Method for extracting lithium and removing impurities from electrolyte by high-pressure heat treatment and application thereof

Abstract

The application belongs to the technical field of new energy material separation and extraction, and relates to a method for extracting lithium and removing impurities from electrolyte through high-pressure heat treatment and application. The method comprises the following steps: solid electrolyte sample pretreatment, functional leaching agent premixing reaction, high-pressure heating and pressure steaming treatment, and three-stage impurity removal treatment. Through optimization of the lithium extraction and impurity removal steps and the composition of the auxiliary agent, the obtained lithium extraction liquid has high leaching rate, small loss rate, few impurities and high purity, and can be applied to lithium extraction of solid electrolyte samples, and has wide application prospect.

Description

Technical Field

[0001] This invention belongs to the field of new energy material separation and extraction technology, and relates to a method and application of lithium extraction and impurity removal by high-pressure heat treatment of electrolytes. More specifically, it relates to a method for efficiently extracting lithium from an electrolyte system under high-pressure heat treatment conditions using functional additives. Background Technology

[0002] With the widespread application of lithium batteries in new energy vehicles, energy storage, and 3C electronics, the efficient development and recycling of lithium resources has become a key link in the industrial chain. During processes such as lithium salt synthesis, hydrometallurgy, battery recycling, and by-product treatment, large amounts of lithium-rich solid electrolyte residues are often generated, including dried electrolyte precipitates, thermal decomposition byproducts, membrane fouling, and dried residual liquid. In these solid samples, lithium is typically in the form of Li. + It exists in the form of bound salts or complexes, with a content between 2% and 15%, accompanied by a large number of insoluble or co-precipitated impurities, such as Al. 3+ Fe 3+ Mg 2+ Ca 2+ Na + F - PO4 3- These substances, with their complex composition and dense structure, often exist in particulate or aggregate form, posing a significant obstacle to the efficient release and subsequent extraction of lithium.

[0003] Current methods for extracting lithium from these solid electrolytes mainly include acid leaching-lithium precipitation, calcination-water leaching, solvent extraction, and membrane separation. However, these methods generally suffer from a series of technical bottlenecks: First, acid leaching easily causes impurities to dissolve simultaneously, making lithium-impurity separation difficult; second, the calcination-water leaching method requires high-temperature treatment, resulting in high energy consumption and numerous side reactions; while membrane methods and extraction technologies have poor adaptability to solid-liquid systems, low processing efficiency, and are sensitive to systems with coexisting impurities. Especially in high-impurity environments, traditional methods struggle to achieve highly selective lithium extraction, often resulting in high lithium loss rates and low purity of lithium-rich solutions, severely restricting subsequent resource utilization.

[0004] To address the aforementioned issues, recent research has increasingly focused on introducing functional additives or auxiliary leaching agents during lithium extraction from solid-state electrolytes to regulate the dissolution behavior and separation mechanism of lithium at the liquid-solid interface. These functional reagents, such as chelating agents, structure-directing agents, and complexing stabilizers, can enhance lithium migration and inhibit impurity co-dissolution under certain conditions. However, most additives exhibit poor stability under strong acid or high-temperature, high-pressure conditions, easily becoming inactive or captured by impurities, or even reacting with impurities to form precipitates, leading to secondary lithium encapsulation or adsorption, thus exacerbating lithium loss. This is especially true in high-pressure heat treatment systems, where reagent temperature resistance and selectivity are even more critical. Therefore, there is an urgent need to develop a functional additive system suitable for lithium extraction from solid-state electrolytes, and to achieve efficient lithium extraction and low-loss impurity removal by regulating the lithium dissolution pathway and impurity separation methods. Summary of the Invention

[0005] To address the aforementioned shortcomings, this invention provides a method for lithium extraction and impurity removal via high-pressure heat treatment of electrolytes, along with its application. This extraction method achieves high lithium leaching rate, low loss rate, few impurities, and high purity, and can be applied to lithium extraction from solid electrolyte samples, demonstrating broad application prospects.

