South Africa - Inkaba.org
South Africa - Inkaba.org
South Africa - Inkaba.org
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Low Enthalpy Geothermal Energy purification of Acid Mine<br />
Drainage, and storage of potable water in the deep gold mines<br />
of <strong>South</strong> <strong>Africa</strong><br />
1 T.Ntholi, 2 M.de Wit<br />
1. AEON- University of Cape Town, <strong>South</strong> <strong>Africa</strong>, thakane.ntholi@gmail.com<br />
2. AEON- University of Cape Town, <strong>South</strong> <strong>Africa</strong>, maarten.dewit@uct.ac.za<br />
ABSTRACT<br />
The total volume of interconnected voids beneath the Witwatersrand, as a result of more than a century of deep<br />
gold mining, is ≈ 6x10 6 -9x10 6 ML, at least double the volume of the Vaal dam. Most Witwatersrand mines<br />
experience undesired water inflow from overlying aquifers. Operating mines invest resources to pump out the<br />
water but abandoned mines are left to fill. The inflowing water evolves into acid mine water (AMW) as a result of<br />
acid mine drainage (AMD). The AMD results from the hydrolysis and oxidation of pyrite and other sulphide<br />
minerals, producing high acidity, sulphate ions and dissolution of heavy metal ions from their host minerals. The<br />
AMW will continue to fill the mines until it eventually intersects the overlying water table and contaminate ground<br />
water. In the East and Far West Rand, AMW is already decanting into natural rivers systems while in areas like the<br />
Central Rand, it will do so in the near future.<br />
We explore the viability of an in-situ, geothermally driven AMW purification system that can treat the AMW<br />
within the mines before it reaches the water table. With such a scheme the voids can be allowed to naturally fill up<br />
with water without posing a threat to the fresh ground water resources. The mines can then be used as underground<br />
water reservoirs for the Gauteng region. The added benefit is that residual gold and other metals could be<br />
chemically recovered from this system, and there will be no evaporation loss from this water reservoir.<br />
The Witwatersrand basin has low geothermal gradient ≈18⁰C/km. The mines reach depths up to 4000m, and the<br />
available geothermal energy is near renewable if exploited carefully. Whilst this low enthalpy geothermal energy<br />
may not be high enough for electricity generation, it is enough to drive localised chemical purification systems.<br />
KEYWORDS: Gauteng, deep gold mines, geothermal energy, Acid Mine Drainage, Geochemistry, fresh water<br />
reservoirs<br />
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