Method for recovering phosphorus and aluminum from lithium iron phosphate battery lithium extraction waste residue

Abstract

The present application relates to a method for recovering phosphorus and aluminum from lithium iron phosphate battery lithium extraction waste residue, the preparation method comprising the following steps: (1) mixing lithium iron phosphate battery lithium extraction waste residue and alkali liquor, after the first leaching reaction, obtaining phosphorus aluminum leaching solution and leaching residue; (2) mixing the phosphorus aluminum leaching solution obtained in step (1) with calcium salt, after reaction, obtaining aluminate solution and phosphorus-rich residue. The present application extracts the phosphorus and aluminum components in lithium iron phosphate battery lithium extraction waste residue simultaneously, obtaining recyclable aluminate solution and phosphorus-rich residue, wherein the P2O5 content in the phosphorus-rich residue is ≥30%, which can be directly used as high-grade phosphate ore for wet-process phosphoric acid production. Through the above recovery steps, the recovery rate of phosphorus and aluminum elements both reaches more than 92%, realizing the high-value utilization of lithium iron phosphate battery lithium extraction waste residue; the recovery process and equipment are relatively conventional, the operation is simple and easy to implement, and it has strong practicality.

Description

Technical Field

[0001] This invention relates to the field of solid waste resource recycling technology, and in particular to a method for recovering phosphorus and aluminum from lithium iron phosphate battery lithium extraction waste residue. Background Technology

[0002] LiFePO4 batteries are widely used in the new energy vehicle sector due to their high safety, low cost, and relatively environmental friendliness. However, after prolonged use, LiFePO4 batteries experience problems such as cathode material aging, electrolyte decomposition, and passivation of interfacial side reactions, rendering them unusable and requiring disposal. Recycling valuable elements from spent LiFePO4 batteries through effective methods can achieve resource recycling.

[0003] Hydrometallurgical recycling of waste LiFePO4 batteries offers advantages such as strong raw material adaptability, simple industrial operation, and low environmental pollution, making it a mainstream recycling process. The main process involves pre-treating the LiFePO4 batteries to obtain black powder primarily composed of positive and negative electrode powders. This black powder is then acid-leached to extract lithium. The leachate is then purified, concentrated, and lithium precipitated to obtain lithium carbonate. During the leaching process, neutralization and purification with alkali typically produce a neutralization residue primarily composed of phosphorus, aluminum, iron, and fluorine. Recoverable phosphorus and aluminum mainly exist as amorphous aluminum phosphate and aluminum hydroxide. Since the leaching and neutralization / purification processes are often continuous, the leaching residue and neutralization / purification residue are usually mixed together to form lithium extraction waste. This waste essentially contains no economically valuable lithium and is therefore primarily stored as general solid waste. This not only poses a potential environmental pollution hazard but also results in the failure to recover and utilize resources such as phosphorus, aluminum, and negative electrode graphite, leading to significant resource waste.

[0004] CN113896211A discloses a method for the resource recovery of waste lithium iron phosphate batteries. This method involves leaching lithium from positive and negative electrode powders, then performing a two-step acid dissolution process on the leaching residue to recover negative electrode graphite, and finally recovering phosphorus and iron from the acid solution after multiple impurity removal steps. Although this method recovers phosphorus and iron resources from waste LiFePO4 batteries, the acid process used in the entire process route results in numerous impurity removal processes and stringent process requirements, leading to high industrial production costs and making it difficult to promote.

[0005] CN118637569A discloses a method for the comprehensive recovery of P, Fe, and Li from lithium iron phosphate battery black powder. This method involves adding quartz to the lithium iron phosphate battery black powder and performing side-blowing melting at high temperature to obtain volatile phosphorus; adding limestone to the above smelting slag and melting it at high temperature to obtain molten iron; and then leaching lithium from the slag using a hydrometallurgical process. This method uses a pyrometallurgical process to recover P and Fe from lithium iron phosphate battery black powder, which suffers from high energy consumption, demanding equipment requirements, and the inability to guarantee product purity.

