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Continuous electrowinning of zinc
Abstract
Synthetic and pure zinc solution produced from laboratory leached oxidised zinc ores, under controlled temperature and pH were subjected to continuous elctrowinning operations until the least possible zinc concentration was reached. Conventional DC electrolysis technique, PC and PCR procedures were examined. The effect of organic additives and some of the impurity foreign cations were also investigated. Current efficiencies of more than 95% were obtained from acid sulphate solutions electrolysed at 45 mA cm−2 and 25°C for DC and PC techniques. Electrowinning of zinc from relatively concentrated solutions (160 g dm−3) could be achieved, successively, with acceptable current efficiencies down to a concentration of 40 g dm−3. Copper additives were found to decrease the current efficiency and worsen the quality of the cathode deposits. Manganese and silica were found to have limited effects on both current efficiency and morphology of the deposit. Iron was found to have a deleterious effect on both the current efficiency and the deposit features. Organic additives, gelatine and thiourea, have good leveling effects on the cathode deposits. Gelatine was found to improve the current efficiency especially in the presence of a mixture of foreign cations.
... The present-day more than 80% of the world's primary zinc production is dominated by electrodeposition. However, the zinc electrodeposition process is particularly sensitive to many solution impurities such as cobalt and nickel [2][3][4][5][6][7], manganese [8], antimony [9][10][11][12][13][14], copper [2,[15][16][17], iron [16,17], cadmium [16], germanium [2,18,19] and tin [20]. Low levels of these impurities greatly interfere the zinc deposition process, leading to a decrease in zinc current efficiency (CE) and to changes in deposits' morphology [9] and cathodic polarization [21]. ...
... The present-day more than 80% of the world's primary zinc production is dominated by electrodeposition. However, the zinc electrodeposition process is particularly sensitive to many solution impurities such as cobalt and nickel [2][3][4][5][6][7], manganese [8], antimony [9][10][11][12][13][14], copper [2,[15][16][17], iron [16,17], cadmium [16], germanium [2,18,19] and tin [20]. Low levels of these impurities greatly interfere the zinc deposition process, leading to a decrease in zinc current efficiency (CE) and to changes in deposits' morphology [9] and cathodic polarization [21]. ...
... To counteract the harmful effects of these metallic impurities, the use of additives in electrolytic baths is inevitable. Appropriate amounts of additives are necessary for the formation of fine-grained, smooth and compact deposits [17,22,23]. However, the literature information on the effect of impurities on zinc electrodeposition is with respect to CE and deposit structural characteristics. ...
The effects of some common impurities such as copper, iron, nickel, cobalt, lead and their interaction with an ionic liquid additive 1-butyl-3-methylimidazolium hydrogen sulfate-[BMIM]HSO4 on zinc electrodeposition from acidic sulfate electrolyte were characterized in terms of the polarization behavior and the kinetics of zinc deposition using cyclic voltammetry and potentiodynamic polarization measurements. The results showed that these metallic impurities studied exerted some different changes in cyclic and cathodic polarization voltammograms. The addition of [BMIM]HSO4 was observed to counteract the detrimental effects of these impurities and induced a blocking effect on the zinc electrodeposition process through its cathodic adsorption on the electrode surface. The adsorption of this additive shifted the electroreduction potential of zinc ions towards more negative values, restricted impurities ions from being electroreduced, and inhibited hydrogen evolution. Moreover, the kinetics analysis of cathodic polarization suggested that the presence of these impurities alone and in combination with [BMIM]HSO4 had no effect on the Tafel slope and transfer coefficient but affected the exchange current density for the zinc deposition.
... Once the reagents that present the best characteristics for the solution purification stage have been selected, a final experimentation stage is carried out to define the type and concentration of oxidant necessary to achieve solutions with Fe concentrations lower than 50 ppm, according to the requirements of the Zn electrowinning process [10]. ...
... The technological challenge that guided the development of this work was to determine, for each reagent tested, the appropriate operating conditions to achieve iron removals greater than 90%, keeping the Zn losses at values around 20%. The Zn concentrate leaching solutions that were treated were characterized by high concentrations of Fe, between 5 g/L and 23 g/L, with Fe/Zn ratios between 0.1 and 0.5, and the oxidation stage is incorporated to ensure a residual iron concentration of 50 ppm [10]. ...
Autoclave leaching of zinc concentrate (Sphalerite) is an environmentally friendly process compared to roasting, which discharges pollutants into the atmosphere. Due to the amount of iron in the final product, a study is proposed to evaluate different reagents for eliminating iron from the autoclave outcome, minimizing Zn losses. The colloid formation, zinc losses, iron removal, phase separation stage characteristics (sedimentation and filtering), and reagent costs were used to evaluate six-iron precipitating reagents: CaO, Na2CO3, CaCO3, NaOH, MgO, and Ca(OH)2. CaO shows 99.5% iron removal and 87% zinc recovery. Although CaO was one of the reagents with significant zinc recovery, it presented operational difficulties in the filtration stage due to the high viscosity of the mixtures. Finally, Ca(OH)2 is the reagent recommended due to its ease of use, zinc yield recovery, electrowinning efficiency, and iron precipitate filtration rate. Zinc recovery was above 80%, while the iron concentration in the solution was below 50 ppm.
... Zinc electrodeposition is well established in the industry and has been used extensively in electroplating, corrosion protection and automotive vehicles [11,12,[15][16][17]. At present, conventional baths for zinc electrodeposition are still mainly based on zincate (alkaline) [18], chloride (acid) [19][20][21] and sulphate [22][23][24][25][26][27][28][29][30] in the electroplating industry. ...
... These reactions are facilitated with specific cell architectures under different circumstances. Unlike other proposed systems, most zinc-based flow batteries do not require catalysts for typical operation [26,30]. In all systems, the negative elec trode reaction relies on zinc electrodeposition, which takes place in flowing electrolytes as in other hybrid flow batteries. ...
Zinc-based hybrid flow batteries are one of the most promising systems for medium- to large-scale energy storage applications, with particular advantages in terms of cost, cell voltage and energy density. Several of these systems are amongst the few flow battery chemistries that have been scaled up and commercialized. The existing zinc-based systems rely on zinc electrodeposition in flowing electrolytes as the negative electrode reaction, which is coupled with organic or inorganic positive active species in either solid, liquid or gaseous phases. These reactions are facilitated with specific cell architectures under certain circumstances. To improve the performance and cycle life of these batteries, this review provides fundamental information on zinc electrodeposition and summarizes recent developments in the relevant flow battery chemistries, along with recent applications. The future challenges and opportunities for this technology are discussed.
... F test of variance analysis (Minitab software, version 15) was used to verify the equality of media. Applying Faraday law, the theoretical mass of zinc was calculated using the equation: (10) ...
... Energy consumption (kWh/ton) was calculated using the expression: 5 Vm.8.4. 10 10.CE (2) where Vm is the average potential (V), and CE the current efficiency (%). Cyclic voltammetry tests were performed using a potentiostat/galvanostat AUTOLAB PGSTAT 30. ...
Electrolytic zinc used in galvanizing processes is obtained using zinc electrowinning from sulfate solutions. The
presence of impurities in the electrolyte is a major problem for the zinc electrowinning industry. The impurities on zinc
electrolysis can reduce the current efficiency and increase the energy consumption. In this work, the effect of iron on the
zinc electrodeposition using galvanostatic deposition and cyclic voltammetry is studied. Contents of 5, 10, and 15 mg.L-1 of
iron were added in the electrolyte of zinc sulfate and in an industrial acid electrolyte. Using the industrial electrolyte, iron
addition is detrimental to the zinc electrowinning, increasing the energy consumption and decreasing the current efficiency.
Key words: Electrolysis; Energy consumption; Electrolytic zinc.
... The electrowinning of zinc onto a cathode material is a critical stage of industrial zinc production and it is desirable for this process to occur at high current densities while rendering level and uniform zinc deposits [1] that can be easily stripped from the cathode substrate [2]. In practice, zinc can be electrodeposited from different electrolytes (industrial and non-industrial) and onto a variety of cathodes [3][4][5][6][7][8] and the characteristics of deposition can be influenced by factors including electrolyte concentration and composition [9][10][11][12][13][14][15][16][17][18][19][20][21], electrolyte impurities [22][23][24][25], current density and temperature [26,27], as well as pH [28]. These factors may affect the morphology and roughness of a zinc deposit and are important considerations for the operating practices of a zinc production plant. ...
