Zinc Deposition Current Efficiency Research Articles

Synergistically achieving particulate matter reduction and production performance optimization for zinc electrolysis by ultrasonication coupling anode-coated MnO2

Abating particulate matter (PM) from electrolysis processes is significant because this PM poses occupational threats to workers and has a negative impact on air quality. However, it remains a challenge to synergize the reduction of PM production and the improvement of electrolysis performance. This study developed a green method, termed as the coupling of ultrasonication and pre-coating MnO2 anode treatment (UMT). The effects on PM generation rate and electrolysis performance indicators were estimated using the bench-scale zinc electrolysis device, and the synergistic mechanism of UMT was expanded from the perspective of electrochemical reactions and bubble characteristics using analysis of reaction products, camera technique, and PM generation prediction models. The results showed UMT not only overcame the degradation of deposited zinc quality caused by the ultrasonication treatment but also solved the increased PM generation by the pre-coating MnO2 film treatment. The UMT simultaneously reduced PM (33.9 %-57.5 %), decreased zinc impurity content by (11.2 %-54.3 %), improved current efficiency of zinc deposition (0.19 %-1.71 %), and conserved electrolysis energy (0.27 %-1.01 %). The optimal performance of UMT occurred at 80 kHz. The UMT suppressed the gas evolution reactions and prematurely bursting bubbles, in favor of reducing the number and size of bubbles, to reduce PM generation. Meanwhile, the UMT improved the electrolysis performance by inhibiting the corrosion of lead-based anodes, promoting the mass transfer rate of Zn2+, providing more active surfaces, and decreasing the overpotential of reactions. The findings may provide references for the green development of the metal electrolysis industry.

Ultrasonication to reduce particulate matter generated from bursting bubbles: A case study on zinc electrolysis

Particulate matters (PM) generated from bursting bubbles during electrolysis are hazardous and undesirable. Cleaner production technologies to reduce these PM by controlling bubble characteristics need to be explored. This study applied an ultrasonication method to reduce PM generated from zinc electrolysis. The results showed that the reduction efficiencies for total suspended particulates increased with the increase in ultrasonic power. The reduction mechanism was also investigated from the perspective of behavior of the bubble. The results showed that the number and size of microbubbles were both inversely related to the ultrasonic power, while positively related to the total mass of PM. Ultrasonication reduced PM by decreasing the number and size of microbubbles in two steps: i) during gas generation, ultrasonication inhibited anodic oxygen evolution and cathodic hydrogen evolution to reduce the gas amount; ii) after the formation of microbubbles, the mechanical effects of ultrasonication probably prematurely detach the microbubbles on electrode and directly burst microbubbles in electrolyte. Moreover, ultrasonication was also beneficial for increasing the current efficiency of zinc deposition and for lowering the energy consumption. The findings provided indications for ultrasonication technology to reduce PM from electrolysis and paved the road for exploring other clean PM reduction methods.

Influence of additives on the electrodeposition of zinc from a deep eutectic solvent

The effects of nicotinic acid (NA), boric acid (BA) and benzoquinone (BQ) on the electrodeposition of Zn have been studied in a choline chloride (ChCl) ethylene glycol (EG) based deep eutectic solvent (DES), (1ChCl:2 EG), and for the first time a bright zinc coating has been achieved when NA was used.In metal electroplating processes, small-molecule additives are often included in the plating bath to improve properties of coating such as brightness, roughness, thickness, hardness and resistance to corrosion. The effects of additives on the electrodeposition of Zn from aqueous solution have been extensively investigated. However, very few studies have considered the effects of additives on the electrodeposition of Zn from ionic liquids or deep eutectic solvents. The electrochemical properties of the plating liquid have been studied here using cyclic voltammetry, chronocoulometry, chronoamperometry and microgravimetry (EQCM). Redox peak currents decrease when additives were included in the Zn solution and total charge was also reduced in experiments where additives were present. The Zn deposition in the absence of additive is in good agreement with an instantaneous growth mechanism at short experimental time scales (being indeterminate over longer periods), however, this changes to one of a progressive growth mechanism when additives were included in the coating bath. The current efficiency of zinc deposition in the DES without additives was 95%, which was reduced when additives were included. The resultant surface morphologies, thickness, topography, roughness and crystal structure of the Zn coating were revealed by scanning electron microscopy (SEM), atomic force microscopy (AFM) and X-ray diffraction (XRD), demonstrating that those additives serve as effective brighteners that can produce highly uniform and smooth zinc deposits.

