Zoti Bemba wrote:Is the problem with the mine heavy metals? I thought it was sulfides, which are a whole different order of pollutants than sewage runoffs, especially if your concern is wild rice beds.
Acid Mine Drainage (AMD) consists of heavy metals AND
low pH levels (the H+), and in the case of pyrite (iron disulfide), sulphuric acid as well.
Fe3+ in this case.
HOWEVER: even in an iron mine, mine operators release a whole range of heavy metals, as copper, zinc, etc., etc. in the ore body and overburden also undergo a series of cascading reactions paralleling the equations defining that process for Fe (below).
So Acid Mine Drainage is most often a soup of heavy metals with multiple cascading chemical reactions occurring at different stages. And it is permanent. The reactions don't run out of fuel, and once started continue in anaerobic environments (i.e., underwater) using chemical energy to stoke their own fires, so to speak. Joseph Skulan posted a stellar explanation on facebook a week or so back.
The following oxidation and reduction reactions express the breakdown of pyrite that leads to acid mine drainage:
1. 2FeS2 + 7O2 + 2H2O -> 2FeSO4 + 2H2SO4
2. 2Fe2+ + 1/2 O2 + 2H+ -> 2Fe3+ + H2O
3. Fe3+ + 3H2O -> Fe(OH)3 + 3H+
4. FeS2 (s) + 15/4 O2 + 7/2 H2O <--> 4H+ + 2SO4- +Fe(OH)3 (s)