A system treatment process and method for fluorine-containing wastewater

Abstract

The application provides a system treatment process for fluorine-containing wastewater, which comprises the following steps: a fluorine-containing wastewater treatment process, a sludge treatment process, a defluorination filter material regeneration process and a sludge waste liquid treatment process. The system treatment process for fluorine-containing wastewater has the advantages of low sludge yield, low flocculant consumption, low treatment cost, high adsorption capacity, greatly prolonged adsorption time of the adsorbent, reduced regeneration frequency, no discharge of regeneration liquid, and effectively solved problem of difficult treatment of by-products of traditional treatment processes.

Description

Technical Field

[0001] This invention belongs to the field of water treatment technology, specifically relating to a system treatment process and method for fluoride-containing wastewater. Background Technology

[0002] Many industries generate fluoride-containing wastewater during industrial production, such as glass processing, electronic semiconductor processing, coal mining, polysilicon photovoltaic processing, coal chemical industry, electroplating industry, fluorochemical wastewater, metal smelting fluoride-containing wastewater, and pesticide chemical fluoride-containing wastewater. Different industries have relatively stringent emission standards. Taking mine water from coal mining as an example, the volume is large, and the requirements for fluoride content are high (a coal mining base in Northwest my country requires that the fluoride content of discharged mine water meet the standard of Class III surface water, i.e., fluoride content ≤1mg / L).

[0003] Fluoride is highly harmful to the human body. Long-term excessive intake of fluoride can lead to fluorosis, including dental fluorosis and skeletal fluorosis. It can also interfere with the activity of various enzymes and disrupt the metabolic balance of calcium and phosphorus. In my country, it is generally more prevalent in areas with excessively high fluoride levels in groundwater. Endemic fluorosis is related to the abundance of fluoride in the geographical environment. Therefore, fluoride removal from mine water, groundwater, and fluoride chemical wastewater is directly related to public health. Furthermore, in some areas, large volumes of mine water and groundwater contain fluoride levels between 5 and 10 mg / L, far exceeding the fluoride requirements for drinking water and surface water. Therefore, economical, efficient, and safe fluoride-containing water treatment technologies are crucial for safeguarding public health.

[0004] The common methods for treating fluorides are as follows: (1) Chemical precipitation: This method utilizes F - With Ca 2+ The generated CaF2 has low solubility, but this method has limited effect on the treatment of fluoride ions. Lime milk or calcium chloride can only reduce the total fluoride content in wastewater to about 10 mg / L, which cannot meet the relevant emission limits. (2) Flocculation and sedimentation method: This method uses aluminum salts as flocculants and utilizes Al 3+ With F - The complexation of aluminum salt hydrolysis intermediates and the final Al(OH)3(am) flocs remove fluoride ions from water through ligand exchange, physical adsorption, and sweeping. Although this method can effectively remove fluoride ions from water... - However, if the standard of ≤1mg / L is reached, the flocculant dosage is large, the sludge production is large, and the Al in the water is high. 3+The residual amount is large, so flocculation and sedimentation is not the best treatment method for fluoride-containing wastewater with slightly excessive emissions and high discharge standards. (3) Adsorption method: This method uses activated alumina, clinoptilolite, activated magnesium oxide, hydroxyapatite, zirconium oxide, defluorination resin, etc. to adsorb fluoride-containing wastewater. However, all of them have problems such as low adsorption capacity, high cost of adsorbent, difficulty in regenerating adsorbent, rapid decline in adsorbent capacity, and difficulty in treating regenerated liquid.

[0005] Therefore, it is necessary to develop a systematic treatment process for fluoride-containing wastewater to solve problems such as low adsorption capacity, high cost of adsorbents, difficulty in adsorbent regeneration, rapid decline in adsorbent capacity, and difficulty in treating regenerated liquid. Summary of the Invention

[0006] The purpose of this invention is to provide a system treatment process and method for fluoride-containing wastewater. This system treatment process produces less sludge, uses less flocculant, has low treatment costs, high adsorption capacity, significantly extends the adsorption time of the adsorbent, reduces the regeneration frequency, and eliminates the discharge of regenerated liquid, effectively solving the problem of difficult-to-treat byproducts in traditional treatment processes. To achieve the above objectives, this invention provides the following technical solution:

[0007] The system treatment process for fluoride-containing wastewater includes the following steps: fluoride-containing wastewater treatment process, sludge treatment process, fluoride removal filter media regeneration process, and sludge waste liquid treatment process.