... There are numerous studies that have characterized a wide range of zinc deposits using high-resolution surface probes. For example, zinc deposits produced on various substrates and from different electrolytes have been widely characterized with SEM [2,7,8,10,15,16,18,19,21,22,24,26,[30][31][32][33][34] to gain insight into the morphological structure of surfaces under different deposition parameters. Zinc deposits have also been studied with 3-dimensional techniques such as AFM [4,13,[33][34][35] which not only offer a topographical view of the surface but can also be used to quantify roughness properties such as the rms variation of surface heights. ...
The morphology and roughness of zinc electrodeposits produced on an aluminum cathode from an industrial acid sulfate electrolyte have been characterized with scanning electron microscopy (SEM), atomic force microscopy (AFM), and scaling analysis. SEM and AFM images provided a topographical view of the deposit, while scaling analysis was used to determine the mechanism of surface growth and to quantify surface characteristics including the root-mean-squared (rms) roughness and periodicity. For an electrolyte with a fixed composition of additives, both the rms roughness and the width of the surface features increased with deposition time and the mechanism of surface growth was dominated by surface diffusion. However, when the deposition time was fixed but the concentration of glue in the electrolyte was increased between 3 and 60 mg L−1, a marked change in the deposition mechanism was observed. Here, small elevations in glue had minimal influence on the rms roughness but reduced the width of surface features thereby producing rougher deposits. At glue concentrations above 30 mg L−1, the scaling analysis plot changed considerably and corresponded to samples with two distinct deposit morphologies on a single surface, an observation that was not apparent from the SEM images alone. The features include large zinc islands with numerous small zinc features on their surfaces, which indicate competing mechanisms of nucleation and surface diffusion, respectively. The results show that scaling analysis offers complementary information to SEM characterization and can render additional information on the mechanism of zinc deposition under industrial conditions.
Graphical Abstract
... F test of variance analysis (Minitab software, version 15) was used to verify the equality of media. Applying Faraday law, the theoretical mass of zinc was calculated using the equation: (10) ...
... Energy consumption (kWh/ton) was calculated using the expression: 5 Vm.8.4. 10 10.CE (2) where Vm is the average potential (V), and CE the current efficiency (%). Cyclic voltammetry tests were performed using a potentiostat/galvanostat AUTOLAB PGSTAT 30. ...
Electrolytic zinc used in galvanizing processes is obtained using zinc electrowinning from sulfate solutions. The presence of impurities in the electrolyte is a major problem for the zinc electrowinning industry. The impurities on zinc electrolysis can reduce the current efficiency and increase the energy consumption. In this work, the effect of iron on the zinc electrodeposition was studied using galvanostatic deposition and cyclic voltammetry. Contents of 5, 10, and 15 mg.L-1 of iron were added in the electrolyte of zinc sulfate and in an industrial acid electrolyte. Using the industrial electrolyte, iron addition was detrimental to the zinc electrowinning, increasing the energy consumption and decreasing the current efficiency.
... In the field of electrowinning, the equations that describe the electrolytic cells have often been outlined 1-10 , but have seldom been applied to specific industrial processes. Some experiments were carried out to validate the electrowinning cell for equation sets [11][12][13][14][15] . ...
... ? Equation [12] relates the overpotential for each species to the rate of reaction expressed in terms of current density. It assumes that the rate determining step is the charge transfer at the electrode surface and not the mass transfer of the species to the surface . ...
... The cyclic voltammograms obtained for the zinc sulfate solutions showed a cathodic peak due to zinc deposition and hydrogen reduction (Saba and Elsherif, 2000) or the formation of hydrogenated phases (Munford, 1998). The onset of depostion occurs at -1040 mV vs.(Ag/AgCl) occurs. ...
... This energy consumpton is evident in the first scan. The cyclic voltammograms exhibited a hysteresis loop of nucleation (Saba and Elsherif, 2000;Munford, 1998). ...
Zinc electrowinning is performed with the application of a current through insoluble electrodes (Pb-Ag), causing the electrolysis of zinc sulfate, with or without impurities, and zinc deposition on the cathode of aluminum. The impurities can reduce the current efficiency and increase the energy consumption in zinc electrolysis. In this work, the effect of nickel and magnesium on zinc electrodeposition was studied using the electrochemical techniques of galvanostatic deposition and cyclic voltammetry. Additions of nickel, magnesium or both cations in zinc sulfate electrolyte resulted in a marginal increase in current efficiency. Addition of nickel or magnesium polarizes the cathode; however, the extent of polarization in the presence of magnesium is more than that of nickel. Addition of magnesium to the zinc electrolyte caused zinc reduction at a more negative potential. The addition of nickel to the zinc electrolyte increased the current density of the anodic peaks, thus increasing the dissolution of zinc and hydrogenated phases. The addition of nickel to the zinc and magnesium solutions decreased the nucleation loop, facilitating zinc deposition.
... Elsayed and his CMRDI coworker at the chemical and electro processing department [39][40][41][42][43][44][45][46][47][48][49] performed electrochemical studies on the electrowinning (EW) and removal of harmful metals from IWW, electroextraction, from leather processing, toxic Cr 6+ from electroplating wastewater, zinc liquors, and copper refiners for the treatment of industrial wastewater. ...
... In an another research zinc powder was also produced from Zn-Pb ores by alkaline treatment [12]. Continuous electrowinning of zinc was done Saba and Elsherief [13] and showed the applicability of sodium zincate in zinc powder formation. From zinc dross zinc was recovered by electrochemical method by in a recent study [14]. ...
Direct electro winning of zinc containing waste under anodic material may be useful in electrowinning of zinc powder. The present invention deals with the electrolytic zinc powder preparation from zinc dross in sodium zincate solution. The zinc dross was first expose to SEM-XRD for micrographic study and then subjected for wet chemical analysis. It was observed that most of the zinc is in metallic state with few amount of zinc is associated with iron. Different parameters such as current density, current efficiency, voltage and concentration of electrolyte have been studied to establish the process. It was observed that at 5 amp/dm 2 current density the formation of zinc powder is possible with 1.23 kWh per kg of energy consumption. The corresponding impressed voltage was found 1.2 V and with a current efficiency of 90 %.
... For bioleaching, it was assumed that 90% of the metals are brought into solution by the microorganisms (Brierley, 2008). For the extraction process and for electrowinning in particular, an efficiency of between 95 and 97% was assumed over a longer period of time (Beukes and Badenhorst, 2009;Saba and Elsherief, 2000;Sinclair, 2005). To facilitate simplified calculation, 100% is assumed for the latter part. ...
Bioleaching has been a well-established technique for the extraction of various metals since the 1990s. In particular, leaching in continuously stirred tank reactors (CSTR) facilitates the rapid and environmentally friendly extraction of different metals. This work investigates the economic feasibility of this technology when carried out using a suitable process and sulphide concentrate from a mining operation in the Erzgebirge region of Germany. The process is based on assumptions and tests are pending. The focus is on recovering zinc, copper and, in particular, indium from zinc sulphide. Based on the defined process characteristics of the bioleaching step as well as down- and upstream processes, investment costs and operating costs of the necessary plant structure were determined. After determining the potential profits based on given metal concentrations and current market prices of zinc, copper and indium, a net present value (NPV) and the corresponding internal rate of return (IRR) were calculated to ensure comparability with other investments. Both values are positive, showing that an investment in the proposed bioleaching plant pays off even with low process volumes.
... Since optimizing zinc-bromine batteries cells are important to correct these problems, zinc ions deposition were impinged onto the electrode surface that cause deterioration and mechanical abrasion for these cells. As a result of this, it is necessary to improve the performance and the uptake of ZnBr 2 cells systems for utility-scales electrical storage system [34][35][36][37] by introducing fluidized bed zinc electrodes to these cells anode-sides as the only electroplating devices that could prevent dendrites formation. ...
