Method for preparing iron monatomic catalyst by upgrading retired lithium iron phosphate battery and application of iron monatomic catalyst

Abstract

The invention provides a method for preparing an iron monatomic catalyst by upgrading a retired lithium iron phosphate battery and application of the iron monatomic catalyst. The preparation method comprises the following steps: combining retired lithium iron phosphate powder and an electrolytic solution with a graphene aerogel GA electrode and an Ag / AgCl reference electrode, and connecting into an electrochemical workstation; adding a surfactant into the electrolytic solution, introducing oxygen for electrolysis, performing electrochemical leaching on the retired lithium iron phosphate, performing solid-liquid separation to obtain a leaching solution and filter residues, and performing a recovery process on the leaching solution to obtain iron phosphate and lithium carbonate products; and adding a nitrogen source into the obtained recycled waste, and carrying out ball milling and high-temperature roasting to obtain the iron monatomic catalyst. According to the method disclosed by the invention, the leaching of Li and Fe in the retired lithium iron phosphate battery is enhanced by utilizing H2O2 generated by electricity, so that the stepped recovery of lithium carbonate, iron phosphate and recovered waste is realized. And active oxygen (ROS) is produced in the process of activating peroxymonosulfate (PMS), so that deep degradation of bisphenol A pollutants (BPA) can be realized.

Description

Technical Field

[0001] The present invention relates to the technical field of water pollution treatment, and in particular to a method for preparing an iron single-atom catalyst by upgrading retired lithium iron phosphate batteries and an application thereof. Background Art

[0002] With the rapid development of the new energy vehicle industry, the demand for power batteries, mainly lithium iron phosphate batteries, has increased rapidly, but it is also facing the problem of disposing of more and more retired lithium iron phosphate batteries. In 2023, my country produced a total of 168,000 tons of retired power batteries. It is estimated that by 2030, my country will produce more than 1 million tons of retired power batteries, of which more than 60% will be lithium iron phosphate batteries. Therefore, the rational and efficient treatment and recycling of retired lithium iron phosphate batteries can not only recycle a large amount of non-ferrous metal resources such as lithium, iron, nickel and cobalt, but also avoid the irreversible harm of heavy metals and fluorine-containing electrolytes to the ecological environment.

[0003] At present, hydrometallurgy has become the mainstream process for disposing of retired lithium iron phosphate batteries. The valuable metals in retired lithium iron phosphate batteries are ionized using acidic solvents (organic or inorganic acids), and then recycled in stages through chemical precipitation, extraction, membrane separation, adsorption and other means. In order to cope with the stable olivine structure (FeLiPO4) and coating (conductive agent, binder and graphite), strong acid leaching agents (HCl and H2SO4) and oxidants (H2O2, Cl2 and active oxygen) are used to enhance the decomposition of retired lithium iron phosphate batteries. However, after the valuable metals are leached, the remaining graphite and iron phosphate are often ignored and not recycled because they are difficult to separate and have low value.

[0004] The advanced oxidation process (AOP) based on peroxymonosulfate (PMS) is widely regarded as an effective method for eliminating organic pollutants in wastewater. The reactive oxygen species (ROS) generated by the activation of PMS is a strong oxidant with high pollutant degradation ability. Since traditional physical methods (such as ultraviolet rays, gamma rays, ultrasound, microwaves, heat, etc.) mean a lot of energy consumption, single-atom catalysts are superior in activation methods. Among them, metal nitrogen-carbon catalysts made of transition metals (such as iron, copper, nickel, cobalt, manganese, etc.) and nitrogen-co-doped carbon materials have significant advantages in repairing water environments due to their high atomic utilization, uniform active sites and high stability.

[0005] For example, CN 119076036A prepares a N-coordinated metal organic framework by a precipitation method using Cu salts and N-containing organic ligands, and then pyrolyzes the metal at 300-800°C to obtain a metal single atom catalyst (i.e., CuO@CN catalyst) supported on a metal oxide and a carbon-nitrogen composite support, which effectively improves its catalytic activation efficiency for persulfate degradation of phenol.

[0006] For another example, CN 118949990A utilizes the strong metal-support interaction between synthesized titanium dioxide nanosheets and Co single atoms, and obtains titanium dioxide nanosheets loaded with Co single atoms (i.e., Co / TiO2NS catalyst) after air calcination. Among them, Co single atoms can efficiently activate peroxymonosulfate as catalytic sites to produce highly oxidizing hydroxyl radicals, thereby achieving efficient oxidative degradation of new antibiotic pollutants. However, the above-mentioned single-atom catalysts all have the obvious disadvantages of complex processes and high costs.

