Electrochemical Behaviour of Industrial IrO2-Ta2O5 Anodes for Copper Electrowinning

Abstract

Lead-based anodes are widely used in copper electrowinning (EW). However, lead can induce contamination of the electrolyte during copper EW due to the corrosion of the anode [1]. Furthermore, corrosion while at high current densities will finally lead to the failure of the anode since the overvoltage for oxygen evolution reaction (OER) on lead is still rather high, and the service life of lead-based anodes is quite limited in industrial copper plants [2]. Besides, lead and lead compounds are toxic, which means the use of lead-based anodes is not environmentally friendly. Dimensionally stable anodes (DSAs) with IrO2-Ta2O5 oxides coated on titanium substrates hold excellent electrocatalytic activity and electrochemical stability, and have the most potential to replace lead-based anode in copper EW industry. In this work, different types of commercially available electrode samples with IrO2-Ta2O5 coating were studied. The studies focused on investigating the impact of surface microstructure on electrocatalytic activity. Surface morphology and chemical composition of DSA samples were analyzed using scanning electron microscopy (SEM, Hitachi S-3400N) combined with energy dispersive spectroscopy (EDS). X-ray diffraction (XRD) studies were carried out using Bruker AXS D8Advance with grazing incident angle at 3°. The crystalline structure and phase composition were analyzed by varying the 2θ angle from 10° to 80°. The electrochemical experiments were carried out in aqueous solution with 0.9 M H2SO4 and 1.2 M CuSO4. A Teflon holder giving a 1 cm2 electrode surface area was used. All experiments were conducted at 60 °C. Cyclic voltammetry (CV) measurements were recorded in a range between 0.55 V and 1.35 V vs. SHE with varying sweep rate from 300 mV/s to 1 mV/s. The scan rate for all polarization measurement was 0.5 mV/s. The ohmic (IR) drop during the testing was corrected for by measuring the electrolyte resistance using electrochemical impedance spectroscopy (EIS) at high frequency. Electrocatalytic activity for anodes as a function of composition and preparation method was determined by steady state polarization analysis. The durability of the anodes was investigated by accelerated lifetime tests, which were carried out in 0.9 M H2SO4 solution at the constant current density of 2 A/cm2. In the present work, commercial DSAs were used instead of samples fabricated in the laboratory. This offers not only valuable results for DSAs research but also a consideration for DSAs manufacturers to improve the quality of the DSA. [1] M. Clancy, C. J. Bettles, A. Stuart, N. Birbilis, Corrosion behaviour and catalytic effectiveness of Pb–Ca–Sn, RuO2 –IrO2 /Ti and IrO2 –Ta2O5/Ti anodes for copper electrowinning, Hydrometallurgy 131-132 (2013) 144. [2] G. N. Martelli, R. Ornelas, G. Faita, Deactivation mechanisms of oxygen evolving anodes at high current densities, Electrochim. Acta 39 (1994) 1551.