A recycling and treatment process for organic fluorine-containing waste liquid

Abstract

This application belongs to the field of wastewater treatment technology, specifically relating to a recycling and treatment process for organic fluoride-containing wastewater. The invention employs a stepped treatment process: Fenton pre-oxidation treatment—anaerobic biological treatment—aerobic biological treatment—deep adsorption with mixed metal oxides, efficiently and systematically removing fluoride ions from organic fluoride-containing wastewater. Using magnesium-aluminum composite oxides or lanthanum-zirconium-doped magnesium-aluminum composite oxides as adsorbents allows for precise removal of fluoride ions, unaffected by interference from other ions, effectively improving the fluoride ion removal rate. The use of lanthanum and zirconium-doped magnesium-aluminum composite oxides ensures that the resulting lanthanum-zirconium-doped magnesium-aluminum composite oxides maintain high fluoride removal activity over a wide pH range of 3-9, effectively reducing the cost of wastewater treatment.

Description

Technical Field

[0001] This application belongs to the field of wastewater treatment technology, specifically relating to a recycling and treatment process for organic fluorine-containing waste liquid. Background Technology

[0002] Due to their excellent chemical stability, thermal stability, and unique physicochemical properties, organofluorine compounds are used in various industrial fields such as semiconductor manufacturing, photovoltaic industry, fluorochemicals, lithium-ion battery production, and fluorine pesticide synthesis. However, the production, processing, and cleaning of these products generate large amounts of organofluorine wastewater. The CF bond energy in organofluorine compounds is extremely high (up to 485 kJ / mol), resulting in extremely strong chemical stability. They are difficult for microorganisms to degrade in the natural environment, with half-lives reaching decades. This leads to long-term accumulation and migration through the food chain, causing serious impacts on both the natural environment and human health. Furthermore, fluorine wastewater is highly corrosive, accelerating the depreciation of industrial equipment and increasing production and maintenance costs for enterprises. Therefore, this places extremely high demands on the depth and stability of organofluorine wastewater treatment.

[0003] Currently, the main technologies for treating organic fluoride-containing wastewater include physicochemical methods, advanced oxidation methods, and biological methods. Chemical precipitation can generate fluoride precipitates by adding reagents such as calcium salts and aluminum salts, which is suitable for the pretreatment of high-concentration fluoride-containing wastewater. However, it is only effective for free fluoride ions and cannot react with organic fluoride. Moreover, the fluoride concentration in the treated wastewater is difficult to reduce to below 10 mg / L. Adsorption methods use adsorbents such as activated alumina, modified bone char, and special resins to retain organic fluorides. They are simple to operate and suitable for low-concentration wastewater, but the adsorbent capacity is limited. Advanced oxidation methods degrade organic fluorides by generating strong free radicals to attack CF bonds, including electrocatalytic oxidation and ozone catalytic oxidation. Although they can convert some organic fluoride into inorganic fluoride ions, they have high requirements for equipment materials, high energy consumption, and the catalyst is prone to deactivation and difficult to recover. In existing treatment processes for organic fluoride-containing wastewater, activated alumina adsorbents exhibit low adsorption capacity and slow adsorption rate, resulting in long hydraulic retention times. Furthermore, these adsorbents are typically only effective under weakly acidic conditions with a pH of 5-6, while the pH of industrial wastewater fluctuates significantly, further reducing adsorption efficiency. In addition, competing ions such as sulfate and carbonate in the wastewater occupy adsorption sites, leading to a substantial decrease in the adsorbent's fluoride removal efficiency.

[0004] Chinese patent application CN118684392A discloses a process for treating hazardous organic waste containing fluoride, including pretreatment, waste liquid adsorption, defluorination treatment, evaporation and concentration, purification treatment, and discharge recovery. The defluorination treatment step removes fluoride ions from the waste liquid by adding a reactant to form an insoluble precipitate with fluoride ions. However, this method can only remove free fluoride ions and cannot react with organic fluorides in the waste liquid. The defluorination efficiency and depth are insufficient, making it difficult to meet stringent emission standards. Furthermore, this process requires a large amount of reactant, leading to increased treatment costs. Other metal ions in the wastewater may also compete with the reactant for reaction, further reducing the defluorination efficiency. Summary of the Invention

[0005] In order to solve the technical problems existing in the prior art, such as low defluorination efficiency, pH limitation, and the influence of competing ions, the purpose of this invention is to provide a recycling and treatment process for organic fluorine-containing waste liquid.

