Method for extracting lithium from lithium iron phosphate black powder material by wet process

Abstract

According to the wet-process lithium extraction method of the lithium iron phosphate black powder material, the characteristic that distribution differences of all components of black powder in different particle sizes are large is utilized, the proportion of the black powder particles in different particle sizes is adjusted through a compounding technology, then the content of all the components in a system is regulated and controlled, the content of active substances is selectively increased, and therefore the leaching rate of main elements is increased. Specifically, the mass content of particles with the particle size smaller than 75 micrometers is adjusted to be larger than 25%, and meanwhile the mass content of particles with the particle size ranging from 75 micrometers to 300 micrometers is adjusted to be larger than 40%, so that the flotation efficiency is guaranteed, and the leaching efficiency is also guaranteed.

Description

Technical Field

[0001] The invention belongs to the field of battery recycling, and in particular relates to a method for wet-process lithium extraction from lithium iron phosphate black powder material. Background Art

[0003] The recycling of used batteries is mainly divided into pyrolysis, wet processing, bioleaching and mechanical treatment. Compared with other recycling methods, wet processing is more widely used. Wet recycling uses solvents to extract the required metal elements and recovers metals and their salts through precipitation. The advantages are simple process, low energy consumption, low equipment requirements, and suitable for large-scale production.

[0004] At present, the battery recycling industry generally believes that wet processing is a more mature lithium extraction process, but the types of solvents used in the leaching system are diverse, each with its own advantages and disadvantages. The "sulfuric acid + hydrogen peroxide" system is the most widely used. This process has problems such as high impurity leaching rate, low main element leaching rate, and easy introduction of sulfate ions, resulting in excessive sulfur content in the product. Therefore, it is particularly important to develop a lithium iron phosphate black powder lithium extraction process with good economic benefits and no introduction of other impurities. Summary of the invention

[0005] Waste lithium iron phosphate batteries are finely disassembled and calcined without oxygen, and then pre-treated by coarse crushing and fine crushing, and then further sieved and separated from large pieces of aluminum foil current collectors. The screened material is mainly lithium iron phosphate black powder, and the black powder particle size distribution is in the range of 20~400 μm. Conventional pretreatment and separation methods cannot accurately control the content of each component in the system, so acid leaching cannot selectively improve the extraction efficiency of the main elements. The present invention utilizes the large difference in the distribution of each component of black powder in different particle sizes, and adjusts the proportion of black powder particles of different particle sizes through a compounding process, thereby regulating the content of each component in the system, selectively increasing the content of active substances, and thus improving the leaching rate of the main elements.

[0006] To this end, the present invention proposes a method for wet lithium extraction from lithium iron phosphate black powder material, comprising the following steps: S1, pre-treating the waste lithium iron phosphate battery to obtain lithium iron phosphate black powder; S2, ball-milling and sieving the black powder to obtain black powder particles with particle sizes ranging from less than 75 μm, 75 to 300 μm, and more than 300 μm; S3, compounding the black powder particles of different particle sizes obtained above, so that the mass content of particles below 75 μm is greater than 25%, and the mass content of particles of 75-300 μm is greater than 40%, to obtain compound black powder; S4. The composite black powder is homogenized, floated, and acid-leached to remove impurities to obtain a battery-grade lithium carbonate product.

[0007] In order to improve the leaching rate of lithium iron phosphate black powder, technicians in this field usually crush and grind the black powder to reduce the particle size, so that the contact area with the leaching solution can be increased during leaching, thereby improving the leaching rate. However, after the inventors ball-milled the black powder into small particles, they found that although the leaching rate of the main element increased, the leaching rate of the impurity elements also increased, resulting in subsequent impurity removal difficulties. In order to selectively improve the leaching rate of the main element, the inventors conducted a lot of research on the relationship between the particle size and leaching rate of the black powder, and finally found that: the ductility of elemental aluminum is good, and it is mainly distributed in black powder particles with a particle size of more than 300 μm; lithium iron phosphate is mainly distributed in particles with a particle size of less than 100 μm; carbon has a low hardness and is easily turned into small particles during ball milling, crushing, and screening, resulting in carbon being mainly distributed in particles with a particle size of less than 50 μm. In order to fully recover the main elements and various impurity elements, the inventors thought of taking advantage of the fact that the distribution of various components of black powder in different particle sizes is quite different. Through a compounding process, the proportion of black powder particles with different particle sizes is adjusted, and then the content of each component in the system is regulated, the content of active substances is selectively increased, thereby improving the leaching rate of the main elements.

