Iron and lithium separation method of waste lithium iron phosphate positive electrode material

Abstract

The invention belongs to the field of battery waste recovery, and particularly relates to an iron and lithium separation method of a waste lithium iron phosphate positive electrode material, which comprises the following steps: mixing black powder to be treated containing the waste lithium iron phosphate positive electrode material, an auxiliary agent (shown in the formula 1) and water to obtain mixed slurry, continuously blowing an oxygen-containing atmosphere into the mixed slurry for leaching treatment, and then carrying out solid-liquid separation, lithium leaching liquid and iron-containing slag are obtained; in the formula 1, X1 and X2 are independently C1-C6 carbon chains, in R1 and R2, one substituent group is-COOH,-SO3H or-SO4H, and the other substituent group is H,-COOH,-SO3H or-SO4H; a <-> is Cl <->, Ac <->, HSO4 <->, BF4 <->, PF6 <-> or CF3COO <->; the concentration of the formula 1 in the mixed slurry is 0.02 M or above, and the leaching process is 70 DEG C or above. According to the method disclosed by the invention, the crystal structure of the lithium iron phosphate can be selectively disintegrated, and the selective separation of lithium and iron can be realized with high selectivity.

Description

Technical Field

[0001] The present invention belongs to the field of waste battery material recycling, and particularly relates to the field of waste lithium iron phosphate recycling. Background Art

[0002] Currently, hydrometallurgical processes are well-developed and can efficiently extract valuable metals from spent lithium-ion batteries. These processes offer advantages such as simple operation, high metal recovery rates, and low carbon emissions. The key to the hydrometallurgical process lies in suitable and efficient leaching agents, whose leaching efficiency and metal selectivity significantly influence the recovery of valuable metals from spent lithium-ion batteries.

[0003] There are some prior art processes for preferentially extracting lithium through oxidative acid leaching. For example, Chinese patent document CN114865129A discloses a wet method for recovering retired lithium iron phosphate battery powder to extract lithium and prepare lithium carbonate. Specifically, the method includes adding retired LiFePO4 and an oxidant into a container, and then adding water to form a mixed solution; heating the mixed solution to 40-80°C, adding acid solution for acid leaching and dissolution, maintaining the mixture for reaction, stopping heating, and filtering to obtain a lithium-containing filtrate and iron phosphate residue.

[0004] For example, publication number CN116814984A discloses a method for extracting lithium from waste lithium iron phosphate batteries, wherein fine powder of waste lithium iron phosphate is calcined at high temperature in a rotary kiln, and then mechanically crushed and ball-milled to obtain calcined and crushed fine powder; the calcined and crushed fine powder clinker is fully stirred with an acid solution for leaching, and after adjusting the pH, solid-liquid separation is performed to obtain a lithium-containing solution and leached residue.

[0005] Although the existing lithium extraction process for waste lithium iron phosphate batteries can achieve good lithium extraction results, the separation selectivity of iron and lithium still needs to be improved. In addition, the efficiency of the existing leaching process is not ideal, and the leaching agent is difficult to recycle. Summary of the Invention

[0006] To solve the above problems, the first purpose of the present invention is to provide a method for separating iron and lithium from waste lithium iron phosphate positive electrode materials, aiming to provide a method that can achieve efficient, mild and highly selective separation of lithium and iron in waste lithium iron phosphate.

[0007] The unit cell structure of lithium iron phosphate belongs to the orthorhombic system, with a space group of Pnma. The unit cell contains four Li atoms, four Fe atoms, four P atoms, and sixteen O atoms. The Fe atom is located at the 4a site of the unit cell, the Li atom is located at the 8c site, the P atom is located at the 4b site, and the O atom is located at the 16e site. The lithium and iron in this crystalline compound are difficult to separate efficiently and selectively. To address this problem, the present invention provides a green lithium extraction method:

[0008] A method for separating iron and lithium from waste lithium iron phosphate positive electrode materials comprises mixing black powder to be treated containing waste lithium iron phosphate positive electrode materials, an additive of formula 1, and water to obtain a mixed slurry, continuously blowing an oxygen-containing atmosphere into the mixed slurry for leaching treatment, and then performing solid-liquid separation to obtain a lithium leachate and iron-containing slag;

[0009] Formula 1

[0010] In Formula 1, X1 and X2 are independently C1-C6 carbon chains; among R1 and R2, one of the substituents is -COOH, -SO3H or -SO4H, and the other substituent is H, -COOH, -SO3H or -SO4H; the A - Cl - 、Ac - 、HSO4 - 、BF4 - PF6 - or CF3COO - ;

[0011] The concentration of Formula 1 in the mixed slurry is above 0.02M, and the leaching process is above 70°C.

