A process for full immersion of waste lithium iron phosphate black powder

Abstract

This invention discloses a full leaching process for waste lithium iron phosphate (LFP) black powder, belonging to the field of LFP black powder recycling. The process includes the following steps: S1, raw material pretreatment: obtaining pretreated black powder with a moisture content ≤1%; S2, preparation of an organic acid leaching agent; S3, first iron-phosphorus leaching; S4, filtering the reaction system of step S3 using a 0.22μm plate and frame filter to obtain an iron-phosphorus leaching solution and lithium-containing solid filter residue; S5, subsequent lithium leaching; S6, filtering the reaction system of step S5 using a 0.22μm plate and frame filter to obtain a lithium leaching solution and solid residue; S7, adjusting the pH of the iron-phosphorus leaching solution to 3.5–4.0 with ammonia water, removing impurities, and crystallizing to obtain battery-grade iron phosphate; concentrating the lithium leaching solution under reduced pressure at 45–50℃, adding diammonium hydrogen phosphate to precipitate lithium, and crystallizing to obtain battery-grade lithium phosphate. This invention involves no strong acids or toxic reagents throughout the entire process, resulting in minimal equipment corrosion.

Description

Technical Field

[0001] This invention belongs to the field of lithium iron phosphate black powder recycling, and relates to a full immersion process for waste lithium iron phosphate black powder. Background Technology

[0002] In the leaching process of lithium iron phosphate black powder, the inorganic acid (such as sulfuric acid and hydrochloric acid) system commonly used in the current wet process will continuously corrode the equipment during the production process, and will also produce substances with safety and environmental risks such as sulfur dioxide, chlorine and hydrogen. Summary of the Invention

[0003] The purpose of this invention is to provide a full immersion process for waste lithium iron phosphate black powder, which solves the problems of equipment corrosion and environmental safety caused by the current widespread use of inorganic acids in wet processes.

[0004] The technical solution adopted in this invention is as follows: A process for fully impregnating waste lithium iron phosphate black powder includes the following steps: S1. Raw material pretreatment: Dry the waste lithium iron phosphate battery powder at 65-75℃ for 1-2 hours, grind it and pass it through a 200-mesh sieve to obtain pretreated black powder with a moisture content of ≤1%; S2. Preparation of organic acid leaching agent: Using deionized water as solvent, add 70-90 g / L of citric acid, 30-50 g / L of itaconic acid, 3-5 g / L of anhydrous glucose, 8-15 g / L of hydroxyethylated sodium carboxymethyl cellulose, and 5-10 g / L of carboxylated chitosan by mass-volume ratio, and stir at room temperature until completely dissolved and a uniform gel-like liquid is formed. The resulting leaching agent is obtained by stirring at room temperature. S3. Pre-iron and phosphorus leaching: The pretreated black powder and organic acid leaching agent are mixed at a solid-liquid ratio of 1:(5~6) g / mL and reacted at a stirring rate of 350~400r / min and a temperature of 55~60℃ for 1.2~1.5h to achieve preferential leaching of iron and phosphorus. S4. Filter the reaction system of step S3 using a 0.22μm plate and frame filter to obtain iron-phosphorus leachate and lithium-containing solid filter residue. S5. Lithium leaching: The lithium-containing solid filter residue is mixed with the organic acid leaching agent prepared in step S2 at a solid-liquid ratio of 1:(4-5) g / mL, and reacted at a stirring rate of 350-400 r / min and a temperature of 65-70℃ for 0.8-1 h to achieve lithium leaching. S6. Filter the reaction system of step S5 using a 0.22μm plate and frame filter to obtain lithium leaching solution and solid residue; S7. The pH of the iron-phosphorus leaching solution is adjusted to 3.5-4.0 with ammonia water, and after impurity removal and crystallization, battery-grade iron phosphate is obtained; the lithium leaching solution is concentrated under reduced pressure at 45-50℃, and diammonium hydrogen phosphate is added to precipitate lithium, and then crystallized to obtain battery-grade lithium phosphate.

[0005] Further, the hydroxyethylated sodium carboxymethyl cellulose is prepared by the following method: sodium carboxymethyl cellulose is dissolved in deionized water, ethylene oxide and pH adjuster are added, and the mixture is stirred and reacted at 45-50℃ and pH 8±0.5 for 2-3 hours. The mixture is then dried under reduced pressure and ground to obtain hydroxyethylated sodium carboxymethyl cellulose.

