ROLE OF THE INTERFACE IN THE KINETICS AND MECHANISM OF NICKEL EXTRACTION WITH CERTAIN HALOGEN-SUBSTITUTED AND ALKYL-SUBSTITUTED 8-QUINOLINOLS

Halogen- or alkyl-substitution of the chelating extractant 8-quinolinol raises the distribution constant of the neutral ligand and, therefore, the interfacial activity of the corresponding ligand anion. This, in turn, results in a systematic change in the rate-determining step in the extraction of nickel with 8-quinolinols from a combination of bulk aqueous phase and interfacial reactions to reaction solely at the liquid-liquid interface. In systems in which a bulk and interfacial reaction of the ligand occur simultaneously, the rate constant associated with the interfacial reaction is typically an order of magnitude larger than that for the bulk reaction.