SETAC Globe - Environmental Quality Through Science
 
  9 June 2011
Volume 12 Issue 6
 

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Mining Water is Threatening Freshwater Supply in South Africa

Vernon Somerset, CSIR Natural Resources and the Environment

In South Africa, a country that is known for its mineral wealth, a new crisis is emerging as abandoned and existing mining activities are generating mega-litres of acidic mine drainage (AMD) that is severely impacting freshwater and groundwater resources. South Africa’s water resources are limited. Some parts of the country are semi-arid, while in other parts communities depend on groundwater sources for drinking water and agricultural activities.

The mining of several minerals, including gold, coal, copper and nickel, is associated with the formation of AMD. AMD is formed when sulphide-bearing material in unprocessed ore, exposed ore and abandoned mining sites is exposed to oxygen and water. Various mining activities can promote the formation of AMD. Sulphate-reducing bacteria also play an important role. Ultimately, the presence of AMD can be very detrimental to the surrounding aquatic environment due to its low pH, and presence of toxic contaminants such as cyanides, heavy metals, sulphates, and phosphates that, in turn, influence human health and lead to serious ecological impacts[1-4].

Figure 1.	A dam receiving raw mine water in the West Rand Area, Gauteng Province, South Africa (Photo: Stephan Du Toit)
Figure 1. A dam receiving raw mine water in the West Rand Area, Gauteng Province, South Africa (Photo: Stephan Du Toit)

The South African AMD problems occur in specific locations within the Witwatersrand area in Gauteng Province. This area has been the main focus of gold mining activities since 1886. After changing to the cyanide extraction process in 1916, the landscape has never been the same. Recent studies of freshwater and groundwater quality in the areas impacted by AMD has shown that the most important source of pollution in the area is the pyrite (FeS2) present in the tailings dumps. Pyrite exposed to the atmosphere during mining and excavation reacts with oxygen and water in a bacterially-mediated process that forms sulfate, resulting in AMD. The groundwater that seeps from the dumps has low pH and Eh, and a high dissolved solids load (high electrical conductivity readings). When the AMD comes in contact with surface water, everything turns red over time due to the precipitation of iron, as can be seen in the Fig. 1.

The government through the Department of Water Affairs, mining companies, research organisations, universities and several non-governmental organisations have been active in advocating for a fast-and-effective approach in dealing with AMD. However, action has been slow and with infrastructure problems experienced at municipal level, there is a growing threat to human and environmental health. In order to limit the adverse effects on the aquatic environment and associated human health concerns, many researchers and lobbyists are calling for fast action.

Despite all the negative publicity on AMD and criticism given to the Departments of Water Affairs and Mining, a plan is on the table and several ministerial task groups have been established to deal with the crisis. Every bit of help is needed to turn the tide, though, and everyone that is following the story on the AMD threat to the environment is asked to help constructively.

Author contact information: VSomerset@csir.co.za

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[1] Akcil A, Koldas S. 2006. Review article. Acid Mine Drainage (AMD): causes, treatment and case studies. Journal of Cleaner Production. 14:1139-1145.
[2] Cheng H, Hu Y, Luo J, Xu B, Zhao J. 2009. Review. Geochemical processes controlling fate and transport of arsenic in acid mine drainage (AMD) and natural systems. Journal of Hazardous Materials. 165:13-26.
[3] Gray NF. 1997. Environmental impact and remediation of acid mine drainage: a management problem. Environmental Geology. 30(1/2):62-71.
[4] Tutu H, McCarthy TS, Cukrowska E. 2008. The chemical characteristics of acid mine drainage with particular reference to sources, distribution and remediation: The Witwatersrand Basin, South Africa as a case study. Applied Geochemistry. 23:3666-3684.
 
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