Catalytic Effect of Ionic Surfactants on the Extraction Rate of Nickel(II) and Palladium(II) with 2-(5-Bromo-2-pyridylazo)-5-diethylaminophenol in the Toluene/Water System

Abstract

The effects of the surfactants on the extraction rate of nickel(II) and palladium(II) with 2-(5-bromo-2-pyridylazo)-5-diethyaminophenol (5-Br-PADAP) in the toluene/water system were investigated by the centrifugal liquid membrane (CLM) method. The extraction rates of the metal(II) ions were increased by the addition of the ionic surfactants having a charge opposite to the metal(II) species in the aqueous solution. The stronger the interfacial activity of the surfactant, the larger the acceleration effect became. The acceleration was explained by the increase in the interfacial concentration of metal ions by an electrostatic attraction between the metal species and the ionic surfactant adsorbed at the interface. On the other hand, the extraction rates of metal(II) ions were reduced by the addition of an ionic surfactant having the same charge as the metal(II) species and the nonionic surfactant.