Witwatersrand gold tailings and acid mine drainage

PhytoremediationField scale, 2003–2010

Tamarix usneoides, Searsia lancea, Searsia pendulina, Combretum erythrophyllum, Eucalyptus spp.

Mine Woodlands Project (University of the Witwatersrand with AngloGold Ashanti): trees planted in the seepage pathways of tailings dams to raise evapotranspiration, exert hydraulic control over the drainage and immobilise contaminants in biomass and rhizosphere. Trials began in 2003 at the Vaal River and West Wits mining operations; 48 indigenous tree species were assessed to limit the use of exotics, with potentially invasive species excluded.

Outcome Trees with roots in shallow water tables transpired 1,000–1,400 mm a year, against about 570 mm of evapotranspiration from grass-dominated vegetation; over deep water tables they were limited to about 700 mm. Good survival and reasonable growth for Tamarix usneoides, Searsia lancea, Searsia pendulina and Combretum erythrophyllum. For a 484 ha tailings dam at Vaal River, with seepage estimated at 547,500 m³ a year, 137 ha of trees might be enough to match it. The authors report sequestration of sulphur and metals and name salt build-up in the root zone, fire and pathogens as risks.

• Acid mine drainage
• Sulphates

• Dye P.J., Weiersbye I.M. The Mine Woodlands Project in the Witwatersrand Basin gold fields of South Africa: strategy and progress. In: Wolkersdorfer & Freund (eds), Mine Water and Innovative Thinking, IMWA 2010, Sydney NS, pp. 471–474, imwa.info, 2010