Evaluation by Means of Electrochemical Impedance Spectroscopy of the Transport of Phosphate Ions through a Heterogeneous Anion-Exchange Membrane at Different pH and Electrolyte Concentration

Electrodialysis is an innovative technique to reclaim phosphates from municipal wastewater. However, chemical reactions accompany the transport of these ions through ion-exchange membranes. The present study investigates the dependence of these phenomena on the initial pH and concentration of the phosphate-containing solution using a heterogeneous anion-exchange membrane. Linear sweep voltammetry, electrochemical impedance spectroscopy, and chronopotentiometry experiments were conducted for different phosphate-containing systems. For the most diluted solution, two limiting current densities (i(lim)) have been observed for pH 5 and 7.2, while only one i(lim) for pH 10, and correlated with the appearance of Gerischer arcs in EIS spectra. For pH 7.2, sub-arcs of Gerischer impedance were separated by a loop, indicating the involvement of the membrane functional groups. Increasing the phosphate concentration changed the system's characteristics, reporting a single i(lim). In the EIS spectra, the absence of Gerischer elements determined the attenuation of chemical reactions, followed by the development of a diffusion boundary layer, as indicated by the finite-length Warburg arcs. Chronopotentiometry clarified the mass transport mechanism responsible for distorting the diffusion boundary layer thickness at lower concentrations. The obtained results are expected to contribute to the phosphates recovery using electrodialysis in the most varied conditions of pH and concentration available in the environment.

Automated summary

Electrodialysis is an innovative technique for phosphates recovery from municipal wastewater. This study investigated the dependency of chemical reactions during ion transport on initial pH and concentration using a heterogeneous anion-exchange membrane. The results showed that different pH and concentration conditions affected the system's characteristics, leading to variations in limiting current density and the appearance of Gerischer arcs in electrochemical impedance spectroscopy spectra. The obtained findings are expected to contribute to the utilization of electrodialysis in phosphates recovery under various environmental conditions.