Fluorine-containing wastewater treatment method

Abstract

The invention relates to a fluorine-containing wastewater treatment method, which comprises: (1) introducing a fluorine removal agent into fluorine-containing wastewater, adjusting the pH value to 6.0-7.5, carrying out a stirring reaction, standing, and separating the precipitate to obtain primary fluorine-removed wastewater; and (2) introducing an inorganic-organic hybrid flocculant into the primary defluorination wastewater, stirring to react, standing, and separating out precipitate to obtain secondary defluorination wastewater. And (3) introducing the polysilicic acid aluminum chloride-cationic polyacrylamide composite material into the secondary defluorination wastewater, stirring to react, standing, and separating out precipitate to obtain purified effluent. The method disclosed by the invention is high in pollutant removal rate, simple and convenient to operate and relatively low in investment and operation cost.

Description

Technical Field

[0001] The invention belongs to the technical field of water pollution control, and particularly relates to a method for treating fluorine-containing wastewater. Background Art

[0002] Excessive fluoride ion levels in wastewater can cause severe corrosion of equipment, harm the environment, and affect crop growth and human bone health. The first-level standard of the Integrated Wastewater Discharge Standard (GB 8798-1996) stipulates a maximum permissible fluoride discharge concentration of 10 mg / L. Therefore, simple, low-cost, and efficient treatment of fluoride ions in wastewater is of great significance.

[0003] Traditional fluoride removal methods include chemical precipitation, coagulation-sedimentation, adsorption, reverse osmosis, electrodialysis, etc. Among them, reverse osmosis and electrodialysis have high process costs and are difficult to achieve large-scale industrial promotion and application; adsorption is more suitable for the treatment of low-fluoride wastewater and deep treatment of fluoride-containing wastewater; the combined chemical-coagulation-precipitation method is currently the most widely studied and applied in the treatment of fluoride-containing wastewater.

[0004] Chemical precipitation method usually adds calcium-containing reagents such as CaCl2, Ca(OH)2 and CaO to fluoride-containing wastewater. 2+ and F - When the concentration reaches an oversaturated state, CaF2 precipitate will be generated. Since CaF2 is a slightly soluble mineral, the homogeneous nucleation and crystallization of CaF2 requires a high reaction kinetics, and the resulting calcium fluoride sludge is amorphous, has a high water content, and has a poor sedimentation effect, resulting in unsatisfactory final fluoride removal effect. Limited by the solubility of CaF2, the chemical precipitation method can generally reduce the fluoride ion concentration in the wastewater to between 20-30 mg / L. Deep removal of fluoride ions, that is, reducing the fluoride ion concentration to below 10 mg / L, often requires further coagulation and sedimentation methods. Since excessive amounts of calcium-containing reagents are usually added in the treatment of fluoride-containing wastewater, the residual calcium ions need to be further treated for hardness removal. In addition, the generated CaF2 precipitate, coagulation precipitate, and hardness precipitate are newly generated suspended matter and also need further turbidity removal treatment. Therefore, for the treatment of fluoride-containing wastewater, regardless of whether the initial wastewater contains hardness ions and suspended matter, there are usually hardness removal and turbidity removal sections in the process flow.

[0005] CN210764753U discloses a zero-emission pretreatment system for high-salt wastewater from coal coking. In the fluoride removal process, calcium chloride, ferric chloride, polyacrylamide, and other reagents must be added in two steps. This method usually produces a fine fluoride precipitate, and its separation relies on the addition of large amounts of coagulants and flocculants. In the hardness removal process, liquid caustic soda, sodium carbonate, ferric chloride, polyacrylamide, and other reagents must be added in steps, resulting in high reagent consumption and complex process flow. In addition, because acidic pH is suitable for fluoride removal and alkaline pH is suitable for hardness removal, the invention involves the addition of both alkali and acid, resulting in high acid and alkali consumption and increasing the burden of subsequent membrane treatment for desalination.

[0006] Therefore, to address the above problems, simple, low-cost, and efficient methods for removing fluorine, hardness, and turbidity from wastewater remain to be developed. Summary of the Invention

[0007] To address the shortcomings of existing fluorine-containing wastewater treatment technologies, such as complex processes for removing fluorine, hardness, and turbidity, and high chemical consumption, the present invention provides a method for treating fluorine-containing wastewater. This method not only achieves a high pollutant removal rate, but also is simple to operate and has low investment and operating costs.

