Dynamic evolution of structure–activity of anode on lead release and overpotential change in zinc electrowinning

Abstract

Anode is the main source of lead (Pb) contaminations in zinc (Zn) electrowinning, also greatly affects the energy consumption due to the high dependence of overpotential for the oxygen evolution reaction (OER) on anodic oxide film (AOF). Herein, continuous tracking of the Pb-based anode was conducted for 60 d to reveal the evolution of structure–activity relationship with the growth of AOF. Results showed that three competitive reactions including Pb corrosion reaction, Mn2+ oxidation reaction and OER on the anode had complex interactive influences on the characteristic evolution of AOF as time increased periodically. With the continuous formation and coverage of AOF (PbSO4/ PbO2/MnO2) during the early 15 d, the Pb-based anode exhibited obvious self-protection effects of less Pb released and less MnO2-containing waste generated, which were attributed to the physically blocking effect of AOF against the excessive exposure of Pb surface by the dense and reticular structure and the electrochemically inhibiting effect for the Mn2+ oxidation by abundant Mn3+ and oxygen vacancy (Ov) of MnO2. Density-Functional-Theory (DFT) calculation indicated that the PbSO4 with higher energy band gap (4.19 eV) and lower formation energy (-1.51 eV atom−1) was prone to form and accumulate, which caused increasing voltage and accelerating release of Pb in the late stage due to over-thickness and structure instability of AOF. This study can provide inspiration for the future design or reconstruction of highly effective AOF structure to synergistically reduce pollution generation of Pb and anode slime and decrease OER overpotential.