Salt leaching-extraction method for cascade cycle recovery of lithium iron phosphate and ternary lithium battery powder

Abstract

The invention discloses a salt leaching-extraction method for cascade recycling of lithium iron phosphate and ternary lithium battery powder, and belongs to the technical field of waste lithium battery recycling. The method adopts iron salt as a leaching agent, constructs a circulation mechanism through the conversion of the valence state of iron ions, and realizes the cascade leaching cycle of waste lithium iron phosphate and nickel cobalt manganese oxide battery powder. Through multiple rounds of leaching cycles, a concentrated enrichment solution containing lithium, nickel, cobalt and manganese and crude iron phosphate and graphite can be obtained. During the leaching cycle, a mixed solvent is developed as an extractant for iron ions, and after the leaching solution containing iron salts is extracted and stripped with hydrochloric acid, both the leaching agent and the extractant can be recycled. The method efficiently leaches the valuable metals in the waste battery powder under milder reaction conditions, and effectively reduces the consumption of chemicals such as acid, alkali, leaching agent, oxidant and extractant through the study of the circulation mechanism, significantly reduces the cost, and has good environmental and economic benefits.

Description

Technical Field

[0001] The invention relates to the technical field of waste lithium battery recycling, and in particular to a salt leaching-extraction method for cascade cycle recycling of lithium iron phosphate and ternary lithium battery powder. Background Art

[0002] With the improvement of consumers' environmental awareness and the performance of new energy vehicle products, the scale of the new energy vehicle market has continued to expand in the past five years, and the demand for precious metals such as lithium, nickel, cobalt and manganese has increased. Therefore, the recycling of mainstream batteries of new energy vehicles such as lithium iron phosphate (LFP) and lithium nickel cobalt manganese oxide (NCM) is imperative. However, the current standardization and recycling efficiency of new energy vehicle power batteries are relatively low, and it is necessary to develop a green and efficient metal recycling method.

[0003] At present, the commonly used metal recovery methods include pyrometallurgy and hydrometallurgy. Pyrometallurgy is not conducive to sustainable economic development due to its high energy consumption and pollution. Hydrometallurgy is more favored by researchers for its advantages such as high recovery rate, high purity and easy regulation. Hydrometallurgy usually requires excessive leaching agent to achieve high leaching efficiency, and inorganic acids (such as CN118026222A, CN117776130B, etc.), organic acids (such as CN117446770A, etc.) or alkalis (such as CN106299526B) are often used as metal ion leaching agents. The metals in the positive electrode of NCM batteries are mostly present as high-valent compounds, and the direct leaching efficiency is low. Reducing agents (such as H2O2, NaHSO3 and ascorbic acid, etc.) are often used to reduce them to low-valent states to promote metal leaching; but for the positive electrode of LFP batteries, additional oxidants (such as H2O2 and (NH4)2S2O8) are required to promote lithium ion release. H2O2, used as an oxidizing or reducing agent, often needs to be added in excess, but it is easily decomposed by heat catalysis, posing a safety risk, so the concentration used needs to be controlled.

[0004] In order to save resources, researchers have proposed a joint recovery strategy for LFP and NCM battery powders. CN118782952A uses sulfuric acid as a leaching agent to jointly recover the LFP and NCM mixture, eliminating the addition of reducing agents and oxidizing agents; however, it is necessary to add chemical reagents such as hydrogen peroxide, sodium phosphate and alkali to oxidize divalent iron ions to obtain iron phosphate precipitation, introducing new cationic impurities, resulting in a complex purification process and high production costs; and the leaching agent cannot be recycled. There is also CN112374550A that uses iron salts to simultaneously leach LFP and NCM battery powders, and regenerates the iron salt leaching agent, but the process still cannot directly generate iron phosphate, and the leaching rate and leaching efficiency are low; there are a large number of iron impurities in the leachate and the leaching residue, and a large amount of acid, alkali and oxidizing agents are further required for impurity removal and purification, which has high production costs, and the large amount of iron hydroxide colloid produced is very easy to clog the filter cloth and pipelines, significantly reducing production efficiency. Although the patent proposes the idea of ​​recycling the leaching agent, using alkali to precipitate the iron in the leaching solution and acid to dissolve the iron hydroxide in the leaching residue to regenerate the iron salt leaching agent, its recycling consumes a large amount of disposable acid and alkali reagents, has low regeneration efficiency, and still generates a large raw material cost. Summary of the invention

[0005] In view of the shortcomings of the prior art, the present invention proposes a salt leaching-extraction method for cascade circulation recovery of lithium iron phosphate and ternary lithium battery powder.

