Methods for removing chloride ions from water by catalytic oxidation

Abstract

This invention relates to a method for removing chloride ions from water by catalytic oxidation, belonging to the field of water treatment technology. The method includes: Step S1, electrolyzing a chlorine-containing solution to electrocatalytically oxidize chloride ions in the solution to form chlorine gas; simultaneously, adding persulfate to the chlorine-containing solution; Step S2, activating the persulfate to generate sulfate radicals and hydroxyl radicals, utilizing these radicals to catalytically oxidize chloride ions to form chlorine gas; Step S3, collecting and treating the chlorine gas. The embodiments of this invention utilize electrocatalytic oxidation and the catalytic oxidation of chloride ions by strong oxidizing radicals generated after persulfate activation to oxidize chloride ions into easily treatable chlorine gas. This method can efficiently remove chloride ions from water, requires no complex equipment, has low energy consumption, can be used for a long time, and is simple to operate, safe, clean, and pollution-free.

Description

Technical Field

[0001] This invention relates to the field of water treatment technology, and in particular to a method for removing chloride ions from water by catalytic oxidation. Background Technology

[0002] Industrial processes in industries such as chemical production, metallurgy, printing and dyeing, papermaking, mining, and petroleum generate and discharge large amounts of chlorine-containing wastewater. The chloride ion concentration in this wastewater can reach as high as 2000–40000 mg / L. The accumulation of these chloride ions can severely corrode metal equipment and pipelines, reduce product quality, and cause salinization of water bodies and soil. Therefore, removing chloride ions from wastewater is crucial in wastewater treatment.

[0003] Currently, common methods for removing chloride ions from water include evaporation crystallization, precipitation, membrane separation, and ion exchange. Among these, ion exchange resins are commonly used as ion exchange agents, but they have low adsorption capacity and weak regeneration ability, and the desorbed chloride-containing solution still requires further treatment. Evaporation crystallization is often combined with membrane separation to evaporate and crystallize the high-chlorine solution concentrated by membrane separation, resulting in mixed salts. These mixed salts are of low quality and difficult to sell, thus becoming solid waste. In precipitation methods, the ultra-high lime-alumina method commonly used for chloride removal produces Freund's salt precipitates that are difficult to separate into solid and liquid phases, have high water content, and are generated in large quantities, thus becoming solid waste.

[0004] Most existing methods involve concentrating and enriching chloride ions, which typically exist as mixed salts or precipitates, becoming solid waste that is difficult to treat. Furthermore, these methods suffer from complex processes and high treatment costs. Summary of the Invention

[0005] Based on the above analysis, the present invention aims to provide a method for removing chloride ions from water by catalytic oxidation, in order to solve at least one of the problems of existing treatment methods, such as complex processes, high costs, and the generation of solid wastes such as mixed salts or precipitates that are difficult to treat.

[0006] This invention provides a method for catalytic oxidation to remove chloride ions from water, comprising: step S1, electrolyzing a chlorine-containing solution to electrocatalytically oxidize chloride ions in the chlorine-containing solution to form chlorine gas; simultaneously, adding persulfate to the chlorine-containing solution; step S2, activating the persulfate to generate sulfate radicals and hydroxyl radicals, and using the sulfate radicals and hydroxyl radicals to catalytically oxidize chloride ions to form chlorine gas; and step S3, collecting and treating the chlorine gas.

[0007] Based on further improvements to the above method, in step S2, the persulfate is activated by: heating the chlorine-containing solution with added persulfate; and / or adding a transition metal catalyst to the chlorine-containing solution; and / or sonicating the chlorine-containing solution with added persulfate.

[0008] Further improvements to the above method involve heating the chlorine-containing solution to 50–90°C; and / or, using a transition metal catalyst comprising oxides and / or hydroxides of transition metal elements; and / or, using an ultrasonic treatment with an ultrasonic frequency of 20–800 kHz and an ultrasonic density of 33–200 W / cm³. 2 .

[0009] Based on further improvements to the above method, chloride ions in the chlorine-containing solution are catalytically oxidized to obtain a treated low-chlorine solution; the method also includes: step S4, using a capacitor deionization method to concentrate the low-chlorine solution to obtain a concentrated solution and a qualified purified solution; step S5, returning the concentrated solution to step S1 for catalytic oxidation treatment.

[0010] Based on further improvements to the above method, in step S4, the low-chlorine solution is concentrated using a capacitor deionization method, including: assembling a capacitor deionization device, which includes a reaction chamber, an anode, and a cathode; continuously supplying the low-chlorine solution to the reaction chamber; applying power to the anode and cathode to electrochemically adsorb chloride ions onto the anode, forming a purified solution in the reaction chamber; continuously discharging the purified solution from the reaction chamber; and when the anode is saturated with adsorption, switching the positive and negative electrodes of the power supply to desorb the chloride ions adsorbed on the anode, forming a concentrated solution in the reaction chamber.

[0011] Based on further improvements to the above method, the electrode material of the anode includes: layered metal hydroxide or layered metal oxide.

[0012] Based on further improvements to the above method, the method also includes: preparing layered metal hydroxides or layered metal oxides; mixing the layered metal hydroxides or layered metal oxides with a conductive agent and a binder to obtain an electrode material; and coating the electrode material onto a conductive substrate to obtain an electrode.

[0013] Further improvements to the above method include the collection and treatment of chlorine gas, including: conveying chlorine gas to an absorption washing liquid for at least one absorption treatment until the treated gas meets emission standards.

[0014] Based on further improvements to the above method, the absorbent washing solution includes saturated lime water or sodium hydroxide solution.

[0015] Based on further improvements to the above method, when the content of calcium hypochlorite or sodium hypochlorite in the absorbent washing solution reaches a predetermined percentage, the absorbent washing solution is concentrated and crystallized; after concentration and crystallization, the crystallization mother liquor is separated, and the absorbent washing solution is prepared using the crystallization mother liquor.

[0016] Compared with the prior art, the method for removing chloride ions of the present invention can achieve at least one of the following beneficial effects:

[0017] 1. The embodiments of the present invention utilize electrocatalytic oxidation and the strong oxidizing free radicals generated by the activation of persulfate to oxidize chloride ions into easily treatable chlorine gas. This can efficiently remove chloride ions from water, requires no complex equipment, consumes little energy, can be used for a long time, and is simple to operate, safe, clean, and pollution-free.

[0018] 2. In embodiments of the present invention, catalytic oxidation and capacitive deionization technologies are coupled to perform multi-stage dechlorination treatment on chlorine-containing solutions, achieving a chloride ion removal rate of over 95%. Specifically, the low-chlorine solution obtained from catalytic oxidation dechlorination is concentrated using capacitive deionization technology to obtain a concentrated high-chlorine solution and treated water. The concentrated high-chlorine solution can be returned to the original chlorine-containing solution for further catalytic oxidation, while the treated water is ready for normal use.

[0019] 3. In the embodiments of the present invention, chloride ions are oxidized by electrocatalytic oxidation and strong oxidizing free radicals to generate chlorine gas. The generated chlorine gas is then passed into an absorption washing liquid for absorption, generating a solution containing hypochlorite. This solution product can be used in industrial applications such as oxidation and disinfection in water treatment, thereby solving the problem that existing technologies for treating chloride ions generate precipitates and mixed salts, which are difficult to utilize, and realizing the resource utilization of chloride ions.