[0008] The present invention provides a method for treating fluorine-containing wastewater, comprising the following steps:

[0009] (1) introducing a defluoridating agent into the fluorine-containing wastewater, adjusting the pH to 6.0-7.5, stirring the reaction, and then allowing the mixture to stand, separating the precipitate, and obtaining first-level defluoridated wastewater;

[0010] (2) Introducing an inorganic-organic hybrid flocculant into the primary defluoridation wastewater, stirring the reaction and then allowing it to stand, separating the precipitate, and obtaining the secondary defluoridation wastewater.

[0011] (3) Introducing a polysilicate aluminum chloride-cationic polyacrylamide composite material into the secondary defluoridation wastewater, stirring the reaction and then allowing it to stand, separating the precipitate to obtain purified water.

[0012] In step (1) of the present invention, the concentration of fluoride ions in the wastewater is 50-100 mg / L, the hardness is 0-300 mg / L, and the turbidity is 0-20 NTU.

[0013] In step (1) of the present invention, the defluoridating agent is a calcified substance, preferably at least one of calcium chloride, calcium hydroxide, calcium oxide, etc., and the dosage of the defluoridating agent is 300-800 mg / L in terms of calcium.

[0014] In step (1) of the present invention, the pH of the wastewater is adjusted from the initial pH to 6.0-7.5, preferably 6.5-7.5; the stirring reaction rate is 200-500 rpm, the stirring time is 10-60 minutes, and the standing time is 30-60 minutes.

[0015] In step (2), the inorganic-organic hybrid flocculant is prepared by the following method:

[0016] (a) preparing an inorganic flocculant or an inorganic flocculant colloidal solution, adding an inorganic salt modifier, and then adding an organic monomer to obtain a mixed solution;

[0017] (b) placing the mixed solution in a constant temperature water bath, introducing nitrogen or an inert gas, and then adding an initiator to start a polymerization reaction, thereby obtaining an inorganic-organic hybrid polymer gel;

[0018] (c) dissolving the inorganic-organic hybrid polymer gel and then extracting it to obtain a precipitate;

[0019] (d) drying the precipitate and grinding it to obtain the inorganic-organic hybrid flocculant.

[0020] The inorganic flocculant in step (a) is at least one of aluminum hydroxide, ferric hydroxide, polyaluminum chloride, polyferric sulfate, polyaluminum silicate, polyaluminum ferric silicate, etc., preferably at least one of aluminum hydroxide, polyaluminum chloride, polyaluminum silicate, polyaluminum ferric silicate, more preferably a mixture of aluminum hydroxide and polyaluminum silicate in a mass ratio of (2-5):1.

[0021] The concentration of the inorganic flocculant or inorganic flocculant colloidal solution in step (a) is 0.05-2 mol / L, calculated as the molar concentration of Al or Fe.

[0022] The inorganic salt described in step (a) is an inorganic oxyacid ion, specifically selected from at least one of the soluble salts of phosphate, monohydrogen phosphate, dihydrogen phosphate, metaphosphate, hypophosphite, citrate, borate, tartrate, acetate, ethylenediaminetetraacetic acid root, etc., preferably at least one of the soluble sodium salts of phosphate, more preferably a mixture of disodium hydrogen phosphate and sodium dihydrogen phosphate in a mass ratio of (1-5): 1.

[0023] The amount of the inorganic salt in step (a) is 0.5%-10% of the mass of the organic monomer.

[0024] The inorganic salt in step (a) is added dropwise for 10-60 minutes.

[0025] The organic monomer in step (a) comprises a cationic quaternary ammonium salt monomer and acrylamide in a mass ratio of 1:9-1:1, wherein the cationic quaternary ammonium salt monomer is selected from at least one of dimethyldiallylammonium chloride, acryloylethoxytrimethylammonium chloride, methacryloylethoxytrimethylammonium chloride, (3-acrylamidopropyl)-trimethylammonium chloride and N,N,N-trimethyl-3-(2-methylallylamino)-1-propylammonium chloride, and preferably a mixture of dimethyldiallylammonium chloride and (3-acrylamidopropyl)-trimethylammonium chloride in a mass ratio of (6-9):1.

