ACID MINE DRAINAGE
Introduction
Currently, the world is living in an era of consequences. Nowadays, it is already common to hear news about different calamities and natural disasters from different parts of the globe, primarily because of the increasing impact of global warming and climate change. The level of pollutions in the world is mostly in highest level due to the different factories and facilities which are implementing and using approaches and methods that are harmful to the environment, at the same time, there are different products and services that are still being used and consumed by individual consumers which affect the environment.
The mining industry is considered as one of the industries that are greatly affected by global warming and climate change. For the past months, there are numerous news about injuries and deaths of miners, due to accident as well as natural calamities or disasters. One of the most vital environmental challenges which the industry is facing as of today is the increased in the level of metals in the environment because of different activities related to milling and refining. Mine waters, tailings, waste rock piles adds to the formation and creation of deleterious wastes, which may be released into the surrounding environment, which include surface and ground waters, and even the soils. Release of some dissolved metals is worsen and aggravated by the formation of acid drainage or also known as the acid drainage (AMD). It is the outcome of the oxidation of sulphide bearing minerals, which include pyrite and pyrrhotite, which are normally found in tailings and waste rock piles (Clyde and Queen’s University 2008).
This essay will focus on investigating the prevalence of AMD in national and international level, its impact on the environment, the reasons behind its occurrence and recommendations of possible solutions for the problem.
What is Acid Mine Drainage (AMD)?
ACD can also be called as acid rock drainage and acid drainage. It is defined as the water with a low pH and heavy metal content (Moran 2007). This is formed from chemical reaction between water and rocks which contain sulphur-bearing minerals. The runoff formed is commonly acidic and normally comes from places where ore or coal mining activities have exposed rocks, which contain pyrite, a sulphur bearing mineral (US Environmental Protection Agency n.d.). When underground sources of pyrite-rich coal are mined, the coal becomes exposed to water and the atmosphere. As a result, the pyrite reacts with the oxygen and water, which form the acid (Girard 2010, p. 203).
The term AMD was originated as a term which pertains on the waters coming from abandoned or operating mines (Moran 2007). AMD is considered as one of the most vital threats and risks to the environment of the world. This is because, it will not just affect the country which is undertaking mining activities, but also affect their neighbouring countries, because their environment can be greatly affect by the migrating pollution. The report of the U.S. Environmental Protection Agency showed that AMD is one of the major reason of pollution of ground and surface water and it renders streams and whole river systems to be used by human and other life form. These are the reasons why, countries are using huge amount of money to plan and implement strategies and methods to solve this problem (Fraser 2001).
National and International Incidence of Acid Mine Drainage
AMD is considered as one of the major environmental problems in the world. It is important to take note that it is commonly due to the abandoned mines owned by both public and private sector. In the US alone, there are more or less 560,000 abandoned mines, which are considered as dangerous particularly for those individuals and groups who will attempt to explore the place without any knowledge and training about mining (People, Land and Water 2007). The U.S. Forest Service (USFS) approximate those between 20,000 to 50,000 mines are forming acid on lands that are being managed by the agency, which affect about 8,000 to 16,000 km of body of water (Forest Service 1993). Most of these mines are small abandoned facilities that are placed in remote areas of the western part of the country, which was established even before the modern environmental controls, while some of the huge mines established in the latter half of the 20th century have declared bankruptcy, which leave the tax payers and the government to treat the acid waters within the vicinity, which include the Zortman Landusky Mine (Montana), the Summitville Mine (Colorado) and Brohm Mine (South Dakota) (Jennings, Neuman and Blicker 2008). The same condition can be found in Canada, wherein the government is spending $2 to $5 billion dollars in order to handle its environmental impacts. In 1986 alone, the government of Canada estimated that acid-generating tailings cover more or less 12,000 hectares and 350 million tons of mine waste rock (MEND 2001 cited in Jennings and Neumann 2008).
In addition, the draft report of Mining for the Future by the International Institute for Environment and Development, there is 134 abandoned asbestos mines and 400 asbestos mine dumps which supply a constant flow of asbestos dust in the region. Furthermore, the report of the United Nations Environment Programme (2000) about Mining and Sustainable Development IL’ Challenges and Perspectives, Sweden is recorded to have more than 1,000 abandoned mines, while the Japan’s national survey showed that the country has a total of 5,500 abandoned mines, and 300 of which are Chilean trailing storage facilities that have been abandoned without cleaning the sites (cited in Fields 2003).
In the UK, AMD is also one of the major environment problems. According to Jackson (2000) mining and mineral extraction resulted to ground movements and emissions, which polluted flows of water. Because of the sink shafts and pump mine water from 14th century in order to extract coal, sinks are already in depth of more or less 1,000m (Wilcock 1975) and it is estimated that the extraction of 4,800 million tonnes left more or less 1,000 million m2 of voids (Norton 1996). With this, the UK has a vital legacy of mining, and most of it are now inactive. The abandonment of these mines resulted to the production of acidic mine wasters, which pollute the water system and flow of the UK. According to Jarvis and Younger (2000) it was estimated that there are more or less 700km of streams and rivers that are affected by the discharges of acid mine drainage. These mine wasters differ in nature between mines, but the common denominators is the production of acidic and metal contaminants (Pentreath 1994) and the production of orangey-brown deposit that covers the sediment (Bradley 2008).
