Method for extracting lithium from waste lithium battery black powder by co-crystal molten salt based roasting and deconstruction

Abstract

This invention relates to the field of waste lithium-ion battery recycling technology, specifically to a method for extracting lithium from waste lithium battery black powder through roasting and deconstruction using eutectic molten salt. The specific technical solution includes the following steps: S1: Mixing waste lithium battery black powder with eutectic molten salt uniformly to obtain a mixture; S2: Roasting the mixture under a nitrogen or argon protective atmosphere to obtain a roasted product; S3: Extracting lithium from the roasted product through water leaching, followed by solid-liquid separation to obtain a lithium-containing solution and a fluorine-containing transition metal leaching residue; S4: Adding sodium carbonate to the obtained lithium-containing solution to obtain lithium carbonate precipitate; S5: Mixing the fluorine-containing transition metal leaching residue from step S3 with sulfuric acid and then ultrasonically treating it, followed by solid-liquid separation to obtain a transition metal leaching solution and a fluorine-containing residue. This invention effectively solves the problems of high processing temperature, high energy consumption, low lithium resource utilization, and fluorine impurity pollution in the waste lithium battery recycling process.

Description

Technical Field

[0001] This invention relates to the field of waste lithium-ion battery recycling technology, specifically to a method for extracting lithium from waste lithium battery black powder by roasting and deconstructing solid fluoride based on eutectic molten salt. Background Technology

[0002] Lithium-ion batteries, due to their high energy density and structural stability, have been widely adopted driven by multiple factors, including the electrification of global transportation and the transition to cleaner energy. With the booming development of the industry, the contradiction between resource consumption and the shortage of key metals such as lithium, nickel, and cobalt has become increasingly prominent. The enrichment of key metals in waste lithium batteries is far higher than in natural minerals. Calculations show that the lithium metal recovered from 28 tons of waste lithium batteries is equivalent to the yield from 250 tons of lithium ore or 750 tons of brine. Therefore, the recycling and regeneration of lithium and transition metals from waste ternary batteries has significant resource and economic value and can promote the sustainable development of the industry. However, waste lithium batteries not only contain a large amount of precious metals but also fluorine-containing substances such as polyvinylidene fluoride (PVDF), lithium hexafluorophosphate (LiPF6), and lithium fluoride (LiF). If not properly disposed of, this will lead to fluorine leakage and environmental pollution, as well as a waste of lithium resources.

[0003] In existing technologies, one approach involves utilizing residual fluorine-containing components such as PVDF and LiPF6 in spent lithium batteries to participate in the reaction during reduction roasting, thereby converting lithium into soluble lithium salts and achieving preferential lithium extraction through water leaching. However, during this process, the fluorine in PVDF and LiPF6 is converted into fluorine-containing substances such as HF and LiF. HF easily causes equipment corrosion and environmental pollution, increasing the pressure on waste gas treatment; LiF, being poorly soluble in water, is difficult to remove effectively during water leaching, thus reducing lithium recovery efficiency and causing resource waste. Another approach involves first pre-treating the spent lithium battery materials at low temperatures to remove organic electrolytes and binders, and then roasting and deconstructing the pre-treated black powder. However, some fluorine remains in the black powder in the form of LiF and LiPF6 and enters subsequent processing units, leading to difficulties in controlling fluorine pollution and lithium resource loss during subsequent deconstruction and leaching processes. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention provides a method for extracting lithium from waste lithium battery black powder by roasting and deconstructing it based on eutectic molten salt. This method solves the problems of high roasting temperature, high energy consumption, low lithium resource utilization, and difficulty in controlling fluorine-containing pollutants in the existing waste lithium battery black powder treatment process.