The penetration of renewable sources (solar and wind power) into the power system network has been increasing in the recent years. As a result of this, there have been serious concerns over reliable and satisfactory operation of the power systems. One of the solutions being proposed to improve the reliability and performance of these systems is to integrate energy storage devices into the power system network. Zinc-bromine batteries systems among other energy storage technologies has appeared as one of the best options. This paper presents the performance of three different electrodes feeder materials (carbon, nickel and a titanium) coupled and investigated within a fabricated ZnBr2 cell system via numerical modelling, DDPM+DEM model in ANSYS Fluent to simulate an incorporated anode zinc-electrode and COMSOL Multiphysics for the electrochemical behavior of the cell. After introducing briefly other alternatives to store energy, ZnBr2 cell systems, and its mode of operation were then discussed, before focusing on the numerical modelling and simulation and the laboratory experiments. Several extensive electrochemical experiments were implemented on the cell to achieve fast deposition of zinc onto the electrode surface during charge and fast dissolution during discharge for high performance. The mechanical action of the fluidised design of electrode is intended to improve deposit morphology, obviate the risk of dendrite growth and provide high transport rates of reactant to and from the active electrode surface. In conclusion, this paper has analyzed electrochemical techniques like chronopotentiometry, cyclic voltammetry (CV), and electrochemical impedance spectroscopy that were used to understand the behavior of the zinc bromide cells at a particular flow rate of 166.7cm³ min⁻¹ required to give good fluidization of the anode.
... We could get the reaction rate of zinc production (r ZN 2+ ) and hydrogen (r H + ) by the following equation [34] : ...
This paper proposes a model-free Deep Deterministic Policy Gradient (DDPG) learning controller for zinc electrowinning processes (ZEP) to save energy consumption during the current switching periods. To overcome the problems such as inaccurate modeling and various time delays, the proposed DDPG controller utilizes various control periods and parameters for different working conditions. Strategies such as action boundary setting, reward function definition, state normalization are applied to ensure its learning performance. Simulations and experiments show that the DDPG learning controller can significantly decrease energy consumption during the ZEP current switching periods. The optimal control policy will be learnt for different working conditions with only one group hyperparameters. Furthermore, the smoother control actions of the DDPG controller will improve the stability and reduce more energy consumption by comparing with traditional proportional-integral (PI) controller, model predictive control (MPC) and artificial experiences. The artificial intelligence-based optimal control framework brings both energy saving and intelligence to zinc manufacturing plants.
... In an another research zinc powder was also produced from Zn-Pb ores by alkaline treatment [12]. Continuous electrowinning of zinc was done Saba and Elsherief [13] and showed the applicability of sodium zincate in zinc powder formation. From zinc dross zinc was recovered by electrochemical method by in a recent study [14]. ...
Residue (zinc dross) generated during galvanization of steel contains about >80 wt% zinc metal. In present paper, zinc powder is produced from zinc dross in an alkaline medium by electrolysis using zinc dross as a consumable anode. In an electrolytic cell various parameters such as current density, current efficiency, voltage and concentration of electrolyte etc. have been optimized. The electrolytic cell was operated at room 2 temperature using 16 g/L Zn, 200 g/L NaOH at current density of 5 A/dm. The current efficiency was found to be 90% and the purity of zinc powder is 99.5%. This process offers single step recovery of zinc in the form of powder from galvanizing waste.
... In zinc electrowinning, Fe is a traditionally considered as unfavorable element since it can decrease energy efficiency due to the reduction of Fe 3+ to Fe 2+ at the cathode and is typically removed prior to zinc electrodeposition. [50][51][52] Consequently -in addition to the recovery of silver from battery leaching solution by EDRR -this research also investigates whether the presence of Fe also has a similar influence on the EDRR process as is observed with EW process. ...
In this study, the electrodeposition-redox replacement (EDRR) method was studied for the recovery of minor concentrations of silver from dilute solutions. The parameter optimization was carried out with synthetic solutions similar to silver oxide button battery recycling effluents, consisting of sulfuric acid and concentrated base metal (10 g·L⁻¹ H2SO4, 60 g/L Zn²⁺) with a minor amount of silver (100 ppm) and a varying amount of Fe³⁺ ions. Results of these experiments were analyzed both electrochemically and by use of SEM-EDS. The role of dissolved Fe³⁺ ions was studied by varying the concentration from 0 to 1000 ppm and the results showed that although the presence of Fe ions decreased silver recovery efficiency, final product purity was found to increase slightly. The EDRR process was also found to be more effective for Ag recovery and has less energy consumption when Fe³⁺ concentrations are relatively low (≤ 100 ppm) when compared with conventional direct current electrowinning. In the final stage, silver was successfully recovered via EDRR, using the optimized conditions, from a real pregnant leaching solution (PLS) obtained from the leaching of silver oxide batteries.
... Based on the electrochemical kinetics [15], the reaction rates of the three equations are proportional to the current density and the current efficiency. Therefore, the following equations can be derived: ...
This paper is concerned with the optimal control problem for the zinc electrowinning process during the current switching period. A mathematical model is developed to reveal the dynamic characteristics of the whole plant of the zinc electrowinning process and an energy consumption model is established to set the expected set points of the concentrations of the zinc ion and the sulfuric acid under different current. Furthermore, an optimal control problem is constructed in the light of free initial time, free terminal time, and fixed system switching time during the zinc electrowinning process. A novel time-scaling transformation based control parametrization method is introduced to transform the optimal control problem into a multiple parameters optimization selection problem, which can be effectively solved by the optimization algorithm. The applications on the electrowinning process of a zinc hydrometallurgy plant demonstrate the validity of proposed method.
... The electrochemical formation of lamellar tin is unique and the growth mechanism is postulated in this research. Gelatin was found to improve the current efficiency and flatness of tin deposits [15,16]. Schmid [17] reported that gelatin molecules could adsorb on the substrate by forming a surface film that acts as a physical barrier or by interacting with the surface and participating in the electrochemical reactions. ...
Lamellar tin deposits were prepared by galvanostatical electroplating from the aqueous acidic-sulfate bath, with gelatin and benzalacetone dissolved in ethanol (ABA+EtOH) as additive, and their morphologies were investigated by scanning electron microscopy. Cathodic polarization curves revealed that the absorbability of ABA+EtOH on the cathode surface was higher than that of gelatin. X-ray diffraction analysis indicated preferred orientations of tin growth led to the formation of lamellar structure and distortion of tin lattice. The growth mechanism of lamellar tin was also discussed.
... The zinc powder was obtained with purity higher than 99.5%. Saba and Elsherief [9] made an extensive study on continuous electrowinning of zinc from laboratory leached oxidize zinc ore. They have also studied the effect of organic additives like gelatin, thiourea and foreign cations like copper and iron on the current efficiency and morphology of the zinc deposit. ...
The electrodeposition of zinc from sulphate bath was studied in ammonical medium. The electrolytic conditions for zinc deposition were optimized at room temperature. The effect of acetone on current efficiency, morphology, stability and particle size of deposited zinc powder was studied. The current efficiency as well as stability of the electrolytically deposited zinc powder was found to decrease with increase in acetone concentration. The distribution of particle size of zinc powder and SEM results were presented for those powders obtained from ammoniac-acetone medium and also with the organic additive, triethylbenzyl ammonium chloride (TEBAC). The optimized operating parameters for powder preparation are presented. The average particle size of the deposited powder was found to decrease with increase in of acetone concentration. The Avrami-Erofeyev kinetic parameters were determined. The kinetic order of the process increases with the increasing concentration of acetone.
... The presence of iron in solution greatly affects the zinc current efficiency as can be observed in Fig 8, where current efficiency of zinc deposition at -300 and -700 mA with and without iron is compared. This effect is also observed by other authors [16,17]. The decrease in current efficiency observed in the presence of iron for both current values, is associated with the reverse redox system of Fe +2 /Fe +3 taking place at the two electrodes consuming high amounts of energy [18], and to the enhancement of the HER process, which also competes with zinc electrodeposition. ...
The performance of an electrochemical reactor for zinc recovery from the spent pickling solutions coming from the hot dip galvanizing industry in galvanostatic operation is studied in this paper. These solutions mainly contain ZnCl 2 and FeCl 2 in aqueous HCl media. The effect of the applied current on the figures of merit (fractional conversion, current efficiency, space–time yield and specific energy consumption) of the electrochemical reactor is analyzed and compared with the values obtained in the potentiostatic operation. The applied current was selected in order to obtain similar electrode potential values to those applied in the potentiostatic operation and ranged between −150 and −700 mA. In the absence of iron in solution, as the current value was shifted towards more negative values, the space– time yield of zinc and its fractional conversion increased because of the increase in the zinc reduction rate, the electrode roughness and the hydrogen turbulence-promoting action. However, the increase in current values makes current efficiency to decrease due to the hydrogen evolution reaction (HER), which causes an increment in the specific energy consumption. The presence of iron in synthetic solutions led to a decrease in current efficiency associated with the reverse redox Fe 2+ /Fe 3+ system and to the enhancement of the HER, which also induced increments in the local pH and the subsequent zinc redissolution. These adverse effects related to the presence of iron are greater in galvanostatic mode than in potentiostatic one. On the contrary, the additives present in the real spent pickling baths improve the zinc electrodeposition rate compared with the behavior of synthetic mixtures of zinc and iron solutions but the zinc redissolution is enhanced.
