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

End-of-life printed circuit boards have been subjected to proprietary pyrolysis resulting in a copper-rich char containing liberated metals. For downstream processing and copper recovery, the char was exposed to two different leaching solutions: one containing mixed microbial consortia originating from bioleaching of coal spoils and a cell-free chemical solution for comparative purpose. The influence of char pre-treatment, reactor type, temperature and type of leaching solution on the dissolution of the zero-valent copper was studied. It was found out, that for bringing copper in solution, the type of leaching solution had less pronounced effect than the type of reactor. Other than ferric iron concentration and temperature, the bacterial presence has shown effect on copper leaching kinetics and process efficiency. The fact that copper was continuously dissolved by ferric iron at initial concentrations well below the stoichiometric required ratio, demonstrated microbial regeneration of ferric iron and its back-cycling in the system. In case of the absence of microbe, the regeneration of ferric iron is driven by oxidation in the presence of O-2 and H+. A simplified kinetic model of copper dissolution suggested that the reaction order depends upon the initial concentration of ferric iron.