[0006] The purpose of this invention is to provide a method for lithium extraction and impurity removal through high-pressure heat treatment of electrolytes, the method comprising the following steps: (1) After mechanically crushing the solid electrolyte sample, dry it for later use; (2) Mix the pretreated solid raw material from step (1) with the functional leaching agent solution and stir the mixture under normal pressure for 30-60 min; (3) Transfer the premixed reaction system from step (2) into a sealed reactor and cook under high pressure for 1-4 hours. (4) Cool the system after high-pressure treatment in step (3) to room temperature, and separate the solid and liquid to obtain a lithium-rich liquid; (5) Add impurity remover A to the lithium-rich solution obtained in step (4) for primary impurity removal, add impurity remover B for secondary impurity removal, add impurity remover C for tertiary impurity removal, filter after treatment, and obtain lithium extraction solution.

[0007] This invention first pretreats the solid electrolyte sample for lithium extraction to ensure that the functional leaching agent penetrates into the particles and avoids side reactions and scaling problems caused by water or impurities during subsequent pressure cooking. Then, the functional leaching agent promotes the migration of lithium ions from the solid sample to the liquid phase and forms a weak complex with lithium, thereby improving the efficiency of subsequent pressure cooking and inhibiting the co-dissolution of impurities. Next, high-pressure heat treatment is performed to partially break the solid sample structure, and the lithium ions encapsulated inside migrate to the liquid phase under the synergistic effect of the functional leaching agent. During this process, the complexation between lithium and the additives is in dynamic equilibrium, while some coexisting impurities such as magnesium ions and sodium ions remain in the solid phase due to the formation of ineffective complexes. Finally, a stepwise impurity removal method combining acidic impurity removal, alkaline impurity removal, and complexation impurity removal is used to remove various soluble impurities. The resulting lithium extraction solution has a high lithium leaching rate, low lithium loss rate, low impurity ion content, and high lithium extraction efficiency.

[0008] Preferably, in step (1) of the above technical solution, the solid electrolyte sample is crushed to a particle size of -200 mesh with a volume ratio greater than 60%, and dried at 80℃ for 4-8 hours. After pretreatment, the sample has a uniform texture and a clean surface, which is conducive to the full contact between the functional leaching agent and the effective lithium component in the solid sample in the subsequent reaction, thereby improving the leaching efficiency.

[0009] Preferably, in step (2) of the above technical solution, the solid raw material and the functional leaching agent solution are mixed at a solid-liquid ratio of 1:10-20.

[0010] Preferably, in step (2) of the above technical solution, the functional leaching agent is at least one of sodium polyacrylate, ASDA, sodium fluoroacetate, and ATMP-type additives. Among them, sodium polyacrylate (PAA-Na) can provide carboxyl complex sites to weakly chelate Li. + Inhibit Ca 2+ ASDA (aspartic acid-N,N-diacetic acid) for Li + It has strong affinity; sodium fluoroacetate can enhance the selective migration of lithium; ATMP (triphosphonic acid) type adjuvants can provide multi-toothed complexation, all of which can promote lithium leaching.

[0011] Preferably, in step (2) of the above technical solution, the concentration of the functional leachate solution is 1.0-5.0 g / L, and more preferably 2.0-3.5 g / L.

[0012] Preferably, in step (3) of the above technical solution, the pressure cooking conditions are: temperature 120-160℃, pressure 0.3-0.8MPa. Pressure cooking under high pressure heating conditions can accelerate the dissolution of lithium and improve efficiency.

[0013] Preferably, in step (5) of the above technical solution, the impurity removal agent A is sodium citrate with a concentration of 2-3 g / L, and the reaction conditions for primary impurity removal are: pH 4.0-4.5, temperature 30-40℃, and time 30-60 min.

