Alternate solutions for acid mine drainage – making profit from waste (2017)

Kym.L Morton * and John. Bewsey **
*KLM Consulting Services Pty Ltd
**Trailblazer Technologies

Abstract
Acid mine drainage (AMD) has been documented along the Witwatersrand since 1903. Acidic mine-water is created when water and oxygen come into contact with the sulphide mineral pyrite (FeS2), which occurs in underground workings, outcrop, and all mine waste residue dumps. When exposed to oxygen in the vadose zone, mine workings and shafts where water levels fluctuate are the main sources of acidic water. The AMD contains high concentrations of metals, sulphates, and salts.
The current government initiative is to pump out the AMD and add lime. The Department of Water and Sanitation (DWS) has spent over R3 billion on equipping three shafts to raise 166 Ml of water per day from the West, Central, and Eastern basins. This water, which has a pH of around 3, and is then treated by the addition of expensive and scarce lime to a pH of 8 or 9. The water is still not fit for use (drinking or agriculture) but is pumped directly into the nearest watercourse. The change in pH enables some metals to precipitate out, and a super-toxic sludge is dumped at the headwaters of the streams. The released water has extremely high sulphate levels (>2000mg/l) (Department of Water Affairs, 2016).
The government plans a second phase of treatment of the pumped water. Four conventional treatment methods are being considered and the Water Research Commission (WRC) is investigating other less well-known options. All are power-hungry and expensive.
Continuous pumping is cited as a solution to the Gauteng region’s AMD problem, but this exposes more pyrite to oxygen and water, thus increasing the amount of polluted water.

Morton, K.L. & Bewsey, J. (2017) ‘Alternate solutions for acid mine drainage—making profit from waste’, South African Institute of Mining and Metallurgy Water Conference Proceedings, July 2017.