A circulating treatment method for fluorine-containing wastewater

Abstract

The present invention provides a cyclic treatment method for fluorine-containing wastewater, comprising the following steps: introducing the fluorine-containing wastewater into column A to obtain effluent from column A; detecting whether the fluoride ion concentration of the effluent from column A is greater than a first preset fluoride ion concentration, wherein filler A is provided in column A; if so, introducing the effluent from column A into column B to obtain effluent from column B; detecting whether the fluoride ion concentration of the effluent from column B is greater than a second preset fluoride ion concentration, wherein filler B is provided in column B; if so, stopping the introduction of the fluorine-containing wastewater, draining the liquids in columns A and B into a recovery device, adding a first crystallization solution to both columns A and B, allowing them to react, recovering the first crystallization solution, and cleaning the fillers A and B; and after cleaning, adding a second crystallization solution to both columns A and B, allowing them to react, and repeating the above steps. This effectively reduces the ion concentration and turbidity of the effluent.

Description

Technical Field

[0001] The invention belongs to the technical field of wastewater treatment, and in particular relates to a circulating treatment method for fluorine-containing wastewater. Background Art

[0002] Fluoride ions in fluoride-containing wastewater primarily originate from the following sources: the processing of fluoride-containing ores (such as fluorspar); processes using fluoride salts, fluoric acid, and fluorides as additives or raw materials; byproducts from the fluorine chemical industry; and release during various pickling, etching, refining, and separation processes. Fluoride wastewater resource recovery technology has become a hot research topic. A common treatment method is to add calcium ions to the fluoride-containing wastewater to generate calcium fluoride, an important chemical raw material. By recovering calcium fluoride, fluoride ions are reused as a resource and the discharge of fluoride-containing sludge is reduced. However, due to the low solubility of calcium fluoride, the solution must be supersaturated to precipitate calcium fluoride. To achieve precipitation, the product of the fluoride and calcium ion concentrations in the system must exceed their solubility product (Ksp). Therefore, in fluoride-containing wastewater with low fluoride concentrations, the addition of calcium ions alone is insufficient to drive precipitation. Fluoride enrichment or wastewater concentration may be necessary to enhance the precipitation-driving capacity. However, this approach results in effluent fluoride concentrations exceeding 10 mg / L, which does not meet discharge standards and results in turbidity. Summary of the Invention

[0003] The technical problem to be solved by the present invention is to provide a circulating treatment method for fluorine-containing wastewater, aiming to solve the problems of high ion concentration and high turbidity of effluent water.

[0004] To solve the above technical problems, the present invention is implemented as follows: a method for circulating fluorine-containing wastewater is proposed, comprising the following steps:

[0005] S1. Introducing fluorine-containing wastewater into column A and maintaining it for 3 to 60 minutes to obtain effluent from column A, and detecting whether the fluoride ion concentration of the effluent from column A is greater than a first preset fluoride ion concentration, wherein filler A is provided in column A and is used to treat fluoride ions;

[0006] S2. If yes, introducing the effluent from column A into column B for 3 to 60 minutes to obtain effluent from column B, and detecting whether the fluoride ion concentration of the effluent from column B is greater than a second preset fluoride ion concentration, wherein column B is provided with a packing B for treating fluoride ions;

[0007] S3. If yes, stop introducing the fluorine-containing wastewater, drain the liquid in the column A and the column B into a recovery device, add the first crystallization solution to both the column A and the column B, let them stand for 0.5 to 3 hours, recover the first crystallization solution, and clean the packing A and the packing B;

[0008] S4. After cleaning, add a second crystallization solution to both column A and column B. After standing for 3 to 5 hours, recover the second crystallization solution. Mix the recovered second crystallization solution with the liquid in the recovery device and perform step S1 until the fluoride ion concentration of the effluent from column A is less than or equal to the first preset fluoride ion concentration or the fluoride ion concentration of the effluent from column B is less than or equal to the second preset fluoride ion concentration.

[0009] In some embodiments, the filler A includes at least one of silica, hollow ceramic balls, natural clay, sea sand, activated alumina, activated carbon, hydroxyapatite, resin, sawdust, and zirconia-alumina core-shell particles; the filler B includes at least one of activated alumina, activated carbon, hydroxyapatite, and resin; and the volume fractions of the filler A and the filler B in the column A and the column B, respectively, are 50 to 80%.

[0010] In some embodiments, the first crystallization solution includes at least one of calcium chloride, magnesium chloride, calcium nitrate, magnesium nitrate, ammonium bicarbonate, sodium citrate, and calcium fluorophosphate; the second crystallization solution includes at least one of sodium hydroxide, aluminum sulfate, sodium carbonate, and aluminum acetate; the volume ratio of the first crystallization solution to the filler A is (0.5-3):1; and the volume fraction of the second crystallization solution is 0.75-1%.

[0011] In some embodiments, step S1 includes:

[0012] S1.1. Divide the interior of column A into three layers from bottom to top: the bottom layer is composed of zirconia-alumina core-shell particles, the middle layer is composed of hydroxyapatite particles, and the top layer is composed of a mixture of alumina and silica;

[0013] S1.2. Inject the fluorine-containing wastewater into column A and allow it to stand for 10-30 minutes. Then, initiate a low-speed pulsating flow cycle at a flow rate of 0.5-1.5 L / min for 3-5 minutes. Allow it to stand again for 10-20 minutes. Then, inject disodium hydrogen phosphate solution into the bottom layer of column A. After allowing it to stand for 10-20 minutes, obtain the effluent from column A.

