Method for recovering lithium phosphate from lithium iron phosphate black powder

Abstract

The invention discloses a method for recovering lithium phosphate from lithium iron phosphate black powder. The method comprises the following steps: mixing black powder recovered from waste lithium iron phosphate batteries with sodium persulfate, and calcining; adding water into the obtained calcined product, dissolving, filtering to obtain water extract A and leaching residues, washing the leaching residues with water, and calcining at high temperature to obtain battery-grade iron phosphate; adding a sodium hydroxide solution into the water extract A, and reacting to obtain a water extract B; adding a trisodium phosphate solution into the water immersion liquid B, fully reacting, performing suction filtration to obtain lithium phosphate and filtrate, and cleaning and drying the lithium phosphate to obtain battery-grade lithium phosphate; and freezing and denitrifying the filtrate to obtain a denitrified solution, and adding the denitrified solution into the sodium hydroxide solution for recycling. The method does not generate wastes, recycles the filtrate in the whole process, theoretically realizes zero loss of the lithium element, prevents the iron element from entering the solution, simplifies the preparation steps of the lithium phosphate, and has the advantages of cost reduction and environmental protection.

Description

Technical Field

[0001] The present invention relates to the field of recycling of waste power lithium-ion batteries, and particularly to a method for recovering lithium phosphate from lithium iron phosphate black powder. Background Art

[0002] LiFePO4 batteries have attracted wide attention and applications due to their excellent thermal stability and cycling performance, especially in the field of new energy vehicles. Lithium batteries have been replaced by LiFePO4 batteries and applied to new energy vehicles. The rapidly growing market will inevitably lead to a large number of battery retirements, and the electrolyte is the main pollution source of the batteries. Therefore, a large number of waste batteries need to be processed. Properly treating waste LiFePO4 batteries can reduce the pollution caused by harmful components to the environment, and can also efficiently recover high-value components in the batteries, especially elements such as lithium and iron, promote resource utilization, and contribute to economic growth. Currently, the demand for lithium elements has been increasing, but natural lithium resources are limited and cannot meet the current production needs. Therefore, it is very necessary to recycle waste LiFePO4 batteries.

[0003] Traditional hydrometallurgy has the advantages of high recovery rate, good selectivity, and low cost, but the recycling process consumes too many chemicals and has a greater impact on the environment. There are existing technologies for recycling waste lithium iron phosphate batteries by acid leaching. Patent CN108899601B discloses a method for recovering lithium and iron from lithium iron phosphate. To recover lithium from lithium iron phosphate, lithium elements are selectively leached, sulfuric acid is added during the process, and iron is removed by adjusting the PH to form hydroxides; the precipitate generated during the leaching process is mainly a compound mainly composed of iron phosphate, which is further prepared into battery-grade iron phosphate, and the lithium phosphate recovered from the lithium carbonate mother liquor can be further prepared into lithium carbonate. This process has a high lithium recovery rate, but the acid leaching solution contains a small amount of iron, resulting in an additional step of removing iron with an oxidant, and the purity of the recovered lithium is not high. A large amount of acid is consumed during the recovery process, causing pollution to the environment. Therefore, it is necessary to establish a more perfect recycling and treatment system for retired batteries, simplify the process operation, ensure that these batteries can be safely treated, realize the recycling of resources, and create higher economic value. Summary of the Invention

[0004] Aiming at the above-mentioned existing technologies, the purpose of the present invention is to provide a method for recovering lithium phosphate from lithium iron phosphate black powder.

[0005] To achieve the above purpose, the present invention adopts the following technical solutions: (1) Mix the lithium iron phosphate black powder separated from waste batteries with sodium persulfate by ball milling evenly, and calcine at high temperature under an inert atmosphere; (2) Add water to the obtained calcined product, fully dissolve it and then filter to obtain a water leaching solution A and leaching residues. Wash the leaching residues and then calcine at high temperature under an oxygen-containing atmosphere to obtain battery-grade iron phosphate; (3) Add sodium hydroxide solution to the water leaching solution A, and obtain water leaching solution B after reaction; (4) Add trisodium phosphate solution to the water leaching solution B, carry out suction filtration after sufficient reaction, obtain lithium phosphate and filtrate, and the lithium phosphate is the battery-grade lithium phosphate after washing and drying; (5) The filtrate is obtained after freezing and denitrification, and can be added to the aforementioned sodium hydroxide solution for recycling.

[0006] Preferably, the mass ratio of the recovered black powder of waste lithium iron phosphate battery to sodium persulfate is 1:1 - 1.5.

