Preparation And Electrochemical Performance Of Aluminum - Based Lead Alloy Composite Anodes

In the modern hydrometallurgy of nonferrous metal, the corrosion rate and oxygen evolution reaction (OER) potential of anodes is the key to influence cathodic product quality and energy comsumption. With the increasing requirements of cathodic product quality and increasing serious energy problem, the conventional Pb alloy anodes have not meet the needs of industrial production. In this paper, based on the higher conductivity of Al and higher electrocatalytic of Co ions, WC and CO3O4particles, the Al/Pb, Al/Pb-0.8%Ag, Al/Pb-0.75%Ag-0.03%Co, Al/Pb-Sn, Al/Pb-WC, Al/Pb-Co3O4and Al/Pb-Sn-WC composite anodes for low OER potential and corrosion rate have been prepared by direct current electrodeposition in lead methanesulfonate electrolyte.The electrochemical properties of Al/Pb, Al/Pb-0.8%Ag and Al/Pb-0.75%-0.03%Co composite anodes in H2SO4-ZnSO4electrolyte and of Al/Pb-Sn, Al/Pb-WC, Al/Pb-Co3O4and Al/Pb-Sn-WC composite anodes in H2SO4-CuSO4electrolyte have been established by anode poalrization curves, Tafel curves, cyclic voltammograms, EIS and time-potential curves analysis. XRD and SEM analysis represent the phase and microstructure of anodes. The preparation method and process on anodes with low potential and corrosion rate have been researched. The results are as fllowing:1) Cu and Ni transfer layersCu and Ni with higher conductivity can be used as transfer layers of Al/Pb composite anodes. The electrochemical analysis shows that with an increase of thickness of transfer layer the Al/Pb composite anode polarizes more easily, leading to higher OER over-potential during zinc electro winning. The Al/Pb composite anode with41um thick Ni transfer layer reprents the lowest corrosion rate and OER potential.2) Al/Pb composite anodeWith an increase of Pb electrolyte temperature the corrosion rate and OER over-potential of Al/Pb composite anode increase. As the Pb planting electrolyte temperature is40℃, the highest OER potential of Al/Pb composite anode is0.6785V. With an increase of Pb planting current density the corrosion rate and OER potential of Al/Pb composite anode decrease. The experimental data of corrosion rate data are correspond to the derivation of kinetics of electrode reaction.3) Al/Pb-Ag and Al/Pb-Ag-Co composite anodesCompared with conventional Pb-0.8%Ag alloy anode, Al/Pb-0.75%Ag-0.03%Co and Al/Pb-0.8%Ag composite anodes represent lower corrosion rate. The OER potential of Al/Pb-0.75%Ag-0.03%Co composite anode is decreased by about22mV, and of Al/Pb-0.8%Ag composite anode is decreased by about lOmV as compared conventional Pb-0.8%Ag anode. Pb-0.75%Ag-0.03%Co composite coating represents denser microstructure and smaller crystal size than Pb-0.8%Ag composite coating before anodic polarization. Anodic layer of Al/Pb-0.75%Ag-0.03%Co composite anode is consisted of fairy globular crystal particles, and anodic layer of Al/Pb-0.8%Ag composite anode is consisted of dendritic crystal particles after24h of anodic polarization. The globular Ag crystals of Al/Pb-0.75%Ag-0.03%Co anode adhere to the surface of Pb-0.75%Ag-0.03%Co composite coating, and the elliposoid Ag crystals of Al/Pb-0.8%Ag anode are covered with Pb on the surface of Pb-0.8%Ag composite coating.4) Al/Pb-Sn composite anodesWith an increase of Sn content the OER potential of Al/Pb-Sn composite anode decreases. The OER potential of Al/Pb-0.62%Sn composite anode is1.411V. With an increase of Sn content the corrosion rate decreases, then increases. The Al/Pb-0.32%Sn composite anode represents the highest corrosion rate. Al/Pb-0.41%Sn composite anode represents the lowest corrosion rate. With an increase of Sn content the crystal size of Pb-Sn composite coating increases before anodic polarization. The anodic layer of Al/Pb-0.32%Sn and Al/Pb-0.41%Sn composite anodes mainly represent linear vug consisited of rectangular microcrystals, and the anodic layer of Al/Pb-0.49%Sn and Al/Pb-0.62%Sn composite anodes mainly represent bigger size of rhombus crystals after24h of anodic polarization.5) Al/Pb-WC and Al/Pb-Co3O4composite anodesCompared with conventional Pb-Ca-0.6%Sn anode, Al/Pb-Co3O4composite anode represents the highest electrocatalytic activity and the Al/Pb-WC represents the lowest corrosion rate. CO3O4particles are mainly distributed in the grain boundary of coating, constituting a reticular structure which is similar to Pb-Sb alloy, and WC particles are relatively evenly distributed in the Pb-WC composite coating surface before anodic polarization. Anodic layer of Al/Pb-Co3O4composite anode is mainly represents that the linear microcrystalline devide uniform quadrangular crystal into areas, and of Al/Pb-WC composite anode is mainly represents the uniform quadrangular crystal with less crystallite after24h of anodic polarization.6) Al/Pb-Sn-WC composite anodeCompared with Pb-Ca-0.6%Sn, Al/Pb-Sn and Al/Pb-WC anodes, Al/Pb-Sn-WC composite anode represents the lowest corrosion rate (9.48mgdm-2h-1) and OER potential (1.297V). The surface feature of Al/Pb-Sn-WC composite anode is the irregular crystal that is full of flake crystallite before anodic polarization. The anodic layer surface feature of Al/Pb-Sn-WC anode is quadrangular crystal that is full of granular crystallite.In this paper, Al/Pb-0.75%Ag-0.03%Co is the best composite anode with the lowest OER potential (1.411V) and corrosion rate for zinc electrowinning, and Al/Pb-Sn-WC composite is the best composite anode with the lowest OER potential(1.297V) and corrosion rate (9.48mgdm-2h-1) for copper electrowinning. The preparation and electrochemical properties analysis of the two composite anodes provide a direction in preparing anodes with lower potential and corrosion rate for nonferrous metal electrowinning.