Pb-Ag Anode Research Articles

Effect of Silver Content in Pb-Ag Anodes on the Performance of the Anodes During Zinc Electrowinning

The efficiency of the electrowinning process of zinc depends on the performance of oxygen evolution reaction, anode quality and corrosion resistance oflead anodes. The original surfaces of rolled commercial lead-silver anodes were examined using conventional polarization methods in acid zinc sulfate electrolyte with MnS04 at 38°C. The self-discharge method (potential decay) following 5 hours of polarization at 50 mA. cm-2 was considered to evaluate electrochemical activity, oxygen overpotential and anode stability. The influence of silver content is compared to that of the microstructure, the fabrication process and the composition of the corrosion products. Polished anode samples have also been examined for microstructural and corrosion performance studies. The experiments show that the duration of the plateau at 1600 mV/SHE, the potential level (active corrosion state/corrosion potential region) and the rate Δ corr/ Δt during the decay could be a good indicator to compare the corrosion rates of the anodes in industrial zinc electrolytes.

New oxygen evolution anodes for metal electrowinning: MnO2 composite electrodes

Several modifications of manganese dioxide (MnO2) were investigated for use in composite electrode materials for oxygen evolution, the target application being anodes for the industrial electrowinning of metals. It is demonstrated that the performance of this material depends strongly on the modifications of MnO2. All modifications investigated were found to be more active than the usual anode of lead alloyed with silver (PbAg) used in zinc electrowinning. A composite sample containing chemical manganese dioxide (CMD) was found to give an oxygen evolution overpotential 0.25 V lower than the standard PbAg anode material. In the second part of the article, we investigate the effect of varying several parameters of the composite electrode assembly, including the size of the catalyst particles and percentage of the catalyst material used. A model is proposed where the performance of the material is proportional to the total length of the boundaries between the lead matrix material and the MnO2 catalyst particles. Physicochemical processes contributing to the observed data are discussed.

A Novel Porous Pb-Ag Anode for Energy-saving in Zinc Electrowinning

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Kinetics of oxygen evolution on Pb and Pb-Ag anodes during zinc electrowinning

The behaviour of lead and lead-silver alloy anodes during oxygen evolution in H 2SO 4ZnSO 4 or H 2SO 4ZnSO 4MnSO 4 electrolytes, has been studied by electrochemical impedance spectroscopy. A reaction model of anodic processes is presented, which quantitatively fits the experimental data. It is concluded that the presence of silver in lead modifies both the kinetic parameters of the main reaction of oxygen evolution, and the potential dependence of the oxide layer conductivity. It is also shown that the reaction of oxygen evolution is inhibited by a silver salt adsorbate. The electrode coverage by this adsorbate appears to be increased in the Mn 2+-containing electrolyte, thus changing the inhibition into a passivation process.

Kinetics of Pb and Pb-Ag anodes for zinc electrowinning—II. Oxygen evolution at high polarization

Electrochemical impedance spectroscopy, scanning electron microscopy, X-ray diffraction and secondary ionisation mass spectroscopy (SIMS) have been utilized to investigate the mechanism of reactions taking place on Pb and Pb-Ag alloy anodes in acidic zinc sulphate electrolytes, in the potential domain above 1.16 V sse. At these polarizations, the main reaction is oxygen evolution on a porous deposit of PbO 2, or PbO 2 + MnO 2 in Mn 2+-containing electrolytes. In all cases, the electrode impedance reveals a slow electrode activation with increasing polarization, probably related to the deposit conductivity. With lead-silver anodes it also appears an inhibition process of the main reaction, which becomes more important and turns into passivation, when the electrolyte contains Mn 2+ ions. This process has been assigned to the formation of inhibiting adsorbates on the oxide layers.

Kinetics of Pb and PbAg anodes for zinc electrowinning—I. Formation of PbSO 4 layers at low polarization

Electrochemical impedance spectroscopy and scanning electron microscopy have been utilized to investigate the mechanism of reactions taking place on Pb and PbAg alloy anodes in acidic zinc sulphate electrolytes, during the formation of PbSO 4 layers in the potential domain (0.9 to 1.1 V/SSE). Independent of the Ag content, the anode behaviour is essentially determined by the electrolysis time. From a comparison of experimental data to a kinetic model for the frsol| Pb/ PbO n / PbSO 4 electrode, it is shown that the layer growth is first controlled by the solid state diffusion of SO 2− 4ions, and then by a chemical step associated with a change in charge carriers, from O 2+ v vacancies in the PbO n sublayer into Pb 2+ions in the PbSO 4 layer. In Mn 2+-containing electrolytes, the additional formation of MnO 2 occurs under diffusion control of the Mn 2+ oxidation, and it modifies both the layer properties and the kinetics of reactions.

