A method and system for treating high-alkali silicon-containing wastewater during granular silicon production.

Abstract

This invention discloses a method and system for treating high-alkali silicon-containing wastewater during granular silicon production, comprising a wastewater collection tank, a multi-stage coagulation sedimentation tank, a clarification tank, a sludge storage tank, an activated carbon filter, a multi-media filter, and a plate and frame filter press. The wastewater collection tank is connected to the multi-stage coagulation sedimentation tank; the effluent from the multi-stage coagulation sedimentation tank is connected to the clarification tank; the clarification tank, activated carbon filter, and multi-media filter are connected sequentially; the sludge outlet at the bottom of the multi-stage coagulation sedimentation tank is connected to the sludge storage tank, and the sludge storage tank is connected to the plate and frame filter press. This invention selects a two-stage coagulation sedimentation process to effectively remove silica and suspended solids (SS), and after the coagulation sedimentation process, an activated carbon filtration process is selected to effectively degrade COD in the water, ensuring the water quality requirements for the evaporation system are met.

Description

Technical Field

[0001] This invention belongs to the field of high-alkali silicon-containing wastewater treatment for granular silicon, specifically relating to a method and system for treating high-alkali silicon-containing wastewater during the production of granular silicon. Background Technology

[0002] A small amount of silane gas is emitted during the production of granular silicon. This emitted silane gas requires harmless treatment. It is sent to a scrubbing tower for washing. The silane waste gas scrubbing device uses 31% liquid alkali diluted to approximately 15% to wash the silane gas. Currently, the daily emission is approximately 68 m³. 3 With a total silicon content of approximately 72,000 mg / L, it quickly clogs the heat exchanger when it enters the zero-emission system.

[0003] Silane washing wastewater (sodium silicate high-alkaline wastewater) contains 8% to 12% sodium silicate and has a pH of approximately 12-13. It is highly disruptive to any system and has a strong tendency to form scale, which is not conducive to the stable operation of the system and the current environmental protection requirements of zero discharge. There is currently no mature and effective treatment process.

[0004] Taking a 100,000-ton-per-year granular silicon project as an example, the silane waste gas scrubbing device uses 31% liquid alkali diluted to about 15% to scrub the silane gas, with a daily emission of approximately 60-70 cubic meters. 3 / d, approximately 2-5m per hour 3 The following parameters are present: pH≈12-13, turbidity approximately 3 NTU, conductivity approximately 80000 μS / cm, chloride ion approximately 5000 mg / L, TDS approximately 190000~200000 mg / L, total silicon content approximately 84000 mg / L, COD approximately 600~800 mg / L, SS content approximately 1000~4000 mg / L, and silica content approximately 60000~84000 mg / L. These parameters, when entering a zero-emission system, quickly clog the heat exchanger, causing the equipment to malfunction.

[0005] If the silane gas scrubbing device cannot effectively replace and discharge the gas, the silane gas will not be thoroughly scrubbed. The silane gas will be carried out through the vent pipe and ignited when it encounters air and suitable conditions, causing the vent pipe to catch fire.

[0006] After a large amount of silane gas is washed with liquid alkaline solution, it tends to become saturated. Once saturated, it needs to be effectively replaced. The high-alkaline sodium silicate wastewater after replacement cannot be disposed of by the current system, and environmental and safety issues urgently need to be addressed. Summary of the Invention

[0007] Purpose of the invention: The technical problem to be solved by the present invention is to provide a method and system for effectively treating high-alkali silicon-containing wastewater in the production process of granular silicon, in order to efficiently treat high-alkali silicon-containing wastewater, ensure that the silane gas scrubbing device can effectively replace and discharge, and ensure that there is no emission after thorough silane gas scrubbing.

