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29 August 2013

AMD Debate Technical solutions and funding models for the Acid Mine Drainage problems of South Africa. 29 August 2013. “Sophistication creates Simplicity”. The Challenge.

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29 August 2013

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  1. AMD DebateTechnical solutions and funding models for theAcid Mine Drainage problems of South Africa 29 August 2013

  2. “Sophistication creates Simplicity”

  3. The Challenge Active mining and dewatering of the mines along the East, Central and West Rand mining basins declined and essentially ceased in 2010 The underground voids have been filling with water which interacts with the exposed rock (pyrite) to form AMD In 2002 – AMD from the Western Basin started decanting into surface streams Decanting is expected to occur in 2013 in the Central Basin and 2014 in the Eastern Basin AMD is of poor quality and poses a definite threat to the environment and to the water resources of the Crocodile West and Vaal River Systems

  4. Current Short Term Solution • Upgrading and construction of HDS (lime neutralisation) plants in the Western, Central & Eastern Basin • pH increases & metals precipitate as insoluble metal oxides and hydroxides • Precipitates are removed from the water via large clarifiers and deposited on waste storage facilities • Advantages: • Proven, established process • Can be adapted to variable water qualities and quantities • Process is relatively stable and relatively easy to control • Disadvantages: • Large volumes of mixed hydroxide and gypsum sludge • Large plant footprints with associated CAPITAL costs • Excessive “scaling” potential in down stream pipelines & processes • DOES NOT remove the salts (desalinate) the water • Long term de-stabilisation of waste residues unknown!!

  5. Alternative Short Term Solution • Neutralization of & metals removal from AMD – using waste water from existing gold recovery processing • pH increases & metals precipitate as insoluble metal oxides and hydroxides • Precipitates are deposited with the gold tailings onto tailings storage facilities (TSF) and water is recovered from the TSF • Advantages: • Combines two waste streams to solve both problems • Disposal of solid waste is simplified • Disadvantages: • Not yet fully developed process • Long term de-stabilisation of waste residues unknown!! • Effects of low density gold tailings onto conventional gold TSF’s not fully understood • DOES NOT remove the salts (desalinate) the water • Can only be operated in areas where there are operational gold processing plants

  6. The Challenge Should AMD, which has not been desalinated, be discharged into the Vaal River System, the salt load will require large dilution-releases to be made from the Vaal Dam to achieve fit-for-use objectives This will result in unusable surpluses developing in the Lower Vaal River In addition, should the dilution releases still be required after 2015, the acceptable levels of assurance of water supply from the Vaal dam will be threatened This means that there will be an increasing risk of water restrictions in the Vaal River Supply area

  7. Medium & Long Term Solutions • PHYSICAL Processes • HDS followed by conventional RO • MIWATEK Process • Electrocoagulation & Precipitation • CHEMICAL Processes • Alkali-Barium-Calcium (ABC) Process • Ettringite Process (SAVMIN) • BIOLOGICAL Processes • Biological Sulphate Reduction (Biosure) Process • Biological Sulphate Reduction (Paques) Process

  8. HDS & Conventional RO • HDS for neutralisation & metals precipitation and multi stage RO for desalination • Advantages: • “Proven” process • Only process that has been installed at scale required for treatment of Wits AMD • Disadvantages: • Process has not yet been “proven” on gold AMD • Large volumes of mixed hydroxide and gypsum sludge to dispose of • Large plant footprints with associated CAPITAL costs • Excessive “scaling” potential in down stream pipelines & processes • Long term de-stabilisation of waste residues unknown!! • Large volumes of lime required • Energy intensive • Final “brine” difficult to treat

  9. MIWATEK • Multi stage chemical pre-treatment, metals precipitation & RO • Advantages: • Analysis driven design, flexible and modular • Does not use lime for neutralisation and therefore does not have any of the negative downstream effects • Chemicals used in the pre-treatment/neutralisation can be recovered from the final “brine” • Final “brine” stream can be processed to produce industrial quality reagents • Dramatically reduced solid waste production • Majority/total solid waste can be used by large industry as feed stock • Unique & exclusive South African developed equipment producing rapid and complete chemical reactions resulting in dramatically reduced plant footprint and Capital costs • Unique & exclusive low pressure first stage RO • Process already piloted and demonstrated on Western Basin gold AMD water • Disadvantages: • Not yet at “Proven” status

  10. Funding Models DBOOM – Design, Build, Own, Operate & Maintain DBOM – Design, Build, Operate & Maintain

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