An electrochemical method for continuous removal of ions from a solution without membranes

Abstract

The application discloses an electrochemical method for continuously removing ions in a solution without a membrane, and belongs to the technical field of water treatment and ion separation. The method comprises the following steps: setting two parallel plate anodes and a circular point cathode in a central position; setting a liquid flow channel between the plate cathodes and provided with a solution inlet, a solution outlet and a depleted liquid extraction port; injecting a to-be-processed solution into the solution inlet, flowing through the circular point cathode through the liquid flow channel, and under the action of an electric field, ions in the to-be-processed solution migrate to form a depleted flow with a decreased ion concentration and two enrichment flows with an increased ion concentration on both sides; continuously extracting the depleted liquid from the depleted liquid extraction port, and naturally flowing out the residual solution from the solution outlet. The application does not need a selective permeation membrane, avoids problems of membrane pollution, frequent cleaning and elution regeneration, has a simple structure, low operation cost, can realize efficient, green and continuous removal of ion-type organic matters and heavy metal ions such as copper, zinc and lead, and has a wide application prospect.

Description

Technical Field

[0001] This invention belongs to the field of water treatment and ion separation technology, specifically relating to an electrochemical method for continuous removal of ions from solution without a membrane. Background Technology

[0002] With the rapid development of industry, industries such as electroplating, mining, and chemicals generate large amounts of wastewater containing metal ions. These metal ions (such as copper, nickel, cobalt, chromium, and lead) are non-biodegradable, have cumulative toxicity, and are persistent, posing a threat not only to human health but also to the balance of ecosystems. Therefore, efficient and environmentally friendly removal of metal ions from solutions has significant economic and social value.

[0003] In existing technologies, methods for removing metal ions from solutions mainly include chemical precipitation, solvent extraction, adsorption, membrane separation, and electrochemical methods. Among these, chemical precipitation and solvent extraction are simple to operate and have low costs, but their treatment efficiency is limited, the effluent is difficult to meet stringent discharge standards, and the generated sludge and extract can easily cause secondary pollution. Adsorption methods have a certain removal effect on low concentrations of metal ions, but the adsorbent capacity is limited, requiring frequent regeneration or replacement, resulting in high operating costs. Membrane separation methods have high separation efficiency and excellent effluent quality, but their investment and operating costs are extremely high, and the membrane modules are prone to scaling and fouling, requiring regular cleaning and maintenance.

[0004] Electrochemical methods, with their simple operation, high treatment efficiency, lower cost compared to traditional chemical methods, and minimal or no chemical additives and sludge production, have become a research focus in the field of heavy metal ion removal in recent years. Currently, commonly used electrochemical techniques for metal ion removal in industry and laboratories mainly include electrodialysis, electrodeposition, and capacitive deionization. For example, patent document CN105492108A discloses a method based on ion concentration polarization, which applies an electric field between two parallel ion exchange membranes (cation or anion exchange membranes) with the same charge to form an ion depletion zone (desalination pure flow) and an ion enrichment zone (concentrated brine flow), achieving water desalination / purification and pre-enrichment of biological agents. Martin Z. Bazant et al. at MIT applied shock electrodialysis to water purification, successfully separating solutions containing metal ions such as lead, sodium, strontium, and cobalt into ion enrichment and depletion flows by setting cation-selective permeable membranes inside the anode and cathode.

[0005] In existing electrochemical methods, ion-selective permeation membranes (such as cation exchange membranes, anion exchange membranes, or bipolar membranes) are almost indispensable core components. Their main function is to separate the anode and cathode chambers, preventing the mixing and interference of reaction products; and, based on selective permeation, to allow the directional migration of specific metal ions. However, the purchase cost of these membranes is high, and their selective permeation performance decreases and transmembrane resistance increases after long-term operation, requiring regular cleaning, maintenance, and even replacement. This increases the difficulty of designing and assembling electrochemical devices, and raises the overall cost. Therefore, there is a need to develop electrochemical methods with simple structures that do not require ion-selective permeation membranes, to achieve the goal of efficient, low-cost, and stable removal of metal ions from solution. Summary of the Invention

[0006] The purpose of this invention is to provide an electrochemical method for the continuous removal of ions from solutions without a membrane, which solves the problems of high cost, easy pollution, and secondary sludge generation caused by the selection of permeable membranes and adsorbents in existing methods. It can be used for the efficient and continuous removal of fluorescent ions and heavy metal ions in solutions.

