Method for comprehensively recovering valuable elements in waste lithium iron phosphate black powder by acid process

Abstract

The invention provides a method for comprehensively recycling valuable elements in waste lithium iron phosphate black powder through an acid process, and belongs to the crossing field of metallurgy and chemical engineering. The method comprises the steps that the lithium iron phosphate black powder is subjected to acid leaching through a nitric acid solution after being activated at low temperature, and after ferrophosphorus is precipitated in leaching liquid, the lithium element is recycled through impurity removal and lithium precipitation to prepare lithium carbonate; the crude iron phosphate prepared by precipitating ferrophosphorus is dissolved with acid, battery-grade iron phosphate is prepared after ferrophosphorus precipitation, and lithium precipitation mother liquor and phosphorus precipitation mother liquor can be recycled. The method is suitable for recycling the lithium iron phosphate black powder obtained from the positive electrode material of the waste lithium iron phosphate battery, the process can comprehensively recycle valuable elements, the process flow is simple, acid and alkali can be recycled, and the consumption of reagents and the production cost are greatly reduced.

Description

Technical Field

[0001] This invention belongs to the fields of metallurgy and chemical engineering, and specifically relates to a method for the comprehensive recovery of valuable elements in waste lithium iron phosphate black powder using an acid process. Background Technology

[0002] Due to their advantages such as low production cost, long cycle life, and high safety performance, lithium iron phosphate (LFP) batteries have been widely used in the new energy vehicle industry in recent years, resulting in a large amount of waste LFP batteries. The LiFePO4 cathode material in these batteries is rich in lithium, phosphorus, and iron, and has a higher lithium content than ordinary lithium ore, making it a lithium-rich secondary resource. Therefore, recycling LFP cathode materials can not only reduce resource loss but also effectively alleviate the environmental pressure caused by waste batteries. Currently, the main recycling methods for cathode materials fall into three categories: pyrometallurgical, hydrometallurgical, and regeneration and remediation, with hydrometallurgical being the mainstream process. The mainstream hydrometallurgical process can be divided into selective lithium extraction technology and wet total leaching technology based on the different leaching products. Selective leaching refers to adding an appropriate amount of H2O2 as an oxidant and adjusting the solution pH during the acid leaching of LiFePO4, so that lithium is extracted as LiFePO4. + The lithium exists in the liquid phase, while iron and phosphorus are retained in the leaching residue as FePO4 precipitate. The wet total leaching extraction technology goes a step further, selectively extracting lithium and then recovering the phosphorus and iron from the leaching residue. While these processes offer high lithium recovery rates and can recover almost all metals from the cathode material, they also have several drawbacks: ① In reality, the sources of recycled waste batteries are complex and often severely damaged. Due to the characteristics of selective lithium extraction, a large amount of metallic impurities remain in the carbon-containing iron phosphate leaching residue. This type of black residue contains many types of impurities in high concentrations, lacking a reasonable and effective reuse method, resulting in a waste of phosphorus and iron resources; ② Although the wet total leaching extraction technology can recover phosphorus and iron resources, the method is very complex and consumes large amounts of acids, alkalis, iron powder, and other reagents; ③ The wet total leaching extraction technology generates a large amount of wastewater during the recovery process, requiring additional costs for wastewater treatment, thus increasing the recovery cost.

[0003] Chinese patent (CN119315157A) discloses a method and application for recovering metals from spent lithium iron phosphate batteries based on advanced oxidation. This method involves grinding the positive electrode material from spent lithium iron phosphate batteries, then reacting the positive electrode material powder with an oxidant and water in a reactor under certain conditions. Lithium ions are released into the aqueous solution, and then evaporation and filtration are performed by adding sodium carbonate to recover the lithium as lithium carbonate. While this method is simple and efficient, it does not further utilize the remaining lithium-extracting iron phosphate / carbon powder solids, resulting in a significant waste of iron phosphate resources.

