The presence of sulfide minerals in acid mine drainage AMD can significantly affect the pH and metal concentration of surface water in the surrounding area. This is mainly due to the oxidation of sulfide minerals, particularly pyrite FeS2 , which is commonly found in mining waste and tailings. The oxidation process generates acidity and releases metal ions into the environment, leading to the contamination of surface water.The oxidation of sulfide minerals can be represented by the following chemical reactions:1. Pyrite FeS2 reacts with oxygen O2 and water H2O to form ferrous iron Fe2+ , sulfate ions SO42- , and acidity H+ :FeS2 + 7/2 O2 + H2O Fe2+ + 2 SO42- + 2 H+2. Ferrous iron Fe2+ can further react with oxygen O2 and water H2O to form ferric iron Fe3+ and acidity H+ :4 Fe2+ + O2 + 4 H+ 4 Fe3+ + 2 H2O3. Ferric iron Fe3+ can react with additional pyrite FeS2 and water H2O to form ferrous iron Fe2+ , sulfate ions SO42- , and acidity H+ :FeS2 + 14 Fe3+ + 8 H2O 15 Fe2+ + 2 SO42- + 16 H+These reactions result in the release of metal ions, such as iron Fe , copper Cu , zinc Zn , and other heavy metals, into the surrounding water. The release of H+ ions during the oxidation process leads to a decrease in pH, making the water more acidic. Acidic water can further enhance the dissolution of other minerals, releasing even more metal ions and increasing the metal concentration in the water.The presence of sulfide minerals in AMD can have several negative impacts on the surrounding environment:1. Lower pH levels can harm aquatic life, as many organisms are sensitive to changes in pH and cannot survive in highly acidic conditions.2. High concentrations of metals can be toxic to aquatic organisms, causing direct harm or bioaccumulation in the food chain, which can eventually affect humans who consume contaminated fish or other aquatic organisms.3. The formation of metal hydroxides, such as iron hydroxide Fe OH 3 , can lead to the precipitation of solid particles that can smother aquatic habitats and clog the gills of fish and other organisms.To mitigate the impacts of AMD, various treatment methods can be employed, such as the addition of alkaline materials e.g., limestone to neutralize acidity, the use of constructed wetlands to promote the precipitation of metals, or the installation of passive or active water treatment systems to remove metals and acidity from the water.