Low-concentration fluorine-containing wastewater treatment process

Abstract

The invention discloses a low-concentration fluorine-containing wastewater treatment process, and belongs to the field of sewage treatment. The process comprises the following steps: pumping the low-concentration fluorine-containing wastewater with the fluorine ion concentration of 10-20 mg / L into an acid-base adjusting tank, adding sulfuric acid and a caustic soda solution according to the pH value of the solution, and adjusting the pH value of the solution to 6.3-6.8; after acid-base adjustment, pumping the mixed solution into a defluorination reaction tank, adding an aluminum-based defluorination agent, and carrying out a defluorination stirring reaction; after defluorination reaction, pumping into an adsorption tank, and adding an inorganic adsorbent for adsorption and condensation reaction; after the adsorption and coagulation reaction is finished, pumping into a flocculation basin, and adding an organic flocculant into the flocculation basin to carry out a flocculation reaction; after the flocculation reaction is finished, pumping into a sedimentation tank, standing, taking supernate, measuring the fluorine ion concentration, and reducing the fluorine ion concentration to 0.5-2 mg / L after the reaction; and part of the inorganic adsorbent is recovered from the precipitate after solid-liquid separation after precipitation by a recovery device, so that the problems of poor dosage of a single aluminum-based defluorination agent, poor flocculate settling performance and high sludge yield are solved.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of sewage treatment, and particularly relates to a low-concentration fluorine-containing wastewater treatment process. BACKGROUND

[0002] With the development of industrialization, metal processing, glass, semiconductor manufacturing, smelting, electroplating and many other industries are involved in the production and discharge of fluorides, and the discharge of fluorine-containing wastewater is increasing. At present, the main defluorination technologies include ion exchange, chemical precipitation, membrane filtration, coagulation sedimentation, adsorption and bioremediation, among which coagulation sedimentation and adsorption are two important technologies for defluorination. The general process of defluorination is to form fluorine-containing compounds by adding chemicals to water. The most common method is to add calcium ions (Ca 2+ ) to fluorine-containing water, which reacts with fluorides to form calcium fluoride precipitate (fluorite), thereby achieving the purpose of removing fluorides. However, according to the solubility of fluorite (Ksp = 3.46×10 -11 ), when the fluoride concentration in wastewater is less than 100 mg / L, calcium fluoride precipitate is not easy to form, and the final concentration of fluorides after treatment by precipitation method can only reach 10-20 mg / L. Therefore, calcium precipitation method is only suitable for the treatment of high-concentration fluorine-containing industrial wastewater in electronic and photovoltaic industries. According to the hard-soft acid-base theory of Pearson, fluorine ions have high electronegativity and small ion radius (hard base) and have strong affinity with aluminum ions (hard acid). Therefore, aluminum-containing materials have been widely used in the study of removing fluorides from water.

[0003] Coagulation sedimentation technology has been widely applied due to its low cost, high efficiency and simple operation, but it still has the disadvantages of large amount of coagulant dosage, poor settling performance of reaction products, and large amount of sludge produced. Adsorption technology is also commonly used for defluorination of drinking water due to its simple operation, low cost and easy access to adsorbents (such as alumina, activated carbon, ion exchange resins, natural materials such as clay, and low-cost materials such as fly ash, bone char, metal iron, nanomaterials, etc.). However, the composition of industrial wastewater is more complex, and the selective adsorption performance of adsorbent materials is more easily affected by the complex components in wastewater. In addition, factors such as surface modification process and preparation conditions of adsorbents limit their large-scale application in wastewater.

[0004] Patent with publication number CN 120271181 A proposes a high-concentration fluorine-containing wastewater treatment process based on in-situ calcium ion generation. The invention uses calcium ions to remove fluorine, adjusts the pH of the reaction solution in stages to improve the efficiency of calcium ion fluorine removal, and adds more than 2000 mg / L of polyaluminum chloride to further remove fluoride ions. Although the invention increases the concentration of calcium hydroxide in the solution by adjusting the pH of the solution, thereby increasing the efficiency of the reaction with fluoride ions, during the acid adjustment process, if the pH is too low, it can easily cause corrosion of the equipment in the reaction container. On the other hand, the calcium ion reaction increases the hardness of the solution, causing fouling and clogging of the membrane module during subsequent membrane filtration, affecting equipment stability. Calcium-based defluorination agents such as calcium oxide (CaO), calcium hydroxide (Ca(OH)2), or calcium salt (CaSO4, CaCl2) mainly rely on the reaction of calcium hydroxide with fluoride ions to generate fluorite (CaF2) to remove fluorides. Due to the low solubility of calcium hydroxide, on the one hand, a large amount of calcium-containing defluorination agent needs to be added to maintain the concentration of calcium hydroxide in the solution, which can easily lead to an increase in solution hardness. On the other hand, fluorite has high solubility and is prone to hydrolysis, which can reduce the efficiency of defluorination and increase the amount of defluorination agent used and the cost of treatment.

