Induced crystallization defluorination device and method

Abstract

The invention belongs to the technical field of wastewater treatment, and discloses an induced crystallization defluorination device and method.The induced crystallization defluorination device comprises a crystal growth pond, a precipitation separation pond and a composite absorption tower, the bottom of the crystal growth pond is connected with a seed crystal inlet of the precipitation separation pond through a seed crystal flow guide pipe, and a stop valve III is arranged on the seed crystal flow guide pipe; the bottom of the precipitation separation tank is communicated with the crystal growth tank through a seed crystal return pipe, a return pump, a flow meter and a stop valve IV are arranged on the seed crystal return pipe, and the flow meter and the stop valve IV are positioned on the outlet side of the return pump; a water outlet of the precipitation separation tank is connected with a wastewater inlet of the composite absorption tower through a water outlet pipe. According to the method, a seed crystal induction defluorination system is adopted, aluminum salt and sodium salt are added into the wastewater, the molar ratio is accurately regulated and controlled, fluorine ions are directly converted into high-purity cryolite (Na3AlF6), defluorination and resource utilization are achieved, and meanwhile it is guaranteed that the effluent quality reaches the national standard.

Description

Technical Field

[0001] This invention belongs to the field of wastewater treatment technology, specifically relating to an induced crystallization defluorination device and method. Background Technology

[0002] Fluoride-containing wastewater mainly originates from industries such as aluminum smelting, glass manufacturing, fertilizer production, semiconductor processing, and metal surface treatment. If fluoride ions are discharged directly without treatment, they will cause serious harm to the environment and human health, such as dental fluorosis and skeletal fluorosis. The current "Standards for Drinking Water Quality" (GB5749-2022) stipulates that the fluoride concentration in effluent should be below 1.5 mg / L, but existing processes are difficult to consistently meet this standard over the long term.

[0003] Currently, calcium salt precipitation combined with coagulation is commonly used in engineering applications to remove fluoride ions by generating calcium fluoride (CaF2). Although this method is simple to operate, it has the following drawbacks: small precipitate particle size, making solid-liquid separation difficult; high reagent consumption, generating a large amount of sludge; low added value of by-products, which are mostly discarded as waste; and sensitivity to fluctuations in influent water quality, making it difficult for effluent to consistently meet standards over a long period.

[0004] Therefore, the existing calcium salt precipitation method is difficult to achieve both efficient fluoride removal and resource utilization, and a new treatment scheme is urgently needed to improve it. Summary of the Invention

[0005] The purpose of this invention is to overcome the problems of existing calcium salt precipitation defluorination processes, such as difficulties in solid-liquid separation, large sludge volume, low added value of products, and unstable effluent. This invention proposes an induced crystallization defluorination device and method. The device employs a seed-induced defluorination system, which adds aluminum and sodium salts to the wastewater and precisely controls the molar ratio to directly convert fluoride ions into high-purity cryolite (Na3AlF6), achieving both defluorination and resource utilization, while ensuring that the effluent quality meets national standards.

[0006] To achieve the above objectives, the present invention employs the following technical solution: A defluorination device for induced crystallization includes a crystal growth tank, a precipitation separation tank, and a composite absorption tower. The bottom of the crystal growth tank is connected to the seed inlet of the precipitation separation tank via a seed guide pipe, and a shut-off valve III is installed on the seed guide pipe. The bottom of the precipitation separation tank is connected to the crystal growth tank via a seed return pipe, and a return pump, a flow meter, and a shut-off valve IV are installed on the seed return pipe. The flow meter and shut-off valve IV are located on the outlet side of the return pump. The outlet of the precipitation separation tank is connected to the wastewater inlet of the composite absorption tower via an outlet pipe.

[0007] Preferably, the sedimentation separation tank is equipped with a multi-stage sieve-type crystallization carrier at the bottom. The upper layer of the multi-stage sieve-type crystallization carrier is a vibrating corrugated screen plate assembly with a pore size gradient of 40-60 μm. The middle layer of the multi-stage sieve-type crystallization carrier is a surface-modified ceramic packing layer coated with hydroxyapatite, with a specific surface area ≥500 m². 2 / m 3 The surface roughness Ra = 1.5-2.5μm; the lower layer of the multi-stage sieve crystallization carrier is a conical mud collection cavity structure with an inclination angle of 30°-45°, and the inner wall is coated with wear-resistant polytetrafluoroethylene.

[0008] Preferably, the induced crystallization defluorination device of the present invention further includes an inlet pump I, an electromagnetic flow meter I at the outlet of the inlet pump I, the outlet of the electromagnetic flow meter I being connected to the first inlet of the crystal growth tank via a first branch, and a shut-off valve I on the first branch; the outlet of the electromagnetic flow meter I being connected to the second inlet of the sedimentation separation tank via a second branch, and a shut-off valve II on the second branch.

[0009] Preferably, the sedimentation separation tank is equipped with an ultrasonic sludge level gauge for measuring the position of the sludge at the bottom of the sedimentation separation tank.

[0010] Preferably, the crystal growth tank is equipped with a first stirrer and a first temperature / pH sensor, and the precipitation separation tank is equipped with a second stirrer and a second temperature / pH sensor.

[0011] Preferably, the crystal growth pool is provided with a first dosing interface.

[0012] Preferably, the wastewater inlet of the composite absorption tower is located at the bottom of the composite absorption tower. The bottom of the composite absorption tower has a water distribution net, and a clear water buffer layer is formed between the water distribution net and the bottom of the composite absorption tower. A modified alumina reaction layer is located above the water distribution net in the composite absorption tower. A support plate I is located above the modified alumina reaction layer in the composite absorption tower. An activated carbon filter layer is located above the support plate I in the composite absorption tower. A support plate II is located above the activated carbon filter layer in the composite absorption tower. A clear water layer is located above the support plate II in the composite absorption tower. An outlet is located at the top of the clear water layer in the composite absorption tower.

