Method for obtaining lithium sulfate by low-temperature sulfating roasting of waste lithium batteries

Abstract

This invention discloses a method for obtaining lithium sulfate through low-temperature sulfation roasting of spent lithium batteries, comprising: mixing concentrated sulfuric acid with water, adding ammonium sulfate and sodium sulfate to dissolve, and stirring to obtain a composite sulfate solution; atomizing the composite sulfate solution onto the surface of the positive electrode material of the spent lithium batteries, and drying to obtain homogeneous microspheres; mixing the homogeneous microspheres with distiller's grains and roasting them under a protective atmosphere to obtain a roasting product; grinding the roasting product and mixing it with water to obtain a slurry; adding a pH adjuster to the slurry, and separating the solid and liquid to obtain a lithium sulfate solution. This invention utilizes low-temperature sulfation roasting, which is simple to operate, safe and reliable, requires less acid, and has low production costs. It achieves efficient and low-carbon recycling of lithium resources from spent lithium batteries on an industrial scale, providing a disruptive solution for building a green closed loop throughout the battery lifecycle.

Description

Technical Field

[0001] This invention belongs to the field of waste lithium battery recycling technology, and relates to a method for obtaining lithium sulfate by low-temperature sulfation roasting of waste lithium batteries. Background Technology

[0002] With the explosive growth of the new energy vehicle industry, the large-scale processing of spent lithium-ion batteries (LIBs) has become a global challenge. Among them, the proportion of lithium batteries rich in high-value metals such as nickel, cobalt, and manganese is increasing year by year, and their efficient recycling is of both strategic resource significance and rigid environmental protection requirements. Existing recycling technologies are mainly pyrometallurgy and hydrometallurgy, but both face significant bottlenecks: traditional pyrometallurgical processes can process whole battery packs, but they suffer from high energy consumption and low lithium recovery rates, resulting in a large loss of lithium elements in the form of slag, while generating fluorine-containing waste gas that requires a complex tail gas treatment system; hydrometallurgical processes require thorough disassembly of the battery and separation of the positive electrode active material beforehand. The pretreatment process has two major pain points: difficulty in removing PVDF binder and difficulty in controlling aluminum foil corrosion. High-temperature roasting to remove PVDF easily causes aluminum foil oxidation, forming an inert spinel phase that hinders lithium leaching; strong alkali dissolution generates fluorine-containing waste liquid, increasing treatment costs; and the large amount of aluminum dissolved during acid leaching will contaminate the leaching solution, making subsequent aluminum removal processes complex and prone to loss of target metals.

[0003] Patent CN118792507A discloses a method for selective lithium extraction from manganese-containing cathode materials of spent lithium batteries via sulfation roasting. Specifically, the manganese-containing cathode material from spent lithium batteries is mixed evenly with deionized water, then concentrated sulfuric acid is added to react and the mixture is dried. Following this, a sulfation roasting treatment is performed under a protective atmosphere, and the roasted product is then immersed in water to obtain the final product. This process is known for its short flow and low cost, but it requires roasting at 600–1100 °C for 15–180 min, resulting in high energy consumption and costs.

[0004] Patent CN114277251A discloses a method for separating and recycling metals from waste lithium batteries. Specifically, the positive electrode powder obtained by flotation of waste lithium battery mixed powder is mixed with sulfur and then roasted at 300~1000℃. Finally, the lithium salt solution and metal sulfide enriched residue are obtained by water leaching. Although the lithium leaching rate reaches 97%, the roasting process has high energy consumption, and sulfur is prone to sublimation.

[0005] Low-temperature conversion technology is not yet mature. Although some studies have attempted low-temperature sulfation roasting pretreatment, problems such as low lithium conversion rate, incomplete sulfate decomposition, and excessive acid usage are common. The core difficulty lies in achieving selective and directional lithium conversion at low temperatures while suppressing aluminum foil corrosion and the secondary coating effect of PVDF pyrolysis products.

[0006] Conventional low-temperature conversion technology has limited effectiveness in recovering lithium from spent lithium batteries, and improvements are necessary. Summary of the Invention

[0007] In view of this, the present invention proposes a method for obtaining lithium sulfate by low-temperature sulfation roasting of spent lithium batteries, to solve or at least partially solve the technical problems existing in the prior art. The present invention mixes concentrated sulfuric acid with ammonium sulfate and sodium sulfate to prepare a composite sulfate solution. This composite sulfate solution is then atomized and sprayed onto the surface of the positive electrode material of spent lithium batteries and dried. The obtained homogeneous microspheres are mixed with distiller's grains and subjected to low-temperature sulfation roasting under a protective atmosphere using a fluidized bed process to obtain the roasted product. Finally, a lithium sulfate solution is obtained by water leaching. The method of the present invention is simple, not only efficiently recovering lithium from spent lithium-ion batteries, but also effectively reducing production and equipment operating costs due to its simplified process.

