A method for preferentially extracting lithium from waste ternary lithium batteries to prepare lithium carbonate and a lithium carbonate product

Abstract

This application discloses a method for preferentially extracting lithium from waste ternary lithium batteries to prepare lithium carbonate and the lithium carbonate product, belonging to the field of solid waste recycling and treatment technology. The method includes the following steps: (1) mixing and roasting ternary lithium battery black powder and carbon powder to obtain roasting product; (2) stirring and washing the roasting product to form a slurry, adding oxalic acid to obtain a mixture, leaching to obtain a leaching mixture, and filtering the leaching mixture for the first time to obtain leaching filtrate and primary leaching residue; (3) adding lithium oxalate seed crystals to the leaching filtrate to obtain lithium oxalate crystals and cold crystallization mother liquor; (4) roasting and converting the lithium oxalate crystals to obtain lithium carbonate; (5) stirring and washing the primary leaching residue to form a slurry and filtering to obtain primary washing liquid and secondary leaching residue; (6) stirring and washing the secondary leaching residue to form a slurry and filtering to obtain secondary washing liquid. Carbothermic reduction roasting combined with selective oxalic acid leaching is used to achieve efficient separation of lithium from nickel, cobalt, and manganese, thereby improving the lithium leaching rate. Oxalic acid is used instead of strong acid, resulting in low corrosiveness and recyclability. The lithium recovery rate is further improved through closed-loop circulation of secondary slag washing and mother liquor.

Description

Technical Field

[0001] This application relates to a method for preferentially extracting lithium from waste ternary lithium batteries to prepare lithium carbonate and the lithium carbonate product, belonging to the field of solid waste recycling and treatment technology. Background Technology

[0002] With the rapid development of new energy vehicles and the energy storage industry, the number of waste lithium-ion batteries, especially ternary lithium batteries, is increasing significantly year by year. If waste ternary lithium batteries cannot be efficiently and environmentally recycled, it will not only waste valuable metal resources such as lithium, nickel, cobalt, and manganese, but also cause potential environmental pollution. Therefore, developing green, efficient, and highly selective lithium extraction processes is of great significance for realizing the recycling of battery materials.

[0003] After being discharged, dismantled, crushed, sorted, and separated, the black mixture obtained from waste nickel-cobalt-manganese ternary lithium batteries is called ternary black powder. Ternary black powder contains a large amount of valuable metals such as nickel, cobalt, manganese, and lithium. Hydrometallurgical processes are typically used to recover these valuable metals. These processes include an acid leaching step, where the battery powder reacts with water and sulfuric acid to obtain a leachate containing nickel, cobalt, manganese, and lithium. However, conventional acid leaching processes tend to result in long lithium extraction times, large wastewater volumes, and significant lithium loss, making it difficult to obtain high-purity lithium products while maintaining a high recovery rate.

[0004] Chinese patent CN 117446839 A discloses a method for preferentially extracting lithium from waste lithium battery materials to prepare lithium carbonate. Specifically, it discloses adding black powder to a certain amount of water, then adding a certain concentration of oxalic acid solution for leaching, and filtering after the reaction to obtain a lithium oxalate solution and leaching residue. This method directly leaches the black powder with oxalic acid solution, but it has the following drawbacks: 1. Low lithium leaching rate: Relying solely on the acidic portion of oxalic acid to break down the black powder's crystal lattice, the lattice destruction is incomplete, leaving some lithium elements embedded in the incompletely destroyed lattice, resulting in low lithium leaching rate. 2. Large sludge production: Subsequent use of hydrogen peroxide (for oxidative leaching) and liquid alkali (for pH adjustment and impurity removal) generates a large amount of sludge, such as iron and aluminum hydroxides, increasing environmental treatment costs. 3. Damage to metal morphology: The leaching process generates nickel oxalate, cobalt oxalate, and manganese oxalate precipitates, altering the original oxide morphology of the metals. Additional purification or conversion processes are required, increasing process complexity.

