Overall mass transfer approach for electrodialysis-based acid recovery

The reclamation of low-concentration waste acid (e.g., pH > 0.5) has garnered significant attention due to its prevalence, substantial output, and considerable potential value. Notably, a further concentration of the separated acid is typically required for practical applications, for which electrodialysis (ED) has been widely acknowledged as an effective method. However, various factors, including proton leakage, complicate the application of ED in acid systems compared to salt systems. This study presents a novel modeling approach for ED-based acid recovery utilizing the overall mass transfer (OMT) methodology for the first time. Importantly, regression models incorporating initial concentration and current density as independent variables have been developed to calculate the OMT coefficients and cell resistance following a quantitative analysis of the effects of acid media and electric field on mass transport phenomena, based on a series of carefully designed experiments. Subsequent predictions regarding a typical ED-based acid recovery process were conducted, yielding results that align closely with experimental data. For instance, the relative deviations for concentration and volume evolution were found to be less than ±8.4 % and ±7.9 %, respectively. Additionally, the relative deviations for energy consumption were recorded at 8.2 % and 3.2 % for the overall process and the ED stack, respectively. Furthermore, simulations were performed to evaluate the impacts of operational conditions on ED performance using the derived models. In conclusion, the efficacy of the OMT approach for modeling the ED process in acid systems has been substantiated. It is reasonable to assert that the developed models will be beneficial for production management and the optimization of operating conditions in ED-based acid recovery processes.