CN110745913B - Method for electro-membrane extraction and enrichment of chromium (VI) by quaternary ammonium salt type polymer ionic liquid membrane - Google Patents
Method for electro-membrane extraction and enrichment of chromium (VI) by quaternary ammonium salt type polymer ionic liquid membrane Download PDFInfo
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Abstract
The invention discloses an electric membrane extraction and enrichment method of a quaternary ammonium salt polymer ionic liquid membrane for chromium (VI), which comprises the steps of carrying out reactive blending on polyvinyl chloride and tri-n-octylamine in an organic solvent in the presence of a plasticizer, volatilizing to remove the solvent to prepare the quaternary ammonium salt polymer ionic liquid membrane, and carrying out electric membrane extraction mass transfer and continuous extraction and enrichment of chromium (VI) under the coupling of the quaternary ammonium salt polymer ionic liquid membrane and an external electric field. The quaternary ammonium salt type polymer ionic liquid membrane provided by the invention has the advantages of simple and convenient preparation process, high selectivity, strong stability, difficult leakage of membrane phase under the voltage impact of an external electric field and the mechanical shearing force of liquid and strong tolerance. Under the condition of the operation of the electric membrane extraction, the mass transfer rate of the chromium (VI) passing through the polymer ion liquid membrane is higher than that of the common membrane extraction technology, the operation is simple, convenient and flexible, the energy consumption is low, and no secondary pollution is caused. Is a high-stability membrane product with higher selectivity and faster mass transfer rate to chromium (VI) and a separation method thereof.
Description
Technical Field
The invention belongs to the technical field of environmental monitoring, protection and wastewater treatment, and relates to a preparation method of a high-stability quaternary ammonium salt polymer ionic liquid membrane modified by a plasticizer, and an electric membrane extraction technology for chromium (VI) under the coupling drive of an external electric field.
Background
The industrial wastewater such as heavy metals of chromium, lead, mercury, cadmium and the like has rich sources. For example, in various industrial processes such as tanning, papermaking, cooling tower pollution discharge, electroplating, electrolysis, anodic oxidation tanks and the like, a large amount of chromium (VI) containing wastewater is generated. However, chromium (VI) is a toxic heavy metal, the emission limit of China to industrial chromium is 1mg/L, and the maximum allowable limit of chromium (VI) in inland water areas and drinking water is only below 0.1 and 0.05 mg/L. Therefore, the comprehensive treatment technology of chromium (VI) wastewater has been a relatively sensitive concern in the related industry field.
In the patent technology N104030478A, FeSO is added into chromium (VI) -containing wastewater4、NaHSO3、SO2Iron powder or the like reduces chromium (VI) to chromium (III), and adjusts the pH value to produce Cr (OH)3Precipitating to finally reduce the chromium (VI) concentration to below 0.5 mg/L. The method has good effect of removing chromium (VI) and simple and convenient process. However, the technologies or methods for removing chromium (VI) such as chemical precipitation and coagulation can only simply cure chromium and other metals into mixed solid waste, and not only needs more chemical substances and is difficult to reach the standard, but also cannot effectively recycle valuable metals including chromium, and secondary pollution exists. Extraction, adsorption and other methods are selective extraction technologies for effectively recycling low-concentration substances. In patent technology CN105986125A, a method of back extraction with organic reducing agent ethanol by using trialkyl ammonium chloride, trioctyl ammonium chloride and methyl trioctyl ammonium chloride as extracting agents is proposed to treat chromium (VI) -containing wastewater. The method realizes the standard removal of chromium (VI) in the wastewater through two-step one-stage or multi-stage countercurrent extraction and back extraction. However, the operation process provided by the patent is complicated, a large amount of protective agents such as n-octane and ethanol, and chemical substances such as a back extractant are used in the extraction process, and the regenerated raffinate of the extractant also brings serious harm to the environment. Compared with liquid-liquid extraction, the liquid membrane extraction technology can synchronously carry out extraction and back extraction, the operation is simple and convenient, and the secondary pollution is less. In the research on hexavalent chromium separation by a back-extraction phase pre-dispersion supported liquid membrane and a mass transfer mechanism thereof (leiying, master thesis of Harbin Industrial university, 2015), tris (octyl-decyl) alkyl tertiary amine (N235) is used as an extractant to remove chromium (VI) in water by a back-extraction phase pre-dispersion supported liquid membrane method, and a foundation is provided for resource separation and recovery of heavy metals to a certain extent. But the instability of the supported liquid membrane limits the further industrial application of the process.
