Method for treating low-concentration fluorine-containing organic wastewater based on advanced oxidation-magnetic coagulation sedimentation

Abstract

The invention relates to the technical field of wastewater treatment, and discloses a method for treating low-concentration fluorine-containing organic wastewater based on advanced oxidation-magnetic coagulation precipitation, which comprises the following steps: firstly, adding potassium ferrate into wastewater and stirring to promote the potassium ferrate to decompose to generate hydroxyl free radicals (. OH), oxidizing and degrading organic matters in the wastewater, and removing the organic matters in the wastewater; then adding a saturated sodium sulfite solution to quench the residual oxidant; and then adjusting the pH value of the wastewater, adding polyaluminum chloride, modified imidazoline and Fe3O4, stirring, standing, settling, and separating the precipitate. Polyaluminum chloride (PAC) is dissolved in water to generate high polymers such as [Al (OH) (H2O) 5] < 2 + >, [Al8 (OH) 20 (H2O) x] < 4 + > and the like, the high polymers and F <-> form a complex through a hydroxyl bridging effect, and Al-F precipitate (such as AlF3. 3H2O) is further generated. The low-concentration fluorine-containing organic wastewater is efficiently purified through the oxidation-magnetic coagulation synergistic effect.

Description

Technical Field

[0001] The present invention relates to the technical field of wastewater treatment, in particular to a method for treating low-concentration fluorine-containing organic wastewater based on advanced oxidation-magnetic coagulation precipitation. Background Art

[0002] In the field of industrial wastewater treatment, the comprehensive treatment of fluorinated organic wastewater has always been a technical challenge. Fluoride, as a key raw material, is widely used in fields such as metallurgy, glassmaking, and electronics. However, the fluorinated organic wastewater generated during its production process has complex pollutant composition, stable fluorine-organic complexes, and is difficult to remove simultaneously using conventional processes, easily causing cumulative ecological pollution. Existing treatment technologies are generally plagued by bottlenecks such as large reagent dosages, harsh reaction conditions, and low solid-liquid separation efficiency.

[0003] The current mainstream treatment processes are mainly divided into two technical directions: oxidation and decomposition, and coagulation and sedimentation. Oxidation and decomposition technology: Potassium ferrate (K2FeO4) is used for simultaneous degradation of organic matter and defluorination due to its strong oxidizing properties (oxidation potential of 2.2V) and the coagulation properties of its reduction products. However, it is easy to self-decompose in the aqueous phase (half-life <2h), and the actual dosage far exceeds the theoretical value (requiring an excess of 50%-100%), resulting in a significant increase in operating costs. Coagulation and sedimentation technology: Polyaluminium chloride (PAC) removes pollutants through electrical neutralization and adsorption bridging. However, for low-concentration fluorine-containing organic wastewater (F concentration <50mg / L), it has problems such as small floc particle size and slow sedimentation rate (usually 30-60 minutes), and it is difficult to effectively break the stable complex structure of fluorine-organic matter.

[0004] Existing patented technologies also have significant limitations. For example, Publication No. CN117699936B discloses a defluoridating agent for acidic fluoride-containing wastewater and its preparation method. This defluoridating agent exhibits excellent fluidity in acidic fluoride-containing wastewater and can efficiently adsorb fluoride ions from the solution. In neutral or slightly alkaline conditions, it rapidly swells and solidifies into a physical gel, thereby achieving a coagulation and precipitation effect. However, it relies on a multi-component composite agent (containing aluminosilicates, modified cellulose, etc.), resulting in high raw material costs and significant difficulty in the subsequent disposal of the gel-like precipitate. Publication No. CN111018072A discloses a composite defluoridating agent for fluoride-containing wastewater, its preparation method, and its application. This agent utilizes a humic acid-CaO-PAC composite material for enhanced fluoride removal, but its insufficient oxidizing capacity limits its removal of organic fluoride, making it difficult to meet increasingly stringent emission standards.

