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

Abstract

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^?2 (currently used in practice) and also 6 h of potential decay were made to represent electrowinning periods of maintenance both at 38°C. During the 5 h polarisation, the average double layer capacity of Pb–0·56Ag alloy was higher (～9%) 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 (～52%) than that of Pb–0·56Ag anode.     

Formation and study of the properties of finishing coatings of a circuit board with tin–zinc alloy instead of tin–lead alloy coatings

A formation technique of electroplating coatings of tin–zinc alloy (50) based on using low-toxicity lactic acid as surfactant, ligand, and buffer addition was developed. The dependences of alloy composition and cathodic yield on the alloy current and the coating quality on the concentration of tin and zinc ions in the solution, the content of lactic acid, the solution acidity (pH), the temperature, and the current cathodic density were investigated. The optimum conditions of the process carrying out were determined. The performance characteristics of obtained coatings were investigated. It was proven that the coating with this alloy meets the requirements of GOST (State Standard) 23752–79 “Circuit Boards. General Technical Specifications” and can be used for the circuit boards of products of the instrument-making industry instead of tin–lead alloy, which will make it possible to reduce the environmental risk of production, as well as increase the efficiency and maintainability of devices and systems.     

Effect of solution components on stability of protective PbO2 layers on Pb–Ca–Sn anodes for copper electrowinning

Abstract

Potential–time curves have been carried out in CuSO₄–H₂SO₄ electrolytes to establish the effect of various impurities and additives on the stability of the protective PbO₂ layer formed on Pb–Ca–Sn alloys used in copper electrowinning. The most important effects are those of guar and Fe(III). Acting separately, they tend to stabilise the protective layer, whereas Co(II) and Mn(II) do not. The effect of Fe(III) can be explained by its strong oxidising power; the effect of guar, by its ability to form a protective barrier of organic molecules adsorbed on the PbO₂ layer. The effects of both guar and Fe(III) are diminished by the presence of other species in solution: reducing species diminish the effect of ferric ions and guar is degraded by oxidising species.     

Electrosynthesis and physicochemical properties of α–PbO2–CeO2–TiO2 composite electrodes

In order to investigate the effect of solid particles dopants on physicochemical properties of α-PbO₂ electrodes, α-PbO₂ composite electrodes doped with nano-TiO₂ and nano-CeO₂ particles were respectively prepared on Al/conductive coating electrodes in 4 mol/L NaOH solution with addition of PbO until saturation by anodic codeposition. The electrodeposition mechanism, morphology, composition and structure of the composite electrodes were characterized by cyclic voltammogram (CV), SEM, EDAX and XRD. Results show that the doping solid particles can not change reaction mechanism of α-PbO₂ electrode in alkaline or acid plating bath, but can improve deposition rate and reduce oxygen evolution potential. The doping solid particles can inhibit the growth of α-PbO₂ unit cell and improve specific surface area. The diffraction peak intensity of α-PbO₂-CeO₂-TiO₂ composite electrode is lower than that of pure α-PbO₂ electrode. The electrocatalytic activity of α-PbO₂-2.12%CeO₂-3.71%TiO₂ composite electrode is the best. The Guglielmi model for CeO₂ and TiO₂ codeposition with α-PbO₂ is also proposed.     

Corrosion behaviour and catalytic effectiveness of Pb–Ca–Sn,RuO2–IrO2/Ti and IrO2–Ta2O5/Ti anodes for copper electrowinning

Abstract

The dependence of the corrosion rate on cell current density (CD) for three anode materials (Pb–Ca–Sn, RuO₂–IrO₂/Ti and IrO₂–Ta₂O_5/Ti) in a laboratory scale copper electrowinning cell has been studied by means of short term weight loss tests, scanning electron microscopy observations and energy dispersive spectroscopy analysis. The lead anodes (Pb–Ca–Sn) corroded at all the studied cell CDs, and their corrosion rate increased with increasing cell CD. The precious metal oxide anodes (RuO₂–IrO₂ and IrO₂–Ta₂O₅) only exhibited corrosion at the highest tested cell CD (1000 A m^?2), and their corrosion rates were about a quarter of the lead corrosion rate at the same cell CD. The electrocatalytic properties of the three anode materials were characterised by means of potentiodynamic experiments. The overall results pointed to IrO₂–Ta₂O₅/Ti as the best anode material of choice, although plant tests would be required before deciding on any specific commercial use.     

