What is Acid Mine Drainage?

1. What is Acid Mine Drainage? • Acid mine drainage, sometimes referred to as AMD, results when the mineral pyrite (FeS2) is exposed to air and water, resulting in the formation of sulfuric acid and iron hydroxide. For chemists, the equation for AMD formation is: FeS2 + 3.75 O2 + 3.5 H2O <-------> Fe(OH)3 + 2 H2SO4 • Pyrite is commonly present in coal seams and in the rock layers overlying coal seams. AMD formation occurs during surface mining when the overlying rocks are broken and removed to get at the coal. It can also occur in deep mines which allow the entry of oxygen to pyrite-bearing coal seams. • The products of AMD formation, acidity and iron, can devastate water resources by lowering the pH and coating stream bottoms with iron hydroxide, forming the familiar orange colored "yellow boy" common in areas with abandoned mine drainage. • Many areas also contain naturally occurring limestone (CaCO3) deposits which neutralizes acidity. To determine whether or not a mine will create acidic drainage, coal companies must analyze how much pyrite and neutralizers are in the rocks which will be disturbed by mining. Then DEP can determine whether or not a site can be mined without harming the environment. • By law, DEP cannot issue a permit for new coal mining where it is determined mining will cause acid mine drainage.