[0006] To achieve the above objectives, the technical solution of the present invention is as follows:

[0007] A process for recycling and treating organic fluorine-containing waste liquid includes the following steps:

[0008] S1: The organic fluorine-containing waste liquid is subjected to Fenton oxidation, then flocculant is added for flocculation and sedimentation, filter pressure is applied, and the filter residue is recovered to obtain filtrate I;

[0009] S2: The filtrate I obtained in step S1 is subjected to anaerobic and aerobic biochemical treatments, filtered, and the filter residue is recovered to obtain filtrate II;

[0010] S3: Add adsorbent to filtrate II obtained in step S2, stir for 1-2 hours, let stand for 3-4 hours, filter, recover the filter residue, and discharge the filtrate;

[0011] The adsorbent is a mixed metal oxide, and the amount of adsorbent used is 3-5 g / L.

[0012] The above scheme employs a step-by-step treatment process: Fenton pre-oxidation, anaerobic biochemical treatment, aerobic biochemical treatment, and deep adsorption with mixed metal oxides. This process efficiently and systematically removes fluoride ions from organic fluorine-containing wastewater. During Fenton oxidation, hydroxyl radicals are used to oxidize organic fluorine, converting large-molecule organic fluorine into small-molecule or partially inorganic fluorine, while simultaneously reducing the toxicity of the wastewater. This solves the problem of organic fluorine inhibiting microorganisms and creates suitable conditions for subsequent biochemical treatment. The combined anaerobic and aerobic biochemical treatment processes specifically degrade organic pollutants in the wastewater. The anaerobic stage can efficiently decompose high-concentration large-molecule organic matter, while the aerobic stage further degrades small-molecule pollutants and also degrades some easily biodegradable organic fluorine components. Finally, mixed metal oxide adsorption is used to achieve precise removal of fluoride ions, greatly improving the fluoride removal efficiency.

[0013] Furthermore, the mixed metal oxide is a magnesium-aluminum composite oxide, and the preparation method of the magnesium-aluminum composite oxide is as follows: magnesium nitrate hexahydrate and aluminum nitrate nonahydrate are dissolved in deionized water to form a solution with a metal ion concentration of 0.05-0.10 mol / L. The solution is placed in a constant temperature water bath, and a mixed solution of sodium hydroxide and sodium carbonate is slowly added dropwise at 30-35℃ and a stirring speed of 200-300 rpm. The pH of the system is maintained at 9.5-10.5. The mixture is stirred and aged for 14-16 hours, filtered, washed, dried, calcined at 450-550℃ for 2-3 hours, and cooled to obtain the magnesium-aluminum composite oxide.

[0014] In the above scheme, magnesium salt and aluminum salt are co-precipitated under alkaline conditions to generate a hydrotalcite-like precursor, which is then calcined at 450-550℃ to remove interlayer water and carbonate ions, forming an aluminum-magnesium composite oxide. When the aluminum-magnesium composite oxide comes into contact with an aqueous solution of fluoride ions, it will attempt to restore its layered structure, thereby adsorbing or embedding fluoride ions into its crystal lattice, achieving a precise removal effect of fluoride ions.

[0015] In the preparation of magnesium-aluminum composite oxide, a low-concentration (0.05-0.10 mol / L) solution environment is used to reduce the supersaturation of the solution and slow down the growth rate of crystal nuclei, so that the precursor forms thinner and more uniform nanosheets, avoiding excessively thick crystal stacking. This gives the precursor a larger specific surface area, and the composite oxide formed after sintering has more active alkaline sites exposed on the surface, allowing fluoride ions to easily attach through electrostatic attraction and ion exchange, thereby improving the utilization rate of adsorbent per unit mass. After the reaction, the aging time is extended to dissolve the small crystals and redeposit them at the edges of the large crystals, forming flower-like microspheres with specific channels. Through self-assembly, a hierarchical pore structure is formed. At the same time, the micron-sized flower-like structure formed by this self-assembly increases the apparent particle size, allowing the adsorbent to settle to the bottom of the pool more quickly after wastewater treatment, facilitating the discharge of clear liquid and solid recovery.

