1 Flotation method

Flotation method is a commonly used method for purifying minerals. Due to the difficulty of water infiltration on the surface of graphite, it has good floatability and is easy to separate from impurity minerals. In China, flotation method is generally used for beneficiation of graphite.

The flotation of graphite raw ore generally uses the positive flotation method first, followed by reverse flotation of the positive flotation concentrate. High grade graphite concentrate can be obtained by using flotation method. The grade of flotation graphite concentrate can usually reach 80% to 90%, and the purity can reach around 98% by using multi-stage grinding.

The commonly used collectors for flotation of crystalline graphite are kerosene, diesel, heavy oil, sulfonic acid esters, sulfate esters, phenols, and carboxylic acid esters. The commonly used foaming agents are 2 # oil, 4 # oil, terpineol oil, ether alcohol, and butyl ether oil. The adjusting agents are lime and sodium carbonate, and the inhibitors are water glass and lime. The commonly used collector for flotation of cryptocrystalline graphite is coal tar, the commonly used foaming agents are camphor oil and pine oil, the commonly used adjusting agent is sodium carbonate, and the commonly used inhibitors are water glass and sodium fluorosilicate.

The grade of graphite concentrate purified by flotation can only reach a certain range, as some impurities are extremely fine grained and disseminated in graphite scales, and even fine grinding cannot completely dissociate the monomers. Therefore, it is difficult to completely remove these impurities using physical beneficiation methods, which are generally only used as the first step of graphite purification. Further methods for purifying graphite usually include chemical or high-temperature methods.

2 Alkali acid method

Alkali acid method is the main method for chemical purification of graphite and is currently a relatively mature process method. This method includes systems such as NaOH HCl, NaOH H2SO4, and NaOH HC l-HNO3. The NaOH HCl method is the most common among them.

The principle of alkaline acid method for purifying graphite is to mix NaOH and graphite in a certain proportion and calcine them evenly. At high temperatures of 500-700e, impurities such as silicates, aluminosilicates, quartz, and other components in the graphite react chemically with sodium hydroxide to generate soluble sodium silicate or acid soluble sodium aluminosilicate. Then, they are removed by washing with water to achieve the purpose of desilication; Another part of impurities, such as metal oxides, remain in the graphite after alkali melting. The product after desilication is leached with acid to convert the metal oxides into soluble metal compounds. Impurities such as carbonates in the graphite and acid soluble compounds formed during the alkali leaching process react with acid and enter the liquid phase, which is then separated from the graphite through filtration and washing. Graphite has high chemical inertness and good stability. It is insoluble in organic and inorganic solvents and does not react with alkaline solution; Except for strong oxidizing acids such as nitric acid and concentrated sulfuric acid, it does not react with many acids, especially with hydrofluoric acid resistance; Under 6000 ℃, it does not react with water and steam. Therefore, the properties of graphite remain unchanged during the purification process.