A method for preparing lithium carbonate by roasting lepidolite

Abstract

The present invention discloses a method for preparing lithium carbonate by roasting lepidolite. The method uses a roasting-leaching process to prepare lithium carbonate from lepidolite. The sodium sulfate-containing waste liquid generated during the preparation process is treated by bipolar membrane electrodialysis to convert it into dilute sulfuric acid and sodium hydroxide solution. The dilute sulfuric acid is then converted into calcium sulfate and sodium hydroxide into sodium carbonate, respectively, which are recycled as auxiliary materials in the process for preparing lithium carbonate from lepidolite. The present invention has a high conversion rate of sodium sulfate, a byproduct of lithium extraction from lepidolite, which not only solves the environmental problems caused by sodium sulfate and reduces adverse environmental impacts, but also ensures the sustainability of lithium carbonate production and reduces the cost of pharmaceuticals in the production process, in line with the development strategy of green manufacturing.

Description

Technical Field

[0001] The invention relates to the technical field of preparing lithium carbonate from lepidolite, and in particular to a method for preparing lithium carbonate by calcining lepidolite. Background Art

[0002] Yichun City, Jiangxi Province, is leveraging its abundant lepidolite resources to vigorously develop its lithium-ion battery industry. According to incomplete statistics, Yichun's production of lepidolite concentrate and lithium carbonate reached approximately 2.7 million tons and 133,000 tons, respectively, in 2022. By 2025, these figures are projected to reach 7 million tons and over 500,000 tons, respectively.

[0003] At present, the preparation of lithium carbonate from lepidolite mainly adopts the salt method or acid salt method roasting-leaching process. Every ton of lithium carbonate produced produces about 10 tons of alum (mainly sodium sulfate), of which about 70% can be recycled as auxiliary materials and 30% needs to be sold outside.

[0004] In 2022, there were approximately 20 sodium sulfate manufacturers nationwide, with a production capacity exceeding 10 million tons. There were also over 50 by-product sodium sulfate manufacturers, producing approximately 3 million tons, with supply and demand generally balanced (China Sodium Sulfate Industry Research and Investment Strategy Report, 2022). Based on Yichun's lithium carbonate production of 133,000 tons in 2022, a total of 400,000 tons of sodium sulfate would need to be sold externally; by 2025, it is estimated that Yichun will need to sell 1.5 million tons of sodium sulfate externally. This means that by 2025, sodium sulfate sold externally from lepidolite smelting in Yichun will account for half of the total national by-product sodium sulfate in 2022. The concentrated production of large quantities of sodium sulfate in a single location can lead to an oversupply in that region, resulting in a price drop (currently around 300 yuan / ton). Failure to sell sodium sulfate in a timely manner can lead to inventory stagnation at lepidolite smelters, disrupting lithium carbonate production and causing a series of environmental problems. Therefore, it is urgent to develop a process that can convert sodium sulfate (sodium sulfate) into high-value-added products or can be directly used for lithium extraction from lepidolite. The industrial application of the process is in line with my country's green manufacturing development strategy and also ensures the sustainable production of lithium extraction 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 roasting lepidolite.

[0006] The present invention provides a method for preparing lithium carbonate by calcining lepidolite, comprising the following steps:

[0007] S1, lepidolite, sodium sulfate, calcium sulfate are mixed, dried and then high-temperature roasted, and clinker is obtained after cooling; the clinker is crushed, ground and water-soaked to obtain slurry; the slurry is filtered to obtain filtrate A; appropriate amount of caustic soda and soda ash are added to the filtrate A to fully react and generate a precipitate, and filtrate is obtained to obtain filtrate B; the filtrate B is subjected to ion exchange to remove divalent metal ions to obtain a purified liquid; the purified liquid is saturated with sodium carbonate to sink lithium, and after sinking lithium, it is filtered to obtain lithium carbonate precipitation and sinking lithium mother liquor;

[0008] S2, first add sulfuric acid to the lithium mother liquor to fully react and neutralize carbonate ions, then adjust the pH to 8-10, and then filter through a precision filter to purify the obtained filtrate to meet the design requirements for entering bipolar membrane electrodialysis;

[0009] S3, subjecting the filtrate obtained in S2 to bipolar membrane electrodialysis to obtain a sodium hydroxide solution and a dilute sulfuric acid solution;

[0010] S4, CO2 gas is introduced into the sodium hydroxide solution to obtain a sodium carbonate solution, which is then concentrated to obtain a saturated sodium carbonate solution, which is returned to the lithium sinking step in S1 for recycling;

[0011] S5. Add calcium oxide or calcium carbonate to the dilute sulfuric acid solution, filter and dry the solution after sufficient reaction to obtain calcium sulfate, which is then returned to the roasting step in S1 for recycling.