[0005] Patent with publication number CN 110372075 A proposes a new type of high-efficiency defluorination agent, which is made from polyferric chloride, polyferric sulfate, polyaluminum sulfate, polyaluminum ferric sulfate, polyaluminum chloride, tea leaf iron, modified fly ash, modified zeolite, calcium hydrogen phosphate, and coagulant. The mixture of iron-based and aluminum-based polymers improves the defluorination efficiency, and the modification of related inorganic materials improves the reaction efficiency of the defluorination agent. In this patent, the modification process of zeolite and fly ash involves calcium hydroxide treatment, which can easily cause calcium to adhere to the materials, affecting their porosity, and the combination efficiency of calcium and fluorine is low, thus affecting the overall defluorination effect. In addition, the modification of zeolite with hydrochloric acid can cause the precipitation of Al atoms in the zeolite, leading to the collapse of the crystal structure and affecting its adsorption performance. Traditional aluminum-based defluorination agents (such as alum, polyaluminum sulfate, and polyaluminum chloride) will preferentially form aluminum hydroxide (Al(OH)3) precipitates in neutral and weak alkaline solutions, adsorb fluoride ions to form complexes, and precipitate by adding flocculants. On the one hand, a large dose of aluminum-based defluorination agent needs to be added to ensure the defluorination effect, and a large amount of aluminum-containing sludge will be produced. On the other hand, the form of aluminum in the aluminum-based defluorination agent affects the defluorination efficiency and reaction time, and the efficiency of removing fluoride ions by aluminum hydroxide is low. Therefore, during the defluorination process, especially in the deep defluorination process, it is necessary to not only meet the requirements of high-efficiency defluorination but also avoid the accumulation of calcium-containing and aluminum-containing agents in the solution and sludge. SUMMARY

[0006] The present application aims to provide a defluorination process for industrial low-concentration fluorine-containing wastewater (10-20 mg / L), to solve the problems of low-concentration fluorine-containing industrial wastewater, such as single aluminum-based defluorination agent dosage, poor flocculation performance, and high sludge yield. The defluorination agent of the present application forms a metal oxide precipitate with a three-dimensional structure in water through high-valent metal cations, and removes fluorine ions in water through adsorption and co-precipitation reactions. The defluorination agent of the present application has a small dosage, a fast treatment process, can significantly improve the defluorination efficiency, and reduce the aluminum residual concentration. The solution of the present application is as follows: A low-concentration fluorine-containing wastewater treatment process, comprising the following steps: S1, acid-base adjustment: pump low-concentration fluorine-containing wastewater with a fluorine ion concentration of 10-20 mg / L into an acid-base adjustment tank, add sulfuric acid and caustic soda solution according to the pH value of the solution, and adjust the pH of the solution to 6.3-6.8; S2, defluorination reaction: pump the mixed solution after acid-base adjustment into a defluorination reaction tank, and add an aluminum-based defluorination agent for defluorination stirring reaction; S3, adsorption and coagulation: after defluorination reaction, pump into an adsorption tank and add inorganic adsorbent for adsorption and coagulation reaction; S4, flocculation: after the adsorption and coagulation reaction is completed, pump into a flocculation tank, and add an organic flocculating agent for flocculation reaction; S5, precipitation: after the flocculation reaction is completed, pump into a precipitation tank for standing, and measure the fluorine ion concentration of the supernatant. The fluorine ion concentration after reaction is reduced to 0.5-2 mg / L; S6, inorganic adsorbent recovery: after the precipitation, the precipitate after solid-liquid separation is recovered by a recovery device.

[0007] The defluorination agent of the present application can, through the interaction of aluminum-based defluorination agent, inorganic adsorbent, and organic flocculating agent, in a relatively short time, perform sweeping, electric neutralization, ion exchange, and adsorption bridging on low-concentration fluorine ions in the solution, and the formed fluorine-containing complex and insoluble substance are removed by rapid precipitation. Compared with existing defluorination agents, the treatment process is simple, the amount of agent used is less, the precipitation effect is good, the defluorination efficiency is high, and the aluminum residual content is low.

