Recovery method of waste proton exchange membrane electrolyzed water membrane electrode

Abstract

The invention provides a recycling method of a waste proton exchange membrane electrolyzed water membrane electrode, and relates to the technical field of recycling method.The recycling method comprises the steps that the waste proton exchange membrane electrolyzed water membrane electrode is put into a container, an alcohol-water mixed reagent is poured, and a proton exchange membrane, solid residues A and filtrate are obtained after suspension liquid is subjected to solid-liquid separation; adding the solid slag A into a sodium potassium salt reagent and soaking for a period of time to obtain solid slag B; dissolving the solid slag B in an autoclave for a period of time by using a polar solvent, and carrying out solid-liquid separation to obtain solid slag C and a perfluorosulfonic acid resin solution; reacting the solid slag C with sulfuric acid for a period of time, and performing solid-liquid separation to obtain solid slag D; fully dissolving the solid slag D with hydrochloric acid and an oxidizing agent, and carrying out solid-liquid separation to obtain a chloroplatinic acid solution and iridium oxide; mixing iridium oxide with elemental sulfur, and performing high-temperature closed reaction to obtain solid slag F; and fully dissolving the solid slag F with hydrochloric acid and an oxidizing agent to obtain an iridium-containing solution. According to the scheme, the perfluorosulfonic acid proton exchange regeneration membrane is good in performance, and the platinum group metal recovery rate is high.

Description

Technical Field

[0001] The present application relates to the technical field of recycling methods, and particularly relates to a method for recycling waste proton exchange membrane electrolytic water membrane electrodes. Background Art

[0002] The proton exchange membrane electrolytic water hydrogen production technology has the advantages of high hydrogen purity, no pollution, high conversion efficiency, high safety, etc., and has become one of the most promising "green hydrogen" production methods. The core component of this technology is the membrane electrode, which is mainly composed of a proton exchange membrane, an anode and a cathode catalyst layer. The proton exchange membrane mainly uses a perfluoropolymer proton exchange membrane with high proton conductivity, good electrochemical performance and excellent thermal stability. The catalyst layers are distributed on both sides of the proton exchange membrane. The anode uses an iridium dioxide (IrO2) catalyst, and the cathode is mainly a platinum-carbon catalyst. Platinum group metals are scarce resources and their use price is very expensive.

[0003] Existing methods for recycling waste proton exchange membrane electrolytic water membrane electrodes have problems such as directly roasting without separating the perfluorosulfonic acid resin binder, resulting in pollution by toxic gas hydrogen fluoride (HF); directly dissolving the perfluorosulfonic acid resin under high pressure, which destroys some sulfonic acid groups, causing significant reduction in key properties such as the ion exchange capacity, swelling ratio, and conductivity of the proton exchange regenerated membrane material; in the dissolution and recovery of the iridium catalyst, the alkali fusion leaching method has strong corrosion to equipment and high reagent costs, and other methods such as pressure leaching or oxidative and reductive leaching of iridium have poor effects and low recovery rates. Summary of the Invention

[0004] The purpose of the embodiments of the present application is to provide a method for recycling waste proton exchange membrane electrolytic water membrane electrodes to solve the technical problem of low recycling efficiency of waste proton exchange membrane electrolytic water membrane electrodes in the prior art. The specific technical solutions are as follows: The present application provides a method for recycling waste proton exchange membrane electrolytic water membrane electrodes, including: Step 1: Place the waste proton exchange membrane electrolytic water membrane electrode into a container, pour in an alcohol-water mixed reagent, and react for a period of time under mechanical stirring or ultrasonic action to obtain a proton exchange membrane and a suspension. The suspension is subjected to solid-liquid separation to obtain a proton exchange membrane, solid residue A, and a filtrate; Step 2: Add the solid residue A obtained in Step 1 to a sodium-potassium salt reagent and soak for a period of time, perform solid-liquid separation, and wash the filter cake to neutrality to obtain solid residue B; Step 3: Dissolve the solid residue B obtained in Step 2 in a polar solvent in an autoclave for a period of time, perform solid-liquid separation to obtain solid residue C and a perfluorosulfonic acid resin solution. The perfluorosulfonic acid resin solution is used to prepare a proton exchange regenerated membrane; Step 4: React the solid residue C obtained in Step 3 with sulfuric acid for a period of time, perform solid-liquid separation to obtain solid residue D; Step 5: Dissolve the solid residue D obtained in Step 4 with hydrochloric acid and an oxidant, and perform solid-liquid separation to obtain a chloroplatinic acid solution and iridium oxide. The chloroplatinic acid solution is used as a platinum catalyst precursor solution after concentration / dilution and pH adjustment. Step 6: Mix the iridium oxide obtained in Step 5 with elemental sulfur, and perform a high-temperature sealed reaction for a period of time to obtain a solid residue F. Step 7: Dissolve the solid residue F obtained in Step 6 with hydrochloric acid and an oxidant to obtain an iridium-containing solution, which is used as an iridium catalyst precursor solution after ammonium chloride precipitation-secondary dissolution.

