A method for selectively defluorinating a fluorine-containing solution

Abstract

This invention discloses a method for selectively removing fluoride from a fluoride-containing solution. The apparatus for removing fluoride ions from the fluoride-containing solution includes a hermetically sealed electrolytic cell. An anode, an activated carbon / fluoride ion conductor composite electrode, and a cathode are concentrically installed from the inside out within the electrolytic cell. The activated carbon / fluoride ion conductor composite electrode is cylindrical and has an inner and outer two-layer structure: an inner fluoride ion conductor layer and an outer activated carbon layer. The activated carbon / fluoride ion conductor composite electrode is installed between the anode and cathode, dividing the electrolytic cell into an inner chamber and an outer chamber. During defluorination, an electrolyte is filled into the inner chamber, and a fluoride-containing solution is filled into the outer chamber. By controlling the voltage difference between the cathode and anode in the electrolytic cell and the voltage difference between the activated carbon / fluoride ion conductor composite electrode and the cathode, fluoride ions in the fluoride-containing solution in the outer chamber are made to migrate through the activated carbon / fluoride ion conductor composite electrode into the inner chamber. The method of this invention has a selective and efficient removal effect on fluoride ions.

Description

Technical Field

[0001] This invention relates to the field of solution purification technology, and more specifically to a method for selectively removing fluoride from fluoride-containing solutions. Background Technology

[0002] With rapid industrialization, wastewater discharge problems have become increasingly serious, among which fluoride-containing wastewater is particularly concerning. Fluorine is an element with unique chemical properties and has wide applications in industry, agriculture, and medicine. However, when fluoride is discharged into the environment as wastewater, it causes severe pollution, affecting human health and ecological balance. Therefore, removing fluoride ions from fluoride-containing wastewater has become an urgent need for environmental protection and sustainable development.

[0003] Fluoride-containing wastewater mainly originates from industries such as phosphate fertilizer production, aluminum electrolysis, steel smelting, glass manufacturing, and electroplating. These industries generate wastewater containing fluoride ions during their production processes. If discharged directly without treatment, this wastewater will pollute surface water, groundwater, and soil. To address the environmental problems caused by fluoride-containing wastewater, researchers have developed various defluorination technologies. Currently commonly used defluorination methods include chemical precipitation, ion exchange, adsorption, and membrane separation. A search reveals the following representative methods:

[0004] Chinese patent CN109626482A discloses an apparatus and method for electro-induced adsorption removal of fluoride and chloride ions from solution. The apparatus includes an intermediate electrode composed of an adsorbent material, specifically activated carbon and zeolite in a 1:(1-5) ratio. The method utilizes this intermediate electrode. The apparatus and method provided by this invention utilize solution turbulence and electrostatic forces to create localized concentration polarization of the solution ions. The electrostatic force at the anode enhances both non-specific and specific adsorption of the electrical double layer, while the exchange reaction at the intermediate electrode promotes the adsorption of fluoride and chloride, thus producing an "electro-induced" effect. This increases the adsorption capacity of fluoride and chloride ions per unit mass of the anode region in the system, achieving a fluoride removal rate ≥90% and a chloride removal rate ≥60%, while zinc ions in the solution remain unaffected. The method described in this invention is simple to operate and has a good adsorption effect on fluoride ions, but the regeneration and replacement of the adsorbent require certain costs.

[0005] Patent CN 105905999A discloses a method for removing chloride ions from a sulfuric acid system using a three-dimensional electrode electroadsorption. Specifically, activated carbon is filled into the anode region as the third electrode for anodic polarization. A titanium plate is used as the anode, and a lead plate as the cathode. An insulating diaphragm isolates the cathode and anode regions. Chlorine-containing wastewater with a chloride ion concentration of 800–1200 mg / L is adjusted to a pH of 1–4 and introduced into the three-dimensional electrode. The anode polarization potential is controlled to be between 1.0V and 1.5V. A peristaltic pump is used to introduce wastewater from an external circulation tank into the reactor. The reacted wastewater is then returned to the circulation tank. After a period of circulation, circulating water meeting the circulating cooling water quality standard (300 mg / L) is obtained. While this method is highly effective in treating high-concentration chloride-containing wastewater in sulfuric acid systems, it still involves the regeneration and replacement of the adsorbent.

