Why is open pit mining so devastating to the environment?
One of the adverse effects of open-pit mining stems from removing vegetation, soil, and rock overlying the mineral deposits. It severely degrades the landscape, eventually affecting the region's air and water quality.
Effect on Water Quality
Open-pit mining affects water quality and the availability of water resources in the area. One of the effects of open-pit mining is the occurrence of acid mine drainage. It occurs when pyrite, an iron sulfide, is exposed and reacts with water and air to form sulfuric acid and dissolved iron. When water precipitates, these iron are left at the bottom of mine drainage. Acid runoff dissolves heavy metals, such as mercury, copper, and lead, which can seep into the groundwater and surface water. Dissolved metals become harmful when they reach drinking water, affect the growth of aquatic plants and animals, and corrode infrastructures in nearby communities.
Even in cases where acidic conditions do not occur, processing ore materials can produce toxic substances (e.g., arsenic, selenium, and other metals). Chemicals from leaching (chemical treatment of ores) and blasting can also result in elevated levels of cyanide and nitrogen compounds (e.g., ammonia, nitrate, and nitrite) in waters in and near the mine sites.
Effects on Air Quality
Airborne emissions occur throughout the mining operations, from excavation, blasting, material transportation, and dust from tailing facilities. The wind disperses these tiny particles to other areas beyond the mining site to reach farther areas and can generate hazardous air pollutants. Furthermore, fuel combustion from stationary and mobile sources, explosions, and mineral processing add to air pollution. These pollutants can be a source of monoxide and volatile organic compounds contributing to the formation of ground-level ozone. Inhaling this can eventually trigger throat irritation, coughing, and chest pain and eventually worsen asthma and bronchitis.
In addition to open-pit mining's environmental impacts on air and water, rocks in the area are also subjected to intensive weathering. It makes sediments more easily mobilized, increasing the incidence of landslides and destruction of ledges.
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Aside from the extensive environmental impacts of open-pit mining, there are other disadvantages and issues associated with this mining method. This includes the following:
- Extreme weather disturbances, such as hurricanes and extensive rainfall, can be detrimental to mining operations.
- It requires a large waste disposal area due to the significant amount of waste it produces. Large mines can produce almost one million tons of ore and waste rocks, while small mines can still generate waste of a few thousand tons.
- Dewatering or removal of groundwater was also associated with the formation of sinkholes. A case study in an open-pit mine in Eastern Turkey showed how the significant decrease in pore water pressure and increased vertical stress during drainage borehole operation cause rocks to collapse and form sinkholes.
- Most open-pit mines operate 24/7, producing excessive vibration, noise, and light pollution from blasting, drilling, and hauling. These factors affect the quality of life of humans and wildlife near the site.
- Water, air, and soil contamination threaten food availability in the area, increasing the risk of malnourishment for people in the vicinity. Pollution and contamination also increase the incidence of tuberculosis, asthma, and gastrointestinal diseases.
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Two of the largest producers of copper in the United States use open-pit mining for extraction:
- Bingham Canyon Mine (also known as Kennecott Copper Mine) — is the deepest and one of the largest open-pit mines in the world, with a width of approximately 2.48 mi (4 km) and a depth of more than 0.74 mi (1.2 km). It is located southwest of Salt Lake in Utah. In 2021, it produced 59,400 tons of copper, 139,500 ounces of gold, and 2.22 million ounces of silver.
- Morenci Copper Mine — is another large producer of copper in North America. It is located in Greenlee County, Arizona, and is expected to operate until 2041. It processes about 700,000 tons of rocks daily and produces 840 million pounds of copper yearly. It also produces molybdenum as a byproduct.
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Open-pit mining refers to the process of extracting metallic and nonmetallic ores directly from the surface after removing the overlying vegetation, topsoil, and rocks. It uses a series of level surfaces (also called benches or berms) to reach the ore body until it eventually forms an open pit with stepped walls. Ore materials are transported to a separate processing site, where they are treated with chemicals or heat to obtain the metals they contain. Aluminum, copper, iron, and phosphate are some of the numerous materials derived from an open-pit mine. The deepest and one of the largest open-pit mines in the world is the Bingham Canyon Mine, also known as the Kennecott Copper Mine, located in Utah.
Open-pit mines have higher productivity, lower operating costs, and safer mining operations, but it is also one of the most damaging mining methods. It has adverse effects on the landscape by removing all vegetation and topsoil in the mining site. For one, it affects the water quality and availability in the region due to acid mine drainage — a process where iron sulfides react with water and air to form sulfuric acid and dissolved iron. This dissolves metals that can seep through the groundwater and surface waters. Moreover, particular matter produced during mining operations can be dispersed by winds and generate harmful air pollutants. Poor air and water quality eventually affect the lives of communities and wildlife near the site.
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Frequently Asked Questions
What are the disadvantages of open-pit mining?
Open-pit mining has several disadvantages, which include the following:
(1) It generates thousands to millions of tons of waste and requires a large disposal area to accommodate them.
(2) It has been associated with the formation of sinkholes due to excessive removal of groundwater.
(3) It produces excessive noise and light pollution that can negatively affect the quality of life of humans and wildlife nearby.
Is open-pit mining better for the environment?
Open-pit mining is one of the most destructive mining methods because it requires extensive vegetation, topsoil, and rock removal to extract the ore deposits. It also produces a large amount of waste and has by-products that can adversely affect air and water quality.
How does open-pit mining affect air pollution?
Open-pit mining produces particulate matter from excavation, blasting, transportation, and fuel emissions. These tiny particles can generate hazardous air pollutants and contribute to the formation of ground-level ozone.
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