CN114950151B - Flat membrane, membrane assembly, membrane distillation device and method for concentrating copper-containing wastewater - Google Patents
Flat membrane, membrane assembly, membrane distillation device and method for concentrating copper-containing wastewater Download PDFInfo
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D69/00—Semi-permeable membranes for separation processes or apparatus characterised by their form, structure or properties; Manufacturing processes specially adapted therefor
- B01D69/06—Flat membranes
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D61/00—Processes of separation using semi-permeable membranes, e.g. dialysis, osmosis or ultrafiltration; Apparatus, accessories or auxiliary operations specially adapted therefor
- B01D61/36—Pervaporation; Membrane distillation; Liquid permeation
- B01D61/364—Membrane distillation
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D63/00—Apparatus in general for separation processes using semi-permeable membranes
- B01D63/08—Flat membrane modules
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D63/00—Apparatus in general for separation processes using semi-permeable membranes
- B01D63/08—Flat membrane modules
- B01D63/081—Manufacturing thereof
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D67/00—Processes specially adapted for manufacturing semi-permeable membranes for separation processes or apparatus
- B01D67/0002—Organic membrane manufacture
- B01D67/0009—Organic membrane manufacture by phase separation, sol-gel transition, evaporation or solvent quenching
- B01D67/0011—Casting solutions therefor
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D67/00—Processes specially adapted for manufacturing semi-permeable membranes for separation processes or apparatus
- B01D67/0002—Organic membrane manufacture
- B01D67/0009—Organic membrane manufacture by phase separation, sol-gel transition, evaporation or solvent quenching
- B01D67/0013—Casting processes
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D67/00—Processes specially adapted for manufacturing semi-permeable membranes for separation processes or apparatus
- B01D67/0081—After-treatment of organic or inorganic membranes
- B01D67/0088—Physical treatment with compounds, e.g. swelling, coating or impregnation
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- C—CHEMISTRY; METALLURGY
- C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F1/00—Treatment of water, waste water, or sewage
- C02F1/44—Treatment of water, waste water, or sewage by dialysis, osmosis or reverse osmosis
- C02F1/447—Treatment of water, waste water, or sewage by dialysis, osmosis or reverse osmosis by membrane distillation
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D2323/00—Details relating to membrane preparation
- B01D2323/12—Specific ratios of components used
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D2325/00—Details relating to properties of membranes
- B01D2325/30—Chemical resistance
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- C—CHEMISTRY; METALLURGY
- C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F2101/00—Nature of the contaminant
- C02F2101/10—Inorganic compounds
- C02F2101/20—Heavy metals or heavy metal compounds
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- C—CHEMISTRY; METALLURGY
- C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F2103/00—Nature of the water, waste water, sewage or sludge to be treated
- C02F2103/10—Nature of the water, waste water, sewage or sludge to be treated from quarries or from mining activities
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
- Y02P10/00—Technologies related to metal processing
- Y02P10/20—Recycling
Abstract
The invention provides a preparation method of a hydrophobic flat membrane suitable for concentrating copper-containing wastewater, which comprises the following steps: s1, mixing an organic substance in a semi-crystalline polymer state, a pore-forming additive and an organic solvent at 50-70 ℃ to obtain a liquid to be defoamed; then, defoaming the liquid to be defoamed to obtain a casting film liquid; s2, performing preforming treatment on the casting film liquid to obtain a primary film; then, the primary membrane is soaked in alcohol weak non-solvent with the concentration of 60-80% and water in sequence to obtain a hydrophobic flat membrane with a mastoid structure; wherein the soaking time of the primary membrane in the alcohol weak non-solvent is 10-20s. Based on the preparation method, the hydrophobic flat membrane with the mastoid rough structure is obtained, has better mechanical property, hydrophobic property, anti-pollution property and copper interception property, has higher copper concentration efficiency, and is suitable for membrane distillation of copper-containing wastewater.
Description
Technical Field
The invention relates to membrane separation of copper in copper-containing wastewater, in particular to a flat membrane, a membrane assembly, a membrane distillation device and a method for concentrating copper-containing wastewater.
Background
Copper is widely used in industry or daily life as one of the first metals mined and used by humans. Currently, the grade of copper ores available for exploitation is lower and lower, and the exponentially increased copper yield leads to a large amount of copper-containing wastewater generated in the copper ore exploitation process, which can cause harm to the environment and even human health if the wastewater is not treated. The copper-containing wastewater is concentrated, so that the influence of the copper-containing wastewater on the environment can be reduced, and the treated copper concentrate can be recycled into a solvent extraction process, so that the problem that the solvent extraction treatment of low-concentration copper-containing wastewater has no economic benefit is solved.
In hydrometallurgy, the traditional copper concentration process usually adopts an ion exchange method, a precipitation method, solvent extraction and the like, but the traditional copper concentration process has the problems of complex process, economy, technology and efficiency limitation. The membrane distillation is used as a novel membrane separation technology, and uses the steam pressure difference at two sides of a hydrophobic membrane as a driving force to realize the separation of water and other non-volatile or low-volatile substances and simultaneously produce high-quality reuse water.