[0006] Based on the redox mechanism, the present invention proposes a cascade cycle leaching process, and uses ferric chloride as an intermediate leaching agent to make LFP and NCM serve as each other's reducing agent and oxidizing agent, thereby realizing the step-by-step cascade leaching cycle of waste LFP and NCM battery powders. The step-by-step leaching can not only convert the iron and phosphorus in LFP into iron phosphate precipitate, but also the precipitate has a relatively single component and high purity, which can achieve the selective leaching of LFP; it can also enable NCM to obtain a higher leaching rate, and a high-purity crude graphite product can be directly obtained from the leached residue, reducing the energy consumption of secondary purification; the iron ions as the main component of the leaching agent can also stably exist in the solution, promoting the leaching cycle. In addition, for further leaching of NCM battery powder, the recovery rate of valuable metals in waste NCM battery powder can be further improved by adding a small amount of dilute hydrochloric acid without affecting the precipitation of iron phosphate during the LFP leaching process.

[0007] In view of the recycling and regeneration of the leaching agent, the present invention develops a mixed solvent for the extraction and stripping regeneration of iron ions, in which di(2-ethylhexyl) phosphate (P204) and 2-thenoyltrifluoroacetone (HTTA) are combined under the action of hydrogen bonds. Compared with the P204 extractant commonly used in traditional extraction processes, the mixed solvent of P204 and HTTA has better selectivity for iron ions without the need for alkaline solution saponification, which is conducive to the highly selective separation and extraction of iron ions from the leached enrichment solution. Compared with the chemical precipitation method, the one-time consumption of chemical reagents is reduced, and the obtained iron ion-rich extraction phase can be reused after hydrochloric acid stripping. The acid consumed in the stripping can be recycled for the leaching and stripping process after purification by reduced pressure distillation, thereby realizing the recycling of chemical reagents, reducing the consumption of acid and alkali in the circulation process, and reducing the cost of raw materials.

[0008] The salt leaching-extraction method for cascade cycle recovery of lithium iron phosphate and ternary lithium battery powder of the present invention comprises the following steps:

[0009] 1) Mix the waste lithium iron phosphate battery positive electrode powder and the iron salt leaching agent, stir them thoroughly to react, and separate them by filtration to obtain the leachate S L1 and leached residue R L1 ;

[0010] 2) The leaching solution S in step 1) L1 Mix with the positive and negative mixed powders of waste nickel cobalt manganese oxide lithium batteries, add hydrochloric acid and hydrogen peroxide, stir well to react, and separate by filtration to obtain leachate S N1 and leached residue R N1 ;

[0011] 3) Step 1) and step 2) are recorded as one cycle of leaching; the leaching solution S N1 As the iron salt leaching agent, the next batch of waste lithium iron phosphate battery positive electrode powder is leached again according to step 1) to enter the next round of leaching cycle; in the nth round of leaching cycle, the waste lithium iron phosphate battery powder is leached to obtain the leachate S Ln and leached residue R Ln , the mixed powder of positive and negative electrodes of waste nickel cobalt manganese oxide lithium battery is leached to obtain leachate S Nn and leached residue R Nn ;

[0012] 4) When the lithium leaching rate of any step in a certain round of cyclic leaching process is less than the set threshold, the cycle is terminated after the current round of cyclic leaching; the leaching residues obtained in step 1) of each round of cyclic leaching process are combined into leaching residue R L , the leaching residue obtained in step 2) is combined into leaching residue R N ;

[0013] 5) The leached residue R in step 4) NMix with hydrochloric acid, stir thoroughly to react, and separate by filtration to obtain leachate S N’ and leached residue R N’ ;

[0014] 6) The last cycle leaching solution S of step 4) Nn and the leaching solution S in step 5) N’ After merging, the two phases are mixed with an extractant to obtain a raffinate phase and an iron-enriched extraction phase; the raffinate phase is an enriched solution of lithium, nickel, cobalt and manganese;

[0015] 7) Adding hydrochloric acid to the extraction phase in step 6) for stripping to obtain an organic phase and an aqueous phase enriched in iron; the organic phase is recovered as the extractant in step 6) for extraction; the aqueous phase is subjected to reduced pressure distillation to obtain a regenerated iron salt leaching agent.

