CRITICAL MINERALSWork Toward a Cleaner Way to Purify Critical Metals
Rare-earth elements are everywhere in modern life. However, purifying these critical metals from ores with complex mixtures is a nasty business involving strong acids and hazardous solvents, and is primarily conducted in China. Sandia team studies selective sponges for rare-earth elements.
Rare-earth elements are everywhere in modern life, found in everything from the smart device you’re likely reading this on to the LED lightbulbs overhead and neodymium magnets in electric vehicles and wind turbines.
However, purifying these critical metals from ores with complex mixtures is a nasty business involving strong acids and hazardous solvents, and is primarily conducted in China. Over the past three years, a team of researchers from Sandia has been pioneering an environmentally friendly method to separate these rare-earth elements from watery mixtures.
Initially, the team made and modified tinker-toy-like molecules called metal-organic frameworks or MOFs to test their ability to adsorb these vital metals. They then used computer simulations and X-ray-based experiments to investigate how the rare-earth elements interact with the synthesized sponges. The team’s ultimate goal is to design sponges that selectively absorb one rare earth metal while excluding others. Their findings were recently published in a series of scientific papers, including one published recently in ACS Applied Materials and Interfaces.
“We synthesized MOFs with variable surface chemistry and were able to show through adsorption experiments that these MOFs can pick out rare-earth elements from a mixture of other metals,” said Anastasia Ilgen, a Sandia geochemist and project lead. “They are more selective for the rare earths — that’s good. Importantly, we illustrated that their ability to pick out metals can be fine-tuned by adding chemical groups on their surfaces.”
Synthesizing Stable Sponges
The researchers selected two zirconium-based tinker-toy-like MOFs for the project. These MOFs are highly stable in water and easily adjustable, according to Dorina Sava Gallis, a Sandia materials chemist involved in the project.
MOFs consist of metal hubs and carbon-based linker rods, which can be interchanged to create nanosized sponges with different properties. Also, chemists can add different chemical groups within MOFs to modify their properties or engineer structures with missing rods, Dorina said.
In their study, published in the scientific journal Chemical Communications, Dorina and her team experimented with two types of MOFs featuring zirconium hubs. They attached new chemical groups to the linkers in one MOF building block, while attaching them to the metal hub in another.
