Zinc Electrolyte Research Articles

Electrolytic Zinc Composite Coatings: Ultrasound Assisted Deposition for Morphological and Composition Modification

Protection of steel by sacrificial coatings is of primary importance in the industry, to extend the lifetime of steel structure parts. This is frequently obtained by zinc coatings, after galvanization or electrodeposition, but pure zinc is sometimes not resistant enough when high protective properties are required. Indeed, zinc corrosion rate is quite important, even if corrosion products play an important role in protection. Therefore, Zn alloys deposition is a privileged process. However, the metallic alloy elements used for codeposition are frequently composed of harmful substances, which use is more and more regulated. In a global strategy of employees and environment protection, and to anticipate more drastic restriction, the European plating shop leader Electropoli proposed a partnership to the research institute UTINAM. The project Zincadher intended to propose an alternative to zinc alloys plating by a zinc matrix, reinforced by silica and PMMA particles which main function is to increase corrosion resistance and adhesion. To overcome the lack of availability of PMMA (poly (methyl methacrylate)) nanoparticles at a reasonable price, an original synthesis of the PMMA particles was first developed [1]. It involves the use of a custom-made ultrasonic system, were MMA (methyl methacrylate) and water mixtures are exposed to different ultrasonic systems and successive sonication steps as follows: 20 kHz → 580 kHz → 858 kHz → 1138 kHz. Then, polymerization of the droplets is conducted, in order to obtain the largest possible concentration of PMMA particles of sub micrometer size range of different electrokinetic properties [2]. In a second part of the study, electrochemical study of acid zinc electrolyte with PMMA and/or silica particle have been carried out. As ultrasound is known to improve greatly mass transfer and coating characteristics as well as particles dispersion [3], a calibration of acoustic streaming at the surface of the working electrode is conducted, to be able to compare with classical mechanical stirring with the concept of equivalent velocity. Then, after particles dispersion in an acid zinc bath, composite coatings are elaborated. The plating parameters (current density, particles nature, hydrodynamic source…) on the morphology and composition of the coatings are evaluated by SEM/EDS and XRD characterization. Acknowledgement: The authors would like to thank Electropoli Group for funding this project and the ANRT for the CIFRE convention. [1] K. Nakabayashi, T. Fuchigami, M. Atobe, Electrochimica Acta. 110 593–598 (2013) [2] L Baissac, CC Buron, L Hallez, P Berçot, JY Hihn, L Chantegrel, G Gosse Ultrasonics sonochemistry 40, 183-192 (2018) [3] JY Hihn, F Touyeras, ML Doche, C Costa, BG Pollet in Power Ultrasound in Electrochemistry: From Versatile Laboratory Tool to Engineering Solution, John Wiley & Sons, Ltd, 169-214 (2012) Figure 1

Anodic behavior of zinc in aqueous borate electrolytes

The behavior of zinc in aqueous borate electrolytes at anodic polarization in galvanostatic regime was investigated. Induction periods and voltage breakdown phenomena were observed in the respective kinetic curves. The dependence of the duration of these induction periods on the polarization conditions (j = 5 ÷ 60 mA cm−2; H3BO3 content = 0.1 ÷ 3 wt %; pH 5.8 ÷ 8.2; t = 10 ÷ 30 °C) was studied. The registered breakdown voltages obey the law of Burger and Wu, and exceeded 200 V. Clear periodical oscillations of the forming voltage were registered at high current densities. The obtained films were submitted to X-ray diffractometry (XRD), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS) and attenuated total reflectance Fourier transformed infrared spectroscopy (ATR-FTIR). The data obtained by these observations have revealed that these layers are composed of amorphous 2ZnO.3BO3.7H2O. Furthermore, on the basis of the scanning electron microscopy (SEM) observations a conceptual model was developed for qualitative explanation of the film growth mechanism. The appearance of high amplitude oscillations was explained by complete disjoining of the layer due to accumulation of mechanical stress. These conclusions were confirmed by obtained atomic force microscopy (AFM) images and (ICP-OES) measurements of the electrolytes after the respective polarizations.