[0006] Zhang Ailin et al. from Hebei University (Zhang Ailin. Research on the combined process of CDI (capacitive deionization) and EDI (electrodeionization) for treating saline heavy metal wastewater. 2017) proposed a CDI-EDI combined process, utilizing multiple effects of electroadsorption, ion exchange, and electromigration to remove anions and cations. The experiment used a self-made CDI-EDI device to treat saline heavy metal wastewater, using a self-made Ti / CAC capacitor electrode as the anode and a Ti mesh as the cathode. Anion and cation exchange resins were filled into the anion and cation chambers, respectively, and the deionization effects of the cation, anion, and concentration chambers were studied. Experimental results showed that for Cu... 2+ Ni 2+ The removal effect is good, and the effluent is stable. However, it only has a good removal effect on heavy metal cations. Although the paper also uses Ti / CAC electrode for dechlorination experiments in MCDI (membrane capacitor deionization) process, the results show that appropriately increasing the charging current can improve the dechlorination effect, but it does not use CDI-EDI combined process to remove anions.

[0007] Inspired by the working principles of electro-deionization and fluoride-ion batteries, the inventors of this application developed a cylindrical structure component consisting of a central electrode, activated carbon / fluoride ion conductor composite electrode, and peripheral electrode. This three-electrode control chamber structure selectively removes fluoride ions. By controlling the electrode potential, it drives the directional movement of fluoride ions to accumulate in the central region, making it particularly suitable for the selective defluorination of high-salt solutions containing a small amount of fluoride ions. Summary of the Invention

[0008] The technical problem to be solved by the present invention is to provide a method for selectively removing fluoride from a fluoride-containing solution, which has the effect of selectively and efficiently removing fluoride ions.

[0009] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0010] A method for selectively removing fluoride from a fluoride-containing solution includes an apparatus for removing fluoride ions from the solution, comprising a hermetically sealed electrolytic cell. The electrolytic cell contains an anode, a cathode, and an activated carbon / fluoride ion conductor composite electrode. The activated carbon / fluoride ion conductor composite electrode is cylindrical and has an inner and outer two-layer structure, wherein the inner layer is a fluoride ion conductor layer and the outer layer is an activated carbon layer. The anode, cathode, and activated carbon / fluoride ion conductor composite electrode are concentrically installed, with the anode installed at the center of the electrolytic cell and the cathode installed close to the inner wall of the electrolytic cell. The combined electrode is installed between the anode and cathode, dividing the electrolytic cell into two independent inner and outer chambers. During defluorination, the inner chamber is filled with electrolyte, and the outer chamber is filled with a fluoride-containing solution. The electrolytic cell is then started, and the voltage difference between the cathode and anode in the electrolytic cell is controlled to be 1.4–15V, and the voltage difference between the activated carbon / fluoride ion conductor composite electrode and the cathode is controlled to be 0.9–1.2V. This allows fluoride ions in the fluoride-containing solution in the outer chamber to migrate through the activated carbon / fluoride ion conductor composite electrode into the inner chamber until the concentration of fluoride ions in the solution in the outer chamber reaches the required level.

[0011] The activated carbon / fluoride ion conductor composite electrode involved in the defluorination method of the present invention is prepared according to the following method:

[0012] 1) Using activated carbon as raw material, a columnar carbon electrode blank is prepared;

[0013] 2) Weigh out lanthanum fluoride and barium fluoride according to the specified ratio, mix them evenly, and then pre-sinter them under high temperature conditions. After crushing, obtain the chemical formula La. 1-x Ba x F 3-x Fluoride ion conductor powder, wherein x = 0.05–0.1;

[0014] 3) Add sintering aid to fluoride ion conductor powder, mix evenly, and then adjust into a paste with polyvinyl alcohol aqueous solution. Coat the inner side of the carbon electrode blank with the resulting paste to obtain activated carbon / fluoride ion conductor laminate.

