A method for recovering lithium from waste lithium iron phosphate positive electrode material

Abstract

The invention discloses a method for recovering lithium in waste lithium iron phosphate positive electrode materials. The method includes mixing the pretreated positive electrode material with a leaching agent, directly leaching lithium by stirring, and obtaining a mixed slurry of lithium leachate and leaching residue; the lithium leachate obtained after the solid-liquid separation of the mixed slurry is allowed to settle for 5-10 hours to precipitate byproducts, and filtered to obtain a pure lithium-containing liquid; the pure lithium-containing liquid is concentrated into a high-concentration lithium-rich liquid; sodium carbonate is added to the high-concentration lithium-rich liquid, solids are collected after the reaction, and pure lithium carbonate is obtained by washing and drying; the leaching residue obtained after the solid-liquid separation of the mixed slurry is washed, dried, and sieved to obtain a pure aluminum foil current collector and iron phosphate. The present invention can achieve a lithium leaching rate of more than 95% and a lithium selectivity of more than 99%. The obtained lithium-rich liquid obtains pure lithium carbonate by simple dosing, and the residue is a pure aluminum foil current collector and iron phosphate that are automatically separated, which can be separated by simple screening, and the iron phosphate and aluminum foil recovery rates are both more than 98%.

Description

[0001] Technology Neighborhood

[0002] The present invention belongs to the technical field of resource recovery and relates to a method for recovering lithium from waste lithium iron phosphate positive electrode materials. Background Art

[0003] The carbon neutrality agenda is driving the rapid development of electric vehicles and plug-in hybrid electric vehicles. Lithium iron phosphate (LiFePO4) is an excellent cathode active material, offering advantages such as fast response, long life, and improved resource availability. It has attracted considerable attention as a preferred cathode material for automotive power lithium batteries. Statistics show that the global stock of electric vehicles (including both EVs and PHEVs) is growing rapidly, and the number of lithium batteries is expected to grow nearly linearly over the next 30 years. LiFePO4 batteries have a lifespan of 5-8 years, and the disposal of large quantities of spent LiFePO4 batteries is foreseeable to become a critical component of the new energy sector. On the one hand, the accumulation of these spent lithium batteries poses significant environmental risks, such as leakage of organic electrolytes, which can seriously impact the atmosphere and soil, and ultimately human health. On the other hand, spent LiFePO4 batteries contain lithium, a strategic metal resource in short supply in my country with high recycling value. Therefore, achieving efficient recycling of spent LiFePO4 batteries is of strategic importance for alleviating my country's lithium resource shortage and ensuring the green and circular development of the country's lithium-ion battery industry.

[0004] Conventional processing techniques for spent lithium iron phosphate batteries primarily include discharge-pyrometallurgy and discharge-disassembly-crushing-positive electrode material enrichment-hydrometallurgy. The pyrometallurgical recovery method involves slag smelting of spent lithium-ion batteries using materials such as construction cement. The smelting temperature reaches temperatures exceeding 1200°C, at which point cobalt, copper, nickel, and iron are present as elemental metals, while lithium and aluminum are not recovered. The advantage of this method is that it requires minimal battery sorting, and even pre-processing such as disassembly may not be necessary. The disadvantage is that lithium enters the slag, making it difficult to recover.

[0005] The discharge-disassembly-crushing-positive electrode material enrichment-hydrometallurgical process mainly includes discharging, disassembling, and separating the waste batteries into positive and negative electrode sheets, and then subjecting the positive electrode sheets to high temperature or alkaline treatment to separate the positive electrode active material and the current collector aluminum foil. After that, all metals in the positive electrode active material are leached indiscriminately under extreme conditions such as strong acid or strong alkali. The lithium-containing strong acid leachate needs to be neutralized with a large amount of sodium hydroxide to precipitate impurities, and the purified liquid is precipitated with sodium carbonate under alkaline conditions to prepare lithium carbonate. This route can achieve high-value recovery of lithium, but the processing links are lengthy, the process is cumbersome, the amount of reagents used is large, the amount of residue and waste liquid generated is large, and it is easy to cause secondary pollution, which does not meet the carbon emission reduction requirements under the background of carbon neutrality. For example, Chinese patent CN103280610A discloses a method for recovering aluminum, iron and lithium in positive electrode sheets in the acid and alkali stages. The method comprises the following steps: subjecting the positive electrode sheets obtained by pre-treatment of waste lithium iron phosphate batteries to alkali treatment, dissolving the aluminum and filtering to recover the filtrate, subjecting the filter residue obtained by the alkali treatment to acid leaching to leach the lithium therein into the solution, adding alkali to adjust the pH value and remove impurities, and then adding a precipitant to precipitate and recover the leached lithium ions.