[0008] The technical solution adopted in this invention is as follows: A method for obtaining lithium sulfate by low-temperature sulfation roasting of waste lithium batteries includes the following steps: Concentrated sulfuric acid is mixed with water, then ammonium sulfate and sodium sulfate are added to dissolve them, and the mixture is stirred to obtain a complex sulfate solution. The composite sulfate solution was atomized and sprayed onto the surface of the positive electrode material of a waste lithium battery, and then dried to obtain homogeneous microspheres. The homogeneous microspheres were mixed with distiller's grains and roasted under a protective atmosphere to obtain the roasted product. The roasted product is ground and then mixed with water to obtain a slurry. A pH adjuster is added to the slurry, and the liquid is collected after solid-liquid separation to obtain a lithium sulfate solution.

[0009] Furthermore, the mass ratio of concentrated sulfuric acid to water is 5~10:1; the molar ratio of ammonium sulfate to sodium sulfate is 6:4~8:2; and the mass ratio of the composite sulfate to the waste lithium cobalt oxide battery cathode material is 0.5~1.5:1.

[0010] Furthermore, the composite sulfate solution is atomized through a high-pressure three-fluid nozzle and sprayed onto the surface of the cathode material of the waste lithium battery, forming homogeneous microspheres with a water content of ≤2% under hot air convection drying conditions.

[0011] Furthermore, the waste lithium battery cathode material is one or more of the following: waste lithium cobalt oxide cathode material, waste lithium iron phosphate cathode material, and waste ternary cathode material.

[0012] Furthermore, the mass ratio of the homogeneous microspheres to the distiller's grains is 1:0.2~1.

[0013] Furthermore, the protective atmosphere is an inert atmosphere, the inert gas flow rate is 10–100 mL / min, and the calcination heating rate is 5–15 °C / min. The inert atmosphere is preferably a nitrogen atmosphere, an argon atmosphere, or a vacuum.

[0014] Furthermore, the calcination is carried out in a fluidized bed, with the temperature of the reaction section controlled at 230~550 ℃ and the total residence time of the material at 30~120 min.

[0015] Furthermore, the mass ratio of the calcined product to water is 1:10~30, the water immersion temperature is 25~90 ℃, and the calcined product and water are mixed and reacted at a constant stirring rate of 300~800 rpm for 30~120 min.

[0016] Furthermore, the pH adjustment range is 10~14.

[0017] Furthermore, the pH adjuster is lime or liquid alkali.

[0018] Furthermore, the products obtained from the solid-liquid separation are a lithium sulfate solution and a water-insoluble solid residue.

[0019] Compared with the prior art, the beneficial effects of the present invention are as follows: (1) The method of obtaining lithium sulfate by low-temperature sulfation roasting of waste lithium batteries of the present invention, through low-temperature sulfation roasting, on the one hand, uses spray granulation technology to uniformly coat the surface of the positive electrode material particles with a composite sulfate solution to form a micro-scale sulfate active layer, ensuring molecular-level contact of reactants during low-temperature roasting and breaking through the uniformity bottleneck of traditional mechanical mixing; on the other hand, the ammonium bisulfate generated by the reaction of concentrated sulfuric acid and ammonium sulfate can efficiently dissociate the positive electrode material lattice due to its strong proton acidity, promoting the conversion of lithium ions into soluble lithium sulfate; at the same time, its weak reducing property can avoid excessive dissolution of transition metals such as nickel, cobalt, and manganese. After the introduction of sodium sulfate, by controlling the roasting phase change path, the formation of soluble sulfates of nickel, cobalt, and manganese is directionally suppressed, promoting their conversion into stable insoluble high-temperature oxides, thus avoiding the separation problem caused by the residual transition metal sulfates in traditional processes from the source; finally, low-temperature sulfation roasting is carried out in a protective atmosphere through a fluidized bed process, and through "gas-solid fluidized dynamic roasting", the low-temperature range (230~550) is achieved. Efficient heat and mass transfer of materials is achieved within a temperature range of °C. The selective sulfation reaction of lithium is accelerated by utilizing the eutectic liquid phase of the composite sulfate, while simultaneously generating high-temperature cobalt, nickel, and manganese oxides, ensuring selective separation of the products. By adding distillers' grains as a carbon source during the roasting process, their reducing properties are used to selectively convert high-valence nickel, cobalt, and manganese oxides into insoluble low-valence oxides, thereby synergistically enhancing lithium-ion dissociation through the composite sulfate system. Finally, through a water leaching lithium extraction process, after solid-liquid separation, a lithium sulfate solution and a solid slag containing water-insoluble nickel, cobalt, and manganese oxides are obtained.