[0007] To achieve the above objectives, the present invention adopts the following technical solution:

[0008] This invention provides a membrane-free, continuous electrochemical method for removing ions from solution, comprising the following steps:

[0009] S1. Set two parallel flat plate anodes and a circular cathode located in the center.

[0010] S2. Set up a liquid flow channel located between the flat cathodes and having a solution inlet, a solution outlet, and a depleted liquid extraction port;

[0011] S3. The solution to be treated is injected into the solution inlet at the injection flow rate and flows through the circular cathode through the liquid flow channel. Under the action of the electric field, the ions in the solution to be treated migrate to form a depletion flow with decreasing ion concentration and an enrichment flow with increasing ion concentration on both sides.

[0012] S4. Continuously extract the depleted liquid from the depleted liquid extraction port at the extraction flow rate, and the remaining solution flows out naturally from the solution outlet.

[0013] The principle of this invention is to utilize the electro-convection generated near the dot cathode under the action of an electric field to drive deionization shocks. The ion concentration in the deionization shock wave range near the dot cathode drops sharply, and combined with the liquid flow between the plate anodes, a stable depletion flow and enrichment flow are formed, eliminating the need for the ion-selective permeable membrane in existing methods.

[0014] Preferably, in step S1, the flat plate anode and the dot cathode are selected from one or more of copper electrodes, platinum electrodes, and carbon electrodes, and have no adsorption effect on ions in the solution to be treated.

[0015] More preferably, in step S1, the flat plate anode is a flat plate electrode with a length of 1 mm to 10 cm, and the spacing between the flat plate electrodes is 1 mm to 10 cm; the dot cathode is a dot electrode with a diameter of 10 μm to 1 cm.

[0016] Preferably, in step S2, the fluid flow channel is polydimethylsiloxane (PDMS) containing microfluidic cavities.

[0017] Preferably, in step S2, the depletion liquid extraction port is located between the downstream of the dot cathode and the end of the flat plate anode.

[0018] Preferably, in step S3, the solution to be treated is an ionic organic fluorescent dye or a metal ion solution.

[0019] Preferably, in step S3, the electric field is formed by applying a DC voltage, and the DC voltage exceeds the water electrolysis voltage threshold. By increasing the voltage, the concentration of depleted ions can be reduced and the ion depletion degree can be increased. This is because the flow of the pumped solution can suppress side reactions near the electrode, such as dendrite growth and bubble growth, thus ensuring continuous and stable operation.

[0020] More preferably, in step S3, the DC voltage is 2-20 V and the injection flow rate is 0.05-0.5 μL / s.

[0021] Preferably, in step S4, the ion depletion concentration of the depletion solution is 0.0089-0.0864 mM.

[0022] Preferably, in step S4, the extraction flow rate of the depleted extract is 1% to 50% of the injection flow rate.

[0023] Compared with the prior art, the present invention has the following beneficial effects:

[0024] The electrochemical method for continuous ion removal from solution proposed in this invention only requires placing two parallel flat anodes and a circular electrode into a liquid flow channel. By applying a DC electric field using two pumps, the solution is divided into a depletion flow (decreasing ion concentration) and an enrichment flow (increasing ion concentration on both sides). This method eliminates the need for selectively permeable or semi-permeable membranes, reducing equipment costs. Furthermore, since the electrodes do not adsorb ions, elution is unnecessary after prolonged operation, avoiding membrane fouling, frequent cleaning, and elution regeneration issues. It also eliminates the need for additional chemical reagents such as precipitants. This method achieves efficient, green, and continuous removal of ionic organic compounds and heavy metal ions such as copper, zinc, and lead, and has broad application prospects. Attached Figure Description

[0025] Figure 1 Figure a is a schematic diagram of the ion concentration distribution during the ion removal process in the embodiment. Two flat plate anodes are distributed in parallel, and the dot cathode is located in the center. A depletion flow is formed downstream of the dot cathode. In figure b, the solid line is the concentration value at the position of the yellow line in figure a, and the dashed line is the initial concentration line. The figure is divided into the depletion flow and the enrichment flow on both sides.

