.

[0026] 2. This application controls the intensity and intermittent operation of ultrasound in the reaction zone, and makes the volume power density of bypass ultrasound depolymerization treatment higher than that of ultrasound treatment in the reaction zone. This makes ultrasound in the reaction zone more suitable for promoting liquid-solid mass transfer and crystal nucleus formation, while bypass ultrasound is more suitable for depolymerizing fine particle agglomerates carried out with the overflow. The two ultrasounds act on different stages of the crystallization process and form a continuous combination through reflux, which is beneficial to improving the circulation state of fine crystal nuclei and crystal particles and reducing the continuous loss of fine particles with the liquid phase.

[0027] 3. This application controls the fluidization state of the support in the fluidized bed, the crystal growth conditions, the solid-liquid separation conditions, and the discharge screening and reflux process in a coordinated manner. This allows the formed crystal particles to continue growing in the reactor, and bed crystal particles of suitable size are returned to the reactor to participate in subsequent crystallization. At the same time, the clarifier is used to flocculate and separate residual fluoride-containing particles, silica-containing particles, and suspended particles. This helps to maintain the stability of the bed particle composition and crystallization process, and improves the overall effect of defluorination and desiliconization treatment of polysilicon production wastewater. Attached Figure Description

[0028] Figure 1 This is a flowchart of a method for the combined treatment of defluorination and desiliconization in polysilicon production wastewater provided in this application; Figure 2 This is a graph showing the test results of fluoride ion removal rate provided in this application; Figure 3 This is a graph showing the test results of silica removal rate provided in this application; Figure 4 This is a diagram showing the test results of the overflow suspended solids concentration in the solid-liquid separation zone provided in this application; Figure 5 This is a graph showing the test results of the reflowable particle size distribution provided in this application. Detailed Implementation

[0029] The present application will be further described in detail below with reference to the accompanying drawings and embodiments.

[0030] Technical concept: Polysilicon production wastewater contains high concentrations of fluoride ions and silicon-containing components. When calcium source precipitation is combined with fluidized crystallization for treatment, fluoride ions can form insoluble fluoride-containing crystals with calcium and continue to grow on the surface of the support and the surface of the existing crystal layer. However, during the reaction and crystallization process, fine crystal nuclei and fine crystal particles are easily formed. Some of these fine particles are prone to agglomeration, while others enter the solid-liquid separation zone with the rising liquid flow and are carried out with the overflow. This affects the number of effective crystal nuclei that can continue to participate in crystal growth and the circulation state of the bed particles, thereby limiting the stability of the fluoride and silicon removal process.

[0031] Based on this, this application sequentially sets up a reaction zone, a crystal growth zone, and a solid-liquid separation zone within a fluidized bed crystallization reactor. Lime slurry is added to the reaction zone, and intermittent ultrasound of low intensity is applied to ensure sufficient contact between the calcium source, wastewater, and silica sand support, promoting crystal nucleus formation. The formed crystal nuclei then continue to grow in the crystal growth zone. Simultaneously, a portion of the overflow from the solid-liquid separation zone is introduced into a bypass ultrasonic deagglomeration tank. Ultrasonic intensity higher than that in the reaction zone is used to deagglomerate the fine particle agglomerates carried out with the overflow. The deagglomerated mixture is then returned to the bottom of the fluidized bed to re-participate in the crystallization process. This creates a continuous treatment path for crystal nucleus formation, crystal growth, solid-liquid separation, fine particle deagglomeration, and reflux. Combined with subsequent flocculation and sedimentation to remove residual fluoride-containing particles and silicon-containing components, this improves the circulation state of fine crystal nuclei and crystal particles, enhancing the stability of the synergistic treatment process for defluorination and silicon removal in polysilicon production wastewater.

[0032] Unless otherwise specified, all experimental methods used below are conventional methods. All materials, reagents, methods, and instruments used, unless otherwise specified, are conventional materials, reagents, methods, and instruments in this field, which can be obtained commercially or prepared according to literature methods by those skilled in the art.

[0033] To better understand the above technical solutions, the technical solutions of the present invention will be clearly and completely described below in conjunction with embodiments.

[0034] Please see the appendix Figure 1 The following is a further description with reference to the embodiments: Example 1: A method for the combined treatment of defluorination and silicon removal in polysilicon production wastewater, comprising the following steps: Polysilicon production wastewater is continuously introduced into a homogenization and equalization tank for flow and quality balancing. The effective volume of the equalization and equalization tank is set according to the average treatment flow rate of the wastewater treatment system corresponding to 10 hours of treatment. In the effluent from the equalization and equalization tank entering subsequent treatment processes, the fluoride ion concentration is controlled at 1050 mg / L, the silica concentration at 175 mg / L, and the pH value at 2. During the homogenization and equalization process, the stirring device is activated, and the stirring speed is controlled at 30 rpm to maintain uniform pollutant concentration and acidity in the wastewater, reducing the impact of influent water quality fluctuations on the subsequent crystallization process.

