A method for defluoridation by induced crystallization of high-concentration fluoride wastewater

Abstract

This application relates to the field of industrial wastewater treatment and discloses a method for defluoridation by induced crystallization of high-concentration fluoride-containing wastewater. The method includes filling an induced crystal seed chamber inside a fluidized bed and setting a static bed height; mixing the high-concentration fluoride-containing raw water to be treated with an acid-base adjuster to adjust the pH and then adding the mixture to the inlet to obtain a raw water mixture system; separately introducing a calcium chloride solution into the mixture system; and controlling the upward flow load of the crystallization fluidized bed inner cylinder and the calcium content of the inlet water. 2+ / F ‑ The molar ratio induces a crystallization reaction between the fluoride-containing raw water and the calcium chloride solution in the seed mixing zone, resulting in defluorinated water discharged from the outlet. This application, by separating the feed and controlling the water flow load and influent molar ratio, avoids sedimentation clogging the pipeline, keeps supersaturation within the metastable region, and promotes preferential heterogeneous nucleation and continuous growth on the surface of the induced seed crystals. This reduces the amount of fluoride-containing sludge produced and improves operational stability.

Description

Technical Field

[0001] This application relates to the field of industrial wastewater treatment, specifically a method for induced crystallization of high-concentration fluoride-containing wastewater to remove fluoride. Background Technology

[0002] Industrial production processes often generate wastewater containing high concentrations of fluoride ions. Direct discharge of such wastewater without treatment can damage the ecological environment. Chemical precipitation is a commonly used process for treating high-concentration fluoride wastewater. This typically involves adding calcium salts to the wastewater, where calcium ions react with fluoride ions to form calcium fluoride precipitate, which is then removed through solid-liquid separation. With the development of water treatment technologies, fluidized bed crystallization technology has been introduced into the treatment of fluoride wastewater. This technology aims to utilize fluid dynamics to promote crystallization of the product on a carrier surface, thereby improving the settling performance of the product and reducing sludge volume.

[0003] Conventional induced crystallization processes for fluoride-containing wastewater have revealed several shortcomings in actual operation. In the dosing and influent stages, the conventional integrated mixing and feeding method causes premature contact between the high-concentration fluoride-containing raw water and the calcium source reagent in the influent pipeline, easily leading to direct precipitation and adhesion to the pipe walls, causing pipeline blockage. Simultaneously, the existing process lacks effective control over the system's supersaturation. The supersaturation of the reaction system easily exceeds the metastable region, resulting in a large number of homogeneous spontaneous nucleation phenomena, which in turn produce tiny, amorphous calcium fluoride flocs. These flocs are difficult to settle and separate, resulting in a large amount of fluoride-containing sludge and poor process stability.

[0004] Regarding reactor internal control and water quality conditioning, existing processes lack adequate design for the matching of seed crystal size and static bed height. This results in seed crystals failing to maintain a stable suspended fluidized state under water flow impact, easily leading to loss with the effluent or deposition and aggregation at the bottom. Furthermore, the lack of suitable hydraulic retention time and mass transfer space results in incomplete contact between raw water and reagents, easily causing fluoride ion penetration. In addition, existing acid-base conditioning methods often result in uneven mixing, leading to local pH gradients within the water body, or introducing complexing organic groups and interfering anions during the conditioning process, disrupting the homogeneous water environment required for the crystallization reaction. Therefore, optimizing the feeding and fluidized bed control methods for high-concentration fluoride-containing wastewater to avoid pipeline blockage, inhibit homogeneous nucleation, and improve the treatment efficiency of the induced crystallization process are problems that need to be solved in this field. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this application provides a method for defluorination by induced crystallization of high-concentration fluoride-containing wastewater, which solves the problems of easy clogging of the inlet pipe, difficulty in product sedimentation and separation, and large amount of fluoride-containing sludge generated in existing fluoride-containing wastewater treatment processes.

