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Influence of metallic impurities on zinc electrowinning from sulphate electrolyte
Abstract
The effects of Cd, Fe and Cu impurities on zinc electrowinning from sulphate electrolyte were investigated by means of polarization curves and cyclic voltammetry. The morphology and the structure of the deposits obtained by small-scale electrolysis were determined by SEM and X-ray diffraction analysis and their purity was determined with an energy dispersive X-ray analyzer. The results indicate that the metallic impurities influence the zinc electrodeposition process, exerting a deleterious effect, by influencing the purity and the morphology of the cathodic deposit. Cd and Cu are co-deposited with zinc on the aluminium cathode and facilitate zinc deposition, while Fe inhibits zinc deposition and does not induce significant changes in deposit morphology.
... The current efficiency can be expressed by the ratio of deposited zinc mass and theoretical zinc mass. 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. ...
... (4) The presence of impurities in the electrolyte is a major problem for the zinc electrowinning industry. (5) The synergistic interactions among impurities determine the quality of zinc deposit from the solution. (6) Literature about the effect of impurities on zinc electrowinning is still scarce and restrict to specific impurities such as antimony, (7) nickel, (8) cadmium, iron and copper. ...
... (6) Literature about the effect of impurities on zinc electrowinning is still scarce and restrict to specific impurities such as antimony, (7) nickel, (8) cadmium, iron and copper. (5) A promising development in this area is the application of cyclic voltammetry and of electrochemical impedance spectroscopy to the investigation of the electrodeposition process. (5,9) The aim of this work is to study the effect of iron in the zinc electrowinning process using electrochemical techniques such as galvanostatic deposition and cyclic voltammetry. ...
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 current efficiency can be expressed by the ratio of deposited zinc mass and theoretical zinc mass. 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. ...
... (4) The presence of impurities in the electrolyte is a major problem for the zinc electrowinning industry. (5) The synergistic interactions among impurities determine the quality of zinc deposit from the solution. (6) Literature about the effect of impurities on zinc electrowinning is still scarce and restrict to specific impurities such as antimony, (7) nickel, (8) cadmium, iron and copper. ...
... (6) Literature about the effect of impurities on zinc electrowinning is still scarce and restrict to specific impurities such as antimony, (7) nickel, (8) cadmium, iron and copper. (5) A promising development in this area is the application of cyclic voltammetry and of electrochemical impedance spectroscopy to the investigation of the electrodeposition process. (5,9) The aim of this work is to study the effect of iron in the zinc electrowinning process using electrochemical techniques such as galvanostatic deposition and cyclic voltammetry. ...
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.
... Questo paragrafo offre una panoramica delle caratteristiche e problematiche che si possono presentare quando si decide di effettuare un trattamento sulle polveri FEA 1,4,5,7,8,10,11,12,13,14,15,18,20,22,26,27,28,29,30,31,32,35 . I prelavaggi con acqua sono utili per la rimozione dei cloruri solubili di Na, K, Ca ma in pratica si tende ad evitarli per la grande o le impurezze più elettronegative dello zinco non interferiscono direttamente con il processo di elettrolisi ma, modificando la viscosità della soluzione, influenza lo spessore dello strato di diffusione; ...
... La cementazione 2,3,10,11,18,20,22,31,35 prodotto (y-Xb) T (y-Xb) assuma il minimo valore possibile. Questo vettore si ottiene ...
... ZINCEX); una versione ottimizzata di questo tipo di estrazione che in origine presenta alcuni inconvenienti, è rappresentata dal processo ANPA-Università "La Sapienza" di Roma (non richiede la rimozione del ferro prima dell'estrazione e non presenta i problemi dovuti alla presenza di alogenuri) ed altri recentemente rivisti 31 . E' possibile effettuare delle lisciviazioni selettive utilizzando CaCl 2 (processo Cashman), NaOH (processo Rezada), FeCl 3 in soluzione acida e presenza di ossigeno (Terra Gaia) .Tutti richiedono una purificazione finale.Se lo scopo del processo è quello di ottenere mediante elettrolisi zinco assai puro, è necessario tenere sotto stretto controllo le impurezze presenti nella soluzione destinata ad elettrolisi10. Le impurezze sono letali in quanto non soltanto influenzano l'efficienza energetica del processo, ma causa anche problemi relativi alla qualità e morfologia del metallo che si riduce al catodo. ...
... The values of the nickel and magnesium additions to the electrolyte studied in the present work were selected by a Brazilian zinc industry. Despite that fact that the presence of impurities in the electrolyte is a major problem for the zinc electrowinning industry, literature data are scarce and restricted to specific impurities such as antimony (Tripathy et al, 2003;Ivanov and Stefanov, 2002, a, b;Stefanov et al, 1997), cadmium, iron and copper (Muresan et al, 1996). Cadmium favours zinc deposition by diminishing the nucleation overpotential and is codeposited with zinc on an aluminum cathode (Muresan et al, 1996). ...
... Despite that fact that the presence of impurities in the electrolyte is a major problem for the zinc electrowinning industry, literature data are scarce and restricted to specific impurities such as antimony (Tripathy et al, 2003;Ivanov and Stefanov, 2002, a, b;Stefanov et al, 1997), cadmium, iron and copper (Muresan et al, 1996). Cadmium favours zinc deposition by diminishing the nucleation overpotential and is codeposited with zinc on an aluminum cathode (Muresan et al, 1996). The grain size of the deposit is larger than in the absence of cadmium. ...
... The grain size of the deposit is larger than in the absence of cadmium. Iron increases the nucleation overpotential, inhibiting zinc deposition, but has no significant influence on the morphology of the deposit when glue is present (Muresan et al, 1996). Copper has a harmful effect on zinc electrowinning. ...
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.
... Contrary, the presence of nickel and cobalt leads to perforation of the cathodic deposition and hinders the electrowinning process (Abrasheva and Karoleva, 1984). Any of the metallic impurity decreases the hydrogen overpotential, purity and morphology of the zinc being deposited at cathode (Mureşan et al., 1996). Further, relatively electropositive nature of metallic impurities favors their co-deposition on the cathode during electrolysis (Mureşan et al., 1996). ...
... Any of the metallic impurity decreases the hydrogen overpotential, purity and morphology of the zinc being deposited at cathode (Mureşan et al., 1996). Further, relatively electropositive nature of metallic impurities favors their co-deposition on the cathode during electrolysis (Mureşan et al., 1996). A quality deposition of zinc on the cathode with good productivity can be achieved at higher hydrogen overvoltage which is possible in the absence of impurities (Raghavan et al., 1999). ...