[0014] Preferably, in step (5) of the above technical solution, the impurity remover B is sodium oxalate or ammonium oxalate with a concentration of 1.5-3.5 g / L, and the reaction conditions for secondary impurity removal are: pH 8-11, temperature 50-90℃, and time 30-60 min; the impurity remover C is diethylenetriamine pentamethylphosphonic acid or ammonium polyphosphate with a concentration of 1.0-4.0 g / L, and the reaction conditions for tertiary impurity removal are: temperature 10-60℃ and time 30-60 min. The resulting lithium-rich solution contains, in addition to Li... + In addition, it may also contain various soluble impurities, such as Al. 3+ Fe 3+ Mg 2+ Ca 2+ N + K + F - The lithium solution requires multiple stages and classification methods to remove impurities, ensuring its purity. This technical solution first performs a primary acidic purification process to remove Fe... 3+ And Al 3+ The precipitate is converted into a chelate and removed, followed by a secondary alkaline purification process to precipitate Ca. 2 + Mg 2+ Oxalate is formed, and finally, a three-stage complexation process is performed to remove impurities, leaving residual Mg. 2+ Na + Once a stable complex is formed, it is removed by further filtration.

[0015] The present invention also provides an application of the above-mentioned lithium extraction and impurity removal methods in lithium extraction from solid electrolyte samples.

[0016] Advantages compared to existing technologies: This invention optimizes the lithium extraction process by utilizing a functional leaching agent to promote the migration of lithium ions from the solid sample to the liquid phase and to form a weak complex with lithium, thereby improving the efficiency of subsequent pressure cooking and inhibiting the co-dissolution of impurities. A high-pressure heat treatment is then performed, causing partial rupture of the solid sample structure. The internally encapsulated lithium ions migrate to the liquid phase under the synergistic effect of the functional leaching agent, while some coexisting impurities such as magnesium and sodium ions remain in the solid phase due to the formation of ineffective complexes. Finally, a three-stage impurity removal process (acidic impurity removal, alkaline impurity removal, and complexation impurity removal) removes various soluble impurities, resulting in a lithium extraction solution with high lithium leaching rate, low lithium loss rate, low impurity ion content, and high lithium extraction efficiency.

[0017] The lithium extraction and impurity removal method of this invention is simple, efficient, and widely applicable. It can be applied to lithium extraction from solid electrolyte samples such as lithium fluoride-based solid samples, phosphate-type solid samples, aluminum-silicon mixed salt solid samples, and residual lithium salt by-products. Detailed Implementation

[0018] The above-described technical features of the present invention and the technical features specifically described below (such as in the embodiments) can be combined with each other to form new or preferred technical solutions. However, the present invention is not limited to these embodiments, nor are these embodiments limited in any way.

[0019] Unless otherwise specified, the experimental methods used in the following examples are conventional methods. Unless otherwise specified, the formulations involved in the following examples are all commercially available products that can be purchased from the market.

[0020] The present invention will be further described in detail below with reference to embodiments: Example 1 A method for lithium extraction and impurity removal by high-pressure heat treatment of electrolyte, the method comprising the following steps: (1) After mechanically crushing the lithium fluoride-based solid sample to a volume ratio of -200 mesh greater than 60%, dry it at 80℃ for 4-8 hours for later use; (2) The lithium fluoride-based solid sample pretreated in step (1) was mixed with sodium polyacrylate solution (2.5 g / L) at a solid-liquid ratio of 1:15 and stirred for 45 min under normal pressure. (3) Transfer the premixed reaction system from step (2) into a sealed reactor and cook it under high pressure heating conditions of 140℃ and 0.5MP for 3 hours. (4) Cool the system after high-pressure treatment in step (3) to room temperature, and separate the solid and liquid to obtain a lithium-rich liquid; (5) Add sodium citrate (2 g / L) to the lithium-rich solution obtained in step (4) and perform primary impurity removal at pH 4.0-4.5 and temperature 30℃ for 60 min; then add sodium oxalate (3.5 g / L) and perform secondary impurity removal at pH 8-11 and temperature 50℃ for 60 min; finally add diethylenetriamine pentamethylphosphonic acid (1.0 g / L) and perform tertiary impurity removal at 40℃ for 50 min. After the treatment is completed, filter to obtain lithium extraction solution.

