Extraction of metals from high grade waste printed circuit board by conventional and hybrid bioleaching using Acidithiobacillus ferrooxidans

Bioleaching of selected metals, viz. Cu, Zn, Pb, Ni from e-waste in the form of high grade waste printed circuit board (PCB) of computer is comparatively assessed using pure culture of Acidithiobacillus ferrooxidans with and without the supplementation of lemon juice containing 0.2 M citric acid as active constituent and natural tetradentate chelating agent to simulate hybrid and conventional conditions, respectively. Metal leaching from the comminuted PCB is observed to vary greatly under the conventional and hybrid bioleaching conditions showing better solubilization in the hybrid approach due to the chelating effect of citric acid. At a pulp density of 7.5 g/L and the comminution fines in the size range of 0.075-1 mm, the maximum leaching of 94% Cu, 92% Zn, 64% Pb and 81% Ni are observed at 18 days of hybrid bioleaching with an asymptotic trend from 12 days onward. Measurement of the exopolymeric substances (EPS) production during bioleaching indicates a profound role in the leaching of metals. Extraction through chemical precipitation yields more than 99% of the selected metals from bioleached liquor. Hybrid bioleaching technique followed by chemical precipitation can be deliberated as a complete solution for metal recycling for resource recovery from e-waste.