The polymer-contained film has good stability compared with a supported liquid film, and Kagaya S, Maeno T, Ito K (Analytical Sciences,2017,33(5):643-646) and the like propose a method for removing chromium (VI) by using the polymer-contained liquid film prepared by taking ionic liquid Aliquat 336 as a carrier, but related experiments of the document show that the polymer-contained liquid film taking the ionic liquid as the carrier has the potential of instability. Therefore, the small molecule type liquid membrane technology still has the problems that a liquid phase carrier is easy to leak and the mass transfer process is unstable, and the mass transfer rate of the polymer contained liquid membrane is limited, so that the liquid membrane has a larger bottleneck in the aspect of industrial application due to the reasons.
Disclosure of Invention
The invention aims to provide an electric film extraction and enrichment method for chromium (VI) based on a modified quaternary ammonium salt type polymer ionic liquid film and an electric film extraction and enrichment technology for chromium (VI) under the reinforcement of an external electric field. The invention aims to provide a method for stably, continuously, quickly and selectively removing critical metal chromium (VI) by using an efficient and high-stability quaternary ammonium salt type polymer ionic liquid film and an electromembrane extraction technology. The technology and the method can be used for thoroughly removing and highly enriching the heavy metal chromium in the wastewater.
The invention is realized by the following technical scheme.
An electro-membrane extraction and enrichment method of chromium (VI) by a quaternary ammonium salt type polymer ionic liquid membrane comprises the following steps:
(1) preparation of quaternary ammonium salt type polymer ionic liquid membrane:
mixing 2.0-3.0% of plasticizer, 3.0-3.5% of polyvinyl chloride and 1.5-2.5% of tri-n-octylamine according to the mass ratio, dissolving the mixture in 91.0-93.5% of volatile organic solvent, continuously stirring and reacting for 12-24 h at normal temperature until the solution is homogeneous, spreading the solution in a flat-bottom container, standing and defoaming at room temperature under normal pressure, continuously volatilizing to remove the volatile organic solvent until the film is cured and has constant weight, and obtaining the white opaque film with smooth appearance; acidifying and transforming the membrane in strong acid, and washing with water to obtain a transparent quaternary ammonium salt polymer ionic liquid membrane;
(2) constructing and installing an electric membrane extraction mass transfer device:
fixing and sealing the quaternary ammonium salt type polymer ionic liquid membrane obtained in the step (1) in two hollow polytetrahydrofethylene clamping pieces, installing the clamping pieces between two liquid pools with certain volumes, and separating the liquid pools at two sides by the clamping pieces to ensure that materials in the liquid pools at two sides of the membrane can only transfer mass through the effective area of the membrane at the hollow part;
(3) electromembrane extraction of chromium (VI):
respectively installing platinum electrodes connected with an external electric field by a direct current stabilized voltage supply in the liquid pools on the two sides of the step (2), wherein the negative platinum electrode is arranged in the chromium (VI) containing wastewater pool, and the positive platinum electrode is arranged in the concentration and enrichment pool; the power supply is switched on during mass transfer, and chromium (VI) in the wastewater tank is continuously transmitted into the concentration tank under a specific voltage;
(4) continuous extraction and enrichment of chromium (VI):
and after the content of chromium (VI) in the feed liquid phase of the wastewater pool is lower than the discharge standard, replacing a new chromium (VI) containing solution for continuous mass transfer in the feed liquid phase.
Preferably, the plasticizer is one of dioctyl phthalate, o-nitrophenyl octyl ether or tributyl phosphate.
Preferably, the polyvinyl chloride is polyvinyl chloride with a molecular weight of 15-25 ten thousand.
Preferably, the organic solvent is one or a mixture of tetrahydrofuran and acetone.