[0020] In this invention, the above-described technical solutions can be combined with each other to achieve more preferred combinations. Other features and advantages of this invention will be set forth in the following description, and some advantages may become apparent from the description or be learned by practicing the invention. The objects and other advantages of this invention can be realized and obtained from what is particularly pointed out in the description and drawings. Attached Figure Description

[0021] The accompanying drawings are for illustrative purposes only and are not intended to limit the invention. Throughout the drawings, the same reference numerals denote the same parts.

[0022] Figure 1 This is a schematic flowchart of a method for removing chloride ions from water according to an embodiment of the present invention.

[0023] Figure 2 This is an exploded view of the structure of a capacitor deionization device according to an embodiment of the present invention.

[0024] Figure 3 This is an exploded view of the structure of a capacitor deionization device according to another embodiment of the present invention.

[0025] Figure 4 for Figure 3 A schematic diagram of the dechlorination principle of a medium-capacity deionization device.

[0026] Figure 5 This is an exploded view of the structure of a capacitor deionization device according to yet another embodiment of the present invention.

[0027] Explanation of reference numerals in the attached figures:

[0028] 10-Anode plate; 20-Cathode plate; 30-Silicone plate; 40-Hollow silica gel plate; 50-Electrode fixing plate; 51-Inlet; 52-Outlet; 53-Intermediate outlet; 60-Cation exchange membrane; 70-Anion exchange membrane; 80-Pipeline. Detailed Implementation

[0029] To make the objectives, technical solutions, and advantages of the present invention clearer, exemplary embodiments of the present invention will be described below in conjunction with the accompanying drawings. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention. For clarity and brevity, not all features of actual embodiments are described in the specification.

[0030] It should also be noted that, in order to avoid obscuring the invention with unnecessary details, only the device structure and / or processing steps closely related to the solution according to the invention are shown in the accompanying drawings, while other details that are not closely related to the invention are omitted.

[0031] One embodiment of the present invention provides a method for removing chloride ions from water by catalytic oxidation. The method specifically includes the following steps:

[0032] Step S1 involves electrolyzing the chlorine-containing solution to electrocatalytically oxidize chloride ions in the solution to form chlorine gas; simultaneously, persulfate is added to the chlorine-containing solution.

[0033] Step S2: Activate the persulfate to generate sulfate radicals and hydroxyl radicals, and use the sulfate radicals and hydroxyl radicals to catalyze the oxidation of chloride ions to form chlorine gas;

[0034] Step S3 involves absorbing chlorine gas.

[0035] In embodiments of the present invention, chloride ions in a chlorine-containing solution are catalytically oxidized to form chlorine gas. This catalytic oxidation includes electrocatalytic oxidation in step S1 and strong oxidant catalytic oxidation using free radicals in step S2. The simultaneous electrocatalytic oxidation and strong oxidant catalytic oxidation improve the oxidation efficiency of chloride ions, thereby significantly increasing the chloride ion removal rate and efficiency. Furthermore, the catalytic oxidation of chloride ions to form chlorine gas does not produce difficult-to-treat solid waste such as sodium chloride mixed salts or Freund's salt precipitates. Compared to these solid wastes, chlorine gas is easier to treat into a qualified gas for emission. In addition, the removal method of the present invention requires no complex equipment, has low energy consumption and cost, is simple to operate, safe, clean, and pollution-free, and can be used for a long time.

[0036] In this embodiment, chloride ions are directly oxidized by the electrodes to generate Cl2 during electrolysis. Simultaneously, persulfate is activated to form highly oxidizing sulfate radicals (·SO4) in the chloride-containing solution. － ) and hydroxyl radicals (·OH), chloride ions in ·SO4 － The sulfate radical reacts with ·OH under oxidative action to produce chloride radicals (·Cl), which then combine to form chlorine gas. Specifically, sulfate radicals, hydroxyl radicals, and chloride ions undergo the following reactions:

[0037] SO4 － +Cl － →SO4 2－ +·Cl;

[0038] ·OH+Cl － →OH － +·Cl.

[0039] It should be noted that the chlorine-containing solution processed in the embodiments of the present invention can be any solution containing chloride ions that needs to be treated, including but not limited to chlorine-containing wastewater generated in industrial production.

[0040] In some embodiments of the present invention, when electrolyzing the chlorine-containing solution in step S1, the electrode used can be a commonly used electrode material in the chlor-alkali industry or electrodialysis industry, such as graphite electrode, titanium electrode, platinum electrode, stainless steel electrode, etc.

[0041] Preferably, during electrolysis, the current density is set to 500–800 mA / dm³. 2 For example, 500mA / dm 2 550mA / dm 2 600mA / dm 2 650mA / dm 2 700mA / dm 2 750mA / dm 2800mA / dm 2 The voltage fluctuates between 2 and 3V. This embodiment performs electrolysis within the aforementioned voltage and current density range, which helps improve dechlorination efficiency and reduce dechlorination time.

[0042] In some embodiments of the present invention, the persulfate used includes permonosulfate and / or perdisulfate, which can be activated to generate a large number of persulfate radicals and hydroxyl radicals for the oxidation of chloride ions.

[0043] The persulfate includes at least one of potassium persulfate, sodium persulfate, and ammonium persulfate; the persulfate includes at least one of potassium persulfate, sodium persulfate, and ammonium persulfate. In some embodiments, the selected persulfate can be chosen based on the cations in the chlorine-containing solution, for example, selecting a persulfate that is the same as the cations contained in the chlorine-containing solution to avoid introducing new ions or other impurities into the chlorine-containing solution.

[0044] In some embodiments of the present invention, the amount of persulfate added to the chloride-containing solution is 2–15 g / L. When the amount of persulfate added is too low, its catalytic oxidation reaction rate is slow, and the improvement in chloride ion removal efficiency when used in conjunction with electrocatalysis is not significant. The higher the amount of persulfate added, the more free radicals are generated through activation, thus increasing the oxidation reaction rate and removal rate of chloride ions. However, when the amount added is too high, the oxidation reaction rate and removal rate of chloride ions will reach saturation; at this point, even if the amount added is increased, the removal rate will not increase, and the reagent cost will increase. Considering both the chloride ion removal rate and reagent cost, the present invention sets the addition amount at 2–15 g / L, which ensures both the chloride ion removal rate and controls reagent cost.

[0045] In some embodiments of the present invention, step S2, activating the persulfate, includes: heating the chlorine-containing solution containing the added persulfate; or adding a transition metal catalyst to the chlorine-containing solution and activating the persulfate using the transition metal catalyst; or sonicating the chlorine-containing solution containing the added persulfate.

[0046] When persulfate is activated, the OO bonds in the persulfate break, generating a large number of sulfate radicals and hydroxyl radicals with strong oxidizing properties, which oxidize chloride ions in chlorine-containing solutions.

[0047] The activation method described above for persulfate can rapidly release sulfate and hydroxyl radicals, thereby improving chloride ion removal efficiency and increasing the generation of chloride radicals, thus enhancing chloride ion removal rate. Furthermore, the embodiments of this invention provide various activation methods, allowing for the selection of appropriate methods to activate persulfate for different scenarios and conditions.

