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Graphite has high application value in high-performance materials due to its unique structure and conductivity, heat conduction, lubrication, high temperature resistance, stable chemical properties, etc. It has become an essential non- gold in the development of modern industry and high, new and sharp technologies. Is a material. With the continuous development of technology, ordinary high-carbon graphite products can no longer meet the requirements of various industries, so it is necessary to further improve the purity of graphite.
At present, the methods for purifying graphite at home and abroad mainly include flotation method, alkali acid method, hydrofluoric acid method, chlorination roasting method, high temperature method and the like. Among them, the alkali acid method, the hydrofluoric acid method and the chlorination roasting method belong to the chemical purification method, and the high temperature purification method belongs to the physical purification method.
Scale graphite SEM photo
(1) Flotation method
The flotation of graphite ore is generally carried out by positive flotation followed by reverse flotation of the flotation concentrate. Flotation graphite concentrate grades can usually reach 80% to 90%, using multi-stage grinding, the purity can reach 98%.
Conventional crystalline graphite flotation collector as kerosene, diesel oil, heavy oil, sulfonate, sulfate, phenols, and carboxylic acid ester, a foaming agent commonly used for the oil # 2, # 4 oil, pine oil, an ether Alcohol and butyl ether oil, etc., the adjusting agent is lime and sodium carbonate, and the inhibitors are water glass and lime. The common collector for flotation of cryptocrystalline graphite is coal tar. Commonly used foaming agents are eucalyptus oil and pine oil. The commonly used regulator is sodium carbonate. The commonly used inhibitors are water glass and sodium fluorosilicate.
Advantages: lowest energy consumption and reagent consumption, and lowest cost.
Disadvantages: Only the grade of graphite can be limitedly improved. For scaly graphite, multi-stage grinding can not only dissociate its completely monomer, but also is not conducive to the protection of large scales of graphite.
(2) Alkali acid method
The alkali acid method is the main method for chemical purification of graphite, and it is also a relatively mature process. The method includes a system such as NaOH-HCl, NaOH-H2SO4, NaOH-HCl-HNO3. Among them, the NaOH-HCl method is the most common.
Purification principle graphite base is NaOH acid method in accordance with a certain proportion of the graphite mixed is calcined, graphite impurities such as silicates, aluminates, and quartz components with sodium hydroxide at a high temperature of 500 ~ 700 ℃ A chemical reaction occurs to form soluble sodium silicate or acid-soluble sodium aluminosilicate, which is then removed by washing with water to achieve the purpose of desiliconization; another part of impurities such as metal oxides remain in the graphite after alkali fusion. The product after desiliconization is leached with an acid to convert the metal oxide therein into a soluble metal compound, and impurities such as carbonate in the graphite and the acid-soluble compound formed during the alkali leaching react with the acid to enter the liquid. The phase is separated from the graphite by filtration and washing.
Advantages: The carbon content of graphite purified by alkali acid method can reach more than 99%, with the characteristics of less one-time investment, higher product grade and strong process adaptability. Moreover, it has the advantages of conventional equipment and versatility (in addition to graphite, many non-metallic minerals can be purified by alkaline acid method), and the alkali acid method is the most widely used method in China today.
Disadvantages: high energy consumption, long reaction time, large loss of graphite and serious pollution of wastewater.
(3) Hydrofluoric acid method
Any silicate can be dissolved by hydrofluoric acid, a property that makes hydrofluoric acid a special agent for the treatment of poorly soluble minerals in graphite. Since 1979, the purification methods of gaseous hydrogen fluoride, liquid hydrofluoric acid system and ammonium fluoride salt system have been developed at home and abroad. Among them, liquid hydrofluoric acid method is the most widely used, which uses impurities in graphite and hydrofluoric acid to form It is soluble in fluoride and volatiles to achieve purification.
Advantages: high impurity removal efficiency, high quality of the product obtained, little impact on the performance of graphite products, low energy consumption.
Disadvantages: It is highly toxic and highly corrosive. Strict safety protection measures must be taken during the production process. The strict requirements for equipment and environmental protection investment lead to higher costs.
(4) Chlorination roasting method
The chlorination roasting method is to add a certain amount of reducing agent to the graphite powder, calcine it at a certain temperature and a specific atmosphere, and then pass chlorine gas to carry out a chemical reaction, so that the valuable metal in the material is converted into a gas phase or a condensed phase having a lower melting point. The chloride and the complex escape and separate from the remaining components for the purpose of purifying the graphite.
Advantages: Low calcination temperature and low chlorine consumption reduce the production cost of graphite, while the carbon content of graphite products is comparable to that after treatment with hydrofluoric acid method, compared with the recovery rate of chlorination roasting method.
Disadvantages: Because chlorine is toxic and corrosive, it requires high equipment operation and needs to be tightly sealed. The exhaust gas must be properly disposed of, so it limits its promotion and application to a certain extent.
(5) High temperature purification method
Using the characteristic that the boiling point of graphite is much higher than the boiling point of the silicate containing impurities, the graphite powder is directly charged into the graphite crucible, and heated to 2300 to 3000 ° C in a purification furnace which is supplied with an inert gas and a Freon protective gas to maintain a section. At the time, impurities in the graphite will overflow, thereby purifying the graphite. The high-temperature method generally uses high-carbon graphite containing more than 99% of carbon purified by flotation or chemical method as raw material, and the graphite can be purified to 99.99%. If the process conditions are further improved, the quality of the crucible can be improved, and the purity can reach 99.995%. the above.
Advantages: The carbon content of the product is extremely high, up to 99.995%.
Disadvantages: Specially designed and constructed high-temperature furnaces, expensive equipment, and one-time investment; demanding production conditions limit its application; high energy consumption, high electricity costs increase production costs.
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