Method for preparing Fe3C by using waste lithium iron phosphate batteries, Fe3C and application thereof, and treatment method of organic pollutants

Abstract

The invention provides a method for preparing magnetic Fe3C from a positive electrode and a negative electrode of a waste lithium iron phosphate battery, Fe3C and application thereof, and a treatment method of organic pollutants, and belongs to the field of solid waste recycling. The invention provides a method for preparing magnetic Fe3C by using a waste lithium iron phosphate battery, which comprises the following steps: mixing a positive electrode and a negative electrode in the waste lithium iron phosphate battery to obtain a mixture; the molar ratio of the iron element to the carbon in the mixture is (3-4): 1; the negative electrode contains carbon; in a reducing atmosphere, mixing the mixture with alkali metal salt, and calcining to obtain Fe3C; the alkali metal salt is carbonate and / or bicarbonate. A large amount of Fe contained in the waste lithium iron phosphate battery is mixed with carbon and then calcined to obtain a magnetic material Fe3C with catalytic characteristics.

Description

Technical Field

[0001] The present invention relates to the field of solid waste resource utilization, and in particular to a method for preparing magnetic Fe3C by utilizing waste lithium iron phosphate batteries, Fe3C and its application, and a method for treating organic pollutants. Background Art

[0002] With the vigorous development of new energy vehicles, the use of power lithium batteries has increased rapidly, and the number of retired power batteries has also increased steadily. Lithium iron phosphate batteries are widely used in electric vehicles and energy storage facilities because of their chemical and thermal stability, non-toxicity, economy and easy availability. However, since lithium iron phosphate batteries have a limited lifespan when used as power batteries, a large number of discarded lithium iron phosphate batteries will be generated after the end of their life cycle. Therefore, the subsequent treatment of discarded lithium iron phosphate batteries has important economic value and environmental significance.

[0003] At present, the positive and negative electrodes of waste lithium iron phosphate batteries are used to restore the electrochemical properties of the failed lithium iron phosphate positive electrode materials by replenishing lithium. This method is simple in process, but it also has some defects. First, after thousands of charge and discharge processes, the ratio of lithium, iron, and phosphorus in the used lithium iron phosphate positive electrode is difficult to maintain stability. Secondly, many impurities will also be introduced into the recycled positive electrode. Therefore, compared with the original lithium iron phosphate positive electrode material, the repaired lithium iron phosphate positive electrode material often exhibits poor electrochemical properties. And there is a lack of excellent treatment methods for the recovery of iron elements with higher content. In addition, the negative electrode material of lithium iron phosphate is mainly graphite carbon, and there is currently no good recycling method. Therefore, it is extremely important to develop a method for simultaneously recovering the iron of the positive electrode and the graphite carbon of the negative electrode in waste lithium iron phosphate batteries. Summary of the invention

[0004] The invention provides a method for preparing magnetic Fe3C by using positive and negative electrodes of waste lithium iron phosphate batteries, Fe3C and its application, and a method for treating organic pollutants. The method of the invention realizes resource utilization of iron in waste lithium iron phosphate batteries.

[0005] The present invention provides a method for preparing magnetic Fe3C by using waste lithium iron phosphate batteries, comprising the following steps:

[0006] The positive electrode and the negative electrode of the waste lithium iron phosphate battery are mixed to obtain a mixture; the molar ratio of iron element to carbon in the mixture is 3 to 4:1; the negative electrode contains carbon;

[0007] Under a reducing atmosphere, the mixture is mixed with an alkali metal salt and then calcined to obtain Fe3C; the alkali metal salt is a carbonate and / or a bicarbonate.

[0008] Preferably, the positive electrode comprises the following elements by mass fraction:

[0009] Li 3-5%, Fe 30-35%, P 15-20%, Al 1-5%, O 30-38% and impurity elements 1-6%.

[0010] Preferably, the reducing atmosphere is a mixed gas of protective gas and H2, the volume fraction of the protective gas is 95-98%, and the volume fraction of H2 is 2-5%;

[0011] The calcination temperature is 900-1100° C., the heating rate to the calcination temperature is 5-10° C. / min, and the heat preservation time is 3-5 hours.

