Deep purification method of low-concentration heavy metal chromium (VI)
阅读说明：本技术 一种低浓度重金属铬（vi）的深度净化方法 (Deep purification method of low-concentration heavy metal chromium (VI) ) 是由 孟晓荣 王磊 *** 吕永涛 宋莹莹 李佳文 于 2019-11-04 设计创作，主要内容包括：本发明公开了一种低浓度重金属铬(VI)的深度净化方法,包括以一定质量比的基础聚合物、液相载体、保护剂、有机溶剂共混溶解,通过溶剂挥发相转化法制备固相液膜；以及以固相液膜与外电场协同作用下的电膜萃取技术对低浓度铬(VI)的高效选择性去除方法。本发明所提供的固相液膜制备工艺简便,化学试剂用量较少,成本低廉。电膜萃取过程萃取与反萃同步,速率快,能耗低,操作简便灵活,无污染。本发明提供的铬(VI)的深度净化方法,对铬(VI)的选择性强,去除率高,可实现低浓度铬(VI)的彻底净化。是一种针对重金属铬污染水体的绿色环保处理方法。(The invention discloses a deep purification method of low-concentration heavy metal chromium (VI), which comprises the steps of blending and dissolving a base polymer, a liquid-phase carrier, a protective agent and an organic solvent according to a certain mass ratio, and preparing a solid-phase liquid film by a solvent volatile phase conversion method; and a high-efficiency selective removal method of low-concentration chromium (VI) by an electric membrane extraction technology under the synergistic action of a solid-phase liquid membrane and an external electric field. The solid-phase liquid film provided by the invention has the advantages of simple preparation process, less chemical reagent consumption and low cost. The extraction and the back extraction in the electromembrane extraction process are synchronous, the speed is high, the energy consumption is low, the operation is simple, convenient and flexible, and no pollution is caused. The deep purification method of chromium (VI) provided by the invention has strong selectivity to chromium (VI) and high removal rate, and can realize thorough purification of low-concentration chromium (VI). Is a green and environment-friendly treatment method for the heavy metal chromium polluted water body.)
1. The deep purification method of low-concentration heavy metal chromium (VI) is characterized by comprising the following steps:
(1) preparing a polymer solid-phase liquid film:
mixing 3.0-4.0% of base polymer, 3.0-24.5% of liquid phase carrier, 0-10.0% of protective agent and 61.5-94.0% of volatile organic solvent according to the mass ratio, stirring and dissolving to form a homogeneous phase casting solution, pouring the homogeneous phase casting solution into a flat bottom container, standing at normal pressure, and volatilizing the solvent to constant weight to obtain a solid phase liquid film with the thickness of 100-200 mu m;
(2) constructing an external electric field coupling solid-phase liquid film treatment device:
fixing the solid-phase liquid film obtained in the step (1) on the middle parts of a waste water tank containing a material liquid phase of chromium (VI) and a concentration tank of a stripping phase, and separating liquid tank solutions on two sides by a sealing device; setting acid-base conditions of the solution in the tanks at the two sides of the membrane; respectively installing a cathode electrode and an anode electrode connected with a direct current stabilized voltage power supply of an external electric field in the two tanks, wherein the platinum cathode electrode is arranged in a wastewater tank containing a chromium (VI) material liquid phase, and the platinum anode electrode is arranged in a concentration tank of a chromium (VI) back extraction phase;
(3) separation, removal and enrichment of chromium (VI):
continuously transmitting chromium (VI) in the wastewater pool into a concentration pool by the built external electric field coupling liquid membrane extraction device under the specific voltage of the external electric field until the content of the chromium (VI) in the feed liquid phase reaches the discharge standard; and the alkaline environment of the solution is maintained by periodically supplementing alkali in the stripping phase during the mass transfer process.
2. The method for deeply purifying low-concentration heavy metal chromium (VI) as claimed in claim 1, wherein the base polymer is polyvinyl chloride with average molecular weight of 15-25 ten thousand, vinylidene fluoride with molecular weight of 50 ten thousand or vinylidene fluoride-hexafluoropropylene copolymer with molecular weight of 15-20 ten thousand.
3. The method for deeply purifying low-concentration heavy metal chromium (VI) as claimed in claim 1, wherein the liquid carrier is one or two of tributyl phosphate (TBP), trioctylphosphine oxide (TOPO) and n-Octanol (OCT).
4. The method for the deep purification of low-concentration heavy metal chromium (VI) according to claim 1, wherein the protective agent is kerosene, lauric acid or lauryl alcohol.
