Equilibria and Kinetics of the Extraction of Nickel with 2-Pyridinecarbaldehyde 2-(5-substituted)pyridylhydrazones

Abstract

The equilibria and kinetics of the extraction of nickel ion with benzene solutions of 2-pyridinecarbaldehyde 2-(5-substituted)pyridylhydrazones have been studied at 25±0.1°C and an ionic strength of 0.2. The extracted species was found to be NiL₂ for each hydrazone, where L denotes the undissociable part of the hydrazone. Partition constants of the hydrazones and extraction constants of their nickel complexes between an aqueous and a benzene phase were determined. The rate of extraction was found to be best described by a two-term expression, both terms being first order in nickel ion and HL concentrations. The first term has zero dependence on hydrogen ion concentration, whereas the second is inversely first order with respect to hydrogen ion concentration. These results support the hypothesis that the rate-determining steps involve two concurrent reactions of nickel ion with neutral and anionic forms of the hydrazones. Kinetic data and activation parameters for the first reaction were determined, but those for the second one involving the anion could not be obtained.