Protecting against acid rock drainage is important at mines where sulfide minerals are present. Image: G. Plumlee, USGS Metals-4-1

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 Metals-4-2

Sulfuric acid from oxidation of pyrite causes nearby soil and water to be acidic (acid rock drainage) and can harm habitat. Image: Travis Hudson Metals-4-3

Preventing oxygen from contacting pyrite prevents acid rock drainage. Sulfuric Acid Pyrite Bacteria Images: USGS Metals-4-4

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 Metals-4-5

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. Metals-4-6

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 Metals-4-7

Uncontrolled acid rock drainage is most commonly associated with old mine sites. Image: E. Schneider, ESA Consultants Inc. Metals-4-8

Modern mines use acid rock drainage control and prevention techniques to protect the environment. Image: Kennecott Utah Copper Mine Metals-4-9