铜电积中铅钙锡阳极钝化层的管理

现代铜电解槽中最常用的阳极为铅钙锡合金阳极,在铜电积过程中,PbO_2(过氧化铅)层在阳极表面形成。这层PbO_2的重要性在于保护金属铅阳极不被酸腐蚀,以使析氧反应有一个合理的交换电流密度。然而,在非正常状况或者断电条件下,PbO_2的电化学行为会导致阳极退化,并且导致铜阴极含铅量过高,以及为清除槽底累积的阳极泥而频繁停工。当发生停电或电解槽需要清理而断电时,便会出现非正常状况。某些电解槽为上述情况配置了有限容量的备用整流器。本文描述了PbO_2层形成和损坏的机理,并且确定了维持阳极表面PbO_2层致密性所需要提供的最小电流密度。     

Progressive degradation of noble metal coated titanium anodes in sulphuric acid and acidic copper sulphate electrolytes

Anodes having a nominal loading of 5 g/m² of 70% platinum—30% iridium alloy on a titanium substrate were employed in repetitive galvanostatic runs at 8.1–540 mA/cm² in 2 M H₂SO₄ electrolyte, with and without the addition of 0.5 M CuSO₄. The increase in anode potential with time was attributed to two causes: passivation of the noble metal surface, and oxidation of the substrate metal beneath the coating. Surface platinum loadings were monitored by an X-ray fluorescence technique, and loss rates averaged 1.30 mg/A h, independent of the operating variables of the present investigation. Surface platinum losses were attributed to a direct electrochemical dissolution process, except in the cases where complete anode degradation occurred which was accompanied by substrate attack and spalling of the noble metal coating.     

The corrosion of lead anodes in copper electrowinning

The steady-state corrosion rate of 0.4 pct As-10 pct Sb-Pb anodes in H₂SO₄ copper electro-winning electrolytes was studied. The corrosion rate increases markedly with increasing acid strength and current density, although the corrosion per pound of copper electrowon is affected only slightly by current density. Several ions such as Cu⁺², Mg⁺², Al⁺³, SiO₃ ^-2 and Na+ have no effect on the corrosion while Fe+S and Ni+2 ions have moderate inhibiting effects. Strong corrosion inhibition is brought about by introducing small amounts of Co*2 into the solution or by substituting a Ca-Pb alloy for the conventional antimonial lead anodes.     

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.     

Effect of cobalt added to electrolyte on corrosion rate of Pb-Sb anodes in copper electrowinning

Abstract

Three-layer diffusion couples have been constructed so as to simulate the compositional variations which occur in commercial carbon steels as a result of interdendritic segregation. It has been possible to examine quantitatively the banding behavior in the ternary systems Fe-Si-C, Fe-Mn-C, Fe-Ni-C, Fe-Cr-C, and Fe-P-C both as to the intensity of carbon segregation which occurs in the soaking (austenite) range and during the subsequent γ → a. transformation. The results confirm that the segregation of carbon which occurs before transformation is due to the equalization of the carbon activities. As expected from thermodynamic data, silicon, nickel and phosphorus-rich regions reject carbon while manganese and chromium-rich regions attract it. While this initial segregation is weak, in all cases but nickel it intensifies during transformation. In nickel couples the segregation direction reverses during transformation so that the pearlite-rich regions appear with the nickel. This emphasize s the dominance of constitutional effects in the determination of banding behavior.     

Direct electrowinning of lead from galena concentrate anodes

The results of an investigation of the electrowinning of lead directly from a galena concentrate compact anode employing an acetate bath as the electrolyte are reported. The effects of graphite content in the compact electrode, bath composition, time of electrolysis, temperature of the bath, current density and compaction pressure were studied on a laboratory scale to optimize operating conditions. An electrode containing 6.25% graphite, compacted at 238 MN m^?2 for 5 min, resulted in 70% current efficiency for the dissolution of lead according to the reaction PbS → Pb²⁺ S⁰ + 2e in a bath of ammonium acetate (0.5 M), acetic acid (0.35 M) and lead acetate (0.1 M) when electrolysed at 333 K with a current density of 110.5 A m^?2. The results have formed the basis of a pilot plant design.     

Conductive polymer coating for anodes used in zinc electrowinning

Abstract

In this study polypyrrole was coated on the lead silver alloy (0·5 wt-%) using electrochemical synthesis. The performance of the coating on the lead alloy corrosion behaviour in a severe corrosive electrolyte has been evaluated. Also, the morphology of polypyrrole coating was studied utilising scanning electron microscopy (SEM). The results show that the protective layer of polypyrrole decreases the corrosion rate of the anodes by about 30% for the optimum coating condition.

Dans cette étude, on a recouvert l’alliage de plomb et argent (0·5% en poids) avec du polypyrrole en utilisant la synthèse électrochimique. On a évalué le rendement du revêtement sur le comportement à la corrosion de l’alliage de plomb dans l’électrolyte sévèrement corrosif. On a également étudié la morphologie du revêtement de polypyrrole en utilisant le microscopie électronique à balayage (SEM). Les résultats montrent que la couche protectrice de polypyrrole diminue la vitesse de corrosion des anodes par environ 30% en condition optimale du revêtement.     

