CN116143227B - Method for treating low-concentration heavy metal pollution wastewater by combining adsorption and ultrafiltration - Google Patents
Method for treating low-concentration heavy metal pollution wastewater by combining adsorption and ultrafiltration Download PDFInfo
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Abstract
The invention provides a method for treating low-concentration heavy metal pollution wastewater by combining adsorption and ultrafiltration. The invention can realize the removal rate of heavy metal ions in the metal polluted wastewater of more than 95 percent.
Description
Technical Field
The invention belongs to the technical field of heavy metal pollution wastewater treatment, and particularly relates to a method for treating low-concentration heavy metal pollution wastewater by combining adsorption and ultrafiltration.
Background
The heavy metal pollutant has the characteristics of non-biodegradability, high toxicity, high carcinogenicity, long-term pollution, easy enrichment in vivo and the like.
There are techniques for treating low concentration heavy metal contaminated wastewater in industrial processes such as precipitation, adsorption, ion exchange resins, membrane filtration, electrodialysis, electrodeionization, etc.
The alkaline precipitation method is a common method for treating industrial electroplating wastewater, and has simple operation and high engineering reliability. However, a large amount of chemical reagent needs to be added in the alkaline precipitation process, so that the method has high use cost; the coagulating sedimentation method is also frequently used for removing low-concentration heavy metal ions in wastewater, the method transfers the heavy metal ions from a water phase to a solid phase through adding a coagulant, such as an iron salt coagulant, hydroxyl functional groups generated by hydrolysis of the coagulant have high affinity to heavy metal ions or colloid particles in water, the low-concentration heavy metal ions in the wastewater can be removed through adsorption and coprecipitation, heavy metal-containing sludge generated by the coagulating sedimentation method belongs to typical hazardous waste, and the treatment cost is high. In the resin adsorption method, the adsorbent and the adsorbate interact to form a part of chelate, and the concentration of some metals such as nickel in the adsorbed wastewater cannot reach the emission standard of 0.1mg/L. Membrane pollution in membrane filtration technology restricts its industrial application in wastewater treatment in a number of industries. The selective migration, electrodialysis and electrodeionization of water ions through ion exchange membranes can concentrate heavy metal ions at low concentrations, but at the same time create membrane-related problems such as membrane fouling and concentration polarization.
The industrial wastewater has various pollutant types and high content, the traditional and single water treatment method can not meet the current requirement of water resource recycling, and the combination of multiple water treatment technologies becomes a research hot spot for the deep purification of the industrial wastewater.
Disclosure of Invention
The invention aims to solve the technical problems of the prior art, and provides a method for treating low-concentration heavy metal polluted wastewater by combining adsorption and ultrafiltration, which can realize the removal rate of heavy metal ions in the metal polluted wastewater of more than 95 percent.
In order to solve the technical problems, the invention adopts the following technical scheme: a method for treating low-concentration heavy metal polluted wastewater by combining adsorption and ultrafiltration comprises the following steps:
s1, preparing a multi-active-site cellulose-based adsorbent:
s101, adding microcrystalline cellulose into a 15% NaOH aqueous solution, uniformly stirring, adding tetraethylenepentamine, stirring at a speed of 500 r-600 r/min for 10min, placing in an ice bath, adding epichlorohydrin, continuously stirring for 10-30 min until the mixture forms a solid state, then flushing with high-purity water until the pH value of the filtrate is 7.0, collecting a solid product, drying at 80 ℃ until the constant weight is obtained, and obtaining a cellulose-based adsorbent named M/T;
s102, dispersing bis (carboxymethyl) trithiocarbonate and M/T obtained in S1 in high-purity water, stirring for 5 h at the temperature of 100 ℃, flushing with high-purity water until the pH value of filtrate is 7.0, collecting a solid product, and drying to constant weight at the temperature of 60 ℃ to obtain a multi-active-point cellulose-based adsorbent named M/T-B;
s2, preparing an adsorptive nanofiber membrane:
s201 and TNTs nano adsorbentIs prepared from the following steps: adding TiO into 10mol/L NaOH solution 2 Stirring powder at 60 ℃ for reaction 1h to obtain milky suspension, carrying out ultrasonic treatment 1h, carrying out hydrothermal reaction 72 h in a high-pressure sealed hydrothermal reaction kettle at 160 ℃ and 2.2MPa, cooling to room temperature, washing a white precipitate with high-purity water until the pH value of a filtrate is 7.0, drying at 80 ℃ for 12h, and naturally cooling to room temperature to obtain the TNTs nano adsorbent;
s202, sulfhydryl functional modification of TNTs nano adsorbent:
s20201, preparation of mixture A: mixing the TNTs nano adsorbent obtained in the step S201 with acetone at room temperature, stirring for 1h, and then carrying out ultrasonic treatment on the mixture for 1h to obtain a mixture A;
s20202, preparation of mixture B: MPTMS (HS (CH) 2 ) 3 Si(OCH 3 ) 3 ) Dissolving in high purity water to obtain a mixture B;
s20203, preparation of thiol-modified TNTs: dropwise adding the mixture A obtained in the step S20201 into the mixture B obtained in the step S20202, stirring for 2 hours at room temperature, centrifuging for 15 minutes at a rotating speed of 3000 rpm, collecting the obtained solid substance, washing 3-4 times with acetone, washing 3-4 times with high-purity water, drying 24h the washed solid substance at a temperature of 60 ℃ to obtain mercapto-functional modified TNTs, and naming the TNTs as T/S-NPs;
s203, preparing a nanofiber membrane:
s20301, preparation of PVC film:
drying the PVC at the temperature of 60 ℃ for 24h to obtain dried PVC powder; placing the obtained dried PVC powder into N-methyl pyrrolidone, stirring for 12 hours at the temperature of 60 ℃ to obtain a N-methyl pyrrolidone solution of a PVC polymer with the mass fraction of 13.5%, degassing, scraping a film on a glass plate by a film casting knife, immersing in a high-purity water bath, transferring the film into another high-purity water bath for immersing for 24h after the film on the glass plate is peeled off, and drying at room temperature for 24 hours to obtain a PVC film;
s20302, preparation of spinning solution:
dissolving the dried PVC polymer powder in N-methylpyrrolidone, and stirring for 12 hours at the temperature of 60 ℃ to obtain an N-methylpyrrolidone solution of the PVC polymer with the mass fraction of 15%;
dissolving 1g of the T/S-NPs obtained in S20203 in 30mL of N-methylpyrrolidone, and performing ultrasonic dispersion for 45 min to obtain an N-methylpyrrolidone mixture of the T/S-NPs;
dropwise adding the N-methylpyrrolidone solution of the PVC polymer with the mass fraction of 15% into the N-methylpyrrolidone mixture of the T/S-NPs, stirring for 2 hours at the temperature of 60 ℃, and carrying out degassing treatment to obtain a spinning solution;
s20303, preparation of an adsorptive nanofiber membrane: the PVC film obtained in S20301 was placed on an aluminum foil tray,
electrospinning the spinning solution obtained in the step S20302 on the surface of the PVC film obtained in the step S20301, soaking in a water bath at 25 ℃ after electrospinning, and drying at 60 ℃ after the film is separated from the aluminum foil disc to obtain an adsorptive nanofiber film;
s3, constructing an adsorption-ultrafiltration coupling method:
filling the adsorption column with the M/T-B obtained in the step S102 as a filler;
installing the two adsorption nanofiber membranes obtained in the S20303 into a flat ultrafiltration membrane assembly to form an ultrafiltration membrane assembly;
the wastewater containing low-concentration heavy metal pollutants sequentially passes through the adsorption column and the ultrafiltration membrane component to finish purification; the concentration of each heavy metal ion in the wastewater containing the low-concentration heavy metal pollutants is 0.01-mg/L to 0.1mg/L.
Preferably, the dosage ratio of 15% NaOH aqueous solution, microcrystalline cellulose, tetraethylenepentamine and epichlorohydrin in S101 is 20mL:1g:10g:23g.
Preferably, the mass ratio of the bis (carboxymethyl) trithiocarbonate to the cellulose-based adsorbent in S102 is 1:2.
Preferably, the method comprises the steps of,NaOH solution and TiO solution with concentration of 10mol/L in S201 2 The powder was used in a 50mL:1g ratio.
Preferably, the particle size of the TNTs nano-adsorbent in S201 is 2 nm-5 nm.
Preferably, the dosage ratio of TNTs nano-adsorbent to acetone in S20201 is 1g to 100mL; the dosage ratio of MPTMS to high purity water in S20202 is 12g:50mL; the mass ratio of the TNTs nano-adsorbent to the MPTMS in the S202 is 3:1.
Preferably, the operating conditions of electrospinning described in S20303 are: the flow rate of the spinning solution is 1.5mL/h, the applied voltage is 18kv, the distance between the needle tip and the collector is 18.5cm, and the rotating speed of the collector is 240rpm; the temperature of the chamber in the electrospinning apparatus was 25℃and the relative humidity was 70%.
Preferably, the heavy metal ions in the wastewater containing heavy metal pollutants in S3 comprise Ni 2+ 、Pb 2+ And/or Cd 2+ Ions.
Preferably, the removal rate of each heavy metal ion in the purified wastewater containing heavy metal pollutants in S3 is more than 95%.
Compared with the prior art, the invention has the following advantages:
1. the invention introduces high density amino groups on the surface of microcrystalline cellulose by crosslinking
（-NH 2 ) And carboxyl (-COOH) to prepare the multi-active site cellulose-based adsorbent M/T-B, and the preparation method of the adsorbent is simple, environment-friendly and safe. Microcrystalline cellulose is used as a carrier, has relatively large specific surface area, and can be added by introducing more groups; the prepared adsorbent M/T-B has the group-NH 2 Higher density of-COOH, providing more active sites, the adsorbent is useful for low concentration of Ni in wastewater under test 2+ 、Pb 2+ And/or Cd 2+ Also shows strong adsorptivity.
