A method for preparing iron phosphate by comprehensively recycling waste lithium iron phosphate batteries in an integrated whole-chain manner

Abstract

The present disclosure provides a method for preparing iron phosphate by the whole-chain integrated recycling of waste lithium iron phosphate batteries. The method comprises the following steps: (1) mixing waste lithium iron phosphate materials with a mixed chloride, and heating and melting to obtain a mixed melt; (2) mixing the mixed melt with sodium stearate, then carrying out a blowing reaction, and separating to obtain a carbon-containing lithium iron phosphate scum; (3) mixing the scum with an acid solution, adding hydrogen peroxide for a leaching reaction, and separating the solid and liquid to obtain a lithium-containing solution and a carbon-containing phosphorus iron slag; (4) mixing the carbon-containing phosphorus iron slag with an acid solution, leaching to obtain a phosphorus iron solution, adjusting the phosphorus-iron ratio, adding a complexing agent for a coprecipitation reaction to obtain iron phosphate. The method of the present disclosure can improve the purity of recycled lithium, and at the same time avoid multiple impurity removal processes required in the process of preparing iron phosphate from the phosphorus iron slag after lithium extraction, further improving the purity of iron phosphate prepared from the phosphorus iron slag and the phosphorus-iron recovery rate.

Description

Technical Field

[0001] The present disclosure belongs to the technical field of resource recovery and relates to a method for preparing iron phosphate by integrating the whole chain of recycling waste lithium iron phosphate batteries. Background Art

[0002] Lithium-ion batteries are widely used in fields such as electric vehicles, large-scale energy storage, and electronic devices due to their high capacity and energy density. With the increasingly widespread application of electric vehicles in recent years, a large number of waste lithium-ion batteries will accumulate over time. Recycling these waste lithium-ion batteries can increase the utilization rate of resources and avoid environmental pollution. Among lithium-ion batteries, lithium iron phosphate batteries are widely used in power batteries due to their good stability and low cost.

[0003] Currently, the main method for recycling lithium iron phosphate in waste lithium-ion batteries is to selectively leach and recover lithium, and finally the phosphorus-iron slag obtained after lithium extraction remains. However, the lithium solution obtained by directly leaching waste lithium iron phosphate contains many impurities. Moreover, since the phosphorus-iron slag after lithium extraction contains iron and phosphorus elements, it is necessary to recycle and reuse it.

[0004] CN109250696A discloses a method for recycling nano iron phosphate from lithium iron phosphate batteries: discharging the lithium iron phosphate battery to below 2.0V, crushing and disassembling it to separate the lithium iron phosphate powder, aluminum powder, and copper powder in the battery; putting the lithium iron phosphate powder into a vacuum tube furnace; adding the lithium iron phosphate powder into a dilute hydrochloric acid solution while stirring, and simultaneously dropping hydrogen peroxide and the suspension into a three-neck flask reactor through a peristaltic pump while stirring and ultrasonicating; filtering the mixed solution and taking the filtrate to obtain the leaching solution; synchronously adding the leaching mixed solution and the alkali solution into a mixing reactor through a peristaltic pump to realize the mixing, stirring, and ultrasonicating of the two liquids, and obtaining light yellow powder iron phosphate.

[0005] CN115611250A discloses a method for recycling high-purity iron phosphate from waste lithium iron phosphate cathode powder. The method preliminarily removes impurities through primary acid leaching and first heat preservation self-precipitation to obtain crude iron phosphate, and then obtains iron phosphate through secondary acid leaching and re-dissolution and second heat preservation self-precipitation.

[0006] The above-mentioned solutions adopt wet processing, that is, adding the phosphorus-iron slag into an acidic solution or an alkaline solution for multiple leaching to achieve impurity removal and purification to obtain iron phosphate. Simply using acid leaching or alkali leaching for impurity removal, the prepared iron phosphate still has a high impurity content, and the process flow is long, or using resin adsorption for impurity removal, but the deep impurity removal effect is poor. Summary of the Invention

[0007] The following is an overview of the subject matter described in detail herein. This overview is not intended to limit the scope of protection of the claims.