[0016] Furthermore, in the preparation method of aluminum-magnesium composite oxide, the molar ratio of magnesium nitrate hexahydrate and aluminum nitrate nonahydrate is (2-4):1; the mass percentage of sodium hydroxide in the mixed solution of sodium hydroxide and sodium carbonate is 8%-10%, and the mass percentage of sodium carbonate is 4%-7%; the heating rate of the calcination is 5-10℃ / min.

[0017] Furthermore, the mixed metal oxide can also be a lanthanum-zirconium-doped magnesium-aluminum composite oxide.

[0018] In the above scheme, a lanthanum and zirconium-doped magnesium-aluminum composite oxide is used. Utilizing the extremely high affinity of lanthanum for fluoride (hard acid-hard base theory), it forms a highly insoluble LaF, which specifically and precisely captures fluoride ions from wastewater. This method exhibits strong anti-interference capabilities and avoids interference from impurity ions. The introduction of zirconium improves the chemical stability of the composite oxide, giving the mixed metal oxide excellent acid and alkali resistance and stabilizing the oxide framework. The magnesium-aluminum oxide surface carries a high isoelectric point with a positive charge, which, combined with the high affinity of lanthanum, allows the adsorbent to maintain high fluoride removal activity over a wide pH range of 3-9, effectively reducing the cost of waste treatment.

[0019] Furthermore, the preparation method of the lanthanum-zirconium-doped magnesium-aluminum composite oxide is as follows: magnesium nitrate hexahydrate, aluminum nitrate nonahydrate, lanthanum nitrate and zirconium nitrate are dissolved in deionized water to form a solution with a metal ion concentration of 0.05-0.10 mol / L. Citric acid is added, and the mixture is stirred for 30-40 min. Urea and polyethylene glycol are then added, and the mixture is heated to 140-145℃ and reacted for 10-12 h. The mixture is then centrifuged, the precipitate is washed, dried, calcined, and cooled to obtain the lanthanum-zirconium-doped magnesium-aluminum composite oxide.

[0020] In the above scheme, citric acid forms a stable water-soluble complex with metal ions, which not only inhibits the hydrolysis and precipitation of metal ions, but also attracts different metal ions through its carboxyl groups, ensuring that lanthanum and zirconium are atomically dispersed in the magnesium-aluminum framework, rather than agglomerated into individual oxides. Utilizing the hydrolysis reaction of urea at high temperatures, ammonia and carbon dioxide are slowly released during calcination, achieving uniform precipitation of the precipitate particles and forming a uniform nanosheet structure. The long-chain structure of PEG interspersed between the precipitate particles acts as a steric hindrance. During calcination, PEG decomposes and vaporizes, leaving abundant mesoporous structures in situ, which act as rapid transport channels for fluoride ions, greatly reducing mass transfer resistance. This allows the prepared lanthanum-zirconium-doped magnesium-aluminum composite oxide to not only adsorb fluoride ions on its surface, but also to fully utilize its internal structure, significantly improving adsorption kinetics performance. Furthermore, zirconium and lanthanum ions have different ionic radii and valence states than magnesium and aluminum ions in the matrix. During calcination, the citric acid-assisted dispersion forces lanthanum and zirconium into the magnesium aluminum oxide lattice. This lattice distortion induces a large number of oxygen vacancies, which carry positive charge centers and can efficiently adsorb negatively charged fluoride ions. Moreover, this adsorption mechanism through lattice defects has a higher adsorption capacity and a tighter binding than simple surface hydroxyl exchange adsorption.

[0021] Furthermore, in the preparation method of lanthanum-zirconium-doped magnesium-aluminum composite oxide, the molar ratio of magnesium nitrate hexahydrate, aluminum nitrate nonahydrate, lanthanum nitrate, and zirconium nitrate is (2-4):1:(0.12-0.15):(0.03-0.05); the molar ratio of citric acid to total metal ions is (0.4-0.7):1; the molar ratio of urea to total metal ions is (3-5):1; and the polyethylene glycol is PEG-4000, with the amount of polyethylene glycol being 2%-4% of the total mass of the solution.