Membrane distillation is similar to the mechanism of distillation to some extent, and separation processes applicable to distillation can be theoretically replaced by the membrane distillation, such as fresh water production, wastewater treatment, concentration and crystallization of industrial products, and the like. The intervention of the membrane provides the membrane distillation with some unique advantages over conventional techniques, such as low temperature operation (and thus extended equipment life, suitability for heat sensitive material treatment, etc.), low grade energy use, high concentration levels, space savings, etc. Therefore, the membrane distillation can replace distillation to become one of effective schemes for concentrating copper-containing wastewater, and the concentrated solution is recovered by a traditional hydrometallurgical process. Although the use of membrane distillation for concentrating copper-containing wastewater has the above-described advantages, there are cases where mechanical properties, hydrophobic properties, anti-contamination properties and copper interception properties of the membrane are poor, and copper concentration efficiency is low in the actual concentration of copper-containing wastewater using membrane distillation.
In view of the foregoing, it would be desirable to provide a flat sheet membrane, membrane module, membrane distillation apparatus, and method for concentrating copper-containing wastewater that addresses or at least alleviates the above-described technical drawbacks of poor mechanical properties, hydrophobic properties, anti-fouling properties, and copper rejection properties of the membrane, as well as low copper concentration efficiency.
Disclosure of Invention
The invention aims to provide a flat membrane, a membrane component, a membrane distillation device and a method for concentrating copper-containing wastewater, so as to at least overcome the technical problems of poor mechanical property, hydrophobic property, pollution resistance and copper interception performance of the membrane and low copper concentration efficiency.
To achieve the above object, the present invention provides a method for preparing a hydrophobic flat membrane suitable for concentrating copper-containing wastewater, comprising the steps of:
s1, mixing an organic substance in a semi-crystalline polymer state, a pore-forming additive and an organic solvent at 50-70 ℃ to obtain a liquid to be defoamed; then, defoaming the liquid to be defoamed to obtain a casting film liquid;
s2, performing preforming treatment on the casting film liquid to obtain a primary film; then, the primary membrane is soaked in alcohol weak non-solvent with the concentration of 60-80% and water in sequence to obtain a hydrophobic flat membrane with a mastoid structure;
wherein the soaking time of the primary membrane in the alcohol weak non-solvent is 10-20s.
Further, the step S2 further includes: sequentially soaking the primary membrane in the alcohol weak non-solvent and the water to obtain a membrane to be modified;
and soaking the film to be modified into polydimethylsiloxane modified liquid to obtain the hydrophobic flat film.
Further, the polydimethylsiloxane modified liquid is prepared from polydimethylsiloxane and n-hexane, wherein the weight ratio of the polydimethylsiloxane in the polydimethylsiloxane modified liquid is 1-2%;
the soaking time of the film to be modified in the polydimethylsiloxane modifying liquid is not longer than 2 hours.
Further, the weight ratio of the organic matters in the semi-crystalline polymer state, the pore-forming additive and the organic solvent is 12-15:8-10:75-80;
the organic matter in a semi-crystalline polymer state comprises polyvinylidene fluoride;
the pore-forming additive comprises polyethylene glycol;
the organic solvent comprises N, N-dimethylacetamide;
the alcohol weak non-solvent is prepared from isopropanol and water, wherein the volume of the isopropanol accounts for 60-80% of the volume of the alcohol weak non-solvent.
Further, the defoaming process includes: standing the solution to be defoamed at 50-70 ℃ for 10-12h to obtain the casting solution;
the preforming process comprises the following steps: cooling the casting film liquid to room temperature, and scraping the cooled casting film liquid in a film scraping machine to prepare a film; and then, the film obtained after scraping stays in the air for 10-15s to obtain the primary film.
Further, in the step S2, the soaking time of the primary membrane in water is 24-72 hours.
The invention also provides a hydrophobic flat membrane suitable for concentrating copper-containing wastewater, which is prepared by adopting the preparation method according to any one of the above.
The invention also provides a membrane module suitable for concentrating copper-containing wastewater, comprising a hydrophobic flat membrane as described in any one of the above.
The invention also provides a direct contact membrane distillation device suitable for concentrating copper-containing wastewater, comprising the membrane assembly according to any one of the above.
The invention also provides a method for concentrating copper-containing wastewater, which adopts the membrane distillation device as set forth in any one of the above.
Compared with the prior art, the invention has at least the following advantages:
the invention provides a hydrophobic flat membrane with a mastoid rough structure, which has better mechanical property, hydrophobic property, anti-pollution property and copper interception property and higher copper concentration efficiency. And when polydimethylsiloxane is adopted for modification, low-surface-energy substances can be compounded on the surface of the polydimethylsiloxane, so that the performance of the mastoid rough structure hydrophobic flat membrane is further improved.
