Mine drainage refers to the water that flows from or is pumped out of active or historical mining operations — including open pits, underground workings, waste rock dumps, tailings storage facilities, and heap leach pads — and which may carry dissolved metals, acidity, suspended solids, and other contaminants depending on the mineralogy of the ore and host rock being mined. It is one of the most significant and long-lasting environmental challenges in the global mining industry, affecting gold, coal, iron ore, bauxite, diamond, and base metal mines. The most problematic form is acid mine drainage (AMD), also known as acid rock drainage (ARD), which occurs when sulphide minerals (such as pyrite, FeS₂) present in ore or waste rock are exposed to oxygen and water, triggering oxidation reactions that generate sulphuric acid and mobilize toxic heavy metals such as arsenic, cadmium, lead, zinc, and mercury into drainage waters. Bauxite mining generates drainage that may carry elevated levels of aluminium, silica, and caustic soda from refinery operations. Gold mine drainage may contain dissolved cyanide, thiocyanate, and associated metals from heap leach or CIL operations. Iron ore mine drainage is typically less chemically complex but may carry high suspended solids and iron concentrations. Diamond mine drainage management is focused primarily on controlling tailings dam seepage and maintaining water balance in processing circuits. Mine drainage is managed through a combination of source control (minimizing water contact with reactive materials), interception and collection systems, treatment technologies (lime neutralization, passive wetlands, reverse osmosis), and diversion of clean water away from contaminated areas. Post-closure mine drainage management can continue for centuries and represents a perpetual liability for mine operators and governments.