[0005] Optionally, the process for preparing the proton exchange membrane from the perfluorosulfonic acid resin solution in Step 3 is as follows: Place the perfluorosulfonic acid resin solution in a petri dish, and dry it into a film in a vacuum oven at 160-180°C. Wash the film with 1-5% hydrogen peroxide solution at 25-80°C for 0.5-3 h, and soak it in a 0.1-2 mol / L dilute sulfuric acid solution for 1-24 h to obtain a perfluorosulfonic acid proton exchange membrane.

[0006] Optionally, in the alcohol-water mixed reagent in Step 1, the volume fraction of the alcohol is 30%-90%, and the alcohol is one or more of methanol, ethanol, isopropanol, n-propanol, n-butanol, isobutanol, and tert-butanol. The reaction temperature in Step 1 is 10-50°C, and the reaction time is 1-10 hours.

[0007] Optionally, the concentration of the sodium-potassium salt reagent in Step 2 is 1-6 mol / L, and the types of the sodium-potassium salt reagent include one or more of sodium chloride, potassium chloride, potassium carbonate, potassium bicarbonate, potassium hydroxide, potassium sulfate, potassium phosphate, sodium carbonate, sodium hydroxide, sodium bicarbonate, sodium sulfate, sodium phosphate, sodium sulfite, and sodium thiosulfate. The soaking temperature in Step 2 is 15-30°C, and the soaking time is 3-12 hours.

[0008] Optionally, the polar solvent in Step 3 is one or more of dimethyl sulfoxide, dimethylformamide, acetonitrile, N-methylpyrrolidone, tetrahydrofuran, and ethyl acetate; the reaction temperature in Step 3 is 120-250°C, and the reaction time is 1-4 hours.

[0009] Optionally, the sulfuric acid concentration in Step 4 is 70-98%, the reaction temperature is 70-90°C, and the reaction time is 1-3 hours.

[0010] Optionally, the reaction temperature in Step 5 is 50-80°C, and the reaction time is 1-3 hours.

[0011] Optionally, the reaction gas atmosphere in Step 6 is vacuum or one of nitrogen and argon, the reaction temperature is 400-600°C, the reaction time is 1-3 hours, and the gas pressure is 0.2-1 MPa.

[0012] Optionally, the reaction temperature in Step Seven is 70~90°C, and the reaction time is 1~3 hours.

[0013] Optionally, the oxidant in Step Five and Step Seven is one or more of sodium chlorate, sodium hypochlorite, perchloric acid, hydrogen peroxide, and potassium chlorate.

[0014] Advantages of the present application: The method for recycling waste proton exchange membrane electrolyzed water membrane electrodes provided by the present application has the advantages of simple recycling process, short process flow, no pollution of HF and nitrogen oxides, good performance of perfluorosulfonic acid proton exchange regenerated membranes, high recovery rate of platinum group metals, etc., and can effectively reduce the processing cost of membrane electrodes, the raw material cost of catalysts, and the environmental governance cost. Specific embodiments

[0015] Next, the technical solutions in the embodiments of the present application will be clearly and completely described in conjunction with the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present application without creative efforts shall fall within the protection scope of the present application.

[0016] To solve the problems in the prior art, the present application provides a method for recycling waste proton exchange membrane electrolyzed water membrane electrodes to solve the technical problem of low recycling efficiency of waste proton exchange membrane electrolyzed water membrane electrodes in the prior art.

[0017] Next, a method for recycling waste proton exchange membrane electrolyzed water membrane electrodes provided by the embodiments of the present application will be introduced first.