Specifically, the invention ensures that the hydrophobic flat membrane has a mastoid rough surface structure by regulating and controlling the volume ratio of isopropanol and water in the weak non-solvent, and ensures the mechanical property, the hydrophobic property and the anti-pollution property of the hydrophobic flat membrane, thereby improving the copper concentration rate on the whole. In addition, the invention adopts the surface coating method to introduce the polydimethylsiloxane, so that the flat membrane with good hydrophobicity, pollution resistance cavity and high retention rate can be further and effectively prepared, and the flat membrane has higher use value in the concentration of copper-containing wastewater; in addition, the preparation process is simple, and the material has good film forming performance and excellent performance, so that the material can be well applied to the fields of film separation, copper-containing wastewater concentration, acid mine wastewater treatment and the like.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings that are required in the embodiments or the description of the prior art will be briefly described, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and other drawings may be obtained according to the structures shown in these drawings without inventive effort for a person skilled in the art.
FIG. 1 is a schematic diagram of a direct contact membrane distillation apparatus according to the present invention;
FIG. 2 is a surface SEM image of a PVDF hydrophobic flat membrane of example 1;
FIG. 3 is a surface SEM image of a PVDF hydrophobic flat membrane of comparative example 1;
FIG. 4 is a surface SEM image of a PVDF hydrophobic flat membrane of comparative example 2;
FIG. 5 is a surface SEM image of a PVDF hydrophobic flat membrane of comparative example 3;
FIG. 6 is a surface SEM image of a PVDF hydrophobic flat membrane of example 2;
FIG. 7 is a surface SEM image of a PVDF hydrophobic flat membrane of comparative example 4.
Reference numerals: 1. a constant temperature water bath kettle; 2. a first reservoir; 3. a first peristaltic pump; 4. a first flowmeter; 5. a membrane module; 6. a second peristaltic pump; 7. a second flowmeter; 8. a condenser; 9. an electronic balance; 10. and a second liquid storage container.
The achievement of the object, functional features and advantages of the present invention will be further described with reference to the drawings in connection with the embodiments.
Detailed Description
The following description of the embodiments of the present invention will be made clearly and fully with reference to the accompanying drawings, in which it is evident that the embodiments described are only some, but not all embodiments of the invention. All other embodiments, based on the embodiments of the invention, which are apparent to those of ordinary skill in the art without inventive faculty, are intended to be within the scope of the invention.
Moreover, the technical solutions of the embodiments of the present invention may be combined with each other, but it is necessary to be based on the fact that those skilled in the art can implement the embodiments, and when the technical solutions are contradictory or cannot be implemented, it should be considered that the combination of the technical solutions does not exist, and is not within the scope of protection claimed by the present invention.
Where numerical ranges are provided in the examples, it is understood that unless otherwise stated herein, both endpoints of each numerical range and any number between the two endpoints are significant both in the numerical range. Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs and to which this invention belongs, and any method, apparatus, or material of the prior art similar or equivalent to the methods, apparatus, or materials described in the examples of this invention may be used to practice the invention.
It will be appreciated by those skilled in the art that although the copper feed stock in some embodiments of the present invention is CuSO 4 .5H 2 The concentration of O is prepared according to 100mg/L, but the initial copper content can float within a controllable range due to human errors in the preparation process of copper feed liquid and systematic errors in the measurement process of copper ions.
The invention provides a preparation method of a hydrophobic flat membrane suitable for concentrating copper-containing wastewater, which comprises the following steps:
s1, mixing an organic substance in a semi-crystalline polymer state, a pore-forming additive and an organic solvent at a temperature of 50-70 ℃ (stirring and mixing can be carried out under the heating of a constant-temperature water bath kettle, and the mixing time period can be 10 hours) to obtain a liquid to be defoamed; and then, defoaming the liquid to be defoamed to obtain the casting film liquid.
S2, performing preforming treatment on the casting film liquid to obtain a primary film; and then the primary membrane is soaked in alcohol weak non-solvent with the concentration of 60-80% and water in sequence to obtain the hydrophobic flat membrane with the mastoid structure.
Wherein, the soaking of the primary membrane in the weak non-solvent of alcohols and the soaking in water are coagulation baths. The soaking time of the primary membrane in the alcohol weak non-solvent is 10-20s; the soaking time of the primary membrane in water is 24-72h, and water can be changed for multiple times when the primary membrane is soaked in water, so that residual solvent is removed. In addition, after the completion of the above-described soaking, the primary film after the soaking may be dried in a freeze dryer to obtain the hydrophobic flat sheet film.
It is known that in the research and development process, the invention discovers that after the primary membrane is soaked in alcohol weak non-solvent with the concentration of about 60-80%, the hydrophobic flat membrane can have a mastoid rough structure, so that the hydrophobicity of the hydrophobic flat membrane is improved, and the pollution resistance and copper concentration rate of the hydrophobic flat membrane are ensured.