[0013] The present invention also provides a method for induced crystallization defluorination, which is carried out by the induced crystallization defluorination device of the present invention as described above, and includes the following process: Fluoride-containing wastewater is added to a crystal growth tank and a sedimentation separation tank; Sodium and aluminum salts for generating sodium fluoroaluminate are added to the crystal growth tank to form 20-50 μm supersaturated sodium fluoroaluminate seed crystals. Sodium fluoroaluminate seed crystals in the crystal growth tank are sent into the precipitation separation tank through the seed crystal guide pipe. After the sodium fluoroaluminate seed crystals in the precipitation separation tank are mixed with fluoride-containing wastewater, the fluoride ions in the fluoride-containing wastewater react with the sodium fluoroaluminate seed crystals to induce the formation of 50-100μm cryolite and reduce the fluoride ion concentration in the precipitation separation tank. After the cryolite induced in the sedimentation separation tank settles to a preset height, a portion of the cryolite in the sedimentation separation tank is returned to the crystal growth tank through the seed crystal return pipe, and the remaining cryolite in the sedimentation separation tank is discharged through the sedimentation sludge discharge pipe of the sedimentation separation tank. The supernatant from the sedimentation separation tank is sent to the composite absorption tower through the outlet pipe for further treatment to remove fluoride ions, suspended solids, and organic matter, so that the water meets the standards. The qualified water is finally discharged from the composite absorption tower.

[0014] Preferably, the wastewater inlet of the composite absorption tower is located at the bottom of the composite absorption tower. The bottom of the composite absorption tower has a water distribution net, and a clear water buffer layer is formed between the water distribution net and the bottom of the composite absorption tower. A modified alumina reaction layer is located above the water distribution net in the composite absorption tower. A support plate I is located above the modified alumina reaction layer in the composite absorption tower. An activated carbon filter layer is located above the support plate I in the composite absorption tower. A support plate II is located above the activated carbon filter layer in the composite absorption tower. A clear water layer is located above the support plate II in the composite absorption tower. An outlet is located at the top of the clear water layer in the composite absorption tower. When the supernatant from the sedimentation separation tank is sent to the composite absorption tower for treatment through the effluent pipe, it is evenly distributed through the water distribution network and flows from bottom to top through the modified alumina reaction layer. Under the action of hydroxyapatite-modified activated alumina, the fluoride ion concentration drops to below 1.5 mg / L. The water then flows through the activated carbon filter layer, where residual fluoride ions are further adsorbed and suspended solids and organic matter are removed, making the water meet the standards. The qualified water is finally discharged from the composite absorption tower.

[0015] Preferably, the operating conditions for the crystal growth tank and the sedimentation separation tank include: pH=5.0-6.0 and temperature=24.5-25.5℃; The fluoride concentration in the fluoride-containing wastewater is 800-2500 mg / L, and the pH of the fluoride-containing wastewater is 2.5-6.5; The seed concentration in the crystal growth pool ranges from 50 to 80 g / L.

[0016] The present invention has the following beneficial effects: The induced crystallization defluorination device of this application addresses the core defects of existing calcium salt precipitation processes through precise linkage of a crystal growth tank, a precipitation separation tank, and a composite absorption tower. The specific principle is as follows: Supersaturated sodium fluoroaluminate crystals of 20-50 μm are generated in the crystal growth tank. These crystals are then sent to the precipitation separation tank via a seed guide pipe, inducing fluoride ions in the wastewater to transform into cryolite of 50-100 μm. Compared to the fine precipitates of traditional processes, the particle size is significantly increased, resulting in a substantial improvement in settling performance and fundamentally solving the solid-liquid separation problem. The seed return pipe at the bottom of the precipitation separation tank is connected to the crystal growth tank. With the coordinated control of a return pump, flow meter, and shut-off valve IV, a portion of the cryolite can be returned and reused, ensuring a stable seed concentration in the crystal growth tank and forming an efficient crystallization cycle. This design also relies on precise control of the molar ratio of sodium and aluminum salts to directionally convert fluoride ions into high-purity cryolite, avoiding waste caused by incomplete reagent reactions. Simultaneously, cryolite can be recycled as an industrial raw material, completely changing the problem of low added value of byproducts in traditional processes. The directional crystallization process also reduces sludge production at the source. The supernatant from the sedimentation separation tank enters the composite absorption tower through the effluent pipe, forming a dual guarantee of "crystallization defluorination + deep purification." Even if the influent water quality fluctuates, the sedimentation separation tank can maintain a basic defluorination effect through crystal seed control, while the composite absorption tower further removes residual fluoride ions, suspended solids, and organic matter, ensuring long-term stable compliance of the effluent. The entire device organically combines defluorination, crystallization control, and resource recovery, achieving the synergistic goals of efficient defluorination, low-consumption operation, and resource utilization, demonstrating outstanding technical practicality and economic value. Attached Figure Description

[0017] Figure 1 This is a front view of the induced crystallization defluorination device in an embodiment of the present invention; Figure 2 This is a schematic diagram of the water distribution network in an embodiment of the present invention; Figure 3 This is a schematic diagram of the support plate in an embodiment of the present invention; Figure 4 This is a schematic diagram of a multi-stage sieving crystallization carrier in an embodiment of the present invention.

[0018] In the diagram: 1-Inlet pump I, 2-Electromagnetic flowmeter I, 3-Stop valve I, 4-Stop valve II, 5-Crystal growth tank, 6-First inlet, 7-First mixer, 8-First dosing port, 9-First temperature / pH sensor, 10-Stop valve III, 11-Seedling guide pipe, 12-Intelligent controller, 13-Dual-tank dosing system, 14-Sedimentation separation tank, 15-Second inlet, 16-Second mixer, 17-Ultrasonic sludge level gauge, 18-Second dosing port, 19-Second temperature / pH sensor, 20-Multi-stage sieve crystallization carrier, 21-Seedling return pipe, 22-Stop valve IV, 23-Electromagnetic flowmeter II, 24-Return pump, 25-Sedimentation sludge discharge pipe, 26-Interceptor 27-Stop valve V, 28-Electromagnetic flowmeter III, 29-Outlet pipe, 30-Inlet pump II, 31-Electromagnetic flowmeter IV, 32-Stop valve VI, 33-Composite absorption tower, 34-Outlet, 35-Clear water layer, 36-Support plate II, 37-Activated carbon inlet, 38-Activated carbon filter layer, 39-Water quality sampling port, 40-Online fluoride monitor, 41-Reflux box, 42-Clear water reflux pipe, 42-Activated carbon outlet, 42a-Activated carbon pneumatic discharge valve, 43-Support plate I, 44-Modified activated alumina inlet, 45-Modified alumina reaction layer, 46-Modified activated alumina outlet, 46a-Modified activated alumina pneumatic discharge valve, 47-Water distribution network, 48-Clear water buffer layer. Detailed Implementation

[0019] To enable those skilled in the art to better understand the present invention, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are merely some embodiments of the present invention, not all embodiments, and are not intended to limit the scope of the present invention. Furthermore, in the following description, descriptions of well-known structures and technologies are omitted to avoid unnecessary confusion regarding the concepts disclosed in the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort should fall within the scope of protection of the present invention.

