What Are the Properties of Graphite?

Graphite is an allotrope of carbon. It is a gray-black, opaque solid with a density of 2.25 grams per cubic centimeter, a melting point of 3652 ° C, and a boiling point of 4827 ° C. It has stable chemical properties, corrosion resistance, and is not easy to react with acids and alkalis. Combustion in oxygen produces carbon dioxide at 687 ° C. Can be oxidized by strong oxidants such as concentrated nitric acid and potassium permanganate. Can be used as antiwear agent, lubricant, high purity graphite as neutron moderator in atomic reactor, can also be used in the manufacture of crucible, electrode, brush, dry battery, graphite fiber, heat exchanger, cooler, electric arc furnace, Arc lights, pencil refills, etc. ^[1]

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Chinese name: graphite
English name: graphite
nickname: Stone nirvana, stone black, stone snail, stone dai, thrush stone
Chemical formula: C
Molecular weight: 12.01
CAS Registry Number: 7782-42-5
EINECS registration number: 231-955-3
Melting point: 3652

Boiling point: 4827
Water soluble: not soluble in water
Density: 2.25g / cm³
Exterior: Black solid
Application: Pencil lead, refractory material, conductive material, lubricating material, carbon manufacturing, radiation protection material, etc.
Risk description: Non-toxic, inhalation of dust can cause respiratory disease
Boiling point: 4827
Chemical properties: Stable, corrosion-resistant, difficult to react with acids and alkalis

Introduction to graphite

Graphite structure composition

Graphite is a transitional crystal between atomic crystals, metal crystals and molecular crystals. In the crystal, carbon atoms in the same layer are sp2 hybridized to form a covalent bond. Each carbon atom is connected to three other carbon atoms. Six carbon atoms form a regular hexagonal ring on the same plane and stretch to form a sheet structure. . Carbon atoms in the same plane each have one p orbital, which overlap each other, and the delocalized -bond electrons can move freely in the crystal lattice and can be excited, so graphite has a metallic luster, can conduct electricity and transfer heat. Because the distance between the layers is large, the binding force (Van der Waals force) is small, and the layers can slide, so the density of graphite is smaller than that of diamond, soft and smooth. ^[1]

The distance between each layer of graphite is 3.40 Å, which is combined by van der Waals force, that is, the layer is a molecular crystal.

Molecular structure (3 photos)

The spacing of carbon atoms in the same mesh layer is 1.42 Å. Due to the strong bonding between carbon atoms on the same plane layer, it is extremely difficult to destroy, so the melting point of graphite is also very high, and the chemical properties are also stable. In view of its special way of bonding, it cannot be regarded as a single crystal or a polycrystal, and graphite is now generally considered to be a mixed crystal. ^[2]

Graphite is a hexagonal crystal system with complete layered cleavage. The cleavage surface is dominated by molecular bonds and has a weak attraction to molecules, so its natural floatability is very good. ^[2]

Physical and Chemical Properties of Graphite

Graphite is soft, black and gray, greasy and can contaminate paper. The hardness is 1 to 2, and the hardness can be increased to 3 to 5 with the increase of impurities in the vertical direction. The specific gravity is 1.9 to 2.3. The specific surface area is concentrated in the range of 1-20m ² / g, and its melting point is above 3000 ° C under the condition of isolated oxygen, which is one of the most temperature-resistant minerals. It can conduct electricity and heat. ^[2]

There is no pure graphite in nature, and it often contains impurities such as SiO ₂ , Al ₂ O ₃ , FeO, CaO, P ₂ O ₅ and CuO. These impurities often appear in the form of minerals such as quartz, pyrite, carbonate. In addition, there are gaseous parts such as water, asphalt, CO ₂ , H ₂ , CH ₄ , N ₂ and the like. Therefore, for the analysis of graphite, in addition to the fixed carbon content, the volatile and ash content must be measured simultaneously. ^[2]

Graphite and diamond, carbon 60, carbon nanotubes, graphene, etc. are all simple elements of carbon, and they are allotropics. ^[2]

Special properties of graphite

Because of its special structure, graphite has the following special properties: ^[2]

(1) High temperature resistance

The melting point of graphite is 3850 ± 50 . Even if it is burned by ultra-high temperature arc, the weight loss is very small and the thermal expansion coefficient is very small. The strength of graphite increases with temperature. At 2000 ° C, the strength of graphite doubles. ^[2]

(2) Electrical and thermal conductivity

The conductivity of graphite is one hundred times higher than that of general non-metallic ore. Thermal conductivity exceeds metal materials such as steel, iron, lead

graphite . Thermal conductivity decreases with increasing temperature. Even at extremely high temperatures, graphite becomes a thermal insulator. Graphite can conduct electricity because each carbon atom in the graphite forms only three covalent bonds with other carbon atoms, and each carbon atom still retains one free electron to transfer charge. ^[2]

(3) Lubricity

The lubrication performance of graphite depends on the size of graphite scales. The larger the scale, the smaller the friction coefficient, and the better the lubrication performance. ^[2]

(4) Chemical stability

Graphite has good chemical stability at room temperature and is resistant to acid, alkali and organic solvents. ^[2]

(5) Plasticity

Graphite has good toughness and can be rolled into very thin flakes. ^[2]

(6) Thermal shock resistance

Graphite can withstand severe temperature changes without damage when used at normal temperature. When the temperature changes suddenly, the volume of graphite does not change much and no cracks will occur. ^[2]