For example: as can be seen from example 1, when the coagulation bath (soaking) is carried out by adopting 70% concentration alcohol weak non-solvent, the hydrophobic flat membrane has a mastoid rough surface structure, and the mechanical property and the hydrophobic property of the hydrophobic flat membrane can be ensured.
In order to further improve the use performance of the hydrophobic plate film, the step S2 may further include: sequentially soaking the primary membrane in the weak alcohol non-solvent and water to obtain a membrane to be modified;
and soaking the film to be modified into polydimethylsiloxane modified liquid to obtain the hydrophobic flat film.
The polydimethylsiloxane modified liquid is prepared from polydimethylsiloxane and n-hexane, wherein the weight ratio of the polydimethylsiloxane in the polydimethylsiloxane modified liquid is 1-2%. In addition, the film to be modified generally needs to be freeze-dried before being immersed in the polydimethylsiloxane modifying liquid; after the operation of immersing the film to be modified in the polydimethylsiloxane modifying liquid is completed, the film after the modification is dried and cured in a vacuum drying oven at 60 ℃ for 10 hours, so that the hydrophobic flat plate film is obtained.
The soaking time of the film to be modified in the polydimethylsiloxane modifying liquid is not longer than 2 hours.
From example 2, it can be seen that the hydrophobic flat membrane was modified with Polydimethylsiloxane (PDMS) to increase the hydrophobicity of the hydrophobic flat membrane and obtain superior contamination resistance and copper concentration, based on the 70% concentration of the weak non-solvent of alcohols for coagulation bath.
In the present invention, it is to be understood that the weight ratio of the organic substance in the semi-crystalline polymer state, the pore-forming additive and the organic solvent may be 12-15:8-10:75-80, and may be specifically 15:10:75. The organic matter in a semi-crystalline polymer state comprises polyvinylidene fluoride; the pore-forming additive comprises polyethylene glycol; the organic solvent comprises N, N-dimethylacetamide; the alcohol weak non-solvent is prepared from isopropanol and water, wherein the volume ratio of the isopropanol in the alcohol weak non-solvent is 60-80%. In addition, the organic powder in the semi-crystalline polymer state generally needs to be dried at 60 ℃ for 12 hours to remove moisture before mixing the above several substances.
As an explanation of the defoaming process, the process of the defoaming process includes: and standing the solution to be defoamed at the temperature of 50-70 ℃ for 10-12h to obtain the casting solution.
As an illustration of the preforming process, the preforming process includes: cooling the casting film liquid to room temperature, and scraping the cooled casting film liquid in a film scraping machine to prepare a film; and then, the film obtained after scraping stays in the air for 10-15s to obtain the primary film.
Based on the preparation method, the invention also provides a hydrophobic flat membrane suitable for concentrating copper-containing wastewater, which is prepared by adopting the preparation method according to any one of the above.
The invention also provides a membrane module suitable for concentrating copper-containing wastewater, comprising a hydrophobic flat membrane as described in any one of the above.
The invention also provides a direct contact membrane distillation device suitable for concentrating copper-containing wastewater, comprising the membrane assembly according to any one of the above.
The invention also provides a method for concentrating copper-containing wastewater, which adopts the membrane distillation device as set forth in any one of the above.
It will be appreciated by those skilled in the art that the direct contact membrane distillation apparatus generally comprises a thermal circulation mechanism, a cold circulation mechanism and a membrane module 5, as shown in fig. 1, with the membrane module 5 being divided into relatively isolated hot and cold chambers by flat membranes. Wherein, the hot chamber is communicated with the thermal circulation mechanism and forms a thermal circulation loop together with the thermal circulation mechanism; the cold chamber is communicated with the cold circulation mechanism and forms a cold circulation loop together with the cold circulation mechanism.
In addition, in the thermal cycle mechanism, besides the pipeline for circulation, a constant-temperature water bath 1, a first liquid storage container 2, a first peristaltic pump 3, a first flowmeter 4, a thermometer (T), a pressure gauge (P) and other components are generally required to be arranged; in the cold circulation mechanism, in addition to the piping for circulation, the second peristaltic pump 6, the second flowmeter 7, the condenser 8, the second reservoir 10, the thermometer (T), the pressure gauge (P) and the like are generally required, and of course, an electronic balance 9 and a conductivity meter (K) may be provided to monitor the water in the reservoir.
In the invention, when a test for concentrating copper-containing wastewater is carried out, the copper-containing wastewater (copper feed liquid) is placed in a first liquid storage container 2 of a thermal circulation mechanism, the first liquid storage container 2 is placed in a constant-temperature water bath 1, the copper-containing wastewater is heated to 65 ℃ by the constant-temperature water bath 1, and the copper-containing wastewater circularly flows at a flow rate of 120mL/min (a flow rate flowing to a first flowmeter) under the driving of a first peristaltic pump 3. At this time, deionized water is placed in the second liquid storage container 10 of the cold circulation mechanism, and the deionized water is driven by the second peristaltic pump 6 to flow circularly through the cold chamber of the membrane assembly 5 at a flow rate of 40mL/min (the flow rate flowing to the second flowmeter), and the temperature of the deionized water is reduced to 15 ℃ by the condenser in the circulating flow process.
