System and method for recovering fluorides from fluoride-containing wastewater

Abstract

This application relates to the field of fluoride-containing wastewater treatment technology, and particularly to a system and method for recovering fluorides from fluoride-containing wastewater. The system includes a raw material zone, a sedimentation zone, and a detection zone. The raw material zone includes a first feeding unit for storing the fluoride-containing wastewater and a second feeding unit for storing a precipitant solution. The sedimentation zone includes a sedimentation chamber, and the detection zone includes a detection chamber, the bottom of which is connected to the top of the sedimentation chamber. Fluoride seed crystals are present in the sedimentation chamber. The first feeding unit delivers the fluoride-containing wastewater to the bottom of the sedimentation chamber, and the second feeding unit delivers the precipitant solution to the bottom of the sedimentation chamber. The fluoride-containing wastewater and the precipitant solution mix to form a mixed solution, which then reacts on the surface of the fluoride seed crystals to form fluoride crystals. The detection chamber is used by an operator to detect the fluoride content and turbidity in the mixed solution and to discharge the supernatant. When the reaction is complete, the fluoride crystals in the sedimentation chamber are removed. This system for recovering fluorides from fluoride-containing wastewater exhibits high fluoride recovery efficiency and quality.

Description

Technical Field

[0001] This application relates to the field of fluoride-containing wastewater treatment technology, and in particular to a system and method for recovering fluorides from fluoride-containing wastewater. Background Technology

[0002] Fluorine recovery and utilization from fluoride-containing wastewater generated in industrial manufacturing can not only reduce the harm of fluoride emissions but also promote the sustainable use of fluoride resources and reduce industrial dependence on raw fluoride extraction. Currently, fluoride wastewater treatment processes include coagulation sedimentation, adsorption technology, ion exchange, membrane technology, electrochemical technology, and fluidized bed crystallization. However, with increasingly stringent standards for fluoride recovery in industrial production and environmental treatment, the aforementioned processes and the equipment used are insufficient to meet the demands for high-efficiency and high-quality fluoride recovery. Summary of the Invention

[0003] In view of this, this application provides a system and method for recovering fluorides from fluoride-containing wastewater, which can solve at least one of the above-mentioned technical problems.

[0004] In a first aspect, this application provides a system for recovering fluorides from fluoride-containing wastewater, configured to recover fluorides from fluoride-containing wastewater. The system includes a raw material zone, a sedimentation zone, and a detection zone. The raw material zone includes a first feeding unit and a second feeding unit. The first feeding unit is configured to store the fluoride-containing wastewater. The second feeding unit is configured to store a precipitant solution. The sedimentation zone includes a sedimentation chamber, and the detection zone includes a detection chamber, the bottom of which is connected to the top of the sedimentation chamber. The sedimentation chamber contains fluoride seed crystals, and the first feeding unit is connected to the sedimentation chamber. The bottom surface of the bottom of the first feeding unit allows the fluorine-containing waste liquid to be transported to the sedimentation chamber. The second feeding unit is connected to the side of the bottom of the sedimentation chamber, allowing the precipitant solution to be transported to the sedimentation chamber and mixed with the fluorine-containing waste liquid to form a mixed solution. The fluorine-containing waste liquid and the precipitant solution in the mixed solution react on the surface of the fluoride seed crystals to continuously generate precipitates to form fluoride crystals. The detection chamber is configured to allow the detector to detect the fluorine content and turbidity in the mixed solution and to discharge the supernatant of the mixed solution. It is also configured to allow the detector to remove the fluoride crystals in the sedimentation chamber when the reaction is complete.

[0005] The system for recovering fluorides from fluoride-containing wastewater provided in this application involves feeding both the fluoride-containing wastewater and the precipitant solution from the bottom of the sedimentation chamber into the raw material zone. This allows the fluoride seed crystals to fluidize along the direction of fluid movement within the sedimentation chamber due to the lift of the fluid, forming a fluidized bed reaction site between the sedimentation zone and the detection zone. This fluidized bed reaction site can continuously maintain the suspended fluidized state of the fluoride seed crystals, increasing the solid-liquid contact area and inducing fluoride ions to precipitate with the precipitant solution on the surface of the fluoride seed crystals. Simultaneously, in conjunction with the detection chamber, the operator can detect the residual fluoride content of the mixed solution during the fluoride recovery process, facilitating the optimization of system process parameters to ensure that the fluoride content and turbidity of the mixed solution meet emission standards. Compared to conventional fluoride recovery methods, this system has higher fluoride recovery efficiency and recovery quality.

[0006] In some embodiments, a detection port is provided on the side of the bottom of the detection chamber. This detection port serves as a sampling window for the mixed solution, allowing the operator to detect the fluoride content and turbidity of the mixed solution within the detection chamber. The detection port enables continuous sampling during the precipitation process to detect the fluoride content and turbidity of the mixed solution, providing more accurate identification of the precipitation reaction's progress and facilitating the optimization of the recovery system's process parameters.

[0007] In some embodiments, an outlet is provided on the side of the top of the detection chamber. The outlet is configured to discharge the supernatant when the fluoride content and turbidity in the supernatant meet the discharge standards. The position of the outlet corresponds to the supernatant of the mixed solution, facilitating timely discharge of the supernatant from the detection chamber. The introduction of fluoride-containing waste liquid and precipitant solution into the sedimentation chamber promotes continuous precipitation reaction and improves the fluoride recovery efficiency.