[0005] Therefore, there is an urgent need to develop a new lithium extraction technology for waste ternary lithium batteries that can selectively extract lithium, uses recyclable reagents, has a green and simple process, high lithium recovery rate, and high product purity. Summary of the Invention

[0006] To address the aforementioned issues, a method and product for the preferential extraction of lithium from spent ternary lithium batteries are provided. This method employs carbothermal reduction roasting combined with selective oxalic acid leaching, which preferentially converts lithium into an easily leached form, achieving efficient separation of lithium from nickel, cobalt, and manganese, significantly improving the lithium leaching rate. Oxalic acid is used instead of strong acid, resulting in lower corrosiveness and recyclability, drastically reducing wastewater and waste residue emissions. Secondary slag washing and closed-loop recycling of the mother liquor further enhance lithium recovery, ultimately yielding battery-grade lithium carbonate with a purity ≥99.5%. The overall process is green, efficient, and economical.

[0007] According to one aspect of this application, a method for preferentially extracting lithium from spent ternary lithium batteries to prepare lithium carbonate is provided, comprising the following steps: (1) Mix ternary lithium battery black powder with carbon powder and calcine at 600~950℃ under an inert atmosphere to obtain calcined product; (2) Stir and wash the roasted product to make a slurry, add oxalic acid to obtain a mixture, leach it to obtain a leach mixture, filter the leach mixture for the first time to obtain leach filtrate and primary leach residue; (3) Add lithium oxalate seed crystals to the leachate filtrate to induce crystallization, and separate the solid and liquid to obtain lithium oxalate crystals and cold crystallization mother liquor; (4) Lithium oxalate crystals are calcined and converted to obtain lithium carbonate; (5) The primary leaching residue is stirred, washed, slurried, and filtered to obtain a primary washing liquid and a secondary leaching residue. The primary washing liquid is recycled to step (2) for stirring and slurrying of the roasted product. (6) The secondary leaching residue is stirred, washed, slurried, and filtered to obtain secondary washing liquid. The secondary washing liquid is recycled to step (5) for stirring and slurrying of the leaching residue once.

[0008] Specifically, in step (1), through carbothermic reduction calcination, under an inert atmosphere and at 600~950℃, carbon powder destroys the crystal structure of the ternary lithium battery black powder, reduces the high-valence transition metal, and converts lithium into an easily leached form, forming a calcination product containing lithium compounds and transition metal oxides. In this reaction, carbon powder acts as a reducing agent to reduce Ni 4+ Co 4+ Mn 4+ The lithium is reduced to metallic Ni, metallic Co, and MnO respectively. At the same time, lithium combines with carbon and oxygen in the system to form Li2CO3, achieving the initial separation of lithium from other metals. This lays the foundation for subsequent selective leaching with oxalic acid. The resulting metal residue has high purity and is not contaminated by oxalate, maintaining the original elemental and oxide forms of the metal.

[0009] Step (2) utilizes the selectivity of oxalic acid solution to react only with lithium compounds in the roasting product to generate soluble lithium oxalate. Pressure filtration achieves the initial separation of lithium (leaching filtrate) and transition metal oxides (primary leaching residue). In this step, oxalic acid needs to be continuously added to ensure that there is an excess of oxalic acid.

[0010] Step (3) Relying on the characteristic that the solubility of lithium oxalate decreases with decreasing temperature, the leaching filtrate is cooled and seed crystals are added to induce the crystallization of high-purity lithium oxalate. The cold crystallization mother liquor is retained for recycling. Step (4) Lithium oxalate is decomposed into battery-grade lithium carbonate through medium-temperature calcination. Steps (5) and (6) The lithium remaining in the primary and secondary leaching residues is recovered through secondary stirring and slurrying and pressure filtration. The washing liquid is recycled and reused in sequence to form a closed loop and minimize lithium loss.

[0011] This application achieves efficient and prioritized lithium extraction through step-by-step collaborative operation, significantly improving lithium recovery rate and lithium carbonate purity. Oxalic acid is used instead of traditional strong acids, reducing equipment corrosion and wastewater treatment pressure. Furthermore, the reagents are recyclable, making it environmentally friendly. The process design is simple, with low-temperature crystallization and medium-temperature roasting greatly reducing energy consumption. The closed-loop circulation of secondary slag and washing liquid not only improves lithium recovery rate but also achieves efficient utilization of water resources and reagents. The overall process is highly economical and environmentally friendly, solving the pain points of traditional processes such as metal co-dissolution, complex separation, and significant lithium loss.