[0006] Furthermore, the carboxylated chitosan is prepared by the following method: chitosan is dissolved in a 1% (w / w) acetic acid solution, succinic anhydride is added, and the mixture is stirred at 35-40°C for 1.5-2 hours. After neutralization, filtration, and drying, carboxylated chitosan is obtained.

[0007] Furthermore, the mass ratio of sodium carboxymethyl cellulose to ethylene oxide is 100:12-18.

[0008] Furthermore, the mass ratio of chitosan to succinic anhydride is 25:9-11.

[0009] Furthermore, the mass ratio of citric acid to itaconic acid is 2:1.

[0010] Furthermore, the mass ratio of hydroxyethylated sodium carboxymethyl cellulose to carboxylated chitosan is 1.5:1.

[0011] Furthermore, the ammonia water mentioned in step S7 is a 5% (w / w) dilute ammonia water, and the pH adjustment process is accompanied by low-speed stirring at 150-200 r / min.

[0012] Furthermore, the temperature for vacuum drying is 55–65°C, and the vacuum degree is -0.07–-0.09 MPa.

[0013] Furthermore, the aforementioned full immersion process for waste lithium iron phosphate black powder is suitable for waste lithium iron phosphate black powder with an aluminum and titanium impurity content of ≤2.5%.

[0014] In summary, due to the adoption of the above technical solution, the beneficial effects of the present invention are: 1. This invention provides a full leaching process for waste lithium iron phosphate black powder, primarily using organic acids in combination with hydroxyethylated sodium carboxymethyl cellulose and carboxylated chitosan as acid leaching raw materials. The hydroxyethylated sodium carboxymethyl cellulose intercalates into the lithium iron phosphate lattice, reducing the dismantling activation energy, and, in conjunction with the organic acids, achieves an iron, phosphorus, and lithium leaching rate of ≥98.5%. The carboxylated chitosan achieves gentle complexation and decomplexation of metal ions, avoiding interference from residual organic acids in product synthesis, and ensuring the purity of iron phosphate and lithium phosphate is ≥99.5%. This invention involves no strong acids or toxic reagents throughout the entire process, resulting in minimal equipment corrosion. 2. In this invention, the crystal structure of lithium iron phosphate is LiFePO4, with iron and phosphorus covalently bonded in the same crystal lattice. Leaching iron inevitably involves simultaneous leaching of phosphorus. By employing a "first iron-phosphorus leaching, then lithium leaching" process, iron and phosphorus preferentially enter the liquid phase and are directly used as raw materials for synthesizing battery-grade lithium iron phosphate; lithium remains in the solid phase and is leached separately in subsequent processes to prepare lithium phosphate. This route achieves efficient separation of iron and phosphorus from lithium, preventing phosphorus impurities from entering the lithium product, while ensuring the component matching of the lithium iron phosphate feed solution. Attached Figure Description

[0015] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly described below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort, wherein: Figure 1 This is a flowchart of a process for the complete immersion of waste lithium iron phosphate black powder. Detailed Implementation

[0016] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only for explaining the invention and are not intended to limit the invention; that is, the described embodiments are merely some embodiments of the invention, and not all embodiments. The components of the embodiments of the invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations.

[0017] Therefore, the following detailed description of the embodiments of the invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the invention without inventive effort are within the scope of protection of the invention.

[0018] It should be noted that relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0019] The features and performance of the present invention will be further described in detail below with reference to embodiments.