[0021] Example 2 A method for lithium extraction and impurity removal by high-pressure heat treatment of electrolyte, the method comprising the following steps: (1) After mechanically crushing the phosphate solid sample to a volume ratio of more than 60% of the particle size of -200 mesh, dry it at 80℃ for 4-8 hours for later use; (2) The phosphate-type solid sample pretreated in step (1) was mixed with sodium polyacrylate solution (2.5 g / L) at a solid-liquid ratio of 1:15 and stirred for 45 min under normal pressure. (3) Transfer the premixed reaction system from step (2) into a sealed reactor and cook it under high pressure heating conditions of 140℃ and 0.5MP for 3 hours. (4) Cool the system after high-pressure treatment in step (3) to room temperature, and separate the solid and liquid to obtain a lithium-rich liquid; (5) Add sodium citrate (2 g / L) to the lithium-rich solution obtained in step (4) and perform primary impurity removal at pH 4.0-4.5 and temperature 35℃ for 40 min; then add sodium oxalate (3.5 g / L) and perform secondary impurity removal at pH 8-11 and temperature 70℃ for 40 min; finally add diethylenetriamine pentamethylphosphonic acid (1.0 g / L) and perform tertiary impurity removal at 10℃ for 60 min. After the treatment is completed, filter to obtain lithium extraction solution.

[0022] Example 3 A method for lithium extraction and impurity removal by high-pressure heat treatment of electrolyte, the method comprising the following steps: (1) After mechanically crushing the aluminum-silicon mixed salt solid sample to a volume ratio of more than 60% with a particle size of -200 mesh, dry it at 80℃ for 4-8 hours for later use; (2) The aluminum-silicon mixed salt solid sample pretreated in step (1) was mixed with sodium polyacrylate solution (2.5 g / L) at a solid-liquid ratio of 1:15 and stirred for 45 min under normal pressure. (3) Transfer the premixed reaction system from step (2) into a sealed reactor and cook it under high pressure heating conditions of 140℃ and 0.5MP for 3 hours. (4) Cool the system after high-pressure treatment in step (3) to room temperature, and separate the solid and liquid to obtain a lithium-rich liquid; (5) Add sodium citrate (3g / L) to the lithium-rich solution obtained in step (4) and perform primary impurity removal at pH 4.0-4.5 and temperature 40℃ for 30 min; then add sodium oxalate (1.5g / L) and perform secondary impurity removal at pH 8-11 and temperature 90℃ for 30 min; finally add diethylenetriamine pentamethylphosphonic acid (2.0g / L) and perform tertiary impurity removal at 50℃ for 30 min. After the treatment is completed, filter to obtain lithium extraction solution.

[0023] Example 4 A method for lithium extraction and impurity removal by high-pressure heat treatment of electrolyte, the method comprising the following steps: (1) After mechanically crushing the residual lithium salt by-products to a volume ratio of more than 60% for particles of -200 mesh, dry them at 80℃ for 4-8 hours for later use; (2) The residual lithium salt byproducts after pretreatment in step (1) are mixed with sodium polyacrylate solution (2.5 g / L) at a solid-liquid ratio of 1:15 and stirred for 45 min under normal pressure. (3) Transfer the premixed reaction system from step (2) into a sealed reactor and cook it under high pressure heating conditions of 140℃ and 0.5MP for 3 hours. (4) Cool the system after high-pressure treatment in step (3) to room temperature, and separate the solid and liquid to obtain a lithium-rich liquid; (5) Add sodium citrate (2g / L) to the lithium-rich solution obtained in step (4) and perform primary impurity removal at pH 4.0-4.5 and temperature 40℃ for 30 min; then add sodium oxalate (2g / L) and perform secondary impurity removal at pH 8-11 and temperature 60℃ for 50 min; finally add diethylenetriamine pentamethylphosphonic acid (1.0-4.0g / L) and perform tertiary impurity removal at 30-40℃ for 30-60 min. After treatment, filter to obtain lithium extraction solution.