[0020] (2) The method of obtaining lithium sulfate by low-temperature sulfation roasting of waste lithium batteries of the present invention uses low-temperature sulfation roasting treatment, which is simple to operate, safe and reliable, requires less acid and has low production cost. It realizes efficient and low-carbon recycling of lithium resources in waste lithium batteries on an industrial scale, and provides a disruptive solution for building a green closed loop for the entire life cycle of batteries. Attached Figure Description

[0021] Figure 1 This is a schematic flowchart of a method for obtaining lithium sulfate by low-temperature sulfation roasting of waste lithium batteries in an embodiment of the present invention. Detailed Implementation

[0022] The technical solution of the present invention will be further described clearly and in detail below with reference to specific examples and accompanying drawings.

[0023] like Figure 1 As shown, a method for obtaining lithium sulfate by low-temperature sulfation roasting of waste lithium batteries includes the following steps: (1) After mixing concentrated sulfuric acid with water, ammonium sulfate and sodium sulfate are added to dissolve the mixture, and the mixture is stirred to obtain a composite sulfate solution. The mass ratio of concentrated sulfuric acid to water is 5~10:1; the molar ratio of ammonium sulfate to sodium sulfate is 6:4~8:2; and the mass ratio of the composite sulfate to the waste lithium cobalt oxide battery cathode material is 0.5~1.5:1.

[0024] (2) The composite sulfate solution is atomized and sprayed onto the surface of the waste lithium battery cathode material, and then dried to obtain homogeneous microspheres. The composite sulfate solution is atomized through a high-pressure three-fluid nozzle and sprayed onto the surface of the waste lithium battery cathode material. Under hot air convection drying conditions, homogeneous microspheres with a water content ≤2% are formed. The waste lithium battery cathode material is one or more of waste lithium cobalt oxide cathode material, waste lithium iron phosphate cathode material, and waste ternary cathode material.

[0025] (3) The homogeneous microspheres are mixed with distiller's grains and calcined under a protective atmosphere to obtain the calcined product. The mass ratio of the homogeneous microspheres to the distiller's grains is 1:0.2~1. The protective atmosphere is an inert atmosphere with an inert gas flow rate of 10~100 mL / min and a calcination heating rate of 5~15 ℃ / min. The preferred inert atmosphere is nitrogen, argon, or vacuum. The calcination is carried out in a fluidized bed, with the reaction section temperature controlled at 230~550 ℃ and the total material residence time 30~120 min.

[0026] (4) The calcined product is ground and then mixed with water to obtain a slurry. The mass ratio of the calcined product to water is 1:10~30, the water immersion temperature is 25~90 ℃, and the calcined product and water are mixed and reacted at a constant stirring rate of 300~800 rpm for 30~120 min.

[0027] (5) A pH adjuster is added to the slurry, and the liquid is collected after solid-liquid separation to obtain a lithium sulfate solution. The pH adjustment range is 10-14. The pH adjuster is lime or liquid alkali. The products obtained from the solid-liquid separation are a lithium sulfate solution and a water-insoluble solid residue.

