Method for extracting lithium from waste lithium iron phosphate

Abstract

The invention discloses a method for extracting lithium from waste lithium iron phosphate, and belongs to the technical field of recycling treatment of waste lithium ion batteries. A method for extracting lithium from waste lithium iron phosphate comprises the following steps that S1, aluminum and waste lithium iron phosphate are mixed and subjected to ball milling in a high-energy ball mill, and materials are evenly mixed and subjected to a mechanochemical reaction; s2, uniformly mixing the ball-milled material with water, and filtering for the first time to obtain a first filtrate and a filter cake; s3, heating, evaporating, concentrating and drying the first filtrate; and S4, carrying out heat treatment on the dried solid, adding water, uniformly mixing, carrying out secondary filtration, heating, evaporating and drying the obtained second filtrate to obtain lithium carbonate. According to the method for extracting the lithium from the waste lithium iron phosphate disclosed by the invention, on the basis of a mechanochemical method, metal aluminum is used as a reducing agent, and the recovery of the lithium metal element in the waste lithium iron phosphate material is successfully realized through a mechanochemical reaction.

Description

Technical Field

[0001] The present invention relates to the technical field of waste lithium-ion battery recycling and treatment, and in particular to a method for extracting lithium from waste lithium iron phosphate. Background Art

[0002] With the advancement of modern technology, lithium-ion batteries have significantly impacted our daily lives. Besides being widely used in consumer electronics such as smartphones, digital cameras, and laptops, they also play a crucial role in new energy vehicles and energy storage power stations. Compared to other types of rechargeable batteries, lithium-ion batteries offer advantages such as high energy density, long lifespan, fast charging, environmental friendliness, no memory effect, high operating voltage, and excellent rate capability. They are widely used in the power and energy storage sectors and are considered a key component of future energy storage solutions. With the rapid development of electric vehicles, the lithium battery market is expected to continue growing at a rate of 25% annually. This means a proportional increase in the lithium metal resources required for lithium battery production. However, global lithium resources are limited, and lithium resource shortages are an inevitable issue in the future. Furthermore, the rapid development of electric vehicles and renewable energy storage systems has led to a dramatic increase in the use of lithium-ion batteries. This has resulted in a growing number of used batteries requiring proper disposal. However, currently, less than 5% of used batteries are recycled, making lithium battery recycling a critical technical and economic task.

[0003] At present, the main methods for recycling lithium battery positive electrode materials are mainly divided into pyrometallurgy and hydrometallurgy. Pyrometallurgy is to obtain alloys and slags by smelting batteries at a temperature above 1000°C, in which the alloys are further processed to obtain precious metal elements. In the hydrometallurgical process, valuable metal elements can be recovered with high purity, especially for the recovery of lithium cobalt oxide or ternary materials containing a large amount of transition metal elements. In the research on the recovery of lithium iron phosphate, the main method is to use hydrometallurgy technology, which recovers various metal elements by leaching and precipitation using acid and oxidant.

[0004] Hydrometallurgy generates large amounts of wastewater during the complex multi-step leaching and precipitation process, causing secondary pollution. While the hydrometallurgical techniques described in CN106276842A and CN113501510A can recover cathode materials from lithium iron phosphate batteries, they consume large amounts of acid, alkali, and organic solvents, leading to secondary pollution problems such as acidic or alkaline wastewater, waste gas, and waste residue. The slag from the pyrometallurgical process contains a large amount of lithium metal, which cannot be further recycled, making it an unfriendly method for lithium recovery. In research on lithium iron phosphate recovery technology, lithium metal is clearly more valuable for recycling than iron (because it does not contain metal elements such as nickel and cobalt found in lithium cobalt oxide or ternary materials), and the economic efficiency of lithium metal recovery needs to be considered. Summary of the Invention

[0005] The object of the present invention is to provide a method for extracting lithium from waste lithium iron phosphate, which is simple to operate, does not introduce additional impurities, and has a high lithium element recovery rate.

[0006] The present invention discloses a method for extracting lithium from waste lithium iron phosphate, comprising the following steps:

[0007] S1: Mix aluminum with waste lithium iron phosphate and mill them in a high-energy ball mill to make the materials evenly mixed and cause a mechanochemical reaction;

[0008] S2: mixing the ball-milled material with water and performing a first filtration to obtain a first filtrate and a filter cake;

[0009] S3: heating the first filtrate to evaporate and concentrate, and then drying;

[0010] S4: heat-treating the solid obtained after drying, adding water to mix evenly, filtering for a second time, heating and evaporating the obtained second filtrate, and drying to obtain lithium carbonate.

