Microbial Recycling of Precious and Rare Metals Sourced from Post-Consumer Products

Abstract

We have focused on the metal-reducing bacterium, Shewanella algae that are able to reduce and deposit platinum group metals (Pt (IV), Pd (II) and Rh (III)) and gold (Au (III)) in neutral solutions at room temperature under anaerobic conditions. When processing the aqua regia solution of spent automotive catalysts, the solution pH was adjusted to the optimal range for S. algae activity between pH 4 and 7. After this pH adjustment, the S. algae cells were able to rapidly and selectively reduce and accumulate the platinum group metal ions from the leaching solution into the bacterial cells as metallic nanoparticles. The biotechnological procedure also has the potential to allow the recovery of Au (III) ions from the leaching solution of electronic waste. We also found that the S. algae cells were also applicable to the adsorption of rare metal ions from acidic solutions. We achieved selective adsorption of indium (In (III)) ions on the bacterial cells from the leaching solution of waste liquid crystal displays by adjusting its pH, because the pH range necessary for S. algae to act as an effective adsorbent differs for different metal ions. Our proposed microbial methods enable the rapid and highly efficient recovery of precious and rare metals sourced from post-consumer products.