Acid mine drainage and pollution: two case histories from South Africa

Abstract

Different types of waste waters and effluents may be produced as a result of mining. They arise due to the extraction or preparation of the mineral deposit or from the disposal of associated spoil. 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 the mine or are present in the 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 Transvaal where acidic waters were produced by heaps of pyrite discard. As the mine was due to close, the problem of possible groundwater pollution due to acid mine drainage had to be investigated as part of the environmental management programme. The second case history involves a coal mine in the Eastern Transvaal which was seeping an appreciable load of acidic effluent and salts into the headwaters of the Vaal River, which is a major source of water to the main industrial conurbation of the country. Investigations which included a study of the history of the site, geology, geophysics, hydrology, hydrogeology and geochemistry succeeded in clarifying the sources of the acidic seepage and the remedial measures that would have the greatest chance of success.