Method for removing fluorine from flocculation body after defluorination by aluminum source coagulant and recycling

Abstract

The application discloses a method for defluorination of flocculation body after defluorination by aluminum source coagulant and recycling, which comprises the following steps: adding aluminum source coagulant into fluorine-containing wastewater for coagulation treatment, and filtering to obtain defluorination wastewater and flocculation body; mixing the flocculation body with hydrogen peroxide, adding alkali liquor to adjust pH to 7.5-9.5, stirring and eluting, and filtering to obtain regenerated flocculation body and eluent; and then putting the regenerated flocculation body into the fluorine-containing wastewater, adding acid liquor to adjust pH to 6-7.5, and stirring to remove fluorine. The regenerated flocculation body realizes recycling and recycling of the flocculation body after defluorination by the aluminum source coagulant, avoids water environment pollution and water resource waste caused by direct discharge of the flocculation body, and the eluent is used for recycling sodium fluoride or adding lime to prepare calcium fluoride.

Description

Technical Field

[0001] This invention relates to a method for defluorinating and reusing flocs after defluorination by aluminum-source coagulant. Background Technology

[0002] Fluorine is an essential trace element for the human body, but excessive intake can lead to diseases such as dental fluorosis and skeletal fluorosis. Fluorine in water mainly originates from the dissolution of fluoride-containing minerals in nature and wastewater discharged from human industrial production activities, with industrial wastewater exhibiting the highest fluoride concentration and causing the most severe pollution. Currently, commonly used defluoridation technologies include coagulation, membrane separation, ion exchange, and adsorption. Among these, coagulation is widely used in the treatment of industrial fluoride-containing wastewater due to its high treatment efficiency, low cost, and simple process. Aluminum-based coagulants are widely used agents in coagulation defluorination, such as aluminum sulfate, aluminum chloride, and polyaluminum chloride. Aluminum-based coagulants undergo hydrolysis in water, generating hydrolysis products with different charges and polymerization characteristics. These products remove fluoride ions from the water through adsorption and precipitation, forming flocculent precipitates containing aluminum hydroxide and fluorides.

[0003] The flocs produced after defluorination by aluminum-based coagulants are usually directly discharged or treated as solid waste. The large amount of aluminum hydroxide remaining in the flocs and the adsorbed fluoride ions enter the water body or environment, causing secondary pollution of the water environment and waste of water resources.

[0004] However, existing technologies lack a systematic method for effectively regenerating flocs after defluorination. During the defluorination process, organic pollutants adsorb onto the surface of the flocs, causing the active sites to be covered. At the same time, some hydroxyl active sites undergo transformation or deactivation in the alkaline defluorination environment. If the flocs are reused directly without regeneration, their defluorination adsorption capacity will decrease significantly, making it impossible to guarantee that the treated effluent water quality will consistently meet standards. Summary of the Invention

[0005] The purpose of this invention is to provide a method for defluorinating and reusing flocs after defluorination of aluminum-source coagulants, which can effectively defluorinate and reuse flocs after defluorination of aluminum-source coagulants, and the desorbed flocs have excellent refluorination effect.

[0006] To achieve the above objectives, the technical solutions adopted by the present invention are as follows: A method for defluorinating and reusing flocs after defluorination using aluminum-source coagulants includes the following steps: Coagulation and defluorination: Aluminum-based coagulant is added to fluoride-containing wastewater for coagulation treatment, and the wastewater and flocs are obtained by filtration. Alkaline washing and defluorination: Mix the flocs with hydrogen peroxide, add alkaline solution to adjust the pH to 7.5-9.5, stir and wash, filter to obtain regenerated flocs and eluent; Reuse: The regenerated flocs are added to fluoride-containing wastewater, acid is added to adjust the pH to 6-7.5, and then the mixture is stirred to remove fluoride.

[0007] Preferably, the mass concentration of hydrogen peroxide is 20%-50%, and the flocs and hydrogen peroxide are mixed at a solid-liquid ratio of 1g:(1-4)mL.

[0008] Preferably, the alkaline solution is a 0.5-2 mol / L sodium hydroxide solution.

[0009] Preferably, the stirring and elution time is 10-15 minutes.

