Lithium extraction method of ternary battery black powder

Abstract

The invention discloses a lithium extraction method of ternary battery black powder. The lithium extraction method comprises the following steps of pretreatment alkali washing, adding of organic carbon and concentrated acid, mixing and pyrolysis, primary lithium extraction through water leaching and secondary lithium extraction through acid leaching of filter residues obtained after primary lithium extraction. On the basis of lithium extraction by combining a pyrogenic process and a wet process, secondary acid leaching is performed for lithium extraction, and precipitation of nickel and cobalt ions is reduced while lithium ions are leached by controlling the amount of acid, the reaction temperature and the reaction time; according to the method, the lithium recovery rate is increased to 96% or above, and the leaching rate of nickel and cobalt is lower than 3%; and the high recovery rate of lithium is realized under the condition of low cost.

Description

Technical Field

[0001] The present invention belongs to the field of battery recycling and processing, and in particular relates to a method for extracting lithium from black powder of a ternary battery. Background Art

[0002] The popularity of new energy vehicles has driven rapid development of the entire power battery industry chain. Lithium batteries, due to their excellent electrochemical properties, are widely used as power batteries. However, most lithium batteries have a lifespan of approximately eight years, resulting in a large amount of waste. If these waste batteries are not properly handled, they will not only seriously pollute the environment but also result in a significant waste of resources.

[0003] Ternary lithium batteries are used as a primary power battery due to their high energy density. Their cathode material is primarily nickel-cobalt-manganese oxide. Because the cathode material is the primary component of a battery (15-41%), recycling it is a crucial step in recycling spent lithium batteries.

[0004] After discharging, disassembling and separating the used ternary lithium batteries, the ternary lithium positive electrode active material is obtained, commonly known as ternary black powder. At present, there are two main routes for the recovery of ternary black powder: the full wet method and the combination of the fire-wet method. The full wet method is to dissolve all the metal elements in the black powder through inorganic acids and reducing agents, and then recover manganese, cobalt and nickel in turn through extraction, and finally recover lithium. This not only increases the amount of acid and extractant used, but also reduces the recovery rate of lithium. The combination of the fire-wet method is the current mainstream method. After roasting the ternary black powder, lithium can be preferentially extracted by water, saving the use of auxiliary materials. However, for ternary black materials with complex components and high impurity content, the lithium recovery rate is low, far from meeting the requirements. Summary of the invention

[0005] Purpose of the invention: The technical problem to be solved by the present invention is to provide a new method for extracting lithium from ternary battery black powder, which can fully extract lithium and improve the lithium recovery rate while fully reducing the leaching rate of other metal ions.

[0006] Technical solution: The method for extracting lithium from ternary battery black powder of the present invention comprises the following steps:

[0007] (1) Pretreatment: First, the ternary black powder is fully alkali-washed, filtered, washed and dried to obtain the impurity-free filter residue;

[0008] (2) Mixing: uniformly mixing the filter residue, organic carbon, and acid solution to obtain a mixed slurry, and pyrolyzing the mixed slurry to obtain a roasted product;

[0009] (3) Primary lithium extraction: the roasted product is immersed in water and then filtered to obtain a primary lithium extraction filtrate and a primary lithium extraction residue;

[0010] (4) Secondary lithium extraction: Mix the filter residue from the first lithium extraction with an acid, add water to dissolve, and react for 1 - 2 h at 50 - 70 °C. After filtration and separation, a lithium-containing filtrate and a filter residue are obtained. Among them, the addition amount of the acid is 0.05 - 0.7% of the mass of the filter residue from the first lithium extraction.

[0011] In the present invention, after pre-treating the ternary black powder, it is mixed with organic carbon and an acid solution and pyrolyzed, so as to reduce the contents of aluminum and phosphorus in the ternary battery black powder and enable lithium ions to escape from the layered structure. Subsequently, two-stage lithium extraction is realized through water leaching and acid leaching respectively. That is, after preliminary lithium extraction through water leaching, under the condition that specific acid amount, temperature, and reaction time are all satisfied simultaneously, a high leaching rate of lithium is achieved while reducing the leaching rates of other metal ions (such as nickel and cobalt), achieving the effect of extracting lithium without extracting other metal ions.

[0012] Furthermore, in step (1) of extracting lithium from the ternary black powder in the present invention, the alkali solution used for alkali washing is sodium hydroxide solution or potassium hydroxide solution, and the alkali washing time is 0.5 - 3 h; the washing time is 0.5 - 1 h.

