A method for recycling high-salt dyeing and printing wastewater

Abstract

This invention discloses a method for recycling high-salt dyeing and finishing wastewater, belonging to the field of dyeing wastewater treatment technology. Addressing the problems of traditional coagulants' easy failure in high-salt environments, difficulty in solid-liquid separation, and inability to regenerate and recycle, this invention uses a magnetic composite coagulant for coagulation and sedimentation. Rapid solid-liquid separation is achieved through an external magnetic field, and the separated magnetic composite coagulant is recycled after alternating water washing and desorption. The wastewater is subsequently treated by oxidation, evaporation and crystallization to recover salts, and activated carbon adsorption for deep treatment before being reused in production. The magnetic composite coagulant has a core-shell structure and a temperature-sensitive polymer graft layer, possessing high salt resistance, magnetic response, and temperature-sensitive desorption characteristics. This invention achieves efficient flocculation, rapid magnetic separation, and intelligent desorption and regeneration in high-salt environments, significantly reducing reagent consumption and operating costs. The effluent quality meets the requirements of the "Water Quality Standard for Reclaimed Water in Textile Dyeing and Finishing Industry".

Description

Technical Field

[0001] This invention relates to the field of dyeing wastewater recycling technology, specifically to a method for recycling high-salt dyeing wastewater. Background Technology

[0002] High-salinity dyeing and printing wastewater generated during production processes is characterized by high salinity, deep color, and the presence of complex organic pollutants. Its treatment and resource recovery represent a significant technical challenge for the industry. Currently, conventional recycling processes for this type of wastewater typically follow a technical route of "physicochemical pretreatment - deep oxidation - evaporation and crystallization - deep purification": first, the wastewater's pH is adjusted, and a composite coagulant is added for coagulation and sedimentation to remove suspended solids and some color; then, advanced oxidation treatment is used to degrade residual organic pollutants; next, evaporation and crystallization are used to separate and recover crystalline salts and condensate; finally, the condensate undergoes deep treatment such as activated carbon adsorption before being reused in production.

[0003] However, existing treatment technologies have significant drawbacks in practical applications. First, high-salt environments can cause salting out of traditional polymeric coagulants or severe chain coiling due to electrostatic shielding, resulting in a significant loss of hydration capacity and flocculation activity, leading to a marked decrease in coagulation efficiency. Second, traditional processes rely on lengthy settling times for solid-liquid separation, a slow and difficult process that easily generates large amounts of highly water-content, difficult-to-dehydrate chemical sludge, significantly increasing sludge disposal costs. Furthermore, conventional coagulants have a simple structure and generally have low adsorption capacity for residual dye molecules and fine organic pollutants in wastewater, making deep enrichment and removal difficult. A more prominent problem is that most existing coagulants are single-use consumables, difficult to desorb and regenerate after adsorbing pollutants, and cannot be recycled, resulting in high reagent consumption and high overall operating costs.

[0004] Therefore, developing a novel composite coagulant with excellent high salt resistance, easy and rapid solid-liquid separation, extremely high adsorption capacity, and the ability to achieve intelligent desorption and recycling, and providing a matching method for the recycling of high-salt dyeing and printing wastewater, is of great practical significance for improving the treatment efficiency of dyeing and printing wastewater and reducing operating costs. Summary of the Invention

[0005] To address the problems of traditional coagulants being prone to failure in high-salt wastewater, having difficulty in solid-liquid separation, and being unable to be regenerated and recycled, this invention aims to provide an intelligent magnetic composite coagulant and its wastewater recycling method, achieving efficient flocculation, rapid magnetic field separation, and temperature-sensitive intelligent desorption and regeneration in high-salt environments, significantly reducing reagent consumption and operating costs.

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

[0007] A method for recycling high-salinity dyeing and printing wastewater includes the following steps:

[0008] S1. Adjust the pH value of the high-salt dyeing and printing wastewater to 6.0 to 9.0, add magnetic composite coagulant to the wastewater for coagulation and sedimentation treatment, adsorb and remove suspended solids and some color;

[0009] S2. Apply an external magnetic field to separate the magnetic composite coagulant with adsorbed pollutants from the waste liquid; after the separated magnetic composite coagulant is regenerated by alternating water washing and desorption, it is recycled for use in the front-end coagulation and sedimentation process.

[0010] S3. The wastewater after removing the magnetic composite coagulant is sent to the oxidation unit for oxidation treatment to degrade the residual dyes and organic pollutants therein;

[0011] S4. The wastewater after oxidation treatment is evaporated and crystallized to separate and recover the crystallized salt at the bottom, and the condensate generated during the evaporation process is collected at the same time.

[0012] S5. The collected condensate is treated by activated carbon adsorption and then reused in the printing and dyeing production process.

[0013] The raw materials of the magnetic composite coagulant include the following components in parts by weight: 2.0-2.5 parts of ferric salt hexahydrate, 0.5-0.8 parts of weak acid salt, 1.0-1.5 parts of surfactant, 40-50 parts of alcohol solvent, 0.6-0.8 parts of zirconium salt, 0.4-0.6 parts of amino ligand, 50-60 parts of amide solvent, 5.0-6.0 parts of regulator, 0.7-0.9 parts of haloisobutyryl halide, 0.3-0.5 parts of acid-binding agent, 60-70 parts of halogenated solvent, 1.5-2.0 parts of N-isopropylacrylamide, 0.8-1.2 parts of sulfobetaine methacrylate, 0.05-0.1 parts of catalyst, 0.08-0.15 parts of polymer ligand, and 25-35 parts of mixed solvent.

