The effect of copper on zinc electrowinning from industrial acid sulphate electrolyte

The effect of copper on the electrowinning of zinc from industrial acid sulphate electrolyte was studied using X-ray diffraction, scanning electron microscopy and cyclic voltammetry techniques. Concentrations of copper as high as 50 mg 1^–1 had no effect on the zinc deposition current efficiency for 1-h deposits. Copper co-deposited with zinc and reduced the deposit grain size. The copper content of the zinc deposits increased with increasing copper concentration in the electrolyte and with decreasing current density. The cyclic voltammogram for copper-containing electrolyte was characterized by an appreciable cathodic current in the reverse scan after zinc dissolution indicating the presence of previously deposited copper on the cathode.     

The effect of germanium on zinc electrowinning from industrial acid sulphate electrolyte

The effect ofgermanium on the electrowinning of zinc from industrial acid sulphate electrolyte was studied using X-ray diffraction, scanning electron microscopy and cyclic voltammetry techniques. Germanium concentrations > 0.1 mgl^–1 results in severe re-solution of the zinc deposit and hence decreased the zinc deposition current efficiency. Extreme fluctuations in the current efficiency occurred as a function of electrolysis time. Cyclic voltammograms obtained for Ge-containing electrolytes were characterized by a shoulder in the reverse scan prior to the cross-over potential. Vigorous hydrogen gassing occurred at the shoulder. These results are interpreted in terms of the formation of local Zn-Ge galvanic cells. Germanium concentrations to 0.2 mgl^–1 had no effect on the morphology of the 1-h zinc deposits but the preferred orientation changed from [1 1 4] [1 1 2] for Ge-free electrolyte to [1 1 2] [1 1 0] for electrolytes containing Ge.     

The effect of tin on zinc electrowinning from industrial acid sulphate electrolyte

The effect of tin on the electrowinning of zinc from industrial acid sulphate electrolyte was studied using cyclic voltammetry, X-ray diffraction and scanning electron microscopy techniques. Tin concentrations < 2 mg l^–1 resulted in a rapid decrease in the current efficiency for l-h zinc deposits electrowon at 430 A m^–2; for tin concentration > 2 mg l^–1, the current efficiency remained constant at about 75%. The presence of tin in the electrolyte depolarized the zinc deposition reaction and resulted in a zinc deposit having a preferred [002] orientation. The addition of glue appeared to aggravate rather than counteract the adverse effects of tin.     

Aluminium cathode effects in zinc electrowinning from industrial acid sulphate electrolyte

The effects of aluminum cathode grain size and surface conditioning treatments on zinc electrodeposition from purified industrial acid sulphate electrolyte were investigated. The Al cathode grain size had no effect on the long-time (15–60 min) deposit characteristics although deposits obtained using large-grain Al cathodes were often easier to strip. A study of the initial zinc nucleation (5–80s) showed that fine-grain Al cathodes had more zinc nucleation sites than largegrain cathodes. The influence of cathode preconditioning and glue on the initial zinc nucleation were also determined.     

Characterization of impurity effects in zinc electrowinning from industrial acid sulphate electrolyte

The individual effects of 15 impurities and their interaction with glue on zinc electrowinning from industrial acid sulphate electrolyte were characterized in terms of deposit morphology and preferred deposit orientation and in terms of current efficiency and zinc deposition polarization behaviour. The current efficiency decreased in a cyclical manner with increasing atomic number of the impurity element in each period of the periodic table. This decrease in current efficiency can be correlated to a corresponding increase in the rate of hydrogen evolution on the impurity metal. The various impurities produced four distinct zinc deposit morphologies and orientations and also produced characteristic changes in the cyclic voltammograms for the zinc deposition.     

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 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.     

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 role of zinc and sulfuric acid concentrations on zinc electrowinning from industrial sulfate based electrolyte

The effects of varying simultaneously the zinc/acid concentrations at a fixed total sulfate, on the current efficiency, energy requirements, and deposit physical characteristics for the zinc electrowinning, using Kidd Creek zinc electrolyte, were investigated. The electrowinning experiments were conducted using a laboratory scale apparatus, at plating cycles of 24 and 30 h, a current density of 500 A m^–2 and a temperature of 38 °C. These conditions are typical of those applied at the Kidd Creek zinc tankhouse. The reagents presently used at Kidd Creek, namely strontium carbonate, Saponin, Dowfroth 250, antimony and sodium silicate, were also continuously added to the cell electrolyte at levels similar to Kidd Creek practice. Scanning electron microscopy and X-ray diffraction techniques were used to characterize the deposits with respect to morphology and preferred orientation, respectively. Cyclic voltammetry was used to study the effect of the zinc/acid concentrations on the polarization behaviour of the electrolyte. In addition, the electrical conductivity of the Kidd Creek zinc electrolyte was measured and compared with other industrial sulfate-based zinc electrolytes.     

The effect of cadmium on zinc deposit structures obtained from high purity industrial acid sulphate electrolyte

The effect of cadmium on cathodic zinc crystal growth was studied in high purity industrial electrolyte, with and without additives, in an attempt to establish a correlation between morphology, polarization and the extent of cadmium contamination. Cadmium additions to acid zinc sulphate electrolyte did not have a significant effect on the zinc deposit orientation but did substantially refine the deposit grain size. The refinement in deposit grain size is directly related to the level of cadmium in the zinc deposits. Cadmium, in combination with glue and optimum amounts of glue and antimony, also reduced the deposit grain size: the preferred deposit orientation remained (1 1 2) with a slight tendency to (1 0 1) at high glue concentrations. Cadmium in combination with antimony resulted in an increased depolarization of zinc deposition and a basal (0 0 2) deposit orientation. Lead additions to zinc electrolyte containing cadmium resulted in increased deposition overpotentials and intermediate to vertical deposit orientations.     

