Acid mine drainage AMD is a significant environmental issue caused by the exposure of sulfide minerals, such as pyrite FeS2 , to air and water during mining activities. When these minerals come into contact with water and oxygen, they undergo a series of chemical reactions that result in the formation of sulfuric acid and dissolved metal ions. The release of these substances into the environment leads to a decrease in the pH level of the water, making it more acidic. This change in pH has a direct impact on the concentration of heavy metals in the water, as well as the overall water quality.The pH level plays a crucial role in determining the solubility and mobility of heavy metals in water affected by AMD. As the pH decreases i.e., the water becomes more acidic , the solubility of many heavy metals, such as iron, copper, zinc, and lead, increases. This is because the acidic conditions promote the dissolution of metal-containing minerals and the release of metal ions into the water. Consequently, the concentration of heavy metals in the water increases, posing a threat to aquatic life and human health.The chemical processes that occur during the formation of AMD and the subsequent impact on water quality can be summarized as follows:1. Oxidation of sulfide minerals: When sulfide minerals, such as pyrite, are exposed to air and water, they react with oxygen to form sulfate ions SO4^2- and metal ions e.g., Fe^2+ . This process is known as oxidation. 4FeS2 + 15O2 + 14H2O 4Fe OH 3 + 8SO4^2- + 16H+2. Formation of sulfuric acid: The sulfate ions produced in the oxidation process react with water to form sulfuric acid H2SO4 . SO4^2- + 2H+ H2SO43. Acidification of water: The formation of sulfuric acid leads to a decrease in the pH level of the water, making it more acidic.4. Dissolution of heavy metals: The acidic conditions promote the dissolution of metal-containing minerals, releasing heavy metals into the water. For example, the solubility of iron Fe increases under acidic conditions: Fe OH 3 s + 3H+ Fe^3+ + 3H2OAs a result, the concentration of heavy metals in the water increases, which can have detrimental effects on aquatic life, human health, and the overall water quality.To mitigate the impact of AMD on water quality, 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 increase the pH level of the water, reduce the solubility of heavy metals, and remove them from the water, thereby improving water quality.