[0020] like Figure 1 As shown in the figure, the present invention provides a full immersion process for waste lithium iron phosphate black powder, which includes the following steps: S1. Raw material pretreatment: Dry the waste lithium iron phosphate battery powder at 65-75℃ for 1-2 hours, grind it and pass it through a 200-mesh sieve to obtain pretreated black powder with a moisture content of ≤1%; S2. Preparation of organic acid leaching agent: Using deionized water as solvent, add 70-90 g / L citric acid, 30-50 g / L itaconic acid, 3-5 g / L anhydrous glucose, 8-15 g / L sodium hydroxyethylated carboxymethyl cellulose, and 5-10 g / L carboxylated chitosan in a mass-volume ratio, and stir at room temperature until completely dissolved and a uniform gel-like liquid is formed to obtain the organic acid leaching agent; S3. Pre-iron and phosphorus leaching: The pretreated black powder and organic acid leaching agent are mixed at a solid-liquid ratio of 1:(5~6) g / mL and reacted at a stirring rate of 350~400r / min and a temperature of 55~60℃ for 1.2~1.5h to achieve preferential leaching of iron and phosphorus. S4. Filter the reaction system of step S3 using a 0.22μm plate and frame filter to obtain iron-phosphorus leachate and lithium-containing solid filter residue. S5. Lithium leaching: The lithium-containing solid filter residue is mixed with the organic acid leaching agent prepared in step S2 at a solid-liquid ratio of 1:(4-5) g / mL, and reacted at a stirring rate of 350-400 r / min and a temperature of 65-70℃ for 0.8-1 h to achieve lithium leaching. S6. Filter the reaction system of step S5 using a 0.22μm plate and frame filter to obtain lithium leaching solution and solid residue; S7. The iron-phosphorus leaching solution is adjusted to pH 3.5-4.0 with ammonia water (the ammonia water is 5% by mass, and the pH adjustment process is accompanied by low-speed stirring at 150-200 r / min). After impurity removal and crystallization, battery-grade iron phosphate is obtained. The lithium leaching solution is concentrated under reduced pressure at 45-50℃, and diammonium hydrogen phosphate is added to precipitate lithium. After crystallization, battery-grade lithium phosphate is obtained.

[0021] In the following embodiments, the hydroxyethylated sodium carboxymethyl cellulose was prepared by the following method: sodium carboxymethyl cellulose was dissolved in deionized water, ethylene oxide and a pH adjuster were added, and the mixture was stirred and reacted at 45-50°C and pH 8±0.5 for 2-3 hours. The mixture was then dried under reduced pressure (at a temperature of 55-65°C and a vacuum degree of -0.07 to -0.09 MPa) and ground to obtain hydroxyethylated sodium carboxymethyl cellulose. The mass ratio of sodium carboxymethyl cellulose to ethylene oxide was 100:12-18.

[0022] In the following embodiments, the carboxylated chitosan was prepared by the following method: chitosan was dissolved in a 1% (w / w) acetic acid solution, succinic anhydride was added, and the mixture was stirred at 35-40°C for 1.5-2 hours. After neutralization, filtration, and drying, carboxylated chitosan was obtained. The mass ratio of chitosan to succinic anhydride was 25:9-11.

[0023] In one embodiment, the mass ratio of citric acid to itaconic acid is 2:1.

[0024] In one embodiment, the mass ratio of hydroxyethylated sodium carboxymethyl cellulose to carboxylated chitosan is 1.5:1.

[0025] Example 1

[0026] Based on the above, this embodiment provides a full immersion process for waste lithium iron phosphate black powder, including the following steps: S1. Raw material pretreatment: Dry the waste lithium iron phosphate battery powder at 65-75℃ for 1-2 hours, grind it and pass it through a 200-mesh sieve to obtain pretreated black powder with a moisture content of ≤1%; S2. Preparation of organic acid leaching agent: Using deionized water as solvent, add 70 g / L citric acid, 30 g / L itaconic acid, 3 g / L anhydrous glucose, 8 g / L hydroxyethylated sodium carboxymethyl cellulose, and 5 g / L carboxylated chitosan in the mass-volume ratio, and stir at room temperature until completely dissolved and a uniform gel-like liquid is formed to obtain the organic acid leaching agent. S3. Pre-iron and phosphorus leaching: The pretreated black powder and organic acid leaching agent are mixed at a solid-liquid ratio of 1:6 g / mL and reacted at a stirring rate of 400 r / min and a temperature of 60℃ for 1.5 h to achieve preferential leaching of iron and phosphorus. S4. Filter the reaction system of step S3 using a 0.22μm plate and frame filter to obtain iron-phosphorus leachate and lithium-containing solid filter residue. S5. Post-lithium leaching: The lithium-containing solid filter residue is mixed with the organic acid leaching agent prepared in step S2 at a solid-liquid ratio of 1:5 g / mL, and reacted for 1 h at a stirring rate of 400 r / min and a temperature of 65℃ to achieve lithium leaching. S6. Filter the reaction system of step S5 using a 0.22μm plate and frame filter to obtain lithium leaching solution and solid residue; S7. The iron-phosphorus leaching solution is adjusted to pH 3.5-4.0 with ammonia water (the ammonia water is 5% by mass, and the pH adjustment process is accompanied by low-speed stirring at 150-200 r / min). After impurity removal and crystallization, battery-grade iron phosphate is obtained. The lithium leaching solution is concentrated under reduced pressure at 45-50℃, and diammonium hydrogen phosphate is added to precipitate lithium. After crystallization, battery-grade lithium phosphate is obtained.

