Practical chemistry

This is classic acid mine drainage, the red is Iron III hydroxide. The pH at the effluent interface was around 3. Theres a biological component to how acid mine draininage occurs: Thiobacillus ferrooxidans metabolizes FeS2 to Fe+3 and Sulfuric acid.

 

The bacterium runs this reaction: (half reactions listed because I'm lazy.)

 

FeS2 + 3.5 O2 + H2O --> Fe2+ + 2 SO4(2-) + 2 H+

 

2 Fe2+ + 0.5 O2 + 2 H+ --> 2 Fe3+ + H2O

 

Then the freed Iron III makes the problem even worse by this reaction which happens independent of bacteria.

 

FeS2 + 14 Fe3+ + 8 H2O --> 15 Fe2+ + 2 SO4(2-) + 16 H+

 

Done