[0008] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0009] A high-alkali silicon-containing wastewater treatment system for granular silicon production includes a wastewater collection tank, a multi-stage coagulation sedimentation tank, a clarification tank, a sludge storage tank, an activated carbon filter, a multi-media filter, and a plate and frame filter press. The wastewater collection tank is connected to the multi-stage coagulation sedimentation tank. The effluent from the rear end of the multi-stage coagulation sedimentation tank is connected to the clarification tank. The clarification tank, activated carbon filter, and multi-media filter are connected in sequence. The sludge outlet at the bottom of the multi-stage coagulation sedimentation tank is connected to the sludge storage tank, and the sludge storage tank is connected to the plate and frame filter press.

[0010] Specifically, the multi-stage coagulation sedimentation tank includes a mechanically stirred clarifier, a flocculation tank, and a high-efficiency sedimentation tank connected in sequence; the mechanically stirred clarifier has a coagulant dosing port and a waste hydrochloric acid dosing port; the flocculation tank has a flocculant dosing port; the high-efficiency sedimentation tank has an inclined tube module at the top, through which water is discharged to the clarifier tank; the middle flocculation zone of the high-efficiency sedimentation tank is connected to the flocculation tank; the bottom sludge thickening zone of the high-efficiency sedimentation tank is connected to the mechanically stirred clarifier or the sludge storage tank through sludge return and discharge pipelines, respectively.

[0011] Furthermore, the high-efficiency sedimentation tank is equipped with a sludge scraper in the middle flocculation zone, which is located above the bottom sludge thickening zone.

[0012] Furthermore, a mud level detection system is installed in the central flocculation zone of the high-efficiency sedimentation tank.

[0013] Furthermore, the mechanically stirred clarification tank includes a dosing tank, a first reaction chamber, a second reaction chamber, a flow guiding chamber, and a separation chamber; a coagulant dosing port is provided above the dosing tank, and a waste hydrochloric acid dosing port and a stirrer are provided above the first reaction chamber; an impeller lifting mechanism is provided between the first reaction chamber and the second reaction chamber.

[0014] Furthermore, the separation chamber is equipped with a system where sludge is partially returned to the first reaction chamber via a screw pump, while excess sludge is discharged externally.

[0015] Furthermore, the effluent from the clarification tank is sequentially fed into an activated carbon filter and a multi-media filter for treatment via a clarification tank booster pump; the rear end of the multi-media filter is connected to the filtered water production tank.

[0016] Furthermore, the sludge storage tank is connected to a plate and frame filter press via a sludge lifting pump, and the sludge is transported off-site after being dewatered by the plate and frame filter press.

[0017] Furthermore, the present invention also claims a method for treating highly alkaline silicon-containing wastewater during the production of granular silicon using the above-described system, comprising the following steps:

[0018] S1: Wastewater is collected in a wastewater collection tank, and then passes through a multi-stage coagulation sedimentation tank to remove suspended solids and silica. Then it passes through an activated carbon filter to reduce COD, and then through a multi-media filter to further reduce suspended solids and turbidity, so as to meet the influent water quality requirements of the subsequent evaporation and crystallization system.

[0019] S2: The sludge produced by the multi-stage coagulation sedimentation tank is collected in the sludge storage tank, and then transported away after being dewatered by the plate and frame filter press.

[0020] Specifically, in step S1, the multi-stage coagulation sedimentation tank includes a mechanically stirred clarification tank, a flocculation tank, and a high-efficiency sedimentation tank connected in sequence. High-alkalinity silica-containing wastewater enters the mechanically stirred clarification tank and reacts with coagulant and waste hydrochloric acid, causing suspended solids, colloids, etc. in the water to form flocs. Then it enters the flocculation tank and reacts with the flocculant. The precipitate is finally separated from the water in the form of sludge discharge.

[0021] The surface load of the mechanically stirred clarifier is 2.9–3.6 m. 3 / m 2 •h, with a stay time of 1.2 to 1.5 hours;

[0022] The surface loading of the high-efficiency sedimentation tank is 12-25 m³ / h. 3 / m 2 •h, the stay time is 0.5 to 1h.