Cementation is a prominent purification technique used for removal of copper, cadmium, cobalt, and nickel from impure zinc sulphate solution obtained after leaching of zinc ore. Zinc dust is primarily used for this purpose still the extent of purification is limited. The present study represents the encouraging result in context to utilization of zinc dust for better purification by altering its dosage, size and morphology. The investigations showed that 300% excess zinc dust dosage than stoichiometric results in enhanced cement formation. The study also revealed that fine size and ball milling of zinc dust favors cementation. Zinc dust of −300 mesh (BSS) after 2 h ball milling highly purifies the impure solution within 2 h contact time. The yield of the impurities removal after the optimized cementation is 100, 99.99, 100 and 15% for Cu, Cd, Ni and Co respectively. The kinetics of cementation has been also studied and revealed that the reaction is in mixed controlled mechanism for copper and cadmium cementation. At the same time, for nickel, it is considered to be chemically controlled. The activation energy for the cementation of copper, cadmium and nickel were 38.19, 30.87 and 68.15 kJ /mol, respectively. The estimated activation energies were found within the range which corroborates with the mixed and reaction model and ensures industrial feasibility of the proposed process.
... 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
... The corrosion potential of Zn in a Cu-containing electrolyte is more positive than in an electrolyte without the impurity and a second anodic peak, corresponding to Cu dissolution can be observed in the positive potential region during the reverse scan. The cathodic deposit, obtained in the presence of Cu 2+ ions, is non-adherent with the substrate, and consists of porous microspheres [11]. ...
The influence of copper and ferrous ions on zinc recovery from sulphate electrolytes is investigated. It is found, using cyclic voltammetry that simultaneous deposition of Zn and Cu begins at a potential (vs. SSE) of-1.450 V. Simultaneous deposition of Zn, Fe, and Cu begins at a potential of-1.500 V. Deposition of Cu solely, takes place at more positive potentials. The presence of Cu 2+ and Fe 2+ ions results in Zn redissolution, decreasing the current efficiency of Zn electroextraction. Zn deposit, which contains 2.4 wt.% Cu and 0.25 wt.% Fe, is obtained upon 60 min deposition at-1.600 V in an electrolyte containing Zn 2+-50 g/L, H 2 SO 4-130g/L, Cu 2+-200 mg/L, and Fe 2+-200 mg/L .
... However, the iron ions in the solution have negative effects on the subsequent electrodeposition. Although iron does not induce substantially changes in deposit morphology, its inhibitory effect on the process cannot be ignored (Mureşan et al., 1996). Electrolytes with an iron concentration less than 20 mg L − 1 are an important precondition in zinc electrodeposition (Cui, 2011;Tsakiridis et al., 2010). ...
A clean goethite process for iron removal was proposed to overcome the challenges of large amount of hazardous iron waste and low reaction rate. First, the forms of substances in zinc leaching solution and iron precipitation residue were analyzed by thermodynamic calculation. The process parameters were then optimized by industrial test, and the strengthening mechanism was revealed by numerical simulation. Finally, the industrial application of the process was evaluated. Results indicated that the stable phase of goethite existed in the pH range of 2.8–4.2 at 80 °C. The concentration of iron was reduced from 11.94 g∙L⁻¹ to 2.08 g∙L⁻¹ at 6 h under optimal conditions, and the iron and zinc contents in the residue with needle structure were 49.95 wt.% and 6.02 wt.%, respectively. The shear-enhanced process accelerated the flow rate and improved the gas dispersion, leading to the rapid homogenization of solution and increased reaction rate. In addition, the oxygen utilization rate of the shear-enhanced goethite process was 39.33% higher than that of the traditional process. The shear-enhanced process achieved a 20% reduction in waste residue, and the production cost was 0.85 $∙kg⁻¹.
... A problem with this processing route is the formation of iron sulfate in the concentrate leaching stage. Together with other impurities, this compound generates problems already studied in the subsequent electrowinning process [6][7][8][9]. Even low levels of contaminants influence the sputtering of zinc, which leads to a decrease in current efficiency and changes in the morphology of the deposit. ...
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.
... About 80% of the industrial zinc produced globally is by electrowinning over the metal (Aluminum) cathodes [39][40][41]. Although the metal-based electrodes suffer the problem of pitting even at cathodic potentials due to the presence of impurities of fluoride as well as other anions or cations [42][43][44]. The presence of halides (F, Cl, Br, I) in the catholyte during electrowinning may cause a harmful effect on the lifetime, deposit quality, current efficiency, and electrode surface [45][46][47][48]. ...
The prospects of using a polymer composite electrode the Plastic Chip Electrode (PCE) in high current applications has been reported in this manuscript. PCE is fabricated by a simple solution casting method from a semi-fluidic slurry. This semi-fluidic slurry forms a very compact composite, due to gravitational pull, during drying and hence yielding highly compact and pitless morphology. The viscosity of the polymer has been manipulated in such a way that it balances the weight of the graphite filler. This compact and highly dense morphology of the composite helps to sustain high currents. The electrowinning of zinc from the acidic solutions has been taken as a model for demonstration. The PCE has been found stable at a current density as high as 500 mA cm⁻². The corrosion behavior of PCE has been evaluated. The current efficiency was found to be more than 90% in the presence of HER retardant additive, sodium lauryl sulfate (SLS). The deposited zinc metal has been characterized by various techniques.
... However, the vast of acids were also consumed by other metals including Fe, Ca, Mg, Mn, etc., resulted in the high consumption of acid and especially demand of iron-removing step before zinc electrodeposition [19,20]. Significantly, it was found that the nucleation/crystallization overpotential of zinc was increased when Fe ions were presented in the electrolyte, subsequently increasing the difficulty of Zn electrodeposition [21]. Thus, the alkali leaching possessed a potential advantage due to the iron can remain insoluble. ...