[0005] This invention, based on the principle of eutectic molten salt, proposes a method for calcining and deconstructing waste lithium-ion battery black powder to extract lithium from solid fluoride using a MnCl2-CaCl2 eutectic molten salt. The eutectic molten salt is composed of two or more salts in a specific molar ratio, and its melting point is lower than that of any single salt component. It can form a liquid ionic melt at a lower temperature, thus providing a reaction medium for the low-temperature deconstruction of the positive electrode active material in the black powder. In this invention, MnCl2 serves as a chlorine source, ionizing to generate Cl- in a low-temperature molten state. - and the Li released during the deconstruction process + By combining the formation of water-soluble LiCl, the directional conversion and preferential extraction of lithium are achieved. CaCl2, as a fluorine fixation agent, can synergistically lower the roasting and decomposition temperature while converting fluorine-containing substances such as LiPF6 and LiF in the black powder into stable CaF2, thereby achieving in-situ fixation of fluorine. Subsequently, taking advantage of the difference between CaF2's poor solubility in dilute sulfuric acid and the permissibility of transition metals in the acid leaching solution, the effective separation of CaF2 from the transition metal components is achieved.

[0006] To achieve the above objectives, the present invention provides the following technical solution: This invention discloses a method for extracting lithium from waste lithium battery black powder by roasting and deconstructing solid fluoride based on eutectic molten salt, comprising the following steps: S1: Mix waste lithium battery black powder with eutectic molten salt evenly to obtain a mixture; S2: The mixture is calcined under a protective atmosphere of nitrogen or argon to obtain the calcined product; S3: The roasted product is subjected to water leaching to extract lithium, and the lithium-containing solution and fluorine-containing transition metal leaching residue are obtained by solid-liquid separation. S4: Add sodium carbonate to the obtained lithium solution to obtain lithium carbonate precipitate; S5: The fluorine-containing transition metal leaching residue from step S3 is mixed with sulfuric acid and then subjected to ultrasonic treatment. The transition metal leaching solution and fluorine-containing residue are obtained by solid-liquid separation.

[0007] Preferably, in step S1, the eutectic molten salt is MnCl2 and CaCl2.

[0008] Preferably, in step S1, the molar ratio of MnCl2 to lithium ions in waste lithium battery black powder is 0.40:1-0.80:1; the molar ratio of CaCl2 to fluoride ions in waste lithium battery black powder is 0.40:1-0.80:1.

[0009] Preferably, the molar ratio of MnCl2 to lithium ions in waste lithium battery black powder is 0.50:1-0.70:1; the molar ratio of CaCl2 to fluoride ions in waste lithium battery black powder is 0.50:1-0.70:1.

[0010] Preferably, in step S1, the molar ratio of MnCl2 / (CaCl2+MnCl2) is between 0.2 and 1.

[0011] Preferably, in step S1, the molar ratio of MnCl2 / (CaCl2+MnCl2) is between 0.50 and 0.90.

[0012] Preferably, in step S2, the calcination temperature is 500℃-800℃ and the time is 30min-120min.

[0013] Preferably, in step S3, the water immersion lithium extraction time is 20 min to 120 min, and the solid-liquid ratio of the calcined product to water is 50 g / L to 200 g / L.

[0014] Preferably, in step S4, lithium carbonate is obtained by precipitation with sodium carbonate at 70-90°C.

[0015] Preferably, in step S5, the concentration of the sulfuric acid is 0.5M-2M.

[0016] The present invention has the following beneficial effects: 1. The method of the present invention can achieve gentle decomposition of waste lithium battery black powder and efficient extraction of lithium, while stabilizing and solidifying fluorine in the form of CaF2. This not only helps to reduce the roasting temperature and energy consumption, but also reduces the loss of additives, inhibits the migration of fluorine pollution and avoids the additional introduction of impurity ions, thereby effectively solving the problems of high energy consumption, low lithium recovery rate and serious fluorine pollution in the existing waste lithium battery recycling and treatment.

