Method for preparing battery grade lithium carbonate by utilizing battery material raffinate

Abstract

The invention discloses a method for preparing battery grade lithium carbonate by utilizing battery material raffinate. The method comprises the following steps: S1, removing phosphorus, fluorine and oily substances; s2, removing metal ion impurities; s3, primary concentration: carrying out primary evaporation concentration on the solution treated in the step S2; s4, freezing crystallization: freezing crystallization is performed on the solution subjected to primary concentration; s5, secondary concentration: performing secondary evaporation concentration on the refrigerating fluid; s6, lithium precipitation: carrying out lithium precipitation reaction on the solution subjected to secondary concentration and a lithium precipitation agent to obtain crude lithium carbonate; and stirring, washing and separating the crude lithium carbonate to obtain the battery-grade lithium carbonate. Wherein the conditions of the lithium precipitation reaction are as follows: an inverse addition method is adopted as a charging mode, and the excess coefficient of a lithium precipitation agent is more than 1%. The method can break through the limitation of low-lithium-concentration battery material raffinate, and a high-added-value lithium extraction process which is high in efficiency, low in cost and suitable for large-scale production is realized.

Description

Technical Field

[0001] This invention relates to the field of waste battery material recycling technology, specifically to a method for preparing battery-grade lithium carbonate using residual liquid from battery material extraction. Background Technology

[0002] In recent years, lithium-ion batteries have become an important clean energy storage device due to their significant advantages such as high energy density, low memory effect, and fast charging, and are widely used in many fields, including electric vehicles. It should be noted that the typical lifespan of a lithium-ion battery is 6-8 years. When a large number of used lithium-ion batteries reach their service life, they will inevitably face retirement. These retired batteries contain elements such as nickel (Ni), cobalt (Co), manganese (Mn), and lithium (Li), all of which are valuable mineral resources with extremely high recycling value.

[0003] Currently, hydrometallurgy is the mainstream recycling method for spent lithium-ion batteries, but this method mainly focuses on the recovery of nickel (Ni), cobalt (Co), and manganese (Mn). In actual recycling processes, the mixing of washing solutions and raffinate at each stage leads to the continuous enrichment of impurities, while the lithium concentration is diluted to only 0.5-3 g / L. This situation poses a serious challenge to lithium recovery, as the raffinate contains approximately 50 g / L of sodium (Na₂O₃). + ) and approximately 100 g / L of sulfate ions (SO4) 2- During the evaporation and concentration process, the precipitated sodium sulfate (Na₂SO₄) carries lithium, limiting the lithium concentration to approximately 13 g / L, only about half that of the lithium concentration in the spodumene lithium extraction process. This severely restricts the efficiency and economics of subsequent lithium precipitation. Consequently, the lithium precipitation rate is only about 75%, requiring further treatment of a large amount of mother liquor, which significantly increases recovery costs. Furthermore, the concentrated lithium solution contains sodium (Na₂SO₄). + ) and sulfate ions (SO4) 2- The lithium carbonate is highly saturated, and after lithium precipitation, conventional stirring and washing methods cannot effectively remove these impurities. In the end, only low-quality industrial-grade lithium carbonate or even crude lithium carbonate can be produced, which is difficult to meet the high standard requirements of battery cathode materials.

[0004] Therefore, it is necessary to develop a method for preparing battery-grade lithium carbonate using battery material leaching liquid, clarify the lithium-carrying mechanism of Na2SO4 during the evaporation process, break through the lithium concentration limit, and achieve efficient, economical and large-scale recovery of lithium from battery material leaching liquid with high sodium content and low lithium concentration, so as to realize high-value-added lithium recovery and improve economic benefits. Summary of the Invention

[0005] This invention aims to at least solve one of the technical problems existing in the prior art. To this end, this invention proposes a method for preparing battery-grade lithium carbonate using battery material leaching liquid. This method can overcome the limitation of lithium concentration in the leaching liquid and efficiently and cost-effectively recover lithium from the battery material leaching liquid.

