Low energy consumption electrochemical ion separation and enrichment device and method

Abstract

The application relates to the technical field of electric adsorption and ion separation, and discloses a low-energy-consumption electrochemical ion separation and enrichment device and method, wherein the device comprises an electrochemical membrane stack structure composed of an end plate electrode, an ion exchange membrane, an ion adsorption electrode and a circuit switching control unit. The ion adsorption electrode is a capacitive electrode, a Faraday electrode or the like; the end plate electrode is a hydrophilic carbon felt electrode or a graphite electrode or the like; the redox electrolyte is a reversible redox compound solution such as ferrous / ferric potassium cyanide or ferric citrate; the ion exchange membrane is composed of cation exchange membranes and anion exchange membranes which are alternately stacked; direct current power supply is adopted; and the circuit switching control unit comprises multiple time relays for circuit switching. The application couples the oxidation-reduction reaction and the ion adsorption process, effectively divides the solution resistance through the membrane stack structure design, and relieves the flux attenuation problem in the multistage operation.

Description

Technical Field

[0001] This invention relates to the field of electroadsorption and ion separation technology, specifically to a low-energy-consumption electrochemical ion separation and enrichment device and method. Background Technology

[0002] Electrochemical separation technology, due to its advantages of high efficiency, flexibility, and high selectivity, has been widely used in water treatment, desalination, and resource extraction. Electroadsorption technology utilizes the electric double layer or ion intercalation mechanism on the electrode surface to store ions, typically operating at voltages below 1.2V, and achieving ion adsorption and desorption through periodic charge-discharge cycles. Based on this fundamental principle, researchers have innovatively designed battery structures to achieve efficient ion separation and enrichment. For example, innovative decoupled membrane-free electrochemical battery designs and a rocking chair method integrating adsorption and desorption processes have been developed and combined with electrode materials such as LiFePO4 to achieve selective separation of target ions in brine. However, this technology is limited by the ion storage capacity of the electrode, requiring frequent channel switching to regenerate the electrode, and is prone to ion backmixing during the process, leading to reduced energy utilization.

[0003] Electrodialysis (ED) relies on ion exchange membranes to achieve continuous ion migration under an electric field. However, it typically requires a high voltage to drive the water electrolysis reaction, resulting in high energy consumption and potential corrosion and scaling of electrode and membrane materials. Researchers have developed a redox flow desalination technology by replacing the water electrolysis reaction in ED with a redox couple. This technology can operate at near-0V, reducing energy consumption and enabling continuous operation. However, traditional symmetrical redox flow desalination cells, when constructed into multi-stage stack systems, suffer from low operating voltage and high solution resistance, leading to a decrease in ion flux as the number of stacks increases, thus limiting processing capacity and hindering large-scale application. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention provides a low-energy-consumption electrochemical ion separation and enrichment device and method. By introducing ion adsorption electrodes and circuit switching control, continuous directional migration and enrichment of ions are achieved. An electrochemical membrane stack structure suitable for continuous ion separation is constructed to improve the flux attenuation problem caused by solution resistance. High selective separation of target ions is achieved by utilizing ion exchange membranes (IEMs) or selective ion adsorption electrodes.

[0005] To achieve the above objectives, the present invention provides the following technical solution: The first aspect of this invention provides a low-energy-consumption electrochemical ion separation and enrichment device, the device comprising: An electrochemical membrane stack structure includes two end plate electrodes, an ion adsorption electrode disposed between the two end plate electrodes, and multiple ion exchange membranes alternately stacked between the electrodes. The chamber containing the end plate electrode contains a redox electrolyte; fluid chambers are formed between adjacent ion exchange membranes and between the ion exchange membrane and the ion adsorption electrode for the flow of the liquid to be treated and the concentrate. The circuit switching control unit is electrically connected to the end plate electrode and the ion adsorption electrode, and is used to switch the circuit conduction state between the electrodes at a preset period to drive the target ions to migrate directionally and unidirectionally between the fluid chambers.

[0006] Preferably, the ion adsorption electrode includes a porous current collector that allows ions and water molecules to pass through, and a capacitive electrode material or a Faraday-type electrode material attached to the porous current collector; the porous current collector is a corrosion-resistant metal mesh or titanium mesh; under the drive of the electric field and the circuit switching control unit, the target ions are adsorbed from one side chamber of the ion adsorption electrode and desorbed through the inside of the electrode to the other side chamber.

[0007] Preferably, the electrochemical membrane stack structure is a scalable multi-level stack structure; the multi-level stack structure includes multiple ion adsorption electrodes, which are spaced apart in a fluid chamber formed by multiple ion exchange membranes to divide the overall solution resistance of the electrochemical membrane stack structure.

