Acid Mine Drainage – Socio and Environmental Impacts

Komal M Chougule

ABSTRACT

The most common problem associated with mining and its industrial sector is Acid Mine Drainage (AMD). The main reason for AMD is the formation or presence of pyrite and sulfur-containing minerals. These minerals exposed to air result in Acid Mine Drainage. AMD consists of many harmful metals which are not biodegradable and get stuck with living organisms causing serious health problems which lead to severe Socio-Environmental impacts. Even though, treating mine water has significant challenges there are certain treatment techniques employed. Active and passive treatment techniques are the most conventional techniques. There are various unconventional methods of treatment using waste materials like fly ash, which are economically more affordable and efficient. This article reviews the social and environmental impacts of Acid Mine Drainage and discusses the treatment techniques to be employed for managing and treating Acid Mine Drainage (AMD).

Keywords: Acid mine drainage, mine water, Environmental, Pyrite, Oxidation, Mining, treatment, impacts, waste material, sources

INTRODUCTION

Water is one of the most significant and fundamental assets for supporting life on earth. India receives 4000km³ yearly precipitation. Out of this, only 1123km³ water is accessible as surface and groundwater assets individually 690km³ and 433km³. The water request was 634km³ in the year 2000 and due to the growing population, it might increase to 1093km³ in the year 2025 (central water commission (2011)). All the different types of mines such as coal, metal utilize some amount of water for their mining operations, and then it discharges harmful metals and chemicals such as Iron, copper, cobalt, etc which affects the soil and vegetation cover, also water quality and quantity. From our historic times, mining was executed with the fundamental focus towards the mining benefits and with little thought towards the earth, nearby network, or improvement (ISID (2012)) Mining action has existed since the start of human culture and minerals have contributed to the advancement of human development. The mining business impacts straightforwardly on the large-scale economy by improving foundation, expanding business, creating provincial networks, and empowering new side projects and downstream organizations (FCCI (2013)).

Acid Mine Drainage also called acid rock drainage, acid, metalliferous drainage or mine water occurs naturally within some environments as part of the rock weathering process but is exacerbated by large-scale earth disturbances characteristic of mining and other large construction activities, usually within rocks containing an abundance of sulfide minerals. It is seen all over the world with different ranges of pH values, where acid-forming sulfide minerals are exposed at the surface of the earth Jamal et al. (2015). It is an unavoidable result of the mining and mineral industry which is for the most part described by high convergence of broke up overwhelming metals, sulfate, and low pH as low as 2 and keeps on being a significant water contamination issue in the mining industry around the globe. It additionally alludes to the effluent created from active just as deserted mines. The introduction of rocks comprising of ferrous or ferric sulfide minerals to water and oxygen results in AMD. It is caused by pyrites. The reason behind AMD generation is the presence of sulfide minerals, in form of iron sulfide-aggregated rocks, and exposure of these minerals to water and oxygen (Akcil and Koldas (2006)). However, this is not only the reason behind AMD generation, highway, tunnels and other deep excavations are also part of the reason for AMD.

Primary sources	Secondary sources
My rock dumps	Treatment sludge pounds
Tailings Impoundment	Rock Cuts
Underground and open-pit mine workings	Concentrated load out
Pumped discharged underground water	Stockpiles
Diffuse seeps from overburden in rehabilitated areas	Concentrate spills along roads
Construction rock used in roads, dams, etc	Emergency ponds

After observing the sources of AMD, one would be interested to know about what is the process of AMD generation. The AMD generation process is given in the figure below. The generation mainly takes place due to the oxidation of Pyrite. Oxidation of pyrite (FeS2) through Fig.1 is a key reaction for AMD generation.

Pyrite oxidation leads to the formation of dissolved iron, Sulphate, and Hydrogen. When these mine waters with very high acidic pH are used for certain irrigation purposes, these acidic waters are uptake by plants and different crops which results in dangerous health risks to people and animals who consume these contaminated agricultural products (Kuyucak (2001)).

SOCIO-ENVIRONMENTAL IMPACTS

As known to everyone’s knowledge, mines are very dangerous and are associated with risks. The problem is mostly associated with the areas, where the mines are close nearby to them. But, also it might affect the large distances when the discharged mine water does not undergo any treatment before. Amongst, the problems and impacts caused by these mines and mine water, social and environmental impacts are those which are of major concern. At present, the Indian Government and mines have implemented the socio-environmental legacy for all mining activities which is a cause for harming the environment (EMBC (2006), Jamal et al. (2015)). In general, social and environmental impacts are divided into several fields, such as impacts on biodiversity, poverty alleviation, and others (ELAW (2001)).

