Method for preparing lithium sulfate by using waste ternary lithium battery

Abstract

The application discloses a method for preparing lithium sulfate by using waste ternary lithium batteries, and relates to the technical field of waste battery recycling. The method comprises the following steps: mixing waste ternary black powder and a microwave sensitizing agent, and then performing roasting by microwave carbon thermal reduction to obtain roasted black powder; mixing the roasted black powder and a pre-leaching liquid, and then continuously feeding carbon dioxide to perform leaching to obtain a lithium bicarbonate solution and a leaching residue; performing pyrolysis on the lithium bicarbonate solution to obtain lithium carbonate precipitation and pyrolysis clear liquid; dissolving the lithium carbonate precipitation in dilute sulfuric acid to obtain a lithium sulfate solution; and performing impurity removal and evaporation crystallization on the lithium sulfate solution to obtain lithium sulfate. According to the method, the metal materials in the waste ternary black powder are reduced into lithium carbonate and metal oxides by microwave carbon thermal reduction, then the lithium bicarbonate solution is obtained by using carbon dioxide for auxiliary leaching, finally, high-purity lithium sulfate products can be obtained after pyrolysis separation, impurity removal and evaporation crystallization, and efficient, mild and high-purity extraction of lithium elements is realized.

Description

Technical Field

[0001] This invention relates to the field of waste battery recycling technology, and in particular to a method for preparing lithium sulfate using waste ternary lithium batteries. Background Technology

[0002] With the booming development of the new energy vehicle industry, the recycling and disposal of spent ternary lithium batteries has become an important issue in the field of resource recycling. Spent ternary batteries contain various valuable metal elements such as nickel, cobalt, manganese, and lithium, as well as various impurity metal elements such as calcium and magnesium. This rich elemental composition presents a significant challenge to the extraction of high-purity lithium.

[0003] In recent years, pre-extraction lithium extraction technology has attracted widespread attention as an emerging recycling strategy. Its core idea is to selectively extract lithium from ternary materials first, and then recover valuable metals such as nickel, cobalt, and manganese from the remaining material. Currently, pre-extraction lithium extraction mainly involves reducing ternary black powder and then extracting lithium carbonate through water leaching. However, the aforementioned water leaching method generally suffers from technical bottlenecks in practical applications, including high water consumption, low recovery efficiency, and the risk of combustion and explosion. Therefore, there is an urgent need to develop a more efficient and gentler selective lithium extraction method. Summary of the Invention

[0004] The main objective of this invention is to propose a method for preparing lithium sulfate using waste ternary lithium batteries, aiming to achieve efficient, mild, and high-purity extraction of lithium.

[0005] To achieve the above objectives, this invention proposes a method for preparing lithium sulfate using spent ternary lithium batteries, comprising the following steps: Waste ternary black powder and microwave sensitizer are mixed and then roasted by microwave carbothermal reduction to obtain roasted black powder; wherein, the roasted black powder includes lithium carbonate and metal oxides. After mixing the roasted black powder and the pre-leaching liquid, carbon dioxide is continuously introduced for leaching to obtain a lithium bicarbonate solution and leaching residue. The lithium bicarbonate solution was pyrolyzed to obtain lithium carbonate precipitate and pyrolysis clear liquid. The lithium carbonate precipitate was dissolved in dilute sulfuric acid to obtain a lithium sulfate solution; After removing impurities and evaporating the lithium sulfate solution, lithium sulfate is obtained.

[0006] Preferably, the roasting includes: Under an inert gas atmosphere, the mixed waste ternary black powder and the microwave sensitizer are subjected to a first calcination to obtain a first calcination product. Under an inert gas atmosphere, the first calcined product is heated and subjected to a second calcination by microwave carbothermal reduction to obtain a second calcined product. After cooling, air is introduced for a third roasting to obtain roasted black powder.

[0007] Preferably, the roasting temperature for the first roasting is 300–500°C, and the roasting time is 10–60 min. The second roasting temperature is 600-900℃, and the roasting time is 10-60 min; The third roasting temperature is 400-600℃, and the roasting time is 10-60 minutes.

[0008] Preferably, during the roasting process of the first roasted product, the inert gas is continuously introduced.

[0009] Preferably, the method for preparing lithium sulfate using spent ternary lithium batteries further includes: After washing the leaching residue with water, the residue is filtered to obtain nickel-cobalt-manganese enriched residue and washing water.

[0010] Preferably, the pre-leaching liquid is any one or a combination of two of the pyrolysis solution and the washing water.

