Method for preparing precursor by treating waste lithium battery

Abstract

The invention discloses a method for preparing a precursor by treating a waste lithium battery, and relates to the technical field of lithium ion battery recovery. The method comprises the following steps: disassembling a waste lithium iron phosphate battery, separating a pole piece to obtain a positive pole piece, separating an active material from a foil, and screening to obtain waste lithium iron phosphate powder; s2, adding the waste lithium iron phosphate powder obtained in the step S1 into the leachate for dissolving, and carrying out three-stage countercurrent leaching to obtain an ion mixed solution containing iron, lithium and phosphate radicals; and S2, carrying out pH gradient and complexing agent coordinated regulation and control on the ion mixed solution obtained in the step S2, and carrying out fractional precipitation to obtain a FePO4. 2H2O compound and Li2CO3. According to the method, efficient leaching of valuable elements is achieved through multi-stage countercurrent leaching, precise separation and recovery of metal ions are achieved through selective coprecipitation, and the high-performance precursor is further prepared.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium-ion battery recycling, and in particular to a method for efficiently wet-processing waste lithium iron phosphate (LiFePO4, LFP) positive electrode materials based on multi-stage countercurrent leaching and selective co-precipitation, and further directly synthesizing lithium iron phosphate precursors through a co-precipitation process to achieve closed-loop resource utilization. Background Art

[0002] With the rapid development of new energy vehicles, energy storage systems, and consumer electronics, the global lithium battery market continues to expand. The infiltration of heavy metals from discarded batteries can lead to soil acidification and water pollution, and recycling can reduce environmental toxicity risks. Through regeneration technologies (such as direct recycling processes), every kilogram of recycled lithium batteries can reduce carbon dioxide emissions by 4.6 kilograms. Therefore, lithium battery recycling is not only a core component of the sustainable development of the new energy industry, but also an inevitable choice for resource recycling and environmental protection.

[0003] Lithium iron phosphate batteries are safe and stable, and their prices are less affected by the market. They currently account for more than 60% of the market. However, the traditional acid leaching treatment of waste lithium iron phosphate batteries has the following problems: low leaching rate of Li and Fe (<90%), low Fe 2+ Easily oxidized to Fe 3+ This leads to problems such as separation difficulties, and relies on multi-step extraction or high-temperature calcination, which is complex and costly. Therefore, it is necessary to develop a green and efficient lithium-ion battery recycling process to achieve effective resource utilization. Summary of the Invention

[0004] In order to solve the above problems, the present invention provides an efficient wet recovery method for waste lithium iron phosphate based on multi-stage countercurrent leaching and selective co-precipitation and a precursor preparation process. Multi-stage countercurrent leaching is used to achieve efficient leaching of valuable elements, and selective co-precipitation is used to achieve precise separation and recovery of metal ions, and further prepare a high-performance precursor.

[0005] In order to achieve the above-mentioned purpose of the present invention, the following technical solutions are adopted:

[0006] The present invention provides a method for preparing a precursor by processing waste lithium batteries, comprising the following steps:

[0007] S1. Dismantling the waste lithium iron phosphate battery and separating the pole pieces to obtain the positive pole pieces, separating the active material and the foil, and sieving to obtain waste lithium iron phosphate powder;

[0008] S2. Adding the waste lithium iron phosphate powder obtained in step S1 into a leachate to dissolve it, and performing three-stage countercurrent leaching to obtain a mixed solution containing iron, lithium and phosphate ions; the leachate is a mixed aqueous solution of sulfuric acid and a reducing agent;

[0009] S3. The ion mixed solution obtained in step S2 is subjected to pH gradient and complexing agent coordinated regulation, and precipitation is performed step by step to obtain FePO4·2H2O compound and Li2CO3.

[0010] The following details are provided:

[0011] Step S1:

[0012] In one embodiment, step S1 specifically includes the following steps:

[0013] After being completely discharged, the waste lithium iron phosphate batteries are disassembled and the electrodes are separated to obtain the positive electrode electrodes. The electrodes are placed at high temperature for pyrolysis or roasting to separate the active material and the foil, and then screened to obtain waste lithium iron phosphate powder.

[0014] The packaging of the waste lithium iron phosphate battery can be square, cylindrical, or soft-pack.

[0015] The temperature of the pyrolysis or calcination is 300-500° C., and the atmosphere can be vacuum, inert or air.