Graphite other

Graphite can be divided into two categories: natural graphite and artificial graphite. Natural graphite comes from graphite deposits. Natural graphite can also be divided into flake graphite, earthy graphite, and block graphite. Naturally mined graphite contains a lot of impurities, so it needs beneficiation and can be used after reducing its impurity content. The main use of natural graphite is to produce refractory materials, brushes, flexible graphite products, lubricants, and lithium ion battery anode materials. Some carbon products are sometimes added with a certain amount of natural graphite. ^[3]

In the carbon industry, the largest production is various artificial graphite products. Artificial graphite products generally use petroleum coke and asphalt coke that are easily graphitizable as raw materials. After batching, kneading, molding, baking, graphitization (high temperature heat treatment) and mechanical processing It is made by a series of processes, and the production cycle is dozens of days. ^[3]

There are many types of artificial graphite, such as single crystal graphite, polycrystalline graphite, pyrolytic graphite, highly oriented pyrolytic graphite, polyimide

Graphite (12 photos)

Synthetic graphite, graphite fiber, etc., most artificial graphite products belong to the category of polycrystalline graphite. The main products in artificial graphite are graphite electrodes used in electric arc steelmaking furnaces and mineral thermal electric furnaces. Graphite electrodes are a kind of conductive material that is resistant to high temperatures and corrosion. Artificial graphite is also widely used in many other industrial sectors, such as electric motor brushes, precision casting molds, EDM molds and wear-resistant parts in the mechanical industry, electrical conductors or corrosion-resistant equipment used in electrolytic cells in the chemical industry, High-purity and high-strength artificial graphite is used as a reactor structural material in the nuclear industry sector and as a component for missile rockets. ^[3]

Graphite can also be made of heat dissipation materials, sealing materials, heat insulation materials, and radiation protection materials. Graphite functional materials are widely used in metallurgy, chemical industry, machinery and equipment, new energy vehicles, nuclear power, electronic information, aerospace and defense and other industries. In the report "European Raw Materials At stake" issued by the European Commission, graphite is included in 14 scarce mineral raw materials. ^[4]

Distribution and classification of graphite minerals

Graphite Mineral Distribution

The large and medium-sized graphite deposits discovered in the world are mainly distributed in China, India, Brazil, Czech Republic, Canada, Mexico and other countries. According to the US Geological Survey, the world's graphite reserves are 71 million tons, and China's graphite reserves are 55 million tons, accounting for 77% of the world. Graphite deposits in Brazil are distributed in Minas Gerais, Ceara, and Bahia. The best graphite is distributed in Paidarajul, Minas Gerais ( Pedra Azul), with proven ore reserves of 250 million tons. Graphite mines in India are mainly distributed in the states of Orissa and Rajasthan. According to the Indian Mining Annual Report, the graphite reserves in India are 10.75 million tons and the resources are 15.8025 million tons. Canadian graphite deposits are located in Ontario, British Columbia and Quebec. The Bissett Creek graphite deposit is the largest graphite deposit in North America. Sri Lanka's veined graphite deposits are world-famous and are the only highly graphitized veined graphite deposits in the world, located in the western and southwestern part of the island of Sri Lanka. ^[4]

There are two types of graphite minerals in China: crystalline graphite and cryptocrystalline graphite. According to statistics from the Ministry of Land and Resources, as of the end of 2009, China's crystalline graphite mineral reserves were 30.41 million tons, the basic reserves were 54.32 million tons, and the resources were 13.54 million tons. In the past 20 years, China's crystalline graphite reserves have been increasing, but the large-scale graphite graphite reserves have been reduced to less than 5 million tons. Crystalline graphite is distributed in 20 provinces (autonomous regions) including Heilongjiang, Shandong and Inner Mongolia. ^[4]

Classification of graphite resources

Graphite deposits are mainly medium and small, and the types of deposits are roughly divided into the following five types: layer-like graphite deposits in crystalline schist; graphite deposits in metamorphic coal seams; graphite deposits in nepheline orthoclase; Graphite deposits in karst; vein-like graphite deposits in crystalline schist. ^[5]

There are three types of natural graphite resources. They are block graphite, flake graphite, and earthy graphite (cryptocrystalline graphite). See Table 1 for details. ^[5]

(1) Dense crystalline graphite <br /> Dense crystalline graphite is also called block graphite. Such graphite crystals are clearly visible to the naked eye. The diameter of the particles is greater than 0.1 mm, and the specific surface area is concentrated in the range of 0.1-1 m / g. The crystals are arranged disorderly and have a dense block structure. This type of graphite is characterized by high grades, generally having a carbon content of 60 to 65%, and sometimes 80 to 98%, but its plasticity and smoothness are not as good as flaky graphite. ^[2]

Bulk graphite is the rarest and most valuable graphite mine found mainly in Sri Lanka. ^[5]

(2) Scaly graphite < br Scaly graphite is a combination of many single layers of graphite. It exists as a separate plate in metamorphic rocks, with small reserves and high value. The crystal is scaly, which is at high strength. Degraded under pressure, there are large scales and fine scales. This type of graphite ore is characterized by a low grade, generally between 2 and 3%, or between 10 and 25%. It is one of the most buoyant ores in nature, and can obtain high-grade graphite concentrate after multiple grinding and multiple selection. This type of graphite has superior floatability, lubricity and plasticity than other types of graphite, so it has the largest industrial value. ^[2]

Flake graphite is mainly distributed in Australia, Brazil, Canada, China, Germany and Madagascar. ^{[5] In} recent years, a large number of flake graphite resources have also been found in Africa, Tanzania and Mozambique. Some scholars have studied the flake graphite ore in Ancuaba, Mozambique and Chilalo in Tanzania. The results show that the mineral composition in the graphite ore in Ancuaba and Chilalo is similar, and both are high-quality large-scale graphite resources. ^[6]