Electric arc furnace dust (EAFD) formed during steelmaking in electric arc furnace is rich in iron and zinc. Due to the negative effects of zinc, directly recycling as raw materials for ironmaking does not work so that it is still mostly accumulated. In this study, a novel process was proposed, wherein EAFD was roasted with FeSO4·7H2O followed by water leaching for the effective and selective extraction and separation of zinc and iron from EAFD. The optimal roasting conditions were determined as mass ratio of FeSO4·7H2O/EAFD of 1.5, roasting temperature of 675 °C, holding time of 3h. The transfer mechanism of elements in EAFD was analyzed. 98.79% of zinc and only 0.11% of iron were dissolved in the leaching solution, respectively, avoiding the iron-removing step before the subsequent zinc electrodeposition. Meanwhile, most of Ca, Mg and Mn ions transformed into corresponding sulfates during roasting experiments and then entered leaching solution after water leaching. Thus, the leaching residue with 91.36% mass ratio of Fe2O3 could be applied as raw material for ironmaking industry. In addition, the majority of heavy metals (Pb and Cr) were remained and immobilized in the leaching residue, meeting the requirement of leaching toxicity standard. Results from this work provide a new insight into selective recovery of valuable metals from EAFD while at the same time exploiting the solid waste FeSO4·7H2O.
... It is well known that in aqueous electrolyte, the zinc electrowinning process is very sensitive to the presence of metallic impurities such as copper and nickel [12]. Over the past decades, the effect of copper impurity on the zinc electrodeposition in acidic sulfate electrolyte has been studied [13]. ...
The effect of Cu(I) ions on the electrodeposition of zinc from ChCl-urea-ZnO deep eutectic solvent (DES) was investigated through electrochemical measurement and the deposit characterization. The cyclic voltammetry and cathodic polarization analyses demonstrated that Cu(I) ions obviously decreased the nucleation potential of Zn(II) and promoted the Zn(II) reduction reaction. The analysis of the chronoamperometric transients indicated that the nucleation and growth mode of Zn deposition changed from a three-dimensional progressive nucleation to three-dimensional instantaneous nucleation in the presence of Cu(I) ions. The addition of Cu(I) ions was observed to change the surface morphology, purity, and crystallographic orientation of the zinc deposits.
... This is followed by extensive solution purification processes to remove almost all of the soluble impurities, such as Cu, Co, Ni, Cd, Pb, Sb, As, Ge and Fe, etc. The complete removal of impurities, particularly those which are more electropositive than Zn and those which have low overpotential for H 2 evolution, is essential (Mureş an et al., 1996;Lu et al., 2013;Mackinnon and Fenn, 1984;Hu and Piron, 1992). The impurities in the leach liquor may decrease the current efficiency, deteriorate deposit quality and may increase the energy requirements during the electrowinning process (Alfantazi and Dreisinger, 2001). ...
The main objective of this study is to integrate two energy-intensive metallurgical processes, Cu extraction from CuFeS2 and Zn electrowinning, into a battery-like device that could incentivize renewable energy use at remote mining locations. In this device, Cu extraction and Zn electrowinning occur simultaneously during the charge cycle. During discharge, the device, referred to as a trifunctional battery (TFB), can supply back to an electrical circuit a portion of the stored energy. The re-dissolution of Zn during discharge and reversible reactions at a chalcopyrite slurry electrode are responsible for this energy release. The high initial specific energy (388 Wh–g⁻¹ at 0.5 C discharge rate) registered by this setup decreased to ≈50 Wh–g⁻¹ during the initial 15 galvanostatic charge ̸ discharge cycles and remained almost constant in the subsequent 85 cycles. The low coulombic (≈50%) and energy efficiencies (≈40%) demonstrated by the TFB occurred at maximum (23%) Cu extraction from CuFeS2. A feature of the TFB is that the normally unwanted irreversible reactions that occur in traditional batteries are in fact desirable in the TFB, i.e., they lead to valuable Cu extraction in addition to energy storage.
... The process is rather energy-intensive (3.0-3.3 kWh/kg) due to the high cell voltage [8,13,15,16] and requires a great deal of chemicals with high consumption rates (0.5-2.2 M H 2 SO 4 /kg) [12][13][14]. Moreover, the zinc EW process requires a rather high (50-70 g/L) zinc content in the electrolyte [11,[17][18][19][20] when minimizing the content of impurities [21][22][23][24]. The impurities in Zn electrolyte are often categorized into groups 1-3: category 1 includes the worst impurities, i.e., Ge, Sb, Te, and Se; category 2 consists of worse impurities including As, Ni, Sn, Co, Ag, and Fe; and category 3 includes bad impurities, i.e., Ga, Bi, Cd, Hg, In, and Pb [25]. ...
Electric arc furnace (EAF) dust is globally one of the biggest metal-containing waste fractions, with a composition that challenges the recycling of dust back to the steel process due to the high Zn and Pb content, which also prevents it from being landfilled. The current study presents a process flowsheet with zinc and lead removal from EAF dust via citric acid leaching, lead removal by precipitation, and further solvent extraction (SX) of zinc for recovery. The process produces fractions that can be directly routed back to a steel plant (leach residue), a zinc electrowinning process (pregnant leach solution, PLS), and a lead smelter (lead sulfate, PbSO4 precipitate). Moreover, zinc separation by solvent extraction from citric acid leach solution originating from EAF was performed successfully with minimal impurity content in the final electrolyte, using di(2-ethylhexyl)phosphoric acid (D2EHPA). The total lead removal from PLS was achieved with an addition of only 0.012 M sulfate ion (from sulfuric acid) at room temperature. The optimization of zinc separation via SX was performed at a temperature range of 25–55 °C varying the D2EHPA concentration (10–25 vol-%) with different O/A ratios. With an optimized EAF SX process (pH = 5, t = 15 min, T = 25 °C, CD2EHPA = 20 vol-%, O/A = 1:1) and stripping process (t = 15 min, T = 25 °C, CH2SO4 = 1 M, O/A = 3:1), the zinc content in the electrolyte could be enriched up to 50 g/L, and the amount of impurities in the solution decreased down to a level where they have no adverse effect on the zinc electrowinning process and final zinc recovery. Moreover, the iron-rich leach residue was also shown to be chemically suitable as a raw material for the EAF process. With the proposed roasting-leaching-precipitation-SX-EW unit operation, EAF dust can be converted into three different secondary raw material streams, suitable for integration into state-of-the-art processes.
... Zn is another commercially important metal that is mainly produced via acid leaching of roasted sphalerite (ZnS). The pregnant leach solution is rigorously purified to remove all the soluble metal impurities, particularly those that are electrochemically more noble than Zn and present large kinetic activity towards H2 evolution (Hu & Piron, 1992;Mackinnon, Brannen, & Fenn, 1987;Mureşan, Maurin, Oniciu, & Gaga, 1996). Metal impurities such as Cu, Co, Ni, Cd, Pb, Sb, As, Ge and Fe etc., if they exist in the leach liquor beyond the tolerance limits, can decrease the current efficiency during electrowinning and deteriorate the deposit quality (Alfantazi & Dreisinger, 2001). ...