[0018] The method for recycling waste proton exchange membrane electrolyzed water membrane electrodes of the present application may include the following steps: Step One: Place the waste proton exchange membrane electrolyzed water membrane electrode into a container, pour in an alcohol-water mixed reagent, and react for a period of time under mechanical stirring or ultrasonic action to obtain a proton exchange membrane and a suspension. The suspension is subjected to solid-liquid separation to obtain a proton exchange membrane, solid residue A, and a filtrate; Step Two: Add the solid residue A obtained in Step One to a sodium-potassium salt reagent and soak for a period of time, perform solid-liquid separation, and wash the filter cake to neutrality to obtain solid residue B; Step Three: Dissolve the solid residue B obtained in Step Two in a polar solvent in a pressure reactor for a period of time, perform solid-liquid separation to obtain solid residue C and a perfluorosulfonic acid resin solution, and the perfluorosulfonic acid resin solution is used to prepare a proton exchange regenerated membrane; Step Four: React the solid residue C obtained in Step Three with sulfuric acid for a period of time, perform solid-liquid separation to obtain solid residue D; Step 5: Dissolve the solid residue D obtained in Step 4 with hydrochloric acid and an oxidant, and perform solid-liquid separation to obtain a chloroplatinic acid solution and iridium oxide. The chloroplatinic acid solution is used as a platinum catalyst precursor solution after concentration / dilution and pH adjustment; Step 6: Mix the iridium oxide obtained in Step 5 with elemental sulfur, and perform a high-temperature sealed reaction for a period of time to obtain a solid residue F; Step 7: Dissolve the solid residue F obtained in Step 6 with hydrochloric acid and an oxidant to obtain an iridium-containing solution, which is used as an iridium catalyst precursor solution after ammonium chloride precipitation and secondary dissolution.

[0019] Further, in the alcohol-water mixed reagent in Step 1, the volume fraction of the alcohol is 30% - 90%, and the alcohol is one or more of methanol, ethanol, isopropanol, n-propanol, n-butanol, isobutanol, and tert-butanol. The reaction temperature in Step 1 is 10 - 50 °C, and the reaction time is 1 - 10 hours.

[0020] Further, the concentration of the sodium-potassium salt reagent in Step 2 is 1 - 6 mol / L, and the types of the sodium-potassium salt reagent include one or more of sodium chloride, potassium chloride, potassium carbonate, potassium bicarbonate, potassium hydroxide, potassium sulfate, potassium phosphate, sodium carbonate, sodium hydroxide, sodium bicarbonate, sodium sulfate, sodium phosphate, sodium sulfite, and sodium thiosulfate. The soaking temperature in Step 2 is 15 - 30 °C, and the soaking time is 3 - 12 hours.

[0021] Further, the polar solvent in Step 3 is one or more of dimethyl sulfoxide, dimethylformamide, acetonitrile, N-methylpyrrolidone, tetrahydrofuran, and ethyl acetate; the reaction temperature in Step 3 is 120 - 250 °C, and the reaction time is 1 - 4 hours.

[0022] Further, the sulfuric acid concentration in Step 4 is 70 - 98%, the reaction temperature is 70 - 90 °C, and the reaction time is 1 - 3 hours.

[0023] Further, the reaction temperature in Step 5 is 50 - 80 °C, and the reaction time is 1 - 3 hours.

[0024] Further, the reaction gas atmosphere in Step 6 is vacuum or one of nitrogen and argon, the reaction temperature is 400 - 600 °C, the reaction time is 1 - 3 hours, and the gas pressure is 0.2 - 1 MPa.

[0025] Further, the reaction temperature in Step 7 is 70 - 90 °C, and the reaction time is 1 - 3 hours.

[0026] Further, the oxidant in Step 5 and Step 7 is one or more of sodium chlorate, sodium hypochlorite, perchloric acid, hydrogen peroxide, and potassium chlorate.

[0027] Furthermore, in step three, the process for preparing a proton exchange membrane using a perfluorosulfonic acid resin solution is as follows: placing the perfluorosulfonic acid resin solution in a culture dish, drying the culture dish in a vacuum oven at 160-180° C. to form a membrane, washing the membrane with a 1-5% hydrogen peroxide solution at 25-80° C. for 0.5-3 h, and soaking the membrane in a 0.1-2 mol / L dilute sulfuric acid solution for 1-24 h to obtain a perfluorosulfonic acid proton exchange membrane.

[0028] In the present application, after the catalyst layer and the proton exchange membrane are separated, the hydrogen-type perfluorosulfonic acid resin in the catalyst layer is transformed in advance to obtain a sodium-type or potassium-type perfluorosulfonic acid resin. + or K + By combining with the sulfonic acid group through ionic bonds, the electrostatic interaction between molecules is enhanced, which is beneficial to the stability of the resonance structure between the S atom and the three O atoms, ensuring that the sulfonic acid group does not decompose in a high temperature and high pressure environment; at the same time, the polarity of the sodium or potassium type perfluorosulfonic acid resin is further enhanced. According to the principle of like dissolves like, its solubility in solvents with strong polarity is further improved than that of the hydrogen type, which is beneficial to the dissolution of the perfluorosulfonic acid resin.

