Insoluble anodes used in hydrometallurgy

Ivanov, Ivan B.; Stefanov, Y.; Noncheva, Z.; Petrova, M.; Dobrev, Ts.; Mirkova, L.; Vermeersch, R; Demaerel, J.-P

doi:10.1016/s0304-386x(00)00097-9

Cited by 113 publications

(42 citation statements)

References 4 publications

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“…It has been reported that Cl − forms a compound (AgCl 2 ) sealing the oxide layer and enhancing corrosion resistance. 27 However, Hampson 32 reported that Cl − destabilizes the SO 4 2− in the oxide layer, decreasing the quality of the oxide layer and inhibiting the passivation process, decreasing both the slope of oxygen evolution region and OER potential. Cl − has a very high oxidation potential and destabilizes elements in the oxide layer, displacing them from the anode.…”

Section: Changes In Electrolyte Compositionmentioning

confidence: 99%

Polarization Behavior of Lead-Silver Anodes in Zinc Electrowinning Electrolytes

Tunnicliffe

Mohammadi

Alfantazi

2012

J. Electrochem. Soc.

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Lead anodes performance is important in zinc electrowinning (EW) as it greatly influences the final product quality and operating costs. Pb-based alloys are used in EW because they are cheap, conductive, and relatively stable at high potentials and low pH. In this study, polarization behavior and the oxygen evolution reaction (OER) on a Pb-Ag alloy were examined as a function of H 2 SO 4 , Mn 2+ , Cl − , Zn 2+ concentrations and solution temperature. The slope of the oxygen evolution region and the OER potential were determined using potentiodynamic experiments. Corrosion products were studied using potentiostatic experiments along with scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS) and X-ray diffractometry (XRD). The relationship between surface morphology of the electrode and operating potential was studied.The London Metal Exchange (LME) reported that 12 million tons of metallic zinc was produced in 2007 and, of that, 7 million tons were recovered through aqueous EW. 1 The largest producers were: Australia, Canada, China, Peru, and the United States. 2 Zinc usually exists in nature as sphalerite (ZnS) and is commonly recovered using a roast-leach-EW process. Otherwise, the concentrate is leached in an autoclave, solids and liquids are separated, and zinc is recovered using EW. 3 Fundamentally, EW is an electrolytic process composed of a metallic reduction at the cathode (reaction 1) and oxygen evolution reaction (OER) (reaction 2) at the anode. The standard state thermodynamic cell potential based on these oxidation and reduction reactions is −1.99 V. In order to produce metallic zinc, a constant current between 400 and 600 A/m 2 is applied to the cell which results in a cell potential between 3.2 V and 3.7 V. This high potential is required to achieve desired kinetics during EW.An EW cell contains acidic electrolyte and utilizes Pb-based anodes and aluminum cathodes. Few anode materials are insoluble in sulfate based electrolytes making Pb-based alloys a primary candidate for this application. Pure Pb lacks the physical properties required for anodes but Pb-based alloys are used because they are inexpensive, insoluble, conductive, electrocatalytic, and stable at high potentials. 4 Pb-based alloys have been used as anodes since 1909 when zinc was first produced industrially. 5 A protective corrosion layer creates a physical barrier between the Pb alloy and electrolyte in service. Pb-based anodes' corrosion resistance and physical properties are enhanced by the addition of Ag. Ag improves the Pb alloys electrical conductivity as well as enhances the OER. 4 Ag content varies in electrodes, but industrial anodes commonly contain between 0.5 to 1wt% silver. 4-10 The cost of alloying Pb with Ag becomes substantial because of the high price of metal and the large amount required for the over 10,000 anodes typically used in an EW plant.Assuming that the processing plant is capable of recovering the majority of the used Pb anodes, each new anode costs approximately $300. The cost of ano...

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Section: Changes In Electrolyte Compositionmentioning

confidence: 99%

Polarization Behavior of Lead-Silver Anodes in Zinc Electrowinning Electrolytes

Tunnicliffe

Mohammadi

Alfantazi

2012

J. Electrochem. Soc.

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“…The literature shows many publications on the modification of lead anodes to improve corrosion resistance [16][17][18], to enhance the mechanical properties [19] and to save electrical energy [20][21][22]. There is also interest in improving lead anode performance by pre-treatment [23,24] or by alloying [25].…”

Section: Introductionmentioning

confidence: 99%

New oxygen evolution anodes for metal electrowinning: MnO2 composite electrodes

et al. 2009

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Several modifications of manganese dioxide (MnO 2 ) 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 MnO 2 . 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 MnO 2 catalyst particles. Physicochemical processes contributing to the observed data are discussed.

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“…For Pb-0?56Ag anode, at the beginning time (from 10 min to 1 h), the oxide film layer contains mainly PbO(OH) 2 and PbO(OH), which are colloid and gel conductive. At this time, the oxide film layer has many pores, the ions can pass through the pores, and the reaction is controlled by diffusion phenomenon.…”

Section: Resultsmentioning

confidence: 99%

Electrochemical impedance spectroscopy evaluation of behaviour of Pb–Ag anodes for zinc electrowinning

Zhang

Bounoughaz

Ghali

et al. 2013

Corrosion Engineering, Science and Technology

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Pb-0?5-0?7Ag anodes are widely used in the industry of zinc electrowinning. Two commercial lead anodes containing 0?56 and 0?69%Ag were studied by electrochemical impedance spectroscopy to evaluate their electrochemical activity. An industrial acid zinc sulphate electrolyte containing glue and chloride ion, but without manganese addition, was considered. In this study, 5 h of electrolysis at a density of 50 mA cm 22 (currently used in practice) and also 6 h of potential decay were made to represent electrowinning periods of maintenance both at 38uC. During the 5 h polarisation, the average double layer capacity of Pb-0?56Ag alloy was higher (y9%) than that of Pb-0?69Ag alloy. During the first hour of potential decay, the Warburg impedance controls the electrochemical reaction. For the period from the second to sixth hour, the double layer capacity decreased with immersion time, and the charge transfer resistance increased with time. During the potential decay, the average charge transfer resistance of Pb-0?69Ag anode was higher (y52%) than that of Pb-0?56Ag anode.

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Insoluble anodes used in hydrometallurgy

Cited by 113 publications

References 4 publications

Polarization Behavior of Lead-Silver Anodes in Zinc Electrowinning Electrolytes

Polarization Behavior of Lead-Silver Anodes in Zinc Electrowinning Electrolytes

New oxygen evolution anodes for metal electrowinning: MnO2 composite electrodes

Electrochemical impedance spectroscopy evaluation of behaviour of Pb–Ag anodes for zinc electrowinning

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