[0013] Furthermore, in step (2) of extracting lithium from the ternary black powder in the present invention, the mass ratio of lithium, organic carbon, and acid solution in the filter residue of the mixture is 1:(1 - 3):(10 - 30).

[0014] Furthermore, in step (2) of extracting lithium from the ternary black powder in the present invention, the organic carbon is one or more of glucose, sucrose, starch, cellulose, polyvinyl alcohol, soluble starch, cellulose, ascorbic acid, or phenolic resin.

[0015] Furthermore, in step (2) of extracting lithium from the ternary black powder in the present invention, the acid solution is one or several of sulfuric acid, hydrochloric acid, and nitric acid.

[0016] Furthermore, in step (2) of extracting lithium from the ternary black powder in the present invention, the pyrolysis is to calcine the mixed slurry at 500 - 750 °C for 1 - 5 h. Preferably, the heating rate of this pyrolysis is 2 - 10 °C / min.

[0017] Furthermore, in step (3) of extracting lithium from the ternary black powder in the present invention, the water leaching is to dissolve the calcined product in water and react for 0.5 - 4 h at a water temperature of 25 - 90 °C. Preferably, the solid-liquid ratio of the calcined product to water is 1:(1 - 7).

[0018] Furthermore, in step (4) of extracting lithium from the ternary black powder in the present invention, the acid used in the secondary lithium extraction is an organic acid, and this organic acid is oxalic acid, L-ascorbic acid, glycolic acid, or citric acid.

[0019] Beneficial effects: Compared with the prior art, the significant advantages of the present invention are as follows: Based on the combination of pyrometallurgy and hydrometallurgy for lithium extraction, the present invention realizes two-stage lithium extraction by water leaching and acid leaching respectively. And during the second acid leaching process for lithium extraction, the addition amount of acid, reaction temperature and reaction time are strictly controlled. While achieving high-selectivity lithium extraction and improving the lithium recovery rate (the lithium recovery rate is increased to more than 96%), the precipitation of other metal ions such as nickel and cobalt is avoided (the leaching rate of nickel and cobalt is lower than 3%), realizing the improvement of the lithium recovery rate under low-cost conditions. Specific embodiments

[0020] The technical solution of the present invention will be further described in detail below in conjunction with the embodiments.

[0021] It should be noted that the calculation formulas for the lithium recovery rate and the precipitation rate of other metal ions such as nickel and cobalt in the present invention are as follows:

[0022]

[0023] During the lithium extraction process of ternary battery black powder, even under the same process conditions, certain errors will occur, resulting in fluctuations in the data results. However, after multiple experiments, it is confirmed that the errors will not affect the trend of the leaching rates of lithium, cobalt and nickel.

[0024] The main component contents of the ternary battery black powder used in the following embodiments of the present invention are shown in Table 1 below.

[0025] Table 1 Main component content table of ternary battery black powder

[0026] Main elements Lithium Nickel Cobalt Manganese Iron Aluminum Phosphorus Content / % 4.4 21.89 3.50 4.46 1.82 0.55 2.16

[0027] Example 1

[0028] The method for extracting lithium from ternary battery black powder in this example includes the following steps:

[0029] (1) Pretreatment: Take 100 g of ternary battery black powder and add it to 300 mL of sodium hydroxide solution with a mass fraction of 10%. Under the condition of a stirring speed of 200 r / min, perform alkali washing for 2 h and then filter; subsequently, wash the filter residue with hot water, wash for 30 min at the same stirring speed, and then filter and dry to obtain the filter residue;

[0030] (2) Mixing: Mix the dried filter residue in step (1) with glucose and concentrated sulfuric acid according to the mass ratio of lithium, glucose and concentrated sulfuric acid in the mixed slurry of 1:2:30, and mix evenly in a mortar to obtain a mixed slurry;

[0031] (3) Roasting and pyrolysis: Put the mixed slurry into a crucible, and then put the crucible into a muffle furnace for pyrolysis reaction. The reaction temperature rises from room temperature to 550 °C, the roasting time is 2 h, and the heating rate is 2 °C / min;

[0032] (4) First lithium extraction: Add 104 g of the calcined product to deionized water at a solid-liquid ratio of 1:5, and perform the first water leaching for lithium extraction at a water temperature of 30 °C for 1 h to obtain the first lithium extraction filtrate and the first lithium extraction filter residue;

[0033] (5) Second lithium extraction: Mix 73 g of the first lithium extraction filter residue with oxalic acid, add water to dissolve both, react at 60 °C for 1 h, and obtain a lithium-containing filtrate and 72.20 g of filter residue through filtration and separation; among them, the addition amount of the acid is 0.1% of the first lithium extraction filter residue.

