A method for selective leaching and closed-loop circulation of lithium from spent lithium iron phosphate batteries

Abstract

The present invention discloses a method for selectively leaching and closed-loop recycling of lithium from waste lithium iron phosphate batteries. The specific steps of the method are as follows: a mixture of positive and negative electrode materials (black powder) obtained by disassembling, discharging, crushing and sorting waste lithium iron phosphate batteries is mixed with a chloroisocyanuric acid compound, added to water and reacted to obtain a lithium-containing filtrate and a filter residue. The lithium-containing filtrate can be used to prepare lithium carbonate, and the filter residue is mainly composed of iron phosphate, which can be directly used to prepare lithium iron phosphate positive electrode materials after impurity removal and drying. The method of the present invention recovers iron as iron phosphate, avoiding the defect of the existing technology that requires complex separation and purification of the leachate, and realizes efficient selective recovery and green closed-loop recycling of lithium from the black powder of waste lithium iron phosphate batteries. It has the advantages of a short process, high lithium extraction efficiency, and no secondary pollution, and has excellent prospects for industrial application and promotion.

Description

Technical Field

[0001] The present invention relates to the technical field of recycling retired power batteries, and in particular to a method for selectively leaching lithium from waste lithium iron phosphate batteries and conducting a closed-loop circulation. Background Art

[0002] Lithium iron phosphate batteries typically have a lifespan of 5 to 8 years and are currently facing a massive retirement wave. From the perspective of environmental protection and resource recovery, the development of advanced and efficient recycling technologies is a trend that aligns with the principles of green chemistry. Furthermore, the lithium content in spent lithium iron phosphate battery black powder is far higher than that in primary lithium ore resources, making it highly valuable for recycling.

[0003] Currently, the main recycling processes for spent lithium iron phosphate batteries include pyrometallurgy, biological recycling, and hydrometallurgy. Pyrometallurgy involves recovering metals through a series of physical and chemical processes under high-temperature conditions. There are two general methods: direct regeneration and carbothermal reduction. For lithium iron phosphate, direct regeneration shortens the process but places high demands on raw material purity. Carbothermal reduction, on the other hand, causes the lithium to enter the slag phase, making it difficult to recover. Biological recycling utilizes the metabolic processes of microorganisms to extract the target metals from the raw materials into a solution, which is then separated and recovered using hydrometallurgical techniques. The advantages of biological recycling are lower costs and the generation of no significant wastewater or waste gas compared to traditional methods. However, the disadvantage is the longer microbial cultivation cycle. Hydrometallurgy involves contacting the raw materials with water or other liquids, converting the metals from the raw materials into a liquid phase through a chemical reaction, and then separating the metals from the liquid phase to recover the metal components. The advantages of wet recycling are complete metal recovery and ease of operation, but they also generate significant amounts of wastewater and waste residue.

[0004] Existing hydrometallurgical technology generally uses strong acid or strong base as a leaching agent to leach all the valuable metals in the black powder, and then recovers the lithium by adding a precipitant and adjusting the pH value. For example, Chinese patent CN115784191A mixes an inorganic acid aqueous solution without phosphate radicals with a lithium iron phosphate positive electrode material, dissolving the LiFePO4 in the lithium iron phosphate positive electrode material in the inorganic acid aqueous solution, and filtering to obtain a lithium iron phosphate positive electrode material. + 、Fe 2+ 、HPO4 2- 、H2PO4 - PO4 3-and inorganic acid radicals. Then, the various ions in solution A are separated by adjusting the pH value, and finally, lithium iron phosphate is prepared by a hydrothermal method. This method does not require the addition of any of the phosphate, iron and lithium ions, and has good economic efficiency, but the leaching process will produce wastewater containing strong acid, and the various ions in the solution need to be separated, which makes the operation complicated and tedious. Chinese patent CN114196821A places waste lithium iron phosphate powder and oxalic acid in a ball mill and then soaks it in deionized water for 0.5h to 1h to obtain a leaching solution containing lithium ions and a small amount of iron ions. The method recovers lithium elements in the lithium iron phosphate positive electrode material with a leaching rate of up to 100%, while the leaching rate of iron elements is 12.97%. This method reduces the amount of alkaline solvent required for the subsequent recovery of lithium and iron elements, but the leaching rate of iron cannot be ignored, and lithium and iron separation still needs to be carried out in the subsequent operation process.