2. The nanofiber ultrafiltration membrane with a certain adsorption performance on heavy metal ions is prepared, and the preparation method is simple, safe and environment-friendly. The nanofiber membrane is loaded with a certain amount of sulfhydryl (-SH) groups on the surface, and the groups have a certain adsorption property on heavy metal ions. The ultrafiltration membrane has two functions of removing heavy metal ions in the using process: on one hand, the adsorption function of sulfhydryl groups on the surface of the membrane and on the other hand, the interception function of the ultrafiltration membrane; the removal rate of heavy metal ions is greatly improved under the double functions.
3. The method for treating the low-concentration heavy metal polluted wastewater by utilizing the combination of adsorption and ultrafiltration provided by the invention is a technical combination scheme aiming at the situation that the concentration of heavy metal ions in the wastewater is low, the purification difficulty is increased, and the treated water is difficult to realize large-scale recycling. According to the invention, the wastewater to be treated sequentially passes through the adsorption column filled with the cellulose-based adsorbent with multiple active sites and the nanofiber ultrafiltration membrane with a certain adsorption effect, so that the removal rate of heavy metal ions can reach more than 95%, multiple water indexes of the country and industry are met, the large-scale reuse of the treated water can be realized, and the efficient recycling of water resources is realized. Wherein Ni is 2+ 、Pb 2+ And/or Cd 2+ Concentration of<After passing 0.1mg/L of wastewater through an adsorption column filled with a cellulose-based adsorbent with multiple active sites, ni 2+ 、Pb 2+ And/or Cd 2+ The removal rate of the waste water can reach more than 80 percent; then the wastewater passes through a nanofiber ultrafiltration membrane with a certain adsorption effect, ni 2+ 、Pb 2+ And/or Cd 2+ The removal rate of the wastewater can reach more than 95%, thereby realizing the purification of the wastewater polluted by low-concentration heavy metals.
The present invention will be described in further detail with reference to examples.
Detailed Description
Example 1
The embodiment is a method for treating low-concentration heavy metal polluted wastewater by combining adsorption and ultrafiltration, which comprises the following steps:
s1, preparation of a multi-active site cellulose-based adsorbent (M/T-B):
s101, adding 1g of microcrystalline cellulose (MCC) into 20mL of 15% by mass of NaOH aqueous solution, uniformly stirring, adding 10g of Tetraethylenepentamine (TEPA), stirring at a speed of 500 r/min for 10min, placing in an ice bath, adding 23g of cross-linking agent Epichlorohydrin (ECH), continuously stirring for 30min until the mixture forms a solid state, then flushing with high-purity water until the pH value of the filtrate is 7.0, collecting a solid product, drying to constant weight at a temperature of 80 ℃ to obtain a cellulose-based adsorbent, and naming the cellulose-based adsorbent as M/T;
s102, dispersing 0.25g of bis (carboxymethyl) trithiocarbonate (BCTTC) and 0.5g of M/T obtained in S1 in high-purity water, stirring for 5 h at the temperature of 100 ℃, flushing with high-purity water until the pH value of filtrate is 7.0, collecting a solid product, and drying to constant weight at the temperature of 60 ℃ to obtain a multi-active-point cellulose-based adsorbent named M/T-B;
in the step, bis (carboxymethyl) trithiocarbonate (BCTTC) is grafted on the surface of M/T to prepare a cellulose-based adsorbent M/T-B with multiple active sites (nitrogen, oxygen and sulfur);
in the embodiment, microcrystalline cellulose with larger specific surface area is taken as a carrier, and a large amount of amino groups are introduced to the surface of the microcrystalline cellulose through crosslinking aiming at the chemical characteristics of functional groups and heavy metal ions
（-NH 2 ) And carboxyl (-COOH), amino (-NH) 2 ) And carboxyl (-COOH) are added to greatly improve the Ni content of the microcrystalline cellulose on heavy metal ions in the wastewater 2+ 、Pb 2+ And/or Cd 2+ The adsorption efficiency of the multi-active-site cellulose-based adsorbent is improved, and the preparation method of the multi-active-site cellulose-based adsorbent is simple and easy to operate, and is green and safe.