[0006] According to one aspect of the present invention, a method for preparing battery-grade lithium carbonate using battery material leaching residue is provided, comprising the following steps: S1. Removal of phosphorus, fluorine and oily substances: Pretreatment of the residual liquid from battery material extraction to remove phosphorus, fluorine and oily substances. S2. Remove metal ion impurities: Remove metal ion impurities from the solution after step S1. S3, First Concentration: The solution after step S2 is concentrated by evaporation to control the final lithium concentration to be above 6 g / L; S4. Freeze crystallization: Freeze crystallization of the solution after one concentration. S5. Secondary Concentration: The refrigerant is concentrated by secondary evaporation to control the lithium concentration at the concentration endpoint to be above 20 g / L. S6, Lithium precipitation: The solution after secondary concentration is reacted with a lithium precipitation agent to produce crude lithium carbonate; the crude lithium carbonate is then stirred, washed, and separated to obtain battery-grade lithium carbonate. The conditions for the lithium precipitation reaction include: the feeding method is reverse addition, and the excess coefficient of the lithium precipitation agent is more than 1%.

[0007] According to some embodiments of the present invention, the excess coefficient of the lithium precipitation agent is 1 to 15%.

[0008] According to some embodiments of the present invention, the excess coefficient of the lithium precipitation agent is 5-15%.

[0009] According to some embodiments of the present invention, the lithium precipitation reaction further includes at least one of the following conditions: 1) Feeding time is 1~5 hours; 2) The reaction temperature is 80~95℃; 3) The stirring speed is 100~300 rpm; 4) The mass concentration of sodium carbonate is 200~300g / L.

[0010] According to some embodiments of the present invention, the lithium precipitation reaction further includes at least one of the following conditions: 1) The feeding time is 1~3 hours; 2) The reaction temperature is 85~95℃; 3) The stirring speed is 150~300 rpm; 4) The mass concentration of sodium carbonate is 280~300g / L.

[0011] According to some embodiments of the present invention, the agitation includes the following steps: Water and crude lithium carbonate are mixed into a slurry at a mass ratio of 2-5:1 and then subjected to shearing and crushing.

[0012] According to some embodiments of the present invention, the agitation includes the following steps: Water and crude lithium carbonate are mixed into a slurry at a mass ratio of 2-4:1 and then subjected to shearing and crushing.

[0013] According to some embodiments of the present invention, the agitation includes at least one of the following conditions: 1) The stirring speed is 180~400 rpm; 2) The washing temperature is 80~95℃; 3) The washing time is 30~120 minutes; 4) The shear frequency is 10~50Hz; 5) The number of times to agitate and wash is 1 to 4.

[0014] According to some embodiments of the present invention, the agitation includes at least one of the following conditions: 1) The stirring speed is 180~300 rpm; 2) The washing temperature is 85~95℃; 3) The washing time is 30-60 minutes; 4) The shear frequency is 20~50Hz; 5) The number of times to agitate and wash is 2 to 4.

[0015] According to some embodiments of the present invention, the lithium concentration at the endpoint of the secondary concentration is controlled to be 20~35 g / L.

[0016] According to some embodiments of the present invention, the lithium concentration at the endpoint of the secondary concentration is controlled to be 25~30 g / L.

[0017] According to some embodiments of the present invention, the lithium concentration at the first concentration endpoint is controlled to be 6~14 g / L.

[0018] According to some embodiments of the present invention, the lithium concentration at the primary concentration endpoint is controlled to be 6~13 g / L.

[0019] According to some embodiments of the present invention, the freeze-crystallization temperature is -5 to -20°C.

[0020] According to some embodiments of the present invention, the freeze-crystallization temperature is 0 to -20°C.

[0021] According to some embodiments of the present invention, step S4 further includes the following steps: The frozen residue in step S4 is melted at 40~90℃. After solid-liquid separation, the lithium-containing solution is returned to the front-end process for recycling, and the solid is dried to obtain sodium sulfate.

[0022] According to some embodiments of the present invention, step S4 further includes the following steps: The frozen residue in step S4 is melted at 50~90℃. After solid-liquid separation, the lithium-containing solution is returned to the front-end process for recycling, and the solid is dried to obtain sodium sulfate.

[0023] After the solid is dried, industrial-grade Class I sodium sulfate byproduct can be obtained.

[0024] According to some embodiments of the present invention, the impurity removal conditions in step S2 include at least one of the following conditions: 1) pH range of 10 to 14; 2) temperature of 60 to 90°C; 3) impurity removal reaction time of 30 to 80 min.

[0025] According to some embodiments of the present invention, the impurity removal conditions in step S2 include at least one of the following conditions: 1) pH range of 11 to 13; 2) temperature of 70 to 90°C; 3) impurity removal reaction time of 30 to 60 min.

[0026] According to some embodiments of the present invention, the impurity removal agent used in step S2 is sodium carbonate, and the excess feed coefficient is 1~10%.