[0008] Preferably, the end plate electrode includes a current collector plate and a hydrophilic conductive carbon felt attached to the surface of the current collector plate; the redox electrolyte contains a mixed solution of potassium ferrocyanide and potassium ferrocyanide.

[0009] Preferably, the multiple ion exchange membranes include cation exchange membranes and anion exchange membranes, which are alternately arranged between the endplate electrodes; the cation exchange membranes include monovalent cation exchange membranes or multivalent cation exchange membranes, and the anion exchange membranes include monovalent anion exchange membranes or multivalent anion exchange membranes.

[0010] Preferably, the circuit switching control unit includes multiple time relays; the device also includes multiple DC power supplies, the positive and negative terminals of which are respectively connected to the end plate electrode and the ion adsorption electrode, and the multiple time relays are connected in series in the power supply circuit between the multiple DC power supplies and the electrode.

[0011] The second aspect of this invention provides a method for constructing a low-energy electrochemical ion separation and enrichment device, comprising the following steps: The conductive carbon felt electrode is hydrophilized, cleaned and dried to serve as the end plate electrode, or a carbon cloth or carbon paper electrode supported on a platinum catalyst is used as the end plate electrode. Preparation of ion adsorption electrodes: Capacitive or Faraday electrode materials are mixed with conductive agents and binders in a certain proportion to form a slurry, which is then coated onto a current collector (stainless steel mesh or titanium mesh), dried and compacted for later use. An ion exchange membrane, a sealing gasket, and an ion adsorption electrode are stacked alternately in a preset order to form an electrochemical membrane stack, with end plate electrodes provided at both ends. Inject a reversible redox electrolyte (such as a ferrous / potassium ferricyanide solution or alizarin red solution) into the chamber adjacent to the end plate electrode. Voltage or current is applied to the electrodes by an external DC power supply, and the circuit switching control unit is used to set the periodic switching circuit path to drive the directional migration and enrichment of ions.

[0012] To achieve ion-selective separation, monovalent ion exchange membranes or selective ion adsorption electrodes can be used, and the separation efficiency and throughput can be further improved through multi-stage stack design.

[0013] This invention provides a low-energy-consumption electrochemical ion separation and enrichment device and method, which has the following beneficial effects: 1. This invention couples redox reactions with ion adsorption processes and effectively divides solution resistance through membrane stack structure design, thereby alleviating flux decay problems in multi-stage operations.

[0014] 2. This invention employs ultra-short cycle circuit switching control to achieve pseudo-continuous migration and enrichment of ions, breaking through the capacity limitation of traditional electroadsorption.

[0015] 3. This invention, combined with monovalent ion exchange membranes or selective electrode materials, can achieve continuous desalination or highly efficient selective separation of high-value ions such as lithium, potassium, ammonium, and magnesium.

[0016] 4. This invention operates at low operating voltage, reducing energy consumption and maintaining stable solution pH, which is beneficial for long-term stable operation. Attached Figure Description

[0017] Figure 1 The redox flow desalination (RFD) system of this invention consists of an array of 8 inlet / concentration chambers, with KCl auxiliary chambers and redox electrolyte chambers on both sides; Figure 2 This is a schematic diagram of the low-energy electrochemical ion separation and enrichment device of the present invention. The activated carbon electrode is integrated into the RFD chamber, and the circuit switching is controlled by two relays. Figure 3 A comparison graph showing the current performance of the device of the present invention and the comparative device under different stack numbers; Figure 4 A comparison graph showing the ion flux performance of the device of the present invention and the comparative device under different stack numbers; Figure 5 This is a schematic diagram of the low-energy electrochemical ion separation and enrichment device of the present invention. The AC electrode is placed between the two terminal electrodes, forming a three-electrode series connection. Circuit switching is controlled by two time relays. Note: For clarity, the redox electrolyte chamber, KCl chamber, and part of the ion exchange membrane on the end plate are omitted in the schematic diagram. Figure 6 The graph shows the changes in ion concentration in the inlet chamber and the concentrate chamber at different half-cycle times (6 seconds, 60 seconds, and 600 seconds). Figure 7 To demonstrate long-term desalination performance, we present changes in ion concentration and charge efficiency graphs. Figure 8 This is a schematic diagram of the current structure of the low-energy electrochemical ion separation and enrichment device of the present invention.