[0011] Preferably, the preparation step of the dilute sulfuric acid is as follows: diluting concentrated sulfuric acid in the pyrolysis solution to obtain dilute sulfuric acid; The impurity removal step involves adsorbing impurity ions from the lithium sulfate solution using resin.

[0012] Preferably, in the roasting process, the mass ratio of the waste ternary black powder to the microwave sensitizer is 20:(1-6), and the microwave sensitizer is any one of graphite, acetylene black, semi-coke, lignite, and biomass carbon.

[0013] Preferably, in the leaching process, the mass ratio of the roasted black powder to the pre-leaching liquid is 1:(5-20). The pyrolysis temperature is 70–90°C, and the pyrolysis time is 2–5 hours.

[0014] Preferably, in the washing process, the mass ratio of the leachate residue to the water is 1:(2-5).

[0015] The technical solution of this invention reduces the metal materials in waste ternary black powder into lithium carbonate and metal oxides through microwave carbothermal reduction, and then obtains lithium bicarbonate solution by carbon dioxide-assisted leaching. Finally, after pyrolysis separation, impurity removal and evaporation crystallization, a high-purity lithium sulfate product can be obtained, realizing the efficient, mild and high-purity extraction of lithium. Attached Figure Description

[0016] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the structures shown in these drawings without creative effort.

[0017] Figure 1 This is a schematic flowchart illustrating the method for preparing lithium sulfate from waste ternary lithium batteries provided by the present invention.

[0018] The realization of the objective, functional features and advantages of the present invention will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. 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 a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0020] It should be noted that if the embodiments of the present invention involve directional indicators (such as up, down, left, right, front, back, etc.), the directional indicators are only used to explain the relative positional relationship and movement of the components in a specific posture. If the specific posture changes, the directional indicators will also change accordingly.

[0021] Furthermore, if the embodiments of this invention involve descriptions such as "first" or "second," these descriptions are for descriptive purposes only and should not be construed as indicating or implying their relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined with "first" or "second" may explicitly or implicitly include at least one of those features. Additionally, the use of "and / or" or "and / or" throughout the text includes three parallel solutions. For example, "A and / or B" includes solution A, solution B, or a solution where both A and B are satisfied simultaneously. Furthermore, the technical solutions of the various embodiments can be combined with each other, but this must be based on the ability of those skilled in the art to implement them. When the combination of technical solutions is contradictory or impossible to implement, it should be considered that such a combination of technical solutions does not exist and is not within the scope of protection claimed by this invention.

[0022] Currently, pre-processing lithium extraction mainly involves reducing ternary lithium-ion batteries and then extracting lithium carbonate via water leaching. However, this water leaching method suffers from technical bottlenecks in practical applications, including high water consumption, low recovery efficiency, and the risk of combustion and explosion. Therefore, to achieve efficient, gentle, and high-purity lithium extraction, this invention proposes a method for preparing lithium sulfate using spent ternary lithium-ion batteries, such as... Figure 1 As shown, it includes the following steps: Waste ternary black powder and microwave sensitizer are mixed and then roasted by microwave carbothermal reduction to obtain roasted black powder; wherein, the roasted black powder includes lithium carbonate and metal oxides. After mixing the roasted black powder and the pre-leaching liquid, carbon dioxide is continuously introduced for leaching to obtain a lithium bicarbonate solution and leaching residue. The lithium bicarbonate solution was pyrolyzed to obtain lithium carbonate precipitate and pyrolysis clear liquid. The lithium carbonate precipitate was dissolved in dilute sulfuric acid to obtain a lithium sulfate solution; After removing impurities and evaporating the lithium sulfate solution, lithium sulfate is obtained.

[0023] The proposed method first uses microwave carbothermal reduction to reduce the metal materials in waste ternary black powder into lithium carbonate and metal oxides (i.e., oxides of nickel, cobalt, and manganese, etc.). Then, carbon dioxide-assisted leaching is used to obtain a lithium bicarbonate solution. Finally, after pyrolysis separation, impurity removal, and evaporation crystallization, a high-purity lithium sulfate product can be obtained.

[0024] First, microwave carbothermal reduction utilizes carbon materials (i.e., the microwave sensitizer in this scheme) as a reducing agent under microwave electromagnetic field irradiation to reduce ternary nickel-cobalt-manganese materials to metal oxides, thus converting lithium into lithium carbonate. Because it enables the directional reduction of metals, it significantly enhances the selectivity of lithium in subsequent leaching processes, ensuring that most valuable metals such as nickel, cobalt, and manganese remain in the leaching residue. This facilitates subsequent classification and recycling, thereby improving lithium recovery efficiency.

