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New Gold Extraction Method Uses Cornstarch instead of Cyanide

Sometimes happy little accidents happen in the lab that eventually lead to big changes in the outside world, and a team of Northwestern University scientists may have stumbled upon one that could really clean up the process of gold recovery.

In the movies, you can pick up gold nuggets by hand, or pan out enough in a stream to fill your pocketbook, but in the real world, extracting gold can take a whole lot more work, especially with low-grade ores. Current gold recovery methods use highly toxic cyanides or mercury, which takes a toll on the environment, especially the production of toxic salts and gases from chemical extraction.

But a new “green” method for gold extraction, discovered through scientific “serendipity” while working on a different project, could be the answer for a new inexpensive and benign recovery process.

The researchers, led by Sir Fraser Stoddart, Board of Trustees Professor of Chemistry at Northwestern, found that a solution using common cornstarch was able to selectively isolate gold from other raw materials, while leaving behind the other commingled metals found with gold.

“The elimination of cyanide from the gold industry is of the utmost importance environmentally. We have replaced nasty reagents with a cheap, biologically friendly material derived from starch.” – Stoddart

Not only is the new method more environmentally sound, but it also happens to be more efficient than conventional leaching processes are, and could also be used in the after-market to safely extract gold from components in consumer gadgets and e-waste.

The team found that the new process very quickly produced needle-like structures made out of supramolecular nanowires (just 1.3 nanometers in diameter), and examination of the needles showed an elegant composition:

“In each wire, the gold ion is held together in the middle of four bromine atoms, while the potassium ion is surrounded by six water molecules; these ions are sandwiched in an alternating fashion by alpha-cyclodextrin rings. Around 4,000 wires are bundled parallel to each other and form individual needles that are visible under an electron microscope.”

The results of the study are published at Nature Communications: Selective isolation of gold facilitated by second-sphere coordination with α-cyclodextrin

[Image: subarcticmike]

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