... This additive is a double-edge sword in the traditional zinc electrowinning electrolyte with the casted or rolled Pb-Ag alloy as anode materials (Kruphowa et al., 1977;Verbaan and Mullinder, 1981;Zhang and Cheng, 2007). The Mn 2+ can be oxidized to form a compact and strongly adhesive MnO 2 anodic layer during the electrolysis, which effectively reduces the corrosion of anodes and minimizes the contamination of cathodic zinc by lead (MacKinnon and Brannen, 1991;Newnham, 1992;Saba and Elsherief, 2000;Schierle and Hein, 1993). The MnO 2 slimes also adsorb detrimental ionic impurities, such as Cu 2+ , Co 2+ , Ni 2+ , Sb 3+ (Ivanov, 2004;Ivanov and Stefanov, 2002), and decrease the effect of Cl − (Kelsall et al., 2000). ...
The influence of Mn2+ on oxygen evolution kinetics and corrosion behaviour of Pb/Pb-MnO2 composite anode in sulfuric acid electrolyte was investigated using SEM, XRD, and several electrochemical methods. The results indicate that a high concentration of Mn2+ (e.g. 3.0 g L− 1) in the electrolyte resulted in the formation of a MnO2 layer on the surface of the anode. This layer decreased the oxygen evolution activity of the anode, but at the same time made the underlying PbO2 layer more compact and flat, effectively improving the anodic corrosion resistance. When the Mn2+ concentration was low (e.g. 0.1 g L− 1), no MnO2 layer was formed but the structure of the PbO2 anodic layer was modified. As a result, the oxygen evolution activity and corrosion resistance were both significantly improved. In addition, Mn2+ in the electrolyte did not change the kinetic mechanism of oxygen evolution reaction. The reaction was exclusively controlled by the formation and adsorption of first intermediate, and the adsorption resistance played a dominant part in the whole reaction resistance.
... Calcination: Removing CO 2 from the carbonate feed materials, resulting in so-called calcine, this step is optional ; Leaching of the zinc containing feed using dilute sulphuric acid (Koleini and Moradi, 2002); Purification: removing impurities from the PLS that could affect the quality of the electrolysis process (Yang et al., 2006, Dib and Makhloufi, 2007, Amin et al., 2007. The purified solution is sent to the electrowinning unit to produce zinc metal (Saba and Elsherief, 2000). ...
Mixed sulphide–oxide lead and zinc ores are most often found in the transition, and occasionally in the oxidised, zones of lead–zinc ore-bodies. They are of great importance because there are numerous unexploited or abandoned reserves of these ores in the world.However they present difficulties for conventional mineral processing due to complex mineralogy. In this paper, the specific problems associated with these types of ores are described and methods for solving these problems, combining economic and technical considerations, are discussed.The results of experiments carried out at laboratory scale are presented, in which the dissolution of mixed ore in sulphuric acid without oxidising agents was investigated. The results show the feasibility of zinc recovery from mixed sulphide–oxide lead and zinc ores, which underlines the potential of this approach. We also propose a conceptual flow diagram for the hydrometallurgical processing of these ores.
... A number of studies have been investigated the ways to improve zinc electrowinning process including the effect of free sulphuric acid concentration and current density [8,9], utilizing alkaline electrolysis technique [10] and the effect of additive [1,5,11]. Review ...
Electrical conductivities and densities of acidic zinc, cadmium and manganese sulphate solutions were measured. Empirical
equations have been derived to represent the measured values with high accuracy. Electrical conductivity of solutions has
been shown to be expressed as a logarithmic function of temperature, a second order polynomial function of sulphuric acid
concentration and a linear function of metal ion concentration. It can be deduced that the density of solution can be described
as a linear function of metal ion concentration, temperature and sulphuric acid concentration. These equations could be used
to improve the electrowinning or electrorefining process conditions.
... Electrowinning is currently employed in the production of many pure metals, from a variety of complex ores, including zinc (Han and O'Keefe, 1992;Saba and Elsherief, 2000;Booster, van Sandwijk, and Reuter, 2001), nickel (Gupta and Mukherjee, 1990b;Moskayk and Alfantazi, 2002;Lorenzen et al., 2009), lead (Zhang, O'Keefe, and Yu, 2001), copper (Lemos, Sobrai, and Dutra, 2006), and gold (Barbosa, Sobrai, and Dutra, 2001). This process can also be applied in the extraction of metals from secondary sources, such as zinc from ashes, dross, and electric arc furnace (EAF) dust (Jha, Kumar, and Singh, 2001;Dvorak and Jandova, 2005;Herrero et al., 2010). ...
This review addresses the detrimental effects of fluoride on the various steps which constitute any hydrometallurgical operation. It focuses on the specific examples of apatite flotation, copper bioleaching, zinc electrowinning and the manufacture of phosphoric acid. The presence of fluoride modifies the surface characteristics of minerals altering their effective flotation. Toxicity of fluoride to bacteria directly affects the mechanisms of bioleaching. Fluoride can interfere with the adhesion of metals to cathodes and effect deposit morphology during electrodeposition. In phosphoric acid synthesis from phosphate ores, fluoride affects production efficiency by altering the crystal morphology of the gypsum by-product.
... In addition, lead oxide of low melting point could restrain the volatilization of As 2 O 3 . On the other hand, the contents of impurity such as Ge, Cl and F in secondary zinc oxide are relatively higher than those in zinc calcine, which are harmful to electrolysis processes (Herrero et al., 2010;Saba and Elsherief, 2000;Zhang et al., 2001). It is an uneconomical method to employ hydrometallurgical process alone for the treatment of secondary zinc oxide. ...
Today's society relies on energy storage on a day-to-day basis, e.g. match energy production and demand from renewable sources, power a variety of electronics, and enable emerging technologies. As a result, a vast range of energy storage technologies has emerged in the last decades. Among them, rechargeable Zn–Air batteries have held great promises for a long time. However, the severe challenges related to the reversible O2 reactions and poor cyclability at the positive and negative electrodes, respectively, have severely hindered the success of this technology. Herein, electrically-conducting and semi-flowable Zn semi-solid electrodes are proposed to revive the appealing concept of a mechanically–rechargeable alkaline Zn–Air battery, in which the spent negative electrodes are easily substituted at the end of the discharge process (refillable primary battery). In this proof-of-concept study energy densities of ca. 1500 Wh L⁻¹ (1350 Ah Lelectrode−1 and utilization rate of 85%) are achieved thanks to the compromised flowability of the proposed Zn semi-solid electrodes. In this way, semi-solid Zn electrodes become a type of green energy carrier having intrinsic advantages over gas and liquid fuels. Zn semi-flowable electrode can be generated elsewhere using renewable sources, easily stored, transported, and used to produce electricity.
In recent years, anion storage technology has been regarded as promising alternative for the typical metal ion batteries due to its high energy density in theory, including halogen anions (F⁻, Cl⁻, Br⁻, I⁻) and complex anions (PF6⁻, BF4⁻, FSI⁻, FTFSI⁻, TFSI⁻, FSA⁻, BETI⁻, HSO4⁻, ClO4⁻, AlCl4⁻, NO3⁻, [ZnCl4]²⁻). Research on the storage of anions can not only develop anion batteries, but also extend it to more novel battery concepts such as desalination batteries and dual-ion batteries (DIBs). However, the difference of theoretical and practical performance is a crucial problem for the development of anion storage. Thus, understanding the working mechanism of various batteries and the methods of performance improvement are necessary for the future development of anion battery systems. For this reason, this article reviews the research progress and challenges in electrode materials and electrolytes of various anion storage technologies in detail. Finally, possible development directions in this research area are also proposed.
