An EDTA-Ca,Mg decomplexing method for extracting battery-grade lithium carbonate from retired lithium iron phosphate batteries

Abstract

This application relates to the field of lithium carbonate preparation technology, specifically disclosing a method for extracting battery-grade lithium carbonate from retired lithium iron phosphate batteries using EDTA-Ca and Mg decomplexing, comprising the following steps: S1, adjusting the pH of the lithium precipitation mother liquor; S2, oxidative decomplexing; S3, adjusting polarity for precipitation. This application addresses the difficulty in separating stable complexes formed by EDTA with Ca and Mg by employing a three-step process: acidification to adjust the pH to 0.3-1.0 for decomplexing, oxidation to destroy the structure, and solvent precipitation separation. This process efficiently dissociates the complexes and selectively removes impurity ions, offering advantages such as simple process, low cost, and high efficiency. It can achieve a lithium recovery rate of ≥97% and a calcium removal rate of ≥98%, providing a reliable solution for the production of high-purity battery-grade lithium carbonate and showing promising prospects for industrial application.

Description

Technical Field

[0001] This invention relates to the field of lithium carbonate preparation technology, specifically to an EDTA-Ca and Mg decomplexation method for extracting battery-grade lithium carbonate from retired lithium iron phosphate batteries. Background Technology

[0002] With the continuous expansion of the lithium-ion battery industry, lithium resource consumption is showing a year-on-year growth trend. Although my country's lithium reserves rank among the top in the world, they are mainly concentrated in salt lakes. Salt lake lithium generally suffers from high magnesium-to-lithium ratios and complex impurity composition, making separation and purification difficult. Furthermore, salt lake lithium is mainly distributed in the ecologically fragile northwest region, characterized by harsh natural conditions, high development costs, and weak resource supply stability. In contrast, retired lithium iron phosphate batteries have a high lithium enrichment level, with a mass fraction reaching approximately 1.1%, significantly higher than most natural mineral resources, demonstrating good recycling potential. Related statistics show that the power battery of an electric vehicle with a total weight of 1.3–1.7 tons weighs approximately 500 kg, possessing considerable lithium resource recycling value. Given the current market price of battery-grade lithium carbonate at approximately 130,000 yuan / ton, the efficient recycling of lithium resources from spent lithium iron phosphate batteries has significant economic benefits and strategic importance.

[0003] In the recycling process of spent lithium iron phosphate batteries, the lithium sulfate solution obtained after leaching black powder with sulfuric acid usually requires the addition of carbonate ions for lithium precipitation to prepare lithium carbonate products. To remove impurity ions such as calcium and magnesium ions from the leachate, ethylenediaminetetraacetic acid (EDTA) is often added as a complexing agent to form stable complexes with EDTA, thus retaining them in the mother liquor and preventing them from entering the lithium carbonate product during the precipitation process. The mother liquor obtained after lithium precipitation filtration contains a large amount of EDTA-Ca, EDTA-Mg complexes, and a certain concentration of lithium ions. This mother liquor belongs to a sulfuric acid system and contains trace amounts of characteristic impurities such as iron, phosphorus, and fluorine, making the system complex. Due to the interaction between EDTA and Ca... 2+ Mg 2+ The resulting complexes are extremely stable, with stability constants of lgK = 10.7 for EDTA-Ca and 8.7 for EDTA-Mg, making them difficult to effectively dissociate and remove under normal conditions. If the lithium precipitation mother liquor is directly returned to the leaching system for recycling, the EDTA complexes in the mother liquor will continuously accumulate, leading to the cyclical accumulation of calcium and magnesium impurities in the system, severely affecting the quality of subsequent battery-grade lithium carbonate products. According to industry standards for battery-grade lithium carbonate, the Ca and Mg content in premium-grade lithium carbonate must be controlled below 0.025%, with extremely strict requirements on impurity content. Therefore, how to efficiently and cost-effectively destroy the EDTA complexes, achieve effective separation of calcium and magnesium from lithium, and avoid introducing new impurities is a pressing technical problem to be solved in the treatment of lithium precipitation mother liquor from waste lithium iron phosphate batteries.

