In many fields such as batteries, natural graphite is widely used because of its unique performance, but natural graphite ore often contains various impurities, in order to make it play a better role, the purification process is very important.

The purification process of natural graphite mainly includes several key steps.

The first is flotation purification. The principle of this process is to take advantage of the natural hydrophobicity of graphite. The crushed natural graphite ore is mixed with water to form a slurry, and then a flotation reagent is added. Commonly used flotation reagents are collectors and frothers. The collector can selectively adsorb on the surface of graphite particles to enhance its hydrophobicity, while the foaming agent produces a large number of stable bubbles. Under the stirring and aeration of the flotation equipment, the graphite particles are attached to the bubbles and float to the surface of the pulp, forming a foam layer, while the impurities remain in the pulp and sink. The key technical points are to select the appropriate type and dosage of flotation reagents, and to control the stirring speed, aeration and flotation time of flotation equipment. Appropriate parameters can ensure the sufficient separation of graphite particles from impurities, and improve the flotation efficiency and the recovery rate of graphite.

Next is the acid-base method in the chemical purification method. The principle is the use of natural graphite impurities such as silicon dioxide, aluminum oxide, etc. can react with acid and alkali, and graphite has good chemical stability, under certain conditions do not react with acid and alkali. The graphite after flotation is mixed with strong acid (such as hydrochloric acid) and strong alkali (such as sodium hydroxide) in a certain order and proportion. First, it is treated with hydrochloric acid, which can react with impurities such as metal oxides to form soluble salts, and then these soluble substances are removed by washing. This is followed by treatment with sodium hydroxide, which reacts with acidic impurities such as silica to form soluble silicates. The key technical points are the control of acid-base concentration, treatment temperature and time. Excessive acid-base concentration may cause some damage to the structure of graphite, and the reasonable combination of temperature and time can ensure that the impurities are fully reacted and the graphite is not damaged. At the same time, in the washing process after the reaction, it is necessary to ensure that the soluble substances generated by the reaction are thoroughly cleaned to improve the purity of the graphite.

There is also a high temperature purification method. The principle is based on the difference between the boiling point and sublimation temperature of graphite and impurities. The graphite is heated to a high temperature, generally above 2000°C, at which time impurities such as some low-boiling metallic and non-metallic impurities will volatilize or vaporize, while the graphite remains solid and is further purified. The key technical points are the design of high temperature furnace and the accuracy of temperature control. High temperature furnaces need to have good thermal insulation and temperature uniformity to ensure that the entire graphite material can reach the required high temperature and will not affect the quality of graphite due to local overheating. At the same time, the heating rate in the heating process also needs to be strictly controlled to avoid the damage of graphite structure caused by excessive thermal stress.

In addition, in the whole purification process, it is also necessary to carry out strict quality inspection on the intermediate products and the final products of each step. Through advanced analytical instruments such as X-ray fluorescence spectrometer, inductively coupled plasma mass spectrometer, etc., the impurity content in graphite is accurately analyzed, so as to adjust the purification process parameters in time to ensure that the final natural graphite reaches the required high purity standard.

In short, the purification process of natural graphite is a complex and delicate process, and each purification step has its own unique principle and key technical points. Only through continuous optimization and improvement of these process steps can we produce high-quality natural graphite to meet the growing demand for it in various fields. With the continuous progress of science and technology, it is believed that the purification process of natural graphite will continue to innovate and develop, and make greater contributions to the development of related industries.