Introduction
Upon exposure to oxygen (O2) and water (H2O), metal sulfides undergo oxidation to produce metal-rich acidic effluent. If the pH is low enough to overcome the natural buffering capacity of the surrounding rocks (‘calcium carbonate equivalent’ or ‘acid neutralising capacity’), the surrounding area may become acidic, as well as contaminated with high levels of heavy metals. Though acidophiles have an important place in the iron and sulfur biogeochemical cycles, strongly acidic environments are overwhelmingly anthropogenic in cause, primarily created at the cessation of mining operations where sulfide minerals, such as pyrite (iron disulfide or FeS2), are present.
Acid mine drainage may occur in the mine itself, the spoil heap (particularly colliery spoils from coal mining), or through some other activity that exposes metal sulfides at a high concentration, such as at major construction sites. Banks et al. provide a basic summary of the processes that occur:
- 2FeS2 + 2H2O + 7O2 = 2Fe2+ + 4SO42– + 4H+(aq)
- Pyrite + water + oxygen = ferrous iron + sulfate + acid
Read more about this topic: Acidophiles In Acid Mine Drainage
Famous quotes containing the word introduction:
“The role of the stepmother is the most difficult of all, because you cant ever just be. Youre constantly being testedby the children, the neighbors, your husband, the relatives, old friends who knew the childrens parents in their first marriage, and by yourself.”
—Anonymous Stepparent. Making It as a Stepparent, by Claire Berman, introduction (1980, repr. 1986)
“Such is oftenest the young mans introduction to the forest, and the most original part of himself. He goes thither at first as a hunter and fisher, until at last, if he has the seeds of a better life in him, he distinguishes his proper objects, as a poet or naturalist it may be, and leaves the gun and fish-pole behind. The mass of men are still and always young in this respect.”
—Henry David Thoreau (18171862)
“Do you suppose I could buy back my introduction to you?”
—S.J. Perelman, U.S. screenwriter, Arthur Sheekman, Will Johnstone, and Norman Z. McLeod. Groucho Marx, Monkey Business, a wisecrack made to his fellow stowaway Chico Marx (1931)