Copper Electrowinning Research Articles

Corrosion behaviour and catalytic effectiveness of Pb–Ca–Sn, RuO2–IrO2/Ti and IrO2–Ta2O5/Ti anodes for copper electrowinning

The dependence of the corrosion rate on cell current density (CD) for three anode materials (Pb–Ca–Sn, RuO2–IrO2/Ti and IrO2–Ta2O5/Ti) in a laboratory scale copper electrowinning cell has been studied by means of short term weight loss tests, scanning electron microscopy observations and energy dispersive spectroscopy analysis. The lead anodes (Pb–Ca–Sn) corroded at all the studied cell CDs, and their corrosion rate increased with increasing cell CD. The precious metal oxide anodes (RuO2–IrO2 and IrO2–Ta2O5) only exhibited corrosion at the highest tested cell CD (1000 A m−2), and their corrosion rates were about a quarter of the lead corrosion rate at the same cell CD. The electrocatalytic properties of the three anode materials were characterised by means of potentiodynamic experiments. The overall results pointed to IrO2–Ta2O5/Ti as the best anode material of choice, although plant tests would be required before deciding on any specific commercial use.

The sizing of oxygen bubbles in copper electrowinning

Oxygen bubbles are formed on the anode in the copper electrowinning process. Burst of the bubbles produces acid mist in the tankhouse. While it is well acknowledged that the amount of acid mist is related to the size of the bubble, no systematic measurements have been made to quantify bubble size and its relationship with materials and process variables. This paper presents results of bubble size measurement under different operating conditions. For each of the operating conditions tested, bubbles were detected in a wide size distribution ranging from 20 μm to more than 400 μm in diameter. Statistical analyses on the measurement results showed that addition of FC-1100, a surfactant widely used in copper electrowinning to suppress acid mist, and solution temperature were the two most influential test parameters on the bubble size followed by the age of the anode. In contrast, current density and solution acidity had negligible effect.

Reducing Specific Energy to Shrink the Carbon Footprint in a Copper Electrowinning Facility

Various technologies and strategies to reduce specific energy consumption are examined. Results include 16 harvest cycles for 30 cells, totaling 62 400 cathodes with a weight of 2500 ton. The industrial site was Zaldivar, which is a Barrick mining operation located at 175 km southeast from Antofagasta, Chile. The production averages 140 000 ton/year of copper cathodes. With the technologies tested in this paper, 14 000 MWh and corresponding 14 000 ton of CO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> will be saved per year.

Electrowinning of Copper Using Rotating Cylinder Electrode Utilizing Lead Anode

The effect of lead anode, rotating cylinder electrode (RCE), amount of 1,2-dihydroxypropane (12-DHP), temperature and rotation on the electrowinning of copper from low concentration acidified copper sulphate solution has been investigated. Copper powder was electrodeposited onto RCE that made of pure copper. From cyclic voltammetry experiments, an empirical parameter called the departure percent, S, was obtained which may represent the stability of the organic additive in the given medium and under the experimental conditions. The inhibition percentage, P, was 0.00 - 89.91% depending on the experimental variables. P was affected by temperature and mole fraction of 12-DHP, while rotation did not show any influence on it. Values of activation energy of electrodeposition process, Ea, were found to be less than 28 kJ mol-1 indicating diffusion controlled process. The overall mass transfer correlations under the present conditions have been computed using the dimensional analysis method. The data were valid for 90 < Sh < 1098, 737 < Sc < 59284 and 271 < Re < 7046 and the results agreed with the previous studies of mass transfer to rotating cylinders in turbulent flow regimes. The effect of time, content of 12-DHP, temperature and the speed of rotation on the morphological changes of the electrodeposited copper powder as well as deposits composition and crystallite size have been studied. Various crystallite sizes ranged 7.1 nm - 250.6 nm were obtained and characterized by EDS and XRD. Different topographs proved that the rate of copper electrodeposition increased by increasing deposition time, temperature and the speed of rotation. Also, they proved that the deposition rate decreased by adding 12-DHP to the solution. Therefore, the results obtained by SEM supported those achieved by measuring the limiting current density and follow the normal manner when organic solvents were added to the electrodeposition bath.

