Coal mining is the process of extracting coal from the ground or from a mine. Coal is valued for its energy content and since the 1880s has been widely used to generate electricity. In the United Kingdom and South Africa, a coal mine and its structures are a colliery, a coal mine is called a "pit", and above-ground mining structures are referred to as a "pit head". In Australia, "colliery" generally refers to an underground coal mine.
Coal mining has had many developments in recent years, from the early days of tunneling, digging, and manually extracting the coal on carts to large open-cut and longwall mines. Mining at this scale requires the use of draglines, trucks, conveyors, hydraulic jacks, and shearers.
The coal mining industry has a long history of significant negative environmental impacts on local ecosystems, health impacts on local communities and workers, and contributes heavily to the global environmental crises, such as poor air quality and climate change. Coal mining can cause land degradation, polluted waterways and acid mine drainage, all of these contribute to environmental degradation. Studies show that coal mining is associated with large scale ecological degradation, with most affected land areas experiencing declining environmental quality. For these reasons, coal has been one of the first fossil fuels to be phased out of various parts of the global energy economy. The major coal producing countries, though, such as China, Indonesia, India and Australia, have not reached peak production, with production increases replacing falls in Europe and the United States and proposed mines under development.
As of 2023 the coal mining industry employed over 2.7 million workers, 2.2 million of them in Asia, but declines in global coal production were predicted to greatly decrease the number of coal jobs in coming decades.
Technical and economic feasibility are evaluated based on the following: regional geological conditions; overburden characteristics; coal seam continuity, thickness, structure, quality, and depth; strength of materials above and below the seam for roof and floor conditions; topography, especially altitude and slope; climate; land ownership as it affects the availability of land for mining and access; surface drainage patterns; groundwater conditions; availability of labor and materials; coal purchaser requirements in terms of tonnage, quality, and destination; and capital investment requirements.
Surface mining and deep underground mining are the two basic methods of mining. The choice of mining method depends primarily on depth, density, overburden, and thickness of the coal seam; seams relatively close to the surface, at depths less than approximately 61 m (200 ft), are usually surface mined. Coal that occurs at depths of 55 to 90 m (180 to 300 ft) are usually deep mined, but in some cases surface mining techniques can be used. For example, some western U.S. coal that occur at depths in excess of 60 m (200 ft) are mined by the open pit methods, due to thickness of the seam 20–25 metres (60–90 feet). Coals occurring below 90 m (300 ft) are usually deep mined. However, there are open pit mining operations working on coal seams up to 300–460 metres (1,000–1,500 feet) below ground level, for instance Tagebau Hambach in Germany.
Coal extraction methods vary depending on whether the mine is an underground mine or a surface (also called an open cast) mine. The most economical method of coal extraction for surface mines is the electric shovel or drag line. The most economical form of underground mining is the long wall, which involves using two spinning drums with carbide bits that run along sections of the coal seam.
Many coals extracted from both surface and underground mines require washing in a coal preparation plant.
When coal seams are near the surface, it may be economical to extract the coal using open-cut, also referred to as open-cast, open-pit, mountaintop removal, or strip mining methods. Opencast coal mining recovers a greater proportion of the coal deposit than underground methods, as more of the coal seams in the strata may be exploited. Equipment can include the following: Draglines which operate by removing the overburden, power shovels, large trucks to transport overburden and coal, bucket wheel excavators, and conveyors. In this mining method, explosives are first used in order to break through the surface, or overburden, of the mining area. The overburden is then removed by draglines or by shovel and truck. Once the coal seam is exposed, it is drilled, fractured and thoroughly mined in strips. The coal is then loaded onto large trucks or conveyors for transport to either the coal preparation plant or directly to where it will be used.
Most open cast mines in the United States extract bituminous coal. In Canada, Australia, and South Africa, open cast mining is used for both thermal and metallurgical coals. In New South Wales open casting for steam coal and anthracite is practiced. Surface mining accounts for around 80 percent of production in Australia, while in the US it is used for about 67 percent of production. Globally, about 40 percent of coal production involves surface mining.
Strip mining exposes coal by removing earth above each coal seam. This earth to be removed is referred to as 'overburden' and is removed in long strips. The overburden from the first strip is deposited in an area outside the planned mining area and referred to as out-of-pit dumping. Overburden from subsequent strips is deposited in the void left from mining the coal and overburden from the previous strip. This is known as pit-dumping.
It is often necessary to fragment the overburden by use of explosives. This is accomplished by drilling holes into the overburden, filling the holes with explosives, and detonating the explosive. The overburden is then removed, using large earth-moving equipment, such as draglines, shovel and trucks, excavator and trucks, or bucket-wheels and conveyors. Equipment depends on geological conditions; for example, to remove overburden that is loose or unconsolidated, a bucket wheel excavator might be the most productive. When all the overburden is removed, the underlying coal seam will be exposed (a 'block' of coal). This block of coal may be drilled and blasted (if hard) or otherwise loaded onto trucks or conveyors for transport to the coal preparation (or wash) plant. Once this strip is empty of coal, the process is repeated with a new strip being created next to it. This method is most suitable for areas with flat terrain.
The life of some area mines may be more than 50 years.
The contour mining method consists of removing overburden from the seam in a pattern following the contours along a ridge or around the hillside. This method is most commonly used in areas with rolling to steep terrain. It was once common to deposit the spoil on the downslope side of the bench thus created, but this method of spoil disposal consumed much additional land and created severe landslide and erosion problems. To alleviate these problems, a variety of methods were devised to use freshly cut overburden to refill mined-out areas. These haul-back or lateral movement methods generally consist of an initial cut with the spoil deposited downslope or at some other site, and spoil from the second cut refilling the first. A ridge of undisturbed natural material 15 to 20 ft (5 to 6 m) wide is often intentionally left at the outer edge of the mined area. This barrier adds stability to the reclaimed slope by preventing spoil from slumping or sliding downhill. In certain contour mining operations, extracting multiple coal seams necessitates removing and managing interburden between layers, thereby increasing the complexity of the mining process. However, this still seems to be a common mining approach.
The limitations of contour strip mining are both economic and technical. When the operation reaches a predetermined stripping ratio (tons of overburden/tons of coal), it is not profitable to continue. Depending on the equipment available, it may not be technically feasible to exceed a certain height of highwall. At this point, it is possible to produce more coal with the augering method in which spiral drills bore tunnels into a highwall laterally from the bench to extract coal without removing the overburden.