Acid-base gradient regulation and fractional precipitation method for glyphosate wastewater treatment

Abstract

The invention discloses an acid-base gradient regulation and control and fractional precipitation method for glyphosate wastewater treatment, and belongs to the technical field of industrial wastewater treatment. Aiming at the pollution characteristics of high calcium and magnesium, high organic phosphorus and high heavy metal in the glyphosate wastewater, the method realizes efficient removal of pollutants and resource recovery of glyphosate through an integrated process of coagulation pretreatment, three-stage acid-base gradient regulation and control, fractional precipitation and resource circulation. And a flocculant is combined with precise pH gradient regulation and control to sequentially remove a surfactant, calcium and magnesium ions and heavy metal ions, and finally precise crystallization of glyphosate crystals is realized. The glyphosate recovery rate is greater than or equal to 85%, the purity is greater than or equal to 95%, the calcium and magnesium removal rate is greater than or equal to 85%, the heavy metal removal rate is greater than or equal to 90%, the hydrochloric acid cyclic utilization rate is greater than or equal to 60%, the precipitation product can be recycled, the problems of low recovery rate, serious secondary pollution and high cost of a traditional process are solved, and the method is suitable for glyphosate wastewater treatment under various working conditions.

Description

Technical Field

[0001] This invention relates to the field of industrial wastewater treatment technology, specifically to a method for acid-base gradient control and stepwise sedimentation in the treatment of glyphosate wastewater. It is particularly suitable for the resource-based treatment of glyphosate wastewater under different water quality conditions, such as conventional, high calcium and magnesium, low temperature, high organic phosphorus, and high heavy metal conditions, and can achieve the dual goals of efficient pollutant purification and glyphosate recovery. Background Technology

[0002] As the world's most widely used broad-spectrum herbicide, glyphosate is widely used in agricultural production. However, its production process generates wastewater containing high concentrations of organophosphorus compounds, calcium and magnesium ions, and heavy metals, making wastewater treatment a core pain point for the industry's sustainable development. Currently, about 70% of glyphosate companies still rely on traditional, extensive wastewater treatment processes. This process is based on the core logic of "basic acid-base neutralization + flocculation-extraction": First, industrial-grade acids and bases (mostly 30% concentration liquid alkali or hydrochloric acid) are added to roughly adjust the pH of the wastewater to neutral (6.5-7.5), without precise gradient control design; then, polyaluminum chloride (PAC, usually 400-600 mg / L) and polyacrylamide (8-12 mg / L) are added to form flocs, precipitating and removing some suspended impurities and calcium and magnesium ions; finally, organic solvents such as dichloromethane and ethyl acetate (8%-12% of the wastewater volume) are used to extract and separate glyphosate from the water, and the crude product is obtained after back-extraction and crystallization. This process suffers from three major drawbacks that have been difficult to resolve for a long time: First, the efficiency of pollutant separation is low. Due to crude pH adjustment and poor synergy between flocculation and extraction, the glyphosate recovery rate is generally less than 60%, and the purity of the recovered product is only 75%-85%, which is insufficient to meet industrial-grade reuse standards. A large amount of high-value glyphosate is lost with the wastewater, resulting in a resource loss of over 2 million yuan per plant per year. Second, secondary pollution is a prominent issue. During the reaction, calcium and magnesium ions react with organophosphorus compounds and flocculant residues to form complex salts that are difficult to degrade (such as calcium magnesium phosphate), which cannot be utilized as resources and can only be stockpiled. Furthermore, the residues of flocculants and extractants... The sludge combines with impurities to form hazardous waste sludge, with a single plant producing over 500 tons annually. This type of sludge contains heavy metals and toxic organic solvents, requiring high-temperature incineration or safe landfill for disposal. This not only occupies land resources but may also cause soil and groundwater pollution. Thirdly, the overall cost is high. On the one hand, the annual consumption of reagents such as acids, alkalis, flocculants, and extractants exceeds 1,000 tons, with procurement costs accounting for more than 60% of the total wastewater treatment cost. On the other hand, the disposal cost of hazardous waste sludge is 3,000-5,000 yuan / ton, requiring a single plant to bear over 1.5 million yuan in hazardous waste disposal costs annually. This dual pressure significantly compresses the company's profit margin. While there have been attempts at improvement within the industry to address the aforementioned issues, these efforts have largely focused on optimizing single aspects, such as increasing flocculant dosage to enhance sedimentation or replacing extractants to reduce toxicity. These approaches have failed to resolve the systemic contradictions of "low resource recovery rate, severe secondary pollution, and high cost" from a holistic perspective. Therefore, developing a glyphosate wastewater treatment technology that combines precise control, efficient purification, resource recovery, and cost control has become an urgent need for the industry. Summary of the Invention