[0005] To address these technical limitations, the present invention innovatively proposes a coupled "advanced oxidation-magnetic coagulation and sedimentation" process. By constructing a technical system combining oxidation-decomposition, magnetic flocculation, and gradient separation, this process achieves efficient, coordinated treatment of low-concentration fluorinated organic wastewater. This process significantly shortens hydraulic retention time (HRT) while reducing reagent consumption, offering significant technical and economic advantages. Summary of the Invention

[0006] In response to the deficiencies of the prior art, the present invention provides a method for treating low-concentration fluorine-containing organic wastewater based on advanced oxidation-magnetic coagulation precipitation, which achieves efficient purification of low-concentration fluorine-containing organic wastewater through the synergistic effect of oxidation-coagulation.

[0007] To achieve the above objectives, the present invention provides the following technical solutions: A method for treating low-concentration fluorine-containing organic wastewater based on advanced oxidation-magnetic coagulation precipitation comprises the following steps: S1. Potassium ferrate was added to the wastewater and stirred rapidly for 2-3 minutes at a speed of 300-310 rpm; medium-speed stirring for 10-15 minutes at a speed of 100 -110 r / min to promote the decomposition of potassium ferrate to produce hydroxyl radicals, which oxidatively degrade organic matter. The reaction pH was 7-8.5, and a saturated sodium sulfite solution was added to quench the residual oxidant. S2. Adjust the pH to 7.0-8.0, add polyaluminum chloride and modified imidazoline (0.4-0.6 times the mass of polyaluminum chloride) and Fe3O4 (0.2-0.3 times the mass of polyaluminum chloride), stir slowly for 15-18 minutes at a speed of 50-55 rpm, let it stand for 30-40 minutes, and separate the precipitate.

[0008] Furthermore, the concentration of potassium ferrate in S1 is 4-6 mg / L.

[0009] Furthermore, the concentration of polyaluminium chloride in S2 is 200-300 mg / L.

[0010] Furthermore, the preparation method of the modified imidazoline is: Step 1: Add lauric acid to the reactor, heat it to 160-165°C, add xylene and triethylenetetramine, reflux for 2-3 hours, heat it to 220-230°C and continue to react for 3-4 hours. After the reaction is completed, distill under reduced pressure to obtain a lauric acid imidazoline intermediate; Step 2: Add the lauric acid imidazoline intermediate to anhydrous ethanol solvent, stir and dissolve, add benzyl chloride thereto, heat to 55-65°C and react for 7-9 hours. After the reaction is completed, remove the solvent by rotary evaporation, recrystallize and vacuum dry to obtain lauric acid imidazoline quaternary ammonium salt;

[0011] Step 3: Add trimesoyl chloride and lauric acid imidazoline quaternary ammonium salt into N,N-dimethylformamide solvent, stir and mix, continue to add triethylamine catalyst, stir and react at 80-90°C, and then distill under reduced pressure and wash to obtain modified imidazoline.

[0012] During the above reaction process, the carboxyl group in lauric acid reacts with the amino group in triethylenetetramine to generate an imidazoline group, and then the amino group is introduced to obtain a lauric acid imidazoline intermediate; the tertiary amine in the lauric acid imidazoline intermediate reacts with the chlorine group in benzyl chloride to introduce a quaternary ammonium group to obtain a lauric acid imidazoline quaternary ammonium salt; and the acyl chloride group in trimesoyl chloride reacts with the amino group in the lauric acid imidazoline quaternary ammonium salt to obtain a modified imidazoline.

[0013] Furthermore, in the step 1, the usage ratio of lauric acid, xylene, and triethylenetetramine is 3.9-4.2 g:1.8-2.1 mL:4.6-5.1 g.

[0014] Furthermore, in the step 2, the usage ratio of anhydrous ethanol, lauric acid imidazoline intermediate, and benzyl chloride is 50-75 mL: 4.1-5.2 g: 1.9-2.3 g.