[0008] The fluoride-containing wastewater treatment process is as follows: the coal gasification produced water is sequentially passed through a pH adjustment tank, a spore transfer integrated machine, and a fluoride-containing wastewater adsorption filter before being discharged.

[0009] The sludge treatment process is as follows: the scum generated by the spore transfer integrated machine is squeezed out of the water by a screw press, the filtrate is returned to the pH adjustment tank, and the defluorinated sludge is discharged into the sludge waste liquid treatment tank for further treatment.

[0010] The fluoride removal filter media regeneration process is as follows: the regeneration solution is added to the saturated fluoride-containing wastewater adsorption filter tank through a dosing pump to completely soak the filter media for regeneration. After the regeneration is completed, the regenerated waste liquid is discharged to the sludge waste liquid treatment tank for further treatment.

[0011] The sludge wastewater treatment process is as follows: the defluorinated sludge produced by the screw press and the regeneration wastewater produced by the regeneration process are mixed in the sludge wastewater treatment tank. After mixing, calcium chloride solution is added for treatment. The supernatant is returned to the pH adjustment tank and the sediment is discharged.

[0012] Preferably, after the influent enters the pH adjustment tank, the pH is adjusted to between 6.5 and 7.5.

[0013] Preferably, the pH adjuster in the pH adjustment tank is H2SO4 or HCl with a concentration of 5%.

[0014] The pH adjustment tank is equipped with a mechanical stirrer to ensure that the influent and pH adjuster can react quickly. The influent retention time exceeds 15 minutes. The pH adjustment tank outlet is equipped with online pH monitoring. The amount of pH adjuster added is adjusted every 15 minutes to ensure that the pH of the wastewater at the outlet of the pH adjustment tank is between 6.5 and 7.5.

[0015] Preferably, a polymerizing agent and a focusing agent are added during the processing stage of the spore transfer machine.

[0016] Preferably, the mass ratio of the polymerizing agent to the focusing agent is (10-20):1.

[0017] Preferably, the polymerizing agent is a polymeric metal silicate salt.

[0018] Preferably, the preparation method of the polymeric metal silicate salt is as follows:

[0019] A1. Add hydrochloric acid solution to sodium silicate solution to adjust pH to 2-4, and react for 10-20 hours to obtain polymeric silicate solution;

[0020] A2. Add metal salt solution to polymeric silica solution in sequence, add hydrochloric acid solution to adjust pH to 2-4, stir well and let stand until the solution is colorless and transparent, and dry to obtain polymeric silica metal salt.

[0021] Preferably, the concentration of sodium silicate in the sodium silicate solution is 0.2 to 0.4 mol / L.

[0022] Preferably, the metal salt is AlCl3 and CaCl2.

[0023] Preferably, in the polymeric metal silicate salt, the molar ratio of Si to the metal element is 1:(3-5).

[0024] Preferably, in the polymeric metal silicate salt, the molar ratio of Al to Ca is (1-3):1.

[0025] The inventors discovered that by using a specific method to prepare a polymeric silicate solution, simultaneously introducing aluminum and calcium ions, and controlling the molar ratio of each element, the removal capacity of the prepared polymeric silicate metal salt for chloride ions can be improved, while reducing the turbidity of the wastewater. This is likely because during the polymerization process, silicate molecules cross-link to form diverse spatial structures, thus exhibiting excellent adsorption bridging properties. Furthermore, the introduction of a certain amount of aluminum and calcium ions allows them to interact with the OH groups at the ends of silicate molecules. -Complexation, adsorption, and coordination reactions occurred. These reactions not only inhibited further polymerization of polysilicic acid, ensuring the stability of the resulting polymer, but also tightly bound polysilicic acid, aluminum salt, and calcium salt through specific chemical reactions. The three components exhibit a synergistic effect, resulting in a polysilicic acid metal salt that combines the strong adsorption bridging ability of polysilicic acid, the adsorption-electroneutralization ability of aluminum salt, and the strong bonding ability between calcium salt and fluoride. This significantly improves fluoride removal capacity and reduces wastewater turbidity. The inventors discovered during the preparation process that before adding the metal salt solution, it is necessary to control the concentration of sodium silicate solution, the pH value of the solution, and the reaction time to avoid either excessively rapid polymerization leading to gel formation that hinders the reaction with metal ions or slow polymerization resulting in low reaction efficiency.

