Graphite purification and sorting strategy: from principle to process

In the field of graphite processing and utilization, purification methods are crucial, and can be generally divided into two categories: physical purification and chemical purification.

In terms of physical purification, there are many methods with different principles. Gravity separation is based on the density difference between minerals to achieve separation and purification, but in practical applications, its frequency of use is relatively low. Electrostatic separation is based on the difference in conductivity between minerals for separation, and usually plays a role as a pretreatment step. Flotation, which relies on the difference in physical and chemical properties of the surface of minerals for purification, is the main means of physical purification.

Looking at the chemical purification process, there are many methods, including chlorination roasting, high-temperature purification, hydrofluoric acid method and alkaline acid method. Chlorination roasting takes advantage of the chemical stability of graphite. Under high-temperature heating conditions, impurities will decompose into metal oxides. At this time, the introduction of chlorine can convert high-boiling-point metal oxides into low-boiling-point chlorides, and then separate impurities by low-temperature gasification. High-temperature purification takes advantage of the high melting and boiling points of graphite. After decomposing impurities into metal oxides, they are roasted at high temperature in a specific atmosphere to make the metal oxide impurities escape in the form of gasification, thereby achieving the purpose of separating impurities. The hydrofluoric acid method is to use the acid and alkali resistance of graphite to react with impurity minerals by adding acid to generate soluble products, and finally achieve the separation of impurities. The alkali-acid method is also based on the acid and alkali resistance of graphite. The impurities are first melted with strong alkali to generate soluble salts. After washing to remove impurities, soluble substances are generated by acid leaching, and then washed again to completely remove impurities.

Flotation plays an important role in graphite purification. Because graphite has good floatability, flotation has become an effective and environmentally friendly purification method. The traditional graphite flotation process adopts multiple re-grinding and multiple selection methods. For the flotation of fine flake graphite and cryptocrystalline graphite, the core goal is to improve the yield, fixed carbon content and recovery rate by adopting a reasonable test process and a suitable reagent system.

In graphite selection, natural large flake graphite has unique value. It contains well-crystallized graphite crystals, its industrial value far exceeds that of other types of graphite, and it cannot be synthesized artificially. During the grinding process, once the large flake graphite crystals are destroyed, this process is irreversible. Therefore, in the beneficiation process of large flake graphite, the task is not only to improve the concentrate yield, fixed carbon content and recovery rate, but also to minimize the damage to the large flake graphite during the beneficiation process and ensure that the concentrate contains a sufficient amount of large flake graphite.