[0012] The present invention innovatively adopts functionalized Formula 1 as an auxiliary agent, combined with an oxygen-containing atmosphere airflow-assisted leaching process and the joint control of the concentration of Formula 1 and the leaching temperature, thereby achieving synergy, selectively decomposing the crystal structure of lithium iron phosphate, and achieving selective separation of lithium and iron with high selectivity.

[0013] In the present invention, the waste lithium iron phosphate positive electrode material is the material stripped from the positive electrode of the waste lithium iron phosphate battery. The stripping method can be conventional.

[0014] In the present invention, the black powder to be processed may also contain at least one of a conductive agent, a binder, a separator, and a current collector. Furthermore, the black powder to be processed is material obtained by stripping waste lithium iron phosphate positive electrodes, and for example, contains lithium iron phosphate and a carbonaceous conductive agent.

[0015] In the present invention, the content of lithium iron phosphate in the black powder to be processed is above 50 wt.%, and considering the processing efficiency, it can be further above 80 wt.%, for example, 80-98 wt.%.

[0016] In the present invention, the combination of the auxiliary agent of Formula 1 and the airflow leaching process in an oxygen-containing atmosphere can achieve synergy and can synergistically improve the separation efficiency and selectivity of lithium and iron.

[0017] In the present invention, the structure of formula 1 and A - The combined control method is one of the keys to synergistically enhance the separation of lithium and iron in lithium iron phosphate.

[0018] In the present invention, in the auxiliary agent of formula 1, X1 is a C1~C6 carbon chain, R1 is -COOH or -SO3H, X2 is a C1~C6 carbon chain, and R2 is H.

[0019] Preferably, the A - HSO4 - .

[0020] Preferably, the auxiliary agent of formula 1 is formula 1A;

[0021] Formula 1A.

[0022] In the present invention, the innovative use of formula 1, further combined with the joint control of parameters such as concentration and leaching temperature, helps to further enhance the leaching selectivity of iron and lithium in lithium iron phosphate.

[0023] Preferably, in the mixed slurry, the concentration of the additive of formula 1 is 0.02 to 0.07 M, preferably 0.025 to 0.035 M. In the present invention, the preferred concentration can further enhance the selective leaching effect of lithium and iron in lithium iron phosphate.

[0024] The solid content of the black powder to be processed in the mixed slurry is 1-25 g / L, preferably 5-20 g / L; more preferably 15-20 g / L; and further preferably 15 g / L, 16 g / L, 17 g / L, 18 g / L, 19 g / L, or 20 g / L. In the present invention, the preferred solid content can further enhance the selective leaching of lithium and iron from the lithium iron phosphate.

[0025] In the present invention, the oxygen-containing atmosphere is an atmosphere containing oxygen, preferably at least one of oxygen, an oxygen-protective gas mixture, and air.

[0026] Preferably, the oxygen-containing atmosphere may be, for example, oxygen, wherein the volume content of oxygen may be above 95%.

[0027] In the present invention, the flow rate of the oxygen-containing atmosphere is 0.1 to 5 L / min, preferably 0.5 to 2 L / min.

[0028] In the present invention, the temperature of the leaching process is 70° C. to 100° C., preferably 85° C. to 95° C. In the present invention, the preferred leaching temperature can further enhance the selective leaching effect of lithium and iron in lithium iron phosphate.

[0029] In the present invention, the leaching time is 0.5 h to 5 h, preferably 1 h to 3 h, and further can be 2 h to 2.5 h.

[0030] In the present invention, a solid and a target solution rich in lithium can be obtained by conventional solid-liquid separation (such as filtration, centrifugation, etc.), and the solid is dried and ground.

[0031] In the present invention, after the lithium leaching solution is treated by lithium precipitation, the mother liquor after lithium precipitation is used as a leaching agent and is circulated for leaching the black powder to be treated.

[0032] Beneficial effects

[0033] The present invention innovatively adopts functionalized Formula 1 as an auxiliary agent, combined with an oxygen-containing atmosphere airflow-assisted leaching process, thereby achieving synergy, selectively decomposing the crystal structure of lithium iron phosphate, and achieving selective separation of lithium and iron with high selectivity.

[0034] The present invention eliminates the need for ball milling and calcination activation of lithium iron phosphate, and can control the leaching time to within 2 hours. Under normal pressure, the lithium extraction rate is as high as 99.99%, and the iron leaching rate is less than 0.5%, achieving highly selective lithium separation. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 The XRD patterns of the residue before and after leaching of Example 5C are shown;

[0036] Figure 2 These are SEM images of the slag before and after leaching in Example 5C, wherein Figure a is the SEM image of the black powder before leaching and Figure b is the SEM image of the slag after leaching; DETAILED DESCRIPTION

[0037] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts are within the scope of protection of the present invention.