Statistical analysis of the effect of operating parameters on acid mist generation in copper electrowinning

Acid mist is generated during the final stage of hydrometallurgical metal refining processes including the electrowinning of copper. In this study, the effect of five process parameters and their interactions on the amount of acid mist generated is analysed quantitatively. The amount of acid mist generated was measured under 32 different operating conditions. It was found that solution's temperature and mist suppressant chemical FC-1100 had significant effect on the amount of acid mist generated. More than 90% of the variations in the acid mist generation can be explained by changes in these two parameters and their interaction. To a lesser extent, electrical current density and solution acidity also affected the total amount of acid mist generated. The anode's age and most of the 3, 4, and 5-way parameter interactions were found to have negligible influence on the amount of acid mist. Overall, acid mist was found to increase with temperature and current density. In contrast, increasing the viscosity of the solutions tends to decrease the amount of acid mist.

Experimental Validation of a Computational Fluid Dynamics Model of Copper Electrowinning

The hydrodynamics that occur in the space between the electrode plates in copper electrowinning (EW) are simulated using a computational fluid dynamics model (CFD). The model solves for the phases of gas oxygen bubbles and electrolyte using the Navier–Stokes equations in a CFD framework. An oxygen source is added to the anode, which sets up a recirculation pattern. The gradients in copper near the cathode lead to buoyancy forces, which result in an uplift in the electrolyte close to the cathode. This study investigates the experimental validation of the CFD model using a small/medium-scale real EW system. The predicted fluid velocity profiles are compared with the experimental values, which have been measured along various cross sections of the gap between the anode and the cathode. The results show that the CFD model accurately predicts the velocity profile at several heights in the plate pair. The CFD model prediction of the gas hold-up and the recirculation pattern is compared with visualizations from the experiment. The CFD model prediction is shown to be good across several different operating conditions and geometries, showing that the fundamental underlying equations used in the CFD model transfer to these cases without adjusting the model parameters.

Evaluación de resinas de intercambio iónico para el control del hierro en soluciones de electro-obtención de cobre

Two commercial resins were evaluated for the extraction of iron from a copper electrowinning solution. Both resins efficiently extract iron. TheMonophosphonic resin has a greater charge capacity than the Diphonix resin and the Diphonix resin shows faster kinetics. Experimental results of the interrupted test and tests with different particle size of resins have demonstrated that extraction kinetics is controlled by diffusion into the particle in both resins. A good agreement with Fick’s model for diffusion inside the particles confirms the proposed mechanism. Finally, temperature favors the process kinetics and its effect on the diffusion coefficient follows Arrhenius law, obtaining a value of 4,89 kcal/mol for theMonophosphonic resin and 4,94 kcal/mol for the Dphonix resin. The aforementioned values are close to typical values for the proposed diffusional control which are 6 to 10 kcal/mol.

Nucleation kinetics of selenium (+4) precipitation from an acidic copper sulphate solution

The removal of selenium from copper sulphate solution prior to the electrowinning of copper is desirable in order to minimise contamination of the copper cathodes by selenium and other impurities. The selenium removal is effected by a precipitation process that takes place under high supersaturation conditions, which favour nucleation over any other particle formation processes. There is currently no fundamental information on the nucleation kinetics of this important process. In this study, the nucleation kinetics of selenium (+4) precipitation from an acidic copper sulphate solution was determined using the classical nucleation theory (CNT). Experiments were carried out by varying the levels of supersaturation from 8.66×10 15 to 4.33×10 17 at a temperature of 95 °C under atmospheric pressure. The nucleation rates for four different levels of supersaturation, the nucleation work and the nucleus size were determined. The kinetic constant A was found to be 3.92×10 27 m −3 s −1, which shows that the nucleation process takes place through a homogeneous mechanism. The associated thermodynamic parameter ( B) was determined to be 8.98×10 04.

