Protecting against acid rock Protecting against acid rock drainage is important at mines drainage is important at mines

where sulfide minerals are present.where sulfide minerals are present.

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Image: G. Plumlee, USGS

When pyrite (iron sulfide) comes in When pyrite (iron sulfide) comes in contact with oxygen in air or water, it contact with oxygen in air or water, it “oxidizes” and turns into rusty iron “oxidizes” and turns into rusty iron

oxides and sulfuric acid. Certain bacteria oxides and sulfuric acid. Certain bacteria make this process go faster.make this process go faster.

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Image: Travis Hudson

Sulfuric acid from oxidation of pyrite Sulfuric acid from oxidation of pyrite causes nearby soil and water to be causes nearby soil and water to be acidic (acid rock drainage) and can acidic (acid rock drainage) and can

harm habitat.harm habitat.

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Image: Travis Hudson

Preventing oxygen from Preventing oxygen from contacting pyrite prevents acid contacting pyrite prevents acid

rock drainage.rock drainage.

Oxygen

SulfuricAcid

BacteriaPyrite

Metals-4-4Images: USGS

Covering pyrite-bearing rocks with Covering pyrite-bearing rocks with specially designed soil layers inhibits specially designed soil layers inhibits

infiltration of oxygen-bearing water and infiltration of oxygen-bearing water and neutralizes acidic conditions.neutralizes acidic conditions.

Compacted consolidated wasterock

Uncompacted Lime-amended wasterock

Revegetated Pile Surface

Soil Growth Medium 12”

12”

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Image: Kennecott Utah Copper Mine

Constructed wetlands can remove dissolved Constructed wetlands can remove dissolved metals from certain types of acid rock drainage metals from certain types of acid rock drainage

and prevent continued oxidation of pyrite or and prevent continued oxidation of pyrite or other sulfide minerals.other sulfide minerals.

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Before

AfterImages: ASARCO, Inc.

In some cases, treatment plants add lime In some cases, treatment plants add lime and other chemicals to acid rock and other chemicals to acid rock

drainage that neutralize the acidic waters drainage that neutralize the acidic waters and help remove dissolved metals.and help remove dissolved metals.

Metals-4-7Image: Atlantic Richfield Company

Uncontrolled acid rock drainage is Uncontrolled acid rock drainage is most commonly associated with old most commonly associated with old

mine sites.mine sites.

Metals-4-8Image: E. Schneider, ESA Consultants Inc.

Modern mines use acid rock Modern mines use acid rock drainage control and prevention drainage control and prevention

techniques to protect the techniques to protect the environment.environment.

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Image: Kennecott Utah Copper Mine