[0008] In the present invention, the mass content of particles below 75 μm is adjusted to >25%, and the mass content of particles between 75 and 300 μm is adjusted to >40%, thereby ensuring both flotation efficiency and leaching efficiency.

[0009] Preferably, the mass content of the particles below 75 μm is 30-45%, and the mass content of the particles between 75 and 300 μm is 45-60%.

[0010] In a specific embodiment of the present invention, the particle size range is below 75 μm, preferably 45-75 μm; the particle size range is above 300 μm, preferably 300-400 μm.

[0011] In a specific embodiment of the present invention, the mass ratio of the black powder particles of 75-150 μm to the black powder particles of 150-300 μm in the black powder particles of 75-300 μm is (2-5): 1. Thus, it can be ensured that the active substance content in the black powder within the particle size range is greater than 50%.

[0012] In a specific embodiment of the present invention, the mass ratio of black powder particles with a particle size range of 45-75 μm, 75-300 μm, and above 300 μm is (3-5): (4-6): 1.

[0013] In a specific implementation of the present invention, step S4 is specifically: S41, adding pure water to the compound black powder for homogenization; S42, removing graphite powder from the homogenized slurry by flotation; S43, adding phosphorus-containing concentrated acid to the slurry after flotation, stirring, and performing a primary acid leaching. After the reaction is completed, filtering to obtain a primary leaching residue and a primary leaching liquid; S44, add dilute acid to the primary leaching solution, then slowly add oxidizing substances to perform secondary acid leaching to make Fe 2+ Converted to Fe 3+ , filtering to obtain secondary leaching residue and secondary leaching liquid; S45, adding alkaline substances to the secondary leaching solution, adjusting the pH of the system to remove impurities, and filtering to obtain a neutralized impurity-removing liquid and a neutralized impurity-removing residue; S46, extracting and removing impurities from the neutralized and impurity-removing liquid to obtain a lithium-rich filtrate, and then precipitating lithium to obtain a battery-grade lithium carbonate product.

[0014] In a specific embodiment of the present invention, in step S41, the liquid-to-solid ratio of the homogenate is 1:(1-5), and the homogenization time is 5-30 min.

[0015] In a specific embodiment of the present invention, in step S42, the flotation agent is selected from at least one of pine oil, diethyl phthalate, and butyl ether oil. By flotation, graphite carbon powder can be effectively removed, the adsorption of graphite to active substances can be further reduced, and the main element leaching rate can be increased.

[0016] In a specific embodiment of the present invention, the step S43 further includes at least one of the following technical features: (1) The phosphorus-containing concentrated acid is at least one selected from phosphoric acid, metaphosphoric acid, hypophosphorous acid, and phosphorous acid; (2) The concentration of the phosphorus-containing concentrated acid is 30-85wt%, preferably 50-85wt%; (3) The mass ratio of the added amount of the phosphorus-containing concentrated acid to the black powder is 1 to 10, preferably 5 to 10; (4) The leaching temperature of the first acid leaching is 25-50°C, and the leaching time is 0.5-3 h.

[0017] In the present invention, the purpose of the first acid leaching is to make the impurities copper and aluminum contact with the phosphorus-containing concentrated acid, quickly passivate them, and reduce the leaching rate of impurities. At the same time, the concentrated acid can quickly destroy the structure of lithium iron phosphate, and further improve the reaction efficiency of the main elements in the subsequent leaching process. The main phases of the first leaching residue are elemental carbon, copper oxide, aluminum oxide, and unreacted lithium iron phosphate; the main phases of the first leaching solution are lithium phosphate and ferrous phosphate solution.

