Corrosion of Zinc Ferrite Based Inert Anodes in AlF3-NaF-Al2O3 Melts Under Conditions of Anodic Polarization

ZnFe2O4-based inert anodes were made to conduct the aluminum electrolysis tests. The corrosion behaviors of the inert anodes were examined and discussed. Experiment results prove that: (1) ZnFe2O4-based inert anodes are good corrosion resistant to AlF3-NaF-Al2O3 melts under the conditions of anodic polarization; (2) High anodic current density(＞1.5 A·cm-2), high alumina concentration and low ratio of NaF/AlF3 in the molten salts will be the most important conditions for using inert anode.     

Character of the corrosion destruction of inert anodes during electrolysis of cryolite alumina melt and the reasons for it

The behavior of inert anodes during the electrolysis of the cryolite alumina melt in a laboratory electrolyzer is investigated at 960°C. On the basis of the electrolysis tests of more than 150 anodes with various structures and compositions, the character of their corrosion and possible reasons for it are revealed. It is shown that the physical and physical-chemical processes of the interaction of the molten electrolyte and oxygen evolved from the anode material are the basis of the phenomena of the corrosion destruction of anodes. The requirements for increasing the corrosion stability of the structure of inert anodes are formulated.     

Addition of Cobalt to Lead Anodes Used for Oxygen Evolution—A Literature Review

A review of the literature dealing with the effect of cobalt on lead-based anodes for oxygen evolution during electrolysis of sulfuric acid solutions verifies that the presence of cobalt at the anode–electrolyte interface, either as constituent of the anode material or as ions in the electrolyte, catalyzes the evolution of oxygen and reduces the corrosion of the anodes and the contamination by lead of metal cathodes produced during electrowinning. However, due to harmful effects of cobalt ions on the cathodic reaction in some processes, these benefits are limited to the electrowinning of copper. Efforts to develop a way of introducing cobalt at the anode–electrolyte interface without interfering with the cathodic reactions are reviewed in this paper. The use of lead–cobalt alloy anodes has had limited success due to issues arising from the low solubility of cobalt in lead, segregation during casting of the alloys, and nonuniform distribution of cobalt which affects the integrity of the anodes. This has been overcome in part lately by inclusion of cobalt into only the surface layer of a lead or lead alloy substrate, by thermal treatment of a cobalt salt to form a catalytic cobalt oxide surface species, or by electrodeposition of composite lead–cobalt oxide anodes. The last approach in particular has been actively investigated by several groups, but to our knowledge it is yet to find application in the industry. The review also critically examines the likely reaction mechanisms involved.     

SnO2-Based Gas (Methane) Anodes for Electrowinning of Aluminum

SnO₂-based and carbon-based gas anodes were studied in molten Na₃AlF₆-AlF₃-Al₂O₃ at 1123 K (850 °C) for aluminum electrolysis. Methane was introduced to the porous anodes to take part in a three-phase (anode/electrolyte/methane) boundary reaction. Carbon was used as the cathode. It was observed that the anode potential was reduced by 0.6 V and that the current was increased up to three times in galvanostatic and potentiostatic tests after the introduction of methane on SnO₂-based anodes. A measurable depolarization effect and lower consumption of carbon after the introduction of methane on carbon anodes were also demonstrated.     

Development of an Inert Anode for Electrowinning in Calcium Chloride–Calcium Oxide Melts

Studies were performed investigating the anodic testing of calcium ruthenate for electrowinning in calcium chloride–calcium oxide melts. The results showed that calcium ruthenate may be suitable as an inert anode in calcium chloride containing melts as it exhibited a low rate of corrosion in melts containing a small amount of calcium oxide, capable of producing oxygen on its surface, and did not contaminate the melt. To reduce the amount of ruthenium in the anode, solid solutions of calcium ruthenate in calcium titanate were investigated. At low concentrations, the solid solution is a semiconductor with a relatively low conductivity at room temperature, but at the temperature of operation, 1173 K, the material is an excellent electronic conductor. The other way of reducing the amount of ruthenium is to coat the solid solution onto a substrate. In this way, the substrate would give the mechanical strength while the coating would give the electrical conductivity and corrosion protection. Calcium ruthenate-based anodes can endure long-term use in the laboratory under an applied electrical field with oxygen being liberated on the anode indicating that these materials are candidates for the electrowining in calcium chloride–calcium oxide melts.     

