Open Cast Mining Disadvantages
Jennifer Leos
Open pit mining -- or strip mining -- is an extraction process for ore or fossil fuels that takes place at the surface of a mining site. Worldwide, 40 percent of mining occurs at the surface, according to Greenpeace International. Compared with underground mining, surface mining is much more efficient. Unfortunately, this economy comes with a strict environmental cost because the surface environment is destroyed and polluted during the mining process.
One of the major benefits to open pit mining is the increase in efficiency over deep-shaft mining techniques. Because mining occurs at the surface, no space restrictions from narrow tunnels and shafts affect the rate at which ore can be extracted. Sampling each "bench" -- or level -- in an open pit before mining deeper makes it easy for surveyors to analyze the potential ore yield and avoid safety hazards. Open pit mining also uses larger extraction vehicles, increasing the amount of ore harvested per day. All of these improvements to efficiency work to reduce the cost of mining using an open pit.
Open-pit mining is much safer than shaft mining. In underground mining, the threat of a cave-in or release of toxic gas is a constant concern. When shaft mining was the most common method of ore extraction, thousands died in cave-ins, gas events and accidents involving equipment. In 1907 alone, more than 3,200 deaths related to mining occurred. Today, with safer mining processes, such as open-pit mining, safer equipment and a general increase in safety awareness, mining deaths have fallen considerably. For example, 15 coal mine related deaths were recorded in 2017 in the United States.
An open pit mining operation virtually eliminates any biologic life at the surface. Vegetation is stripped, and the surface at the dig site is left completely barren. Without replanting and restoring the ecosystem, a strip mining site can take decades to recover. Abandoned mining pits can also pose extreme risks. The slope of the mining walls can be steep or even vertical, and the structural stability of access points is constantly changing as erosion occurs. Without vegetation to stabilize the surface, landslides and rockslides can occur without warning.
AMD, or acid mine drainage, is a serious environmental concern associated with strip mining. AMD occurs when sulfide-rich rocks that contain ore are broken down from exposure to water and air at the surface. The sulfides form sulfuric acid, which dissolves nearby rock and releases dangerous metalloids into local streams and groundwater. This polluted water can kill life along water sources for miles. The Questa molybdenum mine in New Mexico, for example, is the root cause for more than eight miles of damage to the Red River.
Our goal is to make science relevant and fun for everyone. Whether you need help solving quadratic equations, inspiration for the upcoming science fair or the latest update on a major storm, Sciencing is here to help.
How they arise and how their effects can be mitigated Overview
Unregulated mining has the potential to release harmful substances into the soil, air, and water. Mission 2016 proposes that governments enforce regulations on companies and use cutting-edge technology to reduce the damage from mining-related sources. As more mines open in countries with varying levels of environmental protection, it is increasingly vital that safeguards established by the Strategic Minerals Association (SMA) are in place before operations proceed (see the international regulation page).
Open pit mining, where material is excavated from an open pit, is one of the most common forms of mining for strategic minerals. This type of mining is particularly damaging to the environment because strategic minerals are often only available in small concentrations, which increases the amount of ore needed to be mined.
Environmental hazards are present during every step of the open-pit mining process. Hardrock mining exposes rock that has lain unexposed for geological eras. When crushed, these rocks expose radioactive elements, asbestos-like minerals, and metallic dust. During separation, residual rock slurries, which are mixtures of pulverized rock and liquid, are produced as tailings, toxic and radioactive elements from these liquids can leak into bedrock if not properly contained.
Underground mining has the potential for tunnel collapses and land subsidence (Betournay, 2011). It involves large-scale movements of waste rock and vegetation, similar to open pit mining. Additionally, like most traditional forms of mining, underground mining can release toxic compounds into the air and water. As water takes on harmful concentrations of minerals and heavy metals, it becomes a contaminant. This contaminated water can pollute the region surrounding the mine and beyond (Miranda, Blanco-Uribe Q., Hernandez, Ochoa G., & Yerena, 1998). Mercury is commonly used in as an amalgamating agent to facilitate the recovery of some precious ores (Miranda et al., 1998). Mercury tailings then become a major source of concern, and improper disposal can lead to contamination of the atmosphere and neighboring bodies of water. Most underground mining operations increase sedimentation in nearby rivers through their use of hydraulic pumps and suction dredges; blasting with hydraulic pumps removes ecologically valuable topsoil containing seed banks, making it difficult for vegetation to recover (Miranda et al., 1998). Deforestation due to mining leads to the disintegration of biomes and contributes to the effects of erosion.