[0006] In summary, the currently available recycling technologies for waste lithium iron phosphate batteries, when attempting to comprehensively recycle the resources in the batteries, generally suffer from problems such as excessively long processes, high reagent consumption, or high energy consumption due to the complex composition of raw materials, making it difficult to achieve industrial promotion. Furthermore, none of them have proposed recycling solutions for aluminum resources in waste lithium iron phosphate batteries.

[0007] Therefore, there is an urgent need to provide a simpler and more energy-efficient method for recovering phosphorus and aluminum from lithium iron phosphate battery lithium extraction waste. Summary of the Invention

[0008] To address the aforementioned technical problems, the present invention aims to provide a method for recovering phosphorus and aluminum from lithium iron phosphate battery lithium extraction waste. The method for recovering phosphorus and aluminum from lithium iron phosphate battery lithium extraction waste described in this invention is simple and efficient, achieving simultaneous and efficient extraction of phosphorus and aluminum resources, with a recovery rate of over 92% for phosphorus and aluminum elements.

[0009] To achieve this objective, the present invention adopts the following technical solution:

[0010] In a first aspect, the present invention provides a method for recovering phosphorus and aluminum from lithium iron phosphate battery lithium extraction waste residue, the preparation method comprising the following steps:

[0011] (1) Mix lithium iron phosphate battery lithium extraction waste residue and alkaline solution, and after the first leaching reaction, obtain phosphorus aluminum leachate and leaching residue;

[0012] (2) The phosphorus aluminum leachate obtained in step (1) is mixed with calcium salt and reacted to obtain aluminate solution and phosphorus-rich slag.

[0013] This invention is based on the differences in solubility of various components in lithium iron phosphate battery lithium extraction waste in an alkaline solution environment. By leaching the lithium iron phosphate battery lithium extraction waste in an alkaline solution, the phosphorus and aluminum components in the waste are dissolved. Calcium salts are added to the phosphorus-aluminum leaching solution to react, causing phosphorus and calcium to form insoluble hydroxyaluminate calcium phosphate, resulting in phosphorus-rich slag. Aluminum remains in the liquid phase, forming a pure aluminate solution that can be used to prepare aluminum products, thus achieving the separation of phosphorus and aluminum components. The resulting phosphorus-rich slag can be directly used as high-grade phosphate rock. Alternatively, the phosphorus-rich slag can be further processed through a wet phosphoric acid process (dissolving with acid) to obtain phosphoric acid solution and calcium slag, thereby achieving comprehensive and efficient utilization of the waste.

[0014] The method provided by this invention enables the simultaneous and efficient extraction of phosphorus and aluminum resources, with a phosphorus and aluminum recovery rate of over 92%.

[0015] The following are preferred technical solutions of the present invention, but are not intended to limit the technical solutions provided by the present invention. The technical objectives and beneficial effects of the present invention can be better achieved and realized through the following preferred technical solutions.

[0016] In some embodiments, the lithium iron phosphate battery lithium extraction waste residue in step (1) includes fluorine, sodium, aluminum, phosphorus, sulfur, calcium, iron, cobalt, nickel and graphite.

[0017] The lithium iron phosphate battery lithium extraction waste residue described in this invention is mainly the waste residue produced by the impurity removal process of the leaching solution during the wet recycling of waste lithium iron phosphate batteries, which often forms waste black powder together with the leaching residue.

[0018] In some embodiments, the alkaline solution comprises a sodium hydroxide solution and / or a potassium hydroxide solution, preferably a sodium hydroxide solution.

[0019] In some embodiments, the concentration of hydroxide ions in the alkaline solution is 1 mol / L to 5 mol / L, for example, it can be 1 mol / L, 1.5 mol / L, 2 mol / L, 2.5 mol / L, 3 mol / L, 3.5 mol / L, 4 mol / L, 4.5 mol / L or 5 mol / L, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable, preferably 1.5 mol / L to 2.5 mol / L.

