Acid Mine Drainage Treatment

[GWJPE]

I'm interested in learning more about treating acid mine drainage (AMD). In my job, I work with group that developed designs for abandoned mine reclamation in Iowa.

I know little about treating AMD, except that I've seen limestone packs and passive wetland treatment systems proposed for such work.

I would enjoy a dialogue with other professionals who may be able to help me learn more about this topic. Perhaps they could suggest a research paper to read. Of particular interest to me is the design criteria. How big for how much flow, pH etc. Anyone out there knowledgeable on this topic?

 

[fattdad]

I think Lee Daniels at Virginia Tech is involved in some of this research. Interesting field, both the generation of the acid run-off and the treatment too.

Yes, I am familiar with the use of limestone to line the drainage ditches, but don't know the design criteria. Just that it works.

f-d

¡papá gordo ain’t no madre flaca!

 

[bimr]

There is significant vollume of materials on line. Here is an example:

http://water.epa.gov/polwaste/nps/acid_mne.cfm

Acid mine drainage water forms through a chemical reaction/ natural bacterial reaction of water (rainwater, snowmelt, pond water) and shallow subsurface water with rocks or waste tailings that contain sulfur-bearing minerals, resulting in sulfuric acid. Heavy metals will then be leached from rocks that come in contact with the acid drainage.

 

[fattdad]

basically, it's pyrite (FeS2) oxidizing (via H20 and 02) into Fex0x and H2SO4, the former being "rust" and the latter being sulfuric acid. Limestone provides a carbonate for the sulfuric acid to react against and carbon dioxide gas is formed along with water and sulfate (I think the sulfate stays in solution - not sure).

This is close.

f-d

¡papá gordo ain’t no madre flaca!

 

[bimr]

2FeS2(s) + 14Fe + 8H2O --> 15Fe + 2SO4 + 16H

Oxidation of iron releases hydrogen (H+) from the water making the water acidic. The H+ combines with sulfate (SO4) present in the water to give H2SO4 (sulfuric acid)


Lime is used to neutralize the sulfuric acid:

Ca(OH)2 + H2SO4 > CaSO4 + 2H2O

 

[fattdad]

I realize that this is not the original topic, but I'm curious about bimr's chemical reaction. When pyrite is underwater it doesn't oxidize and there is no formation of "rust" or sulfuric acid. Therefore, in my mind, the reaction must include O2. Is bimr's reaction actually published, or did you balance the equation from the assumption that pyrite plus water is creating sulfuric acid?

(My earlier reference to chemistry was basically illustrative, but I'd still think O2 is critical to the formation of sulfuric acid.)

f-d

¡papá gordo ain’t no madre flaca!

 

[bimr]

You have to oxidize other metals first to get the H+ ion. With the H+ ion, you now have an acid solution which will enable the oxidation of pyrite.


2FeS2(s) + 7O2(g) + 2H2O 2Fe2+(aq) + 4SO42-(aq) + 4H+(aq) (1)


4Fe2+(aq) + O2(g) + 4H+(aq) Fe3+(aq) + 2H2O (2)

Oxidation of iron releases hydrogen (H+) from the water making the water acidic. The H+ combines with sulfate (SO4) present in the water to give H2SO4 (sulfuric acid)