Investigation of the kinetics and the morphology of cementation products formed during purification of a synthetic zinc sulfate electrolyte

In zinc production, the purity of incoming zinc solution is of great importance. The presence of cobalt in the electrolyte used for zinc production lowers the current efficiency of zinc deposition and affects the purity of the zinc product. For this reason, cobalt must be removed from the electrolyte prior to zinc electrowinning. Cobalt removal is commonly achieved by the addition of metallic zinc dust through a process called cementation. The mechanism by which cementation occurs is not well understood. Parameters, such as cementation time, temperature, solution pH, concentration of activators, concentration of zinc ions in the electrolyte were investigated in this study. It was concluded that cobalt cementation could be described by a first order rate equation with an activation energy of 45 kJ/mol. Temperature played a significant role on the kinetics while the presence of hydrogen, intermediate compound formation, and zinc ions inhibited the cobalt cementation. Cu/Sb activators were cemented within the first 90 s and gave synergistic effect on cobalt cementation. Surface compounds on the cementation product were identified as mainly Zn(OH)2 and ZnSO4. Redissolution of cobalt did not occur from cemented cobalt but from dissolution of intermediate Co(OH)2 and CoSO4 salts.

Electrochemical investigation of electrolyte composition and electrolysis parameters during zinc electrowinning

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

The effects of mixtures of acid mist suppression reagents on zinc electrowinning from spent electrolyte solutions

The effects of Dowfroth 250 (D) and Tennafroth 250 (T) in combination with saponin (S) on zinc deposition current efficiency and power consumption during electrowinning of zinc from industrially supplied spent electrolyte solutions were investigated. The surface morphology and crystallographic orientations of the zinc deposits were also examined by scanning electron microscopy and X-ray diffraction techniques, respectively. Acid mist suppression efficiencies were measured and investigated by frothing behavior of the additives and by surface tension measurements. Concentrations of 5, 10, and 15 ppm of each of the additives were mixed with all possible combinations into spent electrolyte to study the effects. Results showed that addition of Dowfroth 250/Tennafroth 250 as well as saponin decreased the current efficiency, increased the energy consumption while maximum acid mist suppression efficiencies of 86.1% and 87.0% were obtained at D5 + S5 and T5 + S5, respectively. The increase in saponin concentration resulted a change in preferred crystal orientation from (104) (112) (103) (102) (101) at low saponin concentrations to (101) (112) at higher saponin concentration. Bright and compact deposits were obtained at a mixture concentration level of T5 + S5 and D5 + S5.

Distribution of germanium under lead smelting conditions

Germanium is present as a minor element in most mined lead-zinc concentrates, and during subsequent processing part of it is carried in electrolyte to zinc electrowinning. Germanium is well known to reduce drastically the current efficiency of zinc deposition and to cause a multitude of pinholes in the cathode deposit, even at concentrations <0·1 ppm, so it is important to understand how to minimise the amount of germanium proceeding to zinc calcines leaching. This work was aimed at determining the distribution of germanium during lead smelting among lead, slag and gas and generating thermodynamic data for use in process modelling. Lead and a small amount of GeO2 was equilibrated with CaO-SiO2-FeO-Al2O3 slag under oxygen partial pressures from 10-10 to 10-12·5 atm at temperatures from 1150 to 1250ºC. It was found that most germanium is incorporated in the slag, some volatilises and little dissolves into the lead. Germanium is present in the slag predominately as GeO and its activity coefficient in this slag is calculated to be in the range 1·44-2·55. The implications of these findings on processing are also discussed.