[0027] According to some embodiments of the present invention, the impurity remover used in step S2 is sodium carbonate, with an excess coefficient of 5-10%. The impurity remover is added in the form of solid sodium carbonate powder.

[0028] According to some embodiments of the present invention, the pH adjuster used in the pH adjustment process is a liquid alkali solution with a mass concentration of 25-40%.

[0029] According to some embodiments of the present invention, the residual liquid from the battery material extraction in step S1 contains the following components at the following mass concentrations: lithium content of 0.5-3 g / L, sodium content of 20-90 g / L, sulfate content of 50-150 g / L, phosphorus content of 15-60 mg / L, fluorine content of 30-120 mg / L, oily substance content of 15-200 mg / L, and chlorine content of 0.5-3 g / L.

[0030] According to some embodiments of the present invention, the reaction conditions for removing phosphorus, fluorine and oily substances in step S1 include at least one of the following conditions: 1) pH adjustment range of 2-9; 2) temperature adjustment range of 30-90℃; 3) reaction time of 30-120 min.

[0031] According to some embodiments of the present invention, the reaction conditions for removing phosphorus, fluorine and oily substances in step S1 include: pH adjustment range of 3-6, temperature adjustment range of 50-90℃, and reaction time of 30-80min.

[0032] According to some embodiments of the present invention, in step S1, phosphorus removal, fluoride removal and oily substance removal are performed by adding a phosphorus removal agent, a fluoride removal agent and activated carbon, wherein the mass ratio of the phosphorus removal agent, the fluoride removal agent and activated carbon to the battery material extract residue is independently 1-10‰, and the removal of phosphorus, fluoride and oily substances is carried out simultaneously.

[0033] According to some embodiments of the present invention, in step S1, phosphorus removal, fluoride removal and oily substance removal are performed by adding a phosphorus removal agent, a fluoride removal agent and activated carbon, wherein the mass ratio of the phosphorus removal agent, the fluoride removal agent and activated carbon to the battery material extract residue is independently 3-8‰, and the removal of phosphorus, fluoride and oily substances is carried out simultaneously.

[0034] According to some embodiments of the present invention, the dephosphorizing agent is added in solution form, the mass ratio of the dephosphorizing agent to the residual liquid of the battery material is based on the total amount of solution, the mass concentration of the dephosphorizing agent in the dephosphorizing agent solution is 20-40%, and the dephosphorizing agent includes at least one of ferric chloride, aluminum chloride, polyferric chloride or polyaluminum chloride.

[0035] According to some embodiments of the present invention, the defluorinating agent is at least one of lanthanum carbonate, lanthanum oxide, or lanthanum hydroxide.

[0036] According to some embodiments of the present invention, the activated carbon is at least one of coal-derived activated carbon, wood-based activated carbon, or fruit shell activated carbon.

[0037] The method according to embodiments of the present invention has at least the following beneficial effects: the method provided by the present invention can overcome the limitations of low-lithium-concentration battery material extraction residue, and realize a high-efficiency, low-cost, and high-value-added lithium extraction process suitable for large-scale production. Specific analysis is as follows: I. Addressing the characteristics of battery material extraction residue—high sodium, high sulfate, and low lithium—this invention innovatively employs a combined process of "evaporation concentration-freeze crystallization-deep concentration." This process effectively removes sodium sulfate from the system through freeze crystallization, thereby overcoming its limitation on lithium entrainment in subsequent processes and achieving a breakthrough increase in lithium concentration, reaching approximately 30 g / L. Consequently, the primary lithium precipitation rate is significantly increased from 75% to over 85%, not only drastically reducing the processing load on the mother liquor but also improving the overall lithium recovery rate, resulting in significant economic benefits.

[0038] Second, in the washing process, this invention introduces a shear pump, which utilizes the high-frequency shear force generated to effectively break up the agglomerated structure of lithium carbonate crystals, allowing the Na+ crystals encapsulated inside the crystals or adsorbed at the grain boundaries to disperse. + and SO42- This method allows impurities to be fully exposed. It fundamentally solves the problem that conventional agitation can only remove surface impurities and is difficult to remove internal inclusions, enabling impurities to be efficiently removed during subsequent water washing, thereby significantly improving the chemical purity of the final product and ensuring the quality of battery-grade lithium carbonate.