S2, preparing a nanofiber membrane:
s201, preparing a TNTs nano adsorbent: TNTS nano adsorbent is synthesized by adopting a hydrothermal method, and 1g of TiO is added into 50mL of 10mol/L NaOH solution 2 Stirring powder at 60 ℃ for reaction 1h to obtain milky suspension, carrying out ultrasonic treatment 1h, carrying out hydrothermal reaction 72 h in a high-pressure sealed hydrothermal reaction kettle at 160 ℃ and under 2.2MPa, cooling to room temperature, flushing a white precipitate with high-purity water until the pH value of a filtrate is 7.0, drying at 80 ℃ for 12h, and naturally cooling to room temperature to obtain TNTs nano adsorbent with the particle size of 2-5 nm;
TiO in the present embodiment 2 The powder is nano-scale anatase;
s202, sulfhydryl functional modification of TNTs nano adsorbent:
s20201, preparation of mixture A: mixing 1g of the TNTs nano adsorbent obtained in the step S201 with 100mL of acetone at room temperature, stirring for 1h, and performing ultrasonic treatment for 1h to obtain a mixture A;
s20202, preparation of mixture B: 12g of the silane coupling agent MPTMS (HS (CH) 2 ) 3 Si(OCH 3 ) 3 ) Dissolving in 50mL high-purity water to obtain a mixture B;
s20203, preparation of thiol-modified TNTs: dropwise adding the mixture A obtained in the step S20201 into the mixture B obtained in the step S20202, stirring for 2 hours at room temperature, centrifuging for 15 minutes at a rotating speed of 3000 rpm, collecting the obtained solid substance, washing 3 times with acetone, washing 3 times with high-purity water to remove ungrafted MPTMS and other impurities, drying 24h the washed solid substance at a temperature of 60 ℃ to obtain mercapto-functionalized TNTs, and naming the mercapto-functionalized TNTs as T/S-NPs;
the mass ratio of the TNTs nano adsorbent to the MPTMS is 3:1;
s203, preparing a nanofiber membrane: and preparing the nanofiber membrane by taking the PVC membrane as a sublayer and adopting an electrostatic spinning process.
S20301, preparation of PVC film:
drying PVC (DG 800, tianjin Dagu chemical plant) at 60deg.C for 24h to obtain dried PVC powder; placing the obtained dried PVC powder into N-methyl pyrrolidone, stirring for 12 hours at the temperature of 60 ℃ to obtain a N-methyl pyrrolidone solution of a PVC polymer with the mass fraction of 13.5%, degassing, scraping a film on a glass plate by a film casting knife, immersing in a high-purity water bath, transferring the film into another high-purity water bath for immersing for 24h after the film on the glass plate is peeled off, and drying at room temperature for 24 hours to obtain a PVC film; the dried PVC film is cut into rectangular slices of 6 cm multiplied by 9 cm for later use;
s20302, preparation of spinning solution:
dissolving the dried PVC polymer powder in N-methylpyrrolidone, and stirring for 12 hours at the temperature of 60 ℃ to obtain an N-methylpyrrolidone solution of the PVC polymer with the mass fraction of 15%;
dissolving 1g of the T/S-NPs obtained in S20203 in 30mL of N-methylpyrrolidone, and performing ultrasonic dispersion for 45 min to obtain an N-methylpyrrolidone mixture of the T/S-NPs;
dropwise adding the N-methylpyrrolidone solution of the PVC polymer with the mass fraction of 15% into the N-methylpyrrolidone mixture of the T/S-NPs, stirring for 2 hours at the temperature of 60 ℃, and carrying out degassing treatment to obtain a spinning solution;
s20303, preparation of an adsorptive nanofiber membrane: 15mL of the spinning solution obtained in S20302 was extracted by using a syringe equipped with a metal needle, and the syringe was mounted on a syringe pump of an automatic electrospinning apparatus. Placing six prepared PVC films obtained in S20301 in a rectangular shape on 6 rectangular aluminum foils, coiling the aluminum foils on a rotary drum-shaped collector of an electrospinning system, electrospinning on the surface of the PVC films, immersing in a water bath at 25 ℃ after electrospinning to remove residual solvent, separating the residual solvent from the aluminum foils, and drying at 60 ℃ after the films are separated from the aluminum foil discs to obtain nanofiber films;
the operation conditions of the electrospinning are as follows: the flow rate of the spinning solution is 1.5mL/h, the applied voltage is 18kv, the distance between the needle tip and the collector is 18.5cm, and the rotating speed of the collector is 240rpm; the temperature of the chamber in the electrospinning apparatus was 25 ℃ and the relative humidity was 70%;
the nanofiber ultrafiltration membrane with the surface loaded with the sulfhydryl (-SH) is simple, safe and environment-friendly. Thiol (-SH) -loaded nanofiber ultrafiltration membrane for heavy metal ion Ni 2+ 、Pb 2+ And/or Cd 2+ And the like have adsorption performance, so that the ultrafiltration membrane has two functions of removing heavy metal ions in the use process: on one hand, the adsorption function of sulfhydryl groups on the surface of the membrane and on the other hand, the interception function of the ultrafiltration membrane; heavy gold under double actionThe removal rate of the belonging ions is greatly improved.
S3, constructing an adsorption-ultrafiltration coupling method:
filling the adsorption column with the M/T-B obtained in the step S102 as a filler;
two nanofiber membranes obtained in S20303 were mounted to a flat plate ultrafiltration membrane set (GCM-F-04,
forming an ultrafiltration membrane module in national science and technology (Xiamen) limited company;
and (3) sequentially passing the wastewater containing the low-concentration heavy metal pollutants through the adsorption column and the ultrafiltration membrane component to finish purification, wherein the concentration of each heavy metal ion in the wastewater containing the low-concentration heavy metal pollutants is 0.01-mg/L to 0.1mg/L.
