Circulating treatment method of fluorine-containing wastewater

Abstract

The invention provides a fluorine-containing wastewater circulation treatment method, which comprises: introducing fluorine-containing wastewater into a column A to obtain column A effluent, and detecting whether the fluorine ion concentration of the column A effluent is greater than a first preset fluorine ion concentration, the column A being filled with a filler A; if yes, the effluent of the column A is introduced into a column B, effluent of a column B is obtained, whether the fluorine ion concentration of the effluent of the column B is larger than a second preset fluorine ion concentration or not is detected, and filler B is arranged in the column B; if yes, stopping introducing the fluorine-containing wastewater, emptying liquid in the column A and the column B into a recovery device, adding a first crystallization solution into the column A and the column B, standing for reaction, recovering the first crystallization solution, and cleaning the filler A and the filler B; and after cleaning is completed, adding a second crystallization solution into the column A and the column B, standing for reaction, and then circulating the steps. Therefore, the ion concentration and turbidity of the effluent are effectively reduced.

Description

Technical Field

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

[0002] Fluoride ions in fluoride-containing wastewater mainly come from the following aspects: treatment of fluoride-containing ores (such as fluorite); process using fluoride salts, fluoride acid, fluoride as additives or raw materials; by-products of the fluorine chemical industry; release during various pickling, etching, refining, and separation processes. Fluoride-containing wastewater resource treatment technology has become a popular research direction. The common treatment method is to add calcium ions to fluoride-containing wastewater to generate an important chemical raw material-calcium fluoride. By recycling calcium fluoride, the resource recycling of fluoride ions is realized and the discharge of fluoride-containing sludge is reduced. However, due to the low solubility of calcium fluoride, the solution needs to be in a supersaturated state to precipitate calcium fluoride. In order to achieve its precipitation, the product of the fluoride ion and calcium ion concentrations in the system needs to exceed its solubility product (Ksp) value. Therefore, in fluoride-containing wastewater with low fluoride ion concentration, adding calcium ions alone is not enough to drive the precipitation reaction. Sometimes it is necessary to enrich fluoride ions or concentrate wastewater to improve the precipitation driving capacity. However, this method causes the fluoride ion concentration of the treated effluent to be greater than 10 mg / L, which does not meet the discharge standard, and the effluent is relatively turbid. 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 treatment of fluorine-containing wastewater is provided, the steps comprising: S1, introducing fluorine-containing wastewater into column A, maintaining for 3 to 60 minutes, obtaining 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 filler A is used to treat fluoride ions; S2. If yes, the effluent from column A is introduced into column B and kept for 3 to 60 minutes to obtain effluent from column B, and the fluoride ion concentration of the effluent from column B is detected to be greater than a second preset fluoride ion concentration, wherein a filler B is provided in column B, and the filler B is used to treat fluoride ions; S3, if yes, stop introducing the fluorine-containing wastewater, empty the liquid in the column A and the column B into the recovery device, add the first crystallization solution to the column A and the column B, let it stand for 0.5 to 3 hours, then recover the first crystallization solution and clean the filler A and the filler B; S4. After cleaning, add a second crystallization solution to both column A and column B, let it stand for 3 to 5 hours, then recover the second crystallization solution, mix the recovered second crystallization solution with the liquid in the recovery device, and execute 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.

[0005] 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, and 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.

[0006] 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%.

[0007] In some embodiments, step S1 includes: S1.1. The interior of column A is divided into three layers from bottom to top, with the bottom layer being zirconium oxide-alumina core-shell particles, the middle layer being hydroxyapatite particles, and the top layer being a mixture of alumina and silicon dioxide; S1.2, inject the fluorine-containing wastewater and let it stand for 10 to 30 minutes, then start a low-speed pulsating flow circulation with a flow rate of 0.5 to 1.5 L / min for 3 to 5 minutes, let it stand for 10 to 20 minutes again, and then inject disodium hydrogen phosphate solution into the bottom layer of column A, let it stand for 10 to 20 minutes, and obtain the effluent of column A; S1.3. Detect the fluoride ion concentration of the water outlet from the column A to determine whether the fluoride ion concentration of the water outlet from the column A is greater than a preset first fluoride ion concentration, wherein the preset first fluoride ion concentration is 0.1-1.0 mg / L.

