Elucidation of the Structure of Organic Solutions in Solvent Extraction by Combining Molecular Dynamics and X‐ray Scattering

Abstract

Knowledge of the supramolecular structure of the organic phase containing amphiphilic ligand molecules is mandatory for full comprehension of ionic separation during solvent extraction. Existing structural models are based on simple geometric aggregates, but no consensus exists on the interaction potentials. Herein, we show that molecular dynamics crossed with scattering techniques offers key insight into the complex fluid involving weak interactions without any long-range ordering. Two systems containing mono- or diamide extractants in heptane and contacted with an aqueous phase were selected as examples to demonstrate the advantages of coupling the two approaches for furthering fundamental studies on solvent extraction.

Determination of the Structures of Uranyl–Tri‐n‐butyl‐Phosphate Aggregates by Coupling Experimental Results with Molecular Dynamic Simulations

“…The calculated SWAXS intensity profiles are in good agreement with the experimental ones thanks to the use of a polarizable force field, as emphasized in our previous studies . The first I ( q ) peak is well reproduced at 14 nm −1 ; this corresponds to the first‐shell interactions of the aliphatic chains in solution.…”

“…The extraction of uranium from the organic solution leads first to a formation of uranyl/TBP 1:2 and 1:3 complexes, and then, upon increasing the uranium concentration, to the formation of polymetallic aggregates described by [UO 2 (NO 3 ) 2 (TBP) 2 ] n , with n =2 or 3 (and n =4 for the highest TBP and uranyl nitrate concentrations). The organization in these TBP organic phases is quite different from that previously described for diamide organic phases after extraction of water or lanthanide nitrate salts (aggregates are comparable to small reverse micelles with polar cores including water molecules),, or monoamide organic phases after extraction of water or uranyl nitrate salts (extractant aggregation occurs only after UO 2 (NO 3 ) 2 extraction and produces long linear threads of nitrate‐bridged uranyl cations) . Herein, aggregation with TBP is between these two cases, with the formation of 1) simple complexes at low uranium concentration, or 2) aggregates at higher uranium concentration, which could be assimilated into very small reverse micelles, as far as their shape is concerned, but without inclusion of water molecules in the polar core.…”

“…Once agreement of the MD solution densities with the experimental ones had been checked (Table ), SWAXS intensities were calculated from MD trajectories for each solution (Figure , solid lines), following the procedure described in ref. , that is, without any adjustment of the calculated signal.…”

Die zweigesichtige Natur der Wasserstoffbrückenbindung in hydroxylfunktionalisierten ionischen Flüssigkeiten, offenbart durch Neutronendiffraktometrie und Molekulardynamik‐Simulation

“…[36][37][38][39][40] 4 Py] + ein gut polarisierbares Kation ist. [41,42] Die gemessenen Bindungslängen der Wasserstoffbrückenbindungen fürb eide Arten ionischer Wechselwirkungen, die zum einen die Anziehung zwischen entgegengesetzt geladenen Ionen und zum anderen die Abstoßung zwischen Ionen gleicher Ladung beschreiben, werden mit denen von molekularen Flüssigkeiten wie Wasser und Alkoholen verglichen. [29][30][31][32][33][34][35] Ziel dieser Arbeit ist es,d ie (c-a)-( + OÀH···O À )u nd die (c-c)-Wasserstoffbrücken ( + O À H···O + )i nd ieser hydroxylfunktionalisierten IL mittels ND,M olekulardynamik(MD)-Simulationen und quantenchemischen Berechnungen zu charakterisieren.…”

Solvent Extraction: Structure of the Liquid–Liquid Interface Containing a Diamide Ligand

“…These lipophilic extractants are currently used in the nuclear industry to separate f-elements from high-level radioactive liquid waste by LL extraction processes [16] (the DIAMEX process) as well as in the more conventional field of hydrometallurgy to recycle rare-earth elements. [19] Ford iamide in dodecane and in contact with an aqueous phase containing neodymium nitrate salt, the CACo fe xtractant varies between 0.01 and 0.1m depending on the diamide chemistry and the water activity. These extractant molecules have amphiphilic properties [18] that allow first acomplexation of the ligands with specific cations at the interface,second an increase in efficiency of the emulsification that occurs during the solvent extraction process and third astructuration of the oil phase that depends on the extractant concentration and the activity of the various species in the water phase.Due to such surfactant behavior,these molecules indeed form nanoscale structures above ag iven critical aggregation concentration (CAC)w ithin the organic phase such as inverted micelles or reversed aggregates.…”