[0008] The purpose of the present disclosure is to provide a method for the integrated full-chain recycling of waste lithium iron phosphate batteries to prepare iron phosphate. The method of the present disclosure can improve the purity of recycled lithium, and at the same time avoid the multi-step impurity removal processes required in the process of preparing iron phosphate from phosphorus-iron slag after lithium extraction, further improving the purity of iron phosphate prepared from phosphorus-iron slag and the phosphorus-iron recovery rate.

[0009] To achieve this disclosure purpose, the present disclosure adopts the following technical solutions:

[0010] In a first aspect, the present disclosure provides a method for the integrated full-chain recycling of waste lithium iron phosphate batteries to prepare iron phosphate, and the method comprises the following steps:

[0011] (1) Mix waste lithium iron phosphate materials with a mixed chloride, and perform heat melting treatment to obtain a mixed melt;

[0012] (2) After mixing the mixed melt with sodium stearate, perform a blowing reaction, and after separation, obtain a carbon-containing lithium iron phosphate scum on the upper layer;

[0013] (3) Mix the carbon-containing lithium iron phosphate scum with a first acid solution to obtain a mixed solution, add hydrogen peroxide for leaching reaction, and perform solid-liquid separation to obtain a lithium-containing solution and a carbon-containing phosphorus-iron slag;

[0014] (4) Mix the carbon-containing phosphorus-iron slag with a second acid solution, leach to obtain a phosphorus-iron solution, add an iron source and / or a phosphorus source to the phosphorus-iron solution to adjust the phosphorus-iron ratio, and add a complexing agent for coprecipitation reaction to obtain iron phosphate.

[0015] In the process of recycling waste lithium iron phosphate, by placing the steps of removing copper and aluminum impurities before lithium extraction, after mixing and melting the waste lithium iron phosphate powder and mixed chlorides, sodium stearate is added. Since the densities of aluminum and copper impurities contained in the waste lithium iron phosphate are greater than those of lithium iron phosphate and the molten mixed chlorides, they are deposited at the bottom of the molten potassium chloride and sodium chloride mixture. Since the density of lithium iron phosphate is less than that of the sodium chloride and potassium chloride mixture, adding sodium stearate as a surfactant and foaming agent, after blowing in gas, the melt can be stirred. Since the carbon particles are relatively fine and there are many adsorption active sites on their surfaces, they are easily aggregated with lithium iron phosphate into larger slag masses, and can have a strong adsorption phenomenon with the bubbles, so that they can migrate to the surface of the melt together with the bubbles. After the carbon particles carry lithium iron phosphate up to the surface of the melt, larger scum is further formed through collisions. The large scum is difficult to be stirred by gas and brought back into the melt again, finally separating lithium iron phosphate from aluminum and copper impurities. The subsequent phosphorus iron slag obtained after lithium extraction contains less impurities and only contains carbon particles, avoiding the subsequent steps of removing aluminum and copper, and high-purity phosphoric acid iron can be directly obtained through one-step acid leaching. The present disclosure can deeply remove copper and aluminum in waste lithium iron phosphate through one-step reaction, improve the purity of recycled lithium, and avoid multiple impurity removal steps for subsequent phosphorus iron slag, further improving the purity and recovery rate of the recycled phosphoric acid iron.

[0016] In one embodiment, the mixed chlorides in step (1) include potassium chloride and sodium chloride.

[0017] In one embodiment, the mass ratio of potassium chloride to sodium chloride is (0.8 - 1.2):1, for example: 0.8:1, 0.9:1, 1:1, 1.1:1 or 1.2:1, etc.