[0015] Furthermore, in the step 3, the usage ratio of trimesoyl chloride, lauric acid imidazoline quaternary ammonium salt, N,N-dimethylformamide, and triethylamine catalyst is 1.12-1.16 g:3.2-3.5 g:40-55 mL:0.01-0.02 g.

[0016] Furthermore, the reaction time in step three is 4-5 hours.

[0017] (3) Beneficial technical effects The present invention involves adding potassium ferrate to wastewater and stirring; decomposing the potassium ferrate to produce hydroxyl radicals (·OH), which oxidize and degrade organic matter; adding a saturated sodium sulfite solution to quench the residual oxidant; adjusting the pH, adding polyaluminum chloride and modified imidazoline, stirring, allowing the mixture to settle, and separating the precipitate. This invention achieves efficient purification of low-concentration fluorine-containing organic wastewater through the synergistic effect of oxidation and coagulation.

[0018] Potassium ferrate (K2FeO4) decomposes under weakly alkaline conditions (pH 7-8.5) to produce highly oxidizing hydroxyl radicals (·OH), effectively degrading recalcitrant organic matter in wastewater while simultaneously oxidizing some fluoride ions to less toxic forms. The quaternary ammonium groups in the modified imidazoline form magnetic flocs through electrostatic adsorption and ion exchange, synergistically removing fluoride ions. The modified imidazoline, produced by the reaction of trimesoyl chloride with quaternary ammonium laurate imidazoline, possesses high charge density and hydrophobic chain stability, enhancing its selective adsorption capacity for fluoride ions. Potassium ferrate residues can be quenched with sodium sulfite to avoid secondary contamination. The modified imidazoline can be recycled and reused, reducing operating costs.

[0019] Polyaluminium chloride (PAC) dissolves in water to form [Al(OH)(H2O)5] 2+、[Al8(OH) 20 (H2O) X ] 4+ Polymers such as F - Forming a complex, further generating Al-F precipitation (such as AlF3·3H2O). The Al(OH)3 flocs formed by PAC capture F through the "sweep effect" during the sedimentation process. - , forming large particle precipitation. The ferroferric oxide in it has significant magnetic properties, which can quickly separate the flocs formed during the coagulation process through an external magnetic field. It is very efficient in water treatment, significantly shortening the precipitation time and improving treatment efficiency. DETAILED DESCRIPTION

[0020] To make the objectives, technical solutions, and advantages of the embodiments of the present invention more clear, the technical solutions in the embodiments of the present invention are clearly and completely described. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. All other embodiments derived by persons of ordinary skill in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0021] All chemical reagents used in the specific implementation manner are chemically pure.

[0022] The Al2O3 content in polyaluminium chloride is 30%.

[0023] Example 1 A method for treating low-concentration fluorine-containing organic wastewater based on advanced oxidation-magnetic coagulation precipitation comprises the following steps: S1. 3.9 g of lauric acid was added to the reactor, the temperature was raised to 160 ° C, 1.8 mL of xylene and 4.6 g of triethylenetetramine were added thereto, the reaction was refluxed for 2 h, the temperature was raised to 220 ° C and the reaction was continued for 3 h. After the reaction was completed, the mixture was distilled under reduced pressure to obtain a lauric acid imidazoline intermediate; S2. 4.1 g of lauric acid imidazoline intermediate was added to 50 mL of anhydrous ethanol solvent and stirred to dissolve. 1.9 g of benzyl chloride was added thereto and the temperature was raised to 55 ° C for 7 h. After the reaction, the solvent was removed by rotary evaporation, and the mixture was recrystallized and dried in vacuo to obtain lauric acid imidazoline quaternary ammonium salt; S3. 1.12 g of trimesoyl chloride and 3.2 g of lauric acid imidazoline quaternary ammonium salt were added to 40 mL of N, N-dimethylformamide solvent, stirred and mixed, and 0.01 g of triethylamine catalyst was added, and the reaction was stirred at 80 ° C for 4 h. After the reaction, the mixture was distilled under reduced pressure and washed to obtain a modified imidazoline; S4. Potassium ferrate was added to the wastewater to a concentration of 4 mg / L and stirred rapidly for 2 minutes at a speed of 300 rpm. The mixture was then stirred at a moderate speed for 10 minutes at a speed of 100 rpm to promote the decomposition of potassium ferrate to produce hydroxyl radicals, which oxidatively degraded organic matter. The reaction pH was 7, and saturated sodium sulfite solution was added to quench the residual oxidant. S5. Adjust the pH to 7.0, add polyaluminium chloride to a concentration of 200 mg / L, modified imidazoline 0.4 times the mass of polyaluminium chloride, and Fe3O4 0.2 times the mass of polyaluminium chloride, stir slowly for 15 minutes at a speed of 50 r / min, let it stand for 30 minutes, and separate the precipitate.

