Anodic behavior and microstructure of Al/Pb-Ag anode during zinc electrowinning

Anodic behaviors and oxygen evolution kinetics of Pb-0.8%Ag and Al/Pb-0.8%Ag anodes during the initial 24 h zinc electrowinning were investigated with cyclic voltammetry （CV） curves and electrochemical impedance spectroscopy （EIS）. The results reveal that the anodic behaviors and reaction kinetics of the two anodes vary a lot during the anodic polarization which indicate the formation and stabilization of anodic layer. Compared with conventional Pb-0.8%Ag anode, A1/Pb-0.8%Ag anode has longer time of anodic polarization. At the very beginning of anodic polarization, the two anodes all exhibit higher potential of oxygen evolution reaction （OER） since the reaction is controlled by the transformation step of intermediates. Then, its OER potential is largely diminished and OER rate is deduced from the formation and adsorption of the first intermediate （S-OHms）. In the prolonged anodie polarization, the anodie potential of A1/Pb-0.8%Ag gradually decreases and the final value is more stable than that of conventional Pb-0.8%Ag anode. On the anodic layer after 24 h of anodic polarization, the OER potential is controlled by the formation and adsorption of intermediate. The microstructures of A1/Pb-0.8%Ag and Pb-0.8%Ag anodes after 24 h of anodie polarization were analyzed by scanning electron microscope （SEM）.

Effect of impurities in recycling water on Pb-Ag anode passivation in zinc electrowinning process

Effect of impurities in recycling water on Pb-Ag anode passivation in zinc electrowinning process was investigated by linear scan voltammetry.Results show that passivation process would be affected in the presence of Cl^-and F-in recycling water.It was highly advantageous to take H2SO4 concentration as 180g/L,Mn^2＋ concentration as 3-5 g/L and F-less than 42mg/L.However,passivation process would not be affected when Cl^-concentration was less than 13mg/L without any other ions,or when mass ratio of Mn^2＋ to Cl^-existing in electrolyte was 8,where Cl^-concentration could reach up to 625mg/L.

Effect of cooling ways on properties of Al/Pb-0.2%Ag rolled alloy for zinc electrowinning

In order to study the new anode materials for zinc electrowinning,Al/Pb?0.2%Ag rolled alloy was produced by composite casting and hot rolling.Then the effect of cooling ways on properties of Al/Pb?0.2%Ag rolled alloy was investigated.As the results of metallographic test indicated,with the increasing of cooling intensity,both Vickers hardness and yield strength of Al/Pb?0.2%Ag rolled alloy increase.Furthermore,the Al/Pb?0.2%Ag rolled alloy,cooled by ice salt,presents the finest grain size and shows the lowest oxygen evolution potential(1.5902V),while that of alloy cooled by water and air are1.6143V and1.6288V,respectively.However,the corrosion current density and corrosion rate of the Al/Pb?0.2%Ag rolled alloy,cooled by ice salt,are the highest.This can be attributed to its largest specific surface area,which promotes the contact between the anode and electrolyte.

Effect of doping Bi on oxygen evolution potential and corrosion behavior of Pb-based anode in zinc electrowinning

A new anodic material of ternary Pb-0.8%Ag-(0-5.0%)Bi alloy for zinc electrowinning was obtained by doping Bi.The anodic oxygen evolution potential,corrosion rate,surface products after polarization,and microstructures before and after polarization were studied and compared with those of Pb-0.8%Ag anode used in industry.The results show the anodic overpotential decreases with the increase of Bi content in the alloys.When the content of Bi is 1.0%(mass fraction),the anodic overpotential is 40-50 mV lower than that of Pb-0.8%Ag anode.While the corrosion rate decreases and then increases with the increase of Bi content.The Pb-0.8%Ag-0.1%Bi anode has the lowest corrosion rate(0.090 6 mg/(h·cm2).Doping Bi influences the structure of the anodic layer,but does not change the phase.The Pb-0.8%Ag-1.0%Bi anode layer is of a more fine-grained structure compared with Pb-0.8%Ag anode.

Anodic behavior and microstructure of Al/Pb-Ag-Co anode during zinc electrowinning

In order to study the anodic behavior and microstmctures of A1/Pb-Ag-Co anode during zinc electrowinning, by means of potentiodynamic investigations, scanning electron microscopy （SEM） and X-ray diffraction （XRD） analyses, the mechanism of the anodic processes playing on the surface of A1/Pb-0.8%Ag and A1/Pb-0.75%Ag-0.03%Co anodes prepared by electro-deposition from methyl sulfonic acid bath for zinc electrowinning from model sulphate electrolytes have been measured. On the basis of the cyclic voltammograms obtained, information about the corrosion rate of the composite in PbO2 region has been concluded. The microstructures were also observed by means of SEM and XRD which showed Pb-0.75%Ag-0.03%Co alloy composite coating has uniform and chaotic orientation tetragonal symmetry crystallites of PbSO4, but Pb-0.8%Ag alloy composite coating has well-organized orientation crystallites of PbSO4 concentrated in the certain zones after 24 h of anodic polarization. It is important that Al/Pb-0.75%Ag-0.03%Co anode oxide film consists of non-conductive dense MnO2 and PbSO4 and a, fl-PbO2 penetrated into which, in fact, are the active centers of the oxygen evolution after 24 h of anodic polarization.

Fabrication and anodic polarization behavior of lead-based porous anodes in zinc electrowinning

A new type of lead-based porous anode in zinc electrowinning was prepared by negative pressure infiltration. The anodic polarization potential and corrosion rate were studied and compared with those of traditional fiat anodes （Pb-0.8%Ag） used in industry. The anode corrosion rate was determined by anode actual current density and microstructure. The results show that the anodic oxygen evolution potential decreases first and then increases with the decrease of pore diameter. The anodic potential decreases to the lowest value of 1.729 V at the pore diameter of 1.25-1.60 mm. The porous anode can decrease its actual current density and thus decrease the anodic corrosion rate. When the pore diameter is 1.60-2.00 mm, the anodic relative corrosion rate reaches the lowest value of 52.1%.

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.

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.

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.

Electrochemical properties of powder-pressed Pb-Ag-PbO_(2) anodes

Pb?Ag?PbO2 composite anodes with different mass fractions(1%,2%,3%,4%and 5%)ofβ-PbO2 were prepared by powder-pressed(PP)method.The galvanostatic polarization curves,Tafel curves and anodic polarization curves were tested in sulfuric acid solution.The morphologies and phase compositions of the anodic layers formed after galvanostatic polarization were investigated by using scanning electron microscope(SEM)and X-ray diffractometer(XRD),respectively.The results showed thatβ-PbO2 can improve the electrocatalytic activity of anodic oxide.The anode containing 3%β-PbO2 had the lowest overpotential of oxygen evolution reaction(OER)and the best corrosion resistance.The morphologies of the anode surfaces were gradually transformed from regular crystals to amorphous ones as the content ofβ-PbO2 increased in anodes.