Method for purifying microcrystalline graphite

Abstract

The invention discloses a method for purifying microcrystalline graphite, which comprises the following steps: 1) carrying out flotation on microcrystalline graphite ore to obtain medium-carbon microcrystalline graphite with the purity of 80-95%, and crushing and screening to obtain microcrystalline graphite powder with the particle size of-200 meshes; 2) mixing the microcrystalline graphite powder obtained in the step 1) with an auxiliary agent, performing roasting treatment in an inert atmosphere, and performing mineral phase reconstruction on impurities in the microcrystalline graphite powder; (3) stirring the roasted material obtained in the step (2) with acid liquor, reacting at the temperature of 50-90 DEG C, and filtering or centrifugally separating the reacted material to obtain acid-pickled microcrystalline graphite; (4) stirring the acid-washed microcrystalline graphite obtained in the step (3) with alkali liquor, reacting at the temperature of 50-90 DEG C, and filtering or centrifugally separating the reacted material to obtain alkali-washed microcrystalline graphite; 5, the alkali-washed microcrystalline graphite obtained in the step 4 is washed 3-5 times and then dried, and purified microcrystalline graphite is obtained.The method for purifying microcrystalline graphite is low in energy consumption, weak in equipment corrosion and small in acid and alkali consumption.

Description

Technical Field

[0001] The present invention relates to the technical field of graphite purification, and particularly relates to a method for purifying microcrystalline graphite. Background Art

[0002] As a mineral resource, graphite has broad application prospects as a battery anode material or a conductive agent in the field of lithium-ion batteries. Microcrystalline graphite has the advantages of small grain size and strong isotropy, and has good fast charging performance compared with flake graphite. However, natural microcrystalline graphite ore often contains a large amount of impurities. The presence of silicon-based impurities (such as quartz, silicate, etc.) will cause the decline of physical and chemical properties such as the conductivity and thermal stability of microcrystalline graphite, seriously restricting the purity and performance of microcrystalline graphite. It is necessary to purify microcrystalline graphite to more than 99% to meet industrial requirements.

[0003] At present, the main methods for purifying microcrystalline graphite include flotation method, alkali-acid method, hydrofluoric acid method, chlorination roasting method, high-temperature method, etc. Among them, in the alkali-acid method, sodium hydroxide reacts with silicon impurities to form sodium silicate, thereby realizing the removal of silicon. However, the alkali melting process has high requirements for the corrosion resistance of equipment, and the equipment maintenance cost is high. Among them, the hydrofluoric acid method needs to use hydrofluoric acid to remove silicon impurities. There are great potential safety hazards in the operation process, and the amount of waste acid generated is large, significantly increasing the environmental protection pressure. Among them, the chlorination roasting method has high equipment cost and the tail gas will cause pollution. Among them, the high-temperature graphitization process has extremely high energy consumption.

[0004] The existing microcrystalline graphite purification technologies have problems such as equipment corrosion, operation hazards, high energy consumption, and serious pollution. It is urgent to develop an efficient, low-pollution and economical purification method to meet the application requirements of graphite in high-value-added fields. Summary of the Invention

[0005] In order to solve the above technical problems, the present invention provides a method for purifying microcrystalline graphite based on the synergistic effect of ore phase reconstruction and acid-base washing.

[0006] In order to achieve the above purpose, the present invention adopts the following technical solutions: The present invention provides a method for purifying microcrystalline graphite, comprising the following steps: 1) The microcrystalline graphite ore is subjected to flotation to obtain medium-carbon microcrystalline graphite with a purity of 80% - 95%, and the microcrystalline graphite powder with a particle size of -200 mesh is obtained by crushing and screening; 2) The microcrystalline graphite powder obtained in step 1) is mixed with an auxiliary agent and calcined under an inert atmosphere to reconstruct the ore phase of the impurities in the microcrystalline graphite powder; 3) The calcined material obtained in step 2) is stirred with an acid solution and reacted at a temperature of 50°C - 90°C. After the reaction, the material is filtered or centrifuged to obtain pickled microcrystalline graphite; 4) Stir the pickled microcrystalline graphite obtained in step 3) with an alkali solution and react at a temperature of 50°C to 90°C. After the reaction, the material is filtered or centrifuged to obtain alkali-washed microcrystalline graphite; 5) Wash the alkali-washed microcrystalline graphite obtained in step 4) with water 3 to 5 times and then dry it to obtain purified microcrystalline graphite.

[0007] Further, in step 2), the obtained microcrystalline graphite powder and the auxiliary agent are mixed evenly at a mass ratio of 1 to 10:1, and calcined at 600°C to 1000°C in an inert atmosphere to reconstruct the mineral phase of the impurities in the microcrystalline graphite powder.

[0008] Further, in step 2), the auxiliary agent is selected from one or more of zinc oxide, zinc chloride, zinc sulfide, zinc sulfate, zinc carbonate, zinc nitrate, zinc acetate, and zinc hydroxide.

