Activated carbon / flourine ion conductor composite electrode and preparation method thereof

Abstract

The application discloses an active carbon / fluoride ion conductor composite electrode and a preparation method thereof. The method comprises the following steps: 1) taking active carbon as raw material to prepare a column-shaped carbon electrode blank; 2) taking lanthanum fluoride and barium fluoride according to a proportion, uniformly mixing, and then pre-sintering under high-temperature conditions, crushing, and obtaining fluoride ion conductor powder with a chemical formula of La 1‑ x Ba x F 3‑x , x=0.05-0.1; 3) adding a sintering aid into the obtained powder, uniformly mixing, then adjusting into a paste shape with a polyvinyl alcohol aqueous solution, and coating the paste on the inner side of the carbon electrode blank to obtain an active carbon / fluoride ion conductor laminated body; and 4) sintering the obtained active carbon / fluoride ion conductor laminated body under high-temperature conditions, and the composite electrode is obtained. The composite electrode prepared by the method has good fluoride ion conduction capacity, can effectively improve the defluorination efficiency of the electrode, and realizes high-efficiency fluoride ion removal.

Description

Technical Field

[0001] This invention relates to an electrode, specifically to an activated carbon / fluoride ion conductor composite electrode for removing fluoride ions from fluoride-containing wastewater and its preparation method. Background Technology

[0002] Fluoride ions are a common pollutant with a wide range of sources, including industrial wastewater, pesticide residues, and domestic sewage. Long-term excessive intake of fluoride ions can seriously harm human health, causing fluorosis of teeth and bones, and even triggering neurological disorders. Therefore, researching and developing efficient fluoride ion removal technologies is of great significance for environmental protection and human health.

[0003] Currently, methods for removing fluoride ions from solutions mainly include chemical precipitation, adsorption, ion exchange, and electrodialysis. While chemical precipitation can remove some fluoride ions, the resulting precipitates are difficult to treat and can easily cause secondary pollution. Adsorption is simple to operate, but the adsorption capacity of the adsorbent is limited and regeneration is difficult. Ion exchange has good defluorination effects, but it is costly and the exchange resin is easily saturated. Electrodialysis requires a large amount of electrical energy, especially in the presence of large amounts of soluble salts, resulting in high operating costs.

[0004] Developing a highly efficient and cost-effective fluoride ion removal technology has become an urgent problem to be solved. This invention aims to achieve selective and efficient removal of fluoride ions from saline solutions by using innovative electrode materials as intermediate electrodes to couple EDI (electrodeionization) and CDI (capacitive deionization). This provides a new solution for the treatment of fluoride ion pollution in water bodies. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide an activated carbon / fluoride ion conductor composite electrode with good fluoride ion conduction ability for removing fluoride ions from fluoride-containing wastewater and its preparation method.

[0006] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0007] A method for preparing an activated carbon / fluoride ion conductor composite electrode includes the following steps:

[0008] 1) Using activated carbon as raw material, a columnar carbon electrode blank is prepared;

[0009] 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;

[0010] 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.

[0011] 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.

[0012] In step 1) of the preparation method of this invention, 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.

[0013] In step 2) of the preparation method described in this invention, 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 typically 15–25 hours.

[0014] In step 3) of the preparation method of this invention, 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 layer 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.

[0015] In step 4) of the preparation method of the present invention, the high temperature condition refers to 800-900℃, and the sintering time is usually 1-3h.

[0016] The present invention also includes an activated carbon / fluoride ion conductor composite electrode prepared by the above method.

[0017] Compared with the prior art, the present invention is characterized by:

[0018] 1. The activated carbon / fluoride ion conductor composite electrode prepared by 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 high-efficiency fluoride ion removal.

[0019] 2. The method described in this invention is simple and easy to scale up for production.

[0020] 3. Using the composite electrode described in this invention as an intermediate electrode in a specific device enables EDI-CDI coupling. By applying voltage, fluoride ions in fluoride-containing wastewater migrate to the activated carbon surface of the electrode and are adsorbed there. Driven by the EDI voltage, the fluoride ions on the activated carbon side of the adsorbed electrode pass through the fluoride ion conductor, thereby achieving the selective removal of fluoride ions from the solution. This method is particularly suitable for the selective removal of fluoride ions from fluoride-containing wastewater in the presence of large amounts of dissolved salts. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of the composite electrode described in this invention, where (a) is the front view and (b) is the top view.

[0022] Figure 2 This is a schematic diagram of the structure of an electrolytic cell used when applying the composite electrode described in this invention for defluorination.

[0023] The numbers on the map are:

[0024] 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

[0025] 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.

[0026] Example 1: Preparation of the activated carbon / fluoride ion conductor composite electrode of the present invention

[0027] 1) Weigh out activated carbon (with a specific surface area of ​​300-500 m²) at a mass ratio of 75:25. 2 / g) and phenolic resin are mixed evenly and placed in a mold. Using a nickel sheet as the current collector, the mixture is pressed into a hollow cylinder at 130°C to obtain a cylindrical carbon electrode blank with an inner diameter of φ10mm, an outer diameter of φ12mm, and a height of 20cm.

[0028] 2) Weigh lanthanum fluoride and barium fluoride at a mass ratio of 95:5, mix them thoroughly, and then pre-sinter at 800℃ for 20 hours to obtain the chemical formula La. 0.95 Ba 0.05 F 2.95 The fluoride ion conductor was removed, crushed, and passed through a 150-mesh sieve. The sieve residue was collected to obtain the chemical formula La. 0.95 Ba 0.05 F 2.95 Fluoride ion conductor powder;

[0029] 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 5wt% polyvinyl alcohol aqueous solution (the amount of polyvinyl alcohol aqueous solution is 15% of 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) with a coating thickness of 1mm, and obtain an activated carbon / fluoride ion conductor layer composite with an outer layer of activated carbon and an inner layer of fluoride ion conductor.