[0004] For the treatment of lithium-containing mother liquor containing EDTA complexes, several solutions have been proposed in existing technologies. These mainly include the following: 1. Acidification complex-breaking method: Adding strong acid to the solution to lower the pH, relying on hydrogen ions to occupy coordination sites, breaking the binding structure of EDTA with calcium and magnesium, and releasing free calcium and magnesium ions. This process is simple and easy to operate, and is the mainstream industrial method. 2. High-temperature pyrolysis complex-breaking method: Destroying the stable structure of the complex by increasing the solution temperature, weakening the coordination bonds to achieve dissociation. Often used in conjunction with acidification, it significantly improves the decomposition efficiency. 3. Ion replacement complex-breaking method: Introducing metal ions with stronger coordination binding ability, such as iron ions and aluminum ions, to replace the complexed calcium and magnesium ions, followed by unified precipitation to remove impurity ions. 4. Strong oxidative degradation method: Using oxidants such as hydrogen peroxide and sodium hypochlorite to directly oxidize and decompose the EDTA organic framework, breaking the complex system at its source, and thoroughly removing complexing agent residues. 5. Salting-out Concentration and Complex Dissolution Method: This method relies on increasing the salt concentration in the system to change the ion balance, causing the complex to dissociate and precipitate calcium and magnesium ions. It is suitable for the pretreatment of high-concentration lithium-containing solutions. After the above complex dissolution is completed, the impurities can be completely removed by adjusting the alkali and adding carbonate to precipitate free calcium and magnesium, resulting in a highly purified lithium-containing solution. For example, in the prior art, patent CN120793968A discloses a method for removing EDTA-Ca from high-salt, high-chlorine lithium-containing mother liquor. This scheme adopts an acid-adjustment-filtration-alkali-adjustment-oxidation process: First, the pH of the lithium-containing mother liquor is adjusted to acidic and stirred for reaction. Then, it is allowed to stand and filtered to remove the precipitate. Next, the pH of the filtrate is adjusted to alkaline and an oxidant is added for oxidation. Finally, it is heated for a period of time and filtered to remove the precipitate, obtaining the treated lithium-containing mother liquor. The principle of this scheme is: under acidic conditions, the EDTA-Ca complex partially dissociates, releasing Ca... 2+The process involves precipitating and removing calcium and magnesium ions; under alkaline conditions, EDTA is oxidized and degraded using an oxidant, further breaking down the complex structure and causing residual calcium and magnesium to precipitate and be removed as hydroxides. However, the above technical solution has the following shortcomings in practical applications: 1. It requires secondary pH adjustment, which is cumbersome and introduces new impurity ions. After acid-adjusted filtration, the pH of the filtrate needs to be adjusted back from acidic to alkaline. This step inevitably introduces a large amount of alkaline reagents such as NaOH and Na2CO3, resulting in a significant increase in the Na ion concentration in the mother liquor. This not only increases the burden of sodium salt treatment in the subsequent evaporation and crystallization process, but also reduces the lithium carbonate precipitation efficiency in a high-salt system, affecting the overall economic efficiency and product quality. 2. The oxidation efficiency under alkaline conditions is limited, and the complex-breaking effect is not ideal. Under alkaline conditions, the complex stability of EDTA with calcium and magnesium ions is stronger, the complex structure is more stable, and it is more difficult to be oxidized and degraded. Meanwhile, commonly used oxidants are prone to ineffective decomposition under alkaline conditions, reducing their utilization efficiency. If the Fenton system is used to generate OH radicals for oxidation, alkaline conditions are also unfavorable for radical generation and lifetime maintenance, leading to weakened oxidative complex-breaking ability and requiring more oxidant to achieve the desired degradation effect. 3. Heating is required, resulting in high energy consumption. Heating is necessary after the oxidation reaction to promote complete oxidation and sufficient precipitation. After acid conditioning, stirring, and settling, the temperature of the lithium precipitation mother liquor has usually dropped to or near room temperature. Reheating requires a large amount of steam or electricity, significantly increasing energy costs in large-scale industrial production. 4. An intermediate filtration step increases process complexity and lithium mechanical loss. This scheme requires settling and filtration to remove precipitate after acid conditioning, followed by alkaline conditioning and oxidation, and finally filtration to remove precipitate again. The entire process involves two solid-liquid separation operations. Multiple filtrations not only increase equipment investment and floor space requirements but also prolong the process cycle and affect production efficiency. More importantly, intermediate filtration stages can easily cause mechanical entrainment and loss of lithium-containing solutions, reducing lithium recovery rates. 5. Incomplete calcium and magnesium removal fails to meet battery-grade product requirements. Under alkaline conditions, calcium and magnesium ions precipitate as hydroxides. However, in high-salt systems, the solubility of Ca(OH)₂ and Mg(OH)₂ is relatively high, leading to incomplete precipitation reactions and resulting in high residual calcium and magnesium ion content. Furthermore, some intermediate products generated during EDTA oxidation degradation still possess complexing capabilities, potentially forming secondary complexes with calcium and magnesium ions or encapsulating precipitated hydroxides, resulting in incomplete calcium and magnesium removal and failing to meet the stringent impurity content requirements of battery-grade lithium carbonate.