Improving Productivity and Energy Efficiency in Copper Electrowinning Plants

This paper presents strategies to improve energy efficiency and productivity in copper electrowinning (EW) plants. Plant modeling is based on updated technical data and specific measurements obtained in a tankhouse during a complete production cycle (four to five continuous days). The industrial EW plant site examined produces 180 000 ton/year with an operating current density of 300 A/m2 and a current dispersion of 8.5%. Proposals are based on the use of Optibar intercell bars and the reduction of distance between electrodes. Due to these changes, an improvement of +4.3% in energy efficiency combined with an increase of +3.4% in production can be accomplished. The productivity improvement projected for the plant is U.S.$ 10 million/year.

Effect of added cobalt ion on copper electrowinning from sulfate bath using doped polyaniline and Pb-Ag anodes

Effect of added Co 2+(aq) on copper electrowinning was studied using doped polyaniline (Pani) and Pb-Ag(1%) anodes and a stainless steel cathode. The presence of added Co 2+(aq) in the electrolyte solution was found to decrease the anode potentials. The optimum level of Co 2+(aq) concentration in the electrolyte, with respect to the maximum saving of power consumption was established. Linear sweep voltammetry (LSV) was used to study the influence of added Co 2+(aq) on the anodic processes in a copper sulfate-sulfuric acid electrolyte. The oxygen-evolution potential for Pani anode is depolarised at lower current densities (⩽0.01 A/cm 2) and attains saturation at ρ(Co 2+) o≈0.789 g/L; whilst the oxygen-evolution potential for Pb-Ag(1%) anode is depolarised at higher current densities (⩽0.02 A/cm 2) and attains saturation at ρ(Co 2+) o≈1.315 g/L. The preferred orientations of the copper deposits change from (220) to (111) with the addition of 0.394–0.789 g/L Co 2+ but higher concentrations favor (220) orientation again.

An Alternative Copper Electrowinning Process Based on Reactive Electrodialysis (red)

An Alternative Copper Electrowinning Process Based on Reactive Electrodialysis (red)

Evaluation of the Effect of Copper Electrowinning Parameters on Current Efficiency and Energy Consumption Using Surface Response Methodology

The effect of various parameters on the current efficiency and energy consumption during copper electrowinning were studied under relevant conditions to the industrial operations using statistical analysis with the aim of developing statistical models that describe the variation of current efficiency and energy consumption during copper electrowinning. The current efficiency was found to be affected by the ferric concentration, the copper concentration, the current density and the interaction between these parameters. The energy consumption was proved to be a function of the ferric concentration, the copper concentration and the interaction existing between them. These models were proved to predict laboratory test results as well as the output of industrial operations with high accuracy.

Electrowinning of Copper from Copper Cyanide Solutions at Low pH

The electrodeposition of copper from solutions containing free cyanide is difficult under alkaline conditions, but can be substantially enhanced by decreasing the pH due to the formation of the more electroactive aqueous species, Cu(CN)2-. The optimum pH for electrowinning is pH 5, and the electrodeposition of copper is significantly enhanced in an acetate solution due to the minimization of interfacial pH change. Cu(CN)2- was found to be readily oxidized at potentials more positive than 550 mV, and an anode material has yet to be found that promoted oxygen evolution over the oxidation of copper cyanide. At pH 5, the current efficiency increases as the cathode potential shifts to more positive potentials, whilst the copper recovery rate decreases as the potential becomes more positive than -600 mV. The optimum operating cathode potential is between 500 and 600 mV, giving a current efficiency of 90 - 100 % and an average energy consumption of 0.85 - 1.00 kWh/kgCu.

Electrowinning of Copper from Various Copper Cyanide Eluates at Low pH

not Available.

Evaluation of Copper Electrowinning Parameters on Current Efficiency and Energy Consumption Using Surface Response Methodology

not Available.

Study of precipitation hardening in lead calcium tin anodes for copper electrowinning

A suitable yield stress for Pb anodes with 0·07%Ca and 1·3%Sn of 6 mm thickness for copper electrowinning is achieved by means of deformation and precipitation hardening processes, their useful life being dependent on this yield stress. The objective of the present work was to optimise the precipitation hardening, by finding the best cooling conditions for the anodes in the moulds and the optimum hot rolling temperature. The results show that increasing the cooling rate of ingots beyond the rate of natural cooling enhances the precipitation hardening. At least 45 days of aging are necessary to reach stable conditions for the precipitation hardening, with precipitates formation as CaSn3. The hot rolling temperature does not have a significant effect on the precipitation hardening of the anodes.