[0005] In short, most existing technologies have defects such as long processes, complex operations, high separation and purification costs, and low lithium recovery rates. There is an urgent need to develop new processes for selectively and efficiently extracting lithium from waste lithium iron phosphate batteries and then realizing their short-term regeneration. Summary of the Invention

[0006] In response to the above-mentioned problems, the main purpose of the present invention is to provide a method for selectively leaching and closed-loop recycling of lithium from waste lithium iron phosphate batteries. The present invention relates to a method for selectively recovering lithium from waste lithium iron phosphate batteries in a short-range manner. This method recovers iron in the form of iron phosphate through solid-liquid separation, avoiding the disadvantage of the prior art of requiring complex separation and purification of the leachate. It achieves efficient selective recovery and green closed-loop recycling of lithium from waste lithium iron phosphate battery black powder. It has the advantages of a short process, high lithium extraction efficiency, and no secondary pollution, and has excellent prospects for industrial application and promotion.

[0007] The present invention solves the above technical problems through the following technical solutions:

[0008] A method for selectively leaching lithium from spent lithium iron phosphate batteries and conducting a closed-loop circulation, the method comprising the following steps:

[0009] (1) Dismantling waste lithium iron phosphate batteries into battery cells, discharging, crushing and sorting to obtain black powder rich in positive electrode active materials;

[0010] (2) fully mixing the black powder obtained in step (1) with a chloroisocyanuric acid compound, adding the mixture to water and reacting the mixture, and after the reaction is completed, performing solid-liquid separation to obtain a lithium-containing leachate and a filter residue;

[0011] In the present invention, the chloroisocyanuric acid compound described in step (2) is one or a mixture of two or more of trichloroisocyanuric acid, dichloroisocyanuric acid, chlorobromoisocyanuric acid, sodium dichloroisocyanurate, potassium dichloroisocyanurate, sodium trichloroisocyanurate, and potassium trichloroisocyanurate.

[0012] In the present invention, in step (2), the mass ratio of battery black powder to chloroisocyanuric acid compound is 1:0.25-1:10, the amount of water used for leaching is 50-500 mL, the reaction temperature is 20-80° C., the leaching time is 5-180 min, and the initial pH value of the solution during the leaching process is 1-7. Further preferably, in step (2), the mass ratio of battery black powder to chloroisocyanuric acid compound is 1:1-1:5, the amount of water used for leaching is 50-150 mL, the reaction temperature is 20-80° C., the leaching time is 30-120 min, and the initial pH value of the solution during the leaching process is 3-5.

[0013] The present invention also provides a method for selectively leaching lithium from waste lithium iron phosphate batteries and conducting a closed-loop circulation, which further comprises the following steps:

[0014] (3) evaporating and concentrating the lithium-containing leachate obtained in step (2), adding a saturated sodium carbonate solution thereto, recovering the lithium in the form of lithium carbonate precipitate, and obtaining battery-grade lithium carbonate with a purity higher than 99.5% after multiple washing and drying;

[0015] (4) washing and drying the filter residue obtained in step (2) to obtain a powder with iron phosphate as the main component, and preparing a lithium iron phosphate positive electrode material precursor after impurity removal, purification and drying;

[0016] (5) The battery-grade lithium carbonate obtained in step (3) is mixed with the positive electrode material precursor obtained in step (4) and calcined at high temperature to prepare a lithium iron phosphate positive electrode material.

