Fe doped γ-MnO2 of anode for lead release inhibition in zinc electrowinning

Lead (Pb) anode has caused serious environmental pollution and resource waste problems in zinc (Zn) electrowinning. A novel functional Pb-based (Pb/MnO2) anode had been prepared successfully to reduce hazardous wastes of Pb-containing anode slime in our earlier published research. However, the impurity Fe2+ detected in the industrial preparation of this Pb/MnO2 anode was a tricky problem that cannot be ignored. Here, a Fe2+ doped MnO2 (Pb/Fe-MnO2) anode with its controllable preparation was studied. The results showed that Fe2+ participated in the transformation equilibrium reaction between Mn2+ and γ-MnO2, which reduced the deposition efficiency and crystal size of γ-MnO2. The internal structure of γ-MnO2 film had been reconstructed by Fe2+, which increased the concentration of oxygen vacancy (1.6 times) and Mn3+ (5.5 times) on the surface of the composite anode. During 20 d of continuous Zn electrowinning, the anode slime accumulation of the Pb/Fe-MnO2 anode was reduced by 90 % and 40 %, respectively, compared with the traditional Pb anode and Pb/MnO2 anode. The impurity Fe2+ is generally thought to be harmful, but studies have shown that it can promote the OER of the anode surface and improve the reduction of Pb-containing anode slime. The mechanism of reconstruction engineering has revealed that two pathways of Fe2+ may affect the deposition efficiency of MnO2: electrochemical and chemical, while Fe could be involved in the film structure along with γ-MnO2 co-deposition. The controlled impurity Fe2+ effect of MnO2 film anode will have a future application prospect for Pb release inhibition in industrial Zn electrowinning and related hydrometallurgy industries.