New process recovers gold from tailings

A new process for recovering gold from its ores is being developed by scientists from the bp Research Centre at Sunbury, near London, England.

An experimental pilot plant, capable of processing up to a tonne of ore an hour, is operating in Australia. It is processing the tailings from the primitive sluice washing methods of 19th century miners, which allowed small gold particles to escape into rivers and creeks.

As a result of these successful operations, ores from Australia, Canada, Indonesia, France, Brazil and the United States are being examined at Sunbury to seek further uses for the process. Untreated ores, concentrates from gravity treatment plants and old mine waste dumps are all being assessed.

Discovery of the process — known as coal/gold agglomeration or cga — stems from original work carried out from bp Coal. But the payoff came by applying the results to research being caried out for bp Minerals.

The bp Coal research laboratory in Australia was investigating a means of cleaning fine coal by agglomerating it with oil. The process proved uneconomic and the project was closed down but not before it had been scientifically established that gold particles could be gleaned by causing them to adhere to coal/oil agglomerates.

Early in 1985, the bp Minerals Processing Branch at Sunbury was asked to develop the coal/oil agglomeration idea.

Chris Veal, leader of the Minerals Dressing project at Sunbury who, with Iain House, Dave Murgatroyd and Simon Bellamy took over the development, said: “We went back to square one and made a basic investigation into how the different parameters could be manipulated.

“We bought some gold powder and mixed it in minute quantities with sand and attempted to recover it using the coal/oil agglomerates. In the end we came up with a beautifully simple laboratory process with five vessels in which crushed ore is agitated continuously with agglomerates.

“The gold adheres to the agglomerates and can be recovered by burning the result.” Veal added: “Another advantage of the process is an environmental one. Fine gold processing involves the treatment of ores in sodium cyanide solution, which at some stage in the operation requires disposal. With our process, very little chemical is needed so the environmental gain of cga over cyanidation could be an important factor.”

The pilot plant in Australia is working well and needs only slight modification to become a prototype process. “The process looks like being a lot cheaper than conventional methods for many applications and more suitable than any for some types of gold deposits,” said Veal. “It should have a big potential for bp Minerals worldwide.”