Application of carbon cloth assisted bipolar membrane electrodialysis system in removal of low concentration boron in water body

Abstract

The application provides application of a carbon cloth assisted bipolar membrane electrodialysis system in removal of low-concentration boron in a water body. The method comprises the following operation steps: hydrophilic carbon cloth is tailored according to the size of an electrodialysis chamber area; the obtained hydrophilic carbon cloth is respectively placed in corresponding electrode liquid and low-concentration boron-containing solution to be treated for balance; the obtained balanced hydrophilic carbon cloth is filled into the electrodialysis chamber in an electrodialysis device, and a constant current is applied through a direct current power supply, voltage, pH and boron concentration changes in the whole process are recorded, and energy consumption and boron removal effect in the electrodialysis process are quantitatively determined. The application solves the key problems of high energy consumption and poor removal effect in the process of removing low-concentration boron in the water body by electrodialysis.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of water treatment, in particular to application of a carbon cloth assisted bipolar membrane electrodialysis system in removal of low-concentration boron in water bodies. BACKGROUND

[0002] The global water resource shortage problem is increasingly serious, and climate change and population growth aggravate the water supply pressure, prompting seawater desalination to become an important means to alleviate the water resource crisis. Reverse osmosis, as the most mainstream desalination technology at present, is widely used due to its high water salt separation capacity and low energy consumption, but its interception efficiency for neutral small molecules (such as boric acid) is low. The concentration of boron in seawater is about 4-6 mg L -1 , mainly in the form of uncharged boric acid, and reverse osmosis relies on size and charge separation mechanism, and it is difficult to effectively remove such substances. Therefore, the residual boron in the primary effluent of reverse osmosis still needs further post-treatment to meet the water standard. The commonly used post-treatment methods at present include multi-stage reverse osmosis method and ion exchange adsorption method, but both have significant defects. The multi-stage reverse osmosis needs to convert boric acid into borate by adding alkali to improve the interception rate, but the chemical agent consumption is large and the economic cost is greatly increased. The ion exchange resin can selectively adsorb boron, but the adsorption rate is slow, the bed volume is large, and a large amount of acid and alkali is needed in the regeneration process, and the economic efficiency and environmental friendliness are poor. The electric adsorption technology and the electrodialysis technology can remove ions by electric field driving, but boric acid needs to be ionized under high pH conditions to be effectively adsorbed, and the traditional electric adsorption system and electrodialysis system are difficult to stably maintain the required pH, the adsorption rate is slow, and the boron removal effect is not ideal. In addition, the traditional electrodialysis technology has high energy consumption in boron removal when the salt ion concentration is low, which limits its large-scale application.

[0003] It is urgent to develop a boron removal technology that can be used for low-concentration boron in water bodies, realizes fast and low-energy consumption, and overcomes the limitations of the prior art. SUMMARY

[0004] To solve the above technical problems, the application provides application of a carbon cloth assisted bipolar membrane electrodialysis system in removal of low-concentration boron in water bodies. The method for removing low-concentration boron in water bodies has low energy consumption and fast boron removal speed, and can realize efficient treatment of boron in the primary effluent of seawater reverse osmosis, thereby providing a new strategy and method for solving the problem of insufficient boron removal efficiency of traditional reverse osmosis, electric adsorption and electrodialysis.

[0005] A first object of the application is to provide application of a carbon cloth assisted bipolar membrane electrodialysis system in removal of low-concentration boron in water bodies, which comprises the following steps:

[0006] Cutting a hydrophilic carbon cloth according to the size of the electrodialysis chamber area;

[0007] The obtained hydrophilic carbon cloth is respectively placed in the corresponding electrode solution and the low-concentration boron-containing solution to be treated for balancing;

[0008] The obtained balanced hydrophilic carbon cloth is filled in an electrodialysis chamber of an electrodialysis device, and a constant current is applied by a direct current power supply to achieve the purpose of boron removal.

