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Protecting against acid rock
drainage is important at mines
where sulfide minerals are present.
Image: G. Plumlee, USGS
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When pyrite (iron sulfide) comes in
contact with oxygen in air or water, it
“oxidizes” and turns into rusty iron
oxides and sulfuric acid. Certain bacteria
make this process go faster.
Image:
Travis
Hudson
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Sulfuric acid from oxidation of pyrite
causes nearby soil and water to be
acidic (acid rock drainage) and can
harm habitat.
Image: Travis Hudson
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Preventing oxygen from
contacting pyrite prevents acid
rock drainage.
Oxygen
Pyrite
Images: USGS
Bacteria
Sulfuric
Acid
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Covering pyrite-bearing rocks with
specially designed soil layers inhibits
infiltration of oxygen-bearing water and
neutralizes acidic conditions.
Revegetated Pile Surface
Soil Growth Medium
Uncompacted Lime-amended wasterock
12”
12”
Compacted consolidated wasterock
Image: Kennecott Utah Copper Mine
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Constructed wetlands can remove dissolved
metals from certain types of acid rock drainage
and prevent continued oxidation of pyrite or
other sulfide minerals.
Before
After
Images: ASARCO, Inc.
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In some cases, treatment plants add lime
and other chemicals to acid rock
drainage that neutralize the acidic waters
and help remove dissolved metals.
Image: Atlantic Richfield Company
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Uncontrolled acid rock drainage is
most commonly associated with old
mine sites.
Image: E. Schneider, ESA Consultants Inc.
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Modern mines use acid rock
drainage control and prevention
techniques to protect the
environment.
Image: Kennecott Utah Copper Mine
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