[0008] The aluminum-based defluorination agent does not significantly reduce the pH value of the treated water under neutral and weak acid conditions, thereby ensuring the defluorination performance of various polyaluminum hydroxides, and a low aluminum residual content in the solution after reaction. Since the hydrolysis products of Al 13 and Al 30 in the aluminum-based polymer have more positive charges, they have a higher degree of combination with negatively charged F−, and are more stable during stirring reaction, so the removal rate of fluorine ions is also higher. In addition, a large number of hydroxyl groups carried by the inorganic adsorbent can form Al(OH)3 with free Al 3+ , and F -The reaction further reduces the F in the solution. - Concentration and residual aluminum content; on the other hand, because it is alkaline in solution, it can react with H+ in the solution. + The reaction makes the overall solution neutral. After the reaction between the aluminum-based defluorinating agent and the inorganic adsorbent, the organic flocculant acts as a bridging agent, causing the aluminum-based defluorinating agent, the inorganic adsorbent, and the aluminum fluorine hydroxyl compounds formed with fluoride ions to aggregate into larger aggregates, thus destabilizing and precipitating. The solid precipitate is then pumped into the inorganic adsorbent recovery unit.

[0009] Preferably, the aluminum-based defluorinating agent, by weight percentage, includes: Polyaluminum chloride 45-60%; Polyaluminum ferric sulfate 20-40%; Aluminum chloride 5-15%.

[0010] Among them, polyaluminum chloride has an alumina mass fraction of ≥10%, a basicity of 40~60%, and a total iron mass fraction of 1.5%; polyferric sulfate has a total iron mass fraction of 11% and a basicity of 10~19%.

[0011] Preferably, the inorganic adsorbent is a porous material modified by mixing zeolite and metakaolin powder. The mass fraction of zeolite in the inorganic adsorbent is 55-65%, and the mass fraction of metakaolin powder is 35-45%. The modification process is as follows: take metakaolin and zeolite powder that have passed through a 250-mesh sieve, mix them in proportion, add them to a 5% sodium hydroxide solution, stir in a water bath at 60°C for 8 hours, filter, and dry at 105-110°C. The mass ratio of powder to sodium hydroxide is 2:1.

[0012] Preferably, the organic flocculant is selected from at least one of water-soluble cationic chitosan quaternary ammonium salt or polydimethyldiallylammonium chloride.

[0013] Preferably, the amount of aluminum-based defluorinating agent added is 600~1600 mg / L.

[0014] Preferably, the amount of inorganic adsorbent added is 150~300 mg / L.

[0015] Preferably, the amount of organic flocculant added is 0.5~1 mg / L.

[0016] Preferably, the stirring speed in the defluorination reaction is 60~80 r / min, and the reaction time is 2~5 min; Preferably, the stirring speed for the adsorption-coagulation reaction is 25-35 r / min, and the reaction time is 2-5 min.

[0017] Preferably, the stirring speed for the flocculation reaction is 5~15 r / min, the reaction time is 4~7 min, and the settling time in the sedimentation tank is 5~15 min.

[0018] The technical solution of this invention has the following beneficial technical effects: This invention uses an aluminum-based defluorinating agent, polyaluminum chloride, an inorganic adsorbent, and an organic flocculant, anionic polyacrylamide, to form a highly efficient defluorinating agent. It is inexpensive, requires a small dosage, and the inorganic adsorbent is widely available and easy to prepare. It can achieve rapid and efficient removal of fluoride ions in a weakly acidic environment. It features good settling properties, low residual aluminum content, low sludge production, low defluorination cost, and simple operation.

[0019] Under the same fluoride ion removal rate, compared with the fluoride removal process that only adds aluminum-based fluoride removers and organic flocculants, the fluoride removal agent and method of the present invention reduce the dosage of aluminum-based fluoride removers by 15-30%, shorten the reaction and precipitation time by 30-45%, and reduce the overall cost by 15-20% compared with aluminum sulfate, aluminum chloride, and aluminum-based fluoride removers. By adjusting the acid and base to maintain a weakly acidic environment in the solution, the hydrolysis and adsorption of fluoride ions by aluminum hydroxyl groups in the aluminum-based fluoride remover, as well as the formation of Al-F complexes, are promoted. The addition of inorganic adsorbents promotes the formation of Al-F complexes, enhances the removal of fluoride ions from the solution, and neutralizes H+ in the solution. + On the other hand, the inorganic adsorbent, acting as a powder adsorption carrier, increases the adsorption of fluoride ions and suspended solids, while simultaneously increasing the density of agglomerates formed by various complexes and colloids, thereby improving the agglomerate settling rate and shortening the sedimentation time. The addition of a small amount of organic flocculant accelerates the adsorption bridging effect of the flocs, resulting in larger floc sizes, further shortening the sedimentation time and improving reaction efficiency. The industrial wastewater defluoridator of this invention exhibits good removal efficiency for fluoride ion concentrations of 10-20 mg / L. Furthermore, due to the addition of the inorganic adsorbent, the numerous hydroxyl groups on the surface of the inorganic adsorbent can react with metal ions, removing fluoride through adsorption and co-precipitation, demonstrating good defluoridation performance even under high hardness conditions.