[0014] S1.3. Detect the fluoride ion concentration of the water outlet from column A to determine whether the fluoride ion concentration of the water outlet from column A is greater than a first preset fluoride ion concentration, where the first preset fluoride ion concentration is 0.1-1.0 mg / L.

[0015] In some embodiments, after step S1, the method further includes:

[0016] If not, the liquid in the column A is discharged to confirm that the treatment of the fluorine-containing wastewater is completed.

[0017] In some embodiments, step S2 includes:

[0018] S2.1. If the fluoride ion concentration of the effluent from column A is greater than the first predetermined fluoride ion concentration, the effluent from column A is introduced into a buffer reactor containing disodium hydrogen phosphate and calcium chloride, the pH of which is adjusted to 7.2-7.5, and the effluent is allowed to stand for 10-20 minutes before being introduced into column B.

[0019] S2.2. Perform magnetic stirring at the water inlet of column B for 2 to 5 minutes, and then let it stand for 10 to 20 minutes to obtain the water outlet of column B. Detect the fluoride ion concentration of the water outlet of column B to determine whether the fluoride ion concentration of the water outlet of column B is greater than a second preset fluoride ion concentration, which is 0.1 to 1.0 mg / L.

[0020] In some embodiments, after step S2, the method further includes:

[0021] If not, the liquid in the column B is discharged to confirm that the treatment of the fluorine-containing wastewater is completed.

[0022] In some embodiments, step S3 includes:

[0023] S3.1. If the fluoride ion concentration of the effluent from column B is greater than a second predetermined fluoride ion concentration, the introduction of the fluoride-containing wastewater is stopped, and the liquid in columns A and B is drained into a recovery device;

[0024] S3.2. Inject sodium hydroxide solution into columns A and B, adjust the pH to 9.0, and let stand for 5-10 minutes.

[0025] S3.3, injecting the first crystallization solution into the column A and the column B respectively, standing for 0.5 to 3 hours, and recovering the first crystallization solution;

[0026] S3.4. Detecting whether the effective concentration of the recovered first crystallization solution is less than a preset recovery concentration, wherein the preset recovery concentration is 800 to 1000 mg / L;

[0027] S3.5. If yes, increase the first crystallization solution until the predetermined reaction concentration is reached, which is 1500-2000 mg / L, and then execute step S3.4;

[0028] S3.6. If not, place the recovered first crystallization solution in the column A and the column B, and then perform step S3.3;

[0029] S3.7. Steps S3.3 to S3.6 are executed in a loop 1 to 5 times. After the cycle is completed, air flushing and water flushing are performed alternately for 3 to 5 rounds. The air flushing uses 0.2 MPa compressed air for 3 minutes, and the water flushing uses ultrapure water for 5 minutes. The recyclables attached to the filler A and the filler B are collected.

[0030] Compared with the prior art, the circulating treatment method for fluorine-containing wastewater in the present invention has the following beneficial effects:

[0031] Filler A within Column A preferentially captures target ions (fluoride ions) in the wastewater through mechanisms such as charge attraction and coordination reactions. When the fluoride ion concentration in the effluent from Column A exceeds a preset value, the wastewater is introduced into Column B for further treatment. After treatment, a first crystallization solution is injected to induce precipitation, converting residual ions into solid crystals. Subsequent cyclic precipitation with a second crystallization solution further increases the removal rate. The recovered crystal precipitate is removed from the system, significantly reducing the ion concentration in the effluent. Various functional fillers also physically capture suspended particles and colloids in the water, significantly reducing wastewater turbidity. In stages S3 and S4, induced and cyclic crystallization reactions transform ions in the wastewater into insoluble crystals. These crystals are then effectively stripped and recovered after standing, settling, and subsequent washing. This process simultaneously removes fine particles and sediment dispersed in the water, resulting in clearer effluent. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 The figure is a flow chart of a method for recycling treatment of fluorine-containing wastewater in one embodiment of the present invention. DETAILED DESCRIPTION

[0033] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0034] Please refer to Figure 1 The present invention proposes a method for circulating treatment of fluorine-containing wastewater, comprising the following steps:

[0035] S1. Introducing fluoride-containing wastewater into column A and maintaining the flow for 3 to 60 minutes to obtain effluent from column A, and detecting whether the fluoride ion concentration of the effluent from column A is greater than a first preset fluoride ion concentration, wherein filler A is provided in column A. Filler A comprises at least one of silica, hollow ceramic balls, natural clay, sea sand, activated alumina, activated carbon, hydroxyapatite, resin, sawdust, and zirconium oxide-alumina core-shell particles; filler B comprises at least one of activated alumina, activated carbon, hydroxyapatite, and resin; and filler A and filler B respectively account for 50 to 80% of the volume of columns A and B.

[0036] In this method for cyclically treating fluoride-containing wastewater, the core of step S1 is to promote the thorough treatment and initial precipitation of fluoride ions in the wastewater with functional groups on the packing surface within column A through specific packing materials, stratified and zoned operations, and multi-stage disturbance control, thereby reducing the fluoride ion concentration in the effluent and delaying treatment breakthrough. By designing stratified zones and controlling the wastewater transfer state, each treatment site of the packing is fully utilized; by regulating the treatment-precipitation process, premature saturation is avoided, thereby delaying the breakthrough of column A; and by accurately detecting the F⁻ concentration in the effluent, automatic switching to subsequent process steps is achieved.

