PNNL

Image depicting technetium removal by metal organic frameworks, from the cover of a recent issue of Chemical Society Reviews that featured an article on PNNL’s research into MOFs.

It’s long-lived, highly mobile, and a significant risk driver for environmental cleanup—it’s technetium-99, and it’s one of the toughest challenges faced by the DOE in cleaning up millions of gallons of legacy nuclear waste at the Hanford Site in southeastern Washington State. Of special concern is technetium’s ability to move rapidly through the groundwater beneath the Hanford Site, possibly threatening the nearby Columbia River and surrounding communities. Prompted by interest from the DOE Office of River Protection, PNNL researchers think they may have an answer in a promising technique that would use metal organic frameworks or MOFs, to safely remove technetium-99 from Hanford wastes.

Dialing in a Solution

A cornerstone to cleanup at Hanford is the Vit Plant, a multi-billion dollar facility where DOE plans to transform Hanford waste into sturdy glass logs for safe, long-term storage using a process called vitrification. Technetium-99—which is highly volatile, chemically complex, and abundant in Hanford wastes—could complicate things by requiring DOE to add chemical solutions to any waste containing technetium before vitrifying it to prevent potential hazards during waste processing. More waste material means more processing, more glass logs, more time, and more money.

MOFs could change all that, according to principal investigator Praveen Thallapally, who along with other members of the research team recently published two articles on MOFs, including a cover story in the Royal Society of Chemistry’s Chemical Society Reviews.

What makes MOFs so promising? Unlike other methods that DOE could use to tackle technetium, MOFs can be “dialed in” to specifically target and remove technetium simply by changing the MOFs’ chemical makeup, says Thallapally. This may make it possible to use MOFs to remove technetium-99 before vitrification, which could add up to big savings and more efficient Vit Plant operations.

To the Laboratory and Beyond

With encouraging early test results already in hand, Thallapally and the team are back in the lab, exploring their method by sending simulated waste through stainless steel columns packed with MOFs that are chemically configured to target technetium. If things go well, the team will move on to larger scale tests to further demonstrate MOFs' potential at Hanford.

"In my experience, MOFs easily outperform any other class of materials," Thallapally says. "If our results are promising, MOFs could be the next generation of materials for chemical separation and transformations."

PNNL Research Team: Praveen Thallapally, Debasis Banerjee, Michael J Schweiger, and Dong-Sang Kim