Method for recycling all components of lithium iron phosphate waste

Abstract

The invention provides a method for recycling all components of a lithium iron phosphate waste material, which comprises the following steps: mixing the lithium iron phosphate waste material with an acid leaching solution, carrying out first-stage leaching, carrying out solid-liquid separation to obtain a first leaching solution and a first leaching residue, and removing impurities from the first leaching solution to obtain a lithium-rich solution; mixing the first leaching residues with an alkaline leaching solution, carrying out second-stage leaching, carrying out solid-liquid separation to obtain a second leaching solution and second leaching residues, and carrying out impurity removal on the second leaching solution to obtain a phosphorus-rich solution; mixing the lithium-rich solution with the phosphorus-rich solution, carrying out precipitation reaction, and carrying out solid-liquid separation to obtain lithium phosphate and a precipitation mother solution; and mixing the second leaching residue with a precipitation mother solution, carrying out third-stage leaching, carrying out solid-liquid separation to obtain an iron-rich solution, and carrying out evaporative crystallization on the iron-rich solution to obtain the iron-containing product. According to the method disclosed by the invention, efficient separation and all-component closed-loop recovery of lithium, phosphorus and iron elements are realized through a coupling synergistic process of step-by-step precise leaching, directional precipitation and internal circulation collaboration.

Description

Technical Field

[0001] This invention relates to the field of waste lithium-ion battery resource utilization technology, and in particular to a method for the full-component recycling of lithium iron phosphate waste. Background Technology

[0002] With the rapid development of the global energy transition and the new energy vehicle industry, lithium-ion batteries, especially lithium iron phosphate batteries, have become the mainstream choice in the power and energy storage fields due to their high safety, long cycle life, and cost advantages. However, the average lifespan of lithium batteries is about 5-8 years, which means that the first batch of batteries installed on a large scale has entered their retirement period. If they cannot be efficiently and environmentally utilized, it will lead to serious environmental pollution and resource waste. Recycling used lithium iron phosphate batteries can not only build an independent and controllable supply chain, but also avoid the potential harm of heavy metals and electrolytes to the environment, making it a key link in achieving a green, low-carbon, and circular economy.

[0003] Currently, the mainstream recycling technology for waste lithium iron phosphate is "selective lithium extraction," which uses controlled acid leaching conditions to preferentially leach lithium, obtaining a lithium-rich solution for the preparation of lithium salts such as lithium carbonate. However, this process generates a large amount of byproduct—iron phosphate slag. This slag has a complex phase composition, and traditional treatment methods often involve stockpiling or using it as a low-value-added building material raw material. The phosphorus element within it fails to achieve high-value recovery, resulting in the loss of valuable phosphorus resources and creating new solid waste disposal challenges. Furthermore, traditional wet recycling processes typically involve the use of large amounts of acidic and alkaline media, and the resulting saline wastewater can easily cause water pollution if not properly treated. In addition, existing technologies mostly focus on the extraction of single valuable metals (especially lithium), lacking an efficient and economical integrated solution for the synergistic recovery of iron and phosphorus, which constitute a larger proportion of the battery.

[0004] Therefore, developing a new technology that can simultaneously and efficiently recover all components of lithium, phosphorus, and iron from lithium iron phosphate waste, and achieve internal circulation of the medium and near-zero emissions of waste residue, has become an urgent need to break through industry bottlenecks and improve the overall economic and environmental benefits of the recycling industry. Summary of the Invention

[0005] In view of the problems existing in the prior art, the present invention provides a method for the full-component recycling of lithium iron phosphate waste. The method is simple, easy to operate, and highly practical. It can realize the resource utilization of waste lithium-ion batteries at a low cost. At the same time, the pollution of the entire process can be basically zero, effectively avoiding secondary pollution, and has good potential for industrial application.

[0006] To achieve this objective, the present invention adopts the following technical solution:

[0007] In a first aspect, the present invention provides a method for the complete recycling of lithium iron phosphate waste, the method comprising the following steps:

[0008] Lithium iron phosphate waste is mixed with acidic leachate for the first stage of leaching. After solid-liquid separation, the first leachate and the first leachate residue are obtained. The first leachate is then purified to obtain a lithium-rich solution.