[0008] In some embodiments, a feeding port is provided on the side of the bottom of the precipitation chamber. This feeding port is configured to allow a detector to remove the fluoride crystals when the reaction is complete, and to discharge the remaining mixed solution from the precipitation chamber and the detection chamber. Removing the grown fluoride crystals and discharging the fluoride-recovered mixed solution through the feeding port at the bottom of the precipitation chamber facilitates the treatment of the next batch of fluoride-containing wastewater, achieving high-efficiency fluoride recovery.

[0009] In some embodiments, the inner diameter r1 of the sedimentation chamber is smaller than the inner diameter r2 of the detection chamber. When the volumetric flow rates of the sedimentation chamber and the detection chamber are the same, meeting the above-mentioned inner diameter requirements ensures that the inlet flow rate of the detection chamber is lower than that of the sedimentation chamber. This allows the mixed solution in the detection chamber to settle for a longer period, providing suitable reaction time for the effective sedimentation and separation of fluoride seed crystals in the precipitate, thereby achieving efficient solid-liquid separation and fluoride ion recovery.

[0010] Secondly, this application provides a method for recovering fluorides from fluoride-containing wastewater based on the system for recovering fluorides from fluoride-containing wastewater according to any one of the first aspects, comprising the following steps: conveying fluoride-containing wastewater and a precipitant solution to a precipitation chamber and a detection chamber respectively, wherein the precipitation chamber contains fluoride seed crystals, and the fluoride-containing wastewater and the precipitant solution are mixed in the precipitation chamber to form a mixed solution, and the fluoride-containing wastewater and the precipitant solution in the mixed solution continuously generate precipitates on the surface of the fluoride seed crystals to form fluoride crystals; during the precipitation reaction, the fluoride content and turbidity in the mixed solution are sampled and detected through the detection chamber, and the supernatant of the mixed solution is discharged through the detection chamber; when the reaction is completed, the fluoride crystals in the precipitation chamber are removed.

[0011] The recycling method provided in this application has high fluoride recovery efficiency and high recovery quality.

[0012] In some embodiments, the molar ratio of calcium ions to fluoride ions in the mixed solution is 0.55-0.65. Controlling the molar ratio of calcium ions to fluoride ions within this range, according to stoichiometry, one part calcium... 2+ With two F - The formation of precipitates, with an excess of calcium ions, ensures that the precipitation reaction proceeds fully and completely, thereby maximizing the formation of the target precipitate and achieving efficient recovery of fluoride ions.

[0013] In some embodiments, the hydraulic residence time in the detection chamber is greater than that in the sedimentation chamber. Controlling the hydraulic residence time in the sedimentation chamber and the detection chamber helps ensure that the sedimentation reaction proceeds fully. Furthermore, the longer hydraulic residence time in the detection chamber allows for effective aggregation and settling of the precipitate generated in the supernatant of the mixed solution, facilitating the recovery of fluoride crystals from the precipitate and ensuring that the fluoride content of the mixed solution meets emission standards.

[0014] In some embodiments, the fluoride ion concentration of the fluoride-containing wastewater is 150 mg-F / L to 500 mg-F / L. Excessively high or low fluoride ion concentrations can easily lead to the formation of fine fluoride crystals, which are then discharged with the mixed solution, resulting in excessive fluoride content in the wastewater and a waste of fluoride resources. Controlling the mass concentration of the fluoride-containing wastewater within the above range helps maintain a suitable supersaturation, improves the removal rate, ensures system operational stability, and promotes the formation of dense, easily sedimenting fluoride crystals.

[0015] In some embodiments, the fluoride seed crystal is calcium fluoride, and the particle size of the calcium fluoride seed crystal is 100 μm-150 μm. A suitable fluoride seed crystal size can provide an effective precipitation surface area and active sites, thereby inducing the precipitate to crystallize orderly and rapidly on its surface, generating fluoride crystals with uniform particles, dense structure, and easy separation, ultimately improving the recovery rate and purity of fluoride ions. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of the system for recovering fluorides from fluoride-containing wastewater provided in this application.

[0017] Figure 2 This is a comparison chart of the fluorine recovery effects of Example 1 and Comparative Example 1 of this application.

[0018] Figure 3 This document describes the fluoride recovery from fluoride-containing waste liquid in Example 1 and Comparative Example 1 of this application.

[0019] Figure 4 This shows the diameter distribution of calcium fluoride crystals recovered at different times in Example 1 of this application.

[0020] Figure 5 The change of the median diameter (D50) of calcium fluoride crystals in Examples 1 and 2 of this application over time.

[0021] Figure 6 This is a morphology diagram of the calcium fluoride crystals recovered in Example 1 of this application.

[0022] Figure 7 The images show X-ray diffraction patterns of calcium fluoride crystals in Examples 1 and 2 and Comparative Examples 1 and 2 of this application.

[0023] Figure 8 The turbidity of the effluent containing fluoride in Example 1 and Comparative Example 1 of this application is shown.

[0024] Figure 9 This is a comparison chart of the fluorine recovery effects of Example 2 and Comparative Example 2 of this application.

[0025] Figure 10 This document describes the fluoride recovery from fluoride-containing waste liquid in Example 2 and Comparative Example 2 of this application.