[0039] III. By introducing a freeze crystallization step, the Na in the solution is saturated. + and SO4 2- The lithium crystallizes out as sodium sulfate decahydrate (Na₂SO₄·10H₂O). This process not only significantly reduces the concentration of sodium and sulfate ions in the solution, but also achieves pre-enrichment of lithium without consuming additional heat energy due to the large amount of water of crystallization. After this purification and concentration, only low-exponential evaporation is needed to achieve a lithium concentration of approximately 30 g / L, while maintaining a low Na₂SO₄ concentration. + and SO4 2- Therefore, battery-grade lithium carbonate with a purity exceeding 99.65% can be directly obtained through a single-step lithium precipitation reaction, followed by stirring and drying. This greatly simplifies the process and significantly improves the product grade.

[0040] IV. For the solid products generated by freeze crystallization, hot melting and solid-liquid separation can be used for treatment. The resulting lithium-containing solution can be returned to the upstream process for recycling, while the separated solid can be directly used as an industrial-grade Class I first-class sodium sulfate by-product after drying, realizing full recovery and value-added utilization of resources.

[0041] V. The present invention establishes a complete resource recycling system: the condensate generated in the evaporation process is recycled for subsequent washing of crude lithium carbonate and preparation of sodium carbonate solution, while the wash water is also incorporated into the sodium carbonate preparation process, achieving closed-loop utilization of water resources. This process is simple and efficient, significantly reducing fresh water consumption and wastewater treatment costs. It also boasts advantages such as ease of operation, compact process, environmental friendliness, and low cost, making it fully suitable for large-scale industrial applications.

[0042] Additional aspects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Attached Figure Description

[0043] Figure 1 The image shows the XRD pattern of the battery-grade lithium carbonate prepared in Example 1 of this invention.

[0044] Figure 2 The image shows the XRD pattern of the frozen residue and sodium sulfate in Example 1 of this invention.

[0045] Figure 3 The phase diagram is shown for the Li2SO4-Na2SO4-K2SO4-H2O aqueous salt system at 100℃.

[0046] Figure 4 The lithium concentration change in the battery material extract residue after direct freezing and filtration and subsequent evaporation of the cryogenic liquid is shown in Comparative Example 2 of this invention.

[0047] Figure 5 The lithium concentration change in the battery material extract residue after concentration of lithium to 12 g / L and subsequent freezing and filtration in Example 4 of this invention is shown in the figure. Detailed Implementation

[0048] The following will clearly and completely describe the concept and technical effects of the present invention in conjunction with embodiments, so as to fully understand the purpose, features and effects of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, not all of them. Other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are all within the scope of protection of the present invention. Unless otherwise specified, the experimental methods used in the embodiments are conventional methods; the materials and reagents used, unless otherwise specified, are commercially available. Unless otherwise specified, the same parameter value is the same in all embodiments. The embodiments described below are exemplary and are only used to explain the present invention, and should not be construed as limiting the present invention.

[0049] In the description of this invention, references to terms such as "some embodiments" indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. In this specification, illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0050] Unless otherwise specified, "about" in this invention means that the allowable error is within ±2%.

[0051] The battery material extract used in the following examples and comparative examples comes from the same source. Its main components are as follows: Li: 2.5 g / L, P: 0.05 g / L, F: 0.08 g / L, oily substances: 0.06 g / L, Cl: 1.2 g / L, SO42- 2- : 125g / L, Na: 63g / L.

[0052] Example 1 This example provides a method for preparing battery-grade lithium carbonate using residual extract from battery materials. The specific steps are as follows: Heat the battery material extract to 50°C, adjust the pH to 3, and add phosphorus removal agent solution (35% polyferric sulfate solution, mass ratio based on total solution volume), lanthanum carbonate, and coal-derived activated carbon in sequence at mass ratios of 3‰, 3‰, and 3.5‰. After reacting for 30 minutes, filter to complete the preliminary purification.

[0053] Subsequently, the filtrate was heated to 70°C, the pH was adjusted to 11 with 32wt% sodium hydroxide solution, and sodium carbonate powder was added in excess of 5% of the total metal ions (i.e., the excess coefficient was 5%). After reacting for 30 minutes, the solution was filtered to obtain the purified solution.

[0054] The purified solution was concentrated by evaporation once, and evaporation was stopped after the final lithium concentration was controlled at 6 g / L.

[0055] The system was then frozen to -5°C to allow sodium sulfate decahydrate to crystallize out.

[0056] The cryogenic liquid was concentrated by secondary evaporation until the lithium concentration reached 25 g / L, after which evaporation was stopped.