[0025] Furthermore, traditional reduction methods often reduce nickel and cobalt to their metallic state. These reactive metals generate large amounts of hydrogen gas (H2) during subsequent acid leaching, posing a significant fire and explosion hazard. This solution directionally converts nickel, cobalt, and manganese into stable metal oxides. These oxides are stable during subsequent leaching treatments and do not react violently with acids to produce hydrogen gas, fundamentally eliminating this major safety hazard and significantly improving the safety of the process.

[0026] Secondly, this scheme proposes to achieve lithium separation using carbon dioxide-assisted selective leaching. Specifically, carbon dioxide dissolves in water to form weak carbonic acid, H... + CO3 in lithium carbonate crystals 2-The reaction produces HCO3 - , making Li + The lithium bicarbonate is released into the solution, forming soluble lithium bicarbonate. Because co-leaching of impurity metals is avoided, the resulting lithium bicarbonate solution has high purity. High-purity decomposition products can be directly obtained through simple subsequent heating decomposition, eliminating the need for complex purification steps.

[0027] Finally, the core of the traditional water leaching method is to dissolve the lithium carbonate produced after roasting into water. The efficiency of this physical dissolution process is limited by the solubility of lithium carbonate itself. To improve the lithium leaching rate, a large amount of water must be used. In contrast, this method does not simply use water to dissolve lithium carbonate, but instead introduces carbon dioxide into the water, causing it to react with the lithium carbonate and convert into lithium bicarbonate, which has a much higher solubility than lithium carbonate. This allows more lithium to be dissolved with the same amount of water, or to achieve the same leaching effect with less water, thus improving the lithium leaching efficiency.

[0028] To further explain, the roasting includes: Under an inert gas atmosphere, the mixed waste ternary black powder and the microwave sensitizer are subjected to a first calcination to obtain a first calcination product. Under an inert gas atmosphere, the first calcined product is heated and subjected to a second calcination by microwave carbothermal reduction to obtain a second calcined product. After cooling, air is introduced for a third roasting to obtain roasted black powder.

[0029] During the high-temperature reduction process, the PVDF binder in spent ternary lithium batteries decomposes to produce hydrogen fluoride (HF). This HF reacts with the target product, lithium carbonate (Li₂CO₃), to form lithium fluoride (LiF), which is poorly soluble in water. This process easily traps a large amount of lithium in the residue, preventing recovery and resulting in a low lithium leaching rate. Therefore, to address this issue, this solution employs a segmented roasting strategy to directionally control the reduction products. This effectively avoids the formation of lithium fluoride, improves the leaching rate, and prevents excessive reduction of nickel, cobalt, and manganese into elemental metals, thus preventing subsequent leaching. This facilitates subsequent wet leaching while achieving independent separation of lithium elements.

[0030] Specifically, this method first involves a first roasting under an inert atmosphere to preferentially decompose the PVDF binder in the spent ternary batteries before the metal elements are reduced, thus preventing the formation of lithium fluoride during the subsequent reduction process. A second roasting is then performed using microwave carbothermal reduction, reducing the ternary nickel-cobalt-manganese material to elemental metals or metal oxides at high temperatures, and reducing lithium to lithium carbonate. Finally, air is introduced at a lower temperature to convert the elemental metals generated during the reduction process into oxides, ensuring that all valuable metal elements are converted into oxides.

[0031] It should be noted that the inert gas is any one of nitrogen, argon, or helium. This application does not impose any limitation on this gas.

[0032] To further explain, the roasting temperature for the first roasting is 300-500℃, and the roasting time is 10-60 minutes. The second roasting temperature is 600-900℃, and the roasting time is 10-60 min; The third roasting temperature is 400-600℃, and the roasting time is 10-60 minutes.

[0033] In a preferred embodiment of this technical solution, the calcination temperature for the first calcination is preferably 300–500°C, which helps to ensure the effective decomposition of the PVDF binder without a reduction reaction. Simultaneously, the calcination temperature for the third calcination is preferably 400–600°C, which effectively ensures that the over-reduced metal is re-oxidized into oxides without significant side reactions.

[0034] To further explain, during the roasting process of the first roasted product, the inert gas is continuously introduced.

[0035] In another preferred embodiment of this technical solution, the continuous introduction of inert gas can maintain the gas pressure state in the reaction system and promote the timely discharge of hydrogen fluoride gas generated by the decomposition of the binder PVDF, so as to avoid reacting with lithium carbonate during the second calcination process to generate lithium fluoride that is difficult to dissolve in water.