The effect of quality of anodes on the process of electrolytic of manganese dioxide

During the electrosynthesis of manganese dioxide, the anode material and anode current density (i _a) exert the largest influence on the characteristics of electrolysis and the quality of the obtained material. The activation of anodes, which consists of the deposition of the titanium-manganese alloy on the titanium base of the electrode by the thermal-diffusion method, prevents passivation at i _a = 100 and 200 A/m². The electrochemical characteristics of electrolysis for NTMA (a built-up titanium-manganese activated anode) and ATDP (an experimental activated anode with thermodiffusion coating) anodes at i _a = 100 and 200 A/m² have close values. The voltage across the bath does not exceed 2.2–3.0 V, the current efficiency is 95–98%, and electrical power consumption is 1.33–1.80 (kW h)/kg. The chemical composition and the crystalline modification of electrical manganese dioxide corresponds to the requirements of GOST (State Standard) 25823-83. The activated ATDP anodes behave similarly to the known HTMA anodes. After electrolysis, no variations in the surface layer are found on them.     

Electrochemical studies of the performance of different Pb-Ag anodes during and after zinc electrowinning

One Pb-0.25%Ag-0.1%Ca alloy anode and three commercial Pb-0.6%Ag, Pb-0.58%Ag and Pb-0.69%Ag alloys anodes have been studied by conventional electrochemical methods and electrochemical impedance spectroscopy (EIS) in acid zinc sulphate electrolyte with and without MnSO₄ additions to evaluate their activity and corrosion behaviour. At a current density of 50 m Acm⁻² and 38 °C, the polished surface of the anode Pb-0.69%Ag alloy had the lowest overpotential, followed closely by that of anodes Pb-0.6%Ag and Pb-0.58%Ag alloys and then anode Pb-0.25%Ag-0.1%Ca alloy in a bath with and without MnSO₄ additions. Also, during potential decay period after 5 h electrolysis, the polished surfaces showed that anode Pb-0.69%Ag alloy had the lowest corrosion current among the four examined anodes, followed by anodes Pb-0.6%Ag, Pb-0.25%Ag-0.1%Ca alloys and Pb-0.58%Ag alloy.     

铝/空气电池用铝阳极的研究

研究了铝／空气电池用铝阳极中添加合金元素的作用,镓,铟,铋,锡能增大阳极的开路电压,镁,铋钪可增大阳极的抗性。以高纯铝为基体制得的两种铝阳极合金Ａ１,Ａ２基本上达到了碱性铝／空气电池的要求。以普通铝为基体制得的铝合金Ａ３作为铝阳极,其电化学性能良好。     

NiFe_2O_4基惰性阳极的润湿性及气泡析出行为

利用座滴法和双室透明电解槽对NiFe2O4基惰性阳极的润湿性和气泡析出行为进行研究。结果表明,电解质对NiFe2O4基惰性阳极的润湿性要优于碳素阳极。在低电流密度情况下电解,阳极气泡的析出是一个动态过程,它先在阳极表面形核,以球形方式长大,小气泡在长大过程逐渐汇聚偏移,然后逸出。惰性阳极上析出的气泡尺寸比碳素阳极小,在阳极上的逗留时间也更短。大电流密度情况下,气泡的生成速度加快,尺寸降低,很难准确测量气泡的直径。     

Material balance as the basis for process control in electrowinning and electrorefining

Electrowinning and electrorefining, like chemical processes generally, are amenable to comprehensive material balance analysis for purposes of process control. However, current efficiency in electrowinning is insufficient to provide the requisite agreement between current and electrolyte flows on the one hand and observed concentration changes on the other. The many factors contributing to volume change and metal loss is electrowinning determine a “volume efficiency”, as previously defined, which can differ significantly from 100%. Use of volume efficiency in conjuction with current efficiency is illustrated by experimental data for the case of nickel electrowinning employing a porous separator. In electrorefining, anode current efficiency is a major factor in the material balance. The chemical compositions of anodes and cathodes and their respective current efficiencies contribute the source terms for soluble impurity buildup in the electrolyte. An analysis is developed which takes into account the principal mechanisms of extraneous weight loss of anodes, including dissolution of oxide inclusions, disintegration and chemical corrosion. The considerations involved are illustrated for nickel impurity in copper anodes.     

杂散电流对接地材料在陕北土壤模拟溶液中腐蚀行为影响

采用自行设计的杂散电流模拟装置,测试了距离杂散电流源不同距离的纯锌、纯铜和锌/铜耦接结构在陕北土壤模拟溶液中的电位和腐蚀电流,并结合电化学阻抗谱对接地材料腐蚀行为进行分析.研究发现接地材料纯锌表面存在明显的由阴极区向阳极区的过渡,阳极区的试样腐蚀严重;纯铜表面发生电化学反应的阻抗明显高于纯锌,在存在杂散电流的介质中具有更好的耐蚀性;锌作为牺牲阳极与纯铜接地材料耦接后,会使纯铜表面电位整体负移,原来位于杂散电流流出区域的纯铜也进入阴极区受到保护.      

