Acid Mine Drainage

Orange is the color that usually comes to mind when someone mentions acid mine drainage (AMD).  But AMD can manifest itself in many different colors:

	ORANGE:  Orange is the most common AMD color.  The orange material is iron oxide, which is basically rust.
	YELLOW:  When the pH of AMD is raised past 3, either through contact with fresh water or neutralizing minerals, previously soluble Iron(III) ions precipitate as Iron(III) hydroxide, resulting in a yellow-orange solid colloquially known as yellow boy.
	WHITE:  If the AMD discharge is white, it has especially high concentrations of aluminum.  As the water becomes less acidic, the aluminum combines with oxygen to form solid particles that cause a “milky” appearance or white coating.
	BLACK:  If the AMD discharge is black, it has especially high concentrations of manganese.
	CLEAR:  Ironically, the worst AMD is clear because the water is so highly acidic that the minerals remain dissolved and do not precipitate away.  Water bodies that are this acidic cannot support much life.

Acid mine drainage typically has four key characteristics (though not all drainages have all four characteristics):

• High acidity (hence the name “acid mine drainage”)
• High metal concentrations (iron is most common)
• High sulfate levels
• Excessive suspended solids (which smothers insects and other aquatic life)

Adapted from SCRIP

Acid mine drainage (AMD) is the outflow of acidic water from (usually abandoned) metal or coal mines.  AMD may also occur in other areas where the earth has been disturbed, such as construction sites, subdivisions, transportation corridors, etc.  AMD is also typical downstream from coal stocks, coal handling facilities, and coal washeries.

AMD occurs when mineral pyrite (FeS2) is exposed to air and water, resulting in the formation of sulfuric acid and iron hydroxide.

Water that comes in contact with pyrite usually turns a characteristic orange-red or yellow-orange color.  The orange material is iron oxide, which is basically rust.

Adapted from Wikipedia.