Causes of Acid Mine Drainage
It is vital to take note that mining and mineral production operations and procedures, when not properly management can cause contamination of groundwater and surface water, due to AMD, therefore, can affect the overall living of those people and other living things nearby the ear. Those extractive industries, including mineral deposits, oil and gas production, quarrying to build road-making materials, and poorly abandoned or operated mine sites are common sources of minerals or chemicals that when mixed with other chemicals can result to contamination of water.
Acid drainage happens when water, oxygen, certain bacteria and sulphide metals, which include pyrite, marcasite and chalcopyrite come in contact with each other which will produce a telltale “red water” or known as the ferric hydroxide or ochre (http://www.coal.gov.uk/environmental/aboutminewater.cfm) (figure 1), which is considered as one of the first symptoms that early miners used in order to locate mineral deposits. It is vital to take note that natural changes commonly do not create sufficient acidity in order to vitally affect the environment, primarily there is no enough sulphides at the surface, which can be exposed to the air and water. This can be observed on many creeks in the world, particularly in Colorado, which are naturally too acidic to support living things, however, this is natural, thus it has nothing to do with the chemicals and minerals related to mining (Fields 2003).
Other vital oxidation products identified are melanterite (white crystals of FeSO4), copiapite (yellow crystals of ferric sulphate Fe2 (SO4)3, halotrichite (white crystals of iron and/ or magnesium aluminum sulpahte), and alunogenite (white crystals of aluminum sulphate). These minerals are present in the hydrated form, the amount of water varying with the mode of formation (Sharma 2007).
Figure SEQ Figure \* ARABIC 1 How Minewater is Oxidized through the Mining Process
Adapted from: (The Coal Authority n.d.)
The problem is that the mining activities bring large quantities of sulphides towards the surface of the earth, at the same time, break them into smaller pieces, which consequently expose it to more surface area, enough to react with air and water, which create AMD. It is important to add the sulphides are likely to appear in the same geologic conditions, same as those other types of mined metals and coals, this is because when iron sulphide are brought to the surface, then it is exposed towards oxygen and water, which result to oxidation of sulphides which create lots of acidity. This result to sulphuric acids which play a vital role in flourishing microbes, then these microbes will further help and encourage oxidization of the minerals (Fields 2003). The probable involvement of bacteria in forming AMD was reported first by 1919 by Powell and Parr, who found out that coal inoculated with unsterilized sulphate solution, produced drainage with higher concentration and mixture of sulphate than sterile controls. In addition, the study of Colmer et al. showed that bacterial play a vital role in iron oxidation in acid mine water based on observation of the iron oxidation which happen in water samples freed from bacteria by filtration via Scitz filter/Millipore filter or treatment with the different bactericidal agents (The Coal Authority n.d.).
The consequence is chain reaction which will carry on and persist until the sulphides are fully consumed. Depending and based on the mineral deposit, this flow and process can take hundreds and even thousands of years. The speed and duration of this acid-producing reaction is considered as one of the differences between mines. For instance, according to Mr. Paul Ziemkiewicz, the director of the West Virginia Water Research Institute at the West Virginia University, the utmost acid production of coal mine is more or less 10 years, after which, the pyrite will start to expend, while, on the other hand, in coal deposits, because the surrounding rock common have 2% to 5% sulphides, which is extremely high, therefore, it will take longer time (Fields 2003).
Figure SEQ Figure \* ARABIC 2 Some Cases of AMD
Source: (Sharma 2009)
The Environment Impact of Acid Mine Drainage
There is no doubt that AMD offers different disadvantages and risks towards the greater society. Particularly it create damages towards the environment, which affect how those people and other living things manage their daily living.
Once acid drainage is formed, metals will be released into the surrounding environment, which will be available towards all biological organizations. In the body of water, for instance, when fishes are directly exposed to the metals and H4 ions via their gills, they can have impaired respiration due to chronic and acute level of toxicity. Furthermore, fishes are also exposed in indirect manners towards metals via ingestion of some contaminated sediments and foods. In addition, a common enduring product of sulphide oxidation is the shape and creation of iron hydroxide (Fe(OH)3), which is a red or orange coloured substances which can be found in thousand of miles of streams, which is affected by AMD. It is important to take note that those iron hydroxides and oxyhydroxides may actually coat the surface of stream sediments as well as streambeds, which destroy and devastate habitat and living things, which diminish the availability of clean gravels, which is commonly used to spawn and reduce the fish food items, including benthic macro-invertebrates. In general, AMD attributed by metalliferous conditions in water system, which is the cause of physical, chemical as well as biological deprivation of aquatic animals (Jennings and Neuman 2008).
