Optimal Deformation Hardening in Lead Base Anodes for Copper Electrowinning for an Appropiate Working Life

The lead base anodes (Pb-0.07% Ca-1.3% Sn) of 6 mm thick have limited working life due to their loss of thickness and corrosion during the electrowinning process. If this loss of thickness is combined with a low yield stress of the anodes, these are much more likely to suffer premature deformations and distortions in cells. The aim of this study is to optimize the deformation hardening of the anodes, so as to achieve the best combination of yield stress and corrosion resistance to increase their working life. To achieve this the aged anodes were cold rolled to different area reductions from the standard 50% to 75%. To each one of these rolled anodes its yield stress was determined by plane compression tests, their grain sizes was measured by means of optical microscopy and their corrosion rate was determined by coulomb metric assays in a cell using an electrolyte concentration of sulfuric acid of 180 g/l and a oxidation current density of 300 A/m2.It was found that the maximum yield stress of the anodes increases from 58 MPa to 64 MPa when cold reduction goes up from 50% and reach 70% . Regarding the corrosion rate, the maximum and minimum values were 0.33 mm/ year and 0.30 mm / year, i.e., with no significant differences between the different rolled anodes. Based on the above results it is concluded that an increase in the working life of the anodes is obtained simply by giving them greater cold rolling deformation from the current 50% to 70% of area reduction.