[0037] The preparation steps of the zirconium oxide-aluminum oxide core-shell particles are as follows:

[0038] The activated alumina particles were soaked in deionized water for 30 minutes, ultrasonically degassed, rinsed with dilute ammonia water to adjust the surface pH to 6.5-7.5, and dried at 80° C. for 6 hours to obtain alumina particles.

[0039] Weigh zirconium oxychloride particles and dissolve them in deionized water to make a 0.1-0.5 mol / L zirconium salt solution. Add 30-50 vol% ethanol and stir evenly. Slowly add ammonia water to adjust the pH to 9.0-10.5. The system gradually changes from transparent to turbid, and a zirconium oxide precursor colloid begins to form. Continue stirring for 1-2 hours to form a uniform and stable zirconium oxide sol.

[0040] The pretreated alumina particles are immersed in the zirconium oxide sol and stirred for 1 to 2 hours. During this period, the system is kept rotating slowly. Negative pressure filtration is used to promote the zirconium oxide sol to penetrate into the micropores on the surface of the alumina particles. After filtering, the particles are dried at 70 to 90°C for 6 to 12 hours to obtain precursor particles.

[0041] The dried precursor particles are slowly heated to 450~550℃ and kept at a constant temperature for 2~4 hours, and a nitrogen atmosphere is introduced for preservation. During this process, the zirconia sol is converted into a crystalline or quasi-crystalline zirconia shell layer, forming a core-shell structure with tight coating and moderate density.

[0042] Step S1 includes:

[0043] S1.1. Divide the interior of column A into three layers from bottom to top: the bottom layer is set as zirconia-alumina core-shell particles, the middle layer is set as hydroxyapatite particles, and the top layer is a mixture of alumina and silica.

[0044] The surface of the zirconium oxide-alumina core-shell particles in the bottom layer combines the high fluorine affinity of zirconium oxide with the abundant hydroxyl functionality of alumina, allowing them to form stable zirconium-fluorine or aluminum-fluorine complexes with fluoride ions through coordination reactions. This layer primarily serves to capture and immobilize fluoride ions. The hydroxyapatite in the middle layer is highly chemically active and can induce the local formation of precipitation nuclei. This helps promote the reaction of some fluoride ions with calcium or phosphate ions during the treatment process, forming functional nuclei and increasing treatment depth. The top layer provides a large specific surface area and fine pore structure, and has a certain buffering effect, which facilitates initial filtration and balances the flow rate and pH changes of wastewater as it enters each zone.

[0045] S1.2. Inject the fluorine-containing wastewater into column A and allow it to stand for 10 to 30 minutes. Then start a low-speed pulsating flow cycle at a flow rate of 0.5 to 1.5 L / min for 3 to 5 minutes. Allow it to stand for another 10 to 20 minutes. Then, inject disodium hydrogen phosphate solution into the bottom layer of column A. After allowing it to stand for 10 to 20 minutes, the effluent from column A is obtained.

[0046] After initially injecting fluoride-containing wastewater into column A, it is allowed to stand for 10 to 30 minutes to allow the wastewater to fully contact the packing and initially complete the fluoride ion treatment. A low-speed pulsating flow is then initiated at a controlled rate of 0.5 to 1.5 L / min for 3 to 5 minutes to induce micro-perturbation, local mixing, and enhanced mass transfer within the column. The column is then allowed to stand for another 10 to 20 minutes to provide a stable reaction environment for subsequent stages. Following this stand, sodium hydrogen phosphate solution is injected into the bottom layer of column A and allowed to stand for 10 to 20 minutes to induce localized nucleation.

[0047] Ensure sufficient contact between fluoride ions in the wastewater and the surface functional groups of the filler (such as zirconium-hydroxyl, aluminum-hydroxyl, and hydroxyapatite surface active sites), promoting surface adsorption and complexation reactions. During the static period, the locally generated complexed fluoride ions remain stable, which helps to control subsequent precipitation. During the static state, wastewater mass transfer relies on molecular diffusion, and the time window is used to allow the reaction to reach equilibrium.

[0048] Micro-perturbations achieve local mixing of wastewater, breaking down concentration gradients and local dead zones that may occur due to stasis, ensuring that all sites within the packing participate in the reaction. This also helps activate interfaces, prompting the partial release of treated fluoride ions under external disturbances, which are then recaptured by adjacent sites, thereby increasing the overall treatment rate. The shear force and microfluidic effects generated by low-speed pulsating flow achieve uniform mass transfer. This dynamic adjustment optimizes precipitation behavior during chemical reactions and crystal nucleation.

[0049] After the standing period, sodium hydrogen phosphate solution is injected into the bottom layer to help locally regulate pH and ion balance, thereby inducing partial precipitation of fluoride ions and calcium ions in the wastewater, creating favorable conditions for subsequent treatment. Sodium hydrogen phosphate can slightly increase the phosphate ion concentration in a local area, promoting ion exchange reactions mainly characterized by precipitation and crystallization, thereby forming stable crystal nuclei and achieving a synergistic effect of adsorption and precipitation.