Electrochemical Obtaining and Corrosion Behavior of Zinc-Polyaniline (Zn-PANI) Hybrid Coatings

Hybrid zinc-based coatings with embedded polyaniline (PANI) particles in the metal matrix are obtained in a one-step process via electrodeposition on low-carbon steel plates. The aim is directly to use the inhibitor properties of polyaniline for improved protection against corrosion in chloride containing medium (5% NaCl solution). PANI-particles (concentration of 0.025 g/L) are added to the starting zinc electrolyte in dispersed form—the latter being obtained via oxidation polymerization in the presence of stabilizers (polyvinyl pyrrolidone (PVP) or colloidal SiO2). Electrodeposition conditions are equal to those for obtaining an ordinary zinc coating. The surface morphology of the hybrid coatings before and after corrosion treatment in the model medium is characterized with SEM. The influence of the incorporated PANI/PVP- or PANI/SiO2-particles on the protective properties of the coatings is evaluated by the application of electrochemical (potentiodynamic polarization, open-circuit potential, polarization resistance, cyclic voltammetry) as well as X-ray based (X-ray diffraction and X-ray photoelectron spectroscopy) methods. A discussion and some conclusions about the reasons for the improved corrosion resistance and protective ability of the hybrid coatings in that model medium are proposed.

Improved Electrolyte for Negative Side of Zinc-Cerium Redox Flow Batteries

Redox flow batteries (RFBs) are one of the most recent and promising technologies for large-scale energy storage applications. In an RFB, the active materials for the two redox reactions are dissolved in separate electrolytes stored in external tanks. During charge/discharge, these electrolytes are pumped through the cell where the redox reactions occur. Compared to conventional energy storage systems, RFBs are advantageous due to their portability, low maintenance cost, modularity and flexibility [1]. RFBs based on zinc-cerium chemistry are very attractive since they provide the highest cell voltage among flow batteries and thus the highest theoretical energy density [2]. Nevertheless, this system has a number of challenges, the most important of which is the occurrence of side reactions. During charge, hydrogen and oxygen evolution side reactions occur at the negative and positive electrodes, respectively, leading to a lower charge efficiency, wasted energy and eventual premature battery failure [3,4]. During discharge, self-discharge of the zinc deposit due to acid attack also contributes to reduction in the efficiency. Thus, the suppression of these side reactions is necessary for the improvement and ultimate success of zinc-cerium RFBs. Toward this goal, our work focuses on the enhancement of the Zn/Zn(II) redox reaction through the use of a mixed-acid electrolyte. From half-cell experiments on a glassy carbon electrode, we have shown that the introduction of 0.2 – 0.3 mol dm−3 of chloride anions to the conventional methanesulfonic acid electrolyte significantly increases the transport properties of Zn(II), reduces the zinc nucleation overpotential and enhances the exchange current density of the Zn/Zn(II) redox reaction [5]. The same effect is observed when glassy carbon is replaced by polyvinyl ester (PVE), which is a commonly-used negative electrode in Zn-Ce RFBs. The use of this improved electrolyte on the charge, voltage and energy efficiency of a bench-scale zinc-cerium RFB has also been investigated. Similar to results obtained in the half-cell studies, the full-cell experiments show that the mixed methanesulfonate-chloride electrolyte facilitates the zinc redox reaction and thus increases the voltage efficiency of the battery as high as 10%. Additionally, the charge efficiency increases significantly under the conditions where negative half-cell is the limiting reaction. The improvement is more than 20% at an operating current density of 25 mA cm-2. The performance and life-cycle analysis of the battery with this new electrolyte under different operating conditions will also be discussed in this presentation. [1] De Leon, C. P., Frías-Ferrer, A., González-García, J., Szánto, D. A., & Walsh, F. C. (2006). Redox flow cells for energy conversion. Journal of power sources, 160(1), 716-732. [2] Walsh, F. C., Ponce de Léon, C., Berlouis, L., Nikiforidis, G., Arenas‐Martínez, L. F., Hodgson, D., & Hall, D. (2015). The development of Zn–Ce hybrid redox flow batteries for energy storage and their continuing challenges. ChemPlusChem, 80(2), 288-311. [3] Leung, P. K., Ponce-de-León, C., Low, C. T. J., & Walsh, F. C. (2011). Zinc deposition and dissolution in methanesulfonic acid onto a carbon composite electrode as the negative electrode reactions in a hybrid redox flow battery. Electrochimica Acta, 56(18), 6536-6546. [4] Nikiforidis, G., Berlouis, L., Hall, D., & Hodgson, D. (2014). An electrochemical study on the positive electrode side of the zinc–cerium hybrid redox flow battery. Electrochimica Acta, 115, 621-629. [5] Amini, K., & Pritzker, M. D. (2018). Electrodeposition and electrodissolution of zinc in mixed methanesulfonate-based electrolytes. Electrochimica Acta, 268, 448-461.