[0034] Example 2

[0035] The method for extracting lithium from the ternary battery black powder in this example includes the following steps:

[0036] (1) Pretreatment: Take 100 g of ternary battery black powder and add it to 300 mL of a 10% sodium hydroxide solution. Under the condition of a stirring speed of 200 r / min, perform alkali washing for 1 h and then filter; subsequently, wash the filter residue with hot water, wash for 30 min at the same stirring speed, and then filter and dry to obtain the filter residue;

[0037] (2) Mixing: Mix the dried filter residue in step (1) with glucose and concentrated sulfuric acid according to the mass ratio of lithium, glucose, and concentrated sulfuric acid in the mixed slurry of 1:3:25, and mix evenly in a mortar to obtain the mixed slurry;

[0038] (3) Calcination and pyrolysis: Put the mixed slurry into a crucible, and then put the crucible into a muffle furnace for pyrolysis reaction. The reaction temperature rises from room temperature to 650 °C, the calcination time is 2 h, and the heating rate is 5 °C / min;

[0039] (4) First lithium extraction: Add 106 g of the calcined product to deionized water at a solid-liquid ratio of 1:5, and perform the first water leaching for lithium extraction at a water temperature of 30 °C for 1 h to obtain the first lithium extraction filtrate and the first lithium extraction filter residue;

[0040] (5) Second lithium extraction: Mix 74.1 g of the first lithium extraction filter residue with oxalic acid, add water to dissolve both, react at 60 °C for 1 h, and obtain a lithium-containing filtrate and 73.1 g of filter residue through filtration and separation; among them, the addition amount of the acid is 0.5% of the first lithium extraction filter residue.

[0041] Example 3

[0042] The method for extracting lithium from the ternary battery black powder in this example includes the following steps:

[0043] (1) Pretreatment: Take 100 g of ternary battery black powder and add it to 300 mL of sodium hydroxide solution with a mass fraction of 10%. Under the condition of a stirring speed of 200 r / min, perform alkali washing for 2 h and then filter; subsequently, wash the filter residue with hot water, wash for 1 h at the same stirring speed, and then filter and dry to obtain the filter residue;

[0044] (2) Mixing: Mix the dried filter residue in step (1) with glucose and concentrated sulfuric acid according to the mass ratio of lithium, glucose, and concentrated sulfuric acid in the mixed slurry of 1:2:30, and mix evenly in a mortar to obtain the mixed slurry;

[0045] (3) Roasting and pyrolysis: Put the mixed slurry into a crucible, and then put the crucible into a muffle furnace for pyrolysis reaction. The reaction temperature rises from room temperature to 550 °C, the roasting time is 3 h, and the heating rate is 2 °C / min;

[0046] (4) First lithium extraction: Add 105 g of the roasted product to deionized water according to a solid-liquid ratio of 1:4, and perform the first water immersion lithium extraction at a water temperature of 30 °C for 2 h to obtain the first lithium extraction filtrate and the first lithium extraction filter residue;

[0047] (5) Second lithium extraction: Mix 74.1 g of the first lithium extraction filter residue with glycolic acid, add water to dissolve both, and react at 60 °C for 1 h. After filtration and separation, obtain the lithium-containing filtrate and 73 g of filter residue; among them, the addition amount of the acid is 0.2% of the first lithium extraction filter residue.

[0048] Example 4

[0049] The method for extracting lithium from ternary battery black powder in this example includes the following steps:

[0050] (1) Pretreatment: Take 100 g of ternary battery black powder and add it to 300 mL of sodium hydroxide solution with a mass fraction of 10%. Under the condition of a stirring speed of 200 r / min, perform alkali washing for 3 h and then filter; subsequently, wash the filter residue with hot water, wash for 30 min at the same stirring speed, and then filter and dry to obtain the filter residue;

[0051] (2) Mixing: Mix the dried filter residue in step (1) with glucose and concentrated sulfuric acid according to the mass ratio of lithium, glucose, and concentrated sulfuric acid in the mixed slurry of 1:2:30, and mix evenly in a mortar to obtain the mixed slurry;