[0026] The mass ratio of the inorganic flocculant to the organic monomer in step (a) is 1:1-5:1.

[0027] The temperature of the constant temperature water bath in step (a) is 25-90° C. Furthermore, the mixed solution is preferably placed in a constant temperature water bath at 25-50° C. for polymerization reaction. After the reaction for 5-120 minutes, the water bath temperature is raised to 40-90° C. and the reaction is continued for 1-6 hours. After the reaction is completed, an inorganic-organic hybrid polymer gel is obtained.

[0028] The inert gas in step (b) is selected from any one of helium, argon, etc., or a combination of at least two of them.

[0029] The initiator in step (b) is a redox initiator, wherein the oxidizing agent is selected from ammonium persulfate and / or potassium persulfate, and the reducing agent is selected from sodium bisulfite. The mass ratio of the oxidizing agent to the reducing agent is 1.05:1 to 2:1. The mass of the initiator is 0.01% to 3% of the mass of the organic monomer.

[0030] The polymerization reaction time in step (b) is 2-8 hours.

[0031] The inorganic-organic hybrid polymer gel in step (c) is dissolved in deionized water and then extracted with an organic solvent selected from at least one of ethanol, acetone, and the like.

[0032] The drying condition in step (d) is drying at 40-80° C. for 0.5-6 h.

[0033] In step (2) of the present invention, the amount of the inorganic-organic hybrid flocculant added is 10-50 mg / L.

[0034] In step (2) of the present invention, the stirring reaction rate is 100-500 rpm, and the stirring time is 10-30 minutes. More preferably, after adding the flocculant, stirring is first performed at 300-500 rpm for 1-10 minutes, and then at 100-295 rpm for 10-20 minutes.

[0035] In step (3) of the present invention, the polysilicate aluminum chloride-cationic polyacrylamide composite material comprises polysilicate aluminum chloride and cationic polyacrylamide with a degree of hydrolysis of 15%-25%, and the mass ratio of the two is 1:5-1:2, wherein the content of silicon in the polysilicate aluminum chloride is 0.3%-2.0% as SiO2, and the content of aluminum in the polysilicate aluminum chloride is 2%-8% as Al2O3.

[0036] In step (3) of the present invention, the mass ratio of the dosage of the polysilicate aluminum chloride-cationic polyacrylamide composite material to the total hardness in the defluoridation wastewater is 1-5:1.

[0037] In step (3) of the present invention, the stirring reaction rate is 100-500 rpm and the stirring time is 10-30 min. More preferably, after adding the composite material, stirring is first performed at 300-500 rpm for 1-10 min, and then at 100-295 rpm for 10-20 min.

[0038] Compared with the prior art, the present invention has the following beneficial effects:

[0039] (1) To address the shortcomings of fluoride-containing wastewater and the use of calcium-containing defluoridants, the present invention first adjusts the pH to break the complex between calcium ions and complexing agents, scale inhibitors, or hydroxide ions, releasing some free calcium ions to form calcium fluoride seed crystals; on this basis, the inorganic-organic hybrid flocculant described in the present invention is introduced to promote the growth and precipitation of flocs; and further, a polysilicate aluminum chloride-cationic polyacrylamide composite material is introduced to achieve simultaneous removal of hardness and turbidity. After treatment, the fluoride ion concentration in the wastewater is less than 10 mg / L, the total hardness is less than 100 mg / L, and the turbidity is reduced to below 3 NTU, achieving efficient removal of fluoride ions, as well as the introduced hardness and turbidity in the wastewater.

[0040] (2) The inorganic-organic hybrid flocculant prepared by the present invention can, on the one hand, realize the adsorption and coagulation of fluoride ions, which is helpful for the deep removal of fluoride ions; on the other hand, it can realize the growth of flocs and rapid separation in wastewater, and the flocculation effect is better.

[0041] (3) Based on the introduction of inorganic-organic hybrid flocculants, a new type of polysilicate aluminum chloride-cationic polyacrylamide composite material was used to achieve Ca 2+ It can effectively remove fluorine from the water, overcoming the disadvantage of repeated pH adjustment due to the fact that acidic pH is easy to remove fluorine and alkaline pH is easy to remove hardness, effectively reducing the acid and alkali consumption and the desalination load of subsequent sections.

