At present, various methods of graphite purification at home and abroad, mainly flotation, alkali acid, hydrofluoric acid, chlorination roasting and high temperature purification methods, systematically expounded their basic principles, process conditions, research progress and In the actual production of the application of the advantages and disadvantages of various methods in comparison, the improved alkaline acid method is still the best method of industrial purification of graphite.
Key words: graphite purification flotation method, alkali acid hydrofluoric, acid chlorination roasting method, high temperature purification method.
Graphite is a kind of high-energy crystalline carbon material. Because of its unique structure and conductive, thermal conductivity, lubrication, high temperature, chemical stability and so on, it is widely used in metallurgy, Environmental protection, chemical industry, refractory industry, electronics, medicine, military industry and aerospace industry. It has become an indispensable non-metallic material for the development of modern industry and high, new and advanced technology. It is becoming more and more important in the national economic development. Experts predict: the 20th century is the century of silicon, the 21st century will be the carbon century.
To study the method of purification of graphite, we must first find out the content of impurities in the graphite ore composition. Although the natural graphite contains impurity components, but they are not exactly the same compoent, the approximate composition is similar. These impurities are mainly potassium, sodium, magnesium, calcium, aluminum and other silicate minerals. graphite purification process, is to take effective measures to remove this part of the impurities. At present, the method of purification of graphite at home and abroad mainly flotation, alkali acid, hydrofluoric acid, chlorination roasting, high temperature and so on. Among them, alkali acid method, hydrofluoric acid method and chlorination roasting method belong to chemical purification method, high temperature purification method belongs to physical purification method.
1.5 high temperature purification method
Graphite’s Boiling point melting point is the highest in the nature, the melting point of 3850 ± 50 ℃, the boiling point of 4500 ℃, and the boiling point of silicate minerals are 2750 ℃ (quartz boiling point) which is below the graphite boiling point. This characteristic is the theoretical basis of high temperature purification of graphite.
Graphite powder directly into the graphite crucible, in the inert gas and freon shielding gas heating furnace to 2300 ~ 3000 ℃, to maintain a period of time, impurities in graphite will overflow, in order to achieve the purification of graphite. High temperature method generally used by flotation or chemical purification of carbon 99% or more of high-carbon graphite as raw material, the graphite can be purified to 99. 99%, such as by further improving the process conditions, improve the crucible quality, purity can be achieved 99. 995% or more.
High-temperature method can produce more than 99. 99% of ultra-high purity graphite, but the requirements of raw materials to more than 99% of fixed carbon, and expensive equipment, huge investment, limited production scale, electric heating technology demanding, Otherwise, the graphite in the hot air heated to 450 ℃ when it began to be oxidized, the higher the temperature, the greater the loss of graphite. Only the graphite quality requirements of very high special industries (such as defense, aerospace, etc.) using high-temperature small batch production of high-purity graphite.
The biggest advantage of high-temperature method is the high carbon content of products, up to 99. 995% or more, the disadvantage is the need to specifically design and construction of high-temperature furnace, expensive equipment, one-time investment and energy consumption, high electricity The production costs. And the harsh conditions of production of this method is also very limited scope of application, only the defense, aerospace and other products on the purity of graphite have special requirements of the occasion to consider the use of the method of small batch production of graphite, the industry can not achieve promotion. Comparative analysis shows that several methods of graphite purification are different, also have certain defects. Alkali acid method is easy to operate, the production cost is low, the production requirements are lower, but the production of graphite fixed carbon content is low, from the current view can not reach 99.9%. Hydrofluoric acid method impurity effect is good, product fixed carbon content is high, but hydrofluoric acid is highly toxic and strong corrosive to safety protection measures and production conditions are strict, and the wastewater is not easy to handle. Chlorination roasting method due to chlorine poisonous and strong corrosive, also need strict sealing. High-temperature method can produce very high-grade high-purity graphite, but because of their own limitations can not be promoted at present, only a small range of applications.
Due to the shortcomings of high-temperature method itself, the application of this method is extremely limited, the industry can not achieve promotion.
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