[0006] It can be seen that the existing recovery process of valuable metals in waste lithium iron phosphate positive electrode materials has a long and complicated processing flow, extreme experimental conditions and a large amount of reagents. Therefore, it is necessary to develop a new selective lithium recovery process with a small amount of reagents, mild operating conditions and a short process flow, which is of great significance for achieving efficient, green and low-carbon emission treatment of waste lithium iron phosphate batteries. Summary of the Invention

[0007] The present invention addresses the shortcomings of existing waste lithium iron phosphate recycling technology and develops a new process for accurately recycling valuable metals from waste lithium iron phosphate batteries with a short process, high efficiency, mild operating conditions, low carbon emissions, and no acid wastewater generation.

[0008] To achieve the above object, the technical solution adopted by the present invention is:

[0009] A method for recovering lithium from waste lithium iron phosphate positive electrode materials, comprising:

[0010] The pretreated positive electrode material is mixed with a leaching agent, and lithium is directly leached by stirring to obtain a mixed slurry of lithium leaching solution and leaching residue;

[0011] The lithium leaching solution obtained after solid-liquid separation of the mixed slurry is allowed to settle for 5-10 hours to precipitate by-products, and filtered to obtain a pure lithium-containing solution;

[0012] Concentrating the pure lithium-containing solution into a high-concentration lithium-rich solution;

[0013] Sodium carbonate is added to a high-concentration lithium-rich solution, and after the reaction, the solid is collected, washed, and dried to obtain pure lithium carbonate;

[0014] The leached residue obtained after solid-liquid separation of the mixed slurry is washed, dried and sieved to obtain pure aluminum foil current collector and iron phosphate.

[0015] Preferably, the pretreatment is to discharge the waste lithium iron phosphate battery, disassemble and separate the positive electrode sheets, and crush the positive electrode sheets into positive electrode materials of 0.1-1 cm.

[0016] Preferably, the discharging is to discharge the waste lithium iron phosphate battery in a 15% sodium chloride solution for 48 hours.

[0017] Preferably, the leaching agent includes at least one of NaClO, NaDCC, NaClO2, and ClO2.

[0018] Preferably, the ratio of the added molar amount of the leaching agent to the molar amount of the lithium iron phosphate positive electrode material is (1-2):1.

[0019] Preferably, the solid-liquid separation is suction filtration.

[0020] Preferably, the concentration temperature is 60-90°C, more preferably 75-80°C.

[0021] Preferably, the amount of sodium carbonate added is calculated as a molar ratio of carbonate to lithium ions in the lithium-rich solution of (1-3):2, more preferably (1-1.5):2.

[0022] Preferably, the temperature for adding sodium carbonate to the high-concentration lithium-rich solution is 50-100° C., more preferably 75-90° C., and the reaction time is 0.5-4.5 h, more preferably 0.5-2.5 h.

[0023] Preferably, the washing is performed with water, and the temperature of the water washing is 30-100°C, more preferably 65-90°C.