[0020] This invention further controls the concentration of hydroxide ions in the alkaline solution to 1 mol / L-5 mol / L. If the concentration of hydroxide ions is too high, the solubility of Al and P will decrease due to the common ion effect, resulting in a low recovery rate. If the concentration of hydroxide ions is too low, the amount of alkali will be insufficient, the leaching rate of Al and P will be insufficient, and the recovery rate will be low.

[0021] In some embodiments, the liquid-solid mass ratio of the lithium iron phosphate battery lithium extraction waste residue and alkaline solution in step (1) is (1-12):1, for example, it can be 1:1, 2:1, 3:1, 4:1, 5:1, 6:1, 7:1, 8:1, 9:1, 10:1, 11:1 or 12:1, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable, preferably (5-8):1.

[0022] In some embodiments, the first dissolution reaction in step (1) is accompanied by stirring.

[0023] In some embodiments, the temperature of the first dissolution reaction in step (1) is 10℃-100℃, for example, it can be 10℃, 20℃, 30℃, 40℃, 50℃, 60℃, 70℃, 80℃, 90℃ or 100℃, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable, preferably 60℃-90℃.

[0024] This invention further controls the temperature of the first dissolution reaction to be between 10°C and 100°C. Increasing the temperature can accelerate the diffusion of reactants and shorten the reaction time. If the temperature of the first dissolution reaction is too high, the reaction efficiency and recovery rate will not be significantly improved, but energy consumption will increase instead. If the temperature of the first dissolution reaction is too low, the reaction efficiency and recovery rate will be low, affecting the implementation effect.

[0025] In some embodiments, the time for the first dissolution reaction in step (1) is 2 min to 300 min, for example, it can be 2 min, 15 min, 30 min, 50 min, 60 min, 90 min, 120 min, 150 min, 180 min, 210 min, 240 min, 270 min or 300 min, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable, preferably 15 min to 60 min.

[0026] In some embodiments, step (1) after the first leaching reaction is completed and before obtaining the phosphorus aluminum leaching solution and leaching residue, further includes a first solid-liquid separation.

[0027] In some embodiments, the calcium salt in step (2) includes any one or a combination of at least two of calcium oxide, calcium hydroxide, or calcium carbonate. Typical but non-limiting combinations include combinations of calcium oxide and calcium hydroxide, combinations of calcium hydroxide and calcium carbonate, combinations of calcium oxide and calcium carbonate, and combinations of calcium oxide, calcium hydroxide, and calcium carbonate.

[0028] In some embodiments, the molar ratio of calcium in the calcium salt to phosphorus in the aluminum phosphate leachate in step (2) is (0.5-3):1, for example, it can be 0.5:1, 0.8:1, 1:1, 1.2:1, 1.5:1, 1.8:1, 2:1, 2.2:1, 2.5:1, 2.8:1 or 3:1, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable, preferably (1.7-2.2):1.

[0029] This invention further controls the molar ratio of calcium in the calcium salt to phosphorus in the aluminum phosphate leaching solution in step (2) to be (0.5-3):1, Ca 2+ Priority over PO4 3- The calcium-phosphorus aluminate (Ca5(PO4)3(OH)) is formed. The theoretical atomic ratio of calcium to phosphorus is approximately 1.67. The precipitation rate of phosphorus increases with the increase of the Ca / P ratio and then tends to stabilize. If the molar ratio of calcium to phosphorus is too large, the excess calcium is prone to react with aluminum in the solution to form a precipitate, reducing the aluminum recovery rate. If the molar ratio of calcium to phosphorus is too small, the precipitation rate of phosphorus is insufficient, which affects both the recovery rate of phosphorus and the purity of the aluminate solution.

[0030] In some embodiments, the reaction in step (2) is accompanied by stirring.

