Characterization of the liquid-liquid interface and its influence on metal extraction processes.

Abstract

8-Mercaptoquinoline (QSH) exhibited substantial interfacial activity in its neutral form. The interfacial activity of QSH may stem from its zwitterionic form QH⁺S⁻. The interfacial activities of Ni-HPMBP system are in the order Ni(PMBP)₂ > PMBP⁻ > HPMBP. The interfacial rate constant of formation reaction is 4 times greater than the bulk value. The bulk and interfacial rate constants for dissociation reaction of Ni(PMBP)₂ are essentially the same. The centrifugal partition chromatography (CPC) inefficiency as measured by the quantity channel equivalent of a theoretical plate (CETP), reflects the slow chemical kinetics of the back extraction reaction, and increases with the half life of the dissociation reaction. This correlation, for the first time, enables the determination of the interfacial areas generated, and hence the average size of the mobile phase droplets, in the CPC experiments. The interfacial activities of dodecylsalicylaldoxime (HDSO) in its neutral and deprotonated forms and its Ni complex at the hexanes-aqueous interface are very nearly the same. The Ni²⁺ is complexed by HDSO and DSO⁻ in the bulk aqueous and hexanes-aqueous interface. The interfacial rate constants for HDSO and DSO⁻ are 3-5 times smaller than the bulk aqueous values. The interfacial rate constant of the dissociation of Ni(DSO)₂ is an order of magnitude larger than the bulk dissociation rate constant. The CPC efficiencies for the Ni-HDSO system indicate specific interfacial areas of 1350 cm⁻¹ being generated in these experiments corresponding to a mobile phase droplet size of 24 μm. This effect leads to much larger CPC efficiencies than that predicted by the dissociation kinetics in the highly stirred mixture. The interfacial excess of 8-hydroxy-7-iodo-5-quinoline sulfonic acid is about 3 times bigger than its nickel complex, in contrast to the OMNTP which interfacial excess is about 4 times smaller than its barium complex. A new ATR-based method, agar-organic phase model, was developed for the determination of the liquid-liquid (L-L) interfacial adsorption of ligands and their metal-ligand complexes which were useful in L-L extraction.