[0038] In the following case study, the waste lithium iron phosphate cathode powder (also known as black powder) to be processed is the waste cathode component stripped from the cathode of a used lithium iron phosphate battery. Its primary component is lithium iron phosphate, and it also contains a certain amount of conductive agent. As an optional solution, the black powder selected in the following case study has a lithium iron phosphate content between 85% and 90% by weight.

[0039] In the following cases, the oxygen used refers to commercial oxygen with a concentration of more than 95%.

[0040] Example 1

[0041] 2 g of waste lithium iron phosphate positive electrode powder was weighed and placed in a reaction vessel. 200 mL of a leaching agent (an aqueous solution containing Formula 1A, wherein the concentration of Formula 1A was 0.05 M) was added. The temperature was adjusted to 90°C, and oxygen was continuously pumped into the system (at a pumping volume of 1 L / min). After leaching for 2 h, solid-liquid separation was performed.

[0042] The results were: lithium leaching rate was 99.99% and iron leaching rate was 18.66%.

[0043] Example 2

[0044] Compared with Example 1, the only difference is that the leaching time is 2.5 hours; the other operations and parameters are the same as Example 1. The results are: the lithium leaching rate reaches 99.99%, and the iron leaching rate is 16.02%.

[0045] Example 3

[0046] Compared with Example 1, the only difference is that the temperature of the leaching process is changed. The experimental groups are:

[0047] Group A: leaching temperature was 30°C;

[0048] Group B: leaching temperature was 50°C;

[0049] Group C: leaching temperature was 70°C;

[0050] The results are:

[0051] Group A: lithium leaching rate was 88.14%, iron leaching rate was 75.01%;

[0052] Group B: lithium leaching rate was 94.90%, iron leaching rate was 48.31%;

[0053] Group C: lithium leaching rate was 99.99%, and iron leaching rate was 26.80%.

[0054] It can be seen from Example 3 that when the leaching temperature is above 70° C., a good lithium extraction effect can be obtained, with better iron-lithium selectivity.

[0055] Example 4

[0056] Compared with Example 1, the only difference is that the concentration of Formula 1A in the leachate is changed. The experimental groups are:

[0057] Group A: the concentration of Formula 1A in the leachate was 0.01 M;

[0058] Group B: the concentration of Formula 1A in the leachate was 0.03 M;

[0059] Group C: the concentration of Formula 1A in the leachate was 0.07 M;

[0060] The results are:

[0061] Group A: lithium leaching rate was 76.66%, iron leaching rate was 0.09%;

[0062] Group B: lithium leaching rate was 99.99%, iron leaching rate was 4.77%;

[0063] Group C: lithium leaching rate was 99.99%, and iron leaching rate was 23.90%.

[0064] Example 5

[0065] Compared with Example 4B, the only difference is that the amount of black powder is changed. The experimental groups are:

[0066] Group A: black powder dosage was 1g;

[0067] Group B: black powder dosage was 3 g;

[0068] Group C: black powder dosage was 4 g;

[0069] Group D: black powder dosage was 5 g;

[0070] The results are:

[0071] Group A: lithium leaching rate was 99.99%, iron leaching rate was 27.50%;

[0072] Group B: lithium leaching rate was 99.99%, iron leaching rate was 3.90%;

[0073] Group C: lithium leaching rate was 99.99%, and iron leaching rate was 0.22%.

[0074] Group D: lithium leaching rate was 80.40%, and iron leaching rate was 0.26%.

[0075] Example 6

[0076] Compared with Example 5C, the only difference is that the oxygen introduction rate is changed. The experimental groups are:

[0077] Group A: oxygen was pumped at a rate of 0.5 L / min;

[0078] Group B: oxygen was pumped at a rate of 1.5 L / min;

[0079] The results are:

[0080] Group A: lithium leaching rate is 99.99%, iron leaching rate is 1.808%;

[0081] Group B: lithium leaching rate was 99.99%, iron leaching rate was 0.11%;

[0082] The final optimal conditions were leaching time of 2 h, temperature of 90 °C, concentration of Formula 1A of 0.03 M, solid-liquid ratio of 20 g / L, and oxygen rate of 1 L / min.

[0083] Comparative Example 1

[0084] Compared with Example 5C, the only difference is that Formula 1A is not added to the leaching agent, and other operations and parameters are the same as Example 5C.