[0024] Compared with the existing process, the beneficial effects of the present invention are:

[0025] Compared with the prior art, the process of the present invention does not require the separation of the positive electrode material and the current collector in the pretreatment stage. The natural pH of the leachate during the entire leaching and lithium extraction process is weakly alkaline, and the leachate is allowed to stand in situ for precipitation and impurities removal, omitting the alkali-addition and impurity-removal process before the lithium carbonate preparation process in the prior art. The present invention directly subjects the crushed positive electrode material to a leaching reaction, and utilizes the oxidizing property of the active components in the leachate and the protons generated by their hydrolysis to selectively migrate lithium ions in the lithium iron phosphate into the solution. The iron species in the lithium iron phosphate recombine with phosphate radicals in the form of trivalent iron to form solid iron phosphate and leave the surface of the aluminum foil current collector. The aluminum foil in the leaching system is inert to the reaction and will not be corroded or dissolved. The present invention utilizes the special properties of the leaching agent, and the leachate after solid-liquid separation can be allowed to stand to remove residual agents and the generated sodium chloride by-product, thereby greatly reducing the generation of high-salt wastewater and residual leaching agent pollution. Overall, the process of the present invention has the characteristics of a short process flow, a small amount of agent used, no need to add alkali, low equipment requirements, easy parameter control, mild reaction conditions, no acid wastewater discharge, and green environmental protection. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 This is a flow chart of the method for recovering lithium from waste lithium iron phosphate cathode materials of the present invention;

[0027] Figure 2 This is a photo of the lithium leaching mixed slag of the waste lithium iron phosphate positive electrode sheet after screening in the present invention. DETAILED DESCRIPTION

[0028] In order to facilitate understanding of the technical solution of the present invention, the present invention is further described in detail below. However, the following embodiments are merely simplified examples of the present invention and do not represent or limit the scope of protection of the present invention. The scope of protection of the present invention shall be subject to the claims.

[0029] An embodiment of the present invention provides a method for recovering lithium from waste lithium iron phosphate cathode materials, comprising:

[0030] The pretreated positive electrode material is mixed with a leaching agent, and lithium is directly leached by stirring to obtain a mixed slurry of lithium leaching solution and leaching residue;

[0031] The lithium leaching solution obtained after solid-liquid separation of the mixed slurry is allowed to settle for 5-10 hours to precipitate by-products, and filtered to obtain a pure lithium-containing solution;

[0032] Concentrating the pure lithium-containing solution into a high-concentration lithium-rich solution;

[0033] Sodium carbonate is added to a high-concentration lithium-rich solution, and after the reaction, the solid is collected, washed, and dried to obtain pure lithium carbonate;

[0034] The leached residue obtained after solid-liquid separation of the mixed slurry is washed, dried and sieved to obtain pure aluminum foil current collector and iron phosphate.

[0035] It can be seen that after the leaching step in which the positive electrode material reacts with the leaching agent, the lithium leaching solution obtained is a low-concentration lithium-containing solution, and the leaching residue is a mixed residue of iron phosphate / aluminum current collector.

[0036] The embodiment of the present application omits the step of enriching the positive electrode material after pretreatment, that is, the step of separating the positive electrode material from the current collector aluminum foil, and also omits the impurity removal process after the leaching step. Conventional leaching processes in the prior art are carried out under acidic conditions, and are accompanied by leaching pollution of other metal ions besides lithium, resulting in the subsequent impurity removal process usually requiring the addition of agents such as sodium hydroxide to neutralize the pH for impurities. The pH of the leaching step in the embodiment of the present application is 10-11, and nearly 100% selectivity is achieved in this leaching step. Basically, no other metal ion impurities such as iron ions are leached, and there is no need to add agents such as sodium hydroxide to neutralize the pH for impurities. The leachate obtained in the leaching step in the embodiment of the present application can be used to remove impurities from the by-products by static precipitation, which makes the process simpler and reduces the pollution complexity of subsequent wastewater discharge. In the embodiment of the present application, pure aluminum foil and iron phosphate can be obtained by simple screening of the solid leaching residue obtained after leaching. This is a full-process process specifically constructed for the leaching step in the embodiment of the present application.

[0037] The embodiments of the present application utilize the special properties of the leaching agent to remove residual reagents and the generated sodium chloride byproduct by allowing the leachate after solid-liquid separation to stand, greatly reducing the generation of high-salt wastewater and residual leaching agent pollution. As the leaching reaction occurs, the solid ferric phosphate residue falls off the aluminum foil current collector, and the pure aluminum foil and ferric phosphate can be separated by simple screening. The embodiments of the present application effectively simplify the pretreatment process and omit the impurity removal process before the lithium carbonate preparation process. It has the characteristics of a short process flow, low reagent usage, no need to add alkali, low equipment requirements, easy parameter control, mild reaction conditions, no acid wastewater discharge, and green environmental protection.