(3) Cryptocrystalline graphite <br /> Cryptocrystalline graphite is also called microcrystalline graphite or earthy graphite. The crystal diameter of this graphite is generally less than 1 micron, and the specific surface area is concentrated in the range of 1-5m / g. The aggregate of graphite can only be seen under the electron microscope. This type of graphite is characterized by a clay-like surface, lacks gloss, and is slightly inferior to flaky graphite. High grade. Generally 60 to 85%, a few as high as 90%. Generally used in the foundry industry. With the improvement of graphite purification technology, earthy graphite is becoming more and more widely used. ^[2]

Earthy graphite is the one with the most reserves, with small scales and low crystallinity. It is used to produce low-value products. It is the lowest price among the three types of graphite. Earthy graphite is mainly contained in Turkey, China, Europe, Mexico and the United States.

Global graphite reserves in 2015 were 230 million tons, of which Turkey's graphite reserves were 90 million tons, accounting for 39.13% of global reserves, Brazil was 72 million tons, accounting for 31.30% of global reserves, and China was 55 million tons, accounting for global reserves. 23.91%. ^[7]

Types of	Earthy graphite	Flake graphite	Block graphite
Crystalline state	not good	better	well
Crystal size	0.01 0.1m	0.05 1.5 mm (> 1.0 m)	> 0.1 mm
grade	60% 80%, a few as high as 90%	2% 5%, or between 10% 25%	60% to 65%, high up to 80% to 98%
Floatability	not good	it is good	it is good
Origin	Turkey, Europe, China, Mexico, and the United States	Australia, Brazil, Canada, China, Germany, and Madagascar	Sri Lanka

Graphite Industry Overview

Overview of Graphite Mineral Development

In 2010, the world's natural graphite output was 1.1 million tons. China's graphite output is 800,000 tons (crystalline graphite and cryptocrystalline graphite), accounting for 73% of the world's output. In the past 30 years, China's graphite production has ranked first in the world. In 1995, China's graphite output reached a record high of 2.215 million tons, of which crystalline graphite output was 549,000 tons and cryptocrystalline graphite output was 1.656 million tons. In 2008, China s crystalline graphite output reached a record high of 650,000 tons; in 2009, the crystalline graphite output fell to 480,000 tons, while the output of earthy graphite raw ore was about 1 million tons. China's crystalline graphite has been developed in 16 provinces (autonomous regions) including Inner Mongolia, Heilongjiang, Shandong, Hebei, Henan, Hubei, and Sichuan. Important producing areas include Jixi and Luobei in Heilongjiang, Pingdu and Laixi in Shandong, Xinghe, Inner Mongolia, Chicheng, Hebei, Neixiang, Henan, Yichang, Hubei, and Nanjiang, Sichuan. The development of cryptocrystalline graphite in China is mainly in the Yinzhou area of Hunan Province and the Panshi area of Jilin Province. Many companies in Yinzhou area of Hunan Province use ultra-high temperature technology to produce high-purity microcrystalline graphite. ^[4]

India's graphite output ranks second in the world, accounting for 11.6% of the world's graphite output. India's graphite output in 2009 was 130,000 tons. The development of graphite is mainly in Orissa and Rajasthan. The production of graphite in Orissa is 65% to 75%. The main producer is Agrawal Graphite Industry Corporation (Garawudar) and Thailand Two graphite mines in Temtimal; TP Minerals develops graphite mines near Phulbani, Madagudarf and Sargipali. The two companies produce flake graphite and Powder graphite products. Agraval Graphite Industries plans to develop new graphite products for the battery industry. ^[4]

Brazil's graphite output ranks third in the world, accounting for 7.5% of the world's graphite output. Graphite production has been stable in recent years. In 2009, the output of graphite was 76,000 tons. Brazil's National Graphite Co., Ltd. (National de Grafite) is the country's main graphite producer and one of the world's largest producers of natural crystalline graphite. It has 3 crystalline graphite mines in Minas Gerais. The graphite production capacity is 52,000 tons / year, and the output accounts for about two-thirds of Brazil's total output. Each mine has a graphite processing plant. The carbon content of the raw ore of ittaperica graphite mine is 16%. The processing plant production capacity 14,400 tons / year, graphite products are used in batteries, brushes and lubricants; the Salto de Divsa graphite processing plant produces large scale graphite, which is used in refractory materials, crucibles, metallurgical molds and High carbon steel additive, production capacity expanded to 14,400 tons / year; Pedra Azul is Brazil's largest graphite deposit, graphite production capacity of 45,800 tons / year. Brazil National Graphite Co., Ltd. plans to adjust the structure of graphite products, develop and produce new nodular graphite products for the battery industry, including large lithium-ion batteries for electric vehicles. Another important graphite producer in Brazil is Grafita MG Ltd., which is also mining graphite in the Minas Gerais region. The Brazilian refractory company Mag-nesita plans to develop graphite minerals in eastern Brazil. Within two years, the graphite production capacity will reach 40,000 tons / year. The company will develop and expand to upstream mineral raw materials in order to ensure the self-sufficiency of graphite raw material supply. ^[4]