[0024] Example 5 A method for lithium extraction and impurity removal by high-pressure heat treatment of electrolyte, the method comprising the following steps: (1) After mechanically crushing the lithium fluoride-based solid sample to a volume ratio of -200 mesh greater than 60%, dry it at 80℃ for 4-8 hours for later use; (2) The lithium fluoride-based solid sample pretreated in step (1) was mixed with ASDA solution (2.5 g / L) at a solid-liquid ratio of 1:15 and stirred for 45 min under normal pressure. (3) Transfer the premixed reaction system from step (2) into a sealed reactor and cook it under high pressure heating conditions of 140℃ and 0.5MP for 3 hours. (4) Cool the system after high-pressure treatment in step (3) to room temperature, and separate the solid and liquid to obtain a lithium-rich liquid; (5) Add sodium citrate (2 g / L) to the lithium-rich solution obtained in step (4) and perform primary impurity removal at pH 4.0-4.5 and temperature 30℃ for 60 min; then add sodium oxalate (3.5 g / L) and perform secondary impurity removal at pH 8-11 and temperature 50℃ for 60 min; finally add diethylenetriamine pentamethylphosphonic acid (1.0 g / L) and perform tertiary impurity removal at 40℃ for 50 min. After the treatment is completed, filter to obtain lithium extraction solution.

[0025] Example 6 A method for lithium extraction and impurity removal by high-pressure heat treatment of electrolyte, the method comprising the following steps: (1) After mechanically crushing the lithium fluoride-based solid sample to a volume ratio of -200 mesh greater than 60%, dry it at 80℃ for 4-8 hours for later use; (2) The solid raw material after pretreatment in step (1) is mixed with sodium fluoroacetate solution (2.5 g / L) at a solid-liquid ratio of 1:15 and stirred for 45 min under normal pressure; (3) Transfer the premixed reaction system from step (2) into a sealed reactor and cook it under high pressure heating conditions of 140℃ and 0.5MP for 3 hours. (4) Cool the system after high-pressure treatment in step (3) to room temperature, and separate the solid and liquid to obtain a lithium-rich liquid; (5) Add sodium citrate (2g / L) to the lithium-rich solution obtained in step (4) and perform primary impurity removal at pH 4.0-4.5 and temperature 30℃ for 60 min; then add ammonium oxalate (3.5g / L) and perform secondary impurity removal at pH 8-11 and temperature 50℃ for 60 min; finally add diethylenetriamine pentamethylphosphonic acid (1.0g / L) and perform tertiary impurity removal at 40℃ for 50 min. After the treatment is completed, filter to obtain lithium extraction solution.

[0026] Example 7 A method for lithium extraction and impurity removal by high-pressure heat treatment of electrolyte, the method comprising the following steps: (1) After mechanically crushing the lithium fluoride-based solid sample to a volume ratio of -200 mesh greater than 60%, dry it at 80℃ for 4-8 hours for later use; (2) Mix the pretreated solid raw material from step (1) with ATMP solution (2.5 g / L) at a solid-liquid ratio of 1:15 and stir the mixture under normal pressure for 45 min. (3) Transfer the premixed reaction system from step (2) into a sealed reactor and cook it under high pressure heating conditions of 140℃ and 0.5MP for 3 hours. (4) Cool the system after high-pressure treatment in step (3) to room temperature, and separate the solid and liquid to obtain a lithium-rich liquid; (5) Add sodium citrate (2g / L) to the lithium-rich solution obtained in step (4) and perform primary impurity removal at pH 4.0-4.5 and temperature 30℃ for 60 min; then add sodium oxalate (3.5g / L) and perform secondary impurity removal at pH 8-11 and temperature 50℃ for 60 min; finally add ammonium polyphosphate (1.0g / L) and perform tertiary impurity removal at 40℃ for 50 min. After the treatment is completed, filter to obtain lithium extraction solution.