[0024] Example 2 A method for treating low-concentration fluorine-containing organic wastewater based on advanced oxidation-magnetic coagulation precipitation comprises the following steps: S1. 4.2 g of lauric acid was added to the reactor, the temperature was raised to 165 ° C, 2.1 mL of xylene and 5.1 g of triethylenetetramine were added thereto, and the reaction was refluxed for 3 h, then the temperature was raised to 230 ° C and the reaction was continued for 4 h. After the reaction was completed, the mixture was distilled under reduced pressure to obtain a lauric acid imidazoline intermediate; S2. 5.2 g of lauric acid imidazoline intermediate was added to 75 mL of anhydrous ethanol solvent and stirred to dissolve. 2.3 g of benzyl chloride was added thereto and the temperature was raised to 65 ° C for 9 h. After the reaction, the solvent was removed by rotary evaporation, and the mixture was recrystallized and dried in vacuo to obtain lauric acid imidazoline quaternary ammonium salt; S3. 1.16 g of trimesoyl chloride and 3.5 g of lauric acid imidazoline quaternary ammonium salt were added to 55 mL of N, N-dimethylformamide solvent, stirred and mixed, and 0.02 g of triethylamine catalyst was added, and the reaction was stirred at 90 ° C for 5 h. After the reaction, the mixture was distilled under reduced pressure and washed to obtain a modified imidazoline; S4. Potassium ferrate was added to the wastewater to a concentration of 6 mg / L and stirred rapidly for 3 minutes at 310 rpm. Then, the mixture was stirred at a moderate speed for 15 minutes at 110 rpm to promote the decomposition of potassium ferrate to produce hydroxyl radicals, which oxidatively degraded organic matter. The reaction pH was 8.5, and saturated sodium sulfite solution was added to quench the residual oxidant. S5. Adjust the pH to 8.0, add polyaluminium chloride to a concentration of 300 mg / L, 0.6 times the mass of polyaluminium chloride of modified imidazoline, and 0.3 times the mass of polyaluminium chloride of Fe3O4, stir slowly for 18 minutes at a speed of 55 rpm, let it stand for 40 minutes, and separate the precipitate.