[0022] Furthermore, the calcination process described in the preparation method of lanthanum-zirconium-doped magnesium-aluminum composite oxide is as follows: the temperature is increased to 300-400℃ at a rate of 1-4℃ / min, held for 2-3 hours, and then increased to 500-550℃ at a rate of 3-7℃ / min, held for 4-5 hours.

[0023] In the above scheme, low-temperature calcination is first used to avoid the rapid heating that would cause the organic matter to burn violently and generate a large amount of gas, resulting in precursor particle agglomeration and pore structure collapse. During this stage, PEG and citric acid decompose, carbonize and escape, leaving abundant mesoporous channels. Then, high-temperature calcination is used, during which the remaining organic functional groups are further decomposed to ensure carbon-free calcination and avoid carbon impurities covering active sites and affecting adsorption efficiency. In addition, the high-temperature stage can promote the slow diffusion of lanthanum and zirconium into the magnesium aluminum oxide lattice to form a uniformly doped solid solution, thereby enhancing the chemical stability of the composite oxide.

[0024] Furthermore, the specific process of Fenton oxidation in step S1 is as follows: dilute hydrochloric acid is added to the organic fluorine-containing waste liquid to adjust the pH value to 2-4, and Fe... 2+ First, add ferrous sulfate heptahydrate at a molar ratio of 1:(3-10) to H2O2, at a dosage of 1-2 g / L, and stir until dissolved. Then, slowly add hydrogen peroxide solution with a mass fraction of 27%-28% at a dropping rate of 1-2 mL / min. Stir the reaction at 30-40℃ for 60-90 min. After the reaction is completed, add sodium hydroxide solution with a mass percentage of 8%-10% to adjust the pH value to 6.5-7.5.

[0025] The flocculant is composed of calcium chloride and polyaluminum chloride in a mass ratio of 1:(20-30), and the amount added is 200 mg / L.

[0026] Furthermore, in step S2, the reaction temperature for the anaerobic biological treatment is 35-40℃, the hydraulic retention time is 24-48h, and the influent COD volumetric loading rate is 2-5kgCOD / (m³). 3 (d), the reaction pH is 6.5-7.5.

[0027] Furthermore, in step S2, the dissolved oxygen concentration of the aerobic biochemical treatment is 2-4 mg / L, and the aeration intensity of the blower aeration system is 3-5 mg / L. 3 / (m 2 The reaction temperature is 20-30℃, the reaction pH is 7.0-8.0, and the hydraulic retention time is 12-24h.

[0028] Compared with existing technologies, the recycling and treatment process for organic fluorine-containing wastewater provided by this invention has the following technical advantages:

[0029] (1) The present invention adopts a step-by-step treatment process of Fenton pre-oxidation treatment - anaerobic biochemical treatment - aerobic biochemical treatment - deep adsorption of mixed metal oxides to efficiently and orderly remove fluoride ions from organic fluorine-containing waste liquid;

[0030] (2) The present invention uses magnesium aluminum composite oxide or lanthanum zirconium doped magnesium aluminum composite oxide as adsorbent to accurately remove fluoride ions without interference from other ions, and effectively improve the removal rate of fluoride ions.

[0031] (3) The present invention uses lanthanum and zirconium doped magnesium aluminum composite oxide, which enables the prepared lanthanum zirconium doped magnesium aluminum composite oxide to maintain high defluorination activity in a wide range of pH 3-9, effectively reducing the cost of waste treatment. Attached Figure Description

[0032] Figure 1 The process flow diagram of the recycling and treatment process for organic fluorine-containing waste liquid provided by the present invention. Detailed Implementation

[0033] The present application will be further described in detail below with reference to preparation examples, embodiments and comparative examples. All raw materials involved in the present application are commercially available.

[0034] Example 1

[0035] A process for recycling and treating organic fluorine-containing waste liquid includes the following steps:

[0036] S1: The organic fluorine-containing waste liquid is subjected to Fenton oxidation, and then flocculant (calcium chloride and polyaluminum chloride are composed of calcium chloride and polyaluminum chloride in a mass ratio of 1:20, and the amount added is 200mg / L) is added for flocculation and sedimentation, pressure filtration, and the filter residue is recovered to obtain filtrate I;

[0037] The specific process of Fenton oxidation is as follows: dilute hydrochloric acid is added to the organic fluorine-containing waste liquid to adjust the pH value to 2, and Fe is added... 2+Ferrous sulfate heptahydrate was added first at a molar ratio of 1:3 to H2O2, at a dosage of 1 g / L. The mixture was stirred until dissolved, and then a 27% hydrogen peroxide solution was slowly added dropwise at a rate of 1 mL / min. The mixture was stirred at 30°C for 60 min. After the reaction was completed, an 8% sodium hydroxide solution was added to adjust the pH to 6.5.