[0029] The catalyst mixture after separation of perfluorosulfonic acid resin is oxidized with sulfuric acid to remove carbon and dissolve base metals. Compared with the oxidative roasting carbon removal-base metal dissolution process, carbon removal and base metal impurity removal are carried out in the same process, which shortens the process flow and reduces the energy consumption of high-temperature roasting.

[0030] When the iridium catalyst (IrO2) is heated with excess sulfur at high temperature, the S atoms can replace the O atoms in the iridium oxide to form iridium sulfide. This process destroys the stable structure of the dense iridium oxide and converts it into iridium sulfide with dissolution activity. The iridium sulfide is then oxidized and leached to oxidize the negative divalent sulfur to positive hexavalent sulfur, which enters the solution in the form of sulfate, and the iridium ions are dissolved, thereby achieving the smooth dissolution of iridium sulfide.

[0031] In order to illustrate the advancement and innovation of the technology of the present invention and make the technical features of the present invention easier to understand, further description is given in conjunction with specific examples. Example 1

[0032] Step 1: Place the waste proton exchange membrane electrolysis water membrane electrode into a container, pour in 35% alcohol-water mixed reagent, react for 2 hours under mechanical stirring or ultrasonic action, and control the reaction temperature at 15°C to obtain a proton exchange membrane and a suspension. The suspension is subjected to solid-liquid separation to obtain a proton exchange membrane, solid slag A and a filtrate; Step 2: Add the solid residue A obtained in step 1 into a 2 mol / L mixed reagent of sodium chloride and potassium chloride and soak for 4 hours, control the soaking temperature at 20°C, perform solid-liquid separation, and wash the filter cake to neutrality to obtain solid residue B; Step 3: Dissolve the solid residue B obtained in Step 2 in a mixed solution of dimethyl sulfoxide and dimethylformamide in an autoclave for 2 h, control the temperature at 120°C, perform solid-liquid separation to obtain solid residue C and a perfluorosulfonic acid resin solution, and the perfluorosulfonic acid resin solution is used for preparing a proton exchange regeneration membrane; Step 4: React the solid residue C obtained in Step 3 with sulfuric acid at a concentration of 70% for 1 h, control the reaction temperature at 70°C, perform solid-liquid separation to obtain solid residue D; Step 5: Dissolve the solid residue D obtained in Step 4 completely with hydrochloric acid and sodium hypochlorite, perform solid-liquid separation to obtain a chloroplatinic acid solution and iridium oxide. The chloroplatinic acid solution is used as a platinum catalyst precursor solution after concentration / dilution and pH adjustment. The reaction temperature is 50°C and the reaction time is 1 hour; Step 6: Mix the iridium oxide obtained in Step 5 with elemental sulfur, perform a high-temperature closed reaction for a period of time, with an argon gas atmosphere for the reaction, to obtain solid residue F. The reaction temperature is 400°C, the reaction time is 1 hour, and the gas pressure is 0.2 MPa; Step 7: Dissolve the solid residue F obtained in Step 6 completely with hydrochloric acid and sodium chlorate to obtain an iridium-containing solution, which is used as an iridium catalyst precursor solution after ammonium chloride precipitation - secondary dissolution. The reaction temperature is 70°C and the reaction time is 1 hour. Example 2

