A green process for extracting gold
A research team at the University of Saskatchewan has found what may be an inexpensive and environmentally-friendly way of recycling gold from jewelry and electronics. Using a solution of what is essentially reusable table vinegar, the team has shown that for CAD$66 (about US$47) it can produce one kilogram (2.2 lb) of gold with 100 liters (26 gal) of reusable waste water – this is as compared to current methods that can cost over CAD$1,500 (US$1,070) and create 5,000 liters (1,321 gal) of toxic, non-reusable waste.
According to Stephen Foley, associate professor in the Department of Chemistry and leader of the project, 80 percent of the 50 million tons (4.5 million tonnes) of e-waste produced globally each year ends up in landfills, and seriously impacts the environment and surrounding populations as a result.
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The problem with gold is that it's one of the least reactive chemical elements on the planet, which makes it difficult to dissolve. Thus current industry standard methods to remove it from scrap electronics rely on either highly-toxic cyanide solutions that are non-recyclable, or use high heat to burn off the gold, releasing dangerous gases into the air in the process.
The method created by Foley and his team is meant to eventually replace both of those approaches with a less expensive, non-toxic, recyclable solution.
"We use one of the most mass-produced chemicals, acetic acid, at five per cent concentration; it's plain table vinegar," explains Foley. "We use a minute amount of an acid and an oxidant to finish our solution."
Foley points out that the solution developed by his team is the greenest solvent next to water, so it eliminates the vast number of environmental concerns that come with the other long-standing methods of gold extraction.
The next step for the scientists is to identify industry partners who can help them move the process into very large-scale applications for gold recycling from gold-bearing materials. Foley believes that the method could also eventually be used in gold mining, which currently relies on toxic sodium cyanide for extraction.
Over the last several years, research teams elsewhere have developed other solutions for eliminating or reducing the environmental impact of gold mining. These include one utilizing corn starch, another that extracts gold from sewage, and another that involves a mercury recapture system.
Source: University of Saskatchewan