Study of Kinetic Parameters of Uranium (VI) Extraction and Stripping from Phosphoric Acid Medium by Bulk Liquid Membrane Containing Di-2-Ethylhexyl Phosphoric Acid

Facilitated transport kinetics of uranium (VI) from a phosphoric acid medium into another phosphoric acid medium as a receiving phase through a bulk liquid membrane containing di-2-ethylhexyl phosphoric acid (HDEPA) as a carrier was studied. The influence of phosphoric acid concentration in source and receiving phases, carrier concentration, type of solvent, stirring speed and temperature were investigated. The kinetic parameters (ke, ks, tmax, Jmax) were calculated for the interfacial reactions, assuming two consecutive, irreversible first-order reactions. The activation energy values were calculated as 29.40 and 19.51 kJmol-1 for extraction and stripping, respectively. The values of the calculated activation energy indicated that the extraction process was controlled by the mixed regime (both kinetic and diffusion), and the stripping process was merely diffusionally controlled. In comparison with HDEPA optimized conditions, though with adding trioctyl-phosphine oxide into membrane phase as a synergic agent, the extraction rate remained approximately constant but the stripping rate diminished dramatically that led to the decrease of the transport kinetics.