Most modern processes to extract gold from ore or scap use a highly toxic combination of cyanide salts. Researchers at Northwestern University in Chicago have stumbled upon a way of extracting the gold that uses cornstarch instead of cyanide. The process is cheap and does not involve any substances which are ecologically harmful or dangerous.
The team, led by Professor Sir Fraser Stoddart, discovered the method by accident when trying to make three-dimensional nano-cubes out of gold and starch, aiming to use them as storage containers for gases and other small molecules. But they found that, instead of forming cubes, a liquid mixture of dissolved gold-bromide salts and a starch-derived sugar formed needles.
The team decided to try to replicate the process with different sugars.
They found that alpha-cyclodextrin, a starch with six glucose molecules, formed a bundle of needles made up of thousands of nanowires, each 1.3 nanometres in diameter. Each nanowire contained a charged gold atom inside four bromine atoms. This interaction between the starch and the gold allows the gold to be selectively recovered from other materials.
The researchers have already developed a process to isolate gold from scrap metal and they hope this will lead to an environmentally friendly, cheap way of recovering gold from anything.
Professor Stoddard describes the process as "a piece of magic for isolating gold from anything in a green way".