[0007] Preferably, in step (1), the calcination temperature is 500 - 700 °C, and the calcination time is 6 - 8 h.

[0008] Preferably, in step (2), the calcination temperature is 700 - 850 °C, and the calcination time is 3 - 5 h.

[0009] Preferably, in step (3), the addition amount of the sodium hydroxide solution is: added until the solution pH ≥ 14.

[0010] Preferably, in step (4), the trisodium phosphate solution is slowly introduced into the water leaching solution B, and the trisodium phosphate is 2% - 5% in excess.

[0011] The beneficial effects of the present invention: 1. The present invention uses sodium persulfate as the lithium ion leaching agent, and does not use acid in the process, so the process cost is lower than that of the process with acid addition in production. And compared with the traditional wet lithium leaching method, in the present invention, the sodium persulfate powder is first ball-milled and mixed with the black powder, and then leached with water after high-temperature calcination reaction, thus avoiding partial iron ions from entering the lithium-containing water leaching solution, and omitting the subsequent step of removing iron from the water leaching solution used for lithium precipitation. The present invention simplifies the steps for recycling waste lithium iron phosphate battery to prepare battery-grade lithium phosphate, and is more environmentally friendly while reducing costs.

[0012] 2. The present invention separates and recovers all iron ions and lithium ions in the black powder of waste lithium iron phosphate battery, and simultaneously obtains the by-product sodium sulfate. The denitrification solution produced can be recycled later and added to the next batch of sodium hydroxide solution for the preparation of lithium phosphate in multiple batches. The present invention not only theoretically realizes no loss of lithium ions during the recovery process, and the lithium extraction rate reaches 100%, but also no waste and waste liquid are generated throughout the process, is environmentally friendly, and is suitable for large-scale production. Description of the Drawings

[0013] Figure 1 It is a process flow chart for recycling waste lithium iron phosphate battery to prepare battery-grade lithium phosphate and iron phosphate.

[0014] Figure 2XRD pattern of the battery-grade lithium phosphate synthesized in Example 1.

[0015] Figure 3 XRD pattern of the battery-grade lithium phosphate synthesized in Example 2.

[0016] Figure 4 XRD pattern of the battery-grade lithium phosphate synthesized in Comparative Example 1.

[0017] Figure 5 XRD pattern of the battery-grade lithium iron phosphate synthesized in Comparative Example 2. Detailed implementation manners

[0018] It should be noted that the following detailed description is exemplary and is intended to provide further explanation of the present application. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the technical field to which this application belongs.

[0019] The following further describes in detail the specific implementation manners of the present invention in conjunction with the examples. The following detailed description is exemplary and is intended to provide further explanation of the present application rather than limiting the scope of the present invention.

[0020] As described in the background art, in view of the problems of low lithium extraction rate, high cost and environmental unfriendliness in the traditional lithium extraction process of lithium iron phosphate batteries, the present invention provides a method for recovering lithium phosphate from lithium iron phosphate black powder, including the following steps: (1) Mix the lithium iron phosphate black powder separated from waste lithium iron phosphate batteries and sodium persulfate in a mass ratio of 1:(1 - 1.5) by ball milling, and then calcine at 500 - 700 °C for 6 - 8 h in an inert atmosphere; (2) Add water to the calcined product for full dissolution and then filter to obtain the aqueous leaching solution A and the leaching residue. Wash the leaching residue and then calcine at 700 - 850 °C for 3 - 5 h in an oxygen-containing atmosphere to obtain battery-grade lithium iron phosphate; (3) Add sodium hydroxide solution to the aqueous leaching solution A until the solution pH ≥ 14, and obtain the aqueous leaching solution B after the reaction; (4) Add trisodium phosphate solution to the aqueous leaching solution B, fully react and then perform suction filtration to obtain lithium phosphate and the filtrate. After washing and drying the lithium phosphate, it is battery-grade lithium phosphate; (5) Freeze and denitrify the filtrate to obtain the denitrified solution, which can be added to the aforementioned sodium hydroxide solution for recycling.

[0021] In step (1) of the present invention, the reaction occurring during calcination under an inert atmosphere protection is 2LiFePO4 + Na2S2O8 = 2FePO4 + Na2SO4 + Li2SO4, where FePO4 is insoluble in water and is filtered out as leaching residue together with carbon in step (2); the reaction occurring during calcination in step (2) is C + O2 = CO2, removing the carbon in the black powder and obtaining battery-grade FePO4; the reactions occurring in step (3) are 2Na2S2O8 + 4NaOH = 4Na2SO4 + O2 + 2H2O and Li2SO4 + 2NaOH = Na2SO4 + 2LiOH; the reaction occurring in step (4) is 3LiOH + 2Na3PO4 = 3NaOH + 2Li3PO4 to obtain battery-grade Li3PO4.

