Nuclear power has advantages, but if this method of making power is to be viable for the long term, discovering new solutions to radioactive waste disposal and other problems is critical. Otherwise, nuclear power is unlikely to become mainstream.

A team of Northwestern University chemists is focusing 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.

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 of.

“It is a very difficult job to capture strontium in vast amounts of liquid nuclear waste,” said Mercouri G. Kanatzidis, professor of chemistry at Northwestern’s 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.”

According to Kanatzidis, finding strontium in nuclear waste is like finding 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.

In experiments, KMS-1, a free-flowing, black-brown powder, was packaged like tea in a tea bag and then dropped into a solution mixing strontium ions with other ions. The all-important ion exchange followed. The metal sulfide “tea bag” 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,” Kanatzidis said. “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.”

Looking to the future, to be a scaleable and affordable remediation method, the metal in the metal sulfide needs to be inexpensive, readily available and able to make a stable compound.

The group’s 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. If the project continues on pace, the group may prove to have found a better solution for nuclear waste.