Effects of electrodialysis conditions on waste acid reclamation: Modelling and validation

Given its double functions of selective separation and concentration for ions, the potential of electrodialysis (ED) for the reclamation of waste acid has been widely recognized. In view of some differences from the cases of salt systems, a deep grasp on the effects of operating conditions on ED-based acid recovery is urgently required. Moreover, it is also challenging and desirable to effectively address the modelling issue of the membrane process. In this study, the influences of some typical operational factors, including current density, membrane selection, acid concentration of waste effluent, concentration differences between the dilute and concentrating compartments, on ED performances, such as its concentration evolution, current utilization and energy consumption, are systematically investigated. In particular, a fundamental model is established on the basis of the equations of Nernst-Planck, Navier-Stokes and Continuity to understand the influences of operating conditions and predict the relevant work performances. Therein, the proton diffusion coefficient of the used anion exchange membrane (AEM) can be regressed according to its practical performance and input. It is noticed that the obtained proton diffusion efficient is closely related to the AEM selection, but has almost nothing to do with the specific operational conditions and even the acid systems. A series of ED experiments show that the simulation results are in good agreement with the experimental results, which verifies the validity of the proposed model. Especially, this work confirms that proton leakage across AEMs should be the culprit in the non-ideal behaviors of ED-based acid recovery. Hopefully, the new model can contribute to the stack design, process optimization and scale-up of the ED-based acid recovery.