[0036] Furthermore, methods for preparing lithium sulfate using spent ternary lithium batteries also include: After washing the leaching residue with water, the residue is filtered to obtain nickel-cobalt-manganese enriched residue and washing water.

[0037] Following the leaching step in this scheme, nickel-cobalt-manganese enriched slag and washing water can be obtained by washing and filtering the leaching residue. The corresponding metals can be effectively recovered by conventional separation and extraction of the nickel-cobalt-manganese enriched slag. This scheme does not limit this step.

[0038] It should be noted that the washing method in this solution can preferably be agitation washing, that is, washing while agitating.

[0039] To further clarify, the pre-leaching liquid is any one or a combination of two of the pyrolysis solution and the washing water.

[0040] In a preferred embodiment of this technical solution, the pre-leaching liquid can be selected from pyrolysis clear liquid or washing water to achieve water reuse in the reaction system, thereby ensuring the balance of water use in the system and realizing water circulation in the system.

[0041] To further explain, the preparation steps of the dilute sulfuric acid are as follows: diluting concentrated sulfuric acid in the pyrolysis solution to obtain dilute sulfuric acid; The impurity removal step involves adsorbing impurity ions from the lithium sulfate solution using resin.

[0042] In another preferred embodiment of this technical solution, the pyrolysis solution can also be used as a solvent to dilute concentrated sulfuric acid, further saving water. Additionally, the resulting lithium sulfate solution may contain trace amounts of valuable metal ions and / or impurity ions such as calcium and magnesium. In this case, adsorption with resin (such as CH-90 resin or HP705 resin commonly used in the art) allows the resin functional groups to form stable complexes with the aforementioned ions for impurity removal, which is more conducive to improving the purity of the lithium sulfate solution and thus obtaining a higher purity lithium sulfate product.

[0043] To further clarify, in the roasting process, the mass ratio of the waste ternary black powder to the microwave sensitizer is 20:(1-6), and the microwave sensitizer is any one of graphite, acetylene black, semi-coke, lignite, and biomass carbon.

[0044] To further explain, in the leaching process, the mass ratio of the roasted black powder to the pre-leaching liquid is 1:(5-20). The pyrolysis temperature is 70–90°C, and the pyrolysis time is 2–5 hours.

[0045] To further explain, in the washing process, the mass ratio of the leachate residue to the water is 1:(2-5).

[0046] The present invention will be further illustrated below through specific embodiments: Example 1 1. Mix waste ternary black powder and acetylene black at a mass ratio of 10:1; Nitrogen gas was continuously introduced into the reaction system, and the mixed waste ternary black powder and acetylene black were calcined at 400°C for 20 minutes to obtain the first calcined product. Under a nitrogen atmosphere, the first calcined product was heated to 800°C and then subjected to a second calcination for 30 minutes to obtain the second calcined product. After cooling, air is introduced to replace the atmosphere of the reaction system, and a third calcination is carried out at 600℃ for 30 minutes to obtain calcined black powder containing lithium carbonate and metal oxides.

[0047] 2. The roasted black powder and the pre-leaching liquid are mixed at a mass ratio of 1:10, and carbon dioxide is continuously introduced for leaching to obtain lithium bicarbonate solution and leaching residue. 3. The lithium bicarbonate solution is pyrolyzed at 70°C for 3 hours to obtain lithium carbonate precipitate and pyrolysis clear liquid; 4. Dissolve the lithium carbonate precipitate in dilute sulfuric acid to obtain a lithium sulfate solution; 5. After removing impurities and evaporating and crystallizing the lithium sulfate solution using resin adsorption, lithium sulfate with a purity of 99.94% is obtained, and the lithium recovery rate is calculated to be 96.3%.

[0048] Example 2 1. Mix waste ternary black powder and semi-coke at a mass ratio of 10:1; Nitrogen gas was continuously introduced into the reaction system, and the mixed waste ternary black powder and semi-coke were calcined at 450°C for 10 minutes to obtain the first calcined product. Under a nitrogen atmosphere, the first calcined product was heated to 700°C and then calcined for 30 minutes to obtain the second calcined product. After cooling, air is introduced to replace the atmosphere of the reaction system, and a third calcination is carried out at 550℃ for 30 minutes to obtain calcined black powder containing lithium carbonate and metal oxides.

