SOLVENT-EXTRACTION OF PALLADIUM(II) WITH NONCHELATING OXIMES WITH DIFFERENT ALKYL CHAIN LENGTHS

By using four kinds of nonchelating oximes with alkyl chains of different lengths (dodecanal oxime, decanal oxime, octanal oxime, and hexanal oxime), the effects of the hydrophobicity of these extractants on the extraction mechanism of palladium (II) were investigated from the equilibria and kinetic aspects along with the aqueous solubilities and the interfacial adsorption equilibria of the extractants. The loading test showed that palladium(II) was extracted as 1:2 Pd:extractant complexes with all kinds of oximes. The extraction kinetics with dodecanal oxime, which is practically insoluble in the aqueous solution and interfacially active, was reasonably interpreted in terms of the interfacial reaction model. The rate is limited by the formation of the intermediate complex at the interface between the aqueous and organic phases. The extraction kinetics with hexanal oxime with the shortest alkyl chain length, which is of high aqueous solubility and of low interfacial activity, was explained in terms of the classical heterophase homogeneous reaction mechanism controlled by the formation of the intermediate complex in the aqueous phase. The extraction kinetics with two other kinds of oximes was reasonably explained by taking into account the formation of intermediate complexes, which takes place simultaneously at the interface and in the aqueous phase as the rate-determining steps. © 1990, American Chemical Society. All rights reserved.