The effect of some trace metal impurities on the electrowinning of zinc from Kidd Creek electrolyte

The single and combined effects of cobalt (0.15–5 mg/l), arsenic (0.01–5 mg/l) and iron (2.5–50 mg/l) on zinc deposition current efficiency (CE) and polarization behaviour and on the deposit morphology and orientation of 24 h zinc deposits were studied. The in-plant additive mix of 1 mg/1 Saponin, 5 mg/l Dowfroth, 13 mg/l sodium silicate and 0.015 mg/l antimony was employed under the conditions of 60 g/l Zn 2+, 200 g/l H 2SO 4, 500 A/m 2 and 38°C with conditioned PbAg anodes and SrCO 3 additions in bench scale electrolysis (cell volume 300 ml). The CE was sensitive to increasing concentrations of cobalt and arsenic both alone and in combination. Iron alone had very little effect on CE. Iron concentrations greater than 20 mg/l, in combination with arsenic and cobalt, significantly lowered the CE. The nucleation overpotential (NOP) determined from cyclic voltametry did not correlate with the CE results. A prewave in the voltammograms in the presence of some impurities, particulary arsenic, made the determinations of the NOP difficult. Most of the deposits were intermediate (e.g. [101][112][102]) in orientation. The surface of the deposit darkened in appearance as the arsenic concentration increased. At higher cobalt concentrations, the solution side of the deposit appeared normal although significant corroded dark areas starting on the edges were noted on the electrode side.

Passivation du plomb et de ses alliages avec l'argent dans les solutions aqueuses de NaCl

(A) The anodic behaviour of Pb and PbAg alloys (0·82; 4·5; 9·4% Ag) has been studied potentiostatically in 0·1–1·5 N NaCl aqueous solutions. Anodic passivation of these metals occurs over two potential ranges, which show two distinct values of passivation current. Increase of NaCl concentration leads to a decrease of anode current required to give passivation and flowing during passivation and to an increase of the passivation range to higher positive potentials. The apparent overpotential of oxygen on the layer of anodic products found in solutions with different NaCl concentration ( c NaCl) has been established. There is linear relation between the overpotential and log c NaCl. The PbAg anodes give anodic curves almost identical with those given by Pb. (B) Anodic polarization curves in 0·5 N NaCl solution have been determined for different temperatures (10–50°C). The calculated value for the overall energy of activation of the anodic processes occurring in the passive range is 8·3 Kcal/mole, which indicates electrochemical rather than diffusion control. (C) Cathodic depassivation curves have been measured amperostatically for Pb in 0·5 N NaCl solution, after prior passivation in the same solution. The form of the curves indicates electrochemical heterogeneity of the passivating layer. On the basis of the experimental results and from thermodynamic considerations, we suggest that the passive layer consists of lead chloride and lead oxides.

陰極防食用鉛合金陽極の研究 (第7報) 硫酸溶液中の鉛および鉛合金の陽極腐食について

In order to investigate on cathodic protection of steel and stainless steel used for holding sulfuric acid, examination was conducted to check the behavior of pure lead, lead alloys and high-silicon iron in sulfuric acid solution. The experiments were done by measuring the anode potential and analysis of surface film by oxalatimetry.The results obtained are as follows:1) The growth rate of passive film on Pb, Pb-As, etc. follows parabolic law.2) Those on Pb-Te, Pb-Ag, etc. follow the logarithmic law.3) The amount of lead peroxide on Pb-Sn and Pb-Cd electrodes decrease in proportion to the lapse of time.4) Allowable current density for Pb-Ag anode is considered to be approx. 10A/dm2.5) High-silicon iron may be used at the current density of 4A/dm2, while its weight loss caused by corrosion reaches 0.05g/A·hr and is far larger than those of lead alloys examined.