Oregon State University scientists have patented a better and more eco-friendly process for separating two metals that are critical in their pure forms for the semiconductor and atomic energy industries.
Researchers in the OSU College of Science used a water-based solution rather than a toxic organic solvent to separate zirconium, vital in nuclear power generation, from hafnium, which is crucial for both nuclear energy and semiconductor manufacturing.
The study led by graduate research assistant Alex Roseborough and May Nyman, professor of chemistry, explored one of the most difficult separations on the periodic table, made challenging by the elements’ similarity. They are so closely related that the mineral zirconium silicate (ZrSiO4), commonly known as zircon, almost always contains trace amounts of hafnium; zircon mining is the principal economic source of both elements.
But though they are nearly identical, separating one from the other at high purity is necessary for microelectronics and nuclear reactors. Only two facilities in the United States – ATI Specialty Alloys & Components in Albany, Oregon, and Westinghouse Electric in Ogden, Utah – are equipped to perform that separation on an industrial scale, each using millions of pounds of flammable organic solvent annually.
The plants’ liquid-liquid extraction process, the current state of the art for the separation, is energy intensive and also results in roughly 4% of the solvent being lost to the air as noxious pollution, the researchers note.
The separation process developed at Oregon State, however, is based on precipitation: dissolved ions with opposite charges attracting each other to form an insoluble solid.
The basic idea is an aqueous solution that combines natural zirconium, with its few percentage points of hafnium impurity; thiocyanate ligands, which bind to the hafnium and zirconium ions; and choline, an inexpensive, nontoxic chemical commonly used as a food additive.
The result of this low-energy process that involves no organic solvent is a precipitation of hafnium-rich species, with a separation factor much higher than the current industry standard.
As its name suggests, separation factor is a measurement of a process’ ability to separate two components in a mixture. A value greater than one denotes that separation is possible; the higher the number, the better.
The industry standard for zirconium-hafnium separation is between six and seven, and the OSU process produced a top score of 33.
“We describe in atomic-level detail how the separation works and how precipitation-based separations can compete with solvent extraction,” said Nyman, the Terence Bradshaw Chemistry Professor 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.”
Also contributing to the study, which was published in the Journal of the American Chemical Society, were OSU researchers Doctor Stephen, Jack McLaughlin, Lev Zakharov, George Donkor-Gyami and Pere Miró.