[0003] To address the aforementioned technical problems, this invention provides a method for acid-base gradient control and stepwise precipitation in the treatment of glyphosate wastewater. The technical solution of this invention is as follows: A method for acid-base gradient control and stepwise precipitation in glyphosate wastewater treatment, the method comprising the following steps: S1: Coagulation: Add cationic coagulant and stir to form stable flocs; S2 air flotation separation: Wastewater treated by S1 is introduced into a dissolved air system and pressurized. The pressure is reduced by a release device to form microbubbles of 20-50μm. The bubbles adsorb the coagulated flocs and combine with the hydrophobicity of nonionic surfactants, carrying pollutants to the surface to form scum, which is removed by a scum scraper. The removal rate of nonionic surfactants reaches 80%-90%. S3 Primary Acid-Base Regulation: Add 20%-25% liquid alkali (mainly sodium hydroxide) to the wastewater after S2 treatment to precisely adjust the pH to 5.5-6.0. React for 30-40 minutes to preferentially precipitate calcium and magnesium ions and some organic phosphorus impurities in the wastewater, generating phosphate precipitates that can be used as building materials. The calcium and magnesium removal rate is ≥85%. S4 Secondary pH Adjustment: Add 20%-25% liquid alkali to the effluent after S3 treatment and filter press to raise the pH to 9.0-9.5. React for 40-50 minutes to promote the conversion of glyphosate molecules into water-soluble sodium salt, while precipitating and removing heavy metal ions such as iron and zinc, generating recyclable metal hydroxides. The heavy metal removal rate is ≥90%. S5 three-stage acid-base adjustment: The effluent from S4 treatment via pressure filtration is adjusted to pH 2.0-2.5 using 15%-20% hydrochloric acid (60% of which is recycled hydrochloric acid). Based on the characteristic that glyphosate has low solubility (<10g / L) under acidic conditions, the crystallization reaction is carried out for 60-70 minutes to achieve precise crystallization and precipitation of glyphosate crystals with a crystal purity ≥95%. S6 Solid-Liquid Separation and Resource Recycling: The mixed system after crystallization in S5 is filtered to separate glyphosate crystals and saline filtrate; part of the saline filtrate is returned to step S3 for reuse, and the remaining part is discharged after meeting the standards; the phosphate precipitate is used as a building material, and the metal hydroxide is purified and recycled.

[0004] Preferably, in the glyphosate wastewater treatment, the calcium and magnesium ions content is 700-1500 mg / L, the organophosphorus content is 300-500 mg / L, the total heavy metal content is 40-80 mg / L, and the COD is 400-500 mg / L.

[0005] Preferably, in step S1, the cationic coagulant is cationic polyacrylamide (CPAM), and the addition amount is 1-5 mg / L; the preparation method of the cationic polyacrylamide (CPAM) is as follows: acrylamide and methacryloyloxyethyltrimethylammonium chloride are taken at a mass ratio of 7:3, and deionized water is added to prepare a 30% monomer aqueous solution; the pH is adjusted to 6-7, nitrogen gas is purged for 30 min to remove oxygen, and 0.1%-0.3% of ammonium persulfate-sodium bisulfite composite initiator is added, and the mixture is polymerized at a constant temperature of 30-40℃ for 4-6 h; the product is granulated, dried, and pulverized to obtain solid cationic polyacrylamide (CPAM) with a cationicity of 20%-40%.

[0006] Preferably, in step S1, the cationic coagulant is OPTF-1 flocculant, and its preparation method includes the following sub-steps: S1.1. Pre-dispersion and magnetic core preparation: In a 500 mL four-necked flask equipped with a mechanical stirrer, thermometer, and nitrogen delivery tube, 150 parts by weight of deionized water and 5-8 parts by weight of Fe3O4 nanoparticles were added. The mixture was ultrasonically dispersed under nitrogen protection to form a uniform magnetic fluid. Then, 35-45 parts by weight of methacryloyloxyethyltrimethylammonium chloride, 25-30 parts by weight of acrylamide, and 0.1-0.3 parts by weight of crosslinking agent N,N'-methylenebisacrylamide were added sequentially, and the mixture was stirred to allow the monomers to adsorb onto the surface of the magnetic particles. After deoxygenation with pure nitrogen for 30 minutes, the temperature is raised to 60-70℃ in a water bath. 0.5-1.0 parts of ammonium persulfate (APS) are dissolved in 20 parts of water and added dropwise to the system over 30-35 minutes. The mixture is stirred at 300-400 rpm and reacted at a constant temperature of 60-70℃ for 6-8 hours. The supernatant is discarded by magnetic separation. The gel is washed three times with deionized water and ethanol alternately. It is then vacuum dried at 60-70℃ for 10-12 hours and ground to obtain a white powder of Fe3O4@P (methacryloyloxyethyltrimethylammonium chloride-acrylamide). S1.2. Disperse 10 parts of the product from S1.1 in 50-55 parts of N,N-dimethylformamide (DMF), add 0.2-0.4 parts of RAFT chain transfer agent (dithioester) and 8-12 parts of LMA monomer (laurate methacrylate), and sonicate to mix; heat to 70-75℃ under nitrogen protection, add dropwise an ethanol solution initiated by 0.1-0.2 parts of APS, and react at 70-75℃ for 6-8 hours; precipitate the product in a large amount of ice-cold ethanol, collect the solid by magnetic separation, wash with ethanol multiple times, and dry under vacuum to obtain the intermediate product grafted with the hydrophobic arm of PLMA; S1.3. Disperse the above intermediate product in a mixed solvent of 50-70 parts deionized water and 10-15 parts ethanol, add 10-15 parts acrylic acid monomer and 0.1-0.2 parts RAFT chain transfer agent (dithioester); heat to 65-70℃ under nitrogen atmosphere, add APS solution dropwise to initiate polymerization, and react for 6 hours; magnetically separate and purify by washing with ethanol / water to obtain bifunctional microspheres; S1.4. Disperse bifunctional arm microspheres in 100 parts of deionized water, add 5-8 parts of aminotrimethylenephosphonic acid and 4-6 parts of FeCl3·6H2O, adjust the pH to 4.0-4.2 with 1M NaOH; stir the reaction at 40-45℃ and 250-300rpm for 4h, collect the product by magnetic separation, wash with deionized water, dry under vacuum at 60℃, grind and sieve to obtain black powdered OPTF-1 flocculant.

