A method for preparing lithium carbonate by agglomerating and roasting lepidolite

Abstract

This invention provides a method for preparing lithium carbonate by calcining lepidolite agglomerates, relating to the field of lithium carbonate preparation technology from lepidolite. The method includes mixing, agglomeration, calcination, crushing, leaching, filtration and concentration, and impurity removal and lithium precipitation processes, resulting in high lithium-ion leaching rates and high lithium carbonate purity. This invention, by using sulfur to pelletize and calcine lepidolite, not only saves energy but also improves the lithium-ion conversion rate and leaching rate, and yields high-purity lithium carbonate, aligning with the development strategy of green manufacturing.

Description

Technical Field

[0001] This invention relates to the field of lithium carbonate preparation technology from lepidolite, and more particularly to a method for preparing lithium carbonate by calcining lepidolite agglomeration. Background Technology

[0002] With increasing global pressure to reduce carbon emissions, lithium batteries, as a crucial carbon reduction technology, have experienced rapid development. Driven by the growth of the new energy vehicle industry, my country's lithium consumption has maintained a high growth rate in recent years. Currently, my country is the world's largest consumer of lithium, producer of downstream materials, and producer of batteries. Related industries are in the early stages of accelerated growth and face significant strategic opportunities to participate in international competition within the lithium battery industry chain.

[0003] Yichun City, Jiangxi Province, is leveraging its abundant lepidolite resources to vigorously develop lithium battery-related industries. Currently, the main methods for producing lithium carbonate from lepidolite are the salt method or acid salt method roasting-leaching process. The roasting methods primarily employ rotary kilns for bulk materials and tunnel kilns for pressing bricks. Producing one ton of lithium carbonate requires approximately 4,000 cubic meters of natural gas. Bulk rotary kiln roasting is prone to kiln caking, while the clinker after tunnel kiln roasting requires crushing and grinding, a process that consumes a significant amount of electricity.

[0004] Therefore, there is an urgent need to develop a method for preparing lithium carbonate from lepidolite by roasting, which can effectively reduce natural gas consumption and make the roasted clinker easy to crush. The industrial application of this method not only conforms to my country's green manufacturing development strategy, but also ensures the sustainable production of lithium from lepidolite. Summary of the Invention

[0005] Based on the technical problems existing in the background technology, the present invention proposes a method for preparing lithium carbonate by calcination of lithium mica agglomerates.

[0006] The present invention proposes a method for preparing lithium carbonate by calcination of lepidolite agglomerates, comprising the following steps:

[0007] S1. Mixing: Mix lepidolite, sodium sulfate, calcium hydroxide and water evenly to obtain a mixture.

[0008] S2, pelletizing: The mixture of raw materials and sulfur is mixed and pelletized to obtain green pellets;

[0009] S3. Calcination: The green pellets are transferred to a fluidized bed for calcination to obtain clinker, which is then cooled in a cooling kiln to obtain cooled clinker.

[0010] S4. Crushing: The cooled clinker is crushed to obtain crushed clinker;

[0011] S5. Leaching: Mix the crushed clinker with water to obtain a slurry, and leach at room temperature for 40-60 minutes.

[0012] S6. Filtration and Concentration: After filtering the slurry, filtrate A is obtained. Calcium hydroxide and sodium carbonate are added to filtrate A to adjust the pH. After standing and settling, filtrate B is obtained. Filtrate B is passed through a cation exchange resin to obtain a purified liquid. The purified liquid is then concentrated by evaporation to obtain a concentrated purified liquid.

[0013] S7. Lithium precipitation and impurity removal: After mixing the concentrated purified liquid with the saturated sodium carbonate solution evenly, let it stand to precipitate and filter. The resulting liquid is the lithium precipitation mother liquor and the solid is lithium carbonate.

[0014] The method for preparing lithium carbonate by calcination of lepidolite proposed in this invention can be referred to Figure 1 The process flow diagram shown is shown.

[0015] Preferably, in S1, the mass ratio of lepidolite, sodium sulfate, calcium hydroxide, and water is 100:(15-25):(20-30):(8-10).

[0016] Preferably, in S1, the lepidolite has a particle size of less than 104 μm and a water content of no more than 10%.

[0017] Preferably, in S2, the mass ratio of the mixture to sulfur is 100:(25-35); the diameter of the green pellets is (0.1-5) mm.