[0012] Preferably, the particle size of the mixture is 10 to 200 meshes.

[0013] The present invention also provides Fe3C prepared by the method for preparing Fe3C using waste lithium iron phosphate batteries as described in the above technical solution.

[0014] The present invention also provides the application of Fe3C described in the above technical solution in treating organic pollutants.

[0015] The present invention also provides a method for treating organic pollutants, comprising the following steps:

[0016] The electrode loaded with Fe3C is immersed in an electrolyte containing organic pollutants to perform an electrochemical reaction, and the organic pollutants are degraded;

[0017] The Fe3C is the Fe3C described in the above technical solution.

[0018] Preferably, the organic pollutants include one or more of rhodamine B, methylene blue, acid orange, enrofloxacin, ofloxacin, tetracycline, sulfamethoxazole, phenol and bisphenol A.

[0019] Preferably, the current density of the electrochemical reaction is 2-10 mA / cm 2 The initial pH value of the electrolyte containing organic pollutants is 3-11.

[0020] The present invention also provides a method for treating organic pollutants, comprising the following steps:

[0021] mixing wastewater containing organic pollutants, Fe3C and an oxidant, and then subjecting the resulting mixture to an advanced oxidation reaction;

[0022] The Fe3C is the Fe3C described in the above technical solution.

[0023] A large amount of Fe contained in waste lithium iron phosphate batteries is mixed with the negative electrode and calcined to obtain a magnetic material Fe3C with catalytic properties, which has the characteristics of high catalytic oxidation efficiency, wide pH applicable range, metal ions are not easy to lose, and easy water separation. When Fe3C is applied to the treatment of organic wastewater, it not only has the advantages of a wide range of applicable water bodies, mild reaction conditions, and strong ability to remove organic pollutants, but also can be used as a resource for waste lithium iron phosphate solid waste, achieving the purpose of waste treatment, in line with the country's call for sustainable development and energy conservation and emission reduction, and its cost is low and has a wide range of application scenarios. And compared with the traditional method of preparing Fe3C by introducing methane + hydrogen mixed gas, the method of the present invention is simpler, the synthesis path is easy to control, and a large amount of chemical reagents or gases are avoided. It is environmentally friendly and low cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 The present invention is a process flow diagram of a method for preparing Fe3C using waste lithium iron phosphate batteries. DETAILED DESCRIPTION

[0025] The present invention provides a method for preparing Fe3C by using waste lithium iron phosphate batteries, comprising the following steps:

[0026] The positive electrode and the negative electrode of the waste lithium iron phosphate battery are mixed to obtain a mixture; the molar ratio of iron element to carbon in the mixture is 3 to 4:1; the negative electrode contains carbon;

[0027] Under a reducing atmosphere, the mixture is mixed with an alkali metal salt and then calcined to obtain Fe3C; the alkali metal salt is a carbonate and / or a bicarbonate.

[0028] The invention mixes the positive electrode and the negative electrode in the waste lithium iron phosphate battery to obtain a mixture.

[0029] In the present invention, the elements in the positive electrode preferably include, by mass fraction: Li 3-5%. In a specific embodiment of the present invention, the mass fraction of the Li element may be 3%, 4% or 5%.

[0030] In the present invention, the elements in the positive electrode preferably include, by mass fraction: Fe 30-35%. In a specific embodiment of the present invention, the mass fraction of the Fe element may be 30%, 31%, 32%, 33%, 34% or 35%.

[0031] In the present invention, the elements in the positive electrode preferably include, by mass fraction: P15-20%. In a specific embodiment of the present invention, the mass fraction of the P element may be 15%, 16%, 17%, 18%, 19% or 20%.

[0032] In the present invention, the elements in the positive electrode preferably include, by mass fraction: Al 1-5%. In a specific embodiment of the present invention, the mass fraction of the Al element may be 1%, 2%, 3%, 4% or 5%.

[0033] In the present invention, the elements in the positive electrode preferably include, by mass fraction: O30-38%. In a specific embodiment of the present invention, the mass fraction of the O element can be 30%, 31%, 32%, 33%, 34%, 35%, 36%, 37% or 38%.