Zinc removal from dilute solutions using a rotating cylinder electrode reactor

Mine residue recycling processes produce dilute zinc solutions suitable for metal recovery. The rotating cylinder electrode reactor behaviour sequentially followed charge transfer and diffusion control mechanisms, even with solutions contaminated with metals or organic substances. Zinc removal at low pH (∼0) and low concentration (∼2 mg dm−3) is demonstrated. Under galvanostatic operation, the zinc deposition current efficiency in the charge transfer control region attains values up to 77.3%, whereas in the diffusion control region it decreases rapidly to values as low as 0.1%. When a potentio-static mode is used, less energy is required to deposit zinc, even at low current efficiency. The results and possible problems for continuous reactor operation under conditions of powder formation are identified and discussed using knowledge from other zinc industries such as electrowinning, plating and batteries.

Effect of chromate ion on zinc electrowinning from acid sulphate electrolyte

The effect of chromate ion and its interaction with antimony and glue on zinc electrowinning from acid sulphate electrolyte were studied. During electrolysis at 430 A m−2 and 45°C, the chromate ion was found to polarize the cathodic reaction resulting in a refined zinc deposit having a morphology featuring a vertical orientation of the zinc platelets. Although chromium did not codeposit, the current efficiency for zinc deposition was dramatically decreased in the presence of > 1000 mg dm−3. This effect became more pronounced when the electrolyte also contained additives such as antimony and glue.

The effects of foaming agents, and their interaction with antimony, manganese and magnesium, on zinc electrowinning from synthetic acid sulphate electrolyte

The effects of Dowfroth and Saponin, alone and in various combinations with antimony and with manganese and magnesium sulphates, on zinc deposition current efficiency and on the morphology and orientation of 24 h zinc deposits electrowon at 430 A/m 2 and 35°C from synthetic acid sulphate electrolyte were determined. Both Dowfroth and Saponin decreased the zinc deposition current efficiency and also changed the deposit morphology and orientation. Dowfroth and Saponin had a positive interaction with antimony, such that certain combinations of these reagents maximized the current efficiency and improved the deposit quality. The addition of MnSO 4 to an electrolyte containing 10 mg/l Dowfroth increased the current efficiency for zinc deposition and changed the deposit morphology. The current efficiency was further increased by adding antimony, but the addition of MgSO 4 had no effect. The addition of Saponin to an electrolyte containing optimum concentrations of Dowfroth and antimony lowered the current efficiency; however, this current efficiency decrease was more than offset by adding MnSO 4 to the electrolyte.

The effect of some trace metal impurities on the electrowinning of zinc from Kidd Creek electrolyte

The single and combined effects of cobalt (0.15–5 mg/l), arsenic (0.01–5 mg/l) and iron (2.5–50 mg/l) on zinc deposition current efficiency (CE) and polarization behaviour and on the deposit morphology and orientation of 24 h zinc deposits were studied. The in-plant additive mix of 1 mg/1 Saponin, 5 mg/l Dowfroth, 13 mg/l sodium silicate and 0.015 mg/l antimony was employed under the conditions of 60 g/l Zn 2+, 200 g/l H 2SO 4, 500 A/m 2 and 38°C with conditioned PbAg anodes and SrCO 3 additions in bench scale electrolysis (cell volume 300 ml). The CE was sensitive to increasing concentrations of cobalt and arsenic both alone and in combination. Iron alone had very little effect on CE. Iron concentrations greater than 20 mg/l, in combination with arsenic and cobalt, significantly lowered the CE. The nucleation overpotential (NOP) determined from cyclic voltametry did not correlate with the CE results. A prewave in the voltammograms in the presence of some impurities, particulary arsenic, made the determinations of the NOP difficult. Most of the deposits were intermediate (e.g. [101][112][102]) in orientation. The surface of the deposit darkened in appearance as the arsenic concentration increased. At higher cobalt concentrations, the solution side of the deposit appeared normal although significant corroded dark areas starting on the edges were noted on the electrode side.