Serum amyloid A protein as a diagnostic marker for viral infections

Polymeric nanocontainers (NCs) impregnated with corrosion inhibitor benzotriazole are formed using layer-by-layer deposition of poly(acrylic acid) and poly(diallyldimethylammonium chloride) onto hematite particles in the presence of 0.1 M NaCl. Electric light scattering and electrophoresis are employed to control the formation and the size of NCs, as well as the stability of their suspensions. The inhibitor loaded NCs are incorporated into the volume of the galvanized coating during the electrodeposition of zinc on the steel substrate to ensure additional self-healing effect in the case of corrosion attack. The surface morphology and the uniformity of this composite coating as well as the lack of aggregation of the nanocontainers is demonstrated by scanning electron microscopy. The influence of NCs present in the zinc electrolyte on the cathodic and anodic processes is investigated by cyclic voltammetry. The corrosion behavior of the composite coatings at conditions of external cathodic and anodic polarization is tested with potentiodynamic measurements and the results are compared to pure zinc coatings. The composite coatings with embedded NCs revealed enhanced corrosion protection of low carbon steel in comparison with the pure zinc coatings in neutral corrosion medium.

Electrochemical Coprecipitation of Zinc and Aluminum in Aqueous Electrolytes for ZnO and AZO Coverage Deposition

The aim of this study is to examine the technological challenge of the electrochemical formation of zinc oxide and Al-doped ZnO films (ZnO:Al, AZO) as transparent conductive oxide coatings with complex architectures for solar cell photoanode materials. A cathodic electrodeposition of AZO was performed using aqueous nitrate electrolytes at 25°C. A significant positive deviation in aluminum percentage in the films was demonstrated by the LAES, EDX, and XPS methods, which originates from aluminum hydroxide sedimentation. The photoluminescent characteristics of the ZnO films reveal low band intensities related to intrinsic defects, while the samples with 1 at.% of aluminum show a strong and wide PL band at 600±80 nm and increase in conductivity.

Zinc Oxidation in Limited Volume of Alkaline Electrolyte

Studies of zinc electrode oxidation under the conditions of limited volume of alkaline electrolyte are carried out. It is shown, that at anodic polarization below 7–8 mV the zinc surface is covered by phase layer of zinc oxides and hydroxides. The last ones hinder diffusion of ions participating in electrochemical reactions. Then, formation of zincate complex [\(\rm{Zn}(OH)\begin{array}{c}2-\\ 4\end{array}\)] starts, with the slow diffusion stage of hydroxide ions to the anode surface. At polarization from 0.08 to 0.12 V formation of supersaturated zincate electrolyte occurs, and its decomposition with formation of the loose zinc oxide layer. At polarization above 0.12 V, nonporous oxide film is formed on zinc surface; zinc oxidation process proceeds by solid-phase mechanism.