[0004] Chinese patent (CN201510372381.0) discloses a method for recovering battery-grade iron phosphate from lithium iron phosphate batteries and for preparing lithium iron phosphate cathode materials from waste lithium iron phosphate batteries. The method involves crushing and heat-treating LiFePO4 lithium-ion battery cathode sheets, dissolving them in sulfuric acid or hydrochloric acid, adding a surfactant to the acid solution, adjusting the pH to 2 with an alkaline solution, precipitating battery-grade iron phosphate, concentrating and heating the filtrate after precipitating the iron phosphate, and precipitating lithium carbonate with sodium carbonate. The recovered lithium iron phosphate and lithium carbonate are then used to prepare lithium iron phosphate cathode materials. This invention recovers the three main valuable elements—lithium, phosphorus, and iron—achieving comprehensive, high-value-added recycling and utilization of waste lithium iron phosphate batteries. However, it consumes large amounts of acid and alkali, generates a large amount of wastewater during the production process, and has high recycling costs.

[0005] Chinese patent (CN 115611251 A) discloses a method for regenerating iron phosphate from waste lithium iron phosphate cathode material lithium extraction slag. The method involves subjecting the waste lithium iron phosphate cathode material lithium extraction slag to two acid dissolution reactions, followed by stirring, heating, holding, and calcination processes to obtain a high-purity iron phosphate product. While this patent can produce qualified iron phosphate, the entire process is lengthy. The first step, calcination, followed by leaching, results in high costs. Furthermore, the raw material being lithium extraction slag makes the process overly complex from the perspective of lithium iron phosphate recovery.

[0006] Existing technologies for recycling valuable elements from waste lithium iron phosphate black powder have significant drawbacks: selective lithium extraction technologies waste phosphorus and iron resources and produce difficult-to-treat black slag; valuable metal recovery rates are low, and wet total dissolution technologies are cumbersome, consume high levels of reagents, and generate large amounts of wastewater requiring additional treatment. It is difficult to simultaneously achieve full resource recovery, low cost, and environmental friendliness. Summary of the Invention

[0007] This invention provides a method for the comprehensive recovery of valuable elements in waste lithium iron phosphate black powder using an acid process, in order to solve the technical problems in the prior art where valuable elements in waste lithium iron phosphate cathode materials cannot be fully recovered, resource utilization is low, the recovery process is complex, and production costs are high.

[0008] To achieve the above-mentioned objectives, the present invention provides the following technical solution:

[0009] A method for the comprehensive recovery of valuable elements from waste lithium iron phosphate black powder using an acid process includes the following steps:

[0010] S1. After low-temperature activation of lithium iron phosphate black powder, acid leaching is performed with nitric acid solution. After solid-liquid separation, leachate 1 and recovered graphite powder are obtained. The low-temperature activation temperature is 100~350℃ and the time is 0.5~4h.

[0011] S2. Add ferric phosphate dihydrate seed crystals to the leachate 1 for the first crystallization. After the reaction is completed, turn off the stirring and let it age. After filtration and washing, crude ferric phosphate and leachate 2 are obtained.

[0012] S3: Add a purification reagent to the leachate 2 and adjust the pH value to 6~7.5 to remove impurities, selectively precipitating out impurity elements such as aluminum. After the impurities in the leachate are precipitated, solid-liquid separation is obtained to obtain the purified precipitate and the purified liquid. Adjust the pH value of the purified liquid to 10~11, add a precipitant to precipitate lithium, precipitating the lithium element in the solution from the liquid. After filtration, washing and drying, lithium carbonate product is obtained. The lithium precipitation mother liquor can be recycled.

[0013] S4: The crude ferric phosphate is dissolved in nitric acid solution to obtain leachate 3. Ferric phosphate dihydrate seed crystals are added to the leachate 3 for a second crystallization. After the reaction is completed, the mixture is filtered to obtain ferric phosphate and phosphorus precipitation mother liquor. The phosphorus precipitation mother liquor can be recycled. The ferric phosphate is washed and dried to obtain battery-grade ferric phosphate.

[0014] Preferably, the concentration of the nitric acid solution in S1 is 0.5~1.5mol / L, the liquid-to-solid ratio of the acid leaching is 2~6:1ml / g, the acid leaching temperature is 30~70℃, and the acid leaching time is 0.5~4h.