[0028] The principle of this invention for obtaining lithium sulfate through low-temperature sulfation roasting of waste lithium batteries is as follows: Firstly, through low-temperature sulfation roasting, a composite sulfate solution is uniformly coated onto the surface of the cathode material particles using spray granulation technology, forming a microscale sulfate active layer. This ensures molecular-level contact of reactants during low-temperature roasting, overcoming the uniformity bottleneck of traditional mechanical mixing. Secondly, the ammonium bisulfate generated from the reaction of concentrated sulfuric acid and ammonium sulfate, due to its strong proton acidity, can efficiently dissociate the cathode material lattice, promoting the conversion of lithium ions into soluble lithium sulfate. Simultaneously, its weak reducing properties prevent excessive dissolution of transition metals such as nickel, cobalt, and manganese. The introduction of sodium sulfate, by controlling the roasting phase transition path, directionally inhibits the formation of soluble sulfates from nickel, cobalt, and manganese, promoting their conversion into stable, insoluble, high-temperature oxides, thus avoiding the separation problems caused by residual transition metal sulfates in traditional processes. Finally, low-temperature sulfation roasting is carried out in a protective atmosphere using a fluidized bed process. Through "gas-solid fluidized dynamic roasting," the process is carried out in the low-temperature range (230~550°C). Efficient heat and mass transfer of materials is achieved within a temperature range of °C. The selective sulfation reaction of lithium is accelerated by utilizing the eutectic liquid phase of the composite sulfate, while simultaneously generating high-temperature cobalt, nickel, and manganese oxides, ensuring selective separation of the products. By adding distillers' grains as a carbon source during the roasting process, their reducing properties are used to selectively convert high-valence nickel, cobalt, and manganese oxides into insoluble low-valence oxides, thereby synergistically enhancing lithium-ion dissociation through the composite sulfate system. Finally, through a water leaching lithium extraction process, after solid-liquid separation, a lithium sulfate solution and a solid slag containing water-insoluble nickel, cobalt, and manganese oxides are obtained.

[0029] The concentration of concentrated sulfuric acid described in the following examples and comparative examples is 98%.

[0030] Example 1 A method for obtaining lithium sulfate by low-temperature sulfation roasting of waste lithium batteries includes the following steps: (1) Slowly add 60 mL of concentrated sulfuric acid to 20 mL of water. After cooling, add 35 g of ammonium sulfate and 15 g of sodium sulfate and stir to dissolve to form a complex sulfate solution.

[0031] (2) The composite sulfate solution is atomized through a high-pressure three-fluid nozzle and sprayed onto the surface of 100 g of waste ternary lithium battery cathode material (NCM523, containing 7.2% Li, 20.1% Ni, 12.3% Co, 11.0% Mn, and 1.5% Al). Under hot air convection drying, homogeneous microspheres with a water content of ≤2% are formed.

[0032] (3) After mixing the homogeneous microspheres with 30 g of distiller's grains, the mixture was calcined in a fluidized bed at a heating rate of 5 °C / min under a nitrogen atmosphere with a gas flow rate of 50 mL / min. The mixture was then kept at 350 °C for 60 min and cooled to obtain the calcined product.

[0033] (4) After grinding the calcined product, it is mixed with 200 mL of deionized water and stirred at a constant temperature of 60℃ and 300 rpm for 30 min to obtain a slurry.

[0034] (5) Add a pH adjuster to the slurry to make pH=12; finally, separate the solid and liquid to obtain the lithium sulfate solution.

[0035] Example 2 The difference from Example 1 is that in step (3), the product is calcined in a fluidized bed at a heating rate of 5 °C / min, held at 350 °C for 90 min, and then cooled to obtain the calcined product.

[0036] Example 3 The difference from Example 1 is that the water immersion temperature in step (4) is 70°C.

[0037] Comparative Example 1 The difference from Example 1 is that in step (3), the product is calcined in a fluidized bed at a heating rate of 5 °C / min, held at 200 °C for 60 min, and then cooled to obtain the calcined product.

[0038] Comparative Example 2 The difference from Example 1 is that in step (3), the product is calcined in a fluidized bed at a heating rate of 5 °C / min, held at 700 °C for 60 min, and then cooled to obtain the calcined product.

[0039] Comparative Example 3 The difference from Example 1 is that sodium sulfate is not added to the reaction in step (1).

[0040] Comparative Example 4 The difference from Example 1 is that in step (1), the concentrated sulfuric acid is 120 mL.

[0041] The test results of each embodiment and comparative example are shown in Table 1: Table 1 - Test results of each embodiment and comparative example As shown in Table 1, the Li leaching rates in Examples 1-3 and Comparative Examples 2-4 were all higher than those in Comparative Example 1, indicating that the temperature during sulfation roasting should not be too low. A low temperature of 200 °C resulted in incomplete sulfuric acid reaction, causing the lithium leaching rate to plummet to 87.8%. Examples 1 and Comparative Example 2 show that under the same conditions, the leaching rate at 700 °C actually decreased to 90.6%, with a dramatic increase in impurity ion dissolution. Ni, Co, Mn, and Al reached 5.8%, 4.2%, 6.1%, and 15.3%, respectively. This is because the excessively high temperature led to the formation of a large amount of Al2(SO4)3, and the partial decomposition of transition metal sulfates. Comparing Examples 1 and Comparative Example 3, it can be seen that under the same conditions, the manganese dissolution rate reached 4.1% without sodium sulfate. Sodium sulfate can promote the conversion of manganese sulfate to manganese oxide by lowering the eutectic point; insufficient sodium sulfate resulted in excessive manganese dissolution. As can be seen from the impurity ion content of Example 1 and Comparative Example 4, the amount of acid used directly affects the control of impurities. When the amount of acid is increased to 120 mL, the dissolution of cobalt impurities is significantly aggravated. High amounts of acid also increase the leaching of aluminum, which in turn reduces selectivity. This indicates that lower amounts of acid are more conducive to suppressing the co-dissolution of impurities.

