Graphite is a critical non-metallic material widely used in lubricants, refractory materials, batteries, foundry operations, pencils, coatings, and other industrial fields. Raw graphite ore shows significant variation in composition. It is usually mixed with impurities such as quartz, illite, kaolinite, andalusite, and sericite. It may also contain minor amounts of pyrite, limonite, tourmaline, and calcite. Removing these impurities is essential for industrial use.
This article introduces commonly used beneficiation and purification techniques, including flotation, gravity separation, electrostatic separation, and selective flocculation, as well as advanced methods such as alkali-acid leaching, acid leaching, chlorination roasting, and high-temperature roasting.
Graphite naturally shows strong floatability and hydrophobicity. With the addition of suitable reagents, graphite particles rise to the gas–liquid interface and separate from gangue minerals. Collectors such as coal tar oil are commonly used, while frothers include pine oil or butyl ether oil. Sodium silicate and sodium fluorosilicate often act as depressants.
For flake graphite, multi-stage grinding and separation are usually applied to protect the flake structure. Flotation can yield graphite grades of 80%–90%, and in some cases up to 95%. The process requires relatively low reagents and energy consumption. However, finely disseminated silicates and minerals containing K, Ca, Na, Mg, and Al may still need further purification.
Graphite flotation equipment: Primarily uses flotation machines (such as XJK, SF, BF, KYF, etc.) and flotation columns (such as FCSMC).
This method separates minerals based on density differences. Gangue minerals associated with graphite generally fall into three categories:
Heavy minerals (density > 3.32, e.g., pyrite, pyrrhotite, limonite, zoisite)
Medium-density minerals (2.9–3.32, e.g., diopside, tremolite, apatite)
Light minerals (density < 2.9)
Gravity separation works well for removing heavy minerals, leaving behind a crude concentrate rich in graphite.
Graphite gravity separation equipment: Primarily uses shaking tables, spiral chutes, and dense medium cyclones (pre-separation).
This technique leverages differences in electrical conductivity. Graphite, being highly conductive, separates easily from poorly conductive gangue minerals such as feldspar, quartz, and pyrite. The typical size range is 0.1–2 mm, but flaky or low-density graphite can be processed up to 5 mm. Wet high-gradient electrostatic separators can even handle particles at the micrometer level.
Graphite electrostatic separation equipment: Primarily uses high-voltage electrostatic separators (such as drum separators), which must be equipped with drying equipment (such as rotary dryers).
In this process, a polymer flocculant is added to a mixed suspension. It selectively adsorbs onto certain minerals, forming flocs through bridging, which makes separation possible.
Common flocculants include sodium silicate, sodium hexametaphosphate, lignin starch, and carboxymethyl cellulose. Sodium silicate often serves as a dispersant. This method is low-cost and simple, but the fixed carbon recovery rate is relatively low—about 40%.
This two-step chemical process combines alkali fusion and acid leaching:
Alkali fusion: At high temperatures, molten alkali reacts with acidic impurities such as silicates, aluminosilicates, and quartz to form soluble salts. These salts are removed through washing.
Acid leaching: Acids dissolve metal oxide impurities, converting them into soluble salts for easy removal.
This method can achieve a graphite grade of 99.5% with simple equipment and low energy consumption. However, issues such as corrosion, wastewater pollution, and potential graphite loss remain significant concerns.
This process involves roasting graphite ore under controlled atmosphere and temperature while adding a reducing agent. During roasting, valuable metals react with chlorine to form volatile or low-melting-point chlorides, which are then separated from the graphite.
Although this method is efficient and cost-effective, it involves the use of highly corrosive and toxic chlorine gas, raising both environmental and safety challenges.
Graphite's melting point (3652°C) and boiling point (4250°C) are much higher than those of most impurities. By heating the ore to 2700–3000°C, impurities volatilize and separate, leaving graphite with a purity of 99.99% or higher. This technique produces extremely high-purity products, but it consumes a substantial amount of energy and requires advanced equipment, as well as high-quality feed material.
Henan 4000 t/a Graphite ore Project
Practical Considerations
For industrial applications, it is crucial to conduct initial mineral assay and testing to understand the graphite ore's characteristics. Based on these results, a tailored purification process should be designed. Proper equipment selection ensures higher efficiency, reduced resource waste, and better economic returns while maximizing resource utilization.
Xinhai has over 30 years of experience in customized mineral processing services and has handled numerous graphite projects in real operations. Contact us today for tailored solutions and equipment to maximize efficiency and recovery.
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