[0035] The effluent from the homogenization equalization tank is continuously fed into the fluidized bed crystallization reactor. The fluidized bed crystallization reactor is arranged from bottom to top as a reaction zone, a crystal growth zone, and a solid-liquid separation zone. The effective volumes of the three zones account for 31.7%, 41.6%, and 26.7% of the total effective volume of the reactor, respectively, and the sum of the three is 100%. The reactor is filled with silica sand support with a particle size of 0.55 mm, and the filling amount accounts for 30% of the effective volume of the reactor. Wastewater enters from the bottom of the reactor and flows upward. Based on the total liquid flow rate entering the bottom of the reactor, the upward flow velocity of the empty tower in the reaction zone is controlled at 11.5 m / h to keep the silica sand support in stable fluidization. During operation, the expansion rate of the support is controlled at 22.5%.

[0036] Lime slurry was continuously added to the reaction zone at a mass concentration of 10%. The amount of lime slurry added was adjusted according to the fluoride ion concentration in the wastewater entering the fluidized bed crystallization reactor and the instantaneous influent flow rate, so that the molar ratio of calcium to fluoride ions entering the reaction zone was controlled at 1:1, and the pH value of the reaction zone was stably controlled at 9. The lime slurry was continuously added via a metering pump, and the addition rate was adjusted based on the online pH detection results of the reaction zone. The hydraulic retention time in the reaction zone was controlled at 15 minutes.

[0037] An ultrasonic transducer is installed in the reaction zone to apply ultrasonic waves during the mixing and reaction of lime slurry and wastewater. The ultrasonic wave operates at a frequency of 30 kHz and has a volumetric power density of 1.25 W / L. The ultrasonic transducer is arranged along the reaction zone. By controlling the installation position and operating range of the transducer, the ultrasonic action area is limited to the reaction zone, and the effective range of the ultrasonic wave does not cross the boundary between the reaction zone and the crystal growth zone. The ultrasonic wave operates in an intermittent pulse mode with a pulse period of 135 seconds, with each pulse period lasting 45 seconds on and 90 seconds off.

[0038] Wastewater, lime slurry, and silica sand support are in full contact within the reaction zone. Under alkaline conditions, fluoride ions in the wastewater react with calcium to form insoluble fluoride-containing crystals, which then undergo heterogeneous nucleation on the surface of the silica sand support and the already formed crystals. Intermittent ultrasonic treatment within the reaction zone enhances mass transfer between the liquid phase and particles and reduces the disordered agglomeration of fine particles formed in local high-supersaturation areas. The mixed liquid treated in the reaction zone continues to flow upward into the crystal growth zone.

[0039] A guide tube is installed in the crystallization growth zone. The inner diameter of the guide tube is 50% of the inner diameter of the fluidized bed crystallizer, and the height of the guide tube is 70% of the height of the crystallization growth zone. Both ends of the guide tube form a funnel-shaped structure with an expansion angle of 45 degrees. The expansion angle is determined based on the axial direction of the guide tube. After the mixed liquid enters the crystallization growth zone, it forms a circulating flow inside and outside the guide tube, so that the micro-crystal nuclei formed in the reaction zone and the crystal layer on the surface of the support continue to contact the calcium ions and fluoride ions in the wastewater and carry out crystal growth. The hydraulic retention time in the crystallization growth zone is controlled to be 30 minutes.

[0040] After crystal growth is completed, the mixed liquid enters the solid-liquid separation zone. The solid-liquid separation zone reduces the liquid phase rising velocity by expanding the effective flow cross-section. The effective flow cross-sectional area is set according to the liquid phase rising velocity of 3 m / h, so that the larger bed crystal particles return to the crystal growth zone and reaction zone under the action of gravity, reducing the loss of crystal particles with the effluent. An overflow weir is set at the top of the solid-liquid separation zone. The load at the overflow weir opening is controlled at 10 cubic meters per meter per hour. The liquid phase after solid-liquid separation is discharged through the overflow weir.

[0041] During the operation of the fluidized bed crystallization reactor, material is discharged from the bottom of the reactor every 8 hours, with the discharge amount controlled at 3% of the total amount of crystallized particles in the reactor bed. The discharged crystallized particles are classified by wet screening. The screening device is equipped with upper and lower screens, with an upper screen aperture of 1.5 mm and a lower screen aperture of 0.3 mm. After screening, the crystallized particles with a particle size of 0.3 to 1.5 mm are returned to the bottom of the fluidized bed crystallization reactor to continue to be used as a crystal growth carrier. Particles with a particle size greater than 1.5 mm are discharged from the system and collected, while fine particles with a particle size less than 0.3 mm enter the sludge collection unit and are not returned to the fluidized bed crystallization reactor.

