A simple purification method of coal-based graphite

Abstract

This invention belongs to the field of quartz sandstone purification technology, specifically relating to a simple purification method for coal-based graphite, comprising the following steps: crushing low-grade coal-based graphite as raw material to obtain crushed coal-based graphite; mixing the crushed coal-based graphite with solid alkali and flux, followed by calcination and alkali fusion treatment to obtain calcined and alkali-fused coal-based graphite; acid leaching the calcined and alkali-fused coal-based graphite, followed by water washing, filtration, and drying to obtain high-grade coal-based graphite. Compared with existing graphite purification technologies, this invention does not require costly and hazardous reaction reagents or harsh conditions of high temperature and high pressure, and has advantages such as high graphite product purity, simple processing, convenient operation, mild conditions, environmental friendliness, and low cost. Using low-grade coal-based graphite with a fixed carbon content of 65%–85% as raw material, the process of this invention can obtain high-purity graphite with a fixed carbon content greater than 99.5%.

Description

Technical Field

[0001] This invention belongs to the field of coal-based graphite purification technology, specifically relating to a simple purification method for coal-based graphite. Background Technology

[0002] Graphite has always been an indispensable strategic resource for modern industrial and military development. Coal-associated graphite is a product of coal subjected to thermal contact metamorphism by magma and tectonic dynamic metamorphism, and is mostly cryptocrystalline graphite, forming an important component of graphite minerals. Compared to crystalline graphite, coal-associated graphite is characterized by concentrated ore bodies, high grade, and ease of development, with enormous potential resources. Coal-associated graphite is inexpensive and its particles are nearly isotropic, making it an excellent raw material for high-tech products such as isostatic graphite and lithium-ion battery anode materials. It can also be used to prepare graphene, thus belonging to the category of strategic emerging minerals.

[0003] The purity of graphite determines the performance and overall quality of deep-processed graphite products; higher purity graphite has higher application value. In recent years, emerging industries such as new energy and new materials have required high-purity coal-based graphite, necessitating new processes for preparing high-grade coal-based graphite. While there is considerable research on the purification of natural flake graphite, research on the purification of coal-based graphite is relatively limited. Furthermore, the high technical difficulty in purifying coal-based graphite is one of the main reasons restricting its application scope.

[0004] Currently, the purification of coal-based graphite largely relies on the purification technology of natural flake graphite. Common purification methods include: (1) flotation; (2) high-temperature method; (3) alkali-acid method; (4) hydrofluoric acid method; and (5) hydrofluoric acid-hydrochloric acid (sulfuric acid) method. Among these, the product grade purified by flotation is generally between 90% and 95%, making it difficult to obtain products with a purity of over 95%. The high-temperature method involves heating the graphite raw material to 1000–1800°C under nitrogen protection, introducing a halogen-containing mixed gas for 0.5–2 hours, and then continuing to heat it to 2000–2300°C before introducing chlorine gas for 1–2 hours. This method can obtain high-purity graphite with a carbon content of over 99.99%, but the high-temperature treatment process consumes too much energy and uses a large amount of halogen gas. Hydrofluoric acid and hydrofluoric acid-sulfuric acid methods have high impurity removal efficiency and relatively low energy consumption, but their application is limited due to the significant safety hazards and prominent environmental problems associated with hydrofluoric acid.

[0005] The acid-base method is currently a relatively good method for graphite purification. However, it still has the following problems: high alkali calcination temperature (700-1000℃), long time (2-3 hours), severe equipment corrosion, and residual graphite adhering to the equipment, affecting its thermal conductivity and service life. While the alkali-acid method can achieve a graphite content of over 99%, impurities in the graphite raw material are often embedded in the graphite flakes, preventing sufficient contact and reaction with the reagents, thus affecting the purification effect. Therefore, it is necessary to provide a simple purification method for coal-based graphite, optimizing process conditions to minimize costs, reduce energy consumption, and improve efficiency. Summary of the Invention

[0006] The purpose of this invention is to provide a simple purification method for coal-based graphite, which has the advantages of high graphite product purity, simple processing, convenient operation, mild conditions, environmental friendliness, and low cost.