[0026] Preferably, the focusing agent is anionic polyacrylamide.

[0027] Preferably, the anionic polyacrylamide has a molecular weight of 10-20 million and a solid content of ≥85%; more preferably, the anionic polyacrylamide has a molecular weight of 15 million and a solid content of ≥88%.

[0028] In some preferred solutions, using specific anionic polyacrylamide as the focusing agent, with a polymerizer-to-focusing agent mass ratio of (10-20):1, can improve overall dechlorination capacity while further improving water quality and reducing turbidity. This may be because the two have a synergistic effect; when used together, they can enhance each other's adsorption effect, improving the overall dechlorination capacity. Furthermore, the colloid formed by polyaluminum silicate combines with the water-purifying gel of polyacrylamide, more effectively precipitating chloride ions along with other substances in the water (such as heavy metal ions and organic pollutants), further improving water quality and reducing turbidity. However, excessive polyaluminum silicate may lead to excessively high concentrations of aluminum and calcium ions in the water, causing pollution to the aquatic environment. Excessive anionic polyacrylamide may make the water viscous, affecting the filtration properties of the flocs and increasing turbidity. Incorrect ratios of the two substances will also lead to poor water treatment results.

[0029] In some preferred embodiments, the anionic polyacrylamide is purchased from Kaifeng Hongyuan Water Treatment Technology Co., Ltd.

[0030] Preferably, the filter media in the fluoride-containing wastewater adsorption filter is high-performance fluoride-removing hydroxyapatite.

[0031] Preferably, the preparation method of the high-performance fluoride-removing hydroxyapatite includes the following steps:

[0032] B1. Dissolve ferric chloride, aluminum chloride and calcium chloride in deionized water to obtain a mixed solution. Heat the solution in a water bath to 40-50°C, then add an equal volume of diammonium hydrogen phosphate solution dropwise, controlling the dropping rate and maintaining the pH of the system at 9-11. After the addition is complete, continue heating and stirring for 2-4 hours, then age at room temperature for 2-4 days. Filter the solution, wash the product with deionized water until neutral, and dry it to constant weight to obtain modified hydroxyapatite.

[0033] B2. Mix modified hydroxyapatite with activated carbon, continuously add polyvinyl alcohol solution to the mixture while stirring continuously until it forms a gel-like solid, then stop adding the solution. Remove the gel-like solid, dry it, and calcine it at 300-400℃ for 4-6 hours under a nitrogen atmosphere. After cooling, the product is obtained.

[0034] Preferably, in the modified hydroxyapatite, the ratio of the total amount of iron, aluminum, and calcium to the amount of phosphorus is 5:3.

[0035] Preferably, the amount of iron and aluminum is 1% to 5% of the amount of calcium.

[0036] Preferably, the molar ratio of iron to aluminum is 1:(0.5-2).

[0037] While traditional hydroxyapatite possesses some fluoride removal capabilities, these are limited and unsuitable for large-scale wastewater treatment. The inventors discovered that simultaneously modifying hydroxyapatite with iron and aluminum ions significantly enhances its fluoride removal capacity. This is likely due to the synergistic effect of the two ions: firstly, by altering the crystal lattice of hydroxyapatite to form amorphous iron oxides, the specific surface area and pore volume of the hydroxyapatite are increased, thereby enhancing its adsorption capacity; secondly, by changing the crystallinity of the hydroxyapatite crystals, the number of adsorption active sites on its surface is increased. Furthermore, Al… 3+ Fe 3+ All will be with F - Complexation reactions occur, forming complexes that enhance the adsorption capacity of modified hydroxyapatite for fluoride ions. However, while modified hydroxyapatite exhibits high adsorption capacity during fluoride removal, its fluoride removal efficiency is low, and it can lead to increased turbidity.

