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Engineering the Future
Research Projects
The Pressing Matter of
Mine-water Clean-up
The treatment and disposal of water in the mining
sector is a ticking time bomb increasingly threatening
South African cities and surrounding communities
while garnering the focus of both media and legislative
bodies. The success of the research project Refining the
BIOX and ASTER processes for Gold, led by Professor
Susan Harrison and Dr Rob van Hille of UCT’s Centre for
Bioprocess Engineering Research in the Department of
Chemical Engineering, is therefore no small feat.
Getting the Mining
–
Cost
–
Environment Balance Right
South Africa’s mineral resources are being depleted,
making it necessary to find ways to extract metals
from increasingly lower-grade resources. This requires
technologies with low energy and processing inputs
that provide a balance between resource beneficiation,
cost efficiency and environmental impact.
South African scientists and engineers – leading
the development of bioprocesses for gold recovery
from sulphidic ores – have in the past achieved
the worldwide commercialisation of BIOX™, a
hydrometallurgical process in which micro-
organisms oxidise iron and sulphur within the gold
mineral concentrate. The outcome is soluble ferric
iron and acid that leach sulphidic minerals from the
concentrate, leaving gold accessible for extraction
with a cyanide solution.
This latest research at UCT focuses on refining this
technology to improve performance and robustness,
with a particular focus on process intensification
through the use of modern molecular tools for
tracking the microbial consortium present in the
process.
Associated with this process is the more recently
launched ASTER™process for microbial remediation
of residual cyanide and thiocyanate formed in the
gold-recovery process.
Another key issue surrounding the mining industry is
that of responsible mine closures following cessation
of mining activities. The ASTER™ process is linked
to both the BIOX™ process for remediation of its
effluents and the maximisation of water recycle
towards zero emissions, as well as associated
precious metal extractions using other upstream
technologies followed by extraction with cyanide
The research, funded through Goldfields, has been
presented in China, Germany and the USA, with a
range of journal papers in preparation, in addition
to industrial application of its findings.
Heap bioleaching technologies can do this, in
addition to having the potential to process waste rock
displaced in the mining operation. The technology
uses available iron and sulphide as an energy source,
and provides leaching agents for metal extraction
from low-grade ore that is crushed and stacked in
large heaps, which are irrigated and aerated so that
micro-organisms grow on the rock surface.
South Africa has played an important role in
the development of technology for “hot heaps”
operating under thermophilic conditions – relatively
high temperatures that cause certain bacteria to
grow. This UCT project focuses on understanding
the micro-environments established within the
heap that can be manipulated to intensify the
leaching process. Through use of custom-designed
equipment, this project has presented the first
rigorous characterisation of microbial growth rates
on whole ore under temperatures ranging from
ambient to 65˚.
The project, now completed, was funded by BHP-
Billiton and led by Professor Susan Harrison, who holds
the NRF/DST SARChI Research Chair in Bioprocess
Engineering Research. A team of researchers from the
Centre for Bioprocess Engineering Research in the
Department of Chemical Engineering have contributed
to this cross-disciplinary study, along with Dr Rob van
Hille, Associate Professor Jochen Petersen, Emmanuel
Ngoma, Nathan van Wyk, Lucinda Bromfield, Frances
Pocock and Lukhanya Mekuto, Cambridge University’s
Dr Andy Sederman, UCT PhD graduate Marijke Fagan,
and Imperial College London’s Professors Jan Cilliers
and Peter Lee.
Five journal papers were published and a further six
were prepared for publication in 2013.