[0007] The objective of this invention is achieved through the following technical solution:

[0008] This invention provides a simple purification method for coal-based graphite, comprising the following steps:

[0009] Step 1: Low-grade coal-based graphite is used as raw material and crushed to obtain crushed coal-based graphite.

[0010] Step 2: The pulverized coal-based graphite is mixed with solid alkali and flux and then subjected to calcination and alkali fusion treatment to obtain calcined and alkali-fused coal-based graphite.

[0011] Step 3: The calcined coal-based graphite after alkali fusion is acid-leached, washed with water, filtered, and dried to obtain high-grade coal-based graphite;

[0012] The low-grade coal-series graphite is coal-series graphite with a fixed carbon content of 65% to 85%, and the high-grade coal-series graphite is coal-series graphite with a fixed carbon content of 99.5% or higher.

[0013] Furthermore, in step 1, the particle size of the coal-based graphite after pulverization is less than 100 μm.

[0014] Furthermore, in step 2, the mass ratio of the solid alkali to the pulverized coal-based graphite is (0.4:1) to (1:1); the mass ratio of the flux to the pulverized coal-based graphite is (0.01:1) to (0.1:1).

[0015] Furthermore, in step 2, the solid alkali is sodium hydroxide or potassium hydroxide; the flux is sodium metaborate or lithium metaborate.

[0016] Furthermore, in step 2, the mixing process is as follows: the coal-based graphite after being crushed in step 1 is placed in a mixing tank, solid alkali and flux are added, and the mixture is mixed at room temperature for 1 to 2 hours to obtain a mixture; the calcination and alkali fusion process is as follows: the mixture is loaded into a sagger and placed in a muffle furnace, and reacted at 300 to 600°C for 1 to 3 hours to carry out calcination and alkali fusion treatment.

[0017] Furthermore, in step 3, the acid leaching involves crushing the calcined alkali-fused coal-based graphite, adding acid to make the solution pH 1-3, stirring evenly, and then allowing it to settle. The water washing involves extracting the upper liquid after acid leaching and adding pure water to wash the acid-leached coal-based graphite until it is neutral.

[0018] Furthermore, in step 3, the acid addition is the addition of hydrochloric acid with a mass concentration of 10-35%; the stirring time is 0.5-2 hours.

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

[0020] This invention provides a simplified purification method for coal-based graphite, yielding graphite with a fixed carbon content greater than 99.5%. Compared to existing graphite purification technologies, this method eliminates the need for costly and hazardous reaction reagents and harsh conditions requiring high temperature and pressure. It offers advantages such as high graphite product purity, simple processing, convenient operation, mild conditions, environmental friendliness, and low cost. The simplified purification method for coal-based graphite utilizes a mixing-calcination-alkali fusion-acid leaching and water washing process. The process is simple, with each step interconnected. After crushing, the gangue minerals and graphite in the raw ore are fully dissociated. After mixing, the gangue minerals and graphite in the raw ore come into full contact with the alkali and flux, facilitating a thorough reaction between the gangue minerals and the alkali during subsequent alkali fusion, thus aiding in the removal of impurities. Traditional high-temperature roasting requires temperatures above 700℃, while the calcination-alkali fusion method of this invention only requires 300–600℃, significantly reducing energy consumption. Attached Figure Description

[0021] Figure 1 A process flow diagram of the simplified purification method for coal-based graphite provided by the present invention. Detailed Implementation

[0022] The following experimental examples and embodiments are used to further illustrate the present invention, but are not limited to the present invention.

[0023] The present invention provides a simple purification method for coal-based graphite, comprising the following steps:

[0024] S1. Using low-grade coal-series graphite from Chenzhou or Lengshuijiang in Hunan Province as raw material, the ore is crushed to a particle size of less than 100μm. After crushing, the gangue minerals and graphite in the original ore are fully dissociated, which facilitates the full reaction between gangue minerals and alkali during subsequent alkali fusion.