[0020] See Figure 1 This embodiment of the induced crystallization defluorination device includes a crystal growth tank 5, a sedimentation separation tank 14, and a composite absorption tower 32. The bottom of the crystal growth tank 5 is connected to the seed inlet of the sedimentation separation tank 14 via a seed guide pipe 11. A shut-off valve III 10 is installed on the seed guide pipe 11. The bottom of the sedimentation separation tank 14 is connected to the crystal growth tank 5 via a seed return pipe 21. A return pump 24, a flow meter, and a shut-off valve IV 23 are installed on the seed return pipe 21. The flow meter and shut-off valve IV 23 are located on the outlet side of the return pump 24. The outlet of the sedimentation separation tank 14 is connected to the wastewater inlet of the composite absorption tower 32 via an outlet pipe 28. Using this embodiment, the induced crystallization defluorination method is as follows: Fluorine-containing wastewater is added to crystal growth tank 5 and sedimentation separation tank 14; wherein the fluorine concentration in the fluorine-containing wastewater is 800-2500 mg / L and the pH of the fluorine-containing wastewater is 2.5-6.5; In crystal growth cell 5, sodium and aluminum salts for generating sodium fluoroaluminate are added to form 20-50 μm supersaturated sodium fluoroaluminate seed crystals. Sodium fluoroaluminate seeds in crystal growth tank 5 are fed into sedimentation separation tank 14 through seed guide pipe 11. After the sodium fluoroaluminate seeds in sedimentation separation tank 14 are mixed with fluoride-containing wastewater, the fluoride ions in the fluoride-containing wastewater react with the sodium fluoroaluminate seeds to induce the formation of cryolite with a diameter of 50-100μm, and reduce the concentration of fluoride ions in sedimentation separation tank 14. During operation of crystal growth tank 5 and sedimentation separation tank 14, the pH is 5.0-6.0 and the temperature is 24.5-25.5℃. After the cryolite induced in the sedimentation separation tank 14 is deposited to a preset height, a portion of the cryolite in the sedimentation separation tank 14 is returned to the crystal growth tank 5 through the seed return pipe 21, maintaining the seed concentration in the crystal growth tank 5 in the range of 50-80 g / L. The remaining cryolite in the sedimentation separation tank 14 is discharged through the sedimentation sludge discharge pipe of the sedimentation separation tank 14. The supernatant from the sedimentation separation tank 14 is sent to the composite absorption tower 32 through the outlet pipe 28 for further treatment to remove fluoride ions, suspended solids and organic matter, so that the water meets the standards. The qualified water is finally discharged from the composite absorption tower 32.

[0021] As a preferred embodiment of the present invention, see Figure 1 and Figure 4 The sedimentation separation tank 14 has a multi-stage sieve-type crystallizing carrier 20 at the bottom. The upper layer of the multi-stage sieve-type crystallizing carrier 20 is a vibrating corrugated screen plate assembly with a pore size gradient of 40-60 μm. The middle layer of the multi-stage sieve-type crystallizing carrier 20 is a surface-modified ceramic packing layer coated with hydroxyapatite, with a specific surface area ≥500 m². 2 / m 3The surface roughness Ra=1.5-2.5μm, so the middle layer can provide more attachment sites, promote seed attachment and growth, improve crystallization speed and sedimentation efficiency, and fluoride ions are more effectively converted into cryolite, improving the defluorination efficiency. On the other hand, in this embodiment, the large specific surface area of ​​the middle layer promotes the interaction between seed crystals and fluoride ions, and the surface roughness ensures stable seed attachment and growth, avoids crystal suspension, improves sedimentation performance, and solves the problems of small crystals and solid-liquid separation in traditional methods. The lower layer of the multi-stage sieve crystallization carrier 20 is a conical mud collection cavity structure with an inclination angle of 30°-45°. The inner wall is provided with a wear-resistant polytetrafluoroethylene coating. The design of this lower layer has the following functions: (1) Conical mud collection cavity structure: The conical structure (inclination angle 30°-45°) effectively collects deposited crystals, accelerates sedimentation, prevents sediment accumulation, and keeps the sedimentation area unobstructed; (2) Polytetrafluoroethylene coating: Strong wear resistance, reduces wear, extends equipment life, and ensures long-term stable operation. The working process of this multi-stage sieving crystallization carrier in this embodiment revolves around "seed interception - crystallization promotion - sludge collection", as detailed below: (1) Upper layer: Cryolite is generated in the screening sedimentation tank to intercept particles larger than 60μm and prevent them from floating or being lost. An amplitude of 0.5-2.0mm avoids clogging of the screen holes and ensures smooth water flow. Small crystals <40μm pass through the screen plate.

[0022] (2) Middle layer: Small seed crystals enter the modified ceramic filler layer. The larger specific surface area and surface roughness provide more crystallization sites for the seed crystals, promote seed crystal attachment and growth into cryolite particles of 50-100μm, and achieve "secondary crystallization".

[0023] (3) Lower layer: Large cryolite particles intercepted in the upper layer and cryolite crystallized in the middle layer fall into the lower sludge collection chamber under the action of gravity. The 30°-45° inclination angle accelerates the sludge sliding down and avoids accumulation; the polytetrafluoroethylene coating reduces cryolite adhesion and ensures smooth crystal aggregation. The aggregated cryolite flows back to the crystal growth tank through the return pipe, and the rest is discharged through the discharge pipe.

