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Non-toxic corn starch could replace cyanide in gold mines


May 14, 2013

A newly-developed process gives gold mines an alternative to using cyanide for extracting gold from ore (Photo: Shutterstock)

A newly-developed process gives gold mines an alternative to using cyanide for extracting gold from ore (Photo: Shutterstock)

In the gold-mining process, the precious metal is often extracted from low-grade ore in a technique known as gold cyanidation. As its name suggests, the process utilizes highly-poisonous cyanide, some of which ends up entering the environment in the mines’ tailings. That’s not so good. Scientists at Illinois’ Northwestern University, however, recently announced their discovery of a new gold recovery process that’s based on a non-toxic component of corn starch.

The process was discovered by accident, when postdoctoral fellow Zhichang Liu was trying to create a tiny cubic structure that could be used to store gases and molecules. He mixed two solutions together at room temperature – one solution contained a dissolved gold salt called aurate, while the other contained alpha-cyclodextrin, which is a corn starch fragment composed of six glucose units.

To his surprise, less than a minute after the solutions were mixed together, the gold content formed into solid needles. These needles were in turn each composed of a bundle of about 4,000 tiny gold wires, each wire measuring 1.3 nanometers in diameter. While the needles were very small themselves, they could be harvested from the rest of the liquid.

The inexpensive process creates relatively innocuous alkali metal salt as a by-product, and reportedly extracts gold more effectively than existing methods. Additionally, it could also be used to reclaim gold from consumer electronic waste.

“Alpha-cyclodextrin is the gold medal winner,” said Sir Fraser Stoddart, the professor of chemistry who led the research. “Zhichang stumbled on a piece of magic for isolating gold from anything in a green way.”

A paper on the research was published today in the journal Nature Communications.

Source: Northwestern University

About the Author
Ben Coxworth An experienced freelance writer, videographer and television producer, Ben's interest in all forms of innovation is particularly fanatical when it comes to human-powered transportation, film-making gear, environmentally-friendly technologies and anything that's designed to go underwater. He lives in Edmonton, Alberta, where he spends a lot of time going over the handlebars of his mountain bike, hanging out in off-leash parks, and wishing the Pacific Ocean wasn't so far away. All articles by Ben Coxworth

I used to prospect and mine Gold. Cyanide has not been used for years.Waste from Sugar refined in Sweden was the prefered method.

Lawrence Roberts

re; Steve Lane

It depends on what you mean by industry. For large corporations the cost of containing the mercury and cyanide is covered by not having to buy so much mercury and cyanide. it is the non industrial mining that produces most of the pollution.


The amount of environmental damage caused by cyanide and mercury gold extraction has been devastating. Far outweighing the value of the gold extracted but the costs are imposed on everyone and any thing but the gold industry. Hopefully this new discovery will go a long way to reducing the horrendous cost to the environment.

Steve Lane

there was a method developed several year back using enzymes which has been adopted, perhaps this will be

Graham HomeMaintenance

Unfortunately there appears to be some confusion here about the role played by cyanide. It is a lixiviant, and as such is responsible for leaching the gold from the ore and dissolving it as an aurocyanide complex in the aqueous phase. The cornstarch has merely sequestered the already dissolved gold - it has therefore replaced the role of activated carbon in this particular case, NOT that of cyanide. Alternative lixiviants for gold have been investigated for many decades - unfortunately the majority of them are even more deleterious to the environment than cyanide, which attenuates in the environment.

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