A method for recycling spent catalyst

Abstract

The application belongs to the technical field of waste catalyst recovery, and discloses a waste catalyst recycling method, which comprises the following steps: S1: material recovery, solid materials are recovered by a magnet or other tools after being saturatedly adsorbed in a hexavalent chromium aqueous solution; S2: drying treatment, the recovered iron-nitrogen-carbon composite material is sent into a drying machine for drying to ensure that the water content is lower than the requirement; and S3: calcination treatment, the dried iron-nitrogen-carbon composite material is calcined to obtain a chromium-doped iron-nitrogen-carbon composite material. The application effectively recovers waste catalysts through the unique strong magnetism of iron-nitrogen-carbon materials, and the recovered waste catalysts can be regenerated into a composite material doped with metals after simple recalcination, and can be applied to activate persulfate in wastewater treatment to solve the problem of pollutants. Through catalyzing persulfate to generate strong oxidizing free radicals, the application can rapidly degrade organic pollutants in wastewater, and achieves the purpose of purifying water quality.

Description

Technical Field

[0001] This invention belongs to the field of waste catalyst recycling technology, specifically a method for recycling and reusing waste catalysts. Background Technology

[0002] Persulfate-based deep oxidation processes (PDS-AOPs) are widely studied in wastewater treatment for degrading various recalcitrant organic pollutants due to their high oxidizing capacity and low energy consumption. Various free radicals, such as hydroxyl radicals (…), are also utilized. OH), sulfate radicals (SO4-) ) and superoxide radicals (O2- Radicals, including singlet oxygen (1O2), high-valence metal oxygen (HVMO), and electron transfer processes (ETP), have been reported to participate in the removal of target pollutants. While radical pathways offer the advantage of efficiently removing micro-pollutants from water, their non-selectivity makes them susceptible to the influence of environmental background substrates such as inorganic salts, halides, and natural organic matter, as well as consumption by other complex pollutants, leading to overuse of oxidants. Non-radical pathways, on the other hand, can rapidly and selectively remove pollutants and effectively address the problem of inhibiting the reaction between radicals and non-target substances. Chromium is one of the most common heavy metals emitted from electroplating, automobile manufacturing, leather tanning, mining, and other industries. Currently, the treatment of hexavalent chromium wastewater mainly relies on adsorption and reduction methods. The added reagents have good adsorption and reduction properties, but due to the large dosage and problems such as reagent aging and deactivation, reagent consumption is increasingly serious, and the disposal of treated reagents is becoming increasingly problematic. Therefore, finding a material that is easily recyclable and reusable is of great significance.

[0003] Fe3C possesses a unique structure composed of carbon atoms occupying interstitial spaces in the iron lattice, granting it excellent properties similar to noble metals. In the field of advanced persulfate oxidation technology, Fe3C can adsorb persulfate, inducing a non-radical-dominated oxidation process with good activity and selectivity even under complex backgrounds. The unique core-shell structure of Fe3C resists iron leaching, solving the problems of iron sludge formation and severe pH-induced performance inhibition seen in previous Fenton-like reactions. However, the electronic structure of Fe3C results in strong adsorption of oxygen and persulfate by the iron active centers. This strong adsorption leads to competition between the two, accelerating catalyst aging. Therefore, a suitable method must be found to balance the adsorption and desorption of oxidants and oxygen by the iron active centers, thereby improving catalyst activity.

[0004] Among the existing technologies, those related to the recycling and reuse of waste materials include: the application of catalysts using waste adsorbents after adsorption-desorption as raw materials in the treatment of high-salt organic wastewater by activated persulfate (CN202011271815); a method for preparing single-atom catalysts using waste adsorbents after adsorption-desorption (CN202011641169); a single-atom catalyst for CO2 reduction based on waste adsorbents and its preparation method (CN202310523090); and the resource utilization of waste chromium adsorbents (CN201710129043).