[0025] Example 3 A method for treating low-concentration fluorine-containing organic wastewater based on advanced oxidation-magnetic coagulation precipitation comprises the following steps: S1. 4.1 g of lauric acid was added to the reactor, the temperature was raised to 162 ° C, 1.9 mL of xylene and 4.8 g of triethylenetetramine were added thereto, the reaction was refluxed for 2.5 h, the temperature was raised to 225 ° C and the reaction was continued for 3 h. After the reaction was completed, the reaction was distilled under reduced pressure to obtain a lauric acid imidazoline intermediate; S2. 4.7 g of lauric acid imidazoline intermediate was added to 65 mL of anhydrous ethanol solvent and stirred to dissolve. 2.1 g of benzyl chloride was added thereto and the temperature was raised to 60 ° C for 8 h. After the reaction, the solvent was removed by rotary evaporation, and the mixture was recrystallized and dried in vacuo to obtain lauric acid imidazoline quaternary ammonium salt; S3. 1.14 g of trimesoyl chloride and 3.3 g of lauric acid imidazoline quaternary ammonium salt were added to 45 mL of N, N-dimethylformamide solvent, stirred and mixed, and 0.015 g of triethylamine catalyst was added, and the reaction was stirred at 85 ° C for 4.5 h. After the reaction, the mixture was distilled under reduced pressure and washed to obtain a modified imidazoline; S4. Potassium ferrate was added to the wastewater to a concentration of 5 mg / L and stirred rapidly for 2.5 minutes at 305 rpm. Then, the mixture was stirred at a moderate speed for 12 minutes at 105 rpm to decompose the potassium ferrate to produce hydroxyl radicals, which oxidized and degraded organic matter. The reaction pH was 7.5, and saturated sodium sulfite solution was added to quench the residual oxidant. S5. Adjust the pH to 7.6, add polyaluminum chloride to a concentration of 250 mg / L, modified imidazoline 0.5 times the mass of polyaluminum chloride, and Fe3O4 0.25 times the mass of polyaluminum chloride, slowly stir for 17 minutes at a speed of 52 rpm, let it stand for 35 minutes, and separate the precipitate.

[0026] Example 4 A method for treating low-concentration fluorine-containing organic wastewater based on advanced oxidation-magnetic coagulation precipitation comprises the following steps: S1. 3.9 g of lauric acid was added to the reactor, the temperature was raised to 160 ° C, 1.8 mL of xylene and 4.6 g of triethylenetetramine were added thereto, the reaction was refluxed for 2 h, the temperature was raised to 220 ° C and the reaction was continued for 3 h. After the reaction was completed, the mixture was distilled under reduced pressure to obtain a lauric acid imidazoline intermediate; S2. 4.1 g of lauric acid imidazoline intermediate was added to 50 mL of anhydrous ethanol solvent and stirred to dissolve. 1.9 g of benzyl chloride was added thereto and the temperature was raised to 55 ° C for 7 h. After the reaction, the solvent was removed by rotary evaporation, and the mixture was recrystallized and dried in vacuo to obtain lauric acid imidazoline quaternary ammonium salt; S3. 1.16 g of trimesoyl chloride and 3.5 g of lauric acid imidazoline quaternary ammonium salt were added to 55 mL of N, N-dimethylformamide solvent, stirred and mixed, and 0.02 g of triethylamine catalyst was added, and the reaction was stirred at 90 ° C for 5 h. After the reaction, the mixture was distilled under reduced pressure and washed to obtain a modified imidazoline; S4. Potassium ferrate was added to the wastewater to a concentration of 4 mg / L and stirred rapidly for 2.5 minutes at 305 rpm. Then, the mixture was stirred at a moderate speed for 12 minutes at 105 rpm to decompose the potassium ferrate to produce hydroxyl radicals, which oxidized and degraded organic matter. The reaction pH was 7.5, and saturated sodium sulfite solution was added to quench the residual oxidant. S5. Adjust the pH to 7.6, add polyaluminum chloride to a concentration of 250 mg / L, modified imidazoline 0.43 times the mass of polyaluminum chloride, and Fe3O4 0.26 times the mass of polyaluminum chloride, stir slowly for 17 minutes at a speed of 52 rpm, let it stand for 35 minutes, and separate the precipitate.

