Water is considered mining’s biggest casualty of all time given the huge scale at which mining of different types are advancing in today’s world. Acid mine drainage (AMD) is one of the largest repercussions of mining on water resources. It is a risk associated with all kinds of hardrock mines for extraction of useful metals and a significant number of coal mines suffer from acid mine drainage.
What is acid mine drainage?
As the name suggests, it is the outflow of acidic water from mining areas. It is identified by appearance of brownish-yellow precipitate with a foul smell and increase in acidity of water. Target ores for metals such as gold, copper, silver etc. or coal sometimes are sulphur bound which are known as ‘metal sulphides’.
Acid mine drainage is most commonly caused by iron sulphide called “pyrite” or “fool’s gold” which is abundantly found with almost all the metal ores. These sulphides are exposed during mining, and undergo oxidation reaction in presence of air and water to form sulphuric acid that is corrosive. The acid run off further dissolves harmful metals such as copper, aluminium, manganese, mercury, lead etc. and poison the ground or surface water system.
Acid mine drainage is an irreversible process that turns undisturbed and relatively unreactive ores into volumes of hazardous waste whose containment is extremely difficult once it reaches a water body. Acid drainage can also occur in non-mining areas such as construction sites, artificially dug areas or naturally weathered rocks termed as ‘acid rock drainage’. The process of pyrite oxidation and acid formation can be further catalysed by bacteria called as ‘extremophiles’ which can thrive in extreme conditions such as acidic environment.
Environmental impacts of acid mine drainage
Acid mine drainage can occur indefinitely for hundreds of years even after the mining activities have ended and thus affects a large horizon – ecologically and economically. The mines continue to produce acidic drainage as long as the rocks are exposed or become devoid of acid producing minerals. It is one of the single biggest non-point sources of pollution.
Some Roman mining sites in Great Britain are still producing problematic acid mine drainage, 2000 years after the stoppage of mining (CNHE, 2017). Moreover, AMD can develop at any point of the mining process – underground working, open pit mine faces, waste rock dumps, tailings deposits and ore stockpiles. In India, acid mine drainage usually comes from coal mines.
Most of the living organisms thrive well in the pH of near neutral which is 7. Acid mine drainage in some of the worst cases could decrease the pH of water to as low as less than 3. Thus it degrades streams, rivers and aquatic life forms in varying degrees depending upon the severity of pH change. It limits the growth of the river ecology in addition to unsuitable use of water for human, agriculture, industrial and recreational activities.
The increase in acidity can cause loss of sodium ions from the blood of fishes, which adversely affects the gill’s function. Prolonged exposure to low pH can be lethal for plants and animals with effects such as stunted growth, lesions, low reproductive rates and deformities (Vyawahre and Rai, 2016). Acid mine drainage is also responsible for loading a huge amount of heavy metals like lead, aluminium, manganese and more into our waterways. Aluminium is toxic to many aquatic animals and limits root development in plants leading to nutrient deficiency.
In addition to increase of acidity and release of toxic metals, neutralisation of the acid water by alkaline rocks could create an additional problem. In case of decrease in acidity, the iron which was in ferrous form turns into ferric and comes out of the water as a yellowish precipitate (solid) called ‘yellowboy’. It effectively chokes the streambed, crevices and prohibits the growth of benthic (bottom dwelling) life forms.
AMD have renouncing affects on the quality of groundwater system if the mines are located in permeable soil formations. The acidic and heavy metal containing water may percolate inside the water aquifers (underground water pockets) and gets spread throughout the underground water system which ultimately reaches human consumption via bore wells.
Prevention, mitigation and treatment of acid mine drainage
Acid mine drainage does bear a significant economic cost and irreversible environmental effects. Prevention of the acid-generating processes seems to be the only way to completely wipe out the problem of acid mine drainage but, stopping of mining is not the viable solution in most cases.
However, sulphuric acid could be stopped from forming by preventing the waste rock and mine tailings to come in contact with air by strategies such as submerging the tailings under water, sealing them behind barriers or burying them underground (groundtruthseeking.org, 2010). Nonetheless, isolating and containing huge amount of the generated waste is practical either above or below ground thus storing it for a future possibility or treating them with the help of technological advancement.
In most cases it is impossible to completely treat the contaminated water from acid mine drainage due to its high cost, inefficient technology and easily diffusible quality of water. But, its consequences could be limited by treating the water before releasing it into the environment through passive and active technologies (Johnson and Hallberg, 2005).