[0009] The first leaching residue is mixed with an alkaline leaching solution for a second leaching process. After solid-liquid separation, a second leaching solution and a second leaching residue are obtained. The second leaching solution is then purified to obtain a phosphorus-rich solution.

[0010] The lithium-rich solution and the phosphorus-rich solution are mixed to carry out a precipitation reaction. After solid-liquid separation, the lithium phosphate and the precipitate mother liquor are obtained.

[0011] The second leaching residue is mixed with the precipitate mother liquor and subjected to a third leaching process. After solid-liquid separation, an iron-rich solution is obtained. The iron-rich solution is then evaporated and crystallized to obtain the iron-containing product.

[0012] This invention achieves efficient separation and closed-loop recovery of lithium, phosphorus, and iron through a coupled and synergistic process of "stepwise precise leaching - directional precipitation - internal circulation synergy." The stepwise leaching sequence and key process parameters are designed to control the separation difficulty from the source, maximize the utilization of endogenous matter and energy, and ultimately achieve efficient and low-consumption recovery of all components. In the first stage of leaching, controlling the H / Li ratio ensures efficient lithium leaching while minimizing premature dissolution of Fe and P, resulting in a pure lithium-rich solution and leaving a relatively intact phosphorus-iron slag for subsequent steps. This avoids the problem of impurity co-dissolution caused by excessive acid leaching in traditional methods and simplifies the subsequent purification process. In the second stage of leaching, a high concentration of OH... - It can efficiently convert phosphorus into PO4 3- The phosphorus and iron are dissolved in a form that simultaneously transforms iron into a stable Fe(OH)3 precipitate, thus achieving efficient and clean separation. The success of this step highly depends on the protection of the phosphorus-iron structure in the first stage. Furthermore, the mother liquor from the precipitate is recycled in a closed loop for iron leaching, significantly reducing the consumption of fresh acid and alkali raw materials and the generation of wastewater and waste salts. This effectively solves the problems of high operating costs and significant secondary pollution risks associated with traditional wet processes. These parameters collectively constitute a precise process window; any deviation will trigger a chain of negative effects, reducing the overall technological value.

[0013] As a preferred embodiment of the present invention, the acidic leachate comprises an inorganic strong acid.

[0014] Preferably, the inorganic strong acid includes any one or a combination of at least two of sulfuric acid, hydrochloric acid, or nitric acid.

[0015] The concentration of the acid solution in this invention can be adjusted according to the type of acid, the lithium content in the lithium iron phosphate, and the inlet / outlet effect, and is not further limited here.

[0016] Preferably, in the acidic leachate, the molar ratio of hydrogen ions to lithium in the lithium iron phosphate waste is (0.8-1.2):1, for example, it can be 0.8:1, 0.9:1, 1.0:1, 1.1:1 or 1.2:1, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0017] Controlling the concentration of hydrogen ions and lithium in lithium iron phosphate waste within this range is key to achieving selective lithium extraction. When the molar ratio is below 0.8, insufficient acid leads to a significant decrease in lithium leaching rate; when the molar ratio is above 1.2, excessive acid disrupts the crystal structure of lithium iron phosphate, resulting in a large amount of co-dissolution of iron and phosphorus, reducing leaching selectivity while increasing the subsequent impurity removal load and cost. This optimized range ensures efficient lithium ion leaching while suppressing the leaching rates of iron and phosphorus at a low level, thereby achieving efficient initial separation of lithium from iron and phosphorus.

[0018] As a preferred technical solution of the present invention, the leaching temperature of the first stage is 50-80℃, for example, it can be 50℃, 55℃, 60℃, 65℃, 70℃, 75℃ or 80℃, etc., but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0019] Preferably, the leaching time for the first stage is 15-120 min, for example, it can be 15 min, 25 min, 35 min, 45 min, 55 min, 65 min, 75 min, 85 min, 95 min, 105 min or 120 min, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0020] As a preferred embodiment of the present invention, the alkaline leachate comprises an inorganic alkali.

[0021] Preferably, the inorganic base includes any one or a combination of at least two of sodium hydroxide, potassium hydroxide, or ammonia water.