[0050] S1.3. Detect the fluoride ion concentration of the water effluent from column A to determine whether the fluoride ion concentration of the water effluent from column A is greater than a first preset fluoride ion concentration, wherein the first preset fluoride ion concentration is 0.1 to 1.0 mg / L. Preferably, the first preset fluoride ion concentration is 1 mg / L.

[0051] After the static and pulsating processes, the fluoride ion concentration in the effluent is monitored in real time using an online fluoride ion detection module located at the base of Column A. Using an ion-selective electrode (ISE) or an automated online fluoride ion monitoring instrument, the test results are compared with a preset fluoride ion concentration threshold (0.8-1.5 mg / L) to determine whether the effluent meets the effluent standard. This ensures real-time and accurate test data, providing a quantitative basis for the treatment and precipitation performance of Column A. It also helps determine whether the packing's adsorption capacity is saturated and whether switching to the next treatment stage is necessary. An electrochemical method (ISE) achieves a selective response to fluoride ions. The electrode surface's response potential to fluoride ions is proportional to the concentration, converting the concentration signal into a digital signal for storage and comparison. If the fluoride ion concentration in the effluent is continuously detected above the preset threshold, an automatic switching process is initiated. This feedback mechanism ensures that the system operates within the optimal operating range, avoiding treatment efficiency reduction due to saturation. By setting a threshold of 1.0 mg / L (adjustable to 0.8-1.5 mg / L), the column's internal state is compared and judgment is made based on the dynamic change curve, forming a closed-loop control system.

[0052] S1.1 treats wastewater in stages under the action of different materials, achieving the synergy of physical filtration, chemical treatment and induced precipitation, making full use of the specific functions of various filler materials, ensuring the efficient capture of fluoride ions and delayed treatment penetration. S1.2 uses static-flow alternating operations to not only ensure sufficient reaction between the filler and the wastewater, but also stimulates a more uniform state through local disturbances, and promotes the formation of crystal nuclei under suitable conditions, laying the foundation for subsequent precipitation steps. S1.3 Real-time data monitoring ensures the continuity and stability of production operations. By accurately detecting and comparing threshold values, the treatment process is switched in time, which helps to achieve full-process automation and energy consumption optimization, and improve the reliability and economy of the overall system.

[0053] If not, that is, the fluoride ion concentration of the effluent from column A is less than the first preset fluoride ion concentration, the liquid in column A is discharged, confirming that the treatment of the fluoride-containing wastewater is completed.

[0054] When the system detects that the fluoride ion concentration in the effluent from column A has fallen below the set first threshold (e.g., 0.1-1.0 mg / L), it indicates that filler A still has the ability to treat fluoride ions and the fluoride ion concentration in the wastewater has fallen to a safe / compliant range. The system can then terminate further treatment steps (e.g., without switching to column B or entering the crystallization / regeneration step), thereby avoiding energy consumption, manpower, and reagent waste, implementing an on-demand intelligent control strategy, and improving the overall operational efficiency and economic efficiency of the treatment system. The first preset fluoride ion concentration set in this step serves as the safety lower limit criterion. If two consecutive monitorings show that the fluoride ion concentration is below this threshold (e.g., 1.0 mg / L), the system can automatically determine that the current wastewater has been treated and can be safely discharged or transferred to downstream links. This step serves as the termination signal point for the entire process flow, realizing the closed-loop logic of the treatment system.

[0055] This judgment mechanism allows the system to flexibly determine the depth of treatment based on the different batches and concentrations of influent water. For wastewater with inherently low fluoride ion concentrations, a single treatment in Column A can meet the standard without requiring the full, time-consuming steps of dual columns, crystallization, and regeneration. This significantly improves the system's adaptability to fluctuating water quality in practical engineering applications, avoiding a one-size-fits-all approach. When a detection system (such as ISE / IC) detects that the fluoride ion concentration is stable below the standard, the system automatically records the end of treatment and proceeds sequentially through the following steps: stopping water inflow, draining the system, backflushing with clean water, and entering standby mode. This system can be integrated into a control system, enabling 24-hour unattended intelligent treatment.

[0056] S2. If yes, introduce the effluent from column A into column B and keep it for 3 to 60 minutes to obtain the effluent from column B, and detect whether the fluoride ion concentration of the effluent from column B is greater than a second preset fluoride ion concentration, wherein filler B is provided in column B.

[0057] Step S2 includes:

[0058] S2.1. If the fluoride ion concentration of the effluent from column A is greater than the first preset fluoride ion concentration, the effluent from column A is introduced into a buffer reactor containing disodium hydrogen phosphate and calcium chloride, and the pH is adjusted to 7.2-7.5. The effluent is allowed to stand for 10-20 minutes before being introduced into column B.

[0059] When the fluoride ion concentration in the effluent from column A exceeds a first preset fluoride ion concentration, the effluent from column A is automatically introduced into a buffer reactor within the system. A mixture containing disodium hydrogen phosphate and calcium chloride is adjusted to a pH of 7.2-7.5 to establish a relatively stable neutral reaction environment. The mixture is allowed to stand in the buffer reactor for 10-20 minutes, allowing some fluoride ions attached to the surface of filler A in the wastewater to be released under localized controlled conditions. These fluoride ions then combine with calcium ions and phosphate ions to induce the formation of primary crystal nuclei. Subsequently, the conditioned wastewater is introduced into column B. The addition of disodium hydrogen phosphate and calcium chloride creates a localized ionic environment within the buffer reactor, encouraging some fluoride ions to react with calcium ions to form primary calcium fluoride or fluorapatite nuclei. This not only reduces the fluoride ion concentration in the wastewater but also provides anchoring sites for the nuclei for subsequent treatment. Based on ion equilibrium and solubility product theory, under neutral conditions of pH 7.2-7.5, the reaction rate of calcium and fluoride ions to form precipitation is increased, while phosphate ions contribute to the formation of a stable nucleus structure. After buffer pretreatment, fluoride ions in the wastewater are more evenly distributed, reducing local concentration differences, thereby facilitating more consistent treatment results in column B. Buffering agents, which adjust pH and ion concentration, alleviate uneven loading caused by uneven water inflow or localized saturation of the packing surface, allowing subsequent treatment processes to proceed along a more uniform reaction interface.