[0048] In some embodiments, the above activation methods can be used in combination to further improve the removal efficiency of chloride ions and the release of free radicals, thereby greatly enhancing the removal effect of chloride ions.

[0049] In some embodiments of the present invention, when heating the chlorine-containing solution, the solution can be heated to 50–90°C. Energy is generated through heating, causing the O₂ bonds in the persulfate to break and produce SO₄²⁻. － And ·OH. In the embodiments of the present invention, heating the chlorine-containing solution to 50-90°C can not only effectively catalyze the activation of persulfate to generate a large number of free radicals and increase the generation of chlorine free radicals, but also effectively control the heat treatment cost and avoid excessively low heat utilization efficiency.

[0050] In some embodiments of the present invention, the transition metal catalyst added to the chlorine-containing solution comprises oxides and / or hydroxides of transition metal elements. When persulfate is activated using a transition metal catalyst, the single-electron transfer of the transition metal accelerates the formation of SO4 from the persulfate. － The reaction mixture with ·OH effectively promotes the generation of free radicals, and the reaction system is simple, the reaction conditions are mild, the energy consumption is low, and no external heat source is required. For example, the transition metal element may include at least one of Co, Ni, Mn, and Fe, and the transition metal catalyst is an oxide and / or hydroxide containing at least one of Co, Ni, Mn, and Fe.

[0051] In some embodiments, the amount of transition metal catalyst added is 2–8 g / L. If the amount added is too low, the catalytic activation rate is slow; if the amount added is too high, the catalytic activation rate for persulfate will reach saturation. This invention, considering both the activation rate for persulfate and reagent costs, sets the amount of transition metal catalyst added to 2–8 g / L, which ensures both the activation rate and control of reagent costs.

[0052] Ultrasonic treatment is used to activate chlorine-containing solutions containing added persulfate, avoiding the problems of harsh conditions and secondary pollution. In some embodiments of the present invention, the ultrasonic frequency of the ultrasonic treatment is 20–800 kHz, and the ultrasonic density is 33–200 W / cm³. 2 Higher ultrasonic frequencies are also beneficial for SO4. － The generation of ·OH. For example, an electrolytic cell containing a chlorine-containing solution can be placed inside an ultrasonic generator for ultrasonic treatment.

[0053] In some embodiments, the catalytic oxidation treatment time for chloride ions in chlorine-containing solutions is 15 to 20 minutes. In the embodiments of the present invention, chloride ions are oxidized by a combination of electrocatalytic oxidation and catalytic oxidation with strong free radical oxidants, which shortens the time for oxidizing chloride ions and can achieve the removal of chloride ions from water in only 15 to 20 minutes.

[0054] In some embodiments of the present invention, before step S1, the method further includes: adjusting the chlorine-containing solution to acidity, thereby ensuring that chloride ions are removed by catalytic oxidation under acidic conditions, so that the generated ·Cl can combine to generate chlorine gas and escape, thus avoiding the reaction of chlorine gas with alkali, which would lead to a decrease in the chloride ion removal effect.

[0055] Specifically, the acidity of the chlorine-containing solution can be adjusted to above 20 g / L. It should be noted that for acidic chlorine-containing solutions with an acidity above 20 g / L, no acidity adjustment is necessary; persulfate can be added directly to remove chlorine. For neutral and alkaline chlorine-containing solutions, acid should be added to adjust the acidity to above 20 g / L before adding persulfate.

[0056] Preferably, when adjusting the acidity, the acid added to the chlorine-containing solution can be sulfuric acid, so as to avoid introducing chloride ions into the solution.

[0057] In some embodiments of the present invention, during the collection and treatment of chlorine gas in step S3, the chlorine gas can be transported to an absorption washing liquid for at least one absorption treatment until the treated gas meets the emission standards. This embodiment utilizes the absorption washing liquid to perform multi-stage absorption treatment of chlorine gas, ensuring that the discharged gas meets the emission standards and avoiding environmental pollution from waste gas.

[0058] The absorption and washing liquid includes saturated lime water or sodium hydroxide solution. Chlorine reacts with the absorption and washing liquid to produce calcium hypochlorite or sodium hypochlorite, thereby effectively absorbing chlorine and ensuring that the gas collected during the catalytic oxidation of chloride ions meets emission standards. Simultaneously, the calcium hypochlorite or sodium hypochlorite chemical products generated during the absorption and treatment process can be comprehensively recovered for reuse or sale, achieving resource utilization of chloride ions, resulting in good economic benefits and solving the problem of unusable waste generated from traditional chloride ion treatment methods.

[0059] To achieve resource recycling, during the absorption treatment of chlorine gas, once the content of calcium hypochlorite or sodium hypochlorite in the absorption washing liquid reaches a predetermined percentage, the absorption washing liquid can be concentrated and crystallized. After concentration and crystallization, the mother liquor is separated and used to prepare the absorption washing liquid, thereby achieving product recycling. The predetermined percentage can be 15% or higher.

[0060] Optionally, once the hypochlorite content in the washing solution reaches a predetermined percentage, the washing solution can be directly used in other processes of chlorine-containing solution treatment or in wastewater treatment for oxidation, disinfection, and deodorization. The dechlorination method of this embodiment is not only simple in process but also allows for the comprehensive recovery of calcium hypochlorite or sodium hypochlorite chemical products for reuse or sale. Therefore, it generates less waste, eliminates sodium chloride accumulation, is easy to operate, and offers good socio-economic benefits.

[0061] In some embodiments of the present invention, in order to collect and treat chlorine gas and avoid pollution caused by chlorine gas leakage, the catalytic oxidation process for removing chloride ions in steps S1 and S2 can be carried out in a closed electrolytic cell. The electrolytic cell is provided with an inlet and an outlet for inputting the chlorine-containing solution and discharging the low-chlorine solution after catalytic oxidation treatment, respectively. Furthermore, the electrolytic cell is also provided with an exhaust port, which is connected to a gas treatment container containing the absorption washing liquid via a pipe, thereby transporting the generated chlorine gas to the absorption washing liquid for absorption treatment.

[0062] In some embodiments of the present invention, such as Figure 1 As shown, chloride ions in a chlorine-containing solution are catalytically oxidized to obtain a treated low-chlorine solution; the method for removing chloride ions in this embodiment further includes the following steps:

[0063] Step S4: The low-chlorine solution is concentrated using a capacitor deionization method to obtain a concentrated solution and a qualified purified solution.

[0064] Step S5: Return the concentrate to step S1 for catalytic oxidation treatment.

[0065] This invention couples catalytic oxidation deionization technology with capacitive deionization technology to perform multi-stage treatment on chlorine-containing solutions, thereby improving the chloride ion removal rate to over 95%. Specifically, this invention achieves dechlorination of chlorine-containing solutions by electrocatalysis and strong oxidant catalytic oxidation of chloride ions in water. The dechlorinated low-chlorine solution is then concentrated using capacitive deionization to further remove chloride ions, resulting in treated water suitable for normal use. The remaining portion is concentrated into a high-concentration concentrate, which can be returned to step S1 for further catalytic oxidation treatment. This multi-stage treatment of chlorine-containing solutions is simple and highly efficient.