Preferably, the thickness of the solution spread in a flat-bottom container is controlled to be 1.0-2.0 mm, the solvent is volatilized for 12 h-24 h to constant weight under the conditions of room temperature of 25-35 ℃ and normal pressure, and the thickness of the obtained quaternary ammonium salt type polymer ionic liquid film is 150-200 mu m and is in a semitransparent state. The acidifying and transforming agent is 0.1-1M hydrochloric acid solution, and the transformed quaternary ammonium salt polymer ionic liquid film is in a transparent state.
Preferably, the chromium-containing wastewater in the tanks at the two sides of the membrane is a feed liquid tank and a chromium (VI) stripping phase receiving tank, and the acid-base conditions in the tanks at the two sides of the membrane are respectively adjusted by hydrochloric acid and sodium hydroxide, wherein the wastewater is adjusted to be 0.1-1M sodium hydroxide solution, the pH of the chromium (VI) containing concentration tank is adjusted to be 1-3 by hydrochloric acid, and mechanical stirring is applied to keep the ion diffusion rate in the two-phase solution the same.
Preferably, the operating voltage of the direct current power supply is 30-50V; the concentration of chromium (VI) ions is 6.0-60 mg/L for mass transfer.
In the process of continuous mass transfer and enrichment aiming at chromium (VI), sodium hydroxide is quantitatively supplemented in a receiving phase of a concentration tank to maintain the alkaline condition of a back extraction solution of a wastewater tank so as to ensure the continuous and stable extraction condition of the chromium (VI); after the concentration of chromium (VI) in the receiving phase connected with the concentration tank meets the recovery requirement, a new stripping phase can be replaced; in the mass transfer process, when the current density value is overlarge and a large number of bubbles generated by hydrolysis appear in the liquid pools at the two sides, the extraction is stopped, and mass transfer is carried out after a new quaternary ammonium salt polymer ionic liquid membrane is replaced.
The invention has the advantages and innovations that the technical scheme is implemented as follows:
(1) the invention provides an electric membrane extraction of chromium (VI) by a quaternary ammonium salt type polymer ionic liquid membrane, which is characterized in that the quaternary ammonium salt type polymer ionic liquid membrane is coupled with an external electric field, and the HCrO of chromium (IV) in a feed liquid phase is accelerated by a cathode of the electric field4 -The molded body rapidly reaches the membrane phase and exchanges with acid radical chloride ions in the quaternary ammonium salt polymer ionic liquid in the membrane phase to form new HCrO4 -After the ionic liquid complex is formed, the electric field further promotes the dissociation of the complex to diffuse in the membrane, and promotes the dissociation of the complex, and the dissociated HCrO4 -Can jump to the inner membrane to newly generate new anion exchange with the adjacent polymer ionic liquid, reaches the stripping phase side of the quaternary ammonium salt polymer ionic liquid membrane under the double drive of electric field potential and ligand concentration through repeated complexation-dissociation jump mass transfer process, and realizes the reverse gradient mass transfer of chromium (VI) from the feed liquid phase to the stripping phase through the decomplexing of a stripping agent. Based on the principle, the invention provides that chromium (VI) is converted into HCrO by the cathode potential of an applied electric field4 -Compared with the common membrane extraction technology, the mass transfer process of the anion can effectively separate the chromium (VI) from the coexisting cation, has higher separation selectivity on the chromium (VI), and provides convenience for the complete removal and the regeneration and the reuse of the chromium (VI).
(2) The invention provides a plasticizing agentThe quaternary ammonium salt type polymer ionic liquid film has a loose film structure due to the introduction of the plasticizer and the low degree of polymer crystallinity, so that the resistance of the film in the mass transfer process is smaller, and the mass transfer speed is higher than that of the common non-plasticized quaternary ammonium salt type polymer ionic liquid film. In the invention, because the chemical bonding effect exists between the polymer type ionic liquid serving as the carrier in the membrane and the polymer matrix, the carrier can not leak and has higher electric drive mass transfer stability, and the problem of unstable mass transfer of a polymer contained liquid membrane formed by the traditional liquid phase carrier is effectively improved. Is easier to be popularized industrially. The quaternary ammonium salt type polymer ionic liquid membrane prepared according to the invention can be applied to the membrane with 6-100mg L in a lower operating voltage range-1The chromium (VI) in the feed liquid phase with the Cr (VI) concentration range reaches the enrichment of dozens of times or even hundreds of times.
