Comparative study on aqueous acid free UO2 dissolution-extraction using DHOA adduct into room temperature ionic liquid/supercritical carbon dioxide/n-hexane

Abstract

Abstract Feasibility was established for direct dissolution-extraction of uranium employing adduct of N,N-dihexyl octanamide (DHOA), thus eliminating discrete aqueous phase and free acid usage. Various aspects of dissolution of solid uranium dioxide and extraction of uranium into molecular diluent viz. n-hexane and neoteric solvents viz. room temperature ionic liquid (RTIL) and supercritical carbon dioxide (SC CO2) were studied. The organic adduct was found to have composition DHOA.(HNO3)0.78(H2O)0.4. Adduct miscibility and UO2 dissolution behavior was markedly different for RTIL and n-hexane. The dissolution process, studied by monitoring UV–Vis spectra, was found to be pseudo first order with a rate constant of of 0.074 min−1 and 0.036 min−1 for n-hexane and RTIL respectively. Irrespective of medium, dissolution-extraction efficiency of ≥90% was achievable. Using RTIL for dissolution-extraction medium and SC CO2 for stripping is promising in terms of overall efficiency as well as RTIL recovery by avoiding aqueous cross contamination.