[0034] In the present invention, the elements in the positive electrode preferably include, by mass fraction: 1 to 6% of impurity elements. In a specific embodiment of the present invention, the mass fraction of the impurity elements may be 1%, 2%, 3%, 4%, 5% or 6%; the impurities preferably include one or more of K, Ca, V and Ti.

[0035] In the present invention, the particle size of the mixture is preferably 10-200 mesh. In a specific embodiment of the present invention, the particle size of the mixture can be 10 mesh, 50 mesh, 80 mesh, 100 mesh, 150 mesh, 180 mesh or 200 mesh.

[0036] In the present invention, the molar ratio of iron element to carbon element in the mixture is 3 to 4:1. In a specific embodiment of the present invention, the molar ratio of iron element to carbon element in the mixture can be 3:1, 3.2:1, 3.4:1, 3.6:1, 3.8:1 or 4:1.

[0037] After obtaining the mixture, the present invention mixes the mixture with an alkali metal salt under a reducing atmosphere and then calcines the mixture to obtain Fe3C.

[0038] In the present invention, the mass ratio of the mixture to the alkali metal salt is preferably 4 to 7:1. In a specific embodiment of the present invention, the mass ratio may be 4:1, 5:1, 6:1 or 7:1. The alkali metal salt is a carbonate and / or a bicarbonate, and the alkali metal salt is a carbonate and / or a bicarbonate.

[0039] The role of the alkali metal salt is to break the chemical bonds of lithium iron phosphate.

[0040] In the present invention, the reducing atmosphere is a mixed gas of protective gas and H2, the volume fraction of the protective gas is preferably 95-98%, and the volume fraction of H2 is preferably 2-5%.

[0041] In the present invention, the calcination temperature is preferably 900-1100°C. In a specific embodiment of the present invention, the calcination temperature may be 900°C, 920°C, 940°C, 960°C, 980°C or 1100°C; the insulation time may be 3h, 4h or 5h; the heating rate to the calcination temperature is preferably 5-10°C / min. In a specific embodiment of the present invention, the heating rate may be 5°C / min, 6°C / min, 7°C / min, 8°C / min, 9°C / min or 10°C / min.

[0042] In the present invention, the calcination is preferably performed under closed conditions.

[0043] In the present invention, after the calcination is completed, the product is preferably cooled and magnetically separated to obtain pure Fe3C.

[0044] The present invention also provides Fe3C prepared by the method for preparing Fe3C using waste lithium iron phosphate batteries as described in the above technical solution.

[0045] The present invention also provides the use of Fe3C described in the above technical solution in electrochemical treatment of organic pollutants.

[0046] The present invention also provides a method for treating organic pollutants, comprising the following steps:

[0047] The electrode loaded with Fe3C is immersed in an electrolyte containing organic pollutants to perform an electrochemical reaction, and the organic pollutants are degraded;

[0048] The Fe3C is the Fe3C described in the above technical solution.

[0049] In the present invention, the Fe3C loading in the Fe3C loaded electrode is preferably 0.5 to 10 mg / cm 2 In a specific embodiment of the present invention, the loading amount can be 0.5 mg / cm 2 , 1mg / cm 2 , 5mg / cm 2 , 6mg / cm 2 , 7mg / cm 2 , 8mg / cm 2 , 9mg / cm 2 or 10mg / cm 2 ; The substrate of the electrode preferably comprises carbon paper.

[0050] In the present invention, the method for preparing the electrode preferably comprises the following steps:

[0051] Fe3C, ethanol, water and perfluorinated resin Nafion 117 naphthol solution were mixed and dropped onto the electrode and then dried.

[0052] In the present invention, the organic pollutants preferably include one or more of rhodamine B, methylene blue, acid orange, enrofloxacin, ofloxacin, tetracycline, sulfamethoxazole, phenol and bisphenol A.

