Characterization of reversed micelles formed in solvent extraction of thorium(IV) by bis(2-ethylhexyl) phosphoric acid. Transforming from rodlike to wormlike morphology

Abstract

Abstract The reversed micelles formed in solvent extraction of thorium(IV) by bis(2-ethylhexyl) phosphoric acid (HDEHP) in n-heptane were studied. IR spectra, dynamic/static light scattering and zero shear viscosity measurements indicated that thorium complexes formed rodlike reversed micelles, and both the size of aggregates and the viscosity of the organic phase increased with the increasing loadage of thorium(IV). The entanglement of reversed micelles resulted in their transformation to wormlike reversed micelles, inducing the very high viscosity of the organic phase. The structural composition of thorium complexes was proposed to be Th(DEHP)3(NO3) according to the results of log -log  plot and job method analysis. Furthermore, molecular modeling was employed to clarify the structures of reversed micelles as well as the state of water inside. It was found that the complexes linked together via hydrogen bonding and van der Waals forces and that the existence of NO3 – and H2O improved the stability of reversed micelles.