Method for preparing high-purity magnesium fluoride by solid-liquid phase reaction

Abstract

The application belongs to the technical field of high-purity chemical preparation, and provides a method for preparing high-purity magnesium fluoride by solid-liquid phase reaction, mainly comprising the following steps: mixing and reacting a magnesium raw material and a solvent under a protective atmosphere, separating to obtain a magnesium compound, converting the magnesium compound into a magnesium-containing solid under a certain temperature and pressure, then reacting the magnesium-containing solid with hydrofluoric acid, and finally filtering, washing and drying to obtain high-purity magnesium fluoride. The whole process is simple and easy to control, low in cost and friendly to the environment, can effectively avoid problems such as difficulty in separating fluorinated products from gel, and the purity of the magnesium fluoride product can reach more than 99.999%, which can meet the purity requirements of the crystal material and optical material fields.

Description

Technical Field

[0001] This invention belongs to the field of high-purity chemical preparation technology, specifically relating to a method for preparing high-purity magnesium fluoride by solid-liquid phase reaction. Background Technology

[0002] Magnesium fluoride possesses chemical inertness, a wide bandgap, low refractive index, strong thermal shock resistance, and corrosion resistance, making it an important material for optical windows, lenses, and coatings. Currently, the main methods for preparing magnesium fluoride include the magnesium carbonate method, magnesium sulfate method, magnesium halide method, and magnesium oxide method. The magnesium-containing raw materials used are primarily derived from magnesite or salt lake brine, resulting in complex compositions and often containing impurities such as Fe, Mn, Ni, Si, Ca, and halogens, which are extremely difficult to separate and remove. Furthermore, the prepared magnesium fluoride products exhibit severe gelation and agglomeration, making secondary purification difficult. This leads to industrial magnesium fluoride products having a purity level that cannot meet the demands of high-end optical materials and other fields, limiting their use to applications such as electrolytic metal additives, smelting metal fluxes, and anti-corrosion coatings. With the rapid development of technologies such as high-precision imaging, high-power lasers, semiconductor lithography, fiber optic communication, and infrared guidance, the demand for high-purity magnesium fluoride is increasing daily.

[0003] CN106745111A discloses a method for preparing magnesium fluoride from magnesium alkoxides. The method involves mixing magnesium alkoxides, a coagulant, and a polyol, refluxing the mixture, adding a fluorinating agent for fluorination to obtain a sol, allowing it to stand for aging for at least 24 hours to obtain a solid gel, and then drying and calcining it to obtain magnesium fluoride. CN106669742A discloses a method for preparing a magnesium fluoride catalyst from magnesium alkoxides. This method involves contacting an organic magnesium salt solution with an HF ether and / or alcohol solution. The reaction product is dried to obtain a precursor, which is then treated with a three-stage fluorination method to obtain magnesium fluoride with a high specific surface area. CN113955778A discloses a method for preparing high-purity magnesium fluoride powder. This method involves mixing and reacting metallic magnesium raw materials and an alcohol solvent under a protective atmosphere, separating the magnesium alkoxide, and then further hydrolyzing it with water. After introducing carbon dioxide gas, an intermediate precipitate is separated, which is then reacted with hydrofluoric acid. The resulting product is filtered, washed, dried, and sintered to obtain high-purity magnesium fluoride. The above methods still have problems to varying degrees, such as high cost, complex process, severe gelation of the product which is difficult to separate, large amount of waste liquid discharge, and low product purity. Developing a method for preparing high-purity magnesium fluoride has become an urgent technical need. Summary of the Invention

[0004] The purpose of this invention is to provide a method for preparing high-purity magnesium fluoride by solid-liquid phase reaction, and the purity of the product can meet the requirements of crystal materials, special glass, optical materials, special ceramics and other fields.

[0005] The technical solution of the present invention:

[0006] A method for preparing high-purity magnesium fluoride by solid-liquid phase reaction, comprising the following steps:

[0007] Step 1: Under a protective atmosphere, the magnesium raw material, solvent 1 and reaction aid are mixed and stirred at a certain temperature. After the reaction is complete, the reaction mixture is filtered, evaporated and concentrated to obtain a magnesium compound solution.

[0008] Step 2: Place the magnesium compound solution obtained in Step 1 into a reaction vessel, add the reaction solvent, and perform solvent heat treatment at a certain temperature and pressure for 4 to 18 hours. After cooling to room temperature, filter the mixture to separate the magnesium-containing solids, and distill the obtained solution to achieve solvent 1 recycling.

