Non-toxic corn starch could replace cyanide in gold mines
By Ben Coxworth
May 14, 2013
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