Canadian graphite production is 25,000 tons. The major graphite producers are Timcal and Eagle Graphite. Timcal Canada's mines and processing facilities are located in Lac des Iles, and its production capacity is kept secret. In 2007, many developers in Canada planned to build graphite production bases. Due to the financial crisis, the graphite development projects of these companies were suspended. In 2010, the demand for graphite in the international market increased, and graphite prices rose. Industrial Minerals Corporation (IMI) develops the Bissett Creek flaky graphite mine, located in Maria City, Ontario. The company aims to become the largest flaky graphite producer in North America. FortuneGraphite Inc. develops cryptocrystalline and flaky graphite. The mine is located in the Kootenay area in southeastern British Columbia. Quinto Mining Corp. develops the LacGueret graphite deposit, located in the Cotenord region of northeastern Quebec, with a graphite grade of 15% to 40%. Global Graphite Co., Ltd. develops the Superior graphite deposit, which is flake graphite with an ore reserve of 55 million tons. ^[4]

The graphite mine in North Korea is buried deep and needs underground mining. It is not easy to increase mine production. In recent years, graphite production has stabilized at 30,000 tons; the graphite developers in Madagascar are Societe Miniere de la Grande Ile and Establissments Gallois. In 2008, graphite production was reduced to 50 thousand tons. The graphite deposits in Ukraine are distributed in KirovogradOblast. The graphite developer is Zavalivsky Grafitovy Kombinat. The graphite production in Ukraine ranges from 75,000 to 10,000 tons. Sri Lanka has a world-renowned vein shape. Graphite deposits are located in the western and southwestern parts of the island of Sri Lanka. The graphite veins are buried deep and require underground mining. Bogala Graphite SriLanka is a subsidiary of German GK. The company imported new equipment from the UK and equipped with a graphite processing plant. There are 2 graphite developers in the Czech Republic, Coynur Graphite and Tyne Graphite. , Located in southern Bohemia, has been processing graphite products since the 17th century. Coinur Graphite Mining Corporation processes and processes flake graphite. Tyne Graphite is a subsidiary of German GK Company. The company has been producing graphite products since 1965. In recent years, it has focused on developing high-purity graphite, especially graphite products for batteries; ^[4] Grafitbergbau Kaiserberg, Austria The open-cast graphite mine is located in Kaiserberg and Trieben. The graphite processing plant operations include drying, classification, grinding and flotation and ultra-fine grinding. The plant has a cryptocrystalline graphite flotation plant. With a processing capacity of 30,000 tons, the company supplies fine graphite, large particle graphite, flake graphite, and synthetic graphite; ^[4] Timcal, Switzerland is the world's leading manufacturer of vertically integrated graphite. Graphite development is distributed in Canada, Europe and Asia, and product distribution agencies are distributed in South Africa, Australia, India, Malaysia and Thailand. The company has obtained 85% equity of Baotou Epistar Graphite Company in China; ^[4] Australia does not currently mine graphite. It is possible to develop and produce graphite products in the future. Eagle Bay Resources owns the Uley graphite deposit, with a carbon content of 7.4% and a reserve of 3.77 million tons, a carbon content of 13.7% and a reserve of 2.44 million tons. There is a processing plant near the deposit. The plant ceased production in 1993, mainly Because the graphite price in the international market is low. The Munglinup graphite deposit has large scale graphite, which is owned by a subsidiary of lithium concentrate producer Gwalia. The graphite mine was mined between 1953 and 1956 because of graphite prices. Production has been suspended for low reasons. The estimated and estimated resources are 1.4 million tons, with an average grade of 18.2% and a depth of 55 meters. ^[4]

Overview of graphite production and consumption

Affected by the recovery of the world economy on the graphite industry, world graphite demand has steadily increased in recent years. According to the US Geological Survey (USGS), in 2012, the world's major graphite producing countries were China, India, Brazil, Canada, North Korea, Russia and the Czech Republic. ^[4]

China has the largest output of 750,000 tons, accounting for 68% of world graphite production. The main exporters of natural graphite are China, Mexico, Canada, Brazil, and Madagascar. These countries export 97% of the world's graphite, accounting for 90% of graphite exports. Earthy graphite is mainly exported from Mexico, bulk graphite is exported from Sri Lanka, China, Canada, and Madagascar export crystalline flake graphite. ^[4]

With the advancement of heating technology and acid leaching technology, the purity of graphite that can be obtained is getting higher and higher, opening up new applications of graphite in the field of high-tech technology. The innovation of purification technology has made graphite more widely used in carbon composite materials, electronics industry, friction materials, lubrication and other fields. The flexible graphite industry represented by graphite paper has a good market prospect, and the widespread application of a large number of fuel cells has increased the amount of graphite. ^[4]

China is a large graphite producer and consumer, but it is not a graphite power. The current backward processing and purification technology in the graphite industry is extremely unevenly developed in China. In some areas, there are no graphite purification companies at all, and they are still selling graphite resources. For some high-tech natural graphite products, some need to develop from graphite-free resources Country imports. The passive situation that China Carbon Graphite is sold to foreign investors at a cheap price, and then high-purity graphite or graphite deep-processing products are purchased from foreign investors at dozens of times the price we export. ^[4]

In order to transform our country from a big graphite country to a strong graphite country, we must follow the graphite deep processing industry route and process graphite raw materials into graphite materials. To achieve this goal, we must first strengthen the research on graphite purification technology. ^[5]

Problems with graphite

As early as the early 20th century, China has begun to use graphite materials. Due to China's large graphite reserves and concentrated production areas, it has provided many convenient conditions for the development of graphite in China. At present, the development and utilization of new graphite technology in China has entered a stage of rapid development. Many new graphite products and new technologies have been highly utilized and developed. At present, China's graphite industry has the following problems: ^[8]