[0060] S2.2. Perform magnetic stirring at the water inlet of column B for 2 to 5 minutes. Let the water stand for 10 to 20 minutes to obtain the water outlet of column B. Detect the fluoride ion concentration of the water outlet of column B to determine whether the fluoride ion concentration of the water outlet of column B is greater than a second preset fluoride ion concentration, which is 0.1 to 1.0 mg / L.

[0061] A magnetic stirring device is installed at the inlet of column B. Using a magnetic stirring bar or ultrasonic pulse device, the wastewater entering column B is uniformly mixed. Magnetic stirring is initiated for 2-5 minutes, followed by a 10-20 minute standstill to ensure sufficient contact between the wastewater and the packing material within column B. After this standstill, a sample is collected from the outlet of column B for fluoride ion concentration testing to determine whether it has reached the second preset fluoride ion concentration (0.1-1.0 mg / L). Magnetic stirring effectively eliminates local concentration gradients caused by uneven flow in column B, ensuring that fluoride ions in the wastewater are evenly distributed throughout the column and ensuring that packing material B fully utilizes its treatment capacity. The disturbance generated by magnetic stirring not only enhances contact between the wastewater and the packing material surface but also reduces competition caused by localized high concentrations, allowing the remaining fluoride ions to more effectively bind to functional groups on packing material B (such as activated alumina or activated carbon). The alternating stirring and settling modes achieve sufficient homogenized mass transfer in a short period of time, while also providing a stable reaction environment during the settling period, promoting the full development of the adsorption and induced precipitation processes and reducing the fluoride ion concentration in the effluent from column B. This operating mode utilizes the alternating dynamic and static characteristics of the liquid to, on the one hand, break the concentration dead zone during the stirring period, and on the other hand, allow the system to approach equilibrium during the settling period, thereby optimizing the entire treatment process.

[0062] If not, that is, the fluoride ion concentration of the effluent from column B is less than the second preset fluoride ion concentration, the liquid in column B is discharged, confirming that the treatment of the fluoride-containing wastewater is complete. By online monitoring of the fluoride ion concentration of the effluent from column B, dynamic closed-loop control is achieved. When the wastewater has reached below the second preset fluoride ion concentration, treatment is confirmed to be complete and the wastewater is discharged.

[0063] In one embodiment, the following calculation method is proposed to calculate the specific standing time required in column A or column B and the specific mass of filler A or filler B:

[0064]

[0065]

[0066] in, It is the fluoride ion concentration (mg / L) of the fluoride-containing wastewater that has not entered column A or column B, and is measured by an online fluoride electrode and an ion selective electrode. It is the fluoride ion concentration (mg / L) of the effluent from column A or column B, obtained by online monitoring or regular sampling. is the treatment time (min), which starts from the time when the fluorine-containing wastewater begins to flow into column A / B and can range from 0 to 60 min. is the flow rate (mL / min), which can be read from a flow meter or rotor flowmeter and can range from 500 to 1500 mL / min. The processing capacity (mg or g) is obtained by statistical fitting of a large number of repeated experimental data with fluoride ion solutions of known concentrations, and can range from 2 to 10 mg or g. is the first rate constant (1 / min), which is obtained by statistical fitting of a large number of repeated experimental data with fluoride ion solutions of known concentrations, and can range from 0.001 to 0.05 (1 / min). The larger the value, the faster the processing kinetics and the higher the reaction efficiency. is the 50% penetration time (min) of packing A or packing B. Predict at what time the liquid in column A or column B will reach =0.5 , judging that the function of filler A or filler B in column A or column B in treating fluoride ions is close to saturation, and the fluoride ion concentration decreases slowly, which is used to indicate the risk of decreased efficiency of filler A and filler B in treating fluoride ion concentration. This is especially important for continuously operating industrial systems and can serve as an important parameter for determining whether to switch to column B or recover. is the second rate constant (mL / (mg·min)), which is obtained by statistical fitting of a large number of repeated experimental data with multiple fluoride ion solutions of known concentrations and can range from 0.01 to 0.2 mL / (mg·min). is the mass of filler A / B (g), used to determine whether filler A / B is more suitable for treating the current fluoride ion concentration and the amount of fluoride-containing wastewater. In one embodiment, the range can be 200-800 g.

[0067] S3. If yes, stop introducing fluorine-containing wastewater, drain the liquid in columns A and B into the recovery device, add the first crystallization solution to both columns A and B, let them stand for 0.5 to 3 hours, then recover the first crystallization solution and clean packing A and packing B.