[0026] Figure 2 Figure a shows the concentration distribution of the fluorescent ionic dye (Alexa Fluor 488, Invitrogen) before and after applying a constant voltage of 10 V when the initial concentration of the dye was 0.1 mM and the injection flow rate was 0.05 μL / s. Figure b shows the fluorescence intensity and concentration distribution at the yellow arrow in figure a.

[0027] Figure 3 The maximum removal rate of fluorescent dye ions in the solution under different flow rates and operating voltages in the examples is shown.

[0028] Figure 4 Figure a shows the copper ion concentration and depletion degree in the depletion solution extracted under different operating voltages when the initial copper ion concentration is 0.1 mM, the injection flow rate is 0.2 μL / s, and the depletion solution extraction flow rate is 0.02 μL / s in the example; Figure b shows the copper ion concentration and depletion degree in the depletion solution extracted under different injection flow rates when the operating voltage is 10 V and the depletion solution extraction flow rate is 0.02 μL / s; Figure c shows the change of current over time under different voltages in figure a; Figure d shows the change of current over time under different injection flow rates in figure b.

[0029] Figure 5 Figure 1 shows the zinc ion concentration and depletion rate in the depletion solution under different operating voltages when the initial zinc ion concentration is 0.1 mM, the injection flow rate is 0.2 μL / s, and the depletion solution extraction flow rate is 0.02 μL / s in the example; Figure 2 shows the change of current over time under different voltages.

[0030] Figure 6Figure 1 shows the zinc ion concentration and depletion degree in the depletion solution under different operating voltages when the initial lead ion concentration is 0.1 mM, the injection flow rate is 0.2 μL / s, and the depletion solution extraction flow rate is 0.02 μL / s in the example; Figure 2 shows the change of current over time under different voltages. Detailed Implementation

[0031] To more fully understand and demonstrate the technical solutions, objectives, and advantages of the present invention, the technical effects produced by the present invention will be further described in detail and completely below with reference to the accompanying drawings and specific embodiments. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. It should be noted that other embodiments obtained by those skilled in the art without departing from the concept of the present invention are all within the protection scope of the present invention.

[0032] The following examples provide an electrochemical method for continuous removal of ions from solution without a membrane, comprising the following steps:

[0033] S1. Set two parallel flat plate anodes and a circular cathode located in the center.

[0034] S2. Set up a liquid flow channel located between the flat cathodes and having a solution inlet, a solution outlet, and a depleted liquid extraction port;

[0035] S3. The solution to be treated is injected into the solution inlet at the injection flow rate and flows through the liquid flow channel to the circular cathode. Under the action of the electric field, the ions in the solution to be treated migrate to form a depletion flow with a decrease in ion concentration and an enrichment flow with an increase in ion concentration on both sides.

[0036] S4. Extract the depleted liquid continuously from the depleted liquid extraction port at a fixed extraction speed, and the remaining solution flows out naturally from the solution outlet.

[0037] In some embodiments, the device consists of two parallel flat anodes and a centrally located dot cathode, as well as a liquid flow channel located between the flat anodes and having a solution inlet, a solution outlet, and a depletion liquid extraction port. A pump is used to pump the solution to be treated from the solution inlet and through the dot cathode at a constant speed. Under the action of an electric field, the ions in the solution to be treated are driven away from the dot cathode, forming a depletion flow with decreasing ion concentration downstream and an enrichment flow with increasing ion concentration on both sides.

[0038] In some implementations, the depletion solution with different ion depletion concentrations is obtained by changing the operating voltage and the injection flow rate of the solution to be treated; another pump is used to pump the depletion solution out from the outlet of the liquid flow channel, and the remaining solution flows out naturally from the outlet at the end of the plate anode; by maintaining the stable operation of the electric field and the two pumps, the continuous removal of ions from the solution is achieved.