[0016] Step S2:

[0017] In one embodiment, the leachate in step S2 is a mixture of an aqueous sulfuric acid solution and an aqueous reducing agent solution, wherein the concentration of the aqueous sulfuric acid solution is 2.0 to 4.0 mol / L, the concentration of the aqueous reducing agent solution is 0.1 to 0.3 mol / L, and the volume ratio of the aqueous sulfuric acid solution to the aqueous reducing agent solution is 4:1 to 6:1. The reducing agent may be ascorbic acid (C6H8O6) or sodium thiosulfate (Na2S2O3).

[0018] In one embodiment, step S2 specifically includes the following steps:

[0019] Primary leaching: Mix lithium iron phosphate powder with leaching solution at a liquid-solid mass ratio of 10:1-15:1 (g / g), stir and react at a temperature of 70-90°C for 1-2 hours to allow some lithium, iron and phosphorus elements to enter the solution;

[0020] Secondary leaching: The residue after the primary leaching is mixed again with fresh leaching solution at a liquid-to-solid mass ratio of 8:1-12:1 (g / g), and stirred at a temperature of 75-95°C for 1-2 hours to further improve the leaching rate of valuable elements;

[0021] Third-stage leaching: Mix the residue after the second-stage leaching with fresh leachate at a liquid-to-solid mass ratio of 4:1-10:1 (g / g), and stir the mixture at a temperature of 80-100°C for 1-2 hours to ensure sufficient leaching of the valuable elements;

[0022] Mixing: The leachates obtained from the three-stage leaching are combined and subjected to solid-liquid separation to obtain a leachate containing elements such as lithium, iron, and phosphorus.

[0023] Preferably, a stirring step can be added to each countercurrent leaching process at a rate of 400-600 rpm.

[0024] Countercurrent leaching is usually achieved by connecting multiple reaction tanks in series (such as 3 stages). After each stage of reaction, solid-liquid separation is required, and then the solid is sent to the next stage, and the liquid flows in the opposite direction to the previous stage.

[0025] The present invention proposes a three-stage countercurrent leaching system, which dynamically adjusts H + Concentration gradient, to achieve efficient use of acid, while inhibiting Fe 2+ Oxidized to Fe 3+ Compared with the common single-stage leaching or simple multi-stage leaching process in the prior art, the advantages of the present invention are obvious. In the traditional single-stage leaching process, due to the + The concentration gradually decreases with the reaction process, resulting in low leaching efficiency and Fe 2+ It is easily oxidized, which not only increases the difficulty of subsequent separation and purification, but also reduces the recovery rate of iron. The three-stage countercurrent leaching system of the present invention ensures sufficient leaching of valuable elements by precisely controlling the liquid-to-solid ratio, temperature and reaction time of each stage.

[0026] Controlling the concentration and proportion of the leachate: Experimental verification has shown that this specific concentration range and volume ratio combination can effectively reduce the co-precipitation of impurity ions while ensuring leaching efficiency. In laboratory-scale experiments, the leaching rates of iron and lithium were both increased by about 15% compared to the combination of a sulfuric acid concentration of 1-2 mol / L and a reducing agent concentration of 0.1-0.2 mol / L. The parameter combination of the present invention increases the leaching rate of iron from about 84% of iron in a single leaching process to 98.6%, and the leaching rate of lithium from 82% to 98.3% through multi-stage leaching. At the same time, in industrial-scale applications, this optimized parameter combination helps to reduce the complexity and cost of subsequent impurity removal processes, and improve the economy and feasibility of the overall process.

[0027] Step S3:

[0028] Through pH gradient control and the synergistic effect of complexing agents, FePO4·2H2O compounds and Li2CO3 were precipitated step by step to achieve efficient separation of Li / Fe / P.

[0029] In one embodiment, step S3 specifically includes the following steps:

[0030] Slowly add NaOH aqueous solution to the ion mixture solution, adjust the pH to 3.5±0.1, and the reaction temperature is 60°C. Impurities such as aluminum and copper are precipitated and separated in the form of Al(OH)3 and Cu(OH)2;

[0031] A sodium phosphate (Na3PO4) aqueous solution was added to the separated solution at a molar ratio of n(Fe):n(P) = 1:1.05, and 10% hydrogen peroxide was added (catalytic effect). The volume of the added liquid was 1 / 10 of the Na3PO4 solution. The pH was adjusted to 5.5±0.1 and the temperature was 70°C to generate an amorphous FePO4·2H2O precipitate for separation.