[0066] In some embodiments of the present invention, when concentrating the low-chlorine solution using the capacitive deionization method in step S4, the specific steps include:

[0067] Step S41: Assemble the capacitor deionization device; the capacitor deionization device includes a reaction chamber, an anode, and a cathode;

[0068] Step S42: The low-chlorine solution is continuously supplied to the reaction chamber of the capacitor deionization device. Power is applied to the anode and cathode to electrochemically adsorb chloride ions onto the anode, thereby forming a purified solution in the reaction chamber.

[0069] Step S43: Continuously discharge the purification liquid from the reaction chamber;

[0070] Step S44: When the anode adsorption is saturated, the positive and negative electrodes of the power supply are switched to desorb the chloride ions adsorbed on the anode and form a concentrated solution in the reaction chamber.

[0071] The capacitive deionization method of this invention can further remove chloride ions from low-chlorine solutions and obtain a qualified purified solution. The method has simple operation steps, can be implemented at room temperature and pressure, and has low production energy consumption and cost.

[0072] In some embodiments, the electrode material of the anode in the capacitive deionization device includes layered metal hydroxides or layered metal oxides. Using layered metal hydroxides or metal oxides as electrode materials is not only cost-effective but also allows for high adsorption capacity of chloride ions, effectively removing chloride ions from water.

[0073] Specifically, the outer layer of the layered metal hydroxide consists of metal plates formed by different metal ions, exhibiting positive charge; the interlayer is filled with some water molecules and anions, exhibiting negative charge; therefore, the material as a whole is electrically neutral. When metal hydroxide is used as the electrode material for the anode, the positive and negative terminals of the power supply are connected to the electrode to supply power. Under the action of the electric field, the metal plates of the metal hydroxide change from a low valence state to a high valence state, and its positive charge is enhanced; chloride ions in the water move towards the anode under the action of the electric field, and after reaching the anode surface, they are embedded in the interlayer of the metal plates. After the interlayer embedding is saturated, a double electric layer adsorption is formed on the electrode surface, thereby achieving the removal of chloride ions from the water.

[0074] Most of the interlayer anions in layered metal oxides are eliminated. Due to the structural memory effect, when they come into contact with low-chlorine solutions, they can re-adsorb and bind chloride ions, thus restoring the layered structure. Simultaneously, under the influence of an electric field, the metal plates of the restored layered metal oxide change from low valence states to high valence states, further adsorbing chloride ions and increasing the rate of chloride ion adsorption. Furthermore, metal oxides possess abundant pore structures and a larger specific surface area, which is even more conducive to chloride ion adsorption.

[0075] In some embodiments of the present invention, the anode can be regenerated after chloride ion insertion and adsorption saturation, thereby achieving recycling. Specifically, the electrode can be disconnected from the power supply, or the positive and negative terminals of the power supply can be reversed with the electrode, so that what was originally the anode becomes the cathode. This causes the metal plates of the metal hydroxide or metal oxide to change from a high valence state to a low valence state, weakening the positive charge. The chloride ions inserted between the plates and adsorbed on the material surface are desorbed from the anode, thereby achieving electrode regeneration.

[0076] Currently, capacitive deionization technology is mainly used for desalination, with silver and bismuth being the primary anode materials for adsorbing chloride ions. These materials remove chloride ions from water by reacting with chloride ions to form a new phase. However, during the cyclic adsorption and regeneration process, the charging and discharging cycles cause continuous changes between the new and old phases, resulting in significant volume changes in the electrode material. This damages the electrode material's structure, reduces cycle stability, and lowers the chloride removal performance.

[0077] To avoid the aforementioned problems when using silver and bismuth as anode materials, embodiments of the present invention use layered metal hydroxides or metal oxides as electrode materials in capacitive deionization devices. This fully utilizes the intercalation and deintercalation characteristics of anions within the layered structure, i.e., the intercalation capability of anions, to achieve the adsorption and removal of chloride ions. Furthermore, the layers are connected by electrostatic interactions, resulting in high electrode stability and recyclability. This overcomes the structural instability caused by large volume changes before and after chloride ion removal when using silver chloride and bismuth oxychloride as anode materials. In addition, embodiments of the present invention utilize the valence state changes of variable-valence metals in the layered metal hydroxides or metal oxides during energization, enhancing the adsorption capacity for chloride ions and thus improving the chloride ion removal rate from water.

[0078] In some embodiments of the present invention, the layered metal hydroxide / layered metal oxide comprises: a first metal ion and a second metal ion. The first metal ion is a divalent metal ion, including Ni. 2+ Co 2+ Ti 2+ Cr 2+ In 2+ Zn 2 + and Mg 2+ At least one of the following; the second metal ion is a trivalent or tetravalent metal ion, including Fe. 3+ Mn 3+ Ti 3+ Cr 3+ Al 3 + In 3+ Co 3+ and Ti 4+At least one of the above. Embodiments of the present invention utilize the tunability of the metal layers of layered metal hydroxides and metal oxides. By employing the aforementioned multiple metal ions, various electrodes can be prepared, thus making them suitable for water treatment in different situations and exhibiting excellent adaptability.

[0079] To assemble a capacitive deionization device, the method of this invention further includes: preparing layered metal hydroxides or layered metal oxides; mixing the layered metal hydroxides or layered metal oxides with a conductive agent and a binder to obtain an electrode material; and coating the electrode material onto a conductive substrate to obtain an electrode. The embodiments of this invention use layered hydroxides and layered metal oxides to prepare the electrode, which can be used as the anolyte of a capacitive deionization device for the electrochemical adsorption of chloride ions in a low-chlorine solution.

[0080] In some embodiments of the present invention, the mass ratio of layered metal hydroxide / layered metal oxide, conductive agent, and binder is 6–8:1–2:1–2. Preferably, the mass ratio is 8:1:1, which can ensure the stability and good conductivity of the electrode even with a large amount of active material.

[0081] In some embodiments, the layered metal hydroxide / layered metal oxide, conductive agent, and binder can be mixed and ground to ensure uniform mixing. The resulting slurry can be dried under vacuum to obtain electrode material for capacitor deionization, facilitating storage and use. The drying temperature can be 60–80°C, and the drying time can be 12–24 hours.

[0082] Preferably, the conductive agent can be conductive carbon black, which can effectively improve the conductivity of the electrode material. Preferably, the binder includes polyvinylidene fluoride (PVDF). Specifically, PVDF can be mixed with the solvent N-methylpyrrolidone to obtain the binder. The mass ratio of PVDF to N-methylpyrrolidone is 3% to 6%.

[0083] In some embodiments of the present invention, the conductive substrate used for the electrode can be carbon paper or a titanium plate. After mixing to obtain an electrode material slurry, the slurry can be coated onto the carbon paper or titanium plate and then vacuum dried to obtain the electrode. The coating thickness of the electrode material is 100–150 μm, the drying temperature is 60–80 °C, and the drying time is 12–24 hours.

[0084] In some embodiments, layered metal hydroxides can be prepared by: mixing the metal salts corresponding to the first metal ion and the second metal ion and preparing a salt solution; mixing the salt solution with an alkaline solution and carrying out a crystallization reaction or a hydrothermal reaction to obtain the metal hydroxide. The embodiments of the present invention employ a co-precipitation method or a hydrothermal method to prepare layered metal hydroxides, which is simple and low-cost.