[0018] The present disclosure selects potassium chloride and sodium chloride, and controlling their mass ratio can reduce the melting point of the mixed salt, enabling the mixed materials to reach the molten state at a lower temperature. Using the melt as a medium, the density of the melt is appropriate, achieving the separation of aluminum and copper impurities and carbon-containing lithium iron phosphate while saving energy.

[0019] In one embodiment, the mass ratio of the waste lithium iron phosphate material to the mixed chlorides is 1:(5 - 10), for example: 1:5, 1:6, 1:7, 1:8 or 1:10, etc.

[0020] In one embodiment, the temperature of the heating and melting treatment in step (1) is 300 - 400°C, for example: 300°C, 320°C, 350°C, 380°C or 400°C, etc.

[0021] In one embodiment, the time of the heating and melting treatment is 10 - 30 min, for example: 10 min, 15 min, 20 min, 25 min or 30 min, etc.

[0022] In one embodiment, the mass ratio of sodium stearate to the waste lithium iron phosphate material in step (2) is (2 - 10):100, for example: 2:100, 4:100, 6:100, 8:100, or 10:100, etc.

[0023] In one embodiment, the gas for the blowing reaction includes argon and / or nitrogen.

[0024] In one embodiment, the gas flow rate of the blowing reaction is 10 - 100 mL / s, for example: 10 mL / s, 20 mL / s, 50 mL / s, 80 mL / s, or 100 mL / s, etc.

[0025] In one embodiment, the time of the blowing reaction is 10 - 30 min, for example: 10 min, 15 min, 20 min, 25 min, or 30 min, etc.

[0026] In one embodiment, the separation in step (2) includes fishing out the upper - layer solid of the melt with a filter screen to obtain carbon - containing lithium iron phosphate scum.

[0027] In one embodiment, the first acid solution in step (3) includes sulfuric acid.

[0028] In one embodiment, the mass ratio of the carbon - containing lithium iron phosphate scum to the first acid solution is 1:(1.2 - 1.8), for example: 1:1.2, 1:1.4, 1:1.5, 1:1.6, or 1:1.8, etc.

[0029] In one embodiment, the pH of the mixed solution is 1.5 - 2, for example: 1.5, 1.6, 1.7, 1.8, or 2, etc.

[0030] In one embodiment, the molar ratio of hydrogen peroxide to lithium iron phosphate in step (3) is (0.3 - 0.8):1, for example: 0.3:1, 0.4:1, 0.5:1, 0.6:1, or 0.8:1, etc.

[0031] In one embodiment, the time of the leaching reaction is 2 - 3 h, for example: 2 h, 2.2 h, 2.5 h, 2.8 h, or 3 h, etc.

[0032] In one embodiment, after the leaching reaction, alkali is added to adjust the pH for reaction.

[0033] In one embodiment, the pH is 4 - 6, for example: 4, 4.5, 5, 5.5, or 6, etc.

[0034] In one embodiment, the time of the reaction is 0.5 - 1 h, for example: 0.5 h, 0.6 h, 0.8 h, 0.9 h, or 1 h, etc.

[0035] In one embodiment, the second acid solution in step (4) includes any one or a combination of at least two of sulfuric acid, nitric acid, or phosphoric acid.

[0036] In one embodiment, the concentration of the second acid solution is 0.8 - 1.2 mol / L, for example: 0.8 mol / L, 0.9 mol / L, 1 mol / L, 1.1 mol / L, or 1.2 mol / L, etc.

[0037] In one embodiment, during the leaching process, the concentration of hydrogen ions in the system ≥ 0.8 mol / L.

[0038] In one embodiment, the leaching time is 1 - 2 h, for example: 1 h, 1.2 h, 1.5 h, 1.8 h, or 2 h, etc.

[0039] In one embodiment, the iron source in step (4) includes ferrous sulfate.

[0040] In one embodiment, the phosphorus source includes phosphoric acid.

[0041] In one embodiment, the adjusted P:Fe ratio of phosphorus to iron is 1.0 - 1.1, for example: 1, 1.02, 1.05, 1.08, or 1.1, etc.