[0012] Specifically, before step (1), there are also steps of sieving and high-speed mixing of black powder and toner.

[0013] Optionally, in step (1), the mass of the carbon powder is 5% to 20% of the mass of the ternary lithium battery black powder, the calcination time is 1 to 3 hours, and the inert atmosphere is nitrogen or argon.

[0014] Specifically, carbon powder, acting as a reducing agent, accounts for 5% to 20% of the black powder in ternary lithium batteries. It can precisely provide the amount of reducing agent required for the reduction reaction—meeting the needs of both disrupting the crystal structure of ternary materials and reducing high-valence Co. 4+ Mn 4+ The requirements for transition metal ions are met, while avoiding excessive carbon powder which would increase the difficulty of subsequent filter residue treatment, or insufficient carbon powder which would lead to incomplete reduction and insufficient lithium release. The temperature and time of calcination are limited to ensure that the reduction reaction is fully carried out, so that lithium is completely converted into easily leached Li2CO3 or Li2O, while avoiding the increase in energy consumption caused by excessively long calcination time.

[0015] Optionally, in step (2), the solid-liquid ratio of the slurry is 1:(1~5), the concentration of oxalic acid in the mixture is 0.6~3mol / L, the leaching temperature is 75~85℃, and the leaching time is 1~4h.

[0016] Specifically, this application specifies the leaching parameters, including the concentration of oxalic acid, ensuring moderate acidity to fully react with lithium-containing compounds in the roasted product to form soluble lithium oxalate, without reacting with transition metal oxides, thus avoiding equipment corrosion and reagent waste; a leaching temperature of 75~85℃ to accelerate the reaction rate while preventing the decomposition and volatilization of oxalic acid; and a leaching time of 1~4h, matching the concentration and temperature to ensure sufficient lithium leaching and avoid excessively long or short leaching times that could affect efficiency.

[0017] Optionally, in step (3), the leaching filtrate is cooled to 15~25°C before adding lithium oxalate seed crystals to induce crystallization.

[0018] Specifically, the solubility of lithium oxalate decreases as the temperature decreases. Cooling the leaching filtrate to 15~25℃ can reduce the solubility of lithium oxalate, creating conditions for its crystallization and precipitation.

[0019] Optionally, in step (4), the roasting temperature is 400~500℃ and the roasting time is 1~3h.

[0020] Specifically, this application limits the roasting temperature and time, which can promote the full decomposition and conversion of lithium oxalate to generate battery-grade lithium carbonate and release CO, while avoiding excessively high temperature and time, which would increase energy consumption and cause product deterioration, or excessively low temperature and time, which would result in incomplete decomposition.

[0021] Optionally, in step (5), the solid-liquid ratio of the pulping process is 1:(2~4), and the pulping time is ≥30min; in step (6), the solid-liquid ratio of the pulping process is 1:(2~4), and the pulping time is ≥30min.

[0022] Specifically, a solid-liquid ratio of 1:(2~4) allows the leaching residue to come into full contact with the washing solution, which can dissolve the residual lithium in the residue and avoid the slurry being too thick to be difficult to stir and too thin to increase the processing load. The stirring time is ≥30min, which can ensure that the residual lithium in the residue is fully dissolved, avoid the loss of lithium due to incomplete washing of the residue, and provide a guarantee for the recycling of the washing solution and the improvement of the overall lithium recovery rate.

[0023] Optionally, in step (6), the mixing liquid for stirring and slurrying is the cold crystallization mother liquor in step (3); in step (5), the initial mixing liquid for stirring and slurrying is the cold crystallization mother liquor in step (3) to start the subsequent washing liquid circulation.

[0024] Specifically, the cold crystallization mother liquor contains trace amounts of unprecipitated lithium oxalate and oxalic acid solution. Using it as the stirring and washing solution in step (6) can dissolve the residual lithium in the secondary leaching residue and achieve secondary lithium recovery. The initial batching in step (5) uses this mother liquor, which can quickly start the washing liquid circulation between the primary and secondary washing residues, forming a closed loop. This fully utilizes the lithium and oxalic acid in the mother liquor, reduces reagent consumption, maximizes the recovery of residual lithium in the residue, further improves the lithium recovery rate, and ensures the continuity and economy of the process cycle.