ISL mining has environmental and safety advantages over conventional mining in that the ore body is dissolved and then pumped out, leaving minimal surface disturbance and no tailings or waste rock (World Nuclear Association, 2012). There is no ore dust or direct ore exposure to the environment and a lower consumption of water is needed in the mining process (International Atomic Energy Agency [IAEA], 2005). However, the strong acids used to dissolve the ore body commonly dissolve metals in the host rock as well. The fluids remaining after the leaching process commonly contain elevated concentrations of metals and radioactive isotopes, posing a significant risk to nearby ground and surface water sources (IAEA, 2005). Additionally, the low pH of ISL mining wastewater can result in acidification of the surrounding environment.
Environmental issues with heap leaching are centered on the failure to keep process solutions within the heap leaching circuit. Release of toxic heap leaching fluids into the environment can affect the health of both the surrounding ecosystem and human population (Reichardt, 2008). Water balance is crucial in heap leaching projects because of the possibility of the overflow of solutions containing toxic concentrations of heavy metals after a heavy rainfall or rapid snowmelt (Norman & Raforth, 1994). In some cases cyanide is used to extract metals from oxidized ores and the resulting leach ponds have caused significant wildlife mortality, including the deaths of about 7,613 animals between 1980 and 1989 at cyanide-extraction ponds in California, Nevada, and Arizona (Eisler, 1991).
Brine mining involves extracting and evaporating the brine solutions to remove harmful elements and compounds (Gruber et al., 2011), potentially releasing them into the environment. The drilling and transport of brine solutions can disrupt existing ecosystems and well casings, pipelines, and storage tanks are subject to corrosion due to the high salinity content of the solutions that they are exposed to, which can lead to leaks and contamination of adjacent bodies of water (New York State Division of Mineral Resources, 1988) Currently, there is no economically plausible plan to clean up contamination of an aquifer by sodium chloride and harmful concentrations of chloride inhibit plant growth and can cause fish kills (Division of Mineral Resources, 1988).
All REE-bearing minerals contain low levels of the radioactive isotopes that can become concentrated in mine tailings. Radionuclides are released as dust during mining or from exposed waste rock stockpiles where they are least containable (and mostly airborne). Radiation can also leak into the ground, and nearby water sources after they have been separated into tailings, if the tailings are not stored safely. Once radionuclides are in an ecosystem, they accumulate in plants, where the higher concentrations are ingested and ascend the levels of the food chain (Paul & Campbell, 2011).Radioactive contamination has become such a problem that monazite mining has been banned by China and the United States has imposed strict regulations effectively accomplishing the same (Schuler, Buchert , Liu , Stefanie & Merz, 2011).
When companies break up materials during mining, the dust can release a variety of heavy metals commonly associated with health problems. As dust, these minerals (such as the asbestos-like mineral riebeckite) can be absorbed into lung tissue, causing problems like pneumoconiosis and silicosis, commonly known as "Black Lung" (Paul & Campbell, 2011). Another example of harmful dust generated is flue dust, a byproduct of mining fluorine. According to the Chinese Society of Rare Earths, every ton of REE produced generates 8.5 kilograms of fluorine and 13 kilograms of flue dust, waste materials which contain the heavy metals discussed above (Schuler et al, 2011).
The following chart details how these contaminants enter the environment during mining and refining. Current mining and refining techniques make contaminant release common. Note: the two columns that involve waste rock and the column labeled, "No site rehabilitation after cease of mining operation" all involve mining specifically.
Mining, like most heavy industries, is dependent on fossil fuels, which generate the energy needed to operate a mine. To combat these carbon emissions, some countries have enacted regulations requiring emission credits, but many countries do not have codes dealing with carbon output ("Molycorp, inc.," 2010). Some form of environmental standards are needed for larger countries like China and Russia, and other developing countries that mine large volumes of strategic minerals.
c80f0f1006