[0014] Furthermore, the specific operation of the alternating water washing desorption regeneration is as follows: the separated magnetic composite coagulant is washed 5 times alternately with deionized water under environmental conditions below 20 degrees Celsius and above 50 degrees Celsius.

[0015] Furthermore, the hexahydrate ferric salt is selected from one or more of ferric chloride hexahydrate, ferric nitrate hexahydrate, and ferric sulfate hexahydrate;

[0016] The weak acid salt is selected from one or more of anhydrous sodium acetate, anhydrous sodium formate, and anhydrous sodium carbonate;

[0017] The surfactant is selected from one or more of polyethylene glycol, polyvinylpyrrolidone, and polyvinyl alcohol;

[0018] The alcohol solvent is selected from one or more of ethylene glycol, propylene glycol, and butanediol;

[0019] The zirconium salt is selected from one or more of zirconium tetrachloride, zirconium oxynitrate, and zirconium oxysulfate.

[0020] The amino ligand is selected from one or more of 2-aminoterephthalic acid, 2-aminotriphenyl oleic acid, and 2-aminoisophthalic acid.

[0021] Furthermore, the preparation method of the magnetic composite coagulant includes the following steps:

[0022] A1. Dissolve 2.0-2.5 parts by weight of ferric salt hexahydrate and 0.5-0.8 parts by weight of weak acid salt in 40-50 parts by weight of alcohol solvent, add 1.0-1.5 parts by weight of surfactant, stir for 30 minutes, then transfer to a high-pressure reactor lined with polytetrafluoroethylene, react at 190-200 degrees Celsius for 10-12 hours, cool and then perform magnetic separation, wash three times alternately with deionized water and anhydrous ethanol, and vacuum dry to obtain magnetic nanospheres;

[0023] A2. Take 0.5 parts by weight of the magnetic nanospheres prepared in A1 and disperse them in 50-60 parts by weight of an amide solvent. Disperse them by ultrasonication for 30 minutes. Add 0.6-0.8 parts by weight of zirconium salt and 0.4-0.6 parts by weight of amino ligand in sequence, and add 5.0-6.0 parts by weight of regulator dropwise. Stir at room temperature for 1 hour, then transfer to a reaction vessel and react at 120 degrees Celsius for 24 hours. After the reaction, extract the solid by magnetic separation and perform Soxhlet extraction with methanol for 24 hours. Dry it under vacuum at 60 degrees Celsius to obtain a core-shell structured carrier with amino active sites on the surface.

[0024] A3. Disperse 0.3 parts by weight of the core-shell structured support prepared in A2 in 60-70 parts by weight of a halogen-containing solvent, add 0.3-0.5 parts by weight of an acid-binding agent, and slowly add 0.7-0.9 parts by weight of a haloisobutyryl halide under an ice bath and nitrogen atmosphere. After the addition is complete, continue the reaction at room temperature for 12 hours. After the reaction is completed, perform magnetic separation extraction, wash thoroughly with anhydrous ethanol, and then vacuum dry to obtain a macromolecular initiator with initiation sites grafted on its surface.

[0025] A4. Disperse 0.2 parts by weight of the macromolecular initiator prepared in A3 in 25-35 parts by weight of a mixed solvent, and sequentially add 1.5-2.0 parts by weight of N-isopropylacrylamide, 0.8-1.2 parts by weight of sulfobetaine methacrylate, 0.05-0.1 parts by weight of catalyst, and 0.08-0.15 parts by weight of polymer ligand. After the mixture is thoroughly deoxygenated by three cycles of freezing, evacuation, and thawing, it is protected by argon gas and subjected to constant temperature stirring at 60 degrees Celsius for 24 hours to carry out an atom transfer radical polymerization reaction. After the reaction is completed, the product is magnetically separated and washed alternately with deionized water at temperatures below 20 degrees Celsius and above 50 degrees Celsius. After freeze-drying, the magnetic composite coagulant is obtained.

[0026] Furthermore, the Soxhlet extraction time in step A2 is 24-26 hours;

[0027] The A4 section consists of 5 alternating washes.

[0028] Furthermore, the acid-binding agent is selected from one or more of triethylamine, pyridine, and N,N-diisopropylethylamine;

[0029] The catalyst is selected from one or more of cuprous bromide, cuprous chloride, and cuprous iodide;

[0030] The polymer ligand is selected from one or more of N,N,N',N'',N''-pentamethyldiethylenetriamine, 2,2'-bipyridine, and 1,1,4,7,10,10-hexamethyltriethylenetetramine.

[0031] Furthermore, the magnetic field strength of the applied external magnetic field is 0.5 Tesla, and the solid-liquid separation is completed within 10 seconds after the magnetic field is applied.

[0032] Furthermore, the oxidation unit employs Fenton oxidation, ozone oxidation, or photocatalytic oxidation processes;

[0033] The evaporation crystallization process employs multi-effect evaporation or mechanical vapor recompression evaporation, and the main component of the recovered crystalline salt is sodium chloride.

[0034] Furthermore, the Fenton oxidation operation method is as follows: the pH value of the wastewater obtained in S2 is adjusted to 3.0-5.0, ferrous sulfate heptahydrate and hydrogen peroxide are added to the wastewater, the amount of ferrous sulfate heptahydrate added is 0.05%-0.2% of the wastewater mass, the amount of hydrogen peroxide added is 0.1%-0.5% of the wastewater mass, the reaction temperature is controlled at 20-40 degrees Celsius, the reaction is stirred for 30-60 minutes, after the reaction is completed, the pH value is adjusted to neutral, and the generated iron sludge is removed by settling.