[0010] Preferably, the stirring defluorination is carried out by first stirring at 500-700 rpm for 2-4 minutes, and then stirring at 100-300 rpm for 15-20 minutes.

[0011] Preferably, the acid solution is dilute nitric acid.

[0012] Preferably, the aluminum source in the aluminum-based coagulant is one or more of aluminum sulfate, aluminum chloride, aluminum nitrate, aluminum stearate, aluminum triethanolamine, polyaluminum sulfate, polyaluminum chloride, polyaluminum phosphate, polyaluminum silicate iron, polyaluminum phosphate iron, and basic aluminum silicate sulfate; the concentration of the aluminum-based coagulant is 15-25 g / L.

[0013] Preferably, in the coagulation and defluorination step, the dosage of aluminum source coagulant is 0.04-0.1 times the volume of fluoride-containing wastewater, and the fluoride ion concentration in the fluoride-containing wastewater is 10-50 ppm; In the reuse step, the ratio of regenerated flocs to fluoride-containing wastewater is (0.35-1)g:(200-1000)mL, and the fluoride ion concentration in the fluoride-containing wastewater is 10-50 ppm.

[0014] Preferably, the process further includes a step of recovering the eluent, which involves concentrating and crystallizing the eluent to recover sodium fluoride from the eluent, or adding lime to the eluent to obtain calcium fluoride.

[0015] Preferably, in the reuse step, the flocs obtained after the defluorination treatment of the regenerated flocs are used for defluorination of fluoride-containing wastewater after repeated alkaline washing defluorination steps.

[0016] The present invention has the following beneficial effects: By adding hydrogen peroxide to the defluorinated flocs and using an alkaline solution for stirring and elution, the adsorbed fluoride ions in the flocs are released. Simultaneously, the hydrogen peroxide oxidizes and removes organic pollutants adsorbed on the floc surface, cleans active sites, and promotes the regeneration of hydroxyl groups on the floc surface, restoring the floc's adsorption activity. After filtration, regenerated flocs are obtained. These regenerated flocs can be reused in defluorination treatment of fluoride-containing wastewater, achieving resource recovery and reuse of flocs after defluorination with aluminum-based coagulants. This avoids water pollution and water resource waste caused by direct discharge of flocs, while also recovering residual aluminum salt resources from the flocs.

[0017] The elution pH is adjusted to 7.5-9.5 using an alkaline solution. Hydroxide ions compete with fluoride ions for adsorption sites on the floc surface, thereby displacing and releasing fluoride ions from the floc and achieving defluorination and regeneration of the floc. At the same time, the oxidative cleaning effect of hydrogen peroxide significantly increases the number of active hydroxyl groups on the floc surface, thus enhancing the adsorption and exchange efficiency of fluoride ions by the regenerated floc.

[0018] After the regenerated flocs are reintroduced into the fluoride-containing wastewater, acid is added to adjust the pH to 6-7.5. Rapid stirring is performed in the early stage to break up the regenerated flocs and increase their specific surface area to enhance adsorption. Slow stirring is performed in the later stage to promote the regeneration and aggregation of the broken flocs, forming flocs with good settling properties. This ensures that the regenerated flocs have stable adsorption and settling effects during the re-fluoride removal process.

[0019] By recycling the eluent, sodium fluoride can be directly recovered from the eluent, or lime can be added to the eluent to obtain calcium fluoride, thus realizing the recycling of fluorine resources, reducing processing costs, and reducing secondary pollution. Detailed Implementation

[0020] This invention provides a method for defluorinating and reusing flocs after defluorination by aluminum-source coagulants, comprising the following steps: S1: Coagulation treatment.

[0021] Aluminum-based coagulants are added to fluoride-containing wastewater for coagulation treatment.

[0022] The aluminum source in the aluminum-based coagulant is one or more of the following: aluminum sulfate, aluminum chloride, aluminum nitrate, aluminum stearate, aluminum triethanolamine, polyaluminum sulfate, polyaluminum chloride, polyaluminum phosphate, polyaluminum silicate iron, polyaluminum phosphate iron, and basic aluminum silicate sulfate, with a concentration of 15-25 g / L. The solvent is water.

