A method for preparing high-purity graphite using natural graphite

Abstract

The present invention relates to the technical field of the preparation of high-purity graphite, and particularly relates to a method for preparing high-purity graphite by using natural graphite. In the present invention, a fluoride salt, an additive and natural graphite powder are uniformly mixed at room temperature, and then heated to a certain temperature and kept at a constant temperature for a certain time, and a hydrothermal reaction is carried out under a certain pressure to complete the reaction and removal process of impurities. After cooling, the above reaction product is separated, and then the separated graphite is washed with deionized water to remove residual impurities such as Na2SiF6, K2SiF6 or CaSiF6. Compared with the existing process, this method overcomes the problem that the obtained graphite cannot meet the market demand due to the low purity of chemical purification; in addition, the used reagent (fluoride salt) has weaker corrosiveness and less addition amount, and the reaction time can be shortened and the corrosion effect can be increased by adjusting the temperature and pressure, which is easy to operate. Most importantly, the required equipment is simple, the energy consumption is low, and the cost is low.

Description

Technical Field

[0001] The present invention relates to the technical field of the preparation of high-purity graphite, and specifically relates to a method for preparing high-purity graphite using natural graphite. Background Art

[0002] Graphite has many advantages such as low density, corrosion resistance, radiation resistance, self-lubrication, and resistance to high and low temperatures, and has important applications in the fields of aerospace, aviation, military, electronics, nuclear energy, metallurgy, etc. With the continuous development of new technologies and new processes, ordinary high-purity graphite materials can no longer meet the needs of many industries. The quality of graphite purification determines the use characteristics and comprehensive performance of graphite materials. The higher the graphite purity, the higher the application value.

[0003] Currently, the main methods for graphite purification at home and abroad are chemical methods, including flotation method, alkali-acid method, hydrofluoric acid method, chlorination roasting method, etc. The physical method mainly refers to the high-temperature method. Among them, the high-temperature method can increase the purity of graphite powder to 99.99%, but it has high requirements for equipment, and the working temperature must be at least above 3000 °C, which greatly increases the cost. Chemical purification uses a large amount of strong acids such as sulfuric acid, hydrofluoric acid, hydrochloric acid and strong bases such as sodium hydroxide. The strict requirements for equipment also lead to an increase in cost; moreover, the preparation process of chemical purification has more steps, and more waste acids and waste alkalis are easily generated during the preparation process, resulting in an increase in wastewater discharge and production costs. Summary of the Invention

[0004] In order to improve the deficiencies of the existing technology, the present invention provides a method for preparing high-purity graphite using natural graphite. Compared with the existing process, this method has low energy consumption, is more environmentally friendly, is simpler and easier to operate, and has lower manufacturing costs while ensuring the graphite purity.

[0005] The object of the present invention is achieved by the following technical solutions:

[0006] A method for preparing high-purity graphite using natural graphite, the method comprising the following steps:

[0007] (1) Add natural graphite powder, fluorine salt, water and additive into a reaction kettle and stir evenly, and carry out hydrothermal reaction to prepare a slurry; the fluorine salt is a composition of a low-boiling fluorine salt and a high-boiling fluorine salt;

[0008] (2) Separate the slurry in step (1) to obtain a mixture containing graphite and impurities;

[0009] (3) Wash the mixture in step (2) with deionized water until neutral, and dry it to prepare high-purity graphite.

[0010] According to an embodiment of the present invention, in step (1), the carbon content of the natural graphite powder is ≥90%, and the particle size of the natural graphite powder is ≤100 μm.

[0011] According to an embodiment of the present invention, in step (1), the mass ratio of the natural graphite powder, the fluoride salt, water, and the additive is 1:(0.3 - 0.8):(1.5 - 3):(0.01 - 0.05).

[0012] Exemplarily, the mass ratio of the natural graphite powder, the fluoride salt, water, and the additive is 1:(0.3, 0.4, 0.5, 0.6, 0.7, or 0.8):(1.5, 1.6, 1.7, 1.8, 1.9, 2, 2.1, 2.2, 2.3, 2.4, 2.5, 2.6, 2.7, 2.8, 2.9, or 3):(0.01, 0.02, 0.03, 0.04, or 0.05).

[0013] According to an embodiment of the present invention, in step (1), the low-boiling fluoride salt is selected from at least one of NH4F and NH4HF2; the high-boiling fluoride salt is selected from at least one of NaF, KF, and CaF2.