[0042] The overflow generated in the solid-liquid separation zone is diverted, with 17.5% of the overflow entering the bypass ultrasonic depolymerization tank and the remaining 82.5% being sent to the clarification tank. The bypass diversion ratio is controlled based on the cumulative water volume entering the bypass ultrasonic depolymerization tank during a complete operating cycle and the total overflow volume of the solid-liquid separation zone during the same period.

[0043] The bypass ultrasonic depolymerization tank operates in a batch process. The overflow entering the bypass contains fine crystal nuclei and fine crystalline particles carried out with the liquid phase. The ultrasonic operating frequency of the bypass ultrasonic depolymerization tank is 30kHz, and the volumetric power density is 3.25W / L, which is higher than the volumetric power density of 1.25W / L in the reaction zone. Each operating cycle consists of liquid feeding, ultrasonic treatment, drainage, and standby, with a liquid feeding time of 10 minutes, ultrasonic treatment time of 10 minutes, drainage time of 6.5 minutes, and standby time of 3.5 minutes. During the ultrasonic treatment, the fine particle agglomerates in the overflow are depolymerized, dispersing the agglomerates into fine particles that can continue to participate in the crystallization reaction. After ultrasonic depolymerization, the mixture is returned to the bottom of the fluidized bed crystallizer during the drainage stage and enters the reaction zone together with the effluent from the homogenization equalization tank, thus forming a bypass depolymerization reflux cycle.

[0044] Overflow that does not enter the bypass ultrasonic depolymerization tank is sent to the clarifier for flocculation and sedimentation; the surface load of the clarifier is controlled at 1.15 cubic meters per square meter per hour, and the hydraulic retention time is 1.75 hours. Polyaluminum chloride and anionic polyacrylamide are added to the inlet pipe of the clarifier; the mass concentration of polyaluminum chloride, calculated as alumina, is 10%, and it is continuously added at a dosage of 1.5L per cubic meter of wastewater; the molecular weight of anionic polyacrylamide is 11.5 million Daltons, and it is prepared into a homogeneous aqueous solution and added to the inlet pipe of the clarifier at a dosage of 0.75 mg / L based on the effective ingredient.

[0045] After the flocculant is added, the wastewater enters the clarification tank and forms flocs. The fine fluoride-containing particles, silica-containing particles and other suspended particles remaining after fluidized bed crystallization treatment settle to the bottom of the clarification tank with the flocs. Clarified effluent is formed at the top of the clarification tank. The effluent is reused or discharged according to the water quality requirements for production water. The sludge deposited at the bottom of the clarification tank is discharged periodically.

[0046] Example 2: This example differs from Example 1 above in that: The effective volume of the equalization tank is set according to the average treatment flow rate of the wastewater treatment system corresponding to the treatment volume in 12 hours; the fluoride ion concentration in the effluent of the equalization tank is 2000 mg / L, the silica concentration is 300 mg / L, the pH value is 3, and the stirring speed is 40 rpm.

[0047] In the fluidized bed crystallization reactor, the effective volumes of the reaction zone, crystal growth zone, and solid-liquid separation zone account for 35%, 45%, and 20% of the total effective volume of the reactor, respectively; the silica sand support particle size is 0.8 mm, and the support filling amount accounts for 40% of the effective volume of the reactor; the upward flow velocity of the empty tower in the reaction zone is 15 m / h, and the support expansion rate is 30%.

[0048] Lime slurry with a mass concentration of 15% was added to the reaction zone, the molar ratio of calcium to fluoride ions was controlled at 1.2:1, the pH value of the reaction zone was controlled at 9.5, and the hydraulic retention time was 20 minutes.

[0049] The ultrasonic working frequency in the reaction zone is 40kHz, the volume power density is 2W / L, and the ultrasonic action range is limited to the reaction zone; the ultrasonic pulse period is 180 seconds, with 60 seconds on and 120 seconds off in each cycle.

[0050] The inner diameter of the guide tube in the crystallization growth zone is 60% of the inner diameter of the fluidized bed crystallization reactor, the height of the guide tube is 80% of the height of the crystallization growth zone, the expansion angle of the bell mouths at the upper and lower ends is 60 degrees, and the hydraulic residence time in the crystallization growth zone is 40 minutes.

[0051] The effective cross-sectional area of ​​the solid-liquid separation zone is set according to the liquid phase rising velocity of 4 m / h, and the load of the top overflow weir is 15 cubic meters per meter per hour.

[0052] The fluidized bed crystallizing reactor discharges material from the bottom every 12 hours, with each discharge amount controlled at 5% of the total amount of crystallized particles in the reactor bed. Wet screening uses two layers of screens with apertures of 1.5 mm and 0.3 mm, and bed crystallized particles with a particle size of 0.3 to 1.5 mm are returned to the bottom of the reactor.

