Biogenic production of cyanide and its application to gold recovery

Chromobacterium violaceum is a cyanogenic (cyanide-producing) microorganism . Cyanide is used on an industrial scale to complex and recover gold from o res or concentrates of ores bearing the precious metal. A potentially usefu l approach in gold mining operations could be to produce cyanide biological ly in relatively small quantities at the ore surface. In this study, C. vio laceum grown in nutrient broth formed a biofilm and could complex and solub ilize 100% of the gold on glass test slides within 4-7 days. Approximately 50% of the cyanide-recoverable gold could be mobilized from a biooxidized s ulfidic-ore concentrate. Complexation of cyanide in solution by gold appear ed to have a beneficial effect on cell growth - viable cell counts were nea rly two orders of magnitude greater in the presence of gold-coated slides o r biooxidized ore substrates than in their absence. C. violaceum was cyanog enic when grown in alternative feedstocks, When grown in a mineral salt sol ution supplemented with 13.3% v/v swine fecal material (SFM), cells exhibit ed pigmentation and suspended cell concentrations comparable to cultures gr own in nutrient broth. Glycine supplements stimulated production of cyanide in 13.3% v/v SFM. In contrast, glycine was inhibitory when added at the ti me of inoculation in the more concentrated SFM, decreasing cell numbers and reducing ultimate bulk-solution cyanide concentrations. However, aeration and addition of glycine to stationary phase cells grown on 13.3% v/v SFM an aerobically resulted in rapid production and high concentrations (up to 38 mg l(-1)) of cyanide. This indicates that biogenesis of cyanide may be supp orted in remote areas using locally produced and inexpensive agricultural f eedstocks in place of commercial media.