[0018] In the present invention, phosphoric acid leaching is used to avoid the introduction of sulfate ions and reduce the risk of excessive sulfur content in the product.

[0019] In a specific embodiment of the present invention, the step S44 further includes at least one of the following technical features: (1) The dilute acid is dilute phosphoric acid; (2) The concentration of the dilute acid is 5-15wt%; (3) The mass ratio of the amount of the diluted acid added to the black powder is 1 to 10, preferably 5 to 10; (4) The oxidizing substance is at least one selected from hydrogen peroxide, oxygen, and sodium persulfate; (5) The amount of the oxidizing substance added is 2-5% of the mass of the black powder.

[0020] In the present invention, the main phases of the secondary leaching residue are elemental carbon and iron phosphate, and the secondary leaching solution is mainly a lithium sulfate solution.

[0021] In a specific embodiment of the present invention, the step S45 further includes at least one of the following technical features: (1) The alkaline substance is at least one selected from sodium hydroxide, sodium carbonate, and ammonium carbonate; (2) The impurity removal temperature is 25-80°C, preferably 40°C, the impurity removal time is 0.5-4 h, preferably 2 h; the system pH is 2.0-5.5, preferably 5.0.

[0022] In step S45, the remaining trivalent iron and metal cations such as calcium and magnesium are mainly removed; the main phase of the neutralization and impurity removal liquid is lithium sulfate solution; the main phase of the neutralization and impurity removal slag is iron hydroxide, calcium hydroxide, magnesium hydroxide and other metal hydroxides.

[0023] In a specific embodiment of the present invention, in step S46, the extraction agent is at least one of P204 and sulfonated kerosene. The impurity elements are further removed through extraction to ensure that the impurity element content in the lithium-rich filtrate is low.

[0024] In a specific embodiment of the present invention, the pretreatment includes: discharging, crushing, and screening the waste lithium iron phosphate batteries, and then high-temperature oxygen-free roasting to remove fluorine impurities, followed by cooling and sorting to obtain lithium iron phosphate black powder.

[0025] Beneficial effects: (1) The present invention provides a method for wet extraction of lithium from lithium iron phosphate black powder material, which can achieve comprehensive and efficient recovery of the Li element. The whole process can achieve a total recovery rate of Li ≥ 95%, achieving the purpose of full resource utilization; (2) The present invention proposes for the first time that there is a correlation between the particle size of lithium iron phosphate black powder and the element content. By adjusting the particle size of lithium iron phosphate black powder, the content of impurity elements and the content of main elements in the black powder can be adjusted, the content of main elements can be selectively increased, and the leaching rate can be further improved. (3) In the process of the present invention, the impurity elements can be passivated by adjusting the acid concentration, further reducing the impurity leaching rate (<30%). At the same time, the concentrated acid can quickly destroy the lithium iron phosphate structure and increase the main element leaching rate; (4) The process of the present invention achieves a Li leaching rate of >99% through secondary leaching; (5) The process flow of the present invention is simple, the leaching rate of main elements is high, and the leaching rate of impurity elements is low. It is a lithium extraction process for lithium iron phosphate black powder with good economic benefits. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 This is a process flow chart for wet lithium extraction from lithium iron phosphate black powder material provided by the present invention. DETAILED DESCRIPTION