Hydrometallurgical processes, i.e., Cu extraction from a mineral concentrate and Zn electrowinning, are coupled in a battery-like system. A naturally-sourced CuFeS2 concentrate mixed with activated carbon is used as a positive slurry electrode separated by a membrane from the negative compartment. The Zn is deposited on the negative Al current collector from the circulating solution containing 100 g L-1 Zn 2+ in 0.2 M H2SO4. In this battery-like system, both CuFeS2 oxidation and Zn deposition are possible during the charging cycle. The additional benefit of this setup is the energy storage if discharged by re-dissolving the Zn in the negative compartment. Cyclic charge/discharge testing revealed oxidation of the mineral concentrate supported by the Zn 2+ /Zn redox reaction. The coulombic and energy efficiencies increased monotonically to 95.6% and 43%, respectively, with approximately 7% Cu extraction during the first 10 charge/discharge cycles (completed in 2.4 hours). The discharge energy density also increased from 2.7 to 36.2 mWh L-1. In the following 90 cycles, the low energy (~14%) and coulombic (~33%) efficiencies that were obtained confirmed the progress of irreversible reactions e.g. Cu extraction from the mineral concentrate. Overall, approximately 16% Cu was extracted from the mineral concentrate over 100 charge/discharge cycles (or about 12.2 hours).
... 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.
... Over the past decades, many scholars have conducted a large number of studies with regard to the effect of numerous impurities on zinc electrodeposition. Low concentrations of nickel Liu et al. 2012), cobalt (Cachet et al. 1999;Krause and Sandenbergh 2015), copper (Mureşan et al. 1996), antimony (Ivanov 2004;Alkatsev et al. 2015), iron (Lins et al. 2010;Adcock 2017), cadmium (Moradkhani et al. 2012), and germanium Alkatsev et al. 2014) have been regarded not only as influential in the zinc electrodeposition efficiency of cathode but also make a difference in the characteristics of zinc product microcosmic morphology and cathodic polarization. ...
The influence of Mn²⁺ ions on the generation of heavy metal anode slime during zinc electrolysis industry was extensively investigated using several electrochemical methods, electron microscope technologies, and particle size analysis. Results showed that the Mn²⁺ could obviously promote oxygen evolution reaction (OER) and thereby weaken oxidation efficiency of Mn²⁺ (ηMnO2) and dissolution of Pb²⁺. The significant improvement in kinetic parameters for OER was found in electrolytes of 1 and 3 g/L Mn²⁺, but became unstable as the Mn²⁺ concentration increased to 10 g/L. This result was correlated with much different properties of oxide layers that its changes of microstructure are involved in, since it confirmed that the positive role of compact oxide layers in contributing to high corrosion resistance and activity for OER, but excessive Mn²⁺, resulted in its micromorphology of overthickness and instability. Such differences resulted from the effect of the Mn²⁺ concentration fluctuation on kinetic rates of the nucleation growth process. The formation and adsorption of intermediate MnO2–OHads identified as the controlled step for Mn²⁺ catalyzing OER was also recommended. The generation mechanism of anode slime was found to be changed in essence due to varying Mn²⁺ concentrations. In electrolyte of 1 g/L Mn²⁺, results revealed that the root cause of excessive small suspended anode slime (around 20 μm) was the change of the initial pathway of Mn²⁺ electro-oxidation, whereas, it showed great improvement in the settling performance as the Mn²⁺ concentration was increased to 10 g/L. Considering the potential of optimizing Mn²⁺ concentrations as a cleaner approach to control anode slime, deepening the understanding of the impact mechanism of Mn²⁺ can provide new insights into intervention in the generation of anode slime.
... Many of the known physical and physicochemical methods of zinc melts refining from metallic impurities (Fe, Pb, Cu, etc.) are low productive and difficult from the point of view of constructive-technological realiza-tion [8][9][10][11][12][13][14]. The method of liquation refining draws the greatest interest towards production of zinc melts of a low content of iron and other metallic impurities as it is easily adapted to the conditions of the acting industrial enterprises. ...
The methodology of selection of additive elements for purification of zinc melts from iron impurity by liquation refining is proposed. Calculations of the effectiveness assessing the possibility of application of the formula of the periodic process of extracting to a single stage of extraction are performed. The extracting ability of the additives chosen is established. The experimental results show that the highest efficiency of unalloyed zinc purification from iron impurity is achieved by using silicon as an extraction additive. Aluminum and manganese are recommended to be used as extracting additives in zinc alloys refining from iron.
... The results dealing with the time evolution of the zinc fractional conversion depicted in Fig. 14 show higher zinc deposition rates when EW is carried out with the previously treated stripping solution. This fact may be related to the change in the main composition of the SPB after their treatment by the MBSX technique, as the chloride reduction or the elimination of other heavy metals present in the SPB, which affects negatively to zinc deposition [24,25], or the elimination of the organic additives used in the SPB [2]. However, the main difference between SPB and the stripping solution is related to the Zn/Fe molar ratio which has values of 1.56 and 20, respectively. ...
... Leaching the concentrates liberates zinc ions and impurities such as iron, copper, cadmium, cobalt and nickel that must be purified before electrowinning. 2,3 Metallic impurities play complex roles during the zinc electrowinning from acidic sulfate solutions. The zinc electrodepositions from bathes, especially the bright plating bathes, are very sensitive to impurities such as Ge, Sb, Ni, Co, Bi, Cu, As and Sn. ...
The neutralised zinc sulfate solution obtained from hydrometallurgical process of Angouran zinc concentrate has cadmium, nickel and cobalt impurities that must be purified before electrowinning. Therefore, cadmium and nickel are usually cemented out by addition of zinc dust under cold purification conditions. The present research aims to introduce a new technique for determination of effective parameters and optimisation of zinc electrolyte cold purification process using statistical design of experiments. The Taguchi’s method, based on orthogonal array design (OAD), was used to arrange the experiments. The experimental conditions addressed in the study were: the temperature range of 45–65uC for reaction temperature (T), one to five series for zinc dust particle size distributions (S), 15–75 min for reaction time (t), 1– 2?5gL21 for zinc powder concentration (M), and 200–600 rev min21 (R) for stirring speed. Optimum conditions for cold purification obtained in this study were T4 (60uC), S1 (series 1), t3 (45 min), M5 (2?5gL21), and R1 (200 rev min21).