[0068] This step, which occurs after the column's processing capacity has been saturated, aims to recover residual fluoride ions from the material; induce crystallization to stabilize the fluoride ions; clean the packing surface and restore performance; and achieve the recycling of the adsorption-precipitation system. Its key value lies in coupling adsorption, induced crystallization, and desorption cleaning into a continuous process, maximizing system processing efficiency and material regeneration performance.

[0069] Step S3 includes:

[0070] S3.1. If the fluoride ion concentration of the effluent from column B is greater than the second preset fluoride ion concentration, the introduction of fluoride-containing wastewater is stopped, and the liquid in columns A and B is drained into the recovery device.

[0071] When online detection shows that the fluoride ion concentration in the effluent of column B is greater than the preset second threshold value (0.1~1.0 mg / L), the system automatically stops introducing fluoride-containing wastewater; then the drain valves of column A and column B are opened to empty all the liquid in the two columns into a dedicated recovery device for subsequent treatment or waste liquid management. Timely cessation of water inflow can prevent further saturation of the filler and avoid the attachment sites being completely occupied by residual fluoride ions, thereby affecting subsequent regeneration and the next round of treatment. Emptying the liquid can make the environment in the column reach a clean state, remove unnecessary impurities and by-products, and create a more uniform working base for subsequent pH adjustment and crystallization precipitation. Real-time monitoring combined with automatic emptying operation ensures stable operation of the system and a closed-loop data feedback loop, meeting the requirements of automated continuous processing. The recovery device can be set as a dedicated recovery chamber. The specific structure is known to those skilled in the art and will not be described here.

[0072] S3.2. Inject sodium hydroxide solution into columns A and B respectively, adjust the pH to 9.0, and let it stand for 5 to 10 minutes.

[0073] The injection of sodium hydroxide solution shifts the column environment from neutral or slightly acidic to alkaline (approximately pH 9.0), helping to disrupt some of the already formed zirconium-fluorine or aluminum-fluorine complex bonds, partially releasing fluoride ions from the packing surface and enhancing the activity of the subsequent crystallization reaction. Under alkaline conditions, some of the adsorbed fluoride ions can be converted to a free state, providing sufficient free fluoride ions to react with the calcium ions in the injected crystallization solution. This chemical regeneration step creates more ideal reaction conditions for inducing crystallization.

[0074] The first crystallization solution induces the formation of crystal nuclei in the column through the calcium ions, magnesium ions, and phosphate ions in the solution and the released fluoride ions, forming calcium fluoride, magnesium fluoride or fluorapatite precipitation. This not only further reduces the fluoride ion concentration in the wastewater, but also forms a recyclable solid phase on the surface of the filler, which has resource value. After the end, the first crystallization solution is recovered and can be used for the next cycle after appropriate adjustment, playing a role in resource recovery and reuse. Utilizing the solubility product principle and supersaturation conditions, a sparingly soluble salt precipitate is generated in a stable alkaline environment, while auxiliary ions are used to induce the formation of a composite crystal phase. This step uses the method of ion-induced crystallization to control precipitation and optimizes the process parameters to ensure that the crystal nuclei are initially generated and further grow to a recyclable particle size range. After the static reaction, the first crystallization solution recovered can be recycled for the next batch of wastewater treatment after appropriate adjustment, reducing drug consumption and operating costs. Utilizing the principle of conservation of matter and solution regulation, after multiple cycles, the concentration of active components in the solution is maintained within the appropriate range through online testing and regular replenishment of drugs, thereby maximizing the utilization of chemical resources.

[0075] S3.3. Inject the first crystallization solution into column A and column B, respectively. After standing for 0.5 to 3 hours, recover the first crystallization solution. The first crystallization solution comprises at least one of calcium chloride, magnesium chloride, calcium nitrate, magnesium nitrate, ammonium bicarbonate, sodium citrate, and calcium fluorophosphate. The volume ratio of the first crystallization solution to filler A is (0.5 to 3):1.

[0076] S3.4. Detect whether the effective concentration of the recovered first crystallization solution is less than a preset recovery concentration, wherein the preset recovery concentration is 800-1000 mg / L.

[0077] A significant decrease in the active ingredient (<800 mg / L) indicates that a significant amount of calcium ions and other ions have been consumed by precipitation, the crystallization reaction is complete, and a large amount of crystal nuclei have been deposited. Concentration testing can be used to determine whether the solution in that round of crystallization is reactive enough for reuse and serves as a basis for implementing multiple cycles. When nuclei are generated to treat calcium / phosphate ions, the free ion concentration in the solution decreases, forming a quantitative criterion. As a function of reaction rate, concentration can quantitatively reflect the system entering the precipitation plateau phase.

[0078] If yes, increase the first crystal concentration until it reaches the preset reaction concentration, which is 1500-2000 mg / L, and then execute step S3.4.

[0079] This addition method extends the life of the first crystallization solution, achieving a closed-loop resource cycle. Maintaining a supersaturated state prevents slow nucleation rates and inadequate precipitation, thereby improving reaction consistency. Maintaining the calcium ion / fluoride ion ratio within the ideal reaction range (e.g., 2:1) is essential for ensuring continuous calcium fluoride precipitation. Dynamically adjusting the reactant concentration is a chemical buffering method that prevents the reaction from entering a diffusion / equilibrium-limited phase.

[0080] S3.6. If not, place the recovered first crystallization solution in columns A and B, and then perform step S3.3.

