Case studies

Witwatersrand Central Basin

Acid Mine Drainage Treatment Plant.

Proxa's treatment plant to maintain Acid Mine Drainage

THE CHALLENGE

The main objective of the treatment plant is to maintain the Acid Mine Drainage (AMD) below the Environmental Critical Level to prevent flooding risks to shallow groundwater, flooding of underground infrastructure, increased seismic activity and decanting, which would impact major river systems.

OUR SOLUTION

An Acid Mine Drainage Treatment Plant designed for a maximum treatment capacity of 84 Ml/day.

TREATMENT PROCESSES & CAPACITIES

The AMD neutralisation process entails a modified High Density Sludge process

  • Pre-neutralisation of the feed AMD using limestone to remove free acidity, aluminium associated acidity and a fraction of feed iron.
  • Aeration to oxidise the ferrous iron and manganese.
  • Conditioning of recycled sludge using lime.
  • Final neutralisation with lime.
  • Gypsum crystallisation of the excess supersaturated calcium sulphate.
  • Solid separation in dedicated clarifiers/thickeners.
  • Handling and disposal of waste sludge, mainly containing metals hydroxides and gypsum.

PROCESS RELIABILITY

PROXA is responsible for operations of the AMD plant within the guidelines as set by the Department of Water Affairs (DWA) and National Department of Environment Affairs (DEA). Responsibility also includes preventative and corrective maintenance of the AMD plant and equipment.

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