Like other industrial processes, hot-dip galvanizing of steel generates some by-products and wastes. Secondary materials contain a relatively high percentage of zinc being valuable sources of the metal. Solid by-products like zinc ash, bottom dross, and top dross are currently sold to pyrometallurgical recycling plants, although zinc ash consisting of easy leachable components is suitable for hydrometallurgical treatment. In turn, flux skimming is deposited in landfills for hazardous wastes, but it could be leached for zinc recovery. Waste aqueous solutions from pretreatment steps, such as spent baths from pickling, stripping, and fluxing, or washing waters can be also regenerated by hydrometallurgical methods instead of going to landfills. This chapter presents the characteristics of main secondary raw materials originating from hot-dip galvanizing lines and reviews hydrometallurgical methods developed for their recycling or regeneration.KeywordsBottom drossFlux skimmingRecyclingSpent pickling solutionZinc ash
The morphology and composition of cemented products formed by Cu cementation in a ZnSO4 solution containing Cu²⁺ using Zn as the cementation agent were investigated. The influence of several factors on the characteristics of the cemented products, such as the temperature and pH of solution, ultrasound field, and suspended SiO2 particles, was studied separately. The cemented products were characterized using optical microscopy, scanning electron microscopy with energy dispersive X-ray, and X-ray diffraction. The Cu²⁺ content in the solution after the cementation process was determined using inductively coupled plasma-atomic emission spectroscopy. The results show that the cemented products can be effectively removed from the Zn surface when the rotating Zn sample is immersed in the solution containing suspended SiO2 particles, enhancing the Cu cementation and increasing the utilization efficiency of Zn especially for its addition near the stoichiometric amount. The high-power ultrasound can form a cemented product layer with large cracks favoring a solution permeation through the product layer; additionally the formation of basic Zn salts is enhanced, which are detrimental to Cu cementation. The pH of the solution greatly impacts on the morphology and composition of the cemented product on the Zn surface in the pH range of 0.5–4.5; a low pH of 0.5 or 1 can expose a large fraction of the Zn surface without the cemented product coverage. The enhanced Cu cementation at a higher temperature was confirmed by more cemented product obtained after 4-h cementation at 60 °C than those at lower temperatures.
The nonferrous metal electrowinning process is energy intensive due to the sluggish dynamics of the oxygen evolution reaction (OER) on the anode. Developing novel anode materials with high OER activity and stability is imperative. Herein, we propose a novel Pb-ceramic composite anode by introducing ZnFe2O4. In this work, Pb-ZnFe2O4 and PS-Pb anodes were prepared through powder pressing and sintering processes. The effects of ZnFe2O4 particles on the phase composition, surface morphology and inner structure of the oxide layer formed on Pb-ZnFe2O4 anodes were investigated. Furthermore, the role of ZnFe2O4 in the anodic potential and stability of Pb-ZnFe2O4 anodes was discussed. The results show that as the ZnFe2O4 content increases, the oxide layer formed on Pb-ZnFe2O4 anodes exhibits higher surficial compactness, higher integrity, and much smaller thickness. ZnFe2O4 exhibits a trivial impact on the oxygen evolution dynamics. However, the anodic potential of the Pb-ZnFe2O4 anode declines as the ZnFe2O4 content increases, which could be attributed to the higher compactness and smaller thickness of the oxide layer. As the ZnFe2O4 content increases, the weight loss of the Pb-ZnFe2O4 composite anode increases, suggesting the unsatisfactory stability of Pb-ZnFe2O4, which could be attributed to the inevitable dissolution of ZnFe2O4 particles, smaller thickness of the oxide layer and larger porosity of the substrate. Although Pb-ZnFe2O4 composite anodes have the potential to reduce energy consumption, their unsatisfactory stability limits the feasibility of Pb-ZnFe2O4 anodes in the electrowinning industry.
A new process for recycling zinc and copper from the smelting slag of waste brass was investigated in this study. The zinc and copper present in the smelting slag were dissolved in a ZnCl2–NH4Cl solution system. To recycle copper, the lixivium was purified by a novel method termed as electrochemistry and chemistry synergetic (ECS) purification. After deep purification of the ECS-treated lixivium by zinc powder cementation, zinc in the lixivium was extracted by electrowinning to obtain a zinc plate. The effects of the leaching temperature, reaction time, and liquid–solid ratio on the extraction percentages of zinc and copper were examined. The results revealed that the extraction percentages of zinc and copper were 88.37% and 90.85%, respectively, at a leaching temperature of 95 °C, reaction time of 90 min, and liquid–solid ratio of 8:1 mL/g. Further, effects of the current density, temperature, and reaction time on the recovery ratio of copper by ECS method were examined. The results revealed that 98.51% of copper could be extracted from the lixivium and that the purity of the extracted copper was 96.7% at a temperature of 70 °C and cathode current density of 75 A/m² after a reaction for 4 h. In the deep purification process, 0.3 g/L zinc powder was used to completely remove impurities from the ECS-treated lixivium. In the zinc electrowinning process, a current efficiency of 95.79% was achieved at 70 °C and 400 A/m²; the purity of the obtained zinc product was greater than 99.95%, and the direct energy consumption was 2966.59 kW·h/t-Zn.
Top ash from hot-dip galvanizing plant was investigated as a source of secondary zinc to be returned to galvanizing bath. The waste material contained 63% Zn as metallic, oxide and hydroxychloride phases. It was leached in H2SO4 solutions (20% and 25%) at various bath loadings (100−300 g/L). Leaching behaviors of zinc, manganese, iron and chloride ions were investigated. A few strategies of iron elimination from leaching liquors were examined. Flocculant addition was harmful for subsequent filtration of iron precipitates due to increased viscosity of solution, while a combination of zinc oxide and calcium carbonate for rising pH resulted in the formation of dense suspension unenforceable to separate from zinc sulphate solution. Zinc electrowinning was carried out at different pH (from −0.5 to 2.8) using a range of current densities (3−10 A/dm²). Optimal conditions for pure metal recovery were: leaching in 20% H2SO4 solution at zinc ash content 100−150 g/L, Fe2O3·xH2O precipitation using H2O2 and CaCO3, zinc electrowinning at pH of 0.1−1.0 at 3−6 A/dm². Correlations between pH and free H2SO4 concentration in electrolyte solutions were also discussed. pH−acid concentration dependence for zinc electrolyte was between experimental and calculated curves for pure H2SO4 solutions, while the curve was shifted towards lower pH if ferric ions were in the solution.