[0015] Preferably, the mass of the iron phosphate dihydrate seed crystal in S2 is 0.05~0.2% of the leachate 1, and the temperature of the first crystallization is 70~100℃, and the time is 1~4h.

[0016] Preferably, the aging time in S2 is 0.5~3h, the liquid-to-solid ratio in the washing process is 2~5:1ml / g, the washing temperature is 60~90℃, and the washing time is 0.5~2h.

[0017] Preferably, the impurity removal reagent in S3 is one of lithium hydroxide, sodium carbonate, and sodium hydroxide, and the impurity removal temperature is 45~65℃, and the impurity removal time is 1~4h.

[0018] Preferably, the precipitant in S3 is carbon dioxide, and the lithium precipitation temperature is 45~65℃, and the time is 1~4h.

[0019] Preferably, the concentration of the nitric acid solution in S4 is 1.5~3.0 mol / L, the liquid-to-solid ratio of the acid dissolution is 2~6:1 ml / g, the temperature is 50~70℃, and the time is 0.5~4h.

[0020] Preferably, the mass of the iron phosphate dihydrate seed crystals in S4 is 0.05~0.2% of the leachate 3.

[0021] Preferably, the temperature for the second crystallization in S4 is 70~100℃ and the time is 1~4h.

[0022] Preferably, the liquid-to-solid ratio in the washing process S4 is 2~5:1 ml / g, the washing temperature is 60~90℃, and the washing time is 0.5~2h.

[0023] Lithium iron phosphate (LiFePO4) exhibits unique properties in highly acidic environments, especially nitric acid. In low-temperature, high-concentration nitric acid environments, nitric acid reacts with ferric phosphate, dissolving it in the solution. As the temperature rises, the heat destroys this unstable solvate, causing the ferric phosphate to recrystallize and precipitate from the solution. By controlling the process conditions, the dissolution and precipitation of ferric phosphate can be achieved. Furthermore, after activation treatment, the raw material (lithium iron phosphate) can achieve selective dissolution under mild conditions, increasing the leaching rate of valuable metals and thus improving their recovery rate. Low-temperature activation effectively removes inert substances from the material surface without damaging the lithium iron phosphate crystal structure, thereby opening channels and allowing the subsequent leaching agent to react smoothly with the internal useful components, which is beneficial for the leaching of ferric phosphate.

[0024] The method of this invention can obtain battery-grade lithium carbonate and lithium iron phosphate products. It not only achieves full recovery of the main valuable elements in waste lithium iron phosphate cathode materials, improving resource utilization, but also features a simple and easy-to-implement recycling process. Furthermore, it allows for the recycling of acids and alkalis, significantly reducing reagent consumption, generating no wastewater, and is energy-saving and environmentally friendly. This maximizes resource utilization while greatly reducing production costs. This efficient and concise process expands new avenues for the development of lithium iron phosphate cathode material black powder, possessing advantages such as being green, low-carbon, and environmentally friendly, and demonstrating significant socio-economic value.

[0025] The technical solution of the present invention has at least the following beneficial effects compared with the prior art:

[0026] The method of this invention uses lithium iron phosphate black powder obtained from the recycling of waste lithium iron phosphate battery cathode material as raw material, combined with specific processing steps. Specifically, the lithium iron phosphate black powder is activated at low temperature and then leached with nitric acid. The leaching solution is used to precipitate iron phosphate, and then the lithium element is recovered by removing impurities and precipitating lithium to prepare lithium carbonate. The crude iron phosphate prepared by precipitating iron phosphate is dissolved with acid and then precipitated with iron phosphate to prepare battery-grade iron phosphate. Both the lithium precipitation mother liquor and the phosphorus precipitation mother liquor can be recycled.

[0027] The method of this invention can comprehensively recover valuable elements from lithium iron phosphate black powder with a simple process flow, and can recycle acids and alkalis, reducing reagent consumption while generating no wastewater or waste gas, making it green and environmentally friendly. The materials used in this invention are all common industrial products, easy to purchase and inexpensive; the entire process flow is short, low-cost, low-energy-consumption, easy to scale up, and easy to industrialize. Attached Figure Description

[0028] Figure 1 This is a schematic diagram of a method for the comprehensive recovery of valuable elements in waste lithium iron phosphate black powder using an acid process, as described in this invention. Detailed Implementation

[0029] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the described embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0030] The analysis results of each component of the lithium iron phosphate black powder recovered from the waste lithium iron phosphate batteries used in the following examples are shown in Table 1.

