Method for preparing high-purity lithium fluoride from crude lithium carbonate

Abstract

The invention relates to the technical field of lithium fluoride preparation, and particularly discloses a method for preparing high-purity lithium fluoride from crude lithium carbonate, the method comprises eight steps of material taking, acidification, primary filtration, pH adjustment, two-stage filtration, evaporation and concentration, dissolution and reaction, and final filtration and drying to prepare the high-purity lithium fluoride, in the dissolution and reaction step, a pyridine solution is adopted as a solvent, as the lithium fluoride is slightly soluble in water, insoluble or insoluble in pyridine and alcohol, compared with a traditional method for separating out the lithium fluoride from water, the yield of the lithium fluoride is higher, the industrial byproduct crude lithium carbonate is adopted, and the production cost can be reduced.

Description

Technical Field

[0001] The invention relates to the technical field of lithium fluoride preparation, and in particular to a method for preparing high-purity lithium fluoride by utilizing crude lithium carbonate. Background Art

[0002] Lithium fluoride (LiF), as an important lithium salt, not only plays an important role in the electrolyte additive of lithium batteries to improve battery safety and cycle stability, but is also widely used in the semiconductor industry, optical materials and neutron moderators of nuclear reactors.

[0003] The traditional method for preparing lithium fluoride mainly adopts the direct preparation method, which is generally based on solid Li 2 CO 3 and hydrofluoric acid solution as raw materials. Since lithium carbonate has low solubility in water, the solid-liquid reaction efficiency is low. Although there is an application of carbonizing it with carbon dioxide to generate lithium bicarbonate with high solubility to turn it into a liquid-liquid reaction to improve the conversion rate, this method is not very effective for solid Li 2 CO 3 The quality requirements are very high. The higher the purity of Li 2 CO 3 The more expensive the price. At the same time, in the production process of this method, lithium is precipitated from water, and lithium fluoride is slightly soluble in water, so the yield of lithium fluoride is relatively low. Moreover, the system contains aqueous hydrofluoric acid, which is extremely corrosive and requires corrosion-resistant equipment for reaction. The price of corrosion-resistant equipment is more expensive, which increases the investment cost. Summary of the invention

[0004] The object of the present invention is to provide a method for preparing high-purity lithium fluoride using crude lithium carbonate, so as to solve the problems of high input cost and low yield in the production process of lithium fluoride.

[0005] In order to solve the above problems, the technical solutions provided are as follows:

[0006] A method for preparing high-purity lithium fluoride using crude lithium carbonate comprises the following steps:

[0007] S1: Take materials: weigh crude lithium carbonate containing 70-80% lithium carbonate and industrial hydrochloric acid,

[0008] S2: Acidification: Gradually add crude lithium carbonate to industrial hydrochloric acid and stir at room temperature for 1-3 hours;

[0009] S3: Primary filtration: The solution of S2 is initially filtered to remove insoluble impurities;

[0010] S4: pH adjustment: add alkali solution to the solution after the initial filtration to adjust the pH to 10-12;

[0011] S5: Two-stage filtration: The solution after pH adjustment is subjected to two-stage precision filtration to form a purified solution;

[0012] S6: Evaporation and concentration: The purified liquid is concentrated by vacuum evaporation for 4 hours to precipitate lithium chloride crystals, which are dried in a drying oven at a pressure of less than -0.1 MPa and a temperature of 80 to 85°C to obtain lithium chloride solids;

[0013] S7: dissolving and reacting: dissolving lithium chloride solid in pyridine solution, and then slowly adding the pyridine solution of lithium chloride to the hydrogen fluoride solution for reaction, the reaction temperature is 20-50° C., and lithium fluoride crystals are precipitated;

[0014] S8: Finally filtering and drying: Filter the solution in step S7, and after filtering, vacuum dry the lithium fluoride crystals at a pressure lower than -0.1 MPa and a temperature of 80-85° C. to obtain high-purity lithium fluoride.