[0008] In some embodiments, 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.

[0009] In some embodiments, step S2 includes: S2.1. If the fluoride ion concentration of the effluent from column A is greater than the preset first fluoride ion concentration, the effluent from column A is connected to a buffer reactor containing disodium hydrogen phosphate and calcium chloride, the pH is adjusted to 7.2-7.5, and the effluent is introduced into column B after standing for 10-20 minutes; 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 preset second fluoride ion concentration, which is 0.1 to 1.0 mg / L.

[0010] In some embodiments, 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.

[0011] In some embodiments, step S3 includes: S3.1. If the fluoride ion concentration of the effluent from column B is greater than the preset second fluoride ion concentration, the introduction of fluoride-containing wastewater is stopped, and the liquid in the columns A and B is drained into the recovery device; S3.2, inject sodium hydroxide solution into column A and column B respectively, 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 solubility of the first crystallization solution recovered is less than a preset recovery concentration, wherein the preset recovery concentration is 800-1000 mg / L; S3.5. If yes, increase the first crystallization solution until the preset reaction concentration is reached, the preset reaction concentration is 1500-2000 mg / L, and then execute step S3.4; S3.6, if not, placing the recovered first crystallization solution in the column A and the column B, and then performing step S3.3; S3.7, 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.

[0012] Compared with the prior art, the circulating treatment method for fluorine-containing wastewater in the present invention has the following beneficial effects: The filler A set in column A can preferentially capture the target ions (fluoride ions) in the wastewater through mechanisms such as charge attraction and coordination reaction. When the fluoride ion concentration in the effluent of column A exceeds the preset value, the wastewater is introduced into column B for treatment again. After the treatment is completed, the residual ions are converted into solid crystals by injecting the first crystallization solution to induce crystal precipitation, and the removal rate is further improved by the subsequent circulation precipitation of the second crystallization solution. The recovered crystal precipitate is removed from the system, thereby significantly reducing the ion concentration in the effluent. A variety of functional fillers can also capture suspended particles and colloids in the water through physical interception, significantly reducing the turbidity of the wastewater. In the S3 and S4 stages, the ions in the wastewater are converted into insoluble crystals through induction and circulation crystallization reactions, and these crystals are effectively stripped and recovered after standing, settling and subsequent washing. This process can simultaneously remove tiny particles and sediments dispersed in the water, making the effluent clearer. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 It is a schematic flow chart of a method for circulating treatment of fluorine-containing wastewater in one embodiment of the present invention. DETAILED DESCRIPTION

[0014] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with 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.

[0015] Please refer to Figure 1 The present invention provides a method for circulating treatment of fluorine-containing wastewater, the steps comprising: S1. Introduce fluorine-containing wastewater into column A, keep it for 3 to 60 minutes, obtain column A effluent, and detect whether the fluoride ion concentration of the column A effluent is greater than the first preset fluoride ion concentration, wherein filler A is provided in column A. Filler A includes 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, and filler B includes at least one of activated alumina, activated carbon, hydroxyapatite, and resin, and the volume fractions of filler A and filler B in column A and column B are 50 to 80%, respectively.

[0016] In the method for cyclic treatment of fluorine-containing wastewater, the core of step S1 is to promote the full treatment and initial induction precipitation of fluoride ions in the wastewater with the functional groups on the surface of the filler in column A through specific filling fillers, stratified and zoned operations, and multi-stage disturbance control, so as to achieve the purpose of reducing the fluoride ion concentration in the effluent and delaying the treatment penetration. Through stratified area design and control of wastewater transfer state, each treatment site of the filler is fully utilized; by regulating the treatment-precipitation process, premature saturation is avoided, thereby delaying the penetration of column A; by accurately detecting the F⁻ concentration in the effluent, automatic switching to subsequent process steps is achieved.

