Recovery of low-concentration waste acid by electrodialysis: Modeling and validation

In light of the operational principles of Electrodialysis (ED), it is anticipated that this technology would significantly contribute to the recovery of waste acids through selective separation and subsequent proton concentration. However, the imperfect proton leakage characteristics of anion exchange membranes (AEMs) not only detrimentally affect the efficacy of ED-based acid recovery systems but also present considerable challenges for modeling endeavors. This study introduces a model based on the Nernst-Plank Equation at the cell pair scale, aimed at predicting ED performance. The model incorporates an empirical expression that links operational parameters, such as acid concentration and the concentration ratio between the concentrate and dilute compartments, to the permselectivities of AEMs in terms of anion transport numbers. Furthermore, both numerical and experimental analyses are performed to evaluate energy consumption across various operating conditions. The simulation outcomes derived from the proposed model exhibit a strong correlation with experimental data concerning acid transport (where the acid concentration increases from 0.25 M to 1.1 M through a two-stage concentration process), water migration (which demonstrates a nearly linear increase over time with applied currents, specifically a 15% increase under low-current conditions and a 100% increase under high-current conditions), and energy consumption. It is hoped that this model will aid in the design and optimization of ED-based acid reclamation processes, thereby enhancing their practical applications.