[0038] S2: The filtrate I obtained in step S1 is subjected to anaerobic and aerobic biochemical treatments, filtered, and the filter residue is recovered to obtain filtrate II;

[0039] The anaerobic biological treatment reaction temperature was 35℃, the hydraulic retention time was 24h, and the influent COD volumetric loading rate was 2kgCOD / (m³). 3 (d) The reaction pH was 6.5; the dissolved oxygen concentration in the aerobic biochemical treatment was 2 mg / L, and the aeration intensity of the blower aeration system was 3 m³ / s. 3 / (m 2 The reaction temperature was 20℃, the reaction pH was 7.0, and the hydraulic retention time was 12h.

[0040] S3: Add adsorbent to filtrate II obtained in step S2. The amount of adsorbent is 3g / L. Stir for 1 hour, let stand for 3 hours, filter, recover the filter residue, and discharge the filtrate.

[0041] The adsorbent is a magnesium-aluminum composite oxide. The preparation method of the magnesium-aluminum composite oxide is as follows: magnesium nitrate hexahydrate and aluminum nitrate nonahydrate are dissolved in deionized water at a molar ratio of 2:1 to form a solution with a metal ion concentration of 0.05 mol / L. The solution is placed in a constant temperature water bath and a mixed solution of sodium hydroxide and sodium carbonate is slowly added dropwise at 30°C and a stirring speed of 200 rpm. The mass percentage of sodium hydroxide is 8% and the mass percentage of sodium carbonate is 4%. The pH of the system is maintained at 9.5. The mixture is stirred and aged for 14 h, filtered, washed, dried, heated to 450°C at a heating rate of 5°C / min, calcined for 2 h, and cooled to obtain the magnesium-aluminum composite oxide.

[0042] Example 2

[0043] A process for recycling and treating organic fluorine-containing waste liquid includes the following steps:

[0044] S1: The organic fluorine-containing waste liquid is subjected to Fenton oxidation, and then flocculant (calcium chloride and polyaluminum chloride are composed of calcium chloride and polyaluminum chloride in a mass ratio of 1:30, and the amount added is 200mg / L) is added for flocculation and sedimentation, pressure filtration, and the filter residue is recovered to obtain filtrate I;

[0045] The specific process of Fenton oxidation is as follows: dilute hydrochloric acid is added to the organic fluorine-containing waste liquid to adjust the pH value to 4, and Fe... 2+Ferrous sulfate heptahydrate was added first at a molar ratio of 1:10 to H2O2 at a dosage of 2 g / L. The mixture was stirred until dissolved, and then 28% hydrogen peroxide solution was slowly added dropwise at a rate of 2 mL / min. The mixture was stirred at 40°C for 90 min. After the reaction was completed, 10% sodium hydroxide solution was added to adjust the pH to 7.5.

[0046] S2: The filtrate I obtained in step S1 is subjected to anaerobic and aerobic biochemical treatments, filtered, and the filter residue is recovered to obtain filtrate II;

[0047] The anaerobic biological treatment reaction temperature was 40℃, the hydraulic retention time was 48h, and the influent COD volumetric loading rate was 5kgCOD / (m³). 3 (d) The reaction pH was 7.5; the dissolved oxygen concentration in the aerobic biochemical treatment was 4 mg / L, and the aeration intensity of the blower aeration system was 5 m³ / s. 3 / (m 2 The reaction temperature was 30℃, the reaction pH was 8.0, and the hydraulic retention time was 24h.

[0048] S3: Add adsorbent to filtrate II obtained in step S2. The amount of adsorbent is 5g / L. Stir for 2 hours, let stand for 4 hours, filter, recover the filter residue, and discharge the filtrate.