[0015] 4) The obtained activated carbon / fluorine ion conductor composite is sintered under high temperature conditions to obtain the activated carbon / fluorine ion conductor composite electrode.

[0016] In step 1) of the above-mentioned method for preparing an activated carbon / fluoride ion conductor composite electrode, the carbon electrode blank is prepared using conventional methods, typically by adding an appropriate amount of phenolic resin to activated carbon and then pressing it into a cylindrical shape. Specifically, activated carbon and phenolic resin are mixed evenly at a mass ratio of 70-80:30-20, placed in a mold, current collector wires are introduced, and the mixture is pressed into a cylindrical shape at 120-150°C; wherein, the specific surface area of ​​the activated carbon is preferably 300-1000 m². 2 / g, more preferably, is made from bamboo with a specific surface area of ​​300-600m². 2 / g of activated carbon. In this application, the shape of the carbon electrode blank can be a cylinder with a circular cross-section or a column with a square cross-section.

[0017] In step 2) of the above method for preparing activated carbon / fluoride ion conductor composite electrode, the ratio of lanthanum fluoride and barium fluoride is determined according to the chemical formula of the desired fluoride ion conductor powder. In this application, the value of x in the chemical formula is preferably 0.05. In this step, the high temperature condition refers to 800–900°C, and the pre-sintering time is usually 15–25 h.

[0018] In step 3) of the above-mentioned method for preparing activated carbon / fluoride ion conductor composite electrodes, the sintering aid is the same as in the prior art, preferably potassium fluoride; the amount of sintering aid added is preferably 0.9 to 1.1 times the mass of barium fluoride in step 2). The molecular weight of the polyvinyl alcohol is usually 2000 to 5000, and the concentration of the polyvinyl alcohol aqueous solution is preferably 2 to 5 wt%. Typically, a 10 to 30% polyvinyl alcohol aqueous solution, equivalent to the total weight of the fluoride ion conductor powder and the sintering aid, is used to prepare the mixture of fluoride ion conductor powder and sintering aid into a paste. The resulting paste is uniformly coated on the inner side of the carbon electrode blank, resulting in an activated carbon / fluoride ion conductor composite with a two-layer structure in cross-section, namely an activated carbon layer and a fluoride ion conductor layer. Taking a cylindrical carbon electrode blank as an example, the resulting paste is uniformly coated on the inner circumferential surface of the carbon electrode blank. The coating thickness of the paste is determined as needed, for example, it can be equivalent to the thickness of the carbon electrode blank.

[0019] In step 4) of the above method for preparing activated carbon / fluoride ion conductor composite electrode, the high temperature condition refers to 800-900℃, and the sintering time is usually 1-3h.

[0020] In the defluorination method of the present invention, it is preferable to control the voltage difference between the cathode and the anode in the electrolytic cell to be 6-15V, and to control the voltage difference between the activated carbon / fluoride ion conductor composite electrode and the cathode in the electrolytic cell to be 1.0-1.2V.

[0021] In the defluorination method described in this invention, the electrolyte is typically a 0.5–1.0 mol / L sodium hydroxide solution. After the fluoride-containing solution (i.e., fluoride-containing wastewater) is introduced into the outer chamber, the anions and cations in the outer chamber are driven by the cathode and the activated carbon / fluoride ion conductor composite electrode to accumulate on the surface of the activated carbon / fluoride ion conductor composite electrode. Fluoride ions pass through the activated carbon / fluoride ion conductor composite electrode into the inner chamber, where they accumulate, thus achieving the purpose of removing fluoride ions from the fluoride-containing solution.

[0022] To improve the removal efficiency of fluoride ions, a cation exchange membrane can be separately installed on the inner wall of the cathode, or ion exchange fibers can be separately filled in the outer chamber. Furthermore, in addition to installing a cation exchange membrane, ion exchange fibers can be filled in the outer chamber to further improve the removal efficiency of fluoride ions. The ion exchange fibers can be anion exchange fibers and / or cation exchange fibers. The applicant's experimental results show that it is preferable to simultaneously fill with anion exchange fibers and cation exchange fibers, and more preferably, the ratio of anion exchange fibers to cation exchange fibers is 1:1 by volume.