[0022] As a preferred embodiment of the present invention, the concentration of alkali in the second leaching system is 3-15 mol / L, for example, it can be 3 mol / L, 5 mol / L, 7 mol / L, 9 mol / L, 11 mol / L, 13 mol / L or 15 mol / L, etc., but is not limited to the listed values, and other unlisted values ​​within the range are also applicable; the liquid-solid ratio of the second leaching system is (3-10) mL / g, for example, it can be 3 mL / g, 4 mL / g, 5 mL / g, 6 mL / g, 7 mL / g, 8 mL / g, 9 mL / g or 10 mL / g, etc., but is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0023] This invention controls the liquid-to-solid ratio within this range, which is key to balancing leaching efficiency, process economy, and subsequent processing load. When the liquid-to-solid ratio is below 3 mL / g, the system viscosity is too high, resulting in poor solid-liquid mixing and mass transfer, which easily leads to a decrease in phosphorus leaching rate and is not conducive to solid-liquid separation. When the liquid-to-solid ratio is above 10 mL / g, although it is beneficial to mass transfer, it significantly increases the volume of subsequent solution processing, leading to a sharp increase in evaporation and concentration energy consumption, reducing equipment utilization, and increasing operating costs. Within this preferred liquid-to-solid ratio range, both efficient phosphorus leaching and reasonable material throughput and process energy consumption can be ensured, which is conducive to achieving the economic feasibility and engineering operability of the overall process.

[0024] Preferably, the leaching temperature of the second stage is 50-90℃, for example, it can be 50℃, 55℃, 60℃, 65℃, 70℃, 75℃, 80℃, 85℃ or 90℃, etc., but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0025] Preferably, the leaching time for the second stage is 15-120 min, for example, it can be 15 min, 25 min, 35 min, 45 min, 55 min, 65 min, 75 min, 85 min, 95 min, 105 min or 120 min, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0026] As a preferred technical solution of the present invention, the molar ratio of lithium ions to phosphorus ions in the precipitation reaction is (3.0-3.2):1, for example, it can be 3.0:1, 3.1:1 or 3.2:1, etc., but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0027] Preferably, the temperature of the precipitation reaction is 60-95℃, for example, it can be 60℃, 65℃, 70℃, 75℃, 80℃, 85℃, 90℃ or 95℃, etc., but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0028] Preferably, the endpoint pH value of the precipitation reaction is 10-12, for example, it can be 10, 11 or 12, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0029] As a preferred technical solution of the present invention, after the precipitation reaction is completed, the product is aged at the reaction temperature for 2-4 hours, for example, 2 hours, 2.5 hours, 3 hours, 3.5 hours or 4 hours, etc., but not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0030] As a preferred technical solution of the present invention, the leaching temperature of the third stage is 50-80℃, for example, it can be 50℃, 55℃, 60℃, 65℃, 70℃, 75℃ or 80℃, etc., but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0031] Preferably, the free acid concentration of the iron-rich solution is 0.1-0.5 mol / L, for example, it can be 0.1 mol / L, 0.2 mol / L, 0.3 mol / L, 0.4 mol / L or 0.5 mol / L, etc., but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0032] As a preferred technical solution of the present invention, the evaporation crystallization includes: evaporating and concentrating the iron-rich solution, and then slowly cooling it to 20-30°C to crystallize.

[0033] As a preferred technical solution of the present invention, the lithium iron phosphate waste includes the positive electrode active material obtained after decommissioned lithium iron phosphate batteries are crushed and sorted.

[0034] Compared with existing technical solutions, the present invention has at least the following beneficial effects:

[0035] (1) This invention achieves efficient separation and closed-loop recovery of lithium, phosphorus and iron elements through a coupled efficiency enhancement process of “stepwise precise leaching-directional precipitation-internal circulation synergy”. The leaching rate of lithium and phosphorus can reach more than 99.9%. Moreover, the method is simple, easy to operate and highly practical, and can realize the resource utilization of waste lithium-ion batteries at a low cost.