[0026] Figure 11 This shows the diameter distribution of calcium fluoride crystals recovered at different times in Example 2 of this application.

[0027] Figure 12 The turbidity of the effluent containing fluoride in Example 2 and Comparative Example 2 of this application is shown.

[0028] Explanation of key component symbols: 10. A system for recovering fluorides from fluoride-containing wastewater; 1. Raw material area; 11. First feeding unit; 12. Second feeding unit; 13. First pipeline; 14. Second pipeline; 15. First feed pump; 16. Second feed pump; 2. Sedimentation zone; 21. Sedimentation chamber; 22. Feed outlet; 3. Detection area; 31. Detection chamber; 32. Detection port; 33. Water outlet. Detailed Implementation

[0029] The technical solutions of the embodiments of this application will be described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments.

[0030] To address the issue that existing fluoride recovery equipment cannot meet the current demand for high-quality recovery, please refer to... Figure 1 This application provides a system 10 for recovering fluorides from fluorine-containing wastewater, which has high fluoride recovery efficiency and high fluoride recovery quality.

[0031] The system 10 for recovering fluoride from fluoride-containing wastewater includes a raw material zone 1, a sedimentation zone 2, and a detection zone 3. The raw material zone 1 is used to store fluoride-containing wastewater and precipitant solution. The sedimentation zone 2 is used to provide a sedimentation site and collect sedimentation products. The detection zone 3 is used to detect whether the fluoride content of the effluent after fluoride recovery from the mixed solution formed by the fluoride-containing wastewater and precipitant solution meets the required standard. That is, through the cooperation of the three, a systematic fluoride recovery process of feeding, sedimentation, and detection is realized, and the resource recovery of fluoride is realized simultaneously in this process.

[0032] The raw material area 1 includes a first feeding unit 11 and a second feeding unit 12. The first feeding unit 11 is configured to store fluorine-containing waste liquid, and the second feeding unit 12 is configured to store precipitant solution. Both the first feeding unit 11 and the second feeding unit 12 can be tank structures. The arrangement position, quantity, and tank structure size of the first feeding unit 11 and the second feeding unit 12 can be selected according to actual needs. For example, only one first feeding unit 11 and one second feeding unit 12 can be set up, thereby reducing the arrangement space required for the raw material area 1. Alternatively, at least two first feeding units 11 and two feeding units 12 can be set up, so that the raw material area 1 can buffer a large amount of raw materials, achieve a continuous and stable supply of raw materials, and improve the fluoride recovery efficiency.

[0033] The precipitation zone 2 includes an elongated precipitation chamber 21 that extends approximately vertically. The detection zone 3 includes a detection chamber 31, the bottom of which is connected to the top of the precipitation chamber 21. Fluoride seed crystals can be introduced from the top of the detection chamber 31. The precipitation chamber 21 contains fluoride seed crystals. A first feeding unit 11 is connected to the bottom surface of the precipitation chamber 21 and is used to transport fluoride-containing waste liquid to the precipitation chamber 21. A second feeding unit 12 is connected to the side surface of the bottom of the precipitation chamber 21 and is used to transport a precipitant solution to the precipitation chamber 21 and mix it with the fluoride-containing waste liquid to form a mixed solution. Both the fluoride-containing waste liquid and the precipitant solution are injected from the bottom of the sedimentation chamber 21. When the mixed solution enters the sedimentation chamber 21, the liquid level rises from bottom to top, allowing the mixed solution to enter the detection chamber 31. The mixed solution can apply an upward fluid force to the fluoride seed crystals, and the fluoride seed crystals are lifted by the water flow to achieve fluidization. When the apparent velocity of the water flow is between the minimum fluidization velocity and the terminal settling velocity of the fluoride seed crystals, the fluoride seed crystals are suspended in the rising water flow. At this time, the fluoride-containing waste liquid and the precipitant solution in the mixed solution react on the surface of the fluoride seed crystals to generate new precipitates. The fluoride seed crystals continue to grow until they can overcome the drag force of the water flow and then settle to the bottom of the sedimentation chamber 21, thereby obtaining precipitated fluoride crystals.

[0034] This application does not limit the liquid level in detection chamber 31. During the deposition process, fluoride seed crystals in the precipitate continuously grow. As the system continues to operate, the concentration of fluoride ions in the effluent remains relatively stable for a certain period of time. That is, the mixed solution in detection chamber 31 is mainly the supernatant after fluoride recovery. This supernatant contains a small amount of fluoride ions and powdery fluoride particles flowing out with the supernatant. At this time, detection chamber 31 is configured for the inspector to sample and detect the fluoride content and turbidity in the mixed solution. When the fluoride content and turbidity meet the discharge requirements, the supernatant of the mixed solution is discharged. When the reaction is complete, the fluoride crystals in precipitation chamber 21 are removed. This application does not limit the discharge requirements for the mixed solution. For example, it can be from 1.0 mg-F / L to 10 mg-F / L, and can be selected according to local requirements and industry standards.

