Taking the tarnish off gold mining
Toxic cyanide spills may become a thing of the past, if research into a non-toxic chemical for gold extraction is put to use.
Dr Matthew Jeffrey, a chemical engineer from Australia's Monash University, is developing a new technique that uses thiosulfate in the presence of ammonia, instead of toxic cyanide, in the extraction of gold from ore.
He presented his results at the ScienceNOW! conference currently underway in Melbourne.
'Thiosulfate is slightly less reactive than cyanide, but in sufficient quantities is as effective in the gold extraction process," said Dr Jeffrey.
"It is the only non-toxic chemical that will effectively leach gold."
Cyanide is poisonous because it reacts with haemoglobin, reducing the oxygen-carrying capacity of blood.
However, alternatives to cyanide extraction have not been researched until now because, according to Dr Jeffrey, it is a "generally effective process".
Cyanide attaches to minute particles of gold to form water-soluble goldcyanide compounds from which gold is later recovered. Leftover cyanide is stored in tailing dams and re-used indefinitely, which makes it a cost-effective procedure.
The mining industry has long argued that the dilute cyanide concentrations employed and the rapid ultraviolet decomposition of cyanide into relatively non-toxic compounds make cyanide extraction safe.
However, many of the breakdown compounds, while generally less toxic than the original cyanide, are known to be toxic to aquatic organisms, and may persist in the environment.
The disastrous effects of cyanide were felt early last year when a tailing dam collapsed at Baia Mare in Romania due to an unprecedented volume of snow melt. The cyanide cocktail was released into the Tisza and Danube Rivers, killing virtually all aquatic life.
Gold mines are often located in regions that are unsuitable for tailing dam construction, such as Papua New Guinea where frequent earthquakes occur. Cyanide has also been known to leach into the surrounding groundwater after prolonged storage, affecting town water supplies.
Dr Jeffrey discovered that thiosulfate is an effective alternative to cyanide using a instrument called a rotating electrochemical quartz crystal microbalance, which accurately measures how rapidly gold reacts with specific chemicals.
Commonly used in photography and paper manufacture, thiosulfate decomposes into sulfate, which is harmless under the alkaline conditions used in the research, said Dr Jeffrey. In fact, "thiosulfate was once used as an antidote to cyanide poisoning", he said.
The research is funded by the Australian Research Council and the Australian gold industry.