Influence of Mn2+ ions on the corrosion mechanism of lead-based anodes and the generation of heavy metal anode slime in zinc sulfate electrolyte

Abstract

The influence of Mn ions on the generation of heavy metal anode slime during zinc electrolysis industry was extensively investigated using several electrochemical methods, electron microscope technologies, and particle size analysis. Results showed that the Mn could obviously promote oxygen evolution reaction (OER) and thereby weaken oxidation efficiency of Mn (η) and dissolution of Pb. The significant improvement in kinetic parameters for OER was found in electrolytes of 1 and 3 g/L Mn, but became unstable as the Mn concentration increased to 10 g/L. This result was correlated with much different properties of oxide layers that its changes of microstructure are involved in, since it confirmed that the positive role of compact oxide layers in contributing to high corrosion resistance and activity for OER, but excessive Mn, resulted in its micromorphology of overthickness and instability. Such differences resulted from the effect of the Mn concentration fluctuation on kinetic rates of the nucleation growth process. The formation and adsorption of intermediate MnO-OH identified as the controlled step for Mn catalyzing OER was also recommended. The generation mechanism of anode slime was found to be changed in essence due to varying Mn concentrations. In electrolyte of 1 g/L Mn, results revealed that the root cause of excessive small suspended anode slime (around 20 μm) was the change of the initial pathway of Mn electro-oxidation, whereas, it showed great improvement in the settling performance as the Mn concentration was increased to 10 g/L. Considering the potential of optimizing Mn concentrations as a cleaner approach to control anode slime, deepening the understanding of the impact mechanism of Mn can provide new insights into intervention in the generation of anode slime.

Ti/Ti4O7 Anodes for Efficient Electrodeposition of Manganese Metal and Anode Slime Generation Reduction

“…This led to lead contamination and the occurrence of hydrolysis sludge, which would affect the purity of the electrolytic product. 9 For the microstructure of the MnO 2 layer on the Ti/Ti 4 O 7 anode ( Figure 7 b), the surface of MnO 2 was smooth and dense, which uniformly covered the surface of the anode. This physically isolated the Ti/Ti 4 O 7 substrate from the electrolyte and effectively improved the corrosion resistance of the anode coating.…”

“…The microstructure of the MnO 2 layer on the Pb anode is shown in Figure a, and a rough and porous surface and fluffy accumulation of the manganese oxide layer were observed. This led to lead contamination and the occurrence of hydrolysis sludge, which would affect the purity of the electrolytic product . For the microstructure of the MnO 2 layer on the Ti/Ti 4 O 7 anode (Figure b), the surface of MnO 2 was smooth and dense, which uniformly covered the surface of the anode.…”

“…In the actual production of manganese, a lead-based quaternary alloy anode (Pb–Ag–Sn-Sb) is widely used as an anode. The lead-based anode undergoes oxidation reaction in the acid system to form a smooth and dense oxide layer, which is resistant to corrosion and highly conductive, and has the stability of continuous operation. − However, the lead-based anode has a high oxygen evolution potential (OEP), which leads to the violent occurrence of anode side reactions, resulting in a large amount of anode slime. , The anode slime layer deposited on the anode surface is mainly α-MnO 2 with poor conductivity, which leads to the increase of cell voltage and energy consumption. In addition, the anode slime (MnO 2 particles) suspended in the solution can block the diaphragm and cause the short circuit of the cathode and anode. , More seriously, the lead-based anode will continue to be electro-oxidized and dissolved during the process of manganese electrowinning, and the α-MnO 2 layer is loose and porous, which cannot effectively protect the lead-based anode substrate, resulting in the anode slime becoming an industrial hazardous waste containing lead .…”

“… 5 − 7 However, the lead-based anode has a high oxygen evolution potential (OEP), which leads to the violent occurrence of anode side reactions, resulting in a large amount of anode slime. 8 , 9 The anode slime layer deposited on the anode surface is mainly α-MnO 2 with poor conductivity, which leads to the increase of cell voltage and energy consumption. In addition, the anode slime (MnO 2 particles) suspended in the solution can block the diaphragm and cause the short circuit of the cathode and anode.…”

Polyoxometalate/Lead Composite Anode for Efficient Oxygen Evolution in Zinc Electrowinning

“…4a and 4b indicated Tafel plots of OER, and presented two distinct linear segments in the low-potential and high-potential regions due to partially evolved O 3 . 46,47 The Tafel formula was calculated for both slopes and exchange current densities based on the data of the low-potential region in Table I.…”