[0017] 2. The binary eutectic molten salt used in this invention remains in a liquid state at the eutectic temperature, which is beneficial to the diffusion of lithium ions after the thermal decomposition of the cathode material and improves the efficiency of preferential separation and recovery of lithium. Attached Figure Description

[0018] Figure 1 The phase diagram of MnCl2-CaCl2 eutectic salt; Figure 2 This is a flowchart of the deconstruction and solid fluorine extraction process for Example 1; Figure 3 The X-ray diffraction (XRD) spectra of the mixture, roasting product, and lithium extraction tailings after water leaching in Example 1 are shown. Figure 4 The XRD pattern of the lithium carbonate product obtained in Example 1; Figure 5 The image shows the XRD pattern of the CaF2 residue from Example 1. Detailed Implementation

[0019] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0020] Unless otherwise specified, the technical means used in the implementation examples are conventional means well known to those skilled in the art.

[0021] This invention provides a method for calcining and deconstructing waste lithium-ion battery black powder to extract lithium from solid fluoride using a eutectic molten salt. The addition amounts of MnCl2 and CaCl2 are determined based on the lithium-ion and fluoride ion content in the waste lithium-ion battery black powder, and the calcination temperature is selected using the MnCl2-CaCl2 eutectic molten salt phase diagram. At the specified molar ratio, the eutectic melting temperature of the binary lithium battery is significantly lower than the melting point temperature of the single component, effectively reducing the thermal deconstruction temperature of the waste lithium-ion battery. The MnCl2 in the binary eutectic salt acts as a chlorine source, decomposing into MnCl2 in a low-temperature molten state. 2+ and Cl - The generated Cl - With the Li released during the deconstruction process + By combining the formation of water-soluble LiCl, the directional conversion and preferential extraction of lithium can be achieved; metallic manganese ions exist in waste lithium battery black powder and can be directly recycled and regenerated in subsequent processing; CaCl2 is used as a solid fluoride agent to generate CaF2; the binary eutectic molten salt remains liquid at the eutectic temperature, which is conducive to the diffusion of lithium ions after thermal decomposition of the cathode material and improves the efficiency of preferential separation and recovery of lithium.

[0022] The specific process is as follows: S1: Mixing: The waste lithium battery black powder and eutectic molten salt are mixed evenly to obtain a mixed material; the waste lithium battery black powder refers to the positive electrode active material of waste lithium battery positive electrode material that retains its original crystal structure after removing PVDF, electrolyte, electrolyte and other substances; the eutectic molten salt is MnCl2 and CaCl2.

[0023] The molar ratio of MnCl2 to lithium ions in waste lithium battery black powder is 0.40:1-0.80:1, preferably 0.50:1-0.70:1; the molar ratio of CaCl2 to fluoride ions in waste lithium battery black powder is 0.40:1-0.80:1, preferably 0.50:1-0.70:1. The molar ratio of MnCl2 / (CaCl2+MnCl2) is 0.2-1, preferably 0.50-0.90.

[0024] S2: Calcination: The mixture is calcined under a protective atmosphere of nitrogen or argon to obtain a calcined product; the calcination temperature is 500℃-800℃, preferably 600℃-700℃; the treatment time is 30min-120min, preferably 60min-90min.

[0025] S3: Lithium extraction by water leaching: The roasted product is subjected to lithium extraction by water leaching, and a lithium-containing solution and a fluorine-containing transition metal leaching residue are obtained by solid-liquid separation; the lithium extraction time is 20 min-120 min, preferably 40-60 min; the solid-liquid ratio of the roasted product to water is 50 g / L-200 g / L, preferably 100 g / L-150 g / L.

[0026] S4: Lithium precipitation: Add sodium carbonate solution dropwise to the obtained lithium solution at 70-90℃ until no more precipitate appears, to obtain lithium carbonate precipitate; S5: Sulfuric acid leaching: The fluorine-containing transition metal leaching residue from step S3 is mixed with sulfuric acid and then ultrasonically treated for 1 hour. Solid-liquid separation is then performed to obtain a transition metal (containing nickel, cobalt, and manganese) leaching solution and a fluorine-containing residue. The concentration of the sulfuric acid is 0.5M-2M, preferably 0.5-1M.

