Graphite is an important non-metallic mineral. After purification, it can be used in many fields such as optics, energy, aerospace, environment, new materials, etc. Therefore, its mineral processing and purification has important strategic significance.

Graphite ore (picture from the Internet)

Quartz, illite, kaolinite, andalusite, sericite, and a small amount of pyrite, limonite, tourmaline, and calcite are often associated with graphite ore. It needs to be purified and removed before it can be applied. Common graphite Purification methods include selective flocculation method, flotation method, alkaline acid method, acid leaching method, chlorination roasting method and high-temperature roasting method.

1. Selective flocculation of graphite ore

The selective flocculation method requires the addition of a polymer flocculant to a suspension containing two or more components, so that the flocculant can selectively adsorb a certain component in the suspension, and Flocculation and sedimentation are produced by bridging, so as to achieve the purpose of component separation.

The main flocculants are sodium silicate, sodium hexametaphosphate, lignin starch, carboxymethyl cellulose and water glass as dispersants, and tapioca flour, acorn powder, sodium alginate, and polyacrylamide as flocculants Purify graphite ore.

The graphite ore selective flocculation purification method and equipment are relatively simple and low in cost, but the fixed carbon recovery rate is low, only about 40%.

2. Graphite ore flotation method

Flotation is a common method for the purification of graphite ore. It mainly enriches selected target minerals in the gas-liquid interface by adding a series of flotation agents to achieve separation from impurity minerals to achieve the purpose of purification.

Graphite itself has good natural floatability and hydrophobicity, so conventional graphite ore can be purified by flotation technology. In the purification process, in order to protect the large scales of graphite, the process generally adopts the process of multi-stage grinding, multiple separation, and regrind and reselection of coarse concentrate.

The commonly used collectors in graphite ore flotation process mostly use coal tar, the foaming agents mostly use terpineol oil or butyl ether oil, and the inhibitors mostly use water glass and sodium fluorosilicate.

Purification of graphite ore flotation method can make the graphite grade reach 80%~90%, or even about 95%, and this method has low chemical consumption, low energy consumption and low cost. However, when the graphite ore is mixed with very fine silicate minerals and potassium, calcium, sodium, magnesium, aluminum and other elements, the monomer dissociation cannot be achieved in the grinding stage, and it needs to be purified again by other processes after the flotation method. .

3. Graphite ore alkaline acid method

Purification of graphite ore by acid-base method is a relatively mature process at present, which can be divided into two processes: alkali melting and acid leaching.

Alkali melting process: Under high temperature conditions, the alkali in the molten state and the acid impurities in the graphite (silicate, aluminosilicate, quartz) are chemically reacted to form soluble salts. , And then use washing method to remove impurities.

Acid leaching process: Use acid to react with metal oxide impurities to convert some of the impurities that did not react during the alkali fusion process into soluble salts, and then wash the impurities to make them and graphite Separation to improve graphite purity.

Purification of graphite ore by alkaline acid method can make graphite taste up to 99.5%, with simple equipment, low energy consumption and small one-time investment. However, the acid and alkali of this method are highly corrosive to the equipment, and the wastewater after purification is seriously polluted. In addition, there are drawbacks of graphite loss.

4. Graphite ore acid leaching method

The acid leaching method can be used to purify graphite ore by methods such as sulfuric acid, hydrochloric acid, nitric acid, and hydrofluoric acid. Among them, sulfuric acid and hydrochloric acid are more suitable for leaching acid, with strong leaching ability, but some sulfates are less soluble, and hydrochloric acid is more expensive; nitric acid has strong oxidation and volatility, and is easy to decompose when exposed to light and is easy to produce highly toxic phosgene. It is easy to explode at high temperatures; hydrofluoric acid cannot undergo oxidation or reduction reactions. The point is that it can effectively dissolve SiO2 and silicate. After graphite and hydrofluoric acid are fully mixed, hydrofluoric acid will be mixed with impurities in graphite After the reaction, water-soluble compounds and volatiles are generated, and then the soluble impurities are removed by the water washing method to obtain high-purity graphite.

The hydrofluoric acid purification of graphite ore can effectively remove impurities in minerals and has low energy consumption. However, this method is highly toxic and causes great environmental pollution.

5. Graphite ore chlorination roasting method

Purification of graphite ore by the chlorination roasting method is mainly to add an appropriate amount of reducing agent to the graphite ore, and then roast it at a high temperature under a specific atmosphere and equipment, so that the valuable metals in the mineral are combined with chlorine and converted into a low melting point boiling point The gas phase or condensed phase metal chlorides are separated out and separated from other components to obtain high-purity graphite.

The purification of graphite ore by chlorination roasting has high efficiency, low energy consumption and low cost. However, in this method, chlorine gas is highly corrosive and toxic, and pollutes the environment.

6. High temperature roasting method of graphite ore

The melting point of graphite ore is very high (melting point is 3652℃, boiling point is 4250℃), which is much higher than other impurity minerals. The high-temperature roasting method is used to purify graphite by using the melting point difference of graphite. The graphite ore is heated to 2700~3000℃, most of the impurities have been vaporized, so graphite can be effectively separated from impurities.

The high-temperature roasting method to purify graphite ore can achieve a taste of 99.99% or even higher, but the energy consumption is high, the requirements for equipment are very high, and there are certain requirements for the purity of the graphite ore.

The above are the six common graphite ore purification methods. Which one to choose depends on various factors such as the nature of the graphite ore, the processing plant conditions, and the investment budget. It is recommended that when selecting the process, the graphite ore beneficiation test should be carried out first, and the purification process should be selected according to the test report in order to strive for the ideal technical and economic benefits.