Intensifying transition metal ion removal and recovery from acidic wastewater via electrodialysis (ED) -based process

Industrial use of critical metals such as cobalt (Co) and manganese (Mn) generates metal-containing wastewater. Sustainable and effective solutions are yet to be developed to recover these elements in reusable forms, mainly due to the low metal ion concentration and presence of organics (e.g., in green plastic production). Thus, this study aimed to explore the feasibility of metal ion recovery from synthetic wastewater containing metal ions (e.g., Mn²⁺, Co²⁺) and high content of organic acid using electrodialysis (ED)-based process, with a specific focus to understand the fundamental performance constrains and find effective routes to intensify the recovery efficiency. The parametric study in the conventional ED demonstrated that the choice of more electrically conductive receiving solution greatly promoted the metal ion transport rate (ITR) by ∼26 % and reduced the energy consumption to 0.0045 kWh/kg metal recovered; while an optimal applied voltage of 1 V was chosen to avoid energy penalty through water splitting. Nevertheless, inherent limitations to further improvement of mass transfer of metal ions were identified in conventional ED. To this end, the adverse effect of concentration polarization was overcome by applying a pulsed electric field (PEF) in ED, reaching Co²⁺ ITR of 0.537mg·cm^-2·h^-1, which was 40 % higher than the optimal in conventional ED. Also, the competitive ion (H⁺ from acetic acid in this study) transport was found to impede the effective transfer of metal ions across the membrane. Thus, a novel integration of ED with a pretreatment method (i.e., super critical water gasification (SCWG)) was proposed to remove the acid for significantly intensifying the metal ion recovery with 50 % shorter treatment time, which was simulated to demonstrate the potential of energy self-sufficiency. The findings highlight the importance of advancing beyond traditional process optimization to address the complexities of real-world wastewater treatment, contributing to the development of unconventional and more sustainable treatment technologies and closed-loop industrial solutions.