[0007] Preferably, in step S1, the cationic coagulant is OPTF-1 flocculant, and the addition amount ranges from 1 to 5 mg / L.

[0008] Preferably, in step S1, the pH needs to be controlled between 6 and 8 during the addition of cationic coagulant. During stirring, the cationic coagulant neutralizes the negatively charged anionic surfactant, adsorbs and bridges the suspended matter and some nonionic surfactants, forming stable flocs.

[0009] Preferably, in step S2, the bubbles are 20-50 μm in size, and the nonionic surfactant removal rate after step S2 is 80%-90%. The bubbles adsorb the coagulated flocs, and due to the hydrophobicity of the nonionic surfactants, they carry the pollutants to the surface to form scum, which is then removed by a scum scraper.

[0010] Preferably, in step S3, the pH of the glyphosate wastewater is adjusted to 5.5-6.0 using 20%-25% liquid alkali. This preferentially precipitates calcium and magnesium ions and some organic phosphorus impurities in the wastewater, generating phosphate precipitates that can be used as building materials, thus avoiding the formation of difficult-to-treat complex salts in subsequent reactions. The calcium and magnesium removal rate can reach over 85%.

[0011] Preferably, in step S4, the wastewater obtained from the primary regulation is filtered and then effluent is supplemented with liquid alkali to raise the pH to 9.0-9.5, which promotes the conversion of glyphosate molecules into water-soluble sodium salt, while precipitating and removing heavy metal ions such as iron and zinc, generating recyclable metal hydroxides, with a heavy metal removal rate of ≥90%.

[0012] Preferably, in step S5, the effluent from the wastewater obtained by secondary regulation after pressure filtration is adjusted to pH 2.0-2.5 using 15%-20% hydrochloric acid. Based on the characteristic that glyphosate has low solubility (<10g / L) under acidic conditions, glyphosate crystals are accurately crystallized and precipitated with a purity ≥95%, meeting the industrial-grade reuse standard.

[0013] Preferably, the parameter optimization rules for different water quality conditions are as follows: For high-calcium and magnesium wastewater with calcium and magnesium ions ≥1200 mg / L, the specific parameters are as follows: S3, add 25% liquid alkali, adjust pH to 6.0, reaction time 40 min, and increase stirring speed to 80 r / min; S4, add 25% liquid alkali, adjust pH to 9.5, and reaction time 50 min; S5, add 20% hydrochloric acid, adjust pH to 2.5, and crystallization time 70 min. The specific parameters for low-temperature operation (ambient temperature ≤10℃) are as follows: S3 and S4 reaction tanks are auxiliary heated to 20℃; S3 is added with 23% liquid alkali, pH is adjusted to 5.7, and the reaction time is 35 min; S4 is added with 23% liquid alkali, pH is adjusted to 9.3, and the reaction time is 45 min; S5 is added with 17% hydrochloric acid, pH is adjusted to 2.2, the temperature is maintained at 25℃, and the crystallization time is 65 min. For high organic phosphorus wastewater (organic phosphorus ≥ 400 mg / L), the specific parameters are as follows: S3: Add 24% liquid alkali, adjust pH to 5.9, stir at 75 r / min, and react for 45 min; S4: Add 24% liquid alkali, adjust pH to 9.4, stir at 65 r / min, and react for 40 min; S5: Add 17% hydrochloric acid, adjust pH to 2.3, stir at 55 r / min, and crystallize for 65 min. For wastewater with heavy metal concentrations ≥70 mg / L, the specific parameters are as follows: S3: Add 23% liquid alkali, adjust pH to 5.8, stir at 70 r / min, and react for 35 min; S4: Add 23% liquid alkali, adjust pH to 9.5, stir at 65 r / min, and react for 45 min; S5: Add 18% hydrochloric acid, adjust pH to 2.4, stir at 50 r / min, and crystallize for 70 min.

[0014] Beneficial effects of the present invention Compared with existing technologies, the innovations of this invention are: first, it constructs a highly targeted three-level acid-base regulation system to achieve efficient stepwise separation of pollutants; second, it develops a special flocculant with a "core-shell-dual-functional arm" structure to improve flocculation efficiency and selectivity; third, it designs a full-process resource recycling system to reduce costs and environmental risks; and fourth, it optimizes parameters for complex working conditions to improve industrial applicability. The resource recycling design of this invention achieves a 60% hydrochloric acid recycling rate, reducing the amount of new hydrochloric acid purchased; precipitated products are recycled, with phosphate precipitates used in building materials and metal hydroxides recovered, purified, and reused, forming a closed-loop resource recycling system.