Potentiostatic studies of the influence of temperature on lead-silver anodes during electrowinning and decay period

ABSTRACTThe electrochemical behaviour of the Pb-0.7% Ag anode has been investigated in zinc sulphuric acid electrolyte containing 5, 8, 12 g/L Mn2+ by electrochemical measurements at different temperatures of 35°C, 40°C, 45°C. It was observed by cyclic voltammetry before electrolysis that temperature increase from 35°C to 45°C resulted in a decrease in the oxidation peak I (Pb → PbSO4) and an increase in the oxygen evolution peak II (2H2O → O2 + 4H+ + 4e). At 2.01 V/SHE, the current densities of Pb-0.7% Ag anode in sulphuric acid solution containing 8 g/L Mn2+ at 35°C, 40°C and 45°C increased from 26.5 at 35°C to 28.5 and 37.7 mA/cm2 at 40 and 45°C, respectively. In the presence of ZnSO4 addition to the sulphuric acid solution, the anodic current of oxygen evolution at 2.01 V/SHE decreased by ∼ 18% at 40°C. After 2 h of potentiostatic polarisation in the presence of zinc sulphate addition at 2.01 V/SHE, electrochemical Noise Measurements showed that the admittance (corrosion rate) of the Pb-0.7% Ag anode in the zinc electrolyte increased with the increase in temperatures during decay. This tendency was also confirmed by linear polarisation and impedance measurements.

Lead-silver anode behavior for zinc electrowinning in sulfuric acid solution

Abstract In recent years, a renewed interest in studying the electrochemical corrosion behavior of lead anodes during zinc electrowinning is probably due to the particularly high sulfuric acid concentrations in zinc electrolyte where lead alloy anodes have high cell voltage and high corrosion rate of lead. The high corrosion rate of lead alloy resulted in Pb contamination on zinc deposit. In zinc electrometallurgy, the electrolyte from a zinc-rich ore contains a significant amount of Mn2+. Mn2+ in the zinc electrolyte results in forming an oxide film on lead anodes during electrolysis. Pb-0.7% Ag anode is generally used in the zinc industry. To improve the technical performance and decrease product cost, other anodes, such as Pb-Ca or Pb-Ag-Ca or Pb-Ag-Ti or Pb-Ag-Se alloys were tested. Till now, none of them has succeeded in the substitution of Pb-Ag anodes in the zinc electrowinning. As an alloying element, silver in small quantities is considered because of the benefits that generates on the anode during electrolysis. During zinc electrolysis, lead dissolution into the zinc electrolyte can be harmful to the quality of zinc deposit. However, the lead silver alloy anode can decrease the lead content in the zinc deposit by pre-treated methods such as blasting and preconditioning.

Selective determination of trace cobalt in zinc electrolytes by second-derivative catalytic polarography

We report herein a highly selective method for directly determining the trace Co2+ in highly concentrated zinc electrolyte. This novel method is based on a second derivative wave of catalytic adsorptive polarography generated by complexing Co2+ with dimethylglyoxime and nitrite onto a dropping mercury electrode. By employing a medium with NH3-NH4Cl buffer, DMG and NaNO2 during determining the trace Co2+, any interferences of highly concentrated Zn2+ and other coexisting metal ions in the electrolyte are completely eliminated due to the selective masking effect of EDTA. When the concentration of Co2+ is within 1.0×10–10–3.2×10–7 mol/L range, it shows a good linear relationship with the current peak. Detection limit is 1.0×10–11 mol/L, and RSD ≤2.7% for six successive assays. We have compared the efficiency of the current method to that obtained by cobalt nitroso-R-salt spectrophotometry, and the absolute values of relative deviations are ≤4.2%. The method developed and described herein has been successfully employed in determining the trace Co2+ in actual zinc electrolyte.

Influence of F-Doped β-PbO2 Conductive Ceramic Layer on the Anodic Behavior of 3D Al/Sn Rod Pb−0.75%Ag for Zinc Electrowinning

In this study, a 3D Al/Sn rod Pb−0.75%Ag anode was prepared by continuous extrusion coating technique, and a conductive ceramic layer was formed by anodic oxidation in a fluoride-containing H2SO4 solution. The phase composition and surface microstructure of the oxide layer were examined by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and energy dispersive spectrometer (EDS), indicating the presence of F-doped β-PbO2 ceramic layer. The electrocatalytic characteristics and electrochemical stability of the anodes were explored by cyclic voltammetry, anodic polarization curves, electrochemical impedance spectroscopy (EIS) and the accelerated life test in the zinc electrolyte. It was found that the F-doped β-PbO2 layer has good electrocatalytic activity and corrosion resistance. The fence-like 3D Al/Sn rod Pb−0.75%Ag/F-doped β-PbO2 anode plate was continuously used in the zinc electrolyte for 15 days; in addition, it was found that compared to the traditional Pb-0.75%Ag anode plate, the ultimate tensile strength improved by about 31.45%, the average cell voltage decreased by 53 mV, and the output of zinc increased by 3.09%, confirming its feasibility in practical applications for zinc EW.