[0053] 25% of the total overflow from the solid-liquid separation zone enters the bypass ultrasonic depolymerization tank. The bypass ultrasonic operating frequency is 40kHz, and the volumetric power density is 4W / L. In each batch operation cycle, the liquid feeding time is 15 minutes, the ultrasonic treatment time is 15 minutes, the drainage time is 10 minutes, and the standby time is 5 minutes. The mixture after ultrasonic depolymerization is returned to the bottom of the fluidized bed crystallizer.

[0054] The surface loading rate of the clarifier is 1.5 cubic meters per square meter per hour, and the hydraulic retention time is 2.5 hours. The mass concentration of polyaluminum chloride (calculated as alumina) is 12%, and 2L is added per cubic meter of wastewater. The molecular weight of anionic polyacrylamide is 15 million Daltons, and the dosage based on the effective ingredient is 1 mg / L.

[0055] Example 3: This example differs from Example 1 above in that: The effective volume of the equalization tank is set according to the average treatment flow rate of the wastewater treatment system corresponding to the treatment volume in 8 hours; the fluoride ion concentration in the effluent of the equalization tank is 100 mg / L, the silica concentration is 50 mg / L, the pH value is 1, and the stirring speed is 20 rpm.

[0056] In the fluidized bed crystallization reactor, the effective volumes of the reaction zone, crystal growth zone, and solid-liquid separation zone account for 25%, 45%, and 30% of the total effective volume of the reactor, respectively; the silica sand support particle size is 0.3 mm, and the support filling amount accounts for 20% of the effective volume of the reactor; the upward flow velocity of the empty tower in the reaction zone is 8 m / h, and the support expansion rate is 15%.

[0057] Lime slurry with a mass concentration of 5% was added to the reaction zone, the molar ratio of calcium to fluoride ions was controlled at 0.8:1, the pH value of the reaction zone was controlled at 8.5, and the hydraulic retention time was 10 minutes.

[0058] The ultrasonic working frequency in the reaction zone is 20kHz, the volume power density is 0.5W / L, and the ultrasonic action range is within the reaction zone; the ultrasonic pulse period is 90 seconds, with 30 seconds on and 60 seconds off in each cycle.

[0059] The inner diameter of the guide tube in the crystallization growth zone is 40% of the inner diameter of the fluidized bed crystallization reactor, the height of the guide tube is 60% of the height of the crystallization growth zone, the expansion angle of the bell mouths at the upper and lower ends is 30 degrees, and the hydraulic residence time in the crystallization growth zone is 20 minutes.

[0060] The effective cross-sectional area of ​​the solid-liquid separation zone is set according to the liquid phase rising velocity of 2m / h, and the load of the top overflow weir is 5 cubic meters per meter per hour.

[0061] The fluidized bed crystallization reactor discharges material from the bottom every 4 hours, with each discharge amount controlled at 1% of the total amount of crystallized particles in the reactor bed. Wet screening uses two layers of screens with apertures of 1.5 mm and 0.3 mm, and bed crystallized particles with a particle size of 0.3 to 1.5 mm are returned to the bottom of the reactor.

[0062] 10% of the total overflow from the solid-liquid separation zone enters the bypass ultrasonic depolymerization tank; the bypass ultrasonic operating frequency is 20kHz, and the volumetric power density is 2.5W / L; in each batch operation cycle, the liquid feeding time is 5 minutes, the ultrasonic treatment time is 5 minutes, the drainage time is 3 minutes, and the standby time is 2 minutes. The mixture after ultrasonic depolymerization is returned to the bottom of the fluidized bed crystallizer.

[0063] The surface loading rate of the clarifier is 0.8 cubic meters per square meter per hour, and the hydraulic retention time is 1 hour; the mass concentration of polyaluminum chloride (calculated as alumina) is 8%, and 1L is added per cubic meter of wastewater; the molecular weight of anionic polyacrylamide is 8 million Daltons, and the dosage based on the effective ingredient is 0.5 mg / L.

[0064] Comparative Example 1: A method for treating polysilicon production wastewater by removing fluoride and silicon, including the following processes: The same polysilicon production wastewater as in Example 1 was used as the treatment target. The wastewater was continuously introduced into a homogenization and equalization tank for flow and quality balancing. The effective volume of the homogenization and equalization tank was set according to the average treatment flow rate of the wastewater treatment system corresponding to the treatment volume over 10 hours. The fluoride ion concentration in the effluent from the homogenization and equalization tank was 1050 mg / L, the silica concentration was 175 mg / L, the pH value was 2, and the stirring speed of the stirring device during homogenization and equalization was 30 rpm.

[0065] The effluent from the homogenization and equalization tank enters a conventional mechanically stirred sedimentation reactor. No fluidized bed crystallization reactor is installed, no silica sand support is used, and no ultrasonic treatment is performed. A 10% (w / w) lime slurry is continuously added to the sedimentation reactor. The amount of lime slurry added is controlled based on the fluoride ion concentration in the wastewater and the influent flow rate to maintain a 1:1 molar ratio of calcium to fluoride ions, and the pH of the reaction system is controlled at 9. The hydraulic retention time in the sedimentation reactor is controlled at 45 minutes to allow the fluoride ions to precipitate with the calcium.