[0005] In the technology of using waste adsorbent after adsorption-desorption as raw material for the treatment of high-salt organic wastewater by activated persulfate (CN202011271815), the waste biomass adsorbent that has repeatedly adsorbed heavy metals is recovered and then mixed with a nitrogen source for calcination to regenerate the waste adsorbent-based catalyst. This catalyst is then applied to the persulfate advanced oxidation system to efficiently resolve persistent organic matter in high-salt organic wastewater through a non-radical mechanism. This technology not only solves the problem that adsorbents saturated with heavy metal ions cannot effectively treat pollutants, but also provides a new way to degrade pollutants through a non-radical process by activated persulfate. It is simple to operate, low in cost, and can effectively help solve environmental problems while also utilizing waste.

[0006] In a method for preparing single-atom catalysts using waste adsorbents after adsorption-desorption (CN202011641169), the waste biomass adsorbent saturated with heavy metals is recovered and then mixed with a nitrogen source for calcination to regenerate the single-atom catalyst. The single-atom catalyst obtained by this invention exhibits uniform metal single-atom distribution and good dispersion, avoiding secondary pollution from the waste adsorbent after heavy metal adsorption, alleviating the pressure of solid waste disposal, and protecting the environment. The operation is simple and low-cost, and the prepared product has high metal single-atom loading and good dispersion, providing a new approach for the large-scale production of single-atom catalysts.

[0007] In the technology of a single-atom catalyst for CO2 reduction based on waste adsorbent and its preparation method (CN202310523090), a single-atom catalyst is obtained by mixing waste carbon-based adsorbent that has adsorbed heavy metals with nitrogen-containing organic matter for CO2 reduction. This catalyst has low cost, good conductivity, excellent selectivity for CO, and greatly reduces the environmental harm of solid waste and heavy metals, thus having broad market prospects.

[0008] In a technology for the resource utilization of waste chromium adsorbents (CN201710129043), a catalyst is prepared by calcining the waste composite mesoporous chromium adsorbent after chromium adsorption, which is then used for the catalytic decomposition of methanethiol. This catalyst not only significantly reduces the decomposition temperature of methanethiol but also significantly improves its lifespan, achieving the goal of "treating waste with waste" and showing promising application prospects.

[0009] However, the above technologies all overlook the difficulties in recycling carbon-based materials in water and the limitations in improving catalyst performance after adding a nitrogen source. Although current technologies for recycling and reusing waste materials in water mainly focus on the regeneration and calcination of carbon-based adsorbents, the structure of carbon-based adsorbents is relatively simple. Although adding a nitrogen source can effectively improve the treatment efficiency, it is still insufficient to meet the ideal treatment efficiency of polluted wastewater. Therefore, a new recycling and reuse method is urgently needed to solve the above problems. Summary of the Invention

[0010] The purpose of this invention is to provide a method for recycling and reusing spent catalysts to solve the problems mentioned in the background art. To achieve the above objective, this invention provides the following technical solution: A method for recycling and reusing spent catalysts, comprising the following steps:

[0011] S1: Material recycling, which involves recycling the solid material saturated with hexavalent chromium in an aqueous solution of iron, nitrogen, and carbon using a magnetic tool;

[0012] S2: Drying process, the recovered iron-nitrogen-carbon composite material is sent into the dryer for drying to ensure that the moisture content is lower than the requirement;

[0013] S3: Calcination treatment, the dried iron-nitrogen-carbon composite material is calcined to obtain chromium-doped iron-nitrogen-carbon composite material;

[0014] S4: Catalyze the removal of tetracycline hydrochloride from water using sodium persulfate. Mix chromium-doped iron-nitrogen-carbon composite material, tetracycline hydrochloride solution, and sodium persulfate, and the mixture undergoes a degradation reaction.

[0015] As a further technical solution of the present invention, the iron-nitrogen-carbon material is a catalyst with a core-shell structure having iron carbide as the active center and carbon layer as the outer shell, prepared from ferric chloride, melamine, glucose or other iron, nitrogen and carbon sources.