[0015] The beneficial effects of the above technical solution are as follows:

[0016] 1. Compared with the existing high-purity Li 2 CO 3 Compared with the preparation of lithium fluoride, this scheme uses crude lithium carbonate produced as an industrial byproduct and hydrochloric acid to react to obtain high-purity lithium fluoride. The crude lithium carbonate produced as an industrial byproduct is cheap, which can reduce production costs.

[0017] 2. Compared with the direct preparation method using lithium carbonate and hydrogen fluoride, Li is converted into lithium chloride with high solubility, and then reacted with the fluorinating agent in pyridine in a liquid-liquid reaction. There is no water in the pyridine system, and the reaction conditions are milder than the reaction using hydrofluoric acid as solvent.

[0018] 3. Since lithium fluoride is slightly soluble in water and poorly soluble or insoluble in pyridine and alcohol, the yield of lithium fluoride is higher than the traditional method of precipitating lithium fluoride from water.

[0019] 4. By using alkaline solution to adjust the pH of the acidified liquid to 10-12, within this pH range, divalent metal ions such as calcium and magnesium will precipitate out in the form of hydroxides. After two-stage precision filtration, the purified liquid can be obtained to achieve the purpose of impurity removal.

[0020] Furthermore, in step S1, the molar ratio of crude lithium carbonate to hydrochloric acid is 1:1 to 2.2.

[0021] Furthermore, the alkali solution used in step S4 is one or more of sodium hydroxide or lithium hydroxide.

[0022] Furthermore, the two-stage precision filtration in step S5 uses precision filters with filter element pore sizes of 1 μm and 3 μm respectively.

[0023] Furthermore, in step S7, the molar ratio of lithium chloride to hydrogen fluoride is 1:1 to 1.5.

[0024] Furthermore, the filtrate filtered out in step S8 enters a distillation system to separate a pyridine solution and an HCl solution, the pyridine solution is put into step S7 for recycling, and the HCl solution is put into step S2 for recycling. Pyridine and HCl are recycled, further reducing production costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 Schematic diagram of the process flow of an embodiment of the present invention. DETAILED DESCRIPTION

[0026] The following is further described in detail through specific implementation methods:

[0027] The embodiment is basically as shown in the attached Figure 1 As shown:

[0028] The specific implementation process is as follows:

[0029] Example 1

[0030] A method for preparing high-purity lithium fluoride using crude lithium carbonate comprises the following steps:

[0031] S1: Taking materials: weighing 500 g of crude lithium carbonate with a lithium carbonate content of 70% and 1265.99 g of industrial hydrochloric acid (hydrochloric acid content of 30%), the molar ratio of crude lithium carbonate to hydrochloric acid is 1:2.2;

[0032] S2: Acidification: Gradually add crude lithium carbonate to industrial hydrochloric acid and stir at room temperature for 1 hour;

[0033] S3: Primary filtration: The solution of S2 is filtered through a precision filter to remove insoluble impurities;

[0034] S4: pH adjustment: lithium hydroxide solution is added to the solution after the initial filtration to adjust the pH to 12;

[0035] S5: Two-stage filtration: The solution after adjusting the pH value is filtered through two-stage precision filters with pore sizes of 1μm and 3μm respectively to form a purified solution;

[0036] S6: Evaporation and concentration: The purified liquid is concentrated by vacuum evaporation for 4 hours to precipitate lithium chloride crystals, which are dried in a drying oven at a pressure of less than -0.1 MPa and a temperature of 80 to 85°C to obtain lithium chloride solids;

[0037] S7: dissolving and reacting: dissolving lithium chloride solid in pyridine solution, and then slowly adding the pyridine solution of lithium chloride to the hydrogen fluoride solution for reaction, the molar ratio of lithium chloride to hydrogen fluoride is 1:1.1, the reaction temperature is 25°C, and lithium fluoride crystals are precipitated;

[0038] S8: Finally filtering and drying: Filter the solution in step S7, and dry the filtered lithium fluoride crystals in vacuum at a pressure lower than -0.1 MPa and a temperature of 80-85° C. to obtain 238 g of high-purity lithium fluoride. The yield of lithium fluoride is calculated to be 98.46%.