[0009] Further, in step 2), the mass ratio of the microcrystalline graphite powder to the auxiliary agent is (1 to 10):1, the calcination temperature is 600°C to 1000°C, and the calcination time is 2 to 10 h.

[0010] Further, in step 3), the acid solution is one or more of sulfuric acid, hydrochloric acid, acetic acid, hydrofluoric acid, and nitric acid.

[0011] Further, in step 3), the concentration of the acid solution is 0.5 to 5 mol / L, and the liquid-solid ratio is 3 to 10 mL / g.

[0012] Further, in step 4), the alkali solution is one or more of sodium hydroxide solution and ammonia water.

[0013] In summary, the beneficial effects of the present invention are as follows: In the process of purifying microcrystalline graphite using a zinc-containing compound in the present invention, zinc reacts with silicate impurities in the microcrystalline graphite at high temperature, causing the mineral phase of the silicate impurities to be reconstructed to form zinc silicate. After acid leaching treatment, zinc silicate dissolves, destroying the silicate framework structure for removal. The process of the present invention is green, safe, simple, and efficient.

[0014] Compared with the high-temperature method, the alkali-acid method, and the hydrofluoric acid method, the method for purifying microcrystalline graphite of the present invention has lower energy consumption, weaker corrosion to equipment, and less consumption of acids and alkalis. It solves the problem that it is difficult to remove impurities, especially silicon impurities, in microcrystalline graphite, and provides a new purification process. Specific embodiments

[0015] To make the objectives, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be described clearly and completely below. Apparently, the described embodiments are some, but not all, of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0016] The present invention provides a method for purifying microcrystalline graphite, comprising the following steps: 1) The microcrystalline graphite ore is subjected to flotation to obtain medium-carbon microcrystalline graphite with a purity of 80% - 95%, and then the -200 mesh microcrystalline graphite powder is obtained through crushing and screening; 2) The microcrystalline graphite powder obtained in step 1) is mixed with an auxiliary agent and calcined under an inert atmosphere to reconstruct the mineral phase of the impurities in the microcrystalline graphite powder; 3) The calcined material obtained in step 2) is stirred with an acid solution and reacted at a temperature of 50°C - 90°C. After the reaction, the material is filtered or centrifuged to obtain pickled microcrystalline graphite; 4) The pickled microcrystalline graphite obtained in step 3) is stirred with an alkali solution and reacted at a temperature of 50°C - 90°C. After the reaction, the material is filtered or centrifuged to obtain alkali-washed microcrystalline graphite; 5) The alkali-washed microcrystalline graphite obtained in step 4) is washed with water 3 - 5 times and then dried to obtain the purified microcrystalline graphite.

[0017] Further, in step 2), the obtained microcrystalline graphite powder and the auxiliary agent are mixed evenly at a mass ratio of 1 - 10:1, and calcined at 600°C - 1000°C under an inert atmosphere to reconstruct the mineral phase of the impurities in the microcrystalline graphite powder.

[0018] Further, in step 2), the auxiliary agent is selected from one or more of zinc oxide, zinc chloride, zinc sulfide, zinc sulfate, zinc carbonate, zinc nitrate, zinc acetate, and zinc hydroxide.

[0019] Further, in step 2), the mass ratio of the microcrystalline graphite powder to the auxiliary agent is (1 - 10):1, the calcination temperature is 600°C - 1000°C, and the calcination time is 2 - 10 h.

[0020] Further, in step 3), the acid solution is one or more of sulfuric acid, hydrochloric acid, acetic acid, hydrofluoric acid, and nitric acid.

[0021] Further, in step 3), the concentration of the acid solution is 0.5 - 5 mol / L, and the liquid-solid ratio is 3 - 10 mL / g.

[0022] Further, in step 4), the alkali solution is one or more of sodium hydroxide solution and ammonia water. Embodiment

[0023] Mix 50 g of microcrystalline graphite with a carbon content of 87% and 16 g of zinc oxide evenly, and then put them into a tubular furnace. Roast them at 900 °C for 6 h under a nitrogen atmosphere. Add the roasted material into 1 mol / L sulfuric acid solution, and stir and heat the reaction at 80 °C for 6 h. After the reaction is completed, filter the material, add the filter cake into 0.5 mol / L sodium hydroxide solution, and stir and heat the reaction at 80 °C for 2 h. Wash and filter the slurry, and then dry it to obtain purified microcrystalline graphite, and its purity is detected to be 99.6%. Example

[0024] Mix 50 g of microcrystalline graphite with a carbon content of 85% and 27 g of zinc chloride evenly, and then put them into a tubular furnace. Roast them at 900 °C for 3 h under an argon atmosphere. Add the roasted material into 2 mol / L sulfuric acid solution, and stir the reaction at 80 °C for 4 h. After the reaction is completed, filter the material, add the filter cake into 1 mol / L sodium hydroxide solution, and stir and heat the reaction at 80 °C for 3 h. Wash and filter the slurry, and then dry it to obtain purified microcrystalline graphite, and its purity is detected to be 99.75%. Example