[0005] In summary, existing methods for treating lithium precipitation mother liquor containing EDTA complexes generally suffer from problems such as cumbersome process steps, the need for repeated pH adjustments, the introduction of additional impurity ions, high energy consumption, and incomplete removal of calcium and magnesium. These methods are insufficient to meet the high-efficiency, low-cost, and high-purity processing requirements of waste lithium iron phosphate battery recycling processes. Therefore, there is an urgent need to develop a novel method for lithium extraction from lithium precipitation mother liquor by decomposing EDTA complexes, in order to overcome the shortcomings of the existing technologies. Summary of the Invention

[0006] To address the shortcomings of existing technologies, this invention provides an EDTA-Ca and Mg decomplexing method for extracting battery-grade lithium carbonate from retired lithium iron phosphate batteries. This process can solve the problems of cumbersome processes, introduction of additional impurity ions, incomplete removal of calcium and magnesium, and high energy consumption and cost in existing decomplexing technologies.

[0007] To address the aforementioned problems, this invention provides a method for extracting battery-grade lithium carbonate from retired lithium iron phosphate batteries using EDTA-Ca and Mg decomplexation, comprising the following steps: S1. A method for extracting battery-grade lithium carbonate from retired lithium iron phosphate batteries using EDTA-Ca and Mg decomplexation, characterized by comprising the following steps: S1. Adjusting the pH of lithium precipitation mother liquor: Add acid to the lithium precipitation mother liquor containing EDTA-Ca and Mg complex to adjust the pH of the lithium precipitation mother liquor to acidic, and obtain acidic lithium-containing mother liquor. S2, Oxidative decomposition: An oxidant is added to the acidic lithium-containing mother liquor obtained in S1, and an oxidative decomposition reaction is carried out under stirring conditions to obtain a decomposition mother liquor; S3, Polarity Adjustment Precipitation: Add an organic solvent to the mother liquor obtained in S2 after decomplexation. By adjusting the polarity of the mother liquor after decomplexation, calcium and magnesium ions are precipitated. Then, solid-liquid separation is performed to obtain a purified lithium solution.

[0008] Furthermore, in S1, the pH value of the acidic lithium-containing mother liquor is 0.3~1.0, and the acid includes one or more of sulfuric acid, phosphoric acid, hydrochloric acid, oxalic acid, and acetic acid.

[0009] Further, in S1, the mass fraction of the acid is 98%, and the amount of acid added is 10.0-20.0g per 100g of lithium precipitation mother liquor.

[0010] Furthermore, in S2, the oxidant includes one or more of the following: hydrogen peroxide, permanganate, dichromate, persulfate, potassium chlorate, periodic acid, and oxygen.

