TECHNICAL INFO

WHAT IS AMD? (a tutorial)

PUBLISHED PAPERS (select from list to view in PDF format)

• Sustained Treatment of AMD Containing Al and Fe 3+ with Limestone Aggregate
  Neil Wolfe, Robert Hedin and Ted Weaver
• Passive Treatment of Acidic Coal Mine Drainage: The Anna S Mine Passive Treatment Complex
  Robert Hedin, Ted Weaver, Neil Wolfe and Kimberly Weaver
• Optimizing the Design and Operation of Self-flushing Limestone Systems from Mine Drainage Treatment
  Hedin Environmental
• Iron Removal by a Passive System Treating Alkaline Coal Mine Drainage (Lowber)
  Robert S. Hedin
• Recovery of Marketable Iron Oxide from Mine Drainage
  Robert S. Hedin
• Acid Mine Drainage Flowing from Abandoned Gas Wells
  Robert S. Hedin, Sherry L. Stafford, and Theodore J. Weaver
• Technology and Design Advancement in Passive Treatment System Flushing
  Kimberly R. Weaver, P.E., Kathleen Langanese, P.E., and Robert S. Hedin, Ph.D.
• The Use of Measured and Calculated Acidity Values to Improve the Quality of Mine Drainage Datasets
  Robert S. Hedin
• IC 9389 Passive Treatment of Coal Mine Drainage
  Robert S. Hedin, Robert W. Nairn, and Robert L. P. Kleinmann
• DOE/NETL The Passive Treatment of Coal Mine Drainage
  George Watzlaf, Karl T. Schroeder, Robert L. P. Kleinmann, Candace L. Kairies, and Robert W. Nairn
• A Method for Predicting the Alkalinity Generated by Anoxic Limestone Drains
  George Watzlaf and Robert S. Hedin
• Passive Treatment of Acid Mine Drainage with Limestone
  Robert S. Hedin, George R. Watzlaf and Robert W. Nairn

 

WHAT IS AMD?

The Definitions

• OK, So What Is AMD?
• The Chemistry
• Why is AMD Harmful?
• AMD Treatment
• For More In-depth Information on AMD Chemistry and Treatment, click HERE.

The Definitions

AMD most commonly refers to Acid Mine Drainage.  This means water that is net acidic, usually containing metals such as iron, manganese, and aluminum, as well has high levels of sulfate.  However, not all polluted water that comes from mines is acidic.  

Therefore, AMD can also mean Alkaline Mine Drainage.  While this water may still be contaminated with iron, manganese, and sulfate, it is net alkaline and does not contain aluminum.

In order to encompass both of these pollution types, some people define AMD as Abandoned Mine Drainage.  This terminology, however, fails to acknowledge pollution that is generated on active mines (thus the possibility Active Mine Drainage).

OK, So What IS AMD?

AMD is polluted water that has resulted from some type of mining or earth disturbance.  In Pennsylvania, AMD is most often associated with surface or deep coal mining.  AMD is caused when iron and sulfur-containing minerals are exposed to air and water.  Pyrite, commonly called "Fool's Gold,"  is one such mineral.  Pyrite is often found in rocks near coal seams, so when the coal is mined, the pyrite is exposed, beginning a series of chemical reactions.  Although the pH of AMD may be nearly neutral, it is not uncommon for the pH of AMD to be around 2. 

The Chemistry

For the chemically inclined, the following reactions detail steps in the formation of AMD.  Not all reactions occur on all sites, but these are the primary reactions that occur.

pyrite oxidation	FeS2 + 7/2 O2 + H2O—>Fe2+ + 2SO42- + 2H+
acid dissolution of clays	Clay + H+ —> SiO2 + Al3+ + Mg2+ + Ca2+ + Mn2+
acid neutralization by calcite	CaCO3 + 2H+—> Ca2+ + H2O + CO2
ferrous iron oxidation	Fe2+ + ¼ O2 + H+—> Fe3+ + ½ H2O
ferric iron hydrolysis (produces "Yellow Boy")	Fe3+ + 3OH —> Fe(OH)3
aluminum hydrolysis	Al3+ + 3OH —>Al(OH)3
summed iron oxidation and hydrolysis reactions	Fe2+ + ¼ O2 + 5/2 H2O>>Fe(OH)3 + 2H+
acid neutralization by bicarbonate ion	H+ + HCO3 —> H2O + CO2
acid neutralization by hydroxyl ion	H+ + OH —>H2O

Note: Equations are for illustration only and may not be balanced.

Why Is AMD Harmful?

AMD can be harmful to humans and ecosystems for the following reasons:

• Aluminum is toxic to humans (though this is not well understood) and is highly toxic to fish and other aquatic organisms.

• Most aquatic organisms require net alkaline, neutral pH conditions for survival, and AMD is often net acidic with very low pH.

• Iron forms a solid and coats the bottoms of streams, smothering aquatic bugs and organisms that form the base of the food chain.  This solid can also coat the gills of fish, choking them.

• High sulfate levels cause

• Iron and manganese cause problems with domestic water systems (scale, clogged pipes, orange clothing).

• AMD-polluted water cannot be used for industrial purposes.

• High sulfate levels can cause taste and odor problems in drinking water, and may cause digestive problems.

AMD Treatment

The type of AMD treatment that is most appropriate depends upon the type of AMD, the amount (flow rate of AMD), and the space available for treatment.  Before the 1980's, expensive chemical plants were the only way to treat AMD.  However, techniques developed since that time, collectively called Passive Treatment, use nature's own products to treat AMD.  Hedin Environmental specializes in the design and implementation of effective, reliable passive treatment systems.  Click HERE for a more in-depth discussion on Passive Treatment.

TO TOP