[0023] Beneficial effects:

[0024] (1) Compared with the traditional coagulation and sedimentation process, the present invention selects a two-stage coagulation and sedimentation combination process to effectively remove silica and SS; the COD in high-alkaline silica-containing wastewater is high, which will affect the normal operation of the subsequent evaporation system. After the coagulation and sedimentation process, the activated carbon filtration process is selected to effectively degrade the COD in the water to ensure the water quality requirements of the evaporation system.

[0025] (2) Using this system, the silane gas scrubbing device can effectively replace and discharge the gas. After thorough scrubbing, there is no discharge of silane gas, which will not cause safety and environmental protection problems. The venting pipeline will not catch fire, resulting in zero risk. After a large amount of silane gas is scrubbed by the liquid alkali solution, it tends to become saturated. After saturation, it is effectively replaced. The high-alkaline sodium silicate wastewater after replacement is scrubbed by the high-alkaline silicon-containing wastewater system, and the environmental and safety issues are successfully resolved. The generated high-alkaline silicon-containing wastewater is neutralized by waste hydrochloric acid to produce silicic acid. Silicic acid is chemically stable and does not react with any substance except strong alkali and hydrofluoric acid. Silicic acid has various molecular compositions, such as disilicate (H2Si2O5), metasilicic acid, orthosilicic acid (Si(OH)4 or H4SiO4), etc. It is a milky white precipitate and appears as colloidal particles, precipitates, or gels. Some water evaporates from the gel, resulting in a porous dry solid gel, namely the common silica gel. It can be effectively separated under the filtration of a plate and frame filter press, thereby reducing the total silicon content. The clear liquid is reused in the zero-discharge system for recycling. Attached Figure Description

[0026] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments, and the advantages of the present invention in the above and / or other aspects will become clearer.

[0027] Figure 1 This is a schematic diagram of the overall structure of the high-alkali silicon-containing wastewater treatment system in the production process of granular silicon according to the present invention.

[0028] The reference numerals in the attached figures represent:

[0029] 1-Wastewater collection tank; 2-Wastewater lift pump; 3-Mechanically stirred clarification tank; 4-High-efficiency sedimentation tank; 5-Clarified water tank; 6-Sludge storage tank; 7-Sludge lift pump; 8-Plate and frame filter press; 9-Clarified water tank lift pump; 10-Activated carbon filter; 11-Multi-media filter; 12-Filtered water production tank; 13-Flocculation tank; 14-Inclined tube module; 15-Bottom sludge thickening zone; 16-Middle flocculation zone; 17-Sludge return and discharge pipeline; 18-Sludge level detection system. Detailed Implementation

[0030] The present invention can be better understood from the following embodiments.

[0031] Taking a 100,000-ton-per-year granular silicon project as an example, in order to ensure the effective replacement and emission of the silane gas scrubbing device while meeting environmental protection standards, it is necessary to discharge the highly alkaline silicon-containing wastewater, replace it with liquid alkali and repeat the scrubbing process to ensure that the silane gas is not carried out from the venting pipeline and flash-ignites upon contact with air. The highly alkaline silicon-containing wastewater is then degraded in terms of total silicon content, pH, and other indicators before entering the zero-emission system. This prevents blockage of the zero-emission system and ensures the safe, environmentally friendly, and stable operation of the silane gas scrubbing device.

