New material can find a needle in a nuclear waste haystack

The rising price of oil and worries about the environment have renewed interest in nuclear power generation. Nuclear power, though, comes with a big problem: What to do about nuclear waste? A team of Northwestern University chemists is the first to focus on metal sulfide materials as a possible source for nuclear waste remediation methods. Their new material is extremely successful in removing strontium from a sodium-heavy solution, which has concentrations similar to those in real liquid nuclear waste. Strontium-90, a major waste component, is one of the more dangerous radioactive fission materials created within a nuclear reactor. The results are published in the Proceedings of the National Academy of Sciences. By taking advantage of ion exchange, the new method captures and concentrates 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 Kanatzidis, Charles E. and Emma H. Morrison Professor of Chemistry in the Weinberg College of Arts and Sciences, Northwestern University, and the paper’s senior author. “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.”

Strontium is like a needle in a haystack: Sodium ions outnumber strontium ions by more than a million to one. The material developed at Northwestern — 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.” KMS-1 works at the extremes of the pH scale — in very basic and very acidic solutions, the conditions common in nuclear waste — and everywhere in between. Metal oxides and polymer resins, the materials currently used in nuclear waste remediation, perform reasonably well but are more limited than KMS-1: each typically works in either basic or acidic conditions but not both and definitely not across the pH