[0085] Specifically, when preparing metal hydroxides using the co-precipitation method, the soluble metal salts corresponding to the first and second metal ions can be dissolved in water to prepare a mixed salt solution. Then, a certain concentration of alkaline solution is prepared and added to the salt solution to adjust the pH value of the salt solution to the range of 7–11, thereby initiating a crystallization reaction. Within this pH range, the nucleation and growth of metal hydroxide crystals are favorable. Preferably, the concentration of the first metal ion in the mixed salt solution can be 0.1–1 mol / L, and the molar ratio of the first and second metal ions can be 1–3.

[0086] In some embodiments of the present invention, the alkaline solution can be added dropwise to the mixed salt solution to initiate a crystallization reaction. Adding the solution dropwise allows the alkaline solution to react slowly with the salt solution, helping to control the reaction rate and preventing localized overheating or uneven precipitation due to excessively rapid reaction. It also allows for more precise control of the pH value of the mixed solution, helping to reduce impurities and improve the purity of the final product. Preferably, the crystallization reaction can be carried out at a temperature of 70–130°C for 12–36 hours. Within this temperature range, the metal ions can react fully, crystallizing to form metal hydroxides.

[0087] When preparing metal hydroxides using a hydrothermal method, the soluble metal salts corresponding to the first and second metal ions can be dissolved in water to prepare a mixed salt solution; then, a certain concentration of alkali solution is prepared, and the salt solution and alkali solution are mixed and placed in a hydrothermal reactor for hydrothermal reaction. Preferably, the reaction temperature of the hydrothermal reaction is 100–170°C, and the reaction time is 12–36 hours. Preferably, the concentration of the first metal ion in the mixed salt solution can be 0.1–1 mol / L, and the molar ratio of the first metal ion to the second metal ion can be 1–6.

[0088] In addition, after the crystallization reaction or hydrothermal reaction is completed, the separated crystals can be washed with deionized water until neutral to remove residual impurities on their surface, and then dried to obtain metal hydroxide.

[0089] In some embodiments of the present invention, the alkaline solution used is a sodium hydroxide solution or a urea solution. Specifically, when preparing metal hydroxides using the co-precipitation method, the alkaline solution used can be a sodium hydroxide solution or a urea solution; when preparing metal hydroxides using the hydrothermal method, the alkaline solution used can be a urea solution. The embodiments of the present invention use a urea solution as the alkaline solution to adjust the pH value of the metal salt solution, and can ensure that the pH value in the solution remains consistent, thereby facilitating the preparation of metal hydroxide crystals with high crystallinity and regular interlayer structure.

[0090] In some embodiments of the present invention, in order to prepare layered metal oxides as electrode materials, the layered metal hydroxides prepared above can be calcined to obtain layered metal oxides. Specifically, the calcination temperature of the layered metal hydroxides can be 250℃ to 550℃. The layered metal oxides obtained after calcination have a richer pore structure and a larger specific surface area, which can expose more active sites, thereby facilitating the adsorption of chloride ions.

[0091] In some embodiments of the present invention, the electrodes described above can be used to assemble various types of capacitive deionization devices, and different numbers of ion exchange membranes can be provided in the capacitive deionization devices, for example, 0, 1, or 2.

[0092] like Figure 2 As shown, the membrane-free capacitive deionization device in this embodiment of the invention includes a stacked anode plate 10, a cathode plate 20, a silica gel plate 30, a hollow silica gel plate 40, and an electrode fixing plate 50. The hollow silica gel plate 40 is disposed between the anode plate 10 and the cathode plate 20. Two electrode fixing plates 50 are symmetrically disposed on both sides of the hollow silica gel plate 40 and located on the outermost layer of the capacitive deionization device. Two silica gel plates 30 are symmetrically disposed outside the anode plate 10 and the cathode plate 20. The hollow portion of the hollow silica gel plate 40 constitutes the reaction chamber of the device. The anode plate 10 can be the electrode prepared in the above embodiment, the cathode plate 20 can be a titanium plate coated with activated carbon material, and the silica gel plate 30 can serve as a gasket to improve the sealing of the device and prevent leakage. The various plates of the device are stacked and connected and fixed by insulating connectors (e.g., insulating screws) to assemble the capacitive deionization device.

[0093] like Figure 2 As shown, the electrode fixing plate 50 is provided with an inlet 51 and an outlet 52. Both the silicone plate 30 and the electrode plate are provided with through holes so that the low-chlorine solution to be treated input from the inlet 51 can enter the reaction chamber through the through holes, and the treated purified liquid can be transported to the outlet 52 for discharge through the through holes.

[0094] Adopting such Figure 2 When the capacitor deionization device shown processes a low-chlorine solution, the low-chlorine solution is continuously input from the inlet 51 on the electrode fixing plate 50. After the power is turned on and an electric field is applied, chloride ions move toward the anode plate 10 coated with the above-mentioned electrode material (layered metal hydroxide or oxide), while other cations move toward the cathode plate 20 coated with activated carbon material. Chloride ions are electrochemically adsorbed on the anode plate, thereby reducing the chloride ion concentration in the solution and forming a purified liquid in the reaction chamber. The purified liquid is continuously discharged from the outlet 52 on the electrode fixing plate 50.

[0095] Once the anode plate 10 is saturated with adsorption, the outlet 52 is connected to the electrolytic cell in step S1. Then, the positive and negative electrodes of the power supply are switched, causing the electric field to reverse. Chloride ions desorb from the anode plate 10, and the resulting concentrated solution is returned to the electrolytic cell for catalytic oxidation treatment, thereby regenerating the anode plate 10. After the anode plate 10 is regenerated, the positive and negative electrodes of the power supply are switched again, allowing the anode plate 10 to continue adsorbing chloride ions.

[0096] In some embodiments of the present invention, a single-membrane capacitive deionization device can also be assembled. This device further includes a cation exchange membrane, with an anode and a cathode respectively disposed on opposite sides of the cation exchange membrane, forming a reaction chamber on each side. During the electrochemical adsorption process, a purified solution is formed in the reaction chamber on the anode side, and a concentrated solution is formed in the reaction chamber on the cathode side. Each reaction chamber is provided with an outlet for discharging the purified solution and the concentrated solution, respectively.

[0097] Specifically, such as Figure 3 As shown, compared to membrane-free capacitive deionization devices, the capacitive deionization device in this embodiment further includes a cation exchange membrane 60. An anode plate 10 and a cathode plate 20 are respectively disposed on both sides of the cation exchange membrane 60. Hollow silica gel plates 40 are respectively disposed between the anode plate 10 and the cation exchange membrane 60, and between the cathode plate 20 and the cation exchange membrane 60, thereby forming a reaction chamber on each side of the cation exchange membrane 60. In this embodiment, both the anode plate 10 and the cathode plate 20 can use the electrode materials (layered metal hydroxides or oxides) described in the above embodiments. In this embodiment, the electrode fixing plates 50 on both sides are provided with outlets 52 to discharge the solutions from the two reaction chambers respectively.