[0014] According to an embodiment of the present invention, in step (1), the mass ratio of the high-boiling fluoride salt to the low-boiling fluoride salt is (0.1 - 0.5):1. Exemplarily, the mass ratio of the high-boiling fluoride salt to the low-boiling fluoride salt is 0.1:1, 0.2:1, 0.3:1, 0.4:1, or 0.5:1.

[0015] According to an embodiment of the present invention, in step (1), the additive is selected from at least one of hydroxyethylidene diphosphonic acid (C2H8O7P2), (1-hydroxyethylidene) diphosphonic acid, and histamine phosphate (C5H 15 N3O8P2).

[0016] According to an embodiment of the present invention, in step (1), the temperature of the hydrothermal reaction is 150°C - 300°C. Exemplarily, the temperature of the hydrothermal reaction is 150°C, 160°C, 170°C, 180°C, 190°C, 200°C, 210°C, 220°C, 230°C, 240°C, 250°C, 260°C, 270°C, 280°C, 290°C, or 300°C; the time of the hydrothermal reaction is 1 h - 10 h, for example, 1 h, 2 h, 3 h, 4 h, 5 h, 6 h, 7 h, 8 h, 9 h, or 10 h.

[0017] According to an embodiment of the present invention, in step (1), during the hydrothermal reaction, the pressure in the reaction kettle is greater than 1 atmosphere.

[0018] According to an embodiment of the present invention, in step (2), the impurity is at least one of Na2SiF6, K2SiF6, or CaSiF6.

[0019] According to an embodiment of the present invention, in step (2), the slurry in step (1) is separated by centrifugation; for example, water in the graphite is centrifuged out using a centrifuge to separate a mixture of graphite and impurities containing 10% - 30% moisture.

[0020] According to an embodiment of the present invention, in step (3), the drying temperature is 100°C - 200°C, and the drying time is 6 - 12 h.

[0021] According to an embodiment of the present invention, in step (3), the carbon content of the obtained high-purity graphite > 99%. Preferably, the carbon content of the obtained high-purity graphite ≥ 99.9%.

[0022] According to an embodiment of the present invention, the present invention uses a composition of high-boiling fluorides and low-boiling fluorides as a reagent for removing impurity components in natural graphite. The low-boiling fluoride (NH4F or NH4HF2) in this reagent can decompose to generate HF gas at a temperature above 100°C. Under the action of the pressure in the reaction kettle, the HF gas dissolves in water to form a strong HF acid solution. Metal oxides (mica, kaolinite, and calcite) in silicates in natural graphite enter the solution in the form of soluble salts, and at the same time, SiF4 gas escapes continuously with water vapor, ensuring that the reaction channel is unobstructed and enabling the chemical reaction of graphite purification to proceed more thoroughly; the high-boiling fluorides NaF, KF, or CaF2 can supplement F - in the solution, so that the HF concentration in the system remains constant, and can also promote the formation of impurities such as Na2SiF6, K2SiF6, or CaSiF6 from silicon oxides (SiOx, 2 ≥ x > 0), and the precipitate adheres to the surface of the graphite. This precipitate will dissolve in water and be removed during the water washing process.

[0023] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0024] (1) The present invention uniformly mixes fluorides, additives, and natural graphite powder at room temperature, then heats to a certain temperature and keeps it constant for a certain time, and conducts a hydrothermal reaction under a certain pressure to complete the reaction and removal process of impurities. After cooling, the above reaction products are separated, and then the separated graphite is washed with deionized water to remove residual impurities such as Na2SiF6, K2SiF6, or CaSiF6.

[0025] (2) The additives added in the present invention can form stable complexes with various metal ions such as iron, copper, aluminum, and zinc obtained after the reaction, further removing trace metal elements in graphite and significantly improving the purity of graphite. Compared with the existing processes, this method overcomes the problem that the obtained graphite cannot meet the market demand due to the low purity of chemical purification; in addition, the corrosiveness of the used reagent (fluoride salt) is weaker, the addition amount is less, the reaction time can be shortened by adjusting the temperature and pressure, the corrosion effect can be increased, and it is easy to operate. Most importantly, the required equipment is simple, the energy consumption is low, and the cost is low. Detailed implementation manners

[0026] The technical solutions of the present invention will be further described in detail below with reference to specific embodiments. It should be understood that the following embodiments are only for illustrative explanation of the present invention and should not be construed as limiting the protection scope of the present invention. All technologies implemented based on the above content of the present invention are covered within the scope of protection intended by the present invention.