[0025] Mix 50 g of microcrystalline graphite with a carbon content of 88% and 32 g of zinc sulfate evenly, and then put them into a tubular furnace. Roast them at 880 °C for 6 h under an argon atmosphere. Add the roasted material into 2 mol / L hydrochloric acid solution, and stir the reaction at 80 °C for 4 h. After the reaction is completed, filter the material, add the filter cake into 1 mol / L ammonia water solution, and stir and heat the reaction at 80 °C for 2 h. Wash and filter the slurry, and then dry it to obtain purified microcrystalline graphite, and its purity is detected to be 99.6%.

[0026] The method for purifying microcrystalline graphite of the present invention selects medium-carbon microcrystalline graphite with a carbon content of 80% - 95% as the raw material, and obtains microcrystalline graphite powder with a mesh size of -200 through crushing and screening. Mix the microcrystalline graphite powder with a roasting aid, and after high-temperature heat treatment, pickling, alkali washing, water washing, filtering and drying of the mixed material, purified microcrystalline graphite is obtained. The present invention can solve the problems that it is difficult to remove silicon impurities in microcrystalline graphite and the equipment corrosion or acid-base pollution is serious during the purification process, and can purify medium-carbon microcrystalline graphite to more than 99.5%.

[0027] In the method for purifying microcrystalline graphite of the present invention, during the process of using zinc-containing compounds to purify microcrystalline graphite, zinc reacts with silicate impurities in microcrystalline graphite at high temperature, so that the silicate impurities are mineral-phase reconstructed to form zinc silicate. After acid leaching treatment, zinc silicate dissolves to destroy the silicate framework structure for removal. The process of the present invention is green, safe, simple and efficient.

[0028] The method for purifying microcrystalline graphite of the present invention, compared with the high-temperature method, the alkali-acid method, and the hydrofluoric acid method, has lower energy consumption, weaker corrosion to equipment, and less consumption of acids and alkalis in the process, solves the problem that it is difficult to remove impurities, especially silicon impurities, in microcrystalline graphite, and provides a new purification process.

[0029] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit the protection scope of the present invention. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that the technical solutions of the present invention can be modified or equivalently replaced without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A method for purifying microcrystalline graphite, characterized in that: The following steps are involved: 1) The microcrystalline graphite ore is flotated to obtain medium carbon microcrystalline graphite with a purity of 80% to 95%, and then crushed and screened to obtain -200 mesh microcrystalline graphite powder; 2) mixing the microcrystalline graphite powder obtained in step 1) with an additive, and calcining the mixture under an inert atmosphere to reconstruct the mineral phase of the impurities in the microcrystalline graphite powder; 3) stirring the calcined material obtained in step 2) with an acid solution, reacting at a temperature of 50° C. to 90° C., filtering or centrifuging the material after the reaction to obtain acid-washed microcrystalline graphite; 4) stirring the acid-washed microcrystalline graphite obtained in step 3) with an alkali solution, reacting at a temperature of 50° C. to 90° C., filtering or centrifuging the reaction material to obtain alkali-washed microcrystalline graphite; 5) Wash the alkaline washed microcrystalline graphite ink obtained in step 4) for 3 to 5 times and then dry it to obtain purified microcrystalline graphite.

2. The method for purifying microcrystalline graphite according to claim 1, characterized in that: In the step 2), the obtained microcrystalline graphite powder and the auxiliary agent are uniformly mixed in a mass ratio of 1 to 10:1, and calcined at 600° C. to 1000° C. in an inert atmosphere to reconstruct the mineral phase of impurities in the microcrystalline graphite powder.

3. The method for purifying microcrystalline graphite according to claim 1, characterized in that: In the step 2), the auxiliary agent is selected from one or more of zinc oxide, zinc chloride, zinc sulfide, zinc sulfate, zinc carbonate, zinc nitrate, zinc acetate, and zinc hydroxide.

4. The method for purifying microcrystalline graphite according to claim 1, characterized in that: In the step 2), the mass ratio of the microcrystalline graphite powder to the auxiliary agent is (1-10):1, the calcination temperature is 600°C-1000°C, and the calcination time is 2-10 hours.

5. The method for purifying microcrystalline graphite according to claim 1, characterized in that: In the step 3), the acid solution is one or more of sulfuric acid, hydrochloric acid, acetic acid, hydrofluoric acid, and nitric acid.

6. The method for purifying microcrystalline graphite according to claim 1, characterized in that: In the step 3), the concentration of the acid solution is 0.5-5 mol / L, and the liquid-to-solid ratio is 3-10 mL / g.

7. The method for purifying microcrystalline graphite according to claim 1, characterized in that: In the step 4), the alkali solution is one or more of sodium hydroxide solution and ammonia water.