Expedite extraction of Pb2+ from low-strength wastewater in the half-wave rectified alternating current electrochemical method by accelerating lead electrodeposition kinetics

The half-wave rectified alternating current electrochemical (HWACE) method is feasible for high-capacity extractions of heavy metal ions (HMI) from low-strength wastewater but exhibits sluggish extraction kinetics. Herein, to expedite Pb2+ extraction, carbon felts (CFs) were modified with well-aligned polyaniline (PANI) actiniae-like nanoarrays and used as cathodes. Consequently, Pb2+ was exclusively extracted (∼99.9%) from binary-component solutions [Pb2+-Na+ (50–500 mg/L)] within 12 h with highest extraction rates of 14.35 mg L−1∙h−1, better than that of CF (88.4%, 9.7 mg L−1∙h−1). Characterizations and COSMOL Multiphysics simulations demonstrated that PANI/CF electrodes enhanced electric fields, promoted Pb2+ mass transfer, and reduced nucleation overpotential, accelerating Pb2+ electrodeposition kinetics and thereby expediting Pb2+ extraction. Moreover, the qualitative discrepancies of Pb2+ diffusion coefficients under Na+ (0.368)/Ca2+ (0.355) interference caused faster Pb2+ extractions in Na+. During extraction, Pb2+ was continuously electrodeposited as lead crystals onto electrodes under Na+/Ca2+ interference, achieving high-capacity extractions of >4000 mg/g, ∼70% of them were recovered using a tweezer, and well-maintained 6-cycle-extraction performance. Kinetic analysis and density functional theory demonstrated that stronger leadophilicity of Pb(111) than electrode surfaces caused Pb2+ extraction a self-accelerating process. This work gives fresh insights to expedite HMI extraction in the HWACE method.