[0042] In one embodiment, the complexing agent includes ammonia water.

[0043] In one embodiment, the pH of the coprecipitation reaction is 1.8 - 2.2, for example: 1.8, 1.9, 2, 2.1, or 2.2, etc.

[0044] As an alternative of the present disclosure, the method includes the following steps:

[0045] (1) Mix the waste lithium iron phosphate material with mixed chlorides at a mass ratio of 1:(5 - 10), and heat and melt at 300 - 400 °C for 10 - 30 min to obtain a mixed melt, where the mixed chlorides include potassium chloride and sodium chloride with a mass ratio of (0.8 - 1.2):1;

[0046] (2) After mixing the mixed melt with sodium stearate at a mass ratio of 100:(2 - 10), blow air at a speed of 10 - 100 mL / s for reaction for 10 - 30 min, and after separation, the upper layer obtains carbon - containing lithium iron phosphate scum;

[0047] (3) Mix the carbon-containing lithium iron phosphate dross and the first acid solution at a mass ratio of 1:(1.2 - 1.8) to obtain a mixed solution with a pH of 1.5 - 2. Add hydrogen peroxide for leaching reaction for 2 - 3 h, add alkali to adjust the pH to 4 - 6 and react for 0.5 - 1 h, and perform solid-liquid separation to obtain a lithium-containing solution and carbon-containing phosphorus iron slag;

[0048] (4) Mix the carbon-containing phosphorus iron slag with a second acid solution with a concentration of 0.8 - 1.2 mol / L, control the hydrogen ion concentration in the system ≥ 0.8 mol / L for leaching for 1 - 2 h to obtain a phosphorus iron solution. Add an iron source and / or a phosphorus source to the phosphorus iron solution to adjust the phosphorus-iron ratio, add ammonia water, and adjust the pH to 1.8 - 2.2 for coprecipitation reaction to obtain iron phosphate.

[0049] Compared with the prior art, the present disclosure has the following beneficial effects:

[0050] (1) The method of the present disclosure can improve the purity of recycled lithium, and at the same time avoid multiple impurity removal processes required in the process of preparing iron phosphate from phosphorus iron slag after lithium extraction, further improving the purity of iron phosphate prepared from phosphorus iron slag and the phosphorus-iron recovery rate.

[0051] (2) The method of the present disclosure recycles waste lithium iron phosphate materials, and the obtained lithium purity can reach more than 97.8%, the iron phosphate purity can reach more than 99.5%, among which the iron content can reach more than 29.85%, the P content can reach more than 16.82%, at the same time the aluminum content can reach less than 0.001%, the copper content can reach less than 0.004%, the iron recovery rate can reach more than 99.3%, and the phosphorus recovery rate can reach more than 99.2%, realizing deep impurity removal and efficient recovery of lithium iron phosphate materials.

[0052] Other aspects can be understood after reading and understanding the detailed description. Specific embodiments

[0053] The technical solution of the present disclosure will be further described below through specific embodiments. Those skilled in the art should understand that the embodiments are only for helping to understand the present disclosure and should not be regarded as specific limitations on the present disclosure.

[0054] Example 1

[0055] This example provides a method for the integrated full-chain recycling of waste lithium iron phosphate batteries to prepare iron phosphate. The method includes the following steps:

[0056] (1) Ball-mill the waste lithium iron phosphate powder, sieve it through a 50-mesh sieve to obtain waste lithium iron phosphate powder, put the lithium iron phosphate powder into a furnace, add a mixture of sodium chloride and potassium chloride with a mass ratio of 1:1, and keep it at a temperature of 350 °C for 20 min, where the mass ratio of lithium iron phosphate to the potassium chloride-sodium chloride mixture is 1:7;