[0035] Furthermore, the ozone oxidation operation method is as follows: the wastewater obtained in S2 is transported to the ozone contact oxidation tower, ozone gas is introduced through a microporous aerator, the ozone dosage is 100-300 mg / L, the gas-water ratio is controlled at 3:1 to 8:1, the reaction time is 15-45 minutes, the wastewater temperature is maintained at 15-35 degrees Celsius during the reaction, and the tail gas is discharged after being treated by an ozone destroyer.

[0036] Furthermore, the photocatalytic oxidation operation method is as follows: Titanium dioxide photocatalyst is added to the wastewater obtained in S2 at a dosage of 0.5-2.0 g / L; the pH value of the wastewater is adjusted to 6.0-8.0; and the reaction is carried out under ultraviolet light irradiation with continuous stirring for 1-3 hours. The dominant wavelength of the ultraviolet light is 254 nm or 365 nm, and the light intensity is 20-50 mW / cm². 2 After the reaction is complete, the photocatalyst is recovered by centrifugation or filtration, and the effluent enters the next treatment unit.

[0037] The activated carbon adsorption deep treatment adopts a granular activated carbon fixed bed adsorption process.

[0038] A high-salt dyeing and printing wastewater recycling system includes a pH adjustment tank, a magnetic coagulation reaction tank, a magnetic separation device, a desorption and regeneration device, an advanced oxidation tank, an evaporation and crystallization device, an activated carbon adsorption tower, and a recycled water tank, which are connected in sequence by pipelines.

[0039] Furthermore, the magnetic composite coagulant separated by the magnetic separation device is processed by the desorption and regeneration device and then returned to the magnetic coagulation reaction tank for recycling via pipeline.

[0040] The magnetic composite coagulant of this invention exerts a multi-response mechanism through a thermosensitive polymer grafted onto the surface of a core-shell structured carrier: in high-salt dyeing wastewater, the copolymer segments formed by sulfobetaine methacrylate and N-isopropylacrylamide exhibit salt-responsive characteristics. The zwitterionic groups in the sulfobetaine structure can bind to dye molecules and organic pollutants in the high-salt wastewater through electrostatic interactions. Simultaneously, the N-isopropylacrylamide segments maintain an extended conformation at room temperature to enhance hydration capacity and adsorption capacity. The magnetic nanosphere coagulant is superparamagnetic to achieve magnetic field response. After coagulation and adsorption are completed, a 0.5 Tesla external magnetic field can be applied to achieve rapid solid-liquid separation between the magnetic composite coagulant and the waste liquid within 10 seconds. In the desorption and regeneration stage, the thermosensitive phase change characteristics of N-isopropylacrylamide are utilized. By washing the polymer chain segments with deionized water at temperatures below 20 degrees Celsius and above 50 degrees Celsius five times alternately, the polymer chain segments undergo a reversible transition between hydrophilic extension and hydrophobic contraction states, thereby achieving the desorption of adsorbed pollutants and efficient regeneration of the coagulant. The regenerated magnetic composite coagulant can be recycled back to the magnetic coagulation reaction tank for reuse after magnetic separation, significantly reducing reagent consumption and operating costs.

[0041] Compared with the prior art, the beneficial effects of the present invention are:

[0042] First, the magnetic composite coagulant of the present invention has high salt resistance. By combining sulfobetaine methacrylate and N-isopropylacrylamide, it effectively overcomes the problem of loss of hydration capacity and flocculation activity caused by salting out or electrostatic shielding effect in high-salt environments of traditional polymer coagulants, thereby improving the coagulation effect and pollutant removal efficiency in high-salt dyeing and printing wastewater.

[0043] Second, this invention achieves rapid solid-liquid separation between magnetic composite coagulant and waste liquid through the core-shell structure design of magnetic nanospheres and the action of an external magnetic field. The separation process is completed within 10 seconds after the magnetic field is applied, which solves the problems of traditional processes that rely on long static settling, slow and difficult separation, and the generation of a large amount of chemical sludge with high water content, and significantly reduces the cost of sludge disposal.

[0044] Third, the magnetic composite coagulant of the present invention can be recycled in the front-end coagulation and sedimentation process after alternating water washing and desorption regeneration due to the reversible phase change characteristics of the temperature-sensitive polymer, thereby realizing regeneration and recycling, reducing the amount of reagents consumed and lowering the overall operating cost. Attached Figure Description

[0045] Figure 1 This is a comparison chart of the SS removal rate retention rate and color removal rate retention rate between the embodiments of the present invention and the comparative examples. Detailed Implementation

[0046] The technical solution of the present invention will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are merely some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0047] Preparation Example 1

[0048] Preparation of magnetic composite coagulant:

[0049] 1. Raw material components by weight:

[0050] 2.2 parts of ferric chloride hexahydrate (ferric salt hexahydrate);

[0051] 0.6 parts of anhydrous sodium acetate (weak acid salt);

[0052] Polyvinylpyrrolidone (surfactant) 1.2 parts;

[0053] 45 parts of ethylene glycol (an alcohol solvent);

[0054] Zirconium tetrachloride (zirconium salt) 0.7 parts;

[0055] 0.5 parts of 2-aminoterephthalic acid (amino ligand);

[0056] 55 parts of N,N-dimethylformamide (amide solvent);

[0057] 5.5 parts of glacial acetic acid (modifier);

[0058] 0.8 parts of 2-bromoisobutyryl bromide (haloisobutyryl halide);

[0059] Triethylamine (acid-binding agent) 0.4 parts;

[0060] 65 parts of dichloromethane (containing halogenated solvent);

[0061] 1.8 parts of N-isopropylacrylamide;

[0062] 1.0 part of sulfobetaine methacrylate;

[0063] 0.08 parts of cuprous bromide (catalyst);

[0064] 0.12 parts of N,N,N',N'',N''-pentamethyldiethylenetriamine (polymer ligand);

[0065] 30 parts of a mixture of deionized water and methanol (volume ratio 1:1, mixed solvent).