[0027] Comparative Example 1 A method for lithium extraction and impurity removal by high-pressure heat treatment of electrolyte, the method differs from Example 1 in that step (2) is: the lithium fluoride-based solid sample pretreated in step (1) is mixed with deionized water at a solid-liquid ratio of 1:15 and stirred under normal pressure for 45 min.

[0028] Comparative Example 2 A method for lithium extraction and impurity removal by high-pressure heat treatment of electrolyte, the method differs from Example 1 in that step (2) is: the lithium fluoride-based solid sample pretreated in step (1) is mixed with a 20% concentration mixed solution of aluminum sulfate and NaCl (molar ratio of 1:1) at a solid-liquid ratio of 1:15, and stirred for 45 min under normal pressure.

[0029] Comparative Example 3 A method for lithium extraction and impurity removal by high-pressure heat treatment of electrolyte, the method differs from Example 1 in that step (5) is: adding a pH adjuster to adjust to 4.5-6.5 to the lithium-rich solution obtained in step (4), adding aluminum hydroxide (4.0 g / L) at 35°C for impurity removal, filtering, and obtaining lithium extraction solution.

[0030] Comparative Example 4 A method for lithium extraction and impurity removal by high-pressure heat treatment of electrolyte, the method differs from that in Example 1 in that step (5) is: the lithium-rich liquid obtained in step (4) is filtered to remove impurities, and lithium extraction liquid is obtained.

[0031] Test case The lithium and impurities in the lithium extraction solutions obtained in Examples 1-7 and Comparative Examples 1-4 were tested, and the lithium leaching rate, lithium loss rate, and impurity residue were calculated. The results are shown in Table 1. Among them, lithium was determined by atomic absorption spectrometry.

[0032] Table 1 Test Results

[0033] As can be seen from the results in Table 1, the lithium extraction and impurity removal methods of Examples 1-7 using the present invention resulted in lithium liquids with high leaching rates, low impurity residues, and low lithium loss rates. Specifically, in Examples 1-4, for different electrolyte solid sample types, the lithium leaching rate consistently reached over 94%, with lithium loss rates controlled between 3-6%, and the impurity ions (Al) were also effectively reduced. 3+ Fe 3+ Mg 2+ The content of lithium (etc.) was all below 80 ppm, indicating that the lithium extraction and impurity removal method of the present invention is feasible, and the leaching agent has good versatility for various solid sample systems, with high and stable lithium extraction efficiency. In Examples 1 and 5-7, the lithium leaching rate of different functional leaching agents was above 92%, but sodium polyacrylate showed the best performance in lithium loss control, while ATMP had slightly worse impurity control ability. This indicates that the selectivity of functional leaching agents for lithium is structure-related, and the weak complexation of lithium by polycarboxylic acid additives is more conducive to dissolution and subsequent separation. These further prove the superiority and feasibility of the lithium extraction and impurity removal method of the present invention.