[0066] After the sedimentation reaction is complete, the mixture enters a clarifier for flocculation and sedimentation. The surface loading rate of the clarifier is 1.15 cubic meters per square meter per hour, and the hydraulic retention time is 1.75 hours. Polyaluminum chloride and anionic polyacrylamide are added to the inlet pipe of the clarifier. The polyaluminum chloride has a mass concentration of 10% based on alumina, and is added at 1.5 L per cubic meter of wastewater. The anionic polyacrylamide has a molecular weight of 11.5 million Daltons, and is added at 0.75 mg / L based on the effective ingredient. The fluoride-containing precipitate, silica-containing precipitate, and suspended particles formed by flocculation settle in the clarifier. The effluent from the top of the clarifier is used as treated effluent, and the sludge at the bottom is discharged periodically.

[0067] Comparative Example 2: This comparative example differs from Example 1 above in that: No ultrasound is applied within the reaction zone.

[0068] 17.5% of the total overflow from the solid-liquid separation zone still enters the bypass ultrasonic depolymerization tank. The bypass ultrasonic depolymerization tank operates at a frequency of 30kHz and has a volumetric power density of 3.25W / L. In each operating cycle, the liquid inlet time is 10 minutes, the ultrasonic treatment time is 10 minutes, the drainage time is 6.5 minutes, and the standby time is 3.5 minutes. The mixed liquid after ultrasonic depolymerization is returned to the bottom of the fluidized bed crystallizer.

[0069] Comparative Example 3: This comparative example differs from Example 1 above in that: The reaction zone continued to be subjected to ultrasound in accordance with the method of Example 1. The ultrasound working frequency was 30kHz, the volume power density was 1.25W / L, and it was operated in an intermittent pulse mode with a pulse period of 135 seconds, 45 seconds on and 90 seconds off.

[0070] 17.5% of the total overflow from the solid-liquid separation zone still enters the bypass ultrasonic depolymerization tank, but the ultrasonic device in the bypass ultrasonic depolymerization tank is not activated; the overflow entering the bypass ultrasonic depolymerization tank undergoes 10 minutes of liquid inlet, 10 minutes of settling, 6.5 minutes of drainage, and 3.5 minutes of standby in sequence, and the mixed liquid after the settling is returned to the bottom of the fluidized bed crystallization reactor, and the rest is the same as in Example 1.

[0071] Comparative Example 4: This comparative example differs from Example 1 above in that: The ultrasonic operating frequency in the reaction zone remains 30kHz, the volumetric power density remains 1.25W / L, and the pulse operation mode is the same as in Example 1.

[0072] The ultrasonic working frequency in the bypass ultrasonic depolymerization tank remains at 30kHz, but the volumetric power density is adjusted from 3.25W / L to 1.25W / L so that the volumetric power density of the bypass ultrasonic treatment is the same as that of the ultrasonic treatment in the reaction zone.

[0073] Comparative Example 5: This comparative example differs from Example 1 above in that: The ultrasonic working frequency in the reaction zone is 30kHz, and the volumetric power density is increased to 3.25W / L. The ultrasonic working frequency in the bypass ultrasonic depolymerization tank is 30kHz, and the volumetric power density is reduced to 1.25W / L. This makes the volumetric power density of the ultrasonic treatment in the reaction zone higher than that of the bypass ultrasonic treatment.

[0074] The reaction zone still operates in an intermittent pulse mode with a pulse cycle of 135 seconds, 45 seconds on and 90 seconds off. The bypass diversion ratio is 17.5%. The bypass ultrasonic depolymerization tank has a liquid inlet time of 10 minutes, an ultrasonic treatment time of 10 minutes, a drainage time of 6.5 minutes, and a standby time of 3.5 minutes for each operating cycle. The mixed liquid after ultrasonic treatment is returned to the bottom of the fluidized bed crystallizer. The rest is the same as in Example 1.

[0075] Performance testing: Polysilicon production wastewater treatment tests were conducted using the methods corresponding to Examples 1 to 3 and Comparative Examples 1 to 5, respectively. Example 1 and Comparative Examples 1 to 5 used the same batch of polysilicon production wastewater as the treatment object, and controlled the fluoride ion concentration entering the treatment system to 1050 mg / L, the silica concentration to 175 mg / L, and the pH value to 2, in order to reduce the impact of the difference in raw water quality on the comparison results; Example 2 and Example 3 were treated according to the influent water quality and operating conditions in the corresponding examples.

[0076] Each treatment system ran continuously for 72 hours. The first 48 hours were used to allow the system to reach a stable operating state. From the 48th hour onwards, samples were collected every 8 hours for a total of 4 times. The fluoride ion removal rate and silica removal rate were calculated using the effluent from the homogenization equalization tank and the clarification tank. The concentration of suspended solids in the overflow of the solid-liquid separation zone was detected using the overflow of the solid-liquid separation zone of the fluidized bed crystallizer. The proportion of recyclable particle size was detected using the bed crystallized particles discharged during stable operation. Each test was repeated 3 times, and the average value of each test result was taken.