[0057] (2) Add sodium stearate with a mass of 6% of the mass of lithium iron phosphate into the furnace, blow argon into the melt at the lower part of the furnace for reaction for 20 min, control the gas flow rate at 50 mL / s, and carbon and lithium iron phosphate form a slag phase floating on the upper layer, while copper and aluminum impurities deposit at the bottom of the melt. Subsequently, use a filter screen to fish out the lithium iron phosphate and carbon scum floating on the upper layer from above to separate the aluminum and copper impurities from the carbon-containing lithium iron phosphate;

[0058] (3) Wash the obtained carbon-containing lithium iron phosphate and add it to a sulfuric acid solution, control the pH at 1.7, the solid-liquid ratio at 1:1.5, and then slowly add hydrogen peroxide with a molar amount 0.5 times that of lithium iron phosphate to react for 2.5 h to selectively leach lithium. After the reaction ends, add alkali to adjust the pH to 5 and react for 0.7 h, and then perform solid-liquid separation to obtain a lithium-containing solution and a carbon-containing phosphorus-iron slag;

[0059] (4) Add the carbon-containing phosphorus-iron slag to a sulfuric acid solution with a concentration of 1 mol / L and control the hydrogen ion concentration in the solution at 0.8 mol / L, carry out leaching reaction for 2 h, and perform solid-liquid separation after the reaction is completed to obtain a high-purity phosphorus-iron solution. Add ferrous sulfate or phosphoric acid to the obtained phosphorus-iron solution to adjust the phosphorus-iron ratio to P:Fe = 1.05, add ammonia water to adjust the pH to 2 for coprecipitation reaction, and perform solid-liquid separation after the reaction is completed to obtain high-purity iron phosphate.

[0060] Example 2

[0061] This example provides a method for the full-chain integrated recycling of waste lithium iron phosphate batteries to prepare iron phosphate, and the method includes the following steps:

[0062] (1) Ball-mill the waste lithium iron phosphate powder, sieve it through a 40-mesh sieve to obtain waste lithium iron phosphate powder, put the lithium iron phosphate powder into the furnace, add a mixture of sodium chloride and potassium chloride with a mass ratio of 1:1, keep it warm at 300 °C for 30 min, and the mass ratio of lithium iron phosphate to the sodium chloride and potassium chloride mixture is 1:5;

[0063] (2) Add sodium stearate with a mass of 2% of the mass of lithium iron phosphate into the furnace, blow argon into the melt at the lower part of the furnace for reaction for 10 min, control the gas flow rate at 100 mL / s, and carbon and lithium iron phosphate form a slag phase floating on the upper layer, while copper and aluminum impurities deposit at the bottom of the melt. Subsequently, use a filter screen to fish out the lithium iron phosphate and carbon scum floating on the upper layer from above to separate the aluminum and copper impurities from the carbon-containing lithium iron phosphate;

[0064] (3) Wash the obtained carbon-containing lithium iron phosphate and add it to a sulfuric acid solution, control the pH at 1.5, the solid-liquid ratio at 1:1.5, and then slowly add hydrogen peroxide with a molar amount 0.3 times that of lithium iron phosphate to react for 2.5 h to selectively leach lithium. After the reaction ends, add alkali to adjust the pH to 4 and react for 0.5 h, and then perform solid-liquid separation to obtain a lithium-containing solution and a carbon-containing phosphorus-iron slag;

[0065] (4) Add carbon-phosphorus-iron slag to sulfuric acid solution with a concentration of 1.2 mol / L, control the hydrogen ion concentration in the solution to be 1.2 mol / L, carry out leaching reaction for 1.5 h, after the reaction is completed, carry out solid-liquid separation to obtain a high-purity phosphorus-iron solution, add ferrous sulfate or phosphoric acid to the obtained phosphorus-iron solution to adjust the phosphorus-iron ratio to P:Fe = 1, add ammonia water to adjust the pH to 1.8 for co-precipitation reaction, and after the reaction is completed, carry out solid-liquid separation to obtain high-purity iron phosphate.

