Introduction to ACID ROCK DRAINAGE

Oxidation of sulphides exposed to water and oxygen in waste rock piles or mine workings

Oxidation of pyrite by oxygenFeS2 + 7/2 O2 + H2O

= Fe2+ + 2SO42- + 2H+

Oxidation of Fe2+ to Fe3+

Fe2+ + 1/4 O2 + H+ = Fe3+ + ½H2O

Further oxidation of pyriteFeS2 + 14Fe3+ + 8H2O = 15Fe2+ + 2SO4

2- + 16H+

Metal Solubility vs pHMany toxic metals are mobile in acidic water

Sol

ubili

ty

pH

1 2 3 4 5 6 7 8 9 10 11 12

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

Dry Cover:Layers of non acid generating (NAG) carbonate rich rock

and clay covered with vegetation. Prevents water percolating through

Problems: Erosion, subsidence, slope failureNot 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

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/sullivan_mine.htm• See MEND 13th annual BC Workshop File

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