[0015] This invention boasts superior treatment efficiency, achieving calcium and magnesium removal rates of ≥85%, heavy metal removal of ≥91%, and organophosphorus removal of ≥90%. Glyphosate recovery rate is ≥85%, with a purity of ≥95.2%. It offers a win-win situation for both economic and environmental protection. The 60% hydrochloric acid recycling reduces reagent costs by 40%-60%, the precipitated products are recycled, no hazardous waste is generated, and the effluent COD is ≤180mg / L, meeting national standards. Compared to traditional and simplified processes, reagent consumption is reduced by 30%-40%. For a single plant treating 100,000 tons of wastewater annually, reagent costs are reduced by over 500,000 yuan. Solid waste emissions are reduced by over 80%, and hazardous waste disposal costs are reduced by over 300,000 yuan annually. Simultaneously, the recovery of glyphosate crystals generates 1-1.5 million yuan in annual revenue, and phosphate precipitation adds an additional 20,000-30,000 yuan. The total annual cost per plant decreases by 25%-30%, with an investment payback period of 1-2 years. The effluent quality consistently meets the "Emission Standard for Pollutants from Pesticide Industry," alleviating environmental governance pressure. Glyphosate recovery rate is increased to over 85%, reducing the demand for technical grade pesticides and energy consumption, indirectly reducing carbon emissions by 100-200 tons per plant annually. This invention is comprehensively superior in terms of adaptability to operating conditions, treatment efficiency, economy, and environmental friendliness. It can be directly applied industrially, promoting the transformation of the glyphosate industry from "end-of-pipe treatment" to "resource recycling," and can also be extended to other high-salt and high-organophosphorus chemical wastewater treatment fields. Detailed Implementation

[0016] The technical solution of the present invention will be further explained and described below with reference to specific embodiments. It is worth noting that the following embodiments are only preferred embodiments of the present invention and should not be construed as limiting the present invention. The scope of protection of the present invention should be determined by the contents of the claims. Modifications and substitutions made by those skilled in the art to the technical solution of the present invention without creative effort all fall within the scope of protection of the present invention.

[0017] The following examples and comparative examples are all based on a 1 m³ / h pilot plant. The flocculant preparation methods used in the examples and comparative examples: Preparation process of cationic polyacrylamide (CPAM): Acrylamide and cationic monomer methacryloyloxyethyltrimethylammonium chloride are mixed at a mass ratio of 7:3, and deionized water is added to prepare a 30% monomer aqueous solution; the pH is adjusted to 6, nitrogen gas is purged for 30 min to remove oxygen, and 0.2% of the total mass of the monomer is added as an ammonium persulfate-sodium bisulfite composite initiator (the mass ratio of ammonium persulfate to sodium bisulfite is 1:1). Polymerization is carried out at a constant temperature of 30-40℃ for 5 h; the product is granulated, dried and pulverized to obtain solid CP acrylamide-PAM with a cationicity of 30%.

[0018] The preparation method of OPTF-1 flocculant includes the following steps: S1.1 Pre-dispersion and magnetic core preparation: In a 500 mL four-necked flask equipped with a mechanical stirrer, thermometer, and nitrogen delivery tube, 150 parts of deionized water and 5-8 parts of Fe3O4 nanoparticles were added. The mixture was ultrasonically dispersed (300 W, 40 kHz) for 30 min under nitrogen protection to form a homogeneous magnetic fluid. Then, 40 parts of methacryloyloxyethyltrimethylammonium chloride, 25 parts of acrylamide, and 0.2 parts of crosslinking agent N,N'-methylenebisacrylamide were added sequentially, and the mixture was stirred slowly at 200 rpm. The monomer was adsorbed onto the surface of the magnetic particles; after deoxygenation by purging with high-purity nitrogen for 30 min, the temperature was raised to 60±1℃ in a water bath; 0.8 parts of ammonium persulfate (APS) were dissolved in 20 parts of warm water and added dropwise to the system within 30 min; the mixture was stirred at 300 rpm and reacted at a constant temperature of 60℃ for 6 h; the supernatant was discarded by magnetic separation; the gel was washed three times with deionized water and ethanol alternately; it was dried under vacuum at 60℃ for 12 h; and then ground to obtain Fe3O4@P (methacryloyloxyethyltrimethylammonium chloride-acrylamide) white powder. S1.2. Grafting of hydrophobic arms: 10 parts of the product from S1.1 were dispersed in 50 parts of N,N-dimethylformamide (DMF), 0.3 parts of RAFT chain transfer agent and 10 parts of LMA monomer were added, and the mixture was sonicated for 15 min to mix. Under nitrogen protection, the temperature was raised to 70±1℃, and an ethanol solution initiated by 0.1 parts of APS was slowly added dropwise. The reaction was carried out at 70℃ for 8 h. The product was precipitated by pouring a large amount of ice-cold ethanol, and the solid was collected by magnetic separation. After washing with ethanol several times, the product was dried under vacuum to obtain the intermediate product grafted with hydrophobic arms of PLMA. S1.3. Hydrophilic arm grafting: The above intermediate product was dispersed in a mixed solvent of 50 parts deionized water and 10 parts ethanol, and 10-15 parts acrylic acid monomer and 0.15 parts RAFT chain transfer agent were added; the temperature was raised to 65±1℃ under a nitrogen atmosphere, and APS solution was added dropwise to initiate polymerization. The reaction was carried out for 6 hours; the product was magnetically separated and purified by washing with ethanol / water to obtain microspheres with "bifunctional arms". S1.4. Phosphonic acid functionalization: Bifunctional arm microspheres were dispersed in 100 parts of deionized water, 6 parts of aminotrimethylene phosphonic acid and 5 parts of FeCl3·6H2O were added, and the pH was adjusted to 4.0±0.2 with 1M NaOH. The reaction was stirred at 40℃ and 250rpm for 4h, the product was collected by magnetic separation, washed with deionized water until the conductivity was stable, dried under vacuum at 60℃, and then ground through a 200-mesh sieve to obtain black powdered OPTF-1 flocculant.

