Mining
Mining Pollution
The mining industry accounts for approximatly 5% of the global GDP, with evidence of mining being present for thousands of years. As mining practices have improved in efficiency since the industrial revolution more materials have been mined with mines increasing in size as well as depth as the techniques and equiptment used allows. However, mining also produces a large amount of waste that contains concentrations of metals and other substances that can be extremely damaging to the natural environment.
Many techniques have been employed to prevent the spread of these contaminants to the wider environment including the use of tailings dams, where the mine waste is covered by a layer of water seperate from other surface water preventing the spread of contamination. There are however examples across the globe of poor management of these waste materials leading to the contamination of surface water and major environmental damages. Another issue related to the mining industry originates from historic mining sites, as seen across the U.K. with historic mining sites being prevelent, these sites are often poorly maintained allowing for contamination to enter surface water for hundreds of years.
Dependant on the products that are mined, drainage from the site can become contaminated leading to changes in the pH of the water leading to the processes of Acid Mine Drainage and Neutral Mine Drainage. Acid mine drainage occurs when water comes into contact with sulfur rich minerals forming sulfuric acid and metals dependant on the compounds that are found, As the concentration of the sulfuric acid increases as more of the minerals come into contact with water the pH of the water drops below 7 leading to the contamination of both surface and groundwater resources. Neutral mine drainage also occurs in similar mining setting with the main causes occuring from pyrite oxidation and the dissolution of carbonate minerals. following these processes there is an increase in the concentration of heavy metals within the environment while the acidic nature of pyrite oxidation is neutralised leading to mine drainage that is equal to or more basic than a pH of 7.
Pollutants
There are a wide range of pollutants that originate from mining these include:
Sulphur rich minerals - Minerals such as pyrite and galena that are rich in both heavy metals and sulphur lead to the processes of Acid mine drainage and Neutral mine drainage that greatly impact the environmental health of a river system.
Heavy metals - Including metals such as lead, zinc and cadmium these metals that are generated throughout the mining process can cause major environmental impacts once they enter the wider environment.
Environmental Impact
Acid Mine Drainage (AMD)
Acid mine drainage leads to a lower natural pH of surface and groundwater resources as well as an increase in the concentration of heavy metals that can be environmentally damaging. The process of acid mine drainage has been linked to the loss of biodiversity in the affected catchments with the reductions in the number of total fauna species ranging from invertebrates to fish species severly impacting the function of the environment. The contaminated drainage also severly impacts the flora species of the affected region with the plants taking in the contaminated, acidic water leading to the decay of organic matter in the catchment. As a byproduct of acid mine drainage a large portion of heavy metals including lead, arsenic, aluminium and manganese are produced, many of these metals have major impacts on both environmental and human health with the potential to bioaccumulate within organic tissue leading to further health concerns.
Neutral Mine Drainage (NMD)
Although there is less awareness around neutral mine drainage this process has major environmental impacts with the pH of surface and groundwater becoming more basic just greater than a pH of 7. Throughout the process of neutral mine drainage a large concentration of heavy metals including iron and zinc are produced these metals can have a negative impact on the natural environment through their bioaccumulation in organic material. The higher concentration of these minerals in the environment also leads to a deterioration in the overall quality of water greatly impacting the chemical status of the water
Heavy metals
heavy metals such as lead, iron, cadmium, zinc, arsenic and manganese can be found in many forms within the environment as a result of mining activity as such there are a wide array of environmental impacts associated with their concentrations in the wider environment. The environmentally persistent metals can be located in dust form transported through wind processes if the waste materials are not maintained well such as without the use of tailing dams or other treatment techniques. These metals remain within the environment leading to the detiroration of the biota as the metal bioaccumulates within organic tissue, this not only greatly impacts the overall environmental health of an ecosystem but can also lead to major concerns for human health.
Mitigation
Mitigating the environmental threat of mining can be quite a challenging task with modern mining operations choosing to impement methods such as the use of a tailings dam that prevent the spread of contaminated material to wider environment, however, there is some potential for the failure of these structures leading to widespread environmental damage. As such, it is imperative to employ effective maintainace practices across these sites to reduce the risk of catestrophic failure such as the collapse of the dam leading to environmental contamination.
However, the major cause for concern originates from many of the old, abandoned mining systems the waste material and mine tailing were dumped in piles along the mining site as well as exposed unused mining operation allowing for the flow of water along exposed minerals leading to a large level of exposure to these minerals that in turn leads to processes such as AMD and NMD. Therefore, the many diffuse and point sources across the sites must be identified on an individual basis with bespoke methods of mitigation being designed implemented.