[0033] Step 1: Place the waste proton exchange membrane electrolyzed water membrane electrode in a container, pour in a 60% alcohol-water mixed reagent, react under mechanical stirring or ultrasonic action for 5 h, control the reaction temperature at 35°C to obtain a proton exchange membrane and a suspension. The suspension undergoes solid-liquid separation to obtain a proton exchange membrane, solid residue A, and a filtrate; Step 2: Add the solid residue A obtained in Step 1 to a mixed solution of potassium phosphate and sodium carbonate at 4 mol / L, soak for 7.5 h while controlling the soaking temperature at 22°C, perform solid-liquid separation, and wash the filter cake to neutrality to obtain solid residue B; Step 3: Dissolve the solid residue B obtained in Step 2 in a mixed solution of acetonitrile, N-methylpyrrolidone, and tetrahydrofuran in an autoclave for 2.5 h, control the temperature at 200°C, perform solid-liquid separation to obtain solid residue C and a perfluorosulfonic acid resin solution, and the perfluorosulfonic acid resin solution is used for preparing a proton exchange regeneration membrane; Step 4: React the solid residue C obtained in Step 3 with sulfuric acid at a concentration of 85% for 2 h, control the reaction temperature at 80°C, perform solid-liquid separation to obtain solid residue D; Step 5: Dissolve the solid residue D obtained in Step 4 completely with a mixed solution of hydrochloric acid, hydrogen peroxide, and potassium chlorate, perform solid-liquid separation to obtain a chloroplatinic acid solution and iridium oxide. The chloroplatinic acid solution is used as a platinum catalyst precursor solution after concentration / dilution and pH adjustment. The reaction temperature is 65°C and the reaction time is 2 hours; Step 6: Mix the iridium oxide obtained in Step 5 with elemental sulfur, and carry out a high-temperature sealed reaction for a period of time. The reaction gas atmosphere is nitrogen to obtain solid residue F. The reaction temperature is 500 °C, the reaction time is 2 hours, and the gas pressure is 0.5 MPa; Step 7: Dissolve the solid residue F obtained in Step 6 fully with hydrochloric acid and perchloric acid to obtain an iridium-containing solution, which is used as an iridium catalyst precursor solution after ammonium chloride precipitation - secondary dissolution. The reaction temperature is 70 °C and the reaction time is 1 hour. Example 3

[0034] Step 1: Put the waste proton exchange membrane electrolyzed water membrane electrode into a container, pour in an 85% alcohol-water mixed reagent, and react for 10 h under mechanical stirring or ultrasonic action. Control the reaction temperature at 48 °C to obtain a proton exchange membrane and a suspension. The suspension is subjected to solid-liquid separation to obtain a proton exchange membrane, solid residue A, and a filtrate; Step 2: Add the solid residue A obtained in Step 1 to a mixed solution of 6 mol / L potassium sulfate and sodium thiosulfate, soak for 11 h while controlling the soaking temperature at 30 °C, carry out solid-liquid separation, and wash the filter cake to neutrality to obtain solid residue B; Step 3: Dissolve the solid residue B obtained in Step 2 in an ethyl acetate solution in a pressure reactor for 4 h, control the temperature at 245 °C, and carry out solid-liquid separation to obtain solid residue C and a perfluorosulfonic acid resin solution. The perfluorosulfonic acid resin solution is used to prepare a proton exchange regenerated membrane; Step 4: React the solid residue C obtained in Step 3 with 96% concentrated sulfuric acid for 3 h, control the reaction temperature at 90 °C, and carry out solid-liquid separation to obtain solid residue D; Step 5: Dissolve the solid residue D obtained in Step 4 fully with hydrochloric acid and perchloric acid, carry out solid-liquid separation to obtain a chloroplatinic acid solution and iridium oxide. The chloroplatinic acid solution is used as a platinum catalyst precursor solution after concentration / dilution and pH adjustment. The reaction temperature is 79 °C and the reaction time is 3 hours; Step 6: Mix the iridium oxide obtained in Step 5 with elemental sulfur, and carry out a high-temperature sealed reaction for a period of time. The reaction gas atmosphere is vacuum to obtain solid residue F. The reaction temperature is 600 °C and the reaction time is 3 hours; Step 7: Dissolve the solid residue F obtained in Step 6 fully with hydrochloric acid and perchloric acid to obtain an iridium-containing solution, which is used as an iridium catalyst precursor solution after ammonium chloride precipitation - secondary dissolution. The reaction temperature is 90 °C and the reaction time is 3 hours.

[0035] It should be noted that in this text, relational terms such as first and second are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the term "comprising", "including" or any other variant thereof is intended to cover non-exclusive inclusion, such that a process, method, article or device comprising a series of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article or device. Without further limitation, an element defined by the statement "comprising an..." does not exclude the presence of additional identical elements in the process, method, article or device comprising the said element.

[0036] Each embodiment in this specification is described in a related manner. For the same or similar parts among the embodiments, reference can be made to each other. Each embodiment focuses on the differences from other embodiments. In particular, for the device embodiments, since they are basically similar to the method embodiments, the description is relatively simple, and reference can be made to the corresponding parts of the method embodiments for the relevant content.

[0037] The above description is only a preferred embodiment of the present application and is not intended to limit the protection scope of the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application are all included within the protection scope of the present application.

