Elucidation\nof the Decomplexation and Reverse Migration\nMechanism of Uranyl Ions from the Oil Phase to the Aqueous Phase Using\nMicrosecond (0.2 μs) Molecular Dynamics Simulations

Interphase ion transfer is ubiquitous in chemistry, physics,\nbiology,\nand various engineering sciences. Ion transfer from the aqueous phase\nto the oil phase or vice versa is a complex chemical phenomenon, and\nits fundamental understanding is crucial for efficient and economical\nmass transfer. This ion transfer is much more complex for radionuclide\nmetal ions. Therefore, an attempt has been made to elucidate the decomplexation\nand mechanism of reverse migration of uranyl ions from the loaded\noil phase to the aqueous phase using large time-scale molecular dynamics\nsimulations (microseconds) and density functional theory (DFT). The\nstrength of the metal–ligand complex is the key factor for\nstripping among other mass transfer parameters. Stronger the metal–ligand\ncomplex, the lower the tendency for reverse migration into the aqueous\nphase, which was demonstrated by three different ligands for reverse\nmigration using water as the stripping agent. The interaction energy\nof the metal–ligand complex has been calculated using DFT.\nThe reverse migration is validated by the distance between the centers\nof mass. Higher interface thickness and lower interfacial tension\nbelong to <i>N</i>,<i>N</i>,<i>N</i>′,<i>N</i>′-tetra-octyldiglycolamide (TODGA),\nwhich are favorable for mass transfer across the liquid–liquid\ninterface. The computed distribution coefficient (K<sub>D</sub>) is\nfavorable for tributyl phosphate (TBP) and tri-iso-amyl phosphate\n(TiAP), whereas TODGA shows a higher K<sub>D</sub>, indicating a less\nfavorable value for reverse migration. The distance between the uranyl\nion and the TODGA molecule confirms that the entrapment of uranyl\nions in the TODGA phase might be attributed to aggregation. Further,\nthe aggregation tendency of TODGA molecules reduces the back extraction\nand the recovery of uranyl ions into the aqueous phase. The present\nMD results might be important for predicting an efficient back-extracting\nagent for the recovery of the metal ions from the oil phase.