The traditional method of extracting gold from other materials, first discovered more than two hundred years ago, involves cyanide. Cyanide is very toxic. But now, scientists have stumbled upon a method of extracting gold by using alpha-cyclodextrin, a carbohydrate that can be derived from corn starch. The gold forms tiny nanowires. From a press release:
The supramolecular nanowires, each 1.3 nanometers in diameter, assemble spontaneously in a straw-like manner. 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.
This method can be used, among other things, to recycle gold from consumer electronics. Hopefully they can find a way to make it work for ores, since the initial mining still accounts for the majority of gold cyanidation, and consequent environmental danger. One of the co-authors of this paper, Dennis Cao, is on reddit answering questions about the research.