[0023] In the defluorination method of the present invention, the anode can be a carbon rod, usually a cylindrical carbon rod; the cathode can be a cylindrical component made of stainless steel with a shape matching the inner wall of the electrolytic cell.

[0024] This invention also includes the electrolytic cell used in the above method. The electrolytic cell is equipped with an anode, a cathode, and an activated carbon / fluoride ion conductor composite electrode. The activated carbon / fluoride ion conductor composite electrode is cylindrical and has an inner and outer two-layer structure, wherein the inner layer is a fluoride ion conductor layer and the outer layer is an activated carbon layer. The anode, cathode, and activated carbon / fluoride ion conductor composite electrode are concentrically installed, with the anode installed at the center of the electrolytic cell, the cathode installed close to the inner wall of the electrolytic cell, and the activated carbon / fluoride ion conductor composite electrode installed between the anode and the cathode, dividing the electrolytic cell into two independent inner and outer chambers. The anode, cathode, and activated carbon / fluoride ion conductor composite electrode involved in this electrolytic cell are all the same as those described above.

[0025] Compared with the prior art, the present invention is characterized by:

[0026] 1. The activated carbon / fluoride ion conductor composite electrode used in the method of the present invention combines the adsorption properties of activated carbon and La. 1-x Ba x F 3-x The material exhibits excellent fluoride ion conductivity, which can effectively improve the defluorination efficiency of the electrode and achieve selective and highly efficient fluoride ion removal.

[0027] 2. In this invention, an activated carbon / fluoride ion conductor composite electrode is used in conjunction with the cathode and anode to form an EDI nested CDI coupling structure in the electrolytic cell (specifically, the cathode is connected to the negative terminal of the DC power supply, and there is a voltage difference between the anode and the activated carbon / fluoride ion conductor composite electrode, wherein the anode and the fluoride ion conductor layer of the activated carbon / fluoride ion conductor composite electrode constitute a CDI, while the cathode and the activated carbon layer of the activated carbon / fluoride ion conductor composite electrode constitute half of the EDI). This EDI nested CDI coupling structure achieves selective and efficient removal of fluoride ions.

[0028] 3. The method described in this invention only consumes electrical energy and does not require the addition of reagents. The ion exchange fiber is regenerated in situ and does not need to be replaced. After the removal of fluoride ions, the fluoride content in the solution can be less than 1 ppm.

[0029] 4. The method described in this invention is particularly suitable for the selective removal of fluoride ions under high-concentration salt conditions. Attached Figure Description

[0030] Figure 1 This is a schematic diagram of the electrolytic cell used in the method described in this invention.

[0031] The numbers on the map are:

[0032] 1 Cathode, 2 Activated carbon / fluorine ion conductor composite electrode, 201 Activated carbon layer, 202 Fluorine ion conductor layer, 3 Anode, 4 Ion exchange fiber, 5 Cation membrane, 6 Outer chamber, 7 Inner chamber. Detailed Implementation

[0033] To better explain the technical solution of the present invention, the present invention will be further described in detail below with reference to the embodiments, but the implementation of the present invention is not limited thereto.