[0081] Reusing the same batch of crystallization solution multiple times significantly reduces the consumption of reagents such as calcium chloride, aligning with the concept of green chemistry. The reused crystallization solution still contains high concentrations of calcium ions, phosphate ions, and other ions, providing continuous reaction power over multiple cycles.

[0082] After the first crystallization solution is collected, it is weighed, dissolved, and the residual calcium ions are titrated with a standard ethylenediaminetetraacetic acid (EDTA) solution. This allows the calculation of the residual calcium ion concentration of the first crystallization solution introduced in the first cycle. The residual calcium ion concentration of the first crystallization solution introduced in multiple cycles can also be calculated. The calculation formula is as follows:

[0083]

[0084] in, is the residual calcium ion concentration in the recovered first crystallization solution (mg / L), is the titer of the EDTA standard solution (mg / L), obtained by titrating with a standard calcium ion solution of known concentration. is the volume of EDTA consumed in titration (L), is the volume consumed by blank pure water titration (L), is the volume of EDTA standard solution (L).

[0085] The residual calcium ion concentration of the first crystallization solution after multiple cycles can help determine whether the cycle should be terminated. If the detected residual calcium ion concentration is lower than 20 mg / L, it can be discharged directly. If the residual calcium ion concentration is higher than 50 mg / L, it needs to be recovered and retained.

[0086] S3.3, steps S3.3 to S3.6 are executed in a cycle for 1 to 5 times. After the cycle, air flushing and water flushing are performed alternately for 3 to 5 rounds. The air flushing uses 0.2 MPa compressed air for 3 minutes, and the water flushing uses ultrapure water for 5 minutes. The recyclables attached to the filler A and the filler B are collected.

[0087] Alternating air and water flushing operations can utilize the dual effects of physical impact and liquid flushing to remove and collect crystals on the surface and pores of the packing, restoring the packing's original specific surface area and treatment sites. The air flush provides an instantaneous high-pressure impact to destroy the adhesive layer on the packing surface, while the water flush utilizes the penetration and flow rate effects of water to effectively remove and collect scattered crystals, thereby reducing the risk of packing clogging. After thorough cleaning, the packing can be reused in the next cycle of wastewater treatment, ensuring long-term stable operation of the system and reducing operating costs. Through alternating flushing, not only physical cleaning is achieved, but also, to a certain extent, the passivation of the packing active sites by chemical residues is avoided, thereby extending the packing's service life.

[0088] S4. After cleaning, add a second crystallization solution to both columns A and B. After standing for 3-5 hours, recover the second crystallization solution. Mix the recovered second crystallization solution with the liquid in the recovery device and perform step S1 until the fluoride ion concentration of the water outlet from column A is less than or equal to the first preset fluoride ion concentration or the fluoride ion concentration of the water outlet from column B is less than or equal to the second preset fluoride ion concentration. The second crystallization solution includes at least one of sodium hydroxide, aluminum sulfate, sodium carbonate, and aluminum acetate, and the volume fraction of the second crystallization solution is 0.75-1%.

[0089] If some fluoride ions remain in the filler pores, surface microregions, or in an unconverted complex state during the S3 treatment process, a 3-5 hour quiescent crystallization reaction allows further crystallization and precipitation reactions to occur in this local microenvironment. A reaction-inducing layer (e.g., calcium phosphate / calcium fluoride microcrystals) is deposited on the filler surface, providing a nucleation template for the next round of fluoride-containing wastewater entering the system, improving the initial efficiency of the fluoride ion reaction and achieving an effect similar to surface crystallization pre-activation. Under static conditions, the first crystallization solution maintains a high calcium and phosphate ion environment, causing fluoride ions in the wastewater (both attached and in solution) to precipitate. The surface of the nucleation inducer (e.g., fluorapatite) provides ordered crystal faces, accelerating the heterogeneous nucleation process and improving the rate and uniformity of crystal formation.

[0090] By organically linking filler regeneration, crystallization precipitation, and crystallization solution reuse with the next treatment cycle, a fully closed loop is formed. Before executing S1 again, the surfaces of fillers A / B are already coated with an induced crystal nucleation layer, resulting in a higher initial adsorption reaction rate and more controllable reaction conditions, helping the system operate quickly and stably when entering the next treatment cycle.

[0091] The present invention has been tested multiple times to obtain data on chemical content in effluent. Based on local requirements for effluent to meet Class III standards in the "Surface Water Environmental Quality Standards," the process of the present invention was judged to determine whether it can be integrated into subsequent water treatment processes. The results, as shown in the table below, show that the effluent from the present invention is more effective in treating fluoride-containing wastewater than the effluent from coagulation and sedimentation. It can replace traditional coagulation and sedimentation processes and be integrated with subsequent treatment processes such as biochemical ponds and constructed wetlands. The specific content of the above standards is well known to those skilled in the art and will not be elaborated on here.

[0092]

[0093] It can be seen that the defluorination efficiency of the effluent of the embodiment of the present invention is significantly improved to meet the national standard, while the traditional process is unqualified. The effluent turbidity is extremely low, much lower than that of the traditional method, which is conducive to further membrane treatment or standard discharge.

[0094] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for recycling fluorine-containing wastewater, characterized in that the steps include: S1. Introducing fluorine-containing wastewater into column A and maintaining it for 3 to 60 minutes to obtain effluent from column A, and detecting whether the fluoride ion concentration of the effluent from column A is greater than a first preset fluoride ion concentration, wherein filler A is provided in column A and is used to treat fluoride ions; Step S1 includes: S1.