(1) Graphite mining planning and coordination are not in place

China's graphite reserves rank second in the world, but because there is no unified investment and planning for graphite mining, there is no unified pricing and overall management of graphite in China. Mining scale and output value are not high. The development and utilization of graphite mainly rely on the production and research and development of high-tech products to obtain greater added value and profits. In the current development and utilization of graphite in China, the development and utilization of new products have shown a disorderly state, and planning and overall planning cannot be related Combine to maximize benefits. ^[8]

(2) Lack of channels for the development and utilization of graphite resources

Graphite resources are a kind of non-renewable resources. Only by continuously increasing the development and utilization of graphite resources can greater product added value be obtained. At present, China lacks channels for the development and utilization of graphite resources, and there are many primary productions of graphite, but there is no channel for the research and development and utilization of high-tech materials. The combination of the most efficient products in the market and production and processing can produce more maximum profits, both of which are indispensable. The combination of graphite resources and high-tech products will inevitably play an irreplaceable role in promoting the graphite industry. At present, there are relatively few channels for the development and utilization of graphite resources in China, and market demand is not combined with product research and development. ^[8]

(3) There is no unified plan for the establishment of graphite mining rights

Graphite is a mining product that has severe damage to the mining environment. China has not set up a unified plan for graphite mining rights, resulting in a large amount of disorderly mining and waste of resources. Graphite mining has the same characteristics as other mining operations. The initial investment in production capital is large and the impact on the environment is very serious. Only the unified planning of graphite mining and reducing unnecessary repetitive inputs can appropriately increase the ratio of input to output. ^[8]

(4) Serious misappropriation

Illegal mining in non-graphite mining areas is very serious. Graphite is a non-renewable resource, and the mining utilization rate determines the direct economic benefits of mining. The probability of reuse of graphite mining that has been stolen is negligible. At present, China's crackdown on the illegal mining of graphite is very strong, but in the face of high profits, many small mining owners still ignore it. Strengthening the crackdown on graphite mining is of great significance for the protection of graphite mining. ^[8]

Graphite purification method

The premise of the graphite deep processing industry is purification. Graphite purification is a complex physical and chemical process. Its purification methods mainly include flotation, alkaline acid, hydrofluoric acid, chlorination roasting, and high temperature methods. ^[5]

Graphite flotation

Flotation is a commonly used and important beneficiation method. Graphite has good natural floatability. Basically, all graphite can be purified by flotation. To protect graphite flakes, graphite flotation mostly uses a multi-stage process. Graphite flotation collector is generally selected from kerosene, and the amount is 100-200g / t. Foaming agent is generally pinanol oil or butyl ether oil, and the amount is 50-250g / t. ^[5]

The value and application of large scale graphite is much greater than that of fine scale graphite, and once destroyed, it cannot be recovered. Protecting the large scale of graphite in graphite beneficiation is a problem that cannot be ignored in the beneficiation process. ^[5] Because graphite has good natural buoyancy, the flotation method can improve the grade of graphite to 80% to 90%, or even up to about 95%. The biggest advantage of this method is that it has the least energy consumption, reagent consumption and lowest cost among all purification schemes. However, silicate minerals and compounds of potassium, calcium, sodium, magnesium, aluminum and other elements contained in graphite flakes in an extremely fine state cannot be dissociated by grinding, and it is not conducive to protecting the large graphite flakes. . Therefore, the flotation method is only the primary method for graphite purification. If high carbon graphite with a carbon content of more than 99% is required, other methods must be used for purification. ^[5]

Graphite alkaline acid method

The alkaline acid method includes two reaction processes: an alkali melting process and an acid leaching process. The alkali melting process is to use high temperature conditions to make a chemical reaction between the alkali in the molten state and the acidic impurities in graphite, especially silicon-containing impurities (such as silicates, aluminosilicates, quartz, etc.) to generate soluble salts. After washing to remove impurities, the purity of graphite can be improved. The basic principle of the acid leaching process is to use the acid and metal oxide impurities to react. This part of the impurities does not react with the alkali during the alkali melting process. The metal oxide is converted into a soluble salt, and then washed to separate it from graphite. The combination of alkali melting and acid leaching has a better effect on graphite purification. ^[5]

Various alkaline substances can remove graphite impurities. The stronger the alkaline, the better the purification effect. The alkaline acid method mostly uses NaOH with a small melting point and strong alkalinity. The acid used in the acid leaching process can be HCl, H ₂ SO 4, HNO ₃ or a mixture of them. Among them, HCl is widely used. ^[5]

For some graphites with high silicon content, the purification of graphite by alkali melting method can also realize the comprehensive recycling of silicon. The solution after acid leaching is acidic, and the silicon impurities in the solution are converted into silicic acid. Silicic acid can be extracted by adding a certain amount of alum, and then calcined at 900 ° C to obtain pure silica. ^[5]

Alkali acid method is the most widely used method in China's graphite purification industrial production. It has the characteristics of less one-time investment, higher product quality, and strong adaptability, as well as simple equipment and strong versatility. The disadvantages are the need for high temperature calcination, large energy consumption, long process flow, severe equipment corrosion, large graphite loss and serious wastewater pollution. Therefore, it is very important to use graphite to purify wastewater to produce polyaluminum ferric silicate silicate. ^[5]

Graphite hydrofluoric acid method

Hydrofluoric acid is a strong acid that can react with almost any impurity in graphite, and graphite has good acid resistance, especially hydrofluoric acid, which determines that graphite can be purified with hydrofluoric acid. The main process of the hydrofluoric acid method is the mixing of graphite and hydrofluoric acid. Hydrofluoric acid and impurities react for a period of time to produce soluble substances or volatiles. The impurities are washed to remove the impurities, and purified graphite is obtained after dehydration and drying. ^[5]