Cyclic voltammetry (CV) for Pd electrodeposition on Au from PdCl2+HCl solution between +1.100 and –0.400 V vs Ag/AgCl (3M NaCl) was performed. The CVs exhibit nucleation loop (NL), which can be characterized by higher cathodic current density (j) in the reverse scan rather than that in the forward scan. The reasons for the appearance of NL are investigated by making use of the surface condition of electrode and overpotential (η). Since it is difficult to estimate η during CV, it was obtained by potentiostatic electrodepositions (ED) on the substrates with similar surface conditions as those within NL. These substrates were produced by a potential sweep in (i) forward (FS) and (ii) forward+reverse (RS) scans from open circuit potential up to a representative potential (+0.330 V) within NL. These FS and RS substrates possess partial and significant Pd coverage, respectively. ED at +0.330 V on these substrates shows similar j trends in the initial stages as in NL. η during ED is estimated from the equilibrium potentials and the potential drop due to solution resistance (Rs). Rs is obtained from electrochemical impedance spectroscopy at +0.330 V. The estimated η is higher on RS, supporting higher j during electrodeposition on RS and reverse scan of CV within NL. Electrochemical and morphological analyses suggest that Pd deposition on the FS is nucleation driven whereas that on the RS is growth driven with the surface condition playing an important role in the appearance of NL during CV.
Les poussières d'aciérie électriques sont générées lors du recyclage de l'acier en four à arc électrique. La présence de métaux tels que le zinc, le plomb, le cadmium ou le chrome fait de ces poussières des déchets toxiques devant subir un traitement d'inertage permettant leur acceptation en centre d'enfouissement technique de classe I. La production mondiale annuelle de poussières constitue un gisement de zinc de 910 000 t. l'objectif du procédé étudié est d'extraire des poussières les métaux valorisables, en laissant intacte la matrice ferreuse qui pourra être valorisée vers la sidérurgie. Les formes minéralogiques des éléments majoritaires sont : Fe3O4, ZnO, ZnFe2O4, PbOHCl. Le procédé étudié s'appuie sur un traitement hydrométallurgique, basé sur la lixiviation sélective du zinc et du plomb. Dans un premier temps, on réalise une lixiviation douce utilisant un réactif complexant l'ion nitrilotriacétate N(CH2-COO)3 [exposant]3-, utilisé sous sa forme protonnée HNTA [exposant]2-. Le traitement d'un échantillonnage représentatif de poussières permet l'extraction de la totalité du zinc présent sous forme ZnO à température ambiante. Le taux de fer extrait est inférieur à 3 %. La récupération du zinc et du plomb dans le lixiviat est réalisée par précipitation de sulfures métalliques valorisables en métallurgie, le réactif lixiviant pouvant être recycle en début du procédé. Le test AFNOR X31-210 appliqué aux résidus solides confirme leur acceptation C.E.T. de classe I. Cependant, ils contiennent encore une quantité importante de zinc sous forme ZnFe2O4. Le ferrite de zinc est alors traité par du chlorure ferrique hexahydraté FeCl3, 6H2O. La réaction qui consiste en un échange de particules O [exposant]-2 / Cl [exposant]- permet de récupérer le zinc sous forme de ZnCl2 et le fer sous forme Fe2O3. La séparation des produits est obtenue par simple lixiviation aqueuse. La totalité de ZnFe2O4 est extraite pour un traitement à 150°C. Le résidu solide ultime, concentré en fer, peut être dirige vers la sidérurgie
The effect of Ir(IV) ions on the electrowinning of zinc from acid sulfate electrolytes was studied using scanning electron microscopy and electrochemical measurements. The change in the surface morphology of the deposits, cathodic current efficiency, polarization behavior, and cathodic potential were investigated. The results showed that Ir(IV) ions in the electrolyte co-deposited with zinc on the cathode and significantly reduced the hydrogen overpotential from − 1.022 V to − 0.99 V vs. saturated calomel electrode (SCE). The cathodic current efficiency decreased from 85% to less than 3% when the Ir(IV) ion concentration was 2.0 mg dm− 3. The presence of Ir(IV) ions also affected the surface macro- and microstructure of the zinc deposits. In the presence of Ir(IV) ions, a large number of circular holes were found on the surface of the zinc deposits. This result confirmed that Ir(IV) ions have a significant negative influence on the electrowinning of zinc.
The electrochemical performance of the zinc half-cell is strongly linked to the quality and morphology of zinc electrodeposits generated during the charging phase. The structure of the zinc plating also dictates performance characteristics such as efficiencies, charge densities and peak current values during the subsequent discharge phase. The previous chapter described and analyzed the considerations arising from chemical reactions occurring at the zinc-side electrode. Following from that point, this chapter describes the underlying reasons why different zinc plating morphologies are obtained under different conditions and how certain behavior such as dendritic growth can be detrimental to Zn/Br performance. Promising methods for solving such issues are then identified from a wide range of literature including studies directly related to redox flow batteries as well as from the highly established electroplating industry. The primary means of controlling zinc crystal structure involves the use of organic additives to achieve a specific growth template and rate. Additionally, the merits and drawbacks of alternative strategies such as controlling deposition rates are investigated in this chapter.
Thiadiazolines and Thiosemicarbazones represent classes of well-known molecular structures with important biological activities. The set of twenty structures, synthesized in our lab, was characterized about lipophilicity by reverse phase thin layer chromatography (RPTLC) and tested for their antimicrobial activities. These molecular properties were modeled by using topological and quantum descriptors, in the frame of a hypermolecule, with the meaning of a "mean molecule" in the set. A general procedure for developing and validating the models using the above concept is given. Within this frame, a method of data reduction (i.e., selection of relevant descriptors) was exemplified.
The present study is focused on the electrochemical recovery of zinc anodic remnants from Zn-MnO 2 waste batteries and the development of a combined flow scheme that allows the recovery of zinc by electrodeposition with satisfactory energy consumption related to the amount of Zn deposited. Batch laboratory experiments were performed to evaluate the electrochemical dissolution/winning parameters (electrolyte composition, pH, current density) in acidic medium. The proposed flow scheme aims at the electrodissolution of anodic remnants from waste batteries. Using the electrochemical method were achieved a high cathodic current efficiencies, approximately 98 % for Zn electrodeposition and also an improvement of the solubilization degree in comparison with the chemical solubilization using as anode Zn remnants in 0.5 M H 2SO 4.
The basic method for the electrolyte zinc production is an electrowinning process based on sulfate solutions. The presence of the impurities in the electrolyte is a major problem for the zinc electrowinning industry. They decrease the current efficiency, increase the energy consumption and deteriorate the quality of cathode deposited zinc. In this work the influence of the concentration of germanium in the synthetic or industrial electrolyte from 0 to 3.17 mg/L and 0.04 to 3.21 mg/L respectively, without and in the present of antimony (4.95 mg/L) on zinc electrodepositing has been studied. For this purpose, two electrochemical techniques have been used: a cyclic voltammetry and a galvanostatic deposition. It has been established that the increase of germanium concentration in the zinc sulfate electrolyte above 0.05 mg/l leds to essential decreasing of hydrogen overpotential and intensive reverse anodic dissolution of zinc. The presence of germanium ions in the electrolyte, significantly decreases the current efficiency and the quality of the electrodeposited zinc. The harmful effect of germanium in the electrolyte is increased in the presence of antimony.
A high-performance thin-layer chromatographic method combined with a sample preparation procedure and digital images processing has been developed for simultaneous determination of parabens in pharmaceutical suspensions. For the quantitative evaluation of the chromatographic spots, three different software that combines 2D (ImageDecipher-TLC and Sorbfil TLC) and respectively 3D (JustTLC) image analysis were investigated. The statistical parameters of the linear relation between the applied concentrations and both the peaks area and volume respectively, revealed no statistical significant differences in terms of the regression determination coefficient (R 2). The lowest limits of detection and quantification values were obtained for ethylparaben and butylparaben using the ImageDecipher-TLC software. Also, by using ImageDecipher-TLC software with conversion of color images of chromatographic plates into grey scale, the precision of the developed method increased in all cases. The results obtained for commercial samples showed that the proposed method, using new UV-Vis TLC scanner device with ImageDecipher-TLC software, is suitable for rapid routine analysis of parabens in pharmaceutical suspensions.