(3) The preparation technology of the quaternary ammonium salt type polymer ionic liquid membrane provided by the invention is implemented by one-step method in the preparation process of the quaternary ammonium salt type polymer ionic liquid, namely trioctylammonium chloride polyvinyl chloride ammonium and the membrane thereof, the process is simple and convenient, the operation is convenient, the complicated steps of separation, purification and the like of the product are omitted, and the by-products and the environmental pollution of the by-products are reduced. Is a scientific green preparation technology.
Drawings
FIG. 1 is an infrared spectrum of the quaternary ammonium salt type polymer ionic liquid membrane prepared by the present invention.
Detailed Description
The following examples further illustrate the embodiments of the present invention in detail.
The invention relates to an electric membrane extraction and enrichment method of a quaternary ammonium salt type polymer ionic liquid membrane for chromium (VI), which comprises the following steps:
step 1: preparation of quaternary ammonium salt type polymer ionic liquid membrane:
mixing 2.0-3.0% of plasticizer (dioctyl phthalate, o-nitrophenyl octyl ether or tributyl phosphate) with 3.0-3.5% of polyvinyl chloride with the molecular weight of 15-25 ten thousand and 1.5-2.5% of tri-n-octylamine, dissolving in 91.0-93.5% of organic solvent (tetrahydrofuran, 1, 4-dioxane or acetone), continuously stirring at 25-35 ℃ and normal pressure to generate nucleophilic addition reaction solvent volatilization for 12-24 h to constant weight, keeping the spreading thickness of 1.0-2.0 mm in a flat-bottomed glass or polytetrafluoroethylene container after the solution is homogeneous, covering the upper part of the container to prevent water vapor from entering, standing at 25-35 ℃ and normal pressure, defoaming, volatilizing the solvent for more than 12h, and curing to constant weight to obtain a white opaque film with flat appearance and the thickness of 150-200 mu m; and (3) acidifying and transforming the obtained opaque film in 0.1-1M hydrochloric acid solution, washing with water to remove redundant acid on the surface to obtain a transparent plasticizing polymer type ionic liquid film, and sealing and storing the film for later use, wherein the film is shown in figure 1.
Step 2: constructing and installing an electric membrane extraction mass transfer device:
and (3) fixing and sealing the plasticized polymer type ionic liquid membrane obtained in the step (1) on two hollow polytetrafluoroethylene clamping pieces with edges lined with tetrafluoroethylene sealing gaskets, and ensuring that no gap exists between the clamping pieces and the membrane. The clamping pieces are arranged in the middle parts of the two liquid pools with certain volumes, and the liquid pools on the two sides are separated by the clamping pieces, so that the mass transfer of the solutions on the two sides can only be carried out through the quaternary ammonium salt type polymer ionic liquid membrane, and the effective mass transfer area of the membrane is determined by the area of the hollow parts of the clamping pieces. Wherein, the feed liquid pool and the receiving pool are both provided with an upper inlet and a lower inlet and are communicated with the feed liquid storage tank and the receiving phase storage tank through a diaphragm pump, and the liquid pool, the liquid storage tank and the like are made of polymers or other non-conductive materials. The material liquid phase (or chromium-containing waste water) containing chromium (VI) and the back extraction phase (concentration tank or receiving phase) containing chromium (VI) are respectively placed in the tanks at the two sides of the membrane. Adjusting acid-base conditions in the tanks at two sides of the membrane by using hydrochloric acid and sodium hydroxide, wherein the pH of the chromium (VI) containing material liquid phase solution is regulated to be 1-3 by preferably using 0.1-1M hydrochloric acid solution, and the concentration of hydroxide ions of the strip phase solution is regulated to be 0.1-1.0M by preferably using 0.1-1M sodium hydroxide. The diffusion rate of ions in the two-phase solution is maintained by magnetic stirring, and the rotating speed is not less than 300 rmp.