[0077] Fluoride ion removal rate test: The fluoride ion concentration in the effluent of the equalization tank and the clarifier were measured separately; the fluoride ion removal rate was calculated as the percentage of the difference between the fluoride ion concentration in the equalization tank effluent and the fluoride ion concentration in the clarifier effluent.

[0078] Silica removal rate test: The total silicon concentration in the effluent from the equalization tank and the clarifier was measured and converted into silica concentration. The silica removal rate was calculated as a percentage of the silica concentration in the equalization tank effluent minus the silica concentration in the clarifier effluent.

[0079] Detection of suspended solids concentration in the solid-liquid separation zone overflow: Overflow samples from the solid-liquid separation zone of the fluidized bed crystallizer were taken, filtered through a pre-weighed filter membrane, and then dried at 105°C to constant weight. The suspended solids concentration was calculated based on the change in filter membrane mass before and after filtration and the sample volume. A lower concentration of suspended solids in the solid-liquid separation zone overflow indicates a lower degree of loss of fine crystals and particles with the overflow. Comparative Example 1 did not include a fluidized bed crystallizer, therefore this test was not performed.

[0080] Recycled particle size distribution test: During the stable operation of each treatment system, bed crystallization particles discharged over three discharge cycles were continuously collected and wet-screened using two layers of sieves with apertures of 1.5 mm and 0.3 mm. Particles of each size were collected separately and dried to constant weight. The percentage of the dry mass of bed crystallization particles with a diameter of 0.3 to 1.5 mm relative to the total dry mass of discharged bed crystallization particles was defined as the recycled particle size distribution. A higher recycled particle size distribution indicates that more bed crystallization particles are within the suitable particle size range that can continue to return to the reactor to participate in crystal growth. Comparative Example 1 did not have a fluidized bed crystallization reactor, therefore this test was not performed.

[0081] The test results are shown in Table 1.

[0082] Table 1: Performance test results of each embodiment and comparative example

[0083] In conjunction with Examples 1 to 3 and Comparative Example 1, and in conjunction with Table 1 and Appendix Figure 2 and attached Figure 3 It can be seen that by using a fluidized bed crystallization reactor and setting up a silica sand support, fluoride-containing substances in wastewater can undergo heterogeneous nucleation and subsequent crystal growth on the surface of the support and the surface of the existing crystal layer, so that some fluoride-containing substances are transformed from micro-precipitates to bed crystal particles. At the same time, the fluidized bed crystallization treatment is connected with the subsequent flocculation and sedimentation, which is conducive to further removing residual fluoride-containing particles and silica-containing substances, so that both fluoride ions and silica maintain a good removal effect.

[0084] In conjunction with Example 1 and Comparative Example 2, and in conjunction with Table 1 and Appendix Figure 2 To be continued Figure 5 It can be seen that setting intermittent ultrasound in the reaction zone can maintain sufficient contact between lime slurry, wastewater and silica sand support, and promote the transfer of reactants in the liquid phase to the particle surface, so that the formed fine crystal nuclei are more uniformly dispersed in the reaction system. After the ultrasound in the reaction zone is removed, the tendency of fine particles to be lost with overflow increases, and the number of bed crystal particles in the appropriate reflux particle size range decreases accordingly, indicating that ultrasound in the reaction zone is beneficial to providing more stable crystal nuclei conditions for subsequent crystal growth.

[0085] In conjunction with Example 1 and Comparative Example 3, and in conjunction with Table 1 and Appendix Figure 2 To be continued Figure 5 It can be seen that the fine crystal nuclei and fine crystal particles carried in the overflow of the solid-liquid separation zone can be redispersed after bypass ultrasonic deagglomeration and return to the bottom of the fluidized bed with the reflux liquid to continue participating in the subsequent crystallization process. After bypass ultrasonic deagglomeration is cancelled, some fine particles return to the reactor in an agglomerated state, and the number of dispersed particles that can continue to participate in crystal growth is reduced accordingly. At the same time, the trend of fine particles being lost with the overflow increases, indicating that bypass ultrasonic deagglomeration is beneficial to maintaining the recycling of crystal nuclei and the continuous growth of bed particles.

[0086] In conjunction with Example 1, Comparative Example 2 and Comparative Example 3, and in conjunction with Table 1 and Appendix Figure 2 To be continued Figure 5 It can be seen that the ultrasonic treatment in the reaction zone and the ultrasonic treatment in the bypass zone act on different stages of the crystallization cycle. The ultrasonic treatment in the reaction zone mainly acts on the liquid-solid mass transfer and crystal nucleation process after the addition of lime slurry, while the ultrasonic treatment in the bypass zone mainly acts on the fine particle agglomerates carried out with the overflow and causes the deagglomerated particles to return to the reaction zone. The two ultrasonic treatments are connected in the process of crystal nucleation, particle deagglomeration, reflux and continued growth, so that fine particles can circulate and participate in the crystallization process inside the fluidized bed. This is beneficial to balance the removal effect of fluorine and silicon, reduce the loss of fine particles and maintain a suitable composition of bed crystallization particles.