硫酸介质中阴离子膜电解氧化铈的电极选择

报导了硫酸介质中电解氧化铈的阴阳极选择。从电极的耐蚀性、电极对阳极电流效率及槽电压影响三方面的比较 ,可以得出 :在阴离子交换膜体系中 ,1#铅合金在所比较的三种阳极材料中是最佳的 ,可以在该体系中作阳极。铜作阴极是可行的 ,既有高的电流效率又有低的溶解性和槽电压 ,可以保证电解的顺利进行。     

锌电积用惰性阳极材料的研究现状

锌电积长期采用Ph—Ag合金为阳极。该阳极存在析氧过电位高、易腐蚀且污染阴极锌等问题,因此人们研究了各类新型阳极。阐述了国内外铅及铅合金阳极、复合电催化铅基阳极、钛基DSA阳极及其他基体阳极材料的研究现状,着重指出了铝基阳极材料具有较好的发展前景,并对未来锌电积用惰性阳极材料的发展趋势进行了展望。     

A Mineralogical overview of the behavior of nickel during copper electrorefining

Nickel-bearing copper anodes and anode slimes were studied using a variety of mineralogical and chemical techniques. In anodes containing <;0.3 pct Ni, the nickel occurs only in solid solution in the copper matrix. This nickel dissolves simultaneously with the copper during electrorefining, but a small amount reprecipitates as copper-nickel sulfate or a complex Ni-bearing Cu-Ag-As-Se-S oxidate phase in the anode slimes. In anodes containing >0.3 pct Ni, NiO crystals also form. The presence of the Cu-Ni-Sb oxide, kupferglimmer, in the anode depends on its antimony content. Kupferglimmer is prevalent in nickel-rich anodes with high Sb contents (>200 ppm) but is not found in similar anodes with Sb contents <200 ppm. Various Cu-Ni and Ca-Cu-Ni silicate inclusions are present. Depending on the iron content of the anode, Fe-bearing NiO, NiFe₂O₄, and other Ni-bearing iron oxide phases also may be present. All of the oxidate nickel phases remain largely undissolved during electrorefining and concentrate in the anode slimes.     

铝棒低银铅合金表面陶瓷化复合阳极的制备与性能

为获得一种锌电积用低成本、低析氧电位和高催化活性的阳极,在铝棒表面通过挤压复合技术包覆Pb-0.2% Ag合金得到Al棒Pb-0.2% Ag阳极.在含氟的硫酸溶液中,通过阳极氧化在Pb-0.2% Ag合金和Al棒Pb-0.2% Ag合金阳极表面形成具有高催化性能的膜层,采用显微图像分析仪和数显显微硬度计表征了膜层的厚度及硬度,并通过电子拉伸试验对比了两种阳极的极限抗拉强度.采用X射线衍射、扫描电子显微镜、循环伏安法、阳极极化和交流阻抗法等技术手段研究了Al棒Pb-0.2% Ag与Pb-0.2% Ag阳极表面氧化膜层的物相、形貌以及电化学性能.结果表明:Al棒Pb-0.2% Ag阳极相比Pb-0.2% Ag阳极表面易生成致密较厚的氧化膜层,且膜层硬度提升了41.64%,其氧化膜层主要物相均为电催化活性良好的β-PbO₂.新型阳极的极限抗拉强度是传统阳极的1.3倍,大大改善了阳极材料的机械性能.阳极极化曲线数据显示Al棒Pb-0.2% Ag/PbO₂阳极在电积锌体系中具有较低的析氧电位(1.35 V vs MSE,500 A·m-2)和较高的交换电流密度(7.079×10-5 A·m-2).循环伏安曲线和交流阻抗数据显示Al棒Pb-0.2% Ag/PbO₂阳极具有较高的电催化活性、较大的表面粗糙度和较小的电荷传质电阻.在电积锌实验中,栅栏型Al棒Pb-0.2% Ag/PbO₂阳极相比传统Pb-0.2% Ag阳极平均槽电压下降了75 mV,而且大大减少了阳极泥的产生.      