[0057] A 280 g / L sodium carbonate solution with an excess coefficient of 5% was pre-added to a lithium precipitation reactor. The stirring speed was controlled at 150 rpm and the temperature at 85°C. Then, the secondary concentrate was added dropwise to the reactor over one hour. After the reaction was complete, solid-liquid separation was performed to obtain crude lithium carbonate. Water and crude lithium carbonate were mixed at a mass ratio of 3:1 and slurryed at a stirring speed of 190 rpm and a temperature of 85°C. The mixture was then washed twice with a shear pump at a frequency of 20 Hz, for 30 minutes each time. After solid-liquid separation, the resulting solid was dried to obtain battery-grade lithium carbonate.

[0058] In addition, the sodium sulfate decahydrate crystals produced by freeze crystallization are melted at 60°C and then subjected to solid-liquid separation. The liquid is returned to the previous process for recycling, and the solid is dried to obtain industrial-grade Class I first-class sodium sulfate by-product.

[0059] Example 2 This example provides a method for preparing battery-grade lithium carbonate using residual extract from battery materials. The specific steps are as follows: The residual liquid from the battery material extraction was heated to 60°C and the pH was adjusted to 4. Phosphorus removal agent solution (30% polyferric sulfate solution, mass ratio based on total solution volume), lanthanum hydroxide, and coconut shell activated carbon were added sequentially at mass ratios of 4‰, 3.5‰, and 5‰. After reacting for 40 minutes, the mixture was filtered to complete the preliminary purification.

[0060] Subsequently, the filtrate was heated to 80°C, the pH was adjusted to 12 with 32wt% sodium hydroxide solution, sodium carbonate powder was added with an excess coefficient of 7% for the total metal ions, and the mixture was filtered after reacting for 45 minutes to obtain the purified solution.

[0061] The purified solution was concentrated by evaporation once, and evaporation was stopped after the final lithium concentration was controlled at 10 g / L.

[0062] The system was then frozen to -10°C to allow sodium sulfate decahydrate to crystallize out. The cryogenic solution was then concentrated by secondary evaporation until the lithium concentration reached 27 g / L, at which point evaporation was stopped.

[0063] A sodium carbonate solution with an excess of 8% (280 g / L) was pre-added to a lithium precipitation reactor. The stirring speed was controlled at 200 rpm and the temperature at 90°C. Then, the secondary concentrate was added dropwise to the reactor over two hours. After the reaction was complete, solid-liquid separation was performed to obtain crude lithium carbonate. The crude lithium carbonate was mixed with water at a liquid-to-solid ratio of 3.5:1, and the mixture was slurried at 200 rpm and 90°C. The mixture was then washed three times with a shear pump at 40 Hz for 50 minutes each time. After solid-liquid separation, the resulting solid was dried to obtain battery-grade lithium carbonate.

[0064] Sodium sulfate decahydrate crystals produced by freeze crystallization are melted at 70°C and then subjected to solid-liquid separation. The liquid is returned to the previous process for recycling, and the solid is dried to obtain industrial-grade Class I first-class sodium sulfate by-product.

[0065] Example 3 This example provides a method for preparing battery-grade lithium carbonate using residual extract from battery materials. The specific steps are as follows: The residual liquid from the battery material was heated to 80°C and the pH was adjusted to 6. Phosphorus removal agent solution (36% polyferric chloride solution, mass ratio based on total solution volume), lanthanum hydroxide, and wood-based activated carbon were added sequentially at mass ratios of 5‰, 6‰, and 4‰. After reacting for 50 minutes, the mixture was filtered to complete the preliminary purification.

[0066] Subsequently, the filtrate was heated to 85°C, the pH was adjusted to 13 with 32wt% sodium hydroxide solution, sodium carbonate powder was added with an excess coefficient of 9% for the total metal ions, the reaction was carried out for 60 minutes, and then filtered to obtain the purified solution.

[0067] The purified solution was concentrated by evaporation once, and evaporation was stopped after the final lithium concentration was controlled at 13 g / L.

[0068] The system was then frozen to -15°C to allow sodium sulfate decahydrate to crystallize out.

[0069] The cryogenic liquid was concentrated by secondary evaporation until the lithium concentration reached 30 g / L, and then evaporation was stopped.

[0070] A 280 g / L sodium carbonate solution with an excess coefficient of 10% was pre-added to a lithium precipitation reactor. The stirring speed was controlled at 250 rpm and the temperature at 90°C. Then, the secondary concentrate was added dropwise to the reactor over 3 hours. After the reaction was complete, solid-liquid separation was performed to obtain crude lithium carbonate. The crude lithium carbonate was mixed with water at a liquid-to-solid ratio of 4:1, and the mixture was slurried at a stirring speed of 1300 rpm and a temperature of 90°C. The mixture was then washed four times with a shear pump at a frequency of 50 Hz, for 40 minutes each time. After solid-liquid separation, the resulting solid was dried to obtain battery-grade lithium carbonate.