[0006] To address the above problems, this application provides the following technical solution:

[0007] This application provides a method for defluoridation of high-concentration fluoride-containing wastewater by induced crystallization, employing the following technical solution: A method for defluoridation of high-concentration fluoride-containing wastewater by induced crystallization includes the following steps: A crystallization fluidized bed with a preset bed layer is obtained by filling the fluidized bed with induced crystal seeds and setting the static bed height. The high-concentration fluoride-containing raw water to be treated is mixed with an acid-base regulator to adjust the pH, resulting in pH-adjusted fluoride-containing raw water. The pH-adjusted fluoride-containing raw water is then added to the inlet of the crystallization fluidized bed of the preset bed layer to obtain a raw water mixing system. A calcium chloride solution is separately introduced into the raw water mixing system. The rising water flow load inside the crystallization fluidized bed of the preset bed layer is controlled, and the dosage of the calcium chloride solution is adjusted to control the Ca content of the water entering the raw water mixing system. 2+ / F - The molar ratio induces the pH-adjusted fluoride-containing raw water and the calcium chloride solution to undergo an induced crystallization reaction in the seed mixing zone, resulting in reaction water. The reaction water is then discharged from the outlet at the top of the pre-set crystallization fluidized bed to obtain defluorinated water.

[0008] By adopting the above technical solution, the design of separating the high-concentration fluoride-containing raw water to be treated from the calcium chloride solution and feeding them separately into the crystallization fluidized bed avoids premature contact and precipitation of high-concentration fluoride ions and calcium ions in the inlet water delivery pipeline, thereby reducing the risk of pipeline blockage; and by controlling the rising water flow load and the Ca... 2+ / F - The molar ratio-induced crystallization process controls the supersaturation in the reaction system within the metastable region, allowing newly generated calcium fluoride to preferentially undergo heterogeneous nucleation and continuous growth on the surface of the fluidized induced seed crystals. This significantly inhibits the formation of tiny amorphous flocs from homogeneous spontaneous nucleation. As a result, the process achieves stable fluoride removal efficiency, produces dense calcium fluoride crystals that are easy to settle and separate, and significantly reduces the amount of fluoride-containing sludge generated, thereby improving the long-term operational stability of the water treatment process.

[0009] Preferably, in the step of filling the seed crystals and setting the height of the static bed, the particle size of the seed crystals is 100 to 120 mesh.

[0010] By adopting the above technical solution, the particle size of 100 to 120 mesh provides a suitable specific surface area to facilitate the attachment and growth of crystals, and also enables the particles to maintain fluidized mechanical balance under the rising water flow load, preventing the induced seed crystals from being lost with the water flow due to excessively small particle size, or the bottom deposition and hydraulic channeling phenomenon caused by excessively large particle size.

[0011] Preferably, in the step of filling the seed crystals and setting the height of the static bed, the height of the static bed is 38cm to 50cm.

[0012] By adopting the above technical solution and setting the static bed height to 38cm to 50cm, the bed can form a seed mixing zone with suitable hydraulic residence time and mass transfer space after the fluid impacts and expands upwards. This promotes the contact reaction between the calcium chloride solution and the high-concentration fluoride-containing raw water to be treated, reducing the fluoride ion penetration caused by incomplete mass transfer.

[0013] Preferably, before the step of mixing the high-concentration fluoride-containing raw water to be treated with an acid-base regulator to adjust the pH, the method further includes a step of preparing the high-concentration fluoride-containing raw water to be treated: mixing and stirring a deionized water stock solution containing sodium fluoride with basic tap water to obtain the high-concentration fluoride-containing raw water to be treated.

[0014] By adopting the above technical solution and introducing the basic tap water for raw water preparation, it is possible to introduce ions with coexisting background hardness and alkalinity to simulate the water system matrix of industrial fluoride-containing wastewater, and test the anti-interference ability of the induced crystallization defluorination method under specific water quality conditions.

[0015] Preferably, in the step of preparing the high-concentration fluoride-containing raw water to be treated, the initial concentration of fluoride ions in the high-concentration fluoride-containing raw water to be treated is 110 mg / L to 120 mg / L.

[0016] By adopting the above technical solution, the initial concentration of fluoride ions in the raw water is limited to 110 mg / L to 120 mg / L, covering the load range of high-concentration fluoride-containing wastewater. This allows the crystallization fluidized bed to maintain a suitable local supersaturation gradient at this concentration, thereby achieving stable crystal growth and reaction.