And step 3: electro-membrane extraction of chromium (VI) by quaternary ammonium salt type polymer ionic liquid membrane:
and (3) respectively installing platinum electrodes in the two side cells in the step 2 and connecting the platinum electrodes with an external electric field through a direct current stabilized power supply. The negative pole of the power supply is connected with the liquid receiving tank, and the positive pole of the power supply is connected with the receiving phase (back extraction tank). Selecting an operation voltage between 30 and 50V; the concentration of chromium (VI) ions in the chromium (VI) -containing aqueous phase solution is 6.0-60 mg/L. And stopping mass transfer until the concentration of chromium (VI) in the feed liquid phase pool reaches the removal standard.
And 4, step 4: continuous extraction and enrichment of chromium (VI):
and 3, continuously operating until the content of chromium (VI) in the feed liquid phase is lower than a certain value or reaches the discharge standard, and replacing a new chromium (VI) containing solution to continuously transfer mass in the feed liquid phase. During the continuous mass transfer, the alkaline condition of the strip liquor is maintained by quantitatively supplementing sodium hydroxide in the receiving phase so as to ensure the continuous and stable extraction condition of chromium (VI). After the concentration of chromium (VI) in the receiving phase reaches the recovery requirement, a new stripping phase can be replaced. In the mass transfer process, the current density change condition of the electric membrane extraction system is observed, when the current density value is overlarge and a large amount of bubbles generated by hydrolysis appear in the liquid pools at the two sides, the extraction is stopped, and mass transfer is carried out after a new quaternary ammonium salt polymer ionic liquid membrane is replaced.
The invention is further illustrated by the following specific examples.
Example 1:
the mass transfer of the plasticized quaternary ammonium salt polymer ionic liquid film with dioctyl phthalate (DOP) as a plasticizer to chromium (VI).
According to the mass percentage, 3.47 percent of polyvinyl chloride, 2.08 percent of dioctyl phthalate, 1.85 percent of tri-n-octylamine and 92.6 percent of tetrahydrofuran are mixed and magnetically stirred to form a homogeneous transparent casting solution, the mixture is continuously stirred at 25 ℃ to carry out nucleophilic addition reaction for 15 hours, the casting solution is poured into a flat-bottom closed container which is horizontally placed and has the diameter of 55mm, the flat-bottom closed container is kept communicated with the atmosphere, and the mixture is volatilized at 25 ℃ to constant weight to obtain a liquid film. The solution is immersed in 0.1mol/L hydrochloric acid solution for 12 hours and then taken out. The resulting plasticized quaternary ammonium salt-type polymer ionic liquid membrane was fixed to the central connecting portion of the permeation device. Wherein the effective membrane area is 3.14cm2The thickness was 150. mu.m. Chromium (VI) -containing solution with a volume of 80mL and a concentration of 12mg/L was adjusted to pH 1.3 with hydrochloric acid and used as a feed liquid phase. Volume is 80ml, concentration is 0.25mol L-1Sodium hydroxide solution ofThe solution was used as the analysis phase. The rotating speed of the two-phase magnetons is controlled to be 300rmp, the voltage is 50V, the concentration of the chromium (VI) in the feed liquid phase is reduced to 0.18mg/L after 9 hours of mass transfer, and the industrial discharge standard is reached. The mass transfer permeability coefficient is 34.65 mu m s-1Compared with the common liquid film mass transfer rate which is not driven by voltage, the mass transfer rate is improved by about 5 times.