[0027] In order to make the technical problems, technical solutions and beneficial effects solved by the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0028] Example 1 This embodiment provides a method for wet lithium extraction from black powder material of lithium iron phosphate battery, comprising the following steps: (1) Discharging, crushing, and screening the waste lithium iron phosphate batteries, and then calcining them at high temperature without oxygen to remove fluorine impurities, followed by cooling and sorting to obtain lithium iron phosphate black powder; (2) ball milling and sieving the lithium iron phosphate black powder to obtain black powder particles with particle sizes ranging from 45 to 75 μm, 75 to 150 μm, 150 to 300 μm, and above 300 μm; (3) The black powder particles of different particle sizes obtained above are fully mixed in a mixer at a mass ratio of 3:4:2:1 to obtain composite lithium iron phosphate black powder; (4) Add pure water to the composite lithium iron phosphate black powder for homogenization, adjust the liquid-to-solid ratio to 1:5, and homogenize for 30 minutes; (5) adding pine oil as a flotation agent to the slurry to remove graphite powder by flotation; (6) Add concentrated phosphoric acid (>85 wt%) to the slurry, stir, and perform a primary leaching at a leaching temperature of 50°C and a leaching time of 2 h. After the reaction is completed, filter and separate to obtain a primary acid leaching residue and a primary leaching liquid; (7) Add dilute phosphoric acid (5 wt%) to the primary leachate and adjust the Fe 2+ Concentration <50g / L, avoid Fe 2+The high concentration caused the temperature to be too high when hydrogen peroxide was added. Then hydrogen peroxide was slowly added to react for 20 minutes, and the secondary acid leaching residue was removed by filter pressing to obtain the secondary leaching solution; (8) adding sodium hydroxide (4 mol / L) to the secondary leaching solution to adjust the pH of the system to 4.5, reacting at 40°C for 2 h, filtering and separating to obtain a neutralization and impurity removal liquid, and removing the neutralization and impurity removal residue by filter pressing; (9) P204 is added to the neutralization and impurity removal liquid for extraction and impurity removal operations, and the impurity elements are deeply removed and separated to ensure that the impurity element content in the lithium-rich filtrate is low; (10) Conduct elemental testing on the lithium-rich filtrate to determine the lithium content therein, so as to calculate the comprehensive recovery rate of Li, and subsequently prepare battery-grade lithium carbonate products.

[0029] The ICP-OES (inductively coupled plasma atomic emission spectrometry) method was used to detect the elements of the black powder and lithium-rich filtrate. The test results are shown in Table 1.

[0030] Table 1 Element and content analysis

[0031] Note: “—” in the table means that the element is below the detection limit of the instrument and is not detected (ND) Example 2 This embodiment provides a method for wet lithium extraction from black powder material of lithium iron phosphate battery, comprising the following steps: (1) Discharging, crushing, and screening the waste lithium iron phosphate batteries, and then calcining them at high temperature without oxygen to remove fluorine impurities, followed by cooling and sorting to obtain lithium iron phosphate black powder; (2) ball milling and sieving the lithium iron phosphate black powder to obtain black powder particles with particle sizes ranging from 45 to 75 μm, 75 to 150 μm, 150 to 300 μm, and above 300 μm; (3) The black powder particles of different particle sizes obtained above are fully mixed in a mixer at a mass ratio of 4.5:3:1.5:1 to obtain composite lithium iron phosphate black powder; (4) Add pure water to the composite lithium iron phosphate black powder for homogenization, adjust the liquid-to-solid ratio to 1:4, and homogenize for 10 minutes; (5) adding a flotation agent, diethyl phthalate, to the slurry to remove graphite powder by flotation; (6) Add mixed acid (mass ratio: phosphoric acid: hypophosphorous acid = 1:1) to the slurry, stir, and perform a primary leaching at a leaching temperature of 40°C and a leaching time of 5 h. After the reaction is completed, filter and separate to obtain a primary acid leaching residue and a primary leaching liquid; (7) Add dilute phosphoric acid (5 wt%) to the primary leachate and adjust the Fe 2+ The concentration is less than 50g / L, and then hydrogen peroxide is slowly added to react for 30 minutes, and the secondary acid leaching residue is removed by filter pressing to obtain the secondary leaching solution; (8) adding sodium hydroxide (3 mol / L) to the secondary leaching solution to adjust the pH of the system to 5.5, reacting at 40°C for 1 h, filtering and separating to obtain a neutralization and impurity removal liquid, and removing the neutralization and impurity removal residue by filter pressing; (9) P204 is added to the neutralization and impurity removal liquid for extraction and impurity removal operations, and the impurity elements are further deeply removed and separated to ensure that the impurity element content in the lithium-rich filtrate is low; (10) Conduct elemental testing on the lithium-rich filtrate to determine the lithium content in it, so as to calculate the comprehensive recovery rate of Li and subsequently prepare battery-grade lithium carbonate products. The black powder and lithium-rich filtrate were subjected to elemental testing, and the test results are shown in Table 2.