[0020] Furthermore, other beneficial effects of the present invention will be mentioned in the specific embodiments. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of a low-concentration fluoride-containing wastewater treatment process in this scheme; In order to make the objects, technical solutions and advantages of the present application clearer, the technical solutions in the present application will be described clearly and completely below in conjunction with the drawings in the present application. Obviously, the described embodiments are some of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative work fall within the protection scope of the present application. DETAILED DESCRIPTION

[0022] In order to make the objects, technical solutions and advantages of the present application clearer, the technical solutions in the present application will be described clearly and completely below in conjunction with the drawings in the present application. Obviously, the described embodiments are some of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative work fall within the protection scope of the present application.

[0023] As shown in Figure 1 , a low-concentration fluorine-containing wastewater treatment process comprises the following steps: S1, acid-base adjustment: pump 10-20 mg / L of low-concentration fluorine-containing wastewater into an acid-base adjustment tank, and add sulfuric acid / alkali solution according to the pH value of the solution to adjust the pH of the solution to 6.3-6.8; S2, defluorination reaction: pump the mixed solution after the acid-base adjustment into a defluorination reaction tank, and add 600-1600 mg / L of aluminum-based defluorination agent to perform defluorination stirring reaction, with a stirring speed of 60-80 r / min and a mixing reaction time of 2-5 min.

[0024] The aluminum-based defluorination agent comprises, in terms of mass percentage: 45-60% of polyaluminum chloride, 20-40% of polyaluminum ferric sulfate, and 5-15% of aluminum chloride. In all the embodiments of the present solution, the aluminum-based defluorination agent comprises 60% of polyaluminum chloride, 30% of polyaluminum ferric sulfate, and 10% of aluminum chloride, wherein the polyaluminum chloride has an alumina mass fraction of ≥10%, a basicity of 40-60%, and a total iron mass fraction of 1.5%; the polyaluminum ferric sulfate has a total iron mass fraction of 11% and a basicity of 10-19%.

[0025] Due to the low aluminum content of the aluminum-based polymer, a small amount of aluminum chloride is added to the polymer to increase the monomer Al 3+ concentration in the defluorination process and further improve the defluorination efficiency. In addition, the polyaluminum chloride and the polyaluminum ferric sulfate with basicities of 40-60% and 10-19% respectively contain more medium-polymerized aluminum hydroxyl (Al 13 ) and high-polymerized aluminum hydroxyl (Al 30 ), wherein Al 13 and Al 30Al possesses high positive charge density and good coagulation performance, making it an important form for removing low concentrations of fluoride ions. 13 Belonging to the category of highly charged nanoscale molecules, these molecules possess multiple coordinating hydroxyl groups. In neutral solutions, they can adsorb F ions onto the Al surface through hydrogen bonding and ion exchange, forming Al-F complexes. 30 In a weakly acidic environment, it can hydrolyze into an aluminum hydroxide colloidal system, primarily adsorbing fluoride ions through trapping and charge neutralization. This creates overall charge neutrality in the adsorption region, causing the adsorption system to become unstable and precipitate. Different aluminum hydroxyl groups in the aluminum-based polymer can react with fluoride ions not only through valence bonds and coordination interactions, but also through electrostatic interactions to form bridging and charge neutralization with other substances in the solution, forming larger flocs that remove fluorides and suspended solids. Furthermore, the iron in polyaluminum ferric sulfate forms hydroxides in the solution, further enhancing the removal of fluoride ions.

[0026] S3. Adsorption and coagulation: After the fluoride removal reaction, the solution is pumped into the adsorption tank and 150~300 mg / L of inorganic adsorbent is added to carry out the adsorption and coagulation reaction. The stirring speed is 25~35 r / min and the reaction time is 2~5 min.

[0027] Inorganic adsorbents are porous materials modified from a mixture of zeolite and metakaolin powder, mainly containing SiO2, Al2O3, Fe2O3, etc. The mass fractions of zeolite (>250 mesh) and metakaolin powder (>250 mesh) in the inorganic adsorbent are 55-65% and 35-45%, respectively.

[0028] In all embodiments of this scheme, the mass fractions of zeolite and metakaolin powder in the inorganic adsorbent are 55% and 45%, respectively.

[0029] The inorganic adsorbent modification process is as follows: A certain amount of metakaolin and zeolite powder that have passed through a 250-mesh sieve are mixed in a certain proportion and then added to a 5% sodium hydroxide solution. The mixture is stirred in a water bath at 60°C for 8 hours, filtered, and then dried at 105~110°C. The mass ratio of powder to sodium hydroxide is 2:1.