[0018] Preferably, in step S3, before the green pellets are transferred to the fluidized bed for calcination, the green pellets are dried at 100-110°C for 2-5 minutes.

[0019] Preferably, in step S3, the roasting process specifically involves: introducing natural gas into the fluidized bed to raise the temperature in the fluidized bed to 870–950°C, stopping the introduction of natural gas, switching to air, and roasting the green pellets in the fluidized bed.

[0020] Preferably, in S3, the pressure difference between the upper and lower parts of the fluidized bed is 4.5 to 12 kPa.

[0021] More preferably, in S3, the pressure difference between the upper and lower parts of the fluidized bed is 4.5 to 5 kPa.

[0022] Preferably, in step S4, 80 wt% of the crushed clinker has a particle size of less than 106-150 μm.

[0023] Preferably, in step S5, the mass ratio of crushed clinker to water is 1:1.

[0024] Preferably, in step S6, the mass ratio of calcium hydroxide to sodium carbonate is 1:(10-15), so that the pH of the solution is not less than 11.

[0025] Preferably, in step S6, the lithium oxide content in the concentrated purified liquid is not less than 20 g / L.

[0026] Preferably, in step S7, the mass ratio of the concentrated purified liquid to the saturated sodium carbonate solution is 1:3.

[0027] Preferably, in step S7, the lithium precipitation mother liquor, after neutralization, filtration, and evaporation processes, yields sodium sulfate which can be returned to step S1 for reuse.

[0028] In this invention, a schematic diagram of the fluidized bed used for green pellet roasting is shown below. Figure 2 As shown, by controlling the size of the green pellets and the pressure difference between the upper and lower parts of the fluidized bed, the green pellets exhibit the following states in the fluidized bed: a descending state in region 1, a suspended state in region 2, and a boiling state in region 3. The gases generated during the roasting process can be desulfurized, defluorinated, and denitrified by a tail gas absorption device, meeting the emission standards.

[0029] The beneficial effects of this invention are as follows:

[0030] (1) This invention uses a mixing-agglomeration-roasting-leaching-filtration-concentration-impurity removal and lithium precipitation process to prepare lithium carbonate from lepidolite. The process route is reasonably designed, and the production of lithium carbonate has the characteristics of low energy consumption and low processing cost. The roasting method of this invention avoids the problems of severe equipment corrosion and large equipment investment caused by the sulfuric acid process, and also alleviates the problems of large natural gas consumption and difficult crushing required for rotary kiln roasting and brick pressing tunnel kiln roasting.

[0031] (2) This invention uses a mixture of lepidolite, auxiliary salts (sodium sulfate, calcium hydroxide), and water, mixed with sulfur to form green pellets. By controlling the size of the green pellets and the pressure difference between the upper and lower parts of the fluidized bed, the green pellets are roasted in the fluidized bed. When the temperature in the fluidized bed reaches 870-950°C, the natural gas supply is stopped. Sulfur, acting as fuel, undergoes an exothermic reaction, allowing the temperature in the fluidized bed to be maintained at 870-950°C for continued roasting without the need for continuous natural gas supply. Furthermore, since the reaction between sulfur and lepidolite in the pellets is a solid-solid reaction, the heat generated by the sulfur directly fuels the reaction of the lepidolite. Therefore, compared to tunnel kiln and rotary kiln roasting methods, this roasting method saves 10-20 cubic meters of natural gas per ton of clinker produced. In addition, because sulfur is converted into gas during roasting, the pellets develop a loose and porous structure. This structure not only facilitates the uniform distribution of roasting heat but also facilitates the crushing of the clinker at the downstream end, saving energy required for crushing. Therefore, the introduction of sulfur in this invention can save energy and is in line with my country's green manufacturing development strategy.

[0032] (3) No additional sulfuric acid is needed during the leaching process. The residual oxidation products of sulfur in the pellets during the roasting process make the leachate weakly acidic (pH 4.5-6), which helps to leach lithium ions from lepidolite and improve the leaching rate. Attached Figure Description

[0033] Figure 1 This is a schematic diagram of the process flow for preparing lithium carbonate by calcining lepidolite agglomerates, as proposed in this invention.