[0066] 2. Preparation method:

[0067] A1. Preparation of magnetic nanospheres:

[0068] 2.2 parts by weight of ferric chloride hexahydrate and 0.6 parts by weight of anhydrous sodium acetate were dissolved in 45 parts by weight of ethylene glycol. 1.2 parts by weight of polyvinylpyrrolidone were added, and the mixture was stirred at 600 rpm for 30 minutes at room temperature until uniformly dispersed. The mixture was transferred to a 100 mL high-pressure reactor lined with polytetrafluoroethylene (PTFE), with a filling density of 70%. After sealing, the reactor was placed in a forced-air drying oven, and the temperature was increased to 195 °C at a rate of 2 °C / min, and maintained at this temperature for 11 hours. After the reaction, the mixture was cooled to room temperature at a rate of 1 °C / min. The product was then subjected to magnetic separation under an external magnetic field (magnetic field strength 0.5 Tesla, provided by an electromagnet). The supernatant was discarded, and the black solid product was collected. The product was washed three times alternately with deionized water and anhydrous ethanol (50 mL of washing solution was added each time, and the product was ultrasonically dispersed for 5 minutes and then magnetically separated). Finally, the product was placed in a vacuum drying oven and vacuum dried at 60 °C for 12 hours to obtain magnetic nanospheres with a particle size of 200-300 nm.

[0069] A2. Preparation of core-shell structured carriers:

[0070] Take 0.5 parts by weight of the magnetic nanospheres prepared in step A1 and ultrasonically disperse them in 55 parts by weight of N,N-dimethylformamide. The ultrasonic power is 200W and the frequency is 40kHz. The dispersion is carried out for 30 minutes until uniform dispersion. Add 0.7 parts by weight of zirconium tetrachloride and 0.5 parts by weight of 2-aminoterephthalic acid sequentially, and add 5.5 parts by weight of glacial acetic acid as a regulator. Stir at 400 rpm for 1 hour at room temperature. Transfer the mixture to a 100 mL polytetrafluoroethylene-lined reactor, seal it, and place it in an oven. Increase the temperature to 120°C at a rate of 2°C / min and react at this temperature for 24 hours. After the reaction, cool to room temperature at a rate of 1°C / min. Extract the solid product by magnetic separation (magnetic field strength 0.5 Tesla, provided by an electromagnet) and perform Soxhlet extraction with 100 mL of methanol for 24 hours (extraction temperature 65°C) to remove unreacted ligands and impurities. After extraction, the product was placed in a vacuum drying oven at 60℃ and dried under vacuum for 12 hours to obtain a core-shell structured carrier with amino active sites on its surface.

[0071] A3. Preparation of macromolecular initiators:

[0072] 0.3 parts by weight of the core-shell structured support prepared in step A2 was dispersed in 65 parts by weight of dichloromethane, and 0.4 parts by weight of triethylamine was added as an acid-binding agent. The mixture was placed in an ice bath environment, and 0.8 parts by weight of 2-bromoisobutyryl bromide was slowly added dropwise under a nitrogen atmosphere at a rate of 1-2 drops per second for about 30 minutes. After the addition was complete, the ice bath was removed, and the reaction was continuously stirred at 300 rpm for 12 hours at room temperature. After the reaction was completed, the solid product was extracted by magnetic separation (magnetic field strength 0.5 Tesla, provided by an electromagnet), washed thoroughly 5 times with anhydrous ethanol (50 mL each time, sonicated for 5 minutes and then magnetically separated), and magnetic separation was performed after each washing (magnetic field strength 0.5 Tesla, provided by an electromagnet). Finally, the product was placed in a vacuum drying oven and dried under vacuum at 40°C for 8 hours to obtain a macromolecular initiator with initiation sites grafted on its surface.

[0073] A4. Preparation of magnetic composite coagulant:

[0074] Disperse 0.2 parts by weight of the macromolecular initiator prepared in step A3 in 30 parts by weight of a mixture of deionized water and methanol (volume ratio 1:1). Then, add 1.8 parts by weight of N-isopropylacrylamide, 1.0 parts by weight of sulfobetaine methacrylate, 0.08 parts by weight of cuprous bromide, and 0.12 parts by weight of N,N,N',N'',N''-pentamethyldiethylenetriamine sequentially. Freeze the mixture in a liquid nitrogen / ethanol bath to -78°C, evacuate to below 10 Pa, and thaw to room temperature. Repeat this freezing-evacuation-thawing cycle three times to ensure complete deoxygenation. After deoxygenation, high-purity argon gas was introduced into the system for protection. The temperature was increased to 60°C at a rate of 2°C / min under argon atmosphere, and the mixture was stirred at a constant temperature of 200 rpm for 24 hours. After the reaction, the product was magnetically separated (magnetic field strength 0.5 Tesla, provided by an electromagnet), and washed five times alternately with deionized water at 15°C and 55°C, each wash lasting 10 minutes, using 50 mL of washing solution each time. Magnetic separation was then performed again after washing (magnetic field strength 0.5 Tesla, provided by an electromagnet). Finally, the product was placed in a freeze dryer and freeze-dried at -50°C and 10 Pa for 24 hours to obtain the magnetic composite coagulant.

