Preparation And Characterization Of Sandwich Plate Anode For Zinc Electrowinning

Lead and lead based alloys have been widely applied as insoluble anode for hydrometallurgical non-ferrous electrowinning due to their high stability in H2SO4solution. However, lead based alloys also show several problems such as easy to creep, high oxygen evolution over-potential and unsatisfactory corrosion resistance. In response to these problems, coating anodes, novel lead alloy anodes and porous anodes are developed, in spite of some beneficial results, they can not completely meet the requirements of industrial applications.Aimed at the shortcoming mentioned above, a sandwich plate anode Al/Pb-Ag-RE with Al core was developed. Laboratory preparation of sandwich plate anode has been designed, and its surface alloy composition was optimized. On this basis, laboratory simulation experiment was conducted to evaluate the performance of Al/Pb-Ag-RE sandwich plate anode. The main results are as follows:(1)Sandwich flat anode was successfully prepared and corresponding equipment was developed. Al/Pb-Ag-RE sandwich flat anode was successfully prepared. The alloy casting equipment has been improved and the casting parameter has been optimized to diminish the oxidation loss of RE. The optimized parameter for casting process was as follow:smelting temperature650℃, smelting time2h, Ar pressure0.8MPa, rotate speed250r/min. Using lead plating molten salt technology and anti-gravity casting technology, a sandwich flat anode was prepared, Al and Pb alloy core layers formed good metallurgical bonding. Anodic yield strength and tensile strength were increased by77.39%and57.18%, and weight was decreased by approximately11%.(2) In order to optimize the Ag and RE content of Pb-Ag-RE alloy the influence of Ag content and RE content on the electrochemical performance of Pb-Ag-RE anodes has been investigated. The optimistic alloy composition is Pb-Ag0.4wt.%-RE0.02wt.%, which presents higher oxygen evolution reactivity, low stable anodic potential after72h galvanostatic polarization (1.365V vs. Hg/Hg2SO4/sat. K2SO4), compact anodic surface film, uniform base corrosion, less intergranular corrosion and satisfactory corrosion rate (average corrosion rate is2.569g/m2·h).(3) Al/Pb-Ag-RE sandwich plate anode is prepared, and its laboratory simulation experiments are performed. The results shows: After joining the Al core, the anode voltage is reduced by about30mV, the energy consumption is decreased by55.43kWh/t-Zn. On the other hand, the corrosion of the anode is accelerated, and Pb content of the anode slime and cathode Zn is increased due to the existence of Cl element during the chemical lead-plating process.In summary, Al/Pb-Ag-RE sandwich plate anode could improve the mechanical property, conductivity and oxygen evolution over-potential of Pb-Ag-RE anode. However, the sandwich plate anode presents slightly higher corrosion rate due to the introduction of Cl ions during the Pb plating in molten salts. The preparation method of sandwich plate anode should be further improved.