[0031] Table 1. Component analysis results of a certain lithium iron phosphate black powder

[0032]

[0033] Example 1

[0034] like Figure 1 As shown, a method for the comprehensive recovery of valuable elements from waste lithium iron phosphate black powder using an acid process specifically includes the following steps:

[0035] S1. The lithium iron phosphate black powder is activated at 200℃ for 2 hours in a suspension activation furnace for low-temperature activation. The treated raw material is then acid-leached with a 1.2 mol / L nitric acid solution at a liquid-to-solid ratio of 4:1 ml / g, a leaching temperature of 50℃, and a leaching time of 2 hours. After the reaction is complete, solid-liquid separation is performed to obtain leachate 1 and recovered graphite powder. The recovered graphite powder is acid-washed until the impurity content is less than 1%. Preferably, the selected lithium iron phosphate black powder has a Li content of 1.5~4 wt%, a P content of 8~12 wt%, and an Fe content of 16~20 wt%.

[0036] S2. The leachate 1 obtained in S1 is heated to 85°C, and 0.1% of ferric phosphate dihydrate seed crystals by mass of leachate 1 are added for the first crystallization. After stirring for 2 hours, the stirring is turned off and the mixture is aged for 2 hours. After the reaction is completed, the precipitate obtained by filtration is washed 3 times with water at a liquid-to-solid ratio of 3:1, at a washing temperature of 85°C and a washing time of 0.5 hours, to obtain crude ferric phosphate and leachate 2.

[0037] S3. Lithium hydroxide is added to the leachate 2 obtained in S2 as a purification reagent to adjust the pH to 7.0. The reaction temperature is 55℃ and the reaction time is 2h. Impurities such as aluminum are selectively precipitated. After the impurities in the leachate are precipitated, solid-liquid separation is performed to obtain the purified precipitate and the purified liquid. Lithium hydroxide is added to adjust the pH of the purified liquid to 11. Carbon dioxide is introduced as a precipitant at a flow rate of 0.3L / min to precipitate lithium elements from the liquid. The precipitation temperature is 55℃ and the precipitation time is 2h. After filtration, washing and drying are performed to obtain lithium carbonate product. The washing liquid-to-solid ratio is 3:1, the washing temperature is 55℃ and the washing time is 0.5h. The lithium precipitation mother liquor is recycled.

[0038] The crude ferric phosphate obtained from S4 and S2 was dissolved in 2 mol / L nitric acid solution at a liquid-to-solid ratio of 4:1, at a reaction temperature of 50℃, and for 2 hours. The solution was filtered to obtain leachate 3. Leachate 3 was heated to 85℃, and 0.1% of ferric phosphate dihydrate seed crystals by mass of leachate 3 were added for a second crystallization. The reaction was stirred for 2 hours, then the stirring was turned off, and the mixture was aged for 2 hours. After the reaction was completed, the filtered ferric phosphate was washed three times with water at a liquid-to-solid ratio of 3:1 at a washing temperature of 85℃ and a washing time of 0.5 hours. The prepared ferric phosphate dihydrate was dried and sold as battery-grade ferric phosphate. The mother liquor from the phosphate precipitation was recycled.

[0039] In this embodiment, the leaching rates of lithium, phosphorus, and iron in S1 were 99.28%, 98.01%, and 98.24%, respectively; the precipitation rates of lithium, phosphorus, and iron in S2 were 0.47%, 99.28%, and 98.71%, respectively; the precipitation rate of lithium in S3 was 95.49%; and the leaching rates of phosphorus and iron in S4 were 98.20% and 97.64%, respectively. The resulting lithium carbonate had a main content of 99.53%, and the prepared iron phosphate dihydrate had an Fe content of 29.6% and a P content of 16.7%.

