Different types of waste waters and effluents may be produced as a result of mining. Generally, the major pollutants are suspended solids, dissolved salts or acidity. In the latter case, acid mine drainage refers to the oxidation of sulphide minerals, notably pyrite, which are exposed in a mine or are present in spoil. The primary oxidation products of pyrite are ferric and ferrous sulphates, and sulphuric acid. Two case histories are provided which deal with the problem of acid mine drainage associated with mines in South Africa. The first refers to a tin mine in the North West Province where acidic waters were produced by heaps of pyrite discard. The second refers to a mine in the Witbank Coalfield where acid groundwater emerges from the mine as springs and to has led to the decimation of vegetation, and to the eradication of aquatic flora and fauna in a nearby stream.
The term acid mine drainage is used to describe natural oxidation of sulphide minerals which occur in mine rock or waste which are exposed to air and water. This is a consequence of the oxidation of sulphur in the minerals to a higher oxidation state. If acid mine drainage is not controlled it can pose a serious threat to the aquatic environment since acid generation can lead to elevated levels of heavy metals and sulphate in the water which obviously has a detrimental effect on its quality. Certain conditions including the right combination of mineralogy, water and oxygen are necessary for the development of acid mine drainage. Such conditions do not always exist. The ability of a particular mine rock or waste to generate net acidity depends on the relative content of acid generating minerals and acid consuming or neutralizing minerals.