[0012] The method for preparing lithium carbonate by calcining lepidolite proposed in the present invention can refer to Figure 1 Schematic diagram of the process flow shown.

[0013] Preferably, in S1, the mass ratio of lepidolite, sodium sulfate and calcium sulfate is 100:(15-25):(25-35).

[0014] Preferably, in S1, the high temperature calcination temperature is 850-1000° C. and the time is 50-80 min.

[0015] Preferably, in S1, the volume ratio of the purified liquid to the saturated sodium carbonate solution is 1:(2.5-3.5).

[0016] Preferably, in S2, the design requirements for entering bipolar membrane electrodialysis are as follows: TSS content is less than 0.1 mg / L; the sum of divalent and multivalent cation contents is less than 0.3 mg / L; SiO2 content is less than 40 mg / L; there is no acetone, tetrahydrofuran, dichloromethane, or toluene; and phenol content is less than 1 mg / L.

[0017] Preferably, in S3, the operating parameters of the bipolar membrane electrodialysis include: a current density of 1 mA / cm 2 ~20mA / cm 2, voltage is 1.7V~2.0V, and processing time is 60min~200min.

[0018] In the present invention, bipolar membrane electrodialysis treatment can be carried out by Figure 2 The bipolar membrane electrodialysis device shown in the figure consists of a positive electrode, a BP membrane, an A membrane, a C membrane, a BP membrane, and a negative electrode, arranged in this order. The BP membrane represents the bipolar membrane, which is composed of a composite of an anion exchange membrane and a cation exchange membrane; the A membrane represents the anion exchange membrane; the C membrane represents the cation exchange membrane; the compartment between the A membrane and the BP membrane near the positive electrode is the acid compartment; the compartment between the A membrane and the C membrane is the salt compartment; and the compartment between the C membrane and the BP membrane near the negative electrode is the base compartment. When using this device for bipolar membrane electrodialysis, the filtrate obtained from S2 (primarily containing sodium sulfate) is fed into the salt compartment. Under the action of a DC electric field, sulfate ions migrate through the A membrane to the acid compartment, where they combine with hydrogen ions generated on the anode side of the bipolar membrane to form sulfuric acid. Sodium ions migrate through the C membrane to the base compartment, where they combine with hydroxide ions generated on the cathode side of the bipolar membrane to form sodium hydroxide. Finally, dilute sulfuric acid solution and sodium hydroxide solution are discharged from the acid compartment and base compartment, respectively.

[0019] The beneficial effects of the present invention are as follows:

[0020] The present invention uses a roasting-leaching process to prepare lithium carbonate from lepidolite, and treats the sodium sulfate-containing waste liquid generated during the preparation process by bipolar membrane electrodialysis to convert it into dilute sulfuric acid and sodium hydroxide solution. The dilute sulfuric acid is then converted into calcium sulfate and the sodium hydroxide into sodium carbonate, respectively, for recycling as auxiliary materials in the process of preparing lithium carbonate from lepidolite. The present invention converts sodium sulfate, a byproduct generated by lithium extraction from lepidolite, into an auxiliary material that can be directly used for lithium extraction from lepidolite and reuses it in the production of lithium carbonate from lepidolite. The conversion and utilization rate of sodium sulfate, a byproduct of lithium extraction from lepidolite, is high, thereby solving the environmental problems caused by sodium sulfate and reducing adverse environmental impacts. It also ensures the sustainability of lithium carbonate production and reduces the cost of reagents in the production process, thus complying with the development strategy of green manufacturing. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 The figure is a schematic diagram of the process flow of the method for preparing lithium carbonate by roasting lepidolite proposed in the present invention.

[0022] Figure 2 The figure is a schematic diagram of the working principle of preparing dilute sulfuric acid and sodium hydroxide solution by bipolar membrane electrodialysis of sodium sulfate solution in the present invention. DETAILED DESCRIPTION

[0023] The technical solution of the present invention is described in detail below through specific embodiments.