[0024] The advantages of the multi-stage sieving crystallization carrier 20 design in this embodiment are as follows: It optimizes the process of fluoride ion conversion into cryolite, ensuring effective crystal growth and smooth sedimentation. Through multi-stage sieving, it separates crystal seeds of different sizes, promotes secondary crystallization of smaller seeds, and ultimately collects and recovers high-purity cryolite. This design improves crystal formation efficiency, enhances system stability, and solves problems such as difficult sedimentation and excessive sludge production in traditional defluorination processes.

[0025] As a preferred embodiment of the present invention, see Figure 1This embodiment improves upon the above embodiment by adding an inlet pump I1. An electromagnetic flowmeter I2 is installed at the outlet of inlet pump I1. The outlet of electromagnetic flowmeter I2 is connected to the first inlet 6 of crystal growth tank 5 via a first branch, and a shut-off valve I3 is installed on the first branch. The outlet of electromagnetic flowmeter I2 is connected to the second inlet 15 of sedimentation separation tank 14 via a second branch, and a shut-off valve II4 is installed on the second branch. Inlet pump I1 can pump fluoride-containing wastewater into crystal growth tank 5 and sedimentation separation tank 14. Electromagnetic flowmeter I2 can accurately measure the flow rate at the outlet of inlet pump I1. Shut-off valves I3 and II4 can control the flow ratio of fluoride-containing wastewater in the first and second branches, thereby adjusting the proportion of fluoride-containing wastewater entering crystal growth tank 5 and sedimentation separation tank 14.

[0026] As a preferred embodiment of the present invention, see Figure 1 This embodiment is an improvement on the above embodiment. The sedimentation separation tank 14 is equipped with an ultrasonic sludge level gauge 17 for measuring the sludge level at the bottom of the sedimentation separation tank 14. Based on the value measured by the ultrasonic sludge level gauge 17, it is determined whether the sludge at the bottom of the sedimentation separation tank 14 has reached the discharge time. When the value measured by the ultrasonic sludge level gauge 17 is greater than or equal to the preset value, the sludge at the bottom of the sedimentation separation tank 14 is discharged. Part of it is discharged and part of it is sent to the crystal growth tank 5 through the seed return pipe 21. The return pump 24 on the seed return pipe 21 provides power. The flow meter is used to measure the return flow rate. The flow meter can be an electromagnetic flow meter II 23. The shut-off valve IV 22 is used to control the return flow rate, which helps to control the reaction process in the crystal growth tank 5.

[0027] As a preferred embodiment of the present invention, see Figure 1 This embodiment is an improvement upon the above embodiment. The crystal growth tank 5 is equipped with a first stirrer 7 and a first temperature / pH sensor 9, while the sedimentation separation tank 14 is equipped with a second stirrer 16 and a second temperature / pH sensor 19. The stirrer accelerates the reaction process in the crystal growth tank 5 and the sedimentation separation tank 14. The temperature / pH sensor integrates temperature and pH detection; however, these sensors can also be separate. This invention does not impose specific limitations; the main requirement is the ability to detect the temperature and pH in the crystal growth tank 5 and the sedimentation separation tank 14 to control the reaction conditions.

[0028] As a preferred embodiment of the present invention, see Figure 1This embodiment is an improvement upon the above embodiment. The crystal growth tank 5 is provided with a first dosing port 8, and the sedimentation separation tank 14 is provided with a second dosing port 18. The first dosing port 8 and the second dosing port 18 facilitate the dosing of chemicals into these two tanks. Furthermore, a dual-tank dosing system 3 can be equipped to dosing chemicals into the crystal growth tank 5 and the sedimentation separation tank 14. The first dosing tank 13(a) of the dual-tank dosing system 3 is used to dosing chemicals into the crystal growth tank 5, and the second dosing tank 13(b) of the dual-tank dosing system 3 is used to dosing chemicals into the sedimentation separation tank 14.

[0029] As a preferred embodiment of the present invention, see Figure 1 This embodiment is an improvement on the above embodiment. The wastewater inlet of the composite absorption tower 32 is located at the bottom of the composite absorption tower 32. The bottom of the composite absorption tower 32 has a water distribution net 47. A clear water buffer layer 48 is formed between the water distribution net 47 and the bottom of the composite absorption tower 32. A modified alumina reaction layer 45 is provided above the water distribution net 47 in the composite absorption tower 32. A support plate I 43 is provided above the modified alumina reaction layer 45 in the composite absorption tower 32. An activated carbon filter layer 37 is provided above the support plate I 43 in the composite absorption tower 32. A support plate II 35 is provided above the activated carbon filter layer 37 in the composite absorption tower 32. A clear water layer 34 is provided above the support plate II 35 in the composite absorption tower 32. An outlet 33 is provided at the top of the clear water layer 34 in the composite absorption tower 32. In this embodiment, when the supernatant from the sedimentation separation tank 14 is sent to the composite absorption tower 32 for treatment through the outlet pipe 28, it is evenly distributed through the water distribution net 47 and flows from bottom to top through the modified alumina reaction layer 45. Under the action of hydroxyapatite modified activated alumina, the fluoride ion concentration drops to below 1.5 mg / L. The water then flows through the activated carbon filter layer 37, where residual fluoride ions are further adsorbed and suspended solids and organic matter are removed, so that the water meets the standards. The qualified water is finally discharged from the composite absorption tower 32.

[0030] As a preferred embodiment of the present invention, see Figure 1 This embodiment is an improvement on the above embodiment. The composite absorption tower 32 has a modified active alumina inlet 44 at the upper part of the modified alumina reaction layer 45 and a modified active alumina outlet 46 at the lower part of the modified alumina reaction layer 45. The modified active alumina outlet 46 has a modified active alumina pneumatic discharge valve 46a. By setting the modified active alumina inlet 44, the modified alumina reaction layer 45 can be fed and replenished. By setting the modified active alumina outlet 46, the modified alumina reaction layer 45 can be discharged. The modified active alumina pneumatic discharge valve 46a can control the timing of discharge. The composite absorption tower 32 has an activated carbon inlet 36 at the upper part of the activated carbon filter layer 37 and an activated carbon outlet 42 at the lower part of the activated carbon filter layer 37. The activated carbon outlet 42 is equipped with an activated carbon pneumatic discharge valve 42a. The activated carbon inlet 36 can be used to add and replenish the activated carbon filter layer 37, and the activated carbon outlet 42 can be used to discharge the activated carbon filter layer 37. The activated carbon pneumatic discharge valve 42a can control the timing of the discharge.