[0040] Example 2

[0041] like Figure 1 As shown, a method for the comprehensive recovery of valuable elements from waste lithium iron phosphate black powder using an acid process specifically includes the following steps:

[0042] S1. The lithium iron phosphate black powder is activated at 100℃ for 4 hours in a suspension activation furnace for low-temperature activation. The treated raw material is then acid-leached with a 1.5 mol / L nitric acid solution at a liquid-to-solid ratio of 2:1 ml / g, a leaching temperature of 70℃, and a leaching time of 0.5 hours. After the reaction is complete, solid-liquid separation is performed to obtain leachate 1 and recovered graphite powder. The recovered graphite powder is then acid-washed until the impurity content is less than 1%. Preferably, the selected lithium iron phosphate black powder has a Li content of 1.5~4 wt%, a P content of 8~12 wt%, and an Fe content of 16~20 wt%.

[0043] S2. The leachate 1 obtained in S1 is heated to 70°C, and 0.05% of the mass of ferric phosphate dihydrate seed crystals are added to the leachate 1 for the first crystallization. After stirring for 4 hours, the stirring is turned off and the mixture is aged for 0.5 hours. After the reaction is completed, the precipitate obtained by filtration is washed 3 times with water at a liquid-to-solid ratio of 2:1, at a washing temperature of 60°C and a washing time of 2 hours to obtain crude ferric phosphate and leachate 2.

[0044] S3. Add sodium carbonate as a purification reagent to the leachate 2 obtained in S2, adjust the pH to 6.0, the reaction temperature is 45℃, and the reaction time is 4h to selectively precipitate impurities such as aluminum. After the impurities in the leachate are precipitated, solid-liquid separation is performed to obtain the purified precipitate and the purified liquid. Add lithium hydroxide to adjust the pH of the purified liquid to 10.5, and introduce carbon dioxide as a precipitant at a flow rate of 0.3L / min to precipitate lithium elements from the liquid. The precipitation temperature is 45℃ and the precipitation time is 4h. After filtration, washing and drying are performed to obtain lithium carbonate product. The washing liquid-to-solid ratio is 3:1, the washing temperature is 55℃, and the washing time is 0.5h. The lithium precipitation mother liquor is recycled.

[0045] The crude ferric phosphate obtained from S4 and S2 was dissolved in 1.5 mol / L nitric acid solution at a liquid-to-solid ratio of 6:1, at a reaction temperature of 55℃, and for 4 hours. The solution was filtered to obtain leachate 3. The leachate 3 was heated to 70℃, and 0.05% of ferric phosphate dihydrate seed crystals by mass of leachate 3 were added for a second crystallization. The reaction was stirred for 4 hours, then the stirring was turned off, and the mixture was aged for 2 hours. After the reaction was completed, the filtered ferric phosphate was washed three times with washing water at a liquid-to-solid ratio of 2:1 at a washing temperature of 60℃ for 1 hour. The prepared ferric phosphate dihydrate was dried and sold as battery-grade ferric phosphate. The mother liquor from the phosphate precipitation was recycled.

[0046] In this embodiment, the leaching rates of lithium, phosphorus, and iron in S1 were 92.81%, 88.24%, and 89.59%, respectively; the precipitation rates of lithium, phosphorus, and iron in S2 were 0.75%, 96.46%, and 95.81%, respectively; the precipitation rate of lithium in S3 was 80.64%; and the leaching rates of phosphorus and iron in S4 were 99.16% and 99.03%, respectively. The resulting lithium carbonate had a main content of 98.61%, and the iron phosphate dihydrate contained 29.51% Fe and 16.64% P.

[0047] Example 3

[0048] like Figure 1 As shown, a method for the comprehensive recovery of valuable elements from waste lithium iron phosphate black powder using an acid process specifically includes the following steps:

[0049] S1. The lithium iron phosphate black powder is activated at 350℃ for 0.5h in a suspension activation furnace for low-temperature activation. The treated raw material is then acid-leached with 0.5mol / L nitric acid solution at a liquid-to-solid ratio of 6:1ml / g, a leaching temperature of 30℃, and a leaching time of 4h. After the reaction is complete, solid-liquid separation is performed to obtain leachate 1 and recovered graphite powder. The recovered graphite powder is acid-washed until the impurity content is less than 1%. Preferably, the selected lithium iron phosphate black powder has a Li content of 1.5~4wt%, a P content of 8~12wt%, and an Fe content of 16~20wt%.

