Remediation of acidic zinc mine tailing leachate with capacitive deionization: role of carbon electrodes, membranes and pretreatment

Remediating acidic mine drainage is essential to mitigate environmental concerns due to its acidity and elevated heavy metal concentration. This study investigates the performance of capacitive deionization (CDI) and membrane CDI (MCDI) for remediating acidic zinc mine tailing leachate from Australian mining sites, specifically focusing on the roles of fabricated carbon-based electrodes and carbon nanotube (CNT) membrane. Among the four fabricated electrodes, activated carbon + carbon nanotubes (AC + CNT) electrode achieved the highest metal removal at a rapid rate (30–65% Al 3+ , Fe 3+ , Zn 2+ , salt adsorption rate 0.78 mg·g −1 ·min −1 ). This was attributed to AC + CNT electrode's superior capacitance (9.0 F·g −1 ), and markedly reduced internal resistances (148.7 Ω, vs AC's 208.2 Ω,), contributing to enhanced ion transport pathways compared to AC and carbon black electrodes. While polymer-coated membrane electrodes initially hindered ion transport, embedding CNTs within the membrane restored charge-transfer pathways, enabling 67–88% removal of major metals (Al 3+ , Fe 3+ , Zn 2+ ) from zinc tailing. Membrane reuse evaluation indicated inevitable metal oxidation, leading to precipitation on membrane. To address this, a granular activated carbon (GAC) pretreatment step was implemented upstream, reducing bulk metal loading by ~62% The integrated configuration of MCDI with CNT membrane upon GAC pretreatment maintained high metal removal efficiencies (97–98%) across multiple cycles of adsorption and chemical-free desorption, while producing an acidic stream (pH 1.1 ± 0.2) suitable for mining reuse. Overall, these findings demonstrate the potential of electrochemical processes for rapid acid mine drainage (AMD) remediation, while concurrently supporting acid recovery. • Combined AC + CNT carbon electrode exhibited superior metal removal in CDI. • CNT membrane MCDI achieved high metal removal from acidic zinc mine tailing. • GAC pretreatment prevented CNT membrane fouling by lowering feed ion concentrations. • GAC–MCDI process achieved 98% metal removal, yielding an acidic effluent. • The electrochemical approach enabled rapid and low-chemical AMD remediation.