[0030] After modification, the metakaolin and zeolite powder in the inorganic adsorbent can enhance the performance of the OH- in the alkaline solution. -The Si-O bond in the crystal structure in the powder reacts to generate Si(OH)4 and related products, replacing the Si atoms in the crystal structure, on the one hand, to cause vacancies in the original crystal structure, increase the internal active adsorption channels and points, thereby increasing the specific surface area and pore volume of the metakaolin and zeolite powder, and being able to adsorb various suspended and colloidal substances in the solution and attract and agglomerate into larger flocs; on the other hand, the Al in the modified crystal can be complexed with the fluoride ions in the solution to form Al-F complexes, and through the precipitation process, the fluoride ions are removed from the solution. In addition, the modified powder surface has a large number of hydroxyl groups, which can be ion exchanged with fluoride ions in the solution, and at the same time, combined with metal cations to form larger metal hydroxide precipitates, thereby enhancing the trapping effect of fluoride ions in the precipitation process. Due to the stirring and mixing effect, the powder adsorbent not only can increase the collision frequency of various suspended substances in the solution, promote the coagulation between particles, form larger flocs, and accelerate the settling, but also can act as a coagulation nucleus and adsorption carrier of the flocs in the solution, increase the density of the suspended flocs in the reaction solution, further increase the settling speed of the flocs, and shorten the reaction time.

[0031] S4, flocculation: after the reaction, the solution is pumped into a flocculation tank, and an organic flocculant is added to the flocculation tank at a dosage of 0.5-1 mg / L for flocculation reaction, the stirring speed is 5-15 r / min, and the reaction time is 4-7 min.

[0032] The organic flocculant is at least one of water-soluble cationic chitosan quaternary ammonium salt and polydimethyl diallyl ammonium chloride; in the embodiment of the present scheme, the organic flocculant is polydimethyl diallyl ammonium chloride; S5, flocculation: after the reaction, the solution is pumped into a precipitation tank and left to stand for 5-15 min, the supernatant is taken to measure the fluoride ion concentration, and the fluoride ion concentration after the reaction can be reduced to 0.5-2 mg / L; S6, inorganic adsorbent recovery: the precipitate after solid-liquid separation is recovered by a recovery device. The inorganic adsorbent is added into the defluorination reaction process device at a dosage of 4-8% of the reaction water volume, and participates in the defluorination reaction process again. The recovery device includes a high-speed shearing machine and a cyclone separator. The aluminum fluoride hydroxide on the surface and in the interstices of the solid precipitate after the reaction can be removed by the recovery device, the adsorption performance is restored, and the inorganic adsorbent is continuously added into the defluorination reaction process at a small proportion, so that the use amount of the inorganic adsorbent can be reduced, the concentration of the solid coagulation nucleus in the reaction process can be ensured, the flocculation and precipitation effect can be strengthened, and the reaction and precipitation time can be shortened.

[0033] Hereinafter, the examples of the present application will be described. The examples described below are illustrative and are not to be taken as limiting of the present application. Where specific technical or conditions are not mentioned in the examples, the techniques or conditions described in the literature in the field or according to the product manual are used. Where the manufacturer of a reagent or instrument is not mentioned, it is not to be construed as being a limitation of the present application, but rather a routine choice. First Embodiment,

[0034] 1. A certain industrial wastewater was taken, and the fluoride ion concentration was measured to be 14.8 mg / L, the total hardness (CaCO3) was 1750 mg / L, and the pH was 7.36.

[0035] 2. The fluoride-containing wastewater with a known fluoride ion concentration was pumped into the adjusting tank, and dilute sulfuric acid solution was added to adjust the pH of the solution to 6.3. 3. After the pH adjustment, the mixed solution was pumped into the defluorination tank, and aluminum-based defluorination agent was added at 1400 mg / L for defluorination stirring reaction, the stirring speed was 60 r / min, and the mixing reaction time was 2 min. 4. After the defluorination reaction, the mixed solution was pumped into the adsorption tank, and inorganic adsorbent was added at 200 mg / L for adsorption and coagulation reaction, the stirring speed was 25 r / min, and the reaction time was 2 min. 5. After the adsorption reaction, the mixed solution was pumped into the flocculation tank and organic flocculating agent was added at 0.75 mg / L for flocculation reaction, the stirring speed was 5 r / min, and the reaction time was 4 min. 6. After the flocculation reaction, the supernatant was pumped into the sedimentation tank for sedimentation and standing for 15 min, the pH of the supernatant was 6.89, the fluoride ion concentration of the supernatant was measured, and the fluoride ion concentration after the reaction was 0.86 mg / L.

[0036] 7. After the solid precipitate passed through the solid recovery device, part of the inorganic adsorbent was recovered and added to the next defluorination reaction at a proportion of 4%.