[0017] The preparation steps of the zirconium oxide-aluminum oxide core-shell particles are as follows: 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.

[0018] Weigh zirconium oxychloride particles and dissolve them in deionized water to make a 0.1~0.5 mol / L zirconium salt solution. Add 30~50vol% 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.

[0019] 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 out, the particles are dried at 70 to 90°C for 6 to 12 hours to obtain precursor particles.

[0020] The dried precursor particles are slowly heated to 450-550°C and kept at a constant temperature for 2-4 hours, and a nitrogen atmosphere is introduced for preservation. During this process, the zirconium oxide sol is converted into a crystalline or quasi-crystalline zirconium oxide shell layer, forming a core-shell structure with tight coating and moderate density.

[0021] Step S1 includes: S1.1. The interior of column A is divided into three layers from bottom to top, with the bottom layer being zirconium oxide-aluminum oxide core-shell particles, the middle layer being hydroxyapatite particles, and the top layer being a mixture of aluminum oxide and silicon dioxide.

[0022] The surface of the zirconium oxide-aluminum oxide core-shell particles in the bottom layer contains both the high fluorine affinity of zirconium oxide and the rich hydroxyl functions of alumina, which can form stable zirconium-fluorine or aluminum-fluorine complexes with fluoride ions through coordination reactions. This layer mainly plays the role of capturing and fixing fluoride ions. The hydroxyapatite in the middle layer has high chemical activity and can induce the local formation of precipitation nuclei, which helps to promote the reaction of some fluoride ions with calcium ions or phosphate ions during the treatment process to form functional nuclei and increase the treatment depth. The top layer provides a large specific surface area and fine pore structure, and has a certain buffering effect, which helps to initially filter and balance the flow rate and pH changes of wastewater when it enters each zone.

[0023] S1.2. Inject the fluorine-containing wastewater and let it stand for 10 to 30 minutes. Then start a low-speed pulsating flow circulation with a flow rate of 0.5 to 1.5 L / min for 3 to 5 minutes, let it stand for 10 to 20 minutes again, and then inject disodium hydrogen phosphate solution into the bottom layer of column A. After standing for 10 to 20 minutes, the effluent from column A is obtained.

[0024] After the fluorine-containing wastewater is initially injected into column A, it is allowed to stand for 10 to 30 minutes to allow the wastewater to fully contact the filler and initially complete the treatment of fluoride ions. Then, a low-speed pulsating flow is started with a flow rate controlled at 0.5 to 1.5 L / min and run for 3 to 5 minutes to cause micro-disturbance, local mixing and mass transfer upgrade of the wastewater in the column. It is allowed to stand for another 10 to 20 minutes to provide a stable reaction environment for the subsequent stages; after the standing is completed, a disodium hydrogen phosphate solution is injected into the bottom layer of column A and allowed to stand for 10 to 20 minutes to induce local nucleation.

[0025] Ensure that the fluoride ions in the wastewater are in full contact with the surface functional groups of the filler (such as zirconium-hydroxyl, aluminum-hydroxyl, and hydroxyapatite surface active sites), which promotes surface adsorption and complexation reactions; the locally generated complexed fluoride ions are in a stable state during the static period, which is helpful for subsequent precipitation control. The mass transfer of wastewater in the static state depends on molecular diffusion, and the time window is used to make the reaction reach a balanced state.

[0026] Through micro-perturbation, local mixing of wastewater is achieved, breaking the concentration gradient and local dead zone that may occur due to static state, ensuring that all sites inside the filler participate in the reaction; at the same time, it helps to activate the interface, causing the treated fluoride ions to be partially released under external disturbances, and then recaptured by adjacent sites, thereby increasing the overall treatment rate. The shear force and microfluidic effect generated by low-speed pulsating flow are used to achieve uniform mass transfer. This dynamic adjustment can optimize precipitation behavior during chemical reactions and crystal nucleation.

