Degradation of metal cyanide complexes by micrcoorganisms

The use of cyanide to extract gold from ores is widespread. In the process of extracting gold, cyanide may form metal cyanide complexes with a variety of other metals present in the ore. This study was carried out to investig ate the biodegradation of the Cu(I)-cyanide complex and tetracyanonickelate under varying pH and nutrient additions. Detailed studies using shake-flas k cultures and bioreactors showed that naturally occurring bacteria residin g on gold-leach-pad ore utilized the Cu(I)-cyanide complex (CuCN) and tetra cyanonickelate, Na-2(NiCN4), as carbon and/or nitrogen sources. Ammonium-ni trogen (NH4+-N) and/or cyanate (CNO-) accumulated in solution as the metal cyanide complexes were degraded. The accumulation of cyanate as a product i s a concern due to its toxicity. Degradation rates were increased if a grow th substrate (peptone, 0.1%) was added to the medium or if bioreactors were primed with peptone before addition of the metal-cyanide complex. Tetracya nonickelate was degraded at pH 8 without added peptone, but it was not degr aded at pH 10. The addition of peptone was required for degradation of the Cu(I)-cyanide complex at pH 8 and pH 10. At pH 8, the addition of peptone r esulted in the accumulation of cyanate, whereas, at pH 10, cyanate was not detected in the cultures. Biodegradation of metal-cyanide complexes was fas ter (approximately 1.5 to ten times faster) in bioreactors than in shake-fl ask cultures. The addition of peptone was not required for degradation of m etal-cyanide complexes in bioreactors. However, priming the bioreactor with peptone resulted in higher metal-cyanide degradation rates over multiple c ycles.