Abstract
Factors which play a role in acid mine drainage (AMD) formation were investigated over a period of 12 months. These include climatic, mineralogical, hydrological and oxygen diffusion parameters. The oxygen diffusion data reveal that the flow of oxygen in the Witwatersrand tailings dams is controlled by secondary porosity (i.e. cracks caused by roots on the dam surface). The age of the dam does not have a significant bearing on the extent to which the oxidised zone development and subsequently AMD can progress. Most of these processes take place within the first 3 m of the dams. The amount of rainfall plays a crucial role in determining the extent to which an oxidised zone progresses. The average oxidised zone in the 5 sites is 2.4 m ranging from 2.2 to 3.5 m. Water SA Vol.32 (4) 2006: pp.499-506
Highlights
In tailings storage facilities, acid mine drainage (AMD) occurs when sulphide minerals in tailings are oxidised, because of exposure to moisture and oxygen
Sulphuric acid was added to each sample for preservation
Paste pH done at the PHD Inc. laboratory involved making a 1:10 ratio of sample to water, measured after 24 h, which allowed for a more realistic determination of the current pH and allowed reactions to be more complete than an instantaneous or 10 min analysis
Summary
AMD occurs when sulphide minerals in tailings are oxidised, because of exposure to moisture and oxygen. This results in the generation of sulphates, metals and acidity that can have manifold environmental consequences. When AMD is generated, it can have undesirable effects on the ecosystem. Results can include contaminated water, disrupted growth and reproduction of aquatic plants and animals. Dissolved metals and acidity can affect plant and animal populations. Seven sites across the Witwatersrand Basin were identified for this study.
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