Water-based chemistry offers greener way to split zirconium from hafnium

Chemists at Oregon State University have patented a water-based method for separating zirconium from hafnium, two elements so chemically alike that pulling them apart has long ranked among the hardest challenges on the periodic table. The new process, described in the Journal of the American Chemical Society, replaces the flammable, toxic organic solvents used at the only two U.S. facilities capable of industrial-scale separation with an inexpensive, nontoxic precipitation chemistry that delivers a separation factor roughly five times better than the current industry standard.

Zirconium and hafnium occupy adjacent positions in the periodic table, and their outer electron shells are so similar that they behave almost identically in most chemical reactions. That resemblance is more than a curiosity for chemists; it has real industrial consequences. Natural zirconium silicate, the mineral zircon, almost always carries trace amounts of hafnium, and zircon mining is the principal economic source of both elements. Yet for microelectronics and nuclear reactors, the two must be separated to very high purity, because their nearly identical chemistry conceals dramatically different nuclear behavior.

In a nuclear reactor, zirconium is prized for its transparency to neutrons, making it ideal for fuel cladding, while hafnium absorbs neutrons so strongly that it is used in control rods. If hafnium contaminates zirconium cladding, the material’s neutron economy is compromised. In semiconductor manufacturing, hafnium compounds serve as high-k dielectric gate materials in modern transistors, demanding exceptional purity. Only two facilities in the United States, ATI Specialty Alloys & Components in Albany, Oregon, and Westinghouse Electric in Ogden, Utah, are equipped to perform the separation on an industrial scale, and each consumes millions of pounds of flammable organic solvent annually.

The current state-of-the-art technique, liquid-liquid extraction, is energy intensive and also loses roughly four percent of the solvent to the air as noxious pollution. The Oregon State team, led by graduate research assistant Alex Roseborough and Terence Bradshaw Chemistry Professor May Nyman, set out to demonstrate that precipitation-based separations can compete with solvent extraction. Precipitation relies on a simple principle: dissolved ions with opposite charges attract each other and form an insoluble solid that can be filtered out of solution.

The patented process combines an aqueous solution of natural zirconium, which contains a few percentage points of hafnium impurity, with thiocyanate ligands that bind to both the hafnium and zirconium ions, and choline, an inexpensive, nontoxic chemical commonly used as a food additive. The result is a low-energy process involving no organic solvent, producing a precipitation of hafnium-rich species with a separation factor much higher than the industry standard.

Separation factor measures a process’s ability to divide two components in a mixture. A value greater than one means separation is possible, and the higher the number, the better. The industry standard for zirconium-hafnium separation sits between six and seven; the Oregon State process produced a top score of 33. The team also captured the separation in atomic-level detail, showing how the different nuclearity, or the number of metal atoms clustered together in the aqueous thiocyanate molecules, controls which species precipitate. Crystals in the precipitates take on distinct shapes depending on their hafnium concentration, providing visual evidence of the molecular selectivity at work.

We describe in atomic-level detail how the separation works and how precipitation-based separations can compete with solvent extraction, Nyman said. 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.

The study, published on 7 September 2026 under the title Emergent Hf-Selective Precipitation of Aqueous (Zr,Hf) Thiocyanate Molecules through Nuclearity Control, also included contributions from OSU researchers Doctor Stephen, Jack McLaughlin, Lev Zakharov, George Donkor-Gyami and Pere Miró. The U.S. Department of Energy and the Murdock Charitable Trust supported the research, and Roseborough is now a metallurgist with the department’s National Energy Technology Laboratory.

The implications reach well beyond the laboratory bench. As demand grows for both advanced microelectronics and carbon-free nuclear power, a greener, cheaper and more selective separation chemistry could ease a supply chain bottleneck that has persisted for decades. By eliminating millions of pounds of organic solvent each year and cutting the energy cost of one of chemistry’s most stubborn separations, the Oregon State process offers the semiconductor and nuclear industries a path toward cleaner production of two metals on which modern technology quietly depends.

The difficulty of the zirconium-hafnium separation stems from a phenomenon chemists call the lanthanide contraction. Because hafnium sits directly below zirconium in the periodic table, the added electrons in hafnium are balanced by the contraction of its atomic radius, leaving the two elements with nearly identical ionic sizes and charge densities. This means that reagents designed to grab one metal almost invariably grab the other, which is why conventional separation schemes have relied on brute-force methods that cycle enormous volumes of material through many extraction stages. Any chemistry that can discriminate between the two elements in a single, simple step therefore represents a meaningful departure from decades of practice.

