Effect of Aqueous Antimony Species on Corrosion of Pb–Sn–Ca Alloy in Copper Electrowinning

Abstract

Copper electrowinning is important not only for the solvent extraction – electrowinning process (SX-EW), which produces primary copper metal from copper oxide minerals, but also for the copper recycling process, which comprises smelting, leaching, and electrowinning. The electrolyte used in the copper recycling process contains various impurities that are usually negligible in the electrolyte used in the SX-EW process. In this study, the effect of aqueous antimony species on the corrosion of a Pb–Sn–Ca alloy in copper electrowinning was investigated using galvanostatic electrolysis, followed by X-ray diffractometry, scanning electron microscopy – energy dispersive X-ray spectroscopy, and inductively coupled plasma – optical emission spectrometry analyses. The electrolysis was conducted at various current densities in a synthetic copper electrolyte containing H₂SO₄, Cu(II), Ni(II), Co(II), and 0–4.1 mmol·dm⁻³ of Sb(III) at 65°C. When the electrolyte did not contain any antimony species, the anode surface was covered with scale comprised of αPbO₂ and βPbO₂. The PbO₂ scale grew along the grain boundaries, and its growth rate was considerably slow. In contrast, when the electrolysis was conducted in an electrolyte containing Sb(III), scale consisting of Sb₂O₅ and αPbO₂ formed on the anode surface. A laminated Sb₂O₅–αPbO₂ mixture scale was observed on the anode surface, and its growth rate was significantly faster than that of the PbO₂ scale. The flakes of the Sb₂O₅–αPbO₂ mixture scale periodically fell from the anode surface, and consequently, the corrosion of the Pb–Sn–Ca alloy anode was accelerated. The oxidation of Sb(III) to Sb₂O₅ was likely caused by an anode reaction rather than by direct reaction with the oxygen formed on the anode surface. The formation of Sb₂O₅ on the Pb–Sn–Ca alloy resulted in a considerable decrease in aqueous antimony in the copper electrolyte, indicating its effectiveness in enhancing the electrowinning process targeting pure copper cathode production, copper liberation, and antimony removal from the tailing electrolyte in copper electrorefining.