[0049] The adsorbent is a magnesium-aluminum composite oxide. The preparation method of the magnesium-aluminum composite oxide is as follows: magnesium nitrate hexahydrate and aluminum nitrate nonahydrate are dissolved in deionized water at a molar ratio of 4:1 to form a solution with a metal ion concentration of 0.10 mol / L. The solution is placed in a constant temperature water bath and a mixed solution of sodium hydroxide and sodium carbonate is slowly added dropwise at 35°C and a stirring speed of 300 rpm. The mass percentage of sodium hydroxide is 10% and the mass percentage of sodium carbonate is 7%. The pH of the system is maintained at 10.5. The mixture is stirred and aged for 16 h, filtered, washed, dried, heated to 550°C at a heating rate of 10°C / min, calcined for 3 h, and cooled to obtain the magnesium-aluminum composite oxide.

[0050] Example 3

[0051] A process for recycling and treating organic fluorine-containing waste liquid includes the following steps:

[0052] S1: The organic fluorine-containing waste liquid is subjected to Fenton oxidation, and then flocculant (calcium chloride and polyaluminum chloride are composed of calcium chloride and polyaluminum chloride in a mass ratio of 1:26, and the amount added is 200mg / L) is added for flocculation and sedimentation, pressure filtration, and the filter residue is recovered to obtain filtrate I;

[0053] The specific process of Fenton oxidation is as follows: dilute hydrochloric acid is added to the organic fluorine-containing waste liquid to adjust the pH value to 3, and Fe... 2+Ferrous sulfate heptahydrate was added first at a molar ratio of 1:7 to H2O2, with an addition amount of 1.8 g / L. The mixture was stirred until dissolved, and then a 27.5% hydrogen peroxide solution was slowly added dropwise at a rate of 1.5 mL / min. The mixture was stirred at 35 °C for 80 min. After the reaction was completed, a 9% sodium hydroxide solution was added to adjust the pH value to 7.

[0054] S2: The filtrate I obtained in step S1 is subjected to anaerobic and aerobic biochemical treatments, filtered, and the filter residue is recovered to obtain filtrate II;

[0055] The anaerobic biological treatment reaction temperature was 38℃, the hydraulic retention time was 32h, and the influent COD volumetric loading rate was 4kgCOD / (m³). 3 (d) The reaction pH was 7; the dissolved oxygen concentration in the aerobic biochemical treatment was 3 mg / L, and the aeration intensity of the blower aeration system was 4 m³ / s. 3 / (m 2 The reaction temperature was 25℃, the reaction pH was 7.5, and the hydraulic retention time was 20h.

[0056] S3: Add adsorbent to filtrate II obtained in step S2. The amount of adsorbent is 4 g / L. Stir for 1.5 h, let stand for 3.5 h, filter, recover the filter residue, and discharge the filtrate.

[0057] The adsorbent is a magnesium-aluminum composite oxide. The preparation method of the magnesium-aluminum composite oxide is as follows: magnesium nitrate hexahydrate and aluminum nitrate nonahydrate are dissolved in deionized water at a molar ratio of 3:1 to form a solution with a metal ion concentration of 0.08 mol / L. The solution is placed in a constant temperature water bath and a mixed solution of sodium hydroxide and sodium carbonate is slowly added dropwise at 32°C and a stirring speed of 250 rpm. The mass percentage of sodium hydroxide is 9% and the mass percentage of sodium carbonate is 6%. The pH of the system is maintained at 10. The mixture is stirred and aged for 15 h, filtered, washed, dried, heated to 500°C at a heating rate of 7°C / min, calcined for 2.5 h, and cooled to obtain the magnesium-aluminum composite oxide.

[0058] Example 4

[0059] A recycling process for organic fluorine-containing wastewater is similar to that in Example 1. The difference between this example and Example 1 is that the adsorbent is a lanthanum-zirconium-doped magnesium-aluminum composite oxide. The preparation method of the lanthanum-zirconium-doped magnesium-aluminum composite oxide is as follows: magnesium nitrate hexahydrate, aluminum nitrate nonahydrate, lanthanum nitrate, and zirconium nitrate are dissolved in deionized water at a molar ratio of 2:1:0.12:0.03 to form a solution with a metal ion concentration of 0.05 mol / L, and citric acid is added (the molar ratio of citric acid to total metal ions is 0.4:1). Stir for 30 min, then add urea (molar ratio of urea to total metal ions is 3:1) and PEG-4000 (2% of the total mass of the solution). Heat to 140℃ and react for 10 h. Centrifuge to separate the contents, wash with deionized water until neutral, then wash twice with anhydrous ethanol. Dry at 80℃, heat to 300℃ at a rate of 1℃ / min, hold for 2 h, then heat to 500℃ at a rate of 3℃ / min, hold for 4 h, and cool to obtain lanthanum-zirconium-doped magnesium-aluminum composite oxide.