[0034] Figure 1 The following are schematic diagrams of the electrolytic cells involved in the embodiments. Figure 1As shown, the electrolytic cell is cylindrical, and contains a cylindrical anode 3, a cathode 1, and an activated carbon / fluoride ion conductor composite electrode 2. The activated carbon / fluoride ion conductor composite electrode 2 has an inner and outer two-layer structure, with an inner fluoride ion conductor layer 202 and an outer activated carbon layer 201. The anode 3, cathode 1, and activated carbon / fluoride ion conductor composite electrode 2 are concentrically installed, with the anode 3 positioned at the center of the electrolytic cell. The cathode 1 is installed close to the inner wall of the electrolytic cell, and a cation exchange membrane 5 is provided on the inner wall of the cathode 1. The activated carbon / fluoride ion conductor composite electrode 2 is installed between the anode 3 and the cathode 1 (the activated carbon layer 201 of the activated carbon / fluoride ion conductor composite electrode 2 is adjacent to the cathode 1, and the fluoride ion conductor layer 202 of the activated carbon / fluoride ion conductor composite electrode 2 is adjacent to the anode 3), dividing the electrolytic cell into inner and outer layers. The electrolytic cell comprises two independent chambers: an outer chamber 6 and an inner chamber 7. The outer chamber 6 is formed by the outer wall of the activated carbon / fluoride ion conductor composite electrode 2, the inner wall of the cathode 1, and the top and bottom surfaces of the electrolytic cell between the outer wall of the activated carbon / fluoride ion conductor composite electrode 2 and the inner wall of the cathode 1. The inner chamber 7 is formed by the inner wall of the activated carbon / fluoride ion conductor composite electrode 2, the outer wall of the anode 3, and the top and bottom surfaces of the electrolytic cell between the inner wall of the activated carbon / fluoride ion conductor composite electrode 2 and the outer wall of the anode 3. The inner chamber 7 is filled with an electrolyte (a 0.5–1.0 mol / L sodium hydroxide solution), and the outer chamber 6 is filled with a fluoride-containing solution. Ion exchange fibers 4 are filled in the outer chamber 6. The cathode 1 in the electrolytic cell is connected to the negative terminal of the power supply, and the anode 3 is connected to the positive terminal. The anode 3 in the electrolytic cell is a carbon rod, and the cathode 1 is made of stainless steel. The activated carbon / fluoride ion conductor composite electrode 2 is prepared according to the following method:

[0035] 1) Weigh out activated carbon (with a specific surface area of ​​300-600 m²) at a mass ratio of 75:25. 2 / g) and phenolic resin are mixed evenly and placed in a mold. A nickel sheet is introduced as a current collector wire and pressed into a hollow cylinder at 130°C to obtain a cylindrical carbon electrode blank of the required size and specifications.

[0036] 2) Weigh out lanthanum fluoride and barium fluoride according to the specified ratio, mix them evenly, and pre-sinter at 800–900℃ for 15–25 hours. After pre-sintering, remove the mixture and crush it to obtain the chemical formula La. 1-x Ba x F 3-x Fluoride ion conductor powder, wherein x = 0.05–0.1;

[0037] 3) Add potassium fluoride to the obtained fluoride ion conductor powder in the same amount as barium fluoride used in step 2), mix evenly, and then use a polyvinyl alcohol aqueous solution with a concentration of 2-5 wt% (the amount of polyvinyl alcohol aqueous solution is 0.9-1.1 times the total weight of fluoride ion conductor powder and potassium fluoride) to make a paste. Coat the obtained paste on the inner circumferential surface of the carbon electrode blank obtained in step 1) (the coating thickness is determined as needed) to obtain an activated carbon / fluoride ion conductor layer composite with an outer layer of activated carbon layer 201 and an inner layer of fluoride ion conductor layer 202.

[0038] 4) The obtained activated carbon / fluorine ion conductor layer composite is placed at 800-900℃ for sintering for 1-3 hours, taken out, and its shape is trimmed to obtain a cylindrical activated carbon / fluorine ion conductor composite electrode 2 with an inner fluorine ion conductor layer 202 and an outer activated carbon layer 201.

[0039] In a specific application example, the height of the electrolytic cell is 20cm; the diameter of the anode 3 (carbon rod) is 6mm; the inner diameter of the activated carbon / fluoride ion conductor composite electrode 2 is 10mm, and the thickness is 2mm, wherein the thickness of the fluoride ion conductor layer 202 is 1mm (the main material is La). 0.95 Ba 0.05 F 2.95 The electrode contains fluoride ion conductor powder, and the activated carbon layer 201 has a thickness of 1 mm. The inner diameter of the cathode 1 (made of stainless steel plate) is 18 mm. The distance between the inner wall of the cathode 1 and the outer wall of the activated carbon / fluoride ion conductor composite electrode 2 is 2 mm. The heights of the anode 3, cathode 1, and activated carbon / fluoride ion conductor composite electrode 2 are the same as the height of the electrolytic cell. The electrolyte used in the inner chamber 7 is a 0.5 mol / L sodium hydroxide solution, and the outer chamber 6 is filled with a mixture of anion exchange fibers and cation exchange fibers in a 1:1 volume ratio.

