Earthy graphite is also called amorphous graphite, cryptocrystalline graphite or microcrystalline graphite. The crystal diameter of this kind of graphite is generally less than 1 micron, and the specific surface area is concentrated in the range of 1-5m2 / g. it is an aggregate of microcrystalline graphite, and the crystal form can be seen only under the electron microscope. The earthy graphite ore is grayish black and steel gray, generally dull, with dense massive, earthy, layered and sheet-like structures. This kind of graphite lacks luster, its lubricity is lower than that of flake graphite and its selectivity is poor. However, the grade is high, the carbon content is generally 60% ~ 80%, and a few are more than 90%, the ash content is 15% ~ 22%, the volatile content is 1% ~ 2%, and the water content is 2% ~ 7%.
Microcrystalline graphite is divided into two categories: iron free and iron free. It is divided into more than 60 grades according to the fixed carbon content and maximum particle size of the products. The appearance of various grades of graphite products requires that there shall be no visible wood chips, iron chips, stone particles and other sundries in the products, and the products shall not be contaminated by other substances.
The content of acid soluble iron in microcrystalline graphite is not more than 1%, which is mainly used for the ingredients of pencils, batteries, welding rods, graphite emulsions, graphite bearings and raw materials of battery carbon rods; Microcrystalline graphite without iron requirements is mainly used for casting materials, refractory materials, dyes, electrode paste and other raw materials.
Natural microcrystalline graphite is usually converted from coal under the geological environment of high temperature and high pressure. Therefore, natural microcrystalline graphite is usually associated with coal. The transition area from anthracite to natural microcrystalline graphite can often be seen in the natural microcrystalline graphite ore body. The mineral composition is mainly graphite, accompanied by andalusite, hydromica, sericite and a small amount of pyrite, tourmaline, limonite and calcite.
The grade of Aphanitic Graphite Ore varies greatly. The average content of fixed carbon in the ore of each deposit is 12.17% ~ 85.39%, with an average of about 70.8%. There are 5 deposits with rich average grade (ore fixed carbon content is 71% ~ 86%), including 1 large mine, 2 medium mines and 2 small mines. The total reserves account for 76% of the total reserves of aphanitic graphite, mainly distributed in deposits in Hunan and Guangdong. There are 3 deposits with medium average grade (the fixed carbon content of ore is 60% ~ 70%), including 1 medium-sized mine and 2 small-sized mines. The retained reserves account for 13% of the total retained ore reserves of cryptocrystalline graphite. There are 5 deposits with low average grade (fixed carbon content of ore is 12% ~ 56%), including 2 medium-sized mines and 3 small-sized mines. The total reserves account for 11% of the total reserves of cryptocrystalline graphite, which are distributed in deposits in Guangdong, Shaanxi, Jilin, Beijing and other places. The content of main harmful impurity sulfur in aphanitic graphite ore is generally low, mostly 0.26% ~ 1.16%.
Earthy graphite is one of the most abundant graphite, with small scale and low crystallinity. It is used to produce low-value products and is the lowest price among graphite; It is mainly contained in Türkiye, China, Europe, Mexico and the United States.
Earthy graphite is widely used in casting coatings, oil field drilling, battery carbon rods, steel, casting materials, refractory materials, dyes, fuels, electrode pastes, and as ingredients for pencils, welding rods, batteries, graphite emulsions, desulfurizing agents, preservatives and antiskid agents, smelting carburizing agents, ingot injection protective fluxes, graphite bearings and other products. Its most common uses are three: first, mixing a certain amount of soil (the main component of silica) to press into pencil lead; Second, as a lubricant for some mechanical devices or industrial production; Third, as the electrode of electrolysis, electroplating or storage battery; In addition, it is also a raw material for the artificial production of various other allotropes (such as soccer ball, diamond, carbon nanotubes).
When it is used as a carburizing agent, the steel plant calls it graphite ball or earth graphite carburizing agent when purchasing. 50% of the iron and steel enterprises will basically use earthy graphite with a content of C ≥ 80%, while the other manufacturers have applied C: 83, 85 and 86%. The particle size used is more diversified, including 10-30mm, 20-50mm spherical, and 1-3mm, 1-5mm, 3-6mm, and 3-15mm granular materials. The monthly purchase volume is also adjusted according to the specific needs of production. The high monthly consumption is more than 100 tons, and the low consumption is 5 tons and 10 tons. However, most iron and steel enterprises do not use earthy graphite as a carburizing agent. It is understood that earthy graphite emits smoke when used in the steel-making process. At the same time, the carbon content is low and the price does not have much advantage.