(177g) Atomistic Simulation of Water Extraction by TBP/Dodecane

Solvent extraction is the workhorse process in industrial nuclear fuel reprocessing. Metal ions, acid, and water are typically co-extracted from the aqueous phase into the organic phase, such as TBP/dodecane, a prevalent solvent mixture. As a first step to understand and quantify this process, we investigate the process of water extraction and interfacial properties using full atomistic force field models, including a recently developed force field model for TBP. We conduct large scale simulations involving a few tens to a few hundred thousand atoms to investigate the process of water molecule transfer from the interface region into the organic phase. We find that the breaking of hydrogen bonds at the interface is a crucial step in determining the rate of extraction. To this end, we have carried out molecular simulation at various temperatures and ambient pressure to investigate the effect of temperature on the process and the rate of extraction. In addition, we have thoroughly characterized the aqueous/organic interface to gain deep insight into the extraction process. Specifically, we have determined the density profiles of water, TBP, and dodecane across the interface, the preferential orientation of polar molecule (group) at the interface, and the enrichment of TBP molecules in the interfacial region, as well as the interfacial tension. Finally, we have conducted long calculations (~100 ns) to investigate the whole molecular process of water extraction into the organic phase as well as determining the saturated water concentration in the organic phase (solubility).