Determination of mass transfer coefficients of 99Tc(VII) in forward and backward transport in PUREX-relevant systems by using analytical ultracentrifugation

Abstract

The lack of published data on the extraction kinetics of Tc(VII) in the system U(VI)/HNO3//TBP/dodecane prompted us to investigate its transport behaviour in detail. The aim was to improve the U(VI)/Tc(VII) separation in the PUREX process. We choose the method of analytical ultracentrifugation to determine the concentration gradient profile, the initial flux density and the integral mass transport for both sides of the unstirred liquid-liquid interface as well as the overall mass transfer coefficients as a function of Tc(VII)-, U(VI)-concentrations and temperature from time-dependent changes of the refractive index gradients. The results were supplemented by comparing the experimental with calculated concentration profiles, obtained by modeling a diffusion-limited extraction process. In some of the investigated systems, the transport at the interface is reaction-limited after phase contact. The determined values of J max, I, and α are discussed in terms of the extraction conditions.