The following are some of the social impacts of AMD (ELAW (2001)):

• Displacement of houses
• People moving out from place to place (resettlement)
• Employment problems
• Health and safety
• Ecosystem services
• Socio-political conflicts

Large-scale mining projects and activities are completely interlinked, complex, and difficult to process. Mining activities in India can create many opportunities for jobs, roads and can increase the need for these mined materials in distinct areas. But, when these benefits are not equally shared amongst people it can lead to social impacts or conflicts. Because of extensive mining activities that take place in India, people have to leave their houses and have to settle at some other place. Displaced communities are often settled in areas without adequate resources or are left near mines, where they may face pollution and contamination. Displaced community people having cultural and spiritual ties to their lands will find it very difficult when they migrate (Downing (2002)) “Breaking new ground: Mining, Minerals, and sustainable development”. When this happens, it might also create conflicts between people who are already living there and the newcomers (Singh et al. (2016)).

Many hazardous and polluting substances are emitted from acid mine drainage, causing many health risks and negative impacts to humans as well as animals. The World health organization (WHO) defines health as a “state of complete physical, mental and social well-being, and not merely the absence of disease or infirmity” (WHO (1946)).

These hazardous substances cause serious health issues, an illness that is sometimes not curable, and other dangerous diseases such as tuberculosis, asthma, chronic bronchitis, and gastrointestinal diseases. The social impacts(air, land, water, geology, community, and biodiversity) are often combined or a result of environmental impacts as well. Major environmental impacts are:

• Land
• Water accessibility, water quality, and quantity
• Air quality
• Land disturbance
• Waste generation
• Loss in Biodiversity

One of the major environmental impacts would be on water sources that are near to mine dumps. From different types of mines in India, a large amount of harmful and hazardous waste will be generated which should be properly stored, treated, and then disposed of. But, because of a lack of rules and regulations large amount of mine waste is directly discharged into water bodies, rivers, lakes which results in damaging the water quality and causes a lot of contamination (DashAshis (2012)).

As we all are aware harmful metals and gases released from AMD such as sulfur, As, Hg, cyanide, and lead will be deposited into the underground surface and will be contaminating the groundwater and also soil quality. These harmful metals not only contaminate the groundwater but also causes serious water pollution and destroy terrestrial habitats in areas surrounded by mines (Jamal et al. (2015)). Water sources, their environmental impacts on quality and quantity are the most discussed aspects in the mining field these days. “The problems of water quality and quantity have led to many conflicts between miners and communities” (Bebbington and Williams (2008)).

Certain mines release a lot of dust during their operations polluting the air quality. These mines release methane, which is a greenhouse gas that results in potential problems for humans and animals. Also, other heavy metals, sulfur gases, and other pollutants are the cause of environmental impact polluting the

air (Zambrano (2021)). An example of environmental impact or damage has taken place in Karnataka state in southern India. The company named Kundremukh iron ore company limited (KIOCL) in Western Ghats mountain ranges was responsible for the huge destruction of hills, which further caused pollution in groundwater and also severely affected Kundremukh National Park. The other important environmental impact is pollution which is caused by unused and abandoned mines. In the region named Jharia and Raniganj coalfields in Bihar, India there are more than 500 abandoned mines constituting an area of about 1800 hectares (Singh R. S. and D. (2012)).

When severe mining activities will be going on, it causes very high overburden pressure on the land surface. This pressure leads to high environmental impacts. The material over the main mineral which needs to be extracted will be removed. This causes land disturbance (Zambrano (2021)). Not only land disturbance, water quality, but air quality also come under environmental impacts of AMD also impacts wildlife fauna and especially fisheries too. Mining heavily disturbs the wildlife because of destroying forests for mining, land disturbance, ecosystem damage, etc. It also leads to the death or displacement of certain species such as reptiles, invertebrates, etc, which is a detrimental impact. As the land or place where wildlife survives is being banged up for mining, it leads to the migration of native species of wildlife. Due to extremely low pH, the water’s being highly acidic; AMD affects the aquatic plants and animals intensively. Amongst them, fishes are caused a huge disturbance and result in deaths, problems in their growth rates, and reproduction (Kimmel (1983)). Due to heavy metals present in AMD, the oxygen present in the aquatic water is used up which leads to anoxia and death of fishes, due to adverse choking effects on fish gills (Morris et al. (1989)). Also, because of the loss of sodium ions in the blood, fish deaths may occur.

