The use of pyrite as a source of lixiviant in the bioleaching of electronic waste

Electronic waste (e-waste) contains a wide range of elements, many of which are highly toxic to environmental and human health. On the other hand e-waste represents a significant potential source of valuable metals. This study used microbial oxidation of pyrite to generate a biolixiviant. Its efficiency in the dissolution of metals from printed circuit boards (PCBs) was evaluated as well as the effects of metals and PCB concentrations on microbial activity. The addition of elemental metals (Cu, Cr, Ni, Sn, Zn) had an immediate inhibitory effect on pyrite oxidation, though leaching recovered after a period of adaptation. Bioleaching was inhibited initially by the addition of 1 % (w/v) ground PCB, but recovered rapidly, whereas pulp densities of ≥ 5 % had sustained negative impacts on culture activity and viability. The loss of culture viability meant that only abiotic copper dissolution occurred at ≥ 5 % PCB. Final copper recoveries declined with increasing PCB pulp density. The relatively high content of elemental iron caused a lag period in copper solubilisation possibly due to displacement reactions. Leptospirillum ferriphilum was primarily responsible for pyrite oxidation, and most affected by both the pure metals (particularly Ni and Cu) and PCB.