5. The method for deeply purifying low-concentration heavy metal chromium (VI) according to claim 1, wherein the volatile organic solvent is one or a mixture of two of acetone, dichloroethane, chloroform and tetrahydrofuran.
6. The deep purification method of low-concentration heavy metal chromium (VI) according to claim 1, wherein in the step (1), the spreading thickness of the homogeneous casting solution in a flat-bottom container is 1.0-2.0mm, the solvent volatilization temperature is 25-35 ℃, and the thickness of the obtained solid-phase liquid film is controlled to be 100-200 μm.
7. The method for deeply purifying low-concentration heavy metal chromium (VI) according to claim 1, wherein in the step (2), the concentration of Cr (VI) in the chromium (VI) -containing wastewater pool is in the range of 6-15mg L-1And adjusting the pH value of the back extraction phase to 0.5-5 by hydrochloric acid.
8. The method for deeply purifying low-concentration heavy metal chromium (VI) according to claim 1, wherein in the step (2), the stripping phase in the concentration tank is sodium acetate, acetic acid/sodium acetate buffer solution or 0.1M sodium hydroxide solution.
9. The deep purification method of low-concentration heavy metal chromium (VI) according to claim 1, wherein in the step (3), the voltage is 10-90V.
Technical Field
The invention belongs to the technical field of environmental protection and industrial wastewater treatment, and relates to a green method and technology for deep purification of low-concentration heavy metal chromium (VI) and application thereof in deep purification and comprehensive treatment of drinking water or industrial wastewater.
Background
Chromium (VI) is harmful to the human body and the ecological environment. Chromium (VI) in water can cause irreversible damage to the stream ecological environment and ingestion of lethal doses of chromate by animals can lead to cardiovascular failure. Chromium (VI) has abundant industrial sources and is widely used in leather making, paper making, cooling tower pollution discharge, electroplating, electrolysis, anodic oxidation tanks and the like, and various industrial cleaning processes. The discharge limit of China to industrial chromium (VI) is 1mg/L, and the maximum allowable limit of the chromium (VI) in inland water areas and drinking water is 0.1 mg/L and 0.05mg/L respectively.
The traditional treatment method of the chromium-containing wastewater comprises chemical precipitation, coagulation, ion exchange, adsorption and the like. However, the high chemical requirements of large volumes of chromium (VI) -containing wastewater and the inability of most conventional processes to achieve complete or complete removal have limited the wide spread and application of these conventional techniques or processes. For example, in patent technology CN1032328A, sodium hydroxide is used as a precipitant, and an acid is added to the etching waste liquid in the aluminum nameplate production, and after an aluminum reaction, the treatment agent is prepared by filtering and adding an alkali to adjust the pH value. Then passing through ferrous salt and AlCl in the treating agent3、FeCl2、Al2(SO4)3Reducing chromium (VI) to chromium (III) to form Cr (OH)3Precipitating to remove chromium (VI) in the wastewater, and finally reducing the chromium (VI) in the water from 1200mg/L to 0.05 mg/L. However, the method has complicated treatment process, is easy to generate secondary pollution, and is extremely not suitable for the advanced treatment and purification process of the low-concentration chromium (VI) containing water body. For the treatment of the low-concentration chromium water body, the patent technology CN102849816A provides an adsorption process. The process modifies carbon nano-tubes through mixed acid, and then the modified carbon nano-tubes are used for adsorbing chromium (VI) in chromium-containing wastewaterWhen the amount of the modified carbon nano tube is 0.2g, the removal rate of the modified carbon nano tube to 25mL of chromium (VI) solution with the concentration of 50mg/L reaches 98.61%, but the operation of the subsequent regeneration process of the carbon nano tube adsorbent is complicated, a large amount of nitric acid and sulfuric acid are required to be consumed only in the step of mixed acid treatment, and the carbon nano tube is expensive and has low economic applicability. In recent years, with the rise of liquid membrane separation technology, certain research has been conducted on the treatment of chromium-containing wastewater. The patent technology CN109095500A utilizes the dication quaternary ammonium type extractant to extract chromium (VI), realizes the extraction rate of more than 96 percent of the chromium (VI) within the pH value of 2-8, creates a road for extracting and recovering the Cr (VI) under the neutral condition, and can be widely applied to the extraction of the Cr (IV) in neutral soil and surface water. However, the liquid-liquid extraction technology cannot synchronize extraction and stripping, and the regeneration of the extractant requires a large amount of stripping agent and acid-base reagent. In the literature, "research on recovery of hexavalent chromium ions in electroplating wastewater by extraction" (Wanfang, Master thesis of Jiangnan university, 2009), a method for removing chromium (VI) in wastewater by using a back-extraction pre-dispersed hollow fiber supported liquid membrane is adopted. The method takes a common polypropylene (PP) hollow fiber membrane as a membrane material and di (2-ethylhexyl) phosphate (D2EHPA) as a carrier, and the extraction rate of chromium ions can reach over 96 percent after the continuous operation for 5 hours. The method has the advantages that the extraction and the back extraction are carried out synchronously, and the treatment process has better cleaning property. However, the supported liquid membrane has poor stability in long-term operation and can not continuously transfer mass, thereby limiting the industrial application of the supported liquid membrane. Compared with a supported liquid membrane, the polymer solid-phase liquid membrane has good stability, but the lower diffusion coefficient is always a great obstacle in the application of the solid-phase liquid membrane. The invention provides an operation technology for removing low-concentration metal ions by driving a solid-phase liquid film through an external electric field. The method can effectively improve the transmission rate of the liquid film and the thoroughness of removal by applying an external power supply on two sides of the solid-phase film and driving with voltage. Solves the problem of slow mass transfer rate of the solid-phase liquid film, and is an efficient, green and environment-friendly heavy metal pollution treatment method.