[0034] In Comparative Example 1, without the addition of a functional leaching agent, the lithium leaching rate was only 61.5%, with an impurity content as high as 200 ppm and a lithium loss rate of 12.5%, indicating that the functional leaching agent is crucial for improving lithium mobility and selectivity. Comparative Example 2, using a traditional auxiliary agent, showed lower lithium leaching rate, loss rate, and impurity removal effect compared to Example 1, demonstrating that the design of the functional leaching agent in this invention is significantly superior to traditional small-molecule auxiliary systems. Comparative Example 3, using a traditional impurity removal agent (NaOH pH adjustment + Al(OH)3 precipitation), had an impurity residue of 140 ppm, a removal rate of only 80.7%, and a lithium loss rate of 9.2%. Compared to Example 1, with an impurity residue of 72 ppm, a removal rate of 95.4%, and a lithium loss rate of 4.3%, its lithium extraction effect was significantly worse, likely due to the removal of Fe. 3+ And Al 3+ But for Mg 2+ and Ca 2+ It had no effect. In Comparative Example 4, the final step was simply filtration of the over-rich lithium solution, which did not remove subsequent impurity ions, resulting in low lithium purity in the lithium extraction solution.

[0035] In summary, this invention optimizes the lithium extraction and impurity removal process by combining sample pretreatment, functional leaching agent premixing reaction, high-pressure heating and steaming treatment, and three-stage impurity removal treatment. Simultaneously, it optimizes the composition of the leaching agent and impurity remover, resulting in a lithium extraction solution with high lithium leaching rate, low loss rate, few impurities, and high purity. This solution can be applied to lithium extraction from solid electrolyte samples and has broad application prospects.

[0036] Finally, it should be emphasized that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention can have various changes and modifications. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for lithium extraction and impurity removal through high-pressure heat treatment of an electrolyte, characterized in that, The method includes the following steps: (1) Crush the solid electrolyte sample to a particle size of 200 mesh with a volume ratio greater than 60%, and dry it at 80°C for 4-8 hours; (2) Mix the pretreated solid raw material from step (1) with the functional leaching agent solution and stir the mixture under normal pressure for 30-60 minutes; the functional leaching agent is at least one of sodium polyacrylate, ASDA, sodium fluoroacetate, and ATMP type additives. (3) Transfer the premixed reaction system from step (2) into a sealed reactor and cook it under high pressure heating conditions of 140℃ and 0.5MPa for 1-4 hours. (4) Cool the system after high-pressure treatment in step (3) to room temperature, and separate the solid and liquid to obtain a lithium-rich liquid; (5) Add impurity remover A to the lithium-rich solution obtained in step (4) for primary impurity removal, add impurity remover B for secondary impurity removal, add impurity remover C for tertiary impurity removal, filter after treatment to obtain lithium extraction solution; the impurity remover A is sodium citrate with a concentration of 2-3 g / L; the impurity remover B is sodium oxalate or ammonium oxalate with a concentration of 1.5-3.5 g / L; the impurity remover C is diethylenetriamine pentamethylphosphonic acid or ammonium polyphosphate with a concentration of 1.0-4.0 g / L.

2. The method for lithium extraction and impurity removal by high-pressure heat treatment of electrolyte according to claim 1, characterized in that, In step (2), the solid raw material and the functional leaching agent solution are mixed at a solid-liquid ratio of 1:10-20.

3. The method for lithium extraction and impurity removal by high-pressure heat treatment of an electrolyte according to claim 1, characterized in that, In step (2), the concentration of the functional leaching agent solution is 1.0-5.0 g / L.

4. The method for lithium extraction and impurity removal by high-pressure heat treatment of an electrolyte according to claim 3, characterized in that, The concentration of the functional leachate solution is 2.0-3.5 g / L.

5. The method for lithium extraction and impurity removal by high-pressure heat treatment of an electrolyte according to claim 1, characterized in that, In step (5), the reaction conditions for primary impurity removal are: pH 4.0-4.5, temperature 30-40℃, and time 30-60min.

6. The method for lithium extraction and impurity removal by high-pressure heat treatment of electrolyte according to claim 1, characterized in that, In step (5), the reaction conditions for secondary impurity removal are: pH 8-11, temperature 50-90℃, and time 30-60min; the reaction conditions for tertiary impurity removal are: temperature 10-60℃ and time 30-60min.

7. The application of the lithium extraction and impurity removal method as described in any one of claims 1-6 in lithium extraction from solid electrolyte samples.

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