Kinetic study of chromium(VI) facilitated transport through a bulk liquid membrane using tri-n-butyl phosphate as carrier

The facilitated transport of Cr(VI) through a bulk liquid membrane (BLM) is investigated, using the commercially available solvent tri-n-butyl phosphate (TBP) as mobile carrier. The influences of the carrier concentration in the liquid membrane phase, the HCl concentration of the feed phase, and the stripping concentration on the mass transfer process are studied. The transport rate of Cr(VI) increases with increasing the TBP concentration and HCl concentration. The increasing of the stripping concentration improves the stripping process until a plateau is reached. A kinetic model is used to describe the Cr(VI) transport behavior, assuming that it obeys the kinetic laws of two consecutive irreversible first-order reactions. The experimental data fits reasonable well with the derived model. The analysis of the accumulation of Cr(VI) in the liquid membrane phase and the discussion of the rate-controlling step under different experimental conditions are carried out. The magnitude of the value of ke and ks is found to be 10−4–10−5 s−1, and is well in agreement with other studies.