1. Divide the interior of column A into three layers from bottom to top: the bottom layer is composed of zirconia-alumina core-shell particles, the middle layer is composed of hydroxyapatite particles, and the top layer is composed of a mixture of alumina and silica; S1.

2. Inject the fluorine-containing wastewater into column A and allow it to stand for 10-30 minutes. Then, initiate a low-speed pulsating flow cycle at a flow rate of 0.5-1.5 L / min for 3-5 minutes. Allow it to stand again for 10-20 minutes. Then, inject disodium hydrogen phosphate solution into the bottom layer of column A. After allowing it to stand for 10-20 minutes, obtain the effluent from column A. S1.

3. Detecting the fluoride ion concentration of the effluent from column A to determine whether the fluoride ion concentration of the effluent from column A is greater than a first preset fluoride ion concentration, wherein the first preset fluoride ion concentration is 0.1 to 1.0 mg / L; S2. If yes, introducing the effluent from column A into column B for 3 to 60 minutes to obtain effluent from column B, and detecting whether the fluoride ion concentration of the effluent from column B is greater than a second preset fluoride ion concentration, wherein column B is provided with a packing B for treating fluoride ions; S3. If yes, stop introducing the fluorine-containing wastewater, drain the liquid in the column A and the column B into a recovery device, add the first crystallization solution to both the column A and the column B, let them stand for 0.5 to 3 hours, recover the first crystallization solution, and clean the packing A and the packing B; S4. After cleaning, add a second crystallization solution to both column A and column B. After standing for 3 to 5 hours, recover the second crystallization solution. Mix the recovered second crystallization solution with the liquid in the recovery device and perform step S1 until the fluoride ion concentration of the effluent from column A is less than or equal to the first preset fluoride ion concentration or the fluoride ion concentration of the effluent from column B is less than or equal to the second preset fluoride ion concentration.

2. The method for circulating fluorine-containing wastewater according to claim 1, characterized in that: The filler B includes at least one of activated alumina, activated carbon, hydroxyapatite, and resin, and the volume fractions of the filler A and the filler B in the column A and the column B are 50-80%, respectively.

3. The method for circulating fluorine-containing wastewater according to claim 1, characterized in that: The first crystallization solution includes at least one of calcium chloride, magnesium chloride, calcium nitrate, magnesium nitrate, ammonium bicarbonate, sodium citrate, and calcium fluorophosphate; the second crystallization solution includes at least one of sodium hydroxide, aluminum sulfate, sodium carbonate, and aluminum acetate; the volume ratio of the first crystallization solution to the filler A is (0.5-3):1, and the volume fraction of the second crystallization solution is 0.75-1%.

4. The method for circulating fluorine-containing wastewater according to claim 1, characterized in that: After step S1, the method further includes: If not, the liquid in the column A is discharged to confirm that the treatment of the fluorine-containing wastewater is completed.

5. The method for circulating treatment of fluorine-containing wastewater according to claim 1, characterized in that: Step S2 includes: S2.

1. If the fluoride ion concentration of the effluent from column A is greater than the first predetermined fluoride ion concentration, the effluent from column A is introduced into a buffer reactor containing disodium hydrogen phosphate and calcium chloride, the pH of which is adjusted to 7.2-7.5, and the effluent is allowed to stand for 10-20 minutes before being introduced into column B. S2.

2. Perform magnetic stirring at the water inlet of column B for 2 to 5 minutes, and then let it stand for 10 to 20 minutes to obtain the water outlet of column B. Detect the fluoride ion concentration of the water outlet of column B to determine whether the fluoride ion concentration of the water outlet of column B is greater than a second preset fluoride ion concentration, which is 0.1 to 1.0 mg / L.

6. The method for circulating treatment of fluorine-containing wastewater according to claim 1, characterized in that: After step S2, the method further includes: If not, the liquid in the column B is discharged to confirm that the treatment of the fluorine-containing wastewater is completed.

7. The method for circulating treatment of fluorine-containing wastewater according to claim 1, characterized in that: Step S3 includes: S3.

1. If the fluoride ion concentration of the effluent from column B is greater than a second predetermined fluoride ion concentration, the introduction of the fluoride-containing wastewater is stopped, and the liquid in columns A and B is drained into a recovery device; S3.

2. Inject sodium hydroxide solution into columns A and B, adjust the pH to 9.0, and let stand for 5-10 minutes. S3.3, injecting the first crystallization solution into the column A and the column B respectively, standing for 0.5 to 3 hours, and recovering the first crystallization solution; S3.

4. Detecting whether the effective concentration of the recovered first crystallization solution is less than a preset recovery concentration, wherein the preset recovery concentration is 800 to 1000 mg / L; S3.

5. If yes, increase the first crystallization solution until the predetermined reaction concentration is reached, which is 1500-2000 mg / L, and then execute step S3.4; S3.

6. If not, place the recovered first crystallization solution in the column A and the column B, and then perform step S3.3; S3.

7. Steps S3.3 to S3.6 are executed in a loop 1 to 5 times. After the cycle is completed, air flushing and water flushing are performed alternately for 3 to 5 rounds. The air flushing uses 0.2 MPa compressed air for 3 minutes, and the water flushing uses ultrapure water for 5 minutes. The recyclables attached to the filler A and the filler B are collected.

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