Environmental Impact of Acid Mine Drainage and overview of the Treatment Techniques
Dr A Gangagni Rao, Chief Scientist, CSIR – IICT; Dr Sandeep Panda, SERB National Post Doc Fellow, CSIR – IICT; Sameena Begum, Royal Melbourne Institute of Technology, Australia
This article focuses on the origin, causes, environmental impact of acidic wastewater generated from the mining industry, also known as the Acid Mine Drainage. The article also gives an overview of the treatment techniques of such wastewater.
Acidic wastewaters generated from the mining industries are referred to as Acid Mine Drainage (AMD) and are known to be associated with serious environmental problems. The dissolution of heavy metals and toxic substances into the environment, as a result of AMD, cause serious concerns to the waterways and biodiversity. Over the years, several treatment techniques have surfaced for AMD management and safe treatment. The present article focuses on the origin, causes, environmental impact of AMD along with an overview of the available treatment techniques.
Mining activities have been practised for centuries for the commercial exploitation of mineral resources to meet the growing demand for metals. Extensive mining activities for extraction of metals, like - copper, gold, nickel etc., from their sulphides, results in the generation of wastes such as “waste rocks” and “mine tailings” at the mine site, which is dumped( 1). The dumped wastes at the mine site generally come in contact with air and water (ground or rain water) that results in its weathering. This generates acids and toxic substances. The weathering of the metal sulphides can
be chemical, hydrological or microbiological( 2). Waters generated either from the waste dumps or abandoned mines are highly acidic and have elevated levels of heavy metals due to the weathering of the sulphide minerals. Acid Mine Drainage (AMD) is thus an acidic wastewater, rich in metals and other toxic substances, generated from a mining site (example - coal or any metal sulphide mine). The dissolved metals and acids seep and mix into nearby water bodies causing concerns to the waterways and biodiversity.
The mining sector in India plays an important role in the country’s economy. India stands to be the third largest producer of coal. For the year 2018, production of coal in the country has been estimated to be 676.51 million tonnes. In terms of production of iron ore, India stands to be in the 4th position globally with a production reported to 210 million tonnes FY 2018.( This indicates that iron ores
6) or iron as part of other ores constitute to be a major element of the mineral deposits. Generally, iron is seen as iron pyrites (FeS ) when it occurs in sulphide form
(details discussed below w.r.t. AMD formation). AMD is a common problem in coal or other sulphide-rich mines and reports on its treatment in India are scarce. Recently, Vyawahre and Rai (2016) have attempted two types of passive treatment methods for treatment of AMD from Durgapur mines, Maharashtra. It is believed that, in the coming years, treatment of AMD will be an attractive area of research in India.