[0035] The system 10 provided in this application for recovering fluorides from fluoride-containing wastewater includes a raw material zone 1 where the fluoride-containing wastewater and precipitant solution are fed into the sedimentation chamber 21 from the bottom. This causes the fluoride seed crystals in the sedimentation chamber 21 to be fluidized along the direction of fluid movement due to the lift generated by the fluid flow. In other words, the sedimentation zone 2 and the detection zone 3 form a fluidized bed reaction site. This fluidized bed reaction site can continuously maintain the suspended fluidized state of the fluoride seed crystals, increasing the solid-liquid contact area and inducing fluoride ions and precipitant solution to form precipitates on the surface of the fluoride seed crystals. At the same time, in conjunction with the detection chamber 31, the operator can detect the residual fluoride content of the mixed solution during the fluoride recovery process, which facilitates the optimization of system process parameters to ensure that the fluoride content of the mixed solution meets the emission standards (e.g., fluoride content is less than 10 mg / L). Compared with conventional fluoride recovery methods, this system has higher fluoride recovery efficiency and fluoride recovery quality.

[0036] In some embodiments, a detection port 32 is provided on the side of the bottom of the detection chamber 31. The detection port 32 is configured to provide a sampling window for the mixed solution, allowing the operator to detect the fluoride content and turbidity of the mixed solution in the detection chamber 31 through the sampled sample. The setting of the detection port 32 allows for continuous sampling during the precipitation process to detect the fluoride content and turbidity of the mixed solution, more accurately identifying the progress of the precipitation reaction and facilitating the optimization of the process parameters of the recovery system.

[0037] In some embodiments, an outlet 33 is provided on the side of the top of the detection chamber 31. The outlet 33 is configured to discharge the supernatant when the fluoride content and turbidity in the supernatant meet the discharge standards. The position of the outlet 33 corresponds to the supernatant of the mixed solution, which facilitates the timely discharge of the supernatant in the detection chamber 31. Fluoride-containing waste liquid and precipitant solution are introduced into the sedimentation chamber 21, which is conducive to continuous precipitation reaction in the sedimentation chamber 21 and improves the fluoride recovery efficiency.

[0038] In some embodiments, a feeding port 22 is provided on the side of the bottom of the precipitation chamber 21. The feeding port 22 is configured to remove fluoride crystals through the feeding port 22 when the reaction is complete, and the remaining mixed solution in the precipitation chamber 21 and the detection chamber 31 is discharged from the feeding port 22. By removing the grown fluoride crystals and discharging the mixed solution after fluorine recovery through the feeding port 22 at the bottom of the precipitation chamber 21, the treatment process of the next batch of fluorine-containing waste liquid is facilitated, achieving high-efficiency recovery of fluorides.

[0039] In some embodiments, the inner diameter r1 of the sedimentation chamber 21 is smaller than the inner diameter r2 of the detection chamber 31. The mixed solution enters the detection chamber from the bottom of the sedimentation chamber 21 upwards. When the volumetric flow rates of the sedimentation chamber 21 and the detection chamber 31 are the same, satisfying the above-mentioned inner diameter requirement ensures that the inlet flow rate of the detection chamber 31 is lower than that of the sedimentation chamber 21. The mixed solution in the detection chamber 31 can undergo sedimentation for a longer period of time, providing a suitable reaction time for the effective sedimentation and separation of fluoride seed crystals in the precipitate, thereby achieving efficient solid-liquid separation and fluoride ion recovery.

[0040] In some embodiments, the raw material zone 1 further includes a first pipe 13 and a second pipe 14. The first pipe 13 is equipped with a first feed pump 15, and the second pipe 14 is equipped with a second feed pump 16. The first feed unit 11 is connected to the bottom surface of the sedimentation chamber 21 through the first pipe 13, and the first pipe 13 transports fluorine-containing waste liquid. The second feed unit 12 is connected to the side surface of the bottom of the sedimentation chamber 21 through the second pipe 14, and the second pipe 14 transports a precipitant solution. With the cooperation of the first feed pump 15 and the second feed pump 16, the instantaneous and cumulative dosage of the fluorine-containing waste liquid and the precipitant solution can be precisely controlled, ensuring real-time matching of the flow rate or fluorine content changes of the precipitant solution and the fluorine-containing waste liquid, thereby improving the fluorine recovery effect.

[0041] Secondly, this application provides a recovery method for a system 10 for recovering fluorides from fluoride-containing wastewater based on any one of the first aspects, comprising the following steps: In step S10, the fluorine-containing waste liquid and the precipitant solution are respectively transported to the precipitation chamber 21 and the detection chamber 31. The precipitation chamber 21 contains fluoride seed crystals, so that the fluorine-containing waste liquid and the precipitant solution are mixed in the precipitation chamber 21 to form a mixed solution, and the fluorine-containing waste liquid and the precipitant solution in the mixed solution continuously generate precipitates on the surface of the fluoride seed crystals to form fluoride crystals.

[0042] In step S20, during the precipitation reaction, the fluoride content and turbidity in the mixed solution are sampled and detected through the detection chamber 31, and the supernatant of the mixed solution is discharged through the detection chamber 31. When the reaction is completed, the fluoride crystals in the precipitation chamber 21 are removed.

[0043] In step S10, the molar ratio of calcium ions to fluoride ions in the mixed solution within the precipitation chamber 21 is 0.55-0.65. Optionally, the molar ratio of calcium ions to fluoride ions in the mixed solution can specifically be 0.55, 0.56, 0.57, 0.58, 0.59, 0.60, 0.61, 0.62, 0.63, 0.64, and 0.65, or any value or range within the above range. Controlling the molar ratio of calcium ions to fluoride ions to the above values, according to stoichiometry, one part of Ca... 2+ With two F -The formation of precipitates, with an excess of calcium ions, ensures that the precipitation reaction proceeds fully and completely, thereby maximizing the formation of the target precipitate and achieving efficient recovery of fluoride ions.