[0039] Example 1: Membrane-free electrochemical removal of fluorescent ions

[0040] This embodiment provides a method for the continuous removal of dye ions from solution using an electrochemical method, the steps of which are as follows:

[0041] (1) A device is constructed by placing two parallel flat copper plates (1 cm × 2 mm) and one round copper plate (100 μm in diameter) in a polydimethylsiloxane (PDMS) containing a microfluidic cavity. The flat copper plates are spaced 4 mm apart, and the round copper plate is located at the center. The flat copper plates serve as the anode, and the round copper plate serves as the cathode. Figure 1 As shown, 0.01 mM of an ionic fluorescent dye (Alexa Fluor 488, Invitrogen) was introduced. After calibration, the fluorescence intensity showed a linear relationship with the dye molecule concentration. The dye removal effect was visualized in real time and in situ using a fluorescence microscope (AXIO Zoom.V16, Zeiss), demonstrating the maximum removal rate. Since Example 1 only demonstrated the ion removal effect of the system in situ, only one pump was used to inject the solution, and the depletion of the solution was not involved.

[0042] (2) Using a micro-injection pump, inject the fluorescent dye solution into the device at a flow rate of 0.05 μL / s, and apply a DC voltage of 10V. Figure 2 As shown, the fluorescent dye is displaced from the vicinity of the cathode, forming a depletion current downstream of the cathode to remove ions, and an enrichment current at the two parallel anodes. The initial concentration of the fluorescent dye, c0, is 0.1 mM, and the minimum concentration of the depletion current, c... min The maximum removal rate (also known as the maximum depletion rate) is 0.0099 mM (f dep =(c0-c min The ratio (c0) is 0.901, indicating that 90% of the ions were removed.

[0043] (3) The minimum concentration and maximum removal rate in the depletion zone under different injection flow rates and voltages are as follows: Figure 3 As shown, different combinations of injection flow rates of 0.05 to 0.5 μL / s and DC voltages of 2-20 V resulted in a minimum depletion concentration range of 0.0089 to 0.0864 mM, with corresponding maximum removal rates between 0.136 and 0.911. Therefore, the membrane-free, continuous electrochemical method for ion removal from solution proposed in this invention is applicable to various ion depletion requirements.

[0044] Example 2

[0045] This embodiment demonstrates a method for continuously removing copper ions and extracting the ion-depleted solution, as detailed below:

[0046] (1) Prepare a CuSO4 solution with a concentration of 0.1 mM.

[0047] (2) Example 2 involves the extraction of depleted liquid. Compared with Example 1, an additional pump is added to extract the solution in the depleted flow at a set rate. The extraction port is located at the outlet downstream of the dot cathode.

[0048] (3) Copper ion depletion effect under different working voltages. CuSO4 solution (c0 = 0.1 mM) was injected into the device at a constant flow rate of 0.2 μL / s. After applying a constant voltage, the depleted solution was extracted at a flow rate of 0.02 μL / s. Figure 4 a shows the Cu in the extract under a voltage of 5-20 V. 2+ Concentration (c) ex ) and depletion degree (depletion degree = (c0 - c) ex As the voltage increased from 5 V to 20 V, the depletion percentage increased from 0.66 to 0.81, indicating that 81% of the Cu in the depleted solution was depleted. 2+ The fact that it was cleared indicates that the higher the operating voltage, the more obvious the depletion effect.

[0049] (4) Copper ion depletion effect at different injection flow rates. 0.1 mM CuSO4 solution was injected into the device at a constant flow rate. After applying 10 V, the depleted solution was extracted at a flow rate of 0.02 μL / s. Figure 4 b shows the Cu in the extract at injection flow rates of 0.2, 0.5, and 0.8 μL / s. 2+ Concentration and depletion. As the injection flow rate increased, the depletion decreased from 0.73 to 0.45. Although the depletion effect decreased slightly with the increase of the injection flow rate, the processing capacity per unit time was improved.

[0050] Example 3

[0051] This embodiment demonstrates a method for continuously removing zinc ions and extracting ion-depleted solution. The apparatus is the same as in Embodiment 2, except that the solution is replaced with zinc ions.