Five supporting electrolytes were studied for their viability as alternatives in the zinc half-cell of a zinc/bromine (Zn/Br) flow battery. The secondary electrolytes studied included sodium salts of the following anions: Br-, SO42-, H2PO4-and NO3-, which were compared against the conventionally employed Cl-. Cyclic voltammetry and Tafel analysis showed improved electrochemical performance from electrolytes containing NaBr, Na2SO4 and NaH2PO4. Consequently, these chemicals are proposed as potential alternatives in future Zn/Br design work. Electrochemical impedance spectroscopy revealed that the lowering of charge-Transfer resistance and diffusion limitation was the contributing reason toward improved performance from those electrolytes. Scanning electron microscopy and X-ray diffraction of zinc electrodeposits obtained during charging showed the type of supporting electrolyte present alters zinc crystallinity. Generation of smaller crystals was related to observations of good half-cell performance during voltammetry. Mossy deposits were linkedwith higher nucleation overpotentials between zinc plating/de-plating. Thewell-performing Na2SO4 supporting electrolyte produced mossy deposits, suggesting that contrary to common assumption, such deposition behavior is possibly unrelated to poor zinc-side performance. While the proposed compounds are intended for Zn/Br flow battery applications, they are possibly adaptable to other types of flow batteries utilizing the Zn2+/Zn redox couple.
An investigation into the suitability of carbon materials, metallic lead and its alloys as substrates for the zinc electrode in acid Zn-PbO2 flow batteries was performed. No maximum current appears on the potentiostatic current transients recorded for the zinc deposition on the lead and its alloys. With increasing the overpotential, the progressive nucleation turns to be the 3D-instantaneous nucleation process employed for the resin-graphite composite. Hydrogen evolution on the graphite composite is effectively suppressed due to the doping of polymer resins. The rate of hydrogen evolution reaction on the lead is relatively weak, but on the lead alloys, the hydrogen evolution conversely becomes serious to a certain degree. Though the exchange current density of the zinc deposition and dissolution process on the graphite composite is relatively low, the zinc corrosion is weakened to a great extent. With the increase of deposition time, the zinc deposits tend to be more compact. Zinc galvanostatic charge-discharge cycling on the graphite composite reveals that the coulombic of over 90% can be found, exhibiting an excellent cycling stability.
Hot dip galvanizing processes offer a simple and effective method for corrosion protection of steel. In this process, during the pickling step, HCl reacts with iron and iron oxides. Spent pickling baths contain hydrochloric acid, ZnCl 2 and FeCl 2 as principal compounds. Due to the inadequate existing techniques to treat the spent pickling solutions, the decrease of natural reserves of non-ferrous metals and the requirement of environmental protection, in the present work, the cathodic electrodeposition of zinc present in the spent pickling baths coming from hot dip galvanizing industries is studied. As the electrode potential was shifted towards more negative values, the fractional conversion increased. Simultaneously, the specific energy consumption decreased initially due to the increase in the zinc conversion rate but decreased for the most cathodic potential value due to hydrogen evolution reaction. Even though iron deposition does not take place for any experimental condition under study.
Nucleation and growth orientation of zinc electrodeposition in Zn(II)–NH3–NH4Cl–H2O solutions were studied. XRD and SEM were used to characterize the structure and morphology of deposited-Zn films on cathodes. TEM and HRTEM were used to characterize the structure of zinc nuclei electrodeposited on a copper grid directly. Cyclic voltammetry was applied to investigate the nucleation process of zinc crystals. The growth orientation was assessed using Lotgering factor f according to the peaks of XRD patterns. The results showed that the addition of gelatin played a role in controlling the {110} orientation of the zinc crystal with maximum Lotgering factor f of 0.71 during zinc deposition. Change of overpotential, difference in stripping potential of different crystal orientation, controllable shape and size of zinc nuclei were observed with increase of the content of gelatin. The shape of the zinc nuclei was changed from fiber to particles when the content of gelatin was 75 mg L−1 in solution.
The effect of the ionic liquid additive 1-butyl-3-methylimidazolium hydrogen sulfate ([BMIM] HSO4) on the kinetics of oxygen evolution during zinc electrowinning from an acidic sulfate solution was investigated. We used potentiodynamic polarization, electrochemical impedance spectroscopy, scanning electron microscopy, and X-ray diffraction for this study. Potentiodynamic polarization curves and the corresponding kinetic parameter analysis show that [BMIM]HSO4 has a catalytic effect on oxygen evolution by stimulating the reaction rate constant. Impedance data reveal that [BMIM]HSO4 can markedly reduce the oxygen evolution charge transfer resistance. The addition of 5 mg·L-1 [BMIM]HSO4 obviously decreased the resistance value by at least 50% over the studied potential range from 1.85 to 2.10 V. In addition, the results of the impedance measurements also suggest an inhibition effect of [BMIM]HSO4 on the secondary reactions and this is due to the adsorption of the additive on the anode surface, which decreased the amount of active sites for anion adsorption. All electrochemical results were corroborated with a morphological and orientation analysis of the anodic surface after 120 h of anodic polarization. The addition of [BMIM]HSO4 inhibited the generation of the intermediate product β-PbO2 and it promoted the generation of larger, loose, and porous α-PbO2, which benefited the oxygen evolution reaction.
Background
The pulsed bed electrode (PBE) has been used successfully for copper electrodeposition from highly concentrated acidic electrolytes. Advantages of this electrode include high space-time yield (Y) and simple operation and maintenance. In this work, the effects of operational conditions were investigated in an attempt to achieve current efficiencies (CE) higher than 76.7%, which was the maximum value obtained in a previous study.ResultsThe results showed that use of a high current density and low acid concentration provided the best operational conditions for maximizing CE and Y, and minimizing the energy consumption (EC). Nonetheless, the highest current density was limited to 3000 A cm−2 and the lowest acid concentration was limited to 110 g L−1, due to limitations such as metal dissolution, dendrite growth, and short circuiting. The highest CE achieved was 77.7%, using 2838 A m−2. According to a statistical model, the maximum CE value that could be achieved is 82.4%, with application of 3000 A cm−2. This suggests that further improvement of CE would lead to values of EC lower than those found in electrowinning plants.Conclusions
Electrowinning using a pulsed-bed electrode is an excellent method for copper production, but additional improvements are required to increase CE.
Using existing models, a zinc electrowinning cell house was simulated including electrowinning cells, electrolyte storage, and cooling towers. Optimisations and applications of the simulation were investigated as applicable to a cell house. Conditions were identified for achieving optimal current efficiency, energy consumption, and zinc production rate for a single cell and the entire cell house. The minimal energy consumption of the cell house was found to be larger than single cells primarily due to the lack of available control of the acid concentration. Water loss through cooling towers and the movement of a well-mixed non-interacting impurity was also tracked.
The stability of ionic liquid additive 1-butyl-3-methylimidazolium hydrogen sulfate ([BMIM]HSO4) during zinc electrowinning from acidic sulfate solution was investigated by cyclic voltammetry, electrochemical impedance spectroscopy and scanning electron microscopy. Compared with the traditional industrial additives, gelatine and gum arabic, [BMIM]HSO4 has more excellent chemical and thermal stabilities. The inhibition effects of gelatine and gum arabic on the zinc electrocrystallization are observed to markedly weaken due to their part degradation after 12 h longtime successive electrolysis and high temperature (90 °C) treatments. In contrast, the activity of [BMIM]HSO4 is practically unaffected after 24 h longtime successive electrolysis and high temperature treatments. These results are corroborated with the corresponding morphological analysis of the cathodic deposits.
Electrodeposition and dissolution of zinc in sulfuric acid were studied as the negative electrode reactions in acidic zinc-based redox flow batteries. The zinc deposition and dissolution is a quasi-reversible reaction with a zinc ion diffusion coefficient of 4.6 × 10−6 cm2 s−1 obtained. The increase of acid concentration facilitates an improvement in the kinetics of zinc electrodeposition–dissolution process. But too high acid concentration would result in a significant decrease in charge efficiency. The performance of the zinc electrode in a three-electrode system with magnetic stirring was also studied as a function of Zn(II) ion concentration, sulfuric acid concentration, current density, and the addition of additives in 1 M H2SO4 medium. The optimum electrolyte composition is suggested at high zinc(II) concentration (1.25 M) and moderate sulfuric acid concentration (1.0–1.5 M) at a current density range of 20–30 mA cm−2. Whether in acid-free solution or in sulfuric acid solution with or without additives, no dendrite formation is observed after zinc electrodeposition for 1 h at 20 mA cm−2. The energy efficiency is improved from 77 % in the absence of additives in 1 M H2SO4 medium to over 80 % upon the addition of indium oxide or SLS–Sb(III) combined additive as hydrogen suppressants.
