Highly Efficient Removal of Americium(III) from High-Level Waste Using Novel Phenanthroline Diamide Ligands

The most important problem of atomic energy is the reprocessing of spent nuclear fuel and management of high-level radioactive waste (HLW). The separation of americium(III) from HLW remains a severe problem, the solution of which is necessary for the sustainable development of nuclear energetics. Two novel phenantrolinediamide ligands having methyl groups in the ortho-positions of the aryl fragments demonstrate record values for the separation factors of Am(III) and light lanthanides(III) including HLW imitator solution containing 10.7 g/L of lanthanides(III), 0.5 g/L of Pd, and 0.2 g/L of Zr in 3 mol/L nitric acid solution. They also have a high extraction equilibrium rate, high radiolytic stability, and fully reversible extraction, which allows americium back-extraction to be performed using dilute nitric acid. The mechanism of complexation using SC-XRD and DFT calculations was investigated to demonstrate the importance of formation complexes having a ligand:metal 2:1 ratio.