[0024] Example 1

[0025] A method for preparing lithium carbonate by roasting lepidolite, characterized in that it comprises the following steps:

[0026] S1. Mixing lepidolite, sodium sulfate and calcium sulfate in a mass ratio of 100:20:30, drying and high-temperature roasting at 900°C for 60 min, and cooling to obtain clinker; crushing, grinding and soaking the clinker to obtain slurry; filtering the slurry to obtain filtrate A; adding appropriate amounts of caustic soda and soda ash to the filtrate A to fully react to generate a precipitate, and filtering to obtain filtrate B; subjecting the filtrate B to ion exchange to remove divalent metal ions and obtain a purified liquid; mixing the purified liquid with a saturated sodium carbonate solution in a volume ratio of 1:3 to precipitate lithium, filtering after the lithium precipitation is completed to obtain lithium carbonate precipitate and lithium precipitation mother liquor;

[0027] S2, first add sulfuric acid to the lithium precipitation mother liquor to fully react and neutralize carbonate ions, then adjust the pH to 8-10, and then filter through a precision filter with a pore size of 2 μm, and purify the obtained filtrate through a sodium cation exchange resin with a resin diameter of 0.8-1.0 mm to meet the design requirements for entering bipolar membrane electrodialysis: TSS content is less than 0.1 mg / L; the sum of divalent and multivalent cation content is less than 0.3 mg / L; SiO2 content is less than 40 mg / L; no acetone, tetrahydrofuran, dichloromethane, toluene; phenol content is less than 1 mg / L;

[0028] S3, the filtrate obtained in S2 is subjected to bipolar membrane electrodialysis to obtain sodium hydroxide solution and dilute sulfuric acid solution; wherein the current density of the bipolar membrane electrodialysis treatment is 10mA / cm 2 , voltage is 1.8V, and processing time is 100min;

[0029] S4, CO2 gas is introduced into the sodium hydroxide solution to obtain a sodium carbonate solution, which is then concentrated to obtain a saturated sodium carbonate solution, which is returned to the lithium sinking step in S1 for recycling;

[0030] S5. Add calcium oxide or calcium carbonate to the dilute sulfuric acid solution, filter and dry the solution after sufficient reaction to obtain calcium sulfate, which is then returned to the roasting step in S1 for recycling.

[0031] Example 2

[0032] A method for preparing lithium carbonate by roasting lepidolite, characterized in that it comprises the following steps:

[0033] S1. Mixing lepidolite, sodium sulfate and calcium sulfate in a mass ratio of 100:15:25, drying and high-temperature roasting, the roasting temperature is 850°C, the roasting time is 80min, and cooling to obtain clinker; crushing, grinding and soaking the clinker to obtain slurry; filtering the slurry to obtain filtrate A; adding appropriate amounts of caustic soda and soda ash to the filtrate A to fully react to generate a precipitate, and filtering to obtain filtrate B; subjecting the filtrate B to ion exchange to remove divalent metal ions to obtain a purified liquid; mixing the purified liquid with a saturated sodium carbonate solution in a volume ratio of 1:2.5 to precipitate lithium, filtering after the lithium precipitation is completed to obtain lithium carbonate precipitate and lithium precipitation mother liquor;

[0034] S2, first add sulfuric acid to the lithium precipitation mother liquor to fully react and neutralize carbonate ions, then adjust the pH to 8-10, and then filter through a precision filter with a pore size of 2 μm, and purify the obtained filtrate through a sodium cation exchange resin with a resin diameter of 0.8-1.0 mm to meet the design requirements for entering bipolar membrane electrodialysis: TSS content is less than 0.1 mg / L; the sum of divalent and multivalent cation content is less than 0.3 mg / L; SiO2 content is less than 40 mg / L; no acetone, tetrahydrofuran, dichloromethane, toluene; phenol content is less than 1 mg / L;

[0035] S3, the filtrate obtained in S2 is subjected to bipolar membrane electrodialysis to obtain sodium hydroxide solution and dilute sulfuric acid solution; wherein the current density of the bipolar membrane electrodialysis treatment is 5mA / cm 2 , voltage is 1.7V, and processing time is 200min;

[0036] S4, CO2 gas is introduced into the sodium hydroxide solution to obtain a sodium carbonate solution, which is then concentrated to obtain a saturated sodium carbonate solution, which is returned to the lithium sinking step in S1 for recycling;

[0037] S5. Add calcium oxide or calcium carbonate to the dilute sulfuric acid solution, filter and dry the solution after sufficient reaction to obtain calcium sulfate, which is then returned to the roasting step in S1 for recycling.

[0038] Example 3

[0039] A method for preparing lithium carbonate by roasting lepidolite, characterized in that it comprises the following steps:

[0040] S1. Mixing lepidolite, sodium sulfate and calcium sulfate in a mass ratio of 100:25:35, drying and then high-temperature roasting at a roasting temperature of 1000°C for 50 min, and cooling to obtain clinker; crushing, grinding and soaking the clinker to obtain a slurry; filtering the slurry to obtain a filtrate A; adding an appropriate amount of caustic soda and soda ash to the filtrate A to fully react to generate a precipitate, and filtering to obtain a filtrate B; subjecting the filtrate B to ion exchange to remove divalent metal ions to obtain a purified liquid; mixing the purified liquid with a saturated sodium carbonate solution in a volume ratio of 1:3.5 to precipitate lithium, and filtering after the lithium precipitation to obtain a lithium carbonate precipitate and a lithium precipitation mother liquor;