[0032] Table 2 Element and content analysis

[0033] Note: “—” in the table means that the element is below the detection limit of the instrument and is not detected (ND) Example 3 This embodiment provides a method for wet lithium extraction from black powder material of lithium iron phosphate battery, comprising the following steps: (1) Discharging, crushing, and screening the waste lithium iron phosphate batteries, and then calcining them at high temperature without oxygen to remove fluorine impurities, followed by cooling and sorting to obtain lithium iron phosphate black powder; (2) ball milling and sieving the lithium iron phosphate black powder to obtain black powder particles with particle sizes ranging from 45 to 75 μm, 75 to 150 μm, 150 to 300 μm, and above 300 μm; (3) The black powder particles of different particle sizes obtained above are fully mixed in a mixer at a mass ratio of 3:5:1:1 to obtain composite lithium iron phosphate black powder; (4) Add pure water to the composite lithium iron phosphate black powder for homogenization, adjust the liquid-to-solid ratio to 1:5, and homogenize for 30 minutes; (5) adding pine oil as a flotation agent to the slurry to remove graphite powder by flotation; (6) Add concentrated phosphoric acid (>85 wt%) to the slurry, stir, and perform a primary leaching at a leaching temperature of 50°C and a leaching time of 2 h. After the reaction is completed, filter and separate to obtain a primary acid leaching residue and a primary leaching liquid; (7) Add dilute phosphoric acid (5 wt%) to the primary leachate and adjust the Fe2+ The concentration is less than 50g / L, and then hydrogen peroxide is slowly added to react for 20 minutes, and the secondary acid leaching residue is removed by filter pressing to obtain the secondary leaching solution; (8) adding sodium hydroxide (4 mol / L) to the secondary leaching solution to adjust the pH of the system to 4.5, reacting at 40°C for 2 h, filtering and separating to obtain a neutralization and impurity removal liquid, and removing the neutralization and impurity removal residue by filter pressing; (9) P204 is added to the neutralization and impurity removal liquid for extraction and impurity removal operations, and the impurity elements are deeply removed and separated to ensure that the impurity element content in the lithium-rich filtrate is low; (10) Conduct elemental testing on the lithium-rich filtrate to determine the lithium content therein, so as to calculate the comprehensive recovery rate of Li, and subsequently prepare battery-grade lithium carbonate products.

[0034] The black powder and lithium-rich filtrate were subjected to elemental testing, and the test results are shown in Table 3.

[0035] Table 3 Element and content analysis

[0036] Note: “—” in the table means that the element is below the detection limit of the instrument and is not detected (ND) Comparative Example 1 This embodiment provides a method for wet lithium extraction from black powder material of lithium iron phosphate battery, comprising the following steps: (1) Discharging, crushing, and screening the waste lithium iron phosphate batteries, and then calcining them at high temperature without oxygen to remove fluorine impurities, followed by cooling and sorting to obtain lithium iron phosphate black powder; (2) ball milling and sieving the lithium iron phosphate black powder to select black powder particles with a particle size range of 45 to 75 μm; (3) The black powder particles obtained above are fully mixed by a mixer to ensure the uniformity of the black powder; (4) Add pure water to the lithium iron phosphate black powder for homogenization, adjust the liquid-to-solid ratio to 1:5, and homogenize for 30 minutes; (5) adding pine oil as a flotation agent to the slurry to remove graphite powder by flotation; (6) Add concentrated phosphoric acid (>85 wt%) to the slurry, stir, and perform a primary leaching at a leaching temperature of 50°C and a leaching time of 2 h. After the reaction is completed, filter and separate to obtain a primary acid leaching residue and a primary leaching liquid; (7) Add dilute phosphoric acid (5 wt%) to the primary leachate and adjust the Fe 2+ The concentration is less than 50g / L, and then hydrogen peroxide is slowly added to react for 20 minutes, and the secondary acid leaching residue is removed by filter pressing to obtain the secondary leaching solution; (8) adding sodium hydroxide (4 mol / L) to the secondary leaching solution to adjust the pH of the system to 4.5, reacting at 40°C for 2 h, filtering and separating to obtain a neutralization and impurity removal liquid, and removing the neutralization and impurity removal residue by filter pressing; (9) P204 is added to the neutralization and impurity removal liquid for extraction and impurity removal operations, and the impurity elements are deeply removed and separated to ensure that the impurity element content in the lithium-rich filtrate is low; (10) Conduct elemental testing on the lithium-rich filtrate to determine the lithium content therein, so as to calculate the comprehensive recovery rate of Li, and subsequently prepare battery-grade lithium carbonate products.