[0034] Figure 2 This is a schematic diagram of the fluidized bed used in the roasting of green pellets according to the present invention;

[0035] Figure 2 In the diagram, 1 represents the feed inlet, 2 represents the exhaust outlet, 3 represents the fluidized bed body, 4 represents the first zone, 5 represents the second zone, 6 represents the third zone, 7 represents the bellows, and 8 represents the air / natural gas inlet. Detailed Implementation

[0036] The technical solution of the present invention will be described in detail through specific embodiments.

[0037] In the following examples and comparative examples, the specific information regarding the raw materials used is as follows:

[0038] Cation exchange resin: Manufacturer: Lanxiao, Brand: series;

[0039] Sulfur: Manufacturer: Shanghai Testing, Grade: Chemically Pure.

[0040] Example 1

[0041] The chemical composition of the lepidolite used in this embodiment is shown in Table 1.

[0042] Table 1 Chemical composition of lepidolite in Example 1

[0043] Testing items <![CDATA[Li2O(%)]]> <![CDATA[Rb2O(%)]]> <![CDATA[Cs2O(%)]]> F(％) <![CDATA[K2O(%)]]> <![CDATA[Na2O(%)]]> <![CDATA[SiO2(%)]]> Detection value 2.53 0.92 0.14 3.59 9.20 1.12 50.50

[0044] A method for preparing lithium carbonate by calcination of lepidolite agglomerates includes the following steps:

[0045] S1. Mixing: Lithium mica, sodium sulfate, calcium hydroxide and water are mixed evenly in a mass ratio of 100:15:22:8 to obtain a mixture, wherein the particle size of lithium mica is less than 45μm.

[0046] S2. Agglomeration: Mix the mixture and sulfur at a mass ratio of 100:30 and agglomerate them. Roll the mixture in the agglomeration machine until the diameter of the green pellets is 2mm.

[0047] S3. Calcination: The green pellets are transported to the dryer via a bucket elevator and dried at 100°C for 2 minutes. The heat required for drying is provided by the heat from the cooling kiln through a heat exchanger. The dried green pellets are then transported to the fluidized bed feed inlet via the bucket elevator. Natural gas is introduced into the fluidized bed to raise the temperature to 870°C. The natural gas supply is then stopped, and air is introduced instead, creating a pressure difference of 4.5 kPa between the top and bottom of the fluidized bed. The green pellets are then calcined in the fluidized bed for 22 minutes, and the clinker is produced from the bottom side of the fluidized bed. The clinker enters from the top of the cooling kiln and is thoroughly mixed with the rising air. The clinker is produced from the bottom of the cooling kiln, while the hot air flows out from the top of the cooling kiln, providing the heat required for drying. The clinker contains 1.59% soluble lithium and 1.72% total lithium, i.e., a conversion rate of 93%.

[0048] S4. Crushing: The cooled clinker is crushed to obtain crushed clinker, and the particle size of the crushed clinker is less than 106μm, accounting for 80wt%.

[0049] S5. Leaching: The crushed clinker and water are mixed evenly at a mass ratio of 1:1 to obtain a slurry, and the leaching reaction is carried out at room temperature for 50 minutes; the lithium ion leaching rate is 98%.

[0050] S6. Filtration and Concentration: After filtering the slurry, filtrate A is obtained. Calcium hydroxide and sodium carbonate with a mass ratio of 1:11 are added to filtrate A to adjust the pH to 11. After standing and settling, filtrate B is obtained. Filtrate B is passed through a cation exchange resin to remove divalent metal ions to obtain a purified solution. The purified solution is then concentrated by evaporation to obtain a concentrated purified solution. The concentrated purified solution contains 22.0 g / L of lithium oxide.

[0051] S7. Lithium precipitation and impurity removal: After the concentrated purified liquid is mixed evenly with the saturated sodium carbonate solution, it is allowed to stand and precipitate, and then filtered. The resulting liquid is the lithium precipitation mother liquor, and the solid is lithium carbonate. The lithium precipitation mother liquor is neutralized, filtered, and evaporated to obtain sodium sulfate, which can be returned to S1 for reuse. The purity of the obtained lithium carbonate is 98.6%.

[0052] Example 2

[0053] The chemical composition of the lepidolite used in this embodiment is shown in Table 2.

