Properties of Al/Conductive Coating/α-PbO2-CeO2-TiO2/β-PbO2-WC-ZrO2 Composite Anode for Zinc Electrowinning

The properties of Al/conductive coating/α-PbO2-CeO2-TiO2/β-PbO2-WC-ZrO2 composite anode for zinc electrowinning were investigated. The electrochemical performance was studied by Tafel polarization curves（Tafel）, electrochemical impedance spectroscopy（EIS） and corrosion rate obtained in an acidic zinc sulfate electrolyte solution. Scanning electron microscopy（SEM）, X-ray diffraction（XRD）, and energy dispersive X-ray spectroscopy（EDXS） were used to observe the microstructural features of coating. Anodes of Al/conductive coating/α-PbO2-CeO2-TiO2/β-PbO2, Al/conductive coating/α-PbO2-CeO2-TiO2/β-PbO2-WC, Al/conductive coating/α-PbO2-CeO2-TiO2/β-PbO2-ZrO2, and Pb-1%Ag anodes were also researched. The results indicated that the Al/conductive coating/α-PbO2-CeO2-TiO2/β-PbO2-WC-ZrO2 showed the best catalytic activity and corrosion resistant performance; the intensity of diffraction peak exhibited the highest value as well as a new PbWO4 phase; the content of WC and ZrO2 in coating showed the highest value as well as the finest grain size.

Behavior of arsenic in zinc electrowinning

The effects of arsenic on the cathode polarization process in zinc electrowinning,its kinetics equation,parameters and polarization mechanism were studied by multiple electrochemistry approaches.The experimental results show that,if[As 3+]≥3 mg/L,electrowinning first enters into stationary passivation range,and then enters into precipitation range,which indicates that the depolarization function of impurity arsenic is zinc electrowinning.

Polyaniline anode for zinc electrowinning from sulfate electrolytes

Polyaniline(Pani)anode is tested to highlight the feasibility of reduction of both energy consumption and capital costs in zinc electrowinning from sulfate solution without any modification to the existing plant.Current density,electrolyte temperature, added gelatin,added Mn 2+ ,oxygen-evolution potential,cell potential and long duration tests were investigated.The zinc deposits were also studied by means of scanning electron microscope(SEM)and X-ray diffraction(XRD).The results show that current density and added gelatin change the preferred crystal orientations of the zinc deposits.Compared with Pb-Ag(1%)anode used in industry,the cell voltage decreases by 0.15-0.30 V,energy consumption of Zn is 2.46-2.70 kW·h/kg which results in 20%energy savings.Long duration tests show that Pani anode can represent a good alterative ability for zinc electrowinning.Zinc deposits obtained have no Pb pollution.The additions of Mn2 +ions and gelatin also change the surface morphology and deposit quality of the electrodeposited zinc,affecting the crystal orientation.These researches demonstrate that Pani anode has distinct advantages over acidic electrowinning process.

Electrochemical Properties and Microstructure of Al/Pb–Ag and Al/Pb–Ag–Co Anodes for Zinc Electrowinning

The Al/Pb-0.8%Ag and Al/Pb-0.75%Ag-0.03%Co （in mass fraction） anodes used in zinc electrowinning are prepared through the electrodeposition of lead methanesulfonate electrolyte onto an aluminum matrix. The results of anode polarization curves, Tafel curves, and EIS characterizations indicated that the Al/Pb-0.75%Ag-0.03%Co anode has higher electrocatalytic activity and corrosion resistance than the Al/Pb-0.8%Ag anode. SEM observations on the fruit surfaces demonstrated the crystals on the Al/Pb-0.8%Ag anode are larger than on the Al/Pb-0.75%Ag-0.03%Co anode. After 24 h of anodic polarization, SEM observations and XRD analysis showed that the MnO2-PbO2 layer on the Al/Pb-0.75%Ag- 0.03%Co anode surface is characterized by dendritic crystals, and the PbSO4-PbO2 layer under the MnO2-PbO2 layer is characterized by uniform and chaotic orientation tetragonal symmetry crystallites of PbSO4. However, the MnO2-PbO2 layer on the Al/Pb-0.8%Ag anode surface is characterized by granular crystals, and the PbSO4-PbO2 layer under the MnO2 PbO2 layer is characterized by well-organized orientation crystallites of PbSO4, which are concentrated in certain zones.