Effect of chemical pretreatment on the biodegradation of cyanides

The application of Fenton's reagent (H2O2; Fe2+) as a chemical pretreatment for acceleration of biological degradation of cyanides in soil-containing systems has been studied. In slurries of topsoil freshly amended with radiolabeled free cyanide (K14CN) at pH 7.2, about 100% of the compound was removed from the system by the combination of chemical oxidation and biodegradation. In slurry of manufactured gas plant (MGP) soil, the extent of combined chemical-biological treatment was 50%. At the same time, approximately 15% of the cyanide was lost from the system by protonation and evolution of formed HCN. In slurries of both topsoil and MGP soil amended with radiolabeled K4[Fe(CN)6], less than 20% was degraded. In soils previously equilibrated with free and complex cyanide, the highest extent of degradation resulted from chemical-biological treatment did not exceed 15%. To avoid massive evolution of HCN, the cyanide-amended topsoil was maintained at a pH of 10.0. At this pH, nearly 35% of the cyanides were removed from the system by combined chemical-biological treatment