[0039] The filtrate filtered out in step S8 enters the distillation system to separate the pyridine solution and the HCl solution. The pyridine solution is put into step S7 for recycling, and the HCl solution is put into step S2 for recycling.

[0040] Example 2

[0041] A method for preparing high-purity lithium fluoride using crude lithium carbonate comprises the following steps:

[0042] S1: Taking materials: weighing 500 g of crude lithium carbonate with a lithium carbonate content of 70% and 1265.99 g of industrial hydrochloric acid (hydrochloric acid content of 30%), the molar ratio of crude lithium carbonate to hydrochloric acid is 1:2.2;

[0043] S2: Acidification: Gradually add crude lithium carbonate to industrial hydrochloric acid and stir at room temperature for 1 hour;

[0044] S3: Primary filtration: The solution of S2 is filtered through a precision filter to remove insoluble impurities;

[0045] S4: pH adjustment: lithium hydroxide solution is added to the solution after the initial filtration to adjust the pH to 10;

[0046] S5: Two-stage filtration: The solution after adjusting the pH value is filtered through two-stage precision filters with pore sizes of 1μm and 3μm respectively to form a purified solution;

[0047] S6: Evaporation and concentration: The purified liquid is concentrated by vacuum evaporation for 4 hours to precipitate lithium chloride crystals, which are dried in a drying oven at a pressure of less than -0.1 MPa and a temperature of 80 to 85°C to obtain lithium chloride solids;

[0048] S7: dissolving and reacting: dissolving lithium chloride solid in pyridine solution, and then slowly adding the pyridine solution of lithium chloride to the hydrogen fluoride solution for reaction, the molar ratio of lithium chloride to hydrogen fluoride is 1:1.1, the reaction temperature is 25°C, and lithium fluoride crystals are precipitated;

[0049] S8: Finally filtering and drying: Filter the solution in step S7, and vacuum dry the filtered lithium fluoride crystals at a pressure lower than -0.1 MPa and a temperature of 80-85° C. to obtain 236 g of high-purity lithium fluoride. The yield of lithium fluoride is calculated to be 97.22%.

[0050] The filtrate filtered out in step S8 enters the distillation system to separate the pyridine solution and the HCl solution. The pyridine solution is put into step S7 for recycling, and the HCl solution is put into step S2 for recycling.

[0051] Example 3

[0052] A method for preparing high-purity lithium fluoride using crude lithium carbonate comprises the following steps:

[0053] S1: Take materials: weigh 500g of crude lithium carbonate with a lithium carbonate content of 70% and 1265.99g of industrial hydrochloric acid (hydrochloric acid content of 30%), the molar ratio of crude lithium carbonate to hydrochloric acid is 1:2.2

[0054] S2: Acidification: Gradually add crude lithium carbonate to industrial hydrochloric acid and stir at room temperature for 1-3 hours;

[0055] S3: Primary filtration: The solution of S2 is filtered through a precision filter to remove insoluble impurities;

[0056] S4: pH adjustment: add alkali solution to the solution after the initial filtration to adjust the pH to 12;

[0057] S5: Two-stage filtration: The solution after adjusting the pH value is filtered through two-stage precision filters with pore sizes of 1μm and 3μm respectively to form a purified solution;

[0058] S6: Evaporation and concentration: The purified liquid is concentrated by vacuum evaporation for 4 hours to precipitate lithium chloride crystals, which are dried in a drying oven at a pressure of less than -0.1 MPa and a temperature of 80 to 85°C to obtain lithium chloride solids;

[0059] S7: dissolving and reacting: dissolving lithium chloride solid in aqueous solution, and then slowly adding lithium chloride aqueous solution to hydrogen fluoride solution for reaction, the molar ratio of lithium fluoride to hydrogen fluoride is 1:1.1, the reaction temperature is 25°C, and lithium fluoride crystals are precipitated;

[0060] S8: Finally filtering and drying: Filter the solution in step S7, and after filtering, vacuum dry the lithium fluoride crystals at a pressure lower than -0.1 MPa and a temperature of 80-85° C. to obtain 229 g of high-purity lithium fluoride. The yield of lithium fluoride is calculated to be 94.73%.