[0044] In step S10, the hydraulic residence time in detection chamber 31 is greater than that in sedimentation chamber 21. Controlling the hydraulic residence time of sedimentation chamber 21 and detection chamber 31 helps ensure the reaction proceeds fully. Furthermore, the longer hydraulic residence time in detection chamber 31 allows for effective aggregation and settling of the precipitate generated in the supernatant of the mixed solution, facilitating the recovery of fluoride crystals from the precipitate and ensuring that the fluoride content of the mixed solution meets emission standards. Optionally, the hydraulic residence time in sedimentation chamber 21 is 3 minutes, and the hydraulic residence time in detection chamber 31 is 24 minutes.

[0045] In some embodiments, the mass concentration of fluoride ions in the fluoride-containing wastewater is 150 mg-F / L to 500 mg-F / L. Optionally, the specific mass concentration of fluoride ions can be 150 mg-F / L, 200 mg-F / L, 250 mg-F / L, 300 mg-F / L, 350 mg-F / L, 400 mg-F / L, 450 mg-F / L, and 500 mg-F / L, or other values ​​within this range. Excessively high or low fluoride ion concentrations can easily lead to the formation of fine fluoride crystal particles, which are then discharged with the mixed solution, resulting in excessive fluoride content in the wastewater and a waste of fluoride resources. Controlling the mass concentration of the fluoride-containing wastewater within the above range helps maintain a suitable supersaturation, improves the removal rate and ensures the stability of system operation, promotes the formation of dense and easily sedimented fluoride crystal precipitates, and improves the quality of fluoride recovery.

[0046] In step S10, the fluoride seed crystal is calcium fluoride, and the particle size of the calcium fluoride seed crystal is 100μm-150μm. Optionally, the particle size of the calcium fluoride seed crystal can be 100μm, 110μm, 120μm, 130μm, 140μm, and 150μm, or other values ​​within this range. Using calcium fluoride as the seed crystal, corresponding to the type of target precipitate generated in the reaction, ensures that the precipitation process grows specific crystals with the required purity, crystal form, and particle size in the most controllable way with minimal energy consumption. Furthermore, the suitable fluoride seed crystal size provides an effective precipitation surface area and active sites, thereby inducing the precipitate to crystallize orderly and rapidly on its surface, generating uniform, dense, and easily separable fluoride precipitate crystals, ultimately improving the recovery rate and purity of the fluoride.

[0047] In step S10, the total influent flow rate of the sedimentation chamber 21 is 17.58 L / h, and the influent flow velocity is 14 m / h. The total influent flow rate is the sum of the first influent flow rate of the first feeding unit and the second influent flow rate of the second feeding unit, wherein the first influent flow rate is 16.6 L / h and the second influent flow rate is 0.98 L / h. By controlling the flow rate and velocity of the sedimentation chamber 21, it is beneficial to regulate the mixing and contact state and reaction time of the fluoride-containing waste liquid and the precipitant solution in the reaction system, so that the molar ratio of calcium ions to fluoride ions in the mixed solution is 0.55-0.65, thereby promoting the formation of a well-structured precipitate that is easy to separate subsequently.

[0048] In step S10, the height h1 of the precipitation chamber 21 is 70 cm and the inner diameter r1 is 2 cm; the height h2 of the detection chamber 31 is 35 cm and the inner diameter r2 is 8 cm. Controlling the dimensions of the precipitation chamber 21 and the detection chamber 31 provides suitable physical space and reaction time for the effective sedimentation and separation of the fluoride crystals in the precipitate, ensuring smooth flow during the transport of the mixed solution. The suitable space allows for sufficient contact between the solid and liquid, enabling the precipitant solution and fluoride ions to react fully and generate a precipitate. The generated fluoride crystals can aggregate and settle to the bottom of the precipitation chamber 21, thereby achieving efficient solid-liquid separation and fluoride ion recovery.

[0049] In step S20, the discharge of the supernatant continues as the precipitation reaction proceeds. That is, while the precipitant solution and fluorine-containing waste liquid are continuously transported to the precipitation chamber 21, the supernatant is also continuously discharged from the detection chamber 31.

[0050] In some embodiments, when the precipitation reaction continues and the fluoride seed crystals reach the recovery standard, new fluoride seed crystals need to be replaced. The recovery standard includes at least one of the following: whether the fluoride content in the mixed solution continues to rise; whether the crystal particle size of the precipitate exceeds a preset growth size; and whether the height of the precipitate layer exceeds a preset deposition height. For example, if the effluent fluoride concentration continues to rise (exceeding a set value), the system's fluoride recovery is poor, and new fluoride seed crystals with smaller particle sizes need to be replaced to restart the reaction; or, the bed pressure difference in the fluidized bed formed in the precipitation chamber 21 increases, and the fluidization resistance increases, indicating that the physical state of the fluoride seed crystals has changed adversely; or, the fluoride seed crystal particle size exceeds a certain size; or, the height of the precipitate layer formed at the bottom of the precipitation chamber 21 exceeds a preset deposition height.