[0025] S2. The coal-based graphite pulverized in step S1 is mixed with solid alkali (the mass ratio of solid alkali to pulverized coal-based graphite is (0.4:1) to (1:1)) and flux (the mass ratio of flux to pulverized coal-based graphite is (0.01:1) to (0.1:1)). The mixture is then placed in a muffle furnace for calcination and alkali fusion treatment. The mixing process is as follows: the coal-based graphite pulverized in step S1 is placed in a mixing tank, solid alkali and flux are added, and the mixture is mixed at room temperature for 1 to 2 hours. After mixing, the gangue minerals and graphite in the original ore can fully contact the alkali and flux, which is beneficial for the subsequent removal of impurities. The calcination and alkali fusion process is as follows: the mixture is loaded into a sagger and placed in a muffle furnace, and reacted at 300 to 600°C for 1 to 3 hours for calcination and alkali fusion treatment. Traditional high-temperature roasting requires a temperature of over 700°C. Compared with traditional high-temperature roasting, this invention greatly reduces energy consumption.

[0026] S3. The coal-based graphite after calcination and alkali fusion in step S2 is subjected to acid leaching, followed by water washing, filtration, and drying to obtain high-grade coal-based graphite. The acid leaching process is as follows: the coal-based graphite after calcination and alkali fusion in step S2 is crushed, acid is added to make the pH of the solution 1-3, the mixture is stirred evenly and allowed to settle, the upper liquid is extracted and pure water is added, the acid-leached minerals are washed with water until neutral, and the solution is filtered and dried to obtain high-grade graphite.

[0027] Low-grade coal-series graphite generally includes gangue minerals in addition to graphite, such as quartz, feldspar, calcite, clay minerals, and small amounts of iron-titanium minerals. It should be noted that low-grade coal-series graphite in the above method refers to coal-series graphite with a fixed carbon content of 65%–85%; high-grade graphite refers to graphite with a fixed carbon content of 99.5% or higher.

[0028] In step S2, the solid alkali is sodium hydroxide or potassium hydroxide, and the flux is sodium metaborate or lithium metaborate; in step S3, the added acid is hydrochloric acid with a mass concentration of 10-35%, and the stirring time is 0.5-2 hours.

[0029] The following embodiments are used to further illustrate the present invention, but are not limited to the present invention. The process flow diagram of the simplified purification method for coal-based graphite in the present invention is shown below. Figure 1 As shown.

[0030] Example 1

[0031] In this embodiment, coal-based graphite with a fixed carbon content of 85% from Chenzhou, Hunan Province, was used as raw material. 100g of coal-based graphite was weighed and crushed to 100μm to achieve a certain degree of dissociation between gangue and graphite in the raw ore. Then, 40g of sodium hydroxide, 1g of sodium metaborate flux, and 100g of crushed coal-based graphite were added to a mixing tank and mixed for 1 hour. The mixture was then placed in a sagger and placed in a muffle furnace and reacted at 300℃ for 1 hour for calcination and alkali fusion treatment. The alkali-fused product was crushed, and 10% dilute hydrochloric acid was slowly added to adjust the pH of the solution to 3. After stirring for 0.5 hours, the solution was allowed to settle, the supernatant was extracted, and then deionized water was added to wash until neutral. The solution was filtered and dried to obtain 84.29g of graphite product with a fixed carbon content of 99.77%.

[0032] Example 2

[0033] In this embodiment, coal-based graphite with a fixed carbon content of 65% from Chenzhou, Hunan Province, was used as raw material. 100g of coal-based graphite was weighed and crushed to 60μm to achieve a certain degree of dissociation between gangue and graphite in the raw ore. Then, 100g of sodium hydroxide, 10g of lithium metaborate flux, and 100g of crushed coal-based graphite were added to a mixing tank and mixed for 2 hours. The mixture was then placed in a sagger and placed in a muffle furnace and reacted at 600℃ for 3 hours for calcination and alkali fusion treatment. The alkali-fused product was crushed, and 35% dilute hydrochloric acid was slowly added to adjust the pH of the solution to 1. After stirring for 2 hours, the solution was allowed to settle, the supernatant was extracted, and then deionized water was added to wash until neutral. The solution was filtered and dried to obtain 63.26g of graphite product with a fixed carbon content of 99.83%.