[0071] Sodium sulfate decahydrate crystals produced by freeze crystallization are melted at 90°C and then separated into solid and liquid components. The liquid is returned to the previous process for recycling, and the solid is dried to obtain industrial-grade Class I first-class sodium sulfate by-product.

[0072] Example 4 This example provides a method for preparing battery-grade lithium carbonate using residual liquid from battery material extraction. The difference between this method and Example 3 is that during the single evaporation and concentration of the purified liquid, the evaporation is stopped after controlling the final lithium concentration to 12 g / L.

[0073] Comparative Example 1 This example provides a method for preparing battery-grade lithium carbonate using residual extract from battery materials. The specific steps are as follows: The residual liquid from the battery material was heated to 80°C and the pH was adjusted to 6. Phosphorus removal agent solution (36% polyferric chloride solution, mass ratio based on total solution volume), lanthanum hydroxide, and wood-based activated carbon were added sequentially at mass ratios of 5‰, 6‰, and 4‰. After reacting for 50 minutes, the mixture was filtered to complete the preliminary purification.

[0074] Subsequently, the filtrate was heated to 85°C, the pH was adjusted to 13 with 32wt% sodium hydroxide solution, sodium carbonate powder was added with an excess coefficient of 9% for the total metal ions, the reaction was carried out for 60 minutes, and then filtered to obtain the purified solution.

[0075] The purified liquid was concentrated, and evaporation was stopped after the final lithium concentration was controlled at 13 g / L. Solid-liquid separation was performed to obtain concentrated liquid and concentrated residue.

[0076] Subsequently, a 280 g / L sodium carbonate solution with an excess coefficient of 10% was pre-added to the lithium precipitation reactor. The stirring speed was controlled at 250 rpm and the temperature at 90°C. Then, the secondary concentrate was added dropwise to the reactor over 3 hours. After the reaction was completed, solid-liquid separation was performed to obtain crude lithium carbonate. The crude lithium carbonate was mixed with water at a liquid-to-solid ratio of 4:1, and the mixture was stirred and washed four times at a stirring speed of 1300 rpm and a temperature of 90°C, each time for 50 minutes.

[0077] After solid-liquid separation, the resulting solid is dried to obtain industrial-grade lithium carbonate. The concentrated residue is then dried to obtain industrial-grade sodium sulfate as a byproduct.

[0078] Comparative Example 2 This example provides a method for preparing battery-grade lithium carbonate using residual liquid from battery material extraction. The difference from Example 3 is that the purified liquid is first frozen to -15°C to allow sodium sulfate decahydrate to crystallize out. The frozen liquid is then evaporated and concentrated, and after solid-liquid separation, the concentrated liquid is de-lithium precipitated.

[0079] The compositional analysis of lithium carbonate prepared in Examples 1, 2, 3, 4 and Comparative Examples 1 and 2 is shown in Table 1.

[0080] Table 1. Compositional Analysis of Battery-Grade Lithium Carbonate Standards, Examples, and Comparative Examples Prepared by Lithium Carbonate

[0081] As shown in Table 1, the lithium carbonate prepared in different examples has high purity, few impurities, and good quality, fully meeting the requirements of the national standard (YS / T 582-2023 "Battery-grade Lithium Carbonate") for battery-grade lithium carbonate. However, the lithium carbonate prepared in the comparative example still contains large amounts of Na and SO4. 2- It only meets the standard of industrial-grade lithium carbonate, grade II.

[0082] The component analysis of sodium sulfate prepared in Examples 1, 2, 3, 4 and Comparative Examples 1 and 2 is shown in Table 2.

[0083] Table 2. Standards, Examples, and Comparative Examples of Industrial Grade Class I First-Class Sodium Sulfate Preparation: Composition Analysis

[0084] As shown in Table 2, the sodium sulfate prepared in all embodiments of this invention meets the industrial-grade Class I first-class standard, while the sodium sulfate prepared in the comparative example only meets the industrial-grade Class II first-class standard. This indicates that this method can successfully prepare battery-grade lithium carbonate as the main product, while also producing higher-quality sodium sulfate by-products, achieving value-added recycling throughout the entire process.

