1. Protecting against acid rock drainage is important at mines where sulfide minerals are present.
Image: G. Plumlee, USGS
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2. 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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3. 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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4. Preventing oxygen from contacting pyrite prevents acid rock drainage.
Sulfuric
Acid
Pyrite
Bacteria
Images: USGS
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5. Covering pyrite-bearing rocks with specially designed soil layers inhibits infiltration of oxygen-bearing water and neutralizes acidic conditions.
Revegetated Pile Surface
12”
Soil Growth Medium
Uncompacted Lime-amended wasterock
12”
Compacted consolidated wasterock
Image: Kennecott Utah Copper Mine
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6. 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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7. 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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8. Uncontrolled acid rock drainage is most commonly associated with old mine sites.
Image: E. Schneider, ESA Consultants Inc.
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9. Modern mines use acid rock drainage control and prevention techniques to protect the environment.
Image: Kennecott Utah Copper Mine
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