ELECTROPHYSICAL PROPERTIES OF ZINC SULFATE SOLUTIONS IN PRESENCE OF WATER DISPERSION OF MULTI-LAYERED CARBON NANOTUBES

Multi-layered carbon nanotubes were synthesized via hydrocarbons pyrolysis method in the presence of argon overpressure in the reaction system. With the use of the scanning electron microscope method, a morphology of the obtained materials were investigated. Synthetized nanotubes were modified by treating with solutions of various reagents: sodium hydroxide (10 mass. %), azotic (40 mass. %) and perchloric (40 mass. %) acids, chloroform. The sample was placed in the reagent solution with the volume of 10 ml and exposed for 24 h. Electrophysical investigation of multi-layered carbon nanotubes dispersions with zinc sulfate additions was carried with the use of the impedance meter Z - 1500J in a range of frequencies of 10 Hz - 2 MHz. It was found that the carbon nanomaterials effect on the electrophysical properties of zinc electrolyte. A change in electrical conductivity of zinc sulfate solutions with the addition of multi-layered carbon nanotubes with various morphology and surface modifications was studied. With the use of impedance spectroscopy method, there were examined the electrophysical properties of zinc electrolyte with additions of carbon nanotubes in the presence of various components concentration and pH level of the environment, that was obtained via the original technique. It is shown that electron conduction increases with the rise of nanotubes concentration, but substantially levels with the rise of zinc sulfate concentration. Moreover, insertion of multi-layered carbon nanotubes in the solution changes a state of equivalent circuit and its elements. It is concluded that insert of multi-layered carbon nanotubes has unambiguous impact on the electrophysical properties of zinc sulfate solutions. Based on the obtained data, a scheme of electrolyte and nanotubes interaction is offered.

Simultaneous determination of trace Cu2+, Cd2+, Ni2+ and Co2+ in zinc electrolytes by oscillopolarographic second derivative waves

Abstract Simultaneous determination of impurity metal ions in high concentration zinc solution is very important for zinc hydrometallurgy, and the purpose is to establish a method for determining the trace Cu2+, Cd2+, Ni2+ and Co2+ in zinc electrolytes at the same time using the second derivative waves of single sweep oscillopolarography. Factors affecting the derivative waves of the ions were researched in a medium of dimethylglyoxime (DMG)-sodium citrate-sodium tetraborate. The results indicated that the interferences of a high concentration of Zn2+ and most other coexisting ions on the determination can be eliminated; when the Cu2+, Cd2+, Ni2+ and Co2+ are in the ranges of 1×10−7-3×10−4, 6×10−7-2×10−4, 2×10−8-1×10−5 and 1×10−8-3×10−5 mol/L, respectively, the relationships between the peak currents of the second derivative waves and the concentrations are linear; the detection limits to determine the Cu2+, Cd2+, Ni2+ and Co2+ are 8×10−8, 2×10−7, 6×10−9 and 4×10−9 mol/L, respectively. Without any sample pretreatment, the method was used to directly determine the trace Cu2+, Cd2+, Ni2+ and Co2+ in actual zinc electrolytes with satisfactory results. The method is simple, sensitive and rapid.

Anti-Corrosion and High Temperature Thermal Treatment of SiO2 Crystal Induced on Zinc Electrolyte on Mild Steel

The effects of SiO2 nanoparticles on the electroplating of Zn–Nb2O5 coatings of mild steel were considered in this research work. The hardness performance and corrosion resistance of the coated samples were analysed using Emco-test microhardness tester and Autolab PGSTAT 101 Metrohmpotentiostat/galvanostat. The results of the research showed that Zn–10Nb2O5–SiO2 coatings displayed preferable hardness property and corrosion resistance compared to Zn–10Nb2O5 coating. Also, the incremental addition of SiO2 nanoparticles improved the hardness behaviour and corrosion resistance of Zn–10Nb2O5 coatings.