[0066] Example 3

[0067] This example provides a method for preparing iron phosphate by integrally recycling waste lithium iron phosphate batteries in a full-chain manner. The method includes the following steps:

[0068] (1) Ball-mill waste lithium iron phosphate powder, sieve it through a 60-mesh sieve to obtain waste lithium iron phosphate powder, put the lithium iron phosphate powder into a furnace, add a mixture of sodium chloride and potassium chloride with a mass ratio of 1:1, keep it warm at 400 °C for 10 min, and the mass ratio of lithium iron phosphate to the sodium chloride-potassium chloride mixture is 1:10;

[0069] (2) Add sodium stearate with a mass of 10% of the mass of lithium iron phosphate to the furnace, blow argon into the melt at the lower part of the furnace for reaction for 30 min, control the gas flow rate to be 10 mL / s, carbon and lithium iron phosphate form a slag phase floating on the upper layer, and copper and aluminum impurities deposit at the bottom of the melt. Subsequently, use a filter screen to fish out the floating lithium iron phosphate and carbon slag from above to separate aluminum and copper impurities from carbon-containing lithium iron phosphate;

[0070] (3) Wash the obtained carbon-containing lithium iron phosphate and add it to sulfuric acid solution, control the pH to 2, the solid-liquid ratio is 1:1.5, and then slowly add hydrogen peroxide with a molar amount 0.8 times that of lithium iron phosphate to react for 3 h to selectively leach lithium. After the reaction is completed, add alkali to adjust the pH to 6 and react for 1 h, and then carry out solid-liquid separation to obtain a lithium-containing solution and carbon-phosphorus-iron slag;

[0071] (4) Add carbon-phosphorus-iron slag to sulfuric acid solution with a concentration of 1.5 mol / L, control the hydrogen ion concentration in the solution to be 0.8 mol / L, carry out leaching reaction for 1 h, after the reaction is completed, carry out solid-liquid separation to obtain a high-purity phosphorus-iron solution, add ferrous sulfate or phosphoric acid to the obtained phosphorus-iron solution to adjust the phosphorus-iron ratio to P:Fe = 1.1, add ammonia water to adjust the pH to 2.2 for co-precipitation reaction, and after the reaction is completed, carry out solid-liquid separation to obtain high-purity iron phosphate.

[0072] Example 4

[0073] The difference between this example and Example 1 is only that the mass of sodium stearate is 1% of the mass of lithium iron phosphate, and other conditions and parameters are exactly the same as those in Example 1.

[0074] Example 5

[0075] The difference between this example and Example 1 is only that the mass of sodium stearate is 12% of the mass of lithium iron phosphate, and other conditions and parameters are exactly the same as those in Example 1.

[0076] Comparative Example 1

[0077] This comparative example provides a method for recycling waste lithium iron phosphate materials to prepare iron phosphate, and the method includes the following steps:

[0078] (1) Ball-mill the waste lithium iron phosphate powder and sieve it through a 50-mesh sieve to obtain waste powder.

[0079] (2) Add the above-mentioned waste lithium iron phosphate powder into a sulfuric acid solution, control the pH at 1.7, and the solid-liquid ratio at 1:1.5. Then slowly add hydrogen peroxide with a molar amount 0.5 times that of lithium iron phosphate and react for 2.5 h to selectively leach lithium. After the reaction is completed, add alkali to adjust the pH to 5 and react for 0.7 h, and then perform solid-liquid separation to obtain a lithium-containing solution and phosphorus-iron slag.

[0080] (3) Add the phosphorus-iron slag obtained in step (2) into a sulfuric acid solution with a concentration of 1 mol / L to control the hydrogen ion concentration in the solution at 0.8 mol / L, and carry out a leaching reaction for 2 h. After the reaction is completed, perform solid-liquid separation to obtain a phosphorus-iron solution.

