Graphite purification and beneficiation scheme

Graphite is often associated with quartz, illite, kaolinite, rhodochrosite, sericite, and a small amount of pyrite, limonite, tourmaline, and calcite. Purification and dressing are required before application.

Graphite beneficiation programs mainly include flotation, gravity separation, electric separation, selective flocculation, alkali-acid, acid leaching, chlorination roasting, high-temperature roasting, etc.

Among them, flotation, gravity separation and electric separation are commonly used in graphite beneficiation process, while alkali-acid method, chlorination roasting method and high-temperature roasting method are used for deep processing of graphite concentrate.

01 Graphite flotation separation method

Graphite has good natural buoyancy and hydrophobic properties. Therefore, most processing plants use flotation to purify graphite ore, that is, add a series of flotation reagents to the gas-liquid interface to enrich graphite ore on the gas-liquid interface, thereby separating it from impurity minerals. A commonly used collector is coal tar. The foaming agent is mainly pine oil or butyl ether oil, and the corrosion inhibitor is mostly water glass and sodium fluorosilicate.

The flotation process of flake graphite ore mostly adopts multi-stage grinding, multiple separation, coarse concentrate regrinding, and separation process to protect the scales.

Graphite flotation beneficiation can make graphite grade reach 80%-90%, even close to 95%. And it was found that the method has the characteristics of low chemical consumption, low energy consumption and low cost. However, for graphite ore containing extremely fine silicate minerals and elemental compounds such as potassium, calcium, sodium, magnesium, and aluminum, the monomer dissociation cannot be achieved in the grinding stage, and it needs to be purified again by other processes after flotation.

02 Graphite gravity separation method

Graphite gravity separation is sorted according to the specific gravity difference between graphite ore and gangue. The paragenetic minerals in graphite ore can be divided into heavy minerals, medium heavy minerals and light minerals according to specific gravity. Among them, heavy minerals (specific gravity > 3.32) mainly include pyrite, pyrrhotite, limonite, zoisite, etc., followed by titanite, zircon, white titanium, monazite, and scheelite. Minerals with medium specific gravity (with a specific gravity between 2.9 and 3.32) mainly include diopside, tremolite, and occasionally apatite. Among the light minerals (specific gravity<2.9), there is a difference in the specific gravity of graphite and its associated minerals. Therefore, heavy minerals can be separated by gravity separation to obtain rough concentrate mainly composed of graphite.

03 Graphite electroseparation method

Electric separation is a physical separation method that utilizes the different electrical properties of various minerals and materials for separation. For graphite ore beneficiation, graphite ore has good conductivity, while gangue minerals such as feldspar, quartz, pyrite, etc. have poor conductivity. Based on this difference, graphite and other minerals can be separated by electroseparation.

The effective treatment particle size of electric separation method is usually 0.1-2mm. However, for flake or low-density graphite ore, the upper limit of processing particle size can reach 5mm. The processing particle size of the wet high-gradient electric separator can be reduced to the micron level.

04 Graphite selective flocculation method

Purification of graphite ore by selective flocculation requires adding a polymer flocculant to a suspension containing two or more components, so that the flocculant selectively adsorbs a certain component in the suspension and generates Flocculation and precipitation, so as to achieve the purpose of component separation.

In production practice, commonly used flocculants mainly include sodium silicate, sodium hexametaphosphate, lignin starch, carboxymethyl cellulose, and dispersants mainly include water glass.

Purification of graphite ore by selective flocculation has relatively simple equipment and low cost, but the recovery rate of fixed carbon is low, only about 40%.

05 Graphite alkali acid method

The acid-base purification of graphite ore is a relatively mature method, which is divided into two processes: alkali fusion and acid leaching.

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

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

06 Graphite chlorination roasting method

The graphite chlorination roasting method is mainly to add an appropriate amount of reducing agent to the graphite raw ore, and then perform high-temperature roasting in a specific atmosphere and equipment. After the valuable metals in the minerals are combined with chlorine, they are transformed into low-melting and low-boiling gas phase or condensed phase metal chlorides, which are effectively separated from other components to obtain high-purity graphite.

The purification of graphite ore by chlorination roasting has the advantages of high efficiency, low energy consumption and low cost. However, the chlorine gas in this method has strong corrosiveness and toxicity, which has caused great pollution to the environment.

07 Graphite high temperature roasting method

The melting point of graphite ore is very high (melting point 3652°C, boiling point 4250°C), much higher than other impurity minerals. The graphite high-temperature roasting method is to use the melting point difference between graphite and other impurity minerals to separate. When graphite ore is heated to 2700~3000℃, most of the impurities are gasified, which can effectively separate graphite and impurities.

The grade of graphite ore purified by high-temperature roasting method can reach 99.99% or even higher, but there are still disadvantages such as high energy consumption, high equipment requirements, and high purity requirements of graphite raw ore.