[0042] (4) Compared with existing processes, the process of the present invention shortens the process flow, reduces reagent consumption and slag production. Therefore, the method has low operating costs, simple operation, and good application prospects. DETAILED DESCRIPTION

[0043] The technical solution of the present invention and its effects are further illustrated below with reference to specific examples. The examples are implemented based on the technical solution of the present invention, and provide detailed implementation methods and specific operating processes, but the scope of protection of the present invention is not limited to the following examples.

[0044] The experimental methods in the following examples, unless otherwise specified, are all conventional methods in the art. The experimental materials used in the following examples, unless otherwise specified, were purchased from conventional biochemical reagent stores.

[0045] In the present invention, the fluoride ion concentration in the wastewater was measured using a multi-parameter water quality analyzer (Seven Excellence, Mettler Toledo, Switzerland), the total hardness of the wastewater was measured using EDTA complexometric titration, and the turbidity of the wastewater was measured using a turbidimeter (TL2300EPA, Hach, USA). The polyaluminum chloride silicate-cationic polyacrylamide composite material was the composite material described in CN117304632A.

[0046] Example 1

[0047] The wastewater treated in this example had a pH of 8.2, a fluoride ion concentration of 80 mg / L, a hardness of 46 mg / L, and a turbidity of 4.03 NTU. The treatment was performed using the following steps:

[0048] (1) 500 mg / L (calcium) calcium chloride was added to the wastewater, the pH of the wastewater was adjusted to 7.0, and the mixture was stirred at 300 rpm for 30 minutes. Testing revealed that the total hardness of the wastewater was 1130 mg / L and the turbidity was 1005 NTU. After the reaction, the wastewater was allowed to settle for 1 hour, and the precipitate was separated to obtain primary defluoridated wastewater.

[0049] (2) Add 35 mg / L of inorganic-organic hybrid flocculant to the primary defluoridation wastewater, stir at 400 rpm for 5 min, then stir at 200 rpm for 15 min, let it stand for 30 min, separate the precipitate, and obtain secondary defluoridation wastewater.

[0050] The preparation method of the inorganic-organic hybrid flocculant is as follows: (a) A 0.4 mol / L (in terms of Al molar concentration) Al(OH)3 colloidal solution is prepared, and sodium phosphate (Na3PO4) modifier is added dropwise over a 20-minute period. After the addition is complete, acrylamide (AM) and dimethyldiallyl ammonium chloride (DMDAAC) are added to obtain a mixed solution. The mass ratio of aluminum hydroxide to organic monomer is 1:9, the mass ratio of DMDAAC to AM is 1:9, and the mass of Na3PO4 is 1% of the mass of the organic monomer. (b) The mixed solution is placed in a 25°C constant temperature water bath and aerated with high-purity nitrogen for approximately 30 minutes. Subsequently, a mixed solution of ammonium persulfate ((NH4)2S2O8) and sodium bisulfite (NaHSO3) is added. The reaction system is sealed, and the polymerization reaction is continued for 3 hours before termination, yielding an inorganic-organic hybrid polymer gel. The mass of the initiator is 0.1% of the mass of the organic monomer, and the mass ratio of (NH₄)₂S₂O₈ to NaHSO₃ is 1.5:1. (c) The inorganic-organic hybrid polymer gel is dissolved in deionized water and added dropwise to acetone for extraction to obtain a precipitate. (d) The precipitate is dried at 60°C for 1 hour and ground to obtain the inorganic-organic hybrid flocculant powder.

[0051] (3) A polysilicate aluminum chloride-cationic polyacrylamide composite material (the composite material prepared by Example 1 of CN117304632A) was added to the secondary defluoridation wastewater, with a mass ratio of the composite material to the total hardness in the defluoridation wastewater being 1.5:1. The mixture was stirred at 500 rpm for 5 minutes, and then stirred at 250 rpm for 15 minutes. The mixture was then allowed to stand for 0.5 hours, and the precipitate was separated to obtain purified water.

[0052] After testing, the fluoride ion concentration in the outlet water was 9.81 mg / L, the total hardness was 78 mg / L, and the turbidity was 1.32 NTU.