[0031] As a preferred embodiment of the present invention, see Figure 1 This embodiment is an improvement upon the above embodiment. The composite absorption tower 32 has a water sampling port 38 located above the activated carbon filter layer 37. The composite absorption tower 32 has a reflux tank 40 for receiving the water from the water sampling port 38, and an online fluoride monitor 39 for detecting water quality at the water sampling port 38. The reflux tank 40 is connected to the bottom of the modified alumina reaction layer 45 via a clean water return pipe 41. The wastewater treated by the activated carbon filter layer 37, which performs the final treatment of fluoride-containing wastewater, can be released through the water sampling port 38. The online fluoride monitor 39 detects fluoride ions in the water sample collected at the water sampling port 38. The water sample collected at the water sampling port 38 and the water sample detected by the online fluoride monitor 39 are collected in the reflux tank 40. The reflux tank 40 can return any substandard water samples to the modified alumina reaction layer 45 for treatment via the clean water return pipe 41, thus preventing environmental pollution after discharge.

[0032] As a preferred embodiment of the present invention, see Figure 1 , Figure 2 and Figure 3 This embodiment is an improvement upon the above embodiment. The opening ratio of the water distribution net 47 is 40%-50%, and uniformly distributed flow nozzles 47-a are evenly distributed on the water distribution net 47, with the nozzles of the uniformly distributed flow nozzles 47-a pointing upwards. The support plate I 43 adopts a porous structure with a pore size range of 0.1~0.5mm and an opening ratio of 30%~40%. The support plate II 35 adopts a hydrophilic modified composite ultrafiltration UF membrane made of PVDF material with a pore size of 1.5-2μm. The modified alumina reaction layer 45 is filled with hydroxyapatite modified activated alumina, and the particle size of the activated alumina carrier is 600~900μm, with a specific surface area of ​​200~300m². 2 / g; Activated carbon filter layer 37 is filled with microporous activated carbon with an iodine value ≥1000mg / g and a particle size ≤2nm.

[0033] As a preferred embodiment of the present invention, see Figure 1This embodiment is an improvement upon the above embodiment. An inlet pump II 29 is installed on the outlet pipe 28, and a flow meter and a shut-off valve VI 31 are installed on the outlet pipe 28 at the outlet side of the inlet pump II 29. The inlet pump II 29 pumps the supernatant from the sedimentation separation tank 14 into the composite absorption tower 32. The shut-off valve VI 31 on the outlet pipe 28 controls the flow rate of wastewater entering the composite absorption tower 32, and the flow meter can be used to detect the flow rate. Furthermore, an electromagnetic flow meter IV 30 can be used as the flow meter.

[0034] Example 1 like Figure 1 As shown, the induced crystallization defluorination device in this embodiment is equipped with a crystal growth tank 5, a precipitation separation tank 14, and a composite absorption tower 32.

[0035] The device is equipped with an inlet pipe. The raw water is pressurized by the inlet pump I1 and metered by the electromagnetic flowmeter I2 before being pumped into the crystal growth tank 5 and the sedimentation separation tank 14.

[0036] The crystal growth tank 5 is equipped with a first inlet 6, a first agitator 7, a first dosing interface 8, a first temperature / pH sensor 9, a shut-off valve III 10, a seed crystal guide pipe 11 and a seed crystal return pipe 21, a shut-off valve IV 22, an electromagnetic flow meter II 23, and a return pump 24. Specifically, the crystal growth tank 5 has a first inlet 6 at the top, a first agitator 6 at the center of the interior, a first dosing interface 8 on the side wall connecting to the dosing system, a built-in temperature / pH sensor 9 interlocked with an intelligent controller 12, and a seed crystal guide pipe 11 and a seed crystal return pipe 21 at the bottom. The seed crystal guide pipe 11 and the seed crystal return pipe 21 are connected to the lower end of the sedimentation separation tank 14. The seed crystal guide pipe 11 is equipped with a shut-off valve III 10, and the seed crystal return pipe 21 is equipped with a pneumatic shut-off valve IV 22, an electromagnetic flow meter II 23, and a return pump 24 in sequence.

[0037] The sedimentation separation tank 14 is equipped with a second inlet 15, a second agitator 16, an ultrasonic sludge level gauge 17, a second chemical dosing port 18, a second temperature / pH sensor 19, a multi-stage sieve-type crystallizing carrier 20, a sedimentation sludge discharge pipe 25, a shut-off valve V 26, an electromagnetic flowmeter III 27, an outlet pipe 28, an inlet pump II 29, an electromagnetic flowmeter IV 30, and a shut-off valve VI 31. Specifically, the shut-off valve V 26 and the electromagnetic flowmeter III 27 are located at the outlet at the bottom of the sedimentation separation tank 14, and the seed crystal return pipe 21 is connected to the outlet side of the electromagnetic flowmeter III 27. The sedimentation separation tank 14 is connected to the crystal growth tank 5. The sedimentation separation tank 14 is equipped with a second water inlet 15 at the top, a second agitator 16 at the center of the interior, an ultrasonic sludge level gauge 17 installed on the side wall, a multi-stage screening crystallization carrier 20 and a sedimentation sludge discharge pipe 25 at the bottom, and is equipped with a shut-off valve V 26 and an electromagnetic flow meter III 27. The second dosing port 18 on the side wall is connected to the dosing system. The built-in second temperature / pH sensor 19 is connected to the intelligent controller 12. The supernatant in the sedimentation separation tank 14 is connected to the lower end of the composite adsorption tower (i.e., composite absorption tower 32) through the water outlet pipe 28. The water outlet pipe 28 is equipped with a water inlet pump II 29, an electromagnetic flow meter IV 30, and a shut-off valve VI 31 in sequence.