[0011] Further, in S2, the mass fraction of the oxidant is 27%, and the amount of the oxidant added is 10.0-50.0g per 100g of lithium precipitation mother liquor.

[0012] Furthermore, in S2, the stirring rate is 300~600 rpm; the oxidative decomposition reaction time is 1~3 hours, and the reaction temperature is room temperature 25±5℃.

[0013] Furthermore, in S3, the organic solvent includes one or more of the following: ethanol, isopropanol, n-propanol, ethyl acetate, ethyl lactate, etc.

[0014] Further, in S3, the addition of organic solvent includes: stopping the addition of organic solvent when the reaction system becomes turbid and produces flocculent precipitate; the solid-liquid separation includes: filtering after flocculent precipitate appears in the reaction system, the obtained filter cake is calcium and magnesium precipitate, and the obtained filtrate is purified lithium solution.

[0015] Furthermore, in S3, the purified lithium solution is returned to S1 as lithium-containing mother liquor to be processed for recycling.

[0016] Furthermore, in S1, the lithium precipitation mother liquor is obtained by leaching sulfuric acid, precipitating lithium with sodium carbonate, and complexing with EDTA after the recovery of black powder from retired lithium iron phosphate batteries.

[0017] Compared with existing technologies, this solution has the following advantages: 1. No need for alkali adjustment of pH, avoiding the introduction of impurity ions. This invention only adds acid to the lithium precipitation mother liquor to adjust the pH to acidic, and there is no need to adjust the pH back to alkaline in subsequent steps, thus avoiding the introduction of Na+. + K + Using alkali metal ions will not increase the salt content of the system or the processing burden of subsequent evaporation and crystallization, which is beneficial to improving the lithium precipitation efficiency and the quality of lithium carbonate products.

[0018] 2. Oxidation under acidic conditions significantly improves complex-breaking efficiency. This invention involves directly adding the oxidant after adjusting the pH, and then carrying out the oxidation reaction under acidic conditions. On one hand, EDTA undergoes carboxylation under acidic conditions, reducing its coordination ability with calcium and magnesium, resulting in a looser complex structure that is more easily oxidized and degraded. On the other hand, oxidants such as H₂O₂ are more stable under acidic conditions and have stronger effective oxidizing power. The acidic decomposition and acidic oxidation produce a synergistic effect, completing acid decomposition and oxidative complex breaking in one step without repeated pH adjustments. The complex-breaking efficiency is significantly better than that of oxidation schemes under alkaline conditions.

[0019] 3. No heat treatment required, low energy consumption. This invention utilizes the high efficiency of oxidation and complex breaking under acidic conditions, allowing the oxidation reaction to proceed efficiently at room temperature without additional heating to accelerate it; the polarity adjustment and precipitation of organic solvents can also be achieved at room temperature without heating to promote precipitation. Compared to existing technologies that require heat treatment, this invention significantly reduces energy consumption, simplifies equipment requirements, and lowers production costs.

[0020] 4. Simplified process, requiring only one solid-liquid separation, reducing lithium loss. This invention employs a continuous operation flow of acid conditioning → oxidation → polarity adjustment → solid-liquid separation, eliminating the need for intermediate filtration between steps. The entire process involves only one solid-liquid separation operation. Compared to existing technologies that require two solid-liquid separations followed by acid conditioning and filtration, plus alkali conditioning and oxidation followed by filtration, this invention reduces equipment investment and operating time, shortens the process cycle, and avoids mechanical entrainment and loss of lithium-containing solution caused by intermediate filtration, thereby improving lithium recovery rate.