Characteristics and properties of surface coated nano-TiO_2

1Introduction Nano-TiO2,as a new inorganic material,has many excellent properties,such as nontoxic,stable in chemistry and high efficient photocatalytic effect[1,2].As fine particles,it is easy to agglomerate in practical use,especially difficult to dispe…     

Fabrication of TiO2 nanotube arrays on biologic titanium alloy and properties

The vertically aligned highly ordered TiO2 nanotube arrays were fabricated by potentiostatic anodization of biologic Ti alloys（TLM） and pure Ti substrates, followed by annealing at 480 and 550 ℃ for 6 h. High-resolution scanning electron microscopy （SEM） was applied to characterize the original films. The phase of the film was characterized by XRD. The interfacial adhesion and bond strength between thin films coating and substrate were tested by scratch method. The results show that the films on the TLM alloy have high adhesion strength compared with them on pure Ti.     

Preparation and properties of Os–Ir–Al alloy for impregnated tungsten cathodes

Os–Ir–Al alloy was fabricated by powder metallurgy technique.IrAl and OsIr interalloys were synthesized to reduce the Al evaporation and ensure the composition of the ternary alloy.Analysis on microstructures shows that each component is distributed homogeneously,and the green density reaches 94.9%.Ba–W cathodes with Os–Ir–Al alloy magnetic sputtered on the tips are prepared and directly current density tests are carried out on these cathodes.It is found that at 1,050℃,the average zero field emission density of the cathode reaches up to 20 Aácm-2.The improvements of cathodic current density and stability may indicate the prosperous application of Os–Ir–Al alloy on cathode.     

Sulphidization flotation for recovery of lead and zinc from oxide-sulfide ores

A new flowsheet was developed to recover the valuable minerals from oxide or oxide-sulfide ores of lead and zinc. The flowsheet consisted of flotation of sulfide minerals, desliming and sulphidization-flotation of oxide minerals. The corresponding reagent system and techniques to the flowsheet were investigated. Batch and continuous tests show that the dosage of sodium sulfide, temperature, and collector type are main affecting factors on the recovery of smithsonite and cerussite. For the flotation of cerussite, there is an appropriate dosage of sodium sulfide at which the recovery reaches its maximum value. The required sodium sulfide for smithsonite flotation is higher than that for cerussite and the recovery of smithsonite flotation increases with the dosage of sodium sulfide at low level and becomes insensitive at high dosage. The appropriate temperature for smithsonite and cerussite flotation is found to be 25 ～ 40℃. Amines are found to be the effective collectors for the flotation of smithsonite after sulphidization. Investigation also shows that desliming prior to sulphidization-flotation is essential to the effective recovery of smithsonite and cerussite, and the desliming process of two-stage hydrocyclon is well feasible and effective for the treatment of lead-zinc oxide ores. A further treatment on the cerussite flotation concentrate by shaking table is proposed to obtain higher lead grade.     

Mechanical properties and microstructures of hot extruded AE42 alloy with addition of zinc

Mechanical properties and microstructures of AE42 magnesium alloy with addition of Zn and subjected to hot extrusion at 370 ℃ and an extrusion ratio of 8：1 were investigated. The results show that for the AE42 alloy, the addition of Zn can obviously improve its elongation as well as the ultimate tensile and yield strengths below 150 ℃. The addition of Zn can refine the mierostructure of the AE42 alloy, and result in the precipitation of Mg17Al12 and MgZn2 phases. Due to the addition of Zn to the AE42 alloy, the amount of Al11RE3 phase decreases, while the Al11RE3 phase becomes short rod-shaped from acicular and block, and distributes along the grain boundaries, which will have a stronger effect on the tensile properties of the alloy at elevated temperature. In addition, with the presence of MgZn2 precipitates, the sliding of grain boundaries is restrained and the strength of the alloy gets enhanced.     

Physicochemical and environmental properties of arsenic sulfide sludge from copper and lead−zinc smelter

Physicochemical properties of arsenic sulfide sludge (ASS) from copper smelter (ASS-I) and lead−zinc smelter (ASS-II) were examined by XRD, Raman spectroscopy, SEM−EDS, TG−DTA, XPS and chemical phase analysis method. The toxicity characteristic leaching procedure (TCLP), Chinese standard leaching tests (CSLT), three-stage sequential extraction procedure (BCR) and batch leaching experiments (BLE) were used to investigate the environmental stability. The ASSs from different smelters had obviously different physicochemical and environmental properties. The phase composition and micrograph analysis indicate that ASS-I mainly consists of super refined flocculent particles including amorphous arsenic sulfide adhered with amorphous sulfur and that ASS-II mainly consists of amorphous arsenic sulfide. The valence state of arsenic in both sludges is trivalent, but the valence composition of sulfur is quite different. The ASSs have thermal instability properties. The results of TCLP and CSLT indicate that the concentrations of As and Pd in the leaching solution exceed the standard limits. More than 5% and 90% of arsenic are in the form of acid soluble and oxidizable fractions, respectively, which explains the high arsenic leaching toxicity and environmental activity of ASS. This research provides comprehensive information for the disposal of ASS from copper and lead−zinc smelter.     