[0038] The composite adsorption tower is equipped with an outlet 33, a clear water layer 34, a support plate II 35, an activated carbon inlet 36, an activated carbon filter layer 37, a water quality sampling port 38, an online fluoride monitor 39, a reflux box 40, a clear water reflux pipe 41, an activated carbon outlet 42, a support plate I 43, a modified activated alumina inlet 44, a modified alumina reaction layer 45, a modified activated alumina outlet 46, a water distribution network 47, and a clear water buffer layer 48. Specifically, the composite adsorption tower is located downstream of the sedimentation tank (i.e., sedimentation separation tank 14). The composite adsorption tower, from bottom to top, includes: a clear water buffer layer 48, a water distribution network 47, a modified alumina reaction layer 45, a support plate I 43, an activated carbon filter layer 37, a support plate II 35, and a clear water layer 34. The external functional interfaces of the composite adsorption tower unit include: a modified activated alumina inlet 44, a modified activated alumina outlet 46, an activated carbon inlet 36, an activated carbon outlet 42, a water quality sampling port 38, an online fluoride monitor 39, a reflux box 40, a clear water reflux pipe 41, and a water outlet 33.

[0039] Preferred, refer to Figure 1 In this embodiment, a split-flow water inlet is adopted. The raw water is metered by electromagnetic flowmeter I2 and then passes through a valve to achieve a precise 10%:90% split.

[0040] Preferred, refer to Figure 1In this embodiment, the diameter-to-height ratio of the crystal growth tank 5 and the sedimentation separation tank 13 is 1:2 to 1:4. The flow velocity in both tanks is controlled at 0.6-1.0 m / s, and the rotation speed of the first agitator 7 and the second agitator 16 is 100-200 r / min. The operating conditions for both tanks are pH 5.0-6.0 and temperature 25±0.5℃.

[0041] Preferred, refer to Figure 1 This embodiment is applicable to the treatment of high-fluoride wastewater with a fluoride concentration of 800-2500 mg / L and a pH of 2.5-6.5.

[0042] Preferred, refer to Figure 1 and Figure 4 In this embodiment, an ultrasonic sludge level gauge 17 is installed in the sedimentation separation tank to monitor the height of the cryolite sedimentation layer in real time. The multi-stage sieve crystallizing carrier 20, ultrasonic sludge level gauge 17, shut-off valve V 26, and electromagnetic flowmeter III 27 are connected to an intelligent controller 12. When the height reaches 30%–50% of the effective depth of the sedimentation separation tank 14, the intelligent controller 12 automatically controls the multi-stage sieve crystallizing carrier 20 to operate and the shut-off valve V 26 to open, thereby discharging the crystals from the sedimentation separation tank 14 through the sedimentation sludge discharge pipe 25. The sludge discharge time is controlled in a closed loop by feedback from the electromagnetic flowmeter III 27. The above control process is a conventional process, and this invention does not impose specific limitations.

[0043] Preferred, refer to Figure 1 and Figure 4 In this embodiment, the multi-stage sieve-type crystallization carrier 20 has an upper layer 20-a that is a vibrating corrugated sieve plate assembly (made of 316L stainless steel, with a pore size gradient of 40-60μm and an amplitude of 0.5-2.0mm); and a middle layer 20-b that is a surface-modified ceramic filler layer (treated with hydroxyapatite coating, with a specific surface area ≥500m²). 2 / m 3 The surface roughness Ra = 1.5-2.5μm); the lower layer 20-c is a conical mud collection cavity structure (the inclination angle is 30°-45°, and the inner wall is coated with wear-resistant polytetrafluoroethylene).

[0044] Preferred, refer to Figure 1 In this embodiment, the seed concentration in the crystal growth cell is 50-80 g / L, the flow rate of the seed guide tube 11 is 5-15 L / min, and the reflux ratio of the seed return tube 21 is 10%-30%.

[0045] Preferred, refer to Figure 1In this embodiment, the height of the modified alumina reaction layer 45 accounts for 30%-40%; the height of the activated carbon filter layer 37 accounts for 30%-40%; the height of the clear water layer 34 accounts for 20%-30%; a purified water outlet is provided at the top, wherein the horizontal center line of the purified water outlet is aligned with the middle position of the clear water layer; and the ratio of the outlet pipe diameter of the purified water outlet 33 to the tower diameter is 1:8-1:10.

[0046] Preferred, refer to Figure 1 In this embodiment, the modified alumina reaction layer 45 is filled with hydroxyapatite-modified activated alumina with a particle size of 600~900μm; the activated carbon filter layer 37 is filled with microporous activated carbon with an iodine value ≥1000mg / g and a particle size ≤2nm.

[0047] Preferred, refer to Figure 1 In this embodiment, the modified alumina inlet 44 and the activated carbon inlet 36 are located at approximately 2% of the total height of their respective packing layers in the composite absorption tower 32. Both adopt a 45° inclined upward feed pipe, with the length extending into the tower being 1 / 5 to 1 / 4 of the tower diameter. The activated carbon outlet 42 and the modified alumina outlet 46 are respectively located on the upper edge of the support plate I 43 and the water distribution net 47. Both are downward inclined conical material collection structures with a cone angle of 50±5°, with the pipe openings tilted downwards and equipped with pneumatic discharge valves 42a and 46a.

[0048] Preferred, refer to Figure 1 and Figure 2 In this embodiment, the clear water buffer layer of the composite absorption tower is provided with a multi-layer water distribution network 47 and a uniformly distributed flow nozzle 47-a. The opening rate of the multi-layer water distribution network plate is 40%-50%, and the spacing of the uniformly distributed flow nozzle is 2-3 times the nozzle diameter.

[0049] Preferred, refer to Figure 1 and Figure 3 In this embodiment, the support plate I 43 in the composite absorption tower adopts a high-precision stainless steel porous structure with a pore size range of 0.1~0.5mm and an open rate of 30%~40%. The support plate II 35 adopts a hydrophilic modified composite ultrafiltration (UF) membrane made of PVDF material with a pore size of 1.5-2μm.