[0085] Figure 1 This is the XRD powder diffraction pattern of the battery-grade lithium carbonate prepared in Example 1. Figure 1 It can be seen that the diffraction peaks of the sample are completely consistent with the standard diffraction card for battery grade, and no diffraction peaks of other impurities were observed, which indicates that the prepared lithium carbonate is a high-purity phase.

[0086] Figure 2 The image shows the XRD powder diffraction patterns of the frozen residue and sodium sulfate from Example 1. Figure 2 It can be seen that the main component of the frozen residue is Na2SO4·10H2O, therefore, a large amount of Na and SO4 were removed by freezing. 2-The slag also contains a small amount of lithium-containing double salt Na3Li(SO4)2·6H2O. By directly melting the frozen slag, a lithium-containing saturated sodium sulfate solution and anhydrous sodium sulfate solid (sodium sulfate) are formed. The lithium-containing solution is returned to the upstream process for recovery, and the solid is dried to obtain industrial-grade Class I sodium sulfate byproduct. XRD patterns also show that the prepared sodium sulfate perfectly matches the Na2SO4 standard card, and no diffraction peaks were observed for Na2SO4·10H2O and Na3Li(SO4)2·6H2O, indicating that the hot-melt recovery of the frozen slag is feasible.

[0087] Figure 3 The phase diagram is shown for the Li2SO4-Na2SO4-K2SO4-H2O aqueous salt system at 100℃. Figure 3 Phase diagram analysis shows that during the evaporation process, when the battery material raffinate is concentrated to a lithium concentration of 12-13 g / L (corresponding to point A in the figure), the system is on the eutectic line of Na₂SO₄ and LiNaSO₄, and lithium-containing double salt LiNaSO₄ begins to precipitate. This phenomenon not only directly causes lithium loss, but also limits the further increase of lithium concentration in the liquid phase from the perspective of phase equilibrium, becoming a key factor restricting lithium recovery efficiency.

[0088] Figure 4 The change in lithium concentration after direct freeze-filtration of the residual battery material in Comparative Example 2, followed by evaporation of the cryogenic liquid. Figure 4 It is known that if the battery material extract liquid is directly frozen, even if the freezing liquid is subsequently evaporated and concentrated to 4.57 times, the lithium concentration can only reach about 19.6 g / L. If the concentration continues, lithium-containing complex salts of LiNaSO4 will precipitate again, and it will never be able to reach a high lithium concentration level comparable to that of lithium extraction from ore.

[0089] Figure 5 This represents the change in lithium concentration after the residual lithium in the battery material extract of Example 4 of the present invention was concentrated to 12 g / L, then frozen and filtered, and the resulting liquid evaporated. Figure 5 As can be seen, in this embodiment of the invention, the raffinate is first concentrated to a lithium concentration of 12 g / L, saturating the sodium sulfate. During the subsequent freezing process, a large amount of sodium sulfate decahydrate precipitates out, efficiently removing sodium and sulfate impurities, while further increasing the lithium concentration in the freezing liquid. Afterward, only a low-multiplication (approximately 2x) secondary concentration is needed to increase the lithium concentration to 30 g / L, achieving a level comparable to that of spodumene lithium extraction processes.

[0090] The above results indicate that the evaporation-freezing-evaporation integrated process constructed by the present invention is a reliable path for the efficient recovery of lithium resources from the residual liquid of battery materials with high sodium, high sulfate and low lithium concentrations and the preparation of battery-grade lithium carbonate.

[0091] This application's solution utilizes a freeze-crystallization process between two evaporation and concentration cycles, achieving a breakthrough increase in lithium concentration to approximately 30 g / L and a lithium precipitation rate increase of over 10%. This significantly reduces the mother liquor processing load and improves the overall lithium yield. Furthermore, this invention allows for one-step lithium precipitation to obtain battery-grade lithium carbonate without thermal decomposition, greatly simplifying the recovery process and improving recovery efficiency.

[0092] The embodiments of the present invention have been described in detail above, but the present invention is not limited to the above embodiments. Within the scope of knowledge possessed by those skilled in the art, various changes can be made without departing from the spirit of the present invention.