[0016] In the method of the present invention, steps 1) to 5) all involve leaching operations, and the temperature and time of the leaching operation can be selected according to the operating conditions well known in the art; preferably, the temperature of the leaching operation can be a water bath condition of 20 to 70° C., and the time of the leaching operation can be 5 to 60 min.

[0017] In the above method, the number of cyclic leaching rounds is greater than one, and the specific number of rounds is determined based on the lithium leaching rate. When the lithium leaching rate in step 1) or step 2) of a certain round of cyclic leaching is less than the set threshold, it means that the leaching cycle is poor. If the cyclic leaching continues, the production efficiency will decrease. Therefore, the method of the present invention terminates the cycle after the cyclic leaching round in which this situation occurs, and enters the leaching agent extraction regeneration process. Among them, the set threshold can be selected according to the actual production needs. Typically, but not limited, the set threshold can be set to 90%.

[0018] Compared with the prior art, the present invention has the following beneficial effects:

[0019] (1) The advantage of the present invention is that iron salts are used instead of strong acids to ensure high leaching efficiency while reducing the amount of acid used, and directly obtaining a high-purity crude iron phosphate product, solving the problem of difficulty in recovering phosphorus and iron elements, and reducing the subsequent separation and purification costs. In the first round of circulation, the leaching rate of lithium in the positive electrode powder of waste lithium iron phosphate batteries can reach 99.58%, and the leaching rates of lithium, nickel, cobalt and manganese in the positive and negative mixed powders of waste nickel-cobalt-manganese oxide lithium batteries can reach 99.70%, 92.98%, 97.14% and 99.80%, respectively. After multiple rounds of circulation and a small amount of acid leaching, the total leaching rates of lithium, nickel, cobalt and manganese reach 99.74%, 99.93%, 99.54% and 99.40%, respectively.

[0020] (2) By using iron salt as a leaching intermediate and through the cyclic conversion mechanism of trivalent iron and divalent iron, the cascade recovery of waste lithium iron phosphate and lithium nickel cobalt manganese oxide battery powders was innovatively achieved. The lithium iron phosphate battery powder and lithium nickel cobalt manganese oxide battery powder were cleverly used as the reducing agent and oxidizing agent for leaching each other, which greatly reduced the use of redox agents.

[0021] (3) In the leaching cycle process, the recycling mechanism significantly reduces the cost of using the leaching agent. Based on the calculation of six rounds of leaching with fresh leaching agent, the cost of the leaching cycle process is 15% of the cost of combined salt leaching and 65% of the cost of independent acid leaching when leaching the same amount of waste lithium iron phosphate and lithium nickel cobalt manganese oxide battery materials. In addition, the concentration of valuable metals such as lithium, nickel, cobalt, and manganese in the leachate produced by the recycling process is high, and the energy consumption and wastewater volume required for subsequent separation and purification are reduced accordingly.

[0022] (4) With regard to the recycling of the leaching agent, the present invention has developed a more efficient mixed solvent system for the extraction-stripping process of iron ions, which can recover the iron in the leaching enrichment solution to regenerate the iron salt leaching agent solution for circulating leaching, thereby reducing the cost of the leaching agent raw materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 This is a process flow chart of the salt leaching-extraction method for cascade cycle recovery of lithium iron phosphate and ternary lithium battery powder provided by the present invention.

[0024] Figure 2 The leaching rate of valuable metals in the cascade recovery of waste lithium iron phosphate and lithium nickel cobalt manganese oxide battery powders in Example 1.

[0025] Figure 3 This is the leaching rate of valuable metals in the cascade recovery of waste lithium iron phosphate and lithium nickel cobalt manganese oxide battery powders in Example 2. DETAILED DESCRIPTION

[0026] In the present invention, iron salt is used as a leaching intermediate, lithium iron phosphate is used as a reducing agent, and lithium nickel cobalt manganese oxide is used as an oxidant. Through the redox process design, iron ions are cyclically converted in the form of trivalent iron and divalent iron during the leaching process, and waste lithium iron phosphate and lithium nickel cobalt manganese oxide battery powders are continuously leached. The main reaction equation is as follows:

[0027] ;

[0028] ;

[0029] Among them, x and y are both greater than 0 and less than 1.