[0037] The black powder and lithium-rich filtrate were subjected to elemental testing, and the test results are shown in Table 4.

[0038] Table 4 Element and content analysis

[0039] Note: “—” in the table means that the element is below the detection limit of the instrument and is not detected (ND) Comparative Example 2 This embodiment provides a method for wet lithium extraction from black powder material of lithium iron phosphate battery, comprising the following steps: (1) Discharging, crushing, and screening the waste lithium iron phosphate batteries, and then calcining them at high temperature without oxygen to remove fluorine impurities, followed by cooling and sorting to obtain lithium iron phosphate black powder; (2) ball milling and sieving the lithium iron phosphate black powder to select black powder particles with a particle size range of 75 to 300 μm; (3) The black powder particles obtained above are fully mixed by a mixer to ensure the uniformity of the black powder; (4) Add pure water to the lithium iron phosphate black powder for homogenization, adjust the liquid-to-solid ratio to 1:5, and homogenize for 30 minutes; (5) adding pine oil as a flotation agent to the slurry to remove graphite powder by flotation; (6) Add concentrated phosphoric acid (>85 wt%) to the slurry, stir, and perform a primary leaching at a leaching temperature of 50°C and a leaching time of 2 h. After the reaction is completed, filter and separate to obtain a primary acid leaching residue and a primary leaching liquid; (7) Add dilute phosphoric acid (5 wt%) to the primary leachate and adjust the Fe 2+ The concentration is less than 50g / L, and then hydrogen peroxide is slowly added to react for 20 minutes, and the secondary acid leaching residue is removed by filter pressing to obtain the secondary leaching solution; (8) adding sodium hydroxide (4 mol / L) to the secondary leaching solution to adjust the pH of the system to 4.5, reacting at 40°C for 2 h, filtering and separating to obtain a neutralization and impurity removal liquid, and removing the neutralization and impurity removal residue by filter pressing; (9) P204 is added to the neutralization and impurity removal liquid for extraction and impurity removal operations, and the impurity elements are deeply removed and separated to ensure that the impurity element content in the lithium-rich filtrate is low; (10) Conduct elemental testing on the lithium-rich filtrate to determine the lithium content therein, so as to calculate the comprehensive recovery rate of Li, and subsequently prepare battery-grade lithium carbonate products.

[0040] The black powder and lithium-rich filtrate were subjected to elemental testing, and the test results are shown in Table 5.