[0021] 5. Selective separation of calcium, magnesium, and lithium is achieved by adjusting the polarity of the organic solvent, resulting in more thorough removal. This invention adjusts the polarity of the system by adding an organic solvent after oxidation, utilizing the difference in polarity to achieve selective precipitation: calcium and magnesium salts and EDTA degradation products, due to their high polarity, exhibit significantly reduced solubility and precipitate after the addition of the organic solvent; while lithium salts maintain a certain solubility in the mixed system containing the organic solvent, thus achieving efficient separation of calcium, magnesium, and lithium. Compared to the method of precipitating calcium and magnesium as hydroxides under alkaline conditions, the solvent precipitation method is not limited by the high solubility of Ca(OH)₂ and Mg(OH)₂ in high-salt systems, resulting in more thorough removal of calcium and magnesium and meeting the stringent requirements for impurity content in battery-grade lithium carbonate. Furthermore, the organic solvents used, such as ethanol, isopropanol, n-propanol, and ethyl acetate, have low boiling points and can be recycled through distillation, reducing production costs.

[0022] 6. Acidic oxidation and organic solvent polarity adjustment have a synergistic effect. The steps in this invention are not simply additive, but rather synergistic: oxidation under acidic conditions leads to the efficient degradation of EDTA, releasing Ca... 2+ / Mg 2+ In a free state; at this point, adding an organic solvent directly to adjust the polarity will release the free Ca. 2+ / Mg 2+ Due to their high polarity, the solubility of EDTA degradation products drops sharply in low-polarity environments, causing them to precipitate immediately. This forms a highly efficient combination of acidic complex breaking and polar precipitation, completing decomplexing and separation in one continuous step without the need for alkali adjustment, heating, or intermediate filtration, thus significantly improving the overall process efficiency. Attached Figure Description

[0023] Figure 1 This is a process flow diagram of the present invention. Detailed Implementation

[0024] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0025] The lithium precipitation mother liquor used in the embodiments of the present invention is all the mother liquor obtained by leaching sulfuric acid, precipitating lithium with sodium carbonate, and complexing with EDTA after the black powder of retired lithium iron phosphate batteries is recycled.

[0026] Example 1 like Figure 1 As shown, this embodiment provides an EDTA-Ca,Mg decomplexing method for extracting battery-grade lithium carbonate from retired lithium iron phosphate batteries: Take 100g of lithium precipitation mother liquor (pH=8.54), add 12.28g of 98% sulfuric acid to adjust the pH to 0.55. The solution becomes clear. Add 45.25g of 27% hydrogen peroxide and stir at 550rpm for 3 hours to ensure the EDTA structure is fully destroyed. Then, add ethanol in two steps: first, add 50.25g of ethanol. After white bubbles appear, add another 24.08g of ethanol. The system becomes turbid and flocculent precipitate forms. Then, perform solid-liquid separation to obtain filtrate and filter residue, and analyze the composition of filtrate and filter residue.

[0027] Example 2 Take 100g of lithium precipitation mother liquor, pH=8.54, add 14.60g of 98% sulfuric acid, adjust the pH to 0.58, the solution becomes clear, add 21.23g of 27% hydrogen peroxide, stir at 550rpm for 3h, add 21.11g of ethanol, a white substance is produced, the system separates into layers, then solid-liquid separation is performed to obtain filtrate and filter residue, and the composition of filtrate and filter residue is analyzed.

[0028] Example 3 Take 100g of lithium precipitation mother liquor, pH=8.62, add 10.96g of 98% sulfuric acid, adjust the pH to 0.48, add 10.73g of 27% hydrogen peroxide, stir at 550rpm for 3h, add 42.37g of ethanol, the system becomes turbid, a white salt-like precipitate appears at the bottom of the beaker, and small white flocculent matter is suspended in the system. Then perform solid-liquid separation to obtain filtrate and filter residue, and analyze the composition of filtrate and filter residue.

[0029] Example 4 Take 100g of lithium precipitation mother liquor, pH=8.62, add 13.61g of 98% sulfuric acid, adjust the pH to 0.52, add 20.08g of 27% hydrogen peroxide, stir at 550rpm for 3h, add 43.15g of ethanol, the system becomes turbid and large white flocculents appear, then perform solid-liquid separation to obtain filtrate and filter residue, and analyze the composition of filtrate and filter residue.