[0075] Preparation Example 2

[0076] The magnetic composite coagulant was prepared by referring to the preparation method of Preparation Example 1, except that ferric chloride hexahydrate was replaced with ferric nitrate hexahydrate, and the rest remained the same as in Preparation Example 1.

[0077] Preparation Example 3

[0078] The magnetic composite coagulant was prepared by referring to the preparation method of Preparation Example 1, except that zirconium tetrachloride was replaced with zirconium oxynitrate, and the rest remained the same as in Preparation Example 1.

[0079] Preparation Example 4

[0080] The magnetic composite coagulant was prepared by referring to the preparation method of Preparation Example 1, except that 2-aminoterephthalic acid was replaced with 2-aminoisophthalic acid, and the rest remained the same as in Preparation Example 1.

[0081] Comparative Preparation Example 1

[0082] The magnetic composite coagulant was prepared according to the preparation method of Preparation Example 1, except that N-isopropylacrylamide was not added, and the rest were the same as in Preparation Example 1.

[0083] Comparative Preparation Example 2

[0084] The magnetic composite coagulant was prepared according to the preparation method of Preparation Example 1, except that N,N,N',N'',N''-pentamethyldiethylenetriamine was not added, and the rest remained the same as in Preparation Example 1.

[0085] Comparative preparation example 3

[0086] The magnetic composite coagulant was prepared according to the preparation method of Preparation Example 1, except that sulfobetaine methacrylate was not added, and the rest were the same as in Preparation Example 1.

[0087] Comparative preparation example 4

[0088] The magnetic composite coagulant was prepared by referring to the preparation method of Preparation Example 1, except that sulfobetaine methacrylate was replaced with 2-hydroxyethyl methacrylate, and the rest remained the same as in Preparation Example 1.

[0089] Comparative preparation example 5

[0090] The magnetic composite coagulant was prepared by referring to the preparation method of Preparation Example 1, except that N-isopropylacrylamide was replaced with acrylamide, and the rest remained the same as in Preparation Example 1.

[0091] Comparative preparation example 6

[0092] The preparation of the magnetic composite coagulant is the same as in Preparation Example 1, except that step A1 is omitted and Fe3O4 is used directly, while the rest remains the same as in Preparation Example 1.

[0093] The examples and comparative examples use high-salt dyeing wastewater from a dyeing and printing factory. The specific parameters are shown in Table 1.

[0094] Table 1

[0095] parameter numerical values Test methods pH value 9.2 GB / T6920-1986 Glass Electrode Method Chemical oxygen demand (COD) 2850mg / L HJ828-2017 Dichromate Method <![CDATA[Biochemical Oxygen Demand (BOD5)]]> 680mg / L HJ505-2009 Dilution and Inoculation Method Color 450 times GB / T11903-1989 Dilution Factor Method Suspended solids (SS) 320mg / L GB / T11901-1989 Gravimetric Method <![CDATA[Ammonia nitrogen (NH3-N)]]> 45mg / L HJ535-2009 Nessler's Reagent Spectrophotometric Method Total nitrogen (TN) 78mg / L HJ636-2012 Alkaline Potassium Persulfate Digestion Ultraviolet Spectrophotometry Total dissolved solids (TDS) 28500mg / L GB / T5750.4-2006 Total Soluble Solids by Weighing Method electrical conductivity 42500μS / cm GB / T5750.4-2006 Electrode Method Sodium chloride content 18600mg / L GB / T5750.5-2006 Silver nitrate titration method <![CDATA[Sulfate ion (SO4 2- )]]> 4200mg / L GB / T5750.5-2006 Barium Sulfate Turbidimetric Method Reactive Brilliant Red dye (calculated as Reactive Brilliant Red X-3B) 125mg / L GB / T17592-2011 Extraction Spectrophotometry water temperature 28℃ Thermometer method

[0096] Example 1

[0097] A method for recycling high-salinity dyeing and printing wastewater:

[0098] The specific processing steps are as follows:

[0099] S1. Coagulation and sedimentation treatment: The high-salt dyeing wastewater was introduced into a pH adjustment tank, and a 1 mol / L hydrochloric acid solution was added to adjust the pH of the wastewater to 7.5. The pH-adjusted wastewater was then pumped into a magnetic coagulation reactor, and the magnetic composite coagulant (prepared in Preparation Example 1) was added to the wastewater at a dosage of 0.15% of the wastewater mass (i.e., 1.5 kg / m³). 3 (Wastewater). Turn on the agitator and control the agitation speed at 150 rpm. Stir for 20 minutes to allow the magnetic composite coagulant to fully contact the suspended solids, dye molecules, and organic pollutants in the wastewater and undergo coagulation and adsorption.

[0100] S2. Magnetic Separation and Desorption Regeneration: The wastewater treated by coagulation and sedimentation is introduced into the magnetic separation device. An external magnetic field is applied by activating the electromagnet, with the magnetic field strength controlled at 0.5 Tesla. Under the action of the magnetic field, the magnetic composite coagulant, which adsorbs pollutants, rapidly migrates and accumulates in the direction of the magnetic field, resulting in solid-liquid separation between the magnetic composite coagulant and the wastewater. The separated wastewater enters the subsequent treatment unit, while the collected magnetic composite coagulant enters the desorption and regeneration device.