Hydrofluoric acid reacts with metal oxides such as Ca, Mg, and Fe to form a precipitate. The H ₂ SiF ₆ produced by ^{[5] is} dissolved in the solution, and impurities such as Ca, Mg, and Fe can be removed. ^[5] Hydrofluoric acid is highly toxic and seriously pollutes the environment. Purifying graphite with other acids can effectively reduce the amount of hydrofluoric acid. Hydrofluoric acid purification of graphite has the advantages of simple process flow, high product quality, relatively low cost, and small impact on the performance of graphite products. However, hydrofluoric acid is highly toxic and must have safety protection measures during use. The generated wastewater must be treated before it can be discharged to the outside, otherwise it will cause serious pollution to the environment. ^[5]

Graphite chlorination roasting method

The chlorination roasting method is to mix graphite with a certain reducing agent and roast at high temperature in a specific equipment and atmosphere. The valuable metals in the material are converted into metal chlorides in the gas phase or condensed phase, and separated from the other components to make graphite. Purification process. ^[5]

Impurities in graphite can be decomposed into oxides with higher melting points under high temperature conditions, such as SiO ₂ , Al ₂ O ₃ , Fe ₂ O ₃ , CaO, MgO. These oxides are subjected to chlorine gas at a certain high temperature and atmosphere, and the metal oxides and chlorine gas react to form chlorides with lower melting points. So at a lower temperature, these chlorides can be gasified and escaped to achieve separation from graphite, so that graphite can be purified. ^[5]

The advantages of the chlorination roasting method are energy saving, high purification efficiency (> 98%), and high recovery rate. However, there are also problems with chlorine gas being toxic, severely corrosive, and seriously polluting the environment. The purity of graphite produced in the process is limited, and the process stability is not good, which affects the application of the chlorination method in actual production, and needs to be further improved and improved. ^[5]

Graphite high temperature purification method

The melting point of graphite is 3850 ± 50 , which is one of the substances with the highest melting point in nature, far higher than the boiling point of impurity silicate. Utilizing the difference in their melting points, graphite is placed in a graphitized graphite crucible, and in a certain atmosphere, it is heated to 2700 ° C with specific instruments and equipment, so that impurities can escape from the graphite and achieve a purification effect. . This technology can purify graphite to more than 99.99%. ^[5]

There are many factors that affect the purification of graphite by high temperature method: The impurity content of graphite raw material has the most influence on the purification effect of high temperature method. The impurity content of the raw material is different, and the ash content of the product is different. Graphite with carbon content of 99% or more after purification by flotation method or alkaline acid method is often used as the raw material; The carbon content of graphite crucible is also an important factor affecting the purification effect. Crucible ash content is lower than graphite ash content, which helps graphite Ash in the medium escapes; the use of large currents, graphite heats up quickly, is conducive to graphite purification, it is best to use high-power electrode raw materials, and high temperature treatment at 2800 ; graphite particle size also has a certain effect on purification. ^[5]

High-temperature method for the purification of graphite, high product quality, carbon content can reach more than 99.995%, which is the biggest feature of the high-temperature method, but at the same time, high energy consumption, high requirements for equipment, requires special design, large investment, purified graphite Raw materials also have certain requirements. Only graphite used in high-tech fields such as national defense, aerospace, and nuclear industry can be purified by this method. ^[5]

Graphite applications

Graphite can be used in the production of refractory materials, conductive materials, wear-resistant materials, lubricants, high-temperature-resistant sealing materials, corrosion-resistant materials, thermal insulation materials, adsorption materials, friction materials, and radiation protection materials. , Machinery industry, electronics industry, nuclear industry and national defense. ^[9]

Graphite refractory

In the iron and steel industry, graphite refractories are used in refractory linings for electric arc blast furnaces and oxygen converters, ladle refractory linings, etc .; graphite refractories are mainly monolithic casting materials, magnesium carbon bricks and aluminum graphite refractories. Graphite is also used in powder metallurgy and metal casting film-forming materials. Graphite powder is added to molten steel to increase the carbon content of steel, so that high carbon steel has many excellent properties. ^[9]

Graphite conductive material

In the electrical industry, it is used as the anode for manufacturing electrodes, brushes, carbon rods, carbon tubes, mercury current flowers, graphite gaskets, telephone parts, and coatings for television picture tubes. ^[9]

Graphite wear-resistant lubricating material

Graphite is often used as a lubricant in the machinery industry. Lubricating oil often cannot be used under high-speed, high-temperature, high-pressure conditions, and graphite wear-resistant materials can work at high sliding speeds at temperatures of -200 to 2000 ° C without lubricants. Many equipments for transporting corrosive media widely use graphite materials to make piston cups, seals and bearings. They do not need to be added with lubricant when running. Graphite milk is also a good lubricant for many metal processing (drawing, drawing). ^[9]

Graphite corrosion-resistant material

Specially processed graphite has the characteristics of corrosion resistance, good thermal conductivity, and low permeability. It is widely used in the manufacture of heat exchangers, reaction tanks, condensers, combustion towers, absorption towers, coolers, heaters, and filters. , Pump equipment. Widely used in petrochemical, wet metallurgy, acid and alkali production, synthetic fiber, papermaking and other industrial sectors, can save a lot of metal materials. ^[9]

