Reducing oxidative stress in bacteria and suppressing microbial-metal interaction enhance bioleaching of platinum group metals at a high pulp density

Abstract

Although bioleaching has shown promise for the recovery of platinum group metals (PGM) from metal-bearing solid wastes, high pulp density (i.e., the solid mass to liquid volume ratio) poses a significant challenge. This study aimed to enhance PGM biorecovery from spent automotive catalysts (SAC) under such a condition. A novel two-step bioleaching approach has been devised that notably improved PGM extraction efficiency in the presence of elevated metal concentrations. This was achieved by mitigating oxidative stress in bacteria through the addition of the antioxidant glutathione (GSH) and minimizing bacteria-metal interactions and metal sorption onto bacterial cells using the dispersant polyvinylpyrrolidone (PVP). Our newly developed strategy yielded higher Pt, Pd, and Rh recoveries, reaching 68 %, 74 %, and 86 %, respectively, at a pulp density of 4 % w/v, compared to 30 %, 33 %, and 62 %, respectively, in the absence of GSH and PVP.