The heavy metal ions in the wastewater containing heavy metal pollutants comprise Ni 2+ 、Pb 2+ And/or Cd 2+ Ions;
the removal rate of each heavy metal ion in the purified wastewater containing heavy metal pollutants is more than 95 percent.
In this example, the heavy metal removal capacity of the adsorption-ultrafiltration coupling method was verified in two modes, namely laboratory preparation simulation wastewater and industrial wastewater (experimental test results are shown in example 2).
Laboratory simulated wastewater experimental design:
respectively by NiCl 2 ·6H 2 O、PbCl 2 、CdCl 2 Preparation of Ni for raw materials 2+ 、Pb 2+ And Cd 2+ The simulated wastewater with the concentration of 0.1mg/L is designed, the pH=6.5 of the wastewater is designed, the peristaltic pump is used for controlling the flow rate of the wastewater to be 5, 10, 20 and 50mL/min at room temperature, the wastewater sequentially passes through an adsorption column filled with cellulose-based adsorbent with multiple active sites and a nanofiber ultrafiltration membrane with heavy metal adsorption performance, water is collected, and the concentration of heavy metal ions in the wastewater is tested. The removal rates of the various heavy metal ions are shown in table 1.
TABLE 1 removal Rate of heavy Metal ions from wastewater at different flow rates of example 1
Example 2
The embodiment is a method for treating low-concentration heavy metal polluted wastewater by combining adsorption and ultrafiltration, which comprises the following steps:
s1, preparation of a multi-active site cellulose-based adsorbent (M/T-B):
s101, adding 1g of microcrystalline cellulose (MCC) into 20mL of 15% by mass of NaOH aqueous solution, uniformly stirring, adding 10g of Tetraethylenepentamine (TEPA), stirring at a speed of 500 r/min for 10min, placing in an ice bath, adding 23g of cross-linking agent Epichlorohydrin (ECH), continuously stirring for 10min until the mixture forms a solid state, then flushing with high-purity water until the pH value of the filtrate is 7.0, collecting a solid product, drying to constant weight at a temperature of 80 ℃ to obtain a cellulose-based adsorbent, and naming the cellulose-based adsorbent as M/T;
s102, dispersing 0.25g of bis (carboxymethyl) trithiocarbonate (BCTTC) and 0.5g of M/T obtained in S1 in high-purity water, stirring for 5 h at the temperature of 100 ℃, flushing with high-purity water until the pH value of filtrate is 7.0, collecting a solid product, and drying to constant weight at the temperature of 60 ℃ to obtain a multi-active-point cellulose-based adsorbent named M/T-B;
in the step, bis (carboxymethyl) trithiocarbonate (BCTTC) is grafted on the surface of M/T to prepare a cellulose-based adsorbent M/T-B with multiple active sites (nitrogen, oxygen and sulfur);
s2, preparing a nanofiber membrane:
s201, preparing a TNTs nano adsorbent: TNTS nano adsorbent is synthesized by adopting a hydrothermal method, and 1g of TiO is added into 50mL of 10mol/L NaOH solution 2 Stirring powder at 60 ℃ for reaction 1h to obtain milky suspension, carrying out ultrasonic treatment 1h, carrying out hydrothermal reaction 72 h in a high-pressure sealed hydrothermal reaction kettle at 160 ℃ and under 2.2MPa, cooling to room temperature, flushing a white precipitate with high-purity water until the pH value of a filtrate is 7.0, drying at 80 ℃ for 12h, and naturally cooling to room temperature to obtain TNTs nano adsorbent with the particle size of 2-5 nm;
TiO in the present embodiment 2 The powder is nano-scale anatase;
s202, sulfhydryl functional modification of TNTs nano adsorbent:
s20201, preparation of mixture A: mixing 1g of the TNTs nano adsorbent obtained in the step S201 with 100mL of acetone at room temperature, stirring for 1h, and performing ultrasonic treatment for 1h to obtain a mixture A;
s20202, preparation of mixture B: 12g of the silane coupling agent MPTMS (HS (CH) 2 ) 3 Si(OCH 3 ) 3 ) Dissolving in 50mL high-purity water to obtain a mixture B;
s20203, preparation of thiol-modified TNTs: dropwise adding the mixture A obtained in the step S20201 into the mixture B obtained in the step S20202, stirring for 2 hours at room temperature, centrifuging for 15 minutes at a rotating speed of 3000 rpm, collecting the obtained solid substance, washing with acetone for 4 times, washing with high-purity water for 4 times to remove ungrafted MPTMS and other impurities, and drying the washed solid substance at a temperature of 60 ℃ for 24h to obtain mercapto-functionalized TNTs, which are named as T/S-NPs;
the TNTs nanosorbent and MPTMS (HS (CH) 2 ) 3 Si(OCH 3 ) 3 ) The mass ratio of (2) to (1);
s203, preparing a nanofiber membrane: and preparing the nanofiber membrane by taking the PVC membrane as a sublayer and adopting an electrostatic spinning process.