[0061] From the lithium fluoride yield data obtained from Examples 1 to 3, it can be seen that the lithium fluoride yields of Examples 1 and 2 are higher than that of Example 3. Therefore, using pyridine solution as a solvent, the lithium fluoride yield is higher, and pyridine and HCl solutions can also be extracted and recycled, further reducing production costs.

[0062] The above is only an embodiment of the present invention, and the common knowledge such as the known specific structure and characteristics in the scheme is not described in detail here. It should be pointed out that for those skilled in the art, several deformations and improvements can be made without departing from the structure of the present invention, which should also be regarded as the protection scope of the present invention, and these will not affect the effect of the implementation of the present invention and the practicality of the patent. The scope of protection required by this application shall be based on the content of its claims, and the specific implementation methods and other records in the specification can be used to interpret the content of the claims.

Claims

1. A method for preparing high-purity lithium fluoride using crude lithium carbonate, characterized in that: The following steps are involved: S1: Take materials: weigh crude lithium carbonate containing 70-80% lithium carbonate and industrial hydrochloric acid, S2: Acidification: Gradually add crude lithium carbonate to industrial hydrochloric acid and stir at room temperature for 1-3 hours; S3: Primary filtration: The solution of S2 is initially filtered to remove insoluble impurities; S4: pH adjustment: add alkali solution to the solution after the initial filtration to adjust the pH to 10-12; S5: Two-stage filtration: The solution after pH adjustment is subjected to two-stage precision filtration to form a purified solution; S6: Evaporation and concentration: The purified liquid is concentrated by vacuum evaporation for 4 hours to precipitate lithium chloride crystals, which are dried in a drying oven at a pressure of less than -0.1 MPa and a temperature of 80 to 85°C to obtain lithium chloride solids; S7: dissolving and reacting: dissolving lithium chloride solid in pyridine solution, and then slowly adding the pyridine solution of lithium chloride to the hydrogen fluoride solution for reaction, the reaction temperature is 20-50° C., and lithium fluoride crystals are precipitated; S8: Finally filtering and drying: Filter the solution in step S7, and after filtering, vacuum dry the lithium fluoride crystals at a pressure lower than -0.1 MPa and a temperature of 80-85° C. to obtain high-purity lithium fluoride.

2. A method for preparing high-purity lithium fluoride using crude lithium carbonate according to claim 1, characterized in that: In step S1, the molar ratio of crude lithium carbonate to hydrochloric acid is 1:1 to 2.

2.

3. A method for preparing high-purity lithium fluoride using crude lithium carbonate according to claim 2, characterized in that: The alkali solution used in step S4 is one or more of sodium hydroxide and lithium hydroxide.

4. A method for preparing high-purity lithium fluoride using crude lithium carbonate according to claim 3, characterized in that: The two-stage precision filtration in step S5 uses precision filters with filter element pore sizes of 1 μm and 3 μm respectively.

5. A method for preparing high-purity lithium fluoride using crude lithium carbonate according to claim 4, characterized in that: In step S7, the molar ratio of lithium chloride to hydrogen fluoride is 1:1 to 1.

5.

6. A method for preparing high-purity lithium fluoride using crude lithium carbonate according to claim 5, characterized in that: The filtrate filtered out in step S8 enters the distillation system to separate the pyridine solution and the HCl solution. The pyridine solution is put into step S7 for recycling, and the HCl solution is put into step S2 for recycling.

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