[0050] S2. The leachate 1 obtained in S1 is heated to 100℃, and 0.2% of the mass of ferric phosphate dihydrate seed crystals are added to leachate 1 for the first crystallization. After stirring for 1 hour, the stirring is turned off and the mixture is aged for 3 hours. After the reaction is completed, the precipitate obtained by filtration is washed 3 times with water at a liquid-to-solid ratio of 5:1, at a washing temperature of 90℃ and a washing time of 1.5 hours to obtain crude ferric phosphate and leachate 2.

[0051] S3. Add sodium hydroxide as a purification reagent to the leachate 2 obtained in S2, adjust the pH to 7.5, the reaction temperature is 65℃, and the reaction time is 1h to selectively precipitate aluminum and other impurities. After the impurities in the leachate are precipitated, solid-liquid separation is performed to obtain the purified precipitate and the purified liquid. Add lithium hydroxide to adjust the pH of the purified liquid to 11, and introduce carbon dioxide as a precipitant at a flow rate of 0.3L / min to precipitate lithium from the liquid at a precipitation temperature of 65℃ and a precipitation time of 1h. After filtration, washing and drying are performed to obtain lithium carbonate product. The washing liquid-to-solid ratio is 3:1, the washing temperature is 55℃, and the washing time is 0.5h. The lithium precipitation mother liquor is recycled.

[0052] The crude ferric phosphate obtained from S4 and S2 was dissolved in 3 mol / L nitric acid solution at a liquid-to-solid ratio of 2:1, at a reaction temperature of 70℃, and for 0.5 h. The solution was filtered to obtain leachate 3. Leachate 3 was heated to 100℃, and 0.2% of ferric phosphate dihydrate seed crystals by mass of leachate 3 were added for a second crystallization. The reaction was stirred for 1 h, then the stirring was turned off, and the solution was aged for 2 h. After the reaction was completed, the filtered ferric phosphate was washed three times with washing water at a liquid-to-solid ratio of 5:1 at a washing temperature of 90℃ for 2 h. The prepared ferric phosphate dihydrate was dried and sold as battery-grade ferric phosphate. The mother liquor from the phosphate precipitation was recycled.

[0053] In this embodiment, the leaching rates of lithium, phosphorus, and iron in S1 were 95.17%, 90.89%, and 92.25%, respectively; the precipitation rates of lithium, phosphorus, and iron in S2 were 0.34%, 99.70%, and 99.16%, respectively; the precipitation rate of lithium in S3 was 94.68%; and the leaching rates of phosphorus and iron in S4 were 82.92% and 80.77%, respectively. The resulting lithium carbonate had a main content of 99.62%, and the prepared iron phosphate dihydrate had an Fe content of 29.83% and a P content of 16.74%.

[0054] Comparative Example 1

[0055] The preparation process of this comparative example is similar to that of Example 1. The difference is that in step S1 of this comparative example, the lithium iron phosphate black powder is not activated at low temperature, but is directly leached with a 1.2 mol / L nitric acid solution.

[0056] In this comparative example, the leaching rates of lithium, phosphorus, and iron in S1 were 63.25%, 28.51%, and 59.10%, respectively.

[0057] Comparative Example 2

[0058] The preparation process of this comparative example is similar to that of Example 1, except that in step S1 of this comparative example, the lithium iron phosphate black powder is activated at 600°C.

[0059] In this comparative example, the leaching rates of lithium, phosphorus, and iron in S1 were 93.84%, 73.25%, and 17.27%, respectively.

[0060] Comparative Example 3

[0061] The preparation process of this comparative example is similar to that of Example 1, except that the temperature of the second crystallization in step S4 of this comparative example is 50°C, and ferric phosphate dihydrate is obtained.