Environmental impacts are frequently intense, unplanned releases of wastes from mines, transitory or chronic (long term, extracted from waste disposal). Environmental impacts are responsible for affecting surface ecology (Atkins and Singh (1982)). Therefore, there are many foreseen and unforeseen environmental impacts, and these problems should be addressed as early as possible for a balanced and good development of the mining sector

CONVECTIONAL TREATMENT TECHNIQUES

As we are aware of the fact that water is an important natural resource and essential component for all living organisms. It plays an important role in domestic, industrial, agricultural and environmental purposes. Due to these utilities, mine water requires treatment (Jamal et al. (2015)). As mine waters are highly acidic with pH 2-4 and contain many hazardous, toxic metals which cause harm to humans, the environment, and problems of reproduction of aquatic plants and animals (Jamal et al. (2015)). Due to the precipitation of ferric hydroxide, the turbidity of mine water increases, causing high toxicity of mine water, which in turn affects the life cycle of fisheries. Because of these particular reasons’ treatment of mine water is important.

Active and passive treatments are the conventional methods of treating AMD. They are further subdivided into different procedures. Active treatment consists of different procedures such as Aeration, Neutralization, Reverse osmosis, Ion exchange, Electrodialysis, and Zeolites. Passive treatments consist of Aerobic wetlands, anaerobic wetlands, Open limestone channels, and Anoxic limestone drains.

Aeration

Aeration, the word itself indicates it’s a treatment procedure associated with air or oxygen. In this method, initially purified air is sent into mine water’s as this air consists of oxygen molecules, which get consolidated with metals and form oxides, which later get accelerated. Amongst the different types of aerators available we select the mechanical surface aerators as it is used to treat exceptionally acidic and diminished water. With the help of its blades oxygen is reached to water in the aeration basin. The aerator creates some disturbance, scatter’s air bubbles, and holds iron floc in suspension. High-velocity spray nozzles are utilized to improve contact between air and water. However, the effectiveness of aerators depends on pH, as inorganic oxidation is delayed below pH 5. Therefore, this procedure is combined with adding a base to neutralize pH (Skousen et al. (1998)).

Neutralization

The name itself indicates bringing the water or a compound to a neutral state by the addition of suitable chemicals. Here, we consider limestone. Limestone is the most commonly used chemical in neutralization

and it is also very economic (Heathfield et al. (1971)). As limestone is a base, it consumes hydrogen ions increases the pH, and also adds bicarbonate ions to bring the water to a neutral state (Younger et al. (2002)). Further, after these additions it mainly precipitates, forming hydroxides and oxyhydroxides.

• CaCO3 + 2H+ → Ca+2 + H2O +CO2
• CaCO3 +H2CO3 → Ca+2 +2 HCO3

TREATMENT WITH WASTE MATERIALS

As we are aware of the fact that water is an important natural resource and essential component for all living organisms. It plays an important role in domestic, industrial, agricultural and environmental purposes. Due to these utilities, mine water requires treatment (Jamal et al. (2015)). As mine waters are highly acidic with pH 2-4 and contain many hazardous, toxic metals which cause harm to humans, the environment, and problems of reproduction of aquatic plants and animals (Jamal et al. (2015)). Due to the precipitation of ferric hydroxide, the turbidity of mine water increases, causing high toxicity of mine water, which in turn affects the life cycle of fisheries. Because of these particular reasons’ treatment of mine water is important.

Active and passive treatments are the conventional methods of treating AMD. They are further subdivided into different procedures. Active treatment consists of different procedures such as Aeration, Neutralization, Reverse osmosis, Ion exchange, Electrodialysis, and Zeolites. Passive treatments consist of Aerobic wetlands, anaerobic wetlands, Open limestone channels, and Anoxic limestone drains.