[0032] The generated highly alkaline silicon-containing wastewater is neutralized with waste hydrochloric acid to produce silicic acid. Silicic acid is a weak acid, a glassy, ​​colorless, transparent amorphous particle. It is sparingly soluble in water and alcohol, insoluble in acids, but soluble in caustic alkali solutions. It decomposes into silicon dioxide when heated to 150℃. Silicic acid is chemically stable and does not react with any substance except strong bases and hydrofluoric acid. Silicic acid has various molecular compositions, such as disiliac acid (H₂Si₂O₅), metasilicic acid, and orthosilicic acid (Si(OH)₄ or H₄SiO₄), etc. The most commonly used silicic acid is the stable metasilicic acid H₂SiO₃. The ionization equilibrium constant of metasilicic acid is K₁ = 2 × 10⁻⁶. -10 At room temperature, orthosilicic acid is stable in the pH range of 2-3. However, if a supersaturated H4SiO4 solution is left for a long time, amorphous silica precipitates will form, which are milky white and appear as colloidal particles, precipitates, or gels. Some water evaporates from the gel, yielding a porous, dry solid gel, commonly known as silica gel. This silica gel can be effectively separated using a plate and frame filter press, thereby reducing the total silica content and allowing the clarified liquid to be reused in a zero-discharge system for recycling.

[0033] The influent water for this invention is surface water with high TDS, silica content of approximately 60,000–84,000 mg / L, high SS, and relatively high COD. To ensure that the treated water meets the influent requirements of the evaporation crystallization system, a two-stage coagulation sedimentation + filtration process is employed to ensure that the effluent meets discharge standards.

[0034] Combination Figure 1 The high-alkali silicon-containing wastewater treatment system for the granular silicon production process of this invention includes a wastewater collection tank 1, a multi-stage coagulation sedimentation tank, a clarification tank 5, a sludge storage tank 6, an activated carbon filter 10, a multi-media filter 11, and a plate and frame filter press 8. The wastewater collection tank 1 is connected to the multi-stage coagulation sedimentation tank; the effluent from the rear end of the multi-stage coagulation sedimentation tank is connected to the clarification tank 5; the clarification tank 5, the activated carbon filter 10, and the multi-media filter 11 are connected in sequence; the sludge outlet at the bottom of the multi-stage coagulation sedimentation tank is connected to the sludge storage tank 6, and the sludge storage tank 6 is connected to the plate and frame filter press 8.

[0035] The multi-stage coagulation sedimentation tank includes a mechanically stirred clarifier 3, a flocculation tank 13, and a high-efficiency sedimentation tank 4 connected in sequence. The mechanically stirred clarifier 3 has a coagulant inlet and a waste hydrochloric acid inlet. The flocculation tank 13 is equipped with a flocculant inlet. The high-efficiency sedimentation tank 4 is equipped with an inclined tube module 14 at the top, through which water is discharged to the clarification tank 5. The middle flocculation zone 16 of the high-efficiency sedimentation tank 4 is connected to the flocculation tank 13. The bottom sludge thickening zone 15 of the high-efficiency sedimentation tank 4 is connected to the mechanically stirred clarifier 3 or the sludge storage tank 6 through sludge return and discharge pipelines, respectively.

[0036] Wastewater collection tank 1 is connected to mechanically stirred clarification tank 3 via wastewater lift pump 2.

[0037] The inclined tube module 14 is connected to the clarification tank 5 through a water collection tank and a water channel.

[0038] The middle flocculation zone 16 of the high-efficiency sedimentation tank 4 is equipped with a sludge scraper, which is located above the bottom sludge thickening zone 15.

[0039] A sludge level detection system 18 is installed in the middle flocculation zone 16 of the high-efficiency sedimentation tank 4.

[0040] After softening in the mechanically stirred clarifier 3, the wastewater is rapidly mixed with coagulant PAC and enters the flocculation tank 13, where it mixes with the returned sludge from the flocculation zone 16 in the middle of the sedimentation tank. In the flocculation tank 13, coagulant PAM is added to complete the flocculation reaction. The effluent then flows into the sedimentation zone via a plug flow method. In the sedimentation zone, the sludge settles, and the clarified water is further separated by the inclined tube module 14 and collected by the collection tank. The settled sludge is concentrated in the bottom sludge thickening zone 15. The upper layer of the concentrated sludge is returned to the mechanically stirred clarifier 3 by a screw pump for mixing to maintain optimal solids concentration. Excess sludge at the bottom is pumped out by a screw pump.