Precipitation itself is one of the oldest tools in the chemist’s repertoire, but its use in high-precision metal refining has been limited by a lack of selectivity. The Oregon State team’s insight was that selectivity could emerge not from a specially engineered synthetic ligand but from the way the metals organize themselves in solution. In the presence of thiocyanate, the zirconium and hafnium ions assemble into clusters of different nuclearity, meaning different numbers of metal atoms are joined into a single molecular unit. Because hafnium-rich clusters adopt structures that fall out of solution preferentially, the separation arises from the self-assembly behavior of the mixture rather than from a one-to-one binding event. This emergent selectivity, as the study’s title suggests, is what allows a simple precipitation to rival a multi-stage solvent extraction plant.

The choice of choline as the counter-ion is also notable from a sustainability standpoint. Choline is produced on an industrial scale, is recognized as safe in food applications, and is readily biodegradable, which stands in sharp contrast to the organic diluents and extractants used in conventional liquid-liquid extraction. Those solvents, typically flammable hydrocarbon mixtures, pose fire hazards in addition to the volatile emissions already noted, and their disposal adds cost and regulatory burden. A process whose main reagents are water, thiocyanate salt, and choline would be far easier to permit and operate, particularly if the thiocyanate and choline can be recovered and recycled from the mother liquor after the hafnium-rich solid is removed.

The separation factor of 33 deserves some context. In industrial separations, each incremental improvement in this metric translates into fewer processing stages, smaller equipment, and lower energy consumption, because the amount of material that must be recycled or reprocessed shrinks. A fivefold improvement over the standard value of six to seven could, in principle, compress a separation train that currently requires many repeated extraction and scrubbing cycles into a much shorter sequence. The researchers caution, however, that laboratory-scale separation factors do not translate directly into plant performance; questions of crystal handling, throughput, reagent recovery, and the behavior of real zircon feedstocks with their full complement of trace impurities remain to be resolved.

The demand backdrop strengthens the case for such advances. Zirconium alloys have long been the material of choice for nuclear fuel cladding because of their combination of neutron transparency, corrosion resistance, and mechanical strength, and a renewed interest in nuclear energy as a low-carbon power source is expected to sustain or grow that demand. On the semiconductor side, hafnium-based dielectrics became standard in advanced logic transistors after the industry transitioned away from silicon dioxide gate insulators, and hafnium consumption has grown with each generation of chip manufacturing. Both supply chains currently funnel through the same narrow refining bottleneck, which is why a chemistry that could be adopted more broadly, without the scale and hazard of solvent extraction plants, would be strategically significant.

The atomic-level characterization reported in the study also carries methodological weight. By determining the structures of the precipitated species and correlating crystal morphology with hafnium content, the researchers provided a mechanistic account of why the separation works, rather than merely demonstrating that it does. That kind of understanding is what allows a laboratory discovery to be optimized rationally, since future work can target the specific cluster geometries and solution conditions that favor hafnium enrichment. The team’s acknowledgment that questions remain suggests they view the current result as a foundation rather than a finished technology, with the path forward involving refinement of the precipitation conditions and demonstration at larger scales.

Funding from the U.S. Department of Energy reflects the national-security and energy dimensions of the work, since domestic production of reactor-grade zirconium has long been considered a strategic capability. With only two industrial separation facilities in the country, the supply chain for both nuclear fuel and semiconductor-grade hafnium is unusually concentrated, and any disruption at either site would ripple through both industries. A precipitation-based alternative that could be implemented at smaller scale, with lower capital intensity and without flammable solvents, would add resilience to that chain while reducing the environmental footprint of a process that has remained essentially unchanged in principle for many decades.

Subject of Research: Green chemistry separation of zirconium and hafnium for semiconductor and nuclear industries

Article Title: Semiconductor, nuclear industries poised for green boost thanks to chemistry breakthrough

Article References: Semiconductor, nuclear industries poised for green boost thanks to chemistry breakthrough. (n.d.). Original publication

Image Credits: AI Generated

DOI: Not provided

Keywords: zirconium, hafnium, green chemistry, semiconductors, nuclear energy, precipitation, Oregon State University, separation factor, thiocyanate, materials science, Semiconductor, nuclear