Claims

1. A method for recycling waste proton exchange membrane electrolytic water membrane electrodes, characterized in that Including: Step 1: Put the waste proton exchange membrane electrolyzed water membrane electrode into a container, pour in the alcohol-water mixed reagent, and react for a period of time under mechanical stirring or ultrasonic action to obtain a proton exchange membrane and a suspension. The suspension is subjected to solid-liquid separation to obtain a proton exchange membrane, solid residue A, and filtrate; Step 2: Add the solid residue A obtained in Step 1 to the sodium-potassium salt reagent and soak for a period of time, perform solid-liquid separation, and wash the filter cake to neutrality to obtain solid residue B; Step 3: Dissolve the solid residue B obtained in Step 2 in a polar solvent in a pressure reactor for a period of time, perform solid-liquid separation to obtain solid residue C and a perfluorosulfonic acid resin solution. The perfluorosulfonic acid resin solution is used to prepare a proton exchange regenerated membrane; Step 4: React the solid residue C obtained in Step 3 with sulfuric acid for a period of time, perform solid-liquid separation to obtain solid residue D; Step 5: Dissolve the solid residue D obtained in Step 4 sufficiently with hydrochloric acid and an oxidant, perform solid-liquid separation to obtain a chloroplatinic acid solution and iridium oxide. The chloroplatinic acid solution is used as a platinum catalyst precursor solution after concentration / dilution and pH adjustment; Step 6: Mix the iridium oxide obtained in Step 5 with elemental sulfur, and perform a high-temperature sealed reaction for a period of time to obtain solid residue F; Step 7: Dissolve the solid residue F obtained in Step 6 sufficiently with hydrochloric acid and an oxidant to obtain an iridium-containing solution, which is used as an iridium catalyst precursor solution after ammonium chloride precipitation-secondary dissolution.

2. The method according to claim 1, wherein The process for preparing a proton exchange membrane from the perfluorosulfonic acid resin solution in Step 3 is as follows: Place the perfluorosulfonic acid resin solution in a petri dish, and dry the petri dish in a vacuum oven at 160-180 °C to form a film. Wash the film with 1-5% hydrogen peroxide solution at 25-80 °C for 0.5-3 h, and soak it in a 0.1-2 mol / L dilute sulfuric acid solution for 1-24 h to obtain a perfluorosulfonic acid proton exchange membrane.

3. The method according to claim 1, wherein In the alcohol-water mixed reagent in Step 1, the volume fraction of alcohol is 30%-90%, and the alcohol is one or more of methanol, ethanol, isopropanol, n-propanol, n-butanol, isobutanol, and tert-butanol. The reaction temperature in Step 1 is 10-50 °C, and the reaction time is 1-10 hours.

4. The method according to claim 1, wherein The concentration of the sodium-potassium salt reagent in Step 2 is 1-6 mol / L. The types of sodium-potassium salt reagents include one or more of sodium chloride, potassium chloride, potassium carbonate, potassium bicarbonate, potassium hydroxide, potassium sulfate, potassium phosphate, sodium carbonate, sodium hydroxide, sodium bicarbonate, sodium sulfate, sodium phosphate, sodium sulfite, and sodium thiosulfate. The soaking temperature in Step 2 is 15-30 °C, and the soaking time is 3-12 hours.

5. The method according to claim 1, characterized in that, The polar solvent in Step 3 is one or more of dimethyl sulfoxide, dimethylformamide, acetonitrile, N-methylpyrrolidone, tetrahydrofuran, and ethyl acetate; the reaction temperature in Step 3 is 120-250 °C, and the reaction time is 1-4 hours.

6. The method according to claim 1, wherein The concentration of sulfuric acid in Step 4 is 70%-98%, the reaction temperature is 70-90 °C, and the reaction time is 1-3 hours.

7. The method according to claim 1, wherein The reaction temperature in Step 5 is 50-80 °C, and the reaction time is 1-3 hours.

8. The method according to claim 1, characterized in that, The reaction gas atmosphere in Step 6 is vacuum or one of nitrogen and argon, the reaction temperature is 400 - 600 °C, the reaction time is 1 - 3 hours, and the gas pressure is 0.2 - 1 MPa.

9. The method according to claim 1, wherein The reaction temperature in Step 7 is 70 - 90 °C, and the reaction time is 1 - 3 hours.

10. The method according to claim 1, characterized in that, The oxidizing agent in Step 5 and Step 7 is one or more of sodium chlorate, sodium hypochlorite, perchloric acid, hydrogen peroxide, and potassium chlorate.