Acid Mine Drainage

Photo: Distribution of coal-bearing strata in
the Appalachian region study area. Dots
indicate corehole locations. Green, areas
having a low potential for acid mine
drainage (AMD) from surface mining; red,
areas having high AMD potential; yellow,
areas having intermediate AMD potential.

Acid mine drainage in a watershed can be a consequence of mining coal or mineral deposits. A significant amount of scientific research has been conducted to determine the chemical reactions that create acidity and lead to the precipitation of dissolved metals, but despite improvements in both prediction and prevention methods, acid mine drainage problems persist. The acidity of coal-mine drainage is caused primarily by the oxidation of the mineral pyrite (FeS₂), which is found in coal, coal overburden, and mine waste piles. The rate of pyrite oxidation depends on the following: reactive surface area of the pyrite, the oxygen concentration and pH of the water, the forms of pyrite, and the presence of Fe-oxidizing bacteria (Thiobacillus ferroxidans).

Many passive and active treatment systems have been developed to treat coal-mine drainage in order to raise the pH of the water and to control the precipitation of dissolved metals. However, predicting and preventing acid mine drainage from occurring is preferable to having to perform remedial treatment once the problem has occurred. Both static and kinetic chemical tests have been developed to aid in predicting potentially acidic drainages. Acid-base accounting of the rock strata that is disturbed (overburden) is commonly determined. One test measure resulting from these chemical analyses is the neutralization potential (NP), which can be combined with other parameters such as maxiumum potential acidity to provide a predictive guide as to whether acidic drainage will be created. 

Photo: An example of acid mine
drainage water.

Although mining-related environmental degradation of streams occurs throughout the Appalachian Basin, problems are most acute where mining occurs in upper Middle and Upper Pennsylvanian age strata. The USGS and WV Geological and Economic Survey conducted a pilot study to core these strata and examine the mineralogy and neutralization potential of the rocks with analyses conducted on one-foot intervals of rock in order to examine the spatial variability of the deleterious materials over the northern and southern coal fields of WV. In this study, the results using down-hole geochemical wireline logging (GCL) were compared to the core analyses. GCL has the advantage of "real-time" anlaysis and provides a down-hole log of net neutralization potential. Results of CGL showed a good qualitative record of iron, sulfur, and calcium but could not be quantitatively compared to the core analyses.

References

Dulong, F.T., Fedorko, Nick, Renton, J.J., and Cecil, C.B., 2002, Chemical and Mineralogical Analyses of Coal-Bearing Strata in the Appalachian Basin: U.S. Geological Survey Open-File Report 02-489.
http://pubs.er.usgs.gov/usgspubs/ofr/ofr02489

Sue Tewalt
Project Chief

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Manganese Remediation System

Manganese Remediation System

High metal concentrations are common in coal mine drainage; greatest concentrations are generally iron, aluminum, and manganese. Manganese is an aesthetically undesirable metallic element that is very difficult to remove from mine drainage that has acidic to neutral pH. In spite of the thermodynamic prediction that oxygen in the atmosphere or in solution should oxidize dissolved manganese (Mn2+) to an oxide or a... [+]

Photo: USGS personnel at the main
entrance to the Mine Drainage Limestone
Treatment facility at Little Toby Creek, PA.

hydroxide, this does not happen in acidic aqueous solutions. The capability of ozone to oxidize and precipitate manganese as anoxide was proven in bench-scale experiments at U.S. Geological Survey (USGS) labs, and the process was granted U.S. patent no. 6,485,696. In addition to manganese, the treatment should also precipitate as oxides or hydroxides: iron, nickel, cobalt, lead, silver, palladium, bismuth and thallium, if they are present in the water. USGS personnel involved in developing the methodology were Dr. Motoaki Sato and Dr. Eleanora Robbins, both presently retired from the USGS.

A prototype system was built to test the method of manganese remediation in a field test on mine drainage. The USGS installed the pilot-scale treatment system at the Little Toby Creek Treatment Plant in Elk County, PA, which is a limestone-based acid mine drainage treatment plant run by the Pennsylvania Department of Environmental Protection. The manganese treatment system was commissioned in March 2004.

Photos: The prototype USGS manganese (Mn) remediation system at Little Toby, which uses ozone to oxidize Mn and precipitate it from the mine drainage.

Mine drainage water samples, collected prior to and following ozone treatment, were analyzed for manganese and trace metals and showed that manganese concentrations were lowered by about 98 percent, iron by 99 percent, cobalt by 78 percent, and nickel by 8 percent. Measurements of Eh-pH values in the water samples subjected to ozone treatment demonstrate a shift from the Mn2+ field into the manganese dioxide (Mn4+) stability field.

The prototype system was removed from Little Toby Creek Treatment Plant and shipped to James Madison University (JMU) in Harrisonburg, VA. A Technical Assistance Agreement between the USGS and JMU existed from 2006 through February, 2011. Currently JMU has a research patent license and students in the College of Integrated Science and Technology (CISAT) continue to work with the equipment on further refinements and innovations to the methodology. The USGS has also entered into an exclusive license agreement with Ozone Technology Inc. on U.S. Patent No. 6,485,696.

USGS Links

USGS Mine Drainage Activities

USGS Microbiology of Acid Mine Drainage

USGS Public Health Website

USGS Health and Environment Fact Sheets

Energy Resources Program - Produced Waters

Energy Resources Program - Mercury and Selenium

External Links

Acid Drainage Technology Initiative

American Society of Mining and Reclamation

Office of Surface Mining