[0052] (3) Roasting and pyrolysis: Put the mixed slurry into a crucible, and then put the crucible into a muffle furnace for pyrolysis reaction. The reaction temperature rises from room temperature to 550 °C, the roasting time is 2 h, and the heating rate is 2 °C / min;

[0053] (4) First lithium extraction: 110 g of the calcined product was added to deionized water at a solid-liquid ratio of 1:6, and the water immersion was carried out at a water temperature of 30 °C for 1 h for the first time to obtain the filtrate of the first lithium extraction and the residue of the first lithium extraction;

[0054] (5) Second lithium extraction: 74.5 g of the residue of the first lithium extraction was mixed with L-ascorbic acid, and water was added to dissolve them. Then, the reaction was carried out at 60 °C for 1.5 h, and after filtration and separation, a lithium-containing filtrate and 73.5 g of residue were obtained; among them, the addition amount of the acid was 0.4% of the residue of the first lithium extraction.

[0055] Example 5

[0056] The method for extracting lithium from the ternary battery black powder in this example includes the following steps:

[0057] (1) Pretreatment: 100 g of the ternary battery black powder was added to 300 mL of a sodium hydroxide solution with a mass fraction of 10%, and the alkali washing was carried out for 2 h at a stirring speed of 200 r / min and then filtered; subsequently, the filter residue was washed with hot water, and after washing for 1 h at the same stirring speed, it was filtered and dried to obtain the filter residue;

[0058] (2) Mixing: The dried filter residue in step (1) was mixed with glucose and concentrated sulfuric acid in a mass ratio of lithium, glucose, and concentrated sulfuric acid in the mixed slurry of 1:3:30, and the mixture was uniformly mixed in a mortar to obtain the mixed slurry;

[0059] (3) Calcination pyrolysis: The mixed slurry was put into a crucible, and then the crucible was put into a muffle furnace for pyrolysis reaction. The reaction temperature was raised from room temperature to 550 °C, the calcination time was 2 h, and the heating rate was 10 °C / min;

[0060] (4) First lithium extraction: 107 g of the calcined product was added to deionized water at a solid-liquid ratio of 1:5, and the water immersion was carried out at a water temperature of 30 °C for 1 h for the first time to obtain the filtrate of the first lithium extraction and the residue of the first lithium extraction;

[0061] (5) Second lithium extraction: 74.2 g of the residue of the first lithium extraction was mixed with citric acid, and water was added to dissolve them. Then, the reaction was carried out at 60 °C for 2 h, and after filtration and separation, a lithium-containing filtrate and 74.1 g of residue were obtained; among them, the addition amount of the acid was 0.7% of the residue of the first lithium extraction.

[0062] Example 6

[0063] The method for extracting lithium from the ternary battery black powder in this example includes the following steps:

[0064] (1) Pretreatment: Take 100 g of ternary battery black powder and add it to 300 mL of sodium hydroxide solution with a mass fraction of 10%. Under the condition of a stirring speed of 200 r / min, perform alkali washing for 2 h and then filter; subsequently, wash the filter residue with hot water, and under the same stirring speed, wash for 30 min and then filter and dry to obtain the filter residue;

[0065] (2) Mixing: Mix the dried filter residue in step (1) with glucose and concentrated sulfuric acid according to the mass ratio of lithium, glucose, and concentrated sulfuric acid in the mixed slurry of 1:2:30, and mix evenly in a mortar to obtain the mixed slurry;

[0066] (3) Roasting and pyrolysis: Put the mixed slurry into a crucible, and then put the crucible into a muffle furnace for pyrolysis reaction. The reaction temperature rises from room temperature to 550 °C, the roasting time is 2 h, and the heating rate is 7 °C / min;

[0067] (4) First lithium extraction: Add 106 g of the roasted product to deionized water according to a solid-liquid ratio of 1:6, and under the condition of a water temperature of 30 °C, perform water immersion for 2 h for the first water immersion lithium extraction to obtain the first lithium extraction filtrate and the first lithium extraction filter residue;

[0068] (5) Second lithium extraction: Mix 75 g of the first lithium extraction filter residue with glacial acetic acid, add water to dissolve both, and react at 60 °C for 2 h. After filtration and separation, obtain the lithium-containing filtrate and 74.1 g of filter residue; among them, the addition amount of the acid is 0.6% of the first lithium extraction filter residue.

