Exploring the solvation of water molecules around radioactive elements in nuclear waste water treatment

Abstract

Abstract Nuclear waste water contains many actinides which coordinate with water molecules to form complexes. The hydration of water molecules with varying coordination numbers and modes makes it interesting and intriguing in understanding the extraction process of these radioactive ions. In order to separate these complexes from the nuclear waste water, many organic ligands are being used. However, prior knowledge on the nature of electronic environment of these hydration patterns will help us to understand the extraction mechanism. Therefore, a series of complexes such as [Np(H2O)9]4+, [Cm(H2O)9]3+, [Am(H2O)9]3+, [Pu(H2O)9]4+, [Pu(H2O)9]3+, [U(H2O)9]3+, [NpO2(H2O)5]+, [UO2(H2O)5]2+ and [PuO2(H2O)5]2+ have been calculated by means of relativistic DFT. Bond length analysis and energy decomposition analysis are executed with the intention to comprehend the bonding situation of these complexes. To account for the stabilizing interactions amid the radioactive ion and the water molecules, a detailed QTAIM investigation is done. It is seen that the metals having higher oxidation state readily complex with water molecules. Energy decomposition analysis throws light on the significant orbital interactions in the [M(H2O)9] n complexes, whereas in the metal oxide complexes significant contribution is resulted from electrostatic interactions. In summary, this investigation brings out the nuances of coordination modes of solvation in nuclear waste water which will help us to explore and design novel extraction techniques in near future.