电积法生产铜粉的开发与研制

试验研究了以硫酸铜为原料,采用电积法生产铜粉的各种工艺条件,并依据试验研究确定的工艺条件,制备出了符合国家标准的铜粉,产品能满足电解铜粉使用领域的要求。     

Bed performance in the direct electrowinning of lead from suspension galena anodes

Additive effects have been examined in the performance of suspension electrolysis of galena concentrate anode. A better conducting additive of properly selected size fraction, compatible with the relative size and specific gravity of galena, was found to improve the dissolution characteristics. With optimization of parameters such as current density, lead ion additions to the bath, electrolysis time,etc., and by withdrawing accumulated elemental sulfur intermittently, it was possible to dissolve lead with 79 pct current efficiency and energy consumption of 0.54 Kwh per kilogram of lead.     

Physico-chemical properties of copper electrorefining and electrowinning electrolytes

Densities, viscosities, electrical conductivities and specific heats of solutions containing copper, nickel, arsenic, iron and sulphuric acid in the concentration ranges of copper electrorefining and electrowinning electrolytes have been measured. Equations are presented for calculating these properties as a function of electrolyte composition and temperature. DEREK C. PRICE, formerly Research Associate, Department of Mining and Metallurgical Engineering, McGill University, Montreal, Canada     

Interactions of variables in the fluidised-bed electrowinning of copper

The effects of certain variables on the current efficiency and power consumption of a small fluidised-bed electrowinning cell treating dilute copper sulphate solutions have been studied. A factorial experimental design in two levels has been used to investigate the effects of cell current, sulphuric acid concentration, temperature and the presence of iron in the electrolyte, and the results have been analysed by the Yates technique.It is shown that an increase in temperature and the presence of iron in solution both decrease the current efficiency, while an increase in the cell current increases the current efficiency, for conditions where the cathode is not polarized with respect to copper ions. Significant interaction effects on the current efficiency are shown to exist for the case of cell current and iron concentration and for cell current and temperature. These main effects and interactions can be accounted for by a model in which three simultaneous reduction reactions occur at the cathode involving cupric ions, ferric ions and oxygen, with the latter two occurring at their diffusion limited rates.Significant main effects on the power consumption of the cell are shown to exist for cell current, iron concentration and acid concentration. Increasing either of the former two variables increases the power consumption whereas an increase in the latter causes a marked decrease in power consumption, and significant interactions occur between cell current and iron concentration and cell current and acid concentration.An increase in temperature is shown to lead to an increase in the amount of metal deposited on the feeder electrode.The paper concludes with a discussion of the application of fluidised-bed cathodes to the recovery of copper by electrowinning from various types of solutions.     

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.     

Dissolution kinetics of copper sulphide anodes

Constant current and voltammetric experiments were carried out with synthetic and natural chalcocite and synthetic digenite anodes in a variety of electrolytes. Rapid dissolution of copper occurred at low potentials until limited by the rate at which copper could be transported from the reaction zone by diffusion through electrolyte held within the porous product layer. At this point, the potential rose sharply (galvanostatic) or the current began to fall (voltammetric) corresponding to the formation of elemental sulphur. Quantitative support for this mechanism was obtained using a simplified model of the pore diffusion process. The complexity of the solid-state reactions occurring in the anode product was revealed by a novel technique which enabled direct observation of the product profile during electrolysis.     

The mineralogical characterization of tellurium in copper anodes

A mineralogical study of a «normal» commercial copper anode and six tellurium-rich copper anodes from the CCR Refinery of the Noranda Copper Smelting and Refining Company was carried out to identify the tellurium carriers and their relative abundances. In all the anodes, the major tellurium carrier is the Cu₂Se-Cu₂Te phase which occurs as a constituent of complex inclusions at the copper grain boundaries. In tellurium-rich anodes, the molar tellurium content of the Cu₂Se-Cu₂Te phase can exceed that of selenium. Although >85 pct of the tellurium occurs as the Cu₂Se-Cu₂Te phase, minor amounts are present in Cu-Pb-As-Bi-Sb oxide, Cu-Bi-As oxide, and Cu-Te-As oxide phases which form part of the grain-boundary inclusions. About 1 pct of the tellurium content of silver-rich anodes occurs in various silver alloys, but gold tellurides were never detected. Surprising is the fact that 2 to 8 pct of the total tellurium content of the anodes occurs in solid solution in the copper-metal matrix, and presumably, this form of tellurium dissolves at the anode interface during electrorefining.     