[0025] Optionally, a precision filtration and resin impurity removal step may be included between step (2) and step (3) to remove impurity ions from the leachate.

[0026] Specifically, precision filtration can remove trace suspended impurities and unreacted fine particles from the filtrate, preventing them from affecting lithium oxalate crystallization; resin purification can specifically adsorb Mg²⁺ from the filtrate. + Cu² + Impurity ions are removed to prevent impurities from mixing into lithium oxalate crystals, ensuring that high-purity lithium oxalate is obtained through subsequent low-temperature crystallization, thereby guaranteeing the purity of the final battery-grade lithium carbonate and avoiding impurities from affecting product quality and subsequent applications.

[0027] Optionally, an exhaust gas treatment step may be included between steps (1) and (2).

[0028] Specifically, during the carbothermic reduction roasting step (1), toxic gases such as fluorine-containing waste gas and CO are generated. Adding a tail gas treatment step can effectively remove the above-mentioned harmful gases, avoid their emission and pollution of the environment and harm to human health, and at the same time prevent corrosive waste gas from damaging subsequent equipment.

[0029] According to another aspect of this application, a lithium carbonate product prepared by the above method is also provided, wherein the lithium carbonate is battery grade, with Li2CO3 purity ≥99.5% and lithium recovery rate ≥95%.

[0030] Specifically, the process effectively removes impurity ions and trace impurities through selective oxalic acid leaching, precision filtration to remove impurities, low-temperature crystallization purification, and medium-temperature roasting conversion, ensuring that the product meets battery-grade standards and satisfies the needs of high-end applications such as power batteries. The lithium recovery rate is limited to ≥95% because the process fully releases lithium through carbothermal reduction, recovers residual lithium through secondary slag washing, and uses a closed-loop circulation system to minimize lithium loss and achieve efficient recovery of lithium resources.

[0031] The beneficial effects of this application include, but are not limited to: 1. A method for preferentially extracting lithium from spent ternary lithium batteries to prepare lithium carbonate according to this application, through carbothermic reduction roasting combined with selective oxalic acid leaching, can precisely destroy the lattice of ternary materials under an inert atmosphere, so that lithium is preferentially converted into an easily leached form, while inhibiting transition metals such as nickel, cobalt, and manganese from entering the leaching solution and not introducing new impurity ions, thus achieving highly selective extraction of lithium; combined with low-temperature crystallization and medium-temperature roasting conversion, battery-grade lithium carbonate is finally obtained to meet the needs of high-end power battery materials; combined with secondary slag washing and multi-stage closed-loop circulation of mother liquor, the lithium recovery rate is improved, achieving efficient resource utilization, and the overall process has both high purity and high recovery rate.

[0032] 2. According to the present application, a method for preferentially extracting lithium from waste ternary lithium batteries to prepare lithium carbonate uses oxalic acid instead of traditional strong acid, which greatly reduces equipment corrosion and wastewater treatment pressure. Oxalic acid can be recycled through thermal decomposition, which significantly reduces reagent consumption and environmental impact. At the same time, the process adopts inert atmosphere roasting and tail gas treatment technology to effectively remove HF, CO and fluorine-containing waste gas, which is green and environmentally friendly.

[0033] 3. The method for preparing lithium carbonate from waste ternary lithium batteries according to this application has a simplified process, strong process repeatability, and is suitable for continuous industrial production. The recycling logic of washing residue and mother liquor is perfect, which can effectively reduce production costs and lithium loss, and has good economic benefits and promotion value.

[0034] 4. A lithium carbonate product prepared by preferentially extracting lithium from waste ternary lithium batteries according to this application has high purity, meets battery-grade standards, and satisfies the needs of high-end applications such as power batteries. Attached Figure Description

[0035] The accompanying drawings, which are included to provide a further understanding of this application and form part of this application, illustrate exemplary embodiments and are used to explain this application, but do not constitute an undue limitation of this application. In the drawings: Figure 1 This is a process flow diagram of the method for preferentially extracting lithium from waste ternary lithium batteries to prepare lithium carbonate in Embodiment 1 of this application. Detailed Implementation

[0036] The present application is described in detail below with reference to the embodiments, but the present application is not limited to these embodiments.