[0030] The technical solution of the present invention is further explained below in conjunction with a specific implementation method.

[0031] The described embodiments are merely illustrative of the present disclosure and do not represent or limit the protection scope of the present invention. The protection scope of the present invention shall be subject to the claims.

[0032] In the following examples, flame atomic absorption spectrometer (FAAS, Thermo Fisher) was used to detect the metal concentration in the solution. In the wet leaching stage, the leaching rate of valuable metal elements was calculated as follows:

[0033]

[0034] Where, L is the leaching efficiency, %; c a is the concentration of valuable metal ions in the leachate, mg / L; V is the volume of the leachate, L; ω i is the mass fraction of each element in the battery powder obtained by dissolving and detecting with aqua regia; m is the mass of the waste battery powder, g; i represents the target element, which is Li, Ni, Co, Mn and Fe in this embodiment.

[0035] Figure 1 The process flow chart of the cascade recovery of valuable metals from waste lithium iron phosphate and nickel cobalt manganese oxide battery powders by cyclic salt leaching of the present invention is shown. Figure 1 As shown, as a preferred embodiment of the method of the present invention, it comprises the following steps:

[0036] 1) Mix the waste lithium iron phosphate cathode powder and ferric chloride solution according to the solid-liquid ratio of 10-200 g / L, stir and react for 5-60 min in a water bath at 20-70 °C, and separate the leaching solution S by filtration. L1 and leached residue R L1 ;

[0037] 2) According to the conversion molar ratio of waste lithium iron phosphate battery positive electrode powder and waste nickel cobalt manganese oxide battery positive and negative electrode mixed powder 1: (0.5~2), waste nickel cobalt manganese oxide battery positive and negative electrode mixed powder and leaching solution S L1 Mix, add hydrochloric acid and hydrogen peroxide, stir and react for 5-60 min in a water bath at 20-70℃, and separate by filtration to obtain the leachate S N1 and leached residue R N1 ;

[0038] 3) Step 1) and step 2) are recorded as one cycle of leaching, and the leaching solution S N1 As the iron salt leaching agent, the next batch of waste lithium iron phosphate battery positive electrode powder is leached again as in step 1), and the next round of leaching is entered; in the nth round of leaching, the waste lithium iron phosphate battery powder is leached to obtain the leachate S Ln and leached residue R Ln, the mixed powder of positive and negative electrodes of waste nickel cobalt manganese oxide lithium battery is leached to obtain leachate S Nn and leached residue R Nn ;

[0039] 4) Step 3) The cycle can be performed for n (n>1) rounds. If the lithium leaching rate of any step in a certain round of leaching is less than the set threshold value of 90%, the cycle is terminated after the current round of leaching to obtain the final round of leaching solution S Nn and leached residue R Nn ; The leaching residues obtained in step 1) of each round of leaching process are combined into leaching residue R L , the leaching residue obtained in step 2) is combined into leaching residue R N ;

[0040] 5) The leached residue R is mixed with water according to the solid-liquid ratio of 10-200 g / L. N Mix with 0.5~3 mol / L hydrochloric acid, stir and react for 5~60 min in a water bath at 20~70℃, and separate by filtration to obtain the leaching solution S N’ and leached residue R N’ ;

[0041] 6) The last cycle leaching solution S of step 4) Nn and the leachate S in step 5) N’ After merging, adding P204 and HTTA mixed solvent, placing in a water bath constant temperature oscillator, extracting at 10-30°C for 5-30 min, and obtaining a raffinate phase and an iron-enriched extraction phase; the raffinate phase is an enriched solution for recovering valuable metals in waste battery powder;

[0042] 7) The extract phase of step 6) is added with 2-6 mol / L hydrochloric acid for back extraction, placed in a water bath constant temperature oscillator, and back extracted at 10-50°C for 5-30 min to obtain an organic phase and an aqueous phase enriched in iron; the organic phase can be used again as the extractant of step 6) for extraction; the aqueous phase mainly contains ferric chloride and hydrochloric acid, and the regenerated iron salt is obtained after reduced pressure distillation and recycled as the leaching agent of step 1) in the first round of leaching.