[0019] Example 1: Conventional glyphosate wastewater treatment Wastewater quality: calcium and magnesium ions 800 mg / L, organic phosphorus 300 mg / L, total heavy metals 50 mg / L, COD 450 mg / L.

[0020] Operating steps: S1: Add 3 mg / L CPAM, control the system pH=7.0, and continuously stir to form stable flocs. The removal rate of surfactant pollutants is 88%. S2: After pressurized dissolved air system, 30μm microbubbles are generated through release device, and scum is separated by air flotation, with a nonionic surfactant removal rate of 89%; S3: Add 22% liquid alkali, precisely adjust the pH to 5.8, react for 30 minutes, the calcium and magnesium ion removal rate is 88%, and phosphate precipitate is generated; S4: Add 22% liquid alkali to raise the pH to 9.2, react for 40 minutes, heavy metal removal rate is 92%, metal hydroxide precipitate is generated; S5: Add 18% recycled hydrochloric acid (60% recycling rate) to adjust the pH back to 2.3 and allow the crystallization reaction to proceed for 60 minutes; S6: Glyphosate crystals were obtained by pressure filtration (purity 96.5%, recovery rate 87%), 60% of the saline filtrate was returned to S3 for reuse, and the remaining filtrate COD=150mg / L, which met the discharge standards; the phosphate precipitate was sold as a building material.

[0021] Example 2: Treatment of high-calcium-magnesium glyphosate wastewater Wastewater quality: calcium and magnesium ions 1500 mg / L, organic phosphorus 400 mg / L, total heavy metals 65 mg / L, COD 480 mg / L.

[0022] Operating steps: S1: Add 4 mg / L CPAM, control the system pH=7.5, and the removal rate of surfactant pollutants is 85%; S2: The dissolved air system generates 40μm microbubbles, and the nonionic surfactant removal rate is 87% after air flotation separation; S3: Add 25% liquid alkali to adjust the pH to 6.0, increase the stirring speed to 80 r / min, react for 40 min, the calcium and magnesium ion removal rate is 86%, and the phosphate precipitation yield is increased by 40% compared with Example 1; S4: Add 25% liquid alkali to raise the pH to 9.5, react for 50 minutes, and the heavy metal removal rate is 91%; S5: Add 20% circulating hydrochloric acid to adjust the pH back to 2.5, and allow the crystallization reaction to proceed for 70 minutes; S6: Glyphosate crystals (purity 95.2%, recovery rate 85%) are obtained by pressure filtration. After purification, metal hydroxides are used to recover metals such as zinc and iron. The effluent COD is 180 mg / L, which meets the discharge standards.

[0023] Example 3: Glyphosate wastewater treatment under low-temperature conditions Wastewater quality: calcium and magnesium ions 1000 mg / L, organic phosphorus 350 mg / L, total heavy metals 55 mg / L, COD 460 mg / L; ambient temperature 10℃.

[0024] Operating steps: S1: Add 3 mg / L CPAM, control the system pH=7.2, and the removal rate of surfactant pollutants is 86%; S2: The dissolved air system generates 35μm microbubbles, and the nonionic surfactant removal rate is 88% after air flotation separation; S3: Add 23% liquid alkali to adjust the pH to 5.7, heat the reaction tank to 20℃, react for 35 minutes, and the calcium and magnesium ion removal rate is 87%; S4: Add 23% liquid alkali to raise the pH to 9.3, keep the temperature at 20℃ for 45 minutes, and the heavy metal removal rate is 93%; S5: Add 17% circulating hydrochloric acid to adjust the pH back to 2.2, and maintain the temperature at 25℃ for 65 minutes for crystallization reaction; S6: Glyphosate crystals were obtained by pressure filtration (purity 96.1%, recovery rate 86%), with no decrease in crystallization efficiency. The reagent consumption was the same as under normal temperature conditions, and the effluent COD was 160 mg / L, meeting the discharge standards.

[0025] Example 4: Application of OPTF-1 flocculant as an alternative The wastewater quality is the same as in Example 1. Step S1 is replaced by adding 2 mg / L OPTF-1 flocculant and controlling the system pH to 5.9. The parameters of the remaining steps are the same as in Example 1.

[0026] Treatment results: After S1 treatment, COD removal rate was 92%, total phosphorus (TP) removal rate was 55%, and surfactant removal rate was 90%; after S4 treatment, Zn² + The removal rate was 98.5%; after S5 treatment, the purity of glyphosate crystals was 98%, and the recovery rate was 95%. Compared with Example 1, the purity of glyphosate increased by 1.5%, the recovery rate increased by 8%, and the amount of flocculant used was reduced by 30%.

[0027] Comparative Example 1: Traditional acid-base neutralization + flocculation extraction process The wastewater quality is the same as in Example 1. The operation steps are as follows: add 30% liquid alkali to adjust the pH to 7.0, add 500mg / L PAC and 10mg / L PAM for flocculation, and let stand for 30 minutes; use 10% of the wastewater volume of dichloromethane to extract glyphosate, and then crystallize after back-extraction.