[0053] Example 2

[0054] The wastewater treated in this example has a pH of 8.0, a fluoride ion concentration of 50 mg / L, and no hardness or turbidity. The treatment was performed using the following steps:

[0055] (1) 350 mg / L (calcium) calcium chloride was added to the wastewater, the pH of the wastewater was adjusted to 7.5, and the mixture was stirred at 200 rpm for 50 min. Testing revealed that the total hardness of the wastewater was 750 mg / L and the turbidity was 826 NTU. After the reaction, the wastewater was allowed to settle for 1 h, and the precipitate was separated to obtain primary defluoridated wastewater.

[0056] (2) Add 25 mg / L of inorganic-organic hybrid flocculant to the primary defluoridation wastewater, stir at 500 pm for 5 minutes, then stir at 150 rpm for 15 minutes, let it stand for 30 minutes, separate the precipitate, and obtain secondary defluoridation wastewater.

[0057] The preparation method of the inorganic-organic hybrid flocculant is as follows: (a) A polyferric sulfate solution with a concentration of 0.4 mol / L (based on the molar concentration of Fe) is prepared, and a sodium phosphate (Na3PO4) modifier is added dropwise over a 20-minute period. After the addition is complete, acrylamide (AM) and dimethyldiallyl ammonium chloride (DMDAAC) are added to obtain a mixed solution. The mass ratio of polyferric sulfate to organic monomer is 1:9, the mass ratio of DMDAAC to AM is 1:9, and the mass of Na3PO4 is 1% of the mass of the organic monomer. (b) The mixed solution is placed in a 25°C constant temperature water bath and aerated with high-purity nitrogen for approximately 30 minutes. Subsequently, a mixed solution of ammonium persulfate ((NH4)2S2O8) and sodium bisulfite (NaHSO3) is added. The reaction system is sealed, and the polymerization reaction is continued for 3 hours before termination, resulting in an inorganic-organic hybrid polymer gel. The initiator is present in an amount of 0.1% by weight of the organic monomer, and the mass ratio of (NH4)2S2O8 to NaHSO3 is 1.5:1. (c) The inorganic-organic hybrid polymer gel is dissolved in deionized water and then dropwise added to acetone for extraction to obtain a precipitate. (d) The extracted precipitate is dried at 60°C for 1 hour and ground to obtain the inorganic-organic hybrid flocculant powder.

[0058] (3) A polysilicate aluminum chloride-cationic polyacrylamide composite material (the composite material prepared by Example 2 of CN117304632A) was added to the secondary defluoridation wastewater, with a mass ratio of the composite material to the total hardness in the defluoridation wastewater being 1.5:1. The mixture was stirred at 500 rpm for 5 minutes, and then stirred at 250 rpm for 15 minutes. The mixture was then allowed to stand for 0.5 hours, and the precipitate was separated to obtain purified water.

[0059] After testing, the fluoride ion concentration in the outlet water was 9.93 mg / L, the total hardness was 76 mg / L, and the turbidity was 2.36 NTU.

[0060] Example 3

[0061] The wastewater treated in this example had a pH of 8.5, a fluoride ion concentration of 90 mg / L, a hardness of 87 mg / L, and a turbidity of 8.6 NTU. The treatment was performed using the following steps:

[0062] (1) 600 mg / L (calcium) calcium chloride was added to the wastewater, the pH of the wastewater was adjusted to 6.5, and the mixture was stirred at 400 rpm for 20 minutes. Testing revealed that the total hardness of the wastewater was 1326 mg / L and the turbidity was 1032 NTU. After the reaction, the wastewater was allowed to settle for 1 hour, and the precipitate was separated to obtain primary defluoridated wastewater.

[0063] (2) Add 50 mg / L of inorganic-organic hybrid flocculant to the primary defluoridation wastewater, stir at 300 rpm for 10 min, then stir at 200 rpm for 15 min, let it stand for 30 min, separate the precipitate, and obtain secondary defluoridation wastewater.