[0054] Table 2 Chemical composition of lepidolite in Example 2

[0055] Testing items <![CDATA[Li2O(%)]]> <![CDATA[Rb2O(%)]]> <![CDATA[Cs2O(%)]]> F(％) <![CDATA[K2O(%)]]> <![CDATA[Na2O(%)]]> <![CDATA[SiO2(%)]]> Detection value 1.53 - - 2.21 6.03 2.88 60.11

[0056] A method for preparing lithium carbonate by calcination of lepidolite agglomerates includes the following steps:

[0057] S1. Mixing: Lithium mica, sodium sulfate, calcium hydroxide and water are mixed evenly in a mass ratio of 100:25:22:8 to obtain a mixture, wherein the particle size of lithium mica is less than 45μm.

[0058] S2. Agglomeration: Mix the raw materials and sulfur at a mass ratio of 100:25 and agglomerate them. Roll the mixture in the agglomeration machine until the diameter of the green pellets is 0.9 mm.

[0059] S3. Calcination: The green pellets are transported to the dryer via a bucket elevator and dried at 100°C for 2 minutes. The heat required for drying is provided by the heat from the cooling kiln through a heat exchanger. The dried green pellets are then transported to the fluidized bed feed inlet via the bucket elevator. Natural gas is introduced into the fluidized bed to raise the temperature to 900°C. The natural gas supply is then stopped, and air is introduced instead, creating a pressure difference of 4.5 kPa between the top and bottom of the fluidized bed. The green pellets are then calcined in the fluidized bed for 22 minutes, and the clinker is produced from the bottom side of the fluidized bed. The clinker enters from the top of the cooling kiln and is thoroughly mixed with the rising air. The clinker is produced from the bottom of the cooling kiln, while the hot air flows out from the top of the cooling kiln, providing the heat required for drying. The clinker contains 0.93% soluble lithium and 1.03% total lithium, i.e., a conversion rate of 90.3%.

[0060] S4. Crushing: The cooled clinker is crushed to obtain crushed clinker, and the particle size of the crushed clinker is less than 106μm, accounting for 80wt%.

[0061] S5. Leaching: The crushed clinker and water are mixed evenly at a mass ratio of 1:1 to obtain a slurry, and the leaching reaction is carried out at room temperature for 60 minutes; the lithium ion leaching rate is 97%.

[0062] S6. Filtration and Concentration: After filtering the slurry, filtrate A is obtained. Calcium hydroxide and sodium carbonate with a mass ratio of 1:15 are added to filtrate A to adjust the pH to 11. After standing and settling, filtrate B is obtained. Filtrate B is passed through a cation exchange resin to remove divalent metal ions to obtain a purified solution. The purified solution is then concentrated by evaporation to obtain a concentrated purified solution. The concentrated purified solution contains 18.7 g / L of lithium oxide.

[0063] S7. Lithium precipitation and impurity removal: After the concentrated purified liquid is mixed evenly with the saturated sodium carbonate solution, it is allowed to stand and precipitate, and then filtered. The resulting liquid is the lithium precipitation mother liquor, and the solid is lithium carbonate. The lithium precipitation mother liquor is neutralized, filtered, and evaporated to obtain sodium sulfate, which can be returned to S1 for reuse. The purity of the obtained lithium carbonate is 98.5%.

[0064] Example 3

[0065] The chemical composition of the lepidolite used in this embodiment is shown in Table 3.

[0066] Table 3 Chemical composition of lepidolite in Example 3

[0067] Testing items <![CDATA[Li2O(%)]]> <![CDATA[Rb2O(%)]]> <![CDATA[Cs2O(%)]]> F(％) <![CDATA[K2O(%)]]> <![CDATA[Na2O(%)]]> <![CDATA[SiO2(%)]]> Detection value 2.01 0.63 - 5.67 8.20 3.19 53.68

[0068] A method for preparing lithium carbonate by calcination of lepidolite agglomerates includes the following steps:

[0069] S1. Mixing: Lithium mica, sodium sulfate, calcium hydroxide and water are mixed evenly in a mass ratio of 100:25:20:8 to obtain a mixture, wherein the particle size of lithium mica is less than 45μm.

[0070] S2. Agglomeration: Mix the mixture and sulfur at a mass ratio of 100:35 and agglomerate them. Roll the mixture in the agglomeration machine until the diameter of the green pellets is 5mm.