[0081] (4) Add an iron source or a phosphorus source to the phosphorus-iron solution obtained in step (3) to adjust the phosphorus-iron ratio to P:Fe = 1.05, add ammonia water to adjust the pH to 2 for coprecipitation reaction, and perform solid-liquid separation after the reaction is completed to obtain high-purity iron phosphate.

[0082] Comparative Example 2

[0083] The difference between this comparative example and Example 1 is only that sodium stearate is not added, and other conditions and parameters are exactly the same as those in Example 1.

[0084] Performance test:

[0085] Test the purity of the recovered lithium, the iron phosphate index and its recovery rate obtained in the test examples and comparative examples. The test results are shown in Table 1:

[0086] Table 1

[0087]

[0088] As can be seen from Table 1, according to Examples 1-3, for the method described in the present disclosure for recycling waste lithium iron phosphate materials, the lithium purity can reach over 97.8%, and the iron phosphate purity can reach over 99.5%. Among them, the iron content can reach over 29.85%, the P content can reach over 16.82%. At the same time, the aluminum content can reach below 0.001%, the copper content can reach below 0.004%, the iron recovery rate can reach over 99.3%, and the phosphorus recovery rate can reach over 99.2%, achieving deep impurity removal and efficient recovery of lithium iron phosphate materials.

[0089] By comparing Example 1 with Examples 4-5, it can be obtained that during the process of recycling waste lithium iron phosphate materials to prepare iron phosphate in the present disclosure, the addition amount of sodium stearate will affect the recycling effect. Controlling the addition amount of sodium stearate at 2-10% of the mass of lithium iron phosphate results in a better recycling effect. If the addition amount of sodium stearate is too large, a large amount of sticky and fine foam will be formed to adsorb impurity metals, which is not conducive to the separation of lithium iron phosphate and aluminum and copper impurities. If the addition amount of sodium stearate is too small, the foaming rate is too low and the number of bubbles is too small, which is not conducive to bringing lithium iron phosphate and carbon to the slag layer, thus reducing the flotation efficiency.

[0090] By comparing Example 1 with Comparative Example 1, it can be obtained that the present disclosure selects potassium chloride and sodium chloride, and controlling the mass ratio of the two can reduce the melting point of the mixed salt, enabling the mixed material to reach a molten state at a lower temperature. Using the melt as the medium, the density of the melt is appropriate, achieving the separation of aluminum and copper impurities and carbon-containing lithium iron phosphate while saving energy.

Claims

1. A method for preparing iron phosphate by the full-chain integrated recycling of waste lithium iron phosphate batteries, the method comprising the following steps: (1) Mix the waste lithium iron phosphate material with a mixed chloride, and perform a heating and melting treatment to obtain a mixed melt; (2) After mixing the mixed melt with sodium stearate, perform a blowing reaction, and after separation, obtain a carbon-containing lithium iron phosphate scum on the upper layer; (3) Mix the carbon-containing lithium iron phosphate scum with a first acid solution to obtain a mixed solution, add hydrogen peroxide for a leaching reaction, and perform solid-liquid separation to obtain a lithium-containing solution and a carbon-containing phosphorus-iron slag; (4) Mix the carbon-containing phosphorus-iron slag with a second acid solution, leach to obtain a phosphorus-iron solution, adjust the phosphorus-iron ratio by adding an iron source and / or a phosphorus source, and add a complexing agent for a coprecipitation reaction to obtain iron phosphate; In step (1), the mixed chloride includes potassium chloride and sodium chloride, the mass ratio of potassium chloride to sodium chloride is (0.8 - 1.2):1, and the temperature of the heating and melting treatment is 300 - 400 °C.

2. The method according to claim 1, wherein The mass ratio of the waste lithium iron phosphate material to the mixed chloride is 1:(5 - 10).

3. The method according to claim 1, wherein The time of the heating and melting treatment is 10 - 30 min.

4. The method according to claim 1, wherein In step (2), the mass ratio of sodium stearate to the waste lithium iron phosphate material is (2 - 10):

100.

