Acid drainage, especially acid mine drainage is the process whereby water combines with the sulfide minerals like pyrite which is iron plus sulfur (high in sulfur) to produce sulfuric acid (iron plus sulfur plus oxygen so oxidation of the sulfide like pyrite is part of the process) which is deleterious to the environment so where mine waste contains pyrite then it must be isolated and neutralized with say limestone or submerged in water to prevent the development of sulfuric acid.
