A method for removing chloride ions using a flow electrode capacitive deionization device

Abstract

The application discloses a method for removing chlorine ions by a flow electrode capacitive deionization device, and belongs to the technical field of regenerated water resource treatment technology. The flow electrode capacitive deionization device is built, carbon material and divalent iron ions are used as conductive agents, and through the synergistic effect of capacitive, membrane filtration, activated carbon adsorption and the like, the chlorine ions in the regenerated water are removed through a simple process of device construction, electrode selection and chlorine ion removal. The application has the advantages of mild reaction condition, simple operation, environmental friendliness, low cost, and the like, can significantly improve the use range of the flow electrode capacitive deionization device, reduce the chlorine ion removal energy consumption, and has very important practical significance for removing the chlorine ions in the regenerated water.

Description

Technical Field

[0001] This invention belongs to the field of reclaimed water resource treatment technology, specifically relating to a method for removing chloride ions from water using a flowing electrode capacitor deionization device. Background Technology

[0002] Reclaimed water treatment can increase available water resources and solve the freshwater supply crisis; among these, chloride ion removal is a crucial issue in reclaimed water treatment and resource utilization. Chloride ions in reclaimed water originate from domestic sewage, industrial wastewater, and reagents added during wastewater treatment (such as coagulants, disinfectants, and antifouling agents). Chloride in water can cause corrosion and scaling in pipelines, contribute to salinization of freshwater and soil, inhibit plant growth, and lead to crop yield losses. However, due to the high solubility, small ionic radius, low charge, and limited bioavailability of chloride ions, the effective removal of chloride ions in water bodies through secondary treatment and conventional tertiary treatment technologies (such as coagulation, biological filtration, and microfiltration) is challenging. Researching methods for chloride ion removal in reclaimed water is of significant practical importance.

[0003] Among the existing methods for removing chloride ions from reclaimed water, such as the "A method for removing chloride ions from reclaimed water and a method for preparing an electrode" published on August 18, 2020, with publication number CN111547824A, the method disclosed is as follows: activated carbon fiber is used as the negative electrode, and the modified material formed by calcining activated carbon fiber with titanium dioxide and polyaniline at 400℃ for 1 to 4 h is used as the positive electrode. 254 mg / L of raw water is injected into the electroadsorption module, and adsorption treatment is carried out at 2 V for 70 min, with a chloride ion removal rate of 80.42% in the water. The main disadvantages of this method are: (1) The positive electrode material is modified by calcining activated carbon fiber, titanium dioxide and polyaniline at 400 °C for 1-4 h. The production of the positive electrode requires additional production processes and equipment, which increases production costs; (2) Activated carbon fiber and modified materials are used as solid positive and negative electrodes. The adsorption capacity of the electrode is affected by the limited adsorption capacity of the solid carbon electrode. The adsorption capacity of the raw water with a chloride ion concentration of 254 mg / L is 16.88 mg / g, which affects the chloride ion removal efficiency; (3) After the solid electrode is saturated with chloride ions, the electrode needs to be regenerated by applying a reverse voltage, which leads to intermittent operation of the equipment and increases energy consumption, thus increasing operating costs. Summary of the Invention

[0004] The purpose of this invention is to address the shortcomings of existing methods for removing chloride ions from reclaimed water by providing a flow electrode capacitor deionization device and its method for removing chloride ions. This method features normal operating conditions (temperature and pressure), few and simple operation steps, low energy consumption and cost, and high chloride ion removal rate.

[0005] The mechanism of this invention is as follows: carbon materials and redox-active ferrous ions serve as conductive agents, forming electrode particles that, together with electrolyte water, constitute a flowing electrode. Under the influence of an electric field, the redox reaction of ferrous ions accelerates the rapid and reversible reaction in the electrodialysis process, mediating charge transfer in the flowing electrode and improving electrode conductivity in the electric field. Simultaneously, it accelerates the capacitive deionization process, directly driving chloride ion migration, reducing charge transfer resistance, ion adsorption resistance, and internal device resistance, thereby increasing the chloride ion migration rate. During this process, an electric double layer and pseudocapacitive adsorption are formed on the electrode particles; negatively charged chloride ions in the desalination chamber migrate directionally through the ion exchange membrane into the anolyte, achieving chloride ion removal from the raw water.