[0041] The mechanically stirred clarifier 3 includes a dosing tank, a first reaction chamber, a second reaction chamber, a guide chamber, and a separation chamber. A coagulant dosing port is located above the dosing tank, and a waste hydrochloric acid dosing port and a mixer are installed above the first reaction chamber. An impeller lifting mechanism is installed between the first and second reaction chambers. The mechanically stirred clarifier 3 utilizes the lifting effect of mechanical stirring to complete sludge recirculation and contact reaction. Raw water from the dosing tank enters the first reaction chamber and reacts with several times its volume of circulating sludge under the agitation of the impeller blades. The sludge is then lifted by the impeller to the second reaction chamber for further reaction, forming larger flocs, which then pass through the guide chamber into the separation chamber for sedimentation and separation. A portion of the settled sludge is recirculated back to the first reaction chamber using a screw pump, while excess sludge is discharged.

[0042] The separation chamber is equipped with a screw pump that partially returns the sludge to the first reaction chamber, while the excess sludge is discharged.

[0043] The effluent from the clarification tank 5 is sequentially fed into the activated carbon filter 10 and the multi-media filter 11 by the clarification tank booster pump 9 for treatment; the rear end of the multi-media filter 11 is connected to the filtered water production tank 12.

[0044] The activated carbon filter 10 utilizes granular activated carbon to further remove residual suspended solids and impurities from the raw water. It exhibits significant removal effects on odors, organic matter, colloids, iron, and residual chlorine, providing favorable influent conditions for subsequent treatment. The activated carbon filter 10 primarily utilizes activated carbon organic flocculants with high carbon content, large molecular weight, and large specific surface area to physically adsorb impurities in the water. When water flows through the pores of the activated carbon, various suspended particles and organic matter are adsorbed into the pores under the action of van der Waals forces. Simultaneously, residual chlorine and hypochlorous acid adsorbed on the activated carbon surface undergo a chemical reaction, being reduced to chloride ions, thus effectively removing residual chlorine and ensuring that the residual chlorine content in the effluent is less than 0.1 ppm, meeting the operating conditions for subsequent membrane treatment. Over time, the amount of material trapped within the pores and between the particles of the activated carbon gradually increases, causing the pressure difference across the filter to rise until it fails. When the activated carbon filter's normal operation is affected by excessive impurities, its performance can be restored through backwashing. Backwashing loosens the filter media by using reverse water flow, allowing adhering debris to peel off and be carried away by the backwash. This facilitates the removal of sediment and suspended solids from the filter media, prevents caking, and fully restores its interception capacity. The backwashing cycle depends on the effluent turbidity. When the activated carbon reaches its saturation adsorption capacity and becomes completely ineffective, it should be regenerated or replaced to meet system requirements.

[0045] Multi-media filters 11 are used in industrial water treatment systems to remove suspended solids and colloids from water. The multi-media filter 11 primarily uses quartz sand and anthracite as filter media. Through interception, sedimentation, inertia, diffusion, and hydrodynamic forces, suspended particles migrate to the filter media surface. Under the influence of van der Waals forces, electrostatic forces, chemical bonds, and chemisorption forces, they adhere to the surface of the filter media particles or particles already adhering to the filter media surface. Through the dirt-holding and intercepting capacity of the filter media, the turbidity and SDI value of the water are further reduced. After a period of filtration, the gaps between the surface filter media gradually become clogged with pollutant particles, forming a filter membrane. This causes a sharp increase in filtration resistance, a sharp decrease in filtration rate, or even the possibility of filter membrane cracks, leading to pollutant penetration. Therefore, the multi-media filter 11 should be backwashed promptly after a period of operation. Combined air-water backwashing is often used, which yields good backwashing results.