[0016] By effectively recovering iron, nitrogen, and carbon materials from spent catalysts, resource reuse is achieved, reducing waste and aligning with the principles of circular economy and sustainable development. Spent catalysts may contain harmful substances or heavy metals; recycling and reuse methods can reduce environmental pollution and harm, protecting the ecological environment. The chromium-doped iron-nitrogen-carbon composite material obtained after calcination possesses certain catalytic properties and can be used to catalytically degrade organic matter in water, such as tetracycline hydrochloride, thereby purifying water quality and achieving environmental protection goals. The calcined chromium-doped iron-nitrogen-carbon composite material can achieve efficient degradation of organic matter during catalysis, realizing the effective reuse of resources and improving material utilization efficiency. Recycling and reusing spent catalysts can reduce waste treatment costs and also provide an economical and efficient way to prepare new materials, lowering production costs.

[0017] As a further technical solution of the present invention, the hexavalent chromium aqueous solution has potassium dichromate as the solute, water as the solvent, and a concentration of 20 mg / L.

[0018] As a further technical solution of the present invention, the hexavalent chromium aqueous solution is adjusted to a pH between 2 and 4 using 0.1 mM hydrochloric acid.

[0019] As a further technical solution of the present invention, the dosage of iron, nitrogen and carbon materials in the hexavalent chromium aqueous solution is 300 mg / L.

[0020] As a further technical solution of the present invention, during the drying process, the drying temperature range should be controlled to be 100-120 ℃ and the drying time should be 10-12 h.

[0021] As a further technical solution of the present invention, the calcination treatment shall be carried out under a protective atmosphere, namely nitrogen or argon. The temperature range during calcination shall be controlled at 700-900 ℃, the rate of heating to the calcination temperature shall be 4-6 ℃ / min, and the calcination time shall be 1-2 h.

[0022] As a further technical solution of the present invention, when sodium persulfate is used to remove tetracycline hydrochloride from water, the concentration of sodium persulfate in the mixed solution is in the range of 0.5-5 mmol / L, the pH value of the degradation reaction is 3-11, and the temperature range of the degradation reaction is 15-55 ℃.

[0023] This invention provides a method for recycling and reusing iron-nitrogen-carbon (Fe3C) materials after chromium adsorption to synthesize chromium-doped Fe3C-carbon composite materials and their applications. Unlike the simple structure of carbon-based materials, Fe3C materials, with Fe3C as the active center and a carbon-encased core-shell structure, possess strong stability and high catalytic activity, maintaining good activity over a wide pH range. The confined structure also effectively prevents iron sludge leaching. The strong magnetism of Fe3C itself provides more efficient recycling methods such as magnetic adsorption. Due to its excellent performance, Fe3C-carbon materials are currently attracting significant attention from researchers and various industries, and their application scope is gradually expanding. Therefore, the recycling and reuse of this type of material has higher cost-effectiveness and forward-looking potential. Furthermore, the chromium doping method of this invention not only adsorbs and enriches hexavalent chromium but also recovers and calcines it into a novel catalyst, altering the electronic structure and charge density of the original catalyst, realizing the transformation from a free radical pathway to a non-free radical electron transfer pathway, improving electron transfer capacity, and simultaneously enhancing oxygen evolution capacity. It increases oxygen vacancies while enhancing oxidant adsorption, improving catalytic activation performance, achieving dual utilization and a green and environmentally friendly effect, showing promising prospects.

[0024] The iron-nitrogen-carbon material mentioned in this invention uses iron as a key active center, exhibiting superior catalytic performance unmatched by carbon-based materials. Furthermore, its porous structure enables excellent adsorption of chromium metal, providing both adsorption and catalytic oxidation capabilities. Secondly, addressing the current challenge of adsorbent recovery, existing technologies often rely on filtration to recover solid materials from water. However, the iron-nitrogen-carbon material possesses strong magnetism, allowing for efficient recovery through simple magnetic attraction, significantly simplifying the complex recovery process and reducing both difficulty and cost. Finally, addressing the issue that most currently discovered iron-nitrogen-carbon catalysts rely primarily on free radical mechanisms, making them susceptible to oxygen influence and occupying oxidant adsorption sites, the chromium doping method of this invention not only improves the electronic structure of the iron-nitrogen-carbon material but also enhances the adsorption of oxidants such as persulfate, shifting the free radical pathway to a non-free radical pathway and resulting in better selectivity.