[0028] Treatment results: calcium and magnesium ion removal rate 62%, heavy metal removal rate 75%, glyphosate recovery rate 58%, purity 88%; generated hazardous waste sludge 0.8 kg / m³, requiring professional disposal; reagent cost (including extractant and flocculant) is 2.8 times that of Example 1; effluent COD=280 mg / L, which does not meet the discharge standard and requires secondary treatment.

[0029] Comparative Example 2: Simplified Process Without Hydrochloric Acid Circulation The wastewater quality was the same as in Example 1, and the operating procedures were consistent with Example 1, except that step S5 used 18% fresh hydrochloric acid instead of recycled hydrochloric acid. The removal rates of calcium and magnesium ions were 87%, heavy metals 91%, organophosphorus compounds 89%, and glyphosate recovery 86%, which are close to the indicators in Example 1 (88% calcium and magnesium, 92% heavy metals, 90% organophosphorus compounds, and 87% recovery). However, the purity of glyphosate crystals decreased to 90%, the reagent cost increased by 30%, and the amount of solid waste generated increased by 15%, highlighting the importance of hydrochloric acid recycling.

[0030] Comparative Example 3: Sulfuric Acid Substitution for Hydrochloric Acid Process The wastewater quality is the same as in Example 1, and the operation steps are the same as in Example 1, except that in step S5, 20% sulfuric acid is used instead of hydrochloric acid.

[0031] Treatment results: The purity of glyphosate crystals decreased to 94%, and ion chromatography showed that the crystals contained sulfate impurities; the crystals became more viscous and prone to clumping, making them unusable for direct reuse; the subsequent saline filtrate, due to the presence of sulfate, could not be returned to S3 for reuse, thus disrupting the resource recycling system.

[0032] Comparative Example 4: OPTF-2 flocculant Based on Example 1, step S1 was replaced by adding 2 mg / L OPTF-2 flocculant, and the pH of the system was controlled at 5.9. The parameters of the remaining steps were the same as in Example 1.

[0033] OPTF-2 flocculant uses the exact same functional monomers as OPTF-1 flocculant, but through a one-step random copolymerization process. The specific steps are as follows: Monomer solution preparation: Add 150 parts of deionized water to a 250 mL beaker. Under low-speed magnetic stirring, dissolve 40 parts of methacryloyloxyethyltrimethylammonium chloride, 25 parts of AM (acrylamide), and 2 parts of AA (acrylic acid) in sequence. Then, under strong ultrasonic emulsification (400 W), slowly add 10 parts of LMA monomer to the above aqueous solution to form a milky white microemulsion system.

[0034] Reaction initialization: The above monomer microemulsion was transferred to a 500 mL four-necked flask. 0.2 parts of crosslinking agent MBA (N,N'-methylenebisacrylamide) were added, and high-purity nitrogen was introduced for 30 minutes to completely remove oxygen. Subsequently, the mixture was heated in a water bath to 60±1℃.

[0035] Polymerization initiation: Dissolve 0.8 parts APS in 20 parts warm water and slowly and evenly add the solution dropwise into the reaction system over 40 minutes using a constant pressure funnel. Maintain a constant temperature of 60°C and stir at 300 rpm for 8 hours.

[0036] Product post-processing: After the reaction was completed, a viscous colloidal product was obtained. It was repeatedly precipitated and washed three times with anhydrous ethanol to remove unreacted monomers. The resulting white gel was dried in a vacuum drying oven at 60°C for 24 hours, and finally pulverized and passed through a 200-mesh sieve to obtain a white powdered OPTF-2 flocculant.

[0037] Treatment effect: Compared with Example 4 (OPTF-1), the treatment effect was significantly reduced: after S1, COD removal rate was 78%, TP removal rate was 22%, and surfactant removal rate was 75%; after S4, Zn 2+ The removal rate was 82%; after S5, the glyphosate purity was 92.3% and the recovery rate was 82%, but the effluent COD was 210 mg / L, which did not meet the standard. Furthermore, it lacks a magnetic nucleus, requiring 30 minutes of natural sedimentation for solid-liquid separation, resulting in a 93% decrease in efficiency compared to the 2-minute magnetic separation of OPTF-1.

[0038] One-step random copolymerization leads to the failure of functional group synergy, lack of directional bifunctional arms, poor surfactant removal; lack of Fe3O4 magnetic core, resulting in low separation efficiency; inability to construct complexation sites targeting organophosphorus compounds, leading to a sharp reduction in total phosphorus removal.

[0039] Comparative Example 5: OPTF-3 flocculant Based on Example 1, step S1 was replaced with the addition of 2 mg / L LOPTF-3 flocculant, and the pH of the system was controlled at 5.9. The parameters of the remaining steps were the same as those in Example 1.

[0040] The difference between OPTF-3 flocculant and OPTF-1 flocculant is that the final "phosphonic acid functionalization" step is omitted in a complete replication of Example 1. This comparative example aims to demonstrate that even with a perfect structural framework, the lack of the crucial "phosphonic acid metal ternary complex arm" results in insufficient targeted capture ability of organophosphorus compounds.

[0041] Preparation steps: S1.1-S1.3: This step is completely consistent with the S1.1-S1.3 steps of OPTF-1 flocculant, and Fe3O4@P(DMC-AM) white powder is prepared.