[0009] In some specific embodiments of the present application, the hydrophilic carbon cloth is a carbon fiber fabric of one or more of W0S1011, HCP330N and CCD; 5 pieces of W0S1011 type carbon cloth are needed to fill one electrodialysis chamber.

[0010] In some specific embodiments of the present application, the electrodialysis chamber includes three chambers in total, one of which is a concentrated water chamber, the concentrated water chamber is the water body to be treated, and the other two are electrode solution chambers, the electrode is a titanium electrode, and the electrode solution is 0.5 M K2SO4;

[0011] The membrane used in the three chambers of the electrodialysis is respectively ASTOM AHA anion exchange membrane and fumasep FBM bipolar membrane.

[0012] In some specific embodiments of the present application, the thickness of the silica gel gasket of the electrodialysis device is 0.5-3 mm, the thickness of the tetrafluoroethylene gasket is 0.5-3 mm, and the chamber area is 1 cm 2 ~1 m 2 .

[0013] In some specific embodiments of the present application, the material of the silica gel gasket is a conventional material in the field, which can be one or more of tetrafluoroethylene, polypropylene, polyethylene and polyvinyl chloride.

[0014] In some specific embodiments of the present application, the electrode solution is 0.1-1 M K2SO4 or Na2SO4, and the low-concentration boron-containing solution includes a mixed solution of 0.2 mM-1 mM H3BO3 and 2 mM-5 mM NaCl simulating the primary effluent of reverse osmosis.

[0015] In some specific embodiments of the present application, the balancing time of the hydrophilic carbon cloth placed in the corresponding electrode solution and the low-concentration boron-containing solution to be treated is 2-24 h.

[0016] In some specific embodiments of the present application, the flow rate of the electrode solution and the low-concentration boron-containing solution to be treated is 0.5 ml·min -1 ~2 ml·min -1 .

[0017] In some specific embodiments of the present application, the current density of the constant current ranges from 1.0 mA·cm -22.0 mA·cm -2 .

[0018] In some embodiments of the application, the voltage of the electrodialysis system is recorded by a direct current power supply, and the pH is recorded by a pH meter.

[0019] In some embodiments of the application, the boron concentration of the water is determined by ICP-OES.

[0020] Further, the carbon cloth assisted bipolar membrane electrodialysis device is used for removing low concentration boron in water bodies, and the specific steps are as follows:

[0021] (1) The constructed carbon cloth assisted bipolar membrane electrodialysis device is connected to the electrode solution and the low concentration boron-containing water body to be treated through a peristaltic pump;

[0022] (2) A constant current is applied to the electrodialysis device, the real-time voltage is recorded by a direct current power supply, the real-time pH is recorded by a pH meter, the effluent is collected at a time, and the boron concentration of the effluent is determined;

[0023] Further, the flow rate of the electrode solution and the low concentration boron-containing solution to be treated is 0.5-2 ml·min -1 ;

[0024] Further, the direct current power supply is eTM-L303SPL (30V3A), and the current density range of the applied constant current is 1.0-2.0 mA cm -2 .

[0025] Further, the pH meter is SX620 acidity meter, and the measurement range is 0-14.

[0026] Further, the boron concentration determination method is ICP-OES.

[0027] In the application, based on the Second-Wien effect of the bipolar membrane under the action of an electric field, H + and OH - are generated on both sides of the membrane, so that the boric acid in the water body can be converted into negatively charged borate ions without adding acid and base. The hydrophilic carbon cloth is used as a porous conductive material with high specific surface area, which can effectively reduce the overall working voltage of the electrodialysis system, and the rich oxygen-containing functional groups on the surface of the carbon cloth can maintain the pH of the boron removal chamber at an alkaline level. Thus, a high-efficiency, stable and low-energy-consumption electrodialysis technology for removing low-concentration boron in water bodies is constructed.