Disclosure of Invention
The invention aims to provide a green treatment technology and a method which can rapidly remove low-concentration critical metal chromium (IV), have good stability and are convenient to operate. The invention provides a method for improving the mass transfer efficiency of a solid-phase liquid film by driving of an external electric field, and completely removing, highly enriching and selectively extracting low-concentration chromium (VI). The technology and the method can be used for deeply removing, enriching and regenerating heavy metal chromium (VI) in the wastewater in drinking water and industrial wastewater.
In order to achieve the technical purpose, the invention is realized by the following technical scheme.
A deep purification method of low-concentration heavy metal chromium (VI) comprises the following steps:
(1) preparing a polymer solid-phase liquid film:
mixing 3.0-4.0% of base polymer, 3.0-24.5% of liquid phase carrier, 0-10.0% of protective agent and 61.5-94.0% of volatile organic solvent according to the mass ratio, stirring and dissolving to form a homogeneous phase casting solution, pouring the homogeneous phase casting solution into a flat bottom container, standing at normal pressure, and volatilizing the solvent to constant weight to obtain a solid phase liquid film with the thickness of 100-200 mu m;
(2) constructing an external electric field coupling solid-phase liquid film treatment device:
fixing the solid-phase liquid film obtained in the step (1) on the middle parts of a feed liquid phase (wastewater pool) containing chromium (VI) and a stripping phase (concentration pool), and separating the solutions of the liquid pools at two sides by a sealing device; setting acid-base conditions of the solution in the tanks at the two sides of the membrane; the two tanks are respectively provided with a cathode electrode and an anode electrode which are connected with a direct current stabilized voltage power supply of an external electric field, wherein the platinum cathode electrode is arranged in a chromium (VI) containing material liquid phase (a wastewater tank), and the platinum anode electrode is arranged in a concentration tank of a chromium (VI) back extraction phase;
(3) separation, removal and enrichment of chromium (VI):
in the external electric field coupling liquid membrane extraction device built in the step (2), a direct current power supply of an external electric field is switched on, and chromium (VI) in the wastewater tank is continuously transmitted into the concentration tank under a specific voltage until the content of chromium (VI) in the feed liquid phase reaches the discharge standard; during the mass transfer process, alkali can be supplemented in the stripping phase at regular time to keep the alkaline environment of the solution, so as to ensure the continuous and stable mass transfer rate.
In the method for preparing the solid-phase liquid film:
the basic polymer is polyvinyl chloride with the average molecular weight of 15-25 ten thousand, cellulose triacetate, vinylidene fluoride with the molecular weight of 50 ten thousand or a vinylidene fluoride-hexafluoropropylene copolymer with the molecular weight of 15-20 ten thousand, wherein the polyvinyl chloride is preferred.
The liquid phase carrier is one or a mixture of tributyl phosphate (TBP), trioctylphosphine oxide (TOPO) or n-Octanol (OCT), wherein TOPO and OCT are preferred.
The protective agent is kerosene, lauric acid or lauryl alcohol, wherein the kerosene is preferred.
The volatile organic solvent is one or two of acetone, dichloroethane, chloroform or tetrahydrofuran, wherein tetrahydrofuran is preferred.
Preferably, the homogeneous casting solution is spread in a flat-bottomed container to a thickness of 1.0-2.0mm, and is volatilized at 25-35 ℃, and finally the thickness of the solid-phase liquid film is controlled to be 100-200 mu m.