[0018] In this diagram, 1 is a DC power supply; 2 and 3 are time relays; 4 and 5 are end plate electrodes; 6 is an ion adsorption electrode; 7 and 8 are porous end plate electrodes; 9 and 14 are cation exchange membranes; 10 and 13 are anion exchange membranes; 11 and 12 are monovalent cation exchange membranes; ① and ⑦ are chambers containing redox electrolytes; ② and ⑥ are chambers containing auxiliary electrolytes; ③ is the inlet water chamber; ④ is the buffer solution chamber; and ⑤ is the concentrate chamber. Detailed Implementation

[0019] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0020] Reference Figures 1-8 This invention provides a low-energy-consumption electrochemical ion separation and enrichment device, the core of which is a multi-stage scalable electrochemical membrane stack structure. This electrochemical membrane stack structure ingeniously integrates redox flow desalination (RFD) technology with electroadsorption (ES) technology. By introducing an ion adsorption electrode 6, which acts as an ion relay station, into the membrane stack and cooperating with high-frequency circuit switching, pseudo-continuous unidirectional migration of target ions is achieved.

[0021] Specifically, the hardware structure of the device includes a DC power supply 1, time relays 2 and 3, end plate electrodes 4 and 5, porous end plate electrodes 7 and 8, ion adsorption electrode 6, and multiple ion exchange membranes stacked alternately (including cation exchange membranes 9 and 14, anion exchange membranes 10 and 13, and monovalent cation exchange membranes 11 and 12). These components work together to sequentially divide the device into chambers ① and ⑦ containing the redox electrolyte, chambers ② and ⑥ containing the auxiliary electrolyte, chamber ③ containing the inlet water, chamber ④ containing the buffer solution, and chamber ⑤ containing the concentrate.

[0022] Endplate electrodes 4 and 5 are respectively disposed at the left and right ends of the electrochemical membrane stack. Both are typically current collectors made of dense metal plates or graphite plates resistant to electrochemical corrosion. To further reduce interfacial contact resistance and increase the active area for the redox reaction, porous endplate electrodes 7 and 8 are tightly attached to the inner sides of endplate electrodes 4 and 5, respectively. The porous endplate electrodes 7 and 8 are preferably hydrophilically treated conductive carbon felt. In actual construction, the conductive carbon felt is pre-treated with a mixed solution of sulfuric acid and nitric acid for hydrophilic modification, and after thorough cleaning and drying, it is filled into chambers ① and ⑦ at both ends. A redox electrolyte is continuously circulated into chambers ① and ⑦. In this embodiment, a mixed solution of potassium ferrocyanide and potassium ferrocyanide with equimolar concentrations (e.g., both at 100 mM) is preferably used. This reversible redox couple can undergo a stable redox reaction at extremely low voltage, replacing the energy-intensive and gas-generating water electrolysis reaction in traditional electrodialysis, thereby maintaining the overall operating voltage of the redox flow desalination (RFD) system at a low level.

[0023] Regarding the internal fluid chamber construction of the membrane stack, from left to right, a cation exchange membrane 9, an anion exchange membrane 10, a monovalent cation exchange membrane 11, an ion adsorption electrode 6, a monovalent cation exchange membrane 12, an anion exchange membrane 13, and a cation exchange membrane 14 are arranged. These ion exchange membranes and electrodes are connected by perforated acrylic plates or insulating gaskets, forming independent chambers for the flow of various liquids. Chambers ② and ⑥ are circulated with an auxiliary electrolyte, preferably a 200mM potassium chloride solution in this embodiment, to provide basic conductivity and maintain the system's charge balance. Chamber ③ serves as the inlet chamber, circulated with the solution to be treated, such as a mixed brine solution containing a high proportion of magnesium chloride and lithium chloride (e.g., a low-quality brine with a Mg / Li ratio of 40). Chamber ④ contains the buffer solution. Chamber ⑤ contains the concentrate, used to collect high-purity target enriched ions.