[0041] Table 5 Element and content analysis

[0042] Note: “—” in the table means that the element is below the detection limit of the instrument and is not detected (ND) Comparative Example 3 This embodiment provides a method for wet lithium extraction from black powder material of lithium iron phosphate battery, comprising the following steps: (1) Discharging, crushing, and screening the waste lithium iron phosphate batteries, and then calcining them at high temperature without oxygen to remove fluorine impurities, followed by cooling and sorting to obtain lithium iron phosphate black powder; (2) ball milling and sieving the lithium iron phosphate black powder to obtain black powder particles with particle sizes ranging from 45 to 75 μm, 75 to 150 μm, 150 to 300 μm, and above 300 μm; (3) The black powder particles of different particle sizes obtained above are fully mixed in a mixer at a mass ratio of 1:2:1:6 to obtain composite lithium iron phosphate black powder; (4) Add pure water to the lithium iron phosphate black powder for homogenization, adjust the liquid-to-solid ratio to 1:5, and homogenize for 30 minutes; (5) adding pine oil as a flotation agent to the slurry to remove graphite powder by flotation; (6) Add concentrated phosphoric acid (>85 wt%) to the slurry, stir, and perform a primary leaching at a leaching temperature of 50°C and a leaching time of 2 h. After the reaction is completed, filter and separate to obtain a primary acid leaching residue and a primary leaching liquid; (7) Add dilute phosphoric acid (5 wt%) to the primary leachate and adjust the Fe 2+ The concentration is less than 50g / L, and then hydrogen peroxide is slowly added to react for 20 minutes, and the secondary acid leaching residue is removed by filter pressing to obtain the secondary leaching solution; (8) adding sodium hydroxide (4 mol / L) to the secondary leaching solution to adjust the pH of the system to 4.5, reacting at 40°C for 2 h, filtering and separating to obtain a neutralization and impurity removal liquid, and removing the neutralization and impurity removal residue by filter pressing; (9) P204 is added to the neutralization and impurity removal liquid for extraction and impurity removal operations, and the impurity elements are deeply removed and separated to ensure that the impurity element content in the lithium-rich filtrate is low; (10) Conduct elemental testing on the lithium-rich filtrate to determine the lithium content therein, so as to calculate the comprehensive recovery rate of Li, and subsequently prepare battery-grade lithium carbonate products.

[0043] The black powder and lithium-rich filtrate were subjected to elemental testing, and the test results are shown in Table 6.

[0044] Table 6 Element and content analysis

[0045] Note: “—” in the table means that the element is below the detection limit of the instrument and is not detected (ND) Comparative Example 4 This embodiment provides a method for wet lithium extraction from black powder material of lithium iron phosphate battery, comprising the following steps: (1) Discharging, crushing, and screening the waste lithium iron phosphate batteries, and then calcining them at high temperature without oxygen to remove fluorine impurities, followed by cooling and sorting to obtain lithium iron phosphate black powder; (2) ball milling and sieving the lithium iron phosphate black powder to obtain black powder particles with particle sizes ranging from 45 to 75 μm, 75 to 150 μm, 150 to 300 μm, and above 300 μm; (3) The black powder particles of different particle sizes obtained above are fully mixed in a mixer at a mass ratio of 6:2:1:1 to obtain composite lithium iron phosphate black powder; (4) Add pure water to the lithium iron phosphate black powder for homogenization, adjust the liquid-to-solid ratio to 1:5, and homogenize for 30 minutes; (5) adding pine oil as a flotation agent to the slurry to remove graphite powder by flotation; (6) Add concentrated phosphoric acid (>85 wt%) to the slurry, stir, and perform a primary leaching at a leaching temperature of 50°C and a leaching time of 2 h. After the reaction is completed, filter and separate to obtain a primary acid leaching residue and a primary leaching liquid; (7) Add dilute phosphoric acid (5 wt%) to the primary leachate and adjust the Fe 2+ The concentration is less than 50g / L, and then hydrogen peroxide is slowly added to react for 20 minutes, and the secondary acid leaching residue is removed by filter pressing to obtain the secondary leaching solution; (8) adding sodium hydroxide (4 mol / L) to the secondary leaching solution to adjust the pH of the system to 4.5, reacting at 40°C for 2 h, filtering and separating to obtain a neutralization and impurity removal liquid, and removing the neutralization and impurity removal residue by filter pressing; (9) P204 is added to the neutralization and impurity removal liquid for extraction and impurity removal operations, and the impurity elements are deeply removed and separated to ensure that the impurity element content in the lithium-rich filtrate is low; (10) Conduct elemental testing on the lithium-rich filtrate to determine the lithium content therein, so as to calculate the comprehensive recovery rate of Li, and subsequently prepare battery-grade lithium carbonate products.