[0027] After the standing period, injecting disodium hydrogen phosphate solution into the bottom layer helps to locally regulate pH and ion balance, thereby inducing partial precipitation of fluoride ions and calcium ions in the wastewater, creating favorable conditions for subsequent further treatment. Disodium hydrogen phosphate can slightly increase the concentration of phosphate ions in local areas, prompting ion exchange reactions dominated by precipitation crystallization, thereby forming stable crystal nuclei and achieving the synergistic effect of adsorption and precipitation.

[0028] S1.3, the fluoride ion concentration of the water discharged from column A is detected to determine whether the fluoride ion concentration of the water discharged from column A is greater than a preset first fluoride ion concentration, the preset first fluoride ion concentration is 0.1-1.0 mg / L. The preferred preset first fluoride ion concentration is 1 mg / L.

[0029] After the static and pulsating processes are completed, the fluoride ion concentration in the effluent water is monitored in real time through the online fluoride ion detection module configured at the bottom of column A. The ion selective electrode (ISE) or automatic online fluoride ion monitoring instrument is used to compare the test results with the preset first fluoride ion concentration threshold (0.8-1.5 mg / L) to determine whether the effluent standard is met. Ensure that the test data is real-time and accurate, and form a quantitative basis for the treatment-precipitation effect of column A; help determine whether the adsorption performance of the filler is saturated and whether it is necessary to switch to the next treatment stage. The electrochemical method (ISE) is used to achieve selective response to fluoride ions. The response potential of the electrode surface to fluoride ions is proportional to the concentration, so that the concentration signal is converted into a digital signal for storage and comparison. If the fluoride ion concentration in the effluent water is continuously detected to be greater than the preset threshold, the automatic switching process is started; this feedback mechanism ensures that the system operation is always within the optimal working range, avoiding the reduction of treatment efficiency due to saturation. By setting a threshold of 1.0 mg / L (adjustable to 0.8-1.5 mg / L), comparing the state in the column, and judging according to the dynamic change curve, a closed-loop control is formed.

[0030] 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 efficient capture of fluoride ions and delayed treatment penetration. S1.2 uses static-flow alternating operations to not only ensure full reaction between the filler and the wastewater, but also stimulate a more uniform state through local disturbances, and promote nucleus formation under suitable conditions, laying the foundation for subsequent precipitation steps. S1.3 Real-time data monitoring ensures the continuity and stability of production operations, and timely switches the treatment process through precise detection and threshold comparison, which helps to achieve full process automation and energy consumption optimization, and improve the reliability and economy of the overall system.

[0031] If not, that is, the fluoride ion concentration of the water discharged from column A is less than the preset first fluoride ion concentration, the liquid in column A is discharged, confirming that the treatment of the fluoride-containing wastewater is completed.

[0032] When the system detects that the fluoride ion concentration in the effluent of column A is lower than the set first threshold value (such as 0.1~1.0 mg / L), it means that filler A still has the ability to treat fluoride ions, and the fluoride ion concentration in the wastewater has dropped to the safe / standard range. The system can terminate further processing steps at this time (for example, there is no need to switch column B, and there is no need to enter the crystallization treatment / regeneration step), thereby avoiding energy consumption, manpower and reagent waste, realizing the intelligent control strategy of on-demand operation, and improving the overall operation efficiency and economy of the treatment system. The preset first fluoride ion concentration set in this step is used as the safety lower limit criterion. If two consecutive monitorings show that the fluoride ion concentration is lower than the threshold value (such as 1.0 mg / L), the system can automatically determine that the current wastewater has been treated and can be safely discharged or transferred to the downstream link. This step can be used as the termination signal point of the entire process flow to realize the closed-loop logic of the treatment system.

[0033] This judgment mechanism allows the system to flexibly decide the depth of treatment according to the influent conditions of different batches and different concentrations. If the fluoride ion concentration of some wastewater is low and reaches the standard after one treatment in column A, it does not need to go through the complete double column, crystallization, regeneration and other time-consuming steps. This can significantly improve the system's adaptability to the treatment of fluctuating water quality in actual engineering applications and avoid a one-size-fits-all treatment strategy. When the detection system (such as ISE / IC) detects that the fluoride ion concentration is stable below the standard value, the system can automatically record the end of the treatment, stop the water inlet, empty the system, backwash with clean water, and enter the standby state in turn. It can be integrated into the control system to achieve a 24-hour unattended intelligent treatment mode.