The performance of a one- and two-compartment electrochemical reactor under galvanostatic control for zinc recovery present in the spent pickling solutions is studied in this paper. These solutions, which mainly contain ZnCl2 and FeCl2 in aqueous HCl media, come from the hot dip galvanizing industry. The effect of the anion-exchange membrane (AEM) on the figures of merit of the electrochemical reactor is analyzed.In the absence of iron in solution, as the current value was shifted towards more negative values, the zinc fractional conversion increased because of the increase in the zinc reduction rate. However, the increase in current values made current efficiency decrease due to the hydrogen-reduction side reaction, which caused an increment in the specific energy consumption. The presence of iron in synthetic solutions led to a decrease in current efficiency associated with the reverse redox Fe2+/Fe3+ system and to the enhancement of the HER, which also induced increments in the local pH and the subsequent zinc redissolution. These adverse effects related to the presence of iron could be minimized by the interposition of an AEM. In this case, the zinc redissolution was eliminated which enabled zinc conversion values close to 100% together with higher current efficiencies as the consumption of current by the system Fe2+/Fe3+ was diminished.
Although a number of studies have been reported on the electrical conductivities of sulphate electrolytes for electrowinning
and electrorefining processes, very few have focused on the optimization of these different effective factors. In this study,
a design of experiment (DOE) technique, the Taguchi method, has been used to optimize four main effective factors (temperature
of electrolyte, sulphuric acid concentration, metal ion concentration, impurity concentration) on electrical conductivity
of sulphate solutions. The percentage contributions of these effective factors and their ranking have been revealed. Sulphuric
acid concentration is the main effective factor on electrical conductivity of electrolyte while the temperature of electrolyte
is in the second important factor.
Pure zinc and composite coatings of zinc and nano-sized yttria stabilized zirconia (YSZ) particles were prepared by cathodic electrodeposition from zinc sulphate-based electrolytes containing gelatin. The effects of gelatin on the morphology, crystallographic orientation of the zinc coatings and deposition mechanism of the composite Zn–YSZ coatings were studied. The coatings obtained were studied by scanning electron microscopy (SEM) with energy dispersion spectroscopy (EDS), X-ray diffraction and potentiodynamic polarization measurements. It was shown that the addition of gelatin to the electrolyte significantly changed the microstructure and crystallographic orientation of the zinc deposits and improved the coating microhardness. In the case of the composite coating co-deposition process, the YSZ particles were found to preferentially rest on the edges or macrosteps of the deposited zinc crystals. The incorporation of YSZ particles into the composite coating was enhanced by reducing the solution pH and through the addition of gelatin. The mechanical and electrochemical properties of conventional zinc coatings were observed to be significantly improved by the incorporation of YSZ particles.
An electrochemical reactor was developed to recover zinc from the spent pickling solutions coming from the hot dip galvanizing industry. These solutions mainly contain ZnCl2 and FeCl2 in aqueous HCl media. The effect of the applied potential on the figures of merit (fractional conversion, current efficiency, space–time yield and specific energy consumption) of the electrochemical reactor was analysed. Voltammetric experiments were performed previously in order to select the optimum conditions to be applied in the electrolysis experiments. From the I–V curves it was inferred that bulk zinc deposition started from potential values more cathodic than −0.99 V. The hydrogen evolution reaction (HER) appeared from −0.45 V and masked the zinc cathodic peak C1, related to bulk zinc deposition, at high HCl concentrations. The presence of HCl inhibited iron deposition in synthetic samples. The additives present in the real baths, which diminish the massive hydrogen generation, allowed the observation of peak C1.
Electrodeposition and dissolution of zinc in methanesulfonic acid were studied as the negative electrode reactions in a hybrid redox flow battery. Cyclic voltammetry at a rotating disk electrode was used to characterize the electrochemistry and the effect of process conditions on the deposition and dissolution rate of zinc in aqueous methanesulfonic acid. At a sufficiently high current density, the deposition process became a mass transport controlled reaction. The diffusion coefficient of Zn2+ ions was 7.5×10−6cm2s−1. The performance of the zinc negative electrode in a parallel plate flow cell was also studied as a function of Zn2+ ion concentration, methanesulfonic acid concentration, current density, electrolyte flow rate, operating temperature and the addition of electrolytic additives, including potassium sodium tartarate, tetrabutylammonium hydroxide, and indium oxide. The current-, voltage- and energy efficiencies of the zinc-half cell reaction and the morphologies of the zinc deposits are also discussed. The energy efficiency improved from 62% in the absence of additives to 73% upon the addition of 2×10−3moldm−3 of indium oxide as a hydrogen suppressant. In aqueous methanesulfonic acid with or without additives, there was no significant dendrite formation after zinc electrodeposition for 4h at 50mAcm−2.
High current density zinc eledrowinning was studied using high purity synthetic solutions using 50 dm-3 zinc and 150 dm-3 H2SO4. Cyclic voltammetry and galvanostatic methods were used for this investigation. The effects of high concentrations of copper, iron, manganese and SiO2 on the current efficiency and cathodic zinc quality were evaluated. Gelatine was added separately and in combination with these impurities. A correlation between cyclic voltammetric data obtained and the current efficiency values was observed. The various deposit morphologies obtained under different conditions were studied using the scanning electron microscope.
The zinc electrowinning (EW) process is very sensitive to the presence of impurities. There is only one EW plant in the world that we know of that operates at moderate current efficiency and deposition times without using any additives. All the others must use them continuously. Additives allow zinc EW to occur at high current efficiencies while suppressing excessive acid mist formation. The study of the electrochemical effects of additives in zinc EW is not straightforward. This article presents a review of the experimental techniques currently used at Cominco Research: Cyclic voltammetry, Hull cells, laboratory and mini-cell electrowinning techniques are all described and their relationship to the industrial operation is discussed.
The cathodic reaction during zinc electrodeposition is usually characterized by cyclic voltammetry on the assumption that homogeneous nucleation is taking place on the cathodic substrates. In this present study, this premise was examined for pure Al and its alloys, including AlFe, AlSi, AlFeSiMg and the commercial alloy AlFeSi, by systematic observations of the substrates in the scanning electron microscope, using various modes of detection such as secondary electrons, back scattered electrons, for electron channelling contrast, and X-ray energy dispersive spectrometry. The results clearly show that zinc nuclei form heterogeneously on precipitates rather than on the alumina-coated matrix. Under constant potential, alloys with precipitates had deposition rates a few orders of magnitude larger than in the case of high purity Al. Normalization of the electrochemical data with the volume fraction of precipitates indicates that the deposition rates and morphology of the deposits are affected by the chemistry of the precipitates. The effectiveness of the alumina barrier was demonstrated by the observation that the specific features of the microstructure, such as grain boundaries and plastically deformed substrate, as observed by electron channelling contrast, did not act as locations for zinc nucleation.
The effects of manganese, magnesium, sodium and potassium sulphates on the current efficiency, morphology and orientation of 24 h zinc deposits electrowon at 430 A/m2 and 35°C from synthetic acid sulphate electrolyte have been determined. Increasing concentrations of MnSO4 in the electrolyte decreased the current efficiency and increased the size of the zinc platelets; the preferred deposit orientation remained intermediate, but the [112] and [114] components became more prominent. The addition of MgSO4 to the electrolyte resulted in a slight increase in current efficiency and the deposit orientation changed from intermediate to basal. At 50 g/l MgSO4 the current efficiency decreased slightly and the deposit orientation changed from basal to [101]. Increasing concentrations of MnSO4 in the presence of 50 g/l MgSO4 decreased the current efficiency and changed the deposit orientation from [101] to [112] [114] [102] [103] [101]. The addition of Na2SO4 resulted in a small increase in current efficiency. Although the deposit orientation remained intermediate, the zinc grain size was reduced at high Na2SO4 concentrations. The current efficiency initially decreased with the addition of K2SO4 to the electrolyte, but subsequently increased and reached a maximum value at 5 g/l K2SO4. The current efficiency was always less at a given K2SO4 concentration than for an equivalent concentration of Na2SO4. The presence of K2SO4 resulted in a zinc deposit having a vertical orientation that reverted to intermediate when the electrolyte also contained MnSO4 and MgSO4.
