Graphite is a natural form of carbon characterized by its hexagonal crystalline structure. It is extracted using both open pit and underground mining methods. Although the naturally occurring ore is abundantly found and mined in many countries, including the U.S., the largest producer of graphite is China, followed by India. Natural graphite finds enormous applications in coatings, pencils, batteries, powder metal, castings and lubricants, depending upon the flake characteristic, which is determined by geology and the extraction and purification process employed.
Graphite Types and Mining Techniques
Graphite extraction is based on the degree of weathering of the ore rock and the proximity of the ore to the surface. Around the world, graphite is mined using two techniques: the open pit method (surface quarrying) and the underground method. Natural graphite is classified into flake or microcrystalline graphite, macrocrystalline graphite, and vein or lump graphite based on its underlying physical and chemical properties. These three types of graphite have distinct characteristics as a result of their occurrence in different geological regions. Flake graphite and macrocrystalline graphite are mined open pit and underground, whereas lump graphite, sourced by Sri Lanka, is only mined underground.
Open Pit Mining
Open pit mining involves extracting rock or minerals from an open pit or burrow. Open pit methods are used when the ore is close to the earth and the surface material covering the deposit is thin. Quarrying is a form of surface mining employed to obtain graphite by breaking the rocks either by drilling or by using dynamite explosives to cut open the rocks and compressed air or water to split it. Bore hole mining that is common to both open pit and underground methods involves drilling a hole to reach the ore, making a slurry using water through a tube and pumping back the water and mineral to the storage tank for further processing. Drilling and blasting methods are used on hard rock ore to liberate large-sized graphite flakes that are then crushed and ground before being subjected to flotation. The extracted graphite is brought to the surface by locomotives or, in developing countries, handpicked, shoveled and pulled in a cart and moved to the plant for further processing.
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Underground mining is done when the ore is present at a greater depth. Drift mining, hard rock mining, shaft mining and slope mining are exclusive to underground mining and are employed in graphite extraction.
Underground Methods In Graphite Extraction
Shaft mining is employed to reach the deepest ores. There are shafts or tunnels for miners and heavy equipment to move in and out. A different shaft is used for transportation of extracted ore and an air shaft for ventilation. Slope mining is done with slanted shafts that are not too deep and helps to extract ore that occurs parallel to the ground. Conveyors are used for transporting men and load using separate shafts. Drift mining, mostly done in mountainous regions, is common in the eastern U.S.; it has horizontal tunnels made lower than the mineral vein for gravity-aided extraction.