[0017] In the present invention, in step (3), the temperature of evaporating and concentrating the lithium-containing filtrate is 80-100° C., the amount of the concentrated lithium-containing filtrate is 5-20 mL, the sodium carbonate precipitation time is 60-180 min, and water at 80-100° C. is used when washing the lithium carbonate.

[0018] In the present invention, in step (4), the impurity removal method is mainly flotation, which uses the characteristic of graphite easily floating on water to separate graphite and iron phosphate, and the drying temperature is 80-105°C.

[0019] In the present invention, in step (5), the calcination temperature is 500-750° C., and the calcination time is 3-10 hours.

[0020] Compared with the prior art, the present invention has the following beneficial effects:

[0021] (1) The present invention provides a method for selectively leaching and closed-loop recycling of lithium from waste lithium iron phosphate batteries, which uses chloroisocyanuric acid compounds as leaching agents to selectively leach lithium from waste lithium iron phosphate batteries. Under optimal conditions, the lithium leaching rate reaches 100%, while the iron leaching rate is only 0.05%. The main component of the filter residue is iron phosphate. The precursor of the lithium iron phosphate positive electrode material is prepared by separation, purification and impurity removal. The impurity removal method is mainly flotation, which uses the characteristic of graphite that it easily floats on water to separate graphite and iron phosphate, thereby achieving selective leaching of lithium from waste lithium iron phosphate batteries and closed-loop recycling of the positive electrode material.

[0022] (2) The present invention provides a method for selectively leaching and closed-loop circulation of lithium from waste lithium iron phosphate batteries. After leaching, no additional reagents need to be added to separate lithium and iron, which solves the problem of short-range and efficient recycling of black powder. It has the advantages of low reagent consumption, short process, low cost, and high lithium recovery rate.

[0023] (3) The present invention provides a method for selective leaching and closed-loop circulation of lithium from waste lithium iron phosphate batteries. Starting from the physical and chemical properties of black powder from waste lithium iron phosphate batteries, the entire recycling process is clean and free of secondary pollution. It can effectively improve the recycling rate of battery positive electrode materials, reduce material recycling costs, and has broad prospects for industrial application. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 The figure is a process flow chart for selectively leaching and recovering lithium from waste lithium iron phosphate batteries according to the present invention.

[0025] Figure 2 The XRD pattern of the filter residue obtained in Example 1 is shown.

[0026] Figure 3 This is the XRD pattern of the lithium precipitation product obtained in Example 1. DETAILED DESCRIPTION

[0027] The technical solution of the present invention is described in detail below with reference to the accompanying drawings and embodiments.

[0028] Figure 1 The process flow chart of the present invention for selectively leaching and recovering lithium from waste lithium iron phosphate battery black powder is as follows:

[0029] (1) Dismantling waste lithium iron phosphate batteries into battery cells, discharging, crushing and sorting to obtain black powder rich in positive electrode active materials;

[0030] (2) fully mixing the black powder obtained in step (1) with a chloroisocyanuric acid compound, adding the mixture to water and reacting the mixture, and after the reaction is completed, performing solid-liquid separation to obtain a lithium-containing leachate and a filter residue;

[0031] (3) evaporating and concentrating the lithium-containing leachate obtained in step (2), adding a saturated sodium carbonate solution thereto, recovering the lithium in the form of lithium carbonate precipitate, and obtaining battery-grade lithium carbonate with a purity higher than 99.5% after multiple washing and drying;

[0032] (4) washing and drying the filter residue obtained in step (2) to obtain a powder with iron phosphate as the main component, and preparing a lithium iron phosphate positive electrode material precursor after impurity removal, purification and drying;

[0033] (5) The battery-grade lithium carbonate obtained in step (3) is mixed with the positive electrode material precursor obtained in step (4) and calcined at high temperature to prepare a lithium iron phosphate positive electrode material.