[0043] The waste lithium iron phosphate battery positive electrode powder described in each embodiment of the present invention is obtained by pre-treatment of waste lithium iron phosphate batteries such as discharge, crushing and disassembly, and is allowed to contain a small amount of graphite. The waste lithium iron phosphate battery positive electrode powder is allowed to contain any one or more combinations of copper, manganese, aluminum or carbon elements, and its content range is: Cu element ≤ 0.5wt.%, Mn element ≤ 0.5wt.%, Al element ≤ 1wt.%, carbon element content ≤ 10wt.%. The iron salt leaching agent in the first cycle leaching process of the present invention is preferably ferric chloride, wherein the molar amount of iron is 1 to 2 times the molar amount of effective lithium in the waste lithium iron phosphate battery powder.

[0044] The mixed positive and negative electrode powders of the waste nickel cobalt manganese acid lithium battery described in each embodiment of the present invention are obtained by pre-treatment of the waste nickel cobalt manganese acid lithium battery such as discharge, crushing and disassembly, wherein, in addition to the positive electrode powder and graphite of the nickel cobalt manganese acid lithium battery, it is allowed to contain any one or more of other negative electrode materials, binders, current collectors or electrolytes. The positive electrode powder of the waste nickel cobalt manganese acid lithium battery may include one or more of lithium manganate, lithium nickelate, lithium cobaltate and lithium nickel cobalt manganese acid; the mixed positive and negative electrode powders of the waste nickel cobalt manganese acid lithium battery are allowed to contain any one or more of copper element, aluminum element or carbon element, and the content range is: Cu element ≤ 2wt.%, Al element ≤ 1wt.%, and carbon element content ≤ 40wt.%.

[0045] In each embodiment, the concentration of hydrochloric acid in step 2) is in the range of 3-6 mol / L, and the molar amount of hydrogen ions is 1-3 times the molar amount of the mixed positive and negative electrode powders of the waste nickel cobalt manganese oxide lithium battery. The concentration of hydrogen peroxide solution in step 2) is in the range of 2wt.%-15wt.%, and the molar amount of hydrogen peroxide is 0.05-0.2 times the molar amount of the mixed positive and negative electrode powders of the waste nickel cobalt manganese oxide lithium battery.

[0046] In each embodiment, the mixed solvent in step 6) is a mixed solvent formed by P204 and HTTA, and the molar ratio of P204 to HTTA used is (1-3):1; the mixing temperature is 40-80°C, and the mixing time is 5-30 min.

[0047] According to the present invention Figure 1 The process of the present invention is shown in the flow chart, the leaching residue R L It can be used as crude iron phosphate. N’ Can be used as crude graphite.

[0048] Example 1

[0049] Combine the following Figure 1 , the cascade recovery of valuable metals from waste lithium iron phosphate and lithium nickel cobalt manganese oxide battery powders by cyclic salt leaching of the present invention is demonstrated in detail:

[0050] 1) Mix the waste lithium iron phosphate cathode powder and ferric chloride solution at a solid-liquid ratio of 50 g / L, stir and react for 30 min in a 50°C water bath, and separate the leaching solution S by filtration. L1 and leached residue R L1 ;

[0051] 2) The converted molar amount of the battery is defined by the effective molar amount of lithium in the powder. According to the conversion molar ratio of the positive electrode powder of the waste lithium iron phosphate battery and the positive and negative electrode mixed powder of the waste nickel cobalt manganese oxide battery of 1:1, the waste nickel cobalt manganese oxide positive and negative electrode mixed powder is mixed with the leaching solution SL1 Mix, add 3.75 mL 6 mol / L hydrochloric acid and 0.56 mL 6wt.% hydrogen peroxide to each gram of the mixed powder of the positive and negative electrodes of the waste nickel cobalt manganese oxide lithium battery, stir and react for 30 min in a 50℃ water bath, and separate by filtration to obtain the leachate S N1 and leached residue R N1 ;

[0052] 3) Step 1) and step 2) can be recorded as one cycle of leaching, and the leaching solution S N1 As the iron salt leaching agent, the next batch of waste lithium iron phosphate battery positive electrode powder is leached again according to step 1) to enter the next round of leaching cycle; in the nth round of leaching cycle, the waste lithium iron phosphate battery powder is leached to obtain the leachate S Ln and leached residue R Ln , the mixed powder of positive and negative electrodes of waste nickel cobalt manganese oxide lithium battery is leached to obtain leachate S Nn and leached residue R Nn ;

