Method for preparing iron phosphate by means of full-chain integrated recycling of waste lithium iron phosphate battery

Abstract

Provided in the present disclosure is a method for preparing iron phosphate by means of full-chain integrated recycling of a waste lithium iron phosphate battery. The method comprises the following steps: (1) mixing a waste lithium iron phosphate material with a mixed chloride, and heating and melting the mixture, so as to obtain a mixed melt; (2) mixing the mixed melt with sodium stearate, then subjecting the mixture to a blowing reaction, and separating same to obtain carbon-containing lithium iron phosphate scum; (3) mixing the scum with an acid solution, adding hydrogen peroxide to perform a leaching reaction, and carrying out solid-liquid separation to obtain a lithium-containing solution and carbon-containing phosphorus iron slag; and (4) mixing the carbon-containing phosphorus iron slag with an acid solution, leaching the mixture to obtain a phosphorus iron solution, adjusting the phosphorus iron ratio, and adding a complexing agent to perform a coprecipitation reaction, so as to obtain iron phosphate. The method of the present disclosure can improve the purity of the recycled lithium, also avoid a multi-step impurity-removal process required to be carried out during the process of preparing iron phosphate from the phosphorus iron slag after lithium extraction, and further improve the purity and phosphorus iron recovery rate of the iron phosphate prepared from the phosphorus iron slag.

Description

A method for preparing iron phosphate by recycling waste lithium iron phosphate batteries through full-chain integration Technical Field

[0001] The present invention belongs to the field of resource recovery technology and relates to a method for preparing iron phosphate by recycling waste lithium iron phosphate batteries through full-chain integration. Background Art

[0002] Lithium-ion batteries, due to their high capacity and energy density, are widely used in electric vehicles, large-scale energy storage, and electronic devices. With the increasing adoption of electric vehicles in recent years, a large amount of used lithium-ion batteries has accumulated over time. Recycling these used lithium-ion batteries can increase resource utilization and avoid environmental pollution. Lithium iron phosphate batteries, a type of lithium-ion battery, are widely used in power batteries due to their stable performance and low cost.

[0003] Currently, the primary method for recovering lithium iron phosphate from spent lithium-ion batteries is to extract and recover lithium through selective leaching, leaving behind a ferrophosphorus slag. However, direct leaching of spent lithium iron phosphate produces a lithium solution with high impurities. Furthermore, since the ferrophosphorus slag contains iron and phosphorus, it needs to be recycled and reused.

[0004] CN109250696A discloses a method for recovering nano-iron phosphate from a lithium iron phosphate battery. The method comprises the following steps: discharging the lithium iron phosphate battery to below 2.0V, crushing and disassembling the battery, and separating the lithium iron phosphate powder, aluminum powder, and copper powder in the battery; placing the lithium iron phosphate powder in a vacuum tube furnace; adding the lithium iron phosphate powder to a dilute hydrochloric acid solution while stirring; simultaneously adding hydrogen peroxide and a suspension dropwise to a three-necked flask reactor via a peristaltic pump, and stirring and ultrasonicating the solution; filtering the mixed solution and collecting the filtrate to obtain a leachate; and synchronously adding the leachate mixed solution and an alkaline solution to a mixing reactor via a peristaltic pump, mixing the two liquids, stirring, and ultrasonicating the solution to obtain a light yellow powdered iron phosphate.

[0005] CN115611250A discloses a method for recovering high-purity iron phosphate from waste lithium iron phosphate positive electrode powder. The method performs preliminary impurity removal through a first-stage acid leaching and a first heat preservation self-precipitation to obtain a crude iron phosphate product, and then performs secondary acid leaching, re-dissolution, and a second heat preservation self-precipitation to obtain the iron phosphate.

[0006] The above scheme adopts a wet treatment method, that is, adding ferrophosphorus slag to an acidic solution or an alkaline solution for multiple leaching to remove impurities and purify it to obtain ferric phosphate. If only acid leaching or alkaline leaching is used for impurity removal, the impurity content of the prepared ferric phosphate is still high and the process flow is long. Alternatively, resin adsorption is used for impurity removal, but the deep impurity removal effect is poor.

[0007] Summary of the Invention

[0008] The following is a summary of the subject matter described in detail herein. This summary is not intended to limit the scope of the claims.