[0011] High-energy ball milling is a materials preparation technology that uses the high-speed rotation of a ball mill to cause the grinding balls to strongly impact, shear, and rub the material, thereby achieving various purposes such as material refinement, mixing, alloying, and mechanochemical reactions. Mechanochemical methods are a technical method that uses mechanical forces such as grinding, extrusion, shearing, and friction to induce chemical reactions between solid materials. It focuses on the process of converting mechanical energy into chemical energy in solid matter or at the solid-liquid interface, thereby causing chemical changes. Mechanochemical methods can carry out chemical reactions without the use of solvents, making them environmentally friendly synthesis technologies.

[0012] High-energy ball milling can simplify the recycling process and improve efficiency. Furthermore, the reaction process reduces the use of corrosive liquids, preventing secondary contamination. However, in current battery material recycling applications, this method primarily serves as a pre-treatment (e.g., ball milling) for solid-phase processes and is rarely used directly for lithium recovery from lithium-ion battery materials.

[0013] Furthermore, in step S1, the aluminum includes aluminum foil.

[0014] The current collector used in lithium iron phosphate positive electrode materials is usually aluminum foil, which can be directly used as the reducing agent in the present invention to further reduce the recycling cost.

[0015] Furthermore, the molar ratio of the lithium iron phosphate LiFePO4 powder to aluminum is 1:3.

[0016] Furthermore, in step S1, when the high-energy ball mill performs ball milling, the grinding balls are steel balls, and the ball-to-material ratio of the ball milling is 10:(5~1).

[0017] Using steel balls as grinding balls has the following advantages: High hardness: Steel balls are usually made of high-carbon steel or other high-strength alloys, have high hardness, and can effectively crush and refine materials of various hardnesses. Strong wear resistance: Steel balls are hard and wear-resistant, and can maintain their shape and size during long-term ball milling, reducing pollution caused by wear and extending their service life. Higher density: Steel balls have a higher density, which means that they can provide greater kinetic energy during the ball milling process, which helps to crush and mix materials more effectively. Good cost-effectiveness: Compared with some special material ball milling media (such as zirconia, agate, etc.), steel balls have relatively low cost and are suitable for large-scale industrial production applications.

[0018] An appropriate ball-to-material ratio can ensure a certain ball milling efficiency while avoiding excessive wear of the grinding balls and waste of energy.

[0019] Furthermore, in step S1, the ball milling time is 2-4 hours, and the ball milling speed is 200-500 r / min.

[0020] In step S1, waste lithium iron phosphate and reducing agent aluminum undergo high-energy ball milling mechanochemical reaction with oxygen in ambient air in a high-energy ball mill. The specific chemical reaction that occurs is as follows:

[0021] 2LiFePO4 + 6Al + 0.25O2 → Li2O + Fe2P + AlP + 2.5Al2O3.

[0022] Furthermore, in step S2, after filtration, the filter cake is rinsed with water until the pH of the mixture of the filter cake and water is neutral.

[0023] The residual lithium in the filter cake eventually approaches neutrality (i.e. pH = 7) after multiple washings, indicating that there is almost no residual lithium in the filter cake.

[0024] The chemical reaction occurring in step S1 is as follows.

[0025] The reaction after adding water is:

[0026] Li2O + Al2O3 + H2O → LiOH + Li x AlO x (OH) z + Al2O3.

[0027] During the process of heating, evaporating, concentrating and recrystallizing the first filtrate, the following reaction occurs with CO2 in the air:

[0028] Li x AlO x (OH)z + H2O+ CO2 → Li2Al4(CO3)(OH) 12 ·3H2O.

[0029] During the drying process, LiOH absorbs carbon dioxide in the air and converts it into Li2CO3, and the following reactions occur:

[0030] 2LiOH + CO2 → Li2CO3 + H2O.

[0031] Furthermore, in step S3 and step S4, the temperature of the heating evaporation is 90-100°C.

[0032] Furthermore, in step S3 and step S4, the drying temperature is 60-80° C., and the drying time is 12-16 hours.

[0033] Furthermore, in step S4, the heat treatment temperature is 200-400° C., and the heat treatment time is 1-4 hours.

[0034] Furthermore, in step S4, when adding water and mixing, stirring is required, and the stirring time is 0.5 to 2 hours.

[0035] The chemical reaction of the material under heating conditions in step S4 is:

[0036] Li2Al4(CO3)(OH) 12 ·3H2O → Li2CO3 + 2Al2O3 + 9H2O.