In this study, the roles of tannic acid and gelatin in Zn electrowinning were investigated. The results indicated that the addition of 10 mg/L of gelatin promoted Zn electrowinning and increased its current efficiency (CE) from 89.55% to 91.8%. However, the CE was only 77.47% when the electrolyte contained 50 mg/L of gelatin. As the concentration of tannic acid in the electrolyte increased from 10 mg/L to 400 mg/L, the CE decreased from 85.73% to 72.09%, which represented declines of 4.27% and 19.5%, respectively, compared with that of normal Zn electrowinning conditions in the absence of tannic acid. With increase in the concentrations of tannic acid and gelatin, the cell voltage increased and CE decreased sharply, which eventually resulted in a significant increase in the unit consumption of direct current (DC). The mechanisms by which tannic acid and gelatin inhibited the kinetics of Zn plating were additionally researched using electrochemical methods. The results showed that tannic acid and/or gelatin in high concentrations in the electrolyte significantly inhibited the deposition of Zn on the cathode by increasing the overpotential, reducing the deposition rate, and covering the electrode surface, which led to the appearance of agglomerates and needle-like structures on the surfaces of the Zn sheets.
Solvent extraction process of metals from aqueous solution containing impurities has been the subjects of numerous studies. . In the present work, separation of zinc from solution of filter-cake leaching unit in the presence of Mg impurity was investigated using D2-ethyl hexyl phosphoric acid (D2EHPA) extractant diluted in kerosene. Different experiments were carried out to evaluate the effects of main parameters on recovery and separation of zinc from the sulphate solution. Parameters affecting the extraction process such as pH, D2EHPA concentration, temperature, and organic to aqueous ratio were evaluated. Based on the results obtained at optimal conditions, the pH =2.5-3, [D2EHPA]=20%(vol/vol) and at 40 ° C, the extraction efficiency of zinc and magnesium ions were 95% and 10%, respectively, while the value of ΔpH0.5(Zn-Mg) factor was obtained more than 5.1 under the condition of [D2EHPA]= 20%(v/v). Also for the aqueous to the organic phase ratio (A/O) of 1: 1, an optimum zinc separation factor of 5010 was calculated.
Zinc dust is used for the removal of primary impurities by cementation from the zinc sulphate electrolyte before electrowinning of zinc. However, the industrial zinc electrowinning plants has been reported that the zinc dust consumption is in large excess than the stoichiometric requirement. In the present investigation, morphology of the zinc dust has been altered by ball milling and utilized for the cementation of cadmium, which is one of the major impurity and compared the change in the rate of cementation with original zinc dust. Initially, 325 mesh size zinc dust was used for the optimization of the excess quantity of zinc dust to be used at a temperature of 50 ° C. The chemical analysis of zinc dust before and after ball milling and morphology were studied by scanning electron microscopy (SEM), and the solution was characterized by Atomic Absorption Spectrophotometer. The rate of cementation increased with increase in ball milling time. The residual precipitate obtained after filtration was also characterized by X-ray diffraction analysis. Finally experiments were conducted to study the effect of temperature and kinetics of cadmium cementation using first order reaction kinetics. Based on the integral method, the calculated activation energy for the cadmium cementation with 4-hours ball milled zinc dust was found to be 3.39 KJ/mole.
Three industrial waste materials were examined in terms of their elemental and phase compositions, leaching behaviour in sulphuric acid solutions followed by solution purification and zinc electrowinning. Two dusts being mixtures of metallic zinc and zinc oxide of various proportions and zinc ash, containing simonkolleite additionally, were used. All materials characterized with high zinc percentages (60–80%). Zinc extraction from the materials was high (89–99% in 25% H2SO4) after short time of leaching. In all cases transfer of zinc ions to the leachate was accompanied by different levels of solution contamination in iron, manganese and chloride ions. Leaching of the materials was an exothermic process. Precipitation purification was carried out by using traditional method (oxidation followed by alkalization with CaCO3). Electrolysis parameters (current efficiency, voltage, energy consumption) were typical for zinc electrowinning, but surface morphology of zinc deposits was affected by chloride ions in the electrolyte.
The effect of the main zinc electrolysis parameters from an alkaline zincate solution on the current efficiency and power consumption is studied in laboratory conditions. The zinc concentration (initial and final), current density, and temperature are chosen as variable parameters. Both model (prepared from standard reagents) and actual electrolytes are used. The latter is prepared by leaching the calcined middling product of zinc-bearing dusts processing of ferrous metallurgy. It is shown that the current efficiency can be rather high (higher than 90%) even at the initial zinc concentration in the alkaline electrolyte of 10 g/dm³. However, low current loads (100–400 A/m²) are required in this case, the use of which is unreasonable for industrial electrolysis with the formation of powdered metal, because the actual current density decreases with the development of a cathode deposit surface even lower than the limiting diffusion current of complex ions. The growth of enlarged dendrites with the formation of short-circuited segments in the interelectrode space is expected in this case, which will decrease the current efficiency of zinc. Large-scale laboratory studies on zinc electrolysis from the actual zincate solution make it possible to determine the most power-efficient (with the highest current efficiency of zinc and lowest power consumption) process parameters; notably, the current density is 1000–2000 A/m², the electrolyte temperature is 50–80°C, the initial zinc concentration is 20–50 g/dm³, and the residual zinc concentration is no lower than 15 g/dm³. A high current efficiency (85–95%) and applied power consumption (2.28–3.20 kW h/kgZn) will be provided under these conditions. The maximal current efficiency (higher than 90%) for the “depleted” zincate solution with a zinc content of 10 g/dm³ is implemented at current density j = 125 A/m² close to the diffusion current density (of about 95.7 A/m²). The current efficiency considerably decreases at j > 500 A/m², which is caused by intense hydrogen evolution. When performing studies for the enlarged electrolysis cell, the formed cathode deposit is evaluated qualitatively (by visible crystal sizes).
A novel short process was firstly proposed for the synthesis of nanostructured flower-like metallic Zn from Zn-containing electric arc furnace dust leaching solution. The effects of metal ions coexisting in leachate on the electrodeposition of Zn was investigated. Results indicated that flower-like Zn with a large specific surface area was achieved in the presence of other cations, and the current efficiency reached about 79%. This study may develop a simple way for the direct electrodeposition of metallic Zn from Zn-containing solution with multiple impurity ions.
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 Mn ²⁺ . Mn ²⁺ 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.