Furthermore, it is important to take note that drainage water from acid mine drainage will be clear at first, but will turn into a vivid orange colour as it becomes neutralised due to the precipitation of iron oxides and hydroxides. This precipitate is commonly known as the ochre, which is a very fine, which smothers the river bed with a very find slit, which further influence the life of those small animals at the bottom of the body of water or those benthic organisms, when they can no longer feed, they will be depleted. These animals are considered as the bottom of the aquatic food chain, thus, this will influence the higher level of the food chain, therefore, it affect those larger fish, consequently in the long-term, the body of water will be void of living things (Jennings and Neuman 2008).
AMD can affect a long range of the stream or bed of water. According to Hill (1974), those receiving body of waters may still have pH as low as 2.0 to 4.5 levels, which can still be toxic to most of the life form in the body of water. Studies which connect a given impacts of low pH on growth and reproduction (Fromm 1980) is connected to calcium metabolism and protein synthesis. There are different studies and reports which show that even low pH conditions and levels still affect fishes, for it changes their gill membranes or even change their gill mucus, which cause their death because of hypoxia (cited in Jennings and Neuman 2008).
It is also vital to take note that the extraction decreases the depth of groundwater and natural filtration, which consequently increases the contamination of the groundwater (figure 3).
Figure SEQ Figure \* ARABIC 3 Impact of Extraction in the Contamination of Groundwater
Source: (Sharma 2007)
Releases of acid mine waters affected many landscapes and waterways, which are documented by many organizations. One of the primary results of this is fish kills due to the toxic found in the acid mine waters which contaminate the body of water. For instance, the case of Spain in 1998, when a mine flood accident spilled 6 million m3 of acid water in the Guadiamar River rich with metal and sulphide. Another is the case of large fish kill in Clark Fork River in Montana which killed more than 5000 salmonids because metalliferous tailing and efflorescent metal salts were flushed into the river due to thunderstorm. The Sacramento River of California also experienced different fish kills because of unexpected and swift release of acid water from upstream mine areas, over 20 cases of fish kills were reported since 1963, finally, in 1967, more than 47,000 fish died (Jennings and Neuman 2008).
In the UK, the major case of AMD was the Wheal Jane AMD pollution incident. The mind produced metals and the drainage contained high levels of zinc and cadmium and ubiquitous iron, which turn the water into bright orange and plume of orange pollution was very visible to the onlookers. The incident affected the Fal Estuary (Sharma n.d.).
Solutions to Mitigate the Occurrence of Acid Mine Drainage
There are 2 most popular methods or approaches in treating AMD.
First is to control AMD by reducing and eliminating the source of AMD. This can be done by preventing oxidation by replacing the air in the mine with groundwater. This air-with-water replacement is done by sealing any mine openings with an impermeable grouting material. Popular material used is gas desulphurisation (FGD) materials, which is composed of calcium sulphate (Sharma 2009).
The second focus on treating the AMD itself to remove the negative impact to the entire body of water. This use different buffering agents, which include different carbonate compounds. When these agents are dumped into the body of water, they help to raise the pH, which balance the impacts of acid in the water. One study showed that anoxic limestone drains increase the alkalinity by more 128 to 248 mg L-1. Thus, the bicarbonate ion in limestone (CaCO3) becomes a buffer by lessening the proton acidity because of hydroxylation of metals. Thus, limestone, is considered as the best solution for it is available and inexpensive and reaction which happens in the water is simple. The bases that used commonly dissolve completely in the water help to create hydroxide ions (OH-), when combine with carbonate ions (Co32-) and hydrogen ions (H+) help to neutralize them in the water, which produce water and carbonic acid (H2CO3), which do not offer negative impact on the environment, therefore, this procedure is also friendly to the environment (Lawhorn n.d.).
In some places, wherein ground water has already been contaminated by waste water and AMD, microbial sulphate can be reduced by installing a reactive barriers, which is done by installing a sufficient reactive material into the aquifer in order for the contaminated water to flow via the material (figure 4). The reactive material help to induce the chemical reactions, which therefore, help in order to remove the contaminants from water, or in some cases, cause the alteration of, which lessen the level of toxicity of the water.
Figure SEQ Figure \* ARABIC 4 Underground Mine Sealing
Source: (Sharma 2007)
Conclusion
AMD is considered as one of the major results of past actions of many individuals and organizations, which focus on gaining power and money, without considering the impacts of their action towards the environment, and those living things, particularly the people who are living within the vicinity. As a result, taxpayers and the government are focusing on cleaning their wastes, which takes huge amount of money, effort and time in order to remove, or even just to lessen its horrendous impact to the environment.
There is no doubt that AMD affect the overall condition of the environment, for it affect the quality of water, which influence the life of aquatic resources, then influence those other livings things, which are connected to the food chain, particularly the people. In addition, it is also important to take note of the terrible look of orangey or reddish fluids flowing in the water system, which obviously affect important industry in a given place. Overall AMD affect the environment, social and economic condition of a place. With this, it is vital for governments to focus on establishing policies and standards about mining, at the same time, focus on intensive strategies and actions to clean bodies of water contaminated by AMD.
References
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