New material can find a needle in a nuclear waste haystack
scale.
In earlier work, Kanatzidis and his team had found KMS-1 to be very quick and facile at ion exchange the material gives up an ion and takes another to maintain charge balance). Knowing this and also that the ion exchange process is a removal process, the researchers decided that strontium was an interesting ion with which to test their new material. 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 (nonradioactive strontium, which works the same as the radioactive version, was used in the experiments). 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. KMS-1 does its remarkable work targeting only strontium by taking advantage of two things: Strontium is a heavier ion than calcium, and sulfur (a component of KMS-1) attracts heavier ions; and KMS-1 attracts ions with more charge so it attracts strontium, which has a charge of 2+, and doesn’t attract sodium, which only has a charge of 1+. So, as Kanatzidis likes to say, “Our material beats both sodium and calcium. 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.”
Looking to the future, to be a scaleable and affordable remediation method, the metal in the metal sulfide needs to be inexpensive and readily available and also make a stable compound. “We focused on potassium, manganese and tin because we have been working with them for some time,” said Manolis Manos, a postdoctoral fellow at Northwestern and lead author of the paper. “All three metals make stable compounds and are common and abundant. 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,” added Manos.
-read more in …, “Layered Metal Sulfides: Exceptionally Selective Agents for Radioactive Strontium Removal,” Proceedings of the National Academy of Sciences (3 March 2008) (sub. req.)