5. The method according to claim 1, wherein, The gas for the blowing reaction includes argon and / or nitrogen.

6. The method according to claim 1, wherein The gas flow rate of the blowing reaction is 10 - 100 mL / s.

7. The method according to claim 1, wherein, The time of the blowing reaction is 10 - 30 min.

8. The method according to claim 1, wherein The separation in step (2) includes fishing out the upper-layer solid of the melt with a filter screen to obtain a carbon-containing lithium iron phosphate scum.

9. The method according to claim 1, wherein, The first acid solution in step (3) includes sulfuric acid.

10. The method according to claim 1, wherein The mass ratio of the carbon-containing lithium iron phosphate scum to the first acid solution is 1:(1.2 - 1.8).

11. The method according to claim 1, wherein, The pH of the mixed solution is 1.5 - 2.

12. The method according to claim 1, wherein In step (3), the molar ratio of hydrogen peroxide to lithium iron phosphate is (0.3 - 0.8):

1.

13. The method according to claim 1, wherein The time of the leaching reaction is 2 - 3 h.

14. The method according to claim 1, wherein After the leaching reaction, add alkali to adjust the pH for a reaction.

15. The method according to claim 14, wherein, The pH is 4 - 6.

16. The method according to claim 14, wherein, The time of the reaction is 0.5 - 1 h.

17. The method according to claim 1, wherein, The second acid solution in step (4) includes any one or a combination of at least two of sulfuric acid, nitric acid, or phosphoric acid.

18. The method according to claim 1, wherein, The concentration of the second acid solution is 0.8 - 1.2 mol / L.

19. The method according to claim 1, wherein During the leaching process, the concentration of hydrogen ions in the system ≥ 0.8 mol / L.

20. The method according to claim 1, wherein The time of the leaching is 1 - 2 h.

21. The method according to claim 1, wherein The iron source in step (4) includes ferrous sulfate.

22. The method according to claim 1, wherein, The phosphorus source includes phosphoric acid.

23. The method according to claim 1, wherein, The adjusted phosphorus-iron ratio is P:Fe = 1.0 - 1.

1.

24. The method according to claim 1, wherein, The complexing agent includes ammonia water.

25. The method according to claim 1, wherein, The pH of the coprecipitation reaction is 1.8 - 2.

2.

26. The method according to claim 1, wherein The method includes the following steps: (1) Mix the waste lithium iron phosphate material with a mixed chloride according to a mass ratio of 1:(5 - 10), perform a heating and melting treatment at 300 - 400 °C for 10 - 30 min to obtain a mixed melt, and the mixed chloride includes potassium chloride and sodium chloride with a mass ratio of (0.8 - 1.2):1; (2) Mix the mixed melt with sodium stearate at a mass ratio of 100:(2 - 10), then blow air at a speed of 10 - 100 mL / s for reaction for 10 - 30 min. After separation, the upper layer gives carbon-containing lithium iron phosphate dross; (3) Mix the carbon-containing lithium iron phosphate dross with the first acid solution at a mass ratio of 1:(1.2 - 1.8) to obtain a mixed solution with a pH of 1.5 - 2. Add hydrogen peroxide for leaching reaction for 2 - 3 h, add alkali to adjust the pH to 4 - 6 and react for 0.5 - 1 h, then perform solid-liquid separation to obtain a lithium-containing solution and carbon-containing phosphorus iron slag; (4) Mix the carbon-containing phosphorus iron slag with the second acid solution with a concentration of 0.8 - 1.2 mol / L, control the hydrogen ion concentration in the system ≥ 0.8 mol / L and leach for 1 - 2 h to obtain a phosphorus iron solution. Add an iron source and / or a phosphorus source to the phosphorus iron solution to adjust the phosphorus-iron ratio, add ammonia water, and adjust the pH to 1.8 - 2.2 for coprecipitation reaction to obtain iron phosphate.

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