Biometallurgical recovery of metals from waste printed circuit boards using pure and mixed strains of Acidithiobacillus ferrooxidans and Acidiphilium acidophilum

Abstract

Bioleaching ability of two acidophiles, viz. Acidithiobacillus ferrooxidans, a gammaproteobacteria, and Acidiphilium acidophilum, an alphaproteobacteria in pure and mixed strains was comparatively evaluated for the recovery of metals from waste printed circuit boards (WPCBs) of computer at pulp density in the range of 7.5−15 g/L. Results indicated a variation in metal leachability, showing improved bioleaching by the mixed strain. Mixed strain demonstrated the highest bioleaching of 96% Cu, 94.5% Zn, 75% Ni, and 74.5% Pb from the pulverized particles ranging from 0.075–1 mm size with a pulp density of 7.5 g/L at 18 days with asymptoticity from 12 days onward. Further, the corresponding maximum bioleaching efficiency by the mixed culture for precious and rare earth metals achieved was 46% Ag, 38% Au, and 31% Sc, 27% each of Ce and La, and 24% Nd. Improved bioleaching by the mixed culture may be due to the synergistic growth of the bacterial strains producing a collective effect leading to efficient metal solubilization. Higher production of exopolymeric substances (EPS) by the mixed culture demonstrated their remarkable role in metal bioleaching. A yield of greater than 99% of base metals by fractional chemical precipitation of bioleachate served as a concluding step in metal recovery.