[0034] The chloroisocyanuric acid compound described in step (2) is one or a mixture of two or more of trichloroisocyanuric acid, dichloroisocyanuric acid, chlorobromoisocyanuric acid, sodium dichloroisocyanurate, potassium dichloroisocyanurate, sodium trichloroisocyanurate, and potassium trichloroisocyanurate.

[0035] The mass ratio of battery black powder to chloroisocyanuric acid compounds in the leaching process in step (2) is 1:0.25 to 1:10.

[0036] The amount of water used for leaching in step (2) is 50 to 500 mL.

[0037] The leaching time in step (2) is 5 to 180 minutes.

[0038] The reaction temperature in step (2) is 10-100°C.

[0039] The initial pH value of the solution during the leaching process in step (2) is 1 to 7.

[0040] The temperature for evaporating and concentrating the lithium-containing filtrate in step (4) is 80-100° C., and the amount of the lithium-containing filtrate after concentration is 5-20 mL.

[0041] The precipitation time of adding sodium carbonate in step (4) is 60 to 180 minutes, and the water temperature for washing lithium carbonate is 80 to 100°C.

[0042] The filter residue obtained in step (5) is mainly composed of iron phosphate.

[0043] The temperature of drying the filter residue in step (5) is 80-105°C.

[0044] The calcination temperature in step (6) is 500-750° C., and the calcination time is 3-10 hours.

[0045] Example 1

[0046] A method for selectively leaching lithium from spent lithium iron phosphate batteries and closed-loop recycling, comprising the following steps:

[0047] (1) Determination of metal content in samples

[0048] A 0.1g sample of dried spent lithium iron phosphate battery black powder was placed in a digestion vessel. 6mL of concentrated hydrochloric acid, 2mL of concentrated nitric acid, and 2mL of deionized water were then added. The vessel was then placed in a microwave digester. After digestion, the volume was fixed to 100mL and the solution was diluted 10-fold and 100-fold, respectively. The metal content was then quantitatively determined using an ICP-OES (ICAP700) from ThermoFisher Scientific. The results are shown in Table 1.

[0049] Table 1 Main components of waste lithium iron phosphate battery black powder

[0050] element Li Fe Content (wt.%) 3.30 21.85

[0051] (2) Selective leaching of lithium by sodium dichloroisocyanurate system

[0052] 1g of black powder was placed in a beaker. 3g of sodium dichloroisocyanurate was added to the beaker and mixed thoroughly with the black powder. The mass ratio of black powder to sodium dichloroisocyanurate was controlled at 1:3. The leaching water volume was 100mL, the reaction temperature was 30°C, and the initial pH of the solution was 4. The beaker containing the mixed sample was allowed to stand for 60 minutes before vacuum filtration to separate the lithium-containing filtrate and the residue. The residue was washed with ultrapure water, and the washing solution was added to the filtrate. The metal ion content in the filtrate was measured using ICP-OES. The washed residue was dried in an oven at 105°C for 24 hours and weighed. The phase composition of the residue was then determined using XRD. 0.1g of the sample was digested and the metal ion content in the digestion solution was determined using ICP-OES. The lithium and iron leaching rates were calculated using the following formulas.

[0053]

[0054]

[0055] Where, LE M is the leaching rate of metal M (%);

[0056] C L is the concentration of the metal in the leachate (measured by ICP, g / L);

[0057] V L is the volume of the leachate (L);

[0058] m Z is the mass of the filter residue (weighed after drying at 105 °C for 24 h, g);

[0059] W is the mass fraction of metal in the filter residue (%);

[0060] C Z is the concentration of metal in the digestion solution (measured by ICP, g / L);

[0061] M is the weight of the filter residue (g).

[0062] The leaching rate of lithium using sodium dichloroisocyanurate as the leaching agent was as high as 100%, while the leaching rate of iron was only 0.05%. The filter residue was then tested using XRD (Bruker D8 ADVANCE) from Bruker, Germany. The results are shown in Figure 2. Figure 2 It can be seen that the main phase of the filter residue is iron phosphate. This means that efficient and selective leaching of lithium from waste lithium iron phosphate battery black powder is achieved.