[0087] In conjunction with Example 1 and Comparative Example 4, and in conjunction with Table 1 and Appendix Figure 2 To be continued Figure 5 It can be seen that the ultrasonic deagglomeration process in the reaction zone and the bypass zone has different requirements for the intensity of ultrasonic action. When similar ultrasonic action intensities are used in both zones, the deagglomeration effect of the bypass on the fine particle agglomerates is relatively weakened, and the recycling and subsequent growth of the fine particles are affected to some extent. Making the ultrasonic deagglomeration intensity in the bypass zone higher than that in the reaction zone allows the reaction zone to focus on mass transfer and nucleation, while the bypass focuses on the deagglomeration of particle agglomerates, thus matching the action mode of the two treatment stages with their respective treatment objects.

[0088] In conjunction with Example 1 and Comparative Example 5, and in conjunction with Table 1 and Appendix Figure 2 To be continued Figure 5 It can be seen that by setting a higher intensity ultrasonic action in the reaction zone and reducing the intensity of bypass ultrasonic deagglomeration, the circulation state of the bed crystal particles changes, the tendency of fine particles to be lost with overflow increases accordingly, and the proportion of recirculated particles decreases. This indicates that the treatment effect of the two ultrasonic actions is not simply achieved by increasing the intensity of action, but rather by forming corresponding intensity differences according to the target at different stages. By using relatively low intensity intermittent ultrasound in the reaction zone and relatively high intensity ultrasound in the bypass deagglomeration process, crystal nucleation and particle deagglomeration can be carried out under appropriate conditions.

[0089] In conjunction with Examples 1 to 3 and Comparative Examples 1 to 5, and in conjunction with Table 1 and Appendix Figure 1 To be continued Figure 5 It can be seen that a continuous treatment process is formed through homogenization adjustment, ultrasonic-assisted crystallization in the reaction zone, crystal growth, solid-liquid separation, partial overflow bypass ultrasonic deagglomeration and reflux, and subsequent flocculation and sedimentation. The crystal nuclei generated in the reaction zone enter the crystal growth zone to continue growing. After solid-liquid separation, some fine particles carried out with the overflow are deagglomerated and returned to the reactor through bypass. This makes the crystal nucleus formation, particle growth, fine particle deagglomeration and reflux processes interconnected. At the same time, the residual fluorine-containing particles and silicon-containing substances are removed through subsequent flocculation and sedimentation, thereby achieving the synergistic treatment of fluorine and silicon in polysilicon production wastewater.

[0090] This specific embodiment is merely an explanation of this application and is not intended to limit it. After reading this specification, those skilled in the art can make modifications to this embodiment without contributing any inventive step, but such modifications are protected by patent law as long as they fall within the scope of the claims of this application.

Claims

1. A method for the combined treatment of defluorination and silicon removal in polysilicon production wastewater, characterized in that, Includes the following steps: S1. Introduce polysilicon production wastewater into a homogenization and equalization tank to balance the water quantity and quality. S2. The effluent from the homogenization equalization tank is fed into the fluidized bed crystallization reactor. The fluidized bed crystallization reactor is divided into a reaction zone, a crystal growth zone, and a solid-liquid separation zone from bottom to top. The reactor is filled with silica sand support. The wastewater flows from the bottom to the top, so that the support is in a fluidized state. In the reaction zone, lime milk is added to the wastewater as a calcium source precipitant. The pH value in the reaction zone is controlled at 8.5 to 9.5, and ultrasound is applied. The mixed liquid after being treated in the reaction zone enters the crystal growth zone for crystal growth, and then enters the solid-liquid separation zone for solid-liquid separation. S3. A portion of the overflow from the solid-liquid separation zone is sent to a bypass ultrasonic depolymerization tank for ultrasonic depolymerization treatment. The volume power density of the bypass ultrasonic depolymerization treatment is higher than that of the ultrasonic treatment in the reaction zone. The mixture after ultrasonic depolymerization treatment is returned to the bottom of the fluidized bed crystallizer. S4. The remaining portion of the solid-liquid separation zone overflow that does not enter the bypass ultrasonic depolymerization tank is sent to the clarification tank for flocculation and sedimentation. The effluent from the clarification tank is discharged or reused.

2. The method for synergistic treatment of polysilicon production wastewater by defluorination and desiliconization according to claim 1, characterized in that: In step S1, the effective volume of the equalization tank is determined by the average treatment flow rate of the wastewater treatment system, which corresponds to the treatment volume over 8-12 hours, and the effluent from the equalization tank is controlled at F. - The concentration is 100-2000 mg / L, the SiO2 concentration is 50-300 mg / L, the pH value is 1-3, and the stirring speed of the stirring device in the homogenization tank is 20-40 rpm.