[0046] The black powder and lithium-rich filtrate were subjected to elemental testing, and the test results are shown in Table 7.

[0047] Table 7 Element and content analysis

[0048] Note: “—” in the table means that the element is below the detection limit of the instrument and is not detected (ND) The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for wet lithium extraction from lithium iron phosphate black powder material, characterized in that: The method comprises the following steps: S1, pre-treating the waste lithium iron phosphate battery to obtain lithium iron phosphate black powder; S2, ball-milling and sieving the black powder to obtain black powder particles with particle sizes ranging from less than 75 μm, 75 to 300 μm, and more than 300 μm; S3, compounding the black powder particles of different particle sizes obtained above, so that the mass content of particles below 75 μm is greater than 25%, and the mass content of particles of 75-300 μm is greater than 40%, to obtain compound black powder; S4. The composite black powder is homogenized, floated, and acid-leached to remove impurities to obtain a battery-grade lithium carbonate product.

2. The method according to claim 1, characterized in that The mass ratio of the black powder particles with a particle size range of 75-300 μm to the black powder particles with a particle size range of 75-150 μm and 150-300 μm is (2-5):

1.

3. The method according to claim 1, characterized in that The step S4 is specifically as follows: S41, adding pure water to the compound black powder for homogenization; S42, removing graphite powder from the homogenized slurry by flotation; S43, adding phosphorus-containing concentrated acid to the slurry after flotation, stirring, and performing a primary acid leaching. After the reaction is completed, filtering to obtain a primary leaching residue and a primary leaching liquid; S44, add dilute acid to the primary leaching solution, then slowly add oxidizing substances to perform secondary acid leaching to make Fe 2+ Converted to Fe 3+ , filtering to obtain secondary leaching residue and secondary leaching liquid; S45, adding alkaline substances to the secondary leaching solution, adjusting the pH of the system to remove impurities, and filtering to obtain a neutralized impurity-removing liquid and a neutralized impurity-removing residue; S46, extracting and removing impurities from the neutralized and impurity-removing liquid to obtain a lithium-rich filtrate, and then precipitating lithium to obtain a battery-grade lithium carbonate product.

4. The method according to claim 3, characterized in that In the step S41, the liquid-to-solid ratio of the homogenate is 1:(1-5), and the homogenization time is 5-30 min.

5. The method according to claim 3, characterized in that: In the step S42, the flotation agent is selected from at least one of pine oil, diethyl phthalate, and butyl ether oil.

6. The method according to claim 3, characterized in that In step S43, the phosphorus-containing concentrated acid is selected from at least one of phosphoric acid, metaphosphoric acid, hypophosphorous acid, and phosphorous acid; The concentration of the phosphorus-containing concentrated acid is 30-85wt%; The leaching temperature of the primary acid leaching is 25-50°C, and the leaching time is 0.5-3 h.

7. The method according to claim 3, characterized in that In the step S44, the dilute acid is dilute phosphoric acid; The concentration of the dilute acid is 5-15wt%; The oxidizing substance is selected from at least one of hydrogen peroxide, oxygen and sodium persulfate.

8. The method according to claim 3, characterized in that In step S45, the alkaline substance is selected from at least one of sodium hydroxide, sodium carbonate, and ammonium carbonate; Preferably, the impurity removal temperature is 25-80° C., the impurity removal time is 0.5-4 h, and the system pH is 2.0-5.

5.

9. The method according to claim 3, characterized in that: In the step S46, the extraction agent is at least one of P204 and sulfonated kerosene.

10. The method according to claim 1, characterized in that The pretreatment comprises: discharging, crushing and screening the waste lithium iron phosphate batteries, then high-temperature oxygen-free roasting, and then cooling and sorting to obtain lithium iron phosphate black powder.

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