[0009] The purpose of the present disclosure is to provide a full-chain integrated method for recycling waste lithium iron phosphate batteries to prepare iron phosphate. The method described in the present disclosure can improve the purity of recovered lithium, while avoiding the multi-step impurity removal process required in the process of preparing iron phosphate from ferrophosphorus slag after lithium extraction, further improving the purity of iron phosphate prepared from ferrophosphorus slag and the recovery rate of iron phosphate.

[0010] To achieve this disclosure purpose, the present disclosure adopts the following technical solutions:

[0011] In a first aspect, the present disclosure provides a method for recycling waste lithium iron phosphate batteries to prepare iron phosphate through a full-chain integrated process, the method comprising the following steps:

[0012] (1) mixing waste lithium iron phosphate material with mixed chloride, and performing heating and melting treatment to obtain a mixed melt;

[0013] (2) mixing the mixed melt with sodium stearate, performing air blowing reaction, and obtaining carbon-containing lithium iron phosphate slag on the upper layer after separation;

[0014] (3) mixing the carbon-containing lithium iron phosphate slag with the first acid solution to obtain a mixed solution, adding hydrogen peroxide to carry out a leaching reaction, and performing solid-liquid separation to obtain a lithium-containing solution and carbon-containing iron phosphorus slag;

[0015] (4) mixing the carbon-containing ferrophosphorus slag with a second acid solution, leaching to obtain a ferrophosphorus solution, adding an iron source and / or a phosphorus source to the ferrophosphorus solution to adjust the phosphorus-iron ratio, and adding a complexing agent to carry out a coprecipitation reaction to obtain ferric phosphate.

[0016] The present disclosure discloses a method for recycling waste lithium iron phosphate by placing the copper and aluminum impurity removal step before lithium extraction, and by adding sodium stearate after mixing and melting waste lithium iron phosphate powder and mixed chloride. Since the density of aluminum and copper impurities in the waste lithium iron phosphate is greater than the density of lithium iron phosphate and the density of the molten mixed chloride, 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 the density of the sodium chloride and potassium chloride mixture, sodium stearate is added as a surfactant and foaming agent. After blowing in gas, the melt can be stirred. Since the carbon particles are relatively fine and have many adsorption active sites on their surface, they can easily aggregate with lithium iron phosphate to form larger slag clumps, which can undergo strong adsorption with bubbles and migrate to the surface of the melt along with the bubbles. After the carbon particles carry the lithium iron phosphate to the surface of the melt, they further form larger slag through collision. The large slag is difficult to be brought back into the melt by gas stirring, ultimately separating the lithium iron phosphate and aluminum and copper impurities. The subsequent ferrophosphorus slag obtained after lithium extraction contains low impurities, containing only carbon particles, avoiding the subsequent aluminum and copper removal steps, and can directly obtain high-purity ferric phosphate through a single-step acid leaching. The present disclosure deeply removes copper and aluminum from waste lithium iron phosphate through a single reaction, which can improve the purity of the recovered lithium and avoid the subsequent multi-step impurity removal steps of the ferrophosphorus slag, thereby further improving the purity and recovery rate of the recovered ferric phosphate.

[0017] In one embodiment, the mixed chloride in step (1) includes potassium chloride and sodium chloride.

[0018] 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.

[0019] The present invention selects potassium chloride and sodium chloride, and controlling the mass ratio of the two can reduce the melting point of the mixed salt, so that the mixed material can be molten at a lower temperature. The melt is used as a medium, and the density of the melt is appropriate. While saving energy, the separation of aluminum and copper impurities and carbon-containing lithium iron phosphate is achieved.

[0020] In one embodiment, the mass ratio of the waste lithium iron phosphate material to the mixed chloride is 1:(5-10), for example: 1:5, 1:6, 1:7, 1:8 or 1:10.

[0021] 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.

[0022] In one embodiment, the heating and melting treatment time is 10 to 30 minutes, for example, 10 minutes, 15 minutes, 20 minutes, 25 minutes or 30 minutes.

[0023] In one embodiment, the mass ratio of the sodium stearate and 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.

[0024] In one embodiment, the gas used for blowing the reaction includes argon and / or nitrogen.