[0028] The above technical scheme of the application has the following advantages compared with the prior art:

[0029] The application innovatively constructs a carbon cloth assisted bipolar membrane electrodialysis system. Through the unique cation and anion exchange layer structure of the bipolar membrane, water is dissociated in situ under the action of an electric field, and neutral boric acid in the water body can be efficiently converted into negatively charged borate ions without adding acid and alkali, thereby significantly improving the removal efficiency of boron by electromigration. Compared with the traditional electrodialysis technology, the hydrophilic carbon cloth material introduced in the application can significantly reduce the working voltage of the system, and the rich oxygen-containing functional groups on the surface of the carbon cloth can maintain the pH of the boron removal chamber at a high level of 10.8-11.5, which not only ensures the continuous and efficient ionization of boron, but also avoids the problem of decreased treatment efficiency caused by pH fluctuation in the traditional process. The technical system uses mature commercial membrane materials and hydrophilic carbon cloth raw materials, and has excellent engineering application potential due to its simple assembly process and mild operating conditions. When applied to the boron removal system by electrodialysis, the in-situ pH regulation ability of the bipolar membrane and the dual synergistic effect of the carbon cloth in reducing resistance and stabilizing pH can realize efficient and low-energy consumption purification treatment of low-concentration boron-containing water bodies. BRIEF DESCRIPTION OF DRAWINGS

[0030] In order to make the content of the application more easily understood, the application will be further described in detail below according to specific embodiments of the application and in conjunction with the drawings, in which,

[0031] Figure 1 FIG. 1 is a structural schematic diagram of a carbon cloth assisted bipolar membrane electrodialysis device of the application.

[0032] Figure 2 FIG. 4 is a comparison chart of the average voltage during the boron removal process of the bipolar membrane electrodialysis device without adding carbon cloth and the carbon cloth assisted bipolar membrane electrodialysis device in Example 1 of the application.

[0033] Figure 3 FIG. 5 is a comparison chart of the boron concentration change during the boron removal process of the bipolar membrane electrodialysis device without adding carbon cloth and the carbon cloth assisted bipolar membrane electrodialysis device in Example 1 of the application.

[0034] Figure 4 FIG. 6 is a pH value data chart of the carbon cloth assisted bipolar membrane electrodialysis device during the boron removal process in Example 1 of the application.

[0035] Figure 5 FIG. 7 is a boron concentration data chart of the carbon cloth assisted bipolar membrane electrodialysis device during the boron removal process in Example 1 and Example 2 of the application. DETAILED DESCRIPTION

[0036] The application will be further described below in conjunction with the drawings and specific embodiments, so that those skilled in the art can better understand the application and implement it. However, the embodiments are not limiting to the application.

[0037] Example 1:

[0038] The embodiment provides a construction method of a carbon cloth assisted bipolar membrane electrodialysis system and application of the construction method in removal of low-concentration boron in a water body, and the specific steps are as follows:

[0039] (1) a simulated boron-containing reverse osmosis first-stage effluent containing boron at a concentration of 1 mM and NaCl at a concentration of 5 mM is configured;

[0040] (2) a K2SO4 solution with a concentration of 0.5 M is configured as an electrode solution;

[0041] (3) 15 pieces of W0S1011 carbon cloth are cut into a size of 2 cm x 2 cm according to the size of the electrodialysis chamber;

[0042] (4) 5 pieces of W0S1011 carbon cloth are placed in the simulated boron-containing reverse osmosis first-stage effluent, and 10 pieces of carbon cloth are placed in the electrode solution, and all the carbon cloth is balanced in the solution for 24 h;

[0043] (5) an ASTOM AHA anion exchange membrane is used as an ion exchange membrane close to the anode in the electrodialysis device, and a fumasep FBM bipolar membrane is used as an ion exchange membrane close to the cathode in the electrodialysis device;

[0044] (6) an electrodialysis system is constructed, and 5 pieces of carbon cloth balanced in the corresponding chamber solution are filled in each electrodialysis chamber;

[0045] (7) a peristaltic pump is used to pass the simulated boron-containing reverse osmosis first-stage effluent obtained in step (1) and the electrode solution obtained in step (2), and the flow rate is 0.55 mL·min -1 .

