Studies on Electrochemical Solvent Extraction of Metal Ions at Water/1,2-dichloroethane Interface

Abstract

Solvent extraction mechanisms of some metallic ions, Mn(II), Zn(II), Ni(II), and Co(II), from aqueous phase to 1,2- dichloroethane (DCE) were examined by electrochemical impedance spectroscopy (EIS) and other electrochemical methods. Diffusion-limiting currents were observed in the i-E curves. Such a diffusion-limiting current corresponds to the transfer rate of the metallic ion from the aqueous phase to the DCE phase, and it was found that the extraction rates followed the order of Mn(II)<Zn(II)<Ni(II)<Co(II). The capacitive semicircle due to the time constant of the charge transfer resistance and the interfacial capacitance was described in the electrochemical impedance on the Nyquist plane. A simulation was performed for the experimental result of EIS. The solvent extraction of metallic ions across aqueous phase/DCE phase was discussed by using reaction parameters such as the rate constant and the interfacial capacitance. In the solvent extraction accelerated by an electrochemical driving force, a rate constant increased with the increase of the potential. The value of interfacial capacitance depended on the kind of metallic ions, and it was found out that the interfacial capacitance was related to the amount of the intermediate at the interface.