[0027] Example 2

[0028] Based on the above, this embodiment provides a full immersion process for waste lithium iron phosphate black powder, including the following steps: S1. Raw material pretreatment: Dry the waste lithium iron phosphate battery powder at 65-75℃ for 1-2 hours, grind it and pass it through a 200-mesh sieve to obtain pretreated black powder with a moisture content of ≤1%; S2. Preparation of organic acid leaching agent: Using deionized water as solvent, add 80 g / L citric acid, 40 g / L itaconic acid, 4 g / L anhydrous glucose, 11 g / L sodium hydroxyethylated carboxymethyl cellulose, and 8 g / L carboxylated chitosan in the mass-volume ratio, and stir at room temperature until completely dissolved and a uniform gel-like liquid is formed. The resulting leaching agent is obtained by stirring at room temperature. S3. Preferential leaching of iron and phosphorus: The pretreated black powder and organic acid leaching agent are mixed at a solid-liquid ratio of 1:5.5 g / mL and reacted at a stirring rate of 400 r / min and a temperature of 60℃ for 1.3 h to achieve preferential leaching of iron and phosphorus. S4. Filter the reaction system of step S3 using a 0.22μm plate and frame filter to obtain iron-phosphorus leachate and lithium-containing solid filter residue. S5. Post-lithium leaching: The lithium-containing solid filter residue is mixed with the organic acid leaching agent prepared in step S2 at a solid-liquid ratio of 1:4.5 g / mL, and reacted for 1 h at a stirring rate of 400 r / min and a temperature of 65℃ to achieve lithium leaching. S6. Filter the reaction system of step S5 using a 0.22μm plate and frame filter to obtain lithium leaching solution and solid residue; S7. The iron-phosphorus leaching solution is adjusted to pH 3.5-4.0 with ammonia water (the ammonia water is 5% by mass, and the pH adjustment process is accompanied by low-speed stirring at 150-200 r / min). After impurity removal and crystallization, battery-grade iron phosphate is obtained. The lithium leaching solution is concentrated under reduced pressure at 45-50℃, and diammonium hydrogen phosphate is added to precipitate lithium. After crystallization, battery-grade lithium phosphate is obtained.

[0029] Example 3

[0030] Based on the above, this embodiment provides a full immersion process for waste lithium iron phosphate black powder, including the following steps: S1. Raw material pretreatment: Dry the waste lithium iron phosphate battery powder at 65-75℃ for 1-2 hours, grind it and pass it through a 200-mesh sieve to obtain pretreated black powder with a moisture content of ≤1%; S2. Preparation of organic acid leaching agent: Using deionized water as solvent, add 80 g / L citric acid, 40 g / L itaconic acid, 4 g / L anhydrous glucose, 12 g / L hydroxyethylated sodium carboxymethyl cellulose, and 8 g / L carboxylated chitosan in the mass-volume ratio, and stir at room temperature until completely dissolved and a uniform gel-like liquid is formed. The resulting leaching agent is obtained by stirring at room temperature. S3. Preferential leaching of iron and phosphorus: The pretreated black powder and organic acid leaching agent are mixed at a solid-liquid ratio of 1:5.5 g / mL and reacted at a stirring rate of 400 r / min and a temperature of 60℃ for 1.5 h to achieve preferential leaching of iron and phosphorus. S4. Filter the reaction system of step S3 using a 0.22μm plate and frame filter to obtain iron-phosphorus leachate and lithium-containing solid filter residue. S5. Post-lithium leaching: The lithium-containing solid filter residue is mixed with the organic acid leaching agent prepared in step S2 at a solid-liquid ratio of 1:4.5 g / mL, and reacted for 1 h at a stirring rate of 400 r / min and a temperature of 70 °C to achieve lithium leaching. S6. Filter the reaction system of step S5 using a 0.22μm plate and frame filter to obtain lithium leaching solution and solid residue; S7. The iron-phosphorus leaching solution is adjusted to pH 3.5-4.0 with ammonia water (the ammonia water is 5% by mass, and the pH adjustment process is accompanied by low-speed stirring at 150-200 r / min). After impurity removal and crystallization, battery-grade iron phosphate is obtained. The lithium leaching solution is concentrated under reduced pressure at 45-50℃, and diammonium hydrogen phosphate is added to precipitate lithium. After crystallization, battery-grade lithium phosphate is obtained.