[0009] Step 3: After mixing the magnesium-containing solid obtained in Step 2 and solvent 2 evenly in a polytetrafluoroethylene-lined reactor, hydrofluoric acid is added. After stirring and reacting completely, the mixture is centrifuged, filtered, washed, dried, and calcined to obtain high-purity magnesium fluoride.

[0010] The magnesium raw material in step 1 is magnesium ingot, magnesium rod or magnesium granules with a purity greater than 99%;

[0011] Solvent 1 in step 1 is one of methanol, ethanol, propanol, acetone, formic acid, and acetic acid;

[0012] The mass ratio of magnesium metal to solvent 1 is 1:5 to 1:200; the reaction temperature is 30 to 130℃.

[0013] The reaction aid in step 1 is one of magnesium methoxide, magnesium formate, magnesium acetate, iodine, carbon tetrachloride, and mercuric chloride; the amount of reaction aid used is 0.001 to 0.80% of the mass of the magnesium compound solution.

[0014] The protective atmosphere used in step 1 is high-purity nitrogen or argon;

[0015] The filtration used in step 1 is membrane filtration with a pore size of 0.45–2 μm;

[0016] The reaction solvent in step 2 is one of methanol, ethanol, propanol, butanol, isobutanol, and tert-butanol.

[0017] In step 2, the mass ratio of magnesium compound to solvent is 1:5 to 30;

[0018] The reaction temperature in step 2 is 80–120℃; the reaction pressure is 0.1–2.0 MPa.

[0019] Solvent 2 used in step 3 is one of methanol, ethanol, or water;

[0020] In step 3, the mass ratio of magnesium solid to solvent 2 is 1:0.5 to 1:10.0; the reaction temperature is 5 to 60℃.

[0021] The hydrofluoric acid used in step 3 has a mass fraction of 20-50%; the mass ratio of hydrofluoric acid to magnesium-containing solid is 1:0.2-1:2.5.

[0022] The drying temperature in step 3 is 100–180℃, and the drying time is 5–48 h; the calcination temperature is 400–600℃, and the calcination time is 1–5 h.

[0023] The beneficial effects of this invention are as follows: The process of this invention is simple. Through the conversion of organic magnesium salts as precursors, it can effectively separate various impurities in the raw materials. Furthermore, by converting the raw materials into solid magnesium-containing intermediates before fluorination, it effectively avoids the severe gelation and separation difficulties associated with traditional direct fluorination of magnesium salts. Simultaneously, it allows for solvent recycling. The prepared magnesium fluoride can achieve a purity of over 99.999%. The entire process is simple, easy to control, low-cost, and environmentally friendly. Detailed Implementation

[0024] The specific embodiments of the present invention are described in detail below with reference to the technical solution.

[0025] Example 1

[0026] 65g of magnesium ingots, 5g of magnesium methoxide, and 2000mL of anhydrous methanol were placed in a 5L reactor. Nitrogen gas was continuously introduced to purge the air from the reactor, and the reaction was carried out at approximately 55℃. After no more gas was generated, the liquid was introduced into a positive pressure microporous filter through the outlet at the bottom of the reactor. The filter membrane had a pore size of 1μm. The magnesium compound solution was obtained by filtration under nitrogen protection. The magnesium compound solution was poured into a cleaned polytetrafluoroethylene (PTFE) reactor, and propanol solvent was added. The reaction was carried out at 110℃ and 0.1MPa for 10 hours. After cooling to room temperature, the high-purity magnesium-containing solid and filtrate were obtained by filtration. The magnesium-containing solid was transferred to a 1.5L PTFE reactor, and 350mL of anhydrous methanol was added and stirred to form a dispersion. Then, 200mL of 49% electronic-grade hydrofluoric acid was gradually and slowly added to the reactor through a PTFE feeder. The reaction was carried out by stirring at room temperature to obtain a magnesium fluoride suspension. After multiple filtrations and washings, the sample was dried in a vacuum drying oven at 160℃ for 20 hours. The dried sample was then calcined at 550℃ for 2 hours to obtain high-purity magnesium fluoride powder. The product purity was greater than 99.999%, with the following partial metal impurities: Fe 0.00003%, Ca 0.0002%, Ni 0.00004%, V 0.00006%, Ge 0.00007%, and Mn 0.00003%.