The codeposition of copper into zinc has been studied at a rotating disk electrode. The incorporation of copper from a zinc sulfate solution and from a bright zinc chloride plating solution is diffusion controlled. In a high cyanide zinc plating solution, the codeposition of the copper is an activation controlled process and is affected by changes in the plating surface. In these cyanide solutions, the metal displacement reaction of copper onto zinc is not an effective method for removing copper contaminates.
The effects of Dowfroth alone and in combination with antimony and Saponin on zinc deposition current efficiency and polarization and on the morphology and orientation of 6h and 24h zinc deposits electrowon at 500 Am-2 and 38°C from Kidd Creek zinc electrolyte were determined. Dowfroth, at concentrations as low as 7 mg dm-3, was strongly polarizing, changed the preferred deposit orientation from basal to intermediate and decreased the current efficiency and zinc deposit quality. Dowfroth had a positive interaction with antimony such that certain combinations of these reagents maximized current efficiency and improved the deposit quality. Saponin combined with various concentrations of Dowfroth resulted in a
The individual effects of lead, copper, nickel, cobalt and antimony on zinc electrowinning were evaluated by measurements in high-purity synthetic solutions, free from additives. The coulombic efficiency (QE) of zinc electrodeposition was determined over 2h under mass transfer-controlled conditions at a temperature of 35C and a current density of 400 A m–2 in a solution of 0.8 M ZnSO4+1.07 M H2SO4. Antimony had a very detrimental effect on QE causing decrease of 5 and 50% at 4 and 14 g l–1, respectively. Antimony also exerted a strong grain-refining effect and changed the deposit orientation from random to (112) to (004) with increasing concentration. Lead had a small beneficial effect on QE at the electrode rotation rate employed (20 s–1). It also exerted a grain-refining effect and changed the deposit orientation from random to (102), (103), (104), to strong basal (004), (002) with increasing concentration. Copper, nickel and cobalt had minor effects on QE, with reductions at 5 mg l–1 of 0.8, 0.3 and 0.3%, respectively. The effects of copper on morphology and orientation were very concentration dependent, but with a general trend towards grain-refining and random orientation. Nickel promoted coarse-grained deposits and changed the orientation from random to (114), (102) to (204), (102) with increasing concentration. Cobalt had the least effect on the morphology of the deposit, although it gradually increased the basal plane orientation with increasing concentration.
In this paper, the main factors influencing the morphology of solid metal obtained at the cathode of an electrolytic cell are discussed. Although the presentation is rather fundamental, important practical conclusions are derived. Specific topics linked to electrogalvanizing are stressed.
A novel hydrometallurgical procedure is described for the recovery of zinc from zinc silicate ores which have high acid-soluble
zinc and silica contents. The process is conducted in a continuous concurrent manner at atmospheric pressure and temperatures
of 50 to 95°C. The ore is leached with spent electrolyte from an electrolytic zinc plant to a final pH of approximately 2
to dissolve zinc and the soluble silica. The pH of the leach solution is then raised to 4 to 5.5, using a neutralizing agent,
to precipitate and coagulate the colloidal silica. Finally the coagulated silica is filtered from the solution and washed.
The resulting filtrate is treated conventionally for electrolytic zinc production. This process solves in a simple way the
difficult problem of precipitating large concentrations of colloidal silica(e.g. 25 g SiO2 per liter) in a readily filterable and easily washed form. The process has been tested at up to the 5 tons per day scale
on ores containing willemite and on a laboratory scale with ore containing hemimorphite and smith-sonite.
A comparison is made of three types of circulating particulate electrodes: spouted (circulating) bed (SBE), vortex bed (VBE) and moving bed (MBE). In applications such as metal recovery, all electrodes perform similarly in terms of current efficiency. On the basis of scale-up, it appears that the spouted bed electrode is the preferred system.
The individual effects of 15 impurities and their interaction with glue on zinc electrowinning from industrial acid sulphate electrolyte were characterized in terms of deposit morphology and preferred deposit orientation and in terms of current efficiency and zinc deposition polarization behaviour. The current efficiency decreased in a cyclical manner with increasing atomic number of the impurity element in each period of the periodic table. This decrease in current efficiency can be correlated to a corresponding increase in the rate of hydrogen evolution on the impurity metal. The various impurities produced four distinct zinc deposit morphologies and orientations and also produced characteristic changes in the cyclic voltammograms for the zinc deposition.
The effect of copper on the electrowinning of zinc from industrial acid sulphate electrolyte was studied using X-ray diffraction, scanning electron microscopy and cyclic voltammetry techniques. Concentrations of copper as high as 50 mg 1–1 had no effect on the zinc deposition current efficiency for 1-h deposits. Copper co-deposited with zinc and reduced the deposit grain size. The copper content of the zinc deposits increased with increasing copper concentration in the electrolyte and with decreasing current density. The cyclic voltammogram for copper-containing electrolyte was characterized by an appreciable cathodic current in the reverse scan after zinc dissolution indicating the presence of previously deposited copper on the cathode.
A cyclic voltammetric technique has been developed for approximating the quantities of active chemical species present in
zinc sulfate electrolytes. The experimental apparatus consisted of a Pyrex “H” cell, an aluminum cathode encased in a Teflon
holder, a carbon anode and a mercurous sulfate reference electrode. Voltammograms were obtained using industrial, purified
neutral leach solution (Cominco Ltd., Trail, BC) acidified to give a final concentration of 0.77 M Zn++ and 1 M H2SO4. The polarization curves were then evaluated and used as reference standards to compare with results obtained when various
organic and inorganic additions were made. The deposit morphologies obtained for short-time cathodic cycles were also studied
with the aid of a Scanning Electron Microscope. Changes in concentrations of glue in the 5 to 10 ppm range and of antimony
in the 5 to 10 ppb range were detected using the techniques described.
The effect ofgermanium on the electrowinning of zinc from industrial acid sulphate electrolyte was studied using X-ray diffraction, scanning electron microscopy and cyclic voltammetry techniques. Germanium concentrations > 0.1 mgl–1 results in severe re-solution of the zinc deposit and hence decreased the zinc deposition current efficiency. Extreme fluctuations in the current efficiency occurred as a function of electrolysis time. Cyclic voltammograms obtained for Ge-containing electrolytes were characterized by a shoulder in the reverse scan prior to the cross-over potential. Vigorous hydrogen gassing occurred at the shoulder. These results are interpreted in terms of the formation of local Zn-Ge galvanic cells. Germanium concentrations to 0.2 mgl–1 had no effect on the morphology of the 1-h zinc deposits but the preferred orientation changed from [1 1 4] [1 1 2] for Ge-free electrolyte to [1 1 2] [1 1 0] for electrolytes containing Ge.
Previous processes, both pyrometallurgical and hydrometallurgical, for treating zinc silicate ores are reviewed. Some comparisons
are made with the new continuous leaching process recently developed by the Electrolytic Zinc Company of Australasia Limited.
These comparisons, based on tests with two different zinc silicate ores, demonstrate the simplicity and effectiveness of the
new process.
A series of experiments were conducted to measure the current efficiency of synthetic zinc electrolytes containing additions of nonyl-phenol oxyethylene surfactant. The values of cell voltage were also measured and the energy consumptions were calculated. The surfactant was added in order to prevent the acid mist problem. The experiments were carried out for non-sparged and sparged systems with various surfactant concentrations and with changes in several operating conditions such as current density and zinc/acid ratio. The zinc current efficiency values varied from 56.0 to 90.0 and energy consumptions were in the range of 2900–5200 kWh/t according to operating conditions, surfactant concentrations and system type.
The behaviour of 2-picoline with and without antimony during electrowinning of zinc from acidic sulfate solutions was studied and was compared with that of gum arabic which is commonly used in industry as a levelling agent. The effects of these additives on current efficiency, power consumption, deposit quality, polarization behaviour, crystallographic orientation and surface morphology were determined. The addition of 2-picoline reduced current efficiency, increased power consumption and lowered the surface quality of electrowon zinc. Addition of antimony increased current efficiency, reduced power consumption and produced improved surface morphology and crystal orientations, (101) (112) (102) (103) (114) over a wide range of their combinations.
Plating and surface finishing
- Yao Qi-Xia
Application of Polarisation Measurements in the Control of Metal Deposition
- T Biegler