[0036] (2) This invention provides a convenient and feasible method for obtaining regenerated lithium phosphate. The purity of the obtained lithium phosphate product can reach more than 99.9%. At the same time, the pollution of the whole process can be basically zero, effectively avoiding secondary pollution and having good industrial application potential. Attached Figure Description

[0037] Figure 1 This is a process flow diagram of lithium iron phosphate waste recycling of lithium phosphate according to the present invention. Detailed Implementation

[0038] To facilitate understanding of the present invention, the following embodiments are provided. Those skilled in the art should understand that these embodiments are merely illustrative and should not be construed as limiting the scope of the invention.

[0039] In one specific embodiment, the present invention provides a method for the complete recycling of lithium iron phosphate waste, the method comprising the following steps:

[0040] Preparation of lithium-rich solution: Lithium iron phosphate waste is mixed with a first acidic leachate for the first stage of leaching, wherein the acid is nitric acid, the molar ratio (H / Li) of hydrogen ions to lithium in the lithium iron phosphate waste in the first acidic leachate is (0.8-1.2):1, the temperature of the first stage of leaching is 50-80℃, and the time is 15-120 min; after solid-liquid separation, the first leachate and the first leachate residue are obtained; the first leachate is purified to obtain a lithium-rich solution.

[0041] Preparation of phosphorus-rich solution: The first leaching residue is mixed with the second alkaline leaching solution for a second stage of leaching, wherein the alkali is ammonia water, the liquid-to-solid ratio of the second stage of leaching is (3-10) mL / g, the temperature is 50-90℃, and the time is 15-120 min; after solid-liquid separation, the second leaching solution and the second leaching residue are obtained; the second leaching solution is purified to obtain a phosphorus-rich solution.

[0042] Lithium phosphate preparation: The lithium-rich solution and the phosphorus-rich solution are mixed for precipitation reaction, wherein the molar ratio of lithium ions to phosphorus (Li / P) in the solution is (3.0-3.2):1, the precipitation reaction temperature is 60-95℃, and the final pH value of the reaction is 10-12; after the precipitation reaction is completed, the solution is aged at the reaction temperature for 2-4 h; after solid-liquid separation, lithium phosphate product and third leachate are obtained.

[0043] Preparation of iron-containing products: The second leaching residue is mixed with the third leaching solution for a third-stage leaching, wherein the temperature of the third-stage leaching is 50-80℃; after solid-liquid separation, an iron-rich solution is obtained; when the ferric sulfate solution is evaporated, the free acid concentration of the solution is controlled to be 0.1-0.5 mol / L, and after evaporation and concentration, the solution is slowly cooled to 20-30℃ for crystallization to obtain the iron-containing product.

[0044] It should be clarified that any use of the process provided in the embodiments of the present invention or any substitution or change of conventional data falls within the protection and disclosure scope of the present invention.

[0045] Example 1

[0046] This embodiment provides a method for the complete recycling of lithium iron phosphate waste, the method comprising the following steps:

[0047] Preparation of lithium-rich solution: Lithium iron phosphate waste is mixed with a first acidic leachate for the first stage of leaching, wherein the acid is nitric acid (concentration of 2.0 mol / L), the molar ratio of hydrogen ions to lithium in the lithium iron phosphate waste (H / Li) in the first acidic leachate is 0.8:1, the leaching temperature is 50℃, and the leaching time is 120 min; after solid-liquid separation, the first leachate and the first leachate residue are obtained; the first leachate is purified to obtain a lithium-rich solution.

[0048] Preparation of phosphorus-rich solution: The first leaching residue is mixed with the second alkaline leaching solution for a second stage of leaching, wherein the alkali is potassium hydroxide (concentration of 3.0 mol / L), the liquid-to-solid ratio of the second stage of leaching is 3 mL / g, the temperature is 50℃, and the time is 120 min; after solid-liquid separation, the second leaching solution and the second leaching residue are obtained; the second leaching solution is purified to obtain a phosphorus-rich solution.

[0049] Lithium phosphate preparation: The lithium-rich solution and the phosphorus-rich solution are mixed for precipitation reaction, wherein the molar ratio of lithium ions to phosphorus (Li / P) in the solution is 3.0:1, the precipitation reaction temperature is 60℃, and the final pH value of the reaction is 10; after the precipitation reaction is completed, the mixture is aged at the reaction temperature for 2 h; after solid-liquid separation, lithium phosphate product and third leachate are obtained.

