Acid Mine Drainage :: science

Acid Mine DrainageFor hundreds, even thousands of years, human beings have mined for metals and st one(a)s, and with the advent of great technology as well as greater needs, the demands for these resources continue to grow. While these resources benefit our lives in many ways, the effects of mining can be detrimental, and one such effect is the topic of this essay, acid mine drainage (A.M.D.). The causes of A.M.D. will be discussed, along with some of the physical and biological problems associated with it. Some prevention and remediation treatments will in any case be considered. Acid mine drainage refers to piddle (leachate, drainage or seepage) that has come into contact with oxidised rocks or overburden that contains sulfide material (coal, zinc, copper, lead). (Keller, 2000 U.S.G.S. U.S.E.P.A., 2002). A common sulphide is pyrite, or iron disulfide (FeS2), and throughout this essay it will be pyrite that will be the primary sulphide considered. Acid mine drainage is not a ne w phenomenon, early mining techniques utilized gravity to avoid water pooling, resulting in the water bonnie polluted by acid, iron, sulphur and aluminium (U.S.E.P.A., 2002). It is most commonly associated with coal mining, especially with soft coal, coal that has high sulphur content. The pyrite that is present in coal seams will be accessible after surface mining when the overlying surfaces are removed or in deep mines that allow atomic number 8 access to the previously inaccessible pyrite-containing coal (D.E.P. 1, 1997). After pyrite is exposed to air and water, sulphuric acid and iron hydroxide are formed, creating an acidic outpouring (D.E.P. 1, 1997 2 2002). When the water comes into contact with the pyrite, the chemical reactions that take place causes the water to increase in pH which will dissolve heavy metals which stay in solution. However, when the pH levels reach a certain stage, the iron can then precipitate out, coating sediments with the characteristic yellow, re d or orange colourings (D.E.P. 2, 2002 U.S.G.S. U.S.E.P.A., 2002). The rate that A.M.D. advances is also influenced by the presence of certain bacteria (Doyle U.S.G.S). A.M.D that has dissolved heavy metals such as copper, lead and mercury can contaminate ground and surface water. curiously at risk are mines that are located above the water table (Keller, 2000 D.E.P. 2, 2002). The sources of water that get polluted can be surface water that permeates into the mine, shallow ground water flowing through the mine or any water that comes into contact with the waste tailings produced by mines.