[0064] The preparation method of the inorganic-organic hybrid flocculant is as follows: (a) A 0.05 mol / L (in terms of Al molar concentration) Al(OH)3 colloidal solution is prepared, and sodium phosphate (Na3PO4) modifier is added dropwise over a 10-minute period. After the addition is complete, acrylamide (AM) and dimethyldiallyl ammonium chloride (DMDAAC) are added to obtain a mixed solution. The mass ratio of aluminum hydroxide to organic monomer is 1:5, the mass ratio of DMDAAC to AM is 1:1, and the mass of Na3PO4 is 0.5% of the mass of the organic monomer. (b) The mixed solution is placed in a 40°C constant temperature water bath and aerated with high-purity argon for approximately 30 minutes. A mixture of potassium persulfate (K2S2O8) and sodium bisulfite (NaHSO3) is then added. The reaction system is sealed, and the polymerization reaction is continued for 8 hours before termination, yielding an inorganic-organic hybrid polymer gel. The mass of the initiator is 0.01% of the mass of the organic monomer, and the mass ratio of (NH4)2S2O8 to NaHSO3 is 1.05:1. (c) The inorganic-organic hybrid polymer gel is dissolved in deionized water and added dropwise to acetone for extraction to obtain a precipitate. (d) The extracted precipitate is dried at 40°C for 6 hours and ground to obtain the inorganic-organic hybrid flocculant powder.

[0065] (3) A polysilicate aluminum chloride-cationic polyacrylamide composite material (the composite material prepared using Example 4 of CN117304632A) was added to the secondary defluoridation wastewater, with a mass ratio of the composite material to the total hardness in the defluoridation wastewater being 1.5:1. The mixture was stirred at 500 rpm for 5 minutes, and then stirred at 250 rpm for 15 minutes. The mixture was then allowed to stand for 0.5 hours, the precipitate was separated, and purified water was obtained.

[0066] After testing, the fluoride ion concentration in the outlet water was 9.73 mg / L, the total hardness was 92 mg / L, and the turbidity was 2.98 NTU.

[0067] Example 4

[0068] The same method as Example 1 was used, except that calcium hydroxide was used as the defluoridating agent. Purified effluent was obtained. Testing revealed a fluoride ion concentration of 9.66 mg / L, a total hardness of 69 mg / L, and a turbidity of 2.02 NTU.

[0069] Example 5

[0070] The same method as Example 2 was used, except that calcium oxide was used as the defluoridating agent. Purified effluent was obtained. Testing revealed a fluoride ion concentration of 9.21 mg / L, a total hardness of 81 mg / L, and a turbidity of 1.93 NTU.

[0071] Example 6

[0072] The same method as Example 1 was used, except that in steps (2) and (3), stirring was not performed in stages after the reagent was added, but rather was continued at 250 rpm for 20 minutes. Testing revealed that the fluoride ion concentration in the effluent was 9.89 mg / L, the total hardness was 90 mg / L, and the turbidity was 2.67 NTU.

[0073] Comparative Example 1

[0074] The same method as Example 1 was used, except that an inorganic-organic hybrid flocculant was used in place of the polyaluminum chloride silicate-cationic polyacrylamide composite material. This means that both treatment steps employed an inorganic-organic hybrid flocculant. The test results showed that the fluoride ion concentration in the wastewater was 9.97 mg / L, the total hardness was 636 mg / L, and the turbidity was 5.39 NTU.

[0075] Comparative Example 2

[0076] The same method as Example 1 was used, except that a polyaluminum chloride silicate-cationic polyacrylamide composite material was used in place of the inorganic-organic hybrid flocculant. That is, the polyaluminum chloride silicate-cationic polyacrylamide composite material was used in both treatment steps. The test results showed that the fluoride ion concentration in the wastewater was 23.6 mg / L, the total hardness was 502 mg / L, and the turbidity was 32.86 NTU.

[0077] Comparative Example 3

[0078] The same test was performed as in Example 1, except that the order of adding the inorganic-organic hybrid flocculant and the polyaluminum chloride silicate-cationic polyacrylamide composite material was reversed: the polyaluminum chloride silicate-cationic polyacrylamide composite material was added first, followed by the inorganic-organic hybrid flocculant. The test results showed that the fluoride ion concentration in the wastewater was 15.2 mg / L, the total hardness was 313 mg / L, and the turbidity was 5.51 NTU.