3. The method for synergistic treatment of polysilicon production wastewater by defluorination and desiliconization according to claim 1, characterized in that: In step S2, in the fluidized bed crystallization reactor, the volumes of the reaction zone, the crystal growth zone, and the solid-liquid separation zone account for 25%–35%, 35%–45%, and 20%–30% of the total effective volume of the reactor, respectively, and the sum of the three is 100%; the support is a silica sand support with a particle size of 0.3–0.8 mm, and the support filling rate is 20%–40% of the effective volume of the reactor; based on the total liquid flow rate entering the bottom of the fluidized bed crystallization reactor, the upward flow velocity of the empty tower in the reaction zone is 8–15 m / h, and the support expansion rate is 15%–30%.

4. The method for synergistic treatment of polysilicon production wastewater for defluorination and desilicon removal according to claim 1, characterized in that: In step S2, the calcium source precipitant added to the reaction zone is lime slurry, with a mass concentration of 5% to 15%, and the addition amount is according to n(Ca):n(F) - The ratio is calculated to be 0.8:1 to 1.2:1, and the F... - The amount of F in the wastewater entering the fluidized bed crystallizer is [amount missing]. - The hydraulic residence time in the reaction zone is estimated to be 10–20 minutes.

5. The method for synergistic treatment of polysilicon production wastewater for defluorination and silicon removal according to claim 1, characterized in that: In step S2, when applying ultrasound, the operating frequency of the ultrasound is 20-40kHz, the volume power density is 0.5-2W / L, and the effective distance of the ultrasound does not exceed the height of the reaction zone; the ultrasound operates in an intermittent pulse mode, with a pulse period of 90-180 seconds, and the ultrasound on time is 30-60 seconds and the stop time is 60-120 seconds within each cycle.

6. The method for synergistic treatment of polysilicon production wastewater for defluorination and silicon removal according to claim 1, characterized in that: In step S2, a guide tube is provided in the crystal growth zone. The inner diameter of the guide tube is 40% to 60% of the inner diameter of the reactor, and the height of the guide tube is 60% to 80% of the height of the crystal growth zone. Both the upper and lower ends of the guide tube are flared out in a funnel shape with an expansion angle of 30° to 60°. The hydraulic residence time of the crystal growth zone is 20 to 40 minutes.

7. The method for synergistic treatment of polysilicon production wastewater for defluorination and desilicon removal according to claim 1, characterized in that: In step S2, the effective cross-sectional area of ​​the solid-liquid separation zone is set to ensure that the upward flow velocity of the liquid phase in the solid-liquid separation zone is 2-4 m / h. An overflow weir is provided at the top of the solid-liquid separation zone, and the weir orifice load is 5-15 m. 3 / (m·h).

8. The method for synergistic treatment of polysilicon production wastewater for defluorination and desiliconization according to claim 1, characterized in that: In step S2, the fluidized bed crystallizing reactor discharges material from the bottom every 4 to 12 hours, with each discharge amount being 1% to 5% of the total amount of bed crystallized particles in the reactor. The discharged bed crystallized particles are wet-screened and classified using two layers of screens, with the upper screen having a mesh size of 1.5 mm and the lower screen having a mesh size of 0.3 mm. After classification, bed crystallized particles with a particle size of 0.3 to 1.5 mm are returned to the bottom of the reactor.

9. The method for synergistic treatment of polysilicon production wastewater for defluorination and desilicon removal according to claim 1, characterized in that: In step S3, the portion is 10% to 25% of the total overflow from the solid-liquid separation zone; the frequency of the ultrasonic waves in the bypass ultrasonic depolymerization tank is 20 to 40 kHz, and the volumetric power density is 2.5 to 4 W / L; the bypass ultrasonic depolymerization tank adopts a batch operation, and each operating cycle includes 5 to 15 minutes of liquid inlet, 5 to 15 minutes of ultrasonic treatment, 3 to 10 minutes of drainage, and 2 to 5 minutes of standby.

10. The method for synergistic treatment of polysilicon production wastewater by defluorination and desiliconization according to claim 1, characterized in that: In step S4, the surface loading of the clarification tank is 0.8–1.5 m³. 3 / (m 2 The hydraulic retention time is 1–2.5 hours; the flocculation and sedimentation are carried out by adding polyaluminum chloride and anionic polyacrylamide to the inlet pipe of the clarifier, and the mass concentration of polyaluminum chloride, calculated as Al2O3, is 8%–12%, and the dosage is 1–2 L / m³. 3 For wastewater, anionic polyacrylamide with a molecular weight of 8 million to 15 million Daltons is added at a dosage of 0.5 to 1 mg / L based on the active ingredient.

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