[0006] The technical solution to achieve the purpose of the invention is: a method for removing chloride ions using a flowing electrode capacitive deionization device, which uses carbon materials and ferrous ions as conductive agents, and removes chloride ions from reclaimed water through a simple process of device construction, electrode selection, and chloride ion removal. The specific steps of the method are as follows:

[0007] (1) Construction of chloride ion removal device

[0008] The flowing electrode capacitive deionization device includes a flowing electrode capacitive deionization unit, a raw water storage tank, a cathode storage tank, an anode storage tank, a power supply, and a peristaltic pump. The flowing electrode capacitive deionization unit comprises an anode flowing electrode chamber, a cathode flowing electrode chamber, and a desalination chamber. The anode flowing electrode chamber consists of a graphite current collector, an anion exchange membrane, and an anode electrode solution; the cathode flowing electrode chamber consists of a graphite current collector, a cation exchange membrane, and a cathode electrode solution; the graphite current collector has parallel etched groove channels, and the effective contact area between the grooves and the membrane is 40×40~50×50mm. 2 The spacing between the anion exchange membrane and the cation exchange membrane is 5–10 mm, and they are placed between the flow electrode chamber and the desalination chamber.

[0009] (2) Electrode selection

[0010] After step (1) is completed, firstly, ferrous ions with a mass fraction of 0.125–0.5% are added to the anode flowing electrode chamber, then a conductive agent with a mass concentration of 50–100 g / L and water are added to the anode flowing electrode chamber, and finally, a conductive agent with a concentration of 50–100 g / L is added to the cathode flowing electrode chamber. The ferrous ions in the anode flowing electrode chamber are either ferrous sulfate or ferrous chloride; the conductive agent in the anode flowing electrode solution is either activated carbon with a mesh size of 160–200 mesh, carbon black, carbon nanotubes, or graphene; the conductive agent in the cathode flowing electrode solution is at least one of activated carbon with a mesh size of 160–200 mesh, carbon black, carbon nanotubes, or graphene.

[0011] (3) Chloride ion removal

[0012] After step (2) is completed, firstly, the voltage between the anode flow electrode chamber and the cathode flow electrode chamber is set to 0.5-2.5V. Secondly, the circulation flow rate of the anode and cathode flow electrode liquid is set to 15-35ml / min. Then, chlorine-containing wastewater with an initial mass concentration of 500-1000mg / L is added to the raw water storage tank. Next, the raw water is pumped from the raw water storage tank into the desalination chamber by a peristaltic pump. The circulation flow rate of the chlorine-containing wastewater is set to 15-35ml / min. Then, the power is turned on and the treatment lasts for 30-180 minutes. Finally, the mass concentration of chloride ions in the raw water in the desalination chamber is measured to be 97.15-414.15mg / L, and the chloride ion removal rate is 17.17-80.57%.

[0013] After adopting the above technical solution, the present invention mainly has the following effects:

[0014] (1) This invention uses carbon materials and ferrous ions as conductive agents in the anolyte flow electrode solution, eliminating the need for modification of the carbon materials, reducing production processes and equipment, and lowering production costs. Simultaneously, the addition of redox-active substances triggers a redox reaction in the anolyte flow electrode chamber, generating a pseudocapacitive effect that mediates electron transfer in the flow electrode, enhancing charge transfer between the graphite current collector and the flow electrode, strengthening ion migration, and promoting the adsorption of more chloride ions in the anolyte flow electrode solution. The chloride ion removal rate is 1.62 times that of the flow electrode without added redox-active substances and 1.58 times that of the solid electrode.

[0015] (2) The present invention uses a flow electrode capacitor deionization device. Through the synergistic effect of capacitor, membrane filtration and activated carbon adsorption, the initial mass concentration of chlorine-containing raw water can be increased to 500-1000 mg / L, which significantly expands the application range of the device. Moreover, the energy consumption for chlorine removal is only 0.197 kWh / mol, which is 37.5% lower than that without the addition of redox active substances.