The effects of Dowfroth, antimony and Saponin on zinc electrowinning from Kidd Creek electrolyte

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 <1% change in current efficiency and did not modify the preferred deposit orientation. At optimum Dowfroth + antimony combinations, the addition of Saponin again did not affect significantly the current efficiency. The preferred deposit orientation was either [1 0 1][1 1 2] or [1 0 1] depending on the combination of these reagents employed. Tests run for 24h for selected combinations of Dowfroth, antimony and Saponin confirmed the results obtained for the 6h studies.

The effects of antimony and glue on zinc electrowinning from Kidd Creek electrolyte

The individual and combined effects of antimony and glue on zinc deposition current efficiency and polarization and on the morphology and orientation of 6h zinc deposits electrowon at 500 A m−2 and 38° C from Kidd Creek zinc electrolyte were determined. Glue increased zinc deposition polarization, reduced the deposit grain size, changed the preferred deposit orientation from basal to intermediate, but decreased the current efficiency. At concentrations above 0.02 mgl−1, antimony had a strong depolarizing effect on zinc deposition resulting in a basal deposit orientation and very low current efficiency. Certain combinations of antimony and glue, however, optimized zinc deposition current efficiency and consistently gave an intermediate 〈114〉 〈112〉 〈103〉 〈102〉 〈101〉 preferred deposit orientation. A correlation was observed between the current efficiency (CE) and the nucleation overpotential (NOP) for zinc deposition such that the CE was a maximum when the NOP of the initial cell electrolyte was 120–130 mV and when the NOP of the final cell electrolyte was 100–110 mV.

The behavior of thiourea and flotation reagents in zinc electrowinning circuits

The effect of thiourea and flotation reagents on the electrowinning of zinc from industrial electrolytes was studied, and all the compounds were found to reduce the zinc deposition current efficiency and to change the properties of the zinc deposits. The effectiveness of activated carbon, two-stage cementation, and hot acid leaching on the destruction/removal of the organic compounds also was addressed. Activated carbon pretreatment of thiourea-containing electrolytes restored the current efficiency for 1-hour zinc deposits to values comparable to those obtained for thiourea-free electrolytes. The activated carbon pretreatment, however, altered the deposit morphology and orientation, but produced a cyclic voltammogram similar to that of the thiourea-free solution. Two-stage cementation did not counteract the harmful effects of thiourea. Hot acid leaching destroyed the thiourea but generated large concentrations of ferrous ion that reduced the current efficiency. The ferrous concentrations, however, were readily controlled by KMnO4 or MnO2 oxidation. None of the treatment options (activated carbon, two-stage cementation, or hot acid leaching) was effective in controlling the flotation reagents, and their moderately harmful effect on zinc electrowinning persisted. Even low concentrations of these reagents polarized zinc deposition, and this resulted in a “glue-type” zinc deposit.

The effects of As(III) and As(V) on zinc electrowinning from industrial acid sulphate electrolyte

The effects of As(III) and As(V), with and without glue and glue+antimony additions, on the current effeciency and polarization behaviour of zinc deposition and on the morphology and preferred orientation of 1-h zinc deposits electrowon from industrial acid sulphate electrolyte have been determined. As(III) had no effect on the current efficiency and did not alter significantly either the zinc deposition polarization curve or the zinc deposit morphology and orientation. Increasing concentrations of As(V) resulted in a significant decrease in the current efficiency for zinc deposition from addition-free electrolyte and from electrolytes containing added glue and glue+antimony. As(V) also changed the zinc deposit morphology and orientation, and significantly altered the shape of the zinc deposition cyclic voltammogram.