[0069] Comparative Example 1

[0070] This Comparative Example 1 does not perform pretreatment on the ternary battery black powder, and specifically includes the following steps:

[0071] (1) Mixing: Take 100 g of ternary battery black powder and mix it with glucose and sulfuric acid according to the mass ratio of lithium, glucose, and concentrated sulfuric acid in the mixed slurry of 1:2:30, and mix evenly in a mortar to obtain the mixed slurry;

[0072] (2) Roasting and pyrolysis: Put the mixed slurry into a crucible, and then put the crucible into a muffle furnace for pyrolysis reaction. The reaction temperature rises from room temperature to 550 °C, the roasting time is 2 h, and the heating rate is 6 °C / min;

[0073] (3) First lithium extraction: Add 110 g of the roasted product to deionized water according to a solid-liquid ratio of 1:5, and under the condition of a water temperature of 30 °C, perform water immersion for 1 h for the first water immersion lithium extraction to obtain the first lithium extraction filtrate and the first lithium extraction filter residue;

[0074] (4) Secondary lithium extraction: 92 g of the filter residue from the first lithium extraction is mixed with oxalic acid, and water is added to dissolve both. Then, the reaction is carried out at 60 °C for 1 h, and after filtration and separation, a lithium-containing filtrate and 90 g of filter residue are obtained; among them, the addition amount of the acid is 0.7% of the filter residue from the first lithium extraction.

[0075] Comparative Example 2

[0076] This comparative example does not perform secondary lithium extraction and specifically includes the following steps:

[0077] (1) Pretreatment: 100 g of ternary battery black powder is added to 300 mL of a 10% sodium hydroxide solution by mass. Under the condition of a stirring speed of 200 r / min, it is alkali-washed for 2 h and then filtered; subsequently, the filter residue is washed with hot water, and after washing for 30 min at the same stirring speed, it is filtered and dried to obtain the filter residue.

[0078] (2) Mixing: The dried filter residue in step (1) is mixed with glucose and sulfuric acid according to the mass ratio of lithium, glucose, and concentrated sulfuric acid in the mixed slurry of 1:2:30, and uniformly mixed in a mortar to obtain a mixed slurry.

[0079] (3) Roasting and pyrolysis: The mixed slurry is placed in a crucible, and then the crucible is placed in a muffle furnace for pyrolysis reaction. The reaction temperature is raised from room temperature to 550 °C, the roasting time is 2 h, and the heating rate is 5 °C / min.

[0080] (4) Lithium extraction: 104 g of the roasted product is added to deionized water according to a solid-liquid ratio of 1:5, and the water immersion time is 1 h at a water temperature of 30 °C for water immersion lithium extraction to obtain a lithium extraction filtrate and 75 g of filter residue from the first lithium extraction.

[0081] The lithium and metal ion contents extracted in the above Examples 1-6, Comparative Example 1, and Comparative Example 2 were detected, and the obtained results are shown in Table 2 below.

[0082] Table 2 Lithium leaching rate and nickel-cobalt leaching rate of Examples 1-6 and Comparative Examples 1-2

[0083]

[0084] Parallel test 1 - Addition amount of oxalic acid

[0085] For the addition amount of the acid in the secondary acid leaching, this parallel test was set up to verify the indispensability of the reaction conditions. The reaction temperature for the secondary lithium extraction is 60 °C, the reaction time is 1.5 h, and the remaining steps are the same as those in Example 1. The metal ion leaching rate was calculated, and the results are shown in Table 3 below.

[0086] Table 3 Parallel test of the addition amount of the acid

[0087]

[0088] Parallel test 2 - Reaction temperature of the second lithium extraction by acid leaching

[0089] For the reaction temperature of the second acid leaching, this parallel test was set up to verify the indispensability of the reaction conditions. The addition amount of oxalic acid for the second lithium extraction was 0.3% of the filter residue from the first lithium extraction, the reaction time was 1.5 h, and the remaining steps were the same as those in Example 1. The metal ion leaching rates were calculated, and the results are shown in Table 4 below.