[0060] Example 5

[0061] A recycling process for organic fluorine-containing wastewater is similar to that in Example 2. The difference between this example and Example 2 is that the adsorbent is a lanthanum-zirconium-doped magnesium-aluminum composite oxide. The preparation method of the lanthanum-zirconium-doped magnesium-aluminum composite oxide is as follows: magnesium nitrate hexahydrate, aluminum nitrate nonahydrate, lanthanum nitrate, and zirconium nitrate are dissolved in deionized water in a molar ratio of 4:1:0.15:0.05 to form a solution with a metal ion concentration of 0.10 mol / L, and citric acid is added (the molar ratio of citric acid to total metal ions is 0.7:1). Stir for 40 min, then add urea (molar ratio of urea to total metal ions is 5:1) and PEG-4000 (4% of the total mass of the solution). Heat to 145℃ and react for 12 h. Centrifuge to separate the reaction mixture, wash with deionized water until neutral, then wash twice with anhydrous ethanol. Dry at 80℃, heat to 400℃ at a rate of 4℃ / min, hold for 3 h, then heat to 550℃ at a rate of 7℃ / min, hold for 5 h, and cool to obtain lanthanum-zirconium-doped magnesium-aluminum composite oxide.

[0062] Example 6

[0063] A recycling process for organic fluorine-containing wastewater is similar to that in Example 3. The difference between this example and Example 3 is that the adsorbent is a lanthanum-zirconium-doped magnesium-aluminum composite oxide. The preparation method of the lanthanum-zirconium-doped magnesium-aluminum composite oxide is as follows: magnesium nitrate hexahydrate, aluminum nitrate nonahydrate, lanthanum nitrate, and zirconium nitrate are dissolved in deionized water in a molar ratio of 3:1:0.14:0.04 to form a solution with a metal ion concentration of 0.08 mol / L. Citric acid is then added (the molar ratio of citric acid to total metal ions is 0.6:1), and the mixture is stirred. After 35 min, urea (molar ratio of urea to total metal ions was 4:1) and PEG-4000 (3% of the total mass of the solution) were added. The mixture was heated to 143 °C and reacted for 11 h. After centrifugation, the mixture was washed with deionized water until neutral and then washed twice with anhydrous ethanol. The mixture was dried at 80 °C and heated to 370 °C at a rate of 3 °C / min. The temperature was maintained for 2.5 h, and then increased to 520 °C at a rate of 5 °C / min. The temperature was maintained for 4.5 h, and then cooled to obtain lanthanum-zirconium-doped magnesium-aluminum composite oxide.

[0064] Comparative Example 1

[0065] This comparative example is similar to Example 3, except that the adsorbent used in this comparative example is activated carbon.

[0066] Comparative Example 2

[0067] This comparative example is similar to Example 6, except that the adsorbent used in this comparative example is activated alumina.

[0068] Test case

[0069] Fluoride ion concentration detection and fluoride adsorption capacity calculation: The fluoride concentration in fluoride-containing organic wastewater was determined according to the "Determination of Fluoride in Water - Fluoride Reagent Spectrophotometric Method" (HJ488-2009). The fluoride removal rate was calculated using the following formula, where R... F For fluoride removal rate, c F0 The initial fluoride concentration in the waste liquid (mg / L), c Ft The value represents the residual fluoride concentration (mg / L) in the treated wastewater. The test results are shown in Table 1.

[0070]

[0071] Table 1. Results of Fluoride Ion Concentration Test

[0072]

[0073] As shown in Table 1, the fluoride removal rate of the organic fluoride-containing waste liquid recovery and treatment process provided by the present invention reaches over 97%, which indicates that the organic fluoride-containing waste liquid recovery and treatment process provided by the present invention has a good fluoride removal effect. Compared with traditional adsorbents activated carbon and activated alumina, the fluoride removal rate of the organic fluoride-containing waste liquid recovery and treatment process provided by the present invention is effectively improved.