[0050] Preparation of iron-containing products: The second leaching residue and the third leaching solution are mixed for the third stage of leaching, wherein the temperature of the third stage leaching is 50℃; after solid-liquid separation, an iron-rich solution is obtained; when the ferric sulfate solution is evaporated, the free acid concentration of the solution is controlled to be 0.1 mol / L, and after evaporation and concentration, the solution is slowly cooled to 20℃ for crystallization to obtain the iron-containing product.

[0051] Example 2

[0052] This embodiment provides a method for the complete recycling of lithium iron phosphate waste, the method comprising the following steps:

[0053] Preparation of lithium-rich solution: Lithium iron phosphate waste is mixed with a first acidic leachate for the first stage of leaching, wherein the acid is hydrochloric acid (concentration of 2.0 mol / L), the molar ratio of hydrogen ions to lithium in the lithium iron phosphate waste (H / Li) in the first acidic leachate is 1.2:1, the leaching temperature is 80℃, and the leaching time is 15 min; after solid-liquid separation, the first leachate and the first leachate residue are obtained; the first leachate is purified to obtain a lithium-rich solution.

[0054] Preparation of phosphorus-rich solution: The first leaching residue is mixed with the second alkaline leaching solution for a second stage of leaching, wherein the alkali is ammonia water (concentration of 15 mol / L), the liquid-to-solid ratio of the second stage of leaching is 10 mL / g, the temperature is 90℃, and the time is 15 min; after solid-liquid separation, the second leaching solution and the second leaching residue are obtained; the second leaching solution is purified to obtain a phosphorus-rich solution.

[0055] Lithium phosphate preparation: The lithium-rich solution and the phosphorus-rich solution are mixed for precipitation reaction, wherein the molar ratio of lithium ions to phosphorus (Li / P) in the solution is 3.2:1, the precipitation reaction temperature is 95℃, and the final pH value of the reaction is 12; after the precipitation reaction is completed, the mixture is aged at the reaction temperature for 4 h; after solid-liquid separation, lithium phosphate product and third leachate are obtained.

[0056] Preparation of iron-containing products: The second leaching residue and the third leaching solution are mixed for the third stage of leaching, wherein the temperature of the third stage leaching is 80℃; after solid-liquid separation, an iron-rich solution is obtained; when the ferric sulfate solution is evaporated, the free acid concentration of the solution is controlled to be 0.5 mol / L, and after evaporation and concentration, the solution is slowly cooled to 30℃ for crystallization to obtain the iron-containing product.

[0057] Example 3

[0058] This embodiment provides a method for the complete recycling of lithium iron phosphate waste, the method comprising the following steps:

[0059] Preparation of lithium-rich solution: Lithium iron phosphate waste is mixed with a first acidic leachate for the first stage of leaching, wherein the acid is sulfuric acid (concentration of 1.0 mol / L), the molar ratio of hydrogen ions to lithium in the lithium iron phosphate waste (H / Li) in the first acidic leachate is 1.1:1, the leaching temperature of the first stage is 60℃, and the time is 60 min; after solid-liquid separation, the first leachate and the first leachate residue are obtained; the first leachate is purified to obtain a lithium-rich solution.

[0060] Preparation of phosphorus-rich solution: The first leaching residue is mixed with the second alkaline leaching solution for a second stage of leaching, wherein the alkali is sodium hydroxide (concentration of 4.0 mol / L), the liquid-to-solid ratio of the second stage of leaching is 5 mL / g, the temperature is 80℃, and the time is 60 min; after solid-liquid separation, the second leaching solution and the second leaching residue are obtained; the second leaching solution is purified to obtain a phosphorus-rich solution.

[0061] Lithium phosphate preparation: The lithium-rich solution and the phosphorus-rich solution are mixed to carry out a precipitation reaction, wherein the molar ratio of lithium ions to phosphorus (Li / P) in the solution is 3.1:1, the precipitation reaction temperature is 80℃, and the final pH value of the reaction is 11; after the precipitation reaction is completed, the mixture is aged at the reaction temperature for 3 h; after solid-liquid separation, lithium phosphate product and third leachate are obtained.