[0024] As the core innovative component of this invention, the ion adsorption electrode 6 is disposed between the buffer solution chamber ④ and the concentrate chamber ⑤. Unlike traditional solid plate current collectors, the ion adsorption electrode 6 includes a porous current collector that allows ions and water molecules to pass through freely. The specific construction method is as follows: a corrosion-resistant titanium mesh or stainless steel mesh is used as the porous current collector framework. Capacitive electrode materials (such as high specific surface area activated carbon powder) or Faraday-type electrode materials (such as lithium iron phosphate, Prussian blue analogues, etc.) are mixed with conductive carbon black and polyvinylidene fluoride (PVDF) binder at a mass ratio (e.g., 85:10:5), and then added to N,N-dimethylacetamide and stirred to form a uniform slurry. This slurry is then uniformly coated onto the porous current collector, dried at 120°C, and compacted, controlling the electrode loading to approximately 10 mg / cm³. 2 This porous, permeable structure allows target ions to be adsorbed from chamber ④ on the left side of the electrode into the electrode interior under the drive of an electric field, and then desorbed through the electrode pores to chamber ⑤ on the right side during subsequent electric field switching. Furthermore, because the device is a scalable, multi-level stacked structure, the number of inlet chambers and concentration chambers can be increased in practical large-scale applications, and multiple ion adsorption electrodes 6 can be evenly distributed in the newly added fluid chambers. This effectively mitigates the overall solution resistance accumulated due to the increased number of stacks, overcoming the technical bottleneck of traditional redox flow desalination systems where ion flux decreases sharply with stack expansion.

[0025] In terms of circuit control, this device is equipped with multiple time relays ( Figure 8 The circuit switching control unit consists of time relays 2 and 3. The positive and negative terminals of the DC power supply 1 are connected to the end plate electrodes 4 and 5 and the internal ion adsorption electrode 6, respectively. Time relays 2 and 3 are connected in series in the power supply circuit between the DC power supply 1 and the electrodes.

[0026] Based on the aforementioned low-energy-consumption electrochemical ion separation and enrichment device, this invention also provides a high-efficiency, low-energy-consumption electrochemical ion separation and enrichment method. Taking the extraction of lithium ions from inferior brine with a high magnesium-to-lithium ratio as an example, the specific operating steps and working principle of this method are as follows: Step 1, fluid supply: Start the external peristaltic pump and introduce a mixed solution of potassium ferricyanide and potassium ferrocyanide with equimolar concentration into chambers 1 and 7; introduce potassium chloride auxiliary electrolyte into chambers 2 and 6; introduce a mixed solution containing magnesium chloride and lithium chloride into chamber 3; and introduce the initial collection solution or pure water into chambers 4 and 5.

[0027] The second step is to apply an electric field: Start the DC power supply 1 and apply a constant voltage to the end plate electrodes (4, 5) and the ion adsorption electrode 6. The applied constant voltage range is strictly controlled between 0.4V and 1.2V (preferably set to 1.0V constant voltage mode in this embodiment); or operate in constant current mode (e.g., 5mA) and set the cutoff voltage to 1.0V. This extremely low driving voltage ensures that the system is always within the stable potential window of the redox couple, avoiding the occurrence of side reactions.

[0028] The third step is the separation of periodic switching and pseudo-continuous operation: using time relays 2 and 3, the circuit conduction state between each electrode is automatically switched alternately according to a preset ultra-short period. In this embodiment, the half-cycle time of the preset period is precisely set between 6 seconds and 600 seconds. When high-frequency switching is performed using a 6-second or similar ultra-short period, the system exhibits an extremely excellent pseudo-continuous operating state.

[0029] In the specific microscopic migration process: within one half-cycle, the circuit conduction causes the ion adsorption electrode 6 to exhibit the potential characteristic of attracting cations, and the mixed cations in the inlet chamber ③ are driven by the electric field. Due to the sieving effect of the monovalent cation exchange membrane 11, the smaller monovalent lithium ions preferentially pass through the membrane 11 into the buffer chamber ④, and are quickly adsorbed by the left side surface and internal pores of the porous ion adsorption electrode 6 (while polyvalent magnesium ions are blocked in the inlet chamber ③); then, the time relays 2 and 3 activate to enter the next half-cycle, changing the electric field polarity or circuit connection path of the ion adsorption electrode 6. At this time, the lithium ions adsorbed inside the electrode desorb, and driven by the new electric field, they pass through the mesh of the porous current collector, migrate to the right, and enter the concentrated liquid chamber ⑤ through the porous structure.

[0030] Through the frequent switching of the aforementioned ultra-short cycle, the ion adsorption electrode 6 acts like a pump or relay station, continuously drawing in target ions from the left and expelling them from the right. This mechanism not only overcomes the limited ion storage capacity of traditional electroadsorption materials, avoiding efficiency decline and ion back-mixing caused by electrode saturation, but also makes the change in solution concentration in the fluid chamber exhibit a smooth linear increase or decrease on the macroscopic curve, achieving true continuous directional unidirectional migration.

