Insights into the continuous staggered bioleaching of pure copper from waste printed circuit boards

Recycling precious metals from electronic waste by bioleaching stands out as a sustainable technology for metal solubilisation using microorganisms. In this study, the recovery of pure copper from waste printed circuit boards was performed through an indirect approach by sequential bioleaching and electrowinning. The bacterium Acidithiobacillus ferrooxidans was cultivated in a stirred tank reactor for the continuous production of ferric iron (Fe3+) as the primary leaching agent for batch leaching at pulp densities and temperature up to 8 % w/v and 40 degrees C, respectively. A leaching rate of 50 % copper was achieved at a pulp density of 6 % w/v, 40 degrees C and 96 h spent time. The finding was used as a reference for flow leaching operations in a continuous stirred tank reactor and rates of 100 % and 80 % of copper were leached with and without pH control, respectively, at 40 degrees C, and a hydraulic residence time of 96 h. A rate of 70.85 % of pure copper was then recovered from the metal rich solution by electrowinning using a current density of 0.0168 A/cm2 over 8 h. These results provide valuable insights into the continuous recovery of copper from electronic wastes and contribute to the ongoing strategies of design and scale-up toward industrially viable operations.