[0074] This specific embodiment is merely an explanation of this application and is not intended to limit it. After reading this specification, those skilled in the art can make modifications to this embodiment without contributing any inventive step, but such modifications are protected by patent law as long as they fall within the scope of the claims of this application.

Claims

1. A process for recycling and treating organic fluorine-containing wastewater, characterized in that, Includes the following steps: S1: The organic fluorine-containing waste liquid is subjected to Fenton oxidation, then flocculant is added for flocculation and sedimentation, filter pressure is applied, and the filter residue is recovered to obtain filtrate I; S2: The filtrate I obtained in step S1 is subjected to anaerobic and aerobic biochemical treatments, filtered, and the filter residue is recovered to obtain filtrate II; S3: Add adsorbent to filtrate II obtained in step S2, stir for 1-2 hours, let stand for 3-4 hours, filter, recover the filter residue, and discharge the filtrate; The adsorbent is a mixed metal oxide, and the amount of adsorbent used is 3-5 g / L; The mixed metal oxide is a lanthanum-zirconium-doped magnesium-aluminum composite oxide. The preparation method of the lanthanum-zirconium-doped magnesium-aluminum composite oxide is as follows: magnesium nitrate hexahydrate, aluminum nitrate nonahydrate, lanthanum nitrate, and zirconium nitrate are dissolved in deionized water to form a solution with a metal ion concentration of 0.05-0.10 mol / L. Citric acid is added, and the mixture is stirred for 30-40 min. Urea and polyethylene glycol are then added, and the mixture is heated to 140-145℃ for 10-12 h. The mixture is then centrifuged, the precipitate is washed, dried, calcined, and cooled to obtain the lanthanum-zirconium-doped magnesium-aluminum composite oxide. The magnesium nitrate hexahydrate, aluminum nitrate nonahydrate, lanthanum nitrate, and zirconium nitrate... The molar ratio of zirconium is (2-4):1:(0.12-0.15):(0.03-0.05); the molar ratio of citric acid to total metal ions is (0.4-0.7):1; the molar ratio of urea to total metal ions is (3-5):1; the polyethylene glycol is PEG-4000, and the amount of polyethylene glycol used is 2%-4% of the total mass of the solution; the calcination process is as follows: heat to 300-400℃ at a rate of 1-4℃ / min, hold for 2-3h, and continue to heat to 500-550℃ at a rate of 3-7℃ / min, and hold for 4-5h.

2. The recycling and treatment process for organic fluorine-containing wastewater according to claim 1, characterized in that, The specific process of Fenton oxidation in step S1 is as follows: Dilute hydrochloric acid is added to the organic fluorine-containing waste liquid to adjust the pH value to 2-4, and Fe... 2+ First, add ferrous sulfate heptahydrate at a molar ratio of 1:(3-10) to H2O2, at a dosage of 1-2 g / L, and stir until dissolved. Then, slowly add hydrogen peroxide solution with a mass fraction of 27%-28% at a dropping rate of 1-2 mL / min. Stir the reaction at 30-40℃ for 60-90 min. After the reaction is completed, add sodium hydroxide solution with a mass percentage of 8%-10% to adjust the pH value to 6.5-7.

5. The flocculant is composed of calcium chloride and polyaluminum chloride in a mass ratio of 1:(20-30), and the amount added is 200 mg / L.

3. The recycling and treatment process for organic fluorine-containing wastewater according to claim 1, characterized in that, The anaerobic biological treatment in step S2 has a reaction temperature of 35-40℃, a hydraulic retention time of 24-48h, and an influent COD volumetric loading rate of 2-5kgCOD / (m³). 3 (d), the reaction pH is 6.5-7.

5.

4. The recycling and treatment process for organic fluorine-containing wastewater according to claim 1, characterized in that, In step S2, the dissolved oxygen concentration of the aerobic biochemical treatment is 2-4 mg / L, and the aeration intensity of the blower aeration system is 3-5 m³ / L. 3 / (m 2 The reaction temperature is 20-30℃, the reaction pH is 7.0-8.0, and the hydraulic retention time is 12-24h.

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