Sustainable Electrochemical Extraction of Metal Resources from Waste Streams: From Removal to Recovery

Due to the widespread application of heavy metals in steel making, electronics, batteries, leather tanning, and catalysis, considerable toxic heavy metal-bearing wastewater and solid waste are directly or indirectly discharged into surrounding environments. Recently, electrochemical methods have attracted considerable attention for the remediation of metal pollution, originating from their environmental compatibility, high efficiency/selectivity/feasibility, and cost effectiveness. This review aims at recent advances in electrochemical metal recovery techniques, such as electrodeposition, electrosorption, electrodialysis, electrodeionization, and bioelectrochemical and photoelectrochemical methods. Additionally, the mechanisms and behaviors of different strategies are reviewed and compared, to overcome the limitations of concentration polarization from dilute metal ions, production of dendrites and spongy deposits, sluggish kinetics of ions transportation, and side-reactions from the hydrogen evolution and oxygen reduction reactions. Furthermore, the current challenges and future prospects of electrochemical metal recovery applications are also provided, to establish a process-mechanism-products (PMP) rational design of metal recovery, rather than simple metal removal.