[0017] Preferably, in the step of preparing the high-concentration fluoride-containing raw water to be treated, the deionized water stock solution containing sodium fluoride is prepared by dissolving analytical grade sodium fluoride reagent in deionized water.

[0018] By adopting the above technical solution, the stock mother liquor is prepared using analytical grade sodium fluoride reagent and deionized water, which reduces the interference of impurity ions on the initial induced nucleation stage and facilitates the control of influent fluoride load and the stability of crystallization mechanism conditions.

[0019] Preferably, in the step of mixing the high-concentration fluoride-containing raw water to be treated with an acid-base regulator to adjust the pH, the acid-base regulator is hydrochloric acid or sodium hydroxide.

[0020] By adopting the above technical solution and using hydrochloric acid or sodium hydroxide as the acid-base regulator, it is possible to avoid introducing organic groups with complexing effects or interfering anions, and adjust the high-concentration fluoride-containing raw water to be treated to a suitable pH environment for inducing crystallization.

[0021] Preferably, in the step of mixing the high-concentration fluoride-containing raw water to be treated with an acid-base regulator to adjust the pH, the high-concentration fluoride-containing raw water to be treated is mixed with the hydrochloric acid or sodium hydroxide in a static mixer to adjust the pH.

[0022] By adopting the above technical solution, the continuous fluid deflection and shearing action inside the static mixer is used to achieve uniform mixing of the high-concentration fluoride-containing raw water to be treated and the acid-base regulator in the closed pipeline, thereby reducing the local pH gradient difference of the water and improving the uniformity of acid-base conditions when it enters the crystallization fluidized bed reaction zone.

[0023] Preferably, the Ca introduced into the controlled raw water mixing system 2+ / F - In the molar ratio step, the dosage of the calcium chloride solution is adjusted to control the Ca content of the water entering the raw water mixing system. 2+ / F - The molar ratio is 0.5 to 2.0.

[0024] By adopting the above technical solution, the molar ratio of the reaction system is controlled in the range of 0.5 to 2.0, which not only maintains a suitable calcium ion concentration to provide thermodynamic driving force for the growth of calcium fluoride crystals, but also avoids excessive local calcium ions from causing the supersaturation to exceed the upper limit of the metastable region and triggering homogeneous spontaneous nucleation, thus maintaining the compactness of the product structure.

[0025] Preferably, in the step of controlling the rising water flow load of the inner cylinder of the crystallization fluidized bed in the preset bed, the rising water flow load of the inner cylinder of the crystallization fluidized bed in the preset bed is controlled to be 10 m / h.

[0026] By adopting the above technical solution, the rising water flow load of 10 m / h provides suitable fluid kinetic energy and shear force, enabling the induced seed crystals to overcome gravity and remain in a suspended fluidized state; at the same time, the fluid shear force can continuously peel off the hydration bonding layer attached to the crystal surface, promote the mass transfer and diffusion of internal ions, and prevent the aggregation and agglomeration of particles.

[0027] This application provides a method for defluoridation of high-concentration fluoride-containing wastewater by induced crystallization. It has the following beneficial effects: 1. This application involves adding pH-adjusted fluoride-containing raw water to the inlet and separately introducing calcium chloride solution into the raw water mixing system, combined with controlling the rising water flow load of the crystallizing fluidized bed inner cylinder and the calcium content of the inlet water. 2+ / F- The molar ratio avoids precipitation caused by contact between fluoride-containing raw water and calcium ions in the inlet pipe, which could lead to pipe blockage. It controls the supersaturation within the metastable region, promoting preferential heterogeneous nucleation and continuous growth of fluoride-containing raw water and calcium chloride solution on the surface of induced crystals in the fluidized state. This inhibits the formation of tiny amorphous flocs from spontaneous homogeneous nucleation, resulting in a dense product that is easy to settle and separate. This reduces the amount of fluoride-containing sludge produced and improves the operational stability of the process.