[0053] 4) The cycle of step 3) can be carried out for 6 rounds; during each round of leaching, the leached residue R obtained in step 1) Ln Combined into leaching residue R L , the leaching residue obtained in step 2) is combined into leaching residue R N ; The leached residue R L It is a crude product of iron phosphate;

[0054] 5) The leached residue R is mixed with water according to the solid-liquid ratio of 100 g / L. N Mix with 2 mol / L hydrochloric acid, stir and react in a 50℃ water bath for 30 min, and separate by filtration to obtain the leachate S N’ and crude graphite products;

[0055] 6) Stir P204 and HTTA at 50°C to form a clear and transparent yellow mixed solvent, and combine the sixth cycle leachate S from step 4) N6 and the leaching solution S in step 5) N’ Then add the mixed solvent, place in a water bath constant temperature oscillator, extract at 20°C for 20 min, and obtain a raffinate phase and an iron-enriched extraction phase; the raffinate phase is an enriched solution for recovering valuable metals in waste battery powder ( Figure 1 Li, Ni, Co, Mn enriched solution);

[0056] 7) The extract phase of step 6) is added with 6 mol / L hydrochloric acid for back extraction, placed in a water bath constant temperature oscillator, and back extracted at 50°C for 20 min to obtain an organic phase and an aqueous phase enriched in iron; the organic phase can be used again as the extractant of step 6) for extraction; the aqueous phase mainly contains ferric chloride and hydrochloric acid, and the regenerated iron salt is obtained after reduced pressure distillation as the leaching agent of step 1) of the first round of leaching.

[0057] Example 1 The leaching rate results of cascade recovery of waste lithium iron phosphate and lithium nickel cobalt manganese oxide battery powder are shown in the attached figure. Figure 2 shown.

[0058] from Figure 2 It can be seen that in the first cycle, the method of the present invention can achieve a leaching rate of 99.58% for lithium in the positive electrode powder of waste lithium iron phosphate batteries, and 99.70%, 92.98%, 97.14% and 99.80% for lithium, nickel, cobalt and manganese in the mixed positive and negative electrode powders of waste lithium nickel cobalt manganese oxide batteries. After 6 cycles and a small amount of acid leaching, the total leaching rates of lithium, nickel, cobalt and manganese reached 99.74%, 99.93%, 99.54% and 99.40% respectively.

[0059] Example 2

[0060] 1) Mix the waste lithium iron phosphate cathode powder and ferric chloride solution at a solid-liquid ratio of 200 g / L, stir and react for 30 min in a 50°C water bath, and separate the leaching solution S by filtration. L1 and leached residue R L1 ;

[0061] 2) The converted molar amount of the battery is defined by the effective molar amount of lithium in the powder. According to the conversion molar ratio of the positive electrode powder of the waste lithium iron phosphate battery and the positive and negative electrode mixed powder of the waste nickel cobalt manganese oxide battery of 1:1, the waste nickel cobalt manganese oxide positive and negative electrode mixed powder is mixed with the leaching solution S L1 Mix, add 3.75 mL 6 mol / L hydrochloric acid and 0.56 mL 6wt.% hydrogen peroxide to each gram of the mixed powder of the positive and negative electrodes of the waste nickel cobalt manganese oxide lithium battery, stir and react for 30 min in a 50℃ water bath, and separate by filtration to obtain the leachate S N1 and leached residue R N1 ;

[0062] 3) Step 1) and step 2) can be recorded as one cycle of leaching, and the leaching solution S N1 As the iron salt leaching agent, the next batch of waste lithium iron phosphate battery positive electrode powder is leached again according to step 1) to enter the next round of leaching cycle; in the nth round of leaching cycle, the waste lithium iron phosphate battery powder is leached to obtain the leachate S Ln and leached residue R Ln, the mixed powder of positive and negative electrodes of waste nickel cobalt manganese oxide lithium battery is leached to obtain leachate S Nn and leached residue R Nn ;

[0063] 4) The cycle of step 3) can be carried out for 2 rounds; during each round of leaching, the leached residue R obtained in step 1) Ln Combined into leaching residue R L , the leaching residue obtained in step 2) is combined into leaching residue R N ; The leached residue R L It is a crude product of iron phosphate;