Removal of chloride from simulated acidic wastewater in the zinc production

Abstract The removal of chloride from the zinc electrolyte produced during hydrometallurgical zinc production is challenging. The ion-exchange method is a promising way to remove chloride if the resin washing wastewater can be recycled. This paper focuses on chloride removal from resin washing wastewater to enable its reuse. Various processing factors including the oxygen gas velocity, temperature, and reaction time were investigated systematically. The results show that the optimal conditions for dechlorination are an oxygen gas velocity of 0.5 L·min− 1, a reaction temperature of 80 °C, and a reaction time of 30 min. A dechlorination efficiency of 80% with a residual chloride ion concentration less than 200 mg·L− 1 was achieved, which meets the requirements for the recycling of wastewater. The presence of manganese accelerates the dechlorination by forming a Mn2+–MnO2–MnO4−–Mn2 + redox cycle. In this process, about 15 kg of the MnO2 and all of the zinc can be recovered from 100 m3 wastewater, and the wastewater can be reused, which makes the ion-exchange method a promising technique for chloride removal.

Electrodeposition and electrodissolution of zinc in mixed methanesulfonate-based electrolytes

Zinc electrodeposition and electrodissolution in methanesulfonic acid (MSA) electrolytes mixed with chloride or sulfate are investigated in a 3-electrode cell for eventual use in divided and undivided zinc-cerium redox flow batteries (RFB). Cyclic voltammetry and polarization experiments show that the addition of chloride to methanesulfonate-based electrolytes shifts the nucleation potential in the positive direction, lowers the nucleation overpotential and enhances the kinetics of Zn deposition and subsequent dissolution relative to that achieved when sulfate is added or MSA is the only anion present. In addition, the diffusion coefficient of Zn(II) and the resulting limiting current density for Zn deposition have been found to be moderately higher in mixed methanesulfonate/chloride media than when chloride is absent. The effects of temperature, MSA concentration, Zn(II) concentration and current density on the Zn/Zn(II) system have also been investigated under potentiostatic and galvanostatic conditions. Although an increase in temperature and/or MSA concentration tends to lower the charge efficiency for Zn deposition in both mixed and MSA-only electrolytes due to the higher rate of hydrogen evolution, the amount of zinc deposited, charge and voltage efficiency always remain significantly higher in the mixed methanesulfonate/chloride media than the pure MSA media. Thus, the use of a mixed methanesulfonate/chloride media should enable both divided and undivided zinc-cerium RFBs to operate over a wider range of temperatures and MSA concentrations compared to the case with pure MSA electrolyte. The addition of sulfate to MSA-based electrolytes, however, does not improve the performance of the Zn/Zn(II) system relative to that possible in the MSA-only electrolytes.

Autoclave Precipitation Of Iron From Zinc Sulfate Solutions

<p>Zinc concentrates processing technology that includes high-temperature roasting – leaching of cinder – purification of leached liquor – electrowinning is the most widely used technology. Purified solution, which is fed to the electrowinning stage, has a high sensitivity to such an impurity as iron. The presence of iron in the zinc electrolyte has a negative influence both on the current efficiency and the quality of the cathode zinc. </p><p>The application of autoclave equipment for iron removal from zinc sulfate solutions, obtained after the leaching stage of zinc cinder, is described in this article. All experiments were carried out with a model solution of following composition, g/L: 10-33 H<sub>2</sub>SO<sub>4</sub>, 1.5 Cu, 5 Mn, 110 Zn, 2.5 Fe. Neutralization and purification of the solution was implemented during low-temperature pressure leaching of the zinc cinder. </p><p>The optimum conditions for iron precipitation from zinc solution are following: molar flow rate Zn(cinder) / H<sub>2</sub>SO<sub>4</sub> = 1.3, t = 80 °C, τ = 1 hour, P<sub>O2</sub> = 0.2 MPa. It was found, that the concentration of iron can be reduced up to 1-2 mg/L, whereas 83.5% of Zn and 52.1% of Cu being recovered into the solution from zinc cinder.</p>