[0031] In some embodiments, the temperature of the reaction in step (2) is 10℃-100℃, for example, it can be 10℃, 20℃, 30℃, 40℃, 50℃, 60℃, 70℃, 80℃, 90℃ or 100℃, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable, preferably 70℃-100℃.

[0032] In some embodiments, the reaction time in step (2) is 5 min to 300 min, for example, it can be 5 min, 15 min, 30 min, 50 min, 60 min, 90 min, 120 min, 150 min, 180 min, 210 min, 240 min, 270 min or 300 min, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable, preferably 30 min to 120 min.

[0033] In some embodiments, the pH needs to be maintained at 13 or above during the reaction in step (2).

[0034] In some embodiments, a second solid-liquid separation is included after the reaction described in step (2) and before obtaining the aluminate solution and phosphorus-rich slag.

[0035] As a preferred embodiment of the preparation method of the present invention, the preparation method includes the following steps:

[0036] (1) Mix lithium iron phosphate battery lithium extraction waste residue and sodium hydroxide solution with a concentration of 1.5mol / L-2.5mol / L, and carry out the first dissolution reaction at 60℃-90℃ for 15min-60min under stirring conditions. After the first solid-liquid separation, phosphorus aluminum leachate and leachate residue are obtained. The liquid-solid mass ratio of lithium iron phosphate battery lithium extraction waste residue and alkaline solution is (5-8):1.

[0037] (2) Mix the phosphorus aluminum leachate obtained in step (1) with calcium salt, and react at 70℃-100℃ for 30min-120min under stirring conditions. After the second solid-liquid separation, aluminate solution and phosphorus-rich slag are obtained. The molar ratio of calcium element in calcium salt to phosphorus element in phosphorus aluminum leachate is (1.7-2.2):1.

[0038] The numerical range described in this invention includes not only the point values ​​listed above, but also any point values ​​within the numerical ranges not listed above. Due to space limitations and for the sake of brevity, this invention will not exhaustively list all the specific point values ​​included in the range.

[0039] Compared with the prior art, the present invention has at least the following beneficial effects:

[0040] This invention addresses the problem of wasted phosphorus and aluminum resources caused by the large amount of waste black powder generated during the wet recycling of spent lithium iron phosphate batteries. By simultaneously extracting phosphorus and aluminum components from the lithium extraction waste residue of lithium iron phosphate batteries, recyclable aluminate solutions and phosphorus concentrates are obtained. The recovery rates of phosphorus and aluminum elements both reach over 92%, realizing the high-value utilization of lithium iron phosphate battery lithium extraction waste residue. The recycling process and equipment are relatively conventional, simple to operate, and highly practical. Detailed Implementation

[0041] The technical solution of the present invention will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of the present invention and should not be construed as limiting the invention in any way.

[0042] In this invention, the terms "first aspect," "second aspect," "third aspect," "fourth aspect," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance or quantity, nor should they be construed as implicitly indicating the importance or quantity of the indicated technical features. Moreover, "first," "second," "third," "fourth," etc., serve only as a non-exhaustive enumeration and should be understood not to constitute a closed limitation on the quantity.

[0043] Unless otherwise specified, all reagents and consumables used in the following examples and comparative examples were purchased from conventional reagent manufacturers in the art; unless otherwise specified, the experimental methods and techniques used were conventional methods and techniques in the art.

[0044] In the embodiments and comparative examples provided by the present invention, the chemical composition (by mass percentage) of the lithium iron phosphate battery lithium extraction waste residue is shown in Table 1.

[0045] Table 1

[0046]

[0047] Example 1

[0048] This embodiment provides a method for recovering phosphorus and aluminum from lithium iron phosphate battery lithium extraction waste residue, the method comprising the following steps:

[0049] (1) Mix lithium iron phosphate battery lithium extraction waste residue and sodium hydroxide solution with a concentration of 2 mol / L, and carry out the first dissolution reaction at 90°C for 30 min under stirring conditions. After the first solid-liquid separation, phosphorus aluminum leachate and leachate residue are obtained; the liquid-solid mass ratio of lithium iron phosphate battery lithium extraction waste residue and alkaline solution is 6:1.