[0030] Comparative Example 1 Take 100g of lithium precipitation mother liquor with pH=8.75, add 10.88g of 98% sulfuric acid, adjust the pH to 0.5, the solution changes from yellow-green to sunset yellow and bubbles are generated, add 100g of 27% hydrogen peroxide, stir at 550rpm and react for 3h, add 100g of ethanol, a white suspension layer appears, then perform solid-liquid separation to obtain filtrate and filter residue, and analyze the composition of filtrate and filter residue.

[0031] Comparative Example 2 Take 100g of lithium precipitation mother liquor, pH=8.75, add 6.01g of 98% sulfuric acid, adjust the pH to 0.94, the solution changes from yellow-green to light sunset yellow, and bubbles are generated. Add 100g of 27% hydrogen peroxide, stir at 550rpm, react for 3h, add 100g of ethanol, a white suspension layer appears, the supernatant is turbid in the middle and the bottom is clear. Then perform solid-liquid separation to obtain filtrate and filter residue, and crystals are found at the bottom of the beaker. Analyze the composition of the filtrate, filter residue and crystals.

[0032] Comparative Example 3 Take 100g of lithium precipitation mother liquor, pH=8.66, and crystals precipitate at room temperature. Add 15.55g of 98% sulfuric acid to adjust the pH to 0.56, and the solution becomes clear. Add 100g of 27% hydrogen peroxide, stir at 550rpm, and react for 3h. Add 100g of ethanol, and the solution becomes turbid. Then, perform solid-liquid separation to obtain filtrate and filter residue, and analyze the composition of filtrate and filter residue.

[0033] Comparative Example 4 Take 100g of lithium precipitation mother liquor, pH=8.66, crystals precipitate at room temperature, add 13.28g of 98% sulfuric acid, adjust the pH to 0.57, the solution becomes clear, add 100g of 27% hydrogen peroxide, stir at 550rpm, react for 3h, add 100g of ethanol, the solution turns milky white, then perform solid-liquid separation to obtain filtrate and filter residue, and crystals are found at the bottom of the beaker, and analyze the composition of filtrate, filter residue, and crystals.

[0034] The filtrates and filter residues obtained from Examples 1-4 and Comparative Examples 1-4 were analyzed, and the calcium and lithium recovery rates were calculated, as shown in Table 1 below: Table 1. Filtrate and Filter Residue Conditions of Examples and Comparative Examples

[0035]

[0036] Results analysis: 1. In the lithium solutions finally obtained in Examples 1-4 of the present invention, the lithium recovery rate is as high as 97% or more, while the highest of Comparative Examples 1-4 is only 95% and the lowest is 23%, indicating that their process parameters are unreasonable, resulting in a large amount of lithium co-precipitation or crystallization.

[0037] 2. In the final filter residue obtained in Examples 1-4 of the present invention, the calcium removal rate is as high as 98% or more, while the highest of Comparative Examples 1-4 is only 86% and the lowest is 73%.

[0038] 3. The amount of hydrogen peroxide used in Examples 1-4 of this invention is 10-50g, which is much lower than the 100g used in the comparative example, indicating that the oxidation efficiency is higher under strongly acidic conditions.

[0039] 4. The amount of ethanol used in this embodiment of the invention is lower: 20~75g vs 100g, and it is added gradually until the mixture becomes turbid, thus avoiding excessive use.

[0040] In summary, the strong acid + oxidant + organic solvent polar precipitation scheme represented by Examples 1-4 of this invention shows significant advantages in four aspects—calcium removal efficiency, lithium retention rate, reagent consumption, and precipitation controllability—when treating lithium precipitation mother liquor containing EDTA-calcium / magnesium, compared with the comparative examples where parameters deviated or reagent dosages were inappropriate.

[0041] The above descriptions are merely embodiments of the present invention, and common knowledge regarding specific structures and characteristics is not elaborated upon here. It should be noted that those skilled in the art can make various modifications and improvements without departing from the structure of the present invention, and these should also be considered within the scope of protection of the present invention. These modifications and improvements will not affect the effectiveness of the present invention or the practicality of the patent. The scope of protection claimed in this application should be determined by the content of its claims, and the specific embodiments described in the specification can be used to interpret the content of the claims.