[0027] Example 5 A method for treating low-concentration fluorine-containing organic wastewater based on advanced oxidation-magnetic coagulation precipitation comprises the following steps: S1. 4.2 g of lauric acid was added to the reactor, the temperature was raised to 165 ° C, 2.1 mL of xylene and 5.1 g of triethylenetetramine were added thereto, and the reaction was refluxed for 3 h, then the temperature was raised to 230 ° C and the reaction was continued for 4 h. After the reaction was completed, the mixture was distilled under reduced pressure to obtain a lauric acid imidazoline intermediate; S2. 5.2 g of lauric acid imidazoline intermediate was added to 75 mL of anhydrous ethanol solvent and stirred to dissolve. 2.3 g of benzyl chloride was added thereto and the temperature was raised to 65 ° C for 9 h. After the reaction, the solvent was removed by rotary evaporation, and the mixture was recrystallized and dried in vacuo to obtain lauric acid imidazoline quaternary ammonium salt; S3. 1.14 g of trimesoyl chloride and 3.3 g of lauric acid imidazoline quaternary ammonium salt were added to 45 mL of N, N-dimethylformamide solvent, stirred and mixed, and 0.015 g of triethylamine catalyst was added, and the reaction was stirred at 85 ° C for 4.5 h. After the reaction, the mixture was distilled under reduced pressure and washed to obtain a modified imidazoline; S4. Potassium ferrate was added to the wastewater to a concentration of 6 mg / L and stirred rapidly for 2 minutes at a speed of 300 rpm. The mixture was then stirred at a moderate speed for 10 minutes at a speed of 100 rpm to promote the decomposition of potassium ferrate to produce hydroxyl radicals, which oxidatively degraded organic matter. The reaction pH was 7, and saturated sodium sulfite solution was added to quench the residual oxidant. S5. Adjust the pH to 7.0, add polyaluminium chloride to a concentration of 220 mg / L, modified imidazoline 0.54 times the mass of polyaluminium chloride, and Fe3O4 0.25 times the mass of polyaluminium chloride, stir slowly for 15 minutes at a speed of 50 r / min, let it stand for 30 minutes, and separate the precipitate.

[0028] Comparative Example 1 A method for treating low-concentration fluorine-containing organic wastewater based on advanced oxidation-magnetic coagulation precipitation comprises the following steps: S1. 4.2 g of lauric acid was added to the reactor, the temperature was raised to 165 ° C, 2.1 mL of xylene and 5.1 g of triethylenetetramine were added thereto, and the reaction was refluxed for 3 h, then the temperature was raised to 230 ° C and the reaction was continued for 4 h. After the reaction was completed, the mixture was distilled under reduced pressure to obtain a lauric acid imidazoline intermediate; S2. Potassium ferrate was added to the wastewater to a concentration of 4 mg / L and stirred rapidly for 2 minutes at 300 rpm. The mixture was then stirred at a moderate speed for 10 minutes at 100 rpm to decompose the potassium ferrate to produce hydroxyl radicals, which oxidized and degraded organic matter. The reaction pH was 7, and saturated sodium sulfite solution was added to quench the residual oxidant. S3. Adjust the pH to 7.0, add polyaluminium chloride to a concentration of 200 mg / L, 0.42 times the mass of polyaluminium chloride as the lauric acid imidazoline intermediate, and 0.25 times the mass of polyaluminium chloride as Fe3O4, stir slowly for 15 minutes at a speed of 50 r / min, let it stand for 30 minutes to separate the precipitate.

[0029] Comparative Example 2 A method for treating low-concentration fluorine-containing organic wastewater based on advanced oxidation-magnetic coagulation precipitation comprises the following steps: S1. 4.2 g of lauric acid was added to the reactor, the temperature was raised to 165 ° C, 2.1 mL of xylene and 5.1 g of triethylenetetramine were added thereto, and the reaction was refluxed for 3 h, then the temperature was raised to 230 ° C and the reaction was continued for 4 h. After the reaction was completed, the mixture was distilled under reduced pressure to obtain a lauric acid imidazoline intermediate; S2. 5.2 g of lauric acid imidazoline intermediate was added to 75 mL of anhydrous ethanol solvent and stirred to dissolve. 2.3 g of benzyl chloride was added thereto and the temperature was raised to 65 ° C for 9 h. After the reaction, the solvent was removed by rotary evaporation, and the mixture was recrystallized and dried in vacuo to obtain lauric acid imidazoline quaternary ammonium salt; S3. Potassium ferrate was added to the wastewater to a concentration of 5 mg / L and stirred rapidly for 2 minutes at a speed of 300 r / min; then stirred at a moderate speed for 10 minutes at a speed of 100 r / min to promote the decomposition of potassium ferrate to produce hydroxyl radicals, which oxidatively degraded organic matter. The reaction pH was 7, and saturated sodium sulfite solution was added to quench the residual oxidant; S4. Adjust the pH to 7.0, add polyaluminium chloride to a concentration of 300 mg / L, lauric acid imidazoline quaternary ammonium salt 0.6 times the mass of polyaluminium chloride, and Fe3O4 0.25 times the mass of polyaluminium chloride, stir slowly for 15 minutes at a speed of 50 r / min, let it stand for 30 minutes to separate the precipitate.

