Chemistry
For further information, see Acidophiles in acid mine drainage
The chemistry of oxidation of pyrites, the production of ferrous ions and subsequently ferric ions, is very complex, and this complexity has considerably inhibited the design of effective treatment options.
Although a host of chemical processes contribute to acid mine drainage, pyrite oxidation is by far the greatest contributor. A general equation for this process is:
- 2FeS2 + 7O2 + 2H2O = 2Fe2+ + 4SO42− + 4H+
The oxidation of the sulfide to sulfate solubilizes the ferrous iron (iron(II)), which is subsequently oxidized to ferric iron (iron(III)):
- 4Fe2+ + O2 + 4H+ = 4Fe3+ + 2H2O
Either of these reactions can occur spontaneously or can be catalyzed by microorganisms that derive energy from the oxidation reaction. The ferric irons produced can also oxidize additional pyrite and oxidize into ferrous ions:
- FeS2 + 14Fe3+ + 8H2O = 15Fe2+ + 2SO42− + 16H+
The net effect of these reactions is to release H+, which lowers the pH and maintains the solubility of the ferric ion.
Read more about this topic: Acid Mine Drainage
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