[0016] (3) In the anolyte used in this invention, the conductive agent is activated carbon, and the redox active substance is ferrous sulfate and / or ferrous chloride. The electrode materials are inexpensive, readily available, safe, and do not cause secondary pollution to the environment. Implementation

[0017] The present invention will be further described in detail below with reference to specific embodiments: Example

[0018] The specific steps of a method for removing chloride ions using a flowing electrode capacitive deionization device are as follows:

[0019] (1) Construction of chloride ion removal device

[0020] The flowing electrode capacitive deionization device includes a flowing electrode capacitive deionization unit, a raw water storage tank, a cathode storage tank, an anode storage tank, a power supply, and a peristaltic pump. The flowing electrode capacitive deionization unit comprises an anode flowing electrode chamber, a cathode flowing electrode chamber, and a desalination chamber. The anode flowing electrode chamber consists of a graphite current collector, an anion exchange membrane, and an anode electrode solution; the cathode flowing electrode chamber consists of a graphite current collector, a cation exchange membrane, and a cathode electrode solution; the graphite current collector has parallel etched groove channels, and the effective contact area between the grooves and the membrane is 40×40 mm. 2 The anion exchange membrane and the cation exchange membrane are spaced 10 mm apart and are placed between the flow electrode chamber and the desalination chamber.

[0021] (2) Electrode selection

[0022] After step (1) is completed, 0.5% by mass of ferrous ions is first added to the anode flow electrode chamber, followed by a 50 g / L conductive agent and water. Finally, a 50 g / L conductive agent is added to the cathode flow electrode chamber. The ferrous ions in the anode flow electrode chamber are either ferrous sulfate or ferrous chloride; the conductive agent in the anode flow electrode solution is either 160 mesh activated carbon, carbon black, carbon nanotubes, or graphene; and the conductive agent in the cathode flow electrode solution is at least one of 160 mesh activated carbon, carbon black, carbon nanotubes, or graphene.

[0023] (3) Chloride ion removal

[0024] After step (2) is completed, firstly, the voltage between the anode flow electrode chamber and the cathode flow electrode chamber is set to 2.5V. Secondly, the circulation flow rate of the anode and cathode flow electrode liquid is set to 30ml / min. Then, chlorine-containing wastewater with an initial mass concentration of 500mg / L is added to the raw water storage tank. Next, the raw water is pumped from the raw water storage tank into the desalination chamber by a peristaltic pump. The circulation flow rate of the chlorine-containing wastewater is set to 30ml / min. Then, the power is turned on and the treatment is carried out for 180min. Finally, the mass concentration of chloride ions in the raw water in the desalination chamber is measured to be 97.15mg / L, and the chloride ion removal rate is 80.57%. Example

[0025] A method for removing chloride ions using a flowing electrode capacitive deionization device, similar to Example 1, wherein:

[0026] In step (1), the effective contact area between the groove and the membrane is 50×50mm. 2 The spacing between the ion exchange membranes is 5 mm.

[0027] In step (3), the voltage between the anode and cathode flow electrode chambers was controlled at 2V during the adsorption process, the circulation flow rate of the anode and cathode flow electrode liquid was controlled at 25ml / min, the circulation flow rate of the chlorine-containing wastewater was controlled at 25ml / min, the initial concentration of the chlorine-containing wastewater was controlled at 500 mg / L, the adsorption time was 30min, the mass concentration of chloride ions in the water was measured to be 342.9mg / L, and the chloride ion removal rate was 31.42%. Example

[0028] A method for removing chloride ions using a flowing electrode capacitive deionization device, similar to Example 1, wherein:

[0029] In step (2), the mass fraction of the redox active material in the anolyte flow electrode chamber is controlled to be 0.125%. The concentration of the conductive agent in the anolyte flow electrode solution is 100 g / L, and the mesh size of the activated carbon is 200 mesh. The concentration of the conductive agent in the cathode flow electrode is 100 g / L, and the mesh size of the activated carbon is 200 mesh.

