Breakthrough clean gold mining technique replaces cyanide with... cornstarch!
This accidental discovery will hopefully transform the industryMining gold's a dirty business. To extract gold from raw ore, a lot of cyanide is required, and wherever a lot of cyanide is found, there are also big environmental risks. But what if we could replace all this cyanide with something as benign as cornstarch? Scientists from Northwestern University might have, by accident, figured out a way to do just that.
Zhichang Liu, a postdoctoral fellow in Stoddart's lab and first author of the paper, took two test tubes containing aqueous solutions -- one of the starch-derived alpha-cyclodextrin, the other of a dissolved gold (Au) salt (called aurate) -- and mixed them together in a beaker at room temperature.
Liu was trying to make an extended, three-dimensional cubic structure, which could be used to store gases and small molecules. Unexpectedly, he obtained needles, which formed rapidly upon mixing the two solutions.
"Initially, I was disappointed when my experiment didn't produce cubes, but when I saw the needles, I got excited," Liu said. "I wanted to learn more about the composition of these needles."
"Nature decided otherwise," said Stoddart, a senior author of the paper. "The needles, composed of straw-like bundles of supramolecular wires, emerged from the mixed solutions in less than a minute."
After more tests, it was discovered that alpha-cyclodextrin, a cyclic starch fragment composed of six glucose units, was best at isolating gold from the solution. But not only is this process a lot less toxic than the cyanide leaching process, it also appears to be more efficient at isolating gold.
But that's not all! Like an informercial, there's even more! This process could also be used to recover gold from electronic waste (something that we have a lot of). Before we go mine gold in virgin ore, it makes sense to recycle it from our waste stream.