[0085] During the leaching process, the leaching rate of lithium was 2.88%, and the leaching rate of iron was 0.048%.

[0086] Comparative Example 2

[0087] Compared with Example 5C, the only difference is that the leaching process is carried out in an oxygen atmosphere, but oxygen is not continuously pumped in. Other operations and parameters are the same as those of Example 5C.

[0088] During the leaching process, the leaching rate of lithium was 53.78%, and the leaching rate of iron was 21.91%.

[0089] Comparative Example 3

[0090] Compared with Example 5C, the only difference is that the following comparative compound is used to replace Formula 1A in equal moles, and the other operations and parameters are the same as those of Example 5C; the experimental groups are:

[0091] Group A: Using comparative A Replacement 1A;

[0092] Group B: using contrast B Replacement 1A;

[0093] Group C: using comparative C Replacement 1A;

[0094] The results are:

[0095] Group A: The leaching rate of lithium is 36.85%, and the leaching rate of iron is 0.76%.

[0096] Group B: The leaching rate of lithium was 66.72%, and the leaching rate of iron was 3.70%.

[0097] Group C: The leaching rate of lithium was 39.04%, and the leaching rate of iron was 0.21%.

Claims

1. A method for separating iron and lithium from waste lithium iron phosphate positive electrode materials, characterized in that: The black powder to be treated containing waste lithium iron phosphate positive electrode material, the auxiliary agent of formula 1, and water are mixed to obtain a mixed slurry, and an oxygen-containing atmosphere is continuously blown into the mixed slurry to perform a leaching treatment, followed by solid-liquid separation to obtain a lithium leachate and iron-containing slag; Formula 1; In Formula 1, X1 and X2 are independently C1-C6 carbon chains; among R1 and R2, one of the substituents is -COOH, -SO3H or -SO4H, and the other substituent is H, -COOH, -SO3H or -SO4H; the A - Cl - 、Ac - 、HSO4 - 、BF4 - PF6 - or CF3COO - ; The concentration of Formula 1 in the mixed slurry is above 0.02M, and the leaching process is above 70°C.

2. The method for separating iron and lithium from waste lithium iron phosphate cathode materials according to claim 1, wherein: Waste lithium iron phosphate positive electrode material is the material stripped from the positive electrode of waste lithium iron phosphate batteries; Preferably, the black powder to be processed may further contain at least one component selected from the group consisting of a conductive agent, a binder, a separator, and a current collector. Preferably, the content of lithium iron phosphate in the black powder to be processed is above 50 wt.%.

3. The method for separating iron and lithium from waste lithium iron phosphate cathode materials according to claim 1, wherein: In the additive of formula 1, X1 is a carbon chain of C1 to C6, R1 is -COOH or -SO3H, X2 is a carbon chain of C1 to C6, and R2 is H; Preferably, the A - HSO4 - .

4. The method for separating iron and lithium from waste lithium iron phosphate cathode materials according to claim 3, characterized in that: The auxiliary agent of formula 1 is formula 1A; Formula 1A.

5. The method for separating iron and lithium from waste lithium iron phosphate cathode materials according to claim 1, wherein: In the mixed slurry, the concentration of the additive of formula 1 is 0.02~0.07M; preferably 0.025~0.035M; The solid content of the black powder to be processed in the mixed slurry is 1-25 g / L, preferably 5-20 g / L.

6. The method for separating iron and lithium from waste lithium iron phosphate cathode materials according to claim 1, characterized in that: The oxygen-containing atmosphere is an atmosphere containing oxygen, preferably at least one of oxygen, an oxygen-protective gas mixture, and air; Preferably, the volume content of oxygen in the oxygen-containing atmosphere is above 95%.

7. The method for separating iron and lithium from waste lithium iron phosphate cathode materials according to claim 1, characterized in that: The flow rate of the oxygen-containing atmosphere is 0.1 to 5 L / min, preferably 0.5 to 2 L / min.

8. The method for separating iron and lithium from waste lithium iron phosphate cathode materials according to claim 1, wherein: The temperature during the leaching process is 70°C to 100°C, preferably 85°C to 95°C.

9. The method for separating iron and lithium from waste lithium iron phosphate cathode materials according to claim 1, characterized in that: The leaching time is 0.5h~5h, preferably 1~3h.

10. The method for separating iron and lithium from waste lithium iron phosphate cathode materials according to any one of claims 1 to 9, characterized in that: After the lithium leaching solution is treated with lithium precipitation, the mother liquor after lithium precipitation is used as a leaching agent and is recycled for leaching the black powder to be treated.

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