| The anode of lead-based alloy is always used in industrial production of zinc owing to high concentration of H2SO4 in the electrolyte.However,there are several problems on the lead-based anode such as high oxygen evolution overpotential(about 860mV) which can increase the energy consumption about 1000 kWh/t-Zn(about 30%of the total energy consumption),low corrosion resistance and decrease of zinc quality due to lead dissolution in the electrolyte.Although titanium-based electro-catalytic coating anode can effectively reduce the oxygen evolution potential,it still cannot replace the lead-based anode due to its short life and high cost.Therefore,it still is an important subject to develop new energy-saving anode in the zinc hydrometallurgy.The concept of porous lead-based anode was firstly put forward by the author based on numerous literature investigation.By increasing the anode conductive area to reduce the anodic current density,the porous lead-based anode can reduce the anodic overvoltage,lower the anode corrosion rate and improve the product quality while maintaining the advantages of Pb-Ag alloy anode.In this paper,the equipment and technics of counter-gravity infiltration was developed,the electrochemical properties of porous Pb-Ag(0.8%) anode was evaluated systematically,the effect of current density on the electrochemical behavior of traditional flat anodes was studied thoroughly and a pilot scale electrolysis experiment of porous Pb-Ag(0.8%) was carried out. Based on that,the porous lead-based anode doping metal of electro-catalytic activity was further studied.The main conclusions and results are summarized as follows:(1) The equipment and technics of counter-gravity infiltration for the fabrication of porous lead-based alloy are designed and developed.Filling and crystallization under controllable pressure can effectively avoid the lack and excess of infiltration and solve the problem of wettability and feeding between the lead-based melt and filler particles.The technics for the preparation of porous lead-based anode with controllable pore size and uniform pore structure is set up and the porous materials of Pb-Ag (0.8%) with dimension of 250.0mm×160.0mm×30.0mm are prepared.(2) The electrochemical behavior of porous Pb-Ag(0.8%) anode with different pore diameter is studied systematically and the electrochemical behavior and characteristics of porous anode are revealed. Results show that the oxygen evolution overvoltage and corrosion rate of porous anode are obviously lower than that of flat anode.When the pore diameter is 1.60-2.00mm,its anodic potential is 100mV lower than flat anode and its corrosion rate is about 50%of the flat anode.The lead content of cathode Zn is decreased remarkably by using porous anode. The current efficiency for porous anode is almost same as that for flat anode which is 91%-92%while the porous anode is beneficial for reducing anode slime because the phenomenon of Mn2+ dilution is less obvious.(3) In order to illustrate electrochemical behavior and characteristics of porous anode.The electrochemical behavior of lead-based anode is studied systematically under different current densities and the effect of current density on the anodic potential,the corrosion rate,the composition and microstructure of anodic oxidized layer,the current efficiency,the quantity of anode slime and the quality of cathode zinc is analyzed.In electrolyte of pure ZnSO4-H2SO4,when current density is decreased from 500 A/m2 to 100 A/m2,the anodic potential(VS SCE) decreases from 1.835V to 1.742V and the corrosion rate decreases from 1.620g/m2·h to 0.652g/m2·h.In the electrolyte of ZnSO4-MnSO4-H2SO4, the anodic potential and corrosion rate also decrease with the decrease of current density,the stabilized anodic potential is 1.704V and 1.792V at the current density of 100 A/m2 and 500 A/m2 respectively.(4) The porous Pb-Ag(0.8%) anode with dimension of 200.0mm×100.0mm×6.0mm is tested in pilot scale experiment for 24 days and the anode is found to perform well in industrial electrolysis conditions.The results show that compared with the flat anode,the anodic potential is decreased about 100mV,the corrosion rate is reduced by 80%,the energy consumption is lowered 78kWh/t-Zn,the quantity of anode slime is reduced by 80%and the lead content of cathode Zn is 60%.(5) Bi which is harmful for the electrode of lead-acid battery is introduced to Pb-Ag(0.8%) anode of zinc electrowinning and its effect on anodic potential,corrosion rate and the structure and composition of anodic oxidized layer is analyzed.The optimum content of Bi is found to be 0.8-1.0%.The porous lead-based anode doping metal of electro-catalytic activity is developed.
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