[0034] 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 the second preset fluoride ion concentration, wherein filler B is provided in column B.

[0035] Step S2 includes: S2.1. If the fluoride ion concentration of the effluent from column A is greater than the preset first fluoride ion concentration, the effluent from column A is connected to a buffer reactor containing disodium hydrogen phosphate and calcium chloride, and the pH is adjusted to 7.2-7.5. After standing for 10-20 minutes, the effluent is introduced into column B.

[0036] When the fluoride ion concentration in the effluent of column A is greater than the preset first fluoride ion concentration, the effluent of column A is automatically introduced into the buffer reactor set in the system. The mixed solution containing disodium hydrogen phosphate and calcium chloride is adjusted to pH 7.2~7.5 to establish a relatively stable neutral reaction environment for the system. It is left to stand in the buffer reactor for 10~20 minutes, so that some fluoride ions attached to the surface of filler A in the wastewater are released under local control conditions, and combined with calcium ions and phosphate ions to induce the formation of primary crystal nuclei. Subsequently, the regulated wastewater is introduced into column B. By adding disodium hydrogen phosphate and calcium chloride, a local ion environment is formed in the buffer reactor, which promotes some fluoride ions to react with calcium ions to form primary calcium fluoride crystal nuclei or primary fluoroapatite nuclei. This not only reduces the fluoride ion concentration in the wastewater, but also provides a crystal nucleus anchor point for subsequent treatment. Using the theory of ion balance and solubility product, under neutral conditions of pH 7.2~7.5, the rate of precipitation generated by the reaction of calcium ions and fluoride ions is increased, and at the same time, phosphate ions can participate in the formation of a stable crystal nucleus structure. After buffer pretreatment, the fluoride ions in the wastewater are more evenly distributed, reducing local concentration differences, which is conducive to achieving more consistent treatment effects in column B. The buffer adjusts pH and ion concentration to alleviate the uneven loading problem caused by uneven water inflow or local saturation of the filler surface, allowing subsequent treatment processes to proceed along a more uniform reaction interface.

[0037] S2.2. Perform magnetic stirring at the water inlet of column B for 2 to 5 minutes. Let the mixture 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 the preset second fluoride ion concentration, which is 0.1 to 1.0 mg / L.

[0038] A magnetic stirring device is installed at the water inlet of column B, and a magnetic stirring bar or ultrasonic pulse device is used to make the wastewater entering column B produce a uniform mixing effect. Start the magnetic stirring for 2~5 minutes, then stop the stirring and let it stand for 10~20 minutes to ensure that the wastewater is fully in contact with filler B in column B. After standing, take a sample from the outlet of column B for fluoride ion concentration detection to determine whether it reaches the preset second fluoride ion concentration (0.1~1.0 mg / L). Through magnetic stirring, the local concentration gradient caused by uneven flow in column B is effectively broken, so that the fluoride ions in the wastewater are evenly distributed throughout the column, ensuring that filler B fully exerts its treatment capacity. The disturbance caused by magnetic stirring not only enhances the contact between the wastewater and the filler surface, but also reduces the competition caused by excessive local concentration, so that the remaining fluoride ions can be more effectively combined with the functional groups (such as activated alumina, activated carbon, etc.) on filler B. The alternating stirring and static mode enables sufficient homogenization and mass transfer to be achieved in a short time, and the static period can provide a stable reaction environment, which promotes the adsorption and induced precipitation process to fully develop and reduce the fluoride ion concentration in the effluent of column B. This operation mode uses the characteristics of the liquid's alternating movement and static state to break the concentration dead zone during the stirring period and to allow the system to tend to a balanced state during the static period, thereby optimizing the entire treatment process.