Nickel and cobalt synergism effect in zinc electrowinning from sulphate electrolytes

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.     

Thermodynamic studies on sulphate roasting for zinc electrowinning from carbonate ore

The bulk of the work consists of a theoretical study of the possibility of submitting Umm-Gheig carbonate ore to sulphate roasting. The use of the admixture with pyrites is to enable a carbonate ore to be treated in a similar way to a sulphide ore, and by doing so, to produce a roasted product capable of being treated by orthodox zinc electrowinning methods using sulphate solutions. Thermodynamic studies have been made to find the optimum conditions for sulphate roasting, in either normal air or enriched 36% oxygen air. The results obtained from the experimental work at different roasting temperatures in a tube furnace indicated that a maximum dissolution of 91.2% Zn with a 17.9% Fe could be obtained at a roasting temperature of 650°C for 4 h, followed by leaching in 4% H₂SO₄ (by vol.) at 60°C. The results of the electron microscopic investigation confirmed by metal value data given in the ASTM cards coincide well with results given by chemical analysis.     

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 effect of lead on zinc deposit structures obtained from high purity synthetic and industrial acid sulphate electrolytes

Zinc deposits contaminated with lead were found to have characteristic morphologies and orientations which were dependent on the amount of lead present in the zinc deposits and to a lesser extent on the presence of other impurities such as antimony and glue in the deposits. Increasing lead in the zinc deposits progressively changed the orientations from (1 1 2) to (1 0 1) to (1 0 0) to finally a poorly crystalline (0 0 2) structure. The lead content of the zinc deposits was dependent on both the concentration and chemical composition of lead added to the electrolyte, the current density and also on the presence of antimony or glue in the electrolyte. A relationship was shown to exist between the effect of lead contamination on zinc deposit morphology and orientation and on the overpotentials associated with zinc electrodeposition in the presence of lead.     

Effects of 2-picoline on zinc electrowinning from acidic sulfate electrolyte

The behaviour of 2-picoline with and without antimony during electrowinning of zinc from acidic sulfate solutions was studied and was compared with that of gum arabic which is commonly used in industry as a levelling agent. The effects of these additives on current efficiency, power consumption, deposit quality, polarization behaviour, crystallographic orientation and surface morphology were determined. The addition of 2-picoline reduced current efficiency, increased power consumption and lowered the surface quality of electrowon zinc. Addition of antimony increased current efficiency, reduced power consumption and produced improved surface morphology and crystal orientations, (101) (112) (102) (103) (114) over a wide range of their combinations.     

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

The effects of Saponin alone and in combination with antimony and glue on zinc deposition current efficiency and polarization and on the morphology and orientation of 6h and 24h zinc deposits electrowon at 500 A m^–2 and 38°C from Kidd Creek zinc electrolyte were determined. Saponin, at concentrations to 100mgl^–1, was weakly polarizing, changed the preferred deposit orientation from basal to intermediate and decreased the current efficiency. At optimum glue + antimony levels, Saponin concentrations 5mgl^–1 resulted in an increase in zinc deposition current efficiency and consistently gave either a <114><112><103><102><101> or a <101><112> preferred deposit orientation depending on the antimony + glue combination used. Tests run for 24h for selected combinations of Saponin, antimony and glue confirmed the results obtained for the 6h studies.     

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 importance of cathode zinc morphology as an indicator of industrial electrowinning performance

A number of recent papers have described the use of cyclic voltammetry measurements as a method of controlling the electrowinning step in zinc production. A further advance has been the use of XRD to characterize the crystal orientation of zinc deposits. This paper concerns the use of these techniques by the Electrolytic Zinc Company of Australasia Limited to specify zinc electrowinning conditions during a pilot plant evaluation of a novel zinc plant circuit.Preliminary small scale electrolysis tests gave unsatisfactory deposits and low current efficiencies (<85%). The aforementioned techniques were used diagnostically to make step changes to operating conditions and to cell additives. The approach was successful and current efficiencies of 93% were established. The use of XRD, coupled with extensive experience of zinc electrowinning, proved to be more important than cyclic voltammetry. The preferred conditions generated by the small scale tests were successfully implemented in pilot plant trials using a full sized electrolytic cell producing 0.5 t per day of zinc.Overall, the tests confirmed the expectation that there is a strong correlation between current efficiency and the morphology of zinc deposits.     

Influence of tartaric acid on zinc electrodeposition from sulphate bath

The effect of tartaric acid on zinc electrodeposition from sulphate plating bath was investigated by electrochemical impedance spectroscopy (EIS), stationary polarization curves, X-ray diffraction and SEM imagery. The study shows that it is possible to obtain homogeneous, compact and dendrites-free zinc deposits from sulphate solutions containing tartaric acid. For various hydrodynamic methods (rotating disc electrode and static vertical or horizontal electrode), the results indicate that, the presence of only small quantity of tartaric acid, may induce significant changes on deposition rates and deposit quality.