[0027] The MnCl2-CaCl2 eutectic salt phase diagram is as follows: Figure 1 As shown, the MnCl2-CaCl2 binary system can form a completely molten "BSalt-Liquid" single liquid phase region within a certain composition and temperature range. When the molar ratio of MnCl2 / (MnCl2+CaCl2) is approximately 0.65, the system reaches its lowest liquidus temperature, approximately 590℃, corresponding to its eutectic composition and lowest eutectic temperature. Within this liquid phase region, a homogeneous eutectic molten salt can be formed by controlling the ratio of MnCl2 to CaCl2 and the calcination temperature. Utilizing the molten salt's good fluidity, high reactivity, and enhanced interfacial mass transfer, the structural deconstruction, lithium chloride conversion, and fluoride fixation of waste lithium battery black powder can be promoted. When the system composition deviates from the eutectic composition or the temperature is lower than the corresponding liquidus line, it enters the two-phase region of "BSalt-Liquid+CaCl2(s)" or "BSalt-Liquid+MnCl2(s)" respectively. At this time, the molten salt liquid phase coexists with excess solid CaCl2 or MnCl2, and the system is difficult to achieve complete melting. This may weaken the uniform dispersion, interfacial contact and mass transfer reaction of the salt components, thus hindering the synergistic enhancement of the deconstruction lithium extraction and solid fluorine processes.

[0028] The present invention will be further described below with reference to specific embodiments.

[0029] Example 1 like Figure 2As shown, a method for extracting lithium from waste lithium battery black powder by roasting and deconstructing solid fluoride based on eutectic molten salt includes the following steps: (1) The pretreated waste ternary battery black powder is mixed with MnCl2 and CaCl2 to obtain a mixture, wherein the molar ratio of MnCl2 to lithium ions in the battery black powder is 0.6:1; the molar ratio of CaCl2 to fluoride ions in the battery black powder is 0.5:1; and the molar ratio of eutectic molten salt MnCl2 / (CaCl2+MnCl2) is 0.88. (2) Place the mixture into a tube furnace, and purge with high-purity argon or nitrogen for 20 minutes before heating to ensure that the air in the tube furnace is purged. Calcinate at 650°C for 60 minutes and cool naturally to room temperature to obtain the calcined product. (3) The roasted product was extracted with distilled water at room temperature for 60 min at a solid-liquid ratio of 100 g / L. After solid-liquid separation, a lithium-containing solution was obtained, and a fluorine-containing transition metal leaching residue was obtained. (4) A saturated sodium carbonate solution was added to the lithium-containing solution at 90°C to precipitate lithium carbonate; the obtained lithium carbonate was washed with distilled water at 100°C to remove impurities; the purity of the obtained lithium carbonate is shown in Table 3. The results show that the purity of lithium carbonate is above 99%.

[0030] (5) The fluorine-containing transition metal leaching residue was treated with 1 mol / L sulfuric acid solution. The leaching process was enhanced by ultrasound and the leaching time was 1 h. After solid-liquid separation, the transition metal leaching solution and the fluorine-containing residue (i.e. CaF2 residue) were obtained.

[0031] The X-ray diffraction (XRD) spectra of the mixture, roasting product, and lithium extraction tailings (i.e., fluorine-containing transition metal leaching residue) from the above steps are shown below. Figure 3 As shown, the results indicate that the characteristic peaks of NCM completely disappeared after calcination, followed by the generation of obvious characteristic peaks of LiCl, CaF2, and transition metal oxides, proving that NCM was completely deconstructed and that selective lithium conversion and fluorine fixation were completed.

[0032] The XRD pattern of the lithium carbonate product prepared by the above steps is shown in the figure. Figure 4 As shown, the results indicate that the positions and relative intensities of the main diffraction peaks are highly consistent with the lithium carbonate standard PDF card (No. 01-087-0729), and no obvious impurity phase diffraction peaks were observed, indicating that the obtained product is mainly lithium carbonate with high crystallinity and good phase purity.

