The centrifugal liquid membrane method, which provides an ultra-thin two phase liquid membrane system in a rotating glass cell, was successfully applied for the kinetic study of the liquid-liquid extraction of nickel(II) and zinc(II) with 2-(5-bromo-2-pyridylazo)-5-diethylaminophenol (5-Br-PADAP) in toluene. The initial extraction rate of the metal(II) complexes depended upon the concentrations of the metal(II) ion and ligand. The rate determining step was revealed as 1:1 chelate formation of Ni(II) or Zn(II) with 5-Br-PADAP adsorbed at the liquid-liquid interface. The interfacial complexation rate constants of Ni(II)-5-Br-PADAP and Zn(II)-5-Br-PADAP were determined as (4.1 ± 0.1) x 10 and (2.4 ± 0.6) x 103 M-1 s-1 at pH 6.50 ± 0.02, respectively. (C) 2000 Elsevier Science B.V.
- Centrifugal liquid membrane method
- Extraction kinetics
- Interfacial complexation
- Liquid-liquid extraction