[0028] 2. This application fills the inside of the crystallization fluidized bed with induced crystals of controlled particle size and sets the height of the static bed layer. In conjunction with controlling the rising water flow load inside the crystallization fluidized bed, it provides a suitable specific surface area for attachment and growth of the induced crystallization reaction. This allows the induced crystals to overcome gravity and maintain a stable suspended fluidized state to prevent loss or deposition and aggregation. After the bed expands, a crystal mixing zone with suitable hydraulic residence time and mass transfer space is formed. This promotes the contact between the raw water mixing system and the calcium chloride solution in the crystal mixing zone to induce crystallization reaction, reduces the risk of fluoride ion penetration due to incomplete mass transfer, and improves the defluorination efficiency of the reaction water.

[0029] 3. This application adjusts the pH of the high-concentration fluoride-containing raw water to be treated by mixing it with hydrochloric acid or sodium hydroxide as an acid-base regulator in a static mixer. By utilizing the continuous fluid deflection and shearing action inside the static mixer, uniform mixing of the fluoride-containing raw water and the acid-base regulator is achieved in a closed pipeline. This reduces the local pH gradient difference of the water body, avoids the introduction of complexed organic groups or interfering anions that may interfere with the crystallization nucleation stage, and ensures the uniformity of the pH conditions inside the reaction system when it enters the crystallization fluidized bed. This provides a stable water quality environment for inducing heterogeneous nucleation on the surface of the crystal seeds and improves the overall treatment effect of the crystallization fluidized bed. Attached Figure Description

[0030] Figure 1 This is a schematic diagram of the defluorination device pipeline structure in the embodiments of this application; Figure 2 For different static bed heights in Test Example 1 of this application, F - Removal rate varies with Ca 2+ / F - Graph showing the change in molar ratio; Figure 3 For different static bed heights in Test Example 1 of this application, F - The rate of change of removal rate with Ca 2+ / F - Graph showing the relationship between molar ratio changes.

[0031] The components include: 1. Fluoride-containing water tank; 2. Valve; 3. First peristaltic pump; 4. Static mixer; 5. CaCl2 reagent tank; 6. Second peristaltic pump; 7. Crystallization fluidized bed; 8. Water inlet; 9. Water outlet. Detailed Implementation

[0032] The technical solutions in the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments in this application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of this application.

[0033] The defluorination device pipeline structure used in the various embodiments and test examples of this application is as follows: Figure 1 As shown, the device mainly includes: a fluoride-containing water tank 1 connected sequentially to the inlet of the crystallization fluidized bed 7 via a valve 2, a first peristaltic pump 3, and a static mixer 4; a CaCl2 reagent tank 5 connected separately to the inlet at the bottom of the crystallization fluidized bed 7 via a second peristaltic pump 6; and a water inlet 8 and an outlet 9 on the top outlet pipe of the crystallization fluidized bed 7. Subsequent embodiments and test examples are all based on this device structure and corresponding experimental operations are carried out.

[0034] Preparation Examples 1-3: Preparation Example 1: This preparation example provides a high-concentration fluoride-containing simulated raw water, including the following steps: Weigh out analytical grade sodium fluoride reagent, dissolve it in deionized water prepared by ultrapure water equipment, and prepare a deionized water stock solution containing sodium fluoride for later use.

[0035] Take an appropriate amount of the prepared deionized water stock solution containing sodium fluoride and add it to the base tap water for mixing. The base tap water has the following water quality parameters: calcium hardness 68.00 mg / L, total hardness 86.00 mg / L, alkalinity 65.00 mg / L, turbidity 0.10 NTU, and pH 7.60.

[0036] The mixed water was thoroughly stirred to ensure uniform mixing, thus preparing a high-concentration fluoride-containing raw water for treatment. Testing confirmed that the initial fluoride ion concentration in the prepared influent was stable at 110 mg / L, and it was stored in the fluoride-containing water tank 1.

[0037] Preparation Example 2: This preparation example provides a high-concentration fluoride-containing simulated raw water, including the following steps: Weigh out analytical grade sodium fluoride reagent, dissolve it in deionized water prepared by ultrapure water equipment, and prepare a deionized water stock solution containing sodium fluoride for later use.

