Effects of operational parameters on the bio-assisted leaching of metals from pyrolyzed printed circuit boards

End-of-life printed circuit boards have been subjected to proprietary pyrolysis resulting in a copper-rich char. This study details their downstream processing by hydrometallurgy for copper recovery. The pyrolysed PCBs were reacted with two different bioleaching solutions containing mixed mesophilic microbial consortia and a synthetic chemical solution for comparative purposes. The influence of char pre-treatment, reactor type, working temperature, and the origin of leaching solution on the dissolution of the zero valent copper was studied. It was found, that the type of reactor had a more pronounced effect than the origin of bacterial solution in bringing copper in solution. Characterisation of the leached char confirmed the importance of the pre-treatment step. Other than ferric iron concentration and temperature, the leaching effciency and kinetics were largely influenced by the bacterial activity. The fact that copper was brought into solution by ferric iron at starting concentrations well below the stoichiometric requirement, implies bacterial regeneration of the ferric iron and its cycling in the system.