Characterizing the removal of Pb2+ and Zn2+ from an acidic smelting wastewater using electrocatalytic internal Fe0/C micro-electrolysis

Abstract

The discharge of acid non-ferrous metal smelting wastewater has received unprecedented attention with increasing threat to ecosystems and human health. A combined process of electrocatalytic internal Fe0/C micro-electrolysis (ECIME) fluidized bed was developed at lab scale (2.0L) to investigate the co-removal performance, optimization conditions and reaction characteristics differences of Pb2+ and Zn2+ from acid smelting wastewater. The results of cyclic voltammogram (CV) and XPS reveal that Pb2+ and Zn2+ can be electrodeposited on the carbon microelectrodes surface in ECIME system, and the positive shift degree of the reductive peak potentials under cathodic polarized is positively correlated with the voltage intensity. Metal ions reaction flow direction of ECIME system and SEM, EDS, XPS characterizations indicated that the removal of Pb2+ and Zn2+ were mainly attribute to electroreduction deposition and in-situ iron polymer hydroxyl flocculation, and including four reaction processes of electroreduction on surface of external electrode, iron-carbon particles microelectrode, self-flocculation and secondary flocculation. But the removal of Pb2+ and Zn2+ show different dominant reaction path, Pb2+ removal mainly depended on the electroreduction deposition (64.11%), whereas Zn2+ dominated by iron-based flocculation (62.93%). Response surface optimization based on the average efficiency indicated that the co-removal of Pb2+ and Zn2+ mainly depended on polarization voltage, reaction time, initial pH and electrolyte concentration with optimal conditions of 11.0 V, 58.65 min, 5.0, and 0.08 mol/L, and its optimal average removal efficiency reached 98.52% (initial concentration 100 mg/L), and the residual concentrations were 0.081 mg/L and 1.890 mg/L, respectively. These findings provide insights and theoretical for developing electrochemical platform to realize heavy metal wastewater zero discharge.