In the current study, electrodeposition-redox replacement was applied to a hydrometallurgical solution with the main elements of Ca (13.8 g L⁻¹), Al (4.7 g L⁻¹), Cu (2.5 g L⁻¹), Zn (1.2 g L⁻¹), Fe (1.2 g L⁻¹), S (1 g L⁻¹), Mg (0.8 g L⁻¹), P (0.5 g L⁻¹) and Ag (3.5 ppm). The solution originated from the leaching experiment of incinerator plant bottom ash, which was dissolved into 2 M HCl media at T = 30 °C. The resulting deposit on the electrode surface was analysed with SEM-EDS and the observed Ag/(Cu + Zn) ratio (0.3) indicated remarkable enrichment of silver on the surface, when compared to the ratio of these elements (Ag/(Cu + Zn)) in the solution (6.8 × 10⁻⁵). The enrichment of Ag vs. (Cu + Zn) could be demonstrated to increase ca. 4500 fold compared to the ratio of the elements in solution.
Silver is a metal widely applied in renewable energy applications and therefore subjected for resource scarcity. The paper presents a new approach for recovering silver from zinc containing solutions mimicking hydrometallurgical base metal process solution. By nature, silver present in the ores or concentrates is more noble than zinc and not effectively leached into the sulfate media during zinc hydrometallurgical processing. This paper presents a novel approach for the concentrating and recovering silver present in minor amounts in zinc sulfate media. The electrodeposition-redox re-placement (EDRR) method was investigated in synthetic zinc sulfate solutions ([Zn] = 60 g/L, [Ag] = 1 ppb – 250 ppm, [H2SO4] = 10 g/L) containing silver as low as 1 ppb. The deposited metal coating was analyzed by electrochemical tech-niques and SEM-EDS. As a result, an enrichment of silver as nano- and micro particles on electrode was evident. With the application of multiple EDRR steps (n = 160) the method was shown to result in high purity Ag layer (Ag/Zn ratio ≈ 1500 in the product) from solution with minor Ag content (Ag/Zn ratio ≈ 0.0017 in solution). Moreover, at the concen-tration levels studied, the EDRR method was shown to outperform conventional electrowinning (EW).
The influences of sodium silicate on manganese electrodeposition in sulfate solution were investigated. Manganese electrodeposition experiments indicate that a certain amount of sodium silicate can improve cathode current efficiency and initial pH 7.0–8.0 is the optimized pH for high cathode current efficiency. The analyses of scanning electron microscopy (SEM) and X-ray diffraction (XRD) indicate the compact morphology and nanocrystalline structure of electrodeposits. X-ray photoelectron spectrometry (XPS) analysis shows that the elements of Mn, Si and O exist in the deposit. The solution chemistry calculations of sulfate electrolyte and sodium silicate solution indicate that species of Mn2+, MnSO4, Mn(SO4)2–2, Mn2+, MnSiO3, Mn(NH3)2+, SiO32– and HSiO3− are the main active species during the process of manganese electrodeposition. The reaction trend between Mn2+ and Si-containing ions is confirmed by the thermodynamic analysis. In addition, polarization curve tests confirm that sodium silicate can increase the overpotential of hydrogen evolution reaction, and then indirectly improve the cathode current efficiency.
Stripping solution of Lanping zinc oxide ore was simulated with zinc sulfate and sulphuric acid. The effect of ammonium nitrogen and organic impurities such as 260 solvent oil, β-dione on the current efficiency and quality of electrolytic zinc in different concentrations was investigated. Experimental results show that ammonium nitrogen has no effect on zinc current efficiency or quality of electrolytic zinc, while effect of organic impurities such as 260 solvent oil and β-dione on zinc electrowinning process is larger.
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.
By means of an electrochemical study, the influence of Sb3+ on cathode polarization process in zinc electrowinning and its kinetics equation and parameters have been studied. The results show that antimony has a depolarization function in the presence of [Sb3+] ≥0.5 mg·L-1 in zinc electrowinning, and Sb3+ has a polarization function in zinc electrowinning in the presence of [Sb 3+] ≥1 mg·L-1, the polarization curve enters into the hydrogen evolution range from the activation range, which indicates that the presence of antimony has adverse influence on the zinc electrowinning process.
The solubilization of used batteries components is of great scientific and economic interest, on account of recycling requirement of these wastes and recovery of valuable materials. In this paper, the recovery of zinc and manganese from Zn-ZnCl 2-MnO 2 (Zn-carbon) spent batteries was studied through chemical and electrochemical acid leaching experiments. Experimental parameters, such as acid concentration, solid: liquid ratio (S: L), temperature, time and current intensity were studied related to the dissolution of the black powder of the Zn-MnO 2 batteries. Leaching tests were carried out using H 2SO 4, in order to maximize zinc extraction and minimize Mn and Fe extraction. The best conditions for acid leaching (98% of Zn, 24% of Mn and 18% of Fe) were obtained with 2 M H 2SO 4, S: L= 1:5, room temperature and 1 hour leaching time. The results of electrochemical experiments showed selective leaching of Zn, together with a good recovery of metallic Zn (99.99% purity) at the cathode.
The effects of nickel ions on the cathode polarization process, kinetics equation and parameters in zinc electrowinning have been investigated in this paper. The results of the experiments show that when [Ni2+] <= 4 mg.L-1, the current density increases with increasing concentration of Ni2+ and limiting current of the passive point reach maximum, which indicates that the depolarization function of nickel in zinc electrowinning. And when [Ni2+] >= 4 mg.L-1, owing to the polarization function of nickel, electrowinning enters into stationary passive range at first and then enters into precipitation range because of the polarization function of nickel.
A detailed investigation has been carried out to determine the inhibition behavior of a mixed additive gelatin+thiourea+cresol (GTC) on zinc electrowinning from sulphate solutions containing germanium. The results indicate that zinc redissolution is inhibited because of germanium in existence, current efficiency is increased and surface morphology of cathode zinc is improved using proper GTC in the electrolyte. Cathode polarization curves were traced and analyzed to indicate that additive GTC may inhibit the depolarization and stimulating hydrogen evolution effects of germanium on zinc deposition.
The effects of three novel alkylpyridinium hydrosulfate ionic liquids (ILs)-EpyHSO4, BpyHSO4 and HpyHSO4 on current efficiency (CE), energy consumption (EC), catholic polarization behavior, surface morphology and crystallographic orientation during zinc electrodeposition from acidic sulphate solution were investigated. Addition of these additives was found to increase CE, decrease EC and improve the surface morphology at lower concentrations. Voltammetric studies indicated that these additives had a pronounced inhibiting effect on Zn2+ electroreduction and polarization of the electrode was in the order: HpyHSO4 > BpyHSO4 > EpyHSO4. X-ray diffraction analysis revealed that the presence of additives did not change the structure of the electrodeposited zinc but affected the crystallographic orientation of the crystal planes.