[0101] The separated magnetic composite coagulant was regenerated by alternating washing and desorption with deionized water: first, it was washed for 5 minutes at a low temperature of 15°C, followed by washing for 5 minutes at a high temperature of 55°C. This alternating low-temperature and high-temperature washing was performed a total of 5 times, with the washing solution used each time being 10 times the mass of the magnetic composite coagulant. After desorption and regeneration, the magnetic composite coagulant was recovered by magnetic separation. The regenerated magnetic composite coagulant was then returned to the magnetic coagulation reaction tank for recycling via pipeline.

[0102] S3. Fenton Oxidation Treatment: Wastewater after removing the magnetic composite coagulant is introduced into an advanced oxidation tank. A 1 mol / L sulfuric acid solution is added to adjust the pH to 4.0. Ferrous sulfate heptahydrate is added to the wastewater at a rate of 0.1% of the wastewater mass. After stirring and dissolving, a 30% hydrogen peroxide solution is added at a rate of 0.3% of the wastewater mass. The reaction temperature is controlled at 30℃, the stirring speed at 100 rpm, and the reaction time at 45 minutes to degrade residual dyes and organic pollutants in the wastewater. After the reaction, a 1 mol / L sodium hydroxide solution is added to adjust the pH to 7.0. The mixture is allowed to stand for 30 minutes to remove the generated iron sludge precipitate.

[0103] S4. Evaporation and Crystallization Treatment: The oxidized wastewater is pumped into a triple-effect evaporation and crystallization unit for treatment. The first-effect evaporation temperature is controlled at 95℃, the second-effect at 75℃, and the third-effect at 55℃, with the system vacuum controlled at -0.08MPa. After multi-effect evaporation and concentration, the bottom crystallized salt (mainly sodium chloride) is recovered by centrifugation. The recovered crystallized salt has a purity of over 96% and can be sold as an industrial raw material. The secondary steam generated during the evaporation process is condensed and the condensate is collected.

[0104] S5. Activated Carbon Adsorption Deep Treatment: The collected condensate is introduced into an activated carbon adsorption tower for deep treatment using a fixed-bed granular activated carbon adsorption process. The activated carbon packing height is 1.5m, the empty bed contact time is 15 minutes, and the water flow rate is 6m / h. After activated carbon adsorption treatment, the effluent COD is reduced to 35mg / L, color is reduced by 10 times, turbidity is reduced to 1NTU, and conductivity is reduced to 120μS / cm. All indicators meet the requirements of the "Water Quality Standard for Reclaimed Water in Textile Dyeing and Finishing Industry" (FZ / T01107-2011). The treated reclaimed water is pumped into a reclaimed water tank and reused in the rinsing process of the dyeing and printing production.

[0105] Examples 2-4

[0106] A method for recycling high-salt dyeing and printing wastewater, referring to the method in Example 1, except that the magnetic composite coagulant is replaced sequentially with the products prepared in Preparation Examples 2-4, and the rest remains the same as in Example 1.

[0107] Comparative Examples 1-6

[0108] A method for recycling high-salt dyeing and printing wastewater, referring to the method in Example 1, except that the magnetic composite coagulant is replaced sequentially with the products prepared in Comparative Preparation Examples 1-6, and the rest remains the same as in Example 1.

[0109] Performance testing:

[0110] 1. Cyclic Stability Test: The same batch of magnetic composite coagulant was subjected to 10 consecutive cycles of "adsorption-magnetic separation-desorption regeneration-re-adsorption" according to the method described in Example 1. The removal rates of SS (suspended solids) and color were measured in each cycle, and the performance retention rate after the 10th cycle was calculated.

[0111] ;

[0112] In the formula, η 10 η1 represents the removal rate in the 10th cycle, and η1 represents the removal rate in the first use.

[0113] The tests for SS (suspended solids) and color were conducted according to GB / T11901-1989 - Gravimetric method and GB / T11903-1989 - Dilution factor method, respectively. The data are shown in Table 2.

[0114] 2. Reclaimed water quality compliance test: The final effluent from step S5 was tested according to the following indicators in the standard FZ / T01107-2011 "Reclaimed Water Quality of Textile Dyeing and Finishing Industry": color (dilution factor method), COD (mg / L), turbidity (NTU), conductivity (μS / cm), pH value, iron ion content (mg / L) and total hardness (mg / L, calculated as CaCO3). The data are shown in Table 2.

[0115] Table 2

[0116] index Example 1 Example 2 Example 3 Example 4 Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 Comparative Example 5 Comparative Example 6 <![CDATA[Retention rate R of SS removal 10 (%)]]> 96.5 95.2 95.6 94.8 32.5 72.4 65.2 75.6 35.8 82.5 <![CDATA[Retention rate R of chromaticity removal rate 10 (%)]]> 95.8 94.6 94.9 94.2 30.1 70.5 62.8 73.2 33.4 80.1 Color intensity (multiple) 10 12 11 13 35 25 55 45 32 20 COD (mg / L) 35 38 36 40 85 75 145 115 82 65 Turbidity (NTU) 1 1.2 1.1 1.3 4.5 3.2 8.5 6.4 4.2 2.5 Electrical conductivity (μS / cm) 120 125 122 128 210 185 280 245 205 160 pH value 7.1 7 7.2 7.1 7.2 7.1 6.8 6.9 7 7.1 Iron ions (mg / L) 0.12 0.15 0.14 0.16 0.35 0.28 0.55 0.45 0.32 1.25 Total hardness (mg / L) 15 18 16 20 35 28 45 38 32 25

[0117] Examples 1-4 employ a core-shell structure and a multi-responder formulation. The zwitterionic groups of sulfobetaine methacrylate generate an anti-polyelectrolyte effect under high salinity, with the molecular chains becoming more extended at higher salinity, significantly enhancing the flocculation capacity for high-salt wastewater. N-isopropylacrylamide imparts thermosensitive phase change capability to the material. During washing at 15°C and 55°C, the polymer chains can switch between "hydrophilic extension" and "hydrophobic contraction," effectively "squeezing out" adsorbed impurities. After 10 cycles, the removal retention rates of SS and color are both as high as 94%~96% or more, resulting in excellent effluent quality that fully meets the "Water Quality Standard for Reclaimed Water in Textile Dyeing and Finishing Industry." Furthermore, altering the metal salt precursor has minimal impact on overall performance, demonstrating the system's stability.