[0041] S2, first add sulfuric acid to the lithium precipitation mother liquor to fully react and neutralize carbonate ions, then adjust the pH to 8-10, and then filter through a precision filter with a pore size of 2 μm, and purify the obtained filtrate through a sodium cation exchange resin with a resin diameter of 0.8-1.0 mm to meet the design requirements for entering bipolar membrane electrodialysis: TSS content is less than 0.1 mg / L; the sum of divalent and multivalent cation content is less than 0.3 mg / L; SiO2 content is less than 40 mg / L; no acetone, tetrahydrofuran, dichloromethane, toluene; phenol content is less than 1 mg / L;

[0042] S3, the filtrate obtained in S2 is subjected to bipolar membrane electrodialysis to obtain sodium hydroxide solution and dilute sulfuric acid solution; wherein the current density of the bipolar membrane electrodialysis treatment is 20mA / cm 2 , voltage is 2.0V, and processing time is 60min;

[0043] S4, CO2 gas is introduced into the sodium hydroxide solution to obtain a sodium carbonate solution, which is then concentrated to obtain a saturated sodium carbonate solution, which is returned to the lithium sinking step in S1 for recycling;

[0044] S5. Add calcium oxide or calcium carbonate to the dilute sulfuric acid solution, filter and dry the solution after sufficient reaction to obtain calcium sulfate, which is then returned to the roasting step in S1 for recycling.

[0045] The above description is only a preferred specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any technician familiar with the technical field, within the technical scope disclosed by the present invention, who makes equivalent replacements or changes based on the technical solution and inventive concept of the present invention, should be covered by the scope of protection of the present invention.

Claims

1. A method for preparing lithium carbonate by roasting lepidolite, characterized in that: The following steps are involved: S1, lepidolite, sodium sulfate, and calcium sulfate are mixed, dried, and then high-temperature roasted. After cooling, a clinker is obtained, in which the mass ratio of lepidolite, sodium sulfate, and calcium sulfate is 100: (15-25): (25-35); the clinker is crushed, ground, and soaked in water to obtain a slurry; the slurry is filtered to obtain a filtrate A; an appropriate amount of caustic soda and soda ash are added to the filtrate A to fully react to generate a precipitate, and the filtrate is filtered to obtain a filtrate B; the filtrate B is subjected to ion exchange to remove divalent metal ions to obtain a purified liquid; the purified liquid is mixed with a saturated sodium carbonate solution to precipitate lithium, and after the lithium precipitation is completed, it is filtered to obtain a lithium carbonate precipitate and a lithium precipitation mother liquor; S2, first add sulfuric acid to the lithium mother liquor to fully react and neutralize carbonate ions, then adjust the pH to 8-10, and then filter through a precision filter to purify the obtained filtrate to meet the design requirements for entering bipolar membrane electrodialysis; S3, subjecting the filtrate obtained in S2 to bipolar membrane electrodialysis to obtain a sodium hydroxide solution and a dilute sulfuric acid solution; S4, CO2 gas is introduced into the sodium hydroxide solution to obtain a sodium carbonate solution, which is then concentrated to obtain a saturated sodium carbonate solution, which is returned to the lithium sinking step in S1 for recycling; S5. Add calcium oxide or calcium carbonate to the dilute sulfuric acid solution, filter and dry the solution after sufficient reaction to obtain calcium sulfate, which is then returned to the roasting step in S1 for recycling.

2. The method for preparing lithium carbonate by calcining lepidolite according to claim 1, wherein In S1, the high temperature calcination temperature is 850-1000° C. and the time is 50-80 minutes.

3. The method for preparing lithium carbonate by calcining lepidolite according to claim 1, wherein In S1, the volume ratio of the purified liquid to the saturated sodium carbonate solution is 1:(2.5-3.5).

4. The method for preparing lithium carbonate by calcining lepidolite according to claim 1, wherein In S2, the design requirements for entering bipolar membrane electrodialysis are as follows: TSS content is less than 0.1 mg / L; the sum of divalent and multivalent cation content is less than 0.3 mg / L; SiO2 content is less than 40 mg / L; there is no acetone, tetrahydrofuran, dichloromethane, or toluene; and phenol content is less than 1 mg / L.

5. The method for preparing lithium carbonate by calcining lepidolite according to claim 1, wherein In S3, the operating parameters of the bipolar membrane electrodialysis include: current density of 1 mA / cm 2 ~20mA / cm 2 , voltage is 1.7V~2.0V, and processing time is 60min~200min.

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