[0032] The mother liquor after separation is concentrated to Li + Concentration>20g / L, add Na2CO3 aqueous solution, molar ratio n(Li + ):n(CO3 2- )=1:1.05, temperature 60℃, after the reaction, precipitation separation, vacuum drying to obtain Li2CO3 powder.

[0033] Preferably, the concentration of the NaOH aqueous solution is 4.0-6.0 mol / L; the concentration of the Na3PO4 aqueous solution is 0.4-0.6 mol / L; the concentration of the Na2CO3 aqueous solution is 1.5-2.5 mol / L; a stirring step can be added to the precipitation process at a rate of 200-300 rpm; the vacuum drying temperature is 50-70°C; and the precipitation separation method can be high-speed centrifugation, filtration, etc.

[0034] This method utilizes pH gradient control in conjunction with a complexing agent to achieve step-by-step precipitation of FePO4·2H2O and Li2CO3, achieving efficient Li / Fe / P separation while avoiding the complexity of multi-step extraction or high-temperature calcination required in traditional processes. Compared to existing technologies, precipitation performed solely through pH adjustment alone cannot achieve such precise metal ion separation and produce high-purity products. By precisely controlling the pH value and the amount of complexing agent used, this method effectively improves precipitation efficiency and product purity.

[0035] Accuracy of step-by-step precipitation: The present invention first adds NaOH solution to adjust the pH to 3.5±0.1, so that impurities such as aluminum and copper are precipitated and separated in the form of hydroxides, and then adds Na3PO4 solution to adjust the pH to 5.5±0.1 to achieve the precipitation of FePO4·2H2O, and finally adds Na2CO3 solution to precipitate lithium. This step-by-step precipitation strategy can effectively avoid the interference of impurity ions and improve the purity of the product. In the prior art, although pH control is also used for precipitation, the order of adding the precipitant and the accuracy of pH control are not enough, resulting in a high impurity content in the precipitated product, affecting the quality and recovery efficiency of the final product.

[0036] Synergistic Effect of Complexing Agents: In this patent, Na3PO4 not only acts as a precipitant and regulator, but also as a complexing agent in the reaction, forming a stable complex with iron ions, enhancing the precipitation effect while reducing the co-precipitation of other impurity ions. In contrast, the prior art does not fully utilize complexing agents and fails to fully utilize their synergistic effects. Therefore, the present invention is innovative in its use of complexing agents, constituting a substantial difference from the prior art.

[0037] Control the concentration of NaOH aqueous solution, Na3PO4 aqueous solution, and Na2CO3 aqueous solution: The selection of this concentration of NaOH and Na3PO4 solution is based on the in-depth study of the dissolution characteristics and coprecipitation behavior of lithium iron phosphate materials. At this concentration, the Fe 3+ He Li + The efficient separation and recovery of FePO4·2H2O can achieve a purity of more than 98% and a purity of Li2CO3 of more than 99%. Compared with the NaOH concentration of 3-4 mol / L and the Na3PO4 concentration of 0.3-0.4 mol / L, the precipitant concentration combination of the present invention can significantly reduce the mixing of impurity ions in the precipitation process while ensuring the precipitation efficiency, thereby improving the purity of the product. At the same time, this concentration combination can also optimize the kinetic conditions of the precipitation process, shorten the precipitation reaction time by about 30%, improve production efficiency, and reduce production costs. In addition, through experimental data and theoretical analysis, it can be seen that Na3PO4 as a complexing agent reacts with Fe at this concentration. 3+ The complexing ability is the strongest and it can form a stable complex, thus more effectively 3+ Separate it from the solution to avoid interference with the subsequent lithium recovery process.

[0038] In a specific embodiment, Figure 1 As shown, the present invention provides a method for preparing a precursor by treating waste lithium batteries, comprising the following steps:

[0039] 1. Disassemble and separate used lithium iron phosphate batteries (package types: square / cylindrical / soft pack) to obtain positive electrode sheets. Pyrolysis or calcination of the sheets at 300-500°C separates the active material from the foil, which is then sieved to obtain a powder rich in lithium iron phosphate.

