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.
Receive Daily Updates
Recent Posts
Steve Ovett, the famous British middle-distance athlete, won the 800-metres gold medal at the Moscow Olympics of 1980. Just a few days later, he was about to win a 5,000-metres race at London’s Crystal Palace. Known for his burst of acceleration on the home stretch, he had supreme confidence in his ability to out-sprint rivals. With the final 100 metres remaining,
[wptelegram-join-channel link=”https://t.me/s/upsctree” text=”Join @upsctree on Telegram”]Ovett waved to the crowd and raised a hand in triumph. But he had celebrated a bit too early. At the finishing line, Ireland’s John Treacy edged past Ovett. For those few moments, Ovett had lost his sense of reality and ignored the possibility of a negative event.
This analogy works well for the India story and our policy failures , including during the ongoing covid pandemic. While we have never been as well prepared or had significant successes in terms of growth stability as Ovett did in his illustrious running career, we tend to celebrate too early. Indeed, we have done so many times before.
It is as if we’re convinced that India is destined for greater heights, come what may, and so we never run through the finish line. Do we and our policymakers suffer from a collective optimism bias, which, as the Nobel Prize winner Daniel Kahneman once wrote, “may well be the most significant of the cognitive biases”? The optimism bias arises from mistaken beliefs which form expectations that are better than the reality. It makes us underestimate chances of a negative outcome and ignore warnings repeatedly.
The Indian economy had a dream run for five years from 2003-04 to 2007-08, with an average annual growth rate of around 9%. Many believed that India was on its way to clocking consistent double-digit growth and comparisons with China were rife. It was conveniently overlooked that this output expansion had come mainly came from a few sectors: automobiles, telecom and business services.
Indians were made to believe that we could sprint without high-quality education, healthcare, infrastructure or banking sectors, which form the backbone of any stable economy. The plan was to build them as we went along, but then in the euphoria of short-term success, it got lost.
India’s exports of goods grew from $20 billion in 1990-91 to over $310 billion in 2019-20. Looking at these absolute figures it would seem as if India has arrived on the world stage. However, India’s share of global trade has moved up only marginally. Even now, the country accounts for less than 2% of the world’s goods exports.
More importantly, hidden behind this performance was the role played by one sector that should have never made it to India’s list of exports—refined petroleum. The share of refined petroleum exports in India’s goods exports increased from 1.4% in 1996-97 to over 18% in 2011-12.
An import-intensive sector with low labour intensity, exports of refined petroleum zoomed because of the then policy regime of a retail price ceiling on petroleum products in the domestic market. While we have done well in the export of services, our share is still less than 4% of world exports.
India seemed to emerge from the 2008 global financial crisis relatively unscathed. But, a temporary demand push had played a role in the revival—the incomes of many households, both rural and urban, had shot up. Fiscal stimulus to the rural economy and implementation of the Sixth Pay Commission scales had led to the salaries of around 20% of organized-sector employees jumping up. We celebrated, but once again, neither did we resolve the crisis brewing elsewhere in India’s banking sector, nor did we improve our capacity for healthcare or quality education.
Employment saw little economy-wide growth in our boom years. Manufacturing jobs, if anything, shrank. But we continued to celebrate. Youth flocked to low-productivity service-sector jobs, such as those in hotels and restaurants, security and other services. The dependence on such jobs on one hand and high-skilled services on the other was bound to make Indian society more unequal.
And then, there is agriculture, an elephant in the room. If and when farm-sector reforms get implemented, celebrations would once again be premature. The vast majority of India’s farmers have small plots of land, and though these farms are at least as productive as larger ones, net absolute incomes from small plots can only be meagre.
A further rise in farm productivity and consequent increase in supply, if not matched by a demand rise, especially with access to export markets, would result in downward pressure on market prices for farm produce and a further decline in the net incomes of small farmers.
We should learn from what John Treacy did right. He didn’t give up, and pushed for the finish line like it was his only chance at winning. Treacy had years of long-distance practice. The same goes for our economy. A long grind is required to build up its base before we can win and celebrate. And Ovett did not blame anyone for his loss. We play the blame game. Everyone else, right from China and the US to ‘greedy corporates’, seems to be responsible for our failures.
We have lowered absolute poverty levels and had technology-based successes like Aadhaar and digital access to public services. But there are no short cuts to good quality and adequate healthcare and education services. We must remain optimistic but stay firmly away from the optimism bias.
In the end, it is not about how we start, but how we finish. The disastrous second wave of covid and our inability to manage it is a ghastly reminder of this fact.