[0033] The XRD pattern of the fluorine-containing residue obtained after treating the fluorine-containing transition metal solid with sulfuric acid solution in the above steps is shown below. Figure 5As shown in the figure. The results show that the positions and relative intensities of the main diffraction peaks in the residue are basically consistent with the standard PDF cards (No. 01-070-1469 and No. 01-074-1905) for CaF2 and CaSO4, respectively, and no obvious diffraction peaks of transition metal phases were observed. The results indicate that during acid leaching, F is mainly enriched and retained in the solid phase in the chemically stable form of CaF2, while the transition metals enter the leachate, thus achieving effective separation of F and transition metals.

[0034] Table 1 shows the content of each element, water leaching rate, and fluoride fixation rate in the mixture and lithium-containing solution completely dissolved in aqua regia. The aqua regia dissolution conditions were a solid-liquid ratio of 1:20 g / ml, a time of 2 h, and a temperature of 60 °C. The concentration of each element in the obtained solution was determined by ICP or IC50, and the water leaching rate and fluoride fixation rate of each element were calculated.

[0035] Table 2 shows the Ni, Co, and Mn contents in the fluorine-containing transition metal leaching residue after complete dissolution with aqua regia, and the Ni, Co, and Mn contents in the transition metal leaching solution after sulfuric acid leaching. The aqua regia dissolution conditions were a solid-liquid ratio of 1:20 g / ml, a time of 2 h, and a temperature of 60 °C. The water leaching rate or the transition metal acid leaching rate was calculated using formula (1), and the F ion fixation rate was calculated using formula (2).

[0036] (1) (2) In the formula, Ei is the water immersion efficiency of i (Li, Ni, Co, Mn), and M is the water immersion efficiency of i (Li, Ni, Co, Mn). i For ICP determination of the content (mg / g) of various ions in the feedstock / fluorine-containing transition leaching residue; m i The content (mg / g) of Li, Ni, Co, and Mn in the water leachate or sulfuric acid leachate; M F For IC determination of the content (mg / g) of raw material F; m F The content of F in the aqueous extract (mg / g).

[0037] Table 3 shows the purity of lithium hydrochloride products obtained by normalizing the Li, Ni, Co, Mn, Al, Ca, and F contents obtained after completely dissolving the lithium carbonate products in aqua regia and measuring them using ICP or IC40.

[0038] Table 1. Test results of ion concentration in aqua regia digestion solution and lithium-containing solution of mixed materials.

[0039] Table 2. Test results of ion concentration in transition metal leachate

[0040] Table 3 Lithium carbonate yield and purity

[0041] Example 2 A method for extracting lithium from waste lithium battery black powder by roasting and deconstructing solid fluoride based on eutectic molten salt is the same as in Example 1, except that the roasting temperature is 700℃ and other methods remain unchanged.

[0042] Table 4 shows the content of each element, water extraction rate, and fluoride fixation rate in the mixture and lithium-containing solution completely dissolved with aqua regia. The aqua regia dissolution conditions were a solid-liquid ratio of 1:20 g / ml, a time of 2 h, and a temperature of 60 °C. The concentration of each element in the obtained solution was determined by ICP or IC50, and the water leaching rate and fluoride fixation rate of each element were calculated.

[0043] Table 4. Ion concentration test results of aqua regia digestion solution and lithium-containing solution for mixed materials.

[0044] Example 3 A method for extracting lithium from waste lithium battery black powder by roasting and deconstruction based on eutectic molten salt is the same as in Example 1, except that the molar ratio of MnCl2 to lithium ions in the system is 0.5:1, the roasting time is 90 min, and other methods remain unchanged.

