Acid Mine Water – Can it be a valuable resource?

Waterfall, Witwatersrand National Botanical Gardens

The farm where gold was first discovered in 1886 by that an Australian gold miner, George Harrisonfarmgold 1886

SA mineral reserves and production (% of World) (from: DME, South Africas mineral industry 2006/2007) CommodityReservesProductio n Platinum87.7 (1)59.3 (1) Vanadium31.0 (1)48.0 (1) Zirconium19.4 (2)41.6 (2) Ferro-chromium-40.5 (1) Vermiculite38.9 (2)39.6 (1) Chrome ore72.4 (1)38.7 (1) Alumino-silicates-36.4 (1) Titanium minerals18.3 (2)19.8 (2) Manganese ore80.0 (1)13.3 (2) Gold40.1 (1)11.1 (1) Ferro-Mn/Fe-Si-Mn6.0 (4) Fluorspar16.7 (2)5.0 (4) Coal6.1 (8)4.5 (5)

Water quality of gold mines in Gauteng

Decant water from gold mines in Gauteng BasinFlow rate (Ml/day) Far Western65 Western60 Central100 Eastern120+ Total for Gauteng gold mines 345+ Mpumalanga coal mines 80+

Limited area

Question Can we deal with this problem in a cost-effective way?

Neutralized mine water

CONSEQUENCES OF OVERFLOWING Pyrite (FeS 2 ) or Fools Gold remains stable when deep underground..... but if exposed to 0 ² and H ² 0 (through decanting) it decomposes and forms Acid Mine Drainage (AMD) Environmental Critical Level is approximately 23m below water level – lowest natural spring 10

National Water Act of 1998 Key Principles Decentralization Equitable access Efficiency Sustainability Key instruments: Polluter pays principle Mine closure certificate

Decant started March 2002 – Harmony emergency measures Directives and apportionment (2006) Randfontein Estates Gold Mine (Harmony 46%) West Witwatersrand Gold Mine (DRD 44%) Mogale Gold Mine (Mintails 0.8%) Co-operation agreement between Mintails and DRD Heads of Agreement between Harmony, DRD and Mintails Apportionment 12

What is mine water? What is mine water not?

Components of AMD 4FeS O 2 + 4H 2 O 4FeSO 4 + 4H 2 SO 4 1. Free acid: H 2 SO 4 already partially neutralized 2. Fe(II) acid: Cannot react with limestone/dolomite 3. Low concentrations of heavy metals 4. Salt (Ca, SO 4 )

How does AMD form? 1. Dissolution of limestone/dolomite CaCO 3 + H 2 O Ca 2+ + HCO H + 2. Pyrites oxidation as a result of ingress water running through broken rock; 4FeS O 2 + 4H 2 O 4FeSO 4 + 4H 2 SO 4 3. Neutralization (natural attenuation) H 2 SO 4 + CaCO 3 CaSO 4 + CO 2 + H 2 O 4. Reciprocating contact of pyrites-rich ore with water and oxygen as the water level fluctuates from water being pumped out at a constant rate while the incoming water flow-rate fluctuates with seasonal rainfall.

Water quality of gold mines in Gauteng

Volume of mine water under Johannesburg Kariba Lake = 185 km 3 or Ml

Battery acid AcidAcidity (mg/l CaCO3) Eastern Basin50 Western Basin1800 Central Basin1500 Battery Acid Gas cool drink800

Game Reserve put at risk

Four point plan 1.Encourage mining activities to stimulate job creation (reduced labour cost, beneficiation of raw materials). The pumping and treatment cost should be offset by the value of the mined minerals, the treated water, and dissolved by-products reclaimed from the mine water. 2.Immediate implementation of: – limestone neutralization for removal of free acid, iron(II) and partial desalination. – lime treatment for removal of toxic heavy metals and radioactivity, – In the case of Grootvlei Mine, water is already neutralized due to natural attenuation - Passive treatment 3.Implement desalination to meet water demand by Selected technology based on capital and running costs, performance, process stability. 4.Pumping or not