[0053] In the present invention, the current density of the electrochemical reaction is preferably 2 to 10 mA / cm 2 In a specific embodiment of the present invention, the current density can be 2 mA / cm 2 , 3mA / cm 2 , 4mA / cm 2 , 5mA / cm 2 , 6mA / cm 2 , 7mA / cm 2 , 8mA / cm 2 , 9mA / cm 2 or 10mA / cm 2 ; The initial pH value of the electrolyte containing organic pollutants is preferably 3 to 11. In a specific embodiment of the present invention, the initial pH value can be 3, 4, 5, 6, 7, 8, 9, 10 or 11.

[0054] In the present invention, the method for preparing the electrolyte containing organic pollutants preferably comprises the following steps:

[0055] The organic contaminants are mixed with the electrolyte.

[0056] In the present invention, the electrolyte preferably includes a sodium sulfate solution; the concentration of the sodium sulfate solution is preferably 0.5M.

[0057] The present invention also provides a method for treating organic pollutants, comprising the following steps:

[0058] mixing wastewater containing organic pollutants, Fe3C and an oxidant, and then subjecting the resulting mixture to an advanced oxidation reaction;

[0059] The Fe3C is the Fe3C described in the above technical solution.

[0060] In the present invention, the concentration of the organic pollutants in the mixture is preferably 10 to 30 mg / L. In a specific embodiment of the present invention, the concentration of the organic pollutants may be 10 mg / L, 15 mg / L, 20 mg / L, 25 mg / L or 30 mg / L.

[0061] The concentration of Fe3C in the mixture is 0.5-30 g / L. In a specific embodiment of the present invention, the concentration of Fe3C can be 0.5 g / L, 5 g / L, 10 g / L, 15 g / L, 20 g / L, 25 g / L or 30 g / L.

[0062] In the present invention, the oxidant includes persulfate or hydrogen peroxide; the persulfate preferably includes peroxymonosulfate and / or peroxydisulfate. In the present invention, the persulfate is preferably added in the form of a persulfate aqueous solution; the concentration of the persulfate aqueous solution is preferably 0.1 mol / L.

[0063] In the present invention, the mass percentage of the hydrogen peroxide is preferably 30%. In the present invention, the volume ratio of the persulfate aqueous solution or hydrogen peroxide to the wastewater containing organic pollutants is preferably 0.01 to 0.1:1. In a specific embodiment of the present invention, the volume ratio can be 0.01:1, 0.01:1, 0.02:1, 0.04:1, 0.06:1, 0.08:1 or 0.1:1.

[0064] In the present invention, the mixing process preferably includes: ultrasonically mixing the wastewater containing organic pollutants and Fe3C, and then adding the oxidant; the ultrasonic mixing time is preferably 5 minutes.

[0065] In the present invention, the temperature of the advanced oxidation reaction is preferably room temperature, and the advanced oxidation is preferably carried out under stirring.

[0066] Figure 1 The process flow diagram of the method for preparing Fe3C using waste lithium iron phosphate batteries according to an embodiment of the present invention is as follows:

[0067] Graphite electrode waste is added to the lithium iron phosphate electrode to adjust the iron-carbon ratio, and then ground and screened to obtain a mixed material; the mixed material is roasted to obtain Fe3C, and the Fe3C is ground and magnetically separated to prepare an electrode.

[0068] The following is a detailed description of the method for preparing Fe3C using waste lithium iron phosphate batteries, Fe3C and its application, and the method for treating organic pollutants provided by the present invention in conjunction with the embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0069] Example 1

[0070] At room temperature, the positive electrode (by mass fraction, the elements are Fe 30%, Li 5%, P 20%, Al 1%, O 38% and impurities (K, Ca, V and Ti) 1%) and the negative electrode (by mass fraction, the components are graphite 95%, silicon 3% and other impurities 2%) of the waste lithium iron phosphate battery are ground respectively, and then the iron-carbon ratio is adjusted to 3:1 (molar ratio) to obtain a mixture with a particle size of 200 mesh.