[0050] Preferred, refer to Figure 1 In this invention, the modified alumina layer 45 is filled with hydroxyapatite-modified activated alumina, and the particle size of the activated alumina carrier is 600~900μm, with a specific surface area of ​​200~300m². 2 / g; In this embodiment of the invention, the diameter-to-height ratio of the crystal growth tank and the sedimentation separation tank is 1:2–1:4, and the operating conditions are controlled at pH 5.0–6.0 and temperature 25±0.5℃. The flow velocity in both tanks is 0.6–1.0 m / s, and the stirring speed is 100–200 r / min. The influent is high-fluoride wastewater with a fluoride concentration of 800–2500 mg / L and a pH of 2.5–6.5. An ultrasonic sludge level gauge is installed in the sedimentation separation tank, which is linked to an intelligent controller to monitor the height of the cryolite sedimentation layer in real time. When the height reaches 30%–50% of the effective height, sludge discharge is triggered, and automatic closed-loop control is achieved in conjunction with flow meter feedback. The multi-stage screening crystallization carrier consists of an upper layer of vibrating corrugated screen plate assembly (316L stainless steel, pore size 40–60 μm, amplitude 0.5–2.0 mm), and a middle layer of surface-modified ceramic filler (hydroxyapatite coating, specific surface area ≥500 m²). 2 / m 3 The surface roughness Ra is 1.5–2.5 μm. The lower layer is a conical sludge collection chamber (inclination angle 30°–45°, inner wall covered with a PTFE wear-resistant layer). The seed concentration in the crystal growth tank is 50–80 g / L, the seed conductivity is 5–15 L / min, and the reflux ratio is 10%–30%. The internal structure of the composite absorption tower consists of a modified alumina reaction layer (30%–40%), an activated carbon filter layer (30%–40%), and a clear water layer (20%–30%). The ratio of the purified water outlet pipe diameter to the tower diameter is 1:8–1:10. The modified alumina layer is filled with hydroxyapatite-modified alumina particles with a particle size of 600–900 μm and a specific surface area of ​​200–300 m². 2 / g, the activated carbon layer is filled with microporous activated carbon with an iodine value ≥1000mg / g and a pore size ≤2nm. The feed inlet in the composite absorption tower is located at approximately 2% of the total height of each packing layer, using a 45° inclined upward structure, with the length extending into the tower being 1 / 5–1 / 4 of the tower diameter; the discharge outlet is located at the upper edge of support plate I and the water distribution net, both of which are 50±5° downward inclined conical collection structures equipped with pneumatic valves. The clear water buffer layer is equipped with multiple layers of water distribution nets with an opening rate of 40%–50%, and the spray distance of the evenly distributed nozzles is 2–3 times the nozzle diameter. Support plate I is a stainless steel porous sieve plate with a pore size of 0.1–0.5mm and an opening rate of 30%–40%, while support plate II is a hydrophilic modified composite ultrafiltration (UF) membrane made of PVDF material with a pore size of 1.5–2μm.

[0051] Fluoride-containing wastewater is diverted by an influent pump and an electromagnetic flow meter, with 10% entering the crystal growth tank and the remainder entering the sedimentation separation tank. In the crystal growth tank, the dosing system adds sodium and aluminum salts at a molar ratio of Na:F:Al = 3:1:6, and the dosing flow rate is adjusted to 0.5-2.0 L / min by an intelligent controller. The intelligent controller also controls the temperature, pH, and the first agitator to form 20-50 μm supersaturated sodium fluoroaluminate seed crystals. After the seed crystals are mixed with the wastewater in the sedimentation separation tank, the intelligent controller adds the reagents a second time at the same ratio and starts the second agitator, causing the fluoride ions in the wastewater to react with the sodium fluoroaluminate seed crystals, inducing the formation of 50-100 μm high-purity cryolite (Na3AlF6) and reducing the fluoride ion concentration to 30 mg / L.

[0052] The induced cryolite is deposited on a multi-stage sieve crystallization carrier. An ultrasonic sludge level gauge monitors the height of the sedimentation layer in real time. When the height exceeds the set threshold, the intelligent controller controls the shut-off valves on the seed crystal return pipe and the sedimentation sludge discharge pipe, so that some of the 30-50μm cryolite is returned to the crystal growth tank, and the rest is discharged through the sedimentation sludge discharge pipe.

[0053] The supernatant from the sedimentation separation tank enters the clear water buffer layer of the composite absorption tower and is then evenly distributed through the water distribution mesh plate, flowing from bottom to top through the modified alumina reaction layer. Under the action of hydroxyapatite-modified activated alumina, the fluoride ion concentration drops to below 1.5 mg / L. After completing the second step of adsorption and defluorination, the water flows through the activated carbon layer, further adsorbing residual fluoride ions and removing suspended solids and organic matter. After water quality sampling, water that does not meet the standards is returned to the modified alumina layer for further treatment through the reflux device. Water that meets the standards enters the clear water buffer layer after deep filtration through support plate II and is finally discharged from the purified water outlet.

[0054] In summary, this invention, through a synergistic mechanism of "seedling-directed induction, enhanced circulation, and multi-stage adsorption purification," achieves efficient fluoride removal, stable operation, and resource utilization, resulting in significant environmental and economic benefits.

[0055] Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort should fall within the scope of protection of the present invention.

[0056] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the specific implementation of the present invention. Any modifications or equivalent substitutions that do not depart from the spirit and scope of the present invention should be covered within the protection scope of the claims of the present invention.

Claims

1. A device for induced crystallization and defluorination, characterized in that, The system includes a crystal growth tank (5), a sedimentation separation tank (14), and a composite absorption tower (32). The bottom of the crystal growth tank (5) is connected to the seed inlet of the sedimentation separation tank (14) through a seed guide pipe (11). A stop valve III (10) is provided on the seed guide pipe (11). The bottom of the sedimentation separation tank (14) is connected to the crystal growth tank (5) through a seed return pipe (21). A return pump (24), a flow meter, and a stop valve IV (23) are provided on the seed return pipe (21). The flow meter and the stop valve IV (23) are located on the outlet side of the return pump (24). The outlet of the sedimentation separation tank (14) is connected to the wastewater inlet of the composite absorption tower (32) through an outlet pipe (28).

