What is acid rock drainage?

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What is acid rock drainage?
Image G. Plumlee, USGS
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Rocks that contain useful metals commonly contain
sulfide minerals - minerals that combine metal
with sulfur.
Image Travis Hudson
Sulfide minerals in a rock sample
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The most common sulfide mineral is pyrite - or
Fools Gold - a combination of iron and sulfur.
Image R. Busch
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Pyrite occurs widely in rocks including
disseminations through this entire mountain.
Image G. Plumlee, USGS
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When pyrite comes in contact with oxygen in air
or water it oxidizes or turns into rusty iron
oxides and sulfuric acid. Certain bacteria make
this process go faster.
Oxygen
Sulfuric Acid
Bacteria
Pyrite
Images USGS, DeAtley Design
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The sulfuric acid produced by oxidation of pyrite
makes nearby soil and water acidic - this is acid
rock drainage. Acid rock drainage can harm
habitat.
Image Travis Hudson
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Acid rock drainage occurs naturally and is an
environmental concern where sulfide minerals are
mined. There are several ways to control or
prevent acid rock drainage at mines.
Image Travis Hudson
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