 EPOD - a service of USRA

The Earth Science Picture of the Day (EPOD) highlights the diverse processes
and phenomena which shape our planet and our lives. EPOD will collect and
archive photos, imagery, graphics, and artwork with short explanatory
captions and links exemplifying features within the Earth system. The
community is invited to contribute digital imagery, short captions and
relevant links.


 Archive - Acid Mine Drainage Chemistry

   November 21, 2020

    Acidminedrainagea copy

   Every weekend we present a notable item from our archives. This EPOD
   was originally published November 21, 2003.

   Provided and copyright by:  Enver Murad,  Bayerisches
   Geologisches Landesamt
   Summary author:  Enver Murad

   Pyrite (iron sulfide) is a common constituent of lignites and coals.
   This pyrite oxidizes as it is exposed to the atmosphere in the course
   of mining, leading to the generation of sulfuric acid and dissolved
   iron (acid mine drainage). Besides the detrimental effect that the
   acidity has on the environment, this process often leads to an
   extensive generation of ochreous precipitates.

   In the example shown here, waters draining a sulfide-rich lignite seam
   in the Czech Republic precipitate under different conditions.
   Initially, a bright orange precipitate, consisting mainly of the
   sulfate-containing mineral schwertmannite, forms under acid conditions.
   After merging with alkaline waters (entering from the right-center of
   the picture), iron that has remained in solution precipitates almost
   instantaneously as ferrihydrite, a poorly-crystalline, sulfate-free
   iron oxyhydroxide, leading to a sudden change of precipitate color to
   reddish-brown. The variations in color can thus serve as indicators for
   the precipitate composition, and thereby for the conditions under which
   the precipitates formed.

   For more information on this locality, see the article by  Murad and
   Rojík in American Mineralogist vol. 88, 2003, pp. 1915-1918


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