| Because of the benefits of low cost and simple process, the lead-based alloy anodes have been widely used in the electro-deposition of nonferrous metals, such as Zn. Cu, Ni, etc. But the high anodic over potential for oxygen evolution, high reactive power loss as well as inherent problems like high internal resistance, low creep resistance, non-uniform corrosion and the contamination of the electrolyte and cathode products, has restricted the technological creativity and economic progress for the corresponding hydrometallurgical processes. To solve the problems above, although noble oxide coated Titanium anodes can efficiently improve certain properties, the complex process and high cost make it too hard to become a substitute for lead-base alloy anodes.In this paper, the concept of the Pb-Al laminated composite material as a new energy-saving anode is proposed for the first time. The present research, supported by the National High Technology Research and Development Program of China (national 863 plans projects) and the National Natural Science Foundation of China (NSFC), aims to obtain an energy-saving anode with light weight, high strength, good conductivity, long working period, low power consumption, high current efficiency and high quality cathodic product by a simplified process. By introducing the third element Sn, the immiscible materials Pb and Al are transitionally combined by the hot pressing diffusion technique, forming thin solid solution enhanced interfaces with good electrical conductivity so that the advantages of Pb and Al can be used simultaneously. Stability of physical chemistry of the interfaces is experimentally confirmed. Influence of preparation technology on the interfacial microstructure, the cooperative deformability and electrical resistivity are systematically studied. On this basis, further investigations are carried out on the electrochemical properties of Pb-Al laminated composite anode materials, simulated production of zinc electrowinning is performed, and the energy-saving mechanism of Pb-Al laminated composite anode materials are analyzed. The research results are as follows:(1) Based on the preparation principle of Pb-Al laminated composite anode materials, thermodynamic calculation is carried out to analyze the Pb-Al binary liquid-solid interfacial energy and characteristics of Pb-Sn-Al ternary system. When reaching the upper limit of temperature 753.15K, the minimum interfacial binding energy value is -5.33×104J/mol, with composition of the material is 0.42 at.%,73.55 at.% and 26.03 at.% for Al, Sn and Pb, respectively, and it provides theoretical basis for the preparation of Pb-Al laminated composite anode materials.(2) Al-Sn laminated composite with good bonding interface is obtained by hot dipping Sn on the surface of Al through the mechanical vibration method. when the (200)Al and (211)Sn crystal plane makes an angle of 27.6°between Al phase and Sn phase, there would be a mismatch of 25%. The results of mismatch calculation show that every four interplanar spacings of (211)Sn correspond with three interplanar spacings of (200)Al. That is, every four (211)Sn interplanar spacings have a coincidence lattice position, which makes a relatively low interfacial energy, leading to the stable Al-Sn interface. After the aging treatment of the Al-Sn layered composite material for 150 days, XRD analysis shows that besides small amounts of SnO2, the surface mainly in the form ofβ-Sn.(3) Pb-Al laminated composites are prepared by means of hot pressing diffusion, on the basis of the study of the Al-Sn solder ability. EDS and SEM are carried out to analyze the interface topography and phase structure under varied preparing conditions. The results show that with increasing diffusion temperature and holding time, an alternately distributing continuous multilayered transition structure with a principal phase ofα(Sn-Pb)+β(Sn-Pb) solid solution is ultimately generated on the interface. The fraction of new generated phase increase with temperature and holding time, and the diffusion breadth also changes from a 2.5μm wide primary phase to a 18.4μm multiphase continuous transition diffusion layer. Thermodynamic principles are used to analyze the atom/phase transformation of interfacial diffusion. The results indicate that the Pb-Sn eutectic structure of the principal phase grows through branching and bridging. The a phase grows on theβphase through branching, and simultaneously theβphase grows on the a phase, leading to an ultimate staggered layered structure. Cores of the two phases grow radically since formed, and a final spherical meeting eutectic structure is formed, so that the total system energy remains minimum, and the interfaces possess good thermodynamic stability.(4) Interfacial microhardness analysis, conductivity and integral bending property test are carried out on Pb-Al laminated composite materials obtained under different preparing conditions. The results show that compared with Pb-1% Ag alloy material, the weight of the Pb-Al laminated composite materials is reduced by 32% on average with the same shape and volume, the average bending strength is increased by 70.1%, the average interfacial Vickers hardness is enhanced by 205%. With the alloying extent and interface broadening, the interfacial bond strength is increased but it decreases the conductivity on the other hand. However, thanks to the unit microns level thickness of the interfacial layer, the interface resistance value is from 1.435×10-8Ωto 6.605×10-7Ω. However, it will not have a significant negative impact when the Pb-Al laminated composite materials used as anode to meet the overall conductivity requirements, and it makes Al as the core material can present an excellent electric conductivity for the layered structure anode material matrix. Thus, the internal resistance of the Pb-Al laminated materials is lower than that of the lead alloy anode substrates in the same volume.(5) The results of polarization curves show that compared with the Pb-1% Ag anodes, the anodic polarization potential of the Pb-Al laminated anodes is decreased by 18.2%, it reduces the possibility of self-corrosion. When the apparent current density is 500A/m2, regardless of the existence of Mn2+, the anodic oxygen evolution potential of Pb-Al laminated anodes is lower than Pb-1% Ag alloy anodes, so as to speed up the electrode polarizing process. The Pb-Al laminated composite anodes with dimension of 170mm×110mm×6mm are tested in pilot scale experiment for 24 days and the anodes are found to perform well in industrial electrolysis conditions. The corresponding average current efficiency of Pb-Al laminated composite anodes is about 92%, while the corresponding average current efficiency of Pb-1% Ag alloy anodes is only about 89.74%. The calculating results of energy consumption (per tonne of zinc produced) show that, compared with Pb-1% Ag alloy anodes, Pb-Al laminated composite anodes have reduced energy consumption by 116kWh, energy-saving effects are very obvious, and at the same time, the quantity of anode mud and the anodic corrosion rate is reduced by 90%,80%, respectively. The edge dendrite phenomenon of cathode zinc products has been greatly improved due to the fact that the optimized layered structure design of the composite anodes, and the good conductivity of Al core material. Finally, the aim of saving energy and lowering anodic corrosion has been obtained according to the production practice of Zinc electrolysis.
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