UPHILL TRANSPORT OF PHOSPHATE ION THROUGH AN OXOMOLYBDENUM(V)-TETRAPHENYLPORPHYRIN COMPLEX-CONTAINING BULK LIQUID MEMBRANE - EFFECT OF HALOGEN IONS ON PHOSPHATE ION FLUX

The uphill transport of dihydrogenphosphate ion coupled with the counter-flow of a halogen ion across a bulk liquid membrane was studied by using various potassium halides (KF, KCl, KBr, and KI). The bulk membrane employed consisted of a trichlorobenzene solution containing oxomolybdenum (V) tetraphenylporphyrin complex as a mobile carrier. The feed solution phase was continuously replaced by fresh phosphate solution in order to avoid the accumulation of halogen ions and to hold the phosphate concentration to the initial level. The extraction constant, i.e., the equilibrium constant for the interfacial ligand exchange reaction, was estimated from two-phase liquid-liquid extraction experiments with a trichlorobenzene solution of the complex and an aqueous solution of the various halides. To clarify the relationship between the phosphate flux and the extraction constant, a transport equation was derived by considering aqueous film diffusion, organic film diffusion, and interfacial chemical reaction as simultaneous controlling factors. It was found that the halogen ions influence the flux via a change in the extraction constant according to their species. However, resistances due to the above three rate-controlling steps were independent of the species of halogen ion. Another characteristic of the present membrane system was that, regardless of the species of halogen ions, their concentrations at the aqueous-organic interface on the feed solution side are much larger than that of H2PO4-. © 1990.