Graphite Ore Purification Technologies: A Comprehensive Overview

Graphite, as an important non - metallic material with both metallic and non - metallic properties, is widely used in modern industry. However, natural graphite ores are often associated with a large number of impurities and need to go through efficient purification processes to increase the fixed carbon content and meet the stringent requirements of various industries. Currently, graphite ore purification mainly includes three types of processes: physical, chemical, and combined purification, each with its own technical characteristics and application scenarios.

1. Physical Purification Processes: Separation Methods Based on Physical Property Differences

(1) Flotation Method: The Basic Process for Graphite Ore Dressing

Flotation is the most commonly used physical method for graphite ore dressing, especially suitable for flake graphite. Due to the natural hydrophobicity and good floatability of flake graphite, in the flotation process, kerosene, diesel, etc. are used as collectors, and No. 2 oil, No. 4 oil, etc. are used as frothers. Together with regulators (such as lime and sodium carbonate to adjust the pulp pH to 8 - 9), graphite particles can attach to air bubbles and float up to achieve separation from gangue minerals. Generally, a stage grinding and stage separation process is adopted, such as the common one - roughing, one - scavenging, and seven - cleaning process, which can obtain graphite concentrates with a fixed carbon content of 90% - 97%. For large - flake graphite, in order to protect the integrity of the flakes, rod mills are often selected for rough grinding; while for fine - flake graphite, ball mills can be used, and a finer grinding fineness is selected to improve the concentrate grade.

(2) Gravity Separation Method: A Pretreatment and Preliminary Enrichment Method

Gravity separation is based on the density differences between graphite and impurity minerals for separation and is mainly used for the pretreatment of graphite ores. When the ore contains minerals with relatively large specific gravity such as pyrite, limonite, and garnet, through gravity separation equipment (such as jiggers, chutes, etc.), the heavy - mineral tailings can be removed in advance, achieving preliminary enrichment of graphite. After obtaining the rough concentrate, flotation is used to increase the fixed carbon content further. However, the purification accuracy of gravity separation for graphite is limited, and it is mostly used in combination with flotation in actual production and is rarely used alone.

(3) Electrostatic Separation Method: A Separation Technology Utilizing Conductivity Differences

The good electrical conductivity of graphite forms a sharp contrast with associated gangue minerals (such as quartz, feldspar, mica, etc.). Based on this, electrostatic separation can be used to separate graphite from gangue. In an electric field, graphite particles and gangue minerals are separated due to different charging characteristics. However, electrostatic separation has a small processing capacity and low efficiency. Currently, it is only applied in some specific scenarios (such as some graphite dressing in North Korea) and has not been widely popularized.

2. Chemical Purification Processes: An Effective Path for Deep Impurity Removal

(1) Alkali - Acid Method: A Traditional and Widely Used Chemical Purification Process

In the alkali - acid method, graphite is first mixed with sodium hydroxide in a certain proportion and melted at a high temperature of 700 - 800°C. The impurity elements such as silicon, iron, and aluminum in the graphite react with sodium hydroxide to form water - soluble substances. After washing with water to remove these water - soluble impurities, hydrochloric acid or sulfuric acid is added to further react with the undissolved impurities to form soluble substances, and then washed with water again to completely remove the impurities. This process can increase the graphite purity to 98% - 99.8%. However, it has disadvantages such as high processing temperature, strong corrosiveness of acid - base reagents, large graphite loss during washing, and high costs. Moreover, the product purity is difficult to meet the extremely high requirements for graphite purity in high - end electronics, national defense, and other fields.

(2) Hydrofluoric Acid Method: An Efficient and Low - Consumption Purification Solution

The hydrofluoric acid method uses the reaction between hydrofluoric acid and impurities in graphite (such as SiO₂, metal oxides, etc.) to generate water - soluble fluorides and fluosilicates, and the impurities are removed by washing with water to obtain high - purity graphite products. During the reaction, hydrochloric acid is often added to dissolve the solid products generated by the reaction to promote the reaction. This process has high impurity removal efficiency, high - grade graphite products, little impact on the performance of graphite, and low energy consumption. For example, using the flotation concentrate of flake graphite from a certain place in Madagascar as raw material, under the conditions of a liquid - solid ratio of 3.5 mL/g of the mixed acid composed of hydrochloric acid and hydrofluoric acid to graphite, a HF volume fraction of 40%, and a water - bath reaction at 60°C for 8 hours, the graphite grade can be purified from 94.96% to 99.98%. However, the highly toxic and corrosive nature of hydrofluoric acid requires extremely high production safety protection and environmental protection treatment, increasing the difficulty and cost of process application.

(3) High - Temperature Purification Method: A Key Technology for Preparing Ultra - High - Purity Graphite

The high - temperature purification method takes advantage of the fact that the melting point of graphite (3850 ± 50°C) is much higher than that of impurities. The graphite ore is placed in a graphite crucible, and under an inert gas and protective gas environment, it is heated to about 2700°C through specific equipment to vaporize and escape the impurities, thereby achieving graphite purification. After purification by this process, the graphite purity can be greater than 99.99%. However, this method has high energy consumption, strict requirements for equipment and raw materials, and huge investment. It is only suitable for high - tech fields with extremely high requirements for graphite purity, such as national defense and aerospace, and is difficult to be widely applied in ordinary graphite production.

3. Combined Purification Processes: An Innovative Solution with Complementary Advantages

In order to overcome the limitations of a single purification process, combined purification processes have gradually emerged in recent years. For example, the "flotation - alkali - acid method" combined process first enriches graphite preliminarily through flotation, reducing the impurity content of the raw materials for subsequent chemical treatment. Then, the alkali - acid method is used for deep impurity removal, which can not only reduce the consumption of acid - base reagents and graphite loss but also improve the product purity; the "flotation - hydrofluoric acid method" combination gives play to the advantages of flotation in low - cost and large - scale enrichment and combines the high - efficiency impurity removal ability of the hydrofluoric acid method. High - purity graphite products can be obtained while reducing the use of hydrofluoric acid and environmental risks. The combined process comprehensively utilizes the advantages of different processes and is an important direction for the development of graphite ore purification technology in the future.

The selection of graphite ore purification processes needs to comprehensively consider multiple factors such as ore properties, target product purity requirements, production costs, and environmental protection standards. With the progress of science and technology and the increasing demand for high - purity graphite in the industry, continuously optimizing existing processes and developing green and efficient combined purification technologies will promote the continuous development of the graphite industry towards high - end and refined directions.