In the step (2), the operation of constructing the external electric field coupling solid-phase liquid film treatment device is as follows:
the concentration of Cr (VI) in the chromium (VI) containing wastewater in the feed liquid pool is kept between 6 and 15mg L-1And adjusting the pH of the liquid phase of the material to be 0.5-5 by using hydrochloric acid, wherein the pH is preferably 1.3. The stripping phase in the concentration tank may be sodium acetate, acetic acid/sodium acetate buffer solution with pH 5, or alkaline 0.1M sodium hydroxide solution, and preferably 0.1M sodium hydroxide solution.
In the step (3), the voltage is between 10 and 90V.
The invention has the advantages and innovations that the technical scheme is implemented as follows:
(1) compared with the common traditional water treatment technology for treating chromium (VI), the method for removing the low-concentration toxic heavy metal chromium (VI) in the water body by driving the solid-phase liquid film through the external electric field has the advantages of high chromium (VI) removal rate, thorough removal and large enrichment factor, and can quickly and completely extract and enrich the heavy metal chromium (VI) ions in the wastewater into a receiving phase for further concentration and solidification treatment. The method can realize the extraction and recovery of heavy metal chromium while realizing the treatment of the chromium (VI) containing wastewater, and is a novel green and environment-friendly treatment technology in the true sense.
(2) The invention accelerates the separation technology of extracting chromium by the solid phase membrane through electric field coupling, the dosage of the liquid phase carrier is small, the extraction and the back extraction are synchronous, the carrier does not need to be regenerated, the solid phase liquid membrane can be continuously and repeatedly used, and no secondary pollution exists; the receiving phase does not need high-concentration acid or alkaline solution for back extraction, the process condition is mild, the operation is simple and convenient, the dosage of chemical reagents is less, the electric field voltage is low, and the energy consumption is low; the process equipment requirement is low, the working procedure is simple, and the industrialization expansion is easy. Is a novel treatment technology with energy conservation and emission reduction.
(3) The invention is a multi-technology coupling waste water treatment technology integrating an extraction technology, a membrane treatment technology and an electrophoresis technology, has strong technical innovation, is energy-saving and environment-friendly, can generate great technical innovation for the traditional heavy metal waste water treatment technology and field, and has certain promotion and reference for the technical innovation in the wet metallurgy field.
Drawings
FIG. 1 is a schematic diagram of an electric membrane extraction device coupled by an external electric field.
Detailed Description
The following is a more detailed description of embodiments of the present invention, taken in conjunction with the accompanying drawings and examples.
The invention relates to a deep purification method of low-concentration heavy metal chromium (VI), which comprises the following steps:
(1) preparing a solid-phase liquid film: according to the mass ratio, 3.0-4.0% of base polymer (one of polyvinyl chloride with the average molecular weight of 15-25 ten thousand, polyvinylidene fluoride with the average molecular weight of 30-50, or polyvinylidene fluoride-hexafluoropropylene copolymer with the average molecular weight of 15-20 ten thousand), 3.0-24.5% of liquid phase carrier (one or a mixture of two of tributyl phosphate TBP, trioctylphosphine oxide TOPO or n-octanol OCT), 0-10.0% of protective agent (one of kerosene, lauryl alcohol and lauric acid), and 61.5-94.0% of organic volatile solvent (one or a mixture of two of acetone, dichloroethane, chloroform and tetrahydrofuran) are added. Mixing, stirring and dissolving the substances to form a homogeneous phase casting solution, pouring the homogeneous phase casting solution into a flat-bottomed container made of flat-bottomed glass or polytetrafluoroethylene, spreading the homogeneous phase casting solution to a thickness of 1.0-2.0mm, standing the flat-bottomed container at normal pressure, and volatilizing the solvent to constant weight at 25-35 ℃ to obtain a film with a thickness of 100-200 mu m, namely a solid-phase liquid film.
(2) Constructing an external electric field coupling solid-phase liquid film treatment device: separating the solid-phase liquid film 4 obtained in the step (1) from a chromium (VI) containing wastewater pool 6 (material liquid phase) and a chromium (VI) concentrating pool 3 (back extraction phase), clamping the waste water pool and the chromium (VI) containing wastewater pool by two polytetrafluoroethylene frames with edges lined with sealing gaskets, ensuring no gap, sealing the waste water pool and the concentrating and enriching pool, and placing the waste water pool and the concentrating and enriching pool at two connecting parts, wherein the solution at two sides of the membrane frames is ensured to be seamless, and the solution between the two pools can only transfer mass through the solid-phase liquid film part. The schematic diagram of the electric membrane extraction device is shown in attached figure 1.
