E-waste is a gold mine: research extracts precious metal

At the University of Cornell in the US, researchers have developed a method for extracting gold from electronics waste, to ensure the precious metal isn’t wasted, and then using the recovered metal for converting carbon dioxide (CO2) into organic materials - to provide additional environmental benefits.

Reportedly, this method will provide a sustainable use of the 50 million tonnes of e-waste discarded each year, only 20% of which is recycled according to Amin Zadehnazari, a postdoctoral researcher in the lab of Alireza Abbaspourrad, the Yongkeun Joh Associate Professor of Food Chemistry and Ingredient Technology in the College of Agriculture and Life Sciences.

Low recycling rates reflect the urgency for a new method capable of cutting down e-waste.

In Zadehnazari’s case, he synthesised a pair of vinyl-linked covalent organic frameworks (VCOFs) to remove gold ions and nanoparticles from circuit boards in discarded electronic devices. One of his VCOFs was shown to selectively capture 99.9% of the gold and very little of other metals, that included nickel and copper, from the devices.

“We can then use the gold-loaded COFs to convert CO2 into useful chemicals,” Zadehnazari explained. “By transforming CO2 into value-added materials, we not only reduce waste disposal demands, we also provide both environmental and practical benefits. It’s kind of a win-win for the environment.”

The results of the research, which were published in Nature Communications, were led by Zadehnazari as lead author, and Abbaspourrad as corresponding author. 

Current estimates place a ton of e-waste as containing 10 times more gold than a ton of the ore from which gold is extracted. As 80 million metric tonnes of e-waste are predicted by 2030, finding ways to extract that precious material are ever-more pressing.

Traditional methods of recovering gold from e-waste include the use of harsh chemicals, which pose environmental risks. Zadehnazari’s method is achieved without hazardous chemicals, through the process of chemical adsorption.

As part of the research, Zadehnazari synthesised two VCOFs, using tetrathiafulvalene (TTF) and tetraphenylethylene (TPE) as building blocks, and his research showed that the TTF-COF had superior gold adsorption as it was rich in sulfur. It also withstood 16 washing and reuses with little loss of adsorption efficiency.

Under ambient CO2 pressure at 50 degrees Celsius, the gold-loaded COF efficiently converted CO2 into organic matter via the process of carboxylation.

“Knowing how much gold and other precious metals go into these types of electronics devices, being able to recover them in a way where you can selectively capture the metal you want – in this case, gold – is very important,” Abbaspourrad said, adding that other methods for recovering gold and other precious metals from e-waste aren’t typically as selective as Zadehnazari’s and can result in impurities.

Co-authors on the research include Abbaspourrad lab postdoctoral researcher Amin Zarei; former postdoctoral researcher Ataf Ali Altaf; lab research associate Ahmadreza Khosropour; Saeed Amirjalayer of the University of Munster, Germany; and Florian Auras of Dresden University of Technology, also in Germany.