[0007] In view of this, the present invention is proposed. Summary of the invention

[0008] In order to solve the above technical problems, the present invention provides a method for upgrading retired lithium iron phosphate batteries to prepare iron single atom catalysts and its application. The method provided by the present invention not only provides a sustainable, economical and effective way for recycling retired lithium iron phosphate battery waste, but also has important significance for reducing the treatment cost of organic pollutants such as bisphenol A pollutants (BPA).

[0009] The first object of the present invention is to provide a method for upgrading retired lithium iron phosphate batteries to prepare iron single-atom catalysts, comprising the following steps:

[0010] (1) Adding retired lithium iron phosphate powder into the electrolytic solution, inserting the graphene aerogel GA electrode and the Ag / AgCl reference electrode, and connecting to the electrochemical workstation;

[0011] (2) adding a surfactant to the electrolytic solution of step (1), and continuously introducing oxygen for electrolysis, electrochemically leaching the retired lithium iron phosphate, performing solid-liquid separation on the electrolyzed electrolyte to obtain a leachate and a filter residue, washing and drying the filter residue to obtain a recycled waste containing iron phosphate and graphite, and subjecting the leachate to a recovery process to obtain iron phosphate and lithium carbonate products;

[0012] (3) Adding a nitrogen source to the recycled waste obtained in step (2), ball milling and high-temperature calcination to obtain an iron single-atom catalyst.

[0013] In some embodiments of the present invention, in step (1), the amount of retired lithium iron phosphate powder added is 0.5-2 g / L. The amount of retired lithium iron phosphate powder added is preferably 0.5 g / L, 1 g / L, 1.5 g / L and 2 g / L, or any interval value between any two values.

[0014] In some embodiments of the present invention, in step (1), the electrolytic solution is one or more of sulfuric acid, phosphoric acid, oxalic acid, and acetic acid solutions; preferably a sulfuric acid solution.

[0015] In some embodiments of the present invention, the concentration of the electrolytic solution is 0.01-0.4M, for example, 0.05M, 0.1M, 0.15M, 0.2M, 0.25M, 0.3M and 0.35M, or any interval between any two values.

[0016] In some embodiments of the present invention, in step (2), the surfactant is sodium dodecyl sulfate. The present invention reduces the surface tension of the sulfuric acid medium by adding a surfactant, so that the waste lithium iron phosphate powder is fully dissolved in the low-concentration sulfuric acid electrolyte.

[0017] In some embodiments of the present invention, in step (2), the amount of surfactant added is 0.05-0.3 g / L. The amount of surfactant added is preferably 0.1 g / L, 0.15 g / L, 0.18 g / L and 0.2 g / L, or any interval between any two values.

[0018] In some embodiments of the present invention, in step (2), the electrochemical leaching is an enhanced leaching process for electrically producing H2O2, and the specific parameters include an applied voltage of -1 to -1.5V, an electrolysis time of 2 to 5h, and a stirring speed of 300 to 600rpm. The electrolysis time is preferably 2 to 4h, such as 2h, 2.5h, 3h, 3.5h, 4h, etc., or any interval value between any two values.

[0019] In some embodiments of the present invention, in step (3), the nitrogen source is selected from one or more of dicyandiamide, urea, ethylenediamine, and hydrazine hydrate. Further, dicyandiamide is preferred.

[0020] In some embodiments of the present invention, the amount of the nitrogen source in the recycled waste is 22.5-50 g / g, preferably 25-30 g / g, for example, 25 g / g, 26 g / g, 27 g / g, 28 g / g, 29 g / g and 30 g / g, or any interval value between any two values.

[0021] In some embodiments of the present invention, in step (3), the ball milling speed is 200 to 600 rpm;

[0022] In some embodiments of the present invention, the temperature of high temperature roasting is 600-900°C, and the roasting time is 2-5h. The high temperature roasting is preferably 600°C, 650°C, 700°C, 750°C and 800°C, or any interval between any two values. The roasting time is preferably 2h, 2.5h, 3h, 3.5h and 4h, or any interval between any two values.

