Uranyl Speciation in the Presence of Specific Ion Gradients at the Electrolyte/Organic Interface

Abstract

Uranyl (UO2+ 2 ) speciation at the liquid/liquid interface is an essential aspect of the mech?anism that underlies its extraction as part of spent nuclear fuel reprocessing schemes and environmental remediation of contaminated legacy waste sites. Of particular importance is a detailed perspective of how changing ion concentrations at the liquid interface alter the distribu?tion of hydrated uranyl ion and its interactions with complexing electrolyte counterions relative to the bulk aqueous solution. In this work, classical molecular dynamics simulations have ex?amined uranyl in bulk LiNO3(aq) and in the presence of a hexane interface. UO2+ 2 is observed to have both direct coordination with NO− 3 and outer-sphere interactions via solvent-separated ion-pairing (SSIP), whereas the interaction of Li+ with NO− 3 (if it occurs) is predominantly as a contact ion-pair (CIP). The variability of uranyl interactions with nitrate is hypothesized to prevent dehydration of uranyl at the interface, and as such the cation concentration is un?perturbed in the interfacial region. However, Li+ loses waters of solvation when it is present in the interfacial region, an unfavorable process that causes a Li+ depletion region. Although significant perturbations to ion-ion interactions, solvation, and solvation dynamics are observed in the interfacial region, importantly, this does not change the association constants of uranyl with nitrate. Thus, the experimental association constants, in combination with knowledge of the interfacial ion concentrations, can be used to predict the distribution of interfacial uranyl nitrate complexes. The enhanced concentration of uranyl dinitrate at the interface, caused by excess adsorbed NO− 3 , is highly relevant to extractant ligand design principles as such nitrate complexes are the reactants in ligand complexation and extraction events. File list (2) download file view on ChemRxiv Uranyl_complexation_and_solvation_in_nitrate_f.pdf (1.59 MiB) download file view on ChemRxiv Uranyl_complexation_and_solvation_in_nitrate_SI.pdf (4.00 MiB)

Unexpected inverse correlations and cooperativity in ion-pair phase transfer

“…The Li + and NO 3 − ions were modeled using parameters from Joung et al 39 and Ye et al 40,41 but with a 90% electrostatic continuum correction (ECC) to account for the polarization effects (charges scaled by 10%), as recently reported by Kumar et al 42 to reproduce the interactions with metal ions ( e.g. UO 2 2+ ) in PUREX-like conditions up to 5 M [LiNO 3 ].…”

Contribution of Molecular Dynamics in pNMR for the Structural Determination of AnV and AnVI Complexes in Solution

“…The purpose of this paper is to study flexible actinyle complexes with tetra-ethyl dyglicolamide (TEDGA) as ligand. Herein, in order to explore the different conformations existing in solution and to access the geometric factors needed to determine the χ parameters, classical MDs simulations coupled with NMR and EXAFS spectroscopies have been performed, since this theoretical method has proven its robustness for studying the actinide-ligand interactions. − …”

Adsorbate Organization Characterized by Sublevelset Persistent Homology

“…The LiNO 3(aq) /TBP/hexane systems were equilibrated in NPT and NVT for a minimum of 20 ns using the Nosé-Hoover thermostat and Parrinello–Rahman barostat. , Production runs were performed for more than 150 ns in the NVT ensemble. The electronic continuum correlation (ECC) optimized Li + and NO 3 – force fields were employed in combination with TIP3P water as benchmarked in ref and the optimized TBP force fields taken from Ye et al Long-range electrostatics were handled using Particle-mesh Ewald (PME) summation . A 16 Å cutoff was used for both short-ranged and van der Waals atomic interactions.…”