The concentration of Cr (VI) in the chromium (VI) containing wastewater pool is 6-15mg L-1Setting acid-base conditions of the solution in the tanks at the two sides of the membrane: adjusting the pH of the liquid phase of the material to be 0.5-5 by hydrochloric acid, and preferably adjusting the pH to be 1.3; the concentration tank is filled with neutral deionized water, acetic acid/sodium acetate buffer solution with pH of 5, or 0.1M sodium hydroxide solution, preferably 0.01-0.1M sodium hydroxide solution.
(3) Treating the chromium (VI) containing wastewater by using an external electric field coupling solid-phase liquid membrane: and (3) mounting cathode and anode platinum electrodes 2 in the two side cells of the treatment device built in the step (2) respectively, and connecting the cathode and anode platinum electrodes with a direct current stabilized power supply 1 of an external electric field. Wherein the cathode platinum electrode is arranged in the waste water pool containing chromium (VI), and the anode platinum electrode is arranged in the concentration and enrichment receiving pool. And (3) switching on a direct current power supply, starting magnetic stirring 5 in the two tanks, continuously transmitting the chromium (VI) in the wastewater tank 6 (material liquid phase) to the concentration tank 3 (stripping phase) under the voltage range of 10-90V, and observing the electrolysis behavior of the solution at two sides and the change of current density in the mass transfer process to judge whether the transmission process of the chromium (VI) is influenced by the electrolysis phenomenon. And interrupting the circuit when the chromium (VI) concentration in the feed liquid phase is reduced to the discharge standard until the chromium (VI) content in the feed liquid phase reaches the discharge standard. During the mass transfer process, alkali can be supplemented in the stripping phase at regular time to keep the alkaline environment of the solution, so as to ensure the continuous and stable mass transfer rate.
After the mass transfer is finished, the new chromium-containing wastewater (material liquid phase) can be continuously replaced, and after the concentration of chromium (VI) in the receiving pool reaches a certain value, the solution can be further evaporated and concentrated to the concentration required by chemical precipitation, and then the chromium is solidified and recovered.
The invention provides a selective removal principle of chromium (VI) in heavy metal wastewater, which is based on liquid phase carriers of tributyl phosphate, trioctylphosphine oxide, fatty alcohol and the like in a solid phase liquid film, contains basic electron-donating groups such as hydroxyl, phosphorus oxygen and the like, and can react with an oxyacid radical anion HCrO of chromium (VI)4 -Forming a special hydrogen complex, selectively extracting chromium (VI) from a water body containing heavy metal chromium (VI) into a solid-phase liquid film, transmitting the chromium (VI) through the inside of the solid-phase liquid film and reaching a stripping phase interface, and continuously returning the carrier to the film phase and continuously carrying out mass transfer after the dissociation of substances in the stripping phase. In an electric field, charged ions are accelerated by the electric field potential. In an acidic aqueous system (pH)<6) In, negative anion of chromium (VI) HCrO4 -Has a high distribution coefficient, so that the negative electrode of an external electric field (the cathode of a membrane extraction system) drives the HCrO with negative charge4 -Rapidly gather to the surface of a solid-phase liquid film, and a large amount of HCrO can be rapidly enriched at the interface of the film phase4 -Ions promote the corresponding increase of the membrane phase extraction rate in unit time. At the same time, due to the membrane phase carrier and HCrO4 -The complex and the body of (2) are also negatively charged, so the propagation rate of chromium (VI) in the membrane phase is much higher than that of the common extraction technology. Also, at the stripping interface of the solid liquid film, HCrO4 -The hydrogen bond conjugate with the carrier is deprotonated under neutral or alkaline conditions to form CrO4 2-It can also be accelerated by the electric field potential to be taken away from the membrane phase interface and rapidly moved in the analytic phase to be transferred to the vicinity of the anode. Most metal ions such as copper (II), cobalt (II), nickel (II), zinc (II) and the like exist in the form of positively charged metal cations in aqueous solution, particularly acidic aqueous solution, and the cations cannot be accelerated to the anode by the electric field cathode, so that the cations cannot reach the stripping phase through the solid-phase liquid film by the method, and can be separated from chromium (VI). Thus, the present technology is more selective for the separation of chromium (VI) from other metal ions than other processes. The principle of membrane extraction technology by external electric field coupling is shown in FIG. 1.
The invention is further illustrated by the following specific examples.