[0037] The present invention discloses a method for extracting lithium from waste lithium iron phosphate. The method is based on a mechanochemical method, uses metallic aluminum as a reducing agent, and successfully realizes the recovery of lithium metal elements in waste lithium iron phosphate materials through mechanochemical reactions. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 This is the XRD pattern of the product Li2CO3 obtained in Example 1 of the present invention. DETAILED DESCRIPTION

[0039] In order to make the technical solution of the present invention clearer, the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0040] Waste lithium iron phosphate is obtained from waste lithium-ion batteries. The specific process is as follows:

[0041] First, the used lithium-ion batteries are discharged to ensure safety. Next, the batteries are disassembled to separate the electrode material containing lithium iron phosphate. The separated electrode material is crushed, and then physical methods such as screening are used to remove larger particles of aluminum foil or other impurities, leaving a fine powder mixture.

[0042] Example 1

[0043] A method for extracting lithium from waste lithium iron phosphate, the specific operations are as follows:

[0044] Step S1: 1.33 g of waste lithium iron phosphate powder and 0.67 g of aluminum foil (molar ratio 1:3) were placed in a high-energy ball mill. The grinding balls were 20 g of steel balls, the ball-to-material ratio was 10:1, and the milling was carried out for 3 h at a speed of 400 r / min to ensure that the materials were evenly mixed and reacted.

[0045] Step S2: The material obtained after ball milling is gradually and slowly added to deionized water. After the material is fully reacted, it is filtered using a vacuum pump, and the filter cake is repeatedly washed with deionized water until the pH of the suspension is 7, thereby obtaining a first filtrate.

[0046] Step S3: The obtained first filtrate was evaporated, concentrated and crystallized in a 100°C water bath to obtain a solid, and the obtained solid was dried in an oven at 70°C for 12 hours;

[0047] Step S4: The dried solid was placed in a muffle furnace at 350°C for 3 hours. The solid powder obtained after the heat treatment was then stirred with deionized water for 1 hour and vacuum filtered. The second filtrate was then evaporated and concentrated in a 100°C water bath to recrystallize the Li2CO3. The resulting Li2CO3 crystalline solid was then dried in an oven at 70°C for 12 hours, resulting in a purified Li2CO3 mass of 0.187 g.

[0048] According to ICP testing, the purity of Li2CO3 obtained in Example 1 is 75 wt%.

[0049] Lithium recovery rate calculation method: The starting ball-milled material was weighed without sampling. Since no visible gas release was observed during the ball-milling process, it was assumed that the elemental composition of the sample did not change. Finally, the Li2CO3 recovery ratio was calculated based on the theoretical lithium content present in the starting ball-milled mixed material.

[0050] The theoretical mass of lithium carbonate corresponding to the complete recovery of original waste lithium iron phosphate should be 0.311g, and the recovery rate of lithium element is 60.1wt%.

[0051] like Figure 1As shown, in the XRD pattern of the purified product Li2CO3, the diffraction peak of the product is consistent with the standard card of Li2CO3 (JCPDS: 04-008-5839), and no other diffraction peaks are observed, proving that the product of this technical solution is Li2CO3.

[0052] Example 2

[0053] A method for extracting lithium from waste lithium iron phosphate, the specific operations are as follows:

[0054] Step S1: 1.33 g of waste lithium iron phosphate powder and 0.67 g of aluminum foil (molar ratio 1:3) were placed in a high-energy ball mill with 20 g steel balls and a ball-to-material ratio of 10:1. The milling was performed for 2 h at a speed of 400 rpm to allow the materials to mix evenly and react.

[0055] Step S2: The material obtained after ball milling is gradually and slowly added to deionized water. After the material is fully reacted, it is filtered using a vacuum pump, and the filter cake is repeatedly washed with deionized water until the pH of the suspension is 7 to obtain a first filtrate.

[0056] Step S3: The obtained first filtrate was evaporated, concentrated and crystallized in a 100°C water bath to obtain a solid, and the obtained solid was dried in an oven at 70°C for 12 hours;

[0057] Step S4: The dried solid was placed in a muffle furnace at 350°C for 3 hours. The resulting solid powder was then stirred with deionized water for 1 hour and vacuum filtered. The resulting second filtrate was then concentrated by evaporation in a 100°C water bath to recrystallize the Li2CO3. The resulting Li2CO3 crystalline solid was then dried in a 70°C oven for 12 hours. The resulting purified Li2CO3 had a mass of 0.142 g and a lithium recovery rate of 45.7 wt%. ICP testing showed that the purity of the Li2CO3 obtained in Example 2 was 72 wt%.