[0038] Preferably, the activated carbon has an iodine adsorption value > 800 mg / g and a specific surface area > 700 m². 2 / g, residual chlorine adsorption rate >80%; more preferably, the activated carbon has an iodine adsorption value of 800-1200 mg / g and a specific surface area >850 m² / g. 2 / g, residual chlorine adsorption rate >85%.

[0039] In some preferred embodiments, the activated carbon is purchased from Jiangsu Quanhu Activated Carbon Co., Ltd.

[0040] Preferably, the mass ratio of the modified hydroxyapatite to activated carbon is (5-7):1.

[0041] The inventors discovered that by blending specific activated carbon with modified hydroxyapatite in a mass ratio of (5-7):1, the fluoride removal capacity of modified hydroxyapatite can be further improved while overcoming the turbidity problem caused by its adsorption, thus enhancing the fluoride removal efficiency. This is because activated carbon has a high specific surface area and acts as a carrier during blending, allowing the modified hydroxyapatite to be fully dispersed within it. This enables the modified hydroxyapatite to fully utilize its fluoride ion exchange capacity while simultaneously increasing the contact area with wastewater, thereby improving ion exchange efficiency and preventing an increase in water turbidity. However, since activated carbon itself has a relatively poor fluoride adsorption capacity, its addition amount should not be excessive.

[0042] Preferably, the degree of hydrolysis of the polyvinyl alcohol is 85 mol / % to 90 mol / %, and the viscosity is 20 to 25 MPa·s; more preferably, the degree of hydrolysis of the polyvinyl alcohol is 87 mol / % to 89 mol / %, and the viscosity is 20.5 to 24.5 MPa·s.

[0043] Preferably, the polyvinyl alcohol content in the polyvinyl alcohol solution is 1 wt% to 5 wt%.

[0044] In some preferred embodiments, the polyvinyl alcohol is purchased from Shanxi Sanweishengtai New Material Technology Co., Ltd.

[0045] In some preferred embodiments, this application establishes a specific sludge wastewater treatment process. The defluorination sludge treated by this specific process and the regeneration wastewater generated from the regeneration process are mixed in a sludge wastewater treatment tank. After mixing, calcium chloride solution is added for further treatment. This approach reduces costs while solving the problem of difficult-to-treat byproducts from traditional treatment processes. This is because, on the one hand, the main component of the defluorination sludge is aluminum hydroxide colloid. After mixing with the regeneration wastewater in the sludge wastewater tank, the sludge dissolves, generating a supernatant NaAlO2 solution. This solution is then returned to the pH adjustment tank, where it reacts with H2SO4 or HCl solution in a spore transfer machine to generate new flocs Al(OH)3. This Al(OH)3 floc can be used as a polymerizing agent in the spore transfer machine for flocculation and capture of fluoride in the water. - This reduces the amount of polymerizing and focusing agents used; on the other hand, the F in the sludge - It reacts with CaCl2 solution to form CaF2 precipitate, which can be disposed of by external discharge, making the operation simple. The supernatant is recovered and reused, and the precipitate is discharged externally. The entire treatment process produces no waste liquid, improving economic efficiency while maintaining its simplicity, making it suitable for large-scale treatment of fluoride-containing wastewater. There is no waste liquid treatment throughout the process, with only a small amount of calcium fluoride sludge being transported and disposed of. The fluoride content in the treated water meets the standards for Class III surface water. It also achieves simultaneous silicon and hardness removal.