Aeration

Aeration, the word itself indicates it’s a treatment procedure associated with air or oxygen. In this method, initially purified air is sent into mine water’s as this air consists of oxygen molecules, which get consolidated with metals and form oxides, which later get accelerated. Amongst the different types of aerators available we select the mechanical surface aerators as it is used to treat exceptionally acidic and diminished water. With the help of its blades oxygen is reached to water in the aeration basin. The aerator creates some disturbance, scatter’s air bubbles, and holds iron floc in suspension. High-velocity spray nozzles are utilized to improve contact between air and water. However, the effectiveness of aerators depends on pH, as inorganic oxidation is delayed below pH 5. Therefore, this procedure is combined with adding a base to neutralize pH (Skousen et al. (1998)).

Neutralization

The name itself indicates bringing the water or a compound to a neutral state by the addition of suitable chemicals. Here, we consider limestone. Limestone is the most commonly used chemical in neutralization

and it is also very economic (Heathfield et al. (1971)). As limestone is a base, it consumes hydrogen ions increases the pH, and also adds bicarbonate ions to bring the water to a neutral state (Younger et al. (2002)). Further, after these additions it mainly precipitates, forming hydroxides and oxyhydroxides.

• CaCO3 + 2H+ → Ca+2 + H2O +CO2
• CaCO3 +H2CO3 → Ca+2 +2 HCO3

TREATMENT WITH WASTE MATERIALS

The above-mentioned active and passive treatment techniques are said to be conventional methods that are very costly and require, enhanced maintenance cost even though they give good results. Many researchers have done numerous experiments to confirm the usage of waste materials for the treatment of AMD which are cost-effective and efficient neutralization materials (Gitari et al. (2008)). Some of them are fly ash, metallurgical slag, zero-valent iron (ZVI), cement kiln dust (CKD), organic waste such as peat and rice husk. Further investigations said that amongst the specified waste materials, fly ash was very much more efficient. So we are now going to study about treatment of AMD with fly ash.

Fly ash

Fly ash is said to be a combined product formed from burning coal in electric power plants. During combustion, elements of coal mix in suspension and fly out of the chamber with other gases. Fig.2 depicts the procedure for decontaminating AMD using fly ash. The main principle followed here is adsorption, precipitation, and followed by co-precipitation of the metals (Jianping and Haitao (2014)). Here, the adsorbent is fly ash. This tells that certain metals such as Cu, Pb, and Ni are adsorbed on the surface of fly ash (adsorbent). At this point, the water molecule breaks down into respective ions and precipitation of metals takes place. The co-precipitation shows the formation of important compound Fe (OH)3. During co-precipitation or secondary precipitation after the formation of Fe (OH)3 metals such as Cu+2, Zn+2, and anion SO4-2 are also adsorbed by ferric hydroxide through which metals uptake is done by fly ash (Jianping and Haitao (2014)). Apart from the above-mentioned procedure of decontaminating AMD by fly ash it also has several advantages and uses. It can be used as an alternative to limestone as a pre-treatment agent (Potgieter et al. (2006)). It is not a regular or conventional method which makes it a little bit cheaper and it also does not pollute the environment in comparison to others (Cetin and Pehlivan (2007)). It can remove different heavy metals from the mine water (Polat et al. (2002)).

CONCLUSION

Acid mine drainage is the main problem associated with mining and their industries. However, mining activities are said to be an integral part of societal development. AMD causes severe social and environmental impacts. These impacts have numerous effects imposed on society. Human and animal health is the primary concerns of AMD. It also causes damage to the soil cover, vegetation, available food in mining areas and also pollutes the air. The migration of humans and species also occurs due to unsuitable environmental conditions. These impacts can be considerably reduced by certain treatment techniques. Active and passive treatments are considered always first for the treatment of AMD. Even though they are effective they incur very high installation and adsorbent costs. Besides this, certain methods also require pre-treatment, this further increases the cost. However, the application and selection of waste materials to treat AMD are mostly followed these days because it is economically very cheap, affordable, and also reduces the environmental load. Some of the waste materials are fly ash, slag, ZVI, cement kiln dust, zeolites, etc. After thorough research, it’s concluded that amongst the above-mentioned waste materials, fly ash is very effective and economical due to its adsorption capability, retention time, etc. Government intervention is also very important for the control of AMD. Government should lay certain guidelines for these mining sectors. Moreover, AMD can be controlled by the mining industry becoming environmentally friendly and socially sustainable by reducing impacts of operations and adopting corporate social responsibility.

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