[0023] In some embodiments of the present invention, in step (3), the recovery process of the leachate is a chemical precipitation process including: adjusting the pH of the leachate to about 2.5, adding 5 to 10 g / L of ammonia water and reacting for 2 to 4 hours, and then separating the solid and liquid to obtain iron phosphate; then adding 0.5 to 2 g / L of sodium carbonate and reacting for 2 to 4 hours, filtering, rinsing and drying to obtain lithium carbonate.

[0024] The second object of the present invention is to provide an iron single atom catalyst prepared by the method, wherein the iron single atom catalyst is a carbon-based nanomaterial co-doped with Fe and N (Fe-NC catalyst).

[0025] The third object of the present invention is to provide the use of the iron single atom catalyst in activating peroxymonosulfate to degrade organic pollutants.

[0026] In some embodiments of the present invention, the organic pollutants include one or more of bisphenol A (BPA), phenol (PN), rhodamine B (RhB), ofloxacin (OFC), and tetracycline (TC). 4- ·), hydroxyl radical (·OH) and singlet oxygen ( 1 O2) to achieve deep degradation of pollutants such as BPA.

[0027] In some embodiments of the present invention, the dosage of the iron single atom catalyst is 0.05-0.2 g / L.

[0028] In the present invention, the advanced oxidation technology (AOP) based on Fe-NC catalyst activated peroxymonosulfate (PMS) to degrade bisphenol A pollutants (BPA) includes the following chemical reactions:

[0029]

[0030] In the present invention, a method for upgrading retired lithium iron phosphate batteries to prepare single-atom catalysts and its application is to upgrade the "recycled waste" of retired lithium iron phosphate batteries by electro-oxidation leaching to prepare Fe-NC catalysts to activate peroxymonosulfate (PMS) to efficiently degrade bisphenol A pollutants (BPA). Based on traditional leaching methods, electrochemical leaching technology strengthens the leaching of retired lithium iron phosphate batteries through the produced H2O2. The leached solution is subjected to a series of recovery processes to obtain iron phosphate and lithium carbonate products, and the recycled waste containing iron and graphite is upgraded by nitrogen doping, ball milling and calcination to prepare Fe-NC catalysts. The activation effect of Fe-NC catalyst on PMS is manifested in that the oxygen atoms in the peroxide bond are adsorbed on the Fe active site to site-adsorb PMS, resulting in the cleavage of the OO bond and the generation of sulfate radicals (SO 4-·) and hydroxyl radicals (·OH), while the N active site adsorbs the terminal oxygen single-bonded to the S element on PMS, promoting the singlet oxygen ( 1 O2), the N active sites in the Fe-NC catalyst not only prevent the leaching of Fe and improve the catalyst stability, but also promote the generation of singlet oxygen ( 1 O2) to degrade BPA pollutants. Based on the above-mentioned free radical and non-free radical advanced oxidation technology (AOP), BPA pollutants can be directly degraded into CO2 and H2O. In addition, the Fe-NC catalyst can restore the activity of the deactivated Fe-NC catalyst through the "self-etching" effect under pyrolysis conditions.

[0031] The above technical solution of the present invention has the following advantages compared with the prior art:

[0032] (1) The present invention provides a method for preparing single-atom catalysts for upgrading retired lithium iron phosphate batteries and its application, which avoids secondary pollutants (Cl2 or ClO2) caused by traditional electrochemical oxidation technology by means of "advanced oxidation process" of electrically producing H2O2 and "recycling process" of chemical precipitation. - ), and at the same time realize the cascade recovery of iron phosphate products, lithium carbonate products and recycled waste, which can bring good economic and social benefits and has good application prospects.

[0033] (2) Electrochemical leaching in low-concentration sulfuric acid medium has mild conditions and reduces equipment requirements; low-concentration sulfuric acid medium is conducive to 2e - The electrocatalytic redox reaction (ORR) produces more H2O2, which can enhance the oxidative decomposition of retired lithium iron phosphate batteries; the low-concentration sulfuric acid medium used greatly reduces acid consumption and facilitates subsequent waste liquid treatment.

[0034] (3) The present invention provides a method for upgrading retired lithium iron phosphate batteries to prepare single-atom catalysts and its application, which utilizes "upgrading treatment" to achieve resource reuse of iron-containing waste recovered from retired lithium iron phosphate batteries, and is of great significance to improving the sustainability of waste management of retired lithium iron phosphate batteries.