[0022] The raw materials of the present invention are waste lithium iron phosphate black powder. The reagents used are cheap, the process operation is simple, no waste is generated, the requirements for equipment are low, the denitrification liquid can be recycled, it is environmentally friendly, there is no lithium loss, and it is suitable for large-scale production.

[0023] Unless otherwise defined, the technical terms used in the following examples have the same meanings as commonly understood by those skilled in the art to which the present invention pertains. The test reagents used in the following examples are all conventional biochemical reagents unless otherwise specified; the experimental methods are all conventional methods unless otherwise specified. Example 1

[0024] (1) 500 g of black powder recovered from waste lithium iron phosphate batteries is ball-milled and mixed evenly with 500 g of sodium persulfate, and then calcined at 500 °C under nitrogen protection, with the heating rate maintained at 10 °C / min and the heat preservation time of 6 h. After natural cooling, the calcined product is obtained; (2) Water is added to the calcined product obtained in step (1) for full dissolution and then filtered to obtain a water leaching solution and a leaching residue. The leaching residue is washed with water and then calcined at 700 °C under an air atmosphere, with the heating rate maintained at 10 °C / min and the calcination time of 3 h. After natural cooling, it is powdered to obtain battery-grade iron phosphate; (3) Sodium hydroxide solution is added to water leaching solution A until the solution pH = 14, and water leaching solution B is obtained after the reaction; (4) 510 g of sodium phosphate solution is added to water leaching solution B. After full reaction, it is suction-filtered to obtain lithium phosphate and a filtrate. The lithium phosphate is washed and dried to obtain battery-grade lithium phosphate; (5) The filtrate is frozen and denitrified to obtain a denitrification liquid, which can be added to the sodium hydroxide solution described in step (3) for recycling. Example 2

[0025] (1) 500 g of black powder recovered from waste lithium iron phosphate batteries was mixed with 520 g of sodium persulfate by ball milling, and then calcined at 600 °C under nitrogen protection, with the heating rate maintained at 10 °C / min, the holding time was 6 h, and the calcined product was obtained after natural cooling; (2) adding water to the calcined product obtained in step (1) to fully dissolve it and then filtering it to obtain a water extract and a residue. After washing the residue with water, calcining it at a high temperature in an air atmosphere at a temperature of 800°C, with a heating rate maintained at 10°C / min, and a calcination time of 4 hours. After cooling naturally, pulverizing it to obtain battery-grade iron phosphate; (3) adding sodium hydroxide solution to water extract A until the pH value of the solution is 15, and obtaining water extract B after reaction; (4) Add 520 g of trisodium phosphate solution to the water extract B, filter it after sufficient reaction to obtain lithium phosphate and filtrate, and wash and dry the lithium phosphate to obtain battery-grade lithium phosphate; (5) The filtrate is frozen and denitrated to obtain a denitrified liquid, which can be added to the sodium hydroxide solution in step (3) for recycling. Example 3

[0026] (1) 600 g of black powder recovered from waste lithium iron phosphate batteries was mixed with 800 g of sodium persulfate by ball milling, and then calcined at 700 °C under nitrogen protection, with the heating rate maintained at 10 °C / min, the holding time was 7 h, and the calcined product was obtained after natural cooling; (2) adding water to the calcined product obtained in step (1) to fully dissolve it and then filtering it to obtain a water extract and a residue. After washing the residue with water, calcining it at a high temperature in an air atmosphere at a temperature of 850°C, with a heating rate maintained at 10°C / min, and a calcination time of 5 hours. After cooling naturally, pulverizing it to obtain battery-grade iron phosphate; (3) adding sodium hydroxide solution to water extract A until the pH value of the solution is 14, and obtaining water extract B after reaction; (4) Add 515 g of trisodium phosphate solution to the water extract B, filter it after sufficient reaction, and obtain lithium phosphate and filtrate. The lithium phosphate is washed and dried to obtain battery-grade lithium phosphate; (5) The filtrate is frozen and denitrated to obtain a denitrified liquid, which can be added to the sodium hydroxide solution in step (3) for recycling.