[0090] Table 4 Parallel test of the reaction temperature of the second acid leaching

[0091]

[0092] From the data of Examples 1 - 6 and Parallel tests 1 and 2, it can be seen that when the mass of the acid in the second lithium extraction acid is 0.05 - 0.7% of the mass of the filter residue from the first lithium extraction, the lithium extraction efficiency is relatively high, and at the same time, the dissolution of nickel and cobalt can be inhibited; when the acid amount in the second lithium extraction is less than 0.05% of the mass of the filter residue from the first lithium extraction / or the acid leaching temperature is lower than 50 °C, the lithium leaching rate decreases significantly, while the nickel and cobalt leaching rates increase to a certain extent; when the acid amount in the second lithium extraction is higher than 0.7% of the mass of the filter residue from the first lithium extraction or the acid leaching temperature is higher than 70 °C, the nickel and cobalt leaching rates are obvious. It can be seen that only under the conditions of the acid amount, temperature, and reaction time defined in the present invention can the effect of lithium extraction without extracting other metal ions be achieved.

[0093] In addition to the above examples, the lye used in the pretreatment in step (1) of the lithium extraction method for the ternary battery black powder of the present invention is a common lye, preferably sodium hydroxide, which is used to remove impurities in the ternary battery black powder, and its cleaning time can be 0.5 - 3 h.

[0094] In the mixing in step (2), the mass ratio of lithium, carbon source, and concentrated acid in the filter residue weight of the mixed slurry can be 1:(1 - 3):(10 - 30), and the organic carbon used can also be one or more of sucrose, starch, cellulose, polyvinyl alcohol, soluble starch, cellulose, ascorbic acid, or phenolic resin. Pyrolysis is to calcine the mixed slurry at 500 - 750 °C for 1 - 5 h.

[0095] In the first lithium extraction in step (3), the water leaching temperature of the calcined product can be 25 - 90 °C, and the water leaching time can be 0.5 - 4 h. The solid - liquid ratio of the calcined product to water can be 1:(1 - 7).

[0096] That is, by adopting the preparation process of the present invention and the defined parameter range, the technical effects claimed by the present invention can be achieved, and thus no further separate examples will be listed for verification.

Claims

1. A method for extracting lithium from ternary battery black powder, characterized in that, It includes the following steps: (1) Pretreatment: First, fully alkali-wash the ternary black powder, then filter, wash, and dry it to obtain the impurity-removed filter residue. (2) Mixing: Mix the filter residue, organic carbon, and acid solution evenly to obtain a mixed slurry, and pyrolyze the mixed slurry to obtain a calcined product. (3) First lithium extraction: Immerse the calcined product in water and then filter to obtain a first lithium extraction filtrate and a first lithium extraction filter residue. (4) Second lithium extraction: Mix the first lithium extraction filter residue with an acid, add water to dissolve it, and react at 50 - 70 °C for 1 - 2 h. After filtration and separation, a lithium-containing filtrate and a filter residue are obtained; wherein, the addition amount of the acid is 0.05 - 0.7% of the mass of the first lithium extraction filter residue.

2. The lithium extraction method according to claim 1, wherein In step (1), the alkali solution used for alkali washing is sodium hydroxide solution or potassium hydroxide solution, and the alkali washing time is 0.5 - 3 h; the washing time is 0.5 - 1 h.

3. The lithium extraction method according to claim 1, characterized in that, In the mixture in step (2), the mass ratio of lithium, organic carbon, and acid solution in the filter residue is 1:(1 - 3):(10 - 30).

4. The lithium extraction method according to claim 1 or 3, characterized in that, In step (2), the organic carbon is one or more of glucose, sucrose, starch, cellulose, polyvinyl alcohol, soluble starch, cellulose, ascorbic acid, or phenolic resin.

5. The lithium extraction method according to claim 1 or 3, characterized in that, In step (2), the acid solution is one or several of sulfuric acid, hydrochloric acid, and nitric acid.

6. The lithium extraction method according to claim 1, wherein, In step (2), the pyrolysis is to calcine the mixed slurry at 500 - 750 °C for 1 - 5 h.

7. The lithium extraction method according to claim 6, characterized in that, The heating rate of the pyrolysis is 2 - 10 °C / min.

8. The lithium extraction method according to claim 1, wherein In step (3), the water immersion is to dissolve the calcined product in water and react at a water temperature of 25 - 90 °C for 0.5 - 4 h.

9. The lithium extraction method according to claim 8, wherein The solid-liquid ratio of the calcined product to water is 1:(1 - 7).

10. The lithium extraction method according to claim 1, characterized in that, In step (4), the acid used in the second lithium extraction is an organic acid, and the organic acid is oxalic acid, L-ascorbic acid, glycolic acid, citric acid, or glacial acetic acid.

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