[0037] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of skill in the art. The reagents and raw materials used in this invention are readily available through conventional means, and unless otherwise specified, they shall be used in accordance with conventional methods or product instructions. Furthermore, any methods and materials similar to or equivalent to those described herein may be applied to the methods of this invention. The preferred embodiments and materials described in this patent are for illustrative purposes only. The screening steps for raw materials will not be repeated in the following examples and comparative examples.

[0038] Example 1 A method for preferentially extracting lithium from spent ternary lithium batteries to prepare lithium carbonate. (1) Mix ternary lithium battery black powder with carbon powder, the mass of carbon powder being 5% of the mass of ternary lithium battery black powder, and calcine at 600°C for 3 hours under a nitrogen atmosphere to obtain the calcined product and treat the tail gas. (2) The roasted product was stirred and washed to form a pulp. The solid-liquid ratio of the stirred pulp was 1:1. Oxalic acid was added to obtain a mixed solution with an oxalic acid concentration of 3 mol / L. The mixture was then leached at a temperature of 75°C for 4 hours to obtain a leachate mixture. The leachate mixture was then filtered for the first time to obtain a leachate filtrate and a primary leachate residue. The leachate filtrate was then subjected to precision filtration and resin impurity removal. (3) Cool the leaching filtrate to 15°C, add lithium oxalate seed crystals to the leaching filtrate to induce crystallization, and separate the solid and liquid to obtain lithium oxalate crystals and cold crystallization mother liquor; (4) Lithium oxalate crystals were calcined and converted at a temperature of 400°C for 3 hours to obtain lithium carbonate. (5) The primary leaching residue is stirred and washed to form a pulp. The initial liquid for stirring and washing is the cold crystallization mother liquor in step (3) to start the subsequent washing liquid circulation. The solid-liquid ratio of the stirring and washing pulp is 1:2, the stirring and washing time is 30 min, and the pulp is filtered to obtain the primary washing liquid and the secondary leaching residue. The primary washing liquid is circulated to step (2) for stirring and washing the roasted product. (6) The secondary leaching residue is stirred and washed to form a pulp. The feed liquid is the cold crystallization mother liquor in step (3). The solid-liquid ratio of stirring and washing is 1:2. The stirring and washing time is 30 min. After filtration, a secondary washing liquid is obtained. The secondary washing liquid is recycled to step (5) to stir and wash the leaching residue once.

[0039] Example 2 (1) Mix ternary lithium battery black powder with carbon powder, the mass of carbon powder being 20% ​​of the mass of ternary lithium battery black powder, and calcine at 950°C for 1 hour under an argon atmosphere to obtain the calcined product and treat the tail gas. (2) The roasted product was stirred and washed to form a slurry with a solid-liquid ratio of 1:5. Oxalic acid was added to obtain a mixed solution with an oxalic acid concentration of 0.6 mol / L. The mixture was then leached at a temperature of 85°C for 1 hour to obtain a leaching mixture. The leaching mixture was then filtered for the first time to obtain a leaching filtrate and a primary leaching residue. The leaching filtrate was then subjected to precision filtration and resin impurity removal. (3) Cool the leaching filtrate to 25°C, add lithium oxalate seed crystals to the leaching filtrate to induce crystallization, and separate the solid and liquid to obtain lithium oxalate crystals and cold crystallization mother liquor; (4) Lithium oxalate crystals were calcined and converted at a temperature of 500°C for 1 hour to obtain lithium carbonate. (5) The primary leaching residue is stirred and washed to form a pulp. The initial batching liquid for stirring and washing is the cold crystallization mother liquor in step (3) to start the subsequent washing liquid circulation. The solid-liquid ratio of the stirring and washing pulp is 1:4, the stirring and washing time is 30 min, and the pulp is filtered to obtain the primary washing liquid and the secondary leaching residue. The primary washing liquid is circulated to step (2) for stirring and washing the roasted product. (6) The secondary leaching residue is stirred and washed to form a pulp. The feed liquid is the cold crystallization mother liquor in step (3). The solid-liquid ratio of stirring and washing is 1:4. The stirring and washing time is 30 min. After filtration, a secondary washing liquid is obtained. The secondary washing liquid is recycled to step (5) to stir and wash the leaching residue once.