[0071] A corundum ark is used as a container and placed in a muffle furnace. 5 g of the mixture and 1 g of Na2CO3 are put into the muffle furnace. Under a reducing atmosphere (the volume content of Ar in the reducing atmosphere is 95%, and the volume content of H2 is 5%), the temperature is increased from room temperature to 900°C at a rate of 5°C / min, and the mixture is calcined for 4 hours in a closed state. The mixture is naturally cooled and Fe3C is obtained after magnetic separation using a magnet.

[0072] 0.01 g of Fe3C was placed in a test tube and 710 uL of anhydrous ethanol, 240 uL of deionized water and 50 uL of perfluorinated resin Nafion 117 naphthol solution were added. After ultrasonic treatment for 1 h, 50 uL of the mixed solution was drop-coated on commercial carbon paper (1 cm×2 cm) and then naturally dried to obtain a Fe3C electrode.

[0073] The Fe3C electrode prepared in this example was placed in an electrolytic cell as the negative electrode (the total submerged geometric area of ​​the electrode in the electrolytic cell was 2 cm 2 ), a platinum electrode as the positive electrode, 0.5M Na2SO4 as the electrolyte, norfloxacin as the target pollutant, and a norfloxacin concentration of 20 mg / L. The electrochemical reaction was carried out under a constant current power supply with a current density of 2 mA / cm 2 After 10 min of reaction, norfloxacin was degraded by 90.5%.

[0074] Example 2

[0075] The difference between this embodiment and embodiment 1 is that the calcination temperature of the muffle furnace is 1000° C., and the rest is the same as embodiment 1.

[0076] The Fe3C electrode prepared in this example was placed in an electrolytic cell as the negative electrode (the total submerged geometric area of ​​the electrode in the electrolytic cell was 2 cm 2 ), a platinum electrode as the positive electrode, 0.5M Na2SO4 as the electrolyte, enrofloxacin as the target pollutant, and an enrofloxacin concentration of 20 mg / L. The electrochemical reaction was carried out under a constant current power supply with a current density of 2 mA / cm 2 After 10 min of reaction, the degradation of enrofloxacin was 97.9%.

[0077] Example 3

[0078] The difference between this embodiment and embodiment 1 is that the total submerged geometric area of ​​the electrodes is 1 cm2 , the rest is the same as Example 1.

[0079] The Fe3C electrode prepared in this example was placed in an electrolytic cell as the negative electrode (the total submerged geometric area of ​​the electrode in the electrolytic cell was 2 cm 2 ), platinum electrode as positive electrode, 0.5M Na2SO4 as electrolyte, tetracycline as target pollutant, tetracycline concentration is 20mg / L. Electrochemical reaction is carried out under constant current power supply, current density is 2mA / cm 2 After 30 minutes of reaction, tetracycline was degraded by 94.1%.

[0080] Example 4

[0081] The difference between this embodiment and embodiment 1 is that the iron-carbon ratio is adjusted to 4:1 (molar ratio), and the rest is the same as embodiment 1.

[0082] The Fe3C electrode prepared in this example was placed in an electrolytic cell as the negative electrode (the total submerged geometric area of ​​the electrode in the electrolytic cell was 2 cm 2 ), a platinum electrode as the positive electrode, 0.5M Na2SO4 as the electrolyte, rhodamine B as the target pollutant, and a rhodamine B concentration of 20 mg / L. The electrochemical reaction was carried out under a constant current power supply with a current density of 2 mA / cm 2 After 30 minutes of reaction, Rhodamine B was degraded by 80.6%.

[0083] Example 5

[0084] 10 mg of Fe3C prepared in Example 1 was added to 20 mL of sulfamethoxazole solution, the concentration of sulfamethoxazole was 20 mg / L, and after ultrasonication for 5 min, 200 μL of 0.1 mol / L peroxydisulfate (PDS) solution was added, and magnetic stirring was performed at room temperature. After reacting for 30 min, the degradation rate of sulfamethoxazole was measured to be 88.6%.

[0085] Comparative Example 1

[0086] 10 mg of Fe2O3 was added to 20 mL of Rhodamine B solution, and the concentration of Rhodamine B was 20 mg / L. After 5 minutes of ultrasound, 200 μL of 30% hydrogen peroxide (H2O2) was added and magnetic stirring was performed at room temperature. After 30 minutes of reaction, Rhodamine B was degraded by 68.3%.