[0027] Unless otherwise specified, the experimental methods used in the following embodiments are all conventional methods; unless otherwise specified, the reagents, materials, etc. used in the following embodiments can all be obtained from commercial channels.

[0028] Example 1

[0029] (1) Add 100 g of natural graphite powder (carbon content ≥ 90%, particle size ≤ 100 μm), 40 g of fluoride salt (28 g of NH4F, 12 g of NaF), 200 g of water, and 1 g of hydroxyethylidene diphosphonic acid into a reaction kettle and stir evenly, then heat to 300 °C and keep warm for 12 hours for hydrothermal reaction. During the hydrothermal reaction, the pressure in the reaction kettle is about 2.5 atmospheres. After the reaction is completed, cool to room temperature to obtain a slurry.

[0030] (2) Feed the slurry in step (1) into a centrifuge to spin out about 80% of the water in the graphite, and separate a mixture of graphite containing 20% water and Na2SiF6 from the centrifuge.

[0031] (3) Wash the mixture in step (2) with deionized water until neutral, and dry it at 120 °C for 8 h to obtain high-purity graphite with a purity of 99.92%.

[0032] Example 2

[0033] (1) Add 100 g of natural graphite powder (carbon content ≥ 90%, particle size ≤ 100 μm), 50 g of fluoride salt (40 g of NH4F, 10 g of NaF), 300 g of water, and 3 g of hydroxyethylidene diphosphonic acid into a reaction kettle and stir evenly, then heat to 260 °C and keep warm for 8 hours for hydrothermal reaction. During the hydrothermal reaction, the pressure in the reaction kettle is about 1.8 atmospheres. After the reaction is completed, cool to room temperature to obtain a slurry.

[0034] (2) Feed the slurry from step (1) into a centrifuge to spin out approximately 80% of the moisture in the graphite, and separate a mixture of graphite containing 20% moisture and Na2SiF6 from the centrifuge.

[0035] (3) Wash the mixture from step (2) with deionized water until neutral, and dry it at 150 °C for 6 h to obtain high-purity graphite with a purity of 99.95%.

[0036] Example 3

[0037] (1) Add 100 g of natural graphite powder (carbon content ≥ 90%, particle size ≤ 100 μm), 70 g of fluoride salts (60 g of NH4F and 10 g of NaF), 300 g of water, and 5 g of hydroxyethylidene diphosphonic acid to a reaction kettle and stir evenly. Then heat to 230 °C and keep warm for 8 hours for hydrothermal reaction. During the hydrothermal reaction, the pressure in the reaction kettle is about 1.5 atmospheres. After the reaction, cool to room temperature to obtain a slurry.

[0038] (2) Feed the slurry from step (1) into a centrifuge to spin out approximately 80% of the moisture in the graphite, and separate a mixture of graphite containing 20% moisture and Na2SiF6 from the centrifuge.

[0039] (3) Wash the mixture from step (2) with deionized water until neutral, and dry it at 120 °C for 8 h to obtain high-purity graphite with a purity of 99.97%.

[0040] Comparative Example 1

[0041] (1) Add 100 g of natural graphite powder (carbon content ≥ 90%, particle size ≤ 100 μm), 40 g of fluoride salt (NH4F), and 200 g of water to a reaction kettle and stir evenly. Then heat to 300 °C and keep warm for 12 hours for hydrothermal reaction. During the hydrothermal reaction, the pressure in the reaction kettle is about 2.5 atmospheres. After the reaction, cool to room temperature to obtain a slurry.

[0042] (2) Feed the slurry from step (1) into a centrifuge to spin out approximately 80% of the moisture in the graphite, and separate a graphite mixture containing 20% moisture from the centrifuge.

[0043] (3) Wash the mixture from step (2) with deionized water until neutral, and dry it at 120 °C for 8 h to obtain high-purity graphite with a purity of 97.2%.