[0025] 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.

[0026] In one embodiment, the blowing reaction time is 10 to 30 minutes, for example, 10 minutes, 15 minutes, 20 minutes, 25 minutes or 30 minutes.

[0027] In one embodiment, the separation in step (2) includes removing the solid layer on the upper layer of the melt with a filter to obtain carbon-containing lithium iron phosphate slag.

[0028] In one embodiment, the first acid solution in step (3) comprises sulfuric acid.

[0029] In one embodiment, the mass ratio of the carbon-containing lithium iron phosphate slag 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.

[0030] 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.

[0031] In one embodiment, the molar ratio of the hydrogen peroxide and 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.

[0032] In one embodiment, the leaching reaction time is 2 to 3 hours, for example, 2 hours, 2.2 hours, 2.5 hours, 2.8 hours or 3 hours.

[0033] In one embodiment, after the leaching reaction, alkali is added to adjust the pH to proceed with the reaction.

[0034] In one embodiment, the pH is 4 to 6, for example, 4, 4.5, 5, 5.5 or 6.

[0035] In one embodiment, the reaction time is 0.5 to 1 h, for example, 0.5 h, 0.6 h, 0.8 h, 0.9 h or 1 h.

[0036] In one embodiment, the second acid solution in step (4) comprises any one of sulfuric acid, nitric acid or phosphoric acid, or a combination of at least two of them.

[0037] In one embodiment, the concentration of the second acid solution is 0.8 to 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.

[0038] In one embodiment, during the leaching process, the concentration of hydrogen ions in the system is ≥0.8 mol / L.

[0039] In one embodiment, the leaching time is 1 to 2 hours, for example, 1 hour, 1.2 hours, 1.5 hours, 1.8 hours or 2 hours.

[0040] In one embodiment, the iron source in step (4) comprises ferrous sulfate.

[0041] In one embodiment, the phosphorus source comprises phosphoric acid.

[0042] In one embodiment, the phosphorus-iron ratio is adjusted to P:Fe=1.0-1.1, for example: 1, 1.02, 1.05, 1.08 or 1.1.

[0043] In one embodiment, the complexing agent comprises aqueous ammonia.

[0044] In one embodiment, the pH of the coprecipitation reaction is 1.8 to 2.2, for example, 1.8, 1.9, 2, 2.1 or 2.2.

[0045] As an optional solution of the present disclosure, the method includes the following steps:

[0046] (1) mixing waste lithium iron phosphate material with mixed chloride in a mass ratio of 1:(5-10), heating and melting at 300-400° C. for 10-30 min to obtain a mixed melt, wherein the mixed chloride includes potassium chloride and sodium chloride in a mass ratio of (0.8-1.2):1;

[0047] (2) mixing the mixed melt with sodium stearate in a mass ratio of 100:(2-10), blowing air at a rate of 10-100 mL / s for 10-30 min, and separating the upper layer to obtain carbon-containing lithium iron phosphate slag;

[0048] (3) mixing the carbon-containing lithium iron phosphate slag with the first acid solution in a mass ratio of 1:(1.2-1.8) to obtain a mixed solution with a pH of 1.5-2, adding hydrogen peroxide to carry out a leaching reaction for 2-3 hours, adding alkali to adjust the pH to 4-6 and reacting for 0.5-1 hour, and performing solid-liquid separation to obtain a lithium-containing solution and carbon-containing iron phosphorus slag;

[0049] (4) mixing the carbon-containing ferrophosphorus slag with a second acid solution having a concentration of 0.8 to 1.2 mol / L, controlling the concentration of hydrogen ions in the system to be ≥0.8 mol / L and leaching for 1 to 2 hours to obtain a ferrophosphorus solution, adding an iron source and / or a phosphorus source to the ferrophosphorus solution to adjust the phosphorus-iron ratio, adding ammonia water, and adjusting the pH to 1.8 to 2.2 to perform a coprecipitation reaction to obtain ferric phosphate.

[0050] Compared with the prior art, the present disclosure has the following beneficial effects:

[0051] (1) The method disclosed in the present invention can improve the purity of recovered lithium, while avoiding the multi-step impurity removal process required in the preparation of ferric phosphate from ferrophosphorus slag after lithium extraction, further improving the purity of ferric phosphate prepared from ferrophosphorus slag and the recovery rate of ferrophosphorus.