[0049] 2. The roasted black powder and the pre-leaching liquid are mixed at a mass ratio of 1:10, and carbon dioxide is continuously introduced for leaching to obtain lithium bicarbonate solution and leaching residue. 3. The lithium bicarbonate solution is pyrolyzed at 80°C for 3 hours to obtain lithium carbonate precipitate and pyrolysis clear liquid; 4. Dissolve the lithium carbonate precipitate in dilute sulfuric acid to obtain a lithium sulfate solution; 5. After removing impurities and evaporating the lithium sulfate solution using resin adsorption, lithium sulfate with a purity of 99.93% is obtained, and the lithium recovery rate is calculated to be 95.7%.

[0050] In summary, the proposed method first uses microwave carbothermal reduction to reduce the metal materials in waste ternary black powder into lithium carbonate and metal oxides, then uses carbon dioxide-assisted leaching to obtain a lithium bicarbonate solution, and finally obtains a high-purity lithium sulfate product through pyrolysis separation, impurity removal and evaporation crystallization, thus achieving efficient, mild and high-purity extraction of lithium.

[0051] The above description is merely an exemplary embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent structural transformations made using the contents of the present invention specification and drawings under the technical concept of the present invention, or direct / indirect applications in other related technical fields, are included within the patent protection scope of the present invention.

Claims

1. A method for preparing lithium sulfate using spent ternary lithium batteries, characterized in that, Includes the following steps: Waste ternary black powder and microwave sensitizer are mixed and then roasted by microwave carbothermal reduction to obtain roasted black powder; wherein, the roasted black powder includes lithium carbonate and metal oxides. After mixing the roasted black powder and the pre-leaching liquid, carbon dioxide is continuously introduced for leaching to obtain a lithium bicarbonate solution and leaching residue. The lithium bicarbonate solution was pyrolyzed to obtain lithium carbonate precipitate and pyrolysis clear liquid. The lithium carbonate precipitate was dissolved in dilute sulfuric acid to obtain a lithium sulfate solution; After removing impurities and evaporating the lithium sulfate solution, lithium sulfate is obtained.

2. The method for preparing lithium sulfate using spent ternary lithium batteries as described in claim 1, characterized in that, The roasting includes: Under an inert gas atmosphere, the mixed waste ternary black powder and the microwave sensitizer are subjected to a first calcination to obtain a first calcination product. Under an inert gas atmosphere, the first calcined product is heated and subjected to a second calcination by microwave carbothermal reduction to obtain a second calcined product. After cooling, air is introduced for a third roasting to obtain roasted black powder.

3. The method for preparing lithium sulfate using spent ternary lithium batteries as described in claim 2, characterized in that, The first roasting temperature is 300-500℃, and the roasting time is 10-60 min; The second roasting temperature is 600-900℃, and the roasting time is 10-60 min; The third roasting temperature is 400-600℃, and the roasting time is 10-60 minutes.

4. The method for preparing lithium sulfate using spent ternary lithium batteries as described in claim 2, characterized in that, During the roasting process of the first roasted product, the inert gas is continuously introduced.

5. The method for preparing lithium sulfate using spent ternary lithium batteries as described in claim 1, characterized in that, Also includes: After washing the leaching residue with water, the residue is filtered to obtain nickel-cobalt-manganese enriched residue and washing water.

6. The method for preparing lithium sulfate using spent ternary lithium batteries as described in claim 5, characterized in that, The pre-leaching solution is any one or a combination of two of the pyrolysis solution and the washing water.

7. The method for preparing lithium sulfate using spent ternary lithium batteries as described in claim 1, characterized in that, The preparation steps of the dilute sulfuric acid are as follows: dilute concentrated sulfuric acid in the pyrolysis solution to obtain dilute sulfuric acid; The impurity removal step is as follows: impurity ions in the lithium sulfate solution are adsorbed by resin.

8. The method for preparing lithium sulfate using spent ternary lithium batteries as described in claim 1, characterized in that, In the roasting process, the mass ratio of the waste ternary black powder to the microwave sensitizer is 20:(1-6), and the microwave sensitizer is any one of graphite, acetylene black, semi-coke, lignite, and biomass carbon.

9. The method for preparing lithium sulfate from spent ternary lithium batteries as described in claim 1, characterized in that, In the leaching process, the mass ratio of the roasted black powder to the pre-leaching liquid is 1:(5-20). The pyrolysis temperature is 70–90°C, and the pyrolysis time is 2–5 hours.

10. The method for preparing lithium sulfate using spent ternary lithium batteries as described in claim 5, characterized in that, In the washing process, the mass ratio of the leachate residue to the water is 1:(2-5).

Images