[0087] Comparative Example 2

[0088] Platinum electrodes are placed in the electrolytic cell as positive and negative electrodes (the total submerged geometric area of ​​the electrodes in the electrolytic cell is 2 cm 2), with 0.5M Na2SO4 as the electrolyte, enrofloxacin as the target pollutant, and an enrofloxacin concentration of 20 mg / L. The electrochemical reaction was carried out under a constant current power supply with a current density of 2 mA / cm 2 After 30 min of reaction, enrofloxacin was degraded by 72.4%.

[0089] Comparative Example 3

[0090] The Fe2O3 electrode was placed in the electrolytic cell as the anode, 0.5M Na2SO4 was used as the electrolyte, enrofloxacin was used as the target pollutant, and the concentration of enrofloxacin was 20 mg / L. The electrochemical reaction was carried out under a constant current power supply with a current density of 2 mA / cm 2 , pH value was 11, and after 30 min of reaction, enrofloxacin was degraded by 75.4%.

[0091] Comparative Example 4

[0092] 10 mg of Fe3C prepared in Example 2 of CN118579789A was added to 20 mL of sulfamethoxazole solution, the concentration of sulfamethoxazole was 20 mg / L, and after ultrasonication for 5 min, 200 μL of 0.1 mol / L peroxydisulfate (PDS) solution was added, and magnetic stirring was performed at room temperature. After reacting for 30 min, the degradation rate of sulfamethoxazole was measured to be 85.2%.

[0093] Comparative Example 5

[0094] The difference from Example 1 is that the electrode prepared by using Fe3C prepared in Example 1 of CN118579789A has a degradation rate of only 62.5% for norfloxacin.

[0095] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for preparing magnetic Fe3C using waste lithium iron phosphate batteries, characterized in that: The following steps are involved: The positive electrode and the negative electrode of the waste lithium iron phosphate battery are mixed to obtain a mixture; the molar ratio of iron element to carbon in the mixture is 3 to 4:1; the negative electrode contains carbon; Under a reducing atmosphere, the mixture is mixed with an alkali metal salt and then calcined to obtain Fe3C; the alkali metal salt is a carbonate and / or a bicarbonate.

2. The method according to claim 1, characterized in that: The positive electrode comprises the following elements by mass fraction: Li 3-5%, Fe 30-35%, P 15-20%, Al 1-5%, O 30-38% and impurity elements 1-6%.

3. The method according to claim 1, characterized in that The reducing atmosphere is a mixed gas of protective gas and H2, the volume fraction of the protective gas is 95-98%, and the volume fraction of H2 is 2-5%; The calcination temperature is 900-1100° C., the heating rate to the calcination temperature is 5-10° C. / min, and the heat preservation time is 3-5 hours.

4. The method according to claim 1, characterized in that: The particle size of the mixture is 10 to 200 meshes.

5. Fe3C prepared by the method for preparing Fe3C using waste lithium iron phosphate batteries as described in any one of claims 1 to 4.

6. Use of Fe3C as claimed in claim 5 in treating organic pollutants.

7. A method for treating organic pollutants, characterized in that: The following steps are involved: The electrode loaded with Fe3C is immersed in an electrolyte containing organic pollutants to perform an electrochemical reaction, and the organic pollutants are degraded; The Fe3C is the Fe3C described in claim 5.

8. The processing method according to claim 7, characterized in that: The organic pollutants include one or more of rhodamine B, methylene blue, acid orange, enrofloxacin, ofloxacin, tetracycline, sulfamethoxazole, phenol and bisphenol A.

9. The processing method according to claim 7, characterized in that: The current density of the electrochemical reaction is 2-10 mA / cm 2 The initial pH value of the electrolyte containing organic pollutants is 3-11.

10. A method for treating organic pollutants, characterized in that: The following steps are involved: mixing wastewater containing organic pollutants, Fe3C and an oxidant, and then subjecting the resulting mixture to an advanced oxidation reaction; The Fe3C is the Fe3C described in claim 5.

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