[0046] Compared with the prior art, the advantages and beneficial effects of the present invention are as follows:

[0047] 1. This invention provides a system treatment process for fluoride-containing wastewater. This system produces less sludge, uses less flocculant, has low treatment costs, significantly extends the adsorption time of the adsorbent, reduces the regeneration frequency, and eliminates the discharge of regenerated liquid, effectively solving the problem of difficult-to-treat byproducts in traditional treatment processes. There is no wastewater treatment throughout the process, with only a small amount of calcium fluoride sludge being transported for disposal. The fluoride content in the treated effluent meets the standards for Class III surface water. It also achieves simultaneous silicon and hardness removal.

[0048] 2. This invention uses a specific method to prepare a polymeric silicate solution, while introducing aluminum and calcium ions and controlling the molar ratio between the elements. This can improve the removal capacity of the prepared polymeric silicate metal salt for chloride ions and reduce the turbidity of the wastewater.

[0049] 3. By selecting a specific anionic polyacrylamide as a focusing agent, and when the mass ratio of polymerizer to focusing agent is (10-20):1, this invention can improve the overall dechlorination capacity while further improving water quality and reducing turbidity.

[0050] 4. This invention uses iron ions and aluminum ions to modify hydroxyapatite simultaneously, which can greatly improve the fluoride removal capacity of traditional hydroxyapatite.

[0051] 5. By selecting specific activated carbon and blending modified hydroxyapatite, and when the mass ratio of modified hydroxyapatite to activated carbon is (5-7):1, this invention can further improve the defluorination capacity of modified hydroxyapatite while overcoming the turbidity problem caused by the adsorption of modified hydroxyapatite, thereby improving the defluorination efficiency.

[0052] 6. This application sets up a specific sludge wastewater treatment process, which mixes the defluorinated sludge treated by the specific process and the regeneration wastewater generated by the regeneration process in a sludge wastewater treatment tank, and then adds calcium chloride solution for treatment. This can reduce costs and solve the problem of difficult treatment of by-products of traditional treatment processes. Detailed Implementation

[0053] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0054] All raw materials used in this invention are commercially available, specifically:

[0055] Anionic polyacrylamide, with a molecular weight of 15 million and a solid content of ≥88%, was purchased from Kaifeng Hongyuan Water Treatment Technology.

[0056] Activated carbon with an iodine adsorption value of 800–1200 mg / g and a specific surface area >850 m². 2 / g, residual chlorine adsorption rate >85%, purchased from Jiangsu Quanhu Activated Carbon Co., Ltd.

[0057] Polyvinyl alcohol, with a degree of hydrolysis of 87 mol / % to 89 mol / %, and a viscosity of 20.5 to 24.5 MPa·s, was purchased from Shanxi Sanweishengtai New Material Technology Co., Ltd.

[0058] Example 1

[0059] This embodiment provides a system treatment process for fluoride-containing wastewater, the steps of which are: fluoride-containing wastewater treatment process, sludge treatment process, fluoride removal filter media regeneration process and sludge waste liquid treatment process.

[0060] The fluoride-containing wastewater treatment process is as follows: the coal gasification produced water is sequentially passed through a pH adjustment tank, a spore transfer integrated machine, and a fluoride-containing wastewater adsorption filter before being discharged.

[0061] The sludge treatment process is as follows: the scum generated by the spore transfer integrated machine is squeezed out of the water by a screw press, the filtrate is returned to the pH adjustment tank, and the defluorinated sludge is discharged into the sludge waste liquid treatment tank for further treatment.

[0062] The fluoride removal filter media regeneration process is as follows: the regeneration solution is added to the saturated fluoride-containing wastewater adsorption filter tank through a dosing pump to completely soak the filter media for regeneration. After the regeneration is completed, the regenerated waste liquid is discharged to the sludge waste liquid treatment tank for further treatment.

[0063] The sludge wastewater treatment process is as follows: the defluorinated sludge produced by the screw press and the regeneration wastewater produced by the regeneration process are mixed in the sludge wastewater treatment tank. After mixing, calcium chloride solution is added for treatment. The supernatant is returned to the pH adjustment tank and the sediment is discharged.

[0064] After the influent enters the pH adjustment tank, the pH is adjusted to approximately 7.

[0065] The pH adjusting agent in the pH adjustment tank is 5% HCl.