[0079] Comparative Example 4

[0080] The same as Example 1, except that: the preparation method of the inorganic-organic hybrid flocculant is as follows: (1) (Al(OH)3) colloid with a concentration of 0.4 mol / L (in terms of the molar concentration of Al) is prepared, acrylamide (AM) and dimethyldiallyl ammonium chloride (DMDAAC) are added to obtain a mixed solution, and the mixed solution is placed in a constant temperature water bath at a temperature of 25°C. The mass ratio of aluminum hydroxide to organic monomer is 1:9, the mass ratio of DMDAAC to AM is 1:9, and the mass of Na3PO4 is 1% of the mass of the organic monomer. (2) High-purity nitrogen is introduced for about 30 minutes, and then a mixed solution of ammonium persulfate ((NH4)2S2O8) and sodium bisulfite (NaHSO3) is added. The reaction system is sealed, and the polymerization reaction is continued for 3 hours before termination to obtain an inorganic-organic hybrid polymer gel. The mass of the initiator is 0.1% of the mass of the organic monomer, and the mass ratio of (NH4)2S2O8 to NaHSO3 is 1.5:1. (3) The inorganic-organic hybrid polymer gel was dissolved in deionized water and added dropwise to acetone for extraction to obtain a precipitate. (4) The extracted precipitate was dried at 60°C for 1 hour and ground to obtain the inorganic-organic hybrid flocculant powder. The test results showed that the fluoride ion concentration in the wastewater was 14.9 mg / L, the total hardness was 362 mg / L, and the turbidity was 9.51 NTU.

Claims

1. A method for treating fluorine-containing wastewater, characterized in that The steps include: (1) Introducing a defluoridating agent into the fluorine-containing wastewater, adjusting the pH to 6.0-7.5, stirring the reaction, and then allowing it to stand, separating the precipitate to obtain first-level defluoridated wastewater; (2) Introducing an inorganic-organic hybrid flocculant into the primary defluoridation wastewater, stirring the reaction and then allowing it to stand, separating the precipitate, and obtaining the secondary defluoridation wastewater; (3) Introduce a polysilicate aluminum chloride-cationic polyacrylamide composite material into the secondary defluoridation wastewater, stir the reaction and then let it stand to separate the precipitate to obtain purified water.

2. The method according to claim 1, wherein: The wastewater has a fluoride ion concentration of 50-100 mg / L, a hardness of 0-300 mg / L, and a turbidity of 0-20 NTU.

3. The method according to claim 1, wherein: In step (1), the defluoridating agent is a calcified substance, preferably at least one of calcium chloride, calcium hydroxide, and calcium oxide, and the dosage of the defluoridating agent is 300-800 mg / L in terms of calcium.

4. The method according to claim 1, wherein: In step (1), the stirring reaction rate is 200-500 rpm, the stirring time is 10-60 min, and the standing time is 30-60 min.

5. The method according to claim 1, wherein: In step (2), the inorganic-organic hybrid flocculant is prepared by the following method: (a) preparing an inorganic flocculant or an inorganic flocculant colloidal solution, adding an inorganic salt modifier, and then adding an organic monomer to obtain a mixed solution; (b) placing the mixed solution in a constant temperature water bath, introducing nitrogen or an inert gas, and then adding an initiator to initiate a polymerization reaction, thereby obtaining an inorganic-organic hybrid polymer gel; (c) dissolving the inorganic-organic hybrid polymer gel and then extracting it to obtain a precipitate; (d) drying the precipitate and grinding it to obtain the inorganic-organic hybrid flocculant.

6. The method according to claim 5, characterized in that: The inorganic flocculant in step (a) is at least one of aluminum hydroxide, ferric hydroxide, polyaluminum chloride, polyferric sulfate, polyaluminum silicate, and polyaluminum ferric silicate, preferably at least one of aluminum hydroxide, polyaluminum chloride, polyaluminum silicate, and polyaluminum ferric silicate, more preferably a mixture of aluminum hydroxide and polyaluminum silicate in a mass ratio of (2-5):

1.

7. The method according to claim 5 or 6, characterized in that: The concentration of the inorganic flocculant or inorganic flocculant colloidal solution in step (a) is 0.05-2 mol / L, calculated as the molar concentration of Al or Fe.