[0045] Table 5 shows the content of each element, water leaching rate, and fluorine fixation rate in the lithium extraction solution obtained by completely dissolving the mixture and roasting product in aqua regia. The aqua regia dissolution conditions were a solid-liquid ratio of 1:20 g / ml, a time of 2 h, and a temperature of 60 °C. The concentration of each element in the obtained solution was determined by ICP or IC50, and the water leaching rate and fluorine fixation rate of each element were calculated.

[0046] Table 5. Ion concentration test results of aqua regia digestion solution and lithium-containing solution for mixed materials.

[0047] Note: In Tables 1-5, all elements are present in solution in ionic form. Also, the mixtures used in Examples 1 and 2 are not the same as those in Example 1, but rather experiments were conducted based on the same proportions. Therefore, the data on the aqua regia digestion content differ between Tables 1 and 4.

[0048] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A method for extracting lithium from waste lithium battery black powder by roasting and deconstruction using eutectic molten salt, characterized in that: Includes the following steps: S1: Mix waste lithium battery black powder with eutectic molten salt evenly to obtain a mixture; S2: The mixture is calcined under a protective atmosphere of nitrogen or argon to obtain the calcined product; S3: The roasted product is subjected to water leaching to extract lithium, and the lithium-containing solution and fluorine-containing transition metal leaching residue are obtained by solid-liquid separation. S4: Add sodium carbonate to the obtained lithium solution to obtain lithium carbonate precipitate; S5: The fluorine-containing transition metal leaching residue from step S3 is mixed with sulfuric acid and then subjected to ultrasonic treatment. The transition metal leaching solution and fluorine-containing residue are obtained by solid-liquid separation.

2. The method for extracting lithium from waste lithium battery black powder by roasting and deconstruction based on eutectic molten salt according to claim 1, characterized in that: In step S1, the eutectic molten salt is MnCl2 and CaCl2.

3. The method for extracting lithium from waste lithium battery black powder by roasting and deconstruction based on eutectic molten salt according to claim 2, characterized in that: In step S1, the molar ratio of MnCl2 to lithium ions in waste lithium battery black powder is 0.40:1-0.80:1; the molar ratio of CaCl2 to fluoride ions in waste lithium battery black powder is 0.40:1-0.80:

1.

4. The method for extracting lithium from waste lithium battery black powder by roasting and deconstruction based on eutectic molten salt according to claim 3, characterized in that: The molar ratio of MnCl2 to lithium ions in waste lithium battery black powder is 0.50:1-0.70:1; the molar ratio of CaCl2 to fluoride ions in waste lithium battery black powder is 0.50:1-0.70:

1.

5. The method for extracting lithium from waste lithium battery black powder by roasting and deconstruction based on eutectic molten salt according to claim 2, characterized in that: In step S1, the molar ratio of MnCl2 / (CaCl2+MnCl2) is between 0.2 and 1.

6. The method for extracting lithium from waste lithium battery black powder by roasting and deconstruction based on eutectic molten salt according to claim 5, characterized in that: In step S1, the molar ratio of MnCl2 / (CaCl2+MnCl2) is between 0.50 and 0.

90.

7. The method for extracting lithium from waste lithium battery black powder by roasting and deconstruction based on eutectic molten salt according to claim 1, characterized in that: In step S2, the calcination treatment is carried out at a temperature of 500℃-800℃ for a time of 30min-120min.

8. The method for extracting lithium from waste lithium battery black powder by roasting and deconstruction based on eutectic molten salt according to claim 1, characterized in that: In step S3, the water immersion extraction time for lithium is 20 min to 120 min, and the solid-liquid ratio of the calcined product to water is 50 g / L to 200 g / L.

9. The method for extracting lithium from waste lithium battery black powder by roasting and deconstruction based on eutectic molten salt according to claim 1, characterized in that: In step S4, lithium carbonate is obtained by precipitation with sodium carbonate at 70-90°C.

10. The method for extracting lithium from waste lithium battery black powder by roasting and deconstruction based on eutectic molten salt according to claim 1, characterized in that: In step S5, the concentration of the sulfuric acid is 0.5M-2M.

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