[0052] (2) The method disclosed in the present invention recycles waste lithium iron phosphate materials, and the obtained lithium purity can reach more than 97.8%, and the iron phosphate purity can reach more than 99.5%, among which the iron content can reach more than 29.85%, and the P content can reach more than 16.82%. At the same time, the aluminum content can reach less than 0.001%, and 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%, thereby achieving deep impurity removal and efficient recovery of lithium iron phosphate materials.

[0053] Still other aspects will become apparent upon reading and understanding the detailed description. DETAILED DESCRIPTION

[0054] The technical solution of the present disclosure is further described below through specific implementation methods. Those skilled in the art should understand that the embodiments are only used to help understand the present disclosure and should not be regarded as specific limitations of the present disclosure.

[0055] Example 1

[0056] This embodiment provides a method for recycling waste lithium iron phosphate batteries to prepare iron phosphate in an integrated manner, the method comprising the following steps:

[0057] (1) waste lithium iron phosphate powder is ball-milled and sieved through a 50-mesh sieve to obtain waste lithium iron phosphate powder, the lithium iron phosphate powder is placed in a furnace, a mixture of sodium chloride and potassium chloride in a mass ratio of 1:1 is added, and the mixture is kept at a temperature of 350° C. for 20 minutes, wherein the mass ratio of the lithium iron phosphate to the potassium chloride and sodium chloride mixture is 1:7;

[0058] (2) Sodium stearate, which is 6% of the mass of lithium iron phosphate, is added to the furnace. Argon gas is blown into the melt at the lower end of the furnace for 20 minutes, with the gas flow rate controlled at 50 mL / s. Carbon and lithium iron phosphate form a slag phase that floats on the upper layer, while copper and aluminum impurities are deposited at the bottom of the melt. Subsequently, a filter is used to remove the lithium iron phosphate and carbon slag floating on the upper layer from above, thereby separating the aluminum and copper impurities from the carbon-containing lithium iron phosphate.

[0059] (3) washing the obtained carbon-containing lithium iron phosphate with water and adding it to a sulfuric acid solution, controlling the pH at 1.7 and the solid-liquid ratio at 1:1.5, then slowly adding hydrogen peroxide with a molar amount 0.5 times that of the lithium iron phosphate and reacting for 2.5 hours to selectively leach lithium. After the reaction is completed, adding alkali to adjust the pH to 5 and reacting for 0.7 hours, and then performing solid-liquid separation to obtain a lithium-containing solution and carbon-containing phosphorus iron slag;

[0060] (4) Adding carbon-containing ferrophosphorus slag to a sulfuric acid solution with a concentration of 1 mol / L to control the concentration of hydrogen ions in the solution to 0.8 mol / L, and leaching reaction for 2 hours. After the reaction is completed, solid-liquid separation is performed to obtain a high-purity ferrophosphorus solution. Ferrous sulfate or phosphoric acid is added to the obtained ferrophosphorus solution to adjust the phosphorus-iron ratio to P:Fe=1.05. Ammonia water is added to adjust the pH to 2 for coprecipitation reaction. After the reaction is completed, solid-liquid separation is performed to obtain high-purity ferric phosphate.

[0061] Example 2

[0062] This embodiment provides a method for recycling waste lithium iron phosphate batteries to prepare iron phosphate in an integrated manner, the method comprising the following steps:

[0063] (1) ball-milling waste lithium iron phosphate powder and sieving it through a 40-mesh sieve to obtain waste lithium iron phosphate powder, placing the lithium iron phosphate powder in a furnace, adding a mixture of sodium chloride and potassium chloride in a mass ratio of 1:1, and keeping the temperature at 300° C. for 30 minutes, wherein the mass ratio of the lithium iron phosphate to the potassium chloride and sodium chloride mixture is 1:5;

[0064] (2) Sodium stearate at a mass equivalent to 2% of the mass of lithium iron phosphate is added to the furnace. Argon gas is blown into the melt at the lower end of the furnace for 10 minutes, with the gas flow rate controlled at 100 mL / s. Carbon and lithium iron phosphate form a slag phase that floats on the upper layer, while copper and aluminum impurities are deposited at the bottom of the melt. Subsequently, a filter is used to remove the lithium iron phosphate and carbon slag floating on the upper layer from above, thereby separating the aluminum and copper impurities from the carbon-containing lithium iron phosphate.