[0031] Example 4

[0032] Based on the above, this embodiment provides a full immersion process for waste lithium iron phosphate black powder, including the following steps: S1. Raw material pretreatment: Dry the waste lithium iron phosphate battery powder at 65-75℃ for 1-2 hours, grind it and pass it through a 200-mesh sieve to obtain pretreated black powder with a moisture content of ≤1%; S2. Preparation of organic acid leaching agent: Using deionized water as solvent, add 90 g / L citric acid, 50 g / L itaconic acid, 5 g / L anhydrous glucose, 15 g / L hydroxyethylated sodium carboxymethyl cellulose, and 10 g / L carboxylated chitosan in the mass-volume ratio, and stir at room temperature until completely dissolved and a uniform gel-like liquid is formed. The resulting leaching agent is obtained by stirring at room temperature. S3. Preferential leaching of iron and phosphorus: The pretreated black powder and organic acid leaching agent are mixed at a solid-liquid ratio of 1:5 g / mL and reacted at a stirring rate of 400 r / min and a temperature of 60℃ for 1.2 h to achieve preferential leaching of iron and phosphorus. S4. Filter the reaction system of step S3 using a 0.22μm plate and frame filter to obtain iron-phosphorus leachate and lithium-containing solid filter residue. S5. Post-lithium leaching: The lithium-containing solid filter residue is mixed with the organic acid leaching agent prepared in step S2 at a solid-liquid ratio of 1:4 g / mL, and reacted for 0.8 h at a stirring rate of 400 r / min and a temperature of 70℃ to achieve lithium leaching. S6. Filter the reaction system of step S5 using a 0.22μm plate and frame filter to obtain lithium leaching solution and solid residue; S7. The iron-phosphorus leaching solution is adjusted to pH 3.5-4.0 with ammonia water (the ammonia water is 5% by mass, and the pH adjustment process is accompanied by low-speed stirring at 150-200 r / min). After impurity removal and crystallization, battery-grade iron phosphate is obtained. The lithium leaching solution is concentrated under reduced pressure at 45-50℃, and diammonium hydrogen phosphate is added to precipitate lithium. After crystallization, battery-grade lithium phosphate is obtained.

[0033] Comparative Example 1 1.5 mol / L sulfuric acid was used as the leaching agent, and no organic acids or modified polymers were added. The remaining process parameters were the same as those in Example 1 of this invention.

[0034] Comparative Example 2 A single 120 g / L citric acid extractant was used, without the addition of itaconic acid, hydroxyethylated sodium carboxymethyl cellulose, carboxylated chitosan, or anhydrous glucose. The remaining process parameters were the same as in Example 1 of this invention. 120 g of citric acid was weighed, and about 800 mL of deionized water was added. The mixture was stirred until completely dissolved, and then the volume was adjusted to 1000 mL with deionized water to obtain a 120 g / L citric acid aqueous solution.

[0035] Comparative Example 3 Based on Example 1, the difference between this comparative example and Example 1 is that the organic acid leaching agent in this comparative example does not include sodium hydroxyethylated carboxymethyl cellulose, but all other aspects are the same.

[0036] Comparative Example 4 Based on Example 1, the difference between this comparative example and Example 1 is that the organic acid leaching agent in this comparative example does not include carboxylated chitosan, but all other aspects are the same.