[0030] Comparative Example 3 A method for treating low-concentration fluorine-containing organic wastewater based on advanced oxidation-magnetic coagulation precipitation comprises the following steps: S1. Potassium ferrate was added to the wastewater to a concentration of 4 mg / L and stirred rapidly for 2 minutes at 300 rpm. The mixture was then stirred at a moderate speed for 10 minutes at 100 rpm to decompose the potassium ferrate to produce hydroxyl radicals, which oxidized and degraded organic matter. The reaction pH was 7, and saturated sodium sulfite solution was added to quench the residual oxidant. S2. Adjust the pH to 7.0, add polyaluminium chloride to a concentration of 260 mg / L, triethylenetetramine (0.42 times the mass of polyaluminium chloride), and Fe3O4 (0.25 times the mass of polyaluminium chloride), stir slowly for 15 minutes at a speed of 50 r / min, let it stand for 30 minutes, and separate the precipitate.

[0031] The determination of fluoride removal was carried out in accordance with GB / T 7484-1987 "Water quality - Determination of fluoride - Ion selective electrode method"; the determination of chemical oxygen demand in water was carried out in accordance with HJ 828-2017 "Water quality - Determination of chemical oxygen demand - Dichromate method" Determination of COD: Fluoride ion in the original wastewater is 8.5 mg / L; COD is 180 mg / L.

[0032] Table 1: Fluoride ion concentration determination.

[0033]

[0034] Table 1 shows that Examples 1-5 of the present invention exhibit superior fluoride removal effectiveness compared to Comparative Examples 1-3. Comparative Example 1 uses a lauric acid imidazoline intermediate instead of a modified imidazoline, resulting in higher fluoride ion and COD concentrations compared to Example 5. Comparative Example 2 uses a lauric acid imidazoline quaternary ammonium salt instead of a modified imidazoline, resulting in higher fluoride ion and COD concentrations compared to Example 5. Compared to the modified imidazoline, the lauric acid imidazoline in Comparative Example 1 lacks quaternary ammonium groups and multiple side chains. Therefore, the quaternary ammonium groups are unable to form magnetic flocs with polyaluminum chloride (PAC) through electrostatic adsorption and ion exchange, resulting in a weakened fluoride ion removal effect. Compared to lauric acid imidazoline, the lauric acid imidazoline quaternary ammonium salt in Comparative Example 2 lacks multiple side chains, resulting in a lower charge density and a weaker selective adsorption capacity for fluoride ions. Comparative Example 3 differs from Example 5 in that triethylenetetramine is used instead of a modified imidazoline, resulting in a lower fluoride ion removal rate.

[0035] It should be noted that, in this document, the terms "comprise," "include," or any other variations thereof are intended to encompass non-exclusive inclusion, such that a process, method, article, or apparatus comprising a series of elements includes not only those elements but also other elements not explicitly listed, or elements inherent to such process, method, article, or apparatus. In the absence of further limitations, an element defined by the phrase "comprises a ..." does not preclude the presence of other identical elements in the process, method, article, or apparatus comprising the element.

[0036] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the various embodiments of the present invention.