Example 2:
the invention is different from the embodiment 1 in that the plasticizer is o-nitrophenyloctyl ether (NPOE) and the composition of the quaternary ammonium salt type polymer ionic liquid film is different. The method comprises the following specific steps:
according to the mass percentage, 3.5 percent of polyvinyl chloride, 3.0 percent of o-nitrophenyloctyl ether, 2.5 percent of tri-n-octylamine, 51.0 percent of tetrahydrofuran and 40 percent of acetone are mixed, the mixture is magnetically stirred until homogeneous transparent casting solution is obtained, the mixture is continuously stirred at 25 ℃ to carry out nucleophilic addition reaction for 12 hours, the casting solution is poured into a flat-bottom closed container which is horizontally placed with the diameter of 55mm, the flat-bottom closed container is kept communicated with the atmosphere, and the mixture is volatilized to constant weight at 30 ℃ to obtain a liquid film. Immersing the mixture into 0.5mol/L hydrochloric acid solution for 12h, taking out, sealing and storing. The obtained plasticized quaternary ammonium salt type polymer ionic liquid membrane was fixed to the central connection part of the permeation device. Wherein the effective membrane area is 3.14cm2The thickness was 150. mu.m. Chromium (VI) -containing solution with a volume of 80mL and a concentration of 12mg/L was adjusted to pH 1.3 with hydrochloric acid and used as a feed liquid phase. Volume is 80ml, concentration is 0.1mol L-1As the analysis phase. The rotating speed of the two-phase magnetons is controlled to be 300rmp, the voltage is 30V, the removal rate and the recovery rate of chromium (VI) after 6 hours of mass transfer are 91.39 percent and 55.32 percent respectively, and the permeability coefficient is 42.65 mu m s-1The electric membrane extraction permeability coefficient of the quaternary ammonium salt type polymer ionic liquid membrane added with NPOE is increased by 3.7 times compared with that of the same condition. The concentration of the chromium (VI) in the feed liquid phase is 1mg/L, and the industrial discharge standard is reached.
Example 3:
the present example differs from example 1 in that the plasticizer is tributyl phosphate (TBP) and the quaternary ammonium salt type polymer ionic liquid film composition and mass transfer conditions differ.
According to the mass percentage, 3.0 percent of polyvinyl chloride, 2.5 percent of tributyl phosphate and 1.5 percent ofMixing tri-n-octylamine, 43.0% of tetrahydrofuran and 50% of 1, 4-dioxane, magnetically stirring until the homogeneous transparent casting solution is obtained, continuously stirring at 25 ℃ for nucleophilic addition reaction for 24 hours, pouring the casting solution into a flat-bottom closed container which is horizontally placed and has the diameter of 55mm, keeping the flat-bottom closed container communicated with the atmosphere, and volatilizing at 35 ℃ until the weight is constant to obtain the liquid film. The mixture is immersed in 1mol/L hydrochloric acid solution for 12 hours and then taken out for sealing and storage. The obtained quaternary ammonium salt type polymer ionic liquid membrane is fixed at the central connecting part of the permeation device. Wherein the effective membrane area is 3.14cm2The thickness was 150. mu.m. Chromium (VI) -containing solution with a volume of 80mL and a concentration of 12mg/L was adjusted to pH 1.3 with hydrochloric acid to serve as a feed liquid phase. Volume is 80ml, concentration is 0.1mol L-1As the analysis phase. The rotating speed of the two-phase magnetons is controlled to be 300rmp, the voltage is 40V, the removal rate and the recovery rate of chromium (VI) after 6 hours of mass transfer are respectively 87.92 percent and 37.50 percent, and the permeability coefficient is 31.41 mu m s-1. The electric membrane extraction permeability coefficient of the TBP plasticizing quaternary ammonium salt type polymer ionic liquid membrane prepared by the example is increased by 2.7 times compared with the conventional mass transfer.