S20301, preparation of PVC film:
drying PVC (DG 800, tianjin Dagu chemical plant) at 60deg.C for 24h to obtain dried PVC powder; placing the obtained dried PVC powder into N-methyl pyrrolidone, stirring for 12 hours at the temperature of 60 ℃ to obtain a N-methyl pyrrolidone solution of a PVC polymer with the mass fraction of 13.5%, degassing, scraping a film on a glass plate by a film casting knife, immersing in a high-purity water bath, transferring the film into another high-purity water bath for immersing for 24h after the film on the glass plate is peeled off, and drying at room temperature for 24 hours to obtain a PVC film; the dried PVC film is cut into rectangular slices of 6 cm multiplied by 9 cm for later use;
s20302, preparation of spinning solution:
dissolving the dried PVC polymer powder in N-methylpyrrolidone, and stirring for 12 hours at the temperature of 60 ℃ to obtain an N-methylpyrrolidone solution of the PVC polymer with the mass fraction of 15%;
dissolving 1g of the T/S-NPs obtained in S20203 in 30mL of N-methylpyrrolidone, and performing ultrasonic dispersion for 45 min to obtain an N-methylpyrrolidone mixture of the T/S-NPs;
dropwise adding the N-methylpyrrolidone solution of the PVC polymer with the mass fraction of 15% into the N-methylpyrrolidone mixture of the T/S-NPs, stirring for 2 hours at the temperature of 60 ℃, and degassing to obtain a spinning solution;
s20303, preparation of an adsorptive nanofiber membrane: the spinning solution 20mL obtained in S20302 was extracted with a syringe equipped with a metal needle, and the syringe was fitted to a syringe pump of an automatic electrospinning apparatus. Placing six prepared PVC films obtained in S20301 in a rectangular shape on 6 rectangular aluminum foils, coiling the aluminum foils on a rotary drum-shaped collector of an electrospinning system, electrospinning on the surface of the PVC films, immersing in a water bath at 25 ℃ after electrospinning to remove residual solvent, separating the residual solvent from the aluminum foils, and drying at 60 ℃ after the films are separated from the aluminum foil discs to obtain nanofiber films;
the operation conditions of the electrospinning are as follows: the flow rate of the spinning solution is 1.5mL/h, the applied voltage is 18kv, the distance between the needle tip and the collector is 18.5cm, and the rotating speed of the collector is 240rpm; the temperature of the chamber in the electrospinning apparatus was 25 ℃ and the relative humidity was 70%;
s3, constructing an adsorption-ultrafiltration coupling method:
filling the adsorption column with the M/T-B obtained in the step S102 as a filler;
two nanofiber membranes obtained in S20303 were mounted to a flat plate ultrafiltration membrane set (GCM-F-04,
forming an ultrafiltration membrane module in national science and technology (Xiamen) limited company;
the wastewater containing low-concentration heavy metal pollutants sequentially passes through the adsorption column and the ultrafiltration membrane component to finish purification; the concentration of each heavy metal ion in the wastewater containing the heavy metal pollutants is 0.1-mg/L to 0.01-mg/L.
The heavy metal ions in the wastewater containing heavy metal pollutants comprise Ni 2+ 、Pb 2+ And/or Cd 2+ Ions;
the removal rate of each heavy metal ion in the purified wastewater containing heavy metal pollutants is more than 95 percent.
In the embodiment, the heavy metal removal capacity of the adsorption-ultrafiltration coupling method is verified by two modes of laboratory preparation simulation wastewater and industrial wastewater.
Laboratory simulated wastewater experimental design:
respectively by NiCl 2 ·6H 2 O、PbCl 2 、CdCl 2 Preparation of Ni for raw materials 2+ 、Pb 2+ And Cd 2+ The simulated wastewater with the concentration of 0.1mg/L is designed, the pH=6.5 of the wastewater is designed, the peristaltic pump is used for controlling the flow rate of the wastewater to be 5, 10, 20 and 50mL/min at room temperature, the wastewater sequentially passes through an adsorption column filled with cellulose-based adsorbent with multiple active sites and a nanofiber ultrafiltration membrane with heavy metal adsorption performance, water is collected, and the concentration of heavy metal ions in the wastewater is tested. The removal rates of the various heavy metal ions are shown in table 2.
Table 2 example 2 corresponds to the removal rate of heavy metal ions from wastewater at different flow rates
Industrial wastewater experimental design: the wastewater of a certain farm is treated by an in-farm sewage treatment system to discharge Pb in the wastewater 2+ 、Ni 2+ And Cd 2+ The concentrations were 0.18mg/L, 0.092/mg/L and 0.009 mg/L, respectively, and the metal ion concentrations in the water before and after the deep treatment were as shown in Table 3, respectively, using the adsorption-ultrafiltration combinations of examples 1 and 2, and using a water inflow rate of 20 mL/min.
