Physical purification method of cryptocrystalline graphite

Cryptocrystalline graphite is also called amorphous graphite and earthy graphite. It is named because of its tiny grain size, usually below 1μm. This type of graphite is characterized by an earthy surface, lack of luster, and slightly worse lubricity than flake graphite. The grade of cryptocrystalline graphite ore is generally 60% to 85%. A few are as high as 90% or more.

 With the increasing depletion of regional metamorphic rock-type crystalline graphite resources, coal-based cryptocrystalline graphite will become the focus of future development and an important mineral resource for the preparation of graphene. Because most natural cryptocrystalline graphite ores are often accompanied by quartz, illite, kaolinite and metamorphic minerals, they need to be purified and impurities removed before they can be used in industrial fields such as crucibles, electrodes, electric carbon, pencils, etc.

 Physical purification method of cryptocrystalline graphite

 Selective flocculation method

The basic principle of the selective flocculation method is to add a polymer flocculant to a suspension containing two or more components, so that the flocculant selectively adsorbs a certain component in the suspension, and produces flocculation precipitation through bridging action, thereby achieving the purpose of component separation. Xu Tao first selected sodium silicate, sodium hexametaphosphate, lignin starch, carboxymethyl cellulose and water glass as dispersants, and selected cassava flour, acorn flour, sodium alginate and polyacrylamide as flocculants to purify the cryptocrystalline graphite in Jilin Panshi, and compared the purification effects. The results show that the purification effect is most obvious when sodium silicate is used as a dispersant and polyacrylamide is used as a flocculant.

 Flotation method

This method is one of the commonly used methods for purifying cryptocrystalline graphite at present, mainly using the floatability of natural graphite particles to purify it. The main factors affecting the flotation effect are fine grinding of the original ore, type of collector, type of inhibitor, type of pH adjuster, type of frother, etc.

 High-temperature calcination method

 The high-temperature method uses the properties of graphite's high temperature resistance (sublimation point 4500℃) and the fact that most of the ash in natural graphite can be vaporized and released at high temperatures to purify graphite. In theory, as long as the graphite is heated to above 2700~C, the impurities can be vaporized and removed first by taking advantage of their low boiling point. Although this method can obtain high-purity graphite (carbon content>99.99%) for industrial fields such as semiconductors, high-purity graphite products and spectral electrodes, it is expensive, requires large investments, consumes a lot of energy, and has extremely strict requirements on electric furnace heating technology. Therefore, the application scope of the high-temperature method is smaller than other methods.