Influence of lead dioxide surface films on anodic oxidation of a lead alloy under conditions typical of copper electrowinning

Cyclic voltammograms, current transients at constant potential and potential decay transients have been used to study the formation of lead dioxide surface films in the presence of cobalt ions and their role in decreasing the oxidation rate of a lead alloy under steady state conditions typical of copper electrowinning. The observations in the present work indicate, consistent with the surface film model, that the formation of a continuous PbSO4 + alpha-PbO2 film on the surface of the lead alloy in the presence of cobalt ions hinders further oxidation of the metal. The protectiveness of the film is dynamic in the steady state; the film is continuously forming and dissolving. Also studied was the potential of the oxygen evolution reaction on alpha-PbO2 and beta-PbO2 in 170 g L-1 H2SO4 with and without cobalt ions. The steady state potential for oxygen evolution on beta-PbO2 in 170 g L-1 H2SO4 at 285 A m(-2) decreased in the presence of cobalt ions and the steady state potential of beta-PbO2 was essentially the same as that of (i) the Pb-Ca-Sn alloy and (ii) alpha-PbO2. The implication is that the potential of the Pb-Ca-Sn alloy is determined by the alpha-PbO2 and/or beta-PbO2 on its surface

Effective Copper Diffusion Coefficients in CuSO₄—H₂SO₄ Electrowinning Electrolytes

Mass transport is an important factor in the deposit quality of copper electrowinning. Presently, there is limited diffusivity data available at commercially relevant concentrations between 25 and 40 °C. Linear sweep voltammetry at a rotating disk electrode was used to measure effective diffusion coefficients of cupric ion for a wide range of copper concentrations (10-50 g/L), sulfuric acid concentrations (120-240 g/L), and temperatures (25-60 °C). The results were well correlated by the equation: D, m2/s = 2.977 x 10-10 -5.462 x 10-13 [Cu]-1.212 x 10-12 [H2SO4] + 1.688 x 10-11 x T, where [Cu] and [H2O4] are in g/L, and T is °C. Addition of 20 mg/L Cl- slightly increased effective diffusivity. Other common commercial organic smoothing agents were found to have no effect. The measured diffusivities were used to calculate the maximum permissible current density that can produce smooth dense cathodes as a function of copper concentration and temperature

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

Exploring As-Cast PbCaSn-Mg anodes for improved performance in copper electrowinning

Lead calcium tin (PbCaSn) alloys are the common anodes used in copper electrowinning (Cu EW). Given a large amount of energy consumed in Cu EW process, anodes with controlled oxygen evolution reaction (OER) kinetics and a lower OER overpotential are advantageous for reducing the energy consumption. To date, magnesium (Mg) has never been studied as an alloying element for EW anodes. As-cast PbCaSn anodes with the addition of Mg were examined herein, revealing an improved performance compared to that of the industrial standard PbCaSn anode. The alloy performances in the early stages of anode life and passivation were established from electrochemical studies which were designed to simulate industrial Cu EW process. The 24-hour polarization testing revealed that the Mg alloying depolarizes the anode potential up to 80 mV; thus, resulting in a higher Cu EW efficiency. In addition, scanning electron microscopy and X-ray photoelectron spectroscopy revealed that the alteration of the alloy microstructure and the corresponding interfacial reactions contribute to the changes of the anode electrochemical performances. The present study reveals for the first time the potency of Mg alloying in reducing the overpotential of PbCaSn anode