[0046] (8) an eTM-L303SPL (30V3A) is used to provide a constant current of 1.4 mA cm 2 , and voltage data within 60 min are recorded; the experimental results are shown in Figure 2 .

[0047] (9) an SX620 acidity meter is used to record the pH data within 60 min; the experimental results are shown in Figure 4 .

[0048] (10) the effluent of the simulated boron-containing reverse osmosis first-stage effluent, the effluent of the electrodialysis treatment boron-containing reverse osmosis first-stage effluent chamber at 5 min, 15 min, 30 min, 45 min and 60 min are collected, the boron concentration is analyzed by ICP-OES, and the experimental results are shown in Figure 3 、 Figure 5 .

[0049] Comparative Example 1

[0050] The comparative example is similar to example 1, the difference is that no carbon cloth is used in the entire bipolar membrane electrodialysis device.

[0051] Figure 1 A carbon cloth assisted bipolar membrane electrodialysis system structure diagram constructed by the present application.

[0052] As shown in Figure 2 , it can be seen that the carbon cloth assisted bipolar membrane electrodialysis device constructed by the method of the present example has a significantly lower voltage than the bipolar membrane electrodialysis device without carbon cloth assistance (comparative example 1), which indicates that the carbon cloth assisted bipolar membrane electrodialysis device has a significant advantage in reducing boron removal energy consumption.

[0053] As shown in Figure 3 , it can be seen that the carbon cloth assisted bipolar membrane electrodialysis device constructed by the method of the present example has a significantly improved boron removal effect than the bipolar membrane electrodialysis device without carbon cloth assistance (comparative example 1), which indicates that the carbon cloth assisted bipolar membrane electrodialysis device has a significant advantage in improving boron removal effect.

[0054] As shown in Figure 4 , it can be seen that the carbon cloth assisted bipolar membrane electrodialysis device constructed by the method of the present example can make the pH value of the boron removal chamber rise to above 10.5 within 10 min, converting boric acid into borate.

[0055] As shown in Figure 5 , it can be seen that the carbon cloth assisted bipolar membrane electrodialysis device constructed by the method has good boron removal effect.

[0056] Example 2:

[0057] The present example provides a method for constructing a carbon cloth assisted bipolar membrane electrodialysis system and its application in removing low concentration boron from water bodies, the specific steps are as follows:

[0058] (1) Prepare a simulated boron-containing reverse osmosis primary effluent with a boron concentration of 1 mM and a NaCl concentration of 5 mM;

[0059] (2) Prepare a solution of K2SO4 with a concentration of 0.5 M as an electrode solution;

[0060] (3) Cut 15 pieces of W0S1011 carbon cloth with a size of 2 cm × 2 cm according to the size of the electrodialysis chamber;

[0061] (4) Place 5 pieces of W0S1011 carbon cloth in the simulated boron-containing reverse osmosis primary effluent, and place 10 pieces of carbon cloth in the electrode solution, and all carbon cloths are balanced in the solution for 24 h;

[0062] (5) using ASTOM AHA anion exchange membrane as the ion exchange membrane close to the anode in the electrodialysis device, and fumasep FBM bipolar membrane as the ion exchange membrane close to the cathode in the electrodialysis device;

[0063] (6) constructing an electrodialysis system, and filling 5 pieces of carbon cloth equilibrated in the corresponding chamber solution in each electrodialysis chamber;

[0064] (7) using a peristaltic pump to pass the simulated boron-containing reverse osmosis primary effluent obtained in step (1) and the electrode solution obtained in step (2), at a flow rate of 0.55 mL·min -1 .

[0065] (8) using eTM - L303SPL (30V3A) to provide a constant current of 1.6 mA cm 2 , and recording the voltage data within 60 min at the same time;

[0066] (9) using SX620 acidity meter to record the pH data within 60 min, and the experimental results are shown in Figure 4 .

[0067] (10) collecting the effluent of the boron-containing reverse osmosis primary effluent chamber in the electrodialysis treatment at 5 min, 15 min, 30 min, 45 min and 60 min, and analyzing the boron concentration by ICP - OES, and the experimental results are shown in Figure 5 .