[0065] (3) washing the obtained carbon-containing lithium iron phosphate with water and adding it to a sulfuric acid solution, controlling the pH at 1.5 and the solid-liquid ratio at 1:1.5, then slowly adding hydrogen peroxide with a molar amount 0.3 times that of the lithium iron phosphate and reacting for 2.5 hours to selectively leach lithium. After the reaction is completed, adding alkali to adjust the pH to 4 and reacting for 0.5 hours, and then performing solid-liquid separation to obtain a lithium-containing solution and carbon-containing phosphorus iron slag;

[0066] (4) Adding carbon-containing ferrophosphorus slag to a sulfuric acid solution with a concentration of 1.2 mol / L to control the concentration of hydrogen ions in the solution to 1.2 mol / L, leaching reaction for 1.5 h, solid-liquid separation after the reaction is completed to obtain a high-purity ferrophosphorus solution, adding ferrous sulfate or phosphoric acid to the obtained ferrophosphorus solution to adjust the phosphorus-iron ratio to P:Fe=1, adding ammonia water to adjust the pH to 1.8 for coprecipitation reaction, and solid-liquid separation after the reaction is completed to obtain high-purity ferric phosphate.

[0067] Example 3

[0068] This embodiment provides a method for recycling waste lithium iron phosphate batteries to prepare iron phosphate in an integrated manner, the method comprising the following steps:

[0069] (1) waste lithium iron phosphate powder is ball-milled and sieved through a 60-mesh sieve to obtain waste lithium iron phosphate powder, the lithium iron phosphate powder is placed in a furnace, a mixture of sodium chloride and potassium chloride in a mass ratio of 1:1 is added, and the mixture is kept at a temperature of 400° C. for 10 minutes, wherein the mass ratio of the lithium iron phosphate to the potassium chloride and sodium chloride mixture is 1:10;

[0070] (2) Sodium stearate (10% by mass of lithium iron phosphate) was added to the furnace, and argon gas was blown into the melt at the lower end of the furnace for 30 minutes. The gas flow rate was controlled at 10 mL / s. Carbon and lithium iron phosphate formed a slag phase that floated on the upper layer, while copper and aluminum impurities were deposited at the bottom of the melt. Subsequently, a filter was used to remove the lithium iron phosphate and carbon slag floating on the upper layer from above, thereby separating the aluminum and copper impurities from the carbon-containing lithium iron phosphate.

[0071] (3) washing the obtained carbon-containing lithium iron phosphate with water and adding it to a sulfuric acid solution, controlling the pH at 2 and the solid-liquid ratio at 1:1.5, then slowly adding hydrogen peroxide with a molar amount 0.8 times that of the lithium iron phosphate and reacting for 3 hours to selectively leach lithium. After the reaction is completed, adding alkali to adjust the pH to 6 and reacting for 1 hour, and then performing solid-liquid separation to obtain a lithium-containing solution and carbon-containing phosphorus iron slag;

[0072] (4) Adding carbon-containing ferrophosphorus slag to a sulfuric acid solution with a concentration of 1.5 mol / L to control the concentration of hydrogen ions in the solution to 0.8 mol / L, and leaching reaction for 1 hour. After the reaction is completed, solid-liquid separation is performed to obtain a high-purity ferrophosphorus solution. Ferrous sulfate or phosphoric acid is added to the obtained ferrophosphorus solution to adjust the phosphorus-iron ratio to P:Fe=1.1. Ammonia water is added to adjust the pH to 2.2 for coprecipitation reaction. After the reaction is completed, solid-liquid separation is performed to obtain high-purity ferric phosphate.

[0073] Example 4

[0074] The only difference between this embodiment and embodiment 1 is 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 embodiment 1.

[0075] Example 5

[0076] The only difference between this embodiment and embodiment 1 is 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 embodiment 1.

