Bacteria holds key to more efficient gold processing

Research from the University of Adelaide has found that certain ‘nugget producing’ bacteria could be the key to developing more efficient methods of processing of gold ore.

The university has been investigating the role of microorganisms in gold transformation for more than 10 years.

The precious metal can be dissolved, dispersed and reconcentrated into nuggets through a process called the biogeochemical cycle of gold.

For the fist time, the researchers have identified how long this cycle takes, with the aim of making the process faster in the future.

“Primary gold is produced under high pressures and temperatures deep below the Earth’s surface and is mined, nowadays, from very large primary deposits, such as at the Superpit in Kalgoorlie,” Dr Frank Reith, Australian Research Council Future Fellow in the University of Adelaide’s School of Biological Sciences, said.

“In the natural environment, primary gold makes its way into soils, sediments and waterways through biogeochemical weathering and eventually ends up in the ocean.

“On the way, bacteria can dissolve and re-concentrate gold – this process removes most of the silver and forms gold nuggets.”

Reith added that they have known this process takes place but they are now able to show that the transformation happens in a matter of years or decades.

“That’s a blink of an eye in terms of geological time,” he added.

“These results have surprised us, and lead the way for many interesting applications such as optimising the processes for gold extraction from ore and re-processing old tailings or recycled electronics, which isn’t currently economically viable.”

Dr Reith, together with John and Johno Parsons from the Prophet gold mine in Queensland, professor Gordon Southam from the University of Queensland, Dr Geert Cornelis formerly from the CSIRO, and University of Adelaide postdoctoral researcher Dr Jeremiah Shuster, analysed a number of gold grains from West Coast Creek using high-resolution electron-microscopy.

Their findings, published in the journal Chemical Geology, showed that five ‘episodes’ of gold biogeochemical cycling had occurred on each gold grain.

Each episode was estimated to take between 3.5 and 11.7 years – a total of under 18 to almost 60 years needed to form the secondary gold.

Dr Shuster said understanding this biogeochemical cycle could assist mineral exploration through the development of innovative processing techniques or locating undiscovered gold deposits.

“If we can make this process faster, then the potential for re-processing tailings and improving ore-processing would be game-changing,” he said

“Initial attempts to speed up these reactions are looking promising.”

The researchers added that understanding the cycle could also help verify the authenticity of archaeological gold artefacts compared to fake copies.

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