After the heated copper-containing wastewater flows to the hot chamber of the membrane assembly 5, hot steam in the copper-containing wastewater passes through the hydrophobic flat membrane to enter the cold chamber and is fused into ionized water, so that concentration of copper ions in the copper-containing wastewater is realized.
To facilitate a further understanding of the invention by those skilled in the art, reference is now made to the accompanying drawings, in which:
in the examples and comparative examples described below, PVDF6020 was used, commercially available from Suwei corporation, having a molecular weight of 68 to 80 ten thousand; PDMS used was purchased from Dow Corning; the PEG-400 used was purchased from Tianjin Miou chemical reagent Co., ltd and had an average molecular weight of 400; the copper-containing wastewater contains Cu 2+ 、Ca 2+ 、SO 4 2- 。
Example 1:
in this example, a 70% IPA coagulation bath was used and PDMS modification was not performed.
The method specifically comprises the following steps:
1. preparation of casting solution
Mixing polyvinylidene fluoride (PVDF 6020), polyethylene glycol (PEG-400) and N, N-dimethylacetamide (DMAc) according to weight percentages of 15wt%, 10wt% and 75wt% at 60 ℃ and stirring for 10 hours until uniform; then standing and defoaming for 10 hours at the constant temperature of 60 ℃ in a vacuum drying oven to obtain the casting film liquid.
2. Preparation of PVDF hydrophobic flat membrane
Cooling the casting film liquid to room temperature, and setting the height of a scraper of an automatic film scraping machine to be 500 mu m; then starting an automatic film scraping machine to uniformly coat the casting film liquid on the surface of the glass plate, and standing the scraped film in the air for 15s after the film is scraped by the automatic film scraping machine to obtain a primary film;
soaking the primary membrane in a weak non-solvent coagulation bath for 15s, transferring the primary membrane into a deionized water (DI) coagulation bath for soaking, soaking in deionized water for 3 days to remove residual solvent (three times of water exchange), and freeze-drying at-45 ℃ for 6h after soaking to obtain the PVDF hydrophobic flat membrane.
Wherein, the weak non-solvent is prepared by Isopropanol (IPA) and deionized water (DI) according to a volume ratio of 70:30.
3. Performance test of PVDF hydrophobic flat membrane
The SEM image of the surface of the PVDF hydrophobic flat membrane in this example is shown in fig. 2, and it can be seen by analysis: the PVDF hydrophobic flat membrane surface is formed by mastoid structure;
in this example, the PVDF hydrophobic flat film measured by the contact angle meter test has a water contact angle of: 120.32 °;
the mechanical properties of the PVDF hydrophobic flat membrane in this example are: the elongation at break is 22.67%, the tensile strength is 0.364MPa, and the mechanical property in the embodiment can ensure the normal use of the PVDF hydrophobic flat membrane.
Comparative example 1
In this comparative example, a 0% IPA coagulation bath was used and PDMS modification was not performed.
The method specifically comprises the following steps:
1. preparation of casting solution
Uniformly mixing polyvinylidene fluoride (PVDF 6020), polyethylene glycol (PEG-400) and N, N-dimethylacetamide (DMAc) according to the weight percentages of 15wt%, 10wt% and 75wt% at 60 ℃; then standing and defoaming for 10 hours at the constant temperature of 60 ℃ in a vacuum drying oven to obtain the casting film liquid.
2. Preparation of PVDF flat membrane
Cooling the casting film liquid to room temperature, and setting the height of a scraper of an automatic film scraping machine to be 500 mu m; then starting an automatic film scraping machine to uniformly coat the casting film liquid on the surface of the glass plate, and standing the scraped film in the air for 15s after the film is scraped by the automatic film scraping machine to obtain a primary film;
soaking the primary membrane in a weak non-solvent coagulation bath for 15s, transferring the primary membrane into a deionized water (DI) coagulation bath for soaking, soaking in deionized water for 3 days to remove residual solvent (three times of water exchange), and freeze-drying at-45 ℃ for 6h after soaking to obtain the PVDF flat membrane.
Wherein, the weak non-solvent is prepared by Isopropanol (IPA) and deionized water (DI) according to the volume ratio of 0:100.
3. Performance test of PVDF flat film
The SEM image of the surface of the PVDF flat membrane in this comparative example is shown in fig. 3, and it can be seen from the analysis: the PVDF flat membrane has smooth and compact surface and small porosity;
the PVDF flat film in this comparative example measured the water contact angle by the contact angle meter test as follows: 76.12 °;
the mechanical properties of the PVDF flat membrane in this comparative example are: the elongation at break was 47.67% and the tensile strength was 2.20MPa.
