Acid Mine Drainage

Yellow boy in a stream receiving acid drainage from surface coal mining. An Enviromental problem in coal- Mining region Degrades water quality > Mixing of acid mine water into natural in river Polluted water for human consumption and industrial use Pyrite Air, bacteria and moisture during mining Pyrite Oxidation Formation of AMD Initiator reaction Propagation cycle

The breakdown of pyrite – Leads to the formation of sulfuric acid and ferrous iron – pH values ranging from 2 to 4.5 – Sulfate ion concentrations ranging from 1,000 to 20,000 mg L−1 but a nondetectable ferrous iron concentration – The acid formed attack other minerals associated with the coal and pyrite, causing breakdown of rock fabric Alumunium : Highly toxic

In AMD will be detectable some of acidophilic iron oxidizing thiobacilli. Acidithiobacillus ferrooxidans is involved, pyrite biooxidation proceeds Pyrit Oxidation : Ferric ion oxidation Acidithiobacillus thiooxidans : Oxidized elemental sulfur (S0) and other partially reduced sulfur species : Intermediates in pyrite oxidation to sulfuric acid Metallogenium-like organism that they isolated from AMD ( Walsh and Mitchell (1972) ) - pH drops below 3.5.

An early study by Harrison (1978) Artificial coal spoil Deposit into mound d= 50 cm l= 25cm on plastic tray Absorbed and migrated upward Sampling Inoculated : 20 L of an emulsion of acid soil, drainage water, and mud from a spoil from an old coal strip mine Microbial succession in coal spoil under laboratory conditions

Result... pH had dropped from 7 to 5. pH to just below 5 >> caused by a burst of growth by sulfur-oxidizing bacteria, >> then died off progressively. The heterotrophic population increased again to just below 107 g−1. The sulfur-oxidizing bacteria were assumed to be making use of elemental sulfur resulting from the oxidation of pyrite by ferric sulfate: FeS2 + Fe2(SO4)3 → 3FeSO4 + 2S0 Initial samples : The base of the mound Heterotrophic bacteria. 2 weeks : The population density of ∼ 107 cells g−1 After 8 weeks : heterotrophs were still dominant Between 12 and 20 weeks : The population decreased Near the summit of the mound, First 15 weeks : Heterotrophs predominated Acidithiobacillus thiooxidans and Acidithiobacillus ferrooxidans Higher pH values Protozoans, algae, and arthropod Metallogenium was not seen Between 12 and 20 weeks : The population decreased After 8 weeks : heterotrophs were still dominant

NEW DISCOVERIES RELATING TO ACID MINE DRAINAGE A fairly recent study of abandoned mines at Iron Mountain, California. The ore body at Iron Mountain – various metal sulfides and was a source of Fe, Cu, Ag, and Au. – A signifi cant part of the iron was in the form of pyrite. The drainage currently coming The distribution of Acidithiobacillus ferrooxidans and Leptospirillum ferrooxidans from a pyrite deposit – in the Richmond Mine, seepage from a tailings pile and AMD storage tanks outside this mine

Occurred in slime-based communities at pH >1.3 at temperatures below 30°C Affect precipitation of ferric iron but seemed to have a minor role in acid generation active role in generating ferric iron as an oxidizing agent Acidithiobacillus ferrooxidans Abundant in subsurface slime-based communities. Occurred in planktonic form at pH values in the range of 0.3–0.7 between 30 and 50°C active role in generating ferric iron as an oxidizing agent L. ferrooxidans

The Richmond Mine revealed the presence of Archaea in summer and fall months: Archaea represented ∼ 50% of the total population correlated these population fluctuations with rainfall and conductivity, (dissolved solids), pH, and temperature of the mine water Ferroplasma acidarmanus, grew in slime streamers on the pyrite surfaces. extremely acid-tolerant : pH optimum at 1.2 Its cells lack a wall Archaean order Thermoplasmales