Ferrous Iron (Fe2+) Fact Sheet

Definition: A positively charged metal in water that can easily combine with other compounds .

Background:

  • Most waters contain some iron.
  • The presence of large amounts of iron in water is usually caused by acid mine drainage.
  • Large deposits of iron leech into waterways at iron mining sites
  • Iron solids (precipitates) form a reddish-yellow to yellowish-brown coating on rocks .

If a stream has a yellowish red color, it is indicative of a high iron concentration. Sometimes the streams are nicknamed "yellow boys." This stream is draining out of a hillside where an old coal mine is located.

Image Source: National Mine Land Reclamation Center

Pyrite

  • Pyrite is a solid compound of ferrous iron and sulfur, FeS2(s)
  • Pyrite is usually found in coal mining overburden or spoils (the rock and soil that was removed to get to the coal seam) .
  • When Pyrite is exposed to air and water, it becomes oxidized and hydrogen ions are produced which reduces the pH of the water (makes it more acidic).

Oxidation of Pyrite:

FeS2 +3.75 O2 +3.5 H20 = Fe(OH)3 + 2SO4-2 + 4H+

  • Bacteria called Thiobacillus can catalyze the oxidation reaction by producing enzymes if CO2, O2, Fe and small amounts of N & P are present in the water.

 

Iron Ore Tailings
  • 98-99% of what is mined is useless waste, low in iron concentration.
  • The generated waste product is called iron ore tailings.
  • Tailings are deposed of in tailing ponds such as the one below.

One of the main problems with tailing ponds is that they often overflow due to flooding or poor construction. When a leak or overflow occurs, streams nearby can become heavily polluted by the high concentration of iron.

Image Source: National Mine Land Reclamation Center

Water Quality:

The EPA drinking water standard requires ferrous iron to be less than 0.3 mg/L.