[0042] S1.4' Termination Treatment: The above Fe3O4@P(DMC-AM)-g-(PLMA-b-PAA) bifunctional arm microspheres were dispersed in 100 parts of deionized water. ATMP and FeCl3·6H2O were not added. The mixture was stirred at 250 rpm for 1 hour at room temperature to ensure sufficient hydration and dispersion of the microspheres in the aqueous phase. Subsequently, magnetic separation was performed directly, followed by washing three times with deionized water, vacuum drying at 60°C, and grinding through a 200-mesh sieve to obtain the OPTF-1 derivative (black powder) lacking the phosphonic acid functional arm. This material has the exact same physical structure as the final product (magnetic core, cation shell, hydrophobic arm, and polyacrylic acid hydrophilic arm), but the polyacrylic acid arm does not have a "Fe-ATMP" ternary complexation site, therefore it does not possess the specific capture ability for organophosphorus molecules.

[0043] Compared to Example 4: After S1, COD (89%) and surfactant removal rate (88%) were similar, demonstrating the advantages of the structural framework; however, TP removal rate was only 30%. After S5, glyphosate purity was 94.5% and recovery rate was 88%, with effluent COD = 175 mg / L (meeting standards but slightly high). The absence of the "phosphonic acid functionalization" step resulted in the loss of organophosphorus targeted capture ability, a sharp drop in total phosphorus removal, and consequently, affected glyphosate quality.

[0044] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A method for acid-base gradient regulation and stepwise precipitation of glyphosate wastewater treatment, characterized in that, The method comprises the steps of: S1 coagulation: adding a cationic coagulant to the glyphosate wastewater, stirring, forming stable flocs, and removing surfactant pollutants; S2 air floatation separation: passing the wastewater treated in S1 into a dissolved air system to pressurize and dissolve air, reducing the pressure to form micro-bubbles through a release device, and removing non-ionic surfactants by a slag scraper; S3 primary acid-base regulation: adding liquid alkali to the wastewater treated in S2 to accurately adjust the pH to 5.5-6.0, and precipitating calcium, magnesium ions and part of organic phosphorus impurities in the wastewater; S4 secondary acid-base regulation: supplementing liquid alkali to the filtrate after S3 treatment to increase the pH to 9.0-9.5, promoting the conversion of glyphosate molecules into sodium salt which is easily soluble in water, and precipitating and removing iron, zinc or other heavy metal ions; S5 tertiary acid-base regulation: using hydrochloric acid to adjust the pH of the filtrate after S4 treatment to 2.0-2.5, based on the low solubility of glyphosate under acidic conditions, realizing crystallization reaction, and achieving accurate crystallization of glyphosate crystals; S6 solid-liquid separation and resource recycling: pressure filtration of the mixed system after crystallization in S5 to separate out glyphosate crystals and salt-containing filtrate; part of the salt-containing filtrate is returned to S3 for reuse, and the remaining part is discharged after reaching the standard; the phosphate precipitate is used as a building auxiliary material, and the metal hydroxide is recycled after purification.

2. The acid-base gradient regulation and step precipitation method for glyphosate wastewater treatment according to claim 1, characterized in that: The glyphosate wastewater has the following quality indexes: calcium and magnesium ions 700-1500 mg / L, organic phosphorus 300-500 mg / L, total heavy metal content 40-80 mg / L, and COD 400-500 mg / L.

3. The acid-base gradient regulation and step precipitation method for glyphosate wastewater treatment according to claim 1, characterized in that: In the step S1, the cationic coagulant is cationic polyacrylamide, and the addition amount is 1-5 mg / L; the preparation method of the cationic polyacrylamide is as follows: taking acrylamide and methyl methacryloyloxyethyl trimethyl ammonium chloride at a mass ratio of (5-7):3, adding deionized water to prepare a monomer aqueous solution; adjusting the pH to 6-7, removing oxygen by nitrogen blowing, adding 0.1%-0.3% of the total mass of the monomer of ammonium persulfate-sodium bisulfite composite initiator, and polymerizing at 30-40℃ for 4-6 h; the product is granulated, dried, and crushed to obtain the cationic polyacrylamide.

4. The acid-base gradient regulation and step precipitation method for glyphosate wastewater treatment according to claim 1, characterized in that: In the step S1, the cationic coagulant is OPTF-1 flocculant, and the preparation method comprises the following steps: S1.

1. pre-dispersion and magnetic core preparation: 150 parts of deionized water and 5-8 parts of Fe3O4 nanoparticles are ultrasonically dispersed under nitrogen protection to form a uniform magnetic fluid; 35-45 parts of methyl methacryloyloxyethyl trimethyl ammonium chloride, 25-30 parts of acrylamide and 0.1-0.3 parts of crosslinking agent N,N'-methylene bisacrylamide are added in sequence and stirred; after oxygen removal by nitrogen blowing for 30 min, the water bath is heated to 60-70℃; 0.5-1.0 parts of ammonium persulfate is dissolved in 20 parts of water, and is added dropwise into the system within 30-35 min; stirring is carried out at 300-400 rpm, constant temperature reaction is carried out at 60-70℃ for 6-8 h; the supernatant is discarded by magnetic separation, and the product is washed with deionized water and ethanol alternately, vacuum dried at 60-70℃ for 10-12 h, and ground to obtain Fe3O4@P(methyl methacryloyloxyethyl trimethyl ammonium chloride-acrylamide) white powder; S1.

