Bioleaching: an innovative biotechnology for recovery of metals from electronic wastes
Every year, more than 40 million metric tons of electronic wastes are discarded worldwide and these wastes represent a problem due to their improper treatment. Presence of metals, plastics and ceramics in these wastes pose a threat for health and environment. Pyrometallurgy and hydrometallurgy are employed for metal extraction from these wastes. However, of late, bioleaching is emerging one of the alternatives for recovery of metals. Chemolithotrophic bacterial strains are used and they accomplish bioleaching either by direct or indirect mechanisms. This review deals on the potential bacterial strains, their mechanism of action, factors involved, limitations and perspectives on bioleaching.
Electronic wastes (E-waste) represent a serious pollution problem due to their metal content (1). It has been estimated that in 2014 E-waste accounted to 41.8 million metric tonnes (Mt) and could increase to 50 Mt in 2018 (2). Asia is the major contributor in the generation of E-waste with 16.6 million metric tons (Mt), followed by America, Europa, Africa and Oceania, which generated 11.7 Mt, 11.6 Mt, 1.9 Mt and 0.6 Mt respectively (3). The major concern of E-waste is the release of the different materials of which it is composed, which can be summarized as mainly metals (40%), plastic (30%) and ceramic (30%) (1, 4-6). Its content of metals such as aluminum (Al), cadmium (Cd), copper (Cu), zinc (Zn), nickel (Ni), gold (Au) and silver (Ag) to mention a few, represents a great potential for recovery. It has been reported (7) that approximately 279.93 g of gold, 190.512 kg of copper, 145.152 kg of aluminium and 450 g of silver can be recovered from one ton of printed circuit board (PCB). Methods based on pyrometallurgy and hydrometallurgy are currently used for the recovery of metals from these wastes (8). However, due to the secondary pr ...