- Passive Treatment- It is the use of naturally occurring biological and chemical reactions that could be employed to reduce the acidity of AMD. For example, ‘bioreactors’ which works on use of sulphate-reducing microbes that precipitate out dissolved harmful metals. Another method is the creation of artificial wetlands where microbes can remove the heavy metals from the mine water. Both these methods are limited to small scale mines since it is expensive and requires a huge area of land. However, operation and maintenance of passive treatment system is comparatively lesser as compared to active treatment.
- Active Treatment- It is the typical water treatment system involving the use of alkaline chemicals such as caustic soda, hydrated lime, sodium carbonate etc. to decrease the acidity of mine drainage. Limestone is one very common chemical used due to its low cost and relative abundant availability. On the other hand, continued active treatment due to precipitation increases the rate of total dissolved solid (TDS) which is an important water quality parameter. Moreover, active treatment technologies are expensive due to chemical usage, equipments and huge manpower.
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Petrol in India is cheaper than in countries like Hong Kong, Germany and the UK but costlier than in China, Brazil, Japan, the US, Russia, Pakistan and Sri Lanka, a Bank of Baroda Economics Research report showed.
Rising fuel prices in India have led to considerable debate on which government, state or central, should be lowering their taxes to keep prices under control.
The rise in fuel prices is mainly due to the global price of crude oil (raw material for making petrol and diesel) going up. Further, a stronger dollar has added to the cost of crude oil.
Amongst comparable countries (per capita wise), prices in India are higher than those in Vietnam, Kenya, Ukraine, Bangladesh, Nepal, Pakistan, Sri Lanka, and Venezuela. Countries that are major oil producers have much lower prices.
In the report, the Philippines has a comparable petrol price but has a per capita income higher than India by over 50 per cent.
Countries which have a lower per capita income like Kenya, Bangladesh, Nepal, Pakistan, and Venezuela have much lower prices of petrol and hence are impacted less than India.
“Therefore there is still a strong case for the government to consider lowering the taxes on fuel to protect the interest of the people,” the report argued.
India is the world’s third-biggest oil consuming and importing nation. It imports 85 per cent of its oil needs and so prices retail fuel at import parity rates.
With the global surge in energy prices, the cost of producing petrol, diesel and other petroleum products also went up for oil companies in India.
They raised petrol and diesel prices by Rs 10 a litre in just over a fortnight beginning March 22 but hit a pause button soon after as the move faced criticism and the opposition parties asked the government to cut taxes instead.
India imports most of its oil from a group of countries called the ‘OPEC +’ (i.e, Iran, Iraq, Saudi Arabia, Venezuela, Kuwait, United Arab Emirates, Russia, etc), which produces 40% of the world’s crude oil.
As they have the power to dictate fuel supply and prices, their decision of limiting the global supply reduces supply in India, thus raising prices
The government charges about 167% tax (excise) on petrol and 129% on diesel as compared to US (20%), UK (62%), Italy and Germany (65%).
The abominable excise duty is 2/3rd of the cost, and the base price, dealer commission and freight form the rest.
Here is an approximate break-up (in Rs):
a)Base Price | 39 |
b)Freight | 0.34 |
c) Price Charged to Dealers = (a+b) | 39.34 |
d) Excise Duty | 40.17 |
e) Dealer Commission | 4.68 |
f) VAT | 25.35 |
g) Retail Selling Price | 109.54 |
Looked closely, much of the cost of petrol and diesel is due to higher tax rate by govt, specifically excise duty.
So the question is why government is not reducing the prices ?
India, being a developing country, it does require gigantic amount of funding for its infrastructure projects as well as welfare schemes.
However, we as a society is yet to be tax-compliant. Many people evade the direct tax and that’s the reason why govt’s hands are tied. Govt. needs the money to fund various programs and at the same time it is not generating enough revenue from direct taxes.
That’s the reason why, govt is bumping up its revenue through higher indirect taxes such as GST or excise duty as in the case of petrol and diesel.
Direct taxes are progressive as it taxes according to an individuals’ income however indirect tax such as excise duty or GST are regressive in the sense that the poorest of the poor and richest of the rich have to pay the same amount.
Does not matter, if you are an auto-driver or owner of a Mercedes, end of the day both pay the same price for petrol/diesel-that’s why it is regressive in nature.
But unlike direct tax where tax evasion is rampant, indirect tax can not be evaded due to their very nature and as long as huge no of Indians keep evading direct taxes, indirect tax such as excise duty will be difficult for the govt to reduce, because it may reduce the revenue and hamper may programs of the govt.