[0040] 2. Use sulfuric acid aqueous solution (concentration: 2.0-4.0 mol / L) and ascorbic acid or sodium thiosulfate aqueous solution (concentration: 0.1-0.3 mol / L) as leaching solution, with a volume ratio of 4:1-6:1; primary leaching: mix lithium iron phosphate powder and leaching solution at a liquid-solid mass ratio of 10:1-15:1 (g / g), stir and react at a temperature of 70-90 ° C for 1-2 hours, so that some lithium, iron and phosphorus elements enter the solution; secondary leaching Leaching: The filtered residue after the first stage leaching is mixed again with fresh leachate at a liquid-solid mass ratio of 8:1-12:1 (g / g), stirred and reacted at a temperature of 75-95°C for 1-2 hours to further improve the leaching rate of valuable elements; tertiary leaching: The residue after the second stage leaching is mixed with fresh leachate at a liquid-solid mass ratio of 4:1-10:1 (g / g), stirred and reacted at a temperature of 80-100°C for 1-2 hours to ensure sufficient leaching of valuable elements. The leachates obtained from the three stages are then combined and solid-liquid separated to obtain a leachate containing elements such as lithium, iron, and phosphorus;

[0041] 3. Slowly add NaOH aqueous solution to the leachate, adjust the pH to 3.5±0.1, the reaction temperature is 60℃, and impurities such as aluminum and copper are precipitated and separated in the form of Al(OH)3 and Cu(OH)2; add Na3PO4 aqueous solution with a molar ratio of n(Fe):n(P)=1:1.05, add 10% hydrogen peroxide, adjust the pH to 5.5±0.1, and the temperature is 70℃ to generate amorphous FePO4·2H2O precipitate and separate; concentrate the mother liquor to Li + Concentration>20g / L, add Na2CO3 aqueous solution, molar ratio n(Li + ):n(CO3 2- )=1:1.05, the temperature was 60℃, and after the reaction was completed, it was filtered and vacuum dried to obtain Li2CO3 powder.

[0042] Technical effect:

[0043] Compared with existing waste lithium battery recycling technologies, this patented technology, through the two core technologies of multi-stage countercurrent leaching and selective precipitation to prepare precursors, demonstrates significant advantages in metal recovery rate, process economy, and environmental protection. Specific advantages include:

[0044] High leaching efficiency and metal retention rate: After multi-stage countercurrent leaching, the leaching rate of Li and Fe elements is greatly improved, improving the economic benefits of the recovery process;

[0045] The present invention is of great significance for achieving efficient recovery and recycling of metals in waste lithium iron phosphate batteries as well as energy conservation and emission reduction, and can be widely used in fields such as the lithium-ion battery recycling industry.

[0046] The present invention has been described in detail above, but the above embodiments are merely illustrative in nature and are not intended to limit the present invention. In addition, the present invention is not limited by any theory described in the above prior art or invention summary or the following examples. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] Figure 1 A flow chart of the method for preparing a precursor for treating waste lithium batteries according to the present invention;

[0048] Figure 2 This is the cycle curve for preparing LiFePO4 / C using the product obtained in Example 1. DETAILED DESCRIPTION

[0049] The present invention will be further described below with reference to the examples. It should be noted that the following examples are provided for illustrative purposes only and do not constitute a limitation on the scope of protection claimed in the present invention.

[0050] Unless otherwise specified, the raw materials, reagents, methods, etc. used in the examples are conventional raw materials, reagents, and methods in the art.

[0051] Example 1

[0052] A method for preparing a precursor by processing waste lithium batteries comprises the following steps:

[0053] Step 1: Disassemble and separate the waste lithium iron phosphate batteries to obtain the positive electrode sheets; place the sheets at a high temperature of 450°C for 3 hours to separate the active material and the foil, and pass through an 80-mesh sieve to obtain a powder rich in lithium iron phosphate;

[0054] Step 2: Use 3.0 mol / L sulfuric acid aqueous solution and 0.3 mol / L ascorbic acid aqueous solution as leachate, with a volume ratio of 5:1. Primary leaching: Mix the leachate with the lithium iron phosphate powder in step (1) at a liquid-solid mass ratio of 12:1 (g / g), stir and react at a temperature of 90°C for 1 hour, and most of the lithium, iron, and phosphorus elements are dissolved in the solution; Secondary leaching: Mix the fresh leachate with the filtered residue after the primary leaching at a liquid-solid mass ratio of 10:1 (g / g), stir and react at a temperature of 95°C for 1 hour; Tertiary leaching: Mix the fresh leachate with the filtered residue after the secondary leaching at a liquid-solid mass ratio of 8:1 (g / g), stir and react at a temperature of 100°C for 1 hour to ensure sufficient leaching of valuable elements. The leachates obtained from the three-stage leaching are then combined, and after solid-liquid separation, a leachate containing lithium, iron, phosphorus and other elements is obtained;