[0068] As shown in Figure 4 , it can be seen that the carbon cloth assisted bipolar membrane electrodialysis device constructed by this method can make the pH value of the boron removal chamber rise to above 10.5 within 10 min, so that boric acid is converted into borate.

[0069] As shown in Figure 5 , it can be seen that the carbon cloth assisted bipolar membrane electrodialysis device constructed by this method has good boron removal effect.

[0070] Obviously, the above examples are only examples for clearly illustrating, and are not limitation to the embodiments. For those skilled in the art, other different forms of changes or variations can be made on the basis of the above description. Here, it is not necessary and impossible to enumerate all the embodiments. The obvious changes or variations derived therefrom are still within the protection scope of the present application.

Claims

1. Use of a carbon cloth assisted bipolar membrane electrodialysis system for the removal of low concentrations of boron from a water body, characterized in that, The method comprises the following steps: hydrophilic carbon cloth is tailored according to the size of the electrodialysis chamber; the obtained hydrophilic carbon cloth is respectively placed in the corresponding electrode solution and the low-concentration boron-containing solution to be treated for equilibrium; the obtained equilibrium hydrophilic carbon cloth is filled into the electrodialysis chamber of the electrodialysis device, and a constant current is applied through a direct current power supply to achieve the purpose of boron removal; the hydrophilic carbon cloth is carbon fiber fabric of one or more of W0S1011, HCP330N and CCD; the low-concentration boron-containing solution comprises a mixed solution of 0.2mM-1mM H3BO3 and 2mM-5mM NaCl simulating the primary effluent of reverse osmosis.

2. Use of the carbon cloth assisted bipolar membrane electrodialysis system according to claim 1 for the removal of low concentrations of boron from water bodies, characterized in that, The electrodialysis chamber comprises three chambers in total, one of which is a concentrated water chamber, and the other two are electrode solution chambers. The membranes used in the three chambers of the electrodialysis are anion exchange membranes and bipolar membranes, respectively.

3. Use of the carbon cloth assisted bipolar membrane electrodialysis system according to claim 1 for the removal of low concentrations of boron from water bodies, characterized in that, The silicon gel gasket of the electrodialysis device has a thickness of 0.5-3 mm, the tetrafluoroethylene gasket has a thickness of 0.5-3 mm, and the chamber has an area of 1 cm 2 ~1 m 2 .

4. Use of the carbon cloth assisted bipolar membrane electrodialysis system according to claim 1 for the removal of low concentrations of boron from water bodies, characterized in that, The electrode solution is 0.1-1M K2SO4 or Na2SO4.

5. Use of the carbon cloth assisted bipolar membrane electrodialysis system according to claim 1 for removal of low concentration boron from water bodies, characterized in that, The equilibrium time of the hydrophilic carbon cloth placed in the corresponding electrode solution and the low-concentration boron-containing solution to be treated is 2-24h.

6. Use of the carbon cloth assisted bipolar membrane electrodialysis system as claimed in claim 1 for removal of low concentration boron from water bodies characterized by, The flow rate of the electrode solution and the low-concentration boron-containing solution to be treated is 0.5 ml·min -1 ~ 2 ml·min -1 .

7. Use of the carbon cloth assisted bipolar membrane electrodialysis system as claimed in claim 1 for removal of low concentration boron from water bodies characterized by, The constant current has a current density ranging from 1.0 mA-cm -2 ~ 2.0 mA-cm -2 .

8. Use of the carbon cloth assisted bipolar membrane electrodialysis system as claimed in claim 1 for removal of low concentration boron from water bodies characterized in that, The voltage of the electrodialysis system is recorded by a direct current power supply, and the pH is recorded by a pH meter.

9. Use of the carbon cloth assisted bipolar membrane electrodialysis system as claimed in claim 1 for removal of low concentration boron from water bodies characterized in that, The boron concentration of the effluent is determined by ICP-OES.

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