Concentration of copper(II) ion by liquid membrane with bathocuproine.

Abstract

The distribution ratios of copper(II) ion between an aqueous solution containing a copper salt in the presence of nitrate, chloride or sulfate and an organic phase containing 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (bathocuproine) in 1,2-dichloroethane (DCE) were measured as a fundamental study for establishing the liquid membrane system.The difference in distribution ratio between nitrate and sulfate used in large excess was applied to drive the uphill transport of copper ion. The liquid membrane process consisted of the DCE solvent containing bathocuproine as a transport carrier and the two aqueous copper ion solutions containing a large excess of nitrate and sulfate ions. In this process, reproducible rate data were obtained by using a liquid-film holder in which the liquid membrane was maintained at constant pressure between two sheets of hydrophilic filter to prevent its leakage. The transport rate was examined by the quasi-steady model based on the three mass transfer steps involving a series of formation and dissociation of the copper-bathocuproine ion-pair with nitrate anion that take place instantaneously and reversibly at both interfaces of the liquid membrane. As a result, it became clear that copper ion was concentrated by the extraction through one hydrophilic filter, the diffusion of ion-pair across the liquid membrane and the back-extraction through the opposite filter accompanying the pseudo-first order equilibrium reaction for the complexation of copper with sulfate ion.