[0042] Unless otherwise specified, all materials and reagents used in the above embodiments are commercially available.

[0043] The above description is merely a preferred embodiment of the present invention. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make many possible variations and modifications to the technical solutions of the present invention using the methods and techniques disclosed above, or modify them into equivalent embodiments with equivalent changes, without departing from the scope of the technical solutions of the present invention. Therefore, any simple modifications, equivalent changes, and modifications made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solutions of the present invention shall still fall within the protection scope of the technical solutions of the present invention.

Claims

1. A method for obtaining lithium sulfate by low-temperature sulfation roasting of waste lithium batteries, characterized in that, Includes the following steps: Concentrated sulfuric acid is mixed with water, then ammonium sulfate and sodium sulfate are added to dissolve the mixture. After stirring, a composite sulfate solution is obtained. The sodium sulfate is used to regulate the phase change path during the roasting process to directionally inhibit the formation of soluble sulfates from nickel, cobalt, and manganese, and promote the transformation of nickel, cobalt, and manganese into stable, insoluble, high-temperature oxides. The composite sulfate solution is atomized through a high-pressure three-fluid nozzle and sprayed onto the surface of the positive electrode material of waste lithium batteries. It is then dried by hot air convection to form homogeneous microspheres with a water content of ≤2%. The homogeneous microspheres are mixed with distillers' grains and calcined at 230-550 °C in a protective atmosphere to obtain the calcined product. The distillers' grains are used as a carbon source to selectively convert high-valence oxides of nickel, cobalt, and manganese into insoluble low-valence oxides by utilizing the reducing properties of the distillers' grains. The roasted product is ground and then mixed with water to obtain a slurry. A pH adjuster is added to the slurry, and the liquid is collected after solid-liquid separation to obtain a lithium sulfate solution. The volume ratio of concentrated sulfuric acid to water is 3:1; the molar ratio of ammonium sulfate to sodium sulfate is 6:4 to 8:2; the mass ratio of the composite sulfate to the waste lithium cobalt oxide battery cathode material is 0.5 to 1.5:1; and the calcination is carried out in a fluidized bed.

2. The method of claim 1, wherein the lithium sulfate is obtained by low-temperature sulfuric acidization roasting of the waste lithium battery. The waste lithium battery cathode material is one or more of the following: waste lithium cobalt oxide cathode material, waste lithium iron phosphate cathode material, and waste ternary cathode material.

3. The method for obtaining lithium sulfate by low-temperature sulfation roasting of waste lithium batteries according to claim 1, characterized in that, The mass ratio of the homogeneous microspheres to the distiller's grains is 1:0.2~1.

4. The method for obtaining lithium sulfate by low-temperature sulfation roasting of waste lithium batteries according to claim 1, characterized in that, The protective atmosphere is an inert atmosphere, the inert gas flow rate is 10-100 mL / min, and the calcination heating rate is 5-15 ℃ / min.

5. The method for obtaining lithium sulfate by low-temperature sulfation roasting of waste lithium batteries according to claim 1, characterized in that, The total residence time of materials is 30~120 min.

6. The method for obtaining lithium sulfate by low-temperature sulfation roasting of waste lithium batteries according to claim 1, characterized in that, The mass ratio of the calcined product to water is 1:10~30, the water immersion temperature is 25~90 ℃, and the calcined product and water are mixed and reacted at a constant stirring rate of 300~800 rpm for 30~120 min.

7. The method for obtaining lithium sulfate by low-temperature sulfation roasting of waste lithium batteries according to claim 1, characterized in that, The pH adjustment range is 10~14.

8. The method for obtaining lithium sulfate by low-temperature sulfation roasting of waste lithium batteries according to claim 1, characterized in that, The pH adjuster is lime or liquid alkali.

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