Computational Chemistry Assisted Simulation for Metal Ion Separation in the Aqueous-Organic Biphasic Systems

Understanding the separation of metal ions from the aqueous phase to the organic phase is of great relevanceto basic scientific knowledge, as well as to the development of advanced technology, especially in nuclear waste reprocessing. In that direction, computational chemistry comprising Quantum electronic structure calculations (QESC) and molecular dynamics (MD) simulations technique hasemerged as a strong complimentary tool to the solvent extraction and ion exchnage experiments by providing microscopic pictures at the molecular level. Therefore, the present chapter is devoted to the application of QESC and MD simulations in the microscopic understanding of the ligand-aided metal ion transfer processesand thus its assistance in nuclear waste management.Density functional theory–based quantum electronic structure calculations have been shown to be very useful in interpreting the coordinating environment of different radionuclides towards binding ligating chemical species. Further, the interaction strength of extractant molecules with the radionuclide can be decisively predicted and thus can be used as a prescreening criteria.The preferential selectivity of radionuclide towards a particular extractant can be well predicted by determining the free energy of extraction using thermodynamic cycle, as the free energy of extraction is correlated with the experimentally determined distribution constants as confirmed by determining the free energy of UO₂ ²⁺ and Pu⁴⁺ towards DH2EHA, DHOA, TMDGA, and GO-EGMP. Further, high-fidelity molecular simulations were shown to capture the experimentally observed migration of uranyl nitrate complexes from the aqueous to the aqueous-organic interface to the organic phase. MD simulations on several systems involving various acid models reveal the effect of acid in the aqueous phase, organic phase, and aqueous/organic interface. Simulations with varied TBP and acid concentration yield the trends similar toexperiments, which might be helpful while considering the extraction of many metal ions using TBPs.