Bioleaching of metals from e-waste using immobilized biomass of mesophilic Acidithiobacillus ferrooxidans

Among the secondary post-consumption wastes, e-wastes represent the fastest growing waste stream in the world being heterogeneous and diverse in terms of structure and composition. Consequently, it is difficult to feed such waste into conventional recycling streams. Biometallurgy could prove a competitive and applicable technique for recovering valuable metals from these materials. The objective of the study is to test the feasibility of biometallurgy for recycling secondary raw materials, rendering the presently uneconomic raw materials economically viable, thus contributing directly to the circular economy. Long-term objective is to study the peculiarities of bioleaching of secondary raw materials, reveal the role of bacteria in these processes and develop the concept on the mechanism of bioleaching of secondary raw materials. Comparative chemical leaching of printed circuit boards (PCBs) by ferric sulfate Fe2O12S3xH2Osolution and biogenic Fe3+ obtained by immobilized biomass ofAcidithiobacillus ferrooxidans 61 (Armenia) and Acidithiobacillus GR1 (Bulgaria) has been performed. The intensity of zero valent copper oxidation was correlated to the ratio of Fe3+/Fe2+ ions in the solution. It was revealed that recovery of metals from PCBs by biogenic Fe3+ occurred 2-3 times more intensively than that by Fe2O12S3xH2O solution. The use ofFe2O12S3xH2O solution for leaching of PCBs resulted in intensive precipitation of Fe3+ andgeneration of jarosite, while in case of biogenic Fe3+ the amount of jarosite was significantly lower. It is supposed that Fe3+ in biogenic solution is mainly in the form of complexes with organic compounds produced by bacteria, which prevent its precipitation as jarosite. It is as-sumed that chemical leaching by biogenic Fe3+ integrated into the processes of leaching of PCB's may contribute to intensification of extraction of copper and other valuable metals from different secondary resources.