[0027] Example 2

[0028] 45g of magnesium ingots, 2000mL of anhydrous ethanol, and 20mL of carbon tetrachloride were placed in a 5L reactor. Argon gas was continuously introduced to purge the air from the reactor, and the mixture was heated to approximately 120℃. After no more gas was generated, the mixture was introduced into a positive pressure microporous filter with a 0.45μm pore size. Magnesium-containing solids were obtained through argon-protected filtration and then added to a cleaned polytetrafluoroethylene (PTFE) reactor. Ethanol solvent was added, and the mixture was reacted at 100℃ and 0.2MPa for 11 hours. After the reaction was completed, the mixture was cooled to room temperature and filtered to obtain high-purity magnesium-containing solids and filtrate. The magnesium-containing solids were transferred to a 1.5L PTFE reactor, and 250mL of anhydrous ethanol was added and stirred to form a dispersion. 150mL of 40% hydrofluoric acid was gradually and slowly added to the PTFE reactor through a PTFE feeder, and the mixture was stirred at 50℃ to obtain a magnesium fluoride suspension. After multiple filtrations and washings, the product was dried in a vacuum drying oven at 150℃ for 18 hours. The dried sample was then calcined at 450℃ for 1 hour to obtain high-purity magnesium fluoride powder. The product purity was greater than 99.999%, with the following partial metal impurities: Fe 0.00005%, Ca 0.0001%, Ni 0.00007%, V 0.00005%, Ge 0.00004%, and Mn 0.00003%.

[0029] Example 3

[0030] 6g of magnesium granules, 0.5g of magnesium formate, and 300mL of anhydrous methanol were placed in a 500mL three-necked flask. Nitrogen gas was introduced to purge the air from the reactor, and the mixture was then heated in a water bath at 60℃. When no more gas was produced, the three-necked flask was removed, and the reaction mixture was transferred to a microporous filter (1μm pore size) to obtain a clear liquid. The clear liquid was poured into a cleaned polytetrafluoroethylene (PTFE) reactor, and ethanol was added. The reaction was carried out at 90℃ and 0.4MPa for 14 hours. After completion, the mixture was cooled to room temperature and filtered to obtain magnesium-containing solids and a filtrate. The magnesium-containing solids were transferred to a 100mL PTFE reactor, and 50mL of anhydrous methanol was added and stirred to form a dispersion. 20mL of 49% electronic-grade hydrofluoric acid was gradually and slowly added to the reactor through a PTFE feeder, and the mixture was stirred at 30℃ to obtain a magnesium fluoride suspension. After multiple filtrations and washings, the sample was dried in an oven at 110℃. The dried sample was then calcined at 500℃ for 2 hours to obtain high-purity magnesium fluoride. The obtained magnesium fluoride product had a purity greater than 99.999%, with the following partial metal impurities: Fe 0.00008%, Ca 0.0002%, Ni 0.00006%, V 0.00004%, Ge 0.00004%, and Mn 0.00005%.

[0031] Example 4

[0032] 15g of magnesium granules, 1500mL of anhydrous ethanol, and 0.01g of iodine were placed in a 2000mL reactor. Nitrogen gas was introduced to purge the air from the reactor, and the mixture was heated under reflux until no gas was generated. The reaction solution was then transferred to a microporous filter to obtain magnesium-containing solids. The microporous filter membrane had a pore size of 2μm. The magnesium ethoxide solid was poured into a cleaned polytetrafluoroethylene (PTFE) reactor, and ethylene glycol solvent was added. The reaction was carried out at 120℃ and 0.6MPa for 16 hours. After completion, the mixture was cooled to room temperature and filtered to obtain magnesium-containing solids and a filtrate. The magnesium-containing solids were transferred to a 1000mL PTFE reactor, and 500mL of anhydrous ethanol was added and stirred to form a dispersion. 100mL of 35% hydrofluoric acid was gradually and slowly added to the reactor through a PTFE feeder, and the mixture was stirred at 45℃ to obtain a magnesium fluoride suspension. After multiple filtrations and washings, the sample was dried in a vacuum drying oven at 140℃ for 20 hours. The dried sample was then calcined at 400℃ for 2 hours to obtain high-purity magnesium fluoride powder. The product purity was greater than 99.999%, with the following partial metal impurities: Fe 0.00007%, Ca 0.0003%, Ni 0.00004%, V 0.00007%, Ge 0.00005%, and Mn 0.00008%.