[0077] Comparative Example 1

[0078] This comparative example provides a method for recycling waste lithium iron phosphate material to prepare iron phosphate, the method comprising the following steps:

[0079] (1) Waste lithium iron phosphate powder is ball-milled and sieved through a 50-mesh sieve to obtain waste powder.

[0080] (2) The above-mentioned waste lithium iron phosphate powder was added to a sulfuric acid solution, the pH was controlled at 1.7, the solid-liquid ratio was 1:1.5, and then hydrogen peroxide with a molar amount 0.5 times that of lithium iron phosphate was slowly added and reacted for 2.5 hours to selectively leach lithium. After the reaction was completed, alkali was added to adjust the pH to 5 and reacted for 0.7 hours, and then solid-liquid separation was performed to obtain a lithium-containing solution and ferrophosphorus slag.

[0081] (3) The ferrophosphorus slag obtained in step (2) was added to a sulfuric acid solution with a concentration of 1 mol / L to control the concentration of hydrogen ions in the solution to 0.8 mol / L, and the leaching reaction was carried out for 2 h. After the reaction was completed, solid-liquid separation was performed to obtain a ferrophosphorus solution.

[0082] (4) adding an iron source or a phosphorus source to the ferrophosphorus solution obtained in step (3) to adjust the phosphorus-iron ratio to P:Fe=1.05, adding ammonia water to adjust the pH to 2 for coprecipitation reaction, and after the reaction is completed, solid-liquid separation is performed to obtain high-purity ferric phosphate.

[0083] Comparative Example 2

[0084] The only difference between this comparative example and Example 1 is that sodium stearate is not added, and other conditions and parameters are exactly the same as those in Example 1.

[0085] Performance testing:

[0086] The purity of recovered lithium, iron phosphate index and recovery rate obtained from the test examples and comparative examples are shown in Table 1:

[0087] Table 1

[0088] As can be seen from Table 1, from Examples 1-3, the method disclosed in the present invention recycles waste lithium iron phosphate materials, and the obtained lithium purity can reach more than 97.8%, and the iron phosphate purity can reach more than 99.5%, among which the iron content can reach more than 29.85%, and the P content can reach more than 16.82%. At the same time, the aluminum content can reach less than 0.001%, and 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%, thereby achieving deep impurity removal and efficient recovery of lithium iron phosphate materials.

[0089] By comparing Example 1 with Examples 4-5, it can be seen that in the process of recycling waste lithium iron phosphate materials to prepare iron phosphate in the present disclosure, the amount of sodium stearate added will affect the recovery effect. When the amount of sodium stearate added is controlled at 2-10% of the mass of the lithium iron phosphate, the recovery effect is better. If the amount of sodium stearate added 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 amount of sodium stearate added 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, thereby reducing the flotation efficiency.

[0090] By comparing Example 1 and Comparative Example 1, it can be seen 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, so that the mixed material can be molten at a lower temperature. The melt is used as a medium, and the density of the melt is appropriate. While saving energy, the separation of aluminum and copper impurities and carbon-containing lithium iron phosphate is achieved.

Claims

1. A method for preparing iron phosphate by recycling waste lithium iron phosphate batteries in a full-chain integrated manner, the method comprising the following steps: (1) mixing waste lithium iron phosphate material with mixed chloride, and performing heating and melting treatment to obtain a mixed melt; (2) mixing the mixed melt with sodium stearate, and then performing an air blowing reaction, and obtaining a carbon-containing lithium iron phosphate slag on the upper layer after separation; (3) mixing the carbon-containing lithium iron phosphate slag with the first acid solution to obtain a mixed solution, adding hydrogen peroxide to carry out a leaching reaction, and performing solid-liquid separation to obtain a lithium-containing solution and carbon-containing iron phosphorus slag; (4) mixing the carbon-containing ferrophosphorus slag with a second acid solution, leaching to obtain a ferrophosphorus solution, adding an iron source and / or a phosphorus source to the ferrophosphorus solution to adjust the phosphorus-iron ratio, and adding a complexing agent to perform a coprecipitation reaction to obtain ferric phosphate.

2. The method of claim 1, wherein: The mixed chloride in step (1) includes potassium chloride and sodium chloride.

3. The method according to claim 1 or 2, wherein: The mass ratio of potassium chloride to sodium chloride is (0.8-1.2):

1.