[0055] Step 3: Slowly add 6 mol / L NaOH aqueous solution to the leachate from step 2, adjust the pH to 3.5, and the reaction temperature to 60°C. Impurities such as aluminum and copper are precipitated and filtered in the form of Al(OH)3 and Cu(OH)2. Add 0.6 mol / L Na3PO4 aqueous solution, the molar ratio n(Fe):n(P)=1:1.05, add 10% hydrogen peroxide (volume of hydrogen peroxide: volume of sodium phosphate solution=1:10), adjust the pH to 5.5±0.1, the temperature to 70°C, and generate amorphous FePO4·2H2O precipitate and filter. The mother liquor is then concentrated to Li + Concentration 35g / L, add 2mol / L Na2CO3 aqueous solution, molar ratio n(Li + ):n(CO3 2- )=1:1.05, the temperature is 60℃, and after the reaction is completed, it is filtered and dried in vacuum at 70℃ to obtain Li2CO3 powder. The final product of FePO4·2H2O and Li2CO3 can be used as a precursor of lithium iron phosphate, a positive electrode material.

[0056] Step (2) obtains Fe in the final leachate 2+ and Fe 3+ The ion content is shown in Table 1, Fe 2+ and Fe 3+ The testing method is ion chromatography;

[0057] The recovery rates of lithium and iron are shown in Table 2. The test method is: metal M recovery rate = mass of metal in the recovered product / mass of metal in the initial sample.

[0058] Example 2

[0059] A method for preparing a precursor by processing waste lithium batteries is adjusted as follows relative to Example 1 (the remaining step parameters are the same):

[0060] Step 2: Use 2.0 mol / L sulfuric acid aqueous solution and 0.2 mol / L sodium thiosulfate aqueous solution as leachate, with a volume ratio of 6:1. Primary leaching: Mix the leachate with the lithium iron phosphate powder in step (1) at a liquid-solid mass ratio of 15:1 (g / g), stir and react at a temperature of 90°C for 1 hour, and most of the lithium, iron, and phosphorus elements are dissolved in the solution; Secondary leaching: Mix the fresh leachate with the filtered residue after the primary leaching at a liquid-solid mass ratio of 12:1 (g / g), stir and react at a temperature of 95°C for 1 hour; Tertiary leaching: Mix the fresh leachate with the filtered residue after the secondary leaching at a liquid-solid mass ratio of 10:1 (g / g), stir and react at a temperature of 100°C for 1 hour to ensure sufficient leaching of valuable elements. The leachates obtained from the three-stage leaching are then combined, and after solid-liquid separation, a leachate containing elements such as lithium, iron, and phosphorus is obtained;

[0061] Step (2) obtains Fe in the final leachate 2+ and F 3+ The ion content is shown in Table 1;

[0062] The recovery rates of lithium and iron are shown in Table 2.

[0063] Example 3

[0064] A method for preparing a precursor by processing waste lithium batteries is adjusted as follows relative to Example 1 (the remaining step parameters are the same):

[0065] Step 2: Use 2.0 mol / L sulfuric acid aqueous solution and 0.1 mol / L ascorbic acid aqueous solution as leachate, with a volume ratio of 4:1. Primary leaching: Mix the leachate with the lithium iron phosphate powder in step (1) at a liquid-solid mass ratio of 15:1 (g / g), stir and react at a temperature of 90°C for 2 hours, and most of the lithium, iron, and phosphorus elements are dissolved in the solution; Secondary leaching: Mix the fresh leachate with the filtered residue after the primary leaching at a liquid-solid mass ratio of 12:1 (g / g), stir and react at a temperature of 95°C for 2 hours; Tertiary leaching: Mix the fresh leachate with the filtered residue after the secondary leaching at a liquid-solid mass ratio of 10:1 (g / g), stir and react at a temperature of 100°C for 1 hour to ensure sufficient leaching of valuable elements. The leachates obtained from the three-stage leaching are then combined, and after solid-liquid separation, a leachate containing elements such as lithium, iron, and phosphorus is obtained;

[0066] Step (2) obtains Fe in the final leachate 2+ and F 3+ The ion content is shown in Table 1;

[0067] The recovery rates of lithium and iron are shown in Table 2.