[0064] 5) The leached residue R is mixed with water according to the solid-liquid ratio of 100 g / L. N Mix with 2 mol / L hydrochloric acid, stir and react in a 50℃ water bath for 30 min, and separate by filtration to obtain the leachate S N’ and crude graphite products;

[0065] 6) Stir P204 and HTTA at 50°C to form a clear and transparent yellow mixed solvent, and combine the second round of leaching solution S from step 4) N2 and the leaching solution S in step 5) N’ Then add the mixed solvent, place in a water bath constant temperature oscillator, extract at 20°C for 20 min, and obtain a raffinate phase and an iron-enriched extraction phase; the raffinate phase is an enriched solution for recovering valuable metals in waste battery powder ( Figure 1 Li, Ni, Co, Mn enriched solution);

[0066] 7) The extract phase of step 6) is added with 6 mol / L hydrochloric acid for back extraction, placed in a water bath constant temperature oscillator, and back extracted at 50°C for 20 min to obtain an organic phase and an aqueous phase enriched in iron; the organic phase can be used again as the extractant of step 6) for extraction; the aqueous phase mainly contains ferric chloride and hydrochloric acid, and the regenerated iron salt is obtained after reduced pressure distillation and recycled as the leaching agent of the first round of leaching step 1).

[0067] Example 2 The leaching rate results of cascade recovery of waste lithium iron phosphate and lithium nickel cobalt manganese oxide battery powder are shown in the attached Figure 3 shown.

[0068] from Figure 3 It can be seen that in the first cycle, the method of the present invention can achieve a lithium leaching rate of 98.55% in the positive electrode powder of waste lithium iron phosphate batteries, and the leaching rates of lithium, nickel, cobalt and manganese in the positive and negative mixed powders of waste lithium nickel cobalt manganese oxide batteries reach 97.64%, 92.80%, 91.05% and 94.16%, respectively.

[0069] In the leaching cycle process of the present invention, the use cost of the leaching agent is greatly reduced through the circulation mechanism. Based on the calculation of 6 rounds of leaching by fresh leaching agent in Example 1, compared with leaching of the same amount of waste lithium iron phosphate and lithium nickel cobalt manganese oxide battery materials, the cost of the leaching cycle process is 15% of the cost of combined salt leaching and 65% of the cost of independent acid leaching. In addition, the concentration of valuable metals such as lithium, nickel, cobalt, and manganese in the leachate generated by the circulation process is high, and the energy consumption and wastewater volume required for subsequent separation and purification are correspondingly reduced.

[0070] The present invention develops and adopts a more efficient mixed solvent system for the extraction-stripping process of iron ions, which can recover the iron in the leaching enrichment solution to regenerate the iron salt leaching agent solution for cyclic leaching, thereby reducing the cost of the leaching agent raw materials.

[0071] The applicant declares that the above is only a specific implementation mode of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention shall fall within the protection scope and disclosure scope of the present invention.

Claims

1. A salt leaching-extraction method for recovering lithium iron phosphate and ternary lithium battery powder by cascade circulation, characterized in that: The method comprises the following steps: 1) Mix the waste lithium iron phosphate battery positive electrode powder and the iron salt leaching agent, stir them thoroughly to react, and separate them by filtration to obtain the leachate S L1 and leached residue R L1 ; 2) The leaching solution S in step 1) L1 Mix with the positive and negative mixed powders of waste nickel cobalt manganese oxide lithium batteries, add hydrochloric acid and hydrogen peroxide, stir well to react, and separate by filtration to obtain leachate S N1 and leached residue R N1 ; 3) Step 1) and step 2) are recorded as one cycle of leaching; the leaching solution S N1 As the iron salt leaching agent, the next batch of waste lithium iron phosphate battery positive electrode powder is leached again according to step 1) to enter the next round of leaching cycle; in the nth round of leaching cycle, the waste lithium iron phosphate battery powder is leached to obtain the leachate S Ln and leached residue R Ln , the mixed powder of positive and negative electrodes of waste nickel cobalt manganese oxide lithium battery is leached to obtain leachate S Nn and leached residue R Nn ; 4) When the lithium leaching rate of any step in a certain round of cyclic leaching process is less than the set threshold, the cycle is terminated after the current round of cyclic leaching; the leaching residues obtained in step 1) of each round of cyclic leaching process are combined into leaching residue R L , the leached residue obtained in step 2) is combined into leached residue R N ; 5) The leached residue R in step 4) N Mix with hydrochloric acid, stir thoroughly to react, and separate by filtration to obtain leachate S N’ and leached residue R N’ ; 6) The last cycle leaching solution S of step 4) Nn and the leaching solution S in step 5) N’ After merging, the mixture is mixed with an extractant to obtain a raffinate phase and an iron-enriched extraction phase; the raffinate phase is an enriched solution of lithium, nickel, cobalt and manganese; 7) Adding hydrochloric acid to the extraction phase in step 6) for stripping to obtain an organic phase and an aqueous phase enriched in iron; the organic phase is recovered as the extractant in step 6) for extraction; the aqueous phase is subjected to reduced pressure distillation to obtain a regenerated iron salt leaching agent.

