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article imageGold processing bacteria help to recycle electronics

By Tim Sandle     May 7, 2017 in Science
Adelaide - There are species of bacteria that efficient at processing of gold ore. Applications include recycling electronics as well as use in exploration for new deposits. A new study demonstrates the advantages.
The study has been undertaken at the University of Adelaide and it has been running for ten years. The focus is with how gold can be dissolved, dispersed and re-concentrated into nuggets by the activities of microorganisms; a process called biogeochemical processing.
One area of interest is how long the cycle takes to complete and whether the process can be optimized, including speeding up the conversion process. This is with a view to industrializing the microbial activity on a larger scale.
The process is described by Dr Frank Reith in a research brief: “In the natural environment, primary gold makes its way into soils, sediments and waterways through biogeochemical weathering and eventually ends up in the ocean.”
With the role of microbes, he adds: “On the way bacteria can dissolve and re-concentrate gold -- this process removes most of the silver and forms gold nuggets.”
The bacterium that undertakes the process most efficiently is called Delftia acidovorans. The organism has a King Midas-like touch, and this is a natural part of the organism’s self-defense mechanism. Dissolved gold is toxic to the organism, so it has evolved a mechanism to turn poisonous ions into harmless gold particles that eventually accumulate outside of the bacterial cell. A second bacterium species called Cupriavidus metallidurans can also produce gold nuggets.
What the researchers hope is to find an economically viable way of performing gold extraction from ore and re-processing old tailings or recycled electronics. At present this process is costly, meaning that many electronic devices simply end up in landfill sites rather than being recycled for their potentially valuable competes.
The reason the process is costly is because it takes considerable amounts of time. This time is very short in geological terms, but it is too long for any person to make it commercially effective. Through the use of high-resolution electron-microscopy, the time taken for the microbial processing is anything between 3.5 and 11.7 years for each stage of the process, meaning that it could be up to 60 years before gold is completely recovered and processed.
However, new insights into the process mean that innovative processing techniques could be achieved and this represents the next phase of the continuing research project.
The research is published in the journal Chemical Geology, under the heading “Secondary gold structures: Relics of past biogeochemical transformations and implications for colloidal gold dispersion in subtropical environments.”
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