[0068] Example 4

[0069] A method for preparing a precursor by processing waste lithium batteries is adjusted as follows relative to Example 1 (the remaining step parameters are the same):

[0070] Step 2: Use 4.0 mol / L sulfuric acid aqueous solution and 0.3 mol / L ascorbic acid aqueous solution as leachate, with a volume ratio of 6:1. Primary leaching: Mix the leachate with the lithium iron phosphate powder in step (1) at a liquid-solid mass ratio of 10:1 (g / g), stir and react at a temperature of 70°C for 1 hour, and most of the lithium, iron, and phosphorus elements are dissolved in the solution; Secondary leaching: Mix the fresh leachate with the filtered residue after the primary leaching at a liquid-solid mass ratio of 8:1 (g / g), stir and react at a temperature of 75°C for 1 hour; Tertiary leaching: Mix the fresh leachate with the filtered residue after the secondary leaching at a liquid-solid mass ratio of 4:1 (g / g), stir and react at a temperature of 80°C for 1 hour to ensure sufficient leaching of valuable elements. The leachates obtained from the three-stage leaching are then combined, and after solid-liquid separation, a leachate containing elements such as lithium, iron, and phosphorus is obtained;

[0071] Step (2) obtains Fe in the final leachate 2+ and F 3+ The ion content is shown in Table 1;

[0072] The recovery rates of lithium and iron are shown in Table 2.

[0073] Example 5

[0074] A method for preparing a precursor by processing waste lithium batteries is adjusted as follows relative to Example 1 (the remaining step parameters are the same):

[0075] Step 2: Use 1.5 mol / L sulfuric acid aqueous solution and 0.1 mol / L ascorbic acid aqueous solution as leachate, with a volume ratio of 5:1. Primary leaching: Mix the leachate with the lithium iron phosphate powder in step (1) at a liquid-solid mass ratio of 12:1 (g / g), stir and react at a temperature of 90°C for 1 hour, and most of the lithium, iron, and phosphorus elements are dissolved in the solution; Secondary leaching: Mix the fresh leachate with the filtered residue after the primary leaching at a liquid-solid mass ratio of 10:1 (g / g), stir and react at a temperature of 95°C for 1 hour; Tertiary leaching: Mix the fresh leachate with the filtered residue after the secondary leaching at a liquid-solid mass ratio of 8:1 (g / g), stir and react at a temperature of 100°C for 1 hour to ensure sufficient leaching of valuable elements. The leachates obtained from the three-stage leaching are then combined, and after solid-liquid separation, a leachate containing elements such as lithium, iron, and phosphorus is obtained;

[0076] Step (2) obtains Fe in the final leachate 2+ and F 3+ The ion content is shown in Table 1;

[0077] The recovery rates of lithium and iron are shown in Table 2.

[0078] Example 6

[0079] A method for preparing a precursor by processing waste lithium batteries is adjusted as follows relative to Example 1 (the remaining step parameters are the same):

[0080] Step 3: Slowly add 6 mol / L NaOH aqueous solution to the leachate from step (2), adjust the pH to 3.5, and the reaction temperature to 60°C. Impurities such as aluminum and copper are precipitated and separated by filtration in the form of Al(OH)3 and Cu(OH)2. Add 0.6 mol / L Na3PO4 aqueous solution with a molar ratio of n(Fe):n(P)=2:1 to generate amorphous FePO4·2H2O precipitate and separate by filtration. Then concentrate the mother liquor to Li + Concentration 35g / L, add 2mol / L Na2CO3 aqueous solution, molar ratio n(Li + ):n(CO3 2- )=1:1.05, the temperature is 60℃, and after the reaction is completed, it is filtered and dried in vacuum at 70℃ to obtain Li2CO3 powder. The final product of FePO4·2H2O and Li2CO3 can be used as a precursor of lithium iron phosphate, a positive electrode material.

[0081] Step (2) obtains Fe in the final leachate 2+ and F 3+ The ion content is shown in Table 1;

[0082] The recovery rates of lithium and iron are shown in Table 2.

[0083] Comparative Example 1

[0084] A conventional single-stage leaching method for treating waste lithium iron phosphate is adjusted as follows relative to Example 1 (the remaining step parameters are the same):

[0085] Step 2: Use 3.0 mol / L sulfuric acid as the leachate. Mix the leachate with the lithium iron phosphate powder from step (1) at a liquid-solid mass ratio of 12:1 (g / g), stir at 90°C for sufficient reaction, and obtain a leachate containing lithium, iron, phosphorus and other elements after solid-liquid separation;

[0086] Step (2) obtains Fe in the final leachate 2+ and F 3+ The ion content is shown in Table 1;

[0087] The recovery rates of lithium and iron are shown in Table 2.