[0062] Preparation of iron-containing products: The second leaching residue and the third leaching solution are mixed for the third stage of leaching, wherein the temperature of the third stage leaching is 70℃; after solid-liquid separation, an iron-rich solution is obtained; when the ferric sulfate solution is evaporated, the free acid concentration of the solution is controlled to be 0.3 mol / L, and after evaporation and concentration, the solution is slowly cooled to 20℃ for crystallization to obtain the iron-containing product.

[0063] Example 4

[0064] This embodiment provides a method for the complete recycling of lithium iron phosphate waste. The only difference between this method and Embodiment 3 is that the molar ratio of hydrogen ions in the acidic leachate to lithium in the lithium iron phosphate waste is changed to 0.7:1. All other aspects are the same as in Embodiment 3.

[0065] Example 5

[0066] This embodiment provides a method for the complete recycling of lithium iron phosphate waste. The only difference between this method and Embodiment 3 is that the molar ratio of hydrogen ions in the acidic leachate to lithium in the lithium iron phosphate waste is changed to 1.3:1. All other aspects are the same as in Embodiment 3.

[0067] Example 6

[0068] This embodiment provides a method for the complete recycling of lithium iron phosphate waste. The only difference between this method and Example 3 is that the liquid-to-solid ratio of the second leaching system is 2 mL / g, while the rest are the same as in Example 3.

[0069] Example 7

[0070] This embodiment provides a method for the complete recycling of lithium iron phosphate waste. The only difference between this method and Example 3 is that the liquid-to-solid ratio of the second leaching system is 11 mL / g, while the rest are the same as in Example 3.

[0071] Example 8

[0072] This embodiment provides a method for the complete recycling of lithium iron phosphate waste. The only difference between this method and Example 3 is that the molar ratio of lithium ions to phosphorus ions in the precipitation reaction is 2.9:1, while the rest are the same as in Example 3.

[0073] Example 9

[0074] This embodiment provides a method for the complete recycling of lithium iron phosphate waste. The only difference between this method and Example 3 is that the molar ratio of lithium ions to phosphorus ions in the precipitation reaction is 3.3:1, while the rest are the same as in Example 3.

[0075] Performance testing

[0076] The samples provided in the examples and comparative examples were tested and analyzed, including the leaching rate of lithium in the first stage of leaching, the leaching rates of iron and phosphorus in the second stage of leaching, and the purity of lithium phosphate and iron-containing products. The results are shown in Table 1.

[0077] Table 1

[0078]

[0079] As can be seen from Table 1, the method provided by the present invention can effectively recover lithium phosphate from lithium iron phosphate waste, and significantly improve the recovery rate of lithium and phosphorus and the purity of the product.

[0080] A comprehensive comparison of Examples 3 and 4-9 shows that the core parameter ranges defined in this invention (the molar ratio of hydrogen ions in the acidic leachate to lithium in the lithium iron phosphate waste is (0.8-1.2):1, the liquid-to-solid ratio of the second-stage leaching system is (3-10) mL / g, and the molar ratio of lithium ions to phosphorus ions in the precipitation reaction is (3.0-3.2):1) are crucial for ensuring the high efficiency, high purity, and economic feasibility of the entire process. A low H / Li ratio leads to reduced lithium and phosphorus leaching rates; a high ratio destroys selectivity and introduces impurities. A low liquid-to-solid ratio deteriorates operability and separation efficiency; a high ratio drastically increases energy consumption and reduces economic efficiency. A low Li / P ratio introduces competitive precipitation, damaging the purity of lithium phosphate; a high ratio leads to lithium contamination of the ferric sulfate product and lithium loss. These parameters collectively constitute a precise process window; any deviation will trigger a chain of negative effects, reducing the overall technical value.

[0081] In summary, the method provided by this invention has at least the following advantages:

[0082] (1) Through the coupled efficiency enhancement process of “stepwise precise leaching-directional precipitation-internal circulation synergy”, the efficient separation of lithium, phosphorus and iron elements and the closed-loop recovery of all components were achieved, which significantly improved the efficiency of comprehensive resource utilization.