[0038] Take an appropriate amount of the prepared deionized water stock solution containing sodium fluoride and add it to the base tap water for mixing. The base tap water has the following water quality parameters: calcium hardness 68.00 mg / L, total hardness 86.00 mg / L, alkalinity 65.00 mg / L, turbidity 0.10 NTU, and pH 7.60.

[0039] The mixed water was thoroughly stirred to ensure uniform mixing, thus preparing a high-concentration fluoride-containing raw water for treatment. Testing confirmed that the initial fluoride ion concentration in the prepared influent was stable at 115 mg / L, and it was stored in the fluoride-containing water tank 1.

[0040] Preparation Example 3: This preparation example provides a high-concentration fluoride-containing simulated raw water, including the following steps: Weigh out analytical grade sodium fluoride reagent, dissolve it in deionized water prepared by ultrapure water equipment, and prepare a deionized water stock solution containing sodium fluoride for later use.

[0041] Take an appropriate amount of the prepared deionized water stock solution containing sodium fluoride and add it to the base tap water for mixing. The base tap water has the following water quality parameters: calcium hardness 68.00 mg / L, total hardness 86.00 mg / L, alkalinity 65.00 mg / L, turbidity 0.10 NTU, and pH 7.60.

[0042] The mixed water was thoroughly stirred to ensure uniform mixing, thus preparing a high-concentration fluoride-containing raw water for treatment. Testing confirmed that the initial fluoride ion concentration in the prepared influent was stable at 120 mg / L, and it was stored in the fluoride-containing water tank 1.

[0043] Examples 1-6: Example 1: This embodiment provides a method for defluoridation of high-concentration fluoride-containing wastewater by induced crystallization, comprising the following steps: S1. Fill the crystallization fluidized bed 7 with a height of 1.2m and a diameter of 5cm with induced crystal seeds with a particle size of 100 mesh, and set the static bed height to 38cm; S2. The raw water of Preparation Example 1 stored in the fluoride-containing water tank 1 is transported through valve 2 and first peristaltic pump 3, mixed with hydrochloric acid or sodium hydroxide in static mixer 4 to adjust the pH, and then added to the inlet of the crystallization fluidized bed 7. S3. The calcium chloride solution in the CaCl2 tank 5 is introduced separately from the bottom of the crystallization fluidized bed 7 via the second peristaltic pump 6. The upward water flow load inside the crystallization fluidized bed 7 is controlled at 10 m³ / h. The dosage of calcium chloride is adjusted to ensure that the influent CaCl2 solution in the system is within acceptable limits. 2 + / F -The molar ratio is 0.5; the fluoride-containing raw water and the calcium-containing reagent are in full contact in the seed mixing zone, and an induced crystallization reaction occurs, and then the water is discharged from the outlet 9 at the top of the crystallization fluidized bed 7.

[0044] Example 2: This embodiment provides a method for defluoridation of high-concentration fluoride-containing wastewater by induced crystallization, comprising the following steps: S1. Fill the crystallization fluidized bed 7 with a height of 1.2m and a diameter of 5cm with induced crystal seeds with a particle size of 110 mesh, and set the static bed height to 38cm. S2. The raw water of Preparation Example 2 stored in the fluoride-containing water tank 1 is transported through valve 2 and first peristaltic pump 3, mixed with hydrochloric acid or sodium hydroxide in static mixer 4 to adjust the pH, and then added to the inlet of the crystallization fluidized bed 7. S3. The calcium chloride solution in the CaCl2 tank 5 is introduced separately from the bottom of the crystallization fluidized bed 7 via the second peristaltic pump 6. The upward water flow load inside the crystallization fluidized bed 7 is controlled at 10 m³ / h. The dosage of calcium chloride is adjusted to ensure that the influent CaCl2 solution in the system is within acceptable limits. 2 + / F - The molar ratio is 0.65; the fluoride-containing raw water and the calcium-containing reagent are in full contact in the seed mixing zone, and an induced crystallization reaction occurs, and then the water is discharged from the outlet 9 at the top of the crystallization fluidized bed 7.