[0044] Comparative Example 2

[0045] (1) Add 100 g of natural graphite powder (carbon content ≥ 90%, particle size ≤ 100 μm), 40 g of fluoride salt (NH4F), 200 g of water, and 1 g of hydroxyethylidene diphosphonic acid to a reaction kettle and stir evenly. Then heat to 300 °C and keep warm for 12 hours for hydrothermal reaction. During the hydrothermal reaction, the pressure in the reaction kettle is about 2.5 atmospheres. After the reaction, cool to room temperature to obtain a slurry;

[0046] (2) Feed the slurry from step (1) into a centrifuge to spin out about 80% of the water in the graphite, and separate a mixture of graphite containing 20% water and Na2SiF6 from the centrifuge;

[0047] (3) Wash the mixture from step (2) with deionized water until neutral, and dry at 120 °C for 8 h to obtain high-purity graphite with a purity of 97.8%.

[0048] Comparative Example 3

[0049] (1) Add 100 g of natural graphite powder (carbon content ≥ 90%, particle size ≤ 100 μm), 40 g of fluoride salt (NaF), 200 g of water, and 1 g of hydroxyethylidene diphosphonic acid to a reaction kettle and stir evenly. Then heat to 300 °C and keep warm for 12 hours for hydrothermal reaction. During the hydrothermal reaction, the pressure in the reaction kettle is about 2.5 atmospheres. After the reaction, cool to room temperature to obtain a slurry;

[0050] (2) Feed the slurry from step (1) into a centrifuge to spin out about 80% of the water in the graphite, and separate a mixture of graphite containing 20% water and Na2SiF6 from the centrifuge;

[0051] (3) Wash the mixture from step (2) with deionized water until neutral, and dry at 120 °C for 8 h to obtain high-purity graphite with a purity of 95.4%.

[0052] Comparative Example 4

[0053] (1) Add 100 g of natural graphite powder (carbon content ≥ 90%, particle size ≤ 100 μm), 40 g of fluoride salt (NH4F 28 g, NaF 12 g), and 200 g of water to a reaction kettle and stir evenly. Then heat to 300 °C and keep warm for 12 hours for hydrothermal reaction. During the hydrothermal reaction, the pressure in the reaction kettle is about 2.5 atmospheres. After the reaction, cool to room temperature to obtain a slurry;

[0054] (2) Feed the slurry from step (1) into a centrifuge to spin out about 80% of the water in the graphite, and separate a mixture of graphite containing 20% water and Na2SiF6 from the centrifuge;

[0055] (3) Wash the mixture in step (2) with deionized water until neutral, and dry it at 120 °C for 8 h to obtain high-purity graphite with a purity of 98.6%.

[0056] As described above, the embodiments of the present invention have been described. However, the present invention is not limited to the above embodiments. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for preparing high-purity graphite from natural graphite, the method comprising the following steps: (1) Adding natural graphite powder, fluoride salt, water and an additive into a reaction kettle, stirring evenly, and carrying out hydrothermal reaction to prepare a slurry; the fluoride salt is a composition of a low-boiling-point fluoride salt and a high-boiling-point fluoride salt; (2) Separating the slurry obtained in step (1) to obtain a mixture containing graphite and impurities; (3) Washing the mixture obtained in step (2) with deionized water until neutral, and drying to prepare high-purity graphite; In step (1), the low-boiling-point fluoride salt is selected from at least one of NH4F and NH4HF2; the high-boiling-point fluoride salt is selected from at least one of NaF, KF and CaF2; In step (1), the mass ratio of the high-boiling-point fluoride salt to the low-boiling-point fluoride salt is (0.1~0.5):1; In step (1), the additive is selected from at least one of hydroxyethylidene diphosphonic acid and histamine phosphate.

2. The method according to claim 1, wherein In step (1), the carbon content of the natural graphite powder is ≥90%, and the particle size of the natural graphite powder is ≤100μm.

3. The method according to claim 1, wherein, In step (1), the mass ratio of the natural graphite powder, fluoride salt, water and additive is 1:(0.3~0.8):(1.5~3):(0.01~0.05).

4. The method according to any one of claims 1 to 3, wherein, In step (1), the temperature of the hydrothermal reaction is 150°C~300°C; the time of the hydrothermal reaction is 1h~10h.

5. The method according to any one of claims 1-3, wherein, In step (2), the impurity is at least one of Na2SiF6, K2SiF6 or CaSiF6.

6. The method according to any one of claims 1 to 3, wherein, In step (2), the slurry obtained in step (1) is separated by a centrifugal separation method.

7. The method according to any one of claims 1-3, wherein, In step (3), the carbon content of the obtained high-purity graphite is >99%.

8. The method according to claim 7, wherein In step (3), the carbon content of the obtained high-purity graphite is ≥99.9%.