Mining Impacts · impact
Acid mine drainage
Water · Both
- Category
- Water
- Timescale
- Both
Mitigation
Flooding old workings to exclude oxygen, capping and lining waste rock, adding limestone to neutralise; where the load is too large, treating the water indefinitely.
Case
The Richmond mine at Iron Mountain, California has produced the most acidic water ever measured — pH as low as −3.6, with dissolved metals up to 200 g/L (Nordstrom & Alpers, 2000).
Mechanism
Sulfide minerals — pyrite above all — oxidise on contact with air and water to sulfuric acid, and the acid then dissolves metals out of the surrounding rock. Bacteria accelerate the reaction by orders of magnitude. Once it starts it sustains itself for as long as sulfide and oxygen last, which is centuries.
Where
Open pitUndergroundTailings storage
Open on the Mining Impacts shelf — the interactive card, the filters, and everything alongside it.