Metal solubilization from metal-containing solid materials by cyanogenic Chromobacterium violaceum.

Different cyanogenic bacterial strains (Chromobacterium violaceum, Pseudomonas fluorescens, Bacillus megaterium) were cultivated under cyanide-forming conditions in the presence of metal-containing solids such as nickel powder or electronic scrap. All microorganisms were able to form water-soluble metal cyanides, however, with different efficiencies. C. violaceum was able to mobilize nickel as tetracyanonickelate [Ni(CN)4(2-)] from fine-grained nickel powder. Gold was microbially solubilized as dicyanaoaurate [Au(CN)2-] from electronic waste. Additionally, cyanide-complexed copper was detected during biological treatment of shredded printed circuit boards scrap. Regarding the formation of tetracyanonickelate, C. violaceum was more effective than P. fluorescens or B. megaterium. Besides a few previous reports on gold solubilization from gold-containing ores or native gold by C. violaceum, the findings demonstrate for the first time the microbial mobilization of metals other than gold from solid materials and represent a novel type of microbial metal mobilization based on the ability of certain microbes to form HCN. The results might have the potential for industrial applications (biorecovery, bioremediation) regarding the treatment of metal-containing solids since metal cyanides can easily be separated by chromatographic means and be recovered by sorption onto activated carbon.