TABLE 3 removal Rate of heavy Metal ions before and after advanced treatment of aquaculture wastewater
Comparing the heavy metal index GB31574-2015 (see Table 4) of the industrial sewage discharge standard with the heavy metal index GB5749-2006 (see Table 4) of the sanitary standard of the residential drinking water, the concentration of the heavy metal in the discharged water of the farm is found to meet the heavy metal concentration related index of the industrial sewage discharge standard GB31574-2015, and the discharge requirement is met. However, after further treatment by the adsorption-ultrafiltration combination described in embodiments 1 and 2, the concentration of heavy metal ions therein completely meets the heavy metal concentration specified by the sanitary standard GB5749-2006 of resident drinking water, so the adsorption-ultrafiltration coupling method can realize the purification of low-concentration heavy metal polluted wastewater.
TABLE 4 heavy metal index excerpt from industry wastewater discharge Standard and resident drinking Water sanitation Standard
In the invention, ni 2+ 、Pb 2+ And/or Cd 2+ After the wastewater with the concentration of 0.01-mg/L to 0.1mg/L passes through an adsorption column filled with cellulose-based adsorbent with multiple active sites, ni 2+ 、Pb 2+ And/or Cd 2+ The removal rate of the waste water can reach more than 80 percent; then the wastewater passes through a nanofiber ultrafiltration membrane with heavy metal adsorption performance, ni 2+ 、Pb 2+ And/or Cd 2+ The removal rate of the wastewater can reach more than 95%, thereby realizing the purification of the wastewater polluted by low-concentration heavy metals.
The method for treating the low-concentration heavy metal polluted wastewater by the combined use of adsorption and ultrafiltration provided by the invention is a technical combined use scheme aiming at the situation that the concentration of heavy metal ions in the wastewater is low, the purification difficulty is increased, and the treated water is difficult to realize the large-scale recycling. The removal rate of heavy metal ions can reach more than 95% after the adsorption-ultrafiltration combination of the low-concentration heavy metal pollution wastewater is used, so that a plurality of water use indexes of the country and industry are met, and further the industrial treatment water is expected to be reused in a large range, and the efficient recycling of water resources is realized.
The above description is only of the preferred embodiments of the present invention, and is not intended to limit the present invention. Any simple modification, variation and equivalent variation of the above embodiments according to the technical substance of the invention still fall within the scope of the technical solution of the invention.
Claims (7)
1. A method for treating low-concentration heavy metal polluted wastewater by combining adsorption and ultrafiltration is characterized by comprising the following steps:
s1, preparing a multi-active-site cellulose-based adsorbent;
the preparation method of the multi-active-site cellulose-based adsorbent in S1 comprises the following steps:
s101, adding microcrystalline cellulose into a 15% NaOH aqueous solution, uniformly stirring, adding tetraethylenepentamine, stirring at a speed of 500 r-600 r/min for 10min, placing in an ice bath, adding epichlorohydrin, continuously stirring for 10-30 min until the mixture forms a solid state, then flushing with high-purity water until the pH value of the filtrate is 7.0, collecting a solid product, drying at 80 ℃ until the constant weight is obtained, and obtaining a cellulose-based adsorbent named M/T;
s102, dispersing bis (carboxymethyl) trithiocarbonate and M/T obtained in S101 in high-purity water, stirring for 5 h at the temperature of 100 ℃, flushing with high-purity water until the pH value of filtrate is 7.0, collecting a solid product, and drying to constant weight at the temperature of 60 ℃ to obtain a multi-active-point cellulose-based adsorbent named M/T-B;
s2, preparing an adsorptive nanofiber membrane;
the preparation method of the adsorptive nanofiber membrane in the S2 comprises the following steps:
s201, preparing a TNTs nano adsorbent: adding TiO into 10mol/L NaOH solution 2 Stirring the powder at 60deg.C for reaction 1h to obtain milky suspension, ultrasonic treating 1h, and hydrothermal reacting in a sealed hydrothermal reaction kettle at 160deg.C under 2.2MPaAfter 72 to h, cooling to room temperature, washing the white precipitate with high-purity water until the pH of the filtrate is 7.0, drying the washed white precipitate at 80 ℃ for 12 to h, and naturally cooling to room temperature to obtain the TNTs nano adsorbent; the particle size of the TNTs nano adsorbent in S201 is 2 nm-5 nm;
s202, sulfhydryl functional modification of TNTs nano adsorbent:
s20201, preparation of mixture A: mixing the TNTs nano adsorbent obtained in the step S201 with acetone at room temperature, stirring for 1h, and then carrying out ultrasonic treatment on the mixture for 1h to obtain a mixture A;
s20202, preparation of mixture B: dissolving MPTMS in high-purity water to obtain a mixture B;