[0051] In some embodiments, after the same system has undergone long-term and multiple fluoride recovery operations, the operating experience cycle can be determined based on data statistics and other methods. Once the system has reached the operating cycle, the grown fluoride seed crystals can be removed through the feed port 22 at the bottom of the precipitation chamber 21.

[0052] In some embodiments, the system for recovering fluorides from fluoride-containing wastewater of this application further includes additional defluorination equipment, which may be an ion exchange device or a coagulation and precipitation device, such that the defluorination equipment is configured to perform deep defluorination on the discharged mixed solution, thereby further reducing the fluoride concentration of the fluoride-containing wastewater.

[0053] The recycling method provided in this application has high fluoride recovery efficiency and high fluoride recovery quality.

[0054] In practical applications, the first feed pump 15 and the second feed pump 16 are turned on. The first feed pump 15 is controlled to allow the fluorine-containing waste liquid to enter the sedimentation chamber 21, and the second feed pump 16 is controlled to allow the precipitant solution to enter the sedimentation chamber 21 and mix with the fluorine-containing waste liquid to form a mixed solution. In the sedimentation chamber 21, the precipitant solution and fluoride ions form precipitates on the surface of fluoride seed crystals. The fluoride seed crystals grow continuously to obtain fluoride crystals, thus realizing the recovery of fluoride ions.

[0055] In some embodiments, effluent refers to the liquid or solid phase product that flows out after the waste liquid to be treated passes through a certain treatment unit or system. For example, in this application, effluent refers to the process of the mixed solution in the detection chamber 31 being discharged after precipitation to form a supernatant (containing a small amount of fluoride ions and powdered calcium fluoride particles flowing out with the supernatant). The effluent concentration includes the fluoride ion concentration in the effluent, the concentration of fluoride powder particles in the effluent, and the concentration of fluoride recovered by the feed port 22.

[0056] The solution of this application will be described below with reference to specific embodiments: Example 1: (1) Prepare a simulated fluoride waste liquid with a fluoride ion mass concentration of 250 mg-F / L using sodium fluoride and store it in the first feed unit 11. Prepare a precipitant solution with a calcium ion mass concentration of 5200 mg-Ca / L using calcium chloride and store it in the second feed unit 12.

[0057] (2) Add calcium fluoride seed crystals with a particle size of 100μm~150μm and an initial dosage of 30g from the top of the outlet 32, wherein the density of the calcium fluoride seed crystals is 3.18g / cm³. 3 .

[0058] (3) Turn on the first feed pump 15 and control the influent flow rate of the simulated fluoride waste liquid into the sedimentation chamber 21 to be 16.6 L / h and the influent velocity to be 14 m / h; turn on the second feed pump 16 and set the influent flow rate of the precipitant solution into the sedimentation chamber 21 to be 0.98 L / h, so as to achieve Ca in the mixed solution 2+ / F - The molar ratio is 0.6.

[0059] (4) The hydraulic residence time of the mixed solution in the sedimentation chamber 21 is 3 min and the hydraulic residence time of the mixed solution in the detection chamber 31 is 24 min. Under fluidized conditions, fluoride ions and calcium ions in the mixed solution come into contact on the surface of calcium fluoride seed crystals. Since the calcium fluoride seed crystals and the precipitate have the same crystal lattice structure, the ions tend to undergo heterogeneous nucleation on the existing crystal surface, and calcium fluoride precipitate is precipitated on the surface of the calcium fluoride seed crystals. Using the calcium fluoride seed crystals as templates, the calcium fluoride crystals are grown layer by layer along the seed direction. The fluoride concentration in the mixed solution is detected through the detection port 32, and the fluoride removal rate and fluoride recovery rate are calculated.

[0060] (5) Take out the calcium fluoride crystal and test the purity of the calcium fluoride on the calcium fluoride crystal.

[0061] Example 2: (1) The difference in Example 1 is that sodium fluoride is used to prepare a simulated fluoride waste liquid with a fluoride ion mass concentration of 150 mg-F / L, and calcium chloride is used to prepare a precipitant solution with a calcium ion mass concentration of 3200 mg-Ca / L. Other steps and parameters are the same as in Example 1.

[0062] Comparative Example 1: (1) The difference from Example 1 is that no calcium fluoride seed crystals are added in the precipitation chamber, and the other steps and parameters are the same as in Example 1.

[0063] Comparative Example 2: (1) The difference from Example 2 is that no calcium fluoride seed crystals are added in the precipitation chamber, and the other steps and parameters are the same as in Example 2.