Claims

1. A method for extracting battery-grade lithium carbonate from retired lithium iron phosphate batteries using EDTA-Ca and Mg decomplexation, characterized in that: Includes the following steps: S1. Adjusting the pH of lithium precipitation mother liquor: Add acid to the lithium precipitation mother liquor containing EDTA-Ca and Mg complex to adjust the pH of the lithium precipitation mother liquor to acidic, and obtain acidic lithium-containing mother liquor. S2, Oxidative decomposition: An oxidant is added to the acidic lithium-containing mother liquor obtained in S1, and an oxidative decomposition reaction is carried out under stirring conditions to obtain a decomposition mother liquor; S3, Polarity Adjustment Precipitation: Add an organic solvent to the mother liquor obtained in S2 after decomplexation. By adjusting the polarity of the mother liquor after decomplexation, calcium and magnesium ions are precipitated. Then, solid-liquid separation is performed to obtain a purified lithium solution.

2. The EDTA-Ca and Mg decomplexing method for extracting battery-grade lithium carbonate from retired lithium iron phosphate batteries according to claim 1, characterized in that: In S1, the pH value of the acidic lithium-containing mother liquor is 0.3~1.0, and the acid includes one or more of sulfuric acid, phosphoric acid, hydrochloric acid, oxalic acid, and acetic acid.

3. The EDTA-Ca and Mg decomplexing method for extracting battery-grade lithium carbonate from retired lithium iron phosphate batteries according to claim 1, characterized in that: In S1, the mass fraction of the acid is 98%, and the amount of acid added is 10.0-20.0g per 100g of lithium precipitation mother liquor.

4. The EDTA-Ca and Mg decomplexing method for extracting battery-grade lithium carbonate from retired lithium iron phosphate batteries according to claim 1, characterized in that: In S2, the oxidant includes one or more of the following: hydrogen peroxide, permanganate, dichromate, persulfate, potassium chlorate, periodic acid, and oxygen.

5. The EDTA-Ca and Mg decomplexing method for extracting battery-grade lithium carbonate from retired lithium iron phosphate batteries according to claim 1, characterized in that: In S2, the oxidant has a mass fraction of 27%, and the amount of oxidant added is 10.0-50.0g per 100g of lithium precipitation mother liquor.

6. The EDTA-Ca,Mg decomplexing method for extracting battery-grade lithium carbonate from retired lithium iron phosphate batteries according to claim 1, characterized in that: In S2, the stirring rate is 300~600 rpm; the oxidative decomposition and complexation reaction time is 1~3 hours, and the reaction temperature is room temperature 25±5℃.

7. The EDTA-Ca and Mg decomplexing method for extracting battery-grade lithium carbonate from retired lithium iron phosphate batteries according to claim 1, characterized in that: In S3, the organic solvent includes one or more of the following: ethanol, isopropanol, n-propanol, ethyl acetate, ethyl lactate, etc.

8. The EDTA-Ca and Mg decomplexing method for extracting battery-grade lithium carbonate from retired lithium iron phosphate batteries according to claim 1, characterized in that: In S3, the addition of organic solvent includes: stopping the addition of organic solvent when the reaction system becomes turbid and produces flocculent precipitate; the solid-liquid separation includes: filtering after flocculent precipitate appears in the reaction system, the obtained filter residue is calcium and magnesium precipitate, and the obtained filtrate is purified lithium solution.

9. The EDTA-Ca and Mg decomplexing method for extracting battery-grade lithium carbonate from retired lithium iron phosphate batteries according to claim 1, characterized in that: In S3, the purified lithium solution is returned to S1 as lithium-containing mother liquor to be processed and recycled.

10. The EDTA-Ca,Mg decomplexing method for extracting battery-grade lithium carbonate from retired lithium iron phosphate batteries according to claim 1, characterized in that: In S1, the lithium precipitation mother liquor is obtained by leaching sulfuric acid, precipitating lithium with sodium carbonate, and complexing with EDTA after the recovery of black powder from retired lithium iron phosphate batteries.

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