[0034] Example 3

[0035] In this embodiment, coal-based graphite with a fixed carbon content of 71% from Lengshuijiang, Hunan Province, was used as raw material. 50g of coal-based graphite was weighed and crushed to 80μm to achieve a certain degree of dissociation between gangue and graphite in the raw ore. Then, 40g of potassium hydroxide, 2g of lithium metaborate flux, and 50g of crushed coal-based graphite were added to a mixing tank and mixed for 1.5h. The mixture was then placed in a sagger and placed in a muffle furnace and calcined and alkali-fused at 400℃ for 2h. The alkali-fused product was crushed, and 15% dilute hydrochloric acid was slowly added to adjust the pH of the solution to 2. After stirring for 1h, the solution was allowed to settle, the supernatant was extracted, and then deionized water was added to wash until neutral. The solution was then filtered and dried to obtain 35.16g of graphite product with a fixed carbon content of 99.72%.

[0036] Example 4

[0037] In this embodiment, coal-based graphite with a fixed carbon content of 82% from Lengshuijiang, Hunan Province, was used as raw material. 50g of coal-based graphite was weighed and crushed to 50μm to achieve a certain degree of dissociation between gangue and graphite in the raw ore. Then, 30g of potassium hydroxide, 1.5g of sodium metaborate flux, and 50g of crushed coal-based graphite were added to a mixing tank and mixed for 1 hour. The mixture was then placed in a sagger and placed in a muffle furnace and reacted at 500℃ for 2 hours for calcination and alkali fusion treatment. The alkali-fused product was crushed, and 25% dilute hydrochloric acid was slowly added to adjust the pH of the solution to 2. After stirring for 1 hour, the solution was allowed to settle, the supernatant was extracted, and then deionized water was added to wash until neutral. The solution was then filtered and dried to obtain 40.81g of graphite product with a fixed carbon content of 99.84%.

[0038] In summary, the simplified purification method for coal-based graphite of this invention, through a mixing-calcination-alkali fusion-acid leaching and water washing process, is simple and interconnected. After crushing, the gangue minerals and graphite in the raw ore are fully dissociated. After mixing, the gangue minerals and graphite in the raw ore are in full contact with the alkali and flux, facilitating the reaction between the gangue minerals and alkali during subsequent alkali fusion and promoting the removal of impurities. After acid washing, high-grade graphite with a fixed carbon content greater than 99.5% is obtained. This purification method of the present invention has advantages such as low cost, low requirements on the grade of the raw coal-based graphite, simple processing, convenient operation, mild conditions, environmental friendliness, and low cost.

[0039] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A simple purification method of coal-based graphite, characterized by, The method comprises the following steps: Step 1: low-grade coal-based graphite is crushed as raw material to obtain crushed coal-based graphite; Step 2: the crushed coal-based graphite is mixed with solid alkali and fluxing agent, and then calcined alkali fusion treatment is performed to obtain calcined alkali fusion coal-based graphite; Step 3: the calcined alkali fusion coal-based graphite is subjected to acid immersion, and then water washing, filtration and drying are performed to obtain high-grade coal-based graphite; The low-grade coal-based graphite has a fixed carbon content of 65-85%, and the high-grade coal-based graphite has a fixed carbon content of more than 99.5%; In step 1, the particle size of the crushed coal-based graphite is less than 100 μm; In step 2, the mass ratio of the solid alkali to the crushed coal-based graphite is (0.4:1)-(1:1), and the mass ratio of the fluxing agent to the crushed coal-based graphite is (0.01:1)-(0.1:1); In step 2, the solid alkali is sodium hydroxide or potassium hydroxide, and the fluxing agent is sodium metaborate or lithium metaborate; In step 2, the mixing is performed as follows: the crushed coal-based graphite obtained in step 1 is placed in a mixing tank, solid alkali and fluxing agent are added, and mixing is performed at room temperature for 1-2 h to obtain a mixture; the calcined alkali fusion process is as follows: the mixture is loaded into a sagger and placed in a muffle furnace, and calcined alkali fusion treatment is performed at 300-600 ℃ for 1-3 h; In step 3, the acid immersion is performed as follows: the calcined alkali fusion coal-based graphite is crushed, acid is added, the pH value of the solution is adjusted to 1-3, and then uniform stirring is performed and the solution is allowed to stand and settle; the water washing is performed as follows: after the acid immersion, the upper liquid is removed, and pure water is added to wash the acid-immersed coal-based graphite to neutral; In step 3, the acid added has a mass concentration of 10-35%, and the stirring time is 0.5-2 h.

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