[0064] Test results and analysis: With a hydraulic retention time of 3 minutes in the sedimentation zone and 24 minutes in the detection zone, refer to Figure 2 In Example 1, the fluoride ion concentration in the effluent was below 10 mg / L for the first 45 hours, with a removal rate of 96.6%, demonstrating excellent water purification and fluoride removal effects. (Refer to...) Figure 3 In Example 1, the fluoride recovery rate was approximately 51% in the first 45 hours (first stage), with approximately 45.7% of the fluoride being powdery fluoride particles suspended in the effluent. In the following 24 hours (second stage), as calcium fluoride seed crystals grew, the fluoride recovery rate increased to 84.8%. (Refer to...) Figure 4 and Figure 5 It can be seen that after the recovery system of Example 1 ran for 77 hours, the median diameter D50 of the recovered calcium fluoride crystals increased from 140.3 μm to 405.3 μm, and the maximum size reached approximately 850 μm. Figure 4 Furthermore, the volume of these calcium fluoride crystals is mostly larger than the added calcium fluoride seed crystals, indicating that the calcium fluoride precipitate grows on the surface of the calcium fluoride seed crystals. (Refer to...) Figure 6 Among them, (a) is the morphology of the original calcium fluoride seed crystal, (b) is the morphology of the calcium fluoride crystal recovered after 1 hour of treatment, (c) is the morphology of the calcium fluoride crystal recovered after 72 hours of treatment, and (d) is the morphology of the surface of the calcium fluoride crystal recovered after 72 hours. It can be seen that after the calcium fluoride seed crystal in Example 1 is placed in the precipitation chamber for 1 hour, its smooth surface becomes uneven, forming many square structures, which gradually evolve into spheres, and finally transform into larger crystals with a similar morphology to the original calcium fluoride seed crystal; in addition, referring to Figure 6 (d) The calcium fluoride crystal of Example 1 exhibits numerous voids containing growing crystals within its interior. These voids gradually form protruding spherical structures. This observation indicates that the calcium fluoride crystal of Example 1 will separate when its growth diameter reaches a critical threshold, and the movement under fluid action further enhances the separation and growth; and combined with Figure 7 As can be seen, X-ray diffraction analysis of the calcium fluoride crystals obtained in Example 1 confirmed the presence of calcium fluoride without impurity peaks. The calcium fluoride crystals recovered using calcium fluoride seeds had a purity as high as 92%, indicating high-quality fluoride recovery. Furthermore, referring to... Figure 8 In Example 1, the effluent turbidity continuously decreased during the first 54 hours of operation, reaching a minimum of approximately 30 NTU. Subsequently, the effluent turbidity began to rise, reaching 90 NTU at the 72nd hour. However, after the calcium fluoride crystal recovery was completed at the 72nd hour, the effluent turbidity rapidly decreased back to approximately 30 NTU. Figure 3 Two conclusions can be drawn: first, the reduction in effluent turbidity is significantly negatively correlated with the increase in fluoride recovery rate; second, timely recovery of calcium fluoride seed crystals is beneficial to stabilizing the effluent turbidity control, fluoride recovery effect, and fluoride recovery quality of this system.

[0065] With a hydraulic retention time of 3 minutes in the sedimentation zone and 24 minutes in the detection zone, refer to Figure 9 It was found that in Example 2, the fluoride concentration in the effluent after 96 hours was approximately 15-20 mg / L, with a removal rate between 86.7% and 90%. The fluoride removal effect fluctuated slightly compared to Example 1. (Refer to...) Figure 10 As can be seen, the recovery rate of fluoride in Example 2 was approximately 49.2% in the first 45 hours (first stage), and increased to 68.1% in the following 24 hours (second stage). Referring again... Figure 7 X-ray diffraction analysis of the precipitate obtained in Example 2 confirmed the presence of calcium fluoride without impurity peaks, and the purity of the crystals recovered using calcium fluoride seeds was as high as 92%. (Refer to...) Figure 11 It was found that the calcium fluoride crystal growth in Example 2 was slower than that in Example 1, and the growth tended to stabilize after 96 hours; the final median diameter D50 was 329.9 μm at 125 hours. (Refer to...) Figure 12It can be seen that the effluent turbidity of Example 2 basically showed a continuous decreasing trend during the 144 hours of operation, fluctuating between 30-35 NTU, and there was a negative correlation between effluent turbidity and fluoride recovery rate.

[0066] With a hydraulic retention time of 3 minutes in the sedimentation zone and 24 minutes in the testing zone, and then referring to... Figure 2 In Comparative Example 1, the fluoride concentration in the effluent after the first 45 hours was approximately 15 mg / L, with a removal rate of 90%, lower than the fluoride removal level in Example 1. This indicates that introducing calcium fluoride seed crystals can further improve the fluoride removal effect compared to not adding calcium fluoride seed crystals. (Reference) Figure 3 It can be seen that in Comparative Example 1, virtually no calcium fluoride crystals were effectively recovered in the first 45 hours (first stage) and the last 24 hours (second stage). Therefore, the fluoride recovery rate can be ignored. Figure 8 It was found that the reason for this situation is that over 85% of the calcium fluoride exists as powdery particles suspended in the effluent and is discharged from the reactor with the effluent, making recovery impossible. This indicates that adding calcium fluoride seed crystals can significantly improve the recovery of calcium fluoride crystals, rather than causing fluoride to be lost with the effluent as fluoride ions and fine powdery particles (crystals in a non-recoverable state, with low recovery value and not ideal products), resulting in fluoride waste. (See also...) Figure 7 It can be seen that the crystals recovered from the reactor in Comparative Example 1 showed a wider peak width than those in Example 1. This indicates that the calcium fluoride crystal deposits obtained in Example 1 have higher crystallinity, demonstrating that adding calcium fluoride seeds can effectively improve the crystallinity of the recovered calcium fluoride seeds.

