Liquid gold - the future of biotechnology in gold exploration and processing
A recent review article co-authored by Dr Carla Zammit, Institute for Mineral and Energy Resources (IMER), has highlighted the potential for biotechnology to transform the gold mining industry. Dr Zammit and her colleagues are working on a project led by Dr Frank Reith, IMER, to develop a microbial-based biosensor to aid in gold exploration and processing.
''Microbes have been perfecting their biochemical pathways for more than 3.5 billion years and we're just starting to realise their potential," said Dr Zammit.
Biological agents are currently used in the mining industry for bioleaching and bioremediation but there are a number of new ways that biotechnology may be used to benefit the mining industry. Microbial-based biosensors and bioindicators are being developed to improve gold exploration and processing.
Bioindicators rely on resident organisms in the mineralisation zone, and/or those that are sensitive to metal, and could be developed in two different ways. Firstly through phylogenetic fingerprinting, which involves the identification of all of the microbes present in the environment and comparing the microbial profile to those associated with environmental parameters like heavy-metal containing soils. Bioindicators could also be developed by searching for specific genes, proteins and/or metabolites that are associated with the ability of microbes to resist or detoxify heavy metals.
''It's rare to have a system without microbes, but now we're paying more attention to their role in metal cycling,'' Dr Zammit said.
Biosensors, similar to those that monitor blood glucose levels or detect illicit drugs, are also under development to enhance gold exploration. Biosensors can be developed into inexpensive devices that are simple to operate, portable, highly selective and give immediate results in the field. This will give exploration teams the ability to determine gold concentrations from environmental samples instantaneously rather than weeks later.
Biosensors could also improve mineral processing by analysing the minerals within ores in real time and increasing recovery rates. Cupriavidus (Ralstonia) metallidurans has been isolated from metal-rich environments in many countries. It has been detected in biofilms on gold grains in Australia and shows potential as a gold biosensor.
Gold processing could also benefit by putting microbes to work in gold mines. Traditional gold processing has relied on cyanide leaching and/or roasting but these methods are becoming increasingly difficult due to technical and legislative concerns. As the price of gold rises, there is increased interest in processing higher volumes of lower grade ore - increasing the amount of cyanide needed by the industry.
Cyanide is produced by microbes at the end of their growth phase and there is potential to use bioreactors to produce cyanide on site for use in place of synthetic cyanide. Although it is unlikely that microbes will be able to provide the mining industry with all its cyanide needs, there is enormous potential for microbial production of cyanide directly on the surface of gold-containing minerals.
Dr Zammit is currently working on the development of gold biosensors and bioleaching under high salt level conditions and microbial-based leaching of gold in situ.
Microbes can directly attach to the surface of gold, form a biofilm and begin producing cyanide which dissolves the gold into solution. Cyanide-producing microbes can be coupled with existing technologies like biooxidation to assist in the leaching of gold and may also have the potential for bioleaching. This would reduce the amount of cyanide required and the problems associated with cyanide transport.
"There is no doubt that in situ leaching of gold will be a very promising up and coming technology," said Dr Zammit.
Biotechnology has enormous potential to help develop ‘greener' and more efficient gold processing and extraction techniques. Continued understanding and use of molecular analysis techniques and interactions between microbes and gold in the environment will help researchers identify opportunities for using biotechnology in gold processing.
Dr Zammit and colleagues' review of the future of biotechnology for gold exploration can be accessed online or contact:
Dr Carla Zammit
Institute for Mineral and Energy Resources
Centre of Tectonics, Resources and Exploration (TRaX)
School of Earth and Environmental Sciences
The University of Adelaide, Adelaide SA 5005
Ph: +61 8 434 894 040
Email: carla.zammit@adelaide.edu.au
Dr Frank Reith
Institute for Mineral and Energy Resources
Centre of Tectonics, Resources and Exploration (TRaX)
Waite Laboratories
Waite Road, Gate 4
Urrbrae, South Australia 5064, Australia
Ph: +61 8 8303 8469
Email: Frank.Reith@csiro.au
Zammit, C.M., Cook, N., Brugger, J., Ciobanu, C.L., Reith, F. (2012). The future of biotechnology for gold exploration and processing. Minerals Engineering 32, pp. 45-53.
Carla Zammit and Joël Brugger sampling from an Australian salt lake.
