Electrochemical removal of lead and zinc ion from mining wastewater with manganese-carbon composite electrodes: performance and coupling mechanism

A multi-layer porous manganese-carbon composite electrode was prepared and used in the electrochemical system for the efficient removal of Pb2+ and Zn2+ from mining wastewater. The prepared electrode was optimized with Mn/C ratio of 1:3 and coating density of 12.55 mg/cm2 by mediating the physicochemical and electrochemical characteristics. The electrode represented excellent electrochemical behavior with improved capacitance and reduced Warburg impedance accompanied by porous structure and hydrophilicity. The electrochemical system performed efficient Pb2+ and Zn2+ removal with the corresponding removal efficiency of 94.52% and 87.27% as well as exceptional selectivity toward Pb2+ and Zn2+. The distinction of removal mechanism was presented between Pb2+ and Zn2+. Rapid Pb2+ removal was achieved via a synergetic mechanism of dual pathways in terms of adsorption at anode and reduction-dominated processes coupling of electrosorption at cathode. In contrast, Zn2+ removal was dominated by electric double layer adsorption at cathode with partial reduction. Rapid electromobility of Pb2+ and the reduction-dominated removal processes promoted mutually and consecutively, while the electromobility rate of Zn2+ underwent a gradual decline. The mechanism disparity in the removal of Pb2+ and Zn2+ was governed by the differences in electrochemical processes and electrode properties. Moreover, the prepared electrode exhibited robust stability and long-term performance. The study provides valuable information and insights into the preparation of specific electrode and electrochemical treatment of heavy metal wastewater.