Introduction to ACID ROCK DRAINAGE

1
Introduction to ACID ROCK DRAINAGE
Oxidation of sulphides exposed to water and
oxygen in waste rock piles or mine
workings Oxidation of pyrite by oxygen FeS2
7/2 O2 H2O Fe2 2SO42- 2H Oxidation
of Fe2 to Fe3 Fe2 1/4 O2 H Fe3
½H2O Further oxidation of pyrite FeS2 14Fe3
8H2O 15Fe2 2SO42- 16H
2
Metal Solubility vs pHMany toxic metals are
mobile in acidic water
Solubility
1 2 3 4 5 6 7 8
9 10 11 12
pH
3
Neutralization of Acid RockDrainage

• Carbonate dissolution
• CaCO3 H ? Ca2 HCO3- pH 7-8

Or exclude either oxygen or water with either a
dry or a wet cover over waste rock pile or
tailings
4
Dry Cover

• Layers of non acid generating (NAG) carbonate
  rich rock and clay covered with vegetation.
  Prevents water percolating through
• Problems Erosion, subsidence, slope failure
• Not completely impermeable as clay cracks when
  dry
• Lack of oxygen, recognised after four deaths at
  Sullivan Mine, Cranbrook.
• Reducing environment can mobilize arsenic Snow
  Lake

5
Sullivan Pb-Zn Mine Accident

• Four people were killed at a decommissioned mine
  May 2006, Kimberley, SE BC.
• Douglas Erickson, 48, a contractor from nearby Ha
  Ha Creek. Robert Newcombe, 49, a Teck Cominco
  employee who lived in Cranbrook,
• Kim Weitzel, 44, a paramedic from Kimberley.
  Shawn Currier, 21, a paramedic who lived in
  Cranbrook.
• The victims apparently succumbed to fumes in a
  small building at the decommissioned Sullivan
  mine, where Erickson had been testing the water.
• Initially H2S was suspected to be the cause.
• The shed, which measures just 9m2, has a hole in
  its floor through which technicians perform
  monthly tests on water draining from the former
  Pb, Zn, Ag Sullivan mine owned by Teck Cominco.
• Erickson was apparently overcome by fumes when he
  entered the pump house shed on Monday to perform
  tests. His spouse sounded the alert when he
  hadn't been heard from two days later.
• Newcombe then went into the shed, saw Erickson's
  body floating in the well and called 911 for help
  before collapsing himself.
• The two paramedics who rushed to the scene also
  succumbed to fumes in the shed.
• All four bodies were recovered by a fire rescue
  crew equipped with oxygen masks.
• Fred Hermann, B.C.'s chief mines inspector,
  wouldn't speculate about the exact cause of the
  deaths.
• "We do know there was an oxygen-deficient
  atmosphere inside the shed," Hermann said.
• http//www.mediaroom.gov.bc.ca/sullivan_mine/sulli
  van_mine.htm
• See MEND 13th annual BC Workshop File

6
Wet Cover

• Keep O2 out by submerging tailings
• Environment remains
• reduced, and oxidation
• does not happen.
• Problem
• Keeping water level
• high over a long period
• of time
• Old dykes built to hold solids not water e.g.
  Ruttan Mine, Leaf Rapids