[0098] Adopting such Figure 3 In the capacitor deionization device shown, a low-chlorine solution is continuously input from the inlet 51 on the electrode fixing plate 50, and the outlet on one side of the cathode plate 10 is connected to the electrolytic cell in step S1. Figure 4 As shown, after the power is turned on and an electric field is applied, chloride ions in the low-chlorine solution move toward the anode plate 10 and are adsorbed onto the layered metal hydroxide or oxide, while cations move toward the cathode plate 20 and can pass through the cation exchange membrane 60 to reach the reaction chamber on the cathode side. This results in the formation of a purified solution after chloride ion removal in the reaction chamber on the anode plate 10 side. The purified solution is continuously discharged from the outlet 52 on the anode plate 20 side, and a concentrated solution is formed in the reaction chamber on the cathode plate 20 side. The concentrated solution is continuously returned to the electrolytic cell from another outlet 52 for catalytic oxidation treatment.

[0099] When the anode plate 10 becomes saturated, the interfaces of the two outlets 52 are swapped, so that the outlet 52 on one side of the anode plate 20 is connected to the electrolytic cell. Then, the positive and negative terminals of the power supply are swapped, and the electric field is reversed. At this time, the anode plate 10 becomes the cathode, and the cathode plate 20 becomes the anode. After the electric field is reversed, the previously saturated anode plate 10 is regenerated, and at the same time, the cathode plate 20 begins to adsorb chloride ions. The above process is repeated until the cathode plate 20 is also saturated.

[0100] By repeatedly exchanging the positive and negative terminals of the power supply, the electrodes are continuously regenerated and chloride ions are adsorbed. When the positive and negative terminals of the power supply are exchanged, the interfaces of the two outlets 52 also need to be exchanged.

[0101] The embodiments of this invention reduce the repulsion effect of common ions during adsorption by adding a cation exchange membrane, allowing both the anode and cathode to use the prepared layered metal hydroxide or oxide as electrode materials. Furthermore, the capacitive deionization device enables simultaneous electrochemical adsorption and regeneration, achieving efficient enrichment and concentration of chloride ions while purifying, significantly shortening the processing time. It offers advantages such as low cost, large adsorption capacity, and ease of continuous processing, thereby improving the removal capacity and efficiency of chloride ions.

[0102] In some embodiments of the present invention, a dual-membrane capacitive deionization device can also be assembled. This device further includes a cation exchange membrane and an anion exchange membrane. The cation exchange membrane is disposed between the anode and cathode, and the anion exchange membrane is disposed between the cation exchange membrane and cathode. The device forms three reaction chambers: a reaction chamber on the anode side, a reaction chamber on the cathode side, and a reaction chamber formed between the two membranes. Each reaction chamber is provided with an outlet for discharging the treated purified liquid and concentrated liquid, respectively. The anode can be made of the aforementioned layered metal hydroxide or oxide as the electrode material.

[0103] Specifically, such as Figure 5 As shown, compared to the membrane-free capacitive deionization device, the capacitive deionization device in this embodiment further includes a cation exchange membrane 60 and an anion exchange membrane 70. The electrode fixing plate 50, silica gel plate 30, anode plate 10, cation exchange membrane 60, hollow silica gel plate 40, anion exchange membrane 70, cathode plate 20, another silica gel plate 30, and another electrode fixing plate 50 are sequentially stacked. The anode plate 10 is a titanium plate coated with the layered metal hydroxide or oxide described in the above embodiment, and the cathode plate 20 is a titanium plate coated with activated carbon material.

[0104] In this embodiment, an intermediate reaction chamber, called the concentrate chamber, is formed between the cation exchange membrane 60 and the anion exchange membrane 70; two side reaction chambers, called desalination chambers, are formed between the cation exchange membrane 60 and the silica gel plate 30, and between the anion exchange membrane 70 and the silica gel plate 30. Both electrode fixing plates 50 are provided with outlets (not shown in the figure) to discharge the solutions in the side reaction chambers; simultaneously, the electrode fixing plate 50 is also provided with an intermediate outlet 53, which is connected to the intermediate reaction chamber through a pipe 80 to discharge the solution in the intermediate reaction chamber.

[0105] Adopting such Figure 5 In the capacitor deionization device shown, a low-chlorine solution is continuously fed into the inlet 51 on the electrode fixing plate 50, and the middle outlet 53 of the concentrate chamber is connected to the electrolytic cell in step S1. After the power is turned on and an electric field is applied, chloride ions in the low-chlorine solution move towards the anode plate 10. Some chloride ions (chloride ions on the anode side) are adsorbed onto the anode plate 10, while other chloride ions (chloride ions on the cathode side) move towards the anode plate 10 and pass through the anion exchange membrane 70 to reach the concentrate chamber. Cations in the low-chlorine solution move towards the cathode plate 20 and pass through the cation exchange membrane 60 to reach the concentrate chamber. The purified liquid formed in the desalination chambers on both sides is continuously discharged, and the concentrated liquid formed in the middle concentrate chamber is continuously discharged and returned to the electrolytic cell for catalytic oxidation treatment.

[0106] When the anode plate 10 becomes saturated with chloride ions, the outlets of the freshwater chambers on both sides are connected to the electrolytic cell, and the positive and negative electrodes of the power supply are exchanged. The anode plate 10, which previously adsorbed chloride ions, becomes the new cathode. Chloride ions desorb from the saturated anode plate 10, forming a concentrated solution in the freshwater chamber. The concentrated solution is continuously discharged from the outlet into the electrolytic cell, while the purified solution formed in the concentrated water chamber is continuously discharged from the middle outlet 53. After the anode plate 10 is regenerated, the positive and negative electrodes of the power supply are exchanged again, allowing the anode plate 10 to continue adsorbing chloride ions.

[0107] To illustrate the feasibility of the above embodiments of the present invention, the method for removing chloride ions from water provided by the present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0108] Example 1

[0109] Prepare 500mL Cl at room temperature - A sodium chloride simulated solution with a concentration of 4000 mg / L and a sulfuric acid concentration of 50 g / L was used as a chlorine-containing solution for treatment.

[0110] The simulated sodium chloride solution was placed in an electrolytic cell for electrolysis, and 7g of solid potassium persulfate was added simultaneously and stirred thoroughly. Titanium electrodes were used during electrolysis, and the current density was approximately 800 mA / dm³. 2 The voltage is approximately 2-3V.

[0111] The electrolytic cell was placed in an ultrasonic generator for ultrasonic treatment for 20 minutes. The ultrasonic generator had a frequency of 20 kHz, a power of 36 W, and an ultrasonic density of 100 W / cm³. 2 Potassium persulfate is activated by ultrasound to generate sulfate radicals and hydroxyl radicals.

[0112] In a chlorine-containing solution, chloride ions are electrocatalytically oxidized and free radical catalytically oxidized to generate chlorine gas, thereby reducing the chloride ion concentration in the solution. The chlorine gas generated in the electrolytic cell is discharged through an exhaust port to an absorption and scrubbing liquid for three-stage absorption treatment. The first-stage absorption and scrubbing liquid is saturated lime water, while the second and third-stage absorption and scrubbing liquids are 5% sodium hydroxide solutions, which absorb chlorine gas to form sodium hypochlorite solution and calcium hypochlorite solution, respectively. The qualified gas after multi-stage absorption treatment is directly discharged.