[0063] (3) Lithium carbonate recovery

[0064] The lithium-containing filtrate and washing liquid obtained after leaching were collected, evaporated and concentrated to 15 mL at 95°C, and saturated sodium carbonate solution was added thereto to obtain a lithium precipitated product. The product was dried in an oven at 105°C for 24 h and then detected by XRD (Bruker D8 ADVANCE) from Bruker, Germany. The results are shown in FIG. Figure 3 It can be seen that the main phase of lithium precipitation products is lithium carbonate.

[0065] (4) Synthesis of lithium iron phosphate

[0066] The resulting filter residue is washed with pure water, dried, and then, utilizing graphite's tendency to float on water, removed by flotation to produce the cathode material precursor. A certain amount of lithium carbonate and cathode material precursor, ensuring a lithium:iron molar ratio of 1:1, are mixed and calcined under a nitrogen atmosphere at 650°C for 9 hours to obtain lithium iron phosphate.

[0067] Example 2

[0068] This embodiment differs from Example 1 in that the mass ratio of battery black powder to sodium dichloroisocyanurate in the leaching experiment in step (2) is 1:5, the reaction temperature is 40° C., and the initial pH of the leaching solution is 7. Other conditions are the same as in Example 1. The leaching rate of lithium in the sodium dichloroisocyanurate system was measured to be 98.85%, while the leaching rate of iron was 0.57%, thus achieving efficient and selective leaching of lithium from waste lithium iron phosphate battery black powder.

[0069] Example 3

[0070] This embodiment differs from Example 1 in that the mass ratio of battery black powder to sodium dichloroisocyanurate in the leaching experiment in step (2) is 1:1, the reaction temperature is 80° C., and the initial pH of the leaching solution is 5. Other conditions are the same as in Example 1. The leaching rate of lithium in the sodium dichloroisocyanurate system was measured to be 100%, while the leaching rate of iron was 0.18%, thus achieving efficient and selective leaching of lithium from waste lithium iron phosphate battery black powder.

[0071] Example 4

[0072] This embodiment differs from Example 1 in that the chloroisocyanuric acid compound used in step (2) is trichloroisocyanuric acid, and the other steps are the same as in Example 1. The lithium leaching rate in the trichloroisocyanuric acid system was measured to be 97.31%, while the iron leaching rate was 0.42%, thus achieving efficient and selective leaching of lithium from waste lithium iron phosphate battery black powder.

[0073] Comparative Example 1

[0074] This comparative example differs from Example 1 in that, in step (2), aqueous hydrogen peroxide was used instead of a chloroisocyanuric acid compound, and the initial pH of the leaching solution was 7. All other conditions were the same as in Example 1. The measured lithium leaching rate was 44.09%, and the iron leaching rate was 0.06%. Efficient lithium leaching was not possible in this case, so the use of a chloroisocyanuric acid compound as the leaching agent in the leaching process is a key feature of the present invention.

[0075] Comparative Example 2

[0076] This comparative example differs from Example 1 in that the mass ratio of battery black powder to sodium dichloroisocyanurate in the leaching experiment in step (2) was 1:0.25, and all other conditions were the same as in Example 1. The measured lithium leaching rate was 42.77%, while the iron leaching rate was 0.04%. Efficient lithium leaching was not achieved at this point, so the appropriate mass ratio between battery black powder and sodium dichloroisocyanurate during the leaching process is an important factor affecting the selective leaching of lithium.

[0077] Comparative Example 3

[0078] This comparative example differs from Example 1 in that the pH value of the leaching experiment in step (2) was 8; otherwise, the same as in Example 1 was used. The measured lithium leaching rate was 43.37%, while the iron leaching rate was 0.03%. Efficient lithium leaching was not achieved at this point, so the appropriate pH value during the leaching process is an important factor affecting the selective leaching of lithium.