Microstructure and properties of aging Cu–Cr–Zr alloy

The crystallography and morphology of precipitate particles in a Cu matrix were studied using an aged Cu–Cr–Zr alloy by transmission electron microscopy(TEM) and high-resolution transmission electron microscopy(HRTEM). The tensile strength and electrical conductivity of this alloy after various aging processes were tested. The results show that two kinds of crystallographic structure associated with chromium-rich phases, fcc and bcc structure, exist in the peak-aging of the alloy. The orientation relationship between bcc Cr precipitate and the matrix exhibits Nishiyama–Wasserman orientation relationship. Two kinds of Zr-rich phases(Cu4Zr and Cu5Zr)can be identified and the habit plane is parallel to {111}Cu plane during the aging. The increase in strength is ascribed to the precipitation of Cr- and Zr-rich phase.     

Electrochemical corrosion behaviour and surface morphology of electrodeposited zinc,zinc–cobalt and their composite coatings

Abstract

The electrochemical behaviour as well as the surface morphology characteristics of electrodeposited Zn and Zn-Co (≈3 wt-%) alloy coatings on low carbon steel samples, with and without included nanoparticles of organic co-polymers in their structure, are discussed. Their corrosion resistance and protective properties were studied in a model corrosion medium, 5 wt-% NaCl, using electrochemical methods such as polarisation resistance (R _p) measurements and potentiodynamic (PD) polarisation curves. Scanning electron microscopy (SEM) was performed to examine the surface morphology changes of the samples before and after the corrosion treatment. Some conclusions are drawn about the influence and importance of the organic nanoparticles on the corrosion behaviour of the coatings presented.     

Microstructure and mechanical properties of ZrB2–Nb composite

The high relative density of the ZrB₂-based composite toughened by 25 vol.%Nb (ZN) was hot-pressed at reduced temperatures with low pressure of 30 MPa. Compared with the toughness of 2.3–3.5 MPa m^1/2 and strength of 350 MPa of the monolithic ZrB₂, the toughness and strength of the ZN composite were improved to 6.7 MPa m^1/2 and 773 MPa, respectively, due to the addition of ductile Nb. The toughening mechanisms are crack deflection and branching as well as stress relaxation near the crack tip. Furthermore, the densification mechanism was analyzed and discussed. The results here pointed to a potential method for improving fracture toughness and strength of ZrB₂-based ceramics.     

Preparation and electrocatalytic properties of Ti/IrO2-Ta2O5 anodes for oxygen evolution

1 Introduction Oxygen and chlorine evolution reaction are the common and most important electrochemical reactions in electrolysis industry. As the Ti/RuO2-TiO2 anode has been successfully developed and widely employed in the electrochemical industry, the …     

Al2O3–TiO2 composite coatings with enhanced anticorrosion properties for 316L stainless steel

316L stainless steel is used as an important structural material in various industries. However, its service life is limited in the presence of chloride ions due to severe chemical corrosion. Herein, a facile radiofrequency magnetron sputtering process is reported for the synthesis of various Al₂O₃–TiO₂ composite coatings as an anticorrosion layer for 316L stainless steel substrates. The enhanced chemical stability of Al₂O₃–TiO₂ composite coatings was investigated by X-ray photoelectron spectroscopy, electron paramagnetic resonance, and X-ray diffraction measurements. Moreover, the high specific surface area of Al₂O₃–TiO₂ composite coatings displayed better hydrophobic property which can be confirmed by scanning electron microscopy and contact angle measurements. Finally, the direct characterization of anticorrosion properties was carried out using electrochemical tests. All of the above results exhibited the enhanced anticorrosion properties of Al₂O₃ coating after the incorporation of TiO₂. Significantly, the Al₂O₃–TiO₂ composite coatings with 15.56% Ti content provided the best corrosion resistance for 316L stainless steel.     

Study of the proportioning design method and mechanical properties of a cBN–TiN composite

This study provides a proportioning design method for the polycrystalline cubic boron nitride (PcBN) composite based on dense packing theory with the use of the Horsfield dense filling theory and Dinger–Funk equation. Subsequently, three proportioning schemes of the cBN–TiN system were designed with different titanium nitride content. The samples were analysed through X-ray diffraction, scanning electron microscopy and transmission electron microscopy for density, hardness and actual cutting performance, respectively. The predicted optimal values were consistent with the experimental results, which proved the validity of the method. Three samples designed from the method had sufficient sintering reaction under high pressure and high temperature to form a uniform and compact sintering structure, which had excellent mechanical properties to meet the industrial application. A surface reaction zone was formed on the W grains and the substitution reaction between cBN and TiN occurs and directly combines with each other to form an obvious grain boundary. It also indicated that appropriate PcBN proportioning scheme, workpiece characteristics, and cutting parameters should be sufficiently considered and reasonably adjusted in order to achieve a higher tool life and excellent workpiece surface roughness in the actual cutting application.