A faster technique to purify the elements

Actinides, the chemical elements in the last row of the periodic table, are used in applications ranging from medical treatment to space exploration and nuclear power generation. But the purification of the target element so that it can be used, separating contaminants and other elements, can be difficult and time consuming.

Researchers at the Berkeley Lab's National Lawrence Berkeley Laboratory have developed a new method of separation that is much more efficient than conventional processes, paving the way for faster discovery of new elements, more Easier reprocessing of nuclear fuel and a better way to get actinium-225, a promising therapeutic isotope for the treatment of cancer.

The research entitled "Strategic actinide separation determined by an ultra-selective ligand" was published in the journal Nature Communications. The authors are Gauthier Deblonde, Abel Ricano and Rebecca Abergel from the Chemical Sciences Division of Berkeley Lab. "The proposed approach offers a paradigm shift for the production of strategic elements," the authors wrote.

"The process we propose seems much more efficient than existing processes, involves fewer steps and can be used in aqueous environments, so it does not require corrosive chemicals," said Abergel, head of Berkeley Lab Heavy Element Chemistry Group. "I think it's really important and it will be useful for many applications."

Berkeley Lab is part of a handful of institutions around the world that study the nuclear and chemical properties of the heaviest elements. Most of them have actually been discovered in the Berkeley lab over the past century. The Abergel group has previously published findings on berkelium and plutonium and treatments for radioactive contamination.

Abergel noted that the new separation method allows for separation factors several orders of magnitude higher than current state of the art methods. The separation factor is a measure of the ability of an element to be separated from a mixture. "The higher the separation factor, the fewer contaminants," she said. "Usually, when you purify an element, you cycle through it several times to reduce contaminants."

With a higher separation factor, fewer steps and fewer solvents are needed, which makes the process faster and more cost effective. For example, scientists demonstrated for one of the three systems that they purified the possibility of reducing the 25-step process to two steps.

Berkeley Lab researchers first introduced their method to actinium 225, an isotope of actinium that has shown very promising applications in radiotherapy. It works by killing cancer cells but not healthy cells by targeted delivery.

DOE's isotope program actively employs increasing the production of actinium-225 in all national laboratory accelerators. This new method of separation could be an alternative to chemical processes under development. "With any production process, you have to purify the final isotope," said Abergel. "Our method could be used right after production, before distribution."

The other two actinides purified in this study were plutonium and berkelium. An isotope of plutonium, plutonium 238, is used for the production of energy in the robots sent to explore Mars. Plutonium isotopes are also present in waste generated by nuclear power plants, where they must be separated from uranium in order to recycle uranium.

Finally, berkelium is important for basic scientific research. One of its uses is as a target for the discovery of new elements.

The process relies on the unprecedented ability of synthetic ligands – small molecules that bind metal atoms – to be highly selective for binding to metal cations (positive ions) depending on the size and charge of the metal.

The next step, said Abergel, is to explore the use of the process on other medical isotopes. "On the basis of what we have seen, this new method can really be generalized, as long as we have different loads on the metals we want to separate," she said. "Having a good purification process available could simplify everything in terms of post-production processing and availability."