A team of Northwestern University chemists has developed a method that can remove strontium - a dangerous radioactive fission material, from nuclear waste.
The new method takes the advantage of ion exchange to capture and concentrate strontium as a solid material, leaving clean liquid behind.
In the case of actual nuclear waste remediation, the radioactive solid could then be dealt with separately - handled, moved, stored or recycled - and the liquid disposed.
"It is a very difficult job to capture strontium in vast amounts of liquid nuclear waste," said Mercouri G. Kanatzidis, Charles E. and Emma H. Morrison Professor of Chemistry in the Weinberg College of Arts and Sciences.
"Sodium and calcium ions, which are nonradioactive, are present in such enormous amounts compared to strontium that they can be captured instead of the radioactive material, interfering with remediation," he added.
But, the material developed at Northwestern University - a layered metal sulfide made of potassium, manganese, tin and sulfur called KMS-1 - attracts strontium but not sodium."
The metal sulfide did much, much better than we expected at removing strontium in such an excess of sodium," said Kanatzidis.
"We were really amazed at how well it discriminates against sodium and think we have something special. As far as we can tell, this is the best material out there for this kind of application," he added.
The solution the researchers used in the lab contained strontium and two "interfering" ions, sodium and calcium, in concentrations like those found in the nuclear waste industry.
KMS-1, a free flowing black-brown powder, was packaged like tea in a teabag and then dropped into the solution. The all-important ion exchange followed: the metal sulfide "teabag" soaked up the strontium and gave off potassium, which is not radioactive, into the liquid.
"The nuclear power process generates enormous amounts of radioactive liquid waste, which is stored in large tanks," said Kanatzidis. "If we can concentrate the radioactive material, it can be dealt with and the nonradioactive water thrown away. I can imagine our material as part of a cleansing filter that the solution is passed through," he added.
According to J. Manos, a postdoctoral fellow at Northwestern and lead author of the study, "Our next step is to do systematic studies, including using an actual waste solution from the nuclear power industry, to learn how KMS-1 works and how to make even better metal sulfides."