[0040] Example 1

[0041] Prepare a fluoride-containing solution: Weigh out a certain amount of sodium fluoride and sodium sulfate and dissolve them in water. Control the concentration of sodium fluoride in the resulting solution to be 1 g / L and the concentration of sodium sulfate to be 20 g / L.

[0042] A 0.5 mol / L sodium hydroxide solution was pumped into the inner chamber of the electrolytic cell, and a fluorine-containing solution was pumped into the outer chamber. The electrolytic cell was then started, and the voltage difference between the cathode and anode was maintained at 15 V, and the voltage difference between the activated carbon / fluoride ion conductor composite electrode and the cathode was maintained at 1.2 V. The flow rate was controlled at 2 mL / min. After operating under these conditions for 20 minutes, the solution was drained from the outer chamber, and the concentration of fluoride ions in the effluent was found to be 0.89 ppm.

[0043] Example 2

[0044] Prepare a fluoride-containing solution: Weigh out a certain amount of sodium fluoride and ammonium sulfate and dissolve them in water. Control the concentration of sodium fluoride in the resulting solution to be 0.5 g / L and the concentration of ammonium sulfate to be 20 g / L.

[0045] A 0.5 mol / L sodium hydroxide solution was pumped into the inner chamber of the electrolytic cell, and a fluorine-containing solution was pumped into the outer chamber. The electrolytic cell was then started, and the voltage difference between the cathode and anode was maintained at 5 V, and the voltage difference between the activated carbon / fluoride ion conductor composite electrode and the cathode was maintained at 1.2 V. The flow rate was controlled at 2 mL / min. After operating under these conditions for 20 minutes, the solution was drained from the outer chamber, and the concentration of fluoride ions in the effluent was found to be 0.42 ppm.

[0046] Example 3

[0047] Fluorine-containing solution: Fluorine-containing wastewater from flotation electrolytic aluminum carbon slag was used as the fluorine-containing solution. The concentration of fluoride ions in the solution was found to be 15.6 mg / L.

[0048] A 0.5 mol / L sodium hydroxide solution was pumped into the inner chamber of the electrolytic cell, and a fluorine-containing solution was pumped into the outer chamber. The electrolytic cell was then started, and the voltage difference between the cathode and anode was maintained at 5 V, and the voltage difference between the activated carbon / fluoride ion conductor composite electrode and the cathode was maintained at 1.2 V. The flow rate was controlled at 1 mL / min. After operating under these conditions for 20 minutes, the solution was drained from the outer chamber, and the concentration of fluoride ions in the effluent was found to be 0.24 ppm.

[0049] Example 4

[0050] Fluorine-containing solution: Fluorine-containing wastewater from flotation electrolytic aluminum carbon slag was used as the fluorine-containing solution. The concentration of fluoride ions in the solution was found to be 15.6 mg / L.

[0051] A 0.5 mol / L sodium hydroxide solution was pumped into the inner chamber of the electrolytic cell, and a fluorine-containing solution was pumped into the outer chamber. The electrolytic cell was then started, and the voltage difference between the cathode and anode was maintained at 1.4 V, and the voltage difference between the activated carbon / fluoride ion conductor composite electrode and the cathode was maintained at 0.9 V. The flow rate was controlled at 1 mL / min. After operating under these conditions for 20 minutes, the solution was drained from the outer chamber, and the concentration of fluoride ions in the effluent was found to be 8.75 ppm.

