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6 Graphite ore purification methods

2023-01-30 Xinhai (132)

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

Graphite ore is often associated with quartz, illite, kaolinite, andalusite, sericite, pyrite, limonite, tourmaline, calcite, etc., which need to be purified and removed before use. Standard graphite purification methods include:

selective flocculation

flotation

Alkali method

pickling

Chlorination Roasting

High temperature baking

Graphite beneficiation

1. Selective flocculation

Purification of graphite ore by selective flocculation requires adding a polymer flocculant to the suspension containing two or more components, so that the flocculant can selectively adsorb specific elements in the suspension and pass through the bridge chain. This action produces flocculation and precipitation to achieve the purpose of component separation.

The flocculants mainly include sodium silicate, sodium hexametaphosphate, lignin starch, etc. Carboxymethyl cellulose and water glass were used as dispersants. Tapioca flour, acorn flour, sodium alginate and polyacrylamide were used as flocculants to purify graphite ore.

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

2. Graphite ore flotation

Flotation is a standard method for graphite ore purification, mainly by adding a series of flotation reagents to enrich the selected target minerals at the gas-liquid interface and separate them from impurity minerals, so as to achieve the purpose of purification.

Graphite has good natural buoyancy and hydrophobicity, so conventional graphite ore can be purified by flotation. In the purification process, in order to protect large pieces of graphite, processes such as multi-stage grinding, multiple separations, and re-grinding of coarse concentrates are generally used.

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

Flotation purification of graphite ore can make graphite grade reach 80%~90% or even 95%. The method has the advantages of less medicine consumption, low energy consumption and low cost. Graphite ore contains very fine silicate minerals and compounds of potassium, calcium, sodium, magnesium, aluminum and other elements. Monomer dissociation cannot be achieved in the grinding stage, and it needs to be purified again by other processes after flotation.

3. Basic acid

The acid-base purification of graphite ore is a relatively mature process, which can be divided into alkali fusion and acid leaching.

Alkali fusion method: Under high temperature conditions, the molten alkali reacts chemically with acidic impurities (silicate, aluminosilicate, quartz) in graphite to form soluble salts, and then removes impurities by washing with water.

Acid leaching method: use acid to react with metal oxide impurities, convert some unreacted impurities in the alkali melting process into soluble salts, and then remove impurities by washing with water to separate them from graphite and improve the purity of graphite.

The alkali-acid purification of graphite ore can make the graphite grade reach 99.5%, the equipment is simple, the energy consumption is low, and the one-time investment is small. However, the acid and alkali in this method are highly corrosive to the equipment, and the purified wastewater is seriously polluted. In addition, there is the disadvantage of graphite loss.

4. Pickling

Acid leaching can be used to purify graphite ore by sulfuric acid, hydrochloric acid, nitric acid, hydrofluoric acid and other methods.

Sulfuric acid and hydrochloric acid are more suitable for leaching and have strong leaching ability. Some sulfuric acid leaching methods can also be used to purify graphite ore with sulfuric acid, hydrochloric acid, nitric acid, hydrofluoric acid, etc.

Sulfuric acid and hydrochloric acid are more suitable for leaching and have strong leaching ability. However, some sulfates have low solubility and hydrochloric acid is more expensive.

Nitric acid is highly oxidizing and volatile, easily decomposes when exposed to light, easily produces highly toxic phosgene, and is prone to explosion at high temperatures.

Hydrofluoric acid can neither carry out oxidation reaction nor reduction reaction. The key point is that it effectively dissolves silica and silicates. After graphite and hydrofluoric acid are fully mixed, hydrofluoric acid will react with impurities in graphite to form water-soluble compounds and volatiles, and then wash with water to remove soluble impurities to obtain high-purity graphite.

Hydrofluoric acid purification of graphite ore can effectively remove impurities in minerals with low energy consumption. However, this method has high toxicity and great environmental pollution.

5. Chlorination roasting

Purification of graphite ore by chlorination roasting method is mainly to add an appropriate amount of reducing agent to graphite ore. And high-temperature roasting is carried out under a specific atmosphere and equipment, so that the valuable metals in the minerals are combined with chlorine, and converted into gas phase or deposits with low melting point and boiling point. It is then precipitated and effectively separated from other components to obtain high-purity graphite.

The chlorination roasting method for purifying graphite ore has high efficiency, low energy consumption and low cost. However, chlorine gas in this method has strong corrosiveness and toxicity, and causes great external pollution.

6. High temperature baking

The melting point of graphite ore is very high (melting point 3652°C, boiling point 4250°C), much higher than other impurity minerals. The high-temperature roasting method for purifying graphite is selected by utilizing the difference in the melting point of graphite. When graphite ore is heated to 2700~3000°C, most of the impurities have been gasified, so graphite and impurities can be effectively separated.

The high-temperature roasting method can purify graphite ore with a grade of 99.99% or even higher. However, it consumes a lot of energy, requires high equipment, and has specific requirements for the purity of graphite ore.

The above are the standard six graphite ore purification methods. According to the ore properties of the graphite ore, the conditions of the processing plant, and the investment budget, choose which method to use. When selecting the process, the graphite ore beneficiation test should be carried out first. Through the test report, select the purification process in a targeted manner to strive for excellent technical and economic benefits.


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