2. The induced crystallization defluorination device according to claim 1, characterized in that, The sedimentation separation tank (14) is equipped with a multi-stage sieve-type crystallizing carrier (20) at the bottom. The upper layer of the multi-stage sieve-type crystallizing carrier (20) is a vibrating corrugated screen plate assembly with a pore size gradient of 40-60 μm. The middle layer of the multi-stage sieve-type crystallizing carrier (20) is a surface-modified ceramic packing layer coated with hydroxyapatite, with a specific surface area ≥500 m². 2 / m 3 The surface roughness Ra = 1.5-2.5μm; the lower layer of the multi-stage sieve crystallization carrier (20) is a conical mud collection cavity structure with an inclination angle of 30°-45°, and the inner wall is provided with a wear-resistant polytetrafluoroethylene coating.

3. The induced crystallization defluorination device according to claim 1, characterized in that, It also includes an inlet pump I (1), the outlet of which is equipped with an electromagnetic flow meter I (2), the outlet side of which is connected to the first inlet (6) of the crystal growth tank (5) through a first branch, and a shut-off valve I (3) is provided on the first branch; the outlet side of the electromagnetic flow meter I (2) is connected to the second inlet (15) of the sedimentation separation tank (14) through a second branch, and a shut-off valve II (4) is provided on the second branch.

4. The induced crystallization defluorination device according to claim 1, characterized in that, An ultrasonic sludge level gauge (17) is installed in the sedimentation separation tank (14) to measure the position of the sludge at the bottom of the sedimentation separation tank (14).

5. The induced crystallization defluorination device according to claim 1, characterized in that, The crystal growth tank (5) is equipped with a first stirrer (7) and a first temperature / pH sensor (9), and the sedimentation separation tank (14) is equipped with a second stirrer (16) and a second temperature / pH sensor (19).

6. The induced crystallization defluorination device according to claim 1, characterized in that, The crystal growth pool (5) is equipped with a first dosing interface (8).

7. The induced crystallization defluorination device according to claim 1, characterized in that, The wastewater inlet of the composite absorption tower (32) is located at the bottom of the composite absorption tower (32). The bottom of the composite absorption tower (32) has a water distribution net (47). A clear water buffer layer (48) is formed between the water distribution net (47) and the bottom of the composite absorption tower (32). A modified alumina reaction layer (45) is located above the water distribution net (47) in the composite absorption tower (32). A support plate I (43) is located above the modified alumina reaction layer (45) in the composite absorption tower (32). An activated carbon filter layer (37) is located above the support plate I (43) in the composite absorption tower (32). A support plate II (35) is located above the activated carbon filter layer (37) in the composite absorption tower (32). A clear water layer (34) is located above the support plate II (35) in the composite absorption tower (32). An outlet (33) is located at the top of the clear water layer (34) in the composite absorption tower (32).

8. A method for induced crystallization to remove fluoride, characterized in that, This method is carried out using the induced crystallization defluorination apparatus according to any one of claims 1-7, and includes the following processes: Fluorine-containing wastewater is added to the crystal growth tank (5) and the sedimentation separation tank (14); In the crystal growth pool (5), sodium and aluminum salts for generating sodium fluoroaluminate are added to form 20-50 μm supersaturated sodium fluoroaluminate seed crystals in the crystal growth pool (5). Sodium fluoroaluminate seed crystals in crystal growth tank (5) are sent into sedimentation separation tank (14) through seed crystal guide pipe (11). After the sodium fluoroaluminate seed crystals in sedimentation separation tank (14) are mixed with fluoride-containing wastewater, the fluoride ions in the fluoride-containing wastewater react with the sodium fluoroaluminate seed crystals to induce the formation of 50-100μm cryolite and reduce the fluoride ion concentration in sedimentation separation tank (14). After the cryolite induced in the sedimentation separation tank (14) is deposited to a preset height, part of the cryolite in the sedimentation separation tank (14) is returned to the crystal growth tank (5) through the seed return pipe (21), and the remaining cryolite in the sedimentation separation tank (14) is discharged through the sedimentation sludge discharge pipe of the sedimentation separation tank (14). The supernatant from the sedimentation separation tank (14) is sent to the composite absorption tower (32) through the outlet pipe (28) for further treatment to remove fluoride ions, suspended solids and organic matter, so that the water meets the standards. The qualified water is finally discharged from the composite absorption tower (32).

9. The method for induced crystallization and defluorination according to claim 8, characterized in that, The wastewater inlet of the composite absorption tower (32) is located at the bottom of the composite absorption tower (32). The bottom of the composite absorption tower (32) has a water distribution net (47). A clear water buffer layer (48) is formed between the water distribution net (47) and the bottom of the composite absorption tower (32). A modified alumina reaction layer (45) is located above the water distribution net (47) in the composite absorption tower (32). A support plate I (43) is located above the modified alumina reaction layer (45) in the composite absorption tower (32). An activated carbon filter layer (37) is located above the support plate I (43) in the composite absorption tower (32). A support plate II (35) is located above the activated carbon filter layer (37) in the composite absorption tower (32). A clear water layer (34) is located above the support plate II (35) in the composite absorption tower (32). An outlet (33) is located at the top of the clear water layer (34) in the composite absorption tower (32). When the supernatant from the sedimentation separation tank (14) is sent to the composite absorption tower (32) for treatment through the outlet pipe (28), it is evenly distributed through the water distribution network (47) and flows from bottom to top through the modified alumina reaction layer (45). Under the action of hydroxyapatite modified activated alumina, the fluoride ion concentration drops to below 1.5 mg / L. The water then flows through the activated carbon filter layer (37), where the activated carbon filter layer (37) further adsorbs residual fluoride ions and removes suspended solids and organic matter, so that the water meets the standards. The qualified water is finally discharged from the composite absorption tower (32).

10. A method for induced crystallization to remove fluoride according to claim 8 or 9, characterized in that, The operating conditions for the crystal growth tank (5) and the sedimentation separation tank (14) include: pH=5.0-6.0 and temperature of 24.5-25.5℃; The fluoride concentration in the fluoride-containing wastewater is 800-2500 mg / L, and the pH of the fluoride-containing wastewater is 2.5-6.5; The seed concentration in the crystal growth pool (5) ranges from 50 to 80 g / L.

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