[0062] The lithium carbonate in this comparative example had a main content of 99.61%, while the prepared iron phosphate dihydrate had an Fe content of 28.8% and a P content of 16.4%. This was mainly because the crystallization temperature was too low, resulting in more impurities being carried over and precipitated.

[0063] The above are merely specific embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. The scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A method for the comprehensive recovery of valuable elements from waste lithium iron phosphate black powder using an acid process, characterized in that, Includes the following steps: S1. After low-temperature activation of lithium iron phosphate black powder, acid leaching is performed with nitric acid solution. After solid-liquid separation, leachate 1 and recovered graphite powder are obtained. The low-temperature activation temperature is 100~350℃ and the time is 0.5~4h. S2. Add ferric phosphate dihydrate seed crystals to the leachate 1 to perform the first crystallization. After the reaction is completed, the crude ferric phosphate and leachate 2 are obtained by aging, filtration and washing. S3: Add a purification reagent to the leachate 2, adjust the pH value to 6~7.5 to remove impurities, separate the solid and liquid to obtain the purified precipitate and the purified liquid, adjust the pH value of the purified liquid to 10~11, add a precipitant to precipitate lithium, filter, wash and dry to obtain lithium carbonate product. S4: The crude ferric phosphate is dissolved in nitric acid solution to obtain leachate 3. Ferric phosphate dihydrate seed crystals are added to the leachate 3 for a second crystallization. After the reaction is completed, the mixture is filtered to obtain ferric phosphate and precipitated phosphate mother liquor. The ferric phosphate is washed and dried to obtain battery-grade ferric phosphate.

2. The method for comprehensive acid recovery of valuable elements in waste lithium iron phosphate black powder according to claim 1, characterized in that, The concentration of the nitric acid solution in S1 is 0.5~1.5mol / L, the liquid-to-solid ratio of the acid leaching is 2~6:1 ml / g, the acid leaching temperature is 30~70℃, and the acid leaching time is 0.5~4h.

3. The method for comprehensive acid recovery of valuable elements in waste lithium iron phosphate black powder according to claim 1, characterized in that, The mass of the iron phosphate dihydrate seed crystals in S2 is 0.05~0.2% of the leachate 1, and the temperature of the first crystallization is 70~100℃, and the time is 1~4h.

4. The method for comprehensive acid recovery of valuable elements in waste lithium iron phosphate black powder according to claim 1, characterized in that, The aging time in S2 is 0.5~3h, the liquid-solid ratio in the washing process is 2~5:1ml / g, the washing temperature is 60~90℃, and the washing time is 0.5~2h.

5. The method for comprehensive acid recovery of valuable elements in waste lithium iron phosphate black powder according to claim 1, characterized in that, The impurity removal reagent mentioned in S3 is one of lithium hydroxide, sodium carbonate, and sodium hydroxide. The impurity removal temperature is 45~65℃, and the impurity removal time is 1~4h.

6. The method for comprehensive acid recovery of valuable elements in waste lithium iron phosphate black powder according to claim 1, characterized in that, The precipitant in S3 is carbon dioxide, and the lithium precipitation temperature is 45~65℃, and the time is 1~4h.

7. The method for comprehensive acid recovery of valuable elements in waste lithium iron phosphate black powder according to claim 1, characterized in that, The concentration of the nitric acid solution in S4 is 1.5~3.0 mol / L, the liquid-to-solid ratio of the acid dissolution is 2~6:1 ml / g, the temperature is 50~70℃, and the time is 0.5~4h.

8. The method for comprehensive acid recovery of valuable elements in waste lithium iron phosphate black powder according to claim 1, characterized in that, The mass of the iron phosphate dihydrate seed crystals in S4 is 0.05~0.2% of the leachate 3.

9. The method for comprehensive acid recovery of valuable elements in waste lithium iron phosphate black powder according to claim 1, characterized in that, The second crystallization described in S4 is carried out at a temperature of 70~100℃ for 1~4 hours.

10. The method for comprehensive acid recovery of valuable elements in waste lithium iron phosphate black powder according to claim 1, characterized in that, The liquid-to-solid ratio for washing described in S4 is 2~5:1 ml / g, the washing temperature is 60~90℃, and the washing time is 0.5~2h.

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