s20203, preparation of thiol-modified TNTs: dropwise adding the mixture A obtained in the step S20201 into the mixture B obtained in the step S20202, stirring for 2 hours at room temperature, centrifuging for 15 minutes at a rotating speed of 3000 rpm, collecting the obtained solid substance, washing 3-4 times with acetone, washing 3-4 times with high-purity water, drying 24h the washed solid substance at a temperature of 60 ℃ to obtain mercapto-functional modified TNTs, and naming the TNTs as T/S-NPs;
s203, preparing a nanofiber membrane:
s20301, preparation of PVC film:
drying the PVC at the temperature of 60 ℃ for 24h to obtain dried PVC powder; placing the obtained dried PVC powder into N-methyl pyrrolidone, stirring for 12 hours at the temperature of 60 ℃ to obtain a N-methyl pyrrolidone solution of a PVC polymer with the mass fraction of 13.5%, degassing, scraping a film on a glass plate by a film casting knife, immersing in a high-purity water bath, transferring the film into another high-purity water bath for immersing for 24h after the film on the glass plate is peeled off, and drying at room temperature for 24 hours to obtain a PVC film;
s20302, preparation of spinning solution:
dissolving the dried PVC polymer powder in N-methylpyrrolidone, and stirring for 12 hours at the temperature of 60 ℃ to obtain an N-methylpyrrolidone solution of the PVC polymer with the mass fraction of 15%;
dissolving 1g of the T/S-NPs obtained in S20203 in 30mL of N-methylpyrrolidone, and performing ultrasonic dispersion for 45 min to obtain an N-methylpyrrolidone mixture of the T/S-NPs;
dropwise adding the N-methylpyrrolidone solution of the PVC polymer with the mass fraction of 15% into the N-methylpyrrolidone mixture of the T/S-NPs, stirring for 2 hours at the temperature of 60 ℃, and carrying out degassing treatment to obtain a spinning solution;
s20303, preparation of an adsorptive nanofiber membrane: the PVC film obtained in S20301 was placed on an aluminum foil tray,
electrospinning the spinning solution obtained in the step S20302 on the surface of the PVC film obtained in the step S20301, soaking in a water bath at 25 ℃ after electrospinning, and drying at 60 ℃ after the film is separated from the aluminum foil disc to obtain an adsorptive nanofiber film;
the operating conditions for electrospinning described in S20303 are: the flow rate of the spinning solution is 1.5mL/h, the applied voltage is 18kv, the distance between the needle tip and the collector is 18.5cm, and the rotating speed of the collector is 240rpm; the temperature of the chamber in the electrospinning apparatus was 25 ℃ and the relative humidity was 70%;
s3, constructing an adsorption-ultrafiltration coupling method:
filling an adsorption column with the multi-active-site cellulose-based adsorbent obtained in the step S1 as a filler;
installing the two adsorption nanofiber membranes obtained in the step S2 into a flat ultrafiltration membrane assembly to form an ultrafiltration membrane assembly;
the wastewater containing low-concentration heavy metal pollutants sequentially passes through the adsorption column and the ultrafiltration membrane component to finish purification; the concentration of each heavy metal ion in the wastewater containing the low-concentration heavy metal pollutants is 0.01-mg/L to 0.1mg/L.
2. The method for treating wastewater polluted by low concentration heavy metal as claimed in claim 1, wherein the heavy metal ions in the wastewater containing low concentration heavy metal pollutant in S3 include Ni 2+ 、Pb 2+ And/or Cd 2+ Ions.
3. The method for treating wastewater polluted by low concentration heavy metal by combined use of adsorption and ultrafiltration as claimed in claim 2, wherein the removal rate of each heavy metal ion in the wastewater containing low concentration heavy metal pollutant in S3 is more than 95%.
4. The method for treating wastewater polluted by low concentration heavy metals by combined use of adsorption and ultrafiltration as claimed in claim 1, wherein the dosage ratio of 15% NaOH aqueous solution, microcrystalline cellulose, tetraethylenepentamine and epichlorohydrin in S101 is 20mL:1g:10g:23g.
5. The method for treating wastewater contaminated with low concentration of heavy metals by combined use of adsorption-ultrafiltration according to claim 1, wherein the mass ratio of the bis (carboxymethyl) trithiocarbonate to the cellulose-based adsorbent in S102 is 1:2.
6. The method for treating wastewater polluted by low concentration heavy metal by combined use of adsorption and ultrafiltration as claimed in claim 1, wherein the concentration of NaOH solution and TiO in S201 is 10mol/L 2 The powder was used in a 50mL:1g ratio.
7. The method for treating wastewater polluted by low concentration heavy metals by combined use of adsorption and ultrafiltration according to claim 1, wherein the dosage ratio of the TNTs nano adsorbent to the acetone in S20201 is 1g to 100mL; the usage ratio of MPTMS and high purity water in S20202 was 12g:50mL; the mass ratio of the TNTs nano-adsorbent to the MPTMS in the S202 is 3:1.
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