[0039] If not, that is, the fluoride ion concentration of the effluent from column B is less than the preset second fluoride ion concentration, the liquid in column B is discharged to confirm 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 preset second fluoride ion concentration, the treatment is confirmed to be complete and the wastewater is discharged.

[0040] 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: 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, which is obtained by online monitoring or timed sampling. is the treatment time (min), which starts from the time when the fluorine-containing wastewater starts 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 flow meter 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 the range can be 2~10 mg or g. is the first rate constant (1 / min), 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 filler A or filler B. Predict at what time point 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 decrease of fluoride ion concentration slows down, 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 running industrial systems and can be used as an important parameter for whether to switch to column B or recycle. is the second rate constant (mL / (mg·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 0.01 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 may be 200-800 g.

[0041] 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 into columns A and B, let the reaction stand for 0.5 to 3 hours, then recover the first crystallization solution and clean filler A and filler B.

[0042] This step belongs to the treatment stage after the column treatment function is saturated. The purpose is to recover the residual fluoride ions on the material; to achieve induced crystallization so that the fluoride ions are precipitated in a stable form; to clean the surface of the filler and restore the performance; and to achieve the recycling of the adsorption-precipitation system. Its key value lies in coupling adsorption, induced crystallization, and desorption cleaning into a continuous process to maximize the system treatment efficiency and material regeneration performance.

[0043] Step S3 includes: S3.1. If the fluoride ion concentration of the effluent from column B is greater than the preset second 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.

[0044] When the online detection shows that the fluoride ion concentration in the outlet water 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 drain 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 data feedback closed loop, meeting the requirements of automated continuous processing. The recovery device can be set as a special recovery chamber. The specific structure is known to those skilled in the art and will not be repeated here.

[0045] S3.2. Inject sodium hydroxide solution into columns A and B respectively, adjust the pH to 9.0, and let stand for 5 to 10 minutes.

[0046] The injection of sodium hydroxide solution adjusts the column environment from neutral or slightly acidic to alkaline (about pH 9.0), which helps to destroy some of the zirconium-fluorine or aluminum-fluorine complex bonds that have been formed, partially release fluoride ions from the surface of the filler, and improve the activity of the subsequent crystallization reaction. Under alkaline conditions, some of the adsorbed fluoride ions can be converted into a free state, thereby providing enough 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.

[0047] The first crystallization solution induces the formation of crystal nuclei in the column through calcium ions, magnesium ions, phosphate ions in the solution and the released fluoride ions to form calcium fluoride, magnesium fluoride or fluoroapatite 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 the solution can be used for the next cycle after appropriate adjustment, which plays a role in resource recovery and reuse. Using the solubility product principle and supersaturation conditions, a sparingly soluble salt precipitate is generated in a stable alkaline environment, and the formation of a composite crystal phase is assisted by auxiliary ions. This step uses the method of ion-induced crystallization to control precipitation, and optimizes the process parameters to ensure that the crystal nucleus is born and further grows to a recyclable particle size range. The first crystallization solution recovered after the static reaction can be recycled for the next batch of wastewater treatment after appropriate adjustment, reducing the consumption of reagents and operating costs. Using the principle of conservation of matter and solution regulation, after multiple cycles of use, the concentration of active components in the solution is kept within a suitable range through online detection and regular replenishment of medicines, so as to maximize the utilization of chemical resources.

[0048] S3.3, inject the first crystallization solution into column A and column B respectively, and recover the first crystallization solution after standing for 0.5 to 3 hours. The first crystallization solution includes at least one of calcium chloride, magnesium chloride, calcium nitrate, magnesium nitrate, ammonium bicarbonate, sodium citrate, and calcium fluorophosphate, and the volume ratio of the first crystallization solution to filler A is (0.5 to 3):1.

[0049] S3.4. Detect whether the effective solubility of the recovered first crystallization solution is less than a preset recovery concentration, wherein the preset recovery concentration is 800-1000 mg / L.

