Solvent Extraction Mechanism of Co(II)-8-hydroxyquinoline Complex Investigated by Electrochemical Impedance Spectroscopy

Abstract

The solvent extraction of Co(II) was investigated by electrochemical methods. It was found in the measurement of i-E curves that the extraction rate was in proportion to the Co(II) concentration in aqueous phase and 8-hydroxyquinoline (HQ) concentration in organic phase and that the Co(II) formed a 1:1 complex with HQ. Furthermore, the electrochemical impedance spectroscopy (EIS) was applied to the kinetic investigation. The capacitive semicircle due to the time constant of charge transfer resistance and the interfacial capacitance was described in the electrochemical impedance on the Nyquist plane at low extraction rate. The apparent Warburg impedance was shown on the Nyquist plane at high extraction rate, indicating that the diffusion process contributes to the total extraction rate. On the basis of experimental results by the electrochemical methods and the numerical simulation, the solvent extraction mechanism of Co(II) was discussed.