Mining
Mining Basics
Mining involves the extraction of geologic materials, such as ores that contain valuable mineral deposits, from the Earth. The minerals within ores that are mined are often metal, but are not always. Resources such as coal can be mined as well.
When discussing mining, the mine's reserve is often referenced; this is the amount of the resource left to mine. A reserve can be depleted if there is none left, and it can also be economically depleted if it is not profitable to continue to mine what is remaining.
As ore is a rock or sediment that contains valuable minerals inside, there is waste left over once the minerals are extracted - this is known as tailings. Slag, another type of waste from mining, is a byproduct of smelting ores. This waste is typically stored in tailing ponds which are large, man-made reservoirs; they hold toxic materials and can cause environmental harm via contaminating groundwater and killing wildlife.
Surface Mining
When the resource is found in a relatively shallow mineral deposit, surface mining is used. In order to get to the resource, soil, plants, and rocks need to be removed - this is known as overburden. The overburden that is removed is usually left in a pile known as a spoil. The removal of overburden can lead to habitat destruction, topsoil erosion, and decreases in water and air quality due to things like PM in the air and increased stream turbidity.
Surface mining is used for the vast majority of mining in the US, and there are a variety of different types of surface mining.
Open Pit Mining centers around using machines to dig a large pit where ores are removed.
Strip Mining involves digging thin, horizontal strips above the desired resource. After the resource is extracted, a parallel strip is dug and its overburden is dumped into the previous strip. This process is then continually repeated.
Mountaintop Removal Mining uses explosives to destroy the top of a mountain, after which waste is plowed into valleys below. This method is especially damaging to the environment.
Subsurface Mining
As surface deposits are depleted, it becomes necessary to move deeper to find the resource. Subsurface mining involves extracting deep materials through the use of underground tunnels and shafts. Machines are then used to return mined resources back to the surface.
This method is actually far less environmentally damaging than surface mining. It disturbs a fraction of the land and produces far less waste. It is, however, significantly more expensive and dangerous for miners. There are risks of falling rocks/cave-ins, explosions, higher risks of respiratory ailments (such as "black lung" which is caused by miners breathing in coal dust), and suffocation from poor ventilation. In addition, subsidence can occur, which is when the land above the mines collapses, which can cause a variety of issues.
Environmental Impacts of Mining
There are a variety of environmental problems that are associated with both types of mining. Roughly 3/4 of all US solid waste is produced by mining. While surface mining produces more, that does not mean that subsurface doesn't produce any. One particularly damaging result of this is acid mine drainage which is when rainwater leaks into the mine or the spoils piles and mixes with the sulfuric acid produced by anaerobes as a by-product of their metabolism. When this sulfuric acid is introduced to nearby streams and groundwater, it lowers the pH of the water. This alone can harm organisms if it brings them outside their range of tolerance, but it also makes toxic metals (such as mercury and aluminum which can be obtained through mining) more soluble in water, which can kill aquatic organisms.
In addition, mining of all kinds can release methane (a greenhouse gas), particulate matter (a respiratory irritant), habitat loss, and increases erosion along with the effects caused by that.
Mine Reclamation
Mine reclamation is a method that works to make mining a more sustainable process by limiting the long-term environmental damage. Essentially, it involves returning the mined area to its original state as best as possible, with the ultimate goal of restoring the community to as close to what is was before mining as they can.
The general process involves filling the holes and shafts, removing tailings, restoring the contours of the land, returning topsoil, and then replanting native plants.
In addition to mine reclamation, it is possible to be more sustainable by using the mined resources more sustainably. The main strategy is the three Rs - reducing our need for them, reusing when possible, and recycling the minerals.