[0037] Comparative Example 5 Based on Example 1, the difference between this comparative example and Example 1 is that unmodified sodium carboxymethyl cellulose is used instead of hydroxyethylated sodium carboxymethyl cellulose in the organic acid leaching agent of this comparative example, while all other aspects are the same.

[0038] Comparative Example 6 Based on Example 1, the difference between this comparative example and Example 1 is that unmodified chitosan is used instead of carboxylated chitosan in the organic acid leaching agent of this comparative example, while the rest are the same.

[0039] Experimental Example 1 Waste lithium iron phosphate black powder: aluminum impurity content 2.0%, titanium impurity content 1.5%, moisture content 3.2%, particle size D50=25μm; Total immersion process: Examples 1-4, Comparative Examples 1-6.

[0040] Leaching rate: The contents of Fe, P and Li in the leachate were detected by ICP-OES (inductively coupled plasma optical emission spectrometry), and the leaching rate was calculated; the results are shown in Table 1; Product purity: X-ray fluorescence spectrometry (XRF) was used for detection. Impurity content ≤0.5% was judged to be battery grade; the results are shown in Table 1.

[0041] Table 1 Process Efficiency Testing Iron leaching rate (%) Phosphorus leaching rate (%) Lithium leaching rate (%) Iron phosphate purity (%) Lithium phosphate purity (%) Example 1 98.2～98.5 98.4～98.7 98.1～98.4 Compliant with battery grade Compliant with battery grade Example 2 98.7～99.0 98.9～99.2 98.8～99.1 Compliant with battery grade Compliant with battery grade Example 3 99.1～99.3 99.2～99.4 99.0～99.2 Compliant with battery grade Compliant with battery grade Example 4 98.9～99.1 99.1～99. 98.8～99.0 Compliant with battery grade Compliant with battery grade Comparative Example 1 91.8～92.5 91.5～92.2 92.6～93.3 Not compatible with battery grade Not compatible with battery grade Comparative Example 2 93.7～94.4 93.3～94.0 94.0～94.5 Not compatible with battery grade Not compatible with battery grade Comparative Example 3 95.7～96.3 95.5～96.1 95.9～96.4 Not compatible with battery grade Not compatible with battery grade Comparative Example 4 96.2～96.8 96.0～96.5 96.1～96.6 Not compatible with battery grade Not compatible with battery grade Comparative Example 5 94.9～95.5 94.7～95.3 94.8～95.4 Not compatible with battery grade Not compatible with battery grade Comparative Example 6 95.2～95.8 95.0～95.6 95.1～95.7 Not compatible with battery grade Not compatible with battery grade Experimental Example 2 According to GB / T 10124 "Metallic Materials Laboratory Uniform Corrosion Full Immersion Test Method", the corrosion of 316L stainless steel hanging sheets by the leaching agent in Examples 1-4 and Comparative Examples 1-6 on 316L stainless steel hanging sheets was tested by the 316L stainless steel hanging sheet weight loss method. The results are shown in Table 2. 316L stainless steel hanging plate: 316L stainless steel, 50 mm × 25 mm × 2 mm, accurately weighed after degreasing, cleaning and drying; Testing conditions: Static immersion at 60℃ for 72 hours; Remove the test piece, clean it to remove corrosion products, dry it, weigh it again, and calculate the corrosion rate. ; Corrosion rate, in g / (m²·h); Mass loss, g; : Surface area of ​​the test piece, m²; Soaking time, in hours; Slight corrosion; the equipment is safe and usable. Significant corrosion and high equipment wear and tear.

[0042] Table 2 Leaching Agent Corrosion Detection Example 1 Example 2 Example 3 Example 4 Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 Comparative Example 5 Comparative Example 6 Corrosion level Slight corrosion Slight corrosion Slight corrosion Slight corrosion Significant corrosion Corrosion level Slight corrosion Slight corrosion Slight corrosion Slight corrosion In summary, the leaching agent of this application has low corrosivity to equipment and good leaching effect.