Graphite high temperature metallurgical material

Because graphite has a small thermal expansion coefficient and can withstand rapid and rapid changes, it can be used as a mold for glassware. After using graphite, ferrous metal can obtain precise casting dimensions and high surface finish. It can be used without processing or a little processing. Save a lot of metal. Production of powder metallurgy processes such as cemented carbide, graphite materials are usually used to make stampers and porcelain boats for sintering. Crystal growth crucibles for single crystal silicon, regional refining vessels, holder fixtures, induction heaters, etc. are all processed with high-purity graphite. In addition, graphite can also be used for vacuum smelting of graphite heat insulation board and base, high temperature resistance furnace tube and other components. ^[9]

Graphite Atomic Energy and Defense Industry

Graphite has a good neutron moderator used in atomic reactors. Uranium-graphite reactors are one of the most widely used atomic reactors. As a deceleration material in a nuclear power reactor for power, it should have high melting point, stability, and corrosion resistance. Graphite can completely meet the above requirements. The purity of graphite used in atomic reactors is very high, and the impurity content should not exceed tens of ppm. In particular, the boron content should be less than 0.5 ppm. In the defense industry, graphite is also used to make nozzles for solid fuel rockets, nose cones for missiles, parts for space navigation equipment, thermal insulation materials and anti-ray materials. ^[9]

(1) Graphite can also prevent boiler scaling. Unit tests have shown that adding a certain amount of graphite powder (about 4 to 5 grams per ton of water) can prevent scaling on the boiler surface. In addition, graphite can be applied to metal chimneys, roofs, bridges and pipes to prevent corrosion and rust. ^[9]

(2) Graphite is gradually replacing copper as the material of choice for EDM electrodes. ^[9]

(3) The graphite deep-processing products are added to plastic products and rubber products, which can prevent plastic products and rubber products from generating static electricity. Many industrial products need to have anti-static and shielding electromagnetic radiation functions. Graphite products have both functions. Graphite Applications in plastic products, rubber products and other related industrial products will also increase. ^[9]

In addition, graphite is also a polishing agent and rust inhibitor for glass and paper in the light industry. It is an indispensable raw material for the manufacture of pencils, inks, black paints, inks and artificial diamonds and diamonds. It is a very good energy-saving and environmental-friendly material, and it has been used as a car battery in the United States. With the development of modern science and technology and industry, the application field of graphite is still expanding. It has become an important raw material for new composite materials in the high-tech field and plays an important role in the national economy. ^[9]

Graphite graphite deep processing

Graphite Status

Due to the continuous growth of China's metallurgical steel industry and the rapid development of the world's lithium-ion batteries, the demand for graphite raw materials has been stimulated. At the same time, the industry and government's increasing emphasis on the role of graphite strategic resources has caused the price of graphite ore products to rise rapidly and reversed 20 The abnormal situation in which other mineral products have been increasing prices over the years, but graphite has continued to reduce prices, has not only increased the efficiency of the graphite industry, but also caused some social funds to continue to flow into the graphite industry. This great situation is certainly a good time for the development of the graphite industry, but if it is not scientifically planned and reasonably guided, and blindly expanded the volume of extraction, there may be another "black storm" in the late 1980s. Caused significant losses to the development of the graphite industry. ^[10]

China is a large country of graphite resources, but for a long time the vicious competition of low-tech levels of production and prices within the graphite industry has caused serious shortages of capital and technology inputs. The main focus is on the production of low-end products of raw ore and beneficiation. This situation has caused China's graphite deep processing technology and products to lag behind developed countries, while large resource countries are weak deep processing countries. This is incompatible with the rapid development of China's economy and science and technology. At present and for a long time to come, it is a promising cause to protect and scientifically use graphite, a precious strategic resource, to develop graphite deep-processing technology and products. ^[10]

The development of deep processing technology of flaky graphite in China already has a certain foundation. The national science and technology research and support plans of the "Eighth Five-Year Plan" to "Eleventh Five-Year Plan" of the Ministry of Science and Technology have been included in non-metallic ore and western development projects. Obvious results. At present, there are already a number of good (scale) graphite deep-processing enterprises in China. The largest flexible graphite enterprises are mainly distributed in Jiangsu and Zhejiang regions, and battery material companies such as anode materials are mainly distributed in the Pearl River Delta and Yangtze River Delta regions such as Shenzhen. ^[10]

China's original microcrystalline graphite deep processing technology is basically blank. Recent studies have found that because the crystals of microcrystalline graphite are tiny (1m), there are many microcrystals randomly packed in each graphite particle, which makes the particles exhibit isotropy. This makes it an excellent raw material for anode materials and isotropic graphite of lithium-ion batteries (especially power batteries), and has important application value in high-tech fields such as new energy, nuclear energy, and military industry. Tsinghua University has carried out original scientific research and development in this regard, and is cooperating with related enterprises to build production lines of microcrystalline graphite purification and deep processing products. ^[10]

Graphite product form

(1) High-purity graphite

It is mainly used for stabilizers in military and industrial materials and industrial catalysis for other industries. It has crystal integrity and very good thermal conductivity. ^[8]

(2) Isostatic graphite

Isostatic graphite is an extension of high-purity graphite. It is mainly processed from high-purity graphite. It has the characteristics of high-purity graphite, low thermal expansion rate, and excellent thermal conductivity after heating. ^[8]

(3) Expandable graphite

The expandable graphite is mainly selected from naturally arranged natural flake graphite, and interlayer compounds mainly subjected to acid oxidation treatment. The body has the advantages of high temperature resistance and high heat resistance, and the graphite expandability is increased. ^[8]

(4) fluorinated graphite

Fluoride graphite is a new type of graphite product that combines performance and benefit. Graphite functional material with high added value and unique quality, widely used in many fields. ^[8]

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Graphite development direction