The behavior of thiourea and flotation reagents in zinc electrowinning circuits

The effect of thiourea and flotation reagents on the electrowinning of zinc from industrial electrolytes was studied, and all the compounds were found to reduce the zinc deposition current efficiency and to change the properties of the zinc deposits. The effectiveness of activated carbon, two-stage cementation, and hot acid leaching on the destruction/removal of the organic compounds also was addressed. Activated carbon pretreatment of thiourea-containing electrolytes restored the current efficiency for 1-hour zinc deposits to values comparable to those obtained for thiourea-free electrolytes. The activated carbon pretreatment, however, altered the deposit morphology and orientation, but produced a cyclic voltammogram similar to that of the thiourea-free solution. Two-stage cementation did not counteract the harmful effects of thiourea. Hot acid leaching destroyed the thiourea but generated large concentrations of ferrous ion that reduced the current efficiency. The ferrous concentrations, however, were readily controlled by KMnO₄ or MnO₂ oxidation. None of the treatment options (activated carbon, two-stage cementation, or hot acid leaching) was effective in controlling the flotation reagents, and their moderately harmful effect on zinc electrowinning persisted. Even low concentrations of these reagents polarized zinc deposition, and this resulted in a “glue-type” zinc deposit.     

Thermodynamic behavior of bismuth in copper pyrometallurgy: Molten matte,white metal and blister copper phases

This study developed thermodynamic data relating to the behavior of bismuth in copper smelting, converting and refining processes. The activity of bismuth was set by establishing a known vapor pressure of bismuth over melts of various phases. The melts were equilibrated with the vapor, and the resulting bismuth content used to establish bismuth activity coefficients. Experiments were carried out, under controlled oxygen potentials, at 1200 and 1250 °C. Results show that bismuth deviates positively from Raoult's Law at both 1200 and 1250 °C in copper (γ_Bi = 2.17, 2.27), white metal (γ_Bi = 6.1, 6.1), Cu₂S with 2 wt pct FeS (γ_Bi = 8.0, 8.0), Cu₂S with 4 to 6 wt pct FeS (γ_Bii = 16.4, 16.4) and Cu2S with 8 to 70 wt pct FeS (γ_Bi = 13.6, 13.6), respectively. Sabri Arac formerly Research Assistant at University of Arizona Gordon H. Geiger formerly head of the Department of Metallurgical Engineering at the University of Arizona     

The behavior of thiourea and flotation reagents in zinc electrowinning circuits

The effect of thiourea and flotation reagents on the electrowinning of zinc from industrial electrolytes was studied, and all the compounds were found to reduce the zinc deposition current efficiency and to change the properties of the zinc deposits. The effectiveness of activated carbon, two-stage cementation, and hot acid leaching on the destruction/removal of the organic compounds also was addressed. Activated carbon pretreatment of thiourea-containing electrolytes restored the current efficiency for 1-hour zinc deposits to values comparable to those obtained for thiourea-free electrolytes. The activated carbon pretreatment, however, altered the deposit morphology and orientation, but produced a cyclic voltammogram similar to that of the thiourea-free solution. Two-stage cementation did not counteract the harmful effects of thiourea. Hot acid leaching destroyed the thiourea but generated large concentrations of ferrous ion that reduced the current efficiency. The ferrous concentrations, however, were readily controlled by KMnO₄ or MnO₂ oxidation. None of the treatment options (activated carbon, two-stage cementation, or hot acid leaching) was effective in controlling the flotation reagents, and their moderately harmful effect on zinc electrowinning persisted. Even low concentrations of these reagents polarized zinc deposition, and this resulted in a “glue-type” zinc deposit.     

Behavior of antimony(III) during copper electrowinning in chloride solutions

Contamination of cathodic copper by Sb during electrowinning in chloride solutions is a surface phenomenon. A digitized scanning electron microscopy (SEM) micrograph indicates that the Sb is concentrated on the surface of the cathode. Energy-dispersive X-ray (EDX) analysis reveals that the Sb-containing layer is a complex salt of Cu, Sb, Cl, and O. Electrochemical measurements show-that the adsorption of Sb or Cu species decreases with the increase of acidity of the solution when the solution contains antimony chloride or cuprous chloride. The adsorption increases with the increase of the acidity when the solution contains both Sb and Cu. The discharge of cuprous ions in the adsorbed complex salt releases antimonious ions and then forms a new layer of the complex salt with cuprous ions from the solution. This newly formed complex salt is readsorbed on the surface of the cathode. Thus, Sb concentrates on the surface of the cathode instead of being evenly distributed throughout the copper product. This suggested mechanism also explains the fact that the presence of Sb in the electrolyte enhances the electrodeposition of Cu.     

The stacking fault energy in noble metal alloys

A model for the stacking fault energy, γ, in noble metals and their alloys is developed which qualitatively explains many features of experimental observations. The model is based on bothd band and free electron contributions to the cohesion. An important prediction of the model is that γ can be decreased in noble metal alloys by the addition of a solute with an emptyd band withZ = 1 (i.e., lithium in silver). Measurements of γ were made as a function of lithium concentration in a series of Ag-Li alloys up to 25 at. pct Li using the node method. The results show that γ decreases with the addition of lithium in a manner predicted by the model.