[0040] Example 3 (1) Mix ternary lithium battery black powder with carbon powder, the mass of carbon powder being 10% of the mass of ternary lithium battery black powder, and calcine at 750°C under nitrogen atmosphere for 2 hours to obtain calcined product, and then treat the tail gas. (2) The roasted product was stirred and washed to form a slurry with a solid-liquid ratio of 1:5. Oxalic acid was added to obtain a mixed solution with an oxalic acid concentration of 0.6 mol / L. The solution was then leached at a temperature of 80°C for 2 hours to obtain a leaching mixture. The leaching mixture was then filtered for the first time to obtain a leaching filtrate and a primary leaching residue. The leaching filtrate was then subjected to precision filtration and resin impurity removal. (3) Cool the leaching filtrate to 20°C, add lithium oxalate seed crystals to the leaching filtrate to induce crystallization, and separate the solid and liquid to obtain lithium oxalate crystals and cold crystallization mother liquor; (4) Lithium oxalate crystals were calcined and converted at a temperature of 450°C for 2 hours to obtain lithium carbonate. (5) The primary leaching residue is stirred and washed to form a pulp. The initial batching liquid for stirring and washing is the cold crystallization mother liquor in step (3) to start the subsequent washing liquid circulation. The solid-liquid ratio of the stirring and washing pulp is 1:3, the stirring and washing time is 30 min, and the pulp is filtered to obtain the primary washing liquid and the secondary leaching residue. The primary washing liquid is circulated to step (2) for stirring and washing the roasted product. (6) The secondary leaching residue is stirred and washed to form a pulp. The feed liquid is the cold crystallization mother liquor in step (3). The solid-liquid ratio of stirring and washing is 1:3. The stirring and washing time is 30 min. After filtration, a secondary washing liquid is obtained. The secondary washing liquid is recycled to step (5) to stir and wash the leaching residue once.

[0041] Example 4 The difference between Example 4 and Example 3 is that the mass of the toner is 2% of the mass of the ternary lithium battery black powder, while the rest are the same.

[0042] Comparative Example 1 The difference between Example 1 and Example 3 is that sulfuric acid is used instead of oxalic acid in step (2), while the rest are the same.

[0043] Comparative Example 2 The difference between Comparative Example 2 and Example 3 is that the washing and slurry preparation steps (5) and (6) and the washing liquid circulation steps are not included; the rest are the same.

[0044] Experimental Example 1 In this experimental example, the purity of lithium carbonate was determined by ICP-OES according to GB / T11075-2013, and the impurity content was determined by EDTA titration. The purity was calculated by combining the results. Lithium recovery was determined by ICP-OES analysis of the lithium content in the raw material black powder, leachate, crystallization mother liquor, and washing circulating liquid, and material balance calculations were performed. All tests were performed in triplicate, and the average value was taken. The test results are shown in Table 1.

[0045] Table 1 Test Results

[0046] Table 1 shows that the lithium carbonate purity in Examples 1-3 was above 99.5%, and the lithium recovery rate was above 94.5%, with Example 3 being the best example. In Example 4, the lithium recovery rate decreased significantly. The reason for this was insufficient carbon powder, which failed to fully disrupt the crystal structure of the ternary lithium battery black powder. The reduction of high-valence Ni, Co, and Mn ions was incomplete, leaving some lithium trapped in the crystal lattice and unable to be released, resulting in a significant decrease in lithium recovery rate. The lithium carbonate purity also decreased slightly. This was because a small amount of incompletely reduced transition metal oxides entered the leaching filtrate, remaining even after precision filtration and resin impurity removal, leading to a reduction in lithium carbonate purity. In Comparative Example 1, both purity and recovery rate decreased. The reason for this was that sulfuric acid is a strong acid with no selective leaching capability. While leaching lithium, it also leaches transition metals such as Ni, Co, and Mn simultaneously. Even with precision filtration and resin purification, it is difficult to completely remove impurity ions, leading to a decrease in lithium carbonate purity. In addition, strong acid leaching exacerbates equipment corrosion and increases the difficulty of separating transition metal ions from lithium ions. Some lithium is lost with the precipitate of impurities, resulting in a lower lithium recovery rate. In Comparative Example 2, the lithium recovery rate decreased significantly. The reason for this was that after eliminating the washing solution circulation, the soluble lithium remaining in the primary and secondary leaching residues could not be recovered, directly leading to increased lithium loss and a lower recovery rate.