[0118] Comparative Example 1 did not add NIPAm, and Comparative Example 5 replaced NIPAm with ordinary acrylamide. Both lost the temperature-sensitive desorption mechanism. Due to the lack of temperature-sensitive NIPAm segments, the coagulant could not achieve reversible conformational shrinkage and expansion of the polymer chain during alternating washing at 15℃ and 55℃. As a result, the adsorbed dye molecules and suspended matter were locked in the pores and chain segment network of the coagulant and could not be washed away. After the 10th cycle, the R10 retention rate dropped sharply to about 30%~35%, and the front-end coagulation effect was severely reduced, resulting in the final effluent COD and color exceeding the standard.

[0119] Comparative Example 3, without SBMA, and Comparative Example 4, with SBMA replaced by HEMA (which is hydrophilic but lacks zwitterionic characteristics), lost their high-salt resistance. The TDS of the dyeing and printing wastewater reached as high as 28,500 mg / L. In this high-salt environment, ordinary polymers (such as HEMA) will suffer from severe chain curling and aggregation due to electrostatic shielding and salting-out effects, resulting in a loss of hydration capacity and flocculation activity. The internal salt structure of SBMA is the key to resisting high salt. Without SBMA, the coagulation process is ineffective, and a large amount of unremoved organic matter and suspended solids directly impact the downstream treatment unit, resulting in the worst final effluent quality, with COD reaching 115-145 mg / L, color reaching 45-55 times higher, and turbidity and conductivity also significantly higher.

[0120] Comparative Example 2 did not add polymer ligand (PMDETA), which led to the uncontrolled polymerization process. PMDETA is the core ligand for atom transfer radical polymerization. Without it, the polymerization reaction becomes random "free radical dead polymerization". This results in the functional polymer chains grafted onto the surface of the magnetic carrier having varying lengths and extremely low grafting density. Its high-salt flocculation and temperature-sensitive desorption capabilities are greatly reduced, the R10 retention rate drops to about 70%, and the COD of the effluent is on the verge of failing to meet the standards.

[0121] Comparative Example 6 omitted the autoclave solvothermal synthesis of magnetic microspheres and directly used commercially available or bare Fe3O4, resulting in an unstable core carrier. The bare Fe3O4, which was not finely encapsulated, had extremely poor binding force in the subsequent grafting reaction and was easily dissolved in the slightly acidic environment (pH~4.0) of Fenton oxidation. Although other indicators were acceptable, the iron ion concentration in the final effluent abnormally rose to 1.25 mg / L, far exceeding the 0.3 mg / L limit of the recycled water standard, and the magnetic response capability gradually decreased, with R10 dropping to about 80%.

[0122] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for recycling high-salinity dyeing and printing wastewater, characterized in that, Includes the following steps: S1. Adjust the pH value of the high-salt dyeing and printing wastewater to 6.0 to 9.0, add magnetic composite coagulant to the wastewater for coagulation and sedimentation treatment, adsorb and remove suspended solids and some color; S2. Apply an external magnetic field to separate the magnetic composite coagulant with adsorbed pollutants from the waste liquid; after the separated magnetic composite coagulant is regenerated by alternating water washing and desorption, it is recycled for use in the front-end coagulation and sedimentation process. S3. The wastewater after removing the magnetic composite coagulant is sent to the oxidation unit for oxidation treatment to degrade the residual dyes and organic pollutants therein; S4. The wastewater after oxidation treatment is evaporated and crystallized to separate and recover the crystallized salt at the bottom, and the condensate generated during the evaporation process is collected at the same time. S5. The collected condensate is treated by activated carbon adsorption and then reused in the printing and dyeing production process. The raw materials of the magnetic composite coagulant include the following components in parts by weight: 2.0-2.5 parts of ferric salt hexahydrate, 0.5-0.8 parts of weak acid salt, 1.0-1.5 parts of surfactant, 40-50 parts of alcohol solvent, 0.6-0.8 parts of zirconium salt, 0.4-0.6 parts of amino ligand, 50-60 parts of amide solvent, 5.0-6.0 parts of regulator, 0.7-0.9 parts of haloisobutyryl halide, 0.3-0.5 parts of acid-binding agent, 60-70 parts of halogenated solvent, 1.5-2.0 parts of N-isopropylacrylamide, 0.8-1.2 parts of sulfobetaine methacrylate, 0.05-0.1 parts of catalyst, 0.08-0.15 parts of polymer ligand, and 25-35 parts of mixed solvent.

2. The method for recycling high-salinity dyeing and printing wastewater according to claim 1, characterized in that, The specific operation of the alternating water washing desorption regeneration is as follows: the separated magnetic composite coagulant is washed 5 times alternately with deionized water under environmental conditions below 20 degrees Celsius and above 50 degrees Celsius.