[0027] Comparative Example 1: (1) 600 g of black powder recovered from waste lithium iron phosphate batteries was mixed with 900 g of sodium persulfate by ball milling, and then calcined at 700 °C under nitrogen protection, with the heating rate maintained at 10 °C / min, the holding time was 7 h, and the calcined product was obtained after natural cooling; (2) Add water to the calcined product obtained in step (1) for full dissolution and then filter to obtain a water leaching solution and leaching residue. Wash the leaching residue and then perform high-temperature calcination in an air atmosphere at a temperature of 700 °C, with a heating rate maintained at 10 °C / min and a calcination time of 3 h. After natural cooling, powder it to obtain battery-grade iron phosphate; (3) Add sodium hydroxide solution to the water leaching solution A until the solution pH = 14, and obtain water leaching solution B after the reaction; (4) Add 510 g of trisodium phosphate solution to the water leaching solution B. After full reaction, perform suction filtration on it to obtain lithium phosphate and a filtrate. After washing and drying the lithium phosphate, it is battery-grade lithium phosphate; (5) Freeze and denitrify the filtrate to obtain a denitrified solution, which can be added to the sodium hydroxide solution described in step (3) for recycling.

[0028] Comparative Example 2: (1) Mix 600 g of black powder recovered from waste lithium iron phosphate batteries and 850 g of sodium persulfate evenly by ball milling, and then calcine at 650 °C under nitrogen protection, with a heating rate maintained at 10 °C / min and an insulation time of 7 h. After natural cooling, obtain a calcined product; (2) Add water to the calcined product obtained in step (1) for full dissolution and then filter to obtain a water leaching solution and leaching residue. Wash the leaching residue and then perform high-temperature calcination in an air atmosphere at a temperature of 700 °C, with a heating rate maintained at 5 °C / min and a calcination time of 3 h. After natural cooling, powder it to obtain battery-grade iron phosphate; (3) Add sodium hydroxide solution to the water leaching solution A until the solution pH = 14, and obtain water leaching solution B after the reaction; (4) Add 525 g of trisodium phosphate solution to the water leaching solution B. After full reaction, perform suction filtration on it to obtain lithium phosphate and a filtrate. After washing and drying the lithium phosphate, it is battery-grade lithium phosphate; (5) Freeze and denitrify the filtrate to obtain a denitrified solution, which can be added to the sodium hydroxide solution described in step (3) for recycling.

[0029] After collecting the lithium phosphates of Example 1, Comparative Example 1, and Comparative Example 2, use the ICP-OES method to measure the main content of the prepared lithium phosphate to obtain the purity of the lithium phosphate. The measurement results are shown in Table 1: Table 1: Grouping Lithium Phosphate Purity (%) Example 1 Group 99.7 Comparative Example 1 Group 99.6 Comparative Example 2 Group 99.7 The above are only the preferred embodiments of the present application and are not used to limit the present application. For those skilled in the art, the present application can have various changes and modifications. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A method for recovering lithium phosphate from black lithium iron phosphate powder, characterized in that, It includes the following steps: (1) Mix the lithium iron phosphate black powder separated from waste batteries and sodium persulfate evenly by ball milling, and calcine at high temperature under an inert atmosphere; (2) Add water to the obtained calcined product, filter after fully dissolving, to obtain the water leaching solution A and the leaching residue. Wash the leaching residue and calcine at high temperature under an oxygen-containing atmosphere to obtain battery-grade iron phosphate; (3) Add sodium hydroxide solution to the water leaching solution A, and obtain the water leaching solution B after reaction; (4) Add trisodium phosphate solution to the water leaching solution B, carry out suction filtration after sufficient reaction, to obtain lithium phosphate and the filtrate. After lithium phosphate is washed and dried, it is battery-grade lithium phosphate; (5) After the filtrate is frozen and denitrified, the denitrified solution is obtained, which can be added to the aforementioned sodium hydroxide solution for recycling.

2. The method according to claim 1, wherein In step (1), the mass ratio of the recovered black powder of waste lithium iron phosphate batteries to sodium persulfate is 1:1 - 1.

5.

3. The method according to claim 1, characterized in that, In step (1), the calcination temperature is 500 - 700 °C, and the calcination time is 6 - 8 h.

4. The method according to claim 1, wherein In step (2), the calcination temperature is 700 - 850 °C, and the calcination time is 3 - 5 h.

5. The method according to claim 1, wherein In step (3), the addition amount of the sodium hydroxide solution is: added until the solution pH ≥ 14.

6. The method according to claim 1, wherein In step (4), the trisodium phosphate solution is slowly introduced into the water leaching solution B, and the trisodium phosphate is in excess by 2% - 5%.

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