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
Components of AMD 4FeS 2 + 14O 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 3 - + H + 2. Pyrites oxidation as a result of ingress water running through broken rock; 4FeS 2 + 14O 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.
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 2014. Selected technology based on capital and running costs, performance, process stability. 4.Pumping or not