[0025] Compared with existing technologies, this invention regenerates chromium-doped iron-nitrogen-carbon catalysts by recovering waste iron-nitrogen-carbon catalysts that have adsorbed hexavalent chromium. This method not only utilizes the magnetic properties of iron-nitrogen-carbon materials to make the recovery process simple and easy, but also this chromium doping method can modify the original catalyst, changing its configuration and electronic structure, so that the activation mechanism changes from a free radical mechanism to a non-free radical mechanism, enhancing the electron transfer ability of the original catalyst and improving its catalytic oxidation performance.

[0026] The beneficial effects of this invention are as follows:

[0027] 1. This invention utilizes the unique strong magnetic properties of iron-nitrogen-carbon materials to effectively recover waste catalysts. After recovery, the catalysts can be regenerated into metal-doped composite materials through simple recalcination. These composite materials can be applied to wastewater treatment to activate persulfate and solve pollutant problems. By catalyzing persulfate to generate highly oxidizing free radicals, the organic pollutants in wastewater can be rapidly degraded, thereby achieving the purpose of purifying water quality.

[0028] 2. This invention sets different iron, nitrogen, and carbon materials, making them different from the simple structure of carbon-based materials. With Fe3C as the active center, the core-shell structure wrapped by carbon layers gives the material strong stability and high catalytic activity. It can maintain good activity over a wide pH range, and the confined structure also effectively prevents the leaching of iron mud.

[0029] 3. This invention changes the chromium doping method, enabling it not only to adsorb and enrich hexavalent chromium, but also to recover and calcine it into a new type of catalyst. This alters the electronic structure and charge density of the original catalyst, transforming the free radical pathway into a non-free radical electron transfer pathway, thereby improving electron transfer capacity and simultaneously enhancing oxygen evolution capacity. By increasing oxygen vacancies, it also enhances the adsorption of oxidants, improving catalytic activation performance and achieving dual utilization and a green and environmentally friendly effect. Attached Figure Description

[0030] Figure 1 A diagram illustrating the effect of iron-nitrogen-carbon materials on adsorbing hexavalent chromium in water.

[0031] Figure 2 The leaching effect of hexavalent chromium in water on chromium-doped iron-nitrogen-carbon materials;

[0032] Figure 3 TEM images of iron-nitrogen-carbon materials and chromium-doped iron-nitrogen-carbon materials;

[0033] Figure 4 TEM-Mapping of chromium-doped iron-nitrogen-carbon material;

[0034] Figure 5 X-ray diffraction (XRD) pattern of chromium-doped iron-nitrogen-carbon material;

[0035] Figure 6 Raman spectroscopy for chromium-doped iron-nitrogen-carbon materials;

[0036] Figure 7 Vibrating sample magnetometer (VSM) image of chromium-doped iron-nitrogen-carbon material;

[0037] Figure 8 A schematic diagram of sodium persulfate activation for the removal of tetracycline hydrochloride from iron-nitrogen-carbon materials and chromium-doped iron-nitrogen-carbon materials;

[0038] Figure 9A diagram illustrating the quenching effect of chromium-doped iron-nitrogen-carbon materials;

[0039] Figure 10 EPR diagrams of iron-nitrogen-carbon and chromium-doped iron-nitrogen-carbon materials;

[0040] Figure 11 Open circuit potential-time (OCPT) curves for chromium-doped iron-nitrogen-carbon materials;

[0041] Figure 12 A schematic diagram illustrating the effect of different pH values ​​on the removal of tetracycline hydrochloride from chromium-doped iron-nitrogen-carbon materials.