Focus on deep processing, realize some important engineering projects, build a complete industrial chain, and guide the healthy and scientific development of the graphite industry. ^{[10] The} first is the transformation of outdated technology and equipment; the second is the current hot technology products for the development of carbon graphite materials, such as the industrialization and intensification of lithium ion battery anode materials, isotropic graphite, and high thermal conductivity graphite. ^[10]

(1) Renewal of graphite mining technology

China's graphite mining and dressing technology and equipment have basically not improved since the 1960s, and they have lagged behind other minerals in terms of energy consumption and mineral recovery rate. The graphite mining and dressing technology equipment is simpler than other minerals, but because of the low long-term industry benefits and lack of funds, there is no replacement. Combining powerful mineral design and research institutes with mining and dressing enterprises, introducing advanced mining and dressing technology and equipment from other minerals, designing and constructing advanced graphite mining and dressing production lines, in energy consumption, recovery rate, large scale protection, water conservation and utilization, Significant improvements have been made in technical and economic indicators such as mine processing. After successful operation, it will be promoted in the industry, and the advanced technical and economic indicators will be used as indicators for industry access and elimination of backward technology equipment. ^[10]

(2) Construction of advanced large-scale graphite purification production line

The country already has advanced acid-base purification and energy-saving high-temperature purification technologies that are environmentally friendly and energy-saving. Government-led, industry-university-research integration, and construction of different types of large-scale graphite purification production lines based on resource characteristics. Strictly restrict the use of hydrofluoric acid, which seriously pollutes the environment in chemical purification. ^[10]

(3) Industrial scale of natural graphite anode materials for lithium batteries and research and development of anode materials for power and energy storage batteries

There are already domestic companies producing anode materials after spheroidal graphite flakes, such as Bertrand; Tsinghua University and other universities have technology for preparing anode materials with microcrystalline graphite, but the industrial scale and product quality cannot meet lithium ion batteries. Rapidly developing needs. A large number of domestically produced spherical graphites are mainly exported to Japan and South Korea for foreign companies to produce high-quality anode materials. Relying on resources, scale up the industry of natural graphite lithium ion battery anode materials, and research and develop different quality anode materials for the needs of different grades of batteries, so as to serialize the products; develop safe and long life natural graphite power and energy storage battery anodes material. With the rapid growth of demand for lithium-ion batteries, the market prospect of anode materials is very broad. ^[10]

(4) Industrialization of natural graphite-based isotropic graphite

Isotropic graphite is widely used in nuclear energy, silicon crystal preparation, electric discharge machining, continuous steel casting, aerospace and other fields. It is a high-end product and strategic material for carbon materials. China currently imports 2/3 of the isotropic graphite it needs. The preparation of isotropic graphite by traditional technology is complicated and costly. Microcrystalline graphite mineral particles are isotropic, which is a good raw material for preparing isotropic graphite, and can simplify the process and reduce the cost. Industrial-sized samples have been prepared with isotropic parameters of 1.04 (the highest required nuclear Graphite 1.05); flake graphite also has the potential to produce isotropic graphite after spheroidizing. Tsinghua University and others already have their own original patented technology and are cooperating with enterprises to implement industrialization. ^[10]

(5) Natural graphite-based high thermal conductivity material

The miniaturization of electronic equipment requires the increasing integration of electronic devices, making heat dissipation a key technology for the IT industry, and increasing demand for lightweight and highly thermally conductive materials. Flexible graphite has been widely used in LED displays and many electronic products as a soaking and thermally conductive material; using the excellent thermal conductivity of natural graphite to prepare high-end thermally conductive materials with thermal conductivity comparable to or higher than copper, and only 1/4 the density of copper, Wuhan Technology Universities, Shanxi Coal Chemical Research Institute, Tsinghua University, etc. already have related technologies. It is recommended to combine production, learning and research to achieve industrialization. ^[10]

(6) Research on serialization of flexible graphite products

China's flexible graphite production has a certain scale, and has a number of cooperation with foreign advanced enterprises. However, most of our products are low-end and mid-range products, with less than one-fifth of foreign specifications. It is suggested that the combination of production, teaching and research should be used to develop high-end products according to the requirements of use, perfect the specifications and make them serialized and standardized. ^[10]

(7) Industrialization of expanded graphite environmental protection materials

Expansion graphite has a lot of research results on the adsorption and control of water pollution. In the treatment of oil and organic pollution in water, expanded graphite is far more effective and economical than ordinary activated carbon currently used. However, expanded graphite is inconvenient to transport and needs to be prepared at the application site. The preparation, use, recycling, and regeneration of expanded graphite environmentally friendly materials have certain technical difficulties. In addition, due to insufficient attention to environmental protection in the past, expanded graphite environmentally friendly materials have not been industrialized. The 18th National Congress of the Communist Party of China proposed to build a beautiful China and strengthened environmental protection, making the industrialization of expanded graphite environmentally-friendly materials possible. Now the technical basis for the industrialization of expanded graphite environmental protection materials is available, and this project can be carried out from two technical levels. ^[10]

In water-polluted enterprises, such as steel, chemical, printing and dyeing, and food-intensive areas, build a service network for the production, use, recycling, and regeneration of expanded graphite environmentally friendly materials. The combined use of expanded graphite environmentally friendly materials and other treatment methods will greatly improve the degree and benefit of water pollution treatment. For the increasingly frequent emergencies of oil and organic water pollution, build comprehensive water environmental protection special ships, combine traditional fencing, suction and other treatment methods with the efficient oil absorption performance of expanded graphite, and improve pollution control capabilities. ^[10]