Comparative example 2
In this comparative example, 50% IPA coagulation bath was used and PDMS modification was not performed.
The method specifically comprises the following steps:
1. preparation of casting solution
Uniformly mixing polyvinylidene fluoride (PVDF 6020), polyethylene glycol (PEG-400) and N, N-dimethylacetamide (DMAc) according to the weight percentages of 15wt%, 10wt% and 75wt% at 60 ℃; then standing and defoaming for 10 hours at the constant temperature of 60 ℃ in a vacuum drying oven to obtain the casting film liquid.
2. Preparation of PVDF hydrophobic flat membrane
Cooling the casting film liquid to room temperature, and setting the height of a scraper of an automatic film scraping machine to be 500 mu m; then starting an automatic film scraping machine to uniformly coat the casting film liquid on the surface of the glass plate, and standing the scraped film in the air for 15s after the film is scraped by the automatic film scraping machine to obtain a primary film;
soaking the primary membrane in a weak non-solvent coagulation bath for 15s, transferring the primary membrane into a deionized water (DI) coagulation bath for soaking, soaking in deionized water for 3 days to remove residual solvent (three times of water exchange), and freeze-drying at-45 ℃ for 10h after soaking to obtain the PVDF hydrophobic flat membrane.
Wherein, the weak non-solvent is prepared by Isopropanol (IPA) and deionized water (DI) according to the volume ratio of 50:50.
3. Performance test of PVDF hydrophobic flat membrane
The SEM image of the surface of the PVDF hydrophobic flat membrane in this comparative example is shown in fig. 4, and it can be seen from the analysis: the PVDF hydrophobic flat membrane surface is compact, and the mastoid structure is not completely formed;
the PVDF hydrophobic flat film in this comparative example measured the water contact angle by the contact angle meter test as follows: 90 °;
the mechanical properties of the PVDF hydrophobic flat membrane in this comparative example are: the elongation at break was 50.72% and the tensile strength was 0.67MPa.
Comparative example 3
In this comparative example, 100% IPA coagulation bath was used and PDMS modification was not performed.
The method specifically comprises the following steps:
1. preparation of casting solution
Uniformly mixing polyvinylidene fluoride (PVDF 6020), polyethylene glycol (PEG-400) and N, N-dimethylacetamide (DMAc) according to the weight percentages of 15wt%, 10wt% and 75wt% at 60 ℃; then standing and defoaming for 10 hours at the constant temperature of 60 ℃ in a vacuum drying oven to obtain the casting film liquid.
2. Preparation of PVDF hydrophobic flat membrane
Cooling the casting film liquid to room temperature, and setting the height of a scraper of an automatic film scraping machine to be 500 mu m; then starting an automatic film scraping machine to uniformly coat the casting film liquid on the surface of the glass plate, and standing the scraped film in the air for 15s after the film is scraped by the automatic film scraping machine to obtain a primary film;
soaking the primary membrane in a weak non-solvent coagulation bath for 15s, transferring the primary membrane into a deionized water (DI) coagulation bath for soaking, soaking in deionized water for 3 days to remove residual solvent (three times of water exchange), and freeze-drying at-45 ℃ for 10h after soaking to obtain the PVDF hydrophobic flat membrane.
Wherein, the weak non-solvent is prepared by Isopropanol (IPA) and deionized water (DI) according to the volume ratio of 100:0.
3. Performance test of PVDF hydrophobic flat membrane
The SEM image of the surface of the PVDF hydrophobic flat membrane in this comparative example is shown in fig. 5, and it can be seen from the analysis: the PVDF hydrophobic flat membrane surface is composed of mutually connected spherulitic particles, and the pores are larger;
the PVDF hydrophobic flat film in this comparative example measured the water contact angle by the contact angle meter test as follows: 136.23 °;
the mechanical properties of the PVDF hydrophobic flat membrane in this comparative example are: elongation at break of 21.57% and tensile strength of 0.144MPa; the PVDF hydrophobic flat membrane in this comparative example had poor mechanical properties and could not be used normally.
Example 2
In this example, a 70% IPA coagulation bath was used to modify 1% PDMS.
The method specifically comprises the following steps:
1. preparation of casting solution
Uniformly mixing polyvinylidene fluoride (PVDF 6020), polyethylene glycol (PEG-400) and N, N-dimethylacetamide (DMAc) according to the weight percentages of 15wt%, 10wt% and 75wt% at 60 ℃; then standing and defoaming for 10 hours at the constant temperature of 60 ℃ in a vacuum drying oven to obtain the casting film liquid.