[0042] Figure 13 A schematic diagram illustrating the effect of different oxidant dosages on the removal of tetracycline hydrochloride from chromium-doped iron-nitrogen-carbon materials;

[0043] Figure 14 A schematic diagram illustrating the effect of different catalyst dosages on the removal of tetracycline hydrochloride by chromium-doped iron-nitrogen-carbon materials;

[0044] Figure 15 The effect of chromium-doped iron-nitrogen-carbon material in removing different pollutants. Detailed Implementation

[0045] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0046] like Figures 1 to 15 As shown in the embodiment of the present invention, a method for recycling and reusing waste catalyst includes the following steps:

[0047] S1: Material recycling, which involves recycling the solid material saturated with hexavalent chromium in an aqueous solution of iron, nitrogen, and carbon using a magnetic tool;

[0048] S2: Drying process, the recovered iron-nitrogen-carbon composite material is sent into the dryer for drying to ensure that the moisture content is lower than the requirement;

[0049] S3: Calcination treatment, the dried iron-nitrogen-carbon composite material is calcined to obtain chromium-doped iron-nitrogen-carbon composite material;

[0050] S4: Catalyze the removal of tetracycline hydrochloride from water using sodium persulfate. Mix chromium-doped iron-nitrogen-carbon composite material, tetracycline hydrochloride solution, and sodium persulfate, and the mixture undergoes a degradation reaction.

[0051] By effectively recovering iron, nitrogen, and carbon materials from spent catalysts, resource reuse is achieved, reducing waste and aligning with the principles of circular economy and sustainable development. Spent catalysts may contain harmful substances or heavy metals; recycling and reuse methods can reduce environmental pollution and harm, protecting the ecological environment. The chromium-doped iron-nitrogen-carbon composite material obtained after calcination possesses certain catalytic properties and can be used to catalytically degrade organic matter in water, such as tetracycline hydrochloride, thereby purifying water quality and achieving environmental protection goals. The calcined chromium-doped iron-nitrogen-carbon composite material can achieve efficient degradation of organic matter during catalysis, realizing the effective reuse of resources and improving material utilization efficiency. Recycling and reusing spent catalysts can reduce waste treatment costs and also provide an economical and efficient way to prepare new materials, lowering production costs.

[0052] The iron-nitrogen-carbon material is a catalyst with a core-shell structure, consisting of iron carbide as the active center and a carbon layer as the outer shell, prepared from ferric chloride, melamine, glucose, or other iron, nitrogen, and carbon sources.

[0053] The hexavalent chromium aqueous solution contains potassium dichromate as the solute, water as the solvent, and has a concentration of 20 mg / L.

[0054] The hexavalent chromium aqueous solution is adjusted to a pH between 2 and 4 using 0.1 mM hydrochloric acid.

[0055] The dosage of iron, nitrogen, and carbon materials in the hexavalent chromium aqueous solution is 300 mg / L.

[0056] During the drying process, the drying temperature should be controlled within the range of 100-120 ℃, and the drying time should be 10-12 h.

[0057] The calcination process shall be carried out under a protective atmosphere, namely nitrogen or argon. The temperature range during calcination shall be controlled at 700-900 ℃, the rate of heating to the calcination temperature shall be 4-6 ℃ / min, and the calcination time shall be 1-2 h.

[0058] In the process of removing tetracycline hydrochloride from water by catalytic sodium persulfate, the concentration of sodium persulfate in the mixed solution is in the range of 0.5-5 mmol / L, the pH value of the degradation reaction is 3-11, and the temperature range of the degradation reaction is 15-55 ℃.