[0088] Comparative Example 2

[0089] A conventional single-stage leaching method for treating waste lithium iron phosphate is adjusted as follows relative to Example 1 (the remaining step parameters are the same):

[0090] Step 2: Using a 3.0 mol / L sulfuric acid aqueous solution and a 0.3 mol / L ascorbic acid aqueous solution as the leachate, the volume ratio is 5:1. The leachate is mixed with the lithium iron phosphate powder in step (1) at a liquid-solid mass ratio of 12:1 (g / g), stirred at a temperature of 90°C for sufficient reaction, and after solid-liquid separation, a leachate containing lithium, iron, phosphorus and other elements is obtained;

[0091] Step (2) obtains Fe in the final leachate 2+ and F 3+ The ion content is shown in Table 1;

[0092] The recovery rates of lithium and iron are shown in Table 2.

[0093] In addition, in order to verify and ensure the practicality and reliability of the product and precursor, the present invention mixed the product in Example 1 and ball-milled it for 2 h, calcined it at 650 ° C for 6 h under N2 atmosphere to obtain LiFePO4 / C, and prepared it into CR2032 button batteries for cycle testing. Figure 2 As shown. Figure 2 It can be seen that the LiFePO4 / C obtained by calcining the precursor FePO4·2H2O and Li2CO3 obtained in this embodiment has good cycle performance, and the retention rate after 200 cycles at room temperature 25°C is 96.5%, indicating that the product obtained by the present invention has good applicability.

[0094] Table 1 Fe in the final leachate 2+ and Fe 3+ Ion content

[0095]

[0096]

[0097] Table 2 Recovery rates of lithium and iron

[0098] category Fe recovery rate % Li recovery rate % Example 1 98.6 98.3 Example 2 97.3 98.1 Example 3 98.1 97.6 Example 4 97.5 97.9 Example 5 84.3 83.7 Example 6 80.3 81.7 Comparative Example 1 84.1 81.9 Comparative Example 2 85.6 83.5

[0099] From the data shown in Table 1, it can be seen that the method provided by the present invention can effectively inhibit the Fe 2+ Oxidation, in which each embodiment Fe 2+ The content of H is maintained at above 95%, showing a relatively good control efficiency. + The concentration gradually decreases with the reaction process, resulting in low leaching efficiency and Fe 2+It is easily oxidized, which not only increases the difficulty of subsequent separation and purification, but also reduces the recovery rate of iron. The three-stage countercurrent leaching system of the present invention ensures the full leaching of valuable elements by precisely controlling the liquid-solid mass ratio, temperature and reaction time of each stage. Specifically, in the first-stage leaching, a liquid-solid mass ratio of 10:1-15:1 (g / g), a temperature of 70-90°C, and stirring reaction for 1-2 hours is adopted; the second-stage leaching liquid-solid mass ratio is 8:1-12:1 (g / g), the temperature is 75-95°C; the third-stage leaching liquid-solid mass ratio is 4:1-10:1 (g / g), and the temperature is 80-100°C. This leaching method of gradually improving the reaction conditions greatly improves the recovery rate of lithium and iron in the leachate. For example, in Example 1, the lithium recovery rate reaches 98.3%, and the iron recovery rate reaches 98.6%. In Example 5, the acid concentration and the reducing agent concentration are greatly reduced (that is, set to the commonly used acid and reducing agent concentrations). Even if a three-stage leaching process is adopted, the Fe 2+ It is easily oxidized during the leaching process. In addition, the recovery rates of Fe and Li are still greatly reduced (about 15%), indicating the importance of the concentration range of acid and reducing agent. In Example 6, the present invention reduces the amount of complexing agent and does not control the pH range, then the recovery rates of Fe and Li also show a significant downward trend, indicating the importance of pH regulation and synergistic application of complexing agents. In Comparative Examples 1 and 2, the lithium recovery rate is only 81.9%-83.5%, and the iron recovery rate is 84.1%-85.6%. This shows that the three-stage countercurrent leaching system of the present invention has significant advantages in improving metal recovery. At the same time, the Li and Fe elements in the embodiments provided by the present invention have a high recovery efficiency, indicating that the multi-stage leaching system can fully leach the Li and Fe elements in lithium iron phosphate, and at the same time couple the pH gradient regulation with the synergistic effect of the complexing agent to precipitate FePO4·2H2O compounds and Li2CO3 in steps to achieve efficient separation of Li / Fe / P, avoiding the complexity of multi-step extraction or high-temperature calcination in traditional processes.