[0035] (4) The present invention provides a method for upgrading retired lithium iron phosphate batteries to prepare single-atom catalysts and its application. The obtained Fe single-atom catalyst (i.e., Fe-NC catalyst) exhibits high catalytic activity, strong stability, low Fe ion leaching and excellent recycling performance, and can be recycled for a long time.

[0036] (5) The present invention provides a method for preparing a single-atom catalyst for upgrading retired lithium iron phosphate batteries and its application. Compared with single-atom catalysts of Cu, Ag, Co and Mn, Fe-NC catalyst has the advantages of being easy to obtain, non-toxic, environmentally friendly and low-cost.

[0037] (6) The present invention provides a method for upgrading retired lithium iron phosphate batteries to prepare single-atom catalysts and its application, based on the advanced oxidation technology of Fe-NC catalyst activated peroxymonosulfate (PMS)

[0038] (AOP), by producing reactive oxygen species (ROS), it can achieve deep degradation of bisphenol A pollutants (BPA), and is expected to be suitable for treating other organic pollutants such as phenol (PN), rhodamine B (RhB), ofloxacin (OFC), tetracycline (TC), etc. The biodegradability of the treated organic wastewater is greatly improved, and it has good environmental applicability. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] In order to make the content of the present invention more clearly understood, the present invention is further described in detail below according to specific embodiments of the present invention in conjunction with the accompanying drawings, wherein:

[0040] Figure 1 It is a process flow chart of a method for upgrading retired lithium iron phosphate batteries to prepare iron single atom catalysts and its application provided by the present invention.

[0041] Figure 2 The present invention is about the effect of the sulfuric acid medium concentration on the Li and Fe leaching rate (a) and the electrochemical H2O2 production (b) in retired lithium iron phosphate batteries (Example 1, Example 2 and Comparative Examples 1-2).

[0042] Figure 3 The present invention is a 0.1M sulfuric acid medium, under different experimental conditions (without H2O2, with H2O2 and electrochemical) Li and Fe leaching rate differences and quenching experiments in retired lithium iron phosphate batteries

[0043] (Example 1 and Comparative Examples 3-4).

[0044] Figure 4 The addition amount of dicyandiamide in the present invention has an effect on the degradation of bisphenol A pollutants by Fe single atom catalyst

[0045] The influence of (BPA) on the catalytic performance (Example 1, Example 5 and Comparative Examples 8-9).

[0046] Figure 5 This is a spherical aberration projection electron microscope image of the Fe single atom catalyst of the present invention. DETAILED DESCRIPTION

[0047] The present invention is further described below in conjunction with the accompanying drawings and specific embodiments so that those skilled in the art can better understand the present invention and implement it, but the embodiments are not intended to limit the present invention.

[0048] In some embodiments of the present invention, the process of degrading bisphenol A (BPA) organic pollutants comprises the following steps:

[0049] Organic pollutants such as BPA pollutants were weighed, ultrasonically heated for 1 h, and dissolved in 1 L of aqueous solution to obtain a 50 μM BPA pollutant.

[0050] Prepare 10 centrifuge tubes, add 0.05 mL of 1.0 M sodium thiosulfate solution (quencher), and transfer 5 mL of 50 μM BPA contaminant to a centrifuge tube, which is marked as S1.

[0051] 100 mL of BPA pollutant was measured in a beaker, and 0.1 g / L of Fe-NC catalyst was dispersed in the BPA pollutant. Ultrasonic dispersion was performed for 10 min, and then magnetic stirring was performed. After 15 min and 30 min, 5 mL of BPA solvent was taken into centrifuge tubes respectively, marked as S2 and S3.

[0052] Then, 0.5 mL of 0.2 M PMS solution was added to start the reaction and 5 mL of BPA solvent was taken into centrifuge tubes at 10 s, 20 s, 40 s, 60 s, 2 min, 4 min, and 8 min, respectively, and marked as S4 to S10.

[0053] The solutions in 10 centrifuge tubes were filtered with a filter head and added into a liquid phase vial (0.5-1 mL). The concentration change of BPA in the solvent was tested by high performance liquid chromatography to evaluate the catalytic performance of the Fe-NC catalyst.