[0043] The above description is merely a preferred embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, and improvements made by those skilled in the art within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A process for the complete immersion of waste lithium iron phosphate black powder, characterized in that: Includes the following steps: S1. Raw material pretreatment: Dry the waste lithium iron phosphate battery powder at 65-75℃ for 1-2 hours, grind it and pass it through a 200-mesh sieve to obtain pretreated black powder with a moisture content of ≤1%; S2. Preparation of organic acid leaching agent: Using deionized water as solvent, add 70-90 g / L of citric acid, 30-50 g / L of itaconic acid, 3-5 g / L of anhydrous glucose, 8-15 g / L of hydroxyethylated sodium carboxymethyl cellulose, and 5-10 g / L of carboxylated chitosan by mass-volume ratio, and stir at room temperature until completely dissolved and a uniform gel-like liquid is formed. The resulting leaching agent is obtained by stirring at room temperature. S3. Pre-iron and phosphorus leaching: The pretreated black powder and organic acid leaching agent are mixed at a solid-liquid ratio of 1:(5~6) g / mL and reacted at a stirring rate of 350~400r / min and a temperature of 55~60℃ for 1.2~1.5h to achieve preferential leaching of iron and phosphorus. S4. Filter the reaction system of step S3 using a 0.22μm plate and frame filter to obtain iron-phosphorus leachate and lithium-containing solid filter residue. S5. Lithium leaching: The lithium-containing solid filter residue is mixed with the organic acid leaching agent prepared in step S2 at a solid-liquid ratio of 1:(4-5) g / mL, and reacted at a stirring rate of 350-400 r / min and a temperature of 65-70℃ for 0.8-1 h to achieve lithium leaching. S6. Filter the reaction system of step S5 using a 0.22μm plate and frame filter to obtain lithium leaching solution and solid residue; S7. The pH of the iron-phosphorus leaching solution is adjusted to 3.5-4.0 with ammonia water, and after impurity removal and crystallization, battery-grade iron phosphate is obtained; the lithium leaching solution is concentrated under reduced pressure at 45-50℃, and diammonium hydrogen phosphate is added to precipitate lithium, and then crystallized to obtain battery-grade lithium phosphate.

2. The process for full immersion of waste lithium iron phosphate black powder according to claim 1, characterized in that: The hydroxyethylated sodium carboxymethyl cellulose was prepared by the following method: sodium carboxymethyl cellulose was dissolved in deionized water, ethylene oxide and pH adjuster were added, and the mixture was stirred and reacted at 45-50℃ and pH 8±0.5 for 2-3 hours. The mixture was then dried under reduced pressure and ground to obtain hydroxyethylated sodium carboxymethyl cellulose.

3. The process for full immersion of waste lithium iron phosphate black powder according to claim 1, characterized in that: The carboxylated chitosan was prepared by the following method: chitosan was dissolved in a 1% (w / w) acetic acid solution, succinic anhydride was added, and the mixture was stirred at 35-40°C for 1.5-2 hours. After neutralization, filtration, and drying, the carboxylated chitosan was obtained.

4. The process for full immersion of waste lithium iron phosphate black powder according to claim 2, characterized in that: The mass ratio of sodium carboxymethyl cellulose to ethylene oxide is 100:12-18.

5. The process for full immersion of waste lithium iron phosphate black powder according to claim 3, characterized in that: The mass ratio of chitosan to succinic anhydride is 25:9-11.

6. The process for full immersion of waste lithium iron phosphate black powder according to claim 1, characterized in that: The mass ratio of citric acid to itaconic acid is 2:

1.

7. The process for full immersion of waste lithium iron phosphate black powder according to claim 1, characterized in that: The mass ratio of hydroxyethylated sodium carboxymethyl cellulose to carboxylated chitosan is 1.5:

1.

8. The process for full immersion of waste lithium iron phosphate black powder according to claim 1, characterized in that: The ammonia solution mentioned in step S7 is a 5% (w / w) dilute ammonia solution, and the pH adjustment process is accompanied by low-speed stirring at 150-200 r / min.

9. The process for full immersion of waste lithium iron phosphate black powder according to claim 2, characterized in that: The temperature for vacuum drying is 55–65℃, and the vacuum degree is -0.07–-0.09 MPa.

10. The process for full immersion of waste lithium iron phosphate black powder according to claim 1, characterized in that: Suitable for waste lithium iron phosphate black powder with aluminum and titanium impurities content ≤2.5%.

Images