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Comment Separation Processes

Extracting gold without cyanide

By Paul Grad |

The first gold using a process without cyanide and without mercury has been produced using technology from CSIRO Minerals Technology (www.csiro.au) at a demonstration plant in the Western Australian goldfields town of Menzies.

Cyanide is used in more than 90% of global gold production, but producers are facing increasingly tough regulations restricting the use of cyanide due to environmental and health concerns. The CSIRO technology replaces cyanide with thiosulfate, a nontoxic, mobile-plant alternative. It is a simple vat-and-heap-leach process involving low capital cost. CSIRO gold processing team leader Paul Breuer says the CSIRO process targets small high-grade deposits with good gold liberation at a coarse grind size suitable for the gravity tails to be vat-leached. A tank-leach process using this leach system is under development for demonstration next year. This will have the potential to open up the application of the technology to a greater range of ore types and will be scalable to larger projects.

The process concepts entail a mobile plant, vat leach for coarse material, tank leach with thickener/filter as parallel circuit to treat fines, “dry” tails stacking, and plug-and-play modules tailored for different ore types. The mobile plant would allow junior miners and smaller players to process their own gold, explains Breuer. The ability to pack up the plant inside shipping containers gives the process a mobility no other plant could achieve, he says.

The A$2.1-million (A$1.00 = $0.71) demonstration plant at Menzies was made possible through funding from the Science and Industry Endowment fund and an Australian Government Innovation Connections grant. According to CSIRO, a typical cyanide-based processing plant costs about A$30 million, whereas the new technology involves a capital investment of A$2–2.5 million.

The CSIRO team behind the innovation has already enjoyed commercial success with another cyanide-free gold solution developed with Barrick Gold for its Goldstrike Mine in Nevada.

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