[0046] The method for treating high-alkali silicon-containing wastewater during granular silicon production using the above system includes the following steps:

[0047] S1: Wastewater is collected in a wastewater collection tank, and then passes through a multi-stage coagulation sedimentation tank to remove suspended solids and silica. Then it passes through an activated carbon filter to reduce COD, and then through a multi-media filter to further reduce suspended solids and turbidity, so as to meet the influent water quality requirements of the subsequent evaporation and crystallization system.

[0048] S2: The sludge produced by the multi-stage coagulation sedimentation tank is collected in the sludge storage tank, and then transported away after being dewatered by the plate and frame filter press.

[0049] In step S1, the multi-stage coagulation sedimentation tank includes a mechanically stirred clarification tank, a flocculation tank, and a high-efficiency sedimentation tank connected in sequence. High-alkalinity silica-containing wastewater enters the mechanically stirred clarification tank and reacts with coagulant and waste hydrochloric acid, causing suspended solids, colloids, etc. in the water to form flocs. Then it enters the flocculation tank and reacts with the flocculant. The precipitate is finally separated from the water in the form of sludge discharge.

[0050] The surface load of the mechanically stirred clarifier is 2.9–3.6 m. 3 / m 2 •h, with a stay time of 1.2 to 1.5 hours;

[0051] The surface loading of the high-efficiency sedimentation tank is 12-25 m³ / h. 3 / m 2 •h, the stay time is 0.5 to 1h

[0052] The sludge storage tank 6 is connected to the plate and frame filter press 8 via the sludge lifting pump 7. After the sludge is dewatered by the plate and frame filter press 8, it is transported out. The moisture content of the treated sludge can be controlled to below 70%.

[0053] This invention's system boasts advantages such as small footprint, low construction cost, and resistance to shock loads. It can be integrated with filtration systems to produce high-quality, stable effluent. Simultaneously, the system discharges sludge with a high solids content, which can be directly fed into dewatering equipment after collection. It utilizes waste hydrochloric acid in a cascaded manner to neutralize highly alkaline, silicon-containing wastewater. The silane gas scrubbing device effectively replaces and discharges the silane gas, resulting in thorough scrubbing with no emissions, thus avoiding safety and environmental issues. The venting pipeline will not ignite, providing a zero-risk solution to safety and environmental problems. The pH level decreases from influent 12-13 to effluent 6.5-9, SS level decreases from influent 1000-4000 mg / L to effluent ≤10 mg / L, COD level decreases from influent 600-800 mg / L to effluent ≤100 mg / L, and silica level decreases from influent 60000-84000 mg / L to ≤200 mg / L.

[0054] This invention provides a method and system for treating high-alkali silicon-containing wastewater during granular silicon production. Many methods and approaches exist for implementing this technical solution; the above description is merely a preferred embodiment. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of this invention, and these improvements and modifications should also be considered within the scope of protection of this invention. All components not explicitly stated in this embodiment can be implemented using existing technologies.

Claims

1. A system for treating high-alkali silicon-containing wastewater during granular silicon production, characterized in that, The system includes a wastewater collection tank (1), a multi-stage coagulation sedimentation tank, a clarification tank (5), a sludge storage tank (6), an activated carbon filter (10), a multi-media filter (11), and a plate and frame filter press (8); the wastewater collection tank (1) is connected to the multi-stage coagulation sedimentation tank; the effluent from the rear end of the multi-stage coagulation sedimentation tank is connected to the clarification tank (5); the clarification tank (5), the activated carbon filter (10), and the multi-media filter (11) are connected in sequence; the sludge outlet at the bottom of the multi-stage coagulation sedimentation tank is connected to the sludge storage tank (6), and the sludge storage tank (6) is connected to the plate and frame filter press (8); The multi-stage coagulation sedimentation tank includes a mechanically stirred clarifier (3), a flocculation tank (13), and a high-efficiency sedimentation tank (4) connected in sequence; the mechanically stirred clarifier (3) has a coagulant inlet and a waste hydrochloric acid inlet; the flocculation tank (13) is provided with a flocculant inlet; the high-efficiency sedimentation tank (4) is provided with an inclined tube module (14) at the top, and water is discharged to the clarification tank (5) through the inclined tube module (14); the middle flocculation zone (16) of the high-efficiency sedimentation tank (4) is connected to the flocculation tank (13); the bottom sludge thickening zone (15) of the high-efficiency sedimentation tank (4) is connected to the mechanically stirred clarifier (3) or the sludge storage tank (6) through sludge return and discharge pipelines (17).