Claims

1. A method for preparing battery-grade lithium carbonate using residual extract from battery materials, characterized in that: Includes the following steps: S1. Removal of phosphorus, fluorine and oily substances: Pretreatment of the residual liquid from battery material extraction to remove phosphorus, fluorine and oily substances. S2. Remove metal ion impurities: Remove metal ion impurities from the solution after step S1. S3, First Concentration: The solution after step S2 is concentrated by evaporation to control the final lithium concentration to be above 6 g / L; S4. Freeze crystallization: Freeze crystallization of the solution after one concentration. S5. Secondary Concentration: The refrigerant is concentrated by secondary evaporation to control the lithium concentration at the concentration endpoint to be above 20 g / L. S6, Lithium precipitation: The solution after secondary concentration is reacted with a lithium precipitation agent to produce crude lithium carbonate; the crude lithium carbonate is then stirred, washed, and separated to obtain battery-grade lithium carbonate. The conditions for the lithium precipitation reaction include: the feeding method is reverse addition, and the excess coefficient of the lithium precipitation agent is more than 1%.

2. The method for preparing battery-grade lithium carbonate using battery material extraction residue according to claim 1, characterized in that: The excess coefficient of the lithium precipitation agent is 1-15%; and / or, the lithium precipitation reaction further includes at least one of the following conditions: 1) Feeding time is 1~5 hours; 2) The reaction temperature is 80~95℃; 3) The stirring speed is 100~300 rpm; 4) The mass concentration of sodium carbonate is 200~300g / L.

3. The method for preparing battery-grade lithium carbonate using battery material extraction residue according to claim 1 or the method described above, characterized in that: The washing process includes the following steps: water and crude lithium carbonate are mixed into a slurry at a mass ratio of 2-5:1 and then subjected to shearing and crushing.

4. The method for preparing battery-grade lithium carbonate using battery material extraction residue according to claim 3, characterized in that: The agitation includes at least one of the following conditions: 1) The stirring speed is 180~400 rpm; 2) The washing temperature is 80~95℃; 3) The washing time is 30~120 minutes; 4) The shear frequency is 10~50Hz; 5) The number of times to agitate and wash is 1 to 4.

5. The method for preparing battery-grade lithium carbonate using battery material extraction residue according to claim 1 or the method described above, characterized in that: The lithium concentration at the endpoint of the secondary concentration is controlled at 20~35 g / L; and / or, the lithium concentration at the endpoint of the primary concentration is controlled at 6~14 g / L.

6. The method for preparing battery-grade lithium carbonate from battery material raffinate according to any one of claims 1 to 5, characterized in that: Step S4 further includes the following steps: The frozen residue in step S4 is melted at 40~90℃. After solid-liquid separation, the lithium-containing solution is returned to the front-end process for recycling, and the solid is dried to obtain sodium sulfate.

7. The method for preparing battery-grade lithium carbonate from battery material raffinate according to any one of claims 1 to 5, characterized in that: The impurity removal conditions in step S2 include at least one of the following conditions: 1) pH range of 10-14; 2) temperature of 60-90℃; 3) impurity removal reaction time of 30-80 min.

8. The method for preparing battery-grade lithium carbonate from battery material raffinate according to any one of claims 1 to 5, characterized in that: The residual liquid from the battery material extraction in step S1 contains the following components at the following mass concentrations: lithium content 0.5-3 g / L, sodium content 20-90 g / L, sulfate content 50-150 g / L, phosphorus content 15-60 mg / L, fluorine content 30-120 mg / L, oily substance content 15-200 mg / L, and chlorine content 0.5-3 g / L; and / or, the reaction conditions for removing phosphorus, fluorine, and oily substances in step S1 include at least one of the following conditions: 1) pH adjustment range of 2-9; 2) temperature adjustment range of 30-90℃; 3) reaction time of 30-120 min.

9. The method for preparing battery-grade lithium carbonate from battery material raffinate according to any one of claims 1 to 5, characterized in that: In step S1, phosphorus removal, fluoride removal and oily substance removal are performed by adding phosphorus removal agent, fluoride removal agent and activated carbon. The mass ratio of phosphorus removal agent, fluoride removal agent and activated carbon to battery material extract residue is 1-10‰, and phosphorus removal, fluoride removal and oily substance removal are performed simultaneously.

10. The method for preparing battery-grade lithium carbonate using battery material extraction residue according to claim 9, characterized in that: The phosphorus removal agent is added in solution form, and the mass ratio of the phosphorus removal agent to the residual liquid from battery material extraction is based on the total amount of solution. The mass concentration of the phosphorus removal agent in the solution is 20-40%. The phosphorus removal agent includes at least one of ferric chloride, aluminum chloride, polyferric chloride, or polyaluminum chloride; and / or, the defluorinating agent is at least one of lanthanum carbonate, lanthanum oxide, or lanthanum hydroxide; and / or, the activated carbon is at least one of coal-derived activated carbon, wood-based activated carbon, or fruit shell activated carbon.

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