Developments in anodes for pure copper electrowinning from solvent extraction produced electrolytes

The adoption of solvent extraction (SX) techniques in copper recovery flowsheets has resulted in the production of electrolytes from which extremely pure copper may be obtained directly by electrowinning. The necessity to use high acid content strip solutions however may result in attack of conventional lead anodes and therefore in cathode contamination by anode material. Extensive studies have been carried out to determine methods of preventing lead anode dissolution and various alternative lead and non-lead anode materials which are capable of operating under tankhouse conditions have been examined. Non-lead anode materials, which it has been suggested may replace conventional anodes, are described and the effect on capital and operating cost of installing and using higher cost non-lead anodes is examined in comparison with lower cost lead anode alternatives.     

Electrochemical and surface studies on zircaloy-4 exposed to concentrated nitric acid medium

Zircaloy-4 has been considered as a candidate material for dissolver and evaporators in nuclear fuel reprocessing plants involving nitric acid of high concentrations at high temperatures. The present work deals with the electrochemical studies and surface analysis of passive films on zircaloy-4 and its welds in 11.5 M nitric acid medium. Potentiodynamic polarization technique was employed to study the corrosion behaviour of the alloy in both base and welded (Manual TIG and electron beam (EB) welding) conditions. The polarization curves for zircaloy-4 and its welds exhibited a distinct breakdown of passivity at 1.5 V (SCE) and repassivation, after showing a region of stable passivation. The characterization of passive films by SEM, XRD and LRS, grown at different potentials in 11.5 M nitric acid are presented. The surface morphology and phase analysis of passive films grown at higher potentials showed the presence of monoclinic ZrO₂. The phases present in the passive film grown electrochemically in 11.5 M nitric acid at 2.0 V and by autoclaving are found to be similar. The presence of characteristic 1040 cm⁻¹ Raman peak from the sample passivated at 1.2 V indicate that the oxide present consist of nanometer size grains of monoclinic zirconia.     

Influence of silver content and MnSO4 addition on performance of different lead–silver alloys during polarisation and decay periods

Abstract

The electrochemical activity and the corrosion properties of five commercial lead anodes were examined by the conventional polarisation methods and the electrochemical impedance spectroscopy method. The results show that the anode Pb–0·62Ag alloy had a lower overpotential for anode reaction than the others. The corrosion resistance after polarisation of the anode Pb–0·62Ag alloy was higher than that of the Pb–0·29Ag–0·1Ca alloy, Pb–0·58Ag alloy and Pb–0·67Ag alloy, but lower than that of the anode Pb–0·72Ag alloy. However, the anode Pb–0·72Ag alloy had the highest overpotential. When anodes Pb–0·72Ag alloy and Pb–0·62Ag alloy were used, the cathode current efficiencies were higher, while anodes Pb–0·29Ag–0·1Ca alloy, Pb–0·58Ag alloy and Pb–0·67Ag alloy gave lower current efficiency. Regarding these several factors, the anode Pb–0·62Ag alloy is the best choice.

On a examiné l’activité électrochimique et les propriétés de corrosion de cinq anodes commerciales en plomb, au moyen des méthodes conventionnelles de polarisation et de la méthode de spectroscopie d’impédance électrochimique. Les résultats montrent que l’anode de Pb–0·62Ag avait une surtension plus basse que celle des autres pour la réaction de l’anode. La résistance à la corrosion après la polarisation de l’anode de Pb–0·62Ag était plus élevée que pour l’anode de Pb–0·29Ag–0·1Ca, l’anode de Pb–0·58Ag ou l’anode de Pb–0·67Ag, mais plus basse que celle de l’anode de Pb–0·72Ag. Cependant, l’anode de Pb–0·72Ag avait la surtension la plus élevée. Lorsqu’on utilisait les anodes de Pb–0·72Ag ou de Pb–0·62Ag, le rendement du courant de la cathode était plus élevé, alors que les anodes de Pb–0·29Ag–0·1Ca, de Pb–0·58Ag et de Pb–0·67Ag donnaient un rendement de courant plus bas. Par rapport aux divers facteurs, l’anode de Pb–0·62Ag constitue le meilleur choix.     

湿法提铜电积工程实践及添加剂优化探讨

总结了国内外铜电积的工程实践,对铜电积过程添加剂进行优化。结果表明,铜电积液添加Co2+有利于减缓阳极腐蚀速度和降低阳极电位,合适的Co2+浓度为100mg/L;古尔胶有利于生成表面光滑、平整的阴极铜,适宜用量为每吨铜50g;硫脲在不同的电流密度下对阴极铜质量影响不同;铜电积液不适宜添加盐酸。