[0050] (2) The phosphorus aluminum leachate obtained in step (1) is mixed with calcium hydroxide and reacted at 80°C for 90 min under stirring conditions. After the second solid-liquid separation, an aluminate solution and phosphorus-rich slag are obtained. The molar ratio of calcium in calcium hydroxide to phosphorus in phosphorus aluminum leachate is 2:1.

[0051] Example 2

[0052] This embodiment provides a method for recovering phosphorus and aluminum from lithium iron phosphate battery lithium extraction waste residue, the method comprising the following steps:

[0053] (1) Mix lithium iron phosphate battery lithium extraction waste residue and sodium hydroxide solution with a concentration of 1.5 mol / L, and carry out the first dissolution reaction at 60°C for 60 min under stirring conditions. After the first solid-liquid separation, phosphorus aluminum leachate and leachate residue are obtained; the liquid-solid mass ratio of lithium iron phosphate battery lithium extraction waste residue and alkaline solution is 8:1.

[0054] (2) The phosphorus aluminum leachate obtained in step (1) is mixed with calcium oxide and reacted at 100°C for 120 min under stirring conditions. After the second solid-liquid separation, an aluminate solution and phosphorus-rich slag are obtained. The molar ratio of calcium in calcium oxide to phosphorus in phosphorus aluminum leachate is 1.6:1.

[0055] Example 3

[0056] This embodiment provides a method for recovering phosphorus and aluminum from lithium iron phosphate battery lithium extraction waste residue, the method comprising the following steps:

[0057] (1) Mix lithium iron phosphate battery lithium extraction waste residue and sodium hydroxide solution with a concentration of 2.5 mol / L, and carry out the first dissolution reaction at 100℃ for 15 min under stirring conditions. After the first solid-liquid separation, phosphorus aluminum leachate and leach residue are obtained; the liquid-solid mass ratio of lithium iron phosphate battery lithium extraction waste residue and sodium hydroxide solution is 5:1.

[0058] (2) The phosphorus aluminum leachate obtained in step (1) is mixed with calcium carbonate and reacted at 70°C for 30 min under stirring conditions. After the second solid-liquid separation, an aluminate solution and phosphorus-rich slag are obtained. The molar ratio of calcium in calcium carbonate to phosphorus in phosphorus aluminum leachate is 2.2:1.

[0059] Example 4

[0060] This embodiment provides a method for recovering phosphorus and aluminum from lithium iron phosphate battery lithium extraction waste residue, the method comprising the following steps:

[0061] (1) Mix lithium iron phosphate battery lithium extraction waste residue and sodium hydroxide solution with a concentration of 5 mol / L, and carry out the first dissolution reaction at 100℃ for 30 min under stirring conditions. After the first solid-liquid separation, phosphorus aluminum leachate and leach residue are obtained; the liquid-solid mass ratio of lithium iron phosphate battery lithium extraction waste residue and sodium hydroxide solution is 5:1.

[0062] (2) The phosphorus aluminum leachate obtained in step (1) is mixed with calcium hydroxide and reacted at 100°C for 300 min under stirring conditions. After the second solid-liquid separation, an aluminate solution and phosphorus-rich slag are obtained. The molar ratio of calcium in calcium hydroxide to phosphorus in phosphorus aluminum leachate is 3:1.

[0063] Example 5

[0064] This embodiment provides a method for recovering phosphorus and aluminum from lithium iron phosphate battery lithium extraction waste residue. The only difference from Embodiment 1 is that the molar ratio of calcium in calcium hydroxide to phosphorus in aluminum phosphate leaching solution in step (2) is adjusted from 2:1 to 0.1:1, while the other steps remain unchanged.

[0065] Example 6

[0066] This embodiment provides a method for recovering phosphorus and aluminum from lithium iron phosphate battery lithium extraction waste residue. The only difference from Embodiment 1 is that the molar ratio of calcium in calcium hydroxide to phosphorus in aluminum phosphate leaching solution in step (2) is adjusted from 2:1 to 4:1, while the other steps remain unchanged.