8. The method according to claim 5, characterized in that: The inorganic salt in step (a) is an inorganic oxygen-containing acid ion, specifically selected from at least one of phosphate, monohydrogen phosphate, dihydrogen phosphate, metaphosphate, hypophosphite, citrate, borate, tartrate, acetate, and ethylenediaminetetraacetic acid, preferably at least one soluble sodium salt of phosphate, more preferably a mixture of disodium hydrogen phosphate and sodium dihydrogen phosphate in a mass ratio of (1-5):

1.

9. The method according to claim 5 or 8, characterized in that: The amount of the inorganic salt in step (a) is 0.5%-10% of the mass of the organic monomer; the inorganic salt is added dropwise for 10-60 minutes.

10. The method according to claim 5, characterized in that: The organic monomer in step (a) comprises a cationic quaternary ammonium salt monomer and acrylamide in a mass ratio of 1:9 to 1:1, wherein the cationic quaternary ammonium salt monomer is selected from at least one of dimethyldiallylammonium chloride, acryloylethoxytrimethylammonium chloride, methacryloylethoxytrimethylammonium chloride, (3-acrylamidopropyl)-trimethylammonium chloride and N,N,N-trimethyl-3-(2-methylallylamino)-1-propylammonium chloride, and preferably a mixture of dimethyldiallylammonium chloride and (3-acrylamidopropyl)-trimethylammonium chloride in a mass ratio of (6-9):

1.

11. The method according to claim 5, wherein: The mass ratio of the inorganic flocculant to the organic monomer in step (a) is 1:1-5:

1.

12. The method according to claim 5, wherein: The temperature of the constant temperature water bath in step (a) is 25-90°C; preferably, the mixed solution is placed in a constant temperature water bath at 25-50°C for polymerization reaction. After the reaction for 5-120 minutes, the water bath temperature is increased to 40-90°C and the reaction is continued for 1-6 hours. After the reaction is completed, an inorganic-organic hybrid polymer gel is obtained.

13. The method according to claim 5, wherein: The inert gas in step (b) is selected from any one of helium and argon, or a combination of at least two of them.

14. The method according to claim 5, wherein: The initiator in step (b) is an oxidation-reduction initiator, the oxidizing agent is selected from ammonium persulfate and / or potassium persulfate, and the reducing agent is selected from sodium bisulfite; the mass ratio of the oxidizing agent to the reducing agent is 1.05:1-2:1; and the mass of the initiator is 0.01%-3% of the mass of the organic monomer.

15. The method according to claim 5, characterized in that: The inorganic-organic hybrid polymer gel in step (c) is dissolved in deionized water; after dissolution, it is extracted with an organic solvent, and the organic solvent is selected from at least one of ethanol and acetone; and the drying condition is drying at 40-80° C. for 0.5-6 hours.

16. The method according to claim 1, wherein: In step (2), the amount of the inorganic-organic hybrid flocculant added is 10-50 mg / L.

17. The method according to claim 1 or 16, characterized in that: In step (2), after adding the flocculant, the stirring reaction rate is 100-500 rpm, and the stirring time is 10-30 min. More preferably, after adding the flocculant, the stirring is first performed at 300-500 rpm for 1-10 min, and then at 100-295 rpm for 10-20 min.

18. The method according to claim 1, wherein: In step (3), the polysilicate aluminum chloride-cationic polyacrylamide composite material comprises polysilicate aluminum chloride and cationic polyacrylamide having a degree of hydrolysis of 15%-25%, with a mass ratio of the two being 1:5-1:2, wherein the content of silicon in the polysilicate aluminum chloride is calculated as SiO2 and is 0.3%-2.0%, and the content of aluminum in the polysilicate aluminum chloride is calculated as Al2O3 and is 2%-8%.

19. The method according to claim 1 or 18, wherein: In step (3), the mass ratio of the dosage of the polysilicate aluminum chloride-cationic polyacrylamide composite material to the total hardness in the defluoridation wastewater is 1-5:

1.

20. The method according to claim 1, wherein: In step (3), after adding the composite material, the stirring reaction rate is 100-500 rpm, and the stirring time is 10-30 min. It is further preferred that after adding the composite material, the stirring is first performed at 300-500 rpm for 1-10 min, and then at 100-295 rpm for 10-20 min.