Claims

1. A method for selectively defluorinating a fluorine-containing solution, characterized by, The device for removing fluoride ions from a fluoride-containing solution comprises an electrolytic cell capable of being sealed, which is provided with an anode, a cathode and an activated carbon / fluoride ion conductor composite electrode, the activated carbon / fluoride ion conductor composite electrode is in a columnar shape and has an inner layer and an outer layer, wherein the inner layer is a fluoride ion conductor layer and the outer layer is an activated carbon layer; the anode, the cathode and the activated carbon / fluoride ion conductor composite electrode are concentrically installed, wherein the anode is installed at the center of the electrolytic cell, the cathode is installed in close contact with the inner wall of the electrolytic cell, and the activated carbon / fluoride ion conductor composite electrode is installed between the anode and the cathode, thereby separating the electrolytic cell into an inner chamber and an outer chamber; when defluorination is performed, electrolyte is filled in the inner chamber and a fluoride-containing solution is filled in the outer chamber, the electrolytic cell is started to work, the voltage difference between the cathode and the anode in the electrolytic cell is controlled to be 1.4-15 V, and the voltage difference between the activated carbon / fluoride ion conductor composite electrode and the cathode is controlled to be 0.9-1.2 V, so that the fluoride ions in the fluoride-containing solution in the outer chamber migrate to the inner chamber through the activated carbon / fluoride ion conductor composite electrode until the concentration of the fluoride ions in the solution in the outer chamber reaches a required value; wherein the activated carbon / fluoride ion conductor composite electrode is prepared by the following method: 1) an activated carbon is used as a raw material to prepare a carbon electrode blank in a columnar shape; 2) Take fluorinated lanthanum and barium by proportion, mix uniformly, and then pre-sinter under high temperature condition, crush, to obtain fluorine ion conductor powder with chemical formula of La 1-x Ba x F 3-x , wherein x = 0.05 ~ 0.1; 3) a sintering aid is added to the fluoride ion conductor powder, the mixture is uniformly mixed, and then a polyvinyl alcohol aqueous solution is used to adjust the mixture into a paste, the obtained paste is coated on the inner side of the carbon electrode blank to obtain an activated carbon / fluoride ion conductor laminate; 4) the obtained activated carbon / fluoride ion conductor laminate is sintered under high temperature conditions to obtain the activated carbon / fluoride ion conductor composite electrode.

2. The method of claim 1, wherein, In steps 2) and 4), the high temperature conditions refer to 800-900 ℃.

3. The method of claim 1 wherein, The sintering aid is potassium fluoride, and the addition amount of the sintering aid is 0.9-1.1 times the mass of the barium fluoride in step 2).

4. The method of claim 1 wherein, In step 3), the molecular weight of the polyvinyl alcohol is 2000-5000, and the concentration of the polyvinyl alcohol aqueous solution is 2-5 wt%.

5. The method of claim 1 wherein, The voltage difference between the cathode and the anode in the electrolytic cell is controlled to be 6-15 V.

6. The method of claim 1 wherein, The voltage difference between the activated carbon / fluoride ion conductor composite electrode and the cathode in the electrolytic cell is controlled to be 1.0-1.2 V.

7. The method of claim 1 wherein, In the electrolytic cell, a cationic membrane is arranged on the inner wall of the cathode.

8. The method of claim 1 wherein, The outer chamber is filled with anion exchange fibers and / or cation exchange fibers.

9. The electrolytic cell used in the process according to any one of claims 1 to 8, characterized in that, The device for removing fluoride ions from a fluoride-containing solution comprises an electrolytic cell capable of being sealed, which is provided with an anode, a cathode and an activated carbon / fluoride ion conductor composite electrode, the activated carbon / fluoride ion conductor composite electrode is in a columnar shape and has an inner layer and an outer layer, wherein the inner layer is a fluoride ion conductor layer and the outer layer is an activated carbon layer; the anode, the cathode and the activated carbon / fluoride ion conductor composite electrode are concentrically installed, wherein the anode is installed at the center of the electrolytic cell, the cathode is installed in close contact with the inner wall of the electrolytic cell, and the activated carbon / fluoride ion conductor composite electrode is installed between the anode and the cathode, thereby separating the electrolytic cell into an inner chamber and an outer chamber.

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