[0066] Mechanical agitation is installed in the pH adjustment tank to ensure rapid reaction between the influent and the pH adjuster. The influent retention time exceeds 15 minutes. Online pH monitoring is set at the outlet of the pH adjustment tank, and the amount of pH adjuster added is adjusted every 15 minutes to ensure that the pH of the wastewater at the outlet of the pH adjustment tank is approximately 7.

[0067] The spore transfer machine incorporates polymerizing agents and focusing agents during its processing stage.

[0068] The mass ratio of the polymerizer to the focusing agent is 15:1.

[0069] The polymerizing agent is a polymeric metal silicate salt.

[0070] The preparation method of the polymeric metal silicate salt is as follows:

[0071] A1. Add hydrochloric acid solution to sodium silicate solution to adjust pH to 3, and after reacting for 15 hours, a polymeric silicate solution is obtained.

[0072] A2. Add metal salt solution to polymeric silica solution in sequence, add hydrochloric acid solution to adjust pH to 3, stir well and let stand until the solution is colorless and transparent, and dry to obtain polymeric silica metal salt.

[0073] The concentration of sodium silicate in the sodium silicate solution is 0.3 mol / L.

[0074] The metal salts are AlCl3 and CaCl2.

[0075] In the polymeric metal silicate salt, the molar ratio of Si to the metal element is 1:4.

[0076] In the polymeric metal silicate salt, the molar ratio of Al to Ca is 2:1.

[0077] The focusing agent is anionic polyacrylamide.

[0078] The filter media in the fluoride-containing wastewater adsorption filter is high-performance fluoride-removing hydroxyapatite.

[0079] The preparation method of the high-performance fluoride-removing hydroxyapatite includes the following steps:

[0080] B1. Ferric chloride, aluminum chloride and calcium chloride were dissolved in deionized water to obtain a mixed solution. The solution was heated to 45°C in a water bath, and an equal volume of diammonium hydrogen phosphate solution was added dropwise. The dropping rate was controlled and the pH of the system was kept at 10. After the addition was completed, the mixture was heated and stirred for 3 hours. The mixture was then aged at room temperature for 3 days, filtered, and the product was washed with deionized water until neutral. It was then dried to constant weight to obtain modified hydroxyapatite.

[0081] B2. Mix modified hydroxyapatite with activated carbon, continuously add polyvinyl alcohol solution to the mixture while stirring continuously until it forms a gel-like solid, then stop adding the solution. Remove the gel-like solid, dry it, and calcine it at 350°C for 5 hours under a nitrogen atmosphere. After cooling, the product is obtained.

[0082] In the modified hydroxyapatite, the ratio of the total amount of iron, aluminum, and calcium to the amount of phosphorus is 5:3.

[0083] The amount of iron and aluminum is 3% of the amount of calcium.

[0084] The molar ratio of iron to aluminum is 1:1.

[0085] The mass ratio of the modified hydroxyapatite to activated carbon is 6:1.

[0086] The polyvinyl alcohol content in the polyvinyl alcohol solution is 3 wt%.

[0087] Example 2

[0088] The difference between this embodiment and Embodiment 1 is that the mass ratio of the polymerizing agent to the focusing agent is 18:1.

[0089] Example 3

[0090] The difference between this embodiment and Embodiment 1 is that the mass ratio of the modified hydroxyapatite to activated carbon is 5:1.

[0091] Comparative Example 1

[0092] The difference between this comparative example and Example 1 is that the mass ratio of the polymerizing agent to the focusing agent is 5:1.

[0093] Comparative Example 2

[0094] The difference between this comparative example and Example 1 is that the metal salt is AlCl3.

[0095] Comparative Example 3

[0096] The difference between this comparative example and Example 1 is that in the polymeric silicate metal salt, the molar ratio of Si to the metal element is 1:2.

[0097] Comparative Example 4

[0098] The difference between this comparative example and Example 1 is that the preparation method of the polymeric metal silicate salt involves the following steps:

[0099] A1. Add hydrochloric acid solution to sodium silicate solution to adjust pH to 5, and after reacting for 8 hours, a polymeric silicate solution is obtained.