Formation of ZnO nanowires during anodic oxidation of zinc in bicarbonate electrolytes

Dense arrays of ZnO nanowires were obtained by one-step anodic oxidation of metallic Zn in bicarbonate electrolytes followed by 2h of annealing in air at 200°C. A detailed inspection of the anode morphology at the initial stages of anodizations was performed. It was confirmed that nanowire bundles are initially formed both inside and outside the pits created during the anodic dissolution of the metallic substrate. In consequence, root-like structures are formed inside the cavities. However, no roots are observed for nanowire bundles formed outside the pits, directly on the surface of Zn. The effect of anodizing conditions on the growth of nanowires was studied. It was found that applying higher anodizing potentials and more concentrated electrolytes result in not only the significantly faster nanowires growth, but also the formation of denser NW films. In addition, the electrolyte agitation can also increase the rate of nanowires formation. Finally, we proved for the first time that the previous usage of electrolyte and the orientation of electrodes, can significantly affect the morphology of as-formed anodic films. Thermal treatment of as-anodized samples resulted in the successful conversion of the carbonate-containing precursor to crystalline wurtzite ZnO without the loss of nanowire morphology.

Electrochemical investigation of electrolyte composition and electrolysis parameters during zinc electrowinning

The effect of different Mn2+ and Pb2+ concentrations added to the zinc sulfate acid electrolyte during zinc electrowinning process was investigated. Operating parameters such as zinc ion concentration, acid concentration, current density, electrolyte agitation, and temperature were investigated in the presence of Mn2+ and Pb2+. Galvanostatic polarization, potentiodynamic polarization, cyclic voltammetry, and electrochemical impedance spectroscopy studies were performed to examine the cathodic behavior. Scanning electron microscopy (SEM) and X-ray diffraction (XRD) were employed to characterize the surface of the zinc deposit. The addition of lead ions to the zinc electrolyte led to an increase in the cathodic potential and current efficiencies of the zinc deposition. The addition of Mn2+ to the zinc electrolyte resulted in a decrease in the cathodic potential and current efficiency of zinc deposition. An increase in the current density from 45 to 60 mA cm−2 and in electrolyte agitation from 60 to 412 rpm resulted in an increase in the cathodic potential and decrease in current efficiencies. A temperature increase from 35 to 45 °C led to a decrease in the cathodic potential. After a short initial electrodeposition (2–4 h) using a Pb–0.7%Ag anode, the lead content in the zinc deposit was higher than that obtained with a Pt anode (0.15 mg L−1 Pb2+). A long deposition period of more than 72 h was also considered, and Pb content was almost the same in the zinc deposit for Pb2+ quantities (0.15 or 0.2 mg L−1).

Selective removal of halides from spent zinc sulfate electrolyte by diffusion dialysis

Zinc metal is mainly produced by a hydrometallurgical process, in which zinc electrolyte is recirculated, and impurities especially halides are accumulated then, which have dreadful impacts on the process and product. Until now numerous efforts have been made to remove halides from the electrolyte, but none of them are fully satisfying, and it is still a big issue for the industry. As a conventional membrane technology, diffusion dialysis (DD) is originally designed to recover free acid from acid-salt mixture by concentration gradient. In this work, we proposed a novel process to selectively remove these halide impurities from the spent zinc electrolyte by DD directly. Significant Cl- and F- permselectivities over HSO4- are observed in this process. The removal efficiencies are as high as 50–70% and 30–42% for chloride and fluoride, respectively, while the zinc loss is less than 1%. The flow intensity in the current work is much higher than that in conventional DD, which reduces the overall cost immensely. The mechanism of this selective mass transfer is also studied intensively to understand influence of flow intensity, charge number and hydrated radii of ions on the permselectivity. The results here are not confined to provide a superior method to remove halide impurities for the zinc industry, but also extend new applications and deepen understandings for the well-established DD process in selective ion separation. This capability is very likely to become a new growth point and future direction for the DD process besides acid/alkali recovery.