[0083] (2) By recycling the medium within the process (such as using the third leaching solution for iron leaching), the consumption of fresh acid and alkali raw materials and the generation of wastewater and waste salt are greatly reduced, effectively solving the problems of high operating costs and high risk of secondary pollution in traditional wet processes.

[0084] (3) By precisely controlling the reaction interface and mass transfer conditions at each stage, the core product lithium phosphate can directly meet the purity requirements of battery-grade precursors, while the by-product ferric sulfate can meet industrial water treatment standards, realizing the high-value-added directional conversion of the entire process products.

[0085] (4) This method is simple, easy to operate and highly practical. It can realize the resource utilization of waste lithium-ion batteries at a low cost. At the same time, the pollution of the whole process can basically achieve zero emission, effectively avoiding secondary pollution, and has good industrial application potential.

[0086] The present invention has been illustrated with the above embodiments to illustrate its detailed structural features. However, the present invention is not limited to the above detailed structural features, that is, it does not mean that the present invention must rely on the above detailed structural features to be implemented. Those skilled in the art should understand that any improvements to the present invention, equivalent substitutions for the components used in the present invention, additions of auxiliary components, and selection of specific methods, etc., all fall within the protection scope and disclosure scope of the present invention.

Claims

1. A method for the complete recycling of lithium iron phosphate waste, characterized in that, The method includes the following steps: Lithium iron phosphate waste is mixed with acidic leachate for the first stage of leaching. After solid-liquid separation, the first leachate and the first leachate residue are obtained. The first leachate is then purified to obtain a lithium-rich solution. The first leaching residue is mixed with an alkaline leaching solution for a second leaching process. After solid-liquid separation, a second leaching solution and a second leaching residue are obtained. The second leaching solution is then purified to obtain a phosphorus-rich solution. The lithium-rich solution and the phosphorus-rich solution are mixed to carry out a precipitation reaction. After solid-liquid separation, lithium phosphate and precipitate mother liquor are obtained. The second leaching residue is mixed with the precipitate mother liquor and subjected to a third leaching stage. After solid-liquid separation, an iron-rich solution is obtained. The iron-rich solution is then evaporated and crystallized to obtain an iron-containing product.

2. The method according to claim 1, characterized in that, The acidic leachate includes a strong inorganic acid; Preferably, the inorganic strong acid includes any one or a combination of at least two of sulfuric acid, hydrochloric acid, or nitric acid; Preferably, the molar ratio of hydrogen ions in the acidic leachate to lithium in the lithium iron phosphate waste is (0.8-1.2):

1.

3. The method according to claim 1 or 2, characterized in that, The leaching temperature in the first stage is 50-80℃; Preferably, the leaching time for the first stage is 15-120 min.

4. The method according to any one of claims 1 to 3, characterized in that, The alkaline leachate includes an inorganic alkali; Preferably, the inorganic base includes any one or a combination of at least two of sodium hydroxide, potassium hydroxide, or ammonia water.

5. The method according to any one of claims 1 to 4, characterized in that, The concentration of alkali in the second leaching system is 3-15 mol / L, and the liquid-to-solid ratio is (3-10) mL / g; Preferably, the leaching temperature in the second stage is 50-90℃; Preferably, the leaching time for the second stage is 15-120 min.

6. The method according to any one of claims 1 to 5, characterized in that, The molar ratio of lithium ions to phosphorus ions in the precipitation reaction is (3.0-3.2):1; Preferably, the precipitation reaction is carried out at a temperature of 60-95°C; Preferably, the final pH value of the precipitation reaction is 10-12.

7. The method according to any one of claims 1 to 6, characterized in that, After the precipitation reaction is completed, the mixture is aged at the reaction temperature for 2-4 hours.

8. The method according to any one of claims 1 to 7, characterized in that, The leaching temperature in the third stage is 50-80℃; Preferably, the free acid concentration of the iron-rich solution is 0.1-0.5 mol / L.

9. The method according to any one of claims 1 to 8, characterized in that, The evaporation crystallization process includes: evaporating and concentrating the iron-rich solution, and then slowly cooling it to 20-30°C to crystallize it.

10. The method according to any one of claims 1 to 9, characterized in that, The lithium iron phosphate waste includes the positive electrode active material obtained from the crushing and sorting of retired lithium iron phosphate batteries.

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