HEAVY ELEMENT SEPARATION AND EXTRACTION IN BI-PHASIC SOLVENT SYSTEMS

Extraction and separation of heavy elements remains a significant challenge in regards to increasing efficiency and decreasing waste. Molecular level simulations are being applied to gain a detailed microscopic understanding of the inherent interactions that govern and control the factors of separation in aqueous – organic biphasic systems important to modern extraction methods. In this presentation, the role of interfacial structure and solvent structure about heavy element ion molecular complexes is characterized with respect to partitioning. Molecular dynamics simulations are used to determine the free energy difference via the work function, also known as the potential of mean force, that give a measure of partitioning. Molecular details of interface structure provide critical information of how various isomers of organic solvents contribute to the facility or hindrance of partitioning. The structure of the interface is investigated together with the role of counter ion solubility, the role of chelating ligands, and how solvent modifying agents affect partitioning. Specifically, this work reviews the role of simple counter ions and diketone chelates in facilitating transport of neptunium (Np) across aqueous - hexane (isomer) interfaces as determined by the potential of mean force based on molecular dynamics simulations and the umbrella integration technique.