Zirconium and hafnium are so alike that zircon, the mineral zirconium silicate (ZrSiO4), almost always carries traces of hafnium. Zircon mining is the main economic source of both. Yet semiconductor makers and nuclear reactor builders need one cleanly parted from the other.
Oregon State University researchers say they have patented a greener way to do it. They use a water-based solution where industry now uses a toxic organic solvent. The work was led by graduate research assistant Alex Roseborough and May Nyman, a professor of chemistry, in the College of Science, and it appeared in the Journal of the American Chemical Society.
The problem with the current method
Zirconium matters for nuclear power generation. Hafnium matters for both nuclear energy and chip manufacturing. Only two plants in the United States can separate them at industrial scale: ATI Specialty Alloys & Components in Albany, Oregon, and Westinghouse Electric in Ogden, Utah. Each burns through millions of pounds of flammable organic solvent a year.
Their liquid-liquid extraction is the state of the art. It also eats energy, and about 4% of the solvent escapes into the air as noxious pollution, the researchers note.
Precipitation instead
The OSU method relies on precipitation, where dissolved ions with opposite charges attract and form an insoluble solid. Under the hood, the recipe is an aqueous solution of natural zirconium (with its few percentage points of hafnium impurity), thiocyanate ligands that bind to both metals’ ions, and choline, a cheap, nontoxic food additive. Hafnium-rich species drop out as a solid. The process is low-energy and uses no organic solvent.
The detail that matters is the separation factor, which measures how well a process pulls two components apart. Anything above one means separation works, and higher is better. The industry standard sits between six and seven. The OSU process hit 33.
“We describe in atomic-level detail how the separation works and how precipitation-based separations can compete with solvent extraction,” said Nyman, who holds the Terence Bradshaw Chemistry Professorship at Oregon State. “We still have questions to answer and milestones to achieve, but these findings are really exciting and impactful, especially as society must move toward more carbon-free and high-density electricity generation, including nuclear energy.”
Other OSU researchers on the study were Doctor Stephen, Jack McLaughlin, Lev Zakharov, George Donkor-Gyami and Pere Miró. The U.S. Department of Energy and the Murdock Charitable Trust funded the work. Roseborough now works as a metallurgist at the department’s National Energy Technology Laboratory.
Sources
- Semiconductor, nuclear industries poised for green boost thanks to chemistry breakthrough | Newsroom