[0030] In step (3), the power supply is turned on, and the voltage between the anode flow electrode chamber and the cathode flow electrode chamber is controlled at 1.5V during the adsorption process. The circulation flow rate of the anode and cathode flow electrode liquid is controlled at 15 ml / min, the circulation flow rate of the chlorine-containing wastewater is controlled at 15 ml / min, the initial concentration of the chlorine-containing wastewater is controlled at 500 mg / L, the adsorption treatment time is 180 min, the mass concentration of chloride ions in the water is measured to be 178.7 mg / L, and the chloride ion removal rate is 64.26%. Example

[0031] A method for removing chloride ions using a flowing electrode capacitive deionization device, similar to Example 1, wherein:

[0032] In step (3), the voltage between the anolyte flow electrode chamber and the cathode flow electrode chamber was controlled at 0.5V during the adsorption process, the redox active substance mass fraction in the anolyte flow electrode chamber was controlled at 0.5%, the circulation flow rate of the anolyte and cathode flow electrode liquid was controlled at 35ml / min, the circulation flow rate of the chlorine-containing wastewater was controlled at 35ml / min, the initial concentration of the chlorine-containing wastewater was controlled at 1000mg / L, the adsorption treatment time was 180min, the chloride ion mass concentration in the water was measured to be 349.25mg / L, and the chloride ion removal rate was 30.15%.

[0033] Experimental results

[0034] 1. Effect of different applied voltages on chloride ion removal

[0035] serial number Applied voltage (V) Ferrous chloride mass fraction (%) Flow rate (ml / min) Chloride ion concentration (mg / L) Removal rate (%) 1 0.5 0.5 25 500 17.17 2 1.0 0.5 25 500 36.59 3 1.5 0.5 25 500 58.03 4 2.0 0.5 25 500 71.46 5 2.5 0.5 25 500 80.57

[0036] 2. Effect of different ferrous chloride mass fractions on chloride ion removal

[0037] serial number Applied voltage (V) Ferrous chloride mass fraction (%) Flow rate (ml / min) Chloride ion concentration (mg / L) Removal rate (%) 1 2 0 25 500 49.64 2 2 0.125 25 500 52.26 3 2 0.250 25 500 57.26 4 2 0.375 25 500 71.84 5 2 0.500 25 500 76.63

[0038] 3. Effect of different flow rates on chloride ion removal

[0039] serial number Applied voltage (V) Ferrous chloride mass fraction (%) Flow rate (ml / min) Chloride ion concentration (mg / L) Removal rate (%) 1 2 0.5 15 500 40.05 2 2 0.5 20 500 45.79 3 2 0.5 25 500 74.01 4 2 0.5 30 500 77.76 5 2 0.5 35 500 66.18

[0040] The above experiments show that: This invention uses 160-mesh activated carbon as a conductive agent with a concentration of 50 g / L. During the adsorption process, the voltage between the anode and cathode flow electrode chambers is controlled at 2.5 V, the ferrous chloride mass fraction in the anode flow electrode chamber is controlled at 0.5%, the circulation flow rate of the anode and cathode flow electrode solutions is controlled at 30 ml / min, the circulation flow rate of the chlorine-containing wastewater is controlled at 30 ml / min, the initial concentration of the chlorine-containing wastewater is controlled at 500 mg / L, and the adsorption time is 180 min. The chloride ion mass concentration in the water is reduced to 97.15 mg / L, and the chloride ion removal rate is 80.57%. The redox reaction of ferrous ions mediates electron transfer in the flow electrode, effectively improving electron transfer and ion migration rates. The electrode solution in the anode flow electrode chamber can adsorb more chloride ions, improving the chloride ion removal effect and reducing the operating cost of chloride ion removal. The energy consumption is only 0.197 kWh / mol, which is 37.5% lower than that without the addition of ferrous ions. The reaction conditions are mild, the operation is simple, the environment is friendly and the cost is low, and the operation is stable without the need to replace the new electrode, which reduces operating costs.