[0031] After long-term desalination and enrichment operation monitoring, the device has maintained an extremely high current efficiency of over 80% for extended periods. Furthermore, when treating influent with a Mg / Li ratio as high as 40, the lithium-magnesium selective separation ratio reaches an astonishing 8636, with lithium extraction energy consumption of only approximately 9.2 kWh / kg Li. Simultaneously, the pH value of the solution in each chamber remains highly stable, avoiding membrane scaling and electrode corrosion problems caused by hydrolysis reactions, thus extending the device's service life and industrial application potential.

Claims

1. A low-energy-consumption electrochemical ion separation and enrichment device, characterized in that, include: An electrochemical membrane stack structure includes two end plate electrodes, an ion adsorption electrode disposed between the two end plate electrodes, and multiple ion exchange membranes alternately stacked between the electrodes. The chamber containing the end plate electrode contains a redox electrolyte; fluid chambers are formed between adjacent ion exchange membranes and between the ion exchange membrane and the ion adsorption electrode for the flow of the liquid to be treated and the concentrate. The circuit switching control unit is electrically connected to the end plate electrode and the ion adsorption electrode, and is used to switch the circuit conduction state between the electrodes at a preset period to drive the target ions to migrate directionally and unidirectionally between the fluid chambers.

2. The low-energy electrochemical ion separation and enrichment device according to claim 1, characterized in that, The ion adsorption electrode includes a porous current collector that allows ions and water molecules to pass through, and a capacitive electrode material or a Faraday-type electrode material attached to the porous current collector; the porous current collector is a corrosion-resistant metal mesh or titanium mesh; under the drive of the electric field and the circuit switching control unit, the target ions are adsorbed from one side chamber of the ion adsorption electrode and desorbed through the inside of the electrode to the other side chamber.

3. The low-energy electrochemical ion separation and enrichment device according to claim 1, characterized in that, The electrochemical membrane stack structure is a scalable multi-level stack structure; the multi-level stack structure includes multiple ion adsorption electrodes, which are spaced apart in a fluid chamber formed by multiple ion exchange membranes to divide the overall solution resistance of the electrochemical membrane stack structure.

4. The low-energy electrochemical ion separation and enrichment device according to claim 1, characterized in that, The end plate electrode includes a current collector plate and a hydrophilic conductive carbon felt attached to the surface of the current collector plate; the redox electrolyte contains a mixed solution of potassium ferrocyanide and potassium ferricyanide.

5. The low-energy electrochemical ion separation and enrichment device according to claim 1, characterized in that, The multiple ion exchange membranes include cation exchange membranes and anion exchange membranes, which are alternately arranged between the end plate electrodes; the cation exchange membranes include monovalent cation exchange membranes or multivalent cation exchange membranes, and the anion exchange membranes include monovalent anion exchange membranes or multivalent anion exchange membranes.

6. The low-energy electrochemical ion separation and enrichment device according to claim 1, characterized in that, The circuit switching control unit includes multiple time relays; the device also includes multiple DC power supplies, the positive and negative terminals of which are respectively connected to the end plate electrode and the ion adsorption electrode, and the multiple time relays are connected in series in the power supply circuit between the multiple DC power supplies and the electrode.

7. A low-energy electrochemical ion separation and enrichment method, applied to the low-energy electrochemical ion separation and enrichment apparatus according to any one of claims 1-6, characterized in that, Includes the following steps: Fluid supply: A redox electrolyte is introduced into the chamber where the end plate electrodes are located, and the solution to be treated and auxiliary electrolyte are introduced into the fluid chamber; Apply an electric field: Apply a constant voltage or constant current to the end plate electrode and the ion adsorption electrode through a DC power supply; Periodic switching: The circuit switching control unit alternately switches the circuit conduction state between the end plate electrode and the ion adsorption electrode according to a preset period, controlling the target ions to enter and penetrate the ion adsorption electrode and migrate to the adjacent fluid chamber.

8. The low-energy electrochemical ion separation and enrichment method according to claim 7, characterized in that, In the step of applying an electric field, the constant voltage applied by the DC power supply is in the range of 0.4V to 1.2V, or the constant current applied by the DC power supply is set to 1.0V and the cutoff voltage is set to 1.0V.

9. The low-energy electrochemical ion separation and enrichment method according to claim 7, characterized in that, In the cycle switching step, the half-cycle time of the preset cycle for the circuit switching control unit to perform the circuit switching is set to 6 seconds to 600 seconds.

10. A low-energy electrochemical ion separation and enrichment method according to claim 7, characterized in that, The solution to be treated is a mixed solution containing magnesium chloride and lithium chloride; the auxiliary electrolyte is a potassium chloride solution; and the redox electrolyte is a mixed solution of potassium ferricyanide and potassium ferrocyanide with equimolar concentrations.

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