[0113] The chlorine-containing solution in the electrolytic cell is catalytically oxidized to form Cl. - A low-chlorine solution with a concentration of 350 mg / L, using a combination of electrolysis and catalytic oxidation with a strong free radical oxidant, achieved a chloride ion removal rate of 91%.

[0114] Example 2

[0115] The low-chlorine solution obtained in Example 1 was transported to, as... Figure 2 The membrane-free capacitive deionization device shown is used for concentration treatment. The membrane-free capacitive deionization device includes a stacked anode plate, cathode plate, silica gel plate, hollow silica gel plate, and electrode fixing plate. The hollow portion of the hollow silica gel plate constitutes the reaction chamber of the device. The anode plate is a titanium electrode coated with nickel-titanium layered hydroxide, wherein the mass ratio of nickel-titanium layered hydroxide, conductive carbon black, and binder is 8:1:1, the coating thickness is 100 μm, and it is vacuum dried at 60°C for 24 h after coating. The cathode plate is a titanium plate coated with activated carbon. The active area of ​​the electrode material of the anode plate is 4×4 cm, the distance between the anode and cathode plates is approximately 1 mm, and a power supply with a voltage of 1.2 V is connected between the anode and cathode plates.

[0116] Specifically, the low-chlorine solution in the electrolytic cell is continuously supplied to the reaction chamber through the inlet on the electrode fixing plate. Under the influence of the electric field, the low-chlorine solution in the reaction chamber moves towards the anode plate and is electrochemically adsorbed onto the electrode material, forming a qualified purified solution. This purified solution is continuously discharged through the outlet on the electrode fixing plate and is ready for normal use. During the treatment process, the chloride ion concentration of the purified solution at the outlet is monitored in real time. When the decrease in chloride ion concentration compared to the initial concentration of the low-chlorine solution is significantly reduced, the anode plate is considered saturated.

[0117] After the saturated or low-chlorine solution on the anode plate is completely transported to the capacitor deionization device, the outlet is connected to the electrolytic cell. At the same time, the positive and negative terminals of the power supply are switched, so that the anode plate becomes the cathode. The chloride ions adsorbed on the anode plate are desorbed and a concentrated solution is formed in the reaction chamber. The concentrated solution is a chlorine-containing solution with a chloride ion concentration of 2000 mg / L. Finally, the concentrated solution is returned to the electrolytic cell through the outlet for further catalytic oxidation treatment.

[0118] After capacitive deionization, the final discharged purified solution has a chloride ion concentration of less than 200 mg / L, with a chloride ion removal rate of 95%. The chloride ion concentration in the purified solution was detected by ion chromatography.

[0119] Example 3

[0120] Prepare 500mL Cl at room temperature - A sodium chloride simulated solution with a concentration of 3500 mg / L and a sulfuric acid concentration of 30 g / L was used as a chlorine-containing solution for treatment.

[0121] The simulated sodium chloride solution was placed in an electrolytic cell for electrolysis, and 5g of solid potassium persulfate was added and stirred until homogeneous. Platinum electrodes were used during electrolysis, and the current density was approximately 500 mA / dm³. 2 The voltage is approximately 2-3V.

[0122] 4g of cobalt tetroxide was added to the electrolytic cell to initiate the catalytic activation reaction, which lasted for 20 minutes. Potassium persulfate was activated under the catalysis of a transition metal catalyst to generate sulfate radicals and hydroxyl radicals.

[0123] In a chlorine-containing solution, chloride ions are electrocatalytically oxidized and free radical catalytically oxidized to generate chlorine gas. The chlorine gas generated in the electrolytic cell is discharged through an exhaust port to a sodium hydroxide solution for two-stage absorption treatment, forming a sodium hypochlorite solution. The first stage of absorption treatment uses a 15% sodium hydroxide solution, and the second stage uses a 5% sodium hydroxide solution. The qualified gas after two-stage absorption treatment is directly discharged.

[0124] Chloride ions are catalytically oxidized in the electrolytic cell to form Cl. - A low-chlorine solution with a concentration of 320 mg / L achieved a chloride ion removal rate of 90%.

[0125] The low-chlorine solution in the electrolytic cell is transferred to a single-membrane capacitive deionization device for concentration. This device includes a cation exchange membrane, and both the anode and cathode electrodes are made of cobalt-titanium layered hydroxide. All other conditions are the same as in Example 2. The purified solution that has passed the treatment is discharged, and the resulting concentrate is returned to the electrolytic cell for further catalytic oxidation. The chloride ion concentration in the concentrate is 1000 mg / L.

[0126] After treatment, the final discharged purified liquid has a chloride ion concentration of less than 150 mg / L, and the chloride ion removal rate reaches 96%.

[0127] Example 4

[0128] Prepare 500mL Cl at room temperature - A sodium chloride simulated solution with a concentration of 2000 mg / L and a sulfuric acid concentration of 20 g / L was used as a chlorine-containing solution for treatment.

[0129] The simulated sodium chloride solution was placed in an electrolytic cell for electrolysis, and 3g of solid potassium persulfate was added and stirred until homogeneous. Platinum electrodes were used during electrolysis, and the current density was approximately 600 mA / dm³. 2 The voltage is approximately 2-3V.

[0130] The simulated sodium chloride solution in the electrolytic cell was heated to 50°C and reacted at this temperature for 20 minutes. Potassium persulfate was activated at high temperature to generate sulfate radicals and hydroxyl radicals.

[0131] In a chlorine-containing solution, chloride ions are electrocatalytically oxidized and catalytically oxidized by free radicals to generate chlorine gas, thereby reducing the chloride ion concentration in the solution. The chlorine gas generated in the electrolytic cell is discharged through the exhaust port into saturated limewater for absorption treatment, forming a calcium hypochlorite solution. The qualified gas after absorption treatment is directly discharged.

[0132] The chlorine-containing solution in the electrolytic cell is catalytically oxidized to form Cl. - A low-chlorine solution with a concentration of 150 mg / L achieved a chloride ion removal rate of 93%.

[0133] The low-chlorine solution formed after catalytic oxidation in the electrolytic cell is transported to a membrane-free capacitive deionization unit for concentration. The electrode material of the anode plate in the capacitive deionization unit is cobalt-magnesium-aluminum layered hydroxide, and the electrode material of the cathode plate is activated carbon; all other conditions are the same as in Example 2. The purified solution that has passed the treatment is discharged, and the resulting concentrated solution is returned to the electrolytic cell for further catalytic oxidation. The chloride ion concentration in the concentrated solution is 780 mg / L.

[0134] After treatment, the final discharged purified liquid has a chloride ion concentration of less than 50 mg / L, and the chloride ion removal rate reaches 98%.

[0135] Example 5

[0136] Prepare 500mL Cl at room temperature - A sodium chloride simulated solution with a concentration of 2000 mg / L and a sulfuric acid concentration of 20 g / L was used as a chlorine-containing solution for treatment.

[0137] The simulated sodium chloride solution was placed in an electrolytic cell for electrolysis, and 3g of solid potassium persulfate was added simultaneously and stirred thoroughly. Platinum electrodes were used during electrolysis, and the current density was approximately 700 mA / dm³. 2 .

[0138] The simulated sodium chloride solution in the electrolytic cell was heated to 50°C and reacted at this temperature for 20 minutes. Potassium persulfate was activated at high temperature to generate sulfate radicals and hydroxyl radicals.