[0037] 8. Under the same conditions, defluorination reaction, aluminum-based defluorination agent, inorganic adsorbent addition, and 4% of the recovered adsorbent addition were carried out, and after the organic flocculating agent and the sedimentation and standing, the fluoride ion concentration of the supernatant was measured, and the fluoride ion concentration after the reaction was 0.62 mg / L. Second Embodiment,

[0038] 1. A certain industrial wastewater was taken, and the fluoride ion concentration was measured to be 16 mg / L, the total hardness (CaCO3) was 1900 mg / L, and the pH was 7.81.

[0039] 2. The fluoride-containing wastewater with a known fluoride ion concentration was pumped into the adjusting tank, and dilute sulfuric acid solution was added to adjust the pH of the solution to 6.5. 3、pH adjustment, pump into the defluorination pool, and add aluminum-based defluorination agent 1600 mg / L, defluorination stirring reaction, stirring speed 60 r / min, mixed reaction 5 min; 4、After defluorination reaction, add inorganic adsorbent 300 mg / L to the adsorption pool for adsorption and coagulation reaction, stirring speed 35 r / min, reaction 4 min; 5、After adsorption reaction, add organic flocculating agent 1 mg / L to the flocculation pool for flocculation reaction, stirring speed 15 r / min, reaction 7 min; 6、After flocculation reaction, precipitate in the sedimentation pool for 15 min, the supernatant pH=7.19, take the supernatant to measure the fluoride ion concentration, the fluoride ion concentration after reaction is 0.67 mg / L.

[0040] 7、After the solid precipitate passes through the solid recovery device, part of the inorganic adsorbent is recovered and added to the next defluorination reaction at a ratio of 4%.

[0041] 8、Under the same conditions, defluorination reaction, aluminum-based defluorination agent, inorganic adsorbent addition, and 4% recovered adsorbent addition are carried out, after organic flocculating agent and sedimentation, take the supernatant to measure the fluoride ion concentration, the fluoride ion concentration after reaction is 0.50 mg / L. Third embodiment,

[0042] 1、Take some industrial wastewater, the fluoride ion concentration is 10 mg / L, the total hardness (CaCO3) is 1678 mg / L, and the pH is 8.35.

[0043] 2、Pump the fluoride-containing wastewater with known fluoride ion concentration into the adjustment pool, add dilute sulfuric acid solution, and adjust the solution pH to 6.8; 3、After pH adjustment, add aluminum-based defluorination agent 1000 mg / L to the defluorination pool for defluorination stirring reaction, stirring speed 70 r / min, mixed reaction 3 min; 4、After defluorination reaction, add inorganic adsorbent 250 mg / L to the adsorption pool for adsorption and coagulation reaction, stirring speed 30 r / min, reaction 5 min; 5、After adsorption reaction, add organic flocculating agent 1 mg / L to the flocculation pool for flocculation reaction, stirring speed 7 r / min, reaction 5 min; 6、After flocculation reaction, precipitate in the sedimentation pool for 15 min, the supernatant pH=7.03, take the supernatant to measure the fluoride ion concentration, the fluoride ion concentration after reaction is 0.50 mg / L.

[0044] 7、After the solid precipitate passes through the solid recovery device, part of the inorganic adsorbent is recovered and added to the next defluorination reaction at a ratio of 8%.

[0045] 8. The same conditions are used for defluorination reaction and aluminum-based defluorination agent addition, and 8% of the recovered adsorbent is added. The inorganic adsorbent is added at a dosage of 150 mg / L. After organic flocculants and sedimentation, the supernatant is taken to measure the fluoride ion concentration. The fluoride ion concentration after the reaction is 0.50 mg / L. Fourth embodiment,

[0046] 1. A certain industrial wastewater is taken, and the fluoride ion concentration is measured to be 10.3 mg / L. The total hardness (calculated as CaCO3) is 1678 mg / L, and the pH is 8.35.

[0047] 2. The fluorine-containing wastewater with a known fluoride ion concentration is pumped into the conditioning tank, and dilute sulfuric acid solution is added to adjust the solution pH to 6.5. 3. After pH adjustment, aluminum-based defluorination agent is added to the defluorination tank at a dosage of 600 mg / L, and defluorination stirring reaction is carried out. The stirring speed is 80 r / min, and the mixing reaction time is 3 min. 4. After the defluorination reaction, inorganic adsorbent is added to the adsorption tank at a dosage of 150 mg / L for adsorption and coagulation reaction. The stirring speed is 30 r / min, and the reaction time is 5 min. 5. After the adsorption reaction, organic flocculants are added to the flocculation tank at a dosage of 0.5 mg / L for flocculation reaction. The stirring speed is 7 r / min, and the reaction time is 5 min. 6. After the flocculation reaction, the supernatant is taken to measure the fluoride ion concentration. The fluoride ion concentration after the reaction is 1.50 mg / L.

[0048] 7. After the solid precipitate passes through the solid recovery device, part of the inorganic adsorbent is recovered and added to the next defluorination reaction at a proportion of 6%.