[0023] The dosage of aluminum-based coagulant is 0.04-0.1 times the volume of fluoride-containing wastewater, and the fluoride ion concentration in the fluoride-containing wastewater is 10-50 ppm.

[0024] When aluminum-based coagulants are added to fluoride-containing wastewater, they undergo a hydrolysis reaction, generating hydrolysis products with different charges and polymerization properties. These products remove fluoride ions from the water through adsorption and precipitation, forming flocs containing aluminum hydroxide and fluorides. After coagulation, the wastewater is filtered to obtain defluorinated wastewater and flocs, which contain aluminum hydroxide precipitates that have adsorbed fluoride ions. The fluoride ion concentration in the defluorinated wastewater is measured to verify the coagulation and defluorination effect.

[0025] S2: Alkali washing for defluorination and regeneration.

[0026] Hydrogen peroxide and alkaline solution were added to the flocs obtained in S1 and the mixture was stirred and eluted.

[0027] The mass concentration of hydrogen peroxide is 20%-50%, and the solid-liquid ratio of flocs to hydrogen peroxide is 1g:(1-4)mL.

[0028] The alkaline solution is a 0.5-2 mol / L sodium hydroxide solution.

[0029] Hydrogen peroxide is added, and the pH of the elution system is adjusted to 7.5-9.5 using an alkaline solution. The mixture is slowly stirred for 10-15 minutes to release fluoride ions from the flocs. Hydroxide ions in the alkaline solution compete with fluoride ions for adsorption sites on the floc surface, displacing the fluoride ions. The hydrogen peroxide oxidizes and removes adsorbed organic pollutants from the floc surface, cleaning the active sites and promoting the regeneration of hydroxyl groups on the floc surface. After stirring and elution, the mixture is filtered to obtain regenerated flocs and eluent. The sodium fluoride in the eluent can be directly recovered, or lime can be added to the eluent to obtain calcium fluoride, thus achieving the recovery and utilization of fluorine resources.

[0030] S3: Acid-modified activation.

[0031] The regenerated flocs obtained from S2 are then reintroduced into the fluoride-containing wastewater. Acid is added to adjust the pH of the system to 6-7.5; the acid is dilute nitric acid (obtained by mixing 68% concentrated nitric acid and water at a volume ratio of 1:13). This environment activates the adsorption activity of the regenerated flocs, preparing them for further fluoride removal.

[0032] S4: Defluorination again.

[0033] First, rapid stirring is performed to break up the regenerated flocs, increasing the specific surface area of ​​the flocs to enhance the adsorption effect.

[0034] The rapid stirring speed is 500-700 rpm, and the rapid stirring time is 2-4 minutes. Then, slow stirring is carried out to allow the broken flocs to regrow and aggregate, forming flocs with good settling properties. The slow stirring speed is 100-300 rpm, and the slow stirring time is 15-20 minutes.

[0035] After slow stirring, the wastewater was filtered to obtain the treated fluoride-containing wastewater. The fluoride ion concentration in the treated wastewater was measured to verify the effectiveness of the secondary fluoride removal.

[0036] All flocs obtained in the following examples are based on dry weight.

[0037] Example 1: A method for defluorinating and reusing flocs after aluminum chloride coagulation and defluorination, comprising the following steps: 350 ml of 20 g / L aluminum chloride solution was added to 5000 mL of raw water containing 20 ppm fluoride. The mixture was stirred rapidly at 200 rpm for 2 minutes, and then slowly stirred at 40 rpm for 15 minutes. After filtration, defluoridated wastewater and flocs were obtained. The concentration of fluoride ions in the defluoridated wastewater was measured to be 1.4 mg / L.

[0038] Transfer the flocs to a beaker, add 30% hydrogen peroxide at a solid-liquid ratio of 1g:2mL, and adjust the pH of the elution system to 8 by adding 0.5mol / L sodium hydroxide solution. Stir slowly for 10 minutes, filter, and obtain regenerated flocs and eluent.

[0039] Lime was added to the eluent at a solid-liquid ratio of 1g:30mL for resource utilization.