[0052] (1) Prepare a ZnCl2 solution with a concentration of 0.1 mM.

[0053] (2) Zinc ion depletion effect under different working voltages. A 0.1 mM ZnCl2 solution was injected into the device at a constant flow rate of 0.2 μL / s. After applying a constant voltage, the depleted solution was extracted at a flow rate of 0.02 μL / s. Figure 5 a shows the Zn content in the extract under a voltage of 5-15 V. 2+ Concentration and depletion rate. As the voltage increased from 5 V to 15 V, the depletion rate increased from 0.38 to 0.73, indicating that 73% of the Zn in the depleted solution was depleted. 2+ It was deleted.

[0054] Example 4

[0055] This embodiment demonstrates a method for continuously removing lead ions and extracting ion-depleted solution. The apparatus is the same as in Embodiment 2, except that the solution is replaced with lead ions.

[0056] (1) Prepare a PbCl2 solution with a concentration of 0.1 mM.

[0057] (2) Lead ion depletion effect under different working voltages. 0.1 mM PbCl2 solution was injected into the device at a constant flow rate of 0.2 μL / s. After applying a constant voltage, the depleted solution was extracted at a flow rate of 0.02 μL / s. Figure 6 a shows the Pb in the depletion flow extract under a voltage of 5-15 V. 2+ Concentration and depletion rate. As the voltage increased from 5 V to 15 V, the depletion rate increased from 0.88 to 0.96, indicating that 96% of the Pb in the depleted solution was depleted. 2+ It was deleted.

[0058] The above are merely preferred embodiments of the present invention and are not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A membrane-free, continuous electrochemical method for removing ions from solution, characterized in that, Includes the following steps: S1. Set two parallel flat plate anodes and a circular cathode located in the center. S2. Set up a liquid flow channel located between the flat cathodes and having a solution inlet, a solution outlet, and a depleted liquid extraction port; S3. The solution to be treated is injected into the solution inlet at the injection flow rate and flows through the circular cathode through the liquid flow channel. Under the action of the electric field, the ions in the solution to be treated migrate to form a depletion flow with decreasing ion concentration and an enrichment flow with increasing ion concentration on both sides. S4. Continuously extract the depleted liquid from the depleted liquid extraction port at the extraction flow rate, and the remaining solution flows out naturally from the solution outlet.

2. The electrochemical method for continuous removal of ions from solution without a membrane according to claim 1, characterized in that, In step S1, the flat plate anode and the dot cathode are selected from one or more of copper electrodes, platinum electrodes, and carbon electrodes, and have no adsorption effect on ions in the solution to be treated.

3. The electrochemical method for continuous removal of ions from solution without a membrane according to claim 1, characterized in that, In step S2, the fluid flow channel is a polydimethylsiloxane containing a microfluidic cavity.

4. The electrochemical method for continuous removal of ions from solution without a membrane according to claim 1, characterized in that, In step S2, the depletion liquid extraction port is located between the downstream of the dot cathode and the end of the flat plate anode.

5. The electrochemical method for continuous removal of ions from solution without a membrane according to claim 1, characterized in that, In step S3, the solution to be treated is an ionic organic fluorescent dye or a metal ion solution.

6. The electrochemical method for continuous removal of ions from solution without a membrane according to claim 1, characterized in that, In step S3, the electric field is formed by applying a DC voltage, and the DC voltage exceeds the water electrolysis voltage threshold.

7. The electrochemical method for continuous removal of ions from solution without a membrane according to claim 6, characterized in that, In step S3, the DC voltage is 2-20 V and the injection flow rate is 0.05-0.5 μL / s.

8. The electrochemical method for continuous removal of ions from solution without a membrane according to claim 1, characterized in that, In step S4, the ion depletion concentration of the depletion solution is 0.0089-0.0864 mM.

9. The electrochemical method for continuous removal of ions from solution without a membrane according to claim 1, characterized in that, In step S4, the extraction flow rate of the depleted extract is 1% to 50% of the injection flow rate.

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