2. The method according to claim 1, characterized in that Step 1) The waste lithium iron phosphate battery positive electrode powder is obtained by discharging, crushing and disassembling the waste lithium iron phosphate battery, and is allowed to contain one or more of copper, manganese, aluminum or carbon elements, and the content range is: Cu element ≤ 0.5wt.%, Mn element ≤ 0.5wt.%, Al element ≤ 1wt.%, carbon element content ≤ 10wt.%.

3. The method according to claim 1, characterized in that In the first round of leaching, the iron salt leaching agent in step 1) is a ferric chloride solution; the molar amount of iron is 1 to 2 times the molar amount of effective lithium in the waste lithium iron phosphate battery powder; the leaching solid-liquid ratio in step 1) is 10 to 200 g / L.

4. The method according to claim 1, characterized in that: Step 2) The mixed positive and negative electrode powders of waste nickel cobalt manganese oxide batteries are obtained by discharging, crushing and disassembling waste nickel cobalt manganese oxide batteries, including one or more of lithium nickel oxide, lithium cobalt oxide, lithium manganese oxide and lithium nickel cobalt manganese oxide; wherein the mixed powders are allowed to contain any one or more of copper element, aluminum element or carbon element, and the content range is: Cu element ≤ 2wt.%, Al element ≤ 1wt.%, and carbon element content ≤ 40wt.%.

5. The method according to claim 1, characterized in that The converted molar amount is defined by the molar amount of effective lithium in the powder. In the same cycle leaching, the converted molar amount ratio of the mixed positive and negative electrode powder of the waste nickel cobalt manganese oxide lithium battery in step 2) to the positive electrode powder of the waste lithium iron phosphate battery in step 1) is 0.5-2.

6. The method according to claim 5, characterized in that In step 2), the concentration of hydrochloric acid is in the range of 3-6 mol / L, and the molar amount of hydrogen ions is 1-3 times the molar amount of the mixed positive and negative electrode powders of the waste nickel cobalt manganese oxide lithium battery; the concentration of hydrogen peroxide solution in step 2) is in the range of 2wt.%-15wt.%, and the molar amount of hydrogen peroxide is 0.05-0.2 times the molar amount of the mixed positive and negative electrode powders of the waste nickel cobalt manganese oxide lithium battery; the leaching solid-liquid ratio in step 2) is 10-200 g / L.

7. The method according to claim 1, characterized in that The hydrochloric acid concentration in step 5) is in the range of 0.5-3 mol / L; the leaching solid-liquid ratio in step 5) is 10-200 g / L.

8. The method according to claim 1, characterized in that: The extractant in step 6) is a mixed solvent formed by di(2-ethylhexyl) phosphate and 2-thenoyltrifluoroacetone; the molar ratio of di(2-ethylhexyl) phosphate to 2-thenoyltrifluoroacetone is (1-3):1; and the mixture is stirred at a constant temperature of 40-80°C for 5-60 min.

9. The method according to claim 1, characterized in that: Step 6) During the extraction process, the volume ratio of the extracted organic phase to the aqueous phase is (1-2):1; the extraction is a single-stage or multi-stage extraction.

10. The method according to claim 1, characterized in that Step 7) The hydrochloric acid concentration ranges from 0.5 to 6 mol / L; during the stripping process, the volume ratio of the extracted organic phase to the aqueous phase is (1 to 2):1; the stripping is single-stage or multi-stage stripping.

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