Coordination complexes that can remove radioactive elements from the environment have been developed by US scientists.

The dwindling supply of fossil fuels means we must look towards alternative sources of energy such as nuclear power. However, the use of radioactive actinides such as uranium and plutonium has led to a host of waste and environmental contamination issues.

Most of the current systems used for extracting actinides work only at acidic pH. However, natural waters are at near neutral to basic pH, and much of the currently stored wastes are at very caustic conditions.

Now, Anne Gorden and colleagues at Auburn University, Alabama, US, have made simple compounds, which are stable under basic conditions, and could be used to remove toxic, heavy metals from contaminated water supplies or nuclear waste.

Gorden's team synthesized a uranyl Schiff base complex. Schiff base compounds are versatile ligands that can act as extractants by complexing to the metal that needs to be removed. 

The compound [(UO₂)₂(Salpro)(OH)(Solvent)₂] is resistant to nucleophilic addition and substitution reactions. This means that the uranium metal complex is more stable than expected under basic conditions, in contrast to Schiff base complexes with transition metals. 'Salpro' is a pentadentate chelating agent having five groups capable of attachment to a metal ion. It is this extended chelation as well as the bridging hydroxyl group that provides stability to the overall complex.

 'Investigations like this will broaden our understanding of the chemical behaviour of the actinides and enable the development of new sensors and sensing materials for improved detection and isolation of actinides from fuel wastes or contaminated environmental sites,' said Gorden.

Sarah Corcoran