Recovery and Upgrading of Gold as Nanoparticles from Leachates of Waste Printed Circuit Boards through Biosorption Using Baker's Yeast

Abstract Commercially available baker's yeast is used for the recovery and upgrading of Au as nanoparticles (NPs) from aqua regia leachates of waste printed circuit boards (PCBs). For downstream processing after the biosorption of Au from the PCB leachates, the yeast cells are used as the starting material for synthesizing Au NPs, which are a high‐value‐added product of waste PCBs. Two different chemical approaches are developed for the reductive synthesis of Au NPs from the yeast cells. First, aqueous NaBH₄ solution and aqueous HCOONa solution are used to reduce the biosorbed Au ions at room temperature for 24 h. Second, HCOOH vapor is used at 90 °C for 10 min. Both these chemical approaches provide spherical Au NPs of 5–10 nm in diameter on the yeast cells. Moreover, a microbial approach is proposed to synthesize Au NPs without addition of chemical reducing agents, which is called biomineralization. This microbial approach provides rods, cubes, and bipyramids of Au NPs with an edge length of 100–200 nm when the yeast cells are simply left to stand at room temperature for 22 days. This study presents simple and eco‐friendly approaches for synthesizing Au NPs from PCB leachates through biosorption.