[0049] 8. The same conditions are used for defluorination reaction and aluminum-based defluorination agent and inorganic adsorbent addition, and 6% of the recovered adsorbent is added. After organic flocculants and sedimentation, the supernatant is taken to measure the fluoride ion concentration. The fluoride ion concentration after the reaction is 1.12 mg / L. Fifth embodiment,

[0050] 1. A certain industrial wastewater is taken, and the fluoride ion concentration is measured to be 14.3 mg / L. The total hardness (calculated as CaCO3) is 1780 mg / L, and the pH is 7.65.

[0051] 2. The fluorine-containing wastewater with a known fluoride ion concentration is pumped into the conditioning tank, and dilute sulfuric acid solution is added to adjust the solution pH to 6.5. 3. After pH adjustment, aluminum-based defluorination agent is added to the defluorination tank at a dosage of 600 mg / L, and defluorination stirring reaction is carried out. The stirring speed is 70 r / min, and the mixing reaction time is 3 min. 4. After the defluorination reaction, inorganic adsorbent 150 mg / L was added to the adsorption tank for adsorption and coagulation reaction, the stirring speed was 30 r / min, and the reaction time was 5 min; 5. After the adsorption reaction, organic flocculant 1 mg / L was added to the flocculation tank for flocculation reaction, the stirring speed was 7 r / min, and the reaction time was 5 min; 6. After the flocculation reaction, the supernatant was taken for fluorine ion concentration measurement, and the fluorine ion concentration after the reaction was 2.00 mg / L.

[0052] 7. After the solid precipitate passed through the solid recovery device, part of the inorganic adsorbent was recovered and added to the next defluorination reaction at a proportion of 6%.

[0053] 8. Under the same conditions, defluorination reaction and aluminum-based defluorination agent and inorganic adsorbent addition were carried out, and 6% of the recovered adsorbent was added. After the organic flocculant and the sedimentation were added, the supernatant was taken for fluorine ion concentration measurement, and the fluorine ion concentration after the reaction was 1.50 mg / L. Sixth embodiment,

[0054] 1. A certain industrial wastewater was taken, and the fluorine ion concentration was measured to be 20 mg / L, the total hardness (calculated as CaCO3) was 1780 mg / L, and the pH was 7.65.

[0055] 2. The fluorine-containing wastewater with known fluorine ion concentration was pumped into the adjusting tank, and dilute sulfuric acid solution was added to adjust the solution pH to 6.5; 3. After the pH adjustment, aluminum-based defluorination agent 1200 mg / L was added to the defluorination tank for defluorination stirring reaction, the stirring speed was 70 r / min, and the mixing reaction time was 3 min; 4. After the defluorination reaction, inorganic adsorbent 300 mg / L was added to the adsorption tank for adsorption and coagulation reaction, the stirring speed was 30 r / min, and the reaction time was 5 min; 5. After the adsorption reaction, organic flocculant 0.5 mg / L was added to the flocculation tank for flocculation reaction, the stirring speed was 7 r / min, and the reaction time was 5 min; 6. After the flocculation reaction, the supernatant was taken for fluorine ion concentration measurement, and the fluorine ion concentration after the reaction was 1.16 mg / L.

[0056] 7. After the solid precipitate passed through the solid recovery device, part of the inorganic adsorbent was recovered and added to the next defluorination reaction at a proportion of 4%.

[0057] 8. The same conditions are used for defluorination reaction and aluminum-based defluorination agent, inorganic adsorbent addition, and 4% recovered adsorbent addition. After organic flocculant and sedimentation, the supernatant is taken to measure the fluoride ion concentration. The fluoride ion concentration after reaction is 0.83 mg / L. First Comparative Example,

[0058] 1. A certain industrial wastewater is taken, and the fluoride ion concentration is measured to be 14.3 mg / L, the total hardness (CaCO3) is 1780 mg / L, and the pH is 7.65.

[0059] 2. The fluoride-containing wastewater with known fluoride ion concentration is pumped into the conditioning tank, and dilute sulfuric acid solution is added to adjust the solution pH to 6.5. 3. After pH adjustment, aluminum-based defluorination agent is added to the defluorination tank at 800 mg / L for defluorination stirring reaction, with stirring speed of 70 r / min and mixing reaction time of 3 min. 4. After defluorination reaction, organic flocculant is added to the flocculation tank at 1 mg / L for flocculation reaction, with stirring speed of 7 r / min and reaction time of 5 min. 6. After flocculation reaction, the supernatant is taken to measure the fluoride ion concentration. The fluoride ion concentration after reaction is 4.36 mg / L. Second Comparative Example,

[0060] 1. A certain industrial wastewater is taken, and the fluoride ion concentration is measured to be 19.3 mg / L, the total hardness (CaCO3) is 1780 mg / L, and the pH is 7.65.