[0067] With a hydraulic retention time of 3 minutes in the sedimentation zone and 24 minutes in the detection zone, refer to Figure 9 It can be seen that the fluoride concentration in the effluent of Comparative Example 2 in the first 96 hours was approximately 20 mg / L-25 mg / L, with a removal rate between 83.3% and 86.7%, slightly lower than the fluoride removal level of Example 2. This indicates that introducing calcium fluoride seeds can further improve the fluoride recovery effect compared to not adding calcium fluoride seeds. The calcium fluoride recovery rate in Comparative Example 2 was negligible in the first 45 hours (first stage) and the last 24 hours (second stage), with over 85% of the calcium fluoride existing as powdery particles suspended in the effluent. Figure 12 It was found that the reason for this situation is that over 85% of the calcium fluoride exists as powdery particles suspended in the effluent and is discharged from the reactor with the effluent, making recovery impossible. This indicates that adding calcium fluoride seed crystals can significantly improve the recovery of calcium fluoride crystals, rather than allowing fluoride to be lost with the effluent as fluoride ions and fine powdery particles (crystals in a non-recoverable state, with low recovery value and not ideal products), thus wasting fluoride. Meanwhile, referencing... Figure 7It can be seen that the crystals recovered in Comparative Example 2 showed a wider peak width than those in Example 2, which indicates that the calcium fluoride crystal deposits obtained in Example 2 have higher crystallinity, demonstrating that adding calcium fluoride seeds can effectively improve the crystallinity of the recovered calcium fluoride seeds.

[0068] Furthermore, those skilled in the art should recognize that the above embodiments are merely illustrative of this application and are not intended to limit this application. Any appropriate changes and variations made to the above embodiments within the essential spirit and scope of this application fall within the scope of this application's disclosure.

Claims

1. A system for recovering fluorides from fluoride-containing wastewater, configured to recover fluorides from fluoride-containing wastewater, characterized in that, The system for recovering fluorides from fluoride-containing waste liquid includes a raw material area, a sedimentation area, and a detection area; The raw material area includes a first feeding unit and a second feeding unit. The first feeding unit is configured to store the fluorine-containing waste liquid, and the second feeding unit is configured to store the precipitant solution. The precipitation zone includes a precipitation chamber, and the detection zone includes a detection chamber. The bottom end of the detection chamber is connected to the top end of the precipitation chamber. The precipitation chamber contains fluoride seed crystals. The first feeding unit is connected to the bottom surface of the precipitation chamber to transport the fluoride-containing waste liquid to the precipitation chamber. The second feeding unit is connected to the side surface of the bottom of the precipitation chamber to transport the precipitant solution to the precipitation chamber and mix it with the fluoride-containing waste liquid to form a mixed solution. The fluoride-containing waste liquid and the precipitant solution in the mixed solution react on the surface of the fluoride seed crystals to continuously generate precipitates to form fluoride crystals. The detection chamber is configured to allow the detector to detect the fluoride content and turbidity in the mixed solution and to discharge the supernatant of the mixed solution. It is also configured to allow the detector to remove the fluoride crystals in the precipitation chamber when the reaction is complete.

2. The system for recovering fluorides from fluoride-containing wastewater according to claim 1, characterized in that, The bottom side of the detection chamber is provided with a detection port, which is a sampling window for the mixed solution, so that the tester can detect the fluoride content and turbidity of the mixed solution in the detection chamber.

3. The system for recovering fluorides from fluoride-containing wastewater according to claim 2, characterized in that, The detection chamber has an outlet on the top side, which is configured to discharge the upper clear liquid when the fluoride content and turbidity in the upper clear liquid meet the discharge standards.

4. The system for recovering fluorides from fluoride-containing wastewater according to claim 1, characterized in that, The bottom side of the precipitation chamber is provided with a feeding port, which is configured to allow the tester to remove the fluoride crystals when the reaction is complete, and is also configured to discharge the remaining mixed solution in the precipitation chamber and the test chamber.

5. The system for recovering fluorides from fluoride-containing wastewater according to claim 1, characterized in that, The inner diameter of the precipitation chamber is smaller than the inner diameter of the detection chamber.

6. A method for recovering fluorides from fluoride-containing wastewater based on the system described in any one of claims 1-5, characterized in that, Includes the following steps: Fluorine-containing waste liquid and precipitant solution are respectively transported to a precipitation chamber and a detection chamber. The precipitation chamber contains fluoride seed crystals, so that the fluorine-containing waste liquid and the precipitant solution are mixed in the precipitation chamber to form a mixed solution. In the mixed solution, the fluorine-containing waste liquid and the precipitant solution continuously generate precipitates on the surface of the fluoride seed crystals to form fluoride crystals. During the precipitation reaction, the fluoride content and turbidity in the mixed solution are sampled and detected through the detection chamber, and the supernatant of the mixed solution is discharged through the detection chamber. When the reaction is complete, the fluoride crystals in the precipitation chamber are removed.

7. The recycling method according to claim 6, characterized in that, The molar ratio of calcium ions to fluoride ions in the mixed solution is 0.55-0.

65.

8. The recycling method according to claim 6, characterized in that, The hydraulic residence time in the detection chamber is greater than the hydraulic residence time in the sedimentation chamber.

9. The recycling method according to claim 6, characterized in that, The fluoride ion concentration in the fluoride-containing waste liquid is 150 mg-F / L to 500 mg-F / L.

10. The recycling method according to claim 6, characterized in that, The fluoride seed crystal is calcium fluoride, and the particle size of the calcium fluoride seed crystal is 100μm-150μm.

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