From E-Waste to Gold Dust

Tossing precious metals like gold, silver, and copper into a landfill seems counterintuitive, but it happens even after electronic products containing these valuables are recycled. 

Brajendra Mishra, PhD, Kenneth G. Merriam Professor of Mechanical Engineering and director of Center for Resource Recovery and Recycling (CR3), is exploring how to recover more valuable materials from e-waste, par­ticularly large appliances such as dishwashers and laundry dryers, and electronics, including cell phones and comput­ers. When they are discarded, these products can be shred­ded and then melted in high-temperature furnaces to sepa­rate out some of their materials, including metals. But the process produces a lot of fine materials, or flue dust, that is now often landfilled.

Discarded with those “fines,” however, are a number valuable metals, particularly gold, silver, copper, and iron, says Mishra, who came to WPI from Colorado School of Mines in 2015 with a background in process metallurgy.

Mishra’s lab is working with Aurubis, a German-based copper producer and recycler, to look for ways to separate this metallurgical wheat from the chaff. Using flue dust samples supplied by the company, his team is testing a number of physical and chemical techniques, including magnets, electrostatic processes, and density separation, to see if they can enhance the extraction of metals from the fines.

“We have been quite successful doing that,” says Mishra, who notes that flue dust can contain up to 10 percent copper and a few thousand parts per million of silver and gold. If that sounds like a modest return, consider that while a ton of quality ore can yield 35 grams of pure gold, after processing, a ton of old cell phones contains 350 grams of already purified gold, along with silver and copper.

“Without industry support, we can’t do this,” Mishra says. “They’re looking for solutions to handle all the effluents and waste that they create. On a society level, people are looking for ways of recovering valuable materials from something that’s used up or not working anymore. It makes sense to recover metals, but you need structures like the CR3 to do it.”