[0045] Example 3: This embodiment provides a method for defluoridation of high-concentration fluoride-containing wastewater by induced crystallization, comprising the following steps: S1. Fill the crystallization fluidized bed 7 with a height of 1.2m and a diameter of 5cm with induced crystal seeds with a particle size of 120 mesh, and set the static bed height to 38cm. S2. The raw water of Preparation Example 3 stored in the fluoride-containing water tank 1 is transported through valve 2 and first peristaltic pump 3, mixed with hydrochloric acid or sodium hydroxide in static mixer 4 to adjust the pH, and then added to the inlet of the crystallization fluidized bed 7. S3. The calcium chloride solution in the CaCl2 tank 5 is introduced separately from the bottom of the crystallization fluidized bed 7 via the second peristaltic pump 6. The upward water flow load inside the crystallization fluidized bed 7 is controlled at 10 m³ / h. The dosage of calcium chloride is adjusted to ensure that the influent CaCl2 solution in the system is within acceptable limits. 2 + / F - The molar ratio is 0.8; the fluoride-containing raw water and the calcium-containing reagent are fully in contact in the seed mixing zone, and an induced crystallization reaction occurs, and then the water is discharged from the outlet 9 at the top of the crystallization fluidized bed 7.

[0046] Example 4: This embodiment provides a method for defluoridation of high-concentration fluoride-containing wastewater by induced crystallization, comprising the following steps: S1. Fill the crystallization fluidized bed 7 with a height of 1.2m and a diameter of 5cm with induced crystal seeds with a particle size of 100 mesh, and set the static bed height to 50cm. S2. The raw water of Preparation Example 1 stored in the fluoride-containing water tank 1 is transported through valve 2 and first peristaltic pump 3, mixed with hydrochloric acid or sodium hydroxide in static mixer 4 to adjust the pH, and then added to the inlet of the crystallization fluidized bed 7. S3. The calcium chloride solution in the CaCl2 tank 5 is introduced separately from the bottom of the crystallization fluidized bed 7 via the second peristaltic pump 6. The upward water flow load inside the crystallization fluidized bed 7 is controlled at 10 m³ / h. The dosage of calcium chloride is adjusted to ensure that the influent CaCl2 solution in the system is within acceptable limits. 2 + / F - The molar ratio is 1.0; the fluoride-containing raw water and the calcium-containing reagent are fully in contact in the seed mixing zone, and an induced crystallization reaction occurs, and then the water is discharged from the outlet 9 at the top of the crystallization fluidized bed 7.

[0047] Example 5: This embodiment provides a method for defluoridation of high-concentration fluoride-containing wastewater by induced crystallization, comprising the following steps: S1. Fill the crystallization fluidized bed 7 with a height of 1.2m and a diameter of 5cm with induced crystal seeds with a particle size of 110 mesh, and set the static bed height to 50cm. S2. The raw water of Preparation Example 2 stored in the fluoride-containing water tank 1 is transported through valve 2 and first peristaltic pump 3, mixed with hydrochloric acid or sodium hydroxide in static mixer 4 to adjust the pH, and then added to the inlet of the crystallization fluidized bed 7. S3. The calcium chloride solution in the CaCl2 tank 5 is introduced separately from the bottom of the crystallization fluidized bed 7 via the second peristaltic pump 6. The upward water flow load inside the crystallization fluidized bed 7 is controlled at 10 m³ / h. The dosage of calcium chloride is adjusted to ensure that the influent CaCl2 solution in the system is within acceptable limits. 2 + / F - The molar ratio is 1.5; the fluoride-containing raw water and the calcium-containing reagent are fully in contact in the seed mixing zone, and an induced crystallization reaction occurs, and then the water is discharged from the outlet 9 at the top of the crystallization fluidized bed 7.

