AMD occurs when sulphide-bearing minerals in rock are exposed to air and water, changing the sulphide to sulphuric acid. This acid can dissolve heavy metals found in waste rock and tailings such as lead, zinc, copper, arsenic, selenium, mercury, and cad-mium, into ground and surface water. Certain bacteria, naturally present, can significantly increase the rate of this reaction. AMD and heavy metals pollution can poison ground and drinking water. AMD can destroy aquatic life and habitat.
Acid drainage can and does occur naturally at specific sites.
It happens when sulfide minerals are exposed to weathering and react with water and oxygen to produce sulfuric acid, which is carried away in runoff. Acid generation results from exposure to air and water. This means that the more surface area of rock exposed, the greater the amount of acid. During the mining process, hundreds, sometimes thousands of tons of rock are dug up and crushed each day. The acid then leaches through the ground and releases heavy metals such as lead, zinc, copper, arsenic, selenium, mercury and cadmium.