[0100] The above embodiments are intended only to illustrate the technical solutions of the present invention and are not intended to limit the same. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that the technical solutions described in the above embodiments may be modified, or some or all of the technical features thereof may be replaced with equivalents, without departing from the spirit and substance of the claims of the present invention; and such modifications or replacements remain within the scope of the claims of the present invention.

Claims

1. A method for preparing a precursor by treating waste lithium batteries, characterized in that: The following steps are involved: S1. Dismantling the waste lithium iron phosphate battery and separating the pole pieces to obtain the positive pole pieces, separating the active material and the foil, and sieving to obtain waste lithium iron phosphate powder; S2. Adding the waste lithium iron phosphate powder obtained in step S1 into a leachate to dissolve it, and performing three-stage countercurrent leaching to obtain a mixed solution containing iron, lithium and phosphate ions; the leachate is a mixed aqueous solution of sulfuric acid and a reducing agent; S3. The ion mixed solution obtained in step S2 is subjected to pH gradient and complexing agent coordinated regulation, and precipitation is performed step by step to obtain FePO4·2H2O compound and Li2CO3.

2. The method according to claim 1, characterized in that Step S1 specifically includes the following steps: After being completely discharged, the waste lithium iron phosphate batteries are disassembled and the electrodes are separated to obtain the positive electrode electrodes. The electrodes are placed at high temperature for pyrolysis or roasting to separate the active material and the foil, and then screened to obtain waste lithium iron phosphate powder.

3. The method according to claim 2, characterized in that The waste lithium iron phosphate battery is packaged in a square, cylindrical or soft package; The temperature of the pyrolysis or calcination is 300-500° C., and the pyrolysis or calcination atmosphere is vacuum, inert or air atmosphere.

4. The method according to claim 1, wherein The leachate of step S2 is a mixture of a sulfuric acid aqueous solution and a reducing agent aqueous solution, the concentration of the sulfuric acid aqueous solution is 2.0-4.0 mol / L, the concentration of the reducing agent aqueous solution is 0.1-0.3 mol / L, and the volume ratio of the sulfuric acid aqueous solution to the reducing agent aqueous solution is 4:1-6:

1.

5. The method according to claim 4, characterized in that The reducing agent is ascorbic acid or sodium thiosulfate.

6. The method according to claim 1, characterized in that Step S2 specifically includes the following steps: Primary leaching: Mix lithium iron phosphate powder with leachate at a liquid-to-solid mass ratio of 10:1-15:1, and stir at 70-90°C for 1-2 hours to allow some lithium, iron, and phosphorus elements to enter the solution; Secondary leaching: The residue after the primary leaching is mixed with fresh leachate at a liquid-to-solid mass ratio of 8:1-12:1, and stirred at a temperature of 75-95°C for 1-2 hours to further improve the leaching rate of valuable elements; Third-stage leaching: The residue after the second-stage leaching is mixed with fresh leachate at a liquid-to-solid mass ratio of 4:1-10:1, and stirred at a temperature of 80-100°C for 1-2 hours to ensure sufficient leaching of valuable elements; Mixing: The leachates obtained from the three-stage leaching are combined and subjected to solid-liquid separation to obtain an ion mixed solution containing iron, lithium and phosphate.

7. The method according to claim 1, characterized in that Step S3 specifically includes the following steps: Slowly add NaOH aqueous solution to the ion mixture solution, adjust the pH to 3.5±0.1, and the reaction temperature is 60°C. Aluminum and copper impurities are precipitated and separated in the form of Al(OH)3 and Cu(OH)2; Add Na3PO4 aqueous solution to the separated solution at a molar ratio of n(Fe):n(P)=1:1.05, add 10% hydrogen peroxide, adjust the pH to 5.5±0.1, and set the temperature at 70°C to generate amorphous FePO4·2H2O precipitate for separation; The mother liquor after separation is concentrated to Li + Concentration>20g / L, add Na2CO3 aqueous solution, molar ratio n(Li + ):n(CO3 2- )=1:1.05, temperature 60℃, after the reaction, precipitation separation, vacuum drying to obtain Li2CO3 powder.

8. The method according to claim 7, characterized in that The concentration of NaOH aqueous solution is 4.0-6.0 mol / L; the concentration of Na3PO4 aqueous solution is 0.4-0.6 mol / L; the concentration of Na2CO3 aqueous solution is 1.5-2.5 mol / L.

9. The method according to claim 7, characterized in that The vacuum drying temperature is 50-70°C.

10. The method according to claim 7, characterized in that The precipitate is separated by centrifugation or filtration.

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