[0059] This invention provides a method for recycling and reusing iron-nitrogen-carbon (Fe3C) materials after chromium adsorption to synthesize chromium-doped Fe3C-carbon composite materials and their applications. Unlike the simple structure of carbon-based materials, Fe3C materials, with Fe3C as the active center and a carbon-encased core-shell structure, possess strong stability and high catalytic activity, maintaining good activity over a wide pH range. The confined structure also effectively prevents iron sludge leaching. The strong magnetism of Fe3C itself provides more efficient recycling methods such as magnetic adsorption. Due to its excellent performance, Fe3C-carbon materials are currently attracting significant attention from researchers and various industries, and their application scope is gradually expanding. Therefore, the recycling and reuse of this type of material has higher cost-effectiveness and forward-looking potential. Furthermore, the chromium doping method of this invention not only adsorbs and enriches hexavalent chromium but also recovers and calcines it into a novel catalyst, altering the electronic structure and charge density of the original catalyst, realizing the transformation from a free radical pathway to a non-free radical electron transfer pathway, improving electron transfer capacity, and simultaneously enhancing oxygen evolution capacity. It increases oxygen vacancies while enhancing oxidant adsorption, improving catalytic activation performance, achieving dual utilization and a green and environmentally friendly effect, showing promising prospects.

[0060] The iron-nitrogen-carbon material mentioned in this invention uses iron as a key active center, exhibiting superior catalytic performance unmatched by carbon-based materials. Furthermore, its porous structure enables excellent adsorption of chromium metal, providing both adsorption and catalytic oxidation capabilities. Secondly, addressing the current challenge of adsorbent recovery, existing technologies often rely on filtration to recover solid materials from water. However, the iron-nitrogen-carbon material possesses strong magnetism, allowing for efficient recovery through simple magnetic attraction, significantly simplifying the complex recovery process and reducing both difficulty and cost. Finally, addressing the issue that most currently discovered iron-nitrogen-carbon catalysts rely primarily on free radical mechanisms, making them susceptible to oxygen influence and occupying oxidant adsorption sites, the chromium doping method of this invention not only improves the electronic structure of the iron-nitrogen-carbon material but also enhances the adsorption of oxidants such as persulfate, shifting the free radical pathway to a non-free radical pathway and resulting in better selectivity.

[0061] Compared with existing technologies, this invention regenerates chromium-doped iron-nitrogen-carbon catalysts by recovering waste iron-nitrogen-carbon catalysts that have adsorbed hexavalent chromium. This method not only utilizes the magnetic properties of iron-nitrogen-carbon materials to make the recovery process simple and easy, but also this chromium doping method can modify the original catalyst, changing its configuration and electronic structure, so that the activation mechanism changes from a free radical mechanism to a non-free radical mechanism, enhancing the electron transfer ability of the original catalyst and improving its catalytic oxidation performance.

[0062] Example 1:

[0063] Dissolve 3.0 g of anhydrous ferric chloride in 40 mL of solvent (composed of anhydrous ethanol and water in a 1:1 volume ratio) and stir until completely dissolved to obtain anhydrous ferric chloride solution. Dissolve 3.0 g of glucose in 20 mL of water and stir until completely dissolved, then add 40 mL of anhydrous ethanol and mix well to obtain glucose solution. Add 2.0 g of melamine to a 250 mL beaker containing 100 mL of solvent (composed of anhydrous ethanol and water in a 1:1 volume ratio), place the beaker on a thermostatic magnetic stirrer, and stir at 60 ℃ at a rate of 50 r / min until the solution becomes colorless to obtain melamine solution.

[0064] Anhydrous ferric chloride solution and glucose solution were added to melamine solution, stirred at 50 r / min for 20 min, and then 0.5 g of carbon nanotubes were added. The mixture was stirred at 60 ℃ for 2 h to obtain a homogeneous solution. The solution was dried in an oven at 180 ℃ for 12 h to obtain a material precursor solid. The material precursor solid was ground into powder and placed in a ceramic boat. The boat was placed in a tube furnace and heated to 800 ℃ at a rate of 5 ℃ / min under a N2 atmosphere. After holding at 800 ℃ for 3 h, the tube furnace was cooled to room temperature. After the tube furnace cooled, the ceramic boat was removed, and the black solid in the boat was ground into powder particles with a particle size of approximately 1.3 μm to obtain the iron-nitrogen-carbon material.