[0048] Example 6: This embodiment provides a method for defluoridation of high-concentration fluoride-containing wastewater by induced crystallization, comprising the following steps: S1. Fill the crystallization fluidized bed 7 with a height of 1.2m and a diameter of 5cm with induced crystal seeds with a particle size of 120 mesh, and set the static bed height to 50cm. S2. The raw water of Preparation Example 3 stored in the fluoride-containing water tank 1 is transported through valve 2 and first peristaltic pump 3, mixed with hydrochloric acid or sodium hydroxide in static mixer 4 to adjust the pH, and then added to the inlet of the crystallization fluidized bed 7. S3. The calcium chloride solution in the CaCl2 tank 5 is introduced separately from the bottom of the crystallization fluidized bed 7 via the second peristaltic pump 6. The upward water flow load inside the crystallization fluidized bed 7 is controlled at 10 m³ / h. The dosage of calcium chloride is adjusted to ensure that the influent CaCl2 solution in the system is within acceptable limits. 2 + / F - The molar ratio is 2.0; the fluoride-containing raw water and the calcium-containing reagent are in full contact in the seed mixing zone, and an induced crystallization reaction occurs, and then the water is discharged from the outlet 9 at the top of the crystallization fluidized bed 7.

[0049] Comparative Examples 1-2: Comparative Example 1: Compared with Example 2, the difference is that the height of the static bed layer is set to 25cm, while the other parameters and steps are the same.

[0050] Comparative Example 2: Compared with Example 5, the difference is that the height of the static bed layer is set to 38cm, while the other parameters and steps are the same.

[0051] Test Example 1: Experimental description: Investigating different influent Ca 2+ / F - The specific influence of the combination of molar ratio and static bed height on the defluorination efficiency and reagent utilization rate of crystallizing fluidized bed.

[0052] Experimental steps: During the system operation tests of each embodiment and comparative example, samples were taken and measured every 30 minutes at the inlet of the crystallizing fluidized bed 7 and the outlet 8 of the pipeline. Ca in water samples was determined using atomic absorption spectrometry and EDTA titration. 2+ Concentration was determined by using an ion meter to detect F in the water sample. - concentration; The pH and turbidity of the water samples were measured using a pH meter and a turbidity meter, respectively. The supersaturation of CaF2 in the system was calculated based on the measured ion concentration. The calculation is based on: ; in, This indicates the degree of supersaturation of CaF2 in the solution; Indicates the amount of Ca in the solution 2+ The concentration is expressed in mol / L. Indicates F in the solution- The concentration is expressed in mol / L. Let be the solubility product constant of CaF2 at 25℃. The value is 10 10.31 .

[0053] Experimental data: Table 1. Parameters and Effect Data of Fluidized Bed Defluorination Process

[0054] Note: "-" in the table indicates that this data item was not included in the statistics for this test group.

[0055] Experimental conclusion: Combination Figure 2 Monitoring data shows that in the influent Ca 2+ / F - Under conditions where the molar ratio is ≤0.8, the height of the static bed significantly affects the defluorination effect. Comparing the test results of Comparative Example 1 with Examples 1 to 3, when the static bed height is 25 cm, the F... - The overall removal rate was low; after increasing the height of the static bed to 38cm, F - The removal rate showed a significant increase. (From...) Figure 2 The changing trend shows that within this molar ratio range, the treatment effects of a 38cm bed and a 50cm bed are basically the same, indicating that increasing the bed thickness has a limited effect on improving the defluorination rate under this condition, and a 38cm bed can meet the contact requirements for sufficient crystallization.

[0056] Combination Figure 3 The change curve shows that when the influent Ca 2+ / F - When the molar ratio is >0.8, F - The rate of change in removal rate decreased to below 20. At this point, Ca... 2+ / F - molar ratio relative to F - The influence of removal rate weakens, and the height of the stagnant bed becomes the main factor affecting defluorination efficiency. This is due to the increased supersaturation within the system and the presence of free Ca in the water. 2+ The content increases accordingly, combined with Figure 2 The results of Comparative Examples 2 and Examples 4 to 6 show that, compared to a 38cm static bed, a 50cm static bed increases the effective contact area between free ions and the crystal surface, providing more heterogeneous nucleation and crystal growth sites. This increased contact area can meet the crystallization requirements under high supersaturation conditions, promoting the formation of F... - The removal rate is significantly improved, with the highest removal rate reaching 89%.