[0038] The lithium leaching rate of the embodiment of the present application reaches more than 95%, and the purity of the obtained lithium carbonate product reaches more than 99%; the aluminum foil recovery rate is more than 98%, and the purity is more than 99%; the iron phosphate recovery rate reaches 98%, and the purity reaches 99%.

[0039] It should be noted that the pretreatment of the positive electrode material in this application is a common pretreatment method in the field, namely, first discharging the waste lithium iron phosphate battery, disassembling and separating the positive electrode sheets, and then crushing the positive electrode sheets into 0.1-1 cm positive electrode materials. The discharge method can be to discharge the waste lithium iron phosphate battery in a 15% sodium chloride solution for 48 hours.

[0040] The leaching agent is selected from a reagent with strong oxidizing properties under alkaline conditions, such as at least one of NaClO, NaDCC, NaClO2, ClO2, etc.

[0041] In a preferred embodiment, in order to make lithium leaching more complete, the ratio of the added molar amount of the leaching agent to the molar amount of the lithium iron phosphate positive electrode material is (1-2):1.

[0042] In a preferred embodiment, the solid-liquid separation method used is suction filtration. More preferably, after solid-liquid separation, the leached residue (i.e., the iron phosphate / aluminum collector mixed residue) is washed with pure water. In order to minimize lithium loss, a low-concentration lithium-containing solution obtained by solid-liquid separation is added to the washing liquid.

[0043] In a preferred embodiment, the concentration temperature when the pure lithium-containing solution is concentrated into a high-concentration lithium-rich solution is 60-90°C, preferably 75-80°C.

[0044] In a preferred embodiment, the amount of sodium carbonate added is (1-3):2, more preferably (1-1.5):2, based on the molar ratio of carbonate to lithium ions in the lithium-rich solution.

[0045] In a preferred embodiment, the temperature of adding sodium carbonate to the high-concentration lithium-rich solution is 50-100°C, more preferably 75-90°C, and the reaction time is 0.5-4.5 hours, more preferably 0.5-2.5 hours. The washing is performed with water, and the temperature of the water washing is 30-100°C, more preferably 65-90°C.

[0046] In a preferred embodiment, when screening the leached residue, the dried iron phosphate / aluminum current collector mixed residue is screened through a 5-mesh sieve to obtain pure aluminum foil current collector and iron phosphate.

[0047] To clarify the technical solution of this application, the following describes a method for recovering lithium from waste lithium iron phosphate cathode materials and its effectiveness through specific examples. The experimental methods described below, unless otherwise specified, are routine laboratory methods. The experimental materials described below, unless otherwise specified, were commercially available.

[0048] Example: Method for recovering lithium from waste lithium iron phosphate cathode material

[0049] (1) Safe discharge of used lithium iron phosphate batteries

[0050] The collected waste lithium iron phosphate batteries were immersed in a 15% sodium chloride salt solution and disassembled to separate the positive electrode sheets;

[0051] (2) Broken

[0052] Put 1kg of positive electrode sheet into the shear crusher and crush it for 3 minutes. The particle size of the crushed material is about 0.1-1cm.

[0053] (3) Direct leaching

[0054] 5 g of the crushed material was transferred to a reaction tank, 3.2993 g of NaDCC and 25 ml of water were added, and the mixture was reacted at 18°C ​​for 0.5 h. The pH was maintained at a natural value (10-11) throughout the process to obtain a lithium-containing solution.