Claims

1. A method for removing chloride ions using a flow electrode capacitive deionization device, comprising: The method comprises the following steps: (1) Construction of a chloride ion removal device The flow electrode capacitive deionization device comprises a flow electrode capacitive deionization device component, a raw water storage tank, a cathode storage tank, an anode storage tank, a power supply and a peristaltic pump; the flow electrode capacitive deionization device component comprises an anode flow electrode chamber and a cathode flow electrode chamber and a desalination chamber; the anode flow electrode chamber is composed of a graphite current collector plate, an anion exchange membrane and an anode electrode solution; the cathode flow electrode chamber is composed of a graphite current collector plate, a cation exchange membrane and a cathode electrode solution; the graphite current collector plate contains parallel etched groove channels, and the groove has an effective contact area of 40*40-50*50mm with the membrane 2 ; the distance between the anion exchange membrane and the cation exchange membrane is 5-10mm, and the membranes are arranged between the flow electrode chambers and the desalination chamber. After the first step is completed, first add 0.125-0.5% of divalent iron ions by mass fraction to the anode flow electrode chamber, add 50-100 g / L of a conductive agent and water to the anode flow electrode chamber, and finally add a conductive agent with a concentration of 50-100 g / L to the cathode flow electrode chamber; the source of the divalent iron ions in the anode flow electrode chamber is one of ferrous sulfate and ferrous chloride; the conductive agent in the anode flow electrode chamber is one of activated carbon, carbon black, carbon nanotubes, and graphene with a mesh size of 160-200 mesh; the conductive agent in the cathode flow electrode chamber is at least one of activated carbon, carbon black, carbon nanotubes, and graphene with a mesh size of 160-200 mesh; (3) Chloride ion removal After the second step is completed, first set the voltage between the anode flow electrode chamber and the cathode flow electrode chamber to 0.5-2.5 V, second set the circulating flow rate of the anode and cathode flow electrode liquid to 15-35 ml / min, then add the chloride-containing wastewater with an initial mass concentration of 500-1000 mg / L to the raw water storage tank, next pump the raw water from the raw water storage tank into the desalination chamber through a peristaltic pump, set the circulating flow rate of the chloride-containing wastewater to 15-35 ml / min, then connect the power supply, process for 30-180 min, and finally measure the mass concentration of chloride ions in the raw water in the desalination chamber to be 97.15-414.15 mg / L.

2. The method according to claim 1, wherein: In the second step, first add 0.5% of divalent iron ions by mass fraction to the anode flow electrode chamber, add 50 g / L of a conductive agent and water to the anode flow electrode chamber, and finally add a conductive agent with a concentration of 50 g / L to the cathode flow electrode chamber; the source of the divalent iron ions in the anode flow electrode chamber is one of ferrous sulfate and ferrous chloride; the conductive agent in the anode flow electrode chamber is activated carbon with a mesh size of 160 mesh; the conductive agent in the cathode flow electrode chamber is activated carbon with a mesh size of 160 mesh; In step (1), the effective contact area of the graphite current collector plate groove and the membrane is 40 x 40 mm 2 ; the distance between the anion exchange membrane and the cation exchange membrane is 10 mm; In the third step, first set the voltage between the anode flow electrode chamber and the cathode flow electrode chamber to 2.5 V, second set the circulating flow rate of the anode and cathode flow electrode liquid to 30 ml / min, then add the chloride-containing wastewater with an initial mass concentration of 500 mg / L to the raw water storage tank, next pump the raw water from the raw water storage tank into the desalination chamber through a peristaltic pump, set the circulating flow rate of the chloride-containing wastewater to 30 ml / min, then connect the power supply, process for 180 min, and finally measure the mass concentration of chloride ions in the raw water in the desalination chamber to be 97.15 mg / L.

3. The method according to claim 1, wherein: ​ In step (1), the recess has an effective contact area of 50 x 50 mm with the membrane 2 The spacing of the ion exchange membranes is 5 mm. In the step (3), the voltage between the anode flow electrode chamber and the cathode flow electrode chamber is controlled to be 2V, the circulating flow rate of the anode and cathode flow electrode liquid is controlled to be 25ml / min, the circulating flow rate of the wastewater containing chlorine is controlled to be 25ml / min, the initial concentration of the wastewater containing chlorine is controlled to be 500mg / L, the adsorption treatment time is 30min, and the mass concentration of the chlorine ion in the water body is measured to be 342.9mg / L.