[0079] The leaching rate data of lithium and iron in Examples 1 to 4 are summarized in Table 2.

[0080] Table 2 Lithium and iron leaching rates in different embodiments

[0081] Metal leaching rate (%) Example 1 Example 2 Example 3 Example 4 lithium 100 98.85 100 97.31 iron 0.05 0.57 0.18 0.42

[0082] As shown in Table 2, using chloroisocyanuric acid compounds as leaching agents for waste lithium iron phosphate battery black powder effectively achieves selective leaching of lithium. This effectively solves the problem of existing technologies requiring additional lithium and iron separation in the leachate, achieving efficient and selective leaching of lithium from waste lithium iron phosphate battery black powder.

[0083] The basic principles, main features and advantages of the present invention are shown and described above. It should be understood by those skilled in the art that the present invention is not limited to the above embodiments. The above embodiments and descriptions are merely illustrative of the principles of the present invention. Various changes and modifications may be made to the present invention without departing from the spirit and scope of the present invention. Such changes and modifications are intended to fall within the scope of the present invention, which is defined by the appended claims and their equivalents.

Claims

1. A method for selectively leaching lithium from waste lithium iron phosphate batteries, characterized in that: The method comprises the following steps: (1) Dismantle the waste lithium iron phosphate battery into battery cells, and obtain black powder rich in positive electrode active materials after discharge, crushing and sorting; (2) The black powder obtained in step (1) is fully mixed with a chloroisocyanuric acid compound, and then added to water for reaction. After the reaction is completed, solid-liquid separation is performed to obtain a lithium-containing leachate and a filter residue; wherein: The chloroisocyanuric acid compound described in step (2) is one or a mixture of two or more of trichloroisocyanuric acid, dichloroisocyanuric acid, chlorobromoisocyanuric acid, sodium dichloroisocyanurate, potassium dichloroisocyanurate, sodium trichloroisocyanurate, and potassium trichloroisocyanurate; the mass ratio of battery black powder to chloroisocyanuric acid compound is 1:1~1:5, the amount of water used for leaching is 50~150mL, the reaction temperature is 20~80℃, the leaching time is 30~120min, and the initial pH value of the solution during the leaching process is 3~5.

2. A method for selective leaching and closed-loop circulation of lithium from waste lithium iron phosphate batteries according to claim 1, characterized in that: The following steps are also included: (3) evaporating and concentrating the lithium-containing leachate obtained in step (2), adding a saturated sodium carbonate solution thereto, recovering the lithium in the form of lithium carbonate precipitate, and obtaining battery-grade lithium carbonate with a purity higher than 99.5% after multiple washing and drying; (4) washing and drying the filter residue obtained in step (2) to obtain a powder with iron phosphate as the main component, and preparing a lithium iron phosphate positive electrode material precursor after impurity removal, purification and drying; (5) The battery-grade lithium carbonate obtained in step (3) is mixed with the cathode material precursor obtained in step (4) and calcined at high temperature to prepare a lithium iron phosphate cathode material.

3. The method for selective leaching and closed-loop circulation of lithium from waste lithium iron phosphate batteries according to claim 2, characterized in that: In step (3), the temperature of the evaporation and concentration of the lithium-containing leachate is 80-100°C, the amount of the concentrated lithium-containing leachate is 5-20 mL, the precipitation time of adding sodium carbonate is 60-180 min, and the temperature of the water when washing the lithium carbonate is 80-100°C.

4. The method for selective leaching and closed-loop circulation of lithium from waste lithium iron phosphate batteries according to claim 2, characterized in that: In step (4), the impurity removal method is mainly flotation, which uses the characteristic of graphite that it easily floats on water to separate graphite and iron phosphate, and the drying temperature is 80~105℃.

5. The method for selective leaching and closed-loop circulation of lithium from waste lithium iron phosphate batteries according to claim 2, characterized in that: In step (5), the calcination temperature is 500-750°C, and the calcination time is 3-10 hours.

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