[0139] In a chlorine-containing solution, chloride ions are electrocatalytically oxidized and catalytically oxidized by free radicals to generate chlorine gas, thereby reducing the chloride ion concentration in the solution. The chlorine gas generated in the electrolytic cell is discharged through the exhaust port into saturated limewater for absorption treatment, forming a calcium hypochlorite solution. The qualified gas after absorption treatment is directly discharged.

[0140] The chlorine-containing solution in the electrolytic cell is catalytically oxidized to form Cl. - A low-chlorine solution with a concentration of 130 mg / L achieved a chloride ion removal rate of 93.5%.

[0141] The low-chlorine solution formed after catalytic oxidation in the electrolytic cell is transported to a single-membrane capacitive deionization device for concentration. The anode and cathode plates of the capacitive deionization device are both made of cobalt-magnesium-aluminum layered hydroxide, and the device is equipped with a cation exchange membrane; all other conditions are the same as in Example 2. The purified solution that has passed the treatment is discharged, and the resulting concentrated solution is returned to the electrolytic cell for further catalytic oxidation. The chloride ion concentration in the concentrated solution is 850 mg / L.

[0142] After treatment, the final discharged purified liquid has a chloride ion concentration of less than 30 mg / L, and the chloride ion removal rate reaches 98.5%.

[0143] Example 6

[0144] Prepare 500mL Cl at room temperature - A sodium chloride simulated solution with a concentration of 2000 mg / L and a sulfuric acid concentration of 20 g / L was used as a chlorine-containing solution for treatment.

[0145] The simulated sodium chloride solution was placed in an electrolytic cell for electrolysis, and 3g of solid potassium persulfate was added simultaneously and stirred thoroughly. Platinum electrodes were used during electrolysis, and the current density was approximately 700 mA / dm³. 2 .

[0146] The simulated sodium chloride solution in the electrolytic cell was heated to 50°C and reacted at this temperature for 20 minutes. Potassium persulfate was activated at high temperature to generate sulfate radicals and hydroxyl radicals.

[0147] In a chlorine-containing solution, chloride ions are electrocatalytically oxidized and catalytically oxidized by free radicals to generate chlorine gas, thereby reducing the chloride ion concentration in the solution. The chlorine gas generated in the electrolytic cell is discharged through the exhaust port into saturated limewater for absorption treatment, forming a calcium hypochlorite solution. The qualified gas after absorption treatment is directly discharged.

[0148] The chlorine-containing solution in the electrolytic cell is catalytically oxidized to form Cl. - A low-chlorine solution with a concentration of 130 mg / L achieved a chloride ion removal rate of 93.5%.

[0149] The low-chlorine solution formed after catalytic oxidation in the electrolytic cell is transported to a dual-mode capacitive deionization device for concentration. The capacitive deionization device includes a cation exchange membrane and an anion exchange membrane; the electrode materials for both the anode and cathode are cobalt-magnesium-aluminum layered hydroxide, and the remaining conditions are the same as in Example 2. The purified solution that has passed the treatment is discharged, and the resulting concentrated solution is returned to the electrolytic cell for further catalytic oxidation. The chloride ion concentration in the concentrated solution is 1000 mg / L.

[0150] After treatment, the final discharged purified liquid has a chloride ion concentration of less than 25 mg / L, and the chloride ion removal rate reaches 98.7%.

[0151] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for removing chloride ions from water by catalytic oxidation, characterized in that, include: Step S1: Electrolyze the chlorine-containing solution to electrocatalytically oxidize the chloride ions in the chlorine-containing solution to form chlorine gas; Simultaneously, persulfate is added to the chlorine-containing solution; Step S2: The persulfate is activated to generate sulfate radicals and hydroxyl radicals. The sulfate radicals and hydroxyl radicals are used to catalytically oxidize the chloride ions to form chlorine gas. After the chloride ions in the chlorine-containing solution are electrocatalytically oxidized and catalytically oxidized by the sulfate radicals and hydroxyl radicals, a treated low-chlorine solution is obtained. Step S3: Collect and process the chlorine gas; Step S4: The low-chlorine solution is concentrated using a capacitor deionization method to obtain a concentrated solution and a qualified purified solution. Step S5: Return the concentrate to step S1 to perform catalytic oxidation treatment on the concentrate; In step S1, the current density of the electrolysis is 500–750 mA / dm³. 2 The voltage is 2~3V; In the capacitor deionization device used in the capacitor deionization method, the electrode material of the anode includes: layered metal hydroxide or layered metal oxide. The layered metal hydroxide / layered metal oxide comprises: a first metal ion and a second metal ion, wherein the first metal ion is a divalent metal ion, including Co. 2+ and Mg 2+ The second metal ion is a trivalent metal ion, including Al. 3+ ; The method for preparing the anode includes the following steps: (1) Preparation of the layered metal hydroxide or layered metal oxide: Mix the metal salts corresponding to the first metal ion and the second metal ion and prepare a salt solution; mix the salt solution with an alkaline solution and carry out a crystallization reaction or a hydrothermal reaction to obtain the metal hydroxide; (2) The layered metal hydroxide or the layered metal oxide is mixed with a conductive agent and a binder to obtain an electrode material; (3) The electrode material is coated onto a conductive substrate to obtain an electrode.

2. The method according to claim 1, characterized in that, In step S2, the persulfate is activated, including: The chlorine-containing solution containing the added persulfate is subjected to heat treatment; and / or, Add a transition metal catalyst to the chlorine-containing solution; and / or, The chlorine-containing solution with added persulfate is subjected to ultrasonic treatment.

3. The method according to claim 2, characterized in that, Heating the chlorine-containing solution includes: heating the chlorine-containing solution to 50-90°C; and / or, The transition metal catalyst comprises oxides and / or hydroxides of transition metal elements; and / or, The ultrasonic treatment uses an ultrasonic frequency of 20~800kHz and an ultrasonic density of 33~200W / cm³. 2 .

4. The method according to claim 1, characterized in that, In step S4, the low-chlorine solution is concentrated using a capacitive deionization method, including: Assemble a capacitor deionization device, the capacitor deionization device including a reaction chamber, an anode and a cathode; The low-chlorine solution is continuously supplied to the reaction chamber, and a power source is applied to the anode and cathode to cause the chloride ions to be electrochemically adsorbed onto the anode, thereby forming the purified liquid in the reaction chamber. The purification liquid in the reaction chamber is continuously discharged; Once the anode is saturated with adsorption, the positive and negative terminals of the power supply are switched, causing the chloride ions adsorbed on the anode to desorb and form the concentrated solution in the reaction chamber.

5. The method according to claim 1, characterized in that, The collection and treatment of the chlorine gas includes: The chlorine gas is fed into an absorption washing liquid for at least one absorption treatment until the treated gas meets the emission standards.

6. The method according to claim 5, characterized in that, The absorbent washing solution includes saturated lime water or sodium hydroxide solution.

7. The method according to claim 6, characterized in that, Once the content of calcium hypochlorite or sodium hypochlorite in the absorbent washing solution reaches a predetermined percentage, the absorbent washing solution is concentrated and crystallized. After concentration and crystallization, the mother liquor is separated and used to prepare the absorption and washing solution.

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