[0067] Example 7

[0068] This embodiment provides a method for recovering phosphorus and aluminum from lithium iron phosphate battery lithium extraction waste residue. The only difference from Embodiment 1 is that the concentration of the sodium hydroxide solution in step (1) is adjusted from 2 mol / L to 0.5 mol / L, while the other steps remain unchanged.

[0069] Example 8

[0070] This embodiment provides a method for recovering phosphorus and aluminum from lithium iron phosphate battery lithium extraction waste residue. The only difference from Embodiment 1 is that the concentration of the sodium hydroxide solution in step (1) is adjusted from 2 mol / L to 8 mol / L, while the other steps remain unchanged.

[0071] Comparative Example 1

[0072] This comparative example provides a method for recovering phosphorus and aluminum from lithium iron phosphate battery lithium extraction waste. The only difference from Example 1 is that calcium oxide was not added in step (2) when preparing the lithium iron phosphate battery lithium extraction waste to recover phosphorus and aluminum.

[0073] test:

[0074] The aluminum and phosphorus contents of the aluminate solution and phosphorus-rich slag obtained in step (2) of the examples and comparative examples were tested, and the recovery rate (%) was calculated as follows: (c i ×v i ) / m i m i Represents the mass of aluminum or phosphorus in the raw material, (c i ×vi The product of the volume of the aluminate solution and the concentration of aluminum or the product of the mass of phosphorus-rich slag and the mass content of phosphorus in the slag is used. The element content in the solid phase is measured by ICP-OES after acid digestion, and the element content in the liquid phase is measured by ICP-OES.

[0075] The test results are shown in Table 2 below.

[0076] Table 2

[0077]

[0078] The test results show that:

[0079] (1) As can be seen from Examples 1-4, this invention is based on the difference in solubility of each component in lithium iron phosphate battery lithium extraction waste residue under alkaline solution conditions. By leaching the lithium iron phosphate battery lithium extraction waste residue in alkaline solution, the phosphorus and aluminum components in the residue are dissolved. Calcium salts are added to the phosphorus-aluminum leachate to react, so that phosphorus and calcium form insoluble hydroxyaluminate calcium phosphate, becoming phosphorus-rich residue, while aluminum remains in the liquid phase to form a pure aluminate solution that can be used to prepare aluminum products, thereby achieving the separation of phosphorus and aluminum components. The resulting phosphorus-rich residue can be directly used as high-grade phosphate rock. The method achieves simultaneous and efficient extraction of phosphorus and aluminum resources, with a phosphorus and aluminum element recovery rate of over 92%.

[0080] (2) By comparing Example 1 with Examples 5-6, it can be seen that the present invention further controls the molar ratio of calcium in the calcium salt to phosphorus in the aluminum phosphate leaching solution in step (2) to be (0.5-3):1, Ca 2+ Priority over PO4 3- The calcium-phosphorus aluminate (Ca5(PO4)3(OH)) is formed. The theoretical atomic ratio of calcium to phosphorus is approximately 1.67. The precipitation rate of phosphorus increases with the increase of the Ca / P ratio and then tends to stabilize. If the molar ratio of calcium to phosphorus is too large, the excess calcium is prone to react with aluminum in the solution to form a precipitate, reducing the aluminum recovery rate. If the molar ratio of calcium to phosphorus is too small, the precipitation rate of phosphorus is insufficient, which affects both the recovery rate of phosphorus and the purity of the aluminate solution.

[0081] (3) By comparing Example 1 with Examples 7-8, it can be seen that the present invention further controls the concentration of hydroxide ions in the alkaline solution to 1mol / L-5mol / L. If the concentration of hydroxide ions is too high, the solubility of Al and P will decrease due to the common ion effect, resulting in a low recovery rate. If the concentration of hydroxide ions is too low, the amount of alkali will be insufficient, the leaching rate of Al and P will be insufficient, and the recovery rate will be low.