[0100] A2. Add metal salt solution to polymeric silica solution in sequence, add hydrochloric acid solution to adjust pH to 5, stir well and let stand until the solution is colorless and transparent, and dry to obtain polymeric silica metal salt.

[0101] The concentration of sodium silicate in the sodium silicate solution is 0.5 mol / L.

[0102] Comparative Example 5

[0103] The difference between this comparative example and Example 1 is that the preparation method of the high-performance fluoride-removing hydroxyapatite includes the following steps:

[0104] B1. Dissolve ferric chloride and calcium chloride in deionized water to obtain a mixed solution. Heat the solution in a water bath to 45°C, then add an equal volume of diammonium hydrogen phosphate solution dropwise, controlling the dropping rate and maintaining the pH of the system at 10. After the addition is complete, continue heating and stirring for 3 hours, then age at room temperature for 3 days. Filter the solution, wash the product with deionized water until neutral, and dry it to constant weight to obtain modified hydroxyapatite.

[0105] B2. Mix modified hydroxyapatite with activated carbon, continuously add polyvinyl alcohol solution to the mixture while stirring continuously until it forms a gel-like solid, then stop adding the solution. Remove the gel-like solid, dry it, and calcine it at 350°C for 5 hours under a nitrogen atmosphere. After cooling, the product is obtained.

[0106] In the modified hydroxyapatite, the ratio of the total amount of iron and calcium to the amount of phosphorus is 5:3.

[0107] The amount of iron is 3% of the amount of calcium.

[0108] Comparative Example 6

[0109] The difference between this comparative example and Example 1 is that the molar ratio of iron to aluminum is 1:3.

[0110] Comparative Example 7

[0111] The difference between this comparative example and Example 1 is that the mass ratio of the modified hydroxyapatite to activated carbon is 4:1.

[0112] Performance testing

[0113] Wastewater from a factory in Beijing was tested. The fluoride content was measured according to GB 3838-2002 "Environmental Quality Standard for Surface Water," and the result was 8.4 mg / L. The turbidity was measured according to GB / T 19923-2005 "Water Quality Standard for Industrial Water Used in Urban Wastewater Reuse," and the result was 1789 NTU. This is far below the surface water discharge standard, which requires a fluoride content of ≤1 mg / L and a turbidity of ≤5 NTU for industrial water used in urban wastewater reuse. The fluoride content and turbidity of the wastewater after treatment using the processes described in Examples 1 to 7 of this application are shown in Table 1.

[0114] Table 1 Measurement Results

[0115]

[0116] According to statistics, the wastewater treated by the system treatment process for fluoride-containing wastewater prepared in Examples 1-3 of this invention meets the discharge standards for both fluoride content and turbidity. However, in Comparative Example 1, the amount of polymerizing agent added was too small; in Comparative Example 2, calcium ions were not introduced; in Comparative Example 3, the amount of metal element introduced was too small; in Comparative Example 4, the pH value was too high, the reaction time was too short, and the sodium silicate concentration was too high during the preparation of the polymerized metal silicate, affecting the polymerization effect; in Comparative Example 5, aluminum ions were not introduced to modify hydroxyapatite; in Comparative Example 6, the amount of aluminum ions added was too high; and in Comparative Example 7, the amount of activated carbon added was too high. The fluoride content and turbidity of the wastewater treated by the above methods did not fully meet the requirements. Therefore, the system treatment of fluoride-containing wastewater using the method described in this application can achieve the fluoride content and turbidity standards for Class III surface water, with less sludge production, less flocculant usage, lower treatment costs, significantly extended adsorption time of the adsorbent, reduced regeneration frequency, and no regeneration liquid discharge, effectively solving the problem of difficult-to-treat byproducts of traditional treatment processes. There is no waste liquid treatment throughout the process, with only a small amount of calcium fluoride sludge being transported off-site for disposal.

