Computational chemistry study of zirconium monomers in low acid concentration aqueous solutions

Zirconium and hafnium have to be separated prior to their use in nuclear energy reactors. Therefore, a lot of research has been done on the solvent extraction of zirconium. However, most of this research involved screening studies that focused on finding suitable solvent extraction processes, rather than attempting to gain insights into the extraction mechanisms. An important part of understanding extraction mechanisms is knowing which zirconium species are present in aqueous solutions since these are the species with which extractants react. In this study, we used density functional theory based molecular dynamics calculations to model zirconium monomers in low acid concentration solutions. Specifically, we modelled aqua and hydroxo zirconium complexes using an explicit solvent approach. By calculating radial distribution functions for each of these zirconium complexes, using either 10, 20, 30, 40 or 50 explicit solvent water molecules, we were able to determine that at least about 30 solvent water molecules are needed to model the first two solvation spheres of a zirconium ion during an explicit solvent approach. We anticipate that this work will be useful for further explicit solvent based computational chemistry studies on the solvent extraction mechanisms of zirconium and hafnium.