¿Cómo se extrae el grafito?

Graphite is a key non-metallic mineral, which has excellent properties such as electrical conductivity and lubricity. You can widely use it in battery, aerospace and other industries. However, grafito natural needs complex extraction, and understanding its process is significant for resource utilization and industrial development.

Preparations Before Extraction

Geological Exploration Techniques

The technique of geological exploration is very important in searching for graphite deposits, and the basis is geological mapping. By observing and measuring the surface rocks, strata and other elements to draw maps, delineate the possible mineralization area. Geophysical exploration includes resistivity method and induced polarization method. The former uses the difference of resistivity between graphite and surrounding rock to find ore. While the latter uses the polarization effect of graphite in electric field to identify the ore body. Geochemical exploration is used to locate graphite deposits by analyzing soil and other sample elements.

Analysis of Ore Properties

After determining the location of graphite ore, we need to urther analyze the ore properties. First carry out chemical composition analysis to understand the graphite content and associated elements.As there are many impurities containing sulfur and iron, it is necessary to consider the impurity removal method. Then analyze the mineral composition, and clarify the symbiosis and distribution of graphite and quartz minerals. In addition, analyze the physical properties such as hardness and density to provide a basis for subsequent processes.

Methods of Graphite Mining

Open-pit Mining

You can use this method when the graphite deposit is shallow buried and the ore body is large and concentrated. In the early stage, you should do the site preparation work. Such as clearing vegetation, topsoil and regolith, building transport roads and drainage systems. Then use electric shovel, hydraulic excavator and other large equipment to excavate. When mining, according to a certain step height from top to bottom stratified operation. The extracted ore is delivered directly to the concentrator by truck or belt conveyor.

Open-pit mining has low cost, high efficiency, relatively low ore loss rate and dilution rate, so it is conducive to large-scale mining. But it also has obvious the disadvantages, such as disrupting the surface environment and occupying a lot of land. It is also subject to climatic conditions, and bad weather will affect the progress of mining.

Underground Mining

Underground mining is for deeply buried graphite ore. First of all, we must carry out development projects, dig shafts, inclined shafts, adits and other channels. And build a perfect transportation, ventilation, drainage and power supply system. Then select the mining method according to the occurrence condition and shape of the ore body. When the ore body is thin and the roof is stable, usually use the room pillar mining method. If the ore body is thick and the ore has poor stability, we choose the sublevel caving method. It divides the ore body according to its height and draws it from top to bottom. Although underground mining can make use of deep resources, it has high cost, complicated technology, safety risk and high ore loss rate.

Graphite Extraction Processes

Flotation Method

Basic Principles

This way is based on the differences in physical and chemical properties of mineral surfaces. Because graphite is naturally hydrophobic, and most gangue minerals are hydrophilic. When flotation, adding collector to pulp, it will selectively adsorb on graphite surface, strengthen its hydrophobicity. At the same time, add the foaming agent will produce stable bubbles. Then hydrophobic graphite particles attached to the bubbles floated to the surface of the pulp to form a foam layer. And hydrophilic gangue minerals remained in the pulp to achieve separation.

Process Flow

First, break and grind the mined graphite ore to make the particle size meet the requirements of monomer dissociation. And the general -200 mesh accounts for 60%-80%. Then put the ground pulp into the mixing tank, add water, collector and foaming agent to stir fully. So that the agent and the mineral fully function. Then put the pulp into the flotation machine, aerated and stirred to produce bubbles to complete the flotation separation. Finally, select the foam product several times to improve the grade of graphite concentrate and obtain qualified products.

Influencing Factors

Grinding particle size is important, too coarse graphite and gangue dissociation is not sufficient, low grade of concentrate. Excessive granularity of grinding leads to excessive grinding, increases energy consumption and pharmaceutical consumption, and affects flotation index. The type and dosage of collector affect the recovery and grade of graphite. And the amount of foaming agent affects the size and stability of bubbles. In addition, pulp concentration, flotation time and temperature will also have an effect on the flotation effect. You need to optimize them through test and practice.

Chemical Purification Method

Acid-Base Method

This is using the reaction of acid and base with impurities to dissolve impurities to purify the graphite. Mix the graphite concentrate with a certain concentration of hydrochloric acid and hydrofluoric acid, stirring reaction at a specific temperature. Hydrochloric acid dissolves metal oxide impurities, and hydrofluoric acid removes siliceous impurities. After the reaction, filter and wash it, and then neutralize the residual acid with sodium hydroxide and remove some impurities. After several times of washing, graphite with a purity of over 99% can be obtained. However, the acid and base consumption of this method is large. And the waste water produced by this method pollutes the environment and needs to be treated strictly.

Chlorination Roasting Method

Calcine graphite at high temperature by mixing with chlorinating agents such as calcium chloride and sodium chloride. During roasting, graphite impurities react with chlorination agents to form gaseous or volatile chlorides, so as to separate from graphite. Such as iron, aluminum impurities into chloride volatilization. This method has low energy consumption, high purification efficiency and can effectively remove many impurities. However, it will produce toxic chloride gas and seriously corrode the equipment. So it needs to be equipped with perfect exhaust gas treatment and anti-corrosion measures.

Physical Purification Method (High-temperature Purification)

This is purified by using the high melting point of graphite and the low melting point of impurities. Put the graphite raw materials into a special high temperature furnace, heating up to 2500-3000℃. Under the protection of argon, nitrogen and other inert gases, impurities such as ash in the graphite melt, vaporize and escape at high temperatures. This can increase the purity of graphite to more than 99.9%. And it is suitable for high-end electronics, aerospace and other areas with high purity requirements for ultra-high purity graphite production. However, the equipment investment of this method is huge, the energy consumption is high, and the production scale is relatively small.

Conclusión

The extraction of graphite includes exploration, mining, beneficiation and purification. Existing technologies have their own characteristics and meet different needs. In the future, its extraction technology will develop towards green, efficient and intelligent development.

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