2. Preparation of the film to be modified
Cooling the casting film liquid to room temperature, and setting the height of a scraper of an automatic film scraping machine to be 500 mu m; then starting an automatic film scraping machine to uniformly coat the casting film liquid on the surface of the glass plate, and standing the scraped film in the air for 15s after the film is scraped by the automatic film scraping machine to obtain a primary film;
the primary film was immersed in a weak non-solvent coagulation bath for 15s, then transferred to a deionized water (DI) coagulation bath for immersing, and immersed in deionized water for 3 days to remove the residual solvent (three times of water exchange in between), and freeze-dried at-45 ℃ for 10 hours after the immersing was completed, to obtain the film to be modified.
Wherein, the weak non-solvent is prepared by Isopropanol (IPA) and deionized water (DI) according to a volume ratio of 70:30.
3. Modified preparation of PVDF flat membrane
Immersing the membrane to be modified into 1% PDMS modified liquid for 1h, and after the immersing is completed, putting the membrane into a vacuum drying oven for drying and curing at 60 ℃ for 10h to obtain the PVDF hydrophobic flat membrane.
Wherein, the PDMS modified liquid is prepared from Polydimethylsiloxane (PDMS) and n-hexane (solvent) according to the following ratio of 1:99 is prepared by mixing at normal temperature.
4. Performance test of PVDF hydrophobic flat membrane
The SEM image of the surface of the PVDF hydrophobic flat membrane in this example is shown in fig. 6, and it can be seen by analysis: the PVDF hydrophobic flat membrane surface consists of mastoid structures; the mastoid structure is coated with a PDMS coating;
in this example, the PVDF hydrophobic flat film measured by the contact angle meter test has a water contact angle of: 123.17 °;
the mechanical properties of the PVDF hydrophobic flat membrane in this example are: the elongation at break can reach 41.75%, the tensile strength is 0.563MPa, and compared with the unmodified example 1, the stress and strain are greatly improved while the water contact angle is ensured.
Example 3
Direct contact Membrane distillation concentration copper-containing wastewater experiments on PVDF hydrophobic Flat Membrane in example 2
1. CuSO in copper feed solution 4 .5H 2 The concentration of O is 100mg/L, caCl 2 The concentration of (C) is 40mg/L. Carrying out direct contact membrane distillation concentration on copper feed liquid by adopting the PVDF hydrophobic flat membrane in the embodiment 2, wherein the concentration time is 8 hours;
the results showed that the permeation flux at 1h was 13.6kg/m 2 ·h 1 The permeation flux at 8h is 14.73kg/m 2 ·h 1 The method comprises the steps of carrying out a first treatment on the surface of the After 8h of concentration, cu 2+ The concentration is increased from 31.42mg/L to 39.62mg/L, and the concentration efficiency is 1.26 times.
2. CuSO in copper feed solution 4 .5H 2 The concentration of O is 150mg/L, caCl 2 The concentration of (C) is 40mg/L. Carrying out direct contact membrane distillation concentration on copper feed liquid by adopting the PVDF hydrophobic flat membrane in the embodiment 2, wherein the concentration time is 8 hours;
the results showed that the permeation flux at 1h was 13.93kg/m 2 ·h 1 The permeation flux at 8h was 11.33kg/m 2 ·h 1 The method comprises the steps of carrying out a first treatment on the surface of the After 8h of concentration, cu 2+ The concentration is improved from 43.13mg/L to 55.38mg/L, and the concentration efficiency is 1.28 times.
3. CuSO in copper feed solution 4 .5H 2 The concentration of O is 200mg/L, caCl 2 The concentration of (C) is 40mg/L. Carrying out direct contact membrane distillation concentration on copper feed liquid by adopting the PVDF hydrophobic flat membrane in the embodiment 2, wherein the concentration time is 8 hours;
the results showed that the permeation flux at 1h was 13.13kg/m 2 ·h 1 The permeation flux at 8h is12.73kg/m 2 ·h 1 The method comprises the steps of carrying out a first treatment on the surface of the After 8h of concentration, cu 2+ The concentration is increased from 59.15mg/L to 74.05mg/L, and the concentration efficiency is 1.35 times.
Comparative example 4
In this comparative example, 2% PDMS modification was performed using a 90% IPA coagulation bath.
The method specifically comprises the following steps:
1. preparation of casting solution
Uniformly mixing polyvinylidene fluoride (PVDF 6020), polyethylene glycol (PEG-400) and N, N-dimethylacetamide (DMAc) according to the weight percentages of 15wt%, 10wt% and 75wt% at 60 ℃; then standing and defoaming for 10 hours at the constant temperature of 60 ℃ in a vacuum drying oven to obtain the casting film liquid.
2. Preparation of the film to be modified
Cooling the casting film liquid to room temperature, and setting the height of a scraper of an automatic film scraping machine to be 500 mu m; then starting an automatic film scraping machine to uniformly coat the casting film liquid on the surface of the glass plate, and standing the scraped film in the air for 15s after the film is scraped by the automatic film scraping machine to obtain a primary film;
the primary film was immersed in a weak non-solvent coagulation bath for 15s, then transferred to a deionized water (DI) coagulation bath for immersing, and immersed in deionized water for 3 days to remove the residual solvent (three times of water exchange in between), and freeze-dried at-45 ℃ for 10 hours after the immersing was completed, to obtain the film to be modified.