4. The method according to any one of claims 1 to 3, wherein: The mass ratio of the waste lithium iron phosphate material to the mixed chloride is 1:(5-10).

5. The method according to any one of claims 1 to 4, wherein: The temperature of the heating and melting treatment in step (1) is 300-400°C.

6. The method according to any one of claims 1 to 5, wherein: The heating and melting treatment takes 10 to 30 minutes.

7. The method according to any one of claims 1 to 6, wherein: The mass ratio of the sodium stearate and the waste lithium iron phosphate material in step (2) is (2-10):

100.

8. The method according to any one of claims 1 to 7, wherein: The gas for the blowing reaction includes argon and / or nitrogen.

9. The method according to any one of claims 1 to 8, wherein: The gas flow rate of the blowing reaction is 10 to 100 mL / s.

10. The method according to any one of claims 1 to 9, wherein: The blowing reaction time is 10 to 30 minutes.

11. The method according to any one of claims 1 to 10, wherein: The separation in step (2) includes removing the solid on the upper layer of the melt with a filter to obtain carbon-containing lithium iron phosphate slag.

12. The method according to any one of claims 1 to 11, wherein: Step (3) the first acid solution comprises sulfuric acid; Optionally, the mass ratio of the carbon-containing lithium iron phosphate slag to the first acid solution is 1:(1.2-1.8); Optionally, the pH of the mixed solution is 1.5-2.

13. The method according to any one of claims 1 to 12, wherein: The molar ratio of hydrogen peroxide to lithium iron phosphate in step (3) is (0.3-0.8):1; Optionally, the leaching reaction time is 2 to 3 hours; Optionally, after the leaching reaction, alkali is added to adjust the pH to carry out the reaction; Optionally, the pH is 4 to 6; Optionally, the reaction time is 0.5 to 1 h.

14. The method according to any one of claims 1 to 13, wherein: Step (4) the second acid solution comprises any one of sulfuric acid, nitric acid or phosphoric acid, or a combination of at least two thereof; Optionally, the concentration of the second acid solution is 0.8 to 1.2 mol / L; Optionally, during the leaching process, the concentration of hydrogen ions in the system is ≥0.8 mol / L; Optionally, the leaching time is 1 to 2 hours.

15. The method according to any one of claims 1 to 14, wherein: The iron source in step (4) includes ferrous sulfate; Optionally, the phosphorus source includes phosphoric acid; Optionally, the phosphorus-iron ratio is adjusted to P:Fe=1.0-1.1; Optionally, the complexing agent includes aqueous ammonia; Optionally, the pH of the coprecipitation reaction is 1.8 to 2.

2.

16. The method according to any one of claims 1 to 15, wherein: The method comprises the following steps: (1) mixing waste lithium iron phosphate material with mixed chloride in a mass ratio of 1:(5-10), heating and melting at 300-400° C. for 10-30 min to obtain a mixed melt, wherein the mixed chloride includes potassium chloride and sodium chloride in a mass ratio of (0.8-1.2):1; (2) mixing the mixed melt with sodium stearate in a mass ratio of 100:(2-10), blowing air at a speed of 10-100 mL / s for reaction for 10-30 min, and separating the upper layer to obtain carbon-containing lithium iron phosphate slag; (3) mixing the carbon-containing lithium iron phosphate slag with the first acid solution in a mass ratio of 1:(1.2-1.8) to obtain a mixed solution with a pH of 1.5-2, adding hydrogen peroxide to carry out a leaching reaction for 2-3 hours, adding alkali to adjust the pH to 4-6 and reacting for 0.5-1 hour, and performing solid-liquid separation to obtain a lithium-containing solution and carbon-containing phosphorus iron slag; (4) mixing the carbon-containing ferrophosphorus slag with a second acid solution having a concentration of 0.8 to 1.2 mol / L, controlling the concentration of hydrogen ions in the system to be ≥ 0.8 mol / L and leaching for 1 to 2 hours to obtain a ferrophosphorus solution, adding an iron source and / or a phosphorus source to the ferrophosphorus solution to adjust the phosphorus-iron ratio, adding ammonia water, and adjusting the pH to 1.8 to 2.2 to perform a coprecipitation reaction to obtain ferric phosphate.

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