[0061] 2. The fluoride-containing wastewater with known fluoride ion concentration is pumped into the conditioning tank without pH adjustment. After pumping into the defluorination tank, aluminum-based defluorination agent is added at 800 mg / L for defluorination stirring reaction, with stirring speed of 70 r / min and mixing reaction time of 3 min. 3. After defluorination reaction, inorganic adsorbent is added to the adsorption tank at 300 mg / L for adsorption and coagulation reaction, with stirring speed of 30 r / min and reaction time of 5 min. 4. Then organic flocculant is added to the flocculation tank at 1 mg / L for flocculation reaction, with stirring speed of 7 r / min and reaction time of 5 min. 5. After flocculation reaction, the supernatant is taken to measure the fluoride ion concentration. The fluoride ion concentration after reaction is 5.26 mg / L.

[0062] For a better understanding of the present application, numerous specific details are given in the above description. One skilled in the art will understand that the application can be practiced without the specific details, or with some variations. In some instances, methods, devices, elements and circuits that are well known to those skilled in the art are not described in detail in order to avoid obscuring the present application.

[0063] The above description is only specific embodiments of the present application, but the protection scope of the present application is not limited thereto, any person skilled in the art can easily think of changes or replacements within the technical range disclosed by the present application, which should be covered in the protection scope of the present application. Therefore, the protection scope of the present application should be subject to the protection scope of the claims.

Claims

1. A process for treating low concentration fluorine-containing wastewater, characterized by, The method comprises the following steps: S1, acid-base adjustment: low-concentration fluorine-containing wastewater with a fluorine ion concentration of 10-20 mg / L is pumped into an acid-base adjustment tank, and according to the pH value of the solution, sulfuric acid and caustic soda solution are added to adjust the pH value of the solution to 6.3-6.8; S2, defluorination reaction: the mixed solution after the acid-base adjustment is pumped into a defluorination reaction tank, and an aluminum-based defluorination agent is added for defluorination stirring reaction; S3, adsorption and coagulation: after the defluorination reaction, the solution is pumped into an adsorption tank, and an inorganic adsorbent is added for adsorption and coagulation reaction; S4, flocculation: after the adsorption and coagulation reaction, the solution is pumped into a flocculation tank, and an organic flocculating agent is added for flocculation reaction; S5, precipitation: after the flocculation reaction, the solution is pumped into a precipitation tank for standing, and the fluorine ion concentration of the supernatant is measured, and the fluorine ion concentration after the reaction is reduced to 0.5-2 mg / L; S6, inorganic adsorbent recovery: the precipitate after the solid-liquid separation is recovered by a recovery device.

2. The low concentration fluorochemical wastewater treatment process according to claim 1, wherein, The aluminum-based defluorination agent comprises, by mass percentage: polyaluminum chloride 45-60%; polyaluminum ferric sulfate 20-40%; aluminum chloride 5-15%.

3. The low concentration fluorochemical wastewater treatment process of claim 1, wherein, The inorganic adsorbent is a porous material made of modified zeolite and metakaolin powder, the mass fraction of the zeolite in the inorganic adsorbent is 55-65%, and the mass fraction of the metakaolin powder is 35-45%; the modification process is as follows: the metakaolin and zeolite powder sieved through a 250-mesh sieve are mixed according to the proportion, then added into a 5% sodium hydroxide solution, stirred in a 60°C water bath for 8 hours, filtered, and dried at 105-110°C; the mass ratio of the powder to the sodium hydroxide is 2:

1.

4. The low concentration fluorochemical wastewater treatment process of claim 1, wherein, The organic flocculating agent is at least one selected from water-soluble cationic chitosan quaternary ammonium salt and polydimethyl diallyl ammonium chloride.

5. The low concentration fluorochemical wastewater treatment process of claim 1, wherein, The addition amount of the aluminum-based defluorination agent is 600-1600 mg / L.

6. The low concentration fluorochemical wastewater treatment process of claim 1, wherein, The addition amount of the inorganic adsorbent is 150-300 mg / L.

7. The low concentration fluorochemical wastewater treatment process of claim 1, wherein, The addition amount of the organic flocculating agent is 0.5-1 mg / L.

8. The low concentration fluorochemical wastewater treatment process of claim 1, wherein, The stirring speed in the defluorination reaction is 60-80 r / min, and the reaction time is 2-5 min.

9. The low concentration fluorochemical wastewater treatment process of claim 1, wherein, The stirring speed in the adsorption and coagulation reaction is 25-35 r / min, and the reaction time is 2-5 min.

10. The low concentration fluorochemical wastewater treatment process of claim 1, wherein, The stirring speed in the flocculation reaction is 5-15 r / min, the reaction time is 4-7 min, and the standing time in the precipitation tank is 5-15 min.

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