[0033] Example 5

[0034] 5g of magnesium granules, 200mL of acetone, and 1g of mercuric chloride were placed in a 500mL three-necked flask. Argon gas was introduced to purge the air from the flask, and the mixture was heated in a water bath at 30℃. After the reaction was complete, the reaction solution was transferred to a microporous filter to obtain magnesium-containing solid. The microporous filter membrane had a pore size of 2μm. The magnesium pinacol solid was poured into a cleaned polytetrafluoroethylene (PTFE) reactor, and methanol solvent was added. The reaction was carried out at 80℃ and 0.3MPa for 4 hours. After the reaction was completed, the mixture was cooled to room temperature and filtered to obtain magnesium-containing solid and filtrate. The magnesium-containing solid was transferred to a 100mL PTFE reactor, and 40mL of anhydrous ethanol was added and stirred to form a dispersion. 20mL of 20% hydrofluoric acid was gradually and slowly added to the reactor through a PTFE feeder, and the mixture was stirred at room temperature to obtain a magnesium fluoride suspension. After multiple filtrations and washings, the sample was dried in a vacuum drying oven at 180℃ for 5 hours. The dried sample was then calcined at 500℃ for 5 hours to obtain high-purity magnesium fluoride powder. The product purity was greater than 99.999%, with the following partial metal impurities: Fe 0.00005%, Ca 0.0005%, Ni 0.00008%, V 0.00003%, Ge 0.00007%, and Mn 0.00006%.

[0035] Example 6

[0036] 25g of magnesium rod, 5000mL of anhydrous methanol, and 0.01g of iodine were placed in a 7L reactor. Nitrogen gas was introduced to purge the air from the reactor, and the mixture was heated under reflux until no gas was generated. The reaction solution was then transferred to a microporous filter to obtain magnesium-containing solids. The microporous filter membrane had a pore size of 1μm. The methanol-magnesium solids were poured into a cleaned polytetrafluoroethylene (PTFE) reactor, and butanol solvent was added. The reaction was carried out at 90℃ and 0.8MPa for 18 hours. After completion, the mixture was cooled to room temperature and filtered to obtain magnesium-containing solids and a filtrate. The magnesium-containing solids were transferred to a 500mL PTFE reactor, and 150mL of anhydrous methanol was added and stirred to form a dispersion. 200mL of 30% hydrofluoric acid was gradually and slowly added to the reactor through a PTFE feeder, and the mixture was stirred at 5℃ to obtain a magnesium fluoride suspension. After multiple filtrations and washings, the sample was dried in a vacuum drying oven at 100℃ for 48 hours. The dried sample was then calcined at 600℃ for 4 hours to obtain high-purity magnesium fluoride powder. The product purity was greater than 99.999%, with the following partial metal impurities: Fe 0.00009%, Ca 0.0004%, Ni 0.00002%, V 0.00006%, Ge 0.00004%, and Mn 0.00007%.

Claims

1. A method for preparing high-purity magnesium fluoride via a solid-liquid phase reaction, characterized in that, The steps are as follows: Step 1: Under a protective atmosphere, the magnesium raw material, solvent 1 and reaction aid are mixed and stirred at a certain temperature. After the reaction is complete, the reaction mixture is filtered, evaporated and concentrated to obtain a magnesium compound solution. The raw materials for metallic magnesium are magnesium ingots, magnesium rods, or magnesium granules with a purity greater than 99%. Solvent 1 is one of methanol, ethanol, propanol, acetone, formic acid, and acetic acid; The mass ratio of magnesium metal to solvent 1 is 1:5 to 1:200; the reaction temperature is 30 to 130°C. The reaction aid is one of magnesium methoxide, magnesium formate, magnesium acetate, iodine, carbon tetrachloride, and mercuric chloride. The amount of reaction aid used is 0.001~0.80% of the mass of the magnesium compound solution; The protective atmosphere used in step 1 is high-purity nitrogen or argon; The filtration used in step 1 is membrane filtration with a pore size of 0.45~2μm; Step 2: Place the magnesium compound solution obtained in Step 1 into a reaction vessel, add the reaction solvent, and perform solvent heat treatment at a certain temperature and pressure for 4 to 18 hours. After cooling to room temperature, filter the mixture to separate the magnesium-containing solids, and distill the obtained solution to achieve solvent 1 recycling. The reaction solvent is one of methanol, ethanol, propanol, butanol, isobutanol, and tert-butanol. The mass ratio of magnesium compound to solvent is 1:5~30; The reaction temperature is 80~120℃; the reaction pressure is 0.1~2.0 MPa. Step 3: After mixing the magnesium-containing solid obtained in Step 2 and solvent 2 evenly in a polytetrafluoroethylene-lined reactor, add hydrofluoric acid, stir until the reaction is complete, and then centrifuge, filter, wash, dry and calcine to obtain high-purity magnesium fluoride. Solvent 2 is one of methanol, ethanol, or water; The mass ratio of magnesium-containing solid to solvent 2 is 1:0.5 to 1:10.0; The reaction temperature is 5~60℃; The mass fraction of hydrofluoric acid is 20-50%; the mass ratio of hydrofluoric acid to magnesium-containing solid is 1:0.2 to 1:2.

5. The drying temperature is 100~180℃, and the drying time is 5~48h; the calcination temperature is 400~600℃, and the calcination time is 1~5h.