Instability mechanisms of supported liquid membranes for copper (II) ion extraction

The instability of supported liquid membranes (SLMs) for use in copper (II) ion extraction was investigated in this paper. The degradation behavior of these SLMs was monitored in situ by electrochemical impedance spectroscopy (EIS). The electrical properties of a SLM cell can be described by an equivalent circuit, R_s(C_mR_m)Q. The model parameters, membrane resistance (R_m) and membrane capacitance (C_m) can be used to characterize the degradation behavior of SLMs. Experimental data for R_m and C_m indicated that the loss of membrane liquid (ML) during the mass transfer process consists of three stages. Results also suggest that emulsion formation was the dominant instability mechanism for these SLMs. The solubility and osmotic pressure were also shown to not be major factors contributing to the instability although both contributed to the loss of the liquid membrane. The pore size of the polymeric support increased during the first run but remained almost constant in subsequent runs.