[0040] 4g of regenerated flocs were collected and added to 5000mL of wastewater containing 20ppm fluoride. Dilute nitric acid was added dropwise to adjust the pH to 7. The mixture was stirred rapidly at 700rpm for 2 minutes and then slowly at 100rpm for 15 minutes. After filtration, the fluoride ion concentration in the water was measured to be 4.92mg / L.

[0041] Example 2: The regenerated flocs from the fluoride-containing wastewater treated in Example 1 were repeated with the above-mentioned alkaline washing defluorination regeneration steps for secondary regeneration. Then, 4g of the regenerated flocs were added to 5000mL of wastewater containing 20ppm fluoride, and dilute nitric acid was added dropwise to adjust the pH to 7. The mixture was stirred rapidly at 700rpm for 2 minutes and then slowly stirred at 100rpm for 15 minutes. After filtration, the treated fluoride-containing wastewater was obtained, and the fluoride ion concentration was measured to be 5.68mg / L.

[0042] Example 3: A method for defluorinating and reusing flocs after aluminum chloride coagulation and defluorination, comprising the following steps: 350 ml of 20 g / L aluminum chloride solution was added to 5000 mL of raw water containing 20 ppm fluoride. The mixture was stirred rapidly at 200 rpm for 2 minutes, and then slowly stirred at 40 rpm for 15 minutes. After filtration, defluoridated wastewater and flocs were obtained. The concentration of fluoride ions in the defluoridated wastewater was measured to be 1.4 mg / L.

[0043] Transfer the flocs to a beaker, add 40% hydrogen peroxide at a solid-liquid ratio of 1g:1.5mL, and adjust the pH of the elution system to 9 by adding 1mol / L sodium hydroxide solution. Stir slowly for 10 minutes, filter, and obtain regenerated flocs and eluent.

[0044] Lime was added to the eluent at a solid-liquid ratio of 1g:30mL for resource utilization.

[0045] 4g of regenerated flocs were added to 5000mL of wastewater containing 20ppm fluoride. Dilute nitric acid was added dropwise to adjust the pH to 7. The mixture was stirred rapidly at 700rpm for 2 minutes and then slowly at 100rpm for 15 minutes. After filtration, the concentration of fluoride ions in the water was measured to be 5.36mg / L.

[0046] Comparative Example 1: A method for direct reuse of flocs after defluorination by aluminum chloride coagulation, comprising the following steps: 350 ml of 20 g / L aluminum chloride solution was added to 5000 mL of raw water containing 20 ppm fluoride. The mixture was stirred rapidly at 200 rpm for 2 minutes, followed by slow stirring at 40 rpm for 15 minutes. After filtration, defluoridated wastewater and flocs were obtained. The fluoride ion concentration in the defluoridated wastewater was measured to be 1.4 mg / L. Without alkaline washing and defluorination regeneration treatment, 4 g of flocs were directly added to 5000 mL of wastewater containing 20 ppm fluoride. Dilute nitric acid was added dropwise to adjust the pH to 7. The mixture was stirred rapidly at 700 rpm for 2 minutes, followed by slow stirring at 100 rpm for 15 minutes. After filtration, the fluoride ion concentration in the water was measured to be 11.23 mg / L.

[0047] Comparative Example 2: A method for defluorinating and reusing flocs after aluminum chloride coagulation and defluorination, comprising the following steps: 350 ml of 20 g / L aluminum chloride solution was added to 5000 mL of raw water containing 20 ppm fluoride. The mixture was stirred rapidly at 200 rpm for 2 minutes, and then slowly stirred at 40 rpm for 15 minutes. After filtration, defluoridated wastewater and flocs were obtained. The concentration of fluoride ions in the defluoridated wastewater was measured to be 1.4 mg / L.

[0048] Transfer the flocs to a beaker, add 30% hydrogen peroxide at a solid-liquid ratio of 1g:2mL, and adjust the pH of the elution system to 10 by adding 0.5mol / L sodium hydroxide solution. Stir slowly for 10 minutes, filter, and obtain regenerated flocs and eluent.

[0049] Lime was added to the eluent at a solid-liquid ratio of 1g:30mL for resource utilization.