[0082] (4) As can be seen from Example 1 and Comparative Example 1, the present invention can achieve the technical effect of separating phosphorus and aluminum components by adding calcium salt to the phosphorus aluminum leachate obtained in step (1). However, when calcium salt is not used or is lacking, it cannot achieve the technical effect of obtaining directly recyclable aluminate solution and phosphorus enrichment.

[0083] In summary, this invention addresses the problem of wasted phosphorus and aluminum resources caused by the large amount of waste black powder generated during the wet recycling of spent lithium iron phosphate batteries. By simultaneously extracting phosphorus and aluminum components from the lithium extraction waste residue of lithium iron phosphate batteries, recyclable aluminate solutions and phosphorus concentrates are obtained. The recovery rates of phosphorus and aluminum elements both reach over 92%, achieving high-value utilization of lithium iron phosphate battery lithium extraction waste residue. The recycling process and equipment are relatively conventional, simple to operate, and highly practical.

[0084] The applicant declares that the above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

Claims

1. A method for recovering phosphorus and aluminum from lithium iron phosphate battery lithium extraction waste, characterized in that, The preparation method includes the following steps: (1) Mix lithium iron phosphate battery lithium extraction waste residue and alkaline solution, and after the first leaching reaction, obtain phosphorus aluminum leachate and leaching residue; (2) The phosphorus aluminum leachate obtained in step (1) is mixed with calcium salt and reacted to obtain aluminate solution and phosphorus-rich slag.

2. The method according to claim 1, characterized in that, The alkaline solution in step (1) includes sodium hydroxide solution and / or potassium hydroxide solution; And / or, the concentration of hydroxide ions in the alkaline solution in step (1) is 1 mol / L-5 mol / L.

3. The method according to claim 1 or 2, characterized in that, In step (1), the liquid-solid mass ratio of the lithium iron phosphate battery lithium extraction waste residue and alkaline solution is (1-12):

1.

4. The method according to any one of claims 1-3, characterized in that, In step (1), the temperature of the first dissolution reaction is 10℃-100℃; And / or, the time for the first dissolution reaction in step (1) is 2 min to 300 min.

5. The method according to any one of claims 1-4, characterized in that, Step (1) includes a first solid-liquid separation after the first leaching reaction is completed and before obtaining the phosphorus aluminum leaching solution and leaching residue.

6. The method according to any one of claims 1-5, characterized in that, In step (2), the molar ratio of calcium in the calcium salt to phosphorus in the aluminum phosphate leachate is (0.5-3):

1.

7. The method according to any one of claims 1-6, characterized in that, The reaction temperature in step (2) is 10℃-100℃.

8. The method according to any one of claims 1-7, characterized in that, The reaction time in step (2) is 5 min to 300 min.

9. The method according to any one of claims 1-8, characterized in that, Step (2) includes a second solid-liquid separation after the reaction and before obtaining the aluminate solution and phosphorus-rich slag.

10. The method according to any one of claims 1-9, characterized in that, The preparation method includes the following steps: (1) Mix lithium iron phosphate battery lithium extraction waste residue and sodium hydroxide solution with a concentration of 1.5mol / L-2.5mol / L, and carry out the first dissolution reaction at 60℃-90℃ for 15min-60min under stirring conditions. After the first solid-liquid separation, phosphorus aluminum leachate and leachate residue are obtained. The liquid-solid mass ratio of lithium iron phosphate battery lithium extraction waste residue and alkaline solution is (5-8):

1. (2) Mix the phosphorus aluminum leachate obtained in step (1) with calcium salt, and react at 70℃-100℃ for 30min-120min under stirring conditions. After the second solid-liquid separation, aluminate solution and phosphorus-rich slag are obtained. The molar ratio of calcium element in calcium salt to phosphorus element in phosphorus aluminum leachate is (1.7-2.2):1.

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