| In the zinc electrowinning industry, Pb-Ag anode is widely used as the anode materials. It can meet the basic requirements, but still has several problems such as high oxygen evolution over-potential (0.8-1.0 V), unsatisfactory service life and mechanical strength, and low purity of cathodic product. Inspired by the advantages of dimensionally stable anode(DSA) such as high oxygen evolution activity and good mechanical strength, this paper came up with the idea of molten-salt electroless Pb plating on Al substrate-composite electrodeposition of Pb-based, PbO-based composite coating, and prepared Al/Pb/Pb-MnO2 or Al/Pb/PbO2-MnO2 composite electrocatalysis energy-saving anode. The ultimate aim is to improve the oxygen evolution activity and prolong service life of anode mateirals in zinc electro-winning industry, reduce the consumption of raw materials and the preparation cost of anode and make beneficial contribute to zinc hydrometallurgy.(1) Pb/Pb-MnO2 composite anode(the content of particles is 6%-8%) was prepared using cathodic composite electrodeposition technique. During the initial stage of galvanostatic polarization, the anodic oxygen evolution potential was 300 mV lower than that of pure Pb anode. And the stable potential was 100-150 mV lower than that of pure Pb anode after galvanostatic polarization for 72h, which is comparable to the industrial Pb-Ag (1.0%) anode. Besides, the anodic layer of Pb/Pb-MnO2 composite anode after galvanostatic polarization for 72 h was more dense and uniform than that of Pb-Ag anode, and the content of P-PbO2 was much higher in the phase composition. Electrochemical testing shows that the anodic film could effectively inhibit the Pb substrate from contacting the electrolyte and oxidation dissolution. Thus the anodic corrosion resistance was significantly improved. Furthermore, the oxygen evolution reaction was controlled by the formation and adsorption of oxygen-containing intermediate S-OHads, and its adsorption impedance Rαwas much smaller than that of Pb and Pb-Ag anode, which might be the cause of high oxygen evolution activity of the composite anode;(2) Simultaneous oxidation and composite electrodeposition techniques were adopted to prepare Pb/PbO2-MnO2 composite anode in pyrophosphate bath and went through electrochemical performance test. The results show that compared with Pb/PbO2 anode, the composite coating deposited using simultaneous oxidation technique is more leveling, smooth and compact, and its catalytic properties are improved. The surface morphology of the composite coating deposited using composite electrodeposition technique is typically porous. The specific surface area is remarkably increased, and the catalytic property of hydrogen evolution is improved. During the pre-galvanostatic polarization for 90 min, the anodic potential is 150-200 mV decreased comparing with PbO2 deposit. Tafel and EIS testing results show that the oxygen evolution reaction on the composite anode was also controlled by the formation and adsorption of oxygen-containing intermediate S-OHads, and its adsorption impedance Rαwas much smaller than that of Pb/PbO2 anode;(3) Using the A1/Pb composite material as the matrix, composite electrodeposition technique was used to prepare A1/Pb/Pb-MnO2 composite anode containing about 5% MnO2, and went through small-sized industrial simulation experiment in laboratory. The results show that when the addition of Mn2+ in electrolyte is 0.1 g L"1, The anodic potential and cell voltage of composite anode in stable electrowinning is 50-100 mV lower than that of industrial Pb-Ag anode, and the current efficiency is obviously increased by 5%, and the energy consumption is markably decreased. Besides, the surface layer of the composite anode formed after electrolysis for 120 h is dense and homogeneous, and the corrosion resistance is significantly improved. Less lead is dissolved in the electrolyte and quality of the cathodic zinc product is improved. Results of the accelerated life test show that the service life of Al/Pb/Pb-MnO2 composite anode can be as long as 238d, which can meet the requirements of zinc electro-winning industry. |
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