[0058] This shows that a shorter ball milling time will lead to incomplete reaction, reducing the recovery rate and purity of Li2CO3.

[0059] Example 3

[0060] A method for extracting lithium from waste lithium iron phosphate, the specific operations are as follows:

[0061] Step S1: 1.33 g of waste lithium iron phosphate powder and 0.67 g of aluminum foil (molar ratio 1:3) were placed in a high-energy ball mill. The grinding balls were 20 g of steel balls, the ball-to-material ratio was 10:1, and the milling was carried out for 3 h at a speed of 400 r / min to ensure that the materials were evenly mixed and reacted.

[0062] Step S2: The material obtained after ball milling is gradually and slowly added to deionized water. After the material is fully reacted, it is filtered using a vacuum pump, and the filter cake is repeatedly washed with deionized water until the pH of the suspension is 7 to obtain a first filtrate.

[0063] Step S3: The obtained first filtrate was evaporated, concentrated and crystallized in a 100°C water bath to obtain a solid, and the obtained solid was dried in an oven at 70°C for 12 hours;

[0064] Step S4: The dried solid was placed in a muffle furnace at 250°C for 3 hours. The resulting solid powder was then stirred with deionized water for 1 hour and vacuum filtered. The resulting second filtrate was then concentrated by evaporation in a 100°C water bath to recrystallize the Li2CO3. The resulting Li2CO3 crystalline solid was then dried in a 70°C oven for 12 hours. The resulting purified Li2CO3 had a mass of 0.122 g and a lithium recovery rate of 39.2 wt%. ICP testing showed that the purity of the Li2CO3 obtained in Example 3 was 71 wt%.

[0065] It shows that the reduction of the reaction temperature during the muffle furnace heat treatment will lead to the intermediate Li2Al4(CO3)(OH) 12 Incomplete decomposition of 3H2O also reduces the recovery rate and purity of Li2CO3.

[0066] The above-described embodiments merely illustrate several implementations of the present invention, and while their descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that a person skilled in the art would be able to make numerous variations and improvements without departing from the spirit of the present invention, all of which fall within the scope of protection of the present invention. Therefore, the scope of protection of the present invention shall be determined by the appended claims.

Claims

1. A method for extracting lithium from waste lithium iron phosphate, characterized in that: The following steps are involved: S1: Mix aluminum with waste lithium iron phosphate and mill them in a high-energy ball mill to make the materials evenly mixed and cause a mechanochemical reaction; S2: mixing the ball-milled material with water and performing a first filtration to obtain a first filtrate and a filter cake; S3: heating the first filtrate to evaporate and concentrate, and then drying; S4: heat-treating the solid obtained after drying, adding water to mix evenly, filtering for a second time, heating and evaporating the obtained second filtrate, and drying to obtain lithium carbonate.

2. The method for extracting lithium from waste lithium iron phosphate according to claim 1, characterized in that: In the step S1, the aluminum includes aluminum foil.

3. The method for extracting lithium from waste lithium iron phosphate according to claim 2, characterized in that: The molar ratio of the lithium iron phosphate LiFePO4 powder to aluminum is 1:

3.

4. The method for extracting lithium from waste lithium iron phosphate according to claim 1, characterized in that: In the step S1, when the high-energy ball mill is used for ball milling, the grinding balls are steel balls, and the ball-to-material ratio of the ball milling is 10:(5-1).

5. The method for extracting lithium from waste lithium iron phosphate according to claim 4, characterized in that: In step S1, the ball milling time is 2-4 hours, and the ball milling speed is 200-500 r / min.

6. The method for extracting lithium from waste lithium iron phosphate according to claim 1, characterized in that: In the step S2, after filtering, the filter cake is washed with water until the pH of the mixture of the filter cake and water is neutral.

7. The method for extracting lithium from waste lithium iron phosphate according to claim 1, characterized in that: In the step S3 and the step S4, the temperature of the heating evaporation is 90-100°C.

8. The method for extracting lithium from waste lithium iron phosphate according to claim 7, characterized in that: In step S3 and step S4, the drying temperature is 60-80° C., and the drying time is 12-16 hours.

9. The method for extracting lithium from waste lithium iron phosphate according to claim 1, characterized in that: In step S4, the heat treatment temperature is 200-400° C., and the heat treatment time is 1-4 hours.

10. The method for extracting lithium from waste lithium iron phosphate according to claim 1, characterized in that: In step S4, when adding water and mixing, stirring is required, and the stirring time is 0.5 to 2 hours.

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