29 August 2013

AMD DebateTechnical solutions and funding models for theAcid Mine Drainage problems of South Africa

“Sophistication creates Simplicity”

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

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!!

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

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

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

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

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

Funding Models

• DBOOM – Design, Build, Own, Operate & Maintain• DBOM – Design, Build, Operate & Maintain