[0071] S3. Calcination: The green pellets are transported to the dryer via a bucket elevator and dried at 100°C for 2 minutes. The heat required for drying is provided by the heat from the cooling kiln through a heat exchanger. The dried green pellets are then transported to the fluidized bed feed inlet via the bucket elevator. Natural gas is introduced into the fluidized bed to raise the temperature to 950°C. The natural gas supply is then stopped, and air is introduced instead, creating a pressure difference of 5 kPa between the top and bottom of the fluidized bed. The green pellets are then calcined in the fluidized bed for 30 minutes, and the clinker is produced from the bottom side of the fluidized bed. The clinker enters from the top of the cooling kiln and is thoroughly mixed with the rising air. The clinker is produced from the bottom of the cooling kiln, while the hot air flows out from the top of the cooling kiln, providing the heat required for drying. The clinker contains 1.25% soluble lithium and 1.36% total lithium, i.e., a conversion rate of 92%.

[0072] S4. Crushing: The cooled clinker is crushed to obtain crushed clinker, and the particle size of the crushed clinker is less than 106μm, accounting for 80wt%.

[0073] S5. Leaching: The crushed clinker and water are mixed evenly at a mass ratio of 1:1 to obtain a slurry, and the leaching reaction is carried out at room temperature for 60 minutes; the lithium ion leaching rate is 97%.

[0074] S6. Filtration and Concentration: After filtering the slurry, filtrate A is obtained. Calcium hydroxide and sodium carbonate with a mass ratio of 1:10 are added to filtrate A to adjust the pH to 11. After standing and settling, filtrate B is obtained. Filtrate B is passed through a cation exchange resin to remove divalent metal ions to obtain a purified solution. The purified solution is then concentrated by evaporation to obtain a concentrated purified solution. The concentrated purified solution contains 23.4 g / L of lithium oxide.

[0075] S7. Lithium precipitation and impurity removal: After the concentrated purified liquid is mixed evenly with the saturated sodium carbonate solution, it is allowed to stand and precipitate, and then filtered. The resulting liquid is the lithium precipitation mother liquor, and the solid is lithium carbonate. The lithium precipitation mother liquor is neutralized, filtered, and evaporated to obtain sodium sulfate, which can be returned to S1 for reuse. The purity of the obtained lithium carbonate is 98.3%.

[0076] Comparative Example 1

[0077] The difference between Comparative Example 1 and Example 1 is that sulfur was not added to form aggregates. The chemical composition of the lepidolite used in Comparative Example 1 is shown in Table 1.

[0078] A method for preparing lithium carbonate by calcination of lepidolite agglomerates includes the following steps:

[0079] S1. Mixing: Lithium mica, sodium sulfate, calcium hydroxide and water are mixed evenly in a mass ratio of 100:15:22:8 to obtain a mixture, wherein the particle size of lithium mica is less than 45μm.

[0080] S2. Agglomeration: The mixture is directly agglomerated and rolled in the agglomeration machine until the diameter of the green pellets is 2mm;

[0081] S3. Calcination: The green pellets are transported to the dryer via a bucket elevator and dried at 100°C for 2 minutes. The heat required for drying is provided by the heat from the cooling kiln through a heat exchanger. The dried green pellets are then transported to the fluidized bed feed inlet via the bucket elevator. Natural gas is introduced into the fluidized bed to raise the temperature to 870°C. The natural gas supply is then stopped, and air is introduced instead, creating a pressure difference of 4.5 kPa between the top and bottom of the fluidized bed. The green pellets are then calcined in the fluidized bed for 22 minutes, and the clinker is produced from the bottom side of the fluidized bed. The clinker enters from the top of the cooling kiln and is thoroughly mixed with the rising air. The clinker is produced from the bottom of the cooling kiln, while the hot air flows out from the top of the cooling kiln, providing the heat required for drying. The clinker contains 1.53% soluble lithium and 1.70% total lithium, i.e., a conversion rate of 90%.

[0082] S4. Crushing: The cooled clinker is crushed to obtain crushed clinker, and the particle size of the crushed clinker is less than 106μm, accounting for 80wt%.

[0083] S5. Leaching: The crushed clinker and water are mixed evenly at a mass ratio of 1:1 to obtain a slurry, and the leaching reaction is carried out at room temperature for 50 minutes; the lithium ion leaching rate is 95%.