The effects of nickel and cobalt and their interaction with antimony on zinc electrowinning from industrial acid sulphate electrolyte

The effects of nickel and cobalt and their interaction with antimony on the electrowinning of zinc from industrial acid sulphate electrolyte were studied using X-ray diffraction, scanning electron microscopy and cyclic voltammetry. Concentrations of cobalt as high as 20 mgl−1 had no effect on the zinc deposition current efficiency. The current efficiency decreased rapidly when the electrolyte contained >5 mgl−1 nickel. Neither cobalt or nickel had an effect on the morphology of the 1-h zinc deposits. Nickel and cobalt caused characteristic changes in the cyclic voltammograms for zinc deposition. As a result this technique might provide a rapid means for evaluating the electrolyte prior to zinc electrowinning. The combined presence of cobalt and antimony in the zinc electrolyte was more deleterious to zinc electrowinning than was the combined presence of nickel and antimony. The presence of 0.08 mgl−1 antimony in the electrolyte counteracted the effect of nickel both on the current efficiency for 1-h deposits and on the zinc deposition polarization curves.

Bubble Enhanced Mass Transfer of Electrodeposited Zinc from Acid Solutions

Abstract The efficiency of zinc electrodeposition with simultaneous hydrogen evolution was determined in an electrolytic cell using variable H2SO4 and ZnSO4 concentration and current densities of 500,680 and 800 A m−2. The chemical properties of the solution determine the rate of hydrogen evolution. Overall mass transfer coefficients for Zn2+ were calculated from the measured zinc flux and were found to vary with the rate of hydrogen evolution at the cathode surface. These coefficients are enhanced by bubble generation due to microconvection effects but at the detriment of the current efficiency of zinc deposition. Jannsen's model for the estimation of the concentration layer thickness was found to be consistent with the observed results. Resume On a mesure le rendement faradique de l'electroextraction du zinc en presence de concentrations variables de H2SO4 et de ZnSO4 aux densites de courant de 500, 680 et 800A m−2.Les proprietes chimiques de la solution determinent le taux de degagement d'hydrogene a l...

Zinc electrowinning from aqueous chloride electrolytes

Smooth, compact, dendrite-free zinc deposits can be electrowon from acid zinc chloride electrolyte using a diaphragm cell featuring catholyte agitation by air sparging. A correlation exists between the degree of zinc deposition polarization and the zinc deposit structure and orientation that can be used to evaluate the effectiveness of addition agents and, ultimately, to control deposit quality. The effect of impurities on the current efficiency for zinc deposition and on the morphology and orientation of 24h zinc deposits is discussed.

Influence of oxygen reduction in the electrowinning of zinc

The electrodeposition of zinc from an acid zinc sulphate electrolyte similar to those used in commercial zinc electrowinning has been studied at a rotating aluminium cathode. The presence of dissolved oxygen is shown to lower the current efficiency for zinc deposition, and the influence of current density, rotation speed, and oxygen concentration indicates that the mass-transfer-controlled electrochemical reduction of oxygen is responsible. The mass-transport parameters of oxygen in the zinc electrolyte are deduced from voltammetric studies on carbon, aluminium, and platinum cathodes. The influence of dissolved oxygen on current efficiency in a practical electrowinning cell is estimated to be in the order of 1%, with the main uncertainties being in the mass-transfer coefficients and in possible oxygen supersaturation.

A Solution Quality Analyser for Zinc Sulphate Electrolyte

An instrument which continuously measures the purity of a zinc sulphate electrolyte is described. It consists essentially of a rotating bipolar electrode which determines the current efficiency of zinc deposition. Experimental evidence is presented to demonstrate the performance of the analyser under various operating conditions and a comparison is made between the measured and theoretical response of the instrument to a step change in solution purity.