Kinetics of Extraction and Back-Extraction of Nickel Dodecylsalicylaldoxime and Its Correlation with Centrifugal Partition Chromatographic Efficiencies

Abstract

Ni 2+ is complexed in the rate limiting step by dodecylsalicylaldoxime in its neutral (HDSO) and deprotonated (DSO-) forms in the bulk aqueous and hexane-aqueous interface. The interfacial rate constants for HDSO and DSO- are 3-5 times smaller than the bulk aqueous values, in contrast to the other ligand systems studied previously where the opposite was the case. The rate limiting step in the dissociation of Ni(DSO) 2 complex is the reaction of Ni(DSO) + with H + . This reaction has a bulk and interfacial component as well, with the interfacial rate constant being an order of magnitude larger than the bulk rate constant. The interfacial activities of HDSO and DSO- forms and Ni(DSO) 2 at the hexane-aqueous interface are very nearly the same as indicated by their interfacial excess (Γ) values. These Γ values are among the largest measured to date for ligands and metal complexes of interest in solvent extraction. The centrifugal partition chromatographic (CPC) efficiencies for the Ni-HDSO system at an aqueous mobile phase flow rate of 0.4 mL/min indicate the generation of a specific interfacial area of 1350 cm -1 corresponding to an aqueous mobile phase droplet size of 24 μm.