[0117] The above description represents the preferred embodiments of the present invention. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A system treatment process for fluoride-containing wastewater, characterized in that the steps include: include: Fluorine-containing wastewater treatment process, sludge treatment process, fluoride removal filter media regeneration process, and sludge waste liquid treatment process; The fluoride-containing wastewater treatment process is as follows: the coal gasification produced water is sequentially passed through a pH adjustment tank, a spore transfer integrated machine, and a fluoride-containing wastewater adsorption filter before being discharged. The sludge treatment process is as follows: the scum generated by the spore transfer integrated machine is squeezed out of the water by a screw press, the filtrate is returned to the pH adjustment tank, and the defluorinated sludge is discharged into the sludge waste liquid treatment tank for further treatment. The regeneration process of the defluorination filter media is as follows: The regeneration solution is added to a saturated fluoride-containing wastewater adsorption filter tank via a dosing pump to completely immerse the filter media for regeneration. After regeneration, the regenerated waste liquid is discharged to a sludge wastewater treatment tank for further treatment. The filter media in the fluoride-containing wastewater adsorption filter tank is high-performance defluorination hydroxyapatite. The preparation method of the high-performance defluorination hydroxyapatite includes the following steps: B1. Dissolve ferric chloride, aluminum chloride and calcium chloride in deionized water to obtain a mixed solution. Heat the solution in a water bath to 40-50°C, then add an equal volume of diammonium hydrogen phosphate solution dropwise, controlling the dropping rate and maintaining the pH of the system at 9-11. After the addition is complete, continue heating and stirring for 2-4 hours, then age at room temperature for 2-4 days. Filter the solution, wash the product with deionized water until neutral, and dry it to constant weight to obtain modified hydroxyapatite. B2. Mix modified hydroxyapatite with activated carbon, continuously add polyvinyl alcohol solution to the mixture while stirring continuously until it forms a gel-like solid, then stop adding the solution. Take out the gel-like solid, dry it, and calcine it at 300~400℃ for 4~6 hours under a nitrogen atmosphere. After cooling, the product is obtained. In the modified hydroxyapatite, the total molar ratio of iron, aluminum, and calcium to phosphorus is 5:3; the activated carbon has an iodine adsorption value >800 mg / g and a specific surface area >700 m². 2 / g, residual chlorine adsorption rate >80%; The sludge waste liquid treatment process is as follows: the defluorinated sludge produced by the screw press and the regeneration waste liquid produced by the regeneration process are mixed in the sludge waste liquid treatment tank. After mixing, calcium chloride solution is added for treatment. The supernatant is returned to the pH adjustment tank and the sediment is discharged. The spore transfer machine incorporates a polymerizing agent and a focusing agent during its processing stage; the mass ratio of the polymerizing agent to the focusing agent is (10~20):1; the polymerizing agent is a polymeric metal silicate salt; and the preparation method of the polymeric metal silicate salt is as follows: A1. Add hydrochloric acid solution to sodium silicate solution to adjust pH to 2-4, and react for 10-20 hours to obtain polymeric silicate solution; A2. Add metal salt solution to polymeric silica solution in sequence, add hydrochloric acid solution to adjust pH to 2-4, stir evenly and let stand until the solution is colorless and transparent, and dry to obtain polymeric silica metal salt. The metal salts are AlCl3 and CaCl2; in the polymeric metal silicate salt, the molar ratio of Si to the metal element is 1:(3~5); in the polymeric metal silicate salt, the molar ratio of Al to Ca is (1~3):1; the focusing agent is anionic polyacrylamide; the molecular weight of the anionic polyacrylamide is 10 million to 20 million, and the solid content is ≥85%.

2. The system treatment process for fluoride-containing wastewater according to claim 1, characterized in that, The pH adjusting agent in the pH adjustment tank is 5% H2SO4 or HCl.

3. The system treatment process for fluoride-containing wastewater according to claim 1, characterized in that, The amount of iron and aluminum is 1% to 5% of the amount of calcium.

4. The system treatment process for fluoride-containing wastewater according to claim 1, characterized in that, The molar ratio of iron to aluminum is 1:(0.5~2).

5. The system treatment process for fluoride-containing wastewater according to claim 1, characterized in that, The mass ratio of the modified hydroxyapatite to activated carbon is (5~7):1.

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