[0084] S6. Filtration and Concentration: After filtering the slurry, filtrate A is obtained. Calcium hydroxide and sodium carbonate with a mass ratio of 1:11 are added to filtrate A to adjust the pH to 11. After standing and settling, filtrate B is obtained. Filtrate B is passed through a cation exchange resin to remove divalent metal ions to obtain a purified solution. The purified solution is then concentrated by evaporation to obtain a concentrated purified solution. The concentrated purified solution contains 19.5 g / L of lithium oxide.

[0085] S7. Lithium precipitation and impurity removal: After the concentrated purified liquid is mixed evenly with the saturated sodium carbonate solution, it is allowed to stand and precipitate, and then filtered. The resulting liquid is the lithium precipitation mother liquor, and the solid is lithium carbonate. The lithium precipitation mother liquor is neutralized, filtered, and evaporated to obtain sodium sulfate, which can be returned to S1 for reuse. The purity of the obtained lithium carbonate is 98.5%.

[0086] As can be seen from Examples 1-3, the method for preparing lithium carbonate by calcination of lepidolite provided by the present invention has a high lithium-ion leaching rate and high lithium carbonate purity. As can be seen from Example 1 and Comparative Example 1, the addition of sulfur has virtually no effect on the conversion rate, but the lithium-ion leaching rate is 3% higher with sulfur added than without. Furthermore, sulfur can partially replace natural gas, saving approximately 13 m³ of natural gas. 3 / ton of clinker.

[0087] In summary, the method for preparing lithium carbonate by calcining lepidolite using sulfur and lepidolite pellets not only saves energy but also improves the lithium ion leaching rate and yields high-purity lithium carbonate, which aligns with the development strategy of green manufacturing.

[0088] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A method for preparing lithium carbonate by calcination of lepidolite agglomerates, characterized in that, Includes the following steps: S1. Mixing: Lithium mica, sodium sulfate, calcium hydroxide, and water are mixed evenly to obtain a mixture; the mass ratio of lepidolite, sodium sulfate, calcium hydroxide, and water is 100:(15~25):(20~30):(8~10); wherein, the particle size of lepidolite is less than 104μm and the water content does not exceed 10%; S2. Pelletizing: The mixture and sulfur are mixed and pelletized to obtain green pellets; the diameter of the green pellets is 0.1~5mm; the mass ratio of the mixture and sulfur is 100:(25~35); S3. Calcination: The green pellets are transferred to a fluidized bed for calcination to obtain clinker, which is then cooled in a cooling kiln to obtain cooled clinker. The specific steps of the calcination process are as follows: natural gas is introduced into the fluidized bed to raise the temperature in the fluidized bed to 870~950℃, the natural gas is stopped and replaced with air, and the green pellets are calcined in the fluidized bed. The pressure difference between the upper and lower gas levels in the fluidized bed is 4.5~12KPa. S4. Crushing: The cooled clinker is crushed to obtain crushed clinker; S5. Leaching: Mix the crushed clinker with water to obtain a slurry, and leach at room temperature for 40-60 minutes. S6. Filtration and Concentration: After filtering the slurry, filtrate A is obtained. Calcium hydroxide and sodium carbonate are added to filtrate A to adjust the pH. After standing and settling, filtrate B is obtained. Filtrate B is passed through a cation exchange resin to obtain a purified liquid. The purified liquid is then concentrated by evaporation to obtain a concentrated purified liquid. S7. Lithium precipitation and impurity removal: After mixing the concentrated purified liquid with the saturated sodium carbonate solution evenly, let it stand to precipitate and filter. The resulting liquid is the lithium precipitation mother liquor and the solid is lithium carbonate.

2. The method for preparing lithium carbonate by calcination of lepidolite according to claim 1, characterized in that, In S4, 80 wt% of the crushed clinker has a particle size of less than 106 μm.

3. The method for preparing lithium carbonate by calcination of lepidolite according to claim 1, characterized in that, In S5, the mass ratio of crushed clinker to water is 1:

1.

4. The method for preparing lithium carbonate by calcination of lepidolite according to claim 1, characterized in that, In S6, the lithium oxide content in the concentrated purified liquid is not less than 20 g / L.

5. The method for preparing lithium carbonate by calcination of lepidolite according to claim 1, characterized in that, In S7, the mass ratio of the concentrated purified liquid to the saturated sodium carbonate solution is 1:3.

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