[0050] 4g of regenerated flocs were added to 5000mL of wastewater containing 20ppm fluoride. Dilute nitric acid was added dropwise to adjust the pH to 7. The mixture was stirred rapidly at 700rpm for 2 minutes and then slowly at 100rpm for 15 minutes. After filtration, the concentration of fluoride ions in the water was measured to be 9.85mg / L.

[0051] In Example 1, the flocs regenerated after alkaline washing and defluorination, when used for the first cycle, could treat fluoride-containing wastewater to 4.92 mg / L under the condition that the pH of the washing system was 8. In Example 2, the regenerated flocs, after a second regeneration, still showed a good defluorination effect. In Example 3, when the pH of the washing system increased to 9, the defluorination effect of the regenerated flocs decreased to some extent, but the treatment effect was still relatively excellent.

[0052] In Comparative Example 1, when the flocs without alkaline washing and defluorination regeneration were used directly, the fluoride ion concentration in the treated fluoride-containing wastewater was 11.23 mg / L, significantly lower than that of the flocs after alkaline washing and regeneration. In Comparative Example 2, when the pH of the elution system increased to 10, the defluorination effect of the regenerated flocs significantly decreased, and the fluoride ion concentration in the treated fluoride-containing wastewater was 9.85 mg / L. This is because the pH was too high, resulting in excessive OH- ions. - It can seize adsorption sites and even damage the floc structure, thus reducing the defluorination effect of the regenerated floc.

[0053] The above description is merely a preferred embodiment of the present invention. It should be noted that those skilled in the art can make various modifications without departing from the principles of the present invention, and these modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for defluorinating and reusing flocs after defluorination with aluminum-source coagulant, characterized in that, Includes the following steps: Coagulation and defluorination: Aluminum-based coagulant is added to fluoride-containing wastewater for coagulation treatment, and the wastewater and flocs are obtained by filtration. Alkaline washing and defluorination: Mix the flocs with hydrogen peroxide, add alkaline solution to adjust the pH to 7.5-9.5, stir and wash, filter to obtain regenerated flocs and eluent; Reuse: The regenerated flocs are added to fluoride-containing wastewater, acid is added to adjust the pH to 6-7.5, and then the mixture is stirred to remove fluoride.

2. The method according to claim 1, characterized in that, The mass concentration of hydrogen peroxide is 20%-50%, and the flocs and hydrogen peroxide are mixed at a solid-liquid ratio of 1g:(1-4)mL.

3. The method according to claim 1, characterized in that, The alkaline solution is a 0.5-2 mol / L sodium hydroxide solution.

4. The method according to claim 1, characterized in that, The stirring and elution time is 10-15 minutes.

5. The method according to claim 1, characterized in that, For defluorination by stirring, first stir at 500-700 rpm for 2-4 minutes, then stir at 100-300 rpm for 15-20 minutes.

6. The method according to claim 1, characterized in that, The acid solution is dilute nitric acid.

7. The method according to claim 1, characterized in that, The aluminum source in the aluminum-based coagulant is one or more of the following: aluminum sulfate, aluminum chloride, aluminum nitrate, aluminum stearate, aluminum triethanolamine, polyaluminum sulfate, polyaluminum chloride, polyaluminum phosphate, polyaluminum silicate iron, polyaluminum phosphate iron, and basic aluminum silicate sulfate; the concentration of the aluminum-based coagulant is 15-25 g / L.

8. The method according to claim 1, characterized in that, In the coagulation and defluorination step, the dosage of aluminum source coagulant is 0.04-0.1 times the volume of fluoride-containing wastewater, and the fluoride ion concentration in the fluoride-containing wastewater is 10-50 ppm; In the reuse step, the ratio of regenerated flocs to fluoride-containing wastewater is (0.35-1)g:(200-1000)mL, and the fluoride ion concentration in the fluoride-containing wastewater is 10-50 ppm.

9. The method according to claim 1, characterized in that, It also includes a step of recovering the eluent, which involves concentrating and crystallizing the eluent to recover sodium fluoride from the eluent, or adding lime to the eluent to obtain calcium fluoride.

10. The method according to claim 1, characterized in that, In the reuse step, the flocs obtained after the defluorination treatment of the regenerated flocs are repeatedly subjected to an alkaline washing defluorination step and then used for defluorination of fluoride-containing wastewater.