3. The method for recycling high-salinity dyeing and printing wastewater according to claim 1, characterized in that, The hexahydrate ferric salt is selected from one or more of ferric chloride hexahydrate, ferric nitrate hexahydrate, and ferric sulfate hexahydrate; The weak acid salt is selected from one or more of anhydrous sodium acetate, anhydrous sodium formate, and anhydrous sodium carbonate; The surfactant is selected from one or more of polyethylene glycol, polyvinylpyrrolidone, and polyvinyl alcohol; The alcohol solvent is selected from one or more of ethylene glycol, propylene glycol, and butanediol; The zirconium salt is selected from one or more of zirconium tetrachloride, zirconium oxynitrate, and zirconium oxysulfate. The amino ligand is selected from one or more of 2-aminoterephthalic acid, 2-aminotriphenyl oleic acid, and 2-aminoisophthalic acid.

4. The method for recycling high-salinity dyeing and printing wastewater according to claim 1, characterized in that, The preparation method of the magnetic composite coagulant includes the following steps: A1. Dissolve 2.0-2.5 parts by weight of ferric salt hexahydrate and 0.5-0.8 parts by weight of weak acid salt in 40-50 parts by weight of alcohol solvent, add 1.0-1.5 parts by weight of surfactant, stir for 30 minutes, then transfer to a high-pressure reactor lined with polytetrafluoroethylene, react at 190-200 degrees Celsius for 10-12 hours, cool and then perform magnetic separation, wash three times alternately with deionized water and anhydrous ethanol, and vacuum dry to obtain magnetic nanospheres; A2. Take 0.5 parts by weight of the magnetic nanospheres prepared in A1 and disperse them in 50-60 parts by weight of an amide solvent. Disperse them by ultrasonication for 30 minutes. Add 0.6-0.8 parts by weight of zirconium salt and 0.4-0.6 parts by weight of amino ligand in sequence, and add 5.0-6.0 parts by weight of regulator dropwise. Stir at room temperature for 1 hour, then transfer to a reaction vessel and react at 120 degrees Celsius for 24 hours. After the reaction, extract the solid by magnetic separation and perform Soxhlet extraction with methanol for 24 hours. Dry it under vacuum at 60 degrees Celsius to obtain a core-shell structured carrier with amino active sites on the surface. A3. Disperse 0.3 parts by weight of the core-shell structured support prepared in A2 in 60-70 parts by weight of a halogen-containing solvent, add 0.3-0.5 parts by weight of an acid-binding agent, and slowly add 0.7-0.9 parts by weight of a haloisobutyryl halide under an ice bath and nitrogen atmosphere. After the addition is complete, continue the reaction at room temperature for 12 hours. After the reaction is completed, perform magnetic separation extraction, wash thoroughly with anhydrous ethanol, and then vacuum dry to obtain a macromolecular initiator with initiation sites grafted on its surface. A4. Disperse 0.2 parts by weight of the macromolecular initiator prepared in A3 in 25-35 parts by weight of a mixed solvent, and sequentially add 1.5-2.0 parts by weight of N-isopropylacrylamide, 0.8-1.2 parts by weight of sulfobetaine methacrylate, 0.05-0.1 parts by weight of catalyst, and 0.08-0.15 parts by weight of polymer ligand. After the mixture is thoroughly deoxygenated by three cycles of freezing, evacuation, and thawing, it is protected by argon gas and subjected to constant temperature stirring at 60 degrees Celsius for 24 hours to carry out an atom transfer radical polymerization reaction. After the reaction is completed, the product is magnetically separated and washed alternately with deionized water at temperatures below 20 degrees Celsius and above 50 degrees Celsius. After freeze-drying, the magnetic composite coagulant is obtained.

5. A method for recycling high-salinity dyeing and printing wastewater according to claim 4, characterized in that, The Soxhlet extraction time in step A2 is 24-26 hours; The A4 section consists of 5 alternating washes.

6. The method for recycling high-salinity dyeing and printing wastewater according to claim 4, characterized in that, The acid-binding agent is selected from one or more of triethylamine, pyridine, and N,N-diisopropylethylamine; The catalyst is selected from one or more of cuprous bromide, cuprous chloride, and cuprous iodide; The polymer ligand is selected from one or more of N,N,N',N'',N''-pentamethyldiethylenetriamine, 2,2'-bipyridine, and 1,1,4,7,10,10-hexamethyltriethylenetetramine.

7. The method for recycling high-salinity dyeing and printing wastewater according to claim 1, characterized in that, The applied magnetic field strength is 0.5 Tesla, and the solid-liquid separation is completed within 10 seconds after the magnetic field is applied.

8. The method for recycling high-salinity dyeing and printing wastewater according to claim 1, characterized in that, The oxidation unit employs Fenton oxidation, ozone oxidation, or photocatalytic oxidation processes. The evaporation crystallization process employs multi-effect evaporation or mechanical vapor recompression evaporation, and the main component of the recovered crystalline salt is sodium chloride. The activated carbon adsorption deep treatment adopts a granular activated carbon fixed bed adsorption process.

9. A high-salinity dyeing and printing wastewater recycling system, characterized in that, The system includes a pH adjustment tank, a magnetic coagulation reaction tank, a magnetic separation device, a desorption and regeneration device, an advanced oxidation tank, an evaporation and crystallization device, an activated carbon adsorption tower, and a recycled water tank, which are connected in sequence by pipelines.

10. A high-salinity dyeing and printing wastewater recycling system according to claim 9, characterized in that, The magnetic composite coagulant separated by the magnetic separation device is processed by the desorption and regeneration device and then returned to the magnetic coagulation reaction tank for recycling via pipeline.

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