In zinc hydrometallurgy, an advanced copper removal process purifies zinc sulfate solution through a series of chemical reactions with recycled underflow by using zinc powder in zinc hydrometallurgy. This paper focuses on the kinetic modeling of the competitive-consecutive reaction system in the copper removal process, and proposes an adaptive parameter optimal selection strategy for different industrial conditions. In the system model, copper cementation, one of the removal reactions, is described by a surface controlled pseudo-first-order rate equation; cuprous oxide precipitation, the other removal reaction, is described by a shrinking core model of a noncatalytic fluid–solid reaction. Because there are several kinetic parameters in the system model, parameter estimation plays an essential role. Because of the complexity and variation in the practical removal process, the kinetic parameters are usually sensitive to alterations in the process conditions. This work solves the parameter estimation problem using an optimal selection strategy. In the strategy, the industrial conditions are classified adaptively according to the system model performance, then the kinetic parameters are selected optimally by evolutionary and particle swarm optimization algorithms for different industrial conditions. Three different representative industrial data sets are used to test the effectiveness and flexibility of the proposed modeling and parameter optimal selection approach in various situations. Finally, the kinetic model is applied to the soft measurement of the practical copper removal process with underflow, and the results demonstrate that the model effectively captures the trends of the removal reactions.
The polarization characteristics of acid zinc sulphate electrolytes containing various amounts of germanium and cobalt were examined by cyclic voltammetry. The effects of zinc and acid concentration, temperature, and surface preparation were also investigated. Small concentrations of impurities are shown to cause measurable changes in polarization behaviour. Levels as low as 0.02 mgl–1 Ge and 0.1 mgl–1 Co can be detected using this technique. The actual mechanism of impurity behaviour is more clearly delineated using this technique and evaluation of the data from these tests indicate that germanium and cobalt form local galvanic cells. The results of these short-term tests are shown to correlate with classical long-term efficiency tests. The deposit morphologies obtained for short-time cathodic cycles were also studied using scanning electron microscopy.
Using an electrolysis cell with separate compartments, the polarization and impedance of the zinc electrode have been investigated in highly acidic sulfate electrolytes. It is shown that (i) zinc deposition implies a multi-step mechanism and takes place when hydrogen evolution remains passivated on the deposit surface, and (ii) the presence of Ni2+ ions and/or H2O2 molecules in the electrolyte depassivates the reaction of hydrogen evolution and enhances the rate of zinc corrosion. The experimental results have been simulated on the basis of a reaction model in which hydrogen evolution on the oxidized adsorbates (ZnOad or ZnOHad) generated near the corrosion potential is clearly distinct from hydrogen evolution on the metal surface involving ZnHad, which inhibits zinc deposition. Then the passivation of hydrogen evolution is associated with the reduction of oxidized adsorbates. The progressive adsorption of Ni2+ ions competes with the formation of oxidized adsorbates to slow down the passivation process, thus widening the potential domain where hydrogen evolution predominates.
An investigation of the effects of some additives on zinc electrowinning from a weak acidic sulphate electrolyte prepared from an industrial waste product has been carried out. Experiments were done in the presence of additives such as aluminium sulphate, animal glue and an extract of horse-chestnut nuts (HCE), used alone or in different mixtures.Using a rotating disc electrode (RDE) and cyclic voltammetry, the influence of the additives on the polarization curves and on the voltammograms was studied. SEM was used to determine the structure and the morphology of deposits.The results indicated that the additives tested exert a beneficial effect on the quality of the zinc deposits. They increase the cathodic polarization and promote levelling. Al2(SO4)3 influences the reduction of zinc ions, increasing the nucleation overpotential and the deposition rate of zinc on the cathode. The conjoint use of Al2(SO4)3, animal glue and HCE results in smooth, slightly bright deposits, showing a beneficial effect of the mixture on zinc electrodeposition. The analysis of deposit purity suggested that the additives inhibit the discharge rate of impurity metal ions, such as copper and lead, whose deposition is diffusion controlled.
Measurements of coulombic efficiency (QE) for zinc electrodeposition were carried out under mass-transfer controlled conditions using a rotating disk electrode. Zinc deposits were produced over 2h in acidic zinc sulfate solutions prepared from analytical grade or high-purity reagents under the following conditions: 25° or 35°C, 400 A m-2, and an electrode rotation rate of 20 s-1. It was found that, on its own, trace lead had only a small beneficial effect on QE, which was not expected to be significant at the levels encountered in practice. However, in combination with antimony, a strong interactive effect was observed with the lead 'masking' the deleterious effect of antimony on QE, to an extent dependent on the lead concentration.
Lignin sulphonate and an extract of horse chestnut are added to a lead fluorosilicate electrolyte in order to improve the levelling of cathodic lead electrodeposits. By inducing a strong overpotential, these additives suppress totally the various forms of dendritic growth. The resulting smooth layers present weak fibre textures with characteristic morphologies. An original and simple method based on X-ray diffraction was developed in order to evaluate the texture quality. These levellers have different dependence on potential and rotation rate of the disk electrode. In particular, electrolyte agitation tends to increase the inhibition efficiency for one compound and to decrease it for the other. The conjoint use of the two additives ensures a good levelling, even for very thick lead electrodeposits.
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.
From galvanostatic potential-time curves, voltammograms and impedance measurements, it is shown that the destabilization of the zinc deposition process by Ni2+ ions present in the acidic sulphate electrolyte is considerably favoured in the absence of a diaphragm separating the anode and cathode compartments. It is concluded that the deleterious influence of Ni2+ ions is enhanced by the anodically formed products which interfere with the slow interfacial processes taking place at the cathode surface. A stronger synergetic influence of nickel and oxidized species is demonstrated when using an aluminium cathode containing Fe impurities.
An investigation has been made on the mechanism and kinetics of the electrochemical processes occurring during zinc electrowinning from sulphuric acid electrolytes containing Ni2+, Co2+ and mixtures of the two impurities. The electrochemical nature of the synergism effect manifested by the common action of these two metal impurities has been established. It has been demonstrated that as a result of specific adsorption of (Co(SO4))(2n-2)– anions onto the zinc electrode, the partial discharge rate of Ni2+ is catalyzed, leading to an increase of its bulk content in the zinc deposits.
- D R Fosnacht
- T J Keefe
Fosnacht, D.R. and O'Keefe, TJ., J. Appl. Electrochem., 10 (1980): 495-504.