Example 4:
the implementation is the concentration and enrichment of the low-concentration chromium (VI) containing wastewater
According to the mass percentage, 3.0 percent of polyvinyl chloride, 3.0 percent of dioctyl phthalate, 2.5 percent of tri-n-octylamine and 91.5 percent of tetrahydrofuran are mixed and magnetically stirred to form a homogeneous transparent casting solution, the mixture is continuously stirred at 30 ℃ to carry out nucleophilic addition reaction for 18 hours, the casting solution is poured into a flat-bottom closed container which is horizontally placed and has the diameter of 55mm, the flat-bottom closed container is kept communicated with the atmosphere, and the mixture is volatilized at 35 ℃ until the weight is constant to obtain a liquid film. The solution is immersed in 0.1mol/L hydrochloric acid solution for 12 hours and then taken out. The resulting plasticized quaternary ammonium salt-type polymer ionic liquid membrane was fixed to the central connecting portion of the permeation device. Wherein the effective membrane area is 3.14cm2The thickness was 150. mu.m. Adjusting the pH of a solution with the volume of 1000mL and the concentration of 12mg/L chromium (VI) to 1.3 by using nitric acid, introducing the solution into a feed liquid pool of a chromium electro-membrane extraction pool from a feed liquid tank through a pump, simultaneously filling 100mL of 0.25mol/L sodium hydroxide solution into an analysis pool, starting a magnetic stirring device in the pools at two sides, and enabling the feed liquid poolThe platinum electrode in the analysis pool is connected with the cathode of a direct current power supply, the platinum electrode in the analysis pool is connected with the anode of the direct current power supply, the direct current power supply is switched on, the mass transfer is started after the voltage is adjusted to 50V, and after 80 hours of continuous extraction, the concentration of chromium (VI) in the material liquid phase is reduced to 0.5mg L-1The concentration of chromium (VI) in the analysis phase reaches 110.78mg L-1The method meets the requirement of removing chromium (VI) in the feed liquid (the chromium (VI) in the feed liquid reaches below 1mg/L of the industrial discharge standard). The enrichment factor of chromium (VI) in the analysis phase was 9.5.
Example 5:
this example is directed to the selective separation of chromium (VI)
According to the mass percentage, 3.0 percent of polyvinyl chloride, 2.0 percent of phthalate, 1.5 percent of tri-n-octylamine and 93.5 percent of tetrahydrofuran are mixed and magnetically stirred until homogeneous transparent casting solution is formed, the mixture is continuously stirred at 35 ℃ to carry out nucleophilic addition reaction for 12 hours, the casting solution is poured into a flat-bottom closed container which is horizontally placed and has the diameter of 55mm, the flat-bottom closed container is kept communicated with the atmosphere, and the mixture is volatilized at 30 ℃ until the constant weight is achieved, thus obtaining the liquid film. The mixture is immersed in 0.1M HCl for 12h, taken out and sealed for storage. Selecting a membrane with the thickness of 200 mu m for mass transfer, installing the membrane in a two-phase osmotic device with the same volume after fixing and sealing by a hollow clamping piece, separating liquid pools at two sides by the clamping piece, and screwing by a sealing gasket and a screw to ensure that the solutions at two sides can only carry out mass transfer through the quaternary ammonium salt type polymer ionic liquid membrane. The material liquid phase is a mixed solution of Cd (II), Mg (II), Ni (II) and Cr (VI) with the volume of 80mL and the pH value of 1 concentration of 12Mg/L, and the analysis phase is 80mL of NaOH solution with the concentration of 0.1 mol/L. The mass transfer device was placed on a constant temperature magnetic stirrer, and the two phase rotor speed was maintained at 300rmp, with the two phase temperature controlled at 30 ℃. + -. 0.5 ℃. Platinum electrodes are respectively arranged in the two-phase solution, a cathode is arranged in a material liquid phase, and an anode is used for analyzing the phase. The selective extraction and stripping process of chromium is carried out under the voltage of 50V. After continuous extraction for 9h, the concentration of each metal in the feed liquid phase is 0.5mg L of chromium (VI)-1While Cd (II), Mg (II) and Ni (II) are still 12Mg L-1The concentration of chromium (VI) in the analysis phase was 6mg L-1And selective separation of chromium (VI) is realized.
The present invention is not limited to the above-mentioned embodiments, and based on the technical solutions disclosed in the present invention, those skilled in the art can make some substitutions and modifications to some technical features without creative efforts according to the disclosed technical contents, and these substitutions and modifications are all within the protection scope of the present invention.