2. The high-alkali silicon-containing wastewater treatment system for granular silicon production according to claim 1, characterized in that, The high-efficiency sedimentation tank (4) is equipped with a sludge scraper in the middle flocculation zone (16), which is located above the bottom sludge thickening zone (15).

3. The high-alkali silicon-containing wastewater treatment system for granular silicon production according to claim 1, characterized in that, The high-efficiency sedimentation tank (4) is equipped with a mud level detection system (18) in the middle flocculation zone (16).

4. The high-alkali silicon-containing wastewater treatment system for granular silicon production according to claim 1, characterized in that, The mechanically stirred clarification tank (3) includes a dosing tank, a first reaction chamber, a second reaction chamber, a flow guiding chamber, and a separation chamber; a coagulant dosing port is provided above the dosing tank, and a waste hydrochloric acid dosing port and a stirrer are provided above the first reaction chamber; an impeller lifting mechanism is provided between the first reaction chamber and the first reaction chamber.

5. The high-alkali silicon-containing wastewater treatment system for granular silicon production according to claim 4, characterized in that, The separation chamber is equipped with a screw pump that partially returns sludge to the first reaction chamber, while excess sludge is discharged externally.

6. The high-alkali silicon-containing wastewater treatment system for granular silicon production according to claim 1, characterized in that, The effluent from the clarification tank (5) is sequentially fed into the activated carbon filter (10) and the multi-media filter (11) by the clarification tank booster pump (9); the rear end of the multi-media filter (11) is connected to the filtered water production tank (12).

7. The high-alkali silicon-containing wastewater treatment system for granular silicon production according to claim 1, characterized in that, The sludge storage tank (6) is connected to the plate and frame filter press (8) via the sludge lifting pump (7), and the sludge is transported out after being dewatered by the plate and frame filter press (8).

8. A method for treating high-alkali silicon-containing wastewater during granular silicon production using the system described in claim 1, characterized in that, Includes the following steps: S1: Wastewater is collected in wastewater collection tank (1), and then passes through multi-stage coagulation sedimentation tank to remove solid suspended matter and silica in the water. Then it passes through activated carbon filter (10) to reduce COD, and then through multi-media filter (11) to further reduce solid suspended matter and turbidity, so as to meet the water quality requirements of the subsequent evaporation crystallization system. S2: The sludge produced by the multi-stage coagulation sedimentation tank is collected in the sludge storage tank (6), and then transported away after being dewatered by the plate and frame filter press (8).

9. The method for treating high-alkali silicon-containing wastewater during granular silicon production according to claim 8, characterized in that, In step S1, the multi-stage coagulation sedimentation tank includes a mechanically stirred clarification tank (3), a flocculation tank (13), and a high-efficiency sedimentation tank (4) connected in sequence. High-alkali silica-containing wastewater enters the mechanically stirred clarification tank (3) and reacts with coagulant and waste hydrochloric acid, causing suspended solids, colloids, etc. in the water to form flocs. Then it enters the flocculation tank (13) and reacts with the flocculant. The precipitate is finally separated from the water in the form of sludge discharge. The surface load of the mechanically stirred clarifier (3) is 2.9–3.6 m. 3 / m 2 •h, with a stay time of 1.2 to 1.5 hours; The surface loading of the high-efficiency sedimentation tank (4) is 12-25 m³ / h. 3 / m 2 •h, the stay time is 0.5 to 1h.

Images