Chapter 17 – Electrowinning

Publisher Summary This chapter explains how the Cu2+ ions in CuSO4–H2SO4 electrolyte are reduced and electrowon as pure metallic copper in the form of cathodes through the process of electrowining (EW). EW entails applying an electrical potential between inert Pb-alloy anodes and stainless steel (occasionally copper) cathodes in CuSO4–H2SO4 electrolyte. Pure copper electroplates on the cathodes. O2 and H2SO4 are generated at the anodes. The copper is stripped from the cathode and sold. The O2 joins the atmosphere. The Cu2+ -depleted electrolyte is returned to solvent extraction as the spent electrolyte for stripping Cu2+ from the loaded organic phase and replenishment of Cu22+ in the advance electrolyte. Electrowon copper is as pure as or purer than electrorefined copper. Its only significant impurities are S (4 or 5 ppm) and Pb and Fe (1 or 2 ppm each). Careful control and attention to detail in housekeeping and tankhouse management can decrease these impurity concentrations to the low end of these ranges. Modern trends in copper EW include: increasing current densities above 450 A/m2, reducing energy consumption, increasing automation and robotic control and monitoring of the process, and the use of a new generation of anodes.