[0065] A 20 mg / L hexavalent chromium aqueous solution was adjusted to pH 3 with 0.1 mM hydrochloric acid. Then, 300 mg / L iron carbide was added. After ultrasonic adsorption for 20 min, the iron carbide was recovered from the water using a magnet. The solution was then dried in an oven at 100 °C for 12 h to obtain a chromium-doped iron-nitrogen-carbon precursor solid. The precursor solid was ground into powder and placed in a ceramic boat. The boat was then placed in a tube furnace and heated to 800 °C at a rate of 5 °C / min under a N2 atmosphere. After holding at 800 °C for 1 h, the tube furnace was cooled to room temperature. Once cooled, the ceramic boat was removed, and the black solid inside was ground into powder particles with a particle size of approximately 1.3 μm to obtain the chromium-doped iron-nitrogen-carbon catalyst.

[0066] Example 2:

[0067] The prepared chromium-doped iron-nitrogen-carbon catalyst was added to a 0.1 mM tetracycline hydrochloride aqueous solution, and persulfate was added at a dosage of 0.5 mM. After mixing evenly, the mixture was reacted for 60 min under shaking conditions at 25 ℃ and pH 4.5 to degrade and remove tetracycline hydrochloride from the water. The catalyst concentration was 150 mg / L.

[0068] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for recycling and reusing spent catalysts, characterized in that: Includes the following steps: S1: Material recycling, which involves recycling the solid material saturated with hexavalent chromium in an aqueous solution of iron, nitrogen, and carbon using a magnetic tool; S2: Drying process, the recovered iron-nitrogen-carbon composite material is sent into the dryer for drying to ensure that the moisture content is lower than the requirement; S3: Calcination treatment, the dried iron-nitrogen-carbon composite material is calcined to obtain chromium-doped iron-nitrogen-carbon composite material; S4: Catalyze sodium persulfate to remove tetracycline hydrochloride from water. Mix chromium-doped iron-nitrogen-carbon composite material, tetracycline hydrochloride solution and sodium persulfate, and the mixture undergoes a degradation reaction. The iron-nitrogen-carbon material is a catalyst with a core-shell structure, consisting of iron carbide as the active center and a carbon layer as the outer shell, prepared from ferric chloride, melamine, glucose, or other iron, nitrogen, and carbon sources.

2. The method for recycling and reusing spent catalysts according to claim 1, characterized in that: The hexavalent chromium aqueous solution has potassium dichromate as the solute, water as the solvent, and a concentration of 20 mg / L.

3. The method for recycling and reusing spent catalysts according to claim 1, characterized in that: The hexavalent chromium aqueous solution was adjusted to a pH between 2 and 4 using 0.1 mM hydrochloric acid.

4. The method for recycling and reusing spent catalyst according to claim 1, characterized in that: The dosage of iron, nitrogen, and carbon materials in the hexavalent chromium aqueous solution is 300 mg / L.

5. The method for recycling and reusing spent catalysts according to claim 1, characterized in that: During the drying process, the drying temperature should be controlled within the range of 100-120 ℃, and the drying time should be 10-12 h.

6. The method for recycling and reusing spent catalysts according to claim 1, characterized in that: The calcination process should be carried out under a protective atmosphere, such as nitrogen or argon. The temperature range during calcination should be controlled at 700-900 ℃, the rate of heating to the calcination temperature should be 4-6 ℃ / min, and the calcination time should be 1-2 h.

7. The method for recycling and reusing spent catalyst according to claim 1, characterized in that: When catalytic sodium persulfate removes tetracycline hydrochloride from water, the concentration of sodium persulfate in the mixed solution is in the range of 0.5-5 mmol / L, the pH value of the degradation reaction is 3-11, and the temperature range of the degradation reaction is 15-55 ℃.

Images