[0057] Furthermore, data from Examples 4 to 6 show that F in the fluidized bed effluent - With Ca 2+ The removal molar ratio remained consistently above 2. This indicates that, under conditions of increased bed height and high calcium agent dosage, the added calcium salts in the system were completely consumed. The reaction process promoted the conversion of free ions into CaF2 crystals and their attachment to the seed crystal surface, avoiding the problem of large amounts of high-moisture sludge caused by excessive reagents in conventional precipitation methods, thus ensuring the stable defluorination performance of the fluidized bed system.

Claims

1. A method for defluoridation of high-concentration fluoride-containing wastewater by induced crystallization, characterized in that, Includes the following steps: Induced crystal seeds are filled inside the crystallization fluidized bed (7) and the static bed height is set to obtain a crystallization fluidized bed with a preset bed layer; The high-concentration fluoride-containing raw water to be treated is mixed with an acid-base regulator to adjust the pH, resulting in pH-adjusted fluoride-containing raw water. The pH-adjusted fluoride-containing raw water is then added to the inlet of the crystallization fluidized bed of the preset bed layer to obtain a raw water mixing system. The calcium chloride solution is separately introduced into the raw water mixing system, the upflow water load on the inner cylinder of the preset bed crystallization fluidized bed is controlled, the addition amount of the calcium chloride solution is adjusted, the Ca 2+ / F - The molar ratio is used to make the pH-adjusted raw water containing fluorine fully contact with the calcium chloride solution in the seed mixing area to induce a crystallization reaction, and a reaction water body is obtained. The reaction water body is discharged from the water outlet (9) at the top of the preset bed crystallization fluidized bed, and a defluorinated water body is obtained.

2. The defluorination method according to claim 1, characterized in that, In the step of filling the seed crystals and setting the height of the static bed, the particle size of the seed crystals is 100 to 120 mesh.

3. The defluorination method according to claim 1, characterized in that, In the step of filling the seed crystals and setting the height of the static bed, the height of the static bed is 38cm to 50cm.

4. The defluorination method according to claim 1, characterized in that, Before the step of mixing the high-concentration fluoride-containing raw water to be treated with an acid-base adjuster to adjust the pH, the process also includes a step of preparing the high-concentration fluoride-containing raw water to be treated: The deionized water stock solution containing sodium fluoride is mixed and stirred with basic tap water to obtain the high-concentration fluoride-containing raw water to be treated.

5. The defluorination method according to claim 4, characterized in that, In the step of preparing the high-concentration fluoride-containing raw water to be treated, the initial concentration of fluoride ions in the high-concentration fluoride-containing raw water to be treated is 110 mg / L to 120 mg / L.

6. The defluorination method according to claim 4, characterized in that, In the step of preparing the high-concentration fluoride-containing raw water to be treated, the deionized water stock solution containing sodium fluoride is prepared by dissolving analytical grade sodium fluoride reagent in deionized water.

7. The defluorination method according to claim 1, characterized in that, In the step of mixing the high-concentration fluoride-containing raw water to be treated with an acid-base regulator to adjust the pH, the acid-base regulator is hydrochloric acid or sodium hydroxide.

8. The defluorination method according to claim 7, characterized in that, In the step of mixing the high-concentration fluoride-containing raw water to be treated with an acid-base regulator to adjust the pH, the high-concentration fluoride-containing raw water to be treated is mixed with the hydrochloric acid or sodium hydroxide in a static mixer (4) to adjust the pH.

9. The defluorination method according to claim 1, characterized in that, Ca in the water entering the controlled raw water mixing system 2+ / F - In the molar ratio step, the dosage of the calcium chloride solution is adjusted to control the Ca content of the water entering the raw water mixing system. 2+ / F - The molar ratio is 0.5 to 2.

0.

10. The defluorination method according to claim 1, characterized in that, In the step of controlling the rising water flow load of the inner cylinder of the crystallization fluidized bed in the preset bed layer, the rising water flow load of the inner cylinder of the crystallization fluidized bed in the preset bed layer is controlled to be 10 m / h.

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