[0047] The above description is merely an embodiment of this application, and the scope of protection of this application is not limited to these specific embodiments, but is determined by the claims of this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the technical concept and principles of this application should be included within the scope of protection of this application.

Claims

1. A method for preferentially extracting lithium from spent ternary lithium batteries to prepare lithium carbonate, characterized in that, Includes the following steps: (1) Mix ternary lithium battery black powder with carbon powder and calcine at 600~950℃ under an inert atmosphere to obtain calcined product; (2) Stir and wash the roasted product to make a slurry, add oxalic acid to obtain a mixture, leach it to obtain a leach mixture, filter the leach mixture for the first time to obtain leach filtrate and primary leach residue; (3) Add lithium oxalate seed crystals to the leachate filtrate to induce crystallization, and separate the solid and liquid to obtain lithium oxalate crystals and cold crystallization mother liquor; (4) Lithium oxalate crystals are calcined and converted to obtain lithium carbonate; (5) The primary leaching residue is stirred, washed, slurried, and filtered to obtain a primary washing liquid and a secondary leaching residue. The primary washing liquid is recycled to step (2) for stirring and slurrying of the roasted product. (6) The secondary leaching residue is stirred, washed, slurried, and filtered to obtain secondary washing liquid. The secondary washing liquid is recycled to step (5) to stir and slurry the leaching residue once.

2. The method for preferentially extracting lithium from spent ternary lithium batteries to prepare lithium carbonate according to claim 1, characterized in that, In step (1), the mass of the carbon powder is 5% to 20% of the mass of the ternary lithium battery black powder, the calcination time is 1 to 3 hours, and the inert atmosphere is nitrogen or argon.

3. The method for preferentially extracting lithium from spent ternary lithium batteries to prepare lithium carbonate according to claim 1, characterized in that, In step (2), the solid-liquid ratio of the slurry is 1:(1~5), the concentration of oxalic acid in the mixture is 0.6~3mol / L, the leaching temperature is 75~85℃, and the leaching time is 1~4h.

4. The method for preferentially extracting lithium from spent ternary lithium batteries to prepare lithium carbonate according to claim 1, characterized in that, In step (3), the leaching filtrate is cooled to 15~25°C before adding lithium oxalate seed crystals to induce crystallization.

5. The method for preferentially extracting lithium from spent ternary lithium batteries to prepare lithium carbonate according to claim 1, characterized in that, In step (4), the roasting temperature is 400~500℃ and the roasting time is 1~3h.

6. The method for preferentially extracting lithium from spent ternary lithium batteries to prepare lithium carbonate according to claim 1, characterized in that, In step (5), the solid-liquid ratio of the pulping process is 1:(2~4), and the pulping time is ≥30min; in step (6), the solid-liquid ratio of the pulping process is 1:(2~4), and the pulping time is ≥30min.

7. The method for preferentially extracting lithium from spent ternary lithium batteries to prepare lithium carbonate according to claim 1, characterized in that, In step (6), the mixing liquid for stirring and washing the pulp is the cold crystallization mother liquor in step (3); in step (5), the initial mixing liquid for stirring and washing the pulp is the cold crystallization mother liquor in step (3) to start the subsequent washing liquid circulation.

8. A method for preferentially extracting lithium from spent ternary lithium batteries to prepare lithium carbonate according to claim 1, characterized in that, Between steps (2) and (3), there are also steps of precision filtration and resin impurity removal to remove impurity ions from the leachate.

9. A method for preferentially extracting lithium from spent ternary lithium batteries to prepare lithium carbonate according to claim 1, characterized in that, The process between steps (1) and (2) also includes a step of exhaust gas treatment.

10. A lithium carbonate product prepared by the method according to any one of claims 1 to 9, characterized in that, The lithium carbonate is battery grade, with Li2CO3 purity ≥ 99.5% and lithium recovery rate ≥ 95%.

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