KINETICS OF EXTRACTION AND BACK-EXTRACTION OF NICKEL DODECYLSALICYLALDOXIME AND ITS CORRELATION WITH CENTRIFUGAL PARTITION CHROMATOGRAPHIC EFFICIENCIES

Ni2+ is complexed in the rate limiting step by dodecylsalicylaldoxime in its neutral (HDSO) and deprotonated (DSO-) forms in the bulk aqueou s and hexane-aqueous interface. The interfacial rate constants for HDS O and DSO- are 3-5 times smaller than the bulk aqueous values, in cont rast 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 b ulk and interfacial component as well, with the interfacial rate const ant being an order of magnitude larger than the bulk rate constant. Th e interfacial activities of HDSO and DSO- forms and Ni(DSO)(2) at the hexane-aqueous interface are very nearly the same as indicated by thei r interfacial excess (Gamma) values. These Gamma values are among the largest measured to date for ligands and metal complexes of interest i n solvent extraction. The centrifugal partition chromatographic (CPC) efficiencies for the Ni-HDSO system at an aqueous mobile phase flaw ra te of 0.4 mL/min indicate the generation of a specific interfacial are a of 1350 cm(-1) corresponding to an aqueous mobile phase droplet size of 24 mu m. This area is 6 times larger than the maximum area generat ed in the highly mechanically stirred hexane-H2O mixture. This in effe ct leads to much larger CPC efficiencies than that predicted by the ki netics of formation and dissociation of Ni(DSO)(2) in the highly stirr ed mixture.