Biomobilization of silver, gold, and platinum from solid waste materials by HCN-forming microorganisms

Cyanogenic Chromobacterium violaceum, Pseudomonas fluorescens, and P. plecoglossicida were able to mobilize silver, gold, and platinum when grown in the presence of various metal-containing solids such as gold-containing electronic scrap, silver-containing jewelry waste, or platinum-containing automobile catalytic converters. Five percent of silver was microbially mobilized from powdered jewelry waste as dicyanoargentate after one day, although complete dissolution was obtained when non-biological cyanide leaching was applied. Dicyanoargentate inhibited growth at concentrations of > 20 mg/L. Gold was bacterially solubilized from shredded printed circuit boards. Maximum dicyanoaurate concentration corresponded to 68.5% dissolution of the total gold added. Additionally, cyanide-complexed copper was detected during treatment of electronic scrap due to its high copper content of approximately 100 g/kg scrap. However, only small amounts of platinum (0.2%) were mobilized from spent automobile catalytic converter after 10 days probably due to passivation of the surface by an oxide film. In summary, all findings demonstrate the potential of microbial mobilization of metals as cyanide complex from solid materials and represent a novel type of microbial metal mobilization (termed “biocyanidation”) which might find industrial application.