[0050] If the effective ingredients drop significantly (<800 mg / L), it means that a large amount of calcium ions and other ions have been consumed by precipitation, the crystallization reaction is sufficient, and the amount of crystal nuclei deposited is large. Concentration detection can be used to determine whether the crystallization solution of this round has the reaction capacity to be used again, which is the basis for implementing multiple cycles. When the crystal nuclei are generated to treat calcium ions / phosphate ions, the free ion concentration in the solution will decrease, forming a quantitative criterion. The concentration, as a function of the reaction rate, can quantitatively reflect that the system has entered the precipitation reaction plateau period.

[0051] S3.5. If yes, increase the first crystal solubility until reaching the preset reaction concentration, the preset reaction concentration is 1500-2000 mg / L, and then execute step S3.4.

[0052] The addition method can extend the service life of the first crystallization solution and realize a closed-loop circulation of resources. Maintaining a supersaturated state prevents the problem of slow nucleation rate and insufficient precipitation, and improves the consistency of the reaction. Maintaining the calcium ion / fluoride ion ratio in the ideal reaction ratio range (for example, 2:1) is a necessary condition to ensure the continuous precipitation of calcium fluoride. Dynamically adjusting the concentration of the reactant is a chemical buffering method to prevent the reaction from entering the diffusion / equilibrium limited stage.

[0053] S3.6. If not, place the recovered first crystallization solution in columns A and B, and then perform step S3.3.

[0054] The same batch of crystallization solution can be used multiple times, which significantly reduces the consumption of reagents such as calcium chloride, which is in line with the concept of green chemistry. The reused crystallization solution still contains high concentrations of calcium ions, phosphate ions, etc., which can continuously provide reaction power in multiple cycles.

[0055] 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, so that the residual concentration of calcium ions introduced into the first crystallization solution in the first cycle can be calculated. The residual concentration of calcium ions introduced into the first crystallization solution in multiple cycles can also be calculated. The calculation formula is as follows: in, is the residual calcium ion concentration in the first crystallization solution recovered (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).

[0056] 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.

[0057] 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.

[0058] The alternating air and water flushing operation can utilize the dual effects of physical impact and liquid flushing to remove and collect crystals on the surface and pores of the filler, and restore the original specific surface area and treatment sites of the filler. The air flushing provides an instantaneous high-pressure impact to destroy the adhesion layer on the surface of the filler, while the water flushing utilizes the penetration and flow rate effects of water to effectively carry away and collect the scattered crystals, thereby reducing the risk of filler blockage. The thoroughly cleaned filler can be reused for the next cycle of wastewater treatment, ensuring the long-term stable operation of the system and reducing operating costs. By alternating flushing, not only physical cleaning is achieved, but also the passivation of the active sites of the filler by chemical residues is avoided to a certain extent, thereby extending the service life of the filler.

[0059] S4. After cleaning, add the second crystallization solution to both column A and column B, let it stand for 3 to 5 hours, then 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 of column A is less than or equal to the first preset fluoride ion concentration or the fluoride ion concentration of the water outlet of 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%.

[0060] If some fluoride ions still remain in the pores of the filler, the surface micro-regions or the unconverted complex state during the S3 treatment process, the crystallization reaction can continue to cause the crystallization precipitation reaction in the local microenvironment by standing for 3 to 5 hours. A reaction induction layer (such as calcium phosphate / calcium fluoride microcrystals) is deposited on the surface of the filler to provide a nucleation template for the next round of fluoride-containing wastewater entering the system, improve the starting efficiency of the fluoride ion reaction, and achieve an effect similar to surface crystallization pre-activation. Under static conditions, the second crystallization solution maintains a high calcium ion and phosphate ion environment, so that the fluoride ions in the wastewater (including the attached state and the solution state) undergo precipitation reactions, and the surface of the crystal nucleation inducer (such as fluoroapatite) provides an ordered crystal plane, which accelerates the heterogeneous nucleation process and improves the crystal generation rate and uniformity.