[0054] Embodiment 1:

[0055] This embodiment provides a method for upgrading retired lithium iron phosphate batteries to prepare single-atom catalysts and its application, including the following steps:

[0056] (1) 0.1 g of retired lithium iron phosphate powder was added to 100 mL of 0.1 M sulfuric acid electrolyte, and graphene aerogel GA electrodes (i.e., working electrode and counter electrode) and Ag / AgCl reference electrode were inserted and connected to an electrochemical workstation;

[0057] (2) adding 0.1 g / L sodium dodecyl sulfate to the electrolytic solution in step (1), and continuously introducing oxygen, electrochemically leaching the retired lithium iron phosphate under the conditions of a voltage of -1.2 V, an electrolysis time of 2 h, and a stirring speed of 400 rpm, and washing and drying the filter residue to obtain recycled waste, and the leachate is subjected to a recovery process to obtain iron phosphate and lithium carbonate products;

[0058] (3) Weighing 0.2 g of the recycled waste obtained in step (2), adding 25 g / g of dicyandiamide (recycled waste), ball milling at a speed of 400 rpm for 4 h, and then calcining at a temperature of 700° C. and a calcination time of 4 h in a N2 atmosphere to prepare an Fe single atom catalyst (i.e., Fe-NC catalyst);

[0059] Performance testing:

[0060] The Fe-NC catalyst obtained in step (3) was used to activate peroxymonosulfate (PMS) and effectively degrade 50 μM bisphenol A pollutant (BPA) under the conditions of a reaction temperature of 25° C. and a reaction time of 8 min.

[0061] After testing, 6.8mM H2O2 was produced after 2h of electrolysis, the lithium leaching rate in retired lithium iron phosphate batteries reached 99.8%, and the iron leaching rate reached 98.5%. At the same time, the removal efficiency of BPA pollutants by the Fe-NC / PMS system reached 98.5%.

[0062] Embodiment 2:

[0063] This embodiment provides a method for upgrading retired lithium iron phosphate batteries to prepare single-atom catalysts and its application, which is basically the same as Example 1, except that: in step (1), the concentration of sulfuric acid electrolysis medium is 0.05M.

[0064] Performance testing:

[0065] After testing, 6.5mM H2O2 was produced after 2h of electrolysis, the lithium leaching rate in retired lithium iron phosphate batteries reached 99.5%, and the iron leaching rate reached 98.2%. At the same time, the removal efficiency of BPA pollutants by the Fe-NC / PMS system was higher than 98%.

[0066] Embodiment 3:

[0067] This embodiment provides a method for upgrading retired lithium iron phosphate batteries to prepare single-atom catalysts and its application, which is basically the same as Example 1, except that: in step (2), the amount of sodium dodecyl sulfate added is 0.2 g / L.

[0068] Performance testing:

[0069] After testing, the lithium leaching rate in retired lithium iron phosphate batteries reached 99.9%, and the iron leaching rate reached 98.8%.

[0070] Embodiment 4:

[0071] This embodiment provides a method for upgrading retired lithium iron phosphate batteries to prepare single-atom catalysts and its application, which is basically the same as Example 1, except that: in step (2), the electrolysis time is 4 hours.

[0072] Performance testing:

[0073] After testing, 11.5mM H2O2 was produced after 4h of electrolysis, and the leaching rate of lithium in retired lithium iron phosphate batteries reached 99.9%, and the leaching rate of iron reached 98.8%. Obviously, the electrolysis of 2h to produce H2O2 can fully oxidize and decompose retired lithium iron phosphate batteries and recycle resources, and extending the electrolysis time will increase energy consumption.

[0074] Embodiment 5:

[0075] This embodiment provides a method for upgrading retired lithium iron phosphate batteries to prepare single-atom catalysts and its application, which is basically the same as Example 1, except that: in step (3), the amount of dicyandiamide added is 30 g / g (recycled waste).

[0076] Performance testing:

[0077] According to the test, the Fe-NC / PMS system has a removal efficiency of 99.5% for BPA pollutants. In addition, the Fe content in the treated liquid is less than 0.1 mg / L. The N active sites in the Fe-NC catalyst not only prevent Fe leaching and improve the catalyst stability, but also promote the singlet oxygen ( 1 O2) to degrade BPA pollutants.

[0078] Embodiment 6:

[0079] This embodiment provides a method for preparing a single-atom catalyst for upgrading retired lithium iron phosphate batteries and its application, which is basically the same as Example 1, except that: in step (3), the calcination temperature is 800°C.

[0080] Performance testing:

[0081] The Fe-NC / PMS system has a removal efficiency of 98.2% for BPA pollutants. In addition, the Fe content in the treated liquid is less than 0.1 mg / L.