Wherein, the weak non-solvent is prepared by Isopropanol (IPA) and deionized water (DI) according to the volume ratio of 90:10.
3. Modified preparation of PVDF flat membrane
Immersing the membrane to be modified into 2% PDMS modified liquid for 1h, and after the immersing is completed, putting the membrane into a vacuum drying oven for drying and curing at 60 ℃ for 10h, thus obtaining the PVDF hydrophobic flat membrane.
Wherein, the PDMS modified liquid is prepared by mixing Polydimethylsiloxane (PDMS) and n-hexane (solvent) according to the weight ratio of 2:98 at normal temperature.
4. Performance test of PVDF hydrophobic flat membrane
The SEM image of the surface of PVDF hydrophobic flat membrane in this comparative example is shown in fig. 7, and it can be seen from the analysis: the PVDF hydrophobic flat membrane surface consists of mutually connected spherulitic particles; the spherulitic structure is covered by a PDMS coating;
the PVDF hydrophobic flat film in this comparative example measured the water contact angle by the contact angle meter test as follows: 140.44 °;
the mechanical properties of the PVDF hydrophobic flat membrane in this comparative example are: the elongation at break was 57.78% and the tensile strength was 0.771MPa.
5. Direct contact type membrane distillation copper-containing wastewater concentration experiment for PVDF hydrophobic flat membrane
CuSO in copper feed solution 4 .5H 2 The concentration of O is 100mg/L, caCl 2 The concentration of (C) is 40mg/L. The PVDF hydrophobic flat membrane in the comparative example is adopted to carry out direct contact membrane distillation concentration on copper feed liquid, and the concentration time is 8 hours;
the results showed that the permeation flux at 1h was 21.53kg/m 2 ·h 1 The permeation flux at 8h was 26.27kg/m 2 ·h 1 The method comprises the steps of carrying out a first treatment on the surface of the After 8h of concentration, cu 2+ The concentration is improved from 29.5mg/L to 32.46mg/L, and the concentration efficiency is 1.1 times.
In the above technical solution of the present invention, the above is only a preferred embodiment of the present invention, and therefore, the patent scope of the present invention is not limited thereto, and all the equivalent structural changes made by the description of the present invention and the content of the accompanying drawings or the direct/indirect application in other related technical fields are included in the patent protection scope of the present invention.
Claims (3)
1. A method for concentrating copper-containing wastewater, which is characterized in that a direct contact type membrane distillation device is adopted for concentrating copper-containing wastewater, and a membrane component of the direct contact type membrane distillation device comprises a hydrophobic flat membrane;
the preparation method of the hydrophobic flat membrane comprises the following steps:
s1, mixing an organic substance in a semi-crystalline polymer state, a pore-forming additive and an organic solvent at 50-70 ℃ to obtain a liquid to be defoamed; then, defoaming the liquid to be defoamed to obtain a casting film liquid;
the weight ratio of the organic matters in the semi-crystalline polymer state, the pore-forming additive and the organic solvent is 12-15:8-10:75-80; the organic matter in a semi-crystalline polymer state comprises polyvinylidene fluoride; the pore-forming additive comprises polyethylene glycol; the organic solvent comprises N, N-dimethylacetamide;
s2, performing preforming treatment on the casting film liquid to obtain a primary film;
sequentially soaking the primary membrane in an alcohol weak non-solvent with the concentration of 60-80% and water to obtain a membrane to be modified; soaking the membrane to be modified into polydimethylsiloxane modified liquid to obtain a hydrophobic flat membrane with a mastoid structure;
wherein the alcohol weak non-solvent is prepared from isopropanol and water, and the volume of the isopropanol accounts for 60-80% of the alcohol weak non-solvent; the soaking time of the primary membrane in the alcohol weak non-solvent is 10-20s; the soaking time of the primary membrane in water is 24-72h;
the weight ratio of the polydimethylsiloxane to the polydimethylsiloxane modified liquid is 1-2%, and the soaking time of the film to be modified in the polydimethylsiloxane modified liquid is 1-2h.
2. The method of concentrating copper-containing wastewater of claim 1 wherein the polydimethylsiloxane modification solution is formulated from polydimethylsiloxane and n-hexane.
3. The method for concentrating copper-containing wastewater according to claim 1, wherein the defoaming treatment comprises: standing the solution to be defoamed at 50-70 ℃ for 10-12h to obtain the casting solution;
the preforming process comprises the following steps: cooling the casting film liquid to room temperature, and scraping the cooled casting film liquid in a film scraping machine to prepare a film; and then, the film obtained after scraping stays in the air for 10-15s to obtain the primary film.
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