[0055] (4) Separation

[0056] The slurry after the leaching reaction is filtered, the leached residue is washed and dried at 80°C, and then sieved to obtain pure iron phosphate and aluminum foil current collector respectively. The washing liquid is added to the lithium-containing solution and allowed to stand for 10 hours to remove impurities in situ;

[0057] (5) Concentration to obtain lithium-rich solution

[0058] At 80° C., concentrating the lithium solution obtained in step (3) to obtain a lithium-rich solution;

[0059] (5) Recycling into lithium carbonate products

[0060] The lithium-containing solution was allowed to stand for 10 hours and then filtered to remove impurities. Solid sodium carbonate was added to the lithium-rich solution obtained in step (4) at 90°C according to a molar ratio of carbonate to lithium ion of 1.1:2. After reacting for 1 hour, the solution was filtered, washed with water at 95°C, and dried to obtain a lithium carbonate product.

[0061] After testing and calculation, in this embodiment, the lithium leaching rate reaches 96.83% (8.6377×0.025÷1000÷(5×4.66%)=96.83%), the iron / aluminum leaching rate is approximately 0, and the purity of the obtained lithium carbonate product reaches 99.9%.

[0062] It should be noted that the embodiments described above are only used to explain the present invention and do not constitute any limitation of the present invention. The present invention has been described with reference to typical embodiments, but it should be understood that the words used therein are descriptive and explanatory words, rather than restrictive words. The present invention may be modified as specified within the scope of the claims of the present invention, and the present invention may be revised without departing from the scope and spirit of the present invention. Although the present invention described therein relates to specific methods, materials and embodiments, it does not mean that the present invention is limited to the special examples disclosed therein. On the contrary, the present invention can be extended to all other methods and applications with the same function.

Claims

1. A method for recovering lithium from waste lithium iron phosphate cathode materials, characterized in that: It consists of the following steps: The pretreated positive electrode material is mixed with the leaching agent NaDCC, the pH is maintained at 10-11, and lithium is directly leached by stirring to obtain a mixed slurry of lithium leachate and leaching residue; The lithium leaching solution obtained after solid-liquid separation of the mixed slurry is allowed to settle for 5-10 hours to precipitate by-products, and filtered to obtain a pure lithium-containing solution; Concentrating the pure lithium-containing solution into a high-concentration lithium-rich solution; Sodium carbonate is added to a high-concentration lithium-rich solution, and after the reaction, the solid is collected, washed, and dried to obtain pure lithium carbonate; The leached residue obtained after solid-liquid separation of the mixed slurry is washed, dried and sieved to obtain pure aluminum foil current collector and iron phosphate.

2. The recycling method according to claim 1, wherein The pretreatment is to discharge the waste lithium iron phosphate battery, disassemble and separate the positive electrode sheets, and crush the positive electrode sheets into positive electrode materials of 0.1-1 cm.

3. The recycling method according to claim 2, wherein: The discharge is to discharge the waste lithium iron phosphate battery in a 15% sodium chloride solution for 48 hours.

4. The recycling method according to claim 1, wherein The ratio of the added molar amount of the leaching agent to the molar amount of the lithium iron phosphate positive electrode material is (1-2):

1.

5. The recycling method according to claim 1, wherein: The solid-liquid separation is suction filtration.

6. The recycling method according to claim 1, wherein: The concentration temperature is 60-90°C.

7. The recycling method according to claim 6, wherein: The concentration temperature is 75-80°C.

8. The recycling method according to claim 1, wherein: The amount of sodium carbonate added is calculated based on the molar ratio of carbonate to lithium ions in the lithium-rich solution to be (1-3):

2.

9. The recycling method according to claim 8, wherein: The amount of sodium carbonate added is calculated based on the molar ratio of carbonate to lithium ions in the lithium-rich solution to be (1-1.5):

2.

10. The recycling method according to claim 1, wherein: The reaction temperature for adding sodium carbonate to the high-concentration lithium-rich solution is 50-100° C., and the reaction time is 0.5-4.5 hours.

11. The recycling method according to claim 10, wherein: The reaction temperature of adding sodium carbonate to the high-concentration lithium-rich solution is 75-90° C., and the reaction time is 0.5-2.5 h.

12. The recycling method according to claim 1, wherein: The washing is performed with water, and the temperature of the water washing is 30-100°C.

13. The recycling method according to claim 12, wherein: The washing is performed with water, and the temperature of the water washing is 65-90°C.

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