[0082] Embodiment 7:

[0083] This embodiment provides a method for preparing a single-atom catalyst for upgrading retired lithium iron phosphate batteries and its application, which is basically the same as Example 1, except that: in step (3), the calcination time is 3 hours.

[0084] Performance testing:

[0085] The Fe-NC / PMS system has been tested to remove BPA pollutants at a removal efficiency of 98.6%. In addition, the Fe content in the treated liquid is less than 0.1 mg / L.

[0086] Comparative Example 1:

[0087] This comparative example provides a method for upgrading retired lithium iron phosphate batteries to prepare single-atom catalysts and its application, which is basically the same as Example 1, except that: in step (1), the concentration of sulfuric acid electrolysis medium is 0.5M.

[0088] Performance testing:

[0089] After testing, it was found that only 2.6 mM H2O2 was produced after 2 hours of electrolysis. The leaching rate of lithium in retired lithium iron phosphate batteries was 80.5%, and the leaching rate of iron was 83%.

[0090] Comparative Example 2:

[0091] This comparative example provides a method for upgrading retired lithium iron phosphate batteries to prepare single-atom catalysts and its application, which is basically the same as Example 1, except that: in step (1), the concentration of sulfuric acid electrolysis medium is 1M.

[0092] Performance testing:

[0093] After testing, it was found that only 4.2 mM H2O2 was produced after 2 hours of electrolysis. The leaching rates of lithium and iron in retired lithium iron phosphate batteries were 71.5% and 71.5%, respectively.

[0094] Comparative Example 3:

[0095] This embodiment provides a method for upgrading retired lithium iron phosphate batteries to prepare single-atom catalysts and its application, which is basically the same as Example 1, except that: in step (1), the mixed solution of retired lithium iron phosphate powder and sulfuric acid medium is not electrochemically leached.

[0096] Performance testing:

[0097] After testing, the lithium leaching rate in retired lithium iron phosphate batteries was 38%, and the iron leaching rate was 39%.

[0098] Comparative Example 4:

[0099] This comparative example provides a method for upgrading retired lithium iron phosphate batteries to prepare single-atom catalysts and its application, which is basically the same as Example 1, except that: in step (1), the mixed solution of retired lithium iron phosphate powder and sulfuric acid medium is not electrochemically leached, but 6.8mM H2O2 is added.

[0100] Performance testing:

[0101] After testing, the leaching rate of lithium in retired lithium iron phosphate batteries is 60%, and the leaching rate of iron is 42%. In addition, in the presence of a quencher (quenching of H2O2), the leaching rate of lithium in the comparative example is 38%, and the leaching rate of iron is 28%. However, in Example 1, in the presence of a quencher (quenching of H2O2), the leaching rate of lithium is 87%, and the leaching rate of iron is 85%. According to the results of the quenching experiment, the in-situ production of H2O2 during the electrochemical leaching process is different from the method of adding additional H2O2. Under the action of "electro-oxidation enhanced leaching", lithium and iron in retired lithium iron phosphate batteries can achieve efficient leaching.

[0102] Comparative Example 5:

[0103] This comparative example provides a method for upgrading retired lithium iron phosphate batteries to prepare single-atom catalysts and its application, which is basically the same as Example 1, except that: in step (2), the amount of sodium dodecyl sulfate added is 0 g / L.

[0104] Performance testing:

[0105] After testing, the lithium leaching rate in retired lithium iron phosphate batteries was 88.5%, and the iron leaching rate was 86%.

[0106] Comparative Example 6:

[0107] This comparative example provides a method for upgrading retired lithium iron phosphate batteries to prepare single-atom catalysts and its application, which is basically the same as Example 1, except that: in step (2), the electrolysis time is 1 hour.

[0108] Performance testing:

[0109] After testing, the lithium leaching rate in retired lithium iron phosphate batteries was 62%, and the iron leaching rate was 80.5%.

[0110] Comparative Example 7:

[0111] This comparative example provides a method for upgrading retired lithium iron phosphate batteries to prepare single-atom catalysts and its application, which is basically the same as Example 1, except that: in step (2), the electrolysis time is 1.5 hours.

[0112] Performance testing:

[0113] After testing, the lithium leaching rate in retired lithium iron phosphate batteries was 65%, and the iron leaching rate was 82%.

[0114] Comparative Example 8:

[0115] This comparative example provides a method for upgrading retired lithium iron phosphate batteries to prepare single-atom catalysts and its application, which is basically the same as Example 1, except that in step (3), the amount of dicyandiamide added is 15 g / g (recycled waste).