Claims (6)
1. An electro-membrane extraction and enrichment method of chromium (VI) by a quaternary ammonium salt type polymer ionic liquid membrane is characterized by comprising the following steps:
(1) preparation of quaternary ammonium salt type polymer ionic liquid membrane:
mixing 2.0-3.0% of plasticizer, 3.0-3.5% of polyvinyl chloride and 1.5-2.5% of tri-n-octylamine according to the mass ratio, dissolving the mixture in 91.0-93.5% of volatile organic solvent, continuously stirring and reacting for 12-24 h at normal temperature until the solution is homogeneous, spreading the solution in a flat-bottom container, standing and defoaming at normal pressure and normal temperature, continuously volatilizing to remove the volatile organic solvent until the film is cured and constant in weight, and obtaining a white opaque film with smooth appearance; acidifying and transforming the membrane in strong acid, and washing with water to obtain a transparent quaternary ammonium salt polymer ionic liquid membrane;
the plasticizer is one of dioctyl phthalate, o-nitrophenyl octyl ether or tributyl phosphate;
the molecular weight of the polyvinyl chloride is 15-25 ten thousand;
the organic solvent is one or a mixture of tetrahydrofuran and acetone;
(2) constructing and installing an electric membrane extraction mass transfer device:
fixing and sealing the quaternary ammonium salt type polymer ionic liquid membrane obtained in the step (1) in two hollow polytetrahydrofethylene clamping pieces, installing the clamping pieces between two liquid pools with certain volumes, and separating the liquid pools at two sides by the clamping pieces to ensure that materials in the liquid pools at two sides of the membrane can only transfer mass through the effective area of the membrane at the hollow part;
(3) electromembrane extraction of chromium (VI):
respectively installing platinum electrodes connected with an external electric field by a direct current stabilized voltage supply in the liquid pools on the two sides of the step (2), wherein the negative platinum electrode is arranged in the chromium (VI) containing wastewater pool, and the positive platinum electrode is arranged in the concentration and enrichment pool; continuously transmitting chromium (VI) in the wastewater tank to the concentration tank at a specific voltage;
(4) continuous extraction and enrichment of chromium (VI):
after the content of chromium (VI) in the feed liquid phase of the wastewater pool is lower than the discharge standard, a new chromium (VI) containing solution is replaced to continuously transfer mass in the feed liquid phase.
2. The method for electro-membrane extraction and enrichment of chromium (VI) by using the quaternary ammonium salt type polymer ionic liquid membrane as claimed in claim 1, wherein the thickness of the solution spread in a flat-bottom container is controlled to be 1.0-2.0 mm, the solvent is volatilized for 12-24 h to constant weight at room temperature of 25-35 ℃ and under normal pressure, and the thickness of the obtained quaternary ammonium salt type polymer ionic liquid membrane is 150-200 μm and is in a semitransparent state.
3. The method for electro-membrane extraction and enrichment of chromium (VI) by using the quaternary ammonium salt polymer ionic liquid membrane as claimed in claim 1, wherein in the step (1), the membrane is immersed in 0.1-1M hydrochloric acid solution for transformation to form a transparent quaternary ammonium salt polymer ionic liquid membrane.
4. The method for electro-membrane extraction and enrichment of chromium (VI) by using the quaternary ammonium salt type polymer ionic liquid membrane as claimed in claim 1, wherein hydrochloric acid and sodium hydroxide are respectively used for adjusting acid-base conditions in tanks at two sides of the membrane, the concentration of alkaline aqueous solution is 0.1-1M sodium hydroxide, and hydrochloric acid is used for adjusting the pH value of the chromium (VI) -containing aqueous phase solution to 1-3; mechanical agitation was applied to keep the ion diffusion rate in the biphasic solution the same.
5. The method for electro-membrane extraction and enrichment of chromium (VI) by using the quaternary ammonium salt type polymer ionic liquid membrane as claimed in claim 1, wherein the operating voltage of a direct current power supply is 30-50V; the concentration of chromium (VI) ions in the chromium (VI) -containing aqueous phase solution is 6.0-60 mg/L.
6. The method for the electro-membrane extraction and enrichment of chromium (VI) by the quaternary ammonium salt type polymer ionic liquid membrane as claimed in claim 1, wherein sodium hydroxide is quantitatively supplemented in the receiving phase of the concentration tank to maintain the alkaline condition of the back extraction solution of the wastewater tank during the continuous mass transfer process; after the concentration of chromium (VI) in the receiving phase meets the recovery requirement, replacing a new stripping phase of the wastewater tank; and in the mass transfer process, when the current density value is overlarge and a large number of bubbles generated by hydrolysis appear in the liquid pools at the two sides, stopping extraction, replacing a new quaternary ammonium salt polymer ionic liquid membrane, and then carrying out mass transfer.
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