Biotechnological neutralization of cyanides and thiocyanates in cyanidation tails of gold ores and concentrates

摘要

The role played by a bacterial community composed of Pseudomonasputida, strain 21; Pseudomonas stutzeri, strain 18; and Pseudomonas sp., strain 5, and by physical and chemical factors in the degradation of CN~- and SCN~- was studied. It was shown that the degradation of CN~- is determined both by the action of bacteria and by abiotic physical and chemical factors (pH, O_2, temperature, the medium agitation rate, etc.). The contribution of chemical degradation was found to increase drastically at pH below 9.0; when air was blown through the medium (irrespective of the pH value); under active agitation of the medium; and when the medium surface interfacing air was increased. Even at elevated pH values (9.0-9.2), suboptimal for bacterial growth, the microbial degradation could account for at most 20-25 mg/l of CN~-, regardless of its initial concentration. When CN~- or SCN~- were concurrently present in the medium or in the pulp, the former compound was the first to be degraded by microorganisms. CN~- and SCN~- were utilized by bacteria solely as nitrogen sources. The detoxification of cyanide-containing pulps could be achieved by the combination of chemical degradation of cyanide, resulting in the decrease of its concentration, and the subsequent oxidation of SCN~- and the residual CN~- by a community of heterotrophic bacteria.