[0116] Performance testing:

[0117] The Fe-NC / PMS system has a removal efficiency of 92% for BPA pollutants. However, the Fe concentration in the treated solution is 0.3 mg / L. The low N doping level leads to the instability of the Fe single atom catalyst and the easy leaching of Fe.

[0118] Comparative Example 9:

[0119] This comparative example provides a method for upgrading retired lithium iron phosphate batteries to prepare single-atom catalysts and its application, which is basically the same as Example 1, except that in step (3), the amount of dicyandiamide added is 20 g / g (recycled waste).

[0120] Performance testing:

[0121] The results showed that the Fe-NC / PMS system had a removal efficiency of 96% for BPA pollutants. However, the Fe concentration in the treated solution was 0.15 mg / L.

[0122] Comparative Example 10:

[0123] This comparative example provides a method for upgrading retired lithium iron phosphate batteries to prepare single-atom catalysts and its application, which is basically the same as Example 1, except that: in step (3), the calcination temperature is 500°C.

[0124] Performance testing:

[0125] The results showed that the removal efficiency of Fe-NC / PMS system for BPA pollutants was 76%.

[0126] Comparative Example 11:

[0127] This comparative example provides a method for upgrading retired lithium iron phosphate batteries to prepare single-atom catalysts and its application, which is basically the same as Example 1, except that: in step (3), the calcination time is 1 hour.

[0128] Performance testing:

[0129] According to the test, the removal efficiency of BPA pollutants by Fe-NC / PMS system is 65%.

[0130] Obviously, the above embodiments are merely examples for clear explanation and are not intended to limit the implementation methods. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the implementation methods here. The obvious changes or modifications derived from these are still within the protection scope of the invention.

Claims

1. A method for upgrading retired lithium iron phosphate batteries to prepare iron single-atom catalysts, characterized in that: The following steps are involved: (1) Adding retired lithium iron phosphate powder into the electrolytic solution, inserting the graphene aerogel GA electrode and the Ag / AgCl reference electrode, and connecting to the electrochemical workstation; (2) adding a surfactant to the electrolytic solution of step (1), and continuously introducing oxygen for electrolysis, electrochemically leaching the retired lithium iron phosphate, performing solid-liquid separation on the electrolyzed electrolyte to obtain a leachate and a filter residue, washing and drying the filter residue to obtain a recycled waste containing iron phosphate and graphite, and subjecting the leachate to a recovery process to obtain iron phosphate and lithium carbonate products; (3) adding a nitrogen source to the recycled waste obtained in step (2), and subjecting the recycled waste to ball milling and high-temperature calcination to obtain an iron single-atom catalyst.

2. The method according to claim 1, characterized in that In step (1), the amount of the retired lithium iron phosphate powder added is 0.1 to 5 g / L; The electrolytic solution is one or more of sulfuric acid, phosphoric acid, oxalic acid and acetic acid solution; The concentration of the electrolytic solution is 0.01-0.4M.

3. The method according to claim 1, characterized in that In step (2), the surfactant is sodium dodecyl sulfate; The added amount of the surfactant is 0.05-0.3 g / L.

4. The method according to claim 1, characterized in that: In step (2), the electrochemical leaching is an electro-oxidation enhanced leaching process for producing H2O2, and the specific parameters include an applied voltage of -1 to -1.5V, an electrolysis time of 2 to 5h, and a stirring speed of 300 to 600rpm.

5. The method according to claim 1, characterized in that In step (3), the nitrogen source is selected from one or more of dicyandiamide, urea, ethylenediamine, and hydrazine hydrate; The amount of the nitrogen source used in the recycled waste is 22.5-50 g / g.

6. The method according to claim 1, characterized in that In step (3), the ball milling speed is 200-600 rpm ； The high temperature calcination temperature is 550-900°C and the calcination time is 2-5h.

7. The method according to claim 1, characterized in that In step (3), the recovery process of the leachate is a chemical precipitation process.

8. An iron single atom catalyst, characterized in that Prepared by the method described in any one of claims 1 to 7, the iron single-atom catalyst is a carbon-based nanomaterial co-doped with Fe and N.

9. Use of the iron single atom catalyst according to claim 8 in activating peroxymonosulfate to degrade organic pollutants.

10. The use according to claim 9, characterized in that The organic pollutants include one or more of bisphenol A, phenol, rhodamine B, ofloxacin or tetracycline.

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