TBP Assisted Uranyl Extraction in Water-Dodecane Biphasic System: Insights from Molecular Dynamics Simulation

Abstract

Abstract In the PUREX (Plutonium Uranium Recovery by Extraction Process) process, the extraction of uranyl ion from dissolver solution to the organic phase is influenced by co extraction of the other species, such as water and nitric acid and it is assumed that the presence of water or acid droplets in the organic phase intensifies the coordination mechanism of TBP. The present study illustrates the uranyl extraction from the aqueous phase to the organic phase using molecular dynamics (MD) simulation. Here, we consider the biphasic systems to gain insights into the characteristics of the interface and humidity of the organic phase under different acidic and neutral conditions. MD being a force field method, can’t satisfactorily model the bond making and breaking process therefore a priori choice has been made concerning the different status of proton for the acidic phase. Further, the importance of charge species transferability during uranyl-TBP complexation have been investigated considering two different models of uranyl nitrate; united UO2(NO3)2 complex and separate UO2 2+ and NO3 – ions. From the results, it is recommended to use the ionic uranyl model with separate UO2 2+ and NO3 – to study the structural and dynamical properties of extracted uranyl ions in the organic phase. Also, it was noticed that extracted uranyl ions in the organic phase are not completely dehydrated but are surrounded by water molecules. In other words the results show co extraction of other species such as water and acid molecules to the organic phase. Most remarkably, the present study evident that the neutral HNO3 effectively represents the acidity effect for the receiving phase in terms of acid/water extraction and their aggregation to form water droplet, especially when ionic model of uranyl nitrate is considered.