Acid mine drainage AMD is a major environmental issue caused by the exposure of sulfide minerals, such as pyrite FeS2 , to water and oxygen during mining activities. When these minerals are exposed to water and oxygen, they undergo a series of chemical reactions that result in the release of acidic water containing high concentrations of dissolved metals and sulfate ions. This acidic water can significantly affect the pH level of the surrounding water bodies, making them more acidic and potentially harmful to aquatic life and water quality.The primary chemical reactions involved in the formation of acid mine drainage are:1. Oxidation of pyrite FeS2 by oxygen:FeS2 + 7/2 O2 + H2O Fe2+ + 2 SO42- + 2 H+2. Oxidation of ferrous iron Fe2+ to ferric iron Fe3+ by oxygen:4 Fe2+ + O2 + 4 H+ 4 Fe3+ + 2 H2O3. Hydrolysis of ferric iron Fe3+ :Fe3+ + 3 H2O Fe OH 3 s + 3 H+4. Oxidation of additional pyrite by ferric iron Fe3+ :FeS2 + 14 Fe3+ + 8 H2O 15 Fe2+ + 2 SO42- + 16 H+The overall reaction can be summarized as:FeS2 + 15/4 O2 + 7/2 H2O Fe OH 3 s + 2 SO42- + 4 H+As a result of these reactions, the pH level of the water is lowered due to the production of hydrogen ions H+ . The acidic water can dissolve other minerals and metals in the surrounding rocks, further contaminating the water and exacerbating the problem.To mitigate the effects of acid mine drainage, several treatment methods can be employed, such as:1. Neutralization: Adding alkaline materials like limestone CaCO3 or lime Ca OH 2 to the acidic water to increase the pH and precipitate dissolved metals as hydroxides or sulfides.2. Passive treatment systems: Constructing wetlands, anoxic limestone drains, or other passive systems that promote the natural attenuation of acidity and metal concentrations.3. Active treatment systems: Using chemical or biological processes to remove metals and acidity from the water, such as chemical precipitation, ion exchange, or biological sulfate reduction.Overall, acid mine drainage can significantly affect the pH level of water in a particular region, and understanding the chemical reactions involved is crucial for developing effective treatment strategies to mitigate its environmental impacts.