[0030] 4) The obtained activated carbon / fluoride ion conductor composite was sintered at 860℃ for 2 hours, then removed and shaped to obtain a cylindrical activated carbon / fluoride ion conductor composite electrode with a circular cross-section, such as... Figure 1 As shown.

[0031] Example 2: Preparation of the activated carbon / fluoride ion conductor composite electrode of the present invention

[0032] 1) Weigh out activated carbon (with a specific surface area of ​​400-600 m²) at a mass ratio of 70:30. 2 / g) and phenolic resin are mixed evenly and placed in a mold. Using a nickel sheet as the current collector wire, it is pressed into a hollow square at 150°C to obtain a square carbon electrode blank with an inner diameter of 12mm, an outer diameter of 14mm, and a height of 20cm.

[0033] 2) Weigh lanthanum fluoride and barium fluoride at a mass ratio of 90:10, mix them thoroughly, and then pre-sinter at 820℃ for 25 hours to obtain the chemical formula La. 0.9 Ba 0.1 F 2.9 The fluoride ion conductor was removed, crushed, and passed through a 150-mesh sieve. The sieve residue was collected to obtain the chemical formula La. 0.9 Ba 0.1 F 2.9 Fluoride ion conductor powder;

[0034] 3) Weigh out the fluoride ion conductor powder and neutralize the potassium fluoride at a mass ratio of 90:9. After mixing evenly, use a 3wt% polyvinyl alcohol aqueous solution (the amount of polyvinyl alcohol aqueous solution is 20% of the total weight of the fluoride ion conductor powder and potassium fluoride) to make a paste. Coat the resulting paste onto the inner circumferential surface of the carbon electrode blank obtained in step 1) with a coating thickness of 1mm. This results in an activated carbon / fluoride ion conductor layer composite with an outer activated carbon layer and an inner fluoride ion conductor layer in cross-section.

[0035] 4) The obtained activated carbon / fluorine ion conductor composite was sintered at 850℃ for 3 hours, then removed and shaped to obtain a columnar activated carbon / fluorine ion conductor composite electrode with a square cross section.

[0036] Example 3: Defluorination test using the activated carbon / fluoride ion conductor composite electrode described in this invention.

[0037] Figure 2 The following are schematic diagrams of the electrolytic cells involved in the embodiments. Figure 2As 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 into 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, the cathode 1 is made of stainless steel, and the activated carbon / fluoride ion conductor composite electrode 2 is prepared according to the method described in Example 1 of this invention. In the electrolytic cell of this structure, an activated carbon / fluoride ion conductor composite electrode 2 is used in conjunction with cathode 1 and anode 3 to form an EDI nested CDI coupling structure (specifically, cathode 1 is connected to the negative terminal of a DC power supply, anode 3 has a voltage difference with activated carbon / fluoride ion conductor composite electrode 2, wherein anode 3 and the fluoride ion conductor layer 202 of activated carbon / fluoride ion conductor composite electrode 2 constitute a CDI, while cathode 1 and the activated carbon layer 201 of activated carbon / fluoride ion conductor composite electrode 2 constitute half of an EDI). This EDI nested CDI coupling structure achieves selective and efficient removal of fluoride ions.

[0038] 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 2.95The 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 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.

[0039] Fluorine-containing wastewater from the flotation of aluminum electrolytic carbon slag was used as the fluorine-containing solution (the concentration of fluoride ions was measured to be 15.6 mg / L). Figure 2 The electrolytic cell with the structure shown was used for a defluorination test.

[0040] A 0.5 mol / L sodium hydroxide solution was pumped into the inner chamber 7 of the electrolytic cell, and a fluorine-containing solution was pumped into the outer chamber 6. The electrolytic cell was then started, and the voltage difference between cathode 1 and anode 3 was maintained at 5V, and the voltage difference between activated carbon / fluoride ion conductor composite electrode 2 and cathode 1 was maintained at 1.2V. 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 6, and the concentration of fluoride ions in the effluent was found to be 0.24 ppm.

Claims

1. A method for preparing an activated carbon / fluoride ion conductor composite electrode, comprising the following steps: 1) Using activated carbon as raw material, a columnar carbon electrode blank is prepared; 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; 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. 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.

2. The preparation method according to claim 1, characterized in that, In step 2), x = 0.

05.

3. The preparation method according to claim 1 or 2, characterized in that, In steps 2) and 4), the high-temperature conditions refer to 800–900°C.

4. The preparation method according to claim 1 or 2, characterized in that, In step 3), the sintering aid is potassium fluoride.

5. The preparation method according to claim 1 or 2, characterized in that, In step 3), the amount of sintering aid added is 0.9 to 1.1 times the mass of barium fluoride in step 2).

6. The preparation method according to claim 1 or 2, characterized in that, In step 3), the molecular weight of polyvinyl alcohol is 2000-5000, and the concentration of the polyvinyl alcohol aqueous solution is 2-5 wt%.

7. The preparation method according to claim 1 or 2, characterized in that, In step 1), the carbon electrode blank is cylindrical in shape.

8. The activated carbon / fluoride ion conductor composite electrode prepared by the method according to any one of claims 1 to 7.

Images