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Qingdao Tennry Carbon Co.,Ltd
Address: Xiaobeiqu Community, Chengyang Street, Chengyang District, Qingdao, Shandong, China
Contact person: Fujun Pei
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Graphite Purification Method

Graphite is a kind of  high-energy crystal carbon material, because of its unique structure and  conductivity, thermal conductivity, lubrication, high temperature,  chemical stability and other characteristics, so that it has high  application value in high-performance materials, widely used in  metallurgy, Environmental protection, chemical industry,  refractory, electronics, medicine, military and aerospace and other  fields, become a modern industry and high, new and sharp technology  development essential non-metallic materials, the status of national  economic development more and more important, Experts predict that the twentieth century is the century of silicon, the 21st century will be the century of carbon.

China's natural graphite  forming geological conditions are well distributed, rich in resources,  good quality, reserves and production are ranked first in the world, is  one of China's dominant minerals.

Natural graphite  according to its different degree of crystallization, can be divided  into crystalline graphite (scaly) and aphanitic graphite (soil) two  categories. Crystalline graphite ore is characterized by  high grade, fixed carbon content is generally not more than 10%, local  special enrichment up to 20% or more, but the kind of graphite ore  optional, flotation concentrate grade up to More than 85%, is one of the best ore in nature. Aphanitic graphite grade is higher, fixed carbon content is generally 60% to 80%, up to 95%, but the ore optional poor.

To study the method of purification of graphite, we must first identify the impurities present in the graphite ore composition. Although  the natural graphite contains impurities in the composition is not  exactly the same, but the general composition is similar. These  impurities are mainly potassium, sodium, magnesium, calcium, aluminum  and other silicate minerals, graphite purification process, is to take  effective means to remove this part of the impurities. At  present, domestic and foreign methods of refining graphite mainly  flotation method, alkaline acid method, hydrofluoric acid method,  chlorination roasting method, high temperature method and so on. The  alkali acid method, hydrofluoric acid method and chlorination roasting  method are chemical purification method, high temperature purification  method belongs to the physical purification method.

1 flotation method

Flotation  method is a more commonly used method of refining minerals, because the  graphite surface is not easy to water infiltration, so it has a good  floatability, easy to make it with the separation of impurities and  minerals in China are basically using flotation method of graphite For beneficiation.

Graphite ore flotation generally first use the flotation method, and then positive flotation concentrate for reverse flotation. The use of flotation method can get higher grade graphite concentrate. Flotation graphite concentrate grade is usually up to 80% to 90%, using multi-stage grinding, the purity of up to 98%.

Flotation  crystal graphite commonly used collector for the kerosene, diesel,  heavy oil, sulfonate, sulfuric acid esters, phenols and carboxylic acid  esters, commonly used foaming agent for the 2 # oil, 4 # oil, Butyl ether oil, etc., the regulator for the lime and sodium carbonate, the inhibitor is water glass and lime. Flotation of cryptocrystalline graphite commonly used collector is  coal tar, commonly used foaming agent is camphor oil and pine oil,  commonly used regulator is sodium carbonate, commonly used inhibitors  are water glass and sodium fluorosilicate.

The  use of flotation method of pure graphite concentrate, grade can only  reach a certain range, because some of the impurities were very fine  grain dip in the graphite scale, even if the fine grinding can not be  completely dissociated, so the use of physical mineral processing method  is difficult to completely remove This  part of the impurities, generally only as the first step in the  purification of graphite, further purification of graphite methods are  usually chemical or high temperature method.


2 alkaline method

Alkali acid method is the main method of chemical purification of graphite, is also more mature process. The method includes NaOH-HCl, NaOH-H2SO4, NaOH-HC l-HNO3 and other systems. NaOH-HCl method is the most common.

Alkaline  method to improve the principle of graphite is NaOH and graphite in a  certain proportion of mixing evenly calcined at 500 ~ 700 e high  temperature graphite impurities such as silicate, aluminosilicate,  quartz and other components and sodium hydroxide Chemical  reaction, the formation of soluble sodium silicate or acid-soluble  sodium aluminosilicate, and then washed with water to remove it to  achieve the purpose of desilication; another part of the impurities such  as metal oxides, after alkali melting remains in the graphite ,  The product after desilication is leached with acid to convert the  metal oxide into a soluble metal compound, and impurities such as  carbonates in graphite and the acid-soluble compound formed during the  alkali leaching process react with the acid to enter the liquid Phase, and then through the filter, washing and graphite to achieve separation. The  graphite is chemically inert and has good stability. It is insoluble in  organic solvents and inorganic solvents and does not react with lye; it  does not react with many acids except for strong oxidizing acids such  as nitric acid and concentrated sulfuric acid. Resistant hydrofluoric acid; below 6000 ℃, does not react with water and water vapor. Therefore, the nature of the graphite in the purification process remains unchanged.


3 hydrofluoric acid method

Any  silicate can be dissolved by hydrofluoric acid, which makes  hydrofluoric acid a special agent for the treatment of insoluble  minerals in graphite. Since 1979, at home and  abroad have developed a gaseous hydrogen fluoride, liquid hydrofluoric  acid system and ammonium fluoride salt system purification method,  which, the most widely used liquid hydrofluoric acid method, it uses  graphite impurities and hydrofluoric acid reaction Soluble in water fluoride and volatile matter to achieve the purpose of purification


4 chlorination roasting method


Chlorination  roasting method is the graphite powder mixed with a certain amount of  reducing agent, in a certain temperature and specific atmosphere  roasting, and then through the chlorine gas for chemical reaction, the  material in the valuable metal into a lower melting point of the gas  phase or condensed phase Of chlorides and  complexes and escape, and thus separated from the rest of the components  to achieve the purpose of purification of graphite.

Graphite  impurities in the high temperature heating, in the role of reducing  agent can be decomposed into simple oxides such as SiO2, Al2O3, Fe2O3,  CaO, MgO, etc., the melting point of these oxides higher, see Table 1,  and their chlorine The melting point of the metal complex  (such as CaFeCl4, NaAlCl4, KMgCl3, etc.) formed by the chemical or other  trivalent metal chloride is low, see Table 2. The vaporization of these chlorides escapes, improving the purity of the graphite.

The  metal complexes emitted in a gaseous state are quickly turned into  condensed phases due to the temperature drop, and the removal of the  exhaust gas can be carried out using this property


5 high temperature purification method

Graphite  is one of the highest melting points in nature, the melting point of  3850 ± 50 ℃, the boiling point of 4500 ℃, and silicate minerals boiling  at 2750 ℃ (quartz boiling point), the boiling point of graphite is  much higher than the impurities The boiling point of the silicate. This characteristic is the theoretical basis of high temperature method for the purification of graphite.

The  graphite powder is directly charged into the graphite crucible, heated  to 2300 to 3000 ° C in a purification furnace which is passed with an  inert gas and a freon-protected gas, and the impurities in the graphite  are overflowed for a period of time to effect the purification of the  graphite. High-temperature  method generally used by flotation or chemical purification of  carbon-containing 99% or more high-carbon graphite as a 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. More than 995%.

High  temperature method to produce more than 99. 99% of ultra-high purity  graphite, but the requirements of raw materials to be more than 99% of  fixed carbon, and expensive equipment, huge investment, production scale  has been limited, electric furnace heating technology requires strict, Otherwise  the graphite in the hot air to 450 ℃ when the temperature began to be  oxidized, the higher the temperature, the greater the loss of graphite. Only  the graphite quality requirements are very high special industries  (such as defense, aerospace, etc.) using high-temperature production of  high-purity graphite

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