[0037] Those skilled in the art will appreciate that the foregoing descriptions are merely specific embodiments of the present invention, and not exhaustive. It should be noted that numerous variations and modifications are possible for those skilled in the art, and all such variations and modifications that do not exceed the scope of the claims should be considered within the scope of protection of the present invention.

Claims

1. A method for treating low-concentration fluorine-containing organic wastewater based on advanced oxidation-magnetic coagulation precipitation, characterized in that: The following steps are involved: S1. Potassium ferrate was added to the wastewater and stirred rapidly for 2-3 minutes at a speed of 300-310 rpm; medium-speed stirring for 10-15 minutes at a speed of 100 -110 r / min to promote the decomposition of potassium ferrate to produce hydroxyl radicals, which oxidatively degrade organic matter. The reaction pH was 7-8.5, and a saturated sodium sulfite solution was added to quench the residual oxidant. S2. Adjust the pH to 7.0-8.0, add polyaluminum chloride and modified imidazoline (0.4-0.6 times the mass of polyaluminum chloride) and Fe3O4 (0.2-0.3 times the mass of polyaluminum chloride), stir slowly for 15-18 minutes at a speed of 50-55 rpm, let it stand for 30-40 minutes, and separate the precipitate.

2. The method for treating low-concentration fluorine-containing organic wastewater based on advanced oxidation-magnetic coagulation precipitation according to claim 1, characterized in that: The concentration of potassium ferrate in the S1 is 4-6 mg / L.

3. The method for treating low-concentration fluorine-containing organic wastewater based on advanced oxidation-magnetic coagulation precipitation according to claim 1, characterized in that: The concentration of polyaluminium chloride in the S2 is 200-300 mg / L.

4. The method for treating low-concentration fluorine-containing organic wastewater based on advanced oxidation-magnetic coagulation precipitation according to claim 1, characterized in that: The preparation method of the modified imidazoline is: Step 1: Add lauric acid to the reactor, heat it to 160-165°C, add xylene and triethylenetetramine, reflux for 2-3 hours, heat it to 220-230°C and continue to react for 3-4 hours. After the reaction is completed, distill under reduced pressure to obtain a lauric acid imidazoline intermediate; Step 2: Add the lauric acid imidazoline intermediate to anhydrous ethanol solvent, stir and dissolve, add benzyl chloride thereto, heat to 55-65°C and react for 7-9 hours. After the reaction is completed, remove the solvent by rotary evaporation, recrystallize and vacuum dry to obtain lauric acid imidazoline quaternary ammonium salt; Step 3: Add trimesoyl chloride and lauric acid imidazoline quaternary ammonium salt into N,N-dimethylformamide solvent, stir and mix, continue to add triethylamine catalyst, stir and react at 80-90°C, and then distill under reduced pressure and wash to obtain modified imidazoline.

5. The method for treating low-concentration fluorine-containing organic wastewater based on advanced oxidation-magnetic coagulation precipitation according to claim 4, characterized in that: In the step 1, the usage ratio of lauric acid, xylene, and triethylenetetramine is 3.9-4.2 g:1.8-2.1 mL:4.6-5.1 g.

6. The method for treating low-concentration fluorine-containing organic wastewater based on advanced oxidation-magnetic coagulation precipitation according to claim 4, characterized in that: In the step 2, the usage ratio of anhydrous ethanol, lauric acid imidazoline intermediate, and benzyl chloride is 50-75 mL: 4.1-5.2g:1.9-2.3g.

7. The method for treating low-concentration fluorine-containing organic wastewater based on advanced oxidation-magnetic coagulation precipitation according to claim 4, characterized in that: In the step 3, the usage ratio of trimesoyl chloride, lauric acid imidazoline quaternary ammonium salt, N,N-dimethylformamide, and triethylamine catalyst is 1.12-1.16 g: 3.2-3.5 g: 40-55 mL: 0.01-0.02 g.

8. The method for treating low-concentration fluorine-containing organic wastewater based on advanced oxidation-magnetic coagulation precipitation according to claim 4, characterized in that: The reaction time in step 3 is 4-5h.

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