2. Disperse 10 parts of the product of S1.1 in 50-55 parts of N,N-dimethylformamide, add 0.2-0.4 parts of a RAFT chain transfer agent and 8-12 parts of LMA monomer, and mix uniformly under ultrasonic; under nitrogen protection, warm to 70-75°C, and dropwise add an ethanol solution initiated by 0.1-0.2 parts of APS, and react at 70-75°C for 6-8 hours; pour the product into a large amount of ice ethanol to precipitate, magnetically separate and collect the solid, wash with ethanol for multiple times, and vacuum dry to obtain an intermediate product of the grafted PLMA hydrophobic arm; S1.

3. Disperse the above intermediate product in 50-70 parts of a mixed solvent of deionized water and 10-15 parts of ethanol, add 10-15 parts of acrylic acid monomer and 0.1-0.2 parts of a RAFT chain transfer agent; under nitrogen atmosphere, warm to 65-70°C, and dropwise add an APS solution to initiate polymerization, and react for 6 hours; magnetically separate and purify by washing with ethanol / water to obtain the bifunctional microspheres; S1.

4. Disperse the bifunctional arm microspheres in 100 parts of deionized water, add 5-8 parts of aminotri(methylene) phosphonic acid and 4-6 parts of FeCl36H2O, and adjust the pH to 4.0-4.2 with 1M NaOH; react at 40-45°C under stirring at 250-300 rpm for 4 hours, magnetically separate and collect the product, wash with deionized water, vacuum dry at 60°C, and grind and sieve to obtain the OPTF-1 flocculant.

5. The acid-base gradient regulation and step precipitation method for glyphosate wastewater treatment according to claim 1, characterized in that: The parameter optimization rules for different water quality conditions are as follows: High calcium and magnesium wastewater - calcium and magnesium ions ≥1200mg / L, specific parameters: S3, add 25% liquid alkali, adjust pH to 6.0, reaction time 40min, stirring speed increased to 80r / min; S4, add 25% liquid alkali, adjust pH to 9.5, reaction time 50min; S5, add 20% hydrochloric acid, adjust pH to 2.5, crystallization time 70min; Low temperature condition - ambient temperature ≤10°C, specific parameters: S3, S4 reaction tank is assisted to heat to 20°C, S3, add 23% liquid alkali, adjust pH to 5.7, reaction time 35min; S4, add 23% liquid alkali, adjust pH to 9.3, reaction time 45min; S5, add 17% hydrochloric acid, adjust pH to 2.2, keep warm at 25°C, crystallization time 65min; High organic phosphorus wastewater - organic phosphorus ≥400mg / L, specific parameters: S3, add 24% liquid alkali, adjust pH to 5.9, stirring speed 75r / min, reaction time 45min; S4, add 24% liquid alkali, adjust pH to 9.4, stirring speed 65r / min, reaction time 40min; S5, add 17% hydrochloric acid, adjust pH to 2.3, stirring speed 55r / min, crystallization time 65min; High heavy metal wastewater - heavy metal ≥70mg / L, specific parameters: S3, add 23% liquid alkali, adjust pH to 5.8, stirring speed 70r / min, reaction time 35min; S4, add 23% liquid alkali, adjust pH to 9.5, stirring speed 65r / min, reaction time 45min; S5, add 18% hydrochloric acid, adjust pH to 2.4, stirring speed 50r / min, crystallization time 70min.

6. The acid-base gradient regulation and step precipitation method for glyphosate wastewater treatment according to claim 1, characterized in that: The hydrochloric acid in the step S5 is preferably recycled hydrochloric acid, and the recycling rate is greater than or equal to 60%; and sulfuric acid is prohibited to replace hydrochloric acid to avoid introducing sulfate impurities to affect the purity of glyphosate crystals and subsequent resource utilization.

7. The acid-base gradient regulation and step precipitation method for glyphosate wastewater treatment according to claim 1, characterized in that, In the step S2, the bubble is 20-50 μm, and the removal rate of non-ionic surfactant after the step S2 is 80%-90%.

8. The acid-base gradient regulation and step precipitation method for glyphosate wastewater treatment according to claim 1, characterized in that, In the step S3, 20%-25% liquid alkali is used to adjust the pH of the glyphosate wastewater to 5.5-6.

0. The calcium and magnesium ions and part of the organic phosphorus impurities in the wastewater are preferentially precipitated to generate phosphate precipitates which can be used as building materials, thereby avoiding the generation of complex salts which are difficult to handle in subsequent reactions, and the removal rate of calcium and magnesium is greater than or equal to 85%.

9. The acid-base gradient regulation and step precipitation method for glyphosate wastewater treatment according to claim 1, characterized in that, In the step S4, the effluent after pressure filtration of the wastewater obtained by the first regulation is added with liquid alkali to adjust the pH to 9.0-9.5, so as to promote the conversion of glyphosate molecules into sodium salt which is easily soluble in water, and to remove iron, zinc and other heavy metal ions to generate recyclable metal hydroxides, and the removal rate of heavy metals is greater than or equal to 90%.

10. The acid-base gradient regulation and step precipitation method for glyphosate wastewater treatment according to claim 1, characterized in that, In the step S5, the effluent after pressure filtration of the wastewater obtained by the second regulation is adjusted to pH 2.0-2.5 by using 15%-20% hydrochloric acid, based on the low solubility of glyphosate under acidic conditions, the precise crystallization of glyphosate crystals is realized, the purity is greater than or equal to 95%, and the industrial recycling standard is met.