Graphite is a black lustrous mineral formed in a range of metamorphic and hydrothermal environments. Natural graphite can be divided into crystalline graphite (flake graphite) and cryptocrystalline graphite (earth graphite) according to the crystal form.
The characteristic of crystalline graphite minerals is that the grade is not high, and the stable carbon content generally does not exceed 10%, and some special accumulation areas reach more than 20%, but this kind of graphite minerals are easy to grind, and the grade of flotation titanium concentrate is more than 85%, which is the most common in nature. One of the minerals with very good flotation properties. The price of conductive graphite materials, aphanitic graphite is higher, and the stable carbon content is generally 60-80%, up to 95%.
Graphite is an allotrope of carbon and is a transitional crystal composed of carbon atoms. In graphite crystals, carbon atoms in the same layer form covalent bonds in the form of SP hybridization, and six carbon atoms form a hexagonal ring and extend to form a layered structure. Delocalized π-bond electrons formed by overlapping the remaining p orbitals of carbon atoms in the same plane Can move freely in the crystal lattice. This is why graphite has excellent electrical conductivity.
The graphitic structural layers are connected by van der Waals force with an interlayer spacing of 0.3354 nm. It is the layered structure and chemical bond type that determine its unique physical and chemical properties, making it a strategic mineral resource with a wide range of uses. It is not only the basic mineral raw material necessary for traditional industries and strategic emerging industries, but also an important strategic resource to support the development of high-tech. Graphite is therefore an important raw material for industrial applications, especially in energy storage.
Graphite resources are widely used in defense industry, chemical industry, machinery and many other fields due to their excellent high temperature resistance, good electrical, lubricating and chemical stability. These fields require graphite with a purity higher than or equal to 99%. However, pure graphite does not exist in nature. Natural graphite minerals often contain impurities such as SiO 2 , Al 2 O 3 , Fe 2 O 3 , CaO and P 2 O 5 . These impurities are usually in the form of minerals such as quartz, mica, pyrite and carbonates. These result in lower purity grades that cannot be used directly. Therefore, with the increasing demand for high-purity natural graphite, it is of great significance to find an energy-saving, environmentally friendly, and high-speed purification technology that uses natural graphite as raw material to produce high-purity graphite.
At present, many technologies have been developed and applied to remove impurities in natural graphite. Commonly used methods include flotation, alkali-acid method, hydrofluoric acid method, chloride roasting method, and high-temperature purification method. Due to the non-polar surface of natural graphite, flotation is often used as the first step in removing impurities from natural graphite in many methods. Natural graphite does not easily attach to water dipoles and therefore has a natural buoyancy. Therefore, natural graphite can be physically purified by utilizing the difference in surface properties between graphite and impurities. However, fine silicate mineral particles and impurities such as K, Ca, Mg, Al, Fe, S compounds dispersed in natural graphite still remain in the concentrate after flotation. Therefore, it is necessary to further improve the purity of natural graphite by means of chemical or high-temperature purification. High purity graphite higher than 99% can be obtained by hydrofluoric acid method and chloride roasting method.
Natural graphite can be obtained with high purity by high temperature method, which can reach 99.99%. But the required temperature is higher than 2700℃. The alkali-acid method has become a promising purification method for the production of high-purity graphite due to its simple experimental equipment, operation process and ideal graphite purity.
© 2021 Yantai KZ Mining Processing Technology & Equipment Inc.