Acid mine drainage AMD is a major environmental issue associated with mining activities. It occurs when sulfide minerals, such as pyrite FeS2 , are exposed to water and oxygen, resulting in the formation of sulfuric acid H2SO4 and dissolved metal ions. This process can significantly affect the pH level and metal concentrations of nearby bodies of water, such as rivers, lakes, and groundwater.The chemical processes involved in acid mine drainage can be summarized in the following steps:1. Oxidation of sulfide minerals: When sulfide minerals are exposed to water and oxygen, they undergo oxidation. For example, pyrite reacts with water and oxygen to form ferrous iron Fe2+ and sulfate ions SO42- . 4FeS2 + 14O2 + 4H2O 4Fe2+ + 8SO42- + 8H+2. Formation of sulfuric acid: The ferrous iron Fe2+ produced in the previous step can further react with oxygen and water to form ferric iron Fe3+ and more sulfate ions. This reaction also produces hydrogen ions H+ , which contribute to the acidity of the water. 4Fe2+ + O2 + 4H+ 4Fe3+ + 2H2O3. Hydrolysis of ferric iron: Ferric iron Fe3+ can undergo hydrolysis, producing more hydrogen ions H+ and further increasing the acidity of the water. Fe3+ + 3H2O Fe OH 3 + 3H+4. Dissolution of metals: The low pH conditions created by the sulfuric acid promote the dissolution of other metal-containing minerals present in the mine waste, such as those containing copper, zinc, lead, and aluminum. These metals are released into the water as dissolved ions, increasing their concentrations in nearby bodies of water.The overall effect of acid mine drainage on nearby bodies of water is a significant decrease in pH levels increased acidity and increased concentrations of metals. This can have severe consequences for aquatic ecosystems, as the acidic conditions and high metal concentrations can be toxic to many aquatic organisms, including fish, invertebrates, and plants. Additionally, the increased metal concentrations can contaminate drinking water sources, posing risks to human health.To mitigate the effects of acid mine drainage, various treatment methods can be employed, such as neutralization with alkaline materials e.g., limestone , passive treatment systems e.g., constructed wetlands , and active treatment systems e.g., chemical precipitation . These methods aim to raise the pH of the affected water and remove or reduce the concentrations of dissolved metals.