A combination between membrane selectivity and photoelectrochemistry to the separation of copper, zinc and nickel in aqueous solutions

The transport phenomena through ion exchange membrane may be improved by the application of different forces inside or outside the systems. The electrical current, produced by synthetic photo electrode, is applied to enhance the separation of metallic ions. The cation exchange membrane placed between the two compartments permitted the separation and concentration of the ions M2+ (=Cu2+, Zn2+ and Ni2+). The movements of M2+ from the aqueous solution to the membrane and inside the membrane are followed by the flux determinations and the potential measurements. In this study, the three cations are studied alone or as binary and ternary systems. It was observed that the illuminated CdS electrode leads to an increasing of the transport flux at least 10 times more than that calculated in the obscurity. Moreover, in all the cases the potential of the first specie electrode M/M2+ in the feed compartment increases until a maximal value reached at ∼100 min above which it undergoes a diminution. The membrane is more selective to Zn2+; this selectivity decreases in the binary and ternary systems. On the other hand, the photo electrochemical properties of the hexagonal CdS showed strong light absorption of wave lengths shorter than 520 nm. The shape of the intensity potential curve under illumination and the negative flat band potential (−1.02 VSCE) provide unambiguous evidence of n-type conductivity. The conduction band, located at −1.25 VSCE leads to a thermodynamically M2+ reduction under visible light and accentuates the diffusion process.