Optimal Precipitation Hardening Conditions in Lead Base Anodes for Copper Electrowinning

The suitable yield stress of Pb-0.07%Ca-1.3%Sn anodes of 6 mm thickness for copper electrowinning is achieved by means of deformation and precipitation hardening processes, being its useful life dependant of this yield stress. In such sense the objective of the present work is to optimize the precipitation hardening, finding for this purpose the best cooling conditions of the anodes in the molds and of the hot rolling temperature. The results show that increasing cooling rate of ingots from natural cooling the precipitation hardening is enhanced, with increases of 10% and 12.5 % on the yield stress and working life of the anodes respectively, and that a minimum of 45 days of ageing is necessary to reach stable conditions for the precipitation hardening, with precipitates formation as CaSn3. The hot roll temperature as not significant effect on the precipitation hardening of the anodes.

Addition of Cobalt to Lead Anodes Used for Oxygen Evolution—A Literature Review

A review of the literature dealing with the effect of cobalt on lead-based anodes for oxygen evolution during electrolysis of sulfuric acid solutions verifies that the presence of cobalt at the anode–electrolyte interface, either as constituent of the anode material or as ions in the electrolyte, catalyzes the evolution of oxygen and reduces the corrosion of the anodes and the contamination by lead of metal cathodes produced during electrowinning. However, due to harmful effects of cobalt ions on the cathodic reaction in some processes, these benefits are limited to the electrowinning of copper. Efforts to develop a way of introducing cobalt at the anode–electrolyte interface without interfering with the cathodic reactions are reviewed in this paper. The use of lead–cobalt alloy anodes has had limited success due to issues arising from the low solubility of cobalt in lead, segregation during casting of the alloys, and nonuniform distribution of cobalt which affects the integrity of the anodes. This has been overcome in part lately by inclusion of cobalt into only the surface layer of a lead or lead alloy substrate, by thermal treatment of a cobalt salt to form a catalytic cobalt oxide surface species, or by electrodeposition of composite lead–cobalt oxide anodes. The last approach in particular has been actively investigated by several groups, but to our knowledge it is yet to find application in the industry. The review also critically examines the likely reaction mechanisms involved.

Electrochemical and physical characterisation of lead-based anodes in comparison to Ti–(70%) IrO2/(30%) Ta2O5 dimensionally stable anodes for use in copper electrowinning

The suitability of various dimensionally stable anodes (DSAs®) was investigated in comparison to the conventional lead alloy anodes in the electrowinning of copper. DSA® plate and mesh specimens of composition Ti–(70%) IrO2/(30%) Ta2O5 and lead–(6%) antimony were evaluated. The electrochemical behaviour of these anodes was studied by carrying out open circuit potential measurements, galvanostatic chronopotentiometry, cyclic voltammetry and chronoamperometry. Physical characterisation was done using a scanning electron microscope. It was observed that the DSA® plate anode exhibited the highest corrosion resistance followed by the DSA® mesh and lead anodes, respectively. The results also showed that during copper electrowinning using lead anodes, dissolution of the anode occurs while for both DSAs® marginal loss of coating was observed. The lead anode had the highest anode potential followed by the DSA® plate and mesh anodes, respectively. Overall, it was demonstrated that the DSA® plate anode is the most suitable anode for copper electrowinning.

Effect of solution components on stability of protective PbO2 layers on Pb–Ca–Sn anodes for copper electrowinning

Potential–time curves have been carried out in CuSO4–H2SO4 electrolytes to establish the effect of various impurities and additives on the stability of the protective PbO2 layer formed on Pb–Ca–Sn alloys used in copper electrowinning. The most important effects are those of guar and Fe(III). Acting separately, they tend to stabilise the protective layer, whereas Co(II) and Mn(II) do not. The effect of Fe(III) can be explained by its strong oxidising power; the effect of guar, by its ability to form a protective barrier of organic molecules adsorbed on the PbO2 layer. The effects of both guar and Fe(III) are diminished by the presence of other species in solution: reducing species diminish the effect of ferric ions and guar is degraded by oxidising species.