The Elements of Innovation Discovered

Extracting green gold, PGMs from waste

Metal Tech News - April 5, 2024

Researchers develop a highly efficient and selective method of extracting precious metals from e-waste, catalytic converters, and ore.

Scientists at the University of Illinois Urbana-Champaign have developed a cleaner and more efficient method of recovering gold and platinum group metals (PGMs) from electronic waste and other discarded materials.

Even though it costs anywhere from $925 to $4,500 to buy just one ounce of these precious metals, gold and PGMs have special properties that make them worth their high price for electronics and clean energy technologies.

Gold is highly conductive, does not tarnish or corrode, and is malleable enough to be made into ultra-thin wires and coatings for connectors, switches, relays, and contacts in electronics.

It is estimated that high-tech devices account for about 8% of gold's overall demand.

PGMs – platinum, palladium, rhodium, ruthenium, iridium, and osmium – on the other hand, are highly valued for their catalytic abilities.

Since the mid-1970s, platinum and palladium have been used to scrub pollutants from the exhaust of automobiles. As the world transitions from fossil fuels to cleaner energy sources, the catalytic properties of PGMs are being used to produce clean-burning hydrogen from water and other sources.

A University of Illinois Urbana-Champaign team led by chemical and biomolecular engineering professor Xiao Su has developed a way to selectively extract gold and PGM ions from a liquid containing dissolved e-waste, catalytic converters, and even ore from mining.

How it works

Xiao Su

A schematic diagram detailing the electrochemical extraction device used to extract gold in Professor Su's laboratory.

The precious metal extraction and separation process developed by Professor Su and his team is called electrochemical liquid-liquid extraction, or e-LLE.

"Our work is envisioned as a pathway towards a broader class of industrially applicable liquid-liquid extraction-based electrochemical separations," the researchers wrote in a paper published in the scientific journal Nature.

In the lab, the team dissolved catalytic converters, e-waste, and simulated mine ores containing gold and PGMs using an organic solvent. The system then streams these dissolved electronics and other precious metal-rich products through three consecutive extraction columns – one for oxidation, one for leaching and one for reduction.

This method is able to selectively pull 90% of the dissolved gold and PGMs from the solution.

"The metals are then converted to solids using electroplating, and the leftover liquid can be treated to capture the remaining metals and recycle the organic solvent," Su said. "The stream containing the organic extractant is then pumped back to the first extraction column, closing the loop, which greatly minimizes waste."

Green gold and PGMs

An economic analysis demonstrates that the new method runs at a cost of two orders of magnitude lower than current industrial processes. This could significantly improve the economics of recycling precious metals. It is estimated that 90% of the gold used in electronics in the U.S. winds up in landfills instead of recycling facilities.

"The social value of this work is really its ability to produce green gold quickly in a single step, greatly improving transparency and trust in conflict-free recycled precious metals," said postdoctoral researcher Stephen Cotty, the first author of the study.

This highly efficient and clean method of pulling precious metals out of dissolved waste and ore also happens to be highly selective, meaning a nearly pure product is produced.

"We can pull gold and platinum group metals out of the stream, but we can also separate them from other metals like silver, nickel, copper and other less valuable metals to increase purity greatly – something other methods struggle with."

Fred Zwicky

University of Illinois Urbana-Champaign researchers (left to right) Johannes Elbert, Aderiyike Faniyan, Stephen Cotty, and Xiao Su.

The University of Illinois Urbana-Champaign team is working to perfect this precious metals recovery method by improving the engineering design and solvent selection.

The U.S. Department of Energy supported this work.

Author Bio

Shane Lasley, Metal Tech News

Author photo

With more than 16 years of covering mining, Shane is renowned for his insights and and in-depth analysis of mining, mineral exploration and technology metals.

 

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