[0061] The filler regeneration, crystal precipitation, and crystal liquid reuse are organically connected with the next treatment cycle to form a closed loop of the entire process. Before executing S1 again, the surface of filler A / B is already attached with an induced crystal nucleus layer, the initial adsorption reaction rate is higher, and the reaction conditions are more controllable, which helps the system to run quickly and stably when entering a new round of treatment cycle.

[0062] The present invention obtains the chemical content data in the effluent through multiple embodiments, and refers to the local requirement that the effluent meet the Class III standard of the "Surface Water Environmental Quality Standard" to determine whether the process of the present invention can be connected to the subsequent water treatment process. The results are shown in the following table. The effluent of the embodiment of the present invention has a better treatment effect on fluorine-containing wastewater than the coagulation and sedimentation effluent, and can replace the traditional coagulation and sedimentation process, and be combined with subsequent treatment processes such as biochemical pools and artificial wetlands. The specific content of the above standards is known to those skilled in the art and will not be repeated here.

[0063] 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, the traditional process is unqualified, and the effluent turbidity is extremely low, far lower than the traditional method, which is conducive to further membrane treatment or standard discharge.

[0064] 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 protection scope of the present invention.

Claims

1. A method for circulating treatment of fluorine-containing wastewater, characterized in that the steps include: S1, introducing fluorine-containing wastewater into column A, maintaining for 3 to 60 minutes, obtaining 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 filler A is used to treat fluoride ions; S2. If yes, the effluent from column A is introduced into column B and kept for 3 to 60 minutes to obtain effluent from column B, and the fluoride ion concentration of the effluent from column B is detected to be greater than a second preset fluoride ion concentration, wherein a filler B is provided in column B, and the filler B is used to treat fluoride ions; S3, if yes, stop introducing the fluorine-containing wastewater, empty the liquid in the column A and the column B into the recovery device, add the first crystallization solution to the column A and the column B, let it stand for 0.5 to 3 hours, then recover the first crystallization solution and clean the filler A and the filler B; S4. After cleaning, add a second crystallization solution to both column A and column B, let it stand for 3 to 5 hours, then recover the second crystallization solution, mix the recovered second crystallization solution with the liquid in the recovery device, and execute 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 treatment of fluorine-containing wastewater according to claim 1, characterized in that: 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 fillers A and B in the column A and the column B are 50-80%, respectively.

3. The method for circulating treatment of 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 treatment of fluorine-containing wastewater according to claim 1, characterized in that: Step S1 includes: S1.

1. The interior of column A is divided into three layers from bottom to top, with the bottom layer being zirconium oxide-alumina core-shell particles, the middle layer being hydroxyapatite particles, and the top layer being a mixture of alumina and silicon dioxide; S1.2, inject the fluorine-containing wastewater and let it stand for 10 to 30 minutes, then start a low-speed pulsating flow circulation with a flow rate of 0.5 to 1.5 L / min for 3 to 5 minutes, let it stand for 10 to 20 minutes again, and then inject disodium hydrogen phosphate solution into the bottom layer of column A, let it stand for 10 to 20 minutes, and obtain the effluent of column A; S1.

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

5. The method for circulating treatment of 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.

6. 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 preset first fluoride ion concentration, the effluent from column A is connected to a buffer reactor containing disodium hydrogen phosphate and calcium chloride, the pH is adjusted to 7.2-7.5, and the effluent is introduced into column B after standing for 10-20 minutes; 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 preset second fluoride ion concentration, which is 0.1 to 1.0 mg / L.

7. 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.

8. 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 the preset second fluoride ion concentration, the introduction of fluoride-containing wastewater is stopped, and the liquid in the columns A and B is drained into the recovery device; S3.2, inject sodium hydroxide solution into column A and column B respectively, 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 solubility of the first crystallization solution recovered is less than a preset recovery concentration, wherein the preset recovery concentration is 800-1000 mg / L; S3.

5. If yes, increase the first crystallization solution until the preset reaction concentration is reached, the preset reaction concentration is 1500-2000 mg / L, and then execute step S3.4; S3.6, if not, placing the recovered first crystallization solution in the column A and the column B, and then performing step S3.3; S3.7, 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.

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